Action mechanisms of complementary and alternative medicine therapies for rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized as a chronic inflammatory disease in joints and concomitant destruction of cartilage and bone. Cartilage extracellular matrix components, such as type II collagen and aggrecan are enzymatically degraded by matrix metalloproteinases (MMPs) and aggrecanases in RA. Currently, treatments targeting cytokines, including anti-tumor necrosis factor (TNF) α antibodies, soluble TNF receptor, anti-interleukin (IL)-6 receptor antibody, and IL-1 receptor antagonist, are widely used for treating RA in addition to antiantiinflammatory agents and disease-modifying antirheumatic drugs (DMARDs), such as inflmethotrexate, but these treatments have some problems, especially in terms of cost and the increased susceptibility of patients to infection in addition to the existence of low-responders to these treatments. Therefore, therapeutics that can be safely used for an extended period of time would be preferable. Complementary and alternative medicines including traditional Chinese medicines (TCM) have been used for the arthritic diseases through the ages. Recently, there are many reports concerning the anti-arthritic action mechanisms of TCM-based herbal formulas and crude herbal extracts or isolated ingredients. These natural herbal medicines are thought to moderately improve RA, but they exert various actions for the treatment of RA. In this review, the current status of the mechanism exploration of natural compounds and TCM-based herbal formulas are summarized, focusing on the protection of cartilage destruction in arthritic diseases including RA and osteoarthritis.