Developmental effects of estrogenic chemicals are predicted by an in vitro assay incorporating modification of cell uptake by serum

Importance of relative binding of bisphenol A and bisphenol S to plasma proteins for predicting their in vivo potencies

Many studies suggest that the potential impact of bisphenol S (BPS) as an endocrine disruptor is comparable to that of bisphenol A (BPA). However, in vitro-to-in vivo and from animal to human extrapolations require knowledge of the plasma free fraction of the active endocrine compounds. The present study aimed to characterise BPA and BPS binding to plasma proteins both in humans and different animal species. The plasma protein binding of BPA and BPS was assessed by equilibrium dialysis in plasma from adult female mice, rats, monkeys, early and late pregnant women as well as paired cord blood, early and late pregnant sheep and foetal sheep. The fraction of free BPA was independent of plasma concentrations and ranged between 4% and 7% in adults. This fraction was 2 to 3.5 times lower than that of BPS in all species except sheep, ranging from 3% to 20%. Plasma binding of BPA and BPS was not affected by the stage of pregnancy, BPA and BPS free fractions representing about 4% and 9% during early and late human pregnancy, respectively. These fractions were lower than the free fractions of BPA (7%) and BPS (12%) in cord blood. Our results suggest that similarly to BPA, BPS is extensively bound to proteins, mainly albumin. The higher fraction of free BPS compared to BPA may have implications for human exposure assessment since BPS free plasma concentrations are expected to be 2 to 3.5 times higher than that of BPA for similar plasma concentration.

Integrated recombinant gene yeast bioassay and HPLC-MS analysis for detection of low-dose multi-component residue of hormone-like compounds in environment

Illegal addition of low-dose multi-component residue of hormone-like compounds have sprung up in human activities and production as a cunning strategy to escape from sanitation monitoring, sowing a horrible seed for accidents in food security. Hence, combined strategies with accuracy and efficiency are urgently needed to overcome current circumstance and practical hurdles. Herein, an integrated analysis that compromises recombinant gene yeast bioassay (V400E-YES) and high-performance liquid chromatography-mass spectrometry (HPLC-MS) determination was developed promptly with distinguishing advantage as optimized V400E-YES provides a sum of hormone-like compounds in sample, and subsequent HPLC-MS analysis can accurately quantify the concentration of compounds. In terms of V400E-YES, large-scale random mutagenesis was performed to obtain higher sensitivity hormone receptors. Excitingly, single mutation of estrogen receptor (ER) at V400E and amphimutation of androgen receptor (AR) at G581R/D831E conferred the highest detection sensitivity with a more than 10-fold increase. Subsequently, sensitive HPLC-MS methods for simultaneous detection of eleven estrogens and nine androgens, respectively, were well-constructed. Utilizing this integrated and validated methods, we successfully investigated the hormone residue in environmental samples from farms in Jiangsu, China. Collectively, with multiple estrogens and androgens residue are being widely detected in soil and sewage samples, the feasibility of this method is highlighted, as well as the increasing lurking peril of hormone-like substance residues in environment.

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

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

Isoflavones

Phytoestrogens are naturally occurring nonsteroidal phenolic plant compounds that, due to their molecular structure and size, resemble vertebrate steroids estrogens. This review is focused on plant flavonoids isoflavones, which are ranked among the most estrogenic compounds. The main dietary sources of isoflavones for humans are soybean and soybean products, which contain mainly daidzein and genistein. When they are consumed, they exert estrogenic and/or antiestrogenic effects. Isoflavones are considered chemoprotective and can be used as an alternative therapy for a wide range of hormonal disorders, including several cancer types, namely breast cancer and prostate cancer, cardiovascular diseases, osteoporosis, or menopausal symptoms. On the other hand, isoflavones may also be considered endocrine disruptors with possible negative influences on the state of health in a certain part of the population or on the environment. This review deals with isoflavone classification, structure, and occurrence, with their metabolism, biological, and health effects in humans and animals, and with their utilization and potential risks.

In vivo and in vitro bisphenol A exposure effects on adiposity

In utero exposure to the ubiquitous plasticizer, bisphenol A (BPA) is associated with offspring obesity. As adipogenesis is a critical factor contributing to obesity, we determined the effects of in vivo maternal BPA and in vitro BPA exposure on newborn adipose tissue at the stem-cell level. For in vivo studies, female rats received BPA before and during pregnancy and lactation via drinking water, and offspring were studied for measures of adiposity signals. For in vitro BPA exposure, primary pre-adipocyte cell cultures from healthy newborns were utilized. We studied pre-adipocyte proliferative and differentiation effects of BPA and explored putative signal factors which partly explain adipose responses and underlying epigenetic mechanisms mediated by BPA. Maternal BPA-induced offspring adiposity, hypertrophic adipocytes and increased adipose tissue protein expression of pro-adipogenic and lipogenic factors. Consistent with in vivo data, in vitro BPA exposure induced a dose-dependent increase in pre-adipocyte proliferation and increased adipocyte lipid content. In vivo and in vitro BPA exposure promotes the proliferation and differentiation of adipocytes, contributing to an enhanced capacity for lipid storage. These findings reinforce the marked effects of BPA on adipogenesis and highlight the susceptibility of stem-cell populations during early life with long-term consequence on metabolic homeostasis.

