Central endogenous angiotensin-(1-7) protects against aldosterone/NaCl-induced hypertension in female rats

Mas receptor: a potential strategy in the management of ischemic cardiovascular diseases

MasR is a critical element in the RAS accessory pathway that protects the heart against myocardial infarction, ischemia-reperfusion injury, and pathological remodeling by counteracting the effects of AT1R. This receptor is mainly stimulated by Ang 1-7, which is a bioactive metabolite of the angiotensin produced by ACE2. MasR activation attenuates ischemia-related myocardial damage by facilitating vasorelaxation, improving cell metabolism, reducing inflammation and oxidative stress, inhibiting thrombosis, and stabilizing atherosclerotic plaque. It also prevents pathological cardiac remodeling by suppressing hypertrophy- and fibrosis-inducing signals. In addition, the potential of MasR in lowering blood pressure, improving blood glucose and lipid profiles, and weight loss has made it effective in modulating risk factors for coronary artery disease including hypertension, diabetes, dyslipidemia, and obesity. Considering these properties, the administration of MasR agonists offers a promising approach to the prevention and treatment of ischemic heart disease.Abbreviations: Acetylcholine (Ach); AMP-activated protein kinase (AMPK); Angiotensin (Ang); Angiotensin receptor (ATR); Angiotensin receptor blocker (ARB); Angiotensin-converting enzyme (ACE); Angiotensin-converting enzyme inhibitor (ACEI); Anti-PRD1-BF1-RIZ1 homologous domain containing 16 (PRDM16); bradykinin (BK); Calcineurin (CaN); cAMP-response element binding protein (CREB); Catalase (CAT); C-C Motif Chemokine Ligand 2 (CCL2); Chloride channel 3 (CIC3); c-Jun N-terminal kinases (JNK); Cluster of differentiation 36 (CD36); Cocaine- and amphetamine-regulated transcript (CART); Connective tissue growth factor (CTGF); Coronary artery disease (CAD); Creatine phosphokinase (CPK); C-X-C motif chemokine ligand 10 (CXCL10); Cystic fibrosis transmembrane conductance regulator (CFTR); Endothelial nitric oxide synthase (eNOS); Extracellular signal-regulated kinase 1/2 (ERK 1/2); Fatty acid transport protein (FATP); Fibroblast growth factor 21 (FGF21); Forkhead box protein O1 (FoxO1); Glucokinase (Gk); Glucose transporter (GLUT); Glycogen synthase kinase 3β (GSK3β); High density lipoprotein (HDL); High sensitive C-reactive protein (hs-CRP); Inositol trisphosphate (IP3); Interleukin (IL); Ischemic heart disease (IHD); Janus kinase (JAK); Kruppel-like factor 4 (KLF4); Lactate dehydrogenase (LDH); Left ventricular end-diastolic pressure (LVEDP); Left ventricular end-systolic pressure (LVESP); Lipoprotein lipase (LPL); L-NG-Nitro arginine methyl ester (L-NAME); Low density lipoprotein (LDL); Mammalian target of rapamycin (mTOR); Mas-related G protein-coupled receptors (Mrgpr); Matrix metalloproteinase (MMP); MAPK phosphatase-1 (MKP-1); Mitogen-activated protein kinase (MAPK); Monocyte chemoattractant protein-1 (MCP-1); NADPH oxidase (NOX); Neuropeptide FF (NPFF); Neutral endopeptidase (NEP); Nitric oxide (NO); Nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB); Nuclear-factor of activated T-cells (NFAT); Pancreatic and duodenal homeobox 1 (Pdx1); Peroxisome proliferator- activated receptor γ (PPARγ); Phosphoinositide 3-kinases (PI3k); Phospholipase C (PLC); Prepro-orexin (PPO); Prolyl-endopeptidase (PEP); Prostacyclin (PGI2); Protein kinase B (Akt); Reactive oxygen species (ROS); Renin-angiotensin system (RAS); Rho-associated protein kinase (ROCK); Serum amyloid A (SAA); Signal transducer and activator of transcription (STAT); Sirtuin 1 (Sirt1); Slit guidance ligand 3 (Slit3); Smooth muscle 22α (SM22α); Sterol regulatory element-binding protein 1 (SREBP-1c); Stromal-derived factor-1a (SDF); Superoxide dismutase (SOD); Thiobarbituric acid reactive substances (TBARS); Tissue factor (TF); Toll-like receptor 4 (TLR4); Transforming growth factor β1 (TGF-β1); Tumor necrosis factor α (TNF-α); Uncoupling protein 1 (UCP1); Ventrolateral medulla (VLM).

