Biochemical evaluation of the renin-angiotensin system: the good, bad, and absolute?

Counter-regulatory renin-angiotensin system in cardiovascular disease

The renin-angiotensin system is an important component of the cardiovascular system. Mounting evidence suggests that the metabolic products of angiotensin I and II - initially thought to be biologically inactive - have key roles in cardiovascular physiology and pathophysiology. This non-canonical axis of the renin-angiotensin system consists of angiotensin 1-7, angiotensin 1-9, angiotensin-converting enzyme 2, the type 2 angiotensin II receptor (AT₂R), the proto-oncogene Mas receptor and the Mas-related G protein-coupled receptor member D. Each of these components has been shown to counteract the effects of the classical renin-angiotensin system. This counter-regulatory renin-angiotensin system has a central role in the pathogenesis and development of various cardiovascular diseases and, therefore, represents a potential therapeutic target. In this Review, we provide the latest insights into the complexity and interplay of the components of the non-canonical renin-angiotensin system, and discuss the function and therapeutic potential of targeting this system to treat cardiovascular disease.

Renin-angiotensin system in osteoarthritis: A new potential therapy

Osteoarthritis (OA) is one of the most common chronic joint diseases. However, the mechanism remains unclear. The traditional renin-angiotensin system (RAS) is an important system for regulating homeostasis and controlling balance. In recent years, RAS-related components have played an important role in the occurrence of OA. The purpose of this review is to summarize the research results of RAS-related components that are associated with OA. This study systematically searched e-medical databases such as PubMed, Embase, Medline, and Web of Science. The search targets included English publications describing the effects of RAS-related components in OA, including the role of renin, angiotensin-converting enzyme (ACE), Angiotensin II (Ang II), and angiotensin receptor (ATR). Additionally, this study summarizes the potential pathways for RAS-related components to intervene in OA. This study found that RAS-related components including renin, ACE, Ang II, AT1R and AT2R are involved in inflammation and chondrocyte hypertrophy in OA. RAS is involved in signaling pathways including the NF-κB, JNK, VEGFR/Tie-2, and the Axna2/Axna2R axis ones, which may be potential targets for the treatment of OA. Although there are few studies on RAS in the field of OA, the pathogenic effect of RAS-related components is still an important topic in OA treatment, and great progress may be made in this aspect in future studies.

Brain renin-angiotensin system in broiler chickens with cold-induced pulmonary hypertension

1. The relative expression of angiotensinogen (AGT), renin, angiotensin-converting enzyme (ACE) and angiotensin II type 1 receptor (AT₁R) was determined using quantitative real-time PCR on tissue from the brain (forebrain, midbrain and hindbrain) to investigate the effect of cold-induced pulmonary hypertension syndrome (PHS) in broilers aged 42 days. Brain angiotensin II (Ang II) and AT₁R levels were measured using enzyme immunoassay. 2. The right ventricle/total ventricles (RV/TV) ratio of the heart was increased in broilers exposed to cold stress (PHS group) at the end of the experiment. 3. ACE and renin transcripts in three parts of the brain were significantly increased in the PHS group at 42 d of age compared to controls while AGT transcript was significantly increased only in the hindbrain of PHS birds. The amount of AT1R transcript did not differ between control and PHS groups. 4. The amount of Ang II significantly decreased only in the midbrain of PHS birds compared with controls while the amounts of AT₁R were not different between treatments in the three segments of the brain. 5. It was concluded that brain gene expression of AGT (in the hindbrain), renin, and ACE was upregulated in broilers with PHS whereas Ang II and AT1R levels were not changed. These results provided evidence of diminished involvement of the renin-angiotensin system in the pathogenesis of chicken pulmonary hypertension.

Losartan and isoproterenol promote alterations in the local renin-angiotensin system of rat salivary glands

Renin-angiotensin system (RAS) systemically or locally collaborates with tissue homeostasis, growth and development, which has been extensively studied for its pharmacological implications. This study was primarily aimed at finding and characterizing local RAS in rat parotid, sublingual and submandibular glands. It was also hypothesized that vasoactive drugs could affect the expression of RAS targets, as well as saliva flow and its composition. Therefore, another objective of this study was to compare the effects of losartan (angiotensin II receptor blocker) and isoproterenol (β-adrenergic receptor agonist). Forty-one Wistar rats were divided into three groups and administered a daily intraperitoneal dose of saline, losartan or isoproterenol solutions for one week. The following RAS targets were studied using qPCR: renin (REN), angiotensinogen (AGT), angiotensin converting enzyme (ACE), ACE-2, elastase-2 (ELA-2), AT1-a and MAS receptors, using RPL-13 as a reference gene. Morphology of glands was analyzed by immunohistochemistry using REN, ACE, ACE-2, AT1, AT2 and MAS antibodies. The volume and total protein content of saliva were measured. Our results revealed that ACE, ACE-2, AT1-a, AT2 and MAS receptors were expressed in all salivary gland samples, but REN and ELA-2 were absent. Losartan decreased mRNA expression of RAS targets in parotid (MAS) and submandibular glands (ACE and both AT receptors), without affecting morphological alterations, and significantly decreased saliva and total protein secretions. Isoproterenol treatment affected gene expression profiles in parotid (ACE, ACE-2, AT1-a, MAS, AGT), and submandibular (ACE, AT2, AGT) glands, thus promoting acinar hypertrophy in serous acini, without significant changes in salivary flow or total protein content. These drugs affected mainly acini, followed by duct systems and myoepithelial cells, whereas blood vessels were not affected. In conclusion, there is a local RAS in major rat salivary glands and losartan, an angiotensin II receptor blocker, affected not only the RAS-target gene expression but also decreased salivary flow and total protein content.

A microanalytical capillary electrophoresis mass spectrometry assay for quantifying angiotensin peptides in the brain

The renin-angiotensin system (RAS) of the brain produces a series of biologically active angiotensinogen-derived peptides involved in physiological homeostasis and pathophysiology of disease. Despite significant research efforts to date, a comprehensive understanding of brain RAS physiology is lacking. A significant challenge has been the limited set of bioanalytical assays capable of detecting angiotensin (Ang) peptides at physiologically low concentrations (2-15 fmol/g of wet tissue) and sufficient chemical specificity for unambiguous molecular identifications. Additionally, a complex brain anatomy calls for microanalysis of specific tissue regions, thus further taxing sensitivity requirements for identification and quantification in studies of the RAS. To fill this technology gap, we here developed a microanalytical assay by coupling a laboratory-built capillary electrophoresis (CE) nano-electrospray ionization (nano-ESI) platform to a high-resolution mass spectrometer (HRMS). Using parallel reaction monitoring, we demonstrated that this technology achieved confident identification and quantification of the Ang peptides at approx. 5 amol to 300 zmol sensitivity. This microanalytical assay revealed differential Ang peptide profiles between tissues that were micro-sampled from the subfornical organ and the paraventricular nucleus of the hypothalamus, important brain regions involved in thirst and water homeostasis and neuroendocrine regulation to stress. Microanalytical CE-nano-ESI-HRMS extends the analytical toolbox of neuroscience to help better understand the RAS.

