Nuclear Receptor Profiling of Bisphenol-A and Its Halogenated Analogues

Emerging regulatory roles of noncoding RNAs induced by bisphenol a (BPA) and its alternatives in human diseases

Bisphenols (BPs), including BPA, BPF, BPS, and BPAF, are synthetic phenolic organic compounds and endocrine-disrupting chemicals. These organics have been broadly utilized to produce epoxy resins, polycarbonate plastics, and other products. Mounting evidence has shown that BPs, especially BPA, may enter into the human body and participate in the development of human diseases mediated by nuclear hormone receptors. Moreover, BPA may negatively affect human health at the epigenetic level through processes such as DNA methylation and histone acetylation. Recent studies have demonstrated that, as part of epigenetics, noncoding RNAs (ncRNAs), including microRNAs (miRNAs), long noncoding RNAs (lncRNAs), circular RNAs (circRNAs), and small nucleolar RNAs (snoRNAs), have vital impacts on BP-related diseases, such as reproductive system diseases, nervous system diseases, digestive system diseases, endocrine system diseases, and other diseases. Moreover, based on the bioinformatic analysis, changes in ncRNAs may be relevant to normal activities and functions and BP-induced diseases. Thus, we conducted a meta-analysis to identify more promising ncRNAs as biomarkers and therapeutic targets for BP exposure and relevant human diseases. In this review, we summarize the regulatory functions of ncRNAs induced by BPs in human diseases and latent molecular mechanisms, as well as identify prospective biomarkers and therapeutic targets for BP exposure and upper diseases.

Prenatal exposure to environmental phenols and fetal growth across pregnancy in the LIFECODES fetal growth study

INTRODUCTION

Environmental phenols are endocrine disrupting chemicals hypothesized to affect early life development. Previous research examining the effects of phenols on fetal growth has focused primarily on associations with measures of size at delivery. Few have included ultrasound measures to examine growth across pregnancy.

OBJECTIVE

Investigate associations between prenatal exposure to phenols and ultrasound and delivery measures of fetal growth.

METHODS

Using the LIFECODES Fetal Growth Study (n = 900), a case-cohort including 248 small-for-gestational-age, 240 large-for-gestational age, and 412 appropriate-for-gestational-age births, we estimated prenatal exposure to 12 phenols using three urine samples collected during pregnancy (median 10, 24, and 35 weeks gestation). We abstracted ultrasound and delivery measures of fetal growth from medical records. We estimated associations between pregnancy-average phenol biomarker concentrations and repeated ultrasound measures of fetal growth using linear mixed effects models and associations with birthweight using linear regression models. We also used logistic regression models to estimate associations with having a small- or large-for-gestational birth.

RESULTS

We observed positive associations between 2,4-dichlorophenol, benzophenone-3, and triclosan (TCS) and multiple ultrasound measures of fetal growth. For example, TCS was associated with a 0.09 (95 % CI: 0.01, 0.18) higher estimated fetal weight z-score longitudinally across pregnancy. This effect size corresponds to a 21 g increase in estimated fetal weight at 30 weeks gestation. Associations with delivery measures of growth were attenuated, but TCS remained positively associated with birthweight z-scores (mean difference: 0.13, 95 % CI: 0.02, 0.25). Conversely, methylparaben was associated with higher odds of a small-for-gestational age birth (odds ratio: 1.45, 95 % CI: 1.06, 1.98).

DISCUSSION

We observed associations between some biomarkers of phenol exposure and ultrasound measures of fetal growth, though associations at the time of delivery were attenuated. These findings are consistent with hypotheses that phenols have the potential to affect growth during the prenatal period.

Does Bisphenol-A play a role in the development of neural tube defects?

OBJECTIVE

In this study, we aimed to evaluate BPA levels in the maternal serum and amniotic fluid of patients diagnosed with NTD. In addition, we wanted to investigate the relationship between neurodevelopmental defects, such as neural tube defects (NTD), and BPA levels.

STUDY DESIGN

This prospective observational study was carried out at Bursa Yüksek İhtisas Training and Research Hospital between April 15, 2021, and April 15, 2022. The study consisted of 92 patients between the ages of 18-45 who had an amniocentesis at 15-22 weeks of gestation. The patients were divided into two groups according to the indications of amniocentesis. Group 1 contained the patients with abnormal maternal serum screening results or cell-free DNA results and abnormal ultrasonography findings (45 patients). Group 2 contained the patients with a pre-diagnosis of NTD (47 patients). The first 5 cc fluids and maternal serum samples taken during the amniocentesis procedure of all patients were delivered to the biochemistry laboratory. The BPA values between groups were compared.

RESULTS

A statistically significant difference was found between the two groups in terms of amniotic fluid BPA levels (36.66 (19.00:82.00) and 39.62 (19.02-73.87)) and maternal blood BPA levels (22.26 (12.60-228) and 47.81 (12.89-228.39)). In cases with NTD, amniotic fluid BPA levels and maternal blood BPA levels were significantly higher than the control group. When AUC values were compared, the AFP numerical value was higher than the amniotic fluid and maternal blood BPA levels.

CONCLUSION

Plastic, which is indispensable for modern life, may negatively affect fetal development in intrauterine life. The data in this study says that high maternal blood BPA may be associated with NTD.

Oestrogens, adipose tissues and environmental exposures influence obesity and diabetes across the lifecycle

Endogenous oestrogens regulate essential functions to include menstrual cycles, energy balance, adipose tissue distribution, pancreatic β-cell function, insulin sensitivity and lipid homeostasis. Oestrogens are a family of hormones which include oestradiol (E2), oestrone (E1) and oestriol (E3). Oestrogens function by binding and activating oestrogen receptors (ERs). Phytoestrogens are plant-derived compounds which exhibit oestrogenic-like activity and can bind to ERs. Phytoestrogens exert potential oestrogenic-like benefits; however, their effects are context-dependent and require cautious consideration regarding generalised health benefits. Xenoestrogens are synthetic compounds which have been determined to disrupt endocrine function through binding to ERs. Xenoestrogens enter the body through various routes and given their chemical structure they can accumulate, posing long-term health risks. Xenoestrogens interfere with endogenous oestrogens and their functions contributing to conditions like cancer, infertility, and metabolic disorders. Understanding the interplay between endogenous and exogenous oestrogens is critical in order to determine their potential health consequences and requires further investigation. This manuscript provides a summary of the role endogenous oestrogens have in regulating metabolic functions. Additionally, we discuss the impact phytoestrogens and synthetic xenoestrogens have on biological systems across various life stages. We highlight their mechanisms of action, potential benefits, risks and discuss the need for further research to bridge gaps in understanding and mitigate exposure-related health risks.

Alterations induced by Bisphenol A on cellular organelles and potential relevance on human health

Bisphenol A (BPA) is a chemical partially soluble in water and exists in a solid state. Its structural similarity with estrogen makes it an endocrine-disrupting chemical. BPA can disrupt signaling pathways at very low doses and may cause organellar stress. According to in vitro and in vivo studies, BPA interacts with various cell surface receptors to cause organellar stress, producing free radicals, cellular toxicity, structural changes, DNA damage, mitochondrial dysfunction, cytoskeleton remodeling, centriole duplication, and aberrant changes in several cell signaling pathways. The current review summarizes the impact of BPA exposure on the structural and functional aspects of subcellular components of cells such as the nucleus, mitochondria, endoplasmic reticulum, lysosome, ribosome, Golgi apparatus, and microtubules and its consequent impact on human health.

Evaluating endocrine disrupting chemicals: A perspective on the novel assessments in CLARITY-BPA

BACKGROUND

The Consortium Linking Academic and Regulatory Insights on Bisphenol A Toxicity (CLARITY-BPA) was a collaborative research effort to better link academic research with governmental guideline studies. This review explores the secondary goal of CLARITY-BPA: to identify endpoints or technologies from CLARITY-BPA and prior/concurrent literature from these laboratories that may enhance the capacity of rodent toxicity studies to detect endocrine disrupting chemicals (EDCs).

METHODS

A systematic literature search was conducted with search terms for BPA and the CLARITY-BPA participants. Relevant studies employed a laboratory rodent model and reported results on 1 of the 10 organs/organ systems evaluated in CLARITY-BPA (brain and behavior, cardiac, immune, mammary gland, ovary, penile function, prostate gland and urethra, testis and epididymis, thyroid hormone and metabolism, and uterus). Study design and findings were summarized, and a risk-of-bias assessment was conducted.

