Developmental neurotoxicity of chlorpyrifos in vivo and in vitro: effects on nuclear transcription factors involved in cell replication and differentiation

Identifying critical windows of prenatal phenol, paraben, and pesticide exposure and child neurodevelopment: Findings from a prospective cohort study

BACKGROUND

This study aimed to investigate how exposure to a mixture of endocrine disrupting chemicals (EDCs) during two points in pregnancy affects early childhood neurodevelopment.

METHODS

We analyzed publicly-available data from a high-risk cohort of mothers and their children (2007-2014) that measured six EDCs including methyl-, ethyl- and propyl parabens (MEPB, ETPB, PRPB), Bisphenol-A (BPA), 3,5,6-trichloro-2-pyridinol (TCPy), 3-phenoxybenzoic acid (3-PBA) in prenatal urine samples during the second and third trimesters. Neurodevelopmental scores were assessed using Mullen Scales of Early Learning (MSEL) at age 3. We used mean field variational Bayes for lagged kernel machine regression (MFVB-LKMR) to investigate the association between trimester-specific co-exposure to the six EDCs and MSEL scores at age 3, stratified by sex.

RESULTS

The analysis included 130 children. For females, the relationship between BPA and 3PBA with MSEL score varied between the two trimesters. In the second trimester, effect estimates for BPA were null but inversely correlated with MSEL score in the third trimester. 3PBA had a negative relationship with MSEL in the second trimester and positive correlation in the third trimester. For males, effect estimates for all EDCs were in opposing directions across trimesters. MFVB-LKMR analysis identified significant two-way interaction between EDCs for MSEL scores in both trimesters. For example, in females, the MSEL scores associated with increased exposure to TCPy were 1.75 units (95%credible interval -0.04, -3.47) lower in the 2nd trimester and 4.61 (95%CI -3.39, -5.84) lower in the third trimester when PRPB was fixed at the 75th percentile compared to when PRPB was fixed at the 25th percentile.

CONCLUSION

Our study provides evidence that timing of EDC exposure within the prenatal period may impact neurodevelopmental outcomes in children. More of these varying effects were identified among females. Future research is needed to explore EDC mixtures and the timing of exposure during pregnancy to enhance our understanding of how these chemicals impact child health.

Determination of organophosphorus compounds in water and food samples using a non-enzymatic electrochemical sensor based on silver nanoparticles and carbon nanotubes nanocomposite coupled with batch injection analysis

This work presents, for the first time, a fast and highly sensitive electrochemical method for determination of three organophosphorus compounds (OPs), diazinon (DZN), malathion (MLT), and chlorpyrifos (CLPF), using a modified pyrolytic graphite electrode (PGE) coupled to batch injection analysis system with multiple pulse amperometric detection (BIA-MPA). The PGE was modified by a nanocomposite based on functionalized carbon nanotubes (CNTf) and silver nanoparticles (AgNPs). The OPs samples were directly analyzed on the modified working electrode surface by BIA-MPA system in Britton-Robinson (BR) buffer 0.15 mol L^-1 at pH 6.0. The MPA detection of DZN, MLT and CLPF was performed using two potential pulses, which were sequentially applied on modified PGE at -1.3 V (100 ms) and +0.8 V (100 ms) for selective determination of these three OPs and working electrode cleaning, respectively. Under optimized conditions, the sensor presented a linear range of 0.1-20 μmol L^-1 for DZN, 1.0-30 μmol L^-1 for MLT and from 0.25 to 50 μmol L^-1 for CLPF. The limits of detection (LOD) and quantification (LOQ) of 0.35 and 1.18 μmol L^-1 for DZN, 0.89 and 2.98 μmol L^-1 for MLT, and 0.53 and 1.78 μmol L^-1 for CLPF were obtained. The proposed method exhibited high sensitivity of 0.068, 0.030 and 0.043 mA L μmol^-1 for DZN, MLT and CLPF detection, respectively. Furthermore, the BIA-MPA system provided an analytical frequency of 71 determinations per hour for direct determination of these OPs in water and food samples. The modified PGE coupled to BIA-MPA system showed a high stability of electrochemical response for OPs detection with relative standard deviation (RSD) of 1.60% (n = 20). The addition-recovery studies of the proposed method were carried out in tap water, orange juice, and apple fruit real samples, which showed suitable recovery values between 77 and 124%. The analytical performance of the developed sensor provides an attractive alternative method for OPs determination with great potential for a fast and sensitive application in contaminated samples with these pesticides.

The growing concern of chlorpyrifos exposures on human and environmental health

Chlorpyrifos (CP) and its highly electrophilic intermediates are principal toxic metabolites. The active form of CP i.e. chlorpyrifos oxon (CP-oxon) is responsible for both the insecticidal activity and is also of greater risk when present in the atmosphere. Thus, the combined effects of both CP, CP-oxan, and other metabolites enhance our understanding of the safety and risk of the insecticide CP. They cause major toxicities such as AChE inhibition, oxidative stress, and endocrine disruption. Further, it can have adverse hematological, musculoskeletal, renal, ocular, and dermal effects. Excessive use of this compound results in poisoning and potentially kills a non-target species upon exposure including humans. Several examples of reactive metabolites toxicities on plants, aquatic life, and soil are presented herein. The review covers the general overview on reactive metabolites of CP, chemistry and their mechanism through toxic effects on humans as well as on the environment. Considerable progress has been made in the replacement or alternative to CP. The different strategies including antidote mechanisms for the prevention and treatment of CP poisoning are discussed in this review. The approach analyses also the active metabolites for the pesticide activity and thus it becomes more important to know the pesticide and toxicity dose of CP as much as possible.

Efficient remediation of chlorpyrifos pesticide from contaminated water by superparamagnetic adsorbent based on Arabic gum-grafted-polyamidoxime

A novel organic/inorganic biosorbent hydrogel nanocomposite based on Arabic Gum-grafted-polyamidoxime and CuFe₂O₄ magnetic nanoparticles (AG-g-PAO/CuFe₂O₄) was prepared in three steps. The prepared hydrogel nanocomposite was well characterized using Fourier transform infrared (FT-IR), energy-dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), CHN, zeta potential, and Brunauer-Emmett-Teller (BET) analyses. The adsorption efficiency of the AG-g-PAO/CuFe₂O₄ for removing an organophosphorus pesticide (OPP) (chlorpyrifos) from aqueous solutions was studied. Effect of different experimental conditions such as the pH of the solution, adsorbent dosage, contact time, initial concentration on adsorption efficiency was evaluated. The experimental adsorption data described well by the Langmuir isotherm model and the maximum adsorption capacity (Q_max) of the prepared biosorbent for chlorpyrifos was found 769.23 mg/g. The adsorption kinetic data were well fitted by the pseudo-second-order model. It was suggested that the chlorpyrifos was adsorbed onto AG-g-PAO/CuFe₂O₄ hydrogel biosorbent mainly through electrostatic interaction and hydrogen bonding. The result of adsorption-desorption experiments revealed that the AG-g-PAO/CuFe₂O₄ can be excellently regenerated and reused after three sequential runs without a considerable decline in its adsorption performance.

The relationship between pesticide exposure during critical neurodevelopment and autism spectrum disorder: A narrative review

Agricultural pesticides have been one of the most extensively used compounds throughout the world. The main sources of contamination for humans are dietary intake and occupational exposure. The impairments caused by agricultural pesticide exposure have been a significant global public health problem. Recent studies have shown that low-level agricultural pesticide exposure during the critical period of neurodevelopment (pregnancy and lactation) is closely related to autism spectrum disorder (ASD). Inhibition of acetylcholinesterase, gut microbiota, neural dendrite morphology, synaptic function, and glial cells are targets for the effects of pesticides during nervous system development. In the present review, we summarize the associations between several highly used and frequently studied pesticides (e.g., glyphosate, chlorpyrifos, pyrethroids, and avermectins) and ASD. We also discusse future epidemiological and toxicological research directions on the relationship between pesticides and ASD.

