Endosulfan induces small but significant changes in the levels of noradrenaline, dopamine and serotonin in the developing rat brain and deficits in the operant learning performance

Investigating open access new approach methods (NAM) to assess biological points of departure: A case study with 4 neurotoxic pesticides

Open access new approach methods (NAM) in the US EPA ToxCast program and NTP Integrated Chemical Environment (ICE) were used to investigate activities of four neurotoxic pesticides: endosulfan, fipronil, propyzamide and carbaryl. Concordance of in vivo regulatory points of departure (POD) adjusted for interspecies extrapolation (AdjPOD) to modelled human Administered Equivalent Dose (AEDHuman) was assessed using 3-compartment or Adult/Fetal PBTK in vitro to in vivo extrapolation. Model inputs were from Tier 1 (High throughput transcriptomics: HTTr, high throughput phenotypic profiling: HTPP) and Tier 2 (single target: ToxCast) assays. HTTr identified gene expression signatures associated with potential neurotoxicity for endosulfan, propyzamide and carbaryl in non-neuronal MCF-7 and HepaRG cells. The HTPP assay in U-2 OS cells detected potent effects on DNA endpoints for endosulfan and carbaryl, and mitochondria with fipronil (propyzamide was inactive). The most potent ToxCast assays were concordant with specific components of each chemical mode of action (MOA). Predictive adult IVIVE models produced fold differences (FD) < 10 between the AEDHuman and the measured in vivo AdjPOD. The 3-compartment model was concordant (i.e., smallest FD) for endosulfan, fipronil and carbaryl, and PBTK was concordant for propyzamide. The most potent AEDHuman predictions for each chemical showed HTTr, HTPP and ToxCast were mainly concordant with in vivo AdjPODs but assays were less concordant with MOAs. This was likely due to the cell types used for testing and/or lack of metabolic capabilities and pathways available in vivo. The Fetal PBTK model had larger FDs than adult models and was less predictive overall.

Repeated endosulfan exposure induces changes in neurochemicals, decreases ATPase transmembrane ionic-pumps, and increased oxidative/nitrosative stress in the brains of rats: Reversal by quercetin

Neurochemical and ATPase deregulations play important role in toxicant-induced neurodegeneration. Previous studies have shown that loss of ATPase ionic-pumps alters neurochemical balance via increased ammonia, oxidative and nitrosative stress. Thus, this study investigated the ameliorative potentials of quercetin on neurochemical, ATPase changes, hyperammonemia and oxidative/nitrosative status in the brains of Wistar rats exposed to endosulfan, a known toxic environmental pesticide that is casually used in many developing countries. Adult rats were divided into five treatment groups (n = 5). Groups 1-2 received normal saline and corn oil (vehicle) (10 mL/kg/day), group 3 received quercetin (20 mg/kg/day) orally for 28 days consecutively. However, animals in groups 4-5 were given endosulfan (5 mg/kg/day, p.o) for 28 days. But, from the 14th to 28th day, group 4 additionally received vehicle (10 mL/kg/day, p.o.), while group 5 was treated with quercetin (20 mg/kg/day, p.o.). Thereafter, brain levels of neurochemicals, ATPase activities, ammonia and oxidative/nitrosative stress were investigated by employing standardized biochemical assay protocols. Quercetin increased endosulfan-induced decreased levels of norepinephrine, dopamine, GABA, and decreased elevated concentrations of glutamate and serotonin. Quercetin normalized the increased levels of acetylcholinesterase and ammonia. Furthermore, quercetin significantly reversed the decrease in Na⁺/K⁺, Ca²⁺, Mg²⁺-ATPase activities induced by endosulfan. Also, quercetin increased superoxide dismutase, catalase and glutathione peroxidase activities, and reduced nitrite and peroxynitrite levels in brains of rats. These findings further provide evidence of the ameliorative potential of quercetin against endosulfan-induced neurotoxicity via attenuation of neurochemical, ATPase changes, and inhibition of acetylcholinesterase activity, ammonia release and oxidative/nitrosative stress in rat brains.

