Role of the renin-angiotensin system in vascular diseases: expanding the field

Aldosterone and angiotensin: Role in diabetes and cardiovascular diseases

The present review shall familiarize the readers with the role of renin-angiotensin aldosterone system (RAAS), which regulates blood pressure, electrolyte and fluid homeostasis. The local RAAS operates in an autocrine, paracrine and/or intracrine manner and exhibits multiple physiological effects at the cellular level. In addition to local RAAS, there exists a complete pancreatic RAAS which has multi-facet role in diabetes and cardiovascular diseases. Aldosterone is known to mediate hyperinsulinemia, hypertension, cardiac failure and myocardial fibrosis while angiotensin II mediates diabetes, endothelial dysfunction, vascular inflammation, hypertrophy and remodeling. As the understanding of this biology of RAAS increases, it serves to exploit this for the pharmacotherapy of diabetes and cardiovascular diseases.

Evaluation of mechanism for antihypertensive action of Clerodendrum colebrookianum Walp., used by folklore healers in north-east India

ETHNOPHARMACOLOGICAL RELEVANCE

The present investigation was aimed to justify the pharmacological basis in traditional use of Clerodendrum colebrookianum as antihypertensive agent in north-east India.

MATERIALS AND METHODS

The aqueous extract (AECc), its aqueous, n-butanol (nBFCc), Ethyl-acetate (EtFCc) and Chloroform fractions of C. colebrookianum leaves were evaluated for antihypertensive potential by using fructose-induced hypertension model in rats and in isolated frog heart. The ex-vivo muscarinic action in isolated rat ileum, in-vitro assay for Rho-kinase (ROCK -II), phosphodiesterase-5 (PDE-5) and angiotension converting enzyme (ACE) were also carried out to establish the mechanism of action of samples. The total phenolic and flavonoied contents in test samples were estimated to establish phyto-pharmacological relationship.

RESULTS

The 100μg/mL test samples were showed calcium antagonism in rat ileum and at 50μg/mL and 75μg/mL doses exhibited ROCK-II and PDE-5 inhibition respectively where, EtFCc was caused maximum 68.62% (ROCK-II) and 52.28% (PDE-5) inhibition, but none of the sample was exhibit effect in ACE at 100μg/mL. The test samples also showed negative inotropic and chronotropic effect on isolated frog heart and significant (P<0.001) reduction in systolic blood pressure and heart rate in hypertensive rats compared to control. The total phenolic content maximum 80μg gallic acid equivalents in nBFCc and flavonoids content maximum 69.57μg Quercetin equivalent in AECc were estimated.

CONCLUSIONS

These observations established the traditional claim and thus C. colebrookianum could be a potent antihypertensive agent for use in future. The antihypertensive effect mediated by cholinergic action and following ROCK - II, PDE-5 inhibition of C. colebrookianum.

Mitochondrial ATP-sensitive potassium channels enhance angiotensin-induced oxidative damage and dopaminergic neuron degeneration. Relevance for aging-associated susceptibility to Parkinson's disease

Recent studies have shown that renin-angiotensin system overactivation is involved in the aging process in several tissues as well as in longevity and aging-related degenerative diseases by increasing oxidative damage and inflammation. We have recently shown that angiotensin II enhances dopaminergic degeneration by increasing levels of reactive oxygen species and neuroinflammation, and that there is an aging-related increase in angiotensin II activity in the substantia nigra in rats, which may constitute a major factor in the increased risk of Parkinson's disease with aging. The mechanisms involved in the above mentioned effects and particularly a potential angiotensin-mitochondria interaction have not been clarified. The present study revealed that activation of mitochondrial ATP-sensitive potassium channels [mitoK(ATP)] may play a major role in the angiotensin II-induced effects on aging and neurodegeneration. Inhibition of mitoK(ATP) channels with 5-hydroxydecanoic acid inhibited the increase in dopaminergic cell death induced by angiotensin II, as well as the increase in superoxide/superoxide-derived reactive oxygen species levels and the angiotensin II-induced decrease in the mitochondrial inner membrane potential in cultured dopaminergic neurons. The present study provides data for considering brain renin-angiotensin system and mitoK(ATP) channels as potential targets for protective therapy in aging-associated diseases such as Parkinson's disease.

The neuroprotective action of candesartan is related to interference with the early stages of 6-hydroxydopamine-induced dopaminergic cell death

Several studies have revealed that manipulation of the renin angiotensin system results in reduced progression of nigrostriatal damage in different animal models of Parkinson's disease. In the present work, the effect of daily treatment of rats with the angiotensin II (Ang II) type 1 (AT(1) ) receptor antagonist candesartan (3 mg/kg per day, s.c.) initiated 7 days before the intrastriatal injection of 6-hydroxydopamine (6-OHDA) was investigated by means of tyrosine hydroxylase-positive cell counts in the substantia nigra, and dopamine and 3,4-dihydroxyphenylacetic acid measurements in the striatum. In this experimental set-up, candesartan protected dopaminergic neurons of the nigrostriatal tract against the neurotoxin-induced cell death. However, the beneficial effects of AT(1) receptor blockade were not confirmed when treatment was started 24 h after the lesion, suggesting that candesartan interferes with the early events of the 6-OHDA-induced cell death. Stimulation of the AT(1) receptor with Ang II increased the formation of hydroxyl radicals in the striatum of intact rats as measured by the in vivo microdialysis salicylate trapping technique. This Ang II-induced production of reactive oxygen species was suppressed by candesartan perfusion. Furthermore, the Ang II-induced production of reactive oxygen species was nicotinamide adenine dinucleotide phosphate - oxidase and protein kinase C dependent as it could be blocked in the presence of apocynin, an nicotinamide adenine dinucleotide phosphate - oxidase inhibitor, and chelerythrine, an inhibitor of protein kinase C. Together, these data further support the hypothesis that Ang II might contribute in an early stage to the neurotoxicity of 6-OHDA by reinforcing the cascade of oxidative stress.

