Differential ANG II generation in plasma and tissue of mice with decreased expression of the ACE gene

Anti-Inflammatory Effects of Ang-(1-7) Bone-Targeting Conjugate in an Adjuvant-Induced Arthritis Rat Model

Rheumatoid arthritis (RA) is a chronic inflammatory condition of synovial joints that causes disability and systemic complications. Ang-(1-7), one of the main peptides in the renin-angiotensin (Ang) system (RAS), imposes its protective effects through Mas receptor (MasR) signaling. It has a short half-life, limiting its feasibility as a therapeutic agent. In this study, we evaluated the anti-inflammatory effects of Ang-(1-7)’s novel and stable conjugate (Ang. Conj.) by utilizing its affinity for bone through bisphosphonate (BP) moiety in an adjuvant-induced arthritis (AIA) rat model. The rats received subcutaneous injections of vehicle, plain Ang-(1-7), or an equivalent dose of Ang. Conj. The rats’ body weights, paws, and joints’ diameters were measured thrice weekly. After 14 days, the rats were euthanized, and the blood and tissue samples were harvested for further analysis of nitric oxide (NO) and RAS components’ gene and protein expression. The administration of Ang. Conj. reduced body weight loss, joint edema, and serum NO. Moreover, the Ang. Conj. treatment significantly reduced the classical arm components at peptide, enzyme, and receptor levels while augmenting them for the protective arm. The results of this study introduce a novel class of bone-targeting natural peptides for RA caused by an inflammation-induced imbalance in the activated RAS. Our results indicate that extending the half-life of Ang-(1-7) augments the RAS protective arm and exerts enhanced therapeutic effects in the AIA model in rats.

Functional ACE2 deficiency leading to angiotensin imbalance in the pathophysiology of COVID-19

SARS-CoV-2, the virus responsible for COVID-19, uses angiotensin converting enzyme 2 (ACE2) as its primary cell-surface receptor. ACE2 is a key enzyme in the counter-regulatory pathway of the broader renin-angiotensin system (RAS) that has been implicated in a broad array of human pathology. The RAS is composed of two competing pathways that work in opposition to each other: the "conventional" arm involving angiotensin converting enzyme (ACE) generating angiotensin-2 and the more recently identified ACE2 pathway that generates angiotensin (1-7). Following the original SARS pandemic, additional studies suggested that coronaviral binding to ACE2 resulted in downregulation of the membrane-bound enzyme. Given the similarities between the two viruses, many have posited a similar process with SARS-CoV-2. Proponents of this ACE2 deficiency model argue that downregulation of ACE2 limits its enzymatic function, thereby skewing the delicate balance between the two competing arms of the RAS. In this review we critically examine this model. The available data remain incomplete but are consistent with the possibility that the broad multisystem dysfunction of COVID-19 is due in large part to functional ACE2 deficiency leading to angiotensin imbalance with consequent immune dysregulation and endothelial cell dysfunction.

Reduced blood pressure in sickle cell disease is associated with decreased angiotensin converting enzyme (ACE) activity and is not modulated by ACE inhibition

Background

Sickle cell disease (SCD) incurs vaso-occlusive episodes and organ damage, including nephropathy. Despite displaying characteristics of vascular dysfunction, SCD patients tend to present relatively lower systemic blood pressure (BP), via an unknown mechanism. We investigated associations between BP and renin-angiotensin-system (RAS) components in SCD and determined whether an inhibitor of angiotensin converting enzyme (ACE; often used to slow SCD glomerulopathy) further modulates BP and RAS components in a murine model of SCD.

Methods

BP was compared in human subjects and mice with/without SCD. Plasma angiotensin II, ACE and renin were measured by immunoassay. BP was reevaluated after treating mice with enalapril (25 mg/kg, 5x/week) for 5 weeks; plasma and organs were stored for angiotensin II and ACE activity measurement, and quantitative real-time PCR.

Results

Diastolic BP and systolic BP were significantly lower in patients and mice with SCD, respectively, compared to controls. Reduced BP was associated with increased plasma renin and markers of kidney damage (mice) in SCD, as well as significantly decreased plasma ACE concentrations and ACE enzyme activity. As expected, enalapril administration lowered BP, plasma angiotensin II and organ ACE activity in control mice. In contrast, enalapril did not further reduce BP or organ ACE activity in SCD mice; however, plasma angiotensin II and renin levels were found to be significantly higher in enalapril-treated SCD mice than those of treated control mice.

Conclusion

Relative hypotension was confirmed in a murine model of SCD, in association with decreased ACE concentrations in both human and murine disease. Given that ACE inhibition has an accepted role in decreasing BP, further studies should investigate mechanisms by which ACE depletion, via both Ang II-dependent and alternative pathways, could contribute to reduce BP in SCD and understand how ACE inhibition confers Ang II-independent benefits on kidney function in SCD.

Children With Short Stature Display Reduced ACE2 Expression in Peripheral Blood Mononuclear Cells

BACKGROUND

The cause of short stature remains often unknown. The renin-angiotensin system contributes to growth regulation. Several groups reported that angiotensin-converting enzyme 2 (ACE2)-knockout mice weighed less than controls. Our case-control study aimed to investigate if children with short stature had reduced ACE2 expression as compared to controls, and its significance.

MATERIALS AND METHODS

children aged between 2 and 14 years were consecutively recruited in a University Hospital pediatric tertiary care center. Cases were children with short stature defined as height SD ≤ -2 diagnosed with growth hormone deficiency (GHD) or idiopathic short stature (ISS), before any treatment. Exclusion criteria were: acute diseases, kidney disease, endocrine or autoimmune disorders, precocious puberty, genetic syndromes, SGA history. ACE and ACE2 expression were measured in peripheral blood mononuclear cells, angiotensins were measured by ELISA.

RESULTS

Children with short stature displayed significantly lower ACE2 expression, being 0.40 fold induction (0.01-2.27) as compared to controls, and higher ACE/ACE2, with no differences between GHD and ISS. ACE2 expression was significantly and inversely associated with the risk of short stature, OR 0.26 (0.07-0.82), and it had a moderate accuracy to predict it, with an AUC of 0.73 (0.61-0.84). The cutoff of 0.45 fold induction of ACE2 expression was the value best predicting short stature, identifying correctly 70% of the children.

CONCLUSIONS

Our study confirms the association between the reduction of ACE2 expression and growth retardation. Further studies are needed to determine its diagnostic implications.

The Impact of the Renin-Angiotensin-Aldosterone System on Inflammation, Coagulation, and Atherothrombotic Complications, and to Aggravated COVID-19

Atherosclerosis is considered a disease caused by a chronic inflammation, associated with endothelial dysfunction, and several mediators of inflammation are up-regulated in subjects with atherosclerotic disease. Healthy, intact endothelium exhibits an antithrombotic, protective surface between the vascular lumen and vascular smooth muscle cells in the vessel wall. Oxidative stress is an imbalance between anti- and prooxidants, with a subsequent increase of reactive oxygen species, leading to tissue damage. The renin-angiotensin-aldosterone system is of vital importance in the pathobiology of vascular disease. Convincing data indicate that angiotensin II accelerates hypertension and augments the production of reactive oxygen species. This leads to the generation of a proinflammatory phenotype in human endothelial and vascular smooth muscle cells by the up-regulation of adhesion molecules, chemokines and cytokines. In addition, angiotensin II also seems to increase thrombin generation, possibly via a direct impact on tissue factor. However, the mechanism of cross-talk between inflammation and haemostasis can also contribute to prothrombotic states in inflammatory environments. Thus, blocking of the renin-angiotensin-aldosterone system might be an approach to reduce both inflammatory and thrombotic complications in high-risk patients. During COVID-19, the renin-angiotensin-aldosterone system may be activated. The levels of angiotensin II could contribute to the ongoing inflammation, which might result in a cytokine storm, a complication that significantly impairs prognosis. At the outbreak of COVID-19 concerns were raised about the use of angiotensin converting enzyme inhibitors and angiotensin receptor blocker drugs in patients with COVID-19 and hypertension or other cardiovascular comorbidities. However, the present evidence is in favor of continuing to use of these drugs. Based on experimental evidence, blocking the renin-angiotensin-aldosterone system might even exert a potentially protective influence in the setting of COVID-19.