RESULTS

Several endpoints and methods were identified as potentially helpful to detect effects of EDCs. For example, molecular and quantitative morphological approaches were sensitive in detecting alterations in early postnatal development of the brain, ovary, and mammary glands. Hormone challenge studies mimicking human aging reported increased susceptibility of the prostate to disease following developmental BPA exposure. Statistical analyses for nonmonotonic dose responses, and computational approaches assessing multiple treatment-related outcomes concurrently in linked hormone-sensitive organ systems, reported effects at low BPA doses.

CONCLUSIONS

This review provided an opportunity to evaluate the unique insights provided by nontraditional assessments in CLARITY-BPA to identify technologies and endpoints to enhance detection of EDCs in future studies.

Different types of bisphenols alter ovarian steroidogenesis: Special attention to BPA

Endocrine disruptors such as bisphenol A (BPA) and some of its analogues, including BPS, BPAF, and BPE, are used extensively in the manufacture of plastics. These synthetic chemicals could seriously alter the functionality of the female reproductive system. Although the number of studies conducted on other types of bisphenols is smaller than the number of studies on BPA, the purpose of this review study was to evaluate the effects of bisphenol compounds, particularly BPA, on hormone production and on genes involved in ovarian steroidogenesis in both in vitro (human and animal cell lines) and in vivo (animal models) studies. The current data show that exposure to bisphenol compounds has adverse effects on ovarian steroidogenesis. For example, BPA, BPS, and BPAF can alter the normal function of the hypothalamic-pituitary-gonadal (HPG) axis by targeting kisspeptin neurons involved in steroid feedback signals to gonadotropin-releasing hormone (GnRH) cells, resulting in abnormal production of LH and FSH. Exposure to BPA, BPS, BPF, and BPB had adverse effects on the release of some hormones, namely 17-β-estradiol (E2), progesterone (P4), and testosterone (T). BPA, BPE, BPS, BPF, and BPAF are also capable of negatively altering the transcription of a number of genes involved in ovarian steroidogenesis, such as the steroidogenic acute regulatory protein (StAR, involved in the transfer of cholesterol from the outer to the inner mitochondrial membrane, where the steroidogenesis process begins), cytochrome P450 family 17 subfamily A member 1 (Cyp17a1, which is involved in the biosynthesis of androgens such as testosterone), 3 beta-hydroxysteroid dehydrogenase enzyme (3β-HSD, involved in the biosynthesis of P4), and cytochrome P450 family 19 subfamily A member 1 (Cyp19a1, involved in the biosynthesis of E2). Exposure to BPA, BPB, BPF, and BPS at prenatal or prepubertal stages could decrease the number of antral follicles by activating apoptosis and autophagy pathways, resulting in decreased production of E2 and P4 by granulosa cells (GCs) and theca cells (TCs), respectively. BPA and BPS impair ovarian steroidogenesis by reducing the function of some important cell receptors such as estrogens (ERs, including ERα and ERβ), progesterone (PgR), the orphan estrogen receptor gamma (ERRγ), the androgen receptor (AR), the G protein-coupled estrogen receptor (GPER), the FSHR (follicle-stimulating hormone receptor), and the LHCGR (luteinizing hormone/choriogonadotropin receptor). In animal models, the effects of bisphenol compounds depend on the type of animals, their age, and the duration and dose of bisphenols, while in cell line studies the duration and doses of bisphenols are the matter.

Global gene expression analysis reveals novel transcription factors associated with long-term low-level exposure of EA.hy926 human endothelial cells to bisphenol A

Bisphenol A (BPA) is an endocrine disruptor that binds to estrogen receptors (ER); however, studies have shown that the ER pathway was not always the primary molecular mechanism of BPA's action in cells and that gene transcription could be altered by different exposure times and doses. Here, we sought to understand the correlation between the BPA-responsive genes that have associated biological functions and the transcription factors (TFs) involved in their regulation by repeatedly exposing human endothelial cells EA.hy926 to three nanomolar concentrations of BPA (10^-9 M, 10^-8 M, and 10^-7 M) for 14 weeks, after which changes in global gene expression were determined by RNA sequencing. Cytoscape plug-in iRegulon was used to infer TFs involved in the control of BPA-deregulated genes. The results show a minimal overlap in deregulated genes between three concentrations of BPA, with 10^-9 M BPA having the highest number of deregulated genes. TF analysis suggests that all three concentrations of BPA were active in the absence of an ER-mediated pathway. A unique set of TFs (NES≥4) has been identified for each BPA concentration, including the NFκB family and CEBPB for 10^-9 M BPA, MEF family, AHR/ARNT, and ZBTB33 for 10^-8 M BPA, and IRF1-7 and OVOL1/OVOL2 for 10^-7 M BPA, whereas STAT1/STAT2 were common TFs for 10^-9 M and 10^-7 M BPA. Overall, our data suggest that long-term low-level exposure of EA.hy926 cells to BPA leads to concentration-specific changes in gene expression that are not controlled by the ER-mediated signaling but rather by other mechanisms.

Bisphenol-A impairs synaptic formation and function by RGS4-mediated negative regulation of BDNF/NTRK2 signaling in the cerebral cortex

Bisphenol-A (BPA) is a representative endocrine disruptor, widely used in a variety of products including plastics, medical equipment and receipts. Hence, most people are exposed to BPA via the skin, digestive system or inhalation in everyday life. Furthermore, BPA crosses the blood–brain barrier and is linked to multiple neurological dysfunctions found in neurodegenerative and neuropsychological disorders. However, the mechanisms underlying BPA-associated neurological dysfunctions remain poorly understood. Here, we report that BPA exposure alters synapse morphology and function in the cerebral cortex. Cortical pyramidal neurons treated with BPA showed reduced size and number of dendrites and spines. The density of excitatory synapses was also decreased by BPA treatment. More importantly, we found that BPA disrupted normal synaptic transmission and cognitive behavior. RGS4 and its downstream BDNF/NTRK2 pathway appeared to mediate the effect of BPA on synaptic and neurological function. Our findings provide molecular mechanistic insights into anatomical and physiological neurotoxic consequences related to a potent endocrine modifier.

Summary: Bisphenol-A (BPA) disrupts normal synaptic transmission and cognitive behavior in mice. Rgs4 transcription factor and its downstream BDNF/NTRK2 pathway appear to mediate the effect of BPA on synaptic and neurological function.

Potential Pro-Tumorigenic Effect of Bisphenol A in Breast Cancer via Altering the Tumor Microenvironment

Simple Summary

Bisphenol A (BPA) is primarily used to produce polycarbonate plastics, such as water bottles. Exposure to BPA has been shown to increase the growth of breast cancer cells that depend on estrogen for growth due to its ability to mimic estrogen. More recent studies have suggested that BPA also affects the cellular and non-cellular components that compose tumor microenvironments (TMEs), namely the environment around a tumor, thereby potentially promoting breast cancer growth via altering the TME. The TME plays an essential role in cancer development and promotion. Therefore, it is crucial to understand the effect of BPA on breast TMEs to assess its role in the risk of breast cancer adequately. This review examines the potential effects of BPA on immune cells, fibroblasts, extracellular matrices, and adipocytes to highlight their roles in mediating the carcinogenic effect of BPA, and thereby proposes considerations for the risk assessment of BPA exposure.

Abstract

BPA, a chemical used in the preparation of polycarbonate plastics, is an endocrine disruptor. Exposure to BPA has been suggested to be a risk factor for breast cancer because of its potential to induce estrogen receptor signaling in breast cancer cells. More recently, it has been recognized that BPA also binds to the G protein-coupled estrogen receptor and other nuclear receptors, in addition to estrogen receptors, and acts on immune cells, adipocytes, and fibroblasts, potentially modulating the TME. The TME significantly impacts the behavior of cancer cells. Therefore, understanding how BPA affects stromal components in breast cancer is imperative to adequately assess the association between exposure to BPA and the risk of breast cancer. This review examines the effects of BPA on stromal components of tumors to highlight their potential role in the carcinogenic effect of BPA. As a result, I propose considerations for the risk assessment of BPA exposure and studies needed to improve understanding of the TME-mediated, breast cancer-promoting effect of BPA.

