Angiotensin-converting enzyme 2 (ACE2) expression and activity in human carotid atherosclerotic lesions

Imbalance between angiotensin II and angiotensin-(1-7) in human coronary atherosclerosis

Objective:

Our previous studies found that angiotensin-(1–7) (Ang-(1–7)) is an endogenous counter-factor of angiotensin II (Ang-II). However, the balance between Ang-II and Ang-(1–7) in the development of human coronary atherosclerosis is not determined.

Methods and results:

The plasma levels of Ang-II and Ang-(1–7) were detected by enzyme-linked immunosorbent assay (ELISA) in 112 patients with known or suspected coronary artery disease (CAD) undergoing coronary angiography. Patients were divided into three groups based on the coronary angiography as follows: (1) normal (n = 13); (2) noncritical CAD (<50% stenosis, n = 17); and (3) critical CAD (⩾50% stenosis, n = 82). The plasma levels of Ang-II, Ang-(1–7) and the ratio of Ang-II and Ang-(1–7) (Ang-II/Ang-(1–7) were comparable between the normal and noncritical CAD groups. However, Ang-II, Ang-(1–7), and especially Ang-II/Ang-(1–7), were elevated in patients with critical CAD, compared with patients with normal or noncritical CAD. The level of Ang-II/Ang-(1–7) was positively associated with serious coronary stenosis, and correlated with tumor necrosis factor-alpha (TNF-α) level.

Conclusion:

Both Ang-II and Ang-(1–7) expression are significantly increased in patients with critical CAD. However, increased Ang-II/Ang-(1–7) ratios may lead to Ang-II over-activation and aggravate atherosclerosis progression.

Diminazene enhances stability of atherosclerotic plaques in ApoE-deficient mice

Angiotensin (Ang) II contributes to the development of atherosclerosis, while Ang-(1-7) has atheroprotective actions. Accordingly, angiotensin-converting enzyme 2 (ACE2), which breaks-down Ang II and forms Ang-(1-7), has been suggested as a target against atherosclerosis. Here we investigated the actions of diminazene, a recently developed ACE2 activator compound, in a model of vulnerable atherosclerotic plaque. Atherosclerotic plaque formation was induced in the carotid artery of ApoE-deficient mice by a shear stress (SS) modifier device. The animals were treated with diminazene (15mg/kg/day) or vehicle. ACE2 was strongly expressed in the aortic root and low SS-induced carotid plaques, but poorly expressed in the oscillatory SS-induced carotid plaques. Diminazene treatment did not change the lesion size, but ameliorated the composition of aortic root and low SS-induced carotid plaques by increasing collagen content and decreasing both MMP-9 expression and macrophage infiltration. Interestingly, these beneficial effects were not observed in the oscillatory SS-induced plaque. Additionally, diminazene treatment decreased intraplaque ICAM-1 and VCAM-1 expression, circulating cytokine and chemokine levels and serum triglycerides. In summary, ACE2 was distinctively expressed in atherosclerotic plaques, which depends on the local pattern of shear stress. Moreover, diminazene treatment enhances the stability of atherosclerotic plaques.

Tissue specific up regulation of ACE2 in rabbit model of atherosclerosis by atorvastatin: role of epigenetic histone modifications

Growing body of evidence points out the crucial role of ACE2 in preventing atherosclerosis. However, data on how atherosclerosis affects ACE2 expression in heart and kidney remains unknown. Atherosclerosis was induced by feeding New Zealand White rabbits with high cholesterol diet (HCD - 2%) for 12 weeks and atorvastatin was administered (5mg/kg/day p.o) in last 3 weeks. ACE2 mRNA and protein expression was assessed by Western blotting and real time PCR. HCD fed rabbits developed atherosclerosis as confirmed by increase in plasma total cholesterol, LDL and triglycerides as well as formation atherosclerotic plaques in arch of aorta. The ACE2 protein but not mRNA expression was reduced in heart and kidney of HCD rabbits. Interestingly, atorvastatin increased the ACE2 protein expression in heart and kidney of HCD rabbits. However, atorvastatin increased ACE2 mRNA in heart but not in kidney of HCD rabbits. Atorvastatin increased the occupancy of histone H3 acetylation (H3-Ac) mark on ACE2 promoter region in heart of HCD rabbits indicating direct or indirect epigenetic up-regulation of ACE2 by atorvastatin. Further, atorvastatin suppressed Ang II-induced contractile responses and enhanced AT2 receptor mediated relaxant responses in atherosclerotic aorta. We propose that atherosclerosis is associated with reduced ACE2 expression in heart and kidney. We also show an unexplored potential of atorvastatin to up-regulate ACE2 via epigenetic histone modifications. Our data suggest a novel way of replenishing ACE2 expression for preventing not only atherosclerosis but also other cardiovascular disorders.

