Hypothesis regarding the pathophysiological role of alternative pathways of angiotensin II formation in atherosclerosis

Diverse biological functions of the renin-angiotensin system

The renin-angiotensin system (RAS) has been widely known as a circulating endocrine system involved in the control of blood pressure. However, components of RAS have been found to be localized in rather unexpected sites in the body including the kidneys, brain, bone marrow, immune cells, and reproductive system. These discoveries have led to steady, growing evidence of the existence of independent tissue RAS specific to several parts of the body. It is important to understand how RAS regulates these systems for a variety of reasons: It gives a better overall picture of human physiology, helps to understand and mitigate the unintended consequences of RAS-inhibiting or activating drugs, and sets the stage for potential new therapies for a variety of ailments. This review fulfills the need for an updated overview of knowledge about local tissue RAS in several bodily systems, including their components, functions, and medical implications.

Lipotoxicity-Related Hematological Disorders in Obesity

Lipotoxicity can mediate endothelial dysfunction in obesity. Altered endothelial cell phenotype during the pathobiological course of the lipotoxicity may lead to hemostatic abnormalities, which is a hallmark of several hematological disorders. Impaired hemostasis could also be directly related to numerous metabolic diseases such as hypertension, diabetes, and atherosclerosis. On the other hand, the local hematopoietic bone marrow (BM) renin-angiotensin system (RAS) contributes to the development of atherosclerosis via acting on the lipotoxicity processes. Local BM RAS, principally an autocrine/paracrine/intracrine hematological system, is located at the crossroads of cellular regulation, molecular interactions, and lipotoxicity-mediated vascular endothelial dysfunction. The positive regulatory role of plasma LDL on AT1 receptor-mediated hematopoietic stem cell (HSC) differentiation and the production of pro-atherogenic monocytes have been described. LDL-regulated HSC function may explain in part hypercholesterolemia-induced inflammation as well as the anti-inflammatory and anti-atherosclerotic effects of AT1 receptor blockers. The role of local adipose tissue RAS is directly related to the pathogenesis of metabolic derangements in obesity. There may be a crosstalk between local BM RAS and local adipose tissue RAS at the genomics and transcriptomics levels. This chapter aims to review hematological alterations propagating the pathological influences of lipotoxicity on the vascular endothelium.

Alterations in Renin-Angiotensin System (RAS) Peptide Levels in Patients with HIV

Chronic HIV infection has long been associated with an increased risk for cardiovascular diseases. The metabolites of the renin−angiotensin system (RAS) such as angiotensin II (AngII) play an important role in regulating blood pressure and fluid dynamics. Cross-sectional analysis of HIV-positive individuals (n = 71, age > 40 years, stable ART > 3 months with HIV viral load < 50 copies/mL) were compared to a similar HIV seronegative group (n = 72). High-resolution B-mode ultrasound images of the right carotid bifurcation (RBIF) and right common carotid artery (RCCA) were conducted to measure the extent of carotid atherosclerotic vascular disease. Plasma RAS peptide levels were quantified using a liquid chromatography-mass spectrometry-based metabolomics assay. RAS peptide concentrations were compared between persons with HIV and persons without HIV, correlating their association with clinical and cardiac measures. Median precursor peptides (Ang(1-12) and AngI) were significantly higher in the HIV-positive group compared to the HIV-negative. Analyses of the patient subgroup not on antihypertensive medication revealed circulating levels of AngII to be four-fold higher in the HIV-positive subgroup. AngII and TNF-alpha levels were found to have a positive association with RCCA, and AngI/Ang(1-12) ratio and TNF-alpha levels were found to have a positive association with RBIF. In both predictive models, AngIII had a negative association with either RCCA or RBIF, which may be attributed to its ability to bind onto AT2R and thus oppose pro-inflammatory events. These results reveal systemic alterations in RAS as a result of chronic HIV infection, which may lead to the activation of inflammatory pathways associated with carotid thickening. RAS peptide levels and cytokine markers were associated with RCCA and RBIF measurements.

Inhibition of perivascular mast cell activation is involved in the atheroprotective effect of rosiglitazone in apolipoprotein E-deficient mice

Activation of perivascular mast cells (MCs) and subsequent release of their abundant inflammatory mediators have been well documented to induce excessive inflammation and subsequent rupture of atherosclerotic plaques. Previous studies have suggested that rosiglitazone affects the stability of plaques, although the precise mechanism of action is not clearly understood. In this study, we evaluated the effects of rosiglitazone on MCs in vivo and in vitro. Apolipoprotein E-deficient (ApoE^-/-) mice were fed a high-fat diet (HFD), with or without rosiglitazone supplemented in the drinking water (1.5 mg/kg/day). Compared with the HFD group, rosiglitazone did not affect blood glucose levels, but it attenuated serum levels of tumor necrosis factor alpha (TNFα) and interleukin-6 (IL-6), ameliorated plaque lipid accumulation and the expression of matrix metalloproteinases-2 and -9, increased the collagen content of plaques, and inhibited perivascular MC degranulation and chymase expression. The in vitro experiments showed that rosiglitazone treatment repressed the expression of TNFα and IL-6 induced by antigen-challenged RBL-2H3 cells in a peroxisome proliferator-activated receptor γ (PPARγ)-independent manner, which was related to the repression of protein kinase C (PKC)-β1 activation. Combined, these results suggest that the plaque-stabilizing effect of rosiglitazone is attributable to its ability to inhibit the activation of perivascular MCs.

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.

