Sensitive neurotoxicity assessment of bisphenol A using double immunocytochemistry of DCX and MAP2

Bisphenol-F and Bisphenol-S (BPF and BPS) Impair the Stemness of Neural Stem Cells and Neuronal Fate Decision in the Hippocampus Leading to Cognitive Dysfunctions

Neurogenesis occurs throughout life in the hippocampus of the brain, and many environmental toxicants inhibit neural stem cell (NSC) function and neuronal generation. Bisphenol-A (BPA), an endocrine disrupter used for surface coating of plastic products causes injury in the developing and adult brain; thus, many countries have banned its usage in plastic consumer products. BPA analogs/alternatives such as bisphenol-F (BPF) and bisphenol-S (BPS) may also cause neurotoxicity; however, their effects on neurogenesis are still not known. We studied the effects of BPF and BPS exposure from gestational day 6 to postnatal day 21 on neurogenesis. We found that exposure to non-cytotoxic concentrations of BPF and BPS significantly decreased the number/size of neurospheres, BrdU+ (proliferating NSC marker) and MAP-2+ (neuronal marker) cells and GFAP+ astrocytes in the hippocampus NSC culture, suggesting reduced NSC stemness and self-renewal and neuronal differentiation and increased gliogenesis. These analogs also reduced the number of BrdU/Sox-2+, BrdU/Dcx+, and BrdU/NeuN+ co-labeled cells in the hippocampus of the rat brain, suggesting decreased NSC proliferation and impaired maturation of newborn neurons. BPF and BPS treatment increases BrdU/cleaved caspase-3+ cells and Bax-2 and cleaved caspase protein levels, leading to increased apoptosis in hippocampal NSCs. Transmission electron microscopy studies suggest that BPF and BPS also caused degeneration of neuronal myelin sheath, altered mitochondrial morphology, and reduced number of synapses in the hippocampus leading to altered cognitive functions. These results suggest that BPF and BPS exposure decreased the NSC pool, inhibited neurogenesis, induced apoptosis of NSCs, caused myelin degeneration/synapse degeneration, and impaired learning and memory in rats.

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.

Glutamate oxidase sheets-Prussian blue grafted amperometric biosensor for the real time monitoring of glutamate release from primary cortical neurons

Glutamate (GLU) is a primary excitatory neurotransmitter, and its dysregulation is associated with several neurodegenerative disorders. A major challenge in GLU estimation is the existence of other biomolecules in the brain that could directly get oxidized at the electrode. Hence, highly selective electroenzymatic biosensors that enable rapid estimation of GLU are needed. Initially, a copolymer, poly(2-dimethylaminoethyl methacrylate- styrene) was synthesized through reversible addition-fragmentation chain transfer polymerization to noncovalently functionalize reduced graphene oxide (rGO), named DS-rGO. Glutamate oxidase macromolecule immobilized DS-rGO formed enzyme nanosheets, which was drop-coated over Prussian blue electrodeposited disposable electrodes to fabricate the GLU biosensor. The interconnectivity between the enzyme nanosheets and the Prussian blue endows the biosensor with enhanced conductivity and electrochemical activity. The biosensor exhibited a linearity: 3.25-250 μM; sensitivity: 3.96 μA mM-1 cm-2, and a limit of detection: 0.96 μM for GLU in the Neurobasal Medium. The biosensor was applied to an in vitro primary rat cortical model to discriminate GLU levels in Neurobasal Medium, before and after KCl mediated depolarization, which provides new insights for elucidating neuronal functioning in the brain.

Single-cell transcriptomic analysis reveals the adverse effects of cadmium on the trajectory of neuronal maturation

Cadmium (Cd) is an extensively existing environmental pollutant that has neurotoxic effects. However, the molecular mechanism of Cd on neuronal maturation is unveiled. Single-cell RNA sequencing (scRNA-seq) has been widely used to uncover cellular heterogeneity and is a powerful tool to reconstruct the developmental trajectory of neurons. In this study, neural stem cells (NSCs) from subventricular zone (SVZ) of newborn mice were treated with CdCl2 for 24 h and differentiated for 7 days to obtain neuronal lineage cells. Then scRNA-seq analysis identified five cell stages with different maturity in neuronal lineage cells. Our findings revealed that Cd altered the trajectory of maturation of neuronal lineage cells by decreasing the number of cells in different stages and hindering their maturation. Cd induced differential transcriptome expression in different cell subpopulations in a stage-specific manner. Specifically, Cd induced oxidative damage and changed the proportion of cell cycle phases in the early stage of neuronal development. Furthermore, the autocrine and paracrine signals of Wnt5a were downregulated in the low mature neurons in response to Cd. Importantly, activation of Wnt5a effectively rescued the number of neurons and promoted their maturation. Taken together, the findings of this study provide new and comprehensive insights into the adverse effect of Cd on neuronal maturation.

