Identification of fatty acid hydroperoxide cofactors in the cytochrome P450-mediated oxidation of estrogens to quinone metabolites. Role and balance of lipid peroxides during estrogen-induced carcinogenesis.

Abstract

Lipid hydroperoxide-supported metabolic redox cycling between diethylstilbestrol (DES) or catechol-estrogens and their corresponding quinones has been postulated previously to play a role in estrogen-induced toxicity and carcinogenesis. As part of an examination of this postulate, we investigated (a) the effectiveness of various lipid hydroperoxides as oxidants in microsome-mediated quinone formation, and (b) the dependence of DES oxidation to quinone on lipid hydroperoxide levels in liver and kidney of hamsters. Kinetic analyses of the lipid hydroperoxide-mediated conversion of DES to DES quinone revealed that of the peroxides tested (9Z,11E,13(S))-13-hydroperoxyoctadecadien-1-oic acid was the most powerful oxidant (Vmax = 10.5 nmol min-1; Km = 21.3 microM) followed by (5(S),6E,8Z,11Z,14Z)-5-hydroperoxyeicosatetra en-1-oic acid (Vmax = 1.0 nmol min-1; Km 10.0 microM). The other pure fatty acid hydroperoxide isomers or mixtures had a lower affinity for the enzyme (Km values ranging from 23.1 to 130 microM) and/or lower maximal velocity (Vmax values ranging from 0.2 to 7.0 nmol min-1). Levels of Z,Z-dienestrol, which arises from spontaneous rearrangement of DES quinone, were not affected in liver of hamsters treated with estradiol implants for 9 days and an injection of 20 mg/kg DES but increased in kidney by 120% over levels observed in animals without implants (5.5 and 12.1 nmol/g of wet tissue, respectively). Z,Z-Dienestrol concentrations correlated directly with lipid hydroperoxide concentrations in liver and kidney of control and estradiol-treated hamsters. The increased conversion of DES to quinone in kidney compared with that in liver was catalyzed by comparable activities of cytochrome P450 IA, the enzyme family catalyzing this oxidation. These results demonstrated that the oxidation of DES to quinone was directly dependent on the lipid hydroperoxide levels in the organ of metabolic conversion in addition to the enzyme activity catalyzing this reaction. The elevated lipid hydroperoxide levels in kidney of estrogen-treated hamsters indicate enhanced estrogen quinone formation and therefore enhanced generation of free radicals by metabolic redox cycling of estrogens in this organ prior to the appearance of malignancy.