Long-term event-related potential changes following organophosphorus insecticide poisoning

Comprehensive Clinical Assessment of Patients With Acute Organophosphorus Poisoning in a Tertiary Care Hospital

Background The use of organophosphorus (OP) compounds as pesticides is widespread, particularly in developing nations such as India. These substances are easily accessible and often linked to suicide poisoning incidents, especially among distressed farmers. In India, OP poisoning remains a significant cause of emergency hospital admissions. This study aims to analyze the clinical profile of patients admitted with OP poisoning, focusing on the various clinically significant characteristics and aspects associated with these cases. Methods Throughout the course of two years (from June 2022 to May 2024), five hospitals with critical care units participated in this prospective observational study. These hospitals referred patients to the Prathima Institute of Medical Sciences, which served as the central facility for the study. The study focused on individuals who arrived at the emergency room within 24 hours of acute exposure to organophosphate pesticides. A total of 150 patients meeting the inclusion criteria were enrolled. Data collection included a comprehensive clinical examination, detailed patient history, and monitoring of the response to intravenous atropine. The severity of the poisoning was evaluated using the Peradeniya Organophosphorus Poisoning (POP) scale, adapted for this study. Statistical analysis was performed using IBM SPSS Statistics for Windows, Version 23 (Released 2015; IBM Corp., Armonk, New York), with descriptive statistics used to summarize the categorical and continuous variables. Results The results of the study demonstrated a notable relationship between the arrival time at the health facility and mortality rates among patients with OP poisoning. Patients who arrived within three hours had a mortality rate of 13.2% (five out of 38 cases), while those arriving between three and six hours had a slightly higher rate of 14.3% (10 out of 70 cases). The mortality rate sharply increased to 28.6% (12 out of 42 cases) for patients who arrived after six hours. Among the OP compounds, monocrotophos showed the highest mortality rate at 80% (eight out of 10 cases), followed by dimethoate with 42.9% (12 out of 28 cases) and dichlorvos with 62.5% (five out of eight cases). The overall mortality rate in the study was 22.7% (34 out of 150 cases). Conclusions Poisoning with OP has primarily impacted young, productive men. Considerable mortality results from a disease condition that is more severe at presentation. It is advised to selectively outlaw the riskier substances that account for a larger percentage of fatalities.

The α4 Nicotinic Acetylcholine Receptor Is Necessary for the Initiation of Organophosphate-Induced Neuronal Hyperexcitability

Acute intoxication with organophosphorus (OP) cholinesterase inhibitors can produce seizures that rapidly progress to life-threatening status epilepticus. Significant research effort has been focused on investigating the involvement of muscarinic acetylcholine receptors (mAChRs) in OP-induced seizure activity. In contrast, there has been far less attention on nicotinic AChRs (nAChRs) in this context. Here, we address this data gap using a combination of in vitro and in vivo models. Pharmacological antagonism and genetic deletion of α4, but not α7, nAChR subunits prevented or significantly attenuated OP-induced electrical spike activity in acute hippocampal slices and seizure activity in mice, indicating that α4 nAChR activation is necessary for neuronal hyperexcitability triggered by acute OP exposures. These findings not only suggest that therapeutic strategies for inhibiting the α4 nAChR subunit warrant further investigation as prophylactic and immediate treatments for acute OP-induced seizures, but also provide mechanistic insight into the role of the nicotinic cholinergic system in seizure generation.

Changes of attention-related brain activity over 6 months after acute organophosphate pesticide poisoning: a prospective follow-up study

CONTEXT

Ingestion of organophosphate (OP) pesticides is a common method of self-harm in developing countries. Apart from acute cholinergic effects, limited evidence implicates OP poisoning in long-term neurocognitive deficits. However, prospective neurophysiological evidence of long-term deficits is scarce in humans. We aimed to determine long-term cognitive changes of acute OP pesticide self-poisoning in a prospective follow-up study, using event-related potentials (ERPs), an electroencephalographic index of cognitive functioning.

METHODS

We recruited 203 patients (147 men) hospitalised with OP pesticide ingestion (OP group; all had significant erythrocyte cholinesterase inhibition) and 50 patients (23 men) with paracetamol overdose (control group) as a means of self-harm. We recorded their ERPs and behavioural performance in a selective attention task at three post-exposure time points: on discharge from hospital (around 14 days post-ingestion), 6 weeks and 6 months post-ingestion. We compared the reaction time and ERP components of the two groups at each time point, adjusting for sex, age, education and comorbid depression in multiple regression models.

