Are all EDC effects mediated via steroid hormone receptors?

Reconsidering "low-dose"-Impacts of oral estrogen exposure during preimplantation embryo development

Perturbations of estrogen signaling during developmental stages of high plasticity may lead to adverse effects later in life. Endocrine-disrupting chemicals (EDC) are compounds that interfere with the endocrine system by particularly mimicking the action of endogenous estrogens as functional agonists or antagonists. EDCs compose synthetic and naturally occurring compounds discharged into the environment, which may be taken up via skin contact, inhalation, orally due to contaminated food or water, or via the placenta during in utero development. Although estrogens are efficiently metabolized by the liver, the role of circulating glucuro- and/or sulpho-conjugated estrogen metabolites in the body has not been fully addressed to date. Particularly, the role of intracellular cleavage to free functional estrogens could explain the hitherto unknown mode of action of adverse effects of EDC at very low concentrations currently considered safe. We summarize and discuss findings on estrogenic EDC with a focus on early embryonic development to highlight the need for reconsidering low dose effects of EDC.

Reproductive toxicity of combined effects of endocrine disruptors on human reproduction

Confluence of environmental, genetic, and lifestyle variables is responsible for deterioration of human fecundity. Endocrine disruptors or endocrine disrupting chemicals (EDCs) may be found in a variety of foods, water, air, beverages, and tobacco smoke. It has been demonstrated in experimental investigations that a wide range of endocrine disrupting chemicals have negative effects on human reproductive function. However, evidence on the reproductive consequences of human exposure to endocrine disrupting chemicals is sparse and/or conflicting in the scientific literature. The combined toxicological assessment is a practical method for assessing the hazards of cocktails of chemicals, co-existing in the environment. The current review provides a comprehensive overview of studies emphasizing the combined toxicity of endocrine disrupting chemicals on human reproduction. Endocrine disrupting chemicals interact with each other to disrupt the different endocrine axes, resulting in severe gonadal dysfunctions. Transgenerational epigenetic effects have also been induced in germ cells, mostly through DNA methylation and epimutations. Similarly, after acute or chronic exposure to endocrine disrupting chemicals combinations, increased oxidative stress (OS), elevated antioxidant enzymatic activity, disrupted reproductive cycle, and reduced steroidogenesis are often reported consequences. The article also discusses the concentration addition (CA) and independent action (IA) prediction models, which reveal the importance of various synergistic actions of endocrine disrupting chemicals mixtures. More crucially, this evidence-based study addresses the research limitations and information gaps, as well as particularly presents the future research views on combined endocrine disrupting chemicals toxicity on human reproduction.

Sex Determination and Ovarian Development in Reptiles and Amphibians: From Genetic Pathways to Environmental Influences

BACKGROUND

Reptiles and amphibians provide untapped potential for discovering how a diversity of genetic pathways and environmental conditions are incorporated into developmental processes that can lead to similar functional outcomes. These groups display a multitude of reproductive strategies, and whereas many attributes are conserved within groups and even across vertebrates, several aspects of sexual development show considerable variation.

SUMMARY

In this review, we focus our attention on the development of the reptilian and amphibian ovary. First, we review and describe the events leading to ovarian development, including sex determination and ovarian maturation, through a comparative lens. We then describe how these events are influenced by environmental factors, focusing on temperature and exposure to anthropogenic chemicals. Lastly, we identify critical knowledge gaps and future research directions that will be crucial to moving forward in our understanding of ovarian development and the influences of the environment in reptiles and amphibians.

KEY MESSAGES

Reptiles and amphibians provide excellent models for understanding the diversity of sex determination strategies and reproductive development. However, a greater understanding of the basic biology of these systems is necessary for deciphering the adaptive and potentially disruptive implications of embryo-by-environment interactions in a rapidly changing world.

Do G-protein coupled estrogen receptor and bisphenol A analogs influence on Leydig cell epigenetic regulation in immature boar testis ex vivo?

Organotypic culture of testicular fragments from 7-day-old male pigs (Polish White Large) was used. Tissues were treated with an antagonist of G-protein coupled estrogen receptor (GPER) (G-15; 10 nM), and bisphenol A (BPA), and its analogs (TBBPA, TCBPA; 10 nM) alone or in combination and analyzed using electron and light (stainings for collagen fibers, lipid droplet and autophagy markers) microscopes. In addition, mRNA and protein abundances and localization of molecules required for miRNA biogenesis and function (Drosha, Exportin 5; EXPO5, Dicer, and Argonaute 2; AGO2) were assessed together with calcium ion (Ca²⁺) and estradiol concentrations. Regardless of GPER blockade and/or treatment with BPA, TBBPA and TCBPA, there were no changes in Leydig cell morphology. Also, there were no changes in lipid droplet content and distribution but there were changes in lipid and autophagy protein abundance. In the interstitial tissue, there was an increase of collagen content, especially after treatment with BPA analogs and G-15 + BPA. Independent of the treatment, there was downregulation of EXPO5 and Dicer genes but the Drosha and AGO2 genes were markedly upregulated as a result of treatment with G-15 + BPA and TCBPA, respectively. There was always a lesser abundance of EXPO5 and AGO2 proteins regardless of treatment. There was markedly greater abundances of Drosha after G-15 + BPA treatment, and this also occurred for Dicer after treatment with G-15 + TCBPA. Immunolocalization of miRNA proteins indicated there was a cytoplasmic-nuclear pattern in control and treated cells. There was an increase of Ca²⁺ concentrations after treatment with G-15 and BPA analogs. Estradiol secretion decreased after antagonist and chemical treatments when these were administered alone, however, there was an increase in estradiol secretion after treatment with combinations of these compounds.

