Catechol estrogen formation in the mouse uterus and its role in implantation

4-Hydroxyestradiol improves mouse embryo quality, epidermal growth factor-binding capability in vitro and implantation rates

Embryo implantation in the uterus is a critical step to achieve success following ART. Despite favorable uterine conditions, a great number of good quality embryos fail to implant, often for reasons that are unknown. Hence, improving the implantation potential of embryos is a subject of great interest. 4-Hydroxyestradiol (4-OH-E2), a metabolic product of estradiol produced by endometrial cells, plays a key role in endometrial-embryonic interactions that are necessary for implantation. Nonetheless, the effects of 4-OH-E2 on embryos obtained in vitro have not been yet described. This study was designed to determine whether culture media enriched in 4-OH-E2 could improve the quality and implantation rate of embryos obtained in vitro, using both in vitro and in vivo models. We also analyzed its effects on the epidermal growth factor (EGF)-binding capability of the embryos. Our results showed that the presence of 4-OH-E2 in the culture media of embryos during the morula to blastocyst transition increases embryo quality and attachment to endometrial cells in vitro. 4-OH-E2 can also improve viable pregnancy rates of mouse embryos produced in vitro, reaching success rates that are similar to those from embryos obtained directly from the uterus. 4-OH-E2 improved the embryos' ability to bind EGF, which could be responsible for the increased embryo implantation potential observed. Therefore, our results strongly suggest that 4-OH-E2 is a strong candidate molecule to supplement human IVF culture media in order to improve embryo implantation. However, further research is required before these findings can be translated with efficacy and safety to fertility clinics.

Epigenetic regulation of uterine biology by transcription factor KLF11 via posttranslational histone deacetylation of cytochrome p450 metabolic enzymes

Endocrine regulation of uterine biology is critical for embryo receptivity and human reproduction. Uterine endometrium depends on extrinsic sex steroid input and hence likely has mechanisms that enable adaptation to hormonal variation. Emerging evidence suggests that sex steroid bioavailability in the endometrium is determined by adjusting their metabolic rate and fate via regulation of cytochrome (CYP) p450 enzymes. The CYP enzymes are targeted by ubiquitously expressed Sp/Krüppel-like (Sp/KLF) transcription factors. Specifically, KLF11 is highly expressed in reproductive tissues, regulates an array of endocrine/metabolic pathways via epigenetic histone-based mechanisms and, when aberrantly expressed, is associated with diabetes and reproductive tract diseases, such as leiomyoma and endometriosis. Using KLF11 as a model to investigate epigenetic regulation of endometrial first-pass metabolism, we evaluated the expression of a comprehensive array of metabolic enzymes in Ishikawa cells. KLF11 repressed most endometrial CYP enzymes. To characterize KLF11-recruited epigenetic regulatory mechanisms, we focused on the estrogen-metabolizing enzyme CYP3A4. KLF11 expression declined in secretory phase endometrial epithelium associated with increased CYP3A4 expression. Additionally, KLF11 bound to CYP3A4 promoter GC elements and thereby repressed promoter, message, protein as well as enzymatic function. This repression was epigenetically mediated, because KLF11 colocalized with and recruited the corepressor SIN3A/histone deacetylase resulting in selective deacetylation of the CYP3A4 promoter. Repression was reversed by a mutation in KLF11 that abrogated cofactor recruitment and binding. This repression was also pharmacologically reversible with an histone deacetylase inhibitor. Pharmacological alteration of endometrial metabolism could have long-term translational implications on human reproduction and uterine disease.

Cadence of procreation: orchestrating embryo-uterine interactions

Embryo implantation in eutherian mammals is a highly complex process and requires reciprocal communication between different cell types of the embryo at the blastocyst stage and receptive uterus. The events of implantation are dynamic and highly orchestrated over a species-specific period of time with distinctive and overlapping expression of many genes. Delayed implantation in different species has helped elucidate some of the intricacies of implantation timing and different modes of the implantation process. How these events are coordinated in time and space are not clearly understood. We discuss potential regulators of the precise timing of these events with respect to central and local clock mechanisms. This review focuses on the timing and synchronization of early pregnancy events in mouse and consequences of their aberrations at later stages of pregnancy.

Physiological and molecular determinants of embryo implantation

Embryo implantation involves the intimate interaction between an implantation-competent blastocyst and a receptive uterus, which occurs in a limited time period known as the window of implantation. Emerging evidence shows that defects originating during embryo implantation induce ripple effects with adverse consequences on later gestation events, highlighting the significance of this event for pregnancy success. Although a multitude of cellular events and molecular pathways involved in embryo-uterine crosstalk during implantation have been identified through gene expression studies and genetically engineered mouse models, a comprehensive understanding of the nature of embryo implantation is still missing. This review focuses on recent progress with particular attention to physiological and molecular determinants of blastocyst activation, uterine receptivity, blastocyst attachment and uterine decidualization. A better understanding of underlying mechanisms governing embryo implantation should generate new strategies to rectify implantation failure and improve pregnancy rates in women.

The effects of estradiol and catecholestrogens on uterine glycogen metabolism in mink (Neovison vison)

