Pharmacokinetic disposition and tissue distribution of bisphenol A in rats after intravenous administration

Molecular insights underlying the adverse effects of bisphenol A on gonadal somatic cells' steroidogenic activity

Bisphenol A (BPA) exposure may impair gonadal steroidogenesis, although the underlying mechanism is not well known. Hereby, we assessed BPA action on human primary granulosa (hGC) and mouse Leydig cells (BLTK-1) proliferation, cytotoxicity, hormone secretion, and steroidogenic enzyme/receptor gene profile. hGC and BLTK-1 cells were stimulated with increasing concentrations of BPA (10^-12 M to 10^-4 M for cell proliferation assay, 10^-8 M to 10^-4 M for LDH-cytotoxicity assay, and 10^-9 M to 10^-5 M for hormone secretion and genes expression analysis). BPA at low concentrations (pM - nM) did not affect cell proliferation in either cell type, although was toxic at higher (µM) concentrations. BPA stimulation at low nM concentrations decreased the production of estradiol (E₂) and testosterone (T) in BLTK-1, E_2, and progesterone in hGCs. BPA down-regulated Star, Cyp11a1, and Hsd17b3, but up-regulated Cyp19a1, Esr1, Esr2, and Gpr30 expression in BLTK-1 cells. In hGC, BPA down-regulated STAR, CYP19A1, PGRMC1, and PAQR7 but up-regulated ESR2 expression. Estrogen receptor degrader fulvestrant (FULV) attenuated BPA inhibition of hormone production in both cell lines. FULV also blocked the BPA-induced Gpr30 up-regulation in BLTK-1 cells, whereas in hGC, failed to reverse the down-regulation of PGRMC1, STAR, and CYP19A1. Our findings provide novel mechanistic insights into environmentally-relevant doses of BPA action through both nuclear estrogen receptor-dependent and independent mechanisms affecting cultured granulosa and Leydig cell steroidogenesis.

Re-evaluation of the risks to public health related to the presence of bisphenol A (BPA) in foodstuffs

In 2015, EFSA established a temporary tolerable daily intake (t-TDI) for BPA of 4 μg/kg body weight (bw) per day. In 2016, the European Commission mandated EFSA to re-evaluate the risks to public health from the presence of BPA in foodstuffs and to establish a tolerable daily intake (TDI). For this re-evaluation, a pre-established protocol was used that had undergone public consultation. The CEP Panel concluded that it is Unlikely to Very Unlikely that BPA presents a genotoxic hazard through a direct mechanism. Taking into consideration the evidence from animal data and support from human observational studies, the immune system was identified as most sensitive to BPA exposure. An effect on Th17 cells in mice was identified as the critical effect; these cells are pivotal in cellular immune mechanisms and involved in the development of inflammatory conditions, including autoimmunity and lung inflammation. A reference point (RP) of 8.2 ng/kg bw per day, expressed as human equivalent dose, was identified for the critical effect. Uncertainty analysis assessed a probability of 57-73% that the lowest estimated Benchmark Dose (BMD) for other health effects was below the RP based on Th17 cells. In view of this, the CEP Panel judged that an additional uncertainty factor (UF) of 2 was needed for establishing the TDI. Applying an overall UF of 50 to the RP, a TDI of 0.2 ng BPA/kg bw per day was established. Comparison of this TDI with the dietary exposure estimates from the 2015 EFSA opinion showed that both the mean and the 95th percentile dietary exposures in all age groups exceeded the TDI by two to three orders of magnitude. Even considering the uncertainty in the exposure assessment, the exceedance being so large, the CEP Panel concluded that there is a health concern from dietary BPA exposure.

The development and function of the brain barriers - an overlooked consideration for chemical toxicity

It is well known that the adult brain is protected from some infections and toxic molecules by the blood-brain and the blood-cerebrospinal fluid barriers. Contrary to the immense data collected in other fields, it is deeply entrenched in environmental toxicology that xenobiotics easily permeate the developing brain because these barriers are either absent or non-functional in the fetus and newborn. Here we review the cellular and physiological makeup of the brain barrier systems in multiple species, and discuss decades of experiments that show they possess functionality during embryogenesis. We next present case studies of two chemical classes, perfluoroalkyl substances (PFAS) and bisphenols, and discuss their potential to bypass the brain barriers. While there is evidence to suggest these pollutants may enter the developing and/or adult brain parenchyma, many studies suffer from confounding technical variables which complicates data interpretation. In the future, a more formal consideration of brain barrier biology could not only improve understanding of chemical toxicokinetics but could assist in prioritizing environmental xenobiotics for their neurotoxicity risk.

Evaluating In Vitro-In Vivo Extrapolation of Toxicokinetics

Prioritizing the risk posed by thousands of chemicals potentially present in the environment requires exposure, toxicity, and toxicokinetic (TK) data, which are often unavailable. Relatively high throughput, in vitro TK (HTTK) assays and in vitro-to-in vivo extrapolation (IVIVE) methods have been developed to predict TK, but most of the in vivo TK data available to benchmark these methods are from pharmaceuticals. Here we report on new, in vivo rat TK experiments for 26 non-pharmaceutical chemicals with environmental relevance. Both intravenous and oral dosing were used to calculate bioavailability. These chemicals, and an additional 19 chemicals (including some pharmaceuticals) from previously published in vivo rat studies, were systematically analyzed to estimate in vivo TK parameters (e.g., volume of distribution [Vd], elimination rate). For each of the chemicals, rat-specific HTTK data were available and key TK predictions were examined: oral bioavailability, clearance, Vd, and uncertainty. For the non-pharmaceutical chemicals, predictions for bioavailability were not effective. While no pharmaceutical was absorbed at less than 10%, the fraction bioavailable for non-pharmaceutical chemicals was as low as 0.3%. Total clearance was generally more under-estimated for nonpharmaceuticals and Vd methods calibrated to pharmaceuticals may not be appropriate for other chemicals. However, the steady-state, peak, and time-integrated plasma concentrations of nonpharmaceuticals were predicted with reasonable accuracy. The plasma concentration predictions improved when experimental measurements of bioavailability were incorporated. In summary, HTTK and IVIVE methods are adequately robust to be applied to high throughput in vitro toxicity screening data of environmentally relevant chemicals for prioritizing based on human health risks.

