Chlorpyrifos inhibits neural induction via Mfn1-mediated mitochondrial dysfunction in human induced pluripotent stem cells

Combined use of multiparametric high-content-screening and in vitro circadian reporter assays in neurotoxicity evaluation

Accumulating evidence indicates that chronic circadian rhythm disruption is associated with the development of neurodegenerative diseases induced by exposure to neurotoxic chemicals. Herein, we examined the relationship between cellular circadian rhythm disruption and cytotoxicity in neural cells. Moreover, we evaluated the potential application of an in vitro cellular circadian rhythm assay in determining circadian rhythm disruption as a sensitive and early marker of neurotoxicant-induced adverse effects. To explore these objectives, we established an in vitro cellular circadian rhythm assay using human glioblastoma (U87 MG) cells stably transfected with a circadian reporter vector (PER2-dLuc) and determined the lowest-observed-adverse-effect levels (LOAELs) of several common neurotoxicants. Additionally, we determined the LOAEL of each compound on multiple cytotoxicity endpoints (nuclear size [NC], mitochondrial membrane potential [MMP], calcium ions, or lipid peroxidation) using a multiparametric high-content screening (HCS) assay using transfected U87 MG cells treated with the same neurotoxicants for 24 and 72 h. Based on our findings, the LOAEL for cellular circadian rhythm disruption for most chemicals was slightly higher than that for most cytotoxicity indicators detected using HCS, and the LOAEL for MMP in the first 24 h was the closest to that for cellular circadian rhythm disruption. Dietary antioxidants (methylselenocysteine and N-acetyl-l-cysteine) prevented or restored neurotoxicant-induced cellular circadian rhythm disruption. Our results suggest that cellular circadian rhythm disruption is as sensitive as cytotoxicity indicators and occurs early as much as cytotoxic events during disease development. Moreover, the in vitro cellular circadian rhythm assay warrants further evaluation as an early screening tool for neurotoxicants.

Exposure to chlorpyrifos interferes with intercellular communication in cumulus-oocyte complexes during porcine oocyte maturation

Chlorpyrifos (CPF), a widely used organophosphorus pesticide (OP) to control pests has been verified reproductive toxicity on mammalian oocytes. However, limited information exists on its correlation with the dysfunction of the intercellular communication in cumulus-oocyte complexes (COCs). Herein, our study utilized porcine COCs as models to directly address the latent impact of CPF on the communication between cumulus cells (CCs) and oocytes during in vitro maturation. The results demonstrated that CPF exposure decreased the rate of the first polar body (PB1) extrusion and blocked meiosis progression. Notably, the cumulus expansion of CPF-exposed COCs was suppressed significantly, accompanied by the down-regulated mRNA levels of cumulus expansion-related genes. Furthermore, the early apoptotic level was raised and the expression of BAX/BCL2 and cleaved caspase 3 was up-regulated in the CCs of CPF-exposed COCs (p < 0.05). Moreover, CPF exposure impaired mRNA levels of antioxidant enzyme-related genes, induced higher levels of reactive oxygen species (ROS) and reduced the levels of mitochondrial membrane potential (MMP) in CCs (p < 0.05). Additionally, the integrated optical density (IOD) rate (cumulus/oocyte) of calcein and the expression of connexin 43 (CX43) was increased in CPF treatment groups (p < 0.05). As well, CPF exposure reduced the expression levels of FSCN1, DAAM1 and MYO10, which resulted in a significant decrease in the number and fluorescence intensity of transzonal projections (TZPs). In conclusion, CPF inhibited the expansion of cumulus and caused oxidative stress and apoptosis as well as disturbed the function of gap junctions (GJs) and TZPs, which eventually resulted in the failure of oocyte maturation.

A detailed review of pharmacology of MFN1 (mitofusion-1)-mediated mitochondrial dynamics: Implications for cellular health and diseases

The mitochondria are responsible for the production of cellular ATP, the regulation of cytosolic calcium levels, and the organization of numerous apoptotic proteins through the release of cofactors necessary for the activation of caspases. This level of functional adaptability can only be attained by sophisticated structural alignment. The morphology of the mitochondria does not remain unchanged throughout time; rather, it undergoes change as a result of processes known as fusion and fission. Fzo in flies, Fzo1 in yeast, and mitofusins in mammals are responsible for managing the outer mitochondrial membrane fusion process, whereas Mgm1 in yeast and optic atrophy 1 in mammals are responsible for managing the inner mitochondrial membrane fusion process. The fusion process is composed of two phases. MFN1, a GTPase that is located on the outer membrane of the mitochondria, is involved in the process of linking nearby mitochondria, maintaining the potential of the mitochondrial membrane, and apoptosis. This article offers specific information regarding the functions of MFN1 in a variety of cells and organs found in living creatures. According to the findings of the literature review, MFN1 plays an important part in a number of diseases and organ systems; nevertheless, the protein's function in other disease models and cell types has to be investigated in the near future so that it can be chosen as a promising marker for the therapeutic and diagnostic potentials it possesses. Overall, the major findings of this review highlight the pivotal role of mitofusin (MFN1) in regulating mitochondrial dynamics and its implications across various diseases, including neurodegenerative disorders, cardiovascular diseases, and metabolic syndromes. Our review identifies novel therapeutic targets within the MFN1 signaling pathways and underscores the potential of MFN1 modulation as a promising strategy for treating mitochondrial-related diseases. Additionally, the review calls for further research into MFN1's molecular mechanisms to unlock new avenues for clinical interventions, emphasizing the need for targeted therapies that address MFN1 dysfunction.

