Gordon I. Smith

Loss of muscle mass with aging is a major public health concern. Omega-3 (n-3) fatty acids stimulate protein anabolism in animals and might therefore be useful for the treatment of sarcopenia. However, the effect of omega-3 fatty acids on human protein metabolism is unknown.The objective of this study was to evaluate the effect of omega-3 fatty acid supplementation on the rate of muscle protein synthesis in older adults.Sixteen healthy, older adults were randomly assigned to receive either omega-3 fatty acids or corn oil for 8 wk. The rate of muscle protein synthesis and the phosphorylation of key elements of the anabolic signaling pathway were evaluated before and after supplementation during basal, postabsorptive conditions and during a hyperaminoacidemic-hyperinsulinemic clamp.Corn oil supplementation had no effect on the muscle protein synthesis rate and the extent of anabolic signaling element phosphorylation in muscle. Omega-3 fatty acid supplementation had no effect on the basal rate of muscle protein synthesis (mean ± SEM: 0.051 ± 0.005%/h compared with 0.053 ± 0.008%/h before and after supplementation, respectively; P = 0.80) but augmented the hyperaminoacidemia-hyperinsulinemia-induced increase in the rate of muscle protein synthesis (from 0.009 ± 0.005%/h above basal values to 0.031 ± 0.003%/h above basal values; P < 0.01), which was accompanied by greater increases in muscle mTOR(Ser2448) (P = 0.08) and p70s6k(Thr389) (P < 0.01) phosphorylation.Omega-3 fatty acids stimulate muscle protein synthesis in older adults and may be useful for the prevention and treatment of sarcopenia. This trial was registered at clinical trials.gov as NCT00794079.

BACKGROUNDAn increase in intrahepatic triglyceride (IHTG) is the hallmark feature of nonalcoholic fatty liver disease (NAFLD) and is decreased by weight loss. Hepatic de novo lipogenesis (DNL) contributes to steatosis in individuals with NAFLD. The physiological factors that stimulate hepatic DNL and the effect of weight loss on hepatic DNL are not clear.METHODSHepatic DNL, 24-hour integrated plasma insulin and glucose concentrations, and both liver and whole-body insulin sensitivity were determined in individuals who were lean (n = 14), obese with normal IHTG content (n = 26), or obese with NAFLD (n = 27). Hepatic DNL was assessed using the deuterated water method corrected for the potential confounding contribution of adipose tissue DNL. Liver and whole-body insulin sensitivity was assessed using the hyperinsulinemic-euglycemic clamp procedure in conjunction with glucose tracer infusion. Six subjects in the obese-NAFLD group were also evaluated before and after a diet-induced weight loss of 10%.RESULTSThe contribution of hepatic DNL to IHTG-palmitate was 11%, 19%, and 38% in the lean, obese, and obese-NAFLD groups, respectively. Hepatic DNL was inversely correlated with hepatic and whole-body insulin sensitivity, but directly correlated with 24-hour plasma glucose and insulin concentrations. Weight loss decreased IHTG content, in conjunction with a decrease in hepatic DNL and 24-hour plasma glucose and insulin concentrations.CONCLUSIONSThese data suggest hepatic DNL is an important regulator of IHTG content and that increases in circulating glucose and insulin stimulate hepatic DNL in individuals with NAFLD. Weight loss decreased IHTG content, at least in part, by decreasing hepatic DNL.TRIAL REGISTRATIONClinicalTrials.gov NCT02706262.FUNDINGThis study was supported by NIH grants DK56341 (Nutrition Obesity Research Center), DK20579 (Diabetes Research Center), DK52574 (Digestive Disease Research Center), and RR024992 (Clinical and Translational Science Award), and by grants from the Academy of Nutrition and Dietetics Foundation, the College of Natural Resources of UCB, and the Pershing Square Foundation.

Although obesity is typically associated with metabolic dysfunction and cardiometabolic diseases, some people with obesity are protected from many of the adverse metabolic effects of excess body fat and are considered "metabolically healthy." However, there is no universally accepted definition of metabolically healthy obesity (MHO). Most studies define MHO as having either 0, 1, or 2 metabolic syndrome components, whereas many others define MHO using the homeostasis model assessment of insulin resistance (HOMA-IR). Therefore, numerous people reported as having MHO are not metabolically healthy, but simply have fewer metabolic abnormalities than those with metabolically unhealthy obesity (MUO). Nonetheless, a small subset of people with obesity have a normal HOMA-IR and no metabolic syndrome components. The mechanism(s) responsible for the divergent effects of obesity on metabolic health is not clear, but studies conducted in rodent models suggest that differences in adipose tissue biology in response to weight gain can cause or prevent systemic metabolic dysfunction. In this article, we review the definition, stability over time, and clinical outcomes of MHO, and discuss the potential factors that could explain differences in metabolic health in people with MHO and MUO - specifically, modifiable lifestyle factors and adipose tissue biology. Better understanding of the factors that distinguish people with MHO and MUO can produce new insights into mechanism(s) responsible for obesity-related metabolic dysfunction and disease.

Age-associated declines in muscle mass and function are major risk factors for an impaired ability to carry out activities of daily living, falls, prolonged recovery time after hospitalization, and mortality in older adults. New strategies that can slow the age-related loss of muscle mass and function are needed to help older adults maintain adequate performance status to reduce these risks and maintain independence.We evaluated the efficacy of fish oil-derived n-3 (ω-3) PUFA therapy to slow the age-associated loss of muscle mass and function.Sixty healthy 60-85-y-old men and women were randomly assigned to receive n-3 PUFA (n = 40) or corn oil (n = 20) therapy for 6 mo. Thigh muscle volume, handgrip strength, one-repetition maximum (1-RM) lower- and upper-body strength, and average power during isokinetic leg exercises were evaluated before and after treatment.Forty-four subjects completed the study [29 subjects (73%) in the n-3 PUFA group; 15 subjects (75%) in the control group]. Compared with the control group, 6 mo of n-3 PUFA therapy increased thigh muscle volume (3.6%; 95% CI: 0.2%, 7.0%), handgrip strength (2.3 kg; 95% CI: 0.8, 3.7 kg), and 1-RM muscle strength (4.0%; 95% CI: 0.8%, 7.3%) (all P < 0.05) and tended to increase average isokinetic power (5.6%; 95% CI: -0.6%, 11.7%; P = 0.075).Fish oil-derived n-3 PUFA therapy slows the normal decline in muscle mass and function in older adults and should be considered a therapeutic approach for preventing sarcopenia and maintaining physical independence in older adults. This study was registered at clinicaltrials.gov as NCT01308957.

Increased dietary LCn−3PUFA (long-chain n−3 polyunsaturated fatty acid) intake stimulates muscle protein anabolism in individuals who experience muscle loss due to aging or cancer cachexia. However, it is not known whether LCn−3PUFAs elicit similar anabolic effects in healthy individuals. To answer this question, we evaluated the effect of 8 weeks of LCn−3PUFA supplementation (4 g of Lovaza®/day) in nine 25–45-year-old healthy subjects on the rate of muscle protein synthesis (by using stable isotope-labelled tracer techniques) and the activation (phosphorylation) of elements of the mTOR (mammalian target of rapamycin)/p70S6K (p70 S6 kinase) signalling pathway during basal post-absorptive conditions and during a hyperinsulinaemic–hyperaminoacidaemic clamp. We also measured the concentrations of protein, RNA and DNA in muscle to obtain indices of the protein synthetic capacity, translational efficiency and cell size. Neither the basal muscle protein fractional synthesis rate nor basal signalling element phosphorylation changed in response to LCn−3PUFA supplementation, but the anabolic response to insulin and amino acid infusion was greater after LCn−3PUFA [i.e. the muscle protein fractional synthesis rate during insulin and amino acid infusion increased from 0.062±0.004 to 0.083±0.007%/h and the phospho-mTOR (Ser2448) and phospho-p70S6K (Thr389) levels increased by ∼50%; all P&amp;lt;0.05]. In addition, the muscle protein concentration and the protein/DNA ratio (i.e. muscle cell size) were both greater (P&amp;lt;0.05) after LCn−3PUFA supplementation. We conclude that LCn−3PUFAs have anabolic properties in healthy young and middle-aged adults.

Insulin resistance is a key factor in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). We evaluated the importance of subcutaneous abdominal adipose tissue (SAAT) inflammation and both plasma and SAAT-derived exosomes in regulating insulin sensitivity in people with obesity and NAFLD.Adipose tissue inflammation (macrophage and T-cell content and expression of proinflammatory cytokines), liver and whole-body insulin sensitivity (assessed using a hyperinsulinemic-euglycemic clamp and glucose tracer infusion), and 24-hour serial plasma cytokine concentrations were evaluated in 3 groups stratified by adiposity and intrahepatic triglyceride (IHTG) content: (1) lean with normal IHTG content (LEAN; N = 14); (2) obese with normal IHTG content (OB-NL; N = 28); and (3) obese with NAFLD (OB-NAFLD; N = 28). The effect of plasma and SAAT-derived exosomes on insulin-stimulated Akt phosphorylation in human skeletal muscle myotubes and mouse primary hepatocytes was assessed in a subset of participants.Proinflammatory macrophages, proinflammatory CD4 and CD8 T-cell populations, and gene expression of several cytokines in SAAT were greater in the OB-NAFLD than the OB-NL and LEAN groups. However, with the exception of PAI-1, which was greater in the OB-NAFLD than the LEAN and OB-NL groups, 24-hour plasma cytokine concentration areas-under-the-curve were not different between groups. The percentage of proinflammatory macrophages and plasma PAI-1 concentration areas-under-the-curve were inversely correlated with both hepatic and whole-body insulin sensitivity. Compared with exosomes from OB-NL participants, plasma and SAAT-derived exosomes from the OB-NAFLD group decreased insulin signaling in myotubes and hepatocytes.Systemic insulin resistance in people with obesity and NAFLD is associated with increased plasma PAI-1 concentrations and both plasma and SAAT-derived exosomes. ClinicalTrials.gov number: NCT02706262 (https://clinicaltrials.gov/ct2/show/NCT02706262).

Women have less muscle than men but lose it more slowly during aging. To discover potential underlying mechanism(s) for this we evaluated the muscle protein synthesis process in postabsorptive conditions and during feeding in twenty-nine 65-80 year old men (n = 13) and women (n = 16). We discovered that the basal concentration of phosphorylated eEF2(Thr56) was approximately 40% less (P<0.05) and the basal rate of MPS was approximately 30% greater (P = 0.02) in women than in men; the basal concentrations of muscle phosphorylated Akt(Thr308), p70s6k(Thr389), eIF4E(Ser209), and eIF4E-BP1(Thr37/46) were not different between the sexes. Feeding increased (P<0.05) Akt(Thr308) and p70s6k(Thr389) phosphorylation to the same extent in men and women but increased (P<0.05) the phosphorylation of eIF4E(Ser209) and eIF4E-BP1(Thr37/46) in men only. Accordingly, feeding increased MPS in men (P<0.01) but not in women. The postabsorptive muscle mRNA concentrations for myoD and myostatin were not different between sexes; feeding doubled myoD mRNA (P<0.05) and halved that of myostatin (P<0.05) in both sexes. Thus, there is sexual dimorphism in MPS and its control in older adults; a greater basal rate of MPS, operating over most of the day may partially explain the slower loss of muscle in older women.

Aging is associated with a decline in strength, endurance, balance, and mobility. Obesity worsens the age-related impairment in physical function and often leads to frailty. The American College of Sports Medicine recommends a multicomponent (strength, endurance, flexibility, and balance) exercise program to maintain physical fitness. However, the effect of such an exercise program on physical fitness in frail, obese older adults is not known. We therefore determined the effect of a 3-month long multicomponent exercise training program, on endurance (peak aerobic capacity (VO(2) peak)), muscle strength, muscle mass, and the rate of muscle protein synthesis (basal rate and anabolic response to feeding) in nine 65- to 80-year-old, moderately frail, obese older adults. After 3 months of training, fat mass decreased (P < 0.05) whereas fat-free mass (FFM), appendicular lean body mass, strength, and VO(2) peak increased (all P < 0.05). Regular strength and endurance exercise increased the mixed muscle protein fractional synthesis rate (FSR) but had no effect on the feeding-induced increase in muscle protein FSR (~0.02%/h increase from basal values both before and after exercise training; effect of feeding: P = 0.02; effect of training: P = 0.047; no interaction: P = 0.84). We conclude that: (i) a multicomponent exercise training program has beneficial effects on muscle mass and physical function and should therefore be recommended to frail, obese older adults, and (ii) regular multicomponent exercise increases the basal rate of muscle protein synthesis without affecting the magnitude of the muscle protein anabolic response to feeding.

The effect of the female sex steroids, estradiol and progesterone, on muscle protein turnover is unclear. Therefore, it is unknown whether the changes in the hormonal milieu throughout the life span in women contribute to the changes in muscle protein turnover and muscle mass (eg, age associated muscle loss).The objective of this study was to provide a comprehensive evaluation of the effect of sex hormones on muscle protein synthesis and gene expression of growth-regulatory factors [ie, myogenic differentiation 1 (MYOD1), myostatin (MSTN), follistatin (FST), and forkhead box O3 (FOXO3)].We measured the basal rate of muscle protein synthesis and the expression of muscle growth-regulatory genes in 12 premenopausal women and four groups of postmenopausal women (n=24 total) who were studied before and after treatment with T, estradiol, or progesterone or no intervention (control group). All women were healthy, and pre- and postmenopausal women were carefully matched on body mass, body composition, and insulin sensitivity.The muscle protein fractional synthesis rate was approximately 20% faster, and MYOD1, FST, and FOXO3 mRNA expressions were approximately 40%-90% greater (all P<.05) in postmenopausal than premenopausal women. In postmenopausal women, both T and progesterone treatment increased the muscle protein fractional synthesis rate by approximately 50% (both P<.01), whereas it was not affected by estradiol treatment and was unchanged in the control group. Progesterone treatment increased MYOD1 mRNA expression (P<.05) but had no effect on MSTN, FST, and FOXO3 mRNA expression. T and estradiol treatment had no effect on skeletal muscle MYOD1, MSTN, FST, and FOXO3 mRNA expression.Muscle protein turnover is faster in older, postmenopausal women compared with younger, premenopausal women, but these age-related differences do not appear to be explained by the age- and menopause-related changes in the plasma sex hormone milieu.

High-protein (HP) intake during weight loss (WL) therapy is often recommended because it reduces the loss of lean tissue mass. However, HP intake could have adverse effects on metabolic function, because protein ingestion reduces postprandial insulin sensitivity. In this study, we compared the effects of ∼10% WL with a hypocaloric diet containing 0.8 g protein/kg/day and a hypocaloric diet containing 1.2 g protein/kg/day on muscle insulin action in postmenopausal women with obesity. We found that HP intake reduced the WL-induced decline in lean tissue mass by ∼45%. However, HP intake also prevented the WL-induced improvements in muscle insulin signaling and insulin-stimulated glucose uptake, as well as the WL-induced adaptations in oxidative stress and cell structural biology pathways. Our data demonstrate that the protein content of a WL diet can have profound effects on metabolic function and underscore the importance of considering dietary macronutrient composition during WL therapy for people with obesity.

BACKGROUND.Data from studies conducted in rodent models have shown that decreased adipose tissue (AT) oxygenation is involved in the pathogenesis of obesity-induced insulin resistance.Here, we evaluated the potential influence of AT oxygenation on AT biology and insulin sensitivity in people. METHODS.We evaluated subcutaneous AT oxygen partial pressure (pO 2 ); liver and whole-body insulin sensitivity; AT expression of genes and pathways involved in inflammation, fibrosis, and branched-chain amino acid (BCAA) catabolism; systemic markers of inflammation; and plasma BCAA concentrations, in 3 groups of participants that were rigorously stratified by adiposity and insulin sensitivity: metabolically healthy lean (MHL; n = 11), metabolically healthy obese (MHO; n = 15), and metabolically unhealthy obese (MUO; n = 20). RESULTS.AT pO 2 progressively declined from the MHL to the MHO to the MUO group, and was positively associated with hepatic and whole-body insulin sensitivity.AT pO 2 was positively associated with the expression of genes involved in BCAA catabolism, in conjunction with an inverse relationship between AT pO 2 and plasma BCAA concentrations.AT pO 2 was negatively associated with AT gene expression of markers of inflammation and fibrosis.Plasma PAI-1 increased from the MHL to the MHO to the MUO group and was negatively correlated with AT pO 2 , whereas the plasma concentrations of other cytokines and chemokines were not different among the MHL and MUO groups.CONCLUSION.These results support the notion that reduced AT oxygenation in individuals with obesity contributes to insulin resistance by increasing plasma PAI-1 concentrations and decreasing AT BCAA catabolism and thereby increasing plasma BCAA concentrations.

