Repeated exposures to subthreshold doses of chlorpyrifos in rats: hippocampal damage, impaired axonal transport, and deficits in spatial learning

Chronic sub lethal nerve agent (Soman) exposure induced long-term neurobehavioral, histological, and biochemical alterations in rats

Organophosphorus (OP) pesticides and insecticides are used in agriculture and other industries can also cause adverse effects through environmental exposures in the people working in agricultural and pesticide industries. OP nerve agent exposures have been associated with delayed neurotoxic effects including sleep disorders, cognitive malfunctions, and brain damage in Gulf War victims, and Japanese victims of terrorist attacks with nerve agents. However, the mechanisms behind such prolonged adverse effects after chronic OP nerve agent's exposures in survivors are not well understood. In the present study, male Wistar rats were subcutaneously exposed to nerve agent soman (0.25XLD50) for 21 consecutive days to evaluate the neurobehavioral, neuropathological and biochemical alterations (oxidative stress and antioxidants levels). Neurobehavioral studies using Elevated Plus Maze (EPM), T-Maze, and rotarod tests revealed that chronic soman exposure produced alterations in behavioral functions including increased anxiety and reduction in working memory and neuromuscular strength. Biochemical studies showed that antioxidants enzyme (glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase (SOD) levels were reduced and oxidative stress (reduced glutathione (GSH) and lipid peroxidation levels (malondialdehyde (MDA)) were significantly increased in brain at 30 days in soman exposed rats as compared to control rats. Neuroselective fluorojade-c stain was used to examine the brain damage after chronic soman exposure. Results demonstrated that chronic soman exposure induced neurodegeneration as brain damage was detected at 30- and 90-days post exposure. The present study results suggest that chronic nerve agent exposures even at low doses may produce long-term adverse effects like neurobehavioral deficits in rats.

Dysregulation of stress granule dynamics by DCTN1 deficiency exacerbates TDP-43 pathology in Drosophila models of ALS/FTD

The abnormal aggregation of TDP-43 into cytoplasmic inclusions in affected neurons is a major pathological hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Although TDP-43 is aberrantly accumulated in the neurons of most patients with sporadic ALS/FTD and other TDP-43 proteinopathies, how TDP-43 forms cytoplasmic aggregates remains unknown. In this study, we show that a deficiency in DCTN1, a subunit of the microtubule-associated motor protein complex dynactin, perturbs the dynamics of stress granules and drives the formation of TDP-43 cytoplasmic aggregation in cultured cells, leading to the exacerbation of TDP-43 pathology and neurodegeneration in vivo. We demonstrated using a Drosophila model of ALS/FTD that genetic knockdown of DCTN1 accelerates the formation of ubiquitin-positive cytoplasmic inclusions of TDP-43. Knockdown of components of other microtubule-associated motor protein complexes, including dynein and kinesin, also increased the formation of TDP-43 inclusions, indicating that intracellular transport along microtubules plays a key role in TDP-43 pathology. Notably, DCTN1 knockdown delayed the disassembly of stress granules in stressed cells, leading to an increase in the formation of pathological cytoplasmic inclusions of TDP-43. Our results indicate that a deficiency in DCTN1, as well as disruption of intracellular transport along microtubules, is a modifier that drives the formation of TDP-43 pathology through the dysregulation of stress granule dynamics.

Gulf War toxicant-induced reductions in dendritic arbors and spine densities of dentate granule cells are improved by treatment with a Nrf2 activator

Gulf War Illness (GWI) is a chronic multi-symptom disorder affecting approximately 30 % of Veterans deployed to the Persian Gulf from 1990 to 91. GWI encompasses a wide spectrum of symptoms which frequently include neurological problems such as learning and memory impairments, mood disorders, and an increased incidence of neurodegenerative disorders. Combined exposure to both reversible and irreversible acetylcholinesterase (AChE) inhibitors has been identified as a likely risk factor for GWI. It is possible that the exposures affected connectivity in the brain, and it was also unknown whether this could benefit from treatment. We assessed chronic changes in dendritic architecture in granule cells of the dentate gyrus following exposure to pyridostigmine bromide (PB, 0.7 mg/kg), chlorpyrifos (CPF, 12.5 mg/kg), and N,N-diethyl-m-toluamide (DEET, 7.5 mg/kg) in male C57Bl/6J mice. We also evaluated the therapeutic effects of dietary administration for eight weeks of 1 % tert-butylhydroquinone (tBHQ), a Nrf2 activator, on long-term neuronal morphology. We found that Gulf War toxicant exposure resulted in reduced dendritic length and branching as well as overall spine density in dentate granule cells at 14 weeks post-exposure and that these effects were ameliorated by treatment with tBHQ. These findings indicate that Gulf War toxicant exposure results in chronic changes to dentate granule cell morphology and that modulation of neuroprotective transcription factors such as Nrf2 may improve long-term neuronal health in the hippocampus.

Is Gulf War Illness a prolonged early phase tauopathy?

The work of the Gulf War Illness (GWI) Consortium and that of basic and clinical researchers across the USA have resulted in a better understanding in recent years of the pathological basis of GWI, as well as of the mechanisms underlying the disorder. Among the most concerning symptoms suffered by veterans with GWI are cognitive decrements including those related to memory functioning. These decrements are not severe enough to meet dementia criteria, but there is significant concern that the mild cognitive impairment of these veterans will progress to dementia as they become older. Recent studies on GWI using human brain organoids as well as a rat model suggest that one potential cause of the cognitive problems may be elevated levels of tau in the brain, and this is supported by high levels of tau autoantibodies in the blood of veterans with GWI. There is urgency in finding treatments and preventive strategies for these veterans before they progress to dementia, with added value in doing so because their current status may represent an early phase of tauopathy common to many neurodegenerative diseases.

Prenatal and Childhood Exposure to Organophosphate Pesticides and Behavior Problems in Adolescents and Young Adults in the CHAMACOS Study

BACKGROUND

We previously reported associations of prenatal exposure to organophosphate (OP) pesticides with poorer neurodevelopment in early childhood and at school age, including poorer cognitive function and more behavioral problems, in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS), a birth cohort study in an agriculture community.

OBJECTIVE

We investigated the extent to which early-life exposure to OP pesticides is associated with behavioral problems, including mental health, in youth during adolescence and early adulthood.

METHODS

We measured urinary dialkylphosphates (DAPs), nonspecific OP metabolites, in urine samples collected from mothers twice during pregnancy (13 and 26 wk) and at five different times in their children (ages 6 months to 5 y). We assessed maternal report and youth report of externalizing and internalizing behavior problems using the Behavior Assessment System for Children, 2nd edition (BASC-2), when the youth were ages 14, 16, and 18 y. Because there was evidence of nonlinearity, we estimated associations across quartiles of DAPs and modeled repeated outcome measures using generalized estimating equations.