Renin-angiotensin system blockade in the COVID-19 pandemic

In the early months of the coronavirus disease 2019 (COVID-19) pandemic, a hypothesis emerged suggesting that pharmacologic inhibitors of the renin–angiotensin system (RAS) may increase COVID-19 severity. This hypothesis was based on the role of angiotensin-converting enzyme 2 (ACE2), a counterregulatory component of the RAS, as the binding site for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), allowing viral entry into host cells. Extrapolations from prior evidence led to speculation that upregulation of ACE2 by RAS blockade may increase the risk of adverse outcomes from COVID-19. However, counterarguments pointed to evidence of potential protective effects of ACE2 and RAS blockade with regard to acute lung injury, as well as substantial risks from discontinuing these commonly used and important medications. Here we provide an overview of classic RAS physiology and the crucial role of ACE2 in systemic pathways affected by COVID-19. Additionally, we critically review the physiologic and epidemiologic evidence surrounding the interactions between RAS blockade and COVID-19. We review recently published trial evidence and propose important future directions to improve upon our understanding of these relationships.

Targeting the Protective Arm of the Renin-Angiotensin System: Focused on Angiotensin-(1-7)

The in vivo application and efficacy of many therapeutic peptides is limited because of their instability and proteolytic degradation. Novel strategies for developing therapeutic peptides with higher stability toward proteolytic degradation would be extremely valuable. Such approaches could improve systemic bioavailability and enhance therapeutic effects. The renin-angiotensin system (RAS) is a hormonal system within the body essential for the regulation of blood pressure and fluid balance. The RAS is composed of two opposing classic and protective arms. The balance between these two arms is critical for the homeostasis of the body's physiologic function. Activation of the RAS results in the suppression of its protective arm, which has been reported in inflammatory and pathologic conditions such as arthritis, cardiovascular diseases, diabetes, and cancer. Clinical application of angiotensin-(1-7) [Ang-(1-7)], a RAS critical regulatory peptide, augments the protective arm and restores balance hampered by its enzymatic and chemical instability. Several attempts to increase the half-life and efficacy of this heptapeptide using more stable analogs and different drug delivery approaches have been made. This review article provides an overview of efforts targeting the RAS protective arm. It provides a critical analysis of Ang-(1-7) or its homologs' novel drug delivery systems using different administration routes, their pharmacological characterization, and therapeutic potential in various clinical settings. SIGNIFICANCE STATEMENT: Ang-(1-7) is a unique peptide component of the renin-angiotensin system with vast potential for clinical applications that modulate various inflammatory diseases. Novel Ang-(1-7) peptide drug delivery could compensate its lack of stability for effective clinical application.

Mast Cell Chymase and Kidney Disease

A sizable part (~2%) of the human genome encodes for proteases. They are involved in many physiological processes, such as development, reproduction and inflammation, but also play a role in pathology. Mast cells (MC) contain a variety of MC specific proteases, the expression of which may differ between various MC subtypes. Amongst these proteases, chymase represents up to 25% of the total proteins in the MC and is released from cytoplasmic granules upon activation. Once secreted, it cleaves the targets in the local tissue environment, but may also act in lymph nodes infiltrated by MC, or systemically, when reaching the circulation during an inflammatory response. MC have been recognized as important components in the development of kidney disease. Based on this observation, MC chymase has gained interest following the discovery that it contributes to the angiotensin-converting enzyme’s independent generation of angiotensin II, an important inflammatory mediator in the development of kidney disease. Hence, progress regarding its role has been made based on studies using inhibitors but also on mice deficient in MC protease 4 (mMCP-4), the functional murine counterpart of human chymase. In this review, we discuss the role and actions of chymase in kidney disease. While initially believed to contribute to pathogenesis, the accumulated data favor a more subtle view, indicating that chymase may also have beneficial actions.

Severe Acute Respiratory Syndrome Coronavirus 2, COVID-19, and the Renin-Angiotensin System: Pressing Needs and Best Research Practices

The coronavirus disease 2019 (COVID-19) pandemic is associated with significant morbidity and mortality throughout the world, predominantly due to lung and cardiovascular injury. The virus responsible for COVID-19-severe acute respiratory syndrome coronavirus 2-gains entry into host cells via ACE2 (angiotensin-converting enzyme 2). ACE2 is a primary enzyme within the key counter-regulatory pathway of the renin-angiotensin system (RAS), which acts to oppose the actions of Ang (angiotensin) II by generating Ang-(1-7) to reduce inflammation and fibrosis and mitigate end organ damage. As COVID-19 spans multiple organ systems linked to the cardiovascular system, it is imperative to understand clearly how severe acute respiratory syndrome coronavirus 2 may affect the multifaceted RAS. In addition, recognition of the role of ACE2 and the RAS in COVID-19 has renewed interest in its role in the pathophysiology of cardiovascular disease in general. We provide researchers with a framework of best practices in basic and clinical research to interrogate the RAS using appropriate methodology, especially those who are relatively new to the field. This is crucial, as there are many limitations inherent in investigating the RAS in experimental models and in humans. We discuss sound methodological approaches to quantifying enzyme content and activity (ACE, ACE2), peptides (Ang II, Ang-[1-7]), and receptors (types 1 and 2 Ang II receptors, Mas receptor). Our goal is to ensure appropriate research methodology for investigations of the RAS in patients with severe acute respiratory syndrome coronavirus 2 and COVID-19 to ensure optimal rigor and reproducibility and appropriate interpretation of results from these investigations.

Novel Insight into the in vivo Function of Mast Cell Chymase: Lessons from Knockouts and Inhibitors

Mast cells are now recognized as key players in diverse pathologies, but the mechanisms by which they contribute in such settings are only partially understood. Mast cells are packed with secretory granules, and when they undergo degranulation in response to activation the contents of the granules are expelled to the extracellular milieu. Chymases, neutral serine proteases, are the major constituents of the mast cell granules and are hence released in large amounts upon mast cell activation. Following their release, chymases can cleave one or several of a myriad of potential substrates, and the cleavage of many of these could potentially have a profound impact on the respective pathology. Indeed, chymases have recently been implicated in several pathological contexts, in particular through studies using chymase inhibitors and by the use of chymase-deficient animals. In many cases, chymase has been shown to account for mast cell-dependent detrimental effects in the respective conditions and is therefore emerging as a promising drug target. On the other hand, chymase has been shown to have protective roles in other pathological settings. More unexpectedly, chymase has also been shown to control certain homeostatic processes. Here, these findings are reviewed.

Multifunctional Role of Chymase in Acute and Chronic Tissue Injury and Remodeling

Chymase is the most efficient Ang II (angiotensin II)-forming enzyme in the human body and has been implicated in a wide variety of human diseases that also implicate its many other protease actions. Largely thought to be the product of mast cells, the identification of other cellular sources including cardiac fibroblasts and vascular endothelial cells demonstrates a more widely dispersed production and distribution system in various tissues. Furthermore, newly emerging evidence for its intracellular presence in cardiomyocytes and smooth muscle cells opens an entirely new compartment of chymase-mediated actions that were previously thought to be limited to the extracellular space. This review illustrates how these multiple chymase-mediated mechanisms of action can explain the residual risk in clinical trials of cardiovascular disease using conventional renin-angiotensin system blockade.