Decreased adipose tissue oxygen tension and increased expression of the transcription factor hypoxia-inducible factor–1α (HIF-1α) can trigger adipose tissue inflammation and dysfunction in obesity. Our current understanding of obesity-associated decreased adipose tissue oxygen tension is mainly focused on changes in oxygen supply and angiogenesis. Here, we demonstrate that increased adipocyte oxygen demand, mediated by activity of the mitochondrial protein adenine nucleotide translocase 2 (ANT2), is the dominant cause of adipocyte hypoxia. Deletion of adipocyte Ant2 (also known as Scl25a5) improves obesity-induced intracellular adipocyte hypoxia by decreasing obesity-induced adipocyte oxygen demand, without effects on mitochondrial number or mass, or oligomycin-sensitive respiration. This effect of adipocyte ANT2 knockout led to decreased adipose tissue HIF-1α expression and inflammation with improved glucose tolerance and insulin resistance in both preventative and therapeutic settings. Our results suggest that ANT2 may be a target for the development of insulin-sensitizing drugs and that ANT2 inhibition might have clinical utility. Obese and dysfunctional adipose tissue is known to be hypoxic. Here the authors show that adipocyte oxygen consumption increases early after onset of high-fat diet feeding owing to activation of the mitochondrial protein ANT2 and that specific inhibition of ANT2 reduces adipose tissue hypoxia, inflammation and insulin resistance.

BackgroundIt is unclear how excess adiposity and insulin resistance affect β cell function, insulin secretion, and insulin clearance in people with obesity.MethodsWe used a hyperinsulinemic-euglycemic clamp procedure and a modified oral glucose tolerance test to evaluate the interrelationships among obesity, insulin sensitivity, insulin kinetics, and glycemic status in 5 groups of individuals: normoglycemic lean and obese individuals with (a) normal fasting glucose and normal glucose tolerance (Ob-NFG-NGT), (b) NFG and impaired glucose tolerance (Ob-NFG-IGT), (c) impaired fasting glucose and IGT (Ob-IFG-IGT), or (d) type 2 diabetes (Ob-T2D).ResultsGlucose-stimulated insulin secretion (GSIS), an assessment of β cell function, was greater in the Ob-NFG-NGT and Ob-NFG-IGT groups than in the lean group, even when insulin sensitivity was matched in the obese and lean groups. Insulin sensitivity, not GSIS, was decreased in the Ob-NFG-IGT group compared with the Ob-NFG-NGT group, whereas GSIS, not insulin sensitivity, was decreased in the Ob-IFG-IGT and Ob-T2D groups compared with the Ob-NFG-NGT and Ob-NFG-IGT groups. Insulin clearance was directly related to insulin sensitivity and inversely related to the postprandial increase in insulin secretion and plasma insulin concentration.ConclusionIncreased adiposity per se, not insulin resistance, enhanced insulin secretion in people with obesity. The obesity-induced increase in insulin secretion, in conjunction with a decrease in insulin clearance, sufficiently raised the plasma insulin concentrations needed to maintain normoglycemia in individuals with moderate, but not severe, insulin resistance. A deterioration in β cell function, not a decrease in insulin sensitivity, was a determinant of IFG and ultimately leads to T2D.CLINICAL TRIALS REGISTRATIONClinicalTrials.gov NCT02706262, NCT04131166, and NCT01977560.FUNDINGNIH (P30 DK056341, P30 DK020579, and UL1 TR000448); American Diabetes Association (1-18-ICTS-119); Longer Life Foundation; Pershing Square Foundation; and Washington University-Centene ARCH Personalized Medicine Initiative (P19-00559).

Although there appear to be no differences in muscle protein turnover in young and middle aged men and women, we have reported significant differences in the rate of muscle protein synthesis between older adult men and women. This suggests that aging may affect muscle protein turnover differently in men and women.We measured the skeletal muscle protein fractional synthesis rate (FSR) by using stable isotope-labeled tracer methods during basal postabsorptive conditions and during a hyperaminoacidemic-hyperinsulinemic-euglycemic clamp in eight young men (25-45 y), ten young women (25-45 y), ten old men (65-85 y) and ten old women (65-85 y).The basal muscle protein FSR was not different in young and old men (0.040 ± 0.004 and 0.043 ± 0.005%·h-1, respectively) and combined insulin, glucose and amino acid infusion significantly increased the muscle protein FSR both in young (to 0.063 ± 0.006%·h-1) and old (to 0.051 ± 0.008%·h-1) men but the increase (0.023 ± 0.004 vs. 0.009 ± 0.004%·h-1, respectively) was ~60% less in the old men (P = 0.03). In contrast, the basal muscle protein FSR was ~30% greater in old than young women (0.060 ± 0.003 vs. 0.046 ± 0.004%·h-1, respectively; P < 0.05) and combined insulin, glucose and amino acid infusion significantly increased the muscle protein FSR in young (P < 0.01) but not in old women (P = 0.10) so that the FSR was not different between young and old women during the clamp (0.074 ± 0.006%·h-1 vs. 0.072 ± 0.006%·h-1, respectively).There is sexual dimorphism in the age-related changes in muscle protein synthesis and thus the metabolic processes responsible for the age-related decline in muscle mass.

Increased plasma branched-chain amino acid concentrations are associated with insulin resistance, and intravenous amino acid infusion blunts insulin-mediated glucose disposal. We tested the hypothesis that protein ingestion impairs insulin-mediated glucose disposal by leucine-mediated mTOR signaling, which can inhibit AKT. We measured glucose disposal and muscle p-mTOR(Ser2448), p-AKT(Ser473), and p-AKT(Thr308) in 22 women during a hyperinsulinemic-euglycemic clamp procedure with and without concomitant ingestion of whey protein (0.6 g/kg fat-free mass; n = 11) or leucine that matched the amount given with whey protein (n = 11). Both whey protein and leucine ingestion raised plasma leucine concentration by approximately twofold and muscle p-mTOR(Ser2448) by ∼30% above the values observed in the control (no amino acid ingestion) studies; p-AKT(Ser473) and p-AKT(Thr308) were not affected by whey protein or leucine ingestion. Whey protein ingestion decreased insulin-mediated glucose disposal (median 38.8 [quartiles 30.8, 61.8] vs. 51.9 [41.0, 77.3] µmol glucose/µU insulin · mL(-1) · min(-1); P < 0.01), whereas ingestion of leucine did not (52.3 [43.3, 65.4] vs. 52.3 [43.9, 73.2]). These results indicate that 1) protein ingestion causes insulin resistance and could be an important regulator of postprandial glucose homeostasis and 2) the insulin-desensitizing effect of protein ingestion is not due to inhibition of AKT by leucine-mediated mTOR signaling.

Dietary fish oil-derived n-3 PUFA supplementation can increase muscle mass, reduce oxygen demand during physical activity, and improve physical function (muscle strength and power, and endurance) in people. The results from several studies conducted in animals suggest that the anabolic and performance-enhancing effects of n-3 PUFA are at least in part transcriptionally regulated. The effect of n-3 PUFA therapy on the muscle transcriptome in people is unknown. In this study, we used muscle biopsy samples collected during a recently completed randomized controlled trial that found that n-3 PUFA therapy increased muscle mass and function in older adults to provide a comprehensive assessment of the effect of n-3 PUFA therapy on the skeletal muscle gene expression profile in these people. Using the microarray technique, we found that several pathways involved in regulating mitochondrial function and extracellular matrix organization were increased and pathways related to calpain- and ubiquitin-mediated proteolysis and inhibition of the key anabolic regulator mTOR were decreased by n-3 PUFA therapy. However, the effect of n-3 PUFA therapy on the expression of individual genes involved in regulating mitochondrial function and muscle growth, assessed by quantitative RT-PCR, was very small. These data suggest that n-3 PUFA therapy results in small but coordinated changes in the muscle transcriptome that may help explain the n-3 PUFA-induced improvements in muscle mass and function.

BACKGROUNDInsulin is a key regulator of metabolic function. The effects of excess adiposity, insulin resistance, and hepatic steatosis on the complex integration of insulin secretion and hepatic and extrahepatic tissue extraction are not clear.METHODSA hyperinsulinemic-euglycemic clamp and a 3-hour oral glucose tolerance test were performed to evaluate insulin sensitivity and insulin kinetics after glucose ingestion in 3 groups: (a) lean subjects with normal intrahepatic triglyceride (IHTG) and glucose tolerance (lean-NL; n = 14), (b) obese subjects with normal IHTG and glucose tolerance (obese-NL; n = 24), and (c) obese subjects with nonalcoholic fatty liver disease (NAFLD) and prediabetes (obese-NAFLD; n = 22).RESULTSInsulin sensitivity progressively decreased and insulin secretion progressively increased from the lean-NL to the obese-NL to the obese-NAFLD groups. Fractional hepatic insulin extraction progressively decreased from the lean-NL to the obese-NL to the obese-NAFLD groups, whereas total hepatic insulin extraction (molar amount removed) was greater in the obese-NL and obese-NAFLD subjects than in the lean-NL subjects. Insulin appearance in the systemic circulation and extrahepatic insulin extraction progressively increased from the lean-NL to the obese-NL to the obese-NAFLD groups. Total hepatic insulin extraction plateaued at high rates of insulin delivery, whereas the relationship between systemic insulin appearance and total extrahepatic extraction was linear.CONCLUSIONHyperinsulinemia after glucose ingestion in obese-NL and obese-NAFLD is due to an increase in insulin secretion, without a decrease in total hepatic or extrahepatic insulin extraction. However, the liver's maximum capacity to remove insulin is limited because of a saturable extraction process. The increase in insulin delivery to the liver and extrahepatic tissues in obese-NAFLD is unable to compensate for the increase in insulin resistance, resulting in impaired glucose homeostasis.TRIAL REGISTRATIONClinicalTrials.gov NCT02706262.FUNDINGNIH grants DK56341 (Nutrition Obesity Research Center), DK052574 (Digestive Disease Research Center), RR024992 (Clinical and Translational Science Award), and T32 DK007120 (a T32 Ruth L. Kirschstein National Research Service Award); the American Diabetes Foundation (1-18-ICTS-119); Janssen Research & Development; and the Pershing Square Foundation.

Hyperglucagonemia, a hallmark in obesity and insulin resistance promotes hepatic glucose output, exacerbating hyperglycemia and thus predisposing to the development type 2 diabetes. As such, glucagon signaling is a key target for new therapeutics to manage insulin resistance. We evaluated glucagon homeostasis in lean and obese mice and people. In lean mice, fasting for 24 h caused a rise in glucagon. In contrast, a decrease in serum glucagon compared to baseline was observed in diet-induced obese mice between 8 and 24 h of fasting. Fasting decreased serum insulin in both lean and obese mice. Accordingly, the glucagon:insulin ratio was unaffected by fasting in obese mice but increased in lean mice. Re-feeding (2 h) restored hyperglucagonemia in obese mice. Pancreatic perfusion studies confirm that fasting (16 h) decreases pancreatic glucagon secretion in obese mice. Consistent with our findings in the mouse, a mixed meal increased serum glucagon and insulin concentrations in obese humans, both of which decreased with time after a meal. Consequently, fasting and re-feeding less robustly affected glucagon:insulin ratios in obese compared to lean participants. The glucoregulatory disturbance in obesity may be driven by inappropriate regulation of glucagon by fasting and a static glucagon:insulin ratio.

Hepatic gluconeogenesis from amino acids contributes significantly to diabetic hyperglycemia, but the molecular mechanisms involved are incompletely understood. Alanine transaminases (ALT1 and ALT2) catalyze the interconversion of alanine and pyruvate, which is required for gluconeogenesis from alanine. We find that ALT2 is overexpressed in the liver of diet-induced obese and db/db mice and that the expression of the gene encoding ALT2 (GPT2) is downregulated following bariatric surgery in people with obesity. The increased hepatic expression of Gpt2 in db/db liver is mediated by activating transcription factor 4, an endoplasmic reticulum stress-activated transcription factor. Hepatocyte-specific knockout of Gpt2 attenuates incorporation of 13C-alanine into newly synthesized glucose by hepatocytes. In vivo Gpt2 knockdown or knockout in liver has no effect on glucose concentrations in lean mice, but Gpt2 suppression alleviates hyperglycemia in db/db mice. These data suggest that ALT2 plays a significant role in hepatic gluconeogenesis from amino acids in diabetes.

Abstract Type 2 diabetes is associated with insulin resistance, impaired pancreatic β-cell insulin secretion, and nonalcoholic fatty liver disease. Tissue-specific SWELL1 ablation impairs insulin signaling in adipose, skeletal muscle, and endothelium, and impairs β-cell insulin secretion and glycemic control. Here, we show that I Cl,SWELL and SWELL1 protein are reduced in adipose and β-cells in murine and human diabetes. Combining cryo-electron microscopy, molecular docking, medicinal chemistry, and functional studies, we define a structure activity relationship to rationally-design active derivatives of a SWELL1 channel inhibitor (DCPIB/SN-401), that bind the SWELL1 hexameric complex, restore SWELL1 protein, plasma membrane trafficking, signaling, glycemic control and islet insulin secretion via SWELL1-dependent mechanisms. In vivo, SN-401 restores glycemic control, reduces hepatic steatosis/injury, improves insulin-sensitivity and insulin secretion in murine diabetes. These findings demonstrate that SWELL1 channel modulators improve SWELL1-dependent systemic metabolism in Type 2 diabetes, representing a first-in-class therapeutic approach for diabetes and nonalcoholic fatty liver disease.

Men have more muscle than women, but most studies evaluating sex differences in muscle protein metabolism have been unable to discern sexual dimorphism in basal muscle protein turnover rates in young and middle-aged adults. We hypothesized that the anabolic response to nutritional stimuli (i.e., amino acids and insulin) would be greater in young/middle-aged men than women. We therefore measured the rates of muscle protein synthesis (MPS) in 16 healthy individuals [8 men and 8 women, matched for age (mean +/- SE: 37.7 +/- 1.5 yr) and body mass index (25.2 +/- 0.7 kg/m2)] after an overnight fast (plasma insulin approximately 5 microU/ml and plasma phenylalanine approximately 60 microM) and during a hyperinsulinemic-hyperaminoacidemic-euglycemic clamp (plasma insulin approximately 28 microU/ml; plasma phenylalanine approximately 110 microM; plasma glucose approximately 5.4 mM). The rates of MPS were not different between men and women (ANOVA main effect for sex; P = 0.49). During the clamp, the rate of MPS increased by approximately 50% (P = 0.003) with no difference in the increases from basal values between men and women (+0.019 +/- 0.004 vs. +0.018 +/- 0.010%/h, respectively; P = 0.93). There were also no differences between men and women in the basal concentrations of muscle phosphorylated Akt(Ser473), Akt(Thr308), mTOR(Ser2448), and p70s6k(Thr389) or in the hyperinsulinemia-hyperaminoacidemia-induced increases in phosphorylation of those signaling elements (P > or = 0.25). We conclude that there are no major differences in the rate of MPS and its intracellular control during basal conditions and during hyperinsulinemia-hyperaminoacidema between young and middle-aged adult men and women.

