Prenatal exposure to bisphenol A impacts neuronal morphology in the hippocampal CA1 region in developing and aged mice

Health risks of Bisphenol-A exposure: From Wnt signaling perspective

Human beings are routinely exposed to chronic and low dose of Bisphenols (BPs) due to their widely pervasiveness in the environment. BPs hold similar chemical structures to 17β-estradiol (E2) and thyroid hormone, thus posing threats to human health by rendering the endocrine system dysfunctional. Among BPs, Bisphenol-A (BPA) is the best-known and extensively studied endocrine disrupting compound (EDC). BPA possesses multisystem toxicity, including reproductive toxicity, neurotoxicity, hepatoxicity and nephrotoxicity. Particularly, the central nervous system (CNS), especially the developing one, is vulnerable to BPA exposure. This review describes our current knowledge of BPA toxicity and the related molecular mechanisms, with an emphasis on the role of Wnt signaling in the related processes. We also discuss the role of oxidative stress, endocrine signaling and epigenetics in the regulation of Wnt signaling by BPA exposure. In summary, dysfunction of Wnt signaling plays a key role in BPA toxicity and thus can be a potential target to alleviate EDCs induced damage to organisms.

Polystyrene microplastics induced disturbances in neuronal arborization and dendritic spine density in mice prefrontal cortex

An increasing use of plastics in daily life leads to the accumulation of microplastics (MPs) in the environment, posing a serious threat to the ecosystem, including humans. It has been reported that MPs cause neurotoxicity, but the deleterious effect of polystyrene (PS) MPs on neuronal cytoarchitectural morphology in the prefrontal cortex (PFC) region of mice brain remains to be established. In the present study, Swiss albino male mice were orally exposed to 0.1, 1, and 10 ppm PS-MPs for 28 days. After exposure, we found a significant accumulation of PS-MPs with a decreased number of Nissl bodies in the PFC region of the entire treated group compared to the control. Morphometric analysis in the PFC neurons using Golgi-Cox staining accompanied by Sholl analysis showed a significant reduction in basal dendritic length, dendritic intersections, nodes, and number of intersections at seventh branch order in PFC neurons of 1 ppm treated PS-MPs. In neurons of 0.1 ppm treated mice, we found only decrease in the number of intersections at the seventh branch order. While 10 ppm treated neurons decreased in basal dendritic length, dendritic intersections, followed by the number of intersections at the third and seventh branch order were observed. As well, spine density on the apical secondary branches along with mRNA level of BDNF was significantly reduced in all the PS-MPs treated PFC neurons, mainly at 1 ppm versus control. These results suggest that PS-MPs exposure affects overall basal neuronal arborization, with the highest levels at 1 and 10 ppm, followed by 0.1 ppm treated neurons, which may be related to the down-regulation of BDNF expression in PFC.

Effect of bisphenol A on the neurological system: a review update

Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC) and one of the most produced synthetic compounds worldwide. BPA can be found in epoxy resins and polycarbonate plastics, which are frequently used in food storage and baby bottles. However, BPA can bind mainly to estrogen receptors, interfering with various neurologic functions, its use is a topic of significant concern. Nonetheless, the neurotoxicity of BPA has not been fully understood despite numerous investigations on its disruptive effects. Therefore, this review aims to highlight the most recent studies on the implications of BPA on the neurologic system. Our findings suggest that BPA exposure impairs various structural and molecular brain changes, promoting oxidative stress, changing expression levels of several crucial genes and proteins, destructive effects on neurotransmitters, excitotoxicity and neuroinflammation, damaged blood-brain barrier function, neuronal damage, apoptosis effects, disruption of intracellular Ca2+ homeostasis, increase in reactive oxygen species, promoted apoptosis and intracellular lactate dehydrogenase release, a decrease of axon length, microglial DNA damage, astrogliosis, and significantly reduced myelination. Moreover, BPA exposure increases the risk of developing neurologic diseases, including neurovascular (e.g. stroke) and neurodegenerative (e.g. Alzheimer's and Parkinson's) diseases. Furthermore, epidemiological studies showed that the adverse effects of BPA on neurodevelopment in children contributed to the emergence of serious neurological diseases like attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorder (ASD), depression, emotional problems, anxiety, and cognitive disorders. In summary, BPA exposure compromises human health, promoting the development and progression of neurologic disorders. More research is required to fully understand how BPA-induced neurotoxicity affects human health.

Effects of prenatal bisphenol S and bisphenol F exposure on behavior of offspring mice

Bisphenol A (BPA) is a representative endocrine-disrupting chemical that exhibits hormonal disturbance reactions. Various alternatives, such as Bisphenol S (BPS) and Bisphenol F (BPF), are being developed. BPS and BPF (which are representative alternatives to BPA) are used in consumer products such as polycarbonate plastics and epoxy resins. They have structures similar to those of BPA and have also been proven to be exogenous endocrine disruptors. However, although there are many studies on BPA, there are few studies on the neurodevelopmental effects of BPS and BPF. Therefore, in this study, we analyzed neurobehavioral changes in offspring mice exposed to BPS and BPF during brain development by administering BPS and BPF to pregnant mice. We found that prenatal exposure to BPS and BPF did not affect anxiety-and depression-like behaviors, locomotion, sociability, memory, or cognition functions in offspring mice. However, exposure to BPS and BPF decreased the preference for social novelty in the offspring mice. Taken together, these findings suggest that perinatal exposure to BPS and BPF affects changes in social behaviors, but not other behavioral changes such as emotion, memory, or cognition in the offspring mice.

Low-dose bisphenols exposure sex-specifically induces neurodevelopmental toxicity in juvenile rats and the antagonism of EGCG

Bisphenols (BPs) can negatively affect neurobehaviors in rats, whereas the mechanism remains unclear. Here, the mechanism of BPs-induced neurodevelopmental toxicity and its effective detoxification measures were investigated in vitro and in vivo. In in vitro experiments, primary hippocampal neurons from neonatal rats of different genders were treated with bisphenol A (BPA), bisphenol S (BPS) and bisphenol B (BPB) at 1 nM-100 μM, epigallocatechin gallate (EGCG) and G15, an antagonist of G protein-coupled estrogen receptor (GPER) for 7 d. Results indicated that BPs affected neuronal morphogenesis, impaired GABA synthesis and Glu/GABA homeostasis. Neuronal morphogenetic damage induced by low-doses BPA may be mediated by GPER. Neurotoxicity of BPS is weaker than BPA and BPB. In in vivo studies, exposure to BPA (0.5 μg/kg·bw/day) on PND 10-40 caused oxidative stress and inflammation in rat hippocampus, disrupted neuronal morphogenesis and neurotransmitter homeostasis, ultimately impaired spatial memory of rats. Males are more sensitive to BPA exposure than females. Both in vivo and in vitro studies indicated that EGCG, a phytoestrogen, can alleviate BPA-induced neurotoxicity. Taken together, low-doses BPA exposure sex-specifically disrupted neurodevelopment and further impaired learning and memory ability in rats, which may be mediated by GPER. Promisingly, EGCG effectively mitigated the BPA-induced neurodevelopmental toxicity.

Hippocampal transcriptome analysis reveals mechanisms of cognitive impairment in beagle dogs with type 1 diabetes

Diabetic encephalopathy is a common complication of type 1 diabetes. However, there have been few studies on cognitive impairment and hippocampal damage in type 1 diabetes mellitus (T1DM) using dogs as experimental animals. To investigate the effects of diabetes on the CNS, 40 adult beagles were divided into streptozotocin/alloxan type 1 diabetes model and control groups. The duration of diabetes in the model group was 120 days. A cognitive dysfunction scale was used to assess cognitive function. Hematoxylin and eosin and Golgi-Cox staining methods were used to observe morphological damage to the hippocampus. Transcriptomics was used to investigate differential gene expression in the hippocampus. The results showed that the cognitive dysfunction score of the model group was significantly higher than that of the control group. In addition, the number of normal neurons, the complexity of dendritic morphology, and the density of dendritic spines were decreased in the hippocampus of diabetic dogs. A total of 672 differentially expressed genes (DEGs) were identified, 289 of which were upregulated, and 383 were downregulated. Modified genes included DBH, IGFBP2, AVPR1A, and DRAXIN. In conclusion, type 1 diabetic dogs exhibit cognitive dysfunction. The DEGs were mainly enriched in metabolic, PI3K-Akt signaling, and neuroactive ligand-receptor interaction pathways.

