Role of the local renin-angiotensin system in cardiac damage: a minireview focussing on transgenic animal models

Role of Vasoactive Hormone-Induced Signal Transduction in Cardiac Hypertrophy and Heart Failure

Heart failure is the common concluding pathway for a majority of cardiovascular diseases and is associated with cardiac dysfunction. Since heart failure is invariably preceded by adaptive or maladaptive cardiac hypertrophy, several biochemical mechanisms have been proposed to explain the development of cardiac hypertrophy and progression to heart failure. One of these includes the activation of different neuroendocrine systems for elevating the circulating levels of different vasoactive hormones such as catecholamines, angiotensin II, vasopressin, serotonin and endothelins. All these hormones are released in the circulation and stimulate different signal transduction systems by acting on their respective receptors on the cell membrane to promote protein synthesis in cardiomyocytes and induce cardiac hypertrophy. The elevated levels of these vasoactive hormones induce hemodynamic overload, increase ventricular wall tension, increase protein synthesis and the occurrence of cardiac remodeling. In addition, there occurs an increase in proinflammatory cytokines and collagen synthesis for the induction of myocardial fibrosis and the transition of adaptive to maladaptive hypertrophy. The prolonged exposure of the hypertrophied heart to these vasoactive hormones has been reported to result in the oxidation of catecholamines and serotonin via monoamine oxidase as well as the activation of NADPH oxidase via angiotensin II and endothelins to promote oxidative stress. The development of oxidative stress produces subcellular defects, Ca2+-handling abnormalities, mitochondrial Ca2+-overload and cardiac dysfunction by activating different proteases and depressing cardiac gene expression, in addition to destabilizing the extracellular matrix upon activating some metalloproteinases. These observations support the view that elevated levels of various vasoactive hormones, by producing hemodynamic overload and activating their respective receptor-mediated signal transduction mechanisms, induce cardiac hypertrophy. Furthermore, the occurrence of oxidative stress due to the prolonged exposure of the hypertrophied heart to these hormones plays a critical role in the progression of heart failure.

Immunoneutralization of human angiotensin-(1-12) with a monoclonal antibody in a humanized model of hypertension

We engineered a monoclonal antibody (mAb) against the human C-terminus of angiotensin-(1-12) [h-Ang-(1-12)] and performed a biochemical characterization in concert with direct in vivo and ex vivo (carotid artery strips) assessments of h-Ang-(1-12) vasoconstrictor activity in 78 (36 females) transgenic rats expressing the human angiotensinogen gene [TGR(hAGT)L1623] and 26 (10 female) Sprague Dawley (SD) controls. The mAb shows high specificity in neutralizing angiotensin II formation from h-Ang-(1-12) and did not cross-react with human and rat angiotensins. Changes in arterial pressure and heart rate in Inactin® hydrate anesthetized rats were measured before and after h-Ang-(1-12) injections [dose range: 75-300 pmol/kg i.v.] prior to and 30-60 minutes after administration of the h-Ang-(1-12) mAb. Neutralization of circulating Ang-(1-12) inhibited the pressor action of h-Ang-(1-12), prevented Ang-(1-12) constrictor responses in carotid artery rings in both SD and TGR(hAGT)L1623 rats, and caused a fall in the arterial pressure of male and female transgenic rats. The Ang-(1-12) mAb did not affect the response of comparable dose-related pressor responses to Ang II, pre-immune IgG, or the rat sequence of Ang-(1-12). This h-Ang-(1-12) mAb can effectively suppress the pressor actions of the substrate in the circulation of hypertensive rats or in carotid artery strips from both SD and transgenic rats. The demonstration that this Ang-(1-12) mAb by itself, induced a fall in arterial pressure in transgenic hypertensive rats supports further exploring the potential abilities of Ang-(1-12) mAb in the treatment of hypertension.

Studies of salt and stress sensitivity on arterial pressure in renin-b deficient mice

Excessive sodium intake is known to increase the risk for hypertension, heart disease, and stroke. Individuals who are more susceptible to the effects of high salt are at higher risk for cardiovascular diseases even independent of their blood pressure status. Local activation of the renin-angiotensin system (RAS) in the brain, among other mechanisms, has been hypothesized to play a key role in contributing to salt balance. We have previously shown that deletion of the alternative renin isoform termed renin-b disinhibits the classical renin-a encoding preprorenin in the brain resulting in elevated brain RAS activity. Thus, we hypothesized that renin-b deficiency results in higher susceptibility to salt-induced elevation in blood pressure. Telemetry implanted Ren-bNull and wildtype littermate mice were first offered a low salt diet for a week and subsequently a high salt diet for another week. A high salt diet induced a mild blood pressure elevation in both Ren-bNull and wildtype mice, but mice lacking renin-b did not exhibit an exaggerated pressor response. When renin-b deficient mice were exposed to a high salt diet for a longer duration (4 weeks), there was a trend for increased myocardial enlargement in Ren-bNull mice when compared with control mice, but this did not reach statistical significance. Multiple studies have also demonstrated the association of environmental stress with hypertension. Activation of the RAS in the rostral ventrolateral medulla and the hypothalamus is required for stress-induced hypertension. Thus, we next questioned whether the lack of renin-b would result in exacerbated response to an acute restraint-stress. Wildtype and Ren-bNull mice equally exhibited elevated blood pressure in response to restraint-stress, which was similar in mice fed either a low or high salt diet. These studies suggest that mechanisms unrelated to salt and acute stress alter the cardiovascular phenotype in mice lacking renin-b.

Loss of Hepatic Angiotensinogen Attenuates Sepsis-Induced Myocardial Dysfunction

Rationale: The renin-angiotensin system (RAS) is a complex regulatory network that maintains normal physiological functions. The role of the RAS in sepsis-induced myocardial dysfunction (SIMD) is poorly defined. Angiotensinogen (AGT) is the unique precursor of the RAS and gives rise to all angiotensin peptides. The effects and mechanisms of AGT in development of SIMD have not been defined. Objective: To determine a role of AGT in SIMD and investigate the underlying mechanisms. Methods and Results: Either intraperitoneal injection of lipopolysaccharide (LPS) or cecal ligation and puncture (CLP) significantly enhanced AGT abundances in liver, heart, and plasma. Deficiency of hepatocyte-derived AGT (hepAGT), rather than cardiomyocyte-derived AGT (carAGT), alleviated septic cardiac dysfunction in mice and prolonged survival time. Further investigations revealed that the effects of hepAGT on SIMD were partially associated with augmented angiotensin II (AngII) production in circulation. In addition, hepAGT was internalized by LDL receptor-related protein 1 (LRP1) in cardiac fibroblasts (CF), and subsequently activated NLRP3 inflammasome via an AngII-independent pathway, ultimately promoting SIMD by suppressing Sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a (SERCA2a) abundances in cardiomyocytes (CM). Conclusions: HepAGT promoted SIMD via both AngII-dependent and AngII-independent pathways. We identified a liver-heart axis by which AGT regulated development of SIMD. Our study may provide a potential novel therapeutic target for SIMD.

