Low-dose bioactivity of xenoestrogens in animals: fetal exposure to low doses of methoxychlor and other xenoestrogens increases adult prostate size in mice

Xeno-Estrogenic Pesticides and the Risk of Related Human Cancers

In recent decades, "environmental xenobiotic-mediated endocrine disruption", especially by xeno-estrogens, has gained a lot of interest from toxicologists and environmental researchers. These estrogen-mimicking chemicals are known to cause various human disorders. Pesticides are the most heavily used harmful xenobiotic chemicals around the world. The estrogen-mimicking potential of the most widely used organochlorine pesticides is well established. However, their effect is not as clearly understood among the plethora of effects these persistent xenobiotics are known to pose on our physiological system. Estrogens are one of the principal risk modifiers of various disorders, including cancer, not only in women but in men as well. Despite the ban on these xenobiotics in some parts of the world, humans are still at apparent risk of exposure to these harmful chemicals as they are still widely persistent and likely to stay in our environment for a long time owing to their high chemical stability. The present work intends to understand how these harmful chemicals may affect the risk of the development of estrogen-mediated human cancer.

Data integration, analysis, and interpretation of eight academic CLARITY-BPA studies

"Consortium Linking Academic and Regulatory Insights on BPA Toxicity" (CLARITY-BPA) was a comprehensive "industry-standard" Good Laboratory Practice (GLP)-compliant 2-year chronic exposure study of bisphenol A (BPA) toxicity that was supplemented by hypothesis-driven independent investigator-initiated studies. The investigator-initiated studies were focused on integrating disease-associated, molecular, and physiological endpoints previously found by academic scientists into an industry standard guideline-compliant toxicity study. Thus, the goal of this collaboration was to provide a more comprehensive dataset upon which to base safety standards and to determine whether industry-standard tests are as sensitive and predictive as molecular and disease-associated endpoints. The goal of this report is to integrate the findings from the investigator-initiated studies into a comprehensive overview of the observed impacts of BPA across the multiple organs and systems analyzed. For each organ system, we provide the rationale for the study, an overview of methodology, and summarize major findings. We then compare the results of the CLARITY-BPA studies across organ systems with the results of previous peer-reviewed studies from independent labs. Finally, we discuss potential influences that contributed to differences between studies. Developmental exposure to BPA can lead to adverse effects in multiple organs systems, including the brain, prostate gland, urinary tract, ovary, mammary gland, and heart. As published previously, many effects were at the lowest dose tested, 2.5μg/kg /day, and many of the responses were non-monotonic. Because the low dose of BPA affected endpoints in the same animals across organs evaluated in different labs, we conclude that these are biologically - and toxicologically - relevant.

Perinatal Exposure to Methoxychlor Affects Reproductive Function and Sexual Behavior in Mice

Numerous chemicals derived from human activity are now disseminated in the environment where their exert estrogenic endocrine disrupting effects, and therefore represent major health concerns. The present study explored whether Methoxychlor (MXC), an insecticide with xenoestrogens activities, given during the perinatal period (from gestational day 11 to postnatal day 8) and at an environmentally dose [20 μg/kg (body weight)/day], would affect reproductive physiology and sexual behavior of the offspring in mice. While MXC exposure did not induce any differences in the weight gain of animals from birth to 4 months of age, a clear difference (although in opposite direction according to the sexes) was observed on the anogenital distance between intact and exposed animals. A similar effect was also observed on preputial separation and vaginal opening, which reflects, respectively, in males and females, puberty occurrence. The advanced puberty observed in females was associated with an enhanced expression of kisspeptin cells in the anteroventral periventricular region of the medial preoptic area. Exposure to MXC did not induce in adult females changes in the estrous cycle or in the weight of the female reproductive tract. By contrast, males showed reduced weight of the epididymis and seminiferous vesicles associated with reduced testosterone levels and seminiferous tubule diameter. We also showed that both males and females showed deficits in mate preference tests. As a whole, our results show that MXC impacts reproductive outcomes.

Fetal bisphenol A and ethinylestradiol exposure alters male rat urogenital tract morphology at birth: Confirmation of prior low-dose findings in CLARITY-BPA

Bisphenol A (BPA) is a contaminant in virtually all Americans. To examine BPA's adverse effects, the FDA-NCTR, NIEHS, and 14 groups of academic scientists formed a consortium: CLARITY-BPA. The purpose of our study was to investigate the effects of a wide range of doses of BPA on fetal development of the NCTR CD-SD male rat urogenital sinus (UGS). Pregnant rats were administered BPA or positive control ethinylestradiol (EE2) daily, via oral gavage, from gestational day 6 through parturition. Tissues were collected on postnatal day 1 and the UGS was analyzed using computer-assisted 3-D reconstruction. Importantly, only low doses of BPA, as well as EE2, significantly changed birth weight and UGS morphology, including an increased size of the colliculus and decreased size of the urethra, consistent with prior reported BPA and EE2 effects. Our findings provide further evidence that BPA mediates nonmonotonic developmental effects on the fetal urogenital sinus.

