In silico binding of 4,4'-bisphenols predicts in vitro estrogenic and antiandrogenic activity

A critical review to identify data gaps and improve risk assessment of bisphenol A alternatives for human health

Bisphenol A (BPA), a synthetic chemical widely used in the production of polycarbonate plastic and epoxy resins, has been associated with a variety of adverse effects in humans including metabolic, immunological, reproductive, and neurodevelopmental effects, raising concern about its health impact. In the EU, it has been classified as toxic to reproduction and as an endocrine disruptor and was thus included in the candidate list of substances of very high concern (SVHC). On this basis, its use has been banned or restricted in some products. As a consequence, industries turned to bisphenol alternatives, such as bisphenol S (BPS) and bisphenol F (BPF), which are now found in various consumer products, as well as in human matrices at a global scale. However, due to their toxicity, these two bisphenols are in the process of being regulated. Other BPA alternatives, whose potential toxicity remains largely unknown due to a knowledge gap, have also started to be used in manufacturing processes. The gradual restriction of the use of BPA underscores the importance of understanding the potential risks associated with its alternatives to avoid regrettable substitutions. This review aims to summarize the current knowledge on the potential hazards related to BPA alternatives prioritized by European Regulatory Agencies based on their regulatory relevance and selected to be studied under the European Partnership for the Assessment of Risks from Chemicals (PARC): BPE, BPAP, BPP, BPZ, BPS-MAE, and TCBPA. The focus is on data related to toxicokinetic, endocrine disruption, immunotoxicity, developmental neurotoxicity, and genotoxicity/carcinogenicity, which were considered the most relevant endpoints to assess the hazard related to those substances. The goal here is to identify the data gaps in BPA alternatives toxicology and hence formulate the future directions that will be taken in the frame of the PARC project, which seeks also to enhance chemical risk assessment methodologies using new approach methodologies (NAMs).

Adverse outcomes of the newly emerging bisphenol A substitutes

BPA and its analogues are facing increasingly stringent regulations restricting their use due to the increasing knowledge of their harmful effects. It is therefore expected that novel BPA analogues and alternatives will replace them in plastic products, cans and thermal paper to circumvent restrictions imposed by legislation. This raises concerns about the safety of "BPA-free" products, as they contain BPA substitutes whose safety has not been sufficiently assessed prior to their market introduction. The regulatory agencies have recognised BPAP, BPBP, BPC2, BPE, BPFL, BPG, BPP, BPPH, BPS-MAE, BPS-MPE, BP-TMC, BPZ and the alternatives BTUM, D-90, UU and PF201 as compound with insufficient data regarding their safety. We demonstrate that the mentioned compounds are present in consumer products, food and the environment, thus exhibiting toxicological risk not only to humans, but also to other species where their toxic effects have already been described. Results of in silico, in vitro and in vivo studies examining the endocrine disruption and other effects of BPA analogues show that they disrupt the endocrine system by targeting various nuclear receptors, impairing reproductive function and causing toxic effects such as hepatotoxicity, altered behaviour and impaired reproductive function. In vitro and in vivo data on BPA alternatives are literally non-existent, although these compounds are already present in commonly used thermal papers. However, in silico studies predicted that they might cause adverse effects as well. The aim of this article is to comprehensively collate the information on selected BPA substitutes to illustrate their potential toxicity and identify safety gaps.