The Potential Role of Osteopontin and Furin in Worsening Disease Outcomes in COVID-19 Patients with Pre-Existing Diabetes

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the ongoing coronavirus disease 2019 (COVID-19) pandemic, with more than 50 million cases reported globally. Findings have consistently identified an increased severity of SARS-CoV-2 infection in individuals with diabetes. Osteopontin, a cytokine-like matrix-associated phosphoglycoprotein, is elevated in diabetes and drives the expression of furin, a proprotein convertase implicated in the proteolytic processing and activation of several precursors, including chemokines, growth factors, hormones, adhesion molecules, and receptors. Elevated serum furin is a signature of diabetes mellitus progression and is associated with a dysmetabolic phenotype and increased risk of diabetes-linked premature mortality. Additionally, furin plays an important role in enhancing the infectivity of SARS-CoV-2 by promoting its entry and replication in the host cell. Here, we hypothesize that diabetes-induced osteopontin and furin protein upregulation results in worse outcomes in diabetic patients with SARS-CoV-2 infection owing to the roles of these protein in promoting viral infection and increasing metabolic dysfunction. Thus, targeting the osteopontin-furin axis may be a plausible strategy for reducing mortality in SARS-CoV-2 patients with diabetes.

The emerging role of angiotensinogen in cardiovascular diseases

Angiotensinogen (AGT) is the unique precursor of all angiotensin peptides. Many of the basic understandings of AGT in cardiovascular diseases have come from research efforts to define its effects on blood pressure regulation. The development of novel techniques targeting AGT manipulation such as genetic animal models, adeno-associated viral approaches, and antisense oligonucleotides made it possible to deeply investigate the relationship between AGT and cardiovascular diseases. In this brief review, we provide contemporary insights into the emerging role of AGT in cardiovascular diseases. In light of the recent progress, we emphasize some newly recognized features and mechanisms of AGT in heart failure, hypertension, atherosclerosis, and cardiovascular risk factors.

Safety evaluation and cardiovascular effect of additional use of spironolactone in hemodialysis patients: a meta-analysis

Objective: To evaluate the safety and cardiovascular effect of low-dose spironolactone administration in end-stage renal failure patients undergoing hemodialysis coupled with conventional treatment.

Methods: We conducted a systematic search for clinical trials on the safety and cardiovascular effect of additional low-dose spironolactone in hemodialysis patients. The search was performed on PubMed, EMBASE, Cochrane Library, and CBM databases. Relevant references (up to February 2016) were retrieved and subsequent results analyzed with a random-effects model or a fixed-effects model.

Results: We identified nine trials with a total sample size of 765 patients. The results did not indicate significant differences regarding safety and serum potassium levels (mean difference [MD]=0.23, P=0.09) between the two treatment options. However, patients receiving low-dose spironolactone exhibited improvements in left venticular mass index (LVMI) (standardized mean difference= –0.58, P<0.00001) and left ventricular ejection fraction (LVEF) (MD=4.91, P<0.0001) with an additional decrease in systolic blood pressure (MD= –6.97, P=0.0001) and diastolic blood pressure (MD= –4.01, P=0.007). Furthermore, the clinical (OR=0.4, P=0.0003) or cardiovascular and cerebrovascular-related (OR=0.4, P=0.002) mortality was significantly lower among those patients.

Conclusion: These results indicated that additional use of low-dose spironolactone associated with conventional treatment does not have a significant impact on serum potassium levels in hemodialysis patients. What’s more, it might exert a protective effect on the cardiovascular system by optimizing LVMI, improving LVEF, decreasing arterial blood pressure and reducing events-related mortality. Further large sample size studies are needed to support these findings.

Is the cardioprotective effect of the ACE2 activator diminazene aceturate more potent than the ACE inhibitor enalapril on acute myocardial infarction in rats?

Myocardial infarction is a major cause of cardiac dysfunction. All components of the cardiac renin-angiotensin system (RAS) are upregulated in myocardial infarction. Angiotensin-converting enzyme (ACE) and ACE2 are key enzymes involved in synthesis of components of RAS and provide a counter-regulatory mechanism within RAS. We compared the cardioprotective effect of the ACE2 activator diminazene aceturate (DIZE) versus the ACE inhibitor enalapril on post acute myocardial infarction (AMI) ventricular dysfunction in rats. Adult male rats received subcutaneous injections of either saline (control) or isoproterenol (85 mg/kg) to induce AMI. Rats with AMI confirmed biochemically and by ECG, were either left untreated (AMI) or administered DIZE (AMI + DIZE) or enalapril (AMI + enalapril) daily for 4 weeks. DIZE caused a significant activation of cardiac ACE2 compared with enalapril. DIZE caused a significantly greater enhancement of cardiac hemodynamics. DIZE also caused greater reductions in heart-type fatty acid binding protein (H-FABP), β-myosin heavy chain (β-MYH), and in heart mass to total body mass ratio. These results indicated that activation of cardiac ACE2 by DIZE enhanced the protective axis of RAS and improved myocardial function following AMI, whereas enalapril was not sufficient to restore all cardiac parameters back to normal.

Intermittent fasting exerts beneficial metabolic effects on blood pressure and cardiac structure by modulating local renin-angiotensin system in the heart of mice fed high-fat or high-fructose diets

Intermittent fasting (IF) sets the preference for fats as fuel and is linked to beneficial metabolic outcomes; however, the effects in the renin-angiotensin system (RAS) in the heart remains to be determined. We hypothesized that IF improves blood pressure and lipid profiles due to a less activated local RAS in the left ventricle of mice, irrespective of the dietary scheme. This study aimed to evaluate the effects of intermittent fasting on cardiovascular parameters and local RAS in the left ventricle (LV) of mice fed either a high-fat (HF) or high-fructose diet (HFru). Metabolic alterations were induced in C57BL/6 mice by providing them free access to a high-fat or a high-fructose (HFru) diet for 8 weeks. Following the 8-week metabolic alteration period, the mice were subjected to the IF protocol in which mice were deprived of food for 24 hours, every other day, for a period of 4 weeks. The IF protocol caused significant reduction in body weight, systolic blood pressure, blood glucose, total cholesterol, and triacylglycerol levels, in addition to augmenting the plasma and urinary uric acid levels, irrespective of the diet. Post IF protocol, beneficial LV remodeling was observed in animals fed either diet and included reduced LV mass, thickness, and cardiomyocyte cross-sectional area. These results comply with the improved RAS modulation, which favored ACE2/MAS receptor axis over the renin/ACE/AT1 axis. In conclusion, the significant decrease in weight brought about as a result of the IF protocol lead to modulation of the local RAS, with the consequential benefit of LV remodeling and reduction in blood pressure, irrespective of the diet.

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.

MicroRNA-221/222 Family Counteracts Myocardial Fibrosis in Pressure Overload-Induced Heart Failure

Pressure overload causes cardiac fibroblast activation and transdifferentiation, leading to increased interstitial fibrosis formation and subsequently myocardial stiffness, diastolic and systolic dysfunction, and eventually heart failure. A better understanding of the molecular mechanisms underlying pressure overload-induced cardiac remodeling and fibrosis will have implications for heart failure treatment strategies. The microRNA (miRNA)-221/222 family, consisting of miR-221-3p and miR-222-3p, is differentially regulated in mouse and human cardiac pathology and inversely associated with kidney and liver fibrosis. We investigated the role of this miRNA family during pressure overload-induced cardiac remodeling. In myocardial biopsies of patients with severe fibrosis and dilated cardiomyopathy or aortic stenosis, we found significantly lower miRNA-221/222 levels as compared to matched patients with nonsevere fibrosis. In addition, miRNA-221/222 levels in aortic stenosis patients correlated negatively with the extent of myocardial fibrosis and with left ventricular stiffness. Inhibition of both miRNAs during AngII (angiotensin II)-mediated pressure overload in mice led to increased fibrosis and aggravated left ventricular dilation and dysfunction. In rat cardiac fibroblasts, inhibition of miRNA-221/222 derepressed TGF-β (transforming growth factor-β)-mediated profibrotic SMAD2 (mothers against decapentaplegic homolog 2) signaling and downstream gene expression, whereas overexpression of both miRNAs blunted TGF-β-induced profibrotic signaling. We found that the miRNA-221/222 family may target several genes involved in TGF-β signaling, including JNK1 (c-Jun N-terminal kinase 1), TGF-β receptor 1 and TGF-β receptor 2, and ETS-1 (ETS proto-oncogene 1). Our findings show that heart failure-associated downregulation of the miRNA-221/222 family enables profibrotic signaling in the pressure-overloaded heart.