Systemic hyperaminoacidemia, induced by either intravenous amino acid infusion or protein ingestion, reduces insulin-stimulated glucose disposal. Studies of mice suggest that the valine metabolite 3-hydroxyisobutyrate (3-HIB), fibroblast growth factor 21 (FGF21), adiponectin, and nonesterified fatty acids (NEFAs) may be involved in amino acid-mediated insulin resistance. We therefore measured in 30 women the rate of glucose disposal, and plasma 3-HIB, FGF21, adiponectin, and NEFA concentrations, under basal conditions and during a hyperinsulinemic-euglycemic clamp procedure (HECP), with and without concomitant ingestion of protein (n = 15) or an amount of leucine that matched the amount of protein (n = 15). We found that during the HECP without protein or leucine ingestion, the grand mean ± SEM plasma 3-HIB concentration decreased (from 35 ± 2 to 14 ± 1 µmol/L) and the grand median [quartiles] FGF21 concentration increased (from 178 [116, 217] to 509 [340, 648] pg/mL). Ingestion of protein, but not leucine, decreased insulin-stimulated glucose disposal (P < 0.05) and prevented both the HECP-mediated decrease in 3-HIB and increase in FGF21 concentration in plasma. Neither protein nor leucine ingestion altered plasma adiponectin or NEFA concentrations. These findings suggest that 3-HIB and FGF21 might be involved in protein-mediated insulin resistance in humans.

It is proposed that impaired expansion of subcutaneous adipose tissue (SAT) and an increase in adipose tissue (AT) fibrosis causes ectopic lipid accumulation, insulin resistance (IR), and metabolically unhealthy obesity. We therefore evaluated whether a decrease in SAT expandability, assessed by measuring SAT lipogenesis (triglyceride [TG] production), and an increase in SAT fibrogenesis (collagen production) are associated with NAFLD and IR in persons with obesity.In vivo abdominal SAT lipogenesis and fibrogenesis, expression of SAT genes involved in extracellular matrix (ECM) formation, and insulin sensitivity were assessed in three groups of participants stratified by adiposity and intrahepatic TG (IHTG) content: (1) healthy lean with normal IHTG content (Lean-NL; n = 12); (2) obese with normal IHTG content and normal glucose tolerance (Ob-NL; n = 25); and (3) obese with NAFLD and abnormal glucose metabolism (Ob-NAFLD; n = 25). Abdominal SAT TG synthesis rates were greater (P < 0.05) in both the Ob-NL (65.9 ± 4.6 g/wk) and Ob-NAFLD groups (71.1 ± 6.7 g/wk) than the Lean-NL group (16.2 ± 2.8 g/wk) without a difference between the Ob-NL and Ob-NAFLD groups. Abdominal SAT collagen synthesis rate and the composite expression of genes encoding collagens progressively increased from the Lean-NL to the Ob-NL to the Ob-NAFLD groups and were greater in the Ob-NAFLD than the Ob-NL group (P < 0.05). Composite expression of collagen genes was inversely correlated with both hepatic and whole-body insulin sensitivity (P < 0.001).AT expandability is not impaired in persons with obesity and NAFLD. However, SAT fibrogenesis is greater in persons with obesity and NAFLD than in those with obesity and normal IHTG content, and is inversely correlated with both hepatic and whole-body insulin sensitivity.

We undertook a comprehensive review of the literature to unravel the nature of the variability in the reported rate of human muscle protein synthesis. We analyzed the results from studies that report the protein fractional synthesis rate (FSR) in the vastus lateralis in healthy, nonobese, untrained adults ≤50 yr of age in the postabsorptive state at rest by using the primed, constant tracer amino acid infusion method according to experimental design characteristics. We hypothesized that if the variability is methodological (rather than physiological) in nature, systematic clustering of FSR values would be evident, and outliers would become apparent. Overall, as expected, the mixed muscle protein FSR values were significantly ( P &lt; 0.001) greater when the muscle vs. the plasma free amino acid enrichment is used as the surrogate precursor pool enrichment, and the average mixed muscle protein FSR values were significantly greater ( P = 0.05) than the myofibrillar/myosin heavy chain FSR values. The within-study variability (i.e., population variance) was somewhat smaller in studies that used plasma amino acid/ketoacid enrichments vs. muscle free amino acid enrichment (∼24 vs. ∼31%), but this was not apparent in all circumstances. Furthermore, the between-study consistency of measured FSR values (i.e., interquartile range) was inversely correlated with the average duration between biopsies. Aside from that, the variation in reported FSR values could not be explained by differences in the experimental design and analytical methods, and none of the most commonly used approaches stood out as clearly superior in terms of consistency of results and/or within-study variability. We conclude that the variability in reported values is in part due to 1) differences in experimental design (e.g., choice of precursor pool) and 2) considerable within-subject variability. The summary of the results from our analysis can be used as guidelines for “normal” average basal FSR values at rest in healthy adults.

Physical activity and eating are two major physiological muscle growth stimuli. Although muscle protein turnover rates are not different in young and middle-aged men and women, we recently found that the basal rate of muscle protein synthesis is greater and the anabolic response to mixed-meal intake is blunted in 65- to 80-yr-old women compared with men of the same age. Whether older women are also resistant to the anabolic effect of exercise is not known.We measured the rate of muscle protein synthesis (both during basal, postabsorptive conditions and during mixed-meal intake) before and after 3 months of exercise training in obese, 65- to 80-yr-old men and women.At the beginning of the study (before training) the basal, postabsorptive muscle protein fractional synthesis rate (FSR) was significantly greater in women than in men (0.064 ± 0.006%·h(-1) vs 0.039 ± 0.006%·h(-1), respectively, P < 0.01), whereas the meal-induced increase in the muscle protein FSR was greater in men than in women (P < 0.05). In men, exercise training approximately doubled the basal muscle protein FSR (P = 0.001) but had no effect on the meal-induced increase in muscle protein FSR (P = 0.78). In women, exercise training increased the muscle protein FSR by ~40% (P = 0.03) and also had no effect on the meal-induced increase in muscle protein FSR (P = 0.51).These results suggest that there is significant sexual dimorphism not only in the basal, postabsorptive rate of muscle protein synthesis but also in the anabolic response to feeding and exercise training in obese, older adults.

Skeletal muscle is the major constituent of lean body mass and essential for the body's locomotor function. Women have less muscle mass (and more body fat) than men and are therefore not able to exert the same absolute maximal force as men. The difference in body composition between the sexes is evident from infancy but becomes most marked after puberty (when boys experience an accelerated growth spurt) and persists into old age. During early adulthood until approximately the fourth decade of life, muscle mass is relatively stable, both in men and women, but then begins to decline, and the rate of loss is slower in women than in men. In this review we discuss the underlying mechanisms responsible for the age-associated sexual dimorphism in muscle mass (as far as they have been elucidated to date) and highlight areas that require more research to advance our understanding of the control of muscle mass throughout life.

Obesity is related to quantitative neuroimaging abnormalities including reduced gray matter volumes and impaired white matter microstructural integrity, although the underlying mechanisms are not well understood.We assessed influence of obesity on neuroinflammation imaging that may mediate brain morphometric changes. Establishing the role of neuroinflammation in obesity will enhance understanding of this modifiable disorder as a risk factor for Alzheimer's disease (AD) dementia.We analyzed brain MRIs from 104 cognitively normal participants (CDR = 0) and biomarker negativity for CSF amyloid or tau. We classified body mass index (BMI) as normal (BMI <25, N = 62) or overweight and obese (BMI ≥25, N = 42). Blood pressure was measured. BMI and blood pressure classifications were related to neuroinflammation imaging (NII) derived edema fraction in 17 white matter tracts. This metric was also correlated to hippocampal volumes and CSF biomarkers of inflammation and neurodegeneration: YKL-40, SNAP25, VILIP, tau, and NFL.Participants with BMI <25 had lower NII-derived edema fraction, with protective effects of normal blood pressure. Statistically significant white matter tracts included the internal capsule, external capsule, and corona radiata, FDR correc-ted for multiple comparisons to alpha = 0.05. Higher NII-derived edema fractions in the internal capsule, corpus callosum, gyrus, and superior fronto-occipital fasciculus were related with smaller hippocampal volumes only in individuals with BMI ≥25. There were no statistically significant correlations between NII-derived edema fraction and CSF biomarkers.We demonstrate statistically significant relationships between neuroinflammation, elevated BMI, and hippocampal volume, raising implications for neuroinflammation mechanisms of obesity-related brain dysfunction in cognitively normal elderly.

Abstract Plasma hyaluronan (HA) increases systemically in type 2 diabetes (T2D) and the HA synthesis inhibitor, 4-Methylumbelliferone, has been proposed to treat the disease. However, HA is also implicated in normal physiology. Therefore, we generated a Hyaluronan Synthase 2 transgenic mouse line, driven by a tet-response element promoter to understand the role of HA in systemic metabolism. To our surprise, adipocyte-specific overproduction of HA leads to smaller adipocytes and protects mice from high-fat-high-sucrose-diet-induced obesity and glucose intolerance. Adipocytes also have more free glycerol that can be released upon beta3 adrenergic stimulation. Improvements in glucose tolerance were not linked to increased plasma HA. Instead, an HA-driven systemic substrate redistribution and adipose tissue-liver crosstalk contributes to the systemic glucose improvements. In summary, we demonstrate an unexpected improvement in glucose metabolism as a consequence of HA overproduction in adipose tissue, which argues against the use of systemic HA synthesis inhibitors to treat obesity and T2D.

Lifestyle therapy (energy restriction and exercise) is the cornerstone of therapy for people with type 2 diabetes (T2D) but is difficult to implement. We conducted an 8-month randomized controlled trial in persons with obesity and T2D (17 women and 1 man) to determine the therapeutic effects and potential mechanisms of intensive lifestyle therapy on cardiometabolic function. Intensive lifestyle therapy was conducted at the worksite to enhance compliance and resulted in marked (17%) weight loss and beneficial changes in body fat mass, intrahepatic triglyceride content, cardiorespiratory fitness, muscle strength, glycemic control, β cell function, and multi-organ insulin sensitivity, which were associated with changes in muscle NAD+ biosynthesis, sirtuin signaling, and mitochondrial function and in adipose tissue remodeling. These findings demonstrate that intensive lifestyle therapy provided at the worksite has profound therapeutic clinical and physiological effects in people with T2D, which are likely mediated by specific alterations in skeletal muscle and adipose tissue biology.

Abstract A bacteriological study was made of 106 patients undergoing elective surgery for gallbladder disease and as a control group, of patients with a normal biliary tract but requiring laparotomy for gastrointestinal disease. The isolation rate of all species of bacteria from the gallbladder and common bile duct in those patients with calculi in the duct system and in those with nonfunctioning gallbladders was considerably higher than in patients with a normal biliary system. Surprisingly, the number of isolates from patients with a history of cholsecystitis or cholelithiasis was no greater than in the control group of patients. Using modern techniques of anaerobic retrieval and culture, only a small number of anaerobes were isolated, and despite the prevalence of Bacteroides species as a normal gut inhabitant and as an opportunistic pathogen, this organism was not recovered from any of the sites investigated. Anaerobic species were Isolated from 8 out of the 106 liver biopsy specimens taken at a very early stage after laparotomy, but in such patients only non-specific liver changes were found by histological examinmation. In 8 patients from whom Escherichia colt or other aerobes were isolated from bile samples, at concentrates ranging from 105 to 107/cm3, the same species of organism were consistently isolated from T tube drainage samples for up to 8 or 9 days despite tetracycline therapy.

Although weight loss ameliorates many of the metabolic abnormalities associated with obesity, there has been reluctance to prescribe weight loss in obese, older individuals because of the fear that it will cause debilitating loss of muscle mass and impair physical function. To gain insight into the mechanisms responsible for the weight loss-induced changes in muscle mass, we measured the rate of muscle protein synthesis (by using stable isotope labeled tracer methodology) during basal, postabsorptive conditions and during mixed meal ingestion in eight obese, older adults: (i) before weight loss therapy, (ii) ~3 months after starting the weight loss intervention (i.e., during the active weight loss phase), when subjects had lost ~7% of their initial body weight, and (iii) after they had lost ~10% of their body weight and maintained this new body weight for ~6 months (~12 months after starting the weight loss intervention). The basal muscle protein fractional synthesis rate (FSR) was not affected by weight loss. Mixed meal ingestion stimulated the rate of muscle protein synthesis, and the anabolic response (i.e., increase in the protein synthesis rate above basal values) was greater (P < 0.05) during negative energy balance and active weight loss at 3 months (0.033 ± 0.012%·per hour, mean ± s.e.m.) than during weight maintenance before and at 12 months of weight loss therapy (0.003 ± 0.003 and 0.008 ± 0.012%·per hour, respectively). We conclude that during dietary calorie restriction and weight loss in older adults, the rate of muscle protein synthesis is not impaired. Thus, the loss of muscle mass must be mediated predominately by adverse effects of dietary calorie restriction on muscle proteolysis.

Sexual dimorphism in plasma triglyceride (TG) metabolism is well established but it is unclear to what extent it is driven by differences in the sex hormone milieu. RESULTS from previous studies evaluating the effects of sex steroids on plasma TG homeostasis are inconclusive because they relied on orally administered synthetic hormone preparations or evaluated only plasma lipid concentrations but not kinetics.The purpose of this study was to evaluate the effects of systemically delivered 17β-estradiol, progesterone, and T on very low density lipoprotein-triglyceride (VLDL-TG) concentration and kinetics in postmenopausal women.VLDL-TG concentration and kinetics were evaluated by using stable isotope-labeled tracer techniques in four groups of postmenopausal women (n = 27 total) who were studied before and after treatment with either 17β-estradiol (0.1 mg/d via continuous delivery skin patch), progesterone (100 mg/d via vaginal insert) and T (12.5 mg/d via skin gel), or no intervention (control group).VLDL-TG concentration and kinetics were unchanged in the control group and not altered by T and progesterone administration. Estradiol treatment, in contrast, reduced VLDL-TG concentration by approximately 30% due to accelerated VLDL-TG plasma clearance (25.1 ± 2.5 vs. 17.4 ± 2.7 mL/min; P < .01).Estradiol, but not progesterone or T, is a major regulator of VLDL-TG metabolism.

The goal of this study was to discover whether using different tracers affects the measured rate of muscle protein synthesis in human muscle. We therefore measured the mixed muscle protein fractional synthesis rate (FSR) in the quadriceps of older adults during basal, postabsorptive conditions and mixed meal feeding (70 mg protein·kg fat-free mass −1 ·h −1 × 2.5 h) by simultaneous intravenous infusions of [5,5,5- 2 H 3 ]leucine and either [ring- 13 C 6 ]phenylalanine or [ring- 2 H 5 ]phenylalanine and analysis of muscle tissue samples by gas chromatography-mass spectrometry. Both the basal FSR and the FSR during feeding were ∼20% greater ( P &lt; 0.001) when calculated from the leucine labeling in muscle tissue fluid and proteins (fasted: 0.063 ± 0.005%/h; fed: 0.080 ± 0.007%/h) than when calculated from the phenylalanine enrichment data (0.051 ± 0.004 and 0.066 ± 0.005%/h, respectively). The feeding-induced increase in the FSR (∼20%; P = 0.011) was not different with leucine and phenylalanine tracers ( P = 0.69). Furthermore, the difference between the leucine- and phenylalanine-derived FSRs was independent of the phenylalanine isotopomer used ( P = 0.92). We conclude that when using stable isotope-labeled tracers and the classic precursor product model to measure the rate of muscle protein synthesis, absolute rates of muscle protein FSR differ significantly depending on the tracer amino acid used; however, the anabolic response to feeding is independent of the tracer used. Thus different precursor amino acid tracers cannot be used interchangeably for the evaluation of muscle protein synthesis, and data from studies using different tracer amino acids can be compared qualitatively but not quantitatively.

