Objective:To investigate the protective effects and underlying mechanisms of Xuebijing Injection (XBJ) on the lung endothelial barrier in hydrogen sulfide (H2S)-induced acute respiratory distress syndrome (ARDS).Methods:Sprague-Dawley rats were exposed to H2S (300 ppm) to establish ARDS model,while human pulmonary microvascular endothelial cells (HPMECs) were incubated with NaHS(a H2S donor,500 μ mol/L) to establish cell model.H2S and XBJ were concurrently administered to the rat and cell models.Lung hematoxylin and eosin staining,immunohistochemistry,transmission electron microscopy and wet/dry ratio measurement were used to confirm ARDS induced by H2S in vivo.The expression levels of claudin-5,phosphorylated protein kinase B (p-AKT)/t-AKT and p-forkhead box transcription factor O1(FoxO1)/t-FoxO1 in vivo and in vitro were also assessed.Paracellular permeability and transepithelial electrical resistance (TEER) were measured to evaluate endothelial barrier function in the cell model.Results:The morphological investigation showed that XBJ attenuated H2S-induced ARDS in rats.XBJ significantly ameliorated both the reduction in TEER and the increased paracellular permeability observed in NaHS-treated HPMECs (P＜0.05).The protective effects of XBJ were blocked by LY294002,a phosphatidylinositol 3-kinase(PI3K)/AKT/FoxO1 pathway antagonist (P＜0.05).Furthermore,XBJ promoted the expression of claudin-5 and increased the levels of p-AKT and p-FoxO1 in vivo and in vitro (P＜0.05).Conclusion:XBJ ameliorated H2S-induced ARDS by promoting claudin-5 expression via the PI3K/AKT/FoxO1 signaling pathway.