Induction of Nrf2/ARE-mediated cytoprotective genes by red ginseng oil through ASK1–MKK4/7E–JNK and p38 MAPK signaling pathways in HepG2 cells

Background: The induction of cellular defensive genes such as phase II detoxifying and antioxidant enzymes is a highly effective strategy for protection against carcinogenesis as well as slowing cancer development. Transcription factor Nrf2 (nuclear factor E2-related factor 2) is responsible for activation of phase II enzymes induced by natural chemopreventive compounds. Methods: Red ginseng oil (RGO) was extracted using a supercritical CO₂ extraction system and chemical profile of RGO was investigated by GC/MS. Effects of RGO on regulation of the Nrf2/antioxidant response element (ARE) pathway were determined by AREeluciferase assay, western blotting, and confocal microscopy. Results: The predominant components of RGO were 9,12-octadecadienoic acid (31.48%), bicyclo[10.1.0] tridec-1-ene (22.54%), and 22,23-dihydrostigmasterol (16.90%). RGO treatment significantly increased nuclear translocation of Nrf2 as well as ARE reporter gene activity, leading to upregulation of heme oxygenase-1 and NAD(P)H:quinone oxidoreductase 1. Phosphorylation of the upstream kinases such as apoptosis signal-regulating kinase (ASK)1, mitogen-activated protein kinase (MAPK) kinase (MKK)4/7, C-Jun N-terminal kinase (JNK), and p38 MAPK were enhanced by treatment with RGO. In addition, RGOmediated Nrf2 expression and nuclear translocation was attenuated by JNK inhibitor SP600125 and p38 MAPK inhibitor SB202190.Conclusion: RGO could be used as a potential chemopreventive agent, possibly by induction of Nrf2/ARE-mediated phase II enzymes via ASK1-MKK4/7-JNK and p38 MAPK signaling pathways.