Vitamin D supplementation alters the expression of genes associated with hypertension and did not induce DNA damage in rats

Vitamin D3 deficiency has been correlated with altered expression of genes associated with increased blood pressure (BP); however, the role of vitamin D3 supplementation in the genetic mechanisms underlying hypertension remains unclear. Thus, the aim of this study was investigate the consequences of vitamin D3 supplemented (10,000 IU/kg) or deficient (0 IU/kg) diets on regulation of expression of genes related to hypertension pathways in heart cells of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) controls. An additional aim was to assess the impact of vitamin D3 on DNA damage and oxidative stress markers. The gene expression profiles were determined by PCR array, DNA damage was assessed by an alkaline comet assay, and oxidative stress markers by measurement of thiobarbituric acid reactive substances (TBARS) and glutathione (GSH) levels. In SHR rats data showed that the groups of genes most differentially affected by supplemented and deficient diets were involved in BP regulation and renin-angiotensin system. In normotensive WKY controls, the profile of gene expression was similar between the two diets. SHR rats were more sensitive to changes in gene expression induced by dietary vitamin D3 than normotensive WKY animals. In addition to gene expression profile, vitamin D3 supplemented diet did not markedly affect DNA or levels of TBARS and GSH levels in both experimental groups. Vitamin D3 deficient diet produced lipid peroxidation in SHR rats. The results of this study contribute to a better understanding of the role of vitamin D3 in the genetic mechanisms underlying hypertension. Abbreviations: AIN, American Institute of Nutrition; EDTA, disodium ethylenediaminetetraacetic acid; GSH, glutathione; PBS, phosphate buffer solution; SHR, spontaneously hypertensive rats; TBARS, thiobarbituric acid reactive substances; WKY, Wistar Kyoto.

Angiotensin-(1-7) inhibits sodium transport via Mas receptor by increasing nitric oxide production in thick ascending limb

Sodium transport in the thick ascending loop of Henle (TAL) is tightly regulated by numerous factors, especially angiotensin II (Ang II), a key end-product of the renin-angiotensin system (RAS). However, an alternative end-product of the RAS, angiotensin-(1-7) [Ang-(1-7)], may counter some of the Ang II actions. Indeed, it causes vasodilation and promotes natriuresis through its effects in the proximal and distal tubule. However, its effects on the TAL are unknown. Because the TAL expresses the Mas receptor, an Ang-(1-7) ligand, which in turn may increase NO and inhibit Na+ transport, we hypothesized that Ang-(1-7) inhibits Na transport in the TAL, via a Mas receptor/NO-dependent mechanism. We tested this by measuring transport-dependent oxygen consumption (VO2 ) in TAL suspensions. Administering Ang-(1-7) decreased VO2 ; an effect prevented by dimethyl amiloride and furosemide, signifying that Ang-(1-7) inhibits transport-dependent VO2 in TAL. Ang-(1-7) also increased NO levels, known inhibitors of Na+ transport in the TAL. The effects of Ang-(1-7) on VO2 , as well as on NO levels, were ameliorated by the Mas receptor antagonist, D-Ala, in effect suggesting that Ang-(1-7) may inhibit transport-dependent VO2 in TAL via Mas receptor-dependent activation of the NO pathway. Indeed, blocking NO synthesis with L-NAME prevented the inhibitory actions of Ang-(1-7) on VO2 . Our data suggest that Ang-(1-7) may modulate TAL Na+ transport via Mas receptor-dependent increases in NO leading to the inhibition of transport activity.

The renin-angiotensin-aldosterone system and its suppression

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

Obesity is Associated with Higher Blood Pressure and Higher Levels of Angiotensin II but Lower Angiotensin-(1-7) in Adolescents Born Preterm

OBJECTIVES

To evaluate if obesity is associated with increased angiotensin II (Ang II) and decreased angiotensin-(1-7) or Ang-(1-7) in the circulation and urine among adolescents born prematurely.

STUDY DESIGN

In a cross-sectional analysis of 175 14-year-olds born preterm with very low birth weight, we quantified plasma and urinary Ang II and Ang-(1-7) and compared their levels between subjects with overweight/obesity (body mass index ≥85th percentile, n = 61) and those with body mass index <85th percentile (n = 114) using generalized linear models, adjusted for race and antenatal corticosteroid exposure.

RESULTS

Overweight/obesity was associated with higher systolic blood pressure and a greater proportion with high blood pressure. After adjustment for confounders, overweight/obesity was associated with an elevated ratio of plasma Ang II to Ang-(1-7) (β: 0.57, 95% CI 0.23-0.91) and higher Ang II (β: 0.21 pmol/L, 95% CI 0.03-0.39) but lower Ang-(1-7) (β: -0.37 pmol/L, 95% CI -0.7 to -0.04). Overweight/obesity was associated with a higher ratio of urinary Ang II to Ang-(1-7) (β: 0.21, 95% CI -0.02 to 0.44), an effect that approached statistical significance.

CONCLUSIONS

Among preterm-born adolescents, overweight/obesity was associated with increased Ang II but reduced Ang-(1-7) in the circulation and the kidney as well as higher blood pressure. Obesity may compound the increased risk of hypertension and cardiovascular disease in individuals born prematurely by further augmenting the prematurity-associated imbalance in the renin-angiotensin system.

The renin-angiotensin system: going beyond the classical paradigms

Thirty years ago, a novel axis of the renin-angiotensin system (RAS) was unveiled by the discovery of angiotensin-(1−7) [ANG-(1−7)] generation in vivo. Later, angiotensin-converting enzyme 2 (ACE2) was shown to be the main mediator of this reaction, and Mas was found to be the receptor for the heptapeptide. The functional analysis of this novel axis of the RAS that followed its discovery revealed numerous protective actions in particular for cardiovascular diseases. In parallel, similar protective actions were also described for one of the two receptors of ANG II, the ANG II type 2 receptor (AT₂R), in contrast to the other, the ANG II type 1 receptor (AT₁R), which mediates deleterious actions of this peptide, e.g., in the setting of cardiovascular disease. Very recently, another branch of the RAS was discovered, based on angiotensin peptides in which the amino-terminal aspartate was replaced by alanine, the alatensins. Ala-ANG-(1−7) or alamandine was shown to interact with Mas-related G protein-coupled receptor D, and the first functional data indicated that this peptide also exerts protective effects in the cardiovascular system. This review summarizes the presentations given at the International Union of Physiological Sciences Congress in Rio de Janeiro, Brazil, in 2017, during the symposium entitled “The Renin-Angiotensin System: Going Beyond the Classical Paradigms,” in which the signaling and physiological actions of ANG-(1−7), ACE2, AT₂R, and alatensins were reported (with a focus on noncentral nervous system-related tissues) and the therapeutic opportunities based on these findings were discussed.