RESULTS

OP group had significantly slower reaction times than the control group on discharge and at 6 weeks, but not at 6 months. On discharge, the OP group also showed significantly prolonged latency of the parietal P3b component, signifying delayed attentional processing. P3b amplitudes were also significantly smaller in the OP group on discharge and at 6 months. Within the OP group, greater clinical severity of poisoning was associated with smaller P3b amplitudes. Early pre-attentive cortical processing (as indexed by N1 ERP component) showed no significant intergroup differences.

CONCLUSIONS

Acute OP pesticide poisoning was associated with impaired behavioural and neurophysiological indices of selective attention. These deficits outlast the cholinergic phase of intoxication. The neurobehavioral impairment disappears over months, but neurophysiological deficits seem to last even after 6 months. This impairment could potentially compromise the performance and safety of patients for months following clinical recovery.

Neuroinflammation as a Therapeutic Target for Mitigating the Long-Term Consequences of Acute Organophosphate Intoxication

Acute intoxication with organophosphates (OPs) can cause a potentially fatal cholinergic crisis characterized by peripheral parasympathomimetic symptoms and seizures that rapidly progress to status epilepticus (SE). While current therapeutic countermeasures for acute OP intoxication significantly improve the chances of survival when administered promptly, they are insufficient for protecting individuals from chronic neurologic outcomes such as cognitive deficits, affective disorders, and acquired epilepsy. Neuroinflammation is posited to contribute to the pathogenesis of these long-term neurologic sequelae. In this review, we summarize what is currently known regarding the progression of neuroinflammatory responses after acute OP intoxication, drawing parallels to other models of SE. We also discuss studies in which neuroinflammation was targeted following OP-induced SE, and explain possible reasons why such therapeutic interventions have inconsistently and only partially improved long-term outcomes. Finally, we suggest future directions for the development of therapeutic strategies that target neuroinflammation to mitigate the neurologic sequelae of acute OP intoxication.

Organophosphate induced delayed neuropathy after an acute cholinergic crisis in self-poisoning

INTRODUCTION

Despite organophosphate pesticide is the most prevalent cause of acute poisoning in low- and middle-income countries, data on organophosphate induced delayed neuropathy (OPIDN) are limited. We aimed to characterize organophosphates' long-term effects on the peripheral nervous system after an acute cholinergic crisis in adults.

METHODS

We performed a prospective observational study in an academic hospital of north India in patients aged 13-40 years with acute organophosphate ingestion. After resolving the cholinergic crisis, the patients were followed for six months with neurologic assessments, including history, neurologic examination, and nerve conduction study (NCS).

RESULTS

Twenty-three patients were recruited to the study. All but one had normal neurological examination and NCS at discharge from hospital a median duration of six days (interquartile range, 3-10) after self-poisoning. Eight (34.8%) developed OPIDN during the six-month follow-up. Three patients had symptomatic neuropathy, and NCS detected subclinical peripheral nerve involvement in five. All cases were associated with chlorpyrifos ingestion (8/17 total chlorpyrifos cases). Two OPIDN cases had foot drop and gait ataxia at three-month which persist at six-month. One patient had distal paresthesia at three months, which improved at a six-month follow-up. NCS in OPIDN cases invariably revealed axonal degeneration, injury to motor fibers more than sensory fibers, and frequent peroneal nerve involvement. None of the baseline characteristics, including the ingested amount, predicted clinical or subclinical OPIDN in chlorpyrifos self-poisoned patients on a univariant analysis.

CONCLUSION

Peripheral nerve involvement is not uncommon after recovery from a cholinergic crisis in chlorpyrifos self-poisoning and debilitating in some patients. Detection of subclinical injury on NCS may provide an early window to prevent severe symptomatic neuropathy.

Subacute and chronic neuropsychological sequalae of acute organophosphate pesticide self-poisoning: a prospective cohort study from Sri Lanka

CONTEXT

Some epidemiological evidence implicates acute organophosphate (OP) pesticide poisoning in long-term neurocognitive deficits. However, no study has prospectively followed up poisoned patients long-term from the time of intoxication. We aimed to determine whether clinically significant acute OP self-poisoning leads to subacute and chronic neurocognitive deficits, in a prospective follow up study.