Effect of olmesartan and amlodipine on serum angiotensin-(1-7) levels and kidney and vascular function in patients with type 2 diabetes and hypertension

BACKGROUND

Recent studies suggest that angiotensin-converting enzyme 2 (ACE2) and angiotensin-(1-7) [Ang-(1-7)] might have beneficial effects on the cardiovascular system. We investigated the effects of olmesartan on the changes in serum ACE2 and Ang-(1-7) levels as well as kidney and vascular function in patients with type 2 diabetes and hypertension.

METHODS

This was a prospective, randomized, active comparator-controlled trial. Eighty participants with type 2 diabetes and hypertension were randomized to receive 20 mg of olmesartan (N = 40) or 5 mg of amlodipine (N = 40) once daily. The primary endpoint was changes of serum Ang-(1-7) from baseline to week 24.

RESULTS

Both olmesartan and amlodipine treatment for 24 weeks decreased systolic and diastolic blood pressures significantly by > 18 mmHg and > 8 mmHg, respectively. Serum Ang-(1-7) levels were more significantly increased by olmesartan treatment (25.8 ± 34.5 pg/mL → 46.2 ± 59.4 pg/mL) than by amlodipine treatment (29.2 ± 38.9 pg/mL → 31.7 ± 26.0 pg/mL), resulting in significant between-group differences (P = 0.01). Serum ACE2 levels showed a similar pattern (6.31 ± 0.42 ng/mL → 6.74 ± 0.39 ng/mL by olmesartan treatment vs. 6.43 ± 0.23 ng/mL → 6.61 ± 0.42 ng/mL by amlodipine treatment; P < 0.05). The reduction in albuminuria was significantly associated with the increases in ACE2 and Ang-(1-7) levels (r =  - 0.252 and r =  - 0.299, respectively). The change in Ang-(1-7) levels was positively associated with improved microvascular function (r = 0.241, P < 0.05). Multivariate regression analyses showed that increases in serum Ang-(1-7) levels were an independent predictor of a reduction in albuminuria.

CONCLUSIONS

These findings suggest that the beneficial effects of olmesartan on albuminuria may be mediated by increased ACE2 and Ang-(1-7) levels. These novel biomarkers may be therapeutic targets for the prevention and treatment of diabetic kidney disease.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05189015.

Counter-regulatory renin-angiotensin system in hypertension: Review and update in the era of COVID-19 pandemic

Cardiovascular disease is the major cause of mortality and disability, with hypertension being the most prevalent risk factor. Excessive activation of the renin-angiotensin system (RAS) under pathological conditions, leading to vascular remodeling and inflammation, is closely related to cardiovascular dysfunction. The counter-regulatory axis of the RAS consists of angiotensin-converting enzyme 2 (ACE2), angiotensin (1-7), angiotensin (1-9), alamandine, proto-oncogene Mas receptor, angiotensin II type-2 receptor and Mas-related G protein-coupled receptor member D. Each of these components has been shown to counteract the effects of the overactivated RAS. In this review, we summarize the latest insights into the complexity and interplay of the counter-regulatory RAS axis in hypertension, highlight the pathophysiological functions of ACE2, a multifunctional molecule linking hypertension and COVID-19, and discuss the function and therapeutic potential of targeting this counter-regulatory RAS axis to prevent and treat hypertension in the context of the current COVID-19 pandemic.

The Impact of Angiotensin-Converting Enzyme-2/Angiotensin 1-7 Axis in Establishing Severe COVID-19 Consequences

The COVID-19 pandemic has put a tremendous stress on the medical community over the last two years. Managing the infection proved a lot more difficult after several research communities started to recognize the long-term effects of this disease. The cellular receptor for the virus was identified as angiotensin-converting enzyme-2 (ACE2), a molecule responsible for a wide array of processes, broadly variable amongst different organs. Angiotensin (Ang) 1-7 is the product of Ang II, a decaying reaction catalysed by ACE2. The effects observed after altering the level of ACE2 are essentially related to the variation of Ang 1-7. The renin-angiotensin-aldosterone system (RAAS) is comprised of two main branches, with ACE2 representing a crucial component of the protective part of the complex. The ACE2/Ang (1-7) axis is well represented in the testis, heart, brain, kidney, and intestine. Infection with the novel SARS-CoV-2 virus determines downregulation of ACE2 and interrupts the equilibrium between ACE and ACE2 in these organs. In this review, we highlight the link between the local effects of RAAS and the consequences of COVID-19 infection as they arise from observational studies.

