Schisandrin B elicits a glutathione antioxidant response and protects against apoptosis via the redox-sensitive ERK/Nrf2 pathway in AML12 hepatocytes

This study examined the effects of (-)schisandrin B [(-)Sch B] on MAPK and Nrf2 activation and the subsequent induction of glutathione antioxidant response and cytoprotection against apoptosis in AML12 hepatocytes. Pharmacological tools, such as cytochrome P-450 (CYP) inhibitor, antioxidant, MAPK inhibitors and Nrf2 RNAi, were used to delineate the signalling pathway. (-)Sch B caused a time-dependent activation of MAPK in AML12 cells, particularly the ERK1/2. The MAPK activation was followed by an enhancement in Nrf2 nuclear translocation and the eliciting of a glutathione antioxidant response. Reactive oxygen species arising from a CYP-catalysed reaction with (-)Sch B seemed to be causally related to the activation of MAPK and Nrf2. ERK inhibition by U0126 or Nrf2 suppression by Nrf2 RNAi transfection almost completely abrogated the cytoprotection against menadione-induced apoptosis in (-)Sch B-pre-treated cells. (-)Sch B pre-treatment potentiated the menadione-induced ERK activation, whereas both p38 and JNK activations were suppressed. Under the condition of ERK inhibition, Sch B treatment did not protect against carbon tetrachloride-hepatotoxicity in an in vivo mouse model. In conclusion, (-)Sch B triggers a redox-sensitive ERK/Nrf2 signalling, which then elicits a cellular glutathione antioxidant response and protects against oxidant-induced apoptosis in AML12 cells.