Bradykinin potentiation by angiotensin-(1-7) and ACE inhibitors correlates with ACE C- and N-domain blockade

Interplay of Angiotensin Peptides, Vasopressin, and Insulin in the Heart: Experimental and Clinical Evidence of Altered Interactions in Obesity and Diabetes Mellitus

The present review draws attention to the specific role of angiotensin peptides [angiotensin II (Ang II), angiotensin-(1-7) (Ang-(1-7)], vasopressin (AVP), and insulin in the regulation of the coronary blood flow and cardiac contractions. The interactions of angiotensin peptides, AVP, and insulin in the heart and in the brain are also discussed. The intracardiac production and the supply of angiotensin peptides and AVP from the systemic circulation enable their easy access to the coronary vessels and the cardiomyocytes. Coronary vessels and cardiomyocytes are furnished with AT1 receptors, AT2 receptors, Ang (1-7) receptors, vasopressin V1 receptors, and insulin receptor substrates. The presence of some of these molecules in the same cells creates good conditions for their interaction at the signaling level. The broad spectrum of actions allows for the engagement of angiotensin peptides, AVP, and insulin in the regulation of the most vital cardiac processes, including (1) cardiac tissue oxygenation, energy production, and metabolism; (2) the generation of the other cardiovascular compounds, such as nitric oxide, bradykinin (Bk), and endothelin; and (3) the regulation of cardiac work by the autonomic nervous system and the cardiovascular neurons of the brain. Multiple experimental studies and clinical observations show that the interactions of Ang II, Ang(1-7), AVP, and insulin in the heart and in the brain are markedly altered during heart failure, hypertension, obesity, and diabetes mellitus, especially when these diseases coexist. A survey of the literature presented in the review provides evidence for the belief that very individualized treatment, including interactions of angiotensins and vasopressin with insulin, should be applied in patients suffering from both the cardiovascular and metabolic diseases.

Knockout of ACE-N facilitates improved cardiac function after myocardial infarction

Angiotensin-converting enzyme (ACE) hydrolyzes N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) into inactive fragments through its N-terminal site (ACE-N). We previously showed that Ac-SDKP mediates ACE inhibitors' cardiac effects. Whether increased bioavailability of endogenous Ac-SDKP caused by knocking out ACE-N also improves cardiac function in myocardial infarction (MI)-induced heart failure (HF) is unknown. Wild-type (WT) and ACE-N knockout (ACE-NKO) mice were subjected to MI by ligating the left anterior descending artery and treated with vehicle or Ac-SDKP (1.6 mg/kg/day, s.c.) for 5 weeks, after which echocardiography was performed and left ventricles (LV) were harvested for histology and molecular biology studies. ACE-NKO mice showed increased plasma Ac-SDKP concentrations in both sham and MI group compared to WT. Exogenous Ac-SDKP further increased its circulating concentrations in WT and ACE-NKO. Shortening (SF) and ejection (EF) fractions were significantly decreased in both WT and ACE-NKO mice post-MI, but ACE-NKO mice exhibited significantly lesser decrease. Exogenous Ac-SDKP ameliorated cardiac function post-MI only in WT but failed to show any additive improvement in ACE-NKO mice. Sarcoendoplasmic reticulum calcium transport ATPase (SERCA2), a marker of cardiac function and calcium homeostasis, was significantly decreased in WT post-MI but rescued with Ac-SDKP, whereas ACE-NKO mice displayed less loss of SERCA2 expression. Our study demonstrates that gene deletion of ACE-N resulted in improved LV cardiac function in mice post-MI, which is likely mediated by increased circulating Ac-SDKP and minimally reduced expression of SERCA2. Thus, future development of specific and selective inhibitors for ACE-N could represent a novel approach to increase endogenous Ac-SDKP toward protecting the heart from post-MI remodeling.

Kidney Angiotensin in Cardiovascular Disease: Formation and Drug Targeting

The concept of local formation of angiotensin II in the kidney has changed over the last 10-15 years. Local synthesis of angiotensinogen in the proximal tubule has been proposed, combined with prorenin synthesis in the collecting duct. Binding of prorenin via the so-called (pro)renin receptor has been introduced, as well as megalin-mediated uptake of filtered plasma-derived renin-angiotensin system (RAS) components. Moreover, angiotensin metabolites other than angiotensin II [notably angiotensin-(1-7)] exist, and angiotensins exert their effects via three different receptors, of which angiotensin II type 2 and Mas receptors are considered renoprotective, possibly in a sex-specific manner, whereas angiotensin II type 1 (AT1) receptors are believed to be deleterious. Additionally, internalized angiotensin II may stimulate intracellular receptors. Angiotensin-converting enzyme 2 (ACE2) not only generates angiotensin-(1-7) but also acts as coronavirus receptor. Multiple, if not all, cardiovascular diseases involve the kidney RAS, with renal AT1 receptors often being claimed to exert a crucial role. Urinary RAS component levels, depending on filtration, reabsorption, and local release, are believed to reflect renal RAS activity. Finally, both existing drugs (RAS inhibitors, cyclooxygenase inhibitors) and novel drugs (angiotensin receptor/neprilysin inhibitors, sodium-glucose cotransporter-2 inhibitors, soluble ACE2) affect renal angiotensin formation, thereby displaying cardiovascular efficacy. Particular in the case of the latter three, an important question is to what degree they induce renoprotection (e.g., in a renal RAS-dependent manner). This review provides a unifying view, explaining not only how kidney angiotensin formation occurs and how it is affected by drugs but also why drugs are renoprotective when altering the renal RAS. SIGNIFICANCE STATEMENT: Angiotensin formation in the kidney is widely accepted but little understood, and multiple, often contrasting concepts have been put forward over the last two decades. This paper offers a unifying view, simultaneously explaining how existing and novel drugs exert renoprotection by interfering with kidney angiotensin formation.

SARS-CoV-2 Infections, Impaired Tissue, and Metabolic Health: Pathophysiology and Potential Therapeutics

The SARS-CoV-2 enters the human airways and comes into contact with the mucous membranes lining the mouth, nose, and eyes. The virus enters the healthy cells and uses cell machinery to make several copies of the virus. Critically ill patients infected with SARS-CoV-2 may have damaged lungs, air sacs, lining, and walls. Since COVID-19 causes cytokine storm, it damages the alveolar cells of the lungs and fills them with fluid, making it harder to exchange oxygen and carbon dioxide. The SARS-CoV-2 infection causes a range of complications, including mild to critical breathing difficulties. It has been observed that older people suffering from health conditions like cardiomyopathies, nephropathies, metabolic syndrome, and diabetes instigate severe symptoms. Many people who died due to COVID-19 had impaired metabolic health [IMH], characterized by hypertension, dyslipidemia, and hyperglycemia, i.e., diabetes, cardiovascular system, and renal diseases making their retrieval challenging. Jeopardy stresses for increased mortality from COVID-19 include older age, COPD, ischemic heart disease, diabetes mellitus, and immunosuppression. However, no targeted therapies are available as of now. Almost two-thirds of diagnosed coronavirus patients had cardiovascular diseases and diabetes, out of which 37% were under 60. The NHS audit revealed that with a higher expression of ACE-2 receptors, viral particles could easily bind their protein spikes and get inside the cells, finally causing COVID-19 infection. Hence, people with IMH are more prone to COVID-19 and, ultimately, comorbidities. This review provides enormous information about tissue [lungs, heart and kidneys] damage, pathophysiological changes, and impaired metabolic health of SARS-CoV-2 infected patients. Moreover, it also designates the possible therapeutic targets of COVID-19 and drugs which can be used against these targets.

