3D models of MBP, a biologically active metabolite of bisphenol A, in human estrogen receptor α and estrogen receptor β

The Conflict between Regulatory Agencies over the 20,000-Fold Lowering of the Tolerable Daily Intake (TDI) for Bisphenol A (BPA) by the European Food Safety Authority (EFSA)

BACKGROUND

The European Food Safety Authority (EFSA) recommended lowering their estimated tolerable daily intake (TDI) for bisphenol A (BPA) 20,000-fold to 0.2  ng / kg  body weight  ( BW ) / day . BPA is an extensively studied high production volume endocrine disrupting chemical (EDC) associated with a vast array of diseases. Prior risk assessments of BPA by EFSA as well as the US Food and Drug Administration (FDA) have relied on industry-funded studies conducted under good laboratory practice protocols (GLP) requiring guideline end points and detailed record keeping, while also claiming to examine (but rejecting) thousands of published findings by academic scientists. Guideline protocols initially formalized in the mid-twentieth century are still used by many regulatory agencies. EFSA used a 21st century approach in its reassessment of BPA and conducted a transparent, but time-limited, systematic review that included both guideline and academic research. The German Federal Institute for Risk Assessment (BfR) opposed EFSA's revision of the TDI for BPA.

OBJECTIVES

We identify the flaws in the assumptions that the German BfR, as well as the FDA, have used to justify maintaining the TDI for BPA at levels above what a vast amount of academic research shows to cause harm. We argue that regulatory agencies need to incorporate 21st century science into chemical hazard identifications using the CLARITY-BPA (Consortium Linking Academic and Regulatory Insights on BPA Toxicity) nonguideline academic studies in a collaborative government-academic program model.

DISCUSSION

We strongly endorse EFSA's revised TDI for BPA and support the European Commission's (EC) apparent acceptance of this updated BPA risk assessment. We discuss challenges to current chemical risk assessment assumptions about EDCs that need to be addressed by regulatory agencies to, in our opinion, become truly protective of public health. Addressing these challenges will hopefully result in BPA, and eventually other structurally similar bisphenols (called regrettable substitutions) for which there are known adverse effects, being eliminated from all food-related and many other uses in the EU and elsewhere. https://doi.org/10.1289/EHP13812.

In silico simulations and molecular descriptors to predict in vitro transactivation potencies of Baikal seal estrogen receptors by environmental contaminants

Baikal seals (Pusa sibirica) are vulnerable to high levels of organic pollutants. Here, we evaluated the transactivation potencies of bisphenols (BPs) and hydroxylated polychlorinated biphenyls (OH-PCBs) via the Baikal seal estrogen receptor α and β (bsERα and bsERβ) using in vitro and in silico approaches. In vitro reporter gene assays showed that most BPs and OH-PCBs exhibited estrogenic activity with bsER sub-type-specific potency. Among the BPs tested, bisphenol AF showed the lowest EC50 for both bsERs. 4'-OH-CB50 and 4'-OH-CB30 showed the lowest EC50 among OH-PCBs tested for bsERα and bsERβ, respectively. 4-((4-Isopropoxyphenyl)-sulfonyl)phenol, 4'-OH-CB72, and 4'-OH-CB121 showed weak bsERα-specific transactivation. Only 4-OH-CB107 did not affect both bsERs. In silico docking simulations revealed the binding affinities of these chemicals to bsERs and partially explained the in vitro results. Using the in silico simulations and molecular descriptors as explanatory variables and the in vitro results as objective variables, the quantitative structure-activity relationship (QSAR) models constructed for classification and regression accurately separated bsER-active compounds from non-active compounds and predicted the in vitro bsERα- and bsERβ-transactivation potencies, respectively. The QSAR models also suggested that chemical polarity, van der Waals surface area, bridging atom structure, position of the phenolic-OH group, and ligand interactions with key residues of the ligand binding pocket are critical variables to account for the bsER transactivation potency of the test compounds. We also succeeded in constructing computational models for predicting in vitro transactivation potencies of mouse ERs in the same manner, demonstrating the applicability of our approach independent of species-specific responses.

Repeated exposure to 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP) accelerates ligand-independent activation of estrogen receptors in long-term estradiol-deprived MCF-7 cells

It was previously identified that there may be an active metabolite of bisphenol A (BPA), 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP). An in vitro system was developed to detect MBP toxicity to the Michigan Cancer Foundation-7 (MCF-7) cells that had been repeatedly exposed to a low dose of the metabolite. MBP profoundly activated estrogen receptor (ER)-dependent transcription as a ligand, with an EC₅₀ of 2.8 nM. Women are continuously exposed to numerous estrogenic environmental chemicals; but their susceptibility to these chemicals may be significantly altered after menopause. Long-term estrogen-deprived (LTED) cells, which display ligand-independent ER activation, are a postmenopausal breast cancer model derived from MCF-7 cells. In this study, we investigated the estrogenic effects of MBP on LTED cells in a repeated exposure in vitro model. The results suggest that i) nanomolar levels of MBP reciprocally disrupt the balanced expression of ERα and ERβ proteins, leading to the dominant expression of ERβ, ii) MBP stimulates ERs-mediated transcription without acting as an ERβ ligand, and iii) MBP utilizes mitogen-activated protein kinase and phosphatidylinositol-3 kinase signaling to evoke its estrogenic action. Moreover, the repeated exposure strategy was effective for detecting low-dose estrogenic-like effects caused by MBP in LTED cells.

System-wide health risk prediction for 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene(MBP), a major active metabolite of environmental pollutant and food contaminant - Bisphenol A

Human exposure to plastic contaminated foods and environmental micro/nano plastic derived chemicals necessitates system-wide health risk assessment. Hence, current study intend to explore the mode of action (MoA) based adverse outcome pathways of 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), the major active metabolite of bisphenol A (BPA). The computational study employed broad range of target prediction, systems biology tools and molecular docking protocols. Further, validation of MBP targets was done using protein-ligand fluorescence quenching assay, endothelial cell culture and chicken embryo vascular angiogenesis models. Interestingly, the current results illustrate that various physiological signaling pathways (MAPK and VEGF related angiogenesis signaling) and disease progression pathways (hypertension, cancer and endocrine disorders) were enriched as potential targets of MBP. Further, docking studies highlights the possible binding mechanism of MBP with important targets including endothelial nitric oxide synthase (eNOS) and serum albumin (BSA). In addition, the validation studies on MBP-BSA interaction (fluorescence quenching), eNOS derived nitric oxide (NOx) generation in endothelial cells and chicken embryo angiogenesis support the system-wide impacts of MBP with highlights on cardiovascular pathogenesis. Thus, the current observation provides novel insights into the system wide impacts of MBP for the futuristic health risk assessment of plastic derived chemicals.

