Differential role of ethanol and acetaldehyde in the induction of oxidative stress in HEP G2 cells: Effect on transcription factors AP-1 and NF-kappaB

The oxidative metabolism of ethanol by the cytochrome P450 2E1 (CYP2E1) has been recognized to contribute to the ethanol-induced deleterious effects t hrough the induction of oxidative stress. This study compared the effect of ethanol and acetaldehyde in the induction of oxidative stress and activati on of transcription factors nuclear factor-kappa B (NF-kappa B) and activat ing protein 1 (AP-1) in HepG2 cells, which do not express CYP2E1, and HepG2 cells transfected with CYP2E1 (E47 cells), Neither ethanol (80 mmol/L) nor acetaldehyde (25-200 mu mol/L) caused oxidative stress in HepG2 cells, an effect that was independent of blocking reduced glutathione (GSH) synthesis with buthionine-L-sulfoximine (BSO), However, BSO preincubation caused an overproduction of peroxides and activation of NF-kappa B and AP-1 in E47 ce lls even in the absence of ethanol, Furthermore, the incubation of E47 cell s with ethanol (80 mmoI/L for up to 4 days) depleted cellular GSH stores in both cytosol and mitochondria, reflecting the induction of oxidative stres s, Ethanol activated NF-kappa B and AP-1 in E47 cells, an effect that was p revented by 4-methylpyrazole, potentiated by cyanamide, and attenuated by t rolox C, Interestingly, however, despite the inability of acetaldehyde to i nduce oxidative stress in HepG2, acetaldehyde activated NF-kappa B and AP-1 ; in contrast, ethanol failed to activate these transcription factors in He pG2. Thus, our findings indicate that activation of NF-kappa B and AP-1 by ethanol and acetaldehyde occurs through distinct mechanisms. CYP2E1 is indi spensable in the induction of oxidative stress from ethanol, whereas the ac tivation of NF-kappa B and AP-1 by acetaldehyde is independent of oxidative stress.