From gene to protein-experimental and clinical studies of ACE2 in blood pressure control and arterial hypertension

Hypertension is a major risk factor for stroke, coronary events, heart and renal failure, and the renin-angiotensin system (RAS) plays a major role in its pathogenesis. Within the RAS, angiotensin converting enzyme (ACE) converts angiotensin (Ang) I into the vasoconstrictor Ang II. An “alternate” arm of the RAS now exists in which ACE2 counterbalances the effects of the classic RAS through degradation of Ang II, and generation of the vasodilator Ang 1-7. ACE2 is highly expressed in the heart, blood vessels, and kidney. The catalytically active ectodomain of ACE2 undergoes shedding, resulting in ACE2 in the circulation. The ACE2 gene maps to a quantitative trait locus on the X chromosome in three strains of genetically hypertensive rats, suggesting that ACE2 may be a candidate gene for hypertension. It is hypothesized that disruption of tissue ACE/ACE2 balance results in changes in blood pressure, with increased ACE2 expression protecting against increased blood pressure, and ACE2 deficiency contributing to hypertension. Experimental hypertension studies have measured ACE2 in either the heart or kidney and/or plasma, and have reported that deletion or inhibition of ACE2 leads to hypertension, whilst enhancing ACE2 protects against the development of hypertension, hence increasing ACE2 may be a therapeutic option for the management of high blood pressure in man. There have been relatively few studies of ACE2, either at the gene or the circulating level in patients with hypertension. Plasma ACE2 activity is low in healthy subjects, but elevated in patients with cardiovascular risk factors or cardiovascular disease. Genetic studies have investigated ACE2 gene polymorphisms with either hypertension or blood pressure, and have produced largely inconsistent findings. This review discusses the evidence regarding ACE2 in experimental hypertension models and the association between circulating ACE2 activity and ACE2 polymorphisms with blood pressure and arterial hypertension in man.

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.

Angiotensin-(1-7) and angiotensin-(1-9): function in cardiac and vascular remodelling

The RAS (renin-angiotensin system) is integral to cardiovascular physiology; however, dysregulation of this system largely contributes to the pathophysiology of CVD (cardiovascular disease). It is well established that AngII (angiotensin II), the main effector of the RAS, engages the AT1R (angiotensin type 1 receptor) and promotes cell growth, proliferation, migration and oxidative stress, all processes which contribute to remodelling of the heart and vasculature, ultimately leading to the development and progression of various CVDs, including heart failure and atherosclerosis. The counter-regulatory axis of the RAS, which is centred on the actions of ACE2 (angiotensin-converting enzyme 2) and the resultant production of Ang-(1-7) [angiotensin-(1-7)] from AngII, antagonizes the actions of AngII via the receptor Mas, thereby providing a protective role in CVD. More recently, another ACE2 metabolite, Ang-(1-9) [angiotensin-(1-9)], has been reported to be a biologically active peptide within the counter-regulatory axis of the RAS. The present review will discuss the role of the counter-regulatory RAS peptides Ang-(1-7) and Ang-(1-9) in the cardiovascular system, with a focus on their effects in remodelling of the heart and vasculature.

