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αIIbβ3 antagonism vs. antiadhesive treatment to prevent platelet interactions with vascular subendothelium

Summary.  Platelets adhering to blood vessels promote coagulation and inflammation, and release growth factors that trigger smooth muscle cell activation. We have therefore studied the pharmacological modification of platelet deposition quantitatively by comparing adhesion of flowing platelets to various subendothelial ligands in the absence or presence of an antiαIIbβ3 antagonist with the effects of antiadhesive treatment consisting of von Willebrand factor (VWF) and fibronectin neutralization or of the combined inhibition of platelet adhesion and aggregation. In vitro, perfusion of anticoagulated human blood over calf skin collagen reiterated that αIIbβ3 antagonism prevents platelet aggregation, but not adhesion per se: single platelets strongly bound to collagen at wall shear rates of both 1300 and 2700 s−1, largely VWF‐independent. When perfused over a human umbilical vein endothelial cell‐derived extracellular matrix, single αIIbβ3‐antagonized platelets primarily adhered to matrix‐bound VWF when perfused at 2700 s−1, but at 1300 s−1 they also adhered significantly to fibronectin. During perfusion of anticoagulated rabbit blood over de‐endothelialized rabbit aorta at a wall shear rate of 1100 s−1, αIIbβ3 antagonism even increased the absolute numbers of adhering platelets and VWF neutralization redirected αIIbβ3‐antagonized platelets towards other vascular ligands. Finally, in vivo, following photochemically induced blood vessel injury in mice, αIIbβ3 antagonism inhibited platelet‐rich thrombus formation, but platelet adhesion was only significantly inhibited when associated with fibronectin neutralization. In conclusion, antiadhesive platelet treatment more potently interferes with platelet deposition on injured blood vessels than αIIbβ3 antagonism, but abrogating platelet adhesion can only be achieved by carefully selected antiplatelet drug combinations.