AT2 receptor-mediated relaxation is preserved after long-term AT1 receptor blockade

Angiotensin-converting enzyme inhibitors: a therapeutic option for controlling blood pressure associated with delayed cognitive processing speed

Antihypertensive treatment (AT) is essential for preventing hypertension-related cognitive decline. The goals of this observational study were to compare cognitive performance (CP) between non-hypertensive (NH) volunteers and hypertensive patients and to evaluate the correlation between CP and antihypertensive drugs (AHD). Three groups were constituted: NH (n = 30) [group 1], hypertensive with systolic blood pressure (SBP) < 140 mmHg and diastolic blood pressure (DBP) < 90 mmHg (n = 54) [group 2] and hypertensive with SBP ≥ 140 or DBP ≥ 90 (n = 31) [group 3]. To analyze the cognitive domains, a neuropsychological battery was applied and the raw performance values in these tests were transformed into z-scores. The domain was considered impaired if it presented a z-score below -1.5 SD. Compared to group 1, both groups of hypertensive were older (51 [ ± 12] years) and showed a worse CP in episodic memory (p = 0.014), language (p = 0.003) and processing speed (PS) [p = 0.05]. Angiotensin-converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARB) were the most used AHD (46.3%, p = 0.01 [group 2] and 64.5%, p = 0.005 [group 3]) and showed correlations with PS. Linear regression models revealed a negative association of PS with the use of ACEi (β = -0.230, p = 0.004), but not with the use of ARB (β = 0.208, p = 0.008). The effect of AT on cognition appears to go beyond the search for lower blood pressure targets and also includes the mechanism of action of AHD on the brain, so that additional benefits may possibly be achieved with simple adaptations in the treatment regimen, particularly in patients without clinically manifest cognitive impairment.

Losartan and metabolite EXP3179 activate endothelial function without lowering blood pressure in AT2 receptor KO mice

BACKGROUND

We have documented profound release of nitric oxide (NO) and endothelium-derived hyperpolarization factor (EDHF) by angiotensin II (ANGII) receptor 1 (AT1) blocker (ARB) losartan and its unique metabolite EXP3179, a pleiotropic effect that may help rationalize the protective properties of ARBs. Since blood pressure (BP) lowering by ARBs likely require an ANGII-dependent switch from AT1 to ANGII receptor 2 (AT2) signaling, a receptor known to stimulate endothelial NO release, we investigated the contribution of AT1 and AT2 to losartan and EXP3179's endothelial function-activating properties.

EXPERIMENTAL APPROACH

Two AT1 ligands were used in an attempt to block the AT1-dependent endothelium-enhancing effects of EXP3179. AT2-null mice were used to evaluate the acute ex vivo and chronic in vivo effects of EXP3179 (20μM) and losartan (0.6 g/l), respectively, on endothelial function, BP and aortic stiffness.

KEY RESULTS

Ex vivo blockade of AT1 receptors did not attenuate EXP3179's effects on NO and EDHF-dependent endothelial function activation. We observed significant reductions in PE-induced contractility with EXP3179 in both WT and AT2 knockout (KO) aortic rings. In vivo, a 1-month chronic treatment with losartan did not affect pulse wave velocity (PWV) but decreased PE-induced contraction by 74.9 % in WT (p < 0.0001) and 47.3 % in AT2 KO (p < 0.05). Presence of AT2 was critical to losartan's BP lowering activity.

CONCLUSION

In contrast to BP lowering, the endothelial function-enhancing effects of losartan and EXP3179 are mostly independent of the classic ANGII/AT1/AT2 pathway, which sheds light on ARB pleiotropism.

Functional crosstalk between angiotensin receptors (types 1 and 2) and relaxin family peptide receptor 1 (RXFP1): Implications for the therapeutic targeting of fibrosis

Class A, rhodopsin-like, G-protein-coupled receptors (GPCRs) are by far the largest class of GPCRs and are integral membrane proteins used by various cells to convert extracellular signals into intracellular responses. Initially, class A GPCRs were believed to function as monomers, but a growing body of evidence has emerged to suggest that these receptors can function as homodimers and heterodimers and can undergo functional crosstalk to influence the actions of agonists or antagonists acting at each receptor. This review will focus on the angiotensin type 1 (AT1) and type 2 (AT2) receptors, as well as the relaxin family peptide receptor 1 (RXFP1), each of which have their unique characteristics but have been demonstrated to undergo some level of interaction when appropriately co-expressed, which influences the function of each receptor. In particular, this receptor functional crosstalk will be discussed in the context of fibrosis, the tissue scarring that results from a failed wound-healing response to injury, and which is a hallmark of chronic disease and related organ dysfunction. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

CGP42112: the full AT2 receptor agonist and its role in the renin-angiotensin-aldosterone system: no longer misunderstood

For years, the AT2R-selective ligand CGP42112 has been erroneously characterized as a partial agonist, partly due to its ability to also interact with the AT1R at high concentrations. As late as 2009, it was still being characterized as an antagonist as well. In this perspective/opinion piece, we try to resolve the ambiguity that surrounds the efficacy of this compound by extensively reviewing the literature, tracing its beginnings to 1989, showing that CGP42112 has never been convincingly shown to be a partial agonist or an antagonist at the AT2R. While CGP42112 is now routinely characterized as an AT2R agonist, regrettably, there is a paucity of studies that can validate its efficacy as a full agonist at the AT2R, leaving the door open for continuing speculation regarding the extent of its efficacy. Hopefully, the information presented in this perspective/opinion piece will firmly establish CGP42112 as a full agonist at the AT2R such that it can once again be used as a tool to study the AT2R.

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

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-(1-9) in hypertension

Angiotensin-(1-9) [Ang-(1-9)] is a peptide of the non-canonical renin-angiotensin system (RAS) synthesized from angiotensin I by the monopeptidase angiotensin-converting enzyme type 2 (ACE2). Using osmotic minipumps, infusion of Ang-(1-9) consistently reduces blood pressure in several rat hypertension models. In these animals, hypertension-induced end-organ damage is also decreased. Several pieces of evidence suggest that Ang-(1-9) is the endogenous ligand that binds and activates the type-2 angiotensin II receptor (AT2R). Activation of AT2R triggers different tissue-specific signaling pathways. This phenomenon could be explained by the ability of AT2R to form different heterodimers with other G protein-coupled receptors. Because of the antihypertensive and protective effects of AT2R activation by Ang-(1-9), associated with a short half-life of RAS peptides, several synthetic AT2R agonists have been synthesized and assayed. Some of them, particularly CGP42112, C21 and novokinin, have demonstrated antihypertensive properties. Only two synthetic AT2R agonists, C21 and LP2-3, have been tested in clinical trials, but none of them like an antihypertensive. Therefore, Ang-(1-9) is a promising antihypertensive drug that reduces hypertension-induced end-organ damage. However, further research is required to translate this finding successfully to the clinic.

Role of the central renin‑angiotensin system in hypertension (Review)

Present in more than one billion adults, hypertension is the most significant modifiable risk factor for mortality resulting from cardiovascular disease. Although its pathogenesis is not yet fully understood, the disruption of the renin-angiotensin system (RAS), consisting of the systemic and brain RAS, has been recognized as one of the primary reasons for several types of hypertension. Therefore, acquiring sound knowledge of the basic science of RAS and the under- lying mechanisms of the signaling pathways associated with RAS may facilitate the discovery of novel therapeutic targets with which to promote the management of patients with cardiovascular and kidney disease. In total, 4 types of angiotensin II receptors have been identified (AT1R-AT4R), of which AT1R plays the most important role in vasoconstriction and has been most extensively studied. It has been found in several regions of the brain, and its distribution is highly associated with that of angiotensin-like immunoreactivity in nerve terminals. The effect of AT1R involves the activation of multiple media and signaling pathways, among which the most important signaling pathways are considered to be AT1R/JAK/STAT and Ras/Raf/MAPK pathways. In addition, the regulation of the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) and cyclic AMP response element-binding (CREB) pathways is also closely related to the effect of ATR1. Their mechanisms of action are related to pro-inflammatory and sympathetic excitatory effects. Central AT1R is involved in almost all types of hypertension, including spontaneous hypertension, salt-sensitive hypertension, obesity-induced hypertension, renovascular hypertension, diabetic hypertension, L-NAME-induced hypertension, stress-induced hypertension, angiotensin II-induced hyper- tension and aldosterone-induced hypertension. There are 2 types of central AT1R blockade, acute blockade and chronic blockade. The latter can be achieved by chemical blockade or genetic engineering. The present review article aimed to high- light the prevalence, functions, interactions and modulation means of central AT-1R in an effort to assist in the treatment of several pathological conditions. The identification of angiotensin-derived peptides and the development of AT-2R agonists may provide a wider perspective on RAS, as well as novel therapeutic strategies.