Maternal hyperthyroidism increases the susceptibility of rat adult offspring to cardiovascular disorders

Suboptimal intrauterine conditions as changed hormone levels during critical periods of the development are considered an insult and implicate in physiological adaptations which may result in pathological outcomes in later life. This study evaluated the effect of maternal hyperthyroidism (hyper) on cardiac function in adult offspring and the possible involvement of cardiac Renin-Angiotensin System (RAS) in this process. Wistar dams received orally thyroxin (12 mg/L) from gestational day 9 (GD9) until GD18. Adult offspring at postnatal day 90 (PND90) from hyper dams presented increased SBP evaluated by plethysmography and worse recovery after ischemia-reperfusion (I/R), as evidenced by decreased LVDP, +dP/dT and -dP/dT at 25 min of reperfusion and by increased infarct size. Increased cardiac Angiotensin I/II levels and AT1R in hyper offspring were verified. Herein, we provide evidences that maternal hyperthyroidism leads to altered expression of RAS components in adult offspring, which may be correlated with worse recovery of the cardiac performance after ischemic insults and hypertension.

Pathophysiology of Myocardial Infarction

Myocardial infarction is defined as sudden ischemic death of myocardial tissue. In the clinical context, myocardial infarction is usually due to thrombotic occlusion of a coronary vessel caused by rupture of a vulnerable plaque. Ischemia induces profound metabolic and ionic perturbations in the affected myocardium and causes rapid depression of systolic function. Prolonged myocardial ischemia activates a "wavefront" of cardiomyocyte death that extends from the subendocardium to the subepicardium. Mitochondrial alterations are prominently involved in apoptosis and necrosis of cardiomyocytes in the infarcted heart. The adult mammalian heart has negligible regenerative capacity, thus the infarcted myocardium heals through formation of a scar. Infarct healing is dependent on an inflammatory cascade, triggered by alarmins released by dying cells. Clearance of dead cells and matrix debris by infiltrating phagocytes activates anti-inflammatory pathways leading to suppression of cytokine and chemokine signaling. Activation of the renin-angiotensin-aldosterone system and release of transforming growth factor-β induce conversion of fibroblasts into myofibroblasts, promoting deposition of extracellular matrix proteins. Infarct healing is intertwined with geometric remodeling of the chamber, characterized by dilation, hypertrophy of viable segments, and progressive dysfunction. This review manuscript describes the molecular signals and cellular effectors implicated in injury, repair, and remodeling of the infarcted heart, the mechanistic basis of the most common complications associated with myocardial infarction, and the pathophysiologic effects of established treatment strategies. Moreover, we discuss the implications of pathophysiological insights in design and implementation of new promising therapeutic approaches for patients with myocardial infarction.

Clinical perspectives and fundamental aspects of local cardiovascular and renal Renin-Angiotensin systems

Evidence for the potential role of organ specific cardiovascular renin-angiotensin systems (RAS) has been demonstrated experimentally and clinically with respect to certain cardiovascular and renal diseases. These findings have been supported by studies involving pharmacological inhibition during ischemic heart disease, myocardial infarction, cardiac failure; hypertension associated with left ventricular ischemia, myocardial fibrosis and left ventricular hypertrophy; structural and functional changes of the target organs associated with prolonged dietary salt excess; and intrarenal vascular disease associated with end-stage renal disease. Moreover, the severe structural and functional changes induced by these pathological conditions can be prevented and reversed by agents producing RAS inhibition (even when not necessarily coincident with alterations in arterial pressure). In this review, we discuss specific fundamental and clinical aspects and mechanisms related to the activation or inhibition of local RAS and their implications for cardiovascular and renal diseases. Fundamental aspects involving the role of angiotensins on cardiac and renal functions including the expression of RAS components in the heart and kidney and the controversial role of angiotensin-converting enzyme 2 on angiotensin peptide metabolism in humans, were discussed.

Interactive roles of NPR1 gene-dosage and salt diets on cardiac angiotensin II, aldosterone and pro-inflammatory cytokines levels in mutant mice

OBJECTIVE

The objective of the present study was to elucidate the interactive roles of guanylyl cyclase/natriuretic peptide receptor-A (NPRA) gene (Npr1) and salt diets on cardiac angiotensin II (ANG II), aldosterone and pro-inflammatory cytokines levels in Npr1 gene-targeted (1-copy, 2-copy, 3-copy, 4-copy) mice.

METHODS

Npr1 genotypes included 1-copy gene-disrupted heterozygous (+/-), 2-copy wild-type (+/+), 3-copy gene-duplicated heterozygous (++/+) and 4-copy gene-duplicated homozygous (++/++) mice. Animals were fed low, normal and high-salt diets. Plasma and cardiac levels of ANG II, aldosterone and pro-inflammatory cytokines were determined.

RESULTS

With a high-salt diet, cardiac ANG II levels were increased (+) in 1-copy mice (13.7 ± 2.8 fmol/mg protein, 111%) compared with 2-copy mice (6.5 ± 0.6), but decreased (-) in 4-copy (4.0 ± 0.5, 38%) mice. Cardiac aldosterone levels were increased (+) in 1-copy mice (80 ± 4 fmol/mg protein, 79%) compared with 2-copy mice (38 ± 3). Plasma tumour necrosis factor alpha was increased (+) in 1-copy mice (30.27 ± 2.32 pg/ml, 38%), compared with 2-copy mice (19.36 ± 2.49, 24%), but decreased (-) in 3-copy (11.59 ± 1.51, 12%) and 4-copy (7.13 ± 0.52, 22%) mice. Plasma interleukin (IL)-6 and IL-1α levels were also significantly increased (+) in 1-copy compared with 2-copy mice but decreased (-) in 3-copy and 4-copy mice.

CONCLUSION

These results demonstrate that a high-salt diet aggravates cardiac ANG II, aldosterone and pro-inflammatory cytokine levels in Npr1 gene-disrupted 1-copy mice, whereas, in Npr1 gene-duplicated (3-copy and 4-copy) mice, high salt did not render such elevation, suggesting the potential roles of Npr1 against salt loading.

Cardiac remodeling during and after renin-angiotensin system stimulation in Cyp1a1-Ren2 transgenic rats

This study investigated renin-angiotensin system (RAS)-induced cardiac remodeling and its reversibility in the presence and absence of high blood pressure (BP) in Cyp1a1-Ren2 transgenic inducible hypertensive rats (IHR). In IHR (pro)renin levels and BP can be dose-dependently titrated by oral administration of indole-3-carbinol (I3C). Young (four-weeks old) and adult (30-weeks old) IHR were fed I3C for four weeks (leading to systolic BP >200 mmHg). RAS-stimulation was stopped and animals were followed-up for a consecutive period. Cardiac function and geometry was determined echocardiographically and the hearts were excised for molecular and immunohistochemical analyses. Echocardiographic studies revealed that four weeks of RAS-stimulation incited a cardiac remodeling process characterized by increased left ventricular (LV) wall thickness, decreased LV volumes, and shortening of the left ventricle. Hypertrophic genes were highly upregulated, whereas in substantial activation a fibrotic response was absent. Four weeks after withdrawal of I3C, (pro)renin levels were normalized in all IHR. While in adult IHR BP returned to normal, hypertension was sustained in young IHR. Despite the latter, myocardial hypertrophy was fully regressed in both young and adult IHR. We conclude that (pro)renin-induced severe hypertension in IHR causes an age-independent fully reversible myocardial concentric hypertrophic remodeling, despite a continued elevated BP in young IHR.

