Increased chymase-dependent angiotensin II formation in human atherosclerotic aorta

The up-regulation of endothelin-1 and down-regulation of miRNA-125a-5p, -155, and -199a/b-3p in human atherosclerotic coronary artery

BACKGROUND

Previous studies have reported important roles of endothelin-1 (ET-1) and angiotensin II (Ang II) in the pathogenesis of atherosclerosis. However, the expression of these two proteins and the underlying mechanisms in human atherosclerotic coronary arteries are largely unknown.

METHODS

We examined the expression of ET-1 and Ang II in pericardial fluid and coronary arteries from 25 individuals (n = 25) using enzyme-linked immuno sorbent assay (ELISA) and immunohistochemistry. Twelve patients died from acute coronary syndrome were classified as atherosclerotic plaque group (AP group) (n = 12), while 13 patients died from other causes were classified as non-AP group (n = 13). Meanwhile, we performed reverse transcription-polymerase chain reaction (RT-PCR) to measure the expression of six microRNAs targeting ET-1 in formalin-fixed, paraffin-embedded coronary arteries.

RESULTS

Our data showed that ET-1 was significantly higher in both pericardial fluid and coronary arteries from AP group. However, Ang II showed no significant difference in pericardial fluid between the two groups, while it was even significantly lower in coronary arteries from AP group. Besides, miR-125a-5p, miR-155, and miR-199a/b-3p, which suppressed the expression of ET-1, were down-regulated in the coronary arteries from AP group.

CONCLUSION

The up-regulation of ET-1, regulated by miR-125a-5p, miR-155, and miR-199a/b-3p, indicated that ET-1 played an important role in human coronary atherosclerosis.

SUMMARY

We focused on the human coronary arteries with atherosclerotic plaques. The expression of ET-1, as well as its upstream miRNAs, was determined. Unlike any of previous study regarding miRNAs expression, we could exclude the discrepancy of artery-bed-specific miRNA expression. Besides, our data indicated, to some degree, that ET-1 might play a more vital role than Ang II in coronary atherosclerosis.

Donor Artery Aneurysm Formation following the Ligation of Haemodialysis Arteriovenous Fistula: A Systematic Review and Case Reports

Purpose

The purpose of this study is to investigate the pathogenesis, presentation and diagnosis of donor artery aneurysm formation following arteriovenous fistula (AVF) ligation and reach a consensus on their management.

Methods

A systematic review of literature in Ovid, MedLine, Embase, Scopus and CINHAL in the English language from 1951 to 2014 was performed. This was accompanied by two case reports. A total of 12 articles with 23 case reports were identified. Variables including patient's demographics, signs, symptoms, fistula type, duration of fistula use, time to aneurysm formation, renal transplantation, diagnostic modality, aneurysm type and size, type of surgery and outcome were reviewed.

Results

The data demonstrate a male predominance (5:1) and a median age of 47 years (range, 27-75 years). The median duration of access was 54 months (range, 6-300 months). The median time from ligation to aneurysm was 120 months (range, 6-280 months). The commonest aneurysm was of the brachial artery (BA, n = 21, 84%). The commonest type of AVF was radiocephalic (n = 15, 60%) followed by brachiocephalic AVF (n = 9, 36%). The management of choice was aneurysmectomy followed by interposition vein grafting (n = 12, 50%) with a median reported patency of 12 months (range, 1-38 months). This was followed by polytetrafluoroethylene (PTFE) grafting (n = 6, 25%) with a median reported patency of 6 months (range, 1-48 months).

Conclusions

The pathogenesis of donor artery aneurysms remains contentious. This review suggests that duplex is the investigative modality of choice and aneurysmectomy with interposition grafting is preferred over bypass.

Generation of a new congenic mouse strain with enhanced chymase expression in mast cells

Mast cells are effector cells best known for their roles in IgE-associated allergy, but they also play a protective role in defense against pathogens. These cells express high levels of proteases including chymase, tryptase and carboxypeptidase. In the present study, we identified a congenic strain of C57BL/6 mice expressing an extraordinarily high level of chymases Mcp-2 and Mcp-4 in mast cells. The overexpression was associated with variant Mcp-2 and Mcp-4 genes originated from DBA/2 mice that also expressed high levels of the two enzymes. Real time PCR analysis revealed that Mcp-2 and Mcp-4 were selectively overexpressed as tryptases, Cpa3 and several other chymases were kept at normal levels. Reporter gene assays demonstrated that single-nucleotide polymorphisms (SNPs) in the promoter region of Mcp-2 gene may be partly responsible for the increased gene transcription. Our study provides a new model system to study the function of mast cell chymases. The data also suggest that expression of chymases differs considerably in different strains of mice and the increased chymase activity may be responsible for some unique phenotypes observed in DBA/2 mice.

Hypoxia-induced collagen synthesis of human lung fibroblasts by activating the angiotensin system

The exact molecular mechanism that mediates hypoxia-induced pulmonary fibrosis needs to be further clarified. The aim of this study was to explore the effect and underlying mechanism of angiotensin II (Ang II) on collagen synthesis in hypoxic human lung fibroblast (HLF) cells. The HLF-1 cell line was used for in vitro studies. Angiotensinogen (AGT), angiotensin converting enzyme (ACE), angiotensin II type 1 receptor (AT1R) and angiotensin II type 2 receptor (AT2R) expression levels in human lung fibroblasts were analysed using real-time polymerase chain reaction (RT-PCR) after hypoxic treatment. Additionally, the collagen type I (Col-I), AT1R and nuclear factor κappaB (NF-κB) protein expression levels were detected using Western blot analysis, and NF-κB nuclear translocation was measured using immunofluorescence localization analysis. Ang II levels in HLF-1 cells were measured with an enzyme-linked immunosorbent assay (ELISA). We found that hypoxia increased Col-I mRNA and protein expression in HLF-1 cells, and this effect could be inhibited by an AT1R or AT2R inhibitor. The levels of NF-κB, RAS components and Ang II production in HLF-1 cells were significantly increased after the hypoxia exposure. Hypoxia or Ang II increased NF-κB-p50 protein expression in HLF-1 cells, and the special effect could be inhibited by telmisartan (TST), an AT1R inhibitor, and partially inhibited by PD123319, an AT2R inhibitor. Importantly, hypoxia-induced NF-κB nuclear translocation could be nearly completely inhibited by an AT1R or AT2R inhibitor. Furthermore pyrrolidine dithiocarbamate (PDTC), a NF-κB blocker, abolished the expression of hypoxia-induced AT1R and Col-I in HLF-1 cells. Our results indicate that Ang II-mediated NF-κB signalling via ATR is involved in hypoxia-induced collagen synthesis in human lung fibroblasts.

