Cardiovasc Pathol. 2013 Jan-Feb;22(1):42-8.  

Expression of angiotensin-converting enzyme 2 and its end product angiotensin 1-7 is increased in diabetic atheroma: implications for inflammation and neovascularization.

K-Raman Purushothaman*, Prakash Krishnan*, Meerarani Purushothaman*, Jose Wiley*, Carlos L. Alviar*, Fernando J. Ruiz*, Yelena Zubatov*, Annapoorna S. Kini*, Samin K. Sharma*, Valentin Fuster*, **, Pedro R. Moreno*.

*The Zena and Michael A. Wiener Cardiovascular Institute, Mount Sinai School of Medicine, New York, NY, USA. **Centro Nacional de Investigaciones Cardiovasculares (CNIC), Madrid, Spain.



Aims The angiotensin-converting enzyme 2 (ACE2) and its end product angiotensin 1-7 (Ang1-7) are key counter regulatory proteins to offset the deleterious effects of angiotensin II. ACE2 is decreased in diabetic kidney disease but over expressed in metabolically active atheroma. We tested the hypothesis that ACE2 is increased in diabetic peripheral atheroma, concomitantly with Ang1-7, angiotensin II receptor 1 (AT1R), proinflammatory cytokines, macrophage infiltration, and plaque neovascularization.

Methods and Results Peripheral atherectomy plaques collected from 12 diabetic (DM) and 12 non-DM patients were immunostained for ACE2, Ang1-7, AT1R, and proinflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). Macrophage infiltration and neovascularization were counted using double-label immunochemistry with CD68/CD3 and CD34, respectively. Quantification was performed blindly by randomly counting positively stained cells in 20 high-power fields using previously validated methods. Tissue content of ACE2, Ang1-7, and AT1R was increased in DM when compared to non-DM (P=0.0001). IL-6 and TNF-α were also increased in DM when compared to non-DM (P=0.0001), as well as macrophage infiltration score and neovessel counting (P=0.0001) (Table).

Conclusion Expression of ACE2 and its end product Ang1-7 is increased in DM atheroma, along with over expression of AT1R, IL6, TNF-α, macrophage infiltration, and neovascularization. These results suggest that the renin–angiotensin system counter regulatory pathway may be preserved in metabolically active atheroma, offering potential targets for future therapies in diabetic atherosclerosis.

Keywords: ACE2, Diabetes mellitus, Inflammation, Neovascularization, Peripheral vascular disease



Angiotensin Converting Enzyme 2 (ACE2) is now considered a key modulator of the renin-angiotensin system in cardiovascular and renal disease 1. This recently discovered homologue of the Angiotensin Converting Enzyme (ACE) 2 is responsible for tissue degradation of Angiotensin II (Ang-II), and the generation of Angiotensin 1-7 (Ang 1-7), a vasodilatory and anti-inflammatory protein that counteracts the actions of Ang-II 3. The proatherogenic effects of Ang-II are mediated by its specific Ang-II receptor type 1 (AT1R) 4. The interaction between Ang-II and AT1R has been linked to atherosclerosis formation, by means of endothelial dysfunction, increased inflammation, macrophage infiltration, and adventitial neovascularization 5, 6. In renal disease, glomerular and tubular ACE2 expression is reduced in patients with Type II diabetes 7. While genetic deletion of ACE2 significantly accelerates atherosclerosis in ApoE KO mice 8, over expression of ACE2 remarkably ameliorated glomerular injury, and improved glycemic control in diabetic mice 9.

Diabetes mellitus is characterized by metabolically active atheroma, with increased inflammation and neovascularization 10, 11. Although poorly studied in human atherosclerosis, recent studies documented increased ACE2 in metabolically active atheroma, including vulnerable plaques 12. Nevertheless, the role of ACE2 in diabetes atherosclerosis has not been studied. This study tested the hypothesis that ACE2 is over expressed in diabetic peripheral atheroma, which in turns leads to an increased production of Ang 1-7. To evaluate possible mediators involved, we simultaneously quantified the expression of the Ang-II receptor1 (AT1R), along with pro-inflammatory cytokine expression, macrophage infiltration, and plaque neovascularization.

The evaluation of peripheral, active atheroma from patients with DM in our study demonstrated increased expression of ACE2, Ang1-7, AT1R, IL-6, and TNF-α, along with enhanced macrophage infiltration, and neovascularization when compared to non-DM specimens. The concomitant over expression of ACE2, Ang1-7, and AT1R, along with inflammatory markers, suggest that the RAS counter-regulatory pathway may be preserved in the metabolically active, DM atheroma (Flow chart). While specific molecular mechanisms remain to be elucidated, further studies are warranted to clarify the potential role of the ACE2 pathway in DM atherosclerosis. It is conceivable that the ACE2 pathway may offer specific targets for novel therapy that could be tested to ameliorate plaque progression in DM atherosclerosis.


Table 1: Immunohistological profile differences between diabetic and non diabetic atheroma.




fig1Figure: Depicts the innate Renin- Angiotensin pathway, ACE/ACE-2 converts Angiotensin I to II furthermore, Angiotensin II parallels increase in Angiotensin 1 receptor expression (AT1R) induces angiogenesis and pro-inflammatory pathway by increasing inflammation. In addition diabetes parse increases smooth muscle cells, endothelial dysfunction and macrophages which augments the production of ACE/ACE-2, which acts as a viscous cycle in inducing Angiotensin II and further inflammation and angiogenesis through the growth factors.



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