Carlo Patrono

ESC Guidelines for the management of acute coronary syndromes in patients presenting without persistent ST-segment elevation : The Task Force for the management of acute coronary syndromes (ACS) in patients presenting without persistent ST-segment elevation of the European Society of Cardiology (ESC).

Coronary artery disease (CAD) is a pathological process characterized by atherosclerotic plaque accumulation in the epicardial arteries, whether obstructive or non-obstructive. This process can be modified by lifestyle adjustments, pharmacological therapies, and invasive interventions designed to achieve disease stabilization or regression. The disease can have long, stable periods but can also become unstable at any time, typically due to an acute atherothrombotic event caused by plaque rupture or erosion. However, the disease is chronic, most often progressive, and hence serious, even in clinically apparently silent periods. The dynamic nature of the CAD process results in various clinical presentations, which can be conveniently categorized as either acute coronary syndromes (ACS) or chronic coronary syndromes (CCS). The Guidelines presented here refer to the management of patients with CCS. The natural history of CCS is illustrated in Figure 1.

This review of the role of platelets in atherothrombosis illuminates the surprisingly numerous activities of these tiny, anucleate cells and stresses their participation in the inflammatory component of atherothrombosis. The information is presented in the context of the prevention of atherothrombosis by antiplatelet agents now in clinical use.

Nonsteroidal antiinflammatory drugs (NSAIDs) are widely used to treat arthritis, menstrual pain, and headache. Although they are effective, their long-term use is limited by gastrointestinal effects such as dyspepsia and abdominal pain and, less often, gastric or duodenal perforation or bleeding. Development of the coxibs, a new group of antiinflammatory drugs, represents a response to the unsatisfactory therapeutic profile of NSAIDs. Both groups of drugs inhibit prostaglandin G/H synthase, the enzyme that catalyzes the transformation of arachidonic acid to a range of lipid mediators, termed prostaglandins and thromboxanes (Figure 1). However, whereas NSAIDs inhibit the two recognized forms of the . . .

Numerous experimental, epidemiologic, and clinical studies suggest that nonsteroidal anti-inflammatory drugs (NSAIDs), particularly the highly selective cyclooxygenase (COX)-2 inhibitors, have promise as anticancer agents. NSAIDs restore normal apoptosis in human adenomatous colorectal polyps and in various cancer cell lines that have lost adenomatous polyposis coli gene function. NSAIDs also inhibit angiogenesis in cell culture and rodent models of angiogenesis. Many epidemiologic studies have found that long-term use of NSAIDs is associated with a lower risk of colorectal cancer, adenomatous polyps, and, to some extent, other cancers. Two NSAIDs, sulindac and celecoxib, have been found to inhibit the growth of adenomatous polyps and cause regression of existing polyps in randomized trials of patients with familial adenomatous polyposis (FAP). However, unresolved questions about the safety, efficacy, optimal treatment regimen, and mechanism of action of NSAIDs currently limit their clinical application to the prevention of polyposis in FAP patients. Moreover, the development of safe and effective drugs for chemoprevention is complicated by the potential of even rare, serious toxicity to offset the benefit of treatment, particularly when the drug is administered to healthy people who have low annual risk of developing the disease for which treatment is intended. This review considers generic approaches to improve the balance between benefits and risks associated with the use of NSAIDs in chemoprevention. We critically examine the published experimental, clinical, and epidemiologic literature on NSAIDs and cancer, especially that regarding colorectal cancer, and identify strategies to overcome the various logistic and scientific barriers that impede clinical trials of NSAIDs for cancer prevention. Finally, we suggest research opportunities that may help to accelerate the future clinical application of NSAIDs for cancer prevention or treatment.

To assess the effects of selective cyclo-oxygenase-2 (COX 2) inhibitors and traditional non-steroidal anti-inflammatory drugs (NSAIDs) on the risk of vascular events.Meta-analysis of published and unpublished tabular data from randomised trials, with indirect estimation of the effects of traditional NSAIDs.Medline and Embase (January 1966 to April 2005); Food and Drug Administration records; and data on file from Novartis, Pfizer, and Merck.Eligible studies were randomised trials that included a comparison of a selective COX 2 inhibitor versus placebo or a selective COX 2 inhibitor versus a traditional NSAID, of at least four weeks' duration, with information on serious vascular events (defined as myocardial infarction, stroke, or vascular death). Individual investigators and manufacturers provided information on the number of patients randomised, numbers of vascular events, and the person time of follow-up for each randomised group.In placebo comparisons, allocation to a selective COX 2 inhibitor was associated with a 42% relative increase in the incidence of serious vascular events (1.2%/year v 0.9%/year; rate ratio 1.42, 95% confidence interval 1.13 to 1.78; P = 0.003), with no significant heterogeneity among the different selective COX 2 inhibitors. This was chiefly attributable to an increased risk of myocardial infarction (0.6%/year v 0.3%/year; 1.86, 1.33 to 2.59; P = 0.0003), with little apparent difference in other vascular outcomes. Among trials of at least one year's duration (mean 2.7 years), the rate ratio for vascular events was 1.45 (1.12 to 1.89; P = 0.005). Overall, the incidence of serious vascular events was similar between a selective COX 2 inhibitor and any traditional NSAID (1.0%/year v 0.9%/year; 1.16, 0.97 to 1.38; P = 0.1). However, statistical heterogeneity (P = 0.001) was found between trials of a selective COX 2 inhibitor versus naproxen (1.57, 1.21 to 2.03) and of a selective COX 2 inhibitor versus non-naproxen NSAIDs (0.88, 0.69 to 1.12). The summary rate ratio for vascular events, compared with placebo, was 0.92 (0.67 to 1.26) for naproxen, 1.51 (0.96 to 2.37) for ibuprofen, and 1.63 (1.12 to 2.37) for diclofenac.Selective COX 2 inhibitors are associated with a moderate increase in the risk of vascular events, as are high dose regimens of ibuprofen and diclofenac, but high dose naproxen is not associated with such an excess.

This review considers the role of low-dose aspirin for the prevention of atherothrombosis, discussing the molecular mechanism of action of aspirin as well as clinical and epidemiologic studies of aspirin as an antiplatelet agent, with special emphasis on the benefits and risks in different patient populations.

The past 10 years have witnessed major changes in our understanding of the pathophysiologic mechanisms underlying vascular occlusion1,2 and considerable progress in the clinical assessment of aspirin and other antiplatelet agents35. The purpose of this review is to describe a rational basis for antithrombotic prophylaxis and treatment with aspirin. Basic information on the molecular mechanism of action of aspirin in inhibiting platelet function will be integrated with the appropriate clinical pharmacologic data and the results of randomized clinical trials.Mechanism of ActionAspirin induces a long-lasting functional defect in platelets, clinically detectable as a prolongation of the . . .

Acetylation of platelet cyclooxygenase by oral aspirin is dose dependent and cumulative with repeated administration. However, no single dose of aspirin has been found to be completely selective of platelet thromboxane (TX) synthesis inhibition in man. We determined the dose dependence, cumulative nature and selectivity of aspirin effects on platelet TXB(2) and renal prostaglandin (PG) and prostacyclin (PGI(2)) production. We measured, by radioimmunoassay, serum TXB(2) levels after whole blood clotting and urinary excretion of PGE(2), PGF(2alpha), and 6-keto-PGF(1alpha), before and after single or repeated oral aspirin doses given to 46 healthy subjects. Single doses of 6-100 mg aspirin resulted in a linear (r = 0.92, P < 0.01) inhibition of platelet TXB(2) production, ranging from 12 to 95% after 24 h. A daily dose of 0.45 mg/kg given for 7 d produced a cumulative and virtually complete inhibition of platelet TXB(2) production, without significantly reducing the urinary excretion of PGE(2), PGF(2alpha), and 6-keto-PGF(1alpha) in both healthy men and women. The platelet inhibitory effect of this regimen was maintained unaltered throughout 1 mo of therapy, with no evidence of cumulative inhibition of renal PG-synthesis. Moreover, furosemide-induced renal PGI(2) synthesis and renin release were unaffected by chronic low-dose aspirin. Following cessation of aspirin therapy, platelet TXB(2) production returned toward control values at a similar rate as after a single higher dose. WE CONCLUDE THAT IN HEALTHY SUBJECTS: (a) aspirin causes a dose-dependent inhibition of platelet TXA(2) production, with no obvious sex-related difference; (b) the inhibitory effect of daily low-dose aspirin is cumulative on platelet TXA(2) but not on renal PG-synthesis; (c) during chronic low-dose aspirin therapy, renal PGI(2)-producing cells are readily activable by furosemide at a time of virtually complete suppression of platelet cyclooxygenase activity.

The use of aspirin for the prevention of thrombotic complications in polycythemia vera is controversial.We enrolled 518 patients with polycythemia vera, no clear indication for aspirin treatment, and no contraindication to such treatment in a double-blind, placebo-controlled, randomized trial to assess the safety and efficacy of prophylaxis with low-dose aspirin (100 mg daily). The two primary end points were the cumulative rate of nonfatal myocardial infarction, nonfatal stroke, or death from cardiovascular causes and the cumulative rate of nonfatal myocardial infarction, nonfatal stroke, pulmonary embolism, major venous thrombosis, or death from cardiovascular causes. The mean duration of follow-up was about three years.Treatment with aspirin, as compared with placebo, reduced the risk of the combined end point of nonfatal myocardial infarction, nonfatal stroke, or death from cardiovascular causes (relative risk, 0.41; 95 percent confidence interval, 0.15 to 1.15; P=0.09) and the risk of the combined end point of nonfatal myocardial infarction, nonfatal stroke, pulmonary embolism, major venous thrombosis, or death from cardiovascular causes (relative risk, 0.40; 95 percent confidence interval, 0.18 to 0.91; P=0.03). Overall mortality and cardiovascular mortality were not reduced significantly. The incidence of major bleeding episodes was not significantly increased in the aspirin group (relative risk, 1.62; 95 percent confidence interval, 0.27 to 9.71).Low-dose aspirin can safely prevent thrombotic complications in patients with polycythemia vera who have no contraindications to such treatment.

Background —Diabetes mellitus (DM) is associated with enhanced lipid peroxidation and persistent platelet activation. We tested the hypothesis that the in vivo formation of the F 2 -isoprostane 8-iso-prostaglandin (PG)F 2α , a bioactive product of arachidonic acid peroxidation, is enhanced in DM and contributes to platelet activation. Methods and Results —Urine samples were obtained from 85 diabetic patients and 85 age- and sex-matched healthy subjects for measurement of immunoreactive 8-iso-PGF 2α and 11-dehydro-thromboxane B 2 (TXM), an in vivo index of platelet activation. Sixty-two had non–insulin-dependent (NID)DM, and 23 had insulin-dependent (ID) DM. Vitamin E supplementation, metabolic control, and cyclooxygenase inhibitors were used to investigate the mechanisms of formation of 8-iso-PGF 2α in this setting. Urinary 8-iso-PGF 2α excretion was significantly higher ( P =0.0001) in NIDDM patients (419±208 pg/mg creatinine; range 160 to 1014) than in age-matched control subjects (208±92; 41 to 433). Urinary 8-iso-PGF 2α was linearly correlated with blood glucose and urinary TXM. 8-iso-PGF 2α excretion was also significantly ( P =0.0001) higher in IDDM patients (400±146; 183 to 702) than in control subjects (197±69; 95 to 353). Vitamin E supplementation (600 mg/d for 14 days) was associated with a statistically significant reduction in both urinary 8-iso-PGF 2α (by 37%) and TXM (by 43%) in 10 NIDDM patients. Improved metabolic control was associated with a significant ( P =0.0001) reduction in 8-iso-PGF 2α and TXM excretion by 32% and 41%, respectively, in 21 NIDDM patients. 8-iso-PGF 2α was unchanged after 2-week dosing with aspirin and indobufen despite profound suppression of TXM excretion. Conclusions —We conclude that DM is associated with increased formation of F 2 -isoprostanes, as a correlate of impaired glycemic control and enhanced lipid peroxidation. This may provide an important biochemical link between impaired glycemic control and persistent platelet activation. These results provide a rationale for dose-finding studies of antioxidant treatment in diabetes.

The clinical course of polycythemia vera is often complicated by thrombosis as well as by the possible transition to myeloid metaplasia with myelofibrosis or acute myeloid leukemia. The aim of this study was to assess the rate of these complications in subjects receiving currently recommended treatments.Overall, 1,638 patients from 12 countries were enrolled onto a large, prospective multicenter project aimed at describing the clinical history of polycythemia vera for the following outcomes: survival, the cumulative rate of cardiovascular death and thrombosis, the cumulative rate of leukemia, myelodysplasia, and myelofibrosis. The mean duration of the disease at entry and the duration of the follow-up were 4.9 and 2.7 years, respectively.The overall mortality rate of 3.7 deaths per 100 persons per year resulted from a moderate risk of cardiovascular death and a high risk of death from noncardiovascular causes (mainly hematologic transformations). Age older than 65 years and a positive history of thrombosis were the most important predictors of cardiovascular events. Antiplatelet therapy, but not cytoreductive treatment, was significantly associated with a lower risk of cardiovascular events. We found a consistent association between age and risk of leukemia, and between duration of the disease with risk of myelofibrosis.The European Collaboration on Low-Dose Aspirin in Polycythemia Vera study documents that large international collaborative studies are feasible in this field, in which few epidemiologic data are available. The persistently high mortality rate from hematologic malignancies characterizes the unmet therapeutic need of polycythemic patients and suggests a priority for future studies in this disease.

<h2>Abstract</h2> We studied the time- and dose-dependence of the inhibitory effect of oral aspirin on platelet production of thromboxane (TX) B₂ in response to endogenously formed thrombin, by allowing the whole blood to clot at 37°C for 30 min and measuring TXB₂ concentrations by radioimmunoassay in the separated serum. The concentrations of generated TXB₂ averaged 222.4 ± 81.3 (SD) ng/ml of serum in 45 healthy subjects, and were highly reproducible in the same subject upon repeated sampling. A single 100-mg aspirin dose reduced serum TXB₂ by 98% during the 1^st hour. Single doses of 100–400 mg aspirin resulted in 94–98% inhibition after 24 and 48 h, and 90–92% after 72h. Thereafter, serum TXB₂ returned to control levels with a time course consistent with platelet turnover. More than 90% inhibition could be maintained, over one month, by giving a 200-mg aspirin dose every 72h. Thus, aspirin can achieve a ceiling effect on TXB₂ production in healthy subjects at a considerably lower dosage than currently employed regimens for antithrombotic therapy.

Sinceour last report on antithrombotic therapy in 1998,1 newinformation has been published on the role of aspirin and otherplatelet-active drugs in the treatment and prevention ofatherothrombosis. These new data can be summarized as follows: (1) alarge randomized study, the Acetylsalicylic Acid and Carotid Endarterectomy (ACE) trial,2 has directly comparedlow-dose and high-dose aspirin for the prevention of ischemic stroke inpatients undergoing carotid endarterectomy; (2) the role of aspirin inprophylaxis of venous thromboembolism (VTE) has to be reassessedin the light of the Pulmonary Embolism Prevention (PEP)trial3; (3) three nonrandomized studies with historicalcontrol subjects4, 5, 6 and one randomizedtrial7 have compared the safety of clopidogrel plusaspirin vs ticlopidine plus aspirin in patients undergoingintracoronary stent implantation; (4) the results of clinical andangiographic follow-up of the patients in the Evaluation of PlateletIIb/IIIa Inhibitors for Stenting (EPISTENT) trial at 6months8 and 1 year9 provide evidence thatstent implantation and platelet glycoprotein (GP) IIb/IIIa blockade byabciximab improve the efficacy and safety of percutaneous coronaryrevascularization; and (5) preliminary reports from three large trialsof long-term GPIIb/IIIa blockade (Orbofiban in Patients with Unstable Coronary Syndromes [OPUS]; Evaluation ofXemilofiban in Controlling ThromboticEvents [EXCITE]10; and sibrafibanvs aspirin to yield maximum protectionfrom ischemic heart events post-acute coronary syndromes[SYMPHONY] (sibrafiban)11) in approximately27,000 patients taking oral drugs for 3 months to 1 year, are largely disappointing in terms of efficacy and/orsafety.

This article discusses platelet active drugs as part of the Seventh American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. New data on antiplatelet agents include the following: (1) the role of aspirin in primary prevention has been the subject of recommendations based on the assessment of cardiovascular risk; (2) an increasing number of reports suggest a substantial interindividual variability in the response to antiplatelet agents, and various phenomena of "resistance" to the antiplatelet effects of aspirin and clopidogrel; (3) the benefit/risk profile of currently available glycoprotein IIb/IIIa antagonists is substantially uncertain for patients with acute coronary syndromes who are not routinely scheduled for early revascularization; (4) there is an expanding role for the combination of aspirin and clopidogrel in the long-term management of high-risk patients; and (5) the cardiovascular effects of selective and nonselective cyclooxygenase-2 inhibitors have been the subject of increasing attention.

It has been suggested that platelet hyperreactivity in patients with diabetes mellitus is associated with increased platelet production of thromboxane. We therefore compared the excretion of a thromboxane metabolite and platelet function in 50 patients with Type II diabetes mellitus who had normal renal function and clinical evidence of macrovascular disease and in 32 healthy controls. The mean (+/- SD) excretion rate of urinary 11-dehydro-thromboxane B2 was significantly higher in the patients than in the controls (5.94 +/- 3.68 vs. 1.50 +/- 0.79 nmol per day; P less than 0.001), irrespective of the type of macrovascular complication. Tight metabolic control achieved with insulin therapy reduced the levels of 11-dehydro-thromboxane B2 by approximately 50 percent. The fractional conversion of exogenous thromboxane B2 (infused at a rate of 4.5, 45.3, or 226.4 fmol per kilogram of body weight per second) to urinary 11-dehydro-thromboxane B2 was assessed in four patients, in whom it averaged 5.4 +/- 0.1 percent; this value did not differ from that measured in healthy subjects. Aspirin in low doses (50 mg per day for seven days) reduced urinary excretion of the metabolite by approximately 80 percent in four patients. The fact that thromboxane biosynthesis recovered over the following 10 days was consistent with a platelet origin of the urinary metabolite.(ABSTRACT TRUNCATED AT 250 WORDS)

Obesity, in particular abdominal adiposity, is associated with increased cardiovascular morbidity and mortality through mechanisms possibly linking the metabolic disorder to platelet and vascular abnormalities.To investigate the clinical and biochemical determinants of lipid peroxidation and platelet activation in obese women.Cross-sectional comparison, conducted between September 1999 and September 2001, of urinary 8-iso prostaglandin F(2alpha) (8-iso PGF(2alpha)) and 11-dehydrothromboxane B2 (11-dehyhdro-TxB2) excretion levels in 93 women: 44 with a body mass index (BMI) higher than 28 and a waist-to-hip ratio (WHR) of 0.86 or higher, android obesity; 25 with a BMI higher than 28 and a WHR lower than 0.86, gynoid obesity; and 24 nonobese women with a BMI lower than 25. An additional study was conducted to determine the short-term effects of weight loss in 20 of the 44 women with android obesity.During a 12-week period, 20 women with android obesity followed a weight loss program to reduce caloric intake to about 1200 kcal/d.Plasma C-reactive protein, insulin and leptin levels, and urinary 8-iso PGF(2alpha) (marker of in vivo lipid peroxidation) and 11-dehyhdro-TxB2 (marker of in vivo platelet activation) excretion. Weight loss was defined as successful when the initial body weight decreased by at least 5 kg after a 12-week period of caloric restriction.Women with android obesity had higher levels of 8-iso PGF(2alpha )(median [interquartile range [IQR]] 523 [393-685] vs 187 [140-225] pg/mg creatinine) and 11-dehyhdro-TxB2 (median [IQR], 948 [729-1296] vs 215 [184-253] pg/mg creatinine) than nonobese women (P<.001). Both 8-iso PGF(2alpha)and 11-dehyhdro-TxB2 were higher in women with android obesity than women with gynoid obesity (P<.001). Based on multiple regression analysis, C-reactive protein levels and WHRs of 0.86 or higher predicted the rate of 8-iso PGF(2alpha) excretion independently of insulin and leptin levels. Of 20 women with android obesity, 11 achieved successful weight loss, which was associated with statistically significant reductions in C-reactive protein (median change, 23%; P<.05), 8-iso PGF(2alpha) (median change, 32%; P =.04) and 11-dehydro-TxB2 (median change, 54%; P =.005).Android obesity is associated with enhanced lipid peroxidation and persistent platelet activation. These abnormalities are driven by inflammatory triggers related to the degree of abdominal adiposity and are, at least in part, reversible with a successful weight-loss program.

This article about currently available antiplatelet drugs is part of the Antithrombotic and Thrombolytic Therapy: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). It describes the mechanism of action, pharmacokinetics, and pharmacodynamics of aspirin, reversible cyclooxygenase inhibitors, thienopyridines, and integrin αIIbβ3 receptor antagonists. The relationships among dose, efficacy, and safety are thoroughly discussed, with a mechanistic overview of randomized clinical trials. The article does not provide specific management recommendations; however, it does highlight important practical aspects related to antiplatelet therapy, including the optimal dose of aspirin, the variable balance of benefits and hazards in different clinical settings, and the issue of interindividual variability in response to antiplatelet drugs. This article about currently available antiplatelet drugs is part of the Antithrombotic and Thrombolytic Therapy: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). It describes the mechanism of action, pharmacokinetics, and pharmacodynamics of aspirin, reversible cyclooxygenase inhibitors, thienopyridines, and integrin αIIbβ3 receptor antagonists. The relationships among dose, efficacy, and safety are thoroughly discussed, with a mechanistic overview of randomized clinical trials. The article does not provide specific management recommendations; however, it does highlight important practical aspects related to antiplatelet therapy, including the optimal dose of aspirin, the variable balance of benefits and hazards in different clinical settings, and the issue of interindividual variability in response to antiplatelet drugs.

HomeCirculationVol. 67, No. 6Analysis of prostacyclin and thromboxane biosynthesis in cardiovascular disease. Free AccessAbstractPDF/EPUBAboutView PDFSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessAbstractPDF/EPUBAnalysis of prostacyclin and thromboxane biosynthesis in cardiovascular disease. G A FitzGerald, A K Pedersen and C Patrono G A FitzGeraldG A FitzGerald Search for more papers by this author , A K PedersenA K Pedersen Search for more papers by this author and C PatronoC Patrono Search for more papers by this author Originally published1 Jun 1983https://doi.org/10.1161/01.CIR.67.6.1174Circulation. 1983;67:1174–1177 Previous Back to top Next FiguresReferencesRelatedDetailsCited By Kratz D, Wilken-Schmitz A, Sens A, Hahnefeld L, Scholich K, Geisslinger G, Gurke R and Thomas D (2022) Post-mortem changes of prostanoid concentrations in tissues of mice: Impact of fast cervical dislocation and dissection delay, Prostaglandins & Other Lipid Mediators, 10.1016/j.prostaglandins.2022.106660, 162, (106660), Online publication date: 1-Oct-2022. 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Isoprostanes are emerging as a new class of biologically active products of arachidonic acid metabolism of potential relevance to human vascular disease. Their formation in vivo seems to reflect primarily, if not exclusively, a nonenzymatic process of lipid peroxidation. Enhanced urinary excretion of 8-iso-PGF2 alpha has been described in association with cardiac reperfusion injury and with cardiovascular risk factors, including cigarette smoking, diabetes mellitus, and hypercholesterolemia. Besides providing a likely noninvasive index of lipid peroxidation in these settings, measurements of specific F2 isoprostanes in urine may provide a sensitive biochemical end point for dose-finding studies of natural and synthetic inhibitors of lipid peroxidation. Although the biological effects of 8-iso-PGF2 alpha in vitro suggest that it and other isoeicosanoids may modulate the functional consequences of lipid peroxidation, evidence that this is likely in vivo remains inadequate at this time.

