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Sevoflurane induces developmental neurotoxicity in mice; however, the underlying mechanisms remain unclear. Triggering receptor expressed on myeloid cells 2 (TREM2) is essential for microglia-mediated synaptic refinement during the early stages of brain development. We explored the effects of TREM2 on dendritic spine pruning during sevoflurane-induced developmental neurotoxicity in mice. Mice were anaesthetized with sevoflurane on postnatal days 6, 8, and 10. Behavioral performance was assessed using the open field test and Morris water maze test. Genetic knockdown of TREM2 and overexpression of TREM2 by stereotaxic injection were used for mechanistic experiments. Western blotting, immunofluorescence, electron microscopy, three-dimensional reconstruction, Golgi staining, and whole-cell patch-clamp recordings were performed. Sevoflurane exposures upregulated the protein expression of TREM2, increased microglia-mediated pruning of dendritic spines, and reduced synaptic multiplicity and excitability of CA1 neurons. TREM2 genetic knockdown significantly decreased dendritic spine pruning, and partially aggravated neuronal morphological abnormalities and cognitive impairments in sevoflurane-treated mice. In contrast, TREM2 overexpression enhanced microglia-mediated pruning of dendritic spines and rescued neuronal morphological abnormalities and cognitive dysfunction. TREM2 exerts a protective role against neurocognitive impairments in mice after neonatal exposures to sevoflurane by enhancing microglia-mediated pruning of dendritic spines in CA1 neurons. This provides a potential therapeutic target in the prevention of sevoflurane-induced developmental neurotoxicity.

Developmental exposures to PCBs are implicated in the etiology of neurodevelopmental disorders (NDDs). This observation is concerning given the continued presence of PCBs in the human environment and the increasing incidence of NDDs. Previous studies reported that developmental exposure to legacy commercial PCB mixtures (Aroclors) or single PCB congeners found in Aroclors caused NDD-relevant behavioral phenotypes in animal models. However, the PCB congener profile in contemporary human samples is dissimilar to that of the legacy Aroclors, raising the question of whether human-relevant PCB mixtures similarly interfere with normal brain development. To address this question, we assessed the developmental neurotoxicity of the Fox River Mixture (FRM), which was designed to mimic the congener profile identified in fish from the PCB-contaminated Fox River that constitute a primary protein source in the diet of surrounding communities. Adult female C57BL/6 J mouse dams (8-10 weeks old) were exposed to vehicle (peanut oil) or FRM at 0.1, 1.0, or 6.0 mg/kg/d in their diet throughout gestation and lactation, and neurodevelopmental outcomes were assessed in their pups. Ultrasonic vocalizations (USVs) and measures of general development were quantified at postnatal day (P) 7, while performance in the spontaneous alternation task and the 3-chambered social approach/social novelty task was assessed on P35. Triiodothyronine (T3) and thyroxine (T4) were quantified in serum collected from the dams when pups were weaned and from pups on P28 and P35. Developmental exposure to FRM did not alter pup weight or body temperature on P7, but USVs were significantly decreased in litters exposed to FRM at 0.1 or 6.0 mg/kg/d in the maternal diet. FRM also impaired male and female pups' performance in the social novelty task. Compared to sex-matched vehicles, significantly decreased social novelty was observed in male and female pups in the 0.1 and 6.0 mg/kg/d dose groups. FRM did not alter performance in the spontaneous alternation or social approach tasks. FRM increased serum T3 levels but decreased serum T4 levels in P28 male pups in the 1.0 and 6.0 mg/kg/d dose groups. In P35 female pups and dams, serum T3 levels decreased in the 6.0 mg/kg/d dose group while T4 levels were not altered. Collectively, these findings suggest that FRM interferes with the development of social communication and social novelty, but not memory, supporting the hypothesis that contemporary PCB exposures pose a risk to the developing brain. FRM had sex, age, and dose-dependent effects on serum thyroid hormone levels that overlapped but did not perfectly align with the FRM effects on behavioral outcomes. These observations suggest that changes in thyroid hormone levels are not likely the major factor underlying the behavioral deficits observed in FRM-exposed animals.

The increasing prevalence of neurodevelopmental disorders has highlighted the need for improved testing methods to determine developmental neurotoxicity (DNT) hazard for thousands of chemicals. This paper proposes the integration of organoid intelligence (OI); leveraging brain organoids to study neuroplasticity in vitro, into the DNT testing paradigm. OI brings a new approach to measure the impacts of xenobiotics on plasticity mechanisms - a critical biological process that is not adequately covered in current DNT in vitro assays. Finally, the integration of artificial intelligence (AI) techniques will further facilitate the analysis of complex brain organoid data to study these plasticity mechanisms. [ABSTRACT FROM AUTHOR]

AbstractBisphenol A (BPA), a synthetic chemical widely used in the production of polycarbonate plastic and epoxy resins, has been associated with a variety of adverse effects in humans including metabolic, immunological, reproductive, and neurodevelopmental effects, raising concern about its health impact. In the EU, it has been classified as toxic to reproduction and as an endocrine disruptor and was thus included in the candidate list of substances of very high concern (SVHC). On this basis, its use has been banned or restricted in some products. As a consequence, industries turned to bisphenol alternatives, such as bisphenol S (BPS) and bisphenol F (BPF), which are now found in various consumer products, as well as in human matrices at a global scale. However, due to their toxicity, these two bisphenols are in the process of being regulated. Other BPA alternatives, whose potential toxicity remains largely unknown due to a knowledge gap, have also started to be used in manufacturing processes. The gradual restriction of the use of BPA underscores the importance of understanding the potential risks associated with its alternatives to avoid regrettable substitutions. This review aims to summarize the current knowledge on the potential hazards related to BPA alternatives prioritized by European Regulatory Agencies based on their regulatory relevance and selected to be studied under the European Partnership for the Assessment of Risks from Chemicals (PARC): BPE, BPAP, BPP, BPZ, BPS-MAE, and TCBPA. The focus is on data related to toxicokinetic, endocrine disruption, immunotoxicity, developmental neurotoxicity, and genotoxicity/carcinogenicity, which were considered the most relevant endpoints to assess the hazard related to those substances. The goal here is to identify the data gaps in BPA alternatives toxicology and hence formulate the future directions that will be taken in the frame of the PARC project, which seeks also to enhance chemical risk assessment methodologies using new approach methodologies (NAMs). [ABSTRACT FROM AUTHOR]

Under regulations such as REACH, testing of novel and established compounds for their (neuro)toxic potential is a legal requirement in many countries. These are largely based on animal-, cost-, and time-intensive in vivo models, not in line with the 3 Rs' principle of animal experimentation. Thus, the development of alternative test methods has also received increasing attention in neurotoxicology. Such methods focus either on physiological alterations in brain development and neuronal pathways or on behavioral changes. An example of a behavioral developmental neurotoxicity (DNT) assay is the zebrafish (Danio rerio) embryo coiling assay, which quantifies effects of compounds on the development of spontaneous movement of zebrafish embryos. While the importance of embryo-to-embryo contact prior to hatching in response to environmental contaminants or natural threats has been documented for many other clutch-laying fish species, little is known about the relevance of intra-clutch contacts for zebrafish. Here, the model neurotoxin rotenone was used to assess the effect of grouped versus separate rearing of the embryos on the expression of the coiling behavior. Some group-reared embryos reacted with hyperactivity to the exposure, to an extent that could not be recorded effectively with the utilized software. Separately reared embryos showed reduced activity, compared with group-reared individuals when assessing. However, even the control group embryos of the separately reared cohort showed reduced activity, compared with group-reared controls. Rotenone could thus be confirmed to induce neurotoxic effects in zebrafish embryos, yet modifying one parameter in an otherwise well-established neurotoxicity assay such as the coiling assay may lead to changes in behavior influenced by the proximity between individual embryos. This indicates a complex dependence of the outcome of behavior assays on a multitude of environmental parameters. [ABSTRACT FROM AUTHOR]

Arsenic (As) is globally detected in drinking water and food products at levels repeatedly surpassing regulatory thresholds. Several neurological and mental health risks linked to arsenic exposure are proposed; however, the nature of these effects and their association with the chemical forms of arsenic are not fully understood. Gaining a clear understanding of the etiologies and characteristics of these effects is crucial, particularly in association with developmental exposures where the nervous system is most vulnerable. In this study, we investigated the effects of early developmental exposure (6- to 120-h postfertilization [hpf]) of larval zebrafish to environmentally relevant concentrations of arsenic species—trivalent/pentavalent, inorganic/organic forms—on developmental, behavioral, and molecular endpoints to determine their effect on stress response and their potential association with stress-related disorders. At 120 hpf, the developing larvae were assessed for a battery of endpoints including survival, developmental malformities, background activity, and behavioral responses to acute visual and acoustic stimuli. Pooled larval samples were analyzed for alterations in the transcript levels of genes associated with developmental neurotoxicity and stress-related disorders. Developmental exposures at target concentrations did not significantly alter survival, overall development, or background activity, and had minor effects on developmental morphology. Sodium arsenate and monomethylarsonic acid exaggerated the behavioral responses of larval zebrafish, whereas sodium arsenite depressed them. Sodium arsenate induced significant effects on molecular biomarkers. This study highlights the effects of developmental exposure to arsenicals on the behavioral stress response, the role chemical formulation plays in exerting toxicological effects, and the possible association with stress-related disorders. [ABSTRACT FROM AUTHOR]

