Differential effects of angiotensin II versus endothelin-1 inhibitions in hypertrophic left ventricular myocardium during transition to heart failure

Endothelial cell dysfunction in cardiac disease: driver or consequence?

The vascular endothelium is a multifunctional cellular system which directly influences blood components and cells within the vessel wall in a given tissue. Importantly, this cellular interface undergoes critical phenotypic changes in response to various biochemical and hemodynamic stimuli, driving several developmental and pathophysiological processes. Multiple studies have indicated a central role of the endothelium in the initiation, progression, and clinical outcomes of cardiac disease. In this review we synthesize the current understanding of endothelial function and dysfunction as mediators of the cardiomyocyte phenotype in the setting of distinct cardiac pathologies; outline existing in vivo and in vitro models where key features of endothelial cell dysfunction can be recapitulated; and discuss future directions for development of endothelium-targeted therapeutics for cardiac diseases with limited existing treatment options.

A multiscale model of cardiac concentric hypertrophy incorporating both mechanical and hormonal drivers of growth

Growth and remodeling in the heart is driven by a combination of mechanical and hormonal signals that produce different patterns of growth in response to exercise, pregnancy, and various pathologies. In particular, increases in afterload lead to concentric hypertrophy, a thickening of the walls that increases the contractile ability of the heart while reducing wall stress. In the current study, we constructed a multiscale model of cardiac hypertrophy that connects a finite-element model representing the mechanics of the growing left ventricle to a cell-level network model of hypertrophic signaling pathways that accounts for changes in both mechanics and hormones. We first tuned our model to capture published in vivo growth trends for isoproterenol infusion, which stimulates β-adrenergic signaling pathways without altering mechanics, and for transverse aortic constriction (TAC), which involves both elevated mechanics and altered hormone levels. We then predicted the attenuation of TAC-induced hypertrophy by two distinct genetic interventions (transgenic Gq-coupled receptor inhibitor overexpression and norepinephrine knock-out) and by two pharmacologic interventions (angiotensin receptor blocker losartan and β-blocker propranolol) and compared our predictions to published in vivo data for each intervention. Our multiscale model captured the experimental data trends reasonably well for all conditions simulated. We also found that when prescribing realistic changes in mechanics and hormones associated with TAC, the hormonal inputs were responsible for the majority of the growth predicted by the multiscale model and were necessary in order to capture the effect of the interventions for TAC.

Murine models of diastolic dysfunction and heart failure with preserved ejection fraction

Left ventricular diastolic dysfunction leads to heart failure with preserved ejection fraction, an increasingly prevalent condition largely driven by modern day lifestyle risk factors. As heart failure with preserved ejection fraction accounts for almost one-half of all patients with heart failure, appropriate nonhuman animal models are required to improve our understanding of the pathophysiology of this syndrome and to provide a platform for preclinical investigation of potential therapies. Hypertension, obesity, and diabetes are major risk factors for diastolic dysfunction and heart failure with preserved ejection fraction. This review focuses on murine models reflecting this disease continuum driven by the aforementioned common risk factors. We describe various models of diastolic dysfunction and highlight models of heart failure with preserved ejection fraction reported in the literature. Strengths and weaknesses of the different models are discussed to provide an aid to translational scientists when selecting an appropriate model. We also bring attention to the fact that heart failure with preserved ejection fraction is difficult to diagnose in animal models and that, therefore, there is a paucity of well described animal models of this increasingly important condition.

Randomized, double-blind, placebo-controlled study of sitaxsentan to improve impaired exercise tolerance in patients with heart failure and a preserved ejection fraction

OBJECTIVES

The purpose of this study was to evaluate the efficacy and safety of the selective endothelin type A (ETA) receptor antagonist sitaxsentan in patients who have heart failure with preserved ejection fraction (HFpEF).

BACKGROUND

Fifty percent of heart failure (HF) patients have a preserved ejection fraction. No treatment has been shown to improve their clinical outcomes. Previous studies have suggested that ETA receptor antagonists might improve diastolic function and exercise tolerance in some forms of HF.

METHODS

In all, 192 HFpEF patients (EF ≥50%) were randomly assigned 2:1 to sitaxsentan 100 mg/day (n = 128) versus placebo (n = 64) for 24 weeks. The primary endpoint was change in treadmill exercise time after 24 weeks of treatment. Secondary objectives included changes in left ventricular mass, transmitral inflow velocity to early diastolic mitral annulus velocity ratio, and Minnesota Living With Heart Failure questionnaire, and New York Heart Association functional class. Subjects were age 65 ± 11 years, 63% female, 29% non-Caucasian, and in functional class II (56.5%) or III (43.5%).

RESULTS

Subjects treated with sitaxsentan had an increase in median treadmill time (90 s) compared with placebo-treated subjects (37 s, p = 0.0302). There was no significant treatment differences in transmitral inflow velocity to early diastolic mitral annulus velocity ratio, left ventricular mass, Minnesota Living With Heart Failure questionnaire, New York Heart Association functional class, deaths, or HF hospital stay. The incidence of adverse events was similar for sitaxsentan and placebo.

CONCLUSIONS

In HFpEF patients, treatment with a selective ETA receptor antagonist increased exercise tolerance but did not improve any of the secondary endpoints such as left ventricular mass or diastolic function. Further studies will be necessary to determine whether ETA receptor antagonists may be useful in the treatment of HFpEF. (A Study of the Effectiveness of Sitaxsentan Sodium in Patients With Diastolic Heart Failure; NCT00303498).

Merits of non-invasive rat models of left ventricular heart failure

Heart failure (HF) is characterized as a limitation to cardiac output that prevents the heart from supplying tissues with adequate oxygen and predisposes individuals to pulmonary edema. Impaired cardiac function is secondary to either decreased contractility reducing ejection (systolic failure), diminished ventricular compliance preventing filling (diastolic failure), or both. To study HF etiology, many different techniques have been developed to elicit this condition in experimental animals, with varying degrees of success. Among rats, surgically induced HF models are the most prevalent, but they bear several shortcomings, including high mortality rates and limited recapitulation of the pathophysiology, etiology, and progression of human HF. Alternatively, a number of non-invasive HF induction methods avoid many of these pitfalls, and their merits in technical simplicity, reliability, survivability, and comparability to the pathophysiologic and pathogenic characteristics of HF are reviewed herein. In particular, this review focuses on the primary pathogenic mechanisms common to genetic strains (spontaneously hypertensive and spontaneously hypertensive heart failure), pharmacological models of toxic cardiomyopathy (doxorubicin and isoproterenol), and dietary salt models, all of which have been shown to induce left ventricular HF in the rat. Additional non-invasive techniques that may potentially enable the development of new HF models are also discussed.

