Role of Nitric Oxide in the Antipruritic Effect of WIN 55,212-2, a Cannabinoid Agonist

Introduction: For centuries, cannabinoids are known to be effective in pain relief. Itch is an unpleasant sensation that provokes a desire to scratch. Since itch and pain are two sensations sharing a lot in common, we aimed to investigate whether the cannabinoid agonist WIN 55,212-2 reduces serotonin-induced scratching behavior and also observe whether modulation of Nitric Oxide (NO) production mediates the antipruritic effect of WIN 55,212-2. Methods: Scratching behavior is induced by intradermal injection of serotonin (50 mu g/50 mu L/mouse) to BALB/c mice. The cannabinoid agonist WIN 55,212-2 (1, 3, 10 mg/kg, IP) was given 30 min before serotonin injection. To observe the effect of NO modulation on the antipruritic effect of cannabinoids, the endothelial nitric oxide synthase (NOS) inhibitor L-NAME (3 mg/kg, IP), the neuronal NOS inhibitor 7-nitroindazole (3 mg/kg, IP), and the NO precursor L-arginine (100 mg/kg, IP) were administered together withWIN 55,212-2. Results: WIN 55,212-2 reduced serotonin-induced scratches at higher doses (3, 10 mg/kg; P<0.0001). The endothelial NOS inhibitor L-NAME, the neuronal NOS inhibitor 7-nitroindazole, and the nitric oxide precursor L-arginine did not influence the antipruritic action of WIN 55,212-2. When NO modulators were used alone, only the neuronal NOS inhibitor 7-nitroindazole attenuated serotonin-induced scratches (P<0.0001). Conclusion: Our findings indicate that exogenous cannabinoids may attenuate serotonin-induced scratches and NO does not mediate the antipruritic effect of WIN 55,212-2. On the other hand, neuronal NOS inhibition may play a role in the production of serotonin-induced scratches. Highlights Exogenous cannabinoids reduce serotonin-induced scratching behavior. Nitric oxide does not mediate the antipruritic action of cannabinoids. Cannabinoids have the potential to be used as antipruritic drugs. Plain Language Summary Cannabinoid drugs are not used effectively due to their potential drug abuse and side effects. For centuries, cannabinoids are known to exert analgesic actions, but they also produce antipruritic effects. There are numerous studies on the mechanisms of the analgesic effects of cannabinoids; however there are only a few research on their antipruritic mechanism of action. In this study, we observed the modulatory role of nitric oxide in the effect of cannabinoids on serotonininduced scratches which nitric oxide did not play role in this action. We induced scratching behavior by administering serotonin intradermally. Then we injected the cannabinoid agonist WIN 55,212-2 and observed the reduction of the scratching behavior. Afterwards, we administered an endothelial nitric oxide synthase inhibitor, a neuronal nitric oxide synthase inhibitor, and a nitric oxide precursor and showed that nitric oxide does not mediate the antipruritic effects of WIN 55,212-2. Whatever the mechanism of action, cannabinoids have the potential to be used as antipruritic drugs, especially if their side effects are reduced.