METHODS

Employing Mini Mental State Examination, Digit Span and Cambridge Neuropsychological Test Automated Battery (CANTAB), we compared multiple cognitive functions in 222 patients hospitalized with acute OP pesticide self-poisoning with a control group of 52 patients hospitalized with paracetamol overdose, at three time points: on discharge following clinical recovery, 6 weeks and 6 months post-ingestion. Intergroup comparisons at each time point were done in multiple regression models, adjusting for sex, age, education and psychiatric comorbidities. OP within-group analysis was done to determine a dose-response relationship.

RESULTS

After adjusting for covariates, the OP poisoned group had significantly poorer working memory (Digit Span) and episodic memory (CANTAB Paired Associates Learning); impaired spatial planning (CANTAB Stocking of Cambridge); and slower response speed in the sustained attention task (CANTAB Rapid Visual Information Processing), in the post-discharge assessment. Only working memory and episodic memory measures were impaired in the OP group at 6 weeks, whereas no significant intergroup differences were observed at 6 months. The OP subgroup who had complete red cell acetylcholinesterase inhibition on admission had poorer episodic memory when tested post-discharge than those who had partial inhibition, but no significant subgroup differences were observed at 6 weeks or 6 months.

DISCUSSION

Acute OP pesticide poisoning may cause neuropsychological impairment that outlasts the cholinergic phase on a subacute time scale; but does not cause measurable chronic neuropsychological deficits.

P300 development from infancy to adolescence

This article provides an overview of P300 research from infancy through adolescence. First, a brief historical overview is provided highlighting seminal studies that began exploration of the P300 component in developmental groups. Overall, these studies suggest that the P300 can be detected in children and appears to reflect similar cognitive processes to those in adults; however, it is significantly delayed in its latency to peak. Second, two striking findings from developmental research are the lack of a clear P300 component in infancy and differential electrophysiological responses to novel, unexpected stimuli in children, adolescents, and adults. Third, contemporary questions are described, which include P300-like components in infancy, alteration of P300 in atypically developing groups, relations between P300 and behavior, individual differences of P300, and neural substrates of P300 across development. Finally, we conclude with comments regarding the power of a developmental perspective and suggestions for important issues that should be addressed in the next 50 years of P300 research.

Prenatal organophosphate insecticide exposure and infant sensory function

BACKGROUND

Occupational studies suggest that exposure to organophosphate insecticides (OPs) can lead to vision or hearing loss. Yet the effects of early-life exposure on visual and auditory function are unknown. Here we examined associations between prenatal OP exposure and grating visual acuity (VA) and auditory brainstem response (ABR) during infancy.

METHODS

30 OPs were measured in umbilical cord blood using gas chromatography tandem mass spectrometry in a cohort of Chinese infants. Grating visual acuity (VA) (n = 179-200) and auditory brainstem response (ABR) (n = 139-183) were assessed at 6 weeks, 9 months, and 18 months. Outcomes included VA score, ABR wave V latency and central conduction time, and head circumference (HC). Associations between sensory outcomes during infancy and cord OPs were examined using linear mixed models.

RESULTS

Prenatal chlorpyrifos exposure was associated with lower 9-month grating VA scores; scores were 0.64 (95% CI: -1.22, -0.06) points lower for exposed versus unexposed infants (p = 0.03). The OPs examined were not associated with infant ABR latencies, but chlorpyrifos and phorate were both significantly inversely associated with HC at 9 months; HCs were 0.41 (95% CI: 0.75, 0.6) cm and 0.44 (95% CI: 0.88, 0.1) cm smaller for chlorpyrifos (p = 0.02) and phorate (p = 0.04), respectively.

CONCLUSIONS

We found deficits in grating VA and HC in 9-month-old infants with prenatal exposure to chlorpyrifos. The clinical significance of these small but statistically significant deficits is unclear. However, the disruption of visual or auditory pathway maturation in infancy could potentially negatively affect downstream cognitive development.

Assessment of exogenous melatonin action on mouse liver cells after exposure to soman

Melatonin is a hormone with many different biological activities and therefore seems to be an important factor reducing the harmful effects caused by toxic organophosphorus compounds. In this study, we attempted to evaluate the protective effect of melatonin on liver cells of mice challenged with chemical warfare agent-soman. The study was conducted at the level of ultrastructural and biochemical changes (analysis of the activity of model lysosomal enzymes and assessment of the level of lipid peroxidation). Significant biochemical and ultrastructural changes were found in the studied mouse hepatocytes after administration of soman alone, and soman in combination with melatonin, and the scope of the disclosed changes was dependent on the time of action of the examined factors. Melatonin has shown protective action, shielding liver cells from toxic effects of soman, which may result from its antioxidant properties and stimulation of the lysosomal compartment, the system coordinating the isolation and removal of cell-threatening processes.

