On the local cardiac renin angiotensin system. Basic and clinical implications

Increased CaMKII activation and contrast changes of cardiac β1-and β3-Adrenergic signaling pathways in a humanized angiotensinogen model of hypertension

Aims

Upregulation of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) contributes to the pathogenesis of cardiovascular disease, including hypertension. Transgenic rats expressing the human angiotensinogen gene [TGR (hAGT)L1623] are a new novel humanized model of hypertension that associates with declines in cardiac contractile function and β-adrenergic receptor (AR) reserve. The molecular mechanisms are unclear. We tested the hypothesis that in TGR (hAGT)L1623 rats, left ventricular (LV) myocyte CaMKIIδ and β₃-AR are upregulated, but β₁-AR is down-regulated, which are important causes of cardiac dysfunction and β-AR desensitization.

Main methods

We compared LV myocyte CaMKIIδ, CaMKIIδ phosphorylation (at Thr287) (pCaMKIIδ), and β₁-and β₃-AR expressions and determined myocyte functional and [Ca²⁺]_I transient ([Ca²⁺]_iT) responses to β-AR stimulation with and without pretreatment of myocytes using an inhibitor of CaMKII, KN-93 (10^-6 M, 30 min) in male Sprague Dawley (SD; N = 10) control and TGR (hAGT)L1623 (N = 10) adult rats.

Key findings

Hypertension in TGR (hAGT)L1623 rats was accompanied by significantly increased LV myocyte β₃-AR protein levels and reduced β₁-AR protein levels. CaMKIIδ phosphorylation (at Thr287), pCaMKIIδ was significantly increased by 35%. These changes were followed by significantly reduced basal cell contraction (dL/dt_max), relaxation (dR/dt_max), and [Ca²⁺]_iT. Isoproterenol (10^-8 M) produced significantly smaller increases in dL/dt_max, dR/dt_max, and [Ca²⁺]_iT. Moreover, only in TGR (hAGT)L1623 rats, pretreatment of LV myocytes with KN-93 (10^-6 M, 30 min) fully restored normal basal and isoproterenol-stimulated myocyte contraction, relaxation, and [Ca²⁺]_iT.

Significance

LV myocyte CaMKIIδ overactivation with associated contrast changes in β₃-AR and β₁-AR may be the key molecular mechanism for the abnormal contractile phenotype and β-AR desensitization in this humanized model of hypertension.

Prolylcarboxypeptidase Alleviates Hypertensive Cardiac Remodeling by Regulating Myocardial Tissue Angiotensin II

Background Prolonged activation of angiotensin II is the main mediator that contributes to the development of heart diseases, so converting angiotensin II into angiotensin 1-7 has emerged as a new strategy to attenuate detrimental effects of angiotensin II. Prolylcarboxypeptidase is a lysosomal pro-X carboxypeptidase that is able to cleave angiotensin II at a preferential acidic pH optimum. However, insufficient attention has been given to the cardioprotective functions of prolylcarboxylpeptidase. Methods and Results We established a CRISPR/CRISPR-associated protein 9-mediated global prolylcarboxylpeptidase-knockout and adeno-associated virus serotype 9-mediated cardiac prolylcarboxylpeptidase overexpression mouse models, which were challenged with the angiotensin II infusion (2 mg/kg per day) for 4 weeks, aiming to investigate the cardioprotective effect of prolylcarboxylpeptidase against hypertensive cardiac hypertrophy. Prolylcarboxylpeptidase expression was upregulated after 2 weeks of angiotensin II infusion and then became downregulated afterward in wild-type mouse myocardium, suggesting its compensatory function against angiotensin II stress. Moreover, angiotensin II-treated prolylcarboxylpeptidase-knockout mice showed aggravated cardiac remodeling and dampened cardiac contractility independent of hypertension. We also found that prolylcarboxylpeptidase localizes in cardiomyocyte lysosomes, and loss of prolylcarboxylpeptidase led to excessive angiotensin II levels in myocardial tissue. Further screening demonstrated that hypertrophic prolylcarboxylpeptidase-knockout hearts showed upregulated extracellular signal-regulated kinases 1/2 and downregulated protein kinase B activities. Importantly, adeno-associated virus serotype 9-mediated restoration of prolylcarboxylpeptidase expression in prolylcarboxylpeptidase-knockout hearts alleviated angiotensin II-induced hypertrophy, fibrosis, and cell death. Interestingly, the combination of adeno-associated virus serotype 9-mediated prolylcarboxylpeptidase overexpression and an antihypertensive drug, losartan, likely conferred more effective protection than a single treatment protocol to mitigate angiotensin II-induced cardiac dysfunction. Conclusions Our data demonstrate that prolylcarboxylpeptidase protects the heart from angiotensin II-induced hypertrophic remodeling by controlling myocardial angiotensin II levels.

Circadian rhythms of risk factors and management in atherosclerotic and hypertensive vascular disease: Modern chronobiological perspectives of an ancient disease

Atherosclerosis, a chronic inflammatory disease of the arteries that appears to have been as prevalent in ancient as in modern civilizations, is predisposing to life-threatening and life-ending cardiac and vascular complications, such as myocardial and cerebral infarctions. The pathogenesis of atherosclerosis involves intima plaque buildup caused by vascular endothelial dysfunction, cholesterol deposition, smooth muscle proliferation, inflammatory cell infiltration and connective tissue accumulation. Hypertension is an independent and controllable risk factor for atherosclerotic cardiovascular disease (CVD). Conversely, atherosclerosis hardens the arterial wall and raises arterial blood pressure. Many CVD patients experience both atherosclerosis and hypertension and are prescribed medications to concurrently mitigate the two disease conditions. A substantial number of publications document that many pathophysiological changes caused by atherosclerosis and hypertension occur in a manner dependent upon circadian clocks or clock gene products. This article reviews progress in the research of circadian regulation of vascular cell function, inflammation, hemostasis and atherothrombosis. In particular, it delineates the relationship of circadian organization with signal transduction and activation of the renin-angiotensin-aldosterone system as well as disturbance of the sleep/wake circadian rhythm, as exemplified by shift work, metabolic syndromes and obstructive sleep apnea (OSA), as promoters and mechanisms of atherogenesis and risk for non-fatal and fatal CVD outcomes. This article additionally updates advances in the clinical management of key biological processes of atherosclerosis to optimally achieve suppression of atherogenesis through chronotherapeutic control of atherogenic/hypertensive pathological sequelae.

