COMPARATIVE REAL-TIME EFFECTS ON PLATELET-ADHESION AND AGGREGATION UNDER FLOWING CONDITIONS OF IN-VIVO ASPIRIN, HEPARIN, AND MONOCLONAL-ANTIBODY FRAGMENT AGAINST GLYCOPROTEIN IIB-IIIA

Background A real-time in vitro system of human platelet thrombosis un der arterylike flowing conditions similar to those produced in vivo by angioplasty would be useful for the evaluation of potential antiarter ial thrombotic agents in association with in vivo trials. Aspirin, hep arin, and the chimeric monoclonal antibody antigen-binding fragment 7E 3 (c7E3 Fab) directed against platelet glycoprotein (GP) IIb-IIIa have been used in attempts to delay or prevent thrombotic reocclusion of c oronary arteries after angioplasty. We compared the effects of these a gents administered in vivo on GPIb-mediated platelet adhesion to von W illebrand factor (vWF)/collagen type I (as in atherosclerotic subendot helium) and on subsequent GPIIb-IIIa-fibrinogen/vWF-mediated platelet aggregation under flowing conditions analogous to those in constricted coronary arteries. Methods and Results Citrated whole blood containin g mepacrine-labeled platelets from patients and healthy donors was per fused for 1 minute at an abnormally elevated shear rate of 1500 second s(-1) (arterial wall shear stress of 50 to 60 dynes/cm(2)) at 37 degre es C over collagen I/vWF. The number of adherent fluorescent platelets was quantified every 15 seconds with a low-light-level video camera a nd epifluorescent microscopy. After 5 healthy donors had ingested 975 mg aspirin, platelet adhesion was unaffected in the aspirin-treated bl ood compared with the control blood in all experiments (10 of 10), and subsequent aggregation was unchanged in most runs (8 of 10). The bloo d of 3 aspirin-treated patients undergoing angioplasty was analyzed be fore and after a 12 000-U heparin injection and 2 minutes, 2 hours, an d 24 hours after infusion of 0.25 mg/kg of c7E3 Fab. In these patients , the bolus of heparin did not inhibit either platelet adhesion to col lagen I/vWF or subsequent aggregation. In contrast, there was >50% inh ibition of platelet aggregation 2 minutes after the infusion of c7E3 F ab in all 3 patients, and inhibition persisted in 2 of the 3 patients at 2 hours and 24 hours after c7E3 Fab. Conclusions In contrast to asp irin or heparin, the in vivo injection of c7E3 Fab considerably reduce s platelet aggregate formation mediated by the binding of fibrinogen, VWF, or some other ligand to platelet GPIIb-IIIa under conditions of a bnormally increased shear stress analogous to those in narrowed corona ry arteries. Platelet adherence to collagen I/vWF is not affected. Thi s study describes an in vitro model of arterial injury (similar to ang ioplasty) that uses human blood to compare directly, in real time, the precise relative effects of aspirin, heparin, and c7E3 Fab on platele t adhesion and subsequent aggregation.