title: Induction of DNA strand breaks and oxidative stress in HeLa cells by ethanol is dependent on CYP2E1 expression.
abstract: Induction of cytochrome P4502E1 (CYP2E1) is considered to be an important mechanism by which ethanol can cause toxicity related to oxidative stress both in vivo and in vitro. In the current study, we used HeLa cells with doxycycline-regulated CYP2E1 expression to test the hypothesis that induction of CYP2E1 could lead to secondary DNA oxidation that could potentially contribute to the carcinogenicity of ethanol in vivo. Overexpression of CYP2E1 protein was not associated with oxidative stress per se as assessed by markers of lipid peroxidation (cis-parinaric acid oxidation), glutathione depletion and elevation of intracellular reactive oxygen species (dichlorofluoroscin oxidation) in the presence or absence of ethanol substrate (10 mM, 24 h). Furthermore, there was no evidence of elevation of frequency of DNA strand breaks as assessed by the comet assay. In contrast, however, after pre-incubation of cells with L-buthionine-(S,R)-sulphoximine (BSO, 10 microM) which caused a 75% reduction in intracellular reduced glutathione (GSH) levels, CYP2E1 expression resulted in oxidative stress as assessed by all of these markers and DNA strand breaks but only in the presence of ethanol (10 mM). No effect was observed under these conditions in control cells not expressing CYP2E1. Furthermore, these effects could be attenuated by co-incubation with 1-aminobenzotriazole (0.5 mM), a suicide inhibitor of P450 activity. In conclusion, in this in vitro model CYP2E1-mediated interaction with ethanol results in the intracellular oxidative stress and the formation of DNA strand breaks which are detectable in cells pre-sensitized by depletion of intracellular levels of GSH.
authors.affiliation: The School of Biosciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. N.Hodges@bham.ac.uk
authors.forename: Nikolas J
authors.initials: NJ
authors.lastname: Hodges
authors.forename: Richard M
authors.initials: RM
authors.lastname: Green
authors.forename: James K
authors.initials: JK
authors.lastname: Chipman
authors.forename: Mark
authors.initials: M
authors.lastname: Graham
mesh_terms: D015197:Carcinogenicity Tests / Q000379:methods; D020552:Comet Assay; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism*; D053904:DNA Breaks, Single-Stranded / Q000187:drug effects*; D004790:Enzyme Induction / Q000187:drug effects; D000431:Ethanol / Q000633:toxicity*; D005978:Glutathione / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D015227:Lipid Peroxidation / Q000187:drug effects; D008717:Methionine Sulfoximine / Q000031:analogs & derivatives; D018384:Oxidative Stress / Q000187:drug effects*; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; C065566:buthionine sulfoximine ethyl ester; D008717:Methionine Sulfoximine; D000431:Ethanol; D019392:Cytochrome P-450 CYP2E1; D005978:Glutathione