Update on Angiotensin II Subtype 2 Receptor: Focus on Peptide and Nonpeptide Agonists

Angiotensin II (Ang II) is the most dominant effector component of the renin-angiotensin system (RAS) that generally acts through binding to two main classes of G protein-coupled receptors, namely Ang II subtype 1 receptor (AT1R) and angiotensin II subtype 2 receptor (AT2R). Despite some controversial reports, the activation of AT2R generally antagonizes the effects of Ang II binding on AT1R. Studying AT2R signaling, function, and its specific ligands in cell culture or animal studies has confirmed its beneficial effects throughout the body. These characteristics classify AT2R as part of the protective arm of the RAS that, along with functions of Ang (1-7) through Mas receptor signaling, modulates the harmful effects of Ang II on AT1R in the activated classic arm of the RAS. Although Ang II is the primary ligand for AT2R, we have summarized other natural or synthetic peptide and nonpeptide agonists with critical evaluation of their structure, mechanism of action, and biologic activity. SIGNIFICANCE STATEMENT: AT2R is one of the main components of the RAS and has a significant prospective for mediating the beneficial action of the RAS through its protective arm on the body's homeostasis. Targeting AT2R offers substantial clinical application possibilities for modulating various pathological conditions. This review provided concise information regarding the AT2R peptide and nonpeptide agonists and their potential clinical applications for various diseases.

Renin-angiotensin system overactivation in perivascular adipose tissue contributes to vascular dysfunction in heart failure

Perivascular adipose tissue (PVAT) dysfunction is associated with vascular damage in cardiometabolic diseases. Although heart failure (HF)-induced endothelial dysfunction is associated with renin-angiotensin system (RAS) activation, no data have correlated this syndrome with PVAT dysfunction. Thus, the aim of the present study was to investigate whether the hyperactivation of the RAS in PVAT participates in the vascular dysfunction observed in rats with HF after myocardial infarction surgery. Wire myograph studies were carried out in thoracic aorta rings in the presence and absence of PVAT. An anticontractile effect of PVAT was observed in the rings of the control rats in the presence (33%) or absence (11%) of endothelium. Moreover, this response was substantially reduced in animals with HF (5%), and acute type 1 angiotensin II receptor (AT1R) and type 2 angiotensin II receptor (AT2R) blockade restored the anticontractile effect of PVAT. In addition, the angiotensin-converting enzyme 1 (ACE1) activity (26%) and angiotensin II levels (51%), as well as the AT1R and AT2R gene expression, were enhanced in the PVAT of rats with HF. Associated with these alterations, HF-induced lower nitric oxide bioavailability, oxidative stress and whitening of the PVAT, which suggests changes in the secretory function of this tissue. The ACE1/angiotensin II/AT1R and AT2R axes are involved in thoracic aorta PVAT dysfunction in rats with HF. These results suggest PVAT as a target in the pathophysiology of vascular dysfunction in HF and provide new perspectives for the treatment of this syndrome.

LP2, the first lanthipeptide GPCR agonist in a human pharmacokinetics and safety study

Introduction of a lanthionine into a peptide may enhance target affinity, target specificity and proteolytic resistance. This manuscript reports preclinical safety studies and the first-in-human study with the lanthipeptide AT₂R agonist LP2, a structural analog of cAng-(1-7), whose N-terminus was protected against aminopeptidases by the presence of a d-lysine. None of the preclinical studies, including an in vitro multitarget panel, behavioral, respiratory and cardiovascular measurements, genotoxicity and toxicity studies in rat and dog, posed any safety concern. Due to lack of toxicity the maximum tolerated dose was not reached neither in rat nor in dog. In the human dose escalation study, healthy male volunteers received a single 1 mL subcutaneous injection (0.001 mg, 0.01 mg or 0.1 mg) of LP2 or matching placebo. In contrast to angiotensin II which has a T_1/2 in plasma of < 1 min, LP2 has a T_1/2 of approximately 2.1-2.6 hours. The fraction of the dose excreted unchanged in urine ranged from 84.73 ± 10.4 % at a dose of 0.001 mg to 66.4 ± 3.9 % at 0.1 mg. There were no deaths, serious adverse events or subject withdrawals as a result of an adverse event. The incidence of adverse events was 16.7 %; each was mild in severity. One adverse event, peripheral coldness, was considered to be possibly related to LP2 at 0.001 mg LP2. None of the results was considered to pose a clinically relevant safety concern. This study supports the potential for the therapeutic use of lanthipeptides.

Estrogens and the Angiotensin II Type 2 Receptor Control Flow-Mediated Outward Remodeling in the Female Mouse Mesenteric Artery

Flow-mediated outward remodeling (FMR) is involved in postischemic revascularization. Angiotensin II type 2 receptor (AT2R), through activation of T-cell-mediated IL-17 production, and estrogens are involved in FMR. Thus, we investigated the interplay between estrogens and AT2R in FMR using a model of ligation of feed arteries supplying collateral pathways in mouse mesenteric arteries in vivo. Arteries were collected after 2 (inflammatory phase), 4 (diameter expansion phase), and 7 days (remodeling completed). We used AT2R+/+ and AT2R-/- ovariectomized (OVX) female mice treated or not with 17-beta-estradiol (E2). Seven days after ligation, arterial diameter was larger in high flow (HF) compared to normal flow (NF) arteries. FMR was absent in OVX mice and restored by E2. AT2R gene expression was higher in HF than in NF arteries only in E2-treated OVX AT2R+/+ mice. CD11b and TNF alpha levels (inflammatory phase), MMP2 and TIMP1 (extracellular matrix digestion), and NOS3 (diameter expansion phase) expression levels were higher in HF than in NF arteries only in E2-treated AT2R+/+ mice, not in the other groups. Thus, E2 is necessary for AT2R-dependent diameter expansion, possibly through activation of T-cell AT2R, in arteries submitted chronically to high blood flow.

Angiotensin-(1-9) prevents vascular remodeling by decreasing vascular smooth muscle cell dedifferentiation through a FoxO1-dependent mechanism

The renin-angiotensin system, one of the main regulators of vascular function, controls vasoconstriction, inflammation and vascular remodeling. Antagonistic actions of the counter-regulatory renin-angiotensin system, which include vasodilation, anti-proliferative, anti-inflammatory and anti-remodeling effects, have also been described. However, little is known about the direct effects of angiotensin-(1-9), a peptide of the counter-regulatory renin-angiotensin system, on vascular smooth muscle cells. Here, we studied the anti-vascular remodeling effects of angiotensin-(1-9), with special focus on the control of vascular smooth muscle cell phenotype. Angiotensin-(1-9) decreased blood pressure and aorta media thickness in spontaneously hypertensive rats. Reduction of media thickness was associated with decreased vascular smooth muscle cell proliferation. In the A7r5 VSMC cell line and in primary cultures of rat aorta smooth muscle cells, angiotensin-(1-9) did not modify basal proliferation. However, angiotensin-(1-9) inhibited proliferation, migration and contractile protein decrease induced by platelet derived growth factor-BB. Moreover, angiotensin-(1-9) reduced Akt and FoxO1 phosphorylation at 30 min, followed by an increase of total FoxO1 protein content. Angiotensin-(1-9) effects were blocked by the AT2R antagonist PD123319, Akt-Myr overexpression and FoxO1 siRNA. These data suggest that angiotensin-(1-9) inhibits vascular smooth muscle cell dedifferentiation by an AT2R/Akt/FoxO1-dependent mechanism.