RESULTS

There were 335 youths with prenatal maternal DAP measures and 14-. 16-, or 18-y BASC-2 scores. Prenatal maternal DAP concentrations (specific gravity-adjusted median, Q 1 - Q 3 = 159.4 , 78.7 - 350.4  nmol / L ) were associated with higher T-scores (more behavior problems) from maternal report, including more hyperactivity [fourth vs. first quartile of exposure β = 2.32 ; 95% confidence interval (CI): 0.18, 4.45], aggression (β = 1.90 ; 95% CI: 0.15, 3.66), attention problems (β = 2.78 ; 95% CI: 0.26, 5.30), and depression (β = 2.66 ; 95% CI: 0.08, 5.24). Associations with youth report of externalizing problems were null, and associations with depression were suggestive (fourth vs. first quartile of exposure β = 2.15 ; 95% CI: - 0.36 , 4.67). Childhood DAP metabolites were not associated with behavioral problems.

DISCUSSION

We found associations of prenatal, but not childhood, urinary DAP concentrations with adolescent/young adult externalizing and internalizing behavior problems. These findings are consistent with prior associations we have reported with neurodevelopmental outcomes measured earlier in childhood in CHAMACOS participants and suggests that prenatal exposure to OP pesticides may have lasting effects on the behavioral health of youth as they mature into adulthood, including their mental health. https://doi.org/10.1289/EHP11380.

Gestational Exposure to Organophosphate Pesticides and Longitudinally Assessed Behaviors Related to Attention-Deficit/Hyperactivity Disorder and Executive Function

The brain’s prefrontal cortex directs higher-order cognitive and behavioral processes that are important for attention, working memory, and inhibitory control. We investigated whether gestational exposure to organophosphate (OP) pesticides was associated with these abilities in childhood and early adolescence. Between 1999 and 2000, we enrolled pregnant women in a birth cohort drawn from an agricultural region of California. We measured dialkyl phosphate (DAP) metabolites of OP pesticides in maternal pregnancy urine samples (13 and 26 weeks) and estimated associations with behaviors related to attention-deficit/hyperactivity disorder and executive function, assessed longitudinally; 351 families provided neurodevelopmental outcome data at any point when the child was aged 7–12 years. We assessed function across multiple dimensions (e.g., working memory, attention), methods (e.g., behavior reports, child assessment), and reporters (e.g., mothers, teachers, child self-reports). Higher gestational DAP concentrations were consistently associated with behaviors related to attention-deficit/hyperactivity disorder and executive function. For example, a 10-fold increase in gestational DAP concentration was associated with poorer longitudinally assessed Behavior Rating Inventory of Executive Function scores, as reported by mothers (β = 4.0 (95% confidence interval: 2.1, 5.8); a higher score indicates more problems), and Weschler Intelligence Scale for Children—Fourth Edition Working Memory scores (a 3.8-point reduction; β = −3.8 (95% confidence interval: −6.2, −1.3)). Reducing gestational exposure to OP pesticides through public health policy is an important goal.

Acute gene expression changes in the mouse hippocampus following a combined Gulf War toxicant exposure

AIMS

Approximately 30% of the nearly 700,000 Veterans who were deployed to the Gulf War from 1990 to 1991 have reported experiencing a variety of symptoms including difficulties with learning and memory, depression and anxiety, and increased incidence of neurodegenerative diseases. Combined toxicant exposure to acetylcholinesterase (AChE) inhibitors has been studied extensively as a likely risk factor. In this study, we modeled Gulf War exposure in male C57Bl/6J mice with simultaneous administration of three chemicals implicated as exposure hazards for Gulf War Veterans: pyridostigmine bromide, the anti-sarin prophylactic; chlorpyrifos, an organophosphate insecticide; and the repellant N,N-diethyl-m-toluamide (DEET).

MAIN METHODS

Following two weeks of daily exposure, we examined changes in gene expression by whole transcriptome sequencing (RNA-Seq) with hippocampal isolates. Hippocampal-associated spatial memory was assessed with a Y-maze task. We hypothesized that genes important for neuronal health become dysregulated by toxicant-induced damage and that these detrimental inflammatory gene expression profiles could lead to chronic neurodegeneration.

KEY FINDINGS

We found dysregulation of genes indicating a pro-inflammatory response and downregulation of genes associated with neuronal health and several important immediate early genes (IEGs), including Arc and Egr1, which were both reduced approximately 1.5-fold. Mice exposed to PB + CPF + DEET displayed a 1.6-fold reduction in preference for the novel arm, indicating impaired spatial memory.

SIGNIFICANCE

Differentially expressed genes observed at an acute timepoint may provide insight into the pathophysiology of Gulf War Illness and further explanations for chronic neurodegeneration after toxicant exposure.

The cytoskeleton as a non-cholinergic target of organophosphate compounds

Current organophosphate (OP) toxicity research now considers potential non-cholinergic mechanisms for these compounds, since the inhibition of acetylcholinesterase (AChE) cannot completely explain all the adverse biological effects of OP. Thanks to the development of new strategies for OP detection, some potential molecular targets have been identified. Among these molecules are several cytoskeletal proteins, including actin, tubulin, intermediate filament proteins, and associated proteins, such as motor proteins, microtubule-associated proteins (MAPs), and cofilin. in vitro, ex vivo, and some in vivo reports have identified alterations in the cytoskeleton following OP exposure, including cell morphology defects, cells detachments, intracellular transport disruption, aberrant mitotic spindle formation, modification of cell motility, and reduced phagocytic capability, which implicate the cytoskeleton in OP toxicity. Here, we reviewed the evidence indicating the cytoskeletal targets of OP compounds, including their strategies, the potential effects of their alterations, and their possible participation in neurotoxicity, embryonic development, cell division, and immunotoxicity related to OP compounds exposure.

Chlorpyrifos induces cell proliferation in MCF-7 and MDA-MB-231 cells, through cholinergic and Wnt/β-catenin signaling disruption, AChE-R upregulation and oxidative stress generation after single and repeated treatment

Chlorpyrifos (CPF) biocide, is associated with breast cancer. The processes underlying this association have not been elucidated to date. CPF increases MCF-7 and MDA-MB-231 cell proliferation after acute and long-term treatment, partially through KIAA1363 overexpression and aryl-hydrocarbon receptor activation but also through estrogen receptor-alpha activation after 24 h exposure in MCF-7 cells, suggesting other mechanisms may be involved. CPF induces reactive oxygen species (ROS) generation, acetylcholine accumulation, and overexpression of acetylcholinesterase-R/S (AChE-R/S) variants, while it also alters the Wnt/β-catenin pathway, both in vitro and in vivo, in processes different from cancer. These latter mechanisms are also linked to cell proliferation and could mediate this effect induced by CPF. Our results show that CPF (0.01-100 μM), following one-day and fourteen-days treatment, respectively, induced ROS generation and lipid peroxidation, and acetylcholine accumulation due to AChE inhibition, Wnt/β-catenin up- or downregulation depending on the CPF treatment concentration, and AChE-R and AChE-S overexpression, with the latter being mediated through GSK-3β activity alteration. Finally, CPF promoted cell division through ACh and ROS accumulation, AChE-R overexpression, and Wnt/β-catenin signaling disruption. Our results provide novel information on the effect of CPF on human breast cancer cell lines that may help to explain its involvement in breast cancer.