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.

Chymase inhibition and cardiovascular protection

Human chymase, an angiotensin II-forming chymotrypsin-like serine proteinase, posses various biological actions mediating through local angiotensin II formation in the tissue level of many cardiovascular organs. Our previous experimental data have shown that chymase inhibitor increased a survival rate of the hamster post-myocardial infarction model with concomitant improvements of the cardiac function and hypertrophy, decreased hamster aortic atherosclerotic lesion induced by a high fat diet and improved hamster diabetic nephropathy decreasing the proteinuria and increased renal antiotensin II levels. Although chymase inhibitor has not yet been applied for clinical use, clinical cardiovascular diseases above mentioned appear to be the target of chymase inhibitor. The related basal and clinical circumstances are discussed in this review article for chymase inhibitor.

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.

Contributions of leukocyte angiotensin-converting enzyme to development of atherosclerosis

OBJECTIVE

This study determined the role of angiotensin-converting enzyme (ACE) on the development of angiotensin I-induced atherosclerosis and the contribution of leukocyte-specific expression of this enzyme.

APPROACH AND RESULTS

To define the contribution of ACE-dependent activity to angiotensin II synthesis in atherosclerotic development, male low-density lipoprotein receptor(-/-) mice were fed a fat-enriched diet and infused with either angiotensin I or angiotensin II. The same infusion rate of these peptides had equivalent effects on atherosclerotic development. Coinfusion of an ACE inhibitor, enalapril, ablated angiotensin I-augmented atherosclerosis but had no effect on angiotensin II-induced lesion development. ACE protein was detected in several cell types in atherosclerotic lesions, with a predominance in macrophages. This cell type secreted angiotensin II, which was ablated by ACE inhibition. To study whether leukocyte ACE contributed to atherosclerosis, irradiated male low-density lipoprotein receptor(-/-) mice were repopulated with bone marrow-derived cells from either ACE(+/+) or ACE(-/-) mice and fed the fat-enriched diet for 12 weeks. Chimeric mice with ACE deficiency in bone marrow-derived cells had modestly reduced atherosclerotic lesions in aortic arches but had no effects in aortic roots.

CONCLUSIONS

ACE mediates angiotensin I-induced atherosclerosis, and ACE expression in leukocytes modestly contributes to atherosclerotic development in hypercholesterolemic mice.

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

BACKGROUND AND AIM

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Mast cells and vascular diseases

Mast cells are increasingly being recognized as effector cells in many cardiovascular conditions. Many mast-cell-derived products such as tryptase and chymase can, through their enzymic action, have detrimental effects on blood vessel structure while mast cell-derived mediators such as cytokines and chemokines can perpetuate vascular inflammation. Mice lacking mast cells have been developed and these are providing an insight into how mast cells are involved in cardiovascular diseases and, as knowledge increase, mast cells may become a viable therapeutic target to slow progression of cardiovascular disease.

Locally applied leptin induces regional aortic wall degeneration preceding aneurysm formation in apolipoprotein E-deficient mice

OBJECTIVE

Leptin promotes atherosclerosis and vessel wall remodeling. As abdominal aortic aneurysm (AAA) formation involves tissue remodeling, we hypothesized that local leptin synthesis initiates and promotes this process.

METHODS AND RESULTS

Human surgical AAA walls were analyzed for antigen and mRNA levels of leptin and leptin receptor, as well as mRNA for matrix metalloproteinases (MMP)-9 and MMP-12. Leptin and leptin receptor antigen were evident in all AAAs, and leptin, MMP-9, and MMP-12 mRNA was increased relative to age-matched nondilated controls. To simulate in vivo local leptin synthesis, ApoE(-/-) mice were subjected to a paravisceral periaortic application of low-dose leptin. Leptin-treated aortas exhibited decreased transforming growth factor-β and increased MMP-9 mRNA levels 5 days after surgery, and leptin receptor mRNA was upregulated by day 28. Serial ultrasonography demonstrated accelerated regional aortic diameter growth after 28 days, correlating with local medial degeneration, increased MMP-9, MMP-12, and periadventitial macrophage clustering. Furthermore, the combination of local periaortic leptin and systemic angiotensin II administration augmented medial MMP-9 synthesis and aortic aneurysm size.

CONCLUSIONS

Leptin is locally synthesized in human AAA wall. Paravisceral aortic leptin in ApoE(-/-) mice induces local medial degeneration and augments angiotensin II-induced AAA, thus suggesting novel mechanistic links between leptin and AAA formation.

Mast cell chymase and tryptase in abdominal aortic aneurysm formation

Mast cells (MCs) are implicated in the pathogenesis of atherosclerosis and abdominal aortic aneurysm (AAA). MC-specific chymase and tryptase play important roles in inducing endothelial cell expression of adhesion molecules and chemokines to promote leukocyte recruitment, degrading matrix proteins and activating protease-activated receptors to trigger smooth muscle cell apoptosis, and activating other proteases to degrade medial elastin and to enhance angiogenesis. In experimental AAA, the absence or pharmacological inhibition of chymase or tryptase reduced AAA formation and associated arterial pathologies, proving that these MC proteases participate directly in AAA formation. Increased levels of these proteases in human AAA lesions and in plasma from AAA patients suggest that these proteases are also essential to human AAA pathogenesis. Development of chymase or tryptase inhibitors or their antibodies may have therapeutic potential among affected human subjects.

Association of polymorphisms in prolylcarboxypeptidase and chymase genes with essential hypertension in the Chinese Han population

INTRODUCTION

The prolylcarboxypeptidase (PRCP) gene encodes a membrane protein that acts on angiotensin II (Ang II) and kallikrein to release vasoactive peptides. The chymase (CMA1) gene is important for Ang II generation. Therefore, the two genes might be involved in the pathogenesis of essential hypertension (EH).