TRIENNIAL REPRODUCTION SYMPOSIUM: Environmental programming of reproduction during fetal life: Effects of intrauterine position and the endocrine disrupting chemical bisphenol A

During critical periods in fetal life, there is an increased vulnerability to perturbations in endocrine function due to environmental factors. Small shifts in concentrations of hormones that regulate the differentiation of organs, such as estradiol and testosterone, can have permanent effects on morphology, enzymatic activity, and hormone receptors in tissues as well as neurobehavioral effects. These changes can lead to effects throughout life, including impacting the risk for various diseases (referred to as the Developmental Origins of Adult Health and Disease hypothesis). The intrauterine position phenomenon concerns the consequence for fetuses of randomly implanting next to embryos of the same or opposite sex. An intrauterine position next to males vs. females results in small differences in serum testosterone and estradiol during fetal life that are associated with marked effects on life history (such as lifetime fecundity) in both males and females born in litters (mice, rats, gerbils, rabbits, and swine) as well as human twins. Research with mice subsequently demonstrated that a very small experimental change in fetal serum estradiol levels altered organogenesis and caused permanent changes in organ function. Taken together, these findings led to the hypothesis that environmental chemicals that mimic or antagonize hormone action (e.g., endocrine disrupting chemicals) could also be causing harm at very low exposures (the "low dose" hypothesis) within the range of exposure of humans, domesticated animals, and wildlife. There is now extensive evidence from experimental laboratory animals, sheep, and humans that fetal exposure to very low (presumably safe) doses of the endocrine disrupting chemical bisphenol A (BPA), which exhibits estrogenic activity, can cause permanent changes that can increase the risk of a wide array of diseases. The reasons that federal regulatory agencies are ignoring the massive literature showing adverse effects of BPA and other endocrine disrupting chemicals are discussed.

Detection of bisphenol A using palm-size NanoAptamer analyzer

We have demonstrated a palm-size NanoAptamer analyzer capable of detecting bisphenol A (BPA) at environmentally relevant concentrations (<1ng/mL or ppb). It is designed for performing reaction and fluorescence measurement on single cuvette sample. Modified NanoGene assay was used as the sensing mechanism where signaling DNA and QD₆₅₅ was tethered to QD₅₆₅ and magnetic bead via the aptamer. Aptamer affinity with BPA resulted in the release of the signaling DNA and QD₆₅₅ from the complex and hence corresponding decrease in QD₆₅₅ fluorescence measurement signal. Baseline characterization was first performed with empty cuvettes, quantum dots and magnetic beads under near-ideal conditions to establish essential functionality of the NanoAptamer analyzer. Duration of incubation time, number of rinse cycles, and necessity of cuvette vibration were also investigated. In order to demonstrate the capability of the NanoAptamer analyzer to detect BPA, samples with BPA concentrations ranging from 0.0005 to 1.0ng/mL (ppb) were used. The performance of the NanoAptamer analyzer was further examined by using laboratory protocol and commercial spectrofluorometer as reference. Correlation between NanoAptamer analyzer and laboratory protocol as well as commercial spectrofluorometer was evaluated via correlation plots and correlation coefficients.

Review on crosstalk and common mechanisms of endocrine disruptors: Scaffolding to improve PBPK/PD model of EDC mixture

Endocrine disruptor compounds (EDCs) are environment chemicals that cause harmful effects through multiple mechanisms, interfering with hormone system resulting in alteration of homeostasis, reproduction and developmental effect. Many of these EDCs have concurrent exposure with crosstalk and common mechanisms which may lead to dynamic interactions. To carry out risk assessment of EDCs' mixture, it is important to know the detailed toxic pathway, crosstalk of receptor and other factors like critical window of exposure. In this review, we summarize the major mechanism of actions of EDCs with the different/same target organs interfering with the same/different class of hormone by altering their synthesis, metabolism, binding and cellular action. To show the impact of EDCs on life stage development, a case study on female fertility affecting germ cell is illustrated. Based on this summarized discussion, major groups of EDCs are classified based on their target organ, mode of action and potential risk. Finally, a conceptual model of pharmacodynamic interaction is proposed to integrate the crosstalk and common mechanisms that modulate estrogen into the predictive mixture dosimetry model with dynamic interaction of mixture. This review will provide new insight for EDCs' risk assessment and can be used to develop next generation PBPK/PD models for EDCs' mixture analysis.

Molecular targets of developmental exposure to bisphenol A in diabesity: a focus on endoderm-derived organs

Several studies associate foetal human exposure to bisphenol A (BPA) to metabolic/endocrine diseases, mainly diabesity. They describe the role of BPA in the disruption of pancreatic beta cell, adipocyte and hepatocyte functions. Indeed, the complexity of the diabesity phenotype is due to the involvement of different endoderm-derived organs, all targets of BPA. Here, we analyse this point delineating a picture of different mechanisms of BPA toxicity in endoderm-derived organs leading to diabesity. Moving from epidemiological data, we summarize the in vivo experimental data of the BPA effects on endoderm-derived organs (thyroid, pancreas, liver, gut, prostate and lung) after prenatal exposure. Mainly, we gather molecular data evidencing harmful effects at low-dose exposure, pointing to the risk to human health. Although the fragmentation of molecular data does not allow a clear conclusion to be drawn, the present work indicates that the developmental exposure to BPA represents a risk for endoderm-derived organs development as it deregulates the gene expression from the earliest developmental stages. A more systematic analysis of BPA impact on the transcriptomes of endoderm-derived organs is still missing. Here, we suggest in vitro toxicogenomics approaches as a tool for the identification of common mechanisms of BPA toxicity leading to the diabesity in organs having the same developmental origin.

Preparation of 4-butylaniline-bonded attapulgite for pre-concentration of bisphenol A in trace quantity

Ring-opening reaction with synchronous hydrolysis was used to prepare 4-butylaniline-modified attapulgite (abbreviated as BA-ATP) for pre-concentration of bisphenol A (BPA) in trace quantity. The preparation was achieved under mild condition, and the material was characterized by Fourier transform infrared spectroscopy (FT-IR), elemental analysis, nuclear magnetic resonance (NMR) and scanning electron microscopy. BA-ATP was used in solid phase extraction (SPE), and SPE was performed in a neutral condition without regard to ionic strength. The results indicate that BA-ATP has high affinity to BPA with a maximum adsorption amount of 44mg g(-1), and the adsorption can be described by Langmuir isotherm model. The content of bisphenol A in water samples was analyzed by HPLC method with the pre-concentration using BA-ATP. The limit of detection (LOD) can be as low as 3.9ng mL(-1), and the average recoveries are in a range of 93-97% with relative standard deviation (RSD) of less than 2%.