Contrasting effects of pre-training on acquisition of operant and radial arm maze tasks in rats

Performing multiple tasks either simultaneously, in rapid alternation or in succession, is routine in daily life. Further, testing rodents in a battery of tests is common both in drug discovery and behavioral phenotyping research. However, learning of new tasks can be influenced by prior experience(s). There has been some research on 'switching cost' involved in the transition from one behavior to another. However, there has been no specific assessment of the effect of learning an operant paradigm on performance in a spatial memory task and vice versa. Accordingly, we evaluated task switching between two forms of learning paradigms, operant conditioning and radial arm maze (RAM) tasks. In experiment 1, rats were trained for operant conditioning with food reward followed by a partially baited RAM task. In experiment 2, rats were trained first on a RAM task followed by operant learning. Pre-training on the operant task, impaired the acquisition of the RAM. On the contrary, pre-training on the RAM enhanced operant performance. Our study reveals significant effects of the test order on task-switching in rats. This knowledge can be useful when framing test sequences in test batteries for drug discovery research and screening genetically modified mice.

Relative toxicity for indoor semi volatile organic compounds based on neuronal death

BACKGROUND

Semi Volatile Organic Compounds (SVOCs) are contaminants commonly found in dwellings as a result of their use as plasticizers, flame retardants, or pesticides in building materials and consumer products. Many SVOCs are suspected of being neurotoxic, based on mammal experimentation (impairment of locomotor activity, spatial learning/memory or behavioral changes), raising the question of cumulative risk assessment. The aim of this work is to estimate the relative toxicity of such SVOCs, based on neuronal death.

METHOD

SVOCs fulfilling the following conditions were included: detection frequency >10% in dwellings, availability of data on effects or mechanism of action for neurotoxicity, and availability of dose-response relationships based on cell viability assays as a proxy of neuronal death. Benchmark concentration values (BMC) were estimated using a Hill model, and compared to assess relative toxicity.

RESULTS

Of the 58 SVOCs selected, 28 were suspected of being neurotoxic in mammals, and 21 have been documented as inducing a decrease in cell viability in vitro. 13 have at least one dose-response relationship that can be used to derive a BMC based on a 10% fall in neuronal viability. Based on this in vitro endpoint, PCB-153 appeared to be the most toxic compound, having the lowest BMC₁₀ (0.072μM) and diazinon the least toxic compound, having the highest BMC₁₀ (94.35μM). We showed that experimental designs (in particular choice of cell lines) had a significant influence on BMC calculation.

CONCLUSION

For the first time, the relative in vitro toxicity of 13 indoor contaminants belonging to different chemical families has been assessed on the basis of neuronal cell viability. Lack of comparable toxicity datasets limits the number of SVOCs that can be included. More standardized protocols in terms of cell lines, species and exposure duration should be developed with a view to cumulative risk assessment.

The fate of technical-grade chlordane in mice fed a high-fat diet and its roles as a candidate obesogen

Epidemiological studies indicate that exposure to persistent organic pollutants is positively associated with the prevalence of obesity. To delineate the potential role of technical-grade chlordane in obesity development, chlordane metabolism and chlordane-induced metabolic changes were investigated in mice fed high-fat diet (HFD) over a 6-week period. Gas chromatography-electron capture detector analysis showed that HFD induced more accumulation of technical chlordane in the liver, muscle and adipose tissue. The enantioselectivities of oxychlordane in selected tissues were also influenced by HFD. ¹H NMR-based liver metabolome indicated that technical chlordane can enhance the metabolic alterations induced by HFD. Compared with the low-fat diet (LFD) group, no differences were observed in the LFD + chlordane group. However, as many as 16 metabolites were significantly different between the HFD group and HFD + chlordane group. Moreover, compared to the LFD + chlordane group, the abundances of 24 metabolites significantly increased or decreased in the HFD + chlordane group. Twenty metabolites were altered in the HFD group compared to the LFD group. Tryptophan profiling suggested that both chlordane and HFD can disturb tryptophan catabolism. These interactions between technical chlordane and HFD suggest that technical chlordane is a candidate obesogen.

