Interaction of bisphenol A with rat hepatic cytochrome P450 enzymes

Low-dose bisphenols exposure sex-specifically induces neurodevelopmental toxicity in juvenile rats and the antagonism of EGCG

Bisphenols (BPs) can negatively affect neurobehaviors in rats, whereas the mechanism remains unclear. Here, the mechanism of BPs-induced neurodevelopmental toxicity and its effective detoxification measures were investigated in vitro and in vivo. In in vitro experiments, primary hippocampal neurons from neonatal rats of different genders were treated with bisphenol A (BPA), bisphenol S (BPS) and bisphenol B (BPB) at 1 nM-100 μM, epigallocatechin gallate (EGCG) and G15, an antagonist of G protein-coupled estrogen receptor (GPER) for 7 d. Results indicated that BPs affected neuronal morphogenesis, impaired GABA synthesis and Glu/GABA homeostasis. Neuronal morphogenetic damage induced by low-doses BPA may be mediated by GPER. Neurotoxicity of BPS is weaker than BPA and BPB. In in vivo studies, exposure to BPA (0.5 μg/kg·bw/day) on PND 10-40 caused oxidative stress and inflammation in rat hippocampus, disrupted neuronal morphogenesis and neurotransmitter homeostasis, ultimately impaired spatial memory of rats. Males are more sensitive to BPA exposure than females. Both in vivo and in vitro studies indicated that EGCG, a phytoestrogen, can alleviate BPA-induced neurotoxicity. Taken together, low-doses BPA exposure sex-specifically disrupted neurodevelopment and further impaired learning and memory ability in rats, which may be mediated by GPER. Promisingly, EGCG effectively mitigated the BPA-induced neurodevelopmental toxicity.

Systematic multi-omics reveals the overactivation of T cell receptor signaling in immune system following bisphenol A exposure

Bisphenol A (BPA) is pervasive in the environment, and exposure to BPA may increase the incidence of noncommunicable diseases like autoimmune diseases and cancer. Although BPA causes immunological problems at the cellular level, no system-level research has been conducted on this. Hence, in this study, we aimed to gain a better understanding of the biological response to BPA exposure and its association with immunological disorders. For that, we explored the transcriptome and the proteomic modifications at the systems and cellular levels following BPA exposure. Our integrated multi-omics data showed the alteration of the T cell receptor (TCR) signaling pathway at both levels. The proportion of enlarged T cells increased with upregulation of CD69, a surface marker of early T cell activation, even though the number of T cells reduced after BPA exposure. Additionally, on BPA exposure, the levels of pLCK and pSRC increased in T cells, while that of pLAT decreased. Following BPA exposure, we investigated cytokine profiles and discovered that chitinase 3 Like 1 and matrix metalloproteinase 9 were enriched in T cells. These results indicated that T cells were hyperactivated by CD69 stimulation, and phosphorylation of SRC accelerated on BPA exposure. Hence, alteration in the TCR signaling pathway during development and differentiation due to BPA exposure could lead to insufficient and hasty activation of TCR signaling in T cells, which could modify cytokine profiles, leading to increased environmental susceptibility to chronic inflammation or diseases, increasing the chance of autoimmune diseases and cancer. This study enhances our understanding of the effects of environmental perturbations on immunosuppression at molecular, cellular, and systematic levels following pubertal BPA exposure, and may help develop better predictive, preventative, and therapeutic techniques.

Sex-specific oxidative damage effects induced by BPA and its analogs on primary hippocampal neurons attenuated by EGCG

BPA analogs, including bisphenol S (BPS) and bisphenol B (BPB), have been used to replace BPA since it was banned to be added. To investigate whether BPA and its analogs cause oxidative damage effects on primary hippocampal neurons of rats, reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), mitochondrial membrane potential (MMP), apoptosis and cell viability assays were conducted after hippocampal neurons exposure to different concentrations of BPA, BPS, and BPB (1, 10, 100 nM and 1, 10, 100 μM). Moreover, the effects of EGCG (5 and 6 μM for male and female, respectively) added on neurons exposed to BPA were assessed. Results showed that 24 h exposure to these bisphenols (BPs) could increase the levels of ROS and contents of MDA, but reduce the activity of SOD significantly. A decline of cell viabilities accompanied with the increasing of apoptosis rates was observed after 7 d exposure to BPs and the reduction of MMP was also observed after 7 d exposure to BPA. Interestingly, BPS has the lower toxicity to hippocampal neurons compared with BPA and BPB. Non-monotonic dose-effect relationships between the concentrations of BPs and the cytotoxic effects were observed, and the effects of BPs on male hippocampal neurons are greater than those of female ones in general. While EGCG can protect neurons free of oxidative damages. In conclusion, the results suggest that BPs may induce sex-specific neurotoxic effects involving oxidative stress, which can be attenuated by EGCG, and males are more sensitive to BPs than females.