Treatment with Angiotensin-(1-7) reduces inflammation in carotid atherosclerotic plaques

Angiotensin (Ang)-(1-7), acting through the receptor Mas, has atheroprotective effects; however, its role on plaque vulnerability has been poorly studied. Here, we investigated the expression of the renin-angiotensin system (RAS) components in stable and unstable human carotid plaques. In addition, we evaluated the effects of the chronic treatment with an oral formulation of Ang-(1-7) in a mouse model of shear stress-determined carotid atherosclerotic plaque. Upstream and downstream regions of internal carotid plaques were obtained from a recently published cohort of patients asymptomatic or symptomatic for ischaemic stroke. Angiotensinogen and renin genes were strongly expressed in the entire cohort, indicating an intense intraplaque modulation of the RAS. Intraplaque expression of the Mas receptor mRNA was increased in the downstream portion of asymptomatic patients as compared to corresponding region in symptomatic patients. Conversely, AT1 receptor gene expression was not modified between asymptomatic and symptomatic patients. Treatment with Ang-(1-7) in ApoE-/- mice was associated with increased intraplaque collagen content in the aortic root and low shear stress-induced carotid plaques, and a decreased MMP-9 content and neutrophil and macrophage infiltration. These beneficial effects were not observed in the oscillatory shear stress-induced plaque. In vitro incubation with Ang-(1-7) did not affect ICAM-1 expression and apoptosis on cultured endothelial cells. In conclusion, Mas receptor is up regulated in the downstream portions of human stable carotid plaques as compared to unstable lesions. Treatment with the oral formulation of Ang-(1-7) enhances a more stable phenotype in atherosclerotic plaques, depending on the local pattern of shear stress forces.

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

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

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

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Elevated ACE2 activity is a biomarker in heart failure.

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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.

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.

Regulation of cardiovascular remodeling by the counter-regulatory axis of the renin-angiotensin system

The counter-regulatory axis of the renin-angiotensin system (RAS) is a novel therapeutic target in cardiovascular disease. Pathophysiological effects mediated via angiotensin II (Ang II) are well established in regulation of blood pressure, cardiac and vascular remodeling, and renal sodium handling, which lead to disorders such as hypertension and associated end-organ damage, atherosclerosis and heart failure. The counter-regulatory axis of the RAS is centered on the angiotensin-converting enzyme 2/angiotensin-1-7 (Ang-[1-7])/Mas receptor axis and has been shown to inhibit many detrimental phenotypes in cardiovascular disease. More recently, an alternative peptide, angiotensin-(1-9) (Ang-[1-9]), has been reported as a potential new member of this axis. This review will discuss the cardiovascular regulatory roles of Ang-(1-7) and Ang-(1-9) in the counter-regulatory axis of the RAS, and the potential for new therapeutic approaches in cardiovascular disease.

Role of the angiotensin converting enzyme 1/angiotensin II/angiotensin receptor 1 axis in interstitial collagenase expression in human carotid atheroma

BACKGROUND AND AIM

Angiotensin II (AII) receptor 1 (ATR1) and angiotensin converting enzyme 1 (ACE1) blockers have been shown to reduce acute cardiovascular events in patients, improve plaque stability and modify matrix metalloproteinase (MMP) expression. However, the role of the ACE1/AII/ATR1 axis in interstitial collagenase regulation has not been fully explored. In this study, we investigated the effect of ATR1 and ACE1 blockade on the expression and activity of MMP-1, -8 and -13 in human carotid atheroma.

METHODS

Atheroma samples (n = 24) were obtained from patients undergoing carotid endarterectomy. The effects of ATR1 (irbesartan), ACE1 (quinapril), ACE2 (DX600) and MMP (GM6001) blockade on the expression of AII, the interstitial collagenases and soluble elastin fragments were investigated in explant culture supernatants. Paired atheroma samples were incubated with intervention or media control for 4 days. Protein levels (AII, MMP-1, -8, -13 and soluble elastin) were determined by ELISA.

