Enhanced susceptibility to biomechanical stress in ACE2 null mice is prevented by loss of the p47(phox) NADPH oxidase subunit

Myocardial Iron Deficiency and Mitochondrial Dysfunction in Advanced Heart Failure in Humans

Background

Myocardial iron deficiency (MID) in heart failure (HF) remains largely unexplored. We aim to establish defining criterion for MID, evaluate its pathophysiological role, and evaluate the applicability of monitoring it non‐invasively in human explanted hearts.

Methods and Results

Biventricular tissue iron levels were measured in both failing (n=138) and non‐failing control (NFC, n=46) explanted human hearts. Clinical phenotyping was complemented with comprehensive assessment of myocardial remodeling and mitochondrial functional profiles, including metabolic and oxidative stress. Myocardial iron status was further investigated by cardiac magnetic resonance imaging. Myocardial iron content in the left ventricle was lower in HF versus NFC (121.4 [88.1–150.3] versus 137.4 [109.2–165.9] μg/g dry weight), which was absent in the right ventricle. With a priori cutoff of 86.1 μg/g d.w. in left ventricle, we identified 23% of HF patients with MID (HF‐MID) associated with higher NYHA class and worsened left ventricle function. Respiratory chain and Krebs cycle enzymatic activities were suppressed and strongly correlated with depleted iron stores in HF‐MID hearts. Defenses against oxidative stress were severely impaired in association with worsened adverse remodeling in iron‐deficient hearts. Mechanistically, iron uptake pathways were impeded in HF‐MID including decreased translocation to the sarcolemma, while transmembrane fraction of ferroportin positively correlated with MID. Cardiac magnetic resonance with T2* effectively captured myocardial iron levels in failing hearts.

Conclusions

MID is highly prevalent in advanced human HF and exacerbates pathological remodeling in HF driven primarily by dysfunctional mitochondria and increased oxidative stress in the left ventricle. Cardiac magnetic resonance demonstrates clinical potential to non‐invasively monitor MID.

Current Trends and Applications of Food-derived Antihypertensive Peptides for the Management of Cardiovascular Disease

Abstract:

Food derived Antihypertensive peptides is considered as a natural supplement for controlling the hypertension. Food protein not only serve as a macronutrient but also act as raw material for biosynthesis of physiologically active peptides. Food sources like milk and milk products, animal protein such as meat, chicken, fish, eggs and plant derived proteins from soy, rice, wheat, mushroom, pumpkins contain high amount of antihypertensive peptides. The food derived antihypertensive peptides has ability to supress the action of rennin and Angiotesin converting enzyme (ACE) which is mainly involved in regulation of blood pressure by RAS. The biosynthesis of endothelial nitric oxide synthase is also improved by ACE inhibitory peptides which increase the production of nitric oxide in vascular walls and encourage vasodilation. Interaction between the angiotensin II and its receptor is also inhibited by the peptides which help to reduce hypertension. This review will explore the novel sources and applications of food derived peptides for the management of hypertension.

Changes of FGF23 and the Renin-Angiotensin-System in Male Mouse Models of Chronic Kidney Disease and Cardiac Hypertrophy

Serum fibroblast growth factor 23 (FGF23) levels and the renin-angiotensin-aldosterone system (RAAS) are elevated in chronic kidney disease (CKD) patients, and their association with left ventricular hypertrophy (LVH) has been reported. However, whether the FGF23 elevation is the cause or result of LVH remains unclear. At 10 weeks, male C57BL/6J mice were divided into 4 groups: sham, CKD (5/6 nephrectomy), LVH (transaortic constriction), and CKD/LVH group. At 16 weeks, the mice were euthanized, and blood and urine, cardiac expressions of FGF23 and RAAS-related factors, and cardiac histological analyses were performed. Heart weight, serum FGF23 levels, and cardiac expression of FGF23 and RAAS-related factors, except for angiotensin-converting enzyme 2, were more increased in the CKD/LVH group compared to the other groups. A significant correlation between LVH and cardiac expressions of FGF23 and RAAS-related factors was observed. Furthermore, there was a significantly close correlation of the cardiac expression of FGF23 with LVH and RAAS-related factors. The coexisting CKD and LVH increased serum and cardiac FGF23 and RAAS-related factors, and there was a significant correlation between them. A close correlation of cardiac, but not serum FGF23, with LVH and RAAS suggests that local FGF23 levels may be associated with LVH and RAAS activation.

Selective Inhibition of the Interaction between SARS-CoV-2 Spike S1 and ACE2 by SPIDAR Peptide Induces Anti-Inflammatory Therapeutic Responses

Many patients with coronavirus disease 2019 in intensive care units suffer from cytokine storm. Although anti-inflammatory therapies are available to treat the problem, very often, these treatments cause immunosuppression. Because angiotensin-converting enzyme 2 (ACE2) on host cells serves as the receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), to delineate a SARS-CoV-2-specific anti-inflammatory molecule, we designed a hexapeptide corresponding to the spike S1-interacting domain of ACE2 receptor (SPIDAR) that inhibited the expression of proinflammatory molecules in human A549 lung cells induced by pseudotyped SARS-CoV-2, but not vesicular stomatitis virus. Accordingly, wild-type (wt), but not mutated (m), SPIDAR inhibited SARS-CoV-2 spike S1-induced activation of NF-κB and expression of IL-6 and IL-1β in human lung cells. However, wtSPIDAR remained unable to reduce activation of NF-κB and expression of proinflammatory molecules in lungs cells induced by TNF-α, HIV-1 Tat, and viral dsRNA mimic polyinosinic-polycytidylic acid, indicating the specificity of the effect. The wtSPIDAR, but not mutated SPIDAR, also hindered the association between ACE2 and spike S1 of SARS-CoV-2 and inhibited the entry of pseudotyped SARS-CoV-2, but not vesicular stomatitis virus, into human ACE2-expressing human embryonic kidney 293 cells. Moreover, intranasal treatment with wtSPIDAR, but not mutated SPIDAR, inhibited lung activation of NF-κB, protected lungs, reduced fever, improved heart function, and enhanced locomotor activities in SARS-CoV-2 spike S1-intoxicated mice. Therefore, selective targeting of SARS-CoV-2 spike S1-to-ACE2 interaction by wtSPIDAR may be beneficial for coronavirus disease 2019.

Zinc ionophores isolated from Terminalia bellirica fruit rind extract protect against cardiomyocyte hypoxia/reoxygenation injury

The study aimed to isolate and characterize zinc ionophores from Terminalia bellirica fruit using a liposome assay and test its utility in H9c2 rat cardiomyoblasts cells subjected to hypoxia/reoxygenation. Ethyl acetate extract that exhibited zinc ionophore activity was resolved to yield three polyphenols that were characterized as epicatechin-3-gallate (ECG), epigallocatechin-3-gallate (EGCG) and epigallocatechin (EGC) by nuclear magnetic resonance and electrospray ionization-mass spectra. The polyphenols enhanced the uptake of zinc into the liposomes and increased FluoZin-3 fluorescence. These polyphenols in the presence of 10 μM ZnCl₂ enhanced the zinc import into H9c2 cells, whose intracellular zinc levels were otherwise lowered upon hypoxia/reoxygenation. EGCG proved to be more potent than ECG, which indeed was more effective than EGC in improving cellular zinc levels and in attenuating the apoptosis of H9c2 cells after hypoxia/reoxygenation injury. The polyphenols required zinc for anti-apoptotic effect. The cardioprotective effect is indeed due to enhanced zinc uptake mediated by these polyphenols.

Targeting fibrosis in the failing heart with nanoparticles

Heart failure (HF) is a clinical syndrome characterized by typical symptoms and signs caused by a structural and/or functional cardiac abnormality, resulting in a reduced cardiac output and/or elevated intracardiac pressures at rest or during stress. Due to increasing incidence, prevalence and, most importantly mortality, HF is a healthcare burden worldwide, despite the improvement of treatment options and effectiveness. Acute and chronic cardiac injuries trigger the activation of neurohormonal, inflammatory, and mechanical pathways ultimately leading to fibrosis, which plays a key role in the development of cardiac dysfunction and HF. The use of nanoparticles for targeted drug delivery would greatly improve therapeutic options to identify, prevent and treat cardiac fibrosis. In this review we will highlight the mechanisms of cardiac fibrosis development to depict the pathophysiological features for passive and active targeting of acute and chronic cardiac fibrosis with nanoparticles. Then we will discuss how cardiomyocytes, immune and inflammatory cells, fibroblasts and extracellular matrix can be targeted with nanoparticles to prevent or restore cardiac dysfunction and to improve the molecular imaging of cardiac fibrosis.

