Deterioration in brain and heart functions following a single sub-lethal (0.8 LCt50) inhalation exposure of rats to sarin vapor: a putative mechanism of the long term toxicity

Long-Term Anxiety-Like Behavior and Microbiota Changes Induced in Mice by Sublethal Doses of Acute Sarin Surrogate Exposure

Anxiety disorder is one of the most reported complications following organophosphorus (OP) nerve agent (NA) exposure. The goal of this study was to characterize the long-term behavioral impact of a single low dose exposure to 4-nitrophenyl isopropyl methylphosphonate (NIMP), a sarin surrogate. We chose two different sublethal doses of NIMP, each corresponding to a fraction of the median lethal dose (one mild and one convulsive), and evaluated behavioral changes over a 6-month period following exposure. Mice exposed to both doses showed anxious behavior which persisted for six-months post-exposure. A longitudinal magnetic resonance imaging examination did not reveal any anatomical changes in the amygdala throughout the 6-month period. While no cholinesterase activity change or neuroinflammation could be observed at the latest timepoint in the amygdala of NIMP-exposed mice, important modifications in white blood cell counts were noted, reflecting a perturbation of the systemic immune system. Furthermore, intestinal inflammation and microbiota changes were observed at 6-months in NIMP-exposed animals regardless of the dose received. This is the first study to identify long-term behavioral impairment, systemic homeostasis disorganization and gut microbiota alterations following OP sublethal exposure. Our findings highlight the importance of long-term care for victims of NA exposure, even in asymptomatic cases.

Neuroprotection by delayed triple therapy following sarin nerve agent insult in the rat

The development of refractory status epilepticus (SE) induced by sarin intoxication presents a therapeutic challenge. In our current research we evaluate the efficacy of a delayed combined triple treatment in ending the abnormal epileptiform seizure activity (ESA) and the ensuing of long-term neuronal insult. SE was induced in male Sprague-Dawley rats by exposure to 1.2LD50 sarin insufficiently treated by atropine and TMB4 (TA) 1 min later. Triple treatment of ketamine, midazolam and valproic acid was administered 30 min or 1 h post exposure and was compared to a delayed single treatment with midazolam alone. Toxicity and electrocorticogram activity were monitored during the first week and behavioral evaluation performed 3 weeks post exposure followed by brain biochemical and immunohistopathological analyses. The addition of both single and triple treatments reduced mortality and enhanced weight recovery compared to the TA-only treated group. The triple treatment also significantly minimized the duration of the ESA, reduced the sarin-induced increase in the neuroinflammatory marker PGE2, the brain damage marker TSPO, decreased the gliosis, astrocytosis and neuronal damage compared to the TA+ midazolam or only TA treated groups. Finally, the triple treatment eliminated the sarin exposed increased open field activity, as well as impairing recognition memory as seen in the other experimental groups. The delayed triple treatment may serve as an efficient therapy, which prevents brain insult propagation following sarin-induced refractory SE, even if treatment is postponed for up to 1 h.

Lung damage following whole body, but not intramuscular, exposure to median lethality dose of sarin: findings in rats and guinea pigs

Objective: Sarin is an irreversible organophosphate cholinesterase inhibitor and a highly toxic, volatile warfare agent. Rats and guinea pigs exposed to sarin display cholinergic excitotoxicity which includes hyper-salivation, respiratory distress, tremors, seizures, and death. Here we focused on the characterization of the airways injury induced by direct exposure of the lungs to sarin vapor and compared it to that induced by the intramuscularly route. Materials and methods: Rats were exposed to sarin either in vapor (∼1LCT50, 34.2 ± 0.8 µg/l/min, 10 min) or by i.m. (∼1LD50, 80 µg/kg), and lung injury was evaluated by broncho-alveolar lavage (BAL). Results and discussion: BAL analysis revealed route-dependent effects in rats: vapor exposed animals showed elevation of inflammatory cytokines, protein, and neutrophil cells. These elevations were seen at 24 h and were still significantly higher compared to control values at 1 week following vapor exposure. These elevations were not detected in rats exposed to sarin i.m. Histological evaluation of the brains revealed typical changes following sarin poisoning independent of the route of administration. The airways damage following vapor exposure in rats was also compared to that induced in guinea pigs. The latter showed increased eosinophilia and histamine levels that constitutes an anaphylactic response not seen in rats. Conclusions: These data clearly point out the importance of using the appropriate route of administration in studying the deleterious effects of volatile nerve agents, as well as the selection of the appropriate animal species. Since airways form major target organs for the development of injury following inhalation toxicity, they should be included in any comprehensive evaluation of countermeasures efficacy.