RESULTS

ATR1, but not ACE1, blockade significantly reduced MMP-1 and -8 concentrations in atheroma supernatants. ACE2 blockade significantly increased MMP-1 and -8 concentrations in atheroma supernatants. AII concentration in atheroma supernatants significantly increased after ATR1, ACE1 and ACE2 blockade. Release of soluble elastin fragments increased after ATR1 and ACE1 blockade, but was not changed by an MMP inhibitor.

CONCLUSIONS

Our findings suggest that ATR1 blockade alters AII, MMP-1, MMP-8 expression and a marker of elastin degradation in human atheroma, but that the elastin degradation response is not MMP driven. This data contributes to the recognised ability of ATR1 blockade to modify plaque stability.

Angiotensin-(1-7) inhibits vascular calcification in rats

Angiotensin-(1-7) [Ang-(1-7)] is a new bioactive heptapeptide in the renin-angiotensin-aldosterone system (RAAS) with potent protective effects in cardiovascular diseases, opposing many actions of angiotensin II (Ang II) mediated by Ang II type 1 (AT1) receptor. It is produced mainly by the activity of angiotensin-converting enzyme 2 (ACE2) and acts through the Mas receptor. However, the role of Ang-(1-7) in vascular calcification (VC) is still unclear. In this study, we investigated the protective effects of Ang-(1-7) on VC in an in vivo rat VC model induced by vitamin D3 plus nicotine. The levels of ACE2 and the Mas receptor, as well as ACE, AT1 receptor, Ang II type 2 receptor and angiotensinogen, were significantly increased in calcified aortas, and Ang-(1-7) reversed the increased levels. Ang-(1-7) restored the reduced expression of lineage markers, including smooth muscle (SM) α-actin, SM22α, calponin and smoothelin, in vascular smooth muscle cells (VSMCs) and retarded the osteogenic transition of VSMCs by decreasing the expression of bone-associated proteins. It reduced alkaline phosphatase activity and calcium deposition in VC and alleviated the hemodynamic disorders of rats with VC. We provide the first in vivo evidence that Ang-(1-7) can inhibit the development of VC by inhibiting the osteogenic transition of VSMCs, at least in part by decreasing levels of the ACE/Ang II/AT1 axis. The increased expression of ACE2 and the Mas receptor in calcified aortas suggests the involvement of the ACE2/Ang-(1-7)/Mas axis during VC. Ang-(1-7) might be an efficient endogenous vasoprotective factor for VC.

The ACE2 gene: its potential as a functional candidate for cardiovascular disease

The RAS (renin–angiotensin system) plays an important role in the pathophysiology of CVD (cardiovascular disease), and RAS blockade is an important therapeutic strategy in the management of CVD. A new counterbalancing arm of the RAS is now known to exist in which ACE (angiotensin-converting enzyme) 2 degrades Ang (angiotensin) II, the main effector of the classic RAS, and generates Ang-(1–7). Altered ACE2 expression is associated with cardiac and vascular disease in experimental models of CVD, and ACE2 is increased in failing human hearts and atherosclerotic vessels. In man, circulating ACE2 activity increases with coronary heart disease, as well as heart failure, and a large proportion of the variation in plasma ACE2 levels has been attributed to hereditary factors. The ACE2 gene maps to chromosome Xp22 and this paper reviews the evidence associating ACE2 gene variation with CVD and considers clues to potential functional ACE2 variants that may alter gene expression or transcriptional activity. Studies to date have investigated ACE2 gene associations in hypertension, left ventricular hypertrophy and coronary artery disease, but the results have been inconsistent. The discrepancies may reflect the sample size of the studies, the gender or ethnicity of subjects, the cardiovascular phenotype or the ACE2 SNP investigated. The frequent observation of apparent sex-dependence might be of special importance, if confirmed. As yet, there are no studies to concurrently assess ACE2 gene polymorphisms and circulating ACE2 activity. Large-scale carefully conducted clinical studies are urgently needed to clarify more precisely the potential role of ACE2 in the CVD continuum.

