2-hydroxyestradiol and 2-hydroxyestradiol-17-sulfate

Two endogenous antioxidants that are speculated to be defense substances against preeclampsia, 2-hydroxyestradiol (2-OH-E2) and its 17-sulfate, 2-hydroxyestradiol 17-sulfate (2-OH-E2-17-S), were administered to rats to compare their inhibitory effects on hepatic microsomal lipid peroxidation, and the lipid peroxides were determined in NADPH- and ascorbic acid-dependent systems. The two catechols showed a strong inhibitory effect on lipid peroxidation in both systems, and the effect was dose dependent. However, a large difference was observed in their inhibition patterns. After administration of 2-OH-E2, the effect appeared immediately and decreased gradually with time. In contrast, the effect of 2-OH-E2-17-S appeared some time after administration and persisted for a longer time. Both catechols also showed a striking difference in their dynamics. After administration, 2-OH-E2 was detected in the blood together with its metabolites, 2-methoxyestradiol and 2-methoxyestrone, and they disappeared immediately. In contrast, 2-OH-E2-17-S was present in the blood for a longer time together with its O-methylated product, 2-methoxyestradiol 17-sulfate, but disappeared from liver microsomes within 2 h after administration. The results imply no occurrence of a direct inhibition effect of 2-OH-E2-17-S.

Topics: Animals; Dose-Response Relationship, Drug; Estradiol; Estrogens; Lipid Peroxidation; Liver; Male; Microsomes, Liver; Models, Molecular; Molecular Structure; Rats; Rats, Wistar; Time Factors

For identification of microsomal cytochrome P-450 (P-450) enzymes which catalyze 2- or 4-hydroxylations of estrogens in the rat liver, estradiol (E2) and estradiol 17-sulfate (E2-17-S) were selected as the substrates and incubated with various kinds of purified P-450 enzymes: PB-1, PB-2, PB-4 and PB-5 obtained from phenobarbital-treated male rats (Sprague-Dawley); MC-1 and MC-5 from 3-methylcholanthrene-treated male rats; and UT-1, UT-2, UT-4 and UT-5 from untreated animals. The reactions were carried out under the P-450-reconstructed system, and the resulting products were determined by HPLC using electrochemical detection. All the enzymes tested were shown to have varying degrees of catalytic activities for 2-hydroxylation of the two substrates; UT-1 and UT-2 had the highest activity. Of the induced P-450 enzymes, PB-2 and MC-1 showed fairly high catalytic activity for 4-hydroxylation of E2. The P-450 enzymes obtained from the untreated male rats, especially UT-4, showed the highest catalytic activity for 4-hydroxylation of the two substrates. From these results and also from kinetic experiments, the P-450 enzymes which catalyze 2- and 4-hydroxylations of estrogen were considered to be different species. A part of E2 was converted to such metabolites as estrone and those having a hydroxyl group at positions 6 beta, 15 alpha or 16 alpha, each production of which was estimated to be catalyzed by single or multiple P-450s.

Topics: Animals; Chromatography, High Pressure Liquid; Cytochrome P-450 Enzyme System; Estradiol; Estrogens, Catechol; Hydroxylation; Kinetics; Male; Methylcholanthrene; Microsomes, Liver; Phenobarbital; Rats; Rats, Inbred Strains