Grape seed extract prevents chlorpyrifos-induced toxicity in rat liver through the modulation of phase I detoxification pathway

Chlorpyrifos (CPF) poisoning is a public health problem for which there is not currently any effective prophylaxis. In this study, we investigated the protective effect of grape seed extract (GSE) against CPF-induced hepatotoxicity. Rats were daily treated either with CPF (2 mg/kg) or CPF and GSE (20 mg/kg) for 1 week, sacrificed, and their livers dissected for biochemical, molecular, and histopathological analyses. CPF generated liver dysfunction by altering carbohydrate, lipid, amino acid, ammonia and urea metabolism, and provoked mitochondrial impairment through disturbing tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS), and mitochondrial viability. CPF also induced cholinergic excitotoxicity along with oxidative stress and histopathological alterations. Interestingly, treatment with GSE prevented all the detrimental effects of CPF through the regulation of cytochrome P450 (CYP450) gene expression. Molecular docking analysis indicated that GSE-containing polyphenols acted as epigenetic modulators through inhibiting DNA (cytosine-5)-methyltransferase 1 (DNMT1), thus favoring the CYP2C6 detoxification pathway. Thereby, GSE might be a promising strategy in the protection of the liver against CPF toxicity.

Surveillance of pesticide residues in tomato and eggplant and assessment of acute and chronic health risks to the consumers in Pakistan

Pesticide application has become a mandatory requirement of the modern agricultural system, resulting in the objectionable levels of pesticide residues in the treated food commodities and posing health threats to the consumers. This study aimed at optimization and validation of an analytical method which can be reliably applied for routine monitoring of the selected eighteen widely reported pesticides in tomato and eggplant. The principle of quick, easy, cheap, effective, rugged, and safe, i.e., QuEChERS, involving the acetate-buffered extraction followed by cleanup using the primary secondary amines (PSA) was employed. The analytical method was validated at three spiking levels (0.05, 0.01, 0.005 mg/kg) using gas chromatograph-micro electron capture detector (GC-µECD). Gas chromatograph-mass spectrometric detector (GC-MSD) was also used for confirmation and quantification using selective ion monitoring (SIM) mode. The method was applied on fresh samples of tomato (n = 33) and eggplant (n = 27) collected from local markets of Khyber Pakhtunkhwa, Pakistan, in the crop season 2020-2021. Twenty-five (76%) tomato samples and fifteen (56%) eggplant samples were found positive for one or more pesticides. Though the chronic and acute health risk assessments indicate that both of these vegetables are unlikely to pose any unacceptable health threat to their consumers, yet the risks from regular intake of pesticides-contaminated food commodities should be regularly addressed for possible protection of the public health and assurance of safe and consistent agro-trade, alike.

The susceptibility of humans to neurodegenerative and neurodevelopmental toxicities caused by organophosphorus pesticides

The toxicology field is concerned with the impact of organophosphorus (OP) compounds on human health. These compounds have been linked to an increased risk of neurological disorders, including neurodegenerative and neurodevelopmental diseases. This article aims to review studies on the role of OP compounds in developing these neurological disorders and explore how genetic variations can affect susceptibility to the neurotoxicity of these pesticides. Studies have shown that exposure to OP compounds can lead to the development of various neurological disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), attention deficit hyperactivity disorder (ADHD), autism, intellectual disability, and other developmental neurotoxicities. Apart from inhibiting the cholinesterase enzyme, OP compounds are believed to cause other pathological mechanisms at both the extracellular level (cholinergic, serotonergic, dopaminergic, glutamatergic, and GABAergic synapses) and the intracellular level (oxidative stress, mitochondrial dysfunction, inflammation, autophagy, and apoptosis) that contribute to these disorders. Specific genetic polymorphisms, including PON1, ABCB1, NOS, DRD4, GST, CYP, and APOE, have increased the risk of developing OP-related neurological disorders.

Widespread RNA hypoediting in schizophrenia and its relevance to mitochondrial function

RNA editing, the endogenous modification of nucleic acids, is known to be altered in genes with important neurological function in schizophrenia (SCZ). However, the global profile and molecular functions of disease-associated RNA editing remain unclear. Here, we analyzed RNA editing in postmortem brains of four SCZ cohorts and uncovered a significant and reproducible trend of hypoediting in patients of European descent. We report a set of SCZ-associated editing sites via WGCNA analysis, shared across cohorts. Using massively parallel reporter assays and bioinformatic analyses, we observed that differential 3' untranslated region (3'UTR) editing sites affecting host gene expression were enriched for mitochondrial processes. Furthermore, we characterized the impact of two recoding sites in the mitofusin 1 (MFN1) gene and showed their functional relevance to mitochondrial fusion and cellular apoptosis. Our study reveals a global reduction of editing in SCZ and a compelling link between editing and mitochondrial function in the disease.

New Insights into Baicalein's Effect on Chlorpyrifos-Induced Liver Injury in Carp: Involving Macrophage Polarization and Pyropto sis

Chlorpyrifos (CPF) is widely used in agriculture, plants, and buildings to kill pests and worms. Excessive environmental residues of CPF will result in soil and ecological contamination and toxicity to animals and humans. Baicalein (Bai), derived from the root of natural Scutellaria baicalensis, is a potent anti-inflammatory, antioxidant, and antitumor agent. The objective of this paper is to investigate the molecular mechanism by which Bai prevents CPF-induced hepatotoxic injury. Carp were kept in water containing CPF (23.2 μg/L) and/or fed diets containing Bai (0.15 g/kg). We found that Bai attenuated liver tissue damage and vacuolization caused by CPF. We confirmed that CPF causes M1/M2 polarization imbalance in macrophages and hepatocyte pyroptosis, which ultimately leads to liver injury. Further exploration of the internal mechanism shows that CPF participates in liver toxicity damage by destroying the AMPK/SIRT1/pGC-1α pathway and causing mitochondrial biogenesis and mitochondrial dynamics imbalance. Notably, Bai significantly attenuated CPF-induced inhibition of the AMPK/SIRT1/pGC-1α pathway. In summary, our results suggest that Bai alleviates CPF exposure-induced inhibition of the AMPK/SIRT1/pGC-1α pathway, thereby attenuating macrophage M1 hyperpolarization and pyroptosis by inhibiting the NF-κB pathway. These results may provide new insights into the detoxification mechanism of Bai on the same type of organophosphorus pesticides.