High-throughput in-silico prediction of ionization equilibria for pharmacokinetic modeling

Chemical ionization plays an important role in many aspects of pharmacokinetic (PK) processes such as protein binding, tissue partitioning, and apparent volume of distribution at steady state (Vdss). Here, estimates of ionization equilibrium constants (i.e., pKa) were analyzed for 8132 pharmaceuticals and 24,281 other compounds to which humans might be exposed in the environment. Results revealed broad differences in the ionization of pharmaceutical chemicals and chemicals with either near-field (in the home) or far-field sources. The utility of these high-throughput ionization predictions was evaluated via a case-study of predicted PK Vdss for 22 compounds monitored in the blood and serum of the U.S. population by the U.S. Centers for Disease Control and Prevention National Health and Nutrition Examination Survey (NHANES). The chemical distribution ratio between water and tissue was estimated using predicted ionization states characterized by pKa. Probability distributions corresponding to ionizable atom types (IATs) were then used to analyze the sensitivity of predicted Vdss on predicted pKa using Monte Carlo methods. 8 of the 22 compounds were predicted to be ionizable. For 5 of the 8 the predictions based upon ionization are significantly different from what would be predicted for a neutral compound. For all but one (foramsulfuron), the probability distribution of predicted Vdss generated by IAT sensitivity analysis spans both the neutral prediction and the prediction using ionization. As new data sets of chemical-specific information on metabolism and excretion for hundreds of chemicals are being made available (e.g., Wetmore et al., 2015), high-throughput methods for calculating Vdss and tissue-specific PK distribution coefficients will allow the rapid construction of PK models to provide context for both biomonitoring data and high-throughput toxicity screening studies such as Tox21 and ToxCast.

Assumed non-persistent environmental chemicals in human adipose tissue; matrix stability and correlation with levels measured in urine and serum

The aim of this study was to (1) optimize a method for the measurement of parabens and phenols in adipose tissue, (2) evaluate the stability of chemical residues in adipose tissue samples, and (3) study correlations of these compounds in urine, serum, and adipose tissue. Samples were obtained from adults undergoing trauma surgery. Nine phenols and seven parabens were determined by isotope diluted TurboFlow-LC-MS/MS. The analytical method showed good accuracy and precision. Limits of detection (LOD) for parabens and phenols ranged from 0.05 to 1.83ng/g tissue. Good recovery rates were found, even when biological samples remained defrosted up to 24h. Benzophenone-3 (BP-3; range of values: <LOD-1.48ng/g tissue) and methylparaben (MeP; <LOD-1.78ng/g tissue) were detected in >70% of adipose tissue samples, while bisphenol-A (BPA; <LOD-3.28ng/g tissue) and 2-phenylphenol (2-PP; <LOD-0.78ng/g tissue) were detected in >40% of adipose tissue samples. In general, levels were similar between adipose tissue and serum, while a correlation between adipose tissue and urine was only found for BP-3. In conclusion, adipose tissue samples in this study were found to contain environmental chemicals considered to be non-persistent, whose levels were weakly or not at all correlated with the urine burden. Therefore, adipose tissue may potentially provide additional information to that obtained from other biological matrices. Further investigations are warranted to explore whether adipose tissue might be a suitable matrix for assessment of the consequences for human health of mid/long-term exposure to these chemicals.

Influence of Bisphenol A on Type 2 Diabetes Mellitus

Bisphenol A (BPA) is an organic synthetic compound employed to produce plastics and epoxy resins. It is used as a structural component in polycarbonate beverage bottles and as coating for metal surface in food containers and packaging. The adverse effects of BPA on human health are widely disputed. BPA has been recently associated with a wide variety of medical disorders and, in particular, it was identified as potential endocrine-disrupting compound with diabetogenic action. Most of the clinical observational studies in humans reveal a positive link between BPA exposure, evaluated by the measurement of urinary BPA levels, and the risk of developing type 2 diabetes mellitus. Clinical studies on humans and preclinical studies on in vivo, ex vivo, and in vitro models indicate that BPA, mostly at low doses, may have a role in increasing type 2 diabetes mellitus developmental risk, directly acting on pancreatic cells, in which BPA induces the impairment of insulin and glucagon secretion, triggers inhibition of cell growth and apoptosis, and acts on muscle, hepatic, and adipose cell function, triggering an insulin-resistant state. The current review summarizes the available evidences regarding the association between BPA and type 2 diabetes mellitus, focusing on both clinical and preclinical studies.

A dynamic simulation of bisphenol A dosimetry in neuroendocrine organs

Bisphenol A (BPA) is a known xenoestrogen with similar properties to 17b-estradiol. BPA and estrogen are hydrophobic compounds, and this affects the pharmacokinetics of both compounds in mammals. In a previous study we measured the distribution of BPA in female F344 rats exposed to oral doses of 0.1, 10 and 100 mg/kg. The results showed distribution to target neuroendocrine organs at all doses tested. Using these results, we developed a pharmacokinetic model to predict the dynamic uptake and excretion of BPA by various routes of exposure (po, iv, sc, ip). The model was able to simulate the entire time course (48 h) following various routes of exposure in rats over the dose ranges tested. The model indicated that the ultimate tissue uptake of BPA was established by the rapid initial transfer of free BPA into tissues. After free BPA enters the systemic circulation, metabolism and excretion reactions cause a relatively short duration and rapid decline. This period is followed by a slower long-term decline characteristic of BPA’s biphasic pharmacokinetics. Plasma protein and tissue binding reactions established the long-term half-life of BPA in the body. Route differences in tissue uptake were directly related to the competition between transfer and binding reactions during the absorption phase.

