Dynamic Observation of Mechanically-Injured Mouse Femoral Artery Reveals an Antiinflammatory Effect of Renin Inhibitor

OBJECTIVE: The renin-angiotensin-aldosterone system (RAS) plays a central role in atherosclerosis. To investigate the effects of a direct renin inhibitor aliskiren on vascular inflammation, we conducted leukocyte adhesion assays in vivo and in vitro using a novel real-time imaging system. METHODS AND RESULTS: Aliskiren (10 mg/kg/d) or PBS was administered to C57BL/6 mice (6-7 weeks of age; Oriental Yeast, Tokyo, Japan) for 2 weeks via an osmotic pump. Blood pressure was not significantly changed in the 2 groups throughout the experimental period. A perivascular cuff injury was then introduced to the femoral artery and real-time intravital microscopic observation was conducted 24 hours after injury. The number of adherent leukocytes was elevated in the injured mice without aliskiren (43.8+/-9.3/10(-2) mm(2)), whereas that was significantly reduced in the mice with aliskiren (18.4+/-4.4, P<0.05). Treatment of human umbilical vein endothelial cells (HUVECs) with aliskiren significantly reduced the adhesion of THP-1 cells to TNF-alpha-activated HUVECs (P<0.05). Interestingly, TNF-alpha-induced renin activity and angiotensin II production in HUVECs were also blunted by aliskiren. Furthermore, exogenous renin and angiotensin II abrogated the aliskiren-mediated reduction of THP-1 cell adhesion to HUVECs. CONCLUSIONS: Our in vivo and in vitro findings indicate a pivotal role for renin inhibition in vascular inflammation independent of blood pressure.