Fetal programming and the angiotensin-(1-7) axis: a review of the experimental and clinical data

Hypertension is the primary risk factor for cardiovascular disease that constitutes a serious worldwide health concern and a significant healthcare burden. As the majority of hypertension has an unknown etiology, considerable research efforts in both experimental models and human cohorts has focused on the premise that alterations in the fetal and perinatal environment are key factors in the development of hypertension in children and adults. The exact mechanisms of how fetal programming events increase the risk of hypertension and cardiovascular disease are not fully elaborated; however, the focus on alterations in the biochemical components and functional aspects of the renin-angiotensin (Ang) system (RAS) has predominated, particularly activation of the Ang-converting enzyme (ACE)-Ang II-Ang type 1 receptor (AT1R) axis. The emerging view of alternative pathways within the RAS that may functionally antagonize the Ang II axis raise the possibility that programming events also target the non-classical components of the RAS as an additional mechanism contributing to the development and progression of hypertension. In the current review, we evaluate the potential role of the ACE2-Ang-(1-7)-Mas receptor (MasR) axis of the RAS in fetal programming events and cardiovascular and renal dysfunction. Specifically, the review examines the impact of fetal programming on the Ang-(1-7) axis within the circulation, kidney, and brain such that the loss of Ang-(1-7) expression or tone, contributes to the chronic dysregulation of blood pressure (BP) and cardiometabolic disease in the offspring, as well as the influence of sex on potential programming of this pathway.

Causes and Consequences of the Dysregulated Maternal Renin-Angiotensin System in Preeclampsia

A healthy pregnancy outcome depends on the activation of the renin-angiotensin-aldosterone system (RAAS) as a regulated, integrated response to the growing demands of the conceptus. Both the circulating RAAS and the intrarenal renin-angiotensin system (iRAS) play major roles in cardiovascular function and fluid and electrolyte homeostasis. The circulating RAAS becomes dysfunctional in preeclampsia and we propose that dysregulation of the iRAS plays a role in development of the clinical syndrome known as preeclampsia. Experimental studies in animals have shown that placental renin, when released into the maternal circulation, can cause hypertension. We postulate that abnormal placental development is associated with over-secretion of renin and other RAS proteins/angiotensin (Ang) peptides by the placenta/decidua into the maternal circulation. We hypothesise that this is because of increased shedding of exosomes and other placental particles into the maternal circulation that not only contain RAS proteins and peptides but also microRNAs (miRNAs) that target RAS mRNAs, and Ang II type 1 receptor autoantibodies (AT₁R-AAs), that are agonists for, and have the same actions as, Ang II. As a result, there is both suppression of the circulating RAAS that is responsible for maintaining maternal homeostasis and activation of the iRAS. Together with altered vascular reactivity to Ang peptides, the iRAS causes hypertension, renal damage and secondary changes in the neurohumoral control of the maternal circulation and fluid and electrolyte balance, which contribute to the pathophysiology of preeclampsia.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Benchmarking renin suppression and blood pressure reduction of direct renin inhibitor imarikiren through quantitative systems pharmacology modeling

Multiple classes of antihypertensive drugs inhibit components of the renin-angiotensin-aldosterone system (RAAS). The primary physiological effector of the RAAS is angiotensin II (AngII) bound to the AT1 receptor (AT1-bound AngII). There is a strong non-linear feedback from AT1-bound AngII on renin secretion. Since AT1-bound AngII is not readily measured experimentally, plasma renin concentration (PRC) and/or activity (PRA) are typically measured to indicate RAAS suppression. We investigated the RAAS suppression of imarikiren hydrochloride (TAK-272; SCO-272), a direct renin inhibitor currently under clinical development. We employed a previously developed quantitative system pharmacology (QSP) model to benchmark renin suppression and blood pressure regulation with imarikiren compared to other RAAS therapies. A pharmacokinetic (PK) model of imarikiren was linked with the existing QSP model, which consists of a mechanistic representation of the RAAS pathway coupled with a model of blood pressure regulation and volume homeostasis. The PK and pharmacodynamic effects of imarikiren were calibrated by fitting drug concentration, PRA, and PRC data, and trough AT1-bound AngII suppression was simulated. We also prospectively simulated expected mean arterial pressure reduction in a cohort of hypertensive virtual patients. These predictions were benchmarked against predictions for several other (previously calibrated) RAAS monotherapies and dual-RAAS therapies. Our analysis indicates that low doses (5-10 mg) of imarikiren are comparable to current RAAS therapies, and at higher doses (25-200 mg), RAAS suppression may be equivalent to existing dual-RAAS combinations (at registered doses). This study illustrates application of QSP modeling to predict phase II endpoints from phase I data.

A Genomic Survey of Angiotensin-Converting Enzymes Provides Novel Insights into Their Molecular Evolution in Vertebrates

Angiotensin-converting enzymes, ACE and ACE2, are two main elements in the renin⁻angiotensin system, with a crucial role in the regulation of blood pressure in vertebrates. Previous studies paid much attention to their physiological functions in model organisms, whereas the studies on other animals and related evolution have been sparse. Our present study performed a comprehensive genomic investigation on ace and ace2 genes in vertebrates. We successfully extracted the nucleotide sequences of ace and ace2 genes from high-quality genome assemblies of 36 representative vertebrates. After construction of their evolutionary tree, we observed that most of the phylogenetic positions are consistent with the species tree; however, certain differences appear in coelacanths and frogs, which may suggest a very slow evolutionary rate in the initial evolution of ace and ace2 in vertebrates. We further compared evolutionary rates within the entire sequences of ace and ace2, and determined that ace2 evolved slightly faster than ace. Meanwhile, we counted that the exon numbers of ace and ace2 in vertebrates are usually 25 and 18 respectively, while certain species may occur exon fusion or disruption to decrease or increase their exon numbers. Interestingly, we found three homologous regions between ace and ace2, suggesting existence of gene duplication during their evolutionary process. In summary, this report provides novel insights into vertebrate ace and ace2 genes through a series of genomic and molecular comparisons.

