Bioavailability and mammary excretion of bisphenol a in Sprague-Dawley rats

Predictive Performance of Next Generation Physiologically Based Kinetic (PBK) Model Predictions in Rats Based on In Vitro and In Silico Input Data

The goal of the present study was to assess the predictive performance of a minimal generic rat physiologically based kinetic (PBK) model based on in vitro and in silico input data to predict peak plasma concentrations (Cmax) upon single oral dosing. To this purpose, a dataset was generated of 3960 Cmax predictions for 44 compounds, applying different combinations of in vitro and in silico approaches for chemical parameterization, and comparison of the predictions to reported in vivo data. Best performance was obtained when (1) the hepatic clearance was parameterized based on in vitro measured intrinsic clearance values, (2) the method of Rodgers and Rowland for calculating partition coefficients, and (3) in silico calculated fraction unbound plasma and Papp values (the latter especially for very lipophilic compounds). Based on these input data, the median Cmax of 32 compounds could be predicted within 10-fold of the observed Cmax, with 22 out of these 32 compounds being predicted within 5-fold, and 8 compounds within 2-fold. Overestimations of more than 10-fold were observed for 12 compounds, whereas no underestimations of more than 10-fold occurred. Median Cmax predictions were frequently found to be within 10-fold of the observed Cmax when the scaled unbound hepatic intrinsic clearance (Clint,u) was either higher than 20 l/h or lower than 1 l/h. Similar findings were obtained with a test set of 5 in-house BASF compounds. Overall, this study provides relevant insights in the predictive performance of a minimal PBK model based on in vitro and in silico input data.

Investigating the glucuronidation and sulfation pathways contribution and disposition kinetics of Bisphenol S and its metabolites using LC-MS/MS-based nonenzymatic hydrolysis method

Despite showing serious health consequences and widespread exposure, the toxicokinetic information required to evaluate the health risks of BPS is insufficient. Thus, we aim to describe the comprehensive toxicokinetics of BPS and its glucuronide (BPS-G) and sulfate (BPS-S) metabolites in rats. Simultaneous quantification of BPS and its metabolites (authentic standards) was accomplished using UPLC-MS/MS method. BPS displayed rapid absorption, extensive metabolism and fast elimination after oral administration. Following intravenous administration, BPS exhibited CL (8.8 L/h/kg) higher than the rat hepatic blood flow rate suggesting the likelihood of extrahepatic clearance. The CL value differed from those reported previously (sheep and piglets) and the probable reason could be attributed to dose- and/or interspecies differences. BPS was extensively metabolized and excreted primarily through urine as BPS-G (∼56%). BPS and BPS-S exhibited a high protein binding capacity in comparison to BPS-G. In in vitro metabolic stability study, BPS was predominantly metabolized through glucuronidation. The predicted in vivo hepatic clearance of BPS suggested it to be a high and intermediate clearance chemical in rats and humans, respectively. The significant interspecies difference observed in the clearance of BPS between rats and humans indicated that toxicokinetics of BPS should be considered for health risk assessment in humans.

Preliminary toxicokinetic study of BPA in lactating dairy sheep after repeated dietary and subcutaneous administration

Dietary intake is the predominant route of human exposure to bisphenol A and one of the important food commodities is milk. The aim of our study was to preliminarily evaluate the bisphenol A exposure and disposition in sheep milk after repeated dietary and subcutaneous administration of a relatively low dose (100 µg/kg of b. w./day) of bisphenol A to a sheep. On the basis of blood plasma sampling, milk sampling and HPLC analysis, we developed the toxicokinetic model. With the toxicokinetic model we showed that most likely only free bisphenol A passes into the mammary gland and is subsequently conjugated there. The percentage of the dose eliminated with milk was less than 0.1%, regardless of the route of bisphenol A administration. It is proven that the bisphenol A is eliminated through the milk of lactating sheep. However, the amounts excreted in the milk that were detected in this study are minimal.

