Reconstitution of adhesive properties of human platelets in liposomes carrying both recombinant glycoproteins Ia/IIa and Ibα under flow conditions: specific synergy of receptor–ligand interactions

Abstract

Liposomes carrying both recombinant glycoprotein Ia/IIa (rGPIa/IIa) and Ib␣ (rGPIb␣) (rGPIa/IIa-Ib␣-liposomes) instantaneously and irreversibly adhered to the collagen surface in the presence of soluble von Willebrand factor (VWF) at high shear rates, in marked contrast with translocation of liposomes carrying rGPIb␣ alone on the VWF surface. In the absence of soluble VWF, the adhesion of rGPIa/IIa-Ib␣-liposomes to the collagen surface decreased with increasing shear rates, similar to liposomes carrying rGPIa/ IIa alone. While adhesion of liposomes with exofacial rGPIa/IIa and rGPIb␣ densities of 2.17 ؋ 10 3 and 1.00 ؋ 10 4 molecules per particle, respectively, was efficient at high shear rates, reduction in rGPIb␣ density to 5.27 ؋ 10 3 molecules per particle resulted in decreased adhesion even in the presence of soluble VWF. A 50% reduction in the exofacial rGPIa/IIa density resulted in a marked decrease in the adhesive ability of the liposomes at all shear rates tested. The inhibitory effect of antibody against GPIb␣ (GUR83-35) on liposome adhesion was greater at higher shear rates. Further, the anti-GPIa antibody (Gi9) inhibited liposome adhesion more than GUR83-35 at all shear rates tested. These results suggest that the rGPIa/IIa-collagen interaction dominates the adhesion of rGPIa/IIa-Ib␣-liposomes to the collagen surface at low shear rates, while the rGPIa/IIa-collagen and rGPIb␣-VWF interaction complements each other, and they synergistically provide the needed functional integration required for liposome adhesion at high shear rates. This study thus has confirmed for the first time the proposed mechanisms of platelet adhesion to the collagen surface under flow conditions using the liposome system. IntroductionThe basic and important platelet functions for primary hemostasis are adhesion and aggregation, and this can be easily understood from the observations that patients with congenital platelet membrane defects such as Bernard-Soulier syndrome or Glanzmann thrombasthenia are deficient in platelet adhesion or aggregation and have severe bleeding tendencies. The contribution of specific platelet receptors or adhesive proteins to platelet adhesion and aggregation onto immobilized collagen under flow conditions is usually studied with monoclonal antibodies or inhibitors specific to particular platelet receptors or adhesive proteins or, also, with blood from patients with congenital bleeding disorders deficient in specific receptors or adhesive proteins. These analyses indicate that initial platelet adhesion depends on the interaction of glycoprotein (GP) Ib/IX/V complexes on platelets with von Willebrand factor (VWF) adsorbed on the collagen surface. This is a rapid but low-affinity interaction, suggesting that it serves to tether platelets, flowing at high speed in the bloodstream, to the collagen surface. [1][2][3][4] The collagen receptors of the tethered platelets then bind strongly with the collagen surface, activating platelets to form aggregates. This was supported by observations that platelets ...

Platelet receptor interplay regulates collagen-induced thrombus formation in flowing human blood

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Bio‐inspired nanomedicine strategies for artificial blood components

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