Communication Between Cardiomyocytes and Fibroblasts During Cardiac Ischemia/Reperfusion and Remodeling: Roles of TGF-β, CTGF, the Renin Angiotensin Axis, and Non-coding RNA Molecules

Communication between cells is a foundational concept for understanding the physiology and pathology of biological systems. Paracrine/autocrine signaling, direct cell-to-cell interplay, and extracellular matrix interactions are three types of cell communication that regulate responses to different stimuli. In the heart, cardiomyocytes, fibroblasts, and endothelial cells interact to form the cardiac tissue. Under pathological conditions, such as myocardial infarction, humoral factors released by these cells may induce tissue damage or protection, depending on the type and concentration of molecules secreted. Cardiac remodeling is also mediated by the factors secreted by cardiomyocytes and fibroblasts that are involved in the extensive reciprocal interactions between these cells. Identifying the molecules and cellular signal pathways implicated in these processes will be crucial for creating effective tissue-preserving treatments during or after reperfusion. Numerous therapies to protect cardiac tissue from reperfusion-induced injury have been explored, and ample pre-clinical research has attempted to identify drugs or techniques to mitigate cardiac damage. However, despite great success in animal models, it has not been possible to completely translate these cardioprotective effects to human applications. This review provides a current summary of the principal molecules, pathways, and mechanisms underlying cardiomyocyte and cardiac fibroblast crosstalk during ischemia/reperfusion injury. We also discuss pre-clinical molecules proposed as treatments for myocardial infarction and provide a clinical perspective on these potential therapeutic agents.

Angiotensin II receptor type 1 - An update on structure, expression and pathology

The AT₁ receptor, a major effector of the renin-angiotensin system, has been extensively studied in the context of cardiovascular and renal disease. Moreover, angiotensin receptor blockers, sartans, are among the most frequently prescribed drugs for the treatment of hypertension, chronic heart failure and chronic kidney disease. However, precise molecular insights into the structure of this important drug target have not been available until recently. In this context, seminal studies have now revealed exciting new insights into the structure and biased signaling of the receptor and may thus foster the development of novel therapeutic approaches to enhance the efficacy of pharmacological angiotensin receptor antagonism or to enable therapeutic induction of biased receptor activity. In this review, we will therefore highlight these and other seminal publications to summarize the current understanding of the tertiary structure, ligand binding properties and downstream signal transduction of the AT₁ receptor.

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

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

Alteration in the expression of the renin-angiotensin system in the myocardium of mice conceived by in vitro fertilization

Epidemiological studies have revealed that offspring conceived by in vitro fertilization (IVF) have an elevated risk of cardiovascular malformations at birth, and are more predisposed to cardiovascular diseases. The renin-angiotensin system (RAS) plays an essential role in both the pathogenesis of congenital heart disease in fetuses and cardiovascular dysfunction in adults. This study aimed to assess the relative expression levels of genes in the RAS pathway in mice conceived using IVF, compared to natural mating with superovulation. Results demonstrated that expression of the angiotensin II receptor type 1 (AGTR1), connective tissue growth factor (CTGF), and collagen 3 (COL3), in the myocardial tissue of IVF-conceived mice, was elevated at 3 weeks, 10 weeks, and 1.5 years of age, when compared to their non-IVF counterparts. These data were supported by microRNA microarray analysis of the myocardial tissue of aged IVF-conceived mice, where miR-100, miR-297, and miR-758, which interact with COL3, AGTR1, and COL1 respectively, were upregulated when compared to naturally mated mice of the same age. Interestingly, bisulfite sequencing data indicated that IVF-conceived mice exhibited decreased methylation of CpG sites in Col1. In support of our in vivo investigations, miR-297 overexpression was shown to upregulate AGTR1 and CTGF, and increased cell proliferation in cultured H9c2 cardiomyocytes. These findings indicate that the altered expression of RAS in myocardial tissue might contribute to cardiovascular malformation and/or dysfunction in IVF-conceived offspring. Furthermore, these cardiovascular abnormalities might be the result of altered DNA methylation and abnormal regulation of microRNAs.

Blockade of the angiotensin II type 1 receptor increases bone mineral density and left ventricular contractility in a mouse model of juvenile Paget disease

Juvenile Paget disease (JPD1), an autosomal-recessive disorder, is characterized by extremely rapid bone turnover due to osteoprotegerin deficiency. Its extra-skeletal manifestations, such as hypertension and heart failure, suggest a pathogenesis with shared skeletal and cardiovascular system components. In spite of this, the effects of anti-hypertensive drugs on bone morphometry remain unknown. We administered an angiotensin II type 1 receptor blocker, olmesartan (5 mg/kg/day) to 8-week-old male mice lacking the osteoprotegerin gene, with and without 1 μg/kg/min of angiotensin II infusion for 14 days. Olmesartan treatment decreased systolic blood pressure, and echocardiography showed increased left ventricular systolic contractility. Three-dimensional micro-computed tomography scans demonstrated that olmesartan treatment increased trabecular bone volume (sham, +176%; angiotensin II infusion, +335%), mineral density (sham, +150%; angiotensin II infusion, +313%), and trabecular number (sham, +407%; angiotensin II infusion, +622%) in the tibia. Olmesartan increased cortical mineral density (sham, +19%; angiotensin II infusion, +24%), decreased the cortical bone section area (sham, -16%; angiotensin II infusion, -18%), decreased thickness (sham, -18%; angiotensin II infusion, -31%), and decreased the lacunar area (sham, -41%; angiotensin II infusion, -27%) in the tibia. Similar trend was observed in the femur. Moreover, olmesartan decreased angiotensin II-induced increases in tartrate-resistant acid phosphatase concentrations in plasma, but it affected neither type I procollagen N-terminal propeptides, nor the receptor activator of nuclear factor kappa-B ligand. Our data suggest that blockade of the angiotensin II type 1 receptor improves bone vulnerability, and helps to maintain the heart's structural integrity in osteoprotegerin-deficient mice.

Angiotensin II type 2 receptor blocker PD123319 has more beneficial effects than losartan on ischemia-reperfusion injury and oxidative damage in isolated rat heart

Our study aimed to determine the effects of losartan and PD123319 in ischemia-reperfusion (IR) injury in isolated perfused rat heart. The study used 40 male Wistar albino rats that were grouped as Control, IR, and IR treatment groups that received losartan (20 mg/kg), PD123319 (20 mg/kg), and losartan+PD123319. The hearts were attached to Langendorff isolated heart system by employing in situ cannulation method, and cardiodynamic parameters were recorded during the experiment. At the end of experiment, hearts were retained for biochemical analysis and all data were statistically evaluated. A partial recovery of cardiodynamic parameters was observed in all treatment groups. A significant increase in oxidative stress parameters were seen in the IR group, whereas all treatment groups exhibited lower increase. Furthermore, levels of all antioxidant parameters were significantly lower in the IR group, but higher in the treatment groups. Effects on all parameters were much more remarkable in the PD123319 group. Levels of angiotensin II and renin were increased (P < 0.001) with IR application and decreased (P < 0.001) with the treatment of both antagonists. In conclusion, treatment of losartan and PD123319 played a cardioprotective role against IR injury, PD123319 being more effective in this protection.

