Procoagulant circulating microparticles in health and disease

Procoagulant circulating microparticles in health and disease

Introduction

Cellular microparticles (MPs) are fragments of the plasma membrane that are shed by virtually all cell when subject to a number of stress conditions, including cellular activation and apoptosis (Beaudoin and Grondin 1991; Zwaal and Schroit 1997; Freyssinet et al 1999; Hugel et al 2005). Since the description of “platelet dust” by Wolf (1967), numerous studies have reported the presence of subcellular vesicles in centrifuged plasma. Although long considered to be cellular debris, blood MPs are more recently considered reflective of cellular stimulation, activation, and degeneration/apoptosis (Freyssinet 2003; Morel et al 2005; Boulanger et al 2006).

Procoagulant circulating microparticles in health and disease

By general consensus, MPs are small in size (=1.5 µm), expose the anionic phospholipid (PL) phosphatidylserine (PS) on the outer leaflet of their membrane, and bear surface membrane antigens reflecting their cell of origin (Jy et al 2004). MPs that arise from the cellular components of blood and the endothelial lining of blood vessels are referred to as blood MPs. Apart from blood MPs, plasma contains smaller membrane vesicles (40-100 nm) termed exosomes and larger vesicles (>1.5 µm) termed apoptotic bodies that are derived from blood and vascular cells (Heijnen et al 1999; Freyssinet 2003). The aim of this article is to review the technical aspects of characterizing the morphological and functional properties of blood MPs with emphasis on both preanalytical and analytical variables.

All cell type's spontaneously shed blebs from their plasma membranes in an active process that appears to be important for membrane remodeling and antigenic turnover. In resting cells, the negatively charged phospholipids, including PS, are almost exclusively present in the inner leaflet of the cell membrane (Zwaal and Schroit 1997). Among the mechanisms proposed to account for this asymmetry are unidirectional enzymatic movement by an aminophospholipid translocase and/or association between the negatively charged phospholipids and elements in the cytoplasm, including cytoskeletal elements and their accompanying proteins (Bevers et al 1998).

MP release is an integral part of the cell membrane remodeling process whereby the normal asymmetric distribution of phospholipids between the two leaflets of the plasma membrane is lost. Calcium entry, activation of calpain and scramblase activity are thought to be important steps in the loss of lipid asymmetry and microparticle formation, but the exact sequence of events is not completely understood (Fox et al 1990; Yano et al 1994; Dachary-Prigent et al 1995, 1997; Pasquet et al 1996, 1998; Bucki et al 1998, 2006; Kunzelmann-Marche et al 2001). The possible pathways leading to membrane budding and MP release have been recently reviewed (Freyssinet 2003; Boulanger et al 2006).

Shedding processes are found in a variety of blood cells (Beaudoin and Grondin 1991). Human erythrocytes treated with ionophore A23187 in the presence of calcium, respond by budding to release MPs. Normal erythrocytes also release MPs following ATP depletion, heat treatment (49 °C), incubation at pH 5.4 and incubation with diamide (5 mMol/L) (Wagner et al 1986). Erythrocyte MPs are also found to be elevated in ...