Characterization of a nose-only inhaled phosgene acute lung injury mouse model

Abstract

Context: Phosgene's primary mode of action is as a pulmonary irritant characterized by its early latent phase where life-threatening, non-cardiogenic pulmonary edema is typically observed 6-24 h post-exposure.

Objective: To develop an inhaled phosgene acute lung injury (ALI) model in C57BL/6 mice that can be used to screen potential medical countermeasures.

Methods: A Cannon style nose-only inhalation exposure tower was used to expose mice to phosgene (8 ppm) or air (sham). An inhalation lethality study was conducted to determine the 8 ppm median lethal exposure (LCt50) at 24 and 48 h post-exposure. The model was then developed at 1.2 times the 24 h LCt50. At predetermined serial sacrifice time points, survivors were euthanized, body and lung weights collected, and lung tissues processed for histopathology. Additionally, post-exposure clinical observations were used to assess quality of life.

Results and discussion: The 24-hour LCt50 was 226 ppm*min (8 ppm for 28.2 min) and the 48-hour LCt50 was 215 ppm*min (8 ppm for 26.9 min). The phosgene exposed animals had a distinct progression of clinical signs, histopathological changes and increased lung/body weight ratios. Early indicators of a 1.2 times the 24-hour LCt50 phosgene exposure were significant changes in the lung-to-body weight ratios by 4 h post-exposure. The progression of clinical signs and histopathological changes were important endpoints for characterizing phosgene-induced ALI for future countermeasure studies.

Conclusion: An 8 ppm phosgene exposure for 34 min (1.2 × LCt50) is the minimum challenge recommended for evaluating therapeutic interventions. The predicted higher mortality in the phosgene-only controls will help demonstrate efficacy of candidate treatments and increase the probability that a change in survival rate is statistically significant.

Keywords: Inhalation exposure; LCt50; lung injury; model; mouse; pathology; phosgene.

Figure 1

Phosgene and sham exposure system diagram.

Figure 2

Probit dose-response model fit lethality study data at 24 and 48 h.

Figure 3

Representative lung pathology in the 27.5 min duration sham exposed and the 27.5 min phosgene exposed animals 24 h after challenge: lethality study.

Figure 4

Kaplan-Meier survival curves for phosgene exposure groups: model development study.

Figure 5

Fibrin accumulation at 12 h post phosgene exposure (34 min): model development study.

Figure 6

Alveolar macrophage accumulation at 7 days post-phosgene and sham exposure: model development study.