Activation of Endotheiial Cells Induces Platelet Thrombus Formation on Their Matrix Studies of New In Vitro Thrombosis Model with Low Molecular Weight Heparin as Anticoagulant

Previous studies have indicated that activation of endotheiial cells may lead to the production of tissue factor. We have studied the effect of endotheiial cell activation and subsequent tissue factor synthesis on thrombus formation on the extracellular matrix in flowing blood. Endotheiial cells were stimulated with tumor necrosis factor, endotoxln, or phorbol ester. Coversllps with activated cells or their extracellular matrix were introduced Into a perfuslon system and exposed to blood antlcoagulated with 20 U/ml low molecular weight heparin. This concentration allowed manipulation of blood without activation of the coagulation cascade. Platelet deposition and fibrin formation were evaluated by morphometry, and flbrlnopeptlde A formation was assayed as a measure of thrombln generation. Activation of endotheiial cells caused flbrlnopeptlde A generation In the perfusate and some deposition of fibrin on endotheiial cells; however, platelets were not deposited. The matrix of the stimulated endothellum also caused enhanced flbrlnopeptlde A generation, and platelet aggregates and fibrin were deposited on the matrix. Maximal effects were observed with stimulation periods between 4 and 10 hours and were still clearly present after 18 hours. Increase In shear rate, perfusion time, and platelet number resulted In an Increase In platelet adhesion, but platelet aggregate formation as a percentage of adhesion remained constant. Platelet aggregate formation and flbrlnopeptlde A generation were inhibited with antibodies against tissue factor or factor Vila. Platelet aggregate formation alone was Inhibited by antibodies against glycoproteln llb/llla. Polymerization of fibrin on the matrix was best supported In perfuslons at a low shear rate. The new in vitro thrombosis model presented here provides a powerful tool for study of the regulation of thrombogenelty by the vessel wall In response to various stimuli. (Arteriosclerosis 10:49-61, January/February 1990)