Interaction of Bisphenol A and Its Analogs with Estrogen and Androgen Receptor from Atlantic Cod (Gadus morhua)

The widespread use of bisphenol A (BPA) in polycarbonate plastics and epoxy resins has made it a prevalent environmental pollutant in aquatic ecosystems. BPA poses a significant threat to marine and freshwater wildlife due to its documented endocrine-disrupting effects on various species. Manufacturers are increasingly turning to other bisphenol compounds as supposedly safer alternatives. In this study, we employed in vitro reporter gene assays and ex vivo precision-cut liver slices from Atlantic cod (Gadus morhua) to investigate whether BPA and 11 BPA analogs exhibit estrogenic, antiestrogenic, androgenic, or antiandrogenic effects by influencing estrogen or androgen receptor signaling pathways. Most bisphenols, including BPA, displayed estrogenic properties by activating the Atlantic cod estrogen receptor alpha (gmEra). BPB, BPE, and BPF exhibited efficacy similar to or higher than that of BPA, with BPB and BPAF being more potent agonists. Additionally, some bisphenols, like BPG, induced estrogenic effects in ex vivo liver slices despite not activating gmEra in vitro, suggesting structural modifications by hepatic biotransformation enzymes. While only BPC2 and BPAF activated the Atlantic cod androgen receptor alpha (gmAra), several bisphenols exhibited antiandrogenic effects by inhibiting gmAra activity. This study underscores the endocrine-disrupting impact of bisphenols on aquatic organisms, emphasizing that substitutes for BPA may pose equal or greater risks to both the environment and human health.

Screening of the Antagonistic Activity of Potential Bisphenol A Alternatives toward the Androgen Receptor Using Machine Learning and Molecular Dynamics Simulation

Over the past few decades, extensive research has indicated that exposure to bisphenol A (BPA) increases the health risks in humans. Toxicological studies have demonstrated that BPA can bind to the androgen receptor (AR), resulting in endocrine-disrupting effects. In recent investigations, many alternatives to BPA have been detected in various environmental media as major pollutants. However, related experimental evaluations of BPA alternatives have not been systematically implemented for the assessment of chemical safety and the effects of structural characteristics on the antagonistic activity of the AR. To promote the green development of BPA alternatives, high-throughput toxicological screening is fundamental for prioritizing chemical tests. Therefore, we proposed a hybrid deep learning architecture that combines molecular descriptors and molecular graphs to predict AR antagonistic activity. Compared to previous models, this hybrid architecture can extract substantial chemical information from various molecular representations to improve the model's generalization ability for BPA alternatives. Our predictions suggest that lignin-derivable bisguaiacols, as alternatives to BPA, are likely to be nonantagonist for AR compared to bisphenol analogues. Additionally, molecular dynamics (MD) simulations identified the dihydrotestosterone-bound pocket, rather than the surface, as the major binding site of bisphenol analogues. The conformational changes of key helix H12 from an agonistic to an antagonistic conformation can be evaluated qualitatively by accelerated MD simulations to explain the underlying mechanism. Overall, our computational study is helpful for toxicological screening of BPA alternatives and the design of environmentally friendly BPA alternatives.

New environmental factors related to diabetes risk in humans: Emerging bisphenols used in synthesis of plastics

BACKGROUND

Diabetes mellitus (DM) is one of the largest global health emergencies of the 21st century. In recent years, its connection with environmental pollutants, such as bisphenol A (BPA), has been demonstrated; consequently, new structurally similar molecules are used to replace BPA in the plastics industry (BPS, BPF and BPAF).

AIM

To carry out a systematic review to allow coherent evaluation of the state of the art. Subsequently, a meta-analysis was performed to unify the existing quantitative data.

METHODS

Firstly, a systematic review was carried out, using the terms "(bisphenol) AND (Diabetes OR Hyperglycemia)", to maximize the number of results. Subsequently, three authors analyzed the set of articles. Finally, a meta-analysis was performed for each BP, using RevMan software. In addition, funnel plots were developed to study publication bias.

RESULTS

The systematic analysis of the literature revealed 13 recent articles (2017-2023) related to the study paradigm. The qualitative analysis showed interesting data linking diabetes to the three most widely used substitute BPs in the industry: BPS, BPF and BPAF. Finally, the meta-analysis determined a positive relationship with BPS, BPF and BPAF, which was only statistically significant with BPS.

CONCLUSION

There is a need to apply the precautionary principle, regulating the use of new BPs. Therefore, replacing BPA with BPS, BPF or BPAF is unlikely to protect the population from potential health risks, such as DM.

