ObjectiveIn order to determine whether gabexate mesilate, a synthetic protease inhibitor with anticoagulant properties, is useful for the treatment of adult respiratory distress syndrome, we examined its effect on endotoxin-induced pulmonary vascular injury in rats.DesignProspective, randomized, controlled study.SettingResearch laboratory at a university medical center.SubjectsMale Wistar rats (180 to 220 g).InterventionsAnimals received intravenous infusions of endotoxin (5 mg/kg iv) or saline (control). Pulmonary vascular injury was assessed 6 hrs after administration of endotoxin in terms of the increase in vascular permeability. Rats received gabexate mesilate (10 mg/kg ip), heparin, antithrombin III, an inactive derivative of activated factor X (a selective inhibitor of thrombin generation), or N-[2-[4-(2,2-dimethyl-propionyloxy) phenyl-sulfonylamino] benzoyl] aminoacetic acid (ONO-5046) (a potent granulocyte elastase inhibitor) 30 mins before endotoxin administration. Leukocytopenia was induced by administration of methotrexate. The effects of gabexate mesilate on the function of activated neutrophils and the production of tumor necrosis factor-alpha (TNF-alpha) by endotoxin-stimulated monocytes were examined in vitro using neutrophils and monocytes prepared from healthy human volunteers.Measurements and Main ResultsPulmonary vascular permeability was determined by measuring the vascular leakage of intravenously administered125I-labeled bovine serum albumin. Intravenous administration of endotoxin significantly increased pulmonary vascular permeability. Gabexate mesilate significantly inhibited pulmonary vascular injury observed 6 hrs after the administration of endotoxin. Pulmonary vascular injury was not attenuated by the administration of heparin, heparin plus antithrombin III, or the inactive derivative of activated factor X, but pulmonary vascular injury was significantly attenuated in animals with methotrexate-induced leukocytopenia and in those animals treated with N-[2-[4-(2,2-dimethyl-propionyloxy) phenylsulfonylamino] benzoyl] aminoacetic acid. Gabexate mesilate in concentrations of 10minus4 to 10minus3 M inhibited the release of granulocyte elastase and leukocyte aggregation stimulated by N-formyl-methionyl-leucyl-phenylalanine and the opsonized zymosan-activated production of superoxide radical by neutrophils in vitro. Gabexate mesilate significantly inhibited the endotoxin-induced increase in the serum concentration of TNF-alpha in vivo and, at a concentration of 10minus8 M, the production of TNF-alpha by endotoxin-stimulated monocytes in vitro.ConclusionOur findings suggest that gabexate mesilate attenuated endotoxin-induced pulmonary vascular injury mainly by inhibiting TNF-alpha production by monocytes, which may play a central role in sepsis-related lung injury.(Crit Care Med 1996; 24:1047-1053)