Fetal-Perinatal Exposure to Bisphenol-A Affects Quality of Spermatozoa in Adulthood Mouse

Bisphenol-A (BPA) is considered an endocrine disruptor with estrogenic activity. It is described as an environment-polluting industrial chemical whose adverse effects on the male reproductive system depend on the period of exposure (i.e., fetal, prepubertal, or adult life). We exposed male mice to BPA during the fetal-perinatal period (from 10 days post coitum to 31 days post partum) and investigated the impact of this early-life exposure on gamete health in adulthood animals at 78 days of age. Both in control and BPA-exposed mice, viability and motility of spermatozoa, as well as sperm motility acquisition and chromatin condensation of spermatozoa, have been evaluated. Results reveal harmful effect of BPA on viability and motility of sperm cells as well as on chromatin condensation status during epididymal maturation of spermatozoa. In particular, BPA exposure interferes with biochemical mechanism useful to stabilize sperm chromatin condensation, as it interferes with oxidation of thiol groups associated to chromatin.

A New LC-MS/MS Method for Simultaneous and Quantitative Detection of Bisphenol-A and Steroids in Target Tissues: A Power Tool to Characterize the Interference of Bisphenol-A Exposure on Steroid Levels

Bisphenol A (BPA), an endocrine disruptor, may affect in situ steroidogenesis and alter steroids levels. The present work proposes a liquid chromatography tandem mass spectrometry method to simultaneously quantify BPA, 17β-Estradiol and testosterone in two target tissues: testis and visceral fat mass. Analytes were isolated and lipophilic impurities removed by two serial steps: liquid-liquid and solid phase extraction. All compounds were separated in a single gradient run by Kinetex F5 column and detected via multiple reaction monitoring using a triple quadrupole with a TurboIon electrospray source in both negative and positive modes. The method is selective and very sensitive. In the investigated concentration range, the linearity of the detector response is verified in both tissues. The use of specific SPE cartridges for affinity chromatography purification allows obtaining high percentages of process efficiency (68.0-83.3% for testicular tissue; 63.7-70.7% for visceral fat mass). Good repeatability and reproducibility was observed. The validated method can be efficiently applied for direct biological monitoring in testis and visceral fat mass from mice exposed to BPA. The quantification of compounds in a single assay could be achieved without a loss of sensitivity.

Mass spectrometry investigation of DNA adduct formation from bisphenol A quinone metabolite and MCF-7 cell DNA

Bisphenol A (BPA) is a widely used additive in the plastic industry and has been reported to have genotoxicity. A hypothesis that BPA may enhance breast cancer risk through the formation of its metabolic intermediate or DNA adduct has been proposed. In this study, breast cancer cell MCF-7 was cultured and the cellular DNA was extracted from the cells. The adducts of bisphenol A 3,4-quinone (BPAQ) with 2'-deoxyguanosine (dG), calf thymus DNA and MCF-7 cell DNA were investigated. DNA adducts were characterized by using electrospray ionization Orbitrap high-resolution mass spectrometry and tandem mass spectrometry. The BPA-DNA adducts of BPAQ with dG, calf thymus and MCF-7 cell DNA were identified as 3-hydroxy-bisphenol A-N7-guanine (3-OH-BPA-N7Gua). The MS/MS fragmentation pathway of 3-OH-BPA-N7Gua was proposed based on obtained accurate mass data. BPA quinone metabolites can react with MCF-7 cell DNA in vitro. The findings provide evidence that BPA might covalently bind to DNA in MCF-7 cells mediated by quinone metabolites, which may increase our understanding of health risk associated with BPA exposure.

Orally Administered Bisphenol A Disturbed Antigen Specific Immunoresponses in the Naïve Condition

Bisphenol A [2,2-bis(4-hydoxyphenyl)propane; BPA] is an endocrine disrupter widely used in polycarbonate plastics and epoxy resins. We investigated the effects of orally administered BPA on antigen-specific responses of the naïve immune system.BPA was orally administered to T cell receptor transgenic mice, and the antigen-specific responses of immune cells were investigated. Administered BPA moderately reduced interleukin (IL)-2, 4, and interferon (IFN)-gamma secretion and increases in IgA and IgG2a production.Additionally, it was found that orally administered BPA increased antigen-specific IFN-gamma production of T cells and modified whole antigen presenting cells (APCs) to suppress antigen-specific cytokine production from T cells. These findings suggest that BPA can augment the Th1-type responses of naïve immune systems, though the bioavailability of orally administered BPA was low in our experiments.

