Angiotensin II receptor antagonist TCV-116 induces regression of hypertensive left ventricular hypertrophy in vivo and inhibits the intracellular signaling pathway of stretch-mediated cardiomyocyte hypertrophy in vitro

Mechanisms of myocardial reverse remodelling and its clinical significance: A scientific statement of the ESC Working Group on Myocardial Function

Cardiovascular disease (CVD) is the leading cause of morbimortality in Europe and worldwide. CVD imposes a heterogeneous spectrum of cardiac remodelling, depending on the insult nature, that is, pressure or volume overload, ischaemia, arrhythmias, infection, pathogenic gene variant, or cardiotoxicity. Moreover, the progression of CVD-induced remodelling is influenced by sex, age, genetic background and comorbidities, impacting patients' outcomes and prognosis. Cardiac reverse remodelling (RR) is defined as any normative improvement in cardiac geometry and function, driven by therapeutic interventions and rarely occurring spontaneously. While RR is the outcome desired for most CVD treatments, they often only slow/halt its progression or modify risk factors, calling for novel and more timely RR approaches. Interventions triggering RR depend on the myocardial insult and include drugs (renin-angiotensin-aldosterone system inhibitors, beta-blockers, diuretics and sodium-glucose cotransporter 2 inhibitors), devices (cardiac resynchronization therapy, ventricular assist devices), surgeries (valve replacement, coronary artery bypass graft), or physiological responses (deconditioning, postpartum). Subsequently, cardiac RR is inferred from the degree of normalization of left ventricular mass, ejection fraction and end-diastolic/end-systolic volumes, whose extent often correlates with patients' prognosis. However, strategies aimed at achieving sustained cardiac improvement, predictive models assessing the extent of RR, or even clinical endpoints that allow for distinguishing complete from incomplete RR or adverse remodelling objectively, remain limited and controversial. This scientific statement aims to define RR, clarify its underlying (patho)physiologic mechanisms and address (non)pharmacological options and promising strategies to promote RR, focusing on the left heart. We highlight the predictors of the extent of RR and review the prognostic significance/impact of incomplete RR/adverse remodelling. Lastly, we present an overview of RR animal models and potential future strategies under pre-clinical evaluation.

Angiotensin II Receptor Blockers Are Associated With Reduced Valvular Fibrosis in Women With Aortic Stenosis

BACKGROUND

Angiotensin receptor blockers (ARBs) may slow down the progression of aortic stenosis (AS) through their antifibrotic effect. Women present more valvular fibrosis than men, so ARBs may have more effect in females. Our aim was to assess the impact of ARBs on the remodelling of the aortic valve in men and women.

METHODS

We included patients who had an aortic valve replacement with or without coronary bypass grafting from 2006 to 2013. Patients with missing echocardiographic or histologic data were excluded. Warren-Yong and fibrosis scores of the explanted valves were performed. Patients were divided into 4 phenotypes according to their Warren-Yong and fibrosis scores: mild calcification/fibrosis, severe calcification/fibrosis group, predominant fibrosis group, predominant calcification group.

RESULTS

Among the 1321 included patients, the vast majority (89%) has severe AS. Patients in the predominant fibrosis group, compared with the predominant calcium group, were more often female (39% vs 31%; P = 0.008) with bicuspid valves (44% vs 34%; P = 0.002), and less often used ARBs (25% vs 30%; P = 0.046). Female sex was independently associated with being in the predominant fibrosis group (odds ratio 1.45, 95% confidence interval 1.08-1.95; P = 0.01), with a significant interaction between female sex and ARBs. Women taking ARBs compared with women not taking ARBs had significantly lower fibrosis scores (P < 0.001). This difference was not seen in men.

CONCLUSIONS

In this large series of patients with moderate-severe AS, among the women there was a negative association between intake of ARBs and valvular fibrosis. Thus, the possible effects of ARBs may be sex specific, with a larger therapeutic role in women.

Candesartan Cilexetil Attenuates Arrhythmogenicity Following Pressure Overload in Rats via the Modulation of Cardiac Electrical and Structural Remodeling and Calcium Handling Dysfunction

Background

Cardiac hypertrophy is associated with abnormal electrophysiology and increased arrhythmia risk. This study assessed whether candesartan cilexetil, an angiotensin II type 1 receptor blocker, could suppress arrhythmogenecity by attenuating cardiac electrical remodeling and calcium mishandling in rats with pressure‐overload hypertrophy.

Methods and Results

Male Sprague‐Dawley rats were randomly subjected to abdominal aorta banding or sham procedure and received either candesartan cilexetil (3.0 mg/kg per day) or vehicle by gavage for 5 weeks. Pressure overload was characterized by compensated left ventricular (LV) hypertrophy and fibrosis, increased LV pressure and its decay time, and prolonged corrected QT interval, all of which were attenuated by candesartan cilexetil treatment. Candesartan cilexetil–treated banded rat hearts displayed shorter QT intervals and lower vulnerability to atrial and ventricular tachyarrhythmias than vehicle‐treated banded hearts. Candesartan cilexetil prevented banding‐induced prolonged action potential duration and reduced the occurrence of triggered activity in LV papillary muscles. In addition, the prolonged time to 50% cell relengthening and calcium transient decay time were normalized in LV myocytes from candesartan cilexetil–treated banded rats, along with a normalization of decreased SERCA2a (sarco[endo]plasmic reticulum calcium‐ATPase) expression in LV tissues. Furthermore, candesartan cilexetil normalized depressed transient outward potassium current densities and protein and mRNA levels of both voltage‐gated potassium 4.2 and 4.3 channel subunits (Kv4.2 and Kv4.3) in banded rats.

Conclusions

Candesartan cilexetil protects the heart from pressure overload‐induced adverse electrical remodeling by preserving potassium channel densities. In addition, calcium handling and its molecular regulation also improved after treatment. These beneficial effects may contribute to a lower susceptibility to arrhythmias in hearts from candesartan cilexetil–treated pressure‐overloaded rats.

Transcriptomic Response in the Heart and Kidney to Different Types of Antihypertensive Drug Administration

Certain classes of antihypertensive drug may exert specific, blood pressure (BP)-independent protective effects on end-organ damages such as left ventricular hypertrophy, although the overall evidence has not been definitive in clinical trials. To unravel antihypertensive drug-induced gene expression changes that are potentially related to the amelioration of end-organ damages, we performed in vivo phenotypic evaluation and transcriptomic analysis on the heart and the kidney, with administration of antihypertensive drugs to two inbred strains (ie, hypertensive and normotensive) of rats. We chose 6 antihypertensive classes: enalapril (angiotensin-converting enzyme inhibitor), candesartan (angiotensin receptor blocker), hydrochlorothiazide (diuretics), amlodipine (calcium-channel blocker), carvedilol (vasodilating β-blocker), and hydralazine. In the tested rat strains, 4 of 6 drugs, including 2 renin-angiotensin system inhibitors, were effective for BP lowering, whereas the remaining 2 drugs were not. Besides BP lowering, there appeared to be some interdrug heterogeneity in phenotypic changes, such as suppressed body weight gain and body weight-adjusted heart weight reduction. For the transcriptomic response, a considerable number of genes showed prominent mRNA expression changes either in a BP-dependent or BP-independent manner with substantial diversity between the target organs. Noticeable changes of mRNA expression were induced particularly by renin-angiotensin system blockade, for example, for genes in the natriuretic peptide system (Nppb and Corin) in the heart and for those in the renin-angiotensin system/kallikrein-kinin system (Ren and rat Klk1 paralogs) and those related to calcium ion binding (Calb1 and Slc8a1) in the kidney. The research resources constructed here will help corroborate occasionally inconclusive evidence in clinical settings.

Effects of inhibition of the renin-angiotensin system on hypertension-induced target organ damage: clinical and experimental evidence

The dysregulation of renin-angiotensin-system (RAS) plays a pivotal role in hypertension and in the development of the related target organ damage (TOD). The main goal of treating hypertension is represented by the long-term reduction of cardiovascular (CV) risk. RAS inhibition either by angiotensin converting enzyme (ACE)-inhibitors or by type 1 Angiotensin II receptors blockers (ARBs), reduce the incidence of CV events in hypertensive patients. Actually, ACE-inhibitors and ARBs have been demonstrated to be effective to prevent, or delay TOD like left ventricular hypertrophy, chronic kidney disease, and atherosclerosis. The beneficial effects of RAS blockers on clinical outcome of hypertensive patients are due to the key role of angiotensin II in the pathogenesis of TOD. In particular, Angiotensin II through an inflammatory-mediated mechanism plays a role in the initiation, progression and vulnerability of atherosclerotic plaque. In addition, Angiotensin II can be considered the hormonal transductor of the pressure overload in cardiac myocytes, and through an autocrine-paracrine mechanism plays a role in the development of left ventricular hypertrophy. Angiotensin II by modulating the redox status and the immune system participates to the development of chronic kidney disease. The RAS blocker should be considered the first therapeutic option in patients with hypertension, even if ACE-inhibitors and ARBs have different impact on CV prevention. ARBs seem to have greater neuro-protective effects, while ACE-inhibitors have greater cardio-protective action.