Glycogen is a uterine histotroph nutrient synthesized by endometrial glands in response to estradiol. The effects of estradiol may be mediated, in part, through the catecholestrogens, 2-hydroxycatecholestradiol (2-OHE2) and 4-hydroxycatecholestradiol (4-OHE2), produced by hydroxylation of estradiol within the endometrium. Using ovariectomized mink, our objectives were to determine the effects of estradiol, 4-OHE2, and 2-OHE2 on uterine: 1) glycogen concentrations and tissue localization; 2) gene expression levels for glycogen synthase, glycogen phosphorylase, and glycogen synthase kinase-3B; and 3) protein expression levels for glycogen synthase kinase-3B (total) and phospho-glycogen synthase kinase-3B (inactive). Whole uterine glycogen concentrations (mean ± SEM, mg/g dry wt) were increased by estradiol (43.79 ± 5.35), 4-OHE2 (48.64 ± 4.02), and 2-OHE2 (41.36 ± 3.23) compared to controls (4.58 ± 1.16; P ≤ 0.05). Percent glycogen content of the glandular epithelia was three-fold greater than the luminal epithelia in response to estradiol and 4-OHE2 (P ≤ 0.05). Expression of glycogen synthase mRNA, the rate limiting enzyme in glycogen synthesis, was increased by 4-OHE2 and 2-OHE2 (P ≤ 0.05), but interestingly, was unaffected by estradiol. Expression of glycogen phosphorylase and glycogen synthase kinase-3B mRNAs were reduced by estradiol, 2-OHE2, and 4-OHE2 (P ≤ 0.05). Uterine phospho-glycogen synthase kinase-3B protein was barely detectable in control mink, whereas all three steroids increased phosphorylation and inactivation of the enzyme (P ≤ 0.05). We concluded that the effects of estradiol on uterine glycogen metabolism were mediated in part through catecholestrogens; perhaps the combined actions of these hormones are required for optimal uterine glycogen synthesis in mink.

Estrogen-independent actions of environmentally relevant AhR-agonists in human endometrial epithelial cells

The human endometrium is a cyclically regenerating organ under the influence of ovarian steroid hormones. Disturbances in this highly coordinated regulation of endometrial proliferation and differentiation may result in infertility and diseases such as endometriosis and endometrial cancer. Environmental toxins belonging to the group of polyhalogenated aromatic hydrocarbons (PAHs) are lipophilic xenobiotics, which accumulate in biological systems. PAHs have been implicated in the etiology of uterine pathologies, including infertility, endometriosis and endometrial cancer. However, suitable cellular models of the endometrium are lacking and the molecular mechanism of PAH action in the endometrium is not fully understood. In this study, we have characterized a previously established immortalized human telomerase reverse transcriptase (hTERT) endometrial epithelial cell (hTERT-EEC) model as a responsive in vitro cell model to investigate the cellular and molecular mechanisms of selected environmentally relevant PAH in human EECs. We show that dioxin-type PAHs activate the endogenous arylhydrocarbon receptor (AhR) signaling pathway in hTERT-EEC in a time-, concentration- and congener-specific manner and that the induction of AhR target genes is modulated by estrogen. Strikingly, AhR activation did not interfere with estrogenic actions in these EECs. Independent of their ability to bind to AhR, the PAHs investigated here increased cell migration by hTERT-EEC. Furthermore, we have identified several candidates by proteomic analysis, which are involved in heat shock responses and protein modification and turnover. Our data suggest that AhR-activating environmental pollutants directly alter endometrial cell stress responses and metabolism independent of estrogenic actions.

Association of cytochrome P450 1B1 polymorphism with first-trimester miscarriage

OBJECTIVE

To determine whether the cytochrome P450 1B1 (CYP1B1) Val432Leu polymorphism is associated with risk of miscarriage. We also analyzed the possible interaction between this polymorphism and caffeine intake.

DESIGN

The population-based case-control study included 507 women with miscarriage in the first trimester of pregnancy and 908 controls with a normal first-trimester pregnancy. The controls were frequency matched to cases. The material was analyzed taking maternal age, smoking habits, alcohol intake, caffeine intake, fetal karyotype, nausea, and vomiting into consideration.

SETTING

University hospital and primary care facility.

MAIN OUTCOME MEASURE(S)

CYP1B1 Val432Leu genotype frequencies in cases and controls.

RESULT(S)

Carriers of the CYP1B1 432 Val/Val genotype were at a higher risk of miscarriage in the first trimester of pregnancy (odds ratio = 1.46; 95% confidence interval, 1.02-2.08). We also found a significant interaction between genotype and caffeine intake.

CONCLUSION(S)

CYP1B1 Val432Leu polymorphism is associated with first-trimester miscarriage, and it may also modify the risk among coffee drinkers.

Induction of cytochromes P450, caspase-3 and DNA damage by PCB3 and its hydroxylated metabolites in porcine ovary

Polychlorinated biphenyl (PCBs) levels of tens and hundreds of pg/ml for individual congeners are measured in human follicular fluid. PCB3 (4-chlorobiphenyl), caused a significant increase in estradiol secretion in porcine granulose-theca cell co-cultures and its two metabolites, 4-OH-PCB3 and 3,4-diOH-PCB3, were even more potent than PCB3 itself [Ptak, A., Ludewig, G., Lehmler, H.J., Wojtowicz, A.K., Robertson, L.W., Gregoraszczuk, E.L. 2005. Comparison of the actions of 4-chlorobiphenyl and its hydroxylated metabolites on estradiol secretion by ovarian follicles in primary cells in culture. Reprod. Toxicol. 20, 57-64]. The question is whether these follicle cells are potentially able to metabolize PCB3 to hydroxylated and genotoxic or cytotoxic intermediates. We report here that granulose-theca co-cultures express xenobiotic-metabolizing cytochrome P450 activities, with CYP1A1>CYP2B>>CYP1A2. A significant increase in CYP1A1 and 2B, but not CYP1A2, activity was seen in cells that were exposed to 6 ng/ml PCB3 or 20 nM 17-beta-estradiol. An increase in caspase-3 activity, indicative for apoptosis, was only observed in PCB3-exposed cells after 24 h exposure. Genotoxicity, determined with the Comet assay, was initially reduced after 24 h exposure to PCB3 and both metabolites compared to untreated controls, followed by a significant transient increase in Comets at the 4 and 24 h time point with PCB3 and 4-OH-PCB3. 3,4-diOH-PCB3 induced a significant increase only after 72 h of recovery. We hypothesize that these biphasic damage kinetics may be due to cross-links caused by adduct formation. These results show for the first time that granulose-theca cells in co-culture express CYP1A1, 2B and 1A2 activities and that PCBs at concentrations that are reached in the environment induce genotoxicity in granulosa cells.

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.