Background: The brominated flame retardant 2, 2′, 4, 4′-tetrabromodiphenyl ether (PBDE-47) is well known as a developmental neurotoxicant, yet the underlying mechanisms remain elusive. Increasing evidence has demonstrated that brain glucose metabolism perturbation plays a role in neural impairments. Nevertheless, whether this disturbance is involved in PBDE-47-induced neurotoxicity remains unknown. Objectives: To explore the impacts of perinatal PBDE-47 exposure on brain glucose metabolism, and its link to thyroid hormones (THs) levels as well as neurobehavioral changes. Methods: Female Sprague-Dawley rats were orally exposed to PBDE-47 at environmentally relevant levels (0.1, 1.0, and 10.0 mg/kg bw) from pre-pregnancy through weaning of offspring. The male offspring were continued to raise to 88 days after birth for follow-up experiments. Morris water maze and Open field tests were performed to assess the neurobehavioral alterations. The brain glucose metabolism was evaluated using 18F-labeled fluorodeoxyglucose (18F-FDG) positron emission tomography. Serum THs levels were measured via enzyme-linked immunosorbent assay. Results: Perinatal exposure to PBDE-47 induced neurobehavioral impairments in adult male rats as evidenced by learning and memory impairments, hyperactivity and anxiety-like behavior. Moreover, positron emission tomography showed that the glucose metabolism in the whole and the specific brain regions were markedly declined. Interestingly, variations in brain glucose metabolism were associated with the increased serum triiodothyronine (T3) levels, and both were linked to neurobehavioral disorders. Conclusion: Exposure to environmentally related levels of PBDE-47 at critical developmental stages lowers glucose metabolism in the whole brain and in various brain regions, which is associated with behavioral and cognitive deficits in adult male rats. Moreover, the association may be influenced by the disturbance of T3 homeostasis.

The adverse outcome pathway (AOP) framework serves as a practical tool for organising scientific knowledge that can be used to infer cause–effect relationships between stressor events and toxicity outcomes in intact organisms. However, a major challenge in the broader application of the AOP concept within regulatory toxicology is the development of a robust AOPs that can withstand peer review and acceptance. This is mainly due to the considerable amount of work required to substantiate the modular units of a complete AOP, which can take years from inception to completion. The methodology used here consisted of an initial assessment of a single chemical hazard using the Integrated Approach to Testing and Assessment (IATA) framework. An evidence‐based approach was then used to gather empirical evidence combining systematic literature review methods with expert knowledge to ensure the effectiveness of the AOP development methodology. The structured framework used assured transparency, objectivity and comprehensiveness, and included expert knowledge elicitation for the evaluation of key event relationships (KERs). This stepwise approach led to the development of an AOP that begins with binding of chemicals to Voltage Gate Sodium Channels (VGSC/Nav) during mammalian development leading to adverse consequences in neurodevelopment evidenced as deficits in cognitive functions. Disruption of the formation of precise neural circuits by alterations in VGSC kinetics during the perinatal stages of brain development may also underlie neurodevelopmental disorders. Gaps in our understanding include the specific critical developmental windows and the quantitative relationship of binding to VGSC and subsequent disruption and cognitive function. Despite the limited quantitative information at all KER levels, regulatory applications of this AOP for DNT assessment have been identified. [ABSTRACT FROM AUTHOR]

Neonicotinoids are synthetic, nicotine-derived insecticides used worldwide to protect crops and domestic animals from pest insects. The reported evidence shows that they are also able to interact with mammalian nicotine receptors (nAChRs), triggering detrimental responses in cultured neurons. Exposure to high neonicotinoid levels during the fetal period induces neurotoxicity in animal models. Considering the persistent exposure to these insecticides and the key role of nAChRs in brain development, their potential neurotoxicity on mammal central nervous system (CNS) needs further investigations. We studied here the neurodevelopmental effects of different generations of neonicotinoids on CNS cells in mouse fetal brain and primary cultures and in neuronal cells and organoids obtained from human induced pluripotent stem cells (iPSC). Neonicotinoids significantly affect neuron viability, with imidacloprid (IMI) inducing relevant alterations in synaptic protein expression, neurofilament structures, and microglia activation in vitro, and in the brain of prenatally exposed mouse fetuses. IMI induces neurotoxic effects also on developing human iPSC-derived neurons and cortical organoids. Collectively, the current findings show that neonicotinoids might induce impairment during neuro/immune-development in mouse and human CNS cells and provide new insights in the characterization of risk for the exposure to this class of pesticides. [ABSTRACT FROM AUTHOR]

Copyright of Asian Journals of Ecotoxicology is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Clothianidin (CLO), a neonicotinoid that is widely used in forests and agricultural areas, was recently reported to cause toxicity in mammals. Although sensitivity to chemicals varies between sexes and developmental stages, studies that comprehensively evaluate both males and females are limited. Therefore, in this study we utilized murine models to compare the sex-specific differences in behavioral effects following CLO exposure at different developmental stages. We orally administered CLO to male and female mice as a single high-dose solution (80 mg/kg) during the postnatal period (2-week-old), adolescence (6-week-old), or maturity (10-week-old), and subsequently evaluated higher brain function. The behavioral battery test consisted of open field, light/dark transition, and contextual/cued fear conditioning tests conducted at three and seven months of age. After the behavioral test, the brains were dissected and prepared for immunohistochemical staining. We observed behavioral abnormalities in anxiety, spatial memory, and cued memory only in female mice. Moreover, the immunohistochemical analysis showed a reduction in astrocytes within the hippocampus of female mice with behavioral abnormalities. The behavioral abnormalities observed in female CLO-treated mice were consistent with the typical behavioral abnormalities associated with hippocampal astrocyte dysfunction. It is therefore possible that the CLO-induced behavioral abnormalities are at least in part related to a reduction in astrocyte numbers. The results of this study highlight the differences in behavioral effects following CLO exposure between sexes and developmental stages. [ABSTRACT FROM AUTHOR]

Organophosphorus flame retardants (OPFRs) are abundant and persistent in the environment but have limited toxicity information. Their similarity in structure to organophosphate pesticides presents great concern for developmental neurotoxicity (DNT). However, current in vivo testing is not suitable to provide DNT information on the amount of OPFRs that lack data. Over the past decade, an in vitro battery was developed to enhance DNT assessment, consisting of assays that evaluate cellular processes in neurodevelopment and function. In this study, behavioral data of small model organisms were also included. To assess if these assays provide sufficient mechanistic coverage to prioritize chemicals for further testing and/or identify hazards, an integrated approach to testing and assessment (IATA) was developed with additional information from the Integrated Chemical Environment (ICE) and the literature. Human biomonitoring and exposure data were identified and physiologically-based toxicokinetic models were applied to relate in vitro toxicity data to human exposure based on maximum plasma concentration. Eight OPFRs were evaluated, including aromatic OPFRs (triphenyl phosphate (TPHP), isopropylated phenyl phosphate (IPP), 2-ethylhexyl diphenyl phosphate (EHDP), tricresyl phosphate (TMPP), isodecyl diphenyl phosphate (IDDP), tert-butylphenyl diphenyl phosphate (BPDP)) and halogenated FRs ((Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), tris(2-chloroethyl) phosphate (TCEP)). Two representative brominated flame retardants (BFRs) (2,2′4,4′-tetrabromodiphenyl ether (BDE-47) and 3,3′,5,5′-tetrabromobisphenol A (TBBPA)) with known DNT potential were selected for toxicity benchmarking. Data from the DNT battery indicate that the aromatic OPFRs have activity at similar concentrations as the BFRs and should therefore be evaluated further. However, these assays provide limited information on the mechanism of the compounds. By integrating information from ICE and the literature, endocrine disruption was identified as a potential mechanism. This IATA case study indicates that human exposure to some OPFRs could lead to a plasma concentration similar to those exerting in vitro activities, indicating potential concern for human health. [ABSTRACT FROM AUTHOR]

Organic UV filters (OUVFs) have been commonly used in sunscreen and many consumer products. Following dermal application, these compounds can enter circulation and may cause systemic effects in humans. In the present study, we chose four OUVFs frequently detected in the environment, i.e., avobenzone (AVB), benzophenone-3 (BP-3), octocrylene (OC), and octyl methoxycinnamate (OMC), and evaluated their thyroid, neurodevelopmental, and kidney toxicities. For this purpose, zebrafish embryos (

The increasing prevalence of neurodevelopmental disorders has highlighted the need for improved testing methods to determine developmental neurotoxicity (DNT) hazard for thousands of chemicals. This paper proposes the integration of organoid intelligence (OI); leveraging brain organoids to study neuroplasticity in vitro, into the DNT testing paradigm. OI brings a new approach to measure the impacts of xenobiotics on plasticity mechanisms – a critical biological process that is not adequately covered in current DNT in vitro assays. Finally, the integration of artificial intelligence (AI) techniques will further facilitate the analysis of complex brain organoid data to study these plasticity mechanisms.

