Impacts of bisphenol A analogues on zebrafish post-embryonic brain

Developmental neurotoxicity of bisphenol F and bisphenol S in animal model systems: A literature review

Neurodevelopmental disorders have complex etiologies, stemming both from genetic and environmental risk factors, including gestational exposure to bisphenol A (BPA). BPA is an endocrine-disrupting chemical widely used in the synthesis of plastics and epoxy-resins. In 2012, the Food and Drug Administration issued a ban on the use of BPA in certain baby and childhood products, which contributed to the proliferation of BPA-free products. To make products without BPA, plastic and epoxy manufacturers often use chemical analogs, including bisphenol F (BPF) and bisphenol S (BPS). However, the structural and biochemical similarities BPF and BPS share with BPA suggest they may have similar molecular and cellular impacts on the developing nervous system, despite consumers generally regarding BPA-free products as safer alternatives. In this review, we synthesized all available peer-reviewed primary literature to date reporting on the neurodevelopmental impacts of BPF and/or BPS in animal models. In total, 61 papers were identified as relevant to the topic, including evaluation of BPF- and BPS-associated neurodevelopmental phenotypes such as changes in neurodevelopmental gene expression, the proliferation and differentiation of neural stem cells, synaptogenesis, central nervous system morphology, neuronal cell death, and behavior. Though less extensively studied than BPA, the collective works described here indicate that BPF and BPS can act as developmental neurotoxicants in animal models, urging further mechanistic and epidemiological analyses of these bisphenol analogs, as well as a reconsideration by regulatory agencies of policies surrounding their usage.

The biological effects of bisphenol AF in reproduction and development: What do we know so far?

Due to the established endocrine-disrupting effects of Bisphenol A (BPA), alternative bisphenols entered the market. Bisphenol AF (BPAF) is now commonly used in the industrial manufacturing of polycarbonate plastics and epoxy resins. However, BPAF's effects on reproduction and development have not been thoroughly reviewed. We investigated the relationship between BPAF exposure and reproduction and early development. We performed a literature review of studies on BPAF and reproductive physiology. Using keywords, we searched PubMed, Medline, Cochrane Library Database, Embase, and ClinicalTrials.gov for English language literature available until December 2024; we additionally identified and included studies from bibliographies. We included 125 articles, spanning in vitro and in vivo model organism and human studies. BPAF is a selective estrogen receptor modulator and an androgen receptor antagonist and is more potent than BPA. It is detected in urine, blood products, saliva, amniotic fluid, and breast milk. In vitro and in vivo studies demonstrate a spectrum of BPAF-induced endocrine and reproductive changes in both sexes. There is strong evidence of alterations in the hypothalamic-pituitary-gonadal axis and of altered steroidogenesis pathways. Multiple studies using zebrafish, Xenopus, chickens, and rodents, show BPAF's effects on embryogenesis, morphology, and sexual differentiation. Decreased serum testosterone and impaired spermatogenesis and oocyte viability have been demonstrated. The current literature shows clear disruptive effects of BPAF on reproductive health and embryonic development. Though further investigation is warranted, there is ample converging evidence to support limiting the use of BPAF and other similar bisphenols.

Deep learning dives: Predicting anxiety in zebrafish through novel tank assay analysis

Behavior is fundamental to neuroscience research, providing insights into the mechanisms underlying thoughts, actions and responses. Various model organisms, including mice, flies, and fish, are employed to understand these mechanisms. Zebrafish, in particular, serve as a valuable model for studying anxiety-like behavior, typically measured through the novel tank diving (NTD) assay. Traditional methods for analyzing NTD assays are either manually intensive or costly when using specialized software. To address these limitations, it is useful to develop methods for the automated analysis of zebrafish NTD assays using deep-learning models. In this study, we classified zebrafish based on their anxiety levels using DeepLabCut. Subsequently, based on a training dataset of image frames, we compared deep-learning models to identify the model best suited to classify zebrafish as anxious or non anxious and found that specific architectures, such as InceptionV3, are able to effectively perform this classification task. Our findings suggest that these deep learning models hold promise for automated behavioral analysis in zebrafish, offering an efficient and cost-effective alternative to traditional methods.

