Elevated Levels of Cell-Derived Microparticles with Procoagulant Activity in Cocaine Abusers: Association with Increased Thrombin Generation and a Prothrombotic State.

Cocaine abuse is associated with an increased risk of serious cerebral and cardio vascular ischemic events. The underlying mechanisms leading to these complications are not fully understood although intravascular thrombus formation is probable. Several in vitro studies showed that cocaine may induce damage and/or activation of platelets and endothelial cells. A known feature of activated cells is the shedding of microparticles (MP) which support coagulation by exposure of negatively charged phospholipids and possibly tissue factor (TF). Elevated levels of circulating MP have been reported in association with thrombotic disorders. In this work we characterized circulating MP in long-term cocaine users and their relationship with activation of blood coagulation and increased thrombin generation (TG). Eighteen cocaine-dependent subjects (aged 20–49 years, mean age 35 years) and 22 healthy controls (aged 22–65 years, mean age 39 years) were studied (p:0.25); all patients fulfilled DSM-IV criteria for cocaine dependence with drug exposure within the 72 hours prior to blood sampling. Circulating MP were isolated from frozen plasma and their number and cellular source were determined by flow cytometry (FC) using double labeling with specific monoclonal antibodies and annexin V. Procoagulant activity (PCA) was determined in washed MP by conversion of factor X to Xa in the presence of FVIIa. Calibrated automated TG was measured in clotting plasma (Hemker, Thromb Haemost, 2000) without the addition of exogenous phospholipids and TF; under these conditions TG directly depends on the number of MP present in plasma. Monocyte TF expression was determined by FC by double labeling with FITC-labeled anti-CD142 and PE-labeled anti-CD-14. Thrombin anti-thrombin complexes (TAT) were measured by ELISA.

Compared to the controls, circulating MP were significantly elevated in the patient group (1,278±216 vs 703±82 x10³/ml plasma, p: 0.014). TG was higher among the patients with respect to the controls (peak, 149±70 vs 58±21 nM thrombin, p<0.0001). TF expression by circulating monocytes was significantly increased among cocaine-dependent individuals compared to the controls (1.28±0.26 vs 0.88±0.19 MFI, respectively; p:<0.0001). TAT in patients and controls were 2.7±0.7 and 0.7±0.4 μg/L, respectively (p:0.06). TG correlated significantly with the number (r: 0.68; p: 0.0039) and the PCA (r: 0.58; p: 0.0025) of circulating MP. The number of circulating MP were also correlated with TAT levels (r: 0.40; p: 0.04). The results confirm a prothrombotic state in cocaine-dependent individuals demonstrated by increased levels of TAT and expression of TF by monocytes. The increased number of circulating MP and their association with high thrombin generation and activation of the coagulation system, suggest that cell-derived MP may play an important role in the pathogenesis of the thrombotic complications associated with cocaine abuse.