Precision medicine for heart failure based on molecular mechanisms: The 2019 ISHR Research Achievement Award Lecture

Heart failure is a leading cause of death, and the number of patients with heart failure continues to increase worldwide. To realize precision medicine for heart failure, its underlying molecular mechanisms must be elucidated. In this review summarizing the "The Research Achievement Award Lecture" of the 2019 XXIII ISHR World Congress held in Beijing, China, we would like to introduce our approaches for investigating the molecular mechanisms of cardiac hypertrophy, development, and failure, as well as discuss future perspectives.

Targeting cardiac fibrosis in heart failure with preserved ejection fraction: mirage or miracle?

Cardiac fibrosis is central to the pathology of heart failure, particularly heart failure with preserved ejection fraction (HFpEF). Irrespective of the underlying profibrotic condition (e.g. ageing, diabetes, hypertension), maladaptive cardiac fibrosis is defined by the transformation of resident fibroblasts to matrix-secreting myofibroblasts. Numerous profibrotic factors have been identified at the molecular level (e.g. TGFβ, IL11, AngII), which activate gene expression programs for myofibroblast activation. A number of existing HF therapies indirectly target fibrotic pathways; however, despite multiple clinical trials in HFpEF, a specific clinically effective antifibrotic therapy remains elusive. Therapeutic inhibition of TGFβ, the master-regulator of fibrosis, has unfortunately proven toxic and ineffective in clinical trials to date, and new approaches are needed. In this review, we discuss the pathophysiology and clinical implications of interstitial fibrosis in HFpEF. We provide an overview of trials targeting fibrosis in HFpEF to date and discuss the promise of potential new therapeutic approaches and targets in the context of underlying molecular mechanisms.

The role of stretch, tachycardia and sodium-calcium exchanger in induction of early cardiac remodelling

Stretch and tachycardia are common triggers for cardiac remodelling in various conditions, but a comparative characterization of their role in the excitation‐transcription coupling (ETC) and early regulation of gene expression and structural changes is lacking. Here, we show that stretch and tachycardia directly induced hypertrophy of neonatal rat cardiac myocytes and also of non‐myocytes. Both triggers induced similar patterns of hypertrophy but had largely distinct gene expression profiles. ACTA1 served as good hypertrophy marker upon stretch, while RCAN1 was found increased in response to tachycardia in a rate‐dependent fashion. Mechanistically, several calcium‐handling proteins, including the sodium‐calcium exchanger (NCX), contributed to ETC. Phosphorylation of the calcium/calmodulin‐dependent protein kinase II (CaMKII) was elevated and occurred downstream of NCX activation upon tachycardia, but not stretch. Microarray profiling revealed that stretch and tachycardia regulated around 33% and 20% genes in a NCX‐dependent manner, respectively. In conclusion, our data show that hypertrophy induction by stretch and tachycardia is associated with different gene expression profiles with a significant contribution of the NCX.

Nelumbo nucifera Receptaculum Extract Suppresses Angiotensin II-Induced Cardiomyocyte Hypertrophy

Nelumbo nucifera Gaertn. (lotus) is an important medicinal plant, and many parts of the plant have been investigated for their therapeutic effects. However, the therapeutic effect of receptacles of lotuses on pathological cardiomyocyte hypertrophy has not been investigated yet. Therefore, the current study aimed to determine the protective effect of lotus against angiotensin II (Ang II)-induced cardiomyocyte hypertrophy in vitro. Ang II was used to induce hypertrophy of H9c2 cells. The lotus receptacle powder (MeOH extract of receptaculum Nelumbinis; MRN) used in the experiments was prepared by MeOH extraction and subsequent evaporation. To evaluate the effect of MRN on cardiomyocyte hypertrophy, cell size, protein synthesis, and hypertrophic marker expressions were examined. The antioxidant ability of MRN was determined by using CM-H₂DCFDA, a general oxidative stress indicator. Ang II-induced cardiomyocyte hypertrophy was significantly attenuated by 5 µg/mL of MRN, as confirmed by the reductions in cell size, protein synthesis, and hypertrophic marker expression. MRN also attenuated Ang II-induced excessive intracellular reactive oxygen species (ROS) production through the suppression of protein kinase C (PKC), extracellular-signal-regulated kinase (ERK), and NF-κB activation and subsequent type I angiotensin receptor (AT1R), receptor for advanced glycation end products (RAGE), and NADPH oxidase (NOX) expression. MRN exerted a significant protective effect against Ang II-induced cardiomyocyte hypertrophy through suppression of PKC–ERK signaling, and this subsequently led to attenuation of intracellular ROS production.

Relation Between Renin-Angiotensin System Blockers and Survival Following Isolated Aortic Valve Replacement for Aortic Stenosis

Renin-angiotensin system blockers (RASb) improve cardiac remodeling, but their clinical utility after surgical aortic valve replacement (SAVR) for aortic stenosis (AS) is unclear. We aimed to assess the impact of RASb on short- and long-term survival following isolated SAVR for severe AS. From January 2005 to January 2014, 508 consecutive patients had isolated SAVR for severe AS. Patients with RASb (n = 286; 53%) were more often female (p = 0.039), hypertensive (p < 0.0001), and diabetic (p = 0.004), with higher body mass index (p < 0.0001) and EuroSCORE II (p = 0.025), and lower mean aortic pressure gradient (p = 0.011). The 30-day mortality was similar in both groups (RASb: 3% vs no RASb: 5.8%, p = 0.13), but lower under angiotensin receptor blockers (ARB) than angiotensin-converting enzyme inhibitors (ACEi; 0.7% vs 5.6%, p = 0.017). Patients under RASb had a better 8-year survival than those without RASb (83 ± 3% vs 52 ± 5%, p < 0.0001), confirmed in a propensity score-matched pairs analysis (82 ± 4% vs 50 ± 7%, p < 0.0001). Regarding different types of RASb, patients under ARB had lower mortality than those under ACEi (87 ± 3% vs 79 ± 4%, p = 0.028). In multivariate analysis, the use of RASb was associated with improved survival (hazard ratio = 0.31, 95% confidence interval 0.20 to 0.47, p < 0.0001), with lower mortality under ARB than under ACEi (hazard ratio = 0.39, 95% confidence interval 0.18 to 0.85, p = 0.018). In this observational study, the use of RASb was associated with improved long-term outcome after isolated SAVR for severe AS. A randomized clinical trial is mandatory.

Biomechanical Strain Exacerbates Inflammation on a Progeria-on-a-Chip Model

Organ-on-a-chip platforms seek to recapitulate the complex microenvironment of human organs using miniaturized microfluidic devices. Besides modeling healthy organs, these devices have been used to model diseases, yielding new insights into pathophysiology. Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disease showing accelerated vascular aging, leading to the death of patients due to cardiovascular diseases. HGPS targets primarily vascular cells, which reside in mechanically active tissues. Here, a progeria-on-a-chip model is developed and the effects of biomechanical strain are examined in the context of vascular aging and disease. Physiological strain induces a contractile phenotype in primary smooth muscle cells (SMCs), while a pathological strain induces a hypertensive phenotype similar to that of angiotensin II treatment. Interestingly, SMCs derived from human induced pluripotent stem cells of HGPS donors (HGPS iPS-SMCs), but not from healthy donors, show an exacerbated inflammatory response to strain. In particular, increased levels of inflammation markers as well as DNA damage are observed. Pharmacological intervention reverses the strain-induced damage by shifting gene expression profile away from inflammation. The progeria-on-a-chip is a relevant platform to study biomechanics in vascular biology, particularly in the setting of vascular disease and aging, while simultaneously facilitating the discovery of new drugs and/or therapeutic targets.

