Acute pulmonary toxicity following inhalation exposure to aerosolized VX in anesthetized rats.

This study evaluated acute toxicity and pulmonary injury in rats at 3, 6 and 24 h after an inhalation exposure to aerosolized O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX). Anesthetized male Sprague-Dawley rats (250-300 g) were incubated with a glass endotracheal tube and exposed to saline or VX (171, 343 and 514 mg×min/m³ or 0.2, 0.5 and 0.8 LCt50, respectively) for 10 min. VX was delivered by a small animal ventilator at a volume of 2.5 ml × 70 breaths/minute. All VX-exposed animals experienced a significant loss in percentage body weight at 3, 6, and 24 h post-exposure. In comparison to controls, animals exposed to 514 mg×min/m³ of VX had significant increases in bronchoalveolar lavage (BAL) protein concentrations at 6 and 24 h post-exposure. Blood acetylcholinesterase (AChE) activity was inhibited dose dependently at each of the times points for all VX-exposed groups. AChE activity in lung homogenates was significantly inhibited in all VX-exposed groups at each time point. All VX-exposed animals assessed at 20 min and 3, 6 and 24 h post-exposure showed increases in lung resistance, which was prominent at 20 min and 3 h post-exposure. Histopathologic evaluation of lung tissue of the 514 mg×min/m³ VX-exposed animals at 3, 6 and 24 h indicated morphological changes, including perivascular inflammation, alveolar exudate and histiocytosis, alveolar septal inflammation and edema, alveolar epithelial necrosis, and bronchiolar inflammatory infiltrates, in comparison to controls. These results suggest that aerosolization of the highly toxic, persistent chemical warfare nerve agent VX results in acute pulmonary toxicity and lung injury in rats.

Determination of LCt(50)s in anesthetized rats exposed to aerosolized nerve agents.

Nerve agents pose a threat to the respiratory tract with exposure that could result in acute compromised lung performance and death. The determination of toxicity by inhalation is important for the rational development of timely therapeutic countermeasures. This study was designed to deliver aerosolized dilute nerve agents in a dose-response manner to investigate the extent of lethality of nerve agents: soman, sarin, VX and VR. Male rats (240-270 g) were anesthetized intramuscularly with 10 mg/kg xylazine and 90 mg/kg ketamine. Following anesthesia, rats were intubated with a glass endotracheal tube (ET) and placed in a glove box. The ET was connected to a closed circuit nebulizer system (Aeroneb, Aerogen, Inc.) that delivered a particle size of < 2.0 µm and was in series between the ventilator and the ET. Nerve agents were delivered by a small animal ventilator set for a volume of 2.5 mL × 60-80 breaths/min. VX or VR were nebulized and delivered in concentrations ranging from 6.25-800 µg/kg over a 10-min exposure time period. Sarin (GB) or soman (GD), 6.5-1250 µg/kg, were delivered in a similar manner. Lethality by inhalation occurred either during the 10-min exposure period or less than 15 min after the cessation of exposure. Survivors were euthanized at 24 h postexposure. LCt(50) estimates (± 95% confidence intervals [CIs]) were obtained from the sequential stage-wise experiments using the probit analysis. Probit analysis revealed that the LD(50) for VX was 110.7 µg/kg (CI: 73.5-166.7), VR 64.2 µg/kg (CI: 42.1-97.8); soman (GD), 167 µg/kg (CI: 90-310), and sarin (GB), 154 µg/kg (CI: 98-242), respectively. Although VR is a structural isomer of VX, the compounds appear to be markedly different in terms of toxicity when delivered by aerosol. These relationships were converted to actual 10 min LCt(50) equivalents: VX = 632.2, VR = 367, GD = 954.3 and GB = 880 mg·min/m(3). Validation of exposure was verified by the determination of blood levels of acetylcholinesterase (AChE) across doses for the agent VR.

Gas chromatographic-mass spectrometric analysis of sulfur mustard-plasma protein adducts: validation and use in a rat inhalation model.

Sulfur mustard (HD) is an alkylating agent that reacts rapidly with macromolecular targets resulting in the formation of stable adducts providing depots for markers of exposure. The purpose of this study was to validate an analytical procedure for detection of HD-plasma protein adducts and to establish the utility of the method in an HD rat inhalation study. Calibration curves were prepared in human and rat plasma at six levels of HD (12.5 to 400 nM). Correlation coefficients for the mean data were 0.9987 for human and 0.9992 for rat plasma. The percent coefficient of variation (%CV) derived from the mean concentration data ranged from 0.53 to 14.1% in human (n = 5) and 0.57 to 10.63% in rat (n = 6) plasma. Intraday and interday precision and accuracy studies were conducted at three concentration levels (25, 150, 300 nM) to represent low, medium, and high concentrations of HD relative to those employed in the calibration curve. Precision and accuracy were assessed by determining %CV and % error, respectively. For intra- and interday studies, the %CVs and absolute % errors were less than 15%. The limits of quantitation were 20.88 nM for human and 16.73 nM for rat plasma. In animal studies, rats received nebulized HD at six doses. The data indicate a dose-dependent relationship between maximal plasma concentrations and dose administered (R(2) = 0.9728). Results from this study indicate an accurate, precise, and sensitive method. The method was useful in determining plasma protein adduct formation in a rat inhalation model.