Angiotensin-(1-7) as a Potential Therapeutic Strategy for Delayed Cerebral Ischemia in Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is a substantial cause of mortality and morbidity worldwide. Moreover, survivors after the initial bleeding are often subject to secondary brain injuries and delayed cerebral ischemia, further increasing the risk of a poor outcome. In recent years, the renin-angiotensin system (RAS) has been proposed as a target pathway for therapeutic interventions after brain injury. The RAS is a complex system of biochemical reactions critical for several systemic functions, namely, inflammation, vascular tone, endothelial activation, water balance, fibrosis, and apoptosis. The RAS system is classically divided into a pro-inflammatory axis, mediated by angiotensin (Ang)-II and its specific receptor AT₁R, and a counterbalancing system, presented in humans as Ang-(1-7) and its receptor, MasR. Experimental data suggest that upregulation of the Ang-(1-7)/MasR axis might be neuroprotective in numerous pathological conditions, namely, ischemic stroke, cognitive disorders, Parkinson's disease, and depression. In the presence of SAH, Ang-(1-7)/MasR neuroprotective and modulating properties could help reduce brain damage by acting on neuroinflammation, and through direct vascular and anti-thrombotic effects. Here we review the role of RAS in brain ischemia, with specific focus on SAH and the therapeutic potential of Ang-(1-7).

Angiotensin-(1-7) and Mas receptor in the brain

The renin-angiotensin system (RAS) is a key regulator of blood pressure and electrolyte homeostasis. Besides its importance as regulator of the cardiovascular function, the RAS has also been associated to the modulation of higher brain functions, including cognition, memory, depression and anxiety. For many years, angiotensin II (Ang II) has been considered the major bioactive component of the RAS. However, the existence of many other biologically active RAS components has currently been recognized, with similar, opposite, or distinct effects to those exerted by Ang II. Today, it is considered that the RAS is primarily constituted by two opposite arms. The pressor arm is composed by Ang II and the Ang II type 1 (AT1) receptor (AT1R), which mediates the vasoconstrictor, proliferative, hypertensive, oxidative and pro-inflammatory effects of the RAS. The depressor arm is mainly composed by Ang-(1-7), its Mas receptor (MasR) which mediates the depressor, vasodilatory, antiproliferative, antioxidant and anti-inflammatory effects of Ang-(1-7) and the AT2 receptor (AT2R), which opposes to the effects mediated by AT1R activation. Central Ang-(1-7) is implicated in the control of the cardiovascular function, thus participating in the regulation of blood pressure. Ang-(1-7) also exerts neuroprotective actions through MasR activation by opposing to the harmful effects of the Ang II/AT1R axis. This review is focused on the expression and regulation of the Ang-(1-7)/MasR axis in the brain, its main neuroprotective effects and the evidence regarding its involvement in the pathophysiology of several diseases at cardiovascular and neurological level.

Glycopeptide drugs: A pharmacological dimension between "Small Molecules" and "Biologics"

Peptides are an important class of molecules with diverse biological activities. Many endogenous peptides, especially neuropeptides and peptide hormones, play critical roles in development and regulating homeostasis. Furthermore, as drug candidates their high receptor selectivity and potent binding leads to reduced off-target interactions and potential negative side effects. However, the therapeutic potential of peptides is severely hampered by their poor stability in vivo and low permeability across biological membranes. Several strategies have been successfully employed over the decades to address these concerns, and one of the most promising strategies is glycosylation. It has been demonstrated in numerous cases that glycosylation is an effective synthetic approach to improve the pharmacokinetic profiles and membrane permeability of peptides. The effects of glycosylation on peptide stability and peptide-membrane interactions in the context of blood-brain barrier penetration will be explored. Numerous examples of glycosylated analogues of endogenous peptides targeting class A and B G-protein coupled receptors (GPCRs) with an emphasis on O-linked glycopeptides will be reviewed. Notable examples of N-, S-, and C-linked glycopeptides will also be discussed. A small section is devoted to synthetic methods for the preparation of glycopeptides and requisite amino acid glycoside building blocks.

Sex differences in cardiovascular actions of the renin-angiotensin system

Cardiovascular disease (CVD) remains a worldwide public health concern despite decades of research and the availability of numerous targeted therapies. While the intrinsic physiological mechanisms regulating cardiovascular function are similar between males and females, marked sex differences have been established in terms of CVD onset, pathophysiology, manifestation, susceptibility, prevalence, treatment responses and outcomes in animal models and clinical populations. Premenopausal females are generally protected from CVD in comparison to men of similar age, with females tending to develop cardiovascular complications later in life following menopause. Emerging evidence suggests this cardioprotection in females is, in part, attributed to sex differences in hormonal regulators, such as the renin-angiotensin system (RAS). To date, research has largely focused on canonical RAS pathways and shown that premenopausal females are protected from cardiovascular derangements produced by activation of angiotensin II pathways. More recently, a vasodilatory arm of the RAS has emerged that is characterized by angiotensin-(1-7) [(Ang-(1-7)], angiotensin-converting enzyme 2 and Mas receptors. Emerging studies provide evidence for a shift towards these cardioprotective Ang-(1-7) pathways in females, with effects modulated by interactions with estrogen. Despite well-established sex differences, female comparison studies on cardiovascular outcomes are lacking at both the preclinical and clinical levels. Furthermore, there are no specific guidelines in place for the treatment of cardiovascular disease in men versus women, including therapies targeting the RAS. This review summarizes current knowledge on sex differences in the cardiovascular actions of the RAS, focusing on interactions with gonadal hormones, emerging data for protective Ang-(1-7) pathways and potential clinical implications for established and novel therapies.