Targeting ACE2 for COVID-19 Therapy: Opportunities and Challenges

The coronavirus disease (COVID-19) pandemic is sweeping the globe. Even with a number of effective vaccines being approved and available to the public, new cases and escalating mortality are climbing every day. ACE2 (angiotensin-converting enzyme 2) is the primary receptor for the COVID-19 causative virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and its complexation with spike proteins plays a crucial role in viral entry into host cells and the subsequent infection. Blocking this binding event or reducing the accessibility of the virus to the ACE2 receptor, represents an alternative strategy to prevent COVID-19. In addition, the biological significance of ACE2 in modulating the innate immune system and tissue repair cascades and anchors its therapeutic potential for treating the infected patients. In this viewpoint article, we review the current efforts of exploiting ACE2 as a therapeutic target to address this dire medical need. We also provide a holistic view of the pros and cons of each treatment strategy. We highlight the fundamental and translational challenges in moving these research endeavors to clinical applications.

The role of SARS-CoV-2 target ACE2 in cardiovascular diseases

SARS-CoV-2, the virus responsible for the global coronavirus disease (COVID-19) pandemic, attacks multiple organs of the human body by binding to angiotensin-converting enzyme 2 (ACE2) to enter cells. More than 20 million people have already been infected by the virus. ACE2 is not only a functional receptor of COVID-19 but also an important endogenous antagonist of the renin-angiotensin system (RAS). A large number of studies have shown that ACE2 can reverse myocardial injury in various cardiovascular diseases (CVDs) as well as is exert anti-inflammatory, antioxidant, anti-apoptotic and anticardiomyocyte fibrosis effects by regulating transforming growth factor beta, mitogen-activated protein kinases, calcium ions in cells and other major pathways. The ACE2/angiotensin-(1-7)/Mas receptor axis plays a decisive role in the cardiovascular system to combat the negative effects of the ACE/angiotensin II/angiotensin II type 1 receptor axis. However, the underlying mechanism of ACE2 in cardiac protection remains unclear. Some approaches for enhancing ACE2 expression in CVDs have been suggested, which may provide targets for the development of novel clinical therapies. In this review, we aimed to identify and summarize the role of ACE2 in CVDs.

Association of ACE inhibitors and angiotensin type II blockers with ACE2 overexpression in COVID-19 comorbidities: A pathway-based analytical study

Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) outbreak is a major public health concern, which has accounted for >1.7 million deaths across the world. A surge in the case fatality ratio as compared with the infection ratio has been observed in most of the countries. The novel Coronavirus SARS-CoV-2 shares the most common sequence with SARS-CoV, but it has a higher rate of transmission. The SARS-CoV-2 pathogenesis is initiated by the binding of viral spike protein with the target receptor Angiotensin-Converting Enzyme 2 (ACE2) facilitating virus internalization within host cells. SARS-CoV-2 mainly causes alveolar damage ranging from mild to severe clinical respiratory manifestations. Most of the cases have revealed the association of Coronavirus disease with patients having earlier comorbidities like Hypertension, Diabetes mellitus, and Cerebrovascular diseases. Pharmacological investigation of the SARS-Cov-2 patients has revealed the frequent use of drugs belongs to Angiotensin-converting enzyme inhibitors (ACEi) and/or Angiotensin II type I receptor blockers (ARBs). Interestingly, a significant increase in ACE2 expression was noticed in patients routinely treated with the above group of drugs were also reported. To date, the association of ACEi and/or ARBs with the up-regulation of ACE2 expression has not been defined distinctively. The proposed review will focus on the pathways which are responsible for the upregulation of ACE2 and its impact on gravity of SARS-CoV-2 disease.

Outbreak of SARS-CoV2: Pathogenesis of infection and cardiovascular involvement

Since the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) has emerged from China, the infection (novel corona virus disease-2019, COVID-19) has affected many countries and led to many deaths worldwide. Like SARS-CoV, angiotencin converting enzyme (ACE)2 as a functional receptor for SARS-CoV2 is essential for the virus to make an entry into the cell. ACE2 is a part of Renin-Angiotensin-Aldosterone System, which is expressed in several organs that opposes the angiotensin (Ang) II functions by converting Ang II to Ang (1-7), the one with vasodilation effects. The death rate of COVID-19 is estimated to be approximately 3.4%; however, some comorbid conditions like underlying cardiovascular disease, hypertension, and diabetes increase the risk of mortality. In addition, cardiovascular involvement as a complication of SARS-CoV2 could be direct through either ACE2 receptors that are expressed tremendously in the heart, or by the surge of different cytokines or by acute respiratory distress syndrome-induced hypoxia. Traditional risk factors could aggravate the process of COVID-19 infection that urges the triage of these high-risk patients for SARS-CoV2. Currently, there is no effective, proven treatment or vaccination for COVID-19, but many investigators are struggling to find a treatment strategy as soon as possible. Some potential medications like chloroquine by itself or in combination with azithromycin and some protease inhibitors used for the treatment of COVID-19 have cardiovascular adverse effects, which should be kept in mind while the patients taking these medications are being closely monitored.

The Human Explanted Heart Program: A translational bridge for cardiovascular medicine

The progression of cardiovascular research is often impeded by the lack of reliable disease models that fully recapitulate the pathogenesis in humans. These limitations apply to both in vitro models such as cell-based cultures and in vivo animal models which invariably are limited to simulate the complexity of cardiovascular disease in humans. Implementing human heart tissue in cardiovascular research complements our research strategy using preclinical models. We established the Human Explanted Heart Program (HELP) which integrates clinical, tissue and molecular phenotyping thereby providing a comprehensive evaluation into human heart disease. Our collection and storage of biospecimens allow them to retain key pathogenic findings while providing novel insights into human heart failure. The use of human non-failing control explanted hearts provides a valuable comparison group for the diseased explanted hearts. Using HELP we have been able to create a tissue repository which have been used for genetic, molecular, cellular, and histological studies. This review describes the process of collection and use of explanted human heart specimens encompassing a spectrum of pediatric and adult heart diseases, while highlighting the role of these invaluable specimens in translational research. Furthermore, we highlight the efficient procurement and bio-preservation approaches ensuring analytical quality of heart specimens acquired in the context of heart donation and transplantation.

Zinc-dependent changes in oxidative and endoplasmic reticulum stress during cardiomyocyte hypoxia/reoxygenation

Myocardial zinc dyshomeostasis is associated with caspase-3 activation, ErbB2 degradation and apoptosis during hypoxia/reoxygenation. Zinc pyrithione replenishes intracellular zinc, suppresses caspase-3, augments ErbB2 levels and improves cell survival. We hypothesize that zinc is capable of modulating redox and endoplasmic reticulum (ER) stress in the setting of cardiomyocyte hypoxia-reoxygenation. Hypoxia/reoxygenation lowered intracellular zinc, increased ER as well as oxidative stress in H9c2 cells, both of which were effectively attenuated by zinc supplementation. Silencing of gp91phox attenuated oxidative and ER stress, decreased caspase-3 activation and improved cell survival. Mimicking the oxidative insult using 50 μM H2O2 increased the caspase-3 activity that correlated with decreased ErbB2 levels, concomitant with augmented ER stress. N-acetyl cysteine (NAC) administration completely suppressed ER stress as well as caspase-3 activity. Zinc depletion using TPEN also resulted in lowered ErbB2 and increased apoptosis, along with NOX2 mRNA upregulation, increased oxidative and ER stress. Repletion with zinc suppressed NOX2 mRNA, lowered oxidative as well as ER stress and decreased cell death. These results suggest that zinc dyshomeostasis, along with oxidative stress contribute to the unfolded protein response during myocardial H/R and that zinc replenishment corrects zinc homeostasis, alleviates associated stress and improves cardiomyocyte survival.

