Received on July 8, 2005
Accepted on December 22, 2005

Hemostasis and Thrombosis

P-Selectin- and CD63-Exposing Platelet Microparticles Reflect Platelet Activation in Peripheral Arterial Disease and Myocardial Infarction

¹ Department of Cardiology, Academic Medical Center of the University of Amsterdam, Amsterdam, The Netherlands
² Laboratory of Experimental Clinical Chemistry, Academic Medical Center of the University of Amsterdam, Amsterdam, The Netherlands
³ Department of Clinical Chemistry, VU Medical Center, Amsterdam, The Netherlands

^* To whom correspondence should be addressed. E-mail: p.m.vanderzee{at}amc.uva.nl.

Background: Platelet-derived microparticles (PMPs) are generally considered a marker of platelet activation in cardiovascular disease. We studied the extent to which PMP subpopulations parallel platelet activation in vitro and in vivo.

Methods: Using flow cytometry, we analyzed PMP subpopulations from resting and activated platelets in vitro (n = 6) as well as from plasma samples of patients with stable angina, peripheral arterial disease, or myocardial infarction [non-ST-elevation (NSTEMI) and ST-elevation (STEMI)] and from older, age- and sex-matched and young healthy individuals [n = 10 for all groups except NSTEMI (n = 11)]. Coagulation markers prothrombin fragment F_{1 + 2} and thrombin-antithrombin complexes were determined by ELISA. The PMP-associated fraction of soluble (s)P-selectin was estimated by ELISA.

Results: In vitro, stimulation of platelets with thrombin receptor-activating peptide (15 µmol/L) or the calcium ionophore A23187 (2.5 µmol/L) increased fractions of both platelets and PMPs exposing P-selectin or CD63 (P <0.001 for all). Whereas the number of PMPs released by A23187-stimulated platelets increased significantly (P <0.001), the number of PMPs released from thrombin receptor-activating peptide--stimulated platelets remained constant (P >0.05). Ex vivo, numbers of circulating (P)MPs were comparable in all groups. Compared with young persons, P-selectin-exposing PMPs were increased in older persons (P = 0.02) and were further increased in patients with NSTEMI (P = 0.007) and STEMI (P = 0.045). CD63-exposing PMPs were increased in patients with peripheral arterial disease (P = 0.041), NSTEMI (P = 0.001), and STEMI (P = 0.049). Subpopulations exposing P-selectin or CD63 correlated with each other (r = 0.581; P <0.001), but neither correlated with the plasma concentrations of F_{1 + 2} or thrombin-antithrombin complexes. The PMP-associated fraction of sP-selectin constituted only 2.2 (4.7)% [mean (SD)] of total sP-selectin.

Conclusions: PMP subpopulations reflect platelet activation status better than the total number of PMPs. Increased concentrations of circulating PMP subpopulations are found in aging, and further increases are encountered in peripheral arterial disease and myocardial infarction.