Binding and activity of bisphenol analogues to human peroxisome proliferator-activated receptor β/δ

Several studies have indicated metabolic function disruption effects of bisphenol analogues through peroxisome proliferator-activated receptor (PPAR) alpha and gamma pathways. In the present study, we found for the first time that PPARβ/δ might be a novel cellular target of bisphenol analogues. By using the fluorescence competitive binding assay, we found seven bisphenol analogues could bind to PPARβ/δ directly, among which tetrabromobisphenol A (TBBPA, 18.38-fold) and tetrachlorobisphenol A (TCBPA, 12.06-fold) exhibited stronger binding affinity than bisphenol A (BPA). In PPARβ/δ-mediated luciferase reporter gene assay, the seven bisphenol analogues showed transcriptional activity toward PPARβ/δ. Bisphenol AF (BPAF), bisphenol F (BPF) and bisphenol B (BPB) even showed higher transcriptional activity than BPA, while TBBPA and TCBPA showed comparable activity with BPA. Moreover, in human liver HL-7702 cells, the bisphenol analogues promoted the expression of two PPARβ/δ target genes PDK4 and ANGPTL4. Molecular docking simulation indicated the binding potency of bisphenol analogues to PPARβ/δ might depend on halogenation and hydrophobicity and the transcriptional activity might depend on their binding affinity and hydrogen bond interactions. Overall, the PPARβ/δ pathway may provide a new mechanism for the metabolic function disruption of bisphenol analogues, and TBBPA and TCBPA might exert higher metabolic disruption effects than BPA via PPARβ/δ pathway.

Maternal Bisphenol A (BPA) Exposure Alters Cerebral Cortical Morphogenesis and Synaptic Function in Mice

Early-life exposure to bisphenol A (BPA), synthetic compound used in polycarbonate plastic, is associated with altered cognitive and emotional behavior later in life. However, the brain mechanism underlying the behavioral deficits is unknown. Here, we show that maternal BPA exposure disrupted self-renewal and differentiation of neural progenitors during cortical development. The BPA exposure reduced the neuron number, whereas it increased glial cells in the cerebral cortex. Also, synaptic formation and transmission in the cerebral cortex were suppressed after maternal BPA exposure. These changes appeared to be associated with autophagy as a gene ontology analysis of RNA-seq identified an autophagy domain in the BPA condition. Mouse behavioral tests revealed that maternal BPA caused hyperactivity and social deficits in adult offspring. Together, these results suggest that maternal BPA exposure leads to abnormal cortical architecture and function likely by activating autophagy.

Obesity and endocrine-disrupting chemicals

Obesity is now a worldwide pandemic. The usual explanation given for the prevalence of obesity is that it results from consumption of a calorie dense diet coupled with physical inactivity. However, this model inadequately explains rising obesity in adults and in children over the past few decades, indicating that other factors must be important contributors. An endocrine-disrupting chemical (EDC) is an exogenous chemical, or mixture that interferes with any aspect of hormone action. EDCs have become pervasive in our environment, allowing humans to be exposed daily through ingestion, inhalation, and direct dermal contact. Exposure to EDCs has been causally linked with obesity in model organisms and associated with obesity occurrence in humans. Obesogens promote adipogenesis and obesity, in vivo, by a variety of mechanisms. The environmental obesogen model holds that exposure to obesogens elicits a predisposition to obesity and that such exposures may be an important yet overlooked factor in the obesity pandemic. Effects produced by EDCs and obesogen exposure may be passed to subsequent, unexposed generations. This "generational toxicology" is not currently factored into risk assessment by regulators but may be another important factor in the obesity pandemic as well as in the worldwide increases in the incidence of noncommunicable diseases that plague populations everywhere. This review addresses the current evidence on how obesogens affect body mass, discusses long-known chemicals that have been more recently identified as obesogens, and how the accumulated knowledge can help identify EDCs hazards.

Association of placental concentrations of phenolic endocrine disrupting chemicals with cognitive functioning in preschool children from the Environment and Childhood (INMA) Project

Developmental exposure to bisphenol A (BPA) and other phenolic endocrine disrupting chemicals (EDCs) may affect child neurodevelopment, but data on the effects of prenatal exposure to phenols on cognitive function remain sparse. Our aim was to examine the association of placental concentrations of several phenolic EDCs, including BPA, parabens (PBs), and benzophenones (BzPs), with cognitive development in preschool children from the Environment and Childhood (INMA) Project in Spain. Concentrations of BPA, four PBs (methylparaben [MePB], ethylparaben [EtPB], propylparaben [PrPB], and butylparaben [BuPB]), and six BzPs (BzP-1, BzP-2, BzP-3, BzP-6, BzP-8, and 4-hydroxybenzophenone [4-OH-BzP]) were measured in 490 placenta samples randomly selected from five INMA cohorts collected between 2000 and 2008. Neuropsychological assessment of cognitive and motor function was performed with the McCarthy Scales of Children's Abilities (MSCA) at the age of 4-5 years. Associations were assessed in a sub-sample of 191 mother-child pairs using linear and logistic regression models adjusted for confounding factors. PB compounds were detected in more than 71% of placentas, BPA in 62%, 4-OH-BzP in 50%, and the remaining BzPs in <9% of the samples. Because of the low detection frequency of BzP compounds, only 4-OH-BzP was included in the exposure-outcome analyses. After adjustment for confounders, BPA was associated with greater odds of scoring lower (below the 20th percentile) in the verbal (third vs. first exposure tertile: odds ratio [OR] = 2.78, 95% confidence interval [CI] = 1.00; 5.81, p-trend = 0.05) and gross motor (detected vs. undetected: OR = 1.75, 95%CI = 1.06; 9.29) areas, and these associations were only significant for boys. Regarding PB compounds, PrPB was associated with lower scores in memory (detected vs. undetected: β = -4.96, 95%CI = -9.54; -0.31), span memory (OR = 2.50, 95%CI = 0.95; 6.92 and 2.71, 95%CI = 0.97; 6.64, respectively for second and third tertiles, p-trend = 0.03), and motor function (β = -5.15, 95%CI = -9.26; -0.01 for third vs. first exposure tertile, p-trend = 0.04). EtPB and total PBs concentrations in the second tertile were also associated with poorer visual function of posterior cortex and worse quantitative performance, respectively, but linear trends were not statistically significant. The associations of BPA and PrPB with poorer verbal, memory, and motor skills are novel observations that warrant further attention. Larger prospective studies are required to confirm whether prenatal exposure to BPA and other phenolic EDCs is associated with impaired cognitive development.

Long-Term Exposure of Early-Transformed Human Mammary Cells to Low Doses of Benzo[a]pyrene and/or Bisphenol A Enhances Their Cancerous Phenotype via an AhR/GPR30 Interplay

It is of utmost importance to decipher the role of chronic exposure to low doses of environmental carcinogens on breast cancer progression. The early-transformed triple-negative human mammary MCF10AT1 cells were chronically (60 days) exposed to low doses (10⁻¹⁰ M) of Benzo[a]pyrene (B[a]P), a genotoxic agent, and/or Bisphenol A (BPA), an endocrine disruptor. Our study revealed that exposed MCF10AT1 cells developed, in a time-dependent manner, an acquired phenotype characterized by an increase in cancerous properties (anchorage independent growth and stem-like phenotype). Co-exposure of MCF10AT1 cells to B[a]P and BPA led to a significantly greater aggressive phenotype compared to B[a]P or BPA alone. This study provided new insights into the existence of a functional interplay between the aryl hydrocarbon receptor (AhR) and the G protein-coupled receptor 30 (GPR30) by which chronic and low-dose exposure of B[a]P and/or BPA fosters the progression of MCF10AT1 cells into a more aggressive substage. Experiments using AhR or GPR30 antagonists, siRNA strategies, and RNAseq analysis led us to propose a model in which AhR signaling plays a “driver role” in the AhR/GPR30 cross-talk in mediating long-term and low-dose exposure of B[a]P and/or BPA. Retrospective analysis of two independent breast cancer cohorts revealed that the AhR/GPR30 mRNA expression signature resulted in poor breast cancer prognosis, in particular in the ER-negative and the triple-negative subtypes. Finally, the study identified targeting AhR and/or GPR30 with specific antagonists as a strategy capable of inhibiting carcinogenesis associated with chronic exposure to low doses of B[a]P and BPA in MCF10AT1 cells. Altogether, our results indicate that the engagement of both AhR and GPR30 functions, in particular in an ER-negative/triple-negative context of breast cells, favors tumor progression and leads to poor prognosis.

