Early death due to severe organophosphate poisoning is a centrally mediated process

A complete, evidence-based review on novichok poisoning based on epidemiological aspects and clinical management

Background: The whole world has learned about the existence of a highly toxic neuro-paralytic substance called Novichok. A wide range of neuro-paralytic toxins were used during the wars of decades ago, which also had harmful and irreversible effects. Fortunately, the establishment of conventions prohibiting the use of these weapons prevented the adverse clinical consequences of these compounds. What we did in the present study was to evaluate the clinical features of Novichok, how to manage exposure to it, and to evaluate the prognostic aspects associated with this poisoning agent. Methods: The manuscript especial databases including Medline, Web of knowledge, Google scholar, and Scopus were deeply searched by the two blinded investigators for all eligible studies based on the considered keywords. Initially 98 articles were initially collected by database searching that considering eligibility criteria, 83 articles were finally eligible for the final assessment. There is a lack of clinical trials and case-cohort studies on general population about treatment and side effects when it comes to human nerve agents and most of the data in our search is based on animal studies. Results: In evaluating various clinical, auto physiological and prognostic aspects of exposure to these substances, special attention was necessary to the following points. First, Novichok agents are considered more potent than other toxic agents. Pathophysiologically, these agents irreversibly bind acetylcholinesterase and produce a rapid cholinergic toxidrome which is responsible for the clinical manifestations as well as the potential dangerous and life threatening side effects caused by these agents. Uniquely, these agents are thought to also target every neuron in the central and peripheral nervous system. As a managerial and therapeutic approach, early and timely treatment of its related complication along with prevents massive exposure and decontamination in addition to rapid resuscitation can prohibit debilitating neuropathy and death due to facing it. Conclusion: The present review highlights the importance of recognizing the potential acute toxic effects of Novichok agents, diagnostic and therapeutic approaches (life-saving antidotal therapy) to complications and ultimately the application of guidelines to improve the prognosis of exposure to these agents for both victims and medical community.

First meta-analysis study of cholinesterase inhibition in experimental animals by organophosphate or carbamate insecticides under the influence of diphenhydramine

Background and Aim

Diphenhydramine is an H1-antihistamine that counteracts the toxic effects of organophosphate and carbamate insecticides that inhibit cholinesterase (ChE) activity. This meta-analysis aimed to investigate the effects of diphenhydramine on ChE inhibition induced by these insecticides in the plasma, erythrocytes, or whole brain of experimental animals.

Materials and Methods

A data search was performed on erythrocyte, plasma, and brain ChE inhibition caused by organophosphate and carbamate insecticides in experimental animals (mice, rats, and chicks) treated with the antihistamine diphenhydramine in accordance with preferred reporting items for systematic reviews and meta-analysis, which was done by the two-group random-effects model meta-analysis. The meta-analysis included 18 records extracted from six studies that, appeared from 1996 to 2022.

Results

Using the random-effects model, a two-group meta-analysis revealed that the combined effect size (ChE inhibition) was significantly more favorable in the control group than in the diphenhydramine intervention, as shown by a forest plot. The combined effect size (standardized mean difference) was 0.67, with a standard error of 0.3, a lower limit of 0.04, and an upper limit of 1.29 (p = 0.025). The heterogeneity was moderate, as I2 of the combined effect size was 74%, with a significant Cochrane Q-test result (Q = 65, p < 0.0001). Subgroup analysis indicated that, with brain ChE inhibition, the heterogeneity (I2) became 5%, which was lower than ChE inhibition in plasma (84%) and erythrocytes (78%). No publication bias was identified using the funnel plot and Egger's test.

Conclusion

This meta-analysis suggests that, in addition to its documented antidotal action against ChE-inhibiting insecticides, diphenhydramine can also reduce the extent of ChE inhibition, especially in the brain, which is the main site of toxicity of these insecticides. There is a need for additional studies to assess such enzyme inhibition in different parts of the brain.

Organophosphorus Pesticides as Modulating Substances of Inflammation through the Cholinergic Pathway

Organophosphorus pesticides (OPs) are widespread insecticides used for pest control in agricultural activities and the control of the vectors of human and animal diseases. However, OPs’ neurotoxic mechanism involves cholinergic components, which, beyond being involved in the transmission of neuronal signals, also influence the activity of cytokines and other pro-inflammatory molecules; thus, acute and chronic exposure to OPs may be related to the development of chronic degenerative pathologies and other inflammatory diseases. The present article reviews and discusses the experimental evidence linking inflammatory process with OP-induced cholinergic dysregulation, emphasizing the molecular mechanisms related to the role of cytokines and cellular alterations in humans and other animal models, and possible therapeutic targets to inhibit inflammation.

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.

Slow-binding reversible inhibitor of acetylcholinesterase with long-lasting action for prophylaxis of organophosphate poisoning

Organophosphorus (OP) compounds represent a serious health hazard worldwide. The dominant mechanism of their action results from covalent inhibition of acetylcholinesterase (AChE). Standard therapy of acute OP poisoning is partially effective. However, prophylactic administration of reversible or pseudo-irreversible AChE inhibitors before OP exposure increases the efficiency of standard therapy. The purpose of the study was to test the duration of the protective effect of a slow-binding reversible AChE inhibitor (C547) in a mouse model against acute exposure to paraoxon (POX). It was shown that the rate of inhibition of AChE by POX in vitro after pre-inhibition with C547 was several times lower than without C547. Ex vivo pre-incubation of mouse diaphragm with C547 significantly prevented the POX-induced muscle weakness. Then it was shown that pre-treatment of mice with C547 at the dose of 0.01 mg/kg significantly increased survival after poisoning by 2xLD50 POX. The duration of the pre-treatment was effective up to 96 h, whereas currently used drug for pre-exposure treatment, pyridostigmine at a dose of 0.15 mg/kg was effective less than 24 h. Thus, long-lasting slow-binding reversible AChE inhibitors can be considered as new potential drugs to increase the duration of pre-exposure treatment of OP poisoning.