Surveillance and dietary risk assessment of endocrine-disrupting pesticides in eggplant/brinjal and cauliflower in Pakistan

Several pesticides (used in vegetable production) have recently been identified as potential endocrine disruptors. The current study aimed to determine the consumer exposure risk associated with eating contaminated vegetables. The European Union-citrate buffered QuEChERS extraction protocol, validated in accordance with the European Union guidelines, was used to monitor selected endocrine-disrupting pesticides in eggplant/brinjal (Solanum melongena L.) and cauliflower (Brassica oleracea) marketed in Rawalpindi/Islamabad, Pakistan. A total of 80 and 69 percent of eggplant/brinjal (n = 25) and cauliflower (n = 26) samples were found contaminated, respectively. Sixty-five percent of cauliflower samples were found non-contaminated with both European Union (EU) and Codex Alimentarius Commission (CAC) maximum residue limits (MRL), while 20 % of brinjal samples were found to be non-compliant with EU-MRL. Both vegetables contained high levels of the androgen antagonist chlorpyrifos and the thyroid hormone inhibitor cyhalothrin-lambda. The estimated acute health risk associated with dietary exposure to chlorpyrifos and cyhalothrin-lambda in cauliflower for both males and females was found to be greater than 200 % of the FAO/WHO Joint Meeting on Pesticide Residues' (JMPR) established acute reference dose. The estimated chronic health risk for all studied endocrine-disrupting pesticides (0-5.27 %) indicates zero to very low health risk for studied population groups.

Effects of fluoride exposure on mitochondrial function: Energy metabolism, dynamics, biogenesis and mitophagy

Fluoride is ubiquitous in the environment. Furthermore, drinking water represents the main source of exposure to fluoride for humans. Interestingly, low fluoride concentrations have beneficial effects on bone and teeth development; however, chronic fluoride exposure has harmful effects on human health. Besides, preclinical studies associate fluoride toxicity with oxidative stress, inflammation, and apoptosis. On the other hand, it is well-known that mitochondria play a key role in reactive oxygen species production. By contrast, fluoride's effect on processes such as mitochondrial dynamics, biogenesis and mitophagy are little known. These processes modulate the size, content, and distribution of mitochondria and their depuration help to counter the reactive oxygen species production and cytochrome c release, thereby allowing cell survival. However, a maladaptive response could enhance fluoride-induced toxicity. The present review gives a brief account of fluoride-induced mitochondrial alterations on soft and hard tissues, including liver, reproductive organs, heart, brain, lung, kidney, bone, and tooth.

Comparison of the Toxicological Effects of Pesticides in Non-Tumorigenic MCF-12A and Tumorigenic MCF-7 Human Breast Cells

Humans are exposed to residues of organophosphate and neonicotinoid pesticides, commonly used in agriculture. Children are particularly vulnerable and, among possible adverse outcomes, the increased incidence of premature mammary gland development (thelarche) has raised concern. We evaluated the toxicological effects of chlorpyrifos (CPF), imidacloprid (IMI) and glyphosate (GLY) at exposure concentrations occurring in children on the tumorigenic MCF-7 and non-tumorigenic MCF-12A breast cell lines, as representative of the target organ model, assessing cytotoxicity, apoptosis, necrosis, intracellular reactive oxygen species (ROS) and ATP levels, 17β-estradiol secretion and gene expression of nuclear receptors involved in mammary gland development. The pesticides decreased cell vitality in MCF-7 and cell proliferation in MCF-12A cells. ATP levels were decreased in MCF-7 cells by pesticides and apoptosis was increased in MCF-12A cells only by GLY (2.3 nM). ROS production was decreased by pesticides in both cell lines, except IMI (1.6 nM) in MCF-7 cells. Endocrine disrupting activity was highlighted by induction of 17β-estradiol secretion and modulation of the gene expression of estrogen alpha and beta, progesterone, androgen, and aryl hydrocarbon receptors in both cell lines. The use of MCF-7 and MCF-12A cells highlighted dissimilar modes of action of each pesticide at low human relevant concentrations.

Mitochondrial dysfunction by TFAM depletion disrupts self-renewal and lineage differentiation of human PSCs by affecting cell proliferation and YAP response

Genetic mitochondrial dysfunction is frequently associated with various embryonic developmental defects. However, how mitochondria contribute to early development and cell fate determination is poorly studied, especially in humans. Using human pluripotent stem cells (hPSCs), we established a Dox-induced knockout model with mitochondrial dysfunction and evaluated the effect of mitochondrial dysfunction on human pluripotency maintenance and lineage differentiation. The nucleus-encoded gene TFAM (transcription factor A, mitochondrial), essential for mitochondrial gene transcription and mitochondrial DNA replication, is targeted to construct the mitochondrial dysfunction model. The hPSCs with TFAM depletion exhibit the decrease of mtDNA level and oxidative respiration efficiency, representing a typical mitochondrial dysfunction phenotype. Mitochondrial dysfunction leads to impaired self-renewal in hPSCs due to proliferation arrest. Although the mitochondrial dysfunction does not affect pluripotent gene expression, it results in a severe defect in lineage differentiation. Further study in mesoderm differentiation reveals that mitochondrial dysfunction causes proliferation disability and YAP nuclear translocalization and thus together blocks mesoderm lineage differentiation. These findings provide new insights into understanding the mitochondrial function in human pluripotency maintenance and mesoderm differentiation.