Angiotensin converting enzyme 2 and atherosclerosis

Angiotensin converting enzyme 2 (ACE2) is a homolog of angiotensin converting enzyme (ACE) which generates angiotensin II from angiotensin I. ACE, its product angiotensin II and the downstream angiotensin type I receptor are important components of the renin-angiotensin system (RAS). Angiotensin II, the most important component of the RAS, promotes the development of atherosclerosis. The identification of ACE2 in 2000 opened a new chapter of research on the regulation of the RAS. ACE2 degrades pro-atherosclerotic angiotensin II and generates anti-atherosclerotic angiotensin 1-7. In this review, we explored the importance of ACE2 in protecting experimental animals from developing atherosclerosis and its involvement in human atherosclerosis. We also examined the published evidence assessing the importance of ACE2 in different cell types relevant to atherosclerosis and putative underlying cellular and molecular mechanisms linking ACE2 with protection from atherosclerosis. ACE2 shifts the balance from angiotensin II to angiotensin 1-7 inhibiting the progression of atherosclerosis in animal models.

Angiotensin-Converting Enzyme 2 (ACE2) Is a Key Modulator of the Renin Angiotensin System in Health and Disease

Angiotensin-converting enzyme 2 (ACE2) shares some homology with angiotensin-converting enzyme (ACE) but is not inhibited by ACE inhibitors. The main role of ACE2 is the degradation of Ang II resulting in the formation of angiotensin 1–7 (Ang 1–7) which opposes the actions of Ang II. Increased Ang II levels are thought to upregulate ACE2 activity, and in ACE2 deficient mice Ang II levels are approximately double that of wild-type mice, whilst Ang 1–7 levels are almost undetectable. Thus, ACE2 plays a crucial role in the RAS because it opposes the actions of Ang II. Consequently, it has a beneficial role in many diseases such as hypertension, diabetes, and cardiovascular disease where its expression is decreased. Not surprisingly, current therapeutic strategies for ACE2 involve augmenting its expression using ACE2 adenoviruses, recombinant ACE2 or compounds in these diseases thereby affording some organ protection.

Rho kinase inhibition activates the homologous angiotensin-converting enzyme-angiotensin-(1-9) axis in experimental hypertension

BACKGROUND

Angiotensin II (Ang II) levels depend on renin, angiotensin-converting enzyme (ACE), and on the homologous angiotensin-converting enzyme (ACE2). Increased ACE and Ang II levels are associated with higher Rho kinase activity. However, the relationship between Rho kinase activation and ACE2 in hypertension is unknown.

OBJECTIVE

The role of the Rho kinase signaling pathway in both enzymatic activity and aortic gene expression of ACE2 in deoxycorticosterone acetate (DOCA) hypertensive rats was assessed in the present study.

METHODS AND RESULTS

Compared with sham animals, Rho kinase activity was higher by 400% (P<0.05) in the aortic wall of the DOCA hypertensive rats. In addition to blood pressure reduction, the specific Rho kinase inhibitor fasudil reduced aortic Rho kinase activity to levels observed in the sham control group and increased ACE2 enzymatic activity (by 83% in plasma and by 52% in the aortic wall, P<0.05), ACE2, and endothelial nitric oxide synthase (eNOS) aortic mRNA levels (by 340 and 40%, respectively, P<0.05) with respect to the untreated hypertensive DOCA rats. Fasudil also increased significantly plasma levels of Ang-(1-9) in normotensive and in the hypertensive rats. Aortic mRNA and protein levels of transforming growth factor-β1 (TGF-β1), plasminogen activator inhibitor 1 (PAI-1), and monocyte chemoattractant protein 1 (MCP-1) were significantly (P<0.05) higher in the untreated DOCA rats and were normalized by fasudil administration.

CONCLUSION

In experimental hypertension, Rho-associated, coiled-coil containing protein kinase (ROCK) inhibition reduces blood pressure and increases ACE2 levels and activity. At the same time, ROCK inhibition reduces angiotensin II and increases Ang-(1-9) plasma levels. Fasudil also increases vascular eNOS mRNA levels and reduces aortic overexpression of the remodeling promotion proteins TGF-β1, PAI-1, and MCP-1. This effect might additionally contribute to the antihypertensive and antiremodeling effects of ROCK inhibition in hypertension.

