Nordihydroguaiaretic Acid as a Novel Substrate and Inhibitor of Catechol O-Methyltransferase Modulates 4-Hydroxyestradiol-Induced Cyto- and Genotoxicity in MCF-7 Cells

Nordihydroguaiaretic acid (NDGA) is a major lignan metabolite found in Larrea spp., which are widely used in South America to treat various diseases. In breast tissue, estradiol is metabolized to the catechol estrogens such as 4-hydroxyestradiol (4-OHE₂), which have been proposed to be cancer initiators potentially involved in mammary carcinogenesis. Catechol-O-methyltransferase (COMT) catalyzes the O-methylation of catechol estrogens to their less toxic methoxy derivatives, such as 4-O-methylestradiol (4-MeOE₂). The present study investigated the novel biological activities of NDGA in relation to COMT and the effects of COMT inhibition by NDGA on 4-OHE₂-induced cyto- and genotoxicity in MCF-7 human breast cancer cells. Two methoxylated metabolites of NDGA, 3-O-methylNDGA (3-MNDGA) and 4-O-methyl NDGA (4-MNDGA), were identified in the reaction mixture containing human recombinant COMT, NDGA, and cofactors. K_m values for the COMT-catalyzed metabolism of NDGA were 2.6 µM and 2.2 µM for 3-MNDGA and 4-MNDGA, respectively. The COMT-catalyzed methylation of 4-OHE₂ was inhibited by NDGA at an IC₅₀ of 22.4 µM in a mixed-type mode of inhibition by double reciprocal plot analysis. Molecular docking studies predicted that NDGA would adopt a stable conformation at the COMT active site, mainly owing to the hydrogen bond network. NDGA is likely both a substrate for and an inhibitor of COMT. Comet and apurinic/apyrimidinic site quantitation assays, cell death, and apoptosis in MCF-7 cells showed that NDGA decreased COMT-mediated formation of 4-MeOE₂ and increased 4-OHE₂-induced DNA damage and cytotoxicity. Thus, NDGA has the potential to reduce COMT activity in mammary tissues and prevent the inactivation of mutagenic estradiol metabolites, thereby increasing catechol estrogen-induced genotoxicities.

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.

Catecholestradiol Activation of Adrenergic Receptors Induces Endometrial Cell Survival via p38 MAPK Signaling

CONTEXT

Enhanced levels of catecholestradiols, 2-hydroxyestradiol (2-OHE2) or 4-hydroxyestradiol (4-OHE2), are reported in endometriosis. During gestation, catecholestradiol activation of adrenergic receptors (AR) elevates estrogen receptor (ER)-independent proliferation of uterine arterial endothelial cells.

OBJECTIVE

To investigate β-AR-mediated catecholestradiol effects on human endometrial stromal cell (HESC) and epithelial cell survival in endometriosis.

DESIGN

β-AR immunostaining of eutopic and ectopic endometria (n = 9). Assays for cell viability, 5-bromo-2'-deoxyuridine proliferation, apoptosis, quantitative PCR, and estrogenicity (alkaline phosphatase activity), as well as siRNA β-AR silencing and immunoblot analyses of cultured HESCs or Ishikawa cells treated with control or 2-OHE2 or 4-OHE2 ±β-AR antagonist or ±p38 MAPK inhibitor.

SETTING

University research institution.

PATIENTS

Women with or without endometriosis.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

β-AR expression in eutopic vs ectopic endometria and regulation of HESC survival by 2-OHE2 and 4-OHE2.

RESULTS

Eutopic and ectopic endometrial stromal and epithelial cells displayed β2-AR immunoreactivity with increased staining in the functionalis vs basalis layer (P < 0.05). Both 2-OHE2 and 4-OHE2 enhanced HESC and Ishikawa cell survival (P < 0.05), an effect abrogated by β-AR antagonist propranolol, but not ER antagonist ICI182,780. 2-OHE2 or 4-OHE2 failed to induce cell survival and estrogenic activity in ADRB2-silenced HESCs and in Ishikawa cells, respectively. Although 2-OHE2 inhibited apoptosis and BAX mRNA expression, 4-OHE2 induced proliferation and decreased apoptosis (P < 0.05). Both catecholestradiols elevated phospho-p38 MAPK levels (P < 0.05), which was blocked by propranolol, and p38 MAPK inhibitor reversed catecholestradiol-enhanced HESC survival.

CONCLUSIONS

Catecholestradiols increase endometrial cell survival by an ER-independent β-AR-mediated p38 MAPK activation, suggesting that agents blocking β-AR (e.g., propranolol) or inhibiting 2-OHE2- or 4-OHE2-generating enzymes (i.e., CYP1A1/B1) could treat endometriosis.

The role of 17β-estradiol metabolites in chromium-induced oxidative stress

BACKGROUND

The increasing incidence of estrogen-dependent breast cancer and the presence in the environment of a large number of factors that interact with estrogen receptors have sparked interest in chemical influences on estrogen-dependent processes. In a previous work, the authors examined the interaction of estradiol with chromium. In the present article the importance of estradiol biotransformation in these interactions is investigated. There is no information in the available literature about the role of metabolites in exposure to chromium. It seems important because estradiol metabolites have various carcinogenic abilities and their formation during biotransformation could be increased or decreased by environmental enzyme inducers or inhibitors. The metabolites could play a detoxifying role or create a toxic synergism in free radical processes induced by chromium VI (CrVI).

OBJECTIVES

The aim of this study was to evaluate the influence of 2 17β-estradiol metabolites - 4-hydroxyestradiol (4-OHE2) and 16α-hydroxyestrone (16α-OHE1) - in conditions of oxidative stress caused by CrVI.

MATERIAL AND METHODS

Human blood, erythrocytes or mitochondria isolated from human placentas after natural deliveries were used in the experiments. The influence of CrVI, 4-OHE2 and 16-OHE1 on thiobarbituric acid reactive substances (TBARS), the hydroxyl radical (•OH), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione-S-transferase (GST), and the interactions of the metabolites exposed to chromium expressed by these factors were examined.

RESULTS

4-OHE2 reduced the level of TBARS induced by CrVI in mitochondria (p < 0.05) and in erythrocytes (p < 0.05), and increased SOD activity (p < 0.05). 16α-OHE1 increased the activity of GST in erythrocytes exposed to CrVI (p < 0.05).

CONCLUSIONS

The metabolites do not have toxic interactions with CrVI. On the contrary, they exhibited a protective effect. The mechanism of protection varied: 4-OHE2 decreased TBARS and increased SOD activity, while 16α-OHE1 increased GST activity.

4-hydroxy estrogen induces DNA damage on codon 130/131 of PTEN in endometrial carcinoma cells

Catechol estrogens, such as 4-hydroxyestradiol (4-OHE2), are estrogen metabolites that form DNA adducts and may induce mutations and subsequent cell transformation in mammary cells; however, little is known about their roles in endometrial carcinogenesis. Furthermore, it remains unclear whether 4-OHE2 is able to induce DNA damage on specific genes involved in carcinogenesis or a 'pro'-mutation status such as microsatellite instability (MSI). Therefore, we modified terminal transferase-dependent PCR by the application of a capillary sequencer to detect DNA damage at the single base level. Using this method, we demonstrated that 4-OHE2 directly induced DNA damage on codon 130/131 in exon 5 of PTEN, which is a mutation hot spot for PTEN in endometrial carcinoma. Whereas, both estradiol and 4-OHE2 treatment did not affect MSI status in immortalized endometrial glandular cells. 4-OHE2 might contribute to endometrial carcinogenesis by inducing PTEN mutation on codon 130/131.

Quercetin-3-O-glucronide inhibits noradrenaline binding to α2-adrenergic receptor, thus suppressing DNA damage induced by treatment with 4-hydroxyestradiol and noradrenaline in MCF-10A cells

Risk factors for breast cancer include estrogens such as 17β-estradiol (E2) and high stress levels. 4-Hydroxyestradiol (4-OHE2), a metabolite of E2 formed preferentially by cytochrome P450 1B1, is oxidized to E2-3,4-quinone, which reacts with DNA to form depurinating adducts that exert genotoxicity and carcinogenicity. Endogenous catecholamines such as adrenaline (A) and noradrenaline (NA) are released from the adrenal gland and sympathetic nervous system during exposure to stress. Here, we found that treatment with 4-OHE2 (3 μM) and NA (3 nM) significantly induced the phosphorylation of histone H2AX (γ-H2AX), one of the earliest indicators of DNA damage, and apurinic (AP) sites via the α2-adrenergic receptor (α2-AR) in human mammary epithelial MCF-10A cells. As an inverse association between a higher intake of flavonoids and breast cancer risk has previously been suggested from epidemiological studies, we investigated the effects of quercetin-3-O-glucuronide (Q3G), a circulating metabolite of quercetin in the blood, on 4-OHE2- and NA-induced γ-H2AX and AP sites. Q3G (0.1 μM) suppressed their induction and inhibited the binding of [(3)H]-NA to α2-AR. These results suggest that Q3G acts as an α2-AR antagonist and that it could be used as a chemopreventive agent for stress-promoted breast cancer.

