Evaluating the Efficacy of GPVI Receptors on Stored Platelets as an Indicator of Platelet Viability for Vascular Hemostasis.
Platelet receptor GPVI plays an integral role in maintaining vascular hemostasis in response to inflammation and acute injury vascular damage. Traditional storage of platelets at room temperature (RT-22°C) for up to 5 days results in the loss of hemostatic function, known as the platelet storage lesion. These platelets demonstrate a reduced agonist response due to premature activation, receptor shedding, and loss of metabolic function. Current quality indicators are insufficient for evaluating platelet viability prior to transfusion. This dissertation assesses GPVI receptor expression as an indicator of platelet viability and demonstrates the sustained hemostatic and metabolic function of cold-stored platelets up to 21 days of storage. Hyper-concentrated, double apheresis platelets were collected from healthy donors (n=3-7). Platelets were reconstituted using donor-derived plasma (100% plasma) or InterSol platelet additive solution (65% Intersol/35% Plasma). Reconstituted plasma and Intersol AP platelets were split and stored for 21 days at either RT (Plasma RT, Intersol RT) with agitation or 4˚C (Plasma 4C, Intersol 4C) without agitation. Stored platelets were analyzed to determine GPVI receptor expression, hemostatic function, metabolism, and mitochondrial function. RT GPVI receptor expression decreased during storage, corresponding to diminished collagen binding, endothelial repair, and agonist response. The loss of hemostatic function in RT units is attributed to metabolic dysfunction with high lactate, mitochondrial depolarization, and loss of ATP generation. In contrast, GPVI receptor expression was higher in Plasma and Intersol 4C platelets corresponding to sustained collagen binding, endothelial repair, and agonist response up to 21 days of storage. This sustained function is attributed to preserved metabolic competence as demonstrated by low lactate and sustained mitochondrial function to maintain ATP generation. Of the two, Intersol 4C was overall superior, with sustained platelet counts, absence of macroaggregate formation during storage, and superior agonist response compared to Plasma 4C. Altogether, this dissertation demonstrates the correlation between platelet viability and GPVI expression and further supports the extension of cold-stored platelets to 21 days to significantly improve availability and therapeutic platelet transfusion outcomes.