Angiotensin-(1-7) and the renin-angiotensin system

Increasing serum soluble angiotensin-converting enzyme 2 activity after intensive medical therapy is associated with better prognosis in acute decompensated heart failure

BACKGROUND

Angiotensin-converting enzyme 2 (ACE2) is an endogenous counterregulator of the renin-angiotensin system that has been recently identified in circulating form. We aimed to investigate the relationship among changes in soluble ACE2 (sACE2) activity, myocardial performance, and long-term clinical outcomes in patients with acute decompensated heart failure (ADHF). We hypothesized that increasing sACE2 activity levels during intensive medical treatment are associated with improved myocardial performance and long-term clinical outcomes.

METHODS AND RESULTS

In 70 patients admitted to the intensive care unit with ADHF, serum sACE2 activity levels, echocardiographic data, and hemodynamic variables were collected within 12 hours of admission (n = 70) and 48-72 hours after intensive medical treatment (n = 57). The median [interquartile range] baseline and 48-72-hour serum sACE2 activity levels were 32 [23-43] ng/mL and 40 [28-60] ng/mL, respectively. Baseline serum sACE2 activity levels correlated with surrogate measures of right ventricular diastolic dysfunction, including right atrial volume index (RAVi; r = 0.31; P = .010), tricuspid E/A ratio (r = 0.39; P = .007), and B-type natriuretic peptide (r = 0.32; P = .008). However, there were no correlations between serum sACE2 and left ventricular systolic or diastolic dysfunction. After intensive medical therapy, a 50% increase in baseline serum sACE2 levels predicted a significant reduction in risk of death, cardiac transplantation, or ADHF rehospitalization, including after adjustment for baseline age, RAVi, and BNP levels (hazard ratio 0.35, 95% confidence interval 0.12-0.84; P = .018).

CONCLUSIONS

In patients admitted with ADHF, increasing serum sACE2 activity levels during intensive medical therapy predict improved outcomes independently from underlying cardiac indices.

Non-canonical signalling and roles of the vasoactive peptides angiotensins and kinins

GPCRs (G-protein-coupled receptors) are among the most important targets for drug discovery due to their ubiquitous expression and participation in cellular events under both healthy and disease conditions. These receptors can be activated by a plethora of ligands, such as ions, odorants, small ligands and peptides, including angiotensins and kinins, which are vasoactive peptides that are classically involved in the pathophysiology of cardiovascular events. These peptides and their corresponding GPCRs have been reported to play roles in other systems and under pathophysiological conditions, such as cancer, central nervous system disorders, metabolic dysfunction and bone resorption. More recently, new mechanisms have been described for the functional regulation of GPCRs, including the transactivation of other signal transduction receptors and the activation of G-protein-independent pathways. The existence of such alternative mechanisms for signal transduction and the discovery of agonists that can preferentially trigger one signalling pathway over other pathways (called biased agonists) have opened new perspectives for the discovery and development of drugs with a higher specificity of action and, therefore, fewer side effects. The present review summarizes the current knowledge on the non-canonical signalling and roles of angiotensins and kinins.

Angiotensin II receptor antagonists in acute coronary syndromes

BACKGROUND

It is well known that inappropriate or exaggerated activity of the renin-angiotensin system might contribute to the development of systemic hypertension with consequent organ injury and associated increased risk of acute cardiovascular (CV) diseases. This review will discuss evidence form basic research and clinical studies, investigating the efficacy of angiotensin II receptor blockers (ARBs) in the management of acute coronary syndromes (ACS).

MATERIALS AND METHODS

This narrative review is based on the material found on MEDLINE and PubMed up to June 2013. We looked for the terms 'angiotensin, AT1 receptor, ACE inhibitors' in combination with 'acute coronary syndromes, acute myocardial infarction, pathophysiology'.

RESULTS

Preclinical studies showed relevant protective effects of ARBs to reduce adverse cardiac remodelling in animal models of acute cardiac ischaemia. However, although recommended in Consensus guidelines as a good alternative to angiotensin-converting enzyme inhibitors (ACEIs), clinical studies did not confirm a superior efficacy of the ARBs as compared to ACEIs. As a matter of fact for some authors, these drugs might potentially have deleterious effects increasing the CV risk.

CONCLUSIONS

Emerging evidence from clinical trials suggests that the use of ARBs in ACS might be controversial, and caution should be used for their clinical use to replace ACEIs in ACS.

The role of renin-angiotensin system in cellular differentiation: implications in pancreatic islet cell development and islet transplantation

In addition to the well-characterized circulating renin-angiotensin system (RAS), local RAS has been identified recently in diverse tissues and organs. The presence of key components of the RAS in local tissues is important for our understanding of the patho-physiological mechanism(s) of several metabolic diseases, and may serve as a major therapeutic target for cardiometabolic syndromes. Locally generated and physiologically active RAS components have functions that are distinct from the classical vasoconstriction and fluid homeostasis actions of systemic RAS and cater specifically for local tissues. Local RAS can affect islet-cell function and structure in the adult pancreas as well as proliferation and differentiation of pancreatic stem/progenitor cells during development. Differentiation of stem/progenitor cells into insulin-expressing cells suitable for therapeutic transplantation offers a desperately needed new approach for replacement of glucose-responsive insulin producing cells in diabetic patients. Given that the generation of functional and transplantable islet cells has proven to be difficult, elucidation of RAS involvement in cellular regeneration and differentiation may propel pancreatic stem/progenitor cell development and thus β-cell regeneration forward. This review provides a critical appraisal of current research progress on the role of the RAS, including the newly characterized ACE2/Ang-(1-7)/Mas axis in the proliferation, differentiation, and maturation of pancreatic stem/progenitor cells. It is thus plausible to propose that the AT1 stimulation could be a repair mechanism involving the AT2R as well as the ACE2/Ang-(1-7)/Mas axis in directing β-cell development in diabetic patients using genetic and pharmaceutical manipulation of the RAS.

High glucose activates the alternative ACE2/Ang-(1-7)/Mas and APN/Ang IV/IRAP RAS axes in pancreatic β-cells

The activation of the classical angiotensin (Ang)-converting enzyme (ACE)/Ang II/Ang II type 1 receptor (AT1R) axis of the renin-angiotensin system (RAS) has been associated with islet dysfunction and insulin resistance. Hyperglycaemia, hypertension and obesity, major components of metabolic syndrome, are all associated with increased systemic and tissue levels of Ang II. Whereas it is well established that Ang II, by binding to AT1R, impairs glucose-stimulated insulin secretion and insulin signaling, the contribution of alternative RAS axes to β-cell function remains to be fully elucidated. In this study, using the BRIN-BD11 rat insulinoma cell line, we i) examined the basal expression levels of components of classical and alternative RAS axes and ii) investigated the effects of normal (5.5 mM) and elevated (11, 15, 25 mM) glucose concentrations on their expression and/or enzymatic activity by means of reverse transcription quantitative PCR (RT-qPCR), immunoblot analysis and enzymatic activity assays. The results correlated with the insulin production and release. Essential components of all RAS axes were found to be expressed in the BRIN-BD11 cells. Components of the alternative RAS axes, ACE2, neutral endopeptidase 24.11, Mas receptor (Mas), aminopeptidases A (APA) and N (APN) and insulin-regulated aminopeptidase (IRAP) showed an increased expression/activity in response to high glucose. These alterations were paralleled by the glucose-dependent increase in insulin production and release. By contrast, components of the classical RAS axis, ACE, AT1R and Ang II type 2 receptor (AT2R), remained largely unaffected under these conditions. Glucose induced the activation of the alternative ACE2/Ang-(1-7)/Mas and APN/Ang IV/IRAP RAS axes simultaneously with the stimulation of insulin production/release. Our data suggest the existence of a functional link between the local RAS axis and pancreatic β-cell function; however, further studies are required to confirm this hypothesis.