Bisphenol S induces Agrp expression through GPER1 activation and alters transcription factor expression in immortalized hypothalamic neurons: A mechanism distinct from BPA-induced upregulation

The increasing prevalence of obesity around the world has brought concern upon ubiquitously present obesogenic environmental compounds, such as bisphenol A (BPA). Increasingly tightened regulations on the industrial use of BPA have prompted a transition to a structurally similar alternative, bisphenol S (BPS). BPS displays endocrine-disrupting behaviours similar to those of BPA and increases body weight, food intake and the hypothalamic expression of Agrp in vivo. However, the mechanisms behind this deleterious effect are unclear. Here, we report an increase in the mRNA level of Agrp at 4 h following BPS treatment in immortalized murine hypothalamic cell lines of embryonic and adult origin (mHypoE-41, mHypoA-59). BPS-induced changes in the expression of transcription factors and estrogen receptors that occurred concurrently with Agrp upregulation demonstrated similarities to BPA-induced changes, however, there were also changes that were unique to BPS. Specifically, while Chop, Atf3, Atf4, Atf6, Klf4, and Creb1 were upregulated and Gper1 was downregulated by both BPA and BPS, Esr1 mRNA levels were upregulated and Foxo1 and Stat3 levels remained unchanged by BPS. Finally, inhibition of GPER1 by G15 prevented BPS-mediated Agrp upregulation, independent of Atf3 and Klf4 upregulation. Overall, our results demonstrate the ability of BPS to increase Agrp mRNA expression through GPER1 signaling and to alter transcription factor expression in hypothalamic neurons, further elucidating the endocrine-disrupting potential of this alternative industrial chemical.

The bisphenol A metabolite MBP causes proteome alterations in male Cyprinodon variegatus fish characteristic of estrogenic endocrine disruption

The toxicological status of bisphenol A (BPA) is under strong debate. Whereas in vitro it is an agonist of the estrogen receptor with a potency ca. 10⁵-fold lower than the natural female hormone estradiol, in vivo exposure causes only mild effects at concentration thresholds environmentally not relevant and inconsistent among species. By using a proteomic approach, shotgun liver proteome analysis, we show that 7-d exposure to 10 μg/L of the BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), and not the same exposure to the parental molecule BPA, alters the liver proteome of male Cyprinodon variegatus fish. Different physiological and environmental conditions leading to biotransformation of BPA to MBP may partly explain the conflicting results so far reported for in vivo BPA exposures. The pattern of alteration induced by MBP is similar to that caused by estradiol, and indicative of estrogenic endocrine disruption. MBP enhanced ribosomal activity, protein synthesis and transport, with upregulation of 91% of the ribosome-related proteins, and 12 proteins whose expression is regulated by estrogen-responsive elements, including vitellogenin and zona pellucida. Whey acidic protein (WAP) was the protein most affected by MBP exposure (FC = 68). This result points at WAP as novel biomarker for xenoestrogens.

Estrogenic Activity of Tetrazole Derivatives Bearing Bisphenol Structures: Computational Studies, Synthesis, and In Vitro Assessment

The classification of bisphenol A (BPA) as an industrial endocrine disruptor has led to a ban of this ubiquitous critical starting material from food and medical applications. Thus, scientists worldwide are researching to develop non-ER binding starting compounds to fulfill unmet market needs. In line with this trending research topic, the current paper highlights the development of tetrazole derivatives bearing a bisphenol structure (TbB) as a novel weak binder or potential inactive to the estrogen receptor (ER) and androgen receptor (AR). The structure and ligand-based approach supported by binding affinity analysis, electrostatic complementarity, ADMET prediction, and in silico studies identified TbBs as privileged substitutes for BPA. Five TbB ligands were successfully synthesized and subjected to biological testing comprising radioligand competitive binding and functional cellular assays. The measured IC₅₀ value for BPA was found to be 0.24 μM, whereas all the inhibitions were less than 15% for the two TbB ligands, 223-2 and 223-3. As these TbB ligands did not meet the established acceptance criteria of 50% inhibition, they are considered as extremely weak binders to ERα. Steric clashes, the desolvation effect, and the increased total polar surface area (TPSA) of TbB ligands in the hydrophobic binding site are hypothesized to be possible reasons for low binding. Modeling studies complemented by bioassays highlight TbB compounds as privileged prospective BPA replacements. However, more research on TbB ligand toxicity is needed to understand and substantiate that the adverse effects on the hormonal system, for example, via metabolic activation, are not elicited.

Endocrine-Disrupting Chemicals and Their Adverse Effects on the Endoplasmic Reticulum

There is growing concern regarding the health and safety issues of endocrine-disrupting chemicals (EDCs). Long-term exposure to EDCs has serious adverse health effects through both hormone-direct and hormone-indirect ways. Accordingly, some EDCs can be a pathogen and an inducer to the susceptibility of disease, even if they have a very low affinity on the estrogen receptor, or no estrogenic effect. Endoplasmic reticulum (ER) stress recently attracted attention in this research area. Because ER and ER stress could be key regulators of the EDC’s adverse effects, such as the malfunction of the organ, as well as the death, apoptosis, and proliferation of a cell. In this review, we focused on finding evidence which shows that EDCs could be a trigger for ER stress and provide specific examples of EDCs, which are known to cause ER stress currently.

Impact of bisphenol A (BPA) on cells and tissues at the human materno-fetal interface

Bisphenol A (BPA) is an endocrine disruptor extensively used in the production of polycarbonate plastics and epoxy resins and a component of liquid and food containers. It is a hazard in the prenatal period because of its presence in the placenta, fetal membranes, amniotic fluid, maternal and fetal blood and its ability to cross the placenta and reach the fetus. Estimation of the risk of BPA exposure during in utero life is extremely important in order to prevent complications of pregnancy and fetal growth. This review describes in vitro models of the human materno-fetal interface. It also outlines the effects of BPA at doses indicated as "physiological", namely at the concentrations found in the general population, and at "supraphysiological" and "subphysiological" doses, i.e. above and below the physiological range. This work will help clarify the discrepancies observed in studies on the effects of BPA on human reproduction and pregnancy, and it will be useful for the choice of appropriate in vitro models for future studies aimed at identifying the potential impact of BPA on specific functional processes.

Occurrence, Profiles and Ecological Risk of Bisphenol Analogues in a Municipal Sewage Treatment Plant

Due to the strict control on bisphenol A (BPA) in many countries, bisphenol analogues (BPs) are being widely used as alternative materials to manufacture epoxy resins and polycarbonate plastics, resulting in their occurrence in sewage treatment plants (STPs). In this study, the occurrence and distribution of 7 BPs in a large-scale STP in Beijing China was investigated. Wastewater samples were collected from the influents and effluents of each processing unit, and extracted by solid-phase extraction. Target compounds were quantified by ultra-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The total concentrations of seven BPs (ΣBPs) were 400.42 ± 48.12 ng/L in the raw sewage, 438.60 ± 46.50 ng/L in the primary effluent, 17.21 ± 13.12 ng/L in the secondary effluent, and 11.33 ± 4.84 ng/L in the tertiary effluent, respectively. Bisphenol S (BPS) and BPA were the predominant congener in raw sewage with an overall contribution of 29.32% and 70.22% to the ΣBPs, indicating that there was a large amount of BPS and BPA consumption in the study area. During a one-week sampling period, ΣBPs changed slightly at the same sampling site. It was found that high removal efficiencies were achieved for BPs in anoxic and oxic secondary clarifier treatment units, suggesting that biodegradation and sorption played major roles in BPs elimination in the STP. After tertiary treatment, all BPs except BPA were completely removed, suggesting the necessity to investigate the fate and toxicity of BPA in the aquatic environment.