Comparison of in vitro hormone activities of novel flame retardants TBB, TBPH and their metabolites TBBA and TBMEPH using reporter gene assays

The anti-androgenic and anti-thyroid hormonal activities of the two novel brominated flame retardants, TBB and TBPH and of their metabolites TBBA and TBMEPH have been compared using the luciferase reporter gene assays. Only the parent compounds TBB and TBPH exhibited anti-glucocorticoid activity with IC50 values of 1.9 μM and 0.3 μM. Furthermore, mode of action for these two compounds is by direct competing to the glucocorticoid receptor (GR) with IC50 values of 0.03 μM and 0.002 μM. All four tested compounds possess anti-androgenic and anti-thyroid hormonal activities, without agonist activities on the respective receptors. Anti-androgenic activities with IC50 values of 43.5 μM, 0.1 μM, 47.5 μM and 1.3 μM were found for TBB, TBPH, TBBA and TBMEPH. The anti-thyroid hormonal IC50 values of 37.5 μM, 0.1 μM, 22.8 μM and 32.3 μM for TBB, TBPH, TBBA and TBMEPH, together with the above quoted results, indicate that metabolism can modify anti-androgenic, anti-glucocorticoid and anti-thyroid hormonal effects of these novel brominated flame retardants. Furthermore, the parent flame retardants are shown to be able to disrupt the function of the GR as antagonists by direct competition to the receptor.

Tamoxifen persistently disrupts the humoral adaptive immune response of gilthead seabream (Sparus aurata L.)

There is increasing concern about the possible effect of pharmaceutical compounds may have on the fish immune system. Bath exposition of 17α-ethynylestradiol (EE2), a synthetic estrogen used in oral contraceptives, altered the immune response of the gilthead seabream (Sparus aurata L.), a marine hermaphrodite teleost. Tamoxifen (Tmx) is a selective estrogen-receptor modulator used in hormone replacement therapy, the effects of which are unknown in fish immunity. This study aims to investigate the effects of dietary administration of EE2 (5 μg/g food) and Tmx (100 μg/g food) on the immune response of gilthead seabream, and the capacity of the immune system to recover its functionality after a recovery period. The results show for the first time the reversibility of the effect of EE2 and Tmx on the fish immune response. Tmx promoted a transient alteration in hepatic vitellogenin gene expression of a different magnitude to that produced by EE2. Both, EE2 and Tmx inhibited the induction of interleukin-1β gene expression while reversed the inhibition of ROI production in leukocytes following vaccination. However, none of these effects were observed after ceasing EE2 and Tmx exposure. EE2 and Tmx stimulated the antibody response of vaccinated fish although Tmx, but not EE2, altered the antibody response and modulated the percentage of IgM(+) B lymphocytes of vaccinated fish during the recovery phase. Taken together, our results suggest that EE2 and Tmx might alter the capacity of fish to appropriately respond to infection and show that Tmx has a long-lasting effect on humoral adaptive immunity.

Steroids in teleost fishes: A functional point of view

Steroid hormones are involved in the regulation of a variety of processes like embryonic development, sex differentiation, metabolism, immune responses, circadian rhythms, stress response, and reproduction in vertebrates. Teleost fishes and humans show a remarkable conservation in many developmental and physiological aspects, including the endocrine system in general and the steroid hormone related processes in particular. This review provides an overview of the current knowledge about steroid hormone biosynthesis and the steroid hormone receptors in teleost fishes and compares the findings to the human system. The impact of the duplicated genome in teleost fishes on steroid hormone biosynthesis and perception is addressed. Additionally, important processes in fish physiology regulated by steroid hormones, which are most dissimilar to humans, are described. We also give a short overview on the influence of anthropogenic endocrine disrupting compounds on steroid hormone signaling and the resulting adverse physiological effects for teleost fishes. By this approach, we show that the steroidogenesis, hormone receptors, and function of the steroid hormones are reasonably well understood when summarizing the available data of all teleost species analyzed to date. However, on the level of a single species or a certain fish-specific aspect of physiology, further research is needed.

Perinatal 17α-ethinylestradiol exposure affects formalin-induced responses in middle-aged male (but not female) rats

17α-Ethinylestradiol (EE), the main component of the contraceptive pill, is a synthetic estrogen found in rivers of the United States and Europe as an environmental contaminant. It is one of the most studied xenoestrogens due to its possible effect on the reproductive system. In the present study we evaluated the modulation of pain responses induced by formalin injection (licking, flexing, paw-jerk) in 8-month-old male and female offspring of female rats treated with two different doses of EE (4ng/kg/day or 400ng/kg/day) during pregnancy and lactation. Spontaneous behaviors and gonadal hormone levels were also determined. Both concentrations of EE induced an increase of pain behaviors in males only, i.e. higher flexing and licking of the formalin-injected paw than in OIL-exposed rats, during the second, inflammatory, phase of the formalin test. Grooming duration was increased by EE exposure in both males and females. Prenatal EE exposure (both concentrations) decreased estradiol plasma levels in the formalin-injected females but not in the males. These results underline the possibility that exposure to an environmental contaminant during the critical period of development can affect neural processes (such as those involved in pain modulation) during adulthood, indicating long-term changes in brain circuitry. However, such changes may be different in males and females.

Perinatal exposure to methoxychlor enhances adult cognitive responses and hippocampal neurogenesis in mice

During perinatal life, sex steroids, such as estradiol, have marked effects on the development and function of the nervous system. Environmental estrogens or xenoestrogens are man-made chemicals, which animal and human population encounter in the environment and which are able to disrupt the functioning of the endocrine system. Scientific interest in the effects of exposure to xenoestrogens has focused more on fertility and reproductive behaviors, while the effects on cognitive behaviors have received less attention. Therefore, the present study explored whether the organochlorine insecticide Methoxychlor (MXC), with known xenoestrogens properties, administered during the perinatal period (from gestational day 11 to postnatal day 8) to pregnant-lactating females, at an environmentally relevant dose (20 µg/kg (body weight)/day), would also affect learning and memory functions depending on the hippocampus of male and female offspring mice in adulthood. When tested in adulthood, MXC perinatal exposure led to an increase in anxiety-like behavior and in short-term spatial working memory in both sexes. Emotional learning was also assessed using a contextual fear paradigm and MXC treated male and female mice showed an enhanced freezing behavior compared to controls. These results were correlated with an increased survival of adult generated cells in the adult hippocampus. In conclusion, our results show that perinatal exposure to an environmentally relevant dose of MXC has an organizational effect on hippocampus-dependent memory and emotional behaviors.

