Study Of Inducibility Of Phase 2 Enzymes In HepG2 Cells By Quercetin

Objective: To investigate the induction of phase 2 enzymes and chemoprotection against oxidant in human HepG2 cells by quercetin.Methods: The HepG2 cells were treated with various concentrations of quercetin for 6 h and 24 h. The activity of NAD(P)H:quinone oxidore- ductase (NQO1) in HepG2 cells were measured by 2, 6-dichloroindophenol reduction method. The activities of superoxide dismutase (SOD) and catalase (CAT) were determined with the method of chemical colorimetry. The protein expressions of NQO1 and Nrf2 in HepG2 cells were detected by Western blotting. HepG2 cells were damaged by H2O2. MTT method was used to examine cell survival rate. SOD and AST in cell culture fluid were determined to observe the cyto-protective effect of quercetin.Results: Incubation of HepG2 cells with quercetin for 6 hours resulted in a marked concentration-dependent induction of three kinds of phase 2 enzymes, including SOD, CAT, NQO1 (P<0.01, P<0.01, P<0.01), and the activities of those enzymes all decreased at 24 hours. Quercetin treatment of HepG2 cells also caused increase in protein expressions of NQO1 and Nrf2 (P<0.01, P<0.01). Quercetin have significant protective effects on HepG2 cells injured by free-radical produced by H2O2. Obviously elevated intracellular cell viability and SOD level as well as markedly lowered AST level of cultured cell supernatant were observed in drug treatment group vs injury group (P<0.01, P<0.05, P<0.01).Conclusion: This study demonstrates that quercetin can induce a series of phase 2 enzymes in HepG2 cells in a concentration-dependent fashion and increased the resistance to oxidative injury in hepatic cell by H2O2. The mechanism is due to upregulation the activity and protein expressions of phase 2 enzymes by its induction of Nrf2 activation.