Accelerated reduction of serum thyroxine and hippocampal histone acetylation links to exacerbation of spatial memory impairment in aged CD-1 mice pubertally exposed to bisphenol-a

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.

Distinct epigenetic modulation of differentially expressed genes in the adult mouse brain following prenatal exposure to low-dose bisphenol A

Bisphenol A (BPA) is a common component in the manufacture of daily plastic consumer goods. Recent studies have suggested that prenatal exposure to BPA can increase the susceptibility of offspring to mental illness, although the underlying mechanisms remain unclear. In this study, we performed transcriptomic and epigenomic profiling in the adult mouse brain following prenatal exposure to low-dose BPA. We observed a sex-specific transcriptional dysregulation in the cortex, with more significant differentially expressed genes was observed in adult cortex from male offspring. Moreover, the upregulated genes primarily influenced neuronal functions, while the downregulated genes were significantly associated with energy metabolism pathways. More evidence supporting impaired mitochondrial function included a decreased ATP level and a reduced number of mitochondria in the cortical neuron of the BPA group. We further investigated the higher-order chromatin regulatory patterns of DEGs by incorporating published Hi-C data. Interestingly, we found that upregulated genes exhibited more distal interactions with multiple enhancers, while downregulated genes displayed relatively short-range interactions among adjacent genes. Our data further revealed decreased H3K9me3 signal on the distal enhancers of upregulated genes, whereas increased DNA methylation and H3K27me3 signals on the promoters of downregulated genes. In summary, our study provides compelling evidence for the potential health risks associated with prenatal exposure to BPA, and uncovers sex-specific transcriptional changes with a complex interplay of multiple epigenetic mechanisms.

Brain-derived neurotrophic factor (BDNF): an effect biomarker of neurodevelopment in human biomonitoring programs

The present narrative review summarizes recent findings focusing on the role of brain-derived neurotrophic factor (BDNF) as a biomarker of effect for neurodevelopmental alterations during adolescence, based on health effects of exposure to environmental chemical pollutants. To this end, information was gathered from the PubMed database and the results obtained in the European project Human Biomonitoring for Europe (HBM4EU), in which BDNF was measured at two levels of biological organization: total BDNF protein (serum) and BDNF gene DNA methylation (whole blood) levels. The obtained information is organized as follows. First, human biomonitoring, biomarkers of effect and the current state of the art on neurodevelopmental alterations in the population are presented. Second, BDNF secretion and mechanisms of action are briefly explained. Third, previous studies using BDNF as an effect biomarker were consulted in PubMed database and summarized. Finally, the impact of bisphenol A (BPA), metals, and non-persistent pesticide metabolites on BDNF secretion patterns and its mediation role with behavioral outcomes are addressed and discussed. These findings were obtained from three pilot studies conducted in HBM4EU project. Published findings suggested that exposure to some chemical pollutants such as fine particle matter (PM), PFAS, heavy metals, bisphenols, and non-persistent pesticides may alter circulating BDNF levels in healthy population. Therefore, BDNF could be used as a valuable effect biomarker to investigate developmental neurotoxicity of some chemical pollutants.

Genome-wide distribution of histone trimethylation reveals a global impact of bisphenol A on telomeric binding proteins and histone acetyltransferase factors: a pilot study with human and in vitro data

OBJECTIVE

To assess the genetic and epigenetic effects promoted by Bisphenol A (BPA) exposure in adolescent males from the Spanish INMA-Granada birth cohort, and in human cells.

METHODS

DNA methylation was analysed using MEDIP. Repeat number variation in genomic DNA was evaluated, along with the analysis of H3K4me3 by using chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq). Analyses were performed with material extracted from whole blood of the adolescents, complemented by in vitro assessments of human (HeLa) cells exposed to 10 nM BPA, specifically, immunofluorescence evaluation of protein levels, gene expression analysis and ChIP‒qPCR analysis.

