Estrogenicity of halogenated bisphenol A: in vitro and in silico investigations

Occurrence of Chlorinated Derivatives of Bisphenol S in Paper Products and Their Potential Health Risks through Dermal Exposure

The occurrence of chlorinated derivatives of bisphenol S (Clx-BPS) and BPS was investigated in nine types of paper products (n = 125), including thermal paper, corrugated boxes, mail envelopes, newspapers, flyers, magazines, food contact paper, household paper, and business cards. BPS was found in all paper product samples, while Clx-BPS were mainly found in thermal paper (from below the limit of detection ( Collapse

Key Words

• Chlorinated derivatives of bisphenol S
• Dermal exposure
• Paper products
• Paper recycling
• Toxicity

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MESH Headings

• Humans
• Benzhydryl Compounds
• Paper
• Food
• Commerce

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Affiliation(s)

Xiaoxuan Han Research Center for Analytical Sciences, Department of Chemistry, College of Sciences, Northeastern University, Shenyang 110819, China School of Environmental & Municipal Engineering, Qingdao University of Technology, Qingdao 266033, China
Yong Tian School of Environmental & Municipal Engineering, Qingdao University of Technology, Qingdao 266033, China
Haonan Liu School of Environmental & Municipal Engineering, Qingdao University of Technology, Qingdao 266033, China
Xuwei Chen Research Center for Analytical Sciences, Department of Chemistry, College of Sciences, Northeastern University, Shenyang 110819, China
Jian-Hua Wang Research Center for Analytical Sciences, Department of Chemistry, College of Sciences, Northeastern University, Shenyang 110819, China
Jianbo Shi State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
Guibin Jiang State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

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In silico profiling of endocrine-disrupting potential of bisphenol analogues and their halogenated transformation products

Due to its endocrine-disrupting properties, bisphenol A (BPA) is being phased out from plastics, thermal paper and epoxy resins, and its replacements are being introduced into the market. Bisphenols are released into the environment, where they can undergo halogenation. Unlike BPA, the endocrine-disrupting potential of BPA analogues and their halogenated transformation products has not been extensively studied. The aim of this study was to evaluate the endocrine-disrupting potential of 18 BPA analogues and their halogenated derivatives by calculating affinities for 14 human nuclear receptors utilizing the Endocrine Disruptome and VirtualToxLab™ in silico tools. Our simulations identified AR, ERs, and GR as the most favorable targets of bisphenols and their derivatives. Several BPA analogues displayed a higher predicted potential for endocrine disruption than BPA. Our models highlighted BPZ and BPPH as the most hazardous in terms of predicted endocrine activities. Halogenation, in general, was predicted to increase the binding affinity of bisphenols for AR, ERβ, MR, GR, PPARγ, and TRβ. Notably, mono- or 2,2'-di-halogenated bisphenols exhibited the highest potential for endocrine disruption. In vitro corroboration of the obtained results should be the next milestone in evaluating the safety of BPA substitutes and their halogenated transformation products.

Species Differences in Response to Binding Interactions of Bisphenol A and its Analogs with the Modeled Estrogen Receptor 1 and In Vitro Reporter Gene Assay in Human and Zebrafish

Adverse impacts associated with the interactions of numerous endocrine-disruptor chemicals (EDCs) with estrogen receptor 1 play a pivotal role in reproductive dysfunction. The predictive studies on these interactions thus are crucial in the risk assessment of EDCs but rely heavily on the accuracy of specific protein structure in three dimensions. As the three-dimensional (3D) structure of zebrafish estrogen receptor 1 (zEsr1) is not available, the 3D structure of zEsr1 ligand-binding domain (zEsr1-LBD) was generated using MODELLER and its quality was assessed by the PROCHECK, ERRAT, ProSA, and Verify-3D tools. After the generated model was verified as reliable, bisphenol A and its analogs were docked on the zEsr1-LBD and human estrogen receptor 1 ligand-binding domain (hESR1-LBD) using the Discovery Studio and Autodock Vina programs. The molecular dynamics followed by molecular docking were simulated using the Nanoscale Molecular Dynamics program and compared to those of the in vitro reporter gene assays. Some chemicals were bound with an orientation similar to that of 17β-estradiol in both models and in silico binding energies showed moderate or high correlations with in vitro results (0.33 ≤ r²  ≤ 0.71). Notably, hydrogen bond occupancy during molecular dynamics simulations exhibited a high correlation with in vitro results (r²  ≥ 0.81) in both complexes. These results show that the combined in silico and in vitro approaches is a valuable tool for identifying EDCs in different species, facilitating the assessment of EDC-induced reproductive toxicity. Environ Toxicol Chem 2022;41:2431-2443. © 2022 SETAC.