The renin-angiotensin-aldosterone system and its suppression

Chronic activation of the renin-angiotensin-aldosterone system (RAAS) promotes and perpetuates the syndromes of congestive heart failure, systemic hypertension, and chronic kidney disease. Excessive circulating and tissue angiotensin II (AngII) and aldosterone levels lead to a pro-fibrotic, -inflammatory, and -hypertrophic milieu that causes remodeling and dysfunction in cardiovascular and renal tissues. Understanding of the role of the RAAS in this abnormal pathologic remodeling has grown over the past few decades and numerous medical therapies aimed at suppressing the RAAS have been developed. Despite this, morbidity from these diseases remains high. Continued investigation into the complexities of the RAAS should help clinicians modulate (suppress or enhance) components of this system and improve quality of life and survival. This review focuses on updates in our understanding of the RAAS and the pathophysiology of AngII and aldosterone excess, reviewing what is known about its suppression in cardiovascular and renal diseases, especially in the cat and dog.

Serum concentration of renin-angiotensin system components in association with ACE I/D polymorphism among hypertensive subjects in response to ACE inhibitor therapy

Background: Renin-angiotensin system (RAS) is a complex network of enzymes and peptides with the essential role in blood pressure control. The relationships between RAS components, RAS-related genetic polymorphisms and therapy response in essential hypertension (EH) were widely explored but the results were inconclusive. Aim: The aim of this study was to explore the functional role of ACE insertion/deletion (I/D) polymorphism on the systemic quantity of angiotensin-converting enzyme (ACE), its homolog - ACE2, chymase and angiotensin II in EH patients with respect to achieved therapeutic blood pressure control. Results: Genotyping of ACE I/D polymorphism was performed among 140 patients with EH from Bulgaria. The serological analyses reveal the significant elevation of the serum quantity of all investigated enzymes in EH than normotensive controls. In addition, serum ACE2 (183.57 pg/ml; vs. 151.78 pg/ml; p = 0.02) and chymase (68.5 pg/ml; vs. 23.66 pg/ml; p = 0.034) were significantly higher in patients with uncontrolled EH than controlled EH in response to ACE-inhibitory therapy. Also, ACE I/D polymorphism showed a significant impact on the serum ACE and chymase levels. ACE quantity was the highest among carriers of DD-genotype, followed by ID and II-genotype. Contrary, chymase was in the highest quantity in II-genotype compared to ID-genotype (p = 0.025) and DD-genotype (p = 0.044). Conclusions: Our results suggest that insufficient blood pressure control by ACE-inhibitory therapy could be associated with elevation of serum ACE2 and chymase levels. Also, it appears that ACE I/D polymorphism may influence the circulating quantity of chymase in addition to ACE.

Combination of Chymostatin and Aliskiren attenuates ER stress induced by lipid overload in kidney tubular cells

Background

Lipotoxicity plays an important role in the pathogenesis of kidney injury. Our previous study demonstrated that activation of local renin-angiotensin system (RAS) was involved in saturated free fatty acids palmitic acid (PA)-induced tubular cell injuries. The current study aims to investigate whether suppression of RAS by combination of direct renin inhibitor aliskiren and noncanonical RAS pathway chymase inhibitor chymostatin attenuates PA or cholesterol induced-endoplasmic reticulum stress (ER stress) and apopotosis in cultured human proximal tubular HK2 cells.

Methods

HK2 cells were treated with saturated fatty acid PA (0.6 mM) for 24 h or cholesterol (10 μg/ml) for 6d with or without chymostatin and/or aliskiren. Expressions of the ER stress associated proteins and apoptosis markers were detected by western blotting. The mRNA levels of RAS components were measured by real-time qPCR.

Results

Combination treatment of chymostatin and aliskiren markedly suppressed PA or cholesterol-induced ER stress, as reflected by increased BiP, IRE1α, phosphorylated-eIF2α and ATF4 as well as proapoptotic transcription factor CHOP. The ratio of Bax/Bcl-2 and cleaved caspase-3, two markers of apoptosis were upregulated by PA or cholesterol treatment. PA treatment was also associated with increased levels of angiotensinogen and angiotensin type 1 receptor (AT1R) mRNA expression. Combination treatment of chymostatin and aliskiren markedly suppressed PA or cholesterol-induced ER stress and apoptosis. The protective effect of two inhibitors was also observed in primary cultured cortical tubular cells treated with PA. In contrast, chymostatin and/or aliskiren failed to prevent ER stress induced by tunicamycin.

Conclusions

These results suggested that combination treatment of chymostatin and aliskiren attenuates lipid-induced renal tubular cell injury, likely through suppressing activation of intracellular RAS.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0818-1) contains supplementary material, which is available to authorized users.

Mast cell derived carboxypeptidase A3 is decreased among patients with advanced coronary artery disease

BACKGROUND

Coronary artery disease (CAD) affects milions of people and can result in myocardial infarction (MI). Previously, mast cells (MC) have been extensively investigated in the context of hypersensitivity, however as regulators of the local inflammatory response they can potentially contribute to CAD and/or its progression. The aim of the study was to assess if serum concentration of MC proteases: carboxypeptidase A3, cathepsin G and chymase 1 is associated with the extension of CAD and MI.

METHODS

The 44 patients with angiographically confirmed CAD (23 subjects with non-ST-segment elevation MI [NSTEMI] and 21 with stable CAD) were analyzed. Clinical data were obtained as well serum concentrations of carboxypeptidase A3, cathepsin G and chymase 1 were also measured.

RESULTS

Patients with single vessel CAD had higher serum concentration of carboxypeptidase than those with more advanced CAD (3838.6 ± 1083.1 pg/mL vs. 2715.6 ± 442.5 pg/mL; p = 0.02). There were no significant differences in levels of any protease between patients with stable CAD and those with NSTEMI. Patients with hypertension had ≈2-fold lower serum levels of cathepsin G than normotensive individuals (4.6 ± 0.9 pg/mL vs. 9.4 ± 5.8 pg/mL; p = 0.001). Cathepsin G levels were also decreased in sera of the current smokers as compared with non-smokers (3.1 ± 1.2 ng/mL vs. 5.8 ± 1.2 ng/mL, p = 0.02).

CONCLUSIONS

Decreased serum level of carboxypeptidase is a hallmark of more advanced CAD. Lower serum levels of carboxypeptidase A3 and catepsin G are associated with risk factors of blood vessel damage suggesting a protective role of these enzymes in CAD.

Renin angiotensin aldosterone inhibition in the treatment of cardiovascular disease

A collective century of discoveries establishes the importance of the renin angiotensin aldosterone system in maintaining blood pressure, fluid volume and electrolyte homeostasis via autocrine, paracrine and endocrine signaling. While research continues to yield new functions of angiotensin II and angiotensin-(1-7), the gap between basic research and clinical application of these new findings is widening. As data accumulates on the efficacy of angiotensin converting enzyme inhibitors and angiotensin II receptor blockers as drugs of fundamental importance in the treatment of cardiovascular and renal disorders, it is becoming apparent that the achieved clinical benefits is suboptimal and surprisingly no different than what can be achieved with other therapeutic interventions. We discuss this issue and summarize new pathways and mechanisms effecting the synthesis and actions of angiotensin II. The presence of renin-independent non-canonical pathways for angiotensin II production are largely unaffected by agents inhibiting renin angiotensin system activity. Hence, new efforts should be directed to develop drugs that can effectively block the synthesis and/or action of intracellular angiotensin II. Improved drug penetration into cardiac or renal sites of disease, inhibiting chymase the primary angiotensin II forming enzyme in the human heart, and/or inhibiting angiotensinogen synthesis would all be more effective strategies to inhibit the system. Additionally, given the role of angiotensin II in the maintenance of renal homeostatic mechanisms, any new inhibitor should possess greater selectivity of targeting pathogenic angiotensin II signaling processes and thereby limit inappropriate inhibition.