Men and women with hyperandrogenemia have a more proatherogenic plasma lipid profile [e.g., greater triglyceride (TG) and total and low-density lipoprotein-cholesterol and lower high-density lipoprotein-cholesterol concentrations] than healthy premenopausal women. Furthermore, castration of male rats markedly reduces testosterone availability below normal and decreases plasma TG concentration, and testosterone replacement reverses this effect. Testosterone is, therefore, thought to be an important regulator of plasma lipid homeostasis. However, little is known about the effect of testosterone on plasma TG concentration and kinetics. Furthermore, testosterone is a potent skeletal muscle protein anabolic agent in men, but its effect on muscle protein turnover in women is unknown. We measured plasma lipid concentrations, hepatic very low density lipoprotein (VLDL)-TG and VLDL-apolipoprotein B-100 secretion rates, and the muscle protein fractional synthesis rate in 10 obese women before and after trandermal testosterone (1.25 g of 1% AndroGel daily) treatment for 3 wk. Serum total and free testosterone concentrations increased (P < 0.05) by approximately sevenfold in response to testosterone treatment, reaching concentrations that are comparable to those in women with hyperandrogenemia, but lower than the normal range for eugonadal men. Except for a small (∼10%) decrease in plasma high-density lipoprotein particle and cholesterol concentrations (P < 0.04), testosterone therapy had no effect on plasma lipid concentrations, lipoprotein particle sizes, and hepatic VLDL-TG and VLDL-apolipoprotein B-100 secretion rates (all P > 0.05); the muscle protein fractional synthesis rate, however, increased by ∼45% (P < 0.001). We conclude that testosterone is a potent skeletal muscle protein anabolic agent, but not an important regulator of plasma lipid homeostasis in obese women.

The purpose of this study was to determine whether brisk walking improves multiorgan (liver, muscle, adipose tissue) insulin sensitivity in older women. Ten nonobese older women (age: 66.7 ± 1.5 yr, mean ± SE) completed two 2-stage hyperinsulinemic-euglycemic clamp procedures [insulin infusion rate stage 1: 10 mU/m 2 body surface area (BSA) per min; stage 2: 50 mU/m 2 BSA per min] in conjunction with stable isotope-labeled glucose and palmitate tracer infusions: one in the morning after a single, ∼1-h bout of brisk treadmill walking, the other after an equivalent period of rest in the late afternoon of the preceding day. We found that basal glucose rate of appearance (Ra) into plasma was not different after rest and after exercise (17.3 ± 0.8 and 17.1 ± 0.4 μmol/kg fat-free mass per min, respectively). The insulin-mediated decrease in glucose Ra during stage 1 of the clamp was also not different after rest and exercise (82.2% ± 3.4% and 77.7% ± 2.1%, respectively), but glucose rate of disappearance (Rd) during stage 2 of the clamp was significantly greater ( P &lt; 0.05) after exercise than rest (88.0 ± 5.9 and 78.4 ± 6.5 μmol/kg fat-free mass per min, respectively). There were no differences in palmitate Ra during basal conditions or insulin infusion after exercise and after rest. Therefore, we conclude that a single bout of brisk walking for ∼1 h improves muscle insulin sensitivity but has no effect on liver and adipose tissue insulin sensitivity in older women.

Fibroblast growth factor (FGF)19 and FGF21 are secreted by the intestine and liver in response to macronutrient intake. Intestinal resection and reconstruction via bariatric surgery may alter their regulation.We tested the hypothesis that weight loss induced by Roux-en-Y gastric bypass (RYGB) surgery, but not matched weight loss induced by laparoscopic adjustable gastric banding (LAGB), increases postprandial plasma FGF19 and FGF21 concentrations.Glucose kinetics and plasma FGF19 and FGF21 responses to mixed meal ingestion and to glucose-insulin infusion during a hyperinsulinemic-euglycemic clamp procedure, with stable isotope tracer methods, were evaluated in 28 adults with obesity before and after 20% weight loss induced by RYGB (n = 16) or LAGB (n = 12).LAGB- and RYGB-induced weight loss increased postprandial plasma FGF19 concentrations (P < 0.05). However, weight loss after RYGB, but not LAGB, increased postprandial plasma FGF21 concentrations (1875 ± 330 to 2976 ± 682 vs 2150 ± 310 and 1572 ± 265 pg/mL × 6 hours, respectively). The increase in plasma FGF21 occurred ∼2 hours after the peak in delivery of ingested glucose into systemic circulation. Glucose-insulin infusion increased plasma FGF21, but not FGF19, concentrations. The increase in plasma FGF21 during glucose-insulin infusion was greater after than before weight loss in both surgery groups without a difference between groups, whereas plasma FGF19 was not affected by either procedure.RYGB-induced weight loss has unique effects on postprandial FGF21 metabolism, presumably due to rapid delivery of ingested macronutrients to the small intestine and delivery of glucose to the liver.

High protein (particularly leucine-rich whey protein) intake is recommended to mitigate the adverse effect of weight loss on muscle mass. The effectiveness of this approach is unknown.Seventy middle-aged (50-65 years old) postmenopausal women with obesity were randomized to (1) weight maintenance (WM), (2) weight loss and the recommended daily allowance for protein (0.8 g/kg/d) (WL group), or (3) weight loss plus whey protein supplementation (total protein: 1.2 g/kg/d) (WL-PS group). Thigh muscle volume and strength were assessed at baseline and after 5% and 10% weight loss in the weight-loss groups and after matched time periods (∼3 and 6 months, respectively) in the WM group.A 5% weight loss caused a greater decrease in thigh muscle volume in the WL group than the WL-PS group (4.7% ± 0.7% vs. 2.8% ± 0.8%, respectively; P < 0.05). After 10% weight loss, there was no statistically significant difference in muscle mass loss in the two groups, and the total loss was small in both groups (5.5% ± 0.8% and 4.5% ± 0.7%, respectively). The dietary interventions did not affect muscle strength.Whey protein supplementation during diet-induced weight loss does not have clinically important therapeutic effects on muscle mass or strength in middle-aged postmenopausal women with obesity.

Abstract Objective The objective of this study was to evaluate the relative importance of the basal rate of glucose appearance (Ra) in the circulation and the basal rate of plasma glucose clearance in determining fasting plasma glucose concentration in people with obesity and different fasting glycemic statuses. Methods The authors evaluated basal glucose kinetics in 33 lean people with normal fasting glucose (&lt;100 mg/dL; Lean &lt; 100 group) and 206 people with obesity and normal fasting glucose (Ob &lt; 100 group, n = 118), impaired fasting glucose (100–125 mg/dL; Ob 100–125 group, n = 66), or fasting glucose diagnostic of diabetes (≥126 mg/dL; Ob ≥ 126 group, n = 22). Results Although there was a large (up to three‐fold) range in glucose Ra within each group, the ranges in glucose concentration in the Lean &lt; 100, Ob &lt; 100, and Ob 100–125 groups were small because of a close relationship between glucose Ra and clearance rate. However, the glucose clearance rate at any Ra value was lower in the hyperglycemic than the normoglycemic groups. In the Ob ≥ 126 group, plasma glucose concentration was primarily determined by glucose Ra, because glucose clearance was markedly attenuated. Conclusions Fasting hyperglycemia in people with obesity represents a disruption of the precisely regulated integration of glucose production and clearance rates. image

The muscle protein fractional synthesis rate (FSR) is determined by monitoring the incorporation of an amino acid tracer into muscle protein during a constant-rate intravenous tracer infusion. Commonly two sequential muscle biopsies are obtained some time after starting the tracer infusion. However, other protocols, including those with an initial biopsy before starting the tracer infusion to measure the background enrichment and those with only a single biopsy after several hours of tracer infusion have been used. To assess the validity of these approaches, we compared the muscle protein FSR obtained by calculating the difference in [ ring- 2 H 5 ]phenylalanine and [5,5,5- 2 H 3 ]leucine incorporation into muscle protein at ∼3.5 h after starting the tracer infusion and 1) at 60 min; 2) before starting the tracer infusion (background enrichment); 3) a population average muscle protein background enrichment; and 4) by measuring the tracer incorporation into muscle protein at ∼3.5 h assuming essentially no background enrichment. Irrespective of the tracer used, the muscle protein FSR calculated from the difference in the muscle protein labeling several hours after starting the tracer infusion and either the labeling at 60 min or the background enrichment were not different (e.g., 0.049 ± 0.007%/h vs. 0.049 ± 0.007%/h, respectively, with [ 2 H 5 ]phenylalanine; P = 0.99). However, omitting the initial biopsy and assuming no background enrichment yielded average FSR values that were ∼15% (with [ 2 H 5 ]phenylalanine) to 80% (with [ 2 H 3 ]leucine) greater ( P ≤ 0.059); using a population average background enrichment reduced the difference to ∼3% ( P = 0.76) and 22% ( P = 0.52) with [ 2 H 5 ]phenylalanine and [ 2 H 3 ]leucine, respectively. We conclude that during basal, postabsorptive conditions, valid muscle protein FSR values can be obtained irrespective of the timing of the initial biopsy so long as the protein labeling in two sequential biopsies is measured whereas the single biopsy approach should be avoided.

ABSTRACT Matrix-remodeling associated 8 (MXRA8), also known as Dual immunoglobulin domain cell adhesion molecule (DICAM), is a type 1 transmembrane protein that reportedly binds the α V β 3 integrin 1 and regulates the differentiation of osteoclasts 2 and chondrocytes 3 , tumor growth 4 , T cell trafficking 5 , and angiogenesis 6 . MXRA8 is also an essential entry receptor for chikungunya virus and other related arthritogenic alphaviruses. 7-9 We compared MXRA8 expression in 51 tissues in the Human Protein Atlas and found it is most highly expressed in white adipose tissue (WAT), however the function of MXRA8 in WAT is unknown. Here, we found that MXRA8 expression in WAT is increased in people with obesity and that this response is also observed in a mouse model of high fat-diet (HFD)-induced obesity. Single-nucleus RNA sequencing and high-dimensional spectral flow cytometry analyses revealed that MXRA8 is expressed predominantly by adipocyte progenitor (AP) cells and mature adipocytes. MXRA8 mutant primary adipocytes from inguinal (i)WAT exhibited increased expression of Uncoupling protein 1 (UCP1), a thermogenic protein expressed by beige and brown adipocytes that limits obesity pathogenesis. 10-12 Indeed, MXRA8 mutant mice fed a HFD had preserved UCP1 + beige and brown adipocytes and were protected from HFD-induced obesity in a UCP1-dependent manner. Collectively, these findings indicate that MXRA8 promotes whitening of beige and brown adipose tissues to drive obesity pathogenesis and identify MXRA8 as a possible therapeutic target to treat obesity and associated metabolic diseases.

There is considerable heterogeneity in the cardiometabolic abnormalities associated with obesity. We evaluated multi-organ system metabolic function in 20 adults with metabolically healthy obesity (MHO; normal fasting glucose and triglycerides, oral glucose tolerance, intrahepatic triglyceride content, and whole-body insulin sensitivity), 20 adults with metabolically unhealthy obesity (MUO; prediabetes, hepatic steatosis, and whole-body insulin resistance), and 15 adults who were metabolically healthy lean. Compared with MUO, people with MHO had (1) altered skeletal muscle biology (decreased ceramide content and increased expression of genes involved in BCAA catabolism and mitochondrial structure/function); (2) altered adipose tissue biology (decreased expression of genes involved in inflammation and extracellular matrix remodeling and increased expression of genes involved in lipogenesis); (3) lower 24-h plasma glucose, insulin, non-esterified fatty acids, and triglycerides; (4) higher plasma adiponectin and lower plasma PAI-1 concentrations; and (5) decreased oxidative stress. These findings provide a framework of potential mechanisms responsible for MHO and the metabolic heterogeneity of obesity. This study was registered at ClinicalTrials.gov (NCT02706262).

The exact mechanisms responsible for increased plasma triglyceride (TG) concentration in obese people are unclear, and it is not known whether excess energy intake per se is involved in the pathophysiology of this abnormality.The purpose of our study was to examine how excess energy intake from a balanced diet for 1 day affects very-low-density lipoprotein (VLDL)-TG kinetics and its putative regulators hepatic insulin sensitivity and plasma free fatty acid availability.We used stable isotope-labeled tracer methods to evaluate glucose and lipid kinetics in 8 overweight and obese men (age, 38 ± 3 years; body mass index, 33.7 ± 1.7 kg/m(2); means ± SEM) on 2 occasions (randomized crossover design): once, the day after they consumed a balanced diet that provided an amount of energy that matched their energy expenditure, and another time, the day after they consumed a balanced diet that provided 30% excess calories. Eight healthy, lean men (34 ± 1 years; 22.5 ± 0.6 kg/m(2)) were studied under isocaloric conditions only to provide a reference for normal lipid kinetics.VLDL-TG and VLDL-apolipoprotein B-100 (apoB-100) concentrations and secretion rates were significantly greater (P < .01) in overweight/obese compared with lean men. Hypercaloric, compared with isocaloric, feeding in overweight/obese men increased glucose rate of appearance in plasma (904 ± 21 vs 873 ± 26 μmol/min), the hepatic insulin resistance index (10.9 ± 2.2 vs 8.3 ± 1.8), and VLDL-apoB-100 concentration and secretion rate (1.91 ± 0.24 vs. 1.53 ± 0.13 nmol/min), whereas VLDL-apoB-100 plasma clearance rate, VLDL-TG secretion and plasma clearance rates, and free fatty acid rate of appearance in plasma were not affected by overfeeding.One day of moderate overfeeding (30% excess energy intake) stimulates hepatic glucose and VLDL-apo B-100 secretion rates but has no effect on hepatic and adipose tissue fatty acid metabolism in overweight/obese men.

This review will focus on findings from the few studies performed to date in humans to examine changes in muscle protein turnover, lean or muscle mass, and physical function following fish oil-derived omega-3 fatty acid treatment. Although considerable gaps in our current knowledge exist, hypertrophic responses (e.g., improvements in the rate of muscle protein synthesis and mTOR signaling during increased amino acid availability and an increase in muscle volume) have been reported in older adults following prolonged (8 to 24 weeks) of omega-3 fatty acid supplementation. There is also accumulating evidence that increased omega-3 fatty acid levels in red blood cells are positively related to strength and measures of physical function. As a result, increased omega-3 fatty acid consumption may prove to be a promising low-cost dietary approach to attenuate or prevent aging-associated declines in muscle mass and function.

Abstract Insulin resistance increases patients’ risk of developing type 2 diabetes (T2D), non-alcoholic steatohepatitis (NASH) and a host of other comorbidities including cardiovascular disease and cancer. At the molecular level, insulin exerts its function through the insulin receptor (IR), a transmembrane receptor tyrosine kinase. Data from human genetic studies have shown that Grb14 functions as a negative modulator of IR activity, and the germline Grb14-knockout (KO) mice have improved insulin signaling in liver and skeletal muscle. Here, we show that Grb14 knockdown in liver, white adipose tissues, and heart with an AAV-shRNA (Grb14-shRNA) improves glucose homeostasis in diet-induced obese (DIO) mice. A previous report has shown that germline deletion of Grb14 in mice results in cardiac hypertrophy and impaired systolic function, which could severely limit the therapeutic potential of targeting Grb14. In this report, we demonstrate that there are no significant changes in cardiac function as measured by echocardiography in the Grb14-knockdown mice fed a high-fat diet for a period of four months. While additional studies are needed to further confirm the efficacy and to de-risk potential negative cardiac effects in preclinical models, our data support the therapeutic strategy of inhibiting Grb14 to treat diabetes and related conditions.

We conducted this study to quantify the oxidation of exogenous acetate and to determine the effect of increased acetate availability upon fat and carbohydrate utilization in humans at rest. Eight healthy volunteers (6 males and 2 females) completed 2 separate trials, 7 d apart in a single-blind, randomized, crossover design. On each occasion, respiratory gas and arterialized venous blood samples were taken before and during 180 min following consumption of a drink containing either sodium acetate (NaAc) or NaHCO3 at a dose of 2 mmol/kg body mass. Labeled [1,2 -13C] NaAc was added to the NaAc drink to quantify acetate oxidation. Both sodium salts induced a mild metabolic alkalosis and increased energy expenditure (P < 0.05) to a similar magnitude. NaHCO3 ingestion increased fat utilization from 587 +/- 83 kJ/180 min to 693 +/- 101 kJ/180 min (P = 0.01) with no change in carbohydrate utilization. Following ingestion of NaAc, the amount of fat and carbohydrate utilized did not differ from the preingestion values. However, oxidation of the exogenous acetate almost entirely (90%) replaced the additional fat that had been oxidized during the bicarbonate trial. We determined that 80.1 +/- 2.3% of an exogenous source of acetate is oxidized in humans at rest. Whereas NaHCO3 ingestion increased fat oxidation, a similar response did not occur following NaAc ingestion despite the fact both sodium salts induced a similar increase in energy expenditure and shift in acid-base balance.