Cellular Mechanisms of Valvular Thickening in Early and Intermediate Calcific Aortic Valve Disease

Background:

Calcific aortic valve disease is common in an aging population. It is an ac-tive atheroinflammatory process that has an initial pathophysiology and similar risk factors as athero-sclerosis. However, the ultimate disease phenotypes are markedly different. While coronary heart dis-ease results in rupture-prone plaques, calcific aortic valve disease leads to heavily calcified and ossi-fied valves. Both are initiated by the retention of low-density lipoprotein particles in the subendotheli-al matrix leading to sterile inflammation. In calcific aortic valve disease, the process towards calcifica-tion and ossification is preceded by valvular thickening, which can cause the first clinical symptoms. This is attributable to the accumulation of lipids, inflammatory cells and subsequently disturbances in the valvular extracellular matrix. Fibrosis is also increased but the innermost extracellular matrix layer is simultaneously loosened. Ultimately, the pathological changes in the valve cause massive calcifica-tion and bone formation - the main reasons for the loss of valvular function and the subsequent myo-cardial pathology.

Conclusion:

Calcification may be irreversible, and no drug treatments have been found to be effec-tive, thus it is imperative to emphasize lifestyle prevention of the disease. Here we review the mecha-nisms underpinning the early stages of the disease.

Blockade of AT1 type receptors for angiotensin II prevents cardiac microvascular fibrosis induced by chronic stress in Sprague-Dawley rats

To test the effects of chronic-stress on the cardiovascular system, the model of chronic mild unpredictable stress (CMS) has been widely used. The CMS protocol consists of the random, intermittent, and unpredictable exposure of laboratory animals to a variety of stressors, during 3 consecutive weeks. In this study, we tested the hypothesis that exposure to the CMS protocol leads to left ventricle microcirculatory remodeling that can be attenuated by angiotensin II receptor blockade. Male Sprague-Dawley rats were randomly assigned into four groups: Control, Stress, Control + losartan, and Stress + losartan (N = 6, each group, losartan: 20 mg/kg/day). The rats were euthanized 15 days after CMS exposure, and blood samples and left ventricle were collected. Rats submitted to CMS presented increased glycemia, corticosterone, noradrenaline and adrenaline concentration, and losartan reduced the concentration of the circulating amines. Cardiac angiotensin II, measured by high-performance liquid chromatography (HPLC), was significantly increased in the CMS group, and losartan treatment reduced it, while angiotensin 1-7 was significantly higher in the CMS losartan-treated group as compared with CMS. Histological analysis, verified by transmission electron microscopy, showed that rats exposed to CMS presented increased perivascular collagen and losartan effectively prevented the development of this process. Hence, CMS induced a state of microvascular disease, with increased perivascular collagen deposition, that may be the trigger for further development of cardiovascular disease. In this case, CMS fibrosis is associated with increased production of catecholamines and with a disruption of renin-angiotensin system balance, which can be prevented by angiotensin II receptor blockade.

Nicotine and the renin-angiotensin system

Cigarette smoking is the single most important risk factor for the development of cardiovascular and pulmonary diseases (CVPD). Although cigarette smoking has been in constant decline since the 1950s, the introduction of e-cigarettes or electronic nicotine delivery systems 10 yr ago has attracted former smokers as well as a new generation of consumers. Nicotine is a highly addictive substance, and it is currently unclear whether e-cigarettes are "safer" than regular cigarettes or whether they have the potential to reverse the health benefits, notably on the cardiopulmonary system, acquired with the decline of tobacco smoking. Of great concern, nicotine inhalation devices are becoming popular among young adults and youths, emphasizing the need for awareness and further study of the potential cardiopulmonary risks of nicotine and associated products. This review focuses on the interaction between nicotine and the renin-angiotensin system (RAS), one of the most important regulatory systems on autonomic, cardiovascular, and pulmonary functions in both health and disease. The literature presented in this review strongly suggests that nicotine alters the homeostasis of the RAS by upregulating the detrimental angiotensin-converting enzyme (ACE)/angiotensin (ANG)-II/ANG II type 1 receptor axis and downregulating the compensatory ACE2/ANG-(1-7)/Mas receptor axis, contributing to the development of CVPD.

Effects of IQP, VEP and Spirulina platensis hydrolysates on the local kidney renin angiotensin system in spontaneously hypertensive rats

The aim of the present study was to investigate the antihypertensive effects of the bioactive Spirulina platensis peptides Ile‑Gln‑Pro (IQP), Val‑Glu‑Pro (VEP), as well as Spirulina platensis hydrolysates (SH), and assessed whether the synthesis of components of the myocardial and renal local renin angiotensin system (RAS) are regulated differentially in spontaneously hypertensive rats (SHR). The SHR were administrated with IQP, VEP and SH respectively (10 mg/kg/day) for 6 weeks and received continuous monitoring of blood pressure (BP) for two more weeks. During the trial, the rats' kidney tissues were removed from these rats and collected at weeks 3, 6 and 8. The expression of the main components of local kidney RAS was measured at the mRNA levels by reverse transcription‑quantitative polymerase chain reaction, and at the protein levels by ELISA or western blotting. Oral administration of IQP, VEP and SH into SHR resulted in marked antihypertensive effects. IQP, VEP and SH decreased rats' BP by affecting the expression of local kidney RAS components via downregulating the angiotensin‑converting enzyme (ACE), Ang II and angiotensin II (Ang II) and angiotensin type‑1 receptor (AT 1), while upregulating ACE2, Ang (1‑7), Mas and AT 2. The comparisons of SH effects on local tissue RAS demonstrated that local kidney RAS regulated BP via the ACE‑Ang II‑AT 1/AT 2 axis and the ACE2‑Ang (1‑7)‑Mas axis primarily at the mRNA level, while the local myocardium RAS mainly at the protein level. This preliminary study suggests that the main components of local RAS presented different expression levels in myocardium and kidney, which is important to the development of bioactive peptides targeting for lowering BP by changing the levels of some components in local RAS in specific tissues.