Despite the growing epidemiological evidence of an association between toxin exposure and developmental neurotoxicity (DNT), systematic testing of DNT is not mandatory in international regulations for admission of pharmaceuticals or industrial chemicals. However, to date around 200 compounds, ranging from pesticides, pharmaceuticals and industrial chemicals, have been tested for DNT in the current OECD test guidelines (TG-443 or TG-426). There are calls for the development of new approach methodologies (NAMs) for DNT, which has resulted in a DNT testing battery using in vitro human cell-based assays. These assays provide a means to elucidate the molecular mechanisms of toxicity in humans which is lacking in animal-based toxicity tests. However, cell-based assays do not represent all steps of the complex process leading to DNT. Validated models with a multi-organ network of pathways that interact at the molecular, cellular and tissue level at very specific timepoints in a life cycle are currently missing. Consequently, whole model organisms are being developed to screen for, and causally link, new molecular targets of DNT compounds and how they affect whole brain development and neurobehavioral endpoints. Given the practical and ethical restraints associated with vertebrate testing, lower animal models that qualify as 3 R (reduce, refine and replace) models, including the nematode (Caenorhabditis elegans) and the zebrafish (Danio rerio) will prove particularly valuable for unravelling toxicity pathways leading to DNT. Although not as complex as the human brain, these 3 R-models develop a complete functioning brain with numerous neurodevelopmental processes overlapping with human brain development. Importantly, the main signalling pathways relating to (neuro)development, metabolism and growth are highly conserved in these models. We propose the use of whole model organisms specifically zebrafish and C. elegans for DNT relevant endpoints. [ABSTRACT FROM AUTHOR]

Adult neurotoxicity (ANT) and developmental neurotoxicity (DNT) assessments aim to understand the adverse effects and underlying mechanisms of toxicants on the human nervous system. In recent years, there has been an increasing focus on the so-called new approach methodologies (NAMs). The Organization for Economic Co-operation and Development (OECD), together with European and American regulatory agencies, promote the use of validated alternative test systems, but to date, guidelines for regulatory DNT and ANT assessment rely primarily on classical animal testing. Alternative methods include both non-animal approaches and test systems on non-vertebrates (e.g., nematodes) or non-mammals (e.g., fish). Therefore, this review summarizes the recent advances of NAMs focusing on ANT and DNT and highlights the potential and current critical issues for the full implementation of these methods in the future. The status of the DNT in vitro battery (DNT IVB) is also reviewed as a first step of NAMs for the assessment of neurotoxicity in the regulatory context. Critical issues such as (i) the need for test batteries and method integration (from in silico and in vitro to in vivo alternatives, e.g., zebrafish, C. elegans) requiring interdisciplinarity to manage complexity, (ii) interlaboratory transferability, and (iii) the urgent need for method validation are discussed. [ABSTRACT FROM AUTHOR]

Acetamiprid is a pesticide active substance with insecticidal action whose approval was renewed by Commission Implementing Regulation (EU) 2018/113. In January 2022, the EFSA PPR Panel published a statement following a request from the European Commission to advise on human health or the environment based on new scientific evidence presented by France during the decision‐making phase. In July 2022, by means of a further mandate received from the European Commission, EFSA was requested to provide advice if new information and any other scientific evidence that has become available since the assessment conducted for the renewal in 2018 warrant re‐evaluation of (i) toxicological parameters used for the risk assessment of acetamiprid during the renewal process, including toxicological endpoints; (ii) the residue definition for acetamiprid in products of plant origin; and (iii) the safety of existing maximum residue levels (MRLs). Meanwhile, the applicant of acetamiprid in the EU submitted new toxicology studies regarding the toxicological profile of the metabolite IM‐2‐1. Furthermore, the European Commission was made aware that several recent publications in scientific literature were made available after the literature searches conducted by EFSA. As the new data could affect the advice that EFSA was expected to deliver through the 2022 mandate, EFSA was further requested to consider this information by means of a revised mandate received in September 2023. As regards re‐evaluation of point (i) in this statement, this was addressed by an EFSA Working Group integrating all the available evidence. The results of the weight of evidence indicated that there are major uncertainties in the body of evidence for the developmental neurotoxicity (DNT) properties of acetamiprid and further data are therefore needed to come to a more robust mechanistic understanding to enable appropriate hazard and risk assessment. In view of these uncertainties, the EFSA WG proposed to lower the acceptable daily intake (ADI) and acute reference dose (ARfD) from 0.025 to 0.005 mg/kg body weight (per day). A revised residue definition for risk assessment was proposed for leafy and fruit crops as sum of acetamiprid and N‐desmethyl‐acetamiprid (IM‐2‐1), expressed as acetamiprid. Regarding pulses/oilseeds, root crops and cereals, the new data received did not indicate a need to modify the existing residue definition for risk assessment, which therefore remains as parent acetamiprid. Regarding the residue definition for enforcement, the available data did not indicate a need to modify the existing definition because acetamiprid is still a sufficient marker of the residues in all crop groups. Considering the new health‐based guidance values derived in the present statement, a risk for consumer has been identified for 38 MRLs currently in place in the EU Regulation. Consequently, EFSA recommended to lower the existing MRLs for 38 commodities based on the assessment of fall‐back Good Agricultural Practices received within an ad hoc data call. Some fall‐back MRLs proposals require further risk management considerations. [ABSTRACT FROM AUTHOR]

Studies on the effects of glyphosate (GlyP) and glyphosate‐based herbicides (GBHs) on cerebellar development are extremely limited. This study examined the effects of maternal exposure to GlyP and GBH on rat cerebellar development in male offspring. From day 6 of gestation until day 21 postpartum at weaning, dams were given GlyP at 1.5% or 3.0% in diet or GBH at 1.0% in drinking water (corresponding to 0.36% GlyP). At weaning, GBH exposure was linked to increased numbers of DCX+ migrating granule cells in the cortex and TUNEL+ apoptotic cells in the internal granular layer (IGL), suggesting the disappearance of mismigrated granule cells via apoptosis. GBH also upregulated Nr4a3 and downregulated Cdk5 in the cerebellar vermis, suggesting a causal relation with the impaired granule cell development at this time. GlyP (3.0%) tended to increase in the number of DCX+ migrating granule cells in the IGL and upregulated Nr4a3 at weaning. Both compounds also upregulated genes related to granule cell migration (Astn1, Astn2, Nfia, and/or Nfix) at weaning and in adulthood, which might be an ameliorative response to delayed granule cell migration. Moreover, GBH induced Purkinje cell misalignment at weaning, which could be the result of delayed granule cell migration. In adulthood, GBH was associated with upregulation of the reelin signaling‐related genes Reln, Dab1, and Efnb1, suggesting a compensatory response to Purkinje cell misalignment. GlyP induced the same gene expression changes. These results suggest that GBH reversibly disrupts cerebellar development, primarily by targeting granule cell migration and differentiation, whereas GlyP exhibited similar toxic potential as GBH. [ABSTRACT FROM AUTHOR]

Alcohol is toxic to neurons and can trigger alcohol-related brain damage, neuronal loss, and cognitive decline. Neuronal cells may be vulnerable to alcohol toxicity and damage from oxidative stress after differentiation. To consider this further, the toxicity of alcohol to undifferentiated SH-SY5Y cells was compared with that of cells that had been acutely differentiated. Cells were exposed to alcohol over a concentration range of 0–200 mM for up to 24 h and alcohol effects on cell viability were evaluated via MTT and LDH assays. Effects on mitochondrial morphology were examined via transmission electron microscopy, and mitochondrial functionality was examined using measurements of ATP and the production of reactive oxygen species (ROS). Alcohol reduced cell viability and depleted ATP levels in a concentration- and exposure duration-dependent manner, with undifferentiated cells more vulnerable to toxicity. Alcohol exposure resulted in neurite retraction, altered mitochondrial morphology, and increased the levels of ROS in proportion to alcohol concentration; these peaked after 3 and 6 h exposures and were significantly higher in differentiated cells. Protein carbonyl content (PCC) lagged behind ROS production and peaked after 12 and 24 h, increasing in proportion to alcohol concentration, with higher levels in differentiated cells. Carbonylated proteins were characterised by their denatured molecular weights and overlapped with those from adult post-mortem brain tissue, with levels of PCC higher in alcoholic subjects than matched controls. Hence, alcohol can potentially trigger cell and tissue damage from oxidative stress and the accumulation of oxidatively damaged proteins. [ABSTRACT FROM AUTHOR]

Many epidemiological and animal exposure studies have suggested that exposure to environmental substances is a major risk factor for developmental neurotoxicity (DNT), such as in autism, and is related to the increasing relevance of neurodevelopmental disorders. Recent efforts have led to the development of various in vitro approaches that use cell lines and pluripotent stem cells to assess numerous environmental substances. In this study, we developed a method for assessing DNT using a mouse embryonic stem (mES) cell model that focuses on differentiation into neuronal cells (neural cells and astrocytes). Using this model system, we found that six insecticides inhibited the differentiation of neural precursor cells into astrocytes. Our data indicated that the effects of insecticides on glial differentiation were more sensitive than those of several DNT markers reported in previous studies. This mES cell model can make a quick assessment of DNT potential and may be a useful tool for screening substances with potential to induce DNT. [ABSTRACT FROM AUTHOR]