Minocycline suppresses interleukine-6, its receptor system and signaling pathways and impairs migration, invasion and adhesion capacity of ovarian cancer cells: in vitro and in vivo studies

Interleukin (IL)-6 has been shown to be a major contributing factor in growth and progression of ovarian cancer. The cytokine exerts pro-tumorigenic activity through activation of several signaling pathways in particular signal transducer and activator of transcription (STAT3) and extracellular signal-regulated kinase (ERK)1/2. Hence, targeting IL-6 is becoming increasingly attractive as a treatment option in ovarian cancer. Here, we investigated the effects of minocycline on IL-6 and its signaling pathways in ovarian cancer. In vitro, minocycline was found to significantly suppress both constitutive and IL-1β or 4-hydroxyestradiol (4-OH-E2)-stimulated IL-6 expression in human ovarian cancer cells; OVCAR-3, SKOV-3 and CAOV-3. Moreover, minocycline down-regulated two major components of IL-6 receptor system (IL-6Rα and gp130) and blocked the activation of STAT3 and ERK1/2 pathways leading to suppression of the downstream product MCL-1. In female nude mice bearing intraperitoneal OVCAR-3 tumors, acute administration (4 and 24 h) of minocycline (30 mg/kg) led to suppression of IL-6. Even single dose of minocycline was effective at significantly lowering plasma and tumor IL-6 levels. In line with this, tumoral expression of p-STAT3, p-ERK1/2 and MCL-1 were decreased in minocycline-treated mice. Evaluation of the functional implication of minocycline on metastatic activity revealed the capacity of minocycline to inhibit cellular migration, invasion and adhesion associated with down-regulation of matrix metalloproteinases (MMP)-2 and 9. Thus, the data suggest a potential role for minocycline in suppressing IL-6 expression and activity. These effects may prove to be an important attribute to the upcoming clinical trials of minocycline in ovarian cancer.

Reactive oxygen species via redox signaling to PI3K/AKT pathway contribute to the malignant growth of 4-hydroxy estradiol-transformed mammary epithelial cells

The purpose of this study was to investigate the effects of 17-β-estradiol (E2)-induced reactive oxygen species (ROS) on the induction of mammary tumorigenesis. We found that ROS-induced by repeated exposures to 4-hydroxy-estradiol (4-OH-E2), a predominant catechol metabolite of E2, caused transformation of normal human mammary epithelial MCF-10A cells with malignant growth in nude mice. This was evident from inhibition of estrogen-induced breast tumor formation in the xenograft model by both overexpression of catalase as well as by co-treatment with Ebselen. To understand how 4-OH-E2 induces this malignant phenotype through ROS, we investigated the effects of 4-OH-E2 on redox-sensitive signal transduction pathways. During the malignant transformation process we observed that 4-OH-E2 treatment increased AKT phosphorylation through PI3K activation. The PI3K-mediated phosphorylation of AKT in 4-OH-E2-treated cells was inhibited by ROS modifiers as well as by silencing of AKT expression. RNA interference of AKT markedly inhibited 4-OH-E2-induced in vitro tumor formation. The expression of cell cycle genes, cdc2, PRC1 and PCNA and one of transcription factors that control the expression of these genes - nuclear respiratory factor-1 (NRF-1) was significantly up-regulated during the 4-OH-E2-mediated malignant transformation process. The increased expression of these genes was inhibited by ROS modifiers as well as by silencing of AKT expression. These results indicate that 4-OH-E2-induced cell transformation may be mediated, in part, through redox-sensitive AKT signal transduction pathways by up-regulating the expression of cell cycle genes cdc2, PRC1 and PCNA, and the transcription factor - NRF-1. In summary, our study has demonstrated that: (i) 4-OH-E2 is one of the main estrogen metabolites that induce mammary tumorigenesis and (ii) ROS-mediated signaling leading to the activation of PI3K/AKT pathway plays an important role in the generation of 4-OH-E2-induced malignant phenotype of breast epithelial cells. In conclusion, ROS are important signaling molecules in the development of estrogen-induced malignant breast lesions.

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.

Enhanced binding of circulating SLE autoantibodies to catecholestrogen-copper-modified DNA

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease characterized by circulating and tissue fixed autoantibodies reactive with self-antigens, including nucleic acid and other nuclear components. The pathways by which these autoantibodies act as a pathogenic factor remain elusive. Present study has investigated the role of estrogens in SLE etiopathogenesis. Estrogen-modified DNA [4-OHE(2)-Cu(II)-DNA] showed single- and double-strand breaks, hyperchromicity, decrease in Tm, and modification of bases. The 4-OHE(2)-Cu(II)-DNA exhibited increased binding with naturally occurring anti-DNA autoantibodies as compared to the unmodified native form (P < 0.001) as assessed by ELISA, quantitative precipitin titration, and gel retardation assay. The relative affinity of anti-DNA antibodies for modified and native DNA was in the order of 2.1 x 10(-7) M and 1.3 x 10(-6) M, respectively. The data suggested that DNA modified with 4-OHE(2) and Cu(II) may be one of the factors for the induction of circulating anti-DNA autoantibodies in SLE.

Contribution of alpha2-adrenoceptors to the mitogenic effect of catecholestrogen in human breast cancer MCF-7 cells

Catecholestrogens are estrogen metabolites formed by hydroxylation of 17beta-estradiol and estrone at either the C-2 or C-4 position, rivaling the parent estrogens in concentration. The objective of the present work was to assess if their catechol group could make them induce proliferation of human breast cancer cells via alpha(2)-adrenoceptors. In competition studies in human breast cancer MCF-7 cells, high concentrations of 2-hydroxy-estradiol (2-OH-E(2)), 2-hydroxy-estrone (2-OH-E(1)) and 4-hydroxy-estrone (4-OH-E(1)) competed for [(3)H]-rauwolscine binding, whereas 4-hydroxy-estradiol (4-OH-E(2)) did not. The contribution of alpha(2)-adrenoceptors and estrogen receptors (ERs) in proliferation enhancement was analyzed with specific antagonists. The specific alpha(2)-adrenergic antagonist yohimbine partially reversed the effect of catecholestrogens except 4-OH-E(2). The selective ER downregulator ICI-182780 or fulvestrant partially or totally reversed the effect of all hydroxylated catecholestrogens. When analyzing the effect of the combination of both antagonists in MCF-7, the contribution of the alpha(2)-adrenoceptors and ERs for 2-OH-E(2), 2-OH-E(1) and 4-OH-E(1) was mixed, whereas for 4-OH-E(2), the only receptor implied was an ER. In MDA-MB-231 cells (ER-alpha negative) the proliferation stimulation by these three catecholestrogens and reversal by the adrenergic antagonist was also observed. It can be concluded that alpha(2)-adrenoceptors contribute at least in part to the mitogenic effect of 2-OH-E(2), 2-OH-E(1) and 4-OH-E(1).

Biochemical and computational insights into the anti-aromatase activity of natural catechol estrogens

High levels of endogenous estrogens are associated with increased risks of breast cancer. Estrogen levels are mainly increased by the activity of the aromatase enzyme and reduced by oxidative/conjugative metabolic pathways. In this paper, we demonstrate for the first time that catechol estrogen metabolites are potent aromatase inhibitors, thus establishing a link between aromatase activity and the processes involved in estrogen metabolism. In particular, the anti-aromatase activity of a set of natural hydroxyl and methoxyl estrogen metabolites was investigated using biochemical methods and subsequently compared with the anti-aromatase potency of estradiol and two reference aromatase inhibitors. Catechol estrogens proved to be strong inhibitors with an anti-aromatase potency two orders of magnitude higher than estradiol. A competitive inhibition mechanism was found for the most potent molecule, 2-hydroxyestradiol (2-OHE(2)) and a rational model identifying the interaction determinants of the metabolites with the enzyme is proposed based on ab initio quantum-mechanical calculations. A strong relationship between activity and electrostatic properties was found for catechol estrogens. Moreover, our results suggest that natural catechol estrogens may be involved in the control mechanisms of estrogen production.

Ovarian P450 aromatase activity in the catfish Heteropneustes fossilis: seasonal changes and effects of catecholestrogens

Ovarian microsomal aromatase (P450arom) activity was studied in relation to season and incubation of follicles with catecholestrogens [(2-hydroxyestradiol-17beta (2-OHE2) and 2-methoxyestradiol-17 beta (2-methoxyE2)] using a product (estradiol-17 beta) assay. Peak P450arom activity was noticed in late preparatory phase (April) and it decreased significantly in pre-spawning, spawning and post-spawning phases to give the lowest value in resting phase. Apparent Km and Vmax of the enzyme varied significantly and the values were high in the preparatory (vitellogenic) phase (Km 74.62+/-1.73 nM, Vmax 0.81+/-0.01 pmol/mg protein/min) and low in the spawning (post-vitellogenic) phase (Km 62.01+/-1.68 nM, Vmax 0.69+/-0.002 pmol/mg protein/min). The incubation of the ovarian microsomes with 2-OHE2 elicited significant biphasic effects on enzyme activity. In the vitellogenic phase, concentrations of the steroid up to 1 microM inhibited enzyme activity significantly with the highest inhibition at 10nM. However, in the post-vitellogenic ovary, the highest inhibition was registered at 100 nM. The higher concentrations (10 microM or 100 microM) did not elicit any significant change compared to the control groups. A comparison of the aromatase inhibition index (AI50, indicates 50% inhibition of aromatase activity) of fadrozole, a known aromatase inhibitor and 2-OHE2 shows that the AI50 was 4.4 nM for fadrozole and 0.864 nM (vitellogenic phase) and 1.31 nM (post-vitellogenic phase) for 2-OHE2 indicating higher potency of the latter. The incubation of the ovarian microsomes with 2-methoxyE2 increased enzyme activity only at the higher concentrations (1-100 microM). The results show seasonality in the potential of the ovary to synthesize E2 and the potent enzyme inhibiting activity of 2-OHE2, which is reported for the first time.