Effect of N-acetylcysteine on attenuation of chlropyrifos and its methyl analogue toxicity in male rats

The attenuating effect of 150 mg/kg of N-acetylcysteine (NAC) against the oral administration of 7.88 and 202.07 mg/kg/day for 14 days of either chlropyrifos-ethyl (CPE-E) or chlropyrifos-methyl (CPF-M), respectively, in male rat was investigated using biochemical and genetic markers. Biomarkers such as acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), paraoxonase (PON), adenosine 5'-triphosphatase (ATP-ase), glutathione-S-transferase (GST), catalase (CAT), glutathione reduced (GSH) in serum showed a significant decline in their levels, while calcium (Ca⁺²), cytochrome C reduction (CYC-R), lipid peroxidation (LPO), nitric oxide (NO) levels showed a significant increase in serum of treated rats. Regarding the genotoxic parameters, when rats are treated either with CPE-E or CPF-M, liver DNA, chromosomal aberration (CA), and micronucleated polychromatic erythrocytes (MnPCE) significantly increased, while the mitotic index (MI) and polychromatic erythrocytes (PCE)/ normochromatic erythrocytes (NCE) ratio were significantly decreased. However, the administration of NAC following the intoxication of CPF-E or CPF-M attenuated the tested biochemical and genotoxic markers. It can be concluded that NAC can be used to ameliorate the toxicity of certain organophosphorus compounds such as CPF-E and CPF-M.

Effects of chlorpyrifos on cell death and cellular phenotypic specification of human neural stem cells

Chlorpyrifos (CPF) is an organophosphate pesticide widely used in agriculture, whose traditional and well-known mechanism of action is the inhibition of the enzyme Acetylcholinesterase (AChE). Subacute exposures to CPF have been associated with alterations different from the inhibition of AChE. Because of the vulnerability of the developing nervous system, prenatal and early postnatal exposures are of special concern. Human neural stem cells (hNSC) provide the opportunity to study early stages of neural development and may be a valuable tool for developmental neurotoxicology (DNT). In the current work, the cell line hNS1 was used as a model system with the aim of validating this cell line as a reliable testing method. To evaluate the effects of CPF on early developmental stages, hNS1 cells were exposed to different concentrations of the pesticide and cell death, proliferation and cell fate specification were analyzed under differentiation conditions. Since hNS1 cells responded to CPF in a similar way to other human cell lines, we consider it may be a valid model for DNT chemical assessment. CPF induced apoptotic cell death only at the highest doses tested, suggesting that it is not toxic for the specific developmental stage here addressed under short term exposure. In addition, the higher doses of CPF promoted the generation of astroglial cells, without affecting neurogenesis.

Associations of prenatal and childhood chlorpyrifos exposure with Neurodevelopment of 3-year-old children

Chlorpyrifos (CPF), an organophosphate insecticide, has been linked to adverse neurodevelopmental effects in animal studies. However, little is known about long-term neurotoxicity of early-life CPF exposure in humans. We aimed to evaluate the associations of both prenatal and early childhood CPF exposure with neurodevelopment of children. In this observational study based on Sheyang Mini Birth Cohort, pregnant women were recruited from an agricultural region between June 2009 and January 2010, and their children were followed up from birth to age three. Urinary 3,5,6-Trichloro-2-pyridinol (TCPy), a specific metabolite of CPF, was quantified using large-volume-injection gas chromatography-tandem mass spectrometry. Developmental quotients (DQs) of children in motor, adaptive, language, and social areas were assessed by trained pediatricians. Data from 377 mother-child pairs were used in the current study. Associations between CPF exposure and neurodevelopmental indicators were estimated using generalized linear models with adjustment for potential confounders. The median concentrations of TCPy in maternal and children's urine were 5.39 μg/L and 5.34 μg/L, respectively. No statistically significant association was found between maternal urinary TCPy concentrations and children neurodevelopment. While for postnatal exposure, we found lower motor area DQ score 0.61 [95% confidence interval (CI): -1.13, -0.09; p = 0.02] and social area DQ score 0.55 (95% CI: -1.07, -0.03; p = 0.04) per one-unit increase in the ln-transformed childhood urinary TCPy concentrations. Further stratification by sex indicated that the inverse associations were only observed in boys, but not in girls. Our findings suggest that adverse neurodevelopmental effects were associated with early childhood CPF exposure, but not prenatal exposure. Additional longitudinal studies are needed to replicate these results and to further understand the toxicological mechanisms of CPF.

Effects of Chlorpyrifos on Cholinesterase and Serine Lipase Activities and Lipid Metabolism in Brains of Rainbow Trout (Oncorhynchus mykiss)

Chlorpyrifos is an organophosphorus insecticide that elicits acute toxicity through inhibition of acetylcholinesterase (AChE), leading to acetylcholine accumulation and prolonged stimulation of cholinergic receptors throughout the central and peripheral nervous systems. Previous studies have indicated that neurodevelopment may also be impaired through alternative pathways, including reduction of cAMP catalyzed downstream events. The upstream initiating events that underlie non-cholinergic neurological actions of chlorpyrifos and other organophosphorus compounds remain unclear. To investigate the potential role of disruption of fatty acid signaling as a mechanism of toxicity, lipid metabolism and fatty acid profiles were examined to identify alterations that may play a critical role in upstream signaling in the CNS. Juvenile rainbow trout were treated for 7 days with nominal chlorpyrifos concentrations previously reported to diminish olfactory responses (10, 20, and 40 μg/L). While lethality was noted higher doses, measured chlorpyrifos concentrations of 1.38 μg/L (nominal concentration 10 μg/L) significantly reduced the activity of AChE and two serine lipases, monoacylglycerol lipase and fatty acid amide hydrolase in the brain. Reductions in lysophosphatidylethanolamines (16:0; 18:0, 18:1, and 22:6) derived from the phosphatidylethanolamines and free fatty acids (Palmitic acid16:0; Linolenic acid18:3; Eicosadienoic acid 20:2; Arachidonic acid 20:4; and Docosahexaenoic acid 22:6) were also noted, suggesting that chlorpyrifos inhibited the metabolism of selected phospholipid signaling precursors at sublethal concentrations. These results indicate that in addition to AChE inhibition, environmentally relevant chlorpyrifos exposure alters serine lipase activity and lipid metabolites in the trout brain, which may compromise neuronal signaling and impact neurobehavioral responses in aquatic animals.

Effects of three common pesticides on survival, food consumption and midgut bacterial communities of adult workers Apis cerana and Apis mellifera

The acute and chronic toxicity of 3 common pesticides, namely, amitraz, chlorpyrifos and dimethoate, were tested in Apis mellifera and Apis cerana. Acute oral toxicity LC₅₀ values were calculated after 24 h of exposure to contaminated syrup, and chronic toxicity was tested after 15 days of exposure to 2 sublethal concentrations of pesticides. The toxicity of the tested pesticides to A. mellifera and A. cerana decreased in the order of dimethoate > chlorpyrifos > amitraz. A. mellifera was slightly more sensitive to chlorpyrifos and dimethoate than A. cerana, while A. cerana was more sensitive to amitraz than A. mellifera. Chronic toxicity tests showed that 1.0 mg/L dimethoate reduced the survival of the two bee species and the food consumption of A. mellifera, while 1.0 mg/L amitraz and 1.0 mg/L chlorpyrifos did not affect the survival or food consumption of the two bee species. The treatment of syrup with amitraz at a concentration equal to 1/10th of the LC₅₀ value did not affect the survival of or diet consumption by A. mellifera and A. cerana; however, chlorpyrifos and dimethoate at concentrations equal to 1/10th of their respective LC₅₀ values affected the survival of A. cerana. Furthermore, intestinal bacterial communities were identified using high-throughput sequencing targeting the V3V4 regions of the 16S rDNA gene. All major honey bee intestinal bacterial phyla, including Proteobacteria (62.84%), Firmicutes (34.04%), and Bacteroidetes (2.02%), were detected. There was a significant difference in the microbiota species richness of the two species after 15 days; however, after 30 days, no significant differences were found in the species diversity and richness between A. cerana and A. mellifera exposed to 1.0 mg/L amitraz and 1.0 mg/L chlorpyrifos. Overall, our results confirm that acute toxicity values are valuable for evaluating the chronic toxicity of these pesticides to honey bees.

