A rapid and sensitive radioenzymatic assay for catechol estrogens in tissues

Breast cancer risk reduction and membrane-bound catechol O-methyltransferase genetic polymorphisms

Catechol O-methyltransferase (COMT)-catalyzed methylation of catecholestrogens has been proposed to play a protective role in estrogen-induced genotoxic carcinogenesis. We have taken a comprehensive approach to test the hypothesis that genetic variation in COMT might influence breast cancer risk. Fifteen COMT single nucleotide polymorphisms (SNPs) selected on the basis of in-depth resequencing of the COMT gene were genotyped in 1,482 DNA samples from a Mayo Clinic breast cancer case control study. Two common SNPs in the distal promoter for membrane-bound (MB) COMT, rs2020917 and rs737865, were associated with breast cancer risk reduction in premenopausal women in the Mayo Clinic study, with allele-specific odds ratios (OR) of 0.70 [95% confidence interval (CI), 0.52-0.95] and 0.68 (95% CI, 0.51-0.92), respectively. These two SNPs were then subjected to functional genomic analysis and were genotyped in an additional 3,683 DNA samples from two independent case control studies (GENICA and GESBC). Functional genomic experiments showed that these SNPs could up-regulate transcription and that they altered DNA-protein binding patterns. Furthermore, substrate kinetic and exon array analyses suggested a role for MB-COMT in catecholestrogen inactivation. The GENICA results were similar to the Mayo case control observations, with ORs of 0.85 (95% CI, 0.72-1.00) and 0.85 (95% CI, 0.72-1.01) for the two SNPs. No significant effect was observed in the GESBC study. These studies showed that two SNPs in the COMT distal promoter were associated with breast cancer risk reduction in two of three case control studies, compatible with the results of functional genomic experiments, suggesting a role for MB-COMT in breast cancer risk.

HPLC-electrochemical detection of ovarian estradiol-17beta and catecholestrogens in the catfish Heteropneustes fossilis: seasonal and periovulatory changes

A high performance liquid chromatography-electrochemical (HPLC-EC) detection method was used to characterize estradiol-17beta (E2) and its metabolites (2-hydroxyE2, 4-hydroxyE2, and 2-methoxyE2) and investigate their seasonal and periovulatory changes in the ovary of the catfish Heteropneustes fossilis. The retention times in minutes of standards determined by individual and mixture applications are: 2-OHE2-6.6, 4-OHE2-7.0, 4-OHE1-11.2, E2-12.0, and 2-methoxyE2-15.2. Since the retention times of 2-OHE2 and 4-OHE2 merged at higher concentrations, the elution peaks of the sample were taken as due to both (2/4-OHE2) for analysis. The steroids were not detectable in the resting and postspawning phases and 2-methoxyE2 was not detectable in the recrudescent (preparatory, prespawning, and spawning) phases as well. E2 and 2/4-OHE2 have maintained an inverse relationship in the recrudescent phase. The E2 concentration was the highest in the preparatory phase (April) with active vitellogenic activity and declined significantly across prespawning and spawning phases (P<0.001, one way ANOVA; P<0.05, Newman-Keuls' test). On the other hand, the concentration of 2/4-OHE2, which was the lowest in the preparatory phase, increased significantly to the peak level in the spawning phase. A single intraperitoneal injection of hCG (100 IU/fish) stimulated significantly the formation of 2/4-OHE2 at 8 h with a simultaneous reduction in E2. 2-MethoxyE2 was detected only after 16 h of the hCG injection. The functional significance of catecholestrogens in the seasonal reproductive cycle and during the hCG-induced ovulation of the catfish was discussed.

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.

