Role of endothelin in deterioration of heart failure due to cardiomyopathy in hamsters: increase in endothelin-1 production in the heart and beneficial effect of endothelin-A receptor antagonist on survival and cardiac function

Pulmonary Hypertension in Left Heart Diseases: Pathophysiology, Hemodynamic Assessment and Therapeutic Management

Pulmonary hypertension (PH) associated with left heart diseases (PH-LHD), also termed group 2 PH, represents the most common form of PH. It develops through the passive backward transmission of elevated left heart pressures in the setting of heart failure, either with preserved (HFpEF) or reduced (HFrEF) ejection fraction, which increases the pulsatile afterload of the right ventricle (RV) by reducing pulmonary artery (PA) compliance. In a subset of patients, progressive remodeling of the pulmonary circulation resulted in a pre-capillary phenotype of PH, with elevated pulmonary vascular resistance (PVR) further increasing the RV afterload, eventually leading to RV-PA uncoupling and RV failure. The primary therapeutic objective in PH-LHD is to reduce left-sided pressures through the appropriate use of diuretics and guideline-directed medical therapies for heart failure. When pulmonary vascular remodeling is established, targeted therapies aiming to reduce PVR are theoretically appealing. So far, such targeted therapies have mostly failed to show significant positive effects in patients with PH-LHD, in contrast to their proven efficacy in other forms of pre-capillary PH. Whether such therapies may benefit some specific subgroups of patients (HFrEF, HFpEF) with specific hemodynamic phenotypes (post- or pre-capillary PH) and various degrees of RV dysfunction still needs to be addressed.

VEGF-C promotes brain-derived fluid drainage, confers neuroprotection, and improves stroke outcomes

Meningeal lymphatic vessels promote tissue clearance and immune surveillance in the central nervous system (CNS). Vascular endothelium growth factor-C (VEGF-C) is essential for meningeal lymphatic development and maintenance and has therapeutic potential for treating neurological disorders, including ischemic stroke. We have investigated the effects of VEGF-C overexpression on brain fluid drainage, single cell transcriptome in the brain, and stroke outcomes in adult mice. Intra-cerebrospinal fluid administration of an adeno-associated virus expressing VEGF-C (AAV-VEGF-C) increases the CNS lymphatic network. Post-contrast T1 mapping of the head and neck showed that deep cervical lymph node size and drainage of CNS-derived fluids were increased. Single nuclei RNA sequencing revealed a neuro-supportive role of VEGF-C via upregulation of calcium and brain-derived neurotrophic factor (BDNF) signaling pathways in brain cells. In a mouse model of ischemic stroke, AAV-VEGF-C pretreatment reduced stroke injury and ameliorated motor performances in the subacute stage. AAV-VEGF-C thus promotes CNS-derived fluid and solute drainage, confers neuroprotection, and reduces ischemic stroke damage.

Short abstract

Intrathecal delivery of VEGF-C increases the lymphatic drainage of brain-derived fluids confers neuroprotection, and improves neurological outcomes after ischemic stroke.

Therapeutic Challenges and Emerging Treatment Targets for Pulmonary Hypertension in Left Heart Disease

Pulmonary hypertension (PH) attributable to left heart disease (LHD) is believed to be the most common form of PH and is strongly associated with increased mortality and morbidity in this patient population. Specific therapies for PH‐LHD have not yet been identified and the use of pulmonary artery hypertension‐targeted therapies in PH‐LHD are not recommended. Endothelin receptor antagonists, phosphodiesterase‐5 inhibitors, guanylate cyclase stimulators, and prostacyclins have all been studied in PH‐LHD with conflicting results. Understanding the mechanisms underlying PH‐LHD could potentially provide novel therapeutic targets. Fibrosis, oxidative stress, and metabolic syndrome have been proposed as pathophysiological components of PH‐LHD. Genetic associations have also been identified, offering additional mechanisms with biological plausibility. This review summarizes the evidence and challenges for treatment of PH‐LHD and focuses on underlying mechanisms on the horizon that could develop into potential therapeutic targets for this disease.

