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.

Methamphetamine exposure drives cell cycle exit and aberrant differentiation in rat hippocampal-derived neurospheres

Introduction: Methamphetamine (METH) abuse by pregnant drug addicts causes toxic effects on fetal neurodevelopment; however, the mechanism underlying such effect of METH is poorly understood. Methods: In the present study, we applied three-dimensional (3D) neurospheres derived from the embryonic rat hippocampal tissue to investigate the effect of METH on neurodevelopment. Through the combination of whole genome transcriptional analyses, the involved cell signalings were identified and investigated. Results: We found that METH treatment for 24 h significantly and concentration-dependently reduced the size of neurospheres. Analyses of genome-wide transcriptomic profiles found that those down-regulated differentially expressed genes (DEGs) upon METH exposure were remarkably enriched in the cell cycle progression. By measuring the cell cycle and the expression of cell cycle-related checkpoint proteins, we found that METH exposure significantly elevated the percentage of G0/G1 phase and decreased the levels of the proteins involved in the G1/S transition, indicating G0/G1 cell cycle arrest. Furthermore, during the early neurodevelopment stage of neurospheres, METH caused aberrant cell differentiation both in the neurons and astrocytes, and attenuated migration ability of neurospheres accompanied by increased oxidative stress and apoptosis. Conclusion: Our findings reveal that METH induces an aberrant cell cycle arrest and neuronal differentiation, impairing the coordination of migration and differentiation of neurospheres.

Genes Involved in DNA Repair and Mitophagy Protect Embryoid Bodies from the Toxic Effect of Methylmercury Chloride under Physioxia Conditions

The formation of embryoid bodies (EBs) from human pluripotent stem cells resembles the early stages of human embryo development, mimicking the organization of three germ layers. In our study, EBs were tested for their vulnerability to chronic exposure to low doses of MeHgCl (1 nM) under atmospheric (21%O₂) and physioxia (5%O₂) conditions. Significant differences were observed in the relative expression of genes associated with DNA repair and mitophagy between the tested oxygen conditions in nontreated EBs. When compared to physioxia conditions, the significant differences recorded in EBs cultured at 21% O₂ included: (1) lower expression of genes associated with DNA repair (ATM, OGG1, PARP1, POLG1) and mitophagy (PARK2); (2) higher level of mtDNA copy number; and (3) higher expression of the neuroectodermal gene (NES). Chronic exposure to a low dose of MeHgCl (1 nM) disrupted the development of EBs under both oxygen conditions. However, only EBs exposed to MeHgCl at 21% O₂ revealed downregulation of mtDNA copy number, increased oxidative DNA damage and DNA fragmentation, as well as disturbances in SOX17 (endoderm) and TBXT (mesoderm) genes expression. Our data revealed that physioxia conditions protected EBs genome integrity and their further differentiation.

Ipconazole Disrupts Mitochondrial Homeostasis and Alters GABAergic Neuronal Development in Zebrafish

Ipconazole, a demethylation inhibitor of fungal ergosterol biosynthesis, is widely used in modern agriculture for foliar and seed treatment, and is authorized for use in livestock feed. Waste from ipconazole treatment enters rivers and groundwater through disposal and rain, posing potential toxicity to humans and other organisms. Its metabolites remain stable under standard hydrolysis conditions; however, their neurodevelopmental toxicity is unknown. We investigated the potential neurodevelopmental toxicity of ipconazole pesticides in zebrafish (Danio rerio). Our behavioral monitoring demonstrated that the locomotive activity of ipconazole-exposed zebrafish larvae was reduced during early development, even when morphological abnormalities were undetected. Molecular profiling demonstrated that the mitochondrial-specific antioxidants, superoxide dismutases 1 and 2, and the genes essential for mitochondrial genome maintenance and functions were specifically reduced in ipconazole-treated (0.02 μg/mL) embryos, suggesting underlying ipconazole-driven oxidative stress. Consistently, ipconazole treatment substantially reduced hsp70 expression and increased ERK1/2 phosphorylation in a dose-dependent manner. Interrupted gad1b expression confirmed that GABAergic inhibitory neurons were dysregulated at 0.02 μg/mL ipconazole, whereas glutamatergic excitatory and dopaminergic neurons remained unaffected, resulting in an uncoordinated neural network. Additionally, ipconazole-treated (2 μg/mL) embryos exhibited caspase-independent cell death. This suggests that ipconazole has the potential to alter neurodevelopment by dysregulating mitochondrial homeostasis.