Adverse effects of pesticides on central auditory functions in tobacco growers

OBJECTIVE

To investigate the effects of exposure to pesticides on the central auditory functions (CAF) of Brazilian tobacco growers.

DESIGN

This was a cross-sectional study carried out between 2010 and 2012. Participants were evaluated with two behavioural procedures to investigate CAF, the random gap detection test (RGDT) and the dichotic digit test in Portuguese (DDT).

STUDY SAMPLE

A total of 22 growers exposed to pesticides (study group) and 21 subjects who were not exposed to pesticides (control group) were selected.

RESULTS

No significant differences between groups were observed for pure-tone thresholds. A significant association between pesticide exposure and the results for RGDT and DDT was found. Significant differences between pesticide-exposed and nonexposed subjects were found for RGDT frequency average and DDT binaural average, when including age and hearing level as covariates. Age was significantly associated with RGDT frequency average, DDT left ear score, DDT binaural average and DDT right ear advantage. Hearing levels were not significantly associated with any of the test scores. The relative risk of failing the DDT and RGDT for the study group was 1.88 (95% CI: 1.10-3.20) and 1.74 (95% CI: 1.06-2.86), respectively, as compared with the control group.

CONCLUSIONS

The results showed that tobacco growers exposed to pesticides exhibited signs of central auditory dysfunction characterised by decrements in temporal processing and binaural integration processes/abilities.

The synthetic neuroactive steroid SGE-516 reduces status epilepticus and neuronal cell death in a rat model of soman intoxication

Organophosphorus nerve agents (OPNAs) are irreversible inhibitors of acetylcholinesterase that pose a serious threat to public health because of their use as chemical weapons. Exposure to high doses of OPNAs can dramatically potentiate cholinergic synaptic activity and cause status epilepticus (SE). Current standard of care for OPNA exposure involves treatment with cholinergic antagonists, oxime cholinesterase reactivators, and benzodiazepines. However, data from pre-clinical models suggest that OPNA-induced SE rapidly becomes refractory to benzodiazepines. Neuroactive steroids (NAS), such as allopregnanolone, retain anticonvulsant activity in rodent models of benzodiazepine-resistant SE, perhaps because they modulate a broader variety of GABA_A receptor subtypes. SGE-516 is a novel, next generation NAS and a potent and selective GABA_A receptor positive allosteric modulator (PAM). The present study first established that SGE-516 reduced electrographic seizures in the rat lithium-pilocarpine model of pharmacoresistant SE. Then the anticonvulsant activity of SGE-516 was investigated in the soman-intoxication model of OPNA-induced SE. SGE-516 (5.6, 7.5, and 10mg/kg, IP) significantly reduced electrographic seizure activity compared to control when administered 20min after SE onset. When 10mg/kg SGE-516 was administered 40min after SE onset, seizure activity was still significantly reduced compared to control. In addition, all cohorts of rats treated with SGE-516 exhibited significantly reduced neuronal cell death as measured by FluoroJade B immunohistochemistry. These data suggest synthetic NASs that positively modulate both synaptic and extrasynaptic GABA_A receptors may be candidates for further study in the treatment of OPNA-induced SE.

Impact of Exposure to Fenitrothion on Vital Organs in Rats

This study was designed to investigate the impact of oral administration of fenitrothion (10 mg/kg) on liver, kidney, brain, and lung function in rats. The effect was studied on days 7, 14, 21, 28, and 42. Our results have shown deterioration in liver function as evidenced by the elevation in serum ALT, AST, ALP, and bilirubin and reduction in albumin and hepatic glycogen. This was associated with a state of hyperglycemia and hyperlipidemia and increased prothrombin time, while hemoglobin content was reduced. In addition, the kidney function was reduced as indicated by the elevation in serum creatinine, uric acid, and BUN, while the serum levels of magnesium, potassium, and sodium were reduced. This study also showed an impairment in brain neurotransmitter (elevated 5-HT, glutamate, GABA, and reduced dopamine and norepinephrine level). This was associated with a reduction in the barrier capacity in brain and lung. Fenitrothion also caused a decrease in cholinesterase activity in serum, lung, and brain activity associated with a state of oxidative stress in all tested organs and hyperammonemia. These results support the hazards of pesticide use and shows the importance of minimizing pesticide use or discovering new safe pesticides.

