Acute inhalation toxicity of soman and sarin in baboons

Acetylcholinesterase inhibition resulting from exposure to inhaled OP can be prevented by pretreatment with BChE in both macaques and minipigs

More frequent and widespread nerve agent attacks highlight the need for efficacious pre- and post-exposure organophosphate (OP) counter-measures to protect military and civilian populations. Because of critical targeting of acetylcholinesterase (AChE) in the CNS by OPs, a pre-treatment candidate for preventing/reducing poisoning will be a broadly acting molecule that scavenges OPs in blood before they reach their physiological targets. Prophylactic human butyrylcholinesterase (HuBChE), the leading pretreatment candidate, has been shown to protect against multiple LD50's of nerve agents in rodents, macaques, and minipigs. This review describes the development of a HuBChE bioscavenger pretreatment from early proof-of-concept studies to pre-clinical studies with the native injectable enzyme and the development of aerosolized forms of recombinant enzyme, which can be delivered by inhalation nebulizer devices, to effect protection against inhaled OP nerve agents and insecticides. Early animal studies utilized parenteral exposure. However, lungs are the portal of entry for most volatile OP vapors and represent the major means of OP intoxication. In this regard, pretreat-ment with 7.5 mg/kg of HuBChE by IM injection protected minipigs against lethal sarin vapor and prevented AChE inhibition in the blood. This is similar to the five-day protection in macaques by an aerosolized rHuBChE using a nebulizer against aerosolized paraoxon (estimated to be an 8 mg/kg estimated human dose). Importantly, lethal inhaled doses of OP may be smaller relative to the same dose delivered by injection, thus reducing the protective HuBChE dose, while a combination of HuBChE and post-exposure oxime may prolong protection.

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.

Inhalation Apparatus for Generating Sarin and Soman Toxic Vapors

The developed inhalation system is a dynamic and whole-body exposure model designated for generating sarin or soman vapors. It consists of an evaporating apparatus, an inhalation chamber and a carbon filter. The inhalation chamber is made of stainless steel and its total volume is 36 l. The concentration of organophosphorus compound depends on airflow through the chamber, syringe volume of the dosing pump and dosing speed. For determination of organophosphorus compound (OPC) concentration, a modification of Ellman method is used. At generating of vapors in the inhalation chamber the means of the yield were 61.4 ± 6.6 % for sarin and 35.8 ± 3.5 % for soman. The better yield for sarin than for soman, because of the higher volatility of sarin in comparison with soman was achieved. The stable concentration of the OPC for several hours could be maintained in the inhalation chamber when only relatively small amount of the OPC is used. Using the developed inhalation system LCt50 for sarin and for soman in rats was determined. At 1 h exposure the LCt50 values were 4.72 mg.h-1.m-3 for sarin and 4.81 mg.h-1.m-3 for soman. The results presented show that the inhalation chamber successfully fulfils the role of instrument for inhalation intoxication of small laboratory animals with highly toxic OPC.

Post-exposure treatment with the oxime RS194B rapidly reverses early and advanced symptoms in macaques exposed to sarin vapor

Organophosphate (OP) nerve agents and pesticides trigger a common mechanism of neurotoxicity resulting from critical targeting and inhibition of acetylcholinesterases (AChE) in central and peripheral synapses in the cholinergic nervous system. Therapeutic countermeasures have thus focused on either administering an oxime post-exposure, that can rapidly reactivate OP-inhibited AChE, or by preventing OP poisoning through administering pre-exposure treatments that scavenge OPs before they inhibit their physiological AChE targets. While several pyridinium aldoxime antidotes are currently approved, their utility is impaired due to their inability to cross the blood-brain barrier (BBB) efficiently. The present study utilized a macaque (Ma) model to demonstrate the efficacy of a novel zwitterionic and centrally acting oxime RS194B to reactivate sarin- and paraoxon-inhibited macaque AChE and butyrylcholinesterase (BChE) in vitro and to further assess the capacity of RS194B to effect a reversal of clinical symptoms following sarin inhalation in vivo. In vitro, oxime reactivation of MaAChE and MaBChE was shown to be comparable to their human orthologs, while the macaque studies indicated that IM administration of 62.5 mg/kg of RS194B and 0.28 mg/kg atropine after continuous exposure to 49.6 μg/kg sarin vapor, rapidly reactivated the inhibited AChE and BChE in blood and reversed both early and advanced clinical symptoms of sarin-induced toxicity following pulmonary exposure within 1 h. The rapid cessation of autonomic and central symptoms, including convulsions, observed in macaques bodes well for the use of RS194B as an intra- or post-exposure human treatment and validates the macaque model in generating efficacy and toxicology data required for approval under the FDA Animal rule.