The gut-brain axis involved in polystyrene nanoplastics-induced neurotoxicity via reprogramming the circadian rhythm-related pathways

The production of plastic is still increasing globally, which has led to an increasing number of plastic particles in the environment. Nanoplastics (NPs) can penetrate the blood-brain barrier and induce neurotoxicity, but in-depth mechanism and effective protection strategies are lacking. Here, C57BL/6 J mice were treated with 60 μg polystyrene NPs (PS-NPs, 80 nm) by intragastric administration for 42 days to establish NPs exposure model. We found that 80 nm PS-NPs could reach and cause neuronal damage in the hippocampus, and alter the expression of neuroplasticity-related molecules (5-HT, AChE, GABA, BDNF and CREB), and even affect the learning and memory ability of mice. Mechanistically, combined with the results of hippocampus transcriptome, gut microbiota 16 s ribosomal RNA and plasma metabolomics, we found that the gut-brain axis mediated circadian rhythm related pathways were involved in the neurotoxicity of NPs, especially Camk2g, Adcyap1 and Per1 may be the key genes. Both melatonin and probiotic can significantly reduce intestinal injury and restore the expression of circadian rhythm-related genes and neuroplasticity molecules, and the intervention effect of melatonin is more effective. Collectively, the results strongly suggest the gut-brain axis mediated hippocampal circadian rhythm changes involved in the neurotoxicity of PS-NPs. Melatonin or probiotics supplementation may have the application value in the prevention of neurotoxicity of PS-NPs.

Endocrine-Disrupting Chemicals and Hippocampal Development: The Role of Estrogen and Androgen Signaling

Hormones are important regulators of key processes during fetal brain development. Thus, the developing brain is vulnerable to the action of chemicals that can interfere with endocrine signals. Epidemiological studies have pointed toward sexually dimorphic associations between neurodevelopmental outcomes, such as cognitive abilities, in children and prenatal exposure to endocrine-disrupting chemicals (EDCs). This points toward disruption of sex steroid signaling in the development of neural structures underlying cognitive functions, such as the hippocampus, an essential mediator of learning and memory processes. Indeed, during development, the hippocampus is subjected to the organizational effects of estrogens and androgens, which influence hippocampal cell proliferation, differentiation, dendritic growth, and synaptogenesis in the hippocampal fields of Cornu Ammonis and the dentate gyrus. These early organizational effects correlate with a sexual dimorphism in spatial cognition and are subject to exogenous chemical perturbations. This review summarizes the current knowledge about the organizational effects of estrogens and androgens on the developing hippocampus and the evidence for hippocampal-dependent learning and memory perturbations induced by developmental exposure to EDCs. We conclude that, while it is clear that sex hormone signaling plays a significant role during hippocampal development, a complete picture at the molecular and cellular levels would be needed to establish causative links between the endocrine modes of action exerted by EDCs and the adverse outcomes these chemicals can induce at the organism level.

Re-evaluation of the risks to public health related to the presence of bisphenol A (BPA) in foodstuffs

In 2015, EFSA established a temporary tolerable daily intake (t-TDI) for BPA of 4 μg/kg body weight (bw) per day. In 2016, the European Commission mandated EFSA to re-evaluate the risks to public health from the presence of BPA in foodstuffs and to establish a tolerable daily intake (TDI). For this re-evaluation, a pre-established protocol was used that had undergone public consultation. The CEP Panel concluded that it is Unlikely to Very Unlikely that BPA presents a genotoxic hazard through a direct mechanism. Taking into consideration the evidence from animal data and support from human observational studies, the immune system was identified as most sensitive to BPA exposure. An effect on Th17 cells in mice was identified as the critical effect; these cells are pivotal in cellular immune mechanisms and involved in the development of inflammatory conditions, including autoimmunity and lung inflammation. A reference point (RP) of 8.2 ng/kg bw per day, expressed as human equivalent dose, was identified for the critical effect. Uncertainty analysis assessed a probability of 57-73% that the lowest estimated Benchmark Dose (BMD) for other health effects was below the RP based on Th17 cells. In view of this, the CEP Panel judged that an additional uncertainty factor (UF) of 2 was needed for establishing the TDI. Applying an overall UF of 50 to the RP, a TDI of 0.2 ng BPA/kg bw per day was established. Comparison of this TDI with the dietary exposure estimates from the 2015 EFSA opinion showed that both the mean and the 95th percentile dietary exposures in all age groups exceeded the TDI by two to three orders of magnitude. Even considering the uncertainty in the exposure assessment, the exceedance being so large, the CEP Panel concluded that there is a health concern from dietary BPA exposure.

The effects of prenatal bisphenol A exposure on brain volume of children and young mice

Bisphenol A (BPA) is a synthetic chemical used for the manufacturing of plastics, epoxy resin, and many personal care products. This ubiquitous endocrine disruptor is detectable in the urine of over 80% of North Americans. Although adverse neurodevelopmental outcomes have been observed in children with high gestational exposure to BPA, the effects of prenatal BPA on brain structure remain unclear. Here, using magnetic resonance imaging (MRI), we studied the associations of maternal BPA exposure with children's brain structure, as well as the impact of comparable BPA levels in a mouse model. Our human data showed that most maternal BPA exposure effects on brain volumes were small, with the largest effects observed in the opercular region of the inferior frontal gyrus (ρ = -0.2754), superior occipital gyrus (ρ = -0.2556), and postcentral gyrus (ρ = 0.2384). In mice, gestational exposure to an equivalent level of BPA (2.25 μg BPA/kg bw/day) induced structural alterations in brain regions including the superior olivary complex (SOC) and bed nucleus of stria terminalis (BNST) with larger effect sizes (1.07≤ Cohens d ≤ 1.53). Human (n = 87) and rodent (n = 8 each group) sample sizes, while small, are considered adequate to perform the primary endpoint analysis. Combined, these human and mouse data suggest that gestational exposure to low levels of BPA may have some impacts on the developing brain at the resolution of MRI.

Does Bisphenol A Confer Risk of Neurodevelopmental Disorders? What We Have Learned from Developmental Neurotoxicity Studies in Animal Models

Substantial evidence indicates that bisphenol A (BPA), a ubiquitous environmental chemical used in the synthesis of polycarbonate plastics and epoxy resins, can impair brain development. Clinical and epidemiological studies exploring potential connections between BPA and neurodevelopmental disorders in humans have repeatedly identified correlations between early BPA exposure and developmental disorders, such as attention deficit/hyperactivity disorder and autism spectrum disorder. Investigations using invertebrate and vertebrate animal models have revealed that developmental exposure to BPA can impair multiple aspects of neuronal development, including neural stem cell proliferation and differentiation, synapse formation, and synaptic plasticity-neuronal phenotypes that are thought to underpin the fundamental changes in behavior-associated neurodevelopmental disorders. Consistent with neuronal phenotypes caused by BPA, behavioral analyses of BPA-treated animals have shown significant impacts on behavioral endophenotypes related to neurodevelopmental disorders, including altered locomotor activity, learning and memory deficits, and anxiety-like behavior. To contextualize the correlations between BPA and neurodevelopmental disorders in humans, this review summarizes the current literature on the developmental neurotoxicity of BPA in laboratory animals with an emphasis on neuronal phenotypes, molecular mechanisms, and behavioral outcomes. The collective works described here predominantly support the notion that gestational exposure to BPA should be regarded as a risk factor for neurodevelopmental disorders.

Autism-Related Transcription Factors Underlying the Sex-Specific Effects of Prenatal Bisphenol A Exposure on Transcriptome-Interactome Profiles in the Offspring Prefrontal Cortex

Bisphenol A (BPA) is an environmental risk factor for autism spectrum disorder (ASD). BPA exposure dysregulates ASD-related genes in the hippocampus and neurological functions of offspring. However, whether prenatal BPA exposure has an impact on genes in the prefrontal cortex, another brain region highly implicated in ASD, and through what mechanisms have not been investigated. Here, we demonstrated that prenatal BPA exposure disrupts the transcriptome-interactome profiles of the prefrontal cortex of neonatal rats. Interestingly, the list of BPA-responsive genes was significantly enriched with known ASD candidate genes, as well as genes that were dysregulated in the postmortem brain tissues of ASD cases from multiple independent studies. Moreover, several differentially expressed genes in the offspring's prefrontal cortex were the targets of ASD-related transcription factors, including AR, ESR1, and RORA. The hypergeometric distribution analysis revealed that BPA may regulate the expression of such genes through these transcription factors in a sex-dependent manner. The molecular docking analysis of BPA and ASD-related transcription factors revealed novel potential targets of BPA, including RORA, SOX5, TCF4, and YY1. Our findings indicated that prenatal BPA exposure disrupts ASD-related genes in the offspring's prefrontal cortex and may increase the risk of ASD through sex-dependent molecular mechanisms, which should be investigated further.

Maternal exposure to low doses of bisphenol A affects learning and memory in male rat offspring with abnormal N-methyl-d-aspartate receptors in the hippocampus

Bisphenol A (BPA), a component of polycarbonate and epoxy resins, has been reported to induce learning and memory deficits. However, the mechanisms have not been fully elucidated. Growing evidence has suggested that N-methyl-d-aspartate receptors (NMDARs) are involved in cognitive impairments. In this study, BPA was administered to female Sprague-Dawley rats (six per dose group) at concentrations of 0 (control), 4, 40, and 400 μg/kg·body weight/day from gestation day 1 through lactation day 21. Spatial learning was evaluated using the Morris water maze on postnatal day 22. Expression levels of NMDARs were determined using real-time polymerase chain reaction and Western blot. The results showed that male offspring exposed to BPA exhibited increased latency in reaching the platform and reduced time in the target quadrant, and the number of crossing the platform was less, as compared with the control group. The mRNA and protein expression levels of NMDARs in the hippocampus were significantly downregulated when compared with the control group of male offspring. The data showed that maternal exposure to BPA at low dosage can cause cognitive deficits in male rat offspring, probably due to a decrease in NMDARs in the hippocampus.