Transfer and Metabolism of the Xenoestrogen Zearalenone in Human Perfused Placenta

BACKGROUND

Pregnancy is a sensitive condition during which adverse environmental exposures should be monitored thoroughly and minimized whenever possible. In particular, the hormone balance during gestation is delicate, and disturbance may cause acute or chronic long-term health effects. A potential endocrine disruption may be provoked by in utero exposure to xenoestrogens mimicking endogenous estrogens. The mycoestrogen zearalenone (ZEN), a toxic fungal secondary metabolite and mycotoxin found frequently in food and feed, constitutes a prominent example.

OBJECTIVES

We performed a comprehensive assessment of the transfer as well as phase I and phase II metabolism of ZEN at the human placental barrier.

METHODS

Human placentas were perfused with 1μM (318μg/L) ZEN for 6 h. Samples from the maternal and fetal compartment, placental tissue, and fetal plasma were analyzed by a highly sensitive UHPLC-MS/MS assay to detect ZEN as well as nine key metabolites (α-zearalenol, β-zearalenol, zearalanone, α-zearalanol, β-zearalanol, ZEN-14-glucuronide, α-zearalenol-14-glucuronide, β-zearalenol-14-glucuronide, ZEN-14-sulfate).

RESULTS

The model revealed a fast maternofetal transfer of ZEN across the human placental barrier. We also unraveled phase I and phase II metabolism of the parent toxin ZEN into the approximately 70-times more estrogenic α-zearalenol and the less active ZEN-14-sulfate conjugate, which are effectively released into the maternal and fetal circulation in considerable amounts.

CONCLUSIONS

Our findings suggest that exposure to ZEN (such as through consumption of ZEN-contaminated cereal-based products) during pregnancy may result in in utero exposure of the fetus, not only to ZEN but also some of its highly estrogenically active metabolites. In the light of the known affinity of ZEN and potentially co-occurring xenoestrogens to the estrogen receptor, and our results demonstrating placental transfer of ZEN and its metabolites in an ex vivo model, we recommend further research and more comprehensive assessment of gestational exposures in women. https://doi.org/10.1289/EHP4860.

Physiologically Based Pharmacokinetic (PBPK) Modeling of the Bisphenols BPA, BPS, BPF, and BPAF with New Experimental Metabolic Parameters: Comparing the Pharmacokinetic Behavior of BPA with Its Substitutes

BACKGROUND

The endocrine disrupting chemical bisphenol A (BPA) has been facing stricter regulations in recent years. BPA analogs, such as the bisphenols S, F, and AF (BPS, BPF, and BPAF) are increasingly used as replacement chemicals, although they were found to exert estrogenic effects similar to those of BPA. Research has shown that only the parent compounds have affinity to the estrogen receptors, suggesting that the pharmacokinetic behavior of bisphenols (BPs) can influence their potency.

OBJECTIVES

Our goal was to compare the pharmacokinetic behaviors of BPA, BPS, BPF, and BPAF for different age groups after environmentally relevant external exposures by taking into account substance-specific metabolism kinetics and partitioning behavior. This comparison allowed us to investigate the consequences of replacing BPA with other BPs.

METHODS

We readjusted a physiologically based pharmacokinetic (PBPK) model for peroral exposure to BPA and extended it to include dermal exposure. We experimentally assessed hepatic and intestinal glucuronidation kinetics of BPS, BPF, and BPAF to parametrize the model for these BPs and calibrated the BPS model with a biomonitoring study. We used the PBPK models to compare resulting internal exposures and focused on females of childbearing age in a two-dimensional Monte Carlo uncertainty analysis.

RESULTS

Within environmentally relevant concentration ranges, BPAF and BPS were glucuronized at highest and lowest rates, respectively, in the intestine and the liver. The predominant routes of BPS and BPAF exposure were peroral and dermal exposure, respectively. The calibration of the BPS model with measured concentrations showed that enterohepatic recirculation may be important. Assuming equal external exposures, BPS exposure led to the highest internal concentrations of unconjugated BPs.

CONCLUSIONS

Our data suggest that the replacement of BPA with structural analogs may not lower the risk for endocrine disruption. Exposure to both BPS and BPAF might be more critical than BPA exposure, if their respective estrogenic potencies are taken into account. https://doi.org/10.1289/EHP2739.

Twenty-five years after "Wingspread"- Environmental endocrine disruptors (EDCs) and human health

The aim of this paper is to provide the reader with a view of the Endocrine Disruptor Chemical (EDC) research field and its relevance to human health. My perspective is from working on the effects of EDCs that act via the androgen (A) or estrogen (E) signaling pathways in a regulatory agency for the last four decades with the objective of producing data that risk assessors could use to reduce the uncertainty in risk assessment. In vitro and in vivo data from our studies has contributed to regulatory agencies decision-making since the 1990s (https://www3.epa.gov/pesticides/chem_search/cleared_reviews/csr_PC-113201_7-Apr-98_238.pdf). From the start, we were evaluating the utility of in vitro and short-term in vivo effects to predict the adverse effects in developing animals [1; 2]. This approach has expanded greatly to include what is now known as Adverse Outcome Pathways (AOP) and networks (AOPn) [3; 4]. The AOP framework for the effects of chemicals that disrupt androgen signaling during sexual differentiation of the fetal male rat provides biological context for extrapolating mechanistic information from in vitro and in vivo assays in rodents to other species including humans. Such an approach has biological validity because the E and A pathways are highly conserved in vertebrates, including humans and laboratory animals.