Distribution of bisphenol A in the neuroendocrine organs of female rats

The distribution of 14C-bisphenol A (BPA) in plasma and neuroendocrine organs was determined in Fischer 344 female rats following three oral doses (0.1, 10 or 100 mg/kg). Plasma and tissue maximum concentrations (Cmax) were reached within 15-30 min of dosing. Plasma areas-under-the-curve (AUC) ranged from 0.06 to 53.9 mg-h/mL. The AUCs of the pituitary gland and uterus/gonads were 16-21% higher than that of plasma. The AUCs of hypothalamus and the rest of the brain were 43.7% and 77% of the plasma AUCs, respectively. In the brain tissue, the exposure increased linearly with the oral dose, as the dose was increased from 0.1 to 10 and 100 mg/kg; the exposure in the brain relative to the plasma increased by factors of 1, 1.19 and 1.24. This indicates that the brain barrier systems do not limit the access of the lipophilic BPA to the brain. The increases of the uterus/gonads relative to the plasma were 1, 1.07 and 1.04. Tissue partitioning was also examined in vitro by the uptake of 14C-BPA. The BPA tissue/blood partition coefficients were as follows: heart, 7.5; liver, 6.1; kidney, 6.4; fat, 3.6; muscle, 2.6; breast, 3.6; ovaries, 9.1; uterus, 5.9; stomach, 5.1; and small intestine, 6.7. The tissue/cerebrospinal fluid partition coefficients were as follows: pituitary gland, 12.8; brain stem, 6.1; cerebellum, 6.4; hippocampus, 7.1; hypothalamus, 6.1; frontal cortex, 4.9; and caudate nucleus, 6.8.

Bisphenol A exposure is associated with low-grade urinary albumin excretion in children of the United States

Urinary bisphenol A (BPA), a widely used biomarker of exposure to BPA, has been associated with cardiometabolic derangements in laboratory studies and with low-grade albuminuria in Chinese adults. Despite the known unique vulnerability of children to environmental chemicals, no studies have examined associations of urinary BPA with albuminuria in children. As exposure to BPA is widespread in the United States population, we examined data from 710 children in the 2009-10 National Health and Nutrition Examination Survey with urinary BPA measurements and first morning urine samples with creatinine values. Controlled for a broad array of sociodemographic and environmental risk factors as well as insulin resistance and elevated cholesterol, children with the highest compared with the lowest quartile of urinary BPA had a significant 0.91 mg/g higher albumin-to-creatinine ratio, adjusted for the urinary BPA concentration. When the multivariable model was reprised substituting continuous measures of BPA, a significant 0.28 mg/g albumin-to-creatinine ratio increase was identified for each log unit increase in urinary BPA. Thus, an association of BPA exposure with low-grade albuminuria is consistent with previous results found in Chinese adults and documents this in children in the United States. Our findings broaden the array of adverse effects of BPA to include endothelial dysfunction as evidenced by the low-grade albuminuria and support proactive efforts to prevent harmful exposures.

Distribution of bisphenol A into tissues of adult, neonatal, and fetal Sprague-Dawley rats

Bisphenol A (BPA) is an important industrial chemical used in the manufacture of polycarbonate plastic products and epoxy resin-based food can liners. The presence of BPA metabolites in urine of >90% of Americans aged 6-60 suggests ubiquitous and frequent exposure in the range of 0.02-0.2μg/kgbw/d (25th-95th percentiles). The current study used LC/MS/MS to measure placental transfer and concentrations of aglycone (receptor-active) and conjugated (inactive) BPA in tissues from Sprague-Dawley rats administered deuterated BPA (100μg/kg bw) by oral and IV routes. In adult female rat tissues, the tissue/serum concentration ratios for aglycone BPA ranged from 0.7 in liver to 5 in adipose tissue, reflecting differences in tissue perfusion, composition, and metabolic capacity. Following IV administration to dams, placental transfer was observed for aglycone BPA into fetuses at several gestational days (GD), with fetal/maternal serum ratios of 2.7 at GD 12, 1.2 at GD 16, and 0.4 at GD 20; the corresponding ratios for conjugated BPA were 0.43, 0.65, and 3.7. These ratios were within the ranges observed in adult tissues and were not indicative of preferential accumulation of aglycone BPA or hydrolysis of conjugates in fetal tissue in vivo. Concentrations of aglycone BPA in GD 20 fetal brain were higher than in liver or serum. Oral administration of the same dose did not produce measurable levels of aglycone BPA in fetal tissues. Amniotic fluid consistently contained levels of BPA at or below those in maternal serum. Concentrations of aglycone BPA in tissues of neonatal rats decreased with age in a manner consistent with the corresponding circulating levels. Phase II metabolism of BPA increased with fetal age such that near-term fetus was similar to early post-natal rats. These results show that concentrations of aglycone BPA in fetal tissues are similar to those in other maternal and neonatal tissues and that maternal Phase II metabolism, especially following oral administration, and fetal age are critical in reducing exposures to the fetus.

Gestational exposure to bisphenol A and cross-fostering affect behaviors in juvenile mice

Bisphenol-A (BPA) is a component of polycarbonate resins, and, lately, concern has been raised about its potential negative effects on human health. BPA is an estrogen analog and, in addition, it can act as a DNA hypomethylator. We examined the effects of gestational exposure to BPA on several behaviors in C57BL/6J mice. Because BPA affects maternal care, which, may have long-lasting effects on offspring behavior, we tested mice raised by either biological or fostered dams. Both diet and dam affected behavior in juvenile mice in a social novelty task and the elevated plus maze (EPM). In a social novelty task, the amount of time spent interacting with an adult male was affected by sex and gestational diet, but only in juveniles raised by a foster dam. Control females spent less time sniffing a novel adult than did control males or females exposed to BPA during gestation. In the EPM, juveniles reared by foster dams and exposed to BPA during gestation spent less time in the distal half of the open arm as compared with juveniles gestated on a control diet. Adult offspring raised by their biological dams showed the same response pattern; gestational BPA increased anxiety as compared with control diet. Our results show that prenatal BPA exposure affects social behavior and anxiety in the EPM. Moreover, some facet(s) of the infant-maternal interaction may modify these effects.