RESULTS

Adolescents in the high urinary BPA levels group presented a higher level of Satellite A (SATA) repetitive region copy numbers compared to those in the low BPA group and a tendency towards increase in telomere length. We also observed decreased DNA methylation at the promoters of the imprinted genes H19, KCNQ1, and IGF2; at LINE1 retroelements; and at the ARID2, EGFR and ESRRA and TERT genes. Genome-wide sequencing revealed increased H3K4me3 occupancy at the promoters of genes encoding histone acetyltransferases, telomeric DNA binding factors and DNA repair genes. Results were supported in HeLa cells exposed to 10 nM BPA in vitro. In accordance with the data obtained in blood samples, we observed higher H3K4me3 occupancy and lower DNA methylation at some specific targets in HeLa cells. In exposed cells, changes in the expression of genes encoding DNA repair factors (ATM, ARID2, TRP53) were observed, and increased expression of several genes encoding telomeric DNA binding factors (SMG7, TERT, TEN1, UPF1, ZBTB48) were also found. Furthermore, an increase in ESR1/ERa was observed in the nuclei of HeLa cells along with increased binding of ESR1 to KAT5, KMT2E and TERF2IP promoters and decreased ESR1 binding at the RARA promoter. The DNA damage marker p53/TP53 was also increased.

CONCLUSION

In this pilot study, genome-wide analysis of histone trimethylation in adolescent males exposed to BPA revealed a global impact on the expression of genes encoding telomeric binding proteins and histone acetyltransferase factors with similar results in HeLa cells. Nevertheless, larger studies should confirm our findings.

Urinary concentrations of phenols, oxidative stress biomarkers and thyroid cancer: Exploring associations and mediation effects

Phenols have been shown to influence the cellular proliferation and function of thyroid in experimental models. However, few human studies have investigated the association between phenol exposure and thyroid cancer, and the underlying mechanisms are also poorly understood. We conducted a case-control study by age- and sex-matching 143 thyroid cancer and 224 controls to investigate the associations between phenol exposures and the risk of thyroid cancer, and further to explore the mediating role of oxidative stress. We found that elevated urinary triclosan (TCS), bisphenol A (BPA) and bisphenol S (BPS) levels were associated with increased risk of thyroid cancer (all P for trends < 0.05), and the adjusted odds ratios (ORs) comparing the extreme exposure groups were 3.52 (95% confidence interval (CI): 2.08, 5.95), 2.06 (95% CI: 1.06, 3.97) and 7.15 (95% CI: 3.12, 16.40), respectively. Positive associations were also observed between urinary TCS, BPA and BPS and three oxidative stress biomarkers measured by 8-hydroxy-2'-deoxyguanosine (8-OHdG), 8-iso-prostaglandin F_2α (8-isoPGF_2α) and 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA), as well as between urinary 8-isoPGF_2α and HNE-MA and the risk of thyroid cancer. Mediation analysis showed that urinary 8-isoPGF_2α mediated 28.95%, 47.06% and 31.08% of the associations between TCS, BPA and BPS exposures and the risk of thyroid cancer, respectively (all P < 0.05). Our results suggest that exposure to TCS, BPA and BPS may be associated with increased risk of thyroid cancer and lipid peroxidation may be an intermediate mechanism. Further studies are warranted to confirm the findings.

Maternal inflammation induces spatial learning and memory impairment in the F1 and F2 generations of mice via sex-specific epigenetic mechanisms

Mounting evidence indicates that histone modifications are involved in aging-associated cognitive decline (AACD) and can be transmitted to offspring over multiple generations under conditions of stress. Here, we investigated the effects of maternal sub-chronic inflammation caused by lipopolysaccharide (LPS) on AACD and histone modifications in the F1 and F2 generations of experimental mice as well as the potential sex specificity of intergenerational effects. In brief, F0-generation CD-1 dams were exposed to LPS (50 µg/kg) or saline (CON) during late pregnancy. Subsequently, F1 males and females (at 2 months-of-age) from the LPS treatment group were mated with non-littermates from the LPS group or wild-type mice to produce F2 generations of parental- (F2-LPS₂), paternal- (F2M-LPS₁) and maternal-origin (F2F-LPS₁) mice. Then, CON-F1 males and females were mated with wild-type mice to generate F2 generations of paternal- (F2M-CON₁) and maternal-origin (F2F-CON₁). Next, we evaluated the cognitive ability and levels of hippocampal H4K12ac and H3K9me3 in the F1 and F2 offspring at 3- and 13 months-of-age. Overall, F1 male and female LPS groups presented with elevated corticosterone (P < 0.001, P = 0.036, P = 0.025, 0.012, respectively) and cytokine responses, poorer cognitive performance (all P < 0.05) and H3K9 hypermethylation and H4K12 hypoacetylation in the dorsal hippocampus (all P < 0.05); these issues were carried over to the F2 generation via the parents, predominantly in the paternal lineage. Moreover, the levels of H3K9me3 and H4K12ac were significant correlated with cognitive performance (all P < 0.05), regardless of whether inflammatory insults had been incurred directly or indirectly. These findings indicated that gestational inflammatory insults in the F0 generation accelerated AACD in the F2 generation, along with H3K9 hypermethylation and H4K12 hypoacetylation in the hippocampus, and that these issues were derived from the F1 parents, especially from the F1 fathers.