Study of lead-induced neurotoxicity in cholinergic cells differentiated from bone marrow-derived mesenchymal stem cells

The developing brain is susceptible to the neurotoxic effects of lead. Exposure to lead has main effects on the cholinergic system and causes reduction of cholinergic neuron function during brain development. Disruption of the cholinergic system by chemicals, which play important roles during brain development, causes of neurodevelopmental toxicity. Differentiation of stem cells to neural cells is recently considered a promising tool for neurodevelopmental toxicity studies. This study evaluated the toxicity of lead acetate exposure during the differentiation of bone marrow-derived mesenchyme stem cells (bone marrow stem cells, BMSCs) to cholinergic neurons. Following institutional animal care review board approval, BMSCs were obtained from adult rats. The differentiating protocol included two stages that were pre-induction with β-mercaptoethanol (BME) for 24 h and differentiation to cholinergic neurons with nerve growth factor (NGF) over 5 days. The cells were exposed to different lead acetate concentrations (0.1-100 μm) during three stages, including undifferentiated, pre-induction, and neuronal differentiation stages; cell viability was measured by MTT assay. Lead exposure (0.01-100 μg/ml) had no cytotoxic effect on BMSCs but could significantly reduce cell viability at 50 and 100 μm concentrations during pre-induction and neuronal differentiation stages. MAP2 and choline acetyltransferase (ChAT) protein expression were investigated by immunocytochemistry. Although cells treated with 100 μm lead concentration expressed MAP2 protein in the differentiation stages, they had no neuronal cell morphology. The ChAT expression was negative in cells treated with lead. The present study showed that differentiated neuronal BMSCs are sensitive to lead toxicity during differentiation, and it is suggested that these cells be used to study neurodevelopmental toxicity.

Perfluorinated Iodine Alkanes Promoted Neural Differentiation of mESCs by Targeting miRNA-34a-5p in Notch-Hes Signaling

The neurodevelopmental process is highly vulnerable to environmental stress from exposure to endocrine-disrupting chemicals. Perfluorinated iodine alkanes (PFIs) possess estrogenic activities, while their potential neurodevelopmental toxicity remains blurry. In the present study, the effects of two PFIs, including dodecafluoro-1,6-diiodohexane (PFHxDI) and tridecafluorohexyl iodide (PFHxI), were investigated in the neural differentiation of the mouse embryonic stem cells (mESCs). Without influencing the cytobiological process of the mESCs, PFIs interfered the triploblastic development by increasing ectodermal differentiation, thus promoting subsequent neurogenesis. The temporal regulation of PFIs in Notch-Hes signaling through the targeting of mmu-miRNA-34a-5p provided a substantial explanation for the underlying mechanism of PFI-promoted mESC commitment to the neural lineage. The findings herein provided new knowledge on the potential neurodevelopmental toxicities of PFIs, which would help advance the health risk assessment of these kinds of emerging chemicals.

Impact of airborne total suspended particles (TSP) and fine particulate matter (PM2.5 )-induced developmental toxicity in zebrafish (Danio rerio) embryos