Assessment of bisphenol A exposure in Korean pregnant women by physiologically based pharmacokinetic modeling

The objective of this study was to predict the exposure to bisphenol A (BPA) after oral intake in human blood and tissues using physiologically based pharmacokinetic (PBPK) modeling. A refined PBPK model was developed taking into account of glucuronidation, biliary excretion, and slow absorption of BPA in order to describe the second peak of BPA observed following oral intake. This developed model adequately described the second peak and BPA concentrations in blood and various tissues in rats after oral administration. A prospective validation study in rats additionally supported the proposed model. For extrapolation to humans, a daily oral BPA dose of 0.237 mg/70 kg/d or 0.0034 mg/kg/d was predicted to achieve an average steady-state blood concentration of 0.0055 ng/ml (median blood BPA concentration in Korean pregnant women). This dose was lower than the reference dose (RfD, 0.016 mg/kg/d) and the tolerable daily intake established by the European Commission (10 μg/kg/d). Data indicate that enterohepatic recirculation may be toxicologically important as this pathway may increase exposure and terminal half-life of BPA in humans.

Bisphenol A levels in blood depend on age and exposure

We present two approaches to estimate blood concentrations of Bisphenol A (BPA). Simple kinetic principles were applied to calculate steady state plasma concentrations. A physiologically based model was used to simulate the blood concentration time profile in several age groups exploring the influence of not yet fully developed metabolic capacity on the blood concentrations in the newborn. Both approaches gave concordant results and are in excellent agreement with experimental results [Völkel, W., Colnot, T., Csanady, G.A., Filser, J.G., Dekant, W., 2002. Metabolism and kinetics of bisphenol A in humans at low doses following oral administration. Chem. Res. Toxicol. 15, 1281-1287]. The predictions also agree with published results obtained with a different physiologically based model. According to model simulations, BPA is present in the blood of the normal population at concentrations several orders of magnitude lower than most measurements reported in the literature. At the same external exposure level, the newborn is predicted to have 3 times greater blood concentration than the adult. This is due to the not yet fully developed glucuronidation activity in the newborn, not fully compensated by the unimpaired sulfation pathway. For the highest measured external BPA exposure, the predicted blood concentrations of 2.6 pg/ml (steady state concentration) and 8.2 pg/ml (peak concentration) in the adult are lower than the in vitro concentrations at which inhibiting adiponectin release from human adipocytes and stimulation of beta-cell production and secretion were observed.

Predicting plasma concentrations of bisphenol A in children younger than 2 years of age after typical feeding schedules, using a physiologically based toxicokinetic model

BACKGROUND

Concerns have recently been raised regarding the safety of potential human exposure to bisphenol A (BPA), an industrial chemical found in some polycarbonate plastics and epoxy resins. Of particular interest is the exposure of young children to BPA via food stored in BPA-containing packaging.

OBJECTIVES

In this study we assessed the age dependence of the toxicokinetics of BPA and its glucuronidated metabolite, BPA-Glu, using a coupled BPA-BPA-Glu physiologically based toxicokinetic (PBTK) model.

METHODS

Using information gathered from toxicokinetic studies in adults, we built a PBTK model. We then scaled the model to children < 2 years of age based on the age dependence of physiologic parameters relevant for absorption, distribution, metabolism, and excretion.

RESULTS

We estimated the average steady-state BPA plasma concentration in newborns to be 11 times greater than that in adults when given the same weight-normalized dose. Because of the rapid development of the glucuronidation process, this ratio dropped to 2 by 3 months of age. Simulation of typical feeding exposures, as estimated by regulatory authorities, showed a 5-fold greater steady-state BPA plasma concentration in 3- and 6-month-olds compared with adults, reflecting both a reduced capacity for BPA metabolism and a greater weight-normalized BPA exposure. Because of uncertainty in defining the hepatic BPA intrinsic clearance in adults, these values represent preliminary estimates.

CONCLUSIONS

Simulations of the differential BPA dosimetry between adults and young children point to the need for more sensitive analytical methods for BPA to define, with greater certainty, the adult hepatic BPA intrinsic clearance, as well as a need for external exposure data in young children.

Derivation of a bisphenol A oral reference dose (RfD) and drinking-water equivalent concentration