MATERIALS AND METHODS

Eleven tag single nucleotide polymorphisms (SNPs) in the PRCP gene and four tag SNPs and G-1903A (rs1800875) polymorphism in the CMA1 gene were genotyped in the Chinese Han population (n=1020) using a polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

In the PRCP gene, single site analyses indicated that the rs7104980 G allele was a susceptible factor for EH (adjusted odds ratio (OR)=1.98, 95% confidence interval (CI) 1.62-2.43, p=0.3×10(-10)). The protective effect of Hap3 GAGCACTAACA was observed without carrying the susceptible rs7104908 G allele (OR=0.67, 95% CI 0.56-0.81, p=0.3×10(-4)) by haplotype analyses. In the case of the CMA1 gene, no associations with EH were found through single site analyses. However, haplotype analyses showed that Hap16 TTTA significantly increased the risk of EH with OR=3.15 (p=0.0002) which may be driven by interaction with a nearby SNP combination.

CONCLUSIONS

The present results indicated PRCP rs7104980 can be considered as a marker for EH and Hap3 GAGCACTAACA (PRCP) and Hap16 TTTA (CMA1) might be associated with EH in Chinese Han population.

Role of mast cell chymase and tryptase in the progression of atherosclerosis: study in 44 autopsied cases

The aim of this study was to describe the role of mast cell chymase and tryptase in the progression of atherosclerosis. Forty-four sections of aortas were obtained from autopsies. We assessed the macroscopic degree of atherosclerosis, microscopic intensity of lipid deposition in the tunica intima, percentage of collagen in the tunica intima, and density of immunostained mast cells. There was no significant difference between the density of mast cell tryptase and chymase concerning ethnicity, sex, cause of death, or degree of atherosclerosis. The density of mast cell chymase was significantly higher in the nonelderly group. The percentage of collagen was significantly higher in elderly patients. There was a positive and significant correlation between the degree of macroscopic atherosclerosis and lipidosis, the density of mast cell chymase and the percentage of collagen, the density of mast cell tryptase and the percentage of collagen, and lipidosis and the density of mast cell tryptase. The degree of macroscopic lesion of atherosclerosis increased proportionally with the increase in the density of mast cell chymase and tryptase and in the intensity of lipid deposition and with the percentage of collagen in the atherosclerotic plaques. Thus, mast cells may play a crucial role in aggravating atherosclerotic lesions.

Targeting cardiac mast cells: pharmacological modulation of the local renin-angiotensin system

Enhanced production of angiotensin II and excessive release of norepinephrine in the ischemic heart are major causes of arrhythmias and sudden cardiac death. Mast cell-dependent mechanisms are pivotal in the local formation of angiotensin II and modulation of norepinephrine release in cardiac pathophysiology. Cardiac mast cells increase in number in myocardial ischemia and are located in close proximity to sympathetic neurons expressing angiotensin AT1- and histamine H3-receptors. Once activated, cardiac mast cells release a host of potent pro-inflammatory and pro-fibrotic cytokines, chemokines, preformed mediators (e.g., histamine) and proteases (e.g., renin). In myocardial ischemia, angiotensin II (formed locally from mast cell-derived renin) and histamine (also released from local mast cells) respectively activate AT1- and H3-receptors on sympathetic nerve endings. Stimulation of angiotensin AT1-receptors is arrhythmogenic whereas H3-receptor activation is cardioprotective. It is likely that in ischemia/reperfusion the balance may be tipped toward the deleterious effects of mast cell renin, as demonstrated in mast cell-deficient mice, lacking mast cell renin and histamine in the heart. In these mice, no ventricular fibrillation occurs at reperfusion following ischemia, as opposed to wild-type hearts which all fibrillate. Preventing mast cell degranulation in the heart and inhibiting the activation of a local renin-angiotensin system, hence abolishing its detrimental effects on cardiac rhythmicity, appears to be more significant than the loss of histamine-induced cardioprotection. This suggests that therapeutic targets in the treatment of myocardial ischemia, and potentially congestive heart failure and hypertension, should include prevention of mast cell degranulation, mast cell renin inhibition, local ACE inhibition, ANG II antagonism and H3-receptor activation.

Enzymatic processing of angiotensin peptides by human glomerular endothelial cells

The intraglomerular renin-angiotensin system (RAS) is linked to the pathogenesis of progressive glomerular diseases. Glomerular podocytes and mesangial cells play distinct roles in the metabolism of angiotensin (ANG) peptides. However, our understanding of the RAS enzymatic capacity of glomerular endothelial cells (GEnCs) remains incomplete. We explored the mechanisms of endogenous cleavage of ANG substrates in cultured human GEnCs (hGEnCs) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and isotope-labeled peptide quantification. Overall, hGEnCs metabolized ANG II at a significantly slower rate compared with podocytes, whereas the ANG I processing rate was comparable between glomerular cell types. ANG II was the most abundant fragment of ANG I, with lesser amount of ANG-(1-7) detected. Formation of ANG II from ANG I was largely abolished by an ANG-converting enzyme (ACE) inhibitor, whereas ANG-(1-7) formation was decreased by a prolylendopeptidase (PEP) inhibitor, but not by a neprilysin inhibitor. Cleavage of ANG II resulted in partial conversion to ANG-(1-7), a process that was attenuated by an ACE2 inhibitor, as well as by an inhibitor of PEP and prolylcarboxypeptidase. Further fragmentation of ANG-(1-7) to ANG-(1-5) was mediated by ACE. In addition, evidence of aminopeptidase N activity (APN) was demonstrated by detecting amelioration of conversion of ANG III to ANG IV by an APN inhibitor. While we failed to find expression or activity of aminopeptidase A, a modest activity attributable to aspartyl aminopeptidase was detected. Messenger RNA and gene expression of the implicated enzymes were confirmed. These results indicate that hGEnCs possess prominent ACE activity, but modest ANG II-metabolizing activity compared with that of podocytes. PEP, ACE2, prolylcarboxypeptidase, APN, and aspartyl aminopeptidase are also enzymes contained in hGEnCs that participate in membrane-bound ANG peptide cleavage. Injury to specific cell types within the glomeruli may alter the intrarenal RAS balance.

Do Adventitial Mast Cells Contribute to the Pathogenesis of Ascending Thoracic Aorta Aneurysm?

