Catherine A. VandeVoort

Similarity of bisphenol A pharmacokinetics in rhesus monkeys and mice: Relevance for human exposure

Objective Daily adult human exposure to bisphenol A (BPA) has been estimated at < 1 μg/kg, with virtually complete first-pass conjugation in the liver in primates but not in mice. We measured unconjugated and conjugated BPA levels in serum from adult female rhesus monkeys and adult female mice after oral administration of BPA and compared findings in mice and monkeys with prior published data in women. Methods Eleven adult female rhesus macaques were fed 400 μg/kg deuterated BPA (dBPA) daily for 7 days. Levels of serum dBPA were analyzed by isotope-dilution liquid chromatography–mass spectrometry (0.2 ng/mL limit of quantitation) over 24 hr on day 1 and on day 7. The same dose of BPA was fed to adult female CD-1 mice; other female mice were administered 3H-BPA at doses ranging from 2 to 100,000 μg/kg. Results In monkeys, the maximum unconjugated serum dBPA concentration of 4 ng/mL was reached 1 hr after feeding and declined to low levels by 24 hr, with no significant bioaccumulation after seven daily doses. Mice and monkeys cleared unconjugated serum BPA at virtually identical rates. We observed a linear (proportional) relationship between administered dose and serum BPA in mice. Conclusions BPA pharmacokinetics in women, female monkeys, and mice is very similar. By comparison with approximately 2 ng/mL unconjugated serum BPA reported in multiple human studies, the average 24-hr unconjugated serum BPA concentration of 0.5 ng/mL in both monkeys and mice after a 400 μg/kg oral dose suggests that total daily human exposure is via multiple routes and is much higher than previously assumed.

Bisphenol A and Reproductive Health: Update of Experimental and Human Evidence, 2007–2013

Background: In 2007, an expert panel reviewed associations between bisphenol A (BPA) exposure and reproductive health outcomes. Since then, new studies have been conducted on the impact of BPA on reproduction. Objective: In this review, we summarize data obtained since 2007, focusing on a) findings from human and animal studies, b) the effects of BPA on a variety of reproductive end points, and c) mechanisms of BPA action. Methods: We reviewed the literature published from 2007 to 2013 using a PubMed search based on keywords related to BPA and male and female reproduction. Discussion: Because BPA has been reported to affect the onset of meiosis in both animal and in vitro models, interfere with germ cell nest breakdown in animal models, accelerate follicle transition in several animal species, alter steroidogenesis in multiple animal models and women, and reduce oocyte quality in animal models and women undergoing in vitro fertilization (IVF), we consider it an ovarian toxicant. In addition, strong evidence suggests that BPA is a uterine toxicant because it impaired uterine endometrial proliferation, decreased uterine receptivity, and increased implantation failure in animal models. BPA exposure may be associated with adverse birth outcomes, hyperandrogenism, sexual dysfunction, and impaired implantation in humans, but additional studies are required to confirm these associations. Studies also suggest that BPA may be a testicular toxicant in animal models, but the data in humans are equivocal. Finally, insufficient evidence exists regarding effects of BPA on the oviduct, the placenta, and pubertal development. Conclusion: Based on reports that BPA impacts female reproduction and has the potential to affect male reproductive systems in humans and animals, we conclude that BPA is a reproductive toxicant. Citation: Peretz J, Vrooman L, Ricke WA, Hunt PA, Ehrlich S, Hauser R, Padmanabhan V, Taylor HS, Swan SH, VandeVoort CA, Flaws JA. 2014. Bisphenol A and reproductive health: update of experimental and human evidence, 2007–2013. Environ Health Perspect 122:775–786; http://dx.doi.org/10.1289/ehp.1307728

Bisphenol A alters early oogenesis and follicle formation in the fetal ovary of the rhesus monkey

Widespread use of the endocrine disrupting chemical bisphenol A (BPA) in consumer products has resulted in nearly continuous human exposure. In rodents, low-dose exposures have been reported to adversely affect two distinct stages of oogenesis in the developing ovary: the events of prophase at the onset of meiosis in the fetal ovary and the formation of follicles in the perinatal ovary. Because these effects could influence the reproductive longevity and success of the exposed individual, we conducted studies in the rhesus monkey to determine whether BPA induces similar disturbances in the developing primate ovary. The routes and levels of human exposure are unclear; hence, two different exposure protocols were used: single daily oral doses and continuous exposure via subdermal implant. Our analyses of second trimester fetuses exposed at the time of meiotic onset suggest that, as in mice, BPA induces subtle disturbances in the prophase events that set the stage for chromosome segregation at the first meiotic division. Our analyses of third-trimester fetuses exposed to single daily oral doses during the time of follicle formation revealed an increase in multioocyte follicles analogous to that reported in rodents. However, two unique phenotypes were evident in continuously exposed animals: persistent unenclosed oocytes in the medullary region and small, nongrowing oocytes in secondary and antral follicles. Because effects on both stages of oogenesis were elicited using doses that yield circulating levels of BPA analogous to those reported in humans, these findings raise concerns for human reproductive health.