Intracellular renin alters the electrical properties of the intact heart ventricle of adult Sprague Dawley rats

The influence of intracellular renin injection on the electrical properties of the intact left ventricle from adult Sprague Dawley rat heart was investigated. Intracellular renin injection was performed using intracellular microelectrodes filled with solution containing renin (120pM). Pressure pulses (40-70psi) for short periods of time (20ms), were applied to the micropipette while recording the action potential simultaneously from the same fiber. The results indicated that intracellular renin caused a depolarization of ventricular fibers of 7.3±2±mV (n=38) (4 animals) (P<0.05) and a decrease of the action potential duration at 50% and at 90% repolarization, respectively. Moreover, the refractoriness was significantly decreased with consequent generation of triggered activity. The effect of intracellular renin was seen within 3min of enzyme injection. The shortening of the action potential was related to an increase of potassium current which was measured in isolated ventricular myocytes before and after intracellular dialysis of renin (10(-9)M) using a voltage whole cell clamp configuration. Valsartan (10(-8)M) dialyzed together with renin (120pM) into the cell decreased drastically the effect of renin on potassium current. An increment of potassium current was also found when intracellular renin was dialyzed into cardiomyocytes exposed to Krebs solution containing valsartan (10(-8)M) for 10min prior to renin administration. Bis-1 which is a specific inhibitor of PKC, abolished the effect of intracellular renin on potassium current.

IN CONCLUSION

intracellular renin decreases the action potential duration and cardiac refractoriness in the intact left ventricle of adult Sprague Dawley rats. The shortening of the action potential was related to an increase in total potassium current. The effect of renin on total potassium currents was inhibited by valsartan and by Bis-1. Implication for cardiac arrhythmias was discussed.

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

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

The renin-angiotensin system in thyroid disorders and its role in cardiovascular and renal manifestations

Thyroid disorders are among the most common endocrine diseases and affect virtually all physiological systems, with an especially marked impact on cardiovascular and renal systems. This review summarizes the effects of thyroid hormones on the renin-angiotensin system (RAS) and the participation of the RAS in the cardiovascular and renal manifestations of thyroid disorders. Thyroid hormones are important regulators of cardiac and renal mass, vascular function, renal sodium handling, and consequently blood pressure (BP). The RAS acts globally to control cardiovascular and renal functions, while RAS components act systemically and locally in individual organs. Various authors have implicated the systemic and local RAS in the mediation of functional and structural changes in cardiovascular and renal tissues due to abnormal thyroid hormone levels. This review analyzes the influence of thyroid hormones on RAS components and discusses the role of the RAS in BP, cardiac mass, vascular function, and renal abnormalities in thyroid disorders.

The renin-angiotensin system in the breast and breast cancer

Much evidence now suggests that angiotensin II has roles in normal functions of the breast that may be altered or attenuated in cancer. Both angiotensin type 1 (AT1) and type 2 (AT2) receptors are present particularly in the secretory epithelium. Additionally, all the elements of a tissue renin-angiotensin system, angiotensinogen, prorenin and angiotensin-converting enzyme (ACE), are also present and distributed in different cell types in a manner suggesting a close relationship with sites of angiotensin II activity. These findings are consistent with the concept that stromal elements and myoepithelium are instrumental in maintaining normal epithelial structure and function. In disease, this system becomes disrupted, particularly in invasive carcinoma. Both AT1 and AT2 receptors are present in tumours and may be up-regulated in some. Experimentally, angiotensin II, acting via the AT1 receptor, increases tumour cell proliferation and angiogenesis, both these are inhibited by blocking its production or function. Epidemiological evidence on the effect of expression levels of ACE or the distribution of ACE or AT1 receptor variants in many types of cancer gives indirect support to these concepts. It is possible that there is a case for the therapeutic use of high doses of ACE inhibitors and AT1 receptor blockers in breast cancer, as there may be for AT2 receptor agonists, though this awaits full investigation. Attention is drawn to the possibility of blocking specific AT1-mediated intracellular signalling pathways, for example by AT1-directed antibodies, which exploit the possibility that the extracellular N-terminus of the AT1 receptor may have previously unsuspected signalling roles.

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

In the present review we reevaluated the experimental and clinical evidence that there is a local renin angiotensin system in the heart as well as the presence of a functional intracrine component which is activated during pathological conditions like heart failure and hypertension. The implications of these findings for cardiology were discussed. The novel finding that cell swelling impairs cell coupling and impulse propagation through activation of ionic channels with consequent generation of cardiac arrhythmias and the evidence that AT1 receptors are mechanosensors able to alter the heart function independently of Ang II were discussed. Particular attention was given to the role of salt loading on the activation of a local cardiac renin angiotensin and its consequences.

Intracrine action of angiotensin II in the intact ventricle of the failing heart: angiotensin II changes cardiac excitability from within

The influence of intracellular injection of angiotensin II (Ang II) on electrical properties of single right ventricular fibers from the failing heart of cardiomyopathic hamsters (TO2) was investigated in the intact ventricle of 8-month-old animals. Intracellular injection was performed using pressure pulses (40-70 psi) for short periods of time (20 ms) while recoding the action potential simultaneously from the same fiber. The results indicated that intracellular Ang II caused a hyperpolarization of 7.7 mV ± 4.3 mV (n = 39) (4 animals) (P < 0.05) followed by a small fall in membrane potential. The action potential duration was significantly increased at 50% and at 90% repolarization, and the refractoriness was significantly enhanced. The effect of intracellular Ang II on action potential duration was related to the inhibition of potassium conductance through PKC activation because Bis-1 (360 nM), a selective PKC inhibitor, abolished the effect of the peptide. Injections performed in different fibers of the same ventricle showed a variable effect of Ang II on action potential duration and generated spontaneous rhythmicity. The effect of intracellular Ang II on action potential duration and cardiac refractoriness remains for more than 1 h after interruption of the intracellular injection of the peptide.

Potential targets for intervention in radiation-induced heart disease

Radiotherapy of thoracic and chest wall tumors, if all or part of the heart was included in the radiation field, can lead to radiation-induced heart disease (RIHD), a late and potentially severe side effect. RIHD presents clinically several years after irradiation and manifestations include accelerated atherosclerosis, pericardial and myocardial fibrosis, conduction abnormalities, and injury to cardiac valves. The pathogenesis of RIHD is largely unknown, and a treatment is not available. Hence, ongoing pre-clinical studies aim to elucidate molecular and cellular mechanisms of RIHD. Here, an overview of recent pre-clinical studies is given, and based on the results of these studies, potential targets for intervention in RIHD are discussed.