Comparative toxicological assessment of 2 bisphenols using a systems approach: evaluation of the behavioral and transcriptomic responses of Danio rerio to bisphenol A and tetrabromobisphenol A

The zebrafish (Danio rerio) is becoming a critical component of new approach methods (NAMs) in chemical risk assessment. As a whole organism in vitro NAM, the zebrafish model offers significant advantages over individual cell-line testing, including toxicokinetic and toxicodynamic competencies. A transcriptomic approach not only allows for insight into mechanism of action for both apical endpoints and unobservable adverse outcomes, but also changes in gene expression induced by lower, environmentally relevant concentrations. In this study, we used a larval zebrafish model to assess the behavioral and transcriptomic alterations caused by subphenotypic concentrations of 2 chemicals with the same structural backbone, the endocrine-disrupting chemicals bisphenol A and tetrabromobisphenol A. Following assessment of behavioral toxicity, we used a transcriptomic approach to identify molecular pathways associated with previously described phenotypes. We also determined the transcriptomic point of departure for each chemical by modeling gene expression changes as continuous systems which allows for the identification of a single concentration at which toxic effects can be predicted. This can then be investigated with confirmatory cell-based testing in an integrated approach to testing and assessment to determine risk to human health and the environment with greater confidence. This paper demonstrates the impact of using a multi-faceted approach for evaluating the physiological and neurotoxic effects of exposure to structurally related chemicals. By comparing phenotypic effects with transcriptomic outcomes, we were able to differentiate, characterize, and rank the toxicities of related bisphenols, which demonstrates methodological advantages unique to the larval zebrafish NAM.

Transcriptomic analysis reveals the effects of maternal exposure to bisphenol AF on hypothalamic development in male neonatal mice

Fragmented data suggest that bisphenol AF (BPAF), a chemical widely used in a variety of products, might have potential impacts on the hypothalamus. Here, we employed male neonatal mice following maternal exposure to explore the effects of low-dose BPAF on hypothalamic development by RNA-sequencing. We found that maternal exposure to approximately 50 µg/(kg·day) BPAF from postanal day (PND) 0 to PND 15 altered the hypothalamic transcriptome, primarily involving the pathways and genes associated with extracellular matrix (ECM) and intercellular adhesion, neuroendocrine regulation, and neurological processes. Further RNA analysis confirmed the changes in the expression levels of concerned genes. Importantly, we further revealed that low-dose BPAF posed a stimulatory impact on pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus and induced the browning of inguinal white adipose tissue. All findings indicate that developmental exposure to low-dose BPAF could interfere with hypothalamic development and thereby lead to alterations in the metabolism. Interestingly, 5000 µg/(kg·day) BPAF caused slighter, non-significant or even inverse alterations than the low dose of 50 µg/(kg·day), displaying a dose-independent effect. Further observations suggest that the the dose-independent effects of BPAF might be associated with oxidative stress and inflammatory responses caused by the high dose. Overall, our study highlights a risk of low-dose BPAF to human neuroendocrine regulation and metabolism.

Regrettable Substitutes and the Brain: What Animal Models and Human Studies Tell Us about the Neurodevelopmental Effects of Bisphenol, Per- and Polyfluoroalkyl Substances, and Phthalate Replacements

In recent decades, emerging evidence has identified endocrine and neurologic health concerns related to exposure to endocrine-disrupting chemicals (EDCs), including bisphenol A (BPA), certain per- and polyfluoroalkyl compounds (PFASs), and phthalates. This has resulted in consumer pressure to remove these chemicals from the market, especially in food-contact materials and personal care products, driving their replacement with structurally or functionally similar substitutes. However, these "new-generation" chemicals may be just as or more harmful than their predecessors and some have not received adequate testing. This review discusses the research on early-life exposures to new-generation bisphenols, PFASs, and phthalates and their links to neurodevelopmental and behavioral alterations in zebrafish, rodents, and humans. As a whole, the evidence suggests that BPA alternatives, especially BPAF, and newer PFASs, such as GenX, can have significant effects on neurodevelopment. The need for further research, especially regarding phthalate replacements and bio-based alternatives, is briefly discussed.