It has been suggested that leucine is primarily responsible for the increase in muscle protein synthesis after protein ingestion because leucine uniquely activates the mTOR-p70S6K signalling cascade. We compared the effects of ingesting protein or an amount of leucine equal to that in the protein during a hyperinsulinaemic-euglycaemic clamp (to eliminate potential confounding as a result of differences in the insulinogenic effect of protein and leucine ingestion) on muscle anabolic signalling and protein turnover in 28 women. We found that protein, but not leucine, ingestion increased muscle p-mTORSer2448 and p-p70S6KThr389 , although only protein, and not leucine, ingestion decreased muscle p-eIF2αSer51 and increased muscle protein synthesis.It has been suggested that leucine is primarily responsible for the increase in muscle protein synthesis (MPS) after protein ingestion because leucine uniquely activates the mTOR-p70S6K signalling cascade. We tested this hypothesis by measuring muscle p-mTORSer2448 , p-p70S6KThr389 and p-eIF2αSer51 , as well as protein turnover (by stable isotope labelled amino acid tracer infusion in conjunction with leg arteriovenous blood and muscle tissue sampling), in 28 women who consumed either 0.45 g protein kg-1 fat-free mass (containing 0.0513 g leucine kg-1 fat-free mass) or a control drink (n = 14) or 0.0513 g leucine kg-1 fat-free mass or a control drink (n = 14) during a hyperinsulinaemic-euglycaemic clamp procedure (HECP). Compared to basal conditions, the HECP alone (without protein or leucine ingestion) suppressed muscle protein breakdown by ∼20% and increased p-mTORSer2448 and p-p70S6KThr389 by >50% (all P < 0.05) but had no effect on p-eIF2αSer51 and MPS. Both protein and leucine ingestion further increased p-mTORSer2448 and p-p70S6KThr389 , although only protein, and not leucine, ingestion decreased (by ∼35%) p-eIF2αSer51 and increased (by ∼100%) MPS (all P < 0.05). Accordingly, leg net protein balance changed from negative (loss) during basal conditions to equilibrium during the HECP alone and the HECP with concomitant leucine ingestion and to positive (gain) during the HECP with concomitant protein ingestion. These results provide new insights into the regulation of MPS by demonstrating that leucine and mTOR signalling alone are not responsible for the muscle anabolic effect of protein ingestion during physiological hyperinsulinaemia, most probably because they fail to signal to eIF2α to initiate translation and/or additional amino acids are needed to sustain translation.

Overfeeding is associated with insulin resistance. Studies on animals suggest this is likely due to disruption of fatty acid metabolism and increased plasma free fatty acid (FFA) availability during the night. We tested the hypothesis that overfeeding induces insulin resistance and increases nocturnal but not daytime plasma FFA availability in human subjects.We measured plasma glucose, insulin, and FFA concentrations hourly for 24 h during a day of isocaloric feeding and a day of hypercaloric feeding (30% calorie excess) in 8 overweight and obese, nondiabetic men (age: 38±3 years; body mass index: 34±2 kg/m²).Overfeeding had no effect on daytime plasma glucose, insulin, and FFA concentrations compared to isocaloric feeding, but increased nocturnal glucose (P = 0.007) and insulin (P = 0.003) concentrations and decreased nocturnal FFA concentration (P = 0.006). The homeostasis model assessment of insulin resistance score was ∼30% greater the morning after hypercaloric than isocaloric feeding (P = 0.040).One day of overfeeding has no effect on daytime plasma glucose and FFA concentrations but increases nocturnal plasma glucose and insulin concentrations, whereas nocturnal plasma FFA availability is reduced. The acute overfeeding-induced development of insulin resistant glucose metabolism therefore does not appear to be directly mediated by plasma FFA availability.

Accurate measurement of muscle protein turnover is critical for understanding the physiological processes underlying muscle atrophy and hypertrophy. Several mathematical approaches, used in conjunction with a tracer amino acid infusion, have been described to derive protein synthesis and breakdown rates from a two-pool (artery-vein) model. Despite apparently common underlying principles, these approaches differ significantly (some seem to not take into account arterio-venous shunting of amino acids, which comprises ∼80-90% of amino acids appearing in the vein) and most do not specify how tracer enrichment (i.e. mole percent excess (MPE) or tracer-to-tracee ratio (TTR)) and amino acid concentration (i.e. unlabelled only or total labelled plus unlabelled) should be expressed, which could have a significant impact on the outcome when using stable isotope labelled tracers. We developed equations that avoid these uncertainties and used them to calculate leg phenylalanine (Phe) kinetics in subjects who received a [(2) H5 ]Phe tracer infusion during postabsorptive conditions and during a hyperinsulinaemic-euglycaemic clamp with concomitant protein ingestion. These results were compared with those obtained by analysing the same data with previously reported equations. Only some of them computed the results correctly when used with MPE as the enrichment measure and total (tracer+tracee) Phe concentrations; errors up to several-fold in magnitude were noted when the same approaches were used in conjunction with TTR and/or unlabelled concentration only, or when using the other approaches (irrespective of how concentration and enrichment are expressed). Our newly developed equations should facilitate accurate calculation of protein synthesis and breakdown rates.

Abstract Dysfunctional adipose tissue is believed to promote the development of hepatic steatosis and systemic insulin resistance, but many of the mechanisms involved are still unclear. Lipin 1 catalyzes the conversion of phosphatidic acid to diacylglycerol (DAG), the penultimate step of triglyceride synthesis, which is essential for lipid storage. Herein we found that adipose tissue LPIN1 expression is decreased in people with obesity compared to lean subjects and low LPIN1 expression correlated with multi-tissue insulin resistance and increased rates of hepatic de novo lipogenesis. Comprehensive metabolic and multi-omic phenotyping demonstrated that adipocyte-specific Lpin1-/- mice had a metabolically-unhealthy phenotype, including liver and skeletal muscle insulin resistance, hepatic steatosis, increased hepatic de novo lipogenesis, and transcriptomic signatures of nonalcoholic steatohepatitis that was exacerbated by high-fat diets. We conclude that adipocyte lipin 1-mediated lipid storage is vital for preserving adipose tissue and systemic metabolic health and its loss predisposes mice to nonalcoholic steatohepatitis.

Abstract People with obesity who do not have the metabolic syndrome or components of the metabolic syndrome have been characterized as having metabolically healthy obesity (MHO). However, the existence of MHO has been questioned because people with MHO are at greater risk of developing diabetes and fatal cardiovascular disease than people who are lean and healthy. Here we report findings from a 25-year-old woman with rigorously defined MHO (normal oral glucose tolerance, insulin sensitivity [assessed using the hyperinsulinemic-euglycemic clamp procedure], plasma triglyceride, and intrahepatic triglyceride content) evaluated at baseline (body mass index, 37.7 kg/m2) and 5 years later, after a 32% (30.8 kg) increase in body mass (BMI, 49.6 kg/m2). Weight gain did not have adverse effects on fasting plasma glucose, oral glucose tolerance, β-cell function, insulin sensitivity, plasma triglyceride, intrahepatic triglyceride content, or carotid intima-media thickness. Adipose tissue expression of genes involved in extracellular matrix formation remained unchanged. Adipose tissue expression of several inflammation-related genes increased by more than 30%, but was not associated with a corresponding increase in plasma cytokine concentrations, with the exception of IL-6 and C-reactive protein. The present case study demonstrates that some people with obesity are resistant to the adverse cardiometabolic effects of excess adiposity and marked weight gain.

Journal Article The effect of hypothermia on acute coronary occlusion Get access G Smith, G Smith Departments of Surgery and Veterinary Surgery of the University of Glasgow Search for other works by this author on: Oxford Academic Google Scholar D Lawson, D Lawson Departments of Surgery and Veterinary Surgery of the University of Glasgow Search for other works by this author on: Oxford Academic Google Scholar B Penhale B Penhale Departments of Surgery and Veterinary Surgery of the University of Glasgow Search for other works by this author on: Oxford Academic Google Scholar British Journal of Surgery, Volume 44, Issue 186, January 1957, Pages 419–420, https://doi.org/10.1002/bjs.18004418617 Published: 05 December 2005

Although obesity is typically associated with metabolic co-morbidities, some people with obesity do not develop metabolic abnormalities. We evaluated whether modifiable lifestyle factors (i.e., physical activity, dietary composition, and sleep characteristics) can help explain why some people with obesity are metabolically healthy (MHO) and whether metabolically unhealthy obesity (MUO) affects quality of life (QOL). Physical activity and sleep characteristics were assessed by using tri-axial accelerometers and dietary intake, sleep quality, and QOL were evaluated by using validated questionnaires in people stratified into three groups: (1) lean with normal glucose tolerance, plasma triglyceride (TG) concentration and intrahepatic TG (IHTG) content (metabolically healthy lean [MHL]; n = 20); (2) obesity and normal glucose tolerance, plasma TG concentration and IHTG content (MHO; n = 36); and (3) obesity with abnormal glucose metabolism and hepatic steatosis (MUO; n = 43). People with MHO performed ~45-min more light-intensity physical activity/day than the MHL and MUO groups (P < 0.05). QOL, particularly the physical function domain, was higher in the MHO than the MUO group (P < 0.05). Although self-reported intake of starch, dairy, and cured meats were higher in the MUO than the MHO group (P < 0.02), the absolute differences were small and unlikely to have metabolic effects. No differences were found in sleep duration or quality between groups. These data suggest physical activity, but not sleep or dietary intake, contribute to better metabolic health in people with MHO than those with MUO, and that QOL is lower in people with MUO than those with MHO.

In man, after the intravenous infusion of pentagastrin 0.01 μg. per minute per kg. body-weight there was no increase in detectable histamine in the gastric juice or systemic venous blood. The same dose of pentagastrin, however, increased the amount of histamine detected in the venous blood draining the stomach. In all, increased secretion of acid occurred from the stomach. These findings are compatible with the concept that pentagastrin, and presumably gastrin, act on the oxyntic cell through the intermediate release of histamine.

(1) The acid-base status, and the renal excretion of electrolytes has been studied in anaesthetised hypothermic dogs respiring spontaneously and not subjected to surgical procedures. (2) An interpolation technique is described, allowing more precise assessment of acid-base parameters at changing body temperatures. (3) Hypothermia produces an acidosis, having both respiratory and metabolic components. The renal response to this acidosis is paradoxical, serving to augment rather than correct its metabolic component. The secretion of urine more alkaline than the blood plasma has been observed under these conditions. (4) Hypothermia is associated with a marked fall in glomerular nitration rate, and with decreased tubular reabsorption of sodium, potassium, chloride, bicarbonate and phosphate. Possible mechanisms for these changes are discussed.

At rest, administration of the short-chain fatty acid acetate suppresses fat oxidation without affecting carbohydrate utilization. The combined effect of increased acetate availability and exercise on substrate utilization is, however, unclear. With local ethics approval, we studied the effect of ingesting either sodium acetate (NaAc) or sodium bicarbonate (NaHCO3) at a dose of 4 mmol·kg-1 body mass 90 min before completing 120 min of exercise at 50% VO2peak. Six healthy young men completed the trials after an overnight fast and ingested the sodium salts in randomized order. As expected NaAc ingestion decreased resting fat oxidation (mean ± SD; 0.09 ± 0.02 vs. 0.07 ± 0.02 g·min-1 pre- and post-ingestion respectively, p < .05) with no effect upon carbohydrate utilization. In contrast, NaHCO3 ingestion had no effect on substrate utilization at rest. In response to exercise, fat and CHO oxidation increased in both trials, but fat oxidation was lower (0.16 ± 0.10 vs. 0.29 ± 0.11 g·min-1, p < .05) and carbohydrate oxidation higher (1.67 ± 0.35 vs. 1.44 ± 0.22 g·min-1, p < .05) in the NaAc trial compared with the NaHCO3 trial during the first 15 min of exercise. Over the final 75 min of exercise an increase in fat oxidation and decrease in carbohydrate oxidation was observed only in the NaAc trial. These results demonstrate that increasing plasma acetate concentration suppresses fat oxidation both at rest and at the onset of moderate-intensity exercise.

To evaluate the effects of diet-induced changes in energy balance and body weight on in vivo colonocyte fractional proliferation rates (FPR) in people with obesity.In vivo colonocyte FPR was assessed in 31 men and women with obesity (BMI: 35.4 ± 4.0 kg/m2 , age: 52.6 ± 8.9 years) before and after diet-induced weight loss, weight gain, or weight maintenance. Subjects ingested aliquots of 2 H2 O (heavy water) daily for 4 to 7 days, followed by flexible sigmoidoscopy with colon biopsies to assess the incorporation of 2 H into the DNA of dividing colonocytes.Colonocyte FPR averaged 12.7% ± 3.8% per day and correlated directly with intra-abdominal adipose tissue (IAAT) volume (r = 0.364, P = 0.044). Colonocyte FPR decreased in the weight loss group, did not change in the weight maintenance group, and increased in the weight gain group. The change in colonocyte FPR correlated directly with the percent change in body weight (r = 0.409, P = 0.028) and IAAT volume (r = 0.598, P = 0.001).A high-calorie diet and weight gain increase, whereas a low-calorie diet and weight loss decrease, in vivo colonocyte proliferation rate in people with obesity. These results suggest that changes in energy balance influence the risk of developing colon cancer in people with obesity by regulating colonic mucosal growth rates.

Objective This study determined whether striatal dopamine (DA) release is affected by food ingestion and whether the DA response to high‐calorie food images is greater in the fasted than in the fed state in people with obesity. Methods Striatal DA release was evaluated in 10 people with obesity and prediabetes after consuming a meal to satiation and after fasting overnight as well as in response to viewing images of high‐calorie compared with low‐calorie foods after consuming a meal to satiation or fasting overnight by using positron emission tomography with [ 11 C]raclopride injection. Results Striatal DA D2/D3 receptor availability was not different during fasted and fed conditions. Viewing images of high‐calorie foods induced striatal DA release relative to viewing images of low‐calorie foods ( P &lt; 0.05), but there was no difference in the magnitude of the response between fasting and fed conditions. Conclusions People with obesity and prediabetes do not increase striatal DA release after eating a meal to satiation compared with fasting overnight and fail to inhibit DA release in response to high‐calorie food stimuli after eating a meal to satiation. These data suggest that impaired DA signaling contributes to greater energy intake during meals in this population.