Enhancing organophosphate hydrolase efficacy via protein engineering and immobilization strategies

Organophosphorus compounds (OPs), developed as pesticides and chemical warfare agents, are extremely toxic chemicals that pose a public health risk. Of the different detoxification strategies, organophosphate-hydrolyzing enzymes have attracted much attention, providing a potential route for detoxifying those exposed to OPs. Phosphotriesterase (PTE), also known as organophosphate hydrolase (OPH), is one such enzyme that has been extensively studied as a catalytic bioscavenger. In this review, we will discuss the protein engineering of PTE aimed toward improving the activity and stability of the enzyme. In order to make enzyme utilization in OP detoxification more favorable, enzyme immobilization provides an effective means to increase enzyme activity and stability. Here, we present several such strategies that enhance the storage and operational stability of PTE/OPH.

Persistent behavior deficits, neuroinflammation, and oxidative stress in a rat model of acute organophosphate intoxication

Current medical countermeasures for organophosphate (OP)-induced status epilepticus (SE) are not effective in preventing long-term morbidity and there is an urgent need for improved therapies. Rat models of acute intoxication with the OP, diisopropylfluorophosphate (DFP), are increasingly being used to evaluate therapeutic candidates for efficacy in mitigating the long-term neurologic effects associated with OP-induced SE. Many of these therapeutic candidates target neuroinflammation and oxidative stress because of their implication in the pathogenesis of persistent neurologic deficits associated with OP-induced SE. Critical to these efforts is the rigorous characterization of the rat DFP model with respect to outcomes associated with acute OP intoxication in humans, which include long-term electroencephalographic, neurobehavioral, and neuropathologic effects, and their temporal relationship to neuroinflammation and oxidative stress. To address these needs, we examined a range of outcomes at later times post-exposure than have previously been reported for this model. Adult male Sprague-Dawley rats were given pyridostigmine bromide (0.1 mg/kg, im) 30 min prior to administration of DFP (4 mg/kg, sc), which was immediately followed by atropine sulfate (2 mg/kg, im) and pralidoxime (25 mg/kg, im). This exposure paradigm triggered robust electroencephalographic and behavioral seizures that rapidly progressed to SE lasting several hours in 90% of exposed animals. Animals that survived DFP-induced SE (~70%) exhibited spontaneous recurrent seizures and hyperreactive responses to tactile stimuli over the first 2 months post-exposure. Performance in the elevated plus maze, open field, and Pavlovian fear conditioning tests indicated that acute DFP intoxication reduced anxiety-like behavior and impaired learning and memory at 1 and 2 months post-exposure in the absence of effects on general locomotor behavior. Immunohistochemical analyses revealed significantly increased expression of biomarkers of reactive astrogliosis, microglial activation and oxidative stress in multiple brain regions at 1 and 2 months post-DFP, although there was significant spatiotemporal heterogeneity across these endpoints. Collectively, these data largely support the relevance of the rat model of acute DFP intoxication as a model for acute OP intoxication in the human, and support the hypothesis that neuroinflammation and/or oxidative stress represent potential therapeutic targets for mitigating the long-term neurologic sequelae of acute OP intoxication.

Impact of chronic exposure to the pesticide chlorpyrifos on respiratory parameters and sleep apnea in juvenile and adult rats

The widely used organophosphorus pesticide chlorpyrifos (CPF) is often detected in food. CPF inhibits acetylcholinesterase and can modify muscle contractility and respiratory patterns. We studied the effects of chronic exposure to CPF on respiratory parameters and diaphragm contractility in 21- and 60-days old rats. Pregnant rats were exposed to oral CPF (1 or 5 mg/ kg /day: CPF-1 or CPF-5 groups vs vehicle: controls) from gestation onset up to weaning of the pups that were individually gavaged (CPF or vehicle) thereafter. Two developmental time points were studied: weaning (day 21) and adulthood (day 60). Whole-body plethysmography was used to score breathing patterns and apnea index during sleep. Then, diaphragm strips were dissected for the assessment of contractility and acetylcholinesterase activity. Results showed that the sleep apnea index was higher in CPF-exposed rats than in controls. In adult rats, the expiratory time and tidal volume were higher in CPF-exposed animals than in controls. At both ages, the diaphragm’s amplitude of contraction and fatigability index were higher in the CPF-5 group, due to lower acetylcholinesterase activity. We conclude that chronic exposure to CPF is associated with higher sleep apnea index and diaphragm contractility, and modifies respiratory patterns in sleeping juvenile and adult rats.

A primer on nerve agents: what the emergency responder, anesthesiologist, and intensivist needs to know

PURPOSE

The purpose of this review article is to familiarize first responders, anesthesiologists, and intensivists with the medical management of patients exposed to nerve agents.

SOURCE

This review is based on the current medical literature available to the general medical community.

PRINCIPAL FINDINGS

Nerve agents are some of the deadliest substances known to humanity. Though they kill primarily via muscle paralysis, which leads to respiratory arrest, these agents affect virtually every organ system in the body. Their primary mechanism of action is the body-wide inhibition of cholinesterases. This inhibition leads to the accumulation of acetylcholine, stimulating both nicotinic and muscarinic receptors. After decontamination, the primary treatment is with atropine to control muscarinic symptoms and with oximes to reactivate the cholinesterases and treat the nicotinic symptoms. Atropine doses can be much higher than conventionally used. Seizures are generally best treated with benzodiazepines. Patients with substantial exposure may require ventilatory and intensive care unit support for prolonged periods of time.

