Influence of subchronic administration of catechol estrogens on the formation of reactive oxygen species in rat liver microsomes

Metabolic pathways of estrogens are the formation of catechol estrogens (CE; 2- and 4-hydroxy-estrogens), redox cycling of CE and free radical generation, mediated through cytochrome P450 (P450) oxidase/reductase activity. In previous investigations subchronic administration of estrogens showed prooxidative and antioxidative activities in rat liver microsomes (BARTH et al. 1999). To find out whether or not catechol metabolites are responsible for prooxidative activity, we checked 2- and il-hydroxy-estradiol (20H-E-2 and 40H-E-2) and the non-catechol metabolite 6 alpha-hydroxy-estradiol (6 alpha-OH-E-2) for formation of reactive oxygen species in liver microsomes of 30-day-old male Wistar rats after 5 days treatment (1, 10 mg/kg b, wt. orally, once a day). The results were compared with those after treatment of the rats with estradiol (E-2), estradiol valerate (E2V) and ethinylestradiol (EE2). In liver homogenates glutathione- and lipid peroxides were deter mined, in microsomes NADPH-Fe++-stimulated lipid peroxidation (LPO), H2O2 generation and lucigenin (LUC) and luminol (LUM) amplified chemiluminescence (CL) were investigated. In liver 9000 x g supernatants monooxygenase activities were measured. The two catechol estrogens did not show any antioxidative activity, whereas 6 alpha-OH-E-2 significantly diminished lipid peroxides in the liver as well as LPO and LUM-CL in liver microsomes. Among estrogens, only EE, showed antioxidative activity. Both CE inhibited ethoxycoumarin O-deethylation. Peroxidative activity as enhanced LUC-CL was found after 2OH-E-2 (1mg/kg b.wt.) and E-2, but 10 times higher doses of both CE did not change LUC-CL. Microsomal H2O2 generation was enhanced by E-2, E2V and both CE, not by 6 alpha-OH-E-2.(.) The lower level of H2O2 enhancement caused by CE in comparison to E-2 and E2V together with unchanged LUC-CL after high CE doses did not unequivocally prove the CE to be mainly responsible for the prooxidative activities of E-2 and E2V in liver microsomes, at least in 30-day-old male rats. Unchanged GSH in the liver after CE administration supports this hypothesis.