Transcriptional response of rat frontal cortex following acute in vivo exposure to the pyrethroid insecticides permethrin and deltamethrin

Implication of Pyrethroid Neurotoxicity for Human Health: A Lesson from Animal Models

Pyrethroids, synthetic insecticides used in pest management, pose health risks, particularly neurotoxic effects, with studies linking exposure to a neurodegenerative disorder. This review examines the neurotoxic mechanisms of pyrethroids analyzing literature from animal model studies. It identifies critical targets for neurotoxicity, including ion channels, oxidative stress, inflammation, neuronal cell loss, and mitochondrial dysfunction. The review also discusses key therapeutic targets and signaling pathways relevant to Pyrethroids neurotoxicity management, including calcium, Wnt/β-catenin, mTOR, MAPK/Erk, PI3K/Akt, Nrf2, Nurr1, and PPARγ. Our findings demonstrate that pyrethroid exposure triggers multiple neurotoxic pathways that bear resemblance to the mechanisms underlying neurotoxicity. Oxidative stress and inflammation emerge as prominent factors that contribute to neuronal degeneration, alongside disrupted mitochondrial function. The investigation highlights the significance of ion channels as primary neurodegeneration targets while acknowledging the potential involvement of various other receptors and enzymes that may exacerbate neurological damage. Additionally, we elucidate how pyrethroids may interfere with therapeutic targets associated with neuronal dysfunction, potentially impairing treatment efficacy.Also, exposure to these chemicals can alter DNA methylation patterns and histone modifications, ultimately leading to changes in gene expression that may enhance susceptibility to neurological disorders. Pyrethroid neurotoxicity poses a significant public health risk, necessitating future research for protective strategies against pesticide-induced neurological disorders and understanding the interplay between neurodegenerative diseases, potentially leading to innovative therapeutic interventions.

Effects of prenatal pesticide exposure on the fetal brain and placenta transcriptomes in a rodent model

Organophosphate and pyrethroid pesticides are among the most extensively used insecticides worldwide. Prenatal exposures to both classes of pesticides have been linked to a wide range of neurobehavioral deficits in the offspring. The placenta is a neuroendocrine organ and the crucial regulator of the intrauterine environment; early-life toxicant exposures could impact neurobehavior by disrupting placental processes. Female C57BL/6 J mice were exposed via oral gavage to an organophosphate, chlorpyrifos (CPF) at 5 mg/kg, a pyrethroid, deltamethrin (DM), at 3 mg/kg, or vehicle only control (CTL). Exposure began two weeks before breeding and continued every three days until euthanasia at gestational day 17. The transcriptomes of fetal brain (CTL n = 18, CPF n = 6, DM n = 8) and placenta (CTL n = 19, CPF n = 16, DM n = 12) were obtained through RNA sequencing, and resulting data was evaluated using weighted gene co-expression networks, differential expression, and pathway analyses. Fourteen brain gene co-expression modules were identified; CPF exposure disrupted the module related to ribosome and oxidative phosphorylation, whereas DM disrupted the modules related to extracellular matrix and calcium signaling. In the placenta, network analyses revealed 12 gene co-expression modules. While CPF exposure disrupted modules related to endocytosis, Notch and Mapk signaling, DM exposure dysregulated modules linked to spliceosome, lysosome and Mapk signaling pathways. Overall, in both tissues, CPF exposure impacted oxidative phosphorylation, while DM was linked to genes involved in spliceosome and cell cycle. The transcription factor Max involved in cell proliferation was overexpressed by both pesticides in both tissues. In summary, gestational exposure to two different classes of pesticide can induce similar pathway-level transcriptome changes in the placenta and the brain; further studies should investigate if these changes are linked to neurobehavioral impairments.

Neurotoxicity associated with oxidative stress and inflammasome gene expression induced by allethrin in SH-SY5Y cells

