Microparticles adhere to collagen type I, fibrinogen, von Willebrand factor and surface immobilised platelets at physiological shear rates

Abstract

Microparticles (MPs), shed during the storage of platelets, support blood coagulation and could be helpful in restoring the haemostatic system in thrombocytopenic patients. The mechanisms by which MPs support haemostasis under flow conditions were investigated. Fluorescent-labelled MPs were perfused at shear rates of 100 and 1000/s over surfaces coated with collagen, fibrinogen, von Willebrand factor (VWF) or surface-adherent platelets. Adhesion was monitored in real-time by fluorescence microscopy. In addition, thrombin-antithrombin (TAT) complex formation was measured in flowing thrombocytopenic blood. MPs attained the capacity to firmly adhere to collagen, VWF, fibrinogen and surface-adherent platelets at high and low shear rate. Antibodies against glycoprotein Ibalpha and alpha(IIb)beta(3) were used to demonstrate the specificities of these interactions. The addition of MPs to thrombocytopenic blood did not affect platelet adhesion. TAT complex formation was increased in the presence of MPs in capillaries coated with fibrinogen, but not on collagen fibres. We confirmed that MPs adhere to a damaged vascular bed in vivo after infusion in denuded arteries in a mouse model. MPs have platelet-like adhering properties and accelerate thrombin generation. These properties strongly support the notion that MPs can be beneficial in maintaining normal haemostasis when platelet function is impaired or reduced, as in thrombocytopenic patients.

Phosphatidylserine surface expression and integrin αIIbβ3 activity on thrombin/convulxin stimulated platelets/particles of different sizes

“…In our preliminary experiments (Fig 1 and data not shown) we established that low concentrations of Thr/Cvx (0AE005 U/ml/5 ng/ml) are sufficient to induce platelet apoptosis-like events during short stimulation (2 min). Several reports described that activated platelets are not homogeneous (Dachary-Prigent et al, 1993;Pasquet et al, 1998;Tonon et al, 2002;Dale et al, 2005;Remenyi et al, 2005;Leytin et al, 2006;Keuren et al, 2007). Three main platelet populations appeared after Thr/Cvx stimulation.…”

Microparticle formation in apheresis platelets is not affected by three leukoreduction filters

“…A healthy debate is in progress concerning the effect of storage time on patient outcomes and how storage legion affects patient care. Microparticles are thought to have thrombotic and proinflammatory effects and may be involved in antigen trafficking . Leukofiltration of whole blood may incidentally reduce platelet (PLT) concentration and PLT‐derived microparticle (PDMP) formation during storage .…”

Computational Modeling of Thrombotic Microparticle Deposition in Nonparallel Flow Regimes

“…Particles with a 0.5 p m diameter were used as a model MP as sizes reported in the literature range from 0.1 to 1.0 pm . The concentration of particles steadily delivered at the inlet corresponded to 5000 particles/fd based on an experimental study examining platelet derived MP deposition in a parallel plate flow chamber [27]. This is one of a very few studies examining cell-derived MP transport and/or adhesion under controlled flow conditions.…”

“…There is one published in vitro study examin ing the adhesion of platelet derived MPs under well characterized flow conditions. Keuren et al investigated platelet derived MP ad hesion to collagen, von Willebrand factor and a monolayer of pla telets from parallel, streamlined flow of thrombocytopenic blood in a parallel plate chamber under wall shear rates of 100 and 1000 s-1 [27]. The study concluded that platelet MPs adhered to each surface equally at both shear rates; hence, the adhesion was not shear dependent at the conditions employed.…”

“…Using the verified flow solutions, particle injectors were randomly dispersed across the inlet area of the chambers. MP mass flow rates (Tables 1 and 2) were equivalent to a steady concentration of 5000 MPs/ql entering the chamber, sim ilar to experiments by Keuren et al [27], MPs were grouped into packets of particles, called parcels, because it is computationally intensive to calculate trajectories of individual particles. The num ber of particles per parcel (Np) ranges from 82 to 800 for the ste nosis model and from 1 to 86 for the vertical step model.…”