Roles of ERK/Akt signals in mitochondria-dependent and endoplasmic reticulum stress-triggered neuronal cell apoptosis induced by 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene, a major active metabolite of bisphenol A

Bisphenol A (BPA) is recognized as a harmful pollutant in the worldwide. Growing studies have reported that BPA can cause adverse effects and diseases in human, and link to a potential risk factor for development of neurodegenerative diseases (NDs). 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), which generated in the mammalian liver after BPA exposure, is a major active metabolite of BPA. MBP has been suggested to exert greater toxicity than BPA. However, the molecular mechanism of MBP on the neuronal cytotoxicity remains unclear. In this study, MBP exposure significantly reduced Neuro-2a cell viability and induced apoptotic events that MBP (5-15 μM) exhibited greater neuronal cytotoxicity than BPA (50-100 μM). The mitochondria-dependent apoptotic signals including the decrease in mitochondrial membrane potential (MMP) and the increase in cytosolic apoptosis-induced factor (AIF), cytochrome c release, and Bax protein expression were involved in MBP (10 μM)-induced Neuro-2a cell death. Exposure of Neuro-2a cells to MBP (10 μM) also triggered endoplasmic reticulum (ER) stress through the induction of several key molecules including glucose-regulated protein (GRP)78, C/EBP homologous protein (CHOP), X-box binding protein (XBP)-1, protein kinase R-like ER kinase (PERK), eukaryotic initiation factor 2α (eIF2α), inositol-requiring enzyme(IRE)-1, activation transcription factor(AFT)4 and ATF6, and caspase-12. Pretreatment with 4-PBA (an ER stress inhibitor) and specific siRNAs for GRP78, CHOP, and XBP-1 significantly suppressed the expression of these ER stress-related proteins and the activation of caspase-12/-3/-7 in MBP-exposed Neuro-2a cells. Furthermore, MBP (10 μM) exposure dramatically increased the activation of extracellular regulated protein (ERK)1/2 and decreased Akt phosphorylation. Pretreatment with PD98059 (an ERK1/2 inhibitor) and transfection with the overexpression of activation of Akt1 (myr-Akt1) effectively suppressed MBP-induced apoptotic and ER stress-related signals. Collectively, these results demonstrate that MBP exposure exerts neuronal cytotoxicity via the interplay of ERK activation and Akt inactivation-regulated mitochondria-dependent and ER stress-triggered apoptotic pathway, which ultimately leads to neuronal cell death.

Update on the Health Effects of Bisphenol A: Overwhelming Evidence of Harm

In 1997, the first in vivo bisphenol A (BPA) study by endocrinologists reported that feeding BPA to pregnant mice induced adverse reproductive effects in male offspring at the low dose of 2 µg/kg/day. Since then, thousands of studies have reported adverse effects in animals administered low doses of BPA. Despite more than 100 epidemiological studies suggesting associations between BPA and disease/dysfunction also reported in animal studies, regulatory agencies continue to assert that BPA exposures are safe. To address this disagreement, the CLARITY-BPA study was designed to evaluate traditional endpoints of toxicity and modern hypothesis-driven, disease-relevant outcomes in the same set of animals. A wide range of adverse effects was reported in both the toxicity and the mechanistic endpoints at the lowest dose tested (2.5 µg/kg/day), leading independent experts to call for the lowest observed adverse effect level (LOAEL) to be dropped 20 000-fold from the current outdated LOAEL of 50 000 µg/kg/day. Despite criticism by members of the Endocrine Society that the Food and Drug Administration (FDA)'s assumptions violate basic principles of endocrinology, the FDA rejected all low-dose data as not biologically plausible. Their decisions rely on 4 incorrect assumptions: dose responses must be monotonic, there exists a threshold below which there are no effects, both sexes must respond similarly, and only toxicological guideline studies are valid. This review details more than 20 years of BPA studies and addresses the divide that exists between regulatory approaches and endocrine science. Ultimately, CLARITY-BPA has shed light on why traditional methods of evaluating toxicity are insufficient to evaluate endocrine disrupting chemicals.

Complete Genome Sequence of Bisphenol A-Degrading Bacterium Sphingobium sp. Strain A3, Isolated from Contaminated Soil

This study reports the complete genome sequence of bisphenol A-degrading bacterium Sphingobium sp. strain A3, which was isolated from a contaminated soil sample from the site of a factory fire in South Korea. The genome consists of a 6.53-Mbp chromosome and eight plasmid contigs (532,947 bp), with 6,406 protein-coding sequences and a GC content of 63.82%.

This study reports the complete genome sequence of bisphenol A-degrading bacterium Sphingobium sp. strain A3, which was isolated from a contaminated soil sample from the site of a factory fire in South Korea. The genome consists of a 6.53-Mbp chromosome and eight plasmid contigs (532,947 bp), with 6,406 protein-coding sequences and a GC content of 63.82%.

A guide towards safe, functional and renewable BPA alternatives by rational molecular design: structure–property and structure–toxicity relationships

Putting the pieces together: a guide for rational molecular design of safe, functional and renewable BPA alternatives.

Endocrine disruption: Molecular interactions of environmental bisphenol contaminants with thyroid hormone receptor and thyroxine-binding globulin

Many bisphenol A (BPA) analogs have been commercially used recently, such as 2,2-bis(4-hydroxyphenyl)butane (BPB), 4,4′-ethylidenebisphenol, 4,4′-methylenediphenol (BPF), 4,4′-(1,4-phenylenediisopropylidene)bisphenol (BPP), 4,4′-dihydroxydiphenyl sulfone (BPS), 4,4′-cyclohexylidenebisphenol (BPZ), 4,4′-(hexafluoroisopropylidene)diphenol (BPAF), 4,4′-(1-phenylethylidene)bisphenol (BPAP), and 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane (TMBPA), to circumvent adverse effects of BPA. However, their increasing use is also contaminating the environment, which is a potential cause of concern for human health. Thyroid hormone transport and signaling are potential targets for endocrine-disrupting activity of BPA analogs. Thyroxine-binding globulin (TBG) is the major carrier protein for thyroxine (T4) and triiodothyronine (T3) in blood. Thyroid hormones exert their action through thyroid hormone receptors (TRα and TRβ). This report presents the thyroid-disrupting potential of indicated nine BPA analogs from structure-based studies with TBG and TRα. Each BPA analog formed important polar and hydrophobic interactions with a number of residues of TBG and TRα. Majority of TBG residues (77–100%) and TRα residues (70–91%) interacting with BPA analogs were common with those of native ligands T4 and T3, respectively. Majority of BPA analogs interacted with TBG forming a salt bridge interaction at Lys-270. The hydrogen-bonding interaction of T3 with TRα at His-381 was also shared by majority of analogs. The binding energy for BPP, BPB, BPZ, BPAP, and TMBPA with both proteins was closer to binding energy of respective native ligands. The similarity in structural binding characteristics suggested potential disrupting activity of thyroid hormone signaling and transport.