ATF5 deficiency causes abnormal cortical development

Activating transcription factor 5 (ATF5) is a member of the cAMP response element binding protein (CREB)/ATF family of basic leucine zipper transcription factors. We previously reported that ATF5-deficient (ATF5^−/−) mice exhibited behavioural abnormalities, including abnormal social interactions, reduced behavioural flexibility, increased anxiety-like behaviours, and hyperactivity in novel environments. ATF5^−/− mice may therefore be a useful animal model for psychiatric disorders. ATF5 is highly expressed in the ventricular zone and subventricular zone during cortical development, but its physiological role in higher-order brain structures remains unknown. To investigate the cause of abnormal behaviours exhibited by ATF5^−/− mice, we analysed the embryonic cerebral cortex of ATF5^−/− mice. The ATF5^−/− embryonic cerebral cortex was slightly thinner and had reduced numbers of radial glial cells and neural progenitor cells, compared to a wild-type cerebral cortex. ATF5 deficiency also affected the basal processes of radial glial cells, which serve as a scaffold for radial migration during cortical development. Further, the radial migration of cortical upper layer neurons was impaired in ATF5^−/− mice. These results suggest that ATF5 deficiency affects cortical development and radial migration, which may partly contribute to the observed abnormal behaviours.

A Review of Recent Studies on Bisphenol A and Phthalate Exposures and Child Neurodevelopment

Purpose of Review: Bisphenol A and phthalate have been found in the environment, as well as in humans. In this narrative review pre- and postnatal bisphenol A and phthalate exposures, their relationship to neurodevelopment, and the behavioral outcomes of children are elucidated, focusing in particular on the recent case-control, cross-sectional, and longitudinal studies. This review also introduces some of the possible mechanisms behind the observed associations between exposures and outcomes. Recent Findings: Although bisphenol A and phthalate exposure have been reported to influence neurobehavioral development in children, there are various kinds of test batteries for child neurodevelopmental assessment at different ages whose findings have been inconsistent among studies. In addition, the timing and number of exposure assessments have varied. Summary: Overall, this review suggests that prenatal exposure to bisphenol A and phthalates may contribute to neurobehavioral outcomes in children. The evidence is still limited; however, Attention Deficit Hyperactivity Disorder (ADHD) symptoms, especially among boys, constantly suggested association with both prenatal and concurrent exposure to bisphenol A. Although there is limited evidence on the adverse effects of prenatal and postnatal bisphenol A and phthalate exposures provided, pregnant women and young children should be protected from exposure based on a precautionary approach.

Brain Disorders and Chemical Pollutants: A Gap Junction Link?

The incidence of brain pathologies has increased during last decades. Better diagnosis (autism spectrum disorders) and longer life expectancy (Parkinson's disease, Alzheimer's disease) partly explain this increase, while emerging data suggest pollutant exposures as a possible but still underestimated cause of major brain disorders. Taking into account that the brain parenchyma is rich in gap junctions and that most pollutants inhibit their function; brain disorders might be the consequence of gap-junctional alterations due to long-term exposures to pollutants. In this article, this hypothesis is addressed through three complementary aspects: (1) the gap-junctional organization and connexin expression in brain parenchyma and their function; (2) the effect of major pollutants (pesticides, bisphenol A, phthalates, heavy metals, airborne particles, etc.) on gap-junctional and connexin functions; (3) a description of the major brain disorders categorized as neurodevelopmental (autism spectrum disorders, attention deficit hyperactivity disorders, epilepsy), neurobehavioral (migraines, major depressive disorders), neurodegenerative (Parkinson's and Alzheimer's diseases) and cancers (glioma), in which both connexin dysfunction and pollutant involvement have been described. Based on these different aspects, the possible involvement of pollutant-inhibited gap junctions in brain disorders is discussed for prenatal and postnatal exposures.

Bisphenol A and its analogues: A comprehensive review to identify and prioritize effect biomarkers for human biomonitoring

Human biomonitoring (HBM) studies have demonstrated widespread and daily exposure to bisphenol A (BPA). Moreover, BPA structural analogues (e.g. BPS, BPF, BPAF), used as BPA replacements, are being increasingly detected in human biological matrices. BPA and some of its analogues are classified as endocrine disruptors suspected of contributing to adverse health outcomes such as altered reproduction and neurodevelopment, obesity, and metabolic disorders among other developmental and chronic impairments. One of the aims of the H2020 European Human Biomonitoring Initiative (HBM4EU) is the implementation of effect biomarkers at large scales in future HBM studies in a systematic and standardized way, in order to complement exposure data with mechanistically-based biomarkers of early adverse effects. This review aimed to identify and prioritize existing biomarkers of effect for BPA, as well as to provide relevant mechanistic and adverse outcome pathway (AOP) information in order to cover knowledge gaps and better interpret effect biomarker data. A comprehensive literature search was performed in PubMed to identify all the epidemiologic studies published in the last 10 years addressing the potential relationship between bisphenols exposure and alterations in biological parameters. A total of 5716 references were screened, out of which, 119 full-text articles were analyzed and tabulated in detail. This work provides first an overview of all epigenetics, gene transcription, oxidative stress, reproductive, glucocorticoid and thyroid hormones, metabolic and allergy/immune biomarkers previously studied. Then, promising effect biomarkers related to altered neurodevelopmental and reproductive outcomes including brain-derived neurotrophic factor (BDNF), kisspeptin (KiSS), and gene expression of nuclear receptors are prioritized, providing mechanistic insights based on in vitro, animal studies and AOP information. Finally, the potential of omics technologies for biomarker discovery and its implications for risk assessment are discussed. To the best of our knowledge, this is the first effort to comprehensively identify bisphenol-related biomarkers of effect for HBM purposes.

Di-2-ethylhexyl phthalate (DEHP) induces apoptosis of mouse HT22 hippocampal neuronal cells via oxidative stress

Di-2-ethylhexyl phthalate (DEHP) has been widely used as a plasticizer in industry and can affect memory; however, the underlying mechanism remains unclear. In the present study, mouse HT22 cells, an immortalized hippocampal neuronal cell line, was utilized as an in vitro model. We showed that DEHP dramatically inhibited cell viability and increased lactate dehydrogenase (LDH) release from the cells in a dose-dependent manner, suggesting that DEHP could cause cytotoxicity of mouse HT22 cells. The protein levels of cleaved Caspase-8, cleaved Caspase-3, and Bax markedly increased in the DEHP-treated cells, whereas there was a significant decrease in the Bcl-2 protein level, implying that DEHP could induce apoptosis of mouse HT22 cells. DEHP exposure significantly increased the content of malondialdehyde, whereas it markedly decreased the level of glutathione and the activities of glutathione peroxidase and superoxide dismutase, suggesting that DEHP induced oxidative stress of the cells. Compared with the DEHP-treated group, the inhibition of cell viability and the release of LDH were rescued in the N-acetyl-l-cysteine plus DEHP group. Furthermore, inhibition of oxidative stress could rescue the induction of apoptosis by DEHP. Collectively, our results indicated that DEHP could induce apoptosis of mouse HT22 cells via oxidative stress.

Phthalate and Bisphenol Exposure during Pregnancy and Offspring Nonverbal IQ

BACKGROUND

Prenatal exposures to phthalates and bisphenols are associated with impaired brain development in animals. However, epidemiological studies investigating the association between prenatal phthalate or bisphenol exposure and cognition have produced mixed findings and mostly had modest sample sizes and measured the exposure during the third trimester.

OBJECTIVE

We examined the association between pregnancy maternal urinary biomarkers of phthalate or bisphenol exposure and nonverbal intelligence quotient (IQ) in children 6 years of age.

METHOD

The study sample consisted of 1,282 mother-child pairs participating in the Generation R Study, a population-based birth cohort in Rotterdam, Netherlands (enrollment 2002-2006). We measured maternal urinary concentrations of 18 phthalate metabolites and 8 bisphenols at < 18 , 18-25, and > 25  wks of gestation. Child nonverbal IQ was measured at 6 years of age using the Snijders-Oomen Nonverbal Intelligence Test-Revised. Linear regression models were fit for each of the three collection phases separately, the three collection phases jointly, and for the averaged prenatal exposure across pregnancy.

RESULTS

Higher urinary concentrations of phthalate metabolites during early pregnancy were associated with lower child nonverbal IQ score [e.g., B per 10-fold increase in summed low-molecular weight phthalates = - 1.7 (95% CI: - 3.1 , - 0.3 )]. This association remained unchanged when adjusted for mid and late pregnancy exposures. We also observed an inverse association between late pregnancy di-n-octyl phthalate (DNOP) exposure and nonverbal IQ. Maternal urinary concentrations of bisphenols were not associated with child nonverbal IQ. There was no effect estimate modification by sex.

