Background: Microparticles (MPs) have procoagulant properties as shown in vitro and in animal models. Their role in haemostatic system activation at the site of a vascular injury in vivo in humans has not been studied.
Material and methods: In a prospective randomized crossover study, 13 healthy volunteers were given 100 mg acetylsalicylic acid or placebo daily for 7 days. Number and cellular origin, expression of tissue factor (TF) and phosphatidylserine on MPs, and platelet and coagulation activation markers [beta-thromboglobulin (beta-TG), prothrombin fragment f1.2 (f1.2)] were measured in venous blood and in blood from a vascular injury (shed blood) by flow cytometry and immunoassays, respectively.
Results: The number of MPs was significantly higher in shed blood than in venous blood. The majority of MPs were platelet derived. The expression of TF on MPs was low, but higher in shed blood than in venous blood. TF positive MPs were significantly higher in shed blood, which was due to an increase of MPs from platelets (PMPs). In shed blood, the number of TF expressing platelet-derived MPs correlated with beta-TG, but not with f1.2. Low dose acetylsalicylic acid did not affect shedding of PMPs, neither in venous blood nor in shed blood.
Conclusions: The release of PMPs locally at the site of platelet plug formation in humans indicates a possible role of MPs for haemostatic system activation in vivo. Low dose acetylsalicylic acid might not be strong enough to suppress shedding of PMPs in the microcirculation.