Analysis of estrogens and estrogen mimics in edible matrices--a review

This review provides a brief survey of the biological effects of selected endocrine-disrupting compounds that are formed after internal exposure of organisms. Further, the present analytical methods available for the determination of these compounds in foodstuffs are critically evaluated. The attention is primarily devoted to the methods for sample pretreatment, which are the main source of errors and are usually the most time-consuming step of the whole analysis. This review is focused on selected natural and synthetic estrogens, estrogen conjugates, and chemical additives used in the plastic industry that can act as estrogen mimics.

PBDE-47 exposure causes gender specific effects on apoptosis and heat shock protein expression in marine medaka, Oryzias melastigma

Marine medaka (Oryzias melastigma) was fed with a low and high dose of dietary 2,2',4,4'-tetra-bromodiphenyl ether (PBDE-47), over 21 days. Gender specific changes in caspases 3 and 8 in medaka were found as activities in male medaka were significantly increased in both liver and muscle at both low and high exposure levels whereas caspase activity in female medaka tissue remained unchanged. Results of HSP90 and HSP70 immunoassays also showed gender specific related changes as both HSP families were unchanged in liver and muscle of male medaka but significantly increased in liver and muscle of female medaka, following PBDE-47 exposure. The gender specific effects of PBDE-47 on HSP expression profiles could not be explained by inherent differences in the heat shock response of male and female marine medaka, as the HSP profiles in liver and muscle, induced by acute heat shock, were similar in both sexes. The findings from this study provide evidence that PBDE-47 can cause gender specific modulatory effects on mechanisms critical to the apoptotic cascade as well as HSP regulation and expression.

Luteinizing hormone receptor (lhcgr) as a marker gene for characterizing estrogenic endocrine-disrupting chemicals in zebrafish ovarian follicle cells

The adverse effects of endocrine-disrupting chemicals (EDCs) have been well documented; however, the action mechanisms of many EDCs remain elusive and controversial. Furthermore, the highly diversified chemical structures and low environmental concentrations of EDCs present a major challenge to their chemical detection. Clearly, there is an urgent need for simple and reliable bioassays to detect EDCs in the environment and unravel their action mechanisms. We have recently identified luteinizing hormone receptor (lhcgr) as a robust estradiol (E2)-responsive gene in cultured zebrafish ovarian follicle cells. The expression of lhcgr exhibited a distinct biphasic response to E2 over a 24-h time-course treatment, making this a unique system for characterizing estrogenic EDCs. This study was undertaken to validate this platform by testing a wide range of EDCs, including 17α-ethinylestradiol (EE2), diethylstilbestrol (DES), bisphenol A (BPA), genistein (GEN), 1,1,1-trichloro-2-(2-chlorophenyl)-2-(4-chlorophenyl)ethane (o,p'-DDT), vinclozolin (VIN), bis(2-ethylhexyl) phthalate (DEHP), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47). Diethylstilbestrol (DES), EE2 and o,p'-DDT mimicked E2 and induced a biphasic expression of lhcgr while BPA and GEN stimulated a monophasic expression in the 24-h time-course. In contrast, BDE-47, DEHP and VIN had no effect, whereas TCDD decreased lhcgr expression. Dose-response experiment showed that E2, EE2 and DES had the highest potency, which was followed by GEN, BPA and o,p'-DDT. The effects of estrogenic EDCs were further confirmed by their potentiation of hCG-induced activin βA2 subunit (inhbab) expression. In conclusion, the present study showed that the expression of lhcgr in cultured zebrafish follicle cells and its biphasic response to estrogens provide a unique in vitro platform for screening and categorizing estrogenic substances and deciphering their action mechanisms.

Evaluation of the presence of endocrine-disrupting compounds in dissolved and solid wastewater treatment plant samples of Gran Canaria Island (Spain)

Liquid and solid samples from two wastewater treatment plants (WWTPs) on Gran Canaria Island (Spain) have been tested for the presence of compounds with endocrine-disrupting properties. The selected degradation stages were sampled bimonthly from each WWTP over the 12-month period from July 2010 to July 2011. The analytical methods used for the determination of the endocrine-disrupting compounds (EDCs) were based on on-line solid phase extraction, microwave-assisted extraction (MAE), and ultrasonic-assisted extraction (UAE) coupled to UHPLC-MS/MS. All of the hyphenated methodologies employed in this work showed good recoveries (72-104%) and sensitivities, with LODs lower than 7.0 ng L(-1) and 6.3 ng g(-1) for the dissolved and solid fractions, respectively. We have also evaluated the estrogenicity of the samples in terms of their estradiol equivalent concentrations (EEQs). The chemical analysis of the selected EDCs revealed fairly low concentrations for both natural and synthetic oestrogens, alkylphenolic compounds, and bisphenol-A in each of the dissolved, particulate, and sludge samples (ng L(-1) or ng g(-1)). However, the estimated estrogenic activity indicated that the majority of samples could represent an important environmental risk, clearly surpassing the threshold to exert deleterious consequences on living beings.

Transgenic (cyp19a1b-GFP) zebrafish embryos as a tool for assessing combined effects of oestrogenic chemicals

Endocrine disrupting chemicals and especially oestrogen receptor (ER) agonists have been extensively studied over the years due to their potential effects on sexual development and reproduction in vertebrates, notably fish. As ER agonists can exist as complex mixtures in the aquatic environment, evaluating the impact of combined exposure on oestrogenic effects has become increasingly important. Use of predictive models such as concentration addition (CA) and independent action (IA) has allowed assessment of combined estrogenic effects of complex multi-compound mixtures of ER agonists in various fish in vitro and in vivo experimental models. The present work makes use of a transgenic zebrafish strain, tg(cyp19a1b-GFP), which expresses the green fluorescent protein (GFP) under the control of the cyp19a1b (brain aromatase or aromatase B) gene to determine the oestrogenic potency of ER agonists alone or in mixtures. In these studies, tg(cyp19a1b-GFP) zebrafish embryos were exposed for four days (from one to five days post fertilization) to five different oestrogenic chemicals; 17α-ethinylestradiol (EE2), 17β-estradiol (E2), estrone (E1), bisphenol A (BPA) and 4-tert-octylphenol (OP), and three mixtures of up to four of these compounds. The mixture of BPA, OP and E2 was also tested with primary cultures of rainbow trout hepatocytes by analysing the ER-mediated induction of the oestrogenic biomarker vitellogenin in order to compare the performance of the two methods for assessing oestrogenic effects of complex mixtures. The three tested mixtures were predominantly acting in an additive manner on the expression of GFP. Additivity was indicated by the overlap of the 95% confidence interval of the concentration response curves for the observed data with the CA and IA prediction models, and model deviation ratios within a factor of two for a majority of the mixture concentrations. However, minor deviations determined as more than additive effects for the mixture of EE2, E1 and E2 and less than additive effects for the mixture of BPA, OP, EE2 and E1 were observed at the higher mixture concentrations tested. The successful prediction of additivity by CA and IA in tg(cyp19a1b-GFP) zebrafish embryos and deviations at high mixture concentrations seemed to correspond well to results obtained in the rainbow trout hepatocyte assay. The present results clearly show the usefulness of combining predictive modelling and use of in vitro bioassays for rapid screening of oestrogenic effects of complex mixtures and environmental samples.