Bisphenol-A exposure leads to neurotoxicity through upregulating the expression of histone deacetylase 2 in vivo and in vitro

Bisphenol-A (BPA), an environmental endocrine disruptor, is toxic to the central nervous system. Although recent studies have shown BPA-induced neurotoxicity, it is far from clear what precisely epigenetic mechanisms are involved in BPA-induced cognitive deficits. In this study, pheochromocytoma (PC12) cells were treated with BPA at 1 μM for 36 h in vitro. In vivo, C57BL/6 mice were administered to BPA at a dose of 1 mg/kg/day for 10 weeks. The results showed that 1 μM BPA exposure for 36 h impaired neurite outgrowth of PC12 cells through decreasing the primary and secondary branches. Besides, BPA exposure decreased the level of Ac-H3K9 (histone H3 Lys9 acetylation) by upregulating the expression of HDAC2 (histone deacetylases 2) in PC12 cells. Furthermore, treatment of both TSA (Trichostatin A, inhibitor of the histone deacetylase) and shHDAC2 plasmid (HDAC2 knockdown construct) resulted in amelioration neurite outgrowth deficits induced by BPA. In addition, it was shown that repression of HDAC2 could markedly rescue the spine density impairment in the hippocampus and prevent the cognitive impairment caused by BPA exposure in mice. Collectively, HDAC2 plays an essential role in BPA-induced neurotoxicity, which provides a potential molecular target for medical intervention.

Protective Effects of Lignin-Carbohydrate Complexes from Wheat Stalk against Bisphenol a Neurotoxicity in Zebrafish via Oxidative Stress

Lignin-carbohydrate complexes (LCCs) from different lignocellulosic biomass have shown biological qualities as antioxidant and immunostimulant. By contrast, the application of LCCs as protectant against neurotoxicity caused by different compounds is scarce. In this work, two kinds of LCCs with carbohydrate-rich and lignin-rich fractions were obtained from wheat stalk and used to protect against BPA-neurotoxicity in zebrafish. The results showed that BPA at a concentration of 500 µg/L results in neurotoxicity, including significant behavioral inhibition, and prevents the expression of central nervous system proteins in transgenic zebrafish models (Tg (HuC-GFP)). When the zebrafish was treated by LCCs, the reactive oxygen species of zebrafish decreased significantly with the change of antioxidant enzymes and lipid peroxidation, which was due to the LCCs' ability to suppress the mRNA expression level of key genes related to nerves. This is essential in view of the neurotoxicity of BPA through oxidative stress. In addition, BPA exposure had negative effects on the exercise behavior, the catalase (CAT) and superoxide dismutase (SOD) activity, and the larval development and gene expression of zebrafish larvae, and LCC preparations could recover these negative effects by reducing oxidative stress. In zebrafish treated with BPA, carbohydrate-rich LCCs showed stronger antioxidant activity than lignin-rich LCCs, showing their potential as a neuroprotective agents.

Peripubertal Bisphenol A Exposure Imparts Detrimental Age-Related Changes in Body Composition, Cognition, and Hydrogen Sulfide Production Capacities