Exposure to bisphenol A induces neurotoxicity associated with synaptic and cytoskeletal dysfunction in neuro-2a cells

Bisphenol A (BPA) has been reported to injure the developing and adult brain. However, the underlying mechanism still remains elusive. This study used neuro-2a cells as a cellular model to investigate the neurotoxic effects of BPA. Microtubule-associated protein 2 (MAP2) and tau protein maintain microtubule normal function and promote the normal development of the nervous system. Synaptophysin (SYP) and drebrin (Dbn) proteins are involved in regulating synaptic plasticity. Cells were exposed to the minimum essential medium (MEM), 0.01% (v/v) DMSO, and 150 μM BPA for 12, 24, or 36 h. Morphological analysis revealed that the cells in the BPA-treated groups shrank and collapsed compared with those in the control groups. CCK-8 and lactate dehydrogenase assay (LDH) assays showed that the mortality of neuro-2a cells increased as the BPA treatment time was prolonged. Ultrastructural analysis further revealed that cells demonstrated nucleolar swelling, dissolution of nuclear and mitochondrial membranes, and partial mitochondrial condensation following exposure to BPA. BPA also decreased the relative protein expression levels of MAP2, tau, and Dbn. Interestingly, the relative protein expression levels of SYP increased. These results indicated that BPA inhibited the proliferation and disrupted cytoskeleton and synaptic integrity of neuro-2a cells.

Evaluation of p21 expression and related autism-like behavior in Bisphenol-A exposed offspring of Wistar albino rats

BACKGROUND

Bisphenol A (BPA), an endocrine disruptor, may be involved in the etiology of autism spectrum disorders (ASD); however, the mechanism of neuronal and astrocytic damage remains ambiguous. A possible role of altered expression of p21 in autistic-like behavior in rat offspring was examined with prenatal and postnatal BPA exposure.

METHODS

Wistar albino dams were exposed to BPA (5 mg/kg) intraperitoneally throughout pregnancy and until the third postnatal day (PND). Pups were examined on 21st PND for behavioral test. Blood samples were collected for serum lactate levels and pups were sacrificed. Right frontal cortices were dissected out and processed for H&E, immunohistochemical analysis, and gene expression.

RESULTS

Anxiety like behavior and thigmotaxis along with reduction in serum lactate concentrations were observed in pups exposed to BPA. Decline in neuronal number and decreased astrocytic population with reduced dendritic spines were revealed by H&E and immunohistochemical analysis, respectively, in right frontal cortices. Over expression of p21 was also detected in BPA-exposed offspring.

CONCLUSIONS

Over expression of p21 may be associated with autistic behavior. Further studies are recommended to explore the structural alterations in other white matter pathways in frontal cortices.

Evaluation of BPA effects on autophagy in Neuro-2a cells

Bisphenol A (BPA), which is used for the industrial production of polycarbonate plastics and epoxy resins, is found in many commercially available products. Plasticizer BPA produces chemical substances worldwide, and knowledge of its effects on humans and animals is increasing. In the present work, the morphology of cells was observed by optical microscopy and phalloidin staining to evaluate the toxic effect of BPA on Neuro-2a cells. Autophagy has an important role in the regulation of cell metabolism. To study the effect of BPA on the autophagy in Neuro-2a cells, the expression distribution of LC3 was detected by immunofluorescence, and the expression levels of p62 and Beclin1 were determined using western blot and quantitative real-time PCR (qRT-PCR), respectively. Optical microscopy and phalloidin staining revealed that the cells became rounded and small and that the dendritic spine of the cells were reduced at high BPA doses. Immunofluorescence analysis demonstrated that the expression of LC3 fluorescence intensity was weak at increasing BPA concentrations. Western blot results showed that the relative expression of protein p62 increased significantly and that the relative expression levels of the Beclin1 and the LC3 proteins significantly decreased with increasing BPA concentration. qRT-PCR results showed that the relative expression level of autophagy-related p62 mRNA increased significantly and that the relative expression level of Beclin1 mRNA decreased significantly with increasing BPA concentration. The above results indicated that BPA treatment exerted dose-dependent toxic effects on Neuro-2a cells, and BPA inhibited the autophagy level of Neuro-2a cells, thereby providing a new perspective in studying the toxic effect of BPA on Neuro-2a cells.