See corresponding article on page 279. Obesity in older adults (as in the younger population) has become a major public health problem and presents a serious clinical challenge. It affects ∼30–35% of 65- to 85-y-old US adults and is a major risk factor for cardiometabolic disease (including insulin resistance, nonalcoholic fatty liver disease, low-grade inflammation, dyslipidemia, elevated blood pressure, diabetes, ischemic heart disease, and heart failure) and is associated with frailty and reduced quality of life. Dietary calorie restriction–induced weight loss can improve quality of life and improve or even normalize many of the metabolic abnormalities associated with obesity. Nevertheless, the therapeutic value of weight-loss therapy in obese older adults is controversial and has even been referred to as dangerous by some (1–3) because weight loss decreases both fat mass and lean body (including muscle) mass (4) and could therefore increase the risk of sarcopenia. Weight cycling (due to repeated attempts of losing weight coupled with the inability to keep weight off successfully in the long run), in particular, is considered problematic because it is difficult for older adults to recover muscle mass once lost (5, 6). Moreover, obesity in older adults is not (or is only marginally) associated (7, 8), whereas weight loss is associated (9, 10) with increased mortality risk. However, these results are potentially confounded by “survivors’ bias” and unintentional (illness-related) weight loss. In fact, studies that took into account body composition when evaluating the association between body weight status and mortality reported that all-cause and cardiovascular disease mortality risk is greater in sarcopenic (defined as low muscle mass) and obese individuals than in nonsarcopenic and nonobese persons (11). In addition, both sarcopenia and obesity are associated with an increased risk of falls and mobility disability (12, 13). Therefore, it seems prudent to aim for a reduction in fat mass while preserving muscle mass in obese older adults. The 2 key strategies for maintaining adequate muscle mass and physical functioning in older adults are regular physical activity, particularly resistance exercise, and sufficient dietary protein intake. The PROT-AGE Study Group (14) and the European Society for Parenteral and Enteral Nutrition Expert Group (15) recommend 1.0–1.2 g protein/kg body weight per day and a high dietary leucine content (2.0–2.5 g leucine/d) for older adults. However, the efficacy of this approach is uncertain, and it is unclear if it can prevent the loss of muscle mass during calorie restriction. The results from prospective randomized intervention trials demonstrated that increasing protein intake during exercise training in weight-stable older adults does not result in increased muscle mass or strength (16) and exercise training during calorie restriction in older adults reduces but does not abolish the weight-loss–induced loss of lean body and muscle mass when consuming a “standard” weight-loss diet [i.e., despite participating in a vigorous exercise program, obese older adults lost ∼2–3% of their muscle mass, which is 4 times that of the weight-maintenance control group during the same period and ∼20% of total weight lost (4)]. In this issue of the Journal, Verreijen et al. (17) report the results from a double-blind randomized controlled study designed to evaluate the efficacy of a dietary protein supplement to preserve muscle mass in older adults during intentional weight loss achieved by dietary calorie restriction in combination with resistance exercise training (3 times/wk) for 13 wk. They found that consuming the supplement, which contained 20.7 g leucine-rich whey protein (2.8 g leucine), daily as well as 3 times/wk immediately after the exercise bout resulted in ∼30% greater protein intake in the intervention/supplementation group compared with the control group (1.11 vs. 0.85 g/kg body weight per day, respectively, averaged over 1 wk) and completely abolished the weight-loss–induced loss of muscle mass. These results are remarkable and hold promise, although it needs to be noted that the beneficial effects of protein supplementation on muscle mass were not accompanied by differences in strength and physical functioning, which improved to the same extent in both (standard diet and protein supplement) groups. The intervention was short, and the amount of weight lost was small (only ∼3%); therefore, it remains to be seen whether differences emerge during more marked weight loss and whether the beneficial effect of protein supplementation can be sustained long term. Other intriguing questions are whether the beneficial effect of the dietary supplement in the study by Verreijen et al. (17) was due to its high leucine content, the total amount of protein consumed, or the timing of the supplement immediately after the exercise bout. In weight-stable older adults, leucine-rich whey protein acutely stimulates muscle protein synthesis to a greater extent than do other proteins (18), and Esmarck et al. (19) showed that consuming a 10-g protein supplement immediately after a bout of resistance exercise 3 times/wk led to muscle hypertrophy, whereas consuming the supplement later after exercise did not. The results of the reported study by Verreijen et al. (17) almost certainly are not a consequence of the 1.3 g of fiber and 20 μg of vitamin D3 that were added to the supplement (20). A limitation of the study by Verreijen et al. (17) is the absence of a more comprehensive and balanced assessment of benefits vs. potential risks. Although weight loss and high protein intake within the range achieved in the study by Verreijen et al. (17) are considered safe and do not have clinically significant adverse effects on bone and kidneys (1, 14), it is possible that increased protein intake will have adverse effects on insulin sensitivity of glucose metabolism (21, 22) and increase the risk of diabetes. Carefully designed, long-term weight-loss studies are still needed to define optimal protein/amino acid intake to preserve muscle mass and to achieve metabolic health in obese older adults.

Journal Article Gastric secretion and anticholinergic drugs Get access D T Caridis, D T Caridis University of Aberdeen Search for other works by this author on: Oxford Academic Google Scholar G Smith G Smith University of Aberdeen Search for other works by this author on: Oxford Academic Google Scholar British Journal of Surgery, Volume 55, Issue 3, March 1968, Pages 185–189, https://doi.org/10.1002/bjs.1800550306 Published: 06 December 2005

Invited EditorialsSimilar muscle protein synthesis rates in young men and women: men aren't from Mars and women aren't from VenusGordon I. Smith, and Bettina MittendorferGordon I. SmithWashington University, School of Medicine, St. Louis, Missouri, and Bettina MittendorferWashington University, School of Medicine, St. Louis, MissouriPublished Online:01 Jun 2012https://doi.org/10.1152/japplphysiol.00354.2012This is the final version - click for previous versionMoreSectionsPDF (37 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat men have more muscle than women, and several attempts have been made to determine the physiological mechanisms responsible for this phenomenon by measuring the rates of muscle protein synthesis (MPS) and breakdown (MPB) without much luck so far. Except for one group of investigators who reported higher basal rates of MPS in women than in men (8), no one else has found differences between young men and young women in basal rates of muscle protein turnover (2, 3, 9, 14, 17) or rates of MPS during combined hyperinsulinemia and hyperaminoacidemia (17) or immediately after a bout of exercise (2). Aside from the inherent challenges in proving no difference, the studies so far do not provide definitive answers because they did not explore the maximal stimulatory effect of nutrients or take into account the prolonged period of muscle protein anabolism after a bout of exercise (10).West et al. (22) in their study that appears in this issue of the Journal of Applied Physiology attempted to settle this issue by measuring the rate of MPS in young men and young women during overnight fasted conditions and after ingestion of a maximal anabolic dose of whey protein at rest and after exercise, covering almost the entire, if not the entire time period during which MPS is stimulated by increased contractile activity. In support of the general consensus so far, they too report no difference in the rates of MPS between young men and women in the fasted state or the fed state at rest or after exercise. It therefore seems safe to say that West et al. firmly put the final nail in the coffin of the notion that rates of MPS throughout the day are different between healthy young men and women. Although counterintuitive at first glance, this conclusion should probably not surprise us too much. Muscle mass remains steady from young adulthood to middle age in both men and women and the relative muscle growth induced by resistance exercise training is not different between the sexes (16, 21). Consequently, even if one were to find differences in the rates of MPS and MPB between young and middle-aged adult men and women, these differences would only represent differences in the turnover of muscle (i.e., the renewal rate of existing protein) but would not shed any light on why men have more muscle than women. Does this mean research in this area has come to a halt? Certainly not, because there appear to be sex differences in the rates of muscle loss during aging, inactivity, or in catabolic disease states (4, 12, 20, 23). Accordingly, we recently presented some evidence for substantial differences in the rate of MPS in old men and women and their anabolic response to feeding and exercise training (18, 19). A better understanding of the mechanisms responsible for differences in muscle catabolism between men and women deserves the focus of future research because it is essential for designing effective strategies to help curtail the adverse and often debilitating health consequences associated with reduced muscle mass and function.The study by West et al. also provides further insight into the cellular mechanisms that are thought to control the rate of muscle protein turnover. By measuring the activation (phosphorylation) of the Akt-mTOR-p70s6k signaling pathway and the mRNA of the ubiquitin ligases MuRF-1 and atrogin-1 throughout the course of a day during fasted and fed conditions at rest and after exercise, they eliminate the concerns associated with single-snapshot data. Still, West et al. were unable to explain the oscillation of MPS over the course of the day by the changes in anabolic signaling activity; their data therefore adds to the often reported dissociation between the nutrient- and exercise-induced stimulation of MPS and the phosphorylation of anabolic signaling proteins (1, 5–7, 11, 13). Furthermore, although they did not measure rates of MPB, it is quite obvious that the changes in ubiquitin ligase gene expression in the study by West et al. (e.g., decrease in atrogen-1 expression after exercise) do not correspond to the expected changes in muscle protein breakdown [which increases in response to resistance exercise (10, 15)]. These discoveries should not make us dismiss such measurements; however, they should make us think about their utility. The critical involvement of mTOR and its downstream targets in muscle growth is undeniable. However, it now seems clear that relatively small changes in what are considered key anabolic signaling elements are not involved in the fine-tuning of muscle protein turnover rates and cannot and should not be used to predict potential differences in actual muscle protein turnover rates between subjects/conditions. In fact, it seems unlikely that the penultimate control switch can be found as far upstream and in as important a gate keeper for many physiological functions as mTOR.In summary, the answer to the question whether there are differences in muscle protein metabolism between healthy young men and women seems to be no. However, the actual drivers behind the differential response of muscle in men and women to aging, disuse, and catabolic disease remain to be elucidated.DISCLOSURESNo conflicts of interest, financial or otherwise, are declared by the authors.AUTHOR CONTRIBUTIONSAuthor contributions: G.I.S. and B.M. drafted manuscript; G.I.S. and B.M. edited and revised manuscript; G.I.S. and B.M. approved final version of manuscript; B.M. conception and design of research.REFERENCES1. Atherton PJ , Etheridge T , Watt PW , Wilkinson D , Selby A , Rankin D , Smith K , Rennie MJ. Muscle full effect after oral protein: time-dependent concordance and discordance between human muscle protein synthesis and mTORC1 signaling. Am J Clin Nutr 92: 1080–1088, 2010.Crossref | PubMed | ISI | Google Scholar2. Dreyer HC , Fujita S , Glynn EL , Drummond MJ , Volpi E , Rasmussen BB. Resistance exercise increases leg muscle protein synthesis and mTOR signalling independent of sex. 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Moore DR , Robinson MJ , Fry JL , Tang JE , Glover EI , Wilkinson SB , Prior T , Tarnopolsky MA , Phillips SM. Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr 89: 161–168, 2009.Crossref | PubMed | ISI | Google Scholar14. Parise G , Mihic S , MacLennan D , Yarasheski KE , Tarnopolsky MA. Effects of acute creatine monohydrate supplementation on leucine kinetics and mixed-muscle protein synthesis. J Appl Physiol 91: 1041–1047, 2001.Link | ISI | Google Scholar15. Phillips SM , Tipton KD , Aarsland A , Wolf SE , Wolfe RR. Mixed muscle protein synthesis and breakdown after resistance exercise in humans. Am J Physiol Endocrinol Metab 273: E99–E107, 1997.Link | ISI | Google Scholar16. Roth SM , Ivey FM , Martel GF , Lemmer JT , Hurlbut DE , Siegel EL , Metter EJ , Fleg JL , Fozard JL , Kostek MC , Wernick DM , Hurley BF. Muscle size responses to strength training in young and older men and women. J Am Geriatr Soc 49: 1428–1433, 2001.Crossref | PubMed | ISI | Google Scholar17. Smith GI , Atherton P , Reeds DN , Mohammed BS , Jaffery H , Rankin D , Rennie MJ , Mittendorfer B. No major sex differences in muscle protein synthesis rates in the postabsorptive state and during hyperinsulinemia-hyperaminoacidemia in middle-aged adults. J Appl Physiol 107: 1308–1315, 2009.Link | ISI | Google Scholar18. Smith GI , Atherton P , Villareal DT , Frimel TN , Rankin D , Rennie MJ , Mittendorfer B. Differences in muscle protein synthesis and anabolic signaling in the postabsorptive state and in response to food in 65–80 year old men and women. PLos One 3: e1875, 2008.Crossref | PubMed | ISI | Google Scholar19. Smith GI , Villareal DT , Sinacore DR , Shah K , Mittendorfer B. Muscle protein synthesis response to exercise training in obese, older men and women. Med Sci Sports Exerc. In press.ISI | Google Scholar20. Stephens NA , Gray C , Macdonald AJ , Tan BH , Gallagher IJ , Skipworth RJ , Ross JA , Fearon KC , Greig CA. Sexual dimorphism modulates the impact of cancer cachexia on lower limb muscle mass and function. Clin Nutr. In press.ISI | Google Scholar21. Walts CT , Hanson ED , Delmonico MJ , Yao L , Wang MQ , Hurley BF. Do sex or race differences influence strength training effects on muscle or fat? Med Sci Sports Exerc 40: 669–676, 2008.Crossref | ISI | Google Scholar22. West DWD , Burd NA , Churchward-Venne TA , Camera DM , Mitchell CJ , Baker SK , Hawley JA , Coffey VG , Phillips SM. Sex-based comparisons of myofibrillar protein synthesis after resistance exercise in the fed state. J Appl Physiol; doi:10.1152/japplphysiol.00170.2012.ISI | Google Scholar23. Yamamoto T , Sekiya N , Miyashita S , Asada H , Yano Y , Morishima K , Okamoto Y , Goto S , Suzuki Y , Gunji A. Gender differences in effects of 20 days horizontal bed rest on muscle strength in young subjects. J Gravit Physiol 4: S31–S36, 1997.Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: B. Mittendorfer, Division of Geriatrics and Nutritional Science, Washington Univ. School of Medicine, 660 South Euclid Ave., Campus Box 8031, Saint Louis, MO 63110 (e-mail: [email protected]edu). Download PDF Back to Top Next FiguresReferencesRelatedInformation Cited ByTreadmill exercise within lower body negative pressure protects leg lean tissue mass and extensor strength and endurance during bed rest5 August 2016 | Physiological Reports, Vol. 4, No. 15Reduced resting skeletal muscle protein synthesis is rescued by resistance exercise and protein ingestion following short-term energy deficitJosé L. Areta, Louise M. Burke, Donny M. Camera, Daniel W. D. West, Siobhan Crawshay, Daniel R. Moore, Trent Stellingwerff, Stuart M. Phillips, John A. Hawley, and Vernon G. Coffey15 April 2014 | American Journal of Physiology-Endocrinology and Metabolism, Vol. 306, No. 8 More from this issue > Volume 112Issue 11June 2012Pages 1803-1804 Copyright & PermissionsCopyright © 2012 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00354.2012PubMed22442029History Received 19 March 2012 Accepted 19 March 2012 Published online 1 June 2012 Published in print 1 June 2012 Metrics

The Pritikin Program, which provides intensive lifestyle therapy, has been shown to improve cardiometabolic outcomes when provided as a residential program.The purpose of the present study was to conduct a short-term, randomized, controlled trial to evaluate the feasibility and clinical efficacy of treatment with the Pritikin Program in an outpatient worksite setting.Cardiometabolic outcomes were evaluated in people with overweight/obesity and ≥2 metabolic abnormalities (high triglycerides, low high-density lipoprotein (HDL) cholesterol, high blood pressure, HbA1c > 5.7%), before and after they were randomized to 6 weeks of standard care (n = 26) or intensive lifestyle therapy, based on the Pritikin Program (n = 28). Participants in the lifestyle intervention group were provided all food as packed-out meals and participated in group nutrition, behavioral education, cooking classes, and exercise sessions 3 times per week at a worksite location.Compared with standard care, intensive lifestyle therapy decreased body weight (-5.0% vs -0.5%), HbA1c (-15.5% vs +2.3%), plasma total cholesterol (-9.8% vs +7.7%), low-density lipoprotein cholesterol (-10.3% vs +9.3%) and triglyceride (-21.7% vs +3.0%) concentrations, and systolic blood pressure (-7.0% vs 0%) (all P values < .02), and increased exercise tolerance (time to exhaustion walking on a treadmill by +23.7% vs +4.5%; P < .001).This study demonstrates the feasibility and clinical effectiveness of short-term, intensive outpatient lifestyle therapy in people with overweight/obesity and increased risk of coronary heart disease when all food is provided and the intervention is conducted at a convenient worksite setting.

In preclinical models, insulin resistance in the dorsal striatum (DS) contributes to overeating. Although human studies support the concept of central insulin resistance, they have not investigated its effect on consummatory reward-induced brain activity.Taste-induced activation was assessed in the caudate and putamen of the DS with blood oxygen level-dependent (BOLD) functional magnetic resonance imaging. Three phenotypically distinct groups were studied: metabolically healthy lean, metabolically healthy obesity, and metabolically unhealthy obesity (MUO; presumed to have central insulin resistance). Participants with MUO also completed a weight loss intervention followed by a second functional magnetic resonance imaging session.The three groups were significantly different at baseline consistent with the design. The metabolically healthy lean group had a primarily positive BOLD response, the MUO group had a primarily negative BOLD response, and the metabolically healthy obesity group had a response in between the two other groups. Food craving was predicted by taste-induced activation. After weight loss in the MUO group, taste-induced activation increased in the DS.These data support the hypothesis that insulin resistance and obesity contribute to aberrant responses to taste in the DS, which is only partially attenuated by weight loss. Aberrant responses to food exposure may be a barrier to weight loss.