Aims: Peripubertal endocrine disruption has immediate and lifelong consequences on health, cognition, and lifespan. Disruption comes from dietary, environmental, and pharmaceutical sources. The plasticizer Bisphenol A (BPA) is one such endocrine disrupting chemical. However, it is unclear whether peripubertal BPA exposure incites long-lasting physiological, neuro-cognitive, and/or longevity-related metabolic impairments. Catabolism of cysteine via transsulfuration enzymes produces hydrogen sulfide (H2S), a redox-modulating gasotransmitter causative to endocrine and metabolic homeostasis and improved cognitive function with age. As thyroid hormone (TH) regulates hepatic H2S production and BPA is a TH receptor antagonist, we hypothesized that BPA exposure during peripubertal development impairs metabolic and neuro-cognitive/behavioral endpoints in aged mice, in part, due to altered peripheral and/or localized H2S production and redox status. Results: To test this, male C57BL/6J mice at 5 weeks of age were orally exposed daily for 5 weeks to 250 μg BPA/kg, defined as low dose group (LD BPA), or 250 mg BPA/kg, defined as high dose group (HD BPA). Both LD and HD BPA exposure decreased lean mass and increased fat mass accompanied by decreased serum total TH at advanced ages. In addition, LD BPA had an anxiogenic effect whereas HD BPA caused cognitive deficits. Notably, HD BPA disrupted tissue-specific H2S production capacities and/or protein persulfidation, with the former negatively correlated with memory deficits and oxidative stress. Innovation and Conclusion: These findings provide a potential mechanism of action for acute and long-term health impacts of BPA-induced peripubertal endocrine disruption and bolster the need for improved monitoring and limitation of adolescent BPA exposure.

The orphan nuclear receptor Nur77 plays a vital role in BPA-induced PC12 cell apoptosis

Bisphenol A (BPA) is a typical environmental endocrine disruptor that can migrate into organisms through skin contact, breathing, diet and various other approaches. The reproductive toxicity and neurotoxicity of BPA has been confirmed by several toxicological studies. However, the neurotoxicity of BPA is still controversial. In the present study, we used PC12 cells as a model to investigate the mechanism of BPA-induced neuronal apoptosis. BPA exposure reduced cell viability, altered cell morphology and aggravated intracellular Lactate dehydrogenase (LDH) release, intracellular Ca²⁺ concentration, Reactive oxygen species (ROS) levels, apoptosis and the reduction in the mitochondrial transmembrane potential (ΔΨm). Moreover, the results of the Western blot (WB) and Real-time quantitative polymerase chain reaction (RT-qPCR) assays indicated that the expression levels of Nur77 in the BPA group were down-regulated and accompanied by the downregulation of the NF-κb/Bcl-2 proteins and the upregulation of cleaved-caspase 3, which is a marker of apoptosis. However, these changes were significantly reversed with the upregulation of the Nur77 protein by introducing plasmids carrying the nur77 gene. These results indicated that BPA-induced apoptosis was closely related to Nur77-mediated inhibition of the NF-κb/Bcl-2 pathway.

Serum concentration of bisphenol A in elderly cats and its association with clinicopathological findings

OBJECTIVES

Bisphenol A (BPA) has been mentioned as a possible factor contributing to feline hyperthyroidism. Nevertheless, there are no previous studies reporting on the concentration of BPA in feline serum and its association with thyroid function. The objectives of this study were to measure serum BPA concentration in cats aged ⩾7 years, considered as healthy by their owners, and to compare the results with clinicopathological findings.

METHODS

Sixty-nine cats aged ⩾7 years considered as healthy by their owners were enrolled in the study. The concentration of BPA in feline serum was measured using liquid chromatography-tandem mass spectrometry. In all cats, signalment, living environment, diet history, and the results of haematological and biochemical analysis, including thyroxine levels, were available.

RESULTS

The mean serum BPA concentration in feline serum was 1.06 ± 0.908 ng/ml. Significant correlation was found between BPA concentration and haemoglobin (r = 0.3397; P = 0.0043), haematocrit (r = 0.3245; P = 0.0065) and the number of red blood cells (r = 0.2916; P = 0.0151), concentration of total protein (r = 0.2383; P = 0.0486), concentration of calcium (r = 0.3915; P = 0.0009) and level of bilirubin (r = 0.3848; P = 0.0011). No other significant correlations were found. Significant differences (P <0.01) were found between mature (1.28 ± 0.994 ng/ml) and geriatric cats (0.420 ± 0.240 ng/ml), between strictly indoor cats (1.27 ± 0.992 ng/ml) and cats with outdoor access (0.660 ± 0.529 ng/ml), and between cats fed canned food (1.23 ± 0.935 ng/ml) and cats fed non-canned food (0.774 ± 0.795 ng/ml).

CONCLUSIONS AND RELEVANCE

Measurable serum BPA levels were found in all examined samples. The age of the cats was revealed as a significant factor affecting BPA concentration and mature cats had the highest levels. A significantly higher concentration of BPA was found in cats living strictly indoors and in cats fed canned food. No association was found between BPA and thyroid function. Further studies are needed that focus on hyperthyroid cats for better evaluation of this relationship.