Diazinon exposure activated transcriptional factors CCAAT-enhancer-binding proteins α (C/EBPα) and peroxisome proliferator-activated receptor γ (PPARγ) and induced adipogenesis in 3T3-L1 preadipocytes

Environmental chemical exposure could be a contributor to the increasing obesity epidemic. Diazinon, an organophosphate insecticide, has been widely used in the agriculture, and exposure of the general population to diazinon has been reported. Diazinon has been known to induce neurotoxic effects mainly through the inhibition of acetylcholinesterase (AChE). However, its association with dysregulation of adipogenesis has been poorly investigated. The current study aimed to examine the mechanism of diazinon's effect on adipogenesis using the 3T3-L1 preadipocytes combined with a single-cell-based high-content analysis. The results showed that diazinon induced lipid droplet accumulation in a dose-dependent manner. The dynamic changes of adipogenic regulatory proteins and genes were examined at the three stages of adipogenesis (induction, differentiation, and maturation) in 3T3-L1 cells treated with various doses of diazinon (0, 1, 10, 100 μM) using real-time quantitative RT-PCR and Western Blot respectively. Diazinon significantly induced protein expression of transcriptional factors CCAAT-enhancer-binding proteins α (C/EBPα) and peroxisome proliferator-activated receptor γ (PPARγ), their downstream proteins, fatty acid synthase (FASN), acetyl CoA carboxylase (ACC), fatty acid-binding protein 4 (FABP4), lipoprotein lipase (LPL), adiponectin and perilipin in dose and time-dependent manners. Similarly, the adipogenic genes were significantly induced in a dose and time-dependent manner compared to the relative controls. The current study demonstrates that diazinon promotes lipid accumulation and activates the adipogenic signaling pathway in the in vitro model.

Thyroid Function Disruptors: from nature to chemicals

The modern concept of thyroid disruptors includes man-made chemicals and bioactive compounds from food that interfere with any aspect of the hypothalamus-pituitary-thyroid axis, thyroid hormone biosynthesis and secretion, blood and transmembrane transport, metabolism and local action of thyroid hormones. This review highlights relevant disruptors that effect populations through their diet: directly from food itself (fish oil and polyunsaturated fatty acids, pepper, coffee, cinnamon and resveratrol/grapes), through vegetable cultivation (pesticides) and from containers for food storage and cooking (bisphenol A, phthalates and polybrominated diphenyl ethers). Due to the vital role of thyroid hormones during every stage of life, we review effects from the gestational period through to adulthood, including evidence from in vitro studies, rodent models, human trials and epidemiological studies.

Redox imbalance caused by pesticides: a review of OPENTOX-related research

Pesticides are a highly diverse group of compounds and the most important chemical stressors in the environment. Mechanisms that could explain pesticide toxicity are constantly being studied and their interactions at the cellular level are often observed in well-controlled in vitro studies. Several pesticide groups have been found to impair the redox balance in the cell, but the mechanisms leading to oxidative stress for certain pesticides are only partly understood. As our scientific project "Organic pollutants in environment - markers and biomarkers of toxicity (OPENTOX)" is dedicated to studying toxic effects of selected insecticides and herbicides, this review is focused on reporting the knowledge regarding oxidative stress-related phenomena at the cellular level. We wanted to single out the most important facts relevant to the evaluation of our own findings from studies conducted on in vitro cell models.

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.

Recommendation on test readiness criteria for new approach methods in toxicology: Exemplified for developmental neurotoxicity

Multiple non-animal-based test methods have never been formally validated. In order to use such new approach methods (NAMs) in a regulatory context, criteria to define their readiness are necessary. The field of developmental neurotoxicity (DNT) testing is used to exemplify the application of readiness criteria. The costs and number of untested chemicals are overwhelming for in vivo DNT testing. Thus, there is a need for inexpensive, high-throughput NAMs, to obtain initial information on potential hazards, and to allow prioritization for further testing. A background on the regulatory and scientific status of DNT testing is provided showing different types of test readiness levels, depending on the intended use of data from NAMs. Readiness criteria, compiled during a stakeholder workshop, uniting scientists from academia, industry and regulatory authorities are presented. An important step beyond the listing of criteria, was the suggestion for a preliminary scoring scheme. On this basis a (semi)-quantitative analysis process was assembled on test readiness of 17 NAMs with respect to various uses (e.g. prioritization/screening, risk assessment). The scoring results suggest that several assays are currently at high readiness levels. Therefore, suggestions are made on how DNT NAMs may be assembled into an integrated approach to testing and assessment (IATA). In parallel, the testing state in these assays was compiled for more than 1000 compounds. Finally, a vision is presented on how further NAM development may be guided by knowledge of signaling pathways necessary for brain development, DNT pathophysiology, and relevant adverse outcome pathways (AOP).

Prenatal chlorpyrifos leads to autism-like deficits in C57Bl6/J mice

BACKGROUND

Children are at daily risk for exposure to organophosphate insecticides, of which the most common is chlorpyrifos (CPF). Exposure of pregnant women to CPF was linked to decreased birth weight, abnormal reflexes, reduction in IQ, as well as increased maternal reports of signs of pervasive developmental disorder. The aim of current study was to examine the long term effects of prenatal exposure to CPF in C57BL/6 J (B6) mice with specific focus on social and repetitive behavior.

METHODS

B6 female mice were treated with vehicle, 2.5 mg/kg CPF or 5 mg/kg of CPF on gestational days 12-15 by oral gavage. On postnatal days (PND's) 6-12 early development and neuromotor ability were assessed by measuring 3 neonatal reflexes in the offspring. In adulthood, PND 90, social behavior was investigated using the social preference, social novelty and social conditioned place preference tasks. Object recognition and restricted interest, measured by the repetitive novel object contact task (RNOC), were also assessed on PN D 90. In order to rule out the possibility that CPF administration induced alterations in maternal care, the dams' behavior was evaluated via the maternal retrieval task.

RESULTS

CPF treatment resulted in delayed development of neonatal reflexes on PND's 6-12. On PND 90, mice treated prenatally with the 5.0 mg/kg dose exhibited reduced preference towards an unfamiliar conspecific in the social preference test and reduced social conditioned place preference. In the RNOC task, mice exposed prenatally to 2.5 mg/kg dose of CPF showed enhanced restricted interest. CPF administration did not impair dams' behavior and did not cause memory or recognition deficit as was observed in the object recognition task.

CONCLUSIONS

Our data indicate that gestational exposure to CPF has long-term deleterious effects on social behavior and limits exploration of novel objects.