Estrogen Receptor-Independent Catechol Estrogen Binding Activity: Protein Binding Studies in Wild-Type, Estrogen Receptor-α KO, and Aromatase KO Mice Tissues†

Primary evidence for novel estrogen signaling pathways is based upon well-documented estrogenic responses not inhibited by estrogen receptor antagonists. In addition to 17beta-E2, the catechol estrogen 4-hydroxyestradiol (4OHE2) has been shown to elicit biological responses independent of classical estrogen receptors in estrogen receptor-alpha knockout (ERalphaKO) mice. Consequently, our research was designed to biochemically characterize the protein(s) that could be mediating the biological effects of catechol estrogens using enzymatically synthesized, radiolabeled 4-hydroxyestrone (4OHE1) and 4OHE2. Scatchard analyses identified a single class of high-affinity (K(d) approximately 1.6 nM), saturable cytosolic binding sites in several ERalphaKO estrogen-responsive tissues. Specific catechol estrogen binding was competitively inhibited by unlabeled catechol estrogens, but not by 17beta-E2 or the estrogen receptor antagonist ICI 182,780. Tissue distribution studies indicated significant binding differences both within and among various tissues in wild-type, ERalphaKO, and aromatase knockout female mice. Ligand metabolism experiments revealed extensive metabolism of labeled catechol estrogen, suggesting that catechol estrogen metabolites were responsible for the specific binding. Collectively, our data provide compelling evidence for the interaction of catechol estrogen metabolites with a novel binding protein that exhibits high affinity, specificity, and selective tissue distribution. The extensive biochemical characterization of this binding protein indicates that this protein may be a receptor, and thus may mediate ERalpha/beta-independent effects of catechol estrogens and their metabolites.

Catechol estrogen formation in liver microsomes from female ACI and Sprague-Dawley rats: comparison of 2- and 4-hydroxylation revisited

Estradiol (E(2))-hydroxylation was studied in liver microsomes from ACI and Sprague-Dawley female rats, which differ markedly in their susceptibility to E(2)-induced formation of mammary tumors. NADPH-dependent oxidation of E(2) by liver microsomes from ACI and Sprague-Dawley rats produced several metabolites of which 2-hydroxyestradiol (2-OH-E(2)), estrone (E(1)), and 2-hydroxyestrone (2-OH-E(1)) were predominant. Incubations with either low (9 nM) or high (50 microM) concentrations of radiolabeled E(2) and with varying amounts of microsomal protein indicated the formation of only small amounts of 4-hydroxyestradiol (4-OH-E(2)). The ratio of 2-OH-E(2) to 4-OH-E(2) formed with the low concentration of E(2) was about 10:1 regardless of the amount of microsomal protein used, and about 20:1 using a high concentration of E(2). Thus, oxidation of E(2) by liver microsomes from female ACI and Sprague-Dawley rats occurs primarily via 2-hydroxylation, and 4-hydroxylation is only a minor pathway. These results are in disagreement with a recent report indicating substantial 4-hydroxylation of E(2) by liver microsomes from female ACI rats.

Catechol-O-methyltransferase polymorphism and endometriosis

PURPOSE

Catechol-O-methyltransferase (COMT) inactivates the estradiol metabolites, 2-hydroxy and 4-hydroxy catechols, which have been implicated in the pathogenesis of endometriosis. A COMT valine to methionine polymorphism (G-to-A) in exon 4 of the COMT gene is polymorphic in the human population, with 25% of Caucasians being homozygous for the low-activity allele (COMT-L) of the enzyme. In a case-control study we investigated whether this COMT polymorphism is associated with endometriosis.

METHODS

Polymerase chain reaction was performed to analyze the COMT genotype among women with surgically and histologically confirmed endometriosis (study group; n = 91) and in women without evidence of endometriosis confirmed by laparoscopy or laparotomy (control group; n = 92).

RESULTS

Allele frequencies for the low-activity allele (COMT-L) among women with endometriosis and controls were 0.50 and 0.50, respectively (p = 0.999; odds ratio = 1.0, 95% CI: 0.66-1.51).

CONCLUSIONS

Our results suggest that the valine to methionine polymorphism in exon 4 of the COMT gene is not associated with the risk of endometriosis compared to a surgical control population.

Developmental, cellular, and molecular basis of human breast cancer

Breast cancer, which is the most common neoplastic disease in females and accounts for up to one third of all new cases of women's cancer in North America, continues to rise in incidence. In addition, the mortality caused by this disease has remained almost unchanged for the past 5 decades, becoming only second to lung cancer as a cause of cancer-related death. The failure in eradicating this disease is largely due to the lack of identification of a specific etiologic agent, the precise time of initiation, and the molecular mechanisms responsible for cancer initiation and progression. Despite the numerous uncertainties surrounding the origin of cancer, there is substantial evidence that breast cancer risk relates to endocrinologic and reproductive factors. The development of breast cancer strongly depends on the ovary and on endocrine conditions modulated by ovarian function, such as early menarche, late menopause, and parity. However, the specific hormone or hormone combinations responsible for cancer initiation have not been identified, and their role as protective or risk factors is still incompletely understood. A highly significant female hormone is estrogen, which is involved in the development of a variety of cancers, but it is still unclear whether estrogens are carcinogenic to the human breast. An understanding of whether estrogens cause mutations, and, if so, whether they act through hormonal effects activated by receptor binding, cytochrome P450-mediated metabolic activation, or compromise the DNA repair system, is essential for determining whether this steroid hormone is involved in the initiation or progression of breast cancer. This knowledge has to be based on a multidisciplinary approach encompassing studies of the development of the breast, influence of hormones on the differentiation of individual structures, and their interrelations in the pathogenesis of breast cancer. The analysis of the mechanisms involved would require confirmation in the adequate in vitro models and determination of the role played by genomic alterations in both cancer initiation and progression.

Role of DNA adducts in hormonal carcinogenesis

In this review, a mechanism of estrogen-induced cancer has been examined which features a dual role of estrogen as hormone and carcinogen. Evidence exists that estrogens are metabolically activated to 4-hydroxylated metabolites by a specific cytochrome P450 in tissues prone to estrogen-induced cancer. These metabolites and their semiquinone/quinone oxidation products may cause various types of DNA damage. Preliminary data also exist that estrogens induce various genetic mutations. Tumors may develop from cells carrying such mutations and responding to receptor-mediated proliferation signals.