Combination of Bisphenol A and Its Emergent Substitute Molecules Is Related to Heart Disease and Exerts a Differential Effect on Vascular Endothelium

Plastic production, disposal, and recycling systems represent one of the higher challenges for the planet's health. Its direct consequence is the release of endocrine disruptors, such as bisphenol A (BPA), and its emerging substitute molecules, bisphenol F and S (BPF and BPS), into the environment. Consequently, bisphenols are usually present in human biological fluids. Since BPA, BPS, and BPF have structural analogies and similar hormonal activity, their combined study is urgently needed. The present manuscript studied the effect of the mixture of bisphenols (BPmix) in one of the world's largest human cohorts (NHANES cohort). Descriptive and comparative statistics, binomial and multinomial logistic regression, weighted quantile sum regression, quantile g-computation, and Bayesian kernel machine regression analysis determined a positive association between BPmix and heart disease, including confounders age, gender, BMI, ethnicity, Poverty/Income Ratio, and serum cotinine. Endothelial dysfunction is a hallmark of cardiovascular disease; thus, the average ratio of bisphenols found in humans was used to conduct murine aortic endothelial cell studies. The first results showed that BPmix had a higher effect on cell viability than BPA, enhancing its deleterious biological action. However, the flow cytometry, Western blot, and immunofluorescence assays demonstrated that BPmix induces a differential effect on cell death. While BPA exposure induces necroptosis, its combination with the proportion determined in the NHANES cohort induces apoptosis. In conclusion, the evidence suggests the need to reassess research methodologies to study endocrine disruptors more realistically.

Efficient in vivo and in silico assessments of antiandrogenic potential in zebrafish

This study aimed to establish zebrafish-based in vivo and in silico assay systems to evaluate the antiandrogenic potential of environmental chemicals. Zebrafish embryos were exposed to 17α-methyltestosterone (TES) alone or coexposed to TES and representative antiandrogens including flutamide, p,p'-DDE, vinclozolin, fenitrothion, and linuron. We assessed the transcript expression of the androgen-responsive gene sulfotransferase family 2, cytosolic sulfotransferase 3 (sult2st3). The expression of sult2st3 was significantly induced by TES in the later stages of embryonic development. However, the TES-induced expression of sult2st3 was inhibited by flutamide in a concentration-dependent manner (IC₅₀: 5.7 μM), suggesting that the androgen receptor (AR) plays a role in sult2st3 induction. Similarly, p,p'-DDE, vinclozolin, and linuron repressed the TES-induced expression of sult2st3 (IC_50s: 0.35, 3.9, and 52 μM, respectively). At the highest concentration tested (100 μM), fenitrothion also suppressed sult2st3 expression almost completely. Notably, p,p'-DDE and linuron did not inhibit sult2st3 induction due to higher concentrations of TES; instead, they potentiated TES-induced sult2st3 expression. Fenitrothion and linuron, which had relatively low antiandrogenic potentials in terms of sult2st3 inhibition, induced broader toxicities in zebrafish embryos; thus, the relationship between developmental toxicities and antiandrogenic potency was unclear. Additionally, an in silico docking simulation showed that all five chemicals interact with the zebrafish AR at relatively low interaction energies and with Arg702 as a key amino acid in ligand binding. Our findings suggest that a combination of zebrafish-based in vivo and in silico assessments represents a promising tool to assess the antiandrogenic potentials of environmental chemicals.