Angiotensin peptides and nitric oxide in cardiovascular disease

SIGNIFICANCE

The renin-angiotensin system (RAS) plays an important role in the normal control of cardiovascular and renal function in the healthy state and is a contributing factor in the development and progression of various types of cardiovascular diseases (CVD), including hypertension, diabetes, and heart failure.

RECENT ADVANCES

Evidence suggests that a balance between activation of the ACE/Ang II/AT1 receptor axis and the ACE2/Ang-(1-7)/Mas receptor axis is important for the function of the heart, kidney, and autonomic nervous system control of the circulation in the normal healthy state. An imbalance in these opposing pathways toward the ACE/Ang II/AT1 receptor axis is associated with CVD. The key component of this imbalance with respect to neural control of the circulation is the negative interaction between oxidative and NO• mechanisms, which leads to enhanced sympathetic tone and activation in disease conditions such as hypertension and heart failure.

CRITICAL ISSUES

The key mechanisms that disrupt normal regulation of Ang II and Ang-(1-7) signaling and promote pathogenesis of CVD at all organ levels remain poorly understood. The reciprocal relation between ACE and ACE2 expression and function suggests they are controlled interdependently at pre- and post-translational levels. Insights from neural studies suggest that an interaction between oxidative and nitrosative pathways may be key.

FUTURE DIRECTIONS

The role of redox mechanisms in the control of expression and activity of RAS enzymes and Ang receptors may provide important insight into the function of local tissue RAS in health and disease.

The renin angiotensin system regulates Kupffer cells in colorectal liver metastases

Blockade of the renin angiotensin system (RAS) can inhibit tumor growth and this may be mediated via undefined immunomodulatory actions. This study investigated the effects of RAS blockade on liver macrophages (Kupffer cells; KCs) in an orthotopic murine model of colorectal cancer (CRC) liver metastases. Here we showed that pharmacological targeting of the RAS [ANG II (31.25 µg/kg/h i.p.), ANG-(1-7) (24 µg/kg/h i.p.) or the ACE inhibitor; captopril (750 mg/kg/d i.p.)] altered endogenous KC numbers in the tumor-bearing liver throughout metastatic growth. Captopril, and to a lesser extent ANG-(1-7), increased KC numbers in the liver but not tumor. KCs were found to express the key RAS components: ACE and AT1R. Treatment with captopril and ANG II increased the number of AT1R-expressing KCs, although total KC numbers were not affected by ANG II. Captopril (0.1 µM) also increased macrophage invasion in vitro. Additionally, captopril was administered with KC depletion before tumor induction (day 0) or at established metastatic growth (day 18) using gadolinium chloride (GdCl 3; 20 mg/kg). Livers were collected at day 21 and quantitative stereology used as a measure of tumor burden. Captopril reduced growth of CRC liver metastases. However, when captopril was combined with early KC depletion (day 0) tumor growth was significantly increased compared with captopril alone. In contrast, late KC depletion (day 18) failed to influence the anti-tumor effects of captopril. The result of these studies suggests that manipulation of the RAS can alter KC numbers and may subsequently influence progression of CRC liver metastases.

Altered regional blood flow distribution in Mas-deficient mice

BACKGROUND

We have recently shown that the acute infusion of angiotensin-(1-7) [Ang-(1-7)] or chronic increase in plasma Ang-(1-7) produces important changes in regional blood flow in rats.

METHODS

To further assess whether these changes are related to Mas, in this study hemodynamic measurements were performed in Ang-(1-7) receptor Mas knockout C57BL/6 (Mas-KO) mice and age-matched wild type (WT) control mice, using fluorescent microspheres.

RESULTS

Mean arterial pressure in urethane-anesthetized Mas-KO mice (12-16 weeks old) did not differ from that in WT mice (79 ± 2 and 80 ± 2 mmHg respectively). However, pronounced differences were observed in other hemodynamic measurements. Mas-KO mice exhibited a significant decrease in stroke volume (0.03 ± 0.01 versus 0.05 ± 0.01 ml/beat in WT) and decreased cardiac index (0.81 ± 0.08 versus 1.24 ± 0.24 ml/min/g in WT). Strikingly, Mas-KO mice exhibited a marked increase in vascular resistance and a decrease in blood flow in the kidney, lung, adrenal gland, mesentery, spleen and brown fat tissue. The decrease in blood flow ranged from 34% (spleen) to 55% (brown fat tissue).

CONCLUSION

These results suggest that the Ang-(1-7)/Mas axis plays an important role in regional and systemic hemodynamic adjustments in mice.

Angiotensin-converting enzyme 2, angiotensin-(1-7) and Mas: new players of the renin-angiotensin system

Angiotensin (Ang)-(1-7) is now recognized as a biologically active component of the renin-angiotensin system (RAS). Ang-(1-7) appears to play a central role in the RAS because it exerts a vast array of actions, many of them opposite to those attributed to the main effector peptide of the RAS, Ang II. The discovery of the Ang-converting enzyme (ACE) homolog ACE2 brought to light an important metabolic pathway responsible for Ang-(1-7) synthesis. This enzyme can form Ang-(1-7) from Ang II or less efficiently through hydrolysis of Ang I to Ang-(1-9) with subsequent Ang-(1-7) formation by ACE. In addition, it is now well established that the G protein-coupled receptor Mas is a functional binding site for Ang-(1-7). Thus, the axis formed by ACE2/Ang-(1-7)/Mas appears to represent an endogenous counterregulatory pathway within the RAS, the actions of which are in opposition to the vasoconstrictor/proliferative arm of the RAS consisting of ACE, Ang II, and AT(1) receptor. In this brief review, we will discuss recent findings related to the biological role of the ACE2/Ang-(1-7)/Mas arm in the cardiovascular and renal systems, as well as in metabolism. In addition, we will highlight the potential interactions of Ang-(1-7) and Mas with AT(1) and AT(2) receptors.

Cardiac-autonomic imbalance and baroreflex dysfunction in the renovascular Angiotensin-dependent hypertensive mouse

Mouse models provide powerful tools for studying the mechanisms underlying the dysfunction of the autonomic reflex control of cardiovascular function and those involved in cardiovascular diseases. The established murine model of two-kidney, one-clip (2K1C) angiotensin II-dependent hypertension represents a useful tool for studying the neural control of cardiovascular function. In this paper, we discuss the main contributions from our laboratory and others regarding cardiac-autonomic imbalance and baroreflex dysfunction. We show recent data from the angiotensin-dependent hypertensive mouse demonstrating DNA damage and oxidative stress using the comet assay and flow cytometry, respectively. Finally, we highlight the relationships between angiotensin and peripheral and central nervous system areas of cardiovascular control and oxidative stress in the 2K1C hypertensive mouse.