Candesartan abrogates G protein-coupled receptors agonist-induced MAPK activation and cardiac myocyte hypertrophy

The renin-angiotensin-aldosterone system (RAAS) has been identified as a major contributor to the development of cardiac hypertrophy and the subsequent transition to heart failure. G protein-coupled receptors agonists such as angiotensin II (Ang II), endothelin-1 (ET-1) and phenylephrine (PE) have been implicated in hypertrophic responses in ventricular myocytes through the activation of several families of MAP kinases. In this study we examined the effect of candesartan, an Ang II type 1-(AT1)-receptor antagonist, on cardiac hypertrophy by using cultured neonatal rat cardiomyocytes. Stimulation with Ang II (100 nM), ET-1 (100 nM) or PE (1 µM) induced marked increases in [3H]Leucine incorporation (≥ 50%), compatible with enhanced protein synthesis. The addition of candesartan abrogated the increase in [3H]Leucine incorporation in response not only to Ang II but also to ET-1 and PE. To elucidate the mechanisms involved in this antihypertrophic effect of candesartan, we studied the activation of p38-MAPK, extracellular signal-regulated kinases (ERK1/2) and stress-activated protein kinases (SAPKs). Ang II, ET-1 and PE increased the phosphorylation levels of ERK1/2, p54 SAPK and p46SAPK and p38 in a time-dependent manner. This activation was completely blocked in the case of Ang II by pretreatment with candesartan. ET-1-induced activation of ERKs, SAPKs and p38 was also partially, but significantly, reduced by candesartan. PE-induced activation of SAPKs, but not ERKs and p38, was also reduced by candesartan. These results suggest that the hypertrophic response to ET-1 and PE, along with Ang II, is dependent upon a functioning AT1-receptor and may be mediated by AT 1 activation of the MAP kinases.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

The Anrep effect: 100 years later

Myocardial stretch elicits a rapid increase in developed force, which is mainly caused by an increase in myofilament calcium sensitivity (Frank-Starling mechanism). Over the ensuing 10-15 min, a second gradual increase in force takes place. This slow force response to stretch is known to be the result of an increase in the calcium transient amplitude and constitutes the in vitro equivalent of the Anrep effect described 100 years ago in the intact heart. In the present review, we will update and discuss what is known about the Anrep effect as the mechanical counterpart of autocrine/paracrine mechanisms involved in its genesis. The chain of events triggered by myocardial stretch comprises 1) release of angiotensin II, 2) release of endothelin, 3) activation of the mineralocorticoid receptor, 4) transactivation of the epidermal growth factor receptor, 5) increased formation of mitochondria reactive oxygen species, 6) activation of redox-sensitive kinases upstream myocardial Na(+)/H(+) exchanger (NHE1), 7) NHE1 activation, 8) increase in intracellular Na(+) concentration, and 9) increase in Ca(2+) transient amplitude through the Na(+)/Ca(2+) exchanger. We will present the experimental evidence supporting each of the signaling steps leading to the Anrep effect and its blunting by silencing NHE1 expression with a specific small hairpin interference RNA injected into the ventricular wall.

AT1 receptor blockade delays postlactational mammary gland involution: a novel role for the renin angiotensin system

Angiotensin II (AngII), the main effector peptide of the renin-angiotensin system (RAS), participates in multiple biological processes, including cell growth, apoptosis, and tissue remodeling. Since AngII activates, in different cell types, signal transducing pathways that are critical for mammary gland postlactational regression, we investigated the role of the RAS during this process. We found that exogenous administration of AngII in mammary glands of lactating Balb/c mice induced epithelium apoptosis [2.9±0.5% (control) vs. 9.6±1.1% (AngII); P < 0.001] and activation of the proapoptotic factor STAT3, an effect inhibited by irbesartan, an AT(1) receptor blocker. Subsequently, we studied the expression kinetics of RAS components during involution. We found that angiotensin-converting enzyme (ACE) mRNA expression peaked 6 h after weaning (5.7-fold; P<0.01), while induction of angiotensinogen and AT(1) and AT(2) receptors expression was detected 96 h after weaning (6.2-, 10-, and 6.2-fold increase, respectively; P<0.01). To assess the role of endogenously generated AngII, mice were treated with losartan, an AT(1) receptor blocker, during mammary involution. Mammary glands from losartan-treated mice showed activation of the survival factors AKT and BCL-(XL), significantly lower LIF and TNF-α mRNA expression (P<0.05), reduced apoptosis [12.1±2.1% (control) vs. 4.8±0.7% (losartan); P<0.001] and shedding of epithelial cells, inhibition of MMP-9 activity in a dose-dependent manner (80%; P<0.05; with losartan IC(50) value of 6.9 mg/kg/d] and lower collagen deposition and adipocyte invasion causing a delayed involution compared to vehicle-treated mice. Furthermore, mammary glands of forced weaned AT(1A)- and/or AT(1B)-deficient mice exhibited retarded apoptosis of epithelial cells [6.3±0.95% (WT) vs. 3.3±0.56% (AT(1A)/AT(1B) DKO); P<0.05] with remarkable delayed postlactational regression compared to wild-type animals. Taken together, these results strongly suggest that AngII, via the AT(1) receptor, plays a major role in mouse mammary gland involution identifying a novel role for the RAS. angiotensin system.

The cell biology of disease: cellular mechanisms of cardiomyopathy

The heart exhibits remarkable adaptive responses to a wide array of genetic and extrinsic factors to maintain contractile function. When compensatory responses are not sustainable, cardiac dysfunction occurs, leading to cardiomyopathy. The many forms of cardiomyopathy exhibit a set of overlapping phenotypes reflecting the limited range of compensatory responses that the heart can use. These include cardiac hypertrophy, induction of genes normally expressed during development, fibrotic deposits that replace necrotic and apoptotic cardiomyocytes, and metabolic disturbances. The compensatory responses are mediated by signaling pathways that initially serve to maintain normal contractility; however, persistent activation of these pathways leads to cardiac dysfunction. Current research focuses on ways to target these specific pathways therapeutically.

Extracellular matrix of collagen modulates intracellular calcium handling and electrophysiological characteristics of HL-1 cardiomyocytes with activation of angiotensin II type 1 receptor

BACKGROUND

Myocardial fibrosis plays a critical role in heart failure, resulting in cardiac structural and electrical remodeling which can induce atrial arrhythmias. Collagen is the major element of fibrosis. However, it is not clear whether collagen can directly regulate the calcium homeostasis and the electrophysiologic characteristics of cardiomyocytes. The aim of this study was to determine the effects of collagen on calcium homeostasis and the electrical properties of atrial cardiomyocytes.

METHODS AND RESULTS

HL-1 cardiomyocytes were cultured with and without collagen type I (1 or 10 μg/mL) or losartan (10 μmol/L). Whole-cell clamp, indo-1 fluorescence, and Western blotting were used to evaluate the action potential (AP) and ionic currents, intracellular calcium homeostasis, and calcium regulatory proteins. Compared with the control samples, there was no significant difference in collagen (1 μg/mL)-treated HL-1 cardiomyocytes. However, collagen (10 μg/mL)-treated HL-1 cardiomyocytes exhibited larger intracellular calcium ([Ca(2+)](i)) transients by 113% and a larger sarcoplasmic reticulum calcium content by 86%. Collagen (10 μg/mL)-treated HL-1 cardiomyocytes had higher expression of sarcoplasmic reticulum ATPase (SERCA2a) and Thr17-phosphorylated phospholamban but similar protein expressions of the Na(+)/Ca(2+) exchanger and ryanodine receptor. Collagen (10 μg/mL)-treated HL-1 cardiomyocytes (n = 11) had larger AP amplitude (104 ± 5 vs 83 ± 7 mV; P < .05), and shorter 90% of AP duration (25 ± 2 vs 33 ± 2 ms, P < .05) than control cells (n = 11). Moreover, collagen (10 μg/mL)-treated HL-1 cells had larger I(to) and I(Ksus) values than control cells. The administration of losartan (10 μmol/L) attenuated collagen-induced changes in [Ca(2+)](i) transients, [Ca(2+)](i) stores, AP morphology, ionic currents, SERCA2a, and Thr17-phosphorylated phospholamban expressions.

CONCLUSIONS

This study demonstrates that collagen can directly modulate the calcium dynamics and electrical activities of atrial cardiomyocytes, which are associated with the renin-angiotensin system. These findings suggest a critical role of collagen in electrical remodeling during fibrosis.