The effects of different bisphenol derivatives on oxidative stress, DNA damage and DNA repair in RWPE-1 cells: A comparative study

Bisphenol A (BPA) is a well-known endocrine disruptor and it is widely used mainly in the plastics industry. Due to recent reports on its possible impact on health (particularly on the male reproductive system), bisphenol F (BPF) and bisphenol S (BPS) are now being used as alternatives. In this study, RWPE-1 cells were used as a model to compare cytotoxicity, oxidative stress-causing potential and genotoxicity of these chemicals. In addition, the effects of the bisphenol derivatives were assessed on DNA repair proteins. RWPE-1 cells were incubated with BPA, BPF, and BPS at concentrations of 0-600 μM for 24 h. The inhibitory concentration 20 (IC₂₀ , concentration that causes 20% of cell viability loss) values for BPA, BPF, and BPS were 45, 65, and 108 μM, respectively. These results indicated that cytotoxicity potentials were ranked as BPA > BPF > BPS. We also found alterations in superoxide dismutase, glutathione peroxidase and glutathione reductase activities, and glutathione and total antioxidant capacity in all bisphenol-exposed groups. In the standard and modified Comet assay, BPS produced significantly higher levels of DNA damage vs the control. DNA repair proteins (OGG1, Ape-1, and MyH) involved in the base excision repair pathway, as well as p53 protein levels were down-regulated in all of the bisphenol-exposed groups. We found that the BPA alternatives were also cytotoxic and genotoxic, and changed the expressions of DNA repair enzymes. Therefore, further studies are needed to assess whether they can be used safely as alternatives to BPA or not.

Bisphenols (A, S, and F) affect the basic hormonal activity determined for pharmaceuticals - Study of Saccharomyces cerevisiae

Pharmaceuticals and analogs of bisphenol A (BPA) are increasingly threatening environmental pollutants. In this study, mixtures of selected pharmaceuticals (diclofenac sodium salt, chloramphenicol, oxytetracycline hydrochloride, fluoxetine hydrochloride, estrone, ketoprofen, progesterone, gemfibrozil and androstenedione) were prepared with BPA and its two analogs (namely, bisphenols F and S) at such ratios to reflect environmentally detectable levels. Then, the mixture solutions were studied with a XenoScreen YES/YAS assay to determine the variations in the initial hormonal response of each pharmaceutical compound due to the presence of a bisphenol analog. The results obtained were modeled with the concentration addition (CA) and independent action (IA) approaches, the trueness of which was studied with model deviation ratios (MDR). The estrogenic agonistic activity of the drugs studied was most strongly affected by the presence of BPA in solution (twenty-one cases of synergy observed for CA models versus twelve cases of antagonism in the case of IA predictions). BPS shows a strong agonistic estrogenic impact on most of the drugs studied at medium and high concentration levels; androgenic agonistic activity was also impaired with elevated concentrations of BPS. Increasing the concentration of BPF in a reaction mixture also increased the number of YES + synergism incidences (for CA modeling). Estrone, progesterone and androstenedione were mostly affected by the highest BPF concentrations studied in the case of androgenic agonistic research performed.

Plasticizers and bisphenol A, in packaged foods sold in the Tunisian markets: study of their acute in vivo toxicity and their environmental fate

Today, processed and packaged foods are considered as among the major sources of human exposure to plasticizers and bisphenol which migrate from plastic packing. In the present study, a wide range of food products sold on the Tunisian market such as grain and grain products, milk and dairy products, fats and oil, drink, fish, and sweets have been analyzed firstly in order to identify the presence of phthalates and bisphenol. Then, the identified chemical molecules were studied for their environmental fate and tested in vivo for its toxicity in mice models. The food products analyzed using GC-MS/MS indicated the presence of the benzyl butyl phthalate (BBP), dibutyl phthalate (DBP), bis(2-ethylhexyl) phthalate (DEHP), diisodecyl phthalate (DiDP), diisononyl phthalate (DiNP), and 1,2-cyclohexane dicarboxylic acid diisononyl ester (DINC) and which using UPLC-MS/MS demonstrated the presence of bisphenol A of all food products. However, compared to other phthalates, BBP was found at high concentrations in the puff pastry (123 mg/kg), milk (2.59 mg/kg), butter (1.5 mg/kg), yogurt (2.23 mg/kg), oil (6.94 mg/kg), water (0.57 mg/kg), candy 1 (2.35 mg/kg), candy 2 (0.81 mg/kg), orange juice (1.25 mg/kg), peach juice (1.26 mg/kg), fruit juices (0.4 mg/kg), and chocolate (0.884 mg/kg). The obtained data in vivo clearly showed that the acute administration of BBP caused hepatic and renal damage as demonstrated by an increase in biochemical parameters as well as the activities of plasma marker enzymes such as alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, lactate dehydrogenase, blood urea nitrogen, glucose, urea, creatinine, and uric acid when compared to the control group. By the same occurrence, the histopathological study revealed that BBP strongly modified the structure of hepatic and renal tissues. In addition, the plasticizers and BBP will therefore discharge via wastewater treatment plants in aquatic system and could reach marine organisms such as fish. We have followed the fate of BBP in bream Sparus aurata. In fact, chemical analysis showed the contamination of wild S. aurata by BBP from Sousse Coast (1.5 mg/kg) and wild S. aurata from Monastir Coast (0.33 mg/kg).

