Prenatal organophosphates exposure alternates the cleavage plane orientation of apical neural progenitor in developing neocortex

The Preventive Effects of Salubrinal against Pyrethroid-Induced Disruption of Adult Hippocampal Neurogenesis in Mice

Environmental factors, including pesticide exposure, have been identified as substantial contributors to neurodegeneration and cognitive impairments. Previously, we demonstrated that repeated exposure to deltamethrin induces endoplasmic reticulum (ER) stress, reduces hippocampal neurogenesis, and impairs cognition in adult mice. Here, we investigated the potential relationship between ER stress and hippocampal neurogenesis following exposure to deltamethrin, utilizing both pharmacological and genetic approaches. To investigate whether ER stress is associated with inhibition of neurogenesis, mice were given two intraperitoneal injections of eIf2α inhibitor salubrinal (1 mg/kg) at 24 h and 30 min prior to the oral administration of deltamethrin (3 mg/kg). Salubrinal prevented hippocampal ER stress, as indicated by decreased levels of C/EBP-homologous protein (CHOP) and transcription factor 4 (ATF4) and attenuated deltamethrin-induced reductions in BrdU-, Ki-67-, and DCX-positive cells in the dentate gyrus (DG) of the hippocampus. To further explore the relationship between ER stress and adult neurogenesis, we used caspase-12 knockout (KO) mice. The caspase-12 KO mice exhibited significant protection against deltamethrin-induced reduction of BrdU-, Ki-67-, and DCX-positive cells in the hippocampus. In addition, deltamethrin exposure led to a notable upregulation of CHOP and caspase-12 expression in a significant portion of BrdU- and Ki-67-positive cells in WT mice. Conversely, both salubrinal-treated mice and caspase-12 KO mice exhibited a considerably lower number of CHOP-positive cells in the hippocampus. Together, these findings suggest that exposure to the insecticide deltamethrin triggers ER stress-mediated suppression of adult hippocampal neurogenesis, which may subsequently contribute to learning and memory deficits in mice.

Neurotoxic Effect of Fipronil in Male Wistar Rats: Ameliorative Effect of L-Arginine and L-Carnitine

Simple Summary

Insecticides are widely used in agricultural and household environments. They induce wide range of deleterious effects. Fipronil is one of the most widely used phenylpyrazoles insecticides. The neurotoxic effect of such insecticide was tested in the present study with special emphasis on cognitive deficit as well as testing the possible ameliorative impacts of L-arginine and L-carnitine. The study proposed fipronil-induced cognitive deficit as a reflection to oxidative stress and neuro-inflammation. Moreover, L-arginine and L-carnitine exerted ameliorative influence on fipronil induced oxidative stress and neuro-inflammation. Therefore, L-arginine and L-carnitine can be considered as prospective candidates for mitigation of pesticide induced neurotoxicity especially in people with high-risk exposure to pesticide.

Abstract

The ameliorative effect of L-arginine (LA) and L-carnitine (LC) against fipronil (FPN)-induced neurotoxicity was explored. In this case, 36 adult male rats were randomly divided into six groups: group I received distilled water, group II received 500 mg/kg LA, group III received 100 mg/kg LC, group IV received 4.85 mg/kg FPN, group V received 4.85 mg/kg FPN and 500 mg/kg LA and group VI received 4.85 mg/kg FPN and 100 mg/kg LC for 6 weeks. Cognitive performance was assessed using Barnes maze (BM). Serum corticosterone, brain total antioxidant capacity (TAC), malondialdehyde (MDA) and dopamine were measured. Histopathology and immunohistochemistry of ionized calcium-binding adaptor (Iba-1), doublecortin (DCX) and serotonin (S-2A) receptors were performed. Fipronil induced noticeable deterioration in spatial learning and memory performance. In addition, FPN significantly (p < 0.05) diminished brain antioxidant defense system and dopamine coincide with elevated serum corticosterone level. Histopathological examination revealed degenerative and necrotic changes. Furthermore, Iba-1 and DCX were significantly expressed in cortex and hippocampus whereas S-2A receptors were significantly lowered in FPN group. However, administration of LA or LC alleviated FPN-induced deteriorations. In conclusion, LA and LC could be prospective candidates for mitigation of FPN-induced neurotoxicity via their antioxidant, anti-inflammatory and neuropotentiating effects.