Angiotensin receptor blockade mediated amelioration of mucopolysaccharidosis type I cardiac and craniofacial pathology

Mucopolysaccharidosis type I (MPS IH) is a lysosomal storage disease (LSD) caused by inactivating mutations to the alpha-L-iduronidase (IDUA) gene. Treatment focuses on IDUA enzyme replacement and currently employed methods can be non-uniform in their efficacy particularly for the cardiac and craniofacial pathology. Therefore, we undertook efforts to better define the pathological cascade accounting for treatment refractory manifestations and demonstrate a role for the renin angiotensin system (RAS) using the IDUA^-/- mouse model. Perturbation of the RAS in the aorta was more profound in male animals suggesting a causative role in the observed gender dimorphism and angiotensin receptor blockade (ARB) resulted in improved cardiac function. Further, we show the ability of losartan to prevent shortening of the snout, a common craniofacial anomaly in IDUA^-/- mice. These data show a key role for the RAS in MPS associated pathology and support the inclusion of losartan as an augmentation to current therapies.

Elevated Serotonin Interacts with Angiotensin-II to Result in Altered Valve Interstitial Cell Contractility and Remodeling

While the valvulopathic effects of serotonin (5HT) and angiotensin-II (Ang-II) individually are known, it was not clear how 5HT and Ang-II might interact, specifically in the context of the mechanobiological responses due to altered valve mechanics potentiated by these molecules. In this context, the hypothesis of this study was that increased serotonin levels would result in accelerated progression toward disease in the presence of angiotensin-II-induced hypertension. C57/BL6 J mice were divided into four groups and subcutaneously implanted with osmotic pumps containing: PBS (control), 5HT (2.5 ng/kg/min), Ang-II (400 ng/kg/min), and 5HT + Ang-II (combination). Blood pressure was monitored using the tail cuff method. Echocardiography was performed on the mice before surgery and every week thereafter to assess ejection fraction. After three weeks, the mice were sacrificed and their hearts excised, embedded and sectioned for analysis of the aortic valves via histology and immunohistochemistry. In separate experiments, porcine valve interstitial cells (VICs) were directly stimulated with 5HT (10^-7 M), Ang-II (100 nM) or both and assayed for cellular contractility, cytoskeletal organization and collagen remodeling. After three weeks, average systolic blood pressure was significantly increased in the 5HT, Ang-II and combination groups compared to control. Echocardiographic analysis demonstrated significantly reduced ejection fraction in Ang-II and the combination groups. H&E staining demonstrated thicker leaflets in the combination groups, suggesting a more aggressive remodeling process. Picrosirius red staining and image analysis suggested that the Ang-II and combination groups had the largest proportion of thicker collagen fibers. VIC orientation, cellular contractility and collagen gene expression was highest for the 5HT + Ang-II combination treatment compared to all other groups. Overall, our results suggest that 5HT and Ang-II interact to result in significantly detrimental alteration of function and remodeling in the valve.

Local Renin Angiotensin Aldosterone Systems and Cardiovascular Diseases

The presence of local renin angiotensin aldosterone systems (RAAS) in the cardiovascular and renal tissues and their influence in cardiovascular and renal diseases are described. The fundamental role of ACE/Ang II/AT1 receptor axis activation as well the counterregulatory role of ACE2/Ang (1-7)/Mas receptor activation on cardiovascular and renal physiology and pathology are emphasized. The presence of a local RAS and its influence on hypertension is discussed, and finally, the hypothesis that epigenetic factors change the RAAS in utero and induce the expression of renin or Ang II inside the cells of the cardiovascular system is presented.

The Interplay between the Renin Angiotensin System and Pacing Postconditioning Induced Cardiac Protection

Background

Accumulating evidence suggests a cardioprotective role of pacing postconditioning (PPC) maneuvers in animal models and more recently in humans. The procedure however remains to be optimized and its interaction with physiological systems remains to be further explored. The renin angiotensin system (RAS) plays a dual role in ischemia/reperfusion (I/R) injury. The interaction between RAS and PPC induced cardiac protection is however not clearly understood. We have recently demonstrated that angiotensin (1–7) via Mas receptor played a significant role in PPC mediated cardiac protection against I/R injury.

Objective

The objective of this study was to investigate the role of angiotensin converting enzyme (ACE)—chymase—angiotensin II (Ang II)—angiotensin receptor 1 (AT1) axes of RAS in PPC mediated cardiac protection.

Methods

Isolated rat hearts were subjected to I/R (control) or PPC in the presence or absence of Ang II, chymostatin (inhibitor of locally produced Ang II), ACE blocker (captopril) or AT1 antagonist (irbesartan). Hemodynamics data was computed digitally and infarct size was determined histologically using TTC staining and biochemically by measuring creatine kinase (CK) and lactate dehydrogenase levels.

Results

Cardiac hemodynamics were significantly (P<0.001) improved and infarct size and cardiac enzymes were significantly (P<0.001) reduced in hearts subjected to PPC relative to hearts subjected to I/R injury. Exogenous administration of Ang II did not affect I/R injury or PPC mediated protection. Nonetheless inhibition of endogenously synthesized Ang II protected against I/R induced cardiac damage yet did not block or augment the protective effects of PPC. The administration of AT1 antagonist did not alleviate I/R induced damage. Interestingly it abrogated PPC induced cardiac protection in isolated rat hearts. Finally, PPC induced protection and blockade of locally produced Ang II involved enhanced activation of ERK1/2 and Akt components of the reperfusion injury salvage kinase (RISK) pathway.

Conclusions

This study demonstrate a novel role of endogenously produced Ang II in mediating I/R injury and highlights the significance of AT1 signaling in PPC mediated cardiac protection in isolated rodents hearts ex vivo. The interaction between Ang II-AT1 and PPC appears to involve alterations in the activation state of ERK1/2 and Akt components of the RISK pathway.

Role of renin-angiotensin system in liver diseases: an outline on the potential therapeutic points of intervention

The current review aimed to outline the functions of the renin angiotensin system (RAS) in the context of the oxidative stress-associated liver disease. Areas covered: Angiotensin II (Ang II) as the major effector peptide of the RAS is a pro-oxidant and fibrogenic cytokine. Mechanistically, NADPH oxidase (NOX) is a multicomponent enzyme complex that is able to generate reactive oxygen species (ROS) as a downstream signaling pathway of Ang II which is expressed in liver. Ang II has a detrimental role in the pathogenesis of chronic liver disease through possessing pro-oxidant, fibrogenic, and pro-inflammatory impact in the liver. The alternative axis (ACE2/Ang(1-7)/mas) of the RAS serves as an anti-inflammatory, antioxidant and anti-fibrotic component of the RAS. Expert commentary: In summary, the use of alternative axis inhibitors accompanying with ACE2/ Ang(1-7)/mas axis activation is a promising new strategy serving as a novel therapeutic option to prevent and treat chronic liver diseases.