Relationship between emergent BPA-substitutes and renal and cardiovascular diseases in adult population

Plastic waste pollution is one of the leading environmental problems of modern society. Its use, disposal, and recycling lead to the release of xenobiotic compounds such as bisphenol A (BPA), a known endocrine disruptor related to numerous pathologies. Due to the new restrictions on its use, it is gradually being replaced by derived molecules, such as bisphenol F or S (BPF or BPS), whose health risks have not yet been adequately studied. In the present work, significant relationships between the new BPA substitute molecules and renal and cardiovascular diseases have been detected by performing binomial and multinomial logistic regressions in one of the world's largest cohorts of urinary phenols. The results have shown a significant relationship between urinary BPF and renal function or heart disease (specifically congestive heart failure). Urinary BPS has shown a positive relationship with the risk of hypertension and a negative relationship with kidney disease. Consequently, applying new substitute molecules could imply potential health risks equivalent to BPA.

Phytotoxicity and accumulation of BPS to Pistia stratiotes under the influence of microplastics

Bisphenol S (BPS) is a contaminant of emerging concern, its exposure and phytotoxicity towards plants, however, is scarce. This study aimed at revealing the BPS translocation in plants and phytotoxicity in the presence of Polystyrene (PS) microplastics. Results found that BPS and PS showed no effect on plant growth, indicating the tolerance of plants towards BPS and PS co-contamination. In addition, plants enriched BPS from soil, and a major part of absorbed BPS was accumulated in roots, as supported by the higher BCF value in roots compared with leaves. Besides, the low TF (<1) suggested the capacity of plants to accumulate BPS in roots, and less translocation to leaves. PS negatively affected the translocation of BPS in plants. PS with large size (5 μm) also increased the distribution of BPS in organelles. Exposure risk assessment suggested low concern of BPS carried in plants to human health. This study underlines the bioaccumulation of BPS in plants, and the effects of PS in the translocation process.

In Vitro characterization of the endocrine disrupting effects of per- and poly-fluoroalkyl substances (PFASs) on the human androgen receptor

Per- and poly-fluoroalkyl substances (PFASs) are used extensively in a broad range of industrial applications and consumer products. While a few legacy PFASs have been voluntarily phased out, over 5000 PFASs have been produced as replacements for their predecessors. The potential endocrine disrupting hazards of most emerging PFASs have not been comprehensively investigated. In silico molecular docking to the human androgen receptor (hAR) combined with machine learning techniques were previously applied to 5206 PFASs and predicted 23 PFASs bind the hAR. Herein, the in silico results were validated in vitro for the five candidate AR ligands that were commercially available. Three manufactured PFASs namely (9-(nonafluorobutyl)- 2,3,6,7-tetrahydro-1 H,5 H,11 H-pyrano[2,3-f]pyrido[3,2,1-ij]quinolin-11-one (NON), 2-(heptafluoropropyl)- 3-phenylquinoxaline (HEP), and 2,2,3,3,4,4,5,5,5-nonafluoro-N-(4-nitrophenyl)pentanamide (NNN) elicited significant antiandrogenic effects at relatively low concentrations. We further investigated the mechanism of AR inhibition and found that all three PFASs inhibited AR transactivation induced by testosterone through a competitive binding mechanism. We then examined the antiandrogenic effects of these PFASs on AR expression and its responsive genes. Consistently, these PFASs significantly decreased the expression of PSA and FKBP5 and increased the expression of AR, similar to the effects elicited by a known competitive AR inhibitor, hydroxyflutamide. This suggests they are competitive antagonists of AR activity and western blot analysis revealed these PFASs decreased intracellular AR protein in androgen sensitive human prostate cancer cells. Hence, the findings presented here corroborate our published in silico approach and indicate these emerging PFASs may adversely affect the human endocrine system.