Presence of functional angiotensin II receptor and angiotensin converting enzyme in the aorta of the snake Bothrops jararaca

AIM

Angiotensin II (Ang II) interacts with AT(1) and AT(2) receptors and, in some vertebrates, with an Ang II binding site showing low affinity for AT(1) and AT(2) receptor antagonists. This study was carried out to characterize the Ang II receptor, and the presence of an angiotensin-converting enzyme (ACE) in the aorta of the Bothrops jararaca snake.

MAIN METHOD

Contraction induced by Ang I or II in aortic ring from the snake was evaluated in the absence or in the presence of ACE-blocker or Ang II antagonists.

KEY FINDINGS

Ang II analogs, modified at positions 1 and 5, induced vasoconstriction with differences in their potencies. The relative rank order was: [Asp(1), Val(5)] Ang II=[Asp(1), Ile(5)] Ang II>>>[Asn(1), Val(5)] Ang II. ACE-like activity was detected, as well as an Ang II receptor with low affinity for AT(1) and AT(2) selective receptor antagonists (pK(B) values of 5.62±0.23 and 5.08±0.25). A disulfide reducing agent almost abolished the Ang II effect, while an alpha adrenoceptor antagonist, or removing the endothelium, did not modify the Ang II effect. These results indicate that the B. jararaca aorta has an Ang II receptor pharmacologically distinct from AT(1) and AT(2) receptors, and the vasoconstrictor effect observed is independent of catecholamine or endothelium modulation. ACE and the AT receptor in the aorta of B. jararaca may be part of a tissue renin-angiotensin system.

SIGNIFICANCE

The data contribute to the knowledge of the renin-angiotensin system in vertebrate species, and provide insight into the understanding of snake Ang II receptor characteristics and diversity.

Exercise induces renin-angiotensin system unbalance and high collagen expression in the heart of Mas-deficient mice

The renin-angiotensin system (RAS) is involved in the cardiac and vascular remodeling associated with cardiovascular diseases. Angiotensin (Ang) II/AT(1) axis is known to promote cardiac hypertrophy and collagen deposition. In contrast, Ang-(1-7)/Mas axis opposes Ang II effects in the heart producing anti-trophic and anti-fibrotic effects. Exercise training is known to induce cardiac remodeling with physiological hypertrophy without fibrosis. We hypothesize that cardiac remodeling induced by chronic exercise depends on the action of Ang-(1-7)/Mas axis. Thus, we evaluated the effect of exercise training on collagen deposition and RAS components in the heart of FVB/N mice lacking Mas receptor (Mas-KO). Male wild-type and Mas-KO mice were subjected to a moderate-intense swimming exercise training for 6 weeks. The left ventricle (LV) of the animals was sectioned and submitted to qRT-PCR and histological analysis. Circulating and tissue angiotensin peptides were measured by RIA. Sedentary Mas-KO presented a higher circulating Ang II/Ang-(1-7) ratio and an increased ACE2 expression in the LV. Physical training induced in Mas-KO and WT a similar cardiac hypertrophy accompanied by a pronounced increase in collagen I and III mRNA expression. Trained Mas-KO and trained WT presented increased Ang-(1-7) in the blood. However, only in trained-WT there was an increase in Ang-(1-7) in the LV. In summary, we showed that deletion of Mas in FVB/N mice produced an unbalance in RAS equilibrium increasing Ang II/AT(1) arm and inducing deleterious cardiac effects as deposition of extracellular matrix proteins. These data indicate that Ang-(1-7)/Mas axis is an important counter-regulatory mechanism in physical training mediate cardiac adaptations.

The renin-angiotensin system in thyroid disorders and its role in cardiovascular and renal manifestations

Thyroid disorders are among the most common endocrine diseases and affect virtually all physiological systems, with an especially marked impact on cardiovascular and renal systems. This review summarizes the effects of thyroid hormones on the renin-angiotensin system (RAS) and the participation of the RAS in the cardiovascular and renal manifestations of thyroid disorders. Thyroid hormones are important regulators of cardiac and renal mass, vascular function, renal sodium handling, and consequently blood pressure (BP). The RAS acts globally to control cardiovascular and renal functions, while RAS components act systemically and locally in individual organs. Various authors have implicated the systemic and local RAS in the mediation of functional and structural changes in cardiovascular and renal tissues due to abnormal thyroid hormone levels. This review analyzes the influence of thyroid hormones on RAS components and discusses the role of the RAS in BP, cardiac mass, vascular function, and renal abnormalities in thyroid disorders.

Granulocyte colony stimulating factor prevents kidney infarction and attenuates renovascular hypertension

BACKGROUND

G-CSF is a critical regulator of hematopoietic cell proliferation, differentiation and survival. It has been reported that G-CSF attenuates renal injury during acute ischemia-reperfusion. In this study we evaluated the effects of G-CSF on the renal and cardiovascular systems of 2K1C hypertensive mice.

METHODS

Male C57BL/6 mice were subjected to left renal artery clipping (2K1C) or sham operation and were then administered G-CSF (100 μg/kg/day) or vehicle for 14 days.

RESULTS

Arterial pressure was higher in 2K1C + vehicle animals than in 2K1C + G-CSF (150±5 vs. 129±2 mmHg, p<0.01, n=8). Plasma angiotensin I, II and 1-7 concentrations were significantly increased in 2K1C + Vehicle when compared to the normotensive Sham group. G-CSF prevented the increase of these vasoactive peptides. The clipped kidney/contralateral kidney weight ratio showed a less atrophy of the ischemic kidney in the treated group (0.50±0.02 vs. 0.66±0.01, p<0.05). The infarction area in the clipped kidney was completely prevented in 7 out of 8 2K1C + G-CSF mice. Administration of G-CSF protected the clipped kidney from apoptosis.

CONCLUSION

Our data indicate that G-CSF prevents kidney infarction and markedly attenuates the increases in plasma angiotensin levels and hypertension in 2K1C mice, reinforcing the protective effect of G-CSF on kidney ischemia.

Dual RAS blockade normalizes angiotensin-converting enzyme-2 expression and prevents hypertension and tubular apoptosis in Akita angiotensinogen-transgenic mice

We investigated the effects of dual renin-angiotensin system (RAS) blockade on angiotensin-converting enzyme-2 (Ace2) expression, hypertension, and renal proximal tubular cell (RPTC) apoptosis in type 1 diabetic Akita angiotensinogen (Agt)-transgenic (Tg) mice that specifically overexpress Agt in their RPTCs. Adult (11 wk old) male Akita and Akita Agt-Tg mice were treated with two RAS blockers (ANG II receptor type 1 blocker losartan, 30 mg·kg(-1)·day(-1)) and angiotensin-converting enzyme (ACE) inhibitor perindopril (4 mg·kg(-1)·day(-1)) in drinking water. Same-age non-Akita littermates and Agt-Tg mice served as controls. Blood pressure, blood glucose, and albuminuria were monitored weekly. The animals were euthanized at age 16 wk. The left kidneys were processed for immunohistochemistry and apoptosis studies. Renal proximal tubules were isolated from the right kidneys to assess gene and protein expression. Urinary ANG II and ANG 1-7 were quantified by ELISA. RAS blockade normalized renal Ace2 expression and urinary ANG 1-7 levels (both of which were low in untreated Akita and Akita Agt-Tg), prevented hypertension, albuminuria, tubulointerstitial fibrosis and tubular apoptosis, and inhibited profibrotic and proapoptotic gene expression in RPTCs of Akita and Akita Agt-Tg mice compared with non-Akita controls. Our results demonstrate the effectiveness of RAS blockade in preventing intrarenal RAS activation, hypertension, and nephropathy progression in diabetes and support the important role of intrarenal Ace2 expression in modulating hypertension and renal injury in diabetes.