Early changes in M2 muscarinic acetylcholine receptors (mAChRs) induced by sarin intoxication may be linked to long lasting neurological effects

The effect of sarin on the binding parameters (KD & Bmax) of M2 muscarinic acetylcholine receptor (mAChR) was studied 24h and 1 week post exposure. Male & female Sprague-Daweley rats were poisoned with 1XLD50 sarin (80μg/kg, im) followed by treatment of trimedoxime bromide and atropine (7.5:5mg/kg, im) 1min later. Brains were removed and analyzed for M2 mAChR binding, using [³H]AFDX384, an M2 selective antagonist. A significant increase in KD of M2 mAChR was found in the cortex 24h post poisoning, displaying elevation from 4.65±1.16 to 8.45±1.06nM and 5.24±0.93 to 9.29±1.56nM in male and female rats, respectively. A rise in KD was also noted 1 week following exposure from 5.04±1.20 to 11.75±2.78 and from 5.37±1.02 to 11.66±1.73nM, presenting an added increase of 51 and 40% (compared to 24h) in males and females, respectively. Analysis of M2 receptor density (Bmax) revealed a significant reduction of 68% in males and insignificant reduction of 22% in females, 24h after sarin exposure which was followed by 37% recovery in males and 100% recovery in females, 1 week later. These results indicate that sarin induces a long-term decreased affinity in M2 mAChR (elevated KDs) and a transient effect on the number of this receptor subtype (Bmax). We hypothesize that the reduced affinity of the M2 receptors (negative auto-regulatory receptors) may cause long-term brain deficits by impairing the normal regulation release of ACh into the synaptic cleft.

Sarin (GB, O-isopropyl methylphosphonofluoridate) neurotoxicity: critical review

Sarin (GB, O-isopropyl methylphosphonofluoridate) is a potent organophosphorus (OP) nerve agent that inhibits acetylcholinesterase (AChE) irreversibly. The subsequent build-up of acetylcholine (ACh) in the central nervous system (CNS) provokes seizures and, at sufficient doses, centrally-mediated respiratory arrest. Accumulation of ACh at peripheral autonomic synapses leads to peripheral signs of intoxication and overstimulation of the muscarinic and nicotinic receptors, which is described as "cholinergic crisis" (i.e. diarrhea, sweating, salivation, miosis, bronchoconstriction). Exposure to high doses of sarin can result in tremors, seizures, and hypothermia. More seriously, build-up of ACh at neuromuscular junctions also can cause paralysis and ultimately peripherally-mediated respiratory arrest which can lead to death via respiratory failure. In addition to its primary action on the cholinergic system, sarin possesses other indirect effects. These involve the activation of several neurotransmitters including gamma-amino-butyric acid (GABA) and the alteration of other signaling systems such as ion channels, cell adhesion molecules, and inflammatory regulators. Sarin exposure is associated with symptoms of organophosphate-induced delayed neurotoxicity (OPIDN) and organophosphate-induced chronic neurotoxicity (OPICN). Moreover, sarin has been involved in toxic and immunotoxic effects as well as organophosphate-induced endocrine disruption (OPIED). The standard treatment for sarin-like nerve agent exposure is post-exposure injection of atropine, a muscarinic receptor antagonist, accompanied by an oxime, an AChE reactivator, and diazepam.

Possible role for anisodamine in organophosphate poisoning

In cases of organophosphate poisoning, patients are treated with a combination of antidotes. In addition to these poison-directed antidotes, patients may require extra oxygen and artificial ventilation; other modalities may also be needed due to the wide range of toxic effects. Anisodamine is a belladonna alkaloid, and like other drugs from this family is non subtype-selective muscarinic, and a nicotinic cholinoceptor antagonist, which has been employed in traditional Chinese medicine. As a muscarinic antagonist, it displays similar pharmacological effects to atropine and scopolamine. However, anisodamine is not only less potent than atropine and scopolamine but also less toxic. Current in vitro and animal model studies have demonstrated that anisodamine has protective effects in a variety of diseases. Organophosphate poisoning involves not only the central and peripheral nervous systems, but also the cardiac and respiratory systems, as well as activation of inflammatory processes and oxidative stress. Therefore, the anticholinergic and additional activities of anisodamine appear to be relevant and justify its consideration as an addition to the existing remedies. However, more research is needed, as at present data on the role of anisodamine in the management of organophosphate poisoning are limited. Here, we review the beneficial effects of anisodamine on processes relevant to organophosphate poisoning.

