Estrogen receptor independent neurotoxic mechanism of bisphenol A, an environmental estrogen

GGA1 participates in spermatogenesis in mice under stress

BACKGROUND

Infertility is recognized as a common and worrisome problem of human reproduction worldwide. Based on previous studies, male factors account for about half of all infertility cases. Exposure to environmental toxicants is an important contributor to male infertility. Bisphenol A (BPA) is the most prominent toxic environmental contaminant worldwide affecting the male reproductive system. BPA can impair the function of the Golgi apparatus which is important in spermatogenesis. GGA1 is known as Golgi-localized, gamma adaptin ear-containing, ARF-binding protein 1. Previously, it has been shown that GGA1 is associated with spermatogenesis in Drosophila, however, its function in mammalian spermatogenesis remains unclear.

METHODS

Gga1 knockout mice were generated using the CRISPR/Cas9 system. Gga1-/- male mice and wild-type littermates received intraperitoneal (i.p.) injections of BPA (40 µg/kg) once daily for 2 weeks. Histological and immunofluorescence staining were performed to analyze the phenotypes of these mice.

RESULTS

Male mice lacking Gga1 had normal fertility without any obvious defects in spermatogenesis, sperm count and sperm morphology. Gga1 ablation led to infertility in male mice exposed to BPA, along with a significant reduction in sperm count, sperm motility and the percentage of normal sperm. Histological analysis of the seminiferous epithelium showed that spermatogenesis was severely disorganized, while apoptotic germ cells were significantly increased in the Gga1 null mice exposed to BPA. Our findings suggest that Gga1 protects spermatogenesis against damage induced by environmental pollutants.

Bisphenol A single and repeated treatment increases HDAC2, leading to cholinergic neurotransmission dysfunction and SN56 cholinergic apoptotic cell death through AChE variants overexpression and NGF/TrkA/P75NTR signaling disruption

Bisphenol-A (BPA), a widely used plasticizer, induces cognitive dysfunctions following single and repeated exposure. Several studies, developed in hippocampus and cortex, tried to find the mechanisms that trigger and mediate these dysfunctions, but those are still not well known. Basal forebrain cholinergic neurons (BFCN) innervate hippocampus and cortex, regulating cognitive function, and their loss or the induction of cholinergic neurotransmission dysfunction leads to cognitive disabilities. However, no studies were performed in BFCN. We treated wild type or histone deacetylase (HDAC2), P75^NTR or acetylcholinesterase (AChE) silenced SN56 cholinergic cells from BF with BPA (0.001 μM-100 μM) with or without recombinant nerve growth factor (NGF) and with or without acetylcholine (ACh) for one- and fourteen days in order to elucidate the mechanisms underlying these effects. BPA induced cholinergic neurotransmission disruption through reduction of ChAT activity, and produced apoptotic cell death, mediated partially through AChE-S overexpression and NGF/TrkA/P75^NTR signaling dysfunction, independently of cholinergic neurotransmission disruption, following one- and fourteen days of treatment. BPA mediates these alterations, in part, through HDAC2 overexpression. These data are relevant since they may help to elucidate the neurotoxic mechanisms that trigger the cognitive disabilities induced by BPA exposure, providing a new therapeutic approach.

The phenotypic and transcriptomic effects of developmental exposure to nanomolar levels of estrone and bisphenol A in zebrafish

Estrone and BPA are two endocrine disrupting chemicals (EDCs) that are predicted to be less potent than estrogens such as 17β-estradiol and 17α-ethinylestradiol. Human exposure concentrations to estrone and BPA can be as low as nanomolar levels. However, very few toxicological studies have focused on the nanomolar-dose effects. Low level of EDCs can potentially cause non-monotonic responses. In addition, exposures at different developmental stages can lead to different health outcomes. To identify the nanomolar-dose effects of estrone and BPA, we used zebrafish modeling to study the phenotypic and transcriptomic responses after extended duration exposure from 0 to 5 days post-fertilization (dpf) and short-term exposure at days 4-5 post fertilization. We found that non-monotonic transcriptomic responses occurred after extended duration exposures at 1 nM of estrone or BPA. At this level, estrone also caused hypoactivity locomotive behavior in zebrafish. After both extended duration and short-term exposures, BPA led to more apparent phenotypic responses, i.e. skeletal abnormalities and locomotion changes, and more significant transcriptomic responses than estrone exposure. After short-term exposure, BPA at concentrations equal or above 100 nM affected locomotive behavior and changed the expression of both estrogenic and non-estrogenic genes that are linked to neurological diseases. These data provide gaps of mechanisms between neurological genes expression and associated phenotypic response due to estrone or BPA exposures. This study also provides insights for assessing the acceptable concentration of BPA and estrone in aquatic environments.

