Abstract 12116: Angiotensin Ii Releases Procoagulant Microparticles Through Selective At2-Mediated Stimulaton in Human Monocytes/Macrophages
BACKGROUND: Microparticles (MP), i.e. membrane fragments (0.1-1.0 μm) shed by cells stimulated by inflammatory mediators, may predispose to thrombotic complications due to membrane-embedded phospatidylserine (PS), a key component of the prothrombinase complex, and to the presence of Tissue Factor (TF), the main factor of the extrinsic coagulation pathway. That possibility, consistent with increased circulating MP levels in hypertension, raises the issue of the underlying causal mechanisms perhaps including AngII, the final effector of the Renin Angiotensin System (RAS) and a proinflammatory and procoagulant peptide pathophysiologically involved in systemic hypertension and its clinical complications.
AIM: To investigate whether Ang II contributes to procoagulant MP generation by human monocytes/macrophages and to clarify its mechanism of action.
METHODS: Monocytes/macrophages were isolated from the buffy coats of normal blood donors after Ficoll density-gradient centrifugation. MP generation was assessed by measuring PS levels (Hyphen, France). Changes in [Ca++]i from baseline were measured by a fluorometric probe (Molecular Probes Fluo-4 NW Calcium Assay kit) and TF-dependent coagulation was assessed by one-stage clotting assay. RESULTS (Mean±SEM): AngII (1μM, 15 min) increased MP generation (control:0.17±0.03 vs. AngII: 0.27±0.04 nM PS, n=6,p<0.001) in parallel with increased [Ca++]I (+334.6 ΔRFU, n=6, p<0.001) and MP-bound TF-mediated procoagulant activity (control:0.05±0.03 vs AngII:0.16±0.1 UA,n=8, p<0.01). Pre-incubation (30 min) with PD123319 (1μM), an AT2 selective antagonist, inhibited (control: 0.19±0.04; Ang II: 0.29±0.06, p<0.01 vs bas; PD123319+Ang II: 0.20±0.04 nM PS, NS vs bas) and Olmesartan (1μM), an AT1 selective antagonist (control:0.11±0,03;AngII:0.19±0.04; OLM+AngII:0.24±0.07 nM PS,n=8,p<0.05 vs AngII), increased MP generation
CONCLUSIONS: Ang II promotes generation of procoagulant MP by monocytes/macrophages via AT2 receptor stimulation, an effect that AT1 receptor antagonism amplifies. Ang-II mediated MP generation may contribute to the thrombotic complications of systemic hypertension but additional studies are needed to understand the clinical implications of this finding.
- © 2011 by American Heart Association, Inc.