Bilobalide ameliorates carbon tetrachloride-induced oxidative damage in HepG2 cells by the induction of Nrf2-dependent HO-1 expression through PI3K/Akt and P38 pathways

Oxidative stress is implicated in the pathogenesis of hepatic damage induced by various factors. Bilobalide (BB) is a compound extracted from Ginkgo biloba leaf. It has been reported for its anti-oxidative activity and has been tested to treat brain damage. However, it has not been studied whether BB possesses hepatoprotective activity though regulating heme oxygenase-1 (HO-1) which is a key antioxidant defense against reactive oxygen species. In this study, HepG2 cells were stimulated with carbon tetrachloride (CCl4) to induce cellular oxidative damage, and were treated with different concentrations of BB. The viability of the cells and the leakage of ALT and AST were detected to evaluate cell damages. Levels of H2O2, MDA and 8-OHdG in HepG2 cell lysates were measured to assess the cellular oxidative stress. Besides, the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and HO-1 (mRNA and protein) were detected. The results showed that BB attenuated the cellular damage, inhibited the oxidative stress, and increased the expression of Nrf2 and HO-1 in the CCl4-stimulated HepG2 cells. Yet, the cytoprotective effects of BB were abolished by a HO-1 inhibitor zinc protoporphyrin (ZnPP). In addition, Nrf2 knockdown with siNrf2 blocked the induction of HO-1 expression by BB. Furthermore, LY294002 (a PI3K/Akt inhibitor) and SB203580 (a p38 inhibitor) significantly reversed the up-regulation of Nrf2/HO-1 expression and the cytoprotection by BB. Our findings indicated that the hepatoprotective effects of BB were associated with the Nrf2 mediated HO-1 expression. And PI3K/Akt and p38 pathways were involved in the hepatoprotective effects and the regulation of Nrf2/HO-1 signaling by BB. BB may be a useful agent for the treatment of oxidative stress-induced hepatic damage.