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

Baseline physiological data from anesthetized pigs in a VX intoxication model

Over the past fifty years, swine models have been used for organophosphorus intoxication studies. Among these studies and others on the swine model in general, some physiological data, especially cholinesterase activity highly impacted by organophosphorus compounds like nerve agent VX, still need to be completed. To support and compare our model to others, we have published the experimental protocol, the physiological values of 31 juvenile anesthetized pigs, and the 6 h-follow-up of six supplementary anesthetized control animals and 7 VX-intoxicated pigs. We reported hemodynamics and respiratory parameters, blood levels in several biochemical parameters, blood gas, and complete blood count and compared them to the literature. We also focused on tissue and blood cholinesterase activities and detailed them for acetylcholinesterase and butyrylcholinesterase. After establishing a broad physiological data set consistent with the literature, we reported several cardio-respiratory parameters that seem more affected by an organophosphate intoxication, like heart rate, arterial blood pressure, cardiac output, and respiratory rate. Within the blood, oxygen saturation (SpO2), lactatemia, base excess, and glycemia can also be measured and associated with the other parameters to evaluate the life-threatening status. This swine model is currently used to develop and evaluate medical countermeasures against organophosphate nerve agent intoxications.

Efficacy of atropine and scopolamine on airway contractions following exposure to the nerve agent VX

Nerve agents are highly toxic organophosphorus compounds that inhibit acetylcholinesterase resulting in rapid accumulation of the neurotransmitter acetylcholine (ACh) causing a cholinergic syndrome including respiratory failure. In the present study, respiratory responses and antimuscarinic treatment efficacy was evaluated ex vivo using rat precision-cut lung slices (PCLS) exposed to the nerve agent VX. The respiratory effects were evaluated either by adding exogenous ACh directly to the culture medium or by applying electric-field stimulation (EFS) to the PCLS to achieve a release of endogenous ACh from neurons in the lung tissue. The airway contraction induced by both methods was enhanced by VX and resulted in lingering airway recovery, in particular when airways were exposed to a high VX-dose. Both contractions induced by EFS and exogenously added ACh were significantly reduced by administration of the antimuscarinic drugs atropine or scopolamine. Two additions of atropine or scopolamine after maximal ACh-induced airway response was demonstrated effective to reverse the contraction. By adding consecutive doubled doses of antimuscarinics, high efficiency to reduce the cholinergic airway response was observed. However, the airways were not completely recovered by atropine or scopolamine, indicating that non-muscarinic mechanisms were involved in the smooth muscle contractions. In conclusion, it was demonstrated that antimuscarinic treatment reversed airway contraction induced by VX but supplemental pharmacological interventions are needed to fully recover the airways. Further studies should therefore clarify the mechanisms of physiological responses in lung tissue following nerve agent exposures to improve the medical management of poisoned individuals.

Comparative evaluation of antidotal efficacy of 2-PAM and HNK-102 oximes during inhalation of sarin vapor in Swiss albino mice

Efficacy of two oximes treatments evaluated during inhalation of sarin vapor (LCt₅₀, 755.9 mg/min/m³) in simulated real scenario in vivo. Majority of mice either became moribund or died within 1-2 min during exposure to multifold-lethal concentrations of sarin vapor. Protection indices were determined by exposing to sarin vapor in two sessions, 1 min exposure followed by treatments with or without HNK-102 (56.56 mg/kg, im) or 2-PAM (30 mg/kg, im) and atropine (10 mg/kg, ip), and again exposed for remaining 14 min. Protection offered by HNK-102 was found to be four folds higher compared to 2-PAM in the same toxic environment. Secondly, sub-lethal concentration of sarin vapor (0.8 × LCt₅₀ or 605 mg/min/m³), 24 h post investigations revealed that the oximes could not reactivate brain and serum acetylcholinesterase (AChE) activity. The treatments prevented increase in protein concentration (p < .05) and macrophages infiltration compared to sarin alone group in broncho-alveolar lavage fluid. Lung histopathology showed intense peribronchial infiltration and edema with desquamating epithelial lining and mild to moderate alveolar septal infiltration in sarin and atropine groups, respectively. Noticeable peeling-off observed in epithelial lining and sporadic mild infiltration of epithelial cells at bronchiolar region in 2-PAM and HNK-102 groups, respectively. The oximes failed to reactivate AChE activity; however, the mice survived up to 6.0 × LCt₅₀, proved involvement of non-AChE targets in sarin toxicity. Atropine alone treatment was found to be either ineffective or increased the toxicity. HNK-102, exhibited better survivability with lung protection, can be considered as a better replacement for 2-PAM to treat sarin inhalation induced poisoning.