Association between COVID-19 and angiotensin-converting enzyme inhibitors with the spotlight on zinc: an opinion

In the setting of the raging COVID-19 pandemic, the search for innovative therapeutics is desperately sought after. As we learn more about the characteristics and metabolic health of patients and as our understanding of COVID-19 pathophysiology and treatment progresses, so is our understanding of medication effects that might increase disease severity. As of late, ACE inhibitors have been under investigation for a potential increase in illness severity due to ACE2 upregulation. Given our knowledge of other nutrient-pharmaceutical interactions, could the ACE inhibitor impact on COVID be due to something else? In this paper, we discuss the possibility that ACE inhibitors might be affecting COVID-19 patients by causing zinc insufficiency.KEY MESSAGESZinc deficiency caused by chronic ACE inhibitor usage may exacerbate the pathogenicity of COVID-19 in susceptible patients.A multi-center study is needed to assess the zinc levels of patients with COVID-19 who are taking ACE inhibitors and other medications that may result in low zinc levels.

Crosstalk between the renin-angiotensin, complement and kallikrein-kinin systems in inflammation

During severe inflammatory and infectious diseases, various mediators modulate the equilibrium of vascular tone, inflammation, coagulation and thrombosis. This Review describes the interactive roles of the renin–angiotensin system, the complement system, and the closely linked kallikrein–kinin and contact systems in cell biological functions such as vascular tone and leakage, inflammation, chemotaxis, thrombosis and cell proliferation. Specific attention is given to the role of these systems in systemic inflammation in the vasculature and tissues during hereditary angioedema, cardiovascular and renal glomerular disease, vasculitides and COVID-19. Moreover, we discuss the therapeutic implications of these complex interactions, given that modulation of one system may affect the other systems, with beneficial or deleterious consequences.

The renin–angiotensin, complement and kallikrein–kinin systems comprise a multitude of mediators that modulate physiological responses during inflammatory and infectious diseases. This Review investigates the complex interactions between these systems and how these are dysregulated in various conditions, including cardiovascular diseases and COVID-19, as well as their therapeutic implications.

Implications of Endothelial Cell-Mediated Dysfunctions in Vasomotor Tone Regulation

Cardiovascular diseases (CVD) constitute the major cause of death worldwide and show a higher prevalence in the adult population. The human umbilical cord consistsof two arteries and one vein, both composed of three tunics. The tunica intima, lined with endothelial cells, regulates vascular tone through the production/release of vasoregulatory substances. These substances can be vasoactive factors released by endothelial cells (ECs) that cause vasodilation (NO, PGI2, EDHF, and Bradykinin) or vasoconstriction (ET1, TXA2, and Ang II) depending on the cell type (ECs or SMC) that reacts to the stimulus. Vascular studies using ECs are important for the analysis of cardiovascular diseases since endothelial dysfunction is an important CVD risk factor. In this paper, we will address the morphological characteristics of the human umbilical cord and its component vessels. the constitution of the vascular endothelium, and the evolution of human umbilical cord-derived endothelial cells when isolated. Moreover, the role played by the endothelium in the vasomotor tone regulation, and how it may be associated with the existence of CVD, were discussed.

Type 1 Diabetes Mellitus in the SARS-CoV-2 Pandemic: Oxidative Stress as a Major Pathophysiological Mechanism Linked to Adverse Clinical Outcomes

Recent reports have demonstrated the association between type 1 diabetes mellitus (T1DM) and increased morbidity and mortality rates during coronavirus disease (COVID-19) infection, setting a priority of these patients for vaccination. Impaired innate and adaptive immunity observed in T1DM seem to play a major role. Severe, life-threatening COVID-19 disease is characterized by the excessive release of pro-inflammatory cytokines, known as a "cytokine storm". Patients with T1DM present elevated levels of cytokines including interleukin-1a (IL), IL-1β, IL-2, IL-6 and tumor necrosis factor alpha (TNF-α), suggesting the pre-existence of chronic inflammation, which, in turn, has been considered the major risk factor of adverse COVID-19 outcomes in many cohorts. Even more importantly, oxidative stress is a key player in COVID-19 pathogenesis and determines disease severity. It is well-known that extreme glucose excursions, the prominent feature of T1DM, are a potent mediator of oxidative stress through several pathways including the activation of protein kinase C (PKC) and the increased production of advanced glycation end products (AGEs). Additionally, chronic endothelial dysfunction and the hypercoagulant state observed in T1DM, in combination with the direct damage of endothelial cells by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), may result in endothelial and microcirculation impairment, which contribute to the pathogenesis of acute respiratory syndrome and multi-organ failure. The binding of SARS-CoV-2 to angiotensin converting enzyme 2 (ACE2) receptors in pancreatic b-cells permits the direct destruction of b-cells, which contributes to the development of new-onset diabetes and the induction of diabetic ketoacidosis (DKA) in patients with T1DM. Large clinical studies are required to clarify the exact pathways through which T1DM results in worse COVID-19 outcomes.

A comprehensive guide to the pharmacologic regulation of angiotensin converting enzyme 2 (ACE2), the SARS-CoV-2 entry receptor

The recent emergence of coronavirus disease-2019 (COVID-19) as a global pandemic has prompted scientists to address an urgent need for defining mechanisms of disease pathology and treatment. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent for COVID-19, employs angiotensin converting enzyme 2 (ACE2) as its primary target for cell surface attachment and likely entry into the host cell. Thus, understanding factors that may regulate the expression and function of ACE2 in the healthy and diseased body is critical for clinical intervention. Over 66% of all adults in the United States are currently using a prescription drug and while earlier findings have focused on possible upregulation of ACE2 expression through the use of renin angiotensin system (RAS) inhibitors, mounting evidence suggests that various other widely administered drugs used in the treatment of hypertension, heart failure, diabetes mellitus, hyperlipidemias, coagulation disorders, and pulmonary disease may also present a varied risk for COVID-19. Specifically, we summarize mechanisms on how heparin, statins, steroids and phytochemicals, besides their established therapeutic effects, may also interfere with SARS-CoV-2 viral entry into cells. We also describe evidence on the effect of several vitamins, phytochemicals, and naturally occurring compounds on ACE2 expression and activity in various tissues and disease models. This comprehensive review aims to provide a timely compendium on the potential impact of commonly prescribed drugs and pharmacologically active compounds on COVID-19 pathology and risk through regulation of ACE2 and RAS signaling.

Multifunctional angiotensin converting enzyme 2, the SARS-CoV-2 entry receptor, and critical appraisal of its role in acute lung injury

The recent emergence of coronavirus disease-2019 (COVID-19) as a pandemic affecting millions of individuals has raised great concern throughout the world, and the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) was identified as the causative agent for COVID-19. The multifunctional protein angiotensin converting enzyme 2 (ACE2) is accepted as its primary target for entry into host cells. In its enzymatic function, ACE2, like its homologue ACE, regulates the renin-angiotensin system (RAS) critical for cardiovascular and renal homeostasis in mammals. Unlike ACE, however, ACE2 drives an alternative RAS pathway by degrading Ang-II and thus operates to balance RAS homeostasis in the context of hypertension, heart failure, and cardiovascular as well as renal complications of diabetes. Outside the RAS, ACE2 hydrolyzes key peptides, such as amyloid-β, apelin, and [des-Arg9]-bradykinin. In addition to its enzymatic functions, ACE2 is found to regulate intestinal amino acid homeostasis and the gut microbiome. Although the non-enzymatic function of ACE2 as the entry receptor for SARS-CoV-2 has been well established, the contribution of enzymatic functions of ACE2 to the pathogenesis of COVID-19-related lung injury has been a matter of debate. A complete understanding of this central enzyme may begin to explain the various symptoms and pathologies seen in SARS-CoV-2 infected individuals, and may aid in the development of novel treatments for COVID-19.