Bisphenol a induces steatosis in HepaRG cells using a model of perinatal exposure

Human exposure to bisphenol A (BPA) could favor obesity and related metabolic disorders such as hepatic steatosis. Investigations in rodents have shown that these deleterious effects are observed not only when BPA is administered during the adult life but also with different protocols of perinatal exposure. Whether perinatal BPA exposure could pose a risk in human is currently unknown, and thus appropriate in vitro models could be important to tackle this major issue. Accordingly, we determined whether long-term BPA treatment could induce steatosis in human HepaRG cells by using a protocol mimicking perinatal exposure. To this end, the kinetics of expression of seven proteins differentially expressed during liver development was determined during a 4-week period of cell culture required for proliferation and differentiation. By analogy with data reported in rodents and humans, our results indicated that the period of cell culture around day 15 and day 18 after seeding could be considered as the "natal" period. Consequently, HepaRG cells were treated for 3 weeks with BPA (from 0.2 to 2000 nM), with a treatment starting during the proliferating period. BPA was able to induce steatosis with a nonmonotonic dose response profile, with significant effects on neutral lipids and triglycerides observed for the 2 nM concentration. However, the expression of many enzymes involved in lipid and carbohydrate homeostasis was unchanged in exposed HepaRG cells. The expression of other potential BPA targets and enzymes involved in BPA biotransformation was also determined, giving answers as well as new questions regarding the mechanisms of action of BPA. Hence, HepaRG cells provide a valuable model that can prove useful for the toxicological assessment of endocrine disruptors on hepatic metabolisms, in particular in the developing liver. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1024-1036, 2017.

A use of homology modeling and molecular docking methods: to explore binding mechanisms of nonylphenol and bisphenol A with antioxidant enzymes

Bisphenol A (BPA) and nonylphenol (NP) are phenolic compounds used widely by the industries. BPA and NP are endocrine disruptors possessing estrogenic properties. Several studies have reported that BPA and NP induce oxidative stress in various organs or cell types in animals, by inhibiting the activities of antioxidant enzymes like catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase. However, it is not understood how BPA and NP interact with these enzymes and inhibit their functions. Hence, it would be significant to check, whether binding sites are available for NP and BPA in antioxidant enzymes. In the present study three-dimensional structures of antioxidant enzymes, catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase were modeled and docked with BPA and NP. Docking studies revealed that BPA and NP have binding pockets in the antioxidant enzymes. Among the antioxidant enzymes, Catalase was maximally inhibited by BPA and superoxide was maximally inhibited by NP.

Modulation of metabolizing enzymes by bisphenol a in human and animal models

Xenobiotics, such as contaminants and drugs, can be converted to potentially toxic reactive metabolites by phase 1 oxidizing enzymes. These metabolites are further detoxified by phase 2 conjugating enzymes and eliminated from cells by phase 3 transporters. Moreover, many of these xenobiotics are also able to induce or inhibit these enzymes, potentially modulating their own toxicity or that of other chemicals. The present review is focused on bisphenol A, a synthetic monomer used for many industrial applications and exhibiting xenoestrogen properties. The impact of this contaminant on all major classes of metabolizing enzymes (i.e., cytochromes P450, glutathione-S-transferases, sulfotransferases, UDP-glucuronyltransferases, and transporters) was reviewed, with a highlight on the modulation of cytochromes P450 involved in steroid metabolism. Interestingly, most of the studies reported in this review show that BPA is able to induce or inhibit metabolizing enzymes at high doses but also at doses compatible with human exposure.

Bisphenol A induces oxidative stress-associated DNA damage in INS-1 cells

Bisphenol A (BPA), an endocrine disruptor, is widely used to manufacture polycarbonate plastic and epoxy resins. Many studies have demonstrated that BPA can play a role in reproductive toxicity and affect the normal metabolic function. Recent research has shown that BPA can influence the function of pancreatic islets. In this study, our aim is to assess the DNA damage induced by BPA and to clarify the mechanism, by use of rat insulinoma INS-1 cells. INS-1 cells were exposed to different doses of BPA (0, 25, 50, 100 μM). We conducted the single-cell gel electrophoresis (SCGE) assay to measure DNA damage, and studied proteins such as p53 and p-Chk2 (T68) by Western blotting, in order to verify the (geno)toxicity of BPA. Moreover, we examined intracellular reactive oxygen species (ROS) and glutathione (GSH) to discuss the possible mechanism of DNA damage. The results show that BPA caused an increased in DNA strand-breaks along with greater DNA migration from the nucleus into the comet tail. The expression of DNA damage-associated proteins (p53 and p-Chk2 (T68)) was significantly increased. The exposure to various doses of BPA caused a significant increase in intracellular ROS and a significant reduction in the level of GSH. N-Acetyl cysteine, an inhibitor of intracellular ROS formation, can significantly reduce the generation of intracellular reactive oxygen.