Neonatal exposure to ethinylestradiol increases ventral prostate growth and promotes epithelial hyperplasia and inflammation in adult male gerbils

The aim of this study was to analyse morphologically the ventral prostate of adult Mongolian gerbils exposed to ethinylestradiol (EE) during the first week of postnatal development. Lactating females received daily, by gavage, doses of 10 μg/kg of EE diluted in 100 μl of mineral oil from the 1st to 10th postnatal day of the pups (EE group). In the control group (C), the lactating females received only the vehicle. Upon completing 120 days of age, the male offspring were euthanized and the prostates collected for analyses. We employed morphological, stereological-morphometrical, immunohistochemical and ultrastructural methods. The results showed that the postnatal exposure to EE doubled the prostatic complex weight, increasing the epithelial and stromal compartments, in addition to the secretory activity of the ventral lobe of the prostate. All glands exposed to EE showed strong stromal remodelling, and some foci of epithelial hyperplasia and inflammatory infiltrate in both luminal and epithelial or stromal compartments. Cells positive for anti-AR and anti-PCNA reactions increased into the epithelial and stromal tissues. ERα-positive cells, which are normally found in the stromal compartment of intact prostates, were frequently observed in the prostatic epithelium of treated animals. This study demonstrated that the exposure to EE during postnatal development causes histophysiological alterations in this gland, predisposing to the development of prostatic lesions during life. These results are important for public health, considering that women worldwide have commonly used EE. Moreover, the bioaccumulation of this chemical has increased in different ecosystems.

Environmental endocrine disruptors: Effects on the human male reproductive system

Incidences of altered development and neoplasia of male reproductive organs have increased during the last 50 years, as shown by epidemiological data. These data are associated with the increased presence of environmental chemicals, specifically "endocrine disruptors," that interfere with normal hormonal action. Much research has gone into testing the effects of specific endocrine disrupting chemicals (EDCs) on the development of male reproductive organs and endocrine-related cancers in both in vitro and in vivo models. Efforts have been made to bridge the accruing laboratory findings with the epidemiological data to draw conclusions regarding the relationship between EDCs, altered development and carcinogenesis. The ability of EDCs to predispose target fetal and adult tissues to neoplastic transformation is best explained under the framework of the tissue organization field theory of carcinogenesis (TOFT), which posits that carcinogenesis is development gone awry. Here, we focus on the available evidence, from both empirical and epidemiological studies, regarding the effects of EDCs on male reproductive development and carcinogenesis of endocrine target tissues. We also critique current research methodology utilized in the investigation of EDCs effects and outline what could possibly be done to address these obstacles moving forward.

Molecular Mechanisms of Action of BPA

Bisphenol A (BPA) exposure has been associated with serious endocrine-disrupting effects in humans and wildlife. Toxicological and epidemiological studies evidenced that BPA increases body mass index and disrupts normal cardiovascular physiology by interfering with endogenous hormones in rodents, nonhuman primates, and cell culture test systems. The BPA concentration derived from these experiments were used by government regulatory agencies to determine the safe exposure levels of BPA in humans. However, accumulating literature in vivo and in vitro indicate that at concentrations lower than that reported in toxicological studies, BPA could elicit a different endocrine-disrupting capacity. To further complicate this picture, BPA effects rely on several and diverse mechanisms that converge upon endocrine and reproductive systems. If all or just few of these mechanisms concur to the endocrine-disrupting potential of low doses of BPA is at present still unclear. Thus, taking into account that the incidence and/or prevalence of health problems associated with endocrine disruption have increased worldwide, the goal of the present review is to give an overview of the many mechanisms of BPA action in order to decipher whether different mechanisms are at the root of the effect of low dose of BPA on endocrine system.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: the challenge ahead

Low-dose exposures to common environmental chemicals that are deemed safe individually may be combining to instigate carcinogenesis, thereby contributing to the incidence of cancer. This risk may be overlooked by current regulatory practices and needs to be vigorously investigated.

Lifestyle factors are responsible for a considerable portion of cancer incidence worldwide, but credible estimates from the World Health Organization and the International Agency for Research on Cancer (IARC) suggest that the fraction of cancers attributable to toxic environmental exposures is between 7% and 19%. To explore the hypothesis that low-dose exposures to mixtures of chemicals in the environment may be combining to contribute to environmental carcinogenesis, we reviewed 11 hallmark phenotypes of cancer, multiple priority target sites for disruption in each area and prototypical chemical disruptors for all targets, this included dose-response characterizations, evidence of low-dose effects and cross-hallmark effects for all targets and chemicals. In total, 85 examples of chemicals were reviewed for actions on key pathways/mechanisms related to carcinogenesis. Only 15% (13/85) were found to have evidence of a dose-response threshold, whereas 59% (50/85) exerted low-dose effects. No dose-response information was found for the remaining 26% (22/85). Our analysis suggests that the cumulative effects of individual (non-carcinogenic) chemicals acting on different pathways, and a variety of related systems, organs, tissues and cells could plausibly conspire to produce carcinogenic synergies. Additional basic research on carcinogenesis and research focused on low-dose effects of chemical mixtures needs to be rigorously pursued before the merits of this hypothesis can be further advanced. However, the structure of the World Health Organization International Programme on Chemical Safety ‘Mode of Action’ framework should be revisited as it has inherent weaknesses that are not fully aligned with our current understanding of cancer biology.