Human exposure to bisphenol A (BPA) is due to that found in the diet, and BPA and its metabolites were detected at parts per billion (or less) concentrations in human urine, milk, saliva, serum, plasma, ovarian follicular fluid, and amniotic fluid. Adverse health effects in mice and rats may be induced after parenteral injection or after massive oral doses. Controlled ingestion trials in healthy adult volunteers with 5 mg d16-BPA were unable to detect parent BPA in plasma despite exquisitely sensitive (limit of detection = 6 nM) methods, but by 96 h 100% of the administered dose was recovered in urine as the glucuronide. The extensive BPA glucuronidation following ingestion is not seen after parenteral injection; only the parent BPA binds plasma proteins and estrogen receptors (ER). The hypothesis that BPA dose-response may be described by a J- or U-shape curve was not supported by toxicogenomic data collected in fetal rat testes and epididymes (after repeated parenteral exposure at 2-400,000 microg/kg-d), where a clear monotonic dose-response both in the numbers of genes and magnitude of individual gene expression was evident. There is no clear indication from available data that the BPA doses normally consumed by humans pose an increased risk for immunologic or neurologic disease. There is no evidence that BPA poses a genotoxic or carcinogenic risk and clinical evaluations of 205 men and women with high-performance liquid chromatography (HPLC)-verified serum or urinary BPA conjugates showed (1) no objective signs, (2) no changes in reproductive hormones or clinical chemistry parameters, and (3) no alterations in the number of children or sons:daughters ratio. Results of benchmark dose (BMD10 and BMDL10) calculations and no-observed-adverse-effect level (NOAEL) inspections of all available and reproducible rodent studies with oral BPA found BMD and NOAEL values all greater than the 5 mg/kg-d NOAELs from mouse and rat multigeneration reproduction toxicity studies. While allometric and physiologically based pharmacokinetic (PBPK) models were constructed for interspecies scaling of BPA and its interaction with ER, multigeneration feeding studies with BPA at doses spanning 5 orders of magnitude failed to identify signs of developmental toxicity or adverse changes in reproductive tract tissues; the 5-mg/kg-d NOAELs identified for systemic toxicity in rats and mice were less than the oral NOAELs for reproductive toxicity. Thus, it is the generalized systemic toxicity of ingested BPA rather than reproductive, immunologic, neurobehavioral, or genotoxic hazard that represents the point of departure. Using U.S. Environmental Protection Agency (EPA) uncertainty factor guidance and application of a threefold database uncertainty factor (to account for the fact that the carcinogenic potential of transplacental BPA exposure has yet to be fully defined and comprehensive neurobehavioral and immunotoxicologic evaluations of BPA by relevant routes and at relevant doses have yet to be completed) to the administered dose NOAEL results in an oral RfD of 0.016 mg/kg-d. Assuming the 70-kg adult consumes 2 L of water each day and adopting the default 20% U.S. EPA drinking water relative source contribution yields a 100 microg/L BPA total allowable concentration (TAC).

Measurement of bisphenol A concentrations in human colostrum

Bisphenol A (BPA), an estrogenic endocrine disrupting chemical, has been reported to affect embryos and alter their postnatal development. In the present study, we measured the concentrations of BPA in human colostrum by a competitive enzyme-linked immunosorbent assay (ELISA) with the aim of understanding the present status of BPA burden in human breast milk in Shizuoka, Japan. Human colostral samples were collected from 101 healthy mothers within three days after delivery. The BPA concentrations of colostral samples were estimated by ELISA after the acetonitrile extraction and solid phase extraction column purification. BPA in 101 samples was detected in the concentration range of 1-7 ng ml(-1). The mean concentration of BPA was 3.41+/-0.13 (mean+/-SD) ng ml(-1). This is the first demonstration as to what BPA concentrations are in human colostrum. The BPA concentrations in colostrum were higher than those in blood sera samples obtained from healthy women in a previous study. In our study, there was no significant correlation between the concentrations of BPA in colostrum and the age and parity of mothers.

Toxicokinetics of bisphenol A in pregnant DA/Han rats after single i.v. application

Bisphenol A (BPA) is an important chemical in the production of epoxy resins and polycarbonate plastics, and basic monomers which are used for a variety of applications. Consumer exposure to BPA may be possible from migration of BPA from dental sealants or from polycarbonate or epoxy-lined food and drink containers. BPA is known to act as weak estrogen mimic in rodents, and there is a concern of adverse endocrine effects, especially from prenatal exposure to this potential 'endocrine disruptor'. To address this concern, we have studied the disposition and transplacental transfer of BPA in pregnant DA/Han rats on day 18 of gestation. The BPA concentrations were determined by GC/MS analysis in maternal blood, maternal organs (liver, kidney, uterus), placenta and fetuses (fetal liver and residual tissues) at different time-points (5-360 min) after intravenous administration of 10 mg BPA/kg body weight. Total BPA (aglycone and conjugates) was analyzed in all tissue samples after enzymatic hydrolysis and liquid/liquid extraction; in maternal plasma, total BPA and BPA aglycone were analyzed in parallel samples (with/without hydrolysis). Soon (5 min) after the i.v. injection a mean total BPA concentration of 3.8 microg/ml was found in maternal plasma; it declined in the first 2 h to 0.7 microg/ml. Early after injection, the majority of circulating BPA (almost 80%) was still in the aglycone form, but, metabolism by phase II enzymes decreased the BPA aglycone concentration to 0.3 microg/ml after 2 h. Despite this efficient conjugation, BPA was rapidly distributed in the organism: In well perfused organs peak concentrations for total BPA were attained 20-30 min after intravenous administration, with mean values of about 9.7 microg/g in maternal liver, 8.6 microg/g in kidneys, and 6.2 microg/g in the uterus. The peak values in other tissues were lower, with 4.0 microg/g for placenta, 3.3 microg/g for fetal liver, and 2.4 microg/g for residual fetus homogenate. The BPA levels in all tissues thereafter declined more or less in parallel with those in maternal blood. The rather similar concentration time course in placenta and fetal liver indicates that BPA is readily transferred across the placenta of DA/Han rats to the fetus. Our data on BPA disposition in DA/Han rats are discussed in the context of other kinetic studies with BPA in pregnant rats, and in relation to the previous results from our laboratory (Degen et al. Arch Toxicol 76:23-29, 2002a, b, c) demonstrating comparable transplacental transfer of daidzein, a phytoestrogen that accounts for a significant portion of total human exposure to potential endocrine disruptors.