Neuroprotective and Neurorescue Mode of Action of Bacopa monnieri (L.) Wettst in 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-Induced Parkinson's Disease: An In Silico and In Vivo Study

Ethnopharmacological Relevance: Parkinson's disease (PD) is characterized by progressive death of dopaminergic neurons. The presently used medicines only tackle the symptoms of PD, but none makes a dent on the processes that underpin the disease's development. Herbal medicines have attracted considerable attention in recent years. Bacopa monnieri (L.) Wettst (Brahmi) has been used in Indian Ayurvedic medicine to enhance memory and intelligence. Herein, we assessed the neuroprotective role of Bacopa monnieri (L.) Wettst on Parkinson's disease. Aim of the Study: Bacopa monnieri (L.) Wettst, a medicinal herb, is widely used as a brain tonic. We investigated the neuroprotective and neurorescue properties of Bacopa monnieri (L.) Wettst extract (BME) in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mice model of PD. Materials and Methods: The mice model of MPTP-induced PD is used in the study. In the neuroprotective (BME + MPTP) and neurorescue (MPTP + BME) experiments, the animals were administered 40 mg/kg body weight BME orally before and after MPTP administration, respectively. Effect of BME treatment was evaluated by accessing neurobehavioral parameters and levels of dopamine, glutathione, lipid peroxide, and nitrites. An in silico study was performed using AutoDock Tools 1.5.6 (ADT). Results: A significant recovery in behavioral parameters, dopamine level, glutathione level, lipid peroxides, and nitrite level was observed in BME-treated mice. Treatment with BME before or after MPTP administration has a protective effect on dopaminergic neurons, as evidenced by a significant decrease in GFAP immunostaining and expression of inducible nitric oxide synthase (iNOS) in the substantia nigra region; however, the degree of improvement was more prominent in mice receiving BME treatment before MPTP administration. Moreover, the in silico study revealed that the constituents of BM, including bacosides, bacopasides, and bacosaponins, can inactivate the enzyme monoamine oxidase B, thus preventing the breakdown of MPTP to MPP+. Conclusion: Our results showed that BME exerts both neuroprotective and neurorescue effects against MPTP-induced degeneration of the nigrostriatal dopaminergic neurons. Moreover, BME may slow down the disease progression and delay the onset of neurodegeneration in PD.

Gestational exposures to organophosphorus insecticides: From acute poisoning to developmental neurotoxicity

For over three-quarters of a century, organophosphorus (OP) insecticides have been ubiquitously used in agricultural, residential, and commercial settings and in public health programs to mitigate insect-borne diseases. Their broad-spectrum insecticidal effectiveness is accounted for by the irreversible inhibition of acetylcholinesterase (AChE), the enzyme that catalyzes acetylcholine (ACh) hydrolysis, in the nervous system of insects. However, because AChE is evolutionarily conserved, OP insecticides are also toxic to mammals, including humans, and acute OP intoxication remains a major public health concern in countries where OP insecticide usage is poorly regulated. Environmental exposures to OP levels that are generally too low to cause marked inhibition of AChE and to trigger acute signs of intoxication, on the other hand, represent an insidious public health issue worldwide. Gestational exposures to OP insecticides are particularly concerning because of the exquisite sensitivity of the developing brain to these insecticides. The present article overviews and discusses: (i) the health effects and therapeutic management of acute OP poisoning during pregnancy, (ii) epidemiological studies examining associations between environmental OP exposures during gestation and health outcomes of offspring, (iii) preclinical evidence that OP insecticides are developmental neurotoxicants, and (iv) potential mechanisms underlying the developmental neurotoxicity of OP insecticides. Understanding how gestational exposures to different levels of OP insecticides affect pregnancy and childhood development is critical to guiding implementation of preventive measures and direct research aimed at identifying effective therapeutic interventions that can limit the negative impact of these exposures on public health.

Protective effect of fisetin against subchronic chlorpyrifos-induced toxicity on oxidative stress biomarkers and neurobehavioral parameters in adult male albino mice

Chlorpyrifos (CPF), a chlorinated organophosphate insecticide that is widely used in agriculture and public health, has neurotoxic effects in animals. In addition to acetylcholinesterase inhibition, CPF has been shown to induce alterations such as oxidative stress and lipid peroxidation. Fisetin is a dietary flavonol that protects the brain tissue against oxidative stress by modulating the activity of antioxidant enzymes. This study was designed to investigate the protective role of fisetin against brain oxidative damages and neurobehavioral parameters induced by subchronic oral exposure to CPF in albino mice. Adult albino mice (males, n = 32, weighing 20 ~ 25 g) were assigned randomly into 4 groups and treated accordingly for 7 weeks as follows: Group 1(S/OIL): served as the control group and were given 2 ml/kg of soya oil; Group 2 (CPF): received CPF (6.6 mg/kg; 1/5th of the LD₅₀); Group 3 (FIS): fisetin (15 mg/kg) and Group 4 (FIS + CPF): received fisetin at 15 mg/kg, followed by CPF (6.6 mg/kg) 30 min later. Co-treatment with FIS + CPF mitigated the increase in brain malondialdehyde concentration (0.28 ± 0.02 nmol/mg) and orchestrated the increase in the activities of catalase (81.35 ± 7.26 µ/mg), superoxide dismutase (93.03 ± 6.63 IU/mL), glutathione peroxidase (68.76 ± 3.554 nmol/mL) and acetylcholinesterase (11.59 ± 0.72 nmol/min/mL) when compared to the CPF group. The result showed that deficits in motor strength and excitability scores induced by subchronic CPF were mitigated by fisetin administration. It was concluded that fisetin has a protective potential in mitigating against oxidative stress and damages in the brain tissues, induced by subchronic exposure to CPF in adult male albino mice.

Protective Effects of Pelargonium graveolens Essential Oil on Methomyl-Induced Oxidative Stress and Spatial Working Memory Impairment in Association with Histopathological Changes in the Hippocampus of Male Wistar Rats

INTRODUCTION

Methomyl (MET) is a carbamate insecticide, used in agriculture and public health to eliminate harmful insects. Besides its advantages in agriculture, it causes neurotoxic effects. The aim of this study was to evaluate the effect of MET on Spatial Working Memory (SWM), oxidative stress parameters, and histopathological changes in the hippocampus, as well as the possible protective role of Pelargonium graveolens Essential Oil (EO).

METHODS

Male Wistar rats were randomized into four groups of six animals: group I as the control that received the vehicle; group II received EO (75 mg/kg b.w), group III received MET (2 mg/kg b.w); and group IV received both MET and EO. The rats were administered the respective doses orally by gavage for 28 days. SWM was assessed using Y-maze on the day before the first treatment and day 28 after the last dose. They were sacrificed by decapitation and their brains were taken for assessing oxidative stress parameters and histopathological analysis.

RESULTS

MET treatment caused SWM deficits. Furthermore, drastic changes were observed in aspartate transaminase, alanine aminotransferase, and alkaline phosphatase activities. The level of malondialdehyde significantly increased, whereas antioxidant (glutathioneS-transferase and catalase) enzyme activities significantly decreased. The CA1 region of the hippocampus of rats exposed to MET revealed severe histological alterations. However, supplementation with EO improved SWM and partially restored the activities of antioxidant systems and prevented neuronal cell damage.