Bisphenol A alters the development of the rhesus monkey mammary gland

The xenoestrogen bisphenol A (BPA) used in the manufacturing of various plastics and resins for food packaging and consumer products has been shown to produce numerous endocrine and developmental effects in rodents. Exposure to low doses of BPA during fetal mammary gland development resulted in significant alterations in the gland’s morphology that varied from subtle ones observed during the exposure period to precancerous and cancerous lesions manifested in adulthood. This study assessed the effects of BPA on fetal mammary gland development in nonhuman primates. Pregnant rhesus monkeys were fed 400 μg of BPA per kg of body weight daily from gestational day 100 to term, which resulted in 0.68 ± 0.312 ng of unconjugated BPA per mL of maternal serum, a level comparable to that found in humans. At birth, the mammary glands of female offspring were removed for morphological analysis. Morphological parameters similar to those shown to be affected in rodents exposed prenatally to BPA were measured in whole-mounted glands; estrogen receptor (ER) α and β expression were assessed in paraffin sections. Students t tests for equality of means were used to assess differences between exposed and unexposed groups. The density of mammary buds was significantly increased in BPA-exposed monkeys, and the overall development of their mammary gland was more advanced compared with unexposed monkeys. No significant differences were observed in ER expression. Altogether, gestational exposure to the estrogen-mimic BPA altered the developing mammary glands of female nonhuman primates in a comparable manner to that observed in rodents.

Prenatal exposure to bisphenol A impacts midbrain dopamine neurons and hippocampal spine synapses in non-human primates

Prevalent use of bisphenol-A (BPA) in the manufacture of resins, plastics and paper products has led to frequent exposure of most people to this endocrine disruptor. Some rodent studies have suggested that BPA can exert detrimental effects on brain development. However as rodent models cannot be relied on to predict consequences of human exposure to BPA during development, it is important to investigate the effects of BPA on non-human primate brain development. Previous research suggests that BPA preferentially targets dopamine neurons in ventral mesencephalon and glutamatergic neurons in hippocampus, so the present work examined the susceptibility of these systems to low dose BPA exposure at the fetal and juvenile stages of development in non-human primates. Exposure of pregnant rhesus monkeys to relatively low levels of BPA during the final 2 months of gestation, induced abnormalities in fetal ventral mesencephalon and hippocampus. Specifically, light microscopy revealed a decrease in tyrosine hydroxylase-expressing (dopamine) neurons in the midbrain of BPA-exposed fetuses and electron microscopy identified a reduction in spine synapses in the CA1 region of hippocampus. In contrast, administration of BPA to juvenile vervet monkeys (14-18 months of age) was without effect on these indices, or on dopamine and serotonin concentrations in striatum and prefrontal cortex, or on performance of a cognitive task that tests working memory capacity. These data indicate that BPA exerts an age-dependent detrimental impact on primate brain development, at blood levels within the range measured in humans having only environmental contact with BPA.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) modulates function of human luteinizing granulosa cells via cAMP signaling and early reduction of glucose transporting activity

This study examined the changes in cellular glucose uptake, cAMP-dependent protein kinase (PKA), and progesterone production induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in human luteinizing granulosa cells (LGCs) in culture. The role of Ah receptor on TCDD-mediated toxicity in human LGCs was investigated. Treatment of human LGCs with TCDD produced a time- and dose-dependent decrease in the cellular uptake of glucose. The Vmax and the K(m) of glucose transport were decreased by TCDD treatment. Furthermore, cytochalasin B, a specific inhibitor of facilitative glucose transporter proteins, totally abolished the portion of glucose transport activity that is sensitive to TCDD. Pretreatment of the cells with the Ah receptor blockers 4,7-phenanthroline and alpha-naphthoflavone antagonised the effect of TCDD on 3H-Me-glucose uptake. Structure-activity relationship studies with TCDD and three dioxin congeners revealed a rank order for their potency in the inhibition of glucose transport as follows: TCDD > 1,2,3,7,8-PCDD > 1,2,4,7,8-PCDD > 2,7-DCDD. Such a rank order is consistent with the previously determined biological activity of TCDD and the other dioxin congeners. Treatment of cells for 48 h with 10 nM TCDD substantially reduced PKA and progesterone production. The inhibitory effect of TCDD on progesterone production was more pronounced in the presence of insulin (10 micrograms/mL) and D-glucose (13.3 mM). However, cytochalasin B abolished the effect of TCDD on progesterone production. Forskolin (adenylate cyclase activator) abolished the effect of TCDD on glucose uptake and progesterone production but it did not affect the action of TCDD on PKA activity. A relationship between glucose transporting activity and progesterone production in human LGCs treated with TCDD is indicated by several lines of evidence: a) cytochalasin B downregulated glucose transporting activity and progesterone production, b) insulin plus D-glucose downregulated glucose uptake and amplified the negative effect of TCDD on progesterone production, and c) forskolin abolished the negative effect of TCDD on glucose transporting activity and on progesterone production. From the present data we conclude that glucose transporting activity can be used as a sensitive biomarker to detect the very early response to TCDD in human steroid-producing cells and that effect of TCDD on steroid production is mediated through the cAMP-dependent protein kinase.