Comparative Expression of Renin-Angiotensin Pathway Proteins in Visceral Versus Subcutaneous Fat

Body fat distribution contributes to obesity-related metabolic and cardiovascular disorders. Visceral fat is more detrimental than subcutaneous fat. However, the mechanisms underlying visceral fat-mediated cardiometabolic dysregulation are not completely understood. Localized increases in expression of the renin angiotensin system (RAS) in adipose tissue (AT) may be implicated. We therefore investigated mRNA and protein expression of RAS components in visceral versus subcutaneous AT using paired samples from individuals undergoing surgery (N = 20, body mass index: 45.6 ± 6.2 kg/m², and age: 44.6 ± 9.1 years). We also examined RAS-related proteins in AT obtained from individuals on renin angiotensin aldosterone system (RAAS) targeted drugs (N = 10, body mass index: 47.2 ± 9.3 kg/m², and age: 53.3 ± 10.1 years). Comparison of protein expression between subcutaneous and visceral AT samples showed an increase in renin (p = 0.004) and no change in angiotensinogen (p = 0.987) expression in visceral AT. Among proteins involved in angiotensin peptide generation, angiotensin converting enzyme (p = 0.02) was increased in subcutaneous AT while chymase (p = 0.001) and angiotensin converting enzyme-2 (p = 0.001) were elevated in visceral fat. Furthermore, visceral fat expression of angiotensin II type-2 receptor (p = 0.007) and angiotensin II type-1 receptor (p = 0.031) was higher, and MAS receptor (p < 0.001) was lower. Phosphorylated-p53 (p = 0.147), AT fibrosis (p = 0.138) and average adipocyte size (p = 0.846) were similar in the two depots. Nonetheless, visceral AT showed increased mRNA expression of inflammatory (TNFα, p < 0.001; IL-6, p = 0.001) and oxidative stress markers (NOX2, p = 0.038; NOX4, p < 0.001). Of note, mRNA and protein expression of RAS components did not differ between subjects taking or not taking RAAS related drugs. In summary, several RAS related proteins are differentially expressed in subcutaneous versus visceral AT. This differential expression may not alter AngII but likely increases Ang1-7 generation in visceral fat. These potential differences in active angiotensin peptides and receptor expression in the two depots suggest that localized RAS may not be involved in differences in visceral vs subcutaneous AT function in obese individuals. Our findings do not support a role for localized RAS differences in visceral fat-mediated development of cardiovascular and metabolic pathology.

Renal tubular dysgenesis and microcolon, a novel association. Report of three cases

Renal tubular dysgenesis (RTD) is a developmental abnormality of the nephron characterized by fetal anuria, oligohydramnios, and severe postnatal hypotension. Genetic forms have an autosomal recessive inheritance and are caused by mutations in genes encoding key components of the renin-angiotensin pathway. We report three patients from two unrelated families with RTD due to pathogenic variants of the angiotensin-converting enzyme (ACE) gene, in whom RTD was associated with microcolon. We also detail key variations of the renin-angiotensin system in one of these infants. The severe intestinal developmental abnormality culminating in microcolon and early terminal ileum perforation/necrotizing enterocolitis is a novel finding not previously associated with RTD, which points to a role of the renin-angiotensin system in gut development.

Caffeine in Kidney Stone Disease: Risk or Benefit?

Kidney stone disease is a global health care problem, with a high recurrence rate after stone removal. It is thus crucial to develop effective strategies to prevent the formation of new or recurrent stones. Caffeine is one of the main components in caffeinated beverages worldwide (i.e., coffee, tea, soft drinks, and energy drinks). Previous retrospective and prospective studies have reported contradictory effects of caffeine on kidney stone risk. Although it has a diuretic effect on enhancing urinary output, it may slightly increase the stone risk index. However, 3 large cohorts have suggested a preventive role of caffeine in kidney stone disease. In addition, a recent in vitro study has addressed relevant mechanisms underlying the preventive role of caffeine against stone pathogenesis. This review summarizes the relevant data from previous evidence and discusses the association between caffeine consumption and kidney stone risk reduction.

Focus on increased serum angiotensin-converting enzyme level: From granulomatous diseases to genetic mutations

Angiotensin I-converting enzyme (ACE) is a well-known zinc-metallopeptidase that converts angiotensin I to the potent vasoconstrictor angiotensin II and degrades bradykinin, a powerful vasodilator, and as such plays a key role in the regulation of vascular tone and cardiac function. Increased circulating ACE (cACE) activity has been reported in multiple diseases, including but not limited to granulomatous disorders. Since 2001, genetic mutations leading to cACE elevation have also been described. This review takes advantage of the identification of a novel ACE mutation (25-IVS25 + 1G > A) in two Belgian pedigrees to summarize current knowledge about the differential diagnosis of cACE elevation, based on literature review and the experience of our centre. Furthermore, we propose a practical approach for the evaluation and management of patients with elevated cACE and discuss in which cases search for genetic mutations should be considered.

Inappropriate activity of local renin-angiotensin-aldosterone system during high salt intake: impact on the cardio-renal axis

Although there is a general agreement on the recommendation for reduced salt intake as a public health issue, the mechanism by which high salt intake triggers pathological effects on the cardio-renal axis is not completely understood. Emerging evidence indicates that the renin-angiotensin-aldosterone system (RAAS) is the main target of high Na⁺ intake. An inappropriate activation of tissue RAAS may lead to hypertension and organ damage. We reviewed the impact of high salt intake on the RAAS on the cardio-renal axis highlighting the molecular pathways that leads to injury effects. We also provide an assessment of recent observational studies related to the consequences of non-osmotically active Na⁺ accumulation, breaking the paradigm that high salt intake necessarily increases plasma Na⁺ concentration promoting water retention

Novel ACE2-Fc chimeric fusion provides long-lasting hypertension control and organ protection in mouse models of systemic renin angiotensin system activation

Angiotensin-converting enzyme 2 (ACE2) is a carboxypeptidase that potently degrades angiotensin II to angiotensin 1-7. Previous studies showed that injection of the enzymatic ectodomain of recombinant ACE2 (rACE2) markedly increases circulatory levels of ACE2 activity, and effectively lowered blood pressure in angiotensin II-induced hypertension. However, due to the short plasma half-life of rACE2, its therapeutic potential for chronic use is limited. To circumvent this, we generated a chimeric fusion of rACE2 and the immunoglobulin fragment Fc segment to increase its plasma stability. This rACE2-Fc fusion protein retained full peptidase activity and exhibited greatly extended plasma half-life in mice, from less than two hours of the original rACE2, to over a week. A single 2.5 mg/kg injection of rACE2-Fc increased the overall angiotensin II-conversion activities in blood by up to 100-fold and enhanced blood pressure recovery from acute angiotensin II induced hypertension seven days after administration. To assess rACE2-Fc given weekly on cardiac protection, we performed studies in mice continuously infused with angiotensin II for 28 days and in a Renin transgenic mouse model of hypertension. The angiotensin II infused mice achieved sustained blood pressure control and reduced cardiac hypertrophy and fibrosis. In chronic hypertensive transgenic mice, weekly injections of rACE2-Fc effectively lowered plasma angiotensin II and blood pressure. Additionally, rACE2-Fc ameliorated albuminuria, and reduced kidney and cardiac fibrosis. Thus, our chimeric fusion strategy for rACE2-Fc is suitable for future development of new renin angiotensin system-based inhibition therapies.

Angiotensin-(1-7) and Alamandine on Experimental Models of Hypertension and Atherosclerosis

PURPOSE OF REVIEW

The purpose of this review was to summarize the current knowledge on the role of angiotensin-(1-7) [Ang-(1-7)] and alamandine in experimental hypertension and atherosclerosis.