Chlorpyrifos triggers epithelioma papulosum cyprini cell pyroptosis via miR-124-3p/CAPN1 axis

Chlorpyrifos (CPF), a widely used organophosphorus pesticide has caused water pollution, threatening aquatic organisms. MicroRNAs (miRNAs) highly conserved noncoding RNAs, that regulate various cell death processes, including pyroptosis. To investigate the effect of CPF exposure on epithelioma papulosum cyprini (EPC) cell pyroptosis and the role of the miR-124-3p/CAPN1 axis, we established miR-124 overexpression and inhibition EPC cell models of CPF exposure. The target of the miR-124-3p/CAPN1 axis was primarily confirmed by the double luciferase reporter assay. Pyroptosis was demonstrated to occur in CPF-exposed EPC cells and was accompanied by mitochondrial membrane potential depletion, ROS level elevation and pyroptotic indicator expression upregulation. PD150606 was supplied as a CAPN1 inhibitor, alleviating CPF-induced mitochondrial dysfunction, and alleviating the increased expression of NLRP3, CASP1, IL1β and GSDMD. In conclusion, CPF induces pyroptosis by regulating the miR-124-3p/CAPN1 axis. This study enriches the cytotoxicity study of CPF, and provides new theoretical fundamentals for exploration of miRNA and its target protein response to water contaminants.

Exposure to chlorpyrifos leads to spindle disorganization and mitochondrial dysfunction of porcine oocytes during in vitro maturation

Chlorpyrifos (CPF), as one of the most extensively applied organophosphorus pesticides (OPs) in agricultural and domestic settings, causes a potential threat to human and animal health. Various reproductive toxicities of CPF have been reported, however, little information is available on whether CPF exposure could exert toxic effects on mammalian oocytes. Herein, the effects of CPF on the meiotic maturation and developmental capability of porcine oocytes were investigated, and the possible toxic mechanisms of CPF were also explored. Porcine cumulus-oocyte complexes (COCs) were treated with 0, 5, 10, or 20 μM CPF for 44 h during in vitro maturation (IVM), and the results showed that the first polar body (PB1) extrusion rate was significantly decreased, and the subsequent developmental competence of the resulting metaphase II (MII) oocytes was also impaired when the concentration of CPF reached 10 μM. In addition, a higher percentage of CPF-exposed oocytes were arrested at the anaphase-telophase I (ATI) stage, accompanied by misaligned chromosomes and aberrant spindles. Furthermore, higher levels of ROS and upregulated antioxidant-related genes (CAT, SOD1, SOD2, GPX) were detected in CPF-treated oocytes. Additionally, CPF treatment led to the depolarization of mitochondrial membrane potential (MMP) and the release of cytochrome c (Cyt c). Simultaneously, the apoptotic rate of the oocytes was significantly increased, and the expression levels of Bax and CASPASE3 were significantly upregulated after CFP exposure. Together, exposure to 10 μM CPF can disrupt the meiotic cycle progression, lead to aberrant spindles and mitochondrial dysfunction, which eventually induce oxidative stress and apoptosis in porcine oocytes.

Endocrine disruptors also function as nervous disruptors and can be renamed endocrine and nervous disruptors (ENDs)

Endocrine disruption (ED) and endocrine disruptors (EDs) emerged as scientific concepts in 1995, after numerous chemical pollutants were found to be responsible for reproductive dysfunction. The World Health Organization established in the United Nations Environment Programme a list of materials, plasticizers, pesticides, and various pollutants synthesized from petrochemistry that impact not only reproduction, but also hormonal functions, directly or indirectly. Cells communicate via either chemical or electrical signals transmitted within the endocrine or nervous systems. To investigate whether hormone disruptors may also interfere directly or indirectly with the development or functioning of the nervous system through either a neuroendocrine or a more general mechanism, we examined the scientific literature to ascertain the effects of EDs on the nervous system, specifically in the categories of neurotoxicity, cognition, and behaviour. To date, we demonstrated that all of the 177 EDs identified internationally by WHO are known to have an impact on the nervous system. Furthermore, the precise mechanisms underlying this neurodisruption have also been established. It was previously believed that EDs primarily function via the thyroid. However, this study presents substantial evidence that approximately 80 % of EDs operate via other mechanisms. It thus outlines a novel concept: EDs are also neurodisruptors (NDs) and can be collectively termed endocrine and nervous disruptors (ENDs). Most of ENDs are derived from petroleum residues, and their various mechanisms of action are similar to those of "spam" in electronic communications technologies. Therefore, ENDs can be considered as an instance of spam in a biological context.

Evaluation of Barrier Functions in Human iPSC-Derived Intestinal Epithelium

The small intestine plays roles in the absorption and metabolism of orally administered drugs and chemicals. Tight junctions between intestinal epithelial cells, which form a tight barrier preventing the invasion of pathogens and toxins, are essential components of the intestinal defense system. These intestinal functions have generally been evaluated using established cell lines or primary cells in two-dimensional culture. However, these culture systems have not shown the complexity of the three-dimensional structure and diversity of cell types comprising the intestinal epithelial tissue. Here, we report the generation of intestinal organoids using human induced pluripotent stem cells subjected to sequential treatment with different cytokines and compounds. We further describe the tool for evaluating intestinal barrier functions using organoids as a physiologically relevant human platform.