CONCLUSION

P. graveolens EO has the potential in mitigating most of the adverse effects in the hippocampus and prevents SWM impairment induced by MET toxicity.

Chlorpyrifos-induced cell proliferation in human breast cancer cell lines differentially mediated by estrogen and aryl hydrocarbon receptors and KIAA1363 enzyme after 24 h and 14 days exposure

Organophosphate biocide chlorpyrifos (CPF) is involved with breast cancer. However, the mechanisms remain unknown. CPF increases cell division in MCF-7 cells, by estrogen receptor alpha (ERα) activation, although it is a weak ERα agonist, suggesting other mechanisms should be involved. Aromatic hydrocarbon receptor (AhR) activation increases cell division in human breast cancer cells, and CPF strongly activates it. Finally, the KIAA1363 enzyme, which is regulated by CPF, is overexpressed in cancer cells. Accordingly, we hypothesized that CPF or its metabolite chlorpyrifos-oxon (CPFO) could induce cell viability promotion in MCF-7 and MDA-MB-231 cell lines, through mechanisms related to ERα, AhR, and KIAA1363, after 24 h and 14 days treatment. Results show that, after acute and long-term treatment, CPF and CPFO alter differently KIAA1363, AhR, ER and cytochrome P450 isoenzyme 1A1 (CYP1A1) expression. In addition, they induced cell proliferation through ERα activation after 24 h exposure in MCF-7 cells and through KIAA1363 overexpression and AhR activation in MCF-7 and MDA-MB-231 cells after acute and long-term treatment. The results obtained in this work provide new information relative to the mechanisms involved in the CPF toxic effects that could lead to breast cancer disease.

Commercial Formulation of Chlorpyrifos Alters Neurological Behaviors and Fertility

Pesticides are known to result in toxic insult. We aimed to evaluate Judo 40, the commercial formulation of chlorpyrifos on the neurological activities, fertility, and hormone levels of male rats. Male Wistar rats were treated orally with 1 mL of 20 or 50 mg/kg Judo 40. The doses were administered four times, twice a day. Sexual and exploratory behavior indices, fertility indices, serum androgen levels, blood acetylcholinesterase (BChE) levels, and neurological and muscular effects were evaluated. Serum testosterone and luteinizing hormone were significantly reduced in the rats receiving 50 mg/kg Judo 40. A reduction in viable implantation sites and live pups born were evident in the female rats mated with the male rats treated with the highest dose. Similarly, in the rats treated with the highest dose of Judo 40, a significant reduction in plasma BChE enzyme was observed. According to the results, prolonged Judo 40 exposure can cause impairment of the neurological alterations and sex hormones leading to impaired fertility. Therefore, chemical handlers should be educated on protection and risk minimization.

Pesticides, cognitive functions and dementia: A review

Pesticides are widely-used chemicals commonly applied in agriculture for the protection of crops from pests. Depending on the class of pesticides, the specific substances may have a specific set of adverse effects on humans, especially in cases of acute poisoning. In past years, evidence regarding sequelae of chronic, low-level exposure has been accumulating. Cognitive impairment and dementia heavily affect a person's quality of life and scientific data has been hinting towards an association between them and antecedent chronic pesticide exposure. Here, we reviewed animal and human studies exploring the association between pesticide exposure, cognition and dementia. Additionally, we present potential mechanisms through which pesticides may act neurotoxically and lead to neurodegeneration. Study designs rarely presented homogeneity and the estimation of the exposure to pesticides has been most frequently performed without measuring the synergic effects and the possible interactions between the toxicants within mixtures, and also overlooking low exposures to environmental toxicants. It is possible that a Real-Life Risk Simulation approach would represent a robust alternative for future studies, so that the safe exposure limits and the net risk that pesticides confer to impaired cognitive function can be examined. Previous studies that evaluated the effect of low dose chronic exposure to mixtures of pesticides and other chemicals intending to simulate real life exposure scenarios showed that hormetic neurobehavioral effects can appear after mixture exposure at doses considered safe for individual compounds and these effects can be exacerbated by a coexistence with specific conditions such as vitamin deficiency. However, there is an overall indication, derived from both epidemiologic and laboratory evidence, supporting an association between exposure to neurotoxic pesticides and cognitive dysfunction, dementia and Alzheimer's disease.

Proteasome 20S and Rab5 Alteration after 24 h and 14 Days Chlorpyrifos Exposure Lead to β-Amyloid and Tau Protein Level Increases and SN56 Neuronal Cell Death

The biocide chlorpyrifos (CPF) was shown to produce cognition impairment following single and long-term exposure. The complete mechanisms that lead to the CPF induced cognitive disorders remain to be discovered. Aβ and tau proteins production was induced in basal forebrain SN56 cholinergic cells, by CPF, through proteasome 20S inhibition and Rab5 overexpression, leading to cell death both after acute and repeated administration, which was related with cognitive disorders induction. The results obtained in our study procure novel information related to the mechanisms involved in CPF neurodegeneration, which could be responsible for cognitive dysfunction and may lead to a promising alternative treatment of these effects.

Impacts of prolonged chlorpyrifos exposure on locomotion and slow-and fast- twitch skeletal muscles contractility in rats

AIM

Investigate the effect of dietary exposure to chlorpyrifos on locomotion and contraction of soleus andextensor digitorum longus (edl) involved in locomotion. Methods: Rats were fed diets containing 1 or 5 mg kg-1 of chlorpyrifos for six weeks. Locomotion has been assessed weekly using beam walking and beam balance tests. Soleus and edl were removed to study contractile properties, myofibrillar protein content and myosin heavy chain isoforms.

RESULTS

Animals treated with 5 mg kg-1 chlorpyrifos had a decrease body weight. An increase by 28% and 24% in latency time assessed by beam walking test and a decrease by 9% and 13% in the beam balance time was reported after 6 weeks of 1 and 5 chlorpyrifos exposure respectively. The contractile properties in soleus showed an increase in twitch amplitude by 25% and 63% in 1 and 5 doses respectively, without modification in the contraction time and half relaxation time. edl treated with 1 mg kg-1 showed a decrease by 35%, 42% and 22% in twitch amplitude, contraction time and half relaxation time respectively. edl treated with 5 mg kg-1 showed an increase of 23% in twitch amplitude without modification of the other parameters. These changes were associated with modification of myofibrillar protein content in all treated groups. Myosin heavy chain isoforms were altered in both skeletal muscles treated with 1 mg kg-1.

CONCLUSION

Exposure to chlorpyrifos can alter the locomotion and produce physiological changes in a dose and muscle type related manner.