Sympathetic nervous system activation and heart failure: Current state of evidence and the pathophysiology in the light of novel biomarkers

Heart failure (HF) is a complex clinical syndrome characterized by the activation of at least several neurohumoral pathways that have a common role in maintaining cardiac output and adequate perfusion pressure of target organs and tissues. The sympathetic nervous system (SNS) is upregulated in HF as evident in dysfunctional baroreceptor and chemoreceptor reflexes, circulating and neuronal catecholamine spillover, attenuated parasympathetic response, and augmented sympathetic outflow to the heart, kidneys and skeletal muscles. When these sympathoexcitatory effects on the cardiovascular system are sustained chronically they initiate the vicious circle of HF progression and become associated with cardiomyocyte apoptosis, maladaptive ventricular and vascular remodeling, arrhythmogenesis, and poor prognosis in patients with HF. These detrimental effects of SNS activity on outcomes in HF warrant adequate diagnostic and treatment modalities. Therefore, this review summarizes basic physiological concepts about the interaction of SNS with the cardiovascular system and highlights key pathophysiological mechanisms of SNS derangement in HF. Finally, special emphasis in this review is placed on the integrative and up-to-date overview of diagnostic modalities such as SNS imaging methods and novel laboratory biomarkers that could aid in the assessment of the degree of SNS activation and provide reliable prognostic information among patients with HF.

Long-Term Effect of Endothelin Receptor Antagonism With Bosentan on the Morbidity and Mortality of Patients With Severe Chronic Heart Failure: Primary Results of the ENABLE Trials

OBJECTIVES

The objective of this clinical trial was to evaluate the long-term effect of endothelin receptor antagonism with bosentan on the morbidity and mortality of patients with severe chronic heart failure.

BACKGROUND

Endothelin may play a role in heart failure, but short-term clinical trials with endothelin receptor antagonists have reported disappointing results. Long-term trials are lacking.

METHODS

In 2 identical double-blind trials, we randomly assigned 1,613 patients with New York Heart Association functional class IIIb to IV heart failure and an ejection fraction <35% to receive placebo or bosentan (target dose 125 mg twice daily) for a median of 1.5 years. The primary outcome for each trial was clinical status at 9 months (assessed by the hierarchical clinical composite); the primary outcome across the 2 trials was death from any cause or hospitalization for heart failure.

RESULTS

Bosentan did not influence clinical status at 9 months in either trial (p = 0.928 and p = 0.263). In addition, 321 patients in the placebo group and 312 patients in the bosentan group died or were hospitalized for heart failure (hazard ratio [HR]: 1.01; 95% confidence interval [CI]: 0.86 to 1.18; p = 0.90). The bosentan group experienced fluid retention within the first 2 to 4 weeks, as evidenced by increased peripheral edema, weight gain, decreases in hemoglobin, and an increased risk of hospitalization for heart failure, despite intensification of background diuretics. During follow-up, 173 patients died in the placebo group and 160 patients died in the bosentan group (HR: 0.94; 95% CI: 0.75 to 1.16). About 10% of the bosentan group showed meaningful increases in hepatic transaminases, but none had acute or chronic liver failure.

CONCLUSIONS

Bosentan did not improve the clinical course or natural history of patients with severe chronic heart failure and but caused early and important fluid retention.

Na+-H+ exchanger and proton channel in heart failure associated with Becker and Duchenne muscular dystrophies

Cardiomyopathy is found in patients with Duchenne (DMD) and Becker (BMD) muscular dystrophies, which are linked muscle diseases caused by mutations in the dystrophin gene. Dystrophin defects are not limited to DMD but are also present in mild BMD. The hereditary cardiomyopathic hamster of the UM-X7.1 strain is a particular experimental model of heart failure (HF) leading to early death in muscular dystrophy (dystrophin deficiency and sarcoglycan mutation) and heart disease (δ-sarcoglycan deficiency and dystrophin mutation) in human DMD. Using this model, our previous work showed a defect in intracellular sodium homeostasis before the appearance of any apparent biochemical and histological defects. This was attributed to the continual presence of the fetal slow sodium channel, which was also found to be active in human DMD. Due to muscular intracellular acidosis, the intracellular sodium overload in DMD and BMD was also due to sodium influx through the sodium-hydrogen exchanger NHE-1. Lifetime treatment with an NHE-1 inhibitor prevented intracellular Na⁺ overload and early death due to HF. Our previous work also showed that another proton transporter, the voltage-gated proton channel (Hv1), exists in many cell types including heart cells and skeletal muscle fibers. The Hv1 could be indirectly implicated in the beneficial effect of blocking NHE-1.