Differential mechanisms of ang (1-7)-mediated vasodepressor effect in adult and aged candesartan-treated rats

Angiotensin (1-7) (Ang (1-7)) causes vasodilator effects in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) via angiotensin type 2 receptors (AT₂R). However, the role of vascular AT₂R in aging is not known. Therefore, we examined the effect of aging on Ang (1-7)-mediated vasodepressor effects and vascular angiotensin receptor localization in aging. Blood pressure was measured in conscious adult (~17 weeks) and aged (~19 months) normotensive rats that received drug combinations in a randomised fashion over a 4-day protocol: (i) Ang (1-7) alone, (ii) AT₁R antagonist, candesartan, alone, (iii) Ang (1-7) and candesartan, or (iv) Ang-(1-7), candesartan, and the AT₂R antagonist, PD123319. In a separate group of animals, the specific MasR antagonist, A779, was administered in place of PD123319. Receptor localisation was also assessed in aortic sections from adult and aged WKY rats by immunofluorescence. Ang (1-7) reduced blood pressure (~15 mmHg) in adult normotensive rats although this effect was dependant on the background dose of candesartan. This depressor effect was reversed by AT₂R blockade. In aged rats, the depressor effect of Ang (1-7) was evident but was now inhibited by either AT₂R blockade or MasR blockade. At the same time, AT₂R, MasR, and ACE2 immunoreactivity was markedly elevated in aortic sections from aged animals. These results indicate that the Ang (1-7)-mediated depressor effect was preserved in aged animals. Whereas Ang (1-7) effects were mediated exclusively via stimulation of AT₂R in adult WKY, with aging the vasodepressor effect of Ang (1-7) involved both AT₂R and MasR.

New insights and perspectives on intrarenal renin-angiotensin system: focus on intracrine/intracellular angiotensin II

Although renin, the rate-limiting enzyme of the renin-angiotensin system (RAS), was first discovered by Robert Tigerstedt and Bergman more than a century ago, the research on the RAS still remains stronger than ever. The RAS, once considered to be an endocrine system, is now widely recognized as dual (circulating and local/tissue) or multiple hormonal systems (endocrine, paracrine and intracrine). In addition to the classical renin/angiotensin I-converting enzyme (ACE)/angiotensin II (Ang II)/Ang II receptor (AT₁/AT₂) axis, the prorenin/(Pro)renin receptor (PRR)/MAP kinase axis, the ACE2/Ang (1-7)/Mas receptor axis, and the Ang IV/AT₄/insulin-regulated aminopeptidase (IRAP) axis have recently been discovered. Furthermore, the roles of the evolving RAS have been extended far beyond blood pressure control, aldosterone synthesis, and body fluid and electrolyte homeostasis. Indeed, novel actions and underlying signaling mechanisms for each member of the RAS in physiology and diseases are continuously uncovered. However, many challenges still remain in the RAS research field despite of more than one century's research effort. It is expected that the research on the expanded RAS will continue to play a prominent role in cardiovascular, renal and hypertension research. The purpose of this article is to review the progress recently being made in the RAS research, with special emphasis on the local RAS in the kidney and the newly discovered prorenin/PRR/MAP kinase axis, the ACE2/Ang (1-7)/Mas receptor axis, the Ang IV/AT₄/IRAP axis, and intracrine/intracellular Ang II. The improved knowledge of the expanded RAS will help us better understand how the classical renin/ACE/Ang II/AT₁ receptor axis, extracellular and/or intracellular origin, interacts with other novel RAS axes to regulate blood pressure and cardiovascular and kidney function in both physiological and diseased states.

Altered efficacy of AT1R-targeted treatment after spontaneous cancer cell-AT1R upregulation

BACKGROUND

Targeting of the renin angiotensin system (RAS) reduces tumour growth in experimental models of cancer. We aimed to establish if combined targeting of the 'classical' and 'alternative' arms of the RAS could result in synergistic inhibition of colorectal cancer (CRC) liver metastases.

METHODS

Immediately following induction of CRC liver metastases through intrasplenic injection of murine CRC cells, treatment with irbesartan (AT1R blocker; 50 mg/kg/day s.c.), captopril (ACE inhibitor; 750 mg/kg/day i.p.), CGP42112A (AT2R agonist; 0.6 μg/kg/hr i.p.), and/or ANG-(1-7) (24 μg/kg/hr i.p.) began and continued for 21 days. Liver to body weight ratio and/or stereology were used as a measure of tumour burden. Immunohistochemistry was used to determine AT1R and VEGF expression as well as proliferation (Ki67), apoptosis (active caspase 3) and angiogenesis (CD34).

RESULTS

Combined RAS therapies failed to improve upon single arm therapies. However, while irbesartan previously inhibited tumour growth in this model, in the current experiments irbesartan failed to affect tumour burden. Subsequent analysis showed a cancer-cell specific upregulation of the angiotensin II type I receptor (AT1R) in irbesartan-insensitive compared to irbesartan-sensitive tumours. The upregulation of AT1R was associated with an increase in proliferation and VEGF expression by cancer cells. While animals bearing irbesartan-sensitive tumours showed a marked decrease in the number of proliferating cells in the liver and VEGF-expressing infiltrating cells in the tumour following AT1R treatment, these were unchanged by treatment in animals bearing irbesartan-insensitive (high AT1R expressing) tumours.

CONCLUSIONS

Although the results do not support increased efficacy of combined treatment, they provide intriguing evidence of the importance of RAS expression in determining patient response and tumour growth potential and suggest that components of the RAS could be used as biomarkers to aid in patient selection.

(Pro)renin Receptor in Kidney Development and Disease

The renin-angiotensin system (RAS), a key regulator of the blood pressure and fluid/electrolyte homeostasis, also plays a critical role in kidney development. All the components of the RAS are expressed in the developing metanephros. Moreover, mutations in the genes encoding components of the RAS in mice or humans are associated with a broad spectrum of congenital anomalies of the kidney and urinary tract (CAKUT). These forms of CAKUT include renal papillary hypoplasia, hydronephrosis, duplicated collecting system, renal tubular dysgenesis, renal vascular abnormalities, and aberrant glomerulogenesis. Emerging evidence indicates that (pro)renin receptor (PRR), a novel component of the RAS, is essential for proper kidney development and that aberrant PRR signaling is causally linked to cardiovascular and renal disease. This paper describes the role of the RAS in kidney development and highlights emerging insights into the cellular and molecular mechanisms by which the PRR may regulate this critical morphogenetic process.

ACE2 improves right ventricular function in a pressure overload model

BACKGROUND

Right ventricular (RV) dysfunction is a complication of pulmonary hypertension and portends a poor prognosis. Pharmacological therapies targeting RV function in pulmonary hypertension may reduce symptoms, improve hemodynamics, and potentially increase survival. We hypothesize that recombinant human angiotensin-converting enzyme 2 (rhACE2) will improve RV function in a pressure overload model.