Smooth or Risky Revisit of an Old Malaria Drug for COVID-19?

Hydroxychloroquine (HCQ) is an old medication for malaria. In addition to handling this parasitic disease, HCQ is also used to treat a number of autoimmune disorders including rheumatoid arthritis and systemic lupus erythematosus when other medications are not effective. Recently a new viral infection (COVID-19) is rocking the entire world so much that it has already taken more than 200,000 lives throughout the world within the last two months and the World Health Organization was forced to declare it as a pandemic on March 11, 2020. Interestingly, some reports indicate that this wonder drug may be also beneficial for COVID-19 and accordingly, many clinical trials have begun. Here, we discuss different modes of action (anti-inflammatory, antioxidant, inhibition of endosomal acidification, suppression of angiotensin-converting enzyme 2 or ACE2 glycosylation, etc.) of HCQ that might be responsible for its possible anti-COVID-19 effect. On the other hand, this review also makes an honest attempt to delineate mechanisms (increase in vasoconstriction, inhibition of autophagy, depletion of T cells, etc.) indicating how it may aggravate certain conditions and why caution should be taken before granting widespread repurposing of HCQ for COVID-19.

Cardiac fibrosis: potential therapeutic targets

Cardiovascular disease is a leading cause of mortality in the world and is exacerbated by the presence of cardiac fibrosis, defined by the accumulation of noncontractile extracellular matrix proteins. Cardiac fibrosis is directly linked to cardiac dysfunction and increased risk of arrhythmia. Despite its prevalence, there is a lack of efficacious therapies for inhibiting or reversing cardiac fibrosis, largely due to the complexity of the cell types and signaling pathways involved. Ongoing research has aimed to understand the mechanisms of cardiac fibrosis and develop new therapies for treating scar formation. Major approaches include preventing the formation of scar tissue and replacing fibrous tissue with functional cardiomyocytes. While targeting the renin-angiotensin-aldosterone system is currently used as the standard line of therapy for heart failure, there has been increased interest in inhibiting the transforming growth factor-β signaling pathway due its established role in cardiac fibrosis. Significant advances in cell transplantation therapy and biomaterials engineering have also demonstrated potential in regenerating the myocardium. Novel techniques, such as cellular direct reprogramming, and molecular targets, such as noncoding RNAs and epigenetic modifiers, are uncovering novel therapeutic options targeting fibrosis. This review provides an overview of current approaches and discuss future directions for treating cardiac fibrosis.

The sirtuin 6 prevents angiotensin II-mediated myocardial fibrosis and injury by targeting AMPK-ACE2 signaling

Sirtuin 6 (SIRT6) is an important modulator of cardiovascular functions in health and diseases. However, the exact role of SIRT6 in heart disease is poorly defined. We hypothesized that SIRT6 is a negative regulator of angiotensin II (Ang II)-mediated myocardial remodeling, fibrosis and injury. The male Sprague-Dawley rats were randomized to Ang II (200 ng/kg/min) infusion with an osmotic minipump and pretreated with recombinant plasmids adeno-associated viral vector (AAV)-SIRT6 (pAAV-SIRT6) or pAAV-GFP for 4 weeks. Ang II triggered downregulated levels of SIRT6 and angiotensin-converting enzyme 2 (ACE2) and upregulated expression of connective tissue growth factor (CTGF) and proinflammatory chemokine fractalkine (FKN), contributing to enhanced cardiac fibrosis and ultrastructural injury. Reduced levels of phosphorylated pAMPK-α, increased myocardial hypertrophy and impaired heart dysfunction were observed in both Ang II-induced hypertensive rats and ACE2 knockout rats, characterized with increases in heart weight and left ventricular (LV) posterior wall thickness and decreases in LV ejection fraction and LV fractional shortening. More importantly, pAAV-SIRT6 treatment strikingly potentiated cardiac levels of pAMPKα and ACE2 as well as decreased levels of CTGF, FKN, TGFβ1, collagen I and collagen III, resulting in alleviation of Ang II-induced pathological hypertrophy, myocardial fibrosis, cardiac dysfunction and ultrastructural injury in hypertensive rats. In conclusion, our findings confirmed cardioprotective effects of SIRT6 on pathological remodeling, fibrosis and myocardial injury through activation of AMPK-ACE2 signaling and suppression of CTGF-FKN pathway, indicating that SIRT6 functions as a partial agonist of ACE2 and targeting SIRT6 has potential therapeutic importance for cardiac fibrosis and heart disease.

Angiotensin-converting enzyme 2 inhibits high-mobility group box 1 and attenuates cardiac dysfunction post-myocardial ischemia

High-mobility group box 1 (HMGB1) triggers and amplifies inflammation cascade following ischemic injury, and its elevated levels are associated with adverse clinical outcomes in patients with myocardial infarction (MI). Angiotensin-converting enzyme 2 (ACE2), a key member of vasoprotective axis of the renin-angiotensin system (RAS), regulates cardiovascular functions and exerts beneficial effects in cardiovascular disease. However, the association between HMGB1 and ACE2 has not been studied. We hypothesized that overexpression of ACE2 provides cardioprotective effects against MI via inhibiting HMGB1 and inflammation. ACE2 knock-in (KI) mice and littermate wild-type (WT) controls were subjected to either sham or coronary artery ligation surgery to induce MI. Heart function was assessed 4 weeks after surgery using echocardiography and Millar catheterization. Tissues were collected for histology and analysis of the expression of HMGB1, RAS components, and inflammatory cytokines. ACE2 in the heart of the ACE2 KI mice was 58-fold higher than WT controls. ACE2-MI mice exhibited a remarkable preservation of cardiac function and reduction of infarct size in comparison to WT-MI mice. Notably, ACE2 overexpression significantly reduced the MI-induced increase in apoptosis, macrophage infiltration, and HMGB1 and proinflammatory cytokine expression (TNF-α and IL-6). Moreover, in an in vitro study, ACE2 activation prevented the hypoxia-induced cell death and upregulation of HMGB1 in adult cardiomyocytes. This protective effect is correlated with downregulation of HMGB1 and downstream proinflammatory cascades, which could be useful for the development of novel treatment for ischemic heart disease.

A Disintegrin and Metalloprotease 17 in the Cardiovascular and Central Nervous Systems

ADAM17 is a metalloprotease and disintegrin that lodges in the plasmatic membrane of several cell types and is able to cleave a wide variety of cell surface proteins. It is somatically expressed in mammalian organisms and its proteolytic action influences several physiological and pathological processes. This review focuses on the structure of ADAM17, its signaling in the cardiovascular system and its participation in certain disorders involving the heart, blood vessels, and neural regulation of autonomic and cardiovascular modulation.

ACE2 and Microbiota: Emerging Targets for Cardiopulmonary Disease Therapy

The health of the cardiovascular and pulmonary systems is inextricably linked to the renin-angiotensin system (RAS). Physiologically speaking, a balance between the vasodeleterious (Angiotensin-converting enzyme [ACE]/Angiotensin II [Ang II]/Ang II type 1 receptor [AT1R]) and vasoprotective (Angiotensin-converting enzyme 2 [ACE2]/Angiotensin-(1-7) [Ang-(1-7)]/Mas receptor [MasR]) components of the RAS is critical for cardiopulmonary homeostasis. Upregulation of the ACE/Ang II/AT1R axis shifts the system toward vasoconstriction, proliferation, hypertrophy, inflammation, and fibrosis, all factors that contribute to the development and progression of cardiopulmonary diseases. Conversely, stimulation of the vasoprotective ACE2/Ang-(1-7)/MasR axis produces a counter-regulatory response that promotes cardiovascular health. Current research is investigating novel strategies to augment actions of the vasoprotective RAS components, particularly ACE2, in order to treat various pathologies. Although multiple approaches to increase the activity of ACE2 have displayed beneficial effects against experimental disease models, the mechanisms behind its protective actions remain incompletely understood. Recent work demonstrating a non-catalytic role for ACE2 in amino acid transport in the gut has led us to speculate that the therapeutic effects of ACE2 can be mediated, in part, by its actions on the gastrointestinal tract and/or gut microbiome. This is consistent with emerging data which suggest that dysbiosis of the gut and lung microbiomes is associated with cardiopulmonary disease. This review highlights new developments in the protective actions of ACE2 against cardiopulmonary disorders, discusses innovative approaches to targeting ACE2 for therapy, and explores an evolving role for gut and lung microbiota in cardiopulmonary health.

