Microparticles as a circulating source of procoagulant and fibrinolytic activities in the circulation (original) (raw)
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Microparticle analysis in disorders of hemostasis and thrombosis
Cytometry. Part A : the journal of the International Society for Analytical Cytology, 2015
Microparticles (MPs) are submicron vesicles released from the plasma membrane of eukaryotic cells in response to activation or apoptosis. MPs are known to be involved in numerous biologic processes, including inflammation, the immune response, cancer metastasis, and angiogenesis. Their earliest recognized and most widely accepted role, however, is the ability to promote and support the process of blood coagulation. Consequently, there is ongoing interest in studying MPs in disorders of hemostasis and thrombosis. Both phosphatidylserine (PS) exposure and the presence of tissue factor (TF) in the MP membrane may account for their procoagulant properties, and elevated numbers of MPs in plasma have been reported in numerous prothrombotic conditions. To date, however, there are few data on true causality linking MPs to the genesis of thrombosis. A variety of methodologies have been employed to characterize and quantify MPs, although detection is challenging due to their submicron size. F...
Circulating Microparticles Alter Formation, Structure, and Properties of Fibrin Clots
Scientific Reports, 2015
Despite the importance of circulating microparticles in haemostasis and thrombosis, there is limited evidence for potential causative effects of naturally produced cell-derived microparticles on fibrin clot formation and its properties. We studied the significance of blood microparticles for fibrin formation, structure, and susceptibility to fibrinolysis by removing them from platelet-free plasma using filtration. Clots made in platelet-free and microparticle-depleted plasma samples from the same healthy donors were analyzed in parallel. Microparticles accelerate fibrin polymerisation and support formation of more compact clots that resist internal and external fibrinolysis. These variations correlate with faster thrombin generation, suggesting thrombin-mediated kinetic effects of microparticles on fibrin formation, structure, and properties. In addition, clots formed in the presence of microparticles, unlike clots from the microparticle-depleted plasma, contain 0.1-0.5-μm size granular and CD61-positive material on fibres, suggesting that platelet-derived microparticles attach to fibrin. Therefore, the blood of healthy individuals contains functional microparticles at the levels that have a procoagulant potential. They affect the structure and stability of fibrin clots indirectly through acceleration of thrombin generation and through direct physical incorporation into the fibrin network. Both mechanisms underlie a potential role of microparticles in haemostasis and thrombosis as modulators of fibrin formation, structure, and resistance to fibrinolysis. Circulating microparticles (MPs) are 0.1-1-μ m-large phospholipid vesicles 1 released from blood and vascular cells upon activation and apoptosis. The mechanism of MP formation by budding of the outer cell membranes provides them with procoagulant activity, mainly due to phosphatidylserine exposure and tissue factor expression 2,3. Tissue factor-bearing MPs are important for thrombin generation and blood clotting in vitro 4 as well as for thrombus formation in vivo 5-10. MPs are present in the blood under physiological conditions, but the level of circulating MPs is elevated in vascular, infectious, and immune-mediated pathologies 11-16. MPs are heterogeneous in size, composition, density, and cellular origin. MPs derived from different cell types possess unique functional capabilities due to variations of lipids and proteins acquired from parent cells 17-19. The main fraction of circulating MPs in a non-diseased state is reported to be platelet or megakaryocyte-derived MPs 20,21. Circulating MP in the absence of disease likely originate from aging cells 22. Despite many studies on the role of MPs in diseases, the functional importance of normally present MPs is unclear. Circulating MPs in healthy controls were shown to support low-grade thrombin generation by the contact pathway 23. Whether MPs originating under physiological circumstances can provide sufficient activity to support blood coagulation is not clear. Particularly little is known about potential effects of MPs on fibrin clot formation and lysis, the determinant stages of blood clotting. Fibrin is a three-dimensional filamentous
The Role of Microparticles in Inflammation and Thrombosis
Scandinavian Journal of Immunology, 2007
Microparticles (MP) are small membrane-bound vesicles that circulate in the peripheral blood and play active roles in thrombosis, inflammation and vascular reactivity. While MP can be released from nearly every cell type, most investigation has focused on MP of platelet, leucocyte and endothelial cell origin. Cells can release MP during activation or death. Flow cytometry is the usual method to quantify MP; the small size of these structures and lack of standardization in methodology complicate measurement. As MP contain surface and cytoplasmic contents of the parent cells and bear phosphatidylserine, antibodies to specific cell surface markers and annexin V can be used for identification. Through various mechanisms, MP participate in haemostasis and have procoagulant potential in disease. MP contribute to inflammation via their influence on cell-cell interactions and cytokine release, and MP also function in mediating vascular tone. In several disease states characterized by inflammation and vascular dysfunction, MP subpopulations are elevated, correlate with clinical events, and may have important roles in pathogenesis. In the rheumatic conditions such as rheumatoid arthritis and systemic lupus erythematosus, MP are potentially important markers of disease activity and have an increasingly recognized role in immunopathogenesis. It is clear that MP play an important role in atherosclerosis, and study of these structures may provide insight into the link between chronic inflammatory conditions and accelerated atherosclerosis. As biomarkers, MP allow access to usually inaccessible tissues such as the endothelium. Further research will hopefully lead to interventions targeting MP release and function.