Is estradiol a genotoxic mutagenic carcinogen?

The natural hormone 17 beta-estradiol (E2) induces tumors in various organs of rats, mice, and hamsters. In humans, slightly elevated circulating estrogen levels caused either by increased endogenous hormone production or by therapeutic doses of estrogen medications increase breast or uterine cancer risk. Several epigenetic mechanisms of tumor induction by this hormone have been proposed based on its lack of mutagenic activity in bacterial and mammalian cell test systems. More recent evidence supports a dual role of estrogen in carcinogenesis as a hormone stimulating cell proliferation and as a procarcinogen inducing genetic damage. Tumors may be initiated by metabolic conversion of E2 to 4-hydroxyestradiol catalyzed by a specific 4-hydroxylase (CYP1B1) and by further activation of this catechol to reactive semiquinone/quinone intermediates. Several types of direct and indirect free radical-mediated DNA damage are induced by E2, 4-hydroxyestradiol, or its corresponding quinone in cell-free systems, in cells in culture, and/or in vivo. E2 also induces various chromosomal and genetic lesions including aneuploidy, chromosomal aberrations, gene amplification, and microsatellite instability in cells in culture and/or in vivo and gene mutations in several cell test systems. These data suggest that E2 is a weak carcinogen and weak mutagen capable of inducing genetic lesions with low frequency. Tumors may develop by hormone receptor-mediated proliferation of such damaged cells.

Presence of uterine peroxidase activity in the rat early pregnancy

Peroxidase has been associated with estrogen action in the uterus. This enzyme plays an important role in the control of hydrogen peroxide levels and in catechol estrogen production. Since the uterus, during early pregnancy, is subjected to estrogen and progesterone regulation, we analyzed the changes of peroxidase activity in relation to receptivity and uterine early response to the embryo. Soluble and microsomal peroxidase activity were determined in the rat uterus during the estrus phase and early pregnancy (days 3 through 6). Soluble peroxidase activity increased significantly (p < 0.01) from day 3 (1.50 +/- 0.24) to day 4 (3.5 +/- 0.3) and 5 (5 +/- 0.5 U/mg protein, mean +/- S.D., n = 6) of pregnancy. During day 6, a significant decrease was noted in both the implantation site and the nonimplantation uterine tissue. Microsomal calcium-extractable peroxidase showed a similar pattern, with lower specific activity than, the soluble peroxidase. During estrus, the uterine tissue showed the highest activity of calcium-extracted peroxidase (8.7 +/- 1.35 U/mg protein), statistically greater when compared with days 3, 4, 5 and 6 of pregnancy. In conclusion, high peroxidase activity was associated with uterine receptivity. The decrease of activity on day 6 might be due to a progesterone-estrogen interaction, and consequently, hydrogen peroxide can be utilized for hydroxile production by means of the Fenton reaction. Lipoperoxidation may be necessary for changes in membrane fluidity for embryo attachment to endometrial epithelium.

Estrogen receptor null mice: what have we learned and where will they lead us?

All scientific investigations begin with distinct objectives: first is the hypothesis upon which studies are undertaken to disprove, and second is the overall aim of obtaining further information, from which future and more precise hypotheses may be drawn. Studies focusing on the generation and use of gene-targeted animal models also apply these goals and may be loosely categorized into sequential phases that become apparent as the use of the model progresses. Initial studies of knockout models often focus on the plausibility of the model based on prior knowledge and whether the generation of an animal lacking the particular gene will prove lethal or not. Upon the successful generation of a knockout, confirmatory studies are undertaken to corroborate previously established hypotheses of the function of the disrupted gene product. As these studies continue, observations of unpredicted phenotypes or, more likely, the lack of a phenotype that was expected based on models put forth from past investigations are noted. Often the surprising phenotype is due to the loss of a gene product that is downstream from the functions of the disrupted gene, whereas the lack of an expected phenotype may be due to compensatory roles filled by alternate mechanisms. As the descriptive studies of the knockout continue, use of the model is often shifted to the role as a unique research reagent, to be used in studies that 1) were not previously possible in a wild-type model; 2) aimed at finding related proteins or pathways whose existence or functions were previously masked; or 3) the subsequent effects of the gene disruption on related physiological and biochemical systems. The alpha ERKO mice continue to satisfy the confirmatory role of a knockout quite well. As summarized in Table 4, the phenotypes observed in the alpha ERKO due to estrogen insensitivity have definitively illustrated several roles that were previously believed to be dependent on functional ER alpha, including 1) the proliferative and differentiative actions critical to the function of the adult female reproductive tract and mammary gland; 2) as an obligatory component in growth factor signaling in the uterus and mammary gland; 3) as the principal steroid involved in negative regulation of gonadotropin gene transcription and LH levels in the hypothalamic-pituitary axis; 4) as a positive regulator of PR expression in several tissues; 5) in the positive regulation of PRL synthesis and secretion from the pituitary; 6) as a promotional factor in oncogene-induced mammary neoplasia; and 7) as a crucial component in the differentiation and activation of several behaviors in both the female and male. The list of unpredictable phenotypes in the alpha ERKO must begin with the observation that generation of an animal lacking a functional ER alpha gene was successful and produced animals of both sexes that exhibit a life span comparable to wild-type. The successful generation of beta ERKO mice suggests that this receptor is also not essential to survival and was most likely not a compensatory factor in the survival of the alpha ERKO. In support of this is our recent successful generation of double knockout, or alpha beta ERKO mice of both sexes. The precise defects in certain components of male reproduction, including the production of abnormal sperm and the loss of intromission and ejaculatory responses that were observed in the alpha ERKO, were quite surprising. In turn, certain estrogen pathways in the alpha ERKO female appear intact or unaffected, such as the ability of the uterus to successfully exhibit a progesterone-induced decidualization response, and the possible maintenance of an LH surge system in the hypothalamus. [ABSTRACT TRUNCATED]