Molecular interactions of thyroxine binding globulin and thyroid hormone receptor with estrogenic compounds 4-nonylphenol, 4-tert-octylphenol and bisphenol A metabolite (MBP)

AIM

Endocrine disruption due to environmental chemical contaminants is a global human health issue. The aim of present study was to investigate the structural binding aspects of possible interference of commonly detected environmental contaminants on thyroid function.

MATERIAL AND METHODS

Three compounds, 4-tert-octylphenol (4-tert-OP), 4-nonylphenol (4-NP), and 4-methyl-2,4-bis(4-hydroxypentyl)pent-1-ene (MBP) were subjected to induced fit docking (IFD) against thyroxine binding globulin (TBG) and thyroid hormone receptor (THR). Structural analysis included molecular interactions of the amino acid residues and binding energy estimation between the ligands and the target proteins.

KEY RESULTS

All the ligands were successfully placed in the ligand binding pocket of TBG and THR using induced fit docking (IFD). The IFD results revealed high percentage of commonality in interacting amino acid residues between the aforementioned compounds and the native ligand for both TBG and THR. The results of our study further revealed that all the compounds have the potential to interfere with thyroid transport and signaling. However, MBP showed higher binding affinity for both TBG and THR, suggesting higher thyroid disruptive potential as compared to 4-t-OP and 4-NP. Furthermore, our results also suggest that the reported disruptive effects of BPA could actually be exerted through its metabolite; MBP.

SIGNIFICANCE

This work implies that all the three compounds 4-NP, 4-t-OP and especially MBP have the potential to interfere with thyroid hormone transport and signaling. This potentially leads to disruption of thyroid hormone function.

A suggested bisphenol A metabolite (MBP) interfered with reproductive organ development in the chicken embryo while a human-relevant mixture of phthalate monoesters had no such effects

Bisphenol A (BPA) and phthalate diesters are ubiquitous environmental contaminants. While these compounds have been reported as reproductive toxicants, their effects may partially be attributed to metabolites. The aim of this study was to examine reproductive organ development in chicken embryos exposed to the BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP; 100 µg/g egg) or a human-relevant mixture of 4 phthalate monoesters (85 µg/g egg). The mixture was designed within the EU project EDC-MixRisk based upon a negative association with anogenital distance in boys at 21 months of age in a Swedish pregnancy cohort. Chicken embryos were exposed in ovo from an initial stage of gonad differentiation (embryonic day 4) and dissected two days prior to anticipated hatching (embryonic day 19). No discernible effects were noted on reproductive organs in embryos exposed to the mixture. MBP-treated males exhibited retention of Müllerian ducts and feminization of the left testicle, while MBP-administered females displayed a diminished the left ovary. In the left testicle of MBP-treated males, mRNA expression of female-associated genes was upregulated while the testicular marker gene SOX9 was downregulated, corroborating a feminizing effect by MBP. Our results demonstrate that MBP, but not the phthalate monoester mixture, disrupts both male and female reproductive organ development in an avian embryo model.

Genome-Wide Analysis of Low Dose Bisphenol-A (BPA) Exposure in Human Prostate Cells

Endocrine disrupting compounds (EDCs) have the potential to cause adverse effects on wild-life and human health. Two important EDCs are the synthetic estrogen 17α-ethynylestradiol (EE2) and bisphenol-A (BPA) both of which are xenoestrogens (XEs) as they bind the estrogen receptor and dis-rupt estrogen physiology in mammals and other vertebrates. In the recent years the influence of XEs on oncogenes, specifically in relation to breast and prostate cancer has been the subject of considerable study.

Cardiogenesis impairment promoted by bisphenol A exposure is successfully counteracted by epigallocatechin gallate

Exposure to the emerging contaminant bisphenol A (BPA) is ubiquitous and associated with cardiovascular disorders. BPA effect as endocrine disruptor is widely known but other mechanisms underlying heart disease, such as epigenetic modifications, remain still unclear. A compound of green tea, epigallocatechin gallate (EGCG), may act both as anti-estrogen and as inhibitor of some epigenetic enzymes. The aims of this study were to analyze the molecular processes related to BPA impairment of heart development and to prove the potential ability of EGCG to neutralize the toxic effects caused by BPA on cardiac health. Zebrafish embryos were exposed to 2000 and 4000 μg/L BPA and treated with 50 and 100 μM EGCG. Heart malformations were assessed at histological level and by confocal imaging. Expression of genes involved in cardiac development, estrogen receptors and epigenetic enzymes was analyzed by qPCR whereas epigenetic modifications were evaluated by whole mount immunostaining. BPA embryonic exposure led to changes in cardiac phenotype, induced an overexpression of hand2, a crucial factor for cardiomyocyte differentiation, increased the expression of estrogen receptor (esr2b), promoted an overexpression of a histone acetyltransferase (kat6a) and also caused an increase in histone acetylation, both mechanisms being able to act in sinergy. EGCG treatment neutralized all the molecular alterations caused by BPA, allowing the embryos to go on with a proper heart development. Both molecular mechanisms of BPA action (estrogenic and epigenetic) likely lying behind cardiogenesis impairment were successfully counteracted by EGCG treatment.

Neutrophils life under estrogenic and xenoestrogenic control

Over 100 years ago, scientists had identified cells that represent the most abundant population of peripheral blood leukocytes; they called this population neutrophils. Day by day, the knowledge specific to neutrophils is augmented with new and often surprising aspects and facts about neutrophils' life or death. Estrogens (estrone, estriol, and estradiol) are relevant for the regulation of immune responses that are related with neutrophils. An understanding of the molecular mechanism of the action of endogenous hormones allows us to predict the effects of the substances that commonly occur in an environment with estrogen-like properties (xenoestrogens (e.g., bisphenol A, DDT, tributyltin, polychlorinated biphenyls, nonylphenol and octylphenol)). Therefore, we summarize current literature on the impact of estrogens and xenoestrogens, on each aspect of neutrophil life, as well as describe its mechanism of actions in neutrophils.