Bisphenol S Triggers the Migration and Invasion of Pheochromocytoma PC12 Cells via Estrogen-Related Receptor α

Pheochromocytoma (PCC) is a tumor of the adrenal medulla for which surgical resection is the only therapy approach. Risk factors responsible for the tumorigenesis and progression of PCC are not well illustrated. Our present study revealed that an industrial chemical, bisphenol S (BPS), can promote the migration and invasion of PCC PC12 cells, which was evidenced by the upregulation of fibronectin (FN) and matrix metalloproteinases (MMP-2 and MMP-9). The inhibitor of estrogen-related receptor α (ERRα), while not estrogen receptor α/β (ERα/β) or G protein-coupled estrogen receptor (GPER), can attenuate BPS-induced cell migration. Mechanically, BPS can increase the binding between ERRα and promoter of FN1 and then induce the expression of FN in PC12 cells. Further, BPS can induce the expression of miR-10b in PC12 cells via ERRα. The upregulated miR-10b inhibited the expression of KLF4, which can suppress the migration and invasion of cancer cells. BPS can trigger the mRNA and protein expression of ERRα in PC12 cells via a time-dependent manner. Collectively, our study revealed that nanomolar BPS can trigger the migration and invasion of PC12 cells via activation and upregulation of ERRα.

Microarray expression profiling and co-expression network analysis of circulating LncRNAs and mRNAs associated with neurotoxicity induced by BPA

A growing body of evidence has shown bisphenol A (BPA), an estrogen-like industrial chemical, has adverse effects on the nervous system. In this study, we investigated the transcriptional behavior of long non-coding RNAs (lncRNAs) and mRNAs to provide the information to explore neurotoxic effects induced by BPA. By microarray expression profiling, we discovered 151 differentially expressed lncRNAs and 794 differentially expressed mRNAs in the BPA intervention group compared with the control group. Gene ontology analysis indicated the differentially expressed mRNAs were mainly involved in fundamental metabolic processes and physiological and pathological conditions, such as development, synaptic transmission, homeostasis, injury, and neuroinflammation responses. In the expression network of the BPA-induced group, a great number of nodes and connections were found in comparison to the control-derived network. We identified lncRNAs that were aberrantly expressed in the BPA group, among which, growth arrest specific 5 (GAS5) might participate in the BPA-induced neurotoxicity by regulating Jun, RAS, and other pathways indirectly through these differentially expressed genes. This study provides the first investigation of genome-wide lncRNA expression and correlation between lncRNA and mRNA expression in the BPA-induced neurotoxicity. Our results suggest that the elevated expression of lncRNAs is a major biomarker in the neurotoxicity induced by BPA.

Water Quality and Brain Function

In the United States, regulations are in place to ensure the quality of drinking water. Such precautions are intended to safeguard the health of the population. However, regulatory guidelines may at times fail to achieve their purpose. This may be due to lack of sufficient data regarding the health hazards of chronic low dose exposure to contaminants or the introduction of new substances that pose a health hazard risk that has yet to be identified. In this review, examples of different sources of contaminants in drinking water will be discussed, followed by an evaluation of some select individual toxicants with known adverse neurological impact. The ability of mixtures to potentially cause additive, synergistic, or antagonistic neurotoxic responses will be briefly addressed. The last section of the review will provide examples of select mechanisms by which different classes of contaminants may lead to neurological impairments. The main objective of this review is to bring to light the importance of considering trace amounts of chemicals in the drinking water and potential brain abnormalities. There is continued need for toxicology studies to better understand negative consequences of trace amounts of toxins and although it is beyond the scope of this brief overview it is hoped that the review will underscore the paucity of studies focused on determining how long-term exposure to minute levels of contaminants in drinking water may pose a significant health hazard.