Evidence that bisphenol A (BPA) can be accurately measured without contamination in human serum and urine, and that BPA causes numerous hazards from multiple routes of exposure

There is extensive evidence that bisphenol A (BPA) is related to a wide range of adverse health effects based on both human and experimental animal studies. However, a number of regulatory agencies have ignored all hazard findings. Reports of high levels of unconjugated (bioactive) serum BPA in dozens of human biomonitoring studies have also been rejected based on the prediction that the findings are due to assay contamination and that virtually all ingested BPA is rapidly converted to inactive metabolites. NIH and industry-sponsored round robin studies have demonstrated that serum BPA can be accurately assayed without contamination, while the FDA lab has acknowledged uncontrolled assay contamination. In reviewing the published BPA biomonitoring data, we find that assay contamination is, in fact, well controlled in most labs, and cannot be used as the basis for discounting evidence that significant and virtually continuous exposure to BPA must be occurring from multiple sources.

Developmental programming: prenatal BPA treatment disrupts timing of LH surge and ovarian follicular wave dynamics in adult sheep

Developmental exposure to BPA adversely affects reproductive function. In sheep, prenatal BPA treatment induces reproductive neuroendocrine defects, manifested as LH excess and dampened LH surge and perturbs early ovarian gene expression. In this study we hypothesized that prenatal BPA treatment will also disrupt ovarian follicular dynamics. Pregnant sheep were treated from days 30 to 90 of gestation with 3 different BPA doses (0.05, 0.5, or 5mg/kgBW/day). All female offspring were estrus synchronized and transrectal ultrasonography was performed daily for 22days to monitor ovarian follicular and corpora lutea dynamics. Blood samples were collected to assess preovulatory hormonal changes and luteal progesterone dynamics. Statistical analysis revealed that the time interval between the estradiol rise and the preovulatory LH surge was shortened in the BPA-treated females. None of the three BPA doses had an effect on corpora lutea, progestogenic cycles, and mean number or duration of ovulatory and non-ovulatory follicles. However, differences in follicular count trajectories were evident in all three follicular size classes (2-3mm, 4-5mm, and ≥6mm) of prenatal BPA-treated animals compared to controls. Number of follicular waves tended also to be more variable in the prenatal BPA-treated groups ranging from 2 to 5 follicular waves per cycle, while this was restricted to 3 to 4 waves in control females. These changes in ovarian follicular dynamics coupled with defects in time interval between estradiol rise and preovulatory LH release are likely to lead to subfertility in prenatal BPA-treated females.

Low-dose effects of hormones and endocrine disruptors

Endogenous hormones have effects on tissue morphology, cell physiology, and behaviors at low doses. In fact, hormones are known to circulate in the part-per-trillion and part-per-billion concentrations, making them highly effective and potent signaling molecules. Many endocrine-disrupting chemicals (EDCs) mimic hormones, yet there is strong debate over whether these chemicals can also have effects at low doses. In the 1990s, scientists proposed the "low-dose hypothesis," which postulated that EDCs affect humans and animals at environmentally relevant doses. This chapter focuses on data that support and refute the low-dose hypothesis. A case study examining the highly controversial example of bisphenol A and its low-dose effects on the prostate is examined through the lens of endocrinology. Finally, the chapter concludes with a discussion of factors that can influence the ability of a study to detect and interpret low-dose effects appropriately.

Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.

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.

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

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

Visualization of estrogen receptor transcriptional activation in zebrafish

Estrogens regulate a diverse range of physiological processes and affect multiple tissues. Estrogen receptors (ERs) regulate transcription by binding to DNA at conserved estrogen response elements, and such elements have been used to report ER activity in cultured cells and in transgenic mice. We generated stable, transgenic zebrafish containing five consecutive elements upstream of a c-fos minimal promoter and green fluorescent protein (GFP) to visualize and quantify transcriptional activation in live larvae. Transgenic larvae show robust, dose-dependent estrogen-dependent fluorescent labeling in the liver, consistent with er gene expression, whereas ER antagonists inhibit GFP expression. The nonestrogenic steroids dexamethasone and progesterone fail to activate GFP, confirming ER selectivity. Natural and synthetic estrogens activated the transgene with varying potency, and two chemicals, genistein and bisphenol A, preferentially induce GFP expression in the heart. In adult fish, fluorescence was observed in estrogenic tissues such as the liver, ovary, pituitary gland, and brain. Individual estrogen-responsive neurons and their projections were visualized in the adult brain, and GFP-positive neurons increased in number after 17β-estradiol exposure. The transgenic estrogen-responsive zebrafish allow ER signaling to be monitored visually and serve as in vivo sentinels for detection of estrogenic compounds.