Arsenic-Induced Neurotoxicity by Dysfunctioning Cholinergic and Dopaminergic System in Brain of Developing Rats

Chronic exposure to arsenic via drinking water throughout the globe is assumed to cause a developmental neurotoxicity. Here, we investigated the effect of perinatal arsenic exposure on the neurobehavioral and neurochemical changes in the corpus striatum, frontal cortex, and hippocampus that is critically involved in motor and cognition functions. In continuation of previous studies, this study demonstrates that perinatal exposures (GD6-PD21) to arsenic (2 or 4 mg/kg body weight, p.o.) cause hypo-activity in arsenic-exposed rats on PD22. The hypo-activity was found to be linked with a decrease in the mRNA and protein expression of the DA-D2 receptor. Further, a protein expression of tyrosine hydroxylase (TH), levels of dopamine, and its metabolites were also significantly impaired in corpus striatum. The arsenic-exposed groups showed spatial learning and memory significantly below the average in a dose-dependent manner for the controls. Here, we evaluated the declined expression of CHRM2 receptor gene and protein expression of ChAT, PKCβ-1 in the frontal cortex and hippocampus, which are critically involved in cognition functions including learning and memory. A trend of recovery was found in the cholinergic and dopaminergic system of the brain, but changes remained persisted even after the withdrawal of arsenic exposure on PD45. Taken together, our results indicate that perinatal arsenic exposure appears to be critical and vulnerable as the development of cholinergic and dopaminergic system continues during this period.

Neurotoxicity in acute and repeated organophosphate exposure

The term organophosphate (OP) refers to a diverse group of chemicals that are found in hundreds of products worldwide. As pesticides, their most common use, OPs are clearly beneficial for agricultural productivity and the control of deadly vector-borne illnesses. However, as a consequence of their widespread use, OPs are now among the most common synthetic chemicals detected in the environment as well as in animal and human tissues. This is an increasing environmental concern because many OPs are highly toxic and both accidental and intentional exposures to OPs resulting in deleterious health effects have been documented for decades. Some of these deleterious health effects include a variety of long-term neurological and psychiatric disturbances including impairments in attention, memory, and other domains of cognition. Moreover, some chronic illnesses that manifest these symptoms such as Gulf War Illness and Aerotoxic Syndrome have (at least in part) been attributed to OP exposure. In addition to acute acetylcholinesterase inhibition, OPs may affect a number of additional targets that lead to oxidative stress, axonal transport deficits, neuroinflammation, and autoimmunity. Some of these targets could be exploited for therapeutic purposes. The purpose of this review is thus to: 1) describe the important uses of organophosphate (OP)-based compounds worldwide, 2) provide an overview of the various risks and toxicology associated with OP exposure, particularly long-term neurologic and psychiatric symptoms, 3) discuss mechanisms of OP toxicity beyond cholinesterase inhibition, 4) review potential therapeutic strategies to reverse the acute toxicity and long term deleterious effects of OPs.

Organophosphate pesticide chlorpyrifos impairs STAT1 signaling to induce dopaminergic neurotoxicity: Implications for mitochondria mediated oxidative stress signaling events

The organophosphate (OP) pesticide chlorpyrifos (CPF), used in agricultural settings, induces developmental and neurological impairments. Recent studies using in vitro cell culture models have reported CPF exposure to have a positive association with mitochondria-mediated oxidative stress response and dopaminergic cell death; however, the mechanism by which mitochondrial reactive oxygen species (ROS) contribute to dopaminergic cell death remains unclear. Therefore, we hypothesized that STAT1, a transcription factor, causes apoptotic dopaminergic cell death via mitochondria-mediated oxidative stress mechanisms. Here we show that exposure of dopaminergic neuronal cells such as N27 cells (immortalized murine mesencephalic dopaminergic cells) to CPF resulted in a dose-dependent increase in apoptotic cell death as measured by MTS assay and DNA fragmentation. Similar effects were observed in CPF-treated human dopaminergic neuronal cells (LUHMES cells), with an associated increase in mitochondrial dysfunction. Moreover, CPF (10 μM) induced time-dependent increase in STAT1 activation coincided with the collapse of mitochondrial transmembrane potential, increase in ROS generation, proteolytic cleavage of protein kinase C delta (PKCδ), inhibition of the mitochondrial basal oxygen consumption rate (OCR), with a concomitant reduction in ATP-linked OCR and reserve capacity, increase in Bax/Bcl-2 ratio and enhancement of autophagy. Additionally, by chromatin immunoprecipitation (ChIP), we demonstrated that STAT1 bound to a putative regulatory sequence in the NOX1 and Bax promoter regions in response to CPF in N27 cells. Interestingly, overexpression of non-phosphorylatable STAT1 mutants (STAT1Y701F and STAT1S727A) but not STAT1 WT construct attenuated the cleavage of PKCδ and ultimately cell death in CPF-treated cells. Furthermore, small interfering RNA knockdown demonstrated STAT1 to be a critical regulator of autophagy and mitochondria-mediated proapoptotic cell signaling events after CPF treatment in N27 cells. Finally, oral administration of CPF (5 mg/kg) in postnatal rats (PNDs 27-61) induced motor deficits, and nigrostriatal dopaminergic neurodegeneration with a concomitant induction of STAT1-dependent proapoptotic cell signaling events. Conversely, co-treatment with mitoapocynin (a mitochondrially-targeted antioxidant) and CPF rescued motor deficits, and restored dopaminergic neuronal survival via abrogation of STAT1-dependent proapoptotic cell signaling events. Taken together, our study identifies a novel mechanism by which STAT1 regulates mitochondria-mediated oxidative stress response, PKCδ activation and autophagy. In this context, the phosphorylation of Tyrosine 701 and Serine 727 in STAT1 was found to be essential for PKCδ cleavage. By attenuating mitochondrial-derived ROS, mitoapocynin may have therapeutic applications for reversing CPF-induced dopaminergic neurotoxicity and associated neurobehavioral deficits as well as neurodegenerative diseases.

A Novel Method for the Development of Environmental Public Health Indicators and Benchmark Dose Estimation Using a Health-Based End Point for Chlorpyrifos

BACKGROUND

Organophosphorus (OP) compounds are the most widely used group of insecticides in the world. Risk assessments for these chemicals have focused primarily on 10% inhibition of acetylcholinesterase in the brain as the critical metric of effect. Aside from cholinergic effects resulting from acute exposure, many studies suggest a linkage between cognitive deficits and long-term OP exposure.

OBJECTIVE

In this proof-of-concept study, we focused on one of the most widely used OP insecticides in the world, chlorpyrifos (CPF), and utilized an existing physiologically based pharmacokinetic (PBPK) model and a novel pharmacodynamic (PD) dose-response model to develop a point of departure benchmark dose estimate for cognitive deficits following long-term, low-dose exposure to this chemical in rodents.

METHODS

Utilizing a validated PBPK/PD model for CPF, we generated a database of predicted biomarkers of exposure and internal dose metrics in both rat and human. Using simulated peak brain CPF concentrations, we developed a dose-response model to predict CPF-induced spatial memory deficits and correlated these changes to relevant biomarkers of exposure to derive a benchmark dose specific to neurobehavioral changes. We extended these cognitive deficit predictions to humans and simulated corresponding exposures using a model parameterized for humans.

RESULTS

Results from this study indicate that the human-equivalent benchmark dose (BMD) based on a 15% cognitive deficit as an end point is lower than that using the present threshold for 10% brain AChE inhibition. This predicted human-equivalent subchronic BMD threshold compares to occupational exposure levels determined from biomarkers of exposure and corresponds to similar exposure conditions where deficits in cognition are observed.