Role of the ACE2/Angiotensin 1-7 Axis of the Renin-Angiotensin System in Heart Failure

Heart failure (HF) remains the most common cause of death and disability, and a major economic burden, in industrialized nations. Physiological, pharmacological, and clinical studies have demonstrated that activation of the renin-angiotensin system is a key mediator of HF progression. Angiotensin-converting enzyme 2 (ACE2), a homolog of ACE, is a monocarboxypeptidase that converts angiotensin II into angiotensin 1-7 (Ang 1-7) which, by virtue of its actions on the Mas receptor, opposes the molecular and cellular effects of angiotensin II. ACE2 is widely expressed in cardiomyocytes, cardiofibroblasts, and coronary endothelial cells. Recent preclinical translational studies confirmed a critical counter-regulatory role of ACE2/Ang 1-7 axis on the activated renin-angiotensin system that results in HF with preserved ejection fraction. Although loss of ACE2 enhances susceptibility to HF, increasing ACE2 level prevents and reverses the HF phenotype. ACE2 and Ang 1-7 have emerged as a key protective pathway against HF with reduced and preserved ejection fraction. Recombinant human ACE2 has been tested in phase I and II clinical trials without adverse effects while lowering and increasing plasma angiotensin II and Ang 1-7 levels, respectively. This review discusses the transcriptional and post-transcriptional regulation of ACE2 and the role of the ACE2/Ang 1-7 axis in cardiac physiology and in the pathophysiology of HF. The pharmacological and therapeutic potential of enhancing ACE2/Ang 1-7 action as a novel therapy for HF is highlighted.

Antifibrotic therapies to control cardiac fibrosis

Cardiac fibrosis occurs naturally after myocardial infarction. While the initially formed fibrotic tissue prevents the infarcted heart tissue from rupture, the progression of cardiac fibrosis continuously expands the size of fibrotic tissue and causes cardiac function decrease. Cardiac fibrosis eventually evolves the infarcted hearts into heart failure. Inhibiting cardiac fibrosis from progressing is critical to prevent heart failure. However, there is no efficient therapeutic approach currently available. Myofibroblasts are primarily responsible for cardiac fibrosis. They are formed by cardiac fibroblast differentiation, fibrocyte differentiation, epithelial to mesenchymal transdifferentiation, and endothelial to mesenchymal transition, driven by cytokines such as transforming growth factor beta (TGF-β), angiotensin II and platelet-derived growth factor (PDGF). The approaches that inhibit myofibroblast formation have been demonstrated to prevent cardiac fibrosis, including systemic delivery of antifibrotic drugs, localized delivery of biomaterials, localized delivery of biomaterials and antifibrotic drugs, and localized delivery of cells using biomaterials. This review addresses current progresses in cardiac fibrosis therapies.

Genetic Deletion of ACE2 Induces Vascular Dysfunction in C57BL/6 Mice: Role of Nitric Oxide Imbalance and Oxidative Stress

Accumulating evidence indicates that angiotensin-converting enzyme 2 (ACE2) plays a critical role in cardiovascular homeostasis, and its altered expression is associated with major cardiac and vascular disorders. The aim of this study was to evaluate the regulation of vascular function and assess the vascular redox balance in ACE2-deficient (ACE2^-/y) animals. Experiments were performed in 20–22 week-old C57BL/6 and ACE2^-/y male mice. Evaluation of endothelium-dependent and -independent relaxation revealed an impairment of in vitro and in vivo vascular function in ACE2^-/y mice. Drastic reduction in eNOS expression at both protein and mRNA levels, and a decrease in ^•NO concentrations were observed in aortas of ACE2^-/y mice in comparison to controls. Consistently, these mice presented a lower plasma and urine nitrite concentration, confirming reduced ^•NO availability in ACE2-deficient animals. Lipid peroxidation was significantly increased and superoxide dismutase activity was decreased in aorta homogenates of ACE2^-/y mice, indicating impaired antioxidant capacity. Taken together, our data indicate, that ACE2 regulates vascular function by modulating nitric oxide release and oxidative stress. In conclusion, we elucidate mechanisms by which ACE2 is involved in the maintenance of vascular homeostasis. Furthermore, these findings provide insights into the role of the renin-angiotensin system in both vascular and systemic redox balance.

Timing effect of intramyocardial hydrogel injection for positively impacting left ventricular remodeling after myocardial infarction

Intramyocardial injection of various injectable hydrogel materials has shown benefit in positively impacting the course of left ventricular (LV) remodeling after myocardial infarction (MI). However, since LV remodeling is a complex, time dependent process, the most efficacious time of hydrogel injection is not clear. In this study, we injected a relatively stiff, thermoresponsive and bioabsorbable hydrogel in rat hearts at 3 different time points - immediately after MI (IM), 3 d post-MI (3D), and 2 w post-MI (2W), corresponding to the beginnings of the necrotic, fibrotic and chronic remodeling phases. The employed left anterior descending coronary artery ligation model showed expected infarction responses including functional loss, inflammation and fibrosis with distinct time dependent patterns. Changes in LV geometry and contractile function were followed by longitudinal echocardiography for 10 w post-MI. While all injection times positively affected LV function and wall thickness, the 3D group gave better functional outcomes than the other injection times and also exhibited more local vascularization and less inflammatory markers than the earlier injection time. The results indicate an important role for injection timing in the increasingly explored concept of post-MI biomaterial injection therapy and suggest that for hydrogels with mechanical support as primary function, injection at the beginning of the fibrotic phase may provide improved outcomes.

Determinants of ventricular arrhythmias in human explanted hearts with dilated cardiomyopathy

BACKGROUND

The molecular and cellular determinants of ventricular tachycardia (VT) in patients with nonischaemic dilated cardiomyopathy (NIDCM) remain poorly defined.

MATERIALS AND METHODS

We examined 20 NIDCM hearts where VT was reported in 10 cases and VT was absent in 10 cases, using a double-blinded case-control study design, and assessed the molecular and cellular features of the adverse myocardial remodelling.

RESULTS

Explanted hearts from patients with VT showed greater hypertrophic changes based on cardiomyocyte cross-sectional area and expression of disease markers, and increased myocardial fibrosis which extended into the left ventricular and right ventricular outflow tract regions. The VT group also showed increased oxidative stress with reduction in reduced glutathione levels. Connexin 43 levels in the intercalated discs showed increased levels in the VT group with reduced phosphorylation. Microarray mRNA analysis of gene expression in the left ventricle (LV) free wall revealed several families of genes which were differentially upregulated or downregulated in hearts with documented VT compared to hearts without VT. Notably, we identified reduced expression of the Ca(2+) -activated K(+) channel (KCNN2) and increased expression of the transient receptor potential cation channel 7 (TRPM7) and intracellular chloride channel 3. Western blot analysis on LV membrane fractions showed reduced KCNN2 and increased TRPM7 levels in hearts with VT.

CONCLUSIONS

In explanted human hearts with NIDCM, VT is associated with greater hypertrophy, oxidative stress and myocardial fibrosis, differential gene expression, and altered ion channel levels indicative of a distinctive adverse myocardial remodelling process associated with clinically significant VT.

