Therapeutic effect of norisoboldine, an alkaloid isolated from Radix Linderae, on collagen-induced arthritis in mice

The alkaloid fraction of Radix Linderae, the main active component of this herb drug, has been proven to exhibit anti-inflammatory, analgesic and antimicrobial activities. The present study was undertaken to investigate the therapeutic potential of norisoboldine, the major isoquinoline alkaloid present in Radix Linderae, in collagen II -induced arthritis (CIA) of mice as well as the possible mechanisms. CIA was induced in mice by immunization with chicken type II collagen (II). After boosted on day 21, mice were treated with norisoboldine (10, 20, 40 mg/kg) for twenty consecutive days. The clinical scores, body weight changes and joint histopathology were evaluated. Norisoboldine treatment significantly alleviated the severity of the disease, based on the reduced clinical scores and elevated the lowered body weights of model mice. Meanwhile, this alkaloid dose-dependently reduced the infiltration of inflammatory cells, synovial hyperplasia and protected joint from destruction. Additionally, the serum level of anti-CII IgG and the CII-stimulated lymphocyte proliferation were remarkably decreased in the groups administered with norisoboldine. An assessment of Th1 function using the delayed-type hypersensitivity model confirmed that norisoboldine also significantly suppressed the enhanced T cell responses in vivo. These findings suggest that norisoboldine might be a potential therapeutic agent for rheumatoid arthritis, and it functions through protecting joint destruction as well as regulating the abnormal immune responses.