Effect of catecholestrogen administration during adriamycin-induced cardiomyopathy in ovariectomized rat

The therapeutical beneficial effect of estrogen-derived metabolites or catecholestrogens is controversial. These molecules are produced during estrogen therapy based on 17-beta-estradiol treatment. The metabolization of 17-beta-estradiol is carried out in brain, kidney or liver, and triggers different products such as 2- and 4- hydroxyestradiol (2OH and 4OH). These products have shown antioxidant properties against oxidative stress (OS) in several experimental models. Different noxious side effects related to those metabolites have also been observed upon estrogen therapy. In this sense, catecholestrogens seem to be implicated in tumoral and mutagenic process after long treatment with estrogens substitutive therapy. In our study, we have verified that 2OH and 4OH have antioxidant and cardioprotective effects against adriamycin (AD)-induced cardiomyopathy in ovariectomized (OVX) rats. Catecholestrogens diminished the lipid peroxides and carbonyl protein (CO) content, and different enzymes related to cell injury (creatinine kinase, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase) in cardiac tissue from OVX-, AD-, and OVX+AD-treated rats. All these changes were correlated to a recovery on reduced glutathione (GSH), glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT) in heart tissue. The present study showed that 2OH and 4OH reduced all the parameters related to OS, antioxidant depletion and cardiac injury in OVX rats treated or not with AD.

Relative effects of estradiol-17beta (E2), catecholestrogens and clomiphene citrate on in vitro oocyte maturation in the catfish Heteropneustes fossilis (Bloch) and E2 inhibition of 2-hydroxyestradiol-induced maturation

In vitro effects of estradiol-17beta (E(2)), the catecholestrogens 2-hydroxyE(2) (2-OHE(2)) and 2-methoxyE(2), and the nonsteroidal antiestrogen clomiphene citrate (clomid) on oocyte maturation were investigated in the catfish Heteropneustes fossilis. Incubation of postvitellogenic follicles with 2-OHE(2) induced germinal vesicle breakdown (GVBD; 86% at 5 microM for 30 h) and progression of meiosis up to metaphase II, as evident from the presence of Hoechst stained metaphase chromosomes and anti-alpha-tubulin-positive bipolar spindles. The response was both concentration (1, 2.5, 5, 10, and 20 microM)- and duration (0, 3, 6, 12, 24, and 30 h)-dependent. The diameter of the follicles increased and about 20% follicles elicited ovulation. Incubation of the follicles with clomid (20 microM) induced only about 29-35% GVBD at 30 h. This might be due to the dual properties of clomid with estrogenic (cis-isomer) and antiestrogenic (trans-isomer) actions or due to estrogen receptor binding dynamics. Incubations of the follicles with E(2) or 2-methoxyE(2) did not induce oocyte maturation. The higher concentrations of 2-methoxyE(2) caused degenerative changes in the follicles. In competition studies, E(2) inhibited the GVBD response of 2-OHE(2) (5 microM) significantly in a concentration (1, 5, 10, and 20 microM) or duration (2, 4, and 6 h)-dependent manner after pre-incubation with 20 microM E(2) (P<0.001, one-way ANOVA, P<0.05, Newman-Keuls' test). The results show that 2-OHE(2) induces maturational activity while the parent estrogen is a strong inhibitor, alone or in combination with 2-OHE(2).

Estradiol and catecholestrogens protect against adriamycin-induced oxidative stress in erythrocytes of ovariectomized rats

The beneficial effect of estrogens and catecholestrogens against oxidative stress associated tissue injury has been observed in different experimental model. The administration of adriamycin (AD) has been shown to enhance oxidative stress in different tissues. The lack of estrogens during ovariectomy (OVX) also induces oxidative damage in several tissues. However, the antioxidant properties of estrogens and catecholestrogens administration have not been evaluated in erythrocytes and plasma from ovariectomized animals in presence or not of AD toxicity. We have assessed the antioxidant capacity of 17beta-estradiol (17beta) and catecholestrogens against oxidative stress in erythrocytes and plasma induced by OVX in control animals or AD-treated animals. We analyzed the level of lipid peroxides, carbonyl proteins and reduced glutathione (GSH) as well as glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities in plasma and erythrocytes. The results showed that AD, OVX and its combination increased lipid peroxides and carbonyl proteins, as well as reduced glutathione, superoxide dismutase and glutathione peroxidase activities in plasma and erythrocytes. The administration of 17beta and its metabolites (2- and 4-hydroxyestradiol) prevented all markers of oxidative stress induced by OVX in control and AD-treated animals. In conclusion, the administration of estrogens and cathecolestrogens counteract the oxidative stress in erythrocytes and plasma induced by OVX in presence or not toxic injury.

An aryl hydrocarbon receptor agonist amplifies the mitogenic actions of estradiol in granulosa cells: evidence of involvement of the cognate receptors

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that, besides mediating toxic responses, may have a central role in ovarian physiology. Studying the actions of AHR ligands on granulosa cells function, we have found that beta-naphthoflavone amplifies the comitogenic actions of FSH and 17beta-estradiol in a dose-dependent manner. This amplification was even greater in cells that overexpress the AHR and was reversed by cotreatment with the AHR antagonist alpha-naphthoflavone, suggesting that this effect is mediated by the AHR. The estrogen receptor is likewise implicated in this phenomenon, because a pure antiestrogen abolished the described synergism. However, the more traditional inhibitory AHR-estrogen receptor interaction was observed on the estrogen response element-driven transcriptional activity. On the other hand, alpha-naphthoflavone inhibited dose-dependently the mitogenic actions of FSH and 17beta-estradiol. Beta-naphthoflavone induced the expression of Cyp1a1 and Cyp1b1 transcripts, two well-characterized AHR-inducible genes that code for hydroxylases that metabolize estradiol to catecholestrogens. Nevertheless, the positive effect of beta-naphthoflavone on proliferation was not caused by increased metabolism of estradiol to catecholestrogens, because these compounds inhibited the hormonally stimulated DNA synthesis. This latter inhibition exerted by catecholestrogens suggests that these hydroxylases would play a regulatory point in granulosa cell proliferation. Our study indicates that AHR ligands modulate the proliferation of rat granulosa cells, and demonstrates for the first time that an agonist of this receptor is able to amplify the comitogenic action of classical hormones through a mechanism that might implicate a positive cross-talk between the AHR and the estrogen receptor pathways.

Phytochemicals Inhibit Catechol-O-Methyltransferase Activity in Cytosolic Fractions from Healthy Human Mammary Tissues: Implications for Catechol Estrogen-Induced DNA Damage

Phytochemicals are natural dietary constituents of fruits and vegetables. Some of these phytochemicals are known to affect estrogen-metabolizing enzymes. In breast tissue, estradiol can be metabolized to the catechol estrogens 2- and 4-hydroxyestradiol (2-OHE(2) and 4-OHE(2)). Catechol estrogens are suspected carcinogens potentially involved in the etiology of breast cancer. Catechol-O-methyltransferase (COMT) converts the catechol estrogens to their inactive methoxy derivatives (2-MeOE(2) and 4-MeOE(2)). In this study we investigated the effects of several phytochemicals on COMT activity in cytosolic fractions of seven healthy human mammary tissues from reduction mammoplasty. Large interindividual variations were observed in the constitutive levels of COMT activity. However, in all cytosol samples the catalytic efficiency of COMT was greater for 2-MeOE(2) formation than for 4-MeOE(2) formation. The known COMT inhibitor Ro 41-0960 and several phytochemicals with a catechol structure (quercetin, catechin, and (-)-epicatechin) concentration-dependently inhibited COMT activity, while phytochemicals without a catechol structure (genistein, chrysin, and flavone) showed no effect up to 30 microM. Distinct interindividual variations were observed in sensitivity toward COMT inhibition among the various tissue samples, as was shown by the range in IC(50) values for Ro 41-0960 (5-42 nM). The toxicological relevance of COMT inhibition and the effect of reduced inactivation of catechol estrogens was studied by determining the amount of catechol estrogen-induced DNA damage in MCF-7 cells using the comet assay. Catechol estrogens alone caused no increase of DNA damage compared with control treated cells. However, both Ro 41-0960 and quercetin caused a decrease of methoxy estradiol formation and an increase of catechol estrogen-induced DNA damage in MCF-7 cells. This suggests that phytochemicals with a catechol structure have the potential to reduce COMT activity in mammary tissues and may consequently reduce the inactivation of potentially mutagenic estradiol metabolites and increase the chance of DNA damage.