The Pesticide Metabolites Paraoxon and Malaoxon Induce Cellular Death by Different Mechanisms in Cultured Human Pulmonary Cells

Organophosphorus (OP) pesticides are known to induce pulmonary toxicity in both humans and experimental animals. To elucidate the mechanism of OP-induced cytotoxicity, we examined the effects of parathion and malathion and their respective metabolites, paraoxon and malaoxon, on primary cultured human large and small airway cells. Exposure to paraoxon and malaoxon produced a dose-dependent increase in cytotoxicity following a 24-hour exposure, while treatment with parathion or malathion produced no effects at clinically relevant concentrations. Exposure to paraoxon-induced caspase activation, but malaoxon failed to induce this response. Since caspases have a major role in the regulation of apoptosis and cell death, we evaluated OP-induced cell death in the presence of a caspase inhibitor. Pharmacological caspase inhibition protected against paraoxon-induced cell death but not malaoxon-induced cell death. These data suggest that caspase activation is a key signaling element in paraoxon-induced cell death, but not malaoxon-induced cellular death in the pulmonary epithelium.

Exploiting parameter space in MOFs: a 20-fold enhancement of phosphate-ester hydrolysis with UiO-66-NH2

The hydrolysis of nerve agents is of primary concern due to the severe toxicity of these agents. Using a MOF-based catalyst (UiO-66), we have previously demonstrated that the hydrolysis can occur with relatively fast half-lives of 50 minutes. However, these rates are still prohibitively slow to be efficiently utilized for some practical applications (e.g., decontamination wipes used to clean exposed clothing/skin/vehicles). We thus turned our attention to derivatives of UiO-66 in order to probe the importance of functional groups on the hydrolysis rate. Three UiO-66 derivatives were explored; UiO-66-NO2 and UiO-66-(OH)2 showed little to no change in hydrolysis rate. However, UiO-66-NH2 showed a 20 fold increase in hydrolysis rate over the parent UiO-66 MOF. Half-lives of 1 minute were observed with this MOF. In order to probe the role of the amino moiety, we turned our attention to UiO-67, UiO-67-NMe2 and UiO-67-NH2. In these MOFs, the amino moiety is in close proximity to the zirconium node. We observed that UiO-67-NH2 is a faster catalyst than UiO-67 and UiO-67-NMe2. We conclude that the role of the amino moiety is to act as a proton-transfer agent during the catalytic cycle and not to hydrogen bond or to form a phosphorane intermediate.

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.

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.

Protection against paraoxon toxicity by an intravenous pretreatment with polyethylene-glycol-conjugated recombinant butyrylcholinesterase in macaques