Toxic Effects of Bisphenol AF Exposure on the Reproduction and Liver of Female Marine Medaka (Oryzias melastigma)

In recent years, bisphenol AF (BPAF) in aquatic environments has drawn attention to its ecological risks. This study aims to investigate the toxic effects of BPAF (188.33 μg/L) exposure for 30 days on female marine medaka (Oryzias melastigma). On the 10th and 30th day of exposure, the toxicity was evaluated using histological analysis of the liver and ovaries and the transcription levels of genes related to the antioxidant system, immune system, and hypothalamic-pituitary-gonadal (HPG) axis. Findings revealed that (1) BPAF exposure caused vacuolation, karyopyknosis and karyolysis in the liver of marine medaka, and the toxic impact augmented with duration; (2) exposure to BPAF for 10 days facilitated the growth and maturation of primary ova, and this exposure had a comparatively inhibitory effect after 30 days; (3) exposure to BPAF resulted in a biphasic regulation of the transcriptional abundance of genes involved in antioxidant and inflammatory response (e.g., il-8, cat), with an initial up-regulation followed by down-regulation. Additionally, it disrupted the transcriptional pattern of HPG axis-related genes (e.g., 3βhsd, arα). In conclusion, 188.33 μg/L BPAF can alter the expression levels of functionally related genes, impair the structural integrity of marine organisms, and pose a threat to their overall health.

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.

Associations of exposure to bisphenol A and its substitutes with neurodevelopmental outcomes among infants at 12 months of age: A cross-sectional study

BACKGROUND

Bisphenol A (BPA) exposure has been linked to adverse childhood neurodevelopment, but little is known about whether BPA substitutes exposures are also related to childhood neurodevelopment.

OBJECTIVES

To investigate the associations of exposure to BPA and its substitutes with infant neurodevelopment at 12 months.

METHODS

A total of 420 infants at 12 months were included from the Laizhou Wan (Bay) Birth Cohort in Shandong, China. Urinary concentrations of BPA and its substitutes including bisphenol S (BPS), bisphenol B (BPB), bisphenol AF (BPAF), bisphenol AP (BPAP), bisphenol P (BPP) and bisphenol Z (BPZ) were measured. Developmental quotient (DQ) scores based on the Gesell Development Schedules (GDS) were used to evaluate infant neurodevelopment. The multivariable linear regression and weighted quantile sum (WQS) regression were applied to estimate the associations of exposure to individual bisphenols and their mixtures with DQ scores, respectively. Sex-stratified analyses were also performed.

RESULTS

BPA was detected in most infants (89.05%) and had the highest median concentration (0.709 ng/mL) among all bisphenols. BPA substitutes except BPZ were ubiquitous in infants' urine samples (>70%), and BPS showed the highest median concentration (0.064 ng/mL) followed by BPAP (0.036 ng/mL), BPAF (0.028 ng/mL), BPP (0.015 ng/mL) and BPB (0.013 ng/mL). In multivariable linear regression, only BPAF exposure was inversely associated with social DQ scores among all infants (β = -0.334; 95% CI: -0.650, -0.019). After sex stratification, this inverse association was significant in girls (β = -0.605; 95% CI: -1.030, -0.180). Besides, BPA exposure was negatively related to gross motor DQ scores in boys (β = -1.061; 95% CI: -2.078, -0.045). WQS analyses confirmed these results.

CONCLUSIONS

Our study suggests that bisphenol exposure during infancy may be associated with poor infant neurodevelopment, and BPAF as a commonly used BPA substitute contributing the most to this adverse association deserves more attention.

Different types of bisphenols alter ovarian steroidogenesis: Special attention to BPA