Enriched environment enhances histone acetylation of NMDA receptor in the hippocampus and improves cognitive dysfunction in aged mice

The mechanisms of age-associated memory impairment may be associated with glutamate receptor function and chromatin modification. To observe the effect of an enriched environment on the cognitive function of mice with age-associated memory impairment, 3-month-old C57BL/6 male mice ("young" mice) were raised in a standard environment, while 24-month-old C57BL/6 male mice with memory impairment ("age-associated memory impairment" mice) were raised in either a standard environment or an enriched environment. The enriched environment included a variety of stimuli involving movement and sensation. A water maze test was then used to measure cognitive function in the mice. Furthermore, quantitative real-time polymerase chain reaction and western blot assays were used to detect right hippocampal GluN2B mRNA as well as protein expression of GluN2B and CREB binding protein in all mice. In addition, chromatin immunoprecipitation was used to measure the extent of histone acetylation of the hippocampal GluN2B gene promoters. Compared with the young mice, the water maze performance of age-associated memory impairment mice in the standard environment was significantly decreased. In addition, there were significantly lower levels of total histone acetylation and expression of CREB binding protein in the hippocampus of age-associated memory impairment mice in the standard environment compared with the young mice. There were also significantly lower levels of histone acetylation, protein expression, and mRNA expression of GluN2B in the hippocampus of these mice. In contrast, in the age-associated memory impairment mice with the enriched environment intervention, the water maze performance and molecular biological indexes were significantly improved. These data confirm that an enriched environment can improve cognitive dysfunction in age-associated memory impairment mice, and suggest that the mechanisms may be related to the increased expression of CREB binding protein and the increased degree of total histone acetylation in the hippocampus of age-associated memory impairment mice, which may cause the increase of histone acetylation of GluN2B gene promoter and the enhancement of GluN2B mRNA transcription and protein expression in hippocampus. The animal experiment was approved by the Animal Ethics Committee of Yangzhou University, China (approval No. 20170312001) in March 2017.

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.

Bisphenols as Environmental Triggers of Thyroid Dysfunction: Clues and Evidence

Bisphenols (BPs), and especially bisphenol A (BPA), are known endocrine disruptors (EDCs), capable of interfering with estrogen and androgen activities, as well as being suspected of other health outcomes. Given the crucial role of thyroid hormones and the increasing incidence of thyroid carcinoma in the last few decades, this review analyzes the effects of BPS on the thyroid, considering original research in vitro, in vivo, and in humans published from January 2000 to October 2019. Both in vitro and in vivo studies reported the ability of BPs to disrupt thyroid function through multiple mechanisms. The antagonism with thyroid receptors (TRs), which affects TR-mediated transcriptional activity, the direct action of BPs on gene expression at the thyroid and the pituitary level, the competitive binding with thyroid transport proteins, and the induction of toxicity in several cell lines are likely the main mechanisms leading to thyroid dysfunction. In humans, results are more contradictory, though some evidence suggests the potential of BPs in increasing the risk of thyroid nodules. A standardized methodology in toxicological studies and prospective epidemiological studies with individual exposure assessments are warranted to evaluate the pathophysiology resulting in the damage and to establish the temporal relationship between markers of exposure and long-term effects.

The Promises and Challenges of Toxico-Epigenomics: Environmental Chemicals and Their Impacts on the Epigenome

BACKGROUND

It has been estimated that a substantial portion of chronic and noncommunicable diseases can be caused or exacerbated by exposure to environmental chemicals. Multiple lines of evidence indicate that early life exposure to environmental chemicals at relatively low concentrations could have lasting effects on individual and population health. Although the potential adverse effects of environmental chemicals are known to the scientific community, regulatory agencies, and the public, little is known about the mechanistic basis by which these chemicals can induce long-term or transgenerational effects. To address this question, epigenetic mechanisms have emerged as the potential link between genetic and environmental factors of health and disease.

OBJECTIVES

We present an overview of epigenetic regulation and a summary of reported evidence of environmental toxicants as epigenetic disruptors. We also discuss the advantages and challenges of using epigenetic biomarkers as an indicator of toxicant exposure, using measures that can be taken to improve risk assessment, and our perspectives on the future role of epigenetics in toxicology.