Halogenated ingredients of household and personal care products as emerging endocrine disruptors

The everyday use of household and personal care products (HPCPs) generates an enormous amount of chemicals, of which several groups warrant additional attention, including: (i) parabens, which are widely used as preservatives; (ii) bisphenols, which are used in the manufacture of plastics; (iii) UV filters, which are essential components of many cosmetic products; and (iv) alkylphenol ethoxylates, which are used extensively as non-ionic surfactants. These chemicals are released continuously into the environment, thus contaminating soil, water, plants and animals. Wastewater treatment and water disinfection procedures can convert these chemicals into halogenated transformation products, which end up in the environment and pose a potential threat to humans and wildlife. Indeed, while certain parent HPCP ingredients have been confirmed as endocrine disruptors, less is known about the endocrine activities of their halogenated derivatives. The aim of this review is first to examine the sources and occurrence of halogenated transformation products in the environment, and second to compare their endocrine-disrupting properties to those of their parent compounds (i.e., parabens, bisphenols, UV filters, alkylphenol ethoxylates). Albeit previous reports have focused individually on selected classes of such substances, none have considered the problem of their halogenated transformation products. This review therefore summarizes the available research on these halogenated compounds, highlights the potential exposure pathways, and underlines the existing knowledge gaps within their toxicological profiles.

Anti-inflammatory action of betulin and its potential as a dissociated glucocorticoid receptor modulator

Although the medical application of betulin has been presented in previous studies, the potential mechanism of the anti-inflammatory action of betulin should be further investigated. This work aims to confirm the hypothesis that betulin has dexamethasone-like anti-inflammatory action through glucocorticoid receptor (GR)-mediated pathway. Firstly, the binding ability of betulin with GR was measured by a fluorescence polarization-based competitive binding assay, with the IC₅₀ value of 79.18 ± 0.30 mM. Betulin could bind to GR and then induced GR nuclear translocation, but lacked GR transcriptional activity in HeLa cells. Hence, betulin exhibited the potential to be a dissociated modulator for GR, with the loss of glucocorticoid response element (GRE)-associated side effects. In addition, betulin downregulated GRE-driven protein expression of G6P involved in gluconeogenesis, namely side effect. The results of pro-inflammatory cytokines analysis showed that betulin exerted anti-inflammatory action in vitro. Both of the hydrophobic and hydrogen-bonding interactions stabilized the binding between betulin and GR during the simulation process. In conclusion, betulin might be a potential dissociated GR modulator with a reduced side effect profile yet keeping its anti-inflammatory action.

Identification of dicyclohexyl phthalate as a glucocorticoid receptor antagonist by molecular docking and multiple in vitro methods

The potential activities of phthalate esters (PAEs) that interfere with the endocrine system have been focused recently. However, information on modulating the glucocorticoid receptor (GR) of PAEs is scarce. Our aim was to evaluate the agonistic / antagonistic properties of PAEs on human GR. Luciferase reporter gene assay revealed that the tested chemicals displayed no agonistic effects but dicyclohexyl phthalate (DCHP) exerted antagonistic activity in a dose-responsive manner for GR in HeLa cells. The effects of DCHP on dexamethasone (DEX)-induced GR nuclear translocation and gene expression of glucocorticoid-responsive gene expression (G6Pase, PEPCK, FAS, GILZ and MKP-1), as well as protein expression of G6Pase and PEPCK were further examined by RT-qPCR and western blot analysis. DCHP antagonized DEX-induced GR nuclear translocation and suppressed gene expression in both mRNA and protein levels. Furthermore, the results of molecular docking and molecular dynamics simulation showed that DCHP could bind to GR and exhibited potential regulation on this target protein. Collectively, we demonstrate that DCHP may act as a GR antagonist in vitro and is considered to exert endocrine effects via human GR.

