EFFECT OF HEMOGLOBIN VESICLES ON AGONIST-INDUCED PLATELET ACTIVATION IN VITRO

Hemoglobin vesicles (HbV), a type of liposome-encapsulated hemoglobin (LEH), have been recently developed as an artificial oxygen carrier. The efficacy of HbV has been demonstrated in the transfusion of HbV into rodent models of hemorrhagic shock. It is important to evaluate the compatibility of HbV with human blood cells. We examined the effects of HbV on human platelet activation in vitro by estimating the platelet release reaction and expression of platelet surface activation markers in the presence or absence of agonists. HbV concentration in the reaction volume was prepared at 20% or 40%. Preincubation of platelet-rich plasma (PRP) with HbV had no adverse effects on RANTES or serotonin release from platelets. Preincubation of whole blood with HbV also had no effects on exposure of P-selectin on platelets. However, binding of PAC-1, a monoclonal antibody that detects the activation-dependent conformational change of αIIbβ3 to platelets, was amplified by preincubation of whole blood with HbV in the presence of relatively low concentration of ADP. These results suggest that HbV enhances the binding of PAC-1 to platelets. The clinical meaning of this increased binding of PAC-1 needs to be addressed.