Lifetime-dependent effects of bisphenol A on asthma development in an experimental mouse model

BACKGROUND

Environmental factors are thought to contribute significantly to the increase of asthma prevalence in the last two decades. Bisphenol A (BPA) is a xenoestrogen commonly used in consumer products and the plastic industry. There is evidence and an ongoing discussion that endocrine disruptors like BPA may affect human health and also exert alterations on in the immune system. The aim of this study was to investigate age-dependent effects of BPA on the asthma risk using a murine model to explain the controversial results reported till date.

METHODS

BALB/c mice were exposed to BPA via the drinking water for different time periods including pregnancy and breastfeeding. To induce an asthma phenotype, mice were sensitized to ovalbumin (OVA), followed by an intrapulmonary allergen challenge.

RESULTS

BPA exposure during pregnancy and breastfeeding had no significant effect on asthma development in the offspring. In contrast, lifelong exposure from birth until the last antigen challenge clearly increased eosinophilic inflammation in the lung, airway hyperreactivity and antigen-specific serum IgE levels in OVA-sensitized adult mice compared to mice without BPA exposure. Surprisingly, BPA intake during the sensitization period significantly reduced the development of allergic asthma. This effect was reversed in the presence of a glucocorticoid receptor antagonist.

CONCLUSIONS

Our results demonstrate that the impact of BPA on asthma risk is strongly age-dependent and ranges from asthma-promoting to asthma-reducing effects. This could explain the diversity of results from previous studies regarding the observed health impact of BPA.

Perinatal exposure to methoxychlor enhances adult cognitive responses and hippocampal neurogenesis in mice

During perinatal life, sex steroids, such as estradiol, have marked effects on the development and function of the nervous system. Environmental estrogens or xenoestrogens are man-made chemicals, which animal and human population encounter in the environment and which are able to disrupt the functioning of the endocrine system. Scientific interest in the effects of exposure to xenoestrogens has focused more on fertility and reproductive behaviors, while the effects on cognitive behaviors have received less attention. Therefore, the present study explored whether the organochlorine insecticide Methoxychlor (MXC), with known xenoestrogens properties, administered during the perinatal period (from gestational day 11 to postnatal day 8) to pregnant-lactating females, at an environmentally relevant dose (20 µg/kg (body weight)/day), would also affect learning and memory functions depending on the hippocampus of male and female offspring mice in adulthood. When tested in adulthood, MXC perinatal exposure led to an increase in anxiety-like behavior and in short-term spatial working memory in both sexes. Emotional learning was also assessed using a contextual fear paradigm and MXC treated male and female mice showed an enhanced freezing behavior compared to controls. These results were correlated with an increased survival of adult generated cells in the adult hippocampus. In conclusion, our results show that perinatal exposure to an environmentally relevant dose of MXC has an organizational effect on hippocampus-dependent memory and emotional behaviors.

The use of a whole animal biophotonic model as a screen for the angiogenic potential of estrogenic compounds

BACKGROUND

Vascular endothelial growth factor (VEGF) is essential for normal vascular growth and development during wound repair. VEGF is estrogen responsive and capable of regulating its own receptor, vascular endothelial growth factor receptor-2 (VEGFR-2). Several agricultural pesticides (e.g., methoxychlor) have estrogenic potential that can initiate inappropriate physiological responses in estrogenic-sensitive tissues following exposure in vivo. Thus, the current study was designed to determine whether the VEGFR-2-Luciferase (Luc) reporter transgenic mouse is a useful model for evaluating estrogenic tendencies of methoxychlor by monitoring wound healing via VEGFR-2-mediated gene expression using bioluminescence and real-time imaging technology.

RESULTS

VEGFR-2-Luc gene activity peaked by d 7 (P<0.001) in all groups but was not different (P>0.05) between control and estrogen/methoxychlor exposed mice.

CONCLUSIONS

Changes in VEGFR-2-Luc gene activity associated with the dermal wound healing process were able to be measured via photonic emission. The increase in vasculature recruitment and formation is paralleled by the increase of VEGFR-2-Luc activity with a peak on day 7. However, estrogen/methoxychlor did not significantly alter wound healing mediated VEGFR-2-Luc gene expression patterns compared to controls. This suggests that the VEGFR-2-Luc transgenic mouse wound model tested in this study may not be optimal for use as a screen for the angiogenic potential of estrogenic compounds.

