Inhibitory effect of serine protease inhibitors on neutrophil-mediated endothelial cell injury

To investigate the inhibitory effect of serine protease inhibitors (SPI) on neutrophil-mediated endothelial cell (EC) injury, we analyzed the in vitro cytotoxicity of radiolabeled human umbilical vein EC (HUVEC) mediated by n eutrophils in the presence of SPI, The EC injury was inhibited dose-depende ntly by urinary trypsin inhibitor (ulinastatin, UTI) and ONO-5046, which ha ve the ability to inactivate neutrophil elastase, but not by gabexate mesil ate, nafamostat mesilate, aprotinin, and argatroban, which have no ability to inactivate neutrophil elastase, In addition, when UTI and ONO-5046 were added to the tumor necrosis factor alpha -primed neutrophils alone, they sh owed a dose-dependent inhibition of the intracellular elastase activity, bu t the other SPI did not, for either how cytometry or confocal microscopy, T herefore, UTI and ONO-5046 may protect EC against the neutrophil-mediated i njury not only by inactivating the extracellular elastase secreted by neutr ophils, but also by acting directly on neutrophils and suppressing the prod uction and secretion of activated elastase from them.