Interaction between sensory C-fibers and cardiac mast cells in ischemia/reperfusion: activation of a local renin-angiotensin system culminating in severe arrhythmic dysfunction

Renin, the rate-limiting enzyme in the activation of the renin-angiotensin system (RAS), is synthesized and stored in cardiac mast cells. In ischemia/reperfusion, cardiac sensory nerves release neuropeptides such as substance P that, by degranulating mast cells, might promote renin release, thus activating a local RAS and ultimately inducing cardiac dysfunction. We tested this hypothesis in whole hearts ex vivo, in cardiac nerve terminals in vitro, and in cultured mast cells. We found that substance P-containing nerves are juxtaposed to renin-containing cardiac mast cells. Chemical stimulation of these nerves elicited substance P release that was accompanied by renin release, with the latter being preventable by mast cell stabilization or blockade of substance P receptors. Substance P caused degranulation of mast cells in culture and elicited renin release, and both of these were prevented by substance P receptor blockade. Ischemia/reperfusion in ex vivo hearts caused the release of substance P, which was associated with an increase in renin and norepinephrine overflow and with sustained reperfusion arrhythmias; substance P receptor blockade prevented these changes. Substance P, norepinephrine, and renin were also released by acetaldehyde, a known product of ischemia/reperfusion, from cardiac synaptosomes and cultured mast cells, respectively. Collectively, our findings indicate that an important link exists in the heart between sensory nerves and renin-containing mast cells; substance P released from sensory nerves plays a significant role in the release of mast cell renin in ischemia/reperfusion and in the activation of a local cardiac RAS. This culminates in angiotensin production, norepinephrine release, and arrhythmic cardiac dysfunction.

Angiotensin-II-induced apoptosis requires regulation of nucleolin and Bcl-xL by SHP-2 in primary lung endothelial cells

Angiotensin II (Ang II) is a key proapoptotic factor in fibrotic tissue diseases. However, the mechanism of Ang-II-induced cell death in endothelial cells has not been previously elucidated. Using the neutral comet assay and specific receptor antagonists and agonists, we found that Ang-II-mediated apoptosis in primary pulmonary endothelial cells required the AT2 receptor. Ang II caused cytochrome c release from the mitochondria concurrent with caspase-3 activation and DNA fragmentation, and apoptosis was suppressed by an inhibitor of Bax-protein channel formation, implicating mitochondrial-mediated apoptosis. There was no evidence that the extrinsic apoptotic pathway was involved, because caspase-9, but not caspase-8, was activated by Ang-II treatment. Apoptosis required phosphoprotein phosphatase activation, and inhibition of the SHP-2 phosphatase (encoded by Ptpn11) blocked cell death. Reduced levels of anti-apoptotic Bcl-2-family members can initiate intrinsic apoptosis, and we found that Ang-II treatment lowered cytosolic Bcl-x(L) protein levels. Because the protein nucleolin has been demonstrated to bind Bcl-x(L) mRNA and prevent its degradation, we investigated the role of nucleolin in Ang-II-induced loss of Bcl-x(L). RNA-immunoprecipitation experiments revealed that Ang II reduced the binding of nucleolin to Bcl-x(L) mRNA in an AU-rich region implicated in instability of Bcl-x(L) mRNA. Inhibition of SHP-2 prevented Ang-II-induced degradation of Bcl-x(L) mRNA. Taken together, our findings suggest that nucleolin is a primary target of Ang-II signaling, and that Ang-II-activated SHP-2 inhibits nucleolin binding to Bcl-x(L) mRNA, thus affecting the equilibrium between pro- and anti-apoptotic members of the Bcl-2 family.

Attenuation of isoproterenol-induced cardiac fibrosis in transgenic rats harboring an angiotensin-(1-7)-producing fusion protein in the heart

Objective: It has been shown that Ang-(1-7) has cardioprotective actions. To directly investigate the effects of Ang-(1-7) specifically in the heart, we generated and characterized transgenic (TG) rats which express an Ang-(1-7)-producing fusion protein driven by the α-MHC promoter.

Methods and Results: After microinjection of the transgene into fertilized rat zygotes, we obtained four different transgenic lines. Homozygous animals were analyzed with regard to the expression profile of the transgene by ribonuclease protection assay. Transgene expression was detected mainly in the heart with weak or no expression in other organs. Heterozygous TG(hA-1-7)L7301 rats presented a significant increase in cardiac Ang-(1-7) concentration compared with control rats (17.1±2.1 versus 3.9±1.4 pg/mg protein in SD rats). Radiotelemetry analysis revealed that TG rats presented no significant changes in blood pressure and heart rate compared with normal rats. Overexpression of Ang-(1-7) in the heart produced slight improvement in resting cardiac function (+ dT/dt: 81530±1305.0 versus 77470±345.5 g/s bpm in SD rats, p < 0.05), which was in keeping with the enhanced [Ca2+] handling observed in cardiomyocytes of TG rats. TG(hA-1-7)L7301 rats also showed a greater capacity to withstand stress since TG rats showed a less pronounced deposition of collagen type III and fibronectin induced by isoproterenol treatment in the subendocardial area than in corresponding controls. In addition, hearts from TG rats showed reduced incidence and duration of reperfusion arrhythmias in comparison with SD rats.

Conclusion: These results indicate that Ang-(1-7) has blood pressure-independent, antifibrotic effects, acting directly in the heart.

Angiotensin type 1 receptor mediates thyroid hormone-induced cardiomyocyte hypertrophy through the Akt/GSK-3beta/mTOR signaling pathway

Several studies have implicated the renin angiotensin system in the cardiac hypertrophy induced by thyroid hormone. However, whether Angiotensin type 1 receptor (AT1R) is critically required to the development of T3-induced cardiomyocyte hypertrophy as well as whether the intracellular mechanisms that are triggered by AT1R are able to contribute to this hypertrophy model is unknown. To address these questions, we employed a selective small interfering RNA (siRNA, 50 nM) or an AT1R blocker (Losartan, 1 microM) to evaluate the specific role of this receptor in primary cultures of neonatal cardiomyocytes submitted to T3 (10 nM) treatment. The cardiomyocytes transfected with the AT1R siRNA presented reduced mRNA (90%, P < 0.001) and protein (70%, P < 0.001) expression of AT1R. The AT1R silencing and the AT1R blockade totally prevented the T3-induced cardiomyocyte hypertrophy, as evidenced by lower mRNA expression of atrial natriuretic factor (66%, P < 0.01) and skeletal alpha-actin (170%, P < 0.01) as well as by reduction in protein synthesis (85%, P < 0.001). The cardiomyocytes treated with T3 demonstrated a rapid activation of Akt/GSK-3beta/mTOR signaling pathway, which was completely inhibited by the use of PI3K inhibitors (LY294002, 10 microM and Wortmannin, 200 nM). In addition, we demonstrated that the AT1R mediated the T3-induced activation of Akt/GSK-3beta/mTOR signaling pathway, since the AT1R silencing and the AT1R blockade attenuated or totally prevented the activation of this signaling pathway. We also reported that local Angiotensin I/II (Ang I/II) levels (120%, P < 0.05) and the AT1R expression (180%, P < 0.05) were rapidly increased by T3 treatment. These data demonstrate for the first time that the AT1R is a critical mediator to the T3-induced cardiomyocyte hypertrophy as well as to the activation of Akt/GSK-3beta/mTOR signaling pathway. These results represent a new insight into the mechanism of T3-induced cardiomyocyte hypertrophy, indicating that the Ang I/II-AT1R-Akt/GSK-3beta/mTOR pathway corresponds to a potential mediator of the trophic effect exerted by T3 in cardiomyocytes.