Human stem cell-based models for studying autism spectrum disorder-related neuronal dysfunction

The controlled differentiation of pluripotent stem cells (PSCs) into neurons and glia offers a unique opportunity to study early stages of human central nervous system development under controlled conditions in vitro. With the advent of cell reprogramming and the possibility to generate induced pluripotent stem cells (iPSCs) from any individual in a scalable manner, these studies can be extended to a disease- and patient-specific level. Autism spectrum disorder (ASD) is considered a neurodevelopmental disorder, with substantial evidence pointing to early alterations in neurogenesis and network formation as key pathogenic drivers. For that reason, ASD represents an ideal candidate for stem cell-based disease modeling. Here, we provide a concise review on recent advances in the field of human iPSC-based modeling of syndromic and non-syndromic forms of ASD, with a particular focus on studies addressing neuronal dysfunction and altered connectivity. We further discuss recent efforts to translate stem cell-based disease modeling to 3D via brain organoid and cell transplantation approaches, which enable the investigation of disease mechanisms in a tissue-like context. Finally, we describe advanced tools facilitating the assessment of altered neuronal function, comment on the relevance of iPSC-based models for the assessment of pharmaceutical therapies and outline potential future routes in stem cell-based ASD research.

Erythroid Differentiation and Heme Biosynthesis Are Dependent on a Shift in the Balance of Mitochondrial Fusion and Fission Dynamics

Erythropoiesis is the most robust cellular differentiation and proliferation system, with a production of ∼2 × 10¹¹ cells per day. In this fine-tuned process, the hematopoietic stem cells (HSCs) generate erythroid progenitors, which proliferate and mature into erythrocytes. During erythropoiesis, mitochondria are reprogrammed to drive the differentiation process before finally being eliminated by mitophagy. In erythropoiesis, mitochondrial dynamics (MtDy) are expected to be a key regulatory point that has not been described previously. We described that a specific MtDy pattern occurs in human erythropoiesis from EPO-induced human CD34⁺ cells, characterized predominantly by mitochondrial fusion at early stages followed by fission at late stages. The fusion protein MFN1 and the fission protein FIS1 are shown to play a key role in the progression of erythropoiesis. Fragmentation of the mitochondrial web by the overexpression of FIS1 (gain of fission) resulted in both the inhibition of hemoglobin biosynthesis and the arrest of erythroid differentiation, keeping cells in immature differentiation stages. These cells showed specific mitochondrial features as compared with control cells, such as an increase in round and large mitochondrial morphology, low mitochondrial membrane potential, a drop in the expression of the respiratory complexes II and IV and increased ROS. Interestingly, treatment with the mitochondrial permeability transition pore (mPTP) inhibitor, cyclosporin A, rescued mitochondrial morphology, hemoglobin biosynthesis and erythropoiesis. Studies presented in this work reveal MtDy as a hot spot in the control of erythroid differentiation, which might signal downstream for metabolic reprogramming through regulation of the mPTP.

Development of classification models for predicting inhibition of mitochondrial fusion and fission using machine learning methods

Mitochondrial fusion and fission are processes to maintain mitochondrial function when cells respond to environment stresses. Disruption of mitochondrial fusion and fission influences cell health and can cause adverse events such as neurodegenerative disorders. It is critical to identify environmental chemicals that can disrupt mitochondrial fusion and fission. However, experimentally testing all the chemicals is not practical because experimental methods are time-consuming and costly. Quantitative structure-activity relationship (QSAR) modeling is an attractive approach for evaluation of chemicals disrupting potential on mitochondrial fusion and fission. In this study, QSAR models were developed for differentiating chemicals capable of inhibition of mitochondrial fusion and fission using machine learning algorithms (i.e. random forest, logistic regression, Bernoulli naive Bayes, and deep neural network). One hundred iterations of five-fold cross validations and external validations showed that the best model on mitochondrial fusion had area under the receiver operating characteristic curve (AUC) of 82.8% and 78.1%, respectively; and the best model for mitochondrial fission yielded AUC of 84.3% and 97.5%, respectively. Furthermore, 45 and 56 structural alerts were identified for inhibition of mitochondrial fusion and fission, respectively. The results demonstrated that the models and the structural alerts could be useful for screening chemicals that inhibit mitochondrial fusion and fission.

Cytotoxicity comparison of 35 developmental neurotoxicants in human induced pluripotent stem cells (iPSC), iPSC-derived neural progenitor cells, and transformed cell lines

The Organization for Economic Co-operation and Development (OECD) test guideline 426 for developmental neurotoxicity (DNT) of industrial/environmental chemicals depends primarily on animal experimentation. This requirement raises various critical issues, such as high cost, long duration, the sacrifice of large numbers of animals, and interspecies differences. This study demonstrates an alternative protocol that is simple, quick, less expensive, and standardized to evaluate DNT of many chemicals using human induced pluripotent stem cells (iPSC) and their differentiation to neural progenitor cells (NPC). Initially, concentration-dependent cytotoxicity of 35 DNT chemicals, including industrial materials, insecticides, and clinical drugs, were compared among iPSC, NPC, and two transformed cells, Cos-7 and HepG2, using tetrazolium dye (MTS)-reducing colorimetric and ATP luciferase assays, and IC₅₀ values were calculated. Next, inhibitory effects of the 14 representative chemicals (mainly insecticides) on iPSC differentiation to NPC were evaluated by measuring altered expression of neural differentiation and undifferentiation marker genes. Results show that both iPSC and NPC were much more sensitive to most DNT chemicals than the transformed cells, and 14 chemicals induced differential patterns of marker gene expression, highlighting the validity and utility of the protocol for evaluation and classification of DNT chemicals and preclinical DNT tests for safety assessment.