Long-term safety and efficacy of renin-angiotensin blockade in atherosclerotic renal artery stenosis

PURPOSE

The activation of the renin-angiotensin-aldosterone system caused by renal ischaemia in atherosclerotic renal artery stenosis (ARAS) may be responsible for serious cardiovascular and renal consequences. The aim of the study was to assess the long-term safety, tolerability and outcomes of the use of angiotensin I-converting enzyme inhibitors (ACEis) and angiotensin receptor blockers (ARBs) in patients with ARAS.

METHODS

Thirty-six patients with angiographically defined ARAS (managed either with revascularization or only with medical treatment) were prospectively assessed for the safety, tolerability and outcomes of the use of ACEis or ARBs.

RESULTS

The mean period of follow-up was 88.9 ± 37.8 months. A statistically significant reduction in systolic and diastolic blood pressure was recorded over time (P < 0.001). While estimated glomerular filtration rate remained almost stable during the study period (0.816), nuclear EDTA-GFR showed a significant reduction over time (P = 0.03). Mean time from diagnosis/intervention to end-stage renal disease for the cohort of 36 patients was 165.38 ± 13.62 months. Mean overall patient survival was 135.36 ± 15.25 months, with fourteen deaths (38.8%) occurring during the observational period. ACEi/ARB therapy was discontinued transiently in only 4 subjects.

CONCLUSIONS

The use of ACEis/ARBs is safe and effective in patients with ARAS independently of any parameters.

Pharmacological inhibition of βIIPKC is cardioprotective in late-stage hypertrophy

We previously found that in the hearts of hypertensive Dahl salt-sensitive rats, βIIPKC levels increase during the transition from compensated cardiac hypertrophy to cardiac dysfunction. Here we showed that a six-week treatment of these hypertensive rats with a βIIPKC-specific inhibitor, βIIV5-3, prolonged their survival by at least 6weeks, suppressed myocardial fibrosis and inflammation, and delayed the transition from compensated hypertrophy to cardiac dysfunction. In addition, changes in the levels of the Ca(2+)-handling proteins, SERCA2 and the Na(+)/Ca(2+) exchanger, as well as troponin I phosphorylation, seen in the control-treated hypertensive rats were not observed in the βΙΙPKC-treated rats, suggesting that βΙΙPKC contributes to the regulation of calcium levels in the myocardium. In contrast, treatment with the selective inhibitor of βIPKC, an alternative spliced form of βIIPKC, had no beneficial effects in these rats. We also found that βIIV5-3, but not βIV5-3, improved calcium handling in isolated rat cardiomyocytes and enhanced contractility in isolated rat hearts. In conclusion, our data using an in vivo model of cardiac dysfunction (late-phase hypertrophy), suggest that βIIPKC contributes to the pathology associated with heart failure and thus an inhibitor of βIIPKC may be a potential treatment for this disease.

At the heart of tissue: endothelin system and end-organ damage

ET (endothelin)-1 was first described as a potent vasoconstrictor. Since then, many other deleterious properties mediated via its two receptors, ETA and ETB, have been described, such as inflammation, fibrosis and hyperplasia. These effects, combined with a wide tissue distribution of the ET system, its up-regulation in pathological situations and a local autocrine/paracrine activity due to a high tissue receptor binding, make the tissue ET system a key local player in end-organ damage. Furthermore, ET-1 interacts in tissues with other systems such as the RAAS (renin-angiotensin-aldosterone system) to exert its effects. In numerous genetically modified animal models, non-specific or organ-targeted ET-1 overexpression causes intense organ damage, especially hypertrophy and fibrosis, in the absence of haemodynamic changes, confirming a local activity of the ET system. ET receptor antagonists have been shown to prevent and sometimes reverse these tissue alterations in an organ-specific manner, leading to long-term benefits and an improvement in survival in different animal models. Potential for such benefits going beyond a pure haemodynamic effect have also been suggested by clinical trial results in which ET receptor antagonism decreased the occurrence of new digital ulcers in patients with systemic sclerosis and delayed the time to clinical worsening in patients with PAH (pulmonary arterial hypertension). The tissue ET system allows therapeutic interventions to provide organ selectivity and beneficial effects in diseases associated with tissue inflammation, hypertrophy or fibrosis.

Endogenous angiotensin II has fewer effects but neuronal nitric oxide synthase has excitatory effects on renal sympathetic nerve activity in salt-sensitive hypertension-induced heart failure

The effects of endogenous angiotensin II (Ang II) and neuronal nitric oxide synthase (nNOS) on tonic sympathetic activity were studied in salt-sensitive hypertension-induced heart failure. Dahl salt-sensitive rats were fed 8% NaCl diet for 9 weeks to induce chronic heart failure (CHF-DSS). The effects of intravenous administration of a selective nNOS inhibitor, S-methyl-L: -thiocitrulline (SMTC), and an Ang II type 1-receptor blocker, losartan, on renal sympathetic nerve activity (RSNA) were examined in chronically instrumented conscious rats. Baroreceptor (baro)-unloaded RSNA was obtained by decreasing arterial pressure with caval occlusion to determine tonic RSNA. SMTC significantly decreased baro-unloaded RSNA, and subsequent losartan recovered baro-unloaded RSNA to the control level in CHF-DSS rats. To compare the effects of the inhibitors between low- and high-activity states of the renin-angiotensin system (RAS), Sprague-Dawley rats were fed low (0.04%)- or high (8%)-salt diets. A significant difference was found in the effects of SMTC and/or losartan on RSNA between the high- and low-RAS states, which suggested that there is a difference in the effect of endogenous Ang II on RSNA between salt-induced and other-type heart failure. To examine the effects of heart failure on brain-tissue nNOS activity, we measured the activities of the diencephalon in heart-failure rats. Heart failure significantly suppressed diencephalon nNOS activity, which was significantly different from the results in salt-sensitive hypertension without heart failure. These results suggest that endogenous Ang II has fewer effects, but nNOS has excitatory effects on tonic RSNA in salt-sensitive hypertension-induced heart failure.