Experimental depression induces renal oxidative stress in rats

Depression has been associated to inflammatory and oxidative events. Previous report has shown renal oxidative stress in patients with depression. In order to analyze if depressive status is related to renal oxidative and inflammatory events, Sprague Dawley rats were submitted to forced swimming test (FST) and the renal oxidative metabolism, monocyte-macrophage infiltration and Angiotensin II (Ang II) expression were determined. Rats were submitted to FST daily (30 min) for 15 days. Motor activity was analyzed before FST. Kidney sections were homogenized to measure nitric oxide (NO), malondialdehyde (MDA), reduced glutathione (GSH) and catalase activity by enzymatic and biochemical methods. Renal frozen sections were studied for superoxide anion (O2-), monocyte/macrophage infiltration and Ang II expression by histochemical and immunofluorescence methods. In addition, three groups of FST rats were treated with losartan, sertraline or water for 18 days with further renal O2-analysis. In the FST group, struggle time, motor activity, food intake and body weight gain were found decreased. Increased number of glomerular, interstitial and tubular O2-positive cells was observed in FST rats. High renal content of nitrite/nitrate (NO), MDA and decreased amount of GSH were found in FST rats. Values of renal ED-1 or Ang II positive cells in FST rats remained similar to controls; however, AT1 receptor blocking (losartan) and sertraline reduced both depressive-like behavior and renal O2-expression. These data suggests that depression-like behavior in rats is involved in kidney oxidative stress probably mediated by AT1 receptors.

A novel role for calpain in the endothelial dysfunction induced by activation of angiotensin II type 1 receptor signaling

RATIONALE

The cytosolic protease calpain has been recently implicated in the vascular remodeling of angiotensin II (Ang II) type 1 receptor (AT(1)R) signaling. The role of Ang II/AT(1)R/calpain signaling on endothelial function, an important and early determinant of vascular pathology, remains though totally unknown. Accordingly, we investigated the role of calpain in the endothelial dysfunction of Ang II.

OBJECTIVE

To demonstrate a mechanistic role for calpain in the endothelial dysfunction induced by Ang II/AT(1)R signaling. To establish endothelial-expressed calpains as an important target of AT(1)R signaling.

METHODS AND RESULTS

Subchronic administration of nonpressor doses of Ang II to rats and mice significantly increased vascular calpain activity via AT(1)R signaling. Intravital microscopy studies revealed that activation of vascular expressed calpains causes endothelial dysfunction with increased leukocyte-endothelium interactions and albumin permeability in the microcirculation. Western blot and immunohistochemistry studies confirmed that Ang II/AT(1)R signaling preferentially activates the constitutively expressed μ-calpain isoform and demonstrated a calpain-dependent degradation of IκBα, along with upregulation of nuclear factor κB-regulated endothelial cell adhesion molecules. These physiological and biochemical parameters were nearly normalized following inhibition of AT(1)R or calpain in vivo. RNA silencing studies in microvascular endothelial cells, along with knockout and transgenic mouse studies, further confirmed the role of μ-calpain in the endothelial adhesiveness induced by Ang II.

CONCLUSIONS

This study uncovers a novel role for calpain in the endothelial dysfunction of Ang II/AT(1)R signaling and establishes the calpain system as a novel molecular target of the vascular protective action of renin-angiotensin system inhibition. Our results may have significant clinical implications in vascular disease.

Impairment of the Plasmodium falciparum erythrocytic cycle induced by angiotensin peptides

Plasmodium falciparum causes the most serious complications of malaria and is a public health problem worldwide with over 2 million deaths each year. The erythrocyte invasion mechanisms by Plasmodium sp. have been well described, however the physiological aspects involving host components in this process are still poorly understood. Here, we provide evidence for the role of renin-angiotensin system (RAS) components in reducing erythrocyte invasion by P. falciparum. Angiotensin II (Ang II) reduced erythrocyte invasion in an enriched schizont culture of P. falciparum in a dose-dependent manner. Using mass spectroscopy, we showed that Ang II was metabolized by erythrocytes to Ang IV and Ang-(1–7). Parasite infection decreased Ang-(1–7) and completely abolished Ang IV formation. Similar to Ang II, Ang-(1–7) decreased the level of infection in an A779 (specific antagonist of Ang-(1–7) receptor, MAS)-sensitive manner. 10⁻⁷ M PD123319, an AT₂ receptor antagonist, partially reversed the effects of Ang-(1–7) and Ang II. However, 10⁻⁶ M losartan, an antagonist of the AT₁ receptor, had no effect. Gs protein is a crucial player in the Plasmodium falciparum blood cycle and angiotensin peptides can modulate protein kinase A (PKA) activity; 10⁻⁸ M Ang II or 10⁻⁸ M Ang-(1–7) inhibited this activity in erythrocytes by 60% and this effect was reversed by 10⁻⁷ M A779. 10⁻⁶ M dibutyryl-cAMP increased the level of infection and 10⁻⁷ M PKA inhibitor decreased the level of infection by 30%. These results indicate that the effect of Ang-(1–7) on P. falciparum blood stage involves a MAS-mediated PKA inhibition. Our results indicate a crucial role for Ang II conversion into Ang-(1–7) in controlling the erythrocytic cycle of the malaria parasite, adding new functions to peptides initially described to be involved in the regulation of vascular tonus.