Agrochemicals and neurogenesis

Agrochemicals or pesticides are compounds widely used to prevent, destroy or mitigate pests such as insects, rodents, herbs and weeds. However, most of them also act as environmental estrogens, anti-estrogens and/or antiandrogenic chemicals. In addition, both herbicides (such as glyphosate and paraquat) and insecticides (such as pyrethroids, organophosphates, neonicotinoids and rotenone) have been shown to exert significant adverse effects on hippocampal neurogenesis. These effects are particularly important because neurogenesis dysregulation could be associated with cognitive decline and neuropathologies such as Alzheimer's disease. This review focuses on the most commonly used agrochemicals in Argentina and their effects on the hippocampal neurogenesis of mammals. It also discusses the disruption of hormone synthesis and action as a possible mechanism through which these chemical compounds could alter the brain functions. Finally, we propose some lines of research to study the potential endocrine mechanisms involved in the effects of agrochemicals on human health and biodiversity.

Subchronic administration of Parastar insecticide induced behavioral changes and impaired motor coordination in male Wistar rats

Parastar is an insecticide formulation of lambda-cyhalothrin and imidacloprid largely used for crop protection in North West Region of Cameroon. In the present study, we evaluated the behavioral activities and motor function of Wistar male rats after subchronic treatment with the pesticide formulation. To this end, three groups of adult rats were administered Parastar at doses 1.25, 2.49 and 6.23 mg/kg, respectively, for 35 days. A control group was included and received distilled water. At the end of the treatment, the animals were submitted to behavioral and functional tests (open field test, elevated plus maze test, light-dark box test, forced swimming test, tail suspension test, beam-walking test, grid suspension test and wire hang test) for estimation of anxiety, exploration, depression and motor coordination. Results revealed that Parastar, at the higher doses tested, 2.49 and 6.23 mg/kg, induced anxiogenic-like pattern behavior in rats in all behavioral assays including open field test (total distance moved, total lines crossed, frequency and total time in center square were all reduced), elevated plus maze (decreased total time spent in open arms and the number of entries in open arms of the elevated plus maze), and light-dark box (the dark box duration increased, while light box duration time and frequency of transition between dark and light box decreased). Treatment with 2.49 and 6.23 mg/kg Parastar increased the immobility time of animals in both forced swimming test and tail suspension test. The insecticide induced decrease in the distance traveled, foot slip and number of turns of animals in the beam walking test. Parastar also decreased the animal suspension time in both grid suspension grip-strength test and the wire hang test. Taken altogether, these results suggest that subchronic administration of Parastar at the doses of 2.49 and 6.23 mg/kg induced anxiety-like and depressive-like behavior as well as impaired motor coordination and muscle strength in male rats.

Neurotoxicity of pesticides

Pesticides are unique environmental contaminants that are specifically introduced into the environment to control pests, often by killing them. Although pesticide application serves many important purposes, including protection against crop loss and against vector-borne diseases, there are significant concerns over the potential toxic effects of pesticides to non-target organisms, including humans. In many cases, the molecular target of a pesticide is shared by non-target species, leading to the potential for untoward effects. Here, we review the history of pesticide usage and the neurotoxicity of selected classes of pesticides, including insecticides, herbicides, and fungicides, to humans and experimental animals. Specific emphasis is given to linkages between exposure to pesticides and risk of neurological disease and dysfunction in humans coupled with mechanistic findings in humans and animal models. Finally, we discuss emerging techniques and strategies to improve translation from animal models to humans.

Biophysical and biomechanical properties of neural progenitor cells as indicators of developmental neurotoxicity

Conventional in vitro toxicity studies have focused on identifying IC₅₀ and the underlying mechanisms, but how toxicants influence biophysical and biomechanical changes in human cells, especially during developmental stages, remain understudied. Here, using an atomic force microscope, we characterized changes in biophysical (cell area, actin organization) and biomechanical (Young's modulus, force of adhesion, tether force, membrane tension, tether radius) aspects of human fetal brain-derived neural progenitor cells (NPCs) induced by four classes of widely used toxic compounds, including rotenone, digoxin, N-arachidonoylethanolamide (AEA), and chlorpyrifos, under exposure up to 36 h. The sub-cellular mechanisms (apoptosis, mitochondria membrane potential, DNA damage, glutathione levels) by which these toxicants induced biochemical changes in NPCs were assessed. Results suggest a significant compromise in cell viability with increasing toxicant concentration (p < 0.01), and biophysical and biomechanical characteristics with increasing exposure time (p < 0.01) as well as toxicant concentration (p < 0.01). Impairment of mitochondrial membrane potential appears to be the most sensitive mechanism of neurotoxicity for rotenone, AEA and chlorpyrifos exposure, but compromise in plasma membrane integrity for digoxin exposure. The surviving NPCs remarkably retained stemness (SOX2 expression) even at high toxicant concentrations. A negative linear correlation (R² = 0.92) exists between the elastic modulus of surviving cells and the number of living cells in that environment. We propose that even subtle compromise in cell mechanics could serve as a crucial marker of developmental neurotoxicity (mechanotoxicology) and therefore should be included as part of toxicology assessment repertoire to characterize as well as predict developmental outcomes.

Early mitochondrial fragmentation is a potential in vitro biomarker of environmental stress

Mitochondria are essential dynamic organelles that ordinarily balance between fragmentation and fusion. Under stress conditions, a shift toward fragmentation or hyper-fusion is observed as a pro-survival reaction. Fragmentation of mitochondria occurs within minutes or hours after the beginning of the stress and occurs in response to a large number of stress stimuli, including those triggered by environmental contaminants. In this study, we tested whether the change in the mitochondrial phenotype, from tubular to fragmented, could be used as a potential environmental stress biomarker in cells and compared this response with the standard MTT-based viability assay. Firstly, we show that mitochondrial fragmentation induced by selected stressors not only increases with concentrations, but also correlates positively with the cytotoxicity. Secondly, we found that the mitochondrial fragmentation that occurs in the first hour of stress correlated with the viability measured after a 24-h stress, allowing the establishment of a linear relation between mitochondrial fragmentation at 1 h and the predictable associated cytotoxicity of environmental contaminants alone or in mixture. In conclusion, we have succeeded in developing a model of predictable 24 h-cytotoxicity given mitochondrial fragmentation at 1 h with a set of chemicals. This model has been successful applied to three environmental toxicants and to a set of two chemical mixtures. We thus propose that mitochondrial fragmentation is a response that could be used as an early in vitro biomarker of environmental stress for toxicants alone or in mixture.