Kinins and chymase: the forgotten components of the renin-angiotensin system and their implications in COVID-19 disease

The unique clinical features of COVID-19 disease present a formidable challenge in the understanding of its pathogenesis. Within a very short time, our knowledge regarding basic physiological pathways that participate in SARS-CoV-2 invasion and subsequent organ damage have been dramatically expanded. In particular, we now better understand the complexity of the renin-angiotensin-aldosterone system (RAAS) and the important role of angiotensin converting enzyme (ACE)-2 in viral binding. Furthermore, the critical role of its major product, angiotensin (Ang)-(1-7), in maintaining microcirculatory balance and in the control of activated proinflammatory and procoagulant pathways, generated in this disease, have been largely clarified. The kallikrein-bradykinin (BK) system and chymase are intensively interwoven with RAAS through many pathways with complex reciprocal interactions. Yet, so far, very little attention has been paid to a possible role of these physiological pathways in the pathogenesis of COVID-19 disease, even though BK and chymase exert many physiological changes characteristic to this disorder. Herein, we outline the current knowledge regarding the reciprocal interactions of RAAS, BK, and chymase that are probably turned-on in COVID-19 disease and participate in its clinical features. Interventions affecting these systems, such as the inhibition of chymase or blocking BKB1R/BKB2R, might be explored as potential novel therapeutic strategies in this devastating disorder.

COVID-19 and diabetes mellitus: from pathophysiology to clinical management

Initial studies found increased severity of coronavirus disease 2019 (COVID-19), caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), in patients with diabetes mellitus. Furthermore, COVID-19 might also predispose infected individuals to hyperglycaemia. Interacting with other risk factors, hyperglycaemia might modulate immune and inflammatory responses, thus predisposing patients to severe COVID-19 and possible lethal outcomes. Angiotensin-converting enzyme 2 (ACE2), which is part of the renin-angiotensin-aldosterone system (RAAS), is the main entry receptor for SARS-CoV-2; although dipeptidyl peptidase 4 (DPP4) might also act as a binding target. Preliminary data, however, do not suggest a notable effect of glucose-lowering DPP4 inhibitors on SARS-CoV-2 susceptibility. Owing to their pharmacological characteristics, sodium-glucose cotransporter 2 (SGLT2) inhibitors might cause adverse effects in patients with COVID-19 and so cannot be recommended. Currently, insulin should be the main approach to the control of acute glycaemia. Most available evidence does not distinguish between the major types of diabetes mellitus and is related to type 2 diabetes mellitus owing to its high prevalence. However, some limited evidence is now available on type 1 diabetes mellitus and COVID-19. Most of these conclusions are preliminary, and further investigation of the optimal management in patients with diabetes mellitus is warranted.

Targeting Neprilysin (NEP) pathways: A potential new hope to defeat COVID-19 ghost

COVID-19 is an ongoing viral pandemic disease that is caused by SARS-CoV2, inducing severe pneumonia in humans. However, several classes of repurposed drugs have been recommended, no specific vaccines or effective therapeutic interventions for COVID-19 are developed till now. Viral dependence on ACE-2, as entry receptors, drove the researchers into RAS impact on COVID-19 pathogenesis. Several evidences have pointed at Neprilysin (NEP) as one of pulmonary RAS components. Considering the protective effect of NEP against pulmonary inflammatory reactions and fibrosis, it is suggested to direct the future efforts towards its potential role in COVID-19 pathophysiology. Thus, the review aimed to shed light on the potential beneficial effects of NEP pathways as a novel target for COVID-19 therapy by summarizing its possible molecular mechanisms. Additional experimental and clinical studies explaining more the relationships between NEP and COVID-19 will greatly benefit in designing the future treatment approaches.

Targeting the Protective Arm of the Renin-Angiotensin System to Reduce Systemic Lupus Erythematosus Related Pathologies in MRL-lpr Mice

Patients with Systemic Lupus Erythematosus (SLE) suffer from a chronic inflammatory autoimmune disease that results from the body's immune system targeting healthy tissues which causes damage to various organ systems. Patients with lupus are still in need of effective therapies to treat this complex, multi-system disease. Because polymorphisms in ACE are associated with the activity of SLE and lupus nephritis and based on well-documented renal-protective effects of Renin Angiotensin System (RAS)-modifying therapies, ACE-I are now widely used in patients with SLE with significant efficacy. Our research explores alternate ways of modifying the RAS as a potential for systemic therapeutic benefit in the MRL-lpr mouse model of SLE. These therapeutics include; angiotensin (1-7) [A(1-7)], Nor-Leu-3 Angiotensin (1-7) (NorLeu), Losartan (ARB), and Lisinopril (ACE-I). Daily systemic treatment with all of these RAS-modifying therapies significantly reduced the onset and intensity in rash formation and swelling of the paw. Further, histology showed a corresponding decrease in hyperkeratosis and acanthosis in skin sections. Important immunological parameters such as decreased circulating anti-dsDNA antibodies, lymph node size, and T cell activation were observed. As expected, the development of glomerular pathologies was also attenuated by RAS-modifying therapy. Improved number and health of mesenchymal stem cells (MSCs), as well as reduction in oxidative stress and inflammation may be contributing to the reduction in SLE pathologies. Several studies have already characterized the protective role of ACE-I and ARBs in mouse models of SLE, here we focus on the protective arm of RAS. A(1-7) in particular demonstrates several protective effects that go beyond those seen with ACE-Is and ARBs; an important finding considering that ACE-Is and ARBs are teratogenic and can cause hypotension in this population. These results offer a foundation for further pharmaceutical development of RAS-modifying therapies, that target the protective arm, as novel SLE therapeutics that do not rely on suppressing the immune system.

Clinical Implications of SARS-CoV-2 Interaction With Renin Angiotensin System: JACC Review Topic of the Week

Severe acute respiratory-syndrome coronavirus-2 (SARS-CoV-2) host cell infection is mediated by binding to angiotensin-converting enzyme 2 (ACE2). Systemic dysregulation observed in SARS-CoV was previously postulated to be due to ACE2/angiotensin 1-7 (Ang1-7)/Mas axis downregulation; increased ACE2 activity was shown to mediate disease protection. Because angiotensin II receptor blockers, ACE inhibitors, and mineralocorticoid receptor antagonists increase ACE2 receptor expression, it has been tacitly believed that the use of these agents may facilitate viral disease; thus, they should not be used in high-risk patients with cardiovascular disease. Based on the anti-inflammatory benefits of the upregulation of the ACE2/Ang1-7/Mas axis and previously demonstrated benefits of lung function improvement in SARS-CoV infections, it has been hypothesized that the benefits of treatment with renin-angiotensin system inhibitors in SARS-CoV-2 may outweigh the risks and at the very least should not be withheld.