Embryotoxicity induced by diethylstilbestrol in vitro

The embryotoxic potential of diethylstilbestrol (DES) was examined in a whole embryo culture system containing a P-450-dependent bioactivating system. Sprague-Dawley rat embryos were explanted on day 10 and cultured for 24 hours. Concentration-dependent effects of DES on embryonic growth parameters, viability, and embryotoxicity were observed. Concentrations of DES greater than 0.26 mM (final concentration) produced 100% embryolethality, while those below 0.15 mM were without significant effects. At a final concentration of 0.19 mM, DES produced only a slight increase in embryolethality. The same concentration elicited a marked increase in observed embryotoxicity, including prosencephalic hypoplasia, incomplete axial rotation, and open neural tubes. In addition, reductions in embryonic length, somite number, and protein and DNA content were observed. An exogenous P-450-dependent hepatic biotransforming (catechol-generating) system failed to alter either the incidence of observed toxic effects or measured growth parameters. Likewise, exposure of cultured embryos to 20% carbon monoxide (CO) failed to reduce DES-induced embryotoxicity, indicating a lack of participation of an endogenous P-450-dependent embryonic bioactivating system. Arachidonic acid (0.20 mM) and/or indomethacin (0.50 mM) also had no observable effect on DES-induced embryotoxicity, suggesting that prostaglandin synthase was not involved in the embryotoxic activity of DES, as has been proposed to explain its carcinogenic effect. The antioxidants N-acetylcysteine (1.14 mM) and alpha-tocopherol (0.08 mM) failed to protect against DES-induced embryotoxicity, while the anti-estrogen tamoxifen (up to 0.85 mM) actually enhanced this effect of DES in culture. The DES analogs Z,Z-dienestrol (DIES, 0.10 mM) and hexestrol (HES, 0.48 mM) were both embryotoxic in vitro. The presence of an exogenous P-450-dependent hepatic biotransforming system appeared to protect against HES-induced embryolethality but had little effect upon DIES-induced embryotoxicity. The results were consistent with a direct effect of DES independent of either estrogenicity or exogenously generated metabolites.

The possible role of 2-hydroxyestradiol in the development of estrogen-induced striatal dopamine receptor hypersensitivity

In the present study, we have confirmed the existence of a biphasic response in striatal dopamine receptor sensitivity following the administration of estradiol benzoate (EB). This biphasic response consists of a hyposensitive phase 24 h after the last injection of EB, followed by a hypersensitive phase 72 h after the last injection of EB. In contrast to this, the administration of 2-hydroxyestradiol (2-OHE2), a catechol metabolite of estrogen, resulted in a striatal dopamine receptor hypersensitivity at both 24 and 72 h after the last injection of 2-OHE2. Studies on the in vivo metabolism of [3H]estradiol to its [3H]catechol metabolites indicated that the administration of piperonyl butoxide (PBO; a microsomal enzyme inhibitor) significantly decreased the level of [3H]catechol metabolites of [3H]estradiol in the striatum and in the medial basal hypothalamus. In addition, PBO administration resulted in about a 7-fold decrease in the ability of estradiol to induce a striatal dopamine receptor hypersensitivity. These data indicate that the biphasic response in striatal dopamine receptor sensitivity following estrogen, may be mediated by separate molecular mechanisms. The association of the hypersensitive phase with pharmacological doses and/or treatment paradigms, the development of a similar hypersensitivity following the administration of the 2-OHE2 metabolite of estrogen and the attenuation of the estrogen-induced striatal dopamine receptor hypersensitivity in PBO pretreated animals all suggest that this striatal dopamine receptor hypersensitivity may be mediated, at least in part, by the catecholestrogens.

Effect of xenobiotic estrogens and structurally related compounds on 2-hydroxylation of estradiol and on other monooxygenase activities in rat liver