Bisphenol B disrupts testis differentiation partly via the estrogen receptor-mediated pathway and subsequently causes testicular dysgenesis in Xenopus laevis

There is growing concern about adverse effects of bisphenol A alternatives including bisphenol B (BPB) due to their estrogenic activity. However, limited data are available concerning the influences of BPB on male reproductive development in vertebrates, especially in amphibians, which are believed to be susceptible to estrogenic chemicals. The present study investigated the effects of 10, 100 and 1000 nM BPB (2.42, 24.2 and 242 μg/L) on testis development in Xenopus laevis, a model amphibian species for studying gonadal feminization. We found that exposure to BPB from stages 45/46 to 52 resulted in down-regulation of testis-biased gene expression and up-regulation of ovary-biased gene and vitellogenin (vtgb1) expression in gonad-mesonephros complexes (GMCs) of tadpoles at stage 52, coupled with suppressed cell proliferation in testes and reduced gonadal metameres, resembling the effects of 17ß-estradiol. Moreover, an estrogen receptor (ER) antagonist ICI 182780 antagonized BPB-caused up-regulation of ovary-biased gene and vtgb1 expression to some degree, indicating that the effects of BPB on X. laevis testis differentiation could be partly mediated by ER. All observations demonstrate that early exposure to BPB inhibited testis differentiation and exerted certain feminizing effects during gonadal differentiation. When exposure was extended to post-metamorphosis, testes exhibited histological and morphological abnormalities including segmented, discontinuous and fragmented shapes, besides altered sex-dimorphic gene expression. Notably, most of BPB-caused alterations were not concentration-dependent, but the lowest concentration indeed exerted significant effects. Overall, our study for the first time reveals that low concentrations of BPB can disrupt testis differentiation partly due to its estrogenic activity and subsequently cause testicular dysgenesis after metamorphosis, highlighting its reproductive risk to amphibians and other vertebrates including humans. Our finding also implies that estrogenic chemicals-caused testis differentiation inhibition at tadpole stages could predict later testicular dysgenesis after metamorphosis, meaning a possibility of early detection of abnormal testis development caused by estrogenic chemicals.

Structural basis for molecular recognition of G protein-coupled estrogen receptor by selected bisphenols

Complicated ligand-dependent signaling pathways of bisphenol A (BPA) and its analogues involve not only intranuclear estrogen receptor but also membrane receptor G protein-coupled estrogen receptor (GPER). However, the structural basis for molecular recognition of GPER by the environmental chemicals remains unknown. To reveal the structural dependence of GPER recognition by bisphenols, a systematic molecular dynamics simulation study was performed for selected bisphenols with different electron hybrid orbitals and substituents on their C atoms connecting two phenol rings. BPA was used as a control, bisphenol C(BPC) as an example for a connecting C with sp² hybrid orbitals to provide more ligand rigidity, bisphenol E(BPE) and bisphenol F(BPF) for decreased steric hindrance and hydrophobicity around the connecting C, and bisphenol B(BPB) and bisphenol AF(BPAF) for increased hydrophobicity and steric hindrance. All the tested bisphenols can bind with GPER at its classic orthosteric site to obtain GPER-ligand complexes, while van der Waals interactions and direct inter-molecular electrostatic energies provide the driving forces for ligand binding. Bulky substituents and structural rigidity of the connecting C dramatically impair hydrogen bonding between GPER and the bisphenols, which results in decreased contribution of both favorable intermolecular hydrogen bonds and unfavorable polar solvation effect to complex stability of BPB and BPC since decreased number of key residues is expected. Increase in substituent lipophilicity enhances the van der Waals interactions and favorable non-polar solvation effect. The six bisphenols of high structural similarity shared two key recognition residues, Leu137^TM3 and Trp272^TM6, the latter of which was in the highly conserved CWxP motif of TM6 and has been reported as key residue for G protein-coupled receptor activation. Based on the obtained knowledge, GPER affinity and relevant toxicity of BPA alternatives can be easily predicted, and the calculated binding free energies are consistent with the available experimental observations.

