Using a non-invasive assessment of lung injury in a murine model of acute lung injury

Abstract

Arterial oxygen saturation has not been assessed sequentially in conscious mice as a direct consequence of an in vivo murine model of acute lung injury. Here, we report daily changes in arterial oxygen saturation and other cardiopulmonary parameters by using infrared pulse oximetry following intratracheal lipopolysaccharide (IT-LPS) for up to 9 days, and following IT-phosphate buffered saline up to 72 h as a control. We show that arterial oxygen saturation decreases, with maximal decline at 96 h post IT-LPS. Blood oxygen levels negatively correlate with 7 of 10 quantitative markers of murine lung injury, including neutrophilia and interleukin-6 expression. This identifies infrared pulse oximetry as a method to non-invasively monitor arterial oxygen saturation following direct LPS instillations.

Keywords: Neutrophil Biology; Pulmonary oedema; Respiratory Infection.

Figure 1

Weight and cardiopulmonary parameter changes in C57Bl/6 mice post IT-LPS or PBS. Weight changes were assessed in C57Bl/6 instilled via IT route with 50 µg LPS (A) or 50 µL PBS (B). Arterial oxygen saturation (C), heart rate (D) and breath rate (E) were monitored using infrared pulse oximetry following IT-PBS as a control (white bars) compared to IT-LPS instilled mice (black bars). IT-LPS, intratracheal lipopolysaccharide; PBS, phosphate buffered saline.

Figure 2

Markers of lung injury in C57Bl/6 mice post IT-LPS. C57Bl/6 mice were instilled via IT route with 50 µg LPS. Markers of endothelial barrier permeability (A) and alveolar epithelial cell damage by assessing RAGE expression (B) were assessed daily. The total number of granulocytes in BAL fluid was also enumerated per mL (C). The percentage (D) and number (E) of neutrophils were analysed using flow cytometry. ANOVA, analysis of variance; BAL, bronchoalveolar lavage; IT-LPS, intratracheal lipopolysaccharide; RAGE, receptor for advanced glycation end.

Figure 3

Pulmonary cytokine expression in C57Bl/6 mice post IT-LPS. C57Bl/6 mice were instilled via IT route with 50 µg LPS. BAL fluid was collected daily following IT-LPS and the expression of inflammatory cytokines assessed; CXCL1/KC (A), VEGF (B), MIP-2 (C), IL-6 (D), IL-1β (E) and TNFα (F). ANOVA, analysis of variance; BAL, bronchoalveolar lavage; IL, interleukin; IT-LPS, intratracheal lipopolysaccharide; MIP-2, macrophage-inflammatory protein-2; N.D., not detected; TNFα, tumor necrosis factors α; VEGF, vascular endothelial growth factor.

Figure 4

Granulocytic pulmonary infiltrates in C57Bl/6 mice post IT-PBS. C57Bl/6 mice were instilled via IT route with 50 µL PBS. BAL fluid was collected daily and pulmonary granulocytic infiltrates (A) and neutrophilia (B and C) assessed. ANOVA, analysis of variance; BAL, bronchoalveolar lavage; IT, intratracheal; PBS, phosphate buffered saline.