Repeated exposures to chlorpyrifos lead to spatial memory retrieval impairment and motor activity alteration

Chlorpyrifos (CPF) is one of the most commonly used insecticides throughout the world and has become one of the major pesticides detected in farm products. Chronic exposures to CPF, especially at the dosages without eliciting any systemic toxicity, require greater attention. The purpose of this study was, therefore, to evaluate the behavioral effects of repeated low doses (doses that do not produce overt signs of cholinergic toxicity) of CPF in adult rats. Male rats were given 0, 1.0, 5.0 or 10.0mg/kg of CPF through intragastric administration daily for 4 consecutive weeks. The behavioral functions were assessed in a series of behavioral tests, including water maze task, open-field test, grip strength and rotarod test. Furthermore, the present study was designed to evaluate the effects of repeated exposures to CPF on water maze recall and not acquisition. The results showed that the selected doses only had mild inhibition effects on cholinesterase activity, and have no effects on weight gain and daily food consumption. Performances in the spatial retention task (Morris water maze) were impaired after the 4-week exposure to CPF, but the performances of grip strength and rotarod test were not affected. Motor activities in the open field were changed, especially the time spent in the central zone increased. The results indicated that repeated exposures to low doses of CPF may lead to spatial recall impairments, behavioral abnormalities. However, the underlying mechanism needs further investigations.

Delayed reduction of hippocampal synaptic transmission and spines following exposure to repeated subclinical doses of organophosphorus pesticide in adult mice

Agricultural and household organophosphorus (OP) pesticides inhibit acetylcholinesterase (AchE), resulting in increased acetylcholine (Ach) in the central nervous system. In adults, acute and prolonged exposure to high doses of AchE inhibitors causes severe, clinically apparent symptoms, followed by lasting memory impairments and cognitive dysfunction. The neurotoxicity of repeated environmental exposure to lower, subclinical doses of OP pesticides in adults is not as well studied. However, repeated exposure to acetylcholinesterase inhibitors, such as chlorpyrifos (CPF), pyridostigmine, and sarin nerve agent, has been epidemiologically linked to delayed onset symptoms in Gulf War Illness and may be relevant to environmental exposure in farm workers among others. We treated adult mice with a subclinical dose (5 mg/kg) of CPF for 5 consecutive days and investigated hippocampal synaptic transmission and spine density early (2-7 days) and late (3 months) after CPF administration. No signs of cholinergic toxicity were observed at any time during or after treatment. At 2-7 days after the last injection, we found increased synaptic transmission in the CA3-CA1 region of the hippocampus of CPF-treated mice compared with controls. In contrast, at 3 months after CPF administration, we observed a 50% reduction in synaptic transmission likely due to a corresponding 50% decrease in CA1 pyramidal neuron synaptic spine density. This study is the first to identify a biphasic progression of synaptic abnormalities following repeated OP exposure and suggests that even in the absence of acute cholinergic toxicity, repeated exposure to CPF causes delayed persistent damage to the adult brain in vivo.

Auditory event-related potential changes in chronic occupational exposure to organophosphate pesticides

OBJECTIVE

To determine whether chronic occupational exposure to organophosphates (OP) pesticides leads to cognitive impairment using event-related potentials (ERPs).

METHODS

ERPs of 38 vegetable farmers applying OP pesticides and 35 controls were recorded using an auditory oddball paradigm. The N1, P2, N2 and P300 ERP components and the number of counting errors were compared between the groups.

RESULTS

The farmers made significantly more counting errors than controls in the oddball task. The mixed model ANOVA of component latencies revealed a significant componentxgroup interaction, suggesting farmers had a greater delay in later ERP components. Intergroup comparisons of individual components showed significant delays in N2 and P300 latencies. Subsequent ANCOVA showed significant P300 delay even after adjusting for the latency of the preceding component, N2. Intergroup differences of P300 amplitudes were not significant, although there was limited evidence of a difference in scalp topography.

CONCLUSION

Our findings indicate that chronic low-level occupational exposure to OP pesticides is associated with progressively increasing delay in successive ERP components, particularly P300.

SIGNIFICANCE

Chronic exposure to OP pesticides may delay the neurophysiological processes underlying early stages of selective attention and late stages of sensory information processing that include stimulus evaluation and updating of working memory.