Previous study demonstrated that the administration for several days of 1-(o-chlorphenyl)-1-(p-chlorophenyl)-2,2,2-trichloroethane (o,p'DDT) (estrogenic DDT derivative) or of tamoxifen (antiestrogen), but not of 2,2-bis-(p-chlorophenyl)-1,1-dichloroethylene (p,p'DDE) (nonestrogen), to ovariectomized female rats dramatically diminished the induction of uterine ornithine decarboxylase (ODC) by subsequently administered estradiol [W. H. Bulger and D. Kupfer, Archs Biochem, Biophys. 182, 138 (1977)]. The present investigation examines whether the inhibition of ODC induction by o,p'DDT and tamoxifen may have been due to enhanced hydroxylation of estradiol by the hepatic monooxygenase system. Additionally, the effects of other estrogenic and nonestrogenic xenobiotics on the major route of estradiol metabolism (2-hydroxylation) were examined. Treatment of ovariectomized (ovex) rats with o,p'DDT or p,p'DDE caused induction of hepatic estradiol-2-hydroxylation and increased demethylase activities of several substrates. Administration of Kepone (estrogenic) and Mirex (nonestrogenic), both inducers of hepatic monooxygenase, also increased 2-hydroxylation of estradiol. For comparative purposes, the effects on estradiol-2-hydroxylation of administration of classical estrogens (estradiol and diethylstilbestrol) and antiestrogen (tamoxifen) and inducers of monooxygenase activity (phenobarbital and 3-methylcholanthrene) were also studied. Treatment of ovariectomized and adrenalectomized (ovex/adx) or intact female rats with estradiol or ovex/adx animals with diethylstilbestrol had no effect on estradiol-2-hydroxylation. Similarly, tamoxifen did not alter the rate of estradiol-2-hydroxylation. The treatment of ovex/adx rats with 3-methylcholanthrene did not affect the rate of estradiol-2-hydroxylation. By contrast, ovex/adx female or intact male rats treated with phenobarbital exhibited induction of estradiol-2-hydroxylase activity. In the above studies only 2-hydroxyestradiol was found; there was no evidence for the formation of primary metabolites hydroxylated at other sites on estradiol. The current findings exclude the possibility that the previously observed inhibition of estradiol-mediated induction of ODC by pretreatment with o,p'DDT or tamoxifen (see article cited above) was due to enhanced hydroxylation of estradiol by liver monooxygenases. Also, it was concluded that there is no correlation between the ability to induce hepatic microsomal estradiol-2-hydroxylase activity and estrogenic (or antiestrogenic) properties of a given compound.

Estrogen metabolism in neural tissues of six-day-old rats

In vitro incubation of pituitary, hypothalamus and cerebral cortex from 6-day-old rats with [6,7-3H]estradiol revealed that estradiol is actively metabolized in these tissues. Pituitary was found to be more active than hypothalamus and cerebral cortex in metabolizing estradiol in these animals. Covalent binding of estradiol to acid-precipitable proteins was observed in all these tissues from both sexes. While there was no significant sex difference in protein binding of estradiol in any of the tissues tested, treatment with progesterone or estradiol valerate increased protein binding. 2- and 16-hydroxylation and 17 beta-oxidation were demonstrated in all the tissues tested. While there were no significant sex differences observed in 2,16-hydroxylation, 17 beta-oxidation appeared to be more in males. Progesterone treatment of males increased 2-hydroxylation of estradiol 4-fold in pituitary and doubled the levels in hypothalamus. 16-Hydroxylation and 17-oxidation were also elevated significantly in pituitary and hypothalamus by progesterone treatment. Estradiol valerate treatment, however, decreased 2-hydroxylation and 16-hydroxylation in pituitary and hypothalamus; 17-oxidation was increased in pituitary. These results suggest that the estradiol metabolism, and especially 2-hydroxyestradiol formation, can be increased by progesterone and thereby mediate antagonistic effect of progesterone on estrogen-mediated brain sexual differentiation.

Formation of 3H2O from [2-3H]- and [4-3H] estradiol by rat uteri in vitro: possible role of peroxidase

The mitochondrial fraction of diethylstilbestrol-treated rat uteri, known to contain an estrogen-induced peroxidase, was able to catalyze the release of 3H2O from either [2-3H]- or [4-3H]estradiol. Hydrogen peroxide added to this system increased the yield of 3H2O but had no effect on mitochondrial preparations from ovariectomized rat uteri having only very low peroxidase activity. The reaction was inhibited by catalase and also occurred with lactoperoxidase in the presence of H2O2 but 2-hydroxyestradiol was not detected in any of these experiments. Under similar conditions, tyrosinase catalyzed the formation of the catechol estrogen with loss of 3H from [2-3H]- or [2,4,6,7-3H]- but not [4-3H]- or [6,7-3H]estradiol. It is proposed that the formation of 3H2O from 3H-labeled estradiol in the estrogen-treated rat uterus may occur by a peroxidative mechanism which does not necessarily result in hydroxylation of the steroid.