Angiotensin-[1-7] attenuates kidney injury in experimental Alport syndrome

Angiotensin-[1–7] (Ang-[1–7]) antagonize the actions of the renin-angiotensin-system via the Mas receptor and thereby exert renoprotective effects. Murine recombinant angiotensin-converting enzyme (ACE)2 was reported to show renoprotective effects in an experimental Alport syndrome model; however, the protective effect of direct administration of Ang-[1–7] is unknown. Here, we used Col4a3^−/− mice as a model of Alport syndrome, which were treated with saline or Ang- [1–7]; saline-treated wild-type mice were used as a control group. The mice were continuously infused with saline or Ang-[1–7] (25 μg/kg/h) using osmotic mini-pumps. Col4a3^−/− mice showed increased α-smooth muscle actin (SMA), collagen, and fibronectin expression levels, which were attenuated by Ang-[1–7] treatment. Moreover, Ang-[1–7] alleviated activation of transforming growth factor-β/Smad signaling, and attenuated the protein expression of ED-1 and heme oxygenase-1, indicating reduction of renal inflammation. Ang-[1–7] treatment further reduced the expression levels of inflammatory cytokines and adhesion molecules and attenuated apoptosis in human kidney cells. Finally, Ang-[1–7] downregulated TNF-α converting enzyme and upregulated ACE2 expression. Thus, treatment with Ang-[1–7] altered the ACE2-Ang-[1–7]-Mas receptor axis in the kidneys of Col4a3^−/− mice to attenuate the nephropathy progression of Alport syndrome.

Correlation between angiotensin 1-7-mediated Mas receptor expression with motor improvement, activated STAT3/SOCS3 cascade, and suppressed HMGB-1/RAGE/NF-κB signaling in 6-hydroxydopamine hemiparkinsonian rats

In the current investigation, a Parkinson's disease (PD) model was established by a single direct right intrastriatal injection of the 6-hydroxydopamine (OHDA) in male Wistar rats followed by 7 daily unilateral injection of angiotensin (Ang) 1-7 in the striatum. To confirm the putative role of Mas receptor (MasR), the selective antagonist A779 was also injected intrastriatally prior to Ang 1-7 injections and a correlation analysis was performed between MasR expression and the assessed parameters. Ang 1-7 upregulated MasR expression to correlate strongly with the improved rotarod (r = 0.95, p = 0.003) and spontaneous activity task (r = 0.99, p < 0.0001). This correlation extends to involve other effects of Ang 1-7, such as the increased striatal dopamine content (r = 0.98, p = 0.0005), substantia nigra pars compacta tyrosine hydroxylase immune-reactivity (r = 0.97, p = 0.001), active pY705-STAT3 (r = 0.99, p < 0.0001) and SOCS3 (r = 0.99, p < 0.0001). Conversely, Ang 1-7 inhibited inflammatory markers to correlate negatively with NF-κBp65 (r = -0.99, p < 0.0003) and its downstream targets, high mobility group box-1 (HMGB-1; r = -0.97, p = 0.002), receptor for advanced glycation end products (RAGE; r = -0.98, p = 0.0004), and TNF-α (r = -0.99, p < 0.0003), besides poly-ADP-ribose polymerase-1 (r = -0.99, p = 0.0002). In confirmation, the pre-administration of the selective MasR antagonist, A779, partially attenuated Ang 1-7-induced alterations towards 6-OHDA neurodegeneration. Collectively, our findings support a novel role for the anti-inflammatory capacity of the MasR axis to prove potential therapeutic relevance in PD via the upregulation/activation of MasR-dependent STAT3/SOCS3 cascade to negatively control the HMGB-1/RAGE/NF-κB axis hindering PD associated neuro-inflammation along with DA depletion and motor deficits.

Novel Therapeutic Approaches Targeting the Renin-Angiotensin System and Associated Peptides in Hypertension and Heart Failure

Despite the success of renin-angiotensin system (RAS) blockade by angiotensin-converting enzyme (ACE) inhibitors and angiotensin II type 1 receptor (AT1R) blockers, current therapies for hypertension and related cardiovascular diseases are still inadequate. Identification of additional components of the RAS and associated vasoactive pathways, as well as new structural and functional insights into established targets, have led to novel therapeutic approaches with the potential to provide improved cardiovascular protection and better blood pressure control and/or reduced adverse side effects. The simultaneous modulation of several neurohumoral mediators in key interconnected blood pressure-regulating pathways has been an attractive approach to improve treatment efficacy, and several novel approaches involve combination therapy or dual-acting agents. In addition, increased understanding of the complexity of the RAS has led to novel approaches aimed at upregulating the ACE2/angiotensin-(1-7)/Mas axis to counter-regulate the harmful effects of the ACE/angiotensin II/angiotensin III/AT1R axis. These advances have opened new avenues for the development of novel drugs targeting the RAS to better treat hypertension and heart failure. Here we focus on new therapies in preclinical and early clinical stages of development, including novel small molecule inhibitors and receptor agonists/antagonists, less conventional strategies such as gene therapy to suppress angiotensinogen at the RNA level, recombinant ACE2 protein, and novel bispecific designer peptides.

Renal vascular response to angiotensin 1-7 in rats: the role of Mas receptor

Recently a cross talk between angiotensin 1-7 (Ang1-7) receptor (MasR) and angiotensin II receptors types 1 and 2 (AT1R and AT2R) has been highlighted. The effects of MasR antagonist (A779) compared to the vehicle on the renal blood flow (RBF) and renal vascular resistance (RVR) responses to Ang1-7 (300 ng/kg/min) infusion in the absence of Ang II receptors in male and female rats were determined at controlled renal perfusion pressure. Ang1-7 infusion did not alter mean arterial pressure in male and female rats. However, A779 compared to vehicle increased RBF (18% vs 3%) and decreased RVR (13% vs 4%) responses to Ang1-7 infusion significantly (P < 0.05) in male when AngII receptors were blocked. Such observation was not occurred in female animals. Finally it was concluded that renal vascular responses to Ang1-7 administration may not be exerted by MasR in male rats, and these responses are not mediated with AngII receptors.

Kallikrein-kinin system as the dominant mechanism to counteract hyperactive renin-angiotensin system

The renin-angiotensin system (RAS) generates, maintains, and makes worse hypertension and cardiovascular diseases (CVDs) through its biologically active component angiotensin II (Ang II), that causes vasoconstriction, sodium retention, and structural alterations of the heart and the arteries. A few endogenous vasodilators, kinins, natriuretic peptides, and possibly angiotensin (1-7), exert opposite actions and may provide useful therapeutic agents. As endothelial autacoids, the kinins are potent vasodilators, active natriuretics, and protectors of the endothelium. Indeed, the kallikrein-kinin system (KKS) is considered the dominant mechanism for counteracting the detrimental effects of the hyperactive RAS. The 2 systems, RAS and KKS, are controlled by the angiotensin-converting enzyme (ACE) that generates Ang II and inactivates the kinins. Inhibitors of ACE can reduce the impact of Ang II and potentiate the kinins, thus contributing to restore the cardiovascular homeostasis. In the last 20 years, ACE-inhibitors (ACE-Is) have become the drugs of first choice for the treatments of the major CVDs. ACE-Is not only reduce blood pressure, as sartans also do, but by protecting and potentiating the kinins, they can reduce morbidity and mortality and improve the quality of life for patients with CVDs. This paper provides a brief review of the literature on this topic.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Angiotensin-(1-7) Selectively Induces Relaxation and Modulates Endothelium-Dependent Dilation in Mesenteric Arteries of Salt-Fed Rats