A QSAR-ICE-SSD Model Prediction of the PNECs for Per- and Polyfluoroalkyl Substances and Their Ecological Risks in an Area of Electroplating Factories

Per- and polyfluoroalkyl substances (PFASs) are a class of highly fluorinated aliphatic compounds that are persistent and bioaccumulate, posing a potential threat to the aquatic environment. The electroplating industry is considered to be an important source of PFASs. Due to emerging PFASs and many alternatives, the acute toxicity data for PFASs and their alternatives are relatively limited. In this study, a QSAR–ICE–SSD composite model was constructed by combining quantitative structure-activity relationship (QSAR), interspecies correlation estimation (ICE), and species sensitivity distribution (SSD) models in order to obtain the predicted no-effect concentrations (PNECs) of selected PFASs. The PNECs for the selected PFASs ranged from 0.254 to 6.27 mg/L. The ΣPFAS concentrations ranged from 177 to 983 ng/L in a river close to an electroplating industry in Shenzhen. The ecological risks associated with PFASs in the river were below 2.97 × 10⁻⁴.

An in vitro investigation of endocrine disrupting potentials of ten bisphenol analogues

The endocrine disruption potency of BPA was reported elsewhere, but the mechanisms of its analogues have not been fully resolved. In this study, endocrine disruption potentials of nine alternative bisphenol analogues, namely 2,2-bis(4-hydroxyphenyl)butane (BPB), 2,2-Bis(4-hydroxy-3-methylphenyl)propane (BPC), 4,4'-dihydroxydiphenylmethane (BPF), 4,4'-(1,3-Phenylene diisopropylidene)bisphenol (BPM), 4,4'-(1,4-phenylenediisopropylidene)bisphenol (BPP), 4,4'- sulfonyldiphenol (BPS), 4,4' cyclohexylidenebisphenol (BPZ), 4,4' (hexafluoroisopropylidene)-diphenol (BPAF) and 4,4'-(1-phenylethylidene)bisphenol (BPAP), plus 2,2-bis(4-hydroxyphenyl)propane (BPA) were investigated by H295R cell and MVLN cell bioassays. In the H295R cell assay, the endpoints included hormone production and key genes for steroidogenesis (CYP11A, CYP17, CYP19 and 3βHSD2) or metabolism sulfotransferase (SULT1A1, SULT2A1 and SULT2B1) at the molecular level. The results indicated that except for BPP or BPAF, the eight other bisphenols significantly increased the E2/T ratio. In addition, BPB, BPF and BPS significantly up-regulate CYP19 gene expression, and only BPB significantly reduced sulfotransferase gene expression. In the MVLN luciferase gene reporter assay, seven bisphenols induced luciferase activity alone, and are 104 to 108-fold less potent than E2. Their nuclear ERα binding activity is in the order of BPAF > BPZ > BPP > BPB > BPA > BPF > BPS. In summary, all nine tested bisphenols showed endocrine toxicity through different mechanisms. Some had similar potency as BPA, but some had even higher potency. Further research is necessary to evaluate the toxicity of these potential BPA substitutes.

Molecular modelling methods in food safety: Bisphenols as case study

Bisphenol A (BPA), a synthetic compound widely used as a building block for polycarbonate plastics, has been declared in the European Union (EU) as a substance of very high concern (SVHC). A series of BPA alternatives and derivatives (bisphenols/BPs) with similar physical-chemical properties have been produced and used by companies for substituting it. To evaluate the estrogenic and androgenic binding activity of 26 BPs, a non-statistical in silico approach has been applied. The results of molecular docking analyses applied on six different nuclear receptors (NRs) have revealed that: i) some BPA metabolites could lower the harmful effects of BPA exposure; ii) BPS is a lower interactor for all NRs, but it does not appear safer at all for androgen receptor (AR), for which its binding activity is found similar to a pharmacological anti-androgen; iii) only a BP has been found as a safer compound for all NRs considered. Moreover, molecular dynamic simulation of three BPs on ERα have revealed that the presence of negative hydrophobic interactions could induce a decrease in receptor activity. Overall, the present results demonstrate that in silico methods could be a valid approach to screen estrogenic and androgenic activity of food contact materials (FCMs).