RESULTS

rhACE2 administered at 1.8 mg/kg/day improved RV systolic and diastolic function in pulmonary artery banded mice as measured by in vivo hemodynamics. Specifically, rhACE2 increased RV ejection fraction and decreased RV end diastolic pressure and diastolic time constant (p<0.05). In addition, rhACE2 decreased RV hypertrophy as measured by RV/LV+S ratio (p<0.05). There were no significant negative effects of rhACE2 administration on LV function. rhACE2 had no significant effect on fibrosis as measured by trichrome staining and collagen1α1 expression. In pulmonary artery banded mice, rhACE2 increased Mas receptor expression and normalized connexin 37 expression.

CONCLUSION

In a mouse RV load-stress model of early heart failure, rhACE2 diminished RV hypertrophy and improved RV systolic and diastolic function in association with a marker of intercellular communication. rhACE2 may be a novel treatment for RV failure.

An update on the islet renin-angiotensin system

The traditional renin-angiotensin system (RAS) components have been studied extensively since the rate-limiting component of RAS, renin, was first characterized. The ongoing identification of various novel RAS components and signaling pathways continues to elaborate the complexity of this system. Regulation of RAS according to the conventional and contemporary views of its functions in various tissues under pathophysiological conditions is a main treatment strategy for many metabolic diseases. The local pancreatic RAS, first proposed to exist in pancreatic islets two decades ago, could regulate islet function and glycemic control via influences on islet cell mass, inflammation, and ion channels. Insulin secretion, the major function of pancreatic islets, is controlled by numerous factors. Among these factors and of particular interest are glucagon-like peptide-1 (GLP-1) and vitamin D, which may regulate islet function by directly binding receptors on islet beta cells. These factors may work with local RAS signaling in islets to protect and maintain islet function under diabetic and hyperglycemic conditions. In this concise review, the local islet RAS will be discussed with particular attention being paid to recent notable findings.

Angiotensin II and angiotensin-1-7 redox signaling in the central nervous system

Reactive oxygen species (ROS) are important intra-neuronal signaling intermediates in angiotensin II (AngII)-related neuro-cardiovascular diseases associated with excessive sympathoexcitation, including hypertension and heart failure. ROS-sensitive effector mechanisms, such as modulation of ion channel activity, indicate that elevated levels of ROS increase neuronal activity. Nitric oxide, which may work to counter the effects of ROS, particularly superoxide, has been identified as a signaling molecule in angiotensin-1-7 (Ang-(1-7)) stimulated neurons. This review focuses on recent studies that have revealed details on the AngII-activated sources of ROS, the downstream redox-sensitive effectors, Ang-(1-7)-stimulated increase in nitric oxide, and the neuro-cardiovascular (patho)physiological responses modulated by these reactive species. Understanding these intra-neuronal signaling mechanisms should provide insight for the development of new redox-based therapeutics for the improved treatment of angiotensin-dependent neuro-cardiovascular diseases.

Novel regulators and drug targets of cardiac hypertrophy

Cardiac hypertrophy is classically considered as an adaptive and compensatory response enabling cardiomyocytes to increase their work output and thus cardiac function. Biomechanical stress and neurohumoral activation are the most important triggers of pathological hypertrophy and the transition of cardiac hypertrophy to heart failure. Several novel regulators and putative drug targets of cardiac hypertrophy have been found by using gene-modified and acquired models of cardiac hypertrophy. Recent studies have also revealed distinct patterns of cardiac substrate utilization in cardiac hypertrophy and heart failure. The use of novel systems biology techniques such as metabolomics may therefore in future provide insights into the metabolic processes and cardiovascular biology related to cardiac hypertrophy and also extend the ability to discover circulating biomarkers for cardiovascular diseases. The present review discusses current knowledge on molecular mechanisms of cardiac hypertrophy, with special emphasis on novel regulators and putative drug targets of cardiac hypertrophy such as the tissue renin-angiotensin-aldosterone system, calcineurin/nuclear factor of activated T cells pathway, phosphatidylinositol 3-kinase/growth promoting protein kinase B, mammalian target of rapamycin, histone deacetylases, AMPkinases, microRNAs and angiogenetic factors.

The importance of renin-angiotensin blockade in patients with cardio-renal disease

The existence of the renin-angiotensin-aldosterone system was first postulated over 100 years ago. Following the identification of all the major components, came the discovery of their potential pathogenicity in cardiovascular and renal disease. The introduction of drugs that inhibit the synthesis or actions of this system has prompted a number of trials that have largely shaped how cardiovascular and renal disease is managed today. The continued discovery of yet more components of this system promises to further our understanding of its influence on disease processes and herald the development of more highly selective drugs, ensuring that the renin-angiotensin-aldosterone system will continue to be a key area of interest for many years to come.

Differential sympathetic activation induced by intermittent hypoxia and sleep loss in rats: Action of angiotensin (1-7)

The present study attempted to evaluate the effects of chronic intermittent hypoxia (CIH) associated with sleep restriction in hemodynamic parameters and the plasma renin-angiotensin system. Wistar-Hannover rats were submitted to isolated CIH exposure (1000-1600 h), sleep restriction (1600-1000 h), defined as 18-h paradoxical sleep deprivation followed by 6-h sleep permission period and CIH associated to sleep restriction for 21 days. The CIH and sleep restriction group showed a preferential increase in renal sympathetic nervous system (rSNA) associated with a reduction in plasma angiotensin (1-7) concentrations. However, CIH-sleep restriction rats did not modify rSNA and showed a higher angiotensin (1-7) concentration when compared to isolated CIH and sleep restriction. These results suggest that CIH and sleep restriction impaired the cardiovascular system, and its association to sleep loss can modify these effects by partially restoring circulating angiotensin (1-7).

Angiotensin II receptors and drug discovery in cardiovascular disease

Hypertension is one of the cardiovascular diseases that might cause cardiovascular remodeling and endothelial dysfunction besides high blood pressure. Angiotensin II (Ang II) receptors are implicated in hypertension. Genetic and epigenetic manipulations of the Ang II receptors play a crucial part in the programming of cardiovascular diseases, and certain variants of the Ang II type 1 and Ang II type 2 receptors are constitutively predisposed to higher cardiovascular risk and hypertension. In this review, we focus on the expression, mode of action of Ang II receptors, and their role in programming the cardiovascular diseases in utero. In addition, we discuss possible therapeutic interventions of Ang II stimulation. Collectively, this information might lead us to new drug designs against cardiovascular diseases.

Liver regeneration and tumour stimulation: implications of the renin-angiotensin system

Liver resection is the most effective treatment for primary liver tumours and metastasis to the liver, and remains the only potentially long-term curative therapy for patients with colorectal cancer (CRC) liver metastases. Nevertheless, there is a significant incidence of tumour recurrence following liver resection. Cellular and molecular changes resulting from resection and the subsequent liver regeneration process may influence the kinetics of tumour growth, contributing to recurrence. Although commonly associated with the systemic homeostasis of blood pressure, fluid and electrolyte, the renin-angiotensin system (RAS) has recently been shown to play a role in regulating cell proliferation, apoptosis and angiogenesis in local organs as well as in malignancies. An electronic search of the English literature on the role of the RAS in liver regeneration and tumourigenesis was performed using PubMed, with additional relevant articles sourced from reference lists. Studies have shown that the blockade of the RAS pathway stimulates liver regeneration and inhibits tumour progression. An understanding of the role of RAS in liver regeneration and tumourigenesis may enable alternative strategies to improve patient outcome and survival after liver resection. This review will discuss the role of the RAS in liver regeneration and in tumour recurrence post-liver resection. The potential of the RAS as a novel therapeutic target for CRC liver metastases patients undergoing liver resection will be outlined.

