An Updated Weight of the Evidence Evaluation of Reproductive and Developmental Effects of Low Doses of Bisphenol A

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

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experts to call for the lowest observed adverse effect level (LOAEL) to be dropped 20 000-fold from the current outdated LOAEL of 50 000 µg/kg/day.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

In vitro glucuronidation of bisphenol A in liver and intestinal microsomes: interspecies differences in humans and laboratory animals

Bisphenol A (BPA) is an endocrine-disrupting chemical, and is predominantly metabolized into glucuronide in mammals. The present study was conducted in order to examine the hepatic and intestinal glucuronidation of BPA in humans and laboratory animals such as monkeys, dogs, rats, and mice in an in vitro system using microsomal fractions. K_m, V_max, and CL_int values in human liver microsomes were 7.54 µM, 17.7 nmol/min/mg protein, and 2.36 mL/min/mg protein, respectively. CL_int values in liver microsomes of monkey, dogs, rats, and mice were 1.5-, 2.4-, 1.7- and 8.2-fold that of humans, respectively. In intestinal microsomes, K_m, V_max, and CL_int values in humans were 39.3 µM, 0.65 nmol/min/mg protein, and 0.02 mL/min/mg protein, respectively. The relative levels of CL_int in monkey, dogs, rats, and mice to that of humans were 7.0-, 12-, 34-, and 29-fold, respectively. Although CL_int values were higher in liver microsomes than in intestinal microsomes in all species, and marked species difference in the ratio of liver to intestinal microsomes was observed as follows: humans, 118; monkeys, 25; dogs, 23; rats, 5.9; mice, 33. These results suggest that the functional roles of UDP-glucuronosyltransferase (UGT) enzymes expressed in the liver and intestines in the metabolism of BPA extensively differ among humans, monkeys, dogs, rats, and mice.

Bisphenol A and Male Fertility: Myths and Realities

Bisphenol A (BPA) represents the main chemical monomer of epoxy resins and polycarbonate plastics. The environmental presence of BPA is widespread, and it can easily be absorbed by the human body through dietary and transdermal routes, so that more than 90% of the population in western countries display detectable BPA levels in the urine. As BPA is qualified as an endocrine disruptor, growing concern is rising for possible harmful effects on human health. This review critically discusses the available literature dealing with the possible impact of BPA on male fertility. In rodent models, the in vivo exposure to BPA negatively interfered with the regulation of spermatogenesis throughout the hypothalamic-pituitary-gonadal axis. Furthermore, in in vitro studies, BPA promoted mitochondrial dysfunction and oxidative/apoptotic damages in spermatozoa from different species, including humans. To date, the claimed clinical adverse effects on male fertility are largely based on the results from studies assessing the relationship between urinary BPA concentration and conventional semen parameters. These studies, however, produced controversial evidence due to heterogeneity in the extent of BPA exposure, type of population, and enrollment setting. Moreover, the cause-effect relationship cannot be established due to the cross-sectional design of the studies as well as the large spontaneous between- and within-subject variability of semen parameters. The best evidence of an adverse effect of BPA on male fertility would be provided by prospective studies on clinically relevant endpoints, including natural or medically assisted pregnancies among men either with different exposure degrees (occupational/environmental) or with different clinical conditions (fertile/subfertile).

Novel Class of Isoxazole-Based Gelators for the Separation of Bisphenol A from Water and Cleanup of Oil Spills

A series of low-molecular-weight gelators based on an isoxazole backbone were synthesized, which showed robust and phase-selective gelation of a series of oils. Due to their excellent phase-selective and cogelation properties, they were employed for the separation of bisphenol and the recovery of oil spills from water. The driving force and morphology of these gels were characterized by spectroscopic and microscopic studies.

Bisphenol A, Tobacco Smoke, and Age as Predictors of Oxidative Stress in Children and Adolescents

OBJECTIVES

The purpose of this study was to investigate bisphenol A (BPA) and its role in the induction of oxidative stress and confirm the same for tobacco smoke.

METHODS

A total of 223 young, healthy students (7-19 years old) were recruited in Chivasso, Italy. A spot of urine of each subject was analyzed to quantify BPA, cotinine, and 15F2t-isoprostane.

RESULTS

BPA showed a slight increase of concentration proportional with increasing age, even though the 11-14 years age group had slightly lower results, inducing a V-shape. The same trend was observed for 15F2t-isoprostane and cotinine. The result of piecewise linear robust regression shows a break point of the effect of BPA on 15F2t-isoprostane at 6 ng/mg CREA (p < 0.001). At higher levels, 15F2t-isoprostane shows an exponential increase by more than threefold for each one-log unit of BPA. An increase of oxidative stress due to BPA was observed, but only from 6 ng/mg of CREA up. Passive tobacco smoke is also able to induce an increase in oxidative stress.

CONCLUSION

Prevention against BPA and passive tobacco smoke represents an important tool for promoting the highest health standard.

Bisphenol A Affects on the Functional Properties and Proteome of Testicular Germ Cells and Spermatogonial Stem Cells in vitro Culture Model

The endocrine disruptor bisphenol A (BPA) is well known for its adverse effect on male fertility. Growing evidence suggests that BPA may interact with testicular germ cells and cause infertility as a result of its estrogenic activity. Objective of current in vitro study was to investigate the proliferation, survivability and stemness properties of mouse testicular germ cells exposed to BPA, and to evaluate possible expression of cellular proteome. Our results showed that germ cell viability and proliferation were not affected by low concentrations (0.01, 0.1, 1, and 10 µM) although significant reduction observed at 100 µM BPA. Germ cell self-renewal and differentiation related marker proteins expression found unchanged at those concentrations. When BPA-exposed germ cells were transplanted into recipient testes, we observed fewer colonies at higher concentrations (10 and 100 µM). Additionally, a significant frequency of recombination failure during meiosis was observed in 10 µM BPA-exposed germ cell transplanted recipient. Moreover, experiment on continuous BPA-exposed and 100 µM BPA-recovered germ cells suggested that spermatogonial stem cells are more potential to survive in adverse environment. Finally, scrutinizing differentially expressed cellular proteins resulted from our proteomic analysis, we conclude that BPA exposure might be associated with several health risks and infertility.

