Angiotensin II induces the generation of procoagulant microparticles by human mononuclear cells via an angiotensin type 2 receptor-mediated pathway

Introduction: Microparticles are small vesicles shed by cells upon activation and during apoptosis which participate in physiologically relevant phenomena, including blood coagulation. Intracellular calciummobilization is one of the mechanisms of microparticle generation during cell activation. Because the renin-angiotensin system has been proposed as a link between hypertension and increased thrombotic risk,we investigatedwhether angiotensin II upregulates the generation of procoagulant microparticles by human mononuclear cells. Materials and Methods: Human mononuclear cells were exposed to angiotensin II for 15 min. Intracellular calciumconcentrationwas assessed by a Fluo 4 based kit. The supernatants were analyzed for both microparticle content, with a commercially available kit based on phosphatidylserine analysis, and microparticle-associated tissue factor, with a one-stage clotting assay. Results: Intracellular calcium concentration is increased upon exposure of mononuclear cells to angiotensin II. Incubation with angiotensin II stimulates microparticles release; microparticle-associated tissue factor is also upregulated. The effect is inhibited by an angiotensin receptor type 2 antagonist (PD123319) and not by two angiotensin type 1 antagonists (Losartan and Olmesartan). Conclusions: Angiotensin receptor 2-mediated upregulation of tissue factor-bearing, procoagulant microparticle generation represents a novel mechanism linking the renin-angiotensin system to thrombosis.