Antagonism of angiotensin 1-7 prevents the therapeutic effects of recombinant human ACE2

Activation of the angiotensin 1-7/Mas receptor (MasR) axis counteracts angiotensin II (Ang II)-mediated cardiovascular disease. Recombinant human angiotensin-converting enzyme 2 (rhACE2) generates Ang 1-7 from Ang II. We hypothesized that the therapeutic effects of rhACE2 are dependent on Ang 1-7 action. Wild type male C57BL/6 mice (10-12 weeks old) were infused with Ang II (1.5 mg/kg/d) and treated with rhACE2 (2 mg/kg/d). The Ang 1-7 antagonist, A779 (200 ng/kg/min), was administered to a parallel group of mice. rhACE2 prevented Ang II-induced hypertrophy and diastolic dysfunction while A779 prevented these beneficial effects and precipitated systolic dysfunction. rhACE2 effectively antagonized Ang II-mediated myocardial fibrosis which was dependent on the action of Ang 1-7. Myocardial oxidative stress and matrix metalloproteinase 2 activity was further increased by Ang 1-7 inhibition even in the presence of rhACE2. Activation of Akt and endothelial nitric oxide synthase (eNOS) by rhACE2 were suppressed by the antagonism of Ang 1-7 while the activation of pathological signaling pathways was maintained. Blocking Ang 1-7 action prevents the therapeutic effects of rhACE2 in the setting of elevated Ang II culminating in systolic dysfunction. These results highlight a key cardioprotective role of Ang 1-7, and increased Ang 1-7 action represents a potential therapeutic strategy for cardiovascular diseases.

KEY MESSAGES

Activation of the renin-angiotensin system (RAS) plays a key pathogenic role in cardiovascular disease. ACE2, a monocarboxypeptidase, negatively regulates pathological effects of Ang II. Antagonizing Ang 1-7 prevents the therapeutic effects of recombinant human ACE2. Our results highlight a key protective role of Ang 1-7 in cardiovascular disease.

Balance between angiotensin converting enzyme and angiotensin converting enzyme 2 in patients with chronic heart failure

AIM

It has been reported that angiotensin converting enzyme 2 (ACE2) is an endogenous counter-regulator of the renin-angiotensin-aldosterone system. However, angiotensin converting enzyme (ACE)/ACE2 balance in the development of human heart failure is not well established.

METHODS

Here we evaluated the expression of ACE and ACE2 at the mRNA and protein levels in the myocardium of 78 patients with mild or moderate to severe heart failure and in 13 cases with normal myocardium.

RESULTS

In the myocardium of patients with dilated or ischemic cardiomyopathy, ACE and ACE2 expression at the mRNA and protein levels was significantly increased compared with those in normal myocardium (P<0.01, P<0.01, respectively). The ratios of ACE/ACE2 mRNA and ACE/ACE2 were lower in the myocardium of patients with mild heart failure than those in normal myocardium but higher than those in patients with moderate to severe heart failure.

CONCLUSIONS

ACE and ACE2 expression at the mRNA and protein levels are significantly increased in the myocardium of patients with heart failure. The compensatory mechanism of patients with mild heart may cause the decreased ACE/ACE2 ratio. However, increased ACE/ACE2 ratios may induce angiotensin II over-activation and accelerate cardiac remodeling in patients with moderate to severe heart failure.

p47(phox) contributes to albuminuria and kidney fibrosis in mice

Reactive oxygen species (ROS) have an important pathogenic role in the development of many diseases, including kidney disease. Major ROS generators in the glomerulus of the kidney are the p47(phox)-containing NAPDH oxidases NOX1 and NOX2. The cytosolic p47(phox) subunit is a key regulator of the assembly and function of NOX1 and NOX2 and its expression and phosphorylation are upregulated in the course of renal injury, and have been shown to exacerbate diabetic nephropathy. However, its role in nondiabetic-mediated glomerular injury is unclear. To address this, we subjected p47(phox)-null mice to either adriamycin-mediated or partial renal ablation-mediated glomerular injury. Deletion of p47(phox) protected the mice from albuminuria and glomerulosclerosis in both injury models. Integrin α1-null mice develop more severe glomerulosclerosis compared with wild-type mice in response to glomerular injury mainly due to increased production of ROS. Interestingly, the protective effects of p47(phox) knockout were more profound in p47(phox)/integrin α1 double knockout mice. In vitro analysis of primary mesangial cells showed that deletion of p47(phox) led to reduced basal levels of superoxide and collagen IV production. Thus, p47(phox)-dependent NADPH oxidases are a major glomerular source of ROS, contribute to kidney injury, and are potential targets for antioxidant therapy in fibrotic disease.

Angiotensin-converting enzyme 2 as a therapeutic target for heart failure

The renin-angiotensin system (RAS) plays a major role in the pathophysiology of cardiovascular disorders. Angiotensin II (Ang-II), the final product of this pathway, is known for its vasoconstrictive and proliferative effects. Angiotensin-converting enzyme 2 (ACE2), a newly discovered homolog of ACE, plays a key role as the central negative regulator of the RAS. It diverts the generation of vasoactive Ang-II into the vasodilatory and growth inhibiting peptide angiotensin(1-7) [Ang(1-7)], thereby providing counter-regulatory responses to neurohormonal activation. There is substantial experimental evidence evaluating the role of ACE2/Ang(1-7) in hypertension, heart failure, and atherosclerosis. In this review, we aim to focus on the conceptual facts of the ACE2-Ang(1-7) axis with regards to clinical implications and therapeutic targets in cardiovascular disorders, with emphasis on the potential therapeutic role in cardiovascular diseases.

Activation of the ACE2/Ang-(1-7)/Mas pathway reduces oxygen-glucose deprivation-induced tissue swelling, ROS production, and cell death in mouse brain with angiotensin II overproduction

We previously demonstrated that mice which overexpress human renin and angiotensinogen (R+A+) show enhanced cerebral damage in both in vivo and in vitro experimental ischemia models. Angiotensin-converting enzyme 2 (ACE2) counteracts the effects of angiotensin (Ang-II) by transforming it into Ang-(1-7), thus reducing the ligand for the AT1 receptor and increasing stimulation of the Mas receptor. Triple transgenic mice, SARA, which specifically overexpress ACE2 in neurons of R+A+ mice were used to study the role of ACE2 in ischemic stroke using oxygen and glucose deprivation (OGD) of brain slices as an in vitro model. We examined tissue swelling, the production of reactive oxygen species (ROS), and cell death in the cerebral cortex (CX) and the hippocampal CA1 region during OGD. Expression levels of NADPH oxidase (Nox) isoforms, Nox2 and Nox4 were measured using western blots. Results show that SARA mice and R+A+ mice treated with the Mas receptor agonist Ang-(1-7) had less swelling, cell death, and ROS production in CX and CA1 areas compared to those in R+A+ animals. Treatment of slices from SARA mice with the Mas antagonist A779 eliminated this protection. Finally, western blots revealed less Nox2 and Nox4 expression in SARA mice compared with R+A+ mice both before and after OGD. We suggest that reduced brain swelling and cell death observed in SARA animals exposed to OGD result from diminished ROS production coupled with lower expression of Nox isoforms. Thus, the ACE2/Ang-(1-7)/Mas receptor pathway plays a protective role in brain ischemic damage by counteracting the detrimental effects of Ang-II-induced ROS production.

Angiotensin-converting enzyme 2 is a critical determinant of angiotensin II-induced loss of vascular smooth muscle cells and adverse vascular remodeling

Angiotensin-converting enzyme (ACE) 2 is a key negative regulator of the renin-angiotensin system and metabolizes angiotensin II (Ang II) into Ang 1 to 7. Ang II is a vasoactive peptide, which plays an important role in vascular disease. The objective of the present study was to define the role of ACE2 in pathological vascular remodeling. We found upregulation of ACE2 in dilated human aorta with bicuspid aortic valve and in murine aorta in response to Ang II. Ex vivo pressure myography showed increased vascular stiffness in ACE2 knockout (KO) mesenteric arteries in response to Ang II (1.5 mg/kg per day) and with aging. Histological analyses revealed reduced media-to-lumen ratio in ACE2KO mesenteric arteries with loss of vascular smooth muscle cells. Aortic vascular smooth muscle cells from ACE2KO mice showed markedly increased reactive oxygen species and apoptosis in response to Ang II along with increased cleaved caspase-3 and cleaved caspase-8 levels in the ACE2KO aorta. Ang II type 1 receptor blockade and Ang 1 to 7 supplementation prevented the increase in Ang II-induced reactive oxygen species and apoptotic cell death. In the aorta, Ang II resulted in thoracic and abdominal aortic dilation with loss of vascular smooth muscle cell density in ACE2KO aorta as revealed by α-smooth muscle actin, calponin staining, and electron microscopy with increased promatrix metalloproteinase 2, matrix metalloproteinase 2, and matrix metalloproteinase 9 levels. ACE2 is upregulated in vascular diseases, and ACE2 deficiency exacerbates Ang II-mediated vascular remodeling driven by increased reactive oxygen species and vascular smooth muscle cell apoptosis. In conclusion, the key counter-regulatory role of ACE2 against an activated renin-angiotensin system provides novel insights into the role of ACE2 in vascular diseases.