Bisphenol A-associated alterations in the expression and epigenetic regulation of genes encoding xenobiotic metabolizing enzymes in human fetal liver

Alterations in xenobiotic metabolizing enzyme (XME) expression across the life course, along with genetic, nutritional, and environmental regulation, can influence how organisms respond to toxic insults. In this study, we investigated the hypothesis that in utero exposure to the endocrine active compound, bisphenol A (BPA), influences expression and epigenetic regulation of phase I and II XME genes during development. Using healthy 1st to 2nd trimester human fetal liver specimens quantified for internal BPA levels, we examined XME gene expression using PCR Array (n = 8) and RNA-sequencing (n = 12) platforms. Of the greater than 160 XME genes assayed, 2 phase I and 12 phase II genes exhibited significantly reduced expression with higher BPA levels, including isoforms from the carboxylesterase, catechol O-methyltransferase, glutathione S-transferase, sulfotransferase, and UDP-glucuronosyltransferase families. When the promoters of these candidate genes were evaluated in silico, putative binding sites for the E-twenty-six (ETS) and activator protein1 (AP1) related transcription factor families were identified and unique to 97% of all candidate transcripts. Interestingly, many ETS binding sites contain cytosine-guanine dinucleotides (CpGs) within their consensus sequences. Thus, quantitative analysis of CpG methylation of three candidate genes was conducted across n = 50 samples. Higher BPA levels were associated with increased site-specific methylation at COMT (P < 0.005) and increased average methylation at SULT2A1 (P < 0.020) promoters. While toxicological studies have traditionally focused on high-dose effects and hormonal receptor mediated regulation, our findings suggest the importance of low-dose effects and nonclassical mechanisms of endocrine disruption during development.

Characterization and expression of cytochrome p450 cDNA (CYP9AT2) in Chironomus riparius fourth instar larvae exposed to multiple xenobiotics

We identified and characterized a CYP9 family gene, CrCYP9AT2, from Chironomus riparius, an eco-toxicologically important model organism. The 1978 base pair (bp) length CrCYP9AT2 cDNA has an open reading frame of 1587 bp encoding a putative 528 amino acid protein. There was 267 bp 5' and 123 bp 3' untranslated region with a polyadenylation signal site (AATAAA). The putative heme-binding cysteine at position 471 and the typical p450 signature sequence of 463-FGIGPRNCIG-473 were also present. The CrCYP9AT2 transcript was present in all life stages with the highest expression in larvae. The modulation of CrCYP9AT2 was studied using real-time polymerase chain reaction after 24h exposure to cadmium chloride, benzo(a)pyrene; bisphenol A; nonylphenol; chlorpyrifos and ethinylestradiol. Significant up-regulation of CrCYP9AT2 gene was observed after exposure to Cd, B(a)P and CP. However, CrCYP9AT2 was significantly down-regulated after exposure to BPA, NP and EE.

Prediction of human genes and diseases targeted by xenobiotics using predictive toxicogenomic-derived models (PTDMs)

New technologies for systems-level determinants of human exposure to drugs, industrial chemicals, pesticides, and other environmental agents provide an invaluable opportunity to extend the understanding of human health and potential environmental hazards. We report here the development of a new computational-systems toxicology framework, called predictive toxicogenomics-derived models (PTDMs). PTDMs integrate three networks of chemical-gene interactions (CGIs), chemical-disease associations (CDAs) and gene-disease associations (GDAs) to infer chemical hazard profiles, identify exposure data gaps and to incorporate genes and disease networks into chemical safety evaluations. Three comprehensive networks addressing CGI, CDA and GDA extracted from the comparative toxicogenomics database (CTD) were constructed. The areas under the receiver operating characteristics curve ranged from 0.85 to 0.97 and were yielded using our methodology using a 10-fold cross validation by a simulation carried out 100 times. As the illustrated examples show, we predicted new potential target genes and diseases for bisphenol A and aspirin. The molecular hypothesis and experimental evidence from published literature for these predictions were provided. The results demonstrated that our method has potential applications for chemical profiling in human health exposure and environmental hazard assessment.