Candesartan-induced gene expression in five organs of stroke-prone spontaneously hypertensive rats

To test the functional consequences of blocking the local renin-angiotensin system (RAS), we investigated the effects of an angiotensin II type 1 receptor blocker (ARB), candesartan, on the systemic gene expression profile of five important organs (brain, heart, kidney, liver and adipose tissues) in the stroke-prone spontaneously hypertensive rat (SHRSP), an established model of essential hypertension and cardiovascular disorders, and its normotensive control, the Wistar Kyoto (WKY) rat. Rats were treated with candesartan (5 mg/kg/d) for 4 weeks from 12 to 16 weeks of age. DNA microarray technology was used to identify changes in gene expression. Four weeks of treatment with candesartan significantly lowered systolic blood pressure in male rats of both the SHRSP and the WKY strains (p<0.0005). Candesartan differentially modulated the gene expression profile in an organ-specific manner in male SHRSP; of the five organs tested, gene expression was most prominently altered in the hearts of SHRSP. In contrast, candesartan treatment exerted minimal or no significant effects on the gene expression profile of the corresponding organs of male WKY rats. The inter-strain differences in gene expression changes induced by candesartan were considered to be associated with both blood pressure-dependent and independent mechanisms. These results help to delineate the mechanisms that underlie the organ or tissue protection conferred by ARB at the levels of cellular biology and genomics in the context of the local RAS. Further studies are warranted to investigate not only individual genes of interest but also genetic "networks" that involve differential organ- or tissue-specific gene expression induced by the blockade of RAS in essential hypertension. Tokyo, Japan

Exposure to ultrafine carbon particles at levels below detectable pulmonary inflammation affects cardiovascular performance in spontaneously hypertensive rats

BACKGROUND

Exposure to particulate matter is a risk factor for cardiopulmonary disease but the underlying molecular mechanisms remain poorly understood. In the present study we sought to investigate the cardiopulmonary responses on spontaneously hypertensive rats (SHRs) following inhalation of UfCPs (24 h, 172 mug.m-3), to assess whether compromised animals (SHR) exhibit a different response pattern compared to the previously studied healthy rats (WKY).

METHODS

Cardiophysiological response in SHRs was analyzed using radiotelemetry. Blood pressure (BP) and its biomarkers plasma renin-angiotensin system were also assessed. Lung and cardiac mRNA expressions for markers of oxidative stress (hemeoxygenase-1), blood coagulation (tissue factor, plasminogen activator inhibitor-1), and endothelial function (endothelin-1, and endothelin receptors A and B) were analyzed following UfCPs exposure in SHRs. UfCPs-mediated inflammatory responses were assessed from broncho-alveolar-lavage fluid (BALF).

RESULTS

Increased BP and heart rate (HR) by about 5% with a lag of 1-3 days were detected in UfCPs exposed SHRs. Inflammatory markers of BALF, lung (pulmonary) and blood (systemic) were not affected. However, mRNA expression of hemeoxygenase-1, endothelin-1, endothelin receptors A and B, tissue factor, and plasminogen activator inhibitor showed a significant induction (~2.5-fold; p < 0.05) with endothelin 1 being the maximally induced factor (6-fold; p < 0.05) on the third recovery day in the lungs of UfCPs exposed SHRs; while all of these factors - except hemeoxygenase-1 - were not affected in cardiac tissues. Strikingly, the UfCPs-mediated altered BP is paralleled by the induction of renin-angiotensin system in plasma.

CONCLUSION

Our finding shows that UfCPs exposure at levels which does not induce detectable pulmonary neutrophilic inflammation, triggers distinct effects in the lung and also at the systemic level in compromised SHRs. These effects are characterized by increased activity of plasma renin-angiotensin system and circulating white blood cells together with moderate increases in the BP, HR and decreases in heart rate variability. This systemic effect is associated with pulmonary, but not cardiac, mRNA induction of biomarkers reflective of oxidative stress; activation of vasoconstriction, stimulation of blood coagulation factors, and inhibition of fibrinolysis. Thus, UfCPs may cause cardiovascular and pulmonary impairment, in the absence of detectable pulmonary inflammation, in individuals suffering from preexisting cardiovascular diseases.

Serotonin and angiotensin receptors in cardiac fibroblasts coregulate adrenergic-dependent cardiac hypertrophy

By mimicking sympathetic stimulation in vivo, we previously reported that mice globally lacking serotonin 5-HT(2B) receptors did not develop isoproterenol-induced left ventricular hypertrophy. However, the exact cardiac cell type(s) expressing 5-HT(2B) receptors (cardiomyocytes versus noncardiomyocytes) involved in pathological heart hypertrophy was never addressed in vivo. We report here that mice expressing the 5-HT(2B) receptor solely in cardiomyocytes, like global 5-HT(2B) receptor-null mice, are resistant to isoproterenol-induced cardiac hypertrophy and dysfunction, as well as to isoproterenol-induced increases in cytokine plasma-levels. These data reveal a key role of noncardiomyocytes in isoproterenol-induced hypertrophy in vivo. Interestingly, we show that primary cultures of angiotensinogen null adult cardiac fibroblasts are releasing cytokines on stimulation with either angiotensin II or serotonin, but not in response to isoproterenol stimulation, demonstrating a critical role of angiotensinogen in adrenergic-dependent cytokine production. We then show a functional interdependence between AT(1)Rs and 5-HT(2B) receptors in fibroblasts by revealing a transinhibition mechanism that may involve heterodimeric receptor complexes. Both serotonin- and angiotensin II-dependent cytokine production occur via a Src/heparin-binding epidermal growth factor-dependent transactivation of epidermal growth factor receptors in cardiac fibroblasts, supporting a common signaling pathway. Finally, we demonstrate that 5-HT(2B) receptors are overexpressed in hearts from patients with congestive heart failure, this overexpression being positively correlated with cytokine and norepinephrine plasma levels. Collectively, these results reveal for the first time that interactions between AT(1) and 5-HT(2B) receptors coexpressed by noncardiomyocytes are limiting key events in adrenergic agonist-induced, angiotensin-dependent cardiac hypertrophy. Accordingly, antagonists of 5-HT(2B) receptors might represent novel therapeutics for sympathetic overstimulation-dependent heart failure.

Stretch-induced regulation of angiotensinogen gene expression in cardiac myocytes and fibroblasts: opposing roles of JNK1/2 and p38alpha MAP kinases

The cardiac renin-angiotensin system (RAS) has been implicated in mediating myocyte hypertrophy, remodeling, and fibroblast proliferation in the hemodynamically overloaded heart. However, the intracellular signaling mechanisms responsible for regulation of angiotensinogen (Ao), a substrate of the RAS system, are largely unknown. Here we report the identification of JNK1/2 as a negative, and p38alpha as a major positive regulator of Ao gene expression. Isolated neonatal rat ventricular myocytes (NRVM) and fibroblasts (NRFB) plated on deformable membranes coated with collagen IV, were exposed to 20% equiaxial static-stretch (0-24 h). Mechanical stretch initially depressed Ao gene expression (4 h), whereas after 8 h, Ao gene expression increased in a time-dependent manner. Blockade of JNK1/2 with SP600125 increased basal Ao gene expression in NRVM (10.52+/-1.98 fold, P<0.001) and NRFB (13.32+/-2.07 fold, P<0.001). Adenovirus-mediated expression of wild-type JNK1 significantly inhibited, whereas expression of dominant-negative JNK1 and JNK2 increased basal and stretch-mediated (24 h) Ao gene expression, showing both JNK1 and JNK2 to be negative regulators of Ao gene expression in NRVM and NRFB. Blockade of p38alpha/beta by SB202190 or p38alpha by SB203580 significantly inhibited stretch-induced (24 h) Ao gene expression, whereas expression of wild-type p38alpha increased stretch-induced Ao gene expression in both NRVM (8.41+/-1.50 fold, P<0.001) and NRFB (3.39+/-0.74 fold, P<0.001). Conversely, expression of dominant-negative p38alpha significantly inhibited stretch response. Moreover, expression of constitutively active MKK6b (E) significantly stimulated Ao gene expression in the absence of stretch, indicating that p38 activation alone is sufficient to induce Ao gene expression. Taken together p38alpha was demonstrated to be a positive regulator, whereas JNK1/2 was found to be a negative regulator of Ao gene expression. Prolonged stretch diminished JNK1/2 activation, which was accompanied by a reciprocal increase in p38 activation and Ao gene expression. This suggests that a balance in JNK1/2 and p38alpha activation determines the level of Ao gene expression in myocardial cells.

