Estradiol-15 alpha-hydroxylation: a new avenue of estrogen metabolism in peri-implantation pig blastocysts

Preparation of specific antisera to 15alpha-hydroxyestrogens

The synthesis of haptens of 15alpha-hydroxyestrone, 15alpha-hydroxyestradiol, and 15alpha-hydroxyestriol (estetrol) was undertaken, to obtain specific antisera required for enzyme immunoassay. 3-(1-Carboxypropyl) ethers of these 15alpha-hydroxyestrogens were prepared and conjugated with bovine serum albumin and horseradish peroxidase. The specificity of antisera elicited against bovine serum albumin conjugates was checked by the enzyme immunoassay by using horseradish peroxidase-labeled antigen, and proved to be satisfactory in terms of cross-reactivities to related compounds.

Estrogen metabolism in microsomal, cell, and tissue preparations of kidney and liver from Syrian hamsters

The estrogen-treated golden Syrian hamster has been used as an experimental model for estrogen-induced and estrogen-dependent cancers, but pathways to neoplastic transformation remain unknown in this animal. Metabolism of estrogens to activated or reactive compounds, followed by subsequent oxidative damage to the target tissue, remains a potential step in the tumorigenic process. In this study, the extent of estrogen metabolism is compared in three different in vitro preparations from untreated and estrogen-treated Syrian hamsters, primary kidney cell cultures, microsomal preparations, and freshly prepared tissue kidney slices. In primary kidney cell cultures, the amount of catechol estrogens decreased upon increasing estrogen (DES) treatment period, and completely disappeared after about 6 months treatment. This decrease is not a result of formation of less amounts of catechol estrogens, but rather reflects the presence of the enzyme systems to further metabolize any formed catechol estrogens, since the amount of catechol estrogens formed, as detected by 3H2O release, is unchanged. The polar metabolites a, b and c increased with estrogen treatment, and metabolite c appeared only after DES treatment. The appearance of polar metabolite c only in kidney preparations from DES-treated animals implies that it may serve as a marker of cellular transformation. Estriol and estrone were detected, but were not affected by DES treatment, while no methoxyestrogens were isolated. Studies of estradiol metabolism in microsomal preparations showed a very low rate of metabolism, compared to the primary kidney cell cultures. In contrast, estrogen metabolism was extensive in kidney slices from untreated hamsters, with only approx. 30% of the substrate estradiol remaining unmetabolized after 6 h of incubation. While no catechol estrogens were detected, a small quantity of estriol, and a large amount of estrone and methoxyestrogens were isolated. The polar metabolite a was the main polar metabolite detected, with very little of metabolite b and no metabolite c. In kidney slices from 4 month DES-treated hamsters, a much higher amount of polar metabolites was detected, and metabolite c appeared after 6 h incubation. Mass spectrometric analysis and HPLC data of metabolite c indicate that this metabolite is 15 alpha-hydroxyesteradiol. This metabolite may serve as a biomarker for changes occurring in the hamster kidney cells under continuous estrogen exposure. Finally, formation of water soluble conjugates was demonstrated in both kidney slices and liver slices from Syrian hamsters, with glucuronide, sulfate and thioether conjugates of estrone and estradiol and glucuronides of catechol estrogens detected.(ABSTRACT TRUNCATED AT 400 WORDS)

P450 enzymes of estrogen metabolism

Endogenous and exogenous estrogens undergo extensive oxidative metabolism by specific cytochrome P450 enzymes. Certain drugs and xenobiotics have been found to be potent inducers of estrogen hydroxylating enzymes with C-2 hydroxylase induction being greater than that of C-16 hydroxylase. Oxygenated estrogen metabolites have different biological activities, with C-2 metabolites having limited or no activity and C-4 and C-16 metabolites having similar potency to estradiol. Pathophysiological roles for some of the oxygenated estrogen metabolites have been proposed, e.g. 16 alpha-hydroxyestrone and 4-hydroxyestrone. These reactive estrogens are capable of damaging cellular proteins and DNA and may be carcinogenic in specific cells.

The sexually differentiated metabolism of [6,7-3H]17 beta-oestradiol in rats: male-specific 15 alpha- and male-selective 16 alpha-hydroxylation and female-selective catechol formation

The oxygenated-metabolite profiles of exogenous 17 beta-oestradiol (E2) in adult male and female Wistar rats have been characterized and major sex-dependent biotransformations observed which correlate with the regioselectivities of known sexually differentiated hepatic P450. [6,7-3H]E2 (27 micrograms/kg) was given i.v. The metabolites of E2 were rapidly and extensively excreted in bile (46 and 78% of the dose over 1 and 6 h, respectively). Female rats metabolized E2 by one major pathway: oxidation to oestrone (E1) followed by C-2 hydroxylation and O-methylation; the principal aglycones (0-1 h bile collections) were E1 (14%), 2-hydroxyE1 (2-OHE1) (42%) and 2-methoxyE1 (24%). Male rats metabolized E2 principally by two parallel composite pathways of E1 hydroxylation which yielded a complex mixture of mono- and di-oxygenated compounds: 15 alpha-OHE1 (33%), 2,15 alpha-diOHE1 (7%), and 2-methoxy-15 alpha OHE1 (14%); 16 alpha-OHE1 (13%), 2,16 alpha-diOHE1 (4%) and 2-methoxy-16 alpha-OHE1 (2%). 15 alpha-Hydroxylation was unique to males. The balance of aromatic and alkyl hydroxylation in males was dose-dependent: at 3 mg/kg, 15 alpha-hydroxylation was decreased approx. 50% in favour of 2-hydroxylation whilst 16 alpha-hydroxylation was largely unaffected. The male-specific 15 alpha-hydroxylation and male-predominant 16 alpha-hydroxylation of E1 derived from E2 in vivo may be ascribable to the male-specific isoforms P450IIC13 and P450IIC11, respectively.