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

Summary 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 4-hydroxy-estradiol (20H-E 2 and 40H-E 2 ) and the non-catechol metabolite 6α-hydroxy -estradiol (6a-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 (E 2 V) and ethinylestradiol (EE 2 ). In liver homogenates glutathione and lipid peroxides were determined, in microsomes NADPH-Fe ++ -stimulated lipid peroxidation (LPO), H 2 O 2 generation and lucigenin (LUC) and luminol (LUM) amplified chemiluminescence (CL) were investigated. In liver 9000 × g supernatants monooxygenase activities were measured. The two catechol estrogens did not show any antioxidative activity, whereas 6α-OH-E 2 significantly diminished lipid peroxides in the liver as well as LPO and LUM-CL in liver microsomes. Among estrogens, only EE 2 showed antioxidative activity. Both CE inhibited ethoxycoumarin O-deethylation. Peroxidative activity as enhanced LUC-CL was found after 2OH-E 2 (lmg/kg b.wt.) and E 2 but 10 times higher doses of both CE did not change LUC-CL. Microsomal H 2 O 2 generation was enhanced by E 2 , E 2 V and both CE, not by 6α-OH-E 2 . The lower level of H 2 O 2 enhancement caused by CE in comparison to E 2 and E 2 V 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 E 2 V in liver microsomes, at least in 30-day-old male rats. Unchanged GSH in the liver after CE administration supports this hypothesis.