The “Low Dose” Hypothesis: Validity and Implications for Human Risk

In the late 1990s, a “low dose” hypothesis was proposed based on studies that purported to show that hormonally active environmental agents were causing a variety of effects, mainly reproductive and developmental, at “low doses.” The supporters of this hypothesis claim that traditional “high-dose” toxicity studies are not adequate to assess adverse effects from these hormonally active agents in that they do not detect effects that are occurring at “low doses.” In addition, it is claimed that these “low dose” effects are occurring at levels comparable to those to which humans are being exposed. These claims have been controversial and expert panels evaluated the evidence behind them in the early 2000s. Although these panels generally concluded that such “low dose” effects were not conclusively established, proponents of the “low dose” hypothesis assert that a large number of more recent studies now provide clear support for their hypothesis. This review carefully examines both recent and older studies that have been cited to support the “low dose” hypothesis, including their relevance for the human population. These include in vivo and in vitro laboratory studies as well as a very limited number of epidemiological investigations. Based on the evidence, it is concluded that these “low dose” effects have yet to be established, that the studies purported to support these cannot be validly extrapolated to humans, and the doses at which the studies have been performed are significantly higher than the levels to which humans are exposed.

Derivation of an oral Maximum Allowable Dose Level for Bisphenol A

Bisphenol A (BPA) is a high production volume chemical that is used in plastics and epoxy coatings. In 2015, California's Office of Environmental Health Hazard Assessment (OEHHA) added BPA to the Proposition 65 list of chemicals "known to cause reproductive toxicity" based on its Developmental and Reproductive Toxicant Identification Committee's (DART-IC) conclusion that BPA has been shown to cause female reproductive toxicity. A critical factor in determining compliance with Proposition 65 is a Maximum Allowable Dose Level (MADL), which is the exposure level at which a chemical would have no observable reproductive effect even if a person were exposed to 1000 times that level. We performed a comprehensive review of the literature, including the studies reviewed by DART-IC, and derived an oral MADL. Of all the studies we identified, Delclos et al. (2014) is of sufficient quality, has the lowest no observed effect level (NOEL), and results in the most conservative MADL of 157 μg/d. This is generally supported by other studies, including those that were considered by DART-IC. Also, the oral MADL provides a similar margin of safety as OEHHA's dermal MADL and other regulatory guidelines. Taken together, the scientific data support an oral MADL of 157 μg/d.

Experimental Data Extraction and in Silico Prediction of the Estrogenic Activity of Renewable Replacements for Bisphenol A

Bisphenol A (BPA) is a ubiquitous compound used in polymer manufacturing for a wide array of applications; however, increasing evidence has shown that BPA causes significant endocrine disruption and this has raised public concerns over safety and exposure limits. The use of renewable materials as polymer feedstocks provides an opportunity to develop replacement compounds for BPA that are sustainable and exhibit unique properties due to their diverse structures. As new bio-based materials are developed and tested, it is important to consider the impacts of both monomers and polymers on human health. Molecular docking simulations using the Estrogenic Activity Database in conjunction with the decision forest were performed as part of a two-tier in silico model to predict the activity of 29 bio-based platform chemicals in the estrogen receptor-α (ERα). Fifteen of the candidates were predicted as ER binders and fifteen as non-binders. Gaining insight into the estrogenic activity of the bio-based BPA replacements aids in the sustainable development of new polymeric materials.

Exposure of preimplantation embryos to low-dose bisphenol A impairs testes development and suppresses histone acetylation of StAR promoter to reduce production of testosterone in mice

Previous studies have shown that bisphenol A (BPA) is a potential endocrine disruptor and testicular toxicant. The present study focused on exploring the impact of exposure to low dose of BPA on male reproductive development during the early embryo stage and the underlying mechanisms. BPA (20 μg/kg/day) was orally administered to female mice on days 1-5 of gestation. The male offspring were euthanized at PND10, 20, 24, 35 or PND50. We found that the mice exposed to BPA before implantation (BPA-mice) displayed retardation of testicular development with reduction of testosterone level. The diameter and epithelium height of seminiferous tubules were reduced in BPA-mice at PND35. The numbers of spermatogenic cells at different stages were significantly reduced in BPA-mice at PND50. BPA-mice showed a persistent reduction in serum and testicular testosterone levels starting from PND24, whereas GnRH mRNA was significantly increased at PND35 and PND50. The expressions of testicular StAR and P450scc in BPA-mice also decreased relative to those of the controls at PND35 and PND50. Further analysis found that the levels of histone H3 and H3K14 acetylation (Ac-H3 and H3K14ac) in the promoter of StAR were decreased relative to those of control mice, whereas the level of Ac-H3 in the promoter of P450scc was not significantly different between the groups. These results provide evidence that exposure to BPA in preimplantation embryo retards the development of testes by reducing histone acetylation of the StAR promoter to disrupt the testicular testosterone synthesis.

Urinary bisphenol A concentrations positively associated with glycated hemoglobin and other indicators of diabetes in Canadian men

BACKGROUND

Bisphenol A (BPA), an endocrine disrupting chemical (EDC), may pose a risk to human health, including diabetes. However, epidemiological studies from the U.S., China and South Korea showed inconsistent results.