Effect of candesartan treatment on left ventricular remodeling after aortic valve replacement for aortic stenosis

In hypertension, angiotensin receptor blockers can augment regression of left ventricular (LV) hypertrophy. It is not known whether this also is the case after aortic valve replacement (AVR) for severe aortic stenosis (AS). To test the hypothesis that treatment with candesartan in addition to conventional treatment is able to augment LV and left atrial (LA) reverse remodeling in patients with AS undergoing AVR, we studied 114 patients scheduled for AVR. Patients were randomized to treatment with candesartan 32 mg 1 time/day or conventional therapy immediately after AVR. Patients were followed with echocardiographic evaluations 3, 6, and 12 months after surgery. Primary end point was change in LV mass index. At baseline and during follow-up no differences in systolic, diastolic, and pulse pressures were seen between groups. Baseline LV mass index was 134 +/- 41 g/m(2) with no difference between groups. Mean decrease in LV mass index in the control group was 12 +/- 28 g/m(2) compared to 30 +/- 40 g/m(2) in the candesartan group (p = 0.015) during follow-up. After 12 months LV mass index was significantly lower in the candesartan group (103 +/- 29 vs 119 +/- 31 g/m(2), p = 0.01). In addition, the candesartan group had greater improvement in longitudinal LV systolic function assessed by tissue Doppler S' wave (0.6 +/- 0.1-cm/s increase in control group vs 1.4 +/- 0.1 cm/s in candesartan group, p = 0.01, p for trend = 0.02) and a decrease in LA volume (p for trend = 0.01). Treatment had no effect on diastolic E/e' ratio or B-type natriuretic peptide. In conclusion, angiotensin receptor blockade with candesartan after AVR in patients with AS is associated with augmented reverse LV and LA remodeling compared to conventional management.

Felodipine downregulates serum interleukin-18 levels in rats with fructose-induced metabolic syndrome

OBJECTIVE

Human studies suggest that calcium-channel blockers have cardiovascular protection besides reducing blood pressure, and interleukin-18 (IL-18) levels which are elevated in obese population are associated with metabolic syndrome (MetS). The purpose of this research was to study the change of serum IL-18 levels and the effect of felodipine on it in high-fructose diet-fed rats.

METHODS

In this research, 30 Wistar male rats were randomized into 3 groups. A control group (no.=12) was fed with normal feeds, and high-fructose diet was given to a fructose group and a flodioine group (no.=9 in each group). All animals were fed for a period of 32 weeks, during which body weight and systolic blood pressure (BP) were measured once every 4 weeks. Felodipine (5 mg/kg/d) was then administered by gavage daily for 6 weeks to the felodipine group. Before and after treatment with felodipine, fasting plasma lipid, blood glucose, plasma insulin, and serum IL-18 were detected.

RESULTS

Body weight, systolic BP, triglycerides, fasting insulin, and the R-value of homeostasis model (HOMA-R) were significantly increased in high-fructose rats (p<0.01). Serum IL-18 levels were elevated and had significant positive correlation with HOMA-R in rats with fructose-induced MetS (p<0.01). We also found that felodipine may decrease HOMA-R and serum IL-18 levels besides reducing blood pressure (p<0.05, p<0.01).

CONCLUSION

IL-18 plays an important role in the development of MetS, while felodipine exerts an anti-inflammatory effect on rats with fructose-induced MetS by downregulating serum IL-18 levels.

Overexpression of TRB3 gene in adipose tissue of rats with high fructose-induced metabolic syndrome

Insulin resistance is the physiopathologic foundation of metabolic syndrome. TRB3 has been revealed to be involved in insulin resistance in the liver by interacting directly with Akt and blocking its activation. Our investigation aims at exploring the relationship between metabolic syndrome and TRB3 mRNA expression in adipose tissue of rats. Two groups were studied as follows: the control group (CONTROL, n = 12) was fed a standard rodent chow, and the experimental group (Fructose n = 9) was fed a high-fructose diet. Body weight and systolic blood pressure were measured per 4 weeks. At the end of 38 weeks, levels of tribbles mRNAs in adipose tissue were determined by quantitative real-time polymerase chain reaction (PCR), and Akt/phospho-Akt expression was assessed by Western blot. Results show that levels of TRB1-3 mRNAs were expressed in adipose tissue of rats of both groups, and tribbles mRNAs were TRB1 (CONTROL: 0.00515, Fructose: 0.00497), TRB2 (CONTROL: 0.02104, Fructose: 0.01988), and TRB3 (CONTROL: 0.00457, Fructose: 0.00822), respectively. Of the three, TRB3 mRNA alone significantly increased by 94% in adipose tissue of fructose-fed rats compared with those in adipose tissue of the controls (P<0.05), and there was significant positive correlation between TRB3 mRNA levels and HOMA-R in fructose group (r = 0.68, P<0.05). Western blot analysis showed that phospho-Akt (Ser-473) expression was significantly decreased in adipose tissue of fructose-fed rats compared with controls (P<0.001). The present study suggests that TRB3 may be involved in metabolic syndrome by inhibiting activation of Akt in adipose tissue.

Endothelin-1 and angiotensin II contribute to BNP but not c-fos gene expression response to elevated load in isolated mice hearts

The early events in the cardiac hypertrophic process induced by hemodynamic load include activation of B-type natriuretic peptide (BNP) and c-fos gene expression. However, it is unknown whether stretch acts directly or through local paracrine factors to trigger changes in cardiac gene expression. Herein we studied the involvement of endothelin-1 (ET-1) and angiotensin II (Ang II) in load-induced activation of left ventricular BNP and c-fos gene expression using an in vitro stretch model in isolated perfused adult mice hearts. Two-hour stretch induced by increasing coronary flow rate from 2 to 5 ml/min increased the expression of BNP and c-fos genes by 1.9- and 1.5-fold, respectively (P<0.001 and P<0.05). A mixed ET(A/B) receptor antagonist bosentan attenuated the BNP gene expression response to load by 58% (P<0.005). A similar 53% inhibition was observed with the selective ET(A) receptor blocker BQ-123 (P<0.05). Type 1 Ang II receptor antagonist CV-11974 decreased the activation of BNP gene expression by 50% (P<0.05). In contrast, the activation of c-fos gene expression was not inhibited by antagonists of ET(A/B) and AT(1) receptors. Our results show that ET-1 and Ang II play a key role in the induction of BNP, but not c-fos gene expression in response to load in intact adult murine hearts.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Inhibition of NF-κB induces regression of cardiac hypertrophy, independent of blood pressure control, in spontaneously hypertensive rats

The transcription factor nuclear factor (NF)-κB plays a leading role in cardiac hypertrophy associated with heart failure, but whether it is involved in cardiac mass reduction is not known. We evaluated whether inhibiting the NF-κB cascade with pyrrolidine dithiocarbamate (PDTC) in spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto rats (WKYs) affected hypertrophy. We measured NF-κB signaling components [NF-κB translocation, IκBα, p65, mRNA and protein levels, and IκB kinase-β (IKKβ) activity] at 12 and 36 wk in WKYs and SHRs and at 10 wk in PDTC-treated rats ( n = 9). NF-κB activation was also evaluated in rats treated for 10 wk with captopril or hydralazine alone or with either drug plus PDTC. All components were increased in SHRs compared with WKYs. After PDTC treatment, NF-κB activity was inhibited, and heart weight-to-body weight ratio in SHRs was significantly attenuated (3.52 ± 0.04 to 3.32 ± 0.05 mg/kg). Captopril treatment significantly reduced cardiac mass (3.5 vs. 3.05 mg/kg; n = 9) and inhibited NF-κB activity (169.71 ± 5.70 to 106.7 ± 12.44). Hydralazine had no effect on cardiac mass (3.5 vs. 3.42 mg/kg) or NF-κB activity (169.71 ± 5.70 to 155.52 ± 6.11). Hydralazine plus PDTC reduced blood pressure (191.16 ± 1.7 to 158.5 ± 2.36 mmHg) and inhibited NF-κB activity (169.71 ± 5.70 to 97.29 ± 3.65). Our data suggest that 1) cardiac hypertrophy in SHRs is partly due to NF-κB activation, 2) inhibition of NF-κB activity by PDTC parallels regression of hypertrophy, and 3) regression of hypertrophy is partly due to inhibition of NF-κB activity, independent of hypertension. The relationship between NF-κB activity and cardiac remodeling is causal, not coincidental.

Intracellular signaling following myocardial stretch: an autocrine/paracrine loop

The stretch of adult papillary muscle elicits a chain of autocrine/paracrine events in which the Na(+)/H(+) exchanger (NHE-1) activation is the central step. This activation is induced by a sequential angiotensin II-endothelin (Ang II-ET) release and results in an increase in intracellular Na(+) (Na(+)(i)) without significant changes in intracellular pH. The increase in Na(+)(i) negatively shifts the reverse potential of the Na(+)/Ca(2+) exchanger (NCX) thus inducing cell Ca(2+) influx that augments myocardial contractility. This increase in force represents the mechanical counterpart of the autocrine/paracrine mechanism triggered by stretch and has been called the slow force response (SFR) to stretch.