Elastase-2, an angiotensin II-generating enzyme, contributes to increased angiotensin II in resistance arteries of mice with myocardial infarction

BACKGROUND AND PURPOSE

Angiotensin II (Ang II), whose generation largely depends on angiotensin-converting enzyme (ACE) activity, mediates most of the renin-angiotensin-system (RAS) effects. Elastase-2 (ELA-2), a chymotrypsin-serine protease elastase family member 2A, alternatively generates Ang II in rat arteries. Myocardial infarction (MI) leads to intense RAS activation, but mechanisms involved in Ang II-generation in resistance arteries are unknown. We hypothesized that ELA-2 contributes to vascular Ang II generation and cardiac damage in mice subjected to MI.

EXPERIMENTAL APPROACH

Concentration-effect curves to Ang I and Ang II were performed in mesenteric resistance arteries from male wild type (WT) and ELA-2 knockout (ELA-2KO) mice subjected to left anterior descending coronary artery ligation (MI).

KEY RESULTS

MI size was similar in WT and ELA-2KO mice. Ejection fraction and fractional shortening after MI similarly decreased in both strains. However, MI decreased stroke volume and cardiac output in WT, but not in ELA-2KO mice. Ang I-induced contractions increased in WT mice subjected to MI (MI-WT) compared with sham-WT mice. No differences were observed in Ang I reactivity between arteries from ELA-2KO and ELA-2KO subjected to MI (MI-ELA-2KO). Ang I contractions increased in arteries from MI-WT versus MI-ELA-2KO mice. Chymostatin attenuated Ang I-induced vascular contractions in WT mice, but did not affect Ang I responses in ELA-2KO arteries.

CONCLUSIONS AND IMPLICATIONS

These results provide the first evidence that ELA-2 contributes to increased Ang II formation in resistance arteries and modulates cardiac function after MI, implicating ELA-2 as a key player in ACE-independent dysregulation of the RAS.

Cardiac angiotensin-(1-12) expression and systemic hypertension in rats expressing the human angiotensinogen gene

Angiotensin-(1-12) [ANG-(1-12)] is processed into ANG II by chymase in rodent and human heart tissue. Differences in the amino acid sequence of rat and human ANG-(1-12) render the human angiotensinogen (hAGT) protein refractory to cleavage by renin. We used transgenic rats harboring the hAGT gene [TGR(hAGT)L1623] to assess the non-renin-dependent effects of increased hAGT expression on heart function and arterial pressure. Compared with Sprague-Dawley (SD) control rats (n= 11), male homozygous TGR(hAGT)L1623 (n= 9) demonstrated sustained daytime and nighttime hypertension associated with no changes in heart rate but increased heart rate lability. Increased heart weight/tibial length ratio and echocardiographic indexes of cardiac hypertrophy were associated with modest reduction of systolic function in hAGT rats. Robust human ANG-(1-12) immunofluorescence within myocytes of TGR(hAGT)L1623 rats was associated with a fourfold increase in cardiac ANG II content. Chymase enzymatic activity, using the rat or human ANG-(1-12) as a substrate, was not different in the cardiac tissue of SD and hAGT rats. Since both cardiac angiotensin-converting enzyme (ACE) and ACE2 activities were not different among the two strains, the changes in cardiac structure and function, blood pressure, and left ventricular ANG II content might be a product of an increased cardiac expression of ANG II generated through a non-renin-dependent mechanism. The data also underscore the existence in the rat of alternate enzymes capable of acting on hAGT protein. Homozygous transgenic rats expressing the hAGT gene represent a novel tool to investigate the contribution of human relevant renin-independent cardiac ANG II formation and function.

Update on RAAS Modulation for the Treatment of Diabetic Cardiovascular Disease

Since the advent of insulin, the improvements in diabetes detection and the therapies to treat hyperglycemia have reduced the mortality of acute metabolic emergencies, such that today chronic complications are the major cause of morbidity and mortality among diabetic patients. More than half of the mortality that is seen in the diabetic population can be ascribed to cardiovascular disease (CVD), which includes not only myocardial infarction due to premature atherosclerosis but also diabetic cardiomyopathy. The importance of renin-angiotensin-aldosterone system (RAAS) antagonism in the prevention of diabetic CVD has demonstrated the key role that the RAAS plays in diabetic CVD onset and development. Today, ACE inhibitors and angiotensin II receptor blockers represent the first line therapy for primary and secondary CVD prevention in patients with diabetes. Recent research has uncovered new dimensions of the RAAS and, therefore, new potential therapeutic targets against diabetic CVD. Here we describe the timeline of paradigm shifts in RAAS understanding, how diabetes modifies the RAAS, and what new parts of the RAAS pathway could be targeted in order to achieve RAAS modulation against diabetic CVD.

Angiotensin 1-7 significantly reduces diabetes-induced leukocyte recruitment both in vivo and in vitro

OBJECTIVE

Recent studies have demonstrated that Ang1-7 has anti-inflammatory effects. Since the formation of Ang1-7 is significantly altered in the setting of diabetes, here we aimed to evaluate whether Ang1-7 infusion could ameliorate diabetes-induced leukocyte recruitment.

METHODS

Wild-type male Wistar rats were randomly allocated to the following groups: control + saline, control + Ang1-7, diabetes + saline, diabetes + Ang1-7. Diabetes was induced by streptozotocin. Saline and Ang1-7 (576 μg/kg/day) were injected intraperitoneally daily. After 4 weeks leukocyte trafficking was studied in vivo by intravital microscopy in the mesenteric bed, where the expression of pro-oxidative, proinflammatory, and profibrotic molecules was also assessed. In parallel in vitro studies, HUVEC were grown in 5 mM, 22 mM, 30 mM, 40 mM, 50 mM, and 75 mM glucose media for 48 h, 72 h and 6 days and were treated either with placebo, or with Ang1-7, or with Ang1-7 and its inhibitor A779 in order to evaluate the expression of ICAM-1 and VCAM-1. We further studied leukocytes recruitment in vitro by evaluating PMN-HUVEC adhesion.

RESULTS

Ang1-7 prevented in vivo diabetes-induced leukocyte adhesion and extravasation, and it significantly reduced vascular hypertrophy and the other molecular changes due to diabetes. Ang 1-7 prevented also in vitro the hyperglycemia-induced increase of ICAM-1 and VCAM-1 as well as the hyperglycemia-induced PMN adhesion. A779 inhibited Ang 1-7 effects.

CONCLUSIONS

Ang1-7 significantly reduced diabetes-induced leukocyte recruitment both in vivo and in vitro. These findings emphasize the potential utility of ACE2/Ang1-7/Mas repletion as a strategy to reduce diabetes-induced atherosclerosis.

Differential expression of the angiotensin-(1-12)/chymase axis in human atrial tissue

OBJECTIVE

Heart chymase rather than angiotensin converting enzyme has higher specificity for angiotensin (Ang) I conversion into Ang II in humans. A new pathway for direct cardiac Ang II generation has been revealed through the demonstration that Ang-(1-12) is cleaved by chymase to generate Ang II directly. We address here whether Ang-(1-12) and chymase gene expression and activity are detected in the atrial appendages of 44 patients (10 females) undergoing heart surgery for the correction of valvular heart disease, resistant atrial fibrillation or ischemic heart disease.