Angiotensin-converting enzyme 2 is a key modulator of the renin-angiotensin system in cardiovascular and renal disease

PURPOSE OF REVIEW

Angiotensin-converting enzyme 2 (ACE2) has recently emerged as a key regulator of the renin-angiotensin system in both health and disease.

RECENT FINDINGS

ACE2 deficiency is associated with elevated tissue and circulating levels of angiotensin II and reduced levels of angiotensin 1-7. Phenotypically, this results in a modest elevation in systolic blood pressure and left ventricular hypertrophy. In atherosclerosis-prone apolipoprotein E knockout mice, ACE2 deficiency results in augmented vascular inflammation and an inflammatory response that contributes to increased atherosclerotic plaque formation. In the kidney, ACE2 deficiency is associated with progressive glomerulosclerosis. Interventions such as ACE2 replenishment or augmentation of its actions have proven successful in reducing hypertension, plaque accumulation, and renal and cardiac damage in a range of different models. Although promising, the balance of the renin-angiotensin system remains complicated, with some evidence that overexpression of ACE2 may have adverse cardiac effects, and ACE2 and its metabolic products may promote epithelial-to-mesenchymal transition.

SUMMARY

Repletion of ACE2's activities offers a new strategy to complement current clinical interventions in treating hypertension, renal and cardiovascular disease. In particular conditions where ACE inhibition and angiotensin receptor blockade are partially effective, the adjunctive actions of ACE2 may not only reduce clinical escape but also augment the efficacy of interventions.

Angiotensin-converting enzyme 2 deficiency in whole body or bone marrow-derived cells increases atherosclerosis in low-density lipoprotein receptor-/- mice

OBJECTIVE

The renin-angiotensin system contributes to atherosclerotic lesion formation. Angiotensin-converting enzyme 2 (ACE2) catabolizes angiotensin II (Ang II) to angiotensin 1-7 (Ang-(1-7)) to limit effects of the renin-angiotensin system. The purpose of this study was to define the role of ACE2 in atherosclerosis.

METHODS AND RESULTS

Male Ace2(-/y) mice in an low-density lipoprotein receptor-deficient background were fed a high-fat diet for 3 months. ACE2 deficiency increased atherosclerotic area (Ace2(+/y), 17 ± 1; Ace2(-/y), 23 ± 2 mm(2), P < 0.002). This increase was blunted by losartan. To determine whether leukocytic ACE2 influenced atherosclerosis, irradiated low-density lipoprotein receptor-deficient male mice were repopulated with bone marrow-derived cells from Ace2(+/y) or Ace2(-/y) mice and fed a high-fat diet for 3 months. ACE2 deficiency in bone marrow-derived cells increased atherosclerotic area (Ace2(+/y), 1.6 ± 0.3; Ace2(-/y), 2.8 ± 0.3 mm(2); P < 0.05). Macrophages from Ace2(-/y) mice exhibited increased Ang II secretion and elevated expression of inflammatory cytokines. Conditioned media from mouse peritoneal macrophages of Ace2(-/y) mice increased monocyte adhesion to human umbilical vein endothelial cells. Incubation of human umbilical vein endothelial cells with Ang II promoted monocyte adhesion, which was blocked by Ang-(1-7). Coinfusion of Ang-(1-7) with Ang II reduced atherosclerosis.

CONCLUSIONS

These results demonstrate that ACE2 deficiency in bone marrow-derived cells promotes atherosclerosis through regulation of Ang II/Ang-(1-7) peptides.

Gender differences in cardiovascular disease: hormonal and biochemical influences

OBJECTIVE

Atherosclerosis is a complex process characterized by an increase in vascular wall thickness owing to the accumulation of cells and extracellular matrix between the endothelium and the smooth muscle cell wall. There is evidence that females are at lower risk of developing cardiovascular disease (CVD) as compared to males. This has led to an interest in examining the contribution of genetic background and sex hormones to the development of CVD. The objective of this review is to provide an overview of factors, including those related to gender, that influence CVD.

