OBJECTIVETo find the signaling pathway of triptolide (TP)-induced liver injury and to reveal whether NF-E2-related factor 2 (Nrf2) plays an important role in cellular self-protection.

METHODSThe L-02 and HepG2 cells were cultured and treated with various concentrations of TP. The cell viability was observed, and the cell medium was collected for detecting the aspartate aminotransferase (ALT), alanine aminotransferase (AST), lactate dehydrogenase (LDH), superoxide dismutase (SOD) and L-glutathione production (GSH) levels. Nrf2 and its downstream target NAD(P)H: quinine oxidoreductase 1 (NQO1) and heme oxygenase-1 (HO-1) expression, the nuclear translocation of Nrf2, and the binding ability of Nrf2 and antioxidant response element (ARE) were also identified. Meanwhile, shRNA was used to silence Nrf2 in L-02 cells to find out whether Nrf2 plays a protective role.

RESULTSThe viability of the L-02 and HepG2 cells treated with TP decreased in a doseand time-dependent manner, and TP (20-80 μg/mL) markedly induced the release of ALT, AST and LDH (P<0.05 or P<0.01), reduced the levels of SOD and GSH (P<0.01), and increased the intracellular reactive oxygen species. Meanwhile, TP augmented the Nrf2 expression in L-02 and HepG2 cells (P<0.05 or P<0.01), induced Nrf2 nuclear translocation, increased the Nrf2 ARE binding activity, and increased HO-1 and NQO1 expressions. Nrf2 knockdown revealed a more severe toxic effect of TP (P<0.05 or P<0.01).

CONCLUSIONSHuman hepatic cells treated with TP induced oxidative stress, and led to cytotoxicity. Self-protection against TP-induced toxicity in human hepatic cells might be via Nrf2-ARE-NQO1 transcriptional pathway.