Aims:The aim of the present study is to elucidate the mechanism of CYP2E1 induction
as a causative factor of alcoholic hepatitis (AH) and its relationship with inflammation.Background:Chronic alcohol consumption induces CYP2E1, which is involved in the development
of alcoholic hepatitis (AH). However, the mechanisms underlying the induction of CYP2E1
by alcohol remain unclear. Therefore, we herein investigated the induction of drug-metabolizing
enzymes, particularly CYP2E1, by hydrogen peroxide (H2O2), the concentration of which is elevated
under inflammatory conditions.Objective:The mechanisms underlying the induction of CYP2E1 by H2O2 were examined with a
focus on Keap1, a target factor of H2O2.Methods:We assessed changes in the expression of drug-metabolizing enzymes in the human
hepatoma cell line, Hep3B, following treatment with H2O2, and evaluated changes in the expression
of the NFkB-related factor RelA(p65) after the knockdown of Keap1, a regulator of Nrf2
expression by reactive oxygen species. We also performed a promoter analysis using the upstream
region of the CYP2E1 gene. We herein used the GSE89632 series for non-alcoholic hepatitis
(NASH) and the GSE28619 series for AH.Results:The induction of CYP2E1 by H2O2 was significantly stronger than that of other drugmetabolizing
enzymes. On the other hand, the knockdown of Keap1, a target of H2O2, markedly
increased RelA(p65), an NFkB factor. Furthermore, the overexpression of RelA(p65) strongly
induced the expression of CYP2E1. Four candidate p65-binding sequences were identified upstream
of the CYP2E1 gene, and promoter activity assays showed that the third sequence was
responsive to the overexpression of RelA(p65). We used the GSE89632 series for NASH and the
GSE28619 series for AH in the present study. The expression of CYP2E1 mRNA in the liver was
significantly lower in AH patients than in HC patients, but was similar in HC patients and NASH
patients.Conclusion:We herein demonstrated that the expression of CYP2E1 was induced by H2O2. The
overexpression of RelA(p65) also induced CYP2E1 mRNA expression, whereas H2O2 did not
after the knockdown of RelA. These results suggest that H2O2 acts on Keap1 to upregulate RelA
(p65) in the NFkB system. One of the mechanisms underlying the induction of CYP2E1 was dependent
on the H2O2-Keap1-RelA axis. The results of the database analysis revealed that the expression
of CYP2E1 in the liver was significantly lower in AHH patients than in NASH patients,
suggesting that CYP2E1 is not the main cause of AH; however, CYP2E1 may exacerbate the
pathogenesis of AH.