Bacterial biosensors for evaluating potential impacts of estrogenic endocrine disrupting compounds in multiple species

To study the effects and possible mechanisms of suspected endocrine disrupting compounds (EDCs), a wide variety of assays have been developed. In this work, we generated engineered Escherichia coli biosensor strains that incorporate the ligand-binding domains (LBDs) of the β-subtype estrogen receptors (ERβ) from Solea solea (sole), and Sus scrofa (pig). These strains indicate the presence of ligands for these receptors by changes in growth phenotype, and can differentiate agonist from antagonist and give a rough indication of binding affinity via dose-response curves. The resulting strains were compared with our previously reported Homo sapiens ERβ biosensor strain. In initial tests, all three of the strains correctly identified estrogenic test compounds with a high degree of certainly (Z' typically greater than 0.5), including the weakly binding test compound bisphenol A (BPA) (Z' ≈ 0.1-0.3). The modular design of the sensing element in this strain allows quick development of new species-based biosensors by simple LBD swapping, suggesting its use in initial comparative analysis of EDC impacts across multiple species. Interestingly, the growth phenotypes of the biosensor strains indicate similar binding for highly estrogenic control compounds, but suggest differences in ligand binding for more weakly binding EDCs.

Beneficial role of celery oil in lowering the di(2-ethylhexyl) phthalate-induced testicular damage

Di(2-ethylhexyl) phthalate (DEHP), the most abundant phthalate in the environment, is known to be a reproductive toxicant. Considering the therapeutic significance of medicinal plants, this study was conducted to evaluate the effects of administration of celery oil on DEHP-induced testicular toxicity. The experiment was carried out for 8 weeks on 36 male rats that were divided equally into six groups. Group 1 was kept as normal control (given vehicle), while rats of group 2 were administered orally 200 mg/kg/day of celery oil. Groups 3 and 5 were orally given 500 and 1000 mg DEHP/kg/day, respectively. Groups 4 and 6 were treated with similar doses of DEHP as in groups 3 and 5 plus celery oil (200 mg/kg/day). Body and testicular weights, sperm parameters, serum hormones (testosterone, follicle-stimulating hormone, luteinizing hormone and estradiol), antioxidant enzymes (superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT)) and expression of cytochrome P450 aromatase (CYP19) messenger RNA (mRNA) were investigated at the end of 8th week. Treatment with DEHP alone resulted in a significant decrease in body and testicular weights, sperm parameters and serum hormone levels when compared with control. On the other hand, testicular antioxidant enzymes showed a significant dose-dependent increase. The expression of CYP19 mRNA was significantly reduced by increasing the doses of DEHP. Administration of celery oil along with DEHP partially prevented the decrease in body and testicular weights and enhanced epididymal sperm count, serum hormone levels and the expression of CYP19 mRNA along with diminution in the activities of SOD, GPx and CAT enzymes. The obtained results showed that the celery improved the testicular alterations induced by DEHP in albino rats.

Gender-specific modulation of immune system complement gene expression in marine medaka Oryzias melastigma following dietary exposure of BDE-47

BDE-47 is one of the most widely found congeners of PBDEs in marine environments. The potential immunomodulatory effects of BDE-47 on fish complement system were studied using the marine medaka Oryzias melastigma as a model fish. Three-month-old O. melastigma were subjected to short-term (5 days) and long-term (21 days) exposure to two concentrations of BDE-47 (low dose at 290 ± 172 ng/day; high dose at 580 ± 344 ng/day) via dietary uptake of BDE-47 encapsulated in Artemia nauplii. Body burdens of BDE-47 and other metabolic products were analyzed in the exposed and control fish. Only a small amount of debrominated product, BDE-28, was detected, while other metabolic products were all under detection limit. Transcriptional expression of six major complement system genes involved in complement activation: C1r/s (classical pathway), MBL-2 (lectin pathway), CFP (alternative pathway), F2 (coagulation pathway), C3 (the central component of complement system), and C9 (cell lysis) were quantified in the liver of marine medaka. Endogenous expression of all six complement system genes was found to be higher in males than in females (p < 0.05). Upon dietary exposure of marine medaka to BDE-47, expression of all six complement genes were downregulated in males at day 5 (or longer), whereas in females, MBl-2, CFP, and F2 mRNAs expression were upregulated, but C3 and C9 remained stable with exposure time and dose. A significant negative relationship was found between BDE-47 body burden and mRNA expression of C1r/s, CFP, and C3 in male fish (r = -0.8576 to -0.9447). The above findings on changes in complement gene expression patterns indicate the complement system may be compromised in male O. melastigma upon dietary exposure to BDE-47. Distinct gender difference in expression of six major complement system genes was evident in marine medaka under resting condition and dietary BDE-47 challenge. The immunomodulatory effects of BDE-47 on transcriptional expression of these complement components in marine medaka were likely induced by the parent compound instead of biotransformed products. Our results clearly demonstrate that future direction for fish immunotoxicology and risk assessment of immunosuppressive chemicals must include parallel evaluation for both genders.

