Characterization of Angiotensin-(1-7) effects on the cardiovascular system in an experimental model of type-1 diabetes

Although exogenous administration of Angiotensin-(1-7) [Ang-(1-7)] can prevent development of diabetes induced end-organ damage, little is known about the role of endogenous Ang-(1-7) in diabetes and requires further characterization. Here, we studied the effects of chronically inhibiting endogenous Ang-(1-7) formation with DX600, a selective angiotensin converting enzyme-2 (ACE2) inhibitor, on renal and cardiac NADPH Oxidase (NOX) activity, vascular reactivity and cardiac function in a model of Type-1 diabetes. The contribution of endogenous Ang-(1-7) to the protective effects of Losartan and Captopril and that of prostaglandins to the cardiovascular effects of exogenous Ang-(1-7) were also examined. Cardiac and renal NOX activity, vascular reactivity to endothelin-1 (ET-1) and cardiac recovery from ischemia/reperfusion (I/R) injury were evaluated in streptozotocin-treated rats. Chronic treatment with DX600 exacerbated diabetes-induced increase in cardiac and renal NOX activity. Diabetes-induced abnormal vascular reactivity to ET-1 and cardiac dysfunction were improved by treatment with Ang-(1-7) and worsened by treatment with DX600 or A779, a Mas receptor antagonist. Ang-(1-7)-mediated improvement in cardiac recovery or vascular reactivity was attenuated by Indomethacin. Captopril and Losartan-induced improvement in cardiovascular function was attenuated when these drugs were co-administered with A779. Ang-(1-7)-mediated decrease in renal NOX activity was prevented by indomethacin. Losartan also decreased renal NOX activity that could be attenuated with A779 co-treatment. In conclusion, endogenous Ang-(1-7) inhibits diabetes-induced cardiac/renal NOX activity and end-organ damage, and mediates the actions of Captopril and Losartan. Further, prostaglandins are important intermediaries in the beneficial effects of Ang-(1-7) in diabetes. Combining either Losartan or Captopril with Ang-(1-7) had additional beneficial effects in preventing diabetes-induced cardiac dysfunction and this may represent a novel therapeutic strategy. Collectively, these data shed new insights into the likely mechanism of action through which the ACE2/Ang-(1-7)/Mas receptor axis prevents Type 1 diabetes-induced cardiovascular dysfunction.