Endocrine disruptors such as bisphenol A (BPA) and some of its analogues, including BPS, BPAF, and BPE, are used extensively in the manufacture of plastics. These synthetic chemicals could seriously alter the functionality of the female reproductive system. Although the number of studies conducted on other types of bisphenols is smaller than the number of studies on BPA, the purpose of this review study was to evaluate the effects of bisphenol compounds, particularly BPA, on hormone production and on genes involved in ovarian steroidogenesis in both in vitro (human and animal cell lines) and in vivo (animal models) studies. The current data show that exposure to bisphenol compounds has adverse effects on ovarian steroidogenesis. For example, BPA, BPS, and BPAF can alter the normal function of the hypothalamic-pituitary-gonadal (HPG) axis by targeting kisspeptin neurons involved in steroid feedback signals to gonadotropin-releasing hormone (GnRH) cells, resulting in abnormal production of LH and FSH. Exposure to BPA, BPS, BPF, and BPB had adverse effects on the release of some hormones, namely 17-β-estradiol (E2), progesterone (P4), and testosterone (T). BPA, BPE, BPS, BPF, and BPAF are also capable of negatively altering the transcription of a number of genes involved in ovarian steroidogenesis, such as the steroidogenic acute regulatory protein (StAR, involved in the transfer of cholesterol from the outer to the inner mitochondrial membrane, where the steroidogenesis process begins), cytochrome P450 family 17 subfamily A member 1 (Cyp17a1, which is involved in the biosynthesis of androgens such as testosterone), 3 beta-hydroxysteroid dehydrogenase enzyme (3β-HSD, involved in the biosynthesis of P4), and cytochrome P450 family 19 subfamily A member 1 (Cyp19a1, involved in the biosynthesis of E2). Exposure to BPA, BPB, BPF, and BPS at prenatal or prepubertal stages could decrease the number of antral follicles by activating apoptosis and autophagy pathways, resulting in decreased production of E2 and P4 by granulosa cells (GCs) and theca cells (TCs), respectively. BPA and BPS impair ovarian steroidogenesis by reducing the function of some important cell receptors such as estrogens (ERs, including ERα and ERβ), progesterone (PgR), the orphan estrogen receptor gamma (ERRγ), the androgen receptor (AR), the G protein-coupled estrogen receptor (GPER), the FSHR (follicle-stimulating hormone receptor), and the LHCGR (luteinizing hormone/choriogonadotropin receptor). In animal models, the effects of bisphenol compounds depend on the type of animals, their age, and the duration and dose of bisphenols, while in cell line studies the duration and doses of bisphenols are the matter.

Protective effects of cyanidin-3-O-glucoside on BPA-induced neurodevelopmental toxicity in zebrafish embryo model

Bisphenol A (BPA) is ubiquitous in the environment and poses a threat to wildlife and human health. It has been reported that BPA may cause the neurotoxicity during gestational and neonatal periods. Cyanidin-3-O-glucoside (C3G) is one of the most abundant anthocyanins that has shown multiple bio-functions. In this study, the protective effects and possible mechanism of C3G against BPA-induced neurodevelopment toxicity in zebrafish embryos/larvae were studied. The results showed that co-exposure of C3G (25 μg/mL) significantly attenuated BPA-induced deficit in locomotor behavior and restored the BPA-induced aberrant changes in brain morphology of zebrafish larvae. Further studies showed that the defects of central nervous development and the downregulated neurogenesis relative genes induced by BPA were significantly counteracted by co-exposure with 5 μg/mL of C3G. In addition, C3G (25 μg/mL) mitigated the decline of glutathione (GSH) content and enzymatic activities of superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT), attenuated oxidative stress and cell apoptosis induced by BPA in zebrafish. The enhancements of the expression of genes involved in the Nrf2-ARE pathway (Nrf2, HO-1, NQO1, GCLC, and GCLM) were also observed by co-exposure of C3G. The results indicate that C3G exerts protective effects on BPA-induced neurodevelopmental toxicity through improving transcription of neurogenesis related genes, enhancing antioxidative defense system and reducing cell apoptosis by regulation of apoptotic genes in zebrafish larvae. The results suggest that anthocyanins may play important role against the exogenous toxicity for vertebrates.

Oxidative Stress and Apoptosis in Bisphenol AF-Induced Neurotoxicity in Zebrafish Embryos