An Update on the Tissue Renin Angiotensin System and Its Role in Physiology and Pathology

In its classical view, the renin angiotensin system (RAS) was defined as an endocrinesystem involved in blood pressure regulation and body electrolyte balance. However, the emergingconcept of tissue RAS, along with the discovery of new RAS components, increased thephysiological and clinical relevance of the system. Indeed, RAS has been shown to be expressed invarious tissues where alterations in its expression were shown to be involved in multiple diseasesincluding atherosclerosis, cardiac hypertrophy, type 2 diabetes (T2D) and renal fibrosis. In thischapter, we describe the new components of RAS, their tissue-specific expression, and theiralterations under pathological conditions, which will help achieve more tissue- and conditionspecifictreatments.

An Update on the Tissue Renin Angiotensin System and Its Role in Physiology and Pathology

In its classical view, the renin angiotensin system (RAS) was defined as an endocrine system involved in blood pressure regulation and body electrolyte balance. However, the emerging concept of tissue RAS, along with the discovery of new RAS components, increased the physiological and clinical relevance of the system. Indeed, RAS has been shown to be expressed in various tissues where alterations in its expression were shown to be involved in multiple diseases including atherosclerosis, cardiac hypertrophy, type 2 diabetes (T2D) and renal fibrosis. In this chapter, we describe the new components of RAS, their tissue-specific expression, and their alterations under pathological conditions, which will help achieve more tissue- and condition-specific treatments.

Pathological involvement of chymase-dependent angiotensin II formation in the development of cardiovascular disease

Chymase is a potent and specific angiotensin II (Ang II)-forming enzyme in vitro. There is also strong evidence to suggest its importance in vivo. Recent clinical studies have suggested that high serum cholesterol levels are associated with increased vascular chymase activity and this may assist in the development of atherosclerosis. This clinical finding has been reproduced in hamster models. Studies with transgenic mice overexpressing the human chymase gene suggest a direct association between vascular chymase upregulation and atherogenesis. There is also increased chymase activity following various cardiac diseases such as myocardial ischaemia, volume overload cardiac failure, cardiomyopathy and viral myocarditis, suggesting that increased cardiac chymase activity appears to be involved in cardiac remodelling.

Angiotensin II induces the aggregation of native and oxidized low-density lipoprotein

Modifications of low-density lipoprotein (LDL), such as oxidation and aggregation, and angiotensin (Ang) peptides are involved in the pathogenesis of atherosclerosis. Here, we investigated the relationship between one of the Ang peptides, AngII, and two LDL modifications, oxidation and aggregation. Using polyacrylamide gel electrophoresis and aggregation assays, we noted that AngII markedly induced the aggregation of LDL and oxidized LDL (Ox-LDL), and bound to both the aggregated and non-aggregated forms. In contrast, a peptide (AngIII) formed by deletion of N-terminal Asp of AngII induced the aggregation of Ox-LDL but not LDL. From tyrosine fluorescence measurements, we noted that AngII interacted with two major lipid components in LDL and Ox-LDL, phosphatidylcholine (PC) and oxidized PC, while AngIII interacted with oxidized PC, but not with PC and lysophosphatidylcholine. Moreover, results from thiobarbituric acid-reactive substances assay proved that AngII did not induce oxidation of LDL. These results suggest that AngII can be involved in the pathogenesis of atherosclerosis by binding to LDL and Ox-LDL-especially to the major lipid components, PC and oxidized PC-followed by inducing the aggregation of LDL and Ox-LDL and that the N-terminal Asp of AngII is important for the binding and aggregation specificity of LDL and Ox-LDL.

Intracrine angiotensin II functions originate from noncanonical pathways in the human heart

Although it is well-known that excess renin angiotensin system (RAS) activity contributes to the pathophysiology of cardiac and vascular disease, tissue-based expression of RAS genes has given rise to the possibility that intracellularly produced angiotensin II (Ang II) may be a critical contributor to disease processes. An extended form of angiotensin I (Ang I), the dodecapeptide angiotensin-(1-12) [Ang-(1-12)], that generates Ang II directly from chymase, particularly in the human heart, reinforces the possibility that an alternative noncanonical renin independent pathway for Ang II formation may be important in explaining the mechanisms by which the hormone contributes to adverse cardiac and vascular remodeling. This review summarizes the work that has been done in evaluating the functional significance of Ang-(1-12) and how this substrate generated from angiotensinogen by a yet to be identified enzyme enhances knowledge about Ang II pathological actions.

Angiotensin-(1-12): a chymase-mediated cellular angiotensin II substrate

The classical view of biochemical pathways for the formation of biologically active angiotensins continues to undergo significant revision as new data uncovers the existence of important species differences between humans and rodents. The discovery of two novel substrates that, cleaved from angiotensinogen, can lead to direct tissue angiotensin II formation has the potential of radically altering our understanding of how tissues source angiotensin II production and explain the relative lack of efficacy that characterizes the use of angiotensin converting enzyme inhibitors in cardiovascular disease. This review addresses the discovery of angiotensin-(1-12) as an endogenous substrate for the production of biologically active angiotensin peptides by a non-renin dependent mechanism and the revealing role of cardiac chymase as the angiotensin II convertase in the human heart. This new information provides a renewed argument for exploring the role of chymase inhibitors in the correction of cardiac arrhythmias and left ventricular systolic and diastolic dysfunction.

