Caffeic acid induces glutathione synthesis through JNK/AP-1-mediated γ-glutamylcysteine ligase catalytic subunit induction in HepG2 and primary hepatocytes

Previously our research found that caffeic acid (CA) has antioxidant activity in vitro and in vivo. However, the antioxidant mechanism of CA has not been clearly demonstrated. We investigated the protective mechanism of CA on oxidative stress in HepG2 cells and primary hepatocytes. We focused on the effects of CA on glutathione (GSH) synthesis and its mechanisms. Reporter gene assay, transient transfection, quantitative reverse transcription-polymerase chain reaction and western blot were performed to confirm the mechanisms of antioxidant capacity. CA increased GSH level and gamma-glutamylcysteine ligase (gamma-GCL) activity. gamma-Glutamylcysteine ligase catalytic subunit (GCLC) mRNA and protein levels were significantly increased following treatment with CA, whereas no changes were observed in the gamma-GCL modifier subunit levels in HepG2 and rat hepatocytes. CA phosphorylated JNK, and activated the AP-1 transcription factor. These results show that the intracellular GSH levels and GCLC increased through the JNK/AP-1 pathways by CA treatment.