Bisphenol AF (BPAF) is a structural counterpart of bisphenol A that is utilized in the food and beverage industry. The present study investigated the potential mechanisms in BPAF-induced neurotoxicity in zebrafish embryos. The BPAF concentrations (0.03, 0.1, 0.3, and 1.0 µM) had no obvious effect on hatching, mortality, and body length of zebrafish larvae, while curved tail and pericardial edema were observed in the 1.0 μM group at 72 and 96 h postfertilization (hpf). Locomotor activity of the larvae (at 120 hpf) significantly decreased from dark to light but increased from light to dark transitions in BPAF groups (0.1, 0.3, and 1.0 μM). Acridine orange showed that BPAF significantly increased green fluorescence protein intensity (22.6%) in the 1.0 μM group. Consistently, the induced apoptosis significantly up-regulated caspase 3 at 0.3 μM (1.95-fold) and 1.0 μM (2.26-fold) and bax at 0.3 μM (1.60-fold) and 1.0 μM (1.78-fold), whereas bcl-2 expression was significantly decreased at 0.3 μM (0.72-fold) and 1.0 μM (0.53-fold). In addition, increased reactive oxygen species concentrations at 0.3 μM (27%) and 1.0 μM (61.4%) resulted in suppressed superoxide dismutase and catalase activities. Moreover, quantitative polymerase chain reaction results showed that BPAF (0.3 and 1.0 μM) significantly altered normal dopaminergic signaling where dat was up-regulated, while drd2a and th1 were down-regulated, in a concentration-dependent manner. Aberrations in dopamine-related genes were congruous with the dysregulations in neurodevelopment genes (sox11b, pax6a, syn2a, and rob2). Our findings suggest that BPAF-evoked oxidative stress and apoptosis could translate into phenotypical behavioral and neurodevelopmental abnormalities. These highlights could provide theoretical reference for risk assessment and act as an early indicator to BPAF exposure. Environ Toxicol Chem 2022;41:2273-2284. © 2022 SETAC.

Physiologically Based Toxicokinetic Modeling of Bisphenols in Zebrafish (Danio rerio) Accounting for Variations in Metabolic Rates, Brain Distribution, and Liver Accumulation

Bisphenol A (BPA) is an industrial chemical, which has raised human health and environmental concerns due to its endocrine-disrupting properties. BPA analogues are less well-studied despite their wide use in consumer products. These analogues have been detected in water and aquatic organisms around the world, with some analogues showing toxic effects in various species including fish. Here, we present novel organ-specific time-course distribution data of bisphenol Z (BPZ) in female zebrafish (Danio rerio), including concentrations in the ovaries, liver, and brain, a rarely sampled organ with high toxicological relevance. Furthermore, fish-specific in vitro biotransformation rates were determined for 11 selected bisphenols. A physiologically based toxicokinetic (PBTK) model was adapted for four of these bisphenols, which was able to predict levels in the gonads, liver, and brain as well as the whole body within a 2-5-fold error with respect to experimental data, covering several important target organs of toxicity. In particular, predicted liver concentrations improved compared to currently available PBTK models. Predicted data indicate that studied bisphenols mainly distribute to the carcass and gonads and less to the brain. Our model provides a tool to increase our understanding on the distribution and kinetics of a group of emerging pollutants.

Maternal exposure to bisphenol S induces neuropeptide signaling dysfunction and oxidative stress in the brain, and abnormal social behaviors in zebrafish (Danio rerio) offspring

Recent studies show that bisphenol S (BPS) induces multiple adverse effects in exposed organisms; however, the maternal effects of BPS exposure remain poorly understood. Here, we expose adult female zebrafish to environmentally relevant concentrations of BPS (0, 1, 10, 30 μg/L) and 1 μg/L of 17-β-estradiol (E2) as a positive control for 60 days. Females were then paired with BPS-unexposed males and their offspring were raised in control water for 6 months. Maternal exposure to BPS was found to alter social behavior and anxiety response in a dose-specific manner in male offspring. Group preferences and social cohesion were significantly reduced by maternal exposure to 1 and 10 μg/L BPS, respectively. Additionally, maternal exposure to 1 and 30 μg/L BPS and E2 decreased offspring stress responses during the novel tank test. The impaired social behavior was associated with elevated arginine-vasotocin (AVT) level as well as with the altered expression of genes involved in AVT signaling pathway (AVT, avpr1aa) and enzymatic antioxidant genes (cat and Mn-sod) in the brain. Collectively, these results suggest that maternal exposure to environmentally relevant concentrations of BPS alters social behavior in zebrafish offspring, which is likely mediated by oxidative stress and disruption of neuropeptide signaling pathways in the brain.