METHODS

Evidence analysis from PubMed and individual searches concerning biochemical and endocrine influences and gender differences, which affect the origin and development of CVD.

RESULTS

Although still controversial, evidence suggests that hormones including estradiol and androgens are responsible for subtle cardiovascular changes long before the development of overt atherosclerosis.

CONCLUSION

Exposure to sex hormones throughout an individual's lifespan modulates many endocrine factors involved in atherosclerosis.

Angiotensin-converting enzymes and drug discovery in cardiovascular diseases

Angiotensin-converting enzyme (ACE) is a major target in the treatment of cardiovascular diseases (CVDs). In addition to ACE, ACE2 - which is a homolog of ACE and promotes the degradation of angiotensin II (Ang II) to Ang (1-7) - has been recognized recently as a potential therapeutic target in the management of CVDs. This article reviews different metabolic pathways of ACE and ACE2 (Ang I-Ang II-AT1 receptors and Ang I-Ang (1-7)-Mas receptors) in the regulation of cardiovascular function and their potential in new drug development in the therapy of CVDs. In addition, recent progress in the study of angiotensin and ACE in fetal origins of CVD, which might present an interesting field in perinatal medicine and preventive medicine, is briefly summarized.

Advances in the renin angiotensin system focus on angiotensin-converting enzyme 2 and angiotensin-(1-7)

The contribution of the renin angiotensin system to physiology and pathology is undergoing a rapid reconsideration of its mechanisms from emerging new concepts implicating angiotensin-converting enzyme 2 and angiotensin-(1-7) as new elements negatively influencing the vasoconstrictor, trophic, and pro-inflammatory actions of angiotensin II. This component of the system acts to oppose the vasoconstrictor and proliferative effects on angiotensin II through signaling mechanisms mediated by the mas receptor. In addition, a reduced expression of the vasodepressor axis composed by angiotensin-converting enzyme 2 and angiotensin-(1-7) may contribute to the expression of essential hypertension, the remodeling of heart and renal function associated with this disease, and even the physiology of pregnancy and the development of eclampsia.

Eplerenone does not attenuate diabetes-associated atherosclerosis

BACKGROUND

It has been suggested that aldosterone, with its known pro-inflammatory and profibrotic actions, may play a key role in the development and progression of atherosclerosis.

METHOD

In this study, the ability of aldosterone antagonism to reduce atherosclerosis in experimental diabetes was assessed. Diabetes was induced in ApoE knockout mice with streptozotocin, and the mice were treated with the specific aldosterone antagonist, eplerenone, in their feed over 20 weeks (approximately 200 mg/kg per day).

RESULT

En face analysis revealed that eplerenone treatment was unable to attenuate atherosclerosis as assessed by percentage lesion area quantitation in the aortae of these mice compared with untreated diabetic mice (diabetic, 10.7 +/- 1.1; diabetic + eplerenone, 8.8 +/- 1.2%). In contrast, we observed a significant, more than 50% decrease in percentage of plaque area in the nondiabetic control groups. Despite this lack of effect in the diabetic mice, eplerenone treatment was associated with reduced cytosolic superoxide production. However, aortic transcript levels of key molecules implicated in diabetes-associated atherogenesis, such as monocyte chemoattractant protein-1 and vascular cell adhesion molecule-1, were not significantly attenuated by eplerenone.

CONCLUSION

These findings suggest that eplerenone treatment may not be as antiatherosclerotic in the diabetic context.

Angiotensin II reduces membranous angiotensin-converting enzyme 2 in pressurized human aortic endothelial cells

INTRODUCTION

We applied pressure stress to human aortic endothelial cells (HAEC) and investigated whether mechanical pressure stress and/or angiotensin II (Ang II) affected angiotensin-converting enzyme (ACE) 2. We then tested whether the administration of nifedipine had a demonstrable and possibly beneficial effect.

METHODS

A pulsatile atmospheric pressure with or without Ang II was loaded on HAECs. The expression of ACE2 was studied by immunoblots and reverse transcription/real-time polymerase chain reaction.

