Summary: Considerable interest for cell-derived microparticles has emerged, pointing out their essential role in haemostatic response and their potential as disease markers, but also their implication in a wide range of physiological and pathological processes. They derive from different cell types including platelets – the main source of microparticles – but also from red blood cells, leukocytes and endothelial cells, and they circulate in blood. Despite difficulties encountered in analyzing them and disparities of results obtained with a wide range of methods, microparticle generation processes are now better understood. However, a generally admitted definition of microparticles is currently lacking. For all these reasons we decided to review the literature regarding microparticles in their widest definition, including ectosomes and exosomes, and to focus mainly on their role in haemostasis and vascular medicine.

Background— The adenosine diphosphate (ADP) receptor P2Y ₁₂ plays a pivotal role in platelet aggregation, as demonstrated by the benefit conferred by its blockade in patients with cardiovascular disease. Some studies have shown interindividual differences in ADP-induced platelet aggregation responses ex vivo, but the mechanisms underlying this variability are unknown. Methods and Results— We examined ADP-induced platelet aggregation responses in 98 healthy volunteers, and we identified 2 phenotypic groups of subjects with high and low responsiveness to 2 μmol/L ADP. This prompted us to screen the recently identified G _i -coupled ADP receptor gene P2Y ₁₂ for sequence variations. Among the 5 frequent polymorphisms thus identified, 4 were in total linkage disequilibrium, determining haplotypes H1 and H2, with respective allelic frequencies of 0.86 and 0.14. The number of H2 alleles was associated with the maximal aggregation response to ADP in the overall study population ( P =0.007). Downregulation of the platelet cAMP concentration by ADP was more marked in 10 selected H2 carriers than in 10 noncarriers. Conclusions— In healthy subjects, ADP-induced platelet aggregation is associated with a haplotype of the P2Y ₁₂ receptor gene. Given the crucial role of the P2Y ₁₂ receptor in platelet functions, carriers of the H2 haplotype may have an increased risk of atherothrombosis and/or a lesser clinical response to drugs inhibiting platelet function.

Background— We recently described a gain-of-function haplotype, called H2, of the adenosine diphosphate (ADP) receptor P2Y ₁₂ gene associated with increased ADP-induced platelet aggregation ex vivo in healthy volunteers. Because platelets play a key role in atherosclerosis and arterial thrombosis, we tested the possible link between the H2 haplotype and the risk of peripheral arterial disease (PAD) in a case-control study. Methods and Results— We studied 184 consecutive male patients under 70 years of age with PAD and 330 age-matched control subjects free of symptomatic PAD and with no cardiovascular history. Mean age was 57.1±7.2 years (cases) and 56.7±7.6 years (control subjects). The H2 haplotype was more frequent in patients with PAD than in control subjects (30% and 21%, respectively; OR, 1.6; CI, 1.1 to 2.5; P =0.02 in univariate analysis). This association with PAD remained significant in multivariate regression analysis (OR, 2.3; CI, 1.4 to 3.9; P =0.002) after adjustment for diabetes, smoking, hypertension, hypercholesterolemia, and other selected platelet receptor gene polymorphisms. Conclusions— These data point to a role of the H2 haplotype in atherosclerosis and raise the possibility of relative thienopyridine resistance in carriers of the P2Y ₁₂ H2 haplotype.