Airborne total suspended particles (TSP) and particulate matter (PM_2.5 ) threaten global health and their potential impact on cardiovascular and respiratory diseases are extensively studied. Recent studies attest premature deaths, low birth weight, and congenital anomalies in the fetus of pregnant women exposed to air pollution. In this regard, only few studies have explored the effects of TSP and PM_2.5 on cardiovascular and cerebrovascular development. As both TSP and PM_2.5 differ in size and composition, this study is attempted to assess the variability in toxicity effects between TSP and PM_2.5 on the development of cardiovascular and cerebrovascular systems and the underlying mechanisms in a zebrafish model. To explore the potential toxic effects of TSP and PM_2.5 , zebrafish embryos/larvae were exposed to 25, 50, 100, 200, and 400 μg/ml of TSP and PM_2.5 from 24 to 120 hpf (hours post-fertilization). Both TSP and PM_2.5 exposure increased the rate of mortality, malformations, and oxidative stress, whereas locomotor behavior, heart rate, blood flow velocity, development of cardiovasculature and neurovasculature, and dopaminergic neurons were reduced. The expression of genes involved in endoplasmic reticulum stress (ERS), Wnt signaling, and central nervous system (CNS) development were altered in a dose- and time-dependent manner. This study provides evidence for acute exposure to TSP and PM_2.5 -induced cardiovascular and neurodevelopmental toxicity, attributed to enhanced oxidative stress and aberrant gene expression. Comparatively, the effects of PM_2.5 were more pronounced than TSP.

Maternal Benzophenone Exposure Impairs Hippocampus Development and Cognitive Function in Mouse Offspring

Benzophenones are widely supplemented in personal care products, but little is known about its neurodevelopmental toxicity. The previous epidemiological study discovered a negative correlation between maternal exposure to a benzophenone metabolite 4-hydroxybenzophenone (4HBP) and child's neurodevelopment, yet the causal relationship and detailed mechanism remain to be defined. Here, it is reported that prenatal, but not postnatal, exposure to environmentally relevant level of 4HBP impairs hippocampus development and causes cognitive dysfunction in offspring mice. Transcriptomic analyses reveal that 4HBP induces the endoplasmic reticulum stress-induced apoptotic signaling and inflammatory response in hippocampal neural stem cells. Mechanistically, 4HBP exposure activates protein kinase R-like ER kinase (PERK) signaling, which induces CHOP, inhibits IκB translation, and transactivates p65, thereby promoting inflammation and apoptosis on multiple levels. Importantly, genetic or pharmacological inhibition of PERK pathway significantly attenuates 4HBP-induced NFκB signaling and neurodevelopmental abnormalities in mice and in a human brain organoid model. The study uncovers the neurodevelopmental toxicity of BP and cautions its exposure during pregnancy.

Effects of in utero exposure to monosodium glutamate on locomotion, anxiety, depression, memory and KCC2 expression in offspring

In pregnancy, there is a significant risk for developing embryos to be adversely affected by everyday chemicals such as food additives and environmental toxins. In recent times, several studies have documented the detrimental effect of exposure to such chemicals on the behaviour and neurodevelopment of the offspring. This study evaluated the influence of the food additive, monosodium glutamate (MSG), on behaviour and development in mice. Pregnant dams were exposed to MSG 2 or 4 g/kg or distilled water from gestation day 10-20. On delivery, postnatal day 1 (PN 1), 3 pups were sacrificed and whole brain samples assayed for KCC2 expression by western blot. The remaining pups were housed until PN 43 before commencing behavioural assessment. Their weights were measured at birth and at 3 days intervals until PN 42. The impact of prenatal exposure to MSG on baseline exploratory, anxiety and depression behaviours as well as spatial and working memory was assessed. In utero exposure to 4 g/kg MSG significantly reduced exploratory drive and increased depression-like behaviours but did not exert any significant impact on anxiety-like behaviours (p < 0.01). Additionally, there was a two-fold increase in KCC2 expression in both 2 and 4 g/kg MSG-exposed offspring. CONCLUSION: This study indicates that, in utero exposure to MSG increases the expression of KCC2 and causes significant effect on locomotion and depression-like behaviours but only marginally affects memory function.

Chlorpyrifos and other pesticide exposure and suspected developmental delay in children aged under 5 years: a case-control study in Phitsanulok, Thailand

Background: Developmental delay among children under 5 years of age is a serious global public health problem and much research has been carried out to find potential causes. Pesticides - especially organophosphates - are suspected to be one of the main causes of the problem.  This study aimed to investigate the association between pesticide use by the mother during pregnancy and preschool children development using a case-control study.

