title: Effects of storage-induced platelet microparticles on the initiation and propagation phase of blood coagulation.
abstract: Platelets shed microparticles, which support haemostasis via adherence to the damaged vasculature and by promoting blood coagulation. We investigated mechanisms through which storage-induced microparticles might support blood coagulation. Flow cytometry was used to determine microparticle number, cellular origin and surface expression of tissue factor (TF), procoagulant phosphatidylserine (PtdSer) and glycoprotein (GP) Ib-alpha. The influence of microparticles on initiation and propagation of coagulation were examined in activated factor X (factor Xa; FXa) and thrombin generation assays and compared with that of synthetic phospholipids. About 75% of microparticles were platelet derived and their number significantly increased during storage of platelet concentrates. About 10% of the microparticles expressed functionally active TF, as measured in a FXa generation assay. However, TF-driven thrombin generation was only found in plasma in which tissue factor pathway inhibitor (TFPI) was neutralised, suggesting that microparticle-associated TF in platelet concentrates is of minor importance. Furthermore, 60% of all microparticles expressed PtdSer. In comparison with synthetic procoagulant phospholipids, the maximal rate of thrombin formation in TF-activated plasma was 15-fold higher when platelet-free plasma was titrated with microparticles. This difference could be attributed to the ability of microparticles to propagate thrombin generation by thrombin-activated FXI. Collectively, our findings indicate a role of microparticles in supporting haemostasis by enhancement of the propagation phase of blood coagulation.
authors.affiliation: Sanquin Blood Bank Southeast Region, Maastricht, the Netherlands.
authors.forename: Jeffrey F W
authors.initials: JF
authors.lastname: Keuren
authors.forename: Jeffery F W
authors.initials: JF
authors.lastname: Keuren
authors.forename: Elke J P
authors.initials: EJ
authors.lastname: Magdeleyns
authors.forename: José W P
authors.initials: JW
authors.lastname: Govers-Riemslag
authors.forename: Theo
authors.initials: T
authors.lastname: Lindhout
authors.forename: Joyce
authors.initials: J
authors.lastname: Curvers
mesh_terms: D001777:Blood Coagulation / Q000502:physiology*; D001792:Blood Platelets / Q000502:physiology*; D001793:Blood Preservation; D015951:Factor Xa / Q000032:analysis / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D018709:Statistics, Nonparametric; D013917:Thrombin / Q000032:analysis / Q000378:metabolism; D013925:Thromboplastin / Q000032:analysis
chemical_list: D013925:Thromboplastin; D013917:Thrombin; D015951:Factor Xa