Pyrethroids, including allethrin, have largely been used as commercial insecticides. The toxicity of allethrin is little known, but it is assumed that, as occurs with other pyrethroids, it could cause alterations of the nervous system and pose both occupational and non-occupational health hazards. To evaluate the neurotoxicity of allethrin we used the MTT assay of SH-SY5Y neuroblastoma cells to determine cell viability. Dose-dependent reductions of cell viability served to compare the vehicle-group and the IC₅₀ for allethrin, which was 49.19 μM. ROS production increased significantly at concentrations of 10-200 μM of allethrin, and NO levels were significantly increased by the effect of allethrin at a minimum concentration of 50 μM. Lipid peroxidation increased by the effect of allethrin at concentrations of 25, 50, 100, and 200 μM. Caspase 3/7 activity was induced by allethrin concentrations of 50, 100, and 200 μM. Here, we suggest that allethrin might affect the inflammasome complex (Caspase-1, NLRP3, and PYDC1) and apoptosis (Bax and Bcl-2) gene expression by mRNA fold change expression levels shown in Caspase-1 (2.46-fold), NLRP3 (1.57-fold), PYDC1 (1.48-fold), and Bax (2.1-fold). These results demonstrated that allethrin induced neurotoxicity effects on SH-SY5Y cells through activation of inflammasome pathways, cell death, and oxidative stress.

Multigene Biomarkers of Pyrethroid Exposure: Exploratory Experiments

We describe initial development of microarray-based assays for detecting 4 pyrethroid pesticides (bifenthrin, cypermethrin, esfenvalerate, and permethrin) in water. To facilitate comparison of transcriptional responses with gross apical responses, we estimated concentration-mortality curves for these pyrethroids using flow-through exposures of newly hatched Daphnia magna, Pimephales promelas adults, and 24 h posthatch P. promelas. Median lethal concentration (LC50) estimates were below most reported values, perhaps attributable to the use of flow-through exposures or of measured rather than nominal concentrations. Microarray analysis of whole P. promelas larvae and brains from exposed P. promelas adults showed that assays using either tissue type can detect these pyrethroids at concentrations below LC50 values reported for between 72 and 96% of aquatic species, depending on the pesticide. These estimates are conservative because they correspond to the lowest concentrations tested. This suggests that the simpler and less expensive whole-larval assay provides adequate sensitivity for screening contexts where acute aquatic lethality is observed, but the responsible agent is not known. Gene set analysis (GSA) highlighted several Gene Ontology (GO) terms consistent with known pyrethroid action, but the implications of other GO terms are less clear. Exploration of the sensitivity of results to changes in data processing suggests robustness of the detection assay results, but GSA results were sensitive to methodological variations. Environ Toxicol Chem 2019;38:2436-2446. Published 2019 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US government work, and as such, is in the public domain in the United States of America.

Cypermethrin, chlorpyrifos, deltamethrin, and imidacloprid exposure up-regulates the mRNA and protein levels of bdnf and c-fos in the brain of adult zebrafish (Danio rerio)

The aim of the present study is to investigate the toxicity effects of frequently used pesticides, involving cypermethrin, deltamethrin, chlorpyrifos and imidacloprid, on the expression of bdnf and c-fos genes in zebrafish brain tissues. Therefore, brain tissues exposed to intoxication was primarily analyzed by indirect immunofluorescence assay. Afterwards, the mRNA transcription levels of BNDF and c-fos genes and the protein levels were measured by qRT-PCR and Western blotting, respectively. The data of the immunofluorescence assay revealed intensive immunopositivity for bdnf and c-fos genes in the tissues exposed to pesticide intoxication in comparison to the control group (p<0.05). Moreover, the transcription levels of BNDF and c-fos genes, and protein levels were elevated following the intoxication (p<0.05, p<0.01, and p<0.001, respectively). These results showed that the exposure to the acute cypermethrin, deltamethrin, chlorpyrifos and imidacloprid intoxication disrupted the normal neuronal activity, resulting in neurotoxic effect, also DNA-binding Increasing c-fos activation, an oncoprotein from the family of the Nuclear Proteins, is also true of the knowledge that these chemicals are oncogenic in zebrafish brain tissues. Thus, the use of these pesticides poses a potential neuronal and oncogenic risk to the non-target organisms.

Determining Cutoff Point of Ensemble Trees Based on Sample Size in Predicting Clinical Dose with DNA Microarray Data

Background/Aim. Evaluating the success of dose prediction based on genetic or clinical data has substantially advanced recently. The aim of this study is to predict various clinical dose values from DNA gene expression datasets using data mining techniques. Materials and Methods. Eleven real gene expression datasets containing dose values were included. First, important genes for dose prediction were selected using iterative sure independence screening. Then, the performances of regression trees (RTs), support vector regression (SVR), RT bagging, SVR bagging, and RT boosting were examined. Results. The results demonstrated that a regression-based feature selection method substantially reduced the number of irrelevant genes from raw datasets. Overall, the best prediction performance in nine of 11 datasets was achieved using SVR; the second most accurate performance was provided using a gradient-boosting machine (GBM). Conclusion. Analysis of various dose values based on microarray gene expression data identified common genes found in our study and the referenced studies. According to our findings, SVR and GBM can be good predictors of dose-gene datasets. Another result of the study was to identify the sample size of n = 25 as a cutoff point for RT bagging to outperform a single RT.

