β-Lapachone increases phase II antioxidant enzyme expression via NQO1-AMPK/PI3K-Nrf2/ARE signaling in rat primary astrocytes

β-Lapachone (β-LAP) is a naturally occurring quinine that exerts a number of pharmacological actions including antibacterial, antifungal, antimalarial, and antitumor activities. In the present study, we investigated whether β-LAP has an antioxidant effect in rat primary astrocytes. β-LAP suppressed intracellular reactive oxygen species (ROS) production induced by hydrogen peroxide and inhibited astroglial cell death. It also increased astrocytic expression of phase II antioxidant enzymes such as heme oxygenase-1 (HO-1), NAD(P)H:quinone oxidoreductase 1 (NQO1), manganese superoxide dismutase (MnSOD), and catalase. Further mechanistic studies revealed that β-LAP activated AMPK and Akt, and pretreatment of cells with an AMPK inhibitor (compound C) or PI3K/Akt inhibitor (LY294002) suppressed β-LAP-induced antioxidant enzyme expression by inhibiting Nrf2/antioxidant response element (ARE) signaling. Compound C also decreased Akt phosphorylation, suggesting that AMPK is upstream of PI3K/Akt. Furthermore, the AMPK activator 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside mimicked the effect of β-LAP by increasing Akt phosphorylation and ARE-mediated transcription, suggesting that AMPK plays a pivotal role in β-LAP-mediated antioxidant enzyme expression. Because β-LAP effects are usually associated with NQO1 activity, we examined the effect of NQO1 knockdown on antioxidant enzyme expression. Small interfering RNA (siRNA) specific for NQO1 inhibited β-LAP-induced AMPK/Akt phosphorylation and downstream antioxidant enzyme expression. Collectively, the results suggest that β-LAP increases antioxidant enzyme gene expression in astrocytes by modulating NQO1-AMPK/PI3K-Nrf2/ARE signaling.