Recombinant (r) butyrylcholinesterase (rBChE) produced in CHO cells is being developed as a prophylactic countermeasure against neurotoxicity resulting from exposure to organophosphates (OPs) in the form of pesticides and nerve agents. To evaluate the efficacy of a parenteral pretreatment, a PEGylated macaque (Ma) form of rBChE was administered into homologous animals to ensure good plasma retention without immunogenicity. Thus, macaques were administered PEG-rMaBChE at either 5 or 7mg/kg intravenously (i.v.) and exposed subcutaneously to 12μg/kg of the potent pesticide paraoxon (Px) at 1h or at 1 and 72h, respectively. Protection was measured by the ability of rBChE prophylaxis to prevent the inhibition of circulating acetylcholinesterase on red blood cells (RBC-AChE). In rBChE-pretreated animals, no inhibition of RBC-AChE activity after the first Px exposure and only a 10-20% reduction after the second exposure were observed as compared to a 75% RBC-AChE inhibition usually obtained without pretreatment. In addition, these studies raised other interesting issues. The lipophilic nature of Px, appears to result in early and transient inhibition of RBC-AChE as a result of transfer of OP bound to RBC even in BChE-pretreated animals. The protection by a single injection of rBChE against two administrations of Px represents the first example of protection by an i.v. rBChE pretreatment against a pesticide such as Px and bodes well for a parenteral rHuBChE pretreatment as an OP countermeasure in humans.

Aerosolized delivery of oxime MMB-4 in combination with atropine sulfate protects against soman exposure in guinea pigs

We evaluated the efficacy of aerosolized acetylcholinesterase (AChE) reactivator oxime MMB-4 in combination with the anticholinergic atropine sulfate for protection against respiratory toxicity and lung injury following microinstillation inhalation exposure to nerve agent soman (GD) in guinea pigs. Anesthetized animals were exposed to GD (841 mg/m(3), 1.2 LCt(50)) and treated with endotracheally aerosolized MMB-4 (50 µmol/kg) plus atropine sulfate (0.25 mg/kg) at 30 sec post-exposure. Treatment with MMB-4 plus atropine increased survival to 100% compared to 38% in animals exposed to GD. Decreases in the pulse rate and blood O(2) saturation following exposure to GD returned to normal levels in the treatment group. The body-weight loss and lung edema was significantly reduced in the treatment group. Similarly, bronchoalveolar cell death was significantly reduced in the treatment group while GD-induced increase in total cell count was decreased consistently but was not significant. GD-induced increase in bronchoalveolar protein was diminished after treatment with MMB-4 plus atropine. Bronchoalveolar lavage AChE and BChE activity were significantly increased in animals treated with MMB-4 plus atropine at 24 h. Lung and diaphragm tissue also showed a significant increase in AChE activity in the treatment group. Treatment with MMB-4 plus atropine sulfate normalized various respiratory dynamics parameters including respiratory frequency, tidal volume, peak inspiratory and expiratory flow, time of inspiration and expiration, enhanced pause and pause post-exposure to GD. Collectively, these results suggest that aerosolization of MMB-4 plus atropine increased survival, decreased respiratory toxicity and lung injury following GD inhalation exposure.

Pulmonary delivery of an aerosolized recombinant human butyrylcholinesterase pretreatment protects against aerosolized paraoxon in macaques

Butyrylcholinesterase (BChE) is the leading pretreatment candidate against exposure to organophosphates (OPs), which pose an ever increasing public and military health. Since respiratory failure is the primary cause of death following acute OP poisoning, an inhaled BChE therapeutic could prove highly efficacious in preventing acute toxicity as well as the associated delayed neuropathy. To address this, studies have been performed in mice and macaques using Chinese Hamster Ovary cells (CHO)-derived recombinant (r) BChE delivered by the pulmonary route, to examine whether the deposition of both macaque (Ma) and human (Hu) rBChE administered as aerosols (aer) favored the creation and retention of an efficient protective "pulmonary bioshield" that could scavenge incoming (inhaled) OPs in situ thereby preventing entry into the circulation and inhibition of plasma BChE and AChE on red blood cells (RBC-AChE) and in cholinergic synapses. In contrast to parenteral delivery of rBChE, which currently requires posttranslational modification for good plasma stability, an unmodified aer-rBChE pretreatment given 1-40 h prior to >1 LD50 of aer-paraoxon (Px) was able to prevent inhibition of circulating cholinesterase in a dose-dependent manner. These studies are the first to show protection by rBChE against a pesticide such as paraoxon when delivered directly into the lung and bode well for the use of a non-invasive and consumer friendly method of rHuBChE delivery as a human treatment to counteract OP toxicity.