5-Fluorouracil inhibits neural differentiation via Mfn1/2 reduction in human induced pluripotent stem cells

5-fluorouracil (5-FU) has been widely used for the treatment of tumors. Regardless of its widespread use as an anti-cancer drug, 5-FU therapy can cause several side effects, including developmental toxicity and neurotoxicity. However, the potential action of 5-FU at the early fetal stage has not yet been completely elucidated. In the present study, we investigated the effect of 5-FU exposure on neural induction, using human induced pluripotent stem cells (iPSCs) as a model of human fetal stage. 5-FU exposure reduced the expression of several neural differentiation marker genes, such as OTX2, in iPSCs. Since the neural differentiation process requires ATP as a source of energy, we next examined intracellular ATP content using iPSCs. We found that 5-FU decreased intracellular ATP levels in iPSCs. We further focused on the effects of 5-FU on mitochondrial dynamics, which plays a role of ATP production. We found that 5-FU induced mitochondrial fragmentation and reduced the level of mitochondrial fusion proteins, mitofusin 1 and 2 (Mfn1/2). Double knockdown of Mfn1/2 genes in iPSCs downregulated the gene expression of OTX2, suggesting that Mfn mediates neural differentiation in iPSCs. Taken together, these results indicate that 5-FU has a neurotoxicity via Mfn-mediated mitochondria dynamics in iPSCs. Thus, mitochondrial dysfunction in iPSCs could be used as a possible marker for cytotoxic effects of drugs.

Mitochondria as target of endocrine-disrupting chemicals: implications for type 2 diabetes

Type 2 diabetes is a chronic, heterogeneous syndrome characterized by insulin resistance and pancreatic β-cell dysfunction or death. Among several environmental factors contributing to type 2 diabetes development, endocrine-disrupting chemicals (EDCs) have been receiving special attention. These chemicals include a wide variety of pollutants, from components of plastic to pesticides, with the ability to modulate endocrine system function. EDCs can affect multiple cellular processes, including some related to energy production and utilization, leading to alterations in energy homeostasis. Mitochondria are primarily implicated in cellular energy conversion, although they also participate in other processes, such as hormone secretion and apoptosis. In fact, mitochondrial dysfunction due to reduced oxidative capacity, impaired lipid oxidation and increased oxidative stress has been linked to insulin resistance and type 2 diabetes. Herein, we review the main mechanisms whereby metabolism-disrupting chemical (MDC), a subclass of EDCs that disturbs energy homeostasis, cause mitochondrial dysfunction, thus contributing to the establishment of insulin resistance and type 2 diabetes. We conclude that MDC-induced mitochondrial dysfunction, which is mainly characterized by perturbations in mitochondrial bioenergetics, biogenesis and dynamics, excessive reactive oxygen species production and activation of the mitochondrial pathway of apoptosis, seems to be a relevant mechanism linking MDCs to type 2 diabetes development.

Tributyltin Inhibits Neural Induction of Human Induced Pluripotent Stem Cells

Tributyltin (TBT), one of the organotin compounds, is a well-known environmental pollutant. In our recent study, we reported that TBT induces mitochondrial dysfunction, in human-induced pluripotent stem cells (iPSCs) through the degradation of mitofusin1 (Mfn1), which is a mitochondrial fusion factor. However, the effect of TBT toxicity on the developmental process of iPSCs was not clear. The present study examined the effect of TBT on the differentiation of iPSCs into the ectodermal, mesodermal, and endodermal germ layers. We found that exposure to nanomolar concentration of TBT (50 nM) selectively inhibited the induction of iPSCs into the ectoderm, which is the first step in neurogenesis. We further assessed the effect of TBT on neural differentiation and found that it reduced the expression of several neural differentiation marker genes, which were also downregulated by Mfn1 knockdown in iPSCs. Taken together, these results indicate that TBT induces developmental neurotoxicity via Mfn1-mediated mitochondrial dysfunction in iPSCs.

Silver nanoparticles inhibit neural induction in human induced pluripotent stem cells

Silver nanoparticles (AgNPs) have been widely used as consumer products due to their antibacterial activities. Despite their extensive use, AgNPs have been reported to cause various types of cytotoxicity, including neurotoxicity. However, the potential action of AgNPs on early fetal development has not been elucidated. This study determined the effects of AgNPs on neural induction in human induced pluripotent stem cells (iPSCs), used as a model for human fetal stage development. It was observed that exposure to AgNPs reduced the expression of several neural differentiation marker genes, including OTX2, an early biomarker for neurogenesis in iPSCs. Since neural differentiation requires ATP as a source of energy, the intracellular ATP content was also measured. It was observed that AgNPs decreased intracellular ATP levels in iPSCs. Since AgNPs suppressed energy production, a critical mitochondrial function, the effects of AgNPs on mitochondrial dynamics were further studied. The results revealed that AgNPs induced mitochondrial fragmentation and reduced the level of mitochondrial fusion protein mitofusin 1 (Mfn1). Previously, we reported that knockdown of Mfn1 in iPSCs inhibited neural induction via OTX2 downregulation. This suggested that AgNPs could induce cytotoxicity, including neurodevelopmental toxicity, via Mfn1-mediated mitochondrial dysfunction in iPSCs. Thus, mitochondrial function in iPSCs can be used for assessing the cytotoxic effects associated with nanomaterials, including AgNPs.