Effects of methoxychlor and 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane on 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase-3 activities in human and rat testes

Human and rat testis microsomes were used to investigate direct inhibitory activities of methoxychlor (MXC) and its metabolite 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE) on 3β-hydroxysteroid dehydrogenase (3β-HSD) and 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3). The 3β-HSD and 17β-HSD3 enzymes are involved in the reactions that culminate in androgen biosynthesis in Leydig cells. The results demonstrated that MXC and HPTE inhibited human 3β-HSD activity at a concentration of 10 nm. The half maximal inhibitory concentration (IC(50) ) for MXC inhibition of 3β-HSD was 53.21 ± 15.52 μm (human) and 46.15 ± 17.94 μm (rat), and for HPTE, it was 8.29 ± 2.49 μm (human) and 13.82 ± 2.26 μm (rat). At the higher concentration of 100 μm, MXC did not affect human and rat 17β-HSD3 activity. However, the IC(50) for HPTE inhibition of 17β-HSD3 was 12.1 ± 1.9 μm (human) and 32 .0 ± 8.6 μm (rat). The mode of action of MXC and HPTE on 3β-HSD activity was non-competitive with the substrate pregnenolone, but was competitive with the cofactor NAD(+) . The mode of HPTE inhibition of 17β-HSD3 was non-competitive with the substrate androstenedione, but was competitive with the cofactor NADPH. In summary, our results showed that HPTE, which is the biologically active metabolite of MXC, has the capacity for direct inhibition of 3β-HSD and 17β-HSD3 enzyme activity. Inhibition of enzyme activity is presumably associated with suppression of steroidogenesis in gonadal tissues and has implications for testis function.

The impact of neonatal bisphenol-A exposure on sexually dimorphic hypothalamic nuclei in the female rat

Now under intense scrutiny, due to its endocrine disrupting properties, the potential threat the plastics component bisphenol-A (BPA) poses to human health remains unclear. Found in a multitude of polycarbonate plastics, food and beverage containers, and medical equipment, BPA is thought to bind to estrogen receptors (ERs), thereby interfering with estrogen-dependent processes. Our lab has previously shown that exposure to BPA (50mg/kg bw or 50μg/kg bw) during the neonatal critical period is associated with advancement of puberty, early reproductive senescence and ovarian malformations in female Long Evans rats. Here, using neural tissue obtained from the same animals, we explored the impact of neonatal BPA exposure on the development of sexually dimorphic hypothalamic regions critical for female reproductive physiology and behavior. Endpoints included quantification of oxytocin-immunoreactive neurons (OT-ir) in the paraventricular nucleus (PVN), serotonin (5-HT-ir) fiber density in the ventrolateral subdivision of the ventromedial nucleus (VMNvl) as well as ERα-ir neuron number in the medial preoptic area (MPOA), the VMNvl, and the arcuate nucleus (ARC). Both doses of BPA increased the number of OT-ir neurons within the PVN, but no significant effects were seen on 5-HT-ir fiber density or ERα-ir neuron number in any of the areas analyzed. In addition to hypothalamic development, we also assessed female sex behavior and body weight. No effect of BPA on sexual receptivity or proceptive behavior in females was observed. Females treated with BPA, however, weighed significantly more than control females by postnatal day 99. This effect of BPA on weight is critical because alterations in metabolism, are frequently associated with reproductive dysfunction. Collectively, the results of this and our prior study indicate that the impact of neonatal BPA exposure within the female rat hypothalamus is region specific and support the hypothesis that developmental BPA exposure may adversely affect reproductive development in females.

Acute and chronic effects of oral genistein administration in neonatal mice

Soy-based infant formulas are widely used in the United States and some other countries. These formulas contain high levels of the estrogenic isoflavone genistein, leading to concern that neonatal genistein exposure could cause acute and/or long-term adverse effects on reproductive and other organs. However, previous work to assess genistein effects in rodent models has not typically replicated the route of delivery and/or serum genistein concentrations reported for soy formula-fed human infants. Our objective was to develop a mouse model that more closely mimics the oral genistein exposure and total serum genistein concentrations observed in soy formula-fed infants. Mouse pups were dosed orally with genistein in a soy formula-corn oil emulsion from Postnatal Day (PND) 1 to PND 5, then effects on reproductive and non-reproductive organs were assessed after dosing and during subsequent development. Neonatal treatment resulted in changes both at the completion of dosing (PND 5) and in adult animals. At PND 5, neonatal genistein treatment caused increased relative uterine weight and down-regulation of progesterone receptor in uterine epithelia. Estrogenic effects of genistein were also seen in the neonatal ovary and thymus, which had an increase in the incidence of multioocyte follicles (MOFs) and a decrease in thymic weight relative to body weight, respectively. The increased incidence of MOFs persisted into adulthood for neonatally treated genistein females, and estrous cycle abnormalities were seen at 6 mo of age despite normal fertility in these mice. The immediate and long-term effects in this neonatal animal model raise concerns that high serum concentrations of genistein are estrogenic and could potentially impact the development of human infants fed soy formula.

Xenoestrogen-induced regulation of EZH2 and histone methylation via estrogen receptor signaling to PI3K/AKT

Although rapid, membrane-activated estrogen receptor (ER) signaling is no longer controversial, the biological function of this nongenomic signaling is not fully characterized. We found that rapid signaling from membrane-associated ER regulates the histone methyltransferase enhancer of Zeste homolog 2 (EZH2). In response to both 17beta-estradiol (E2) and the xenoestrogen diethylstilbestrol, ER signaling via phosphatidylinositol 3-kinase/protein kinase B phosphorylates EZH2 at S21, reducing levels of trimethylation of lysine 27 on histone H3 in hormone-responsive cells. During windows of uterine development that are susceptible to developmental reprogramming, activation of this ER signaling pathway by diethylstilbestrol resulted in phosphorylation of EZH2 and reduced levels of trimethylation of lysine 27 on histone H3 in chromatin of the developing uterus. Furthermore, activation of nongenomic signaling reprogrammed the expression profile of estrogen-responsive genes in uterine myometrial cells, suggesting this as a potential mechanism for developmental reprogramming caused by early-life exposure to xenoestrogens. These data demonstrate that rapid ER signaling provides a direct linkage between xenoestrogen-induced nuclear hormone receptor signaling and modulation of the epigenetic machinery during tissue development.