Chronic thiamethoxam exposure impairs the HPG and HPT axes in adult Chinese rare minnow (Gobiocypris rarus): Docking study, hormone levels, histology, and transcriptional responses

Thiamethoxam has emerged as an environmental contaminant detected in aqueous environments, and its endocrine-disrupting effect at chronic exposure in teleosts remains unknown. In the present study, a docking experiment and an in vivo test were integrated to systematically explore the toxic mechanisms of thiamethoxam in fish. Histological analysis, plasma VTG and hormone level (E2, 11-KT, T3 and T4) determinations, and HPG and HPT gene expression quantification were performed after Chinese rare minnow (Gobiocypris rarus) was exposed to thiamethoxam (0, 0.5, 5, and 50 μg/L) for 90 days. According to the docking study, thiamethoxam had different interactions with ERα, AR and TRα via hydrogen bonding. A decrease in body length and plasma T4 was observed in both genders. The histological damage in liver and delayed gonadal development were observed in both genders at 50 μg/L thiamethoxam treatment. In males, the following HPG axis genes were upregulated: gnrh and cyp19b in the brain; vtg and cyp19a in the liver; and cyp17 and cyp19a in the gonad. In females, erɑ in the liver was significantly upregulated with 0.5 μg/L thiamethoxam treatment, and cyp17 in the gonad was upregulated with all treatment. The suppression of cyp19a, gnrh, cyp11a, and ttr was observed at the concentration of 5 μg/L in the female liver. Taken together, the endocrine system of Chinese rare minnow might be disrupted after chronic exposure to thiamethoxam.

Evidence for Bisphenol B Endocrine Properties: Scientific and Regulatory Perspectives

BACKGROUND

The substitution of bisphenol A (BPA) by bisphenol B (BPB), a very close structural analog, stresses the need to assess its potential endocrine properties.

OBJECTIVE

This analysis aimed to investigate whether BPB has endocrine disruptive properties in humans and in wildlife as defined by the World Health Organization (WHO) definition used in the regulatory field, that is, a) adverse effects, b) endocrine activity, and c) plausible mechanistic links between the observed endocrine activity and adverse effects.

METHODS

We conducted a systematic review to identify BPB adverse effects and endocrine activities by focusing on animal models and in vitro mechanistic studies. The results were grouped by modality (estrogenic, androgenic, thyroid hormone, steroidogenesis-related, or other endocrine activities). After critical analysis of results, lines of evidence were built using a weight-of-evidence approach to establish a biologically plausible link. In addition, the ratio of BPA to BPB potency was reported from studies investigating both bisphenols.

RESULTS

Among the 36 articles included in the analysis, 3 subchronic studies consistently reported effects of BPB on reproductive function. In rats, the 28-d and 48-week studies showed alteration of spermatogenesis associated with a lower height of the seminiferous tubules, the alteration of several sperm parameters, and a weight loss for the testis, epididymis, and seminal vesicles. In zebrafish, the results of a 21-d reproductive study demonstrated that exposed fish had a lower egg production and a lower hatching rate and viability. The in vitro and in vivo mechanistic data consistently demonstrated BPB's capacity to decrease testosterone production and to exert an estrogenic-like activity similar to or greater than BPA's, both pathways being potentially responsible for spermatogenesis impairment in rats and fish.

CONCLUSION

The available in vivo, ex vivo, and in vitro data, although limited, coherently indicates that BPB meets the WHO definition of an endocrine disrupting chemical currently used in a regulatory context. https://doi.org/10.1289/EHP5200.