A systematic review of Bisphenol A "low dose" studies in the context of human exposure: a case for establishing standards for reporting "low-dose" effects of chemicals

Human exposure to the chemical Bisphenol A is almost ubiquitous in surveyed industrialized societies. Structural features similar to estrogen confer the ability of Bisphenol A (BPA) to bind estrogen receptors, giving BPA membership in the group of environmental pollutants called endocrine disruptors. References by scientists, the media, political entities, and non-governmental organizations to many toxicity studies as "low dose" has led to the belief that exposure levels in these studies are similar to humans, implying that BPA is toxic to humans at current exposures. Through systematic, objective comparison of our current, and a previous compilation of the "low-dose" literature to multiple estimates of human external and internal exposure levels, we found that the "low-dose" moniker describes exposures covering 8-12 orders of magnitude, the majority (91-99% of exposures) being greater than the upper bound of human exposure in the general infant, child and adult U.S. Population. "low dose" is therefore a descriptor without specific meaning regarding human exposure. Where human exposure data are available, for BPA and other environmental chemicals, reference to toxicity study exposures by direct comparison to human exposure would be more informative, more objective, and less susceptible to misunderstanding.

Lactational transfer of bisphenol A in Sprague-Dawley rats

Bisphenol A (BPA), an important industrial chemical to which humans are exposed on a daily basis, has long been associated with endocrine disruption in experimental animal models. Such exposures are of concern, particularly during fetal and early neonatal periods, because of greater vulnerability of developing organs to aberrant endocrine signaling. Although rarely reported, information about internal exposures to the receptor-active aglycone form of BPA during the perinatal period is essential to accurate assessment of potential risks. Lactating Sprague-Dawley dams were treated by daily gavage with 100 μg/kg bw d6-BPA starting at birth. Conjugated and aglycone forms of BPA were then measured by using LC/MS/MS in milk from lactating dams on PND 7 and in serum from dams and their pups on PND 10. All samples were collected 1h after dosing, a time selected to produce nearly maximal levels. While aglycone BPA was detected in all dam serum and milk samples, none was detected in pup serum (<0.2 nM). Doses delivered to pups lactationally, estimated from milk concentrations and body weights, were 300-fold lower than the dose administered to the dams. Similarly, serum concentrations of total BPA in pups were 300-fold lower than those in their dams. Furthermore, plasma concentrations of total BPA in PND 10 rat pups were 500-fold lower than peak levels achieved following direct oral delivery of the same dose to the same age pups. These findings of significant dose attenuation for the active aglycone form of BPA, relative to that of the dam, suggest high potency for toxicological effects derived exclusively from lactational transfer. Alternatively, studies that include lactational exposure and report minimal effects from BPA should consider the possibility that inadequate internal exposures were achieved during the critical postnatal period.

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.

Formation of adducts by bisphenol A, an endocrine disruptor, in DNA in vitro and in liver and mammary tissue of mice

Endocrine disruptors (EDs) represent a major toxicological and public health issue, and the xenoestrogen bisphenol A (BPA) has received much attention due to its high production volume and widespread human exposure. Also, due to its similarity to diethylstilbestrol, a known human carcinogen, BPA has been investigated for its genotoxic and carcinogenic properties, but the results have been either inconclusive or controversial. Metabolically activated BPA has previously been shown to form DNA adducts both in vitro and in rat liver. The present study was designed (a) to assess the sensitivity threshold of DNA-adduct detection by 32P-postlabelling in an acellular system and (b) to evaluate the formation of DNA adducts in both liver and mammary cells of female CD-1 mice receiving BPA in their drinking water (200 mg/kg body weight) for eight consecutive days. The reaction of BPA with calf thymus DNA, in the presence of S9 mix, resulted in a dose-dependent formation of multiple DNA adducts, with a detection limit of approximately 10 ng of this ED under our experimental conditions. Administration of BPA to mice confirmed that DNA adducts are formed in liver (3.4-fold higher levels than in controls). In addition, new evidence is provided that DNA adducts are formed in target mammary cells (4.7-fold higher than in controls). Although DNA adducts do not necessarily evolve into tumours or other chronic degenerative diseases, the formation of these molecular lesions in target mammary cells may bear relevance for the potential involvement of BPA in breast carcinogenesis.