Diverse effects of Ace inhibitors and angiotensin II receptor antagonists on prevention of cardiac hypertrophy and collagen distribution in spontaneously hypertensive rats

This study has compared the effects of two structurally different angiotensin converting enzyme inhibitors (ACEis) such as zofenopril (Zof, with sulfhydrylic group) and lisinopril (Lis, with carboxylic group) and an angiotensin II AT(1) receptor antagonist (losartan, Los) on the prevention of cardiac hypertrophy and collagen distribution in spontaneously hypertensive rats (SHRs). The SHRs were untreated or received: Zof (10 mg/kg/day), Lis (10 mg/kg/day) or Los (20 mg/kg/day) in drinking water starting at 4 weeks of age. At 8, 16 and 24 weeks of age, 8 rats/group were sacrificed for determination of blood pressure, cardiac hypertrophy and collagen distribution. All treatments significantly decreased blood pressure and cardiac indices, expressed as the ventricles to body weight ratio, both variables being significantly correlated. Total ventricular collagen content was similarly decreased in all treated groups. Zof significantly increased the expression of collagen type III and normalized the collagen type I/III ratio. These results suggest that the effects of these drugs on different types of collagen are independent from angiotensin II formation. Similar findings obtained with captopril seem to indicate that the antioxidant sulfhydrylic group of these ACEis can play a role in the distribution of collagen during cardiac hypertrophy.

Atrial natriuretic peptide inhibits cardiomyocyte hypertrophy through mitogen-activated protein kinase phosphatase-1

Cardiac hypertrophy is formed in response to hemodynamic overload. Although a variety of factors such as catecholamines, angiotensin II (AngII), and endothelin-1 (ET-1) have been reported to induce cardiac hypertrophy, little is known regarding the factors that inhibit the development of cardiac hypertrophy. Production of atrial natriuretic peptide (ANP) is increased in the hypertrophied heart and ANP has recently been reported to inhibit the growth of various cell types. We therefore examined whether ANP inhibits the development of cardiac hypertrophy. Pretreatment of cultured cardiomyocytes with ANP inhibited the AngII- or ET-1-induced increase in the cell size and the protein synthesis. ANP also inhibited the AngII- or ET-1-induced hypertrophic responses such as activation of mitogen-activated protein kinase (MAPK) and induction of immediate early response genes and fetal type genes. To determine how ANP inhibits cardiomyocyte hypertrophy, we examined the mechanism of ANP-induced suppression of the MAPK activation. ANP strongly induced expression of MAPK phosphatase-1 (MKP-1) and overexpression of MKP-1 inhibited AngII- or ET-1-induced hypertrophic responses. These growth-inhibitory actions of ANP were mimicked by a cyclic GMP analog 8-bromo-cyclic GMP. Taken together, ANP directly inhibits the growth factor-induced cardiomyocyte hypertrophy at least partly via induction of MKP-1. Our present study suggests that the formation of cardiac hypertrophy is regulated not only by positive but by negative factors in response to hemodynamic load.

Extracellular signal regulated kinase and SMAD signaling both mediate the angiotensin II driven progression towards overt heart failure in homozygous TGR(mRen2)27

Angiotensin (Ang) II is a key player in left ventricular (LV) remodeling and cardiac fibrosis. Its effects are thought to be transferred at least in part by mitogen-activated protein kinases (MAPK), transforming growth factor (TGF) beta1, and the Smad pathway. In this study we sought to elucidate whether Ang II related effects on LV dysfunction and fibrosis in vivo are mediated via MAPK or rather via Smad stimulation. We treated homozygous REN2 rats (7-11 weeks) with placebo, Ang II type 1 (AT1) receptor blocker or tyrphostin A46 (TYR), an inhibitor of epidermal growth factor receptor tyrosine kinase that blocks extracellular signal-regulated kinase (ERK) activity. REN2 rats had LV hypertrophy (LVH) and LV dysfunction that progressed to heart failure between 10 and 13 weeks. Blood pressure normalized over time. Renin, N-terminal atrial natriuretic peptide (N-ANP), and ERK were activated while p38 MAPK was not. Treatment with AT1 receptor blockade prevented LVH and right ventricular hypertrophy, normalized systolic and diastolic d P/d t, N-ANP levels, and reduced collagen apposition. Similarly, TYR reduced LVH, N-ANP levels, and collagen apposition. Myocardial ERK activation did not depend on AT1 receptor signaling as it was not affected by AT1 receptor blockade. TYR abolished myocardial ERK activity. Smad2 activation was inhibited by AT1 receptor blockade but was unaltered by TYR. Ang II induced LV remodeling and fibrosis are dependent on both ERK and Smad2 activation. This process is prevented by both AT1 receptor blockade and TYR, and therefore inhibition of either pathway is equally efficacious in restoring LV function and architecture.

Genetic factors in cardiac hypertrophy

Cardiac hypertrophy is an adaptive response to any cardiac insult or stress that increases hemodynamic load. Cardiac hypertrophy can exist in a state of compensation or progress to a decompensated state (i.e., heart failure) over time. It has been established through transgenic overexpression and gene ablation studies that multiple signaling pathways are involved in the induction of hypertrophy as well as its decompensation. This article reviews the role of G alpha q in the development of pressure overload hypertrophy and discusses the relationships between G alpha q and beta-adrenergic receptors, RGS proteins, and the proapoptotic factor, Nix/Bnip3L.

Amlodipine decreases fibrosis and cardiac hypertrophy in spontaneously hypertensive rats: persistent effects after withdrawal

Our objective was to examine the effect of chronic treatment with amlodipine on blood pressure, left ventricular hypertrophy, and fibrosis in spontaneously hypertensive rats and the persistence of such an effect after drug withdrawal. We investigated the effects of treatment with 2, 8 and 20 mg/kg/day of amlodipine given orally for six months and at three months after drug withdrawal. Systolic blood pressure was measured using the tail-cuff method. At the end of the study period, the heart was excised, the left ventricle was isolated, and the left ventricle weight/body weight ratio was calculated as a left ventricular hypertrophy index. Fibrosis, expressed as collagen volume fraction, was evaluated using an automated image-analysis system on sections stained with Sirius red. Age-matched untreated Wistar-Kyoto and SHR were used as normotensive and hypertensive controls, respectively. Systolic blood pressure was reduced in the treated SHR in a dose-dependent way and after amlodipine withdrawal it increased progressively, without reaching the values of the hypertensive controls. Cardiac hypertrophy was reduced by 8 and 20 mg/kg/day amlodipine, but when treatment was withdrawn only the group treated with 8 mg/kg/day maintained significant differences versus the hypertensive controls. All three doses of amlodipine reduced cardiac fibrosis and this regression persisted with the two highest doses after three months without treatment. We concluded that antihypertensive treatment with amlodipine is accompanied by a reduction in left ventricular hypertrophy and regression in collagen deposition. Treatment was more effective in preventing fibrosis than in preventing ventricular hypertrophy after drug withdrawal.

Comparative effects of valsartan versus amlodipine on left ventricular mass and reactive oxygen species formation by monocytes in hypertensive patients with left ventricular hypertrophy

OBJECTIVES

To compare the effects of the angiotensin receptor blocker (ARB) valsartan versus the calcium channel blocker amlodipine, reactive oxygen species (ROS) formation by monocytes, C-reactive protein (CRP), and left ventricular (LV) mass were studied in 104 hypertensive patients with left ventricular hypertrophy (LVH).

BACKGROUND

There is evidence that ARBs have blood pressure (BP)-independent effects on LV mass. Whether regression of LV mass by ARBs is correlated to ROS formation by monocytes and CRP is not fully understood yet.

METHODS

A cross-sectional and prospective study was performed. Participants were randomly assigned to either the 80-mg valsartan (n = 52) or 5-mg amlodipine (n = 52) group and were treated for eight months. The left ventricular mass index (LVMI) was calculated from two-dimensional M-mode echocardiography. Formation of ROS by monocytes was measured by gated flow cytometry. In addition, CRP, plasma renin activity, plasma aldosterone, and traditional risk factors were assessed.