CONCLUSION

While it is unlikely that most medical practitioners will ever encounter nerve agent poisoning, it is critical to be aware of the presenting symptoms and how best to treat patients exposed to these deadly agents. History has shown that rapid medical treatment can easily mean the difference between life and death for a patient in this situation.

The Effect of Parathion on Red Blood Cell Acetylcholinesterase in the Wistar Rat

Organophosphorus (OP) pesticide poisoning is a significant problem worldwide. Research into new antidotes for these acetylcholinesterase inhibitors, and even optimal doses for current therapies, is hindered by a lack of standardized animal models. In this study, we sought to characterize the effects of the OP pesticide parathion on acetylcholinesterase in a Wistar rat model that included comprehensive medical care. Methods. Male Wistar rats were intubated and mechanically ventilated and then poisoned with between 20 mg/kg and 60 mg/kg of intravenous parathion. Upon developing signs of poisoning, the rats were treated with standard critical care, including atropine, pralidoxime chloride, and midazolam, for up to 48 hours. Acetylcholinesterase activity was determined serially for up to 8 days after poisoning. Results. At all doses of parathion, maximal depression of acetylcholinesterase occurred at 3 hours after poisoning. Acetylcholinesterase recovered to nearly 50% of baseline activity by day 4 in the 20 mg/kg cohort and by day 5 in the 40 and 60 mg/kg cohorts. At day 8, most rats' acetylcholinesterase had recovered to roughly 70% of baseline. These data should be useful in developing rodent models of acute OP pesticide poisoning.

Pharmacotherapy to protect the neuromuscular junction after acute organophosphorus pesticide poisoning

Organophosphorus (OP) pesticide poisoning is a leading cause of morbidity and mortality in the developing world, affecting an estimated three million people annually. Much of the morbidity is directly related to muscle weakness, which develops 1-4 days after poisoning. This muscle weakness, termed the intermediate syndrome (IMS), leads to respiratory, bulbar, and proximal limb weakness and frequently necessitates the use of mechanical ventilation. While not entirely understood, the IMS is most likely due to persistently elevated acetylcholine (ACh), which activates nicotinic ACh receptors at the neuromuscular junction (NMJ). Thus, the NMJ is potentially a target-rich area for the development of new therapies for acute OP poisoning. In this manuscript, we discuss what is known about the IMS and studies investigating the use of nicotinic ACh receptor antagonists to prevent or mitigate NMJ dysfunction after acute OP poisoning.

Respiratory complications of organophosphorus nerve agent and insecticide poisoning. Implications for respiratory and critical care

Organophosphorus (OP) compound poisoning is a major global public health problem. Acute OP insecticide self-poisoning kills over 200,000 people every year, the majority from self-harm in rural Asia. Highly toxic OP nerve agents (e.g., sarin) are a significant current terrorist threat, as shown by attacks in Damascus during 2013. These anticholinesterase compounds are classically considered to cause an acute cholinergic syndrome with decreased consciousness, respiratory failure, and, in the case of insecticides, a delayed intermediate syndrome that requires prolonged ventilation. Acute respiratory failure, by central and peripheral mechanisms, is the primary cause of death in most cases. However, preclinical and clinical research over the last two decades has indicated a more complex picture of respiratory complications after OP insecticide poisoning, including onset of delayed neuromuscular junction dysfunction during the cholinergic syndrome, aspiration causing pneumonia and acute respiratory distress syndrome, and the involvement of solvents in OP toxicity. The treatment of OP poisoning has not changed over the last 50 years. However, a better understanding of the multiple respiratory complications of OP poisoning offers additional therapeutic opportunities.

Comparison of current recommended regimens of atropinization in organophosphate poisoning

Atropine is the mainstay of therapy in organophosphate (OP) toxicity, though research and consensus on dosing is lacking. In 2004, as reported by Eddleston et al. (J Toxicol Clin Toxicol 42(6):865-75, 2004), they noted variation in recommended regimens. We assessed revisions of original references, additional citations, and electronic sources to determine the current variability in atropine dosing recommendations. Updated editions of references from Eddleston et al.'s work, texts of Internal and Emergency Medicine, and electronic resources were reviewed for atropine dosing recommendations. For comparison, recommendations were assessed using the same mean dose (23.4 mg) and the highest dose (75 mg) of atropine as used in the original paper. Recommendations were also compared with the dosing regimen from the World Health Organization (WHO). Thirteen of the original recommendations were updated and 15 additional references were added giving a convenience sample of 28. Sufficient information to calculate time to targeted dose was provided by 24 of these samples. Compared to 2004, current recommendations have greatly increased the speed of atropinization with 13/24 able to reach the mean and high atropine dose within 30 min compared to 1/36 in 2004. In 2004, there were 13 regimens where the maximum time to reach 75 mg was over 18 h, whereas now, there are 2. While only one recommendation called for doubling the dose for faster escalation in 2004, 15 of the 24 current works include dose doubling. In 2004, Eddleston et al. called for an evidence-based guideline for the treatment of OP poisoning that could be disseminated worldwide. Many current recommendations can adequately treat patients within 1 h. While the WHO recommendations remain slow to treat patients with OP poisoning, other authorities are close to a consensus on rapid atropinization.

Biphasic cuirass ventilation is better than bag-valve mask ventilation for resuscitation following organophosphate poisoning

Objective

Exposure to organophosphates (OP) may lead to a life threatening cholinergic crisis with death attributed to a rapidly progressive respiratory failure. In a toxicological mass casualty event involving organophosphate exposure, many of the victims may depend on immediate short-term ventilation to overcome the respiratory distress which may exhaust life supporting resources. In addition, the mandatory use of personal protective gear by first responders emphasizes the need for a noninvasive, easy-to-operate ventilation device. Our objective was to assess the efficacy of MRTX, a Biphasic Cuirass Ventilation device, in comparison with standard bag-valve mask ventilation following acute organophosphate poisoning.