METHODS AND RESULTS

Immunoreactive Ang-(1-12) expression was 54% higher in left atrial compared with right atrial appendages. This was associated with higher abundance of left atrial appendage chymase gene transcripts and chymase activity, but no differences in angiotensinogen mRNA. Atrial chymase enzymatic activity was highly correlated with left atrial but not right atrial enlargement as determined by echocardiography, while both tyrosine hydroxylase and neuropeptide Y atrial appendage mRNAs correlated with atrial angiotensinogen mRNAs.

CONCLUSIONS

Higher Ang-(1-12) expression and upregulation of chymase gene transcripts and enzymatic activity from the atrial appendages connected to the enlarged left versus right atrial chambers of subjects with left heart disease defines a role of this alternate Ang II forming pathway in the processes accompanying adverse atrial and ventricular remodeling.

Development of a sensitive, accurate and robust liquid chromatography/mass spectrometric method for profiling of angiotensin peptides in plasma and its application for atherosclerotic mice

Quantification of angiotensin (Ang) peptides in biological matrices is a challenge due to their low picomolar (pM) concentration and poor analytical performance of current methods. This work aimed to select an optimal strategy for liquid chromatography/mass spectrometry (LC/MS) quantification of major angiotensins in plasma of wild type and atherosclerotic mice. Optimal LC/MS set-up for Ang quantification was chosen, based on analytical performance, from: nanoflow/orbitrap, nanoflow/triple quadrupole and preconcentration nanoflow/triple quadrupole. The best LC/MS configuration (preconcentration nanoflow/triple quadrupole) was validated and used for measurement of angiotensins (Ang I, II, III, IV and (1-7)) in plasma of 6-month-old atherosclerotic apolipoprotein E/LDL receptor double knock-outs (ApoE/LDLR (--/--)) and wild type C57BL/6J (WT) mice. The method established for Ang quantification was selective, accurate and highly sensitive with LLOQ of 5pgmL(-1). The peak area intra-day precisions for Ang II and Ang-(1-7) were in the range 3.0-5.1 and 3.5-5.8, respectively, with corresponding accuracy of 95.4-103.5% and 95.6-106.3%. Plasma angiotensin profile was substantially modified in ApoE/LDLR knock-out mice with increase in concentration of Ang II from 37.6±21.3pgmL(-1) in WT to 200.2±47.6pgmL(-1). Concentrations of Ang I, III and IV were also increased 3-10 fold in ApoE/LDLR (--/--) mice while that of Ang-(1-7) was unchanged. We conclude that the method developed could be effectively used for accurate, comprehensive profiling of angiotensin peptides in mouse plasma. We identified substantial changes in renin-angiotensin system in a genetic mouse model of atherosclerosis consistent with the overactivation of angiotensin converting enzyme (ACE) and the impairment of ACE2.

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.

Interaction of diabetes and ACE2 in the pathogenesis of cardiovascular disease in experimental diabetes

Local and systemic AngII (angiotensin II) levels are regulated by ACE2 (angiotensin-converting enzyme 2), which is reduced in diabetic tissues. In the present study, we examine the effect of ACE2 deficiency on the early cardiac and vascular changes associated with experimental diabetes. Streptozotocin diabetes was induced in male C57BL6 mice and Ace2-KO (knockout) mice, and markers of RAS (renin–angiotensin system) activity, cardiac function and injury were assessed after 10 weeks. In a second protocol, diabetes was induced in male ApoE (apolipoprotein E)-KO mice and ApoE/Ace2-double-KO mice, and plaque accumulation and markers of atherogenesis assessed after 20 weeks. The induction of diabetes in wild-type mice led to reduced ACE2 expression and activity in the heart, elevated circulating AngII levels and reduced cardiac Ang-(1–7) [angiotensin-(1–7)] levels. This was associated structurally with thinning of the LV (left ventricular) wall and mild ventricular dilatation, and histologically with increased cardiomyocyte apoptosis on TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) staining and compensatory hypertrophy denoted by an increased cardiomyocyte cross-sectional area. By contrast Ace2-KO mice failed to increase circulating AngII concentration, experienced a paradoxical fall in cardiac AngII levels and no change in Ang-(1–7) following the onset of diabetes. At the same time the major phenotypic differences between Ace2-deficient and Ace2-replete mice with respect to BP (blood pressure) and cardiac hypertrophy were eliminated following the induction of diabetes. Consistent with findings in the heart, the accelerated atherosclerosis that was observed in diabetic ApoE-KO mice was not seen in diabetic ApoE/Ace2-KO mice, which experienced no further increase in plaque accumulation or expression in key adhesion molecules beyond that seen in ApoE/Ace2-KO mice. These results point to the potential role of ACE2 deficiency in regulating the tissue and circulating levels of AngII and their sequelae in the context of diabetes, as well as the preservation or augmentation of ACE2 expression or activity as a potential therapeutic target for the prevention of CVD (cardiovascular disease) in diabetes.

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.

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.

Uptake and metabolism of the novel peptide angiotensin-(1-12) by neonatal cardiac myocytes

Background

Angiotensin-(1–12) [Ang-(1–12)] functions as an endogenous substrate for the productions of Ang II and Ang-(1–7) by a non-renin dependent mechanism. This study evaluated whether Ang-(1–12) is incorporated by neonatal cardiac myocytes and the enzymatic pathways of ¹²⁵I-Ang-(1–12) metabolism in the cardiac myocyte medium from WKY and SHR rats.

Methodology/Principal Findings

The degradation of ¹²⁵I-Ang-(1–12) (1 nmol/L) in the cultured medium of these cardiac myocytes was evaluated in the presence and absence of inhibitors for angiotensin converting enzymes 1 and 2, neprilysin and chymase. In both strains uptake of ¹²⁵I-Ang-(1–12) by myocytes occurred in a time-dependent fashion. Uptake of intact Ang-(1–12) was significantly greater in cardiac myocytes of SHR as compared to WKY. In the absence of renin angiotensin system (RAS) enzymes inhibitors the hydrolysis of labeled Ang-(1–12) and the subsequent generation of smaller Ang peptides from Ang-(1–12) was significantly greater in SHR compared to WKY controls. ¹²⁵I-Ang-(1–12) degradation into smaller Ang peptides fragments was significantly inhibited (90% in WKY and 71% in SHR) in the presence of all RAS enzymes inhibitors. Further analysis of peptide fractions generated through the incubation of Ang-(1–12) in the myocyte medium demonstrated a predominant hydrolytic effect of angiotensin converting enzyme and neprilysin in WKY and an additional role for chymase in SHR.

Conclusions/Significance

These studies demonstrate that neonatal myocytes sequester angiotensin-(1–12) and revealed the enzymes involved in the conversion of the dodecapeptide substrate to biologically active angiotensin peptides.