Embryos as targets of endocrine disrupting contaminants in wildlife

Environmental contaminants are now a ubiquitous part of the ecological landscape, and a growing literature describes the ability of many of these chemicals to alter the developmental trajectory of the embryo. Because many environmental pollutants readily bioaccumulate in lipid rich tissues, wildlife can attain considerable body burdens. Embryos are often exposed to these pollutants through maternal transfer, and a growing number of studies report long-term or permanent developmental consequences. Many biological mechanisms are reportedly affected by environmental contaminants in the developing embryo and fetus, including neurodevelopment, steroidogenesis, gonadal differentiation, and liver function. Embryos are not exposed to one chemical at a time, but are chronically exposed to many chemicals simultaneously. Mixture studies show that for some developmental disorders, mixtures of chemicals cause a more deleterious response than would be predicted from their individual toxicities. Synergistic responses to low dose mixtures make it difficult to estimate developmental outcomes, and as such, traditional toxicity testing often results in an underestimate of exposure risks. In addition, the knowledge that biological systems do not necessarily respond in a dose-dependent fashion, and that very low doses of a chemical can prove more harmful than higher doses, has created a paradigm shift in studies of environmental contaminant-induced dysfunction. Although laboratory studies are critical for providing dose-response relationships and determining specific mechanisms involved in disease etiology, wildlife sentinels more accurately reflect the genetic diversity of real world exposure conditions, and continue to alert scientists and health professionals alike of the consequences of developmental exposures to environmental pollutants.

Endocrine disrupting chemicals bind to a novel receptor, microtubule-associated protein 2, and positively and negatively regulate dendritic outgrowth in hippocampal neurons

The present study demonstrates a novel high-affinity neuronal target for endocrine disrupting chemicals (EDCs), which potentially cause psychological disorders. EDCs competitively inhibited the binding of bovine serum albumin-conjugated progesterone to recombinant human microtubule-associated protein 2C (rhMAP2C) with an inhibition constant at picomolar levels. In the rhMAP2C-stimulated tubulin assembly assay, agonistic enhancement was observed with dibutyl phthalate and pentachlorphenol and pregnenolone, while an inverse agonistic effect was observed with 4-nonylphenol. In contrast, progesterone and many of the EDCs, including bisphenol A, antagonized the pregnenolone-induced enhancement of rhMAP2C-stimulated tubulin assembly. These agonistic and inverse agonistic actions were not observed in tubulin assembly stimulated with Delta1-71 rhMAP2C, which lacks the steroid-binding site. Using a dark-field microscopy, pregnenolone and pentachlorphenol were observed to generate characteristic filamentous microtubules in a progesterone- or bisphenol A-reversible manner. In cultured hippocampal neurons, similar agonist-antagonist relationships were reproduced in terms of dendritic outgrowth. Fluorescent recovery after photobleaching of hippocampal neurons showed that pregnenolone and agonistic EDCs enhanced, but that 4-nonylphenol inhibited the MAP2-mediated neurite outgrowth in a progesterone- or antagonistic EDC-reversible manner. Furthermore, none of the examined effects were affected by mifepristone or ICI-182,786 i.e. the classical progesterone and estrogen receptor antagonists. Taken together, these results suggest that EDCs cause a wide variety of significant disturbances to dendritic outgrowth in hippocampal neurons, which may lead to psychological disorders following chronic exposure during early neuronal development.

First evidence of estrogenic potential of the cyanobacterial heptotoxins the nodularin-R and the microcystin-LR in cultured mammalian cells

The estrogenic activity of cyanobacterial hepatotoxins microcystin-LR (MC-LR) and nodularin-R (NOD-R) was for the first time investigated invitro in a stably transfect cell line with an estrogen-regulated luciferase gene. Treatment of cells with NOD-R caused a dose-dependent increase in the luciferase activity. NOD-R gave rise to an induction of luciferase activity with an EC(50) value of 66.4 nM, whereas the positive control, 17beta-estradiol (E2) had an EC(50) of 9.6 pM. This indicates that NOD-R is a 6900-fold weaker inducer of luciferase than E2. In contrast, only a slight but significant activation of the luciferase gene was observed with MC-LR between 2.01 and 60.1 nM, and a maximal-induced response was observed with 10.1 nM, approximately 25% of the maximal effect obtained with 1 nM E2. The decrease in the luciferase activity at high MC-LR concentrations can be explained by a cytotoxic effect. No synergistic estrogenic effect was observed when each toxin was co-administrated with E2. However, the induction of the luciferase activity by NOD-R and MC-LR was inhibited by co-treatment with 1 microM of the pure estrogenic receptor (ER) antagonist ICI 182,780, thus proving the ER-dependency of the estrogenic effect.

Modulation of cytokine expression in human myeloid dendritic cells by environmental endocrine-disrupting chemicals involves epigenetic regulation

BACKGROUND

Exposure to environmental endocrine-disrupting chemicals (EDCs) is often associated with dysregulated immune homeostasis, but the mechanisms of action remain unclear.

OBJECTIVES

The aim of this study was to test a hypothesis that EDCs regulate the functions of human dendritic cells, a front-line, immunoregulatory cell type in contact with the environment.

METHODS

We investigated circulating myeloid dendritic cells (mDCs) from five subjects and measured their responses, with or without coculture with autologous T cells, to two common EDCs, nonylphenol (NP) and 4-octylphenol (4-OP). EDC-associated cytokine responses, signaling events, and histone modifications were examined using ELISA, Western blotting, and chromatin immunoprecipitation (ChIP) assays, respectively.

RESULTS

In all cases, mDCs treated with NP or 4-OP demonstrated increased expression of tumor necrosis factor-alpha (TNF-alpha) but decreased baseline and lipopolysaccharide (LPS)-induced (interleukin) (IL)-10 production; the increase in TNF-alpha was partially reversible by an estrogen receptor (ER) antagonist. Activation of the MKK3/6-p38 signaling pathway marked the effect of NP on TNF-alpha expression, concomitant with enhanced levels of methyltranferase complex [mixed-lineage leukemia (MLL) and tryptophan-aspartic acid repeat domain 5 (WDR5)] in the nucleus and of trimethylated H3K4, acetylated H3, and H4 at the TNFA gene locus. Further, up-regulated TNF-alpha expression was significantly suppressed in NP-treated mDCs by a histone acetyltransferase inhibitor. In the presence of NP-treated mDCs, T cells showed increased levels of IL-13 but decreased expression of interferon-gamma.