Concentration dependence of prooxidant and antioxidant properties of catecholestrogens

Estradiol is an established antioxidant in vitro and in vivo. In contrast, prooxidant effects such as 8-hydroxylation of guanine bases of DNA have been induced by various estrogens in hamsters and by 4-hydroxyestradiol or -estrone and a microsomal activating system in vitro. As part of an examination of these conflicting reports, we studied the enhancement or inhibition of lipid peroxidation (conjugated diene formation monitored at 240 nm) by catecholestrogens in human low-density lipoprotein (LDL) incubated with cupric sulfate in phosphate buffer. Addition of 2- or 4-hydroxyestradiol, 2- or 4-methoxyestradiol, or estradiol or estriol (0.5-50 microM) increased lag times for diene formation by 30 to <300% over control values in the absence of estrogens (lag time, 1.6 h). In contrast, low concentrations (5 pM-100 nM) of catecholestrogens decreased lag times by about 40-50%, demonstrating their prooxidant activities. The prooxidant capabilities of catecholestrogens were examined by assaying the reduction by estrogens of Cu(II) to Cu(I) and of Fe(III) to Fe(II). Both 2- and 4-hydroxyestradiol and 2- and 4-methoxyestradiol reduced Cu(II) and Fe(III) ions to their lower oxidation state. In conclusion, the reduction of Cu(II) to Cu(I) by catecholestrogens is proposed to initiate lipid peroxidation and thus oxidation of LDL. In contrast, at high concentrations of catecholestrogens, the scavenging of oxygen radicals may predominate over lipid peroxidation and free radical generation by analogy to the action of similar phenolic antioxidants. With estradiol, estriol, and the methoxyestrogen metabolites, only antioxidant effects were observed.

Coordination of differential effects of primary estrogen and catecholestrogen on two distinct targets mediates embryo implantation in the mouse

In the mouse, estrogen is essential for blastocyst implantation in the progesterone (P4)-primed uterus. The mechanism(s) by which estrogen initiates this response still remains elusive. The present investigation, using delayed implantation in the mouse, examined the differential role of estradiol-17beta (E2) and its catechol metabolite 4-hydroxy-E2 (4-OH-E2) in uterine and blastocyst activation for implantation. The conditions of delayed implantation were induced by ovariectomizing mice on day 4 (day 1 = vaginal plug) of pregnancy or pseudopregnancy and maintaining them with P4 from days 5-7. The binding of EGF to blastocysts was used as a marker for blastocyst activation. Our results show that whereas E2 fails to activate dormant blastocysts (with respect to EGF binding in vitro), 4-OH-E2, cAMP, or prostaglandin E2, is effective in this response. Further, whereas 4-OH-E2 induced-activation is not blocked by an antiestrogen, an inhibitor of PG synthesis, adenylyl cyclase or protein kinase A effectively blocks this activation. These results suggest that 4-OH-E2 effects on blastocysts are mediated by PGs, which, in turn, stimulate cAMP production and thus activation of protein kinase A. Two-fluoro-E2 is a poor substrate and an inhibitor of catecholestrogen synthesis, but it is estrogenic, with respect to uterine growth and gene expression. Using blastocyst transfer experiments, we observed that dormant blastocysts incubated with 4-OH-E2 in vitro, but not with E2, are capable of implanting in P4-treated delayed implanting mice receiving two-fluoro-E2. The results suggest that whereas E2 is necessary for preparation of the uterus, uterine-derived catecholestrogen is important for blastocyst activation for implantation. Indeed, the receptive uterus has the capacity to synthesize 4-OH-E2. Collectively, we demonstrate that the primary ovarian estrogen E2, via its interaction with nuclear estrogen receptors, participates in the preparation of the P4-primed uterus to the receptive state in an endocrine manner, whereas its metabolite 4-OH-E2, produced from E2 in the uterus, mediates blastocyst activation for implantation in a paracrine manner. Our results also establish that these target-specific effects of primary estrogen and catecholestrogen are both essential for implantation and that successful implantation occurs only when the activated stage of the blastocyst coincides with the receptive state of the uterus.

Estrogen receptor mutations

The purpose of this paper is to review potential novel functional pathways by which estradiol and estrogenic compounds elicit biological responses in mammals. We will limit our approach to those novel functions suggested by phenotypes associated with estrogen receptor-alpha (ER alpha) gene mutations and polymorphisms. The study of these pathways has been greatly aided by the availability of ER alpha-minus mice, which lack classic biological responses to estradiol. In addition, the availability of an ER alpha-minus human family, aromatase-minus human families, and in the near future an aromatase-minus mouse model will allow correlations of novel phenotypes with the lack of active ER alpha protein. The ER alpha-minus mice can potentially be used to characterize in depth novel clinical phenotypes that link the functions of estrogens with sexual maturation, cardiovascular disease, osteoporosis, diabetes, and cancer.

Induction of monoamine oxidase B by 17 beta-estradiol in the hamster kidney preceding carcinogenesis

Estrogen-induced kidney tumorigenesis in the male Syrian hamster has been postulated to be mediated by free radicals generated by metabolic redox cycling of catecholestrogen intermediates. This tissue and other rodent tissues in which tumors develop in response to estrogen treatment have been shown to contain high levels of the catecholamine norepinephrine. In this study, we have thus examined the hypothesis that an additional source of free radicals may be hydrogen peroxide formed by the monoamine oxidase (MAO)-catalyzed deamination of catecholamines. We have studied the effect of 17beta-estradiol (25-mg pellet, sc) on MAO activity in the hamster kidney (a target organ) and in the hamster liver and the rat kidney and liver, organs which do not develop tumors under these conditions. 17beta-Estradiol treatment for 2 weeks significantly increased (P < 0.01) MAO activity in the hamster kidney (76.7 +/- 10.0 and 113.0 +/- 10.8% over controls for the substrates tyramine and kynuramine, respectively). MAO activity remained elevated after 4 weeks of 17beta-estradiol treatment. No significant changes were observed in the MAO activity of hamster liver or rat kidney and liver. The addition of Tamoxifen to 17beta-estradiol restored control levels of renal MAO activity. The use of selective MAO A and MAO B inhibitors (clorgyline and deprenyl, respectively) identified the B form as the major component of hamster kidney MAO activity and its hormonal regulation. In conclusion, the estrogen receptor-mediated activation of MAO in conjunction with high catecholamine concentrations in the hamster kidney as previously reported may significantly increase the production of hydrogen peroxide and hydroxyl radicals which are postulated to contribute to tumor initiation.