Evaluating the neurodevelopmental effects of thyroid-disrupting chemicals is challenging. Although some standardized developmental and reproductive toxicity studies recommend serum thyroxine (T4) measures in developing rats, extrapolating between a serum T4 reduction and neurodevelopmental outcomes is not straightforward. Previously, we showed that the blood-brain and blood-cerebrospinal fluid barriers may be affected by developmental hypothyroidism in newborn rats. Here, we hypothesized that if the brain barriers were functionally disturbed by abnormal thyroid action, then small molecules may escape from the brain tissue and into general circulation. These small molecules could then be identified in blood samples, serving as a direct readout of thyroid-mediated developmental neurotoxicity. To address these hypotheses, pregnant rats were exposed to propylthiouracil (PTU, 0 or 3 ppm) to induce thyroid hormone insufficiency, and dams were permitted to give birth. PTU significantly reduced serum T4 in postnatal offspring. Consistent with our hypothesis, we show that tight junctions of the brain barriers were abnormal in PTU-exposed pups, and the blood-brain barrier exhibited increased permeability. Next, we performed serum microRNA Sequencing (miRNA-Seq) to identify noncoding RNAs that may reflect these neurodevelopmental disturbances. Of the differentially expressed miRNAs identified, 7 were upregulated in PTU-exposed pups. Validation by qRT-PCR shows that miR-495 and miR-543-3p were similarly upregulated in males and females. Interestingly, these miRNAs have been linked to cell junction dysfunction in other models, paralleling the identified abnormalities in the rat brain. Taken together, these data show that miR-495 and miR-543-3p may be novel in vivo biomarkers of thyroid-mediated developmental neurotoxicity. [ABSTRACT FROM AUTHOR]

Abstract The adverse outcome pathway (AOP) framework serves as a practical tool for organising scientific knowledge that can be used to infer cause–effect relationships between stressor events and toxicity outcomes in intact organisms. However, a major challenge in the broader application of the AOP concept within regulatory toxicology is the development of a robust AOPs that can withstand peer review and acceptance. This is mainly due to the considerable amount of work required to substantiate the modular units of a complete AOP, which can take years from inception to completion. The methodology used here consisted of an initial assessment of a single chemical hazard using the Integrated Approach to Testing and Assessment (IATA) framework. An evidence‐based approach was then used to gather empirical evidence combining systematic literature review methods with expert knowledge to ensure the effectiveness of the AOP development methodology. The structured framework used assured transparency, objectivity and comprehensiveness, and included expert knowledge elicitation for the evaluation of key event relationships (KERs). This stepwise approach led to the development of an AOP that begins with binding of chemicals to Voltage Gate Sodium Channels (VGSC/Nav) during mammalian development leading to adverse consequences in neurodevelopment evidenced as deficits in cognitive functions. Disruption of the formation of precise neural circuits by alterations in VGSC kinetics during the perinatal stages of brain development may also underlie neurodevelopmental disorders. Gaps in our understanding include the specific critical developmental windows and the quantitative relationship of binding to VGSC and subsequent disruption and cognitive function. Despite the limited quantitative information at all KER levels, regulatory applications of this AOP for DNT assessment have been identified.

BackgroundVolatile anesthetic exposure during development leads to long-term cognitive deficits in rats which are dependent on age and sex. Female rats are protected relative to male rats for the same exposure on postnatal day 7. Here we test our hypothesis that androgens can modulate chloride cotransporter expression to alter the susceptibility to neurotoxicity from GABAergic drugs using female rats with exogenous testosterone exposure.MethodsFemale rats were injected with testosterone (100 μg/animal) or vehicle on postnatal days 1 to 6. On postnatal day 7, the animals were randomized to either isoflurane exposure or sham. Spatial memory was assessed with the Barnes maze starting on postnatal day 41. Western blots were run from testosterone treated postnatal day 7 animals to measure levels of chloride cotransporters sodium-potassium-chloride symporter (NKCC1) and chloride-potassium symporter 5 (KCC2).ResultsExogenous testosterone modulated isoflurane anesthetic neurotoxicity in female rats based on poor performance in the probe trial of the Barnes Maze. By contrast, females with vehicle and isoflurane exposure were able to differentiate the goal position. These behavioral differences corresponded to differences in the protein levels of NKCC1 and KCC2 after exogenous testosterone exposure, with NKCC1 increasing ( P

With the incidence of neurodevelopmental disorders on the rise, it is imperative to screen and evaluate developmental neurotoxicity (DNT) compounds from a large number of environmental chemicals and understand their mechanisms. In this study, DNT qualitative structure-activity relationship (QSAR) study was carried out for the first time based on DNT data of mammals and structural characterization of DNT compounds was preliminarily illustrated. Five different classification algorithms and two feature selection methods were used to construct prediction models. The best model had good predictive ability on the external test set, but a small application domain (AD). Through combining of three different models, both MCC and AD values were improved. Furthermore, electronical properties, van der Waals volume-related properties and S, Cl or P containing substructure were found to be associated with DNT through modeling descriptors analysis and structure alerts (SAs) identification. This study lays a foundation for further DNT prediction of environmental exposures in human and contributes to the understanding of DNT mechanism. Graphical Abstract [ABSTRACT FROM AUTHOR]

Etomidate (ET) is widely used as an anesthetic in clinical practice. The long-term use of ET can lead to negative effects, such as decreased consciousness and cognitive impairment. However, the developmental neurotoxicity of ET on fish remains unclear. To address this issue, zebrafish embryos were exposed to ET from 2 hpf (hours post-fertilization) to 168 hpf at 0. 010, 0. 091, 0. 501, 9. 400, 84. 31 and 664. 4 μg·L-1. The physiological development, behavior and cell apoptosis, and transcriptional expression of genes related to dopamine (DA) and γ-aminobutyric acid (GABA) pathway were detected to investigate the developmental neurotoxicity of ET. The results showed that 664.4 μg·L-1 ET decreased hatching rate at 48 hpf and 60 hpf. 0.091 μg·L-1 and 0.501 μg· L-1 ET decreased body length in larvae at 168 hpf. At 48 hpf, 0.010, 0.091, 0.501, 9.400, 84.31 and 664.4 μg·L-1 ET increased malformation. 0.501, 9.400, 84.31 and 664.4 μg·L-1 ET increased malformation at 96 hpf. Additionally, 0.501, 9.400 and 664.4 μg·L-1 ET increased malformation at 168 hpf. The 0.010 μg·L-1 ET caused cell apoptosis in the brain, while 664.4 μg·L-1 ET inhibited apoptosis. In addition, behavior analysis indicated that ET inhibited touch behavior at all concentrations. The 0.091 μg·L-1 ET enhanced swimming behavior in zebrafish larvae, while 664.4 μg·L-1 ET weakened swimming behavior. ET increased anxious behavior in a concentration-dependent manner. The qPCR data showed that ET up-regulated the transcriptions of genes related to DA and GABA pathway at low concentration, while ET down-regulated the transcriptions of these genes at high concentration. The above results indicate that ET has significant neurodevelopmental toxicity in early development of zebrafish. [ABSTRACT FROM AUTHOR]

The Health and Environmental Sciences Institute Developmental and Reproductive Toxicology (HESI‐DART) group held a hybrid in‐person and virtual workshop in Washington, DC, in 2022. The workshop was entitled, "Interpretation of DART in Regulatory Contexts and Frameworks." There were 154 participants (37 in person and 117 virtual) across 9 countries. The purpose of the workshop was to capture key consensus approaches used to assess DART risks associated with chemical product exposure when a nonclinical finding is identified. The decision‐making process for determining whether a DART endpoint is considered adverse is critical because the outcome may have downstream implications (e.g., increased animal usage, modifications to reproductive classification and pregnancy labeling, impact on enrollment in clinical trials and value chains). The workshop included a series of webinar modules to train and engage in discussions with federal and international regulators, clinicians, academic investigators, nongovernmental organizations, contract research organization scientists, and private sector scientists on the best practices and principles of interpreting DART and new approach methodologies in the context of regulatory requirements and processes. Despite the differences in regulatory frameworks between the chemical and pharmaceutical sectors, the same foundational principles for data interpretation should be applied. The discussions led to the categorization of principles, which offer guidance for the systematic interpretation of data. Step 1 entails identifying any hazard by closely analyzing the data at the study endpoint level, while Step 2 involves assessing risk using weight of evidence. These guiding principles were derived from the collective outcomes of the workshop deliberations. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms are increasing in frequency and intensity globally, and impacting recreational waters as well as waters used for drinking water provisioning. They are sources of bioactive metabolites including retinoids and the neurotoxin anatoxin-a. Here, we investigated the effects of anatoxin-a on a differentiating in vitro human neural stem cell model previously characterised with retinoic acids. Effects on protein and gene expression upon exposure for 9 or 18 days to anatoxin-a alone or in co-exposure with all- trans retinoic acid were evaluated using a panel of neural and glial differentiation biomarkers. Anatoxin-a did not cause distinct developmental neurotoxicity alone, or in co-exposure with retinoic acid. However, in line with its excitotoxicity, in co-exposure with 200 nM all- trans retinoic acid it reduced the differentiation of acetylcholinergic neuron subtypes in the culture at 1000 nM (highest tested concentration). While this could have substantial functional implications for the developing nervous system, there is no indication for developmental neurotoxicity beyond its (excito-)toxicity to acetylcholinergic neurons, which only occurred in co-exposure to all- trans retinoic acid. • ATX does not alter in vitro neurodifferentiation of pluripotent stem cells-derived Neural Stem Cells. • No developmental neurotoxicity was evident. • 1000 nM ATX suppressed differentiation of acetylcholinergic neurons in co-exposure with atRA. [ABSTRACT FROM AUTHOR]

