Suppression of complete Freund＇s adjuvant-induced adjuvant arthritis by cobratoxin

Aim： Cobratoxin （CTX）, the long-chain α-neurotoxin from Thailand cobra venom, has been demonstrated to have analgesic action in rodent pain models. The present study evaluated the anti-inflammatory and anti-nociceptive effects of CTX on adjuvant arthritis （AA） in rats. Methods： Arthritis was induced by injection of complete Freund＇s adjuvant （CFA） in rats. Paw swelling and hyperalgesia of AA rats were measured at various times after CFA administration. Tumor necrosis factor-a （TNF-α）, interleukin-1 （IL-1）, interleukin-2 （IL-2） and interleukin-10 （IL-10） levels in serum were determined with ELISA. Histopathological changes in synoviocytes were examined under a microscope. Involvement of the cholinergic system in the effects of CTX was examined by pretreatment of animals with the α7 nicotinic receptor （α7-nAChR） antagonist methyllycaconitine （MLA）. Results： CFA induced marked paw swelling and reduced thresholds of mechanical and cold-induced paw withdrawal. The levels of TNF-α, IL-1 and IL-2 in the serum of AA rats were increased, whereas the level of IL-10 was decreased. Histopathological examination of synoviocytes showed pronounced inflammation and accumulation of collagen. The administration of CTX （17.0 μg/kg, ip） significantly reduced paw swelling and mechanical and thermal hyperalgesia. CTX also reduced the production ofTNF-α, IL-1, and IL-2 but increased the production of IL-10 and altered pathohistological changes. The analgesic and anti-inflammatory efficacy of CTX was significantly reduced by MLA （3 mg/kg, sc）. Conclusion： These results indicate that CTX has a beneficial effect on CFA-induced arthritis by modulating the production of inflammatory cytokines, α7-nAChR appears to mediate the anti-nociceptive and anti-inflammatory actions of CTX.