Estrogenic responses in estrogen receptor-alpha deficient mice reveal a distinct estrogen signaling pathway

Estrogens are thought to regulate female reproductive functions by altering gene transcription in target organs primarily via the nuclear estrogen receptor-alpha (ER-alpha). By using ER-alpha "knock-out" (ERKO) mice, we demonstrate herein that a catecholestrogen, 4-hydroxyestradiol-17beta (4-OH-E2), and an environmental estrogen, chlordecone (kepone), up-regulate the uterine expression of an estrogen-responsive gene, lactoferrin (LF), independent of ER-alpha. A primary estrogen, estradiol-17beta (E2), did not induce this LF response. An estrogen receptor antagonist, ICI-182,780, or E2 failed to inhibit uterine LF gene expression induced by 4-OH-E2 or kepone in ERKO mice, which suggests that this estrogen signaling pathway is independent of both ER-alpha and the recently cloned ER-beta. 4-OH-E2, but not E2, also stimulated increases in uterine water imbibition and macromolecule uptake in ovariectomized ERKO mice. The results strongly imply the presence of a distinct estrogen-signaling pathway in the mouse uterus that mediates the effects of both physiological and environmental estrogens. This estrogen response pathway will have profound implications for our understanding of the physiology and pathophysiology of female sex steroid hormone actions in target organs.

Synthesis and biological evaluation of 4-(hydroxyalkyl)estradiols and related compounds

A series of synthetic estrogens containing hydroxyalkyl side chains at the C-4 position of the A ring were designed as metabolically stable analogs of 4-hydroxyestradiol, a catechol estrogen. These synthetic steroids would facilitate investigations on the potential biological role of catechol estrogens and also enable further examination of the structural and electronic constraints on the A ring in the interaction of estrogens with the estrogen receptor. Catechol estrogens are implicated as possible causative agents in estrogen-induced tumorigenesis. 4-Hydroxyestradiol has weaker affinity for the estrogen receptor and exhibits lower estrogenic activity in vivo; on the other hand, the catechol estrogens are prone to further oxidative metabolism and can form reactive intermediates. This report describes the synthesis and initial biochemical evaluation of 4-(hydroxyalkyl)estrogens and 4-(aminoalkyl)estradiols. The 4-(hydroxyalkyl)estrogens were prepared by oxidative hydroboration of 4-alkenylestradiols. The alkenylestradiols were obtained via a Stille cross-coupling between a MOM-protected 4-bromoestradiol and an alkenylstannane. The (4-aminoalkyl)estrogens were prepared from the hydroxyalkyl derivatives with phthalimide under Mitsunobu conditions. The substituted estradiols were evaluated for estrogen receptor binding activity in MCF-7 human mammary carcinoma cells, and 4-(hydroxymethyl)estradiol 1 exhibited the highest affinity with an apparent EC50 value of 364 nM. The relative activities for mRNA induction of the pS2 gene in MCF-7 cell cultures by the 4-(hydroxyalkyl)estrogens closely parallel the relative binding affinities. 4-(Hydroxymethyl)estradiol 1 did not stimulate the growth of MCF-7 cells at concentrations up to 1 microM. Thus, 4-(hydroxymethyl)estradiol 1 exhibited similar estrogen receptor affinity as the catechol estrogen, 4-hydroxyestradiol, and may prove useful in the examination of the biological effects of 4-hydroxyestrogens.

Induction of cytochrome P450 1B1 and catechol estrogen metabolism in ACHN human renal adenocarcinoma cells

The catechol estrogen metabolites of 17beta-estradiol (E2), 2-hydroxyestradiol (OHE2) and 4-OHE2, differ in hormonal properties and carcinogenic potential. In Syrian hamster kidney, 4-OHE2 induces clear-cell carcinoma whereas 2-OHE2 does not, and an E2 4-hydroxylase appears to be involved in E2-induced carcinogenesis in these animals. Specific E2 4-hydroxylase activity has been observed in extrahepatic tissues from several species. In humans, cytochrome P450 1B1 (CYP1B1) appears to be an extrahepatic E2 4-hydroxylase under the regulatory control of the aromatic hydrocarbon receptor (AhR). As an initial approach to investigating CYP1B1 expression and E2 4-hydroxylase activity in human kidney, we used the ACHN cell line, derived from a human renal adenocarcinoma. In untreated ACHN cells, a very low level of CYP1B1 mRNA expression was observed and CYP1B1 protein could not be detected; however, in ACHN cells exposed to the high-affinity AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), CYP1B1 mRNA levels were elevated 28-fold, and the CYP1B1 protein was detected by immunoblot analysis. Exposure of ACHN cells to TCDD resulted in minimal induction of the CYP1A1 mRNA, and the CYP1A1 protein was not detectable prior to or after exposure to TCDD. E2 hydroxylase activity could not be detected with microsomes from untreated ACHN cells, although activities at C-4 and, to a lesser extent, at C-2 of E2 were observed with microsomes from TCDD-treated ACHN cells. In experiments with intact ACHN cells, elevated rates of formation of 4-methoxyestradiol (MeOE2) and 2-MeOE2 were observed in response to treatment with TCDD. The EC50 for induction of the CYP1B1 mRNA was 1.5 nM TCDD; EC50s for the stimulation of 2- and 4-MeOE2 formation were 0.68 and 1.1 nM TCDD. These results indicate that the ACHN cell line may be a useful in vitro model system to study the regulation of CYP1B1 expression and the cytotoxic effects associated with E2 4-hydroxylation.