OBJECTIVE

To examine the associations between BPA and indicators of diabetes in the general Canadian population.

METHODS

The analysis was based on cross-sectional data from the Canadian Health Measures Survey (CHMS) Cycle 2 (2009-2011). We included 1915 participants with glycated hemoglobin (HbA1c) measurement and 2405 participants with serum glucose (SG) measurement aged 3-79 years, respectively. Multiple linear regression analyses were performed to model HbA1c and log-transformed SG levels associated with quartiles of urinary BPA concentrations controlling for potential confounders. Further, in adults (age≥18 years), logistic regression analysis was conducted to evaluate the association between BPA and physician-diagnosed diabetes mellitus (DM). Bootstrap weights were applied to all the analyses to account for the complex survey design.

RESULTS

The geometric mean of urinary BPA was 1.21 (±0.05)µg/L. Overall, a positive association was observed between urinary BPA quartiles and HbA1c levels in men after controlling for potential confounders (P<0.05), but not in women and children. Similar patterns were found for the associations of BPA with log-transformed SG levels and doctor-diagnosed DM.

CONCLUSIONS

Higher urinary BPA levels were associated with adverse glucose homeostasis in Canadian men, independent of major covariates. Prospective studies with longitudinal design are needed to further investigate the causality.

Methods for studying human organogenesis

This review details methods for utilizing D & C suction abortus specimens as a source of human fetal organs to study the morphogenetic and molecular mechanisms of human fetal organ development. By this means it is possible to design experiments elucidating the molecular mechanisms of human fetal organ development and to compare and contrast human developmental mechanisms with that of laboratory animals. Finally human fetal organs can be grown in vivo as grafts to athymic mice, thus allowing ethical analysis of potential adverse effects of environmental toxicants.

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

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

Pubertal BPA exposure changes central ERα levels in female mice

Despite many studies on the effects of perinatal Bisphenol A (BPA) exposure on the brain, its effects on brain estrogen receptor (ERα) expression during puberty remain unclear. Here, mice were injected subcutaneously with BPA (50μg/kg), estradiol (10μg 17β-E2/kg) or oil (0.05ml sesame oil) daily during puberty (postnatal days 23-30). Immunohistochemistry was used to examine changes in ERα immunoreactive neurons in different brain regions. Compared to control animals, pubertal exposure to BPA significantly increased ERα immunoreactive neurons in the bed nucleus of the stria terminalis (BST), arcuate hypothalamic nucleus (Arc), ventromedial hypothalamic nucleus (VMH) and medial amygdaloid nucleus (MeA) in females. E2 exposure during puberty also increased ERα immunoreactive neurons in the lateral septum (LS) of females. No effect was detected in males. These results indicate that the effects of estrogenic chemicals on ERα immunoreactive neurons are sex-dependent.

Pre- and postnatal bisphenol A treatment does not alter the number of tyrosine hydroxylase-positive cells in the anteroventral periventricular nucleus (AVPV) of weanling male and female rats

Exposure to Bisphenol A (BPA) may interfere with brain sexual differentiation. Altered numbers of tyrosine hydroxylase (TH) cells in the rodent anteroventral periventricular nucleus (AVPV) after developmental BPA treatment have been reported; however, definitive conclusions are lacking. The current study incorporated many of the guidelines suggested for endocrine disrupter research. Specifically, ethinyl estradiol (EE2) served as a reference estrogen, exogenous environmental estrogen exposure was controlled, BPA was administered orally, and subjects consumed a low phytoestrogen diet. Here, on gestational days 6-21, Sprague-Dawley rats (10-15/group) were gavaged with 2.5 or 25.0 µg BPA/kg/day or 5.0 or 10.0 µg EE2/kg/day or the vehicle (5 ml of 0.3% aqueous carboxymethylcellulose/kg/day). A naïve control group was weighed and restrained, but not gavaged. Beginning on postnatal day (PND) 1 and continuing until PND 21, the 4 pups/sex/litter were orally treated with the same dose their dam had received. On PND 21, 1/sex/litter was perfused and the brain removed. TH immunoreactivity (TH-ir) was counted in 8 images/pup by a technician blind to treatment status. ANOVA results indicated significantly higher TH-ir cells/mm(2) in females (main effect of sex: p<0.01); however, there was no significant effect of treatment or a significant interaction of treatment with sex. In a separate untreated group of PND 21 Sprague-Dawley pups, AVPV volume was quantified and no significant sexual dimorphism was apparent. Similar to our reported results of behavioral assessments, the BPA treatment paradigm used here (2.5 or 25.0 µg BPA/kg/day administered orally) does not appear to cause significant alterations in AVPV TH-ir.

Effects of oral exposure to bisphenol A on gene expression and global genomic DNA methylation in the prostate, female mammary gland, and uterus of NCTR Sprague-Dawley rats

Bisphenol A (BPA), an industrial chemical used in the manufacture of polycarbonate and epoxy resins, binds to the nuclear estrogen receptor with an affinity 4-5 orders of magnitude lower than that of estradiol. We reported previously that "high BPA" [100,000 and 300,000 µg/kg body weight (bw)/day], but not "low BPA" (2.5-2700 µg/kg bw/day), induced clear adverse effects in NCTR Sprague-Dawley rats gavaged daily from gestation day 6 through postnatal day (PND) 90. The "high BPA" effects partially overlapped those of ethinyl estradiol (EE2, 0.5 and 5.0 µg/kg bw/day). To evaluate further the potential of "low BPA" to induce biological effects, here we assessed the global genomic DNA methylation and gene expression in the prostate and female mammary glands, tissues identified previously as potential targets of BPA, and uterus, a sensitive estrogen-responsive tissue. Both doses of EE2 modulated gene expression, including of known estrogen-responsive genes, and PND 4 global gene expression data showed a partial overlap of the "high BPA" effects with those of EE2. The "low BPA" doses modulated the expression of several genes; however, the absence of a dose response reduces the likelihood that these changes were causally linked to the treatment. These results are consistent with the toxicity outcomes.