RESULTS

The pulsatile mechanical pressure increased the expression of ACE2 mRNA by approximately 80%. Supplementation of Ang II (1 microM) with pulsatile mechanical pressure decreased the expression of ACE2 mRNA by approximately 54%. Pulsatile atmospheric pressure increased ACE2 protein, but supplementation of Ang II (1 microM) also increased ACE2 protein, and the latter failed to show significant change compared to pressurized control without Ang II. Ang II administration reduced ACE2 protein in the membranous fraction under pressurized condition. Administration of nifedipine (1 microM) protected cells from this ACE2 protein reduction at the HAEC membrane.

CONCLUSIONS

These results indicate that pulsatile mechanical pressure and Ang II affect ACE2 in HAECs. Our findings suggest that blood pressure reduction with a calcium channel blocker is beneficial for the conservation of ACE2, and may provide a potential therapeutic target beyond blood pressure lowering in hypertensive patients.

Potential enhancement of osteoclastogenesis by severe acute respiratory syndrome coronavirus 3a/X1 protein

Severe acute respiratory syndrome coronavirus (SARS-CoV) causes a lung disease with high mortality. In addition, osteonecrosis and bone abnormalities with reduced bone density have been observed in patients following recovery from SARS, which were partly but not entirely explained by the short-term use of steroids. Here, we demonstrate that human monocytes, potential precursors of osteoclasts, partly express angiotensin converting enzyme 2 (ACE2), a cellular receptor of SARS-CoV, and that expression of an accessory protein of SARS-CoV, 3a/X1, in murine macrophage cell line RAW264.7 cells, enhanced NF-kappaB activity and differentiation into osteoclast-like cells in the presence of receptor activator of NF-kappaB ligand (RANKL). Furthermore, human epithelial A549 cells expressed ACE2, and expression of 3a/X1 in these cells up-regulated TNF-alpha, which is known to accelerate osteoclastogenesis. 3a/X1 also enhanced RANKL expression in mouse stromal ST2 cells. These findings indicate that SARS-CoV 3a/X1 might promote osteoclastogenesis by direct and indirect mechanisms.

Angiotensin-converting enzyme 2: implications for blood pressure and kidney disease

PURPOSE OF REVIEW

Angiotensin-converting enzyme 2 (ACE 2), the main product of which is Ang 1-7, which binds to its receptor, Mas, is an important member of the renin-angiotensin system.

RECENT FINDINGS

A substantial body of research indicates that ACE2 is cardioprotective and renoprotective. ACE2 participates in a pathway that is counterregulatory to the effects of angiotensin II (Ang II). The mechanisms by which the protective effects of ACE2 occur are just beginning to be elucidated.

SUMMARY

As ACE2 appears to exert protective effects within the kidney and vasculature, recent data indicate that how it is expressed, what regulates it, and how it interacts with other biological systems may ultimately have clinical implications.

Angiotensin-converting enzyme 2 in the brain: properties and future directions

Angiotensin (Ang)-converting enzyme (ACE) 2 cleaves Ang-II into the vasodilator peptide Ang-(1-7), thus acting as a pivotal element in balancing the local effects of these peptides. ACE2 has been identified in various tissues and is supposed to be a modulator of cardiovascular function. Decreases in ACE2 expression and activity have been reported in models of hypertension, heart failure, atherosclerosis, diabetic nephropathy and others. In addition, the expression level and/or activity are affected by other renin-angiotensin system components (e.g., ACE and AT1 receptors). Local inhibition or global deletion of brain ACE2 induces a reduction in baroreflex sensitivity. Moreover, ACE2-null mice have been shown to exhibit either blood pressure or cardiac dysfunction phenotypes. On the other hand, over-expression of ACE2 exerts protective effects in local tissues, including the brain. In this review, we will first summarize the major findings linking ACE2 to cardiovascular function in the periphery then focus on recent discoveries related to ACE2 in the CNS. Finally, we will unveil new tools designed to address the importance of central ACE2 in various diseases, and discuss the potential for this carboxypeptidase as a new target in the treatment of hypertension and other cardiovascular diseases.