RNA interference targeting the ACE gene reduced blood pressure and improved myocardial remodelling in SHRs

The purpose of the present study was to investigate the effects on blood pressure and myocardial hypertrophy in SHRs (spontaneously hypertensive rats) of RNAi (RNA interference) targeting ACE (angiotensin-converting enzyme). SHRs were treated with normal saline as vehicle controls, with Ad5-EGFP as vector controls, and with recombinant adenoviral vectors Ad5-EGFP-ACE-shRNA, carrying shRNA (small hairpin RNA) for ACE as ACE-RNAi. WKY (Wistar-Kyoto) rats were used as normotensive controls treated with normal saline. The systolic blood pressure of the caudal artery was recorded. Serum levels of ACE and AngII (angiotensin II) were determined using ELISA. ACE mRNA and protein levels were determined in aorta, myocardium, kidney and lung. On day 32 of the experiment, the heart was pathologically examined. The ratios of heart weight/body weight and left ventricular weight/body weight were calculated. The serum concentration of ACE was lower in ACE-RNAi rats (16.37+/-3.90 ng/ml) compared with vehicle controls and vector controls (48.26+/-1.50 ng/ml and 46.67+/-2.82 ng/ml respectively; both P<0.05), but comparable between ACE-RNAi rats and WKY rats (14.88+/-3.15 ng/ml; P>0.05). The serum concentration of AngII was also significantly lower in ACE-RNAi rats (18.24+/-3.69 pg/ml) compared with vehicle controls and vector controls (46.21+/-5.06 pg/ml and 44.93+/-4.12 pg/ml respectively; both P<0.05), but comparable between ACE-RNAi rats and WKY rats (16.06+/-3.11 pg/ml; P>0.05). The expression of ACE mRNA and ACE protein were significantly reduced in the myocardium, aorta, kidney and lung in ACE-RNAi rats compared with that in vehicle controls and in vector controls (all P<0.05). ACE-RNAi treatment resulted in a reduction in systolic blood pressure by 22+/-3 mmHg and the ACE-RNAi-induced reduction lasted for more than 14 days. In contrast, blood pressure was continuously increased in the vehicle controls as well as in the vector controls. The ratios of heart weight/body weight and left ventricular weight/body weight were significantly lower in ACE-RNAi rats (3.12+/-0.23 mg/g and 2.24+/-0.19 mg/g) compared with the vehicle controls (4.29+/-0.24 mg/g and 3.21+/-0.13 mg/g; P<0.05) and the vector controls (4.43+/-0.19 mg/g and 3.13+/-0.12 mg/g; P<0.05). The conclusion of the present study is that ACE-silencing had significant antihypertensive effects and reversed hypertensive-induced cardiac hypertrophy in SHRs, and therefore RNAi might be a new strategy in controlling hypertension.

Salt-induced cardiac hypertrophy is independent of blood pressure and endothelin in obese, heart failure-prone SHHF rats

The interaction of salt sensitivity and obesity in development of cardiac hypertrophy is incompletely understood. The SHHF/Mcc-fa(cp) (SHHF) rat model was used to examine the effect of high salt on cardiac hypertrophy and expression of endothelin (ET) and nitric oxide synthase (NOS) isoforms. Homozygous lean (+/+) and obese (fa(cp)/fa(cp)) SHHF were fed a low-salt diet (0.3% NaCl) for seven days followed by a high-salt diet (8.0% NaCl) for seven days. To assess the role of ET in mediating cardiac hypertrophy and gene expression with high salt, additional groups were treated with an ET(A)/ET(B) receptor antagonist (bosentan) while on high salt. Obese SHHF showed an increase in systolic blood pressure and cardiac hypertrophy in response to the high-salt diet. High salt resulted in decreased expression of preproET as well as all three NOS isoforms in the Obese, while cytokine induced NOS (iNOS) and neuronal NOS (nNOS) increased in Leans. Though the salt-sensitive component of the hypertension observed in the Obese was prevented by bosentan, cardiac hypertrophy still occurred and expression of all NOS isoforms remained lower in Obese compared to Lean. Endothelial NOS (eNOS) expression increased in the Lean with bosentan. These studies suggest that cardiac hypertrophy is independent of the level of hypertension and may be mediated by altered production of NOS isoforms in salt-sensitive, obese SHHF.

Inflammatory pathways in patients with heart failure and preserved ejection fraction

Immune activation is well established in patients with chronic heart failure and reduced ejection fraction (HF and reduced EF) and is associated with an impaired prognosis. Patients with heart failure and preserved ejection fraction (HF and preserved EF) have an impaired prognosis as well. It is not known whether they have signs of immune activation.

METHODS

We studied patients with HF and preserved EF (n=17, NYHA II [n=7]/III [n=10]) and patients with HF and reduced EF (n=17 NYHA II [n=1]/III [n=16]) and 20 controls. Echocardiography demonstrated preserved ejection fraction (LVEF 59+/-9%), but LV hypertrophy in patients with preserved EF as compared with patients with reduced EF (LVEF 23+/-5%). We evaluated levels of TNFalpha, its receptors (sTNFR-1 and 2), IL-6, IL-10 and NT-proBNP.

RESULTS

TNFalpha, was highest in HF with reduced EF (2.87+/-0.65 vs 1.67+/-0.58 pg/mL, p<0.001) compared to preserved EF and similar between HF with preserved EF and controls. However, sTNFR1 (1618+/-384 vs 1017+/-302 pg/mL, p<0.001) and sTNFR2 levels (3554+/-916 vs 2041+/-586 pg/mL, p<0.001) in HF with preserved EF were significantly higher compared with controls. The same was true for IL-6, IL-10 and NT-proBNP. The highest cytokine and NT-proBNP levels were present in HF with reduced EF. There was a negative correlation between TNFalpha, and LVEF (r=- 0.700; p<0.0001) and positive correlations between sTNFR1 and 2 with NT-proBNP.

CONCLUSION

Patients with HF and preserved EF already show signs of systemic-immune activation which may contribute to the impaired prognosis and the progression to HF with reduced EF.

G-protein coupled receptor signaling in myocardium: not for the faint of heart

Catecholamines, endothelin-1 and angiotensin II are among a diverse group of diffusible extracellular signals that regulate pump function of the heart by binding to G-protein coupled receptors (GPCR). When the body demands a temporary boost of power output or if temporary budgeting of resources is required, these signals can adjust heart rate and contractile strength to maintain continuous perfusion of all vascular beds with nutrient- and oxygen-rich blood. Given adequate time in the face of prolonged challenges, activation of GPCRs can also promote "remodeling of the heart" by increasing cell size, organ size, and chamber dimensions, or by varying tissue composition and altering the expression of protein isoforms controlling excitability and contractility. A common feature of heart disease is the state of chronic activation of GPCR signaling systems. Paradoxically, whereas acute activation is beneficial, chronic activation often contributes to further deterioration of cardiac performance. A better understanding of how chronic GPCR activation contributes to the development of heart disease is needed so that it can be translated into better prevention and therapeutic strategies in the clinic.

Vasoactive peptides in cardiovascular (patho)physiology

Numerous vasoactive agents play an important physiological role in regulating vascular tone, reactivity and structure. In pathological conditions, alterations in the regulation of vasoactive peptides result in endothelial dysfunction, vascular remodeling and vascular inflammation, which are important processes underlying vascular damage in cardiovascular disease. Among the many vasoactive agents implicated in vascular (patho)biology, angiotensin II (Ang II), endothelin (ET), serotonin and natriuretic peptides appear to be particularly important because of their many pleiotropic actions and because they have been identified as potential therapeutic targets in cardiovascular disease. Ang II, ET-1, serotonin and natriuretic peptides mediate effects via specific receptors, which belong to the group of G-protein-coupled receptors. ET, serotonin and Ang II are primarily vasoconstrictors with growth-promoting actions, whereas natriuretic peptides, specifically atrial, brain and C-type natriuretic peptides, are vasodilators with natriuretic effects. Inhibition of vasoconstrictor actions with drugs that block peptide receptors, compounds that inhibit enzymes that generate vasoactive peptides or agents that increase levels of natriuretic peptides are potentially valuable therapeutic tools in the management of cardiovascular diseases. This review focuses on ET, natriuretic peptides and serotonin. The properties and distribution of these vasoactive agents and their receptors, mechanisms of action and implications in cardiovascular (patho)physiology will be discussed.