Comparative neurotoxicity screening in human iPSC-derived neural stem cells, neurons and astrocytes

Induced pluripotent stem cells (iPSC) and their differentiated derivatives offer a unique source of human primary cells for toxicity screens. Here, we report on the comparative cytotoxicity of 80 compounds (neurotoxicants, developmental neurotoxicants, and environmental compounds) in iPSC as well as isogenic iPSC-derived neural stem cells (NSC), neurons, and astrocytes. All compounds were tested over a 24-h period at 10 and 100 μM, in duplicate, with cytotoxicity measured using the MTT assay. Of the 80 compounds tested, 50 induced significant cytotoxicity in at least one cell type; per cell type, 32, 38, 46, and 41 induced significant cytotoxicity in iPSC, NSC, neurons, and astrocytes, respectively. Four compounds (valinomycin, 3,3',5,5'-tetrabromobisphenol, deltamethrin, and triphenyl phosphate) were cytotoxic in all four cell types. Retesting these compounds at 1, 10, and 100 μM using the same exposure protocol yielded consistent results as compared with the primary screen. Using rotenone, we extended the testing to seven additional iPSC lines of both genders; no substantial difference in the extent of cytotoxicity was detected among the cell lines. Finally, the cytotoxicity assay was simplified by measuring luciferase activity using lineage-specific luciferase reporter iPSC lines which were generated from the parental iPSC line. This article is part of a Special Issue entitled SI: PSC and the brain.

Isotonic Regression Based-Method in Quantitative High-Throughput Screenings for Genotoxicity

Quantitative high-throughput screenings (qHTSs) for genotoxicity are conducted as part of comprehensive toxicology screening projects. The most widely used method is to compare the dose-response data of a wild-type and DNA repair gene knockout mutants, using model-fitting to the Hill equation (HE). However, this method performs poorly when the observed viability does not fit the equation well, as frequently happens in qHTS. More capable methods must be developed for qHTS where large data variations are unavoidable. In this study, we applied an isotonic regression (IR) method and compared its performance with HE under multiple data conditions. When dose-response data were suitable to draw HE curves with upper and lower asymptotes and experimental random errors were small, HE was better than IR, but when random errors were big, there was no difference between HE and IR. However, when the drawn curves did not have two asymptotes, IR showed better performance (p < 0.05, exact paired Wilcoxon test) with higher specificity (65% in HE vs. 96% in IR). In summary, IR performed similarly to HE when dose-response data were optimal, whereas IR clearly performed better in suboptimal conditions. These findings indicate that IR would be useful in qHTS for comparing dose-response data.

Parvalbumin and neuropeptide Y expressing hippocampal GABA-ergic inhibitory interneuron numbers decline in a model of Gulf War illness

Cognitive dysfunction is amongst the most conspicuous symptoms in Gulf War illness (GWI). Combined exposure to the nerve gas antidote pyridostigmine bromide (PB), pesticides and stress during the Persian Gulf War-1 (PGW-1) are presumed to be among the major causes of GWI. Indeed, our recent studies in rat models have shown that exposure to GWI-related (GWIR) chemicals and mild stress for 4 weeks engenders cognitive impairments accompanied with several detrimental changes in the hippocampus. In this study, we tested whether reduced numbers of hippocampal gamma-amino butyric acid (GABA)-ergic interneurons are among the pathological changes induced by GWIR-chemicals and stress. Animals were exposed to low doses of GWIR-chemicals and mild stress for 4 weeks. Three months after this exposure, subpopulations of GABA-ergic interneurons expressing the calcium binding protein parvalbumin (PV), the neuropeptide Y (NPY) and somatostatin (SS) in the hippocampus were stereologically quantified. Animals exposed to GWIR-chemicals and stress for 4 weeks displayed reduced numbers of PV-expressing GABA-ergic interneurons in the dentate gyrus and NPY-expressing interneurons in the CA1 and CA3 subfields. However, no changes in SS+ interneuron population were observed in the hippocampus. Furthermore, GABA-ergic interneuron deficiency in these animals was associated with greatly diminished hippocampus neurogenesis. Because PV+ and NPY+ interneurons play roles in maintaining normal cognitive function and neurogenesis, and controlling the activity of excitatory neurons in the hippocampus, reduced numbers of these interneurons may be one of the major causes of cognitive dysfunction and reduced neurogenesis observed in GWI. Hence, strategies that improve inhibitory neurotransmission in the hippocampus may prove beneficial for reversing cognitive dysfunction in GWI.