Repeated Exposure to 4-Methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), an Active Metabolite of Bisphenol A, Aggressively Stimulates Breast Cancer Cell Growth in an Estrogen Receptor β (ERβ)-Dependent Manner

Bisphenol A (BPA), recognized as an endocrine disruptor, is thought to exert its activity through a mechanism involving the activation of estrogen receptors (ERs) α/β However, a major problem is that very high concentrations of BPA are required (i.e., those in excess of environmental levels) for effective activation of ERα/β-mediated transcriptional activities in vitro, despite the BPA-induced estrogenic effects observed in vivo. To elucidate the causal reasons, we successfully identified a BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), which exhibits highly potent estrogenic activity both in vivo and in vitro. We have focused on the biologic relationship between breast tumor promotion and MBP/BPA, because BPA is considered to be a human carcinogen owing to its breast tumor-promoting properties. In general, humans are exposed to many endocrine disruptors, including BPA. In the present study, we used the ERα/β-positive human breast cancer cell line MCF-7 as an experimental model to investigate the effects of repeated exposure to BPA/MBP at concentrations found in the environment on the expression of ERα/β and to determine the particular ER subtype involved. We demonstrated that repeated exposure to MBP, but not to BPA, significantly downregulated ERα protein expression and stimulated the proliferation of MCF-7 cells through the activation of ERβ-mediated signaling.

The promiscuous estrogen receptor: Evolution of physiological estrogens and response to phytochemicals and endocrine disruptors

Many actions of estradiol (E2), the principal physiological estrogen in vertebrates, are mediated by estrogen receptor-α (ERα) and ERβ. An important physiological feature of vertebrate ERs is their promiscuous response to several physiological steroids, including estradiol (E2), Δ⁵-androstenediol, 5α-androstanediol, and 27-hydroxycholesterol. A novel structural characteristic of Δ⁵-androstenediol, 5α-androstanediol, and 27-hydroxycholesterol is the presence of a C19 methyl group, which precludes the presence of an aromatic A ring with a C3 phenolic group that is a defining property of E2. The structural diversity of these estrogens can explain the response of the ER to synthetic chemicals such as bisphenol A and DDT, which disrupt estrogen physiology in vertebrates, and the estrogenic activity of a variety of plant-derived chemicals such as genistein, coumestrol, and resveratrol. Diversity in the A ring of physiological estrogens also expands potential structures of industrial chemicals that can act as endocrine disruptors. Compared to E2, synthesis of 27-hydroxycholesterol and Δ⁵-androstenediol is simpler, leading us, based on parsimony, to propose that one or both of these steroids or a related metabolite was a physiological estrogen early in the evolution of the ER, with E2 assuming this role later as the canonical estrogen. In addition to the well-studied role of the ER in reproductive physiology, the ER also is an important transcription factor in non-reproductive tissues such as the cardiovascular system, kidney, bone, and brain. Some of these ER actions in non-reproductive tissues appeared early in vertebrate evolution, long before the emergence of mammals.

Estrogenic Mechanisms and Cardiac Responses Following Early Life Exposure to Bisphenol A (BPA) and Its Metabolite 4-Methyl-2,4-bis( p-hydroxyphenyl)pent-1-ene (MBP) in Zebrafish

Environmental exposure to Bisphenol A (BPA) has been associated with a range of adverse health effects, including on the cardiovascular system in humans. Lack of agreement on its mechanism(s) of action likely stem from comparisons between in vivo and in vitro test systems and potential multiple effects pathways. In rodents, in vivo, metabolic activation of BPA produces 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP), which is reported to be up to 1000 times more potent as an estrogen than BPA. We investigated the estrogenic effects and estrogen receptor signaling pathway(s) of BPA and MBP following early life exposure using a transgenic, estrogen responsive (ERE-TG) zebrafish and a targeted morpholino approach to knockdown the three fish estrogen receptor (ER) subtypes. The functional consequences of BPA exposure on the cardiovascular system of zebrafish larvae were also examined. The heart atrioventricular valves and the bulbus arteriosus were primary target tissues for both BPA and MBP in the ERE-TG zebrafish, and MBP was approximately 1000-fold more potent than BPA as an estrogen in these tissues. Estrogen receptor knockdown with morpholinos indicated that the estrogenic responses in the heart for both BPA and MBP were mediated via an estrogen receptor 1 (esr1) dependent pathway. At the highest BPA concentration tested (2500 μg/L), alterations in the atrial:ventricular beat ratio indicated a functional impact on the heart of 5 days post fertilization (dpf) larvae, and there was also a significantly reduced heart rate in these larvae at 14 dpf. Our findings indicate that some of the reported adverse effects on heart function associated with BPA exposure (in mammals) may act through an estrogenic mechanism, but that fish are unlikely to be susceptible to adverse effects on heart development for environmentally relevant exposures.

Oxyresveratrol Is a Phytoestrogen Exerting Anti-inflammatory Effects Through NF-κB and Estrogen Receptor Signaling

Recent studies suggest an anti-inflammatory activity of oxyresveratrol, a stilbene extracted from Cortex mori root used in traditional Chinese medicine that also presents estrogen-like activity. We herein tested the hypothesis that oxyreservatrol exerts an anti-inflammatory effect through its estrogenic-like function. In MCF-7 cells, oxyresveratrol significantly induced proliferation, which was accompanied with estrogen receptor (ER)-mediated transcriptional activation, increased estrogen-targeted gene expression (e.g., pS2, PGR, and CTSD), and increased ERα/β proteins. The estrogen-like effect of oxyresveratrol was reversed by the ER inhibitor ICI 182780. Strong ER-binding activities of oxyresveratrol were revealed by negative docking scores. The LPS-induced inflammatory response (e.g., upregulated IκB-α phosphorylation, NF-κB nuclear translocation, and cytokine messenger RNA expression) was significantly suppressed in an ER-dependent manner by oxyresveratrol in RAW264.7 cells. These results suggest that oxyresveratrol may function as an ER agonist and modulate NF-κB signaling.

hCG and Its Disruption by Environmental Contaminants during Human Pregnancy

Human chorionic gonadotropin (hCG) is a hormone of considerable importance in the establishment, promotion and maintenance of human pregnancy. It has been clearly demonstrated that hCG exerts multiple endocrine, paracrine and autocrine actions on a variety of gestational and non-gestational cells and tissues. These actions are directed to promote trophoblast invasiveness and differentiation, placental growth, angiogenesis in uterine vasculature, hormone production, modulation of the immune system at the maternal-fetal interface, inhibition of myometrial contractility as well as fetal growth and differentiation. In recent years, considerable interest has been raised towards the biological effects of environmental contaminants, particularly endocrine disrupting chemicals (EDCs). Emerging evidence suggests that prenatal exposure to selected EDCs can have a deleterious impact on the fetus and long-lasting consequences also in adult life. The results of the in vitro effects of commonly found EDCs, particularly Bisphenol A (BPA) and para-Nonylphenol (p-NP), indicate that these substances can alter hCG production and through this action could exert their fetal damage, suggesting that hCG could represent and become a potentially useful clinical biomarker of an inappropriate prenatal exposure to these substances.

