Effects of capsaicin on the metabolism of rheumatoid arthritis synoviocytes in vitro.

The effects of capsaicin, the ingredient of hot pepper, on rheumatoid arthritis synoviocytes have been studied. Capsaicin was shown to have a direct action on the metabolism of synovial cells. Thus at 10(-6) mol/l and at higher doses DNA synthesis was restored to the control level. Capsaicin at both doses induced an increase in the synthesis of collagenase and at the lower concentration (10(-8) mol/l) only of prostaglandins. These results indicate that the different effects of capsaicin on cellular proliferation and on metabolic activities are dependent on dose. The responses seen in rheumatoid arthritis synoviocytes in vitro might not be mediated by tachykinins if the synovial tissue is still able to produce neuropeptides in the absence of neuronal afferents. These results suggest that capsaicin, in addition to its direct action on the afferent nervous fibres and the consequent release of tachykinins, may also have a direct action on the cells. The mechanisms by which capsaicin stimulates DNA synthesis and production of collagenase and prostaglandin E2, in a manner dependent on dose, remain to be determined.