The platelet storage lesion - Novel approaches to optimise the function and quality of stored platelet concentrates
Routinely, Platelet Concentrates (PC) are stored at 22±2oC, constantly agitated, for up to 7 days with constant bacterial monitoring. Storage conditions stemmed from historical studies and have not differed substantially, despite advances in knowledge and technology. Extracellular vesicles (EVs) are small membrane bound vesicles released from all cells and their roles include cell-to-cell communication. EVs are present within PC, however their actions and roles upon reinfusion is unknown. The aim of this thesis was to assess EVs within PC storage and to optimise the external storage environment to improve platelet function and quality overtime, with the potential to increase storage duration. For this purpose, use of cold storage (4±2oC) and differential oxygen environments were investigated. EVs extracted from PC were characterised using Nanosight tracking analysis and flow cytometry. Direct measurements of oxygen concentration within the storage container and oxygen consumption of platelets was assessed by electron paramagnetic resonance oximetry. Impedance platelet aggregometry was used to assess platelet function. Results from cold storage indicated that platelet aggregometry was not significantly improved compared to conventional storage, however a significant increase in pro-coagulant EV numbers was observed during cold storage which could result in a shortened bleeding time if transfused. A significant finding was oxygen availability in the bag was limited even when incubated at 21% oxygen under standard conditions. Applying the direct measurements made to a mathematical model demonstrated large areas of hypoxia at a relatively short distance from the surface of the container. To address this, predicted by the model, two approaches were taken: reducing platelet concentration or increasing external oxygen concentration. Platelet quality was increased, although elevated oxygen levels gave rise to oxidative stress. This work has provided a new understanding of factors which limit PC storage and point the way forward to improving platelet quality.