Computational insights into the molecular interactions of environmental xenoestrogens 4-tert-octylphenol, 4-nonylphenol, bisphenol A (BPA), and BPA metabolite, 4-methyl-2, 4-bis (4-hydroxyphenyl) pent-1-ene (MBP) with human sex hormone-binding globulin

Environmental contamination has been one of the major drawbacks of the industrial revolution. Several man-made chemicals are constantly released into the environment during the manufacturing process and by leaching from the industrial products. As a result, human and animal populations are exposed to these synthetic chemicals on a regular basis. Many of these chemicals have adverse effects on the physiological functions, particularly on the hormone systems in human and animals and are called endocrine disrupting chemicals (EDCs). Bisphenol A (BPA), 4-tert-octylphenol (OP), and 4-nonylphenol (NP) are three high volume production EDCs that are widely used for industrial purposes and are present ubiquitously in the environment. Bisphenol A is metabolized in the human body to a more potent compound (MBP: 4-Methyl-2, 4-bis (4-hydroxyphenyl) pent-1-ene). Epidemiological and experimental studies have shown the three EDCs to be associated with adverse effects on reproductive system in human and animals. Sex hormone-binding globulin (SHBG) is a circulatory protein that binds sex steroids and is a potential target for endocrine disruptors in the human body. The current study was done in order to understand the binding mechanism of OP, BPA, NP, and MBP with human SHBG using in silico approaches. All four compounds showed high binding affinity with SHBG, however, the binding affinity values were higher (more negative) for MBP and NP than for OP and BPA. The four ligands interacted with 19-23 residues of SHBG and a consistent overlapping of the interacting residues for the four ligands with the residues for the natural ligand, dihydrotestosterone (DHT; 82-91% commonality) was shown. The overlapping SHBG interacting residues among DHT and the four endocrine disruptors suggested that these compounds have potential for interference and disruption in the steroid binding function.

Effects of Bisphenol A Metabolite 4-Methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene on Lung Function and Type 2 Pulmonary Alveolar Epithelial Cell Growth

Bisphenol A (BPA) is recognized as a major pollutant worldwide. 4-Methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP) is a major active metabolite of BPA. The epidemiological and animal studies have reported that BPA is harmful to lung function. The role of MBP in lung dysfunction after BPA exposure still remains unclear. This study investigated whether MBP would induce lung alveolar cell damage and evaluated the role of MBP in the BPA exposure-induced lung dysfunction. An in vitro type 2 alveolar epithelial cell (L2) model and an ex vivo isolated reperfused rat lung model were used to determine the effects of BPA or MBP on cell growth and lung function. MBP, but not BPA, dose-dependently increased the mean artery pressure (Pa), pulmonary capillary pressure (Pc), pulmonary capillary filtration coefficient (K_fc), and wet/dry weight ratio in isolated reperfused rat lungs. MBP significantly reduced cell viability and induced caspases-3/7 cleavage and apoptosis and increased AMP-activated protein kinas (AMPK) phosphorylation and endoplasmic reticulum (ER) stress-related molecules expression in L2 cells, which could be reversed by AMPK-siRNA transfection. These findings demonstrated for the first time that MBP exposure induced type 2 alveolar cell apoptosis and lung dysfunction through an AMPK-regulated ER stress signaling pathway.

Bisphenol A and its analogs: Do their metabolites have endocrine activity?

Structural analogs of bisphenol A are commonly used as its alternatives in industrial and commercial applications. Nevertheless, the question arises whether the use of other bisphenols is justified as replacements for bisphenol A in mass production of plastic materials. To evaluate the influence of metabolic reactions on endocrine activities of bisphenols, we conducted a systematic review of the literature. Knowledge about the metabolic pathways and enzymes involved in metabolic biotransformations is essential for understanding and predicting mechanisms of toxicity. Bisphenols are metabolized predominantly by the glucuronidation reaction, which is considered their most important detoxification pathway, as based on current knowledge, glucuronides do not have activity on endocrine receptors. In contrast, several oxidative metabolites of bisphenols with enhanced endocrine activities are presented, and these findings indicate that oxidative metabolites of bisphenols can still have endocrine activities in humans.

Measured and predicted affinities of binding and relative potencies to activate the AhR of PAHs and their alkylated analogues

Polycyclic aromatic hydrocarbons (PAHs) and their alkylated forms are important components of crude oil. Both groups of PAHs have been reported to cause dioxin-like responses, mediated by aryl hydrocarbon receptor (AhR). Thus, characterization of binding affinity to the AhR of unsubstituted or alkylated PAHs is important to understand the toxicological consequences of oil contamination on ecosystems. We investigated the potencies of major PAHs of crude oil, e.g., chrysene, phenanthrene and dibenzothiophene, and their alkylated forms (n=17) to upregulate expression of AhR-mediated processes by use of the H4IIE-luc transactivation bioassay. In addition, molecular descriptors of different AhR activation potencies among PAHs were investigated by use of computational molecular docking models. Based on responses of the H4IIE-luc in vitro assay, it was shown that potencies of PAHs were determined by alkylation in addition to the number and conformation of rings. Potencies of AhR-mediated processes were generally greater when a chrysene group was substituted, especially in 1-methyl-chrysene. Significant negative correlations were observed between the in vitro dioxin-like potency measured in H4IIE-luc cells and the binding distance estimated from the in silico modeling. The difference in relative potency for AhR activation observed among PAHs and their alkylated forms could be explained by differences among binding distances in the ligand binding domain of the AhR caused by alkylation. The docking model developed in the present study may have utility in predicting risks of environmental contaminants of which toxicities are mediated by AhR binding.

Biological Tools to Study the Effects of Environmental Contaminants at the Feto-Maternal Interface

The identification of reproductive toxicants is a major scientific challenge for human health. Prenatal life is the most vulnerable and important time span of human development. For obvious ethical reasons, in vivo models cannot be used in human pregnancy, and animal models do not perfectly reflect human physiology. This review describes the in vitro test models representative of the human feto-maternal interface and the effects of environmental chemicals with estrogen-like activity, mainly bisphenol A and para-nonylphenol, with a particular emphasis on the effects at low, nontoxic doses similar to concentrations commonly detected in the population.

Androgen and Progesterone Receptors Are Targets for Bisphenol A (BPA), 4-Methyl-2,4-bis-(P-Hydroxyphenyl)Pent-1-Ene--A Potent Metabolite of BPA, and 4-Tert-Octylphenol: A Computational Insight

Exposure to toxic industrial chemicals that have capacity to disrupt the endocrine system, also known as endocrine disrupting chemicals (EDCs), has been increasingly associated with reproductive problems in human population. Bisphenol A (BPA; 4,4'-(propane-2,2-diyl)diphenol) and 4-tert-octylphenol (OP; 4-(1,1,3,3-tetramethylbutyl)phenol) are among the most common environmental contaminants possessing endocrine disruption properties and are present in plastics, epoxy resins, detergents and other commercial products of common personal and industrial use. A metabolite of BPA, 4-Methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP) is about 1000 times more biologically active compared to BPA. Epidemiological, clinical, and experimental studies have shown association of BPA and OP with adverse effects on male and female reproductive system in human and animals. The endocrine disruption activity can occur through multiple pathways including binding to steroid receptors. Androgen receptor (AR) and progesterone receptor (PR) are critical for reproductive tract growth and function. Structural binding characterization of BPA, MBP, and OP with AR and PR using molecular docking simulation approaches revealed novel interactions of BPA with PR, and MBP and OP with AR and PR. For BPA, MBP, and OP, five AR interacting residues Leu-701, Leu-704, Asn-705, Met-742, and Phe-764 overlapped with those of native AR ligand testosterone, and four PR interacting residues Leu-715, Leu-718, Met-756, and Met-759 overlapped with those of PR co-complex ligand, norethindrone. For both the receptors the binding strength of MBP was maximum among the three compounds. Thus, these compounds have the potential to block or interfere in the binding of the endogenous native AR and PR ligands and, hence, resulting in dysfunction. The knowledge of the key interactions and the important amino-acid residues also allows better prediction of potential of xenobiotic molecules for disrupting AR- and PR-mediated pathways, thus, helping in design of less potent alternatives for commercial use.

