Activation in stored platelet concentrates: correlation between membrane expression of P-selectin, glycoprotein...

By using two distinct measurements of alpha-degranulation (surface P-selectin [alpha-granule membrane protein-140] expression and beta-thromboglobulin [beta-TG] release) and quantitation of glycoprotein (GP) IIb/IIIa surface density, stored platelet concentrates were evaluated to determine a) which method of measuring platelet alpha-granule release was more sensitive in detecting early platelet activation; b) whether Day 1 levels of activation predicted the extent of activation or cell lysis on Day 5 of storage; and c) whether changes in surface GPIIb/IIIa density were primarily dependent on platelet activation. By using samples from paired and unpaired units stored for 1, 3, and 5 days, four observations could be made. 1) A flow cytometric assay for the percentage of P-selectin-positive platelets was more sensitive for early detection of platelet activation than was measurement of beta-TG release. This finding was most likely due to enhanced sensitivity in detecting platelets that had undergone partial alpha-granule release. 2) Total P-selectin expression correlated with beta-TG release, which indicated that the extent of alpha-granule membrane fusion with the external platelet membrane was proportional to the amount of alpha-granule contents released into the supernatant. 3) All of the activation measurements on Day 1 predicted the activation values, but did not predict the degree of cell lysis (measured by lactate dehydrogenase discharge), on Day 5 of storage. 4) Surface GPIIb/IIIa density was increased on the subset of P-selectin-positive platelets as compared with the P-selectin-negative subset at all times during storage, but, within each subset, GPIIb/IIIa surface density did not significantly increase over the time of storage.