Selective blockade of TRPA1 channel attenuates pathological pain without altering noxious cold sensation or body temperature regulation

Despite the increasing interest in TRPA1 channel as a pain target, its role in cold sensation and body temperature regulation is not clear; the efficacy and particularly side effects resulting from channel blockade remain poorly understood. Here we use a potent, selective, and bioavailable antagonist to address these issues. A-967079 potently blocks human (IC50: 51 nmol/ L, electrophysiology, 67 nmol/ L, Ca2+ assay) and rat TRPA1 (IC50: 101 nmol/ L, electrophysiology, 289 nmol/L, Ca2+ assay). It is > 1000-fold selective over other TRP channels, and is > 150-fold selective over 75 other ion channels, enzymes, and G-protein-coupled receptors. Oral dosing of A-967079 produces robust drug exposure in rodents, and exhibits analgesic efficacy in allyl isothiocyanate-induced nocifensive response and osteoarthritic pain in rats (ED50: 23.2 mg/kg, p.o.). A-967079 attenuates cold allodynia produced by nerve injury but does not alter noxious cold sensation in naive animals, suggesting distinct roles of TRPA1 in physiological and pathological states. Unlike TRPV1 antagonists, A-967079 does not alter body temperature. It also does not produce locomotor or cardiovascular side effects. Collectively, these data provide novel insights into TRPA1 function and suggest that the selective TRPA1 blockade may present a viable strategy for alleviating pain without untoward side effects. (C) 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.