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.

A Comparison of ToxCast Test Results with In Vivo and Other In Vitro Endpoints for Neuro, Endocrine, and Developmental Toxicities: A Case Study Using Endosulfan and Methidathion

INTRODUCTION

The U.S. Environmental Protection Agency's (EPA's) Toxicity Forecaster (ToxCast) is a potential tool for chemical prioritization, hazard identification, and risk assessment. We conducted a case study to compare ToxCast data with endpoints from other in vitro and in vivo studies for two data-rich pesticides: endosulfan and methidathion.

METHODS

ToxCast assays for endocrine disruption, development (zebrafish), and neurotoxicity were qualitatively compared to traditional neurotoxicity, developmental and reproductive toxicity findings. We also used in vitro-in vivo extrapolation to convert half-maximal activity concentrations in active ToxCast assays to rat oral equivalent doses, and quantitatively compared these to the lowest observable effect level (LOEL) from in vivo studies.

RESULTS

Endosulfan was inactive for GABAA R, unlike in vivo; but active with dopamine transporter assays and was neurotoxic in zebrafish as expected. Methidathion was not active for these endpoints in vivo or in vitro. Acetylcholinesterase inhibition was ToxCast-inactive, although both pesticides are inhibitors in vivo. ToxCast results were generally inactive for endosulfan estrogen receptor agonism and androgen receptor antagonism unlike in vivo. Calculated oral equivalent doses for estrogen receptor and androgen receptor pathways and for zebrafish assays for both compounds were generally consistent with in vivo LOELs. Endosulfan showed neurotoxicity and both pesticides showed developmental effects in the zebrafish assays, although methidathion is not developmentally toxic in vivo.

CONCLUSIONS

ToxCast's predictions showed concordance on some endpoints and nonconcordance, consisting mainly of false inactives, in several critical endpoints, likely due to a lack of metabolic activation and limitations in assay design. Zebrafish assays were good predictors of developmental toxicity and neurotoxicity for endosulfan.

Effects of low dose endosulfan exposure on brain neurotransmitter levels in the African clawed frog Xenopus laevis

Understanding the impact of pesticides in amphibians is of growing concern to assess the causes of their decline. Among pesticides, endosulfan belongs to one of the potential sources of danger because of its wide use and known effects, particularly neurotoxic, on a variety of organisms. However, the effect of endosulfan was not yet evaluated on amphibians at levels encompassing simultaneously brain neurotransmitters and behavioural endpoints. In this context, tadpoles of the African clawed frog Xenopus laevis were submitted to four treatments during 27 d: one control, one ethanol control, and two low environmental concentrations of endosulfan (0.1 and 1 μg L(-1)). Endosulfan induced a significant increase of brain serotonin level at both concentrations and a significant increase of brain dopamine and GABA levels at the lower exposure but acetylcholinesterase activity was not modified by the treatment. The gene coding for the GABA transporter 1 was up-regulated in endosulfan contaminated tadpoles while the expression of other genes coding for the neurotransmitter receptors or for the enzymes involved in their metabolic pathways was not significantly modified by endosulfan exposure. Endosulfan also affected foraging, and locomotion in links with the results of the physiological assays, but no effects were seen on growth. These results show that low environmental concentrations of endosulfan can induce adverse responses in X. laevis tadpoles. At a broader perspective, this suggests that more research using and linking multiple markers should be used to understand the complex mode of action of pollutants.