Cardiovascular Pharmacology of Estradiol Metabolites

A discussion of the role of endogenous estradiol metabolites in mediating important biological actions of estradiol is essentially nonexistent in standard textbooks of pharmacology and endocrinology. Indeed, the prevailing view is that all biological effects of estradiol are initiated by binding of estradiol per se to estrogen receptors and that estradiol metabolites are more or less irrelevant. This orthodox view, which is most likely incorrect, is the fundamental premise (an estrogen is an estrogen is an estrogen) underlying the design of important clinical trials such as the Heart and Estrogen/Progestin Replacement Study and the Women's Health Initiative Study. Accumulating data provide convincing evidence that some metabolites of estradiol, the major estrogen secreted by human ovaries, are biologically active and mediate multiple effects on the cardiovascular and renal systems that are largely independent of estrogen receptors. More specifically, metabolites of estradiol, particularly catecholestradiols and methoxyestradiols, induce multiple estrogen receptor-independent actions that protect the heart, blood vessels, and kidneys from disease. These protective effects are mediated in part by the inhibition of the ability of vascular smooth muscle cells, cardiac fibroblasts, and glomerular mesangial cells to migrate, proliferate, and secrete extracellular matrix proteins, as well as by an improvement in vascular endothelial cell function. The purpose of this review is to highlight the cardiovascular and renal pharmacology of catecholestradiols and methoxyestradiols. The take home message is simple: that when it comes to cardiovascular and renal protection, the concept that all estrogenic compounds are created equal may not be true.

In vitro effects of catecholamines and catecholestrogens on brain tyrosine hydroxylase activity and kinetics in the female catfish Heteropneustes fossilis

Effects of catecholamines and catecholestrogens on tyrosine hydroxylase (TH) activity and kinetics were investigated in the telencephalon and hypothalamus of female Heteropneustes fossilis in gonad quiescent (resting) and recrudescent (preparatory) phases. Dopamine, noradrenaline and adrenaline and the catecholestrogen, 2-hydroxyestradiol-17 beta inhibited TH activity in a concentration-dependent manner in both resting and preparatory phases, with a higher effect in the resting phase. Two- methoxyestradiol-17 beta did not alter TH activity in any season. The catecholamines inhibited TH in a competitive manner increasing apparent K(m) values significantly without altering the apparent V(max). Two-hydroxyestradiol-17 beta inhibited significantly the enzyme in a noncompetitive manner and decreased apparent V(max) without altering apparent K(m) values. The apparent K(i) is higher for dopamine than noradrenaline or adrenaline. The apparent K(i) for 2-hydroxyestradiol-17 beta is not significantly different from that of noradrenaline. The present results suggest an interaction between oestradiol-17beta (E2) and catecholamine metabolism at the level of tyrosine hydroxylation and E2 effects on catecholamines may be mediated through its 2-hydroxylation.

Protection by estrogens of biological damage by 2,2'-azobis(2-amidinopropane) dihydrochloride

We examined by using 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) as a radical generator the ability of estrogens to scavenge carbon-centered and peroxyl radicals. Electron spin resonance signals of carbon-centered radicals from AAPH were diminished by catecholestrogens but not by phenolic estrogens, showing that catecholestrogens efficiently scavenged carbon-centered radicals. However, fluorescent decomposition of R-phycoerythrin by AAPH-derived peroxyl radicals was inhibited by catecholestrogens and phenolic estrogens. Evidently, peroxyl radicals were scavenged by catecholestrogens and by phenolic estrogens. However, the scavenging ability of 4-hydroxyestradiol was less than 2-hydroxyestradiol. Strand break of DNA induced by AAPH was inhibited by catecholestrogens, but not by phenolic estrogens under aerobic and anaerobic conditions. Inactivation of lysozyme induced by AAPH was completely blocked by 2-hydroxyestradiol under aerobic and anaerobic conditions, and by 4-hyroxyestradiol only under anaerobic conditions. Peroxidation of arachidonic acid by AAPH was strongly inhibited by catecholestrogens at low concentrations. Only large amounts of phenolic estrogens markedly inhibited lipid peroxidation. These results show that catecholestrogens were antioxidant against AAPH-induced damage to biological molecules through scavenging both carbon-centered and peroxyl radicals, but phenolic estrogens partially inhibited AAPH-induced damage because they scavenged only peroxyl radicals.

Pro-oxidant and antioxidant potential of catecholestrogens against ferrylmyoglobin-induced oxidative stress

Ferryl heme proteins may play a major role in vivo under certain pathological conditions. Catecholestrogens, the estradiol-derived metabolites, can act either as antioxidants or pro-oxidants in iron-dependent systems. The aim of the present work was (1) to determine the effects of ferrylmyoglobin on hepatocyte cytotoxicity, and (2) to assess the pro/antioxidant potential of a series of estrogens (phenolic, catecholic and stilbene-derived) against ferrylmyoglobin induced lipid peroxidation in rat hepatocytes. Cells were exposed to metmyoglobin plus hydrogen peroxide to form ferrylmyoglobin in the presence of the transition metal chelator diethylentriaminepentaacetic acid. Results showed that ferrylmyoglobin induced an initial oxidative stress, mainly reflected in an early lipid peroxidation and further decrease in GSH and ATP. However, cells gradually adapted to this situation, by recovering the endogenous ATP and GSH levels at longer incubation times. Phenolic and stilbene-derived estrogens inhibited ferrylmyoglobin-induced lipid peroxidation to different degrees: diethylstilbestrol>estradiol>resveratrol. Catecholestrogens at concentrations higher than 1 microM also inhibited lipid peroxidation with similar efficacy. The ability of estrogens to reduce ferrylmyoglobin to metmyoglobin may account for their antioxidant activity. In contrast, physiological concentrations (100 pM-100 nM) of the catecholestrogens exerted pro-oxidant activities, 4-hydroxyestradiol being more potent than 2-hydroxyestradiol. The implications of these interactions should be considered in situations where local myoglobin or hemoglobin microbleeding takes place.

Inhibition of cellular enzymes by equine catechol estrogens in human breast cancer cells: specificity for glutathione S-transferase P1-1

Glutathione S-transferases (GSTs) are a family of detoxification isozymes that protect cells by conjugating GSH to a variety of toxic compounds, and they may also play a role in the regulation of both cellular proliferation and apoptosis. We have previously shown that human GST P1-1, which is the most widely distributed extrahepatic isozyme, could be inactivated by the catechol estrogen metabolite 4-hydroxyequilenin (4-OHEN) in vitro [Chang, M., Shin, Y. G., van Breemen, R. B., Blond, S. Y., and Bolton, J. L. (2001) Biochemistry 40, 4811-4820]. In the present study, we found that 4-OHEN and another catechol estrogen, 4,17beta-hydroxyequilenin (4,17beta-OHEN), significantly decreased GSH levels and the activity of GST within minutes in both estrogen receptor (ER) negative (MDA-MB-231) and ER positive (S30) human breast cancer cells. In addition, 4-OHEN caused significant decreases in GST activity in nontransformed human breast epithelial cells (MCF-10A) but not in the human hepatoma HepG2 cells, which lack GST P1-1. We also showed that GSH partially protected the inactivation of GST P1-1 by 4-OHEN in vitro, and depletion of cellular GSH enhanced the 4-OHEN-induced inhibition of GST activity. In addition, 4-OHEN GSH conjugates contributed about 27% of the inactivation of GST P1-1 by 4-OEHN in vitro. Our in vitro kinetic inhibition experiments with 4-OHEN showed that GST P1-1 had a lower K(i) value (20.8 microM) compared to glyceraldehyde-3-phosphate dehydrogenase (GAPDH, 52.4 microM), P450 reductase (PR, 77.4 microM), pyruvate kinase (PK, 159 microM), glutathione reductase (GR, 230 microM), superoxide dismutase (SOD, 448 microM), catalase (562 microM), GST M1-1 (620 microM), thioredoxin reductase (TR, 694 microM), and glutathione peroxidase (GPX, 1410 microM). In contrast to the significant inhibition of total GST activity in these human breast cancer cells, 4-OHEN only slightly inhibited the cellular GAPDH activity, and other cellular enzymes including PR, PK, GR, SOD, catalase, TR, and GPX were resistant to 4-OHEN-induced inhibition. These data suggest that GST P1-1 may be a preferred protein target for equine catechol estrogens in vivo.