Development of a microinstillation model of inhalation exposure to assess lung injury following exposure to toxic chemicals and nerve agents in Guinea pigs

Respiratory disturbances due to chemical warfare nerve agents (CWNAs) are the starting point of mass casualty and the primary cause of death by these weapons of terror and mass destruction. However, very few studies have been implemented to assess respiratory toxicity and exacerbation induced by CWNAs, especially methylphosphonothioic acid S-(2-(bis(1-methylethyl)amino)ethyl)O-ethyl ester (VX). In this study, we developed a microinstillation technique of inhalation exposure to assess lung injury following exposure to CWNAs and toxic chemicals. Guinea pigs were gently intubated by placing a microcatheter into the trachea 1.5 to 2.0 cm centrally above the bifurcation. This location is crucial to deliver aerosolized agents uniformly to the lung's lobes. The placement of the tube is calculated by measuring the distance from the upper front teeth to the tracheal bifurcation, which is typically 8.5 cm for guinea pigs of equivalent size and a weight range of 250 g to 300 g. The catheter is capable of withstanding 100 psi pressure; the terminus has five peripheral holes to pump air that aerosolizes the nerve agent that is delivered in the central hole. The microcatheter is regulated by a central control system to deliver the aerosolized agent in a volume lower than the tidal volume of the guinea pigs. The average particle size of the nerve agent delivered was 1.48 +/- 0.07 micrometer. The microinstillation technology has been validated by exposing the animals to Coomassie brilliant blue, which showed a uniform distribution of the dye in different lung lobes. In addition, the concentration of the dye in the lungs correlated with the dose/time of exposure. Furthermore, histopathological analysis confirmed the absence of barotraumas following micoinstillation. This novel technique delivers the agent safely, requires less amount of agent, avoids exposure to skin, pelt, and eye, and circumvents the concern of deposition of the particles in the nasal and palette due to the switching of breathing from nasal to oronasal in whole-body dynamic chamber or nose only exposure. Currently, we are using this inhalation exposure technique to investigate lung injuries and respiratory disturbances following direct exposure to VX.

Protective Effects of Aerosolized Scopolamine Against Soman-Induced Acute Respiratory Toxicity in Guinea Pigs

The protective efficacy of the antimuscarinic agent scopolamine was evaluated against soman (o-pinacolyl methylphosphonofluoridate [GD])-induced respiratory toxicity in guinea pigs. Anesthetized animals were exposed to GD (841 mg/m3) by microinstillation inhalation exposure and treated 30 seconds later with endotracheally aerosolized scopolamine (0.25 mg/kg) and allowed to recover for 24 hours. Treatment with scopolamine significantly increased survival and reduced clinical signs of toxicity and body weight loss in GD-exposed animals. Analysis of bronchoalveolar lavage (BAL) fluid showed normalization of GD-induced increased cell death, total cell count, and protein following scopolamine treatment. The BAL fluid acetylcholinesterase and butyrylcholinesterase levels were also increased by scopolamine treatment. Respiratory dynamics parameters were normalized at 4 and 24 hours post–GD exposure in scopolamine-treated animals. Lung histology showed that scopolamine treatment reduced bronchial epithelial and subepithelial inflammation and multifocal alveolar septal edema. These results suggest that aerosolized scopolamine considerably protects against GD-induced respiratory toxicity.