17 beta-estradiol hydroxylation catalyzed by human cytochrome P450 1B1

The 4-hydroxy metabolite of 17 beta-estradiol (E2) has been implicated in the carcinogenicity of this hormone. Previous studies showed that aryl hydrocarbon-receptor agonists induced a cytochrome P450 that catalyzed the 4-hydroxylation of E2. This activity was associated with human P450 1B1. To determine the relationship of the human P450 1B1 gene product and E2 4-hydroxylation, the protein was expressed in Saccharomyces cerevisiae. Microsomes from the transformed yeast catalyzed the 4- and 2-hydroxylation of E2 with Km values of 0.71 and 0.78 microM and turnover numbers of 1.39 and 0.27 nmol product min-1.nmol P450-1, respectively. Treatment of MCF-7 human breast cancer cells with the aryl hydrocarbon-receptor ligand indolo[3,2-b]carbazole resulted in a concentration-dependent increase in P450 1B1 and P450 1A1 mRNA levels, and caused increased rates of 2-, 4-, 6 alpha-, and 15 alpha-hydroxylation of E2. At an E2 concentration of 10 nM, the increased rates of 2- and 4-hydroxylation were approximately equal, emphasizing the significance of the low Km P450 1B1-component of E2 metabolism. These studies demonstrate that human P450 1B1 is a catalytically efficient E2 4-hydroxylase that is likely to participate in endocrine regulation and the toxicity of estrogens.

Equine cytochrome P450 aromatase exhibits an estrogen 2-hydroxylase activity in vitro

Aromatase (estrogen synthetase) is a steroidogenic enzyme complex which catalyzes the conversion of androgens to estrogens (termed aromatization). This enzyme was purified from adult equine testis to homogeneity by five chromatographic steps. The ability of purified and reconstituted equine aromatase to exhibit an estrogen 2-hydroxylase activity was tested and compared to testosterone aromatization. Enzymatic activities were assessed by tritiated water release from labelled estradiol and testosterone. Kinetic analysis of estradiol 2-hydroxylation showed an apparent K(m) of 23 microM and a V(max) of 18 nmol/min/mg, whereas the values for testosterone aromatization were a K(m) of 15.7 nM and a V(max) of 34.6 pmol/min/mg. A specific antiserum raised against purified testicular equine P450arom and known to inhibit aromatase activity [1] was also found to inhibit the estrogen hydroxylase activity of equine placental microsomes in a dose-dependent manner with an IC50 value of 15 microl serum: 0.5 ml incubate. The estrogen hydroxylase activity was inhibited in a dose-dependent manner by two classes of aromatase inhibitors, i.e. steroidal-- (4-hydroxyandrostenedione and 7alpha-([4-aminophenyl]thio)-androst-4-ene-3, 17-dione)--and non-steroidal--(fadrozole and miconazole). The IC50 values were approximately 300 and 890 nM for 4-hydroxyandrostenedione and 7alpha-([4-aminophenyl]thio)-androst-4-ene-3, 17-dione, and 92 and 285 nM, for fadrozole and miconazole, respectively. Furthermore, 4-hydroxyandrostenedione caused a time-dependent inactivation of estrogen hydroxylase activity. We conclude that equine aromatase is able to use estradiol as a substrate, and converts it to catechol estradiol in vitro, possibly using the active site of aromatization. This is the first demonstration that equine aromatase functions as an estrogen 2-hydroxylase, in addition to transforming androgens into estrogen.

4-Hydroxylation of estrogens as marker of human mammary tumors

Estrogen is a known risk factor in human breast cancer. In rodent models, estradiol has been shown to induce tumors in those tissues in which this hormone is predominantly converted to the catechol metabolite 4-hydroxyestradiol by a specific 4-hydroxylase enzyme, whereas tumors fail to develop in organs in which 2-hydroxylation predominates. We have now found that microsomes prepared from human mammary adenocarcinoma and fibroadenoma predominantly catalyze the metabolic 4-hydroxylation of estradiol (ratios of 4-hydroxyestradiol/2-hydroxyestradiol formation in adenocarcinoma and fibroadenoma, 3.8 and 3.7, respectively). In contrast, microsomes from normal tissue obtained either from breast cancer patients or from reduction mammoplasty operations expressed comparable estradiol 2- and 4-hydroxylase activities (corresponding ratios, 1.3 and 0.7, respectively). An elevated ratio of 4-/2-hydroxyestradiol formation in neoplastic mammary tissue may therefore provide a useful marker of benign or malignant breast tumors and may indicate a mechanistic role of 4-hydroxyestradiol in tumor development.

4-Hydroxylation of estradiol by human uterine myometrium and myoma microsomes: implications for the mechanism of uterine tumorigenesis

Estradiol is converted to catechol estrogens via 2- and 4-hydroxylation by cytochrome P450 enzymes. 4-Hydroxyestradiol elicits biological activities distinct from estradiol, most notably an oxidant stress response induced by free radicals generated by metabolic redox cycling reactions. In this study, we have examined 2- and 4-hydroxylation of estradiol by microsomes of human uterine myometrium and of associated myomata. In all eight cases studied, estradiol 4-hydroxylation by myoma has been substantially elevated relative to surrounding myometrial tissue (minimum, 2-fold; mean, 5-fold). Estradiol 2-hydroxylation in myomata occurs at much lower rates than 4-hydroxylation (ratio of 4-hydroxyestradiol/2-hydroxyestradiol, 7.9 +/- 1.4) and does not significantly differ from rates in surrounding myometrial tissue. Rates of myometrial 2-hydroxylation of estradiol were also not significantly different from values in patients without myomata. We have used various inhibitors to establish that 4-hydroxylation is catalyzed by a completely different cytochrome P450 than 2-hydroxylation. In myoma, alpha-naphthoflavone and a set of ethynyl polycyclic hydrocarbon inhibitors (5 microM) each inhibited 4-hydroxylation more efficiently (up to 90%) than 2-hydroxylation (up to 40%), indicating > 10-fold differences in Ki (<0.5 microM vs. > 5 microM). These activities were clearly distinguished from the selective 2-hydroxylation of estradiol in placenta by aromatase reported previously (low Km, inhibition by Fadrozole hydrochloride or ICI D1033). 4-Hydroxylation was also selectively inhibited relative to 2-hydroxylation by antibodies raised against cytochrome P450 IB1 (rat) (53 vs. 17%). These data indicate that specific 4-hydroxylation of estradiol in human uterine tissues is catalyzed by a form(s) of cytochrome P450 related to P450 IB1, which contribute(s) little to 2-hydroxylation. This enzyme(s) is therefore a marker for uterine myomata and may play a role in the etiology of the tumor.