Catechol estrogen metabolites and conjugates in different regions of the prostate of Noble rats treated with 4-hydroxyestradiol: implications for estrogen-induced initiation of prostate cancer

Prostate carcinomas arise in 100% of Noble rats treated with estradiol and testosterone. We hypothesize that estrogens initiate prostate cancer mainly by formation of 4-catechol estrogens (CE), followed by their oxidation to catechol estrogen-3,4-quinones (CE-3,4-Q), which can react with DNA. To avoid cancer initiation, CE can be detoxified by catechol-O-methyltransferase (COMT), and CE-3,4-Q by conjugation with glutathione (GSH) or by reduction to CE, catalyzed by quinone reductase and/or cytochrome P450 reductase. To investigate the prostatic metabolism of estrogens, Noble rats were treated with the CE 4-hydroxyestradiol (4-OHE2) or estradiol-3,4-quinone (E2-3,4-Q), and CE metabolites and conjugates were analyzed in the four regions of the prostate, which differ in susceptibility to carcinoma formation. Following treatment of rats with 4-OHE2 (6 micromol/100 g body weight in 200 microl of trioctanoin/dimethylsulfoxide (4:1) by intraperitoneal injection) for 90 min, the non-susceptible ventral (VP) and anterior (AP) prostate had higher levels of 4-methoxyCE and GSH conjugates than the susceptible dorsolateral prostate (DLP) and periurethral prostate (PUP). After treatment with the same molar amount of E2-3,4-Q, the VP and AP contained more GSH conjugates, 4-CE and 4-methoxyCE than the susceptible DLP and PUP. These results suggest that prostate areas susceptible to carcinoma induction have less protection by COMT, GSH, and quinone reductase and/or cytochrome P450 reductase, favoring reaction of CE-3,4-Q with DNA, presumably to initiate cancer.

Keratinocyte growth factor is up-regulated by estrogen in the porcine uterine endometrium and functions in trophectoderm cell proliferation and differentiation

Keratinocyte growth factor (KGF) is expressed by uterine endometrial epithelial cells during the estrous cycle and during pregnancy in pigs, whereas KGF receptor is expressed in conceptus trophectoderm and endometrial epithelia. In particular, KGF expression in the endometrium is highest on day 12 of pregnancy. This corresponds to the period of maternal recognition of pregnancy in pigs, which is signaled by large amounts of estrogen secreted by conceptus trophectoderm acting on the endometrium. Our hypothesis is that estrogens of conceptus origin stimulate endometrial epithelial KGF expression, and, in turn, secreted KGF stimulates proliferation and differentiation of conceptus trophectoderm. To determine the factors affecting KGF expression in the uterus, endometrial explants from gilts on day 9 of the estrous cycle were cultured in the presence of 17beta-estradiol, catechol estrogens, or progesterone. 17beta-Estradiol stimulated the expression of KGF (P < 0.05), whereas catechol estrogens had no effect (P > 0.05). Between days 9 and 15 of pregnancy, proliferating cell nuclear antigen was abundant in conceptuses, but was barely detectable in uterine endometrial epithelia. To determine the effects of KGF on conceptus trophectoderm, porcine trophectoderm (pTr) cells were treated with recombinant rat KGF (rKGF). rKGF increased the proliferation of pTr cells (P < 0.01) as measured by [(3)H]thymidine incorporation. rKGF elicited phosphorylation of KGF receptor and activated the mitogen-activated protein kinase (ERK1/2) cascade in pTr cells. pTr cell differentiation was affected by rKGF, because it increased expression of urokinase-type plasminogen activator, a marker for differentiation in pTr cells. Collectively, these results indicate that estrogen, the pregnancy recognition signal from the conceptus in pigs, increases uterine epithelial KGF expression, and, in turn, KGF stimulates the proliferation and differentiation of conceptus trophectoderm.

Catechol estrogens induce oxidative DNA damage and estradiol enhances cell proliferation

Estrogen-induced carcinogenesis involves enhanced cell proliferation (promotion) and genotoxic effects (initiation). To investigate the contribution of estrogens and their metabolites to tumor initiation, we examined DNA damage induced by estradiol and its metabolites, the catechol estrogens 2-hydroxyestradiol (2-OHE(2)) and 4-hydroxyestradiol (4-OHE(2)). In the presence of Cu(II), catechol estrogens formed piperidine-labile sites at thymine and cytosine residues in (32)P 5'-end-labeled DNA fragments and induced the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine. NADH markedly enhanced Cu(II)-dependent DNA damage mediated by nanomolar concentrations of catechol estrogens. Catalase and bathocuproine inhibited the DNA damage, suggesting the involvement of H(2)O(2) and Cu(I). These results suggest that H(2)O(2), generated during Cu(II)-catalyzed autoxidation of catechol estrogens, reacts with Cu(I) to form the Cu(I)-peroxide complex, leading to oxidative DNA damage, and that NADH enhanced DNA damage through the formation of redox cycle. To investigate the role of estrogens and their metabolites in tumor promotion, we examined their effects on proliferation of estrogen-dependent MCF-7 cells. Estradiol enhanced the proliferation of MCF-7 cells at much lower concentrations than catechol estrogens. These findings indicate that catechol estrogens play a role in tumor initiation through oxidative DNA damage, whereas estrogens themselves induce tumor promotion and/or progression by enhancing cell proliferation in estrogen-induced carcinogenesis.

Periovulatory changes in catfish ovarian oestradiol-17beta, oestrogen-2-hydroxylase and catechol-O-methyltransferase during GnRH analogue-induced ovulation and in vitro induction of oocyte maturation by catecholoestrogens

In the catfish Heteropneustes fossilis and Clarias batrachus, ovarian oestrogen-2-hydroxylase (OE-2-H) activity increased significantly at 8 h after the injection of an ovulatory dose (0.15 microg/g body weight) of a mammalian GnRH analogue ([d -Ala(6)-Pro(9)]-LHRH ethylamide) and was restored to the 0 h (control) level after egg-stripping at 16 h. On the other hand, ovarian oestradiol-17beta (OE2) level and catechol-O-methyltransferase (COMT) activity decreased significantly at 8 h. While the OE2 level was restored to the 0 h level, COMT activity increased significantly at 16 h. Changes in ovarian OE2 level and enzymes indicate higher synthesis of 2-hydroxylated catecholoestrogens and their degradation during the periovulatory period. Under in vitro conditions, the synthetic catecholoestrogens (CEs, 2- and 4-hydroxylated oestradiol17beta and oestrone (OE1)) induced germinal vesicle break down (GVBD) in a dose- (0.01-10 microg/ml) and duration- (1-36 h) dependent manner, the mean values of the responses being in the order 2-OH OE2>4-OH OE2> 2-OH OE1>4-OH OE1. The CE-induced GVBD response (8 h induction) was not blocked by prior and subsequent incubations with steroid synthesis inhibitors (cyanoketone, epostane and aminoglutethimide) up to 36 h, suggesting that de novo steroidogenesis is not essential for the response. The percentage of GVBD response to 2-h induction by CEs was significantly inhibited by actinomycin D (a transcriptional inhibitor) and cycloheximide (a translational inhibitor), indicating the involvement of both RNA and protein synthesis. The CE-induced 8-h stimulation of GVBD was mildly blocked by propranolol, the beta-adrenergic inhibitor, suggesting the response was partly mediated through a beta-adrenergic receptor mechanism. Incubations with phentolamine, an alpha-adrenergic inhibitor, did not interfere with the CE-induced GVBD response. The results demonstrate CE-related enzymatic changes in teleost (catfish) ovaries and maturation-inducing substance activity of CEs.

Thiols can either enhance or suppress DNA damage induction by catecholestrogens

The estrogen metabolites catecholestrogens (or hydroxyestrogens) are involved in carcinogenesis and the development of resistance to methotrexate. This induction of drug resistance correlates with the relative efficiency of catecholestrogens in the generation of reactive oxygen species (ROS) and the induction of DNA strand breaks. Although antioxidants can neutralize ROS, the generation of these reactive species by catecholestrogens can be enhanced by electron donors like NADH. Therefore, this study was undertaken to determine the ability of different thiol agents (GSH, NAC, DTT, DHLA) to either inhibit or enhance the level of DNA damage induced by the H(2)O(2) generating system 4-hydroxyestradiol/Cu(II). Our results show that GSH, DTT, and DHLA inhibited the induction of the 4-hydroxyestradiol/Cu(II)-mediated DNA damage, with GSH showing the best potential. In contrast, the GSH precursor NAC at low concentrations was able to enhance the level of oxidative damage, as observed with NADH. NAC can reduce Cu(II) to Cu(I) producing the radical NAC&z.rad;, which can generate the superoxide anion. However, the importance of this pathway appears to be relatively minor since the addition of NAC to the 4-hydroxyestradiol/Cu(II) system generates about 15 times more DNA strand breaks than NAC and Cu(II) alone. We suggest that NAC can perpetuate the redox cycle between the quinone and the semiquinone forms of the catecholestrogens, thereby enhancing the production of ROS. In conclusion, this study demonstrates the crucial importance of the choice of antioxidant as potential therapy against the negative biological effects of estrogens.

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

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 (2OH-E2 and 4OH-E2) and the non-catechol metabolite 6alpha-hydroxy-estradiol (6alpha-OH-E2) 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 (E2), estradiol valerate (E2V) and ethinylestradiol (EE2). In liver homogenates glutathione and lipid peroxides were determined, in microsomes NADPH-Fe++-stimulated lipid peroxidation (LPO), H2O2 generation and lucigenin (LUC) and luminol (LUM) amplified chemiluminescence (CL) were investigated. In liver 9000 x g supernatants monooxygenase activities were measured. The two catechol estrogens did not show any antioxidative activity, whereas 6alpha-OH-E2 significantly diminished lipid peroxides in the liver as well as LPO and LUM-CL in liver microsomes. Among estrogens, only EE2 showed antioxidative activity. Both CE inhibited ethoxycoumarin O-deethylation. Peroxidative activity as enhanced LUC-CL was found after 2OH-E2 (1 mg/kg b.wt.) and E2, but 10 times higher doses of both CE did not change LUC-CL. Microsomal H2O2 generation was enhanced by E2, E2V and both CE, not by 6alpha-OH-E2. The lower level of H2O2 enhancement caused by CE in comparison to E2 and E2V together with unchanged LUC-CL after high CE doses did not unequivocally prove the CE to be mainly responsible for the prooxidative activities of E2 and E2V in liver microsomes, at least in 30-day-old male rats. Unchanged GSH in the liver after CE administration supports this hypothesis.