RECENT FINDINGS

The renin-angiotensin system (RAS) is a very complex system, composed of a cascade of enzymes, peptides, and receptors, known to be involved in the pathogenesis of hypertension and atherosclerosis. Ang-(1-7), identified and characterized in 1987, and alamandine, discovered 16 years after, are the newest two main effector molecules from the RAS, protecting the vascular system against hypertension and atherosclerosis. While the beneficial effects of Ang-(1-7) have been widely studied in several experimental models of hypertension, much less studies were performed in experimental models of atherosclerosis. Alamandine has shown similar vascular effects to Ang-(1-7), namely, endothelial-dependent vasorelaxation mediated by nitric oxide and hypotensive effects in experimental hypertension. There are few studies on the effects of alamandine on atherosclerosis.

Regulation, signalling and functions of hormonal peptides in pulmonary vascular remodelling during hypoxia

Hypoxic state affects organism primarily by decreasing the amount of oxygen reaching the cells and tissues. To adjust with changing environment organism undergoes mechanisms which are necessary for acclimatization to hypoxic stress. Pulmonary vascular remodelling is one such mechanism controlled by hormonal peptides present in blood circulation for acclimatization. Activation of peptides regulates constriction and relaxation of blood vessels of pulmonary and systemic circulation. Thus, understanding of vascular tone maintenance and hypoxic pulmonary vasoconstriction like pathophysiological condition during hypoxia is of prime importance. Endothelin-1 (ET-1), atrial natriuretic peptide (ANP), and renin angiotensin system (RAS) function, their receptor functioning and signalling during hypoxia in different body parts point them as disease markers. In vivo and in vitro studies have helped understanding the mechanism of hormonal peptides for better acclimatization to hypoxic stress and interventions for better management of vascular remodelling in different models like cell, rat, and human is discussed in this review.

The renin angiotensin system in liver and lung: impact and therapeutic potential in organ fibrosis

Liver and lung fibrosis are two main organ diseases that are of particular importance in both Egypt and the US. Hepatitis C Virus "HCV" infection and idiopathic pulmonary fibrosis (IPF) are fibrotic diseases of the liver and lung respectively. The liver and lung are reported in literature to share many immune/inflammatory responses to damage through the lung-liver axis. Most importantly, HCV was shown to enhance the development of IPF and is considered one of the risk factors for IPF. The renin angiotensin system (RAS) plays a critical role in the fibrogenesis and inflammation damage of many organs including liver and lung. The relatively recently identified component of RAS, angiotensin converting enzyme-2 (ACE-2), has shown a promising therapeutic potential in models of liver and pulmonary fibrosis. This article reviews the role of RAS in organ fibrosis with focus on role of ACE-2 in fibrotic diseases of the liver and the lung.

The Role of Renin-Angiotensin-Aldosterone System and Its New Components in Arterial Stiffness and Vascular Aging

Many cardiovascular diseases present renin-angiotensin-aldosterone system (RAAS) hyperactivity as an important pathophysiological mechanism to be target in the therapeutic approaches. Moreover, arterial stiffness is currently considered as a new independent risk factor for cardiovascular disease in different clinical conditions, including hypertension and chronic kidney disease. In fact, excessive stimulation of angiotensin type 1 (AT1) receptors, as well as mineralocorticoid receptors, results in cellular growth, oxidative stress and vascular inflammation, which may lead to arterial stiffness and accelerate the process of vascular aging. In the last decades, a vasoprotective axis of the RAAS has been discovered, and now it is well established that new components with antioxidant and anti-inflammatory properties play important roles promoting vasodilation, natriuresis and reducing collagen deposition, thus attenuating arterial stiffness and improving endothelial function. In this review, we will focus on these pathophysiological mechanisms and the relevance of RAAS inhibition by different strategies to increase arterial compliance and to decelerate vascular aging.

Intracrine action of angiotensin II in mesangial cells: subcellular distribution of angiotensin II receptor subtypes AT1 and AT2

Biological effects of angiotensin II (AngII) such as regulation of AngII target genes may be triggered by interaction of AngII with intracellular AngII receptor types 1 and 2 (AT₁ and AT₂), defined as intracrine response. The aim of this study was to examine the presence of AT₁ and AT₂ receptors in nuclear membrane of human mesangial cells (HMCs) and evaluate the possible biological effects mediated by intracellular AT₁ through an intracrine mechanism. Subcellular distribution of AT₁ and AT₂ was evaluated by immunofluorescence and by western blot in isolated nuclear extract. Endogenous intracellular synthesis of AngII was stimulated by high glucose (HG). Effects of HG were analyzed in the presence of candesartan, which prevents AngII internalization. Both receptors were found in nuclear membrane. Fluorescein isothiocyanate (FITC)-labeled AngII added to isolated nuclei produced a fluorescence that was reduced in the presence of losartan or PD-123319 and quenched in the presence of both inhibitors simultaneously. HG induced overexpression of fibronectin and increased cell proliferation in the presence of candesartan, indicating an intracrine action of AngII induced by HG. Results showed the presence of nuclear receptors in HMCs that can be activated by AngII through an intracrine response independent of cytoplasmic membrane AngII receptors.

Sex Differences in Regulation of Blood Pressure

Hypertension is one of the leading risk factors for cardiovascular disease, myocardial infarction, and stroke. There are gender differences in the prevalence of hypertension and in the mechanisms responsible for hypertension in humans. This review will discuss the mechanisms for regulation of blood pressure, sex differences that have been identified in animal studies, and the gender differences that have been identified in humans.

Hypertension regulating angiotensin peptides in the pathobiology of cardiovascular disease

Renin angiotensin system (RAS) is an endogenous hormone system involved in the control of blood pressure and fluid volume. Dysregulation of RAS has a pathological role in causing cardiovascular diseases through hypertension. Among several key components of RAS, angiotensin peptides, varying in amino acid length and biological function, have important roles in preventing or promoting hypertension, cardiovascular diseases, stroke, vascular remodeling etc. These peptides are generated by the metabolism of inactive angiotensinogen or its derived peptides by hydrolyzing action of certain enzymes. Angiotensin II, angiotensin (1-12), angiotensin A and angiotensin III bind primarily to angiotensin II type 1 receptor and cause vasoconstriction, accumulation of inflammatory markers to sub-endothelial region of blood vessels and activate smooth muscle cell proliferation. Moreover, when bound to angiotensin II type 2 receptor, angiotensin II works as cardio-protective peptide and halt pathological cell signals. Other peptides like angiotensin (1-9), angiotensin (1-7), alamandine and angiotensin IV also help in protecting from cardiovascular diseases by binding to their respective receptors.