Methods: Data on prenatal and postnatal pesticide exposure of 442 children with suspected developmental delay, and 413 controls with normal development were included for analysis. The children were matched for gender, age, and residency. Data on pesticide exposure were collected via interview with the mother, and data on pregnancy outcomes abstracted from hospital records.  

Results: Chlorpyrifos exposure significantly increased the risk of developmental delay with an odds ratio (OR) of 3.71 (95% CI 1.03-13.36) for ever use of the pesticide, and an OR of 5.92 (95% CI 1.01-34.68) for postnatal exposure (p <0.05). Some other pesticides also had a positive association with developmental delay but none were statistically significant (p <0.05). Those pesticides were insecticide, fungicide, herbicide, and molluscicide. Individual pesticides with a positive association were glyphosate, paraquat, butachlor, methyl parathion (pholidon), savin, methomyl, endosulfan, carbosulfan, methamidophos, monochrotofos, mancozeb, and bordeaumixture.

Conclusions: This case-control study found that chlorpyrifos and some other pesticides exposure during pregnancy were positively associated with developmental delay in children aged under 5 years. Further research should be conducted to better understand this potential effects of pesticides on child neurodevelopment, and the public - especially those who plan to have families - should be informed.

Human iPSC-Derived 2D and 3D Platforms for Rapidly Assessing Developmental, Functional, and Terminal Toxicities in Neural Cells

With increasing global health threats has come an urgent need to rapidly develop and deploy safe and effective therapies. A common practice to fast track clinical adoption of compounds for new indications is to repurpose already approved therapeutics; however, many compounds considered safe to a specific application or population may elicit undesirable side effects when the dosage, usage directives, and/or clinical context are changed. For example, progenitor and developing cells may have different susceptibilities than mature dormant cells, which may yet be different than mature active cells. Thus, in vitro test systems should reflect the cellular context of the native cell: developing, nascent, or functionally active. To that end, we have developed high-throughput, two- and three-dimensional human induced pluripotent stem cell (hiPSC)-derived neural screening platforms that reflect different neurodevelopmental stages. As a proof of concept, we implemented this in vitro human system to swiftly identify the potential neurotoxicity profiles of 29 therapeutic compounds that could be repurposed as anti-virals. Interestingly, many compounds displayed high toxicity on early-stage neural tissues but not on later stages. Compounds with the safest overall viability profiles were further evaluated for functional assessment in a high-throughput calcium flux assay. Of the 29 drugs tested, only four did not modulate or have other potentially toxic effects on the developing or mature neurospheroids across all the tested dosages. These results highlight the importance of employing human neural cultures at different stages of development to fully understand the neurotoxicity profile of potential therapeutics across normal ontogeny.

Chlorpyrifos and other pesticide exposure and suspected developmental delay in children aged under 5 years: a case-control study in Phitsanulok, Thailand

Background: Developmental delay among children under 5 years of age is a serious global public health problem and much research has been carried out to find potential causes. Pesticides - especially organophosphates - are suspected to be one of the main causes of the problem.  This study aimed to investigate the association between pesticide use by the mother during pregnancy and preschool children development using a case-control study. Methods: Data on prenatal and postnatal pesticide exposure of 442 children with suspected developmental delay, and 413 controls with normal development were included for analysis. The children were matched for gender, age, and residency. Data on pesticide exposure were collected via interview with the mother, and data on pregnancy outcomes abstracted from hospital records.   Results: Chlorpyrifos exposure significantly increased the risk of developmental delay with an odds ratio (OR) of 3.71 (95% CI 1.03-13.36) for ever use of the pesticide, and an OR of 5.92 (95% CI 1.01-34.68) for postnatal exposure (p <0.05). Some other pesticides also had a positive association with developmental delay but none were statistically significant (p <0.05). Those pesticides were insecticide, fungicide, herbicide, and molluscicide. Individual pesticides with a positive association were glyphosate, paraquat, butachlor, methyl parathion (pholidon), savin, methomyl, endosulfan, carbosulfan, methamidophos, monochrotofos, mancozeb, and bordeaumixture. Conclusions: This case-control study found that chlorpyrifos and some other pesticides exposure during pregnancy were positively associated with developmental delay in children aged under 5 years. Further research should be conducted to better understand this potential effects of pesticides on child neurodevelopment, and the public - especially those who plan to have families - should be informed.