Mitochondrial fusion, fission, and mitochondrial toxicity

Mitochondrial dynamics are regulated by two sets of opposed processes: mitochondrial fusion and fission, and mitochondrial biogenesis and degradation (including mitophagy), as well as processes such as intracellular transport. These processes maintain mitochondrial homeostasis, regulate mitochondrial form, volume and function, and are increasingly understood to be critical components of the cellular stress response. Mitochondrial dynamics vary based on developmental stage and age, cell type, environmental factors, and genetic background. Indeed, many mitochondrial homeostasis genes are human disease genes. Emerging evidence indicates that deficiencies in these genes often sensitize to environmental exposures, yet can also be protective under certain circumstances. Inhibition of mitochondrial dynamics also affects elimination of irreparable mitochondrial DNA (mtDNA) damage and transmission of mtDNA mutations. We briefly review the basic biology of mitodynamic processes with a focus on mitochondrial fusion and fission, discuss what is known and unknown regarding how these processes respond to chemical and other stressors, and review the literature on interactions between mitochondrial toxicity and genetic variation in mitochondrial fusion and fission genes. Finally, we suggest areas for future research, including elucidating the full range of mitodynamic responses from low to high-level exposures, and from acute to chronic exposures; detailed examination of the physiological consequences of mitodynamic alterations in different cell types; mechanism-based testing of mitotoxicant interactions with interindividual variability in mitodynamics processes; and incorporating other environmental variables that affect mitochondria, such as diet and exercise.

Aryl- and alkyl-phosphorus-containing flame retardants induced mitochondrial impairment and cell death in Chinese hamster ovary (CHO-k1) cells

Phosphorus-containing flame retardants (PFRs) are increasingly in demand worldwide as replacements for brominated flame retardants (BFRs), but insufficient available toxicological information on PFRs makes assessing their health risks challenging. Mitochondria are important targets of various environmental pollutants, and mitochondrial dysfunction may lead to many common diseases. In the present study, mitochondria impairment-related endpoints were measured by a high content screening (HCS) assay for 11 selected non-halogen PFRs in Chinese hamster ovary (CHO-k1) cells. A cluster analysis was used to categorize these PFRs into three groups according to their structural characteristics and results from the HCS assay. Two groups, containing long-chain alkyl-PFRs and all aryl-PFRs, were found to cause mitochondrial impairment but showed different mechanisms of toxicity. Due to the high correlation between cell death and mitochondrial impairment, two PFRs with different structures, trihexyl phosphate (THP) and cresyl diphenyl phosphate (CDP), were selected and compared with chlorpyrifos (CPF) to elucidate their mechanism of inducing cell death. THP (an alkyl-PFR) was found to utilize a similar pathway as CPF to induce apoptosis. However, cell death induced by CDP (an aryl-PFR) was different from classical necrosis based on experiments to discriminate among the different modes of cell death. These results confirm that mitochondria might be important targets for some PFRs and that differently structured PFRs could function via distinct mechanisms of toxicity.

Clinical effects of chemical exposures on mitochondrial function

Mitochondria are critical for the provision of ATP for cellular energy requirements. Tissue and organ functions are dependent on adequate ATP production, especially when energy demand is high. Mitochondria also play a role in a vast array of important biochemical pathways including apoptosis, generation and detoxification of reactive oxygen species, intracellular calcium regulation, steroid hormone and heme synthesis, and lipid metabolism. The complexity of mitochondrial structure and function facilitates its diverse roles but also enhances its vulnerability. Primary disorders of mitochondrial bioenergetics, or Primary Mitochondrial Diseases (PMD) are due to inherited genetic defects in the nuclear or mitochondrial genomes that result in defective oxidative phosphorylation capacity and cellular energy production. Secondary mitochondrial dysfunction is observed in a wide range of diseases such as Alzheimer's and Parkinson's disease. Several lines of evidence suggest that environmental exposures cause substantial mitochondrial dysfunction. Whereby literature from experimental and human studies on exposures associated with Alzheimer's and Parkinson's diseases exist, the significance of exposures as potential triggers in Primary Mitochondrial Disease (PMD) is an emerging clinical question that has not been systematically studied.

Neurodevelopmental Disorders and Environmental Toxicants: Epigenetics as an Underlying Mechanism

The increasing prevalence of neurodevelopmental disorders, especially autism spectrum disorders (ASD) and attention deficit hyperactivity disorder (ADHD), calls for more research into the identification of etiologic and risk factors. The Developmental Origin of Health and Disease (DOHaD) hypothesizes that the environment during fetal and childhood development affects the risk for many chronic diseases in later stages of life, including neurodevelopmental disorders. Epigenetics, a term describing mechanisms that cause changes in the chromosome state without affecting DNA sequences, is suggested to be the underlying mechanism, according to the DOHaD hypothesis. Moreover, many neurodevelopmental disorders are also related to epigenetic abnormalities. Experimental and epidemiological studies suggest that exposure to prenatal environmental toxicants is associated with neurodevelopmental disorders. In addition, there is also evidence that environmental toxicants can result in epigenetic alterations, notably DNA methylation. In this review, we first focus on the relationship between neurodevelopmental disorders and environmental toxicants, in particular maternal smoking, plastic-derived chemicals (bisphenol A and phthalates), persistent organic pollutants, and heavy metals. We then review studies showing the epigenetic effects of those environmental factors in humans that may affect normal neurodevelopment.