Therapeutic Approaches to the Alternative Angiotensin-(1-7) Axis of the Renin-Angiotensin System

Cardiovascular disease remains the leading cause of death for both men and women in the United States despite the recent advances in drug development, changes in lifestyle and screening protocols. A key target in the treatment of cardiovascular disease and hypertension is the renin-angiotensinsystem (RAS), a circulating and tissue system involved in the regulation of blood pressure, fluid balance and cellular injury. Pharmacologic approaches have traditionally focused on the Ang II-AT1receptor axis of the RAS to prevent the generation of Ang II with angiotensin converting enzyme inhibitors (ACEI) or to block the binding of Ang II to the AT1 receptor (AT1R) with selective antagonists (ARBs).

Renin angiotensin aldosterone inhibition in the treatment of cardiovascular disease

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

Angiotensin II Receptor-Neprilysin Inhibitor Sacubitril/Valsartan Improves Endothelial Dysfunction in Spontaneously Hypertensive Rats

BACKGROUND

We have previously demonstrated that antihypertensive treatment with renin-angiotensin system inhibitors restores the impaired endothelium-dependent hyperpolarization (EDH)-mediated responses in spontaneously hypertensive rats (SHRs). Herein, we investigated whether the angiotensin II receptor-neprilysin inhibitor sacubitril/valsartan (LCZ696) would improve reduced EDH-mediated responses and whether LCZ696 would exert additional effects on endothelium-dependent and endothelium-independent vasorelaxation compared with an angiotensin II type 1 receptor blocker alone during hypertension.

METHODS AND RESULTS

SHRs were treated for 3 months with either LCZ696 or valsartan, from the age of 8 to 11 months. Age-matched, untreated SHRs and Wistar-Kyoto rats served as controls. Membrane potentials and contractile responses were recorded from the isolated superior mesenteric arteries. Acetylcholine-induced, EDH-mediated responses were impaired in untreated SHRs compared with Wistar-Kyoto rats. EDH-mediated responses were similarly improved in the LCZ696- and valsartan-treated SHRs. No difference was observed in acetylcholine-induced, nitric oxide-mediated relaxations among the 4 groups. Endothelium-independent relaxations in response to a nitric oxide donor, sodium nitroprusside, and those to levcromakalim, an ATP-sensitive K+-channel opener, were similar among the 4 groups; however, the sensitivities to levcromakalim were significantly higher in both LCZ696- and valsartan-treated SHRs.

CONCLUSIONS

LCZ696 appears to be as effective as valsartan in improving the impaired EDH-mediated responses during hypertension. LCZ696 and valsartan exert similar beneficial effects on endothelium-independent relaxation via enhanced sensitivity of the ATP-sensitive K+ channel. However, the dual blockade of renin-angiotensin system and neutral endopeptidase with LCZ696 does not appear to provide additional benefit over valsartan alone on vasomotor function in mesenteric arteries of SHRs.

Validation of commercial Mas receptor antibodies for utilization in Western Blotting, immunofluorescence and immunohistochemistry studies

Mas receptor (MasR) is a G protein-coupled receptor proposed as a candidate for mediating the angiotensin (Ang)-converting enzyme 2-Ang (1-7) protective axis of renin-angiotensin system. Because the role of this receptor is not definitively clarified, determination of MasR tissue distribution and expression levels constitutes a critical knowledge to fully understanding its function. Commercially available antibodies have been widely employed for MasR protein localization and quantification, but they have not been adequately validated. In this study, we carried on an exhaustive evaluation of four commercial MasR antibodies, following previously established criteria. Western Blotting (WB) and immunohistochemistry studies starting from hearts and kidneys from wild type (WT) mice revealed that antibodies raised against different MasR domains yielded different patterns of reactivity. Furthermore, staining patterns appeared identical in samples from MasR knockout (MasR-KO) mice. We verified by polymerase chain reaction analysis that the MasR-KO mice used were truly deficient in this receptor as MAS transcripts were undetectable in either heart or kidney from this animal model. In addition, we evaluated the ability of the antibodies to detect the human c-myc-tagged MasR overexpressed in human embryonic kidney cells. Three antibodies were capable of detecting the MasR either by WB or by immunofluorescence, reproducing the patterns obtained with an anti c-myc antibody. In conclusion, although three of the selected antibodies were able to detect MasR protein at high expression levels observed in a transfected cell line, they failed to detect this receptor in mice tissues at physiological expression levels. As a consequence, validated antibodies that can recognize and detect the MasR at physiological levels are still lacking.

Novel Cardiac Intracrine Mechanisms Based on Ang-(1-12)/Chymase Axis Require a Revision of Therapeutic Approaches in Human Heart Disease

PURPOSE OF THE REVIEW

Drugs targeting the renin-angiotensin system (RAS), namely angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers, are the most commonly prescribed drugs for patients with or at risk for cardiovascular events. However, new treatment strategies aimed at mitigating the rise of the heart failure pandemic are warranted because clinical trials show that RAS blockers have limited benefits in halting disease progression. The main goal of this review is to put forward the concept of an intracrine RAS signaling through the novel angiotensin-(1-12)/chymase axis as the main source of deleterious angiotensin II (Ang II) in cardiac maladaptive remodeling leading to heart failure (HF).

RECENT FINDINGS

Expanding traditional knowledge, Ang II can be produced in tissues independently from the circulatory renin-angiotensin system. In the heart, angiotensin-(1-12) [Ang-(1-12)], a recently discovered derivative of angiotensinogen, is a precursor of Ang II, and chymase rather than ACE is the main enzyme contributing to the direct production of Ang II from Ang-(1-12). The Ang-(1-12)/chymase axis is an independent intracrine pathway accounting for the trophic, contractile, and pro-arrhythmic Ang II actions in the human heart. Ang-(1-12) expression and chymase activity have been found elevated in the left atrial appendage of heart disease subjects, suggesting a pivotal role of this axis in the progression of HF. Recent meta-analysis of large clinical trials on the use of ACE inhibitors and angiotensin receptor blockers in cardiovascular disease has demonstrated an imbalance between patients that significantly benefit from these therapeutic agents and those that remain at risk for heart disease progression. Looking to find an explanation, detailed investigation on the RAS has unveiled a previously unrecognized complexity of substrates and enzymes in tissues ultimately associated with the production of Ang II that may explain the shortcomings of ACE inhibition and angiotensin receptor blockade. Discovery of the Ang-(1-12)/chymase axis in human hearts, capable of producing Ang II independently from the circulatory RAS, has led to the notion that a tissue-delimited RAS signaling in an intracrine fashion may account for the deleterious effects of Ang II in the heart, contributing to the transition from maladaptive cardiac remodeling to heart failure. Targeting intracellular RAS signaling may improve current therapies aimed at reducing the burden of heart failure.