Assessment of cellular estrogenic activity based on estrogen receptor-mediated reduction of soluble-form catechol-O-methyltransferase (COMT) expression in an ELISA-based system

Xenoestrogens are either natural or synthetic compounds that mimic the effects of endogenous estrogen. These compounds, such as bisphenol-A (BPA), and phthalates, are commonly found in plastic wares. Exposure to these compounds poses major risk to human health because of the potential to cause endocrine disruption. There is huge demand for a wide range of chemicals to be assessed for such potential for the sake of public health. Classical in vivo assays for endocrine disruption are comprehensive but time-consuming and require sacrifice of experimental animals. Simple preliminary in vitro screening assays can reduce the time and expense involved. We previously demonstrated that catechol-O-methyltransferase (COMT) is transcriptionally regulated by estrogen via estrogen receptor (ER). Therefore, detecting corresponding changes of COMT expression in estrogen-responsive cells may be a useful method to estimate estrogenic effects of various compounds. We developed a novel cell-based ELISA to evaluate cellular response to estrogenicity by reduction of soluble-COMT expression in ER-positive MCF-7 cells exposed to estrogenic compounds. In contrast to various existing methods that only detect bioactivity, this method elucidates direct physiological effect in a living cell in response to a compound. We validated our assay using three well-characterized estrogenic plasticizers - BPA, benzyl butyl phthalate (BBP), and di-n-butyl phthalate (DBP). Cells were exposed to either these plasticizers or 17β-estradiol (E2) in estrogen-depleted medium with or without an ER-antagonist, ICI 182,780, and COMT expression assayed. Exposure to each of these plasticizers (10^-9-10^-7M) dose-dependently reduced COMT expression (p<0.05), which was blocked by ICI 182,780. Reduction of COMT expression was readily detectable in cells exposed to picomolar level of E2, comparable to other in vitro assays of similar sensitivity. To satisfy the demand for in vitro assays targeting different cellular components, a cell-based COMT assay provides useful initial screening to supplement the current assessments of xenoestrogens for potential estrogenic activity.

Daily urinary excretion of bisphenol A

OBJECTIVES

Concerns over dietary exposure to bisphenol A (BPA), an endocrine disruptor, have been raised because BPA is contained in resins and plastics commonly used for the preservation of food and beverages. The purpose of the present study was to assess daily intake levels of BPA in a group of male subjects by measuring total urinary BPA (free BPA plus BPA released by treatment with β-glucuronidase), as well as determining intra-individual variation in BPA excretion.

METHODS

Twenty-four-hour urine was collected from 5 subjects for 5 consecutive days for the evaluation of between-day variation in urinary BPA excretion and from 36 male subjects for the estimation of the level of daily BPA intake. BPA in the urine samples was measured by GC/MS/MS following enzymatic hydrolysis of BPA glucuronate, solid phase extraction, and derivatization.

RESULTS

A large between-day variation was found over 5 days for the daily excretion of urinary BPA in the 5 subjects. The daily excretion of urinary BPA was distributed log-normally in the 36 male subjects, with the median value being 1.2 μg/day (range: <0.21-14 μg/day), which was far below the Tolerable Daily Intake (0.01 mg/kg bw) recommended by a scientific committee in the European Commission in 2002. However, the maximum estimated intake per body weight (0.2 μg/kg/day) was only one order of magnitude lower than the reported lowest level for reproductive/behavioral effects in pregnant mice (2 μg/kg/day).

CONCLUSIONS

Measuring urinary BPA in urine is a suitable approach for estimating short-term BPA intake levels in individuals and/or estimating the average exposure level of populations. Urine analyses will be increasingly important in the human health risk assessment of BPA.

Mouse females devoid of exposure to males during fetal development exhibit increased maternal behavior

Many sex differences can be found in the expression of aggression and parental nurturing behaviors. It is important to determine if these are modulated by prenatal conditions. Here, using assisted reproduction technologies, we generated females that were (mixed-sex) or were not (same-sex) exposed to males during fetal development, raised them by cross fostering among fosters' own female only pups to control for effects of postnatal environment, and compared their reproductive abilities and behavior. There were no differences between females from the two prenatal conditions in estrus cycle length and length of time spent at individual estrus cycle stages. Both types of females had similar ovulation efficiency and bred equally well yielding comparable litter size and progeny sex ratio. Females from the two prenatal conditions were also indistinguishable in social behavior and exhibited normal social responses towards unfamiliar females in the three-chamber social approach and social proximity tests. When urine was collected from both types of females and used as a point source in a scent-marking paradigm, exposed males showed a similar distribution and extent of urinary scent marking in response to urine from each type of female but tended to engage in higher durations of sniffing the urine from same-sex females. When females were tested in a resident-intruder paradigm 3 days after giving birth, same-sex females exhibited enhancement of pup grooming and an overall decrease of non-pup activity prior to male intruder introduction, and after introduction were more defensive as evidenced by higher rates of burying, open-mouth threat/lunges, and attacks towards the male, and decreased latencies to display these defensive behaviors. Our results suggest that females devoid of male exposure during fetal development have reproductive abilities similar to those of females from mixed-sex pregnancies, and have normal social interactions with other females. However, they exhibit hyper-maternal behavior both in terms of the care and defense of pups in front of a male intruder, and potentially produce a pheromonal milieu that renders them more attractive to males during olfactory investigations.