CONCLUSIONS

Quantitative PD models based on neurobehavioral testing in animals offer an important addition to the methodologies used for establishing useful environmental public health indicators and BMDs, and predictions from such models could help inform the human health risk assessment for chlorpyrifos. https://doi.org/10.1289/EHP1743.

Determination of chlorpyrifos and its metabolites in cells and culture media by liquid chromatography-electrospray ionization tandem mass spectrometry

A sensitive method to simultaneously quantitate chlorpyrifos, chlorpyrifos oxon and the detoxified product 3,5,6-trichloro-2-pyridinol (TCP) was developed using either liquid-liquid extraction for culture media samples, or protein precipitation for cell samples. Multiple reaction monitoring in positive ion mode was applied for the detection of chlorpyrifos and chlorpyrifos oxon, and selected ion recording in negative mode was applied to detect TCP. The method provided linear ranges from 5 to 500, 0.2-20 and 20-2000ng/mL for media samples and from 0.5-50, 0.02-2 and 2-200ng/million cells for CPF, CPO and TCP, respectively. The method was validated using selectivity, linearity, precision, accuracy, recovery, stability and dilution tests. All relative standard deviations (RSDs) and relative errors (REs) for QC samples were within 15% (except for LLOQ, within 20%). This method has been successfully applied to study the neurotoxicity and metabolism of chlorpyrifos in a human neuronal model.

Omega-3 fatty acid attenuates oxidative stress in cerebral cortex, cerebellum, and hippocampus tissue and improves neurobehavioral activity in chronic lead-induced neurotoxicity

Objectives: In view of the increasing risk of lead on human health, the present study has been carried out to investigate the neuroprotective effect of omega-3 fatty acid on chronic lead-induced neurotoxicity and behavioral impairment in rats. Methods: Different neurobehavioral parameters, biochemical assays, and histopathological analyses in brain regions of rats were conducted. Results: Rats exposed to different doses of lead (lead acetate 2.5, 5.0, 7.5 mg/kg body weight p.o. for 90 days) caused a significant decrease in body weight, brain weight, and behavioral changes as compared to controls. Abnormal histopathological and increased levels of lead in blood and brain regions increased the levels of ROS, LPO, PCC and decreased the levels of GSH with concomitant reduction in SOD, CAT, and GPx activities in the brain region of rats treated with different doses of lead as compared to controls. Co-treatment of lead with omega-3 fatty acid (500 mg/kg body weight p.o. for 90 days) decreased the levels of ROS, LPO, PCC, and increased the level of GSH, also increased SOD, CAT, and GPx activity and showed improvements in behavioral as well as histopathological changes as compared to lead-treated groups. Discussion: Our results proved that omega-3 fatty acid improved behavioral deficits, altered histopathological and oxidative stress in lead-intoxicated rats. Among three different doses, 2.5 mg/kg b.wt. of lead along with omega-3 fatty acid was the most preventive dose for the neurotoxicity. This work reveals the potential of omega-fatty acid as a protective drug for lead neurotoxicity.

Chlorpyrifos and chlorpyrifos oxon impair the transport of membrane bound organelles in rat cortical axons

Chlorpyrifos (CPF) is an extensively used organophosphorus pesticide that has recently come under increasing scrutiny due to environmental health concerns particularly its association with neurodevelopmental defects. While the insecticidal actions and acute toxicity of CPF are attributed to its oxon metabolite (CPO) which potently inhibits the cholinergic enzyme acetylcholinesterase (AChE), there is significant evidence that CPF, CPO, and other organophosphates may affect a variety of neuronal targets and processes that are not directly related to AChE. Previously, in adult rat sciatic nerves ex vivo and postnatal neurons from rats in vitro we observed that CPF and CPO impaired the movements of vesicles and mitochondria in axons. Here, in embryonic neurons from rats in culture, we evaluated 24h exposures to CPF and CPO across picomolar to micromolar concentrations for effects on fast axonal transport of membrane bound organelles (MBOs) that contained the amyloid precursor protein (APP) tagged with the fluorescent marker, Dendra2 (APPDendra2). The most notable observations of this study were concentration-dependent decreases in the velocity and percentage of MBOs moving in the anterograde direction, an increase in the number of stationary MBOs, and an increased frequency of pauses associated with both CPF and CPO. These effects occurred at concentrations that did not significantly inhibit AChE activity, they were not blocked by cholinergic receptor antagonists, and they were not associated with compromised cell viability. These effects of CPF and CPO may be significant given the importance of axonal transport to neuronal development as well the function of fully developed neurons.

Reprogramming cells from Gulf War veterans into neurons to study Gulf War illness

Gulf War illness (GWI), which afflicts at least 25% of veterans who served in the 1990-1991 war in the Persian Gulf, is thought to be caused by deployment exposures to various neurotoxicants, including pesticides, anti-nerve gas pills, and low-level nerve agents including sarin/cyclosarin. GWI is a multisymptom disorder characterized by fatigue, joint pain, cognitive problems, and gastrointestinal complaints. The most prominent symptoms of GWI (memory problems, poor attention/concentration, chronic headaches, mood alterations, and impaired sleep) suggest that the disease primarily affects the CNS. Development of urgently needed treatments depends on experimental models appropriate for testing mechanistic hypotheses and for screening therapeutic compounds. Rodent models have been useful thus far, but are limited by their inability to assess the contribution of genetic or epigenetic background to the disease, and because disease-vulnerable proteins and pathways may be different in humans relative to rodents. As of yet, no postmortem tissue from the veterans has become available for research. We are moving forward with a paradigm shift in the study of GWI, which utilizes contemporary stem cell technology to convert somatic cells from Gulf War veterans into pluripotent cell lines that can be differentiated into various cell types, including neurons, glia, muscle, or other relevant cell types. Such cell lines are immortal and will be a resource for GWI researchers to pursue mechanistic hypotheses and therapeutics.

Methodological advances in imaging intravital axonal transport

Axonal transport is the active process whereby neurons transport cargoes such as organelles and proteins anterogradely from the cell body to the axon terminal and retrogradely in the opposite direction. Bi-directional transport in axons is absolutely essential for the functioning and survival of neurons and appears to be negatively impacted by both aging and diseases of the nervous system, such as Alzheimer’s disease and amyotrophic lateral sclerosis. The movement of individual cargoes along axons has been studied in vitro in live neurons and tissue explants for a number of years; however, it is currently unclear as to whether these systems faithfully and consistently replicate the in vivo situation. A number of intravital techniques originally developed for studying diverse biological events have recently been adapted to monitor axonal transport in real-time in a range of live organisms and are providing novel insight into this dynamic process. Here, we highlight these methodological advances in intravital imaging of axonal transport, outlining key strengths and limitations while discussing findings, possible improvements, and outstanding questions.