Maternal high-fat diet increases vascular contractility in adult offspring in a sex-dependent manner

A maternal high-fat diet (HFD) is a risk factor for cardiovascular diseases in offspring. The aim of the study was to determine whether maternal HFD causes the epigenetic programming of vascular angiotensin II receptors (ATRs) and leads to heightened vascular contraction in adult male offspring in a sex-dependent manner. Pregnant rats were treated with HFD (60% kcal fat). Aortas were isolated from adult male and female offspring. Maternal HFD increased phenylephrine (PE)-and angiotensin II (Ang II)-induced contractions of the aorta in male but not female offspring. N^G-nitro-L-arginine (ʟ-NNA; 100 μM) abrogated the maternal HFD-induced increase in PE-mediated contraction. HFD caused a decrease in endothelium-dependent relaxations induced by acetylcholine in male but not female offspring. However, it had no effect on sodium nitroprusside-induced endothelium-independent relaxations of aortas regardless of sex. The AT₁ receptor (AT₁R) antagonist losartan (10 μM), but not the AT₂ receptor (AT₂R) antagonist PD123319 (10 μM), blocked Ang II-induced contractions in both control and HFD offspring in both sexes. Maternal HFD increased AT₁R but decreased AT₂R, leading to an increased ratio of AT₁R/AT₂R in HFD male offspring, which was associated with selective decreases in DNA methylation at the AT_1aR promoter and increases in DNA methylation at the AT₂R promoter. The vascular ratio of AT₁R/AT₂R was not significantly different in HFD female offspring compared with the control group. Our results indicated that maternal HFD caused a differential regulation of vascular AT₁R and AT₂R gene expression through a DNA methylation mechanism, which may be involved in HFD-induced vascular dysfunction and the development of a hypertensive phenotype in adulthood in a sex-dependent manner.

Time course of decompensation after angiotensin II and high-salt diet in Balb/CJ mice suggests pulmonary hypertension-induced cardiorenal syndrome

The genetic background of a mouse strain determines its susceptibility to disease. C57BL/6J and Balb/CJ are two widely used inbred mouse strains that we found react dramatically differently to angiotensin II and high-salt diet (ANG II + Salt). Balb/CJ show increased mortality associated with anuria and edema formation while C57BL/6J develop arterial hypertension but do not decompensate and die. Clinical symptoms of heart failure in Balb/CJ mice gave the hypothesis that ANG II + Salt impairs cardiac function and induces cardiac remodeling in male Balb/CJ but not in male C57BL/6J mice. To test this hypothesis, we measured cardiac function using echocardiography before treatment and every day for 7 days during treatment with ANG II + Salt. Interestingly, pulsed wave Doppler of pulmonary artery flow indicated increased pulmonary vascular resistance and right ventricle systolic pressure in Balb/CJ mice, already 24 h after ANG II + Salt treatment was started. In addition, Balb/CJ mice showed abnormal diastolic filling indicated by reduced early and late filling and increased isovolumic relaxation time. Furthermore, Balb/CJ exhibited lower cardiac output compared with C57BL/6J even though they retained more sodium and water, as assessed using metabolic cages. Left posterior wall thickness increased during ANG II + Salt treatment but did not differ between the strains. In conclusion, ANG II + Salt treatment causes early restriction of pulmonary flow and reduced left ventricular filling and cardiac output in Balb/CJ, which results in fluid retention and peripheral edema. This makes Balb/CJ a potential model to study the adaptive capacity of the heart for identifying new disease mechanisms and drug targets.

The renin-angiotensin system: going beyond the classical paradigms

Thirty years ago, a novel axis of the renin-angiotensin system (RAS) was unveiled by the discovery of angiotensin-(1−7) [ANG-(1−7)] generation in vivo. Later, angiotensin-converting enzyme 2 (ACE2) was shown to be the main mediator of this reaction, and Mas was found to be the receptor for the heptapeptide. The functional analysis of this novel axis of the RAS that followed its discovery revealed numerous protective actions in particular for cardiovascular diseases. In parallel, similar protective actions were also described for one of the two receptors of ANG II, the ANG II type 2 receptor (AT₂R), in contrast to the other, the ANG II type 1 receptor (AT₁R), which mediates deleterious actions of this peptide, e.g., in the setting of cardiovascular disease. Very recently, another branch of the RAS was discovered, based on angiotensin peptides in which the amino-terminal aspartate was replaced by alanine, the alatensins. Ala-ANG-(1−7) or alamandine was shown to interact with Mas-related G protein-coupled receptor D, and the first functional data indicated that this peptide also exerts protective effects in the cardiovascular system. This review summarizes the presentations given at the International Union of Physiological Sciences Congress in Rio de Janeiro, Brazil, in 2017, during the symposium entitled “The Renin-Angiotensin System: Going Beyond the Classical Paradigms,” in which the signaling and physiological actions of ANG-(1−7), ACE2, AT₂R, and alatensins were reported (with a focus on noncentral nervous system-related tissues) and the therapeutic opportunities based on these findings were discussed.

Effects of angiotensin-(1-7) and angiotensin II on vascular tone in human cirrhotic splanchnic vessels

Evidence suggests that the renin angiotensin system (RAS) may play a role in the pathological splanchnic vasodilatation that leads to a hyperdynamic circulation in cirrhosis. An impaired contractile response to the angiotensin II peptide of the classical RAS system has been described in animal models of cirrhosis and in vivo in cirrhotic subjects. Furthermore, in experimental cirrhosis, the so-called alternate arm of the RAS was found to be upregulated and its effector peptide, angiotensin-(1-7) was shown to attenuate splanchnic vascular tone. The aim of this study was to explore the relevance of these findings to human disease. Omental arteries from cirrhotic and controls subjects were studied in isolation using a wire myograph. Varied protocols to evaluate the vasoactivity of RAS mediators were enacted. The contractile response to angiotensin II was comparable in cirrhotic vs control splanchnic arteries (61 ± 9 vs 68 ± 11% KPSS, respectively). Despite this, however, arterial contractility of the cirrhotic vessels correlated negatively with Child Pugh score (p = 0.0003, r=-0.83) and there was evidence that angiotensin II-induced contractility was increased in early cirrhosis. Angiotensin II-induced contractility was attenuated by angiotensin-(1-7) in cirrhotic and control arteries, however, adrenergic responses were not affected by angiotensin-(1-7). Contractile responses to angiotensin II are preserved in narrow lumen human cirrhotic splanchnic arteries and are comparatively augmented in early disease. Angiotensin-(1-7) had no vasodilatory effect on adrenergic tone, however, attenuated angiotensin II-induced contractility, possibly through an Ang-(1-7)-AT1R interaction, and thus may contribute to pathological vasodilatation in human cirrhosis.

Predominant Role of Nuclear Versus Membrane Estrogen Receptor α in Arterial Protection: Implications for Estrogen Receptor α Modulation in Cardiovascular Prevention/Safety

BACKGROUND

Although estrogen receptor α (ERα) acts primarily as a transcription factor, it can also elicit membrane-initiated steroid signaling. Pharmacological tools and transgenic mouse models previously highlighted the key role of ERα membrane-initiated steroid signaling in 2 actions of estrogens in the endothelium: increase in NO production and acceleration of reendothelialization.

METHODS AND RESULTS

Using mice with ERα mutated at cysteine 451 (ERaC451A), recognized as the key palmitoylation site required for ERα plasma membrane location, and mice with disruption of nuclear actions because of inactivation of activation function 2 (ERaAF20 = ERaAF2°), we sought to fully characterize the respective roles of nuclear versus membrane-initiated steroid signaling in the arterial protection conferred by ERα. ERaC451A mice were fully responsive to estrogens to prevent atheroma and angiotensin II-induced hypertension as well as to allow flow-mediated arteriolar remodeling. By contrast, ERαAF20 mice were unresponsive to estrogens for these beneficial vascular effects. Accordingly, selective activation of nuclear ERα with estetrol was able to prevent hypertension and to restore flow-mediated arteriolar remodeling.