Nonsteroidal anti-inflammatory drugs and sulfinpyrazone compete dose-dependently with arachidonate for binding to platelet cyclooxygenase. Such a process closely follows systemic plasma drug concentrations and is reversible as a function of drug elimination. Peak inhibition and extent of its reversibility at 24 hr varies consistently with individual pharmacokinetic profile. Inhibition of platelet cyclooxygenase activity by these agents is associated with variable effects on prostaglandin (PG) synthesis in the gastric mucosa and the kidney. Aspirin acetylates platelet cyclooxygenase and permanently inhibits thromboxane (TX) A2 production in a dose-dependent fashion when single doses of 0.1 to 2.0 mg/kg are given. Acetylation of the enzyme by low-dose aspirin is cumulative on repeated dosing. The fractional dose of aspirin necessary to achieve a given level of acetylation by virtue of cumulative effects approximately equals the fractional daily platelet turnover. Serum TXB2 measurements obtained during long-term dosing with 0.11, 0.22, and 0.44 mg/kg aspirin in four healthy subjects could be fitted by a theoretical model assuming identical acetylation of platelet (irreversible) and megakaryocyte (reversible) cyclooxygenase. For a given dose within this range, both the rate at which cumulative acetylation occurs and its maximal extent largely depend upon the rate of platelet turnover. Continuous administration of low-dose aspirin (20 to 40 mg/day) has no statistically significant effect on urinary excretion of either 6-keto-PGF1 alpha or 2,3-dinor-6-keto-PGF1 alpha, i.e., indexes of renal and extrarenal PGI2 biosynthesis in vivo. Whether a selective sparing of extraplatelet cyclooxygenase activity by low-dose aspirin will result in increased antithrombotic efficacy, fewer toxic reactions, or both remains to be established in prospective clinical trials.

Guidelines and Expert Consensus Documents aim to present all the relevant evidence on a particular issue in order to help physicians to weigh the benefits and risks of a particular diagnostic or therapeutic procedure. They should be helpful in everyday clinical decision-making. A great number of Guidelines and Expert Consensus Documents have been issued in recent years by different organizations, the European Society of Cardiology (ESC) and by other related societies. By means of links to web sites of National Societies several hundred guidelines are available. This profusion can put at stake the authority and validity of guidelines, which can only be guaranteed if they have been developed by an unquestionable decision-making process. This is one of the reasons why the ESC and others have issued recommendations for formulating and issuing Guidelines and Expert Consensus Documents. In spite of the fact that standards for issuing good quality Guidelines and Expert Consensus Documents are well defined, recent surveys of Guidelines and Expert Consensus Documents published in peer-reviewed journals between 1985 and 1998 have shown that methodological standards were not complied within the vast majority of cases. It is therefore of great importance that guidelines and recommendations are presented in formats that are easily interpreted. Subsequently, their implementation programmes must also be well conducted. Attempts have been made to determine whether guidelines improve the quality of clinical practice and the utilization of health resources. The ESC Committee for Practice Guidelines ( CPG ) supervises and coordinates the preparation of new Guidelines and Expert Consensus Documents produced by Task Forces, expert groups or consensus panels. The Committee is also responsible for the endorsement of these Guidelines and Expert Consensus Documents or statements. The role of aspirin and other platelet-active drugs in the treatment and prevention of atherothrombosis has been reviewed recently by the Sixth American …

There is considerable evidence that hyperglycemia represents the main cause of complications of diabetes mellitus (DM), and oxidative stress resulting from increased generation of reactive oxygen species plays a crucial role in their pathogenesis. In fact, in the absence of an appropriate response from endogenous antioxidant mechanisms, the redox imbalance causes the activation of stress-sensitive intracellular signaling pathways. The latter play a key role in the development of late complications of DM, as well as in mediating insulin resistance (i.e., resistance to insulin-mediated glucose uptake by some cells) and impaired insulin secretion. This review, focused on lipid peroxidation in DM, will examine the mechanisms and clinical readouts of oxidative stress in this setting, the relationship between lipid peroxidation and antioxidant status in type 1 and type 2 DM, the effects of hyperglycemia and metabolic control on in vivo markers of lipid peroxidation (i.e., isoprostanes), and the association between isoprostane formation and platelet activation. Finally, possible targets of antioxidant therapy for diabetic vascular complications will be discussed.

We investigated whether the glomerular synthesis of prostacyclin modulates the renal blood flow and glomerular filtration rate in chronic glomerular disease. The urinary excretion of 6-keto-prostaglandin F1 alpha, a stable breakdown product of prostacyclin, was significantly (P less than 0.01) reduced in 20 women with chronic glomerular disease, as compared with 19 controls, whereas excretion of urinary prostaglandin E2 was unchanged. In 10 patients randomly assigned to one week of treatment with ibuprofen, excretion of urinary 6-keto-prostaglandin F1 alpha and prostaglandin E2 was reduced by 80 per cent, the level of serum creatinine was increased by 40 per cent, and creatinine and para-aminohippurate clearances were reduced by 28 and 35 per cent, respectively. The reduction of both clearances was inversely related (P less than 0.01) to the basal urinary excretion of 6-keto-prostaglandin F1 alpha but not of prostaglandin E2. No functional changes were detected in five healthy women, despite a similar suppression of renal prostacyclin synthesis by ibuprofen. In contrast, one week of treatment with sulindac did not affect renal prostacyclin synthesis or renal function in the other 10 patients, despite a marked inhibition of extrarenal cyclooxygenase activity. We conclude that in patients with mild impairment of renal function, the renal blood flow and glomerular filtration rate are critically dependent on prostacyclin production. In such patients sulindac may be a safe substitute for other nonsteroidal antiinflammatory drugs.

components of the nephron is based on immunofluorescent microscopy [12][13][14], separation of glomeruli and nephron segments with measurement of prostaglandin synthesis [15][16][17] or by cell cultures of specific components of the nephron with measurement of eicosanoid turnover [18][19][20][21][22].Some species variation exists and the majority of data are based on studies of rat, rabbit, and human kidney.In the cortex, the major sites of

This study was conducted to assess the thromboxane (TX) dependence of biochemical and functional indexes used to monitor the effect of low-dose aspirin. Functional assays of the antiplatelet effects of low-dose aspirin variably reflect the TX-dependent component of platelet aggregation. Previous studies of aspirin resistance were typically based on a single determination of platelet aggregation. We assessed the TXB2dependence of biochemical and functional indexes, as well as their intersubject and intrasubject variability during administration of the drug and after its withdrawal in 48 healthy volunteers randomized to receive aspirin 100 mg daily for 1 to 8 weeks. Serum TXB2was uniformly suppressed by 99% of baseline. Urinary 11-dehydro-TXB2, arachidonic acid-induced aggregation, and VerifyNow Aspirin (Accumetrics Inc., San Diego, California) showed stable, incomplete inhibition (65%, 80%, and 35%, respectively). Adenosine diphosphate- and collagen-induced aggregation was highly variable and poorly affected by aspirin, with an apparent time-dependent reversal. Inhibition of platelet cyclooxygenase activity was nonlinearly related to inhibition of platelet aggregation. Platelet function largely recovered by day 3 post-aspirin, independently of treatment duration. With any functional assay, occasionally “resistant” subjects were found to be “responders” on previous or subsequent determinations. Platelet cyclooxygenase activity, as reflected by serum TXB2levels, is uniformly and persistently suppressed by low-dose aspirin in healthy subjects. However, the effect of aspirin is variably detected by functional assays, potentially leading to misclassification of “responder” as “resistant” phenotypes owing to poor reproducibility of functional measurements. The nonlinearity of the relationship between inhibition of TX production and inhibition of platelet function has important clinical implications.

Interindividual variability in response to aspirin has been popularized as 'resistance'. We hypothesized that faster recovery of platelet cyclooxygenase-1 activity may explain incomplete thromboxane (TX) inhibition during the 24-h dosing interval.To characterize the kinetics and determinants of platelet cyclooxygenase-1 recovery in aspirin-treated diabetic and non-diabetic patients.One hundred type 2 diabetic and 73 non-diabetic patients on chronic aspirin 100 mg daily were studied. Serum TXB(2) was measured every 3 h, between 12 and 24 h after a witnessed aspirin intake, to characterize the kinetics of platelet cyclooxygenase-1 recovery. Patients with the fastest TXB(2) recovery were randomized to aspirin 100 mg once daily, 200 mg once daily or 100 mg twice daily, for 28 days and TXB(2) recovery was reassessed.Platelet TXB(2) production was profoundly suppressed at 12 h in both groups. Serum TXB(2) recovered linearly, with a large interindividual variability in slope. Diabetic patients in the third tertile of recovery slopes (≥ 0.10 ng mL(-1) h(-1) ) showed significantly higher mean platelet volume and body mass index, and younger age. Higher body weight was the only independent predictor of a faster recovery in non-diabetics. Aspirin 100 mg twice daily completely reversed the abnormal TXB(2) recovery in both groups. Interindividual variability in the recovery of platelet cyclooxygenase activity during the dosing interval may limit the duration of the antiplatelet effect of low-dose aspirin in patients with and without diabetes. Inadequate thromboxane inhibition can be easily measured and corrected by a twice daily regimen.

Graft failure occurs in a sizeable proportion of coronary artery bypass conduits. We herein review relevant current evidence to give an overview of the incidence, pathophysiology, and clinical consequences of this multifactorial phenomenon. Thrombosis, endothelial dysfunction, vasospasm, and oxidative stress are different mechanisms associated with graft failure. Intrinsic morphological and functional features of the bypass conduits play a role in determining failure. Similarly, characteristics of the target coronary vessel, such as the severity of stenosis, the diameter, the extent of atherosclerotic burden, and previous endovascular interventions, are important determinants of graft outcome and must be taken into consideration at the time of surgery. Technical factors, such as the method used to harvest the conduits, the vasodilatory protocol, the storage solution, and the anastomotic technique, also play a major role in determining graft success. Furthermore, systemic atherosclerotic risk factors, such as age, sex, diabetes mellitus, hypertension, and dyslipidemia, have been variably associated with graft failure. The failure of a coronary graft is not always correlated with adverse clinical events, which vary according to the type, location, and reason for failed graft. Intraoperative flow verification and secondary prevention using antiplatelet and lipid-lowering agents can help reducing the incidence of graft failure.

The place of aspirin in primary prevention remains controversial, with North American and European organizations issuing contradictory treatment guidelines. More recently, the U.S. Preventive Services Task Force recommended “initiating low-dose aspirin use for the primary prevention of cardiovascular disease (CVD) and colorectal cancer in adults aged 50 to 59 years who have a 10% or greater 10-year CVD risk, are not at increased risk for bleeding, have a life expectancy of at least 10 years, and are willing to take low-dose aspirin daily for at least 10 years.” This recommendation reflects increasing evidence for a chemopreventive effect of low-dose aspirin against colorectal (and other) cancer. The intent of this paper is to review the evidence supporting a chemopreventive effect of aspirin, discuss its potential mechanism(s) of action, and provide a conceptual framework for assessing current guidelines in the light of ongoing studies.

The clinical pharmacology of antiplatelet drugs has been reviewed previously by the European Society of Cardiology (ESC) Task force and by the 8th American College of Chest Physicians (ACCP) Evidence-Based Clinical Practice Guidelines. Moreover, information on the efficacy and safety of antiplatelet drugs in the treatment and prevention of atherothrombosis is provided by collaborative meta-analyses of 287 secondary prevention trials and 6 primary prevention trials. The present document intends to provide practicing physicians with an updated instrument to guide their choice of the most suitable antiplatelet strategy for the individual patient at risk, or with different clinical manifestations, of atherothrombosis.

Abstract Essential thrombocythemia (ET) is characterized by enhanced platelet generation and thrombotic complications. Once-daily low-dose aspirin incompletely inhibits platelet thromboxane A2 (TXA2) in the majority of ET patients. In the present study, we investigated the determinants of aspirin-insensitive platelet TXA2 biosynthesis and whether it could be further suppressed by changing the aspirin dose, formulation, or dosing interval. In 41 aspirin-treated ET patients, the immature platelet count predicted serum TXB2 independently of platelet count, age, JAK-2 V617F mutation, or cytoreduction (β = 3.53, P = .001). Twenty-one aspirin-treated patients with serum TXB2 ≥ 4 ng/mL at 24 hours after dosing were randomized to the following 7-day regimens in a crossover design: enteric-coated aspirin 100 mg twice daily, enteric-coated aspirin 200 mg once daily, or plain aspirin 100 mg once daily. A twice-daily regimen caused a further 88% median (IQR, 78%-92%, P &lt; .001) TXB2 reduction and normalized the functional platelet response to aspirin, as assessed by urinary 11-dehydro-TXB2 excretion and the VerifyNow Aspirin assay. Doubling the aspirin dose reduced serum TXB2 only partially by 39% median (IQR, 29%-54%, P &lt; .05). We conclude that the abnormal megakaryopoiesis characterizing ET accounts for a shorter-lasting antiplatelet effect of low-dose aspirin through faster renewal of platelet cyclooxygenase-1, and impaired platelet inhibition can be rescued by modulating the aspirin dosing interval rather than the dose.

Acetylsalicylic acid (aspirin) is a prototypic cyclooxygenase (COX) inhibitor. It was synthesized serendipitously from a natural compound, i.e., salicylic acid, with known analgesic activity. This chemical modification, obtained for the first time in an industrial environment in 1897, endowed aspirin with the unique capacity of acetylating and inactivating permanently COX-isozymes. Traditional nonsteroidal anti-inflammatory drugs (tNSAIDs) were developed to mimic the pharmacological effects of aspirin, using aspirin-sensitive experimental models of pain and inflammation as the template for screening new chemical entities. Among the tNSAIDs, some were endowed with moderate COX- selectivity (e.g., diclofenac), but no studies of sufficient size and duration were performed to show any clinically relevant difference between different members of the class. Similarly, no serious attempts were made to unravel the mechanisms involved in the shared therapeutic and toxic effects of tNSAIDs until the discovery of COX-2. This led to characterizing their main therapeutic effects as being COX-2-dependent and their gastrointestinal (GI) toxicity as being COX-1-dependent, and provided a rationale for developing a new class of selective COX-2 inhibitors, the coxibs. This review will discuss the clinical pharmacology of tNSAIDs and coxibs, and the clinical read-outs of COX-isozyme inhibition. This article is part of a Special Issue entitled “Oxygenated metabolism of PUFA: analysis and biological relevance.”

BackgroundGastroprotectant drugs are used for the prevention and treatment of peptic ulcer disease and might reduce its associated complications, but reliable estimates of the effects of gastroprotectants in different clinical settings are scarce. We aimed to examine the effects of proton-pump inhibitors (PPIs), prostaglandin analogues, and histamine-2 receptor antagonists (H2RAs) in different clinical circumstances by doing meta-analyses of tabular data from all relevant unconfounded randomised trials of gastroprotectant drugs.MethodsWe searched MEDLINE and Embase from Jan 1, 1950, to Dec 31, 2015, to identify unconfounded, randomised trials of a gastroprotectant drug (defined as a PPI, prostaglandin analogue, or H2RA) versus control, or versus another gastroprotectant. Two independent researchers reviewed the search results and extracted the prespecified outcomes and key characteristics for each trial. We did meta-analyses of the effects of gastroprotectant drugs on ulcer development, bleeding, and mortality overall, according to the class of gastroprotectant, and according to the individual drug within a gastroprotectant class.FindingsWe identified comparisons of gastroprotectant versus control in 849 trials (142 485 participants): 580 prevention trials (110 626 participants), 233 healing trials (24 033 participants), and 36 trials for the treatment of acute upper gastrointestinal bleeding (7826 participants). Comparisons of one gastroprotectant drug versus another were available in 345 trials (64 905 participants), comprising 160 prevention trials (32 959 participants), 167 healing trials (28 306 participants), and 18 trials for treatment of acute upper gastrointestinal bleeding (3640 participants). The median number of patients in each trial was 78 (IQR 44·0–210·5) and the median duration was 1·4 months (0·9–2·8). In prevention trials, gastroprotectant drugs reduced development of endoscopic ulcers (odds ratio [OR] 0·27, 95% CI 0·25–0·29; p<0·0001), symptomatic ulcers (0·25, 0·22–0·29; p<0·0001), and upper gastrointestinal bleeding (0·40, 0·32–0·50; p<0·0001), but did not significantly reduce mortality (0·85, 0·69–1·04; p=0·11). Larger proportional reductions in upper gastrointestinal bleeding were observed for PPIs than for other gastroprotectant drugs (PPIs 0·21, 99% CI 0·12–0·36; prostaglandin analogues 0·63, 0·35–1·12; H2RAs 0·49, 0·30–0·80; phet=0·0005). Gastroprotectant drugs were effective in preventing bleeding irrespective of the use of non-steroidal anti-inflammatory drugs (phet=0·56). In healing trials, gastroprotectants increased endoscopic ulcer healing (3·49, 95% CI 3·28–3·72; p<0·0001), with PPIs more effective (5·22, 99% CI 4·00–6·80) than prostaglandin analogues (2·27, 1·91–2·70) and H2RAs (3·80, 3·44–4·20; phet<0·0001). In trials among patients with acute bleeding, gastroprotectants reduced further bleeding (OR 0·68, 95% CI 0·60–0·78; p<0·0001), blood transfusion (0·75, 0·65–0·88; p=0·0003), further endoscopic intervention (0·56, 0·45–0·70; p<0·0001), and surgery (0·72, 0·61–0·84; p<0·0001), but did not significantly reduce mortality (OR 0·90, 0·72–1·11; p=0·31). PPIs had larger protective effects than did H2RAs for further bleeding (phet=0·0107) and blood transfusion (phet=0·0130).InterpretationGastroprotectants, in particular PPIs, reduce the risk of peptic ulcer disease and its complications and promote healing of peptic ulcers in a wide range of clinical circumstances. However, this meta-analysis might have overestimated the benefits owing to small study bias.FundingUK Medical Research Council and the British Heart Foundation.

Contemporary medicine is shifting towards person rather than disease-oriented care.1 With increasing life expectancy and the ageing of baby boomers, the proportion over 60 years is growing faster than the overall population, with worldwide estimates reaching 2 billion by 2050 (http://www.un.org/esa/population/publications/worldageing19502050).2 In parallel, acute coronary syndromes (ACS) and atrial fibrillation (AF)—the most frequent indications for dual platelet inhibition or anticoagulation—occur mostly in older patients.2–6 There is general agreement that people ≥75 years can be defined ‘elderly’; however, cutoffs as low as 65 years have been applied to important clinical datasets and risk scores.3,7–10 Moreover, ageing is a continuous process and life-span expansion is deflating (http://www.nber.org/papers/w18407). For these reasons, a threshold to define ‘elderly’ has been intentionally avoided in this document. Of note, over one third of patients admitted with acute myocardial infarction (MI) and two thirds dying from MI are over 75 years, but <7% of patients in ACS trials are reported ≥75 years.11 Older patients have multi-organ changes, increased risk of both bleeding and ischaemic events,3,5,12 frequent comorbidities/comedication, and reduced adherence to prescriptions. Given the challenges of antithrombotic treatment in the elderly, the European Society of Cardiology (ESC) Working Group on Thrombosis gathered a task group to address the topic. Antiplatelet, anticoagulant, and fibrinolytic drugs can prevent, postpone, or attenuate the severity of thrombotic events—namely stroke, transient ischaemic attack (TIA), MI, systemic embolism (SE), deep vein thrombosis (DVT), or pulmonary embolism (PE)—and retard cardiovascular and all-cause death, but at the cost of increased bleeding. The critical conundrum is whether, in the older patient, the benefits outweigh the …

Antiplatelet drugs provide first-line antithrombotic therapy for the management of acute ischemic syndromes (both coronary and cerebrovascular) and for the prevention of their recurrence. Their role in the primary prevention of atherothrombosis remains controversial because of the uncertain balance of the potential benefits and risks when combined with other preventive strategies. The aim of this consensus document is to review the evidence for the efficacy and safety of antiplatelet drugs, and to provide practicing cardiologists with an updated instrument to guide their choice of the most appropriate antiplatelet strategy for the individual patient presenting with different clinical manifestations of coronary atherothrombosis, in light of comorbidities and/or interventional procedures.

Post-acute sequelae of SARS-CoV-2 (PASC), also known as Post-Covid Syndrome, and colloquially as Long Covid, has been defined as a constellation of signs and symptoms which persist for weeks or months after the initial SARS-CoV-2 infection. PASC affects a wide range of diverse organs and systems, with manifestations involving lungs, brain, the cardiovascular system and other organs such as kidney and the neuromuscular system. The pathogenesis of PASC is complex and multifactorial. Evidence suggests that seeding and persistence of SARS-CoV-2 in different organs, reactivation, and response to unrelated viruses such as EBV, autoimmunity, and uncontrolled inflammation are major drivers of PASC. The relative importance of pathogenetic pathways may differ in different tissue and organ contexts. Evidence suggests that vaccination, in addition to protecting against disease, reduces PASC after breakthrough infection although its actual impact remains to be defined. PASC represents a formidable challenge for health care systems and dissecting pathogenetic mechanisms may pave the way to targeted preventive and therapeutic approaches.

F2-isoprostanes are bioactive prostaglandin (PG)-like compounds that are produced from arachidonic acid through a nonenzymatic process of lipid peroxidation catalyzed by oxygen free-radicals. 8-Epi-PGF2 alpha may amplify the platelet response to agonists, circulates in plasma, and is excreted in urine. We examined the hypothesis that the formation of 8-epi-PGF2 alpha is altered in patients with hypercholesterolemia and contributes to platelet activation in this setting. Urine samples were obtained from 40 hypercholesterolemic patients and 40 age- and sex-matched control subjects for measurement of immunoreactive 8-epi-PGF2 alpha. Urinary excretion of 11-dehydro-thromboxane (TX) B2, a major metabolite of TXA2, was measured as an in vivo index of platelet activation. Low-dose aspirin, indobufen, and vitamin E were used to investigate the mechanism of formation and effects of 8-epi-PGF2 alpha on platelet activation. Urinary 8-epi-PGF2 alpha was significantly (P = .0001) higher in hypercholesterolemic patients than in control subjects: 473 +/- 305 versus 205 +/- 95 pg/mg creatinine. Its rate of excretion was inversely related to the vitamin E content of LDL and showed a positive correlation with urinary 11-dehydro-TXB2. Urinary 8-epi-PGF2 alpha was unchanged after 2-week dosing with aspirin and indobufen despite complete suppression of TX metabolite excretion. Vitamin E supplementation was associated with dose-dependent reductions in both urinary 8-epi-PGF2 alpha and 11-dehydro-TXB2 by 34% to 36% and 47% to 58% at 100 and 600 mg daily, respectively. We conclude that the in vivo formation of the F2-isoprostane 8-epi-PGF2 alpha is enhanced in the vast majority of patients with hypercholesterolemia. This provides an aspirin-insensitive mechanism possibly linking lipid peroxidation to amplification of platelet activation in the setting of hypercholesterolemia. Dose-dependent suppression of enhanced 8-epi-PGF2 alpha formation by vitamin E supplementation may contribute to the beneficial effects of antioxidant treatment.