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.

Neurodevelopmental toxicity of pyrazinamide to larval zebrafish and the restoration after intoxication withdrawing

To investigate the neurotoxicity of pyrazinamide (PZA) to larval zebrafish, the PZA effects were assessed followed by its mechanism being explored. Same as isoniazid (INH), this compound is a first-line anti-tuberculosis drug and is suggested to be a risk that inducing nerve injury with long-term intoxication. Our findings indicated that zebrafish larvae obtained severe nerve damage secondary to constant immersion in various concentrations of PZA (i.e., 0.5, 1.0, and 1.5 mM) from 4 hpf (hours post fertilization) onwards until 120 hpf. The damage presented as dramatically decrease of locomotor capacity and dopaminergic neuron (DAN)-rich region length in addition to defect of brain blood vessels (BBVs). Moreover, PZA-administrated zebrafish showed a decreased dopamine (DA) level and downregulated expression of neurodevelopment-related genes, such as shha, mbp, neurog1, and gfap. However, secondary to 48 hours' restoration in fish medium (i.e., at 168 hpf), the neurotoxicity described above was prominently ameliorated. The results showed that PZA at the concentrations we tested was notably neurotoxic to larval zebrafish, and this nerve injury was restorable after PZA withdrawing. Therefore, this finding will probably provide a reference for clinical medication.

Di-n-butyl phthalate disrupts neuron maturation in primary rat embryo neurons and male C57BL/6 mice

Di-n-butyl phthalate (DBP) is commonly used as a plasticizer and its usage continues to increase in conjunction with plastic consumption. DBP is readily released into air, drinking water, and soil, and unfortunately, is a potent endocrine disrupter that impairs central nervous system functions. Previously DBP was found to (1) arrest the cell cycle of C17.2 neural progenitor cells (NPCs) at the G1 phase, (2) reduce numbers of newly generated neural stem cells in the mouse hippocampus, and (3) adversely affect learning and memory. Other investigators also noted DBP-mediated neurotoxic effects, but as yet, no study has addressed the adverse effects of DBP on neuronal differentiation. Data demonstrated that at 200 μM DBP induced apoptosis in rat embryo primary neurons by increasing reactive oxygen species levels and inducing mitochondrial dysfunction. However, no significant effect was detected on neurons at concentrations of ≤100 μM. In contrast, doublecortin/microtubule associated protein-2 (DCX/MAP2) immunocytochemistry showed that DBP at 100 μM delayed neuronal maturation by increasing protein levels of DCX (an immature neuronal marker), without markedly affecting cell viability. Further in vivo studies confirmed that DCX⁺ cell numbers were significantly elevated in the hippocampus of DBP-treated mice, indicating that DBP delayed neuronal maturation, which is known to be associated with impaired memory retention. Data demonstrated that DBP might disrupt neuronal maturation, which is correlated with reduced neurocognitive functions.

Comparative toxicities of BPA, BPS, BPF, and TMBPF in the nematode Caenorhabditis elegans and mammalian fibroblast cells