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

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

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

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

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

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

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

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

Heterozygote loss of ACE2 is sufficient to increase the susceptibility to heart disease

Angiotensin-converting enzyme 2 (ACE2) metabolizes Ang II into Ang 1-7 thereby negatively regulating the renin-angiotensin system. However, heart disease in humans and in animal models is associated with only a partial loss of ACE2. ACE2 is an X-linked gene; and as such, we tested the clinical relevance of a partial loss of ACE2 by using female ACE2(+/+) (wildtype) and ACE2(+/-) (heterozygote) mice. Pressure overload in ACE2(+/-) mice resulted in greater LV dilation and worsening systolic and diastolic dysfunction. These changes were associated with increased myocardial fibrosis, hypertrophy, and upregulation of pathological gene expression. In response to Ang II infusion, there was increased NADPH oxidase activity and myocardial fibrosis resulting in the worsening of Ang II-induced diastolic dysfunction with a preserved systolic function. Ang II-mediated cellular effects in cultured adult ACE2(+/-) cardiomyocytes and cardiofibroblasts were exacerbated. Ang II-mediated pathological signaling worsened in ACE2(+/-) hearts characterized by an increase in the phosphorylation of ERK1/2 and JNK1/2 and STAT-3 pathways. The ACE2(+/-) mice showed an exacerbated pressor response with increased vascular fibrosis and stiffness. Vascular superoxide and nitrotyrosine levels were increased in ACE2(+/-) vessels consistent with increased vascular oxidative stress. These changes occurred with increased renal fibrosis and superoxide production. Partial heterozygote loss of ACE2 is sufficient to increase the susceptibility to heart disease secondary to pressure overload and Ang II infusion.

KEY MESSAGE

Heart disease in humans with idiopathic dilated cardiomyopathy is associated with a partial loss of ACE2. Heterozygote female ACE2 mutant mice showed enhanced susceptibility to pressure overload-induced heart disease. Heterozygote female ACE2 mutant mice showed enhanced susceptibility to Ang II-induced heart and vascular diseases. Partial loss of ACE2 is sufficient to enhance the susceptibility to heart disease.

Targeting angiotensin-converting enzyme 2 as a new therapeutic target for cardiovascular diseases

Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that metabolizes several vasoactive peptides, including angiotensin II (Ang-II; a vasoconstrictive/proliferative peptide), which it converts to Ang-(1-7). Ang-(1-7) acts through the Mas receptor to mediate vasodilatory/antiproliferative actions. The renin-angiotensin system involving the ACE-Ang-II-Ang-II type-1 receptor (AT1R) axis is antagonized by the ACE2-Ang-(1-7)-Mas receptor axis. Loss of ACE2 enhances adverse remodeling and susceptibility to pressure and volume overload. Human recombinant ACE2 may act to suppress myocardial hypertrophy, fibrosis, inflammation, and diastolic dysfunction in heart failure patients. The ACE2-Ang-(1-7)-Mas axis may present a new therapeutic target for the treatment of heart failure patients. This review is mainly focused on the analysis of ACE2, including its influence and potentially positive effects, as well as the potential use of human recombinant ACE2 as a novel therapy for the treatment cardiovascular diseases, such as hypertension and heart failure.

New perspectives in the renin-angiotensin-aldosterone system (RAAS) IV: circulating ACE2 as a biomarker of systolic dysfunction in human hypertension and heart failure

Background

Growing evidence exists for soluble Angiotensin Converting Enzyme-2 (sACE2) as a biomarker in definitive heart failure (HF), but there is little information about changes in sACE2 activity in hypertension with imminent heart failure and in reverse remodeling.

Methods, Findings

Patients with systolic HF (NYHAII-IV, enrolled for cardiac resynchronisation therapy, CRT, n = 100) were compared to hypertensive patients (n = 239) and to a healthy cohort (n = 45) with preserved ejection fraction (EF>50%) in a single center prospective clinical study. The status of the heart failure patients were checked before and after CRT. Biochemical (ACE and sACE2 activity, ACE concentration) and echocardiographic parameters (EF, left ventricular end-diastolic (EDD) and end-systolic diameter (ESD) and dP/dt) were measured.

sACE2 activity negatively correlated with EF and positively with ESD and EDD in all patient's populations, while it was independent in the healthy cohort. sACE2 activity was already increased in the hypertensive group, where signs for imminent heart failure (slightly decreased EF and barely increased NT-proBNP levels) were detected. sACE2 activities further increased in patients with definitive heart failure (EF<50%), while sACE2 activities decreased with the improvement of the heart failure after CRT (reverse remodeling). Serum angiotensin converting enzyme (ACE) concentrations were lower in the diseased populations, but did not show a strong correlation with the echocardiographic parameters.

Conclusions

Soluble ACE2 activity appears to be biomarker in heart failure, and in hypertension, where heart failure may be imminent. Our data suggest that sACE2 is involved in the pathomechanism of hypertension and HF.

ACE2: angiotensin II/angiotensin-(1-7) balance in cardiac and renal injury

Our current recognition of the renin-angiotensin system is more convoluted than originally thought due to the discovery of multiple novel enzymes, peptides, and receptors inherent in this interactive biochemical cascade. Over the last decade, angiotensin-converting enzyme 2 (ACE2) has emerged as a key player in the pathophysiology of hypertension and cardiovascular and renal disease due to its pivotal role in metabolizing vasoconstrictive/hypertrophic/proliferative angiotensin II into favorable angiotensin-(1-7). This review addresses the considerable advancement in research on the role of tissue ACE2 in the development and progression of hypertension and cardiac and renal injury. We summarize the results from recent clinical and experimental studies suggesting that serum or urine soluble ACE2 may serve as a novel biomarker or independent risk factor relevant for diagnosis and prognosis of cardiorenal disease. We also review recent proceedings on novel therapeutic approaches to enhance ACE2/angiotensin-(1-7) axis.

Manipulating angiotensin metabolism with angiotensin converting enzyme 2 (ACE2) in heart failure

•

Heart failure is increasing in prevalence associated with a huge economic burden.

•

ACE2 is a negative regulator of the renin–angiotensin system.

•

Elevated ACE2 activity is a biomarker in heart failure.

•

Enhancing ACE2 action may have unique therapeutic effects in patients with heart failure.

Angiotensin converting enzyme 2 (ACE2), is a monocarboxypeptidase which metabolizes several peptides including the degradation of Ang II, a peptide with vasoconstrictive/proliferative/effects, to generate Ang 1–7, which acting through its receptor Mas exerts vasodilatory/anti-proliferative actions. The classical pathway of the RAS involving the ACE-Ang II-AT₁ receptor axis is antagonized by the second arm constituted by the ACE2-Ang 1–7/Mas receptor axis. Loss of ACE2 enhances the adverse pathological remodeling susceptibility to pressure-overload and myocardial infarction. Human recombinant ACE2 is also a negative regulator of Ang II-induced myocardial hypertrophy, fibrosis and diastolic dysfunction and suppresses pressure-overload induced heart failure. Due to its characteristics, the ACE2-Ang 1–7/Mas axis may represent new possibilities for developing novel therapeutic strategies for the treatment of heart failure. Human recombinant ACE2 has been safely administered to healthy human volunteers intravenously resulting in sustained lowering of plasma Ang II levels. In this review, we will summarize the beneficial effects of ACE2 in heart disease and the potential use of human recombinant ACE2 as a novel therapy for heart failure.

Angiotensin 1-7 ameliorates diabetic cardiomyopathy and diastolic dysfunction in db/db mice by reducing lipotoxicity and inflammation

BACKGROUND

The angiotensin-converting enzyme 2 and angiotensin-(1-7) (Ang 1-7)/MasR (Mas receptor) axis are emerging as a key pathway that can modulate the development of diabetic cardiomyopathy. We studied the effects of Ang 1-7 on diabetic cardiomyopathy in db/db diabetic mice to elucidate the therapeutic effects and mechanism of action.