Comparative analysis of human CYP3A4 and rat CYP3A1 induction and relevant gene expression by bisphenol A and diethylstilbestrol: implications for toxicity testing paradigms

Bisphenol A (BPA) and diethylstilbestrol (DES) are endocrine-disrupting chemicals that interact with the human pregnane X receptor (PXR). CYP3A4 enzyme is essential in the hydroxylation of steroid hormones and is regulated by PXR. In the present study, human and rat hepatoma cell lines were exposed to BPA and DES. Both BPA and DES (10-50μM) caused a significant activation of the CYP3A4 promoter via the PXR in the DPX2 human hepatoma cell line. No activation of rat PXR was seen. BPA and DES treated DPX2 cells demonstrated increased expression of CYP3A4 mRNA, and increased enzyme activity. In summary, BPA, in concentrations relevant to current safety levels of human exposure, activates the human PXR and demonstrates an increase in CYP3A4 mRNA expression and enzyme activity. BPA actions in this model system occur to a greater extent than DES. This study raises concerns regarding our current toxicity testing paradigms and species utilization.

Characterization of a cytochrome P450 gene (CYP4G) and modulation under different exposures to xenobiotics (tributyltin, nonylphenol, bisphenol A) in Chironomus riparius aquatic larvae

Cytochrome P450 family members participate in xenobiotic transformation as a detoxification mechanism. We have characterized a CYP gene, assigned to the 4G family, in Chironomus riparius, a reference organism in aquatic toxicology. Due to the potential interest of CYP genes and P450 proteins for monitoring pollution effects at the molecular level, the alterations in the pattern of expression of this gene, induced by different xenobiotics, were analyzed. Different compounds, such as the biocide tributyltin (TBTO) and two other well-known endocrine disruptors, nonylphenol (NP) and bisphenol A (BPA), were tested at different concentrations and acute exposures. Upregulation of the CrCYP4G gene was found after exposures to TBTO (1 ng/L 24h-0.1 ng/L 96 h) and, as measured by RT-PCR mRNA quantification, its level was up to twofold that of controls. However, in contrast, NP (1, 10, 100 μg/L, 24h) and BPA (0.5mg/L 24h-3mg/L 96 h) downregulated the gene (by around a half of the control level) suggesting that this gene responds specifically to particular chemicals in the environment. Glutathione-S-transferase (GST) enzymatic activity was also evaluated for each condition. A fairly good correlation was found with CYP4G gene behavior, as it was activated by TBTO (96 h), but inhibited by NP and BPA (24h). Only the higher concentration of BPA tested activated GST, whereas it inhibited CYP4G activity. The results show that different xenobiotics can induce distinct responses in the detoxification pathway, suggesting multiple xenobiotic transduction mechanisms. This work confirms that specific P450 codifying genes, as well as GST enzyme activities, could be suitable biomarkers for ecotoxicological studies.

Interaction of bisphenol A with human UDP-glucuronosyltransferase 1A6 enzyme

The effects of bisphenol A (BPA) on UDP-glucuronosyltransferase 1A6 (UGT1A6) activities in microsomes from human livers and yeast cells expressing human UGT1A6 (humUGT1A6) were investigated. Serotonin (5-HT) and 4-methylumbelliferone (4-MU) were used as the substrates for UGT1A6. BPA dose-dependently inhibited 5-HT and 4-MU glucuronidation activities in both enzyme sources. The IC(50) values of BPA for 5-HT and 4-MU glucuronidation activities were 156 and 163 microM for liver microsomes, and 84.6 and 80.3 microM for yeast cell microsomes expressing humUGT1A6, respectively. The inhibitory pattern of BPA for 5-HT and 4-MU glucuronidation activities in human liver microsomes exhibited a mixture of competitive and noncompetitive components, with K(i) values of 84.9 and 72.3 microM, respectively. In yeast cell microsomes expressing humUGT1A6, 5-HT glucuronidation activities were noncompetitively inhibited by BPA (K(i) value, 65.5 microM), whereas the inhibition of 4-MU glucuronidation activities by BPA exhibited the mixed type (K(i) value, 42.5 microM). These results suggest that BPA interacts with human UGT1A6 enzyme, and that the interaction may contribute to the toxicity, such as hormone disruption and reproductive effects, of BPA.

In vivo effects of bisphenol A in laboratory rodent studies

Concern is mounting regarding the human health and environmental effects of bisphenol A (BPA), a high-production-volume chemical used in synthesis of plastics. We have reviewed the growing literature on effects of low doses of BPA, below 50 mg/(kg day), in laboratory exposures with mammalian model organisms. Many, but not all, effects of BPA are similar to effects seen in response to the model estrogens diethylstilbestrol and ethinylestradiol. For most effects, the potency of BPA is approximately 10-1000-fold less than that of diethylstilbestrol or ethinylestradiol. Based on our review of the literature, a consensus was reached regarding our level of confidence that particular outcomes occur in response to low dose BPA exposure. We are confident that adult exposure to BPA affects the male reproductive tract, and that long lasting, organizational effects in response to developmental exposure to BPA occur in the brain, the male reproductive system, and metabolic processes. We consider it likely, but requiring further confirmation, that adult exposure to BPA affects the brain, the female reproductive system, and the immune system, and that developmental effects occur in the female reproductive system.