Adverse effects of bisphenol A (BPA) on the dopamine system in two distinct cell models and corpus striatum of the Sprague-Dawley rat

The aim of this study was to examine the effects of bisphenol A (BPA) on the brain dopamine (DA) system utilizing both in vitro models (GH3 cells, a rat pituitary cell line, and SH-SY5Y cells, a human neuroblastoma cell line) and an animal model such as Sprague-Dawley (SD) rats. First, cellular DA uptake was measured 2 or 8 h following BPA exposure (0.1-400 μM) in SH-SY5Y cells, where a significant increase in DA uptake was noted. BPA exerted no marked effect on dopamine active transporter levels in GH3 cells exposed for 8 or 24 h. However, SH-SY5Y cells displayed an increase in dopamine transporter (DAT) levels following 24 h of exposure to BPA. In contrast to DAT levels, BPA exposure produced no marked effect on DA D1 receptor levels in SH-SY5Y cells, yet a significant decrease in GH3 cells following both 8- and 24-h exposure periods was noted, suggesting that BPA exerts differential effects dependent upon cell type. BPA produced no significant effects on prolactin levels at 2 h, but a marked fall occurred at 24 h of exposure in GH3 cells. Finally, to examine the influence of dietary developmental exposure to BPA on brain DA levels in F1 offspring, SD rats were exposed to BPA (0.5-20 mg/kg) through maternal transfer and/or diet and striatal DA levels were measured on postnatal day (PND) 60 using high-performance liquid chromatography (HPLC). Data demonstrated that chronic exposure to BPA did not significantly alter striatal DA levels in the SD rat.

Toxicity study of ochratoxin A using HEK293 and HepG2 cell lines based on microRNA profiling

Ochratoxin A (OTA) induced DNA damage, cytotoxicity, and apoptosis in mammalian cell lines. Micro RNAs (miRNAs) are involved in physiological and developmental processes and contribute to cancer development and progression. In our study, high-throughput miRNA profiling and Kyoto Encyclopedia of Genes and Genomes analysis were applied to comparatively study the toxicity of OTA in HEK293 cells and HepG2 cells treated with 25 μM OTA for 24 h. In these two cells, the same changing miRNAs were mostly related to signal transduction pathways, whereas the different changing miRNAs were mostly related to human cancer pathways. DGCR8, Dicer1, and Drosha were significantly suppressed in HEK293 cells, indicating an impairment of miRNA biogenesis. The damage seemed more extensive in HEK293 cells. Cell models and in vivo models were also compared. Many miRNAs in vitro were markedly different from those in vivo; however, OTA toxicity was observed both in vitro and in vivo. The classification of deregulated pathways is similar. The biogenesis of miRNA was impaired in both lines. In conclusion, deregulated miRNAs in vitro are mostly related to human cancer and signal transduction pathways. The deregulated pathways in vivo are similar to those in vitro.

Assessing estrogenic activity and reproductive toxicity of organic extracts in WWTP effluents

Trace level organic contaminants might not be completely removed from the municipal wastewater and the safety incurred by them had become a concern. These organic pollutants were extracted from water samples and detected by GC-MS. The estrogenic activity of the organic was tested using Yeast Estrogen Screen to detect the transcriptional activation of the estrogen receptor (ER) and immature mouse uterotrophic bioassays to study reproductive toxicity. The results of GC-MS demonstrated the organic extracts in the municipal wastewater and the WWTP effluents Included two major categories, benzenes and Phthalates. The estrogenic activity of organic extracts from the secondary effluent (SE) and tertiary effluent (TE) was below that of the raw wastewater (RW). Results of uterotrophic bioassay demonstrated that SE would bring some potential hazards on animals while TE was relatively safe.

