Discovery and Characterization of Alamandine, a Novel Component of the Renin-Angiotensin System

Rationale: The renin-angiotensin system (RAS) is a key regulator of the cardiovascular system, electrolyte and water balance. Here we report identification and characterization of alamandine, a new heptapeptide generated by catalytic action of ACE2 angiotensin A, or directly from angiotensin-(1-7). Objective: To characterize a novel component of the RAS, alamandine. Methods and Results: Using Mass Spectrometry we observed that alamandine circulates in human blood and can be formed from angiotensin-(1-7) in the heart. Alamandine produces several physiological actions that resemble those produced by angiotensin-(1-7), including vasodilation, anti-fibrosis, anti-hypertensive and central effects. Interestingly, our data reveals that its actions are independent of the known vasodilator receptors of the RAS, Mas and AT2. Rather, we demonstrate that alamandine acts through the Mas-related G-Protein coupled receptor, MrgD. Binding of alamandine to MrgD is blocked by D-Pro7-Ang-(1-7), the MrgD ligand β-alanine and PD-123319, but not by the Mas antagonist A-779. In addition, oral administration of an inclusion compound of alamandine/β-hydroxypropyl cyclodextrin produced a long-lasting anti-hypertensive effect in spontaneously hypertensive rats and anti-fibrotic effects in isoproterenol-treated rats. Alamandine had no noticeable proliferative or anti-proliferative effect in human tumoral cell lines. Conclusions: The identification of these two novel components of the RAS, alamandine and its receptor, provides new insights for the understanding of the physiological and pathophysiological role of the RAS, and may help to develop new therapeutic strategies for treating human cardiovascular diseases and other related disorders.