Alteration of gene expression profile in mouse embryonic stem cells and neural differentiation deficits by ethephon

Ethephon, a member of the organophosphorus compounds, is one of the most widely used plant growth regulators for artificial ripening. Although million pounds of this chemical is being used annually, the knowledge regarding its molecular toxicity is yet not sufficient. The purpose of this study was to evaluate the potential developmental toxicity of ethephon using embryonic stem cell model. The mouse embryonic stem cells (mESCs) were exposed to various concentrations of ethephon and the viability, cell cycle alteration and changes in the gene expression profile were evaluated using high-throughput RNA sequencing. Further, the effect of ethephon on neural differentiation potential was examined. The results showed that ethephon at noncytotoxic doses induced cell cycle arrest in mESCs. Gene ontology enrichment analysis showed that terms related to cell fate and organismal development, including neuron fate commitment, embryo development and cardiac cell differentiation, were markedly enriched in ethephon-treated cells. Neural induction of mESCs in the presence of ethephon was inhibited and the expression of neural genes was decreased in differentiated cells. Results obtained from this work clearly demonstrate that ethephon affects the gene expression profile of undifferentiated mESCs and prevents neural differentiation. Therefore, more caution against the frequent application of ethephon is advised.

Certain ortho-hydroxylated brominated ethers are promiscuous kinase inhibitors that impair neuronal signaling and neurodevelopmental processes

The developing nervous system is remarkably sensitive to environmental signals, including disruptive toxins, such as polybrominated diphenyl ethers (PBDEs). PBDEs are an environmentally pervasive class of brominated flame retardants whose neurodevelopmental toxicity mechanisms remain largely unclear. Using dissociated cortical neurons from embryonic Rattus norvegicus, we found here that chronic exposure to 6-OH-BDE-47, one of the most prevalent hydroxylated PBDE metabolites, suppresses both spontaneous and evoked neuronal electrical activity. On the basis of our previous work on mitogen-activated protein kinase (MAPK)/extracellular signal-related kinase (ERK) (MEK) biology and our observation that 6-OH-BDE-47 is structurally similar to kinase inhibitors, we hypothesized that certain hydroxylated PBDEs mediate neurotoxicity, at least in part, by impairing the MEK-ERK axis of MAPK signal transduction. We tested this hypothesis on three experimental platforms: 1) in silico, where modeling ligand-protein docking suggested that 6-OH-BDE-47 is a promiscuous ATP-competitive kinase inhibitor; 2) in vitro in dissociated neurons, where 6-OH-BDE-47 and another specific hydroxylated BDE metabolite similarly impaired phosphorylation of MEK/ERK1/2 and activity-induced transcription of a neuronal immediate early gene; and 3) in vivo in Drosophila melanogaster, where developmental exposures to 6-OH-BDE-47 and a MAPK inhibitor resulted in offspring displaying similarly increased frequency of mushroom-body β-lobe midline crossing, a metric of axonal guidance. Taken together, our results support that certain ortho-hydroxylated PBDE metabolites are promiscuous kinase inhibitors and can cause disruptions of critical neurodevelopmental processes, including neuronal electrical activity, pre-synaptic functions, MEK-ERK signaling, and axonal guidance.

DNA methylation and copy number variation analyses of human embryonic stem cell-derived neuroprogenitors after low-dose decabromodiphenyl ether and/or bisphenol A exposure