METHODS AND RESULTS

Ang 1-7 was administered to 5-month-old male db/db mice for 28 days via implanted micro-osmotic pumps. Ang 1-7 treatment ameliorated myocardial hypertrophy and fibrosis with normalization of diastolic dysfunction assessed by pressure-volume loop analysis and echocardiography. The functional improvement by Ang 1-7 was accompanied by a reduction in myocardial lipid accumulation and systemic fat mass and inflammation and increased insulin-stimulated myocardial glucose oxidation. Increased myocardial protein kinase C levels and loss of phosphorylation of extracellular signal-regulated kinase 1/2 were prevented by Ang 1-7. Furthermore, Ang 1-7 treatment decreased cardiac triacylglycerol and ceramide levels in db/db mice, concomitantly with an increase in myocardial adipose triglyceride lipase expression. Changes in adipose triglyceride lipase expression correlated with increased SIRT1 (silent mating type information regulation 2 homolog 1) levels and deacetylation of FOXO1 (forkhead box O1).

CONCLUSIONS

We identified a novel beneficial effect of Ang 1-7 on diabetic cardiomyopathy that involved a reduction in cardiac hypertrophy and lipotoxicity, adipose inflammation, and an upregulation of adipose triglyceride lipase. Ang 1-7 completely rescued the diastolic dysfunction in the db/db model. Ang 1-7 represents a promising therapy for diabetic cardiomyopathy associated with type 2 diabetes mellitus.

Angiotensin II induced proteolytic cleavage of myocardial ACE2 is mediated by TACE/ADAM-17: a positive feedback mechanism in the RAS

Angiotensin converting enzyme (ACE) 2 is a key negative regulator of the renin-angiotensin system where it metabolizes angiotensin (Ang) II into Ang 1-7. We hypothesize that Ang II suppresses ACE2 by increasing TNF-α converting enzyme (TACE) activity and ACE2 cleavage. Ang II infusion (1.5 mg/kg/day) in wild-type mice for 2 weeks resulted in substantial decrease in myocardial ACE2 protein levels and activity with corresponding increase in plasma ACE2 activity, prevented by AT1R blockade. Ang II resulted in AT1R-mediated increase in myocardial TACE expression and activity, and membrane translocation of TACE. Ang II treatment in Huh7 cells exhibited AT1R-dependent metalloproteinase mediated shedding of ACE2 while transfection with siTACE prevented shedding of ACE2; cardiomyocyte-specific deletion of TACE also prevented shedding of ACE2. Reactive oxygen species played a key role since p47(phox)KO mice were resistant to Ang II-induced TACE phosphorylation and activation with preservation of myocardial ACE2 which dampened Ang II-induced cardiac dysfunction and hypertrophy. In conclusion, Ang II induces ACE2 shedding by promoting TACE activity as a positive feedback mechanism whereby Ang II facilitates the loss of its negative regulator, ACE2. In HF, elevated plasma ACE2 activity likely represents loss of the protective effects of ACE2 in the heart.

Role of angiotensin-converting enzyme 2 (ACE2) in diabetic cardiovascular complications

Diabetes mellitus results in severe cardiovascular complications, and heart disease and failure remain the major causes of death in patients with diabetes. Given the increasing global tide of obesity and diabetes, the clinical burden of diabetes-induced cardiovascular disease is reaching epidemic proportions. Therefore urgent actions are needed to stem the tide of diabetes which entails new prevention and treatment tools. Clinical and pharmacological studies have demonstrated that AngII (angiotensin II), the major effector peptide of the RAS (renin–angiotensin system), is a critical promoter of insulin resistance and diabetes mellitus. The role of RAS and AngII has been implicated in the progression of diabetic cardiovascular complications and AT1R (AngII type 1 receptor) blockers and ACE (angiotensin-converting enzyme) inhibitors have shown clinical benefits. ACE2, the recently discovered homologue of ACE, is a monocarboxypeptidase which converts AngII into Ang-(1–7) [angiotensin-(1–7)] which, by virtue of its actions on the MasR (Mas receptor), opposes the effects of AngII. In animal models of diabetes, an early increase in ACE2 expression and activity occurs, whereas ACE2 mRNA and protein levels have been found to decrease in older STZ (streptozotocin)-induced diabetic rats. Using the Akita mouse model of Type 1 diabetes, we have recently shown that loss of ACE2 disrupts the balance of the RAS in a diabetic state and leads to AngII/AT1R-dependent systolic dysfunction and impaired vascular function. In the present review, we will discuss the role of the RAS in the pathophysiology and treatment of diabetes and its complications with particular emphasis on potential benefits of the ACE2/Ang-(1–7)/MasR axis activation.

Deletion of angiotensin-converting enzyme 2 promotes the development of atherosclerosis and arterial neointima formation

AIMS

Angiotensin-converting enzyme 2 (ACE2) is known as a negative regulator of the renin-angiotensin system. We aimed to determine the roles of ACE2 on the development of vascular diseases.

METHODS AND RESULTS

Using two diversely different models of vascular diseases, hyperlipidaemia-induced atherosclerosis in apolipoprotein E knockout (KO) mice and mechanical injury-induced arterial neointimal hyperplasia in C57Bl6 mice, we examined whether ACE2 deficiency could affect formation of the vascular lesions. ACE2 deficiency resulted in significantly larger vascular lesions in both aortic atherosclerotic plaques and arterial neointima formation, compared with ACE2(+) control. These ACE2-deficient vascular lesions exhibited enhanced accumulation of macrophages into the lesions and proliferation of vascular smooth muscle cells (VSMCs), accompanied with increased angiotensin-II (Ang-II) levels and enhanced expression of vascular inflammation-related genes, including vascular cell adhesion molecule (VCAM)-1, monocyte chemoattractant protein (MCP)-1, and matrix metalloproteinase (MMP)9 in aorta/artery tissues. Primary bone marrow macrophages and aortic VSMCs isolated from ACE2 KO mice also displayed enhanced pro-inflammatory responsiveness such as up-regulated gene/protein expression of VCAM-1, MCP-1, and MMP9 to stimulation with tumour necrosis factor-α and Ang-II. The similar phenotype was shown in human macrophages and aortic VSMCs that were transfected with ACE2-specific siRNA. In ACE2-deficient VSMCs, inhibition of c-Jun N-terminal kinase (JNK) by pharmacological blockade with SP600125 or genetic knockdown with JNK-specific siRNA significantly attenuated their pro-inflammatory phenotype.

CONCLUSION

ACE2 deficiency promotes the development of vascular diseases associated with Ang-II-mediated vascular inflammation and activation of the JNK signalling, leading to the notion that ACE2 potentially confers protection against vascular diseases.

Angiotensin II and oxidative stress in the failing heart

SIGNIFICANCE

Despite recent medical advances, cardiovascular disease and heart failure (HF) continue to be major health concerns, and related mortality remains high. As a result, investigation of the mechanisms involved in the development of HF continues to be an active field of study.

RECENT ADVANCES

The renin-angiotensin system (RAS) and its effector molecule, angiotensin (Ang) II, affect cardiac function through both systemic and local actions, and have been shown to play a major role in cardiac remodeling and dysfunction in the failing heart. Many of the downstream effects of AngII signaling are mediated by elevated levels of reactive oxygen species (ROS) and oxidative stress, which have also been implicated in the pathology of HF.

CRITICAL ISSUES

Inhibitors of the RAS have proven beneficial in the treatment of patients at risk for and suffering from HF, but remain only partially effective. ROS can be generated from several different sources, and the oxidative state is normally tightly regulated in the heart. How AngII increases ROS levels and causes dysregulation of the cardiac oxidative state has been the subject of considerable interest in recent years.

FUTURE DIRECTIONS

A better understanding of this process and the mechanisms involved should lead to the development of more effective HF therapies and improved outcomes.