RESULTS

Multiple regression analysis showed a significant correlation between LVMI and ROS formation by monocytes and between LVMI and CRP. Treatment reduced BP to a similar extent in both groups. Valsartan significantly reduced LVMI after eight months, but amlodipine had less effect (16% vs. 1.2%, n = 50, p < 0.01). Formation of ROS by monocytes was reduced to a greater extent with valsartan than with amlodipine (28% vs. 2%, n = 50, p < 0.01). Valsartan but not amlodipine reduced CRP levels. A significant correlation between changes in ROS formation by monocytes and LVMI or between CRP and LVMI was observed.

CONCLUSIONS

The ARB valsartan has BP-independent effects on LVH, ROS formation by monocytes, and CRP in hypertensive patients with LVH.

Mechanical stress activates angiotensin II type 1 receptor without the involvement of angiotensin II

The angiotensin II type 1 (AT1) receptor has a crucial role in load-induced cardiac hypertrophy. Here we show that the AT1 receptor can be activated by mechanical stress through an angiotensin-II-independent mechanism. Without the involvement of angiotensin II, mechanical stress not only activates extracellular-signal-regulated kinases and increases phosphoinositide production in vitro, but also induces cardiac hypertrophy in vivo. Mechanical stretch induces association of the AT1 receptor with Janus kinase 2, and translocation of G proteins into the cytosol. All of these events are inhibited by the AT1 receptor blocker candesartan. Thus, mechanical stress activates AT1 receptor independently of angiotensin II, and this activation can be inhibited by an inverse agonist of the AT1 receptor.

Protein kinase C and extracellular signal regulated kinase are involved in cardiac hypertrophy of rats with progressive renal injury

Increased cardiovascular mortality is an unresolved problem in patients with chronic renal failure. Cardiac hypertrophy is observed in the majority of patients with chronic renal failure undergoing haemodialysis. However, the mechanisms, including signal transduction pathways, responsible for cardiac hypertrophy in renal failure remain unknown. We examined the subcellular localization of protein kinase C (PKC) isoforms and phosphorylation activities of 3 mitogen-activated protein (MAP) kinase families in hypertrophied hearts of progressive renal injury rat model by subtotal nephrectomy (SNx). We also examined the effects of a novel angiotensin II type-1 receptor antagonist, CS-866, on the PKC translocation, MAP kinase activity and cardiac hypertrophy in SNx rats. The left ventricle/body weight ratios were significantly larger in SNx rats than in sham rats at 1, 2, and 4 weeks after surgery. The translocation of PKCalpha and epsilon isoforms to membranous fraction was observed in SNx rat hearts at 1, 2, and 4 weeks after surgery. Activation of extracellular signal regulated kinase (ERK) 1/2, but not p38 MAP kinase and c-Jun N-terminal kinase (JNK), was observed at 1 and 2 weeks after surgery. Angiotensin II receptor blockade with CS-866 (1 mg kg-1 day-1) prevented cardiac hypertrophy, PKC translocation and ERK1/2 activation in SNx rats without significant changes in blood pressure. These data suggest that PKC and ERK1/2 are activated by an angiotensin II receptor-mediated pathway and might play an important role in the progression of cardiac hypertrophy in renal failure.

Reduction of bleomycin induced lung fibrosis by candesartan cilexetil, an angiotensin II type 1 receptor antagonist

BACKGROUND

Signalling of angiotensin II via angiotensin II type 1 receptor (AT1) promotes cardiac and renal fibrosis, but its role in lung fibrosis is little understood. Using a rat bleomycin (BLM) induced model of pulmonary fibrosis, we examined the expression of AT1 in the lung and the effect of an AT1 antagonist on pulmonary fibrosis.

METHODS

Adult male Sprague-Dawley rats were given 0.3 mg/kg BLM intratracheally. Two days earlier they had received 10 mg/kg/day of the AT1 antagonist candesartan cilexetil mixed in the drinking water. AT1 expression in the lungs was examined by immunohistochemistry and immunoblot methods. The effect of the AT1 antagonist on pulmonary fibrosis was studied by analysis of bronchoalveolar lavage (BAL) fluid, histopathology, and hydroxyproline assay.

RESULTS

Immunohistochemical studies showed overexpression of AT1 in inflammatory immune cells, alveolar type II cells, and fibroblasts. A quantitative assay for AT1 showed that AT1 expression was significantly upregulated in cells from BAL fluid after day 3 and in the lung homogenates after day 21. Candesartan cilexetil significantly inhibited the increase in total protein and albumin, as well as the increase in total cells and neutrophils in BAL fluid. On day 21 candesartan cilexetil also ameliorated morphological changes and an increased amount of hydroxyproline in lung homogenates. In addition, BLM increased the expression of transforming growth factor (TGF)-beta1 in BAL fluid on day 7; this increase was significantly reduced by candesartan cilexetil.

CONCLUSION

AT1 expression is upregulated in fibrotic lungs. Angiotensin II promotes lung fibrosis via AT1 and, presumably, in part via TGF-beta1.

Altered Effects of Angiotensin II Type 1 and Type 2 Receptor Blockers on Cardiac Norepinephrine Release and Inotropic Responses During Cardiac Sympathetic Nerve Stimulation in Aorto-Caval Shunt Rats

BACKGROUND

Inhibition of the sympathetic nervous and renin - angiotensin systems has become an important strategy in the treatment of chronic heart failure. However, direct evidence of how inhibition of the renin - angiotensin system alters sympathetic activity in a diseased heart is lacking.

METHODS AND RESULTS

Four weeks after abdominal aorto-caval (AV) shunting or sham operation in rats, the hearts were retrogradely perfused in vivo and the left ventricles contracted isovolumetrically at 300 beats/min. Sympathetic nerve stimulation (SNS) was performed in the baseline state and repeated with an infusion of the angiotensin II (A-II) type 1 receptor (AT(1)-R) blocker, losartan, the A-II type 2 receptor (AT(2)-R) blocker, PD123319, or A-II. Norepinephrine (NE) overflow and left ventricular (LV) inotropic responses during baseline SNS were lower in the AV shunt rats. Losartan did not change the NE overflow or the LV inotropic responses to SNS in the sham rats, but did increase them in the AV shunt rats. PD123319 changed neither parameter in the sham rats, but decreased both in the AV shunt rats. A-II enhanced the NE overflow but attenuated the LV inotropic responses to SNS in the sham rats, but attenuated both in the AV shunt rats.

CONCLUSIONS

The effects of A-II via the AT(1)-R and AT(2)-R on the adrenergic drive in the heart were altered significantly in volume overload hypertrophy induced by AV shunting.

The arterial circle of Willis of the mouse helps to decipher secrets of cerebral vascular accidents in the human

The human brain represents an elaborate product of hominizing evolution. Likewise, its supporting vasculature may also embody evolutionary consequences. Thus, it is conceivable that the human tendency to develop cerebral vascular accidents (CVAs) might represent a disease of hominization. In a search for hominizing changes on the arterial circle of Willis (hWAC), we attempted an anatomical comparison of the hWAC with that of the mouse (mWAC) by injecting aliquots of resin into the vasculature of the mouse and then creating vascular endocasts of the mWAC. The internal carotid artery of the mouse (mICA) unites with the mWAC midway between the middle cerebral artery (mMCA) and posterior cerebral artery (mPCA). The mWAC does not complete a circle: the mWAC nourishes the anterior portion of the circle which branches out to the olfactory artery (OlfA) and mPCA, along with the mMCA, and the basilar artery (mBA) does not connect to the mPCA. The OlfA is thicker than the mMCA. The relative brain weight of the mouse was 74 g on average for a 60 kg male and 86 g for a 60 kg female, respectively, as compared with 1424 g for a 60 kg man. These findings are consistent with the mouse being a nocturnal carnivore that lives on olfactory information in contrast to the human that lives diurnally and depends on visual and auditory information. In man, the human ICA (hICA) unites with the hWAC at a point where the human middle cerebral artery (hMCA) branches out, and thus, blood from the hICA does not flow through the hWAC but drains into the hMCA directly. The hMCA is thicker than the anterior cerebral artery. The hPCA receives blood from the hBA rather than from the hICA, and thus, the entire hWAC forms a closed circuit. Since the hICA drains directly into the hMCA without flowing a distance through the hWAC, the capacitor and equalizer functions of the WAC will be mitigated so much that the resultant hemodynamic changes would render the hMCA more likely to contribute to CVAs. Thus, anatomical findings and possibly functions of the arterial circle of Willi may vary from one species to another, depending on one's specific cerebral evolution.

