Platelet interactions with liposomes carrying recombinant platelet membrane glycoproteins or fibrinogen: Approach to platelet substitutes

Liposomes carrying both recombinant platelet membrane glycoproteins GPIa/IIa (rGPIa/IIa) and GPIbα (rGPIbα) (rGPIa/IIa-Ibαliposomes), or fibrinogen (Fbg-liposomes) were prepared. Their interactions with platelets on a collagen surface under flow conditions were evaluated using a recirculating flow chamber, mounted on an epifluorescence microscope, which allows for real-time visualization of fluorescence-labeled liposomes or platelets, interacting with the surface. Adhesion of platelets to the collagen surface increased with increasing the shear rate from 600 to 2400 s^-1. Also, the percentages of surface coverage of rGPIa/IIa-Ibα-liposomes or Fbg-liposomes increased with increasing platelet adhesion. These phenomena were attenuated by a peptide containing arginine-glycine-aspartic acid (RGD-peptide), or prostaglandin E₁ (PGE), but not by a peptide containing arginine-glycine-glutamic acid (RGE-peptide). In a homogeneous solution, rGPIa/IIa-Ibαliposomes and Fbg-liposomes enhanced platelet aggregation in a dose-dependent manner, as evaluated using an aggregometer. These findings suggest that rGPIa/IIa-Ibα-liposomes and Fbgliposomes form aggregates at the site of injury in blood vessels, resulting in stationary adhesion together with activated platelets.