Potential risk of bisphenol A migration from polycarbonate containers after heating, boiling, and microwaving

The migration levels of bisphenol A (BPA) were analyzed in food samples by high-performance liquid chromatography (HPLC) from polycarbonate (PC) bottles subjected to simulated use by heating with microwave, heating in a boiling water bath, or filling them with boiling hot water (100 degrees C). Migration testing performed in PC bottles filled with steamed rice or hot cooked pork, standing at room temperature, or heated in a boiling water bath (100 degrees C) showed that BPA was not detected at the limit of detection (LOD) of 1 microg/L (ppb). In contrast, heating by microwaving to 100 degrees C for 9 min increased BPA migration levels from 6 to 18 ppb and from 5 to 15 ppb for steamed rice or for cooked pork, respectively. In addition, 3 different PC bottles were tested by filling them with boiling hot water (100 degrees C) and leaving them to stand at room temperature for up to 3 h. The mean BPA levels from the bottles increased in a time-dependent manner, with the range of not detected (ND) to 2.5 ppb after 60 min. However, none of the PC bottles released BPA at levels that exceed the recently established specific migration limits (SML) of 600 ppb established by European Union and Korea Food and Drug Administration (KFDA). Data suggest that the use of PC plastic bottles in our daily life is considered safe in Korea.

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).

Downregulation of peritoneal macrophage activity in mice exposed to bisphenol A during pregnancy and lactation

Bisphenol A (BPA) is an environmental endocrine disrupter that is known to be transferred to the fetus via the placenta and to the neonate via milk. In this study, we investigated BPA-induced alterations of the activities of murine peritoneal macrophages in dams and 7 week old offspring of dams exposed to BPA from gestational day 7 until lactation on day 21 after delivery, i.e. 34-36 days. BPA was administered in drinking water at three doses, 15, 75, and 300 mg/L. Dams were sacrificed 21 days after delivery and offspring at the age of 7 weeks. Peritoneal macrophages were cultured in the presence of LPS or LPS plus IFN-gamma for 2 or 4 days. We found that nitric oxide (NO) production by maternal macrophages was significantly decreased in a BPA-dose dependent manner. However, while a significant reduction of NO production by macrophages in the offspring was observed at BPA concentrations of 75 mg/L and 300 mg/L in drinking water, this effect was not seen at the lowest concentration of 15 mg/L. Similar inhibition of tumor necrosis factor-alpha (TNF-alpha) production was observed with macrophages from both BPA-exposed dams and offspring. Thus, our results suggest that exposure to BPA during gestation and lactation induces downregulation of the activities of macrophages in both dams and offspring.

Influence of bisphenol a on developing rat estrogen receptors and some cytokines in rats: a two-generational study

Bisphenol A (BPA) is an industrial chemical with estrogenic activity. In our study, 40 rats were given BPA at 4, 40, and 400 mg/kg per day. Controls were treated with corn oil of same volume until the offspring were 30 d olds. At the end of the experiment, the expression of estrogen receptor (ER)-alpha and the mRNA levels of inerleukin (IL)-2, IL-12, interferon (IFN)-gamma, and tumor necrosis factor (TNF)-alpha in spleens were investigated by Western blotting and real-time reverse-transcription polymerase chain reaction (RT-PCR). The histopathological change of organs was observed. The results showed that bisphenol A reduced the expression of ER-alpha in males of the high-dose group in the F(0) generation and in middle- and high-dose groups of the F(1) generation (p < .05), but increased it in females in the high-dose group of the F(0) generation and in middle- and high-dose groups of the F(1) generation (p < .05). The levels of IL-2, IL-12, IFN-gamma, and TNF-alpha in spleens were downregulated in all groups in contrast to controls (p < .05). We also found some histological changes in spleens, livers, and kidneys. These findings demonstrated that bisphenol A has estrogen-like activity and might affect some immune organs and parameters.