Differentiation of PC12 cells expressing estrogen receptor alpha: a new bioassay for endocrine-disrupting chemicals evaluation

Xeno-estrogens, a class of endocrine disrupting chemicals (EDCs), can disturb estrogen receptor-dependent pathways involved in differentiation, proliferation or protection. Multiple methods have been developed to characterize the disturbances induced by EDCs in different cells or organs. In this study we have developed a new tool for the assessment of estrogenic compounds on differentiation. For this purpose we used the global model of NGF-induced neurite outgrowth of a pseudoneuronal PC12 cell line stably transfected with estrogen receptor alpha (PC12 ER). This new test evidences a new selectivity in which estradiol, genistein and 4-hydroxytamoxifen increased the NGF-induced neurite outgrowth of PC12 ER cells in a dose-dependent manner. In contrast, the strong estrogen agonist 17α-ethynylestradiol, the strong antagonist raloxifene and the agonist bisphenol A were unable to modify the neuritogenesis of PC12 ER cells. Therefore, the analysis of neuritogenesis in PC12 ER cells constitutes a complementary tool for the characterization of xeno-estrogen activity and also serves as a basis for further studies focusing on the mechanisms of EDCs in a neuronal context. Moreover, this test constitutes an alternative to animal testing.

Long-term exposure of 3T3 fibroblast cells to endocrine disruptors alters sensitivity to oxidative injury

When Swiss 3T3 fibroblasts were exposed to bisphenol A (BPA) or nonylphenol (NP) within a range of 0.1-100 nM for 30-45 days, increased resistance to oxidative injury was found. Western blot analysis indicated concomitant increased expression of bcl-2 protein and reduced histone methylation levels in cells after BPA or NP exposure. Using a heterologous expression system, both chemicals could stimulate G protein-coupled receptor 30 (GPR30), a transmembrane estrogen receptor predominantly expressed in 3T3 cells, at lower concentrations, which gave increased survival. Taken together, these results suggest that BPA or NP exposure might cause alterations in cellular activity against oxidative stress, possibly through GPR30.

Low concentrations of o,p'-DDT inhibit gene expression and prostaglandin synthesis by estrogen receptor-independent mechanism in rat ovarian cells

o,p'-DDT is an infamous xenoestrogen as well as a ubiquitous and persistent pollutant. Biomonitoring studies show that women have been internally exposed to o,p'-DDT at range of 0.3-500 ng/g (8.46×10(-10) M-1.41×10(-6) M) in blood and other tissues. However, very limited studies have investigated the biological effects and mechanism(s) of o,p'-DDT at levels equal to or lower than current exposure levels in human. In this study, using primary cultures of rat ovarian granulosa cells, we determined that very low doses of o,p'-DDT (10(-12)-10(-8) M) suppressed the expression of ovarian genes and production of prostaglandin E2 (PGE2). In vivo experiments consistently demonstrated that o,p'-DDT at 0.5-1 mg/kg inhibited the gene expression and PGE2 levels in rat ovary. The surprising results from the receptor inhibitors studies showed that these inhibitory effects were exerted independently of either classical estrogen receptors (ERs) or G protein-coupled receptor 30 (GPR30). Instead, o,p'-DDT altered gene expression or hormone action via inhibiting the activation of protein kinase A (PKA), rather than protein kinase C (PKC). We further revealed that o,p'-DDT directly interfered with the PKA catalytic subunit. Our novel findings support the hypothesis that exposure to low concentrations of o,p'-DDT alters gene expression and hormone synthesis through signaling mediators beyond receptor binding, and imply that the current exposure levels of o,p'-DDT observed in the population likely poses a health risk to female reproduction.

Relationships between urinary biomarkers of phytoestrogens, phthalates, phenols, and pubertal stages in girls