Methods

Pigs were exposed to paraoxon poisoning (1.4 LD₅₀), and treated 8 min later with atropine (0.05 mg/kg). The control group received no further support (n = 9), the two experimental groups received ventilation support initiated 15 min post exposure and lasted for 25 min: one group was ventilated with the commonly used bag-valve mask (Mask group, n = 7) and the other was ventilated with the Biphasic Cuirass Ventilation device (Cuirass group, n = 7). Clinical signs and physiological parameters were monitored during the first hour, and mortality up to 24 h post exposure was recorded.

Results

No mortality was observed in the Cuirass group following OP poisoning, while mortality in the Control and in the Mask groups was high (67% and 71%, respectively). Mouth excretions of the cuirass-ventilated animals were frothy white as in deep suctioning, as opposed to the clear saliva-like appearance of secretions in the other two groups. No further group differences were recorded.

Conclusions

The noninvasive, easy-to-operate Biphasic Cuirass Ventilation device was effective in reducing OP-induced mortality and might be advantageous in an organophosphate mass casualty event. This finding should be validated in further investigations.

Use of OpdA, an organophosphorus (OP) hydrolase, prevents lethality in an African green monkey model of acute OP poisoning

Organophosphorus (OP) pesticides are a diverse class of acetylcholinesterase (AChE) inhibitors that are responsible for tremendous morbidity and mortality worldwide, killing approximately 300,000 people annually. Enzymatic hydrolysis of OPs is a potential therapy for acute poisoning. OpdA, an OP hydrolase isolated from Agrobacterium radiobacter, has been shown to decrease lethality in rodent models of OP poisoning. This study investigated the effects of OpdA on AChE activity, plasma concentrations of OP, and signs of toxicity after administration of dichlorvos to nonhuman primates. A dose of 75 mg/kg dichlorvos given orally caused apnea within 10 min with a progressive decrease in heart rate. Blood AChE activity decreased to zero within 10 min. Respirations and AChE activity did not recover. The mean dichlorvos concentration rose to a peak of 0.66 μg/ml. Treated monkeys received 1.2mg/kg OpdA iv immediately after poisoning with dichlorvos. In Opda-treated animals, heart and respiratory rates were unchanged from baseline over a 240-minute observation period. AChE activity slowly declined, but remained above 25% of baseline for the entire duration. Dichlorvos concentrations reached a mean peak of 0.19 μg/ml at 40 min after poisoning and decreased to a mean of 0.05 μg/ml at 240 min. These results show that OpdA hydrolyzes dichlorvos in an African green monkey model of lethal poisoning, delays AChE inhibition, and prevents lethality.

Open-label randomized clinical trial of atropine bolus injection versus incremental boluses plus infusion for organophosphate poisoning in Bangladesh

Severe organophosphate compound (OPC) poisoning is an important clinical problem in many countries of the world. Unfortunately, little clinical research has been performed and little evidence exists with which to determine the best therapy. A study was therefore undertaken to determine the optimal dosing regimen for atropine in the treatment of OPC poisoning. An open-label randomized clinical trial was conducted in Chittagong Medical College Hospital, Chittagong, Bangladesh, on 156 hospitalized individuals with OPC poisoning from June to September 2006. The aim was to compare the efficacy and safety of conventional bolus doses with individualized incremental doses of atropine for atropinization followed by continuous atropine infusion for management of OPC poisoning. Inclusion criteria were patients with a clear history of OPC poisoning with clear clinical signs of toxicity, i.e. features of cholinergic crisis. The patients were observed for at least 96 h. Immediate outcome and complications were recorded. Out of 156 patients, 81 patients received conventional bolus dose atropine (group A) and 75 patients received rapidly incremental doses of atropine followed by infusion (group B). The mortality in group 'A' was 22.5% (18/80) and in group 'B' 8% (6/75) (p < 0.05). The mean duration of atropinization in group 'A' was 151.74 min compared to 23.90 min for group 'B' (p < 0.001). More patients in group A experienced atropine toxicity than in group 'B' (28.4% versus 12.0%, p < 0.05); intermediate syndrome was more common in group 'A' than in group 'B' (13.6% versus 4%, p < 0.05), and respiratory support was required more often for patients in group 'A' than in group 'B' (24.7% versus 8%, p < 0.05). Rapid incremental dose atropinization followed by atropine infusion reduces mortality and morbidity from OPC poisoning and shortens the length of hospital stay and recovery. Incremental atropine and infusion should become the treatment of choice for OPC poisoning. Given the paucity of existing evidence, further clinical studies should be performed to determine the optimal dosing regimen of atropine that most rapidly and safely achieves atropinization in these patients.

A review of endosulfan, dichlorvos, diazinon, and diuron--pesticides used in Jamaica

The global agricultural sector is the primary user of pesticides, consuming more than three billion kilograms of pesticides annually. Although pesticides are beneficial in controlling the proliferation of pests, they have been associated with adverse human and ecological impacts. Approximately 87% of the annually imported pesticides in Jamaica are applied within agricultural or household settings. However, in Jamaica, the potential impact on humans, their property, and the environment is unknown, as the fate of many of the locally applied pesticides has not been established. This review discusses four pesticides extensively applied in agricultural practices in Jamaica - endosulfan, diazinon, diuron, and dichlorvos. The information presented is essential for the development of fate and transport models of these chemicals. Consequently, health and ecological impact assessments may be conducted from the generated models.