The precise pathogenesis of the ascending aortic aneurysm (AscAA) remains to be determined. Mast cells in the adventitia of human AscAA lesions may play a role in this pathogenesis. Adventitial mast cell density per 10 high-power fields (0.25 mm2) was assessed in multiple biopsy samples, from aneurysmal aortic sections (n = 41) and control (nondilated) aortic specimens (n = 50), stained by orcein-Giemsa method, an inexpensive (<$1) method. In a multivariable adjusted logistic regression model, using AscAA as the dependent variable, mast cell density was found to be an independent predictor of AscAA occurrence (odds ratio = 2.21; 95% confidence interval = 1.58-3.08; P < .001). Receiver operating characteristic curve analysis showed that the proposed cutoff value of ≥3 mast cells per 10 high-power fields was very sensitive to detect AscAA occurrence, yielding a sensitivity of 90% with a specificity of 80%. In conclusion, a significant increase in the number of mast cells in the adventitia of human ascending aortic lesions proposes a role for these cells in the pathogenesis of AscAA.

Emerging role of mast cells and macrophages in cardiovascular and metabolic diseases

Mast cells are essential in allergic immune responses. Recent discoveries have revealed their direct participation in cardiovascular diseases and metabolic disorders. Although more sophisticated mechanisms are still unknown, data from animal studies suggest that mast cells act similarly to macrophages and other inflammatory cells and contribute to human diseases through cell-cell interactions and the release of proinflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. Reduced cardiovascular complications and improved metabolic symptoms in animals receiving over-the-counter antiallergy medications that stabilize mast cells open another era of mast cell biology and bring new hope to human patients suffering from these conditions.

Association between SNP rs1800875, serum chymase and immunoglobulin E levels in patients with coronary heart disease

OBJECTIVE

The gene for mast cell chymase (CMA1) is an ideal candidate for investigating the genetic predisposition to coronary heart disease (CHD), as activated mast cells have been found to be present in a greater proportion in the shoulder region of atheroma than in normal coronary intimae. Previous studies have indicated that CMA1 promoter polymorphism rs1800875 may be involved in regulating immunoglobulin E (IgE) levels in patients with eczema, and it is associated with the progression of immunoglobulin A nephropathy.

METHODS

The association between single nucleotide polymorphism (SNP) rs1800875, serum chymase, and serum IgE levels was examined in 175 CHD subjects and 95 non-CHD subjects.

RESULTS

Statistical analysis indicated no significant difference in allele frequency between CHD and non-CHD. However, a significant association was found between CMA1 genotypes and total IgE levels in CHD subjects. Meanwhile, crossover analysis revealed that, in GG homozygotes, CHD risk was nearly six times higher in those with IgE (U/ml) level <2.58 (natural logarithm conversion), while no association was found with chymase level.

CONCLUSIONS

Polymorphism rs1800875 of CMA1 may be associated with serum IgE level in CHD subjects, but not with chymase level in both groups. In GG homozygotes, high IgE level is a protective factor against coronary disease.

Effects of angiotensin receptor blocker and calcium channel blocker on experimental abdominal aortic aneurysms in a hamster model

Remodeling in the abdominal aortic wall results in abdominal aortic aneurysm (AAA) formation. Many patients with AAA are prescribed antihypertensive drugs. However, the effects of antihypertensive drugs other than their effects on blood pressure control are rarely reported. In this study, we investigated the effects of these drugs on changes in the levels of matrix metalloproteinases (MMPs) and on AAA formation. Experimental AAAs were created in a hamster model by wrapping the abdominal aorta with elastase gauze. Olmesartan medoxomil (angiotensin II receptor antagonist) or azelnidipine (calcium channel antagonist) was administered to the hamsters and then we evaluated the aortic diameter, performed histological analysis, and analyzed the production of MMP-2 and MMP-9 by gelatin zymography. The expansion rate of the aortic diameter was smaller in both treatment groups than in the control group. Elastica van Gieson (EVG) staining showed structural preservation of elastin lamellae in both treatment groups. The active MMP-9 level decreased in both the olmesartan group and the azelnidipine group. Reducing MMP-9 production is important for suppression of AAA formation. Both olmesartan medoxomil and azelnidipine decreased MMP-9 activity, which suppressed degradation of the MMPs and inhibited AAA formation. There are different cascades that determine the production of MMP-9.

Mast cells: pivotal players in cardiovascular diseases

The clinical outcome of cardiovascular diseases as myocardial infarction and stroke are generally caused by rupture of an atherosclerotic plaque. However, the actual cause of a plaque to rupture is not yet established. Interestingly, pathology studies have shown an increased presence of the mast cell, an important inflammatory effector cell in allergy and host defense, in (peri)vascular tissue during plaque progression, which may point towards a causal role for mast cells. Very recent data in mouse models show that mast cells and derived mediators indeed can profoundly impact plaque progression, plaque stability and acute cardiovascular syndromes such as vascular aneurysm or myocardial infarction. In this review, we discuss recent evidence on the role of mast cells in the progression of cardiovascular disorders and give insight in the therapeutic potential of modulation of mast cell function in these processes to improve the resilience of a plaque to rupture.

Contributions of ACE and mast cell chymase to endogenous angiotensin II generation and leucocyte recruitment in vivo

AIMS

In vitro studies suggest that mast cell chymase (MCP) is more important than angiotensin-converting enzyme (ACE) for generating angiotensin II (Ang II) within the cardiovascular system. We investigated in vivo the relative contributions of ACE and MCP to leucocyte recruitment induced by endogenously generated Ang II.

METHODS AND RESULTS

Exposure of the murine cremasteric microcirculation of C57BL/6 mice to Ang I (100 nM for 4 h) induced leucocyte-endothelium interactions. Either losartan (an Ang II receptor-1 antagonist, AT(1)) or enalapril (an ACE inhibitor), but not chymostatin (a chymase inhibitor), inhibited Ang I-induced responses. Mast cell degranulation with compound 48/80 (CMP48/80, 1 μg/mL) also induced leucocyte adhesion but this was only weakly affected by the inhibitors. When Ang I and CMP48/80 were co-administered, AT(1B) receptor expression was increased, MCP-4 was found surrounding the vessel wall, and ACE was detected in the endothelium. Ang I + CMP48/80 induced enhanced leucocyte adhesion that was attenuated by losartan, enalapril, enalapril + chymostatin, and cromolyn (a mast cell stabilizer). The use of male mast cell-deficient WBB6F1/J-Kit(w)/Kit(w-v) mice (C57BL/6 background) confirmed these findings.