Acute Changes in Pulmonary Function Following Microinstillation Inhalation Exposure to Soman in Nonatropenized Guinea Pigs

Barometric whole-body plethysmography (WBP) was used to examine pulmonary functions at 4 and 24 hours postexposure to soman (GD) in guinea pigs without therapeutics to improve survival. Endotracheal aerosolization by microinstillation was used to administer GD (280, 561, and 841 mg/m3) or saline to anesthetized guinea pigs. Significant increases in respiratory frequency (RF), tidal volume (TV), and minute volume (MV) were observed with 841 mg/m3 GD at 4 hours and that were reduced at 24 hours postexposure. A dose-dependent increase in peak inspiration flow and peak expiration flow was present at 4-hour post-GD exposure that was reduced at 24 hours. Time of inspiration and expiration were decreased in all doses of GD exposure at 4 and 24 hours, with significant inhibition at 841 mg/m3. End-expiratory pause (EEP) increased at 280 and 561 mg/m3, but decreased in animals exposed 841 mg/m3 at 24 hours postexposure. Pseudo-lung resistance (Penh) and pause followed similar patterns and increased at 4 hours, but decreased at 24 hours postexposure to 841 mg/m3 of GD compared to control. These studies indicate GD exposure induces dose-dependent changes in pulmonary function that are significant at 841 mg/m3 at 4 hours and remains 24 hours postexposure. Furthermore, at 4 hours, GD induces bronchoconstriction possibly due to copious airway secretion and ongoing lung injury in addition to cholinergic effects, while at 24 hours GD induces bronchodilation a possible consequence of initial compensatory mechanisms.

Acute microinstillation inhalation exposure to sarin induces changes in respiratory dynamics and functions in guinea pigs

This study investigates the toxic effects of sarin on respiratory dynamics following microinstillation inhalation exposure in guinea pigs. Animals are exposed to sarin for 4 minutes, and respiratory functions are monitored at 4 hours and 24 hours by whole-body barometric plethysmography. Data show significant changes in respiratory dynamics and function following sarin exposure. An increase in respiratory frequency is observed at 4 hours post exposure compared with saline controls. Tidal volume and minute volume are also increased in sarin-exposed animals 4 hours after exposure. Peak inspiratory flow increases, whereas peak expiratory flow increases at 4 hours and is erratic following sarin exposure. Animals exposed to sarin show a significant decrease in expiratory time and inspiratory time. End-inspiratory pause is unchanged whereas end-expiratory pause is slightly decreased 24 hours after sarin exposure. These results indicate that inhalation exposure to sarin alters respiratory dynamics and function at 4 hours, with return to normal levels at 24 hours post exposure.

Blood and bronchoalveolar lavage fluid acetylcholinesterase levels following microinstillation inhalation exposure to sarin in Guinea pigs

We determined acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition in the bronchoalveolar lavage fluid (BALF) following inhalation exposure to chemical threat nerve agent (CTNA) sarin. Age- and weight-matched male guinea pigs were exposed to five different doses of sarin (169.3, 338.7, 508, 677.4, and 846.5 mg/m(3)) using a microinstillation inhalation exposure technique for 4 min. The technique involves aerosolization of the agent in the trachea using a microcatheter with a center hole that delivers the agent and multiple peripheral holes that pumps air to aerosolize the agent at the tip. Animals exposed to higher doses of sarin occasionally developed seizures and succumbed to death within 15 min after exposure. The LCt(50) for sarin using the microinstillation technique was determined to be close to 677.4 mg/m(3). Ear blood AChE activity showed a dose-dependent inhibition at 15 min postexposure. The inhibition of blood AChE remained constant over 35 and 55 min after sarin exposure indicating that there was no lung depot effect. Cardiac blood AChE and butyrylcholinesterase (BChE) activity in surviving animals euthanized at 24 h postexposure showed a dose-dependent inhibition with an inhibition of 60% at 677.4 and 846.5 mg/m(3) sarin exposure. AChE and BChE activity in bronchoalveolar lavage fluid (BALF) showed a slight increase at 338.7 to 677.4 mg/m(3) sarin exposure but a marginal inhibition at 169.3 mg/m(3). In contrast, the AChE protein levels determined by immunoblotting showed an increase at 169.3 mg/m(3) in the BALF. The BALF protein level, a biomarker of lung injury, was increased maximally at 338.7 mg/m(3) and that increase was dropped with an increase in the dose of sarin. The BALF protein levels correlated with the AChE and BChE activity. These data suggest that sarin microinstillation inhalation exposure results in respiratory toxicity and lung injury characterized by changes in lavage AChE, BChE, and protein levels.