Neurotoxicity in Preclinical Models of Occupational Exposure to Organophosphorus Compounds

Organophosphorus (OPs) compounds are widely used as insecticides, plasticizers, and fuel additives. These compounds potently inhibit acetylcholinesterase (AChE), the enzyme that inactivates acetylcholine at neuronal synapses, and acute exposure to high OP levels can cause cholinergic crisis in humans and animals. Evidence further suggests that repeated exposure to lower OP levels insufficient to cause cholinergic crisis, frequently encountered in the occupational setting, also pose serious risks to people. For example, multiple epidemiological studies have identified associations between occupational OP exposure and neurodegenerative disease, psychiatric illness, and sensorimotor deficits. Rigorous scientific investigation of the basic science mechanisms underlying these epidemiological findings requires valid preclinical models in which tightly-regulated exposure paradigms can be correlated with neurotoxicity. Here, we review the experimental models of occupational OP exposure currently used in the field. We found that animal studies simulating occupational OP exposures do indeed show evidence of neurotoxicity, and that utilization of these models is helping illuminate the mechanisms underlying OP-induced neurological sequelae. Still, further work is necessary to evaluate exposure levels, protection methods, and treatment strategies, which taken together could serve to modify guidelines for improving workplace conditions globally.

Diisopropylfluorophosphate Impairs the Transport of Membrane-Bound Organelles in Rat Cortical Axons

The extensive use of organophosphates (OPs) is an ongoing environmental health concern due to multiple reports of OP-related neurologic abnormalities. The mechanism of the acute toxicity of OPs has been attributed to inhibition of acetylcholinesterase (AChE), but there is growing evidence that this may not account for all the long-term neurotoxic effects of OPs. In previous experiments (using ex vivo and in vitro model systems) we observed that the insecticide OP chlorpyrifos impaired the movements of vesicles and mitochondria in axons. Here, using a time-lapse imaging technique, we evaluated the OP-nerve agent diisopropylfluorophosphate (DFP) across a wide range of concentrations (subnanomolar to micromolar) for effects on fast axonal transport of membrane-bound organelles (MBOs) that contain the amyloid precursor protein (APP) tagged with the fluorescent marker Dendra2 (APPDendra2). Both 1 and 24 hours of exposure to DFP and a positive control compound, colchicine, resulted in a decrease in the velocity of anterograde and retrograde movements of MBOs and an increase in the number of stationary MBOs. These effects occurred at picomolar (100 pM) to low nanomolar (0.1 nM) concentrations that were not associated with compromised cell viability or cytoskeletal damage. Moreover, the effects of DFP on axonal transport occurred at concentrations that did not inhibit AChE activity, and they were not blocked by cholinergic receptor antagonists. Given the fundamental importance of axonal transport to neuronal function, these observations may explain some of the long-term neurologic deficits that have been observed in humans who have been exposed to OPs.

Repeated exposure to chlorpyrifos leads to prolonged impairments of axonal transport in the living rodent brain

The toxicity of the class of chemicals known as the organophosphates (OP) is most commonly attributed to the inhibition of the enzyme acetylcholinesterase. However, there is significant evidence that this mechanism may not account for all of the deleterious neurologic and neurobehavioral symptoms of OP exposure, especially those associated with levels that produce no overt signs of acute toxicity. In the study described here we evaluated the effects of the commonly used OP-pesticide, chlorpyrifos (CPF) on axonal transport in the brains of living rats using manganese (Mn(2+))-enhanced magnetic resonance imaging (MEMRI) of the optic nerve (ON) projections from the retina to the superior colliculus (SC). T1-weighted MEMRI scans were evaluated at 6 and 24h after intravitreal injection of Mn(2+). As a positive control for axonal transport deficits, initial studies were conducted with the tropolone alkaloid colchicine administered by intravitreal injection. In subsequent studies both single and repeated exposures to CPF were evaluated for effects on axonal transport using MEMRI. As expected, intravitreal injection of colchicine (2.5μg) produced a robust decrease in transport of Mn(2+) along the optic nerve (ON) and to the superior colliculus (SC) (as indicated by the reduced MEMRI contrast). A single subcutaneous (s.c.) injection of CPF (18.0mg/kg) was not associated with significant alterations in the transport of Mn(2+). Conversely, 14-days of repeated s.c. exposure to CPF (18.0mg/kg/day) was associated with decreased transport of Mn(2+) along the ONs and to the SC, an effect that was also present after a 30-day (CPF-free) washout period. These results indicate that repeated exposures to a commonly used pesticide, CPF can result in persistent alterations in axonal transport in the living mammalian brain. Given the fundamental importance of axonal transport to neuronal function, these observations may (at least in part) explain some of the long term neurological deficits that have been observed in humans who have been repeatedly exposed to doses of OPs not associated with acute toxicity.

Subchronic neurotoxicity of chlorpyrifos, carbaryl, and their combination in rats

Anticholinesterase pesticides have been widely used in agricultural and domestic settings and can be detected in the environment after long-term use. Although the acute toxic effects of chlorpyrifos and carbaryl have been well described, little is known about the chronic toxicity of the pesticides mixture. To investigate their chronic neurotoxicity, Wistar rats were exposed to chlorpyrifos, carbaryl, and their mixture (MIX) for 90 consecutive days. The activities of serum cholinesterase (ChE) as well as acetylcholinesterase (AChE) and neuropathy target esterase (NTE) in nerve tissues were determined. Furthermore, the histopathological examination was carried out. The results showed that ChE activity significantly decreased in all treated rats except the rats treated with low dose carbaryl. Treatment with middle- and high-dose chlorpyrifos and MIX in rats significantly inhibited AChE activity in the central nervous tissues, whereas treatment with carbaryl alone did not. In sciatic nerve, AChE activity was significantly inhibited by high-dose carbaryl and MIX, but not by chlorpyrifos alone. No significant NTE inhibition was observed in all treatment groups. Histopathological examination revealed that both chlorpyrifos and MIX treatment induced hippocampal damage. However, no obvious hippocampal damage was found in carbaryl-treated rats. Carbaryl and MIX, but not chlorpyrifos alone, induced pathological damage of sciatic nerve. Taken together, all of the results indicated that chlorpyrifos and carbaryl have different toxicological target tissues in nervous system and showed corresponding effects in the nervous tissues, which may reflect the different sensitivity of central and peripheral nervous tissues to different pesticides individually and in combination.

Effect of monocrotophos, an organophosphorus insecticide, on the striatal dopaminergic system in a mouse model of Parkinson’s disease

Our earlier study had shown that low concentrations of monocrotophos (MCP) elicited dopaminergic features of Parkinson’s disease (PD) in the nematode Caenorhabditis elegans. In the present study, the effect of low doses of MCP on the striatal dopaminergic neurons was investigated using the mouse model system. MCP was initially screened for its ability to cause any neurobehavioral deficits and alterations in the dopaminergic system in Swiss albino mice, aged 8 weeks and weighing 25–30 g, with repeated doses at 0.3 and 0.6 mg/kg body weight (b.w.)/day for 7 days and 30 days. Mice were treated with four intraperitoneal injections for every 2 h with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at the dosage of 14 mg/kg b.w. MCP was administered to these mice at the above-mentioned doses for 7 days. Mice administered with MCP alone revealed a significant ( p < 0.05) reduction in the dopamine (DA) content at both 7 and 30 days and showed a significant ( p < 0.05) increase in neurobehavioral deficits. Interestingly, when MCP was administered for 7 days to MPTP-treated mice, further significant decrease in both DA content and increase in neurobehavioral deficits were apparent. The extent of reactive oxygen species and lipid peroxidation were markedly increased, while the ratio of reduced to oxidized glutathione levels were significantly decreased ( p < 0.05) in the treated mice as compared to the control. Significant histopathological alterations and a marked reduction in the number of tyrosine hydroxylase positive cells were evident in striatum of mice treated with higher doses of MCP. These changes were comparable to that seen in mice treated with MPTP and post-administered lower doses of MCP. Our findings suggest that MCP per se has the propensity to induce pathological changes in the dopaminergic neurons as well as augment the degeneration in a compromised nigrostriatal system such as that in PD.