CONCLUSIONS

We did not observe that maternal biomarkers of bisphenol exposure are associated with nonverbal IQ. We found that phthalate exposure in early pregnancy and DNOP exposure in late pregnancy are associated with lower nonverbal IQ scores in children. Our results might suggest that particularly early pregnancy is a sensitive window of phthalate exposure, but future studies are needed to replicate our findings. https://doi.org/10.1289/EHP6047.

Prenatal exposure to bisphenol A alters the transcriptome-interactome profiles of genes associated with Alzheimer's disease in the offspring hippocampus

Our recent study revealed that prenatal exposure to bisphenol A (BPA) disrupted the transcriptome profiles of genes in the offspring hippocampus. In addition to genes linked to autism, several genes associated with Alzheimer’s disease (AD) were found to be differentially expressed, although the association between BPA-responsive genes and AD-related genes has not been thoroughly investigated. Here, we demonstrated that in utero BPA exposure also disrupted the transcriptome profiles of genes associated with neuroinflammation and AD in the hippocampus. The level of NF-κB protein and its AD-related target gene Bace1 were significantly increased in the offspring hippocampus in a sex-dependent manner. Quantitative RT-PCR analysis also showed an increase in the expression of Tnf gene. Moreover, the reanalysis of transcriptome profiling data from several previously published BPA studies consistently showed that BPA-responsive genes were significantly associated with top AD candidate genes. The findings from this study suggest that maternal BPA exposure may increase AD risk in offspring by dysregulating genes associated with AD neuropathology and inflammation and reveal a possible relationship between AD and autism, which are linked to the same environmental factor. Sex-specific effects of prenatal BPA exposure on the susceptibility of AD deserve further investigation.

Bisphenol-A Exposure during Gestation and Lactation Causes Visual Perception Deficits in Rat Pups Following a Decrease in Interleukin 1β Expression in the Primary Visual Cortex

Bisphenol-A (BPA) exposure can affect cognitive functions of rodents and humans. However, whether information inputs for these functions in the brain are perturbed by BPA remains unclear. Here, visual perception in rats was assessed by testing their ability to discriminate between vertical and horizontal grating. We found that BPA exposure (1 mg/kg/day) during gestation and lactation markedly decreased the grating discrimination ability in rat pups (postnatal 21 days). The results of neuronal functions in the primary visual cortex (V1) showed that the orientation selectivity and signal extraction ability and fidelity were notably decreased after BPA exposure. These effects were accompanied by a reduction in synaptic plasticity (i.e., spine density and maturity) in the V1. According to inflammatory factor expression and glial cell morphology, no increase in inflammatory activation was observed after BPA exposure. However, BPA-exposed rat pups exhibited a significant decrease in IL-1β expression in the V1, accompanied by a decline in P38 phosphorylation. After local injection of IL-1β (10 ng/ml) in the V1, these two visual properties recovered to normal levels. Thus, our findings imply that physiological dysfunction of IL-1β may contribute to orientation perception deficits in BPA-exposed rats.

Bisphenol a Exposure in Utero Disrupts Hypothalamic Gene Expression Particularly Genes Suspected in Autism Spectrum Disorders and Neuron and Hormone Signaling

Bisphenol A (BPA) is an endocrine-disrupting compound detected in the urine of more than 92% of humans, easily crosses the placental barrier, and has been shown to influence gene expression during fetal brain development. The purpose of this study was to investigate the effect of in utero BPA exposure on gene expression in the anterior hypothalamus, the basal nucleus of the stria terminalis (BNST), and hippocampus in C57BL/6 mice. Mice were exposed in utero to human-relevant doses of BPA, and then RNA sequencing was performed on male PND 28 tissue from whole hypothalamus (n = 3/group) that included the medial preoptic area (mPOA) and BNST to determine whether any genes were differentially expressed between BPA-exposed and control mice. A subset of genes was selected for further study using RT-qPCR on adult tissue from hippocampus to determine whether any differentially expressed genes (DEGs) persisted into adulthood. Two different RNA-Seq workflows indicated a total of 259 genes that were differentially expressed between BPA-exposed and control mice. Gene ontology analysis indicated that those DEGs were overrepresented in categories relating to mating, cell-cell signaling, behavior, neurodevelopment, neurogenesis, synapse formation, cognition, learning behaviors, hormone activity, and signaling receptor activity, among others. Ingenuity Pathway Analysis was used to interrogate novel gene networks and upstream regulators, indicating the top five upstream regulators as huntingtin, beta-estradiol, alpha-synuclein, Creb1, and estrogen receptor (ER)-alpha. In addition, 15 DE genes were identified that are suspected in autism spectrum disorders.

Prenatal bisphenol A exposure contributes to Tau pathology: Potential roles of CDK5/GSK3β/PP2A axis in BPA-induced neurotoxicity

Bisphenol A (BPA) is a well-known endocrine disruptor used to manufacture polycarbonate plastics and epoxy resins. BPA exposure especially occupational perinatal exposure to has been linked to numerous adverse effects for the offspring. Available data have shown that perinatal exposure to BPA contributes to neurodegenerative pathological changes; however, the potential mechanisms remain unclear. This study attempted to investigate the long-term consequences of perinatal exposure to BPA on the offspring mouse brain. The pregnant mice were given either a vehicle control or BPA (2, 10, 100 μg/kg/d) from day 6 of gestation until weaning (P6-PND21, foetal and neonatal exposure). At 3, 6 and 9 months of age, the neurotoxic effects in the offspring in each group were investigated. We found that the spine density but not the dendritic branches in the hippocampus were noticeably reduced at 6 and 9 months of age. Meanwhile, p-Tau, the characteristic protein for tauopathy, was dramatically increased in both the hippocampus and cortex at 3-9 months of age. Mechanically, the balance of kinase and protein phosphatase, which plays critical roles in p-Tau regulation, was disturbed. It indicated that GSK3β and CDK5, two critical kinases, were activated in most of the BPA perinatal exposure group, while protein phosphatase 2A (PP2A), one of the important phosphatases, regulated p-Tau expression through its demethylation, methylation and phosphorylation. Taken together, the present study may be translatable to the human occupational BPA exposure due to a similar exposure level. BPA perinatal exposure causes long-term adverse effects on the mouse brain and may be a risk factor for tauopathies, and the CDK5/GSK3β/PP2A axis might be a promising therapeutic target for BPA-induced neurodegenerative pathological changes.

Potentiation of the Glycine Response by Bisphenol A, an Endocrine Disrupter, on the Substantia Gelatinosa Neurons of the Trigeminal Subnucleus Caudalis in Mice

Lamina II, also called the substantia gelatinosa (SG) of the medullary dorsal horn (the trigeminal subnucleus caudalis, Vc), is thought to play an essential role in the control of orofacial nociception because it receives the nociceptive signals from primary afferents, including thin myelinated Aδ- and unmyelinated C-fibers. Glycine, the main inhibitory neurotransmitter in the central nervous system, plays an essential role in the transference of nociceptive messages from the periphery to higher brain regions. Bisphenol A (BPA) is reported to alter the morphological and functional characteristics of neuronal cells and to be an effector of a great number of ion channels in the central nervous system. However, the electrophysiological effects of BPA on the glycine receptors of SG neurons in the Vc have not been well studied. Therefore, in this study, we used the whole-cell patch-clamp technique to determine the effect of BPA on the glycine response in SG neurons of the Vc in male mice. We demonstrated that in early neonatal mice (0-3 postnatal day mice), BPA did not affect the glycine-induced inward current. However, in the juvenile and adult groups, BPA enhanced the glycine-mediated responses. Heteromeric glycine receptors were involved in the modulation by BPA. The interaction between BPA and glycine appears to have a significant role in regulating transmission in the nociceptive pathway.

Maternal exposure to environmental bisphenol A impairs the neurons in hippocampus across generations

Humans from fetal to adult stages are chronically and passively exposed to bisphenol A (BPA, an endocrine disruptor) due to its ubiquitous existence in daily life. To investigate the long-term neurotoxicity of maternal exposure to BPA for offspring, mice were used as the animal model. In this study, pregnant mice (F0) were orally dosed with BPA (i.e. mice from low-, medium- and high-exposed groups were treated with 0.5, 50, 5000 μg/kg·bw of BPA per day) until weaning. Then, the first generation (F1) mice were used to generate the F2 ones. The offspring of mice not exposed to BPA served as the control groups. The Y-maze test, comet assay, hematoxylin-eosin (HE) staining method, Golgi-Cox assay and liquid chromatography-tandem mass spectrometry (LC/MS/MS) were conducted to study any alterations to learning and memory abilities, the morphological variations in hippocampal neurons and transmitter levels of F1 and F2 mice induced by BPA exposure. Results showed that even a low-dose of maternal BPA exposure could sex-dependently and significantly impair the learning and memory ability of F1 male mice, but not of generation F2. Furthermore, decreased neuron quantities and spine densities in hippocampi were observed in both F1 and F2 generations after maternal BPA exposure. However, DNA damage of brain cells were only limited to F1 offspring, in which DNA damage was only observed in the low-exposed male mice and medium-exposed female mice. Additionally, maternal BPA exposure leads to variations in hippocampal neurotransmitter levels, indicated by the decreased ratio of Glu/GABA in F1 offspring. In conclusion, maternal exposure to an environmental dose of BPA resulted in lasting adverse effects on neurological development for offspring mice.