Inhalation of the nerve gas sarin impairs ventilatory responses to hypercapnia and hypoxia in rats

Sarin, a highly toxic nerve gas, is believed to cause bronchoconstriction and even death primarily through respiratory failure; however, the mechanism underlying the respiratory failure is not fully understood. The goals of this study were to ascertain whether sarin affects baseline ventilation (VE) and VE chemoreflexes as well as airway resistance and, if so, whether these changes are reversible. Four groups of F344 rats were exposed to vehicle (VEH) or sarin at 2.5, 3.5, and 4.0 mg h m(-3) (SL, SM, and SH, respectively). VE and VE responses to hypercapnia (7% CO2) or hypoxia (10% O2) were measured by plethysmography at 2 h and 1, 2, and 5 days after VEH or sarin exposure. Total pulmonary resistance (RL) also was measured in anesthetized VEH- and SH-exposed animals 2 h after exposure. Our results showed that within 2 h after exposure 11% of the SM- and 52% of the SH- exposed groups died. Although the SM and SH significantly decreased hypercapnic and hypoxic VE to similar levels (64 and 69%), SH induced greater respiratory impairment, characterized by lower baseline VE (30%; P<0.05), and total loss of the respiratory frequency response to hypercapnia and hypoxia. VE impairment recovered within 1-2 days after sarin exposure; interestingly, SH did not significantly affect baseline RL. Moreover, sarin induced body tremors that were unrelated to the changes in the VE responses. Thus, LC50 sarin causes a reversible impairment of VE that is not dependent on the sarin-induced body tremors and not associated with changes in RL.

Kinetics of sarin (GB) following a single sublethal inhalation exposure in the guinea pig

To improve toxicity estimates from sublethal exposures to chemical warfare nerve agents (CWNA), it is necessary to generate mathematical models of the absorption, distribution, and elimination of nerve agents. However, current models are based on representative data sets generated with different routes of exposure and in different species and are designed to interpolate between limited laboratory data sets to predict a wide range of possible human exposure scenarios. This study was performed to integrate CWNA sublethal toxicity data in male Duncan Hartley guinea pigs. Specific goal was to compare uptake and clearance kinetics of different sublethal doses of sarin (either 0.1 x or 0.4 x LC50) in blood and tissues of guinea pigs exposed to agent by acute whole-body inhalation exposure after the 60-min LC50 was determined. Arterial catheterization allowed repeated blood sampling from the same animal at various time periods. Blood and tissue levels of acetylcholinesterase, butyrylcholinesterase, and regenerated sarin (rGB) were determined at various time points during and following sarin exposure. The following pharmacokinetic parameters were calculated from the graph of plasma or RBC rGB concentration versus time: time to reach the maximal concentration; maximal concentration; mean residence time; clearance; volume of distribution at steady state; terminal elimination-phase rate constant; and area under plasma concentration time curve extrapolated to infinity using the WinNonlin analysis program 5.0. Plasma and RBC t(1/2) for rGB was also calculated. Data will be used to develop mathematical model of absorption and distribution of sublethal sarin doses into susceptible tissues.

Acute toxic effects of nerve agent VX on respiratory dynamics and functions following microinsillation inhalation exposure in guinea pigs