Bisphenol-A: epigenetic reprogramming and effects on reproduction and behavior

Bisphenol A (BPA) is a synthetic compound used in the production of many polycarbonate plastics and epoxy resins. It is one of the most widely produced chemicals in the world today and is found in most canned goods, plastics, and even household dust. Exposure to BPA is almost universal: most people have measurable amounts of BPA in both urine and serum. BPA is similar in structure to estradiol and can bind to multiple targets both inside and outside the nucleus, in effect acting as an endocrine disruptor. Research on BPA exposure has accelerated in the past decade with findings suggesting that perinatal exposure to BPA can negatively impact both male and female reproduction, create alterations in behavior, and act as a carcinogen. BPA can have both short term and long term effects with the latter typically occurring through epigenetic mechanisms such as DNA methylation. This review will draw on both human and animal studies in an attempt to synthesize the literature and examine the effects of BPA exposure on reproduction, behavior, and carcinogenesis with a focus on the potential epigenetic mechanisms by which it acts.

Investigation of the effects of subchronic low dose oral exposure to bisphenol A (BPA) and ethinyl estradiol (EE) on estrogen receptor expression in the juvenile and adult female rat hypothalamus

Concerns have been raised regarding the long-term impacts of early life exposure to the ubiquitous environmental contaminant bisphenol A (BPA) on brain organization. Because BPA has been reported to affect estrogen signaling, and steroid hormones play a critical role in brain sexual differentiation, there is also concern that BPA exposure could alter neural sex differences. Here, we examine the impact of subchronic exposure from gestation to adulthood to oral doses of BPA below the current no-observed-adverse-effect level (NOAEL) of 5 mg/kg body weight (bw)/day on estrogen receptor (ESR) expression in sexually dimorphic brain regions of prepubertal and adult female rats. The dams were gavaged daily with vehicle (0.3% carboxymethylcellulose), 2.5, 25, 260, or 2700 μg BPA/kg bw/day, or 0.5 or 5.0 μg ethinyl estradiol (EE)/kg bw/day from gestational day 6 until labor began. Offspring were then gavaged directly from the day after birth until the day before scheduled sacrifice on postnatal days 21 or 90. Using in situ hybridization, one or more BPA doses produced significant decreases in Esr1 expression in the juvenile female rat anteroventral periventricular nucleus (AVPV) of the hypothalamus and significant decreases in Esr2 expression in the adult female rat AVPV and medial preoptic area (MPOA), relative to vehicle controls. BPA did not simply reproduce EE effects, indicating that BPA is not acting solely as an estrogen mimic. The possible consequences of long-term changes in hypothalamic ESR expression resulting from subchronic low dose BPA exposure on neuroendocrine effects are discussed and being addressed in ongoing, related work.

Developmental exposure of zebrafish (Danio rerio) to bisphenol-S impairs subsequent reproduction potential and hormonal balance in adults

In the recent years, there has been a growing concern about the production and use of bisphenol-A substitute, namely bisphenol-S (BPS). Due to its novel nature, there have been few studies addressing the ability of BPS to disrupt the endocrine system of animals. In the present study, zebrafish (Danio rerio) embryos were exposed to and reared in various concentrations of BPS (0, 0.1, 1, 10 and 100 μg/l) for 75 days. Then adult males and females were paired in spawning tanks for 7 days in clean water and the consequent effects on fish development, reproduction, plasma vitellogenin (VTG), sex steroids and thyroid hormone levels were investigated as endpoints. After 75 days of exposure, there was a skewed sex ratio in favor of females. The results also showed that body length and weight significantly decreased in males exposed to 100 μg/l of BPS. Gonadosomatic index was significantly reduced in fish at ≥ 10 μg/l. Hepatosomatic index exhibited a significant increase in both male and female fish. At ≥ 1 μg/l of BPS, plasma 17β-estradiol levels were significantly increased in both males and females. However, plasma testosterone showed a significant reduction in males exposed to 10 and 100 μg/l of BPS. A significant induction in plasma VTG level was observed in both males and females at ≥ 10 μg/l of BPS. Plasma thyroxine and triiodothyronine levels were significantly decreased at 10 and 100 μg/l of BPS in males, and at 100 μg/l in females. Egg production and sperm count were also significantly decreased in groups received 10 and 100 μg/l of BPS. Moreover, once time to hatching and hatching rates were calculated for fertilized eggs the postponed and decreased rates of hatching were observed. Taken together, these results suggest that developmental exposure to low concentrations of BPS has adverse effects on different parts of the endocrine system in zebrafish.

Bisphenol A and indicators of obesity, glucose metabolism/type 2 diabetes and cardiovascular disease: a systematic review of epidemiologic research

INTRODUCTION

Bisphenol A (BPA), a high-volume chemical with weak estrogenic properties, has been linked to obesity, cardiovascular diseases (CVD) and diabetes mellitus (DM). This review evaluates both the consistency and the quality of epidemiological evidence from studies testing the hypothesis that BPA exposure is a risk factor for these health outcomes.