CONCLUSIONS

Altogether, these results reveal an unexpected prominent role of nuclear ERα in the vasculoprotective action of estrogens with major implications in medicine, particularly for selective nuclear ERα agonist, such as estetrol, which is currently under development as a new oral contraceptive and for hormone replacement therapy in menopausal women.

Update on angiotensin AT2 receptors

PURPOSE OF REVIEW

This review updates major new findings and concepts introduced during the past year on the role of angiotensin II (Ang II) subtype 2 receptors (AT2Rs) in the control of blood pressure and renal function.

RECENT FINDINGS

AT2R activation prevents sodium (Na) retention and lowers blood pressure in the Ang II infusion model of experimental hypertension and prevents salt-sensitive hypertension in the obese Zucker rat model of obesity and the metabolic syndrome. Ang II metabolite, des-aspartyl-Ang II (Ang III) is the predominant AT2R agonist in the kidney and possibly also in the vasculature; a novel synthetic Ang III peptide, β-Pro-Ang III, is vasodepressor and lowers blood pressure in conscious spontaneously hypertensive rats in the presence of low-level Ang II type 1 receptor (AT1R) blockade. Because nitric oxide is a product of AT2R activation, a potential feed-forward loop, wherein nitric oxide increases AT2R transcription, may reinforce the beneficial actions of AT2R in the long term. AT2R activation also reduces proteinuria and oxidative stress in glomerulosclerotic kidneys of high-salt obese Zucker rats.

SUMMARY

Studies during the past year have helped to clarify the physiological and pathophysiological roles of AT2Rs and have enhanced the promise of AT2R agonists in cardiovascular and renal disease.

Understanding the Two Faces of Low-Salt Intake

Fierce debate has developed whether low-sodium intake, like high-sodium intake, could be associated with adverse outcome. The debate originates in earlier epidemiological studies associating high-sodium intake with high blood pressure and more recent studies demonstrating a higher cardiovascular event rate with both low- and high-sodium intake. This brings into question whether we entirely understand the consequences of high- and (very) low-sodium intake for the systemic hemodynamics, the kidney function, the vascular wall, the immune system, and the brain. Evolutionarily, sodium retention mechanisms in the context of low dietary sodium provided a survival advantage and are highly conserved, exemplified by the renin-angiotensin system. What is the potential for this sodium-retaining mechanism to cause harm? In this paper, we will consider current views on how a sodium load is handled, visiting aspects including the effect of sodium on the vessel wall, the sympathetic nervous system, the brain renin-angiotensin system, the skin as "third compartment" coupling to vascular endothelial growth factor C, and the kidneys. From these perspectives, several mechanisms can be envisioned whereby a low-sodium diet could potentially cause harm, including the renin-angiotensin system and the sympathetic nervous system. Altogether, the uncertainties preclude a unifying model or practical clinical guidance regarding the effects of a low-sodium diet for an individual. There is a very strong need for fundamental and translational studies to enhance the understanding of the potential adverse consequences of low-salt intake as an initial step to facilitate better clinical guidance.

Role of the ACE2‑Ang‑(1‑7)‑Mas axis in blood pressure regulation and its potential as an antihypertensive in functional foods (Review)

The renin‑angiotensin system (RAS) serves a critical role in blood pressure regulation and prevention of cardiovascular diseases. Efforts to develop functional foods that enhance the RAS have focused on inhibition of angiotensin‑converting enzyme (ACE) activity in the ACE‑angiotensin II (Ang II)‑Ang II type 1 receptor axis. ACE2 and the Mas receptor are important components of this axis. ACE2 catalyzes Ang II into Ang‑(1‑7), which then binds to the G‑protein‑coupled receptor Mas. In addition, it induces nitric oxide release from endothelial cells and exerts antiproliferative, vasodilatory and antihypertensive effects. The present review examined recent findings regarding the physiological and biological roles of the ACE2‑Ang‑(1‑7)‑Mas axis in the cardiovascular system, discussed potential food‑derived ACE2‑activating agents, and highlighted initiatives, based on this axis, that aim to develop functional foods for the treatment of hypertension.

Structural basis for selectivity and diversity in angiotensin II receptors

Angiotensin II receptors, AT₁R and AT₂R, serve as key components of the renin-angiotensin-aldosterone system. While AT₁R plays a central role in the regulation of blood pressure, the function of AT₂R is enigmatic with a variety of reported effects. To elucidate the mechanisms for the functional diversity and ligand selectivity between these receptors, we report crystal structures of the human AT₂R bound to an AT₂R-selective and an AT₁R/AT₂R-dual ligand, respectively, capturing the receptor in an active-like conformation. Unexpectedly, helix VIII was found in a non-canonical position, stabilizing the active-like state, but at the same time preventing the recruitment of G proteins/β-arrestins, in agreement with the lack of signaling responses in standard cellular assays. Structure-activity relationship, docking and mutagenesis studies revealed the interactions critical for ligand binding and selectivity. Our results thus provide insights into the structural basis for distinct functions of the angiotensin receptors, and may guide the design of novel selective ligands.

AT2 Receptors: Potential Therapeutic Targets for Hypertension

The renin-angiotensin system (RAS) is arguably the most important and best studied hormonal system in the control of blood pressure (BP) and the pathogenesis of hypertension. The RAS features its main effector angiotensin II (Ang II) acting via its 2 major receptors, angiotensin type-1(AT1R) and type-2 (AT2R). In general, AT2Rs oppose the detrimental actions of Ang II via AT1Rs. AT2R activation induces vasodilation and natriuresis, but its effects to lower BP in hypertension have not been as clear as anticipated. Recent studies, however, have demonstrated that acute and chronic AT2R stimulation can induce natriuresis and lower BP in the Ang II infusion model of experimental hypertension. AT2R activation induces receptor recruitment from intracellular sites to the apical plasma membranes of renal proximal tubule cells via a bradykinin, nitric oxide, and cyclic guanosine 3',5' monophosphate signaling pathway that results in internalization and inactivation of sodium (Na+) transporters Na+-H+ exchanger-3 and Na+/K+ATPase. These responses do not require the presence of concurrent AT1R blockade and are effective both in the prevention and reversal of hypertension. This review will address the role of AT2Rs in the control of BP and Na+ excretion and the case for these receptors as potential therapeutic targets for hypertension in humans.

Microvascular vasodilator properties of the angiotensin II type 2 receptor in a mouse model of type 1 diabetes

Diabetes Mellitus is associated with severe cardiovascular disorders involving the renin-angiotensin system, mainly through activation of the angiotensin II type 1 receptor (AT1R). Although the type 2 receptor (AT2R) opposes the effects of AT1R, with vasodilator and anti-trophic properties, its role in diabetes is debatable. Thus we investigated AT2R-mediated dilatation in a model of type 1 diabetes induced by streptozotocin in 5-month-old male mice lacking AT2R (AT2R^−/y). Glucose tolerance was reduced and markers of inflammation and oxidative stress (cyclooxygenase-2, gp91phox p22phox and p67phox) were increased in AT2R^−/y mice compared to wild-type (WT) animals. Streptozotocin-induced hyperglycaemia was higher in AT2R^−/y than in WT mice. Arterial gp91phox and MnSOD expression levels in addition to blood 8-isoprostane and creatinine were further increased in diabetic AT2R^−/y mice compared to diabetic WT mice. AT2R-dependent dilatation in both isolated mesenteric resistance arteries and perfused kidneys was greater in diabetic mice than in non-diabetic animals. Thus, in type 1 diabetes, AT2R may reduce glycaemia and display anti-oxidant and/or anti-inflammatory properties in association with greater vasodilatation in mesenteric arteries and in the renal vasculature, a major target of diabetes. Therefore AT2R might represent a new therapeutic target in diabetes.