In vitro molecular mechanisms of bisphenol A action

Bisphenol A (BPA, 2,2-bis (4-hydroxyphenyl) propane; CAS# 80-05-7) is a chemical used primarily in the manufacture of polycarbonate plastic, epoxy resins and as a non-polymer additive to other plastics. Recent evidence has demonstrated that human and wildlife populations are exposed to levels of BPA which cause adverse reproductive and developmental effects in a number of different wildlife species and laboratory animal models. However, there are major uncertainties surrounding the spectrum of BPA's mechanisms of action, the tissue-specific impacts of exposures, and the critical windows of susceptibility during which target tissues are sensitive to BPA exposures. As a foundation to address some of those uncertainties, this review was prepared by the "In vitro" expert sub-panel assembled during the "Bisphenol A: An Examination of the Relevance of Ecological, In vitro and Laboratory Animal Studies for Assessing Risks to Human Health" workshop held in Chapel Hill, NC, Nov 28-29, 2006. The specific charge of this expert panel was to review and assess the strength of the published literature pertaining to the mechanisms of BPA action. The resulting document is a detailed review of published studies that have focused on the mechanistic basis of BPA action in diverse experimental models and an assessment of the strength of the evidence regarding the published BPA research.

Large effects from small exposures. III. Endocrine mechanisms mediating effects of bisphenol A at levels of human exposure

Over 6 billion pounds per year of the estrogenic monomer bisphenol A (BPA) are used to manufacture polycarbonate plastic products, in resins lining metal cans, in dental sealants, and in blends with other types of plastic products. The ester bond linking BPA molecules in polycarbonate and resins undergoes hydrolysis, resulting in the release of free BPA into food, beverages, and the environment, and numerous monitoring studies now show almost ubiquitous human exposure to biologically active levels of this chemical. BPA exerts estrogenic effects through the classical nuclear estrogen receptors, and BPA acts as a selective estrogen receptor modulator. However, BPA also initiates rapid responses via estrogen receptors presumably associated with the plasma membrane. Similar to estradiol, BPA causes changes in some cell functions at concentrations between 1 pM and 1 nM, and the mean and median range of unconjugated BPA measured by multiple techniques in human pregnant maternal, fetal, and adult blood and other tissues exceeds these levels. In contrast to these published findings, BPA manufacturers persist in describing BPA as a weak estrogen and insist there is little concern with human exposure levels. Our concern with human exposure to BPA derives from 1) identification of molecular mechanisms mediating effects in human and animal tissues at very low doses, 2) in vivo effects in experimental animals caused by low doses within the range of human exposure, and 3) widespread human exposure to levels of BPA that cause adverse effects in animals.

Protein responses in blue mussels (Mytilus edulis) exposed to organic pollutants: a combined CYP-antibody/proteomic approach

Polyclonal antibodies were raised against highly conserved, trans-metazoan sequences of cytochrome P450 (CYP) families 2 and 4 and used to investigate responses in the common blue mussel (Mytilus edulis) exposed to various organic contaminants. The results were evaluated by means of cross-reacting proteins on Western blots of both one- and two-dimensional electrophoresis gels, and by scanning spectroscopy measurements of total CYP content. Furthermore, a proteomic approach was applied aimed at elucidating exposure-related protein changes in a more general term. Identities of isolated proteins were searched by means of peptide mass fingerprints obtained from MALDI-TOF MS analyses. The results demonstrated that both antibodies rendered several cross-reactive bands when probed on Western blots. The most obvious cross-reaction of the CYP2 antibody was with a strongly expressed protein of size approximately 57kDa, pI 4.5-4.6, whereas the CYP4 antibody cross-reacted with a protein of size approximately 55kDa, pI 5.6. However, expression of cross-reacting proteins did not change as a result of the exposures, and resulted only in small and insignificant fluctuations in total CYP content. As a contrast, silver-stained 2DE gels showed that several microsomal proteins were affected in individuals exposed to diallylphthalate as well as crude oil, with and without a spike of alkylphenols and PAHs. Mass spectrometry based analyses of excised, trypsin-digested spots did so far not decipher the identities of the proteins affected by the exposures, nor of those cross-reacting with CYP2 and CYP4 antibodies. This study has underlined the power of the proteomic approach in environmental toxicology, although protein identification was not successful. The missing identities of the proteins cross-reacting with the CYP2- and CYP4-antibodies does not enable a clear conclusion as to whether or not these peptides actually represent CYP iso-enzymes.