Intracellular renin increases the inward calcium current in smooth muscle cells of mesenteric artery of SHR. Implications for hypertension and vascular remodeling

The influence of intracellular renin on the inward calcium current in isolated smooth muscle cells from SHR mesenteric arteries was investigated. Measurements of calcium current were performed using the whole cell configuration of pCLAMP. The results indicated that: 1) renin (100nM) dialyzed into smooth muscle cells, increased the inward calcium current; 2) verapamil (10-9M) administered to the bath inhibited the effect of renin on the inward calcium current; 3) concurrently with the increase of calcium current a depolarization of 6.8+/-2.1mV (n=16)(P<0.05) was found in cells dialyzed with renin; 4) intracellular dialysis of renin (100nM) into smooth muscle cells isolated from mesenteric arteries of normal Wystar Kyoto rats showed no significant change on calcium current; 5) aliskiren (10-9M) dialyzed into the cell together with renin (100nM) abolished the effect of the enzyme on the calcium current in SHR; 6) Ang II (100nM) dialyzed into the smooth muscle cell from mesenteric artery of SHR in absence of renin, decreased the calcium current-an effect greatly reduced by valsartan (10-9M) added to the cytosol; 7) administration of renin (100nM) plus angiotensinogen (100nM) into the cytosol of muscles cells from SHR rats reduced the inward calcium current; 8) extracellular administration of Ang II (100nM) increased the inward calcium current in mesenteric arteries of SHR.

CONCLUSIONS

intracellular renin in vascular resistance vessels from SHR due to internalization or expression, contributes to the regulation of vascular tone and control of peripheral resistance-an effect independently of Ang II. Implications for hypertension and vascular remodeling are discussed.

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

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

Acute Myocardial Response to Stretch: What We (don't) Know

Myocardial stretch, as result of acute hemodynamic overload, is one of the most frequent challenges to the heart and the ability of the heart to intrinsically adapt to it is essential to prevent circulatory congestion. In this review, we highlight the historical background, the currently known mechanisms, as well as the gaps in the understanding of this physiological response. The systolic adaptation to stretch is well-known for over 100 years, being dependent on an immediate increase in contractility—known as the Frank-Starling mechanism—and a further progressive increase—the slow force response. On the other hand, its diastolic counterpart remains largely unstudied. Mechanosensors are structures capable of perceiving mechanical signals and activating pathways that allow their transduction into biochemical responses. Although the connection between these structures and stretch activated pathways remains elusive, we emphasize those most likely responsible for the initiation of the acute response. Calcium-dependent pathways, including angiotensin- and endothelin-related pathways; and cGMP-dependent pathways, comprising the effects of nitric oxide and cardiac natriuretic hormones, embody downstream signaling. The ischemic setting, a paradigmatic situation of acute hemodynamic overload, is also touched upon. Despite the relevant knowledge accumulated, there is much that we still do not know. The quest for further understanding the myocardial response to acute stretch may provide new insights, not only in its physiological importance, but also in the prevention and treatment of cardiovascular diseases.

Role of angiotensin II in stem cell therapy of cardiac disease

INTRODUCTION

The renin angiotensin system (RAS) is closely related to the cardiovascular system, body fluid regulation and homeostasis.

MATERIALS AND METHODS

Despite common therapeutic methods, stem cell/progenitor cell therapy is daily increasing as a term of regenerative medicine. RAS and its pharmacological inhibitors are not only involved in physiological and pathological aspects of the cardiovascular system, but also affect the different stages of stem cell proliferation, differentiation and function, via interfering cell signaling pathways.

RESULTS

This study reviews the new role of RAS, in particular Ang II distinct from other common roles, by considering its regulating impact on the different signaling pathways involved in the cardiac and endothelial tissue, as well as in stem cell transplantation.

CONCLUSIONS

This review focuses on the impact of stem cell therapy on the cardiovascular system, the role of RAS in stem cell differentiation, and the role of RAS inhibition in cardiac stem cell growth and development.

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

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

The impact of age-related dysregulation of the angiotensin system on mitochondrial redox balance

Aging is associated with the accumulation of various deleterious changes in cells. According to the free radical and mitochondrial theory of aging, mitochondria initiate most of the deleterious changes in aging and govern life span. The failure of mitochondrial reduction-oxidation (redox) homeostasis and the formation of excessive free radicals are tightly linked to dysregulation in the Renin Angiotensin System (RAS). A main rate-controlling step in RAS is renin, an enzyme that hydrolyzes angiotensinogen to generate angiotensin I. Angiotensin I is further converted to Angiotensin II (Ang II) by angiotensin-converting enzyme (ACE). Ang II binds with equal affinity to two main angiotensin receptors—type 1 (AT₁R) and type 2 (AT₂R). The binding of Ang II to AT₁R activates NADPH oxidase, which leads to increased generation of cytoplasmic reactive oxygen species (ROS). This Ang II-AT₁R–NADPH-ROS signal triggers the opening of mitochondrial K_ATP channels and mitochondrial ROS production in a positive feedback loop. Furthermore, RAS has been implicated in the decrease of many of ROS scavenging enzymes, thereby leading to detrimental levels of free radicals in the cell. AT₂R is less understood, but evidence supports an anti-oxidative and mitochondria-protective function for AT₂R. The overlap between age related changes in RAS and mitochondria, and the consequences of this overlap on age-related diseases are quite complex. RAS dysregulation has been implicated in many pathological conditions due to its contribution to mitochondrial dysfunction. Decreased age-related, renal and cardiac mitochondrial dysfunction was seen in patients treated with angiotensin receptor blockers. The aim of this review is to: (a) report the most recent information elucidating the role of RAS in mitochondrial redox hemostasis and (b) discuss the effect of age-related activation of RAS on generation of free radicals.