Cardiac protective effects of irbesartan via the PPAR-gamma signaling pathway in angiotensin-converting enzyme 2-deficient mice

BACKGROUND

Angiotensin-converting enzyme 2 (ACE2), a monocarboxypeptidase which metabolizes angiotensin II (Ang II) to generate Ang-(1-7), has been shown to prevent cardiac hypertrophy and injury but the mechanism remains elusive. Irbesartan has the dual actions of angiotensin receptor blockade and peroxisome proliferator-activated receptor-γ (PPARγ) activation. We hypothesized that irbesartan would exert its protective effects on ACE2 deficiency-mediated myocardial fibrosis and cardiac injury via the PPARγ signaling.

METHODS

10-week-old ACE2 knockout (ACE2KO; Ace2(-/y)) mice received daily with irbesartan (50 mg/kg) or saline for 2 weeks. The wild-type mice (Ace2(+/y)) were used to the normal controls. We examined changes in myocardial ultrastructure, fibrosis-related genes and pathological signaling by real-time PCR gene array, Western blotting, Masson trichrome staining and transmission electron microscope analyses, respectively.

RESULTS

Compared with the Ace2(+/y) mice, cardiac expression of PPARα and PPARγ were reduced in Ace2(-/y) mice and the myocardial collagen volume fraction (CVF) and expression of fibrosis-related genes were increased, including transforming growth factor-β1 (TGFβ1), connective tissue growth factor (CTGF), collagen I and collagen III. Moreover, ACE2 deficiency triggered cardiac hypertrophy, increased myocardial fibrosis and adverse ultrastructure injury in ACE2KO hearts with higher levels of atrial natriuretic factor (ANF) and phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2), without affecting cardiac systolic function. Intriguingly, treatment with irbesartan significantly reversed ACE2 deficiency-mediated pathological hypertrophy and myocardial fibrosis in Ace2(-/y) mice linked with enhancement of plasma Ang-(1-7) level and downregulation of AT1 receptor in heart. Consistent with attenuation of myocardial fibrosis and ultrastructure injury, the myocardial CVF and levels of ANF, TGFβ1, CTGF, collagen I, collagen III and phosphorylated ERK1/2 were lower, and expression of PPARγ was higher in ACE2KO mice in response to irbesartan treatment, without affecting cardiac expression of PPARα, PPARδ, β-myosin heavy chain, TGFβ2 and fibronectin.

CONCLUSIONS

We conclude that irbesartan prevents ACE2 deficiency-mediated pathological hypertrophy and myocardial fibrosis in ACE2 mutant mice via activation of the PPARγ signaling and suppression of the TGFβ-CTGF-ERK signaling, resulting in attenuation of myocardial injury. Drugs targeting ACE2 and PPARγ represent potential candidates to prevent and treat myocardial injury and related cardiac disorders.

Angiotensin II downregulates ACE2-mediated enhancement of MMP-2 activity in human cardiofibroblasts

Angiotensin converting enzyme II (ACE2) is a component of the renin-angiotensin system (RAS) that negatively regulates angiotensin II (Ang II). Ang II, in turn, affects the expression of matrix metalloproteinases (MMPs) to induce heart remodeling. The specific mechanisms by which ACE2 regulates MMP-2, however, remain unclear. The aim of this study was to investigate the regulatory relationships between Ang II, ACE2, and MMP-2. ACE2 expression was upregulated and downregulated in human cardiofibroblasts (HCFs) by lentiviral infection. Effects on MMP-2 activity, shed ACE2 activity, extracellular signal-regulated kinase (ERK) signaling pathway, and ADAM metallopeptidase domain 17 (ADAM17) expression were assessed. ACE2 increased MMP-2 activity, and Ang II inhibited this effect through the Ang II type-1 receptor (AT1R) and ERK1/2 signaling pathway. Ang II also reduced the effect of ACE2 on ERK1/2 levels, the activity of shed ACE2, and adam17 expression in HCFs. Additionally, these Ang II-mediated reductions could be attenuated by AT1R antagonist valsartan. In conclusion, these data help to clarify how ACE2 and Ang II interact to regulate MMP-2 and control tissue remodeling in heart disease.

Novel aspects of ROS signalling in heart failure

Heart failure and many of the conditions that predispose to heart failure are associated with oxidative stress. This is considered to be important in the pathophysiology of the condition but clinical trials of antioxidant approaches to prevent cardiovascular morbidity and mortality have been unsuccessful. Part of the reason for this may be the failure to appreciate the complexity of the effects of reactive oxygen species. At one extreme, excessive oxidative stress damages membranes, proteins and DNA but lower levels of reactive oxygen species may exert much more subtle and specific regulatory effects (termed redox signalling), even on physiological signalling pathways. In this article, we review our current understanding of the roles of such redox signalling pathways in the pathophysiology of heart failure, including effects on cardiomyocyte hypertrophy signalling, excitation-contraction coupling, arrhythmia, cell viability and energetics. Reactive oxygen species generated by NADPH oxidase proteins appear to be especially important in redox signalling. The delineation of specific redox-sensitive pathways and mechanisms that contribute to different components of the failing heart phenotype may facilitate the development of newer targeted therapies as opposed to the failed general antioxidant approaches of the past.

Oxidative stress in atrial fibrillation: an emerging role of NADPH oxidase

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Patients with AF have up to seven-fold higher risk of suffering from ischemic stroke. Better understanding of etiologies of AF and its thromboembolic complications are required for improved patient care, as current anti-arrhythmic therapies have limited efficacy and off target effects. Accumulating evidence has implicated a potential role of oxidative stress in the pathogenesis of AF. Excessive production of reactive oxygen species (ROS) is likely involved in the structural and electrical remodeling of the heart, contributing to fibrosis and thrombosis. In particular, NADPH oxidase (NOX) has emerged as a potential enzymatic source for ROS production in AF based on growing evidence from clinical and animal studies. Indeed, NOX can be activated by known upstream triggers of AF such as angiotensin II and atrial stretch. In addition, treatments such as statins, antioxidants, ACEI or AT1RB have been shown to prevent post-operative AF; among which ACEI/AT1RB and statins can attenuate NOX activity. On the other hand, detailed molecular mechanisms by which specific NOX isoform(s) are involved in the pathogenesis of AF and the extent to which activation of NOX plays a causal role in AF development remains to be determined. The current review discusses causes and consequences of oxidative stress in AF with a special focus on the emerging role of NOX pathways.

Loss of p47phox subunit enhances susceptibility to biomechanical stress and heart failure because of dysregulation of cortactin and actin filaments

RATIONALE

The classic phagocyte nicotinamide adenine dinucleotide phosphate oxidase (gp91(phox) or Nox2) is expressed in the heart. Nox2 activation requires membrane translocation of the p47(phox) subunit and is linked to heart failure. We hypothesized that loss of p47(phox) subunit will result in decreased reactive oxygen species production and resistance to heart failure.

OBJECTIVE

To define the role of p47(phox) in pressure overload-induced biomechanical stress.

METHODS AND RESULTS

Eight-week-old male p47(phox) null (p47(phox) knockout [KO]), Nox2 null (Nox2KO), and wild-type mice were subjected to transverse aortic constriction-induced pressure overload. Contrary to our hypothesis, p47(phox)KO mice showed markedly worsened systolic dysfunction in response to pressure overload at 5 and 9 weeks after transverse aortic constriction compared with wild-type-transverse aortic constriction mice. We found that biomechanical stress upregulated N-cadherin and β-catenin in p47(phox)KO hearts but disrupted the actin filament cytoskeleton and reduced phosphorylation of focal adhesion kinase. p47(phox) interacts with cytosolic cortactin by coimmunoprecipitation and double immunofluorescence staining in murine and human hearts and translocated to the membrane on biomechanical stress where cortactin interacted with N-cadherin, resulting in adaptive cytoskeletal remodeling. However, p47(phox)KO hearts showed impaired interaction of cortactin with N-cadherin, resulting in loss of biomechanical stress-induced actin polymerization and cytoskeletal remodeling. In contrast, Nox2 does not interact with cortactin, and Nox2-deficient hearts were protected from pressure overload-induced adverse myocardial and intracellular cytoskeletal remodeling.

CONCLUSIONS

We showed a novel role of p47(phox) subunit beyond and independent of nicotinamide adenine dinucleotide phosphate oxidase activity as a regulator of cortactin and adaptive cytoskeletal remodeling, leading to a paradoxically enhanced susceptibility to biomechanical stress and heart failure.