Angiotensin II type 1A receptors in vascular smooth muscle cells do not influence aortic remodeling in hypertension

Vascular injury and remodeling are common pathological sequelae of hypertension. Previous studies have suggested that the renin-angiotensin system acting through the type 1 angiotensin II (AT(1)) receptor promotes vascular pathology in hypertension. To study the role of AT(1) receptors in this process, we generated mice with cell-specific deletion of AT(1) receptors in vascular smooth muscle cells using Cre/Loxp technology. We crossed the SM22α-Cre transgenic mouse line expressing Cre recombinase in smooth muscle cells with a mouse line bearing a conditional allele of the Agtr1a gene (Agtr1a (flox)), encoding the major murine AT(1) receptor isoform (AT(1A)). In SM22α-Cre(+)Agtr1a (flox/flox) (SMKO) mice, AT(1A) receptors were efficiently deleted from vascular smooth muscle cells in larger vessels but not from resistance vessels such as preglomerular arterioles. Thus, vasoconstrictor responses to angiotensin II were preserved in SMKO mice. To induce hypertensive vascular remodeling, mice were continuously infused with angiotensin II for 4 weeks. During infusion of angiotensin II, blood pressures increased significantly and to a similar extent in SMKO and control mice. In control mice, there was evidence of vascular oxidative stress indicated by enhanced nitrated tyrosine residues in segments of aorta; this was significantly attenuated in SMKO mice. Despite these differences in oxidative stress, the extent of aortic medial expansion induced by angiotensin II infusion was virtually identical in both groups. Thus, vascular AT(1A) receptors promote oxidative stress in the aortic wall but are not required for remodeling in angiotensin II-dependent hypertension.

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.

Location of prorenin receptors in primate substantia nigra: effects on dopaminergic cell death

Angiotensin II acts via angiotensin type 1 receptors and is a major inducer of inflammation and oxidative stress. Local renin-angiotensin systems play a major role in the development of age-related disorders in several tissues. These processes are delayed, but not totally abolished, by blockade of angiotensin signaling. A specific receptor for renin and its precursor prorenin has recently been identified. We previously showed that neurotoxin-induced dopaminergic (DA) cell loss is decreased by inhibition of angiotensin receptors, but the location and functional effects of prorenin receptor (PRR) in the brain, including the DA system, are unknown. In the substantia nigra of Macaca fascicularis and in rat primary mesencephalic cultures, double immunofluorescence analysis revealed PRR immunoreactivity in neurons (including DA neurons) and microglia, but not in astrocytes. Administration of the PRR blocker, handle region peptide, led to a significant decrease in 6-hydroxydopamine-induced DA cell death in the cultures,whereas administration of renin with simultaneous blockade of angiotensin receptors led to an increase in 6-hydroxydopamine-induced cell death. These results suggest that active agent angiotensin II-independent PRR intracellular signaling may contribute to exacerbation of DA cell death in vivo. Therefore, potential neuroprotective strategies for DA neurons in Parkinson disease should address both angiotensin and PRR signaling.

Effects of Angiotensin III on Protein, DNA, and Collagen Synthesis of Neonatal Cardiomyocytes and Cardiac Fibroblasts In Vitro

This study compared angiotensin II (Ang II) and angiotensin III (Ang III) for their effects on rat neonatal cardiomyocytes and cardiac fibroblasts in vitro and discussed the possible role of Ang III in the pathogenesis of cardiac remodeling. To do so, protein synthesis, cardiac fibroblast proliferation, collagen synthesis, and secretion in response to treatment with Ang III and Ang II were investigated. Protein synthesis rate was assessed by 3H-Leucine (3H-Leu) incorporation; the content of DNA was defined by 3H-thymidine (3H-TdR) incorporation; and collagen synthesis and secretion were assessed by 3H-proline (3H-Pro) incorporation. In neonatal cardiomyocytes, Ang III stimulated protein synthesis in a concentration-dependent manner, whereas in neonatal cardiac fibroblasts, DNA synthesis as well as collagen synthesis and secretion were increased in a concentration-dependent manner. Treatment with captopril, selective aminopeptidase A (APA) inhibitor (EC33), or selective aminopeptidase N inhibitor (PC18) had no effect on these outcomes. Treatment with losartan significantly decreased the effects of Ang III, except for cardiomyocyte protein synthesis. Compared with Ang II, Ang III could stimulate cardiomyocyte protein synthesis, cardiac fibroblast proliferation, and collagen synthesis and secretion. Furthermore, 10-7 mol/L Ang II but not Ang III significantly increased APA activity in both cardiomyocytes and fibroblasts. All these results show the bioactive effects of Ang III on myocardial cells and suggest that Ang III could be an important independent factor besides Ang II in the regulation of cardiac function and may affect the pathogenesis of cardiac remodeling.