Human exposure to bisphenol A (BPA)

The plastic monomer and plasticizer bisphenol A (BPA) is one of the highest volume chemicals produced worldwide. BPA is used in the production of polycarbonate plastics and epoxy resins used in many consumer products. Here, we have outlined studies that address the levels of BPA in human tissues and fluids. We have reviewed the few epidemiological studies available that explore biological markers of BPA exposure and human health outcomes. We have examined several studies of levels of BPA released from consumer products as well as the levels measured in wastewater, drinking water, air and dust. Lastly, we have reviewed acute metabolic studies and the information available about BPA metabolism in animal models. The reported levels of BPA in human fluids are higher than the BPA concentrations reported to stimulate molecular endpoints in vitro and appear to be within an order of magnitude of the levels needed to induce effects in animal models.

Toxicokinetics of bisphenol A in rats, monkeys and chimpanzees by the LC–MS/MS method

We examined the toxicokinetics of bisphenol A (BPA) in F344 rats, cynomolgus monkeys and chimpanzees. Serum BPA levels were quantified using the LC-MS/MS method. After oral administration at 10 mg/kg, the maximum concentration in the serum (C(max)) and the area under the serum concentration curve (AUC) of BPA in cynomolgus monkeys and chimpanzees were greater than in rats. After oral administration at 100 mg/kg, AUC during the first 4h (AUC(0-->4h)) in cynomolgus monkeys was greater than in rats. In rats, the serum BPA levels were increased again 6h or later after oral administration at each dose, which suggested the enterohepatic circulation of BPA in rats. After subcutaneous administration at 10 mg/kg, the AUCs were ranked in the following order: cynomolgus monkeys>chimpanzees>rats, and C(max) in cynomolgus monkeys was greater than in rats and chimpanzees. After subcutaneous administration at 100 mg/kg to cynomolgus monkeys and rats, both the C(max) and AUCs in cynomolgus monkeys were greater than in rats. In all species, the oral administration of BPA resulted in much lower C(max) and AUCs than subcutaneous administration at the corresponding doses, indicating the low bioavailability of oral administration. This result suggests that BPA undergoes an extensive first-pass metabolism in these animal species. AUCs of subcutaneous administration and the AUC (0-->4h) of oral administration in the two primates were greater than that in rats. Because the systemic clearance for BPA is assumed to be dependent on the hepatic blood flow-rate, the high AUCs in primates are considered to be due to the lower systemic clearance by a lower hepatic blood flow-rate in primates than in rats. In addition, the toxicokinetics of the metabolites of BPA were examined. After the oral administration of 10 mg/kg BPA, both C(max) and AUCs of BPA metabolites were ranked in the following order: cynomolgus monkeys>chimpanzees>rats, and the terminal elimination half-life (T(1/2)) in rats was greater than that in cynomolgus monkeys and chimpanzees, suggesting the enterohepatic circulation of BPA in rats. From these results, the systemic clearance of BPA in primates is considered to be close to that in humans due to the similarity of the hepatic blood flow-rate. Furthermore, the major elimination route of BPA metabolites in primates is assumed to be renal excretion, as in humans, because the enterohepatic circulation that was observed in rats was not observed. In conclusion, primates are thought to be served as a valuable surrogate model for the toxicokinetics of BPA in humans.

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

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

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.

Xenoestrogens and the induction of proliferative effects in breast cancer cells via direct activation of oestrogen receptor alpha