Exposure to a chemical warfare nerve agent (CWNA) leads to severe respiratory distress, respiratory failure, or death if not treated. We investigated the toxic effects of nerve agent VX on the respiratory dynamics of guinea pigs following exposure to 90.4 mug/m3 of VX or saline by microinstillation inhalation technology for 10 min. Respiratory parameters were monitored by whole-body barometric plethysmography at 4, 24, and 48 h, 7 d, 18 d, and 4 wk after VX exposure. VX-exposed animals showed a significant decrease in the respiratory frequency (RF) at 24 and 48 h of recovery (p value .0329 and .0142, respectively) compared to the saline control. The tidal volume (TV) slightly increased in VX exposed animals at 24 and significantly at 48 h (p = .02) postexposure. Minute ventilation (MV) increased slightly at 4 h but was reduced at 24 h and remained unchanged at 48 h. Animals exposed to VX also showed an increase in expiratory (Te) and relaxation time (RT) at 24 and 48 h and a small reduction in inspiratory time (Ti) at 24 h. A significant increase in end expiratory pause (EEP) was observed at 48 h after VX exposure (p = .049). The pseudo lung resistance (Penh) was significantly increased at 4 h after VX exposure and remained slightly high even at 48 h. Time-course studies reveal that most of the altered respiratory dynamics returned to normal at 7 d after VX exposure except for EEP, which was high at 7 d and returned to normal at 18 d postexposure. After 1 mo, all the monitored respiratory parameters were within normal ranges. Bronchoalveolar lavage (BAL) 1 mo after exposure showed virtually no difference in protein levels, cholinesterase levels, cell number, and cell death in the exposed and control animals. These results indicate that sublethal concentrations of VX induce changes in respiratory dynamics and functions that over time return to normal levels.

Toxic doses of paraoxon alter the respiratory pattern without causing respiratory failure in rats

Respiratory failure, through a combination of muscarinic, nicotinic, and central effects, is the primary cause of death in acute organophosphate poisoning. However, the mechanisms inducing respiratory failure remain unclear. In rats poisoned subcutaneously with paraoxon at doses near the LD(50), we studied the pattern of respiration using whole body plethysmography and the occurrence of respiratory failure using arterial blood gases. Subsequently, we studied the effects of atropine on paraoxon-induced modification of ventilation and arterial blood gases. Fifty and 75%, but not 10% of the subcutaneous LD(50) of paraoxon induced marked and sustained signs and symptoms. At 30min post-injection and throughout the study, there was a significant decrease in the respiratory frequency (34% (50% versus solvent), and 29% (75% versus solvent)) and a significant increase in the expiratory time (72% (50% versus solvent) and 60% (75% versus solvent)) with no modifications of the inspiratory time. The tidal volume was significantly increased for the 75% but not for the 50% dose. Apnea was never detected. Even at the 75% dose, paraoxon had no effects on PaO(2), PaCO(2) or HCO(3)(-); however, a significant decrease in arterial pH was observed at 30min (7.34+/-0.07 versus 7.51+/-0.01, p=0.03). Atropine completely reversed the paraoxon-induced respiratory alterations. We conclude that paraoxon, at doses equal to 50 and 75% of the LD(50), alters ventilation at rest without inducing respiratory failure during the study period.

The automated bioaerosol exposure system: Preclinical platform development and a respiratory dosimetry application with nonhuman primates

INTRODUCTION

Well-characterized inhalation exposure systems are critical for preclinical testing and pathogenesis studies. The automated bioaerosol exposure system (ABES) provides a microprocessor-driven inhalation platform that provides exquisite data acquisition and control over all aspects of inhalation exposures. Because this represents a new technology, the development and characteristics of the ABES are thoroughly discussed. In addition to control over homeostatic and aerosol conditions, the ABES incorporates a dosimetry function based on respiratory performance of the test animal during inhalation.

METHODS

To test the system, rhesus macaques were initially sham-exposed using the ABES in a head-only inhalation configuration. The ABES was subsequently used under biosafety level (BSL)-III conditions in a vaccine efficacy challenge using aerosolized staphylococcal enterotoxin B (SEB) toxin, again using the real-time dosimetry function of the system.

RESULTS

Sham exposure results indicated significant departures from corresponding whole-body plethysmography (WBP) respiratory function estimates taken before the inhalation procedure. The results of the SEB exposure demonstrated the utility of using the ABES to generate consistently accurate and precise inhalation dose.