Environmental and genetic factors influence synapse formation. Numerous animal experiments have revealed that pesticides, including herbicides, can disturb normal intracellular signals, gene expression, and individual animal behaviors. However, the mechanism underlying the adverse outcomes of pesticide exposure remains elusive. Herein, we investigated the effect of maternal exposure to the herbicide glufosinate ammonium (GLA) on offspring neuronal synapse formation in vitro. Cultured cerebral cortical neurons prepared from mouse embryos with maternal GLA exposure demonstrated impaired synapse formation induced by synaptic organizer neuroligin 1 (NLGN1)-coated beads. Conversely, the direct administration of GLA to the neuronal cultures exhibited negligible effect on the NLGN1-induced synapse formation. The comparison of the transcriptomes of cultured neurons from embryos treated with maternal GLA or vehicle and a subsequent bioinformatics analysis of differentially expressed genes (DEGs) identified "nervous system development," including "synapse," as the top-ranking process for downregulated DEGs in the GLA group. In addition, we detected lower densities of parvalbumin (Pvalb)-positive neurons at the postnatal developmental stage in the medial prefrontal cortex (mPFC) of offspring born to GLA-exposed dams. These results suggest that maternal GLA exposure induces synapse pathology, with alterations in the expression of genes that regulate synaptic development via an indirect pathway distinct from the effect of direct GLA action on neurons. [ABSTRACT FROM AUTHOR]

Exposure to metal mixtures is recognized as a real-life scenario, needing novel studies that can assess their complex effects on brain development. There is still a significant public health concern associated with chronic low levels of metal exposure. In contrast to other metals, these three metals (As, Pb, and Mn) are commonly found in various environmental and industrial contexts. In addition to additive or synergistic interactions, concurrent exposure to this metal mixture may also have neurotoxic effects that differ from those caused by exposure to single components. The NMDA receptor and several important signaling proteins are involved in learning, memory, and synaptic plasticity in the hippocampus, including CaMKII, postsynaptic density protein-95 (PSD-95), synaptic Ras GTPase activating protein (SynGAP), a negative regulator of Ras-MAPK activity, and CREB. We hypothesized that alterations in the above molecular players may contribute to metal mixture developmental neurotoxicity. Thus, the aim of this study was to investigate the effect of these metals and their mixture at low doses (As 4 mg, Pb 4 mg, and Mn 10 mg/kg bw/p.o) on NMDA receptors and their postsynaptic signaling proteins during developing periods (GD6 to PD59) of the rat brain. Rats exposed to As, Pb, and Mn individually or at the same doses in a triple-metal mixture (MM) showed impairments in learning and memory functions in comparison to the control group rats. Declined protein expressions of NR2A, PSD-95, p- CaMKII, and pCREB were observed in the metal mix-exposed rats, while the expression of SynGAP was found to be enhanced in the hippocampus as compared to the controls on PD60. Thereby, our data suggest that alterations in the NMDA receptor complex and postsynaptic signaling proteins could explain the cognitive dysfunctions caused by metal-mixture-induced developmental neurotoxicity in rats. These outcomes indicate that incessant metal mixture exposure may have detrimental consequences on brain development. [ABSTRACT FROM AUTHOR]

Introduction: Flame retardants (FRs) are common bodily and environmental pollutants, creating concern about their potential toxicity. We and others have found that the commercial mixture FireMaster® 550 (FM 550) or its individual brominated (BFR) and organophosphate ester (OPFR) components are potential developmental neurotoxicants. Using Wistar rats, we previously reported that developmental exposure to FM 550 or its component classes produced sex- and compound-specific effects on adult socioemotional behaviors. The underlying mechanisms driving the behavioral phenotypes are unknown. Methods: To further mechanistic understanding, here we conducted transcriptomics in parallel with a novel lipidomics approach using cortical tissues from newborn siblings of the rats in the published behavioral study. Inclusion of lipid composition is significant because it is rarely examined in developmental neurotoxicity studies. Pups were gestationally exposed via oral dosing to the dam to FM 550 or the BFR or OPFR components at environmentally relevant doses. Results: The neonatal cortex was highly sexually dimorphic in lipid and transcriptome composition, and males were more significantly impacted by FR exposure. Multiple adverse modes of action for the BFRs and OPFRs on neurodevelopment were identified, with the OPFRs being more disruptive than the BFRs via multiple mechanisms including dysregulation of mitochondrial function and disruption of cholinergic and glutamatergic systems. Disrupted mitochondrial function by environmental factors has been linked to a higher risk of autism spectrum disorders and neurodegenerative disorders. Impacted lipid classes included ceramides, sphingomyelins, and triacylglycerides. Robust ceramide upregulation in the OPFR females could suggest a heightened risk of brain metabolic disease. Conclusions: This study reveals multiple mechanisms by which the components of a common FR mixture are developmentally neurotoxic and that the OPFRs may be the compounds of greatest concern. [ABSTRACT FROM AUTHOR]

We previously performed comprehensive analyses of genes hypermethylated promoter regions and downregulated transcripts in the hippocampal dentate gyrus (DG) of rats upon weaning at postnatal day (PND) 21 after developmental exposure to 6-propyl-2-thiouracil (PTU), valproic acid, and glycidol (GLY), all of which are known to show irreversible effects on hippocampal neurogenesis in adulthood on PND 77. Here, we selected neurotransmitter and neurogenesis-related genes for validation analysis of methylation and expression. As a result, Nrgn by GLY and Shisa7 , Agtpbp1 , and Cyp46a1 by PTU underwent DNA hypermethylation and sustained downregulation. Immunohistochemical analysis of candidate gene products revealed that the number of neurogranin (NRGN)+ granule cells was decreased in the ventral DG by GLY on PND 21 and 77 and by PTU on PND 21. Among the samples of developmental or 28-day young adult-age exposure to known developmental neurotoxicants in humans, i.e., lead acetate, ethanol, and aluminum chloride, a decrease of NRGN+ cells by ethanol was also observed on PND 77 after developmental exposure. Double immunohistochemistry analysis revealed that NRGN was expressed in mature granule cells, and a similar immunoreactive cell distribution was found for phosphorylated calcium/calmodulin-activated protein kinase, a NRGN downstream molecule. After developmental PTU exposure, the number of activity-regulated cytoskeleton-associated protein+ granule cells was also profoundly decreased in the ventral DG in parallel with the decrease in NRGN+ cells on PND 21. These results suggest that NRGN is a potential marker for suppression of synaptic plasticity in mature granule cells in the ventral DG. • DNA hypermethylation and irreversible downregulation were confirmed for four genes. • NRGN among candidate gene products was expressed in mature granule cells. • Developmental GLY exposure irreversibly decreased NRGN+ cells in the ventral DG. • Developmental exposure to PTU or EtOH also decreased NRGN+ cells. • NRGN may be a potential marker for suppression of synaptic plasticity. [ABSTRACT FROM AUTHOR]

Abstract Acetamiprid is a pesticide active substance with insecticidal action whose approval was renewed by Commission Implementing Regulation (EU) 2018/113. In January 2022, the EFSA PPR Panel published a statement following a request from the European Commission to advise on human health or the environment based on new scientific evidence presented by France during the decision‐making phase. In July 2022, by means of a further mandate received from the European Commission, EFSA was requested to provide advice if new information and any other scientific evidence that has become available since the assessment conducted for the renewal in 2018 warrant re‐evaluation of (i) toxicological parameters used for the risk assessment of acetamiprid during the renewal process, including toxicological endpoints; (ii) the residue definition for acetamiprid in products of plant origin; and (iii) the safety of existing maximum residue levels (MRLs). Meanwhile, the applicant of acetamiprid in the EU submitted new toxicology studies regarding the toxicological profile of the metabolite IM‐2‐1. Furthermore, the European Commission was made aware that several recent publications in scientific literature were made available after the literature searches conducted by EFSA. As the new data could affect the advice that EFSA was expected to deliver through the 2022 mandate, EFSA was further requested to consider this information by means of a revised mandate received in September 2023. As regards re‐evaluation of point (i) in this statement, this was addressed by an EFSA Working Group integrating all the available evidence. The results of the weight of evidence indicated that there are major uncertainties in the body of evidence for the developmental neurotoxicity (DNT) properties of acetamiprid and further data are therefore needed to come to a more robust mechanistic understanding to enable appropriate hazard and risk assessment. In view of these uncertainties, the EFSA WG proposed to lower the acceptable daily intake (ADI) and acute reference dose (ARfD) from 0.025 to 0.005 mg/kg body weight (per day). A revised residue definition for risk assessment was proposed for leafy and fruit crops as sum of acetamiprid and N‐desmethyl‐acetamiprid (IM‐2‐1), expressed as acetamiprid. Regarding pulses/oilseeds, root crops and cereals, the new data received did not indicate a need to modify the existing residue definition for risk assessment, which therefore remains as parent acetamiprid. Regarding the residue definition for enforcement, the available data did not indicate a need to modify the existing definition because acetamiprid is still a sufficient marker of the residues in all crop groups. Considering the new health‐based guidance values derived in the present statement, a risk for consumer has been identified for 38 MRLs currently in place in the EU Regulation. Consequently, EFSA recommended to lower the existing MRLs for 38 commodities based on the assessment of fall‐back Good Agricultural Practices received within an ad hoc data call. Some fall‐back MRLs proposals require further risk management considerations.

