Effects of bisphenol A (BPA) on brain-specific expression of cyp19a1b gene in swim-up fry of Labeo rohita

Estrogen regulates numerous developmental and physiological processes and effects are mediated mainly by estrogenic receptors (ERs), which function as ligand-regulated transcription factor. ERs can be activated by many different types endocrine disrupting chemicals (EDCs) and interfere with behaviour and reproductive potential of living organism. Estrogenic regulation of membrane associated G protein-coupled estrogen receptor, GPER activity has also been reported. Bisphenol A (BPA), a ubiquitous endocrine disruptor is present in many household products, has been linked to many adverse effect on sexual development and reproductive potential of wild life species. The present work is aimed to elucidate how an environmentally pervasive chemical BPA affects in vivo expression of a known estrogen target gene, cyp19a1b in the brain, and a known estrogenic biomarker, vitellogenin (Vg) in the whole body homogenate of 30 days post fertilization (dpf) swim-up fry of Labeo rohita. We confirm that, like estrogen, the xenoestrogen BPA exposure for 5-15 days induces strong overexpression of cyp19a1b, but not cyp19a1a mRNA in the brain and increase concentration of vitellogenin in swim-up fry. BPA also induces strong overexpression of aromatase B protein and aromatase activity in brain. Experiments using selective modulators of classical ERs and GPER argue that this induction is largely through nuclear ERs, not through GPER. Thus, BPA has the potential to elevate the levels of aromatase and thereby, levels of endogenous estrogen in developing brain. These results indicate that L. rohita swim-up fry can be used to detect environmental endocrine disruptors either using cyp19a1b gene expression or vitellogenin induction.

Proanthocyanidins Protect Epithelial Cells from Zearalenone-Induced Apoptosis via Inhibition of Endoplasmic Reticulum Stress-Induced Apoptosis Pathways in Mouse Small Intestines

This study evaluated the protective effect of proanthocyanidins (PCs) on reducing apoptosis in the mouse intestinal epithelial cell model MODE-K exposed to zearalenone (ZEA) through inhibition of the endoplasmic reticulum stress (ERS)-induced apoptosis pathway. Our results showed that PCs could reduce the rate of apoptosis in MODE-K cells exposed to ZEA (p < 0.01). PCs significantly increased the ZEA-induced antioxidant protective effects on the enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) and on the content of GSH. PCs also significantly decreased the ZEA-induced increase in the content of malondialdehyde (MDA). The analysis indicated that ZEA increased both mRNA and protein expression levels of C/EBP homologous protein (CHOP), GRP78, c-Jun N-terminal kinase (JNK), and cysteinyl aspartate specific proteinase 12 (caspase-12) (p < 0.05), which are related to the ERS-induced apoptosis pathway. ZEA decreased levels of the pro-apoptotic related protein Bcl-2 (p < 0.05) and increased the anti-apoptotic related protein Bax (p < 0.05). Co-treatment with PCs was also shown to significantly reverse the expression levels of these proteins in MODE-K cells. The results demonstrated that PCs could protect MODE-K cells from oxidative stress and apoptosis induced by ZEA. The underlying mechanism may be that PCs can alleviate apoptosis in mouse intestinal epithelial cells by inhibition of the ERS-induced apoptosis pathway.

Melatonin prevents the estrogenic effects of sub-chronic administration of cadmium on mice mammary glands and uterus

Cadmium (Cd) is a heavy metal classified as a human carcinogen. Occupational exposure, dietary consumption and cigarette smoking are sources of Cd contamination. Cd-induced carcinogenicity depends on its oxidative and estrogenic actions. A possible role of Cd in breast cancer etiology has been recently suggested. Melatonin, because of its antioxidant and antiestrogenic properties could counteract the toxic effects of this metalloestrogen. Our aim was both to determine the effects of relevant doses of Cd on mice mammary glands and uterus and to test whether melatonin would counteract its effects. Female mice of different ages and estrogenic status (prepuberal, adult intact, adult ovariectomized) were treated with CdCl(2) (2-3 mg/kg, i.p.), melatonin (10 microg/mL in drinking water), CdCl(2) + melatonin, or diluents. Whereas in prepuberal animals Cd disturbs mammary ductal growth and reduces the number of terminal end buds, in adults, regardless of the steroidal milieu, Cd exerts estrogenic effects on mammary glands, increasing lobuloalveolar development and ductal branching. Uterine weight also increased as a result of Cd treatment. The effects of Cd are partially inhibited by melatonin. In adult ovariectomized mice, Cd concentration in blood of animals treated with CdCl(2) + melatonin was lower than in mice receiving only Cd; the opposite effects were found in non-castrated animals. As Cd mimics the effect of estrogens, the high incidence of breast cancer in tobacco smokers and women working in industries related with Cd could be explained because of the properties of this metal. The effects of melatonin point to a possible role of this indoleamine as a preventive agent for environmental or occupational Cd contamination.