Mother gestational exposure to organophosphorus pesticide induces neuron and glia loss in daughter adult brain

Chlorpyrifos (CPF) is a widely used organophosphorus pesticide with developmental neurotoxicity such as morphogenesis toxicity. In the present study, we assessed the effects of prenatal CPF exposure on systemic parameters and cytoarchitecture of medial prefrontal cortex (mPFC) in adulthood. Gestational dams were exposed to 5mg/kg/d of CPF during gestational days 13-17, while body weight, organ coefficient, and neuron and glia counts of offspring were determined on postnatal day 60. Our results showed that CPF treatment induced little or no effects on body weight and organ coefficients. There were also no significant pathological changes in mPFC. However, neuron and glia count analysis showed that CPF treatment reduced neuron and glia counts in anterior cingulate, prelimbic, and infralimbic areas of mPFC. The CPF react pattern was similar in both sexes, and there was no statistical difference in most of the sub-regions. Thus, our results revealed an embryonic origin brain deficit induced by gestational mother pesticide exposure.

Chlorpyrifos induces anxiety-like behavior in offspring rats exposed during pregnancy

Chlorpyrifos is a pesticide, member of the organophosphate class, widely used in several countries to manage insect pests on many agricultural crops. Currently, chlorpyrifos health risks are being reevaluated due to possible adverse effects, especially on the central nervous system. The aim of this study was to investigate the possible action of this pesticide on the behaviors related to anxiety and depression of offspring rats exposed during pregnancy. Wistar rats were treated orally with chlorpyrifos (0.01, 0.1, 1 and 10mg/kg/day) on gestational days 14-20. Male offspring behavior was evaluated on post-natal days 21 and 70 by the elevated plus-maze test, open field test and forced swimming test. The results demonstrated that exposure to 0.1, 1 or 10mg/kg/day of chlorpyrifos could induce anxiogenic-like, but not depressive-like behavior at post-natal day 21, without causing fetal toxicity. This effect was reversed on post-natal day 70.

Adverse Associations of both Prenatal and Postnatal Exposure to Organophosphorous Pesticides with Infant Neurodevelopment in an Agricultural Area of Jiangsu Province, China

BACKGROUND

Prenatal exposure to organophosphorous (OP) pesticides has been found to be associated with adverse effects on child neurodevelopment, but evidence on potential effects induced by both prenatal and postnatal OP exposure in infants is limited.

OBJECTIVES

Our aim was to investigate the associations of both prenatal and postnatal OP exposure with birth outcomes and infant neurodevelopment.

METHODS

Exposure to OP in 310 mother-infant pairs was assessed by measuring dimethylphosphate (DM), diethylphosphate (DE), and total dialkylphosphate (DAP) metabolites in urines from pregnant women and their children at 2 years of age. The Gesell Developmental Schedules was administered to examine neurodevelopment of 2-year-old children.

RESULTS

Based on the Gesell Developmental Schedules, the proportions of children with developmental delays were < 6%. Adverse associations between head circumference at birth and prenatal OP exposure were demonstrated. Both prenatal and postnatal OP exposure was significantly associated with increased risk of being developmentally delayed. Specifically, odds ratio (OR) value for prenatal DEs was 9.75 (95% CI: 1.28, 73.98, p = 0.028) in the adaptive area, whereas in the social area, OR values for postnatal DEs and DAPs were 9.56 (95% CI: 1.59, 57.57, p = 0.014) and 12.00 (95% CI: 1.23, 117.37, p = 0.033), respectively. Adverse associations were observed only in boys, not in girls.

CONCLUSIONS

Both prenatal and postnatal OP exposure may adversely affect the neurodevelopment of infants living in the agricultural area. The present study adds to the accumulating evidence on associations of prenatal and postnatal OP exposure with infant neurodevelopment.

CITATION

Liu P, Wu C, Chang X, Qi X, Zheng M, Zhou Z. 2016. Adverse associations of both prenatal and postnatal exposure to organophosphorous pesticides with infant neurodevelopment in an agricultural area of Jiangsu Province, China. Environ Health Perspect 124:1637-1643; http://dx.doi.org/10.1289/EHP196.

An in vivo study in mice: mother's gestational exposure to organophosphorus pesticide retards the division and migration process of neural progenitors in the fetal developing brain

Background: Widely utilized pesticides such as chlorpyrifos (CPF) can cause cognitive abnormalities, neurotransmitter disruptions and brain cytoarchitecture deficits in adulthood due to exposure in the prenatal period, but the mechanism underlying the development and maintenance of such neurotoxicity in embryonic neurogenesis remains largely unclear. Using embryonic neocortex slices, we investigated mitosis population constituents and characteristic interkinetic nuclear migration (INM) to evaluate the CPF effects on the proliferation process of neural progenitors. Methods: Gestational days (GD) 14 and GD 7.5-11.5 ICR dams were exposed to 5 mg kg-1 of CPF to investigate immediate toxicity and sustained toxicity. Proliferating nuclei were labeled with 50 mg kg-1 of Brdu at 1, 3, 6 and 9 hours before samples were collected. The mitoses count and Brdu positive nuclei (BPN) location were measured and analyzed in standard sections of the embryonic dorsolateral cortex. Results: CPF reduced the mitoses count in the primary progenitors but not in the secondary progenitors which are time sustained. CPF retarded BPN migration with a 6-9 μm delay of the relative location in the immediate groups and a 3-6 μm delay in the sustained ones. CPF had no or little effects on the global mitoses count and BPN count. Conclusion: Prenatal CPF exposure disrupts the proliferation process of primary progenitors in the embryonic dorsolateral cortex immediately and with sustained effects, which may contribute to explain the toxicity mechanism in early neurogenesis.

Chlorpyrifos Toxicity in Mouse Cultured Cerebellar Granule Neurons at Different Stages of Development: Additive Effect on Glutamate-Induced Excitotoxicity

OBJECTIVE

Chlorpyrifos (CPF) is a neurotoxic organophosphorus (OP) insecticide. Its mechanism of action includes oxidative stress, excitotoxicity, and inhibition of the acetylcholinesterase enzyme (AChE). The aim of the present study is to investigate CPF toxicity in mature and immature cerebellar granule neurons (CGNs), as well as its effect on glutamate induced excitotoxicity.

MATERIALS AND METHODS

This study was an in vitro experimental study performed on mice cultured CGNs. Immature and mature neurons were exposed to different concentrations of CPF (1-1000 µM) and glutamate (10-600 µM) for 48 hours after which we used the MTT assay to measure cytotoxicity. Immature neurons had exposure to CPF for 5 days in order to evaluate the cytotoxic effect on developing neurons. Mature neurons received sub-lethal concentrations of CPF (10, 100 µM) combined with different concentrations of glutamate. AChE activity and reactive oxygen species (ROS) generation were assessed after treatments.

RESULTS

Immature CGNs had increased sensitivity to CPF toxicity compared to mature neurons. We observed significantly greater ROS production in immature compared to mature neurons, however AChE activity was more inhibited in mature neurons. Although CPF toxicity was not well correlated with AChE inhibition, it correlated well with ROS production. Glutamate toxicity was potentiated by sub-lethal concentration of CPF, however glutamate induced ROS production was not affected. The results suggested that CPF potentiated glutamate toxicity by mechanisms other than oxidative stress.

CONCLUSION

CPF toxicity differed in mature and immature neurons. Potentiated glutamate toxicity by CPF implied that CPF exposure might be a risk factor for neurodegenerative disease.