Male reproductive toxicity of four bisphenol antioxidants in mice and rats and their estrogenic effect

Male mice and rats were fed a diet containing four bisphenol antioxidants, 2,2'-methylenebis(4-ethyl-6-tert-butylphenol) (ME), 2,2'-methylenebis(4-methyl -6-tert-butylphenol) (MM), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol) (BM), or 4,4'-thiobis(3-methyl-6-tert-butylphenol) (TM) at levels of 0.06-0.25% for 2 months. BM and TM decreased epididymal, seminal vesicular, prostate and preputial weights, and injured seminiferous tubules in mice in a dose-dependent fashion. BM and TM also reduced sex accessory organ weights and sperm production capacity in rats, but MM and ME were more toxic to rats than BM and TM. ME and MM did not bind ERalpha up to 10(-3) M, while BM and TM competitively bound ERalpha against beta-estradiol (E2). Fifty percent inhibitory concentrations (IC50 s) of BM, TM, and bisphenol A (positive control) against E2-binding were 7.3 x 10(-6) M, 1.8 x 10(-5) M, and 1.4 x 10(-5) M, respectively. When ovariectomized (OVX) mice were sc administered TM at doses of 60 and 300 mg/kg/day for 4 days, or when OVX mice were fed BM in the diet at a level of 0.25% for 2 months, uterine weight was significantly increased. These results suggest that BM and TM are weakly toxic, possibly through an estrogenic mechanism to male reproductive organs in mice as well as rats, while MM and ME may be the direct testicular toxins in rats but not mice.

QUANTITATION OF BISPHENOL A AND BISPHENOL A GLUCURONIDE IN BIOLOGICAL SAMPLES BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

Bisphenol A (BPA) is a weak estrogen. Pharmacokinetic studies of BPA have demonstrated a rapid and extensive metabolism of BPA to the nonestrogenic BPA-monoglucuronide (BPA-gluc). Some investigators have reported that BPA was found at parts per billion concentrations in the tissues or urine of humans without known exposure to BPA. This work developed a rapid and sensitive method for the determination of BPA and BPA-gluc in plasma and urine based on liquid chromatography-tandem mass spectrometry. The liquid chromatography-electrospray ionization-tandem mass spectrometry method for quantitation of BPA and BPA-gluc uses stable isotope-labeled internal standards. A linear ion trap mass spectrometer permits identification and quantitation of BPA-gluc and BPA without sample workup. Development of separation conditions reduced the BPA-background in solvent samples to below 2.5 pmol/ml for BPA. Limit of quantitation (LOQ) for BPA in control urine was 15 pmol/ml; LOQ for BPA-gluc was 65 pmol/ml. Application of the method to urine samples from human subjects (n = 6) after administration of 25 microg of BPA/person (estimated maximum human daily intake) permitted the determination of excretion kinetics for BPA-gluc; BPA was below the LOD in all except two of the samples. In urine or blood samples of human subjects (n = 19) without intentional exposure to BPA, BPA concentrations were always below the limit of detection ( approximately 2.5 pmol/ml) with or without prior glucuronidase treatment. The results show that care is required for analysis of BPA and its major metabolite BPA-gluc. The LOD obtained and the absence of detectable levels of BPA in samples from individuals suggests that general exposure of humans to BPA is much lower than the worst-case exposure scenario developed.

Evaluation of Oral and Intravenous Route Pharmacokinetics, Plasma Protein Binding, and Uterine Tissue Dose Metrics of Bisphenol A: A Physiologically Based Pharmacokinetic Approach

Bisphenol A (BPA) is a weakly estrogenic monomer used in the production of polycarbonate plastic and epoxy resins, both of which are used in food contact and other applications. A physiologically based pharmacokinetic (PBPK) model of BPA pharmacokinetics in rats and humans was developed to provide a physiological context in which the processes controlling BPA pharmacokinetics (e.g., plasma protein binding, enterohepatic recirculation of the glucuronide [BPAG]) could be incorporated. A uterine tissue compartment was included to allow the correlation of simulated estrogen receptor (ER) binding of BPA with increases in uterine wet weight (UWW) in rats. Intravenous- and oral-route blood kinetics of BPA in rats and oral-route plasma and urinary elimination kinetics in humans were well described by the model. Simulations of rat oral-route BPAG pharmacokinetics were less exact, most likely the result of oversimplification of the GI tract compartment. Comparison of metabolic clearance rates derived from fitting rat i.v. and oral-route data implied that intestinal glucuronidation of BPA is significant. In rats, but not humans, terminal elimination rates were strongly influenced by enterohepatic recirculation. In the absence of BPA binding to plasma proteins, simulations showed high ER occupancy at doses without uterine effects. Restricting free BPA to the measured unbound amount demonstrated the importance of including plasma binding in BPA kinetic models: the modeled relationship between ER occupancy and UWW increases was consistent with expectations for a receptor-mediated response with low ER occupancy at doses with no response and increasing occupancy with larger increases in UWW.

Stimulation of catecholamine synthesis by environmental estrogenic pollutants

Environmental estrogenic pollutants are compounds that have been shown to have estrogenic effects on fetal development and reproductive systems. Less attention, however, has been paid to their influence on neuronal functions. We report here the effects of estrogenic pollutants on catecholamine synthesis in bovine adrenal medullary cells used as a model system of noradrenergic neurons. Treatment of cultured bovine adrenal medullary cells with p-nonylphenol and bisphenol A at 10 nM for 3 d stimulated [14C]catecholamine synthesis from [14C]tyrosine and tyrosine hydroxylase activity, an effect that was not inhibited by ICI 182,780, an antagonist of estrogen receptors. Significant effects of p-nonylphenol on [14C]catecholamine synthesis were observed at 0.1 nM, which is 45 times lower than that of the international regulatory standard (4.5 nM), and the maximum effects were around 10-100 nM. The concentrations (0.1-10 nM) used in the present study are similar to the range observed in rivers in the United States or Europe. On the other hand, short-term treatment of cells with 10 nM p-nonylphenol for 10 min also activated tyrosine hydroxylase, which was suppressed by U0126, an inhibitor of MAPK kinase. Furthermore, treatment of cells with p-nonylphenol for 5 min increased the phospho-p44/42MAPK in a concentration-dependent (1-1000 nM) manner, whereas p-nonylphenol (100 nm, 2 d) enhanced both levels of non-phospho- and phospho-p44/42MAPK. These findings suggest that short-term and long-term treatment of cells with estrogenic pollutants at environmental concentrations stimulates catecholamine synthesis and MAPK through an estrogen receptor-independent pathway.