Evaluation of the Influence of Halogenation on the Binding of Bisphenol A to the Estrogen-Related Receptor γ

Halogenation of organic compounds is one the most important transformations in chemical synthesis and is used for the production of various industrial products. A variety of halogenated bisphenol analogs have recently been developed and are used as alternatives to bisphenol A (BPA), which is a raw material of polycarbonate that has adverse effects in animals. However, limited information is available on the potential toxicity of the halogenated BPA analogs. In the present study, to assess the latent toxicity of halogenated BPA analogs, we evaluated the binding and transcriptional activities of halogenated BPA analogs to the estrogen-related receptor γ (ERRγ), a nuclear receptor that contributes to the growth of nerves and sexual glands. Fluorinated BPA analogs demonstrated strong ERRγ binding potency, and inverse antagonistic activity, similar to BPA. X-ray crystallography and fragment molecular orbital (FMO) calculation revealed that a fluorine-substituted BPA analog could interact with several amino acid residues of ERRγ-LBD, strengthening the binding affinity of the analogs. The ERRγ binding affinity and transcriptional activity of the halogenated BPAs decreased with the increase in the size and number of halogen atom(s). The IC₅₀ values, determined by the competitive binding assay, correlated well with the binding energy obtained from the docking calculation, suggesting that the docking calculation could correctly estimate the ERRγ binding potency of the BPA analogs. These results confirmed that ERRγ has a ligand binding pocket that fits very well to BPA. Furthermore, this study showed that the binding affinity of the BPA analogs can be predicted by the docking calculation, indicating the importance of the calculation method in the risk assessment of halogenated compounds.

Environmental Obesogens and Their Impact on Susceptibility to Obesity: New Mechanisms and Chemicals

The incidence of obesity has reached an all-time high, and this increase is observed worldwide. There is a growing need to understand all the factors that contribute to obesity to effectively treat and prevent it and associated comorbidities. The obesogen hypothesis proposes that there are chemicals in our environment termed obesogens that can affect individual susceptibility to obesity and thus help explain the recent large increases in obesity. This review discusses current advances in our understanding of how obesogens act to affect health and obesity susceptibility. Newly discovered obesogens and potential obesogens are discussed, together with future directions for research that may help to reduce the impact of these pervasive chemicals.

Impact of perinatal bisphenol A and 17β estradiol exposure: Comparing hormone receptor response

Hormonal regulation controls mammary gland (MG) development. Therefore some hormone-related factors can disrupt the early phases of MGs development, making the gland more susceptible to long term modifications in its response to circulating hormones. Endocrine disruptors, such as bisphenol A (BPA), are able to cause alterations in hormone receptor expression, leading to changes in the cell proliferation index, which may expose the tissue to neoplastic alterations. Thus, we evaluated the variations in hormone receptor expression in the MG of 6-month old Mongolian gerbils exposed to BPA and 17β estradiol during the perinatal period. Receptors for estrogen alpha (ERα), beta (ERβ), progesterone (PGR), prolactin (PRL-R), and co-localization of connexin 43 (Cx43) and ERα in gerbils were analyzed, and serum concentrations of estradiol and progesterone were assessed. No alterations in body, liver, and ovary-uterus complex weights were observed. However, there was an increase in epithelial ERα expression in the 17β estradiol (E2) group and in PGR in the BPA group. Although immunohistochemistry did not show alterations in ERβ expression, western blotting revealed a decrease in this protein in the BPA group. PRL-R was more present in epithelial cells in the vehicle control (VC), E2, and BPA groups in comparison to the intact control group. Cx43 was more frequent in E2 and BPA groups, suggesting a protective response from the gland against possible malignancy. Serum concentration of estradiol reduced in VC, E2, and BPA groups, confirming that alterations also impacts steroid levels. Consequently, perinatal exposure to BPA and the reference endogenous estrogen, 17β estradiol, are able to increase the tendency of endocrine disruption in MG in a long term manner, since repercussions are observed even 6 months after exposure.

Dichotomy of bisphenol A-induced expression of peroxisome proliferator-activated receptors in hepatic and testicular tissues in mice

Environmental and dietary exposure to bisphenol A (BPA) and its toxicological consequences are extensively reported. BPA has multiple cellular targets. One of the mechanisms of action of BPA involves interaction with and activation of nuclear receptors (NRs) including peroxisome proliferator activated-receptors (PPARs). PPARs regulate genes involved in adipogenesis, and metabolism of glucose, lipid and cholesterol. Study of tissue and dose specific PPAR expression may decipher the toxicity outcome of BPA exposure. We studied expression of three forms of PPARs in mouse liver and testes exposed to BPA for 14 days. mRNA and protein expression of all forms of PPAR increased linearly (monotonic) with the dose in the liver while non-monotonic but dose specific effects were observed in the testes showing a differential pattern of expression. However, histopathological study showed a dose-dependent pattern of changes in liver as well as testes demonstrating a monotonic effect. These findings imply that other PPAR-independent mechanisms may play a role in BPA-induced pathological changes. The present study warrants exploration of the role of PPARs in BPA-induced effects on male reproductive functions and offers an insight into the peculiar response of BPA at low subchronic levels which may be helpful in designing appropriate risk assessment framework.

Differential activity of BPA, BPAF and BPC on zebrafish estrogen receptors in vitro and in vivo

The high volume production compound bisphenol A (BPA) is of environmental concern largely because of its estrogenic activity. Consequently, BPA analogues have been synthesized to be considered as replacement molecules for BPA. These analogues need to be thoroughly evaluated for their estrogenic activity. Here, we combined mechanism zebrafish-based assays to examine estrogenic and anti-estrogenic activities of BPA and two of its analogues, bisphenol AF (BPAF) and bisphenol C (BPC) in vitro and in vivo. In vitro reporter cell lines were used to investigate agonistic and antagonistic effects of the three bisphenols on the three zebrafish estrogen receptors. The transgenic Tg(5 × ERE:GFP) and Cyp19a1b-GFP zebrafish lines were then used to analyze estrogenic and anti-estrogenic responses of the three bisphenols in vivo. BPA, BPAF and BPC were agonists with different potencies for the three zebrafish estrogen receptors in vitro. The potent zfERα-mediated activity of BPA and BPAF in vitro resulted in vivo by activation of GFP expression in zebrafish larvae in the heart (zfERα-dependent) at lower concentrations, and in the liver (zfERβ-dependent) at higher concentrations. BPC induced zfERβ-mediated luciferase expression in vitro, and the zfERβ agonism led to activation of GFP expression in the liver and the brain in vivo. In addition, BPC acted as a full antagonist on zfERα, and completely inhibited estrogen-induced GFP expression in the heart of the zebrafish larvae. To summarize, applying a combination of zebrafish-based in vitro and in vivo methods to evaluate bisphenol analogues for estrogenic activity will facilitate the prioritization of these chemicals for further analysis in higher vertebrates as well as the risk assessment in humans.

Alternative ligands for thyroid hormone receptors

Thyroid hormone receptors (TRs) are ligand-dependent transcription factors that activate or repress gene transcription, resulting in the regulation of numerous physiological programs. While 3,3',5-L-triiodothyronine is the TR cognate ligand, these receptors can also be activated by various alternative ligands, including endogenous and synthetic molecules capable of inducing diverse active receptor conformations that influence thyroid hormone-dependent signaling pathways. This review mainly discusses current knowledge on 3,5-diiodo-L-thyronine and 3,5,3'-triiodothyroacetic acid, two endogenous molecules that bind to TRs and regulate gene expression; and the molecular interactions between TRs and ligands, like synthetic thyromimetics developed to target specific TR isoforms for tissue-specific regulation of thyroid-related disorders, or endocrine disruptors that have allowed the design of new analogues and revealed essential amino acids for thyroid hormone binding.

Alternative retinoid X receptor (RXR) ligands

Retinoid X receptors (RXRs) control a wide variety of functions by virtue of their dimerization with other nuclear hormone receptors (NRs), contributing thereby to activities of different signaling pathways. We review known RXR ligands as transcriptional modulators of specific RXR-dimers and the associated biological processes. We also discuss the physiological relevance of such ligands, which remains frequently a matter of debate and which at present is best met by member(s) of a novel family of retinoids, postulated as Vitamin A5. Through comparison with other natural, but also with synthetic ligands, we discuss high diversity in the modes of ligand binding to RXRs resulting in agonistic or antagonistic profiles and selectivity towards specific subtypes of permissive heterodimers. Despite such diversity, direct ligand binding to the ligand binding pocket resulting in agonistic activity was preferentially preserved in the course of animal evolution pointing to its functional relevance, and potential for existence of other, species-specific endogenous RXR ligands sharing the same mode of function.