Low-dose bisphenol A exposure impairs learning and memory ability with alterations of neuromorphology and neurotransmitters in rats

To investigate the developmental neurotoxicity of environmental bisphenol A (BPA) exposure for infants and children, postnatal rats were used as the animal model and were divided into four groups. Then, they were treated with different concentrations of BPA (i.e., 0, 0.5, 50, or 5000 μg/kg·bw/day of BPA as the control, low-, medium- and high-exposed group) from postnatal days 7 to 21. Y-maze tests, Golgi-Cox assays and liquid chromatography-tandem mass spectrometry (LC/MS/MS) were performed to test the changes of learning and memory ability, hippocampal neuromorphology and neurotransmitter levels, respectively. The results showed that the BPA-exposed rats, especially the low- and high-exposed rats, needed more trials and longer times to qualify for the learned criterion than the control rats. Additionally, rats after low- or high-exposure to BPA exhibited decreased DG dendritic complexity and reduced CA1 and DG dendritic spine densities in the hippocampus. Low-dosage BPA treatment could significantly alter the neurotransmitter contents in the hippocampus. In male rats, the levels of glutamic acid (Glu) and acetylcholine increased, while the 5-hydroxytryptamine (5-HT) and γ-aminobutyric acid (GABA) levels decreased, which lead to an unbalanced Glu/GABA ratio. However, in female rats, only 5-HT levels decreased. In conclusion, postnatal exposure to BPA could sex- and dose-dependently disrupt dendritic development and neurotransmitter homeostasis in the rat hippocampus. The impaired spatial learning and memory ability of rats induced by low-dose BPA is associated with both disrupted dendritic development and neurotransmitter homeostasis in the hippocampus.

Bisphenol F-Induced Neurotoxicity toward Zebrafish Embryos

In this study, the influence of bisphenol F (BPF) toward central nervous system (CNS) was assessed using zebrafish embryos. We found that BPF could induce significant neurotoxicity toward zebrafish embryos, including inhibited locomotion, reduced moving distance, and CNS cell apoptosis at an effective concentration of 0.0005 mg/L. Immunofluorescence assay showed that both microglia and astrocyte in zebrafish brain were significantly activated by BPF, indicating the existence of neuroinflammatory response. Peripheral motor neuron development was significantly inhibited by BPF at 72 hpf. RNA-seq data indicated that neuronal developmental processes and cell apoptosis pathways were significantly affected by BPF exposure, which was consistent with the phenotypic results. Chip-seq assay implied that the transcriptional changes were not mediated by ERα. Additionally, no significant change was found in neurotransmitter levels (5-hydroxytryptamine, dopamine, and acetylcholine) or acetylcholinesterase (Ache) enzyme activity after BPF exposure, indicating that BPF may not affect neurotransmission. In conclusion, BPF could lead to abnormal neural outcomes during zebrafish early life stage through inducing neuroinflammation and CNS cell apoptosis even at environmentally relevant concentration.

Gestational Exposure to Common Endocrine Disrupting Chemicals and Their Impact on Neurodevelopment and Behavior

Endocrine disrupting chemicals are common in our environment and act on hormone systems and signaling pathways to alter physiological homeostasis. Gestational exposure can disrupt developmental programs, permanently altering tissues with impacts lasting into adulthood. The brain is a critical target for developmental endocrine disruption, resulting in altered neuroendocrine control of hormonal signaling, altered neurotransmitter control of nervous system function, and fundamental changes in behaviors such as learning, memory, and social interactions. Human cohort studies reveal correlations between maternal/fetal exposure to endocrine disruptors and incidence of neurodevelopmental disorders. Here, we summarize the major literature findings of endocrine disruption of neurodevelopment and concomitant changes in behavior by four major endocrine disruptor classes:bisphenol A, polychlorinated biphenyls, organophosphates, and polybrominated diphenyl ethers. We specifically review studies of gestational and/or lactational exposure to understand the effects of early life exposure to these compounds and summarize animal studies that help explain human correlative data.

Bisphenol A triggers axonal injury and myelin degeneration with concomitant neurobehavioral toxicity in C57BL/6J male mice

Bisphenol A (BPA) is a ubiquitously distributed endocrine disrupting chemical (EDC). BPA exposure in humans has been a matter of concern due to its increased application in the products of day to day use. BPA has been reported to cause toxicity in almost all the vital organ systems even at a very low dose levels. It crosses the blood brain barrier and causes neurotoxicity. We studied the effect of BPA on the cerebral cortex of C57BL/6J mice and examined whether BPA exposure alters the expression of axonal and myelin structural proteins. Male mice were dosed orally to 40 μg and 400 μg BPA/kg body weight for 60 days. BPA exposure resulted in memory loss, muscle coordination deficits and allodynia. BPA exposure also caused degeneration of immature and mature oligodendrocytes as evaluated by decreased mRNA levels of 2',3'-cyclic nucleotide 3' phosphodiesterase (CNPase), nestin, myelin basic protein (MBP) and myelin-associated glycoprotein-1 (MAG-1) genes revealing myelin related pathology. It was observed that subchronic BPA exposure caused neuroinflammation through deregulation of inflammatory cytokines mRNA and protein expression which further resulted into neurotoxicity through axonal as well as myelin degeneration in the brain. BPA also caused increased oxidative stress in the brain. Our study indicates long-term subchronic low dose exposure to BPA has the potential to cause axonal degeneration and demyelination in the oligodendrocytes and neurons which may have implications in neurological and neuropsychological disorders including multiple sclerosis (MS), neuromyelitis optica and others.

Transgenerational Bisphenol A Causes Deficits in Social Recognition and Alters Postsynaptic Density Genes in Mice

Bisphenol A (BPA) is a ubiquitous endocrine-disrupting chemical. Developmental exposure produces changes in behavior and gene expression in the brain. Here, we examined social recognition behaviors in mice from the third familial generation (F3) after exposure to gestational BPA. Second-generation mice were bred in one of four mating combinations to reveal whether characteristics in F3 were acquired via maternal or paternal exposures. After repeated habituation to the same mouse, offspring of dams from the BPA lineage failed to display increased investigation of a novel mouse. Genes involved in excitatory postsynaptic densities (PSDs) were examined in F3 brains using quantitative PCR. Differential expression of genes important for function and stability of PSDs were assessed at three developmental ages. Several related PSD genes-SH3 and multiple ankyrin repeat domains 1 (Shank1), Homer scaffolding protein 1c (Homer1c), DLG associated protein 1 (Gkap), and discs large MAGUK scaffold protein 4 (PSD95)-were differentially expressed in control- vs BPA-lineage brains. Using a second strain of F3 inbred mice exposed to BPA, we noted the same differences in Shank1 and PSD95 expression in C57BL/6J mice. In sum, transgenerational BPA exposure disrupted social interactions in mice and dysregulated normal expression of PSD genes during neural development. The fact that the same genetic effects were found in two different mouse strains and in several brain regions increased potential for translation. The genetic and functional relationship between PSD and abnormal neurobehavioral disorders is well established, and our data suggest that BPA may contribute in a transgenerational manner to neurodevelopmental diseases.

Bisphenol-A induces neurodegeneration through disturbance of intracellular calcium homeostasis in human embryonic stem cells-derived cortical neurons

Bisphenol-A (BPA) is a representative exogenous endocrine disruptor, which is extensively composed in plastic products. Due to the capability of passing through the blood-brain barrier, evidence has linked BPA exposure with multiple neuropsychological dysfunctions, neurobehavioral disorders and neurodegenerative diseases. However, the underlying mechanism by which BPA induces neurodegeneration still remains unclear. Our study used human embryonic stem cells-derived human cortical neurons (hCNs) as a cellular model to investigate the adverse neurotoxic effects of BPA. hCNs were treated with 0, 0.1, 1 and 10 μM BPA for 14 days. Impacts of BPA exposure on cell morphology, cell viability and neural marker (MAP2) were measured for evaluating the neurodegeneration. The intracellular calcium homeostasis, reactive oxygen species (ROS) generation and organelle functions were also taken into consideration. Results revealed that chronic exposure of BPA damaged the neural morphology, induced neuronal apoptosis and decreased MAP2 expression at the level of both transcription and translation. The intracellular calcium levels were elevated in hCNs after BPA exposure through NMDARs-nNOS-PSD-95 mediating. Meanwhile, BPA led to oxidative stress by raising the ROS generation and attenuating the antioxidant defense in hCNs. Furthermore, BPA triggered ER stress and increased cytochrome c release by impairing the mitochondrial function. Ultimately, BPA triggered the cell apoptosis by regulating Bcl-2 family and caspase-dependent signaling pathway. Taken together, BPA exerted neurotoxic effects on hCNs by eliciting apoptosis, which might due to the intracellular calcium homeostasis perturbation and cell organellar dysfunction.