Organic UV filters, which are often found in the environment, have been the focus of much public health concern. 2-ethylhexyl-4-methoxycinnamate (EHMC) is one of the most common organic UV filters present in the environment. However, few studies have investigated its developmental neurotoxic (DNT) effects and the underlying molecular mechanisms. In the present study, zebrafish embryos were exposed to low concentration of EHMC (0, 0.01, 0.1, 1 mg/L) in static water starting from 6 h post-fertilization (hpf). Results showed that EHMC exposure caused a reduction in somite count at 13 hpf, a diminishment in head-trunk angle at 30 hpf, a delay in hatching at 48 hpf, and a decrease in head depth and head length at both 30 and 48 hpf. Additionally, EHMC led to abnormal motor behaviors at various developmental stages including altered spontaneous movement at both 23 and 24 hpf, and decreased touch response at 30 hpf. Consistent with these morphological changes and motor behavior deficits, EHMC inhibited axonal growth of primary motor neurons at 30 and 48 hpf, and yielded subtle changes in muscle fiber length at 48 hpf, suggesting the functional relevance of structural changes. Moreover, EHMC exposure induced excessive cell apoptosis in the head and spinal cord regions, increased the production of reactive oxygen species (ROS) and malondialdehyde (MDA), and reduced the level of glutathione (GSH). Defects of lateral line system neuromasts were also observed, but no structural deformity of blood vessels was seen in developing zebrafish. Abnormal expression of axonal growth-related genes (gap43, mbp, shha, and α1-tubulin) and apoptosis-related genes (bax/bcl-2 and caspase-3) revealed potential molecular mechanisms regarding the defective motor behaviors and aberrant phenotype. In summary, our findings indicate that EHMC induced developmental neurotoxicity in zebrafish, making it essential to assess its risks and provide warnings regarding EHMC exposure.

Although their production was banned in the United States in 1977, polychlorinated biphenyls (PCBs) continue to pose significant risks to the developing nervous system. Perinatal exposure to PCBs is associated with increased risk of neuropsychiatric disorders, perhaps due to altered patterns of dendritic arborization of central neurons. Non-dioxin-like (NDL) PCB congeners enhance dendritic arborization of developing mammalian neurons via sensitization of ryanodine receptors (RYR). Structure-activity relationships (SAR) of RYR sensitization by PCBs have been demonstrated using mammalian and rainbow trout (Oncorhynchus mykiss) tissue homogenates. The purpose of this study is to determine whether this SAR translates to developmental neurotoxicity (DNT) of PCBs in vivo, a question that has yet to be tested. To address this gap, we leveraged a zebrafish model to evaluate the developmental neurotoxicity potential of PCBs 28, 66, 84, 95, 138, and 153, congeners previously shown to have broadly different potencies towards sensitizing RYR. We first confirmed that these PCB congeners exhibited differing potency in sensitizing RYR in zebrafish muscle ranging from negligible (PCB 66) to moderate (PCB 153) to high (PCB 95) RYR activity. Next, enzymatically dechorionated embryos were statically exposed to varying concentrations (0.1-10 μM) of each PCB congener from 6 h post-fertilization to 5 days post-fertilization (dpf). Embryos were observed daily using stereomicroscopy to assess mortality and gross malformations and photomotor behavior was assessed in larval zebrafish at 3, 4, and 5 dpf. The body burden of each PCB was measured by gas chromatography. The key findings are: 1) None of these PCBs caused death or overt teratology at the concentrations tested; 2) A subset of these PCB congeners altered photomotor behavior in larval zebrafish and the SAR for PCB behavioral effects mirrored the SAR for RYR sensitization; and 3) Quantification of PCB levels in larval zebrafish ruled out the possibility that congener-specific effects on behavior were due to differential uptake of PCB congeners. Collectively, the findings from this study provide in vivo evidence in support of the hypothesis that RYR sensitization contributes to the DNT of PCBs.

We previously demonstrated that polybrominated diphenyl ethers (PBDEs) inhibit the growth of axons in primary rat hippocampal neurons. Here, we test the hypothesis that PBDE effects on axonal morphogenesis are mediated by thyroid hormone and/or reactive oxygen species (ROS)-dependent mechanisms. Axonal growth and ROS were quantified in primary neuronal-glial co-cultures dissociated from neonatal rat hippocampi exposed to nM concentrations of BDE-47 or BDE-49 in the absence or presence of triiodothyronine (T3; 3-30 nM), N-acetyl-cysteine (NAC; 100 µM), or α-tocopherol (100 µM). Co-exposure to T3 or either antioxidant prevented inhibition of axonal growth in hippocampal cultures exposed to BDE-47 or BDE-49. T3 supplementation in cultures not exposed to PBDEs did not alter axonal growth. T3 did, however, prevent PBDE-induced ROS generation and alterations in mitochondrial metabolism. Collectively, our data indicate that PBDEs inhibit axonal growth via ROS-dependent mechanisms, and that T3 protects axonal growth by inhibiting PBDE-induced ROS. These observations suggest that co-exposure to endocrine disruptors that decrease TH signaling in the brain may increase vulnerability to the adverse effects of developmental PBDE exposure on axonal morphogenesis.

A recent systematic review and dose response meta-analysis, by Iamandii et al., considered the question "Does fluoride exposure affect thyroid function?" The authors concluded that, overall, exposure to high-fluoride drinking water appears to non-linearly affect thyroid function and increase TSH release in children, starting above a threshold of exposure, and to increase the risk of some thyroid diseases. The threshold of exposure for the TSH increase was 2 mg/L, or 2.5 mg/L when the studies with the best quality were considered. Although the lowest-observed-adverse-effect level (LOAEL) observed for TSH was a water fluoride level of approximately 2.5 mg/L, the changes in Total T3 and Total T4, a negative association, were present from very low levels, e.g. a water fluoride level of 0.2 mg/L and did not show a threshold effect. Fluoride in drinking water has been associated, by Hall et al., with an increased risk of hypothyroidism in pregnant women. A 0.5 mg/L increase in drinking water fluoride concentration was associated with a 1.65 (95% confidence interval [CI]: 1.04, 2.60) increased odds of primary hypothyroidism. Children born to women with primary hypothyroidism had lower FSIQ scores compared to children of euthyroid women, especially among boys (B coefficient : -8.42; 95%CI: -15.33, -1.50). The threshold, or point of departure, for fluoride in drinking water varies for different adverse effects such as the development of crippling skeletal fluorosis, dental fluorosis, an elevated TSH, a decreased Total T3 and Total T4, and impaired IQ in children. A recent paper by Grandjean et al. provides evidence that foetal toxicity can occur with a reduction in IQ when the maternal urinary fluoride is above 0.3 mg/L. A BMCL fluoride concentration in maternal urine during pregnancy of about 0.3 mg/L can be estimated to occur with a drinking water fluoride level of 0.24 mg/L, or approximately 0.3 mg/L. These findings suggest that, in order to protect the most vulnerable, a foetus in utero, public health attention should be given to elevated fluoride intakes during pregnancy, whether from drinking water, black tea, or other sources. [ABSTRACT FROM AUTHOR]

Neonicotinoids are synthetic, nicotine-derived insecticides used worldwide to protect crops and domestic animals from pest insects. The reported evidence shows that they are also able to interact with mammalian nicotine receptors (nAChRs), triggering detrimental responses in cultured neurons. Exposure to high neonicotinoid levels during the fetal period induces neurotoxicity in animal models. Considering the persistent exposure to these insecticides and the key role of nAChRs in brain development, their potential neurotoxicity on mammal central nervous system (CNS) needs further investigations. We studied here the neurodevelopmental effects of different generations of neonicotinoids on CNS cells in mouse fetal brain and primary cultures and in neuronal cells and organoids obtained from human induced pluripotent stem cells (iPSC). Neonicotinoids significantly affect neuron viability, with imidacloprid (IMI) inducing relevant alterations in synaptic protein expression, neurofilament structures, and microglia activation in vitro, and in the brain of prenatally exposed mouse fetuses. IMI induces neurotoxic effects also on developing human iPSC-derived neurons and cortical organoids. Collectively, the current findings show that neonicotinoids might induce impairment during neuro/immune-development in mouse and human CNS cells and provide new insights in the characterization of risk for the exposure to this class of pesticides.