CONCLUSION

In vivo, Ang II is primarily generated by ACE under basal conditions, but in inflammatory conditions, the release of MCP amplifies local Ang II concentrations and the associated inflammatory process. Thus, AT(1) receptor antagonists may be more effective than ACE inhibitors for treating ongoing Ang II-mediated vascular inflammation.

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.

Targets of chymase inhibitors

INTRODUCTION

Chymase converts angiotensin I to angiotensin II and it can also convert precursors of TGF-β and MMP-9 to their active forms. Therefore, diseases related to angiotensin II TGF-β, and MMP-9 could potentially be treated with chymase inhibitors.

AREAS COVERED

This review discusses the appropriate targets and safety of chymase inhibitors. Six diseases with notable mortality or morbidity as targets of chymase inhibitors are focused on; abdominal aortic aneurysms (AAAs), nephropathy and retinopathy, cardiomyopathy, nonalcoholic steatohepatitis (NASH), organ fibrosis and intestinal diseases.

EXPERT OPINION

If chymase inhibition proves to be a useful strategy for the attenuation of angiotensin II, TGF-β and MMP-9 in vivo, the application of chymase inhibitors is likely to become widespread in various diseases in the clinical setting. Chymase inhibitors are anticipated not to interfere with the homeostasis of resting tissues, that is, those not affected by injury or inflammation.

Mast cells and metabolic syndrome

Mast cells are critical effectors in the development of allergic diseases and in many immunoglobulin E-mediated immune responses. These cells exert their physiological and pathological activities by releasing granules containing histamine, cytokines, chemokines, and proteases, including mast cell-specific chymase and tryptase. Like macrophages and T lymphocytes, mast cells are inflammatory cells, and they participate in the pathogenesis of inflammatory diseases such as cardiovascular complications and metabolic disorders. Recent observations suggested that mast cells are involved in insulin resistance and type 2 diabetes. Data from animal models proved the direct participation of mast cells in diet-induced obesity and diabetes. Although the mechanisms by which mast cells participate in these metabolic diseases are not fully understood, established mast cell pathobiology in cardiovascular diseases and effective mast cell inhibitor medications used in pre-formed obesity and diabetes in experimental models offer hope to patients with these common chronic inflammatory diseases. This article is part of a Special Issue entitled: Mast cells in inflammation.

Mast cell chymase inhibition reduces atherosclerotic plaque progression and improves plaque stability in ApoE-/- mice

AIMS

mast cells have been shown to accumulate in the adventitia of human atherosclerotic plaques and were recently demonstrated by us to contribute to plaque progression and instability. In this study, we investigated whether selective inhibition of mast cell chymases would affect the lesion development and stability.

METHODS AND RESULTS

the protease inhibitor RO5066852 appeared to be a potent inhibitor of chymase activity in vitro and ex vivo. With this inhibitor, we provide three lines of evidence that chymase inhibition can prevent many pro-atherogenic activities. First, oral administration of RO5066852 reduced spontaneous atherosclerosis in the thoracic aorta of apoE(-/-) mice. Second, chymase inhibition prevented the accelerated plaque progression observed in apoE(-/-) mice that were exposed to repetitive episodes of systemic mast cell activation. Furthermore, RO5066852 enhanced lesional collagen content and reduced necrotic core size. Third, RO5066852 treatment almost completely normalized the increased frequency and size of intraplaque haemorrhages observed in apoE(-/-) mice after acute perivascular mast cell activation in advanced atherosclerosis.

CONCLUSION

our data indicate that chymase inhibition can inhibit pro-atherogenic and plaque destabilizing effects which are associated with perivascular mast cell activation. Our study thus identifies pharmacological chymase inhibition as a potential therapeutic modality for atherosclerotic plaque stabilization.

Modulation of the renin-angiotensin-aldosterone system in sepsis: a new therapeutic approach?

IMPORTANCE OF THE FIELD

Severe sepsis is characterized by relative hypotension associated with a high cardiac output, peripheral vasodilation, and organ dysfunction. The renin-angiotensin-aldosterone system (RAAS) is primarily activated to increase blood pressure, but recently potential pro-inflammatory effects of angiotensin II have attracted interest because of the reported association between angiotensin II levels and organ failure and mortality in sepsis. RAAS antagonists could represent a new therapeutic option in this setting.

AREAS COVERED IN THIS REVIEW

The role of RAAS activation in severe sepsis and septic shock, and the potential benefits (and risks) of using RAAS antagonists.

WHAT THE READER WILL GAIN

Insight into RAAS function in severe sepsis and the potential for RAAS inhibitors to be used as an adjunctive therapy in patients with severe sepsis, with discussion of promising results from animal models of sepsis.

TAKE HOME MESSAGE

Use of RAAS antagonists is an emerging therapeutic option in severe sepsis because these agents may reduce endothelial damage, organ failure, and mortality. However, timing of administration of RAAS antagonists is important because reduced RAAS function may contribute to refractive hypotension later on in septic shock and benefits of RAAS antagonists seem to be restricted to the early phases of sepsis.

Homocysteine-induced oxidative stress upregulates chymase in mouse mastocytoma cells

Reactive oxygen species (ROS) such as hydrogen peroxide (H(2)O(2)), O(*-)(2) and OH(*) participate in the pathogenesis of ischemia/reperfusion injury, inflammation and atherosclerosis. Our previous studies have suggested that increased angiotensin II (Ang II)-forming chymase may be involved in the development of atherosclerosis. However, the regulatory mechanism of chymase expression has not yet been clarified. In this study, we tested whether oxidative stress upregulates mouse mast cell proteinase chymase, mouse mast cell proteinase (MMCP)-5 or MMCP-4. We also examined the expression and activity of these proteins after treatment. Cultured mouse mastocytoma cells (MMC) displaying chymase-dependent Ang II-forming activity were treated with H(2)O(2) and several aminothiols with or without anti-oxidants. The levels of MMCP-5 and MMCP-4 expression were determined by quantitative RT-PCR; the level of chymase-dependent Ang II-forming activity was measured by high performance liquid chromatography using Ang I as a substrate. Treatment of MMC with homocysteine (0.1-3 mmol l(-1)) significantly increased MMCP-5 and MMCP-4 expression, as well as Ang II-forming activity. These effects were significantly inhibited by the addition of catalase and further suppressed by the combination of catalase and superoxide dismutase. Incubation with hydrogen peroxide alone caused a significant increase in Ang II-forming activity, which was completely suppressed by co-treatment with catalase. Furthermore, MMCP-5 and MMCP-4 expression levels were drastically suppressed and chymase induction by homocysteine was diminished under the GATA-inhibited condition. Homocysteine increased mast cell chymase expression and activity through the mechanism of oxidative stress. Our results suggest that there is a biochemical link between oxidative stress and the local Ang II-forming system.