Neurologic dysfunction and genotoxicity induced by low levels of chlorpyrifos

Chlorpyrifos (CPF) is an organophosphorus cholinesterase inhibitor widely used as an insecticide. Neuro and genotoxicity of this agent were evaluated following daily subcutaneous injections at 0.1, 1 and 10mg/kg or its vehicle to laboratory rats during one week, at the end of which somatosensory evoked potentials (SEP) and power spectrum of the electroencephalogram (EEGp) were recorded under urethane anesthesia. In another group of conscious animals, auditory startle reflex (ASR) was evaluated followed, after euthanasia, with measurements of plasma B-esterases, and genotoxicity with the alkaline comet assay (ACA) at the same CPF doses. The results indicated a CPF dose related inhibition of B-esterases. Enhanced inhibition of the ASR by a subthreshold pre-pulse was observed at all doses and ACA showed a significant higher DNA damage than vehicle controls in animals exposed to 10mg/kg CPF. A trend to higher frequencies of EEGp and an increase in amplitude of the first negative wave of the SEP were found at all doses. The first positive wave of the SEP decreased at the CPF dose of 10mg/kg. In summary, a shift to higher EEG frequencies and alterations of somatosensory and auditory input to the central nervous system were sensitive manifestations of CPF toxicity, associated with depression of B-esterases. The changes in electrical activity of the cerebral cortex and DNA damage observed at doses that do not elicit overt toxicity may be useful in the detection of CPF exposure before clinical signs appear.

Repeated exposures to diisopropylfluorophosphate result in impairments of sustained attention and persistent alterations of inhibitory response control in rats

Organophosphate (OP)-based chemicals are used worldwide for many purposes and they have likely saved millions of people from starvation and disease. However, due to their toxicity they can also pose a significant environmental risk. While considerable research has focused on the acute symptoms and long-term consequences of overtly toxic exposures to OPs, less attention has been given to the subject of repeated exposures to levels that are not associated with acute symptoms (subthreshold exposures). There is clinical evidence indicating that this type of OP exposure can lead to prolonged deficits in cognition; however only a few studies have addressed this issue prospectively in animal models. In this study, repeated subthreshold exposures to the OP nerve agent diisopropylfluorophosphate (DFP) were evaluated in a 5-Choice Serial Reaction Time Task (5C-SRTT), an animal model of sustained attention. Adult rats were trained to stably perform the 5C-SRTT and then injected subcutaneously with vehicle or DFP of 0.5mg/kg every other day for 30days. Behavioral testing occurred daily during the DFP-exposure period and throughout a 45day (OP-free) washout period. Compared to vehicle-treated controls, DFP-treated rats exhibited deficits in accuracy, increases in omissions and timeout responses during the OP exposure period, while no significant effects on premature responses, perseverative responses, or response latencies were noted. While the increase in timeout responses remained detectible during washout, all other DFP-related alterations in 5C-SRTT performance abated. When the demands of the task were increased by the presentation of variable intertrial intervals, premature responses were also elevated in DFP-treated rats during the washout period. These results indicate that repeated exposures to subthreshold doses of DFP lead to reversible impairments in sustained attention as well as persistent impairments of inhibitory response control in rats.

Oral intake of hydrogen-rich water ameliorated chlorpyrifos-induced neurotoxicity in rats

Chronic exposure to low-levels of organophosphate (OP) compounds, such as chlorpyrifos (CPF), induces oxidative stress and could be related to neurological disorders. Hydrogen has been identified as a novel antioxidant which could selectively scavenge hydroxyl radicals. We explore whether intake of hydrogen-rich water (HRW) can protect Wistar rats from CPF-induced neurotoxicity. Rats were gavaged daily with 6.75mg/kg body weight (1/20 LD50) of CPF and given HRW by oral intake. Nissl staining and electron microscopy results indicated that HRW intake had protective effects on the CPF-induced damage of hippocampal neurons and neuronal mitochondria. Immunostaining results showed that the increased glial fibrillary acidic protein (GFAP) expression in astrocytes induced by CPF exposure can be ameliorated by HRW intake. Moreover, HRW intake also attenuated CPF-induced oxidative stress as evidenced by enhanced level of MDA, accompanied by an increase in GSH level and SOD and CAT activity. Acetylcholinesterase (AChE) activity tests showed significant decrease in brain AChE activity after CPF exposure, and this effect can be ameliorated by HRW intake. An in vitro study demonstrated that AChE activity was more intense in HRW than in normal water with or without chlorpyrifos-oxon (CPO), the metabolically-activated form of CPF. These observations suggest that HRW intake can protect rats from CPF-induced neurotoxicity, and the protective effects of hydrogen may be mediated by regulating the oxidant and antioxidant status of rats. Furthermore, this work defines a novel mechanism of biological activity of hydrogen by directly increasing the AChE activity.

Chronic dietary exposure to chlorpyrifos causes behavioral impairments, low activity of brain membrane-bound acetylcholinesterase, and increased brain acetylcholinesterase-R mRNA

Chlorpyrifos (CPF) is an organophosphate (OP) insecticide that is metabolically activated to the highly toxic chlorpyrifos oxon. Dietary exposure is the main route of intoxication for non-occupational exposures. However, only limited behavioral effects of chronic dietary exposure have been investigated. Therefore, male Wistar rats were fed a dose of 5mg/kg/day of CPF for thirty-one weeks. Animals were evaluated in spatial learning and impulsivity tasks after 21 weeks of CPF dietary exposure and one week after exposure ended, respectively. In addition, the degree of inhibition of brain acetylcholinesterase (AChE) was evaluated for both the soluble and particulate forms of the enzyme, as well as AChE gene expression. Also, brain acylpeptide hydrolase (APH) was investigated as an alternative target for OP-mediated effects. All variables were evaluated at various time points in response to CPF diet and after exposure ended. Results from behavioral procedures suggest cognitive and emotional disorders. Moreover, low levels of activity representing membrane-bound oligomeric forms (tetramers) were also observed. In addition, increased brain AChE-R mRNA levels were detected after four weeks of CPF dietary exposure. However, no changes in levels of brain APH were observed among groups. In conclusion, our data point to a relationship between cognitive impairments and changes in AChE forms, specifically to a high inhibition of the particulate form and a modification of alternative splicing of mRNA during CPF dietary exposure.