Electrophysiological correlates of respiratory failure in acute organophosphate poisoning: evidence for differential roles of muscarinic and nicotinic stimulation

Background. Respiratory failure in acute organophosphate (OP) poisoning can occur early and also relatively late in the clinical course, and the pathophysiology of respiratory failure at these different phases may have important clinical implications. Objective. To compare the electrophysiological findings in patients with early and late respiratory failure following acute OP poisoning. Methods. A prospective observational case series of consenting symptomatic patients with acute OP poisoning were assessed with daily physical examinations and repetitive nerve stimulation (RNS) studies. RNS was done on right and left median and ulnar nerves at 1, 3, 10, 15, 20, and 30 Hz. Outcomes such as need for ventilation and development of intermediate syndrome (IMS) were noted. Early respiratory failure was defined as occurring within 24 hours of ingestion. Results. Seventy-eight patients were recruited for the clinical and electrophysiological study and of those 59 (75.6%) patients had ingested chlorpyrifos. Seven patients developed respiratory failure within 24 hours of ingestion with overt muscarinic signs. They had no electrophysiological abnormalities at median and ulnar nerves before intubation. Three of them later developed “forme fruste” IMS. Five other patients developed late respiratory failure after 24 hours of ingestion, and all of them showed progressive RNS changes indicating severe IMS prior to intubation. Conclusion. The normal RNS in all patients developing early respiratory failure suggests that it is due to a central nervous system (CNS) and muscarinic effect. This emphasizes the need for early rapid atropinisation as a priority, combating the nicotinic effects being less urgent. This is in contrast with the late respiratory failure, which has been shown to be associated with neuromuscular dysfunction. Further studies are needed to quantify CNS and muscarinic dysfunction to assist in the development of better treatments for the severe and early OP poisoning.

Characterization of status epilepticus induced by two organophosphates in rats

Organophosphates (OPs) inhibit the enzyme cholinesterase and cause accumulation of acetylcholine, and are known to cause seizures and status epilepticus (SE) in humans. The animal models of SE caused by organophosphate analogs of insecticides are not well characterized. SE caused by OPs paraoxon and diisopropyl fluorophosphate (DFP) in rats was characterized by electroencephalogram (EEG), behavioral observations and response to treatment with the benzodiazepine diazepam administered at various stages of SE. A method for SE induction using intrahippocampal infusion of paraoxon was also tested. Infusion of 200nmol paraoxon into the hippocampus caused electrographic seizures in 43/52 (82.7%) animals tested; and of these animals, 14/43 (30%) had self-sustaining seizures that lasted 4-18h after the end of paraoxon infusion. SE was also induced by peripheral subcutaneous injection of diisopropyl fluorophosphate (DFP, 1.25mg/kg) or paraoxon (1.00mg/kg) to rats pretreated with atropine (2mg/kg) and 2-pralidoxime (2-PAM, 50mg/kg) 30min prior to OP injection. SE occurred in 78% paraoxon-treated animals and in 79% of DFP-treated animals. Diazepam (10mg/kg) was administered 10min and 30min after the onset of continuous EEG seizures induced by paraoxon and it terminated SE in a majority of animals at both time points. DFP-induced SE was terminated in 60% animals when diazepam was administered 10min after the onset of continuous EEG seizure activity but diazepam did not terminate SE in any animal when it was administered 30min after the onset of continuous seizures. These studies demonstrate that both paraoxon and DFP can induce SE in rats but refractoriness to diazepam is a feature of DFP induced SE.

Organophosphate-induced brain damage: mechanisms, neuropsychiatric and neurological consequences, and potential therapeutic strategies

Organophosphate (OP)-induced brain damage is defined as progressive damage to the brain, resulting from the cholinergic neuronal excitotoxicity and dysfunction induced by OP-induced irreversible AChE inhibition. This delayed secondary neuronal damage that occurs mainly in the cholinergic regions of the brain that contain dense accumulations of cholinergic neurons and the majority of cholinergic projection, might be largely responsible for persistent profound neuropsychiatric and neurological impairments (memory, cognitive, mental, emotional, motor and sensory deficits) in the victims of OP poisoning. Neuroprotective strategies for attenuating OP-induced brain damage should target different development stages of OP-induced brain damage, and may include but not limited to: (1) Antidote therapies with atropine and related efficient anticholinergic drugs; (2) Anti-excitotoxic therapies targeting attenuation of cerebral edema and inflammatory reaction, blockage of calcium influx, inhibition of apoptosis program, and the control of seizures; (3) Neuroprotective strategies using cytokines, antioxidants and NMDAR antagonists (a single drug or a combination of drugs) to slow down the process of secondary neuronal damage; and (4) Therapies targeting individual symptoms or clusters of chronic neuropsychiatric and neurological symptoms. These neuroprotective strategies may help limit or prevent secondary neuronal damage at the early stage of OP poisoning and attenuate the subsequent neuropsychiatric and neurological impairments, thus reducing the long-term disability caused by exposure to OPs.

Central respiratory effects on motor nerve activities after organophosphate exposure in a working heart brainstem preparation of the rat

The impact of organophosphorus compound (OP) intoxication on the activity of central respiratory circuitry, causing acetylcholinesterase (AChE) inhibition and accumulation of acetylcholine in the respiratory brainstem circuits, is not understood. We investigated the central effect of the OP Crotylsarin (CRS) on respiratory network activity using the working heart brainstem preparation, which specifically allows for the analysis of central drug effects without changes in brainstem oxygenation possibly caused by drug effects on peripheral cardio-respiratory activity. Respiratory network activity was determined from phrenic and hypoglossal or vagal nerve activities (PNA, HNA, VNA). To investigate combined central and peripheral CRS effects hypo-perfusion was used mimicking additional peripheral cardiovascular collapse. Systemic CRS application induced a brief central apnea and complete AChE-inhibition in the brainstem. Subsequently, respiration was characterised by highly significant reduced PNA minute activity, while HNA showed expiratory related extra bursting indicative for activation of un-specified oro-pharyngeal behaviour. During hypo-perfusion CRS induced significantly prolonged apnoea. In all experiments respiratory activity fully recovered after 1h. We conclude that CRS mediated AChE inhibition causes only transient central breathing disturbance. Apparently intrinsic brainstem mechanisms can compensate for cholinergic over activation. Nevertheless, combination of hypo-perfusion and CRS exposure evoke the characteristic breathing arrests associated with OP poisoning.