Cyclooxygenase (COX)-1 or -2 and prostaglandin (PG) synthases catalyze the formation of various PGs and thromboxane (TX) A(2). We have investigated the expression and activity of COX-1 and -2 during human megakaryocytopoiesis. We analyzed megakaryocytes from bone marrow biopsies and derived from thrombopoietin-treated CD34(+) hemopoietic progenitor cells in culture. Platelets were obtained from healthy donors and patients with high platelet regeneration because of immune thrombocytopenia or peripheral blood stem cell transplantation. By immunocytochemistry, COX-1 was observed in CD34(+) cells and in megakaryocytes at each stage of maturation, whereas COX-2 was induced after 6 days of culture, and remained detectable in mature megakaryocytes. CD34(+) cells synthesized more PGE(2) than TXB(2) (214 +/- 50 vs. 30 +/- 10 pg/10(6) cells), whereas the reverse was true in mature megakaryocytes (TXB(2) 8,440 +/- 2,500 vs. PGE(2) 906 +/- 161 pg/10(6) cells). By immunostaining, COX-2 was observed in <10% of circulating platelets from healthy controls, whereas up to 60% of COX-2-positive platelets were found in patients. A selective COX-2 inhibitor reduced platelet production of both PGE(2) and TXB(2) to a significantly greater extent in patients than in healthy subjects. Finally, we found that COX-2 and the inducible PGE-synthase were coexpressed in mature megakaryocytes and in platelets. We conclude that both COX-isoforms contribute to prostanoid formation during human megakaryocytopoiesis and that COX-2-derived PGE(2) and TXA(2) may play an unrecognized role in inflammatory and hemostatic responses in clinical syndromes associated with high platelet turnover.

Journal of Thrombosis and HaemostasisVolume 1, Issue 8 p. 1710-1713 Free Access Aspirin resistance: definition, mechanisms and clinical read-outs C. Patrono, C. Patrono University of Rome 'La Sapienza', Rome, ItalySearch for more papers by this author C. Patrono, C. Patrono University of Rome 'La Sapienza', Rome, ItalySearch for more papers by this author First published: 19 June 2003 https://doi.org/10.1046/j.1538-7836.2003.00284.xCitations: 195 Professor Carlo Patrono, Università di Roma 'La Sapienza, Ospedale Sant'Andrea, Via di Grottarossa 1035, 00189 Roma, Italy. Tel.: +39 0871 541260; fax: +39 0871 541261; e-mail: cpatrono@unich.it AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat The term 'aspirin resistance' has been used to describe a number of different phenomena, including the inability of aspirin to: (i) protect individuals from thrombotic complications; (ii) cause a prolongation of the bleeding time; (iii) inhibit thromboxane (TX) biosynthesis; or (iv) produce an anticipated effect on one or more in vitro tests of platelet function [1]. The fact that some patients may experience recurrent vascular events despite long-term aspirin therapy should be properly labeled as 'treatment failure' rather than aspirin resistance. This is a common phenomenon occurring with any drug (e.g. lipid-lowering or antihypertensive drugs). Given the multifactorial nature of atherothrombosis, it is not surprising that only a fraction (usually one-quarter to one-third) of all vascular complications can be prevented by any single preventive strategy (Fig. 1). Figure 1Open in figure viewerPowerPoint The risk of vascular complications is the major determinant of the absolute benefit of preventive strategies. Data are plotted from placebo-controlled trials of aspirin (○), statins (□) and antihypertensive drugs (▵) in different clinical settings. For each category of patients, the abscissa denotes the absolute risk of experiencing a major vascular event as recorded in the placebo arm of the trial(s). The absolute benefit of the preventive treatment is reported on the ordinate as the number of subjects in whom an important vascular event (non-fatal myocardial infarction, non-fatal stroke, or vascular death) is actually prevented by treating 1000 subjects for 1 year. MI, myocardial infarction; CHD, coronary heart disease; HC, hypercholesterolemic subjects; EH, essential hypertensives. Modified from [1]. Platelet aggregation studies A variable proportion (up to one-quarter) of patients with cerebrovascular disease achieve only partial inhibition of platelet aggregation at initial testing, and some (up to one-third) seem to develop 'resistance' to aspirin over time, even with increasing doses [2-4]. The results of these long-term studies carried out by Helgason et al. are at variance with those of a short-term study of Weksler et al. [5] showing that 40 mg aspirin daily inhibited platelet aggregation and thromboxane A2 (TXA2) formation as effectively as higher doses of aspirin in patients who had recent cerebral ischemia [5]. Variable platelet responses to aspirin have also been described in patients with peripheral arterial disease and with ischemic heart disease. In the study of Buchanan and Brister [6], aspirin 'non-responders' were identified on the basis of bleeding time measurements. Approximately 40% of patients undergoing elective coronary artery bypass grafting showed no prolongation of bleeding time in response to aspirin. This was associated with increased platelet adhesion and 12-HETE synthesis. In contrast, repeated measurements of platelet aggregation carried out over 24 months of placebo-controlled treatment by Berglund and Wallentin [7] demonstrated that 100 patients with unstable coronary artery disease randomized to receive 75 mg aspirin daily in the RISC study had consistently reduced platelet aggregation without attenuation during long-term treatment. Based on measurements of platelet aggregation in response to arachidonate and ADP, 5 and 24% of patients with stable cardiovascular disease who were receiving aspirin (325 mg day−1 for at least 7 days) were defined as 'resistant' and 'semiresponders', respectively [8]. Similar results have been reported using the platelet function analyzer (PFA)-100 system, with approximately 35% of patients with a recent myocardial infarction [9] or ischemic cerebrovascular accident [10] being defined 'non-responders' to aspirin doses in the range of 75–160 mg daily. Platelets from aspirin-resistant patients were found to be more sensitive to the aggregating effect of ADP [11]. Moreover, platelet responsiveness to aspirin was found to be reduced in patients with hyperlipidemia [12]. Using a variety of techniques, including conventional aggregometry, shear stress-induced activation, and the expression of platelet surface receptors, Sane et al. [13] have recently reported that 57% of a group of 88 patients with documented heart failure who had been treated with aspirin 325 mg day−1 for at least 1 month showed 'aspirin-non-responsiveness'. The lack of appropriate controls (e.g. patients treated with another antiplatelet agent) in these studies precludes unequivocal interpretation of their findings. Only a properly controlled, randomized study would allow examining the influence of intrasubject variability in platelet aggregation over time, compliance with study medication and potential drug interactions on the repeated measurements of platelet function. 'Resistance' to thienopyridines has been reported recently [14, 15]. Several relatively small studies (n = 39–180) in stroke patients have suggested that aspirin 'resistance' may contribute to 'treatment failure', i.e. recurrent ischemic events while on antiplatelet therapy, and that doses higher than 500 mg may be more effective than lower doses in limiting this phenomenon [16-18]. The uncontrolled nature and small sample size of these studies makes it difficult to interpret the results. A much larger data-base failed to substantiate a dose-dependent effect of aspirin in stroke prevention [19], an effect that one would theoretically expect if aspirin 'resistance' could be overcome, at least in part, by increasing the daily dose of the drug. The apparent discrepancy between the theoretical predictions originating from studies of aspirin 'resistance' based on platelet aggregation measurements ex vivo and the actual findings of over 70 randomized clinical trials of aspirin prophylaxis in high-risk patients (Table 1) can be reconciled by acknowledging the limitations of platelet function studies. Thus, platelet aggregation as measured by conventional methods ex vivo has less than ideal intra- and intersubject variability and displays limited sensitivity to the effect of aspirin, often considered a 'weak' antiplatelet agent based on such measurements. In addition to technical variables, platelet aggregation responses among normal persons can vary with mental stress, age, gender, race, diet, and hematocrit level, and a person may have different responses on repeated determinations [20]. Moreover, the relevance of changes in this index of capacity to the actual occurrence of platelet activation and inhibition in vivo is largely unknown. Similarly, the bleeding time has serious problems of methodological standardization and is of limited value in predicting hemostatic competence. Table 1. Indirect comparison of aspirin doses reducing vascular events in high risk patients * Aspirin dose (mg day−1) Number of trials Number of patients Odds reduction (%) 500–1500 34 22451 19 ± 3 160–325 19 26513 26 ± 3 75–150 12 6776 32 ± 6 * Data from [ 19]. Interindividual variability in the response to antiplatelet agents As with any drug, it is not surprising that there is some interindividual variability in the response to low-dose aspirin. However, reliable assessment of its occurrence and prevalence would require a long-term controlled study comparing the degree and persistence of the antiplatelet effects of aspirin vis-à-vis another antiplatelet agent in a sizable group of patients requiring antiplatelet therapy. Clopidogrel would be an ideal comparator, because of similarities in the mechanism of action (permanent inactivation of a platelet protein), pharmacokinetics (short half-life of the active moiety) and once-daily regimen as with aspirin [1]. It should be noted, however, that while aspirin is currently used at doses that represent a 2.5- to 10-fold excess over the dose of 30 mg necessary and sufficient to fully inactivate platelet cyclooxygenase (COX)-1 activity upon repeated daily dosing [21], clopidogrel is used routinely at 1 × the dose that appears necessary and sufficient to fully inactivate platelet P2Y12 upon repeated daily dosing [1]. Thus, the main determinants of the interindividual variability in the antiplatelet effects of the two drugs are substantially different (Table 2). Table 2. Main determinants of the interindividual variability in the antiplatelet effects of aspirin and clopidogrel Determinant Aspirin Clopidogrel Dependence on systemic bioavailability No Yes Dependence on liver metabolism to active moiety No Yes Recommended dose: minimum effective dose for full pharmacodynamic effect 2–3 1 Relevance of pharmacodynamic interactions at the target site Yes ? Relevance of extra-platelet sources of the platelet agonist Yes No Reproduced from [1]. Aspirin-resistant thromboxane biosynthesis At least three potential mechanisms may underlie the occurrence of aspirin-resistant TXA2 biosynthesis. The transient expression of COX-2 in newly formed platelets [22] in clinical settings of enhanced platelet turn-over is a potentially important mechanism that deserves further investigation. Extra-platelet sources of TXA2 (e.g. monocyte/macrophage COX-2) may contribute to aspirin-insensitive TXA2 biosynthesis in acute coronary syndromes [23]. Furthermore, Catella-Lawson et al. [24] have recently reported that concomitant administration of non-steroidal anti-inflammatory drugs (NSAIDs) (e.g. ibuprofen) may interfere with the irreversible inactivation of platelet COX-1 by aspirin. This is due to competition for a common docking site within the cyclooxygenase channel (Arg120), which aspirin binds to with weak affinity prior to irreversible acetylation of Ser529 [1]. This pharmacodynamic interaction does not occur with rofecoxib, or diclofenac, drugs endowed with variable COX-2 selectivity [25]. Thus, concomitant treatment with readily available over-the-counter NSAIDs may limit the cardioprotective effects of aspirin and contribute to aspirin 'resistance'. Investigative tools are readily available to evaluate potential sources of aspirin-resistant TXA2 biosynthesis (Table 3). Table 3. Analytical tools for assessing potential sources of aspirin-resistant thromboxane Source of resistance Analytical tool Non-compliance Serum TXB2 (– aspirin in vitro) Interaction with NSAID Serum TXB2 (2 & 24 hr sampling) Extra-platelet sources of TXA2 Urinary TXM (– selective COX-2 inhibitor in vivo) NSAID, nonsteroidal antiinflammatory drug; TXM, thromboxane metabolite (e.g., 11-dehydro-TXB2) Clinical read-outs of aspirin resistance Several recent observational studies suggest that concomitant use of ibuprofen and low-dose aspirin may impair the antithrombotic efficacy of the latter [25, 26], consistently with the pharmacodynamic interaction described by Catella-Lawson et al. [24]. In addition, the clinical relevance of aspirin-resistant TXA2 biosynthesis has been explored by Eikelboom et al. [27] who performed a nested case-control study of baseline urinary thromboxane metabolite excretion in relation to the occurrence of major vascular events in aspirin-treated high-risk patients enrolled in the HOPE trial. After adjustment for baseline differences, the odds for the composite outcome of myocardial infarction, stroke, or cardiovascular death increased with each increasing quartile of 11-dehydro-TXB2 excretion, with patients in the upper quartile having a 1.8-times higher risk than those in the lower quartile (Fig. 2). However, both observational and case-control studies suffer from potential confounding and cannot reliably establish a cause-effect relationship between aspirin-resistant TXA2 biosynthesis and enhanced risk of vascular events. Figure 2Open in figure viewerPowerPoint Association between quartiles of urinary 11-dehydro-TXB2 excretion and composite of myocardial infarction, stroke or cardiovascular death, after adjustment for baseline differences between cases and control high-risk, aspirin-treated patients recruited in the HOPE trial. The P-value is for trend of association. MI, myocardial infarction. Reproduced from [27] with permission from the American Heart Association, Inc. How to test the clinical relevance of aspirin-resistant thromboxane biosynthesis? These interesting findings provide a rationale for testing the efficacy and safety of additional treatments that more effectively block in vivo TXA2 biosynthesis or action in a subset of high-risk patients displaying aspirin-resistant TXA2 biosynthesis. Highly selective COX-2 inhibitors (e.g. rofecoxib, etoricoxib or lumiracoxib: see [25]) could be used in phase II dose-finding studies with a primary biochemical end-point (i.e. urinary 11-dehydro-TXB2 excretion) in the appropriate clinical setting. Although concerns have been expressed on their cardiovascular safety because of inhibition of COX-2-dependent PGI2 production [28], it should be recognized that several endothelial mediators of thromboresistance and vasoregulation exist, including COX-1-dependent PGI2. In addition, any hazard deriving from COX-2 inhibition on top of low-dose aspirin would be shared by any NSAID, regardless of COX-2 selectivity [29]. Thromboxane receptor (TP) antagonists would offer the advantage vis-à-vis coxibs of not interfering with PGI2 production. In addition, they might antagonize the platelet and vascular effects of biologically active F2-isoprostanes acting as incidental ligands of TP receptors [30] (Fig. 3). A draw-back in performing dose-finding studies with a TP antagonist would be the lack of a suitable biochemical end-point related to aspirin-resistant TXA2 biosynthesis. Figure 3Open in figure viewerPowerPoint Antagonism of aspirin-insensitive thromboxane receptor (TP) agonists. The scheme illustrates enzymatic as well as non-enzymatic pathways of arachidonic acid metabolism generating agonists of the platelet and vascular TP receptors that are largely insensitive to inhibition by low-dose aspirin. These include TXA2 derived from COX-2 expressing cells and F2-isoprostanes, e.g. 8-iso-PGF2α.PG, prostaglandin; COX, cyclooxygenase; TX, thromboxane; TP, thromboxane A2 receptor. Conclusions Early reports of aspirin 'resistance' based on platelet aggregation measurements represent descriptive phenomenology of difficult interpretation because of the uncontrolled nature of the observations and lack of a mechanistic insight. It is perhaps important to remember that platelet aggregation measurements have not been particularly useful in describing the human pharmacology of aspirin. In fact, the development of low-dose aspirin as an antiplatelet agent was largely based on measurements of serum TXB2, i.e. a mechanism-based biochemical end-point [31]. On the other hand, recent progress has been made in characterizing aspirin-insensitive or aspirin-resistant TXA2 biosynthesis in terms of potential mechanisms, biochemical and clinical read-outs. Thus, there may be clinical circumstances under which the mechanism(s) and cellular source(s) of TXA2 biosynthesis are inadequately blocked by conventional antiplatelet doses of aspirin. The clinical relevance of this phenomenon deserves further investigation. If we go back to the best characterized example of drug resistance, i.e. resistance to antimicrobial agents, we know that this may be related to: (i) the drug not reaching the target; (ii) the drug being inactivated; and/or (iii) the drug target being altered. If we apply this reading frame to aspirin, we can think of the first possibility concerning the pharmacodynamic interaction with ibuprofen at Arg120 preventing aspirin to access Ser529; the second might apply to aspirin being extensively hydrolyzed by esterases in the gastrointestinal mucosa before it gets a chance of seeing platelets in the portal blood, but we have little evidence for this phenomenon; as far as the third mechanism is concerned, we only have a published example of COX-1 polymorphism that enhances not diminishes aspirin-induced COX-1 inhibition [32]. Physicians should be aware of potential interactions with concurrently (self-)prescribed drugs that may limit the desired pharmacodynamic effect of aspirin. 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Table 1 Incidence rates of major events possibly prevented or caused by COX inhibitors, as assessed in observational studies among non-users Event Incidence rate per 1,000 patient-years Heart failure 2-4 Myocardial infarction 1-4 Upper GI bleeding/perforation 0.6-1.7 Colorectal cancer 0.4-0.7 Acute renal failure 0.02-0.08

Thromboxane A2 (TXA2) biosynthesis is enhanced in the majority of patients with type IIa hypercholesterolemia. Because simvastatin (a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor) was previously shown to reduce platelet aggregation and TXB2 production ex vivo, we investigated TXA2 biosynthesis and platelet function in 24 patients with type IIa hypercholesterolemia randomized to receive in a double-blind fashion simvastatin (20 mg/d) or placebo for 3 months. The urinary excretion of 11-dehydro-TXB2, largely a reflection of platelet TXA2 production in vivo, was measured by a previously validated radioimmunoassay technique. Blood lipid levels and urinary 11-dehydro-TXB2 excretion were significantly (P < .001) reduced by simvastatin. In contrast, placebo-treated patients did not show any statistically significant changes in either blood lipids or 11-dehydro-TXB2 excretion. The reduction in 11-dehydro-TXB2 associated with simvastatin was correlated with the reduction in total cholesterol (r = .81, P < .0001), LDL cholesterol (r = .79, P < .0001), and apolipoprotein B (r = .76, P < .0001) levels. Platelets from patients with type IIa hypercholesterolemia required significantly (P < .01) more collagen and ADP to aggregate and synthesized less TXB2 in response to both agonists after simvastatin therapy. Bleeding time, platelet sensitivity to Iloprost, and blood lipoprotein(a) and HDL cholesterol levels were not significantly affected by either treatment. We conclude that enhanced TXA2 biosynthesis in type IIa hypercholesterolemia is, at least in part, dependent on abnormal cholesterol levels and/or other simvastatin-sensitive mechanisms affecting platelet function.

We have measured the excretion of a major urinary metabolite of thromboxane B2 (TxB2), i.e., 2,3-dinor-TxB2, during the infusion of exogenous TxB2 over a 50-fold dose range to enable estimation of the rate entry of endogenous TxB2 into the bloodstream. Four healthy male volunteers received 6-h i.v. infusions of venhicle alone and TxB2 at 0.1, 1.0, and 5.0 ng/kg X min in random order. They were pretreated with aspirin at a dose of 325 mg/d in order to suppress endogenous TxB2 production. Urinary 2,3-dinor-TxB2 was measured before, during, and up to 24 h after the infusions and in aspirin-free periods, by means of radioimmunoassay. The nature of the extracted immunoreactivity was characterized by thin-layer chromatography and confirmed by negative ion-chemical ionization gas chromatography/mass spectrometry. Aspirin treatment suppressed urinary 2,3-dinor-TxB2 excretion by 80%. The fractional elimination of 2,3-dinor-TxB2 was independent of the rate of TxB2 infusion and averaged 5.3 +/- 0.8%. Interpolation of metabolite values obtained in aspirin-free periods onto the linear relationship between the quantities of infused TxB2 and the amount of metabolite excreted in excess of control values (y = 0.0066x, r = 0.975, P less than 0.001) permitted calculation of the mean rate of entry of endogenous TxB2 into the circulation as 0.11 ng/kg X min. The rate of disappearance of immunoreactive TxB2 from the circulation was monoexponential over the first 10 min with an apparent half-life of 7 min. This corresponded to a maximal estimate of the plasma concentration of endogenous TxB2 of 2.0 pg/ml. These results suggest that ex vivo platelet activation and/or analytical problems confound estimates of endogenous thromboxane release based on plasma TxB2 and provide a rationale for seeking longer-lived enzymatic metabolites of TxB2 in plasma.

The current controversy on the potential cardioprotective effect of naproxen prompted us to evaluate the extent and duration of platelet, monocyte, and vascular cyclooxygenase (COX) inhibition by naproxen compared with low-dose aspirin.We performed a crossover, open-label study of low-dose aspirin (100 mg/d) or naproxen (500 mg BID) administered to 9 healthy subjects for 6 days. The effects on thromboxane (TX) and prostacyclin biosynthesis were assessed up to 24 hours after oral dosing. Serum TXB2, plasma prostaglandin (PG) E2, and urinary 11-dehydro-TXB2 and 2,3-dinor-6-keto-PGF(1alpha) were measured by previously validated radioimmunoassays. The administration of naproxen or aspirin caused a similar suppression of whole-blood TXB2 production, an index of platelet COX-1 activity ex vivo, by 94+/-3% and 99+/-0.3% (mean+/-SD), respectively, and of the urinary excretion of 11-dehydro-TXB2, an index of systemic biosynthesis of TXA2 in vivo, by 85+/-8% and 78+/-7%, respectively, that persisted throughout the dosing interval. Naproxen, in contrast to aspirin, significantly reduced systemic prostacyclin biosynthesis by 77+/-19%, consistent with differential inhibition of monocyte COX-2 activity measured ex vivo.The regular administration of naproxen 500 mg BID can mimic the antiplatelet COX-1 effect of low-dose aspirin. Naproxen, unlike aspirin, decreased prostacyclin biosynthesis in vivo.

The International Consensus Meeting on the Mode of Action of COX-2 Inhibition (ICMMAC) brought together 17 international experts in arthritis, gastroenterology and pharmacology on 5–6 December 1997. The meeting was convened to provide a definition of COX-2 specificity and to consider the clinical relevance of COX-2-specific agents. These compounds are a new class of drugs that specifically inhibit the enzyme COX-2 while having no effect on COX-1 across the whole therapeutic dose range. The objectives of the meeting were to review the currently available data regarding the roles and biology of COX-1 and COX-2, and to foster a consensus definition on COX-2 specificity. At the present time, no guidelines exist for the in vitro and in vivo assessment of COX specificity, and it was felt that consensus discussion might clarify some of these issues. The meeting also reviewed recent clinical data on COX-2-specific inhibitors. The following article reflects discussion at this meeting and provides a consensus definition of COX-2-specific inhibitors.

THE OBJECTIVES OF THIS INVESTIGATION WERE: (a) to characterize the time and dose dependence of the effects of prostacyclin (PGI(2)) on renin release in healthy men; (b) to define whether PGI(2)-induced renin release is secondary to hemodynamic changes; (c) to determine the plasma and urine concentrations of 6-keto-PGF(1alpha) (the stable breakdown product of PGI(2)) associated with renin release induced by exogenous or pharmacologically enhanced endogenous PGI(2). Intravenous PGI(2) or 6-keto-PGF(1alpha) infusions at nominal rates of 2.5, 5.0, 10.0, and 20.0 ng/kg per min were performed in each of six normal human subjects; in three of them, PGI(2) infusion was repeated after beta-adrenergic blockade and cyclooxygenase inhibition. PGI(2), but not 6-keto-PGF(1alpha), caused a time- and dose-dependent increase of plasma renin activity, which reached statistical significance at 5.0 ng/kg per min and was still significantly elevated 30 min after discontinuing the infusion. Although combined propranolol and indomethacin treatment significantly enhanced the hypotensive effects of infused PGI(2), it did not modify the dose-related pattern of PGI(2)-induced renin release. Plasma 6-keto-PGF(1alpha) levels rose from undetectable levels (<7.5 pg/ml) in a stepwise fashion during increasingly higher infusion rates of PGI(2) or 6-keto-PGF(1alpha). The threshold concentration of plasma 6-keto-PGF(1alpha) associated with a statistically significant stimulation of renin release was approximately 200 pg/ml. Upon discontinuing PGI(2) or 6-keto-PGF(1alpha) infusion, the disappearance of 6-keto-PGF(1alpha) from blood showed an identical biphasic behavior, the initial phase having an apparent t((1/2)) of 3.2 min. The intravenous infusion of furosemide, which is known to stimulate renin release via a cyclooxygenase-dependent mechanism, caused a three-to fourfold increase of urinary 6-keto-PGF(1alpha) excretion rate, concomitant with the elevation of plasma renin activity levels, in six healthy women. 6-Keto-PGF(1alpha) remained undetectable in peripheral venous plasma throughout the study. WE CONCLUDE THAT IN HUMAN SUBJECTS: (a) PGI(2)-induced renin release occurs with a dose and time dependence similar to its reported platelet effects; (b) PGI(2)-induced renin release is not mediated by adrenergic stimuli or cyclooxygenase-dependent mechanisms secondary to hemodynamic changes; (c) furosemide-induced renin release is associated with increased renal PGI(2) formation; and (d) PGI(2) appears to act as a local modulator rather than a circulating hormone in controlling juxtaglomerular function.