Critical review of the toxicity mechanisms of bisphenol F in zebrafish (Danio rerio): Knowledge gaps and future directions

Replacement chemicals for bisphenol A, such as bisphenol F (BPF), are detected in aquatic environments worldwide and can potentially exert negative effects on aquatic organisms. We synthesized peer-reviewed literature reporting molecular and physiological responses in zebrafish following exposure to BPF, as BPF is closely related to BPA structure and is a dominant replacement chemical in the marketplace. Global concentrations of BPF in aquatic environments were compiled and compared to physiological and behavioral impacts reported in zebrafish (e.g., developmental abnormalities, oxidative stress, immunotoxicity, endocrine disruption, and neurotoxicity). Using computational approaches, we elucidate BPF-mediated molecular networks and reveal novel biomarkers associated with BPF exposure. Functional classes of proteins including inflammatory cytokines, ATPases, peroxidases, and aromatic l-amino decarboxylases represent novel, underexplored targets of toxicity. Most revealing of this critical review is that few studies report biological responses to BPF at levels present in aquatic environments. Recommendations for future investigations based on knowledge gaps include: (1) Mechanistic studies in the central nervous system of zebrafish to address neurotoxicity; (2) Behavioral assays in zebrafish that assess the effects of BPF on anxiolytic, social, and fear-related behaviors; (3) Studies that broaden understanding of potential endocrine disrupting effects of BPF, for example insulin signaling is predicted to be sensitive to BPF exposure; (4) Studies into metabolic disruption with a focus on glutathione and aromatic amino acids, based upon pathway analysis data; (5) Studies utilizing mixture exposures with other BPA analogs to reflect environmental conditions more accurately.

Bisphenol A Exposure Induces Sensory Processing Deficits in Larval Zebrafish during Neurodevelopment

Because of their ex utero development, relatively simple nervous system, translucency, and availability of tools to investigate neural function, larval zebrafish are an exceptional model for understanding neurodevelopmental disorders and the consequences of environmental toxins. Furthermore, early in development, zebrafish larvae easily absorb chemicals from water, a significant advantage over methods required to expose developing organisms to chemical agents in utero Bisphenol A (BPA) and BPA analogs are ubiquitous environmental toxins with known molecular consequences. All humans have measurable quantities of BPA in their bodies. Most concerning, the level of BPA exposure is correlated with neurodevelopmental difficulties in people. Given the importance of understanding the health-related effects of this common toxin, we have exploited the experimental advantages of the larval zebrafish model system to investigate the behavioral and anatomic effects of BPA exposure. We discovered that BPA exposure early in development leads to deficits in the processing of sensory information, as indicated by BPA's effects on prepulse inhibition (PPI) and short-term habituation (STH) of the C-start reflex. We observed no changes in locomotion, thigmotaxis, and repetitive behaviors (circling). Despite changes in sensory processing, we detected no regional or whole-brain volume changes. Our results show that early BPA exposure can induce sensory processing deficits, as revealed by alterations in simple behaviors that are mediated by a well-defined neural circuit.

Early developmental exposure to bisphenol A and bisphenol S disrupts socio-cognitive function, isotocin equilibrium, and excitation-inhibition balance in developing zebrafish

Dysregulation of the oxytocinergic system and excitation/inhibition (E/I) balance in synaptic transmission and neural circuits are common hallmarks of various neurodevelopmental disorders. Several experimental and epidemiological studies have shown that perinatal exposure to endocrine-disrupting chemicals bisphenol A (BPA) and bisphenol S (BPS) may contribute to a range of childhood neurodevelopmental disorders. However, the effects of BPA and BPS on social-cognitive development and the associated mechanisms remain largely unknown. In this study, we explored the impacts of early developmental exposure (2hpf-5dpf) to environmentally relevant concentrations of BPA, and its analog BPS (0.001, 0.01, and 0.1 μM), on anxiety, social behaviors, and memory performance in 21 dpf zebrafish larvae. Our results revealed that early-life exposure to low concentrations of BPA and BPS elevated anxiety-like behavior, while fish exposed to higher concentrations of these chemicals displayed social deficits and impaired object recognition memory. Additionally, we found that co-exposure with an aromatase inhibitor antagonized BPA- and BPS-induced effects on anxiety levels and social behaviors, while the co-exposure to an estrogen receptor antagonist restored recognition memory in zebrafish larvae. These results indicate that BPA and BPS may affect social-cognitive function through distinct mechanisms. On the other hand, exposure to low BPA/BPS concentrations increased both the mRNA and protein levels of isotocin (zebrafish oxytocin) in the zebrafish brain, whereas a reduction in its mRNA level was observed at higher concentrations. Further, alterations in the transcript abundance of chloride transporters, and molecular markers of gamma-aminobutyric acid (GABA) and glutamatergic systems, were observed in the zebrafish brain, suggesting possible E/I imbalance following BPA or BPS exposure. Collectively, the results of this study demonstrate that early-life exposure to low concentrations of the environmental contaminants BPA and BPS can interfere with the isotocinergic signaling pathway and disrupts the establishment of E/I balance in the developing brain, subsequently leading to the onset of a suite of behavioral deficits and neurodevelopmental disorders.