Amelioration of hypertensive heart failure by amlodipine may occur via antioxidative effects

Although recent clinical studies have suggested that long-acting calcium channel blockers (CCBs) have beneficial effects on heart failure, the precise mechanism is unknown. In this study, Dahl salt-sensitive rats fed a high salt diet were treated with the long-acting CCB amlodipine, the low-molecular-weight membrane permeable superoxide dismutase mimetic 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl (Tempol), or saline from 11 weeks after birth. The cardiac geometry and function, and gene expression profiles were determined at 17 weeks. Dahl salt-sensitive rats fed a high salt diet followed by saline as a non-treatment control (HS group) showed a marked increase in blood pressure and developed concentric hypertrophy at 11 weeks, followed by left ventricular (LV) dilation and congestive heart failure by 17 weeks. The treatment with amlodipine (AMLO group) or Tempol (TEMP group) significantly inhibited the development of LV hypertrophy and cardiac dysfunction. Analysis using an Affymetrix GeneChip U34 revealed that the expression levels of 195 genes were changed by the treatment with amlodipine. Among these 195 genes, 110 genes were increased in HS rats and decreased in AMLO rats. And of these 110 genes, 54 genes were also decreased in TEMP rats. In contrast, 85 genes were decreased in HS rats and increased in AMLO rats. Of these 85 genes, 38 genes were also increased in TEMP rats. Approximately 48% of the genes were changed in similar fashion in AMLO and TEMP rats, suggesting that amlodipine shows beneficial effects on heart failure mainly via antioxidative mechanisms.

Beta-adrenergic pathways in human heart failure

Beta-adrenergic receptor activation plays an important role in the progression of human heart failure and the treatment of patients with beta-blockers has greatly improved the outcome of the disease. However, heart failure still is one of the leading causes of death in various countries and there is an imperative need for additional targets for the treatment of the disease. Recent studies by various groups have analyzed the downstream signaling pathways activated in response to beta-adrenergic stimulation that have the potential to become important targets for future treatments of heart failure. This review focuses on the significance of these pathways in the pathophysiology of heart failure in response to beta-adrenergic stimulation. More specifically the roles of PDE3, phosphorylation of phospholamban, and CaMKII activation are extensively discussed.

Pitavastatin improves cardiac function and survival in association with suppression of the myocardial endothelin system in a rat model of hypertensive heart failure

Statin therapy may be associated with lower mortality in patients with heart failure, but the underlying mechanism of such an association is unknown. We have evaluated the effects of pitavastatin on cardiac function and survival in a rat model of hypertensive heart failure and investigated the molecular mechanism of the observed effects. Dahl salt-sensitive rats fed with high-salt diet from 7 weeks of age developed compensatory left ventricular hypertrophy at 12 weeks and heart failure at 19 weeks. Dahl salt-sensitive rats were treated with either vehicle or pitavastatin (0.3 mg/kg per day) from 7 or 12 weeks. Both early-onset and late-onset pitavastatin treatment reduced left ventricular fibrosis, improved cardiac function, and increased the survival rate apparent at 19 weeks. The increases in the expression levels of hypertrophic, profibrotic, and metalloproteinase genes as well as in gelatinase activities in the heart induced by the high-salt diet were suppressed by pitavastatin treatment. Furthermore, the level of cardiac endothelin-1 was increased in association with the development of heart failure in a manner sensitive to treatment with pitavastatin. Both early and late pitavastatin treatment thus improved cardiac function and survival, with modulation of extracellular matrix remodeling and endothelin-1 signaling possibly contributing to these beneficial effects.

Effect of heart failure on skeletal muscle myofibrillar protein content, isoform expression and calcium sensitivity

BACKGROUND

Alterations in skeletal muscle with heart failure contribute to exercise intolerance and physical disability. The majority of studies to date have examined abnormalities in skeletal muscle oxidative capacity and mitochondrial function. In contrast, less information is available regarding the effect of heart failure on myofibrillar protein metabolism and function. To address this issue, we examined the effect of heart failure on skeletal muscle myofibrillar protein content, isoform distribution and Ca2+ sensitivity.

METHODS

We measured skeletal muscle myosin heavy chain (MHC) and actin protein content and MHC isoform distribution in soleus (SOL), extensor digitorum longus (EDL), plantaris (PL) and diaphragm (DIA) muscles and myofibrillar Ca2+ sensitivity in EDL muscles from Dahl salt-sensitive rats with (high-salt fed: HS; n=10) or without heart failure (low-salt fed: LS; n=8) and assessed the relationship of these variables to markers of disease severity.

RESULTS

No differences in muscle mass were found. Similarly, no differences in MHC (mean+/-SE; SOL: 1353+/-29 vs. 1247+/-52; EDL: 1471+/-31 vs. 1441+/-31; PL: 1207+/-66 vs. 1286+/-36; DIA: 1166+/-42 vs. 1239+/-26 AU/microg protein) or actin (EDL: 348+/-13 vs. 358+/-19; PL: 245+/-20 vs. 242+/-9; DIA: 383+/-9 vs. 376+/-17 AU/microg protein) protein content or the actin-to-MHC ratio were observed, with the exception of lower (P<0.01) actin content in the soleus of LS rats (352+/-7 vs. 310+/-8 AU/microg protein). MHC isoform expression (I, IIa, IIx, IIb) did not differ between groups in SOL (I: 89+/-1% vs. 85+/-2%; IIa: 11+/-1% vs. 15+/-2%), EDL (IIx: 43+/-10% vs. 38+/-10%; IIb: 57+/-10% vs. 62+/-10%), PL (I: 6+/-4% vs. 3+/-3%; IIa: 1+/-1% vs. 1+/-1%; IIx: 31+/-3% vs. 26+/-4%; IIb: 62+/-5% vs. 71+/-6%) or DIA (I: 43+/-6% vs. 36+/-6 %; IIa: 9+/-1% vs. 7+/-1%; IIx: 47+/-6% vs. 56+/-7%; IIb: 2+/-1% vs. 1+/-0.5%) muscles. Moreover, heart failure did not affect the Ca2+ sensitivity (i.e., pCa50) of extensor digitorum longus myofilaments (5.68+/-0.11 vs. 5.65+/-0.09). Finally, MHC and actin content, MHC isoform distribution and myofibrillar Ca2+ sensitivity were not related to markers of disease severity.