Angiotensin-converting-enzyme inhibition counteracts angiotensin II-mediated endothelial cell dysfunction by modulating the p38/SirT1 axis

OBJECTIVE

Oxidative stress has been linked to endothelial dysfunction and angiotensin II stimulates the reactive oxygen species production contributing to several cardiovascular diseases. We have studied the chain of events induced by angiotensin-converting-enzyme (ACE) activation in vascular umbilical vein endothelial cells (HUVECs) by using an ACE inhibitor such as zofenoprilat.

METHODS

We used specific assay to measure the superoxide anion production, tetrazolium bromide (MTT) assay for cell viability, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay for cell apoptosis, and western blot for protein analysis in the study.

RESULTS

Zofenoprilat counteracts the superoxide anion production and cell apoptosis induced by angiotensin I treatment by blocking the extrinsic caspase cascade, NF-kB and p38 activation. p38 inhibitor SB203580 reverted the angiotensin II oxidant effects while the p38 constitutively activation, by MKK6 transfection, abrogated the zofenoprilat effects. Characterizing the zofenoprilat downstream effector we found that zofenoprilat reverted the SirT-1 downregulation induced by angiotensin II. p38 activation by angiotensin II was strictly correlated with SirT1 protein downregulation; SB203580 significantly prevented SirT1 downregulation induced by angiotensin II while the p38 constitutive activation abolished SIRT1 protein basal levels. p38 directly bound SirT1 sequestering it in the cytoplasm. SirT1 inhibition by sirtinol annulled zofenoprilat action while SirT1 overexpression reverted the cytotoxic effects of angiotensin II. Finally, zofenoprilat negatively controlled angiotensin I receptor protein expression through SirT1.

CONCLUSION

The p38-SirT1 axis is found markedly relevant in modulating the cardiovascular benefit deriving from ACE-inhibitors and might represent a novel target for innovative drugs in cardiovascular prevention.

An evolving story of angiotensin-II-forming pathways in rodents and humans

Lessons learned from the characterization of the biological roles of Ang-(1-7) [angiotensin-(1-7)] in opposing the vasoconstrictor, proliferative and prothrombotic actions of AngII (angiotensin II) created an underpinning for a more comprehensive exploration of the multiple pathways by which the RAS (renin-angiotensin system) of blood and tissues regulates homoeostasis and its altered state in disease processes. The present review summarizes the progress that has been made in the novel exploration of intermediate shorter forms of angiotensinogen through the characterization of the expression and functions of the dodecapeptide Ang-(1-12) [angiotensin-(1-12)] in the cardiac production of AngII. The studies reveal significant differences in humans compared with rodents regarding the enzymatic pathway by which Ang-(1-12) undergoes metabolism. Highlights of the research include the demonstration of chymase-directed formation of AngII from Ang-(1-12) in human left atrial myocytes and left ventricular tissue, the presence of robust expression of Ang-(1-12) and chymase in the atrial appendage of subjects with resistant atrial fibrillation, and the preliminary observation of significantly higher Ang-(1-12) expression in human left atrial appendages.

Role of the renin-angiotensin system on abdominal aortic aneurysms

BACKGROUND

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Mast cell chymase and tryptase as targets for cardiovascular and metabolic diseases

Mast cells are critical effectors in inflammatory diseases, including cardiovascular and metabolic diseases and their associated complications. These cells exert their physiological and pathological activities by releasing granules containing histamine, cytokines, chemokines, and proteases, including mast cell-specific chymases and tryptases. Several recent human and animal studies have shown direct or indirect participation of mast cell-specific proteases in atherosclerosis, abdominal aortic aneurysms, obesity, diabetes, and their complications. Animal studies have demonstrated the beneficial effects of highly selective and potent chymase and tryptase inhibitors in several experimental cardiovascular and metabolic diseases. In this review, we summarize recent discoveries from in vitro cell-based studies to experimental animal disease models, from protease knockout mice to treatments with recently developed selective and potent protease inhibitors, and from patients with preclinical disorders to those affected by complications. We hypothesize that inhibition of chymases and tryptases would benefit patients suffering from cardiovascular and metabolic diseases.

Handle Region Peptide Ameliorating Insulin Resistance but Not β Cell Functions in Male Rats Neonatally Treated with Sodium L-Glutamate

Handle region peptide (HRP), which was recognized as a blocker of (pro)renin receptor ((P)RR), may block the function of (P)RR. The aim of this study was to investigate the effect of HRP with a large dose of 1 mg/kg/d on glucose status in the rats treated neonatally with monosodium L-glutamate (MSG). At the age of 8 weeks, the MSG rats were randomly divided into MSG control group, HRP treated group with minipump (MSG-HRP group), losartan treated group (MSG-L group), and HRP and losartan cotreated group (MSG-HRP-L group) and fed with high-fat diet for 4 weeks. Losartan but not HRP increased the levels of insulin releasing and ameliorate glucose status although both losartan and HRP improved insulin sensitivity. On the one hand, both losartan and HRP decreased levels of pancreatic local Ang-II and NADPH oxidase activity as well as its subunits P(22phox). On the other hand, losartan but not HRP decreased α -cell mass and number of PCNA-positive cells located periphery of the islets and decreased picrosirius red stained area in islets. HRP ameliorating insulin resistance but not β -cell functions leads to hyperglycemia in the end in male MSG rats, and the dual characters of HRP may partly account for the phenomenon.

