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 cmH₂O ("lower" tidal volumes of ~7.5 ml/kg; LV_T) or 18 cmH₂O ("higher" tidal volumes of ~15 ml/kg; HV_T). Dexamethasone was intravenously administered at the initiation of HV_T-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 FiO₂ ratios and lung wet to dry ratios. Results: Particularly HV_T-ventilation led to alveolar-capillary barrier dysfunction as reflected by reduced PaO₂ to FiO₂ 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 HV_T-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.