A pharmacokinetic model of cis- and trans-permethrin disposition in rats and humans with aggregate exposure application

Permethrin is a broad-spectrum pyrethroid insecticide and among the most widely used insecticides in homes and crops. Managing the risks for pesticides such as permethrin depends on the ability to consider diverse exposure scenarios and their relative risks. Physiologically based pharmacokinetic models of delta methrin disposition were modified to describe permethrin kinetics in the rat and human. Unlike formulated deltamethrin which consists of a single stereoisomer, permethrin is formulated as a blend of cis- and trans-diastereomers. We assessed time courses for cis-permethrin and trans-permethrin in several tissues (brain, blood, liver, and fat) in the rat following oral administration of 1 and 10mg/kg permethrin (cis/trans: 40/60). Accurate simulation of permethrin in the rat suggests that a generic model structure is promising for modeling pyrethroids. Human in vitro data and appropriate anatomical information were used to develop a provisional model of permethrin disposition with structures for managing oral, dermal, and inhalation routes of exposure. The human permethrin model was used to evaluate dietary and residential exposures in the U.S. population as estimated by EPA's Stochastic Human Exposure and Dose Simulation model. Simulated cis- and trans-DCCA, metabolites of permethrin, were consistent with measured values in the National Health and Nutrition Examination Survey, indicating that the model holds promise for assessing population exposures and quantifying dose metrics.

Mechanisms of pyrethroid insecticide-induced stimulation of calcium influx in neocortical neurons

Pyrethroid insecticides bind to voltage-gated sodium channels (VGSCs) and modify their gating kinetics, thereby disrupting neuronal function. Pyrethroids have also been reported to alter the function of other channel types, including activation of voltage-gated calcium channels. Therefore, the present study compared the ability of 11 structurally diverse pyrethroids to evoke Ca(2+) influx in primary cultures of mouse neocortical neurons. Nine pyrethroids (tefluthrin, deltamethrin, λ-cyhalothrin, β-cyfluthrin, esfenvalerate, S-bioallethrin, fenpropathrin, cypermethrin, and bifenthrin) produced concentration-dependent elevations in intracellular calcium concentration ([Ca(2+)](i)) in neocortical neurons. Permethrin and resmethrin were without effect on [Ca(2+)](i). These pyrethroids displayed a range of efficacies on Ca(2+) influx; however, the EC(50) values for active pyrethroids all were within one order of magnitude. Tetrodotoxin blocked increases in [Ca(2+)](i) caused by all nine active pyrethroids, indicating that the effects depended on VGSC activation. The pathways for deltamethrin- and tefluthrin-induced Ca(2+) influx include N-methyl-D-aspartic acid receptors, L-type Ca(2+) channels, and reverse mode of operation of the Na(+)/Ca(2+) exchanger inasmuch as antagonists of these sites blocked deltamethrin-induced Ca(2+) influx. These data demonstrate that pyrethroids stimulate Ca(2+) entry into neurons subsequent to their actions on VGSCs.

Macrophage inhibitory cytokine-1 (MIC-1/GDF15): a new marker of all-cause mortality