Bisphenol A (BPA) is a chemical compound commonly used in the production of plastics for daily lives and industry. As BPA is well known for its adverse health effects, several alternative materials have been developed. This study comprehensively analyzed the toxicity of BPA and its three substitutes including bisphenol S (BPS), bisphenol F (BPF), and tetramethyl bisphenol F (TMBPF) on aging, healthspan, and mitochondria using an in vivo Caenorhabditis elegans (C. elegans) model animal and cultured mammalian fibroblast cells. C. elegans treated with 1 mM BPA exhibited abnormalities in the four tested parameters related to development and growth, including delayed development, decreased body growth, reduced reproduction, and abnormal tissue morphology. Exposure to the same concentration of each alternative including TMBPF, which has been proposed as a relatively safe BPA alternative, detrimentally affected at least three of these events. Moreover, all bisphenols (except BPS) remarkably shortened the organismal lifespan and increased age-related changes in neurons. Exposure to BPA and BPF resulted in mitochondrial abnormalities, such as reduced oxygen consumption and mitochondrial membrane potential. In contrast, the ATP levels were noticeably higher after treatment with all bisphenols. In mammalian fibroblast cells, exposure to increasing concentrations of all bisphenols (ranging from 50 μM to 500 μM) caused a severe decrease in cell viability in a dose-dependent manner. BPA increased ATP levels and decreased ROS but did not affect mitochondrial permeability transition pores (mPTP). Notably, TMBPF was the only bisphenol that caused a significant increase in mitochondrial ROS and mPTP opening. These results suggest that the potentially harmful physiological effects of BPA alternatives should be considered.

Bisphenol-A inhibits mitochondrial biogenesis via impairment of GFER mediated mitochondrial protein import in the rat brain hippocampus

Mitochondrial biogenesis relies on different protein import machinery, as mitochondrial proteins are imported from the cytosol. The mitochondrial intermembrane space assembly (MIA) pathway consists of GFER/ALR and CHCHD4/Mia40, responsible for importing proteins and their oxidative folding inside the mitochondria. The MIA pathway plays an essential role in complex IV (COX IV) biogenesis via importing copper chaperone COX17, associated with the respiratory chain. BPA, an environmental toxicant, found in consumable plastics, causes neurotoxicity via impairment in mitochondrial dynamics, neurogenesis, and cognitive functions. We studied the levels of key regulatory proteins of mitochondrial import pathways and mitochondrial biogenesis after BPA exposure in the rat hippocampus. BPA caused a significant reduction in the levels of mitochondrial biogenesis proteins (PGC1α, and TFAM) and mitochondrial import protein (GFER). Immunohistochemical analysis showed reduced co-localization of NeuN with GFER, PGC-1α, and TFAM suggesting impaired mitochondrial biogenesis and protein import. BPA exposure resulted in damaged mitochondria with distorted cristae in neurons and caused a significant reduction in GFER localization inside IMS as depicted by immunogold electron microscopy. The reduced levels of GFER resulted in defective COX17 import. The translocation of cytochrome c into the cytosol and increased cleaved caspase-3 levels triggered apoptosis due to BPA toxicity. Overall, our study implicates GFER as a potential target for impaired mitochondrial protein machinery, biogenesis, and apoptosis against BPA neurotoxicity in the rat hippocampus.

Bisphenol A and rotenone induce S-nitrosylation of protein disulfide isomerase (PDI) and inhibit neurite outgrowth of primary cultured cells of the rat hippocampus and PC12 cells

Bisphenol A (BPA) interferes the function and development of the central nervous system (CNS), resulting in behavioral abnormalities and memory loss. S-nitrosylation of protein disulfide isomerase (PDI) is increased in brains with sporadic Alzheimer's disease and Parkinson's disease. The aim of the present study was to clarify the role of nitric oxide (NO) in BPA-induced neurotoxicity. Since rotenone induces NO-mediated neurodegeneration through S-nitrosylation of PDI, it was used as a positive control. First, rats were treated with BPA and rotenone, and S-nitrosylation of PDI was detected in rat brain microsomes. BPA and rotenone decreased RNase oxidation activity of PDI concomitant with S-nitrosylation of PDI. Next, to clarify S-nitrosylation of PDI by BPA and rotenone in rat brains, we treated the rat pheochromocytoma cell line PC12 and primary cultured neuron cells from the rat hippocampus with BPA (5 and 10 μM) and rotenone (100 or 200 nM). BPA induced S-nitrosylation of PDI, while NG-monomethyl-L-arginine (L-NMMA), a NOS inhibitor, exerted the opposite effects. Finally, to evaluate the toxicity of BPA in the CNS, we investigated its effects on neurite outgrowth of PC12 and primary cultured neuron cells. BPA inhibited neurite outgrowth of these cells, while L-NMMA reversed this inhibition. The involvement of PDI activity in neurite outgrowth was also examined, and bacitracin, a PDI inhibitor, is shown to decrease neurite outgrowth. Furthermore, the overexpression of PDI, but not a catalytically inactive PDI mutant, enhanced neurite outgrowth. These results suggested that S-nitrosylation of PDI induced by excessive NO caused BPA-induced neurotoxicity.

