Inhibitory Effect of Baicalin on Collagen-Induced Arthritis in Rats through the Nuclear Factor–kB Pathway

This study focused on the potential therapeutic effect of baicalin on collagen-induced arthritis (CIA) in rats and the underlying mechanisms. The CIA rats were injected with baicalin (50, 100, or 200 mg/kg) once daily for 30 days. The rats were monitored for clinical severity of arthritis, and joint tissues were used for radiographic assessment and histologic examination. We quantified tumor necrosis factor–a (TNF-a) and interleukin-1b (IL-1b) in experimental animals and used Western blots to assess levels of protein abundance, phosphorylation, and acetylation of nuclear factor (NF)-kB p65 and sirtuin 1 (sirt1) protein expression in joint tissues. Human fibroblast-like synoviocytes from rheumatoid arthritis (HFLS-RA) were adopted in further mechanistic investigations. Baicalin intraperitoneal injection for 30 days dose-dependently blocked clinical manifestations of CIA, such as functional impairment and swollen red paws. Meanwhile, it alleviated collageninduced joint inflammation injury and inhibited the secretion of TNF-a and IL-1b in both rat synovium and HFLS-RA. Further mechanistic investigations revealed that baicalin suppresses NF-kB p65 protein expression and phosphorylation in synovial tissue and human-derived synoviocytes. Moreover, the acetylation of NF-kB p65 was downregulated by baicalin, which negatively correlates with the baicalin-induced upregulation of sirt1 expression in the same conditions. The data indicate that CIA in rats can be alleviated by baicalin treatment via relieving joint inflammation, which is related to the suppression of synovial NF-kB p65 protein expression and the elevation of its deacetylation by sirt1.