Olfactory Transcriptional Analysis of Salmon Exposed to Mixtures of Chlorpyrifos and Malathion Reveal Novel Molecular Pathways of Neurobehavioral Injury

Pacific salmon exposed to sublethal concentrations of organophosphate pesticides (OP) have impaired olfactory function that can lead to loss of behaviors that are essential for survival. These exposures often involve mixtures and can occur at levels below those which inhibit acetylcholinesterase (AChE). In this study, juvenile Coho salmon were exposed for 24 h to either 0.1, 0.5, or 2.5 ppb chlorpyrifos (CPF), 2, 10, or 50 ppb malathion (MAL), or binary mixtures of 0.1 CPF:2 ppb MAL, 0.5 CPF:10 ppb MAL, or 2.5 CPF:10 ppb MAL to mimic single and binary environmental exposures. Microarray analysis of olfactory rosettes from pesticide-exposed salmon revealed differentially expressed genes involved in nervous system function and signaling, aryl hydrocarbon receptor signaling, xenobiotic metabolism, and mitochondrial dysfunction. Coho exposed to OP mixtures exhibited a more pronounced loss in detection of a predatory olfactory cue relative to those exposed to single compounds, whereas respirometry experiments demonstrated that exposure to OPs, individually and in mixtures, reduced maximum respiratory capacity of olfactory rosette mitochondria. The observed molecular, biochemical, and behavioral effects occurred largely in the absence of effects on brain AChE. In summary, our results provide new insights associated with the sublethal neurotoxic effects of OP mixtures relevant to environmental exposures involving molecular and cellular pathways of injury to the salmon olfactory system that underlie neurobehavioral injury.

Prenatal drug exposures sensitize noradrenergic circuits to subsequent disruption by chlorpyrifos

We examined whether nicotine or dexamethasone, common prenatal drug exposures, sensitize the developing brain to chlorpyrifos. We gave nicotine to pregnant rats throughout gestation at a dose (3mg/kg/day) producing plasma levels typical of smokers; offspring were then given chlorpyrifos on postnatal days 1-4, at a dose (1mg/kg) that produces minimally-detectable inhibition of brain cholinesterase activity. In a parallel study, we administered dexamethasone to pregnant rats on gestational days 17-19 at a standard therapeutic dose (0.2mg/kg) used in the management of preterm labor, followed by postnatal chlorpyrifos. We evaluated cerebellar noradrenergic projections, a known target for each agent, and contrasted the effects with those in the cerebral cortex. Either drug augmented the effect of chlorpyrifos, evidenced by deficits in cerebellar β-adrenergic receptors; the receptor effects were not due to increased systemic toxicity or cholinesterase inhibition, nor to altered chlorpyrifos pharmacokinetics. Further, the deficits were not secondary adaptations to presynaptic hyperinnervation/hyperactivity, as there were significant deficits in presynaptic norepinephrine levels that would serve to augment the functional consequence of receptor deficits. The pretreatments also altered development of cerebrocortical noradrenergic circuits, but with a different overall pattern, reflecting the dissimilar developmental stages of the regions at the time of exposure. However, in each case the net effects represented a change in the developmental trajectory of noradrenergic circuits, rather than simply a continuation of an initial injury. Our results point to the ability of prenatal drug exposure to create a subpopulation with heightened vulnerability to environmental neurotoxicants.

Biochemical biomarkers of sublethal effects in Rhinella arenarum late gastrula exposed to the organophosphate chlorpyrifos

We determined the biochemical and molecular effects of the organophosphate insecticide chlorpyrifos (CPF) in the late gastrula embryonic stage of the South American toad Rhinella arenarum continuously exposed from fertilization (24 h). Our objective was to evaluate these responses as potential biomarkers at low, sublethal levels of the toxicant. We first established the EC50 for embryo arrest in 21.3 mg/L, with a LOEC of 16 mg/L. At 4 mg/L CPF, some embryos were unable to complete the dorsal lip of the blastopore and the yolk plug became blur, probably because of abnormal cell migration. Acetylcholinesterase activity, the specific biomarker for organophosphates, was unaffected by any of the tested concentrations of CPF (2-14 mg/L). In turn, 2 mg/L CPF increased the reduced glutathione levels and inhibited glutathione-S-transferase activity, suggesting an oxidative stress and antioxidant response. Catalase was induced by CPF exposure at higher concentrations (8 and 14 mg/L). We also studied transcription factor c-Fos as a signaling event related to development in early embryogenesis. Analysis of nuclear c-Fos protein showed two bands, both enhanced in embryos exposed to 2 and 8 mg/L CPF. While nuclear Erk protein was practically unaffected, Mek protein levels were induced by the OP. Transcription factor c-Fos may be then linking oxidative stress with developmental alterations observed due to CPF exposure. These molecular and biochemical responses observed in R. arenarum gastrula at sublethal CPF exposures may replace non-responsive AChE as very early biomarkers in toad gastrula.

Thyroid hormone signaling during early neurogenesis and its significance as a vulnerable window for endocrine disruption

The essential roles of thyroid hormone (TH) in perinatal brain development have been known for decades. More recently, many of the molecular mechanisms underlying the multiple effects of TH on proliferation, differentiation, migration, synaptogenesis and myelination in the developing nervous system have been elucidated. At the same time data from both epidemiological studies and animal models have revealed that the influence of thyroid signaling on development of the nervous system, extends to all periods of life, from early embryogenesis to neurogenesis in the adult brain. This review focuses on recent insights into the actions of TH during early neurogenesis. A key concept is that, in contrast to the previous ideas that only the unliganded receptor was implicated in these early phases, a critical role of the ligand, T3, is increasingly recognized. These findings are considered in the light of increasing knowledge of cell specific control of T3 availability as a function of deiodinase activity and transporter expression. These requirements for TH in the early stages of neurogenesis take on new relevance given the increasing epidemiological data on adverse effects of TH lack in early pregnancy on children's neurodevelopmental outcome. These ideas lead logically into a discussion on how the actions of TH during the first phases of neurogenesis can be potentially disrupted by gestational iodine lack and/or chemical pollution. This article is part of a Special Issue entitled: Nuclear receptors in animal development.

Genomic and phenotypic alterations of the neuronal-like cells derived from human embryonal carcinoma stem cells (NT2) caused by exposure to organophosphorus compounds paraoxon and mipafox

Historically, only few chemicals have been identified as neurodevelopmental toxicants, however, concern remains, and has recently increased, based upon the association between chemical exposures and increased developmental disorders. Diminution in motor speed and latency has been reported in preschool children from agricultural communities. Organophosphorus compounds (OPs) are pesticides due to their acute insecticidal effects mediated by the inhibition of acetylcholinesterase, although other esterases as neuropathy target esterase (NTE) can also be inhibited. Other neurological and neurodevelopmental toxic effects with unknown targets have been reported after chronic exposure to OPs in vivo. We studied the initial stages of retinoic acid acid-triggered differentiation of pluripotent cells towards neural progenitors derived from human embryonal carcinoma stem cells to determine if neuropathic OP, mipafox, and non-neuropathic OP, paraoxon, are able to alter differentiation of neural precursor cells in vitro. Exposure to 1 μM paraoxon (non-cytotoxic concentrations) altered the expression of different genes involved in signaling pathways related to chromatin assembly and nucleosome integrity. Conversely, exposure to 5 μM mipafox, a known inhibitor of NTE activity, showed no significant changes on gene expression. We conclude that 1 μM paraoxon could affect the initial stage of in vitro neurodifferentiation possibly due to a teratogenic effect, while the absence of transcriptional alterations by mipafox exposure did not allow us to conclude a possible effect on neurodifferentiation pathways at the tested concentration.