The Impact of Estrogen and Estrogen-Like Molecules in Neurogenesis and Neurodegeneration: Beneficial or Harmful?

Estrogens and estrogen-like molecules can modify the biology of several cell types. Estrogen receptors alpha (ERα) and beta (ERβ) belong to the so-called classical family of estrogen receptors, while the G protein-coupled estrogen receptor 1 (GPER-1) represents a non-classical estrogen receptor mainly located in the plasma membrane. As estrogen receptors are ubiquitously distributed, they can modulate cell proliferation, differentiation, and survival in several tissues and organs, including the central nervous system (CNS). Estrogens can exert neuroprotective roles by acting as anti-oxidants, promoting DNA repair, inducing the expression of growth factors, and modulating cerebral blood flow. Additionally, estrogen-dependent signaling pathways are involved in regulating the balance between proliferation and differentiation of neural stem/progenitor cells (NSPCs), thus influencing neurogenic processes. Since several estrogen-based therapies are used nowadays and estrogen-like molecules, including phytoestrogens and xenoestrogens, are omnipresent in our environment, estrogen-dependent changes in cell biology and tissue homeostasis have gained attention in human health and disease. This article provides a comprehensive literature review on the current knowledge of estrogen and estrogen-like molecules and their impact on cell survival and neurodegeneration, as well as their role in NSPCs proliferation/differentiation balance and neurogenesis.

Bisphenol-A exposure induced neurotoxicity and associated with synapse and cytoskeleton in Neuro-2a cells

Bisphenol A (BPA) is an environmental chemical that induces neurotoxic effects for human. Synaptophysin (SYP) and drebrin (Dbn) proteins are involved in regulating synaptic morphology. The stability of the cytoskeleton in nerve cells in the brain is regulated by Tau and MAP2. This study aimed to determine the toxicity of BPA to Neuro-2a cells by investigating the synaptic and cytoskeletal damage induced in these cells by 24 h of exposure to 0 (MEM), 50, 100, 150, or 200 μM BPA or DMSO. MTT and LDH assays showed that the death rates of Neuro-2a cells increased, as the BPA concentration increased. Ultrastructural assays revealed that cells underwent nucleolar swelling as well as nuclear membrane and partial mitochondrial dissolution or condensation, following BPA exposure. Morphological analysis further revealed that compared with the cells in the control group, the cells in the BPA-treated groups shrank, became rounded, and exhibited a reduced number of synapses. BPA also significantly decreased the relative protein and mRNA expression levels of Dbn, MAP2 and Tau (P < .01), but increased the relative protein and mRNA expression levels of SYP (P < .01). These results indicated that BPA suppressed the development and proliferation of Neuro-2a cells by disrupting cellular and synaptic integrity and inflicting cytoskeleton injury.

Bisphenols as a Legacy Pollutant, and Their Effects on Organ Vulnerability

Bisphenols are widely used in the synthesis of polycarbonate plastics, epoxy resins, and thermal paper, which are used in manufacturing items of daily use. Packaged foods and drinks are the main sources of exposure to bisphenols. These chemicals affect humans and animals by disrupting the estrogen, androgen, progesterone, thyroid, and aryl hydrocarbon receptor functions. Bisphenols exert numerous harmful effects because of their interaction with receptors, reactive oxygen species (ROS) formation, lipid peroxidation, mitochondrial dysfunction, and cell signal alterations. Both cohort and case-control studies have determined an association between bisphenol exposure and increased risk of cardiovascular diseases, neurological disorders, reproductive abnormalities, obesity, and diabetes. Prenatal exposure to bisphenols results in developmental disorders in animals. These chemicals also affect the immune cells and play a significant role in initiating the inflammatory response. Exposure to bisphenols exhibit age, gender, and dose-dependent effects. Even at low concentrations, bisphenols exert toxicity, and hence deserve a critical assessment of their uses. Since bisphenols have a global influence on human health, the need to discover the underlying pathways involved in all disease conditions is essential. Furthermore, it is important to promote the use of alternatives for bisphenols, thereby restricting their uses.