Discovery of New Protein Targets of BPA Analogs and Derivatives Associated with Noncommunicable Diseases: A Virtual High-Throughput Screening

BACKGROUND

Bisphenol A analogs and derivatives (BPs) have emerged as new contaminants with little or no information about their toxicity. These have been found in numerous everyday products, from thermal paper receipts to plastic containers, and measured in human samples.

OBJECTIVES

The objectives of this research were to identify in silico new protein targets of BPs associated with seven noncommunicable diseases (NCDs), and to study their protein-ligand interactions using computer-aided tools.

METHODS

Fifty BPs were identified by a literature search and submitted to a virtual high-throughput screening (vHTS) with 328 proteins associated with NCDs. Protein-protein interactions between predicted targets were examined using STRING, and the protocol was validated in terms of binding site recognition and correlation between in silico affinities and in vitro data.

RESULTS

According to the vHTS, several BPs may target proteins associated with NCDs, some of them with stronger affinities than bisphenol A (BPA). The best affinity score (the highest in silico affinity absolute value) was obtained after docking 4,4'-bis(N-carbamoyl-4-methylbenzensulfonamide)diphenylmethane (BTUM) on estradiol 17-beta-dehydrogenase 1 (-13.7 kcal/mol). However, other molecules, such as bisphenol A bis(diphenyl phosphate) (BDP), bisphenol PH (BPPH), and Pergafast 201 also exhibited great affinities (top 10 affinity scores for each disease) with proteins related to NCDs.

DISCUSSION

Molecules such as BTUM, BDP, BPPH, and Pergafast 201 could be targeting key signaling pathways related to NCDs. These BPs should be prioritized for in vitro and in vivo toxicity testing and to further assess their possible role in the development of these diseases. https://doi.org/10.1289/EHP7466.

Formation and enhanced photodegradation of chlorinated derivatives of bisphenol A in wastewater treatment plant effluent

There are many reports on the detection and removal of emerging pollutants in the wastewater effluents, while the fate of their chlorinated derivatives generated during chlorination is not well understood. Here we investigated the photodegradation of chlorinated derivatives of bisphenol A (CDBPAs), mainly including 3-chlorobisphenol A, 3,3'-dichlorobisphenol A, 3,5-dichlorobisphenol A, 3,3',5-trichlorobisphenol A, and 3,3',5,5'-tetrachlorobisphenol A, under simulated sunlight. Distinct from BPA, CDBPAs underwent rapid direct photodegradation due to a pronounced bathochromic shift of UV absorption. The photodegradation of CDBPAs was significantly enhanced by effluent organic matter (EfOM) from the wastewater effluent. A series of quenching experiments and laser flash photolysis analysis verified the contribution of triplet states of EfOM (³EfOM∗) for the indirect photodegradation of CDBPAs with rate constant of ∼10⁹ M^-1 s^-1. Both direct and EfOM-induced indirect photodegradation of CDBPAs increased with a higher degree of chlorination. Furthermore, high-resolution mass spectrometry showed similar photoproducts for direct and indirect photodegradation of CDBPAs, mainly ascribed to the cleavage of C-Cl bond and hydroxylation with further cleavage of the benzene ring. The estrogenic activity of the photoproducts was diminished. These findings suggest that photodegradation is an important pathway for the removal and detoxication of CDBPAs from effluents and receiving natural waters under sunlight.