METHODS

We followed the current methodological guidelines for systematic reviews by using two independent researchers to identify, review and summarize the relevant epidemiological literature on the relation of BPA to obesity, CVD, DM, or related biomarkers. Each paper was summarized with respect to its methods and results with particular attention to study design and exposure assessment, which have been cited as the main areas of weakness in BPA epidemiologic research. As quantitative meta-analysis was not feasible, the study results were categorized qualitatively as positive, inverse, null, or mixed.

RESULTS

Nearly all studies on BPA and obesity-, DM- or CVD-related health outcomes used a cross-sectional design and relied on a single measure of BPA exposure, which may result in serious exposure misclassification. For all outcomes, results across studies were inconsistent. Although several studies used the same data and the same or similar statistical methods, when the methods varied slightly, even studies that used the same data produced different results.

CONCLUSION

Epidemiological study design issues severely limit our understanding of health effects associated with BPA exposure. Considering the methodological limitations of the existing body of epidemiology literature, assertions about a causal link between BPA and obesity, DM, or CVD are unsubstantiated.

Mouse strain does not influence the overall effects of bisphenol a-induced toxicity in adult antral follicles

Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC) widely used in common consumer products containing polycarbonate plastics and epoxy resins. Previous studies indicate that other EDCs have species-dependent effects. Furthermore, some EDCs are known to have different effects in different strains within the same species. Little information, however, is known about whether the effects of BPA on the ovary differ by strain. Previous studies have shown that BPA inhibits follicle growth, induces atresia, and inhibits steroidogenesis and expression of steroidogenic enzymes in antral follicles from adult FVB mice. Thus, this study was designed to expand previous work by testing the hypothesis that mouse strain may differentially affect the susceptibility of adult antral follicles to BPA-induced toxicity. To test this hypothesis, antral follicles were mechanically isolated from adult FVB, CD-1, and C57BL/6 mice, individually cultured for 6-120 h and treated with either vehicle control (dimethylsulfoxide) or various concentrations of BPA (1.0 μg/ml, 10 μg/ml, or 100 μg/ml). After culture, media were subjected to measurements of hormone production via ELISA, and follicles were subjected to real-time PCR for analysis of genes known to regulate steroidogenesis, the cell cycle, and atresia. Overall, BPA inhibited follicle growth and steroidogenesis in all tested strains, but CD-1 follicles were slightly more sensitive to BPA at early time points than FVB and C57BL/6 follicles. These data suggest that CD-1, FVB, and C57BL/6 mice can all be used to investigate the effects of BPA on ovarian follicles.

Regulatory decisions on endocrine disrupting chemicals should be based on the principles of endocrinology

For years, scientists from various disciplines have studied the effects of endocrine disrupting chemicals (EDCs) on the health and wellbeing of humans and wildlife. Some studies have specifically focused on the effects of low doses, i.e. those in the range that are thought to be safe for humans and/or animals. Others have focused on the existence of non-monotonic dose-response curves. These concepts challenge the way that chemical risk assessment is performed for EDCs. Continued discussions have clarified exactly what controversies and challenges remain. We address several of these issues, including why the study and regulation of EDCs should incorporate endocrine principles; what level of consensus there is for low dose effects; challenges to our understanding of non-monotonicity; and whether EDCs have been demonstrated to produce adverse effects. This discussion should result in a better understanding of these issues, and allow for additional dialog on their impact on risk assessment.

Sex specific impact of perinatal bisphenol A (BPA) exposure over a range of orally administered doses on rat hypothalamic sexual differentiation

Bisphenol A (BPA) is a high volume production chemical used in polycarbonate plastics, epoxy resins, thermal paper receipts, and other household products. The neural effects of early life BPA exposure, particularly to low doses administered orally, remain unclear. Thus, to better characterize the dose range over which BPA alters sex specific neuroanatomy, we examined the impact of perinatal BPA exposure on two sexually dimorphic regions in the anterior hypothalamus, the sexually dimorphic nucleus of the preoptic area (SDN-POA) and the anterioventral periventricular (AVPV) nucleus. Both are sexually differentiated by estradiol and play a role in sex specific reproductive physiology and behavior. Long Evans rats were prenatally exposed to 10, 100, 1000, 10,000μg/kg bw/day BPA through daily, non-invasive oral administration of dosed-cookies to the dams. Offspring were reared to adulthood. Their brains were collected and immunolabeled for tyrosine hydroxylase (TH) in the AVPV and calbindin (CALB) in the SDN-POA. We observed decreased TH-ir cell numbers in the female AVPV across all exposure groups, an effect indicative of masculinization. In males, AVPV TH-ir cell numbers were significantly reduced in only the BPA 10 and BPA 10,000 groups. SDN-POA endpoints were unaltered in females but in males SDN-POA volume was significantly lower in all BPA exposure groups. CALB-ir was significantly lower in all but the BPA 1000 group. These effects are consistent with demasculinization. Collectively these data demonstrate that early life oral exposure to BPA at levels well below the current No Observed Adverse Effect Level (NOAEL) of 50mg/kg/day can alter sex specific hypothalamic morphology in the rat.