Angiotensin-(1–7) reduces doxorubicin-induced cardiac dysfunction in male and female Sprague-Dawley rats through antioxidant mechanisms

Doxorubicin (Dox) is an effective chemotherapeutic for a variety of pediatric malignancies. Unfortunately, Dox administration often results in a cumulative dose-dependent cardiotoxicity that manifests with marked oxidative stress, leading to heart failure. Adjunct therapies are needed to mitigate Dox cardiotoxicity and enhance quality of life in pediatric patients with cancer. Angiotensin-(1–7) [Ang-(1–7)] is an endogenous hormone with cardioprotective properties. This study investigated whether adjunct Ang-(1–7) attenuates cardiotoxicity resulting from exposure to Dox in male and female juvenile rats. Dox significantly reduced body mass, and the addition of Ang-(1–7) had no effect. However, adjunct Ang-(1–7) prevented Dox-mediated diastolic dysfunction, including markers of decreased passive filling as measured by reduced early diastole mitral valve flow velocity peak ( E) ( P < 0.05) and early diastole mitral valve annulus peak velocity ( e′; P < 0.001) and increased E/e′ ( P < 0.001), an echocardiographic measure of diastolic dysfunction. Since Dox treatment increases reactive oxygen species (ROS), the effect of Ang-(1–7) on oxidative by-products and enzymes that generate or reduce ROS was investigated. In hearts of male and female juvenile rats, Dox increased NADPH oxidase 4 ( P < 0.05), a major cardiovascular NADPH oxidase isozyme that generates ROS, as well as 4-hydroxynonenal ( P < 0.001) and malondialdehyde ( P < 0.001), markers of lipid peroxidation; Ang-(1–7) prevented these effects of Dox. Cotreatment with Dox and Ang-(1–7) increased the antioxidant enzymes SOD1 (male: P < 0.05; female: P < 0.01) and catalase ( P < 0.05), which likely contributed to reduced ROS. These results demonstrate that Ang-(1–7) prevents diastolic dysfunction in association with a reduction in ROS, suggesting that the heptapeptide hormone may serve as an effective adjuvant to improve Dox-induced cardiotoxicity.

NEW & NOTEWORTHY Ang-(1–7) is a clinically safe peptide hormone with cardioprotective and antineoplastic properties that could be used as an adjuvant therapy to improve cancer treatment and mitigate the long-term cardiotoxicity associated with doxorubicin in pediatric patients with cancer.

Central ANG-(1-7) infusion improves blood pressure regulation in antenatal betamethasone-exposed sheep and reveals sex-dependent effects on oxidative stress

Fetal exposure to betamethasone (BMX) as a consequence of glucocorticoid administration to women threatening premature delivery may lead to long-term deleterious effects on the cardiovascular system and dysregulation of blood pressure in exposed adults. Indeed, adult offspring of BMX sheep exhibit increased mean arterial pressure (MAP) and attenuated baroreflex sensitivity (BRS) that are associated with lower medullary and cerebrospinal fluid (CSF) angiotensin-(1-7) [(ANG-(1-7)] content. Thus we determined the effects of ANG-(1-7) supplementation in the CSF on MAP, BRS, blood pressure (BPV) and heart rate variability (HRV) in conscious animals. The peptide or artificial CSF (aCSF) was infused continuously into the lateral ventricle (intracerebroventricular) of 4-mo-old male and female BMX sheep for 2 wk. Analysis of data from males and females combined revealed that intracerebroventricular ANG-(1-7) significantly lowered MAP and heart rate and improved BRS as compared with baseline; intracerebroventricular aCSF did not change these indexes. Similar patterns were observed for altered hemodynamics and autonomic function produced by intracerebroventricular ANG-(1-7) in both sexes. Oxidative stress and MAP kinase (MAPK) activation were lower in tissues from the dorsomedial medulla (DMM) of ANG-(1-7)-treated males but were unchanged in the treated females, when assessed at the end of the treatment period. We conclude that in the face of ANG-(1-7) deficiency in CSF and medullary tissue in BMX sheep intracerebroventricular supplementation of ANG-(1-7) lowers MAP and restores the impaired autonomic function to a similar degree in both males and females; however, the attenuation of MAPK and oxidative stress within the DMM was evident only in males. NEW & NOTEWORTHY We demonstrate that intracerebroventricular angiotensin-(1-7) [(ANG-(1-7)] treatment for 2 wk in antenatal betamethasone-exposed sheep provides beneficial effects on blood pressure and autonomic function. The physiological improvements are accompanied by an attenuation of oxidative stress in males but not females. The finding that ANG-(1-7) supplementation lowers blood pressure and restores the impaired autonomic function in a model of fetal programming previously shown to exhibit a deficiency in cerebrospinal fluid and brain tissue illustrates the potential for new therapeutic strategies for reducing cardiovascular dysfunction arising from prenatal events.

