Annexin V inhibits the procoagulant activity of matrices of TNF-stimulated endothelium under blood flow conditions.

A human ex vivo thrombosis model was used to investigate whether recombinant annexin V (rANV) can prevent thrombus formation under venous and arterial blood flow conditions. In this model, blood from an antecubital vein of healthy donors was allowed to flow directly over the extracellular matrix of tumor necrosis factor-stimulated endothelial cells (TNF-ECMs). TNF-ECMs were preincubated with rANV (2.9 mumol/L) for 30 minutes. With this rANV concentration all binding sites present on TNF-ECMs (1.6 +/- 0.5 x 10(12)/cm2) are occupied, and a maximal inhibition was observed in a tissue factor-dependent clotting assay. Fibrin deposition and platelet and leukocyte adhesion were measured on the rANV-treated and nontreated TNF-ECMs. Nontreated TNF-ECMs were used as controls. rANV inhibited fibrin deposition by 81% at a wall shear rate of 100 s-1. A nonsignificant inhibition was also observed at 650 s-1. Platelet-matrix adhesion, which is more prominent at higher shear rates, was significantly decreased by 60% at 100 s-1 but not at 650 s-1. The average leukocyte adherence was nonsignificantly lowered at 100 s-1. Virtually no leukocytes adhered at 650 s-1. The results demonstrated that rANV can inhibit blood coagulation under venous blood flow conditions and may serve as an antithrombotic drug.