Background & AimsMetabolic dysfunction-associated fatty liver disease (MAFLD) is a common complication of obesity with a hallmark feature of hepatic steatosis. Recent data from animal models of MAFLD have demonstrated substantial changes in macrophage composition in the fatty liver. In humans, the relationship between liver macrophage heterogeneity and liver steatosis is less clear.MethodsLiver tissue from 21 participants was collected at time of bariatric surgery and analyzed using flow cytometry, immunofluorescence, and H&E microscopy. Single-cell RNA sequencing was also conducted on a subset of samples (n=3). Intrahepatic triglyceride content was assessed via MRI and tissue histology. Mouse models of hepatic steatosis were used to investigate observations made from human liver tissue.ResultsWe observed variable degrees of liver steatosis with minimal fibrosis in our participants. Single-cell RNA sequencing revealed four macrophage clusters that exist in the human fatty liver encompassing Kupffer cells (KC) and monocyte-derived macrophages (MdM). The genes expressed in these macrophage subsets were similar to those observed in mouse models of MAFLD. Hepatic CD14+ monocytes/macrophage number correlated with the degree of steatosis. Using mouse models of early liver steatosis we demonstrate recruitment of MdMs precedes KC loss and liver damage. Electron microscopy of isolated macrophages revealed increased lipid accumulation in MdMs and ex vivo lipid transfer experiments suggested that MdMs may serve a distinct role in lipid uptake during MAFLD.ConclusionsThe human liver in MAFLD contains macrophage subsets that align well with those that appear in mouse models of fatty liver disease. Recruited myeloid cells correlate well with the degree of liver steatosis in humans. MdMs appear to participate in lipid uptake during early stages of MALFD.

Abstract Disclosure: M.C. Petersen: None. G.I. Smith: None. J. Yu: None. R.A. Barve: Other; Self; Royalties; PercayAI. J. Yoshino: None. G.I. Shulman: None. S. Klein: Advisory Board Member; Self; Merck, Altimmune. Some people with obesity are resistant to the adverse metabolic effects of excess adiposity and are considered to have “metabolically healthy obesity” (MHO). However, the mechanisms responsible for MHO are not clear. We evaluated whole-body insulin sensitivity (glucose infusion rate/plasma insulin during a hyperinsulinemic-euglycemic clamp) and several putative factors that regulate insulin action, including skeletal muscle diacylglycerol (DAG) and ceramide content and transcriptomic profiles in abdominal subcutaneous adipose tissue (ASAT) and muscle, in three groups separated by adiposity and metabolic function: i) 20 adults with MHO (BMI = 38.6 ± 1.2 kg/m2, normal fasting glucose, oral glucose tolerance, hemoglobin A1c, and intrahepatic triglyceride content); ii) 20 adults with MUO (BMI= 39.5 ± 1.1 kg/m2, prediabetes and hepatic steatosis); and iii) 15 adults who were metabolically-healthy and lean (MHL, BMI= 22.7 ± 0.4 kg/m2). Insulin sensitivity progressively decreased from MHL to MHO to MUO [109 ± 7 to 72 ± 7 to 30 ± 2 (μg glucose/kg FFM/min)/(μU/mL), respectively]. Muscle plasma membrane and total cellular sn-1,2-DAG contents were greater in the MHO and MUO groups compared with the MHL group, with no difference between MHO and MUO groups. In contrast, muscle ceramide content in multiple compartments progressively increased from MHL to MHO to MUO and were inversely correlated with insulin sensitivity among all subjects (plasma membrane, r = -0.61; mitochondria, r = -0.56; endoplasmic reticulum, r = -0.51, all P &amp;lt; 0.001). In ASAT, the expression of genes involved in extracellular matrix (ECM) remodeling and inflammation were greater in MUO than MHO, whereas the expression of genes involved in lipogenesis was greater in MHO than MUO. Sparse partial least-squares discriminant analysis, a classification algorithm, was used to identify the features that best discriminated the MHO and MUO groups. Of 125 variables, fasting plasma C-peptide concentration and skeletal muscle mitochondrial ceramide content were the best discriminants of MHO and MUO. Muscle mitochondrial ceramide content was negatively correlated with muscle transcripts involved in mitochondrial structure/function (e.g., ATP5MG [r = -0.69, P &amp;lt; 0.0001] and MPC1 [r = -0.67, P &amp;lt; 0.0001]) and PAQR4 (r = -0.71, P &amp;lt; 0.0001), which encodes a ceramidase in the adiponectin receptor family. In addition, the muscle transcripts that positively correlated with muscle mitochondrial ceramide content were strongly enriched for ECM and TGFβ-related pathways. Conclusions: Greater whole-body insulin sensitivity in people with MHO than MUO is associated with alterations in adipose tissue and skeletal muscle biology, namely decreased markers of ASAT ECM remodeling and inflammation, decreased skeletal muscle ceramide content, and increased skeletal muscle expression of PAQR4 and genes associated with mitochondrial content/function. Presentation: Friday, June 16, 2023

Hyperglucagonemia is a hallmark in obesity and type 2 diabetes (T2DM). Suppression of glucagon signaling improves glycemic control in T2DM. We evaluated glucagon homeostasis in lean and obese mice and people. Discordant with the canonical rise in glucagon with fasting, our studies show that fasting (4, 8, 16 and 24 h) caused a progressive decrease in serum glucagon in diet-induced obese, hyperglucagonemic mice (P&amp;lt;0.01), yet a progressive increase in serum glucagon in lean mice (P&amp;lt;0.01). Serum insulin decreased with fasting in both lean and obese mice (P&amp;lt;0.01). Accordingly, fasting increased the glucagon:insulin ratio in the lean mouse (P&amp;lt;0.01), but did not affect the glucagon:insulin ratio in the obese mouse. Two hours of re-feeding restored hyperglucagonemia in obese mice (P&amp;lt;0.01). Pancreatic perfusion studies in obese, hyperglucagonemic mice confirm that 16 h of fasting decreases pancreatic glucagon secretion (P&amp;lt;0.01). Consistent with our findings in the mouse, fasting decreased (P&amp;lt;0.05) serum glucagon in obese participants. In contrast, fasting increased serum glucagon concentrations in lean participants (P&amp;lt;0.05). As expected, fasting decreased serum insulin in both lean and obese participants (P&amp;lt;0.05 for both). As a result, fasting induced a more robust rise in the glucagon:insulin ratio in lean compared to obese participants (P&amp;lt;0.01). In addition, mixed meal feeding increased serum glucagon in people with obesity. These findings suggest that the metabolic pathophysiology of obesity may be driven by inappropriate meal-induced regulation of glucagon, resulting in a relatively static glucagon:insulin ratio. Disclosure J.H. Stern: None. G.I. Smith: None. R.H. Unger: None. S. Klein: Stock/Shareholder; Self; Aspire Bariatrics. Consultant; Self; Pfizer Inc.. Research Support; Self; Merck &amp; Co., Inc., Johnson &amp; Johnson Services, Inc., REMD Biotherapeutics. P.E. Scherer: None.

The long-chain omega-3 polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid, which are commonly found in fatty fish such as salmon, mackerel, and sardines or consumed as dietary supplements, are essential to the diet, but in the United States are consumed at well below recommended levels. Early studies focused on the cardiovascular benefits of omega-3 fatty acid intake but more recent studies suggest that omega-3 fatty acids may also positively affect muscle mass, strength, and physical function. For example, in cross-sectional studies higher intake of fatty fish has been associated with improved physical function and strength in older adult, and in prospective studies omega-3 fatty acid supplementation has been found to increase lean body and muscle mass in older adults and attenuate muscle atrophy during cancer cachexia. This chapter will review results from studies examining omega-3 fatty acid-induced changes in muscle protein metabolism, body composition, and strength and function and provide recommendations for future studies where gaps in our knowledge exist.

(Cell Reports 39, 110733; April 26, 2022) In the original published version of this paper, a declaration of interests was accidently omitted: “B.N.F. is a member of the scientific advisory board and has stock in Cirius Therapeutics, which is developing MPC inhibitors for clinical use.” This has been corrected online. The authors apologize for this error. Silencing alanine transaminase 2 in diabetic liver attenuates hyperglycemia by reducing gluconeogenesis from amino acidsMartino et al.Cell ReportsApril 26, 2022In BriefMartino et al. find that alanine transaminase 2 (ALT2), which is encoded by Gpt2, is increased in liver of mice and people with obesity by activating transcription factor 4. Suppression of Gpt2 expression in obese, but not lean mice, lowers blood glucose by suppressing alanine-mediated gluconeogenesis. Full-Text PDF Open Access

In a review of 305 consecutive patients who had undergone truncal vagotomy and gastrojejunostomy for duodenal ulceration 5–15 (mean 10.5) years before, symptomatic and metabolic sequelae were related to a dietary survey in 109 patients. The incidence of post vagotomy symptoms was related to the incidence of weight loss and reduced dietary energy intake. The dietary survey did not show any trends in the incidence of weight loss since operation. Biochemical steatorrhoea occurred in 48% of 96 patients, but this was not related to dietary fat intake, or to weight loss unless diarrhoea was also present. Anaemia was noted in 13% of patients, but the incidence was not related to dietary survey, age, symptoms or post-vagotomy gastric acid output.

Intravenous infusion of an amino acid mixture reduces insulin‐mediated glucose disposal during a hyperinsulinemic‐euglycemic clamp. The mechanisms responsible for the adverse effect of amino acids on insulin‐mediated glucose disposal are unclear and it is not known whether protein ingestion has similar adverse effects. We hypothesized that protein ingestion impairs insulin‐mediated glucose disposal due to leucine‐mediated activation of mTOR and serine‐phosphorylation of IRS1. To test this hypothesis, we conducted hyperinsulinemic‐euglycemic clamps (50 mU insulin/m 2 body surface area/min) in two groups (n = 9/group) of women (age: 58±1 yr, BMI: 35±1 kg/m 2 ) who ingested (in randomized order): a) either 0.6 g of whey protein (containing 0.0684 g of leucine) per kg fat‐free mass (28.1±1.0 g whey protein total) or placebo or b) 0.0684 g leucine per kg fat‐free mass (3.3±0.1 g leucine total) or placebo during the 4‐h clamp. Whey protein ingestion significantly reduced the rate of glucose disposal during insulin infusion (2786±324 vs. 3022±383 µmol/min, respectively, P=0.04) whereas leucine ingestion had no effect on insulin‐mediated glucose disposal (2787±212 vs. 2805±238 µmol/min, respectively, P=0.90). We conclude that: a) protein ingestion impairs insulin‐mediated glucose disposal and b) the insulin desensitizing effect of protein ingestion is not mediated by increased leucine availability. Grant Funding Source : Supported by grants from the NIH and an Ajinomoto Exploratory Research Grant.

We appreciate Dr. Dioguardi’s critical assessment (1) of our recently published article (2). We are a bit perplexed that he considered the outcome from our study predictable. Prompted by the results from intravenous amino acid infusion studies in people that demonstrated that amino acids blunt insulin-mediated glucose disposal (3,4) and studies conducted in cultured myotubes and isolated rat skeletal muscles …

Although there appear to be no differences in muscle protein turnover in young/middle aged men and women, we have reported significant differences in the rate of muscle protein synthesis (MPS) in older adults. This suggests that aging may affect muscle protein turnover differently in men and women. To test this hypothesis we measured rates of MPS (by using stable isotope-labeled tracer methods) during basal postabsorptive conditions and during i.v. insulin/amino acid (AA) infusion in 25–45 y old men and women (n=8 each) and 65–80 y old men and women (n=8 each). The basal rate of MPS was not different in young and old men (0.040 ± 0.004 vs. 0.038 ± 0.004 %/h, respectively; P=0.75) with an increase in the rate of MPS during insulin and AA infusion only observed in young but not old men (to 0.063 ± 0.006 and 0.044 ± 0.007 %/h, respectively; P<0.01). In contrast, the basal rate of MPS was faster in old than young women (0.060 ± 0.004 vs. 0.043 ± 0.004 %/h, respectively; P<0.01) and the rate of MPS during insulin/AA infusion was not different in young and old women (0.075 ± 0.007 vs. 0.076 ± 0.006 %/h, respectively; P=0.70). We conclude that there is sexual dimorphism in the age-associated changes in MPS and thus the metabolic processes responsible for the age-related decline in muscle mass.

We recently reported a greater basal, postabsorptive rate of muscle protein synthesis (MPS) in post‐compared with premenopausal women. This finding suggests that ovarian hormones suppress MPS. In the current study, we tested this hypothesis by measuring the basal rate of MPS (by using stable isotope‐labeled tracer methods) in postmenopausal women before and after treatment with either estradiol (Mylan Pharmaceuticals; 0.1 mg/d delivered transdermally; n=6) or progesterone (Endometrin®; 100 mg/d delivered vaginally; n =5). The MPS rate was unaffected by estrogen treatment (0.063±0.006 vs. 0.063±0.010 %/h, before and after treatment respectively; P=0.99) but was markedly increased after progesterone treatment (0.102±0.018 %/h vs. 0.055±0.007; P=0.02). We conclude that the menopause associated decline in ovarian female sex hormone production is not responsible for the age‐associated increase in MPS in old women. Supported by grants from the NIH.

Skeletal muscle atrophy is a consequence of aging, inactivity, and a number of disease processes including but not limited to: Cancer, AIDS, Chronic Heart Failure, Chronic Obstructive Pulmonary Disease, Sepsis, Denervation, and Amyotrophic Lateral Sclerosis. This loss of muscle mass is a result of a reduction in skeletal muscle protein synthesis and/or an increase in skeletal muscle proteolysis resulting in a net protein degradation. β2-adrenergic agonists have been used in an effort to promote anabolism in animal models and more recently in humans. PURPOSE: to examine the mechanism of action of oral albuterol on skeletal muscle protein metabolism in older adults. METHODS: Seven men and three women (age 68.8±1.5 years; body mass index 24.3±1.6 kg/m2; body mass 76.3±7.0 kg) who were weight stable and on a stable and non-confounding medication regimen participated in this investigation after providing written informed consent. The fractional synthetic rate of mixed muscle protein synthesis (FSR) and whole body protein breakdown was determined in the fasted and fed (Ensure® ingestion) states before and after 10 d supplementation with either albuterol (16 mg/day; n=5) or placebo (n=5). RESULTS: The leucine rate of appearance (Ra), a measure of whole body protein breakdown, was 2.22±0.11 and 2.18±0.09 μmol.kg FFM−1.min−1 pre and post albuterol administration, respectively, and 2.35±0.20 and 2.33±0.21 μmol.kg FFM−1.min−1 pre and post placebo administration, respectively, with no difference between groups (P = 0.53) or change over time (P = 0.67). There was a significant time effect of albuterol supplementation on muscle protein synthesis (∼90% increase in FSR; P = 0.013) pre to post administration (ie. the fasted and fed states combined). Further, the protein synthesis rate during mixed meal feeding was significantly higher post- compared to pre-supplementation (0.132 ± 0.014 %·h−1 vs. 0.061 ± 0.012 %·h−1, respectively; P < 0.05). In contrast, placebo administration had no effect on the rate of muscle protein synthesis (main effect of time P=0.60; interaction P=0.33). CONCLUSIONS: Ten days of albuterol supplementation resulted in a dramatic increase in skeletal muscle protein synthesis while having no effect on whole body proteolysis. These data are the first to our knowledge to document an increase in the rate of muscle protein synthesis as a result of albuterol administration in humans and as such may have important implications for the treatment of muscle atrophy during sarcopenia, unloading, and disease. This research was supported by National Institutes of Health Grants R21 AG25721 (Charles P. Lambert)

Poster presented at the 2017 Health Sciences Research Day which was organized and sponsored by the University of Missouri School of Medicine Research Council and held on November 9, 2017.

