Roles of thrombin and platelet membrane glycoprotein IIb/IIIa in platelet-subendothelial deposition after angioplasty in an ex vivo whole artery model.

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Abstract
BACKGROUND Platelet deposition at the site of injury caused by balloon angioplasty is associated with acute closure and restenosis. METHODS AND RESULTS In a new ex vivo whole artery angioplasty model, we examined the roles of thrombin inhibition with D-Phe-Pro-ArgCH2Cl (PPACK) and inhibition of the platelet membrane fibrinogen receptor glycoprotein IIb/IIIa (GPIIb/IIIa) with monoclonal antibody 7E3 on platelet deposition at the site of balloon injury. Fresh rabbit aortas were mounted in a perfusion chamber. One half of the mounted arterial segment was dilated with a standard angioplasty balloon catheter and the uninjured half served as the control segment. The vessels were perfused with human blood at physiological pressure and shear rates of 180-250 second-1 for 30 minutes. Platelet deposition was measured using 111In-labeled platelets and scanning electron microscopy. With heparin (2 units/ml) anticoagulation, 8.2 +/- 2.2 x 10(6) platelets/cm2 were deposited at the site of balloon injury compared with 0.7 +/- 0.2 x 10(6) platelets/cm2 on uninjured segments (p less than 0.02, n = 7). PPACK was tested at a concentration (10 microM) that totally inhibited platelet aggregation in response to thrombin. 7E3 was tested at a concentration (10 micrograms/ml) that totally inhibited platelet aggregation. Platelet deposition at the site of balloon injury was reduced 47% by PPACK and 70% by 7E3 compared with heparin. CONCLUSIONS At shear rates seen in nonstenotic coronary arteries, PPACK and 7E3 are more effective than heparin in reducing platelet deposition at the site of balloon injury. The significant inhibition of platelet deposition by PPACK demonstrates the importance of heparin-resistant thrombin in platelet thrombus formation. The 7E3 results suggest that approximately 70% of platelet deposition at the site of balloon injury is GPIIb/IIIa dependent and that the remaining 30% results from non-GPIIb/IIIa-mediated platelet-subendothelial adhesion. Finally, the ex vivo whole artery system is a useful model for studying platelet-vessel wall interactions under physiologically defined parameters.

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