Cardiac remodeling in systemic hypertension

Experimental and clinical studies provide evidence that hypertension is causally related to adverse cardiac structural changes, such as LA enlargement, LV hypertrophy and myocardial fibrosis, and functional changes inclusive of LV systolic and diastolic dysfunction. These changes are induced by both hemodynamic and nonhemodynamic factors. There is accumulating evidence from several small and large clinical trials that various classes of antihypertensive therapy prevent and regress LVH and myocardial fibrosis. Prevention and reversal of LVH are associated with an improvement in cardiac function and with a decline in risk of adverse cardiovascular outcomes. Prevention of LVH should be a priority in subjects with hypertension. In patients with hypertensive heart disease, the components of therapy must comprise optimization of BP and regression of LVH. Future targets of therapy in hypertensive heart disease may include regression of myocardial fibrosis, normalization of LA size, and improvement in LV diastolic function.

Different remodelling against left ventricular overload between diabetic and non-diabetic haemodialysis patients

1. Diabetes mellitus is significantly associated with the occurrence of congestive heart failure in end-stage renal disease patients undergoing maintenance haemodialysis. In the present study, we asked whether the left ventricular remodelling against sustained pressure and/or volume overload to the left ventricle may be different between diabetic and non-diabetic haemodialysis patients. 2. Left ventricular parameters, including left ventricular mass index (LVMI), interventricular septal wall thickness (IVST) and relative left ventricular wall thickness (rLVWT), were assessed in 486 patients receiving maintenance haemodialysis (145 diabetic and 341 non-diabetic patients) using transthoracic echocardiography. Plasma concentrations of B-type natriuretic peptide (BNP), measured with an immunoradiometric assay, were used as a humoral parameter indicating left ventricular wall stress. 3. In non-diabetic patients, the plasma BNP concentration correlated with LVMI (r = 0.245; P = 0.0001), IVST (r = 0.250; P = 0.0001) and rLVWT (r = 0.149; P = 0.006). Furthermore, LVMI was correlated with mean blood pressure and pulse pressure and IVST and rLVWT were correlated with pulse pressure. 4. In contrast, none of the measured factors was correlated with LVMI and IVST in diabetic patients. Plasma BNP concentrations were positively correlated with end-systolic and end-diastolic left intraventricular dimensions and were inversely correlated with rLVWT and left ventricular fractional shortening in diabetic patients, but not in non-diabetic patients. 5. In conclusion, a sustained increase in left ventricular wall stress is likely to elicit eccentric left ventricular remodelling in diabetic haemodialysis patients, whereas it causes concentric left ventricular remodelling in non-diabetic haemodialysis patients. This difference in left ventricular remodelling against left ventricular overload may be associated with the high incidence of congestive heart failure in diabetic haemodialysis patients.

Role of host angiotensin II type 1 receptor in tumor angiogenesis and growth

Although the renin angiotensin system (RAS) is a major regulator of vascular homeostasis, the role of the RAS in tumor angiogenesis is little understood. Here we show that host angiotensin II (ATII) type 1 (AT1) receptor plays an important role in angiogenesis and growth of tumor cells engrafted in mice. Subcutaneous B16-F1 melanoma-induced angiogenesis as assessed by tissue capillary density and microangiography was prominent in WT mice but was reduced in AT1a receptor-deficient (AT1a-/-) mice. Consequently, tumor growth rate was significantly slower, and the mouse survival rate was greater, in AT1a-/- mice than in WT mice. Tumor growth was also reduced in WT mice treated with TCV-116, a selective blocker of AT1 receptor. Because the beta-galactosidase gene was inserted into the AT1a gene locus in AT1a-/- mice, the site of beta-galactosidase expression represents the AT1a receptor expression in these mutant mice. In tumor-implanted AT1a-/- mice, the major site of the beta-galactosidase expression was macrophages in tissues surrounding tumors. Moreover, the number of infiltrated macrophages was significantly lower in AT1a-/- mice than in WT mice, and double-immunofluorescence staining revealed that these macrophages expressed VEGF protein intensively. Therefore, the host ATII-AT1 receptor pathway supports tumor-associated macrophage infiltration, which results in enhanced tissue VEGF protein levels. The host ATII-AT1 receptor pathway thereby plays important roles in tumor-related angiogenesis and growth in vivo.

Attenuation of heart failure due to coronary stenosis by ACE inhibitor and angiotensin receptor blocker

It is not known how the angiotensin-converting enzyme (ACE) inhibitor and angiotensin II receptor blocker (ARB) attenuate heart failure (HF) in viable ischemic hearts. To assess HF in a rat coronary stenosis (CS) model, we administered vehicle and quinapril or candesartan (or both) orally for 12 wk. Compared with the sham group, the vehicle group showed impaired myocardial perfusion, impaired coronary endothelial nitric oxide (NO) function in vitro, exhausted myocardial mitochondrial respiration, larger left ventricular (LV) dimensions and lower ejection fraction, lower LV rate of pressure development over time (dP/dt), lower slopes of LV end-systolic pressure-dimension relations (ESPDRs), and increased myocardial fibrosis. Treatment with quinapril or candesartan ameliorated these parameters without modifying the epicardial CS severity. Moreover, their combination maintained similar myocardial perfusion, despite a trend toward lower blood pressure, and showed distinctive neurohumoral modulation, normalized mitochondrial respiration, and increased ESPDR slopes. Thus improved myocardial blood flow and coronary flow reserve by quinapril or candesartan are the key to alleviate CS-induced HF, and their combination may have a therapeutic significance partly through ameliorated mitochondrial respiration and improved LV systolic function.

Effects of diuretic treatment on cardiac and circulating RAS in chronic heart failure post-myocardial infarction in rats

BACKGROUND

Cardiac angiotensin converting enzyme (ACE) is activated by an increase in wall stress and is involved in remodeling processes. Heart failure is often treated with ACE inhibitors and diuretics although diuretic treatment could activate the renin-angiotensin system (RAS).

AIMS

To examine the effects of diuretic treatment on cardiac and circulating RAS in post-infarction chronic heart failure.

METHODS

Myocardial infarction was produced by coronary artery ligation in spontaneously hypertensive rats. The rats were randomly assigned to receive either ramipril (1 mg/kg/day), furosemide (4 mg/kg/day), or combination therapy for 6 weeks, commencing 2 weeks after infarction.

RESULTS

All three treatment protocols equivalently attenuated reactive hypertrophy of the right ventricle and ventricular septum and improved left ventricular systolic function. Both cardiac ACE mRNA and activity were significantly increased in untreated rats. This increase was attenuated by both ramipril and furosemide and further depressed by the combination. The increase in activity was completely inhibited by either agent alone. Plasma renin activity was upregulated by ramipril or ramipril plus furosemide but not influenced by infarction or furosemide alone.

CONCLUSIONS

Furosemide and ramipril significantly reduced cardiac ACE and remodeling. Diuretics work favorably and do not interfere with the effects of ACE inhibitors. Possibly, a reduction in wall stress due to decreased volume overload accounts for the effects of diuretics on cardiac ACE in the treatment of post-infarction remodeling in hypertensive hearts. These data suggest a new mechanism for the frequently observed beneficial effect of diuretics in heart failure.

Circadian gene expression of clock genes and plasminogen activator inhibitor-1 in heart and aorta of spontaneously hypertensive and Wistar-Kyoto rats

OBJECTIVE

Heart and aorta possess biologic clocks, but their involvement in genetic hypertension has been unknown. Plasminogen activator inhibitor-1 (PAI-1) expression is directly regulated by clock genes, while angiotensin II modulates both PAI-1 and clock gene expression. We therefore examined circadian expression of PAI-1 and clock genes, and effects of angiotensin type 1 (AT1) receptor antagonism, in heart and aorta of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats.

METHODS

We examined cardiac and aortic mRNA expression for PAI-1 and clock genes (Per2, Bmal1, Clock, and Dbp) every 4 h throughout the day by quantitative reverse transcription-polymerase chain reaction, and intervention with the AT1 receptor antagonist candesartan and equihypotensive hydralazine.

RESULTS

Cardiac PAI-1 expression was high in the dark, while aortic PAI-1 expression was high in the light. Both cardiac and aortic PAI-1 expression were greater in SHR than in WKY rats. Candesartan treatment decreased cardiac PAI-1 expression only in the dark in WKY rats but throughout the day in SHR. Candesartan but not hydralazine strongly attenuated circadian fluctuation of aortic PAI-1 mRNA in SHR and WKY rats. Clock genes oscillated synchronously in heart and aorta of SHR and WKY rats. Clock gene expression was increased in heart but not aorta of SHR. Candesartan did not affect clock gene expression.