Prenatal bisphenol A exposure alters sex-specific estrogen receptor expression in the neonatal rat hypothalamus and amygdala

Bisphenol A (BPA) exposure is ubiquitous, and in laboratory animals, early-life BPA exposure has been shown to alter sex-specific neural organization, neuroendocrine physiology, and behavior. The specific mechanisms underlying these brain-related outcomes, however, remain largely unknown, constraining the capacity to ascertain the potential human relevance of neural effects observed in animal models. In the perinatal rat brain, estrogen is masculinizing, suggesting that BPA-induced perturbation of estrogen receptor (ESR) expression may underpin later in-life neuroendocrine effects. We hypothesized that prenatal BPA exposure alters sex-specific ESR1 (ERα) and ESR2 (ERβ) expression in postnatal limbic nuclei. Sprague Dawley rats were mated and gavaged on gestational days (GDs) 6-21 with vehicle, 2.5 or 25 μg/kg bw/day BPA, or 5 or 10 μg/kg bw/day ethinyl estradiol. An additional group was restrained but not gavaged (naïve control). Offspring were sacrificed the day after birth to quantify ESR gene expression throughout the hypothalamus and amygdala by in situ hybridization. Relative to the vehicle group, significant effects of BPA were observed on ESR1 and ESR2 expression throughout the mediobasal hypothalamus and amygdala in both sexes. Significant differences in ESR expression were also observed in the mediobasal hypothalamus and amygdala of the naïve control group compared with the vehicle group, highlighting the potential for gavage to influence gene expression in the developing brain. These results indicate that ESR expression in the neonatal brain of both sexes can be altered by low-dose prenatal BPA exposure.

Communicating food risks in an era of growing public distrust: three case studies

The communication and regulation of risk has changed significantly over the past 30 years in Europe and to a noticeable but lesser extent in the United States. In Europe, this is partly due to a series of regulatory mishaps, ranging from mad cow disease in the United Kingdom to contamination of the blood supply in France. In the United States, general public confidence in the American government has been gradually declining for more than three decades, driven by a mix of cultural and political conflicts like negative political advertising, a corrosive news media, and cuts in regulatory budgets. While the former approach is based on an objective assessment of the risk, the latter is driven more by the perception of the risk, consumer sentiment, political will, and sectoral advocacy. In this article, the author examines three U.S.-based food case studies (acrylamide, bisphenol A, and artificial food colorings) where regulations at the local and state levels are increasingly being based on perceived risk advocacy rather than on the most effective response to the risk, be it to food safety or public health, as defined by regulatory interpretation of existing data. In the final section, the author puts forward a series of recommendations for how U.S.-based regulators can best handle those situations where the perceived risk is markedly different from the fact-based risk, such as strengthening the communication departments of food regulatory agencies, training officials in risk communication, and working more proactively with neutral third-party experts.

A critique of the European Commission document, "State of the Art Assessment of Endocrine Disrupters"

In this commentary, we critique a recently finalized document titled "State of the Art Assessment of Endocrine Disrupters" (SOA Assessment). The SOA Assessment was commissioned by the European Union Directorate-General for the Environment to provide a basis for developing scientific criteria for identifying endocrine disruptors and reviewing and possibly revising the European Community Strategy on Endocrine Disrupters. In our view, the SOA Assessment takes an anecdotal approach rather than attempting a comprehensive assessment of the state of the art or synthesis of current knowledge. To do the latter, the document would have had to (i) distinguish between apparent associations of outcomes with exposure and the inference of an endocrine-disruption (ED) basis for those outcomes; (ii) constitute a complete and unbiased survey of new literature since 2002 (when the WHO/IPCS document, "Global Assessment of the State-of-the-Science of Endocrine Disruptors" was published); (iii) consider strengths and weaknesses and issues in interpretation of the cited literature; (iv) follow a weight-of-evidence methodology to evaluate evidence of ED; (v) document the evidence for its conclusions or the reasoning behind them; and (vi) present the evidence for or reasoning behind why conclusions that differ from those drawn in the 2002 WHO/IPCS document need to be changed. In its present form, the SOA Assessment fails to provide a balanced and critical assessment or synthesis of literature relevant to ED. We urge further evidence-based evaluations to develop the needed scientific basis to support future policy decisions.

Evaluation of bisphenol A glucuronidation according to UGT1A1*28 polymorphism by a new LC-MS/MS assay

The endocrine disruptor bisphenol A (BPA) is a frequently used chemical in the manufacture of consumer products. In humans, BPA is extensively metabolized to BPA glucuronide (BPAG) by different UDP-glucuronosyltransferase (UGT) isoforms. The study has been performed with the intention to improve the accuracy of published physiologically based pharmacokinetic models and to improve regulatory risk assessments of BPA. In order to gain insight into intestine, kidney, liver, and lung glucuronidation of BPA, human microsomes of all tested organs were used. BPAG formation followed Michaelis-Menten kinetics in the intestine and kidney, but followed substrate inhibition kinetics in the liver. Human lung microsomes did not show glucuronidation activity towards BPA. While the liver intrinsic clearance was very high (857 mL min(-1)kg body weight(-1)), the tissue intrinsic clearances for the kidney and intestine were less than 1% of liver intrinsic clearance. Since BPA is a UGT1A1 substrate, we postulated that the common UGT1A1*28 polymorphism influences BPA glucuronidation, and consequently, BPA detoxification. Hepatic tissue intrinsic clearances for UGT1A1*1/*1, UGT1A1*1/*28, and UGT1A1*28/*28 microsomes were 1113, 1075, and 284 mL min(-1)kg body weight(-1), respectively. Prior to microsomal experiments, the bioproduction of BPAG and stable isotope-labeled BPAG (BPAG(d16)) was performed for the purpose of the reliable and accurate quantification of BPAG. In addition, a sensitive LC-MS/MS analytical method for the simultaneous determination of BPA and BPAG based on two stable isotope-labeled internal standards was developed and validated. In conclusion, our in vitro results show that the liver is the main site of BPA glucuronidation (K(m) 8.9 μM, V(max) 8.5 nmol min(-1) mg(-1)) and BPA metabolism may be significantly influenced by a person's genotype (K(m) 10.0-13.1 μM, V(max) 3.4-16.2 nmol min(-1) mg(-1)). This discovery may be an important fact for the currently on-going worldwide BPA risk assessments and for the improvement of physiologically based pharmacokinetic models.