Estrogenic activity data extraction and in silico prediction show the endocrine disruption potential of bisphenol A replacement compounds

Bisphenol A (BPA) replacement compounds are released to the environment and cause widespread human exposure. However, a lack of thorough safety evaluations on the BPA replacement compounds has raised public concerns. We assessed the endocrine disruption potential of BPA replacement compounds in the market to assist their safety evaluations. A literature search was conducted to ascertain the BPA replacement compounds in use. Available experimental estrogenic activity data of these compounds were extracted from the Estrogenic Activity Database (EADB) to assess their estrogenic potential. An in silico model was developed to predict the estrogenic activity of compounds lacking experimental data. Molecular dynamics (MD) simulations were performed to understand the mechanisms by which the estrogenic compounds bind to and activate the estrogen receptor (ER). Forty-five BPA replacement compounds were identified in the literature. Seven were more estrogenic and five less estrogenic than BPA, while six were nonestrogenic in EADB. A two-tier in silico model was developed based on molecular docking to predict the estrogenic activity of the 27 compounds lacking data. Eleven were predicted as ER binders and 16 as nonbinders. MD simulations revealed hydrophobic contacts and hydrogen bonds as the main interactions between ER and the estrogenic compounds.

Bisphenol A modulates receptivity and secretory function of human decidual cells: an in vitro study

The human endometrium is a fertility-determining tissue and a target of steroid hormones' action. Endocrine disruptors (EDs) can exert adverse effects on the physiological function of the decidua at the maternal-fetal interface. We examined the potential effects of an ED, bisphenol A (BPA), on endometrial maturation/decidualization, receptivity, and secretion of decidual factors (biomarkers). In vitro decidualized, endometrial stromal cells from six hysterectomy specimens were treated with 1  pM-1  μM of BPA, for 24  h and assessed for cell viability and proliferation. Three non-toxic concentrations of BPA (1  μM, 1  nM, and 1  pM) were selected to study its influence on secretion of cell decidualization biomarkers (IGF-binding protein and decidual prolactin (dPRL)), macrophage migration inhibitory factor (MIF) secretion, and hormone receptors' expression (estrogen receptors (ERα and ERβ); progesterone receptors (PRA and PRB); and human chorionic gonadotropin (hCG)/LH receptor (LH-R)). The results showed a decrease in cell viability (P<0.001) in response to BPA at the level of 1  mM. At the non-toxic concentrations used, BPA perturbed the expression of ERα, ERβ, PRA, PRB, and hCG/LH-R (P<0.05). Furthermore, 1  μM of BPA reduced the mRNA transcription of dPRL (P<0.05). Secretion of MIF was stimulated by all BPA treatments, the lowest concentration (1  pM) being the most effective (P<0.001). The multi-targeted disruption of BPA on decidual cells, at concentrations commonly detected in the human population, raises great concern about the possible consequences of exposure to BPA on the function of decidua and thus its potential deleterious effect on pregnancy.

Bisphenol diglycidyl ethers and bisphenol A and their hydrolysis in drinking water

Epoxy coatings are commonly used to protect the interior (and exterior) surfaces of water mains and storage tanks and can be used on the interior surfaces of water pipes in homes, hospitals, hotels, and other buildings. Common major components of epoxies include bisphenols, such as bisphenol A (BPA) or bisphenol F (BPF), and their reactive prepolymers, bisphenol A diglycidyl ether (BADGE) and bisphenol F diglycidyl ether (BFDGE), respectively. There currently are health concerns about the safety of BPA and BPF due to known estrogenic effects. Determination of key bisphenol leachates, development of a hydrolysis model, and identification of stable hydrolysis products will aid in assessment of human bisphenol exposure through ingestion of drinking water. Liquid chromatography/mass spectrometry (LC/MS/MS) was used for quantitation of key analytes, and a pseudo-first order kinetic approach was used for modeling. In fill-and-dump studies on epoxy-coated pipe specimens, BADGE and a BPA-like compound were identified as leachates. The BADGE hydrolysis model predicts BADGE half-lives at pH 7 and 15, 25, 35, and 40 °C to be 11, 4.6, 2.0, and 1.4 days respectively; the BFDGE half-life was 5 days at pH 7 and 25 °C. The two identified BADGE hydrolysis products are BADGE-H2O and BADGE 2H2O, with BADGE 2H2O being the final end product under the conditions studied.

Measuring the kinetics of the binding of xenoestrogens and estrogen receptor alpha by fluorescence polarization

The mechanism of endocrine disruption by environmental xenoestrogens is unclear. Bisphenol-A (BPA) is an example. Its concentration in human serum is low, and its binding with estrogen receptor (ER) is weak. Yet its effect on prostate and mammary gland development was observed. We investigated whether this effect could be explained in terms of binding kinetics. We used the method of fluorescence polarization anisotropy to measure the kinetic rate constants of the binding of ERα with 19 xenoestrogens. Relative binding affinities (RBA) were also deduced from the kinetics. We drew three observations. First, our RBAs were consistent with published values, thus establishing the validity of our results. Second, our method allowed the determination of low RBAs (∼ 10(-4)) of lipophilic ligands, such as dibutyl phthalate. They could not be measured by steady-state IC50 assays because of their low solubility. Third, we found that BPA had a surprisingly high kon > 10(4) M(-1) s(-1). While its RBA was 1500 times lower than that of 17β estradiol (E2), its kon was >1/90 that of E2. As a result, a 10 min surge of BPA from pM to nM could drive the fraction of BPA-activated ERα to a potent 0.1%. This might help to explain the observable estrogenic impacts of BPA.

Formation mechanism and possible stereocontrol of bisphenol a derivatives: a computational study

Density functional theoretical study elucidates two different pathways for metabolic activation of 2,2'-bis(4-hydroxyphenyl) propane (Bisphenol A; BPA) and consequential formation of 4-methyl-2,4-bis(p-hydroxyphenyl)pent-2-ene (M-1) and 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (M-2, the potential environmental estrogen). Selectivity toward M-1(nontoxic)/M-2(toxic) formation can be controlled by varying the polarity of the reaction medium. We also found the reversal of thermodynamic stability for M-1/M-2 in response to the static polarization of the medium. Moreover, stereocontrol of biologically active M-2 with static polarization as the switch (∼0.005 au) might affect the receptor binding. This analysis may be useful in dictating the prevention of the harmful action of BPA and its metabolites.

