Sinomenine alleviates mechanical hypersensitivity in mice with experimentally induced rheumatoid arthritis

Background and aims We have previously reported that sinomenine, an alkaloid isolated from the root of the plant Sinomenium acutum, had antinociceptive effect in rodent models of acute inflammatory or neuropathic pain. As a traditional medicine, sinomenine is used in China to treat rheumatoid arthritis (RA). Methods In the present study, we evaluated the potential antinociceptive effect of sinomenine in a mouse model of RA, collagen type II antibody (CII Ab) induced arthritis (CAIA) after acute and chronic administration. Results As single administration, sinomenine at 40 or 80 mg/kg significantly reduced mechanical hypersensitivity both at the time of peak joint inflammation (days 11-19 after CII Ab injection) or during the post-inflammatory phase (days 35-54). No tolerance to the effect of 80 mg/kg sinomenine was observed during repeated injection twice a day for 5 days from day 11 to day 19 or from day 49 to day 53 after CII Ab injection in CAIA mice. Conclusions We have shown that sinomenine is effective in alleviating localized and spread hypersensitivities in CAIA mice both during acute inflammation and in post-inflammatory phase. Further, repeated sinomenine administration has elevated the baseline mechanical threshold without producing tolerance. Implications Sinomenine may be clinically useful to treat chronic pain in RA, including wide-spread pain which appears to be a difficult clinical problem despite the improvement in the acute treatment of RA by disease modifying agents.