Clinical relevance of urinary angiotensinogen and renin as potential biomarkers in patients with overt proteinuria

Urinary angiotensinogen (AGT) and renin have been reported to reflect the intrarenal renin-angiotensin system (RAS) activity. However, the adequacy and clinical significance of these markers have not been evaluated in overtly proteinuric patients. In patients with biopsy-proven glomerulonephritis, plasma and urinary AGT and renin were analyzed. A cohort of 75 patients treated with RAS inhibitors was followed for 1 year. Among the 207 patients, 105 had subnephrotic and 102 had nephrotic-range proteinuria. Mean age, estimated glomerular filtration rate (eGFR), and urinary protein-to-creatinine ratio (P/Cr) of all patients were 48 years, 79.7 mL/min/1.73 m(2), and 5.66 mg/mg, respectively. Both natural logarithm of urinary AGT/creatinine (ln [urinary AGT/Cr]) and ln (urinary renin/Cr) showed positive correlations with urinary P/Cr. There was a positive correlation between ln (urinary AGT/Cr) and ln (urinary renin/Cr). Ln (urinary renin/Cr) was not affected by ln (plasma renin) regardless of the degree of proteinuria. The treatment response to RAS inhibitors was greatest in patients with high urinary AGT and renin. However, the predictive value of those parameters was no longer present when the values were adjusted by the degree of proteinuria. Ln (urinary renin/Cr) and initial eGFR were independently associated with the changes in renal function for 1 year. Ln (urinary AGT/Cr) was associated with persistent overt proteinuria after 1 year. Our study suggests that urinary renin may be a better marker in heavy proteinuria, and the treatment response to RAS inhibitors may be enhanced in patients with high urinary renin and AGT. Further studies will be necessary to explore the value of urinary AGT and renin.

Regulation of cell volume and water transport--an old fundamental role of the renin angiotensin aldosterone system components at the cellular level

The expression and the role of renin angiotensin aldosterone system (RAAS) components on regulation of cell volume and water transport on vertebrates and invertebrates were reviewed. The presence of these components even in simple organisms like leeches and their relevance for the control of cellular volume and water transport supports the view that the expression of these components, at cellular level, is an acquisition which was preserved throughout evolution.

Angiotensin-converting enzyme 2 and angiotensin 1-7: novel therapeutic targets

Angiotensin-converting enzyme (ACE) 2 and its product angiotensin 1–7 are thought to have effects that counteract the adverse actions of other, better-known renin–angiotensin system (RAS) components

Numerous experimental studies have suggested that ACE2 and angiotensin 1–7 have notable protective effects in the heart and blood vessels

ACE2-mediated catabolism of angiotensin II is likely to have a major role in cardiovascular protection, whereas the functional importance and signalling mechanisms of angiotensin-1–7-induced actions remain unclear

New pharmacological interventions targeting ACE2 are expected to be useful in clinical treatment of cardiovascular disease, especially those associated with overactivation of the conventional RAS

More studies, especially randomized controlled clinical trials, are needed to clearly delineate the benefits of therapies targeting angiotensin 1–7 actions

Angiotensin-converting enzyme 2, and its product angiotensin 1–7, are thought to have counteracting effects against the adverse actions of the better-known members of the renin–angiotensin system and might, therefore, be useful therapeutic targets in patients with cardiovascular disease. Professor Jiang and colleagues review the evidence for the potential roles of these proteins in various cardiovascular conditions, including hypertension, atherosclerosis, myocardial remodelling, heart failure, ischaemic stroke, and diabetes.

The renin–angiotensin system (RAS) has pivotal roles in the regulation of normal physiology and the pathogenesis of cardiovascular disease. Angiotensin-converting enzyme (ACE) 2, and its product angiotensin 1–7, are thought to have counteracting effects against the adverse actions of other, better known and understood, members of the RAS. The physiological and pathological importance of ACE2 and angiotensin 1–7 in the cardiovascular system are not completely understood, but numerous experimental studies have indicated that these components have protective effects in the heart and blood vessels. Here, we provide an overview on the basic properties of ACE2 and angiotensin 1–7 and a summary of the evidence from experimental and clinical studies of various pathological conditions, such as hypertension, atherosclerosis, myocardial remodelling, heart failure, ischaemic stroke, and diabetes mellitus. ACE2-mediated catabolism of angiotensin II is likely to have a major role in cardiovascular protection, whereas the relevant functions and signalling mechanisms of actions induced by angiotensin 1–7 have not been conclusively determined. The ACE2–angiotensin 1–7 pathway, however, might provide a useful therapeutic target for the treatment of cardiovascular disease, especially in patients with overactive RAS.

Hydrogen sulfide prevents heart failure development via inhibition of renin release from mast cells in isoproterenol-treated rats

AIMS

Cardiac local renin-angiotensin system plays an important role in the development of heart failure and left ventricular (LV) remodeling. We previously reported that hydrogen sulfide (H2S), an endogenous gaseous mediator, regulates renin synthesis and release in juxtaglomerular cells. The present study was designed to investigate whether H2S can protect against isoproterenol (ISO)-induced heart failure via inhibition of local renin activity in rat hearts.

RESULTS

In the present study, we found that an injection of ISO (150 mg/kg) significantly increased plasma lactate dehydrogenase level and hypertrophy index and impaired LV end diastolic pressure. Treatment with NaHS (an H2S donor, 0.056 mg/kg, daily) 3 days before and 2 weeks after the ISO injection attenuated the development of heart failure. Histological staining showed that NaHS decreased ISO-induced collagen deposition. Moreover, NaHS treatment reversed ISO-induced renin elevation in both plasma and LVs. Immunostaining analysis indicated that renin expression co-localized with mast cells in the ventricular tissues. Mast cell counts showed that NaHS treatment decreased the number of degranulated mast cells in cardiac tissue due to down-regulation of leukotriene A4 hydrolase protein expression and leukotriene B4 level. In addition, NaHS treatment also inhibited forskolin-induced renin degranulation from HMC-1.1 mast cells by lowering intracellular cAMP level.

INNOVATION

This study provides evidence for a new pathway in H2S-induced cardioprotection against heart failure development.

CONCLUSIONS

For the first time, we demonstrated that H2S might protect heart during heart failure by suppression of local renin level through inhibition of both mast cell infiltration and renin degranulation.