Estrogenic environmental chemicals and drugs: mechanisms for effects on the developing male urogenital system

Development and differentiation of the prostate from the fetal urogenital sinus (UGS) is dependent on androgen action via androgen receptors (AR) in the UGS mesenchyme. Estrogens are not required for prostate differentiation but do act to modulate androgen action. In mice exposure to exogenous estrogen during development results in permanent effects on adult prostate size and function, which is mediated through mesenchymal estrogen receptor (ER) alpha. For many years estrogens were thought to inhibit prostate growth because estrogenic drugs studied were administered at very high concentrations that interfered with normal prostate development. There is now extensive evidence that exposure to estrogen at very low concentrations during the early stages of prostate differentiation can stimulate fetal/neonatal prostate growth and lead to prostate disease in adulthood. Bisphenol A (BPA) is an environmental endocrine disrupting chemical that binds to both ER receptor subtypes as well as to AR. Interest in BPA has increased because of its prevalence in the environment and its detection in over 90% of people in the USA. In tissue culture of fetal mouse UGS mesenchymal cells, BPA and estradiol stimulated changes in the expression of several genes. We discuss here the potential involvement of estrogen in regulating signaling pathways affecting cellular functions relevant to steroid hormone signaling and metabolism and to inter- and intra-cellular communications that promote cell growth. The findings presented here provide additional evidence that BPA and the estrogenic drug ethinylestradiol disrupt prostate development in male mice at administered doses relevant to human exposures.

Bisphenol A interferes with synaptic remodeling

The potential adverse effects of Bisphenol A (BPA), a synthetic xenoestrogen, have long been debated. Although standard toxicology tests have revealed no harmful effects, recent research highlighted what was missed so far: BPA-induced alterations in the nervous system. Since 2004, our laboratory has been investigating one of the central effects of BPA, which is interference with gonadal steroid-induced synaptogenesis and the resulting loss of spine synapses. We have shown in both rats and nonhuman primates that BPA completely negates the ∼ 70-100% increase in the number of hippocampal and prefrontal spine synapses induced by both estrogens and androgens. Synaptic loss of this magnitude may have significant consequences, potentially causing cognitive decline, depression, and schizophrenia, to mention those that our laboratory has shown to be associated with synaptic loss. Finally, we discuss why children may particularly be vulnerable to BPA, which represents future direction of research in our laboratory.

Bisphenol-A and the great divide: a review of controversies in the field of endocrine disruption

In 1991, a group of 21 scientists gathered at the Wingspread Conference Center to discuss evidence of developmental alterations observed in wildlife populations after chemical exposures. There, the term "endocrine disruptor" was agreed upon to describe a class of chemicals including those that act as agonists and antagonists of the estrogen receptors (ERs), androgen receptor, thyroid hormone receptor, and others. This definition has since evolved, and the field has grown to encompass hundreds of chemicals. Despite significant advances in the study of endocrine disruptors, several controversies have sprung up and continue, including the debate over the existence of nonmonotonic dose response curves, the mechanisms of low-dose effects, and the importance of considering critical periods of exposure in experimental design. One chemical found ubiquitously in our environment, bisphenol-A (BPA), has received a tremendous amount of attention from research scientists, government panels, and the popular press. In this review, we have covered the above-mentioned controversies plus six additional issues that have divided scientists in the field of BPA research, namely: 1) mechanisms of BPA action; 2) levels of human exposure; 3) routes of human exposure; 4) pharmacokinetic models of BPA metabolism; 5) effects of BPA on exposed animals; and 6) links between BPA and cancer. Understanding these topics is essential for educating the public and medical professionals about potential risks associated with developmental exposure to BPA and other endocrine disruptors, the design of rigorously researched programs using both epidemiological and animal studies, and ultimately the development of a sound public health policy.

Transgenerational effects of the endocrine disruptor vinclozolin on the prostate transcriptome and adult onset disease

PURPOSE

The ability of an endocrine disruptor exposure during gonadal sex determination to promote a transgenerational prostate disease phenotype was investigated in the current study.

METHODS

Exposure of an F0 gestating female rat to the endocrine disruptor vinclozolin during F1 embryo gonadal sex determination promoted a transgenerational adult onset prostate disease phenotype. The prostate disease phenotype and physiological parameters were determined for males from F1 to F4 generations and the prostate transcriptome was assessed in the F3 generation.

RESULTS

Although the prostate in prepubertal animals develops normally, abnormalities involving epithelial cell atrophy, glandular dysgenesis, prostatitis, and hyperplasia of the ventral prostate develop in older animals. The ventral prostate phenotype was transmitted for four generations (F1-F4). Analysis of the ventral prostate transcriptome demonstrated 954 genes had significantly altered expression between control and vinclozolin F3 generation animals. Analysis of isolated ventral prostate epithelial cells identified 259 genes with significantly altered expression between control and vinclozolin F3 generation animals. Characterization of regulated genes demonstrated several cellular pathways were influenced, including calcium and WNT. A number of genes identified have been shown to be associated with prostate disease and cancer, including beta-microseminoprotein (Msp) and tumor necrosis factor receptor superfamily 6 (Fadd).