CONCLUSIONS

Our results show that this animal model of heart failure is not characterized by alterations in the quantity or isoform distribution of key skeletal muscle myofibrillar proteins or the Ca2+ sensitivity of isometric force production. These findings suggest that alterations in skeletal muscle myofibrillar protein metabolism do not develop in parallel with myocardial failure in the Dahl salt-sensitive rat.

ACE inhibitors in pediatric patients with heart failure

This article reviews reports of ACE inhibitor use in pediatric heart failure and summarizes the present implications for clinical practice. Captopril, enalapril, and cilazapril are orally active ACE inhibitors, and widely used in pediatric cardiology, although more than ten other ACE inhibitors have been applied clinically in adults. Effects of ACE inhibitors on the renin-angiotensin-aldosterone system in pediatric patients are similar to those in adults. ACE inhibitors lower aortic pressure and systemic vascular resistance, do not affect pulmonary vascular resistance significantly, and lower left atrial and right atrial pressures in pediatric patients with heart failure. In infants with a large ventricular septal defect and pulmonary hypertension, ACE inhibitors decrease left-to-right shunt in those infants with elevated systemic vascular resistance. ACE inhibitors induce a small increase in left ventricular ejection fraction, left ventricular fractional shortening, and systemic blood flow in children with left ventricular dysfunction, mitral regurgitation, and aortic regurgitation. These beneficial effects usually persist long term without the development of tolerance. Therapeutic trials of ACE inhibitors have been reported in children with heart failure and divergent hemodynamics, including myocardial dysfunction, left-to-right shunt, such as large ventricular septal defect and pulmonary hypertension, aortic or mitral regurgitation, and Fontan circulation. Hypotension and renal failure usually occur within 5 days after starting ACE inhibition or increasing the dose and, in most cases, recovery is seen after reduction or cessation of the drug. With all ACE inhibitors, smaller doses are administered initially to prevent excessive hypotension, and doses are increased gradually to the target dose. Captopril is administered orally, usually every 8 hours. Daily doses range from 0.3 to 1.5 mg/kg in children. Enalapril is administered orally, once or twice a day, and daily doses range from 0.1 to 0.5 mg/kg. Enalaprilat is administered intravenously, one to three times a day, in doses ranging from 0.01 to 0.05 mg/kg/dose. For the treatment of chronic heart failure in children, ACE inhibitors are essential along with other medications including diuretics, digoxin, and beta-blockers (beta-adrenoceptor antagonists).

Down-regulation of cardiac apelin system in hypertrophied and failing hearts: Possible role of angiotensin II-angiotensin type 1 receptor system

Cardiac apelin has recently been suggested to contribute to the pathophysiology of heart failure (HF) in humans. In animal experiments, its infusion acutely improved systolic as well as diastolic LV function. Although its deficit could critically determine the cardiac dysfunction, its regulatory mechanism is unknown. Accordingly, we investigated the role and regulation of the cardiac apelin system in the diseased heart using Dahl salt-sensitive rats, which show a distinctive transition from compensatory LV hypertrophy (LVH) to HF. In the compensatory LVH stage, apelin and its receptor APJ mRNA showed no change compared with control animals, while these were markedly down-regulated in the HF stage (72% and 57% decrease, respectively). The rats were chronically treated with telmisartan (angiotensin type 1 receptor blocker [ARB], 5 mg/kg/day, n=9), ONO-4817 (matrix metalloproteinase [MMP] inhibitor, 200 mg/kg/day, n=9), bisoprolol (beta blocker, 3 mg/kg/day, n=6) or vehicle (0.5%CMC, n=9) from the LVH stage. Although the functional improvements were similar among the three treated groups 6 weeks after treatment, restoration of cardiac apelin and APJ expression was observed only in the ARB group. Furthermore, in angiotensin II-infused rats, cardiac apelin mRNA was decreased after 24 h of treatment and its restoration was achieved by treatment with ARB. These results indicate that the cardiac apelin system is markedly down-regulated in experimental HF and may be regulated by the angiotensin II-angiotensin type 1 receptor system directly. Inhibition of the renin-angiotensin system may have beneficial effects, at least in part, through restoration of the cardiac apelin system in the treatment of HF.

Stent revascularization for the prevention of cardiovascular and renal events among patients with renal artery stenosis and systolic hypertension: rationale and design of the CORAL trial

BACKGROUND

Atherosclerotic renal artery stenosis is a problem with no consensus on diagnosis or therapy. The consequences of renal ischemia are neuroendocrine activation, hypertension, and renal insufficiency that can potentially result in acceleration of atherosclerosis, further renal dysfunction, myocardial infarction, heart failure, stroke, and death. Whether revascularization improves clinical outcomes when compared with optimum medical therapy is unknown.

METHODS

CORAL is a randomized clinical trial contrasting optimum medical therapy alone to stenting with optimum medical therapy on a composite cardiovascular and renal end point: cardiovascular or renal death, myocardial infarction, hospitalization for congestive heart failure, stroke, doubling of serum creatinine, and need for renal replacement therapy. The secondary end points evaluate the effectiveness of revascularization in important subgroups of patients and with respect to all-cause mortality, kidney function, renal artery patency, microvascular renal function, and blood pressure control. We will also correlate stenosis severity with longitudinal renal function and determine the value of stenting from the perspectives of quality of life and cost-effectiveness. The primary entry criteria are (1) an atherosclerotic renal stenosis of > or = 60% with a 20 mm Hg systolic pressure gradient or > or = 80% with no gradient necessary and (2) systolic hypertension of > or = 155 mm Hg on > or = 2 antihypertensive medications. Randomization will occur in 1080 subjects. The study has 90% power to detect a 28% reduction in primary end point hazard rate.

CONCLUSIONS

CORAL represents a unique opportunity to determine the incremental value of stent revascularization, in addition to optimal medical therapy, for the treatment of atherosclerotic renal artery stenosis.

Pharmacological and Clinical Studies with Temocapril, an Angiotensin Converting Enzyme Inhibitor that is Excreted in the Bile

Temocapril is an angiotensin converting enzyme inhibitor (ACEI), a prodrug with a thiazepine ring. Its active form, temocaprilat, is slightly more potent than enalaprilat in inhibiting ACE isolated from rabbit lung. The inhibitory potency of temocaprilat on isolated rat aorta is 3 times that of enalaprilat. Temocapril is excreted in the bile and urine and can be used in patients with renal insufficiency. It reduces blood pressure without causing any significant change in heart rate or cardiac output. Temocapril has been reported to improve endothelial dysfunction in vitro by suppressing increased oxidative stress. In vivo it improves reactive hyperemia in patients with essential hypertension. It has been reported to prevent coronary vascular remodeling in vivo by suppressing local ACE and increased oxidative stress. In humans temocapril has been found to improve insulin resistance partly by increasing adiponectin levels. Cardiac remodeling was improved by temocapril not only in experiment animals but also in humans. It improves renal function and decreases urinary albumin excretion in diabetics as well as in hypertensive patients. Temocapril is currently marketed only in Japan. Considering its beneficial effects and unique pharmacokinetics, temocapril, is likely to be introduced in other countries as well.