The renin-angiotensin system in adipose tissue and its metabolic consequences during obesity

Obesity is a worldwide disease that is accompanied by several metabolic abnormalities such as hypertension, hyperglycemia and dyslipidemia. The accelerated adipose tissue growth and fat cell hypertrophy during the onset of obesity precedes adipocyte dysfunction. One of the features of adipocyte dysfunction is dysregulated adipokine secretion, which leads to an imbalance of pro-inflammatory, pro-atherogenic versus anti-inflammatory, insulin-sensitizing adipokines. The production of renin-angiotensin system (RAS) components by adipocytes is exacerbated during obesity, contributing to the systemic RAS and its consequences. Increased adipose tissue RAS has been described in various models of diet-induced obesity (DIO) including fructose and high-fat feeding. Up-regulation of the adipose RAS by DIO promotes inflammation, lipogenesis and reactive oxygen species generation and impairs insulin signaling, all of which worsen the adipose environment. Consequently, the increase of circulating RAS, for which adipose tissue is partially responsible, represents a link between hypertension, insulin resistance in diabetes and inflammation during obesity. However, other nutrients and food components such as soy protein attenuate adipose RAS, decrease adiposity, and improve adipocyte functionality. Here, we review the molecular mechanisms by which adipose RAS modulates systemic RAS and how it is enhanced in obesity, which will explain the simultaneous development of metabolic syndrome alterations. Finally, dietary interventions that prevent obesity and adipocyte dysfunction will maintain normal RAS concentrations and effects, thus preventing metabolic diseases that are associated with RAS enhancement.

The effects of angiotensin II signaling pathway in the systolic response to acute stretch in the normal and ischemic myocardium

Acute myocardial stretch elicits a biphasic increase in contractility: an immediate increase, known as Frank-Starling mechanism (FSM), followed by a progressive increase, regarded as slow force response (SFR). In this study, we characterized the contractile response to acute stretch from 92 to 100% Lmax in rabbit papillary muscles (n=86) under normoxic and ischemic conditions, and its modulation by angiotensin II signaling pathway. Under normoxia, the FSM was independent of Na(+)/H(+)-exchanger, reverse mode of Na(+)/Ca(2+)-exchanger (r-NCX), AT1 receptor, AT2 receptor and PKC. Regarding the SFR, it was mediated by AT1 receptor activation and its downstream effectors PKC, Na(+)/H(+)-exchanger and r-NCX. Ischemia negatively impacted on the FSM and abolished the SFR, with the muscles exhibiting a time-dependent decline in contractility. Under ischemic conditions, FSM was not influenced by AT1 and AT2 receptors or PKC activation. AT1 receptor antagonism rescued the progressive deterioration in contractility, an effect partially dependent on AT2 receptor activation.

Long-term effects of early overnutrition in the heart of male adult rats: role of the renin-angiotensin system

To analyze the long-term effects of early overfeeding on the heart and coronary circulation, the effect of ischemia-reperfusion (I/R) and the role of the renin-angiotensin system (RAS) was studied in isolated hearts from control and overfed rats during lactation. On the day of birth litters were adjusted to twelve pups per mother (controls) or to three pups per mother (overfed). At 5 months of age, the rats from reduced litters showed higher body weight and body fat than the controls. The hearts from these rats were perfused in a Langendorff system and subjected to 30 min of ischemia followed by 15 min of reperfusion (I/R). The myocardial contractility (dP/dt) and the coronary vasoconstriction to angiotensin II were lower, and the expression of the apoptotic marker was higher, in the hearts from overfed rats compared to controls. I/R reduced the myocardial contractily, the coronary vasoconstriction to angiotensin II and the vasodilatation to bradykinin, and increased the expression of (pro)renin receptor and of apoptotic and antiapoptotic markers, in both experimental groups. I/R also increased the expression of angiotensinogen in control but not in overfed rats. In summary, the results of this study suggest that early overnutrition induces reduced activity of the RAS and impairment of myocardial and coronary function in adult life, due to increased apoptosis. Ischemia-reperfusion produced myocardial and coronary impairment and apoptosis, which may be related to activation of RAS in control but not in overfed rats, and there may be protective mechanisms in both experimental groups.

Intracellular angiotensin II increases the total potassium current and the resting potential of arterial myocytes from vascular resistance vessels of the rat. Physiological and pathological implications

The influence of intracellular and extracellular administration of angiotensin II (Ang II; 10(-9) M) on total potassium current of arterial myocytes isolated from mesenteric arteries of Sprague Dawley rats was investigated. Measurements of total potassium current were performed using the voltage clamp whole cell configuration while the effect of intracellular Ang II on the resting potential of arterial myocytes was measured using the current clamp configuration of pCLAMP. The results indicated that: 1) intracellular Ang II (10(-9) M) increased the total potassium current by 73% ± 2.6% (n = 22; P < .05) within 5 minutes; 2) concurrently with the increment of potassium current, the resting potential was increased by 7 ± 1.5 mV (n = 23; P < .05); 3) extracellular administration of Ang II (10(-9) M) reduced the total potassium current by 20% ± 1.6% (n = 21; P < .05) within 5 minutes and depolarized the smooth muscle cells by 9 ± 2.3 mV (n = 26; P < .05); 4) the effects of intracellular Ang II on potassium current and membrane potential were inhibited by dialyzing a PKA inhibitor (10(-9) M) inside the cell together with Ang II (10(-9) M; P > .05); 5) valsartan (10(-9) M) dialyzed into the cell together with Ang II (10(-9) M) abolished the effect of the peptide on potassium current and membrane potential. The presence of endogenous or internalized intracellular Ang II in vascular resistance vessels and its effect on potassium current and resting potential indicates that the peptide present inside the arterial myocytes plays an important role on the regulation of vascular tone and consequently on peripheral resistance, which is a determining factor in the regulation of arterial blood pressure.

Renin-angiotensin system, hypertension, and chronic kidney disease: pharmacogenetic implications

About 80% of CKD (chronic kidney disease) patients are hypertensive, and kidney function and blood pressure are clearly related to both physiologic and pathologic conditions in a "vicious cycle". In this pathologic scenario, there is a renin-angiotensin system (RAS) hyperactivity associated to progression of renal damage. Current guidelines indicate as the first choice of antihypertensive intervention, the pharmacologic blockade of the RAS. Nonetheless, both response to treatment and renal protection have considerable inter-individual variability. The main aims of this review are to describe the genetic characteristics of RAS components and to identify the possible pharmacogenetic implications for RAS-blocker drugs in the hypertension-CKD scenario. To date, RAS polymorphisms have not been consistently associated to antihypertensive response and studies focusing on CKD are scarce. Nonetheless, pharmacogenetic studies for the RAS-blocker drugs could still be further explored, especially with new generation tools and focusing not only on the antihypertensive response, but also on renal protection as well.

