Peptide discovered in human blood circulation
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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 angiotensin-converting enzyme-2 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, antifibrosis, antihypertensive, and central effects. Interestingly, our data reveal that its actions are independent of the known vasodilator receptors of the RAS, Mas, and angiotensin II type 2 receptor. Rather, we demonstrate that alamandine acts through the Mas-related G-protein-coupled receptor, member D. Binding of alamandine to Mas-related G-protein-coupled receptor, member D is blocked by D-Pro(7)-angiotensin-(1-7), the Mas-related G-protein-coupled receptor, member D ligand ?-alanine and PD123319, but not by the Mas antagonist A-779. In addition, oral administration of an inclusion compound of alamandine/?-hydroxypropyl cyclodextrin produced a long-term antihypertensive effect in spontaneously hypertensive rats and antifibrotic effects in isoproterenol-treated rats. Alamandine had no noticeable proliferative or antiproliferative effect in human tumoral cell lines.
CONCLUSIONS: The identification of these 2 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.
In this issue of Circulation Research, Lautner et al report on the biochemical and physiological characterization of a novel peptide of the renin–angiotensin system, the heptapeptide Ala1-Arg2-Val3-Tyr4-Ile5-His6-Pro7 alamandine, in rats, mice, and humans. Just a decade ago, most students of the renin–angiotensin system considered this hormonal system a linear biochemical cascade whereby renin acting on angiotensinogen (Aogen) initiates angiotensin (Ang) II production through the intermediate step of Ang I degradation by angiotensin-converting enzyme. The discovery of the biological actions of Ang-(1–7), the identification of the Mas receptor as the binding protein mediating the inhibitory actions of Ang-(1–7) on Ang II, and the demonstration that the cardioprotective actions of angiotensin-converting enzyme 2 are attributable to its actions on hydrolyzing Ang II into Ang-(1–7) have drastically changed this perception. Not mentioned in this report is the newly discovered Ang-(1–12), which is cleaved from Aogen by a yet-to-be-defined nonrenin enzyme., Ang-(1–12) is then converted to Ang II largely by chymase in the human heart, thus completing a non–renin-dependent Ang II-forming mechanism in human heart tissue. Ang-(1–7), Ang-(1–12), and other Ang peptides, Ang III and Ang IV, originate from 12 amino acids from the 485 amino acids of human Aogen. Although extensive research has confirmed a critical role of renin in the liberation of Ang I from Aogen, numerous other studies have suggested that there exist other proteases capable of cleaving the substrate.
INTRODUCTION: Angiotensin (Ang) A was first identified in human plasma and it differs from Ang II in Ala(1) instead of Asp(1). Here, we hypothesized that the actions of this peptide might explain, at least partially, the limited effects of AT(1)R antagonists in certain cardiovascular diseases. MATERIALS AND METHODS: The effects of Ang A and Ang II on blood pressure (BP) and heart function were compared. Importantly, participation of AT(1)R in these effects was evaluated. Furthermore, the effects of these two peptides on ischemia/reperfusion arrhythmias and involvement of calcium in these effects were investigated.RESULTS:Administration of increasing doses of these peptides caused elevations in BP at comparable magnitude. AT(1)R blockade completely abolished these effects. The actions of these peptides in cardiac function were quite similar although the effects of Ang A were only partially blocked by losartan. Interestingly, Ang II elicited an increase in the duration of ischemia/reperfusion arrhythmias while Ang A had no effect on cardiac rhythm during reperfusion. In accordance, differently to Ang II, Ang A did not induce any significant effect on calcium transient during baseline and ischemic stress conditions. CONCLUSIONS: These data suggest that the existence of alternative peptides of the renin-angiotensin system (RAS) might contribute to the limited effects of angiotensin receptor blockers (ARBs) in certain pathophysiological circumstances.
OBJECTIVE: Angiotensin peptides play a central role in cardiovascular physiology and pathology. Among these peptides, angiotensin II (Ang II) has been investigated most intensively. However, further angiotensin peptides such as Ang 1-7, Ang III, and Ang IV also contribute to vascular regulation, and may elicit additional, different, or even opposite effects to Ang II. Here, we describe a novel Ang II-related, strong vasoconstrictive substance in plasma from healthy humans and end-stage renal failure patients.
METHODS AND RESULTS: Chromatographic purification and structural analysis by matrix-assisted laser desorption/ionisation time-of-flight/time-of-flight (MALDI-TOF/TOF) revealed an angiotensin octapeptide with the sequence Ala-Arg-Val-Tyr-Ile-His-Pro-Phe, which differs from Ang II in Ala1 instead of Asp1. Des[Asp1]-[Ala1]-Ang II, in the following named Angiotensin A (Ang A), is most likely generated enzymatically. In the presence of mononuclear leukocytes, Ang II is converted to Ang A by decarboxylation of Asp1. Ang A has the same affinity to the AT1 receptor as Ang II, but a higher affinity to the AT2 receptor. In the isolated perfused rat kidney, Ang A revealed a smaller vasoconstrictive effect than Ang II, which was not modified in the presence of the AT2 receptor antagonist PD 123319, suggesting a lower intrinsic activity at the AT1 receptor. Ang II and Ang A concentrations in plasma of healthy subjects and end-stage renal failure patients were determined by matrix-assisted laser desorption/ionisation mass-analysis, because conventional enzyme immunoassay for Ang II quantification did not distinguish between Ang II and Ang A. In healthy subjects, Ang A concentrations were less than 20% of the Ang II concentrations, but the ratio Ang A/Ang II was higher in end-stage renal failure patients.
CONCLUSIONS: Ang A is a novel human strong vasoconstrictive angiotensin-derived peptide, most likely generated by enzymatic transformation through mononuclear leukocyte-derived aspartate decarboxylase. Plasma Ang A concentration is increased in end-stage renal failure. Because of its stronger agonism at the AT2 receptor, Ang A may modulate the harmful effects of Ang II.