Contribution of reactive oxygen species to the pathogenesis of left ventricular failure in Dahl salt-sensitive hypertensive rats: effects of angiotensin II blockade

OBJECTIVE

We investigated the contribution of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase-dependent reactive oxygen species (ROS) generation to the pathogenesis of diastolic heart failure (DHF) in Dahl salt-sensitive (DS) hypertensive rats, with the aim of testing our hypothesis that the cardioprotective effects of angiotensin II (Ang II) blockade are provided by the suppression of this pathway.

METHODS

DS rats were maintained on high (H: 8.0% NaCl) or low (L: 0.3% NaCl) salt diets from age 7 to 17 weeks. DS/H rats were also treated with candesartan cilexetil (10 mg/kg per day, orally) or a superoxide dismutase mimetic, tempol (3 mmol/l in drinking water) from age 7 to 17 weeks.

RESULTS

DS/H rats represented hypertension, left ventricular (LV) relaxation abnormality and myocardial stiffening with preserved systolic heart function. As compared with DS/L rats, DS/H rats showed higher levels of transforming growth factor-beta (TGF-beta), connective tissue growth factor (CTGF), p22phox and gp91phox mRNA expression, NADPH oxidase activity and thiobarbituric acid-reactive substance (TBARS) contents in LV tissues. Gene expression of uncoupling protein-2 (UCP-2), an inner mitochondrial membrane proton transporter, was also 2.8 +/- 0.5-fold higher. In DS/H rats, treatment with candesartan did not alter blood pressure, but resulted in a marked improvement of the hemodynamic deterioration; these therapeutic effects were accompanied by decreases in myocardial NADPH oxidase activity, TBARS contents and the expression of TGF-beta, CTGF, p22phox, gp91phox and UCP-2. Similar therapeutic effects were provided by treatment with tempol in DS/H rats.

CONCLUSIONS

Our data suggest that NADPH oxidase-mediated ROS production contributes to the pathogenesis of DHF in DS hypertensive rats, and that the cardioprotective effects of AngII blockade are, at least partially, mediated through the suppression of this pathway.

A beta1-adrenergic receptor CaM kinase II-dependent pathway mediates cardiac myocyte fetal gene induction

Beta-adrenergic signaling plays an important role in the natural history of dilated cardiomyopathies. Chronic activation of beta-adrenergic receptors (beta1-AR and beta2-AR) during periods of cardiac stress ultimately harms the failing heart by mechanisms that include alterations in gene expression. Here, we show that stimulation of beta-ARs with isoproterenol in neonate rat ventricular myocytes causes a "fetal" response in the relative activities of the human cardiac fetal and/or adult gene promoters that includes repression of the human and rat alpha-myosin heavy chain (alpha-MyHC) promoters with simultaneous activation of the human atrial natriuretic peptide (ANP) and rat beta-MyHC promoters. We also show that the promoter changes correlate with changes in endogenous gene expression as measured by mRNA expression. Furthermore, we show that these changes are specifically mediated by the beta1-AR, but not the beta2-AR, and are independent of alpha1-AR stimulation. We also demonstrate that the fetal gene response is independent of cAMP and protein kinase A, whereas inhibition of Ca2+/calmodulin-dependent protein kinase (CaMK) pathway blocks isoproterenol-mediated fetal gene program induction. Finally, we show that induction of the fetal program is dependent on activation of the L-type Ca2+ channel. We conclude that in neonatal rat cardiac myocytes, agonist-occupied beta1-AR mobilizes Ca2+ stores to activate fetal gene induction through cAMP independent pathways that involve CaMK.

B-type natriuretic peptide strongly reflects diastolic wall stress in patients with chronic heart failure: comparison between systolic and diastolic heart failure

OBJECTIVES

We explored the stimulus for B-type natriuretic peptide (BNP) secretion in the clinical setting of heart failure (HF).

BACKGROUND

Increasingly, plasma BNP levels are being incorporated into the clinical assessment and management of systolic heart failure (SHF) as well as diastolic heart failure (DHF). However, heterogeneity in BNP levels among individuals with HF can cause some confusion in interpreting results.

METHODS

In 160 consecutive patients presenting with HF, we measured plasma BNP levels and performed echocardiography and cardiac catheterization. Systolic and diastolic meridional wall stress was calculated from echocardiographic and hemodynamic data.

RESULTS

Although plasma BNP had a significant correlation (r2 = 0.296 [p < 0.001]) with left ventricular end-diastolic pressure (EDP) as previously reported, the correlation between plasma BNP and end-diastolic wall stress (EDWS) (r2 = 0.887 [p < 0.001]) was more robust. In a subanalysis of 62 patients with DHF, a similar result was obtained (r2 = 0.143 for EDP and r2 = 0.704 for EDWS). In a comparison between SHF and DHF, the BNP level was significantly higher in SHF (p < 0.001). Although EDP did not show any difference, EDWS was significantly higher in SHF than in DHF (p < 0.001).

CONCLUSIONS

The present study shows that plasma BNP levels reflect left ventricular EDWS more than any other parameter previously reported, not only in patients with SHF, but also in patients with DHF. The relationship of left ventricular EDWS to plasma BNP may provide a better fundamental understanding of the interindividual heterogeneity in BNP levels and their clinical utility in the diagnosis and management of HF.

Endothelins: Pathophysiology and treatment implications in chronic heart failure

Less than 20 years after its discovery, endothelin is recognized as playing a central role in the pathogenesis of chronic heart failure. Endothelin is not only one of the most potent known vasoconstrictors; it also has multiple other actions. It mediates pathologic hypertrophy and fibrosis of both ventricular and vascular tissues, it potentiates the effects of other neurohormones, and it acts as a proarrhythmic. Endothelin receptor antagonists have been developed to investigate the hypothesis that these adverse effects could be prevented, and experimental studies showed promise in this regard. Clinical studies have confirmed the ability of these new agents to improve hemodynamics, but beneficial effects on clinical outcomes have been more difficult to demonstrate. Further analysis of the data from these trials, as well as other ongoing studies, may provide insight into these disparate findings and guidance for future investigations.

The Role of Endothelin in Heart Failure

Current treatments for heart failure extend the life of the patient but do not stop the progression of the disease process. These treatments may not be addressing the underlying cause of cellular injury. The role of endothelin in cardiac remodeling and inflammation may be important in the progression of failure, and endothelin antagonists may be beneficial in treatment in combination with drugs already in use.

