Abstract:Objective : To investigate the effect of the total flavonoids of orange peel (TFO) against adjuvant arthritis (AA) and the underlying mechanism. Method : AA model was induced in male SD rats by immunization with Freund’s complete adjuvant. Pad thickness was assayed by caliper. Pathological impairment of ankle joint was analysised by hematoxylin and eosin (H&E) staining. Levels of tumor necrosis factor (TNF)-α, Interleukin (IL)-1β and prostaglandin (PG)E2 in serum was detected by radioimmunoassay method. Cyclooxygenase (COX)-2 expression in synovium tissues was measured by Western blot assay. Result : The 75 mg·kg-1 and 150 mg·kg-1 TFO treatment obviously decreased the pad thickness and improve the pathological impairment of ankle joint of AA rats. In addition, abnormal elevation of TNF-α, IL-1β and PGE2 in serum and COX-2 expression in synovium tissues of AA rats were markedly repressed by TFO treatment. Conclusion : TFO can inhibit the development of AA in rats, and the mechanism were likely due to depressing inflammatory mediators production.