Bisphenol A Activates Calcium Influx in Immortalized GnRH Neurons

Bisphenol A (BPA) is one of the most widely used chemicals worldwide, e.g., as a component of plastic containers for food and water. It is considered to exert an estrogenic effect, by mimicking estradiol (E2) action. Because of this widespread presence, it has attracted the interest and concern of researchers and regulators. Despite the vast amount of related literature, the potential adverse effects of environmentally significant doses of BPA are still object of controversy, and the mechanisms by which it can perturb endocrine functions, and particularly the neuroendocrine axis, are not adequately understood. One of the ways by which endocrine disruptors (EDCs) can exert their effects is the perturbation of calcium signaling mechanisms. In this study, we addressed the issue of the impact of BPA on the neuroendocrine system with an in vitro approach, using a consolidated model of immortalized Gonadotropin-Releasing Hormone (GnRH) expressing neurons, the GT1–7 cell line, focusing on the calcium signals activated by the endocrine disruptor. The investigation was limited to biologically relevant doses (nM–µM range). We found that BPA induced moderate increases in intracellular calcium concentration, comparable with those induced by nanomolar doses of E2, without affecting cell survival and with only a minor effect on proliferation.

Terahertz spectroscopy of Bisphenol "A", "AF", "S", "E" and the interrelationship between their molecular vibrations

Bisphenol "A" is a widespread environmental hormone. After the prohibition on the use of BPA in some applications, it is progressively replaced by its variants. However, these variants of Bisphenol "A" are also noxious. It is therefore of the utmost importance to find the similarity among these materials and put all of them under restriction to avoid harmful effects. Therefore, Bisphenol "A", "AF", "E", and "S" are studied by Terahertz spectroscopy (0.5-2.5 THz). Various molecular vibrations are found and assigned based on density-functional-theory calculations. Refractive Indices are calculated as well. The principal component analysis reveals the critical vibrational frequencies for their detection and shows the correlation between them.

Bisphenol A exposure remodels cognition of male rats attributable to excitatory alterations in the hippocampus and visual cortex

Bisphenol A, an environmental xenoestrogen, has been shown sex-specific adverse effects on cognitive function of rodents. However, the specific mechanisms underlying these outcomes remain elusive, limiting our understanding the differences in behavioral impairments due to BPA exposure between genders in humans. The present study chose the juvenile stage (with a stable estrogen level) as the exposure window to explore BPA effects on cognitive behaviors of male and female Sprague-Dawley (SD) rats and related mechanisms. Three dosages of BPA (0.04, 0.4 and 4 mg/kg/day) were chose to make BPA-exposed models. Especially, the mid-dose for rats was close to the current reference daily limit for human exposure given by the U.S. Environmental Protection Agency. Our results showed that male but not female juvenile rats had a marked decline in spatial memory after 0.4 mg/kg/day BPA exposure, which accompanied with downregulation of glutamate receptor (NR2) expression in their hippocampus and primary visual cortex (V1). In the high-dose BPA exposed groups (4 mg/kg/day), there was not only a deficit of spatial memory, but also an anxiety-like behavior of male rats. Additionally, those rats had a significant decline in spine density of pyramidal neurons and a decreased expression of glutamate receptor subtypes (NR2 and GluR1) in the hippocampus. Importantly, such impairments in the hippocampus of male rats were associated with a decrease of glutamate receptor (NR2) expression in the V1, which could perturb the visual information inputs. To some extent, altered ERβ expression within their hypothalamus could contribute to the anxiety-like behavior after high-dose BPA exposure. However, the low-dose BPA exposed juvenile rats didn't present any structural and behavioral changes in our present study. Those results suggests that BPA exerts dose dependent and gender-specific effects on the cognition of juvenile animals. Our findings shed light on mechanisms underlying BPA effects on the juvenile animals.

Exposure to Di-(2-ethylhexyl) Phthalate During Perinatal Period Gender-Specifically Impairs the Dendritic Growth of Pyramidal Neurons in Rat Offspring

Di-(2-ethylhexyl) phthalate (DEHP), as a prevalent xenoestrogen endocrine disrupter, is omnipresent in the environment and commonly used in polyethylene plastic products. Although DEHP has potential adverse effects on multisystem organs, damage to the central nervous system is more significant. However, the consequences and mechanisms of DEHP exposure remain to be explored. The aim of this study was to investigate the effects and related mechanisms of maternal DEHP exposure on dendritic development of hippocampal pyramidal neurons in a rat model. Pregnant Wistar rats were intragastrically administrated either vehicle or DEHP (30, 300, and 750 mg/kg/d) from gestation day 0 to postnatal day (PN) 21. The dendritic length and complexity of dendritic arbors' pattern in pyramidal neurons of the hippocampus were measured using Golgi-Cox staining and Sholl analysis. The expression of dendritic development-related proteins was detected using western blot and immunofluorescence staining. DEHP-treated male but not female pups showed an obvious decrease in the total length and branching numbers of basal dendrites on PN7, PN14, and PN21. The phosphorylation of MAP2c, stathmin, and JNK1 in the male pup hippocampus was significantly decreased in DEHP treatment groups compared to controls. However, protein expression alteration in the hippocampus of female offspring was not observed. In summary, our study indicated that DEHP has a gender-specific negative impact on the dendritic growth of CA1 pyramidal neurons in male offspring of a rat model of DEHP exposure. The adverse impact may be related to the dysregulation of phosphorylated and total MAP2c and stathmin mediated by JNK1.

Does the prenatal bisphenol A exposure alter DNA methylation levels in the mouse hippocampus?: An analysis using a high-sensitivity methylome technique

Background

There is still considerable debate about the effects of exposure to bisphenol A (BPA) an endocrine disrupter at low doses. Recently, many studies using animal models have shown that prenatal BPA exposure induces behavioral and neuronal disorders due to epigenetic changes in the brain. However, striking evidence of epigenomic changes has to be shown.

Methods

To investigate whether low-dose BPA exposure in the fetal stage can alter CpG methylation levels in the central nervous system, the hippocampus of the inbred C57BL/6 J mouse as the target tissue was collected to detect alterations in CpG methylation levels using a highly sensitive method of genome-wide DNA methylation analysis, methylated site display-amplified fragment length polymorphism (MSD-AFLP).

Results

BPA showed the sex-hormone like effects on male reproductive organs. Although we examined the methylation levels of 43,840 CpG sites in the control and BPA (200 μg/kg/day)-treated group (6 mice per group), we found no statistically significant changes in methylation levels in any CpG sites.

Conclusions

At least under the experimental condition in this study, it is considered that the effect of low-dose BPA exposure during the fetal stage on hippocampal DNA methylation levels is extremely small.

Mice exposed to bisphenol A exhibit depressive-like behavior with neurotransmitter and neuroactive steroid dysfunction

Fetal exposure to endocrine disrupting chemicals (EDCs) has been associated with adverse neurobehavioral outcomes across the lifespan and can persist across multiple generations of offspring. However, the underlying mechanisms driving these changes are not well understood. We investigated the molecular perturbations associated with EDC-induced behavioral changes in first (F1) and second (F2) filial generations, using the model EDC bisphenol A (BPA). C57BL/6J dams were exposed to BPA from preconception until lactation through the diet at doses (10 μg/kg bw/d-lower dose or 10 mg/kg bw/d-upper dose) representative of human exposure levels. As adults, F1 male offspring exhibited increased depressive-like behavior, measured by the forced swim test, while females were unaffected. These behavioral changes were limited to the F1 generation and were not associated with altered maternal care. Transcriptome analysis by RNA-sequencing in F1 control and upper dose BPA-exposed adult male hippocampus revealed neurotransmitter systems as major pathways disrupted by developmental BPA exposure. High performance liquid chromatography demonstrated a male-specific reduction in hippocampal serotonin. Administration of the selective serotonin reuptake inhibitor fluoxetine (20 mg/kg bw) rescued the depressive-like phenotype in males exposed to lower, but not upper, dose BPA, suggesting distinct mechanisms of action for each exposure dose. Finally, high resolution mass spectrometry revealed reduced circulating levels of the neuroactive steroid dehydroepiandrosterone in BPA-exposed males, suggesting another potential mechanism underlying the depressive-like phenotype. Thus, behavioral changes associated with early life BPA exposure may be mediated by sex-specific disruptions in the serotonergic system and/or sex steroid biogenesis in male offspring.

Suppressive effects of neonatal bisphenol A on the neuroendocrine system

The aim of this study was to assess the effects of neonatal bisphenol A (BPA) administration on neuroendocrine features (the thyroid–brain axis). BPA (20 or 40 µg/kg) was orally administered to juvenile male albino rats ( Rattus norvegicus) from postnatal days (PNDs) 15 to 30. Both doses resulted in lower serum thyroxine (T4), triiodothyronine (T3), and growth hormone levels and higher thyrotropin level than the control levels at PND 30. In the neonatal cerebellum and cerebrum, vacuolation, pyknosis, edema, degenerative changes, and reductions in the size and number of the cells were observed in both treated groups. Alternatively, elevations in oxidative markers (lipid peroxidation, nitric oxide, and hydrogen peroxide [H2O2]) at both dose levels were recorded at PND 30, along with decreased activities of antioxidant markers (ascorbic acid, total thiol [t-SH], glutathione, glutathione peroxidase, glutathione reductase, glutathione-S-transferase, and catalase) with respect to control levels. Thus, the BPA-induced hypothyroid state may disturb the neonatal thyroid–brain axis via production of free radicals, and this could damage the plasma membrane and cellular components, delaying cerebrum and cerebellum development.

