Nrf2-mediated liver protection by sauchinone, an antioxidant lignan, from acetaminophen toxicity through the PKCδ-GSK3β pathway

BACKGROUND AND PURPOSE Sauchinone, an antioxidant lignan, protects hepatocytes from iron-induced toxicity. This study investigated the protective effects of sauchinone against acetaminophen (APAP)-induced toxicity in the liver and the role of nuclear factor erythroid-2-related factor-2 (Nrf2) in this effect. EXPERIMENTAL APPROACH Blood biochemistry and histopathology were assessed in mice treated with APAP or APAP + sauchinone. The levels of mRNA and protein were measured using real-time PCR assays and immunoblottings. KEY RESULTS Sauchinone ameliorated liver injury caused by a high dose of APAP. This effect was prevented by a deficiency of Nrf2. Sauchinone treatment induced modifier subunit of glutamate-cysteine ligase, NAD(P)H:quinone oxidoreductase-1 (NQO1) and heat shock protein 32 in the liver, which was abolished by Nrf2 deficiency. In a hepatocyte model, sauchinone activated Nrf2, as evidenced by the increased nuclear accumulation of Nrf2, the induction of NQO1-antioxidant response element reporter gene, and glutamate-cysteine ligase and NQO1 protein induction, which contributed to the restoration of hepatic glutathione content. Consistently, treatment of sauchinone enhanced Nrf2 phosphorylation with a reciprocal decrease in its interaction with Kelch-like ECH-associated protein-1. Intriguingly, sauchinone activated protein kinase C-delta (PKC delta), which led to Nrf2 phosphorylation. In addition, it increased the inhibitory phosphorylation of glycogen synthase kinase-3 beta (GSK3 beta), derepressing Nrf2 activity, which was supported by the reversal of sauchinone's activation of Nrf2 by an activated mutant of GSK3 beta. Moreover, phosphorylation of GSK3 beta by sauchinone depended on PKC delta activation. CONCLUSION AND IMPLICATIONS Our results demonstrate that sauchinone protects the liver from APAP-induced toxicity by activating Nrf2, and this effect is mediated by PKC delta activation, which induces inhibitory phosphorylation of GSK3 beta.