Phytoestrogens, phthalates, and phenols are estrogen-disrupting chemicals that have a pronounced effect at puberty. They are exogenous chemicals that are either plant-derived or man-made, and can alter the functions of the endocrine system and cause various health defects by interfering with the synthesis, metabolism, binding, or cellular responses of natural estrogens. Phytoestrogens, phthalates, and phenols are some of the potent estrogens detectable in urine. Phytoestrogens are plant-derived xenestrogens found in a wide variety of food products, like soy-based food, beverages, several fruits, and vegetables. Exposure to phytoestrogens can delay breast development and further lead to precocious puberty. The effect of phytoestrogens is mediated through estrogen receptors α and β or by binding with early immediate genes, such as jun and fos. Phthalates are multifunctional synthetic chemicals used in plastics, polyvinyl chloride products, cosmetics, hair spray, and children’s toys. Phthalates have been shown to cause defeminization, thelarche, precocious puberty, and an increase in breast and pubic hair in pubertal girls. However, reports are also available that show no association of phthalates with precocious puberty in girls. Phthalates can act through a receptor-mediated signaling pathway or affect the production of luteinizing hormone and follicle-stimulating hormone that has a direct effect on estrogen formation. Phenols like bisphenol A are industrial chemicals used mainly in the manufacture of polycarbonates and plastic materials. Bisphenol A has been shown to cause precocious puberty and earlier menarche in pubertal girls. Reports suggest that the neurotoxic effect of bisphenol A can be mediated either by competing with estradiol for binding with estrogen receptors or via the ERK/NK-kappa or ERRγ pathway. This review demonstrates the effects of phytoestrogens, phthalates, and phenols on the development of girls during puberty.

Prenatal environmental exposures, epigenetics, and disease

This review summarizes recent evidence that prenatal exposure to diverse environmental chemicals dysregulates the fetal epigenome, with potential consequences for subsequent developmental disorders and disease manifesting in childhood, over the lifecourse, or even transgenerationally. The primordial germ cells, embryo, and fetus are highly susceptible to epigenetic dysregulation by environmental chemicals, which can thereby exert multiple adverse effects. The data reviewed here on environmental contaminants have potential implications for risk assessment although more data are needed on individual susceptibility to epigenetic alterations and their persistence before this information can be used in formal risk assessments. The findings discussed indicate that identification of environmental chemicals that dysregulate the prenatal epigenome should be a priority in health research and disease prevention.

Effects of estrogens and endocrine-disrupting chemicals on cell differentiation-survival-proliferation in brain: contributions of neuronal cell lines

Estrogens and estrogen receptors (ER) are key actors in the control of differentiation and survival and act on extrareproductive tissues such as brain. Thus, estrogens may display neuritogenic effects during development and neuroprotective effects in the pathophysiological context of brain ischemia and neurodegenerative pathologies like Alzheimer's disease or Parkinson's disease. Some of these effects require classical transcriptional "genomic" mechanisms through ER, whereas other effects appear to rely clearly on "membrane-initiated mechanisms" through cytoplasmic signal transduction pathways. Disturbances of these mechanisms by endocrine-disrupting chemicals (EDC) may exert adverse effects on brain. Some EDC may act via ER-independent mechanisms but might cross-react with endogenous estrogen. Other EDC may act through ER-dependent mechanisms and display agonistic/antagonistic estrogenic properties. Because of these potential effects of EDC, it is necessary to establish sensitive cell-based assays to determine EDC effects on brain. In the present review, some effects of estrogens and EDC are described with focus on ER-mediated effects in neuronal cells. Particular attention is given to PC12 cells, an interesting model to study the mechanisms underlying ER-mediated differentiating and neuroprotective effects of estrogens.

Effect of bisphenol A on human endometrial stromal fibroblasts in vitro

This study evaluated the effects of bisphenol A (BPA) on human endometrial stromal fibroblast (ESF) differentiation and expression of genes involved in oestrogen metabolism. Human ESF from eight hysterectomy specimens were cultured and treated with 5-100 μmol/l of BPA ± oestradiol or 8-br-cAMP for 48 h. mRNA expression was analysed by real-time reverse-transcription PCR. 8-br-cAMP-induced human ESF decidualization was confirmed by expression of insulin-like growth factor binding protein-1 (IGFBP1) and prolactin secretion. Short-term exposure (48 h) decreased human ESF proliferation (P<0.04) not due to apoptosis. High doses of BPA significantly induced IGFBP1 mRNA and protein, decreased P450scc mRNA, reversed the 8-br-cAMP-induced increase in HSD17B2 (oestradiol to oestrone conversion) in a dose-dependent manner and down-regulated HSD17B1 expression (oestrone to oestradiol conversion; P ≤ 0.03). 8-br-cAMP significantly potentiated this effect (P=0.028). BPA had no significant effect on aromatase and PPAR γ expression. The oestrogen-receptor antagonist ICI had no effect on gene expression in BPA-treated cells, and oestrogen receptor α, but not oestrogen receptor β, was significantly down-regulated by high doses of BPA (P=0.028). BPA has an endocrine-disrupting effect on human ESF function and gene expression but the underlying mechanisms appear not to involve oestrogen-mediated pathways.