CONCLUSIONS

These results suggest that NP and 4-OP may have functional effects on the response of mDCs via, in part, the ER, MKK3/6-p38 MAPK signaling pathway, and histone modifications, with subsequent influence on the T-cell cytokine responses.

Occurrence of estrogenic mycotoxin - Zearalenone in aqueous environmental samples with various NOM content

Zearalenone is a mycotoxin produced by some Fusarium species in food and feed. Toxicity of ZEA and its metabolites is related to the chemical structure of the mycotoxins, similar to naturally occurring estrogens. Currently, there is increasing awareness of the significance of fungi and their toxic metabolites in water. Thus it was considered essential to determine the concentration of estrogenic toxin in surface waters, groundwater and wastewater in Poland. The application of ZearalaTest immunoaffinity columns for zearalenone determination by HPLC method in water samples characterized by different natural organic matter (NOM) content gave the recovery rate ranging from 74 to 86%. Obtained results showed that the natural organic micropollutants of water with low molecular masses have an effect on zearalenone recovery. Zearalenone was present in water samples in the range from 0 to 43.7 ngL(-1).

Biotransformation of bisphenol F by human and rat liver subcellular fractions

Bisphenol F [4,4'-dihydroxydiphenyl-methane] (BPF) has a broad range of applications in industry (liners lacquers, adhesives, plastics, coating of drinks and food cans). Free monomers of this bisphenol can be released into the environment and enter the food chain, very likely resulting in the exposure of humans to low doses of BPF. This synthetic compound has been reported to be estrogenic. A study of BPF distribution and metabolism in rats has demonstrated the formation of many metabolites, with multiple biotransformation pathways. In the present work we investigated the in vitro biotransformation of radio-labelled BPF using rat and human liver subcellular fractions. BPF metabolites were separated, isolated by high-performance liquid chromatography (HPLC), and analysed by mass spectrometry (MS), MS(n), and nuclear magnetic resonance (NMR). Many of these metabolites were characterized for the first time in mammals and in humans. BPF is metabolised into the corresponding glucuronide and sulfate (liver S9 fractions). In addition to these phase II biotransformation products, various hydroxylated metabolites are formed, as well as structurally related apolar metabolites. These phase I metabolic pathways are dominant for incubations carried out with liver microsomes and also present for incubations carried out with liver S9 fractions. The formation of the main metabolites, namely meta-hydroxylated BPF and ortho-hydroxylated BPF (catechol BPF) is P450 dependent, as is the formation of the less polar metabolites characterized as BPF dimers. Both the formation of a catechol and of dimeric metabolites correspond to biotransformation pathways shared by BPF, other bisphenols and estradiol.

Assessing and managing risks arising from exposure to endocrine-active chemicals

Managing risks to human health and the environment produced by endocrine-active chemicals (EAC) is dependent on sound principles of risk assessment and risk management, which need to be adapted to address the uncertainties in the state of the science of EAC. Quantifying EAC hazard identification, mechanisms of action, and dose-response curves is complicated by a range of chemical structure/toxicology classes, receptors and receptor subtypes, and nonlinear dose-response curves with low-dose effects. Advances in risk science including toxicogenomics and quantitative structure-activity relationships (QSAR) along with a return to the biological process of hormesis are proposed to complement existing risk assessment strategies, including that of the Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC 1998). EAC represents a policy issue that has captured the public's fears and concerns about environmental health. This overview describes the process of EAC risk assessment and risk management in the context of traditional risk management frameworks, with emphasis on the National Research Council Framework (1983), taking into consideration the strategies for EAC management in Canada, the United States, and the European Union.

Ten years of mixing cocktails: a review of combination effects of endocrine-disrupting chemicals

In the last 10 years, good evidence has become available to show that the combined effects of endocrine disruptors (EDs) belonging to the same category (e.g., estrogenic, antiandrogenic, or thyroid-disrupting agents) can be predicted by using dose addition. This is true for a variety of end points representing a wide range of organizational levels and biological complexity. Combinations of EDs are able to produce significant effect, even when each chemical is present at low doses that individually do not induce observable effects. However, comparatively little is known about mixtures composed of chemicals from different classes of EDs. Nevertheless, I argue that the accumulated evidence seriously undermines continuation with the customary chemical-by-chemical approach to risk assessment for EDs. Instead, we should seriously consider group-wise regulation of classes of EDs. Great care should be taken to define such classes by using suitable similarity criteria. Criteria should focus on common effects, rather than common mechanisms. In this review I also highlight research needs and identify the lack of information about exposure scenarios as a knowledge gap that seriously hampers progress with ED risk assessment. Future research should focus on investigating the effects of combinations of EDs from different categories, with considerable emphasis on elucidating mechanisms. This strategy may lead to better-defined criteria for grouping EDs for regulatory purposes. Also, steps should be taken to develop dedicated mixtures exposure assessment for EDs.

Di-n-butylphthalate and butylbenzylphthalate - urinary metabolite levels and estimated daily intakes: pilot study for the German Environmental Survey on children