Physiologically based modeling of p-tert-octylphenol kinetics following intravenous, oral or subcutaneous exposure in male and female Sprague-Dawley rats

The objective of this study was to develop a physiologically based pharmacokinetic (PBPK) model for p-tert-octylphenol (OP) for understanding the qualitative and quantitative determinants of its kinetics in Sprague-Dawley rats. Compartments of the PBPK model included the liver, richly perfused tissues, poorly perfused tissues, reproductive tissues, adipose tissue and subcutaneous space, in which OP uptake was described as a blood flow- or a membrane diffusion-limited process. The PBPK model successfully simulated previously published data on blood and tissue OP concentrations in Sprague-Dawley rats following oral, intravenous (i.v.) or subcutaneous (s.c.) routes. The model predicted that OP concentrations would reach 6.8, 13.8 and 27.9 ng ml(-1) (male) and 7.2, 14.7 and 31.4 ng ml(-1) (female), 4 h after a single i.v. dose of 2, 4 and 8 mg kg(-1), respectively. The model also predicted that OP concentrations would reach 53.3, 134.8 and 271.2 ng ml(-1) (male) and 87.4, 221.4 and 449.7 ng ml(-1) (female) 4 h after a single oral dose (50, 125 and 250 mg kg(-1)) and that, 4 h after a single s.c. dose (125 mg kg(-1)), OP concentrations would reach 111.3 ng ml(-1) (male) and 121.6 ng ml(-1). A marked sex difference was seen in blood and tissue OP concentrations. This was reflected in the model by a gender-specific maximal velocity of metabolism (V(max)) that was higher (1.77 x) in male than in female rats. Further studies are required to elucidate the mechanism underlying the gender differences and to evaluate whether that is also observed in humans.

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.

Toxicokinetics of p-tert-octylphenol in male and female Sprague-Dawley rats after intravenous, oral, or subcutaneous exposures

This study was undertaken to characterize the toxicokinetics of p-tert-octylphenol (OP), a weak estrogenic compound, in male and female rats. Male and female Sprague-Dawley rats were given a single dose of OP either by oral gavage (50, 125 or 250 mg/kg), by intravenous (iv) injection (2, 4, or 8 mg/kg), or by subcutaneous (sc) injection (125 mg/kg). In a repeated dosing experiment, rats were given OP (oral) daily (25, 50, or 125 mg/kg) for 35 d (female) or 60 d (male). Blood and tissue samples were collected and analyzed for OP content using gas chromatography with detection by mass spectrometry. Blood OP concentrations were generally higher in female than male rats following a single oral or sc administration but were similar following a single iv injection. Tissue OP concentrations were also higher in female than male rats following oral exposure, consistent with the faster metabolism of OP observed in male rat liver microsomes. After subchronic administration, blood OP concentrations were higher at the end of exposure for female (33 d) (2.26-fold, not significant) and male (57 d) (3.47-fold) rats than single dosing but there was no change in the tissue OP concentrations. Gender differences in tissue OP concentrations may contribute, in part, to gender differences in the toxicity of OP in rats. The fact that OP was found in all reproductive tissues confirms its potential for direct endocrine-like effects.

Genistein decreases androgen biosynthesis in rat Leydig cells by interference with luteinizing hormone-dependent signaling

Testicular Leydig cells express estrogen receptors and are the predominant source of the male sex steroid hormone testosterone (T). Previous studies demonstrated that genistein acts through estrogen receptors in Leydig cells. In the present study, pre-treatment of Leydig cells isolated from 35 day-old male Long Evans rats with the epidermal growth factor receptor (EGFR) kinase inhibitor AG 1478 abrogated genistein inhibition of T biosynthesis. Also, incubation of Leydig cells in culture medium containing epidermal growth factor (EGF) decreased T secretion (control: 255+/-16; EGF: 190+/-17ng/10(6) cells, 24h) (P<0.05). However, T secretion by genistein-treated Leydig cells (0.1nM, 10muM; 24h) was rescued by post-treatment incubation with forskolin (control: 275+/-28 versus 325+/-35; 780+/-85; ng/10(6) cells, 3h) and dibutyryl cyclic adenosine 3'-5'-monophosphate (dbcAMP) (control: 370+/-65 versus 580+/-75; 2500+/-200; ng/10(6) cells, 3h) (P>0.05). Furthermore, post-treatment incubation with cholera toxin, an activator of G proteins, caused genistein-treated Leydig cells to produce similar T amounts as untreated control (control: 55+/-5 versus 52+/-2 and 47+/-4; ng/10(6) cells, 3h) (P>0.05). These observations imply that genistein action interferes with coupling of transmembrane luteinizing hormone receptors (LHR) with G proteins. Uncoupling of LHR from G proteins adversely affects adenylate cyclase function and impacts LH-dependent stimulation of Leydig cells. These findings have implications for testicular steroidogenesis in individuals exposed to genistein and soy-based products.

Effects of developmental exposure to bisphenol A on brain and behavior in mice

Bisphenol A (BPA) is a widespread estrogenic chemical used in the production of polycarbonate, and epoxy resins lining food and beverage cans and in dental sealants. During fetal life the intrauterine environment is critical for the normal development, and even small changes in the levels of hormones, such as estradiol or estrogen-mimicking chemicals, can lead to changes in brain function and consequently in behavior. We review here a series of ethological studies on the effects of maternal oral exposure during the last part of gestation (prenatal exposure) or from gestation day 11 to postnatal day 7 (perinatal exposure) to a low, environmentally relevant dose of BPA (10 microg/kg bw/day) on behavioral responses of CD-1 mouse offspring. We examined both male and female offspring and found that maternal exposure to BPA affected: (1) behavioral responses to novelty before puberty and, as adults; (2) exploration and activity in a free-exploratory open field; (3) exploration in the elevated plus maze and (4) sensitivity to amphetamine-induced reward in the conditioned place preference test. A consistent effect of the maternal exposure to BPA is that in all these different experimental settings, while a significant sex difference was observed in the control group, exposure to BPA decreased or eliminated the sex difference in behavior. In addition, exposure of female mice to BPA in both adulthood or during fetal life altered subsequent maternal behavior. These findings, together with those from other laboratories, are evidence of long-term consequences of maternal exposure to low-dose BPA at the level of neurobehavioral development.