Dimerization of AT2 and Mas Receptors in Control of Blood Pressure

PURPOSE OF REVIEW

Angiotensin type 2 receptor (AT2R) and receptor Mas (MasR) are part of the "protective arm" of the renin angiotensin system. Gene and pharmacological manipulation studies reveal that AT2R and MasR are involved in natriuretic, vasodilatory, and anti-inflammatory responses and in lowering blood pressure in various animal models under normal and pathological conditions such as salt-sensitive hypertension, obesity, and diabetes. The scope of this review is to discuss co-localization and heterodimerization as potential molecular mechanisms of AT2R- and MasR-mediated functions including antihypertensive activities.

RECENT FINDINGS

Accumulating evidences show that AT2R and MasR are co-localized, make a heterodimer, and are functionally interdependent in producing their physiological responses. Moreover, ang-(1-7) preferably may be an AT1R-biased agonist while acting as a MasR agonist. The physical interactions of AT2R and MasR appear to be an important mechanism by which these receptors are involved in blood pressure regulation and antihypertensive activity. Whether heteromers of these receptors influence affinity or efficacy of endogenous or synthetic agonists remains a question to be considered.

Angiotensin-(1-7) and Alamandine on Experimental Models of Hypertension and Atherosclerosis

PURPOSE OF REVIEW

The purpose of this review was to summarize the current knowledge on the role of angiotensin-(1-7) [Ang-(1-7)] and alamandine in experimental hypertension and atherosclerosis.

RECENT FINDINGS

The renin-angiotensin system (RAS) is a very complex system, composed of a cascade of enzymes, peptides, and receptors, known to be involved in the pathogenesis of hypertension and atherosclerosis. Ang-(1-7), identified and characterized in 1987, and alamandine, discovered 16 years after, are the newest two main effector molecules from the RAS, protecting the vascular system against hypertension and atherosclerosis. While the beneficial effects of Ang-(1-7) have been widely studied in several experimental models of hypertension, much less studies were performed in experimental models of atherosclerosis. Alamandine has shown similar vascular effects to Ang-(1-7), namely, endothelial-dependent vasorelaxation mediated by nitric oxide and hypotensive effects in experimental hypertension. There are few studies on the effects of alamandine on atherosclerosis.

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

The Link Between Adipose Tissue Renin-Angiotensin-Aldosterone System Signaling and Obesity-Associated Hypertension

Obese individuals frequently develop hypertension, which is for an important part attributable to renin-angiotensin-aldosterone system (RAAS) overactivity. This review summarizes preclinical and clinical evidence on the involvement of dysfunctional adipose tissue in RAAS activation and on the renal, central, and vascular mechanisms linking RAAS components to obesity-associated hypertension.

Significance of angiotensin 1-7 coupling with MAS1 receptor and other GPCRs to the renin-angiotensin system: IUPHAR Review 22

Angiotensins are a group of hormonal peptides and include angiotensin II and angiotensin 1-7 produced by the renin angiotensin system. The biology, pharmacology and biochemistry of the receptors for angiotensins were extensively reviewed recently. In the review, the receptor nomenclature committee was not emphatic on designating MAS1 as the angiotensin 1-7 receptor on the basis of lack of classical G protein signalling and desensitization in response to angiotensin 1-7, as well as a lack of consensus on confirmatory ligand pharmacological analyses. A review of recent publications (2013-2016) on the rapidly progressing research on angiotensin 1-7 revealed that MAS1 and two additional receptors can function as 'angiotensin 1-7 receptors', and this deserves further consideration. In this review we have summarized the information on angiotensin 1-7 receptors and their crosstalk with classical angiotensin II receptors in the context of the functions of the renin angiotensin system. It was concluded that the receptors for angiotensin II and angiotensin 1-7 make up a sophisticated cross-regulated signalling network that modulates the endogenous protective and pathogenic facets of the renin angiotensin system.