Addressing the theoretical and clinical advantages of combination therapy with inhibitors of the renin-angiotensin-aldosterone system: antihypertensive effects and benefits beyond BP control

AIMS

This article reviews the importance of the renin-angiotensin-aldosterone system (RAAS) in the cardiometabolic continuum; presents the pros and cons of dual RAAS blockade with angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs); and examines the theoretical and practical benefits supporting the use of direct renin inhibitors (DRIs) in combination with ACEIs or ARBs.

MAIN METHODS

The author reviewed the literature for key publications related to the biochemical physiology of the RAAS and the pharmacodynamic effects of ACEIs, ARBs, and DRIs, with a particular focus on dual RAAS blockade with these drug classes.

KEY FINDINGS

Although ACEI/ARB combination therapy produces modest improvement in BP, it has not resulted in the major improvements predicted given the importance of the RAAS across the cardiorenal disease continuum. This may reflect the fact that RAAS blockade with ACEIs and/or ARBs leads to exacerbated renin release through loss of negative-feedback inhibition, as well as ACE/aldosterone escape through RAAS and non-RAAS-mediated mechanisms. Plasma renin activity (PRA) is an independent predictor of morbidity and mortality, even for patients receiving ACEIs and ARBs. When used alone or in combination with ACEIs and ARBs, the DRI aliskiren effectively reduces PRA. Reductions in BP are greater with these combinations, relative to the individual components alone.

SIGNIFICANCE

It is possible that aliskiren plus either an ACEI or ARB may provide greater RAAS blockade than monotherapy with ACEIs or ARBs, and lead to additive improvement in BP and clinically important outcomes.

NOX and inflammation in the vascular adventitia

Vascular inflammation has traditionally been thought to be initiated at the luminal surface and progress through the media toward the adventitial layer. In recent years, however, evidence has emerged suggesting that the vascular adventitia is activated early in a variety of cardiovascular diseases and that it plays an important role in the initiation and progression of vascular inflammation. Adventitial fibroblasts have been shown to produce substantial amounts of NAD(P)H oxidase-derived reactive oxygen species (ROS) in response to vascular injury. Additionally, inflammatory cytokines, lipids, and various hormones, implicated in fibroblast proliferation and migration, lead to recruitment of inflammatory cells to the adventitial layer and impairment of endothelium-dependent relaxation. Early in the development of vascular disease, there is clear evidence for progression toward a denser vasa vasorum which delivers oxygen and nutrients to an increasingly hypoxic and nutrient-deficient media. This expanded vascularization appears to provide enhanced delivery of inflammatory cells to the adventitia and outer media. Combined adventitial fibroblast and inflammatory cell-derived ROS therefore are expected to synergize their local effect on adventitial parenchymal cells, leading to further cytokine release and a feed-forward propagation of adventitial ROS production. In fact, data from our laboratory and others suggest a broader paracrine positive feedback role for adventitia-derived ROS in medial smooth muscle cell hypertrophy and neointimal hyperplasia. A likely candidate responsible for the adventitia-derived paracrine signaling across the vessel wall is the superoxide anion metabolite hydrogen peroxide, which is highly stable, cell permeant, and capable of activating downstream signaling mechanisms in smooth muscle cells, leading to phenotypic modulation of smooth muscle cells. This review addresses the role of adventitial NAD(P)H oxidase-derived ROS from a nontraditional, perivascular vantage of promoting vascular inflammation and will discuss how ROS derived from adventitial NAD(P)H oxidases may be a catalyst for vascular remodeling and dysfunction.

Position of fixed‐dose combinations containing an AT1‐receptor blocker and a thiazide diuretic

Treatment of hypertension remains a difficult task despite the availability of different types of medications lowering blood pressure by different mechanisms. In order to reach the target blood pressures recommended today combination therapy is required in most patients. The co-administration of two drugs with different impacts on the cardiovascular system markedly increases the antihypertensive effectiveness without altering adversely tolerability. Fixed low-dose combinations are becoming a valuable option not only as second-line, but also as first-line therapy. In this respect the co-administration of thiazide diuretic with an AT(1)-receptor blocker is particularly appealing. The diuretic-induced decrease in total body sodium activates the renin-angiotensin system, thus rendering blood pressure maintenance angiotensin II-dependent. During blockade of the renin-angiotensin system low doses of thiazides generally suffice, allowing the prevention of undesirable metabolic effects. Also, blockade of the AT(1)-receptor, particularly when angiotensin II production is enhanced in response to diuretic therapy, is expected to be beneficial, since angiotensin II seems to contribute importantly to the pathogenesis of cardiovascular and renal complications of hypertension.

Chymase activity is closely related with plaque vulnerability in a hamster model of atherosclerosis

OBJECTIVE

To test the hypothesis that stimulation of chymase secretion may contribute to plaque vulnerability and inhibition of chymase activity may enhance plaque stability.

METHODS AND RESULTS

Sixty eight-week-old male Syrian golden hamsters were randomly divided into normal control group, high-cholesterol (HC) treated group, HC+ovalbumin treated group and HC+tranilast treated group. The normal control group received a normal diet while the other three intervention groups received a high-cholesterol diet for 15 weeks. Hamsters in the HC+ovalbumin treated group underwent transcatheter pharmacological triggering at the end of week 15 after antigen sensitization and those in the HC+tranilast treated group were given tranilast intragastrically for 3 weeks before euthanasia. Serological, ultrasonographic, pathologic, immunohistochemical, and gene expression studies were performed in all animals. The total number of mast cells, proportion of degranulated mast cells and the number of extracellular granules in plaques, the apoptosis rate of vascular smooth cells, the local activities of chymase, the concentration of Ang II and the expression levels of inflammatory markers as well as plaque vulnerability index all increased significantly in HC+ovalbumin treated group, but remarkably decreased in HC+tranilast treated group, in comparison with the HC treated group. These results suggest that stimulation of chymase secretion contributes to plaque vulnerability while inhibition of chymase activity enhances plaque stability. We conclude that chymase activity provides a promising therapeutic target in the stabilization of atherosclerotic plaques.