Non-muscarinic therapeutic targets for acute organophosphorus poisoning

Organophosphorus (OP) pesticides are a broad class of acetylcholinesterase inhibitors that are responsible for tremendous morbidity and mortality worldwide, contributing to an estimated 300,000 deaths annually. Current pharmacotherapy for acute OP poisoning includes the use of atropine, an oxime, and benzodiazepines. However, even with such therapy, the mortality from these agents is as high as 40%. It is increasingly recognized that not all OPs are the same. Significant differences exist in their toxicity, lipophilicity, and response to oxime therapy. Other non-muscarinic effects of OP pesticides exist, such as acute and chronic neuromuscular junction failure and central respiratory failure. In part because most of the mortality from these chemicals takes place in the developing world, little National Institutes of Health (NIH) research has been directed towards these agents. However, the similar mechanism of action of OP pesticides and the military nerve agents, along with increasing concerns about chemical terrorism has lead to the formation of the NIH Countermeasures Against Chemical Threats (CounterACT) Program. As part of the CounterACT Program, the NIH has recently designated six OP pesticides as "threat agents". This concept paper describes some of the knowledge gaps related to non-muscarinic effects of OP pesticides and highlights needed areas of further research. Leveraging the current NIH interest in these chemicals to medical necessities in the developing world offers the possibility of delivering new therapeutics where they are needed on a daily basis.

CHO cell expression, long-term stability, and primate pharmacokinetics and brain uptake of an IgG-paroxonase-1 fusion protein

Paraoxonase (PON)-1 is the most potent human organophosphatase known, but recombinant forms of human PON1 have been difficult to produce owing to poor secretion by host cells. In the present investigation, human PON1 is re-engineered as an IgG-PON1 fusion protein. The 355 amino acid human PON1 is fused to the carboxyl terminus of the heavy chain of a chimeric monoclonal antibody (MAb) against the human insulin receptor (HIR), and this fusion protein is designated HIRMAb-PON1. The HIRMAb part of the fusion protein enables brain penetration of the PON1, which was considered important, because organophosphate toxicity causes death via a central nervous system site of action. A high producing line of stably transfected Chinese hamster ovary (CHO) cells secreting the HIRMAb-PON1 fusion protein in the absence of serum or lipid acceptors was cloned. The bioreactor generated fusion protein was purified to homogeneity with low impurities by protein A affinity chromatography and anion exchange chromatography. The HIRMAb-PON1 fusion protein was stable as a sterile liquid formulation stored at 4°C for at least 1 year. The plasma pharmacokinetics (PK) of the HIRMAb-PON1 fusion protein was evaluated in Rhesus monkeys, which is the first PK evaluation of a recombinant PON1 protein. The fusion protein was rapidly removed from blood, primarily by the liver. The blood-brain barrier permeation of the HIRMAb-PON1 fusion protein was high and comparable to other HIRMAb fusion proteins. Re-engineering human PON1 as the HIRMAb fusion protein allows for production of a stable, field-deployable formulation of the enzyme that is brain-penetrating.

Kinetics and efficacy of an organophosphorus hydrolase in a rodent model of methyl-parathion poisoning

OBJECTIVES

Organophosphorus (OP) pesticides exert a tremendous health burden, particularly in the developing world. Limited resources, the severity of intentional OP ingestions, and a paucity of beneficial therapies all contribute to the morbidity and mortality of this broad class of chemicals. A novel theoretical treatment for OP poisoning is the use of an enzyme to degrade the parent OP in the circulation after poisoning. The aims of this study were to determine the pharmacokinetics and efficacy of an OP hydrolase (OpdA) in a rodent model of severe methyl-parathion poisoning.

METHODS

Two animal models were used. First, Wistar rats were administered two different doses of the hydrolase (0.15 and 1.5 mg/kg), and the ex vivo hydrolytic activity of plasma was determined by a fluorometric method. Second, an oral methyl-parathion animal poisoning model was developed to mimic severe human poisoning, and the efficacy of postpoisoning OpdA (as measured by survival to 4 and 24 hours) was determined.

RESULTS

The half-life of OpdA in the Wistar rat was dependent on the dose administered and ranged between 45.0 and 57.9 minutes. The poisoning model of three times the lethal dose to 50% of the population (3 x LD(50)) of methyl-parathion resulted in 88% lethality at 4 and 24 hours. Using a single dose of 0.15 mg/kg OpdA 10 minutes after poisoning resulted in 100% survival at 4 hours (p = 0.001 vs. placebo), but 0% at 24 hours postpoisoning (p = NS vs. placebo).

CONCLUSIONS

The OP hydrolase OpdA exhibits pharmacokinetics suitable for repeated dosing and increases short-term survival after severe methyl-parathion poisoning.

