title: The effects of catechol-O-methyltransferase inhibition on estrogen metabolite and oxidative DNA damage levels in estradiol-treated MCF-7 cells.
abstract: Many of the major identified risk factors for breast cancer are associated with exposure to endogenous estrogen. In addition to the effects of estrogen as a growth factor, experimental and epidemiological evidence suggest that catechol metabolites of estrogen also contribute to estrogen carcinogenesis by both direct and indirect genotoxic mechanisms. O-Methylation catalyzed by catechol-O-methyltransferase (COMT) is a Phase II metabolic inactivation pathway for catechol estrogens. We and others have found that a polymorphism in the COMT gene, which codes for a low activity variant of the COMT enzyme, is associated with an increased risk of developing breast cancer; therefore, the goal of the current study was to investigate the role of decreased COMT activity on estrogen catechol levels and on oxidative DNA damage, as measured by 8-hydroxy-2'-deoxyguanosine (8-oxo-dG) levels. MCF-7 cells were pretreated with dioxin as a means to increase estrogen metabolism to catechol estrogens, then treated with estradiol (E2) +/- Ro 41-0960, a COMT-specific inhibitor. After extraction from culture medium, estrogen metabolites were separated using an high-performance liquid chromatography-electrochemical detection method. As expected, dioxin dramatically increased E2 oxidative metabolism, primarily to its 2-OH and 2-methoxy metabolites. The COMT inhibitor blocked 2-methoxy E2 formation. This was associated with increased 2-hydroxy E2 (2-OH E2) and 8-oxo-dG levels. In the presence of COMT inhibition, increased oxidative DNA damage was detected in MCF-7 cells exposed to as low as 0.1 microM E2, whereas in the absence of COMT inhibition, no increase in 8-oxo-dG was detected at E2 concentrations < or =10 microM. This study is the first to show that O-methylation of 2-OH E2 by COMT is protective against oxidative DNA damage caused by 2-OH E2, a major oxidative metabolite of E2.
authors.affiliation: Department of Environmental Health Science, Division of Toxicological Sciences, The Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland 21205-2179, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Lavigne
authors.forename: J E
authors.initials: JE
authors.lastname: Goodman
authors.forename: T
authors.initials: T
authors.lastname: Fonong
authors.forename: S
authors.initials: S
authors.lastname: Odwin
authors.forename: P
authors.initials: P
authors.lastname: He
authors.forename: D W
authors.initials: DW
authors.lastname: Roberts
authors.forename: J D
authors.initials: JD
authors.lastname: Yager
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine; D001577:Benzophenones / Q000494:pharmacology; D001943:Breast Neoplasms / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D065098:Catechol O-Methyltransferase Inhibitors; D004249:DNA Damage; D004273:DNA, Neoplasm / Q000378:metabolism; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000378:metabolism* / Q000494:pharmacology*; D002393:Estrogens, Catechol / Q000378:metabolism*; D006801:Humans; D018384:Oxidative Stress / Q000502:physiology; D014407:Tumor Cells, Cultured
chemical_list: D001577:Benzophenones; D065098:Catechol O-Methyltransferase Inhibitors; D004273:DNA, Neoplasm; D004791:Enzyme Inhibitors; D002393:Estrogens, Catechol; C071721:Ro 41-0960; D004958:Estradiol; D000080242:8-Hydroxy-2'-Deoxyguanosine; D003849:Deoxyguanosine