The intracellular renin-angiotensin system: implications in cardiovascular remodeling

PURPOSE OF REVIEW

The renin-angiotensin system, traditionally viewed as a circulatory system, has significantly expanded in the last two decades to include independently regulated local systems in several tissues, newly identified active products of angiotensin II, and new receptors and functions of renin-angiotensin system components. In spite of our increased understanding of the renin-angiotensin system, a role of angiotensin II in cardiac hypertrophy, through direct effects on cardiovascular tissue, is still being debated. Here, we address the cardiovascular effects of angiotensin II and the role an intracellular renin-angiotensin system might play.

RECENT FINDINGS

Recent studies have shown that cardiac myocytes, fibroblasts and vascular smooth muscle cells synthesize angiotensin II intracellularly. Some conditions, such as high glucose, selectively increase intracellular generation and translocation of angiotensin II to the nucleus. Intracellular angiotensin II regulates the expression of angiotensinogen and renin, generating a feedback loop. The first reaction of intracellular angiotensin II synthesis is catalyzed by renin or cathepsin D, depending on the cell type, and chymase, not angiotensin-converting enzyme, catalyzes the second step.

SUMMARY

These studies suggest that the intracellular renin-angiotensin system is an important component of the local system. Alternative mechanisms of angiotensin II synthesis and action suggest a need for novel therapeutic agents to block the intracellular renin-angiotensin system.

Mice expressing ACE only in the heart show that increased cardiac angiotensin II is not associated with cardiac hypertrophy

In the heart, angiotensin II has been suggested to regulate cardiac remodeling and promote cardiac hypertrophy. To examine this, we studied compound heterozygous mice, called angiotensin-converting enzyme (ACE) 1/8, in which one ACE allele is null, whereas the other ACE allele (the 8 allele) targets expression to the heart. In this model, cardiac ACE levels are about 15 times those of wild-type mice, and ACE expression is reduced or eliminated in other tissues. ACE 1/8 mice have 58% the cardiac ACE of a previous model, called ACE 8/8, but both ACE 1/8 and ACE 8/8 mice have ventricular angiotensin II levels about twofold those of wild-type controls. Despite equivalent levels of cardiac angiotensin II, ACE 1/8 mice do not develop the marked atrial enlargement or the conduction defects previously reported in the ACE 8/8 mice. Six-month-old ACE 1/8 mice have normal cardiac function, as determined by echocardiography and left ventricular catheterization, despite the elevated levels of angiotensin II. ACE 1/8 mice also have normal levels of connexin 43. Both wild-type and ACE 1/8 mice develop similar degrees of cardiac hypertrophy after aortic banding. These data suggest that a moderate increase of local angiotensin II production in the heart does not produce cardiac dysfunction, at least under basal conditions, and that, in response to aortic banding, cardiac hypertrophy is not augmented by a twofold increase of cardiac angiotensin II.

Mast cells in the promotion and limitation of chronic inflammation

Observations of increased numbers of mast cells at sites of chronic inflammation have been reported for over a hundred years. Light and electron microscopic evidence of mast cell activation at such sites, taken together with the known functions of the diverse mediators, cytokines, and growth factors that can be secreted by appropriately activated mast cells, have suggested a wide range of possible functions for mast cells in promoting (or suppressing) many features of chronic inflammation. Similarly, these and other lines of evidence have implicated mast cells in a variety of adaptive or pathological responses that are associated with persistent inflammation at the affected sites. Definitively characterizing the importance of mast cells in chronic inflammation in humans is difficult. However, mice that genetically lack mast cells, especially those which can undergo engraftment with wildtype or genetically altered mast cells, provide a means to investigate the importance of mast cells and specific mast cell functions or products in diverse models of chronic inflammation. Such work has confirmed that mast cells can significantly influence multiple features of chronic inflammatory responses, through diverse effects that can either promote or, perhaps more surprisingly, suppress aspects of these responses.

The intracellular renin-angiotensin system: a new paradigm

More than a century after its discovery, the physiological implications of the renin-angiotensin system (RAS) continue to expand, with the identification of new components, functions and subsystems. These advancements have led to better management and understanding of a broad range of cardiovascular and metabolic disorders. The RAS has traditionally been viewed as a circulatory system, involved in the short-term regulation of volume and blood pressure homeostasis. Recently, local RASs have been described as regulators of chronic tissue effects. Most recently, studies have provided evidence of a complete, functional RAS within cells, described as an 'intracrine' or intracellular system. A more comprehensive understanding of the intracellular RAS provides for new strategies in system regulation and a more efficacious approach to the management of RAS-related diseases.

Role of cardiac overexpression of ANG II in the regulation of cardiac function and remodeling postmyocardial infarction

ANG II has a clear role in development of cardiac hypertrophy, fibrosis, and dysfunction. It has been difficult, however, to determine whether these actions are direct or consequences of its systemic hemodynamic effects in vivo. To overcome this limitation, we used transgenic mice with cardiac-specific expression of a transgene fusion protein that releases ANG II from cardiomyocytes (Tg-ANG II-cardiac) without involvement of the systemic renin-angiotensin system and tested whether increased cardiac ANG II accelerates remodeling and dysfunction postmyocardial infarction (MI), whereas those mice show no evidence of cardiac hypertrophy under the basal condition. Male 12- to 14-wk-old Tg-ANG II-cardiac mice and their wild-type littermates (WT) were subjected to sham-MI or MI by ligating the left anterior descending coronary artery for 8 wk. Cardiac ANG II levels were approximately 10-fold higher in Tg-ANG II-cardiac mice than their WT, whereas ANG II levels in plasma and other tissues did not differ between strains. Systolic blood pressure and heart rate were similar between groups with or without MI. In sham-MI, Tg-ANG II-cardiac mice had increased collagen deposition and decreased capillary density. The differences between strains became more pronounced after MI. Although cardiac function was well preserved in the Tg-ANG II-cardiac mice with sham-MI, cardiac remodeling and dysfunction post-MI were more severe than WT. Our results demonstrate that, independent of systemic hemodynamic effects, cardiac ANG II may act locally in the heart, causing interstitial fibrosis in sham-MI and accelerating deterioration of cardiac dysfunction and remodeling post-MI.

