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Generation of Annexin V+ Microparticles with Stimulus-Dependent Procoagulant Activity During Storage at 4º C

By H Xiao, H Matsubayashi, DP Bonderman, PW Bonderman, RE Speck, R Kovacs, D English, JA McIntyre and D Gao, Methodist Research Inst., Indianapolis IN & Analytical Control Systems, Inc., Fishers, IN.

Platelet factor 3 (PF3) activity and platelet derived microparticles (PDMP) formation were studied in fresh and stored human platelets. Cationic propyl gallate (PG) induced PF3 activity was assessed by activated plasma clotting time (APCT) in platelets and microparticles in a dose dependent manner. Platelet microparticles isolated by filtration from stored platelets possessed enhanced factor 3 activity. While total PG-dependent PF3 activity in platelet samples did not change during prolonged (20 day) platelet storage, levels confined to PDMP increase dramatically as platelet counts fell. This effect correlated with the generation of microparticles during platelet storage. Phosphatidylserine (PS) translocation, as evidenced by increased Annexin V binding, which increased gradually during platelet storage and was induced rapidly by PG stimulation. Thus, platelet storage results in the formation of Annexin V positive microparticles which possess stimulus-dependent procoagulant activity. Microparticles generated by activated human particles may exert a physiologically significant role in thrombosis and hemostasis as a result of exposed phospholipids.