Environmental contamination with a variety of industrial products has been associated with developmental and reproductive abnormalities in wildlife species. Increasing evidence has suggested that bisphenol A (BPA) and 4-nonylphenol (NPH), two major endocrine-disrupting chemicals, might be responsible for adverse effects on humans as a consequence of ubiquitous use together with potential oestrogen-like activity. To provide insight into the oestrogen-like nature of BPA and NPH, their ability to activate a reporter gene construct via an oestrogen response element in the hormone-dependent breast cancer cell lines MCF7 and T47D was ascertained. Both compounds transactivated the endogenous oestrogen receptor (ER) alpha in a direct fashion since the anti-oestrogen 4-hydroxytamoxifen abolished the response. In addition, using steroid-receptor-negative HeLa cells engineered to express ERalpha and ERbeta and the hormone-binding domains of both ERalpha and ERbeta, BPA and NPH confirmed the direct transcriptional activity. Interestingly these properties were supported in MCF7 cells by the ability to autoregulate ERalpha expression as well as to induce its nuclear compartmentalization. We therefore evaluated by reverse transcriptase polymerase chain reaction the expression of oestrogen-controlled genes such as cathepsin D and TFF1 (formerly pS2), which were increased by both chemicals tested. The agonistic effects exhibited in all assays performed prompted the evaluation of a more complex biological response such as the proliferation of MCF7 and T47D cells. The same concentration of xenoestrogens eliciting substantial transcriptional activity significantly stimulated the proliferation of both breast cancer cell lines, although with a reduced effectiveness with respect to the natural hormone 17beta-oestradiol. The results indicate that the biological action of environmental oestrogen such as BPA and NPH should be taken into account for the potential impact on human disease-like hormone-dependent breast cancer. However, further studies are needed to clarify their bioavailability and metabolism as well as whether compound mixtures could produce noticeable effects by synergistic activity.

Exposure to bisphenol A during embryonic/fetal life and infancy increases oxidative injury and causes underdevelopment of the brain and testis in mice

We investigated the modifications in endogenous antioxidant capacity and oxidative damage in the brain, liver, kidney and testis in mice exposed to bisphenol A (BPA), an environmental endocrine disrupter. Mice were exposed to BPA throughout embryonic/fetal life and during lactation by feeding their pregnant/lactating mothers BPA at 5 or 10 microg per milliliter of drinking water. At the age of four weeks, male mice were sacrificed. Exposure to BPA increased the activity of catalase and glutathione peroxidase in the liver and kidney, respectively. It also increased thiobarbituric acid-reactive substances in the brain, kidney and testis, and decreased the wet weight of the brain, kidney and testis. Our results suggest that exposure to BPA throughout embryonic/fetal life and during infancy induces tissue oxidative stress and peroxidation, ultimately leading to underdevelopment of the brain, kidney and testis.

Comparative Study on Toxicokinetics of Bisphenol A in F344 Rats, Monkeys (Macaca fascicularis), and Chimpanzees (Pan troglodytes)

We compared the toxicokinetics of bisphenol A (BPA) among three animal species: rats, cynomolgus monkeys and chimpanzees. Rats and monkeys were administered BPA orally or subcutaneously at 10 or 100 mg/kg body weight, while chimpanzees were administered only 10 mg/kg of BPA. BPA in serum was measured by ELISA. In oral administration of BPA at 10 mg/kg, both C(max) and AUC were rats < chimpanzee < monkeys. In oral administration of BPA at 100 mg/kg, both C(max) and AUC were rats < monkeys. Subcutaneous BPA administrations also revealed similar results, although the values of toxicokinetic parameters in subcutaneous administration were higher than those in oral administration. These results suggest that orally or subcutaneously administered BPA in primates is more easily absorbed than that in rats. We conclude that there are considerable differences in distribution, metabolism, and excretion of BPA between rodents and primates.

Enhanced interleukin-4 production in CD4+ T cells and elevated immunoglobulin E levels in antigen-primed mice by bisphenol A and nonylphenol, endocrine disruptors: involvement of nuclear factor-AT and Ca2+

Bisphenol A (BPA) and p-nonylphenol (NP) are representative endocrine disruptors (EDs) that may have adverse effects on human health. The influence of these compounds on allergic immune responses remains unclear. In this study, we have examined the effects of BPA and NP on production of interleukin-4 (IL-4), a pro-inflammatory cytokine closely associated with allergic immune responses. Both BPA and NP significantly enhanced IL-4 production in keyhole limpet haemocyanin (KLH)-primed CD4+ T cells in a concentration-dependent manner. Treatment with BPA or NP in vivo resulted in significant increase of IL-4 production in CD4+ T cells and of antigen-specific immunoglobulin E (IgE) levels in the sera of KLH-primed mice. Furthermore, BPA and NP enhanced the activation of IL-4 gene promoter in EL4 T cells transiently transfected with IL-4 promoter/reporter constructs, and the enhancing effect mapped to a region in the IL-4 promoter containing binding sites for nuclear factor (NF)-AT. Activation of T lymphocytes by phorbol 12-myristate 13-acetate/ionomycin resulted in markedly enhanced binding activities to the NF-AT site, which significantly increased upon addition of BPA or NP, as demonstrated by the electrophoretic mobility shift assay, indicating that the transcription factor NF-AT was involved in the enhancing effect of BPA and NP on IL-4 production. The enhancement of IL-4 production by BPA or NP was significantly reduced by nitrendipine, a blocker of Ca2+ influx, and by FK506, a calcineurin inhibitor. FK506 inhibited the NF-AT-DNA binding activity and IL-4 gene promoter activity enhanced by BPA or NP. These results represent the first report describing possible enhancement of allergic response by EDs through increasing IL-4 production in CD4+ T cells and antigen-specific IgE levels in the sera via the stimulation of Ca2+/calcineurin-dependent NF-AT activation.