Developmental exposure to the organochlorine insecticide endosulfan alters expression of proteins associated with neurotransmission in the frontal cortex

Exposure to environmental contaminants, such as organochlorine insecticides during critical periods of neurodevelopment has been shown to be a major contributor to several neuropsychological deficits seen in children, adolescence, and adults. Although the neurobehavioral outcomes resulting from exposure to these compounds are known the neurotransmitter circuitry and molecular targets that mediate these endpoints have not been identified. Given the importance of the frontal cortex in facilitating numerous neuropsychological processes, our current study sought to investigate the effects of developmental exposure to the organochlorine insecticide, endosulfan, on the expression of specific proteins associated with neurotransmission in the frontal cortex. Utilizing in vitro models we were able to show endosulfan reduces cell viability in IMR-32 neuroblastoma cells in addition to reducing synaptic puncta and neurite outgrowth in primary cultured neurons isolated from the frontal cortex of mice. Elaborating these findings to an in vivo model we found that developmental exposure of female mice to endosulfan during gestation and lactation elicited significant alterations to the GABAergic (GAT1, vGAT, GABAA receptor), glutamatergic (vGlut and GluN2B receptor), and dopaminergic (DAT, TH, VMAT2, and D2 receptor) neurotransmitter systems in the frontal cortex of male offspring. These findings identify damage to critical neurotransmitter circuits and proteins in the frontal cortex, which may underlie the neurobehavioral deficits observed following developmental exposure to endosulfan and other organochlorine insecticides.

Pesticide exposure and neurodevelopmental outcomes: review of the epidemiologic and animal studies

Assessment of whether pesticide exposure is associated with neurodevelopmental outcomes in children can best be addressed with a systematic review of both the human and animal peer-reviewed literature. This review analyzed epidemiologic studies testing the hypothesis that exposure to pesticides during pregnancy and/or early childhood is associated with neurodevelopmental outcomes in children. Studies that directly queried pesticide exposure (e.g., via questionnaire or interview) or measured pesticide or metabolite levels in biological specimens from study participants (e.g., blood, urine, etc.) or their immediate environment (e.g., personal air monitoring, home dust samples, etc.) were eligible for inclusion. Consistency, strength of association, and dose response were key elements of the framework utilized for evaluating epidemiologic studies. As a whole, the epidemiologic studies did not strongly implicate any particular pesticide as being causally related to adverse neurodevelopmental outcomes in infants and children. A few associations were unique for a health outcome and specific pesticide, and alternative hypotheses could not be ruled out. Our survey of the in vivo peer-reviewed published mammalian literature focused on effects of the specific active ingredient of pesticides on functional neurodevelopmental endpoints (i.e., behavior, neuropharmacology and neuropathology). In most cases, effects were noted at dose levels within the same order of magnitude or higher compared to the point of departure used for chronic risk assessments in the United States. Thus, although the published animal studies may have characterized potential neurodevelopmental outcomes using endpoints not required by guideline studies, the effects were generally observed at or above effect levels measured in repeated-dose toxicology studies submitted to the U.S. Environmental Protection Agency (EPA). Suggestions for improved exposure assessment in epidemiology studies and more effective and tiered approaches in animal testing are discussed.

Effects of prenatal and postnatal exposure to amitraz on norepinephrine, serotonin and dopamine levels in brain regions of male and female rats