Unstable angina is associated with enhanced lipid peroxidation and reduced antioxidant defenses. We have previously reported aspirin failure in the suppression of enhanced thromboxane (TX) biosynthesis in a subset of episodes of platelet activation in this setting. We tested the hypothesis that the in vivo formation of the F(2)-isoprostane 8-iso-prostaglandin (PG)F(2alpha), a bioactive product of arachidonic acid peroxidation, is enhanced in unstable angina and contributes to aspirin-insensitive TX biosynthesis.Urine samples were obtained from patients with unstable angina (n=32), stable angina (n=32), or variant angina (n=4) and from 40 healthy subjects for the measurement of immunoreactive 8-iso-PGF(2alpha) and 11-dehydro-TXB(2). 8-Iso-PGF(2alpha) excretion was significantly higher in patients with unstable angina (339+/-122 pg/mg creatinine) than in matched patients with stable angina (236+/-83 pg/mg creatinine, P:=0.001) and control subjects (192+/-71 pg/mg creatinine, P:<0.0001). In patients with unstable angina, 8-iso-PGF(2alpha) was linearly correlated with 11-dehydro-TXB(2) excretion (rho=0.721, P:<0.0001) and inversely correlated with plasma vitamin E (rho=-0.710, P:=0. 004). Spontaneous myocardial ischemia in patients with variant angina or ischemia elicited by a stress test in patients with stable angina was not accompanied by any change in 8-iso-PGF(2alpha) excretion, thus excluding a role of ischemia per se in the induction of increased F(2)-isoprostane production.These findings establish a putative biochemical link between increased oxidant stress and aspirin-insensitive TX biosynthesis in patients with unstable angina and provide a rationale for dose-finding studies of antioxidants in this setting.

Hypertensive patients with renovascular disease (RVD) may be exposed to increased oxidative stress, possibly related to activation of the renin-angiotensin system.We measured the urinary excretion of 8-iso-prostaglandin (PG) F2alpha and 11-dehydro-thromboxane (TX) B2 as indexes of in vivo lipid peroxidation and platelet activation, respectively, in 25 patients with RVD, 25 patients with essential hypertension, and 25 healthy subjects. Plasma renin activity in peripheral and renal veins, angiotensin II in renal veins, cholesterol, glucose, triglycerides, homocysteine, and antioxidant vitamins A, C, and E were also determined. Patients were also studied 6 months after a technically successful angioplasty of the stenotic renal arteries. Urinary 8-iso-PGF2alpha was significantly higher in patients with RVD (median, 305 pg/mg creatinine; range, 124 to 1224 pg/mg creatinine) than in patients with essential hypertension (median, 176 pg/mg creatinine; range, 48 to 384 pg/mg creatinine) or in healthy subjects (median, 123 pg/mg creatinine; range, 58 to 385 pg/mg creatinine). Urinary 11-dehydro-TXB2 was also significantly higher in RVD patients compared with healthy subjects. In RVD patients, urinary 8-iso-PGF2alpha correlated with 11-dehydro-TXB2 (r(s)=0.48; P<0.05) and renal vein renin (r(s)=0.67; P<0.005) and angiotensin II (r(s)=0.65; P=0.005) ratios. A reduction in 8-iso-PGF2alpha after angioplasty was observed in RVD patients with high baseline levels of lipid peroxidation. Changes in 8-iso-PGF2alpha were related to baseline lipid peroxidation (r(s)=-0.73; P<0.001), renal vein angiotensin II (r(s)=-0.70; P<0.01) and renin (r(s)=-0.63; P<0.05) ratios.Lipid peroxidation is markedly enhanced in hypertensive patients with RVD and is related to activation of the renin-angiotensin system. Moreover, persistent platelet activation triggered or amplified by bioactive isoprostanes may contribute to the progression of cardiovascular and renal damage in this setting.

We have examined the urinary excretion of stable immunoreactive eicosanoids in 23 female patients with systemic lupus erythematosus (SLE), 16 patients with chronic glomerular disease (CGD), and 20 healthy women. SLE patients had significantly higher urinary thromboxane B2 (TXB2) and prostaglandin (PG) E2 excretion and significantly lower 6-keto-PGF1 alpha than did healthy women. In contrast, CGD patients only differed from controls for having reduced 6-keto-PGF1 alpha excretion. The group of SLE patients with active renal lesions differed significantly from the group with inactive lesions for having a lower creatinine clearance and urinary 6-keto-PGF1 alpha and higher urinary TXB2. Higher urinary TXB2 excretion was associated with comparable platelet TXB2 production in whole blood, undetectable TXB2 in peripheral venous blood, and unchanged urinary excretion of 2,3-dinor-TXB2. A significant inverse correlation was found between urinary TXB2 and creatinine clearance rate (CCr). In contrast, the urinary excretion of 6-keto-PGF1 alpha showed a significant linear correlation with both CCr and para-aminohippurate clearance rate (CPAH). In four SLE and seven CGD patients, inhibition of renal cyclooxygenase activity by ibuprofen was associated with a significant reduction in urinary 6-keto-PGF1 alpha and TXB2 and in both CCr and CPAH. However, the average decrease in both clearances was 50% lower in SLE patients than in CGD patients, when fractionated by the reduction in urinary 6-keto-PGF1 alpha or PGE2 excretion. We conclude that the intrarenal synthesis of PGI2 and TXA2 is specifically altered in SLE. Such biochemical alterations are associated with changes in glomerular hemodynamics and may play a role in the progression of SLE nephropathy.

Background Previous studies relating increased thromboxane (TX) biosynthesis to cardiovascular risk factors do not answer the question whether platelet activation is merely a consequence of more prevalent atherosclerotic lesions or reflects the influence of metabolic and hemodynamic disturbances on platelet biochemistry and function. Methods and Results We examined 64 patients with large-vessel peripheral arterial disease and 64 age- and sex-matched control subjects. TXA 2 biosynthesis was investigated in relation to cardiovascular risk factors by repeated measurements of the urinary excretion of its major enzymatic metabolite, 11-dehydro-TXB 2 , by radioimmunoassay. Urinary 11-dehydro-TXB 2 was significantly ( P =.0001) higher in patients with peripheral arterial disease (57±26 ng/h) than in control subjects (26±7 ng/h). Seventy percent of patients had metabolite excretion &gt;2 SD above the normal mean. However, 11-dehydro-TXB 2 excretion was enhanced only in association with cardiovascular risk factors. Multivariate analysis showed that diabetes, hypercholesterolemia, and hypertension were independently related to 11-dehydro-TXB 2 excretion. During a median follow-up of 48 months, 8 patients experienced major vascular events. These patients had significantly ( P =.001) higher 11-dehydro-TXB 2 excretion at baseline than patients who remained event free. Conclusions The occurrence of large-vessel peripheral arterial disease per se is not a trigger of platelet activation in vivo. Rather, the rate of TXA 2 biosynthesis appears to reflect the influence of coexisting disorders such as diabetes mellitus, hypercholesterolemia, and hypertension on platelet biochemistry and function. Enhanced TXA 2 biosynthesis may represent a common link between such diverse risk factors and the thrombotic complications of peripheral arterial disease.

The antiplatelet effect of aspirin reduces the risk of clinical manifestations of atherothrombosis by approximately 25% in secondary prevention settings. Data are limited in primary prevention of coronary heart disease, and even more in women. Here, we estimate the effects of aspirin and non-aspirin nonsteroidal antiinflammatory drugs in the primary prevention of myocardial infarction in postmenopausal women. We followed a cohort of 164,769 women, 50-74 years of age, registered in the General Practice Research Database in the United Kingdom, from January 1991 through December 1995. For aspirin and non-aspirin nonsteroidal antiinflammatory drugs, the risk of myocardial infarction associated with current use was compared with risk in non-users, using a nested case-control analysis. Overall, the relative risk of myocardial infarction associated with current use of aspirin of more than 1 month's duration was 0.56 [95% confidence interval (95% CI) = 0.26-1.21], and that of nonfatal myocardial infarction was 0.28 (95% CI = 0.08-0.91). Chronic use of nonsteroidal antiinflammatory drugs was not associated with a protective effect (relative risk = 1.32; 95% CI = 0.97-1.81). These findings indicate that incomplete and reversible inhibition of platelet cyclooxygenase by non-aspirin nonsteroidal antiinflammatory drugs is not sufficient to produce clinically detectable cardiovascular protection comparable with that achieved by low-dose aspirin through irreversible inactivation of platelet cyclooxygenase.

A B S T R A C T A qualitative platelet abnormality and a bleeding tendency are frequently associated with renal failure and uremia.We demonstrated previously that uremic patients display an abnormal platelet aggregation to arachidonic acid and reduced malondi- aldehyde production in response to thrombin and ar- achidonic acid.The objectives of this investigation were: (a) to compare platelet prostaglandin (PG) and thromboxane (TX) production in whole blood and in platelet-rich plasma (PRP) of 21 uremic patients and 22 healthy subjects; (b) to evaluate the concentration and activity of platelet PG-and TX-forming enzymes; (c) to assess the functional responsiveness of the platelet TXA2/PGH2 receptor; (d) to explore the hemostatic consequences of partially reduced TXA2 production.Platelet immunoreactive TXB2 production during whole blood clotting was significantly reduced, by "60%, in uremic patients as compared to age-and sex-matched controls.Exogenous thrombin (5-30 IU/ ml) failed to restore normal TXB2 production in uremic platelets.Uremic PRP produced comparable or slightly higher amounts of TXB2 than normal PRP at arachidonate concentrations 0.25-1 mM.However, when exposed to substrate concentrations >2 mM, uremic PRP produced significantly less TXB2 than normal PRP.To discriminate between reduced arachidonic acid oxygenation and altered endoperoxide

Leukotrienes C4, D4, and E4 were isolated after incubation of rat brain tissue in vitro with the ionophore A23187 and arachidonic acid. Identification of the compounds was carried out using high-performance liquid chromatography, radioimmunoassay, and bioassay. Average production of leukotrienes C4, D4, and E4 during 10 min of incubation was estimated to 25, 8, and 0.7 pmol per g of brain tissue (wet weight), respectively. Radioimmunoassay determinations indicated in vitro biosynthesis of leukotriene C4 in most regions of the brain, with the highest levels obtained in the hypothalamus and the median eminence. In slices from the caudate nucleus, ionophore A23187 caused a dose-dependent stimulation of leukotriene C4 formation with maximal effect at 5 microM. Leukotriene C4 synthesis of rat brain tissue was inhibited by 30 microM nordihydroguaiaretic acid. Finally, using the indirect immunofluorescence technique, nerve endings in the median eminence and cell bodies in the preoptic area reacting with antibodies raised against leukotriene C4 were observed.

Because of the discrepancy between the capacity of platelets to synthesize thromboxane B2 ex vivo and the actual synthetic rate in vivo, measurement of thromboxane B2 in plasma is highly influenced by sampling-related artifacts. We have developed and validated a radioimmunoassay for a major enzymatic derivative of thromboxane B2 with an extended plasma half-life, i.e., 11-dehydrothromboxane B2. The binding of the tracer is displaced by as low as 1 pg/ml of the homologous ligand, with a high degree of specificity for the open ring structure as well as for the omega side-chain. This method can detect changes in the plasma concentration and urinary excretion of 11-dehydrothromboxane B2 associated with stimulated short-term increases of thromboxane B2 secretion in the human circulation.

We investigated whether platelets prime colon cancer cells for metastasis and whether pharmacological inhibition of platelet function may prevent it. Coculturing HT29 human colon carcinoma cells with human platelets led to the induction of mesenchymal-like cancer cells characterized by downregulation of E-cadherin and upregulation of Twist1, enhanced cell mobility and a proaggregatory action on platelets. These changes were prevented by different antiplatelet agents, aspirin[an inhibitor of cyclooxygenase(COX)-1], DG-041[an antagonist of prostaglandin(PG)E2 EP3 receptor] and ticagrelor (a P2Y12 receptor antagonist). The injection of HT29 cells, exposed to platelets in vitro, into the tail vein of humanized immunodeficient mice led to higher incidence of lung metastasis compared to the injection of untreated HT29 cells. This effect was associated with enhanced systemic biosynthesis of thromboxane(TX)A2 and PGE2in vivo. Platelet COX-1 inhibition by aspirin administration to mice prevented the increased rate of metastasis as well as the enhanced production of TXA2 and PGE2 induced by the in vitro priming of HT29 cells by platelets. In conclusion, targeting platelet COX-1 with low-dose aspirin exerts an antimetastatic action by averting the stem cell mimicry of cancer cells associated with enhanced proaggregatory effects induced by platelet-tumor cell interactions. These effects may be shared by other antiplatelet drugs.

Metabolic syndrome represents a clustering of risk factors related to an elevated risk of cardiovascular disease and type 2 diabetes. Occurrence of both metabolic syndrome and diabetes and their vascular complications share several pathogenetic features including subclinical, low-grade inflammation, altered oxidative/antioxidant status, and persistent platelet activation. Despite the availability of multiple interventions to counteract these metabolic changes, including appropriate diet, regular exercise, weight control and drugs, epidemiological data are witnessing the growing trend of the problem, reflecting both the multifactorial nature of these diseases as well as the scarce compliance of patients to established strategies. Several nutraceuticals used in clinical practice have been shown to target the pathogenesis of diabetes mellitus, metabolic syndrome and their complications and to favorably modulate a number of biochemical and clinical endpoints. These compounds include antioxidant vitamins, such as vitamins C and E, flavonoids, vitamin D, conjugated linoleic acid, omega-3 fatty acids, minerals such as chromium and magnesium, alpha-lipoic acid, phytoestrogens, and dietary fibers. Several areas of concern exist regarding the use of dietary supplements and nutraceuticals in this setting, including product standardization, definition of optimal dosing regimen, potential side effects, drug interactions, and need for evidence-based indications.

Working Group on ThrombosisOświadczenie: Wytyczne ESC reprezentują stanowisko tego towarzystwa i powstały po dokładnym uwzględnieniu wiedzy naukowej i medycznej oraz dowodów dostępnych w

This article is part of a joint Themed section with the British Journal of Pharmacology on Targeting Inflammation to Reduce Cardiovascular Disease Risk: a Realistic Clinical Prospect? The rest of the Themed section will appear in a future issue of BJP and will be available at http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1476-5381 Prostaglandin (PG) H synthase 2 [also referred to colloquially as cyclooxygenase (COX) 2] represents a key enzyme in arachidonic acid metabolism in health and disease. It is both constitutively expressed in several human tissues (e.g. kidney and brain) and induced in various cell types (including monocytes/macrophages, vascular endothelial cells and colorectal cancer cells) in response to inflammatory cytokines, laminar shear stress and growth factors. Products of COX-2 activity (e.g. PGE2 and prostacyclin) are involved in diverse physiological and pathophysiological processes, including renal haemodynamics and the control of blood pressure, endothelial thromboresistance, pain and inflammation, and colorectal tumorigenesis. Therefore, it is not surprising that COX-2 inhibitors display multifaceted clinical effects, ranging from reduced pain and inflammation to increased blood pressure, an increased risk of atherothrombotic events and a decreased risk of colorectal cancer. The aim of the present article was to review the cardiovascular effects of COX-2 inhibitors [traditional nonsteroidal anti-inflammatory drugs (tNSAIDs) and coxibs alike], with a focus on the mechanisms contributing to the clinical readouts of COX-2 inhibition.

Antithrombotic therapy and body mass : an expert position paper of the ESC Working Group on Thrombosis

Inactivation of platelet cyclooxygenase (COX)-1 by low-dose aspirin leads to long-lasting suppression of thromboxane (TX) A2 production and TXA2-mediated platelet activation and aggregation. This effect is necessary and sufficient to explain aspirin's unique (among other COX-1 inhibitors) effectiveness in preventing atherothrombosis, as well as its shared (with other antiplatelet agents) bleeding liability. However, different mechanisms of action have been suggested to explain other beneficial effects of aspirin, such as prevention of venous thromboembolism, chemoprevention of colorectal (and other) cancers, and reduced risk of dementia. These mechanisms include acetylation of other proteins in blood coagulation, inhibition of COX-2 activity, and other COX-independent mechanisms. The intent of this review is to develop the concept that the multifaceted therapeutic effects of low-dose aspirin may reflect pleiotropic consequences of platelet inhibition on pathophysiological tissue repair processes. Furthermore, the clinical implications of this concept will be discussed in terms of current clinical practice and future research.

The benefits of aspirin therapy for the secondary prevention of cardiovascular disease clearly outweigh the risks of bleeding, and low-dose aspirin is uniformly recommended in this setting. However, no clear consensus exists about whether, and if so in whom, aspirin therapy is appropriate for the primary prevention of cardiovascular disease. Three trials of low-dose aspirin versus placebo in three populations at increased risk of myocardial infarction or ischaemic stroke in the absence of established cardiovascular disease were reported in 2018. The ASPREE trial in elderly people was terminated early for futility because aspirin had no effect on disability-free survival but significantly increased the risk of major haemorrhage and, unexpectedly, all-cause mortality. In the ASCEND trial in patients with diabetes mellitus and no evidence of vascular disease, aspirin significantly reduced serious vascular events but increased major bleeding. In the ARRIVE trial in people with multiple risk factors for cardiovascular disease, aspirin had no effect on major cardiovascular events but increased gastrointestinal bleeding. The aim of this Review is to place these new results in the context of previous evidence on aspirin for the primary prevention of cardiovascular disease and to appraise whether the new evidence is likely to enable the more targeted use of aspirin in particular individuals for whom the net benefit is both clinically worthwhile and statistically definite.