Hypothesis-driven weight of evidence framework for evaluating data within the US EPA's Endocrine Disruptor Screening Program

"Weight of Evidence" (WoE) approaches are often used to critically examine, prioritize, and integrate results from different types of studies to reach general conclusions. For assessing hormonally active agents, WoE evaluations are necessary to assess screening assays that identify potential interactions with components of the endocrine system, long-term reproductive and developmental toxicity tests that define adverse effects, mode of action studies aimed at identifying toxicological pathways underlying adverse effects, and toxicity, exposure and pharmacokinetic data to characterize potential risks. We describe a hypothesis-driven WoE approach for hormonally active agents and illustrate the approach by constructing hypotheses for testing the premise that a substance interacts as an agonist or antagonist with components of estrogen, androgen, or thyroid pathways or with components of the aromatase or steroidogenic enzyme systems for evaluating data within the US EPA's Endocrine Disruptor Screening Program. Published recommendations are used to evaluate data validity for testing each hypothesis and quantitative weightings are proposed to reflect two data parameters. Relevance weightings should be derived for each endpoint to reflect the degree to which it probes each specific hypothesis. Response weightings should be derived based on assay results from the test substance compared to the range of responses produced in the assay by the appropriate prototype hormone and positive and negative controls. Overall WoE scores should be derived based on response and relevance weightings and a WoE narrative developed to clearly describe the final determinations.

Effects of early prepubertal exposure to bisphenol A on the onset of puberty, ovarian weights, and estrous cycle in female mice

OBJECTIVE

Bisphenol A (BPA) is a chemical used extensively to manufacture plastics and epoxy resin liners for food and beverage cans. BPA, with properties similar to estrogen, has endocrine-disrupting effects. In the present study, we examined the effects of early prepubertal BPA exposure on the onset of puberty and reproductive parameters such as estrous cycle and reproductive organ weights in female mice.

METHODS

Female mice were injected subcutaneously at postnatal day (PND) 8 with BPA (0.1, 1, 10, 100 mg/kg) in sesame oil or with sesame oil alone. Body weight was measured from PND 10 to 70. Vaginal opening and estrous cycle were monitored from PND 20 to 29. Animals were sacrificed at PND 25, 30, and 70, and the ovary and uterus weights were measured.

RESULTS

Early prepubertal exposure to BPA (10 and 100 mg/kg) significantly decreased body weight from PND 18 to 30. BPA treated mice at testing dose levels showed early opening of the vagina compared to the control group. The number of estrous cycle and days of estrus were significantly decreased in high dose (100 mg/kg) BPA treated mice. The ovary weight at PND 25 and 30 was significantly decreased in all BPA treatment groups.

CONCLUSION

Early prepubertal exposure to BPA accelerated the onset of puberty but decreased reproductive parameters in female mice.

Critical evaluation of key evidence on the human health hazards of exposure to bisphenol A

Despite the fact that more than 5000 safety-related studies have been published on bisphenol A (BPA), there seems to be no resolution of the apparently deadlocked controversy as to whether exposure of the general population to BPA causes adverse effects due to its estrogenicity. Therefore, the Advisory Committee of the German Society of Toxicology reviewed the background and cutting-edge topics of this BPA controversy. The current tolerable daily intake value (TDI) of 0.05 mg/kg body weight [bw]/day, derived by the European Food Safety Authority (EFSA), is mainly based on body weight changes in two- and three-generation studies in mice and rats. Recently, these studies and the derivation of the TDI have been criticized. After having carefully considered all arguments, the Committee had to conclude that the criticism was scientifically not justified; moreover, recently published additional data further support the reliability of the two- and three-generation studies demonstrating a lack of estrogen-dependent effects at and below doses on which the current TDI is based. A frequently discussed topic is whether doses below 5 mg/kg bw/day may cause adverse health effects in laboratory animals. Meanwhile, it has become clear that positive results from some explorative studies have not been confirmed in subsequent studies with higher numbers of animals or a priori defined hypotheses. Particularly relevant are some recent studies with negative outcomes that addressed effects of BPA on the brain, behavior, and the prostate in rodents for extrapolation to the human situation. The Committee came to the conclusion that rodent data can well be used as a basis for human risk evaluation. Currently published conjectures that rats are insensitive to estrogens compared to humans can be refuted. Data from toxicokinetics studies show that the half-life of BPA in adult human subjects is less than 2 hours and BPA is completely recovered in urine as BPA-conjugates. Tissue deconjugation of BPA-glucuronide and -sulfate may occur. Because of the extremely low quantities, it is only of minor relevance for BPA toxicity. Biomonitoring studies have been used to estimate human BPA exposure and show that the daily intake of BPA is far below the TDI for the general population. Further topics addressed in this article include reasons why some studies on BPA are not reproducible; the relevance of oral versus non-oral exposure routes; the degree to which newborns are at higher systemic BPA exposure; increased BPA exposure by infusions in intensive care units; mechanisms of action other than estrogen receptor activation; and the current regulatory status in Europe, as well as in the USA, Canada, Japan, New Zealand, and Australia. Overall, the Committee concluded that the current TDI for BPA is adequately justified and that the available evidence indicates that BPA exposure represents no noteworthy risk to the health of the human population, including newborns and babies.

