Determination of LCt₅₀s in anesthetized rats exposed to aerosolized nerve agents

Abstract

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.

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

“…This study examined the utilization of a newly developed inhalation exposure model for the evaluation of lung injury and pulmonary toxicity following exposure to aerosolized VX in anesthetized intubated rats. In addition to the various biochemical, physiological and histopathological evaluations conducted in this study, clinical gross observations (data not shown) were recorded (Collins et al, 2013). These observations indicated the presence of classical cholinergic signs of intoxication in animals exposed to 171, 343 and 514 mgÂmin/m 3 of VX.…”

“…The LCt 50 of VX was calculated from the real-time LD 50 determinations using the following equation from Weston and Karel (Weston & Karel, 1946): LD 50 ¼ V m  LCt 50, or LCt 50 ¼ LD 50 /V m . LD 50 s (mg) obtained from probit plot analyses of lethality for VX (110 mg/kg) and V m (minute ventilation, m 3 /min), which is the product of respiratory rate (breaths/min)  tidal volume (ml/breath), was used from our previous study (Collins et al, 2013). The t-test was used to calculate the p values.…”

“…All agents were delivered using a recently developed rodent inhalation exposure system (Collins et al, 2013). The system utilizes an aerosolization technique that delivers agent directly into the incubated airway of anesthetized rats through a small animal ventilator (Harvard Model 683, Harvard Apparatus, Holliston, MA) set for a tidal volume of 2.5 ml and a respiratory rate of approximately 70 breaths per minute ( Figure 1).…”

“…Our group recently developed an inhalation model that uses an aerosolization technique to directly introduce the agent into the intubated airway of anesthetized rats (Collins et al, 2013). By delivering the agent directly to the upper airway and lungs under controlled ventilatory conditions, this model bypasses the potential detoxification of the CWNA by high levels of carboxylesterases in the mucus of the nasal cavity of rodents (Caranto et al, 1994;Maxwell & Brecht, 1991).…”

Le VR, version russe du neurotoxique organophosphoré VX

“…Les structures cérébrales montrant le plus d'inhibition varient également en fonction du toxique [33]. Chez le rat anesthésié, le VR administré par aérosol montre une toxicité déterminée par la DL 50 nettement supérieure pour le VR que pour le VX (64,2 g/kg vs 110,7 g/kg) [34]. Les différences expérimentales (voie d'introduction, dose de toxique, espèces utilisées) sont peut-être en partie à la base de ces observations contraires.…”