The Long-Term Effects of Organophosphates Poisoning as a Risk Factor of CVDs: A Nationwide Population-Based Cohort Study

BACKGROUND

Organophosphorus pesticides are widely used throughout the world. Because of their ease of availability, organophosphorus compounds are commonly used for self-poisoning in developing countries. The acute effects of exposure to organophosphorus pesticides are well known, but the chronic effects are unclear. Recent studies suggest that abnormalities of the central and peripheral nervous systems persisted for up to 5 years after acute poisoning due to a single large dose of organophosphates (OPs). However, the long-term effects on cardiovascular diseases are poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

An OPs-exposed cohort (N = 7,561) and an age- and gender-matched control cohort (N = 30,244), both identified from the National Health Insurance Research Database, were compared. We utilized the multivariable Cox proportional model to estimate the risks of developing arrhythmia, coronary artery disease (CAD) and congestive heart failure (CHF). The patients with acute poisoning from OPs had higher incidence rates of arrhythmia (5.89 vs. 3.61 per 1,000 person-years), CAD (9.10 vs. 6.88 per 1,000 person-years), and CHF (3.89 vs. 2.98 per 1,000 person-years) compared with that of the non-OPs poisoning cohort, with a crude subhazard ratio (SHR) of 1.40, 1.13, and 1.12, respectively. Additionally, a significantly higher risk of arrhythmia was observed in the OPs poisoning cohort (adjusted SHR = 1.25) compared with the non-OPs poisoning cohort, particularly in male patients (adjusted SHR = 1.33) and those under 49 years of age (adjusted SHR = 3.16). After accounting for the competing risks of death, there was a higher risk of arrhythmia and CAD during a three year follow-up period (adjusted SHR = 1.50 for arrhythmia; adjusted SHR = 1.10 for CAD). We also found an adjusted SHR of 1.36 associated with developing CHF after 6 years of follow-up for OPs poisoning cohort.

CONCLUSIONS

Acute OPs poisoning may continuously impact human health through mechanisms that are unclear. Any supportive measurements that could contribute to a reduction in the risk of heart disease may be beneficial in cases of OPs poisoning survivors.

Word-finding impairment in veterans of the 1991 Persian Gulf War

Approximately one quarter of 1991 Persian Gulf War Veterans experience cognitive and physiological sequelae that continue to be unexplained by known medical or psychological conditions. Difficulty coming up with words and names, familiar before the war, is a hallmark of the illness. Three Gulf War Syndrome subtypes have been identified and linked to specific war-time chemical exposures. The most functionally impaired veterans belong to the Gulf War Syndrome 2 (Syndrome 2) group, for which subcortical damage due to toxic nerve gas exposure is the suspected cause. Subcortical damage is often associated with specific complex language impairments, and Syndrome 2 veterans have demonstrated poorer vocabulary relative to controls. 11 Syndrome 1, 16 Syndrome 2, 9 Syndrome 3, and 14 age-matched veteran controls from the Seabees Naval Construction Battalion were compared across three measures of complex language. Additionally, functional magnetic resonance imaging (fMRI) was collected during a covert category generation task, and whole-brain functional activity was compared between groups. Results demonstrated that Syndrome 2 veterans performed significantly worse on letter and category fluency relative to Syndrome 1 veterans and controls. They also exhibited reduced activity in the thalamus, putamen, and amygdala, and increased activity in the right hippocampus relative to controls. Syndrome 1 and Syndrome 3 groups tended to show similar, although smaller, differences than the Syndrome 2 group. Hence, these results further demonstrate specific impairments in complex language as well as subcortical and hippocampal involvement in Syndrome 2 veterans. Further research is required to determine the extent of language impairments in this population and the significance of altered neurologic activity in the aforementioned brain regions with the purpose of better characterizing the Gulf War Syndromes.

Sarin-induced brain damage in rats is attenuated by delayed administration of midazolam

Sarin poisoned rats display a hyper-cholinergic activity including hypersalivation, tremors, seizures and death. Here we studied the time and dose effects of midazolam treatment following nerve agent exposure. Rats were exposed to sarin (1.2 LD50, 108 μg/kg, im), and treated 1 min later with TMB4 and atropine (TA 7.5 and 5 mg/kg, im, respectively). Midazolam was injected either at 1 min (1 mg/kg, im), or 1 h later (1 or 5 mg/kg i.m.). Cortical seizures were monitored by electrocorticogram (ECoG). At 5 weeks, rats were assessed in a water maze task, and then their brains were extracted for biochemical analysis and histological evaluation. Results revealed a time and dose dependent effects of midazolam treatment. Rats treated with TA only displayed acute signs of sarin intoxication, 29% died within 24h and the ECoG showed seizures for several hours. Animals that received midazolam within 1 min survived with only minor clinical signs but with no biochemical, behavioral, or histological sequel. Animals that lived to receive midazolam at 1h (87%) survived and the effects of the delayed administration were dose dependent. Midazolam 5 mg/kg significantly counteracted the acute signs of intoxication and the impaired behavioral performance, attenuated some of the inflammatory response with no effect on morphological damage. Midazolam 1mg/kg showed only a slight tendency to modulate the cognitive function. In addition, the delayed administration of both midazolam doses significantly attenuated ECoG compared to TA treatment only. These results suggest that following prolonged seizure, high dose midazolam is beneficial in counteracting adverse effects of sarin poisoning.

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.