Clinical and Hemodynamic Effects of Endothelin Receptor Antagonists in Patients With Heart Failure

The clinical benefit of endothelin receptor antagonists (ERA) for the management of heart failure (HF) remains controversial. To examine this question, we performed a meta-analysis of randomized controlled trials (RCTs) to investigate the clinical and hemodynamic effects of ERA in HF patients.We searched the PubMed, Medline, Embase, and Cochrane Library from inception to March 20, 2016 to identify the pertinent studies. Risk ratio (RR) and weighted mean difference (WMD) were calculated using a fixed or random effect model.A total of 15 RCTs with 3,624 HF patients were included. Compared with control groups, ERA might not improve the mortality (RR 1.12, 95%CI 0.81 to 1.54, P = 0.51) or incidence of worsening HF or cardiovascular events (WHF/ CVE) (RR 1.06, 95%CI 0.94 to 1.19, P = 0.35) in HF patients. Subgroup analysis also suggested that neither nonselective nor selective ERAs had an impact on mortality and WHF/CVE. However, the hemodynamic variables of HF patients, including cardiac index (WMD 0.32, 95%CI 0.22 to 0.43, P < 0.01), pulmonary capillary wedge pressure (WMD -3.10, 95%CI -3.99 to -2.20, P < 0.01), mean pulmonary arterial pressure (WMD -4.42, 95%CI -5.50 to -3.33, P < 0.01), systemic vascular resistance (WMD -276.35, 95%CI -399.62 to -153.09, P < 0.01), and pulmonary vascular resistance (WMD -69.42, 95%CI -105.33 to -33.52, P < 0.01) were significantly improved by ERA.In conclusion, this meta-analysis suggests that ERA therapy could effectively improve cardiac output and pulmonary and systemic hemodynamics, but with less benefit to the clinical outcomes of HF patients.

Deranged Cardiac Metabolism and the Pathogenesis of Heart Failure

Activation of the neuro-hormonal system is a pathophysiological consequence of heart failure. Neuro-hormonal activation promotes metabolic changes, such as insulin resistance, and determines an increased use of non-carbohydrate substrates for energy production. Fasting blood ketone bodies as well as fat oxidation are increased in patients with heart failure, yielding a state of metabolic inefficiency. The net result is additional depletion of myocardial adenosine triphosphate, phosphocreatine and creatine kinase levels with further decreased efficiency of mechanical work. In this context, manipulation of cardiac energy metabolism by modification of substrate use by the failing heart has produced positive clinical results. The results of current research support the concept that shifting the energy substrate preference away from fatty acid metabolism and towards glucose metabolism could be an effective adjunctive treatment in patients with heart failure. The additional use of drugs able to partially inhibit fatty acids oxidation in patients with heart failure may therefore yield a significant protective effect for clinical symptoms and cardiac function improvement, and simultaneously ameliorate left ventricular remodelling. Certainly, to clarify the exact therapeutic role of metabolic therapy in heart failure, a large multicentre, randomised controlled trial should be performed.

Essential role of sympathetic endothelin A receptors for adverse cardiac remodeling

In preclinical studies, endothelin receptor A (ETA) antagonists (ETAi) attenuated the progression of heart failure (HF). However, clinical HF trials failed to demonstrate beneficial effects of ETAi. These conflicting data may be explained by the possibility that established HF drugs such as adrenergic receptor blockers interfered with the mechanism of ETAi action in clinical trials. Here we report that mice lacking ETA only in sympathetic neurons (SN-KO) showed less adverse structural remodeling and cardiac dysfunction in response to pathological pressure overload induced by transverse aortic constriction (TAC). In contrast, mice lacking ETA only in cardiomyocytes (CM-KO) were not protected. TAC led to a disturbed sympathetic nerve function as measured by cardiac norepinephrine (NE) tissue levels and [(124)I]-metaiodobenzylguanidine-PET, which was prevented in SN-KO. In a rat model of HF, ETAi improved cardiac and sympathetic nerve function. In cocultures of cardiomyocytes (CMs) and sympathetic neurons (SNs), endothelin-1 (ET1) led to a massive NE release and exaggerated CM hypertrophy compared with CM monocultures. ETA-deficient CMs gained a hypertrophic response through wild-type SNs, but ETA-deficient SNs failed to mediate exaggerated CM hypertrophy. Furthermore, ET1 mediated its effects indirectly via NE in CM-SN cocultures through adrenergic receptors and histone deacetylases, resulting in activation of the prohypertrophic transcription factor myocyte enhancer factor 2. In conclusion, sympathetic ETA amplifies ET1 effects on CMs through adrenergic signaling pathways. Thus, antiadrenergic therapies may blunt potentially beneficial effects of ETAi. Taken together, this may indicate that patients with β blocker intolerance or disturbed sympathetic nerve function could be evaluated for a potential benefit from ETAi.