Organophosphorus flame retardants (OPFRs) are abundant and persistent in the environment but have limited toxicity information. Their similarity in structure to organophosphate pesticides presents great concern for developmental neurotoxicity (DNT). However, current in vivo testing is not suitable to provide DNT information on the amount of OPFRs that lack data. Over the past decade, an in vitro battery was developed to enhance DNT assessment, consisting of assays that evaluate cellular processes in neurodevelopment and function. In this study, behavioral data of small model organisms were also included. To assess if these assays provide sufficient mechanistic coverage to prioritize chemicals for further testing and/or identify hazards, an integrated approach to testing and assessment (IATA) was developed with additional information from the Integrated Chemical Environment (ICE) and the literature. Human biomonitoring and exposure data were identified and physiologically-based toxicokinetic models were applied to relate in vitro toxicity data to human exposure based on maximum plasma concentration. Eight OPFRs were evaluated, including aromatic OPFRs (triphenyl phosphate (TPHP), isopropylated phenyl phosphate (IPP), 2-ethylhexyl diphenyl phosphate (EHDP), tricresyl phosphate (TMPP), isodecyl diphenyl phosphate (IDDP), tert-butylphenyl diphenyl phosphate (BPDP)) and halogenated FRs ((Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), tris(2-chloroethyl) phosphate (TCEP)). Two representative brominated flame retardants (BFRs) (2,2′4,4′-tetrabromodiphenyl ether (BDE-47) and 3,3′,5,5′-tetrabromobisphenol A (TBBPA)) with known DNT potential were selected for toxicity benchmarking. Data from the DNT battery indicate that the aromatic OPFRs have activity at similar concentrations as the BFRs and should therefore be evaluated further. However, these assays provide limited information on the mechanism of the compounds. By integrating information from ICE and the literature, endocrine disruption was identified as a potential mechanism. This IATA case study indicates that human exposure to some OPFRs could lead to a plasma concentration similar to those exerting in vitro activities, indicating potential concern for human health.

Abstract Background In the European Union (EU), the safety assessment of plant protection products relies to a large extent on toxicity studies commissioned by the companies producing them. By law, all performed studies must be included in the dossier submitted to authorities when applying for approval or renewal of the active substance. Methods For one type of toxicity, i.e. developmental neurotoxicity (DNT), we evaluated if studies submitted to the U.S. Environmental Protection Agency (EPA) had also been disclosed to EU authorities. Results We identified 35 DNT studies submitted to the U.S. EPA and with the corresponding EU dossiers available. Of these, 9 DNT studies (26%) were not disclosed by the pesticide company to EU authorities. For 7 of these studies, we have identified an actual or potential regulatory impact. Conclusions We conclude that (1) non-disclosure of DNT studies to EU authorities, in spite of clear legal requirements, seems to be a recurring phenomenon, (2) the non-disclosure may introduce a bias in the regulatory risk assessment, and (3) without full access to all performed toxicity studies, there can be no reliable safety evaluation of pesticides by EU authorities. We suggest that EU authorities should cross-check their data sets with their counterparts in other jurisdictions. In addition, applications for pesticide approval should be cross-checked against lists of studies performed at test facilities operating under Good Laboratory Practice (GLP), to ensure that all studies have been submitted to authorities. Furthermore, rules should be amended so that future studies should be commissioned by authorities rather than companies. This ensures the authorities’ knowledge of existing studies and prevents the economic interest of the company from influencing the design, performance, reporting and dissemination of studies. The rules or practices should also be revised to ensure that non-disclosure of toxicity studies carries a significant legal risk for pesticide companies.

The Comparative Thyroid Assay (CTA, USEPA) is a screening test for thyroid hormone (TH) disruption in peripheral blood of dams and offspring. Recently, we began investigating feasible improvements to the CTA by adding examination of offspring brain TH concentrations and brain histopathology. In addition, we hypothesize that the number of animals required could be reduced by 50 % while still maintaining sensitivity to characterize treatment related changes in THs. Previously, we showed that the prenatal test cohort of the modified CTA could detect 1000 ppm sodium phenobarbital (NaPB)-induced suppression of brain T3 (by 9 %) and T4 (by 33 %) with no significant changes in serum T3 and T4 (less than 8 %). In the current study we expanded the dose response in a prenatal test cohort. Pregnant SD rats (N = 10/group) were exposed to 0, 1000 or 1500 ppm NaPB in the diet from gestational days (GD) 6 to GD20. Serum THs concentrations in GD20 dams together with serum/brain THs concentrations and brain histopathology in the GD20 fetuses were examined. NaPB dose-dependently suppressed serum T3 (up to −26 %) and T4 (up to −44 %) in dams, with suppression of T3 in serum (up to −26 %) and brain (up to −18 %) and T4 in serum (up to −26 %) and brain (up to −29 %) of fetuses but without clear dose dependency. There were no remarkable findings that deviated significantly from controls in GD20 fetal brain by qualitative histopathology. Overall, the present study suggests that the prenatal test cohort of this modified CTA is able to detect the expected fetal TH disruptions by prenatal exposure to NaPB, while also reducing the number of animals used by 50 %, consistent with the results of our previous study. These findings add to the suggestion that lowering group sizes and adding endpoints may be a useful alternative to the original CTA design.

Fluoride could cause developmental neurotoxicity and significantly affect the intelligence quotient (IQ) of children. However, the systematic mechanism of neuronal damage caused by excessive fluoride administration in offspring is largely unknown. Here, we present a comprehensive integrative transcriptome and metabolome analysis to study the mechanism of developmental neurotoxicity caused by chronic fluoride exposure. Comparing the different doses of fluoride treatments in two generations revealed the exclusive signature of metabolism pathways and gene expression profiles. In particular, neuronal development and synaptic ion transport are significantly altered at the gene expression and metabolite accumulation levels for both generations, which could act as messengers and enhancers of fluoride-induced systemic neuronal injury. Choline and arachidonic acid metabolism, which highlighted in the integrative analysis, exhibited different regulatory patterns between the two generations, particularly for synaptic vesicle formation and inflammatory factor transport. It may suggest that choline and arachidonic acid metabolism play important roles in developmental neurotoxic responses for offspring mice. Our study provides comprehensive insights into the metabolomic and transcriptomic regulation of fluoride stress responses in the mechanistic explanation of fluoride-induced developmental neurotoxicity.

Studies on the comparison of developmental (neuro) toxicity of parabens are currently limited, and unharmonized concentrations between phenotypic observations and transcriptome analysis hamper the understanding of their differential molecular mechanisms. Thus, developmental toxicity testing was conducted herein using the commonly used methyl- (MtP), ethyl- (EtP), and propyl-parabens (PrP) in zebrafish embryos. With a benchmark dose of 5%, embryonic-mortality-based point-of-departure (M-POD) values of the three parabens were determined, and changes in locomotor behavior were evaluated at concentrations of 0, M-POD/50, M-POD/10, and M-POD, where transcriptome analysis was conducted to explore the underlying neurotoxicity mechanism. Higher long-chained parabens were more toxic than short-chained parabens, as determined by the M-POD values of 154.1, 72.6, and 24.2 µM for MtP, EtP, and PrP, respectively. Meanwhile, exposure to EtP resulted in hyperactivity, whereas no behavioral effect was observed with MtP and PrP. Transcriptome analysis revealed that abnormal behaviors in the EtP-exposed group were associated with distinctly enriched pathways in signaling, transport, calcium ion binding, and metal binding. In contrast, exposure to MtP and PrP mainly disrupted membranes and transmembranes, which are closely linked to abnormal embryonic development rather than neurobehavioral changes. According to the changes in the expressions of signature mRNAs, tentative transcriptome-based POD values for each paraben were determined as MtP (2.68 µM), EtP (3.85 µM), and PrP (1.4 µM). This suggests that different molecular perturbations initiated at similar concentrations determined the extent and toxicity outcome differently. Our findings provide insight into better understanding the differential developmental neurotoxicity mechanisms of parabens.