A novel swine model of ricin-induced acute respiratory distress syndrome

Pulmonary exposure to the plant toxin ricin leads to respiratory insufficiency and death. To date, in-depth study of acute respiratory distress syndrome (ARDS) following pulmonary exposure to toxins is hampered by the lack of an appropriate animal model. To this end, we established the pig as a large animal model for the comprehensive study of the multifarious clinical manifestations of pulmonary ricinosis. Here, we report for the first time, the monitoring of barometric whole body plethysmography for pulmonary function tests in non-anesthetized ricin-treated pigs. Up to 30 h post-exposure, as a result of progressing hypoxemia and to prevent carbon dioxide retention, animals exhibited a compensatory response of elevation in minute volume, attributed mainly to a large elevation in respiratory rate with minimal response in tidal volume. This response was followed by decompensation, manifested by a decrease in minute volume and severe hypoxemia, refractory to oxygen treatment. Radiological evaluation revealed evidence of early diffuse bilateral pulmonary infiltrates while hemodynamic parameters remained unchanged, excluding cardiac failure as an explanation for respiratory insufficiency. Ricin-intoxicated pigs suffered from increased lung permeability accompanied by cytokine storming. Histological studies revealed lung tissue insults that accumulated over time and led to diffuse alveolar damage. Charting the decline in PaO2/FiO2 ratio in a mechanically ventilated pig confirmed that ricin-induced respiratory damage complies with the accepted diagnostic criteria for ARDS. The establishment of this animal model of pulmonary ricinosis should help in the pursuit of efficient medical countermeasures specifically tailored to deal with the respiratory deficiencies stemming from ricin-induced ARDS.

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.

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.

Acute toxic effects of inhaled dichlorvos vapor on respiratory mechanics and blood cholinesterase activity in guinea pigs

Using a modified noninvasive volume-displacement plethysmography system, we investigated the effects of inhaled dichlorvos (2,2-dimethyl-dichlorovinyl phosphate, or DDVP) vapor on the respiratory mechanics and blood cholinesterase activity of guinea pigs. Data revealed significant dose-dependent changes in several pulmonary parameters. Animals exposed to a DDVP concentration of 35 mg/m(3) did not show any significant changes in frequency, tidal volume, or minute ventilation. However, animals exposed to 55 mg/m(3) DDVP showed significantly decreased respiratory frequency and significantly increased tidal volume with no significant changes in minute ventilation. Similarly, animals exposed to 75 mg/m(3) DDVP showed significantly decreased respiratory frequency along with significantly increased tidal volume. The decreased respiratory frequency was large enough in the high exposure group to offset the increased tidal volume. This effect resulted in significantly decreased minute ventilation by the end of exposure, which remained attenuated 10 min after exposure. An analysis of whole-blood cholinesterase activity revealed significantly decreased activity for both acetylcholinesterase (AChE) and butyl-cholinesterase (BChE). Peak inhibition occurred for both enzymes at the end of exposure for all three concentrations and rapidly recovered within several minutes of exposure. Analysis of blood samples using gas chromatography-mass spectroscopy (GC-MS) revealed that minute ventilation may only play a minimal role in the dosimetry of inhaled DDVP vapor.

Protective effect of reversible cholinesterase inhibitors (tacrine, pyridostigmine) and eqbuche against VX poisoning and brain acetylcholinesterase inhibition in rats

The protective effect of the reversible cholinesterase inhibitors tacrine and pyridostigmine alone or in combination with different drugs against acetylcholinesterase inhibition in the pontomedullar area and cerebellum of rats caused by VX agent (O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate) in vivo (2xLD50) was studied along with survival of animals pretreated with different combinations of the drugs used. The best prophylactic effect was observed in a combination of pyridostigmine with benactyzine, trihexyphenidyle and HI-6. Tacrine alone or in other combinations has had no better prophylactic effect in comparison with these combinations containing pyridostigmine. Equine butyrylcholinesterase, also protected against VX poisoning very effectively.