Macrophage inhibitory cytokine-1 (MIC-1/GDF15) is a member of the TGF-b superfamily, previously studied in cancer and inflammation. In addition to regulating body weight, MIC-1/GDF15 may be used to predict mortality and/or disease course in cancer, cardiovascular disease (CVD), chronic renal and heart failure, as well as pulmonary embolism. These data suggested that MIC-1/GDF15 may be a marker of all-cause mortality. To determine whether serum MIC-1/GDF15 estimation is a predictor of all-cause mortality, we examined a cohort of 876 male subjects aged 35-80 years, selected from the Swedish Population Registry, and followed them for overall mortality. Serum MIC-1/GDF15 levels were determined for all subjects from samples taken at study entry. A second (independent) cohort of 324 same-sex twins (69% female) from the Swedish Twin Registry was similarly examined. All the twins had telomere length measured and 183 had serum levels of interleukin 6 (IL-6) and C-reactive protein (CRP) available. Patients were followed for up to 14 years and had cause-specific and all-cause mortality determined. Serum MIC-1/GDF15 levels predicted mortality in the all-male cohort with an adjusted odds ratio (OR) of death of 3.38 (95%CI 1.38-8.26). This finding was validated in the twin cohort. Serum MIC-1/GDF15 remained an independent predictor of mortality when further adjusted for telomere length, IL-6 and CRP. Additionally, serum MIC-1/GDF15 levels were directly correlated with survival time independently of genetic background. Serum MIC-1/GDF15 is a novel predictor of all-cause mortality.

Uncovering molecular biomarkers that correlate cognitive decline with the changes of hippocampus' gene expression profiles in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is characterized by a neurodegenerative progression that alters cognition. On a phenotypical level, cognition is evaluated by means of the MiniMental State Examination (MMSE) and the post-mortem examination of Neurofibrillary Tangle count (NFT) helps to confirm an AD diagnostic. The MMSE evaluates different aspects of cognition including orientation, short-term memory (retention and recall), attention and language. As there is a normal cognitive decline with aging, and death is the final state on which NFT can be counted, the identification of brain gene expression biomarkers from these phenotypical measures has been elusive.

METHODOLOGY/PRINCIPAL FINDINGS

We have reanalysed a microarray dataset contributed in 2004 by Blalock et al. of 31 samples corresponding to hippocampus gene expression from 22 AD subjects of varying degree of severity and 9 controls. Instead of only relying on correlations of gene expression with the associated MMSE and NFT measures, and by using modern bioinformatics methods based on information theory and combinatorial optimization, we uncovered a 1,372-probe gene expression signature that presents a high-consensus with established markers of progression in AD. The signature reveals alterations in calcium, insulin, phosphatidylinositol and wnt-signalling. Among the most correlated gene probes with AD severity we found those linked to synaptic function, neurofilament bundle assembly and neuronal plasticity.

CONCLUSIONS/SIGNIFICANCE

A transcription factors analysis of 1,372-probe signature reveals significant associations with the EGR/KROX family of proteins, MAZ, and E2F1. The gene homologous of EGR1, zif268, Egr-1 or Zenk, together with other members of the EGR family, are consolidating a key role in the neuronal plasticity in the brain. These results indicate a degree of commonality between putative genes involved in AD and prion-induced neurodegenerative processes that warrants further investigation.

Splice variant specific increase in Ca2+/calmodulin-dependent protein kinase 1-gamma mRNA expression in response to acute pyrethroid exposure

In mammals, pyrethroids are neurotoxicants that interfere with ion channel function in excitable neuronal membranes. Previous work demonstrated increases in the expression of Ca(2+)/calmodulin-dependent protein kinase 1-gamma (Camk1g) mRNA following acute deltamethrin and permethrin exposure. In the rat, this gene is expressed as two distinct splice variants, Camk1g1 and Camk1g2. The present study tests the hypothesis that changes in Camk1g mRNA expression in the rat following acute pyrethroid exposure are due to a specific increase in the Camk1g1 splice variant and not the Camk1g2 splice variant. Long-Evans rats were acutely exposed to permethrin, deltamethrin, or corn oil vehicle. Frontal cortex was collected at 6 h postdosing. In addition, rats were exposed to permethrin (100 mg/kg) or deltamethrin (3 mg/kg), and frontal cortex was collected at 1, 3, 6, 9, 12, or 24 h along with time-matched vehicle controls. Expression of Camk1g1 and Camk1g2 mRNA was measured by quantitative real-time RT-PCR and quantified using the 2(-Delta Delta C)T method. Dose-dependent increases in Camk1g1 mRNA expression were observed for both pyrethroids at 6 h. In addition, a dose-dependent increase in Camk1g2 was observed at 6 h although it was very small in magnitude. The increases in Camk1g1 expression for deltamethrin and permethrin peak between 3 and 6 h postexposure and returns to control levels by 9 h. There was no increase in CAMK1G1 protein as measured with Western blots. The present data demonstrate that pyrethroid-induced changes in Camk1g are driven mainly by increased expression of the Camk1g1 splice variant.