Time course of serum S100B protein and neuron-specific enolase levels of a single dose of chlorpyrifos in rats

Organophosphate (OP) compounds are a large class of chemicals, many of which are used as pesticides. It is suggested that OPs specifically affect glia and neurons. Effects of acute exposure to chlorpyrifos (CPF), which is a common organophosphorus pesticide used worldwide, on neuron-specific enolase (NSE) and S100B levels in rat blood during 7 days were assessed. Rats were evaluated either before (0 hr) or 2, 12, 24, 48 and 168 hr (7 days) after injection of CPF (279 mg/kg, s.c.) or vehicle (peanut oil, 2 ml/kg, s.c.) for clinical signs of toxicity. Immediately after the evaluation of toxicity, blood samples were taken for biochemical assays. CPF administration produced decreases in body-weight and temperature, which were observed for first time at 12 hr after CPF administration and continued for 168 hr (p < 0.05-0.001). Serum S100B and NSE levels were acutely increased 2 hr after CPF administration and remained high at 12 hr (p < 0.01-0.001). NSE and S100B levels were not different in either CPF or vehicle groups at following time points. Serum butyrylcholinesterase (EC 3.1.1.8; BuChE) activity was dramatically reduced at 2 hr after CPF and remained low at each time points during 7 days (p < 0.01-0.001). Our results suggest that the usefulness of serum levels of these glia- and neuron-specific marker proteins in assessing OP toxicity, specifically CPF-induced toxicity.

Safety methods for chlorpyrifos removal from date fruits and its relation with sugars, phenolics and antioxidant capacity of fruits

The effectiveness of different postharvest wash treatments at two levels (10 and 20 g/l) for different dipping times was determined to remove chlorpyrifos from date fruits treated at concentration of 2 mg/l. The recovered amount of chlorpyrifos was extracted based on the solid phase extraction (SPE) method and then analyzed by gas chromatography with mass spectrometry (GC-MS). The results demonstrate that the removal of chlorpyrifos increased in the order of acetic acid (AA)> citric acid (CA)> hydrogen peroxide (H2O2)> potassium permanganate (KMnO4)> running water (H2O), and the percent of pesticide residue on date fruits depended on the concentration of tested washing treatments and dipping time without the formation of the toxic by-product, chlorpyrifos-oxon. Kinetic studies revealed that chlorpyrifos was found to be more easily removable from date fruits treated with the tested chemical solutions with t1/2 values of 12-29 min compared with roughly 53 min in case of running water. The impact of these washing treatments on quality of date fruits illustrated that all treatments exerted a little negative effect on total sugars content but H2O2 and KMnO4 at level of 2 % had more drastic effect. Whereas, running water, 10 and 20 g/l CA caused significant increases in total phenolic contents, during all the tested contact times compared with control. Except the insignificant effect of KMnO4 treatments, antioxidant capacity of date fruits tended to increase in all wash treatments, when the contact times were 5 or 15 min.

Developmental neurotoxicity of organophosphates targets cell cycle and apoptosis, revealed by transcriptional profiles in vivo and in vitro

Developmental organophosphate exposure reduces the numbers of neural cells, contributing to neurobehavioral deficits. We administered chlorpyrifos or diazinon to newborn rats on postnatal days 1-4, in doses straddling the threshold for barely-detectable cholinesterase inhibition, and evaluated gene expression in the cell cycle and apoptosis pathways on postnatal day 5. Both organophosphates evoked transcriptional changes in 20-25% of the genes in each category; chlorpyrifos and diazinon targeted the same genes, with similar magnitudes of change, as evidenced by high concordance. Furthermore, the same effects were obtained with doses above or below the threshold for cholinesterase inhibition, indicating a mechanism unrelated to anticholinesterase actions. We then evaluated the effects of chlorpyrifos in undifferentiated and differentiating PC12 cells and found even greater targeting of cell cycle and apoptosis genes, affecting up to 40% of all genes in the pathways. Notably, the genes affected in undifferentiated cells were not concordant with those in differentiating cells, pointing to dissimilar outcomes dependent on developmental stage. The in vitro model successfully identified 60-70% of the genes affected by chlorpyrifos in vivo, indicating that the effects are exerted directly on developing neural cells. Our results show that organophosphates target the genes regulating the cell cycle and apoptosis in the developing brain and in neuronotypic cells in culture, with the pattern of vulnerability dependent on the specific stage of development. Equally important, these effects do not reflect actions on cholinesterase and operate at exposures below the threshold for any detectable inhibition of this enzyme.

A comparison of neurotoxicity in cerebellum produced by dermal application of chlorpyrifos in young and adult mice

Chlorpyrifos (CPF), an organophosphate pesticide inhibits acetylcholinesterase (AChE) and causes neuromuscular incoordination among children and elderly. The objectives of the present study were to compare the neurotoxic effects of dermal application of CPF on the cerebellum in the parameters of glial fibrillary acidic protein (GFAP) expression in young and adult mice and to correlate with the changes in acetylcholinesterase levels. Male Balb/c mice, 150 days old (adult) and 18 days old (young) were dermally applied with ½ LD(50) of CPF over the tails for 14 days. Serum AChE concentration was estimated and GFAP immunostaining was performed on sagittal paraffin sections through the vermis of cerebellum. Although reduced in both age-groups exposed to CPF, percentage of reduction in serum AChE was more in adult compared to the young. Under GFAP immunostaining, brown colour fibres and glial cells were observed in cerebellar cortex and medulla in both the experimental groups. The mean GFAP-positive glial cell count in cerebellar medulla per mm(2) of section was significantly (p < 0.05) increased in adult mice exposed to CPF when compared with age-matched control. In conclusion, this study confirmed that dermal exposure of CPF was able to exert neurotoxic effect in both young and adult mice. However, the quantitative results revealed that adult mice showed more GFAP expression in cerebellum when compared with the young, when exposed to CPF.

Critical duration of exposure for developmental chlorpyrifos-induced neurobehavioral toxicity

Developmental exposure of rats to the pesticide chlorpyrifos (CPF) causes persistent neurobehavioral impairment. In a parallel series of studies with zebrafish, we have also found persisting behavioral dysfunction after developmental CPF exposure. We have developed a battery of measures of zebrafish behavior, which are reliable and sensitive to toxicant-induced damage. This study determined the critical duration of developmental CPF exposure for causing persisting neurobehavioral effects. Tests of sensorimotor response (tap startle response and habituation), stress response (novel tank diving test) and learning (3-chamber tank spatial discrimination) were conducted with adult zebrafish after early developmental CPF exposure. The CPF exposure level was 100 ng/ml with durations of 0-1, 0-2, 0-3, 0-4 and 0-5 days after fertilization. Developmental CPF exposure had persisting behavioral effects in zebrafish tested as adults. In the tactile startle test, CPF exposed fish showed decreased habituation to startle and a trend toward increased overall startle response. In the novel tank exploration test, exposed fish showed decreased escape diving response and increased swimming activity. In the 3-chamber learning test, the 0-5 day CPF exposure group had a significantly lower learning rate. There was evidence for persisting declines in brain dopamine and norepinepherine levels after developmental CPF exposure. In all of the measures the clearest persistent effects were seen in fish exposed for the full duration of five days after fertilization. In a follow-up experiment there were some indications for persisting behavioral effects after exposure during only the later phase of this developmental window. This study demonstrated the selective long-term neurobehavioral alterations caused by exposure to CPF in zebrafish. The zebrafish model can facilitate the determination of the molecular mechanisms underlying long-term neurobehavioral impairment after developmental toxicant exposure.