No effect of route of exposure (oral; subcutaneous injection) on plasma bisphenol A throughout 24h after administration in neonatal female mice

Route of administration of chemicals in adults is an important factor in pharmacokinetics of chemicals such as bisphenol A (BPA), the monomer with estrogenic activity used to make polycarbonate plastic products and to line food and beverage cans. Based on findings in adults it has been proposed (CERHR, 2007) that non-oral routes of administration in newborn rodents would also lead to high exposure relative to oral administration. However, in fetuses and neonates, the enzyme that conjugates BPA (UDP-glucuronosyltransferase) is expressed at low levels, suggesting that there may be no differences in pharmacokinetics between oral and non-oral dosing. We thus conducted an analysis of plasma concentrations of unconjugated 3H-BPA after HPLC separation in postnatal day 3 female mice throughout the 24h after administering 3H-BPA orally or via subcutaneous injection at doses above and below the current EPA reference dose. We found no significant difference in plasma BPA based on route of administration in neonatal mice at either dose. However, compared to data from other studies conducted with adults, there was a markedly higher plasma BPA level after oral administration of BPA in newborn mice. This finding sets aside the belief that non-oral administration of BPA renders data as not suitable for consideration of the hazard posed by low-dose exposure to BPA during neonatal life. Therefore the large numbers of BPA studies that used non-oral administration at very low doses during the neonatal period should not be dismissed by scientists or the regulatory community based on route of administration.

Role for estradiol in female-typical brain and behavioral sexual differentiation

The importance of estrogens in controlling brain and behavioral sexual differentiation in female rodents is an unresolved issue in the field of behavioral neuroendocrinology. Whereas, the current dogma states that the female brain develops independently of estradiol, many studies have hinted at possible roles of estrogen in female sexual differentiation. Accordingly, it has been proposed that alpha-fetoprotein, a fetal plasma protein that binds estrogens with high affinity, has more than a neuroprotective role and specifically delivers estrogens to target brain cells to ensure female differentiation. Here, we review new results obtained in aromatase and alpha-fetoprotein knockout mice showing that estrogens can have both feminizing and defeminizing effects on the developing neural mechanisms that control sexual behavior. We propose that the defeminizing action of estradiol normally occurs prenatally in males and is avoided in fetal females because of the protective actions of alpha-fetoprotein, whereas the feminizing action of estradiol normally occurs postnatally in genetic females.

Endocrine-disrupting potential of bisphenol A, bisphenol A dimethacrylate, 4-n-nonylphenol, and 4-n-octylphenol in vitro: new data and a brief review

BACKGROUND

An array of environmental compounds is known to possess endocrine disruption (ED) potentials. Bisphenol A (BPA) and bisphenol A dimethacrylate (BPA-DM) are monomers used to a high extent in the plastic industry and as dental sealants. Alkylphenols such as 4-n-nonylphenol (nNP) and 4-n-octylphenol (nOP) are widely used as surfactants.

OBJECTIVES

We investigated the effect in vitro of these four compounds on four key cell mechanisms including transactivation of a) the human estrogen receptor (ER), b) the human androgen receptor (AR), c) the aryl hydrocarbon receptor (AhR), and d) aromatase activity.

RESULTS

All four compounds inhibited aromatase activity and were agonists and antagonists of ER and AR, respectively. nNP increased AhR activity concentration-dependently and further increased the 2,3,7,8-tetrachlorodibenzo-p-dioxin AhR action. nOP caused dual responses with a weak increased and a decreased AhR activity at lower (10(-8) M) and higher concentrations (10(-5)-10(-4) M), respectively. AhR activity was inhibited with BPA (10(-5)-10(-4) M) and weakly increased with BPA-DM (10(-5) M), respectively. nNP showed the highest relative potency (REP) compared with the respective controls in the ER, AhR, and aromatase assays, whereas similar REP was observed for the four chemicals in the AR assay.

CONCLUSION

Our in vitro data clearly indicate that the four industrial compounds have ED potentials and that the effects can be mediated via several cellular pathways, including the two sex steroid hormone receptors (ER and AR), aromatase activity converting testosterone to estrogen, and AhR; AhR is involved in syntheses of steroids and metabolism of steroids and xenobiotic compounds.

Evidence of altered brain sexual differentiation in mice exposed perinatally to low, environmentally relevant levels of bisphenol A

Humans are routinely exposed to bisphenol A (BPA), an estrogenic chemical present in food and beverage containers, dental composites, and many products in the home and workplace. BPA binds both classical nuclear estrogen receptors and facilitates membrane-initiated estrogenic effects. Here we explore the ability of environmentally relevant exposure to BPA to affect anatomical and functional measures of brain development and sexual differentiation. Anatomical evidence of alterations in brain sexual differentiation were examined in male and female offspring born to mouse dams exposed to 0, 25, or 250 ng BPA/kg body weight per day from the evening of d 8 of gestation through d 16 of lactation. These studies examined the sexually dimorphic population of tyrosine hydroxylase (TH) neurons in the rostral periventricular preoptic area, an important brain region for estrous cyclicity and estrogen-positive feedback. The significant sex differences in TH neuron number observed in control offspring were diminished or obliterated in offspring exposed to BPA primarily because of a decline in TH neuron number in BPA-exposed females. As a functional endpoint of BPA action on brain sexual differentiation, we examined the effects of perinatal BPA exposure on sexually dimorphic behaviors in the open field. Data from these studies revealed significant sex differences in the vehicle-exposed offspring that were not observed in the BPA-exposed offspring. These data indicate that BPA may be capable of altering important events during critical periods of brain development.