Physiologically based pharmacokinetics of bisphenol A

A physiologically based pharmacokinetic (PBPK) model consisting of vein, artery, lung, liver, spleen, kidneys, heart, testes, muscle, brain, adipose tissue, stomach, and small intestine was developed to predict the tissue distribution and blood pharmacokinetics of bisphenol A in rats and humans. To demonstrate the validity of the developed PBPK model, bisphenol A was administered to rats by multiple iv injections to steady state. The PBPK model predicted the steady-state levels of bisphenol A in blood and various tissues observed in rats after multiple iv injections. The PBPK model was further applied to predict blood and various tissue levels of bisphenol A in a 70 kg-human after single iv injection (5-mg dose) and multiple oral administrations to steady state (100-mg doses every 24 h). The simulated steady-state human blood levels (0.9-1.6 ng/ml) were comparable to basal blood levels of bisphenol A reported in literature (1.49 ng/ml). Furthermore, pharmacokinectic parameters of CL (116.6 L/h), Vss (141.8 L), and t1/2 (76.8 min) predicted for humans were comparable to those previously predicted by simple allometric scaling. This PBPK model may provide insights into the tissue distribution characteristics as a result of human exposure to bisphenol A.

Bisphenol-A and estradiol exert novel gene regulation in human MCF-7 derived breast cancer cells

Xenoestrogens such as bisphenol-A (BPA) can mimic endogenous 17beta-estradiol (E2) in vitro and in vivo through binding the estrogen receptor (ER), and modulating target gene expression. In the present study, we compared global gene regulation by BPA and E2 in estrogen responsive (ERalpha-HA) human breast cancer cells derived from the MCF-7 cell line. The ERalpha-HA cells (stably over-expressing ERalpha) were exposed to E2 (10(-8)M) or BPA (10(-6)M), for 3h followed by analysis of global gene expression. More than 40 transcripts were significantly changed in ERalpha-HA cells, with many being unique to BPA. At least 15 genes were modulated by BPA in the ER-null C4-12 cell line, indicating ER independent activity. Utilizing quantitative reverse transcription-polymerase chain reaction (RT-PCR), we confirmed BPA and E2 mediated regulation of four selected genes. A consensus Alu-type estrogen responsive element (ERE) was found in the Wiskott-Aldrich syndrome protein (WASP) gene, which conferred responsiveness to BPA and E2 in a reporter gene assay. Significant stimulation was seen only in ERalpha expressing cells, thus indicating a functional ERE. Taken together these data illustrate novel gene regulation by BPA and E2, which has implications for in vivo actions and previous reports of additive and synergistic effects on breast cancer cell growth.

Inhibition of the norepinephrine transporter function in cultured bovine adrenal medullary cells by bisphenol A

We report here the effects of an environmental estrogen, bisphenol A, on norepinephrine (NE) transporter function in cultured bovine adrenal medullary cells. The effects of bisphenol A were compared to those of 17beta-estradiol. Bisphenol A significantly inhibited [3H]NE uptake by the cells in a concentration-dependent manner (1-100 microM). Kinetic analysis revealed that bisphenol A, as well as 17beta-estradiol, noncompetitively inhibited [3H]NE uptake. Bisphenol A and 17beta-estradiol inhibited the specific binding of [3H]desipramine to plasma membranes isolated from bovine adrenal medulla. As shown by Scatchard analysis of [3H]desipramine binding, bisphenol A increased the dissociation constant (K(d)) and decreased the maximal binding (B(max)), indicating a mixed type of inhibition. 17beta-Estradiol increased the K(d) without altering the B(max), thereby indicating competitive inhibition. The present findings suggest that bisphenol A inhibits the function of the NE transporter by acting on a site different from that of 17beta-estradiol in the adrenal medulla and probably in the brain noradrenergic neurons.

Bisphenol a exposure causes meiotic aneuploidy in the female mouse

BACKGROUND

There is increasing concern that exposure to man-made substances that mimic endogenous hormones may adversely affect mammalian reproduction. Although a variety of reproductive complications have been ascribed to compounds with androgenic or estrogenic properties, little attention has been directed at the potential consequences of such exposures to the genetic quality of the gamete.

RESULTS

A sudden, spontaneous increase in meiotic disturbances, including aneuploidy, in studies of oocytes from control female mice in our laboratory coincided with the accidental exposure of our animals to an environmental source of bisphenol A (BPA). BPA is an estrogenic compound widely used in the production of polycarbonate plastics and epoxy resins. We identified damaged caging material as the source of the exposure, as we were able to recapitulate the meiotic abnormalities by intentionally damaging cages and water bottles. In subsequent studies of female mice, we administered daily oral doses of BPA to directly test the hypothesis that low levels of BPA disrupt female meiosis. Our results demonstrated that the meiotic effects were dose dependent and could be induced by environmentally relevant doses of BPA.

CONCLUSIONS

Both the initial inadvertent exposure and subsequent experimental studies suggest that BPA is a potent meiotic aneugen. Specifically, in the female mouse, short-term, low-dose exposure during the final stages of oocyte growth is sufficient to elicit detectable meiotic effects. These results provide the first unequivocal link between mammalian meiotic aneuploidy and an accidental environmental exposure and suggest that the oocyte and its meiotic spindle will provide a sensitive assay system for the study of reproductive toxins.