CONCLUSIONS

The ability of an endocrine disruptor to promote transgenerational prostate abnormalities appears to involve an epigenetic transgenerational alteration in the prostate transcriptome and male germ-line. Potential epigenetic transgenerational alteration of prostate gene expression by environmental compounds may be important to consider in the etiology of adult onset prostate disease.

DDE-induced changes in aromatase activity in endometrial stromal cells in culture

Environmental toxicants are thought to play a role in several estrogen-dependent diseases including breast cancer and endometriosis. Toxicant-induced increased aromatase activity, an enzyme complex that catalyzes the final rate-limiting step in the conversion of androgens to estrogens, has been reported in assays using placental microsomes and cancer cells in vitro. These data suggest that environmental toxicants can increase aromatase activity and thus increase local tissue estrogen levels, which could have implications for estrogen- dependent functions in target tissues. The objective of this study was therefore to quantify the effect of the stable breakdown product of DDT, 2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE), a toxicant broadly detected in human adipose tissue, serum and follicular fluid, on aromatase activity in the endometrium, an estrogen-sensitive target tissue. Specifically, the effect of increasing log concentrations of p,p'-DDE on aromatase activity was determined in cultures of endometrial stromal cells (ESC). Relative to controls p,p'-DDE treatment significantly increased aromatase activity in ESC (135%). Moreover, ESC cells treated with p,p'-DDE were immunopositive for aromatase, whereas no aromatase staining could be demonstrated in control cultures. Our data demonstrate that p,p'-DDE treatment can increase aromatase activity in ESC in culture.

Estrogenic chemicals in plastic and oral contraceptives disrupt development of the fetal mouse prostate and urethra

Exposure of human fetuses to man-made estrogenic chemicals can occur through several sources. For example, fetal exposure to ethinylestradiol occurs because each year approximately 3% of women taking oral contraceptives become pregnant. Exposure to the estrogenic chemical bisphenol A occurs through food and beverages because of significant leaching from polycarbonate plastic products and the lining of cans. We fed pregnant CD-1 mice ethinylestradiol (0.1 microg/kg per day) and bisphenol A (10 microg/kg per day), which are doses below the range of exposure by pregnant women. In male mouse fetuses, both ethinylestradiol and bisphenol A produced an increase in the number and size of dorsolateral prostate ducts and an overall increase in prostate duct volume. Histochemical staining of sections with antibodies to proliferating cell nuclear antigen and mouse keratin 5 indicated that these increases were due to a marked increase in proliferation of basal epithelial cells located in the primary ducts. The urethra was malformed in the colliculus region and was significantly constricted where it enters the bladder, which could contribute to urine flow disorders. These effects were identical to those caused by a similar dose (0.1 microg/kg per day) of the estrogenic drug diethylstilbestrol (DES), a known human developmental teratogen and carcinogen. In contrast, a 2,000-fold higher DES dose completely inhibited dorsolateral prostate duct formation, revealing opposite effects of high and low doses of estrogen. Acceleration in the rate of proliferation of prostate epithelium during fetal life by small amounts of estrogenic chemicals could permanently disrupt cellular control systems and predispose the prostate to disease in adulthood.

Developmental effects of prenatal exposure to bisphenol a on the uterus of rat offspring

Exposure to estrogenic compounds during critical periods of fetal development could result in adverse effects on the development of reproductive organs that are not apparent until later in life. Bisphenol A (BPA), which is employed in the manufacture of a wide range of consumer products, is a prime candidate for endocrine disruption. We examined BPA to address the question of whether in utero exposure affects the uterus of the offspring and studied the expression and distribution of the estrogen receptors alpha (ERalpha) and beta (ERbeta), because estrogens influence the development, growth, and function of the uterus through both receptors. Gravid Sprague-Dawley dams were administered by gavage either 0.1 or 50 mg/kg per day BPA or 0.2 mg/kg per day 17alpha-ethinyl estradiol (EE2) as reference dose on gestation days 6 through 21. Female offspring were killed in estrus. Uterine morphologic changes as well as ERalpha and ERbeta distribution and expression were measured by immunohistochemistry and Western blot analysis. Striking morphologic changes were observed in the uterine epithelium of postpubertal offspring during estrus of the in utero BPA-treated animals (the thickness of the total epithelium was significantly reduced). ERalpha expression was increased in the 50-mg BPA and EE2-treated group. In contrast, we observed significantly decreased ERbeta expression in all BPA- and EE2-treated animals when compared with the control. In summary, these results clearly indicate that in utero exposure of rats to BPA promotes uterine disruption in offspring. We hypothesize that the uterine disruption could possibly be provoked by a dysregulation of ERalpha and ERbeta.