Cardiac-autonomic imbalance and baroreflex dysfunction in the renovascular Angiotensin-dependent hypertensive mouse

Mouse models provide powerful tools for studying the mechanisms underlying the dysfunction of the autonomic reflex control of cardiovascular function and those involved in cardiovascular diseases. The established murine model of two-kidney, one-clip (2K1C) angiotensin II-dependent hypertension represents a useful tool for studying the neural control of cardiovascular function. In this paper, we discuss the main contributions from our laboratory and others regarding cardiac-autonomic imbalance and baroreflex dysfunction. We show recent data from the angiotensin-dependent hypertensive mouse demonstrating DNA damage and oxidative stress using the comet assay and flow cytometry, respectively. Finally, we highlight the relationships between angiotensin and peripheral and central nervous system areas of cardiovascular control and oxidative stress in the 2K1C hypertensive mouse.

Endothelial dysfunction in the apolipoprotein E-deficient mouse: insights into the influence of diet, gender and aging

Since the early 1990s, several strains of genetically modified mice have been developed as models for experimental atherosclerosis. Among the available models, the apolipoprotein E-deficient (apoE⁻/⁻) mouse is of particular relevance because of its propensity to spontaneously develop hypercholesterolemia and atherosclerotic lesions that are similar to those found in humans, even when the mice are fed a chow diet. The main purpose of this review is to highlight the key achievements that have contributed to elucidating the mechanisms pertaining to vascular dysfunction in the apoE⁻/⁻ mouse. First, we summarize lipoproteins and atherosclerosis phenotypes in the apoE⁻/⁻ mouse, and then we briefly discuss controversial evidence relative to the influence of gender on the development of atherosclerosis in this murine model. Second, we discuss the main mechanisms underlying the endothelial dysfunction of conducting vessels and resistance vessels and examine how this vascular defect can be influenced by diet, aging and gender in the apoE⁻/⁻ mouse.

Insulin alone or with captopril: effects on signaling pathways (AKT and AMPK) and oxidative balance after ischemia-reperfusion in isolated hearts

Insulin and the inhibition of the renin-angiotensin system have independent benefits for ischemia-reperfusion injury, but their combination has not been tested. Our aim was to evaluate the effects of insulin+captopril on insulin/angiotensin signaling pathways and cardiac function in the isolated heart subjected to ischemia-reperfusion. Isolated hearts were perfused (Langendorff technique) with Krebs-Henseleit (KH) buffer for 25 min. Global ischemia was induced (20 min), followed by reperfusion (30 min) with KH (group KH), KH+angiotensin-I (group A), KH+angiotensin-I+captopril (group AC), KH+insulin (group I), KH+insulin+angiotensin-I (group IA), or KH+insulin+angiotensin-I+captopril (group IAC). Group A had a 24% reduction in developed pressure and an increase in end-diastolic pressure vs. baseline, effects that were reverted in groups AC, IA, and IAC. The phosphorylation of protein kinase B (AKT) was higher in groups I and IA vs. groups KH and A. The phosphorylation of AMP-activated protein kinase (AMPK) was ∼31% higher in groups I, IA, and IAC vs. groups KH, A, and AC. The tert-butyl hydroperoxide (tBOOH)-induced chemiluminescence was lower (∼2.2 times) in all groups vs. group KH and was ∼35% lower in group IA vs. group A. Superoxide dismutase content was lower in groups A, AC, and IAC vs. group KH. Catalase activity was ∼28% lower in all groups (except group IA) vs. group KH. During reperfusion of the ischemic heart, insulin activates the AKT and AMPK pathways and inhibits the deleterious effects of angiotensin-I perfusion on SOD expression and cardiac function. The addition of captopril does not potentiate these effects.

Cysteinyl cathepsins and mast cell proteases in the pathogenesis and therapeutics of cardiovascular diseases

The initiation and progression of cardiovascular diseases involve extensive arterial wall matrix protein degradation. Proteases are essential to these pathological events. Recent discoveries suggest that proteases do more than catabolize matrix proteins. During the pathogenesis of atherosclerosis, abdominal aortic aneuryms, and associated complications, cysteinyl cathepsins and mast cell tryptases and chymases participate importantly in vascular cell apoptosis, foam cell formation, matrix protein gene expression, and pro-enzyme, latent cytokine, chemokine, and growth factor activation. Experimental animal disease models have been invaluable in examining each of these protease functions. Deficiency and pharmacological inhibition of cathepsins or mast cell proteases have allowed their in vivo evaluation in the setting of pathological conditions. Recent discoveries of highly selective and potent inhibitors of cathepsins, chymase, and tryptase, and their applications in vascular diseases in animal models and non-vascular diseases in human trials, have led to the hypothesis that selective inhibition of cathepsins, chymases, and tryptase will benefit patients suffering from cardiovascular diseases. This review highlights recent discoveries from in vitro cell-based studies to experimental animal cardiovascular disease models, from protease knockout mice to treatments with recently developed selective and potent protease inhibitors, and from patients with cathepsin-associated non-vascular diseases to those affected by cardiovascular complications.

An update on the islet renin-angiotensin system

The traditional renin-angiotensin system (RAS) components have been studied extensively since the rate-limiting component of RAS, renin, was first characterized. The ongoing identification of various novel RAS components and signaling pathways continues to elaborate the complexity of this system. Regulation of RAS according to the conventional and contemporary views of its functions in various tissues under pathophysiological conditions is a main treatment strategy for many metabolic diseases. The local pancreatic RAS, first proposed to exist in pancreatic islets two decades ago, could regulate islet function and glycemic control via influences on islet cell mass, inflammation, and ion channels. Insulin secretion, the major function of pancreatic islets, is controlled by numerous factors. Among these factors and of particular interest are glucagon-like peptide-1 (GLP-1) and vitamin D, which may regulate islet function by directly binding receptors on islet beta cells. These factors may work with local RAS signaling in islets to protect and maintain islet function under diabetic and hyperglycemic conditions. In this concise review, the local islet RAS will be discussed with particular attention being paid to recent notable findings.