Antioxidant activities of estrogens against aqueous and lipophilic radicals; differences between phenol and catechol estrogens

Natural estrogens have much greater radical-scavenging antioxidant activity than has previously been demonstrated, with activities up to 2.5 times those of vitamin C and vitamin E. The biological significance of this finding remains to be elucidated. In this work the antioxidant activity of a range of estrogens (phenolic, catecholic and stilbene-derived) has been studied. The activity of these substances as hydrogen-donating scavengers of free radicals in an aqueous solution has been determined by monitoring their relative abilities to quench the chromogenic radical cation 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS*+). The results show that the order of reactivity in scavenging this radical in the aqueous phase is dependent on the precise estrogenic structure, with phenolic estrogens being more potent antioxidants than catecholestrogens or diethylstilbestrol. The ability of the same estrogens to scavenge lipid phase radicals has also been assessed, determined by the ex vivo enhancement of the resistance of low-density lipoprotein (LDL) to oxidation; the order of efficacy is different from that in the aqueous phase, with the phenolic estrogens estriol, estrone and 17beta-estradiol being less potent than 2-hydroxyestradiol, 4-hydroxyestradiol, or diethylstilbestrol. In this lipid-based system, phenolic estrogens were found to be unable to regenerate alpha-tocopherol from LDL subjected to oxidative stress, while at the same time 2- and 4-hydroxyestradiol significantly delayed alpha-tocopherol loss. These results indicate that the various estrogens are good scavengers of free radicals generated in both the aqueous and the lipophilic phases. The antioxidant activity of an estrogen depends not only on the hydrophilic or lipophilic nature of the scavenged radical, but also on the phenol and catechol structures of the estrogen compound.

Molecular signaling in uterine receptivity for implantation

Successful implantation is the result of an intimate 'cross-talk' between the blastocyst and uterus in a temporal and cell-specific manner. Thus, both the uterine and embryonic events must be examined to better understand this process. Although various aspects and molecules associated with these events have been explored, a comprehensive understanding of the implantation process is still very limited. In this review, we have highlighted the importance of the blastocyst's activity state and the receptive state of the uterus in determining the 'window' of implantation. In this context, we provide a testable scheme that signifies the important roles of various key molecules in embryo-uterine interactions during implantation.

DNA damage induced by catecholestrogens in the presence of copper (II): generation of reactive oxygen species and enhancement by NADH

Certain estrogen metabolites are involved in carcinogenesis and the development of resistance to methotrexate (MTX). In this study, we determined whether these well-established biological effects correlate with the relative efficiency of several estrogen metabolites to induce DNA strand breaks in the presence of copper, and investigated the potential enhancing effect of reduced nicotinamide adenine dinucleotide (NADH). DNA strand breaks induced by estradiol metabolites were measured by the conversion of supercoiled phage phiX-174 RF1 DNA to open circular and linear forms. The most active catecholestrogens were the 4-hydroxy derivatives, which produced about 2.5 times more DNA double strand breaks than the 2-hydroxy derivatives, while estradiol and 16alpha-hydroxyestrone were inactive. In addition, our results show that 4-hydroxyestradiol (4-OHE2) at physiological concentrations was capable of exhibiting DNA cleaving activity. The formation of these catecholestrogen-induced DNA strand breaks was associated with the utilization of oxygen and the generation of H2O2, because catalase inhibited the DNA cleaving activity of 4-OHE2. Interestingly, we also observed that NADH enhanced the induction of DNA strands breaks by 4-OHE2/Cu(II), probably by perpetuating the redox cycle between the quinone and the semiquinone forms of the catecholestrogen. In conclusion, this study demonstrated that the relative efficiency of 2-, and 4-hydroxyestrogen in carcinogenesis and for the enhancement of MTX resistance correlates with their relative capability to induce DNA strand breaks. In order to inhibit these estrogen-mediated biological effects, it may be important to develop different strategies to block the production of reactive oxygen species by the catecholestrogen-redox cycle.

Antioxidant and prooxidant actions of estrogens: potential physiological and clinical implications

Oxidative stress and free radical-mediated cell death have been linked to diseases such as atherosclerosis, Alzheimer's disease, and cancer. Estrogens may promote, or offer protection against these conditions, by acting both as an antioxidant and prooxidant. Estrogens are converted to catecholestrogens via an oxidation step. Catecholestrogens are precursors of quinones that undergo a reversible oxidation-reduction reaction yielding semiquinones and reactive oxygen species. These semiquinones and reactive oxygen species may act as prooxidants and result in DNA and protein damage that may play a role in initiating tumor growth. Estrogen may also stimulate the peroxidase reaction, thereby promoting prooxidant reactions catalyzed by estrogen. Such reactions may be involved in enhancing the oxidizability of low-density lipoproteins (LDL). This mechanism of oxidation of LDL in plasma may actually lead to increased clearance of LDL by the liver and thereby contribute to estrogens' antiatherogenic action. On the other hand, participation of catecholestrogens in iron redox cycling may contribute to the antioxidant action of estrogens. This action might be important in sites such as the subendothelial space where estrogens are thought to inhibit LDL oxidation. Estrogens may also exert antioxidant effects by acting on genes with response elements for antioxidants. This may in turn inhibit expression of certain proteins involved in disease processes such as atherogenesis. Thus, by acting as an antioxidant and prooxidant, estrogen may produce both beneficial and adverse effects important in the prevention and pathogenesis of disease.

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.

Effect of 2-hydroxyoestradiol on insulin secretion in normal rat pancreatic islets

The possible action of 2-hydroxyoestradiol (2-OHE2) on glucose-induced insulin secretion was evaluated in pancreatic islets isolated from normal rats by collagenase digestion and incubated in KRB buffer. Insulin output in response to either 3.3 or 16.6 mM glucose was measured by radioimmunoassay in the absence or presence of different concentrations of 2-OHE2, norepinephrine (NE), or oestradiol. Islets were also incubated with 2-OHE2, NE, or oestradiol plus a fixed concentration (1 microM) of the alpha 2-adrenergic-receptor blocking agent yohimbine. The results showed that 2-OHE2, oestradiol and NE within a range of 0.1 to 20 microM inhibited glucose-induced insulin secretion in a dose-dependent manner: Ki (microM): 0.04 +/- 0.0001, 0.04 +/- 0.0002, and 0.01 +/- 9.1 E-6 respectively. This suppression was significantly reversed by yohimbine. Contrary to NE and 2-OHE2, oestradiol at lower concentrations (increasing within a range of 0.001 to 0.05 microM) in incubation medium in the same experimental conditions had a significant stimulatory effect on insulin secretion. Thus, it would appear that catecholoestrogens suppress islet insulin release via alpha 2-adrenergic receptors, which suggests that oestrogens may exert a dual modulatory effect on insulin secretion by enhancing release via direct interaction with the cytosolic-oestrogen receptor and inhibiting release after their local hydroxylation and the interaction of their new catechol moiety with alpha 2-adrenergic receptors. Our results suggest that these compounds may play a complementary role to CAs as negative modulators, and they also provide a broader scope for understanding the effect of oestrogens and/or their metabolites in the control of endocrine functions other than those related to reproduction.

Effects of estrogen agonists on amphetamine-stimulated striatal dopamine release

Based upon the observation that estrogen acts in the striatum to rapidly modulate dopamine (DA) neural transmission and DA-mediated behaviors, it has been postulated that these effects of estrogen are mediated by a specific, membrane-bound receptor mechanism. To further characterize the pharmacological specificity of the estrogen binding site, the present experiments examine effects of various estrogen agonists on amphetamine (AMPH)-induced DA release from striatal tissue of ovariectomized female rats, using a superfusion method. Catechol estrogens 4-, and 2-hydroxyestradiol, but not 2-methoxyestradiol, significantly enhance AMPH-induced striatal DA release. Estrogen metabolites, estrone and estriol, and the non-steroidal estrogen analog, diethylstilbestrol, are without effects. Estradiol conjugated to bovine serum albumin (BSA) mimics the effect of estradiol to enhance stimulated striatal DA release. These results indicate that the steroidal configuration and hydroxylation on the A-ring of estrogenic compounds may be important determinants of ligand binding to the putative estrogen binding site in the striatum. Furthermore, the effectiveness of the estradiol conjugated to BSA reinforces the idea of an external membrane-bound receptor binding site in the striatum.