Major role for ACE-independent intrarenal ANG II formation in type II diabetes

Combination therapy of angiotensin-converting enzyme (ACE) inhibition and AT(1) receptor blockade has been shown to provide greater renoprotection than ACE inhibitor alone in human diabetic nephropathy, suggesting that ACE-independent pathways for ANG II formation are of major significance in disease progression. Studies were performed to determine the magnitude of intrarenal ACE-independent formation of ANG II in type II diabetes. Although renal cortical ACE protein activity [2.1 +/- 0.8 vs. 9.2 +/- 2.1 arbitrary fluorescence units (AFU) x mg(-1) x min(-1)] and intensity of immunohistochemical staining were significantly reduced and ACE2 protein activity (16.7 +/- 3.2 vs. 7.2 +/- 2.4 AFU x mg(-1) x min(-1)) and intensity elevated, kidney ANG I (113 +/- 24 vs. 110 +/- 45 fmol/g) and ANG II (1,017 +/- 165 vs. 788 +/- 99 fmol/g) levels were not different between diabetic and control mice. Afferent arteriole vasoconstriction due to conversion of ANG I to ANG II was similar in magnitude in kidneys of diabetic (-28 +/- 3% at 1 microM) and control (-23 +/- 3% at 1 microM) mice; a response completely inhibited by AT(1) receptor blockade. In control kidneys, afferent arteriole vasoconstriction produced by ANG I was significantly attenuated by ACE inhibition, but not by serine protease inhibition. In contrast, afferent arteriole vasoconstriction produced by intrarenal conversion of ANG I to ANG II was significantly attenuated by serine protease inhibition, but not by ACE inhibition in diabetic kidneys. In conclusion, there is a switch from ACE-dependent to serine protease-dependent ANG II formation in the type II diabetic kidney. Pharmacological targeting of these serine protease-dependent pathways may provide further protection from diabetic renal vascular disease.

Inhibition of intracellular angiotensin II formation blocks high glucose effect on mesangial matrix

High glucose causes increased matrix synthesis by glomerular mesangial cells and angiotensin II (Ang II) has been shown to mediate this effect of glucose. These studies investigate whether inhibition of Ang II formation can block high glucose-induced increase in mesangial matrix. Human mesangial cells were incubated with 25 mM glucose (HG) along with captopril, an ACE inhibitor, to block Ang II formation. In other experiments, cells were nucleofected with siRNA to knockdown angiotensinogen (Agt), the precursor of Ang II, and then exposed to high glucose. Captopril blocked high glucose-induced increase in Ang II levels in the cell media (extracellular) but failed to inhibit it in the cell lysate (intracellular). Moreover, captopril treatment did not block the stimulatory effect of high glucose on TGF-beta1 and fibronectin. In contrast, knockdown of the Agt gene prevented high glucose-induced increase in both extracellular and intracellular Ang II levels, and was accompanied by normalization of TGF-beta1 and fibronectin. These data suggest that intracellular Ang II may play an important role in the mediation of the high glucose effect on matrix and that ACE inhibitors may not be effective in blocking intracellular Ang II formation in mesangial cells.

Diversity of pathways for intracellular angiotensin II synthesis

PURPOSE OF REVIEW

The renin-angiotensin system (RAS) has undergone continuous advancement since the initial identification of renin as a pressor agent. Traditionally considered a circulatory system, the RAS is now known to exist as a tissue system as well. Recently, the tissue RAS has been further categorized as intracellular and extracellular. Owing to the unique location, the intracellular RAS encompasses new components, such as cathepsin D and chymase, which participate in intracellular angiotensin (Ang) II synthesis. In this review, evidence of the intracellular RAS and the mechanism of Ang II synthesis in various cell types will be discussed.

RECENT FINDINGS

A physiological role for intracellular Ang II in vascular and cardiac cells has recently been demonstrated. Evidence of intracellular Ang II generation has been shown in several cell types, particularly cardiac, renal, and vascular. Importantly, intracellular synthesis of Ang II is more prominent in hyperglycemic conditions and generally involves angiotensin-converting enzyme-dependent and angiotensin-converting enzyme-independent mechanisms.

SUMMARY

There is significant diversity in the mechanism of intracellular synthesis of Ang II in various cell types and pathological conditions. These observations suggest that a therapeutic intervention to block the RAS should take into consideration the nature of the disorder and the cell type involved.

Angiotensin-converting enzyme-derived angiotensin II formation during angiotensin II-induced hypertension

The extent to which endogenous angiotensin (Ang) II formation is responsible for increasing kidney Ang II content and blood pressure during Ang II-induced hypertension is unknown. To address this, mice were treated with an Ang-converting enzyme (ACE) inhibitor (ACEi) to block endogenous Ang II formation during chronic Ang II infusions. C57BL/6J male mice (8 to 12 weeks) were subjected to Ang II infusions (400 ng/kg per minute) with or without an ACEi (lisinopril, 100 mg/L in the drinking water) for 12 days. Blood pressure was monitored by tail-cuff method and telemetry. Ang II content was determined by radioimmunoanalysis. Ang II infusions increased 24-hour mean arterial pressure significantly (141.0+/-3.7 mm Hg) versus controls (110.0+/-1.0 mm Hg). ACEi prevented the increase in concentration in Ang II-infused mice (Ang II+ACEi; 114.0+/-7.4 mm Hg; P value not significant). Plasma Ang II content was significantly increased by Ang II (367+/-60 fmol/mL) versus controls (128+/-22 fmol/mL; P<0.05); plasma Ang II was not altered by ACEi alone (90+/-31) or in combination with Ang II infusions (76+/-27). Intrarenal Ang II content was significantly increased by Ang II (998+/-143 fmol/g) versus controls (524+/-60 fmol/g; P<0.05), and this was prevented by ACEi (Ang II+ACEi; 484+/-102 fmol/g; P value not significant). Thus, ACEi ameliorates the increases in blood pressure and intrarenal Ang II content caused by Ang II infusions, indicating that endogenous ACE-mediated Ang II formation plays a significant role in the increases of blood pressure and intrarenal Ang II during Ang II-induced hypertension.

The importance of the intrarenal renin-angiotensin system

Evidence suggests that virtually every organ system in the human body possesses a local renin-angiotensin system (RAS). These local systems seem to be independently regulated and compartmentalized from the plasma circulation, perhaps with the exception of the vascular endothelial system, which is responsible for maintaining physiological plasma levels of RAS components. Among these local RASs, the kidney RAS--the focus of this Review--seems to be of critical importance for the regulation of blood pressure and salt balance. Indeed, overactivation of the intrarenal RAS in certain disease states constitutes a pathogenic mechanism that leads to tissue injury, proliferation, fibrosis and ultimately, end-organ damage. Intrarenal levels of angiotensin peptides are considerably higher than those in plasma or any other organ tissue. Moreover, the kidney has a unique capacity to degrade angiotensin peptides, perhaps to maintain its intrinsic homeostasis. Interestingly, each local RAS has a distinct enzymatic profile resulting in different patterns of angiotensin fragment generation in different tissues. A better understanding of the autocrine and paracrine mechanisms involved in the renal RAS and other local RASs might direct future organ-specific therapy.

Renin-Angiotensin system - considerations for hypertension and kidney

The kidneys play a fundamental role in the long-term control of arterial pressure by regulating sodium balance and extracellular fluid volume. The renin-angiotensin system (RAS) is at the center of the regulation of hypertension and progressive renal injury. It has gradually become clear that not only systemic RAS, but also intrarenal RAS has specific effects in the pathogenesis and progression of hypertension and renal damage. All of the RAS components are exhibited in the kidney and intrarenal angiotensin II (Ang II) is formed by multiple mechanisms. The demonstration of much enhanced levels of Ang II within specific renal compartments points out selective local regulation of Ang II in the kidney, showing that intrarenal Ang II levels are regulated in a way different from circulating Ang II. The importance of the RAS in involving proper nephrogenesis is also well known, and suppression of the RAS during fetal development may play a key role in mediating the structural and physiological changes observed in models of fetal programming of hypertension.