The environmental endocrine disruptor, bisphenol A, affects germination, elicits stress response and alters steroid hormone production in kiwifruit pollen

In vitro toxicity of the endocrine disruptor bisphenol A (BPA) to pollen, the male haploid generation of higher plants, was studied. BPA caused significant inhibition of both tube emergence and elongation of kiwifruit pollen in a dose-dependent manner, beginning at 10 mg · l(-1); morphological changes to tubes were also detected. Despite strong inhibition of pollen tube production and growth, a large percentage of treated cells remained viable. Immunoblotting experiments indicated that levels of BiP and 14-3-3, which are proteins involved in stress response, substantially increased in BPA-treated pollen compared to controls. The increases were dose-dependent in the range 10-50 mg · l(-1) BPA, i.e. even when germination ability was completely blocked. Steroid hormones (17 β-estradiol, progesterone and testosterone) were detected in kiwifruit pollen, and their levels increased during germination in basal medium. In a BPA treatment of 30 mg · l(-1), larger increases in both estrogen and testosterone concentrations were detected, in particular, a six-fold increase of 17 β-estradiol over control concentration (30 min). The increased hormone levels were maintained for at least the 90 min incubation. Increasing concentrations of exogenous testosterone and 17 β-estradiol increasingly inhibited pollen tube emergence and elongation. Current data for BPA-exposed kiwifruit pollen suggest a toxicity mechanism that is at least in part based on a dramatic imbalance of steroid hormone production during tube organisation, emergence and elongation. It may be concluded that BPA, a widespread environmental contaminant, can cause serious adverse effects to essential pollen functions. On a broader scale, this chemical poses a potential risk to the reproductive success of higher plants.

Pubertal exposure to bisphenol A disrupts behavior in adult C57BL/6J mice

Bisphenol A (BPA) is a widespread endocrine disrupting chemical that influences adult physiology and behavior after perinatal exposure. However, it is not clear if pubertal exposure to BPA exerts hormone dependent effects on behaviors. Using C57BL/6J mice, we sought to determine how pubertal exposure to BPA affects locomotion, exploration, anxiety and sociability in adulthood. Compared to controls, pubertal exposure to BPA or E(2) (17β-estradiol) significantly altered female exploratory and anxiety behavior. Moreover, BPA and E(2)-treated female mice displayed increased levels of affiliation to female stimulus mice and decreased levels of affiliation to male stimulus mice; while our control males showed affiliation preference to female stimulus. These results indicate that pubertal exposure to BPA or E(2) may masculinize female social and emotional behavior.

Bisphenol A occurred in Kao-Pin River and its tributaries in Taiwan

Bisphenol A (BPA), one of the endocrine-disrupting chemicals, was detected in water collected from Kao-Pin River and its tributaries. Results indicated that 59% of the water samples contained BPA. Concentrations ranged from less than the limit of detection (LOD, 0.037) to 4.23 microg/L. The mean concentrations were 0.16, 0.20, 1.02, 1.30, and 0.30 microg/L for sampling sites S1, S2, S3, S4, and S5, respectively. Concentrations were not significantly different between high and low-flow periods in sites S2, S3, and S4. In site S1, concentrations in the high-flow period were significantly greater than during the lower flow period, and in site S5, BPA concentration in the low-flow period was significantly greater than in the high-flow period. The BPA mass flow rate in site S5 was greater in the high-flow period than in the low-flow period.

Association of urinary bisphenol a concentration with heart disease: evidence from NHANES 2003/06

Background

Bisphenol A (BPA) is a high production volume chemical widely used in food and drinks packaging. Associations have previously been reported between urinary BPA concentrations and heart disease, diabetes and liver enzymes in adult participants of the National Health and Nutrition Examination Survey (NHANES) 2003/04. We aimed to estimate associations between urinary BPA concentrations and health measures in NHANES 2005/06 and in data pooled across collection years.

Methodology and Findings

A cross-sectional analysis of NHANES: subjects were n = 1455 (2003/04) and n = 1493 (2005/06) adults aged 18–74 years, representative of the general adult population of the United States. Regression models were adjusted for age, sex, race/ethnicity, education, income, smoking, BMI, waist circumference, and urinary creatinine concentration. Main outcomes were reported diagnoses of heart attack, coronary heart disease, angina and diabetes and serum liver enzyme levels. Urinary BPA concentrations in 2005/06 (geometric mean 1.79 ng/ml, 95% CI: 1.64 to 1.96) were lower than in 2003/04 (2.49 ng/ml, CI: 2.20 to 2.83, difference p-value = 0.00002). Higher BPA concentrations were associated with coronary heart disease in 2005/06 (OR per z-score increase in BPA = 1.33, 95%CI: 1.01 to 1.75, p = 0.043) and in pooled data (OR = 1.42, CI: 1.17 to 1.72, p = 0.001). Associations with diabetes did not reach significance in 2005/06, but pooled estimates remained significant (OR = 1.24, CI: 1.10 to 1.40, p = 0.001). There was no overall association with gamma glutamyl transferase concentrations, but pooled associations with alkaline phosphatase and lactate dehydrogenase remained significant.

Conclusions

Higher BPA exposure, reflected in higher urinary concentrations of BPA, is consistently associated with reported heart disease in the general adult population of the USA. Studies to clarify the mechanisms of these associations are urgently needed.

The politics of plastics: the making and unmaking of bisphenol a "safety"

Bisphenol A (BPA), a synthetic chemical used in the production of plastics since the 1950s and a known endocrine disruptor, is a ubiquitous component of the material environment and human body. New research on very-low-dose exposure to BPA suggests an association with adverse health effects, including breast and prostate cancer, obesity, neurobehavioral problems, and reproductive abnormalities. These findings challenge the long-standing scientific and legal presumption of BPA's safety. The history of how BPA's safety was defined and defended provides critical insight into the questions now facing lawmakers and regulators: is BPA safe, and if not, what steps must be taken to protect the public's health? Answers to both questions involve reforms in chemical policy, with implications beyond BPA.