Differential effects of estrogen metabolites on bone and reproductive tissues of ovariectomized rats

The effects of 17 beta-estradiol and the important estrogen metabolites, 2-hydroxyestrone (2-OHE1) and 16 alpha-hydroxyestrone (16 alpha-OHE1) on bone, mammary gland, and uterine histology, and on blood cholesterol were investigated in ovariectomized growing rats. Rats were treated with 200 micrograms/kg of body weight/day of each of the test compounds for 3 weeks. Ovariectomy resulted in uterine and mammary gland atrophy, increased body weight, bone turnover and tibia growth, and hypercholesterolemia. 17 beta-estradiol treatment prevented these changes, with the exception that this high dose of estrogen did not prevent hypercholesterolemia. 2-OHE1 had no effect on any of the measurements. 16 alpha-OHE1 resulted in bone measurements that did not differ from the 17 beta-estradiol-treated rats and prevented the increase in serum cholesterol. In contrast, 16 alpha-OHE1 resulted in increases in uterine weight, uterine epithelial cell height, and mammary gland cell proliferation that were significantly less than the 17 beta-estradiol treatment. These findings demonstrate that 16 alpha-hydroxylation of estrone results in tissue-selective estrogen agonistic activity, whereas 2-hydroxylation resulted in no measured activity. Furthermore, they suggest that factors that modulate the synthesis of these metabolites could selectively influence estrogen target tissues.

Female hormones act as natural antioxidants--a survey of our research

The increase in the lipid peroxide level in the serum and liver of female mice after bilateral ovariectomy evidenced antioxidant activities of female hormones. This increase was abolished upon administration of female hormones. Similar increase in the level of lipid peroxide was observed in the serum of women who had undergone bilateral ovariectomy. Injection of 2-hydroxyestradiol suppressed the increase in the lipid peroxide level in the liver of rats receiving whole-body gamma-ray irradiation. Considering that the mechanism of coronary atherosclerosis is ascribed at least in part to the increased level of lipid peroxides, estrogen therapy could be applied to women who had undergone bilateral ovariectomy prior to menopause or to normal women after menopause. 2-Hydroxyestradiol might be applied also to men.

Synergistic induction of DNA strand breakage by catechol-estrogen and nitric oxide: implications for hormonal carcinogenesis

Estrogen is a known risk factor for human breast cancer, although the mechanism by which estrogens induce cancer remains unestablished. We have demonstrated that DNA strand breakage is induced synergistically when pBR322 plasmid DNA is incubated in the presence of both a nitric oxide (NO)-releasing compound (diethylamine NONOate, etc.) and a catechol-estrogen (2- or 4-hydroxyestradiol or -hydroxyestrone). Either the NO-releasing compound or the catechol-estrogen alone induced much fewer strand breaks. Estradiol, estrone, O-methylated catechol-estrogens, and diethylstilbestrol did not exert such DNA damaging effects. Strand breakage induced by NO plus 2- or 4-hydroxyestradiol was inhibited by carboxy-PTIO (an NO-trapping agent) and, to a lesser extent, by superoxide dismutase. Antioxidants (e.g., N-acetylcysteine, ascorbate), but not HO. scavengers, exhibited inhibitory effects. A possible mechanism for this strand breakage would be: (1) NO mediates conversion of catechol-estrogens to quinones, (2) the quinone/hydroquinone redox system produces O2.-, and (3) O2.- reacts with NO to form peroxynitrite, which causes DNA strand breaks. Our results imply that interaction of catechol-estrogens and NO, both known to be formed in human breast and uterus, leads to production of a potent oxidant(s), which could cause damage in cells and DNA, thus playing an important role in hormonal carcinogenesis.

Catechol estrogens as inhibitors of leukotriene synthesis

Estrogens have a beneficial effect on atherosclerosis and osteoporosis after menopause, but their exact mechanism of action is still unknown. The aim of the present study was to investigate the effects of estradiol and its metabolites catechol estrogens on arachidonic acid metabolism in vitro. Estradiol had no effect on arachidonic acid metabolism up to 33 microM in A23187-stimulated human whole blood. All catechol estrogens (2-hydroxyestradiol, 2-hydroxyestrone, 4-hydroxyestradiol and 4-hydroxyestrone) had similar kinds of actions on arachidonic acid metabolism, being over ten times more potent inhibitors of leukotriene synthesis (IC50 values 0.044-0.16 microM) than thromboxane (IC50 values 0.99-2.1 microM) and prostaglandin E2 synthesis (IC50 values 0.84-5.5 microM). It is suggested that some of the protective actions of estrogens--e.g., on atherosclerosis and osteoporosis--may be related to the inhibition of leukotriene synthesis by catechol estrogens.

17Beta-estradiol, its metabolites, and progesterone inhibit cardiac fibroblast growth

Postmenopausal women (PMW) have increased incidence of cardiovascular disease, and estrogen substitution therapy has been shown to have cardioprotective effects. Since abnormal growth of cardiac fibroblasts (CFs) is associated with hypertension and myocardial infarction and estrogen inhibits vascular smooth muscle cell (SMC) growth, it is feasible that estrogen may attenuate cardiac remodeling by inhibiting CF growth, and this possibility was investigated by using cultured CFs. 17Beta-estradiol and progesterone, but not 17alpha-estradiol, estrone, or estriol, inhibited 2.5% FCS-induced proliferation (DNA synthesis and cell number) and collagen synthesis (3H-proline incorporation) in a concentration-dependent manner and to a similar extent in male and female CFs. Compared to 17beta-estradiol, its metabolites 2-hydroxyestradiol and 2-methoxyestradiol were more potent in inhibiting FCS-induced DNA synthesis, collagen synthesis, and cell proliferation. The inhibitory effects of 17beta-estradiol and its metabolites were enhanced in presence of progesterone and 4-hydroxytamoxifen (high-affinity estrogen receptor ligand). Moreover, like estrogens, the dietary phytoestrogens biochanin A and daidzein inhibited FCS-induced growth of CFs. In conclusion, 17beta-estradiol, its metabolites, and progesterone inhibit CF growth in a gender-independent fashion. Moreover, hormone replacement therapy using 17beta-estradiol and progesterone may protect PMW against cardiovascular disease by inhibiting CF growth and cardiac remodeling; whereas estrogens that do not inhibit CF growth may be less effective in protecting PMW against cardiovascular disease. Finally, our studies provide evidence that phytoestrogens inhibit CF growth and may be clinically useful as a substitute for feminizing estrogens in preventing cardiovascular disease in both women and men.

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.

A direct dopaminergic control of aromatase activity in the quail preoptic area

In the quail preoptic area (POA) anatomical and pharmacological data suggest that catecholamines may be implicated in the control of testosterone (T) aromatization into estrogens. The biochemical mechanism(s) mediating this control of the enzyme activity is (are) however unexplored. The present studies were carried out to investigate whether the catecholamines, dopamine (DA) and norepinephrine (NE) are able to directly affect aromatase activity (AA) measured during in vitro incubations of POA homogenates. AA was quantified in the POA-hypothalamus of adult male Japanese quail by measuring the tritiated water production from [1beta-3H]-androstenedione. Enzyme activity was linear as a function of the incubation time and of the protein content of homogenates. It exhibited a typical Michaelis-Menten kinetics, with an apparent Km of 2.8 nM and a Vmax of 266.6 fmol h(-1) mg wet weight(-1). AA was then measured at a substrate concentration of 25 nM in the presence of catecholamines and some of their receptor agonists or antagonists, at two concentrations, 10(-3) and 10(-6) M. Norepinephrine and prazosin (alpha1-adrenergic antagonist) had no or very limited effects on AA at both concentrations. In contrast, DA and some D1 and/or D2 receptor agonists (apomorphine[D1/D2], SKF-38393 [D1] and RU-24213 [D2]) depressed AA by 40 to 70% at the 10(-3) M concentration. One D2 receptor antagonist also produced a major inhibition of AA (sulpiride) while other antagonists either had no significant effect or only produced moderate decreases in enzyme activity (SCH-23390 [D1], spiperone [D2], pimozide [D2]) as did two DA indirect agonists, amfonelic acid and nomifensine. The inhibitory effect of the agonists was not antagonized by the less active antagonists, SCH-23390 [D1] or spiperone [D2]. Taken together these results suggest that the inhibitory effects do not involve specific binding of DA or its agonists/antagonists to dopaminergic receptors mediating changes in cAMP concentration. This conclusion is also supported by the observation that addition of dibutyryl cAMP did not change brain AA. It appears more likely that DA and dopaminergic drugs inhibit AA by a direct effect on the enzyme, as suggested by the competitive nature of DA and SKF-38393 inhibition of AA (Ki's of 59 and 84 microM, respectively). The functional significance of this effect should still be demonstrated but this mechanism may represent an important physiological pathway through which neurotransmitters could rapidly affect steroid-dependent processes such as the neural synthesis of estrogens. This would provide a mean by which environmental stimuli could affect reproductive behavior and physiology.

