Dysregulation of glutathione synthesis during cholestasis in mice: Molecular mechanisms and therapeutic implications

Abstract

Glutathione (GSH) provides important antioxidant defense and regulates multiple critical processes including fibrogenesis. There are conflicting literature studies regarding changes in GSH during cholestasis. Here we examined changes in the GSH synthetic enzymes during bile duct ligation (BDL) in mice and how treatment with ursodeoxycholic acid (UDCA) and/or S‐adenosylmethionine (SAMe) affects the expression of these enzymes and liver injury. The hepatic expression of glutamate‐cysteine ligase (GCL) subunits and GSH synthase (GS) increased transiently after BDL but fell to 50% of baseline by 2 weeks. Nuclear factor‐erythroid 2‐related factor 2 (Nrf2) trans‐activates gene expression by way of the antioxidant response element (ARE), which controls the expression of all three genes. Despite increased Nrf2 nuclear levels, Nrf2 nuclear binding to ARE fell 2 weeks after BDL. Nuclear levels of c‐Maf and MafG, which can negatively regulate ARE, were persistently induced during BDL and the dominant proteins bound to ARE on day 14. UDCA and SAMe induced the expression of GCL subunits and raised GSH levels. They increased nuclear Nrf2 levels, prevented c‐Maf and MafG induction, and prevented the fall in Nrf2 nuclear binding to ARE. Combined treatment had additive effects, reduced liver cell death, and prevented fibrosis. Conclusion: GSH synthesis falls during later stages of BDL due to lower expression of GSH synthetic enzymes. UDCA and SAMe treatment prevented this fall and combined therapy was more effective on preserving GSH levels and preventing liver injury. (HEPATOLOGY 2009.)