CONCLUSIONS

Enhanced expression of clock genes may increase PAI-1 expression in concert with activated renin-angiotensin system in SHR heart. Rather than clock genes, the renin-angiotensin system induces daily fluctuation and increased expression of aortic PAI-1 mRNA in SHR.

Left ventricular regional variations in myosin isoform shift in Dahl salt-sensitive hypertensive rats

To evaluate the effects of chronic pressure overload on different parts of the left ventricle (LV), we examined a myosin isoform shift from V1 to V3 as a biochemical marker of LV hypertrophy in Dahl salt-sensitive (DS) rats. Six-week-old DS rats were fed an 8% (high salt, HS; n = 24) or a 0.3% (low salt, LS; n = 12) NaCl diet. After 2 or 4 weeks, the hearts were dissected and the LVs were separated into four parts (the base and mid-portion of the interventricular septum (IVS), and the base and mid-portion of the LV free wall) for isomyosin analysis. The myosin isoform shift was analyzed by pyrophosphate gel electrophoresis. Both blood pressure and LV/body weight ratio were clearly increased in the HS group. The myosin isoform shift from V1 to V3, which was measured as a decrease in the percentage of V1 isomyosin, was demonstrated only in the base of LV, with significant predominance in the IVS at 2 weeks and in all four parts at 4 weeks in the HS group. In the LS group, a myosin isoform shift was demonstrated only in the basal portion of the LV at 4 weeks. We concluded that, in rats with salt-induced hypertension, the myosin isoform shift from V1 to V3 starts at the base of the LV, and particularly at the base of the IVS, and then spreads across the entire LV. These results suggest that pressure overload from hypertension may be strongest at the base of the IVS, and that LV hypertrophy may originate at the IVS base.

Chronic inhibition of Rho kinase blunts the process of left ventricular hypertrophy leading to cardiac contractile dysfunction in hypertension-induced heart failure

The Gq-RhoA-Rho kinase pathway, activated by neurohormonal factors such as angiotensin II (Ang II), has been proposed to be one of the important signaling pathways involved in the progression of left ventricular (LV) hypertrophy to heart failure. We tested the hypothesis that chronic inhibition of Rho kinase prevents this process. Heart failure was induced in Dahl salt-sensitive (DS) rats fed an 8% NaCl diet from 8 until 17 weeks of age. Y-27632 (5 mg/kg per day), a selective Rho kinase inhibitor, was applied orally to DS rats starting at 10 weeks of age for 7 weeks (DS/Y+). DS rats without Y-27632 (DS/Y-) and Dahl salt-resistant (DR) rats fed the 8% NaCl diet were regarded as non-therapeutic and normotensive controls, respectively. At 17 weeks of age, there was no significant difference in the blood pressure of DS/Y- and DS/Y+ rats. DS/Y- rats exhibited: (1) increases in LV mass, cross-sectional area (CSA) of cardiomyocytes, and interstitial fibrosis; (2) contractile dysfunction, i.e. decreases in LV ejection fraction and % fractional shortening, and prolongation of time to peak tension as well as to 50% relaxation in the twitch contraction of isolated papillary muscle; and (3) increases in the protein expression of Galphaq and Rho kinase in the myocardial membrane fraction. In DS/Y+ rats, the degree of myocardial hypertrophy was significantly inhibited in association with improved contractile function, without a decrease in the degree of interstitial fibrosis. Our results suggest the possibility that the Gq-Rho kinase pathway plays an important role in the process of hypertension-induced LV hypertrophy leading to contractile dysfunction.

Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

Accelerated Cardiac Hypertrophy and Renal Damage Induced by Angiotensin II in Adrenomedullin Knockout Mice

Adrenomedullin (AM) is a potent vasodilating and natriuretic peptide that is thought to play important roles in cardiovascular function. Whether or not AM is involved in the development of cardiac hypertrophy and renal damage remains controversial. In the present study, using heterozygote knockout mice of the AM gene (AM +/-), we analyzed the physiological and pathological roles of the endogenous AM gene. There were no differences in body size or heart and kidney weight compared with wild-type (AM +/+) mice. However, angiotensin II (Ang II) infusion resulted in more severe cardiac hypertrophy in AM +/- mice. The increases in the heart weight-to-body weight ratio and wall thickness of the left ventricle were more prominent in the AM +/- mice. Renal dysfunction characterized by decreased creatinine clearance (C(cr)) was more severe in AM +/- after Ang II infusion. These results suggest that AM plays critical roles in the defense mechanism against cardiac hypertrophy and renal dysfunction. An improved understanding of these roles may pave the way to a novel pharmacological approach for the prevention of cardiovascular diseases.

Angiotensin II type 2 receptor blockade partially negates antihypertrophic effects of type 1 receptor blockade on pressure-overload rat cardiac hypertrophy

We investigated the effects of angiotensin II type 2 (AT2) receptor blockade on the antihypertrophic effects of type 1 receptor (AT1) blockade in pressure-overload cardiac hypertrophy in adult rats. Cardiac hypertrophy was induced by banding the abdominal aorta above the renal arteries. The rats were treated with either an AT1 receptor antagonist TCV-116 (TCV, 10 mg/kg/day), an AT2 receptor antagonist PD123319 (PD, 20 mg/kg/day), or both for 4 weeks after the aortic banding. We measured systolic and diastolic blood pressure (BP), body weight (BW), left ventricular weight (LVW), and serum and cardiac angiotensin converting enzyme (ACE) activities. Aortic banding increased BP and LVW/BW, and TCV reversed both these increases. PD affected neither BP nor LVW/BW. TCV+PD reversed the increase in BP but not LVW/BW. Thus, PD was considered to counteract the antihypertrophic effect of TCV without affecting BP. All three treatments reduced cardiac ACE activity without affecting serum ACE activity. Our data demonstrated that AT2 receptor blockade negates the antihypertrophic effects of AT1 receptor blockade in an adult rat model of pressure-overload cardiac hypertrophy. AT2 receptors may mediate the signaling pathways involved in growth inhibition, which could counteract mediation of the cellular growth signaling pathways by AT1 receptors.

Protection of the cardiovascular system by imidapril, a versatile angiotensin-converting enzyme inhibitor

Imidapril hydrochloride (imidapril) is a long-acting, non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor, which has been used clinically in the treatment of hypertension, chronic congestive heart failure (CHF), acute myocardial infarction (AMI), and diabetic nephropathy. It has the unique advantage over other ACE inhibitors in causing a lower incidence of dry cough. After oral administration, imidapril is rapidly converted in the liver to its active metabolite imidaprilat. The plasma levels of imidaprilat gradually increase in proportion to the dose, and decline slowly. The time to reach the maximum plasma concentration (T(max)) is 2.0 h for imidapril and 9.3 h for imidaprilat. The elimination half-lives (t(1/2)) of imidapril and imidaprilat is 1.7 and 14.8 h, respectively. Imidapril and its metabolites are excreted chiefly in the urine. As an ACE inhibitor, imidaprilat is as potent as enalaprilat, an active metabolite of enalapril, and about twice as potent as captopril. In patients with hypertension, blood pressure was still decreased at 24 h after imidapril administration. The antihypertensive effect of imidapril was dose-dependent. The maximal reduction of blood pressure and plasma ACE was achieved with imidapril, 10 mg once daily, and the additional effect was not prominent with higher doses. When administered to patients with AMI, imidapril improved left ventricular ejection fraction and reduced plasma brain natriuretic peptide (BNP) levels. In patients with mild-to-moderate CHF [New York Heart Association (NYHA) functional class II-III], imidapril increased exercise time and physical working capacity and decreased plasma atrial natriuretic peptide (ANP) and BNP levels in a dose-related manner. In patients with diabetic nephropathy, imidapril decreased urinary albumin excretion. Interestingly, imidapril improved asymptomatic dysphagia in patients with a history of stroke. In the same patients it increased serum substance P levels, while the angiotensin II receptor antagonist losartan was ineffective. These studies indicate that imidapril is a versatile ACE inhibitor. In addition to its effectiveness in the treatment of hypertension, CHF, and AMI, imidapril has beneficial effects in the treatment of diabetic nephropathy and asymptomatic dysphagia. Good tissue penetration and inhibition of tissue ACE by imidapril contributes to its effectiveness in preventing cardiovascular complications of hypertension. The major advantages of imidapril are its activity in the treatment of various cardiovascular diseases and lower incidence of cough compared with some of the older ACE inhibitors.