Effect of estradiol metabolites on the susceptibility of low density lipoprotein to oxidation

The main estradiol metabolites 2-hydroxyestrone, 2-methoxyestrone and 16alpha-hydroxyestrone were investigated in vitro for the susceptibility of low density lipoprotein to oxidation and the effects compared with those of estradiol and vitamin E. 2-hydroxyestrone and 2-methoxyestrone had a greater inhibitory effect than estradiol and vitamin E whereas 16alpha-hydroxyestrone approximates the inhibition of estradiol. These results indicate that 2-hydroxyestrone and 2-methoxyestrone possess non-genomic actions which may play a role in the lipid metabolism.

Induction of granulocytic differentiation in myeloblasts by 17-beta-estradiol involves the leukotriene D4 receptor

17-beta-Estradiol (beta E) causes granulocytic differentiation and neutrophilia in mice. However, the presence of estrogen receptors in myeloblasts and granulocytic progenitor cells has not been reported. beta E can be converted to a bioreactive species, estradiolquinone. We have previously shown that hydroquinone (HQ), via conversion to bioreactive p-benzoquinone (BQ), causes neutrophilia in mice and induces granulocytic differentiation in myeloblasts through interaction with the leukotriene D4 (LTD4) receptor. Therefore, we tested whether beta E could be oxidized by a myeloperoxidase-mediated reaction to a bioreactive intermediate, which might, in turn, induce granulocytic differentiation in mouse myeloblasts by activating the LTD4 receptor, thus obviating the need for LTD4, the downstream intracellular mediator of granulocyte colony-stimulating factor (G-CSF)-induced signal transduction. The interleukin (IL)-3-dependent, G-CSF-inducible normal mouse myeloblastic cell line, 32D cl 3(G), was used to determine the ability of beta E to induce terminal granulocytic differentiation in myeloblasts. Morphological analysis of stage-specific granulocytic differentiation indicated that beta E was capable of the concentration- (10(-8)-10(-4)M) and time-(6d) dependent induction of a complete program of terminal granulocytic differentiation in myeloblasts similar to that seen with G-CSF or LTD4. beta E-induced granulocytic differentiation was prevented by the peroxidase inhibitor, indomethacin, and was completely and competitively inhibited in the presence of a specific LTD4 receptor antagonist, MK-571, suggesting that a bioreactive form of estradiol, such as estradiolquinone, is interacting with the receptor. beta E was shown to cause a similar concentration-dependent induction of granulocytic differentiation in human HL-60 myeloblasts that was also inhibited by the receptor antagonist. Biological effects of beta E in nontarget tissues may result from the interaction of bioreactive estradiolquinone with critical cellular macromolecules involved in normal cellular signaling pathways.

Microsome-mediated 8-hydroxylation of guanine bases of DNA by steroid estrogens: correlation of DNA damage by free radicals with metabolic activation to quinones

Free radical generation by metabolic redox cycling between catechol estrogens and their quinones and subsequent hydroxyl radical damage to DNA have been proposed to mediate estrogen-induced renal carcinogenesis in the hamster. In this study the content of 8-hydroxy-2'-deoxy-guanosine (8-OHdG), a marker product of hydroxyl radical action, was examined in DNA incubated with a liver microsomal activating system and with catechol estrogens, equilenin-3,4-quinone or with parent estrogens. Equilenin-3,4-quinone increased the formation of 8-OHdG by 50% over control levels. 4-Hydroxyestrone and 4-hydroxy-estradiol raised 8-OHdG contents significantly, to 1.61 +/- 0.79 and 1.27 +/- 0.31 8-OHdG/10(5) deoxyguanosine (dG) respectively over controls (0.68 +/- 0.25 8-OHdG/10(5) dG). The corresponding 2-hydroxylated estrogens and the parent hormones estrone, estradiol and equilenin did not affect 8-hydroxylation of guanine bases of DNA. In incubations of catechol estrogens with microsomes and cumene hydroperoxide the 4-hydroxyestrogens were oxidized to quinones more rapidly than the 2-hydroxyestrogens. Our data support a mechanism of hydroxyl radical generation from estrogens by redox cycling between 4-hydroxylated metabolites and their quinones. The rapid oxidation of 4-hydroxylated estrogens to quinones, their redox cycling and hydroxyl radical damage to DNA is consistent with the previously reported carcinogenic activities of 4-hydroxylated, but not of 2-hydroxylated, catechol estrogens.

Sex and gonadal activity modify the effect of 2-hydroxyestradiol on hypothalamic GABA uptake in the rat

The aim of this study was to determine the changes induced by sex and sexual steroids on the effect of the catecholestrogen 2-hydroxyestradiol (2OHE2) upon hypothalamic GABA uptake. For this purpose we have measured [3H]-GABA uptake by crude synaptosomal fractions obtained from normal female and male rats and from ovariectomized and virilized female rats in the presence or absence of increasing concentrations (0.1 to 100 microM) of 20HE2. The results presented in this paper demonstrate that the effect of the catecholestrogen varied according to sex: it potentiated the specific [3H]-GABA uptake in female rats, whereas it clearly inhibited the uptake in male and virilized rats. The enhancing effect of the catecholestrogen was not affected by ovariectomy, but a higher specific GABA uptake was observed in the ovariectomized animals. The present study provides the first evidence that the effect of 2OHE2 on hypothalamic GABA uptake depends on sex, thus suggesting the existence of a sexual dimorphism. Further studies in this field are required to elucidate the physiological significance and the underlying mechanism of the mentioned effect.

Effect of catecholestrogens on [3H]-GABA uptake by hypothalamic crude synaptosomes

Catecholestrogens (CE), 2-hydroxyestradiol, 2-hydroxyestrone and primary estrogens, estradiol and estrone were tested in their ability to compete for the high affinity uptake of [3H]-GABA into crude synaptosomal fractions. Aliquots of the crude synaptosomal fraction obtained from normal rats were incubated for 10 min at 37 degrees C with [3H]-GABA in the presence, or absence, of estrogens and catecholestrogens. Neither estradiol nor estrone modified the specific [3H]-GABA uptake into crude synaptosomal fractions. On the contrary, CE significantly affected the specific [3H]-GABA uptake in a dose-dependent manner: low concentrations of CE enhanced the uptake; this effect disappeared with high concentrations of the compounds. The stimulatory effect of CE on [3H]-GABA uptake was blocked when samples were coincubated with nipecotic acid, thus suggesting that this effect is specific rather than the result of non-specific interactions of CE with the hypothalamic membrane.

On the inhibitory effect of C17-sulfoconjugated catechol estrogens upon lipid peroxidation of rat liver microsomes

The antioxidant effect of C17-sulfoconjugated catechol estrogens was examined under ascorbic acid- or NADPH-dependent lipid peroxidation in rat liver microsomes and compared with that of various estrogens and alpha-tocopherol. Among the estrogens tested, a free catechol estrogen such as 4-hydroxyestradiol showed the strongest effect, followed by 2-hydroxyestradiol, 2-methoxyestradiol and estradiol. Next to these steroids, 2-hydroxyestradiol 17-sulfate, followed by 4-methoxyestradiol, 4-hydroxyestradiol 17-sulfate and estrone also showed a strong inhibitory effect, which was greater than that of alpha-tocopherol. Among the C17-sulfates, the guaiacols (2- and 4-methoxyestradiol 17-sulfate) showed a slightly lower effect than alpha-tocopherol, but estradiol 17-sulfate had almost no effect. The antioxidant activity observed in phenolic or guaiacol steroids was considered to be attributed to the catechols produced by their 2- (or 4-)hydroxylation or their O-demethylation, respectively, during the incubation. This was confirmed by identification of the catechols produced from phenolic or guaiacol estrogens and even from the estrogen C3-sulfates. The mechanism of the inhibition by catechols on lipid peroxidation was speculated to involve their activity as radical scavengers, because of their strong reducing activity for 1,1-diphenyl-2-picrylhydrazyl. The above results suggest that C17-sulfoconjugated catechol estrogens (2- and 4-hydroxyestradiol 17-sulfate), although with slightly lower activity than their free catechols, are promising endogenous antioxidants. The physiological role of these estrogen conjugates during pregnancy is discussed.

Catecholamines in steroid-dependent brain development

Sex-specific peculiarities of catecholamine (CA) content and turnover in neuroendocrine brain areas and their modification with neonatal steroids or prenatal stress (PS) in Wistar rats were studied. No changes in noradrenaline (NA) content and turnover rate were found in the preoptic area (POA), meanwhile dopamine (DA) turnover rates in the POA and mediobasal hypothalamus (MBH) were increased in neonatally androgenized 10-day-old females. Treatment of female neonates with various catecholestrogens increased hypothalamic NA content by 30-95% but only 4-hydroxyestradiol-17 beta induced anovulation. 6-Hydroxydopamine had no significant impact on hypothalamic CA content in neonates and did not prevent testosterone-induced persistent estrous. Maternal stress (restriction for 1 h a day, 15-21st days of pregnancy) resulted in a decrease of hypothalamic NA and blood plasma corticosterone response to acute stress in adult male offspring. Sex differences in CA content in the POA and MBH disappeared in 10-day-old prenatally stressed rats.

CONCLUSIONS

(1) sexual brain differentiation needs co-operative actions of sex steroids and CA to be completed; and (2) early changes in CA content and turnover induced by PS or neonatal steroid exposure predetermine long-term alterations of the stress responsiveness, reproductive behaviour and neuroendocrine control of ovulation.