Cardiac angiotensin II type I and type II receptors are increased in rats submitted to experimental hypothyroidism

This study assessed the behaviour of angiotensin II (Ang II) receptors in an experimental hypothyroidism model in male Wistar rats. Animals were subjected to thyroidectomy and resting for 14 days. The alteration of cardiac mass was evaluated by total heart weight (HW), right ventricle weight (RVW), left ventricle weight (LVW), ratio of HW, RVW and LVW to body weight (BW) and atrial natriuretic factor (ANF) expression. Cardiac and plasma Ang II levels and serum T3 and T4 were determined. The mRNA and protein levels of Ang II receptors were investigated by RT-PCR and Western blotting, respectively. Functional analyses were performed using binding assays. T3 and T4 levels and the haemodynamic parameters confirmed the hypothyroid state. HW/BW, RVW/BW and LVW/BW ratios and the ANF expression were lower than those of control animals. No change was observed in cardiac or plasma Ang II levels. Both AT1/AT2 mRNA and protein levels were increased in the heart of hypothyroid animals due to a significant increase of these receptors in the RV. Experiments performed in cardiomyocytes showed a direct effect promoted by low thyroid hormone levels upon AT1 and AT2 receptors, discarding possible influence of haemodynamic parameters. Functional assays showed that both receptors are able to bind Ang II. Herein, we have identified, for the first time, a close and direct relation of elevated Ang II receptor levels in hypothyroidism. Whether the increase in these receptors in hypothyroidism is an alternative mechanism to compensate the atrophic state of heart or whether it may represent a potential means to the progression of heart failure remains unknown.

The role and regulation of cardiac angiotensin-converting enzyme for noninvasive molecular imaging in heart failure

Congestive heart failure is a pathologic condition characterized by progressive decrease in left ventricular contractility and consequent decline of cardiac output. There is convincing clinical and experimental evidence that the renin-angiotensin system (RAS) and its primary effector peptide, angiotensin II, are linked to the pathophysiology of interstitial fibrosis, cardiac remodeling, and heart failure. In addition to the traditional endocrine or circulating RAS, an active tissue RAS has been characterized. Tissue angiotensin-converting enzyme and locally synthesized angiotensin II, for example, by chymase, exert local trophic effects that modulate gene expression, which regulates growth and proliferation in both myocytes and nonmyocytes. The existence of the tissue RAS offers an opportunity for targeted imaging, which may be of considerable value for guiding medical therapy.

Enhanced cardiac production of matrix metalloproteinase-2 and -9 and its attenuation associated with pravastatin treatment in patients with acute myocardial infarction

Previous experimental studies have demonstrated that MMPs (matrix metalloproteinases) contribute to LV (left ventricular) remodelling. We hypothesized that cardiac MMPs are activated in patients with AMI (acute myocardial infarction) and, if so, MMP production may be attenuated by statins (3-hydroxy-3-methylglutaryl-CoA reductase inhibitors) through their cardiovascular protective actions. We studied 30 patients, ten control patients with stable angina pectoris and 20 patients with AMI, in whom LV catheterization at the chronic stage was performed 22+/-12 days (value is mean+/-S.D.) after the onset of AMI. Blood samples were collected from the CS (coronary sinus) and a peripheral artery. In patients with AMI, the levels of MMP-2 and MMP-9 were significantly (P<0.05) higher in the CS than the peripheral artery (MMP-2, 853+/-199 compared with 716+/-127 ng/ml; MMP-9, 165+/-129 compared with 98+/-82 ng/ml), whereas no significant differences were observed in the patients with angina pectoris. The CS-arterial concentration gradients of MMP-2 and MMP-9 correlated positively with BNP (brain natriuretic peptide) levels (MMP-2, R=0.68, P<0.01; MMP-9, R=0.59, P<0.05) and LV end-diastolic volume index (MMP-2, R=0.70, P<0.01; MMP-9, R=0.70, P<0.01). When patients with AMI treated with 10 mg of pravastatin or without (n=10 in each group) were compared, this statin therapy significantly (P<0.05) decreased the CS-arterial concentration gradients of MMP-2 (69+/-43 compared with 213+/-185 ng/ml) and MMP-9 (14+/-27 compared with 119+/-84 ng/ml). In conclusion, the enhanced production of cardiac MMP-2 and MMP-9 is associated with LV enlargement and elevated BNP levels in patients with AMI. A pleiotropic effect of statins appears to be associated with the modulation of cardiac MMP activation, which may be potentially beneficial in the attenuation of post-infarction LV remodelling.

AT1 receptor blockade is superior to conventional triple therapy in protecting against end-organ damage in Cyp1a1-Ren-2 transgenic rats with inducible hypertension

OBJECTIVE

In the present study we compared the effects of treatment with the AT1 receptor antagonist candesartan and of 'triple therapy' (hydralazine, hydrochlorothiazide, reserpine) on the course of blood pressure, cardiac hypertrophy and angiotensin II concentrations after induction of hypertension in transgenic rats with inducible expression of the mouse renin gene (Cyp1a1-Ren-2 rats).

METHODS

Hypertension was induced in Cyp1a1-Ren-2 rats through dietary administration of the natural xenobiotic indole-3-carbinol (I3C, 0.3%) for 4 days. Starting on the day before administration of I3C, rats were treated either with candesartan or received triple therapy for 9 days. Systolic blood pressure was measured in conscious animals. Rats were decapitated and angiotensin II levels in plasma and in whole kidney and left ventricular tissues were determined by radioimmunoassay.

RESULTS

Administration of I3C resulted in the development of severe hypertension and cardiac hypertrophy that was accompanied by marked elevations of plasma and tissue angiotensin II concentrations. Candesartan treatment prevented the development of hypertension and cardiac hypertrophy and was associated with a reduction of tissue angiotensin II concentrations. In contrast, triple therapy, despite maintaining systolic blood pressure in the normotensive range, did not prevent the development of cardiac hypertrophy and tissue angiotensin II augmentations.

CONCLUSIONS

Our findings indicate that hypertension in Cyp1a1-Ren-2 rats is a clearly angiotensin II-dependent model of hypertension with elevated circulating and tissue angiotensin II concentrations, and that antihypertensive treatment with AT1 receptor blockade is superior to conventional triple therapy in effective protection against hypertension-induced end-organ damage in this rat model.

Dosing Time-Dependent Effect of Temocapril on the Mortality of Stroke-Prone Spontaneously Hypertensive Rats

This study was undertaken to evaluate a dosing time-dependent effect of temocapril, an angiotensin-converting enzyme (ACE) inhibitor, on the mortality of stroke-prone spontaneously hypertensive rats (SHRSP). Temocapril (1 mg/kg/day) prolonged the survival rate of these animals, with a maximum effect after dosing at the early resting period and a minimum effect after dosing at the early active period. The pharmacokinetics of temocaprilat, an active metabolite of temocapril, did not differ significantly between the two dosing times. However, the inhibition of ACE activity in serum and organs (brain and aorta) and the reduction of blood pressure were significantly greater after dosing at the early resting period than at the early active period. These data suggest that the effect of temocapril on the mortality of SHRSP depends on the time of dosing, with a maximum effect seen after dosing at the early resting period. Dosing time-dependent differences in the pharmacodynamics of temocapril might be involved in explaining this phenomenon.

Overexpression of proadrenomedullin N-terminal 20 peptide blunts blood pressure rise and attenuates myocardial hypertrophy and fibrosis in hypertensive rats

We developed a transgenic (Tg) rat model that overexpresses human proadrenomedullin N-terminal 20 peptide (PAMP) only and then compared the effects of unilateral nephrectomy followed by a high salt diet for five weeks in Tg and wild-type rats. We found that systolic blood pressure was significantly lower in Tg UNX rats and cardiac hypertrophy and myocardial fibrosis was also attenuated in Tg rats. Evaluation of gene expression showed suppression of cardiac local renin-angiotensin system (RAS) in Tg rat. These results suggest that in addition to reducing blood pressure, PAMP suppresses cardiac hypertrophy through negative regulation of the local cardiac RAS.