Protective Effects of Silymarin on Triptolide-induced Acute Hepatotoxicity in Rats

Silymarin has been used in the treatment of a number of liver diseases for a long time, but its efficacy in preventing triptolide induced acute hepatotoxicity has not been reported previously. The present study aimed to assess the protective effect of silymarin against triptolide (TP)-induced hepatotoxicity in rats. Rats were orally administrated with silymarin (50, 100 and 200 mg/kg) for 7 days and received intraperitoneal TP (2 mg/kg) on the day 8. Hepatic injuries were comprehensively evaluated in terms of serum parameters, morphological changes, oxidative damage, inflammation and apoptosis. The results demonstrated that TP-induced increases in serum parameters, including alanine transaminase, aspartate aminotransferase, alkaline phosphatase, total cholesterol and γ-glutamyl transpeptidase, which were determined using a biochemical analyzer, and histopathological alterations and hepatocyte apoptosis as determined by hematoxylin and eosin and TUNEL staining, respectively, were prevented by silymarin pretreatment in a dose-dependent manner. TP-induced depletions in the activity of the antioxidant enzymes superoxide dismutase, glutathione peroxidase, glutathione S-transferase and catalase, and glutathione levels, were also significantly reversed by silymarin, as determined using specific kits. Additionally, silymarin dose-dependently exhibited inhibitory effects on malonaldehyde content in the liver. The production of proinflammatory cytokines was investigated using ELISA kits, and the results demonstrated that silymarin dose-dependently inhibited the production of tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-10 and IL-1β in the liver. To determine the mechanism of silymarin, western blot analysis was performed to investigate the protein expression of phosphorylated (p)-p38 and p-c-Jun N-terminal kinase (JNK) of the TNF-α induced inflammatory response and apoptotic pathways. Silymarin significantly blocked p38 and JNK phosphorylation and activation. Additionally, the expression of the proapoptotic proteins cytochrome c, cleaved caspase-3 and Bcl-2-associated X was also reduced following treatment with silymarin, as determined by ELISA, western blotting and immunohistochemistry, respectively. In conclusion, silymarin was demonstrated to dose-dependently protect rat liver from TP-induced acute hepatotoxicity, with the high dose (200 mg/kg) achieving a superior effect. This protective effect may be associated with the improvement of antioxidant and anti-inflammatory status, as well as the prevention of hepatocyte apoptosis. Therefore, silymarin may have the potential to be applied clinically to prevent TP-induced acute hepatotoxicity.