Coimmobilized Native Macromolecular Heparin Proteoglycans Strongly Inhibit Platelet-Collagen Interactions in Flowing Blood

Abstract

Abstract —We coimmobilized mast cell–derived heparin proteoglycans (HEP-PGs) of very high molecular weight (750 kDa) or unfractionated heparin (UFH) on coverslips together with collagen without altering the amount of immobilized collagen. Subsequently, platelet-collagen interactions were studied under both flowing and static conditions in d -phenylalanyl- l -prolyl- l -arginine chloromethyl ketone–anticoagulated blood and platelet-rich plasma (PRP), respectively. At a high shear rate (1600 1/s), the mean platelet deposition (PD) on collagen monomers was 7.5±6.1×10 6 /cm 2 (n=5). When the monomers were coimmobilized with UFH, PD was inhibited by 73% (2.0±1.2×10 6 /cm 2 ), whereas HEP-PG completely blocked it (0.42±0.38×10 6 /cm 2 ; P <0.05). Also, when collagen fibrils were used for coating, HEP-PG significantly inhibited PD. At a low shear rate (200 1/s) and under static conditions in PRP, the inhibitory effect of HEP-PG on PD was less marked. Inhibition of glycoprotein IIb/IIIa did not affect PD on coimmobilized HEP-PG in contrast to coimmobilized UFH or collagen alone. As a sign of inactivation, platelets adhering to the HEP-PG surface released considerably less β-thromboglobulin than did those adhering to pure collagen. In summary, immobilized HEP-PG strongly inhibited PD on collagen by attenuating adhesion-induced platelet activation. The stronger effect on collagen monomers suggests the inhibition of glycoprotein Ia/IIa–mediated activation.