Potential roles of nuclear receptors in mediating neurodevelopmental toxicity of known endocrine-disrupting chemicals in ascidian embryos

Endocrine Disrupting Chemicals (EDCs) are molecules able to interfere with the vertebrate hormonal system in different ways, a major one being the modification of the activity of nuclear receptors (NRs). Several NRs are expressed in the vertebrate brain during embryonic development and these NRs are suspected to be responsible for the neurodevelopmental defects induced by exposure to EDCs in fishes or amphibians and to participate in several neurodevelopmental disorders observed in humans. Known EDCs exert toxicity not only on vertebrate forms of marine life but also on marine invertebrates. However, because hormonal systems of invertebrates are poorly understood, it is not clear whether the teratogenic effects of known EDCs are because of endocrine disruption. The most conserved actors of endocrine systems are the NRs which are present in all metazoan genomes but their functions in invertebrate organisms are still insufficiently characterized. EDCs like bisphenol A have recently been shown to affect neurodevelopment in marine invertebrate chordates called ascidians. Because such phenotypes can be mediated by NRs expressed in the ascidian embryo, we review all the information available about NRs expression during ascidian embryogenesis and discuss their possible involvement in the neurodevelopmental phenotypes induced by EDCs.

The effects of bisphenol A on some plasma cytokine levels and distribution of CD8+ and CD4+ T lymphocytes in spleen, ileal Peyer's patch and bronchus associated lymphoid tissue in rats

The effects of bisphenol A on the some plasma cytokine levels and distribution of CD8⁺ and CD4⁺ T lymphocytes in spleen, ilealPeyer's patch and bronchus-associated lymphoid tissue in rats were investigated. A total of fourty male Wistar Albino rats were divided into five groups including 8 rats in each one: control, vehicle, BPA 5, BPA 50 and BPA 500 groups. Doses of 5, 50 and 500 μg/kg BPA were dissolved in ethanol, then mixed with corn oil. The control group received no treatment. The vehicle group was given the ethanol-corn oil mixture. BPA 5, BPA 50 and BPA 500 groups were given, respectively, 5, 50, and 500 μg/kg/day orally. In blood samples, IL-4, IL-6, IL-10 and TNF-α plasma levels were determined with ELISA. Tissue samples (spleen, ileal Peyer's patches and lung) were processed by means of routine histological techniques. CD4 and CD8 were stained immunohistochemically. Data obtained from this study showed that, BPA causes the alteration on immune parameters including cytokine profile, distribution of CD8⁺ and CD4⁺ T lymhpocytes in spleen and ileal Peyer's patches. Present study indicated that BPA may affect immune systems even at lower doses.Disruption of immun system cells and cytokine levels can result in harmful outcomes triggering autoimmune diseases and immunodeficiencies.

In vivo maternal and in vitro BPA exposure effects on hypothalamic neurogenesis and appetite regulators

In utero exposure to the ubiquitous plasticizer, bisphenol A (BPA) is associated with offspring obesity. As food intake/appetite is one of the critical elements contributing to obesity, we determined the effects of in vivo maternal BPA and in vitro BPA exposure on newborn hypothalamic stem cells which form the arcuate nucleus appetite center. For in vivo studies, female rats received BPA prior to and during pregnancy via drinking water, and newborn offspring primary hypothalamic neuroprogenitor (NPCs) were obtained and cultured. For in vitro BPA exposure, primary hypothalamic NPCs from healthy newborns were utilized. In both cases, we studied the effects of BPA on NPC proliferation and differentiation, including putative signal and appetite factors. Maternal BPA increased hypothalamic NPC proliferation and differentiation in newborns, in conjunction with increased neuroproliferative (Hes1) and proneurogenic (Ngn3) protein expression. With NPC differentiation, BPA exposure increased appetite peptide and reduced satiety peptide expression. In vitro BPA-treated control NPCs showed results that were consistent with in vivo data (increase appetite vs satiety peptide expression) and further showed a shift towards neuronal versus glial fate as well as an increase in the epigenetic regulator lysine-specific histone demethylase1 (LSD1). These findings emphasize the vulnerability of stem-cell populations that are involved in life-long regulation of metabolic homeostasis to epigenetically-mediated endocrine disruption by BPA during early life.

Estrogen receptor-based fluorescence polarization assay for bisphenol analogues and molecular modeling study of their complexation mechanism

A fluorescence polarization (FP) assay based on estrogen receptor was developed for the determination of bisphenol compounds (BPs). The human estrogen receptor α ligand binding domain (hERα-LBD) and coumestrol were employed as recognition element and fluorescent probe, respectively. Competitive displacement of tracer from receptor suggested that BPs exhibited dose-dependent binding to hERα-LBD. In order to elucidate the structural basis for the interaction between BPs and hERα-LBD, molecular dynamics simulations were performed to explore their complexation mechanism. The docked bisphenol compounds adopted agonist/antagonist conformations with varying positions and orientations in the hydrophobic binding pocket, depending on their structural characteristics of bridging moieties. Interestingly, the calculated binding energies were generally correlated with the experimentally measured affinities, indicating a potential advantage of the molecular modeling approach in predicting the binding potencies of putative ligands. Considering that the real samples may contain more than one BP, the established FP assay can potentially be used as a pre-screening method to determine the total amounts of bisphenol compounds.

Hepatic Detoxification of Bisphenol A is Retinoid-Dependent

Bisphenol A (BPA, 2,2-bis(4-hydroxyphenyl) propane) is a widely used industrial chemical. The extensive distribution of BPA in the environment poses risks to humans. However, the molecular mechanisms underlying BPA toxicity as well as its effective detoxification and elimination are not well understood. We have investigated specifically for BPA the notion raised in the literature that the optimal sensing, detoxification, and elimination of xenobiotics requires retinoid (natural derivatives and synthetic analogs of vitamin A) actions. The objective of the study was to explore how retinoids, both those stored in the liver and those originating from recent oral intake, help maintain an optimal xenobiotic detoxification response, affecting mRNA expression and activities of elements of xenobiotic detoxification system upon BPA administration to mice. Wild-type and mice lacking hepatic retinoid stores (Lrat-/-) were acutely treated with BPA (50 mg/kg body weight), with or without oral supplementation with retinyl acetate. Hepatic mRNA expression levels of the genes encoding nuclear receptors and their downstream targets involved in xenobiotic biotransformation, phase I and phase II enzyme activities, and levels of oxidative damage to cellular proteins and lipids in hepatic microsomes, mitochondria and cytosol, were assessed. BPA treatment induced hepatic activities needed for its detoxification and elimination in wild-type mice. However, BPA failed to induce these activities in the livers of Lrat-/- mice. Oral supplementation with retinyl acetate restored phase I and phase II enzyme activities, but accelerated BPA-induced oxidative damage through enhancement of non-mitochondrial ROS production. Thus, the activities of the enzymes involved in the hepatic elimination of BPA require hepatic retinoid stores. The extent of hepatic damage that arises from acute BPA intoxication is directly affected by retinoid administration during the period of BPA exposure and hepatic retinoid stores that have accumulated over the lifetime of the organism.

Bisphenol F Disrupts Thyroid Hormone Signaling and Postembryonic Development in Xenopus laevis

The safety of bisphenol A (BPA) alternatives has attracted much attention due to their wide use. In this study, we investigated the effects of bisphenol F (BPF), an alternative to BPA, on thyroid hormone (TH) signaling and postembryonic development in vertebrates using T3-induced and spontaneous Xenopus metamorphosis as models. We found that in the T3-induced metamorphosis assay, higher concentrations of BPF (100-10000 nM) antagonized T3-induced TH-response gene transcription and morphological changes including intestinal remodeling in a concentration-dependent manner, whereas 10 nM BPF exerted stimulatory effects on T3-induced integral metamorphosis when inhibited T3-induced TH-response gene transcription, demonstrating TH signaling disrupting effects of BPF. In the spontaneous metamorphosis assay, correspondingly, BPF inhibited development at metamorphic climax (with high endogenous TH levels), but promoted pre- and pro-metamorphic development (with low endogenous TH levels), displaying a developmental stage-dependent manner. Importantly, we observed agonistic actions of BPF on Notch signaling in intestines, showing that BPF disrupts vertebrate development possibly via multi pathways besides TH signaling. Thus, we infer the biphasic concentration-response relationship between BPF exposure and T3-induced metamorphosis could result from the interactions of TH signaling with other signaling pathways such as Notch signaling. Our study highlights the adverse influences of BPF on vertebrate development.

