Quantitative increases of extracellular vesicles in prolonged cold storage of platelets increases the potential to enhance fibrin clot formation.

Background: Platelet derived extracellular vesicles (EVs) display a pro-coagulant phenotype and are generated throughout platelet concentrate (PC) storage. Cold storage (CS) of PCs is thought to provide a superior haemostatic advantage over room temperature (RT) storage and could prolong the storage time. However, the effect of storage conditions on EV generation and PC function is unknown. We investigated EV production under CS and RT conditions and assessed whether these EVs exhibited a more pro-coagulant phenotype in model experiments.

Materials and methods: Buffy-coat-derived PCs in a platelet additive solution (PAS) to plasma ratio of approximately 65:35 were stored at RT (22 ± 2°C) or CS (4 ± 2°C) for a prolonged storage duration of 20 days. Impedance aggregometry assessed platelet function. EVs were isolated throughout storage and quantified using nanoparticle tracking analysis. EVs were applied to a coagulation assay to assess the impact on fibrin clot formation and lysis.

Results: CS produced significantly larger EVs from day 4 onwards. EV concentration was significantly increased in CS compared to RT from day 15. EVs, regardless of storage, significantly reduced time to clot formation and maximum optical density measured compared to the no EV control. Clot formation was proportionate to the number of EV applied but was not statistically different across storage conditions when corrected for EV number.

Conclusion: EVs in CS and RT units showed similar clot formation capacity. However, the higher number of larger EVs generated in CS compared to RT suggests PC units derived from CS conditions may overall exhibit a haemostatically superior capacity compared to RT storage.