Relationship between bisphenol A exposure and attention-deficit/ hyperactivity disorder: A case-control study for primary school children in Guangzhou, China

Bisphenol A (BPA) is an endocrine-disrupting chemical. Studies have shown that the exposure to BPA is associated with attention-deficit/hyperactivity disorder (ADHD) during adolescent development. However the direct clinical evidence is limited. To investigate the possible association between environmental BPA exposure and the altered behavior of children, a case-control study was conducted with children aged 6-12 years in Guangzhou, China. Two hundred fifteen children diagnosed with ADHD and 253 healthy children from Guangzhou were recruited as the case and control groups, respectively. Urinary BPA and 8-hydroxy-2'-deoxyguanosine (8-OHdG, a biomarker of oxidative DNA damage) concentrations were determined by high-performance liquid chromatography/tandem spectrometry. The results showed that concentrations of urinary BPA for the case group were significantly higher than those for the control group (3.44 vs 1.70 μg/L; 4.63 vs 1.71 μg/g Crt. p < .001). A stepwise increase in the odds ratios for ADHD was observed with the increasing quartiles of children's urinary BPA (first quartile: reference category; second quartile adjusted OR: 1.79, 95% CI: 0.95-3.37; third quartile adjusted OR: 7.44, 95% CI: 3.91-14.1; fourth quartile adjusted OR: 9.41, 95% CI: 4.91-18.1). When the BPA levels were stratified by gender, the odds of ADHD among boys and girls increased significantly with urinary BPA concentrations (adjusted OR: 4.58, 95% CI: 2.84-7.37; adjusted OR: 2.83, 95% CI: 1.17-6.84). Urinary 8-OHdG concentrations in the ADHD children were significantly higher than those in the control group. Furthermore, the linear regression analysis results indicated that a significant relationship existed between BPA exposure and 8-OHdG levels (R = 0.257, p < .001). Our findings provide direct evidence that childhood BPA exposure may be related to ADHD and 8-OHdG concentrations for children. Moreover, BPA exposure could increase the higher occurrence of ADHD for boy than for girls.

Neurotoxicity of low bisphenol A (BPA) exposure for young male mice: Implications for children exposed to environmental levels of BPA

To investigate the neuron toxicities of low-dose exposure to bisphenol A (BPA) in children, mice were used as an animal model. We examined brain cell damage and the effects of learning and memory ability after BPA exposure in male mice (4 weeks of age) that were divided into four groups and chronically received different BPA treatments for 8 weeks. The comet assay and hippocampal neuron counting were used to detect the brain cell damage. The Y-maze test was applied to test alterations in learning and memory ability. Long term potentiation induction by BPA exposure was performed to study the potential mechanism of performance. The percentages of tail DNA, tail length and tail moment in brain cells increased with increasing BPA exposure concentrations. Significant differences in DNA damage were observed among the groups, including between the low-dose and control groups. In the Y-maze test, the other three groups qualified for the learned standard one day earlier than the high-exposed group. Furthermore, the ratio of qualified mice in the high-exposed group was always the lowest among the groups, indicating that high BPA treatment significantly altered the spatial memory performance of mice. Different BPA treatments exerted different effects on the neuron numbers of different regions in the hippocampus. In the CA1 region, the high-exposed group had a significant decrease in neuron numbers. A non-monotonic relationship was observed between the exposure concentrations and neuron quantity in the CA3 region. The hippocampal slices in the control and medium-exposed groups generated long-term potentiation after induction by theta burst stimulation, but the low-exposed group did not. A significant difference was observed between the control and low-exposed groups. In conclusion, chronic exposure to a low level of BPA had adverse effects on brain cells and altered the learning and memory ability of adolescent mice.

Bisphenol A exposure perturbs visual function of adult cats by remodeling the neuronal activity in the primary visual pathway

Bisphenol A (BPA), a common environmental xenoestrogen, has been implicated in physiological and behavioral impairment, but the neuronal basis remains elusive. Although various synaptic mechanisms have been shown to mediate BPA-induced brain deficits, there are almost no reports addressing its underlying physiological mechanisms at the individual neuron level, particularly in the primary visual system. In the present study, using multiple-channel recording technique, we recorded the responses of single neurons in the primary visual system of cats to various direction stimuli both before and after BPA exposure. The results showed that the orientation selectivity of neurons in the primary visual cortex (area 17, A17) was obviously decreased after 2 h of intravenous BPA administration (0.2 mg/kg). Moreover, there were worse performances of information transmission of A17 neurons, presenting markedly decreased signal-to-noise ratio (SNR). To some extent, these functional decreases were attributable to the altered information inputs from lateral geniculate nucleus (LGN), which showed an increased spontaneous activity. Additionally, local injection of BPA (3.3 μg/ml) in A17 resulted in an obvious increase in orientation selectivity and a decrease in neuronal activity, involving enhanced activity of fast-spiking inhibitory interneurons. In conclusion, our results first demonstrate that acute BPA exposure can restrict the visual perception of cats, mainly depending on the alteration of the LGN projection, not the intercortical interaction. Importantly, BPA-induced-brain deficits might not only be confined to the cortical level but also occur as early as at the subcortical level.

Developmental neurotoxicity test guidelines: problems and perspectives

Epidemiologic evidence has demonstrated associations between early life exposure to industrial chemicals and the occurrence of disease states, including cognitive and behavioral abnormalities, in children. The developing brain in the fetal and infantile periods is extremely vulnerable to chemicals because the blood-brain barrier is not completely formed during these periods. The Organisation for Economic Co-operation and Development (OECD) developmental neurotoxicity (DNT) test guideline, TG426, updated in 2007, comprises in vivo behavioral observational tests and other tests intended to assess DNT induced by exposure to industrial chemicals. These chemicals may enter the market without having been subjected to DNT testing, as DNT test data is not mandated by law at the time of chemical registration. In addition, proprietary rights have led to problems concerning the non-disclosure of industrial chemical toxicity test data, including DNT test data. To overcome the disadvantages of high-cost and low time efficiency of in vivo DNT tests, in vitro or in silico tests are the proposed alternatives, but it is unlikely that the results of such tests would reflect changes in higher brain functions. Accordingly, the current DNT test guidelines need to be revised to avoid overlooking or neglecting the occurrence of DNT induced by exposure to low doses of chemicals. This review also proposes the introduction of novel in vivo DNT testing methods in light of a cost-performance analysis.

Bisphenol A Impairs Synaptic Plasticity by Both Pre- and Postsynaptic Mechanisms

Bisphenol A (BPA), an environmental xenoestrogen, has been reported to induce learning and memory impairments in rodent animals. However, effects of BPA exposure on synaptic plasticity and the underlying physiological mechanisms remain elusive. Our behavioral and electrophysiological analyses show that BPA obviously perturbs hippocampal spatial memory of juvenile Sprague-Dawley rats after four weeks exposure, with significantly impaired long-term potentiation (LTP) in the hippocampus. These effects involve decreased spine density of pyramidal neurons, especially the apical dendritic spine. Further presynaptic findings show an overt inhibition of pulse-paired facilitation during electrophysiological recording, which suggest the decrease of presynaptic transmitter release and is consistent with reduced production of presynaptic glutamate after BPA exposure. Meanwhile, LTP-related glutamate receptors, NMDA receptor 2A (NR2A) and AMPA receptor 1 (GluR1), are significantly downregulated in BPA-exposed rats. Excitatory postsynaptic currents (EPSCs) results also show that EPSC_NMDA, but not EPSC_AMPA, is declined by 40% compared to the baseline in BPA-perfused brain slices. Taken together, these findings reveal that juvenile BPA exposure has negative effects on synaptic plasticity, which result from decreases in dendritic spine density and excitatory synaptic transmission. Importantly, this study also provides new insights into the dynamics of BPA-induced memory deterioration during the whole life of rats.