Thyroid hormone- and estrogen receptor interactions with natural ligands and endocrine disruptors in the cerebellum

Although the effects of phytoestrogens on brain function is widely unknown, they are often regarded as "natural" and thus as harmless. However, the effects of phytoestrogens or environmental pollutants on brain function is underestimated. Estrogen (17beta-estradiol, E2) and thyroid hormones (THs) play pivotal roles in brain development. In the mature brain, these hormones regulate metabolism on cellular and organismal levels. Thus, E2 and THs do not only regulate the energy metabolism of the entire organism, but simultaneously also regulate important homeostatic parameters of neurons and glia in the CNS. It is, therefore, obvious that the mechanisms through which these hormones exert their effects are pleiotropic and include both intra- and intercellular actions. These hormonal mechanisms are versatile, and the experimental investigation of simultaneous hormone-induced mechanisms is technically challenging. In addition, the normal physiological settings of metabolic parameters depend on a plethora of interactions of the steroid hormones. In this review, we discuss conceptual and experimental aspects of the gonadal and thyroid hormones as they relate to in vitro models of the cerebellum.

The measurement of bisphenol A and its analogues, perfluorinated compounds in twenty species of freshwater and marine fishes, a time-trend comparison and human health based assessment

Our previous study in 2011 reported the detection of BPA and PFAAs in 20 species of marine and freshwater fishes. With an emerging evidence to suggest the metabolic-disrupting effects of BPA/PFAAs in animals, the present study was aimed to provide a time-trend analysis to determine the current concentrations of PFAAs and BPA in 20 commercially available Hong Kong species of fishes. Since the manufacture and use of BPA is being prohibited in most nations, the introduction of BPA alternatives has recently been incorporated in the markets. Therefore, the concentrations of BPB, BPF and BPS were determined. In the present study, all freshwater and seawater fish samples showed quantified concentrations [>Limit of Quantification (LOQ<0.5ng/g)] of BPA. BPF was detected in some marine (yellow seafin, bigeye, goldspotted rabbitfish, snubnose pompano, tongue sole, Bleeker's grouper and orange-spotted grouper) and freshwater fishes (mud carp, crucian carp, tilapia, catfish, mandarin fish, grass carp, grey mullet and spotted snakehead). Two of the compounds, BPS and BPB could only be identified in the marine fishes (snubnose pompano, yellow seafin). In PFAA analysis, PFOA, PFDA, PFOS, PFUdA and PFDoA were found in most of the marine and freshwater fishes. PFOS and PFOA were shown to be the two predominant PFAAs in fishes. On the basis of the measured concentrations of bisphenols, BPs (BPA, BPB, BPF, BPS) and PFAAs, the average daily intake for BPs (20.5-31.5ng/kgb.w./day) and PFAAs (1.17-1.83ng/kgb.w./day) were calculated and found to be lower than values of tolerable daily intake (TDI) established in Europe. However, as compared with our previous study in 2011, the present study revealed an approximate 10-fold increase in the concentrations of BPA in the fish samples. Although the hazard ratio of consuming fishes for BPA and PFAA exposure is expected to remain low, possible additive metabolic-disrupting effect of BPA and its analogues as well PFAAs should be taken into consideration for human health risk assessment.

Bisphenol A promotes hepatic lipid deposition involving Kupffer cells M1 polarization in male mice

Bisphenol A (BPA), one of the most common environmental endocrine disruptors, is considered to promote hepatic lipid deposition. However, the mechanism has not been fully elucidated. The polarization of Kupffer cells (KCs) plays an important role in hepatic inflammation by promoting pro-inflammatory M1 phenotype (M1KCs), which contributes to dysregulated lipid metabolism. The purpose of this study is to investigate the role of KC polarization in BPA-induced hepatosteatosis in male mice. In this study, we examined hepatic lipid contents and quantified M1KC in BPA-treated CD1 mice, and further explored the interaction between KCs and hepatocytes using conditional HepG2 cell culture. BPA treatment significantly increased hepatic fat contents in CD1 mice, accompanied by increased number of pro-inflammatory M1KCs and enhanced secretion of inflammatory cytokines. Increased lipid contents were also observed in HepG2 cells treated with BPA. Interestingly, higher TG contents were observed in HepaG2 cells treated with conditional media from BPA-treated KCs, compared with those treated with BPA directly. Incubation of KCs with BPA promoted the polarization of KCs to pro-inflammatory M1 dominant subtypes, which was blocked by estrogen antagonist ICI182780. Taken together, our results revealed that M1KCs polarization is involved in BPA-induced hepatic fat deposition, which is possibly associated with the estrogen receptor signaling pathway.

Prostate Cancer Risk and DNA Methylation Signatures in Aging Rats following Developmental BPA Exposure: A Dose-Response Analysis

BACKGROUND

Previous studies have uncovered heightened prostatic susceptibility to hormone-induced neoplasia from early-life exposure to low-dose bisphenol A (BPA). However, significant data gaps remain that are essential to address for biological relevance and necessary risk assessment.

OBJECTIVES

A complete BPA dose-response analysis of prostate lesions across multiple prostatic lobes was conducted that included internal BPA dosimetry, progression to adenocarcinoma with aging and mechanistic connections to epigenetically reprogramed genes.

METHODS

Male neonatal Sprague-Dawley rats were briefly exposed to 0.1 to 5,000 μg BPA/kg BW on postnatal days (PND) 1, 3, and 5. Individual prostate lobes plus periurethral prostatic ducts were evaluated at 7 mo or 1 y of age without or with adult testosterone plus estradiol (T+E) to promote carcinogenesis. DNA methylation of five genes was quantified by bisulfite genomic sequencing in d-200 dorsal prostates across BPA doses. Serum free-BPA and BPA-glucuronide were quantitated in sera of individual PND 3 pups collected 1 hr postexposure utilizing ultra-high-pressure tandem mass spectrometry (UHPLC-MS-MS).

RESULTS

The lowest BPA dose initiated maximal hormonal carcinogenesis in lateral prostates despite undetectable free BPA 1 hr postexposure. Further, prostatic intraepithelial neoplasia (PIN) progressed to carcinoma in rats given neonatal low-dose BPA with adult T+E but not in rats given adult T+E alone. The dorsal and ventral lobes and periurethral prostatic ducts exhibited a nonmonotonic dose response with peak PIN, proliferation and apoptotic values at 10–100 μg/kg BW. This was paralleled by nonmonotonic and dose-specific DNA hypomethylation of genes that confer carcinogenic risk, with greatest hypomethylation at the lowest BPA doses.

CONCLUSIONS

Developmental BPA exposures heighten prostate cancer susceptibility in a complex dose- and lobe-specific manner. Importantly, elevated carcinogenic risk is found at doses that yield undetectable serum free BPA. Dose-specific epigenetic modifications of selected genes provide a mechanistic framework that may connect early-life BPA to later-life predisposition to prostate carcinogenesis. https://doi.org/10.1289/EHP1050.

Effects of Low-Dose Developmental Bisphenol A Exposure on Metabolic Parameters and Gene Expression in Male and Female Fischer 344 Rat Offspring

BACKGROUND

Bisphenol A (BPA) is an endocrine-disrupting chemical that may contribute to development of obesity and metabolic disorders. Humans are constantly exposed to low concentrations of BPA, and studies support that the developmental period is particularly sensitive.

OBJECTIVES

The aim was to investigate the effects of low-dose developmental BPA exposure on metabolic parameters in male and female Fischer 344 (F344) rat offspring.

METHODS

Pregnant F344 rats were exposed to BPA via their drinking water, corresponding to 0.5 μg/kg BW/d (BPA0.5; n=21) or 50 μg/kg BW/d (BPA50; n=16), from gestational day (GD) 3.5 until postnatal day (PND) 22, and controls were given vehicle (n=26). Body weight (BW), adipose tissue, liver (weight, histology, and gene expression), heart weight, and lipid profile were investigated in the 5-wk-old offspring.