The expression change of glial fibrillary acidic protein and tyrosine hydroxylase in substantia nigra of the Wistar rats exposed to chlorpyrifos: a novel environmental risk factor for Parkinson's disease

Chlorpyrifos (CPF) is one of the most abundant and widely used pesticides in the world. CPF has detrimental effects on brain tissue, so it is possible to generate some neurodegenerative diseases. The aim of this study was to evaluate the effect of CPF on inducing the Parkinson's disease affecting on central nervous system. 6 to 8-week-old animals were categorized into three groups. The first group was normal control which the animals did not received any treatment, while in the second group, CPF were injected (CPF; 5 mg/kg BW for 30 days intraperitoneally) and the sham group as the third group received DMSO. At the end of the CPF treatment, malondialdehyde (MDA) and superoxide dismutase (SOD) levels were measured in the brain tissues of rats. Proportion of neurons was analyzed by crystal violet assays and tunnel assay to detect apoptotic cells. Finally, the expression of GFAP and TH was investigated in the brain of animals. The results witnessed an increase in MDA and a decrease in SOD (P < 0.05) after the CPF treating. Moreover, results indicated that the proportion of neurons decreased in the second group vs. normal and sham groups significantly (P < 0.001). Additionally, in substantia nigra, the expression of GFAP had a significant increase and the TH had a remarkable decrease in CPF injected group in comparison to two other groups (P < 0.001). Furthermore, the numbers of apoptosis cells reduced in substantia nigra (P < 0.001) after the 30-day period of CPF injections. These results demonstrated that repeated exposure to CPF can induce PD via apoptotic cell death, histopathological disruption. It also altered the expression of dopaminergic neuron and changes the levels of oxidant and antioxidant enzymes in substantia nigra region which triggers PD. Hence, the CPF can be introduced as a risk factor for PD.

Specific Effects of Chronic Dietary Exposure to Chlorpyrifos on Brain Gene Expression-A Mouse Study

Chlorpyrifos (CPF) is an organophosphate insecticide used to control pests on a variety of food and feed crops. In mammals, maternal exposure to CPF has been reported to induce cerebral cortex thinning, alteration of long-term brain cognitive function, and Parkinson-like symptoms, but the mechanisms of these processes are not fully understood. In this study, we aimed to gain a deeper understanding of the alterations induced in the brains of mice chronically exposed to CPF by dietary intake. For our purpose, we analysed F1 offspring (sacrificed at 3 and 8 months) of Mus musculus, treated in utero and postnatally with 3 different doses of CPF (0.1-1-10 mg/kg/day). Using RT² Profiler PCR Arrays, we evaluated the alterations in the expression of 84 genes associated with neurodegenerative diseases. In the brains of exposed mice, we evidenced a clear dose–response relationship for AChE inhibition and alterations of gene expression. Some of the genes that were steadily down-regulated, such as Pink1, Park 2, Sv2b, Gabbr2, Sept5 and Atxn2, were directly related to Parkinson’s onset. Our experimental results shed light on the possibility that long-term CPF exposure may exert membrane signalling alterations which make brain cells more susceptible to develop neurodegenerative diseases.

Residential exposure to pesticides as risk factor for childhood and young adult brain tumors: A systematic review and meta-analysis

BACKGROUND

Accumulating evidence suggests a positive association between exposure to non-agricultural pesticides and childhood brain tumors (CBT).

OBJECTIVE

(1) To conduct a systematic review and meta-analysis of published studies on the association between residential/household/domestic exposure to pesticides and childhood brain tumors. (2) To clarify variables that could impact the results.

METHODS

Publications in English were identified from a MEDLINE search through 28 February 2017 and from the reference list of identified publications. Risk estimates were extracted from 18 case-control studies published between 1979 and 2016 and study quality assessments were performed. Summary odds ratios (mOR) were calculated according to fixed and random-effect meta-analysis models. Separate analyses were conducted after stratification for study quality, critical exposure period, exposure location, specific exposures, pesticide category, application methods, type of pest treated, type of CBT, child's age at diagnosis and geographic location.