We analysed urine samples from the 2001/2002 pilot study of the German Environmental Survey on Children (GerES IV) for the concentrations of the di-n-butylphthalate (DnBP) metabolite mono-n-butylphthalate (MnBP) and the butlybenzylphthalate (BBzP) metabolite mono-benzyl-phthalate (MBzP). The study population consisted of 239 children (106 boys, 133 girls) aged between 2 and 14 years (median 8.5 years). We applied two calculation models to estimate the daily intake for the two parent phthalates from metabolite excretion. One was based on the creatinine-related metabolite concentrations; the other was based on the volume-related metabolite concentrations. Median urinary metabolite concentrations were 174 microg/l (136 microg/g creatinine) for MnBP and 19.7 microg/l (15.3 microg/g creatinine) for MBzP. Such levels have been determined in German children before. Compared to the USA, German median MnBP levels were about 3-10 times higher, whereas MBzP levels were in the same range. Median daily intakes calculated with the creatinine-based model were 4.07 (range: 0.66-76.4; 95th percentile: 14.9) microg/kg body weight (bw)/day for DnBP and 0.42 (range: 0.06-13.9; 95th percentile: 2.57) microg/kg bw/day for BBzP. Daily intakes calculated with the volume-based model were approximately two times higher with a median of 7.61 (range: 0.91-110; 95th percentile: 30.5) microg/kg bw/day for DnBP and a median of 0.77 (range: 0.05-31.3; 95th percentile: 4.48) microg/kg bw/day for BBzP. Using the creatinine model, 28 (11.7%) of the 239 children exceeded the TDI for DnBP of 10 microg/kg bw/day defined by the European Union. Employing the volume model, 89 (37.2%) children exceeded the TDI. For BBzP, no preventive limit values (TDI or RfD) were exceeded. For both phthalates and independent of the model, we found increasing daily intakes with decreasing age. Between 25% (creatinine model) and 50% (volume model) of the 2-4-year old children had daily intakes for DnBP above the TDI.

Developmental exposure to xenoestrogen enhances spatial learning in male rats

Steroid hormones have profound effects on the development and function of the nervous system. Environmental estrogens or xenoestrogens are manmade or are natural compounds, which mimics the action of estrogen hormones. The experimental evidence for impairment of cognitive functions in humans and mammals following exposure to xenoestrogens has been fiercely debated. The strongest arguments against such studies have been that the route, time course, and intensity of exposure did not simulate environmental exposure, and that the chemicals tested have additional, non-estrogenic toxic effects, hindering a generalization of actual "xenoestrogenic" effects. Here we show that an environmental-like exposure to the pure estrogen, 17alpha-ethynylestradiol (EE2) during development enhances spatial learning abilities in adult male Sprague-Dawley rats. To simulate an environmental exposure, we used a very low dose (4 ng/kg/day) of EE2 equivalent to concentrations measured in European and US streams which was given orally with a non-invasive method, and we extended the treatment for the entire course of development, from conception to puberty. The animals were tested in a Morris water maze protocol at 6 months of age. Male rats treated with EE2 during development showed a faster learning during the training phase, and remembered better the position of the hidden platform in the short term. Our study demonstrates that actual levels of exposure to xenoestrogens can permanently alter cognitive abilities of a mammalian species.

Hepatic gene expression profiling using Genechips in zebrafish exposed to 17alpha-ethynylestradiol

Genomic, proteomic, and metabolomic technologies continue to receive increasing interest from environmental toxicologists. This interest is due to the great potential of these technologies to identify detailed modes of action and to provide assistance in the evaluation of a contaminant's risk to aquatic organisms. Our experimental model is the zebrafish (Danio rerio) exposed to reference endocrine disrupting compounds in order to investigate compound-induced changes in gene transcript profiles. Adult, female zebrafish were exposed to 0, 15, 40, and 100ng/L of 17alpha-ethynylestradiol (EE2) and concentration and time-dependent changes in hepatic gene expression were examined using Affymetrix GeneChip Zebrafish Genome Microarrays. At 24, 48, and 168h, fish were sacrificed and liver mRNA was extracted for gene expression analysis (24 and 168h only). In an effort to link gene expression changes to effects on higher levels of biological organization, body and ovary weights were measured and blood was collected for measurement of plasma steroid hormones (17beta-estradiol (E2), testosterone (T)) and vitellogenin (VTG) using ELISA. EE2 exposure significantly affected gene expression, GSI, E2, T, and VTG. We observed 1622 genes that were significantly affected (p< or =0.001) in a concentration-dependent manner by EE2 exposure at either 24 or 168h. Gene ontology (GO) analysis revealed that EE2 exposure affected genes involved in hormone metabolism, vitamin A metabolism, steroid binding, sterol metabolism, and cell growth. Plasma VTG was significantly increased at 24, 48, and 168h (p< or =0.05) at 40 and 100ng/L and at 15ng/L at 168h. E2 and T were significantly reduced following EE2 exposure at 48 and 168h. GSI was decreased in a concentration-dependent manner at 168h. In this study, we identified genes involved in a variety of biological processes that have the potential to be used as markers of exposure to estrogenic substances. Future work will evaluate the use of these genes in zebrafish exposed to weak estrogens to determine if these genes are indicative of exposure to estrogens with varying potencies.

Development of a stickleback kidney cell culture assay for the screening of androgenic and anti-androgenic endocrine disrupters

Issues raised by the presence in the environment of chemicals able to mimic or antagonize the action of androgenic hormones are of growing concern. Here we report the development of a novel in vitro test for the screening of (anti-)androgenic chemicals, based on primary cultures of stickleback kidney cells that produce a protein, the spiggin, in response to androgenic stimulation. Cell spiggin content was measured by ELISA. Comparison between cell cultures from quiescent males, photoperiodically stimulated males, control females and dihydrotestosterone (DHT)-primed females led to the selection of cell cultures from DHT-primed females for the development of a standardized protocol. 48h of treatment with androgens proved to be sufficient to induce concentration-dependent increase in spiggin cell content with a high sensitivity. DHT induced a significant spiggin increase at 10(-12)M, while testosterone (T) and the teleost specific androgen 11-ketotestosterone (11-KT) had a significant effect at 10(-10)M. Maximal responses were obtained with 10(-8)M DHT and 10(-6)M T and 11-KT. This indicates a higher sensitivity to DHT than to T and 11-KT, in agreement with previous data on stickleback kidney androgen receptor affinity. No effect was observed with other steroids or thyroid hormone, indicating the androgen specificity of the test. The anabolic steroid 17beta-Trenbolone (TB) was able to stimulate spiggin synthesis in a concentration-dependent manner with a significant effect at a concentration as low as 10(-10)M, and a maximal effect at 10(-6)M. The synthetic human androgen receptor antagonist, flutamide had no effect alone, but concentration-dependently inhibited the stimulatory effect of 10(-8)M 11-KT with a complete inhibition at 10(-6)M flutamide. This cell culture system provides an innovative tool for the rapid and sensitive screening of androgenic and anti-androgenic properties of environmental contaminants.