Combined developmental toxicity of bisphenol A and genistein in micromass cultures of rat embryonic limb bud and midbrain cells

Bisphenol A (BPA), widely used in industry and dentistry, and genistein (GEN), the predominant component of soy product, are both known environmental estrogen. In the present study, we investigated the developmental toxicity of BPA and GEN and their combined effect using micromass test, which is one of three standard alternative developmental toxicity tests recommended by European Center for the Validation of Alternative Methods (ECVAM). The results showed that IC50-P (cell proliferation) and IC50-D (cell differentiation) of BPA and GEN were approximately 20 and 5 μg/ml, respectively. No observed adverse effect level (NOAEL) of BPA and GEN were 10 and 0.94 μg/ml, respectively. The manifestation of BPA as a teratogen was insufficient, although the "low dose" effect should be paid attention to. While the evidence of GEN as a teratogen was solid, especially with the consideration of "high dose" application in clinical treatment. The combined effect of BPA and GEN was generally additive action except that in MB proliferation.

Bisphenol A impairs follicle growth, inhibits steroidogenesis, and downregulates rate-limiting enzymes in the estradiol biosynthesis pathway

Bisphenol A (BPA) is used as the backbone for plastics and epoxy resins, including various food and beverage containers. BPA has also been detected in 95% of random urine samples and ovarian follicular fluid of adult women. Few studies have investigated the effects of BPA on antral follicles, the main producers of sex steroid hormones and the only follicles capable of ovulation. Thus, this study tested the hypothesis that postnatal BPA exposure inhibits antral follicle growth and steroidogenesis. To test this hypothesis, antral follicles isolated from 32-day-old FVB mice were cultured with vehicle control (dimethyl sulfoxide [DMSO]), BPA (4.4-440 μM), pregnenolone (10 μg/ml), pregnenolone + BPA 44 μM, and pregnenolone + BPA 440 μM. During the culture, follicles were measured for growth daily. After the culture, media was subjected to ELISA for hormones in the estradiol biosynthesis pathway, and follicles were processed for quantitative real-time PCR of steroidogenic enzymes. The results indicate that BPA (440 μM) inhibits follicle growth and that pregnenolone cotreatment was unable to restore/maintain growth. Furthermore, BPA 44 and 440 μM inhibit progesterone, dehydroepiandrosterone, androstenedione, estrone, testosterone, and estradiol production. Pregnenolone cotreatment was able to increase production of pregnenolone, progesterone, and dehydroepiandrosterone and maintain androstenedione and estrone levels in BPA-treated follicles compared with DMSO controls but was unable to protect testosterone or estradiol levels. Furthermore, pregnenolone was unable to protect follicles from BPA-(44-440 μM) induced inhibition of steroidogenic enzymes compared with the DMSO control. Collectively, these data show that BPA targets the estradiol biosynthesis pathway in the ovary.

Embryotoxic and teratogenic effects of the combination of bisphenol A and genistein on in vitro cultured postimplantation rat embryos

The potential teratogenic effects and fetal toxicity of environmental estrogenic endocrine disruptors have become a great concern in recent years, and they have yet to be fully characterized. In the present study, the teratogenic effects of bisphenol A (BPA) and genistein (GEN) on rat embryos during their critical period of organogenesis were investigated using a whole-embryo culture experiment. The combined exposure effects of BPA and GEN were explored using a 4 x 4 full factorial design. Both BPA and GEN produced concentration-dependent inhibition of embryonic development, beginning at 32.0 and 10.0 microg/ml, respectively. Full factorial and isobologram analyses revealed a significant synergistic interaction between BPA and GEN for most end points (12 out of 20 tested), as indicated by the enhanced developmental toxicity of BPA after coexposure with different dose levels of GEN. In particular, serious malformations and a higher abnormal frequency of the central nervous system were induced by the combination of BPA and GEN. Our findings suggest that GEN may be embryotoxic and teratogenic to humans. BPA alone may not be a potential teratogen, but these two estrogenic chemicals have a synergistic effect on embryonic development when present together during the critical period of major organ formation. The current findings suggest that pregnant women should not take soy supplements, but more studies are necessary to provide a conclusive recommendation.