This study investigated the acute effects of angiotensin-(1-7) and AVE0991 on active tone and vasodilator responses to bradykinin and acetylcholine in isolated mesenteric arteries from Sprague-Dawley rats fed a high-salt (HS; 4% NaCl) versus a normal salt (NS; 0.4% NaCl) diet. Angiotensin-(1-7) and AVE0991 elicited relaxation, and angiotensin-(1-7) unmasked vasodilator responses to bradykinin in arteries from HS-fed rats. These effects of angiotensin-(1-7) and AVE0991 were inhibited by endothelium removal, A779, PD123319, HOE140 and L-NAME. Angiotensin-(1-7) also restored the acetylcholine-induced relaxation that was suppressed by the HS diet. Vasodilator responses to bradykinin and acetylcholine in the presence of angiotensin-(1-7) were mimicked by captopril and the AT2 receptor agonist CGP42112 in arteries from HS-fed rats. Thus, in contrast to salt-induced impairment of vascular relaxation in response to vasodilator stimuli, angiotensin-(1-7) induces endothelium-dependent and NO-mediated relaxation, unmasks bradykinin responses via activation of mas and AT2 receptors, and restores acetylcholine-induced vasodilation in HS-fed rats. AT2 receptor activation and angiotensin-converting enzyme (ACE) inhibition shared the ability of angiotensin-(1-7) to enhance bradykinin and acetylcholine responses in HS-fed rats. These findings suggest a therapeutic potential for mas and/or AT2 receptor activation and ACE inhibition in restoring endothelial function impaired by elevated dietary salt intake or other pathological conditions.

Heteromerization Between the Bradykinin B2 Receptor and the Angiotensin-(1-7) Mas Receptor: Functional Consequences

Bradykinin B2 receptor (B2R) and angiotensin-(1-7) Mas receptor (MasR)-mediated effects are physiologically interconnected. The molecular basis for such cross talk is unknown. It is hypothesized that the cross talk occurs at the receptor level. We investigated B2R-MasR heteromerization and the functional consequences of such interaction. B2R fused to the cyan fluorescent protein and MasR fused to the yellow fluorescent protein were transiently coexpressed in human embryonic kidney293T cells. Fluorescence resonance energy transfer analysis showed that B2R and MasR formed a constitutive heteromer, which was not modified by their agonists. B2R or MasR antagonists decreased fluorescence resonance energy transfer efficiency, suggesting that the antagonist promoted heteromer dissociation. B2R-MasR heteromerization induced an 8-fold increase in the MasR ligand-binding affinity. On agonist stimulation, the heteromer was internalized into early endosomes with a slower sequestration rate from the plasma membrane, compared with single receptors. B2R-MasR heteromerization induced a greater increase in arachidonic acid release and extracellular signal-regulated kinase phosphorylation after angiotensin-(1-7) stimulation, and this effect was blocked by the B2R antagonist. Concerning serine/threonine kinase Akt activity, a significant bradykinin-promoted activation was detected in B2R-MasR but not in B2R-expressing cells. Angiotensin-(1-7) and bradykinin elicited antiproliferative effects only in cells expressing B2R-MasR heteromers, but not in cells expressing each receptor alone. Proximity ligation assay confirmed B2R-MasR interaction in human glomerular endothelial cells supporting the interaction between both receptors in vivo. Our findings provide an explanation for the cross talk between bradykinin B2R and angiotensin-(1-7) MasR-mediated effects. B2R-MasR heteromerization induces functional changes in the receptor that may lead to long-lasting protective properties.

ACE2 and vasoactive peptides: novel players in cardiovascular/renal remodeling and hypertension

The renin-angiotensin system (RAS) is a key component of cardiovascular physiology and homeostasis due to its influence on the regulation of electrolyte balance, blood pressure, vascular tone and cardiovascular remodeling. Deregulation of this system contributes significantly to the pathophysiology of cardiovascular and renal diseases. Numerous studies have generated new perspectives about a noncanonical and protective RAS pathway that counteracts the proliferative and hypertensive effects of the classical angiotensin-converting enzyme (ACE)/angiotensin (Ang) II/angiotensin type 1 receptor (AT1R) axis. The key components of this pathway are ACE2 and its products, Ang-(1-7) and Ang-(1-9). These two vasoactive peptides act through the Mas receptor (MasR) and AT2R, respectively. The ACE2/Ang-(1-7)/MasR and ACE2/Ang-(1-9)/AT2R axes have opposite effects to those of the ACE/Ang II/AT1R axis, such as decreased proliferation and cardiovascular remodeling, increased production of nitric oxide and vasodilation. A novel peptide from the noncanonical pathway, alamandine, was recently identified in rats, mice and humans. This heptapeptide is generated by catalytic action of ACE2 on Ang A or through a decarboxylation reaction on Ang-(1-7). Alamandine produces the same effects as Ang-(1-7), such as vasodilation and prevention of fibrosis, by interacting with Mas-related GPCR, member D (MrgD). In this article, we review the key roles of ACE2 and the vasoactive peptides Ang-(1-7), Ang-(1-9) and alamandine as counter-regulators of the ACE-Ang II axis as well as the biological properties that allow them to regulate blood pressure and cardiovascular and renal remodeling.

The compensatory renin-angiotensin system in the central regulation of arterial pressure: new avenues and new challenges

Hypertension is a widespread condition that affects millions of people around the world and has a major impact in public health. The classic renin-angiotensin system is a complex system comprised of multiple peptides and pathways that have been the driver of drug development over the years to control hypertension. However, there are still patients whose hypertension is very difficult to control with current drugs and strategies, thus motivating further research in this field. In the past two decades, important discoveries have expanded our knowledge of this system and new pathways are emerging that are helping us understand the complex interaction taking place not only in the periphery, but also in the central nervous system where the renin-angiotensin system is also very active. A new arm, called the ACE2/Ang-(1-7)/Mas receptor axis, was shown to exert antihypertensive properties and serve as a counterbalance to the classic ACE/angiotensin II/AT1 receptor axis, in this way modulating or even counteracting the negative effects of angiotensin II in blood pressure regulation and water retention. Modulation of this new axis through ACE2 activation, ADAM17 regulation or AT1 receptor internalization are some of the novel avenues and challenges that have the potential to become a target for new drug research and development for the treatment of hypertension.

Angiotensin-(1-7) augments endothelium-dependent relaxations of porcine coronary arteries to bradykinin by inhibiting angiotensin-converting enzyme 1

Angiotensin-converting enzyme 2 (ACE2) converts angiotensin II to angiotensin-(1-7) that activates Mas receptors, inhibits ACE1, and modulates bradykinin receptor sensitivity. This in vitro study compared the direct and indirect effects of angiotensin-(1-7), the ACE1 inhibitor captopril, and diminazene aceturate (DIZE) an alleged ACE2 activator in rings of porcine coronary arteries, by measuring changes of isometric tension. Angiotensin-(1-7), captopril, and DIZE did not cause significant changes in tension before or after desensitization of bradykinin receptors in preparations contracted with U46619. Bradykinin caused concentration-dependent and endothelium-dependent relaxations that were not affected by DIZE but were potentiated to a similar extent by angiotensin-(1-7) and captopril, given alone or in combination. Bradykinin responses potentiated by angiotensin-(1-7) and captopril were not affected by the BK1 antagonist SSR240612 and remained augmented in the presence of either N-nitro-L-arginine methyl ester hydrochloride plus indomethacin or TRAM-34 plus UCL-1684. ACE2 was identified in the coronary endothelium by immunofluorescence, but its basal activity was not influenced by DIZE. These results suggest that in coronary arteries, angiotensin-(1-7) and captopril both improves NO bioavailability and enhances endothelium-dependent hyperpolarization to bradykinin solely by ACE1 inhibition. Endothelial ACE2 activity cannot be increased by DIZE to produce local adequate amounts of angiotensin-(1-7) to influence vascular tone.

