PLATELET ACTIVATION IN WHOLE-BLOOD BY ARTIFICIAL SURFACES - IDENTIFICATION OF PLATELET-DERIVED MICROPARTICLES AND ACTIVATED PLATELET BINDING TO LEUKOCYTES AS MATERIAL-INDUCED ACTIVATION EVENTS

Because the lack of thromboresistant vascular biomaterials is in part due to platelet activation, we have attempted, by using fluorescence-a ctivated flow cytometry, to fully characterize the platelet population after in vitro material contact with whole blood. We have used a very simple, near-physiologic system whereby whole blood, anticoagulated w ith D-phenylalanyl-L-prolyl-arginyl chloromethyl ketone (thrombin inhi bitor), contacts materials for 1 hour at 37 degrees C, under low shear . Unlike other tests of platelet compatibility that focus on adherent platelets, this assay evaluates the platelets in the whole blood drain ed from the tube (1.57 mm internal diameter, 25 cm length) after mater ial contact. We demonstrate for the first time significant materials-i nduced microparticle formation. One-hour contact with Silastic, polyet hylene, and polyvinyl alcohol hydrogel surfaces lead to 30 +/- 1, 33 /- 4, and 43 +/- 4 x 10(9) microparticles/L, respectively, whereas res ting blood samples contained only 10 +/- 1 x 10(9) microparticles/L. I n addition, significant increases in activated platelet(s) binding to neutrophils/monocytes after material contact were noted for all surfac es tested. For polyvinyl alcohol hydrogel surfaces a greater than 500% increase in the fluorescent intensity over that of resting whole bloo d was attained. The addition of monoclonal antibodies to GPIIb/IIIa (A 2A9), the tetrapeptide adhesion ligand RGDS (arginine-glycine-aspartat e-serine), or the calcium ion chelator col-bis-(B-aminoethyl-ether)-N, N,N',N'-tetraacetic acid to the whole blood before material contact fu lly inhibited all platelet reactivity noted for all surfaces-platelet microparticles, platelet P-selectin expression, loss of platelets from bulk, and the formation of platelet/leukocyte aggregates-thereby indi cating that material-induced platelet activation is a calcium-dependen t process involving GPIIb/IIIa receptors.