Bisphenols disrupt thyroid hormone (TH) signaling in the brain and affect TH-dependent brain development in Xenopus laevis

There is concern about adverse effects of thyroid hormone (TH) disrupting chemicals on TH-dependent brain development. Bisphenol A (BPA) and its analogues, such as bisphenol F (BPF), are known to have the potential to interfere with TH signaling, but whether they affect TH-dependent brain development is not yet well documented. Here, we conducted the T3-induced Xenopus laevis metamorphosis assay, a model for studying TH signaling disruption, to investigate the effects of BPA and BPF (10-1000 nM) on TH signaling in brains and subsequent brain development. While 48-hr treatment with 1 nM T3 dramatically upregulated TH-response gene expression in X. laevis brains at stage 52, 1000 and/or 100 nM BPA also caused significant transcriptional up-regulation of certain TH-response genes, whereas BPF had slighter effects, suggesting limited TH signaling disrupting activity of BPF in brains relative to BPA at the lack of TH. In the presence of 1 nM T3, 1000 and/or 100 nM of BPF as well as BPA antagonized T3-induced TH-response gene expression, whereas lower concentrations agonized T3 actions on certain TH-response genes, displaying an apparently biphasic effect on TH signaling. After 96 h exposure, T3 induced brain morphological remodeling coupled with cell proliferation and neuronal differentiation, whereas both BPA and BPF generally antagonized T3-induced changes in a concentration-dependent manner, with weak or no effects of bisphenol exposure alone. Overall, all results show that BPA and BPF interfered with TH signaling in Xenopus brains, especially in the presence of TH, and subsequently affected TH-dependent brain development. Given the evolutionary conservation of TH-dependent brain development among vertebrates, our findings from X. laevis warrant further studies to reveal potential influences of bisphenols on TH-dependent brain development in higher vertebrates.

An in vitro investigation of endocrine disrupting potentials of ten bisphenol analogues

The endocrine disruption potency of BPA was reported elsewhere, but the mechanisms of its analogues have not been fully resolved. In this study, endocrine disruption potentials of nine alternative bisphenol analogues, namely 2,2-bis(4-hydroxyphenyl)butane (BPB), 2,2-Bis(4-hydroxy-3-methylphenyl)propane (BPC), 4,4'-dihydroxydiphenylmethane (BPF), 4,4'-(1,3-Phenylene diisopropylidene)bisphenol (BPM), 4,4'-(1,4-phenylenediisopropylidene)bisphenol (BPP), 4,4'- sulfonyldiphenol (BPS), 4,4' cyclohexylidenebisphenol (BPZ), 4,4' (hexafluoroisopropylidene)-diphenol (BPAF) and 4,4'-(1-phenylethylidene)bisphenol (BPAP), plus 2,2-bis(4-hydroxyphenyl)propane (BPA) were investigated by H295R cell and MVLN cell bioassays. In the H295R cell assay, the endpoints included hormone production and key genes for steroidogenesis (CYP11A, CYP17, CYP19 and 3βHSD2) or metabolism sulfotransferase (SULT1A1, SULT2A1 and SULT2B1) at the molecular level. The results indicated that except for BPP or BPAF, the eight other bisphenols significantly increased the E2/T ratio. In addition, BPB, BPF and BPS significantly up-regulate CYP19 gene expression, and only BPB significantly reduced sulfotransferase gene expression. In the MVLN luciferase gene reporter assay, seven bisphenols induced luciferase activity alone, and are 104 to 108-fold less potent than E2. Their nuclear ERα binding activity is in the order of BPAF > BPZ > BPP > BPB > BPA > BPF > BPS. In summary, all nine tested bisphenols showed endocrine toxicity through different mechanisms. Some had similar potency as BPA, but some had even higher potency. Further research is necessary to evaluate the toxicity of these potential BPA substitutes.