Local bone marrow Renin-Angiotensin system and atherosclerosis

Local hematopoietic bone marrow (BM) renin-angiotensin system (RAS) affects the growth, production, proliferation differentiation, and function of hematopoietic cells. Angiotensin II (Ang II), the dominant effector peptide of the RAS, regulates cellular growth in a wide variety of tissues in pathobiological states. RAS, especially Ang II and Ang II type 1 receptor (AT1R), has considerable proinflammatory and proatherogenic effects on the vessel wall, causing progression of atherosclerosis. Recent investigations, by analyzing several BM chimeric mice whose BM cells were positive or negative for AT1R, disclosed that AT1R in BM cells participates in the pathogenesis of atherosclerosis. Therefore, AT1R blocking not only in vascular cells but also in the BM could be an important therapeutic approach to prevent atherosclerosis. The aim of this paper is to review the function of local BM RAS in the pathogenesis of atherosclerosis.

Role of bone marrow renin-angiotensin system in the pathogenesis of atherosclerosis

The renin-angiotensin system (RAS) has been considered to be a circulating hormonal system that regulates blood pressure, blood flow, fluid volume and electrolyte balance. A growing body of evidence indicates local effects of an activated RAS, particularly in the cardiac, vascular, and renal systems. It is now well established that RAS, especially angiotensin II (Ang II) and Ang II type 1 receptor (AT1R) pathway, has significant pro-inflammatory actions on the vessel wall, leading to progression of atherosclerosis. Recent reports suggest that an activated RAS has local effects in bone marrow (BM), which contributes to the regulation of normal and malignant hematologic processes. We reported that AT1aR in BM cells participate in the pathogenesis of atherosclerosis by analyzing several BM chimeric mice whose BM cells were positive or negative for AT1aR. These results suggest that blockade of AT1R not only in vascular cells but also in BM could be an important strategy to prevent atherosclerosis. In this review, we overview recent findings on a role of RAS in the pathogenesis of atherosclerosis, and discuss functional contribution of a local RAS in BM to progression and destabilization of atherosclerotic plaque.

Risk reduction by preventing stroke: need for blockade of angiotensin II and catecholamines?

Angiotensin (AT) II and noradrenaline play major roles in hypertension, stroke and coronary heart disease, which are themselves interlinked. Harmful effects of AT II are not blocked solely by angiotensin-converting enzyme inhibitors, as it is now evident that AT II is generated by other enzymes such as chymase. Angiotensin II also stimulates noradrenaline release modulated by presynaptic receptors on sympathetic nerves. Numerous studies have defined the action of the AT II type 1 receptor blocker (ARB) eprosartan as controlling noradrenergic and adrenergic effects, resulting from actions on the renin-angiotensin-aldosterone system and the sympathetic nervous system. Clinical studies have been carried out to assess the effects of ARBs on morbidity and mortality. The Valsartan Antihypertensive Long-term Use Evaluation (VALUE) trial compared the effects of valsartan and the calcium channel blocker (CCB) amlodipine in over 15,000 patients at high risk of a cardiac event. Results showed that blood pressure was reduced by both treatments and cardiac mortality/morbidity was similar in both groups. By contrast, the Morbidity and mortality after Stroke, Eprosartan compared with nitrendipine for Secondary prevention (MOSES) study (n = 1405) generated results which differed from the VALUE study, in that blood pressure was reduced by both eprosartan and nitrendipine, but eprosartan reduced all cardiovascular and cerebrovascular events to a greater extent than nitrendipine. It is also possible that any delayed clinical benefit of eprosartan could be due to reverse cardiac remodelling. Eprosartan, by blocking AT II receptors, reducing noradrenaline release and blocking catecholamine actions, may, therefore, provide greater protection against vascular events than CCBs or other ARBs.

Renin: at the heart of the mast cell

Cardiac mast cells proliferate in cardiovascular diseases. In myocardial ischemia, mast cell mediators contribute to coronary vasoconstriction, arrhythmias, leukocyte recruitment, and tissue injury and repair. Arrhythmic dysfunction, coronary vasoconstriction, and contractile failure are also characteristic of cardiac anaphylaxis. In coronary atherosclerosis, mast cell mediators facilitate cholesterol accumulation and plaque destabilization. In cardiac failure, mast cell chymase causes myocyte apoptosis and fibroblast proliferation, leading to ventricular dysfunction. Chymase and tryptase also contribute to fibrosis in cardiomyopathies and myocarditis. In addition, mast cell tumor necrosis factor-alpha promotes myocardial remodeling. Cardiac remodeling and hypertrophy in end-stage hypertension are also induced by mast cell mediators and proteases. We recently discovered that cardiac mast cells contain and release renin, which initiates local angiotensin formation. Angiotensin causes coronary vasoconstriction, arrhythmias, fibrosis, apoptosis, and endothelin release, all demonstrated mechanisms of mast-cell-associated cardiac disease. The effects of angiotensin are further amplified by the release of norepinephrine from cardiac sympathetic nerves. Our discovery of renin in cardiac mast cells and its release in pathophysiological conditions uncovers an important new pathway in the development of mast-cell-associated heart diseases. Several steps in this novel pathway may constitute future therapeutic targets.

