Effects of a novel biflavonoid of Lonicera japonica flower buds on modulating apoptosis under different oxidative conditions in hepatoma cells

Background: In our previous work, we purified a novel biflavonoid named Japoflavone D (JFD) from Lonicera japonica flower buds. Biflavonoids are chemical compounds characterized by their high levels of antioxidative activity. Purpose: The present study aimed to investigate the function and molecular mechanism of JFD under different oxidative conditions in hepatoma cells. Methods: MTT assay and apoptosis assay were used to evaluate the cytotoxic effect of JFD. The activities of SOD and CAT were detected to evaluate the oxidative level. Oxidative stress was induced by H2O2 stimulation. The molecular mechanism of JFD was investigated by analyzing relative signaling pathway. Results: JFD inhibited cell viability in all hepatoma cell lines we examined. Under quiescent conditions, JFD treatment of SMMC-7721 cells resulted in upregulation of AKT/mTOR signal pathway and ERK activities and downregulation of KEAP1/NRF2/ARE signaling axis, together with apoptosis. However, under oxidative stress, JFD played a quite different role. Treatment of JFD suppressed the activation of ERK and mTOR and activated the KEAP1/NRF2/ARE signaling axis, which is a predominant regulator of cytoprotective responses to oxidative stress, thereby lessening the damage caused by excess reactive oxygen species (ROS). A molecular docking analysis suggested that JFD may interrupt the interaction between KEAP1 and NRF2 by competitively anchoring to the NRF2 binding site on KEAP1. Conclusion: The results indicate that JFD functions as a potent antioxidant and plays dual roles in modulating apoptosis under different oxidative conditions. JFD has the potential to be developed as a protective drug for diseases related with excess ROS.