RESULTS

Males and females exhibited differential susceptibility to the different doses of BPA. Developmental BPA exposure increased plasma triglyceride levels (0.81±0.10 mmol/L compared with 0.57±0.03 mmol/L, females BPA50 p=0.04; 0.81±0.05 mmol/L compared with 0.61±0.04 mmol/L, males BPA0.5 p=0.005) in F344 rat offspring compared with controls. BPA exposure also increased adipocyte cell density by 122% in inguinal white adipose tissue (iWAT) of female offspring exposed to BPA0.5 compared with controls (68.2±4.4 number of adipocytes/HPF compared with 55.9±1.5 number of adipocytes/HPF; p=0.03) and by 123% in BPA0.5 females compared with BPA50 animals (68.2±4.4 number of adipocytes/high power field (HPF) compared with 55.3±2.9 number of adipocytes/HPF; p=0.04). In iWAT of male offspring, adipocyte cell density was increased by 129% in BPA50-exposed animals compared with BPA0.5-exposed animals (69.9±5.1 number of adipocytes/HPF compared with 54.0±3.4 number of adipocytes/HPF; p=0.03). Furthermore, the expression of genes involved in lipid and adipocyte homeostasis was significantly different between exposed animals and controls depending on the tissue, dose, and sex.

CONCLUSIONS

Developmental exposure to 0.5 μg/kg BW/d of BPA, which is 8-10 times lower than the current preliminary EFSA (European Food Safety Authority) tolerable daily intake (TDI) of 4 μg/kg BW/d and is within the range of environmentally relevant levels, was associated with sex-specific differences in the expression of genes in adipose tissue plasma triglyceride levels in males and adipocyte cell density in females when F344 rat offspring of dams exposed to BPA at 0.5 μg/kg BW/d were compared with the offspring of unexposed controls. https://doi.org/10.1289/EHP505.

Characterization of Adipogenic Chemicals in Three Different Cell Culture Systems: Implications for Reproducibility Based on Cell Source and Handling

The potential for chemical exposures to exacerbate the development and/or prevalence of metabolic disorders, such as obesity, is currently of great societal concern. Various in vitro assays are available to assess adipocyte differentiation, though little work has been done to standardize protocols and compare models effectively. This study compares several adipogenic cell culture systems under a variety of conditions to assess variability in responses. Two sources of 3T3-L1 preadipocytes as well as OP9 preadipocytes were assessed for cell proliferation and triglyceride accumulation following different induction periods and using various tissue culture plates. Both cell line and cell source had a significant impact on potencies and efficacies of adipogenic chemicals. Gene expression analyses suggested that differential expression of nuclear receptors involved in adipogenesis underlie the differences between OP9 and 3T3-L1 cells; however, there were also differences based on 3T3-L1 cell source. Induction period modulated potency and efficacy of response depending on cell line and test chemical, and large variations were observed in triglyceride accumulation and cell proliferation between brands of tissue culture plates. Our results suggest that the selection of a cell system and differentiation protocol significantly impacts the detection of adipogenic chemicals, and therefore, influences reproducibility of these studies.

Fatty acid metabolism in fish species as a biomarker for environmental monitoring

Pollution by Organic Contaminants (OC) in aquatic environments is a relevant issue at the global scale. Lipids comprised of Fatty Acids (FA) play many important roles in the physiology and life history of fishes. Toxic effects of OC are partly dependent on its bioaccumulation in the lipids of aquatic organisms due its physicochemical properties. Therefore, there is an increasing interest to investigate the gene expression as well as the presence and activity of proteins involved in FA metabolism. The attention on Peroxisome Proliferation Activate Receptors (PPARs) also prevails in fish species exposed to OC and in the transport, biosynthesis and β-oxidation of FA. Several studies have been conducted under controlled conditions to evaluate these biological aspects of fish species exposed to OC, as fibrates, endocrine disrupting compounds, perfluoroalkyl acids, flame retardants, metals and mixtures of organic compounds associated with a polluted area. However, only fibrates, which are agonists of PPARs, induce biological responses suitable to be considered as biomarkers of exposure to these pollutants. According to the documented findings on this topic, it is unlikely that these physiological aspects are suitable to be employed as biomarkers with some noticeable exceptions, which depend on experimental design. This emphasises the need to investigate the responses in fish treated with mixtures of OC and in wild fish species from polluted areas to validate or refute the suitability of these biomarkers for environmental or fish health monitoring.

Bisphenol A and Bisphenol S Induce Distinct Transcriptional Profiles in Differentiating Human Primary Preadipocytes

Bisphenol S (BPS) is increasingly used as a replacement plasticizer for bisphenol A (BPA) but its effects on human health have not been thoroughly examined. Recent evidence indicates that both BPA and BPS induce adipogenesis, although the mechanisms leading to this effect are unclear. In an effort to identify common and distinct mechanisms of action in inducing adipogenesis, transcriptional profiles of differentiating human preadipocytes exposed to BPA or BPS were compared. Human subcutaneous primary preadipocytes were differentiated in the presence of either 25 μM BPA or BPS for 2 and 4 days. Poly-A RNA-sequencing was used to identify differentially expressed genes (DEGs). Functional analysis of DEGs was undertaken in Ingenuity Pathway Analysis. BPA-treatment resulted in 472 and 176 DEGs on days 2 and 4, respectively, affecting pathways such as liver X receptor (LXR)/retinoid X receptor (RXR) activation, hepatic fibrosis and cholestasis. BPS-treatment resulted in 195 and 51 DEGs on days 2 and 4, respectively, revealing enrichment of genes associated with adipogenesis and lipid metabolism including the adipogenesis pathway and cholesterol biosynthesis. Interestingly, the transcription repressor N-CoR was identified as a negative upstream regulator in both BPA- and BPS-treated cells. This study presents the first comparison of BPA- and BPS-induced transcriptional profiles in human differentiating preadipocytes. While we previously showed that BPA and BPS both induce adipogenesis, the results from this study show that BPS affects adipose specific transcriptional changes earlier than BPA, and alters the expression of genes specifically related to adipogenesis and lipid metabolism. The findings provide insight into potential BPS and BPA-mediated mechanisms of action in inducing adipogenesis in human primary preadipocytes.

An Emerging Role of micro-RNA in the Effect of the Endocrine Disruptors

Endocrine-disrupting chemicals (EDCs) are diverse natural and synthetic chemicals that may alter various mechanisms of the endocrine system and produce adverse developmental, reproductive, metabolic, and neurological effects in both humans and wildlife. Research on EDCs has revealed that they use a variety of both nuclear receptor-mediated and non-receptor-mediated mechanisms to modulate different components of the endocrine system. The molecular mechanisms underlying the effects of EDCs are still under investigation. Interestingly, some of the effects of EDCs have been observed to pass on to subsequent unexposed generations, which can be explained by the gametic transmission of deregulated epigenetic marks. Epigenetics is the study of heritable changes in gene expression that occur without a change in the DNA sequence. Epigenetic mechanisms, including histone modifications, DNA methylation, and specific micro-RNAs (miRNAs) expression, have been proposed to mediate transgenerational transmission and can be triggered by environmental factors. MiRNAs are short non-coding RNA molecules that post-transcriptionally repress the expression of genes by binding to 3′-untranslated regions of the target mRNAs. Given that there is mounting evidence that miRNAs are regulated by hormones, then clearly it is important to investigate the potential for environmental EDCs to deregulate miRNA expression and action.

"Stockpile" of Slight Transcriptomic Changes Determines the Indirect Genotoxicity of Low-Dose BPA in Thyroid Cells

Epidemiological and experimental data highlighted the thyroid-disrupting activity of bisphenol A (BPA). Although pivotal to identify the mechanisms of toxicity, direct low-dose BPA effects on thyrocytes have not been assessed. Here, we report the results of microarray experiments revealing that the transcriptome reacts dynamically to low-dose BPA exposure, adapting the changes in gene expression to the exposure duration. The response involves many genes, enriching specific pathways and biological functions mainly cell death/proliferation or DNA repair. Their expression is only slightly altered but, since they enrich specific pathways, this results in major effects as shown here for transcripts involved in the DNA repair pathway. Indeed, even though no phenotypic changes are induced by the treatment, we show that the exposure to BPA impairs the cell response to further stressors. We experimentally verify that prolonged exposure to low doses of BPA results in a delayed response to UV-C-induced DNA damage, due to impairment of p21-Tp53 axis, with the BPA-treated cells more prone to cell death and DNA damage accumulation. The present findings shed light on a possible mechanism by which BPA, not able to directly cause genetic damage at environmental dose, may exert an indirect genotoxic activity.