Hazards of bisphenol A -- blocks RNA splicing leading to abnormal testicular development in offspring male mice

This study was conducted to investigate the effects of maternal exposure to BPA on testicular development in offspring males. Pregnant Kunming mice were randomly divided into 7 groups with 20 mice in each group. Group A was the control group and the mice were given distilled water orally. Mice in groups B, C, D, E, F, G received BPA orally at a dose of 0.05 mg/kg/d, 0.5 mg/kg/d, 5 mg/kg/d, 10 mg/kg/d, 20 mg/kg/d, 50 mg/kg/d, respectively. F0 mice were exposed to BPA for 40 days from gestation day 0 to lactation day 21. F1 male mice were sacrificed at weaning (postnatal day 21). Histological observations revealed architectural damages in testis in BPA exposed groups. The testicular organ index increased significantly when the BPA oral exposure dose was above 20 mg/kg/d (P < 0.05). BPA contents in serum of F1 male mice increased significantly when BPA was above 5 mg/kg/d (P < 0.05), while the contents significant increased in maternal serum when BPA was higher than 0.5 mg/kg/d. The damage of cell nuclear DNA of testis was significantly aggravated when BPA was above 5 mg/kg/d. The expression of AR in the testis was significantly increased when BPA was above 20 mg/kg/d (P < 0.05). Transcriptome sequencing showed that the Snrnp 40 which encoding U5 snRNA subunit was significantly up-regulated in spliceosome pathway, and the Hnrnpu which encoding splicing universal protein component was significantly down-regulated. The blockage of spliceosome might be one of the reasons why BPA affects testicular development.

Assessment of the endocrine-disrupting effects of organophosphorus pesticide triazophos and its metabolites on endocrine hormones biosynthesis, transport and receptor binding in silico

Triazophos (TAP) was a widely used organophosphorus insecticide in developing countries. TAP could produce specific metabolites triazophos-oxon (TAPO) and 1-phenyl-3-hydroxy-1,2,4-triazole (PHT) and non-specific metabolites diethylthiophosphate (DETP) and diethylphosphate (DEP). The objective of this study involved computational approaches to discover potential mechanisms of molecular interaction of TAP and its major metabolites with endocrine hormone-related proteins using molecular docking in silico. We found that TAP, TAPO and DEP showed high binding affinity with more proteins and enzymes than PHT and DETP. TAP might interfere with the endocrine function of the adrenal gland, and TAP might also bind strongly with glucocorticoid receptors and thyroid hormone receptors. TAPO might disrupt the normal binding of androgen receptor, estrogen receptor, progesterone receptor and adrenergic receptor to their natural hormone ligands. DEP might affect biosynthesis of steroid hormones and thyroid hormones. Meanwhile, DEP might disrupt the binding and transport of thyroid hormones in the blood and the normal binding of thyroid hormones to their receptors. These results suggested that TAP and DEP might have endocrine disrupting activities and were potential endocrine disrupting chemicals. Our results provided further reference for the comprehensive evaluation of toxicity of organophosphorus chemicals and their metabolites.

Predicting estrogen receptor binding of chemicals using a suite of in silico methods - Complementary approaches of (Q)SAR, molecular docking and molecular dynamics

With the aim of obtaining reliable estimates of Estrogen Receptor (ER) binding for diverse classes of compounds, a weight of evidence approach using estimates from a suite of in silico models was assessed. The predictivity of a simple Majority Consensus of (Q)SAR models was assessed using a test set of compounds with experimental Relative Binding Affinity (RBA) data. Molecular docking was also carried out and the binding energies of these compounds to the ERα receptor were determined. For a few selected compounds, including a known full agonist and antagonist, the intrinsic activity was determined using low-mode molecular dynamics methods. Individual (Q)SAR model predictivity varied, as expected, with some models showing high sensitivity, others higher specificity. However, the Majority Consensus (Q)SAR prediction showed a high accuracy and reasonably balanced sensitivity and specificity. Molecular docking provided quantitative information on strength of binding to the ERα receptor. For the 50 highest binding affinity compounds with positive RBA experimental values, just 5 of them were predicted to be non-binders by the Majority QSAR Consensus. Furthermore, agonist-specific assay experimental values for these 5 compounds were negative, which indicates that they may be ER antagonists. We also showed different scenarios of combining (Q)SAR results with Molecular docking classification of ER binding based on cut-off values of binding energies, providing a rational combined strategy to maximize terms of toxicological interest.