Parkinson's disease (PD) is the fastest-growing neurological disease worldwide, with increases outpacing aging and occurring most rapidly in recently industrialized areas, suggesting a role of environmental factors. Epidemiological, post-mortem, and mechanistic studies suggest that persistent organic pollutants, including the organochlorine pesticide dieldrin, increase PD risk. In mice, developmental dieldrin exposure causes male-specific exacerbation of neuronal susceptibility to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and synucleinopathy. Specifically, in the α-synuclein (α-syn) pre-formed fibril (PFF) model, exposure leads to increased deficits in striatal dopamine (DA) turnover and motor deficits on the challenging beam. Here, we hypothesized that alterations in DA handling contribute to the observed changes and assessed vesicular monoamine transporter 2 (VMAT2) function and DA release in this dieldrin/PFF 2-hit model. Female C57BL/6 mice were exposed to 0.3 mg/kg dieldrin or vehicle every 3 days by feeding, starting at 8 weeks of age and continuing throughout breeding, gestation, and lactation. Male offspring from independent litters underwent unilateral, intrastriatal injections of α-syn PFFs at 12 weeks of age, and vesicular 3H-DA uptake assays and fast-scan cyclic voltammetry were performed 4 months post-PFF injection. Dieldrin-induced an increase in DA release in striatal slices in PFF-injected animals, but no change in VMAT2 activity. These results suggest that developmental dieldrin exposure increases a compensatory response to synucleinopathy-triggered striatal DA loss. These findings are consistent with silent neurotoxicity, where developmental exposure to dieldrin primes the nigrostriatal striatal system to have an exacerbated response to synucleinopathy in the absence of observable changes in typical markers of nigrostriatal dysfunction and degeneration. [ABSTRACT FROM AUTHOR]

Published evidence over the past few decades suggests that general anesthetics could be neurotoxins especially when administered at the extremes of age. The reported pathology is not only at the morphological level when examined in very young and aged brains, given that, importantly, newly developing evidence suggests a variety of behavioral impairments. Since anesthesia is unavoidable in certain clinical settings, we should consider the development of new anesthetics. A promising and safe solution could be a new family of anesthetics referred to as neuroactive steroids. In this review, we summarize the currently available evidence regarding their anesthetic and analgesic properties. [ABSTRACT FROM AUTHOR]

Despite the widespread agricultural use of dithianon as an antifungal agent, its neurotoxic implications for humans and wildlife have not been comprehensively explored. Using zebrafish embryonic development as our model, we found that dithianon treatment induced behavioral alterations in zebrafish larvae that appeared normal. Detailed quantitative analyses showed that dithianon at ≥0.0001 µgmL−1 induced cytoplasmic and mitochondrial antioxidant responses sequentially, followed by the disruption of mitochondrial and cellular homeostasis. Additionally, dithianon at 0.01 and 0.1 µgmL−1 downregulated the expressions of glutamatergic (slc17a6b), GABAergic (gad1b), and dopaminergic (th) neuronal markers. Contrarily, dithianon upregulated the expression of the oligodendrocyte marker (olig2) at concentrations of 0.001 and 0.01 µgmL−1, concurrently suppressing the gene expression of the glucose transporter slc2a1a/glut1. Particularly, dithianon-induced increase in reactive oxygen species (ROS) production was reduced by both N-acetylcysteine (NAC) and betaine; however, only NAC prevented dithianon-induced mortality of zebrafish embryos. Moreover, NAC specifically prevented dithianon-induced alterations in glutamatergic and dopaminergic neurons while leaving GABAergic neurons unaffected, demonstrating that the major neurotransmission systems in the central nervous system differentially respond to the protective effects. Our findings contribute to a better understanding of the neurotoxic potential of dithianon and to developing preventive strategies. [ABSTRACT FROM AUTHOR]

With the vast number of chemicals in commerce, higher throughput strategies are needed to inform risk assessment. The field of toxicology is therefore moving away from traditional in vivo guideline studies towards in vitro new approach methodologies. There has been a great push for such a shift in the field of developmental neurotoxicity, where there is a particular lack of data. A battery of in vitro new approach methodologies has thus been developed to help fill this gap. Included in this battery are assays for numerous processes critical to neurodevelopment, such as proliferation, migration, and synaptogenesis. The current battery of developmental neurotoxicity new approach methodologies still lacks recapitulation of several critical neurodevelopmental processes, including development of neuronal subtypes. With their pluripotency, alongside other advantages, pluripotent stem cells (PSCs) are uniquely suited to address questions of developmental neurotoxicity, as they can recapitulate the different stages of human in vivo neurodevelopment. Among the various neuronal subtypes, development of dopaminergic neurons (DA) is perhaps the best understood and several approaches exist to differentiate PSCs into DA. Herein we review these approaches and propose utilizing PSCs for screening of the impact of environmental chemicals on development of DA. Related techniques and gaps in knowledge are also addressed. [ABSTRACT FROM AUTHOR]

Epidemiological and experimental studies indicate that maternal exposure to environmental pollutants impairs the cognitive and motor functions of offspring in humans and laboratory animals. Infant ultrasonic vocalizations (USVs), the communicative behavior of pups toward caregivers, are impaired in rodent models of neurodevelopmental disorders, suggesting a useful method to evaluate the developmental neurotoxicity of environmental pollutants. Therefore, we investigated USVs emitted by mouse pups of dams exposed to 2-chloro-3,7,8-tribromodibenzofuran (TeXDF) and 1,2,3,7,8-pentabromodibenzofuran (PeBDF), which are detected in the actual environment. The USV duration and number in the pups born to dams administered with TeXDF 40 μg/kg body weight (b.w.), but not 8 μg/kg b.w., on gestational day (GD) 12.5, were significantly lower than those in the corresponding pups on postnatal days 3–9. Conversely, there was no statistical change in the USVs emitted by the pups of dams administered with PeBDF 35 or 175 μg/kg b.w. on GD 12.5. To examine whether maternal exposure leads to behavioral impairments in adulthood, we analyzed exploratory behaviors in a novel environment using IntelliCage, a fully automated testing apparatus for group-housed mice. Neither TeXDF nor PeBDF exposure induced significant differences in offspring exploration. Considered together, our findings revealed that TeXDF induces atypical USV emission in infant mice, suggesting the importance of further studies on the risk assessment of mixed brominated/chlorinated dibenzo-p-dioxins and dibenzofurans. [ABSTRACT FROM AUTHOR]

Fluoride can cause developmental neurotoxicity; however, the precise mechanism has yet to be determined. We aimed to explore the possible role and mechanism of fluoride-induced developmental neurotoxicity, specifically the significance of the lysosomal stress response. As an in vivo model, Sprague Dawley rats were exposed to sodium fluoride (NaF) from embryo to 2 months of age. We found that NaF caused autophagic flux blockage and apoptosis in the rat hippocampus. These results were validated in human neuroblastoma (SH-SY5Y) cells in vitro. In addition, in SH-SY5Y cells, NaF hindered autophagosome-lysosome fusion, decreased lysosomal degradation, and elevated lysosomal pH, which is the most prominent hallmark of a lysosomal stress response. Interestingly, rapamycin promoted autophagosome-lysosome fusion, effectively restoring autophagic flux and reducing apoptosis. Notably, bafilomycin A1, a lysosomal lumen alkalizer, unsurprisingly exacerbated the NaF-induced increase in lysosomal pH and decreased lysosomal degradability, as well as enhanced apoptosis of SH-SY5Y cells. In conclusion, our results suggest that NaF exposure initiates excessive lysosomal stress response, resulting in elevated lysosomal pH, decreased lysosomal degradation, and blocked autophagic flux, which leads to neuronal apoptosis. Thus, the lysosomal stress response may be a promising target for the prevention and treatment of fluoride-induced developmental neurotoxicity. Highlights: 1. NaF caused autophagic flux blockage and apoptosis in vivo and in vitro 2. NaF hindered autophagosome-lysosome fusion and elevated lysosomal pH 3. NaF caused excessive lysosomal stress response and impaired lysosomal degradation [ABSTRACT FROM AUTHOR]

Various forms of pesticides have been reported to be among the environmental toxicants, which are detrimental to human health. The active ingredients of these formulations can enter the human body through air, food, or water. Epidemiological studies suggest that these compounds strongly affect the developing brain in fetal and infant stages due to their ability to breach the underdeveloped blood–brain barrier. Since neural progenitor stem cells (NPCs) in the developing brain are the most vulnerable to these compounds, the mechanisms by which NPCs experience toxicity upon exposure to these chemicals must be investigated. Here, we assessed the viability of human fetal NPCs in 2D cultures in the presence of the active ingredients of six widely used pesticides using Live/Dead® and Hoechst staining. The IC50 values ranged from 4.1–201 μM. A significant drop in cell viability with increasing toxicant concentration (p < 0.01) was noted, with the order of toxicity being malathion < 4-aminopyridine < methoprene < prallethrin < temephos < pyriproxyfen. Changes in cellular biomechanical characteristics (Young’s modulus, tether force, membrane tension, and tether radius) were quantified using atomic force microscopy, whereas cell migration was elucidated over 48 h using a customized wound-healing assay. The Young’s modulus of fetal NPCs exposed to IC50/2 doses of these compounds was reduced by 38–70% and that of those exposed to IC50 doses was reduced by 71–80% (p < 0.001 vs. controls for both; p < 0.01 for IC50 vs. IC50/2 for each compound). Similar patterns were noted for tether forces and membrane tension in fetal NPCs. NPC migration was found to be compound type- and dose-dependent. These results attest to the significant detrimental effects of these compounds on various aspects of the human fetal NPC phenotype, and the utility of cell mechanics as a marker to assess developmental neurotoxicity.