Application of Various Molecular Modelling Methods in the Study of Estrogens and Xenoestrogens

In this review, applications of various molecular modelling methods in the study of estrogens and xenoestrogens are summarized. Selected biomolecules that are the most commonly chosen as molecular modelling objects in this field are presented. In most of the reviewed works, ligand docking using solely force field methods was performed, employing various molecular targets involved in metabolism and action of estrogens. Other molecular modelling methods such as molecular dynamics and combined quantum mechanics with molecular mechanics have also been successfully used to predict the properties of estrogens and xenoestrogens. Among published works, a great number also focused on the application of different types of quantitative structure-activity relationship (QSAR) analyses to examine estrogen's structures and activities. Although the interactions between estrogens and xenoestrogens with various proteins are the most commonly studied, other aspects such as penetration of estrogens through lipid bilayers or their ability to adsorb on different materials are also explored using theoretical calculations. Apart from molecular mechanics and statistical methods, quantum mechanics calculations are also employed in the studies of estrogens and xenoestrogens. Their applications include computation of spectroscopic properties, both vibrational and Nuclear Magnetic Resonance (NMR), and also in quantum molecular dynamics simulations and crystal structure prediction. The main aim of this review is to present the great potential and versatility of various molecular modelling methods in the studies on estrogens and xenoestrogens.

Molecular Image-Based Prediction Models of Nuclear Receptor Agonists and Antagonists Using the DeepSnap-Deep Learning Approach with the Tox21 10K Library

The interaction of nuclear receptors (NRs) with chemical compounds can cause dysregulation of endocrine signaling pathways, leading to adverse health outcomes due to the disruption of natural hormones. Thus, identifying possible ligands of NRs is a crucial task for understanding the adverse outcome pathway (AOP) for human toxicity as well as the development of novel drugs. However, the experimental assessment of novel ligands remains expensive and time-consuming. Therefore, an in silico approach with a wide range of applications instead of experimental examination is highly desirable. The recently developed novel molecular image-based deep learning (DL) method, DeepSnap-DL, can produce multiple snapshots from three-dimensional (3D) chemical structures and has achieved high performance in the prediction of chemicals for toxicological evaluation. In this study, we used DeepSnap-DL to construct prediction models of 35 agonist and antagonist allosteric modulators of NRs for chemicals derived from the Tox21 10K library. We demonstrate the high performance of DeepSnap-DL in constructing prediction models. These findings may aid in interpreting the key molecular events of toxicity and support the development of new fields of machine learning to identify environmental chemicals with the potential to interact with NR signaling pathways.

Protecting Group-Controlled Remote Regioselective Electrophilic Aromatic Halogenation Reactions

Being able to utilize a protecting group to influence remote regiocontrol offers a simple alternative approach to direct late-stage functionalization of complex organic molecules. However, protecting groups that have the ability to influence reaction regioselectivity remote to their local chemical environment are not widely reported in the literature. Herein, we report the development of remote regioselective electrophilic aromatic substitution (S_EAr) reactions that are enabled via the application of the tetrafluoropyridyl (TFP) phenol-protecting group. We demonstrate that through sequential reactions and protection/deprotection of the TFP group, substitution patterns that do not conform to classical S_EAr regioselectivity rules can be readily accessed.

Molecular interactions of vinclozolin metabolites with human estrogen receptors 1GWR-α and 1QKM and androgen receptor 2AM9-β: Implication for endocrine disruption

