Peripheral Effects of Cannabinoids are Mediated via TRPV1 and TRPA1

Objective: To evaluate peripheral effects of cannabinoids in vivo. Our recent data demonstrate that cannabinoids, WIN-55,212 (WIN) can lead to antinociception/antihyperalgesia by dephosphorylating TRPV1 via a calcium-activated calcineurin pathway (Patwardhan et al., Jeske et al., 2006). Using transfected CHO cells and patch clamp analysis, we previously demonstrated that cannabinoid, arachidonyl-2-choloroethylamide (ACEA) activates TRPV1 but not TRPA1 while WIN and AM1241 activate TRPA1 but not TRPV1. Also, ACEA (TRPV1-selective agonist) and WIN and AM1241 (TRPA1-selective agonists) heterologously desensitize mustard oil (MO)- and capsaicin (CAP)-evoked inward currents, respectively in CHO cells as well as sensory neurons (Ruparel et al., Abs Soc Neurosci #622.3; 2005). Methods: 1) The effect of ACEA pretreatment on MO-evoked CGRP release from rat hindpaw skin; 2) The effect of a peripheral dose of ACEA pre-injection on MO-induced nocifensive behavior (ipl injections/grooming and flinching assay) and 3) The effect of a peripheral dose of WIN and AM1241 on CAP-induced nocifensive behavior. Data were analyzed using ANOVA. Results: ACEA(100µM) significantly inhibited MO(0.1%)-evoked CGRP release from skin terminals and this effect was reversed by a TRPV1-selective antagonist, capsazepine(CPZ; 100µM). ACEA(100µg) significantly inhibited MO(0.1%)-induced nocifensive behavior in WT mice and this effect was fully abolished in TRPV1-/- mice. Moreover, ACEA when injected into the contralateral paw did not inhibit MO-induced nocifensive behavior in WT mice indicating a local site of action. Also, WIN(2.5µg) and AM1241(40µg) significantly inhibited CAP (0.5µg)-induced nocifensive behavior in WT mice. This effect was completely reversed in TRPA1-/- mice. WIN and AM1241, when injected into the contralateral paw did not inhibit CAP-induced nocifensive behavior suggesting a local site of action. Conclusions: Our data demonstrate that cannabinoids are able to inhibit nociceptors via TRPV1 and TRPA1 in vivo at the periphery. This supports a new hypothesis of cannabinoid-induced peripheral analgesia at the site of inflammation thereby minimizing cannabinoid-evoked systemic side-effects.