Long-term treatment of spontaneously hypertensive rats with PD123319 and electrophysiological remodeling of left ventricular myocardium

To investigate the effects of PD123319, an antagonist of angiotensin II subtype-2 receptor (AT2R), on the electrophysiological characteristics of the left ventricular hypertrophic myocardium in spontaneously hypertensive rats (SHR). A total of twenty-four 10-week-old male SHR were divided into two groups: PD123319 and non-PD123319 groups (n = 12 in each). Twelve 10-week-old Wistar-Kyoto rats served as the control group. Systolic blood pressure, left ventricular mass index (LVMI), ventricular effective refractory period, and ventricular fibrillation threshold were also measured after 8 weeks. I _Na, I _CaL, I _to, and membrane capacitance were measured in the left ventricular myocytes after 8 weeks by whole-cell patch clamp. PD123319 increased LVMI compared with the non-PD123319 group (PD123319 vs. non-PD123319, 3.83 ± 0.11 vs. 3.60 ± 0.19 mg/g; P < 0.01). PD123319 also decreased the ventricular fibrillation threshold compared with the non-PD123319 group (PD123319 vs. non-PD123319, 14.75 ± 0.65 vs. 16.0 ± 0.86 mA; P < 0.01). PD123319 enhanced membrane capacitance compared with the non-PD123319 group (PD123319 vs. non-PD123319, 283.63 ± 5.80 vs. 276.50 ± 4.28 pF; P < 0.05). PD123319 increased the density of I _CaL compared with the non-PD123319 group (PD123319 vs. non-PD123319, -6.76 ± 0.48 vs. -6.13 ± 0.30 pA/pF; P < 0.05). PD123319 decreased the density of I _to compared with the non-PD123319 group (PD123319 vs. non-PD123319, 11.49 ± 0.50 vs. 12.23 ± 0.36 pA/pF; P < 0.05). Long-term treatment with PD123319 worsened the development of myocyte hypertrophy and associated electrophysiological alterations in spontaneously hypertensive rat.

Comparison of the effects of levocetirizine and losartan on diabetic nephropathy and vascular dysfunction in streptozotocin-induced diabetic rats

This work was designed to investigate the effects of levocetirizine, a histamine H1 receptor antagonist, on diabetes-induced nephropathy and vascular disorder, in comparison to an angiotensin II receptor antagonist, losartan. Diabetes was induced in male Sprague Dawley rats by a single intraperitoneal injection of streptozotocin (50mg/kg). Diabetic rats were divided into three groups; diabetic, diabetic-levocetirizine (0.5mg/kg/day) and diabetic-losartan (25mg/kg/day). Treatments were started two weeks following diabetes induction and continued for additional eight weeks. At the end of the experiment, urine was collected and serum was separated for biochemical measurements. Tissue homogenates of kidney and aorta were prepared for measuring oxidative stress, nitric oxide (NO), transforming growth factor-β1 (TGF-β1) and tumor necrosis factor-α (TNF-α). Moreover, histological analyses were conducted and aortic vascular reactivity was investigated. Levocetirizine improved renal function in diabetic rats (evidenced by mitigation of diabetes-induced changes in kidney to body weight ratio, serum albumin, urinary proteins and creatinine clearance). Moreover, levocetirizine attenuated the elevated renal levels of TNF-α and TGF-β1, ameliorated renal oxidative stress and restored NO bioavailability in diabetic kidney. These effects were comparable to or surpassed those produced by losartan. Moreover, levocetirizine, similar to losartan, reduced the enhanced responsiveness of diabetic aorta to phenylephrine. Histological evaluation of renal and aortic tissues further confirmed the beneficial effects of levocetirizine on diabetic nephropathy and revealed a greater attenuation of diabetes-induced vascular hypertrophy by levocetirizine than by losartan. In conclusion, levocetirizine may offer comparable renoprotective effect to, and possibly superior vasculoprotective effects than, losartan in streptozotocin-diabetic rats.

AT2 receptor activities and pathophysiological implications

Although angiotensin II subtype-2 receptor (AT2R) was discovered over 2 decades ago, its contribution to physiology and pathophysiology is not fully elucidated. Current knowledge suggests that under normal physiologic conditions, AT2R counterbalances the effects of angiotensin II subtype-1 receptor (AT1R). A major obstacle for AT2R investigations was the lack of specific agonists. Most of the earlier AT2R studies were performed using the peptidic agonist, CG42112A, or the nonpeptidic antagonist PD123319. CGP42112A is nonspecific for AT2R and in higher concentrations can bind to AT1R. Recently, the development of specific nonpeptidic AT2R agonists boosted the efforts in identifying the therapeutic potentials for AT2R stimulation. Unlike AT1R, AT2R is involved in vasodilation by the release of bradykinin and nitric oxide, anti-inflammation, and healing from injury. Interestingly, the vasodilatory effects of AT2R stimulation were not associated with significant reduction in blood pressure. In the kidney, AT2R stimulation produced natriuresis, increased renal blood flow, and reduced tissue inflammation. In animal studies, enhanced AT2R function led to reduction of cardiac inflammation and fibrosis, and reduced the size of the infarcted area. Similarly, AT2R stimulation demonstrated protective effects in vasculature and brain.

Hypotensive and sympathoinhibitory responses to selective central AT2 receptor stimulation in spontaneously hypertensive rats

The type 2 angiotensin receptor (AT2R) has been suggested to counterbalance the type 1 angiotensin receptor (AT1R) in the central regulation of blood pressure and sympathetic tone. In the present study we investigated the blood pressure responses to stimulation of central AT2Rs by the selective agonist Compound 21 in conscious spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto rats (WKY rats). We also assessed the impact on noradrenaline [norepinephrine (NE)] plasma levels, autonomic function, spontaneous baroreflex sensitivity, and the possible involvement of the nitric oxide (NO) pathway and the AT1Rs. Chronic intracerebroventricular Compound 21 infusion lowered blood pressure and NE plasma levels in both rat strains. The night-time hypotensive effect was greater in SHRs compared with WKY rats. Compound 21 improved spontaneous baroreflex sensitivity more in SHRs than in WKY rats. These effects were abolished by co-administration of the AT2R antagonist PD123319 or the NO synthase inhibitor Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME). Central AT1R blockade did not enhance the hypotensive response to Compound 21. Chronic selective stimulation of central AT2Rs lowers blood pressure through sympathoinhibition, and improves spontaneous baroreflex sensitivity more in SHRs than in WKY rats. These responses appear to require a functioning central NO pathway, but are not modified by central AT1R blockade. Collectively, the data demonstrate specific beneficial effects of stimulation of central AT2Rs in hypertension associated with increased sympathetic tone, and suggest that central AT2Rs may represent a potential new therapeutic target for the treatment of neurogenic hypertension.

Angiotensin type 1 receptor mediates renal production and conversion of prostaglandins E2 to F2α in conscious diabetic rats

INTRODUCTION

Previous studies demonstrated that stimulation of angiotensin subtype 1 receptor (AT1R) led to increased renal generation of prostaglandins E2 (PGE2) and renal inflammation. In turn, PGE2 increases AT1R activity. The conversion of PGE2 to the less active metabolite prostaglandin F2α (PGF2α) via 9-ketoreductase interrupts this feedback loop. The effects of diabetes on the interface between AT1R, PGE2 and PGF2α are not well established. We hypothesized that in diabetes, an aberrant AT1R activity enhances the biosynthesis of PGE2 and impairs the activity of PGE 9-ketoreductase, leading to accumulation of PGE2.

MATERIALS AND METHODS

Using microdialysis technique, we monitored renal interstitial fluid levels of angiotensin II (Ang II), PGE2 and PGF2α in control and AT1R blocker, valsartan, treated diabetic rats (N=8 each). We utilized the PGF2α to PGE2 ratio as indirect measure of PGE 9-ketoreductase activity.

RESULTS

Diabetes increased renal interstitial fluid levels of Ang II, PGE2 and PGF2α. PGF2α/PGE2 ratio increased by the third week, but declined by the sixth week of diabetes. Valsartan reduced PGE2 and PGF2α levels and increased Ang II and the conversion of PGE2 to PGF2α.

CONCLUSION

Our results suggest that in diabetes, AT1R increases PGE2 generation and reduces conversion of PGE2 to PGF2α with the progression of diabetes.

Compound 21, a selective agonist of angiotensin AT2 receptors, prevents endothelial inflammation and leukocyte adhesion in vitro and in vivo

BACKGROUND AND PURPOSE

Angiotensin AT2 receptors are upregulated in disease states such as atherosclerosis and blockade of the AT2 receptors exacerbates plaque formation. Direct stimulation of these receptors is anti-atherogenic but the mechanisms and pathways involved remain unknown. We examined the effect of direct AT2 receptor stimulation with Compound 21 (C21) on the leukocyte adhesion cascade in vitro, right through to plaque formation in vivo.