Estrogenic Endocrine Disrupting Chemicals Influencing NRF1 Regulated Gene Networks in the Development of Complex Human Brain Diseases

During the development of an individual from a single cell to prenatal stages to adolescence to adulthood and through the complete life span, humans are exposed to countless environmental and stochastic factors, including estrogenic endocrine disrupting chemicals. Brain cells and neural circuits are likely to be influenced by estrogenic endocrine disruptors (EEDs) because they strongly dependent on estrogens. In this review, we discuss both environmental, epidemiological, and experimental evidence on brain health with exposure to oral contraceptives, hormonal therapy, and EEDs such as bisphenol-A (BPA), polychlorinated biphenyls (PCBs), phthalates, and metalloestrogens, such as, arsenic, cadmium, and manganese. Also we discuss the brain health effects associated from exposure to EEDs including the promotion of neurodegeneration, protection against neurodegeneration, and involvement in various neurological deficits; changes in rearing behavior, locomotion, anxiety, learning difficulties, memory issues, and neuronal abnormalities. The effects of EEDs on the brain are varied during the entire life span and far-reaching with many different mechanisms. To understand endocrine disrupting chemicals mechanisms, we use bioinformatics, molecular, and epidemiologic approaches. Through those approaches, we learn how the effects of EEDs on the brain go beyond known mechanism to disrupt the circulatory and neural estrogen function and estrogen-mediated signaling. Effects on EEDs-modified estrogen and nuclear respiratory factor 1 (NRF1) signaling genes with exposure to natural estrogen, pharmacological estrogen-ethinyl estradiol, PCBs, phthalates, BPA, and metalloestrogens are presented here. Bioinformatics analysis of gene-EEDs interactions and brain disease associations identified hundreds of genes that were altered by exposure to estrogen, phthalate, PCBs, BPA or metalloestrogens. Many genes modified by EEDs are common targets of both 17 β-estradiol (E2) and NRF1. Some of these genes are involved with brain diseases, such as Alzheimer's Disease (AD), Parkinson's Disease, Huntington's Disease, Amyotrophic Lateral Sclerosis, Autism Spectrum Disorder, and Brain Neoplasms. For example, the search of enriched pathways showed that top ten E2 interacting genes in AD-APOE, APP, ATP5A1, CALM1, CASP3, GSK3B, IL1B, MAPT, PSEN2 and TNF-underlie the enrichment of the Kyoto Encyclopedia of Genes and Genomes (KEGG) AD pathway. With AD, the six E2-responsive genes are NRF1 target genes: APBB2, DPYSL2, EIF2S1, ENO1, MAPT, and PAXIP1. These genes are also responsive to the following EEDs: ethinyl estradiol (APBB2, DPYSL2, EIF2S1, ENO1, MAPT, and PAXIP1), BPA (APBB2, EIF2S1, ENO1, MAPT, and PAXIP1), dibutyl phthalate (DPYSL2, EIF2S1, and ENO1), diethylhexyl phthalate (DPYSL2 and MAPT). To validate findings from Comparative Toxicogenomics Database (CTD) curated data, we used Bayesian network (BN) analysis on microarray data of AD patients. We observed that both gender and NRF1 were associated with AD. The female NRF1 gene network is completely different from male human AD patients. AD-associated NRF1 target genes-APLP1, APP, GRIN1, GRIN2B, MAPT, PSEN2, PEN2, and IDE-are also regulated by E2. NRF1 regulates targets genes with diverse functions, including cell growth, apoptosis/autophagy, mitochondrial biogenesis, genomic instability, neurogenesis, neuroplasticity, synaptogenesis, and senescence. By activating or repressing the genes involved in cell proliferation, growth suppression, DNA damage/repair, apoptosis/autophagy, angiogenesis, estrogen signaling, neurogenesis, synaptogenesis, and senescence, and inducing a wide range of DNA damage, genomic instability and DNA methylation and transcriptional repression, NRF1 may act as a major regulator of EEDs-induced brain health deficits. In summary, estrogenic endocrine disrupting chemicals-modified genes in brain health deficits are part of both estrogen and NRF1 signaling pathways. Our findings suggest that in addition to estrogen signaling, EEDs influencing NRF1 regulated communities of genes across genomic and epigenomic multiple networks may contribute in the development of complex chronic human brain health disorders.

Impact of Low Dose Oral Exposure to Bisphenol A (BPA) on the Neonatal Rat Hypothalamic and Hippocampal Transcriptome: A CLARITY-BPA Consortium Study

Bisphenol A (BPA) is an endocrine disrupting, high volume production chemical found in a variety of products. Evidence of prenatal exposure has raised concerns that developmental BPA may disrupt sex-specific brain organization and, consequently, induce lasting changes on neurophysiology and behavior. We and others have shown that exposure to BPA at doses below the no-observed-adverse-effect level can disrupt the sex-specific expression of estrogen-responsive genes in the neonatal rat brain including estrogen receptors (ERs). The present studies, conducted as part of the Consortium Linking Academic and Regulatory Insights of BPA Toxicity program, expanded this work by examining the hippocampal and hypothalamic transcriptome on postnatal day 1 with the hypothesis that genes sensitive to estrogen and/or sexually dimorphic in expression would be altered by prenatal BPA exposure. NCTR Sprague-Dawley dams were gavaged from gestational day 6 until parturition with BPA (0-, 2.5-, 25-, 250-, 2500-, or 25 000-μg/kg body weight [bw]/d). Ethinyl estradiol was used as a reference estrogen (0.05- or 0.5-μg/kg bw/d). Postnatal day 1 brains were microdissected and gene expression was assessed with RNA-sequencing (0-, 2.5-, and 2500-μg/kg bw BPA groups only) and/or quantitative real-time PCR (all exposure groups). BPA-related transcriptional changes were mainly confined to the hypothalamus. Consistent with prior observations, BPA induced sex-specific effects on hypothalamic ERα and ERβ (Esr1 and Esr2) expression and hippocampal and hypothalamic oxytocin (Oxt) expression. These data demonstrate prenatal BPA exposure, even at doses below the current no-observed-adverse-effect level, can alter gene expression in the developing brain.

Correlation between antibodies to bisphenol A, its target enzyme protein disulfide isomerase and antibodies to neuron-specific antigens

Evidence continues to increase linking autoimmunity and other complex diseases to the chemicals commonly found in our environment. Bisphenol A (BPA) is a synthetic monomer used widely in many forms, from food containers to toys, medical products and many others. The potential for BPA to participate as a triggering agent for autoimmune diseases is likely due to its known immunological influences. The goal of this research was to determine if immune reactivity to BPA has any correlation with neurological antibodies. BPA binds to a target enzyme called protein disulfide isomerase (PDI). Myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG) are neuronal antigens that are target sites for neuroinflammation and neuroautoimmunity. We determined the co‐occurrence of anti‐MBP and anti‐MOG antibodies with antibodies made against BPA bound to human serum albumin in 100 healthy human subjects. Correlation between BPA to PDI, BPA to MOG, BPA to MBP, PDI to MBP and PDI to MOG were all highly statistically significant (P < 0.0001). The outcome of our study suggests that immune reactivity to BPA‐human serum albumin and PDI has a high degree of statistical significance with substantial correlation with both MBP and MOG antibody levels. This suggests that BPA may be a trigger for the production of antibodies against PDI, MBP and MOG. Immune reactivity to BPA bound to human tissue proteins may be a contributing factor to neurological autoimmune disorders. Further research is needed to determine the exact relationship of these antibodies with neuroautoimmunities. Copyright © 2016 The Authors Journal of Applied Toxicology Published by John Wiley & Sons Ltd.

This study investigated correlation of bisphenol A bound to human albumin antibodies with protein disulfide isomerase antibodies, myelin oligodendrocyte glycoprotein antibodies and myelin basic protein antibodies.

Exposure to endocrine disrupting chemicals and neurodevelopmental alterations

The developing brain is remarkably malleable as neural circuits are formed and these circuits are strongly dependent on hormones for their development. For those reasons, the brain is very vulnerable to the effects of endocrine-disrupting chemicals (EDCs) during critical periods of development. This review focuses on three ubiquitous endocrine disruptors that are known to disrupt the thyroid function and are associated with neurobehavioral deficits: polychlorinated biphenyls, polybrominated diphenyl ethers, and bisphenol A. The human and rodent data suggesting effects of those EDCs on memory, cognition, and social behavior are discussed. Their mechanisms of action go beyond relative hypothyroidism with effects on neurotransmitter release and calcium signaling.

In Utero Bisphenol A Exposure Induces Abnormal Neuronal Migration in the Cerebral Cortex of Mice

Bisphenol A (BPA) has been known to have endocrine-disrupting activity to induce reproductive and behavioral abnormalities in offspring of laboratory animal species. However, morphological basis of this abnormality during brain development is largely unknown. Cerebral cortex plays a crucial role in higher brain function, and its precisely laminated structure is formed by neuronal migration. In the present study, transfecting a plasmid (pCAG-mCherry) by in utero electroporation (IUE), we visualized developing neurons and investigated the possible effects of in utero BPA exposure on neuronal migration. Pregnant mice were exposed to BPA by osmotic pump at estimated daily doses of 0, 40 (BPA-40), or 400 (BPA-400) μg/kg from embryonic day 14.5 (E14.5) to E18.5. IUE was performed at E14.5 and neuronal migration was analyzed at E18.5. Compared with the control group, neuronal migration in the cortical plate was significantly decreased in the BPA-40 group; however, there was no significant difference in the BPA-400 group. Among several neuronal migration-related genes and cortical layer-specific genes, TrkB in the BPA-400 group was found significantly upregulated. In conclusion, in utero exposure to low BPA dose was found to disrupt neuronal migration in the cerebral cortex in a dose-specific manner.