The effects of maternal exposure to amitraz on brain region monoamine levels of male and female offspring rats at 60 days of age were observed. Maternal and offspring body weight, physical and general activity development were unaffected by the exposure of dams to amitraz (20mg/kgbw, orally on days 6-21 of pregnancy and 1-10 of lactation). Male and female offspring were sacrificed at 60 days of age and possible alterations in the content and metabolism of NE, DA and 5-HT were determined in brain regions by HPLC. The results showed that all these neurotransmitter systems were altered in a brain regional-related manner. In male and female offspring, amitraz induced a significant decrease in the prefrontal cortex 5-HT and its metabolite 5-HIAA and DA and its metabolites DOPAC and HVA levels with interaction of sex. Nevertheless, we verified that striatum DA and 5-HT and corresponding metabolite contents decreased in male and female offspring without statistical distinction of sex. In contrast, amitraz did not modify 5-HT content, but caused an increase in 5-HIAA content in the medulla oblongata and hippocampus in male and female offspring. Alterations in the hippocampus DA, DOPAC and HVA levels after amitraz exposure were also observed displaying a sex interaction. NE levels also showed a decrease after amitraz treatment in the prefrontal cortex and striatum without statistical sex interaction, but MHPG levels decreased in both regions with a sex interaction. Amitraz evoked increases in 5-HT turnover in the prefrontal cortex as well as in DA turnover in the striatum and hippocampus but decreases in NE turnover in the hypothalamus, prefrontal cortex and striatum. The present findings indicated that maternal exposure to amitraz altered noradrenergic, serotonergic and dopaminergic neurochemistry in their offspring in the prefrontal cortex, striatum and hippocampus, and those variations could be related to several alterations in the functions in which these brain regions are involved.

Estrogens of multiple classes and their role in mental health disease mechanisms

Gender and sex hormones can influence a variety of mental health states, including mood, cognitive development and function, and vulnerability to neurodegenerative diseases and brain damage. Functions of neuronal cells may be altered by estrogens depending upon the availability of different physiological estrogenic ligands; these ligands and their effects vary with life stages, the genetic or postgenetic regulation of receptor levels in specific tissues, or the intercession of competing nonphysiological ligands (either intentional or unintentional, beneficial to health or not). Here we review evidence for how different estrogens (physiological and environmental/dietary), acting via different estrogen receptor subtypes residing in alternative subcellular locations, influence brain functions and behavior. We also discuss the families of receptors and transporters for monoamine neurotransmitters and how they may interact with the estrogenic signaling pathways.

Differential regulation of dopamine transporter function and location by low concentrations of environmental estrogens and 17beta-estradiol

BACKGROUND

The effects of 17beta-estradiol (E2) and xenoestrogens (XEs) on dopamine transport may have important implications for the increased incidence of neurologic disorders, especially in women during life stages characterized by frequent hormonal fluctuations.

OBJECTIVE

We examined low concentrations of XEs [dieldrin, endosulfan, o', p'-dichlorodiphenyl-ethylene (DDE), nonylphenol (NP), and bisphenol A (BPA)] for nongenomic actions via action of membrane estrogen receptors (ERs).

METHODS

We measured activity of the dopamine transporter (DAT) by the efflux of 3H-dopamine in nontransfected nerve growth factor-differentiated PC12 rat pheochromocytoma cells expressing membrane DAT, ER-alpha, ER-beta, and G-protein-coupled receptor 30. We used a plate immunoassay to monitor trafficking of these proteins.

RESULTS

All compounds at 1 nM either caused efflux or inhibited efflux, or both; each compound evoked a distinct oscillatory pattern. At optimal times for each effect, we examined different concentrations of XEs. All XEs were active at some concentration < 10 nM, and dose responses were all nonmonotonic. For example, 10(-14) to 10(-11) M DDE caused significant efflux inhibition, whereas NP and BPA enhanced or inhibited efflux at several concentrations. We also measured the effects of E2/XE combinations; DDE potentiated E(2)-mediated dopamine efflux, whereas BPA inhibited it. In E2-induced efflux, 15% more ER-alpha trafficked to the membrane, whereas ER-beta waned; during BPA-induced efflux, 20% more DAT was trafficked to the plasma membrane.

CONCLUSIONS

Low levels of environmental estrogen contaminants acting as endocrine disruptors via membrane ERs can alter dopamine efflux temporal patterning and the trafficking of DAT and membrane ERs, providing a cellular mechanism that could explain the disruption of physiologic neurotransmitter function.