HomeCirculationVol. 129, No. 8Nonsteroidal Anti-Inflammatory Drugs and the Heart Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBNonsteroidal Anti-Inflammatory Drugs and the Heart Carlo Patrono, MD and Colin Baigent, BM, BCh Carlo PatronoCarlo Patrono From the Department of Pharmacology, Catholic University School of Medicine, Rome, Italy (C.P.); and Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (C.B.). Search for more papers by this author and Colin BaigentColin Baigent From the Department of Pharmacology, Catholic University School of Medicine, Rome, Italy (C.P.); and Clinical Trial Service Unit and Epidemiological Studies Unit, Nuffield Department of Population Health, University of Oxford, Oxford, UK (C.B.). Search for more papers by this author Originally published25 Feb 2014https://doi.org/10.1161/CIRCULATIONAHA.113.004480Circulation. 2014;129:907–916IntroductionAspirin has been on the market for 115 years. Beginning with the marketing of indomethacin for the treatment of rheumatoid arthritis in 1963, at least 20 other nonsteroidal anti-inflammatory drugs (NSAIDs) with aspirin-like actions have been developed over the past 50 years,1 culminating with the introduction of a new class of selective inhibitors of cyclooxygenase (COX)-2, the coxibs, approximately 15 years ago.2 The NSAIDs represent the single most crowded family of drugs sharing the same therapeutic activities and mechanism of action, perhaps reflecting the unmet therapeutic need in the area of pain management and the large interindividual variability in response to these agents. NSAIDs provide symptomatic relief of pain and inflammation associated with a variety of human disorders, including the rheumatic diseases. Their shared therapeutic actions (ie, analgesic, anti-inflammatory, and antipyretic) are usually accompanied by mechanism-based adverse effects that can, at least in part, be attenuated as a function of individual pharmacokinetic or pharmacodynamic properties.1Nuances in the tolerability of different NSAIDs had been described in the precoxib era on the basis of clinical trials of a few hundred patients treated for up to a few months with soft end points. More recently, however, important differences in safety have been demonstrated in head-to-head randomized comparisons of individual coxibs and 1 or more traditional NSAIDs that involved tens of thousands of patients treated for up to a few years with hard end points. Even more significantly, the interpretation of the effects of NSAIDs has been greatly enhanced by the availability, for the first time, of large, placebo-controlled trials that aimed to assess the potential for chemoprevention of colorectal cancer by rofecoxib or celecoxib.As a result of these developments, the whole field of NSAIDs has been illuminated during the past 15 years. Although epidemiological studies had previously associated regular use of NSAIDs with some aspects of vascular toxicity such as enhanced risk of congestive heart failure,3 a novel aspect of cardiotoxicity associated with COX-2 inhibition emerged from the coxib trials, that is, increased risk of atherothrombotic vascular events.4,5 This was largely unexpected and paradoxical, given that the prototypic COX-2 inhibitor, aspirin, had been clearly shown to be cardioprotective over a wide range of doses up to 1500 mg daily.6The aim of this article is to review the evidence and to discuss the mechanisms underlying the cardiovascular effects of traditional NSAIDs and coxibs, trying to reconcile the pharmacology of COX isozyme inhibition with its clinical readouts. In doing so, we shall rely primarily on the results of the recently completed meta-analysis of individual participant data from randomized trials7 because it provides the most reliable information on the effects of the most widely prescribed NSAIDs on serious clinical outcomes.Arachidonic Acid Metabolism in Human Platelets and EndotheliumStimulation of platelet aggregation by various agonists leads to the activation of membrane phospholipases, with the consequent release of arachidonic acid and its cyclooxygenation to form the prostaglandin (PG) endoperoxides PGG2 and PGH2. PGH2 is further metabolized by thromboxane (TX) synthase (the most abundant PGH2 isomerase in human platelets) to form TXA2 as the prevailing platelet prostanoid.1 The COX isoform involved in this rapid chain of enzymatic reactions is COX-1 in mature human platelets, with transient COX-2 expression being restricted to newly formed platelets.8 Prostanoids are usually not required to produce a functional response but rather to modulate its intensity and duration. Thus, human platelets can aggregate and form a hemostatic plug in response to thrombin even in the absence of TXA2. However, TXA2 amplifies the activation signal by virtue of its being synthesized and released in response to a platelet agonist and in turn inducing platelet aggregation and further TXA2 production through its interaction with the platelet thromboxane receptor.9 Thus, COX-1–dependent generation of TXA2 initiates an amplification loop that propagates the activation signal to adjacent platelets by inducing further platelet activation and TXA2 formation.1,9The rate of TXA2 synthesis and release can increase a few thousand-fold from the resting state and is driven largely by enhanced substrate availability.9 Indeed, the maximal biosynthetic capacity of human platelets to produce TXA2 when challenged by thrombin in vitro (300–400 ng/mL of whole blood in 1 hour) exceeds the basal rate of TXA2 biosynthesis in vivo (0.1 ng·kg−1·min−1) by 3 orders of magnitude.10 The remarkable ability of platelets to increase their production of TXA2 by virtue of an explosive chain reaction may explain, at least in part, the unusual requirement for virtually complete (ie, >97%) suppression of platelet COX-1 activity for pharmacological inhibition to translate into functional impairment11,12 (Figure 1).Download figureDownload PowerPointFigure 1. Maximal biosynthetic capacity of human platelets (left), rate of thromboxane production in healthy subjects (middle), and nonlinear relationship between inhibition of platelet cyclooxygenase activity and thromboxane biosynthesis in vivo (right). Left, Thromboxane production stimulated by endogenous thrombin during whole-blood clotting at 37°C (based on data from Reference 13). Middle, The metabolic fate of thromboxane A2 (TXA2) in vivo and the calculated rate of its production in healthy subjects based on thromboxane B2 (TXB2) infusions and measurement of its major urinary metabolite (data from Reference 10). Right, The nonlinear relationship between inhibition of serum TXB2 measured ex vivo and the reduction in thromboxane metabolite (TXM) excretion measured in vivo (data adapted from Reference 12).Prostacyclin (PGI2) is the major product of COX-catalyzed metabolism of arachidonic acid in human macrovascular endothelium.1 Cultured human endothelial cells synthesize PGI2 (≈20 ng/106 cells) when stimulated with arachidonate in vitro.14 PGI2 is a potent inhibitor of platelet aggregation and a vasodilator.15 Its basal rate of secretion into the systemic circulation is as low as that of TXA2, ≈0.1 ng·kg−1·min−1 in healthy subjects,16 resulting in blood levels (a few picograms per milliliter) that are at least 10-fold lower than the minimal concentration that inhibits platelet function. However, the in vivo biosynthesis of PGI2, as reflected by PGI2 metabolite excretion, is enhanced in patients with severe atherosclerosis and platelet activation,17 suggesting that it functions as a homeostatic response to accelerated platelet–vessel wall interactions.15 The pathophysiological importance of PGI2 has undergone ups and downs during the past 40 years. In 1979, Moncada and Vane15 proposed that vascular homeostasis is determined by a balance between the platelet production of TXA2 and the endothelial production of PGI2 and that the occurrence of thrombotic disorders might be influenced by factors that alter this balance. Lack of specific inhibitors of PGI2 synthesis or action in the preknockout era eventually led to a less enthusiastic view of its role in vascular disorders,18 The hypothesis put forward by Moncada and Vane15 had to wait another 20 years or so before being properly tested by the large, postmarketing trials of coxibs and by the use of mice genetically deficient in the PGI2 receptor.19 The latter approach led FitzGerald’s group to demonstrate for the first time that PGI2 modulates platelet-vascular interactions in vivo and specifically limits the cardiovascular response to TXA2.20Urinary PGI2 metabolite excretion is reduced by 60% to 80% by therapeutic doses of selective COX-2 inhibitors,21–23 implying that PGI2 biosynthesis is largely a COX-2–driven process in humans. The hypothesis that COX-2 is normally expressed by endothelial cells in response to steady laminar shear stress24 is consistent with the finding that deletion of COX-2 in the mouse vasculature reduces the urinary excretion of PGI2 metabolite.25,26Compared with platelets, human endothelial cells have a considerably lower biosynthetic capacity to generate prostanoids. Although the maximal biosynthetic capacity of endothelial cells cannot be assessed ex vivo, one can use the lipopolysaccharide-induced expression of COX-2 in circulating monocytes27 to assess the influence of systemic plasma levels of COX-2 inhibitors on the maximal prostanoid biosynthetic capacity of blood cells exposed to the same inhibitor concentration as vascular endothelial cells. Paired measurements of the inhibition of monocyte COX-2 activity, as assessed ex vivo, and the reduction in urinary PGI2 metabolite excretion, as assessed in vivo, have established a linear relationship between the two,28 in contrast to the strikingly nonlinear relationship between the inhibition of platelet COX-1 activity and the reduction in urinary thromboxane metabolite excretion11,12 (Figure 1). The markedly different requirements for inhibition of TXA2- versus PGI2-dependent functions may have important implications for the interpretation of the cardiovascular effects of different classes of COX inhibitors, as discussed below.Platelet and vascular responses to a PGI2 analog and time to thrombotic carotid arterial occlusion were modulated by PGI2 receptor deletion in a gene/dose-dependent fashion,29 consistent with the concept of a linear relationship between inhibition of PGI2-evoked signaling and reduction in PGI2-mediated functional effects.Mechanism of Action of NSAIDsThe best-characterized mechanism of action of NSAIDs is inhibition of the COX activity of PGH synthase-1 and -2 (also referred to as COX-1 and COX-2; Figure 2).1 Given the role that prostanoids such as PGE2, PGI2, and TXA2 play in the local modulation of many important cellular functions, this mechanism of action is probably sufficient to explain the clinical effects of NSAIDs.1Download figureDownload PowerPointFigure 2. Mechanism of formation and action of prostanoids. Arachidonic acid, a 20-carbon fatty acid containing 4 double bonds, is liberated from the sn2 position in membrane phospholipids by phospholipases, which are activated by diverse stimuli. Arachidonic acid is converted by cytosolic prostaglandin (PG) G/H synthases, which have both cyclooxygenase (COX) and hydroperoxidase activity, to the unstable intermediate PGH2. The synthases are colloquially called cyclooxygenases and exist in 2 forms: COX-1 and COX-2. PGH2 is converted by tissue-specific isomerases to multiple prostanoids. These bioactive lipids activate specific cell membrane receptors of the superfamily of G protein–coupled receptors. cPLA2 indicates cytosolic phospholipase A2; sPLA2, secretory phospholipase A2; EPs, PGE2 receptors; IP, PGI2 receptor; TP, TXA2 receptor; and TX, thromboxane.The administration of PGE2 and PGI2 causes erythema, an increase in local blood flow, and, in concert with other inflammatory mediators (eg, bradykinin), hyperalgesia and enhanced vascular permeability.1 Moreover, PGE2 interacting with its EP3 receptor can produce fever. Thus, prostanoids reproduce the main signs and symptoms of the inflammatory response.1 Because of the redundancy of mediators of this response, it is not surprising that NSAIDs exert only a moderate anti-inflammatory effect, are effective only against pain of low to moderate intensity, reduce fever, but do not interfere with the physiological control of body temperature.1The production of prostanoids involved in these responses appears to be triggered by the immediate availability of constitutively expressed COX-1 and to be amplified and sustained by the local induction of COX-2 in response to inflammatory and mitogenic stimuli.30 Although the analgesic, anti- inflammatory, and antipyretic actions of traditional NSAIDs are closely reproduced by coxibs, this finding does not exclude a potential role for COX-1 in mediating, at least in some individuals, the PG-dependent contribution to pain and inflammation.2The ability of acetaminophen to inhibit COX-1 and COX-2 is importantly conditioned by the peroxide tone of the local environment.31 This may explain, at least in part, the clinical observation that, while sharing the analgesic and antipyretic effects of NSAIDs, acetaminophen has relatively poor anti-inflammatory activity at conventional doses.1 High concentrations of leukocyte-derived peroxides accumulate at sites of inflammation and may impair the ability of acetaminophen to inhibit COX-2.31 However, circulating plasma levels of the drug after the administration of 1000 mg inhibit systemically COX-2 activity to a degree comparable to that of traditional NSAIDs and coxibs.32Clinical Pharmacology of COX Isozyme InhibitionLow-dose aspirin provides a paradigm of COX isozyme–selective and cell-specific inhibition in vivo by virtue of its short half-life and ability to inactivate COX irreversibly.33,34 The relative COX-1 selectivity of low-dose aspirin in vivo arises from both pharmacokinetic determinants such as the acetylation of platelet COX-1 that occurs in portal blood before first-pass metabolism35 and pharmacodynamic determinants such as the cumulative nature of platelet COX-1 inactivation on repeated daily dosing.13,36 Thus, the daily administration of 30 mg aspirin results in virtually complete suppression of platelet TXA2 production after 1 week of dosing through a cumulative process of inactivation of platelet COX-1 by successive daily doses of aspirin.13,36 The unique features of the antiplatelet effect of aspirin explain the highly predictable, virtually complete inhibition of platelet TXA2 biosynthesis in subjects who take the drug regularly,12 the persistence of this effect over the 24-hour dosing interval in the vast majority of subjects with an 8- to 10-day platelet life span,12 and the clinical efficacy of doses as low as 30 to 50 mg daily in high-risk patients.34Traditional NSAIDs lack these unique pharmacokinetic/pharmacodynamic features and do not usually achieve the same degree of persistent platelet COX-1 inhibition as is obtained with low-dose aspirin.34,36 Moreover, several traditional NSAIDs (eg, ibuprofen and diclofenac) are characterized by very short half-lives (1–2 hours), contributing to the transient nature of platelet COX-1 inhibition.34,36The COX isozyme selectivity of a particular inhibitor is critically dependent on its concentration. One can compare the selectivity profiles of different COX-2 inhibitors by plotting the drug concentrations required to inhibit the activity of human platelet COX-1 and those required to inhibit human monocyte COX-2 by 50% (IC50), as measured by widely used whole-blood assays of COX activity27 (Figure 3). This type of analysis established 2 important facts: COX-2 selectivity is a continuous variable that does not justify a dichotomous definition of selective and nonselective inhibitors, and there is an appreciable overlap in COX-2 selectivity between some first-generation coxibs (eg, celecoxib) and some traditional NSAIDs (eg, nimesulide and diclofenac).2 Moreover, there is large variability among NSAID-treated patients in the plasma concentrations of the COX-2 inhibitor after oral administration of a standard therapeutic dose (pharmacokinetic variability) and in the extent of inhibition of each COX isozyme, corresponding to any given concentration of the inhibitor (pharmacodynamic variability). Therefore, one can pragmatically characterize different levels of COX-2 selectivity in terms of the probability of sparing platelet (and presumably gastrointestinal mucosa) COX-1 at therapeutic plasma levels: low (eg, acetaminophen), intermediate (eg, celecoxib, nimesulide, and diclofenac), and high (eg, rofecoxib, etoricoxib, and lumiracoxib; Figure 3).Download figureDownload PowerPointFigure 3. Cyclooxygenase (COX)-2 selectivity as a continuous variable. Concentrations of various COX-2 inhibitors to inhibit the activity of platelet COX-1 and monocyte COX-2 by 50% (IC50) are plotted on the abscissa and ordinate scales, respectively. The solid line describes equipotent inhibition of both COX-1 and COX-2. Symbols to the left of this line denote greater inhibition of COX-1 than COX-2. Symbols to the right of this line indicate progressively greater inhibition of COX-2 than COX-1, that is, increasing degrees of COX-2 selectivity. 6-MNA indicates 6-methoxy-2-naphthylacetic acid, the active metabolite of nabumetone (data adapted from Reference 2).Potential variables contributing to different COX-2- dependent effects include the daily dose of the inhibitor determining the extent of COX-2 inhibition, the half-life and dosing interval of the inhibitor determining the duration of COX-2 inhibition, and the patient substrate, inasmuch as the importance of COX-2–dependent PGI2 biosynthesis is likely to vary in different clinical settings.Although the daily dose, half-life, duration of treatment, and COX-2 selectivity are all continuous variables that could influence the cardiovascular outcomes resulting from COX-2 inhibition, the clinical readouts of such inhibition are constrained by the dichotomy of a nonlinear relationship between the inhibition of platelet COX-1 activity and the downregulation of TXA2-dependent platelet activation (Figure 1). Therefore, inhibiting platelet COX-1 activity by 0% to 20% (as typically achieved with highly selective COX-2 inhibitors), by 20 to 50% (as typically achieved with COX-2 inhibitors endowed with moderate COX-2 selectivity), or by 50% to 90% (as typically achieved with most traditional NSAIDs) will result in only similarly modest suppression of TXA2 biosynthesis in vivo.11,12 Naproxen, when taken regularly at high doses and an adequate dosing interval (ie, 500 mg twice daily), is the only traditional NSAID that has been reported to inhibit platelet COX-1 activity by >95% throughout the dosing interval and to suppress TXA2 biosynthesis in vivo to the same extent as low-dose aspirin.37,38 Lower doses and less frequent dosing of naproxen are not expected to reproduce this aspirin-like antiplatelet effect.38Some NSAIDs favoring COX-1 versus COX-2 inhibition such as ibuprofen and naproxen (Figure 3) may interfere with the antiplatelet effect of low-dose aspirin by competing with acetylsalicylic acid for a common docking site (arginine 120) within the COX-1 channel.39 Prior occupancy of arginine 120 by an NSAID will prevent aspirin from acetylating a serine residue (Ser-529) just below the COX catalytic site of the enzyme, which forms the basis of the unique mechanism of action of aspirin, resulting in permanent inactivation of platelet COX-1.6 Drugs favoring COX-2 versus COX-1 inhibition such as acetaminophen and diclofenac do not interfere with the antiplatelet effect of low-dose aspirin, similar to celecoxib and rofecoxib (Figure 3).39,40 Using a current analysis of the available data, the Food and Drug Administration has issued a statement informing patients and healthcare professionals that ibuprofen can interfere with the antiplatelet effect of low-dose aspirin (81 mg/d), potentially rendering aspirin less effective when used for cardioprotection and stroke prevention (http://www.fda.gov/drugs/drugsafety/postmarketdrugsafetyinformationforpatientsandproviders/ucm110510.htm).Clinical Readouts of COX Isozyme inhibitionClinical evidence from randomized trials is consistent with the available evidence on COX isozyme–specific effects on particular outcomes from laboratory studies. We now describe the relationship between the known pharmacology and evidence from randomized trials as recently summarized by the Coxib and Traditional NSAID (CNT) Collaboration.7Effects on Pain and InflammationThe results of phase 3 randomized trials in osteoarthritis, rheumatoid arthritis, and various clinical models of acute pain have established that the analgesic and anti-inflammatory efficacy of coxibs is similar to that of several NSAID comparators (typically diclofenac, ibuprofen, or naproxen), independently of variable COX isozyme selectivity.1,2 This finding is consistent with the COX-2 dependence of PG-mediated pain and inflammation and similar COX-2 inhibition at comparable doses of different drugs.Effects on Atherothrombotic OutcomesMeta-analyses of randomized trials and observational studies have previously shown that coxibs and some traditional NSAIDs are associated with an increased risk of atherothrombotic events.28,41–43 The CNT Collaboration7 has recently completed meta-analyses of individual participant data from all available randomized trials of an NSAID versus placebo or 1 NSAID regimen versus another NSAID regimen, allowing detailed assessments of the cardiovascular effects of high-dose regimens of the 3 NSAIDs that are most widely prescribed worldwide for chronic inflammatory disorders: naproxen 500 mg twice daily, diclofenac 75 mg twice daily, and ibuprofen 800 mg 3 times daily.7 Compared with placebo, allocation to a coxib (mainly rofecoxib 25 mg daily or celecoxib 400 mg daily) increased the risk of major vascular events by ≈40%, largely as a result of an increase in major coronary events, with no clear evidence of an increase in stroke risk (Figure 4).7 There was no statistically significant heterogeneity in the increased risk of major vascular events associated with rofecoxib and celecoxib despite a 20-fold difference in COX-2 selectivity between the two (Figure 3), consistent with the COX-2 dependence of PGI2-mediated thromboresistance of the vessel wall.26,29 Moreover, there was no significant difference in the incidence of vascular events between a coxib and traditional NSAIDs (with the exception of naproxen [see below]). Given the nonlinear relationship between the inhibition of platelet COX-1 activity and the inhibition of platelet activation in vivo,11,12 it is perhaps not surprising that the cardiovascular safety profiles of coxibs and some traditional NSAIDs appear similar because they both fail to inhibit platelet activation adequately regardless of their COX-2 selectivity.Download figureDownload PowerPointFigure 4. Effects of coxib therapy on major vascular events (MVEs), heart failure, cause-specific mortality, and upper gastrointestinal (GI) complications. Actual numbers for participants are presented, together with the corresponding mean yearly event rate (in parentheses). Participants can contribute only once to the total of MVEs. Major vascular events include myocardial infarction (MI), stroke, or vascular death. CHD indicates coronary heart disease. Rate ratios (RRs) for all trials are indicated by squares; their 99% confidence intervals (CIs), by horizontal lines. Subtotals and their 95% CIs are represented by diamonds. Squares or diamonds to the left of the solid line indicate benefit. *Includes another 25 vs 21 MVEs among patients randomized into trials for which only tabular information was available. Reproduced from Reference 7 with permission from the publisher. Copyright © 2013 Elsevier B.V.Compared with placebo (using indirect comparisons44 and direct comparisons combined), however, high-dose naproxen and other traditional NSAIDs (mostly diclofenac and ibuprofen) had contrasting effects on major vascular events (Figure 5). There was no evidence of atherothrombotic risk from naproxen, consistent with an aspirin-like phenotype conferred by the unique pharmacokinetic/pharmacodynamic features of a twice-daily high-dose naproxen regimen noted above.37,38Download figureDownload PowerPointFigure 5. Effects of naproxen and nonnaproxen nonsteroidal anti-inflammatory drugs (NSAIDs) on major vascular events. Rate ratios (RRs) for all trials are indicated by squares; their 99% confidence intervals (CIs), by horizontal lines. Subtotals and their 95% CIs are represented by diamonds. Squares or diamonds to the left of the solid line indicate benefit. RRs are for comparisons of a traditional (t)NSAID vs placebo, calculated indirectly from ratio of RRs for a coxib vs placebo and RRs for a coxib vs tNSAID, each of which is shown in the vertical columns (see References 7 and 44 for statistical methods).The increased risk of coronary events associated with vascular COX-2 inhibition is mechanistically consistent with the pattern of cardioprotection associated with platelet COX-1 inhibition by low-dose aspirin in low-risk subjects, that is, a clear decrease in coronary risk.45 These findings suggest an important role of PGI2 and TXA2 in modulating platelet activation and its contribution to coronary atherothrombosis.9 A reliable assessment of the role of these prostanoids in cerebrovascular ischemic events requires a much larger number of strokes than available in the CNT database.There was no convincing evidence of a latent period before these vascular hazards emerge, consistent with the proposed mechanism of action4 and with evidence of early hazard observed with intravenous administration of parecoxib followed by oral valdecoxib in 2 short-term trials among patients undergoing coronary bypass surgery.46,47 The CNT analyses did not provide any evidence that the effect of coxib therapy on the risk of major vascular events is attenuated by concomitant aspirin use at baseline.7 A mitigating effect of low-dose aspirin seems biologically plausible because COX-1 knockdown in mice attenuates the prothrombotic effect of COX-2 inhibition.4 Moreover, the neutral coronary phenotype of high-dose naproxen7 suggests that a concomitant aspirin-like antiplatelet effect (ie, profound and persistent inhibition of platelet COX-1 activity throughout the 12-hour dosing interval of a naproxen 500 mg twice daily regimen)37 may mitigate or abolish the prothrombotic consequences of COX-2 inhibition. However, because there was disproportionate underrepresentation of aspirin-treated participants in the coxib trials, this analysis lacked statistical power to assess whether the vascular hazards of a coxib were modified by low-dose aspirin.7Unfortunately, reliable information on the cardiovascular safety of other traditional NSAIDs is lacking. The vast majority of these agents, with the notable exception of indomethacin, failed to achieve >95% inhibition of serum TXB2 after single oral dosing.36 Moreover, both nimesulide48 and meloxicam49 have been reported to inhibit platelet COX-1 activity by <50% on repeated daily dosing. Therefore, the cardiovascular effects of these high-dose agents would not be expected to differ from those of diclofenac and ibuprofen unless convincingly shown otherwise.Effects on Blood Pressure and Renal OutcomesBoth traditional NSAIDs and coxibs have been associated with renal and renovascular adverse events,1,2 which is consistent with the important role of constitutively expressed COX-2 in sustaining the physiological production of vasodilator and natriuretic prostanoids in the kidney.50 Several prostanoids contribute to blood pressure homeostasis, and practically all COX-2 inhibitors have been associated with increased blood pressure or impaired response to antihypertensive drugs.1,4 Furthermore, vascular disruption of COX-2 in mice depressed the expression of endothelial nitric oxide synthase and the consequent release and function of nitric oxide.25Effects on Congestive Heart FailureUse of traditional NSAIDs and coxibs can lead to the development of congestive heart failure in susceptible individuals,3 and in the CNT meta-analysis, there was a doubling of this risk, with no apparent differences in this relative increase associated with different classes of COX-2 inhibitors, consistent with this being a COX-2–dependent hazard unrelated to variable platelet inhibition.7 This is also consistent with the COX-2 dependence of hemodynamic stability and renal function in at-risk individuals and with the role of cardiomyocyte COX-2 in cardiac rhythm and function.51 The finding that coxibs and traditional NSAIDs caused a similar increased risk of heart failure indirectly suggests that the high-dose regimens of these agents used in the coxib trials produced comparable levels of vascular COX-2 inhibition.Effects on Gastroduodenal OutcomesSeveral coxibs have been shown to be associated with a lower incidence of endoscopic gastroduodenal ulcers than doses of traditional NSAIDs with similar analgesic efficacy, which is consistent with the COX-1 dependence of mucosal cytoprotection.1,2 Similarly, in at least 2 independent, large-scale trials, the highly selective COX-2 inhibitors rofecoxib and lumiracoxib were associated with a statistically significant 50% to 60% reduction in ulcer complications (mostly bleeding) compared with ibuprofen and naproxen,52,53 consistent with the COX-1

BackgroundEven though the acetylation of platelet cyclooxygenase (COX)‐1 at serine‐529 is the direct mechanism of action of low‐dose aspirin, its antiplatelet effect has been characterized using indirect indexes of COX‐1 activity.ObjectivesWe performed a clinical study with enteric‐coated low‐dose aspirin (EC‐aspirin), in healthy subjects, to evaluate the effects on the extent and duration of platelet COX‐1 acetylation, using a novel proteomic strategy for absolute protein quantification (termed AQUA), as compared with traditional pharmacokinetic and pharmacodynamic parameters.Subjects and methodsIn a phase I, single‐arm, open‐label study of EC aspirin (100 mg day−1) administered to 24 healthy subjects, we compared, over a 24 h‐period on day 1 and 7, % platelet acetylated COX‐1 (AceCOX‐1) with traditional pharmacokinetic and pharmacodynamics [i.e. serum thromboxane (TX) B2, platelet function by monitoring CEPI(collagen/epinephrine) closure time (CT) using whole‐blood PFA‐100 and urinary excretion of 11‐dehydro‐TXB2] parameters.ResultsAcetylation of platelet COX‐1 was measurable before detection of aspirin levels in the systemic circulation and increased in a cumulative fashion upon repeated dosing. After the last dose of EC‐aspirin, %AceCOX‐1, serum TXB2 and CEPI‐CT values were maximally and persistently modified throughout 24 h; they averaged 76 ± 2%, 99.0 ± 0.4% and 271 ± 5 s, respectively. EC‐aspirin caused 75% reduction in urinary 11‐dehydro‐TXB2 excretion. After chronic dosing with aspirin, the pharmacokinetics of acetylsalicylic acid was completely dissociated from pharmacodynamics.ConclusionsThe demonstrated feasibility of quantifying the extent and duration of platelet COX‐1 acetylation will allow characterizing the genetic, pharmacokinetic and pharmacodynamic determinants of the inter‐individual variability in the antiplatelet response to low‐dose aspirin as well as identifying extra‐platelet sites of drug action.