Role of estrogenic compounds (diethylstibestrol, 17beta-estradiol, and bisphenol A) in the phosphorylation of substrate by protein kinase Calpha

Estrogenic compounds can activate protein kinase C (PKC), which is a calcium and phospholipid-dependent serine/threonine kinase. In the present study, we investigated the role of 17beta-estradiol (E2), diethylstibestrol (DES), and bisphenol A (BPA) in the phosphorylation of substrate by PKCalpha using the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The level of phosphorylated peptide was low in the absence of phosphatidylserine (PS). Moreover, reduction of phosphorylation ratios was identified in the presence of diacylglycerol (DAG) and Ca(2+) or PS and Ca(2+) after adding E2, DES, and BPA. However, no change in phosphorylation ratios was found in the presence of DAG and PS. Addition of E2, DES, and BPA also had no influence on the phosphorylation reaction of substrate by cell or tissue lysate samples. Our study suggests that E2, DES, and BPA can bind to the C2 domain of PKCalpha but have no effects on the phosphorylation reaction of substrates in the presence of DAG and PS.

Mutual synergistic toxicity between environmental toxicants: A study of mercury chloride and 4-nonylphenol

Mercury chloride (HgCl(2)) and 4-nonylphenol (NP) are widespread environmental and industrial pollutants that are known to have toxic effects as well as endocrine disrupting activities. Although the individual effects of HgCl(2) and NP in liver have been relatively well recognized, little is known about the interaction of NP and HgCl(2) during the induction of their toxicity. In the current study, we investigated the synergism between HgCl(2) and NP using HepG2 cells. Surprisingly, the concurrent treatment of HepG2 with HgCl(2) and NP induced a significant cytotoxicity at concentrations where neither of them have any cytotoxic effect when treated alone. The cytotoxicity of NP is enhanced in the presence of HgCl(2) (a shift from 74.9 to 47.4μM in LC(50)) and vice versa (a shift from 94.9 to 66.3μM in LC(50)). Estrogen receptor antagonists such as ICI 182,780 did not protect HepG2 cells from these cytotoxic insults. Whereas the intracellular level of reduced form glutathione (GSH) was considerably decreased upon the co-treatment with NP and HgCl(2). Furthermore, the synergistic cytotoxicity was significantly inhibited by 20-mM N-acetylcysteine (NAC). These results indicate that the mutual synergistic cytotoxicity of HgCl(2) and NP on HepG2 cell is not associated with estrogen receptor signaling but mediated by reactive oxygen species (ROS) generation. In our real life, we are continuously and often simultaneously exposed to many different kinds of environmental pollutants. The present study suggests a mechanism of potential synergistic adverse effects of these toxic pollutants.

Effects of estrogens on proliferation and differentiation of neural stem/progenitor cells

We investigated the effect of the female hormone 17beta-estradiol (E2) and the hormone mimic bisphenol A (BPA) on the proliferation and differentiation of rat neural stem/progenitors cells (NS/PCs) cultured from the telencephalon of embryonic day-15 rats. Basic fibroblast growth factor (FGF-2) is a potent mitogen of early generated NS/PCs, and is used for the proliferation of NS/PCs in vitro. Administration of E2 or BPA alone to the NS/PCs stimulated their proliferation in the absence but not in the presence of FGF-2. E2- or BPA-treatment increased the ratio of the oligodendrocytes generated from the NS/PCs to total cells; however, this ratio did not change when the cells were stimulated with platelet-derived growth factor (PDGF), a mitogen for oligodendrocyte precursors, or with neurotrophin-3, an oligogenic factor for glial progenitor cells. These results suggest that estrogens would influence the fate of NS/PCs when the cells are poorly supplied with mitogens or differentiation factors during the early stages of neurogenesis.