Transcriptional analysis of endocrine disruption using zebrafish and massively parallel sequencing

Endocrine-disrupting chemicals (EDCs), including plasticizers, pesticides, detergents, and pharmaceuticals, affect a variety of hormone-regulated physiological pathways in humans and wildlife. Many EDCs are lipophilic molecules and bind to hydrophobic pockets in steroid receptors, such as the estrogen receptor and androgen receptor, which are important in vertebrate reproduction and development. Indeed, health effects attributed to EDCs include reproductive dysfunction (e.g. reduced fertility, reproductive tract abnormalities, and skewed male:female sex ratios in fish), early puberty, various cancers, and obesity. A major concern is the effects of exposure to low concentrations of endocrine disruptors in utero and post partum, which may increase the incidence of cancer and diabetes in adults. EDCs affect transcription of hundreds and even thousands of genes, which has created the need for new tools to monitor the global effects of EDCs. The emergence of massive parallel sequencing for investigating gene transcription provides a sensitive tool for monitoring the effects of EDCs on humans and other vertebrates, as well as elucidating the mechanism of action of EDCs. Zebrafish conserve many developmental pathways found in humans, which makes zebrafish a valuable model system for studying EDCs, especially on early organ development because their embryos are translucent. In this article, we review recent advances in massive parallel sequencing approaches with a focus on zebrafish. We make the case that zebrafish exposed to EDCs at different stages of development can provide important insights on EDC effects on human health.

Bisphenol A alters β-hCG and MIF release by human placenta: an in vitro study to understand the role of endometrial cells

A proper fetomaternal immune-endocrine cross-talk in pregnancy is fundamental for reproductive success. This might be unbalanced by exposure to environmental chemicals, such as bisphenol A (BPA). As fetoplacental contamination with BPA originates from the maternal compartment, this study investigated the role of the endometrium in BPA effects on the placenta. To this end, in vitro decidualized stromal cells were exposed to BPA 1 nM, and their conditioned medium (diluted 1 : 2) was used on chorionic villous explants from human placenta. Parallel cultures of placental explants were directly exposed to 0.5 nM BPA while, control cultures were exposed to the vehicle (EtOH 0.1%). After 24–48 h, culture medium from BPA-treated and control cultures was assayed for concentration of hormone human Chorionic Gonadotropin (β-hCG) and cytokine Macrophage Migration Inhibitory Factor (MIF). The results showed that direct exposure to BPA stimulated the release of both MIF and β-hCG. These effects were abolished/diminished in placental cultures exposed to endometrial cell-conditioned medium. GM-MS analysis revealed that endometrial cells retain BPA, thus reducing the availability of this chemical for the placenta. The data obtained highlight the importance of in vitro models including the maternal component in reproducing the effects of environmental chemicals on human fetus/placenta.

Bisphenol A modulates the metabolic regulator oestrogen-related receptor-α in T-cells

Bisphenol A (BPA) is a widely used plastics constituent that has been associated with endocrine, immune and metabolic effects. Evidence for how BPA exerts significant biological effects at chronic low levels of exposure has remained elusive. In adult men, exposure to BPA has been associated with higher expression of two nuclear receptors, oestrogen receptor-β (ERβ) and oestrogen-related-receptor-α (ERRα), in peripheral white blood cells in vivo. In this study, we explore the expression of ESR2 (ERβ) and ESRRA (ERRα) in human leukaemic T-cell lymphoblasts (Jurkat cells) exposed to BPA in vitro. We show that exposure to BPA led to enhanced expression of ESRRA within 6 h of exposure (mean±s.e.m.: 1.43±0.08-fold increase compared with the control, P<0.05). After 72 h, expression of ESRRA remained significantly enhanced at concentrations of BPA ≥1 nM. Oxidative metabolism of BPA by rat liver S9 fractions yields the potent oestrogenic metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP). Exposure of cells to 1-100 nM MBP increased the expression of both ESRRA (significantly induced, P<0.05, at 1, 10, 100 nM) and ESR2 (1.32±0.07-fold increase at 100 nM exposure, P<0.01). ERRα is a major control point for oxidative metabolism in many cell types, including T-cells. Following exposure to both BPA and MBP, we found that cells showed a decrease in cell proliferation rate. Taken together, these results confirm the bioactivity of BPA against putative T-cell targets in vitro at concentrations relevant to general human exposure.

3D models of human ERα and ERβ complexed with coumestrol

Coumestrol, a phytoestrogen found in alfalfa, clover, and beans, has nM affinity for both estrogen receptor-α [ERα] and ERβ. Recently, a novel activity of coumestrol was reported: coumestrol binding to human ERβ represses microglia-mediated inflammation, which is associated with various neurodegenerative diseases, such as multiple sclerosis. In contrast, estradiol binding to ERβ had little or no effect on repression of microglia-mediated inflammation. Coumestrol and estradiol have several structural differences, which suggest that each ligand could induce different conformations in ERβ and, thus, different transcriptional responses in brain microglia. To begin to understand how coumestrol binds to ERβ and ERα, we constructed 3D models of coumestrol with human ERβ and ERα, which were compared to the structures of these ERs with estradiol. Of four possible orientations of coumestrol in ERα and ERβ, one orientation had the most favorable contacts with both ERs. Other phytochemicals may activate ERβ and inhibit inflammation in brain microglia and be useful therapeutics for inflammatory conditions in the brain.

Molecular analysis of endocrine disruption in hornyhead turbot at wastewater outfalls in southern california using a second generation multi-species microarray

Sentinel fish hornyhead turbot (Pleuronichthysverticalis) captured near wastewater outfalls are used for monitoring exposure to industrial and agricultural chemicals of ~ 20 million people living in coastal Southern California. Although analyses of hormones in blood and organ morphology and histology are useful for assessing contaminant exposure, there is a need for quantitative and sensitive molecular measurements, since contaminants of emerging concern are known to produce subtle effects. We developed a second generation multi-species microarray with expanded content and sensitivity to investigate endocrine disruption in turbot captured near wastewater outfalls in San Diego, Orange County and Los Angeles California. Analysis of expression of genes involved in hormone [e.g., estrogen, androgen, thyroid] responses and xenobiotic metabolism in turbot livers was correlated with a series of phenotypic end points. Molecular analyses of turbot livers uncovered altered expression of vitellogenin and zona pellucida protein, indicating exposure to one or more estrogenic chemicals, as well as, alterations in cytochrome P450 (CYP) 1A, CYP3A and glutathione S-transferase-α indicating induction of the detoxification response. Molecular responses indicative of exposure to endocrine disruptors were observed in field-caught hornyhead turbot captured in Southern California demonstrating the utility of molecular methods for monitoring environmental chemicals in wastewater outfalls. Moreover, this approach can be adapted to monitor other sites for contaminants of emerging concern in other fish species for which there are few available gene sequences.