HomeJournal of the American Heart AssociationVol. 7, No. 16Off‐Pump Coronary Artery Bypass Grafting: 30 Years of Debate Open AccessReview ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citations ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toOpen AccessReview ArticlePDF/EPUBOff‐Pump Coronary Artery Bypass Grafting: 30 Years of Debate Mario Gaudino, MD, Gianni D. Angelini, MD, Charalambos Antoniades, MD, Faisal Bakaeen, MD, Umberto Benedetto, PhD, Antonio M. Calafiore, MD, Antonino Di Franco, MD, Michele Di Mauro, MD, Stephen E. Fremes, MD, Leonard N. Girardi, MD, David Glineur, MD, Juan Grau, MD, Guo‐Wei He, MD, Carlo Patrono, MD, John D. Puskas, MD, Marc Ruel, MD, MPH, Thomas A. Schwann, MD, Derrick Y. Tam, MD, James Tatoulis, MD, Robert Tranbaugh, MD, Michael Vallely, MD, Marco A. Zenati, MD, Michael Mack, MD, David P. Taggart, MD and Arterial Grafting International Consortium (ATLANTIC) Alliance Mario GaudinoMario Gaudino Department of Cardio‐Thoracic Surgery, Weill Cornell Medicine, New York City, NY Search for more papers by this author , Gianni D. AngeliniGianni D. Angelini Bristol Heart Institute, University of Bristol, United Kingdom Search for more papers by this author , Charalambos AntoniadesCharalambos Antoniades University of Oxford, United Kingdom Search for more papers by this author , Faisal BakaeenFaisal Bakaeen Cleveland Clinic, Cleveland, OH Search for more papers by this author , Umberto BenedettoUmberto Benedetto Bristol Heart Institute, University of Bristol, United Kingdom Search for more papers by this author , Antonio M. CalafioreAntonio M. Calafiore Cardiac Surgery, Pope John Paul II Foundation, Campobasso, Italy Search for more papers by this author , Antonino Di FrancoAntonino Di Franco Department of Cardio‐Thoracic Surgery, Weill Cornell Medicine, New York City, NY Search for more papers by this author , Michele Di MauroMichele Di Mauro Cardiovascular Disease Institute, University of L'Aquila, Italy Search for more papers by this author , Stephen E. FremesStephen E. Fremes Schulich Heart Centre, Sunnybrook Health Science, University of Toronto, Canada Search for more papers by this author , Leonard N. GirardiLeonard N. Girardi Department of Cardio‐Thoracic Surgery, Weill Cornell Medicine, New York City, NY Search for more papers by this author , David GlineurDavid Glineur Division of Cardiac Surgery, Ottawa Heart Institute, Ottawa, Canada Search for more papers by this author , Juan GrauJuan Grau Division of Cardiac Surgery, Ottawa Heart Institute, Ottawa, Canada Search for more papers by this author , Guo‐Wei HeGuo‐Wei He TEDA International Cardiovascular Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Tianjin, China Search for more papers by this author , Carlo PatronoCarlo Patrono Department of Pharmacology, Catholic University School of Medicine, Rome, Italy Search for more papers by this author , John D. PuskasJohn D. Puskas Department of Cardiovascular Surgery, Icahn School of Medicine at Mount Sinai, New York City, NY Search for more papers by this author , Marc RuelMarc Ruel University of Ottawa Heart Institute, Ottawa, Canada Search for more papers by this author , Thomas A. SchwannThomas A. Schwann University of Toledo College of Medicine, Toledo, OH Search for more papers by this author , Derrick Y. TamDerrick Y. Tam Schulich Heart Centre, Sunnybrook Health Science, University of Toronto, Canada Search for more papers by this author , James TatoulisJames Tatoulis Department of Surgery, University of Melbourne, Parkville, Australia Search for more papers by this author , Robert TranbaughRobert Tranbaugh Department of Cardio‐Thoracic Surgery, Weill Cornell Medicine, New York City, NY Search for more papers by this author , Michael VallelyMichael Vallely Sydney Medical School, The University of Sydney, Australia Search for more papers by this author , Marco A. ZenatiMarco A. Zenati Harvard Medical School, Boston, MA Search for more papers by this author , Michael MackMichael Mack The Heart Hospital Baylor Plano, Plano, TX Search for more papers by this author , David P. TaggartDavid P. Taggart University of Oxford, United Kingdom Search for more papers by this author and Arterial Grafting International Consortium (ATLANTIC) Alliance Search for more papers by this author Originally published14 Aug 2018https://doi.org/10.1161/JAHA.118.009934Journal of the American Heart Association. 2018;7:e009934IntroductionOff‐pump coronary artery bypass surgery (OPCAB) has been performed for >30 years.The promotion of OPCAB was based on its potential benefits over some of the limitations of traditional on‐pump coronary artery bypass surgery (ONCAB) by avoiding the trauma of cardiopulmonary bypass (CPB) and by minimizing aortic manipulation. As such, reductions in early mortality and perioperative neurological events, renal failure, blood product transfusions, and hospital length of stay were expected according to the OPCAB proponents. In contrast, critics of OPCAB remain concerned about incomplete and/or poorer quality coronary revascularization with a potential increase in the need for repeat revascularization and late mortality.Despite 3 decades of debate, 115 randomized trials, and >60 meta‐analyses comparing on‐ and off‐pump coronary artery bypass grafting (CABG), controversy on both the role of and indications for OPCAB remains vigorous.In this review, we provide a comprehensive update of the evidence for the differences in the biological effects of off‐ and on‐pump surgery and the comparison of the clinical and angiographic results of the 2 techniques. Furthermore, we critically address the relevant technical aspects of OPCAB, the importance of surgeon experience, and the difference in the costs for the 2 procedures.Search StrategyThe Arterial Grafting International Consortium (ATLANTIC) Alliance is an international writing group on coronary surgery. In January 2018, a comprehensive search to identify studies that evaluated the biological, clinical, angiographic, and economic aspects of OPCAB was performed in the following databases from inception to present: Ovid Medline, Ovid Embase, and the Cochrane Library (Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials [CENTRAL], Cochrane Methodology Register). Search keywords included myocardial revascularization in combination with coronary artery bypass, on pump, off pump, and OPCAB. Relevant abstracts were reviewed, and the related articles function was used for all included studies. References for all selected studies were cross‐checked. The writing group selected the most relevant papers according to both methodological and clinical considerations. Observational series were considered only in the absence of data from randomized controlled trials (RCTs).The Technical Evolution of Beating‐Heart Coronary Artery Bypass SurgeryThe very first direct coronary revascularization procedures in the early 1960s were performed on the beating heart without CPB.1 However, the technique was soon abandoned because of developments in extracorporeal circulation and improvement in myocardial protection that made the surgery safer, standardized, and reproducible. In the early 1980s, 2 South American surgeons, Buffolo2 and Benetti,3 published their extensive series of OPCAB. Most patients received grafts to the left anterior descending coronary artery (LAD) and the main right coronary artery, but with more limited and difficult grafting of coronary arteries on the posterior and lateral wall. In the mid 1990s, a minimally invasive left internal mammary artery (LIMA)–LAD performed through a small left anterior thoracotomy on the beating heart4 was proposed in combination with percutaneous coronary intervention (PCI) for the non‐LAD targets.5Innovative technology played a key role in the development of OPCAB by minimizing the motion of the heart during construction of the anastomosis. Initially, stabilization of the target coronary vessel was obtained by stay sutures, but the advent of mechanical stabilizers, by means of pressure or suction pods, transformed the way OPCAB was performed, accompanied by an evident improvement in surgical results.6 The critical challenge was the exposure of the lateral and inferior walls. Initially, lifting of the heart and exposure of the targets were achieved with multiple slings7 or pericardial stitches, as proposed by Lima and Salerno.8 The commercialization of pressure‐ and vacuum‐assisted positioners further changed the field and allowed minimization of hemodynamic changes during exposure. The use of intracoronary shunts rather than snaring of the target native coronary vessel has been shown to significantly reduce intraoperative myocardial dysfunction and hemodynamic instability during OPCAB.9The use of a transit‐time flowmeter, high‐resolution epicardial ultrasound, or intraoperative fluorescence imaging allowed intraoperative control of the quality of the anastomosis, an issue of particular relevance during the technically more complex OPCAB procedure.10For the future of OPCAB, technology will play an increasingly important role with the adoption of hybrid revascularization and robotic assisted OPCAB. The concept of hybrid coronary revascularization (HCR) stems from the hypothesis that the LIMA‐LAD graft is superior to coronary stenting of the LAD, whereas contemporary drug‐eluting stent–PCI is noninferior to venous bypass grafts used for non‐LAD targets. Although still limited to sporadic experiences in dedicated centers, HCR has the potential to combine the advantages of minimally invasive OPCAB with complete coronary revascularization.The use of robotic assistance during CABG has been associated with superior cosmetic results and reduced postoperative pain but also longer operative times and higher costs.11Differences in Systemic Inflammatory Reaction and Platelet/Coagulation Activation After On‐ and Off‐Pump CABGCABG elicits a complex prothrombotic and proinflammatory response that peaks within a time frame spanning from the end of CPB to the early hours thereafter. These molecular changes may persist for days or weeks after CABG.12 In particular, several studies have described marked and protracted activation of several molecular pathways, reflecting a systemic inflammatory reaction, platelet and coagulation activation, and increased oxidative stress and endothelial dysfunction.13 Interestingly, these changes appear to occur after both ONCAB and OPCAB, with a relatively limited number of these pathways (eg, oxidant stress) showing more pronounced activation in the presence of CPB.13Systemic Inflammatory ReactionPatients undergoing CABG constitute a distinct high‐risk group characterized by advanced atherosclerotic disease, low‐grade systemic inflammation, and the clustering of several other comorbidities.13 The CABG operation per se is a potent triggering factor for cardiovascular events because it elicits major endocrine stress and systemic inflammatory response, which involves the release of acute‐phase proteins and sepsis‐like symptoms during postoperative recovery.14 The inflammatory response during CABG may be related, at least in part, to the use of CPB that induces leukocyte and platelet activation, thrombin and plasmin‐mediated procoagulant and fibrinolytic effects, and a rapid and sustained multifold increase in the circulating levels of proinflammatory mediators.16 Myocardial tissue ischemia as a result of aortic cross‐clamp, reperfusion injury, plaque rupture and microembolization, and other factors (eg, type of anesthesia) also may play a role in CABG‐related inflammation.17If and to what extent avoidance of CPB can reduce or even eliminate the systemic inflammatory reaction after surgery is controversial. Studies that evaluated the circulating levels of proinflammatory cytokines (IL‐6, ‐8, and ‐10) after off‐ and on‐pump‐ surgery reported contradictory results.14The concomitant use of cardiotomy suction or non–heparin‐bounded CPB circuits in some of the trials is a plausible cause of heterogeneity and may partially explain the contradictory results.Interestingly, the severity of the inflammatory response to OPCAB might be affected by the type of anesthesia.23 Inflammation has been proposed to have an important role in determining early postoperative complications (eg, low‐output syndrome, myocardial injury, and atrial fibrillation or stroke). Indeed, increased preoperative CRP (C‐reactive protein) levels are independently associated with early and late mortality in CABG patients.24 In other studies, preoperative levels of IL‐6, IL‐8, and MCP‐1 (monocyte chemoattractant protein 1) predict postoperative atrial fibrillation development in CABG patients.25 Gaudino et al26 described a significant correlation between a single‐base promoter mutation of the polymorphism of the IL6 gene, the postoperative level of IL‐6, and the development of pulmonary and renal complications and atrial fibrillation after CABG. In RCTs, OPCAB has been associated with significantly lower myocardial injury and increase in inflammatory mediators compared with ONCAB,14 although early mortality rates did not differ significantly.27 Nevertheless, it must be noted that the results of pharmacological treatment aimed at reducing the postoperative inflammatory reaction after CABG (corticosteroids, statins) have been mixed,28 so the role of attempts to modulate inflammation in determining postoperative clinical outcome after CABG remains to be determined.Platelet and Coagulation ActivationActivation of the plasmatic and cellular components of the hemostatic system occurs through 2 distinct mechanisms, namely, contact of blood with the surgical wound and contact of blood with the foreign surface of the CPB circuit.30 The former plays a major role in the early activation of the hemostatic system that results in thrombin generation. Besides catalyzing the conversion of fibrinogen to fibrin, thrombin has multiple cellular targets (both in blood [eg, platelets] and the vessel wall) through the interaction with protease‐activated receptors.30 Moreover, there is bidirectional interplay between blood coagulation and inflammation, with activation of the former leading to an inflammatory reaction and vice versa.30 Circulating platelets are activated during CABG by several distinct mechanisms, including thrombin interacting with platelet PAR‐1 (protease‐activated receptor 1), interaction with fibrinogen bound to the CPB circuit, and contact with foreign surfaces. These activation processes eventually lead to reduced numbers of circulating platelets and perioperative platelet dysfunction.30 Moreover, activated platelets release a broad range of inflammatory mediators, thereby reinforcing the inflammatory reaction.31 The increased vascular biosynthesis of the antithrombotic prostanoid prostacyclin (PGI2) represents a homeostatic response to inflammation and platelet activation.32A limited number of studies have compared the effects of ONCAB versus OPCAB on platelet activation and aggregation and failed to demonstrate major differences between them.30 It should be emphasized that these studies relied on measurements of platelet function ex vivo, which do not necessarily reflect the extent of platelet activation in vivo.31A different and more clinically relevant way of assessing the potential hemostatic/prothrombotic differences related to ONCAB versus OPCAB is represented by studies of the pharmacodynamic response to antiplatelet drugs in these settings.32 In a study by Zimmermann et al,33 the antiplatelet effect of aspirin (100 mg/day started on day 1 after surgery) evaluated at day 5 was largely impaired after CPB but not after CABG without CPB; therefore, increased platelet turnover after CPB appears to contribute to transient aspirin “resistance” because an increased number of new platelets might be competent to form Thromboxane A2 (TXA2) within the 24‐hour dosing interval.33 Consistent with this hypothesis, Cavalca et al recently reported impaired aspirin pharmacodynamics early after ONCAB that were associated with significant increases in immature platelets, total platelets, platelet mass, thrombopoieitin, IL‐6, glycocalicin, leukocytes, and high‐sensitivity CRP.32 IL‐6 can control inflammation through CRP and modulate megakaryocyte fragmentation, differentiation, and platelet release directly or through thrombopoieitin.32 Changes in thrombopoietic indexes were largely reversible 3 months after surgery.32 As shown by 3 independent studies, shortening the dosing interval (ie, twice‐daily dosing), but not doubling the dose, safely rescued the impaired antiplatelet effect of low‐dose aspirin and prevented platelet activation associated with acute inflammation and enhanced platelet turnover following cardiac surgery.32To summarize, at present there is no clear‐cut demonstration of a substantial reduction of the postoperative systemic inflammatory reaction and platelet activation after OPCAB. The antiplatelet effect of low‐dose aspirin is transiently impaired following ONCAB because of enhanced platelet turnover.Comparison of Short‐Term Clinical Outcomes of On‐ and Off‐Pump CABGThe benefits and risks of OPCAB have been the subject of several large RCTs, observational studies and registries, and >60 meta‐analyses. In the largest randomized comparisons (CORONARY [CABG Off or On Pump Revascularization] and ROOBY [Randomized On/Off Bypass] trials), there were no differences in the primary study end point at 30 days.27 In CORONARY,27 the primary composite outcome of death, nonfatal stroke, or nonfatal myocardial infarction (MI) was similar between OPCAB and ONCAB (9.8% versus 10.3%, P=0.59). Similarly in ROOBY, the primary composite outcome of 30‐day death or major complications was similar between the 2 arms (7.0% versus 5.6%, P=0.19).38 Furthermore, there was no difference in any individual component of these early composite outcomes (Table 1). Consistent with the purported benefits of off‐pump surgery, several other perioperative complications (transfusion, reoperation for bleeding, acute kidney injury, and respiratory complications) were reduced in the off‐pump patients in CORONARY.Table 1 Early and Late Outcomes of ONCAB Versus OPCABTrialMedian Follow‐upInterventionsEarly OutcomesLate OutcomesMACCE DefinitionMortalityRRStrokeMIMortalityStrokeMIRRMACCECORONARY394.8 yONCAB59/2377 (2.5)4/2328 (0.2)27/2377 (1.1)170/2377 (7.2)322/2377 (13.5)66/2377 (2.8)194/2377 (8.2)55/2377 (2.3)560/2377 (23.6)Death from any cause, nonfatal MI, nonfatal stroke, new renal failure requiring dialysis, RROPCAB60/2375 (2.5)16/2330 (0.7)24/2375 (1.0)158/2375 (6.7)346/2375 (14.6)55/2375 (2.3)178/2375 (7.5)66/2375 (2.8)548/2375 (23.1)ROOBY405 yONCAB13/1099 (1.2)8/1099 (0.7)8/1099 (0.7)17/1099 (1.8)131/1099 (11.9)···105/1099 (9.6)131/1099 (11.9)131/1099 (11.9)Death from any cause, acute MI, RROPCAB18/1104 (1.6)8/1104 (0.7)14/1104 (1.3)15/1104 (1.7)168/1104 (15.2)···134/1104 (12.1)145/1104 (13.1)145/1104 (13.1)GOPCABE411 yONCAB34/1207 (2.8)5/1207 (0.4)32/1207 (2.7)20/1207 (1.7)95/1191 (8)52/1191 (4.4)28/1191 (2.4)24/1191 (2.0)167/1191 (14)Death from any cause, MI, stroke, RR, new renal failure requiring dialysisOPCAB31/1187 (2.6)15/1187 (1.3)26/1187 (2.2)18/1187 (1.5)83/1179 (7)41/1179 (3.5)25/1179 (2.1)36/1179 (3.1)154/1179 (13.1)Data are shown as frequency (percentage). CABG indicates coronary artery bypass grafting; CORONARY, CABG Off‐ or On‐Pump Revascularization; GOPCABE, German Off‐Pump Coronary Artery Bypass Grafting in Elderly Patients; MACCE, major adverse cardiovascular or cerebral events; MI, myocardial infarction; ONCAB, on‐pump coronary artery bypass surgery; OPCAB, off‐pump coronary artery bypass surgery; ROOBY, Randomized On/Off Bypass; RR, repeated revascularization.In GOPCABE (German Off‐Pump CABG in Elderly Trial), a German RCT including only patients aged >75 years, there was no significant difference in the primary composite end point of death, stroke, MI, or new renal replacement therapy (7.8% versus 8.2%, P=0.74) at 30 days41 and no differences in the individual components of the composite end point (Table 1). However, there was an increased number of repeat revascularizations with OPCAB (1.3% versus 0.4%, P=0.04), a finding also observed in CORONARY (0.7% versus 0.2%, P=0.01).Of note, no reduction in stroke was noted both in hospital and at 1 year (CORONARY: 1.5% versus 1.7%; [hazard ratio (HR): 0.90; 95% confidence interval (CI), 0.57–1.41]; GOPCABE: 3.5% versus 4.4%; P=0.26).41At 12 months, the primary composite end point was not different in the OPCAB and ONCAB patients in GOPCABE (13.1% versus 14.0%; P=0.48) or in CORONARY (12.1% versus 13.3%; P=0.24). In ROOBY, the primary outcome favored on‐pump surgery (9.9% versus 7.4%; P=0.04), as did death from cardiac causes (2.7% versus 1.3%; P=0.03).In contrast to the randomized trials, large propensity‐matched databases have reported superior short‐term outcomes with OPCAB, particularly in higher risk patients.Polomsky and associates, using data from the Society of Thoracic Surgeons Adult Cardiac Surgery Database (STS ACSD) on 876 081 elective isolated CABG operations, found that the odds ratios (ORs) for death and most major complications were significantly lower with OPCAB than with ONCAB.43A meta‐analysis of 35 propensity‐matched studies and 123 137 patients found OPCAB to be superior to on‐pump surgery for all short‐term outcomes including mortality.44To summarize, RCTs have reported similar operative risk for off‐ and on‐pump CABG, whereas single‐center studies have reported better outcomes, particularly in high‐risk patients.Comparison of Long‐Term Clinical Outcomes of On‐ and Off‐Pump CABGConflicting evidence exists on whether off‐pump CABG is associated with inferior long‐term outcomes. At 5 years, there was no difference in the primary outcome in the CORONARY trial.39 In the ROOBY trial, however, 5‐year survival was significantly worse in the off‐pump group (15.2% versus 11.9%; P=0.02).40 Event‐free survival was also significantly decreased in the off‐pump group (31.0% versus 27.1%; P=0.05), along with MI and the need for repeat revascularization (Table 1).In a single‐center observational study of 12 812 patients from Emory University, Atlanta, GA, USA, there was no difference in 10‐year mortality between on‐ and off‐pump surgery after propensity score covariate adjustment (HR: 1.00; 95% CI, 0.88–1.14).45 Importantly, the authors reported that the key to long‐term survival was completeness of revascularization in both on‐ and off‐pump patients. Similarly, in 942 propensity score–matched patient pairs from a single Italian center, there was no difference in 10‐year mortality between on‐ and off‐pump surgery (HR: 1.3; 95% CI, 0.91–1.9).46 In a study from the United Kingdom of >13 000 propensity‐matched patients followed for 13 years, there was no difference in survival, suggesting that when OPCAB is performed by highly experienced surgeons, there is no adverse effect on survival.47In contrast, a propensity‐matched single‐institution study from Baylor Research Institute, Dallas, TX, USA showed an elevated risk of late mortality at 10 years with OPCAB (HR: 1.18; 95% CI, 1.02–1.38).48 These concerns about late mortality were further explored in a meta‐analysis of 42 RCTs and 31 risk‐adjusted observational studies that included 1.2 million patients.49 OPCAB was associated with a statistically significant 10% relative increase in the probability of mortality at 5 years (95% CI, 5.0–15.0%) that increased to 14% at 10 years in the observational studies (95% CI, 11.0–17.0%). It is important to note, however, that although statistical significance was reached, the clinical relevance of the reported difference remains to be determined (absolute difference: 0.5% at 5 years and 3% at 10 years).The most recent meta‐analysis including only RCTs with ≥4‐year outcome and pooling data from 8145 participants reported an OR for long‐term mortality of 1.16 for OPCAB (95% CI, 1.02–1.32).50To conclude, long‐term data are discordant. Based on the current evidence, the possibility that off‐pump surgery results in worse clinical outcomes cannot be excluded.OPCAB in Specific Subsets of PatientsHigh‐Risk PopulationsMultiple studies have suggested a benefit of OPCAB in high‐risk patient populations. A recent meta‐analysis of RCTs demonstrated a significant relationship between the patient risk profile and the benefits from OPCAB, with the most benefit derived from reduced perioperative morbidity.51An analysis of the STS ACSD from 1997 to 2007 showed that there were 38% and 55% reductions in the odds of early mortality for patients undergoing off‐pump operations in the third‐ and fourth‐highest risk quartiles, respectively.52 In contrast, a study of the Australian and New Zealand Society of Cardiac and Thoracic Surgeons database for high‐risk patients associated OPCAB with reduced morbidity but showed similar operative mortality as compared to ONCAB.53Impaired Ventricular FunctionAs for patients with low ejection fraction (EF), an analysis of the STS ACSD from 2008 to 2011 of 25 667 patients with low EF (<30%) found that the risks of death, stroke, and major adverse cardiac events (MACE) were lower in the OPCAB group.54 These findings were corroborated by analysis of the Japan Adult Cardiovascular Surgery Database in which OPCAB was associated with reduced early morbidity and mortality in patients with EF <30%.55 A meta‐analysis of observational studies concluded that OPCAB may be associated with lower incidence of early mortality in patients with impaired left ventricular function but noted that the method of handling the conversion‐related mortality in each study was uncertain and may have influenced the results. In addition, incomplete revascularization (IR) in the OPCAB group occurred more often and may explain why the early advantage in mortality was not maintained long term.56Advanced AgeAdvanced age is a known risk factor in CABG.57 In a systematic review of 16 observational studies of CABG in octogenarians (18 685 ONCAB and 8938 OPCAB), in‐hospital mortality (pooled OR: 0.64; 95% CI, 0.44–0.93; P=0.02), and stroke (pooled OR: 0.61; 95% CI, 0.48–0.76; P<0.001) were significantly lower in OPCAB.58 However, results from a Danish registry did not show a difference in outcomes between ONCAB and OPCAB in patients aged >70 years.59 A propensity matched study of 6943 pairs of octogenarians showed a 30% reduction in the odds of stroke with OPCAB using the Nationwide Inpatient Sample (NIS).60 In addition, the largest RCT to date comparing OPCAB and ONCAB in elderly patients (aged ≥75 years), reported no significant difference between ONCAB and OPCAB with regard to the composite outcome of death, stroke, MI, repeat revascularization, or new renal replacement therapy within 30 days and 1 year after surgery.41Female SexNumerous studies report CABG mortality to be higher in women.61 In fact, according to the STS CABG risk model, female sex is associated with increased risk of operative mortality (OR: 1.31), major complications (OR: 1.18), and increased hospital length of stay (OR: 1.24).57 OPCAB, however, may narrow or eliminate this disparity in outcomes between women and men. A large study at an experienced OPCAB US academic center concluded that OPCAB disproportionately benefits women and narrows the sex disparity in outcomes after CABG. Female patients (n=3248) and those treated with OPCAB (n=4492) were older and had more comorbidities than male patients (n=8165) and those treated with ONCAB (n=6921), respectively. Women treated with ONCAB had risk‐adjusted ORs of 1.60 for death (P=0.01) and 1.71 for MACE (P<0.001) compared with men who had ONCAB. In contrast, women treated with OPCAB had outcomes similar to men who had either OPCAB or ONCAB. Among women, OPCAB was associated with a significant reduction in death (OR: 0.39; P=0.001) and MACE (OR: 0.43; P<0.001).63These findings were replicated at a national level in an STS ACSD study of 63 experienced centers that performed >100 OPCAB cases between 2004 and 2005. Women (n=11 785) and those treated with OPCAB (n=16 245) were older and had more comorbidities than men (n=30 662) and those treated with conventional ONCAB (n=26 202), respectively. The risk‐adjusted ORs for death and major complications were significantly lower with OPCAB than with ONCAB. Among ONCAB cases only, women had a significantly greater adjusted risk of death, prolonged ventilation, and longer hospital length of stay than men; however, among OPCAB cases, women had similar outcomes.64 A meta‐analysis of observational studies associated OPCAB with reduced perioperative MI but not with reduction of other morbidities or operative mortality.65 Of note, women undergoing OPCAB received fewer grafts than those undergoing ONCAB.OPCAB may have a selective benefit for women. The underlying mechanism is unclear and is unlikely to be related to avoidance of CPB because there is no major sex difference in outcomes associated with valve surgery.66 It is interesting, however, that women who undergo OPCAB are more likely to receive an internal mammary artery bypass than those undergoing ONCAB.67Neurological RiskThe possible association of OPCAB with reduced stroke with enhanced benefit in higher risk patients67 argues for a potential benefit in patients with a history of atheromatous aorta or cerebrovascular disease. A large single‐center study utilizing propensity‐matched analysis in patients with atheromatous disease of the ascending aorta associated ONCAB with an increased risk of postoperative stroke (OR: 1.4; P=0.05) and operative mortality.68 Another stud

Abstract Essential thrombocythemia (ET) is characterized by abnormal megakaryopoiesis and enhanced thrombotic risk. Once-daily low-dose aspirin is the recommended antithrombotic regimen, but accelerated platelet generation may reduce the duration of platelet cyclooxygenase-1 (COX-1) inhibition. We performed a multicenter double-blind trial to investigate the efficacy of 3 aspirin regimens in optimizing platelet COX-1 inhibition while preserving COX-2–dependent vascular thromboresistance. Patients on chronic once-daily low-dose aspirin (n = 245) were randomized (1:1:1) to receive 100 mg of aspirin 1, 2, or 3 times daily for 2 weeks. Serum thromboxane B2 (sTXB2), a validated biomarker of platelet COX-1 activity, and urinary prostacyclin metabolite (PGIM) excretion were measured at randomization and after 2 weeks, as primary surrogate end points of efficacy and safety, respectively. Urinary TX metabolite (TXM) excretion, gastrointestinal tolerance, and ET-related symptoms were also investigated. Evaluable patients assigned to the twice-daily and thrice-daily regimens showed substantially reduced interindividual variability and lower median (interquartile range) values for sTXB2 (ng/mL) compared with the once-daily arm: 4 (2.1-6.7; n = 79), 2.5 (1.4-5.65, n = 79), and 19.3 (9.7-40; n = 85), respectively. Urinary PGIM was comparable in the 3 arms. Urinary TXM was reduced by 35% in both experimental arms. Patients in the thrice-daily arm reported a higher abdominal discomfort score. In conclusion, the currently recommended aspirin regimen of 75 to 100 once daily for cardiovascular prophylaxis appears to be largely inadequate in reducing platelet activation in the vast majority of patients with ET. The antiplatelet response to low-dose aspirin can be markedly improved by shortening the dosing interval to 12 hours, with no improvement with further reductions (EudraCT 2016-002885-30).