Angiotensin II upregulates acyl-CoA:cholesterol acyltransferase-1 via the angiotensin II Type 1 receptor in human monocyte-macrophages

Angiotensin II (Ang II) is known to accelerate the progression of macrophage-driven atherosclerotic lesions. Acyl-CoA:cholesterol acyltransferase-1 (ACAT1) converts intracellular free cholesterol into cholesterol ester (CE) for storage in lipid droplets, and promotes foam cell formation in atherosclerotic lesions. The present study explored the effect of Ang II on ACAT1 expression as a molecular mechanism of foam cell formation in primary cultured human monocyte-macrophages. Ang II significantly increased ACAT1 protein expression in a time- or concentration-dependent manner. Application of an Ang II type 1 (AT(1)) receptor agonist (L162313), but not an Ang II type 2 (AT(2)) receptor agonist (CGP42112A), mimicked the effects of Ang II treatment in inducing ACAT1 protein expression. ACAT activity and ACAT1 mRNA levels were also significantly increased by Ang II. Two-fold increases in ACAT1 protein expression and ACAT activity with Ang II treatment were completely inhibited by AT(1) receptor antagonists (candesartan, [Sar(1),Ile(8)]-Ang II), but not by an AT(2) receptor antagonist (PD123319). Treatment with a G-protein inactivator (GDP-beta-S), a c-Src tyrosine kinase inhibitor (PP2), a protein kinase C (PKC) inhibitor (rottlerin), or a mitogen activated protein kinase (MAPK) kinase inhibitor (PD98059) significantly reduced Ang II-induced ACAT1 protein expression. Macrophage foam cell formation assessed using acetylated low-density lipoprotein (LDL)-induced CE accumulation was significantly enhanced by Ang II, which was completely inhibited by treatment with candesartan. These results suggested that Ang II enhances foam cell formation by upregulating ACAT1 expression predominantly through the actions of AT(1) receptor via the G protein/c-Src/PKC/MAPK pathway in human monocyte-macrophages.

Effects of maternal undernutrition on renal angiotensin II and chymase in hypertensive offspring

Intrauterine growth restriction (IUGR) can program the future development of hypertension in adulthood. The renin-angiotensin system has been reported to play a role in IUGR-induced hypertension. The aims of this study were to investigate the effects of IUGR on renal angiotensin-converting enzyme (ACE), angiotensin II (Ang II) and chymase in IUGR-induced hypertension. Timed pregnant Sprague-Dawley rats received 50% rations of control food intakes from days 15 to 21 of gestation. Control rats received regular food throughout the pregnancies. Arterial blood pressure and glomerular number were measured and immunohistochemical studies were performed on kidney tissues in adult male offspring at 16 weeks of age. IUGR rats exhibited significantly lower body and kidney weights and reduced number of glomeruli when compared with control rats. IUGR rats had significantly higher systolic blood pressure than control rats. Immunoreactivity of ACE was comparable between control and IUGR rats whereas immunoreactivities of chymase and Ang II were significantly higher in IUGR rats than in control rats. In conclusion, immunohistochemical studies document up-regulation of ACE-independent Ang II and chymase in IUGR kidney and indicate that overactivity of chymase may result in increased intrarenal Ang II production, which could contribute to the development of hypertension in intrauterine undernourished rats.

Current possibilities of ACE inhibitor and ARB combination in arterial hypertension and its complications

The renin-angiotensin-aldosterone system (RAAS) plays a crucial role in blood pressure regulation and hypertension-related complications. Angiotensin-converting enzyme inhibitors (ACEIs) were the first to be used to block the RAAS and now have many compelling indications in the treatment of hypertension and its cardiovascular and renal complications. Angiotensin II receptor blockers (ARBs), introduced 20 years later, have been shown to be equally as effective as antihypertensive treatment and are also associated with a lower number of side effects. Furthermore, in clinical trials ARBs and ACEIs were associated with comparable benefits for their most typical indications. This was confirmed in the 2007 New European Society of Hypertension/European Society of Cardiology (ESH/ESC) guidelines for the management of hypertension by comparable specific recommendations for ARB and ACEI treatment. There is sufficient theoretical background and, in some cases, also clinical evidence that combination therapy with ACEIs and ARBs may be more beneficial than monotherapy with either of the groups alone, both in uncomplicated hypertension and with concomitant heart failure or renal dysfunction. However, the combination of ACEI and ARB was not recommended in the ESH/ESC 2007 Guidelines. This may change after the publication of the Ongoing Telmisartan Alone and in Combination with Ramipril Global End point Trial (ONTARGET) study, the preliminary results of which have just been presented. In heart failure, recent studies have shown that the combination of ACEI and ARB decreases cardiovascular mortality and the number of hospitalizations due to aggravation of heart failure. These results have been reflected in the newest ESC guidelines of the heart failure treatment. Nephroprotective properties of the combination of ACEs and ARBs have been proved both in studies on nondiabetic and diabetic nephropathy. The potential benefits, indications in prespecified groups of patients, the most recent data from clinical trials and latest research regarding dual blockade of RAAS will be reviewed in this article.

