Lung endothelial barrier protection by iloprost in the 2-hit models of ventilator-induced lung injury (VILI) involves inhibition of Rho signaling

Mechanical ventilation at high tidal volume (HTV) may cause pulmonary capillary leakage and acute lung inflammation culminating in ventilator-induced lung injury. Iloprost is a stable, synthetic analog of prostaglandin I2 used to treat pulmonary hypertension, which also showed endothelium-dependent antiedemagenic effects in the models of lung injury. To test the hypothesis that iloprost may attenuate lung inflammation and lung endothelial barrier disruption caused by pathologic lung distension and coagulation system component thrombin, we used cell and animal 2-hit models of ventilator-induced lung injury. Mice received a triple injection of iloprost (2 μg/kg, intravenous instillation) at 0, 40, and 80min after the onset of HTV mechanical ventilation (30mL/kg, 4h), combined with the administration of a thrombin receptor-activating peptide 6 (TRAP6, 3 × 10−7mol/mouse, intratracheal instillation). After 4h of ventilation, bronchoalveolar lavage (BAL), histologic analysis, and measurements of Evans blue accumulation in the lung tissue were performed. The effects of iloprost on endothelial barrier dysfunction were subsequently assessed in pulmonary endothelial cells (ECs) exposed to thrombin and pathologic (18%) cyclic stretch. The combination of HTV and TRAP6 enhanced the accumulation of neutrophils in BAL fluid and lung parenchyma, as well as increased the BAL protein content and endothelial permeability judged by Evans blue extravasation in the lung tissue. These effects were markedly attenuated by iloprost. The application of 18% cyclic stretch to pulmonary ECs enhanced the thrombin-induced EC paracellular gap formation and Rho-GTPase–mediated phosphorylation of regulatory myosin light chains and myosin phosphatase. Iloprost markedly inhibited the Rho-kinase–mediated site-specific phosphorylation of myosin phosphatase, and it prevented cyclic stretch- and thrombin-induced endothelial monolayer disruption. This study characterizes for the first time the protective effects of iloprost in the in vitro and in vivo 2-hit models of VILI and supports consideration of iloprost as a new therapeutic treatment of VILI.