This study aims to investigate the therapeutic effect of alcohol extract of root and root bark of Toddalia asiatica(TAAE) on collagen-induced arthritis(CIA) in rats through phosphatidylinoinosidine-3 kinase/protein kinase B(PI3K/Akt) signaling pathway. To be specific, CIA was induced in rats, and then the rats were treated(oral, daily) with TAAE and Tripterygium Glycoside Tablets(TGT), respectively. The swelling degree of the hind leg joints was scored weekly. After 35 days of administration, the histopathological changes were observed based on hematoxylin and eosin(HE) staining. Enzyme-linked immunosorbent assay(ELISA) was employed to detect the levels of cytokines [tumor necrosis factor-α(TNF-α), interleukin(IL)-6)]. Terminal deoxynucleotidyl transferase dUTP nick end labeling(TUNEL) staining was performed to detect the apoptosis of synoviocytes in rats. Western blot was used to detect the expression levels of apoptosis-related proteins B-cell lymphoma 2(Bcl-2)-associated X(Bax), Bcl-2, and caspase-3 and pathway-related proteins phosphoinositide 3-kinase(PI3K), phosphorylated(p)-PI3K, protein kinase B(Akt), and p-Akt. RT-qPCR was conducted to examine the mRNA levels of Bax, Bcl-2, caspase-3, TNF-α, IL-6, and IL-1β and pathway-related proteins PI3K, p-PI3K, Akt, and p-Akt. TAAE can alleviate the joint swelling in CIA rats, reduce serum levels of inflammatory cytokines, improve synovial histopathological changes, promote apoptosis of synoviocytes, and inhibit synovial inflammation. In addition, RT-qPCR and Western blot results showed that TAAE up-regulated the level of Bax, down-regulated the level of Bcl-2, and activated caspase-3 to promote apoptosis in synoviocytes. TAAE effectively down-regulated the protein levels of p-PI3K and p-Akt. In this study, TAAE shows therapeutic effect on CIA in rats and reduces the inflammation. The mechanism is that it suppresses PI3K/Akt signaling pathway and promotes synoviocyte apoptosis. Overall, this study provides a new clue for the research on the anti-inflammatory mechanism of TAAE and lays a theoretical basis for the better clinical application of TAAE in the treatment of inflammatory and autoimmune diseases.
Keywords: CIA; PI3K/Akt signaling pathway; alcohol extract of root and root bark of Toddalia asiatica; apoptosis; rheumatoid arthritis.