Effect of pravastatin on development of left ventricular hypertrophy in spontaneously hypertensive rats

Endothelin (ET)-1 has been implicated in the development of cardiac hypertrophy. We investigated the effect of pravastatin on development of ventricular hypertrophy in spontaneously hypertensive rats (SHR) and whether the attenuated hypertrophic effect was via reduced ET-1 expression. Normolipidemic SHR were treated with one of the following therapies for 8 wk: vehicle, the nonselective ET receptor antagonists bosentan, pravastatin, mevalonate, hydralazine, or combination of pravastatin + mevalonate from the age of 8 wk at the very early stage of cardiac hypertrophy. Treatment with bosentan and pravastatin significantly decreased left ventricular mass index for body weight and cardiomyocyte sizes isolated by enzymatic dissociation. The myocardial ET-1 levels and preproET-1 mRNA assessed using real-time quantitative RT-PCR were significantly higher (both P < 0.001) in the SHR compared with Wistar-Kyoto rats. The increased tissue ET-1 levels can be inhibited after pravastatin administration. Immunohistochemical analysis confirmed the changes of ET-1. Left ventricular mass index for body weight correlated positively with tissue ET-1 levels (P = 0.0004). A dissociation between the effects of blood pressure and cardiac structure was noted, because pravastatin and hydralazine reduced arterial pressure similarly. Pravastatin-induced effects were reversed by the addition of mevalonate. In conclusion, these results suggest a crucial role of cardiac endothelin system in the early development of ventricular hypertrophy in the SHR. Pravastatin is endowed with cardiac antihypertropic properties that are independent of its hemodynamic and hypolipidemic effects and appear to be related to their capacity to decrease cardiac ET-1 levels, which is linked to mevalonate metabolism.

Sex-specific effects of dual ET-1/ANG II receptor (Dear) variants in Dahl salt-sensitive/resistant hypertension rat model

Essential (polygenic) hypertension is a complex genetic disorder that remains a major risk factor for cardiovascular disease despite clinical advances, reiterating the need to elucidate molecular genetic mechanisms. Elucidation of susceptibility genes remains a challenge, however. Blood pressure (BP) regulatory pathways through angiotensin II (ANG II) and endothelin-1 (ET-1) receptor systems comprise a priori candidate susceptibility pathways. Here we report that the dual ET-1/ANG II receptor gene ( Dear) is structurally and functionally distinct between Dahl salt-sensitive, hypertensive (S) and salt-resistant, normotensive (R) rats. The Dahl S S44/M74 variant is identical to the previously reported Dear cDNA with equivalent affinities for both ET-1 and ANG II, in contrast to Dahl R S44P/M74T variant, which exhibits absent ANG II binding but effective ET-1 binding. The S44P substitution localizes to the ANG II-binding domain predicted by the molecular recognition theory, providing compelling support of this theory. The Dear gene maps to rat chromosome 2 and cosegregates with BP in female F2(R×S) intercross rats with highly significant linkage (LOD 3.61) accounting for 14% of BP variance, but not in male F2(R×S) intercross rats. Altogether, the data suggest the hypothesis that modification of the critical balance between ANG II and ET-1 systems through variant Dear contributes to hypertension susceptibility in female F2(R×S) intercross rats. Further investigations are necessary to corroborate genetic linkage through congenic rat studies, to investigate putative gene interactions, and to show causality by transgenesis and/or intervention. More importantly, the data reiterate the importance of sex-specific factors in hypertension susceptibility.

Endothelin receptor antagonists in heart failure: current status and future directions

Experimental evidence suggests that endothelin substantially contributes to left ventricular remodelling and progression of heart failure. Plasma endothelin (ET)-1 levels are increased in patients with heart failure, independent of the aetiology, and correlate with the severity of the disease. Furthermore, tissue endothelin levels and endothelin receptors are upregulated in myocardium from animals and humans with heart failure. In several experimental models of left ventricular remodelling and/or heart failure, treatment with nonselective ET-A and -B as well as selective ET-A antagonists exerted beneficial cardiovascular effects. In patients with heart failure, short-term studies of treatment with endothelin antagonists demonstrated an improvement of haemodynamic parameters; however, long-term treatment with these drugs did not significantly improve combined morbidity/mortality endpoints. Furthermore, in the recently completed Endothelin-A Receptor Antagonist Trial in Heart Failure (EARTH) trial in patients with chronic heart failure, the selective ET-A receptor antagonist darusentan did not significantly affect left ventricular remodelling as assessed by cardiac magnetic resonance imaging. Potential reasons for the lack of beneficial effects of long-term treatment with ET antagonists in patients with heart failure include the following. Firstly, adverse effects on left ventricular healing have been observed when endothelin antagonist therapy was introduced early after myocardial infarction in rats. Secondly, the role of the ET-B receptor in the pathophysiology of heart failure and remodelling processes has not been clearly defined. Finally, for the detection of improvement in left ventricular remodelling, a study needs to be conducted in patients with recent myocardial infarction and signs of heart failure.

Baseline echocardiographic values for adult male rats

BACKGROUND

Because of safety, repeatability, and portability, clinical echocardiography is well established as a standard for cardiac anatomy, cardiac function, and hemodynamics. Similarly, application of echocardiography in commonly used rat experimental models would be worthwhile. The use of noninvasive ultrasound imaging in the rat is a potential replacement for more invasive terminal techniques. Although echocardiography has become commonly used in the rat, normal parameters for cardiac anatomy and function, and comparison with established human values, have not been reported.

METHODS

A total of 44 Sprague-Dawley male rats had baseline echocardiography replicating a protocol for clinical echocardiography.

RESULTS

Complete 2-dimensional echocardiography for cardiac anatomy and function was obtained in 44 rats. Hemodynamic parameters could be recorded in 85% of rats. The ejection fraction and fractional shortening values of the left ventricle were similar to those reported for healthy human beings. Pulsed Doppler velocities of atrial systole for mitral valve inflow, pulmonary vein reversal, and Doppler tissue of the lateral mitral valve annulus also had similar means as healthy human beings. The calculated left ventricular mass was at the same order of magnitude as a proportion of body weight of rat to man. All other observations in the clinical protocol were different from those reported in healthy human beings.

CONCLUSION

The use of echocardiography for assessment of cardiac anatomy, function, and hemodynamics can be consistently applied to the rat and replicates much of the information used routinely in human echocardiography.

Transplantation of cardiotrophin-1–expressing myoblasts to the left ventricular wall alleviates the transition from compensatory hypertrophy to congestive heart failure in Dahl salt-sensitive hypertensive rats

OBJECTIVES

We investigated whether autologous transplantation of skeletal myoblasts (MB) transferred with cardiotrophin-1 (CT-1) gene could retard the transition to heart failure (HF) in Dahl salt-sensitive (DS) hypertensive rats.