The polybrominated diphenyl ether flame retardants decabromodiphenyl ether (BDE-209) and bisphenol A (BPA) are environmental contaminants that can cross the placenta and exert toxicity in the developing fetal nervous system. Copy number variants (CNVs) play a role in a number of genetic disorders and may be implicated in BDE-209/BPA teratogenicity. In this study, we found that BDE-209 and/or BPA exposure decreased neural differentiation efficiency of human embryonic stem cells (hESCs), although there was a >90% induction of neuronal progenitor cells (NPCs) from exposed hESCs. However, the mean of CNV numbers in the NPCs with BDE-209 + BPA treatment was significantly higher compared to the other groups, whereas DNA methylation was lower and DNA methyltransferase(DNMT1 and DNMT3A) expression were significantly decreased in all of the BDE-209 and/or BPA treatment groups compared with the control groups. The number of CNVs in chromosomes 3, 4, 11, 22, and X in NPCs with BDE-209 and/or BPA exposure was higher compared to the control group. In addition, CNVs in chromosomes 7, 8, 14, and 16 were stable in hESCs and hESCs-derived NPCs irrespective of BDE-209/BPA exposure, and CNVs in chromosomes 20 q11.21 and 16 p13.11 might be induced by neural differentiation. Thus, BDE-209/BPA exposure emerges as a potential source of CNVs distinct from neural differentiation by itself. BDE-209 and/or BPA exposure may cause genomic instability in cultured stem cells via reduced activity of DNA methyltransferase, suggesting a new mechanism of human embryonic neurodevelopmental toxicity caused by this class of environmental toxins.

Exposure to Alumina Nanoparticles in Female Mice During Pregnancy Induces Neurodevelopmental Toxicity in the Offspring

Alumina nanoparticles (AlNP) have been shown to accumulate in organs and penetrate biological barriers which lead to toxic effects in many organ systems. However, it is not known whether AlNP exposure to female mice during pregnancy can affect the development of the central nervous system or induce neurodevelopmental toxicity in the offspring. The present study aims to examine the effect of AlNP on neurodevelopment and associated underlying mechanism. ICR strain adult female mice were randomly divided into four groups, which were treated with normal saline (control), 10 μm particle size of alumina (bulk-Al), and 50 and 13 nm AlNP during entire pregnancy period. Aluminum contents in the hippocampus of newborns were measured and neurodevelopmental behaviors were tracked in the offspring from birth to 1 month of age. Furthermore, oxidative stress and neurotransmitter levels were measured in the cerebral cortex of the adolescents. Our results showed that aluminum contents in the hippocampus of newborns in AlNP-treated groups were significantly higher than those in bulk-Al and controls. Moreover, the offspring delivered by AlNP-treated female mice displayed stunted neurodevelopmental behaviors. Finally, the offspring of AlNP-treated mice demonstrated significantly increased anxiety-like behavior with impaired learning and memory performance at 1 month of age. The underlying mechanism could be related to increased oxidative stress and decreased neurotransmitter levels in the cerebral cortex. We therefore conclude that AlNP exposure of female mice during pregnancy can induce neurodevelopmental toxicity in offspring.

Metabolite profiling study on the toxicological effects of polybrominated diphenyl ether in a rat model

Polybrominated diphenyl ethers (PBDEs) are commonly used to retard the combustion of materials such as foam padding, textiles, or plastics, and numerous studies have confirmed the accumulation thereof in the environment and in fish, mammals, and humans. In this study, we used metabolomics to conduct an environmental risk assessment of the PBDE-209. We profiled the urinary metabolites of control and PBDE-treated rats (exposed to PBDE-209) using nuclear magnetic resonance (NMR) and mass spectrometry (MS). Global metabolic profiling indicated that the effects of PBDE-209 on the urinary metabolic profile were not significant. However, targeted metabolic profiling revealed progressive effects of PBDE-209 over a 7-day PBDE-209 treatment. Moreover, despite the weak PBDE-209 effects, we observed that choline, acetylcholine, 3-indoxylsulfate, creatinine, urea, and dimethyl sulfone levels were decreased, whereas that of pyruvate was significantly increased. Furthermore, we suggest that the increased pyruvate level and decreased levels of choline, acetylcholine, and uremic toxins were suggestive of endocrine disruption and neurodevelopmental toxicity caused by PBDEs. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1262-1272, 2017.