ACE2-Ang-(1-7)-Mas Axis in Brain: A Potential Target for Prevention and Treatment of Ischemic Stroke

The renin-angiotensin system (RAS) in brain is a crucial regulator for physiological homeostasis and diseases of cerebrovascular system, such as ischemic stroke. Overactivation of brain Angiotensin-converting enzyme (ACE) - Angiotensin II (Ang II) - Angiotensin II type 1 receptor (AT1R) axis was found to be involved in the progress of hypertension, atherosclerosis and thrombogenesis, which increased the susceptibility to ischemic stroke. Besides, brain Ang II levels have been revealed to be increased in ischemic tissues after stroke, and contribute to neural damage through elevating oxidative stress levels and inducing inflammatory response in the ischemic hemisphere via AT1R. In recent years, new components of RAS have been discovered, including ACE2, Angiotensin-(1-7) [Ang-(1-7)] and Mas, which constitute ACE2-Ang-(1-7)-Mas axis. ACE2 converts Ang II to Ang-(1-7), and Ang-(1-7) binds with its receptor Mas, exerting benefical effects in cerebrovascular disease. Through interacting with nitric oxide and bradykinin, Ang-(1-7) could attenuate the development of hypertension and the pathologic progress of atherosclerosis. Besides, its antithrombotic activity also prevents thrombogenic events, which may contribute to reduce the risk of ischemic stroke. In addition, after ischemia insult, ACE2-Ang-(1-7)-Mas has been shown to reduce the cerebral infarct size and improve neurological deficits through its antioxidative and anti-inflammatory effects. Taken together, activation of the ACE2-Ang-(1-7)-Mas axis may become a novel therapeutic target in prevention and treatment of ischemia stroke, which deserves further investigations.

The intrarenal renin-angiotensin system: does it exist? Implications from a recent study in renal angiotensin-converting enzyme knockout mice

A large body of evidence supports the presence of local production of angiotensins in the kidney. It is widely believed that renin-angiotensin system (RAS) blockers, through interference with such production and/or the local effects of angiotensin (Ang) II, exert protective renal effects. Yet, whether such production affects blood pressure independently from the circulating RAS is still a matter of debate. To investigate this, a recent study by Gonzalez-Villalobos et al. (J Clin Invest 2013; 123: 2011-2023) has studied the consequences of infusing Ang II or the nitric oxide synthase inhibitor l-NAME in mice lacking renal angiotensin-converting enzyme (ACE). They observed blunted blood pressure and renal responses in the renal ACE knockout mice versus wild-type controls. This review discusses to what degree these findings can be considered as unequivocal evidence for ACE-mediated Ang II formation in the kidney as an independent determinant of 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-converting enzyme 2, angiotensin-(1-7) and Mas: new players of the renin-angiotensin system

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

Powerful vascular protection by combining cilnidipine with valsartan in stroke-prone, spontaneously hypertensive rats

Cilnidipine is an L- and N-type calcium channel blocker (CCB), and amlodipine is an L-type CCB. Valsartan (10 mg kg(-1)), valsartan (10 mg kg(-1)) and amlodipine (1 mg kg(-1)), and valsartan (10 mg kg(-1)) and cilnidipine (1 mg kg(-1)) were administered once daily for 2 weeks to stroke-prone, spontaneously hypertensive rats (SHR-SPs). Blood pressure was significantly reduced by valsartan, and it was further reduced by the combination therapies. Vascular endothelial dysfunction was significantly attenuated in all therapeutic groups, and further significant attenuation was observed in the valsartan+cilnidipine-treated group, but not in the valsartan+amlodipine-treated group. Vascular nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit NOX1 gene expression was significantly attenuated in all therapeutic groups, and significantly greater attenuation was observed in the valsartan+cilnidipine-treated group than in the valsartan-treated group. Compared with the valsartan-treated group, the positive areas for 4-hydroxy-2-nonenal were significantly lower only in the valsartan+cilnidipine-treated group. Plasma renin activity was significantly augmented in the valsartan-treated group, and it was significantly attenuated in the valsartan+cilnidipine-treated group. A significant increase in the ratio of plasma angiotensin-(1-7) to angiotensin II was observed only in the valsartan+cilnidipine-treated group. Vascular angiotensin-converting enzyme (ACE) gene expression was significantly attenuated only in the valsartan+cilnidipine-treated group, but ACE2 gene expression was significantly higher in all of the therapeutic groups. Thus, valsartan and cilnidipine combination therapy might have a powerful protective effect in the vascular tissues via increases in the angiotensin-(1-7)/angiotensin II ratio in plasma.

ACE2/ANG-(1-7)/Mas pathway in the brain: the axis of good

The last decade has seen the discovery of several new components of the renin-angiotensin system (RAS). Among them, angiotensin converting enzyme-2 (ACE2) and the Mas receptor have forced a reevaluation of the original cascade and led to the emergence of a new arm of the RAS: the ACE2/ANG-(1-7)/Mas axis. Accordingly, the new system is now seen as a balance between a provasoconstrictor, profibrotic, progrowth axis (ACE/ANG-II/AT(1) receptor) and a provasodilatory, antifibrotic, antigrowth arm (ACE2/ANG-(1-7)/Mas receptor). Already, this simplistic vision is evolving and new components are branching out upstream [ANG-(1-12) and (pro)renin receptor] and downstream (angiotensin-IV and other angiotensin peptides) of the classical cascade. In this review, we will summarize the role of the ACE2/ANG-(1-7)/Mas receptor, focusing on the central nervous system with respect to cardiovascular diseases such as hypertension, chronic heart failure, and stroke, as well as neurological diseases. In addition, we will discuss the new pharmacological (antagonists, agonists, activators) and genomic (knockout and transgenic animals) tools that are currently available. Finally, we will review the latest data regarding the various signaling pathways downstream of the Mas receptor.

Casein-derived tripeptide Ile-Pro-Pro improves angiotensin-(1-7)- and bradykinin-induced rat mesenteric artery relaxation

AIMS

Milk casein-derived bioactive tripeptides isoleucine-proline-proline (Ile-Pro-Pro) and valine-proline-proline (Val-Pro-Pro) lower blood pressure in animal models of hypertension and humans. In some studies, their angiotensin-converting enzyme (ACE)-inhibitory effect has been demonstrated. Besides classical ACE-angiotensin II-AT(1)-receptor pathway (ACE-Ang II- AT(1)), the significance of ACE2-angiotensin-(1-7)-Mas-receptor (ACE2-Ang-(1-7)-Mas) axis in the blood pressure regulation has now been acknowledged. The present study was aimed to further evaluate the renin-angiotensin system (RAS)-related vascular effects of Ile-Pro-Pro in vitro using rat mesenteric arteries.

