High fragmentation in platelet concentrates impacts the activation, procoagulant, and aggregatory capacity of platelets

Platelets are transfused to patients to prevent bleeding. Since both preparation and storage can impact the hemostatic functions of platelets, we studied platelet concentrates (PCs) with different initial composition in regard to platelet fragmentation and its impact on storage-induced changes in activation potential. Ten whole blood derived PCs were assessed over 7 storage days. Using flow cytometry, platelet (CD41+) subpopulations were characterized for activation potential using activation markers (PAC-1, P-selectin, and LAMP-1), phosphatidylserine (Annexin V), and mitochondrial integrity (DiIC1(5)). Aggregation response, coagulation, and soluble activation markers (cytokines and sGPVI) were also measured. Of the CD41+ events, the PCs contained a median of 82% normal-sized platelets, 10% small platelets, and 8% fragments. The small platelets exhibited procoagulant hallmarks (increased P-selectin and Annexin V and reduced DiIC1(5)). Normal-sized platelets responded to activation, whereas activation potential was decreased for small and abolished for fragments. Five PCs contained a high proportion of small platelets and fragments (median of 28% of CD41+ events), which was significantly higher than the other five PCs (median of 9%). A high proportion of small platelets and fragments was associated with procoagulant hallmarks and decreased activation potential, but, although diminished, they still retained some activation potential throughout 7 days storage. What is the context? ● Platelets are necessary to prevent and stop bleeding. ● Conditions associated with a low platelet count in the circulation, such as during chemotherapy treatment for hematologic cancer, can result in life-threatening bleeding. To prevent this, platelets from blood donors are transfused to these patients. ● The collection and preparation of platelet concentrates and subsequent storage before transfusion can affect the ability of the platelets to prevent bleeding. ● In this study, we investigated platelet concentrates prepared from whole blood and how their activation capacity was affected by the preparation and storage period. What is new? ● We found that the platelet concentrates contained mainly low activated platelets of normal size, but also smaller platelets and platelet fragments. ● Unlike normal-sized platelets, small platelets and fragments exhibited hallmarks that are characteristic of pre-activation. ● Some platelet concentrates contained a relatively high proportion of small platelets and fragments already directly following preparation. ● Investigating several platelet activation markers, we found that platelet concentrates containing a high proportion of small platelets and platelet fragments showed lower activation capacity throughout the storage period. What is the impact? ● We show that some platelet concentrates show lower activation capacity and might contain a substantial fraction of platelets with characteristics that might potentially trigger spontaneous blood coagulation. The variation between different concentrations is high, even though the preparation procedure is the same. ● If these differences will affect the efficacy of platelet transfusion is an important area for future studies.