Arachidonic acid is one of the most abundant and ubiquitous ω-6 polyunsaturated fatty acid, present in esterified form in the membrane phospholipids of all mammalian cells and released from phospholipids by several phospholipases in response to various activating or inhibitory stimuli. Arachidonic acid is the precursor of a large number of enzymatically and non-enzymatically derived, biologically active autacoids, including prostaglandins (PGs), thromboxane (TX) A2, leukotrienes, and epoxyeicosatetraenoic acids (collectively called eicosanoids), endocannabinoids and isoprostanes, respectively. Eicosanoids are local modulators of the physiological functions and pathophysiological roles of blood vessels and platelets. For example, the importance of cyclooxygenase (COX)-1-derived TXA2 from activated platelets in contributing to primary haemostasis and atherothrombosis is demonstrated in animal and human models by the bleeding complications and cardioprotective effects associated with low-dose aspirin, a selective inhibitor of platelet COX-1. The relevance of vascular COX-2-derived prostacyclin (PGI2) in endothelial thromboresistance and atheroprotection is clearly shown by animal and human models and by the adverse cardiovascular effects exerted by COX-2 inhibitors in humans. A vast array of arachidonic acid-transforming enzymes, downstream synthases and isomerases, transmembrane receptors, and specificity in their tissue expression make arachidonic acid metabolism a fine-tuning system of vascular health and disease. Its pharmacological regulation is central in human cardiovascular diseases, as demonstrated by biochemical measurements and intervention trials.

At 125, aspirin still represents the cornerstone of anti-platelet therapy for the acute treatment and long-term prevention of atherothrombosis. The development of a selective regimen of low-dose aspirin for the inhibition of platelet thromboxane production was key to maximizing its antithrombotic efficacy and minimizing its gastrointestinal toxicity. Based on about 50 observational studies, published over the past 30 years, aspirin and other cyclooxygenase inhibitors have been associated with a reduced risk of colorectal cancer, and possibly other digestive tract cancers. The apparent chemopreventive effect of aspirin has been confirmed in post-hoc analyses of randomized cardiovascular trials and their meta-analyses. Moreover, prevention of sporadic colorectal adenoma recurrence was demonstrated by randomized controlled trials of low-dose aspirin and selective cyclooxygenase-2 inhibitors. A single placebo-controlled randomized trial of aspirin has shown long-term colorectal cancer prevention in patients with the Lynch syndrome. The sequential involvement of thromboxane-dependent platelet activation and cyclooxygenase-2-driven inflammatory response in the early stages of colorectal carcinogenesis may explain these clinical benefits. The aim of this mini-review is to analyze the existing evidence for a chemopreventive effect of aspirin and other cyclooxygenase inhibitors and discuss the missing pieces of this mechanistic and clinical puzzle. SIGNIFICANCE STATEMENT: Low-dose aspirin and other cyclooxygenase inhibitors have been associated with a reduced risk of colorectal cancer, and possibly other digestive tract cancers. The sequential involvement of thromboxane-dependent platelet activation and cyclooxygenase-2-driven inflammatory response in the early stages of colorectal carcinogenesis may explain these clinical benefits. The aim of this mini-review is to analyze the evidence for a chemopreventive effect of aspirin and other cyclooxygenase inhibitors and discuss the missing pieces of this mechanistic and clinical puzzle.

Abstract Background Pre-clinical models demonstrate that platelet activation is involved in the spread of malignancy. Ongoing clinical trials are assessing whether aspirin, which inhibits platelet activation, can prevent or delay metastases. Methods Urinary 11-dehydro-thromboxane B 2 (U-TXM), a biomarker of in vivo platelet activation, was measured after radical cancer therapy and correlated with patient demographics, tumour type, recent treatment, and aspirin use (100 mg, 300 mg or placebo daily) using multivariable linear regression models with log-transformed values. Results In total, 716 patients (breast 260, colorectal 192, gastro-oesophageal 53, prostate 211) median age 61 years, 50% male were studied. Baseline median U-TXM were breast 782; colorectal 1060; gastro-oesophageal 1675 and prostate 826 pg/mg creatinine; higher than healthy individuals (~500 pg/mg creatinine). Higher levels were associated with raised body mass index, inflammatory markers, and in the colorectal and gastro-oesophageal participants compared to breast participants ( P &lt; 0.001) independent of other baseline characteristics. Aspirin 100 mg daily decreased U-TXM similarly across all tumour types (median reductions: 77–82%). Aspirin 300 mg daily provided no additional suppression of U-TXM compared with 100 mg. Conclusions Persistently increased thromboxane biosynthesis was detected after radical cancer therapy, particularly in colorectal and gastro-oesophageal patients. Thromboxane biosynthesis should be explored further as a biomarker of active malignancy and may identify patients likely to benefit from aspirin.

Homocystinuria due to homozygous cystathionine beta-synthase deficiency is an inborn error of metabolism characterized by a high incidence of thrombosis and premature atherosclerosis. We evaluated TXA2 biosynthesis in vivo and several in vitro tests of platelet function in 11 homocystinuric patients and 12 healthy controls. In vitro, patients' platelet aggregation was within control values as were TXB2 formation, fibrinogen binding, and ATP secretion in response to thrombin. In contrast, the urinary excretion of 11-dehydro-TXB2, a major enzymatic derivative of TXA2, was > 2 SD of controls in all patients (1,724 +/- 828 pg/mg creatinine, mean +/- SD, in patients vs. 345 +/- 136 in controls, P < 0.001). The administration to four patients of low-dose aspirin (50 mg/d for 1 wk) reduced metabolite excretion by > 80%. The recovery of 11-dehydro-TXB2 excretion over the 10 d that followed aspirin cessation occurred with a pattern consistent with the entry into the circulation of platelets with intact cyclooxygenase activity. Prolonged partial reduction in the abnormally high excretion of both 11-dehydro-TXB2 and 2,3-dinor-TXB2, was also observed in seven patients who ingested 500 mg daily for 3 wk of the antioxidant drug probucol. These results provide evidence for enhanced thromboxane biosynthesis in homocystinuria and for its partial dependence on probucol-sensitive mechanisms. Furthermore, the elevated TXA2 formation in homocystinuria is likely to reflect, at least in part, in vivo platelet activation.

Background We have previously reported aspirin failure in suppressing enhanced thromboxane (TX) biosynthesis in a subset of episodes of platelet activation during the acute phase of unstable angina. The recent discovery of a second prostaglandin H synthase (PGHS-2), inducible in response to inflammatory or mitogenic stimuli, prompted us to reexamine TXA 2 biosynthesis in unstable angina as modified by two cyclooxygenase inhibitors differentially affecting PGHS-2 despite a comparable impact on platelet PGHS-1. Methods and Results We randomized 20 patients (15 men and 5 women aged 59±10 years) with unstable angina to short-term treatment with aspirin (320 mg/d) or indobufen (200 mg BID) and collected 6 to 18 consecutive urine samples. Urinary 11-dehydro-TXB 2 was extracted and measured by a previously validated radioimmunoassay as a reflection of in vivo TXA 2 biosynthesis. Metabolite excretion averaged 102 pg/mg creatinine (median value; n=76) in the aspirin group and 55 pg/mg creatinine (median value; n=99) in the indobufen group ( P &lt;.001). There were 16 samples (21%) with 11-dehydro-TXB 2 excretion &gt;200 pg/mg creatinine among patients treated with aspirin versus 6 such samples (6%) among those treated with indobufen ( P &lt;.001). In vitro and ex vivo studies in healthy subjects demonstrated the capacity of indobufen to largely suppress monocyte PGHS-2 activity at therapeutic plasma concentrations. In contrast, aspirin could only inhibit monocyte PGHS-2 transiently at very high concentrations. Conclusions We conclude that in unstable angina, episodes of aspirin-insensitive TXA 2 biosynthesis may reflect extraplatelet sources, possibly expressing the inducible PGHS in response to a local inflammatory milieu, and a selective PGHS-2 inhibitor would be an ideal tool to test the clinical relevance of this novel pathway of arachidonic acid metabolism in this setting.

Increased platelet thromboxane (TX)A2 production has been described in type IIa hypercholesterolemia. To verify the relevance of these capacity-related measurements to the actual rate of TXA2 biosynthesis in vivo, we studied the urinary excretion of its major enzymatic metabolites in 46 patients with type IIa hypercholesterolemia and 20 age-matched controls.Urinary 11-dehydro-TXB2 and 2,3-dinor-TXB2 were measured by previously validated radioimmunoassays. The excretion rate of 11-dehydro-TXB2 was significantly (p less than 0.001) higher in patients (68.7 +/- 35.1 ng/hr, mean +/- SD) than in controls (22.4 +/- 9.4 ng/hr), with metabolite excretion greater than 2 SD of the normal mean in 74% of the patients. Urinary 11-dehydro-TXB2 was significantly (p less than 0.01) correlated with the threshold aggregating concentration of collagen (r = -0.641) and arachidonate (r = -0.734) and with agonist-induced platelet TXB2 production in vitro (r = 0.647 and 0.748, respectively). Moreover, a statistically significant correlation (r = 0.673, p less than 0.001, n = 66) was found between 11-dehydro-TXB2 excretion and total plasma cholesterol. The enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor simvastatin (20 mg/day for 6 months) significantly reduced cholesterol levels by 22-28% and urinary 11-dehydro-TXB2 excretion by 32-42% in 10 patients. However, the reduction in the latter did not correlate with the reduction in the former and may have resulted from a nonspecific effect of simvastatin. Moreover, selective inhibition of platelet cyclooxygenase activity by low-dose aspirin (50 mg/day for 7 days) was associated with cumulative inhibition of 11-dehydro-TXB2 excretion by approximately 70% in six patients.TXA2 biosynthesis is enhanced in the majority of patients with type IIa hypercholesterolemia; this is, at least in part, a consequence of abnormal cholesterol levels, as suggested by the correlation between the two. Low-dose aspirin can largely suppress increased metabolite excretion, thus suggesting that it reflects TXA2-dependent platelet activation in vivo.

Since our last report on antithrombotic therapy in 1995, 1 Hirsh J Dalen JE Fuster V et al. Aspirin and other platelet-active drugs: the relationship among dose, effectiveness and side effects. Chest. 1995; 108: 247S-257S Abstract Full Text Full Text PDF PubMed Google Scholar new information has been published on the role of aspirin and other platelet-active drugs in the treatment and prevention of atherothrombosis. These new data can be summarized as follows: (1) two large randomized studies have tested the efficacy and safety of aspirin in patients with acute ischemic stroke; 2 International Stroke Trial Collaborative GroupThe International Stroke Trial (IST): a randomised trial of aspirin, subcutaneous heparin, both, or neither among 19,435 patients with acute ischemic stroke. Lancet. 1997; 349: 1569-1581 Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar ,3 CAST (Chinese Acute Stroke Trial) Collaborative GroupCAST: randomised placebo-controlled trial of early aspirin use in 20,000 patients with acute ischemic stroke. Lancet. 1997; 349: 1641-1649 Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar (2) two recent studies have shown that low-dose aspirin therapy is effective and safe in the primary prevention of ischemic heart disease in men at high risk 4 The Medical Research Council's General Practice Research FrameworkThrombosis prevention trial: randomised trial of low-intensity oral anticoagulation with warfarin and low-dose aspirin in the primary prevention of ischemic heart disease in men at increased risk. Lancet. 1998; 351: 233-241 Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar as well as in men and women with hypertension; 4a Hansson L Zanchetti A Carruthers SG et al. Effects of intensive blood-pressure lowering and low-dose aspirin in patients with hypertension: principal results of the Hypertension Optimal Treatment (HOT) randomised trial. Lancet. 1998; 351: 1755-1762 Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar (3) the clinical efficacy of dipyridamole has to be reassessed in the light of the European Stroke Prevention Study-2 (ESPS-2); 5 Diener HC Cunha L Forbes C et al. European Stroke Prevention Study: II. Dipyridamole and acetylsalicylic acid in the secondary prevention of stroke. J Neurol Sci. 1996; 143: 1-13 Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar (4) a novel thienopyridine derivative, clopidogrel, has been shown to be at least as effective as aspirin in one very large phase III trial 6 CAPRIE Steering CommitteeA randomised, blinded, trial of clopidogrel versus aspirin in patients at risk of ischemic events (CAPRIE). Lancet. 1996; 348: 1329-1339 Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar and may be a safer alternative to aspirin than ticlopidine; (5) besides abciximab, now on the market in many countries, several platelet glycoprotein (GP) IIb/IIIa (integrin αIlbβ3) antagonists are in various stages of clinical development and have shown improved efficacy over conventional antithrombotic treatment in high-risk acute coronary settings; 7 Anderson KM Weisman HF Coller BS. Platelet glycoprotein IIb/IIIa receptor inhibitors. in: Hennekens CH Buring JE Manson JE Clinical trials in cardiovascular disease. WB Saunders, Philadelphia1999 Google Scholar and (6) the additive effect of ticlopidine and aspirin in the prevention of coronary stent thrombosis has been demonstrated, 8 STARSN Engl J Med. 1998; (in press) Google Scholar while controversial results have been reported for the combination of low-dose aspirin with low-intensity oral anticoagulation with warfarin. 4 The Medical Research Council's General Practice Research FrameworkThrombosis prevention trial: randomised trial of low-intensity oral anticoagulation with warfarin and low-dose aspirin in the primary prevention of ischemic heart disease in men at increased risk. Lancet. 1998; 351: 233-241 Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar ,9 Coumadin Aspirin Reinfarction Study (CARS) InvestigatorsRandomised double-blind trial of fixed low-dose warfarin with aspirin after myocardial infarction. Lancet. 1997; 350: 389-396 Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar

To investigate early events possibly related to the development of diabetic angiopathy, we examined whether 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha) formation, a marker of in vivo oxidant stress, is altered in different stages of type 1 diabetes (T1DM) and whether it correlates with the rate of thromboxane (TX) A2 biosynthesis, a marker of in vivo platelet activation. We also investigated the relationship between inflammatory markers and F2-isoprostane formation in this setting.A cross-sectional study was performed in 23 insulin-treated patients aged <18 years with new-onset T1DM (<or=6 weeks, group A), matched for age and gender with 23 patients with stable disease (>1 year, group B). Urinary 8-iso-PGF2alpha and 11-dehydro-TXB2 were measured in all patients and in age- and gender-matched controls. Circulating interleukin-6 (IL-6), tumor necrosis factor-alpha, and C-reactive protein were also determined as markers of the inflammatory response. Fifteen of the 23 children in group A were reexamined after 12 months. Compared with either controls or group B, diabetic children in group A showed significantly higher levels of 8-iso-PGF2alpha, 11-dehydro-TXB2, IL-6, tumor necrosis factor-alpha, and C-reactive protein. Statistically significant correlations between IL-6 and both 8-iso-PGF2alpha (r=0.63, P<0.001) and 11-dehydro-TXB2 (r=0.51, P<0.01) were observed. The 15 patients reexamined after 1 year showed a significant reduction in lipid peroxidation and platelet activation (P<0.02 and P<0.001, respectively), consistent with reduced levels of IL-6 and tumor necrosis factor-alpha.These results demonstrate that enhanced lipid peroxidation and platelet activation represent early events in T1DM that are possibly related to an acute inflammatory response. These noninvasive indexes may help in further examining T1DM pathophysiology and monitoring pharmacological interventions to interfere with disease development and progression.

Prostaglandin G and H synthases, or cyclooxygenases (COXs), catalyze the formation of prostaglandins (PGs).Whereas COX-1 is diffusely expressed in lymphoid cells in embryonic day 15.5 thymus, COX-2 expression is sparse, apparently limited to stromal cells.By contrast, COX-2 is predominant in a subset of medullary stromal cells in three-to five-week-old mice.The isozymes also differ in their contributions to lymphocyte development.Thus, experiments with selective COX-1 inhibitors in thymic lobes from normal and recombinase-activating gene-1 knockout mice support a role for this isoform in the transition from CD4 -CD8 -double-negative (DN) to CD4 + CD8 + double-positive (DP).Concordant data were obtained in COX-1 knockouts.Pharmacological inhibition and genetic deletion of COX-2, by contrast, support its role during early thymocyte proliferation and differentiation and, later, during maturation of the CD4 helper T-cell lineage.PGE 2 , but not other PGs, can rescue the effects of inhibition of either isoform, although it acts through distinct EP receptor subtypes.COX-dependent PG generation may represent a mechanism of thymic stromal support for T-cell development.

To test the hypothesis that the vasoconstrictor thromboxane A2 may affect renal hemodynamics in lupus nephritis, we examined the short-term effects of a selective thromboxane-receptor antagonist, BM 13,177, and of low-dose aspirin. In a randomized, double-blind, crossover study, 10 patients with biopsy-proved lupus nephritis were given a 48-hour continuous infusion of BM 13,177 or placebo. At base line, seven patients had markedly elevated urinary levels of thromboxane B2, the breakdown product of thromboxane A2. During the infusion of BM 13,177, the inulin clearance rate, which was 68 ml per minute per 1.73 m2 of body-surface area at base line, increased by an average of 24 percent (range, 12 to 47 percent; P less than 0.01). Para-aminohippurate clearance was increased to the same extent, with no change in the filtration fraction. The bleeding time doubled, indicating an occupancy of platelet thromboxane receptors of more than 95 percent. The hemodynamic changes were associated with a significant increase in sodium excretion from 76 to 118 mmol per day (P less than 0.01) but with no change in arterial blood pressure. In another study, 10 additional patients with lupus nephritis were randomly assigned to receive either placebo or 20 mg of aspirin twice daily for four weeks. The aspirin regimen produced a selective, cumulative inhibition of platelet cyclooxygenase activity and a doubling of bleeding time. However, there was no change in the inulin clearance rate and no change in urinary levels of thromboxane B2 or 6-keto-prostaglandin F1 alpha, which are indicators of renal synthesis of thromboxane A2 and prostacyclin, respectively. We conclude that in lupus nephritis, impairment of renal function is at least in part mediated hemodynamically and is reversible with a thromboxane antagonist. Platelets, however, are not a major source of thromboxane A2 synthesis and action within the kidney.

Rabbits were immunized with a conjugate of leukotriene (LT) C4 and bovine serum albumin prepared by coupling the single free amino group of the hapten to the protein using gluteraldehyde. Binding of [3H]LTC4 to the antibodies obtained is inhibited by 50% with 1.5 ng LTC4. The relative cross-reaction of LTD4 is 16% and of LTC4-methyl ester 3.6%. The validity of the radioimmunoassay was demonstrated by comparison with bioassay using the isolated guinea pig ileum. Using the radioimmunoassay it could be shown that endogenous LTC4 is released in a dose-dependent manner by human polymorphonuclear leucocytes stimulated with the divalent cation ionophore A23187.

1 The present study was undertaken to characterize the spectrum of arachidonic acid metabolites present in synovial effusions of patients with rheumatoid or psoriatic arthritis, and to compare changes in their concentration following a short-term treatment with 6alpha-methyl-prednisolone (6-MeP: 4-8 mg/day) or indoprofen (1.2 g/day), a nonsteroidal anti-inflammatory agent with proven synovial prostaglandin inhibitory effect.2 Measurements of prostaglandin E(2) (PGE(2)), thromboxane (TX) B(2), 6-keto-PGF(1alpha) and PGF(2alpha) were performed by radioimmunoassay techniques in synovial effusions obtained from 23 patients, and validated by thin-layer chromatographic analysis of the extracted immunoreactivity.3 PGE(2) and TXB(2) accounted for more than 60% of the total immunoreactivity in untreated patients. The absence of any constant ratio between the different arachidonic acid metabolites detected in synovial fluid is consistent with a heterogeneous cellular origin of these compounds.4 Indoprofen treatment was associated with a consistent reduction of synovial prostaglandin and thromboxane concentrations, ranging from 36% in the case of 6-keto-PGF(1alpha) to 90% in the case of PGE(2).5 In contrast, 6-MeP caused opposite changes on different metabolites originating via the cyclo-oxygenase pathway. Thus, 6-keto-PGF(1alpha) concentrations were reduced by 35%, PGF(2alpha) concentrations were increased by 30%, while PGE(2) and TXB(2) were unchanged following 6-MeP.6 Although the mechanism(s) underlying the failure of 6-MeP to reduce synovial PGE(2) and TXB(2) levels are uncertain, the results of the present study clearly indicate that therapeutic doses of steroidal and nonsteroidal anti-inflammatory drugs cause quite distinct changes in arachidonic acid metabolism, which might be relevant to their specific therapeutic actions and side-effects.