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on estrogen metabolism in MCF-7 breast cancer cells: evidence for induction of a novel 17 beta-estradiol 4-hydroxylase

Rates of microsomal 17 beta-estradiol (E2) hydroxylation at the C-2, -4, -6 alpha, and -15 alpha positions are each induced greater than 10-fold by treating MCF-7 breast cancer cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The TCDD-induced activities at the C-2, -6 alpha and -15 alpha positions have been attributed to cytochrome P450 1A1 (CYP1A1); however, the low Km 4-hydroxylase induced by TCDD appears to be a distinct enzyme. We report here that antibodies to cytochrome P450-EF (mouse CYP1B1) selectivity inhibited the C-4 hydroxylation of E2 catalyzed by microsomes from TCDD-treated MCF-7 cells. Western blots probed with anti-CYP1B antibodies showed the induction of a 52 kDa microsomal protein in response to treatment with TCDD in MCF-7 cells. Western blots of microsomes from HepG2 cells did not show the TCDD-induced 52 kDa protein, and microsomes from TCDD-treated HepG2 cells did not catalyze a low Km hydroxylation of E2 at C-4. Cellular metabolism experiments also showed induction of both the C-2 and -4 hydroxylation pathways in TCDD-treated MCF-7 cells as evidenced by elevated 2- and 4-methoxyestradiol (MeOE2) formation. In contrast, TCDD-treated HepG2 cells showed 2-MeOE2 formation predominantly over 4-MeOE2. Northern blots of RNA isolated from untreated and TCDD-treated cells, when probed with the human CYP1B1 cDNA, showed induction of a 5.2 kb RNA in MCF-7 cells but not in HepG2 cells in response to treatment with TCDD. These results provide additional evidence for the induction by TCDD of a novel E2 4-hydroxylase in MCF-7 cells but not in HepG2 cells and indicate possible endocrine regulatory roles for the newly discovered group of enzymes of the CYP1B subfamily.

Cell-type specific responses in prostaglandin secretion by glandular and stromal cells from pig endometrium treated with catecholestrogens, methoxyestrogens and progesterone

The pig conceptus and endometrium possess the ability to convert estrogens into catecholestrogens and catecholestrogens into methoxyestrogens. Experiments were carried out to evaluate the effect of catecholestrogens, methoxyestrogens and progesterone on the secretion of prostaglandin (PG) E and F2 alpha by porcine endometrial glandular and stromal cells in vitro. Both 2-hydroxyestradiol (2-OH-E2, 0-20 microM) and 4-hydroxyestradiol (4-OH-E2, 0-20 microM) increased (P less than .05) PGE and PGF2 alpha secretion by stromal cells in a dose response manner. Two-hydroxyestradiol tended (P less than .1) to decrease PGF2 alpha production by glandular cells. Two-methoxyestradiol (20 microM) suppressed (P less than .05) PGF2 alpha secretion by glandular and stromal cells. Four-methoxyestradiol (20 microM) stimulated (P less than .05) PGE production and PGE:PGF2 alpha ratio. Progesterone (.1 microM) suppressed (P less than .05) PG secretion in both cell types. We conclude that catecholestrogens, methoxyestrogens, and progesterone may participate in the establishment of pregnancy by modulating PG production in the endometrium.

Metabolism of [4-14C]estrone in hamster and rat hepatic and renal microsomes: species-, sex- and age-specific differences

The metabolism of [4-14C]estrone (E1) was examined in liver and kidney microsomes of adult castrated male and ovariectomized female hamsters and rats and in neonatal and immature hamster renal microsomes. In castrated male hamster liver microsomes, E1 was metabolized extensively to six major metabolites; 15 beta-hydroxyestrone, 7 alpha-hydroxyestrone, 6 alpha-hydroxyestrone, 6 beta-hydroxyestrone, 2-hydroxyestrone, and delta(9,11)-dehydroestrone, and a nonpolar fraction. Six minor metabolites of E1 were also detected. In contrast, kidney microsomes derived from castrated male hamsters metabolized E1 to mainly 17 beta-estradiol, 2- and 4-hydroxyestrone, 6 alpha-hydroxyestrone, 6 beta-hydroxyestrone and one monohydroxyestradiol metabolite. However, 16 alpha-hydroxyestrone was not detected. A variable, but low amount of estriol was also found. Interestingly, the quantity of 2-hydroxyestrone found in kidney microsomes of the hamster represented 26% of the total amount of metabolites formed, whereas in liver microsomes, only 9% of the overall metabolism resulted in the formation of 2-hydroxyestrone. The ability of kidney microsomes of female ovariectomized hamsters and two different rat strains to metabolize E1 was 5.9- and 9.4-fold lower, respectively, compared to renal microsomes of male castrated hamsters. The onset of oxidative metabolism in newborn hamster kidneys during development was also assessed. The results indicate that the oxidative metabolism of [14C]E1 in renal microsomes of newborn hamsters was 20-fold less than in kidney microsomes of adult hamsters. While catechol E1 metabolites were essentially negligible in hamster kidneys of these ages, it was evident that the conversion of E1 to estradiol via 17 beta-hydroxysteroid dehydrogenase resembles levels seen in the adult animals. Between the age of one and two months, the male hamster kidney exhibited the capacity to metabolize E1 at levels seen in fully mature adult hamsters.