MAIN METHODS

Superior mesenteric arteries of spontaneously hypertensive rat (SHR) were isolated, cut into rings and mounted in standard organ bath chambers. Endothelium-intact arterial rings were incubated in Krebs solution either with Ile-Pro-Pro, proline-proline (Pro-Pro), isoleucine (Ile), proline (Pro) or captopril for 6h at +37°C and vascular reactivity was measured.

KEY FINDINGS

In the presence of AT(1)-antagonist valsartan, Ang II induced vasodilatation, which was more pronounced in the arteries incubated with Ile-Pro-Pro (P<0.05) compared to the other compounds. Ang-(1-7)-induced vasodilatation was augmented by Ile-Pro-Pro or Pro (P<0.001 vs. control). Mas-receptor antagonist A-779 did not alter the responses. Ile-Pro-Pro and Pro augmented also bradykinin-induced relaxations (P<0.001 vs. control). Control arteries and arteries incubated with captopril showed only slight relaxations at higher bradykinin concentrations.

SIGNIFICANCE

Casein-derived tripeptide Ile-Pro-Pro and amino acid Pro enhance the vasodilatory effect of Ang-(1-7) and bradykinin. The role of ACE2-Ang-(1-7)-Mas axis in the modulation of vascular tone by these compounds seems probable.

Reinventing the ACE inhibitors: some old and new implications of ACE inhibition

Since their inception, angiotensin-converting enzyme (ACE) inhibitors have been used as first-line therapy for the treatment of cardiovascular and renal diseases. They restore the balance between the vasoconstrictive salt-retentive and hypertrophy-causing peptide angiotensin II (Ang II) and bradykinin, a vasodilatory and natriuretic peptide. As ACE is a promiscuous enzyme, ACE inhibitors alter the metabolism of a number of other vasoactive substances. ACE inhibitors decrease systemic vascular resistance without increasing heart rate and promote natriuresis. They have been proven effective in the treatment of hypertension, and reduce mortality in congestive heart failure and left ventricular dysfunction after myocardial infarction. They inhibit ischemic events and stabilize plaques. Furthermore, they delay the progression of diabetic nephropathy and neuropathy and act as antioxidants. Ongoing studies have elucidated protective roles for them in both memory-related disorders and cancer. Lastly, N- and C-domain selective ACE inhibitors have led to new uses for ACE inhibitors.

Significance of angiotensin II receptor blockers with high affinity to angiotensin II type 1 receptors for vascular protection in rats

Angiotensin II receptor blockers (ARBs) vary in their binding affinities to angiotensin II type 1 (AT(1)) receptors in in vitro experiments. We compared a high-affinity ARB, olmesartan, and a low-affinity ARB, valsartan, in terms of their vascular protective effects in stroke-prone spontaneously hypertensive rats (SHR-SP). Blood pressure was equally reduced by placebo, olmesartan (1 mg kg(-1)) and valsartan (3 mg kg(-1)) daily for 2 weeks. In another experiment, 12-week-old SHR-SP were fed 8% salt, and olmesartan (1 mg kg(-1)), valsartan (3 mg kg(-1)) or placebo were administered daily until a survival rate of 60% was reached. In the experiment using SHR-SP, the reduction of acetylcholine-induced vascular relaxation and the increase of p22(phox) expression in the placebo-treated group were significantly attenuated by olmesartan and valsartan, but this attenuation was significantly greater for olmesartan. In immunohistological analysis, all areas positive for angiotensin II, p22(phox) and 4-hydroxy-2-nonenal were significantly reduced by olmesartan and valsartan, but again this reduction was significantly greater for olmesartan. In salt-loaded SHR-SP, the number of days to reach a 60% survival rate was 25 and 42 in placebo and valsartan-treated rats, respectively, and this represented a significant difference. The survival rate in olmesartan-treated rats was 95% at day 42, when valsartan-treated rats reached 60% survival, and this difference was also significant. In the surviving rats, olmesartan, but not valsartan, augmented acetylcholine-induced vascular relaxation and attenuated vascular p22(phox) expression. Thus, heterogeneity in binding affinity to AT(1) receptors among ARBs may result in different degrees of vascular protection and lifespan extension.

Olmesartan improves left ventricular function in pressure-overload hypertrophied rat heart by blocking angiotensin II receptor with synergic effects of upregulation of angiotensin converting enzyme 2

It is not clear how the blocking effect of angiotensin II receptors by olmesartan affects the functional recovery of pressure-overload hypertrophied heart. Hypertrophied heart was created by abdominal aortic banding above the celiac artery in Wistar rats at the age of eight weeks. Hypertrophied heart was excised and studied at 10 and 16 weeks after the operation (HT groups). For the last four weeks before the experiment, olmesartan (0.2 mg/kg per day) was administered subcutaneously by osmotic minipumps (Olm groups). Left ventricular function was measured by Langendorff perfusion. The levels of mRNA for angiotensin-converting enzyme (ACE), ACE2 and extracellular signal-regulated kinases (ERKs) in myocardium were analyzed by RT-PCR. Left ventricular systolic (+d P/dtmax, left ventricular systolic pressure) and diastolic functions (-d P/dtmax, tau) were impaired in HT groups, while in Olm groups they were significantly improved. The left ventricle to body weight (LV/BW) ratio increased significantly in HT groups, but in Olm groups the LV/BW ratio decreased significantly in comparison with HT groups. The ACE2 mRNA level was significantly higher in Olm groups as compared with HT groups. Plasma angiotensin II and the ERK mRNA level in HT groups increased significantly, but decreased in Olm groups in comparison with HT groups significantly. Olmesartan improved left ventricular function and hypertrophy through the increase of the ACE2 mRNA and decrease of both angiotensin II and ERK mRNA in pressure-overload rat heart.

Different contributions of the angiotensin-converting enzyme C-domain and N-domain in subjects with the angiotensin-converting enzyme II and DD genotype

BACKGROUND

Angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism-related differences in ACE concentration do not result in differences in angiotensin levels.

METHODS AND RESULTS

To investigate whether this relates to differences in the contribution of the ACE C-domain and N-domain, we quantified, using the C-domain-selective inhibitors quinaprilat and RXPA380, and the N-domain-selective inhibitor RXP407, the contribution of both domains to the metabolism of angiotensin I, bradykinin, the C-domain-selective substrate Mca-BK(1-8), and the N-domain-selective substrate Mca-Ala in serum of IIs, DDs, and 'hyperACE' subjects (i.e., subjects with increased ACE due to enhanced shedding). During incubation with angiotensin I, the highest angiotensin II levels were observed in sera with the highest ACE activity. This confirms that ACE is rate-limiting with regard to angiotensin II generation. C-domain-selective concentrations of quinaprilat fully blocked angiotensin I-II conversion in DDs, whereas additional N-domain blockade was required to fully block conversion in IIs. Both domains contributed to bradykinin hydrolysis in all subjects, and the inhibition profile of RXP407 when using Mca-Ala was identical in IIs and DDs. In contrast, the RXPA380 concentrations required to block C-domain activity when using Mca-BK (1-8) were three-fold higher in IIs than DDs.

CONCLUSION

The contributions of the C-domain and N-domain differ between DDs and IIs, and RXPA380 is the first inhibitor capable of distinguishing D-allele ACE from I-allele ACE. The lack of angiotensin II accumulation in DDs in vivo is not because of the often quoted concept that ACE is a nonrate-limiting enzyme. It may relate to the fact that in IIs both the N-domain and C- domain generate angiotensin II, whereas in DDs only the C-domain converts angiotensin I.