Trophoblast Stem Cells: Models for Investigating Trophectoderm Differentiation and Placental Development

The placenta is an ephemeral organ containing diverse populations of trophoblasts that are all derived from the embryonic trophectoderm but have morphological, functional, and molecular diversity within and across species. In hemochorial placentation, these cells play especially important roles, interfacing with and modifying the cells of the maternal decidua. Within the rapidly growing placenta, it has been shown that there are trophoblast stem cells well characterized in the mouse and postulated but not well understood in primates. This review will discuss the characteristics of candidates for human and nonhuman primate trophoblast stem cells, present the diverse methods of their generation, and propose future prospects for experimental systems in which they can shed light on developmental and pathophysiological processes in human pregnancy.

2,3,7,8-Tetrachlorodibenzo-p-dioxin decreases estradiol production without altering the enzyme activity of cytochrome P450 aromatase of human luteinized granulosa cells in vitro

Abstract This study was designed to examine the in vitro effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on steroid production in human luteinizing granulosa cells (hLGC). TCDD (10 nM) or its solvent was added at the time of changing medium, directly to the cells, every 48 h for 8 days. To test the hypothesis that TCDD reduces estradiol (E2) synthesis by an effect on cytochrome P450 aromatase, aromatase protein and aromatase activity were evaluated. E2 decreased without changing either aromatase protein or its enzyme activity, suggesting that the target of toxicity of TCDD is upstream of aromatase in the steroidogenic pathway. When hLGC were incubated in the presence of labeled E2, no changes in the metabolism of E2 by treatment were observed. Since TCDD did not change progesterone or 17α-hydroxyprogesterone, the inhibition of E2 synthesis by TCDD would seem not to involve steps such as cholesterol transport. Furthermore, the TCDD effect on E2 concentration in these cells disappeared in the presence of excess androgens. We conclude that the inhibition of E2 secretion by TCDD involves intermediate steps, specifically, the provision of androgens for aromatization.

Bisphenol A (BPA) Pharmacokinetics with Daily Oral Bolus or Continuous Exposure via Silastic Capsules in Pregnant Rhesus Monkeys: Relevance for Human Exposures

We measured serum dBPA in non-pregnant and pregnant female rhesus monkeys, fetuses and amniotic fluid. dBPA was administered by a daily oral bolus or sc implantation of Silastic capsules; both resulted in daily average serum unconjugated dBPA concentrations of <1ng/ml. We observed lower serum concentrations of unconjugated dBPA in pregnant females relative to pre-pregnancy values, and generally lower concentrations in fetal serum than in maternal serum. Differences in pharmacokinetics of dBPA were evident between pre-pregnancy, early and late pregnancy, likely reflecting changes in maternal, fetal and placental physiology. The serum ratio of conjugated to unconjugated dBPA after continuous sc release of dBPA was similar to values reported in human biomonitoring studies and markedly lower than with oral administration, suggesting oral bolus exposure is not an appropriate human exposure model. We report elsewhere that there were numerous adverse effects on fetuses exposed to very low serum dBPA in these studies.

Effects of in vitro maturation on gene expression in rhesus monkey oocytes

In vitro oocyte maturation (IVM) holds great promise as a tool for enhancing clinical treatment of infertility, enhancing availability of nonhuman primates for development of disease models, and facilitating endangered species preservation. However, IVM outcomes have remained significantly below the success rates obtained with in vivo matured (VVM) oocytes from humans and nonhuman primates. A cDNA array-based analysis is presented, comparing the transcriptomes of VVM oocytes with IVM oocytes. We observe a small set of just 59 mRNAs that are differentially expressed between the two cell types. These mRNAs are related to cellular homeostasis, cell-cell interactions including growth factor and hormone stimulation and cell adhesion, and other functions such as mRNA stability and translation. Additionally, we observe in IVM oocytes overexpression of PLAGL1 and MEST, two maternally imprinted genes, indicating a possible interruption or loss of correct epigenetic programming. These results indicate that, under certain IVM conditions, oocytes that are molecularly highly similar to VVM oocytes can be obtained; however, the interruption of normal oocyte-somatic cell interactions during the final hours of oocyte maturation may preclude the establishment of full developmental competence.