EXPERIMENTAL APPROACH

Effects of C21 on TNFα-induced inflammation were assessed in human umbilical vein endothelial cells (HUVECs), activation of monocytes, polarisation of monocyte-derived macrophages and in intact mouse aortae.

KEY RESULTS

C21 attenuated TNFα-induced: monocyte adhesion to cultured HUVECs, adhesion molecule expression and abolished TNFα-induced ROS production. TNFα-induced NFκB translocation from the cytoplasm to the nucleus, essential for cytokine production, was prevented by C21. C21 did not influence monocyte activation or macrophage polarisation but did reduce TNFα and IL-6 mRNA expression in M1 macrophages. The anti-inflammatory effects of C21 were abolished by an AT2 receptor antagonist confirming that the effects of C21 were AT2 receptor-mediated. Also, leukocyte adhesion and cytokine gene expression, induced by high-fat diet (HFD), was attenuated in ApoE(-/-) mice treated with C21. Plaque size and stability were improved with C21 treatment with increased smooth muscle cell composition and decreased lipid size, compared with HFD-saline treated mice.

CONCLUSION AND IMPLICATIONS

C21 prevented TNFα-induced and HFD-induced vascular inflammation in vitro and in vivo. Our data provide strong evidence that the anti-atherosclerotic actions of C21 were due to vascular anti-inflammatory effects, mediated by AT2 receptors.

Angiotensin II in inflammation, immunity and rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease that is characterized by increased cardiovascular morbidity and mortality, independent of the traditional risk factors for cardiovascular disease. Although classically known for its role in the regulation of circulatory homeostasis, angiotensin II (Ang II) is recognized to act as a powerful proinflammatory mediator. Some research has showed that Ang II plays important roles in autoimmune diseases, including RA, systemic lupus erythematosus and multiple sclerosis. Ang II blockers prove effective in reducing inflammation and autoimmunity in rheumatic diseases and their relative safety, together with their effects for reducing the cardiovascular disease risk, suggest that Ang II blockers may at least act as effective adjunctive therapy for disease control in patients with RA. The present review focuses systematically on the potential impact of Ang II and its receptors on inflammation and immunomodulation in patients with RA.

Angiotensin-(1-9) reverses experimental hypertension and cardiovascular damage by inhibition of the angiotensin converting enzyme/Ang II axis

BACKGROUND

Little is known about the biological effects of angiotensin-(1-9), but available evidence shows that angiotensin-(1-9) has beneficial effects in preventing/ameliorating cardiovascular remodeling.

OBJECTIVE

In this study, we evaluated whether angiotensin-(1-9) decreases hypertension and reverses experimental cardiovascular damage in the rat.

METHODS AND RESULTS

Angiotensin-(1-9) (600  ng/kg per min for 2 weeks) reduced already-established hypertension in rats with early high blood pressure induced by angiotensin II infusion or renal artery clipping. Angiotensin-(1-9) also improved cardiac (assessed by echocardiography) and endothelial function in small-diameter mesenteric arteries, cardiac and aortic wall hypertrophy, fibrosis, oxidative stress, collagen and transforming growth factor type β - 1 protein expression (assessed by western blot). The beneficial effect of angiotensin-(1-9) was blunted by coadministration of the angiotensin type 2(AT2) receptor blocker PD123319 (36  ng/kg per min) but not by coadministration of the Mas receptor blocker A779 (100  ng/kg per min). Angiotensin-(1-9) treatment also decreased circulating levels of Ang II, angiotensin-converting enzyme activity and oxidative stress in aorta and left ventricle. Whereas, Ang-(1-9) increased endothelial nitric oxide synthase mRNA levels in aorta as well as plasma nitrate levels.

CONCLUSION

Angiotensin-(1-9) reduces hypertension, ameliorates structural alterations (hypertrophy and fibrosis), oxidative stress in the heart and aorta and improves cardiac and endothelial function in hypertensive rats. These effects were mediated by the AT2 receptor but not by the angiotensin-(1-7)/Mas receptor axis.

Metoprolol restores expression and vasodilatation function of AT2R in spontaneously hypertensive rats

Angiotensin II type 2 receptor (AT2R) is thought as an important regulatory target during antihypertensive treatment but its role in vasomotor regulation remains controversial. The interactional relationship between the sympathetic nervous systems and the renin-angiotensin-aldosterone system (RAS) has been revealed but poorly investigated. This work was designed to explore the effect of metoprolol (MET) treatment on the RAS, especially the expression and vasomotor function of AT2R, in spontaneously hypertensive rats (SHR). The results showed that upregulated renin activity and Ang II concentration of plasma in SHR were inhibited by MET treatment. In isolated superior mesenteric arteries from both Wistar-Kyoto rats and SHR, Ang II perfusion induced vasodilatation after AT1R inhibition by telmisartan, although the vasodilatation was harmed in SHR. Furthermore, AT2R inhibitor PD123319 arrested the vasodilatation induced by Ang II. SHR received MET exerted improved vasodilatation mediated by AT2R (47.29% ± 5.16% vs. 24.99% ± 4.93% for MET and SHR, respectively; P < 0.05). Western blot analysis showed that MET restored expression of AT2R in SHR, which may contribute to MET's antihypertensive effect. These results suggested an impact of β-adrenergic blocker on RAS and supported an important role of AT2R in antihypertensive treatment.

Recent insights and therapeutic perspectives of angiotensin-(1-9) in the cardiovascular system

Chronic RAS (renin-angiotensin system) activation by both AngII (angiotensin II) and aldosterone leads to hypertension and perpetuates a cascade of pro-hypertrophic, pro-inflammatory, pro-thrombotic and atherogenic effects associated with cardiovascular damage. In 2000, a new pathway consisting of ACE2 (angiotensin-converting enzyme2), Ang-(1-9) [angiotensin-(1-9)], Ang-(1-7) [angiotensin-(1-7)] and the Mas receptor was discovered. Activation of this novel pathway stimulates vasodilation, anti-hypertrophy and anti-hyperplasia. For some time, studies have focused mainly on ACE2, Ang-(1-7) and the Mas receptor, and their biological properties that counterbalance the ACE/AngII/AT1R (angiotensin type 1 receptor) axis. No previous information about Ang-(1-9) suggested that this peptide had biological properties. However, recent data suggest that Ang-(1-9) protects the heart and blood vessels (and possibly the kidney) from adverse cardiovascular remodelling in patients with hypertension and/or heart failure. These beneficial effects are not modified by the Mas receptor antagonist A779 [an Ang-(1-7) receptor blocker], but they are abolished by the AT2R (angiotensin type 2 receptor) antagonist PD123319. Current information suggests that the beneficial effects of Ang-(1-9) are mediated via the AT2R. In the present review, we summarize the biological effects of the novel vasoactive peptide Ang-(1-9), providing new evidence of its cardiovascular-protective activity. We also discuss the potential mechanism by which this peptide prevents and ameliorates the cardiovascular damage induced by RAS activation.

Attenuation of L-type Ca²⁺ channel expression and vasomotor response in the aorta with age in both Wistar-Kyoto and spontaneously hypertensive rats

Age-related vascular diseases are induced by vascular dysfunction, which involves changes in the vasomotor response. The voltage-dependent L-type calcium channel (VDCC) protein is involved in the regulation of vessel function (contraction/relaxation action). In the present study, we evaluated age-related vasomotor function and expression of the signal-related target proteins, including VDCC, using thoracic aorta from both 8- and 40-week old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). In contraction experiments using aortic rings, vasomotor responses of both phenylephrine-induced contraction and acetylcholine-induced relaxation were significantly attenuated with age in SHR, whereas WKY did not lose activity with age. Contraction induced by angiotensin II was impaired only for the 40-week old SHR among all the rat groups tested, although enhanced AT1R/reduced AT2R expression with age was observed for both WKY and SHR. In contrast, a vasomotor responsiveness to Bay K 8644 (a VDCC agonist) at the initial contraction phase was significantly attenuated in both 40-week WKY and SHR with significant reduction of VDCC protein expression. The reduced VDCC expression in 40-week old rats significantly lowered the relaxation activity of VDCC blockers, such as verapamil and Trp-His, but did not affect that of nifedipine. Taken together, we provided the first evidence that aging caused a reduction of VDCC expression in rat aorta, irrespective of the rat strain, along with diminishment of the therapeutic potential of VDCC blockers.