The antioxidant effect of angiotensin II receptor blocker, losartan, in streptozotocin-induced diabetic rats

We determined the effect of a short-term angiotensin II signaling blockade on vascular endothelial growth factor (VEGF), soluble intercellular adhesion molecule-1 (sICAM-1), nitric oxide (NO), and malondialdehyde (MDA) (index of lipid peroxidation) levels in the systemic circulation and on peroxynitrite generation and insulitis development in the streptozotocin (STZ) diabetic rats' pancreas. Diabetes was induced in Wistar rats by intraperitoneal STZ injection. Diabetic rats were treated for 1 week with losartan (20 mg/kg/body weight/day in the drinking water), and pancreas and blood were collected for histochemical, immunohistochemical, and biochemical studies. Diabetic rats showed greater VEGF, sICAM-1, NO, and MDA levels, a high score of insulitis, increased nitrotyrosine staining, and markedly reduced pancreatic insulin content when compared with controls. Losartan treatment suppressed the excessive NO and lipid peroxidation production systemically without restoring them to that of healthy subjects and reduced VEGF levels while leaving sICAM-1 levels unchanged. The insulitis score and nitrotyrosine staining were reduced, whereas the pancreatic islets and the beta-cell area were increased significantly in the treated group, indicating the reduction of inflammation and nitrosative stress and an early regeneration of beta-cell mass in the pancreas. Conclusively, in the STZ diabetic rat model, even a short-term losartan treatment improves oxidative and nitrosative stress systemically and locally, improving the islets' environment and accelerating beta-cell regeneration.

Maitake mushroom extracts ameliorate progressive hypertension and other chronic metabolic perturbations in aging female rats

OBJECTIVE

We assessed the ability of two commercially-available fractions labeled SX and D derived from the edible maitake mushroom to overcome many age-associated metabolic perturbations such as progressive, age-related elevation of blood pressure, over activity of the renin-angiotensin system (RAS), decreased insulin sensitivity, and inflammation in an in vivo laboratory model.

DESIGN AND METHOD

We divided forty mature, female Sprague-Dawley rats (SD) into five groups of eight. SD ingested regular rat chow containing added sucrose (20% w/w). The groups received baseline diet alone (control) or baseline diet containing captopril, niacin-bound chromium, maitake fraction SX, or maitake fraction D. In addition to blood pressure readings, the following procedures were implemented: losartan and insulin challenges, evaluation of serum ACE activity, glucose tolerance testing, blood chemistries, LNAME challenge, and measurement of various circulating cytokines.

RESULTS

We found that implementation of all test conditions stopped the gradual elevation of systolic blood pressure (SBP) in the SD over the four months of study, even reversing some of the previous elevation that occurred over time. In general, the treatment groups showed decreased activity of the RAS estimated by less lowering of SBP after losartan challenge and decreased serum ACE activity and were more sensitive to exogenous insulin challenge. TNFa levels decreased in all four test groups suggesting a lessening of the inflammatory state.

CONCLUSIONS

We believe our data suggest that maitake mushroom fractions lessen age-related hypertension, at least in part, via effects on the RAS; enhance insulin sensitivity; and reduce some aspects of inflammation--actions that should lead to a longer, healthier life span.

Estrogen and angiotensin interaction in the substantia nigra. Relevance to postmenopausal Parkinson's disease

Epidemiological studies have reported that the incidence of Parkinson's disease (PD) is higher in postmenopausal than in premenopausal women of similar age. Several laboratory observations have revealed that estrogen has protective effects against dopaminergic toxins. The mechanism by which estrogen protects dopaminergic neurons has not been clarified, although estrogen-induced attenuation of the neuroinflammatory response plays a major role. We have recently shown that activation of the nigral renin-angiotensin system (RAS), via type 1 (AT1) receptors, leads to NADPH complex and microglial activation and induces dopaminergic neuron death. In the present study we investigated the effect of ovariectomy and estrogen replacement on the nigral RAS and on dopaminergic degeneration induced by intrastriatal injection of 6-OHDA. We observed a marked loss of dopaminergic neurons in ovariectomized rats treated with 6-OHDA, which was significantly reduced by estrogen replacement or treatment with the AT1 receptor antagonist candesartan. We also observed that estrogen replacement induces significant downregulation of the activity of the angiotensin converting enzyme as well as downregulation of AT1 receptors, upregulation of AT2 receptors and downregulation of the NADPH complex activity in the substantia nigra in comparison with ovariectomized rats. The present results suggest that estrogen-induced down-regulation of RAS and NADPH activity may be associated with the reduced risk of PD in premenopausal women, and increased risk in conditions causing early reduction in endogenous estrogen, and that manipulation of brain RAS system may be an efficient approach for the prevention or coadjutant treatment of PD in estrogen-deficient women.

