Cytochrome P450 2E1 (CYP2E1)-dependent production of a 37-kDa acetaldehyde-protein adduct in the rat liver.

Ethanol-inducible cytochrome P450 2E1 (CYP2E1) has been shown to be involved in the metabolism of both ethanol and acetaldehyde. Acetaldehyde, produced from ethanol metabolism, is highly reactive and can form various protein adducts. In this study, we investigated the role of CYP2E1 in the production of a 37-kDa acetaldehyde-protein adduct. Rats were pairfed an isocaloric control or an alcohol liquid diet with and without cotreatment of YH439, an inhibitor of CYP2E1 gene transcription, for 4 weeks. The soluble proteins from rat livers of each group were separated on SDS-polyacrylamide gels followed by immunoblot analysis using specific antibodies against the 37-kDa protein acetaldehyde adduct. In addition, catalytic activities of the enzymes involved in alcohol and acetaldehyde metabolism were measured and compared with the adduct level. Immunoblot analysis revealed that the 37-kDa adduct, absent in the pair-fed control, was evident in alcohol-fed rats but markedly reduced by YH439 treatment. Immunohistochemical analysis also showed that the 37-kDa adduct is predominantly localized in the pericentral region of the liver where CYP2E1 protein is mainly expressed. This staining disappeared in the pericentral region after YH439 treatment. The levels of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase isozymes were unchanged after YH439 treatment. However, the level of the 37-kDa protein adduct positively correlated with the hepatic content of P4502E1. These data indicate that the 37-kDa adduct could be produced by CYP2E1-mediated ethanol metabolism in addition to the ADH-dependent formation.