Ethanol-induced cytochrome P450 2E1 causes carcinogenic etheno-DNA lesions in alcoholic liver disease

Abstract

Aims: Oxidative stress is thought to play a major role in the pathogenesis of hepatocellular cancer (HCC), the most frequent complication of alcoholic liver disease (ALD). However, its underlying mechanisms are poorly understood. In hepatocytes of patients with ALD, we could recently detect significant levels of carcinogenic exocyclic etheno-DNA adducts that are formed by the reaction of the lipid peroxidation product 4-hydroxynonenal (4-HNE) with nucleobases. Methods and Results: We here show in patients with ALD that 4-HNE and exocyclic etheno-DNA adducts closely correlate with the expression of CYP2E1 expression induced by chronic consumption of alcohol (r=0.93, p<0.01). Increased amounts of exocyclic DNA-adducts were also detectable in the livers of alcohol-fed lean Zucker rats (fa/fa-) and the number of positive nuclei correlated with CYP2E1-expression (r=0.63, p=0.03). To further assess the role of CYP2E1 in the formation of etheno-DNA adducts, HepG2 cells stably transfected with CYP2E1 or vector mock transfected control cells were treated with different concentrations of ethanol with or without the CYP2E1 inhibitor chlormethiazole (CMZ). Ethanol treatment increased etheno-DNA adducts in the nuclei of CYP2E1-transfected HepG2 cells in a dose and time dependent manner, but not in control cells. In addition, CMZ almost completely blocked the generation of etheno-DNA adducts (p<0.01). Conclusion: CYP2E1 plays an important role in ethanol-induced DNA damage. Therefore ethanol-mediated induction of hepatic CYP2E1 may be a central mechanism in HCC development in patients with ALD.