Endosulfan acute toxicity in Bufo bufo gills: ultrastructural changes and nitric oxide synthase localization

Endosulfan is an organochlorine pesticide used in agriculture for a wide range of crops. Endosulfan concentrations of up to 0.7 mg/L can be found in ponds and streams near sprayed agricultural fields. We investigated the short-term toxicity of endosulfan in common toad (Bufo bufo) tadpoles after 24, 48, and 96 h of exposure. Acute toxicity was evaluated at nominal concentrations ranging from 0.01 to 0.6 mg/L: concentrations that could be found after the application of pesticide. Our results show that 0.43 mg/L of endosulfan caused 50% mortality (LC(50)). The effects of a sublethal endosulfan concentration (0.2mg/L) on gill apparatus morphology were evaluated by scanning and transmission electron microscopy. Immunohistochemical methods were also applied to detect the expression pattern of the inducible isoform of nitric oxide synthase (iNOS) in the gills using the confocal laser scanner microscope. Exposure to 0.2mg/L of endosulfan caused an apparent increase in mucus production, the occurrence of secretory vesicles and lamellar bodies, a widening of intercellular spaces and additionally there was evidence of an inflammatory response in the gill apparatus. The morphological alterations occurred after 24h and were more pronounced after 48 and 96 h of exposure. Altered morphology and increased mucus secretion indicate impaired gas exchange and osmoregulation in the gills. In addition, there was an increase of iNOS expression after 24 and 48 h which may reflect hypoxia and inflammation in the gill epithelium. Our results clearly indicate that short-term exposure to a sublethal concentration of endosulfan, near the high end of the environmental range, disrupts gill morphology and function in B. bufo tadpoles.

Effects of in utero and lactational exposure to endosulfan in prefrontal cortex of male rats

The possible neurotoxic effects of the organochlorine pesticide endosulfan have been evaluated on male offspring rats exposed in utero and during lactation. Dams were treated with 0.61mg or 6.12mg endosulfan/(kgday) from the gestation beginning until the weaning. Male offspring rats were sacrificed at post-natal days (PND) 15, 30 and 60, and possible alterations in the content and metabolism of biogenic amines and amino acids were determined in prefrontal cortex using high-performance liquid chromatography (HPLC). Globally, endosulfan induced an increase in amino acid content in prefrontal cortex at PND 15 and PND 30. However, the levels of GABA at PND 15 and those of glutamine at PND 30 were not modified. At PND 60, a significant reduction in the content of GABA and taurine was observed, while the concentration of glutamate, aspartate and glutamine remained constant. Endosulfan did not modify norepinephrine and dopamine content, but serotonin concentration was increased at PND 30 and PND 60 and serotoninergic and dopaminergic metabolism was also modified. These results suggest that pre- and post-natal exposure to endosulfan affects biogenic amines and amino acids in prefrontal cortex, and those variations could be related to several alterations in the functions in which the prefrontal cortex is involved.

Developmental exposure to pesticides zineb and/or endosulfan renders the nigrostriatal dopamine system more susceptible to these environmental chemicals later in life

Several epidemiological studies have suggested a role for environmental pesticide exposures in idiopathic Parkinson's disease. The purpose of this study was to test the hypothesis that exposure to pesticides such as endosulfan and/or zineb during critical periods of postnatal development could result in neuronal dysfunction and enhance the impact of these pesticides during exposure as adults. C57BL/6 mice, exposed daily to each of the pesticides or their mixtures from postnatal days 5 to 19, exhibited insignificant changes in striatal dopamine, acetylcholinesterase and alpha-synuclein levels. However, mice exposed to these pesticides as juveniles and re-exposed at 8 months of age had significantly altered striatum and brain cortex neurotransmitter levels. Thus, mice re-exposed during adulthood to zineb, endosulfan and their mixtures showed a significantly depleted striatal dopamine levels, to 22, 16 and 35% of control, respectively. Acetylcholinesterase activity in the cerebral cortex was significantly increased in all pesticide treated groups (rho< or =0.05) upon repeated exposure, and pesticide mixture treatment also significantly increased levels of normal and aggregated alpha-synuclein. Collectively, these findings support our hypothesis that exposure to pesticides such as endosulfan and zineb during critical periods of postnatal development contributes to neurotransmitter changes upon re-challenge in adulthood.