The brain-heart connection: frontal cortex and left ventricle angiotensinase activities in control and captopril-treated hypertensive rats-a bilateral study

The model of neurovisceral integration suggests that the frontal cortex (FC) and the cardiovascular function are reciprocally and asymmetrically connected. We analyzed several angiotensinase activities in the heart left ventricle (VT) of control and captopril-treated SHR, and we search for a relationship between these activities and those determined in the left and right FC. Captopril was administered in drinking water for 4 weeks. Samples from the left VT and from the left and right FC were obtained. Soluble and membrane-bound enzymatic activities were measured fluorometrically using arylamides as substrates. The weight of heart significantly decreased after treatment with captopril, mainly, due to the reduction of the left VT weight. In the VT, no differences for soluble activities were observed between control and treated SHR. In contrast, a generalized significant reduction was observed for membrane-bound activities. The most significant correlations between FC and VT were observed in the right FC of the captopril-treated group. The other correlations, right FC versus VT and left FC versus VT in controls and left FC versus VT in the captopril group, were few and low. These results confirm that the connection between FC and cardiovascular system is asymmetrically organized.

Aliskiren, at low doses, reduces the electrical remodeling in the heart of the TGR(mRen2)27 rat independently of blood pressure

METHODS

The influence of chronic administration of low doses of aliskiren (5 mg/kg/day, i.p.) for a period of eight weeks on cardiac electrophysiological and structural remodeling was investigated in transgenic (TGR)(mRen-2)27 rats. Cardiac and plasma angiotensin II (Ang II) levels were determined by ELISA before and after administration of the drug. Moreover, histological, electrophysiological and echocardiographic studies were performed in controls and at the end of eight weeks of aliskiren administration.

RESULTS

1) The cardiac Ang II levels were significantly reduced while the plasma Ang II levels were not significantly decreased in rats treated with low doses of aliskiren; 2) echocardographic studies showed a decrease of left ventricle diameter (LVD), left ventricle posterior wall thickness (LVPW), left ventricle end diastolic volume (LVEDV) and increased ejection fraction (EF); 3) aliskiren improved the impulse propagation, increased the cardiac refractoriness and reduced the incidence of triggered activity; 4) perivascular and interstitial fibrosis were greatly reduced, which explains the increase in conduction velocity. All these effects of aliskiren were found independently of blood pressure, suggesting that the beneficial effect of aliskiren was related to an inhibition of the local cardiac renin angiotensin system; and 5) the effect of mechanical stretch on action potential duration, conduction velocity and spontaneous rhythmicity was changed by aliskiren, supporting the hypothesis presented here that the beneficial effect of the drug on cardiac remodeling is related to a decreased sensitivity of cardiac muscle to mechanical stress.

An introduction to murine models of atrial fibrillation

Understanding the mechanism of re-entrant arrhythmias in the past 30 years has allowed the development of almost curative therapies for many rhythm disturbances. The complex, polymorphic arrhythmias of atrial fibrillation (AF) and sudden death are, unfortunately, not yet well understood, and hence still in need of adequate therapy. AF contributes markedly to morbidity and mortality in aging Western populations. In the past decade, many genetically altered murine models have been described and characterized. Here, we review genetically altered murine models of AF; powerful tools that will enable a better understanding of the mechanisms of AF and the assessment of novel therapeutic interventions.

The intracrine renin-angiotensin system

The RAS (renin-angiotensin system) is one of the earliest and most extensively studied hormonal systems. The RAS is an atypical hormonal system in several ways. The major bioactive peptide of the system, AngII (angiotensin II), is neither synthesized in nor targets one specific organ. New research has identified additional peptides with important physiological and pathological roles. More peptides also mean newer enzymatic cascades that generate these peptides and more receptors that mediate their function. In addition, completely different roles of components that constitute the RAS have been uncovered, such as that for prorenin via the prorenin receptor. Complexity of the RAS is enhanced further by the presence of sub-systems in tissues, which act in an autocrine/paracrine manner independent of the endocrine system. The RAS seems relevant at the cellular level, wherein individual cells have a complete system, termed the intracellular RAS. Thus, from cells to tissues to the entire organism, the RAS exhibits continuity while maintaining independent control at different levels. The intracellular RAS is a relatively new concept for the RAS. The present review provides a synopsis of the literature on this system in different tissues.

Intracardiac intracellular angiotensin system in diabetes

The renin-angiotensin system (RAS) has mainly been categorized as a circulating and a local tissue RAS. A new component of the local system, known as the intracellular RAS, has recently been described. The intracellular RAS is defined as synthesis and action of ANG II intracellularly. This RAS appears to differ from the circulating and the local RAS, in terms of components and the mechanism of action. These differences may alter treatment strategies that target the RAS in several pathological conditions. Recent work from our laboratory has demonstrated significant upregulation of the cardiac, intracellular RAS in diabetes, which is associated with cardiac dysfunction. Here, we have reviewed evidence supporting an intracellular RAS in different cell types, ANG II's actions in cardiac cells, and its mechanism of action, focusing on the intracellular cardiac RAS in diabetes. We have discussed the significance of an intracellular RAS in cardiac pathophysiology and implications for potential therapies.

A new look at the renin-angiotensin system--focusing on the vascular system

The renin-angiotensin system (RAS), critically involved in the control of blood pressure and volume homeostasis, is a dual system comprising a circulating component and a local tissue component. The rate limiting enzyme is renin, which in the circulating RAS derives from the kidney to generate Ang II, which in turn regulates cardiovascular function by binding to AT(1) and AT(2) receptors on cardiac, renal and vascular cells. The tissue RAS can operate independently of the circulating RAS and may be activated even when the circulating RAS is suppressed or normal. A functional tissue RAS has been identified in brain, kidney, heart, adipose tissue, hematopoietic tissue, gastrointestinal tract, liver, endocrine system and blood vessels. Whereas angiotensinsinogen, angiotensin converting enzyme (ACE), Ang I and Ang II are synthesized within these tissues, there is still controversy as to whether renin is produced locally or whether it is taken up from the circulation, possibly by the (pro)renin receptor. This is particularly true in the vascular wall, where expression of renin is very low. The exact function of the vascular RAS remains elusive, but may contribute to fine-tuning of vascular tone and arterial structure and may amplify vascular effects of the circulating RAS, particularly in pathological conditions, such as in hypertension, atherosclerosis and diabetes. New concepts relating to the vascular RAS have recently been elucidated including: (1) the presence of functionally active Ang-(1-7)-Mas axis in the vascular system, (2) the importance of the RAS in perivascular adipose tissue and cross talk with vessels, and (3) the contribution to vascular RAS of Ang II derived from immune and inflammatory cells within the vascular wall. The present review highlights recent progress in the RAS field, focusing on the tissue system and particularly on the vascular RAS.