The vasoprotective axes of the renin-angiotensin system: Physiological relevance and therapeutic implications in cardiovascular, hypertensive and kidney diseases

The renin-angiotensin system (RAS) is undisputedly one of the most prominent endocrine (tissue-to-tissue), paracrine (cell-to-cell) and intracrine (intracellular/nuclear) vasoactive systems in the physiological regulation of neural, cardiovascular, blood pressure, and kidney function. The importance of the RAS in the development and pathogenesis of cardiovascular, hypertensive and kidney diseases has now been firmly established in clinical trials and practice using renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, type 1 (AT₁) angiotensin II (ANG II) receptor blockers (ARBs), or aldosterone receptor antagonists as major therapeutic drugs. The major mechanisms of actions for these RAS inhibitors or receptor blockers are mediated primarily by blocking the detrimental effects of the classic angiotensinogen/renin/ACE/ANG II/AT₁/aldosterone axis. However, the RAS has expanded from this classic axis to include several other complex biochemical and physiological axes, which are derived from the metabolism of this classic axis. Currently, at least five axes of the RAS have been described, with each having its key substrate, enzyme, effector peptide, receptor, and/or downstream signaling pathways. These include the classic angiotensinogen/renin/ACE/ANG II/AT₁ receptor, the ANG II/APA/ANG III/AT₂/NO/cGMP, the ANG I/ANG II/ACE2/ANG (1-7)/Mas receptor, the prorenin/renin/prorenin receptor (PRR or Atp6ap2)/MAP kinases ERK1/2/V-ATPase, and the ANG III/APN/ANG IV/IRAP/AT₄ receptor axes. Since the roles and therapeutic implications of the classic angiotensinogen/renin/ACE/ANG II/AT₁ receptor axis have been extensively reviewed, this article will focus primarily on reviewing the roles and therapeutic implications of the vasoprotective axes of the RAS in cardiovascular, hypertensive and kidney diseases.

Future drug discovery in renin-angiotensin-aldosterone system intervention

INTRODUCTION

Renin-angiotensin-aldosterone system inhibitors (RAASIs), including angiotensin-converting enzyme inhibitors, angiotensin AT1 receptor blockers and mineralocorticoid receptor antagonists (MRAs), are the cornerstone for the treatment of cardiovascular and renal diseases. Areas covered: The authors searched MEDLINE, PubMed and ClinicalTrials.gov to identify eligible full-text English language papers. Herein, the authors discuss AT2-receptor agonists and ACE2/angiotensin-(1-7)/Mas-receptor axis modulators, direct renin inhibitors, brain aminopeptidase A inhibitors, biased AT1R blockers, chymase inhibitors, multitargeted drugs, vaccines and aldosterone receptor antagonists as well as aldosterone synthase inhibitors. Expert opinion: Preclinical studies have demonstrated that activation of the protective axis of the RAAS represents a novel therapeutic strategy for treating cardiovascular and renal diseases, but there are no clinical trials supporting our expectations. Non-steroidal MRAs might become the third-generation of MRAs for the treatment of heart failure, diabetes mellitus and chronic kidney disease. The main challenge for these new drugs is that conventional RAASIs are safe, effective and cheap generics. Thus, the future of new RAASIs will be directed by economical/strategic reasons.

The ACE2/Angiotensin-(1-7)/Mas Receptor Axis: Pleiotropic Roles in Cancer

Cancer remains one of the most common causes of death and disability and represents a major economic burden in industrialized nations. The renin-angiotensin system (RAS) has been well-recognized as one of the most important regulators of both normal and pathological physiological processes in the brain, kidney, heart, and blood vessels. The activation of the angiotensin-converting enzyme 2/angiotensin-(1–7)/mitochondrial assembly receptor [ACE2/Ang-(1–7)/MasR] axis, which is one component of the RAS, has recently been identified as a critical component of pulmonary systems, gastric mucosa, and cancer. However, the ability of the ACE2/Ang-(1–7)/MasR axis to suppress or promote cancer has not been fully elucidated. In this review, we focus on recent experimental and clinical studies investigating the basic properties, roles, and mechanisms of ACE2, Ang-(1–7), and the MasR, as well as the axis pathway, to provide insights into possible therapeutic strategies for treating cancer that target the ACE2/Ang-(1–7)/MasR axis.

Skeletal muscle wasting: new role of nonclassical renin-angiotensin system

PURPOSE OF REVIEW

Skeletal muscle can be affected by many physiological and pathological conditions that contribute to the development of muscle weakness, including skeletal muscle loss, inflammatory processes, or fibrosis. Therefore, research into therapeutic treatment alternatives or alleviation of these effects on skeletal muscle is of great importance.

RECENT FINDINGS

Recent studies have shown that angiotensin (1-7) [Ang-(1-7)] - a vasoactive peptide of the nonclassical axis in the renin-angiotensin system (RAS) - and its Mas receptor are expressed in skeletal muscle. Ang-(1-7), through its Mas receptor, prevents or diminishes deleterious effects induced by skeletal muscle disease or injury. Specifically, the Ang-(1-7)-Mas receptor axis modulates molecular mechanisms involved in muscle mass regulation, such as the ubiquitin proteasome pathway, the insulin-like growth factor type 1/Akt (protein kinase B) pathway, or myonuclear apoptosis, and also inflammation and fibrosis pathways.

SUMMARY

Although further research into this topic and the possible side effects of Ang-(1-7) is necessary, these findings are promising, and suggest that the Ang-(1-7)-Mas axis can be considered a possible therapeutic target for treating patients with muscular disorders.

Impact of Non-Human Leukocyte Antigen-Specific Antibodies in Kidney and Heart Transplantation

The presence of donor human leukocyte antigen (HLA)-specific antibodies has been shown to be associated with graft loss and decreased patient survival, but it is not uncommon that donor-specific HLA antibodies are absent in patients with biopsy-proven antibody-mediated rejection. In this review, we focus on the latest findings on antibodies against non-HLA antigens in kidney and heart transplantation. These non-HLA antigens include myosin, vimentin, Kα1 tubulin, collagen, and angiotensin II type 1 receptor. It is suggested that the detrimental effects of HLA antibodies and non-HLA antibodies synergize together to impact graft outcome. Injury of graft by HLA antibodies can cause the exposure of neo-antigens which in turn stimulate the production of antibodies against non-HLA antigens. On the other hand, the presence of non-HLA antibodies may increase the risk for a patient to develop HLA-specific antibodies. These findings indicate it is imperative to stratify the patient’s immunologic risk by assessing both HLA and non-HLA antibodies.

A Fluorometric Method of Measuring Carboxypeptidase Activities for Angiotensin II and Apelin-13

Degradation of the biologically potent octapeptide angiotensin Ang II-(1-8) is mediated by the activities of several peptidases. The conversion of Ang II to the septapeptide Ang-(1-7) is of particular interest as the latter also confers organ protection. The conversion is catalyzed by angiotensin-converting enzyme 2 and other enzymes that selectively cleave the peptide bond between the proline and the phenylalanine at the carboxyl terminus of Ang II. The contribution of various enzyme activities that collectively lead to the formation of Ang-(1-7) from Ang II, in both normal conditions and in disease states, remains only partially understood. This is largely due to the lack of a reliable and sensitive method to detect these converting activities in complex samples, such as blood and tissues. Here, we report a fluorometric method to measure carboxypeptidase activities that cleave the proline-phenylalanine dipeptide bond in Ang II. This method is also suitable for measuring the conversion of apelin-13. The assay detects the release of phenylalanine amino acid in a reaction with the yeast enzyme of phenylalanine ammonia lyase (PAL). When used in cell and mouse organs, the assay can robustly measure endogenous Ang II and apelin-13-converting activities involved in the renin-angiotensin and the apelinergic systems, respectively.