Monocytic fibroblast precursors mediate fibrosis in angiotensin-II-induced cardiac hypertrophy

Angiotensin-II (Ang-II) is an autacoid generated as part of the pathophysiology of cardiac hypertrophy and failure. In addition to its role in cardiac and smooth muscle contraction and salt retention, it was shown to play a major role in the cardiac interstitial inflammatory response and fibrosis accompanying cardiac failure. In this study, we examined a model of Ang-II infusion to clarify the early cellular mechanisms linking interstitial fibrosis with the onset of the tissue inflammatory response. Continuous infusion of Ang-II resulted in increased deposition of collagen in the heart. Ang-II infusion also resulted in the appearance of distinctive small, spindle-shaped, bone marrow-derived CD34(+)/CD45(+) fibroblasts that expressed collagen type I and the cardiac fibroblast marker DDR2 while structural fibroblasts were CD34(-)/CD45(-). Genetic deletion of monocyte chemoattractant protein (MCP)-1 (MCP-1-KO mice) prevented the Ang-II-induced cardiac fibrosis and the appearance of CD34(+)/CD45(+) fibroblasts. Real-time PCR in Ang-II-treated hearts revealed a striking induction of types I and III collagen, TGF-beta1, and TNF mRNA expression; this was obviated in Ang-II-infused MCP-1-KO hearts. In both wild-type and MCP-1-KO mice, Ang-II infusion resulted in cardiac hypertrophy, increased systolic function and hypertension which were not significantly different between the WT and MCP-1-KO mice over the 6-week course of infusion. In conclusion, the development of Ang-II-induced non-adaptive fibrosis in the heart required induction of MCP-1, which modulated the uptake and differentiation of a CD34(+)/CD45(+) fibroblast precursor population. In contrast to the inflammatory and fibrotic response, the hemodynamic response to Ang-II was not affected by MCP-1 in the first 6weeks.

Renin-angiotensin system in human coronavirus pathogenesis

Although initially considered relatively harmless pathogens, human coronaviruses (HCoVs) are nowadays known to be associated with more severe clinical complications. Still, their precise pathogenic potential is largely unknown, particularly regarding the most recently identified species HCoV-NL63 and HCoV-HKU1. HCoVs need host cell proteins to successively establish infections. Proteases of the renin–angiotensin system serve as receptors needed for entry into target cells; this article describes the current knowledge on the involvement of this system in HCoV pathogenesis.

Gene polymorphisms in angiotensin I converting enzyme (ACE I/D) and angiotensin II converting enzyme (ACE2 C-->T) protect against cerebral malaria in Indian adults

To explore the hypothesis that angiotensin II may play a role in the susceptibility to cerebral malaria (CM), we performed a genetic association study of malaria patients in Orissa, India analyzing three SNPs (ACE2 C-->T, iNOS C-->T, eNOS Glu-->Asp) and two I/D polymorphisms (ACE I/D and IL-4 B1/B2). Our results showed that the 'D' allele of ACE I/D polymorphism, responsible for increased Ang II production had a significant association with mild malaria and the ACE2 C-->T substitution had gender specific effect of possibly reduced expression of ACE2 in presence of 'T' allele in women leading to increased level of Ang II and hence protection against CM. Combined genotype analysis of eNOS Glu-->Asp substitution responsible for increased NO production in Plasmodium falciparum infected individuals and ACE I/D polymorphism also showed stronger association of (Glu-Asp+Asp-Asp/ID+DD) genotypes with mild malaria (P<0.0001). Whether by its antiplasmodial activity and/or by some unknown mechanisms, Ang II protects from susceptibility to cerebral malaria remains to be investigated. These genetic findings may contribute to the understanding of malaria pathogenesis.

Vascular metallomics: copper in the vasculature

Owing to recent progress in analytical techniques, metallomics are evolving from detecting distinct trace metals in a defined state to monitor the dynamic changes in the abundance and location of trace metals in vitro and in vivo. Vascular metallomics is an emerging field that studies the role of trace metals in vasculature. This review will introduce common metallomics techniques including atomic absorption spectrometry, inductively coupled plasma-atomic emission spectrometry, inductively coupled plasma-mass spectrometry and X-ray fluorescence spectrometry with a summary table to compare these techniques. Moreover, we will summarize recent research findings that have applied these techniques to human population studies in cardiovascular diseases, with a particular emphasis on the role of copper in these diseases. In order to address the issue of interdisciplinary studies between metallomics and vascular biology, we will review the progress of efforts to understand the role of copper in neovascularization. This recent advance in the metallomics field may be a powerful tool to elucidate the signaling pathways and specific biological functions of these trace metals. Finally, we summarize the evidence to support the notion that copper is a dynamic signaling molecule. As a future direction, vascular metallomics studies may lead to the identification of targets for diagnosis and therapy in cardiovascular disease.

Polymorphism in the angiotensin II type 1 receptor (AGTR1) is associated with age at diagnosis in pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a rare, lethal disease associated with single gene disorders, connective tissue disease, exposures to anorexigens, and often, idiopathic etiology. Genes can modify the risk of PAH: (1) monogenic disorders associated with PAH are incompletely penetrant, and (2) not all patients with associated conditions at increased risk for PAH develop the disease. The renin angiotensin aldosterone system (RAAS) provides a set of candidate genes that could modulate pulmonary vascular disease similar to its effects on renal and peripheral vasculature.

METHODS

We studied 247 patients with PAH, comprising 177 with idiopathic PAH (IPAH), 63 with PAH/connective tissue disease (CTD), and 7 with PAH associated with anorexigens. Patients were genotyped for 5 common polymorphisms in angiotensinogen (AGT), angiotensin-converting enzyme (ACE), cardiac chymase A (CMA1), angiotensin II type 1 receptor (AGTR1), and aldosterone synthase (CYP11B2). Genotypes were tested for associations with age at diagnosis, hemodynamic parameters at diagnosis, and/or response to acute pulmonary vasodilator testing at diagnosis.