Estrogenic activity of polychlorinated biphenyls present in human tissue and the environment

This study evaluated the estrogenicity of polychlorinated biphenyls (PCBs) present in environmental media and human tissue and assessed exposure pathways for PCB-derived estrogenic potency in air, soil, and dust from New Bedford, MA, an area with a PCB-contaminated Superfund site. Thirty-four PCB congeners were assayed for estrogenic potency using E-SCREEN, an assay based on the estrogen-dependent proliferation of MCF-7 cells in vitro. Childhood exposure to estradiol-equivalents via PCBs in environmental media was estimated byweighting previously reported New Bedford congener-specific concentrations by their relative estrogenic potency and published inhalation and soil ingestion rates. Thirteen congeners were weakly estrogenic in E-SCREEN: PCBs 17, 18, 30, 44, 49, 66, 74, 82, 99, 103, 110, 128, and 179. These PCBs were typically 6 orders of magnitude less potent than 17beta-estradiol, with proliferative potencies ranging from 0.0007% to 0.0040%. Of the environmental media assessed, air (inhalation) had the highest PCB-derived estradiol-equivalent exposure. PCB estrogenic potency information from this study provides an important resource both for preliminary estimation of routes of human exposure to xenoestrogens and for application to human health studies focused on estrogen-responsive health outcomes, such as reproductive development and related malignancies.

An extensive new literature concerning low-dose effects of bisphenol A shows the need for a new risk assessment

Bisphenol A (BPA) is the monomer used to manufacture polycarbonate plastic, the resin lining of cans, and other products, with global capacity in excess of 6.4 billion lb/year. Because the ester bonds in these BPA-based polymers are subject to hydrolysis, leaching of BPA has led to widespread human exposure. A recent report prepared by the Harvard Center for Risk Analysis and funded by the American Plastics Council concluded that evidence for low-dose effects of BPA is weak on the basis of a review of only 19 studies; the report was issued after a delay of 2.5 years. A current comprehensive review of the literature reveals that the opposite is true. As of December 2004, there were 115 published in vivo studies concerning low-dose effects of BPA, and 94 of these report significant effects. In 31 publications with vertebrate and invertebrate animals, significant effects occurred below the predicted "safe" or reference dose of 50 microg/kg/day BPA. An estrogenic mode of action of BPA is confirmed by in vitro experiments, which describe disruption of cell function at 10(-12) M or 0.23 ppt. Nonetheless, chemical manufacturers continue to discount these published findings because no industry-funded studies have reported significant effects of low doses of BPA, although > 90% of government-funded studies have reported significant effects. Some industry-funded studies have ignored the results of positive controls, and many studies reporting no significant effects used a strain of rat that is inappropriate for the study of estrogenic responses. We propose that a new risk assessment for BPA is needed based on a) the extensive new literature reporting adverse effects in animals at doses below the current reference dose; b) the high rate of leaching of BPA from food and beverage containers, leading to widespread human exposure; c) reports that the median BPA level in human blood and tissues, including in human fetal blood, is higher than the level that causes adverse effects in mice; and d) recent epidemiologic evidence that BPA is related to disease in women.

Human breast milk and xenoestrogen exposure: a possible impact on human health

Human milk is the best natural and optimal food for neonates with several immunologic, developmental and practical advantages throughout childhood. Although the World Health Organization strongly supports breastfeeding, it recognizes the potential health risks posed by the presence of environmental toxicants in breast milk. Contamination of human milk is widespread and due to decades of inadequately controlled pollution by toxicants, persistent pesticides or chemical solvents. These chemicals tend to degrade slowly in the environment, to bioaccumulate in the food chain and to have long half-lives in humans. Many of these environmental pollutants have estrogen-like activities and, thus they are called environmental estrogen disruptors or xenoestrogens. Certain adverse health and reproductive outcomes are attributed to these chemicals in laboratory animals and in wildlife as well as in humans. Here, we review available data from breast milk monitoring studies suggesting the environmental chemicals that may affect child health through breastfeeding.

The importance of appropriate controls, animal feed, and animal models in interpreting results from low-dose studies of bisphenol A

Interpreting results of studies that report only negative effects is problematic. A number of published studies to determine whether chemicals with estrogenic activity can cause effects at low doses have not taken into account the possibility that the commercial animal feed being used can mask effects of even potent estrogenic drugs such as diethylstilbestrol (DES). In addition, the sensitivity of the strain of animal being used for the specific category of chemical being tested has not always been described. For environmental chemicals, such as the estrogenic polycarbonate plastic monomer bisphenol A, DES is an appropriate positive control for estrogenic effects, and using an appropriate low dose of DES can eliminate the possibility of false-negative conclusions of safety when the above or other variables contribute to the negative outcome. Only when simultaneous positive effects of low doses of a positive control chemical such as DES and negative effects of environmentally relevant low doses of the test chemical are demonstrated within the same experiment are conclusions of no effect of the test chemical warranted, and this has not been reported for bisphenol A in any study. Instead, more than 90 refereed journal publications have reported effects due to exposure to low doses of bisphenol A in a wide variety of animals (for references see: http://rcp.missouri.edu/endocrinedisruptors/vomsaal/vomsaal.html). However, due to lack of attention to the importance of appropriate positive controls, a small number of studies reporting negative effects of bisphenol A have created a false sense of controversy regarding low-dose effects of bisphenol A.