Altered reactivity of resistance vasculature contributes to hypertension in elastin insufficiency

Elastin (Eln) insufficiency in mice and humans is associated with hypertension and altered structure and mechanical properties of large arteries. However, it is not known to what extent functional or structural changes in resistance arteries contribute to the elevated blood pressure that is characteristic of Eln insufficiency. Here, we investigated how Eln insufficiency affects the structure and function of the resistance vasculature. A functional profile of resistance vasculature in Eln(+/-) mice was generated by assessing small mesenteric artery (MA) contractile and vasodilatory responses to vasoactive agents. We found that Eln haploinsufficiency had a modest effect on phenylephrine-induced vasoconstriction, whereas ANG II-evoked vasoconstriction was markedly increased. Blockade of ANG II type 2 receptors with PD-123319 or modulation of Rho kinase activity with the inhibitor Y-27632 attenuated the augmented vasoconstriction, whereas acute Y-27632 administration normalized blood pressure in Eln(+/-) mice. Sodium nitroprusside- and isoproterenol-induced vasodilatation were normal, whereas ACh-induced vasodilatation was severely impaired in Eln(+/-) MAs. Histologically, the number of smooth muscle layers did not change in Eln(+/-) MAs; however, an additional discontinuous layer of Eln appeared between the smooth muscle layers that was absent in wild-type arteries. We conclude that high blood pressure arising from Eln insufficiency is due partly to permanent changes in vascular tone as a result of increased sensitivity of the resistance vasculature to circulating ANG II and to impaired vasodilatory mechanisms arising from endothelial dysfunction characterized by impaired endothelium-dependent vasodilatation. Eln insufficiency causes augmented ANG II-induced vasoconstriction in part through a novel mechanism that facilitates contraction evoked by ANG II type 2 receptors and altered G protein signaling.

Role of the renin-angiotensin system on abdominal aortic aneurysms

BACKGROUND

Abdominal aortic aneurysm (AAA) is a complex degenerative disease, which leads to morbidity and mortality in a large portion of the elderly population. Current treatment options for AAA are quite limited as there is no proven indication for pharmacological therapy and surgery is recommended for AAA larger than 5·5 cm in luminal diameter. Thus, there is a great need to elucidate the underlying pathophysiological cellular and molecular mechanisms to develop effective therapies. In this narrative review, we will discuss recent findings concerning some potential molecular and clinical aspects of the renin-angiotensin system (RAS) in AAA pathophysiology.

MATERIALS AND METHODS

This narrative review is based on the material found on MEDLINE and PubMed up to April 2013. We looked for the terms 'angiotensin, AT1 receptor, ACE inhibitors' in combination with 'abdominal aortic aneurysm, pathophysiology, pathways'.

RESULTS

Several basic research and clinical studies have recently investigated the role of the RAS in AAA. In particular, the subcutaneous infusion of Angiotensin II has been shown to induce AAA in Apo56 knockout mice. On the other hand, the pharmacological treatments targeting this system have been shown as beneficial in AAA patients.

CONCLUSIONS

Emerging evidence suggests that RAS may act as a molecular and therapeutic target for treating AAA. However, several issues on the role of RAS and the protective activities of angiotensin-converting enzyme (ACE) inhibitors and Angiotensin 1 receptors blockers against AAA require further clarifications.

Impact of AT2-receptor stimulation on vascular biology, kidney function, and blood pressure

The angiotensin type 2 receptor (AT2R) and the receptor MAS are receptors within the renin–angiotensin system, which mediate tissue-protective actions such as anti-inflammation, antifibrosis, and antiapoptosis. In recent years, several programs have been launched in order to develop drugs that act as agonists on the AT2R or MAS to take therapeutic advantage of the protective and regenerative properties of these receptors. This review article will focus on recent data obtained in preclinical animal and in vitro models with new AT2R-agonistic molecules (Compound 21 and β-amino acid substituted angiotensin II) and with relevance for blood pressure (BP) regulation or hypertensive end-organ damage. These data will include studies on vasodilation/vasoconstriction in isolated resistance arteries ex vivo, studies on kidney function, studies on vascular remodeling, and studies that measured the net effect of AT2R stimulation on BP in vivo. Current data indicate that although AT2R stimulation causes vasodilation ex vivo and promotes natriuresis, it does not alter BP levels in vivo acutely – at least as long as there is no additional low-dose blockade of AT1R. However, AT2R stimulation alone is able to attenuate hypertension-induced vascular remodeling and reduce arterial stiffening, which in more chronic settings and together with the natriuretic effect may result in modest lowering of BP. We conclude from these preclinical data that AT2R agonists are not suitable for antihypertensive monotherapy, but that this new future drug class may be beneficial in combination with established antihypertensives for the treatment of hypertension with improved protection from end-organ damage.

Activation of the MAS receptor by angiotensin-(1-7) in the renin-angiotensin system mediates mesenteric vasodilatation in cirrhosis

BACKGROUND & AIMS

Splanchnic vascular hypocontractility with subsequent increased portal venous inflow leads to portal hypertension. Although the renin-angiotensin system contributes to fibrogenesis and increased hepatic resistance in patients with cirrhosis, little is known about its effects in the splanchnic vasculature, particularly those of the alternate system in which angiotensin (Ang) II is cleaved by the Ang-converting enzyme-2 (ACE2) to Ang-(1-7), which activates the G-protein-coupled Mas receptor (MasR). We investigated whether this system contributes to splanchnic vasodilatation and portal hypertension in cirrhosis.

METHODS

We measured levels of renin-angiotensin system messenger RNA and proteins in splanchnic vessels from patients and rats with cirrhosis. Production of Ang-(1-7) and splanchnic vascular reactivity to Ang-(1-7) was measured in perfused mesenteric vascular beds from rats after bile-duct ligation. Ang-(1-7) and MasR were blocked in rats with cirrhosis to examine splanchnic vascular hemodynamics and portal pressure response.

RESULTS

Levels of ACE2 and MasR were increased in splanchnic vessels from cirrhotic patients and rats compared with healthy controls. We also observed an ACE2-dependent increase in Ang-(1-7) production. Ang-(1-7) mediated splanchnic vascular hypocontractility in ex vivo splanchnic vessels from rats with cirrhosis (but not control rats) via MasR stimulation. Identical effects were observed in the splanchnic circulation in vivo. MasR blockade reduced portal pressure, indicating that activation of this receptor in splanchnic vasculature promotes portal inflow to contribute to development of portal hypertension. In addition, the splanchnic effects of MasR required nitric oxide. Interestingly, Ang-(1-7) also decreased hepatic resistance.

CONCLUSIONS

In the splanchnic vessels of patients and rats with cirrhosis, increased levels of ACE2 appear to increase production of Ang-(1-7), which leads to activation of MasR and splanchnic vasodilatation in rats. This mechanism could cause vascular hypocontractility in patients with cirrhosis, and might be a therapeutic target for portal hypertension.

