ALPHA-THROMBIN BOUND TO EXTRACELLULAR ENDOTHELIAL MATRIX INDUCES PRONOUNCED FIBRIN DEPOSITION AND PLATELET THROMBUS GROWTH IN FLOWING NONANTICOAGULATED HUMAN BLOOD

Previous studies have shown that thrombin binds to the extracellular e ndothelial matrix and remains biologically active. In the present stud y, the role of matrix-bound alpha-thrombin in thrombus formation was i nvestigated by utilizing a model system of thrombogenesis. Plastic cov er-slips coated with either matrix-bound alpha-thrombin or matrix-boun d active site inactivated thrombin (DIP-alpha-thrombin) were positione d in parallel-plate perfusion chambers and subsequently exposed to non -anticoagulated human blood at a venous wall shear rate of 100/s. The blood was drawn directly from an antecubical vein by a roller pump pla ced distally to the perfusion chamber. The thrombotic deposits on the matrix, fibrin deposition and platelet thrombus volume, were morpholog ically evaluated. Matrix-bound alpha-thrombin enhanced the fibrin depo sition and thrombus volume on matrices of non-stimulated endothelium w ith 91% (P < 0.001) and 94% (P < 0.05), respectively. In contrast, bin ding of DIP-alpha-thrombin to matrices of stimulated endothelium reduc ed the fibrin deposition by 33% (P < 0.05), but had no effect on the p latelet thrombus volume. Translocation of thrombin molecules from upst ream matrix areas to binding sites farther downstream on the matrix wa s indicated in experiments with matrices of stimulated endothelium, wh ich showed enhanced fibrin deposition on downstream areas. Our finding s are compatible with a prominent role for matrix-bound alpha-thrombin in thrombogenesis, and in particular on endothelial matrices without tissue factor. The role of matrix-bound alpha-thrombin on tissue facto r containing matrices appears less prominent, although it is significa nt.