Pharmacokinetics of OpdA, an organophosphorus hydrolase, in the African green monkey

Organophosphorus (OP) pesticides are a broad class of acetylcholinesterase inhibitors that are responsible for tremendous morbidity and mortality worldwide, contributing to an estimated 300,000 deaths annually. Current pharmacotherapy for acute OP poisoning includes the use of atropine, an oxime, and benzodiazepines. However, even with such therapy, the mortality from these agents are as high as 40%. Enzymatic hydrolysis of OPs is an attractive new potential therapy for acute OP poisoning. A number of bacterial OP hydrolases have been isolated. A promising OP hydrolase is an enzyme isolated from Agrobacterium radiobacter, named OpdA. OpdA has been shown to decrease lethality in rodent models of parathion and dichlorvos poisoning. However, pharmacokinetic data have not been obtained. In this study, we examined the pharmacokinetics of OpdA in an African Green Monkey model. At a dose of 1.2mg/kg the half-life of OpdA was approximately 40 min, with a mean residence time of 57 min. As expected, the half-life did not change with the dose of OpdA given: at doses of 0.15 and 0.45 mg/kg, the half-life of OpdA was 43.1 and 38.9 min, respectively. In animals subjected to 5 daily doses of OpdA, the residual activity that was measured 24h after each OpdA dose increased 5-fold for the 0.45 mg/kg dose and 11-fold for the 1.2mg/kg dose. OpdA exhibits pharmacokinetics favorable for the further development as a therapy for acute OP poisoning, particularly for hydrophilic OP pesticides. Future work to increase the half-life of OpdA may be beneficial.

Dichlorvos-induced developmental toxicity in Zebrafish

The present study examined effects of the pesticide dichlorvos (O-(2,2-dichlorovinyl)-O,O dimethylphosphate [DDVP]) on embryonic development of zebrafish. In a first set of experiments, early life stages of zebrafish were exposed to five concentrations (5, 10, 25, 50, and 100 mg/L—1) of DDVP for 96 hours post fertilization (hpf). The 24-hpf LC50 value of DDVP in the semistatic test was 39.75 mg/L-1. Developmental abnormalities have been observed in embryos and larvae, such as no blood flow, cardiac edema, delayed hatching, and vertebra malformations. Most of the onserved effects were increased in a concentration-dependent manner. To investigate the behavior of the larvae, zebrafish exposed to 10 and 25 mg/L-1 DDVP were observed on days 6 and 9 after fertilization. 25 mg L-1 DDVP dose caused significant slowing of swimming activity on day 6 and 9 after fertilization. According to present study results, DDVP exposure during early development caused (i) clear behavioral impairments detectable during the posthatching period and (ii) mortality and developmental abnormalities in zebrafish. Dichlorvos is present in the environment with other similar organophosphate compounds. Additive responses to organophosphate compounds may induce lethal or sub-lethal effects in early life stages of fish chronically exposed to this class of chemicals.

Comparison of two commonly practiced atropinization regimens in acute organophosphorus and carbamate poisoning, doubling doses vs. ad hoc: a prospective observational study

There is a wide variation and lack of evidence in current recommendations for atropine dosing schedules leading to subsequent variation in clinical practice. Therefore, we sought to examine the safety and effectiveness of a titrated vs. ad hoc atropine treatment regimen in a cohort of patients with acute cholinesterase inhibitor pesticide poisoning. A prospective cohort study was conducted in three district secondary referral hospitals in Sri Lanka using a structured data collection form that collected details of clinical symptoms and outcomes of cholinesterase inhibitor pesticide poisoning, atropine doses, and signs of atropinization. We compared two hospitals that used a titrated dosing protocol based on a structured monitoring sheet for atropine infusion with another hospital using an ad hoc regime. During the study, 272 symptomatic patients with anticholinesterase poisoning requiring atropine were admitted to the three hospitals. Outcomes of death and ventilation were analyzed for all patients, 226 patients were prospectively assessed for atropine toxicity. At baseline, patients in the titrated dose cohort had clinical signs consistent with greater toxicity. This in part may be due to ingestion of more toxic organophosphates. They received less pralidoxime and atropine, and were less likely to develop features of atropine toxicity, such as delirium (1% vs. 17%), hallucinations (1% vs. 35%), or either (1% vs. 35%) and need for patient restraint (3% vs. 48%) compared with the ad hoc dose regime. After adjusting for the pesticides ingested, there was no difference in mortality and ventilatory rates between protocols. Ad hoc high dose atropine regimens are associated with more frequent atropine toxicity without any obvious improvement in patient outcome compared with doses titrated to clinical effect. Atropine doses should be titrated against response and toxicity. Further education and the use of a structured monitoring sheet may assist in more appropriate atropine use in anticholinesterase pesticide poisoning.

Chemical Terrorism Attacks: Update on Antidotes

There is well-founded concern that a chemical or radioactive agent will at some point be used as a weapon of terror. There are several antidotes that, if used correctly in a timely fashion, can help lessen the harm caused by these agents. This article is meant to introduce the clinician to several such agents, along with the antidotes useful in the management of exposure to these. It covers the indications, administration, and precautions for using these antidotes.

Organic Phosphorus Compounds—Nerve Agents

The organic phosphorous compounds (OPC) include both the military grade nerve agents and the organic phosphorous pesticides. The major mechanism of OPC toxicity is through inhibition of acetylcholinesterase in neuronal synapses leading to excess acetylcholine and overstimulation of target organs. Signs and symptoms depend on the affinity of the OPC for muscarinic versus nicotinic receptors, and are likely to include both. Muscarinic symptoms may include diarrhea, urination, bronchospasm, bronchorrhea, emesis, and salivation. Nicotinic symptoms such as paralysis and fasciculations may also occur. Central nervous system toxicity may include seizures, altered mental status, and apnea, and require prompt intervention. Treatment includes early airway and ventilatory support as well as antidotal therapy with atropine, pralidoxime, and diazepam. Goals of therapy include prevention and rapid treatment of hypoxia and seizures, as these are linked to patient outcome.