Angiotensin-(1-7)-dependent vasorelaxation of the renal artery exhibits unique angiotensin and bradykinin receptor selectivity

Angiotensin-(1-7) [Ang-(1-7)] exhibits blood pressure lowering actions, inhibits cell growth, and reduces tissue inflammation and fibrosis which may functionally antagonize an activated Ang II-AT₁ receptor axis. Since the vascular actions of Ang-(1-7) and the associated receptor/signaling pathways vary in different vascular beds, the current study established the vasorelaxant properties of the heptapeptide in the renal artery of male Wistar male rats. Ang-(1-7) produced an endothelium-dependent vasodilator relaxation of isolated renal artery segments pre-contracted by a sub-maximal concentration of phenylephrine (PE) (3×10^-7M). Ang-(1-7) induced vasodilation of the rat renal artery with an ED₅₀ of 3±1nM and a maximal response of 42±5% (N=10). The two antagonists (10^-5M each) for the AT₇/Mas receptor (MasR) [D-Pro⁷]-Ang-(1-7) and [D-Ala⁷]-Ang-(1-7) significantly reduced the maximal response to 12±1% and 18±3%, respectively. Surprisingly, the AT₂R receptor antagonist PD123319, the AT₁R antagonist losartan and B₂R antagonist HOE140 (10^-6M each) also significantly reduced Ang-(1-7)-induced relaxation to 12±2%, 22±3% and 14±7%, respectively. Removal of the endothelium or addition of the soluble guanylate cyclase (sGC) inhibitor ODQ (10^-5M) essentially abolished the vasorelaxant response to Ang-(1-7) (10±4% and 10±2%, P <0.05). Finally, the NOS inhibitor LNAME (10^-4M) reduced the response to 13±2% (p<0.05), but the cyclooxygenase inhibitor indomethacin failed to block the Ang-(1-7) response. We conclude that Ang-(1-7) exhibits potent vasorelaxant actions in the isolated renal artery that are dependent on an intact endothelium and the apparent stimulation of a NO-sGC pathway. Moreover, Ang-(1-7)-dependent vasorelaxation was sensitive to antagonists against the AT₇/Mas, AT₁, AT₂ and B₂ receptor subtypes.

Circulating progenitor cells in hypertensive subjects: Effectiveness of a treatment with olmesartan in improving cell number and miR profile in addition to expected pharmacological effects

CD34+ circulating progenitor cells (CD34+CPCs) are a population of multipotent cells which can delay the development of atherosclerosis and cardiovascular disease (CVD) in conditions of increased CV risk. MicroRNAs (miRs) 221 and 222 modulate different genes regulating angiogenesis and inflammation; moreover, miR221/22 have beenshown to participate in differentiation and proliferation of CD34+CPCs, inhibiting cell migration and homing. miR221/222 in CD34+CPCs from hypertensive subjects are also increased and associated with CD34+cell number and reactive oxygen species (ROS). We evaluated CD34+CPC number, intracellular miR221/222 and ROS levels, arterial stiffness (AS)and echocardiography indices at baseline (T0).Then, after a six-month treatment with olmesartan, 20 mg/day (T1), in 57 hypertensive patients with left ventricular hypertrophy (LVH) and with no additional risk factor for CVD, and in 29 healthy controls (baseline),fibrinogen, C-reactive protein (CRP), glucose and lipid profiles were also evaluated.At T1, blood pressure values, CRP and fibrinogen levels, ROS and miR221/222 were significantly decreased (all p <0.001), as were AS indices and LV mass index (p<0.001), while cell number was increased (p<0.001). Olmesartan is effective in reducing miR and ROS levels in CD34+CPCs from hypertensive subjects, as well as in increasing CD34+CPC number, providing multilevel CV protection, in addition to its expected pharmacological effects.

Angiotensin II reduces the surface abundance of KV 1.5 channels in arterial myocytes to stimulate vasoconstriction

KEY POINTS

Several different voltage-dependent K⁺ (K_V ) channel isoforms are expressed in arterial smooth muscle cells (myocytes). Vasoconstrictors inhibit K_V currents, but the isoform selectivity and mechanisms involved are unclear. We show that angiotensin II (Ang II), a vasoconstrictor, stimulates degradation of K_V 1.5, but not K_V 2.1, channels through a protein kinase C- and lysosome-dependent mechanism, reducing abundance at the surface of mesenteric artery myocytes. The Ang II-induced decrease in cell surface K_V 1.5 channels reduces whole-cell K_V 1.5 currents and attenuates K_V 1.5 function in pressurized arteries. We describe a mechanism by which Ang II stimulates protein kinase C-dependent K_V 1.5 channel degradation, reducing the abundance of functional channels at the myocyte surface.

ABSTRACT

Smooth muscle cells (myocytes) of resistance-size arteries express several different voltage-dependent K⁺ (K_V ) channels, including K_V 1.5 and K_V 2.1, which regulate contractility. Myocyte K_V currents are inhibited by vasoconstrictors, including angiotensin II (Ang II), but the mechanisms involved are unclear. Here, we tested the hypothesis that Ang II inhibits K_V currents by reducing the plasma membrane abundance of K_V channels in myocytes. Angiotensin II (applied for 2 h) reduced surface and total K_V 1.5 protein in rat mesenteric arteries. In contrast, Ang II did not alter total or surface K_V 2.1, or K_V 1.5 or K_V 2.1 cellular distribution, measured as the percentage of total protein at the surface. Bisindolylmaleimide (BIM; a protein kinase C blocker), a protein kinase C inhibitory peptide or bafilomycin A (a lysosomal degradation inhibitor) each blocked the Ang II-induced decrease in total and surface K_V 1.5. Immunofluorescence also suggested that Ang II reduced surface K_V 1.5 protein in isolated myocytes; an effect inhibited by BIM. Arteries were exposed to Ang II or Ang II plus BIM (for 2 h), after which these agents were removed and contractility measurements performed or myocytes isolated for patch-clamp electrophysiology. Angiotensin II reduced both whole-cell K_V currents and currents inhibited by Psora-4, a K_V 1.5 channel blocker. Angiotensin II also reduced vasoconstriction stimulated by Psora-4 or 4-aminopyridine, another K_V channel inhibitor. These data indicate that Ang II activates protein kinase C, which stimulates K_V 1.5 channel degradation, leading to a decrease in surface K_V 1.5, a reduction in whole-cell K_V 1.5 currents and a loss of functional K_V 1.5 channels in myocytes of pressurized arteries.