ACE-dependent and chymase-dependent angiotensin II generation in normal and glucose-stimulated human mesangial cells

High glucose (HG) increases angiotensin II (AngII) generation in mesangial cells (MC). Chymase, an alternative AngII-generating enzyme, is upregulated in the glomeruli of diabetic kidneys. In this study, we examined AngII synthesis by human MC via angiotensin-converting enzyme (ACE)-dependent and chymase-dependent pathways under normal glucose (NG, 5 mM) and HG (30 mM) conditions. NG cells expressed ACE and chymase mRNA. Under NG conditions the chymase inhibitor chymostatin reduced AngII levels in cell lysates and in the culture medium, and the ACE inhibitor captopril had no effect. HG induced a 3-fold increase in chymase mRNA and protein but not in ACE mRNA; however, HG induced a 10-fold increase in intracellular ACE activity. The increase in AngII generation induced by HG was found in the cell lysate but not in the culture medium. The rise in intracellular AngII was not prevented by captopril or by chymostatin. Moreover, captopril inhibited extracellular ACE activity but failed to block intracellular ACE activity; these results suggested that captopril was unable to reach intra-cellular ACE. Losartan did not change the intracellular AngII content in either NG or HG conditions, and this lack of change suggested that the increase in AngII was due to intracellular generation. Together these results suggest that chymase may be active in human MC and that both ACE and chymase are involved in increased AngII generation during the HG stimulus by different mechanisms, including an upregulation of chymase mRNA and a rise in intracellular ACE activity, favoring the generation and accumulation of intracellular AngII.

Distinct roles for angiotensin-converting enzyme 2 and carboxypeptidase A in the processing of angiotensins within the murine heart

Angiotensin-converting enzyme 2 (ACE2), a homologue of angiotensin-converting enzyme (ACE), converts angiotensin (Ang) I to Ang(1-9) and Ang II to Ang(1-7), but does not directly process Ang I to Ang II. Cardiac function is compromised in ACE2 null mice; however, the importance of ACE2 in the processing of angiotensin peptides within the murine heart is not known. We determined the metabolism of angiotensins in wild-type (WT), ACE (ACE(-/-)) and ACE2 null mice (ACE2(-/-)). Angiotensin II was converted almost exclusively to Ang(1-7) in the cardiac membranes of WT and ACE(-/-) strains, although generation of Ang(1-7) was greater in the ACE(-/-) mice (27.4 +/- 4.1 versus 17.5 +/- 3.2 nmol(-1) mg h(-1) for WT). The ACE2 inhibitor MLN4760 significantly attenuated Ang II metabolism and the subsequent formation of Ang(1-7) in both strains. In the ACE2(-/-) hearts, Ang II metabolism and the generation of Ang(1-7) were significantly attenuated; however, the ACE2 inhibitor reduced the residual Ang(1-7)-forming activity in this strain. Angiotensin I was primarily converted to Ang(1-9) (WT, 28.9 +/- 3.1 nmol(-1) mg h(-1); ACE(-/-), 49.8 +/- 5.3 nmol(-1) mg h(-1); and ACE2(-/-), 35.9 +/- 5.4 nmol(-1) mg h(-1)) and to smaller quantities of Ang(1-7) and Ang II. Although the ACE2 inhibitor had no effect on Ang(1-9) formation, the carboxypeptidase A inhibitor benzylsuccinate essentially abolished the formation of Ang(1-9) and increased the levels of Ang I in cardiac membranes. In conclusion, our studies in the murine heart suggest that ACE2 is the primary pathway for the metabolism of Ang II and the subsequent formation of Ang(1-7), a peptide that, in contrast to Ang II, exhibits both antifibrotic and antiproliferative actions.

Modulation of the tissue reninangiotensin-aldosterone system in dogs with chronic mild regurgitation through the mitral valve

OBJECTIVE

To investigate whether the tissue and plasma renin-angiotensin-aldosterone system (RAAS) is activated in dogs with mild regurgitation through the mitral valve and determine the contribution of chymase and angiotensin-converting enzyme (ACE) to the activation of the RAAS and potential production of angiotensin II during the chronic stage of mild mitral valve regurgitation.

ANIMALS

5 Beagles with experimentally induced mild mitral valve regurgitation and 6 clinically normal (control) Beagles.

PROCEDURES

Tissue ACE and chymase-like activities and plasma RAAS were measured and the RAAS evaluated approximately 1,000 days after experimental induction of mitral valve regurgitation in the 5 dogs.

RESULTS

Dogs with experimentally induced mitral valve regurgitation did not have clinical signs of the condition, although echocardiography revealed substantial eccentric hyper- trophy. On the basis of these findings, dogs with mitral valve regurgitation were classified as International Small Animal Cardiac Health Council class Ib. Plasma activity of renin and plasma concentrations of angiotensin I, angiotensin II, and aldosterone were not significantly different between dogs with mitral valve regurgitation and clinically normal dogs. Tissue ACE activity was significantly increased and chymase-like activity significantly decreased in dogs with mitral valve regurgitation, compared with values in clinically normal dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

The tissue RAAS was modulated without changes in the plasma RAAS in dogs with mild mitral valve regurgitation during the chronic stage of the condition. An ACE-dependent pathway may be a major route for production of angiotensin II during this stage of the condition.

Angiotensin converting enzyme 2 is primarily epithelial and is developmentally regulated in the mouse lung

Angiotensin converting enzyme (ACE) 2 is a carboxypeptidase that shares 42% amino acid homology with ACE. Little is known about the regulation or pattern of expression of ACE2 in the mouse lung, including its definitive cellular distribution or developmental changes. Based on Northern blot and RT‐PCR data, we report two distinct transcripts of ACE2 in the mouse lung and kidney and describe a 5′ exon 1a previously unidentified in the mouse. Western blots show multiple isoforms of ACE2, with predominance of a 75–80 kDa protein in the mouse lung versus a 120 kDa form in the mouse kidney. Immunohistochemistry localizes ACE2 protein to Clara cells, type II cells, and endothelium and smooth muscle of small and medium vessels in the mouse lung. ACE2 mRNA levels peak at embryonic day 18.5 in the mouse lung, and immunostaining demonstrates protein primarily in the bronchiolar epithelium at that developmental time point. In murine cell lines ACE2 is strongly expressed in the Clara cell line mtCC, as opposed to the low mRNA expression detected in E10 (type I‐like alveolar epithelial cell line), MLE‐15 (type II alveolar epithelial cell line), MFLM‐4 (fetal pulmonary vasculature cell line), and BUMPT‐7 (renal proximal tubule cell line). In summary, murine pulmonary ACE2 appears to be primarily epithelial, is developmentally regulated, and has two transcripts that include a previously undescribed exon. J. Cell. Biochem. 101:1278–1291, 2007. © 2007 Wiley‐Liss, Inc.

A thrombospondin-1 antagonist of transforming growth factor-beta activation blocks cardiomyopathy in rats with diabetes and elevated angiotensin II

In diabetes and hypertension, the induction of increased transforming growth factor-beta (TGF-beta) activity due to glucose and angiotensin II is a significant factor in the development of fibrosis and organ failure. We showed previously that glucose and angiotensin II induce the latent TGF-beta activator thrombospondin-1 (TSP1). Because activation of latent TGF-beta is a major means of regulating TGF-beta, we addressed the role of TSP1-mediated TGF-beta activation in the development of diabetic cardiomyopathy exacerbated by abdominal aortic coarctation in a rat model of type 1 diabetes using a peptide antagonist of TSP1-dependent TGF-beta activation. This surgical manipulation elevates initial blood pressure and angiotensin II. The hearts of these rats had increased TSP1, collagen, and TGF-beta activity, and cardiac function was diminished. A peptide antagonist of TSP1-dependent TGF-beta activation prevented progression of cardiac fibrosis and improved cardiac function by reducing TGF-beta activity. These data suggest that TSP1 is a significant mediator of fibrotic complications of diabetes associated with stimulation of the renin-angiotensin system, and further studies to assess the blockade of TSP1-dependent TGF-beta activation as a potential antifibrotic therapeutic strategy are warranted.