Long-term, high-dosage candesartan suppresses inflammation and injury in chronic kidney disease: nonhemodynamic renal protection

Recent evidence suggests that higher-than-usual antihypertensive dosages of renin-angiotensin-aldosterone system blockers may provide additional protection from progression of chronic renal disease; however, there have been few long-term studies, and the underlying mechanisms remain uncertain. This study examined the effects of long-term (14 mo) administration of ultrahigh dosages of the angiotensin receptor blocker candesartan on the progression of renal injury in spontaneously hypertensive rats (SHR). Beginning 8 wk after birth, SHR underwent unilateral nephrectomy and were given vehicle (control), or candesartan at a standard 5 mg/kg per d (T5), high 25 mg/kg per d (T25), or ultrahigh 75 mg/kg per d dosage (T75). After 2 wk, BP was reduced in all treated groups; however, it was better controlled in the high-dosage groups (T25 and T75). Urinary protein was significantly reduced in T75 after 2 wk of treatment and was also declined in the other two treatment groups but only after 2 mo. Exogenous angiotensin II test showed that complete angiotensin receptor blockade was achieved only in the high-dosage groups. Renal inflammation and macrophage (ED-1) infiltration were significantly ameliorated in both T25 and T75 but not in T5 rats. This was associated with the changes of tubular expression of monocyte chemoattractant protein-1, RANTES (regulated upon expression normal T cell expressed and secreted), and the phosphorylated NF-kappaB, a marker for activation. Suppression of ED-1, monocyte chemoattractant protein-1, and RANTES expression and NF-kappaB activation were greater in T75 as compared with T25. These findings suggest that candesartan has dosage-dependent, anti-inflammatory effects that are mediated by suppression of NF-kappaB activation and chemokine expression. Renal protection with high-dosage therapy may depend on these nonhemodynamic effects.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

ACE Inhibition Lowers Angiotensin-II-Induced Monocyte Adhesion to HUVEC by Reduction of p65 Translocation and AT1 Expression

Angiotensin-converting enzyme (ACE) inhibitors interfere with several key events of vascular inflammation resulting in impressive reductions in coronary vascular events. However, in human arteries ACE inhibitors block the production of angiotensin II (AngII) incompletely because of the involvement of alternative pathways in local AngII formation. Therefore, our study concentrated on the presumed modulation by ACE inhibition of local AngII-mediated inflammatory actions by a mechanism independent of blockage of AngII formation. We analyzed the effect of the ACE inhibitor ramiprilat on AngII-dependent cell adhesion molecule (CAM) expression and adhesion of monocytic THP-1 cells to endothelial cells. AngII induced upregulation of P-selectin, VCAM-1 and ICAM-1 on endothelial cells via activation of AT 1, which was correlated with enhanced THP-1 adhesion in flow chamber assays. Both enhanced adhesion and adhesion molecule expression were significantly reduced by pretreatment with ramiprilat. Ramiprilat reduced AT 1 expression on endothelial cells and decreased the AngII-induced p65 translocation into the nucleus. Diminished AT 1 expression and adhesion molecule expression in response to ramiprilat treatment were partially reversed after incubation with a bradykinin 2 receptor antagonist, suggesting that elevated bradykinin levels under ACE inhibition may be involved in the beneficial effect of ACE inhibitors. Thus, modulation of the local AngII system by ramiprilat may at least in part contribute to the benefits of ACE inhibition in the treatment of atherosclerotic diseases.

Tissue-specific expression of renin-angiotensin system components in IgA nephropathy

BACKGROUND

The renin-angiotensin II system (RAS) has been implicated in the development of glomerulonephritis. The aims of this study were to determine (1) the expression of RAS components, angiotensin (Ang II)-forming enzymes [angiotensin-I-converting enzyme (ACE) and chymase], and Ang II receptors, and (2) the correlation between RAS expression and severity of tissue injury in IgA nephropathy (IgAN).

METHODS

The expression levels of ACE, chymase, and Ang II type 1 and type 2 receptor (AT1R and AT2R) mRNAs were determined by in situ hybridization in renal specimens from 18 patients with IgAN, 5 patients with non-IgA mesangial proliferative glomerulonephritis (non-IgAN) and 10 patients with nonmesangial proliferative glomerulonephritis (minimal change nephrotic syndrome, n = 5, and membranous nephropathy, n = 5). Normal portions of surgically resected kidney served as control.

RESULTS

In normal kidney, a few mesangial cells and glomerular and tubular epithelial cells weakly expressed ACE, chymase and AT1R mRNAs. In IgAN and non-IgAN samples, ACE, chymase, AT1R and AT2R mRNAs were expressed in resident glomerular cells, including mesangial cells, glomerular epithelial cells and cells of Bowman's capsule. The glomerular expressions in IgAN were stronger than in minimal change nephrotic syndrome and membranous nephropathy. In IgAN, the expressions in glomeruli correlated with the degree of mesangial hypercellularity, whereas the expression levels were weaker at the area of mesangial expansion. IgAN with severe tubulointerstitial injury showed expression of ACE, chymase, AT1R and AT2R mRNAs in atrophic tubules and infiltrating cells and such expression correlated with the degree of tubulointerstitial damage.

CONCLUSION

Our results suggest that renal cells can produce RAS components and that locally synthesized Ang II may be involved in tissue injury in IgAN through Ang II receptors in the kidney.