Thyroid hormone action is disrupted by bisphenol A as an antagonist

Bisphenol A (BPA), a monomer of polycarbonate plastics, has been shown to possess estrogenic properties and act as an agonist for the estrogen receptors. Although an epidemiologically based investigation has suggested that some chemicals could disrupt thyroid function in animals, the effects on thyroid hormone receptors (TRs) are unknown. We show here that BPA inhibits TR-mediated transcription by acting as an antagonist. In the transient gene expression experiments, BPA suppressed transcriptional activity that is stimulated by thyroid hormone (T(3)) in a dose-dependent manner. The inhibitory effects were observed in the presence of physiological concentrations of T(3). In contrast, in the case of negatively regulated TSHalpha promoter, BPA activated the gene transcription that is suppressed by T(3). To elucidate possible mechanisms of the antagonistic action of BPA, the effects on T(3) binding and cofactor interaction with TR were examined. The K(i) value for BPA was 200 micro M when assessed by inhibition of [(125)I]T(3) binding to rat hepatic nuclear TRs. In a mammalian two-hybrid assay, BPA recruited the nuclear corepressor to the TR. These results suggest that BPA could displace T(3) from the TR and recruit a transcriptional repressor, resulting in gene suppression. This is the first report that BPA can antagonize T(3) action at the transcriptional level. BPA may disrupt the function of various types of nuclear hormone receptors and their cofactors to disturb our internal hormonal environment.

Pharmacokinetic scaling of bisphenol A by species-invariant time methods

1. The study was performed to predict the pharmacokinetic disposition of bisphenol A in humans using simple allometry and several species-invariant time methods based on animal data. Bisphenol A was injected intravenously to mouse, rat, rabbit and dog (1-2 mg kg(-1) doses). 2. The obtained serum concentration-time profiles were best described by bi-exponential equations in all these animal species, with the mean Cl, V(ss) and t(1/2) of 0.3 l h(-1), 0.1 litres and 39.9 min in mouse, 1.9 l h(-1), 1.3 litres and 37.6 min in rat, 12.6 l h(-1), 7.1 litres and 40.8 min in rabbit, and 27.1 l h(-1), 20.0 litres and 43.7 min in dog, respectively. 3. The human pharmacokinetic parameters of Cl, V(ss) and t(1/2) were predicted by simple allometry as well as by normalization according to species-invariant times of kallynochrons, apolysichrons and dienetichrons. 4. The simple allometric scaling and different time transformation methods predicted the human Cl, V(ss) and t(1/2) ranging from 46.0 to 127.1 l h(-1), 125.3 to 229.7 litres and 43.6 to 196.2 min, respectively. Species-invariant time transformations showed that all animal data from the four species were superimposable. These preliminary parameter values may be useful in interpreting toxicity data in humans on environmental exposure to bisphenol A.

Determination of bisphenol A in rat brain by microdialysis and column switching high-performance liquid chromatography with fluorescence detection

A sensitive column switching HPLC-fluorescence detection for determination of bisphenol A (BPA) in rat brain by coupling with microdialysis was developed. A microdialysis probe was inserted into the hypothalamus of rat brain and an artificial cerebrospinal fluid was used for perfusion. BPA in brain dialysate was subjected to a fluorescent derivatization with 4-(4,5-diphenyl-1H-imidazol-2-yl)benzoyl chloride (DIB-Cl), and the excess reagent was removed by a column-switching technique. Separation was carried out on two ODS semimicro-columns with the mobile phase of acetonitrile-H(2)O-methanol-tetrahydrofuran (55:10:35:2.5, v/v) and acetonitrile-0.1 M acetate buffer (pH 3.0)-methanol (35:10:55, v/v) at a flow rate of 0.10 and 0.15 mL/min for a precolumn and a separation column, respectively. Fluorescence intensity was monitored at 475 nm with excitation of 350 nm. BPA could be sensitively detected at 0.3 ppb in 60 micro L brain microdialysate at a signal-to-noise ratio of 3. By the proposed method, concentrations of BPA in rat brain and plasma were monitored for 8 h after single i.v. or oral administration. It is proved that BPA is capable of penetrating the blood-brain barrier. The ratio of the area under the concentration-time curve of BPA in rat brain to that in blood was estimated to be about 3.0-3.8%.

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.

Bisphenol A inhibits Cl(-) secretion by inhibition of basolateral K+ conductance in human airway epithelial cells

There has been growing concern about the potential threat of hormone-disrupting chemicals like bisphenol A to various aspects of animal and human health. We studied the effects of bisphenol A on the Cl(-) secretion in human airway epithelial Calu-3 cells. Pretreatment with bisphenol A (IC(50) = 60 microM, for 30 min) prevented isoproterenol (10 nM)-generated short-circuit current (I(sc)) more potently than 17beta-estradiol or tamoxifen (IC(50) = 1 mM). 5'-Nitro-2-(3-phenylpropylamino) benzoate-sensitive apical conductance potentiated by isoproterenol was not affected by the pretreatment with either of these estrogenic compounds. The effects of bisphenol A were simulated in I(sc) responses to forskolin (10 microM) and 8-bromo-cAMP (1 mM). Nystatin permeabilization of Calu-3 monolayers revealed that bisphenol A attenuated 8-bromo-cAMP-induced basolateral K+ current, which is sensitive to clotrimazole (30 microM) and insensitive to charybdotoxin (100 nM), without affecting the apical Cl(-) current. Bisphenol A, but neither 17beta-estradiol nor tamoxifen, interrupted the charybdotoxin-sensitive component of I(sc) stimulated by 1-ethyl-2-benzimidazolinone (1-EBIO; 500 microM). The inhibitory effects of bisphenol A on these Cl(-) secretory stimuli were remarkable when applied to the apical rather than the basolateral membrane. Alternatively, long-term incubation of bisphenol A (1 microM; 12-72 h) had no discernible effect on isoproterenol- and 1-EBIO-induced Cl(-) secretion. These findings indicate that short-term exposure to bisphenol A attenuates transepithelial Cl(-) secretion through inhibition of both cAMP- and Ca(2+)-activated K+ channels on the basolateral membrane, interacting from the cytosolic surface in Calu-3 cells.

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.