RESULTS

Associations were demonstrated for AGTR1 and age at diagnosis in IPAH (p = 0.005). Homozygotes for the 1166C allele (n = 13) were associated with an age at diagnosis 26 years later than those with A/A (n = 139) or A/C (n = 90) genotypes. No associations were demonstrated for AGT, ACE, CMA1, or CYP11B2.

CONCLUSIONS

The 1166C polymorphism in AGTR1 appears to be associated with a later age at diagnosis in IPAH, suggesting that this pathway could be involved in the biologic variability that is known to occur in PAH.

Adapter proteins and promoter regulation of the angiotensin AT2 receptor — implications for cardiac pathophysiology

The angiotensin AT 2 receptor (AT2R) represents an important component of the renin-angiotensin system since it is involved in the (patho) physiology of different cardiovascular and neuronal diseases. Furthermore, AT2 receptors can partly mediate beneficial effects of angiotensin AT 1 receptor (AT1R) blockers, and direct pharmacological AT 2 receptor agonism emerges as a novel therapeutic strategy. This review discusses the constitutive and ligand-mediated activity as well as the signal transduction of the AT2 receptor, focusing on adapter proteins which directly bind to this receptor. Direct protein-protein interaction partners of the AT2 receptor described so far include the transcription factor promyelocytic zinc finger protein, AT2 receptor binding protein and the AT1 receptor. In addition, the putative crosstalk of the AT2 receptor with the renin/ prorenin receptor (RER) via the promyelocytic zinc finger protein (PLZF) and the role of oestrogens on the regulation of the AT2 receptor are presented. Conceiving the coupling of the AT2 receptor to different adapter proteins with distinct and partly opposing cellular effects and the implications of its constitutive activity might help to overcome the current controversies on the (patho)physiological role of the AT2 receptor.

Streptococcal zymogen type B induces angiotensin II in mesangial cells and leukocytes

Previous reports have shown that angiotensin II and oxidative stress may be important features in acute poststreptococcal glomerulonephritis (APSGN) and that streptococcal erythrogenic toxin type B (ETB) and its precursor (ETBP) may have an important role in the pathogenesis of APSGN. The aim of this study was to determine the effect of ETBP on the production of angiotensin II and oxidative stress in rat mesangial cells and human mononuclear leukocytes. Mesangial cells and leukocytes were isolated from digested glomeruli and by histopaque gradient, respectively, while ETBP was isolated from nephritogenic streptococcus cultures using a cation exchange column. Angiotensin II was determined by an enzyme-linked immunosorbent assay and by cytometrics. Superoxide anion, reduced glutathione, nitrites, lipid peroxidation and catalase activity were determined by cytochemical, biochemical and enzymatic assays. Inducible nitric oxide synthase expression was determined by cytometrics. An increased production of angiotensin II was observed in ETBP-treated mesangial cell and leukocyte cultures. The ETBP induced an elevated production of superoxide anions and nitrites in mesangial cells and superoxide anions in leukocytes, while this streptococcal protein decreased the expression of inducible nitric oxide synthase in leukocytes. The ETBP was capable of inducing an increased production of angiotensin II and increased oxidative stress, both of which may be important mediators of inflammatory events in the renal tissue and during APSGN.

Vaccine for hypertension: modulating the renin-angiotensin system

Hypertension, which is one of the most common diseases afflicting mankind, is associated to increased morbidity, mortality and cost to society. Cardiovascular disease is the leading cause of death all around the world and hypertension is the most common reversible risk factor for cardiovascular diseases. The renin-angiotensin system (RAS) commands an important role in the regulation of blood pressure, and so, at present, has been a target for clinical control by drugs acting on the system. Despite the fact that effective drugs are available, only about one out of three people has their blood pressure successfully controlled, and the blame goes to the undesirable side effects and the poor oral drug compliance. Keeping in mind the increasing incidence of hypertension and the patients' inconsistency for the polypharmacy, immunization against renin and the angiotensins, although with less success, had been attempted in the past. More recently, immunization against angiotensin-I with PMD-3117 vaccine, angiotensin-II with CYT006-AngQb vaccine and targeting angiotensin-II type 1A receptor with ATR12181 vaccine have provided optimism in the development of a hypertension vaccine. AngQb vaccine has proved to become the first vaccine ever to lower (-9/-4 mm Hg) blood pressure in human beings. Vaccine could induce long lasting effects with a dosing interval of months, increasing patient acceptability and compliance and thus a better control of high blood pressure. Our objective will be to focus on the importance of the RAS and to explore the extent of safety, efficacy and the future implications of vaccine against the RAS.

Hepatocyte expression of angiotensin II type 1 receptor is downregulated in advanced human liver fibrosis

BACKGROUND

The renin-angiotensin system plays an important role in fibrosis. Angiotensin II regulates key steps in tissue remodelling processes through angiotensin II type 1 receptor (AT1R). In bile duct-occluded rats, AT1R expression is significantly decreased in advanced liver fibrosis. Therefore, we studied the AT1R expression in human liver tissue during different stages of fibrosis caused by chronic hepatitis C.

METHODS

Liver biopsy specimens from 85 patients were analysed. Real-time reverse transcription polymerase chain reaction was used to quantify AT1R mRNA. Immunohistochemical labelling of AT1R and double staining for AT1R, CD31, CD68, CD3 and fibulin-2 were performed.

