The role of the renin-angiotensin system in thoracic aortic aneurysms: Clinical implications

Thoracic aortic aneurysms (TAAs) are a potential life-threatening disease with limited pharmacological treatment options. Current treatment options are aimed at lowering aortic hemodynamic stress, predominantly with beta-adrenoceptor blockers. Increasing evidence supports a role for the renin-angiotensin system (RAS) in aneurysm development. RAS blockade would not only lower blood pressure, but might also target the molecular pathways involved in aneurysm formation, in particular the transforming growth factor-beta and extracellular signal-regulated kinase 1/2 pathways. Indeed, the angiotensin II type 1 (AT(1)) receptor blocker losartan was effective in lowering aortic root growth in mice and patients with Marfan's syndrome. RAS inhibition (currently possible at 3 levels, i.e. renin, ACE and the AT, receptor) is always accompanied by a rise in renin due to interference with the negative feedback loop between renin and angiotensin II. Only during AT(1) receptor blockade will this result in stimulation of the non-blocked angiotensin II type 2 (AT(2)) receptor. This review summarizes the clinical aspects of TAAs, provides an overview of the current mouse models for TAAs, and focuses on the RAS as a new target for TAA treatment, discussing in particular the possibility that AT(2) receptor stimulation might be crucial in this regard. If true, this would imply that AT(1) receptor blockers (and not ACE inhibitors or renin inhibitors) should be the preferred treatment option for TAAs. (C) 2011 Elsevier Inc. All rights reserved.