Role of Plasma Factor XIII on Clot Properties of Cold-Stored Platelets

Uncontrolled hemorrhage associated with traumatic injury is the leading cause of preventable death in the United States. Platelets (PLTs) are transfused to prevent bleeding and induce hemostasis, and thus are critical in saving lives following trauma. Currently, PLTs for transfusion are stored at room temperature (RT) for 5-7 days with gentle agitation, despite disadvantages such as loss of function and risk of bacterial contamination. Presumably, cold storage (4°C) of PLTs can mitigate these issues and alleviate PLT shortage since it preserves PLT metabolic reserves, in vitro responses to agonists of activation, aggregation and physiological inhibitors, and adhesion to thrombogenic surfaces better than RT storage. In this dissertation, we tested the hypothesis that coagulation Factor XIII binding to cold stored PLTs during storage modulates the clot mechanical, structural and biochemical properties at all phases of clotting, namely clot evolution and clot retraction phases. Further, we characterized the effect of storage temperature on clot properties by storing PLTs at RT or 4C for 5 days. Mechanical and structural characterization of evolving clots from 4C- stored PLTs was performed using rheometry and scanning electron microscopy in a single variable system using Fresh Frozen plasma (FFP) to avoid any plasma degradation effect during storage. PLT contractile and structural properties were evaluated by clot weight measurements, serum analysis, and imaging after retraction. FXIII inhibitors were used to elucidate the role of FXIII in PLT-mediated clot contraction. We observed that PLTs stored at 4°C showed higher aggregation, formed stronger clots with denser, thinner and straighter fibrin fibers having more branch points, and more lytic resistance at high tissue Plasminogen (tPa) levels than RT stored PLTs. Our clot retraction studies revealed that 4C stored PLT clots were heavier with a highly-organized structure due to superior fibrin-PLT interaction than those from RT-stored PLTs which had a disintegrated structure. Finally, we demonstrate that plasma FXIII binding during cold storage is a principal regulator of both clot formation and contraction processes which contribute to clot stability and strength. In conclusion, our results provide evidence that 4C-stored PLTs represent an attractive alternative to the current standard of care, particularly in mitigating hyperfibrinolysis associated with traumatic hemorrhage.