Administration of long chain n‐3 polyunsaturated fatty acids (LCn‐3PUFA) has been reported to increase whole‐body protein synthesis in burned rats and growing steers. The effects of LCn‐3PUFA on human protein metabolism are unknown. To fill this gap, we measured the skeletal muscle protein fractional synthetic rate (FSR) during basal, postabsorptive conditions and during intravenous infusion of insulin and amino acids in 11 healthy, 65–80 y old adults (BMI: 26 ± 1 kg/m 2 ; means ± SEM) before and after 8 weeks of supplementation with either 4 g·d −1 Lovaza ™ (GlaxoSmithKline) containing 3.36 g of the ethylesters of eicosapentanoic acid [20:5n‐3] and docosahexaenoic acid [22:6n‐3]; n = 6) or corn oil (n = 5). Corn oil supplementation had no effect on either the basal muscle protein FSR (P = 0.62) or the anabolic response to insulin and amino acid infusion (P = 0.58). LCn‐3PUFA supplementation also had no effect on the basal rate of muscle protein synthesis (0.055 ± 0.005 vs. 0.054 ± 0.011 %·h −1 , before and after supplementation, respectively; P= 0.95) but augmented the hyperaminoacidemia hyperinsulinemia‐induced increase in the rate of muscle protein synthesis (from 0.010 ± 0.006 %/h to 0.030 ± 0.004 %·h −1 ; P= 0.04). We conclude that LCn‐3PUFA have anabolic properties in older adults and may be useful for the prevention and treatment of sarcopenia. Supported by grants from the NIH, ASN, AFAR, GSK, and the Longer Life Foundation.

Men have more muscle than women but during aging lose muscle faster than women. To investigate potential mechanisms responsible for this we measured rates of muscle protein synthesis (MPS) with stable isotope‐labeled tracer techniques and the phosphorylation status of anabolic signaling elements during postabsorptive conditions and feeding in men (n=13) and women (n=16) who were matched on age (65–80 y) and body mass index. Postabsorptive MPS was ∼25% less in men than in women (0.045 [0.039; 0.057] vs 0.058 [0.052; 0.072]; %·h −1 ; medians [quartiles]; P =0.02) and feeding increased MPS in men (to 0.071 [0.059; 0.079] %·h −1 ; P &lt;0.01) but not women (0.060 [0.056; 0.089] %·h −1 ). Postabsorptively, muscle phosphorylated Akt Ser473 , p70s6k Thr389 , eIF4E Ser209 and eIF4E‐BP1 Thr37/46 concentrations were not different between sexes but that of eEF Thr56 was less in women, consonant with more activated protein elongation. Accordingly, feeding increased eIF4E Ser209 and eIF4E‐BP1 Thr37/46 phosphorylation in men (both P &lt;0.05) but not in women. Thus, there is sexual dimorphism in MPS and its control in older adults with a diminished basal rate of MPS, which operates over much of the day, potentially explaining the faster loss of muscle in older men. This research was supported by grants from the US NIH, the University of Nottingham, the UK BBSRC, and the European Union.

We have previously shown that albuterol administered at a dose of 16mg/24 h over 12 weeks increased muscle mass by ∼5% without the addition of exercise (Uc et al. Clin. Neuropharmacol. 26(4):207-212, 2003). b2 adrenergic agonists such as albuterol act to increase calpastatin activity which inhibits the calpains. Calpain inhibition has previously been shown to impair insulin stimulated glucose disposal (Sreenan et al. Diabetes 50:2013-2020, 2001). Albuterol administration could lead to impaired insulin sensitivity. Therefore, the present study was undertaken to determine the effects of 7 days of albuterol administration (16mg/24h) on the glucose and the insulin responses to a 75 g oral glucose tolerance test (OGTT). Six elderly individuals (4 men and 2 women) age: 69.3+4.3 yrs, ht: 172.5+10.7 cm, wt: 79.1+20.6 kg, and BMI: 26.2+4.3 kg/m2 participated in this investigation. OGTTs were performed before and after albuterol administration with blood sampled immediately prior to and at 30,60,90, and 120 min post-ingestion of the glucose load. Glucose and insulin responses were compared utilizing a 2 way repeated measures ANOVA. Pre and post glucose and insulin areas under the curve were calculated and compared utilizing a paired t-test. No significant visit by time interaction was observed for the glucose response to the OGTT (p=0.540) or the insulin response to the OGTT (p=0.216). No significant difference between pre and post values was observed for the glucose area under the curve (12966+2413 and 15124+781(mg/dL) X min mean+SE for pre and post albuterol administration, respectively; p=0.427) or the insulin area under the curve (7871+1951and 7470+1603 (μU/ml) X min for pre and post albuterol administration, respectively; p=0.672). In conclusion, short term albuterol administration at a dose of 16 mg/24 h did not significantly alter glucose tolerance or insulin concentrations. Therefore, the administration of albuterol, at least in the short term, would not appear to have the negative effect of impairing glucose tolerance. As a result, albuterol administration should not be contraindicated for this reason.

Feeding a mixed meal doubles muscle protein synthesis (MPS) within 90 min, an effect sufficiently rapid to be mostly due to changes in anabolic signalling. We examined the possibility that feeding may also acutely modulate transcriptional activity of genes controlling muscle mass, viz, MyoD1 and myostatin. We studied the effect of intermittent small meals (Ensure®, to provide 70 mg protein·kg Fat free mass −1 ·h −1 ) in older men and women who were matched for age (65–80 y) and BMI. MPS was measured by incorporation of D3‐leucine into mixed muscle protein (13 men, 16 women). RT‐PCR was used to analyse changes in the expression in quadriceps muscle (7 men, 7 women) of the hypertrophy‐associated transcription factor, MyoD1 and myostatin, a negative regulator of muscle mass, with 28s mRNA used as a reference gene. The rate of postabsorptive MPS was ∼25% less in men than in women (P=0.02). At 2.5 h after beginning feeding, MPS increased by 30% (P&lt;0.01) but only in men. Expression of mRNA for myostatin and MyoD1 were identical in men and women in the postabsorptive state, but feeding decreased expression of myostatin mRNA by 63±9% (P&lt;0.05) and increased that of myoD by 83±5% (P&lt;0.01). Thus, feeding acutely modulates the expression of genes likely to promote a milieu conducive to potential increases in muscle mass but these changes seem not to match the lack of an acute response of MPS to feeding in older women.

We have recently shown that there are considerable sex differences in muscle protein turnover in 65‐80 year old adults. Specifically we found that the basal rate of muscle protein synthesis (MPS) is greater in elderly women than elderly men whereas the anabolic response of MPS to feeding is greater in elderly men than elderly women (PLoS One 3:1875‐83, 2008). The purpose of this study was to determine whether similar differences in muscle protein metabolism exist in younger individuals. We therefore measured the rate of MPS during basal, postabsorptive conditions and during combined hyperinsulinemia and hyperaminoacidemia by using stable isotope‐labeled tracer techniques in 7 men and 5 women, who were matched on age (mean ± SEM: 40 ± 2 y vs 38 ± 3 y, respectively; P = 0.63) and body‐mass index (26.2 ± 1.1 kg.m 2 vs 25.8 ± 1.3 kg.m 2 , respectively; P = 0.84). The basal rate of MPS was not different in men (0.041 ± 0.006 % ·h −1 ) and women (0.040 ± 0.006 % ·h −1 ). Hyperinsulinemia‐hyperaminoacidemia resulted in a significant increase in the rate of MPS (P &lt; 0.001) in both men (to 0.062 ± 0.007 % ·h −1 ) and women (to 0.064 ± 0.010 %·h −1 ) with no difference (P = 0.71) in the magnitude of the anabolic response. Thus, sexual dimorphism in muscle protein turnover is a phenomenon associated with old age. The underlying mechanism(s) remain to be elucidated but are probably due to sex specific hormonal changes that accompany the aging process in men and women. This research was supported by grants from the US NIH.

Oxytocin (OXT), a nine amino acid peptide produced in the hypothalamus and released by the posterior pituitary, has well-known actions in parturition, lactation, and social behavior 1 , and has become an intriguing therapeutic target for diseases like autism and schizophrenia 2 . Exogenous OXT has also been shown to promote weight loss, among other beneficial metabolic effects 1,3 , suggesting that its therapeutic potential may extend to diabetes and obesity 1,4 . It is unclear, however, whether endogenous OXT participates in metabolic homeostasis. Here we show that OXT is a critical regulator of adipose tissue lipolysis in both mice and humans. In addition, OXT serves to license the ability of β- adrenergic agonists to fully promote lipolysis. Most surprisingly, the relevant source of OXT in these metabolic actions is a previously unidentified subpopulation of tyrosine hydroxylase (TH)-positive sympathetic neurons. Our data reveal that OXT from the peripheral nervous system is an endogenous regulator of adipose and systemic metabolism.

OBJECTIVES/SPECIFIC AIMS: People with metabolically abnormal obesity (MAO), defined as those with insulin resistance and high intrahepatic triglyceride, are at high risk for developing type 2 diabetes and cardiovascular disease. Weight loss through reduced energy intake and increased physical activity has profound impacts on improving cardiometabolic function. However, the specific additional effects of exercise training with diet-induced weight loss on metabolic function are equivocal. METHODS/STUDY POPULATION: A comparative trial is ongoing in MAO adults undergoing 8-10% weight loss induced by a very-low fat plant-based (PB) diet with structured exercise training (n=8) compared to the same weight loss induced by the PB diet alone (n=3). RESULTS/ANTICIPATED RESULTS: Preliminary results indicate that, PB diet with or without exercise training results in significant weight loss concomitant with enhanced insulin sensitivity, reduced intrahepatic triglyceride, reduced 24-hour postprandial glucose response, reduced fat mass, and reduced diastolic blood pressure. Those undergoing PB diet with exercise training had greater improvements in muscular strength and cardiorespiratory fitness than those undergoing PB diet alone. Differences between intervention groups for other cardiometabolic measures are not yet known. DISCUSSION/SIGNIFICANCE OF IMPACT: Each of the interventions resulted in improved cardiometabolic measures; however the extent of the differences between the interventions is not yet clear. It is hypothesized that compared with weight loss induced by a PB diet, the same weight loss induced by a PB diet and structured exercise training will i) cause greater improvement in skeletal muscle insulin sensitivity, ii) will attenuate the usual decline in muscle mass while increasing strength, and iii) result in greater increases in left ventricular diastolic function. The long-term objective of this proposal is to provide a foundation for future studies evaluating mechanisms for the effects of exercise in cardiometabolic disease prevention and therapy.

Sodium acetate administration has been shown to increase muscle acetyl-CoA and acetylcarnitine content at rest and during the early stages of exercise. We therefore investigated the effect of sodium acetate ingestion at rest on subsequent substrate utilisation during prolonged exercise. With local ethics approval six healthy males ingested either sodium acetate (NaAc) or sodium bicarbonate (NaHCO3) at a dose of 4 mmol.kg−1 body mass in a randomised order over 90 min prior to 120 min of exercise at 50% V̇O2max. NaAc ingestion decreased resting fat oxidation (0.09 ± 0.02 vs. 0.07 ± 0.02 g.min−1 pre- and post-ingestion respectively, P<0.05) with no effect upon carbohydrate utilisation. In contrast, NaHCO3 ingestion did not affect substrate utilisation at rest. Fat and CHO oxidation increased in both trials when exercise was undertaken, but fat oxidation was lower (0.16 ± 0.10 vs. 0.30 ± 0.10 g.min−1, P<0.05) and carbohydrate oxidation higher (1.75 ± 0.36 vs. 1.50 ± 0.23 g.min−1, P<0.05) in the NaAc compared with the NaHCO3 trial during the first 15 min of exercise. Plasma acetate concentration had returned to baseline after 30 min of exercise in the NaAc trial with no difference in either fat or carbohydrate utilisation between the trials over the last 90 min of exercise. These results demonstrate that increasing plasma acetate concentration suppresses fat oxidation at rest and at the onset of exercise possibly due to changes in acetyl group availability.

Abstract Insulin resistant glucose metabolism is the most common metabolic complication associated with obesity; however, a subset of people with obesity have normal insulin sensitivity and are considered to be metabolically healthy. In rodent models of obesity, adipose tissue (AT) inflammation contributes to whole-body insulin resistance mediated, at least in part, by production of proinflammatory cytokines that are secreted into the systemic circulation. We therefore hypothesized that AT markers of inflammation and plasma concentrations of inflammatory cytokines would be greater in people with metabolically-unhealthy obesity (MUO) and insulin-resistant glucose metabolism than in insulin-sensitive people with metabolically-healthy obesity (MHO). We measured AT expression of genes that encode for proinflammatory proteins by using RNA sequencing and plasma cytokine concentrations assessed serially over 24 hours by using multiplex assays in: i) 28 people with MHO (defined as normal glucose tolerance and normal insulin-stimulated glucose disposal assessed using the hyperinsulinemic-euglycemic clamp procedure [48 ± 2 µmol/kg fat-free mass/min]); and ii) 28 people with MUO (defined as prediabetes and impaired insulin-stimulated glucose disposal [28 ± 1 µmol/kg fat-free mass/min]). AT markers of inflammation (expression of SERPINE1, CCL3, CCL5, CD68, CD74, MRC1, and CXCL16) were greater in the MUO than in the MHO group (all P &amp;lt; 0.05). However, the 24-hour plasma concentration areas-under-the curve (AUC) for TNFα, MCP-1, IL-6, RANTES, IL-1β, IL-17, and IFN-γ were not different between MHO and MUO groups. In contrast, 24-hour plasma plasminogen activator inhibitor 1 (PAI-1) AUC was greater in the MUO (1,759 ± 169 ng/mL x h) group than in the MHO (716 ± 85 ng/mL x h) group (P &amp;lt; 0.001) and plasma PAI-1 was inversely correlated with whole-body insulin sensitivity (r= -0.57; P &amp;lt; 0.001). We conclude that, with the exception of PAI-1, AT inflammation does not contribute to whole-body insulin resistance by increasing systemic circulating inflammatory cytokine levels. However, increased AT production of PAI-1 is associated with whole-body insulin resistance in people with MUO.

SUMMARY Hepatic gluconeogenesis from amino acids contributes significantly to diabetic hyperglycemia, but the molecular mechanisms involved are incompletely understood. Alanine transaminases (ALT1 and ALT2) catalyze the interconversion of alanine and pyruvate, which is required for gluconeogenesis from alanine. We found that ALT2 was overexpressed in liver of diet-induced obese and db/db mice and that the expression of the gene encoding ALT2 ( GPT2 ) was downregulated following bariatric surgery in people with obesity. The increased hepatic expression of Gpt2 in db/db liver was mediated by activating transcription factor 4; an endoplasmic reticulum stress-activated transcription factor. Hepatocyte-specific knockout of Gpt2 attenuated incorporation of 13 C-alanine into newly synthesized glucose by hepatocytes. In vivo Gpt2 knockdown or knockout in liver had no effect on glucose concentrations in lean mice, but Gpt2 suppression alleviated hyperglycemia in db/db mice. These data suggest that ALT2 plays a significant role in hepatic gluconeogenesis from amino acids in diabetes.

Hepatic gluconeogenesis from amino acids contributes significantly to diabetic hyperglycemia, but the molecular mechanisms involved are incompletely understood. Alanine transaminases (ALT1 and ALT2) catalyze the interconversion of alanine and pyruvate, which is required for gluconeogenesis from alanine. We found that ALT2 was overexpressed in liver of diet-induced obese and db/db mice and that the expression of the gene encoding ALT2 (GPT2) was downregulated following bariatric surgery in people with obesity. The increased hepatic expression of Gpt2 in db/db liver was mediated by activating transcription factor 4; an endoplasmic reticulum stress-activated transcription factor. Hepatocyte-specific knockout of Gpt2M attenuated incorporation of 13 C-alanine into newly synthesized glucose by hepatocytes. In vivo Gpt2 knockdown or knockout in liver had no effect on glucose concentrations in lean mice, but Gpt2 suppression alleviated hyperglycemia in db/db mice. These data suggest that ALT2 plays a significant role in hepatic gluconeogenesis from amino acids in diabetes.