DISCUSSION

Until recently, efforts to apply epigenomic data in toxicology and risk assessment were restricted by an incomplete understanding of epigenomic variability across tissue types and populations. This is poised to change with the development of new tools and concerted efforts by researchers across disciplines that have led to a better understanding of epigenetic mechanisms and comprehensive maps of epigenomic variation. With the foundations now in place, we foresee that unprecedented advancements will take place in the field in the coming years. https://doi.org/10.1289/EHP6104.

Bisphenols and Thyroid Hormone

In recent decades, attention has been directed toward the effects of bisphenol A (BPA) on human health. BPA has estrogenic activity and is regarded as a representative endocrine disruptor. In addition, mounting evidence indicates that BPA can disrupt thyroid hormone and its action. This review examined human epidemiological studies to investigate the association between BPA exposure and thyroid hormone levels, and analyzed in vivo and in vitro experiments to identify the causal relationship and its mechanism of action. BPA is involved in thyroid hormone action not only as a thyroid hormone receptor antagonist, but also through several other mechanisms. Since the use of bisphenols other than BPA has recently increased, we also reviewed the effects of other bisphenols on thyroid hormone action.

Embryonic stem cell- and transcriptomics-based in vitro analyses reveal that bisphenols A, F and S have similar and very complex potential developmental toxicities

Bisphenol A (BPA) is a very versatile industrial chemical. Many reports have associated BPA with several health effects. Some bisphenol alternatives have been introduced to replace BPA in its many applications. However, comprehensive toxicological evaluations for these replacements are still lacking. In this study, we examined the potential effects of BPA, bisphenol F (BPF) and bisphenol S (BPS), on embryonic development with an in vitro stem cell toxicology system and transcriptomics analyses. Mouse embryonic stem cells (mESCs) were differentiated via embryoid body formation, either globally towards the three primary germ layers and their lineages, or specifically into neuroectoderm/neural progenitor cells. During the differentiation, cells were treated with BPA, BPF, BPS, or DMSO control. Samples were collected at different time points, for qRT-PCR and RNA-seq analyses. BPA, BPF and BPS disrupted many processes, during mESC global and neural differentiations, in very similar manners. In fact, at each time point the three chemicals differentially regulated analogous gene categories, particularly the ones involved in cell-matrix and cell-cell adhesion, signal transduction pathways, and medical conditions such as cardiovascular diseases and cancer. Our findings demonstrate once more then BPA substitutes may not be very safe. They potentially have a very complex developmental toxicity, similarly to BPA, and seem more toxic than BPA itself. In addition, our results reveal that stem cell-based developmental toxicity assays can be very comprehensive.

Accelerated Deficits of Spatial Learning and Memory Resulting From Prenatal Inflammatory Insult Are Correlated With Abnormal Phosphorylation and Methylation of Histone 3 in CD-1 Mice

Gestational infection causes various neurological deficits in offspring, such as age-related spatial learning and memory (SLM) decline. How inflammation causes age-related SLM dysfunction remains unknown. Previous research has indicated that histone modifications, such as phosphorylation of H3S10 (H3S10p) and trimethylation of H3K9 (H3K9me3) may be involved. In our study, pregnant mice received an intraperitoneal injection of lipopolysaccharide (LPS, 50 or 25 μg/kg) or normal saline during gestational days 15-17. After normal parturition, the offspring were randomly separated into 1-, 6-, 12-, 18-, and 22-month-old groups. SLM performance was assessed using a radial six-arm water maze (RAWM). The hippocampal levels of H3S10p and H3K9me3 were detected using an immunohistochemical method. The results indicated that the offspring had significantly impaired SLM, with decreased H3S10p and increased H3K9me3 levels from 12 months onward. Maternal LPS exposure during late gestation significantly and dose-dependently exacerbated the age-related impairment of SLM, with the decrease in H3S10p and increase in H3K9me3 beginning at 12 months in the offspring. The histone modifications (H3S10p and H3K9me3) were significantly correlated with impairment of SLM. Our findings suggest that prenatal exposure to inflammation could exacerbate age-related impairments of SLM and changes in histone modifications in CD-1 mice from 12 months onward, and SLM impairment might be linked to decreased H3S10p and increased H3K9me3.

