Ulinastatin Ameliorates Pulmonary Capillary Endothelial Permeability Induced by Sepsis Through Protection of Tight Junctions via Inhibition of TNF-α and Related Pathways

Background：Increased permeability of pulmonary capillary is a common consequence of sepsis that leads to acute lung injury. Ulinastatin (UTI), a urinary trypsin inhibitor, is used clinically to mitigate pulmonary edema caused by sepsis. However, the underlying mechanism of UTI in alleviating sepsis-associated pulmonary edema has remained obscure. As tight junctions between the pulmonary microvascular endothelial cells (PMVECs) play a pivotal role in the permeability of pulmonary capillary, the present study was to investigate the effect of UTI on junctional proteins in PMVECs in sepsis. Methods: Male adult SD-rats were subjected to cecal ligation puncture (CLP) and assigned into sham, CLP and UTI-CLP groups. UTI was administered every 8 hourly for 3 days before CLP. At 48h after surgery, Evans blue (EB) was administered to evaluate the pulmonary vascular leakage. Histological sections were prepared for evaluation of lung injury score. By immunofluorescence staining and Western blot, expression of junctional proteins (occludin, claudin-5 and ZO-1) in pulmonary endothelia was assessed. In vitro, PMVECs were divided into: control, lipopolysaccharide (LPS) and UTI-LPS groups. Expression of junctional proteins and TNF-α as well as IκB, P38, JNK and ERK signaling pathways were detected. PMVECs were also treated with TNF-α and TNF-α receptor antagonist and the expression of various junctional proteins was assessed. Results: Compared with CLP group, UTI markedly decreased EB leakage and lung injury score. The expression of occludin, claudin-5 and ZO-1 were decreased in PMVECs of CLP rats and in LPS-treated PMVECs, all of which were reversed by UTI treatment. TNF-α expression was vigorously elevated in the lung of CLP rats and in LPS -challenged PMVECs, which were suppressed by UTI. In addition, TNF-α also reduced occludin, claudin-5 and ZO-1 expression in PMVECs and these effects of TNF-α were antagonized by pretreatment with TNF-α receptor antagonist. Furthermore, UTI inhibited LPS-induced the activation of NF-kB and MAPKs pathways in PMVECs. Conclusion: UTI effectively protects tight junctions and attenuates the permeability of pulmonary capillary endothelial cells during sepsis through inhibiting NF-B and MAPKs signal pathways and TNF-α expression.