Diverse neurotoxicants converge on gene expression for neuropeptides and their receptors in an in vitro model of neurodifferentiation: effects of chlorpyrifos, diazinon, dieldrin and divalent nickel in PC12 cells

Unrelated developmental neurotoxicants can produce similar neurobehavioral outcomes. We examined whether disparate agents affect neuromodulators that control numerous neurotransmitters and circuits, employing PC12 cells to explore the targeting of neuroactive peptides by organophosphates (chlorpyrifos, diazinon), an organochlorine (dieldrin) and a metal (Ni(2+)); we utilized microarrays to profile gene expression for the peptides and their receptors. Chlorpyrifos evoked robust upregulation of cholecystokinin, corticotropin releasing hormone, galanin, neuropeptide Y, neurotensin, preproenkephalin and tachykinin 1; this involved a critical period at the commencement of neurodifferentiation, since the effects were much less notable in undifferentiated PC12 cells. Diazinon targeted a similar but smaller repertoire of neuropeptide genes and the magnitude of the effects was also generally less. Surprisingly, dieldrin shared many of the same neuropeptide targets as the organophosphates and concordance analysis showed significant overlap among all three pesticides. However, dieldrin had more notable effects on neuropeptide receptors, and overlap between diazinon and dieldrin for the receptors led to a stronger resemblance of these two agents than of chlorpyrifos and dieldrin. Ni(2+) was unique, evoking upregulation of only one of the peptides affected by the other agents, while causing downregulation of several others. Nevertheless, there was still significant concordance between Ni(2+) and either diazinon or dieldrin, reflecting similarities toward the receptors. Our results show that neuropeptides are likely to be a prominent target for the developmental neurotoxicity of organophosphates and other neurotoxicants, and further, that the convergence of disparate agents on the same genes and pathways may contribute to similar neurobehavioral outcomes.

Transcriptional profiles for glutamate transporters reveal differences between organophosphates but similarities with unrelated neurotoxicants

The developmental neurotoxicity of organophosphates involves mechanisms other than their shared property as cholinesterase inhibitors, among which are excitotoxicity and oxidative stress. We used PC12 cells as a neurodevelopmental model to compare the effects of chlorpyrifos and diazinon on the expression of genes encoding glutamate transporters. Chlorpyrifos had a greater effect in cells undergoing nerve growth factor-induced neurodifferentiation as compared to undifferentiated PC12 cells, with peak sensitivity at the initiation of differentiation, reflecting a global upregulation of all the glutamate transporter genes expressed in this cell line. In differentiating cells, chlorpyrifos had a significantly greater effect than did diazinon and concordance analysis indicated no resemblance in their expression patterns. At the same time, the smaller effects of diazinon were highly concordant with those of an organochlorine pesticide (dieldrin) and a metal (divalent nickel). We also performed similar evaluations for the cystine/glutamate exchanger, which provides protection against oxidative stress by moving cystine into the cell; again, chlorpyrifos had the greatest effect, in this case reducing expression in undifferentiated and differentiating cells. Our results point to excitotoxicity and oxidative stress as major contributors to the noncholinesterase mechanisms that distinguish the neurodevelopmental outcomes between different organophosphates while providing a means whereby apparently unrelated neurotoxicants may produce similar outcomes.

Toxicogenomic profiling in maternal and fetal rodent brains following gestational exposure to chlorpyrifos

Considering the wide variety of effects that have been reported to occur in the developmental neurotoxicity of chlorpyrifos (CP) and the lack of consensus on their dependence of brain acetylcholinesterase (AChE) activity inhibition, we applied microarray technology to explore dose-dependent alterations in transcriptional response in the fetal and maternal C57BL/6 mouse brain after daily gestational exposure (days 6 to 17) to CP (2, 4, 10, 12 or 15 mg/kg, sc). We identified significantly altered genes across doses and assessed for overrepresentation of Gene Ontology (GO) biological processes and KEGG pathways. We further clustered genes based on their expression profiles across doses and repeated the GO/pathways analysis for each cluster. The dose-effect relationship of CP on gene expression, both at the gene and pathway levels was non-monotonic and not necessarily related to brain AChE inhibition. The largest impact was observed in the 10mg/kg dose group which was also the LOAEL for brain AChE inhibition. In the maternal brain, lower doses (4 mg/kg) influenced GO categories and pathways such as cell adhesion, behavior, lipid metabolism, long-term potentiation, nervous system development, neurogenesis, synaptic transmission. In the fetal brain, lower doses (2 and/or 4 mg/kg) significantly altered cell division, translation, transmission of nerve impulse, chromatin modification, long-term potentiation. In addition, some genes involved in nervous system development and signaling were shown to be specifically influenced by these lower CP doses. Our approach was sensitive and reflected the diversity of responses known to be disrupted by CP and highlighted possible additional consequences of CP neurotoxicity, such as disturbance of the ubiquitin proteasome system.

Organophosphate exposure during a critical developmental stage reprograms adenylyl cyclase signaling in PC12 cells

Early-life organophosphate (OP) exposures elicit neurobehavioral deficits through mechanisms other than inhibiting cholinesterase. Cell signaling cascades are postulated as critical noncholinesterase targets that mediate both the initial alterations in neurodevelopment as well as subsequent abnormalities of synaptic function. We exposed PC12 cells to chlorpyrifos, diazinon or parathion in the undifferentiated state and during neurodifferentiation; we then assessed the function of the adenylyl cyclase (AC) signaling cascade, measuring basal AC activity as well as responses to stimulants acting at G-proteins or on the AC molecule itself. In undifferentiated cells, a 2day exposure to the OPs had no significant effect on AC signaling but the same treatment in differentiating cells produced deficits in all AC measures when exposure commenced at the initiation of differentiation. However, when exposure of the differentiating cells was continued for 6days, AC activities then became supranormal. The same increase was obtained if cells were exposed only for the first two days of differentiation, followed by four subsequent days without the OPs. Furthermore, the OP effects on cell signaling were entirely distinct from those on indices of cell number and neurite outgrowth. These results indicate that OP exposure reprograms the AC pathway during a discrete developmental stage at the commencement of neurodifferentiation, with effects that continue to emerge after OP exposure is discontinued. Importantly, the same sequence is seen with OP exposures in neonatal rats, indicating that direct effects of these agents to reprogram cell signaling provide a major mechanism for functional effects unrelated to cholinesterase inhibition.

Gestational exposure to the organophosphate chlorpyrifos alters social-emotional behaviour and impairs responsiveness to the serotonin transporter inhibitor fluvoxamine in mice

BACKGROUND

The organophosphate chlorpyrifos (CPF) is a pesticide largely used worldwide. Studies from animal models indicate that CPF exposure during development at low doses can target different neurotransmitter systems in the absence of overt cholinergic effects.

METHODS

Late gestational exposure (gestational days 14-17) to CPF at the dose of 6 mg/kg was evaluated in CD-1 mice at adulthood. Neurobehavioural effects likely involving serotonin (5-hydroxytryptamine, 5HT) transmission were assessed both in males and females, through the light-dark exploration test to assess CPF effects on anxiety profiles and the forced swimming test to evaluate the response to the 5HT transporter (5HTT) inhibitor fluvoxamine (30 mg/kg). In females only, we evaluated the effects of gestational exposure to CPF on maternal aggression, under basal condition or after injection of fluvoxamine.

RESULTS

Gestational CPF exposure increased anxiety levels only in female mice, as shown by the augmented thigmotaxis behaviour and the lower latency to enter in the dark compartment. In the forced swimming test, no differences between CPF and control mice were found when assessed under basal condition (saline administration), but both male and female CPF mice missed to show the typical behavioural effects of the 5HTT inhibitor fluvoxamine. During maternal aggression, CPF females showed lower propensity to and intensity of aggressive behaviour, together with mild decreased responsiveness to fluvoxamine administration.

CONCLUSIONS

Overall, the present results confirm a specific and sex-dependent vulnerability of affective/emotional domains to developmental CPF exposure. Furthermore, data provide clear indication on the disrupting effects of prenatal CPF on serotoninergic transmission.