Endocrine disruptors and other inhibitors of 11β-hydroxysteroid dehydrogenase 1 and 2: Tissue-specific consequences of enzyme inhibition

Numerous chemicals in the environment have the ability to interact with the endocrine system. These compounds are called endocrine disruptors (EDs). Exposure to EDs represents one of the hypotheses for decreasing fertility, the increased risk of numerous cancers and obesity, metabolic syndrome and type 2 diabetes. There are various mechanisms of ED action, one of which is their interference in the action of 11β-hydroxysteroid dehydrogenase (11βHSD) that maintains a balance between active and inactive glucocorticoids on the intracellular level. This enzyme has two isoforms and is expressed in various tissues. Inhibition of 11βHSD in various tissues can have different consequences. In the case of EDs, the results of exposure are mainly adverse; on the other hand pharmaceutically developed inhibitors of 11βHSD type 1 are evaluated as an option for treating metabolic syndrome, as well as related diseases and depressive disorders. This review focuses on the effects of 11βHSD inhibitors in the testis, colon, adipose tissue, kidney, brain and placenta.

Developmental exposure to bisphenol A alters expression and DNA methylation of Fkbp5, an important regulator of the stress response

Bisphenol A (BPA), an abundant endocrine disruptor, affects stress-responsiveness and related behaviors in children. In rats, perinatal BPA exposure modifies stress response in pubertal offspring via unknown mechanisms. Here we examined possible epigenetic modifications in the glucocorticoid receptor gene and its regulator Fkbp5 in hypothalamus and hippocampus of exposed offspring. We found increased DNA methylation of Fkbp5 and reduced protein levels in the hippocampus of exposed male rats. Similar effects were obtained in a male hippocampal cell line when exposed to BPA during differentiation. The estrogen receptor (ER) antagonist ICI 182,780 or ERβ knock-down affected Fkbp5 expression and methylation similarly to BPA. Further, BPA's effect on Fkbp5 was abolished upon knock-down of ERβ, suggesting a role for this receptor in mediating BPA's effects on Fkbp5. These data demonstrate that developmental BPA exposure modifies Fkbp5 methylation and expression in male rats, which may be related to its impact on stress responsiveness.

Differences in Bisphenol A and Estrogen Levels in the Plasma and Seminal Plasma of Men With Different Degrees of Infertility

The general population is potentially exposed to many chemicals that can affect the endocrine system. These substances are called endocrine disruptors (EDs), and among them bisphenol A (BPA) is one of the most widely used and well studied. Nonetheless, there are still no data on simultaneous measurements of various EDs along with steroids directly in the seminal fluid, where deleterious effects of EDs on spermatogenesis and steroidogenesis are assumed. We determined levels of BPA and 3 estrogens using LC-MS/MS in the plasma and seminal plasma of 174 men with different degrees of infertility. These men were divided according their spermiogram values into 4 groups: (1) healthy men, and (2) slightly, (3) moderate, and (4) severely infertile men. Estradiol levels differed across the groups and body fluids. Slightly infertile men have significantly higher BPA plasma and seminal plasma levels in comparison with healthy men (p<0.05 and p<0.01, respectively). Furthermore, seminal BPA, but not plasma BPA, was negatively associated with sperm concentration and total sperm count (–0.27; p<0.001 and –0.24; p<0.01, respectively). These findings point to the importance of seminal plasma in BPA research. Overall, a disruption of estrogen metabolism was observed together with a weak but significant impact of BPA on sperm count and concentration.

Bisphenol A Interaction With Brain Development and Functions

Brain development is an organized, but constantly adaptive, process in which genetic and epigenetic signals allow neurons to differentiate, to migrate, and to develop correct connections. Gender specific prenatal sex hormone milieu participates in the dimorphic development of many neuronal networks. Environmental cues may interfere with these developmental programs, producing adverse outcomes. Bisphenol A (BPA), an estrogenic/antiandrogenic endocrine disruptor widely diffused in the environment, produces adverse effects at levels below the acceptable daily intake. This review analyzes the recent literature on the consequences of perinatal exposure to BPA environmental doses on the development of a dimorphic brain. The BPA interference with the development and function of the neuroendocrine hypothalamus and of the nuclei controlling energy balance, and with the hippocampal memory processing is also discussed. The detrimental action of BPA appears complex, involving different hormonal and epigenetic pathways activated, often in a dimorphic way, within clearcut susceptibility windows. To date, discrepancies in experimental approaches and in related outcomes make unfeasible to translate the available information into clear dose-response models for human risk assessment. Evaluation of BPA brain levels in relation to the appearance of adverse effects in future basic studies will certainly give better definition of the warning threshold for human health.

Nuclear receptors in transgenerational epigenetic inheritance

Nuclear Receptors are ligand-activated transcription factors that translate information about the lipid environment into specific genetic programs, a property that renders them good candidates to be mediators of rapid adaptation changes of a species. Lipid-based morphogens, endocrine hormones, fatty acids and xenobiotics might act through this class of transcription factors making them regulators able to fine-tune physiological processes. Here we review the basic concepts and current knowledge on the process whereby small molecules act through nuclear receptors and contribute to transgenerational changes. Several molecules shown to cause transgenerational changes like phthalates, BPA, nicotine, tributylin bind and activate nuclear receptors like ERs, androgen receptors, glucocorticoid receptors or PPARγ. A specific subset of observations involving nuclear receptors has focused on the effects of environmental stress or maternal behaviour on the development of transgenerational traits. While these effects do not involve environmental ligands, they change the expression levels of Estrogen and glucocorticoid receptors of the second generation and consequently initiate an altered genetic program in the second generation. In this review we summarize the available literature about the role of nuclear receptors in transgenerational inheritance.

EPI-001 is a selective peroxisome proliferator-activated receptor-gamma modulator with inhibitory effects on androgen receptor expression and activity in prostate cancer

The androgen receptor (AR) is a driver of prostate cancer (PCa) cell growth and disease progression. Therapies for advanced PCa exploit AR dependence by blocking the production or action of androgens, but these interventions inevitably fail via multiple mechanisms including mutation or deletion of the AR ligand binding domain (LBD). Thus, the development of new inhibitors which act through non-LBD interfaces is an unmet clinical need. EPI-001 is a bisphenol A-derived compound shown to bind covalently and inhibit the AR NH2-terminal domain (NTD). Here, we demonstrate that EPI-001 has general thiol alkylating activity, resulting in multilevel inhibitory effects on AR in PCa cell lines and tissues. At least one secondary mechanism of action associated with AR inhibition was found to be selective modulation of peroxisome proliferator activated receptor-gamma (PPARγ). These multi-level effects of EPI-001 resulted in inhibition of transcriptional activation units (TAUs) 1 and 5 of the AR NTD, and reduced AR expression. EPI-001 inhibited growth of AR-positive and AR-negative PCa cell lines, with the highest sensitivity observed in LNCaP cells. Overall, this study provides new mechanistic insights to the chemical biology of EPI-001, and raises key issues regarding the use of covalent inhibitors of the intrinsically unstructured AR NTD.

An investigation of the endocrine-disruptive effects of bisphenol a in human and rat fetal testes

Few studies have been undertaken to assess the possible effects of bisphenol A (BPA) on the reproductive hormone balance in animals or humans with often contradictory results. We investigated possible direct endocrine disruption by BPA of the fetal testes of 2 rat strains (14.5–17.5 days post-coitum) and humans (8–12 gestational weeks) and under different culture conditions. BPA concentrations of 10^-8M and 10^-5M for 72h reduced testosterone production by the Sprague-Dawley fetal rat testes, while only 10^-5M suppressed it in the Wistar strain. The suppressive effects at 10^-5M were seen as early as 24h and 48h in both strains. BPA at 10^-7-10^-5M for 72h suppressed the levels of fetal rat Leydig cell insulin-like factor 3 (INSL3). BPA exposure at 10^-8M, 10^-7M, and 10^-5M for 72h inhibited testosterone production in fetal human testes. For the lowest doses, the effects observed occurred only when no gonadotrophin was added to the culture media and were associated with a poorly preserved testicular morphology. We concluded that (i) BPA can display anti-androgenic effects both in rat and human fetal testes; (ii) it is essential to ascertain that the divergent effects of endocrine disruptors between species in vitro do not result from the culture conditions used, and/or the rodent strain selected; (iii) the optimization of each in vitro assay for a given species should be a major objective rather than the search of an hypothetical trans-species consensual model-system, as the organization of the testis is intrinsically different between mammalian species; (iv) due to the uncertainty existing on the internal exposure of the human fetal testis to BPA, and the insufficient number of epidemiological studies on the endocrine disruptive effects of BPA, caution should be taken in the extrapolation of our present results to the human reproductive health after fetal exposure to BPA.