Comparison of the Antithrombotic Effect of PEG-Hirudin and Heparin in a Human Ex Vivo Model of Arterial Thrombosis

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Polyethylene glycol (PEG)-hirudin is a derivative of hirudin with a long plasma half-life. We have compared the efficacy of PEG-hirudin with unfractionated heparin (UH) in preventing arterial thrombosis. Arterial thrombus formation was induced ex vivo in 12 healthy human volunteers by exposing a tissue factor-coated coverslip positioned in a parallel-plate perfusion chamber to flowing nonanticoagulated human blood drawn directly from an antecubital vein at an arterial wall shear rate of 2600 s-1 for 3.5 minutes. PEG-hirudin, UH, or saline (as control) were administered ex vivo through a heparin-coated mixing device positioned proximal to the perfusion chamber. Platelet and fibrin deposition was quantified by immunoenzymatic measure of the P-selectin and D-dimer content of dissolved plasmin-digested thrombi, respectively. UH was administered to a plasma concentration of 0.35 IU/mL. This concentration prolonged the activated partial thromboplastin time from 32 +/- 1 seconds to 79 +/- 4 seconds (P<0.01). UH did not significantly prevent platelet deposition. However, fibrin deposition was reduced by 39% (P<0.05). PEG-hirudin in plasma concentrations of 0.5, 2.5, and 5 [micro sign]g/mL prolonged the activated partial thromboplastin time to 48 +/- 2, 87 +/- 4, and 118 +/- 4 seconds, respectively. In contrast to UH, PEG-hirudin prevented both platelet and fibrin deposition in a dose-dependent manner with a >80% reduction at 5 [micro sign]g/mL (P<0.01). Furthermore, the plasma level of PEG-hirudin required to significantly prevent fibrin deposition (0.5 [micro sign]g/mL) corresponded to a much shorter prolongation of activated partial thromboplastin time (48 +/- 2 seconds) than that needed for UH (79 +/- 4 seconds). Thus, our results are compatible with the view that thrombin is greatly involved in recruitment of platelets in evolving thrombi, and that PEG-hirudin is an effective agent for preventing arterial thrombosis in a human ex vivo experimental model. (Arterioscler Thromb Vasc Biol. 1999;19:1348-1353.)

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