Angiotensin-(1-7) and its receptor as a potential targets for new cardiovascular drugs

Effects of genetic deletion of angiotensin-(1-7) receptor Mas on cardiac function during ischemia/reperfusion in the isolated perfused mouse heart

In this study we investigated the role of Mas on cardiac function during ischemia/reperfusion in isolated perfused mouse heart. Following a stabilization period of 30 min, hearts from WT and Mas KO mice were subjected to global ischemia. After 20 min of ischemia, the flow was restarted and the hearts were reperfused for 30 min. An additional group of WT mice was perfused with solution containing the Ang-(1-7) receptor Mas antagonist A-779. Isolated heart of Mas KO and WT treated with A-779 presented an increase in the perfusion pressure in the baseline period. This difference increased with 5 min of reperfusion reaching similar values to baseline period at the end of the reperfusion. Isolated hearts of Mas KO and WT treated with A-779 also presented a decreased systolic tension, +/-dT/dt, and HR. Upon global ischemia WT hearts showed a significant decrease in systolic tension and an increase in diastolic tension. During reperfusion an increase in systolic and diastolic tension was observed in WT mice. Deletion or blockade of Mas markedly attenuated these changes in isolated hearts. These results indicate that Mas plays an important role in cardiac function during ischemia/reperfusion which is in keeping with the cardiac and coronary effects previously described for Ang-(1-7).

Pharmacological Effects of AVE 0991, a Nonpeptide Angiotensin-(1?7) Receptor Agonist

In the last 20 years, our understanding of the physiopathology of the renin-angiotensin system (RAS) has expanded dramatically. Basic and clinical studies showed that this system includes several other components in addition to renin, angiotensin (Ang) II, an-giotensin-converting enzyme (ACE), and Ang II receptors. One of the most interesting new members of RAS is the heptapeptide Ang-(1-7). Many in vitro and in vivo studies have proven that this peptide plays several beneficial effects in the cardiovascular system, which are often opposite to the effects elicited by the main component of the RAS, Ang II. In addition, the recent discovery of the main enzyme involved in the Ang-(1-7) production, ACE2 and the description of the Ang-(1-7) receptor Mas reinforced the biological relevance of this peptide. These findings raised the possibility to develop new drugs based on the ACE2-Ang-(1-7)-Mas axis and directed to cardiovascular and -related diseases. The development of AVE 0991, a nonpeptide Ang-(1-7) receptor Mas agonist, represents an important step for exploration of the effects of Ang-(1-7) and testing of its potential as a cardiovascular drug. Among advantages of this compound in comparison with Ang-(1-7) is the fact that it is orally active and is expected to be resistant to proteolytic enzymes, circumventing an important problem associated with the use of peptides. This article briefly reviews in vitro and in vivo cardiovascular and renal effects of AVE 0991. Moreover, we are pointing to the evidence that ACE2-Ang-(1-7)-Mas axis may represent a putative target for the development of new cardiovascular drugs.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Up-regulation of the Angiotensin II Type 1 Receptor by the MAS Proto-oncogene Is Due to Constitutive Activation of Gq/G11 by MAS

