Microparticles in vascular diseases.

Cellular microparticles (MP) are small membrane vesicles that are released from cells upon activation or apoptosis. They constitute a heterogeneous population of submicron elements differing in cellular origin, number, size, antigenic composition and functional properties. Circulating MP provide an additional procoagulant phospholipid surface enabling the assembly of the clotting enzyme complexes and thrombin generation. Their procoagulant properties rely on the exposure of phosphatidylserine and on the possible presence of tissue factor, the main initiator of blood coagulation. Microparticles constitute the main reservoir of blood-borne tissue factor. Derived from various cells, most notably platelets, erythrocytes, leucocytes and endothelial cells, circulating MP are detectable in the circulation of healthy subjects. Elevated levels are encountered in diseases with vascular involvement and hypercoagulability such as disseminated intravascular coagulation, diabetes, immune-mediated thrombosis, kidney diseases, acute coronary syndromes or systemic inflammatory disease, where they appear indicative of a poor clinical outcome. Converging evidence from experimental and clinical data underlines an involvement of procoagulant MP in the initiation/dissemination of procoagulant and inflammatory responses. In these clinical settings, the pharmacological modulation of MP level or activity provides challenging issues.