Amelioration of rat experimental arthritides by treatment with the alkaloid sinomenine

The effects of treatment with sinomenine, a pure alkaloid extracted from the chinese medical plant Sinomenium acutum, were investigated in rat adjuvant arthritis (AA) and antigen-induced arthritis (AIA). In AA, long-term, intraperitoneal (i.p.) treatment induced significant improvement of arthritic score, hind paw swelling, body weight and erythrocyte sedimentation rate (ESR) beginning past the clinical peak of the disease. In-acute AIA, short and middle-term treatment with sinomenine around and following induction of arthritis induced a dose-dependent decrease of both joint swelling and ESR, starting after the peak of arthritis, and a significant reduction of joint destruction on day 3. There was no rebound of the arthritic signs following suspension of treatment. Long-term treatment of chronic AIA partially ameliorated clinical parameters and significantly counteracted joint destruction. Maximal plasma concentrations of 22.5 micrograms/ml, fast wash out (half-life 4.24 +/- 0.99 h; mean +/- S.E.M.) and no evidence of accumulation of sinomenine were observed following single or repeated i.p. injection of 150 mg/kg. In vitro, sinomenine markedly inhibited proliferation of synovial fibroblasts from AIA or normal rats, both at rest and following activation with either transforming growth factor beta 2 (TGF-beta 2) or interleukin-1 beta (IL-1 beta). The effect was dose-dependent and half-maximal inhibition of proliferation occurred at 20.6 micrograms/ml, that is, within the in vivo therapeutic range of the drug. Late therapeutic effects of sinomenine in rat arthritic models despite early start of treatment may be related to its antiproliferative effects on synovial fibroblasts in addition to its previously reported anti-inflammatory properties.