Background: Vinclozolin (VCZ) is a widely used antifungal agent with capability to enter into the human food chain. VCZ metabolizes into seven metabolites M1-M7. Several studies have shown its effects on reprotoxicity. However, there is limited information available on the interaction of VCZ metabolites with nuclear receptors. In silico studies aimed at identifying interaction of endocrine disruptor with nuclear receptors serve a prescreening framework in risk assessment.Methods: We studied interactive potential of VCZ and its metabolites with human estrogen (ER) and androgen receptor (AR) using molecular docking method. Binding potential of VCZ and its metabolites with estrogen receptors 1GWR-α, 1QKM and androgen receptor 2AM9-β was checked by using Schrodinger Maestro 10.5. Estradiol (E2), a natural ligand of ER and AR was taken as a reference.Results: VCZ and its metabolites showed higher or similar binding efficiency on interaction with target proteins when compared with E2. VCZ and its metabolites also exhibited agonistic effect against 1GWR-α, 1QKM and 2AM9-β with strong binding potential to them.Conclusion: Some VCZ metabolites such as M4 and M5 showed higher binding potencies with 1GWR-α, 1QKM and 2AM9-β than E2. Toxicity data of VCZ is well endowed. However, endocrine disrupting potential of VCZ via nuclear receptor mediated pathway is less understood. This in silico study revealing that not only VCZ but its metabolites have potential to interact with 1GWR-α, 1QKM and 2AM9-β offers a platform for further exploration of VCZ in this direction.

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.

Effects of Bisphenol A on Foxl2 gene expression and DNA damage in adult viviparous fish Goodeaatripinnis

Bisphenol A (BPA) is an emerging pollutant of global concern. Viviparous fish Goodea atripinnis is endemic to the Central Mexican Plateau where BPA was detected; however, few studies examined the influence of this chemical on native viviparous fish. The effects of BPA (sublethal dose) were determined on DNA integrity and Foxl2 expression in G. atripinnis gonads, and interactions of BPA with FOXL2 protein. Genotoxicity analysis revealed that % comets, at 14 and 28 days and comet tail length (at 14 days) were significantly higher in exposed compared to controls. In general, the % DNA tail was not markedly higher in BPA-treated fish; however, tail moment related to tail length exhibited significant increases in DNA damage. RT-qPCR assays showed Foxl2 overexpression after 14 and 28 days of exposure in females; while in males, Foxl2 was overexpressed after 28 days. In silico analysis demonstrated that BPA interacted with seven residues located in FOXL2 homeodomain. In summary, sublethal BPA doses induced DNA damage and changes in Foxl2 expression in gonadal cells of G. atripinnis, which may adversely affect reproduction in BPA-exposed wild populations. Foxl2 overexpression and BPA-FOXL2 interaction suggested alterations in processes involving Foxl2. Viviparous fish may thus serve as potential non-conventional models for assessing pollutants effects.

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.

Saponins as modulators of nuclear receptors

As plant-derived natural products, saponins have been widely applied for the dietary modification of metabolic syndrome. However, the underlying mechanisms of their preventive and therapeutic effects are still largely unclear. Nuclear receptors have been identified as potential pharmaceutical targets for treating various types of metabolic disorders. With similar structure to endogenous hormones, several saponins may serve as selective ligands for nuclear receptors. Recently, a series of saponins are proved to exert their physiological activities through binding to nuclear receptors. This review summarizes the biological and pharmacological activities of typical saponins mediated by some of the most well described nuclear receptors, including the classical steroid hormone receptors (ER, GR, MR, and AR) and the adopted orphan receptors (PPAR, LXR, FXR, and PXR).

In vitro and in silico perspectives on estrogenicity of tanshinones from Salvia miltiorrhiza

This work aims to investigate the structure-activity relationship for binding and activation of human estrogen receptor α ligand binding domain (hERα-LBD) with tanshinones by a combination of in vitro and in silico approaches. The recombinant hERα-LBD was expressed in E. coli strain. The direct binding interactions of tanshinones with hERα-LBD and their ERα agonistic potency were investigated by fluorescence polarization (FP) and reporter gene assays, respectively. FP assay suggested that the tested tanshinones can bind to hERα-LBD as affinity ligands. Tanshinones acted as agonists of hERα as demonstrated by transactivation of estrogen response element (ERE) in transiently transfected MCF-7 cells and by molecular docking of these compounds into the hydrophobic binding pocket of hERα-LBD. Interestingly, comparison of the calculated binding energies versus Connolly solvent-excluded volume and experimental binding affinities showed a good correlation. This work may provide insight into chemical and pharmacological characterization of novel bioactive compounds from Salvia miltiorrhiza.