Endocrine disruptors: from Wingspread to environmental developmental biology

The production and release of synthetic chemicals into the environment has been a hallmark of the "Second Industrial Revolution" and the "Green Revolution." Soon after the inception of these chemicals, anecdotal evidence began to emerge linking environmental contamination of rivers and lakes with a variety of developmental and reproductive abnormalities in wildlife species. The accumulation of evidence suggesting that these synthetic chemicals were detrimental to wildlife, and potentially humans, as a result of their hormonal activity, led to the proposal of the endocrine disruptor hypothesis at the 1991 Wingspread Conference. Since that time, experimental and epidemiological data have shown that exposure of the developing fetus or neonate to environmentally-relevant concentrations of certain synthetic chemicals causes morphological, biochemical, physiological and behavioral anomalies in both vertebrate and invertebrate species. The ubiquitous use, and subsequent human exposure, of one particular chemical, the estrogen mimic bisphenol A (BPA), is the subject of this present review. We have highlighted this chemical since it provides an arresting model of how chemical exposure impacts developmental processes involved in the morphogenesis of tissues and organs, including those of the male and female reproductive systems, the mammary glands and the brain.

Criteria for chemical selection for programs on human milk surveillance and research for environmental chemicals

The people of the United States is exposed to a large number of chemicals in their daily lives. In order to prioritize chemicals that should be considered for surveillance of and/or research in human milk, criteria were developed at the Technical Workshop on Human Milk Surveillance and Research on Environmental Chemicals in the United States. The criteria include (1) lipid solubility and/or persistence in the environment; (2) extensive exposure (e.g., high-production-volume chemicals and chemicals in personal care products); (3) known or suspected toxicity in a biological system; (4) historical interest, trend information; (5) chemicals of emerging concern; and (6) chemicals for medicinal use and chemicals in occupational settings. A working list of chemicals was developed for each of the criteria. It should be noted that more than one criterion may be applicable to a selected chemical, but the selected chemical should possess at least one of these designated criteria. It is hoped that by following a cohort of nursing women through their lactational cycle for a group of these chemicals, data generated will indicate the extent of infant exposure and may suggest methods for risk management to decrease inadvertent exposure for breast-feeding mothers and infants. While not the focus of this article, certain endogenous chemicals in human milk beneficial to the health of the infant warrant study as well.

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.

Effects of bisphenol A and artificial UVB radiation on the early development of Rana temporaria

Ultraviolet-B (UVB) radiation is one environmental factor that may act in concert with other stressors, such as xenobiotics, to produce adverse effect on amphibian populations. Embryos (< 24 h old) of the common frog (Rana temporaria) were exposed to four concentrations (0, 10, 100, or 1000 microg/L) of bisphenol A (BPA), with and without ultraviolet-B (UVB) radiation, for 20 d in the laboratory. Throughout the experiment the biologically effective daily UVB dose, calculated with Setlow's DNA action spectrum, was 2.80 kJ m(-2). UVB radiation as such did not have any significant effect on frog embryos. However, a BPA treatment of 1000 microg/L had a significant effect on embryos in both the UVB and no-UVB treatments, with the effect being greater with UVB. UVB produced a significant decrease in survival in the newly hatched frog larvae at all BPA concentrations. These results demonstrate that simultaneous exposure to these two stress factors is more harmful to R. temporaria larvae than exposure to one stressor alone.

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.