Modulation of Neuropathic and Inflammatory Pain by the Endocannabinoid Transport Inhibitor AM404 [<i>N</i>-(4-Hydroxyphenyl)-eicosa-5,8,11,14-tetraenamide]

The endocannabinoid system may serve important functions in the central and peripheral regulation of pain. In the present study, we investigated the effects of the endocannabinoid transport inhibitor AM404 [<i>N</i>-(4-hydroxyphenyl)-eicosa-5,8,11,14-tetraenamide] on rodent models of acute and persistent nociception (intraplantar formalin injection in the mouse), neuropathic pain (sciatic nerve ligation in the rat), and inflammatory pain (complete Freund9s adjuvant injection in the rat). In the formalin model, administration of AM404 (1–10 mg/kg i.p.) elicited dose-dependent antinociceptive effects, which were prevented by the CB₁ cannabinoid receptor antagonist rimonabant (SR141716A; 1 mg/kg i.p.) but not by the CB₂ antagonist SR144528 (1 mg/kg i.p.) or the vanilloid antagonist capsazepine (30 mg/kg i.p.). Comparable effects were observed with UCM707 [<i>N</i>-(3-furylmethyl)-eicosa-5,8,11,14-tetraenamide], another anandamide transport inhibitor. In both the chronic constriction injury and complete Freund9s adjuvant model, daily treatment with AM404 (1–10 mg/kg s.c.) for 14 days produced a dose-dependent reduction in nocifensive responses to thermal and mechanical stimuli, which was prevented by a single administration of rimonabant (1 mg/kg i.p.) and was accompanied by decreased expression of cyclooxygenase-2 and inducible nitric-oxide synthase in the sciatic nerve. The results provide new evidence for a role of the endocannabinoid system in pain modulation and point to anandamide transport as a potential target for analgesic drug development.