Contribution of Inhibitor of Differentiation and Estrogenic Endocrine Disruptors to Neurocognitive Disorders

The devastating growth in the worldwide frequency of neurocognitive disorders and its allied difficulties, such as decline in memory, spatial competency, and ability to focus, poses a significant psychological public health problem. Inhibitor of differentiation (ID) proteins are members of a family of helix-loop-helix (HLH) transcription factors. ID proteins have been demonstrated to be involved in neurodevelopmental and depressive diseases and, thus, may influence neurocognitive deficiencies due to environmental exposure. Previously, it has been demonstrated that environmental factors, such as estrogenic endocrine disruptors (EEDs), have played an essential role in the influence of various neurocognitive disorders such as Alzheimer’s, dementia, and Parkinson’s disease. Based on this increasing number of reports, we consider the impact of these environmental pollutants on ID proteins. Better understanding of how these ID proteins by which EED exposure can affect neurocognitive disorders in populations will prospectively deliver valuable information in the impediment and regulation of these diseases linked with environmental factor exposure.

Thyroid Function Disruptors: from nature to chemicals

The modern concept of thyroid disruptors includes man-made chemicals and bioactive compounds from food that interfere with any aspect of the hypothalamus-pituitary-thyroid axis, thyroid hormone biosynthesis and secretion, blood and transmembrane transport, metabolism and local action of thyroid hormones. This review highlights relevant disruptors that effect populations through their diet: directly from food itself (fish oil and polyunsaturated fatty acids, pepper, coffee, cinnamon and resveratrol/grapes), through vegetable cultivation (pesticides) and from containers for food storage and cooking (bisphenol A, phthalates and polybrominated diphenyl ethers). Due to the vital role of thyroid hormones during every stage of life, we review effects from the gestational period through to adulthood, including evidence from in vitro studies, rodent models, human trials and epidemiological studies.

Comparative approaches to understanding thyroid hormone regulation of neurogenesis

Thyroid hormone (TH) signalling, an evolutionary conserved pathway, is crucial for brain function and cognition throughout life, from early development to ageing. In humans, TH deficiency during pregnancy alters offspring brain development, increasing the risk of cognitive disorders. How TH regulates neurogenesis and subsequent behaviour and cognitive functions remains a major research challenge. Cellular and molecular mechanisms underlying TH signalling on proliferation, survival, determination, migration, differentiation and maturation have been studied in mammalian animal models for over a century. However, recent data show that THs also influence embryonic and adult neurogenesis throughout vertebrates (from mammals to teleosts). These latest observations raise the question of how TH availability is controlled during neurogenesis and particularly in specific neural stem cell populations. This review deals with the role of TH in regulating neurogenesis in the developing and the adult brain across different vertebrate species. Such evo-devo approaches can shed new light on (i) the evolution of the nervous system and (ii) the evolutionary control of neurogenesis by TH across animal phyla. We also discuss the role of thyroid disruptors on brain development in an evolutionary context.

Effects of BPA on global DNA methylation and global histone 3 lysine modifications in SH-SY5Y cells: An epigenetic mechanism linking the regulation of chromatin modifiying genes

Bisphenol A (BPA), an estrogenic endocrine disruptor, is widely used in the production of polycarbonate plastic and epoxy resins, resulting in high risk on human health. In present study we aimed to investigate the effects of BPA on global and gene specific DNA methylation, global histone modifications and regulation of chromatin modifiying enzymes in human neuroblastoma cells (SH-SY5Y). Cells were treated with BPA at 0.1, 1 and 10μM concentrations for 48 and 96h. IC₅₀ value of BPA was determined as 183 and 129μM in SH-SY5Y cells after 24h by MTT and NRU tests, respectively. We observed significant alterations on the 5-mC% levels (1.3 fold) and 5-hmC% levels (1.67 fold) after 10μM of BPA for 96h. Significant decrease was identified in H3K9me3 and H3K9ac after 10μM of BPA for 96h while decrease was observed in H3K4me3 at 10μM of BPA for 48h. Alterations were observed in chromatin modifiying genes including G9a, EZH2, SETD8, SETD1A, HAT1, SIRT1, DNMT1, RIZ1 and Suv39h1 after 96h of BPA exposure. Taken together, this study suggests that BPA might modulate the epigenetic regulators which would be key molecular events in the toxicity of endocrine disrupting chemicals.