Early management after self-poisoning with an organophosphorus or carbamate pesticide - a treatment protocol for junior doctors

Severe organophosphorus or carbamate pesticide poisoning is an important clinical problem in many countries of the world. Unfortunately, little clinical research has been performed and little evidence exists with which to determine best therapy. A cohort study of acute pesticide poisoned patients was established in Sri Lanka during 2002; so far, more than 2000 pesticide poisoned patients have been treated. A protocol for the early management of severely ill, unconscious organophosphorus/carbamate-poisoned patients was developed for use by newly qualified doctors. It concentrates on the early stabilisation of patients and the individualised administration of atropine. We present it here as a guide for junior doctors in rural parts of the developing world who see the majority of such patients and as a working model around which to base research to improve patient outcome. Improved management of pesticide poisoning will result in a reduced number of suicides globally.

Prenatal exposure to dichlorvos: physical and behavioral effects on rat offspring

The effects of prenatal exposure to dichlorvos (DDVP), an organophosphate (OP) pesticide, on pups' physical and neurobehavioral developments were investigated. Forty pregnant rats were treated by gavage with 8.0 mg/kg DDVP or its vehicle (1 ml/kg) from the 6th to the 15th day of pregnancy. At birth, pups were weighed, the litters culled to eight animals (four male and four female), and then observed for physical (pinna detachment, incisor eruption, eye opening, testes descent, and vaginal opening) and neurobehavioral developments (palmar grasp, surface righting, negative geotaxis, and open-field behaviors). As adults, open-field, apomorphine-induced stereotypy, and passive avoidance behaviors were also assessed. Results showed no differences between the body weight of DDVP and control-treated groups. No differences were observed on the measures of physical and neurobehavioral development. Locomotor activity of male pups at 21 days of age was decreased by DDVP exposure. Adult experimental offspring showed a decreased locomotor frequency and an increased immobility duration on open-field behavior in relation to control animals; the apomorphine-induced stereotyped behavior was decreased by the pesticide exposure as well as performance on the passive avoidance task. These data suggest that prenatal DDVP exposure was able to decrease offspring motor function (adolescence and adults) and conditioned response learning, probably by interference with the cholinergic-dopaminergic balance of activity involved with the control of motor function as well as the cholinergic system that modulates learning process.

Nerve agents: a comprehensive review

Nerve agents are perhaps the most feared of potential agents of chemical attack. The authors review the history, physical characteristics, pharmacology, clinical effects, and treatment of these agents.

Jimson weed extract as a protective agent in severe organophosphate toxicity

Treatment of patients following an organophosphate (OP) exposure can deplete a hospital's entire supply of atropine. Given the possibility of multiple severe exposures after a terrorist attack using OP nerve agents, there exists a need for either greater atropine stores or the development of alternative antidotes. Jimson weed (Datura stramonium) contains atropine and other anticholinergic compounds and is common and readily available. It is used recreationally for its central anticholinergic effects and is made easily into an extract by boiling the crushed seeds. The extract has rapid onset of effects and may be useful for treatment of OP poisoning.

OBJECTIVES

To determine whether pretreatment with an easily stored and prepared Datura seed extract (DSE) will increase survival following a severe OP poisoning.

METHODS

Datura stramonium seeds were collected, crushed, and then heated in water to make a 2-mg/mL atropine solution (100 seeds contain approximately 6 mg of atropine or 0.007 mg/seed). Male rats were randomized to pretreatment with either saline (n = 10) or 7.5 mg/kg DSE (n = 10) given as a single intraperitoneal injection 5 minutes prior to a subcutaneous injection of 25 mg/kg of dichlorvos. The endpoint was time to death recorded by a blinded observer.

RESULTS

The Kaplan-Meier estimates of the 24-hour survival rate was 90% (95% CI = 56% to 100%) for the DSE-pretreated group and 10% (95% CI = 0% to 45%) for the control group. The log-rank test revealed a statistically significant longer survival for the Datura-treated animals (p = 0.0002). Median survival time was 22 minutes 30 seconds for the control group and greater than 24 hours for the DSE-pretreated group.

CONCLUSIONS

Pretreatment with DSE significantly increases survival following severe dichlorvos exposure.

Speed of Initial Atropinisation in Significant Organophosphorus Pesticide Poisoning—A Systematic Comparison of Recommended Regimens

OBJECTIVE

Early deaths from organophosphorus (OP) pesticide self-poisoning result from respiratory failure and cardiovascular collapse. Therapy requires the urgent use of atropine to reverse cholinergic excess, thereby improving respiratory function, heart rate, and blood pressure. We aimed to assess variation in textbook recommendations for early atropinisation and to see whether this variation affected time to stabilisation using model data from 22 severely poisoned patients seen in a Sri Lankan clinical trial.

METHODS

We extracted prospectively recorded data on atropine requirements for 22 OP poisoned patients who required intubation but survived to discharge. We did a systematic search for textbook recommendations for initial atropinisation regimens. These regimens were then applied to data from the Sri Lankan patients.

RESULTS

The patients required a mean of 23.4 mg (standard deviation 22.0, range 1-75 mg) atropine to clear the lungs, raise the pulse above 80 bpm, and restore systolic blood pressure to more than 80 mmHg. Textbook recommendations varied markedly--atropinisation of an average patient, requiring the mean dose of 23.4 mg, would have taken 8 to 1380 mins; atropinisation of a very ill patient, requiring 75 mg, would have taken 25 to 4440 mins. Atropinisation was attained most rapidly with a regimen of increasing bolus doses after failure to respond to the previous bolus.

CONCLUSIONS

There is great variation in recommendations for atropinisation, with some regimens taking hours and even days to stabilise a patient. The guidelines are very flexible--possibly appropriate for experienced emergency physicians or clinical toxicologists, but completely inappropriate for the inexperienced junior doctors who see most cases worldwide. We recommend that a consensus guideline be developed by appropriate organisations to bring order to this important part of OP therapy, while acknowledging the paucity of data to drive the guidelines.