ACE inhibition lowers angiotensin II-induced chemokine expression by reduction of NF-κB activity and AT1 receptor expression

OBJECTIVE

Angiotensin converting enzyme (ACE) inhibitors significantly improve survival in patients with atherosclerosis. Although ACE inhibitors reduce local angiotensin II (AngII) formation, serine proteases form AngII to an enormous amount independently from ACE. Therefore, our study concentrates on the effect of the ACE-inhibitor ramiprilat on chemokine release, AngII receptor (ATR) expression, and NF-kappaB activity in monocytes stimulated with AngII.

METHODS AND RESULTS

AngII-induced upregulation of IL-8 and MCP-1 protein and RNA in monocytes was inhibited by the AT1R-blocker losartan, but not by the AT2R-blocker PD 123.319. Ramiprilat dose-dependently suppressed AngII-induced upregulation of IL-8 and MCP-1. The suppressive effect of ramiprilat on AngII-induced chemokine production and release was in part caused by downregulation of NF-kappaB, but more by a selective and highly significant reduced expression of AT1 receptors as shown in monocytes and endothelial cells.

CONCLUSION

In our study we demonstrated for the first time that ramiprilat reduced expression of AT1R in monocytes and endothelial cells. In addition, ramiprilat downregulated NF-kappaB activity and thereby reduced the AngII-induced release of IL-8 and MCP-1 in monocytes. This antiinflammatory effect, at least in part, may contribute to the clinical benefit of the ACE inhibitor in the treatment of coronary artery disease.

AII antagonists in hypertension, heart failure, and diabetic nephropathy: focus on losartan

The goal of antihypertensive therapy is to prevent cardiovascular complications of hypertension, such as heart failure, stroke, end stage renal disease, and death, not just to normalize blood pressure. Recently, several clinical trials investigated the beneficial effects of angiotensin II antagonists (AIIAs) in patients with hypertension, heart failure or diabetic nephropathy utilizing proven clinical outcomes (e.g., all-cause mortality) rather than surrogate outcomes (e.g., blood pressure or proteinuria). The AIIAs may offer therapeutic advantages with respect to particular outcomes in certain types of patients. Evidence is also emerging that losartan may possess beneficial pharmacological properties such as effects on uric acid, platelets, sexual dysfunction, and cognitive function, that may set it apart from other members of the AIIA class. However, further studies are needed to delineate fully these potential pharmacological differences among the AIIAs and their possible clinical relevance. This paper reviews recent AIIA outcomes studies in patients with hypertension, heart failure, or diabetic nephropathy and also examines data suggesting that molecular differences exist within the AIIA class, differences that may assist in explaining the outcomes achieved in these recent trials.

Effects of candesartan and probucol on restenosis after coronary stenting: results of insight of stent intimal hyperplasia inhibition by new angiotensin II receptor antagonist (ISHIN) trial

The purpose of this study was to determine whether candesartan and its combination with probucol reduce restenosis after coronary stenting. A total of 132 patients who successfully underwent stenting were randomly assigned to a control group (n=45), a candesartan group (8 mg daily, n=43), or a candesartan plus probucol group (+ probucol 500 mg daily, n=44). No differences in late loss were observed between the control and candesartan groups. In the candesartan plus probucol group, late loss was significantly smaller than in the control and candesartan groups (p=0.003, 0.015). The restenosis rate was 27% in the control group, 26% in the candesartan group (p>0.99), and 11% in the candesartan plus probucol group (p=0.104 vs the control group and p=0.103 vs the candesartan group). Intravascular ultrasound revealed no differences in stent area among the 3 groups, and no differences in lumen area or in intimal hyperplasia area between the control and candesartan groups. However, the intimal hyperplasia area in the candesartan plus probucol group was significantly less than that in the control and candesartan groups (p<0.001, p<0.001). This study demonstrated that candesartan failed to inhibit the neointimal hyperplasia and although the combination treatment did reduce neointimal hyperplasia, it did not statistically reduce the restenosis rate.

Vasopeptidase inhibition and Ang-(1-7) in the spontaneously hypertensive rat

BACKGROUND

Omapatrilat, a new vasopeptidase inhibitor, inhibits the activity of angiotensin-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP). Because these two enzymes participate in the degradation of the vasodilator and natriuretic peptide, angiotensin-(1-7) [Ang-(1-7)], we assessed whether omapatrilat treatment is associated with changes in the plasma and urinary excretion rates of the angiotensins.

METHODS

We investigated in spontaneously hypertensive rats (SHR) (0.24 kg body weight) the effect of omapatrilat on plasma and urinary concentrations of angiotensin (Ang) I, Ang II and Ang-(1-7) during 17 days of administration of either the drug (N = 15, 100 micromol/kg/day) or vehicle (N = 14) in the drinking water. Hemodynamic and renal excretory function studies were associated with histological examination of the expression of Ang-(1-7) in the kidneys of both vehicle and omapatrilat-treated SHRs.

RESULTS

Omapatrilat induced a sustained lowering of systolic blood pressure (-68 mm Hg) without changes in cardiac rate. The mild positive water balance produced by omapatrilat did not cause natriuresis or kaliuresis, although it was associated with a significant decrease in urine osmolality. Blood pressure normalization was accompanied by increases in plasma Ang I (2969%), Ang II (57%), and Ang-(1-7) (163%) levels, paralleling pronounced increases in urinary excretion rates of Ang I and Ang-(1-7) but not Ang II. Detection of Ang-(1-7) immunostaining in the kidneys of five other SHR exposed either to vehicle (N = 3) or omapatrilat (N = 2) ascertained the source of the Ang-(1-7) found in the urine. Intense Ang-(1-7) staining, more pronounced in omapatrilat-treated SHR, was found in renal proximal tubules throughout the outer and inner regions of the renal cortex and the thick ascending loop of Henle, whereas no Ang-(1-7)-positive immunostaining was found in glomeruli and distal tubules.