Altered cardiovascular reflexes responses in conscious Angiotensin-(1-7) receptor Mas-knockout mice

This study evaluated the physiological importance of Angiotensin-(1-7) receptor Mas on reflex control of circulation. Experiments were performed in male Mas-knockout (Mas-KO) and Wild Type (WT) conscious mice (12-20 wk of age). Baroreceptor reflex was evaluated by the bradycardic response induced by phenylephrine (0.25 μg/5 μl, i.v.). Bezold-Jarisch reflex was evaluated by phenylbiguanide (0.5 μg/5 μl, i.v.) and chemoreflex by potassium cyanide (2.5 μg/5 μl, i.v.). Baseline mean arterial pressure was higher in Mas-KO (n=14) as compared with WT mice (n=18) (118±1 mmHg vs. 109±2 mmHg); however, heart rate was similar in both strains (615±30 bpm vs. 648±13 bpm). Baroreflex bradycardia was lower (0.78±0.44 ms/mmHg vs. 1.30±0.14 ms/mmHg) in Mas-KO compared with WT mice. The depressor (-17±5 mmHg vs. -45±6 mmHg) and bradycardic (-212±36 bpm vs. -391±29 bpm) components of the Bezold-Jarisch reflex were also lower in Mas-KO mice. In addition, chemoreflex pressor response (+20±3 mmHg vs. +12±0.8 mmHg) and bradycardic response (-250±74 bpm vs. -52±26 bpm) were significantly higher in Mas-KO. These results further advances previous studies by showing that the lack of Mas receptor induced important imbalance in the neural control of blood pressure, altering not only the baroreflex but also the chemo- and Bezold-Jarisch reflexes.

Angiotensin-converting enzyme (ACE) 2 overexpression ameliorates glomerular injury in a rat model of diabetic nephropathy: a comparison with ACE inhibition

The reduced expression of angiotensin-converting enzyme (ACE) 2 in the kidneys of animal models and patients with diabetes suggests ACE2 involvement in diabetic nephrology. To explore the renoprotective effects of ACE2 overexpression, ACE inhibition (ACEI) or both on diabetic nephropathy and the potential mechanisms involved, 50 Wistar rats were randomly divided into a normal group that received an injection of sodium citrate buffer and a diabetic model group that received an injection of 60 mg/kg streptozotocin. Eight wks after streptozotocin injection, the diabetic rats were divided into no treatment group, adenoviral (Ad)-ACE2 group, Ad-green flurescent protein (GFP) group, ACEI group receiving benazepril and Ad-ACE2 + ACEI group. Four wks after treatment, physical, biochemical, and renal functional and morphological parameters were measured. An experiment in cultured glomerular mesangial cells was performed to examine the effects of ACE2 on cellular proliferation, oxidative stress and collagen IV synthesis. In comparison with the Ad-GFP group, the Ad-ACE2 group exhibited reduced systolic blood pressure, urinary albumin excretion, creatinine clearance, glomeruli sclerosis index and renal malondialdehyde level; downregulated transforming growth factor (TGF)-β1, vascular endothelial growth factor (VEGF) and collagen IV protein expression; and increased renal superoxide dismutase activity. Ad-ACE2 and ACEI had similar effects, whereas combined use of Ad-ACE2 and ACEI offered no additional benefits. ACE2 transfection attenuated angiotensin (Ang) II-induced glomerular mesangial cell proliferation, oxidative stress and collagen IV protein synthesis. In conclusion, ACE2 exerts a renoprotective effect similar to that of ACEI treatment. Decreased renal Ang II, increased renal Ang-(1-7) levels, and inhibited oxidative stress were the possible mechanisms involved.

New pathways of the renin-angiotensin system: the role of ACE2 in cardiovascular pathophysiology and therapy

IMPORTANCE OF THE FIELD

The renin-angiotensin system (RAS) is nowadays an important target in cardiovascular diseases and we are currently on the verge of a new interpretation of its role in cardiovascular homeostasis, mainly due to the identification of the new axis ACE2/angiotensin 1 - 7/Mas receptor.

AREAS COVERED IN THIS REVIEW

The main aspects related to ACE2 role in cardiovascular physiology and possible pathological and therapeutic implications are reviewed.

WHAT THE READER WILL GAIN

A description of the new view of the RAS, along with the key findings that support it. In the cardiovascular system, the ACE2/angiotensin 1 - 7/Mas axis, mainly through the inhibition of fibrosis, inflammation, thrombosis and cell proliferation, modulates RAS activity with significant pathophysiological implications in clinical conditions such as hypertension, myocardial ischemia and heart failure. A more complete understanding of this axis has significant therapeutic relevance and a major effort is being carried out in order to pursue this objective.

TAKE HOME MESSAGE

There is increasing evidence that ACE2/angiotensin 1 - 7/Mas receptor axis has a key role in RAS activity regulation with significant pathophysiological implications in several disease states. A therapeutic intervention at this level may open new doors and change the current approach to RAS targeting.

Vascular Relaxation, Antihypertensive Effect, and Cardioprotection of a Novel Peptide Agonist of the Mas Receptor

Mas stimulation with angiotensin (Ang)-(1-7) produces cardioprotective effects and vasorelaxation. Using a computational discovery platform for predicting novel naturally occurring peptides that may activate G protein–coupled receptors, we discovered a novel Mas agonist peptide, CGEN-856S. An endothelium- and NO-dependent vasodilating effect was observed for CGEN-856S in thoracic aorta rings of rats (maximal value for the relaxant effect: 39.99±5.034%), which was similar to that produced by Ang-(1-7) (10 −10 to 10 −6 mol/L). In addition, the vasodilator activity of this peptide depended on a functional Mas receptor, because it was abolished in aorta rings of Mas-knockout mice. CGEN-856S appears to bind the Mas receptor at the same binding domain as Ang-(1-7), as suggested by the blocking of its vasorelaxant effect with the Ang-(1-7) analogue d -Ala 7 -Ang-(1-7), and by its competitive inhibition of Ang-(1-7) binding to Mas -transfected cells. The effect of CGEN-856S on reperfusion arrhythmias and cardiac function was studied on ischemia reperfusion of isolated rat hearts. We found that picomolar concentration of CGEN-856S (0.04 nmol/L) had an antiarrhythmogenic effect, as demonstrated by a reduction in the incidence and duration of reperfusion arrhythmias. Furthermore, acute infusion of CGEN-856S produced a shallow dose-dependent decrease in mean arterial pressure of conscious spontaneously hypertensive rats. The maximum change during infusion was observed at the highest dose. Strikingly, blood pressure continued to drop in the postinfusion period. The results presented here indicate that the novel Mas agonist, CGEN-856S, might have a therapeutic value, because it induces vasorelaxing, antihypertensive, and cardioprotective effects.

