The effects of exogenous surfactant administration on ventilation-induced inflammation in mouse models of lung injury

Abstract

Background: Mechanical ventilation (MV) is an essential supportive therapy for acute lung injury (ALI); however it can also contribute to systemic inflammation. Since pulmonary surfactant has anti-inflammatory properties, the aim of the study was to investigate the effect of exogenous surfactant administration on ventilation-induced systemic inflammation.

Methods: Mice were randomized to receive an intra-tracheal instillation of a natural exogenous surfactant preparation (bLES, 50 mg/kg) or no treatment as a control. MV was then performed using the isolated and perfused mouse lung (IPML) set up. This model allowed for lung perfusion during MV. In experiment 1, mice were exposed to mechanical ventilation only (tidal volume =20 mL/kg, 2 hours). In experiment 2, hydrochloric acid or air was instilled intra-tracheally four hours before applying exogenous surfactant and ventilation (tidal volume =5 mL/kg, 2 hours).

Results: For both experiments, exogenous surfactant administration led to increased total and functional surfactant in the treated groups compared to the controls. Exogenous surfactant administration in mice exposed to MV only did not affect peak inspiratory pressure (PIP), lung IL-6 levels and the development of perfusate inflammation compared to non-treated controls. Acid injured mice exposed to conventional MV showed elevated PIP, lung IL-6 and protein levels and greater perfusate inflammation compared to air instilled controls. Instillation of exogenous surfactant did not influence the development of lung injury. Moreover, exogenous surfactant was not effective in reducing the concentration of inflammatory cytokines in the perfusate.

Conclusions: The data indicates that exogenous surfactant did not mitigate ventilation-induced systemic inflammation in our models. Future studies will focus on altering surfactant composition to improve its immuno-modulating activity.

Figure 1

Experiment 1: Surfactant recovery in lung lavage and surface activity of LA. A: surfactant pool size of TS, LA and SA sub-fractions measured by phosphorous assay. Data are expressed as amount of phospholipids/kg body weight. Within each sub-fraction, *p < 0.05 vs the No Treatment condition. B: minimum surface tension of pooled LA samples during different dynamic compression-expansion cycles. #p < 0.05 versus cycle 1 and 2 within each experimental condition. Values are expressed as mean ± SEM.; n = 6 per group.

Figure 2

Experiment 1: IL-6 levels measured in lung perfusate at 60, 90 and 120 min. Values are expressed as mean ± SEM.; n = 6 per group.

Figure 3

Experiment 2: Peak Inspiratory Pressure (PIP) was measured over the course of MV. Values are expressed as mean ± SEM. +p > 0.05 versus Air No Treatment at the specific time point indicated, *p < 0.05 versus the respective Air control at each time point; n = 6 per group.

Figure 4

Experiment 2: Surfactant recovery in lung lavage and surface activity of crude LA. A: surfactant pool size of TS, LA and SA sub-fractions measured by phosphorous assay. Data are expressed as amount of phospholipids/kg body weight. Within each sub-fraction,*p < 0.05 versus the respective No Treatment condition. B: surface tension of pooled LA samples during different dynamic compression-expansion cycles. §p < 0.05 versus cycle 1 within each experimental condition. Values are expressed as mean ± SEM; n = 6 per group.

Figure 5

Experiment 2: IL-6 levels measured in lung perfusate at 0, 30, 60, 90, 120 min. Data are expressed as mean ± SEM. *p < 0.05 versus respective Air control at each time point; n = 6 per group.