Phosphatidylserine positive microparticles improve hemostasis in in-vitro hemophilia A plasma models
Scientific Reports
Circulating microparticles (MPs) are procoagulant due to the surface containing phosphatidylserine (PS), which facilitates coagulation. We investigated if MPs improve hemostasis in HA plasma models. MPs isolated from pooled normal human plasma were added to severe, moderate and mild HA plasma models (0%, 2.5%, 20% FVIII). The MPs’ effect on hemostasis was evaluated by calibrated automated thrombogram (CAT) and overall hemostasis potential (OHP) assays, while fibrin structure was imaged by standard confocal, stimulated emission depletion (STED) microscopy and scanning electron microscopy (SEM). MPs partially restored thrombin generation and fibrin formation in all HA plasma models. The procoagulant effect of MPs requires PS exposure, to a less extent of contact pathway activation, but not tissue factor exposure or in vitro stimulation of MPs. MPs partially normalized the fibrin structure, and using super-resolution STED, MPs attached to fibrin were clearly resolved. In summary, our r...
Cell-derived microparticles circulate in healthy humans and support low grade thrombin generation
Thrombosis and haemostasis, 2001
We determined the numbers, cellular origin and thrombin-generating properties of microparticles in healthy individuals (n = 15). Microparticles, isolated from fresh blood samples and identified by flow cytometry, originated from platelets [237 x 10(6)/L (median; range 116-565)], erythrocytes (28 x 10(6)/L; 13-46), granulocytes (46 x 10(6)/L; 16-94) and endothelial cells (64 x 10(6)/L; 16-136). They bound annexin V, indicating surface exposure of phosphatidylserine, and supported coagulation in vitro. Interestingly, coagulation occurred via tissue factor (TF)-independent pathways, because antibodies against TF or factor (F)VII were ineffective. In contrast, in our in vitro experiments coagulation was partially inhibited by antibodies against FXII (12%, p = 0.006), FXI (36%, p <0.001), FIX (28%, p <0.001) or FVIII (32%, p <0.001). Both the number of annexin V-positive microparticles present in plasma and the thrombin-generating capacity inversely correlated to the plasma conc...
Thrombosis and Haemostasis, 2010
Endothelial microparticles (EMP) are complex vesicular structures that can be shed by activated or apoptotic endothelial cells. EMP are composed of a phospholipid bilayer that exposes transmembrane proteins and receptors and encloses cytosolic components such as enzymes, transcription factors and mRNA derived from their parent cells. Thus, EMP behave as biological conveyors playing a key role in the tuning of vascular homeostasis. This review focuses on the multifaceted roles of EMP, notably in coagulation, inflammation and angiogenesis and also on the mechanisms that trigger their formation. In this con-text, EMP could compromise vascular homeostasis and then represent key players in the pathogenesis of several inflammatory and thrombotic diseases. Consequently, elucidating their role and their mechanisms of formation will bring new insights into the understanding of endothelial-associated diseases. Moreover, in the future, it can open novel therapeutic perspectives based on the inhibition of EMP release.
Thrombosis and Haemostasis, 2007
Platelet microparticles (PMPs) aresmallv esiclesr eleasedfrom blood platelets upon activation. Thep rocoagulant activity of PMPs has been previously mainlycharacterized by their ability to bindcoagulation factors VIII and Va in reconstructedsystems. It canbesupposed that PMPs can contribute to the development of thromboticcomplicationsinthe pathologic statesassociated with the increase of theirbloodconcentration. In this study, we compared procoagulant properties of calcium ionophore A23187-activatedplatelets and PMPs using several in-vitromodelso fh emostasis. Surface densitieso fp hosphatidylserine, CD61, CD62P and factor Xb oundp er surfacea reau nit were determinedb yf lowc ytometry.Theyw ere2 .7-,8.4-,4.3-,and 13-foldhigher forPMPsthan foractivatedplatelets,respectively.