New and old roles of the peripheral and brain renin-angiotensin-aldosterone system (RAAS): Focus on cardiovascular and neurological diseases

It is commonly accepted that the renin-angiotensin-aldosterone system (RAAS) is a cardiovascular circulating hormonal system that plays also an important role in the modulation of several patterns in the brain. The pathway of the RAAS can be divided into two classes: the traditional pathway of RAAS, also named classic RAAS, and the non-classic RAAS. Both pathways play a role in both cardiovascular and neurological diseases through a peripheral or central control. In this regard, renewed interest is growing in the last years for the consideration that the brain RAAS could represent a new important therapeutic target to regulate not only the blood pressure via central nervous control, but also neurological diseases. However, the development of compounds able to cross the blood-brain barrier and to act on the brain RAAS is challenging, especially if the metabolic stability and the half-life are taken into consideration. To date, two drug classes (aminopeptidase type A inhibitors and angiotensin IV analogues) acting on the brain RAAS are in development in pre-clinical or clinical stages. In this article, we will present an overview of the biological functions played by peripheral and brain classic and non-classic pathways of the RAAS in several clinical conditions, focusing on the brain RAAS and on the new pharmacological targets of the RAAS.

Role of neurons and glia in the CNS actions of the renin-angiotensin system in cardiovascular control

Despite tremendous research efforts, hypertension remains an epidemic health concern, leading often to the development of cardiovascular disease. It is well established that in many instances, the brain plays an important role in the onset and progression of hypertension via activation of the sympathetic nervous system. Further, the activity of the renin-angiotensin system (RAS) and of glial cell-mediated proinflammatory processes have independently been linked to this neural control and are, as a consequence, both attractive targets for the development of antihypertensive therapeutics. Although it is clear that the predominant effector peptide of the RAS, ANG II, activates its type-1 receptor on neurons to mediate some of its hypertensive actions, additional nuances of this brain RAS control of blood pressure are constantly being uncovered. One of these complexities is that the RAS is now thought to impact cardiovascular control, in part, via facilitating a glial cell-dependent proinflammatory milieu within cardiovascular control centers. Another complexity is that the newly characterized antihypertensive limbs of the RAS are now recognized to, in many cases, antagonize the prohypertensive ANG II type 1 receptor (AT1R)-mediated effects. That being said, the mechanism by which the RAS, glia, and neurons interact to regulate blood pressure is an active area of ongoing research. Here, we review the current understanding of these interactions and present a hypothetical model of how these exchanges may ultimately regulate cardiovascular function.

Endotoxin-induced skeletal muscle wasting is prevented by angiotensin-(1-7) through a p38 MAPK-dependent mechanism

Skeletal muscle atrophy induced during sepsis syndrome produced by endotoxin in the form of LPS (lipopolysaccharide), is a pathological condition characterized by the loss of strength and muscle mass, an increase in MHC (myosin heavy chain) degradation, and an increase in the expression of atrogin-1 and MuRF-1 (muscle-specific RING-finger protein 1), two ubiquitin E3 ligases belonging to the ubiquitin-proteasome system. Ang-(1-7) [Angiotensin-(1-7)], through its Mas receptor, has beneficial effects in skeletal muscle. We evaluated in vivo the role of Ang-(1-7) and Mas receptor on the muscle wasting induced by LPS injection into C57BL/10J mice. In vitro studies were performed in murine C2C12 myotubes and isolated myofibres from EDL (extensor digitorum longus) muscle. In addition, the participation of p38 MAPK (mitogen-activated protein kinase) in the Ang-(1-7) effect on the LPS-induced muscle atrophy was evaluated. Our results show that Ang-(1-7) prevents the decrease in the diameter of myofibres and myotubes, the decrease in muscle strength, the diminution in MHC levels and the induction of atrogin-1 and MuRF-1 expression, all of which are induced by LPS. These effects were reversed by using A779, a Mas antagonist. Ang-(1-7) exerts these anti-atrophic effects at least in part by inhibiting the LPS-dependent activation of p38 MAPK both in vitro and in vivo. We have demonstrated for the first time that Ang-(1-7) counteracts the skeletal muscle atrophy induced by endotoxin through a mechanism dependent on the Mas receptor that involves a decrease in p38 MAPK phosphorylation. The present study indicates that Ang-(1-7) is a novel molecule with a potential therapeutic use to improve muscle wasting during endotoxin-induced sepsis syndrome.