Mechanisms of diethylstilbestrol-induced relaxation in rat aorta smooth muscle

The mechanisms of diethylstilbestrol (1 to 30 microM)-induced relaxation on noradrenaline (30 nM)-raised tone in the rat aorta smooth muscle were studied. Neither the increase of calcium content in the medium (3, 6 and 9 mM) nor Bay K 8644 (3, 10 and 100 nM) reversed diethylstilbestrol relaxation. Tamoxifen (3 microM), the quaternary derivate (tamoxifen ethyl bromide, 3 microM), actinomycin D (30 microM), cycloheximide (100 microM), Rp-cAMPS (30 microM), TPCK (1 microM) and difluoromethylornithine (1 mM) inhibited diethylstilbestrol-induced relaxation. Incubation with 2 microg/ml pertussis toxin, propranolol (1 microM), H-7 (10 microM), 2',3'- and 2',5'-dideoxiadenosine (10 and 30 microM, respectively) and methylene blue (10 microM) did not modify diethylstilbestrol-induced relaxation. Our results showed that presumably an activation of membrane mechanisms, protein kinase A activation, genomic mechanisms and polyamine synthesis might participate in diethylstilbestrol-elicited relaxation in addition to the increase in K(ATP) permeability, as previously described. Actinomycin D produces a synergistic effect, with tamoxifen, difluoromethylornithine and glibenclamide antagonizing the effect of diethylstilbestrol. In the case of the association of actinomycin D and glibenclamide, the antagonism of relaxation is complete. The fact that tamoxifen- and difluoromethylornithine-dependent mechanisms participate in diethylstilbestrol relaxation inhibited by glibenclamide suggests that two transduction pathways are involved in the relaxation. Therefore, K(ATP) channels and genomic mechanisms, both modulated by cyclic AMP (cAMP)-dependent mechanisms, are associated with diethylstilbestrol relaxation.

Oestrogenic activity of isobutylparaben in vitro and in vivo

The alkyl esters of p-hydroxybenzoic acid (parabens) are used widely as preservatives in foods, pharmaceuticals and cosmetics to which the human population is exposed. Recent studies have reported that methylparaben, ethylparaben, n-propylparaben and n-butylparaben all possess oestrogenic activity in several in vitro assays and in animal models in vivo. This study reports on the oestrogenic activity of isobutylparaben in a panel of assays in vitro and in vivo. Isobutylparaben was able to displace [(3)H]oestradiol from cytosolic oestrogen receptor alpha of MCF7 human breast cancer cells by 81% at 100 000-fold molar excess. Using a clonal line of MCF7 cells containing a stably transfected oestrogen-responsive ERE-CAT reporter gene, CAT gene expression could be increased by isobutylparaben such that the magnitude of the response was the same at 10(-5) M isobutylparaben as with 10(-8) M 17beta-oestradiol. Isobutylparaben could also increase expression of the endogenous oestrogen-responsive pS2 gene in MCF7 cells and maximal expression at 10(-5) M isobutylparaben could be inhibited with the anti-oestrogen ICI 182 780. The proliferation of two oestrogen-dependent human breast cancer cell lines MCF7 and ZR-75-1 could be increased with isobutylparaben such that at concentrations of 10(-5) M the proliferation response was of the same magnitude as with 10(-8) M 17beta-oestradiol. Evidence for oestrogen receptor mediation of proliferation effects was provided by the inability of isobutylparaben to influence the growth of oestrogen-unresponsive MDA-MB-231 human breast cancer cells and by the ability of the anti-oestrogen ICI 182 780 to inhibit the isobutylparaben effects on MCF7 cell growth. The proliferation response to 10(-10) M 17beta-oestradiol was not antagonized with isobutylparaben at any concentration from 10(-9) M to 10(-4) M in either MCF7 or ZR-75-1 cells. Finally, subcutaneous administration of isobutylparaben was able to increase the uterine weight in the immature mouse after three daily doses of 1.2 or 12.0 mg per mouse. Previous work using linear-alkyl-chain parabens has shown that oestrogenic activity increases with alkyl chain length from methylparaben to n-butylparaben. The results here show that branching of the alkyl chain to isobutylparaben increases oestrogenic activity beyond that of the equivalent length linear alkyl chain in n-butylparaben.