Effects of intracerebroventricular infusion of angiotensin-(1-7) on bradykinin formation and the kinin receptor expression after focal cerebral ischemia-reperfusion in rats

Accumulating evidence suggests that the angiotensin-(1-7) [Ang-(1-7)], is an active member of the brain renin-angiotensin system (RAS). We evaluated the possibility that intracerebroventricular (ICV, lateral ventricle) infusion of exogenous Ang-(1-7) could participate in the potentiation of bradykinin (BK) release and the kinin receptor expression in ischemic brain parenchyma after focal cerebral ischemia-reperfusion in rats. The middle cerebral artery occlusion (MCAO) and sham-operated models were prepared, continuously administrated with Ang-(1-7) or artificial cerebrospinal fluid (aCSF) by implanted Alzet osmotic minipumps into lateral cerebral ventricle after reperfusion in male Sprague-Dawley (SD) rats. Experimental animals were divided into sham-operated group (sham+aCSF), aCSF treatment group (MCAO+aCSF) and Ang-(1-7) treatment groups [MCAO+Ang-(1-7)] at low (1 pmol/0.5 microl/h), medium (100 pmol/0.5 microl/h) or high (10 nmol/0.5 microl/h) dose levels. Cerebral infarction resulted in a significant increase of BK formation from 3 h to 6 h compared with sham-operated group after reperfusion, whereas medium- and high-dose Ang-(1-7) infusion markedly enhanced BK levels from 6 h to 48 h after reperfusion. Medium- and high-dose Ang-(1-7) infusion markedly increased kinin B(2) receptor mRNA and protein expression, whereas only high-dose Ang-(1-7) infusion induced upregulating the expression of B(1) receptor. Low-dose Ang-(1-7) infusion did not modify both the kinin B(1) and B(2) receptor expression compared with aCSF treatment group after focal cerebral ischemia-reperfusion at each time point. The finding might indicate complex interactions between Ang-(1-7) and kallikrein-kinin system in the CNS after focal cerebral ischemia-reperfusion in rats.

New angiotensins

Accumulation of a large body of evidence during the past two decades testifies to the complexity of the renin–angiotensin system (RAS). The incorporation of novel enzymatic pathways, resulting peptides, and their corresponding receptors into the biochemical cascade of the RAS provides a better understanding of its role in the regulation of cardiovascular and renal function. Hence, in recent years, it became apparent that the balance between the two opposing effector peptides, angiotensin II and angiotensin-(1-7), may have a pivotal role in determining different cardiovascular pathophysiologies. Furthermore, our recent studies provide evidence for the functional relevance of a newly discovered rat peptide, containing two additional amino acid residues compared to angiotensin I, first defined as proangiotensin-12 [angiotensin-(1-12)]. This review focuses on angiotensin-(1-7) and its important contribution to cardiovascular function and growth, while introducing angiotensin-(1-12) as a potential novel angiotensin precursor.

Effects of angiotensin II and its metabolites in the rat coronary vascular bed: is angiotensin III the preferred ligand of the angiotensin AT2 receptor?

Aminopeptidases metabolize angiotensin II to angiotensin-(2-8) (=angiotensin III) and angiotensin-(3-8) (=angiotensin IV), and carboxypeptidases generate angiotensin-(1-7) from angiotensin I and II. Angiotensin-converting enzyme (ACE) inhibitors and/or angiotensin II type 1 (AT1) receptor blockers affect the concentrations of these metabolites, and they may thus contribute to the beneficial effects of these drugs, possibly through stimulation of non-classical angiotensin AT receptors. Here, we investigated the effects of angiotensin II, angiotensin III, angiotensin IV and angiotensin-(1-7) in the rat coronary vascular bed, with or without angiotensin AT1 - or angiotensin II type 2 (AT2) receptor blockade. Results were compared to those in rat iliac arteries and abdominal aortas. Angiotensin II, angiotensin III and angiotensin IV constricted coronary arteries via angiotensin AT1 receptor stimulation, angiotensin III and angiotensin IV being approximately 20- and approximately 8000-fold less potent than angiotensin II. The angiotensin AT2 receptor antagonist PD123319 greatly enhanced the constrictor effects of angiotensin III, starting at angiotensin III concentrations in the low nanomolar range. PD123319 enhanced the angiotensin II-induced constriction at submicromolar angiotensin II concentrations only. Angiotensin-(1-7) exerted no effects in the coronary circulation, although, at micromolar concentrations, it blocked angiotensin AT1 receptor-induced constriction. Angiotensin AT2 receptor-mediated relaxation did not occur in iliac arteries and abdominal aortas, and the constrictor effects of the angiotensin metabolites in these vessels were identical to those in the coronary vascular bed. In conclusion, angiotensin AT2 receptor activation in the rat coronary vascular bed results in vasodilation, and angiotensin III rather than angiotensin II is the preferred endogenous agonist of these receptors. Angiotensin II, angiotensin III, angiotensin IV and angiotensin-(1-7) do not exert effects through non-classical angiotensin AT receptors in the rat coronary vascular bed, iliac artery or aorta.

On the mechanism of coronary vasodilation induced by angiotensin-(1-7) in the isolated guinea pig heart

Various mechanisms have been postulated to be involved in angiotensin-(1-7)-induced endothelium-dependent vasodilation. Here, we characterized the vasodilator action of angiotensin-(1-7) in the isolated guinea pig heart. Angiotensin-(1-7) (1-10 nmol, bolus) induced dose-dependent increase in the coronary flow. The coronary vasodilation induced by angiotensin-(1-7) was significantly reduced by the nitric oxide synthase inhibitor, L-N(G)-nitroarginine methyl ester (L-NAME) (100 microM) and abolished by a B(2) receptor antagonist, icatibant (100 nM). Coronary vasodilation induced by bradykinin (3 pmol, bolus) was inhibited by L-NAME and icatibant to similar extent as that induced by angiotensin-(1-7). Neither the selective AT(2) angiotensin receptor antagonist, PD123319 (1 microM), nor the antagonist of a putative angiotensin-(1-7) receptors, [D-alanine-7]-angiotensin-(1-7) (A-779, 1 microM), influenced the response to angiotensin-(1-7). In conclusion, in the isolated guinea pig heart angiotensin-(1-7) induces coronary vasodilation that is mediated by endogenous bradykinin and subsequent stimulation of nitric oxide release through endothelial B(2) receptors. In contrast to other vascular beds, AT(2) angiotensin receptors and specific angiotensin-(1-7) receptors do not appear involved in angiotensin-(1-7)-induced coronary vasodilation in the isolated guinea pig heart.

Angiotensin, bradykinin and the endothelium

Angiotensins and kinins are endogenous peptides with diverse biological actions; as such, they represent current and future targets of therapeutic intervention. The field of angiotensin biology has changed significantly over the last 50 years. Our original understanding of the crucial role of angiotensin II in the regulation of vascular tone and electrolyte homeostasis has been expanded to include the discovery of new angiotensins, their important role in cardiovascular inflammation and the development of clinically useful synthesis inhibitors and receptor antagonists. While less applied progress has been achieved in the kinin field, there are continuous discoveries in bradykinin physiology and in the complexity of kinin interactions with other proteins. The present review focuses on mechanisms and interactions of angiotensins and kinins that deal specifically with vascular endothelium.