BACKGROUND

Although MB is a therapeutic candidate for chronic HF, little is known about the efficiency of this strategy when applied in nonischemic HF. Cardiotrophin-1 has potent hypertrophic and survival effects on cardiac myocytes. We hypothesized that transplantation of CT-1-expressing myoblasts could provide cardioprotective effects against ventricular remodeling in DS hypertensive rats.

METHODS

The DS rats were fed a high salt diet for 6 weeks and developed left ventricular (LV) hypertrophy at 11 weeks. At this stage, animals underwent MB to the myocardium with skeletal myoblasts transferred with CT-1 gene using retrovirus (transplantation of CT-1-expressing myoblasts [MB + CT], n = 31) or myoblasts alone (MB, n = 31). The sham group rats were injected with phosphate-buffered saline (n = 24).

RESULTS

At 17 weeks, MB and MB + CT groups showed a significant alleviation of LV dilation and contractile dysfunction compared with the sham group. The degree of alleviation was significantly greater in the MB + CT group than the MB group (LV end-diastolic dimension: sham 7.06 +/- 0.14 mm, MB 6.51 +/- 0.16 mm, MB + CT 6.24 +/- 0.07 mm; fractional shortening: sham 32.1 +/- 1.4%, MB 38.5 +/- 1.5%, MB + CT 43.2 +/- 0.8%). Histological examination revealed that the myocyte size was 20% larger in the MB + CT group at 17 weeks than in the age-matched sham group. Upregulation of renin-angiotensin and endothelin systems during the transition to HF was attenuated by myoblast transplantation, and this effect was enhanced in the MB + CT group.

CONCLUSIONS

Transplantation of skeletal myoblasts combined with CT-1-gene transfer could be a useful therapeutic strategy for HF.

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 renal ischemia: implications for cardiovascular disease risk

Chronic renal ischemia caused by atherosclerotic renal artery stenosis (RAS) is gaining recognition as a potentially important risk factor for cardiovascular (CV) morbidity and mortality. The etiology of increased risk of CV events is multifaceted and includes direct physiologic changes that increase risk as well as intermediate clinical effects that are associated with worse outcome. Physiologic changes associated with increased CV risk in patients with RAS include increased production of fibrogenic and vasoactive peptides such as renin, angiotensin, endothelin, and catecholamines, as well as endothelial cell dysfunction. Clinical intermediate conditions associated with higher incidences of CV events seen in patients with renal ischemia include hypertension, systemic atherosclerosis, chronic renal failure, and left ventricular hypertrophy and dysfunction. More thorough understanding of the myriad physiologic changes seen in patients with RAS will likely improve patient selection for renal artery revascularization. Clinical trials should examine a full range of CV and renal outcomes, not just blood pressure, to adequately assess the merits of revascularization.

Tissue angiotensin II during progression or ventricular hypertrophy to heart failure in hypertensive rats; differential effects on PKC epsilon and PKC beta

The protein kinase C (PKC) family has been implicated as second messengers in mechanosensitive modulation of cardiac hypertrophy. However, little information is available on the role of expression and activation of specific cardiac PKC isozymes during development of left ventricular hypertrophy (LVH) and failure (LVF). Dahl salt-sensitive rats fed an 8% salt diet developed systemic hypertension and concentric LVH at 11 weeks of age that is followed by left ventricle (LV) dilatation and global hypokinesis at 17 weeks. Among several PKC isozymes expressed in the LV myocardium, only PKC epsilon showed a 94% increase at the LVH stage. At the LVF stage, however, PKC epsilon returned to the control level, whereas PKC beta I and beta II increased by 158% and 155%, respectively. Hearts were studied at each stage using the Langendorff set-up, and a LV balloon was inflated to achieve an equivalent diastolic wall stress. Following mechanical stretch, PKC epsilon was significantly activated in LVH myocardium in which tissue angiotensin II levels were increased by 59%. Pre-treatment with valsartan, an AT(1)-receptor blocker, abolished the stretch-mediated PKC epsilon activation. Mechanical stretch no longer induced PKC epsilon activation in LVF. Chronic administration of valsartan blunted the progression of LVF and inhibited the increase in PKC beta. Mechanosensitive PKC epsilon activation is augmented and therefore may contribute to the development of compensatory hypertrophy. This effect was dependent on activation of tissue angiotensin II. However, this compensatory mechanism becomes inactive in LVF, where PKC beta may participate in the progression to cardiac dysfunction and LV remodeling.

Endothelin antagonism with bosentan: current status and future perspectives

Endothelin receptor antagonists have been proposed for the treatment of a variety of disorders in which the endothelins may act as pathogenic mediators, such as hypertension, congestive heart failure, and cerebral vasospasm. Bosentan is a nonpeptide competitive antagonist, which can be a good tool for studying the endothelin system. It is specific for the endothelin system and blocks the actions of endothelin at both mammalian receptors (A and B). Bosentan has recently moved into Phase III clinical trial. This review will attempt to overview the experimental and clinical effects of bosentan.

The role of endothelin in the pathogenesis of heart failure

In fewer than than 15 years since its discovery, endothelin is now recognized as playing a central role in the pathogenesis of chronic heart failure. This review examines the signaling pathways and mechanism of action of endothelin in relation to the studies that have elucidated this role. Early investigations observed that the endothelin system is markedly upregulated in heart failure, whereas others demonstrated that endothelin is the most potent vasoconstrictor. However, it has multiple other actions, including mediating pathologic hypertrophy and fibrosis of both ventricular and vascular tissues, acting as a proarrhythmic, and potentiating the effects of other neurohormones. Endothelin receptor antagonists were developed to investigate the hypothesis that these adverse effects could be prevented and experimental studies showed promise in this regard. Clinical studies to date have not fulfilled this promise. Further analysis of these trials will hopefully provide insight into these disparate findings and guidance for future investigations.

Proinflammatory effects of angiotensin II and endothelin: targets for progression of cardiovascular and renal diseases

Angiotensin II and endothelin-1 can both be regulated by nuclear factor-kappaB. They are to varying degrees also capable of activating nuclear factor-kappaB and increasing the expression of nuclear factor-kappaB dependent genes. Angiotensin II related vascular effects are in part mediated by endothelin-1. Nitric oxide synthase inhibition facilitates angiotensin II related effects, which can be inhibited both by angiotensin II type 1 receptor blockers and by endothelin system inhibitors. This supports the notion that a combined therapeutic strategy of inhibiting angiotensin II and endothelin-1 generation or blocking their effects at the receptor level would be superior to either strategy alone. Animal studies are encouraging but not without conflicting results. Angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor blockers have a superb track record in experimental animal models and in a host of clinical studies. Selective and nonselective blockers of the endothelin-1 receptors are important research tools and are also undergoing clinical trials. Inhibitors of the endothelin converting enzyme have been developed. The recent elucidation of the endothelin converting enzyme's physical structure should facilitate the development of still more novel compounds to inhibit endothelin-1 generation.