Hormonal, cellular, and molecular control of prostatic development

The prostate is a male accessory sex gland found only in mammals that functions to produce a major fraction of seminal fluid. Interest in understanding the biology of the prostate is driven both by the fascinating nature of the developmental processes that give rise to the prostate and by the high incidence in humans of prostatic diseases, including prostatic adenocarcinoma and benign prostatic hyperplasia. This review summarizes the current state of knowledge of the cellular and molecular processes that control prostatic development. Insight into the mechanisms that control prostatic development has come from experimental embryological work as well as from the study of mice and humans harboring mutations that alter prostatic development. These studies have demonstrated a requirement for androgens throughout prostatic development and have revealed a series of reciprocal paracrine signals between the developing prostatic epithelium and prostatic mesenchyme. Finally, these studies have identified several specific gene products that are required for prostatic development. While research in recent years has greatly enhanced our understanding of the molecular control of prostatic development, known genes cannot yet explain in molecular terms the complex biological interactions that descriptive and experimental embryological studies have elucidated in the control of prostatic development.

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.

Sulfation of Environmental Estrogens by Cytosolic Human Sulfotransferases

It is known that in humans taking soy food, the phytoestrogens, daidzein (DZ) and genistein (GS), exist as sulfates and glucuronides in the plasma and are excreted as conjugates in urine. To investigate which human sulfotransferase (SULT) isoforms participate in the sulfation of these phytoestrogens, the four major cytosolic SULTs, SULT1A1, SULT1A3, SULT1E1, and SULT2A1, occurring in the human liver were bacterially expressed as His-tagged proteins and chromatographically purified to homogeneity in the presence of Tween 20 and glycerol as highly efficient agents for stabilizing the recombinant enzymes. All the SULTs showed sulfating activity toward both DZ and GS. However, k(cat)/K(m) values observed indicated that these phytoestrogens were sulfated predominantly by SULT1A1 and SULT1E1 with K(m) values of 0.3 and 0.7 microM for GS and 1.9 and 3.4 microM for DZ, respectively. DZ and GS strongly inhibited the sulfation of the endogenous substrate, beta-estradiol, by SULT1E1 in a non-competitive manner with K(i) values of 14 and 7 microM, respectively, suggesting that these phytoestrogens might affect tissue levels of beta-estradiol in the human. The phenolic endocrine-disrupting chemicals, bisphenol A (BPA), 4-n-nonylphenol (NP), and 4-t-octylphenol (t-OP), were used as substrates to investigate the possible participation of human SULTs in their metabolism for excretion. High k(cat)/K(m) values were observed for the sulfation of BPA by SULT1A1, NP by SULT1A1 and SULT1E1, and t-OP by SULT1E1 and SULT2A1.

Oestrogenic and antiandrogenic chemicals in the environment: effects on male reproductive health

Exposures of human populations to pesticides and industrial pollutants, and to synthetic chemicals present in foods, beverages, and plastics, have raised concern that these substances can interfere with endogenous sex hormone function. Interference with sex hormone action can, in turn, result in a variety of developmental and reproductive anomalies. Compounds in this class are thus referred to as endocrine disruptors (EDs). EDs that affect reproductive processes in vertebrates act primarily by altering oestrogenic and antiandrogenic activities. The recent cloning of a second oestrogen receptor (ER) subtype (ERbeta) and its widespread tissue distribution pattern indicates that the first ER to be cloned, ERalpha, may not be the only, or even the primary, mediator of oestrogen action. It is anticipated that this discovery will lead to development of antagonist compounds specific to either ER subtype, and help to determine the function of each receptor subtype in reproductive and other tissues. Growing evidence suggests that EDs interfere with reproductive function at low exposure levels and cause distinct effects at different concentrations within the same organ. Developing organisms have increased susceptibility to the actions of EDs because differentiating tissues are more vulnerable to changes in hormonal milieu. Thus, children are at greater risk of toxicant-related illnesses than adults. However, most data are collected from laboratory studies, and it remains to be determined that the levels of chemicals in the environment can impair human reproductive health. There is also significant genetic variability between human and animal species in their reactions to chemicals. The effects of low-dose, chronic, and multiple chemical exposures warrant further investigation in order to characterize the risk of environmental agents to humans. The aims of this review, which will focus on male reproduction, are to: 1) identify synthetic chemicals in the environment that fall into the ED class; 2) describe their mechanisms of toxicity in reproductive tissues; and, 3) outline the direction of future research efforts with respect to EDs.

Soyfoods, soybean isoflavones, and bone health: a brief overview

Soyfoods have received considerable attention during the past 5 years for their role in disease prevention, especially in relation to heart disease, osteoporosis, and cancer. However, limited research also suggests that soy protein favorably affects renal function. Much of the research interest in soy is aimed at establishing the physiological effects of isoflavones. Isoflavones are diphenolic compounds that have a very limited distribution in nature. Soybeans and soyfoods are, for practical purposes, the only nutritionally relevant dietary sources of isoflavones. Isoflavones are weak estrogens in that they bind to estrogen receptors, but they also have important nonhormonal properties as well. Initial speculation that soyfoods, and in particular isoflavones, might promote bone health was based on the estrogenic properties of isoflavones and the similarity in structure between isoflavones and the osteoporosis drug, ipriflavone, which is a synthetic isoflavone. In ovariectomized rodents, isoflavones retard bone loss almost as effectively as estrogen. Most research, but not all, also indicates that soyfoods rich in isoflavones favorably affect bone turnover and spinal bone mineral density in perimenopausal and postmenopausal women. However, studies conducted thus far have been of short duration and involved small numbers of subjects. Furthermore, no studies have actually examined the effect of soy feeding on fracture risk. Thus, although the data in general are encouraging, no firm conclusions can be drawn about the relationship between soy consumption and bone health. In addition to a possible direct effect of isoflavones on bone tissue, soy protein when substituted for animal protein may indirectly enhance bone strength. Several studies have found that in comparison with animal protein, soy protein decreases calcium excretion, a result of the lower sulfur amino acid content of soy protein. Although the high potassium content of soy is a consideration, the evidence clearly indicates that clinicians should consider recommending that their renal patients incorporate soyfoods into their diet.