RESULTS

AT1R mRNA was significantly reduced in human liver tissue with end-stage cirrhosis compared with early fibrosis. In liver cirrhosis, immunohistochemistry revealed a decreased expression of AT1R on hepatocytes, together with an increased staining intensity on myofibroblasts, vascular endothelium and bile duct epithelium.

CONCLUSION

In conclusion, AT1R expression is downregulated in human liver cirrhosis specimens because of the reduced expression levels on hepatocytes. Therefore, antifibrogenic therapy with AT1R blockers may be most promising if initiated during early stages of fibrosis.

Effect of nicotine and nicotine metabolites on angiotensin-converting enzyme in human endothelial cells

Nicotine has been shown to induce endothelial dysfunction, which is an early marker of atherosclerosis. Nicotine undergoes extensive metabolism in the liver, forming a number of major and minor metabolites. There are very limited data on the effect of nicotine metabolites on the cardiovascular system. This study investigates the effects of nicotine and the nicotine metabolites, cotinine, cotinine-N-oxide, nicotine-1'-N-oxide, norcotinine, trans-3'-hydroxycotinine, on angiotensin-converting enzyme (ACE) in human endothelial cells. Cultured endothelial cells obtained from human umbilical cord vein (HUVECs) were stimulated with nicotine or nicotine metabolites in concentrations similar to those observed in plasma during smoking. ACE activity and expression were analyzed using commercial kits. The results showed that nicotine and nicotine metabolites can increase both activity and expression of ACE. However, a marked individual variation in the response to the drugs was observed. This variation was not associated with the ACE insertion/deletion polymorphism. Tobacco contains numerous chemical compounds, and the underlying cause for development of atherosclerosis in smokers is probably multifactorial. The results from this study could explain one cellular mechanism by which smoking exerts negative effect on the vascular system.

[Molecular bases of diabetic nephropathy]

The determinant of the diabetic nephropathy is hyperglycemia, but hypertension and other genetic factors are also involved. Glomerulus is the focus of the injury, where mesangial cell proliferation and extracellular matrix occur because of the increase of the intra- and extracellular glucose concentration and overexpression of GLUT1. Sequentially, there are increases in the flow by the poliol pathway, oxidative stress, increased intracellular production of advanced glycation end products (AGEs), activation of the PKC pathway, increase of the activity of the hexosamine pathway, and activation of TGF-beta1. High glucose concentrations also increase angiotensin II (AII) levels. Therefore, glucose and AII exert similar effects in inducing extracellular matrix formation in the mesangial cells, using similar transductional signal, which increases TGF-beta1 levels. In this review we focus in the effect of glucose and AII in the mesangial cells in causing the events related to the genesis of diabetic nephropathy. The alterations in the signal pathways discussed in this review give support to the observational studies and clinical assays, where metabolic and antihypertensive controls obtained with angiotensin-converting inhibitors have shown important and additive effect in the prevention of the beginning and progression of diabetic nephropathy. New therapeutic strategies directed to the described intracellular events may give future additional benefits.

Angiotensin-converting enzyme (ACE), angiotensinogen (AGT), and angiotensin II type 1 receptor (AT1R) gene polymorphisms in generalized aggressive periodontitis

AIM

Host response to periodontopathic microorganisms can be modulated by genetic factors. Accumulated evidence highlighted the role of renin-angiotensin system (RAS) in inflammatory response thus potential implication of this molecular system in the pathogenesis of periodontitis can be suggested. The present study investigated common genetic variants of molecules within the RAS family namely angiotensin-converting enzyme (ACE), angiotensinogen (AGT) and angiotensin II type 1 receptor (AT1R) in relation to generalized aggressive periodontitis (G-AgP).

METHODS

DNA was obtained from peripheral blood of 103 G-AgP patients and 100 periodontally healthy subjects. ACE I/D, AGT M235T and AT1R A1166C polymorphisms were genotyped by polymerase chain reaction and restriction fragment length polymorphism method. Chi-square, ANOVA and logistic regression were used in statistical analyses.

RESULTS

Both ACE I/D and AT1R polymorphisms were similar in G-AgP and healthy groups (p>0.05). G-AgP subjects exhibited decreased AGT TT genotype and T allele frequency as compared to healthy subjects (p<0.05). The same trend was also observed in the nonsmoker subgroup regarding investigated RAS polymorphisms.

CONCLUSIONS

Present findings suggest that AGT M235T TT genotype and T allele might be associated with decreased risk for G-AgP in Turkish population.

Losartan chemistry and its effects via AT1 mechanisms in the kidney

Besides the importance of the renin-angiotensin system (RAS) in the circulation and other organs, the local RAS in the kidney has attracted a great attention in research in last decades. The renal RAS plays an important role in the body fluid homeostasis and long-term cardiovascular regulation. All major components and key enzymes for the establishment of a local RAS as well as two important angiotensin II (Ang II) receptor subtypes, AT1 and AT2 receptors, have been confirmed in the kidney. In additional to renal contribution to the systemic RAS, the intrarenal RAS plays a critical role in the regulation of renal function as well as in the development of kidney disease. Notably, kidney AT1 receptors locating at different cells and compartments inside the kidney are important for normal renal physiological functions and abnormal pathophysiological processes. This mini-review focuses on: 1) the local renal RAS and its receptors, particularly the AT1 receptor and its mechanisms in physiological and pathophysiological processes; and 2) the chemistry of the selective AT1 receptor blocker, losartan, and the potential mechanisms for its actions in the renal RAS-mediated disease.