Bisphenol A and its methylated congeners inhibit growth and interfere with microtubules in human fibroblasts in vitro

Bisphenol A (BPA), a monomer of polycarbonate plastics and epoxy resins, has previously been reported to induce micronuclei containing whole chromosomes in Chinese hamster V79 cells. In the present study, the aneuploidogenic potential of BPA was investigated in cultured human AG01522C fibroblasts. In contrast to the known aneugens diethylstilbestrol (DES) and 17beta-estradiol, which caused mitotic arrest and the induction of kinetochore-positive micronuclei, BPA did not induce micronuclei and inhibited the proliferation of AG01522C cells in G2 phase and probably also in G1 phase. Fluorescence microscopy of the BPA-treated cells after immunofluorescent staining of microtubules revealed structural abnormalities of the cytoplasmic microtubule complex (CMTC): densely stained rings and loops of tubulin were observed, which increased in number with increasing BPA concentration and were more stable against low temperature than normal microtubules. The mechanisms of the growth inhibition and the interference with microtubules elicited by BPA in AG01522C cells are presently unknown. The formation of rings and loops in the CMTC of AG01522C cells was also observed with two congeners of BPA carrying one and two, respectively, additional methyl groups in ortho-position to the phenolic hydroxyl group at each aromatic ring. However, in contrast to BPA itself, these congeners of BPA behaved "DES-like" by inducing mitotic arrest and kinetochore-positive micronuclei in AG01522C cells.

Aromatase activity modulation by lindane and bisphenol-A in human placental JEG-3 and transfected kidney E293 cells

Aromatase is the cytochrome P-450 involved in converting androgens to estrogens. The cytochrome P-450 family plays a central role in the oxidative metabolism of compounds including environmental pollutants. Since lindane and bisphenol-A (BPA) are two well-characterized endocrine disruptors that have been detected in animals and humans, it was important to learn whether they could affect aromatase activity and consequently estrogen biosynthesis. The present study investigates the effects of BPA and lindane on cytotoxicity, aromatase activity and mRNA levels in human placental JEG-3 cells and transfected human embryonal kidney 293 cells. Both cell lines were exposed to increasing concentrations of lindane (25, 50 and 75 microM) and bisphenol-A (25, 50 and 100 microM) over different time periods (10 min-18 h). As a result, none of these concentrations showed cytotoxicity. After short pre-incubation times (10 min-6 h), aromatase activity was enhanced by both compounds. Longer time incubation (18 h), however, produced dose-related inhibition. Lindane and BPA had no significant effects on CYP19 mRNA levels. Therefore, lindane and BPA modulate aromatase activity suggesting an interaction with the cytochrome P-450 aromatase. This study highlights the endocrine-modulating properties of lindane and bisphenol-A.

Metabolism of the environmental estrogen bisphenol A by plant cell suspension cultures

The metabolism of the environmental estrogen bisphenol A (BPA) was studied in heterotrophic plant cell suspension cultures of soybean (Glycine max), wheat (Triticum aestivum), foxglove (Digitalis purpurea), and thorn apple (Datura stramonium), which were regarded as metabolic model systems for intact plants. Three main metabolic routes of BPA were observed in the tissues. Most of the radioactivity found in the cell extracts consisted of carbohydrate conjugates of BPA amounting to about 85% (foxglove), 80% (wheat), 7% (soybean) and 15% (thorn apple) of applied 14C. The second main route was formation of non-extractable residues. Portions detected were low in foxglove (3.9% of applied 14C), moderate in wheat (13.5%), high in thorn apple (27.4%) and soybean (49.4%). With thorn apple, BPA derived bound residues were preponderantly resistant towards acid treatment; only traces of BPA were released. The third route was the formation of a highly polar, presumably polymeric material detected in media of soybean and thorn apple (29.3% and 36.0% of applied 14C, respectively). The mechanism of its formation remained unknown. In thorn apple, this highly polar material was formed extremely rapidly, and was considerably stable. Only traces of BPA were liberated by hydrolytic treatment with cellulase or acid. During hydrolysis experiments with glycoside fractions, non-extractable residues and highly polar materials, low amounts of presumably primary metabolites of BPA (up to 6% of applied 14C) were detected besides the parent compound; their chemical structures remained unclear.

In vivo effects of bisphenol A on the polecat (mustela putorius)

Bisphenol A (BPA), an environmental estrogen derived from the plastic industry, was given orally via incorporation into the food of 30 male and female polecats at 3 different doses (10, 50, or 250 mg/kg body weight/day) for 2 wk with 10 animals acting as controls. Several hormone levels in the plasma were determined as well as the activities of the phase I and II biotransformation enzymes 7-ethoxyresorufin O-deethylase (EROD), cytosolic glutathione S-transferase (GST), and UDP-glucuronosyltransferase (UDPGT). BPA did not cause any macroscopic effects on body mass or the health of the animals. UDPGT and GST activities increased significantly in direct correlation with increasing BPA exposure in females and UDPGT increased in a dose-related manner in males. There was no change in the plasma T4 and testosterone concentrations of the males with increasing BPA exposure. Discriminant analysis indicated that the group receiving 10 mg BPA/kg body weight/d was not different from the control group but the groups receiving 50 and 250 mg/kg body weight/d were different from the control group. This suggests physiological changes in the groups receiving 50 or 250 mg BPA/kg body weight/d.