Activation of angiotensin-(1-7)/Mas axis in the brain lowers blood pressure and attenuates cardiac remodeling in hypertensive transgenic (mRen2)27 rats

Activation of the peripheral angiotensin-(1-7)/Mas axis of the renin-angiotensin system produces important cardioprotective actions, counterbalancing the deleterious actions of an overactivity of Ang II/AT1 axis. In the present study we evaluated whether the chronic increase in Ang-(1-7) levels in the brain could ameliorate cardiac disorders observed in transgenic (mRen2)27 hypertensive rats through actions on Mas receptor. Sprague Dawley (SD) and transgenic (mRen2)27 hypertensive rats, instrumented with telemetry probe for arterial pressure (AP) measurement were subjected to 14 days of ICV infusion of Ang-(1-7) (200 ng/h) or Ang-(1-7) associated with Mas receptor antagonist (A779, 1 μg/h) or 0.9% sterile saline (0.5 μl/h) through osmotic mini-pumps. Ang-(1-7) infusion in (mRen2)27 rats reduced blood pressure, normalized the baroreflex control of HR, restored cardiac autonomic balance, reduced cardiac hypertrophy and pre-fibrotic alterations and decreased the altered imbalance of Ang II/Ang-(1-7) in the heart. In addition, there was an attenuation of the increased levels of atrial natriuretic peptide, brain natriuretic peptide, collagen I, fibronectin and TGF-β in the heart of (mRen2)27 rats. Furthermore, most of these effects were mediated in the brain by Mas receptor, since were blocked by its selective antagonist, A779. These data indicate that increasing Ang-(1-7) levels in the brain can attenuate cardiovascular disorders observed in (mRen2)27 hypertensive rats, probably by improving the autonomic balance to the heart due to centrally-mediated actions on Mas receptor.

Age-related changes in thirst, salt appetite, and arterial blood pressure in response to aldosterone-dexamethasone combination in rats

This work examined the effects of age on daily water and sodium ingestion and cardiovascular responses to chronic administration of the mineralocorticoid, aldosterone (ALDO) either alone or together with the glucocorticoid, dexamethasone (DEX). Young (4 mo), adult (12 mo), and aged (30 mo) male Brown Norway rats were prepared for continuous telemetry recording of blood pressure (BP) and heart rate (HR). Baseline water and sodium (i.e., 0.3 M NaCl) intake, BP, and HR were established for 10 days. Then ALDO (60 μg/day sc) was infused alone, or together with DEX (2.5 or 20 μg/day sc), for another 10 days. Compared with baseline levels, ALDO stimulated comparable increases in daily saline intake at all ages. ALDO together with the higher dose of DEX (i.e., ALDO/DEX20) increased daily saline intake more than did ALDO, but less so in aged rats. Infusion of ALDO/DEX20 increased mean arterial pressure (MAP), and decreased HR, more than did infusion of ALDO. The changes in MAP in response to both treatments depended on age. For all ages, MAP and saline intake increased simultaneously during ALDO, while MAP always increased before saline intake did during ALDO/DEX20. Contrary to our predictions, MAP did not increase more in old rats in response to either treatment. We speculate that age-related declines in cardiovascular responses to glucocorticoids contributed to the attenuated increases in sodium intake in response to glucocorticoids that were observed in older animals.

Estrogen regulation of the brain renin-angiotensin system in protection against angiotensin II-induced sensitization of hypertension

This study investigated sex differences in the sensitization of angiotensin (ANG) II-induced hypertension and the role of central estrogen and ANG-(1-7) in this process. Male and female rats were implanted for telemetered blood pressure (BP) recording. A subcutaneous subpressor dose of ANG II was given alone or concurrently with intracerebroventricular estrogen, ANG-(1-7), an ANG-(1-7) receptor antagonist A-779 or vehicle for 1 wk (induction). After a 1-wk rest (delay), a pressor dose of ANG II was given for 2 wk (expression). In males and ovariectomized females, subpressor ANG II had no sustained effect on BP during induction, but produced an enhanced hypertensive response to the subsequent pressor dose of ANG II during expression. Central administration of estrogen or ANG-(1-7) during induction blocked ANG II-induced sensitization. In intact females, subpressor ANG II treatment produced a decrease in BP during induction and delay, and subsequent pressor ANG II treatment given during expression produced only a slight but significant increase in BP. However, central blockade of ANG-(1-7) by intracerebroventricular infusion of A-779 during induction restored the decreased BP observed in females during induction and enhanced the pressor response to the ANG II treatment during expression. RT-PCR analyses indicated that estrogen given during induction upregulated mRNA expression of the renin-angiotensin system (RAS) antihypertensive components, whereas both central estrogen and ANG-(1-7) downregulated mRNA expression of RAS hypertensive components in the lamina terminalis. The results indicate that females are protected from ANG II-induced sensitization through central estrogen and its regulation of brain RAS.