Calcium-sensitive potassium channel inhibitors antagonize genistein- and daidzein-induced arterial relaxation in vitro

Estradiol-17beta relaxes rabbit coronary artery rings via large conductance Ca2+-activated K+-channels (K(Ca)). Genistein and daidzein are plant-derived estrogen-like compounds. The aim of the present study was to investigate whether potassium channels participate in the genistein- and daidzein-induced arterial relaxation like they do in the case of estradiol-17beta. Endothelium-denuded superior mesenteric arterial rings from non-pregnant Wistar female rats were used. At a concentration of 10 microM, estradiol-17beta, genistein and daidzein relaxed noradrenaline precontracted arterial rings, (58 +/- 4%, 45 +/- 5% and 31 +/- 3%, respectively; (n=6-8)). Genistein- and daidzein-induced relaxations were inhibited both by iberiotoxin (1-10 nM) and charybdotoxin (30 nM), the antagonists of large conductance Ca2+-activated K+-channels (K(Ca)). Estradiol-17beta-induced relaxation was reduced by iberiotoxin (30 nM). Estradiol-17beta- and daidzein-induced relaxations were also decreased by apamin (0.1-0.3 microM), an antagonist of small conductance Ca2+-activated K+-channels. The antagonists of voltage-dependent K+-channels (K(V)) (4-aminopyridine), ATP-sensitive K+-channels (K(ATP)) (glibenclamide), or inward rectifier K+-channels (KIR) (barium) had no effect on the relaxation responses of any of the compounds studied. Estrogen receptor antagonist tamoxifen did not inhibit the relaxations. In conclusion, in the noradrenaline precontracted rat mesenteric arteries, the relaxations caused by estradiol-17beta, genistein and daidzein were antagonized by large and small conductance K(Ca)-channel inhibitors, suggesting the role of these channels as one of the relaxation mechanisms.

Estrogenic and antiproliferative properties of glabridin from licorice in human breast cancer cells

There is an increasing demand for natural compounds that improve women's health by mimicking the critical benefits of estrogen to the bones and the cardiovascular system but avoiding its deleterious effects on the breast and uterus. The estrogenic properties of glabridin, the major isoflavan in licorice root, were tested in view of the resemblance of its structure and lipophilicity to those of estradiol. The results indicate that glabridin is a phytoestrogen, binding to the human estrogen receptor and stimulating creatine kinase activity in rat uterus, epiphyseal cartilage, diaphyseal bone, aorta, and left ventricle of the heart. The stimulatory effects of 2.5-25 microg/animal glabridin were similar to those of 5 microg/animal estradiol. Chemical modification of glabridin showed that the position of the hydroxyl groups has a significant role in binding to the human estrogen receptor and in proliferation-inducing activity. Glabridin was found to be three to four times more active than 2'-O-methylglabridin and 4'-O-methylglabridin, and both derivatives were more active than 2',4'-O-methylglabridin. The effect of increasing concentrations of glabridin on the growth of breast tumor cells was biphasic. Glabridin showed an estrogen receptor-dependent, growth-promoting effect at low concentrations (10 nM-10 microM) and estrogen receptor-independent antiproliferative activity at concentrations of > 15 microM. This is the first study to indicate that isoflavans have estrogen-like activities. Glabridin and its derivatives exhibited varying degrees of estrogen receptor agonism in different tests and demonstrated growth-inhibitory actions on breast cancer cells.

Octylphenol inhibits testosterone biosynthesis by cultured precursor and immature Leydig cells from rat testes