Arachidonic acid metabolism plays an important role in acute ischemic syndromes affecting the coronary or cerebrovascular territory, as reflected by biochemical measurements of eicosanoid biosynthesis and the results of inhibitor trials in these settings. Two cyclooxygenase (COX)-isozymes have been characterized, COX-1 and COX-2, that differ in terms of regulatory mechanisms of expression, tissue distribution, substrate specificity, preferential coupling to upstream and downstream enzymes, and susceptibility to inhibition by the extremely heterogeneous class of COX-inhibitors. Although the role of platelet COX-1 in acute coronary syndromes and ischemic stroke is firmly established through approximately 20 years of thromboxane metabolite measurements and aspirin trials, the role of COX-2 expression and inhibition in atherothrombosis is substantially uncertain, because the enzyme was first characterized in 1991 and selective COX-2 inhibitors became commercially available only in 1998. In this review, we discuss the pattern of expression of COX-2 in the cellular players of atherothrombosis, its role as a determinant of plaque "vulnerability," and the clinical consequences of COX-2 inhibition. Recent studies from our group suggest that variable expression of upstream and downstream enzymes in the prostanoid biosynthetic cascade may represent important determinants of the functional consequences of COX-2 expression and inhibition in different clinical settings.

F2-isoprostanes are prostaglandin (PG) F2-like compounds that are formed in vivo directly by free radical-catalyzed lipid peroxidation. One of the compounds that can be produced in abundance by such mechanism is 8-epi-PGF2 alpha, a potent vasoconstrictor. We have developed an enzyme immunoassay and a radioimmunoassay for measuring urinary concentrations of 8-epi-PGF2 alpha by raising antibodies against this compound. The antisera presented high titers (> 1/300,000) and provided highly sensitive assays (IC50, 8 and 24 pg/ml, for EIA and RIA, respectively); cross-reactivity with other PG was negligible. The interassay reproducibility of EIA was assessed by measuring the same urine stored frozen in aliquots after solid phase extraction and thin-layer chromatography (17%, n = 13). Measurements of urinary 8-epi-PGF2 alpha by immunoassays were validated using different antisera and by comparison with gas chromatography/mass spectrometry. Healthy volunteers excreted 25 +/- 12 ng of 8-epi-PGF2 alpha/mmol creatinine (n = 19), with no circadian variation over three consecutive 8-hr collection periods (n = 10); preliminary results showed that excretion increased as a function of age. Urinary excretion of 8-epi-PGF2 alpha was unchanged by treatment with two nonsteroidal antiinflammatory drugs, Ibuprofen at 1.2 g/day for 4 days (n = 4) or aspirin as a single administration of 1 g (n = 6). In contrast, the urinary excretion of 11-dehydro-thromboxane B2, a platelet cyclooxygenase-derived metabolite was reduced by more than 80% after aspirin administration.(ABSTRACT TRUNCATED AT 250 WORDS)

We tested the hypothesis that insulin resistance, per se, contributes to increased platelet activation in obesity, independently of underlying inflammation. Obesity, insulin resistance, and atherosclerosis are closely linked phenomena associated with low-grade inflammation. Obesity is associated with persistent platelet activation in otherwise healthy women. We performed a cross-sectional study in 40 obese and 20 non-obese healthy women using urinary thromboxane metabolite excretion as a non-invasive index of platelet activation. An index of insulin sensitivity, SI, and plasma adiponectin, C-reactive protein (CRP), and CD40 ligand (CD40L) levels were measured. Obese women had significantly (p < 0.0001) higher 11-dehydro-thromboxane B2(11-dehydro-TXB2) excretion (median 718 vs. 211 pg/mg creatinine), CRP (1.13 vs. 0.48 mg/l), and CD40L levels (4.45 vs. 0.90 ng/ml) than controls. Obese women had lower SI(median 2.51 vs. 5.0 104min−1/[μU/ml], p < 0.002) and adiponectin (6.3 vs. 10 μg/ml, p < 0.01) than control subjects. On multiple regression analysis, waist-to-hip ratio (β = 0.27, p < 0.05) and SI(β = −0.72, p < 0.04) predicted 11-dehydro-TXB2excretion rate, independently of adiponectin, CRP, CD40L, and lipid patterns. In order to investigate the cause-effect relationship of these associations, we examined the effects of a 12-week weight loss program or a 3-week pioglitazone treatment on urinary 11-dehydro-TXB2in 10 women with impaired SIand visceral obesity. Successful weight loss (0.6 kg loss/week) achieved in 5 subjects was associated with increased SI(+92%) and decreased CD40L (−27%), CRP (−37%), and 11-dehydro-TXB2(−53%) (p < 0.05). Consistently, improvement of insulin sensitivity achieved with pioglitazone significantly decreased urinary 11-dehydro-TXB2excretion (−43%, p < 0.05) without changes in body weight. Insulin resistance is a major determinant of platelet activation in female obesity.

Aspirin has been convincingly shown to reduce the incidence of vascular occlusive events in a wide range of patients at risk of thrombotic complications. These beneficial effects are currently linked to suppression of thromboxane A2-dependent platelet aggregation. This in turn reflects permanent loss of the cyclooxygenase activity of platelet prostaglandin G/H synthase, through acetylation of Ser530. Progress in our understanding of the molecular mechanism of action of aspirin and definition of the clinical pharmacology of its platelet effects has been associated with a downward trend in its daily dosage. This has been reduced by a factor of ten over the last decade, substantially reducing gastrointestinal toxicity, while leaving antithrombotic efficacy virtually unchanged. Carlo Patrono reviews the biochemical, pharmacological and clinical data that form the basis of the present consensus and provide a rationale for clinical trials o f low-dose aspirin.

Thromboxane A2, a potent vasoconstrictor and platelet agonist, is an evanescent cyclooxygenase product of arachidonic acid. Assessment of thromboxane biosynthesis commonly relies upon analysis of the stable but biologically inactive hydration product, thromboxane B2. However, measurement of this compound in plasma is readily confounded by platelet activation ex vivo. We have identified 11-dehydro-thromboxane B2, 11-dehydro-13,14-dihydro-15-keto-thromboxane B2, and 2,3-dinor-thromboxane B2 as enzymatic products of infused thromboxane B2 in the human circulation. Biosynthesis of deuterated standards permitted the development of quantitative analyses for these compounds, employing capillary gas chromatography-negative ion chemical ionization-mass spectrometry. We thus established that the postinfusion half-lives of 11-dehydro-thromboxane B2 and the keto-dihydro metabolite approximated 1 hour, while that of the dinor metabolite ranged from 15 to 17 min. Combined analysis of short- and long-lived enzymatic metabolites of thromboxane B2 promises to bypass the problem of ex vivo platelet activation and enhance the likelihood of relating a discreet clinical event to an alteration in the biosynthesis of thromboxane A2 in the human circulation.

Thromboxane A2 (TxA2), released by aggregating platelets, has been proposed as a potential mediator of coronary vasospasm. We studied six patients with variant angina, a clinical syndrome due to coronary vasospasm, and one patient with frequent recurrent episodes of transient ST-segment depression at rest in whom the spasm was demonstrated angiographically. All patients underwent continuous ECG monitoring for 2 days before and 2 days after a single, low, i.v. dose of aspirin (2 mg/kg), which reduced TxB2 (the stable metabolite of TxA2) to less than 3% of the control values. There were 129 transient ischemic episodes during control and 146 after aspirin, when platelet TxB2 was reduced to negligible levels. The duration, severity and incidence of symptomatic episodes were not significantly affected by TxA2 blockade. We conclude that platelet TxA2 is probably not responsible for the initiation of coronary vasospasm.

Summary A dynamic thrombotic process, coronary spasm or both can be responsible for recurrent episodes of transient reduction of coronary blood flow in unstable angina. We have investigated the temporal relationship between episodic platelet activation, as detected by increased urinary excretion of 11-dehydro-TXB2, and spontaneous myocardial ischemia, assessed by continuous electrocardiographic monitoring and recording in 21 patients with unstable angina pectoris. In order to validate measurements of metabolite excretion as a reflection of intracoronary platelet activation, we have also performed repeated urine sampling from 8 patients undergoing PTCA and from 6 patients with peripheral vascular disease. The latter showed a 16% coefficient of variation in 3 consecutive 8-h urine samples. 11-dehydro-TXB2 increased significantly, by up to 15-fold, in the 2.5- to 5.0-h urine collection encompassing PTCA and decreased by &gt; 50% during the following 2-h period. Patients with unstable angina were characterized by episodic increases (&gt;2 SD of controls) in metabolite excretion, in successive 6-8 h specimens. Paired measurements of 11-dehydro-TXB2 and 2, 3-dinor-TXB2 in 15 urine samples did not reveal evidence of altered metabolic disposition of endogenously released TXB2. A total of 125 ECG ischemic episodes were recorded, of which 64% asymptomatic. We have compared these biochemical and ECG changes in patients randomized to i. v. low-dose aspirin or i.v. isosorbide dinitrate and oral diltiazem. Twenty-five of 56 (i.e. 45%) urine samples obtained in aspirin-free periods showed increased metabolite excretion as compared to 15 of 88 (i.e. 17%) samples collected during aspirin. Of the former, only 3 episodes of enhanced 11-dehydro-TXB2 excretion were associated with ST-segment changes, 7 with chest pain, and 15 with no ECG or clinical changes. Metabolite excretion was approximately 70% lower during aspirin administration than during coronary dilators. However, despite &gt; 95% suppression of platelet cyclooxygenase activity, as monitored ex vivo, incomplete suppression of in vivo TXB2 biosynthesis was occasionally seen during low-dose aspirin therapy. We conclude that in unstable angina, episodic platelet activation is infrequently associated with spontaneous myocardial ischemia. Although the two events may represent functional expressions of the same coronary lesion, they are likely to be triggered by independent mechanisms through different mediators.

Abstract Increased thromboxane (TX) production and modified aspirin sensitivity has been detected in vitro in platelets isolated from patients with polycythemia vera. To verify the relevance of these capacity-related measurements to the actual rate of TXA2 biosynthesis in vivo and its suppression by oral aspirin, we have investigated the urinary excretion of major enzymatic metabolites of TXB2 in 17 patients with polycythemia vera and 23 gender- and age-matched controls. Urinary 11-dehydro-TXB2 and 2,3-dinor-TXB2 were measured by previously validated radioimmunoassays. In addition, urinary immunoreactive leukotriene (LT) E4 was measured to explore the 5-lipoxygenase pathway of arachidonate metabolism. Polycythemic patients had significantly (P &lt; .001) higher excretion rates of both 11-dehydro-TXB2 (1,033 +/- 1,050 v 117 +/- 45 pmol/mmol creatinine; mean +/- SD) and 2,3-dinor-TXB2 (725 +/- 676 v 82 +/- 43 pmol/mmol creatinine) than controls. In contrast, urinary LTE4 was not significantly different. Enhanced metabolite excretion did not correlate with the platelet count or with the hematocrit value, and was not related to the current treatment or to a clinical history of thrombotic complications. Platelet TX receptor studies did not show any significant changes in the binding characteristics of two different ligands. A platelet-selective regimen of aspirin therapy (50 mg/d for 7 to 14 days) was associated with greater than 80% suppression in metabolite excretion in nine patients. These results are consistent with abnormal stimuli operating in polycythemia vera to induce a selective enhancement in the platelet biosynthesis of TXA2 without changes in receptor binding. This in vivo abnormality in platelet biochemistry can be largely suppressed by low doses of aspirin.

Thromboxane (TX) B2, the chemically stable hydration product of pro-aggregatory TXA2, undergoes two major pathways of metabolism in man, resulting in the formation of 2,3-dinor-TXB2 and 11-dehydro-TXB2, respectively. We have measured the excretion of the latter during the infusion of exogenous TXB2 over a 50-fold dose range in order to examine the fractional conversion of TXB2 to urinary 11-dehydro-TXB2 and to re-assess the rate of entry of endogenous TXB2 into the circulation. Four healthy male volunteers receeived 6-h intravenous infusions of the vehicle alone and TXB2 at 0.1, 1.0 and 5.0 ng · kg−1 · min−1 in random order. They were pretreated with aspirin 325 mg/d in order to suppress endogenous TXB2 production. Urinary 11-dehydro-TXB2 and 2,3-dinor-TXB2 were measured before, during and up to 24 h after the infusions and in aspirin-free periods, by means of NICI-GC/MS-validated radioimmunoassays. Aspirin treatment suppressed urinary 11-dehydro-TXB2 by 91%. The fractional elimination of 11-dehydro-TXB2 was independent of the rate of TXB2 infusion and averaged 6.8 ± 0.7%, as compared to 6.4 ± 0.9% for 2,3-dinor-TXB2. Interpolation of 11-dehydro-TXB2 values obtained in aspirin-free periods onto the linear relationship between the quantities of infused TXB2 and the amount of metabolite excreted in excess of control values (y = 0.0058x, r = 0.94, P < 0.001) permitted calculation of the mean rate of entry of endogenous TXB2 into the circulation as 0.12 ng · kg−1 · min−1. We conclude that: (a) urinary 11-dehydro-TXB2 is at least as abundant a conversion product of exogenously infused TXB2 as 2,3-dinor-TXB2; (b) its excretion increases linearly as a function of the rate of entry of TXB2 into the circulation up to approx. 40-fold the calculated rate of secretion of endogenous TXB2; (c) the latter is consistent with previous estimates based on monitoring of the β-oxidation pathway of TXB2 metabolism.

A lack in prostacyclin (PGI2) production due to atherosclerosis may play a role in the pathophysiology of some of the clinical manifestations of ischemic heart disease and in particular, of coronary vasospasm. We therefore evaluated the effects of i.v. PGI2 in nine patients with variant angina and six normal volunteers. In normal subjects, PGI2 (2.5, 5, 10 and 20 micrograms/kg/min) had significant antiplatelet effects, caused a dose-dependent decrease in both systolic and diastolic arterial pressure and a decrease in pulmonary resistance. Heart rate increased in a dose-dependent manner, but no consistent effects on myocardial contractility (evaluated by ultrasound) were observed. Side effects were negligible and readily reversible. Although producing obvious antiplatelet and vasodilatory effects, PGI2 did not affect the number, severity and duration of spontaneous ischemic episodes due to coronary vasospasm in five patients and ergonovine-induced spasm in three. However, the number of ischemic episodes was consistently reduced in one patient during four consecutive periods of PGI2 infusion alternated with placebo. a severe, prolonged ischemic episode with ST elevation and pain was consistently observed in this patient every time PGI2 was discontinued. In the appropriate environment, PGI2 can be administered safely to patients with ischemic heart disease. Occasionally, PGI2 may result in a complete disappearance of ischemic episodes due to coronary vasospasm, but usually it is ineffective. These conflicting results could be related to different etiologies of coronary spasm.

Abstract We tested whether cyclooxygenase 2 (COX-2) expression and unacetylated COX-1 in newly formed platelets might contribute to persistent thromboxane (TX) biosynthesis in aspirin-treated essential thrombocythemia (ET). Forty-one patients on chronic aspirin (100 mg/day) and 24 healthy subjects were studied. Platelet COX-2 expression was significantly increased in patients and correlated with thiazole orange–positive platelets (r = 0.71, P &lt; .001). The rate of TXA2 biosynthesis in vivo, as reflected by urinary 11-dehydro-TXB2 (TXM) excretion, and the maximal biosynthetic capacity of platelets, as reflected by serum TXB2, were higher in patients compared with aspirin-treated healthy volunteers. Serum TXB2 was significantly reduced by the selective COX-2 inhibitor NS-398 added in vitro. Patients were randomized to adding the selective COX-2 inhibitor, etoricoxib, or continuing aspirin for 7 days. Etoricoxib significantly reduced by approximately 25% TXM excretion and serum TXB2. Fourteen of the 41 patients were studied again 21 (± 7) months after the first visit. Serum TXB2 was consistently reduced by approximately 30% by adding NS398 in vitro, while it was completely suppressed with 50μM aspirin. Accelerated platelet regeneration in most aspirin-treated ET patients may explain aspirin-persistent TXA2 biosynthesis through enhanced COX-2 activity and faster renewal of unacetylated COX-1. These findings may help in reassessing the optimal antiplatelet strategy in ET.

Although conceived at the end of the 19th century, aspirin remains the gold standard of antiplatelet therapy. Approximately 100 randomized clinical trials have established its efficacy and safety in the prevention of myocardial infarction, ischemic stroke, and vascular death among high-risk patients treated for a few weeks, at one end of the spectrum, and in low-risk subjects treated up to 10 years at the other. Despite this wealth of data, several issues continue to be debated concerning the use of aspirin as an antiplatelet agent, and novel opportunities appear on the horizon for this 110-year-old drug. These issues include: (1) the optimal dose for cardiovascular prophylaxis; (2) the uncertain threshold of cardiovascular risk for its use in primary prevention; (3) the apparent gender-related difference in its cardioprotective effects; (4) the increasingly popular theme of aspirin "resistance"; (5) the opportunities of chemoprevention in colorectal cancer; and (6) the renewed interest in aspirin as an analgesic agent in osteoarthritic patients at high cardiovascular risk. The aim of this review is to address these issues by integrating our current understanding of the molecular mechanism of action of the drug with the results of clinical trials and epidemiological studies of aspirin as an antiplatelet drug.

This study demonstrates that leukotriene C4, at concentrations in the picomolar range, released luteinizing hormone (LH) but not growth hormone (GH) from dispersed rat anterior pituitary cells. Leukotriene B4, another lipoxygenase pathway product of arachidonic acid, had no effect on LH or GH release. The stimulatory effect of leukotriene C4 could be seen after 0.5 but not after 3 hr of incubation. This was in contrast to the dose-dependent LH-releasing hormone (LHRH)-induced LH release that was not measurable after 0.5 hr but was fully established after incubation for 3 hr. Furthermore, the LH-releasing ability of leukotriene C4 was blocked in the presence of high doses of LHRH. The immunohistochemical analysis revealed leukotriene C4-immunoreactive fibers at all levels of the median eminence, mainly in the lateral parts. These fibers exhibited a marked overlap distribution with LHRH-immunoreactive fibers and elution-restaining experiments revealed identity of at least a large proportion of the leukotriene C4- and LHRH-immunoreactive fibers. Furthermore, cell bodies in the preoptic area contained both leukotriene C4- and LHRH-like immunoreactivities, suggesting localization of these two compounds in the same neurons.

✓Prostaglandin (PGF 2α ) concentrations were measured by radioimmunoassay in serial samples of CSF from patients with subarachnoid hemorrhage, in an attempt to correlate these values with the presence or degree of the arterial spasm. Although elevated concentrations of PGF 2α were found in most of these patients, when compared with a control series, there was no correlation between these values and the appearance of cerebral vasospasm. The results are discussed with reference to previous experimental work suggesting a role of PGF 2α in the pathogenesis of cerebral vasospasm.

Abstract Persistently enhanced platelet activation has been characterized in polycythemia vera (PV) and essential thrombocythemia (ET) and shown to contribute to a higher risk of both arterial and venous thrombotic complications. The incidence of major bleeding complications is also somewhat higher in PV and ET than in the general population. Although its efficacy and safety was assessed in just 1 relatively small trial in PV, low-dose aspirin is currently recommended in practically all PV and ET patients. Although for most patients with a thrombosis history the benefit/risk profile of antiplatelet therapy is likely to be favorable, in those with no such history this balance will depend critically on the level of thrombotic and hemorrhagic risks of the individual patient. Recent evidence for a chemopreventive effect of low-dose aspirin may tilt the balance of benefits and harm in favor of using aspirin more broadly, but the potential for additional benefits needs regulatory scrutiny and novel treatment guidelines. A clear pharmacodynamic rationale and analytical tools are available for a personalized approach to antiplatelet therapy in ET, and an improved regimen of low-dose aspirin therapy should be tested in a properly sized randomized trial.

Summary. Background: Chronic hyperglycemia is a major contributor to in vivo platelet activation in diabetes mellitus. Objectives: To evaluate the effects of acarbose, an α-glucosidase inhibitor, on platelet activation and its determinants in newly diagnosed type 2 diabetic patients. Methods: Forty-eight subjects (26 males, aged 61 ± 8 years) with early type 2 diabetes (baseline hemoglobin A1c ≤ 7% and no previous hypoglycemic treatment) were randomly assigned to acarbose up to 100 mg three times a day or placebo, and evaluated every 4 weeks for 20 weeks. The main outcome measures were urinary 11-dehydro-thromboxane (TX)B2 (marker of in vivo platelet activation) and 8-iso-prostaglandin (PG)F2α (marker of in vivo lipid peroxidation) excretion rate, 2-h postprandial plasma glucose (PPG) after a test meal, and assessment of glucose fluctuations by mean amplitude of glycemic excursions (MAGE). Results: Baseline measurements revealed biochemical evidence of enhanced lipid peroxidation and platelet activation. As compared with the placebo group, patients treated with acarbose had statistically significant reductions in urinary 11-dehydro-TXB2 and 8-iso-PGF2α excretion rate as early as after 8 weeks and at each subsequent time point (between-group P < 0.0001 at 12, 16 and 20 weeks), following earlier decreases in PPG and MAGE. Multiple regression analyses in the acarbose group revealed that PPG was the only significant predictor of 11-dehydro-TXB2 urinary excretion rate (β = 0.39, P = 0.002) and MAGE the only predictor of 8-iso-PGF2α urinary excretion rate (β = 0.42, P = 0.001). Conclusions: Postprandial hyperglycemia is associated with enhanced lipid peroxidation and platelet activation in early type 2 diabetes. A moderate decrease in PPG achieved with acarbose causes time-dependent downregulation of these phenomena, suggesting a causal link between early metabolic abnormalities and platelet activation in this setting.

Low-dose aspirin has been shown to be effective in preventing about one-fifth of atherothrombotic vascular complications (non-fatal myocardial infarction, non-fatal stroke, or vascular death) in a meta-analysis of 16 secondary prevention trials in patients with previous myocardial infarction, stroke, or transient cerebral ischaemia. This corresponds to an absolute reduction of about 10-20 per 1000 patients in the yearly incidence of non-fatal events, and to a smaller, but still definite, reduction in vascular death. Against this benefit, the absolute increase in major extracranial bleeding complications [mostly, gastrointestinal (GI)] is 20- to 50-fold smaller, depending on age and sex. Hence, for secondary prevention, the benefits of antiplatelet therapy substantially exceed the risks. For primary prevention, the balance between vascular events avoided and major bleeds caused by aspirin is substantially uncertain because the risks without aspirin, and hence the absolute benefits of antiplatelet prophylaxis, are at least an order of magnitude lower than in secondary prevention. The aim of this article is to review the updated evidence for the efficacy and safety of low-dose aspirin in primary prevention and to discuss additional health benefits resulting from prolonged antiplatelet therapy in apparently healthy people at low average risk of vascular events.

Observational studies consistently reported an association between plasma total homocysteine concentrations and the risk of vascular events. In contrast, data from randomized trials largely support the hypothesis that mild elevations in homocysteine level have a modest effect on cardiovascular risk. A substantial body of evidence suggests that platelet activation is, at least in part, a transducer of the effects of high homocysteine in promoting atherothrombosis. The larger treatment effect recorded in several supplementation trials by subjects not on antiplatelet agents may support this hypothesis and justify, at least in part, the success of folate therapy in primary prevention. Circulating folate and homocysteine levels as well as MTHFR genotype, while emerging as major predictors of the risk of vascular events and of the efficacy of folic acid therapy, have also proved to be determinants of an interindividual variability in the degree of lipid peroxidation and platelet activation, and of the extent of their downregulation by folic acid. This may justify a variability in folate requirements, to be further characterized with dose-finding studies using biochemical endpoints. The combination of low-dose aspirin and low-dose folate would appear to be ideally suited for the primary prevention of both coronary and cerebrovascular events, and additional clinical trials should assess the efficacy and safety of these agents.