Anti-inflammatory Activity of Formononetin in a Collagen-induced Arthritis Mouse Model ofRheumatoid Arthritis

Background: Rheumatoid arthritis (RA) is a common autoimmune disease characterized by chronic inflammation of the joints, leading to bone erosion and joint dysfunction. Although there are options for the treatment of RA, safer and more effective drugs are still being sought. Formononetin (FMN) is an isoflavonoid compound found in various plants, such as Astragalus propinquus Schischkin and Spatholobus suberectus. It has anti-tumor, anti-bacterial, anti-lipid peroxidation, and estrogen-like activities，and is a noteworthy compound for screening of anti-RA drugs. Methods: To investigate the anti-inflammatory effects of FMN in a collagen-induced arthritis (CIA) mouse model, thirty-six C57BL/6 mice were randomly divided into 6 groups: a healthy control group and 5 CIA groups. Arthritis was induced the CIA groups using chicken collagen type II. The CIA groups were divided in a control group (RA), a tripterygium glycosides (10 mg/kg body weight) treated group (TG), a low-dose (50 mg/kg) FMN group (FMN-L), a middle-dose(100mg/kg) FMN group (FMN-M), and a high-dose (200 mg/kg) FMN group (FMN-H). The control mice and CIA mice in the RA group were treated with an equal volume of 5% carboxymethylcellulose sodium. Drugs were delivered three times a week for four weeks, and the bodyweight, food-uptake, and swelling of the paws were monitored during the treatment process. Inflammatory cytokines and other biochemical indexes in the serum and joint tissues were analyzed, along with the expression levels of NF-κB pathway-related proteins (IκBα, p65, p-p65, TIPE2, and PCNP) in the spleen. Histopathological examinations were processed for the hind limbs. Results: FMN-M dramatically reduced the arthritis index in the CIA mice, inhibited the inflammatory cell infiltration, and prevented damage to the synovium and cartilage. Mechanistic studies suggested that FMN might reduce inflammation by inhibiting IκB-α degradation and by regulating the expression and release of NF-κB p65. Conclusions: These data suggest that FMN might be an active therapeutic agent for RA by preventing bone destruction, regulating inflammatory mediators, and suppressing NF-κB signaling pathways.