Mast cells and inflammatory kidney disease

Inflammatory kidney disease involves a complex network of interactions between resident kidney and infiltrating hematopoietic cells. Mast cells (MCs) are constitutively found in kidneys in small numbers but increase considerably in various renal diseases. While this increase is usually interpreted as a sign of pathological involvement, recent data using MC-deficient animals show their ability to restore kidney homeostasis. In anti-glomerular basement membrane antibody-induced glomerulonephritis, MCs are protective by initiating repair and remodeling functions counteracting the devastating effects of glomerular injury. Protection may also include immunoregulatory capacities to limit autoreactive T-cell responses. MCs also control tubulointerstitial fibrosis by activating tissue remodeling and neutralizing fibrotic factors. Release of mediators by MCs during inflammation, however, could also promote unwanted responses that ultimately lead to destruction of kidney structure, as exemplified by data showing either protection or aggravation in related renal disease models. Similarly, while the action of proteases may initially be beneficial, the generation of fibrosis-promoting angiotensin II by chymase also shows the limits of adaptive responses to achieve homeostasis. Thus, it is likely the physiological context involving the interaction with other cells and inflammatory mediators that determines the final action of MCs in the development of kidney disease.

Effect of ACE inhibitors on angiotensin II in rat mesangial cells cultured in high glucose

This study investigates whether angiotensin converting enzyme (ACE) inhibitors can block high glucose-induced increase of angiotensin II (Ang II) levels in cultured rat mesangial cells. Incubation of cells with high glucose for 5 days increased Ang II in the cell media (extracellular) and cell lysates (intracellular) by approximately 1.5-fold and approximately 2.2-fold, respectively. Captopril blocked high glucose-induced increase in extracellular Ang II levels but not in intracellular Ang II levels. Since the inability of captopril to inhibit intracellular Ang II in intact cells could be explained by failure of the drug to enter the cells, further studies were performed using lysates from cells pre-treated with high glucose for 5 days. Addition of captopril to cell lysates was indeed able to inhibit Ang I conversion to Ang II but only partially. These findings suggest the involvement of non-ACE mechanisms in Ang II formation from Ang I in mesangial cells.

Mast Cell Proteases

Mast cells (MCs) are traditionally thought of as a nuisance for its host, for example, by causing many of the symptoms associated with allergic reactions. In addition, recent research has put focus on MCs for displaying harmful effects during various autoimmune disorders. On the other hand, MCs can also be beneficial for its host, for example, by contributing to the defense against insults such as bacteria, parasites, and snake venom toxins. When the MC is challenged by an external stimulus, it may respond by degranulation. In this process, a number of powerful preformed inflammatory "mediators" are released, including cytokines, histamine, serglycin proteoglycans, and several MC-specific proteases: chymases, tryptases, and carboxypeptidase A. Although the exact effector mechanism(s) by which MCs carry out their either beneficial or harmful effects in vivo are in large parts unknown, it is reasonable to assume that these mediators may contribute in profound ways. Among the various MC mediators, the exact biological function of the MC proteases has for a long time been relatively obscure. However, recent progress involving successful genetic targeting of several MC protease genes has generated powerful tools, which will enable us to unravel the role of the MC proteases both in normal physiology as well as in pathological settings. This chapter summarizes the current knowledge of the biology of the MC proteases.

Small gene effect and exercise training-induced cardiac hypertrophy in mice: an Ace gene dosage study

Small gene effects influence complex phenotypes in a context dependent manner. Here we evaluated whether increasing dosage of the angiotensin I converting enzyme ( Ace) gene influence exercise-induced cardiac hypertrophy. Mice harboring one, two, three, and four copies of the Ace gene were assigned to sedentary (S1–4) and swimming exercise-trained (T1–4) groups (1.5 h twice daily, 5 days/wk, 4 wk). Exercising resulted in comparable bradycardia and elevated skeletal muscle citrate synthase activity, while blood pressure remained unchanged. Left ventricle mass index and cardiomyocyte diameter were similar among sedentary mice and the magnitude of their increase associated to exercising was not influenced by the Ace genotype (T1: 12.6 and 17.9%, T2: 15.2 and 13.8%, T3: 16.9 and 20%, T4: 17 and 19%, respectively). Plasma renin activity (PRA) levels were higher in one vs. three or four copies mice (4.89 ± 0.5 vs. 2.43 ± 0.6 and 2.12 ± 01.1 ng/ml Ang I, P < 0.05), while cardiac ACE activity was higher in three vs. two or one copy mice (5,946 ± 590.8 vs. 2,951.5 ± 328.3 and 3,504.1 ± 258.9 μF·min−1·ml−1, P < 0.05). With exercise, PRA remained unchanged in each group, while cardiac immunostaining for Ang II reached comparable levels. In summary: 1) exercise training led to similar aerobic adaptation regardless of the Ace genotype, and 2) higher number of Ace gene copies per se, which alters cardiac ACE activity, did not influence basal cardiac mass or, most importantly, the magnitude of swimming-induced cardiac hypertrophy. Collectively, these data indicate that small isolated genetic disturbances in ACE cardiac levels can be well compensated under physiological perturbations.

Signaling by the angiotensin-converting enzyme

Inhibition of the angiotensin-converting enzyme (ACE) protects against the progression of several cardiovascular diseases. Because of its dual role in regulating angiotensin II and bradykinin levels, the positive clinical effects of ACE inhibitors were thought to be the consequence of concomitant reductions in the production of angiotensin II and the degradation of bradykinin. Recent evidence suggests that some of the beneficial effects of ACE inhibitors on cardiovascular function and homeostasis can be attributed to novel mechanisms. These include the accumulation of the ACE substrate N-acetyl-seryl-aspartyl-lysyl-proline, which blocks collagen deposition in the injured heart, as well as the activation of an ACE signaling cascade that involves the activation of the kinase CK2 and the c-Jun N-terminal kinase in endothelial cells and leads to changes in gene expression. Moreover, at least one other ACE homologue (ACE2) is proposed to counteract the detrimental effects associated with the activation of the classical renin-angiotensin system. These data reveal hitherto unexpected levels of internal regulation of the renin-angiotensin system.

Advanced glycation end products activate a chymase-dependent angiotensin II-generating pathway in diabetic complications

BACKGROUND

Angiotensin II is a key mediator of diabetes-related vascular disease. It is now recognized that in addition to angiotensin-converting enzyme, chymase is an important alternative angiotensin II-generating enzyme in hypertension and diabetes. However, the mechanism of induction of chymase in diabetes remains unknown.

METHODS AND RESULTS

Here, we report that chymase is upregulated in coronary and renal arteries in patients with diabetes by immunohistochemistry. Upregulation of vascular chymase is associated with deposition of advanced glycation end products (AGEs), an increase in expression of the receptor for AGEs (RAGE), and activation of ERK1/2 MAP kinase. In vitro, AGEs can induce chymase expression and chymase-dependent angiotensin II generation in human vascular smooth muscle cells via the RAGE-ERK1/2 MAP kinase-dependent mechanism. This is confirmed by blockade of AGE-induced vascular chymase expression with a neutralizing RAGE antibody and an inhibitor to ERK1/2 and by overexpression of the dominant negative ERK1/2. Compared with angiotensin-converting enzyme, chymase contributes to the majority of angiotensin II production (>70%, P<0.01) in response to AGEs. Furthermore, AGE-induced angiotensin II production is blocked by the anti-RAGE antibody and by inhibition of ERK1/2 MAP kinase activities.

CONCLUSIONS

AGEs, a hallmark of diabetes, induce chymase via the RAGE-ERK1/2 MAP kinase pathway. Chymase initiates an important alternative angiotensin II-generating pathway in diabetes and may play a critical role in diabetic vascular disease.