Coexpression of the MAS proto-oncogene with the angiotensin II type 1 (AT(1)) receptor in CHO-K1 cells has been reported to increase the number of [(3)H]angiotensin II-binding sites, although MAS does not bind [(3)H]angiotensin II. In HEK293 cells stably expressing AT(1) receptor-cyan fluorescent protein (CFP), MAS-yellow fluorescent protein (YFP) expression from an inducible locus caused strong up-regulation of AT(1) receptor-CFP amounts and [(3)H]angiotensin II binding levels. The time course of AT(1) receptor-CFP up-regulation was also markedly slower than that of induction of MAS expression. These effects were not mimicked by induced expression of I138D MAS-YFP, a mutant unable to cause constitutive loading of [(35)S]guanosine 5'-O-(thiotriphosphate) onto the phospholipase Cbeta-linked G protein Galpha(11). Protein kinase C (PKC) inhibitors and the selective Galpha(q)/Galpha(11) inhibitor YM-254890 fully blocked MAS-induced up-regulation of AT(1) receptor-CFP amounts, whereas the PKC activator phorbol 12-myristate 13-acetate produced strong up-regulation of AT(1) receptor-CFP without induction of MAS-YFP expression and in the presence of I138D MAS-YFP. The C-terminal tail of the AT(1) receptor is a known target for PKC-mediated phosphorylation. In cells stably expressing a C-terminally truncated version of the AT receptor, induction of MAS expression did not up-regulate the truncated construct levels. These data demonstrate that the ability of MAS to up-regulate AT(1) receptor levels reflects the constitutive capacity of MAS to activate Galpha(q)/Galpha(11) and hence stimulate PKC-dependent phosphorylation of the AT(1) receptor.

Impairment of in vitro and in vivo heart function in angiotensin-(1-7) receptor MAS knockout mice

In this study we investigated the effects of the genetic deletion of the angiotensin (Ang)-(1-7) receptor Mas on heart function. Localization of Mas in the mouse heart was evaluated by binding of rhodamine-labeled Ang-(1-7). Cardiac function was examined using isolated heart preparations. Echocardiography was used to confirm the results obtained with isolated heart studies. To elucidate the possible mechanisms involved in the cardiac phenotype observed in Mas(-/-) mice, whole-cell calcium currents in cardiomyocytes and the expression of collagen types I, III, and VI and fibronectin were analyzed. Ang-(1-7) binding showed that Mas is localized in cardiomyocytes of the mouse heart. Isolated heart techniques revealed that Mas-deficient mice present a lower systolic tension (average: 1.4+/-0.09 versus 2.1+/-0.03 g in Mas(+/+) mice), +/-dT/dt, and heart rate. A significantly higher coronary vessel resistance was also observed in Mas-deficient mice. Echocardiography revealed that hearts of Mas-deficient mice showed a significantly decreased fractional shortening, posterior wall thickness in systole and left ventricle end-diastolic dimension, and a higher left ventricle end-systolic dimension. A markedly lower global ventricular function, as defined by a higher myocardial performance index, was observed. A higher delayed time to the peak of calcium current was also observed. The changes in cardiac function could be partially explained by a marked change in collagen expression to a profibrotic profile in Mas-deficient mice. These results indicate that Ang-(1-7)-Mas axis plays a key role in the maintenance of the structure and function of the heart.

Actions of polypeptides at the neuromuscular junction

The effects of several polypeptides, e.g. angiotensin II, substance P, oxytocin and vasopressin, on the isolated frog gastrocnemius, chick biventer cervicis and rat hemodiaphragm preparations were studied using electrophysiological and neurochemical techniques. The effects of angiotensin II, substance P, oxytocin and vasopressin on neuromuscular transmission and muscle contraction were investigated by studying the following parameters: the directly and indirectly-elicited twitch and tetanic contractions, nerve compound action potential, uptake of 3H-methylcholine into nerve-muscle preparations, the contractures produced by depolarizing drugs, e.g. ACh or TEA. The results showed that angiotensin II (10(-10)-10(-6) M) and substance P (10(-7)-10(-6) M) enhanced neuromuscular transmission and muscle contraction by increasing the amplitudes of the indirectly-elicited twitch and tetanic contractions. Oxytocin and vasopressin (1-100 mU/ml-1) both depressed neuromuscular transmission by reducing the contractile and electrical response in the frog, chick and rat skeletal muscle. It was concluded that, like their effects on ganglionic transmission, the peptides can modify neuromuscular transmission. The mechanism by which these peptides produce their effects may be dependent on external calcium concentration. These peptides may affect both pre- and postjunctional mechanisms; prejunctionally by increasing/decreasing the release of ACh, and postjunctionally by affecting the sensitivity of the postjunctional membrane to depolarizing drugs and/or producing a contracture in the skeletal muscle.