DISCUSSION

Taken together, the results of the sham and toxin challenge experiments demonstrate that the dosimetry function of the ABES improves the precision and accuracy of inhaled dose delivery and calculation as compared to predictive WBP conducted before the exposure. The ABES represents a highly adaptable platform for the design of inhalation systems to suit the requirements of a variety of animal models.

Sarin poisoning in Matsumoto, Japan

A presumed terrorist attack with sarin occurred in a residential area of the city of Matsumoto, Japan, on June 27, 1994. About 600 residents and rescue staff were poisoned; 58 were admitted to hospitals, and 7 died. We examined clinical and laboratory findings of 264 people who sought treatment and the results of health examinations on 155 residents done 3 weeks after the poisoning. Findings for severely poisoned people were decreases in serum cholinesterase, acetylcholinesterase in erythrocytes, serum triglyceride, serum potassium and chloride; and increases in serum creatine kinase, leucocytes, and ketones in urine. Slight fever and epileptiform abnormalities on electroencephalogram were present for up to 30 days. Examination revealed no persisting abnormal physical findings in any individual. Acetylcholinesterase returned to normal within 3 months in all people examined. Although subclinical miosis and neuropathy were present 30 days after exposure, almost all symptoms of sarin exposure disappeared rapidly and left no sequelae in most people.

Effect of atropine and bispyridinium oximes on respiratory and circulatory function in guinea-pigs poisoned by sarin

During the past decade the oxime HI 6(1-[[[4-(aminocarbonyl)pyridinio]methoxy]methyl]-2- [(hydroxyimino)methyl] pyridinium dichloride) was shown to improve survival in nerve agent poisoning (in combination with atropine). Recent studies indicate, that HLö 7 (1-[[[4-(aminocarbonyl)pyridinio]methoxy]methyl]-2,4-bis [(hydroxyimino)methyl] pyridinium diiodide or dimethanesulfonate) is also an effective antidote in nerve agent poisoning but, with both oximes, data on restoration of respiration and circulation are scarce. The ability of HLö 7 or HI 6 with atropine to improve the respiratory and circulatory function in sarin-poisoned guinea-pigs was therefore investigated. Female Dunkin-Hartley guinea-pigs were anaesthetised with urethane (1.8 g/kg) and the arteria carotis, vena jugularis and trachea were cannulated. After baseline measurements the animals received 100 or 200 micrograms/kg sarin, and 2 min later the antidotes (all i.v.): 10 mg/kg atropine sulfate or a combination of atropine and HLö 7 or HI 6 (30 mumol/kg, each). Respiratory and circulatory parameters were recorded for the whole experimental period of 60 min or until the death of the animal. Brain and diaphragm acetylcholinesterase (AChE) activity was determined in each animal after the experiment. Poisoning by sarin resulted in a rapid respiratory arrest within 5 min. Atropine treatment was only partially effective in improving respiration after 100 micrograms/kg sarin but was ineffective after 200 micrograms/kg sarin. Therapy of sarin-poisoned animals with atropine plus oxime further improved respiration to various extents, restored circulation and increased survival time, HLö 7 being more effective than HI 6. Diaphragm and brain AChE were reactivated by HLö 7 and, to a minor extent, by HI 6. The results of this investigation suggest, that at equimolar doses (30 mumol/kg) the new bispyridinium dioxime HLö 7 has a higher therapeutic efficacy in sarin-poisoned guinea-pigs when compared to HI 6 (both in combination with atropine).

Chemical warfare agents: II. Nerve agents

Nerve agents are highly potent and rapidly acting organophosphorus compounds that irreversibly bind and inactive acetylcholinesterase. Only rarely have they been used in warfare, but their great lethality and the threat that they pose have encouraged production and stockpiling in large quantities. They differ in a number of important ways from common agricultural organophosphate insecticides. In light of recent threats of chemical warfare and the possibilities of chemical acts of terrorism, North American physicians should be knowledgeable of the effects of these agents and the care of exposure victims.