Tissue renin-angiotensin-aldosterone systems: Targets for pharmacological therapy

The renin-angiotensin-aldosterone system is one of the most important systems in cardiovascular control and in the pathogenesis of cardiovascular diseases. Therefore, it is already a very successful drug target for the therapy of these diseases. However, angiotensins are generated not only in the plasma but also locally in tissues from precursors and substrates either locally expressed or imported from the circulation. In most areas of the brain, only locally generated angiotensins can exert effects on their receptors owing to the blood-brain barrier. Other tissue renin-angiotensin-aldosterone systems are found in cardiovascular organs such as kidney, heart, and vessels and play important roles in the function of these organs and in the deleterious actions of hypertension and diabetes on these tissues. Novel components with mostly opposite actions to the classical renin-angiotensin-aldosterone systems have been described and need functional characterization to evaluate their suitability as novel drug targets.

PKA-mediated effect of MAS receptor in counteracting angiotensin II-stimulated renal Na+-ATPase

We showed previously that angiotensin-(1-7) [Ang-(1-7)] reversed stimulation of proximal tubule Na+-ATPase promoted by angiotensin II (Ang II) through a D-ala(7)-Ang-(1-7) (A779)-sensitive receptor. Here we investigated the signaling pathway coupled to this receptor. According to our data, Ang-(1-7) produces a MAS-mediated reversal of Ang II-stimulated Na+-ATPase by a Gs/PKA pathway because: (1) the Ang-(1-7) effect is reversed by GDPbetaS, an inhibitor of trimeric G protein and Gs polyclonal antibody. Cholera toxin, an activator of Gs protein, mimicked it; (2) in the presence of Ang II, Ang-(1-7) increased the PKA activity 10-fold; (3) the peptide inhibitor of PKA blocked the Ang-(1-7) effect on Ang II-stimulated Na+-ATPase; (4) Ang-(1-7) reverses the Ang II-stimulated PKC activity; (5) cAMP mimicked the Ang-(1-7) effect on the Ang II-stimulated Na+-ATPase. Our results provide new understanding about the signaling mechanisms coupled to MAS receptor-mediated renal Ang-(1-7) effects.

Infusion of angiotensin-(1-7) reduces glomerulosclerosis through counteracting angiotensin II in experimental glomerulonephritis

Recent identification of a counterregulatory axis of the renin-angiotensin system, called angiotensin-converting enzyme 2-angiotensin-(1-7) [ANG-(1-7)]-Mas receptor, may offer new targets for the treatment of renal fibrosis. We hypothesized that therapy with ANG-(1-7) would improve glomerulosclerosis through counteracting ANG II in experimental glomerulonephritis. Disease was induced in rats with the monoclonal anti-Thy-1 antibody, OX-7. Based on a three-dose pilot study, 576 microg x kg(-1) x day(-1) ANG-(1-7) was continuously infused from day 1 using osmotic pumps. Measures of glomerulosclerosis include semiquantitative scoring of matrix proteins stained for periodic acid Schiff, collagen I, and fibronectin EDA+ (FN). ANG-(1-7) treatment reduced disease-induced increases in proteinuria by 75%, glomerular periodic acid Schiff staining by 48%, collagen I by 24%, and FN by 25%. The dramatic increases in transforming growth factor-beta1, plasminogen activator inhibitor-1, FN, and collagen I mRNAs seen in disease control animals compared with normal rats were all significantly reduced by ANG-(1-7) administration (P < 0.05). These observations support our hypothesis that ANG-(1-7) has therapeutic potential for reversing glomerulosclerosis. Several results suggest ANG-(1-7) acts by counteracting ANG II effects: 1) renin expression in ANG-(1-7)-treated rats was dramatically increased as it is with ANG II blockade therapy; and 2) in vitro data indicate that ANG II-induced increases in mesangial cell proliferation and plasminogen activator inhibitor-1 overexpression are inhibited by ANG-(1-7) via its binding to a specific receptor known as Mas.

Brain-selective overexpression of human Angiotensin-converting enzyme type 2 attenuates neurogenic hypertension

RATIONALE

Angiotensin converting enzyme type 2 (ACE2) is a new member of the brain renin-angiotensin system, that might be activated by an overactive renin-angiotensin system.

OBJECTIVE

To clarify the role of central ACE2 using a new transgenic mouse model with human (h)ACE2 under the control of a synapsin promoter, allowing neuron-targeted expression in the central nervous system.

METHODS AND RESULTS

Syn-hACE2 (SA) transgenic mice exhibit high hACE2 protein expression and activity throughout the brain. Baseline hemodynamic parameters (telemetry), autonomic function, and spontaneous baroreflex sensitivity (SBRS) were not significantly different between SA mice and nontransgenic littermates. Brain-targeted ACE2 overexpression attenuated the development of neurogenic hypertension (Ang II infusion: 600 ng/kg per minute for 14 days) and the associated reduction of both SBRS and parasympathetic tone. This prevention of hypertension by ACE2 overexpression was reversed by blockade of the Ang-(1-7) receptor (d-Ala7-Ang-[1-7]; 600 ng/kg per minute). Brain angiotensin II type 2 (AT(2))/AT(1) and Mas/AT(1) receptor ratios were significantly increased in SA mice. They remained higher following Ang II infusion but were dramatically reduced after Ang-(1-7) receptor blockade. ACE2 overexpression resulted in increased NOS and NO levels in the brain, and prevented the Ang II-mediated decrease in NOS expression in regions modulating blood pressure regulation.

CONCLUSIONS

ACE2 overexpression attenuates the development of neurogenic hypertension partially by preventing the decrease in both SBRS and parasympathetic tone. These protective effects might be mediated by enhanced NO release in the brain resulting from Mas and AT(2) receptor upregulation. Taken together, our data highlight the compensatory role of central ACE2 and its potential benefits as a therapeutic target for neurogenic hypertension.

Left ventricular hypertrophy and renin-angiotensin system blockade

The renin-angiotensin system (RAS), an important control system for blood pressure and intravascular volume, also causes left ventricular hypertrophy (LVH) and fibrosis. The main causal mechanism is the increase in blood pressure, which leads to increased left ventricular wall stress; however, aldosterone release from the adrenals and (more controversially) the direct action of angiotensin II on the cardiomyocytes also play a role. Large clinical trials evaluating the blockade of the RAS with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers have demonstrated an ability to prevent progression and induce regression of left ventricular mass, thereby reducing the significant and independent cardiovascular risk conferred by LVH. Regression of left ventricular mass is also achieved by other medication classes, but the RAS blockers have an additional beneficial effect for the same blood pressure reduction, for which the mechanism is not entirely clear. Studies comparing the efficacy of angiotensin-converting enzyme inhibitors versus angiotensin receptor blockers to achieve LVH regression have not demonstrated any clear benefit of one class over the other.