Maternal-fetal disposition of bisphenol a in pregnant Sprague-Dawley rats

This study describes the maternal-fetal disposition of bisphenol A and its distribution into the placenta and amniotic fluid after iv injection (2 mg/kg) to pregnant Sprague-Dawley rats. Bisphenol A was distributed extensively to the placenta and fetus, with their respective AUC values 4.4- and 2.2-fold greater than AUC for the maternal serum. In contrast, the distribution of bisphenol A into the amniotic fluid was low, with the mean amniotic fluid-to-maternal serum AUC ratio of 0.2. The decay curves of bisphenol A in the placenta, fetus, and amniotic fluid paralleled that of the maternal serum during the terminal elimination phase. A five-compartment open model consisting of the maternal central, maternal peripheral, placental, fetal, and amniotic fluid compartments was used to describe the disposition of bisphenol A in pregnant rats, with the elimination occurring from the maternal central and fetal compartments. Based on this model, bisphenol A delivered to the placenta was transferred primarily to the fetus [kpf/(kpf + kpc + kpa) = 65.4 %], with the remaining fraction transported to the maternal central (33.2%) and amniotic fluid (1.4%) compartments. Bisphenol A was eliminated from the amniotic fluid by the fetal (63.9%) and placental (36.1%) routes. On the other hand, bisphenol A was eliminated from the fetus primarily by the placental route back to mother [kfp/(kfp + kfa + kfo) = 100%], with the amniotic route playing an insignificant role in fetal elimination. The percent contribution of the fetal elimination to the total elimination in the maternal-fetal unit was 0.0% [CLfoAUCfetus/(CLcoAUCmaternal serum + CLfoAUCfetus)]. The pharmacokinetic model used in this study provides insights into the routes of elimination of bisphenol A in the maternal-fetal rat upon maternal administration.

Metabolism and interaction of bisphenol A in human hepatic cytochrome P450 and steroidogenic CYP17

The metabolism of bisphenol A (BPA) was determined for 11 forms of human hepatic cytochromes P450 (CYPs) expressed in the yeast Saccharomyces cerevisiae and for human steroidogenic CYP17 expressed in Escherichia coli. Additionally, the effect of BPA on the progesterone 17alpha-chydroxylase activity of CYP17 was investigated. CYP2C18 catalyzed BPA metabolism most efficiently, followed by CYP2C19 and CYP2C9. CYP2C9 and CYP2C18 exhibited the highest affinity (Km=3.9 microM) for BPA metabolism. The Vmax of CYP2C18 (8.10 nmol x min(-1) x nmol CYP(-1)) was 5 times higher than that of CYP2C9. Although the Vmax of CYP2C19 was 1.5 times higher than that of CYP2C18, the affinity of CYP2C19 was 12 times lower than that of CYP2C9 and CYP2C18. Therefore the intrinsic clearance (Vmax/Km) of CYP2C18 was more than 5 times higher than that of CYP2C9 and CYP2C19. On the other hand, BPA exhibited a competitive-type inhibition of the progesterone 17alpha-hydroxylase activity of CYP17 with a Ki value of 71 microM, whereas no metabolism of BPA by CYP17 was detected. These results suggest that BPA is mainly metabolized by the CYP2C subfamily in human liver, and that BPA inhibits human steroidogenic CYP17 activities.

Down-regulation of murine Cyp1a-1 in mouse hepatoma Hepa-1c1c7 cells by bisphenol A

Cultured mouse hepatoma Hepa-1c1c7 cells were treated with either bisphenol A or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or in combination to assess the role of bisphenol A in the process of Cyp1a-1 induction. Treatment of Hepa-1c1c7 cultures with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) induced Cyp1a-1, as determined by analysis of 7-ethoxyresorufin O-deethylase (EROD) activities. Bisphenol A alone did not affect the activity of Cyp1a-1-specific EROD; in contrast, TCDD-induced EROD activities were markedly reduced in the concomitant treatment of TCDD and bisphenol A in a dose-dependent manner. Treatment with tamoxifen, an antiestrogen that acts through the estrogen receptor, did not affect the suppressive effects of bisphenol A on TCDD-induced EROD activity. TCDD-induced Cyp1a-1 mRNA levels were markedly suppressed in the concomitant treatment of TCDD and bisphenol A consistent with their effects on EROD activity. Transient transfection assay using dioxin-response element (DRE)-linked luciferase revealed that bisphenol A reduced transformation of the aryl hydrocarbons (Ah) receptor to a form capable of specifically binding to the DRE sequence in the promoter of the Cyp1a-1 gene. These results suggest the down-regulation of the Cyp1a-1 gene expression by bisphenol A in Hepa-1c1c7 cells might be antagonism of the DRE binding potential of nuclear Ah receptor but not mediated through estradiol receptor.