CONCLUSIONS

Omapatrilat antihypertensive effects caused significant activation of the renin-angiotensin system associated with increases in urinary excretion rates of Ang I and Ang-(1-7). Combined studies of Ang-(1-7) metabolism in urine and immunohistochemical studies in the kidney revealed the existence of an intrarenal source, which may account for the pronounced increase in the excretion rate of the vasodilator heptapeptide. These findings provide further evidence for a contribution of Ang-(1-7) to the regulation of renal function and blood pressure.

Kinetic characterization and inhibition of the rat MAB elastase-2, an angiotensin I-converting serine protease

An elastase-2 has been recently described as the major angiotensin (Ang) II-forming enzyme of the rat mesenteric arterial bed (MAB) perfusate. Here, we have investigated the interaction of affinity-purified rat MAB elastase-2 with some substrates and inhibitors of both pancreatic elastases-2 and Ang II-forming chymases. The Ang II precursor [Pro 11 -D-Ala 12]-Ang I was converted into Ang II by the rat MAB elastase-2 with catalytic efficiency of 8.6 min-1 microM-1, and the chromogenic substrates N-succinyl-Ala-Ala-Pro-Leu-p-nitroanilide and N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide were hydrolyzed by the enzyme with catalytic efficiencies of 10.6 min-1 microM-1 and 7.6 min-1 microM-1, respectively. The non-cleavable peptide inhibitor CH-5450 inhibited the rat MAB elastase-2 activities toward the substrates Ang I (IC50 = 49 microM) and N-succinly-Ala-Ala-Pro-Phe-p-nitroanilide (IC 50 = 4.8 microM), whereas N-acetyl-Ala-Ala-Pro-Leu-chloromethylketone, an effective active site-directed inhibitor of pancreatic elastase-2, efficiently blocked the Ang II-generating activity of the rat MAB enzyme (IC 50 = 4.5 microM). Altogether, the data presented here confirm and extend the enzymological similarities between pancreatic elastase-2 and its rat MAB counterpart. Moreover, the thus far unrealized interaction of elastase-2 with [Pro 11-D-Ala 12]-Ang I and CH-5450, both regarded as selective for chymases, suggests that evidence for the in vivo formation of Ang II by chymases may have been overestimated in previous investigations of Ang II-forming pathways.

Vascular responses to endothelin-1, angiotensin-II, and U46619 in glycerol-induced acute renal failure

Angiotensin II and endothelin-1, major endogenous vasoconstrictors in acute renal failure (ARF), can modulate the effects of each other. This study aimed to evaluate the interaction between these vasoconstrictors in glycerol-induced ARF by evaluating their effects in the isolated perfused kidney in the presence of their respective antagonists. In ARF, angiotensin II (2.5-25 ng) caused an increase in perfusion pressure. Saralasin, 1 microM, a nonselective angiotensin receptor antagonist, reduced these responses by 61+/- 6% (p < 0.05). Surprisingly, SQ29548, 1 microM, a selective PGH2 /thromboxane A2 receptor blocker, also reduced angiotensin II responses (62 +/- 4%; p < 0.05). BQ610 1 microM, an ETA -selective receptor antagonist, was without effect, but BQ788 1 microM, an ETB -selective antagonist, attenuated the response by 70 +/- 4% (p < 0.05). In ARF, in contrast to angiotensin II, vasoconstriction by endothelin-1 (5-25 ng) was diminished. Saralasin further attenuated endothelin-1 response by 65 +/- 2% (p < 0.05), whereas SQ29548 was without effect. BQ788 reduced the responses by 67 +/- 7% (p < 0.05), whereas BQ610 was without effect (42 +/- 30%; p > 0.05). BQ610 and BQ788 combination further reduced vasoconstriction by 89 +/- 3% (p < 0.05). Responses to U46619 were not changed in ARF. However, saralasin and BQ788, but not BQ610, attenuated its vasoconstrictor action. We conclude that vascular responses in ARF may be attributed to enhanced responses to angiotensin II through activation of ETB and/or PGH2 /thromboxane A2 receptors. We also suggest that the vasoconstrictor response to endothelin-1 in ARF is predominantly ETB receptor-mediated.

Angiotensin II and atherosclerosis

Numerous clinical and laboratory data are now available supporting the hypothesis that the renin-angiotensin system is mechanistically relevant in the pathogenesis of atherosclerosis. The traditional role of the renin-angiotensin system in the context of blood pressure regulation has been modified to incorporate the concept that angiotensin II (Ang II) is a potent proinflammatory agent. In vascular cells, Ang II is a potent stimulus for the generation of reactive oxygen species. As a result, Ang II upregulates the expression of many redox-sensitive cytokines, chemokines, and growth factors that have been implicated in the pathogenesis of atherosclerosis. Extensive data now confirm that inhibition of the renin-angiotensin system inhibits atherosclerosis in animal models as well as in humans. These studies provide mechanistic insights into the precise role of Ang II in atherosclerosis and suggest that pharmacologic interventions involving the renin-angiotensin system may be of fundamental importance in the treatment and prevention of atherosclerosis.