Protective effects of total flavonoids of Astragalus against adjuvant-induced arthritis in rats by regulating OPG/RANKL/NF-κB pathway

Astragalus membranaceus Bunge is one of the oldest and most frequently used crude herbs in traditional Chinese medicine. The total flavonoids of Astragalus (TFA) are the main active components isolated from Astragalus membranaceus Bunge. Our recent study has shown its potential immunomodulatory and anti-inflammatory effects in vivo and in vitro. However, its anti-arthritic effects and mechanisms of action involved have not been elucidated. The aim of this study was to evaluate the protective effects and possible mechanisms of TFA on Freund's complete adjuvant (FCA)-induced arthritis in rats. Wistar rats were intradermally injected FCA into the right hind metatarsal footpads to establish adjuvant-arthritic model. The rats were intragastrically administered daily with TFA at 25, 50 and 100 mg/kg for 28 days after FCA induction. Body weight, primary paw swelling, arthritis index, thymus and spleen indices were measured. The levels of serum tumor necrosis factor (TNF)-α, interleukin (IL)-1β, prostaglandin (PG)E2, osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) were determined using ELISA. Histopathological changes and scores in joint tissues were examined using hematoxylin and eosin (H&E). The expression of nuclear factor (NF)-κB p65 in synovial tissues was assayed using immunohistochemical method. TFA significantly increased body weight, attenuated primary paw swelling and arthritis index, decreased thymus and spleen indices of rats induced by FCA. Furthermore, TFA significantly inhibited serum TNF-α, IL-1β, PGE2 and RANKL production, and promoted serum OPG production and OPG/RANKL ratio of rats induced by FCA. Histopathological examination indicated that TFA significantly attenuated inflammatory cell infiltration, synovial hyperplasia, pannus formation, and bone and cartilage damage. Immunohistochemical assay indicated that TFA inhibited NF-κB p65 expression in synovial tissues of rats induced by FCA. These results suggest that TFA exerts potential protective effects against FCA-induced arthritis in rats by regulating OPG/RANKL/NF-κB pathway.