Biocompatibility of hydroxylated metabolites of BISGMA and BFDGE

Unpolymerized dental monomers can leach out into the oral biophase and are bioavailable for metabolism. We hypothesize that metabolites would be less toxic than parent monomers. We first identified the formation of metabolites from bisphenol F diglycidyl ether (BFDGE) and Bisphenol A glycidyl methacrylate (BISGMA) after their exposure to liver S9 fractions. Then, the metabolites and parent compounds were subjected to in vitro cytotoxicity, mutagenicity, and estrogenicity studies. Bisphenol A bis(2,3-dihydroxypropyl) ether and bisphenol F bis(2,3-dihydroxypropyl) ether were the hydroxylated metabolites of BISGMA and BFDGE, respectively. Cytotoxicity against L929 cells showed that the metabolites were significantly (p < 0.05) less cytotoxic than the parent monomers. Only BFDGE was mutagenic in the Ames assay with strain TA100 of Salmonella typhimurium. Parent and metabolite compounds did not stimulate estrogen-dependent MCF-7 cell proliferation above solvent controls. These results indicated that the hydroxylated metabolites were non-mutagenic, non-estrogenic, and less cytotoxic than their parent monomers.

Effects of subchronic exposure to a complex mixture of persistent contaminants in male rats: systemic, immune, and reproductive effects

Human populations throughout the world are exposed daily to low levels of environmental contaminants. The consequences of potential interactions of these compounds to human endocrine, reproductive, and immune function remain unknown. The current study examines the effects of subchronic oral exposure to a complex mixture of ubiquitous persistent environmental contaminants that have been quantified in human reproductive tissues. The dosing solution used in this study contained organochlorines (2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD], polychlorinated biphenyls [PCBs],p,p'-dichlorodiphenoxydichloroethylene [p,p'-DDE],p,p-dichlorodiphenoxytrichloroethane [p,p'-DDT], dieldrin, endosulfan, methoxychlor, hexachlorobenzene, and other chlorinated benzenes, hexachlorocyclohexane, mirex and heptachlor) as well as metals (lead and cadmium). Each chemical was included in the mixture at the minimum risk level (MRL) or tolerable daily intake (TDI) as determined by the U.S. EPA or ATSDR or, for TCDD, at the no observable effect level (NOEL) used to calculate the TDI. Sexually mature male rats were exposed to this complex mixture at 1, 10, 100, and 1000 times the estimated safe levels daily for 70 days. On day 71, all animals were sacrificed and a variety of physiological systems assessed for toxic effects. Evidence of hepatotoxicity was seen in the significant enlargement of the liver in the 1000x group, reduced serum LDH activity (100x), and increased serum cholesterol and protein levels (both 1000x). Hepatic EROD activities were elevated in animals exposed to10x and above. The mixture caused decreased proliferation of splenic T cells at the highest dose and had a biphasic effect on natural killer cell lytic activity with an initial increase in activity at 1x followed by a decrease to below control levels in response to 1000x. No treatment-related effects were seen on bone marrow micronuclei, daily sperm production, serum LH, FSH, or prolactin levels or weights of most organs of the reproductive tract. The weights of the whole epididymis and of the caput epididymis were significantly decreased at 10x and higher doses, although no effect was seen on cauda epididymal weight. The sperm content of the cauda epididymis was increased at the 1x level but not significantly different from control at higher dose levels. A slight, but significant, increase in the relative numbers of spermatids was seen in the animals from the 1000x group with a trend towards reduced proportion of diploid cells at the same dose. Only minor, nondose related changes were seen in parameters related to condensation of chromatin, as determined by flow cytometry, in epididymal sperm. We conclude that the mixture induced effects on the liver and kidney and on general metabolism at high doses but caused only minor effects on immune function, reproductive hormone levels, or general indices of reproductive function measures. These data suggest that additive or synergistic effects of exposure to contaminants resulting in residue levels representative of contemporary human tissue levels are unlikely to result in adverse effects on immune function or reproductive physiology in male rats.

In utero exposure to low doses of bisphenol A lead to long-term deleterious effects in the vagina

The origins of the "endocrine disrupter hypothesis" may be traced to reports on adolescent daughters born to women who had taken the highly potent synthetic estrogen, diethylstilbestrol, while pregnant, and who developed a rare form of vaginal cancer and adenocarcinoma. Bisphenol A (BPA) is an estrogenic chemical that is highly employed in the manufacture of a wide range of consumer products. Some observational studies have suggested that the amounts of BPA to which we are exposed could alter the reproductive organs of developing rodents. We examined the influence of BPA at low doses to address the questions of (a) whether in utero exposure affects the vagina of the offspring and (b) which mechanisms cause the toxic effects. Gravid Sprague-Dawley dams were administered either 0.1 (low dose) or 50 mg/kg per day BPA, the no observed effect level, or 0.2 mg/kg per day 17 alpha-ethinyl estradiol by gavage. Striking morphological changes were observed in the vagina of postpubertal offspring leading us to examine vaginal estrogen receptor (ER) expression because BPA binds to the ER alpha, which is important for growth of the vaginal epithelium. We show that the full-length ER alpha is not expressed during estrus in the vagina of female offspring exposed to either dose of BPA when compared to the control group, whereas ER alpha expression does not differ from the control group during the diestrus stage. ER alpha downregulation seems to be responsible for the observed altered vaginal morphology.