Acute modulation of myocardial function by angiotensin 1-7

Angiotensin 1-7 is a bioactive heptapeptide of the renin-angiotensin system. Its cardiovascular actions have recently acquired growing relevance, mainly due to its counter-regulatory actions in the angiotensin cascade. The aim of the present study was to evaluate the actions of angiotensin 1-7 on myocardial function. Increasing concentrations of angiotensin 1-7 (10(-9) to 10(-5)M) were added to rabbit right papillary muscles: (1) in baseline conditions with intact endocardial endothelium (EE); (2) after selective removal of the EE with Triton X-100 (1s, 0.01%); (3) with intact EE in the presence of the Mas receptor antagonist A-779, the AT(1) receptor antagonist ZD-7155, the AT(2) receptor antagonist PD-123,319 or the nitric oxide synthesis inhibitor NG-nitro-l-arginine (l-NA). Concerning the effects on contractility, we observed a significant decrease on active tension, dT/dt(max), peak shortening and dL/dt(max) of -10.5+/-3.6%, -8.0+/-3.0%, -5.3+/-2.6% and -5.7+/-2.3%, respectively. There was no change on relaxation parameters, namely dT/dt(min) or dL/dt(min). Time to half relaxation was significantly decreased. The presence of ZD-7155 or PD-123,319 did not change these effects. However, angiotensin 1-7 effects on myocardial properties were abolished after selective EE removal and in the presence of A-779 or l-NA. In conclusion, in this animal species, angiotensin 1-7 through its binding to Mas receptor induces a negative inotropic effect modulated by the EE and nitric oxide and independent of AT(1) or AT(2) receptors activation. As the effects described in the present work were influenced by the endocardial endothelium, they may be disrupted in situations associated to endothelial dysfunction, as in heart failure or myocardial ischemia.

Renin-angiotensin system-growth factor cross-talk: a novel mechanism for ureteric bud morphogenesis

The renin-angiotensin system (RAS) plays a critical role in kidney development. Mutations in the genes encoding components of the RAS cause a spectrum of congenital abnormalities of the kidney and renal collecting system, ranging from hypoplasia of the renal medulla and hydronephrosis in mice to renal tubular dysgenesis in humans. However, the mechanisms by which an intact RAS controls proper renal system development and how aberrations in the RAS result in abnormal kidney and renal collecting system development are poorly understood. The renal collecting system originates from the ureteric bud (UB). A number of transcription and growth factors regulate UB branching morphogenesis to ultimately form the ureter, pelvis, calyces, medullary, and cortical collecting ducts. Importantly, UB morphogenesis is a key developmental process that controls organogenesis of the entire metanephros. This review emphasizes emerging insights into the role for the RAS in UB morphogenesis and explores the mechanisms whereby RAS regulates this important process. A conceptual framework derived from recent work indicates that cooperation between the angiotensin II AT(1) receptor and receptor tyrosine kinase signaling performs essential functions during renal collecting system development via control of UB branching morphogenesis.

Relationship between angiotensin-(1-7) and angiotensin II correlates with hemodynamic changes in human liver cirrhosis

AIM: To measure circulating angiotensins at different stages of human cirrhosis and to further evaluate a possible relationship between renin angiotensin system (RAS) components and hemodynamic changes.

METHODS: Patients were allocated into 4 groups: mild-to-moderate liver disease (MLD), advanced liver disease (ALD), patients undergoing liver transplantation, and healthy controls. Blood was collected to determine plasma renin activity (PRA), angiotensin (Ang) I, Ang II, and Ang-(1-7) levels using radioimmunoassays. During liver transplantation, hemodynamic parameters were determined and blood was simultaneously obtained from the portal vein and radial artery in order to measure RAS components.

RESULTS: PRA and angiotensins were elevated in ALD when compared to MLD and controls (P < 0.05). In contrast, Ang II was significantly reduced in MLD. Ang-(1-7)/Ang II ratios were increased in MLD when compared to controls and ALD. During transplantation, Ang II levels were lower and Ang-(1-7)/Ang II ratios were higher in the splanchnic circulation than in the peripheral circulation (0.52 ± 0.08 vs 0.38 ± 0.04, P < 0.02), whereas the peripheral circulating Ang II/Ang I ratio was elevated in comparison to splanchnic levels (0.18 ± 0.02 vs 0.13 ± 0.02, P < 0.04). Ang-(1-7)/Ang II ratios positively correlated with cardiac output (r = 0.66) and negatively correlated with systemic vascular resistance (r = -0.70).

CONCLUSION: Our findings suggest that the relationship between Ang-(1-7) and Ang II may play a role in the hemodynamic changes of human cirrhosis.

The renin-angiotensin system modulates inflammatory processes in atherosclerosis: evidence from basic research and clinical studies

Recent evidence shows that the renin-angiotensin system is a crucial player in atherosclerotic processes. The regulation of arterial blood pressure was considered from its first description of the main mechanism involved. Vasoconstriction (mediated by angiotensin II) and salt and water retention (mainly due to aldosterone) were classically considered as pivotal proatherosclerotic activities. However, basic research and animal studies strongly support angiotensin II as a proinflammatory mediator, which directly induces atherosclerotic plaque development and heart remodeling. Furthermore, angiotensin II induces proatherosclerotic cytokine and chemokine secretion and increases endothelial dysfunction. Accordingly, the pharmacological inhibition of the renin-angiotensin system improves prognosis of patients with cardiovascular disease even in settings of normal baseline blood pressure. In the present review, we focused on angiotensin-convertingenzyme (ACE) inhibitors, angiotensin II receptor blockers (ARBs), and renin inhibitors to update the direct activities of the renin-angiotensin system in inflammatory processes governing atherosclerosis.

Neuronal Angiotensin

Many tissues, including the brain, contain all components of the renin–angiotensin system and generate angiotensin peptides independent of the systemic, circulating system. Within the brain renin, some questions remain as to how the precursor, angiotensinogen, and its processing enzymes interact to produce the active compounds, angiotensin II/III, because they are rarely localized to the same brain nucleus let alone the same cell. These questions aside, there is clear evidence for actions of angiotensin peptides in regions behind the blood–brain barrier. Receptors for angiotensin peptides, including AT₁ and AT₂ receptors, are distributed in a characteristic pattern throughout the brain, with many of these sites behind the blood–brain barrier. Stimulation of these receptors affects multiple physiological functions – actions which often complement the physiological roles established for the systemic renin–angiotensin system. These include effects on fluid and electrolyte homeostasis, autonomic and neuroendocrine regulation, and modulation of sensory function. Moreover, administration of selective receptor antagonists attenuates several of these functions when they are activated in response to physiological stimuli, such as dehydration. Together, these observations point to important roles for brain-derived angiotensin peptides in a wide range of physiological functions.

AT2 receptors: functional relevance in cardiovascular disease

The renin angiotensin system (RAS) is intricately involved in normal cardiovascular homeostasis. Excessive stimulation by the octapeptide angiotensin II contributes to a range of cardiovascular pathologies and diseases via angiotensin type 1 receptor (AT1R) activation. On the other hand, tElsevier Inc.he angiotensin type 2 receptor (AT2R) is thought to counter-regulate AT1R function. In this review, we describe the enhanced expression and function of AT2R in various cardiovascular disease settings. In addition, we illustrate that the RAS consists of a family of angiotensin peptides that exert cardiovascular effects that are often distinct from those of Ang II. During cardiovascular disease, there is likely to be an increased functional importance of AT2R, stimulated by Ang II, or even shorter angiotensin peptide fragments, to limit AT1R-mediated overactivity and cardiovascular pathologies.