Reactive oxygen species in in vitro pesticide-induced neuronal cell (SH-SY5Y) cytotoxicity: role of NFkappaB and caspase-3

Oxidative stress has been implicated in pesticide-induced neurotoxicity, based on its role in the cascade of biochemical changes that lead to dopaminergic neuronal cell death. We have, therefore, examined the role of oxidative stress caused by the pesticides endosulfan and zineb in human neuroblastoma cells (SH-SY5Y) in culture. Upon treatment with 50-200 microM concentrations of either of these pesticides, SH-SY5Y cells generated both superoxide anion and hydrogen peroxide in a dose-and time-dependent manner. Mixtures of the pesticides significantly enhanced the production of these reactive oxygen species compared to individual pesticide exposures. Pesticide treatment decreased superoxide dismutase, glutathione peroxidase, and catalase activities in SH-SY5Y cells. Additionally, these pesticides induced lipid peroxide (thiobarbituric acid reactive products) formation in these cells. While both pesticides individually (at 100 microM) increased caspase-3 activity, cells exposed to a mixture of the pesticides exhibited significantly low levels of this enzyme, probably due to excessive necrotic cell death. Furthermore, exposure to these pesticides increased nuclear NFkappaB activity. Taken together, these findings suggest that the cytotoxicity of endosulfan and zineb, both individually and in mixtures may, at least in part, be associated with the generation of reactive oxygen species with concomitant increased expression of NFkappaB.

Exposure to mixtures of endosulfan and zineb induces apoptotic and necrotic cell death in SH-SY5Y neuroblastoma cells,in vitro

A number of epidemiological studies have demonstrated a strong association between the incidence of Parkinson's disease and pesticide exposure. Earlier it was demonstrated that exposure to the pesticides endosulfan and zineb, alone and in combination, caused neurodegeneration in vivo. It was hypothesized that these pesticides cause neurotoxicity, in part, by enhancing apoptotic cell death. SH-SY5Y human neuroblastoma cells, which retain a catecholaminergic phenotype, were exposed to endosulfan, zineb or a combination of these chemicals, in vitro. For mixture studies, concentrations of pesticides (100 microM each) were chosen based on LC(25) (lethal concentration) that would result in minimum cell death. Exposure to a mixture of pesticides exhibited significantly (P < or = 0.05) higher toxicity than each one alone. Both pesticides were found to cause apoptotic cell death that was concentration (50-400 microM) dependent. A flow cytometric (7-aminoactinomycin D) assay was used to distinguish live, early apoptotic and late apoptotic/necrotic populations. Exposure to mixtures of the pesticides enhanced both early apoptosis and late apoptosis/necrosis compared with either chemical alone. Visual evaluation using a DNA ladder assay and a fluorescence Annexin V/PI assay confirmed the contribution of both apoptotic and necrotic processes. These findings suggest that the cytotoxicity of endosulfan and zineb, both individually and in mixtures, is associated with the occurrence of early and late apoptotic/necrotic processes in SH-SY5Y human neuroblastoma cells and support the contention that pesticide-induced neuronal cell death leading to neurodegenerative disease may, at least in part, be associated with early and late apoptosis of dopaminergic neurons.

A case for revisiting the safety of pesticides: a closer look at neurodevelopment

The quality and quantity of the data about the risk posed to humans by individual pesticides vary considerably. Unlike obvious birth defects, most developmental effects cannot be seen at birth or even later in life. Instead, brain and nervous system disturbances are expressed in terms of how an individual behaves and functions, which can vary considerably from birth through adulthood. In this article I challenge the protective value of current pesticide risk assessment strategies in light of the vast numbers of pesticides on the market and the vast number of possible target tissues and end points that often differ depending upon timing of exposure. Using the insecticide chlorpyrifos as a model, I reinforce the need for a new approach to determine the safety of all pesticide classes. Because of the uncertainty that will continue to exist about the safety of pesticides, it is apparent that a new regulatory approach to protect human health is needed.