Angiotensin II type 2 receptor-mediated and nitric oxide-dependent renal vasodilator response to compound 21 unmasked by angiotensin-converting enzyme inhibition in spontaneously hypertensive rats in vivo

Angiotensin II type 2 receptor (AT2R)-mediated vasodilation has been demonstrated in different vascular beds in vitro and in perfused organs. In vivo studies, however, consistently failed to disclose renal vasodilator responses to compound 21, a selective AT2R agonist, even after angiotensin II type 1 receptor blockade. Here, we investigated in vivo whether angiotensin-converting enzyme inhibition, reducing endogenous angiotensin II levels, could unmask the effects of selective AT2R stimulation on blood pressure and renal hemodynamics in normotensive and hypertensive rats. After pretreatment with the angiotensin-converting enzyme inhibitor captopril, intravenous administration of compound 21 did not affect blood pressure and induced dose-dependent renal vasodilator responses in spontaneously hypertensive but not in normotensive rats. The D1 receptor agonist fenoldopam, used as positive control, reduced blood pressure and renal vascular resistance in both strains. The AT2R antagonist PD123319 and the nitric oxide synthase inhibitor L-NMMA (N(G)-monomethyl-L-arginine acetate) abolished the renal vasodilator response to compound 21 without affecting responses to fenoldopam. The cyclooxygenase inhibitor indomethacin partially inhibited the renal vascular response to compound 21, whereas the bradykinin B2 receptor antagonist icatibant was without effect. Angiotensin-converting enzyme inhibition unmasked a renal vasodilator response to selective AT2R stimulation in vivo, mediated by nitric oxide and partially by prostaglandins. AT2R may have a pathophysiological role to modulate renal hemodynamic effects of angiotensin II in the hypertensive state.

Expression and role of the angiotensin II AT2 receptor in human prostate tissue: in search of a new therapeutic option for prostate cancer

BACKGROUND

Evidence shows that angiotensin II type 1 receptor (AT1R) blockers may be associated with improved outcome in prostate cancer patients. It has been proposed that part of this effect could be due to angiotensin II type 2 receptor (AT2R) activation, the only active angiotensin II receptor in this situation. This study aimed to characterize the localization and expression of AT2R in prostate tissues and to assess its role on cell morphology and number in prostatic epithelial cells in primary culture.

METHODS

AT2R and its AT2R-interacting protein (ATIP) expression were assessed on non-tumoral and tumoral human prostate using tissue microarray immunohistochemistry, binding assay, and Western blotting. AT2R effect on cell number was measured in primary cultures of epithelial cells from non-tumoral human prostate.

RESULTS

AT2R was localized at the level of the acinar epithelial layer and its expression decreased in cancers with a Gleason score 6 or higher. In contrast, ATIP expression increased with cancer progression. Treatment of primary cell cultures from non-tumoral prostate tissues with C21/M024, a selective AT2R agonist, alone or in co-incubation with losartan, an AT1R antagonist, significantly decreased cell number compared to untreated cells.

CONCLUSIONS

AT2R and ATIP are present in non-tumoral human prostate tissues and differentially regulated according to Gleason score. The decrease in non-tumoral prostate cell number upon selective AT2R stimulation suggests that AT2R may have a protective role against prostate cancer development. Treatment with a selective AT2R agonist could represent a new approach for prostate cancer prevention or for patients on active surveillance.

Update on the angiotensin AT(2) receptor

It is quite well established that activation of the AT(2) receptor (AT(2)R) provides a counter-regulatory role to AT(1)R overactivity, particularly during pathological conditions. Indeed, a potential therapeutic role for the AT(2)R is currently being promulgated with the introduction of novel AT(2)R ligands such as compound 21 (C21). In this brief review, we will focus on recent evidence to suggest that AT(2)R exhibits promising organ protection in the context of the heart, kidney and brain, with inflammation and gender influencing outcome. However, this field is not without controversy since the 'flagship' ligand C21 has also come under scrutiny, although it is safe to say there is much evidence to support a potentially important role of AT(2)R in a number of cardiovascular diseases. This report updates recent data in this field.

Opportunities for targeting the angiotensin-converting enzyme 2/angiotensin-(1-7)/mas receptor pathway in hypertension

It is well known that the renin-angiotensin system (RAS) plays a pivotal role in the pathophysiology of cardiovascular diseases. This is well illustrated by the great success of ACE inhibitors and angiotensin (Ang) II AT(1) blockers in the treatment of hypertension and its complications. In the past decade, the classical concept of RAS orchestrated by a series of enzymatic reactions culminating in the linear generation and action of Ang II has expanded and become more complex. From the discoveries of new components such as the angiotensin converting enzyme 2 and the receptor Mas emerged a novel concept of dual opposite branches of the RAS: one vasoconstrictor and pro-hypertensive composed of ACE/Ang II/AT1; and other vasodilator and anti-hypertensive composed of ACE2/Ang-(1-7)/Mas. In this review we will discuss recent findings concerning the biological role of the ACE2/Ang-(1-7)/Mas arm in the cardiovascular system and highlight the initiatives to develop potential therapeutic strategies based on this axis for treating hypertension.

Different cross-talk sites between the renin-angiotensin and the kallikrein-kinin systems

Targeting the renin-angiotensin system (RAS) constitutes a major advance in the treatment of cardiovascular diseases. Evidence indicates that angiotensin-converting enzyme inhibitors and angiotensin AT1 receptor blockers act on both the RAS and the kallikrein-kinin system (KKS). In addition to the interaction between the RAS and KKS at the level of angiotensin-converting enzyme catalyzing both angiotensin II generation and bradykinin degradation, the RAS and KKS also interact at other levels: 1) prolylcarboxypeptidase, an angiotensin II inactivating enzyme and a prekallikrein activator; 2) kallikrein, a kinin-generating and prorenin-activating enzyme; 3) angiotensin-(1-7) exerts kininlike effects and potentiates the effects of bradykinin; and 4) the angiotensin AT1 receptor forms heterodimers with the bradykinin B2 receptor. Moreover, angiotensin II enhances B1 and B2 receptor expression via transcriptional mechanisms. These cross-talks explain why both the RAS and KKS are up-regulated in some circumstances, whereas in other circumstances both systems change in the opposite manner, expressed as an activated RAS and a depressed KKS. As the cross-talks between the RAS and the KKS play an important role in response to different stimuli, taking these cross-talks between the two systems into account may help in the development of drugs targeting the two systems.

Angiotensin II type 2 receptor mediates sex differences in mice renal interlobar arteries response to angiotensin II

OBJECTIVE

Functional sex differences are described in several vascular beds. In the case of renal vessels, sex differences could influence processes like regulation of blood pressure and ion balance. Angiotensin II and nitric oxide are important regulators of renal vascular tone. Females have higher nitric oxide synthase expression, nitric oxide bioavailability and ratio of angiotensin II type 2/type 1 receptors. Thus, our objective was to examine whether renal interlobar arteries present sex differences in their response to angiotensin II, and whether angiotensin II type 2 receptors play a role in such differences.

METHODS

We investigated the isometric contraction and relaxation of interlobar arteries from female and male mice under blockade of nitric oxide synthases and angiotensin II type 2 receptors. We also investigated the expression of angiotensin II receptors (type 1 and 2) and endothelial nitric oxide synthase.

RESULTS

Significantly less intense contraction to angiotensin II were seen in arteries from females in comparison to male mice. Inhibition of nitric oxide synthases and endothelial removal abolished this difference. Angiotensin II type 2 receptors blockade enhanced contraction to angiotensin II in females, but not in males. Endothelial-dependent vasodilation was more dependent on nitric oxide in females than in males. Expression of angiotensin II type 1 and type 2 receptors was similar between sexes. Expression of endothelial nitric oxide synthase was higher in females.

CONCLUSION

A sex-specific, nitric oxide-mediated effect via angiotensin II type 2 receptors underlies the sex differences in the response of interlobar arteries to angiotensin II. Our findings may help understanding sex differences in renal hemodynamics and blood pressure control.

The angiotensin-converting enzyme 2/angiotensin-(1-7)/Mas receptor axis: a potential target for treating thrombotic diseases

Despite many therapeutic advances leading to increasingly effective drug treatments, thrombotic events (such as ischaemic stroke, pulmonary embolism, deep venous thrombosis and acute myocardial infarction) still represent a major worldwide cause of morbidity and mortality. Remarkable effort has been made to identify new drug targets. There is growing evidence indicating that the recently described counter-regulator axis of the renin-angiotensin system (RAS), composed of Angiotensin-Converting Enzyme 2 (ACE2), Angiotensin-(1-7) and the Mas receptor, has protective effects against thrombosis. In addition, it could be considered as a promising target for treating or preventing this disease. In this narrative review, we focused on the recent findings of the role of the ACE2/Angiotensin-(1-7)/Mas axis on the haemostatic process and its therapeutic potential.