Alteration of steroid hormone profile in juvenile turbot (Psetta maxima) as a consequence of short-term exposure to 17alpha-ethynylestradiol

The synthetic estrogen 17alpha-ethynylestradiol (EE2) is among the most potent xenoestrogens found in treated sewage. Adverse effects have been reported in fish exposed to this chemical, such as vitellogenin induction or alteration of gonad structure. In this study, the effects of EE2 on sex steroid profile in juvenile turbot (Psetta maxima) were investigated in a 15-day in vivo experiment. An analytical method was developed for the simultaneous gas chromatography/mass spectrometry determination of 14 steroids in gonads, plasma and bile. The impact of EE2 on the endocrine status of juvenile turbot was sex-dependent, since males were much more sensitive than females. Even at very low concentration (3.5 ng l(-1)), EE2 depressed androgen production as well as plasma levels in males. Androstenedione and 11-ketotestosterone were highly affected by EE2-exposure, since their production was suppressed in EE2-treated males. Furthermore, testis estrogen production and conjugation increased as a consequence of EE2 exposure. Overall, the ratio of androgens to estrogens in EE2-exposed males dropped in testis and plasma and reached values observed in females. These results indicate that juvenile male turbots are susceptible to hormonal imbalance as a consequence of short-term exposure to environmentally relevant EE2 levels.

A repeated 28-day oral dose toxicity study of nonylphenol in rats, based on the 'Enhanced OECD Test Guideline 407' for screening of endocrine-disrupting chemicals

A 28-day repeated oral dose toxicity study of nonylphenol (NP) was performed for an international validation of the 'Enhanced OECD Test Guideline 407' paying particular attention to the sensitivity of individual endocrine-related parameters. Sprague-Dawley rats, each group consisting of ten males and ten females, were administered NP once daily by gavage at doses of 0 (control), 10, 50, or 250 mg/kg body weight. At 250 mg/kg, three females died or became moribund during the experiment. At this dose, hepatic and renal toxicity was evident in both sexes with increase of relative liver and kidney weights as well as histopathological changes, such as centrilobular liver cell hypertrophy and a variety of renal tubular lesions, and alteration of serum biochemical parameters, some of them being evident from 50 mg/kg in females (glucose and inorganic phosphates). Hematologically, development of anemia was evident at 250 mg/kg in both sexes. Regarding endocrine-related effects, increase of thyroid weight in males was detected from 50 mg/kg. At 250 mg/kg, males exhibited reduction of relative weights of the ventral prostate and seminal vesicles, and females developed irregular estrous cyclicity and vaginal mucosal hyperplasia. Although changes in serum hormone levels were detected in both sexes, magnitude of the changes was small to be regarded as a low toxicological significance. In summary, repeated oral doses of NP to rats for 28 days resulted in hepato-renal toxicity from 50 mg/kg and anemia at 250 mg/kg. Effects on the endocrine system were observed from 50 mg/kg, and assessment of weights and histopathology of endocrine-related organs and estrous cyclicity may be valid in a battery for detecting endocrine effects of NP. The no-observed-adverse-effect level of NP was estimated to be 10 mg/kg per day.

Endocrine regulation of HOX genes

Hox genes have a well-characterized role in embryonic development, where they determine identity along the anteroposterior body axis. Hox genes are expressed not only during embryogenesis but also in the adult, where they are necessary for functional differentiation. Despite the known function of these genes as transcription factors, few regulatory mechanisms that drive Hox expression are known. Recently, several hormones and their cognate receptors have been shown to regulate Hox gene expression and thereby mediate development in the embryo as well as functional differentiation in the adult organism. Estradiol, progesterone, testosterone, retinoic acid, and vitamin D have been shown to regulate Hox gene expression. In the embryo, the endocrine system directs axial Hox gene expression; aberrant Hox gene expression due to exposure to endocrine disruptors contributes to the teratogenicity of these compounds. In the adult, endocrine regulation of Hox genes is necessary to enable such diverse functions as hematopoiesis and reproduction; endocrinopathies can result in dysregulated HOX gene expression affecting physiology. By regulating HOX genes, hormonal signals utilize a conserved mechanism that allows generation of structural and functional diversity in both developing and adult tissues. This review discusses endocrine Hox regulation and its impact on physiology and human pathology.

Alteration of steroid hormone balance in juvenile turbot (Psetta maxima) exposed to nonylphenol, bisphenol A, tetrabromodiphenyl ether 47, diallylphthalate, oil, and oil spiked with alkylphenols

In recent years, concern has been raised about the ability of some classes of environmental contaminants to disrupt the endocrine system of both humans and wildlife. In this study, juvenile turbots (Psetta maxima) were exposed under laboratory conditions to selected waterborne contaminants: oil, oil spiked with alkylphenols, bisphenol A, diallylphthalate, tetrabrominated diphenyl ether 47, and p-nonylphenol as a positive control for "estrogenic-type" effects. This work focused on sex steroids, because these hormones play a key role in the reproduction process. Analytical procedures, involving the off-line coupling of solid phase extraction and gas chromatography/mass spectrometry, were developed for the determination of 12 endogenous sex steroids levels in fish plasma, bile, and gonads. Because of the sexual immaturity of the fish used in this study, however, only six steroids could be detected in juvenile turbots. Bisphenol A and p-nonylphenol exhibited the highest potency towards steroids dynamics, lowering the ratio of androgens to estrogens in all three studied matrices. However, these two chemicals had different modes of action, because p-nonylphenol induced a decrease of androstenedione and 11-ketotestosterone levels, whereas bisphenol A exposure led to an elevation of estrone level. Overall, these two chemicals seemingly disrupted the activity of some steroidogenesis enzymes, leading to serious hormonal imbalance in juvenile turbot.

Endocrine disrupting compounds and prostate cancer

Prostate cancer is a major health concern and is treated based on its hormone dependence. Agents that alter hormone action can have substantial biological effects on prostate cancer development and progression. As such, there is significant interest in uncovering the potential effects of endocrine disrupting compound (EDC) exposure on prostate cancer. The present review is focused on agents that alter hormone action in the prostate and how they may impact cancer growth or treatment.