Does the renin-angiotensin system participate in regulation of human vasculogenesis and angiogenesis?

Several lines of evidence suggest that hypertension and angiogenesis may be related phenomena but a functional link remains elusive. Here, we propose that the renin-angiotensin system (RAS), in addition to its central role in arterial hypertension, also regulates blood vessel formation during normal development and cancer. This mechanistic hypothesis is based on reports of biochemical, genetic, clinical, and epidemiologic data reviewed herein. Species differences between the RAS of rodents and humans likely account for why such a fundamental role in angiogenesis went unrecognized for so long. If proven correct, this hypothesis carries many implications for the medical practices of cardiology, oncology, and neonatology.

The effects of ACE inhibitor and angiotensin receptor blocker on clusterin and apoptosis in the kidney tissue of streptozotocin-diabetic rats

Our first aim was to determine the effects of secreted clusterin (sCLU) and nuclear clusterin (nCLU) in diabetic nephropathy. We also aimed to investigate the post-effects of angiotensin II blockage treatment on clusterin expression and to compare these with apoptosis. Five groups of Wistar albino rats were used: First group consisted of healthy controls; the second group included the untreated STZ-diabetics; 30 days of irbesartan or perindopril treated STZ-diabetics formed the third and the fourth groups, respectively; while the subjects receiving a combined treatment with irbesartan and perindopril for 30 days consisted the fifth group. TUNEL method for apoptosis and immunohistochemical staining for TGF-beta1, alpha-SMA, clusterin-beta and clusterin-alpha/beta antibodies were performed. Apoptotic cells especially increased in the kidney tubuli of untreated diabetic group and on the contrary, a significant decrease was observed in the group that received a combined drug treatment. While sCLU was increased in the glomeruli and tubuli of the untreated diabetic group, it was decreased in all the treated groups. An increase in the nCLU immunoreactivity was observed in the podocytes, mesangial cells, and the injured tubule cells of the untreated diabetic group. nCLU immunopositive cells were decreased in all treated diabetic groups. In addition to this, the distribution of nCLU was similar to the distribution of apoptotic cells in the diabetic groups. Our results indicate that sCLU expression in diabetic nephropathy was induced due to renal tissue damage, and the nCLU expression increase in renal tubuli was related to apoptosis. Although irbesartan and perindopril prevented further renal injury in diabetes, a combined application of low-dose ACEI and AT1R blockers revealed more efficient measures, by means of renal damage prevention.

Angiotensin II increases expression of IP-10 and the renin-angiotensin system in endothelial cells

Angiotensin II promotes vascular inflammation, which plays important roles in vascular injury. In this study, we found that angiotensin II-stimulated human endothelial cells increased the release of a CXC chemokine, IP-10, according to an antibody array. IP-10 expression was higher in the endothelium of coronary blood vessels in mice infused with angiotensin II than in control. Quantitative real-time PCR analysis revealed that angiotensin II significantly increased IP-10 mRNA expression compared to control. Pretreatment with valsartan, but not with PD123319, blocked angiotensin II-induced IP-10 mRNA expression. IP-10 levels in conditioned media detected by ELISA increased in response to angiotensin II compared to control, which was blocked by the pretreatment with valsartan. These data indicate that angiotensin II stimulates IP-10 production from endothelial cells via angiotensin II type 1 receptors. In endothelial cells, IP-10 significantly increased mRNA expression of renin, angiotensin-converting enzyme, and angiotensinogen. IP-10 also increased angiotensin II levels in conditioned media compared to control. Angiotensin II significantly increased mRNA expression of renin, angiotensin converting enzyme and angiotensinogen, which was blocked by neutralization of IP-10 with antibody in endothelial cells. IP-10 neutralization with antibody blocked angiotensin II-induced apoptosis and cell senescence in endothelial cells. These data indicate that IP-10 is involved not only in leukocyte-endothelial interaction but also in the circuit of endothelial renin-angiotensin system activation that potentially promotes atherosclerosis.

Deterioration of atherosclerosis in mice lacking angiotensin II type 1A receptor in bone marrow-derived cells

The renin-angiotensin system (RAS) modulates end-organ damages, resulting in cardiovascular and kidney diseases. Experiments both in vitro and in vivo demonstrate that the angiotensin II (Ang II) type 1 (AT1) receptor pathway also exerts pro-inflammatory and pro-atherogenic effects on bone marrow-derived cells (BMDCs). Here, we investigated how AT1 receptor expression by BMDCs contributes to atherosclerosis and kidney injury in vivo by transplanting BM into RAS-activated transgenic mice. There was no difference in the extent of kidney damage between mice receiving BM transplants from mutant mice lacking the angiotensin II type 1a receptor (AT1a) gene and mice receiving transplants from wild-type (WT) mice. However, mice receiving transplants from AT1a 'knockout' (KO) mice displayed accelerated lethality and atherosclerotic lesions. These results indicated that the effects of AT1a receptor on BMDCs are organ dependent. Microarray expression profiling of macrophages from AT1a-KO mice revealed significant changes in the mRNA levels for a number of genes implicated in atherosclerosis. In accordance with the in vivo atherosclerosis results, AT1a-KO macrophages exhibited greater uptake of modified lipoproteins relative to macrophages from WT mice. We propose that the expression of AT1a receptor by BMDCs limits atherosclerosis in vivo.