Disparate developmental neurotoxicants converge on the cyclic AMP signaling cascade, revealed by transcriptional profiles in vitro and in vivo

Cell-signaling cascades are convergent targets for developmental neurotoxicity of otherwise unrelated agents. We compared organophosphates (chlorpyrifos, diazinon), an organochlorine (dieldrin) and a metal (Ni(2+)) for their effects on neuronotypic PC12 cells, assessing gene transcription involved in the cyclic AMP pathway. Each agent was introduced during neurodifferentiation at a concentration of 30 microM for 24 or 72 h and we assessed 69 genes encoding adenylyl cyclase isoforms and regulators, G-protein alpha-and beta,gamma-subunits, protein kinase A subtypes and the phosphodiesterase family. We found strong concordance among the four agents across all the gene families, with the strongest relationships for the G-proteins, followed by adenylyl cyclase, and lesser concordance for protein kinase A and phosphodiesterase. Superimposed on this pattern, chlorpyrifos and diazinon were surprisingly the least alike, whereas there was strong concordance of dieldrin and Ni(2+) with each other and with each individual organophosphate. Further, the effects of chlorpyrifos differed substantially depending on whether cells were undifferentiated or differentiating. To resolve the disparities between chlorpyrifos and diazinon, we performed analyses in rat brain regions after in vivo neonatal exposures; unlike the in vitro results, there was strong concordance. Our results show that unrelated developmental neurotoxicants can nevertheless produce similar outcomes by targeting cell signaling pathways involved in neurodifferentiation during a critical developmental period of vulnerability. Nevertheless, a full evaluation of concordance between different toxicants requires evaluations of in vitro systems that detect direct effects, as well as in vivo systems that allow for more complex interactions that converge on the same pathway.

Benzo[a]pyrene impairs neurodifferentiation in PC12 cells

Animal studies indicate neurobehavioral anomalies after prenatal exposure to benzo[a]pyrene (BaP). In order to determine if BaP directly affects neurodevelopment, we compared its effects to those of the organophosphate insecticide, chlorpyrifos (CPF), in undifferentiated and differentiating neuronotypic PC12 cells, evaluating indices of cell replication, cell number, neurite outgrowth and phenotypic differentiation. Unlike CPF, BaP did not inhibit DNA synthesis in undifferentiated cells. In cells undergoing nerve growth factor-induced differentiation, CPF reduced cell numbers (assessed by DNA content) whereas BaP increased them, suggesting a delay in the transition between cell replication and differentiation. Indices of cell enlargement (total protein/DNA) and neurite outgrowth (membrane protein/DNA) also showed opposite effects of CPF (increases) and BaP (decreases). We directly confirmed BaP impairment of neurodifferentiation by measuring markers for the two neurotransmitter phenotypes expressed by PC12 cells: tyrosine hydroxylase (dopamine phenotype) and choline acetyltransferase (acetylcholine phenotype). BaP significantly reduced both markers in differentiating cells, with a preferentially greater effect on the acetylcholine phenotype. Our results indicate that low, non-toxic levels of BaP can impair neurodifferentiation, resulting in excess cell numbers at the expense of the emergence of neurotransmitter phenotypes. BaP thus has direct actions on developing neuronal cells that could contribute to the adverse neurodevelopmental effects seen with in vivo exposures.

Oxidative and excitatory mechanisms of developmental neurotoxicity: transcriptional profiles for chlorpyrifos, diazinon, dieldrin, and divalent nickel in PC12 cells

BACKGROUND

Oxidative stress and excitotoxicity underlie the developmental neurotoxicity of numerous chemicals.

OBJECTIVES

We compared the effects of organophosphates (chlorpyrifos and diazinon), an organo-chlorine (dieldrin), and a metal [divalent nickel (Ni2+)] to determine how these mechanisms contribute to similar or dissimilar neurotoxic outcomes.

METHODS

We used PC12 cells as a model of developing neurons and evaluated transcriptional profiles for genes for oxidative stress responses and glutamate receptors.

RESULTS

Chlorpyrifos had a greater effect on oxidative-stress-related genes in differentiating cells compared with the undifferentiated state. Chlorpyrifos and diazinon showed significant concordance in their effects on glutathione-related genes, but they were negatively correlated for effects on catalase and superoxide dismutase isoforms and had no concordance for effects on ionotropic glutamate receptors. Surprisingly, the correlations were stronger between diazinon and dieldrin than between the two organophosphates. The effects of Ni2+ were the least similar for genes related to oxidative stress but had significant concordance with dieldrin for effects on glutamate receptors.

CONCLUSIONS

Our results point to underlying mechanisms by which different organophosphates produce disparate neurotoxic outcomes despite their shared property as cholinesterase inhibitors. Further, apparently unrelated neurotoxicants may produce similar outcomes because of convergence on oxidative stress and excitotoxicity. The combined use of cell cultures and microarrays points to specific end points that can distinguish similarities and disparities in the effects of diverse developmental neurotoxicants.

Prenatal chlorpyrifos exposure alters motor behavior and ultrasonic vocalization in CD-1 mouse pups

BACKGROUND

Chlorpyrifos (CPF) is a non-persistent organophosphate (OP) largely used as pesticide. Studies from animal models indicate that CPF is a developmental neurotoxicant able to target immature central nervous system at dose levels well below the threshold of systemic toxicity. So far, few data are available on the potential short- and long-term adverse effects in children deriving from low-level exposures during prenatal life and infancy.

METHODS

Late gestational exposure [gestational day (GD) 14-17] to CPF at the dose of 6 mg/kg was evaluated in CD-1 mice during early development, by assessment of somatic and sensorimotor maturation [reflex-battery on postnatal days (PNDs) 3, 6, 9, 12 and 15] and ultrasound emission after isolation from the mother and siblings (PNDs 4, 7 and 10). Pups' motor skills were assessed in a spontaneous activity test on PND 12. Maternal behavior of lactating dams in the home cage and in response to presentation of a pup previously removed from the nest was scored on PND 4, to verify potential alterations in maternal care directly induced by CPF administration.

RESULTS

As for the effects on the offspring, results indicated that on PND 10, CPF significantly decreased number and duration of ultrasonic calls while increasing latency to emit the first call after isolation. Prenatal CPF also reduced motor behavior on PND 12, while a tendency to hyporeflexia was observed in CPF pups by means of reflex-battery scoring. Dams administered during gestation with CPF showed baseline levels of maternal care comparable to those of controls, but higher levels of both pup-directed (licking) and explorative (wall rearing) responses.

CONCLUSION

Overall our results are consistent with previous epidemiological data on OP neurobehavioral toxicity, and also indicate ultrasonic vocalization as an early marker of CPF exposure during development in rodent studies, with potential translational value to human infants.

Type of cell death and the role of acetylcholinesterase activity in neurotoxicity induced by paraoxon in cultured rat hippocampal neurons

Organophosphate (Ops) neurotoxicity is attributed both to its well-known cholinergic and non-cholinergic effects. In the present study we compared enzymatic and morphologic changes in neurons exposed to paraoxon during one day and one week. The effect of exposure time is important in neurotoxicity of Ops. The longer the exposure time is the more damage is observed in neurons, although there are few investigations about the effect in the post-exposure period. Hippocampal cells were obtained from rat neonates and cultured in Neurobasal/B27. Paraoxon at 50 and 100 microM were added. Inverted microscope and electron microscope were used to study cell morphology and Neutral Red staining was used to measure viability. We also assayed caspase-3 and (acetylcholinesterase) AChE activity. Hoechst staining was utilized to determine the type of cell death. Culture medium was replaced after 24 h in one-day group, however, tests were all carried out at the end of the first week in both group. The results indicate that paraoxon reduced the viability in a dose-dependent manner. Our results do not confirm apoptosis in either group; it seems that the cell death in one-day exposure group was not AChE dependent. In conclusion, present data imply that the toxicity of paraoxon is both dose and duration dependent, which may even remain after the cessation of exposure.