Repeated Episodes of Endosulfan Poisoning

INTRODUCTION

A number of families in a rural area of Jabalpur District (Madhya Pradesh), India, were affected by repeated episodes of convulsive illness over a period of three weeks. The aim of this investigation was to determine the cause of the illness.

METHODS

The investigation included a house-to-house survey, interviews of affected families, discussions with treating physicians, and examination of hospital records. Endosulfan poisoning was suspected as many villagers were using empty pesticide containers for food storage. To confirm this, our team collected blood and food samples, which were transported to the laboratory and analyzed with GC-ECD.

RESULTS

Thirty-six persons of all age groups had illness of varying severity over a period of three weeks. In the first week, due to superstitions and lack of treatment, three children died. In the second week, symptomatic treatment of affected persons in a district hospital led to recovery but recurrence of convulsive episodes occurred after the return home. In the third week, 10 people were again hospitalized in a teaching hospital. Investigations carried out in this hospital ruled out infective etiology but no facilities were available for chemical analysis. All persons responded to symptomatic treatment. The blood and food samples analyzed by our team showed presence of endosulfan, which was confirmed by GCMS. One of the food items (Laddu) prepared from wheat flour was found to contain 676 ppm of alpha-endosulfan.

CONCLUSIONS

Contamination of wheat grains or flour with endosulfan and its consumption over a period of time was the most likely cause of repeated episodes of convulsions, but the exact reason for this contamination could not be determined. This report highlights the unsafe disposal of pesticide containers by illiterate farm workers, superstitions leading to delay in treatment, and susceptibility of children to endosulfan.

Behavioral effects of exposure to endosulfan and methyl parathion in adult rats

Endosulfan (ES) and methyl parathion (MP) are widely used in Latin America, and simultaneous exposure to both products is documented. This exposure may have effects on the nervous system because their targets include the GABAergic and cholinergic systems, which are main modulators of neuronal excitability in the cortex and hippocampus. We tested whether low-level, repeated exposure of adult rats to commercial formulations containing ES and MP disrupts spatial learning in the water maze. Five groups of eight animals received subcutaneously appropriate dilutions of the commercial formulations to yield the following treatments during 10 days: saline, 25 mg/kg ES, 2 mg/kg MP (MP(2)), 25 mg/kg ES plus 1 mg/kg MP (ES+MP(1)) and 25 mg/kg ES plus 2 mg/kg MP (ES+MP(2)). In addition, markers of neurological function, renal and hepatic damage were explored as potential consequences of exposure. In the absence of overt toxicity, the groups exposed to the ES plus MP showed significantly longer escape latencies, higher number of failures to reach the platform and more time in the periphery of the tank than the control and single-exposed groups. This finding shows that commercial formulations of ES and MP have marginal effects when administered individually but can produce behavioral alterations when given in combination.

Levels of dopamine and noradrenaline in the developing of retina--effect of light deprivation

The effect of light deprivation on the levels of dopamine and noradrenaline was studied in the developing rat retina. These transmitters were estimated in three groups of rats: (i) cycling light reared; (ii) dark reared since birth; and (iii) dark reared since birth, but exposed to cycling light for 1 day prior to the estimation of catecholamines. Our results show that (1) there is a progressive decrease in the levels of dopamine and noradrenaline in the cycling light and dark reared rats during postnatal development; (2) dark rearing further reduces the content of dopamine and noradrenaline; and (3) restoration of physiological (light) stimulus in the dark-reared rats during the early postnatal period results in the recovery of noradrenaline to a greater extent than that of dopamine. This study demonstrates a progressive decrease in the plasticity of dopaminergic system during retinal development, while such a decrease is not apparent in the noradrenergic system.