Chlorpyrifos exposure affects fgf8, sox9, and bmp4 expression required for cranial neural crest morphogenesis and chondrogenesis in Xenopus laevis embryos

Chlorpyrifos (CPF) is an organophosphate insecticide used primarily to control foliage and soil-borne insect pests on a variety of food and feed crops. In mammals, maternal exposure to CPF has been reported to induce dose-related abnormalities such as slower brain growth and cerebral cortex thinning. In lower vertebrates, for example, fish and amphibians, teratogenic activity of this compound is correlated with several anatomical alterations. Little is known about the effects of CPF on mRNA expression of genes involved in early development of the anatomical structures appearing abnormal in embryos. This study investigated the effects of exposure to different CPF concentrations (10, 15 and 20 mg/L) on Xenopus laevis embryos from stage 4/8 to stage 46. Some of the morphological changes we detected in CPF-exposed embryos included cranial neural crest cell (NCC)-derived structures. For this reason, we analyzed the expression of select genes involved in hindbrain patterning (egr2), cranial neural crest chondrogenesis, and craniofacial development (fgf8, bmp4, sox9, hoxa2 and hoxb2). We found that CPF exposure induced a reduction in transcription of all the genes involved in NCC-dependent chondrogenesis, with largest reductions in fgf8 and sox9; whereas, in hindbrain, we did not find any alterations in egr2 expression. Changes in the expression of fgf8, bmp4, and sox9, which are master regulators of several developmental pathways, have important implications. If these changes are confirmed to belong to a general pattern of alterations in vertebrates prenatally exposed to OP, they might be useful to assess damage during vertebrate embryo development. Environ. Mol. Mutagen. 57:589-604, 2016. © 2016 Wiley Periodicals, Inc.

Gene Expression Regulation and Pathway Analysis After Valproic Acid and Carbamazepine Exposure in a Human Embryonic Stem Cell-Based Neurodevelopmental Toxicity Assay

Differentiating pluripotent stem cells in vitro have proven useful for the study of developmental toxicity. Here, we studied the effects of anticonvulsant drug exposure in a human embryonic stem cell (hESC)-based neurodevelopmental toxicity test (hESTn). During neural differentiation the cells were exposed, for either 1 or 7 days, to noncytotoxic concentration ranges of valproic acid (VPA) or carbamazepine (CBZ), antiepileptic drugs known to cause neurodevelopmental toxicity. The effects observed on gene expression and correlated processes and pathways were in line with processes associated with neural development and pharmaceutical mode of action. In general, VPA showed a higher number of genes and molecular pathways affected than CBZ. The response kinetics differed between both compounds, with CBZ showing higher response magnitudes at day 1, versus VPA at day 7. With this study, we demonstrated the potential and biological relevance of the application of this hESC-based differentiation assay in combination with transcriptomics, as a tool to study neurodevelopmental toxicity.

Decoding the language of epigenetics during neural development is key for understanding development as well as developmental neurotoxicity

Neural development is a delicate process that can be disrupted by pollution that exerts detrimental impact on neural signaling. This commentary highlights recent discoveries in the arena of research at the interface of environmental toxicology and developmental neuroscience relating to toxicity mechanisms of bisphenol A (BPA), a ubiquitous chemical used in manufacturing of plastics and epoxy resins that is known to bind to and interfere with estrogen receptors, estrogen-receptor-related receptors and other receptors for gonadal steroids. It was recently observed that BPA disrupts the perinatal chloride shift, a key neurodevelopmental mechanism that brings down neuronal chloride from ~100 mM to ~20 mM within weeks. The chloride shift happens in all central nervous systems of vertebrates around parturition. High neuronal chloride supports neuron precursors' migrations, low neuronal chloride is the prerequisite for inhibitory action of neurotransmitters GABA and glycine, and thus an absolute requisite for normal functioning of the mature CNS. One critical contributor to the neuronal chloride shift is the concomitant upregulation of expression of the chloride-extruding transporter molecule, KCC2. We highlight recent findings including our discovery that BPA disrupts the chloride shift in a sex-specific manner by recruiting epigenetics mechanisms. These could be relevant for childhood neuropsychiatric disorders as well as for liability to develop chronic neuropsychiatric diseases later in life.