Angiotensin-converting enzyme 2 and angiotensin 1-7: novel therapeutic targets

Angiotensin-converting enzyme (ACE) 2 and its product angiotensin 1–7 are thought to have effects that counteract the adverse actions of other, better-known renin–angiotensin system (RAS) components

Numerous experimental studies have suggested that ACE2 and angiotensin 1–7 have notable protective effects in the heart and blood vessels

ACE2-mediated catabolism of angiotensin II is likely to have a major role in cardiovascular protection, whereas the functional importance and signalling mechanisms of angiotensin-1–7-induced actions remain unclear

New pharmacological interventions targeting ACE2 are expected to be useful in clinical treatment of cardiovascular disease, especially those associated with overactivation of the conventional RAS

More studies, especially randomized controlled clinical trials, are needed to clearly delineate the benefits of therapies targeting angiotensin 1–7 actions

Angiotensin-converting enzyme 2, and its product angiotensin 1–7, are thought to have counteracting effects against the adverse actions of the better-known members of the renin–angiotensin system and might, therefore, be useful therapeutic targets in patients with cardiovascular disease. Professor Jiang and colleagues review the evidence for the potential roles of these proteins in various cardiovascular conditions, including hypertension, atherosclerosis, myocardial remodelling, heart failure, ischaemic stroke, and diabetes.

The renin–angiotensin system (RAS) has pivotal roles in the regulation of normal physiology and the pathogenesis of cardiovascular disease. Angiotensin-converting enzyme (ACE) 2, and its product angiotensin 1–7, are thought to have counteracting effects against the adverse actions of other, better known and understood, members of the RAS. The physiological and pathological importance of ACE2 and angiotensin 1–7 in the cardiovascular system are not completely understood, but numerous experimental studies have indicated that these components have protective effects in the heart and blood vessels. Here, we provide an overview on the basic properties of ACE2 and angiotensin 1–7 and a summary of the evidence from experimental and clinical studies of various pathological conditions, such as hypertension, atherosclerosis, myocardial remodelling, heart failure, ischaemic stroke, and diabetes mellitus. ACE2-mediated catabolism of angiotensin II is likely to have a major role in cardiovascular protection, whereas the relevant functions and signalling mechanisms of actions induced by angiotensin 1–7 have not been conclusively determined. The ACE2–angiotensin 1–7 pathway, however, might provide a useful therapeutic target for the treatment of cardiovascular disease, especially in patients with overactive RAS.

Update on the Angiotensin converting enzyme 2-Angiotensin (1-7)-MAS receptor axis: fetal programing, sex differences, and intracellular pathways

The renin-angiotensin-system (RAS) constitutes an important hormonal system in the physiological regulation of blood pressure. Indeed, dysregulation of the RAS may lead to the development of cardiovascular pathologies including kidney injury. Moreover, the blockade of this system by the inhibition of angiotensin converting enzyme (ACE) or antagonism of the angiotensin type 1 receptor (AT1R) constitutes an effective therapeutic regimen. It is now apparent with the identification of multiple components of the RAS that the system is comprised of different angiotensin peptides with diverse biological actions mediated by distinct receptor subtypes. The classic RAS can be defined as the ACE-Ang II-AT1R axis that promotes vasoconstriction, sodium retention, and other mechanisms to maintain blood pressure, as well as increased oxidative stress, fibrosis, cellular growth, and inflammation in pathological conditions. In contrast, the non-classical RAS composed of the ACE2-Ang-(1-7)-Mas receptor axis generally opposes the actions of a stimulated Ang II-AT1R axis through an increase in nitric oxide and prostaglandins and mediates vasodilation, natriuresis, diuresis, and oxidative stress. Thus, a reduced tone of the Ang-(1-7) system may contribute to these pathologies as well. Moreover, the non-classical RAS components may contribute to the effects of therapeutic blockade of the classical system to reduce blood pressure and attenuate various indices of renal injury. The review considers recent studies on the ACE2-Ang-(1-7)-Mas receptor axis regarding the precursor for Ang-(1-7), the intracellular expression and sex differences of this system, as well as an emerging role of the Ang1-(1-7) pathway in fetal programing events and cardiovascular dysfunction.

ACE2 alterations in kidney disease

Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that degrades angiotensin (Ang) II to Ang-(1-7). ACE2 is highly expressed within the kidneys, it is largely localized in tubular epithelial cells and less prominently in glomerular epithelial cells and in the renal vasculature. ACE2 activity has been shown to be altered in diabetic kidney disease, hypertensive renal disease and in different models of kidney injury. There is often a dissociation between tubular and glomerular ACE2 expression, particularly in diabetic kidney disease where ACE2 expression is increased at the tubular level but decreased at the glomerular level. In this review, we will discuss alterations in circulating and renal ACE2 recently described in different renal pathologies and disease models as well as their possible significance.