Mast cells modulate the pathogenesis of elastase-induced abdominal aortic aneurysms in mice

Abdominal aortic aneurysm (AAA), an inflammatory disease, involves leukocyte recruitment, immune responses, inflammatory cytokine production, vascular remodeling, neovascularization, and vascular cell apoptosis, all of which contribute to aortic dilatation. This study demonstrates that mast cells, key participants in human allergic immunity, participate in AAA pathogenesis in mice. Mast cells were found to accumulate in murine AAA lesions. Mast cell-deficient KitW-sh/KitW-sh mice failed to develop AAA elicited by elastase perfusion or periaortic chemical injury. KitW-sh/KitW-sh mice had reduced aortic expansion and internal elastic lamina degradation; decreased numbers of macrophages, CD3+ T lymphocytes, SMCs, apoptotic cells, and CD31+ microvessels; and decreased levels of aortic tissue IL-6 and IFN-gamma. Activation of mast cells in WT mice via C48/80 injection resulted in enhanced AAA growth while mast cell stabilization with disodium cromoglycate diminished AAA formation. Mechanistic studies demonstrated that mast cells participated in angiogenesis, aortic SMC apoptosis, and matrix-degrading protease expression. Reconstitution of KitW-sh/KitW-sh mice with bone marrow-derived mast cells from WT or TNF-alpha-/- mice, but not from IL-6-/- or IFN-gamma-/- mice, caused susceptibility to AAA formation to be regained. These results demonstrate that mast cells participate in AAA pathogenesis in mice by releasing proinflammatory cytokines IL-6 and IFN-gamma, which may induce aortic SMC apoptosis, matrix-degrading protease expression, and vascular wall remodeling, important hallmarks of arterial aneurysms.

Does the renin-angiotensin system also regulate intra-ocular pressure?

The renin-angiotensin-aldosterone system is known to play an essential role in controlling sodium balance and body fluid volumes, and thus blood pressure. In addition to the circulating system which regulates urgent cardiovascular responses, a tissue-localized renin-angiotensin system (RAS) regulates long-term changes in various organs. Many recognized RAS components have also been identified in the human eye. The highly vasoconstrictive angiotensin II (Ang II) is considered the key peptide in the circulatory RAS. However, the ultimate effect of RAS activation at tissue level is more complex, being based not only on the biological activity of Ang II but also on the activities of other products of angiotensinogen metabolism, often exerting opposite effects to Ang II action. In recent studies, orally administered angiotensin II type 1 receptor blockers and angiotensin-converting enzyme inhibitors lower intra-ocular pressure (IOP), likewise topical application of these compounds, the effect being more prominent in ocular hypertensive eyes. Based on previous findings and our own experimental data, it can strongly be suggested that the RAS not only regulates blood pressure but is also involved in the regulation of IOP.

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.

Novel roles of intracrine angiotensin II and signalling mechanisms in kidney cells

Angiotensin II (Ang II) has powerful sodium-retaining, growth-promoting and pro- inflammatory properties in addition to its physiological role in maintaining body salt and fluid balance and blood pressure homeostasis. Increased circulating and local tissue Ang II is one of the most important factors contributing to the development of sodium and fluid retention, hypertension and target organ damage. The importance of Ang II in the pathogenesis of hypertension and target organ injury is best demonstrated by the effectiveness of angiotensin- converting enzyme (ACE) inhibitors and AT1-receptor antagonists in treating hypertension and progressive renal disease including diabetic nephropathy. The detrimental effects of Ang II are mediated primarily by the AT1-receptor, while the AT2-receptor may oppose the AT1-receptor. The classical view of the AT1-receptor-mediated effects of Ang II is that the agonist binds its receptors at the cell surface, and following receptor phosphorylation, activates downstream signal transduction pathways and intracellular responses. However, evidence is emerging that binding of Ang II to its cell surface AT1-receptors also activates endocytotic (or internalisation) processes that promote trafficking of both the effector and the receptor into intracellular compartments. Whether internalised Ang II has important intracrine and signalling actions is not well understood. The purpose of this article is to review recent advances in Ang II research with focus on the mechanisms underlying high levels of intracellular Ang II in proximal tubule cells and the contribution of receptor-mediated endocytosis of extracellular Ang II. Further attention is devoted to the question whether intracellular and/or internalised Ang II plays a physiological role by activating cytoplasmic or nuclear receptors in proximal tubule cells. This information may aid future development of drugs to prevent and treat Ang II-induced target organ injury in cardiovascular and renal diseases by blocking intracellular and/or nuclear actions of Ang II.

Treatment of hypertension with olmesartan medoxomil, alone and in combination with a diuretic: an update

Olmesartan medoxomil is an angiotensin II (Ang II) receptor blocker (ARB) that has been approved by the US Food and Drug Administration (FDA) for the treatment of hypertension. It is a prodrug that is hydrolysed in the gut into its active metabolite, olmesartan (RNH-6270). Olmesartan is highly selective for the Ang II type 1 receptor (AT1) to which it binds completely and insurmountably and has very little affinity for the other receptor subtypes AT2 and AT4. After oral administration, in animals and humans, it achieves a maximal blood drug concentration within a maximal time of approximately 2 h. It is then slowly eliminated in the urine and faeces. His half-life is approximately 13 h, which makes it suitable for once-daily administration. Olmesartan medoxomil given orally in single daily doses of 20-40 mg has demonstrated significant blood pressure (BP) lowering effects in hypertensive patients. A medline search for the preparation of this manuscript was conducted and revealed 128 references, from 2000 to 2007. Of these, only 16 well-designed prospective clinical trials were selected. The remaining were either animal studies, reviews or studies in progress. In well-designed clinical trials, olmesartan medoxomil has demonstrated similar antihypertensive actions to the other antihypertensive drugs, as well as other members of its class given the highest recommended doses. In addition, the BP lowering effect of olmesartan, like the other members of its class, is greatly enhanced in combination with a diuretic. Its safety profile is similar to the other ARBs and no different than placebo.

Role of the renin-angiotensin system in the development of abdominal aortic aneurysms in animals and humans

The mediators for the initiation, progression, and rupture of abdominal aortic aneurysms (AAAs) have not been defined. Recent evidence has demonstrated that chronic infusion of angiotensin II via subcutaneously placed osmotic pumps can reproducibly form AAAs in mice. The evolution of AngII-induced AAAs in these mice is complex. Rapid medial macrophage accumulation precedes transmedial breaks and large lumen expansion, which are restricted to the suprarenal aorta. After this initial phase, there is a more gradual rate of lumen expansion that is progressive with continued AngII exposure. There is extensive aortic remodeling during this gradual expansion phase. An initial prominent thrombus gradually resolves and is replaced by fibrous tissue containing several types of inflammatory cells. At prolonged intervals of AngII infusion, internal aortic diameters of the suprarenal aorta can increase up to fourfold compared to the same region in saline-infused mice. The extrapolation of these data in mice to the development of human AAAs remains to be determined. However, there are a considerable number of drugs available to potentially test the efficacy of inhibiting the renin-angiotensin system on the progression of the human disease.