Dexamethasone Attenuates VEGF Expression and Inflammation but Not Barrier Dysfunction in a Murine Model of Ventilator-Induced Lung Injury

Background: Ventilator-induced lung injury (VILI) is characterized by vascular leakage and inflammatory responses eventually leading to pulmonary dysfunction. Vascular endothelial growth factor (VEGF) has been proposed to be involved in the pathogenesis of VILI. This study examines the inhibitory effect of dexamethasone on VEGF expression, inflammation and alveolar-capillary barrier dysfunction in an established murine model of VILI. Methods: Healthy male C57Bl/6 mice were anesthetized, tracheotomized and mechanically ventilated for 5 hours with an inspiratory pressure of 10 cmH(2)O ("lower" tidal volumes of similar to 7.5 ml/kg; LVT) or 18 cmH(2)O ("higher" tidal volumes of similar to 15 ml/kg; HVT). Dexamethasone was intravenously administered at the initiation of HVT-ventilation. Non-ventilated mice served as controls. Study endpoints included VEGF and inflammatory mediator expression in lung tissue, neutrophil and protein levels in bronchoalveolar lavage fluid, PaO2 to FiO(2) ratios and lung wet to dry ratios. Results: Particularly HVT-ventilation led to alveolar-capillary barrier dysfunction as reflected by reduced PaO2 to FiO(2) ratios, elevated alveolar protein levels and increased lung wet to dry ratios. Moreover, VILI was associated with enhanced VEGF production, inflammatory mediator expression and neutrophil infiltration. Dexamethasone treatment inhibited VEGF and pro-inflammatory response in lungs of HVT-ventilated mice, without improving alveolar-capillary permeability, gas exchange and pulmonary edema formation. Conclusions: Dexamethasone treatment completely abolishes ventilator-induced VEGF expression and inflammation. However, dexamethasone does not protect against alveolar-capillary barrier dysfunction in an established murine model of VILI.