4-tert-octyphenol (OP) is a surfactant additive widely used in the manufacture of a variety of detergents and plastic products. OP has been reported to mimic the actions of estrogen in many cellular systems. The present studies evaluated the direct effects of OP on human chorionic gonadotropin (hCG)-stimulated testosterone biosynthesis by cultured precursor and immature Leydig cells from 23-day old (prepubertal) rats. Exposure to increasing OP concentrations (1 to 2000 nM) progressively decreased hCG-stimulated testosterone formation in both precursor and immature Leydig cells at higher OP concentrations (100 or 500 to 2000 nM). Testosterone levels were reduced approximately 30 to 70% below control at the highest concentration in both cell types. Similar reductions in testosterone associated with OP exposure were observed in cells stimulated with 1 mM 8-Br-cAMP, suggesting that the main actions of OP occur after the generation of cAMP. Increasing concentrations of 17beta-estradiol (1 to 1000 nM) had no effect on hCG-stimulated testosterone formation in both precursor and immature Leydig cells and the inclusion of 100 nM ICI 182,780, a pure estrogen antagonist, in precursor and immature Leydig cells exposed to OP and hCG, did not alter the inhibition by higher OP concentrations of testosterone formation in both cell types. These results suggest that OP is a hormonally active agent, but that some of its actions are distinct from those of 17beta-estradiol and are not mediated through the estrogen receptor alpha or beta pathway. To further localize the potential site(s) of action of OP, cultured precursor and immature Leydig cells were exposed to increasing concentrations of OP and hCG for 24 h. Next, fresh media containing 1 microM 22(R)-hydroxycholesterol, 1 microM pregnenolone, 1 microM progesterone, or 1 microM androstenedione was added, and the conversion of each substrate to testosterone was determined after incubation for 4 h. The conversion of androstenedione to testosterone was unaffected by exposure to OP, suggesting that the 17beta-hydroxysteroid dehydrogenase step is not inhibited. However, the conversion of 22(R)-hydroxycholesterol, pregnenolone and progesterone all were inhibited by prior exposure to OP and hCG. This finding suggests that the 17alpha-hydroxylase/c17-20-lyase step, which converts progesterone to androstenedione, is inhibited by OP, and that the cholesterol side-chain cleavage and 3beta-hydroxysteroid dehydrogenase -isomerase steps, which convert cholesterol to pregnenolone and pregnenolone to progesterone, respectively, are other potential sites of OP action. Because concomitant exposure to the antioxidants alpha-tocopherol or ascorbate did not alter the inhibition of testosterone formation by higher OP concentrations, it does not appear that OP is acting as a pseudosubstrate for the generation of free radicals, which can damage P450 enzymes.

The antiestrogen ICI 182,780 abolishes developmental injury for murine embryos exposed in vitro to o,p'-DDT(1)

Previously, we reported that in vitro exposure of murine embryos to 0.1 microg/ml o,p'-DDT (an estrogenic pesticide) significantly reduced development to blastocyst and mean cell number per embryo, and increased percent cell death by 96 h of culture. The objective of the present study was to determine if developmental injury induced by o,p'-DDT resulted from estrogenic, antiestrogenic, or unrelated adverse biologic mechanisms. Toward this objective, pronuclear embryos from CD-1 mice were cultured 96 h in medium supplemented with 0.1% ethanol (control) or 0.1 microg/ml o,p'-DDT, 17beta-estradiol, or ICI 182,780 dissolved in ethanol as single agents or as paired mixtures. As single agents, development to blastocyst and mean cell numbers were significantly reduced and percent apoptosis was significantly increased for embryos cultured in the presence of o,p'-DDT or ICI 182,780. Development to blastocyst was significantly reduced for embryos cultured in the presence of 17beta-estradiol. Beneficial interaction occurred when the receptor antagonist ICI 182,780 was combined with either receptor agonist (o,p'-DDT or 17beta-estradiol). In contrast, interaction was not significant when the two agonists were combined. The results indicate that developmental injury due to the estrogenic pesticide o,p'-DDT was abolished by the addition of the receptor antagonist ICI 182,780 and not by the receptor agonist 17beta-estradiol. The findings underscore the utility of the model for uncovering mechanisms of developmental injury.

Interaction of naturally occurring nonsteroidal estrogens with expressed recombinant human estrogen receptor

The interaction between the recombinant human estrogen receptor and a variety of nonsteroidal estrogens was studied using a transient transfection assay in mammalian cells. Eight naturally occurring compounds were confirmed to stimulate the transcriptional activity of the human estrogen receptor and to compete for the binding of radiolabeled 17 beta-estradiol to this protein. In order of biological potency, these were zearalenone, beta-zearalenol, coumestrol, genistein, daidzein, phloretin, formononetin, and biochanin A. As with steroidal estrogens, the hormonal activity of these compounds was specific for the estrogen receptor and sensitive to inhibition by 4-hydroxytamoxifen and ICI-164,384. Evidence is also presented to indicate that the stimulatory activity of genistein is unrelated to the protein tyrosine kinase inhibitory activity of this isoflavone. These results demonstrate that a significant number of structurally diverse plant and fungal secondary metabolites exist in nature that may contribute to the total estrogen exposure of the human population.