RESULTS

Statistically significant associations were observed with CBT after combining all studies (mOR: 1.26; 95% CI: 1.13-1.40) without evidence of inconsistency between study results or publication bias. Specifically, increased risks were observed for several groupings and more particularly for gliomas and exposure involving insecticides. Statistical significance was also reached for high quality studies, for all exposure periods, for indoor exposure and, more particularly, during the prenatal period for all stratifications involving insecticides (except for outdoor use), for pet treatments, for flea/tick treatment, for studies from USA/Canada and studies from Europe (borderline) as well as for data from studies including children of up to 10years at diagnosis and of up to 15years.

CONCLUSIONS

Our findings support an association between residential exposure to pesticides and childhood brain tumors. Although causality cannot be established, these results add to the evidence leading to recommend limiting residential use of pesticides and to support public health policies serving this objective.

Developmental neurotoxicity of succeeding generations of insecticides

Insecticides are by design toxic. They must be toxic to effectively kill target species of insects. Unfortunately, they also have off-target toxic effects that can harm other species, including humans. Developmental neurotoxicity is one of the most prominent off-target toxic risks of insecticides. Over the past seven decades several classes of insecticides have been developed, each with their own mechanisms of effect and toxic side effects. This review covers the developmental neurotoxicity of the succeeding generations of insecticides including organochlorines, organophosphates, pyrethroids, carbamates and neonicotinoids. The goal of new insecticide development is to more effectively kill target species with fewer toxic side effects on non-target species. From the experience with the developmental neurotoxicity caused by the generations of insecticides developed in the past advice is offered how to proceed with future insecticide development to decrease neurotoxic risk.

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 exposure affects fgf8, sox9, and bmp4 expression required for cranial neural crest morphogenesis and chondrogenesis in Xenopus laevis embryos

Chlorpyrifos (CPF) is an organophosphate insecticide used primarily to control foliage and soil-borne insect pests on a variety of food and feed crops. In mammals, maternal exposure to CPF has been reported to induce dose-related abnormalities such as slower brain growth and cerebral cortex thinning. In lower vertebrates, for example, fish and amphibians, teratogenic activity of this compound is correlated with several anatomical alterations. Little is known about the effects of CPF on mRNA expression of genes involved in early development of the anatomical structures appearing abnormal in embryos. This study investigated the effects of exposure to different CPF concentrations (10, 15 and 20 mg/L) on Xenopus laevis embryos from stage 4/8 to stage 46. Some of the morphological changes we detected in CPF-exposed embryos included cranial neural crest cell (NCC)-derived structures. For this reason, we analyzed the expression of select genes involved in hindbrain patterning (egr2), cranial neural crest chondrogenesis, and craniofacial development (fgf8, bmp4, sox9, hoxa2 and hoxb2). We found that CPF exposure induced a reduction in transcription of all the genes involved in NCC-dependent chondrogenesis, with largest reductions in fgf8 and sox9; whereas, in hindbrain, we did not find any alterations in egr2 expression. Changes in the expression of fgf8, bmp4, and sox9, which are master regulators of several developmental pathways, have important implications. If these changes are confirmed to belong to a general pattern of alterations in vertebrates prenatally exposed to OP, they might be useful to assess damage during vertebrate embryo development. Environ. Mol. Mutagen. 57:589-604, 2016. © 2016 Wiley Periodicals, Inc.

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.

Adoptive Autophagy Activation: a Much-Needed Remedy Against Chemical Induced Neurotoxicity/Developmental Neurotoxicity

The profound significance of autophagy as a cell survival mechanism under conditions of metabolic stress is a well-proven fact. Nearly a decade-long research in this area has led scientists to unearth various roles played by autophagy other than just being an auto cell death mechanism. It is implicated as a vital cell survival pathway for clearance of all the aberrant cellular materials in case of cellular injury, metastasis, disease states, cellular stress, neurodegeneration and so on. In this review, we emphasise the critical role of autophagy in the environmental stressors-induced neurotoxicity and its therapeutic implications for the same. We also attempt to shed some light on the possible protective role of autophagy in developmental neurotoxicity (DNT) which is a rapidly growing health issue of the human population at large and hence a point of rising concern amongst researchers. The intimate association between DNT and neurodegenerative disorders strongly indicates towards adopting autophagy activation as a much-needed remedy for DNT.