Effects of selective endothelin (ET)-A receptor antagonist versus dual ET-A/B receptor antagonist on hearts of streptozotocin-treated diabetic rats

AIMS

The aim was to study the differences in the effectiveness of two types of endothelin (ET) receptor antagonists (selective ET-A or dual ET-A/B antagonists) on the hearts of streptozotocin (STZ)-induced diabetic rats (type I diabetes) at functional and biochemical/molecular levels.

MAIN METHODS

Citrate saline (vehicle) or STZ was injected into rats. The ET-A/B dual receptor antagonist (SB209670, 1mg/kg/day) and the ET-A receptor antagonist (TA-0201, 1mg/kg/day) were then administered to these rats. One week after injection, the animals were separated into those receiving SB209670, TA-0201 or vehicle by 4-week osmotic mini-pump.

KEY FINDINGS

The VEGF level and percent fractional shortening in the diabetic heart were significantly decreased compared to the non-diabetic heart, whereas SB209670 and TA-0201 treatments greatly and comparably prevented this decrease. SB209670 treatment was more effective in reversing decreased expressions of KDR and phosphorylated AKT, downstream of VEGF angiogenic signaling, than TA-0201 treatment. The eNOS levels in hearts were significantly higher in diabetic rats than in healthy rats, and this increase was significantly reduced by TA-0210 but not by SB209670 treatment.

SIGNIFICANCE

Improvement of KDR mRNA and pAKT levels by SB209670 but not TA-0201 suggests that dual ET-A/-B blockade may be effective in improving intracellular systems of these components in the diabetic rat heart. However, the present study also showed that TA-0201 or SB209670 improved percent fractional shortening and VEGF levels of the diabetic hearts to a similar extent, suggesting that ET-A blockade and dual ET-A/-B blockade are similarly effective in improving cardiac dysfunction in the diabetic rats.

The role of endothelin-1 in the sympathetic nervous system in the heart

Endothelin-1 (ET1) is a peptide that was initially identified as a strong inductor of vascular contraction. In the last 25 years, there have been several biological processes identified in which ET1 seems to play a critical role. In particular, genetic studies have unveiled that ET1 is important for neuronal development, growth and function. Experimental studies identified ET1 as a regulator of the interaction between sympathetic neurons and cardiac myocytes. This might be of clinical importance since patients suffering from heart failure are characterized by disrupted norepinephrine homeostasis in the heart. This review summarizes the important findings on the role of ET1 for sympathetic neurons and norepinephrine homeostasis in the heart.

Pulmonary hypertension in canine degenerative mitral valve disease

Pulmonary hypertension secondary to degenerative mitral valve disease has been recognized clinically for many years in veterinary medicine, and clinical diagnosis of this syndrome in dogs has been enhanced greatly by widespread use of echocardiography and Doppler echocardiography. Medical therapy is now available to treat this clinical complication of mitral valve disease, making timely diagnosis even more important to patient longevity and quality of life.

Noninvasive detection of left-ventricular systolic dysfunction by acoustic cardiography in atrial fibrillation

Objectives. Assessment of left ventricular (LV) systolic function in patients with atrial fibrillation can be difficult. Acoustic cardiography provides several parameters for quantifying LV systolic function. We evaluated the ability of acoustic cardiography to detect LV systolic dysfunction in patients with and without atrial fibrillation. Design. We studied 194 patients who underwent acoustic cardiography and cardiac catheterization including measurement of angiographic ejection fraction (EF) and maximum LV dP/dt. LV systolic dysfunction was defined as LV maximum dP/dt <1600 mmHg/s. Acoustic cardiographic parameters included electromechanical activation time (EMAT) and the systolic dysfunction index (SDI). Results. Acoustic cardiography detected systolic dysfunction with high specificity and moderate sensitivity with similar performance to EF (sensitivity/specificity without afib: EMAT 30/96, SDI 40/90, EF at 35% 30/96; sensitivity/specificity with afib: EMAT 64/82, SDI 59/100, EF at 35% 45/82). Conclusions. Acoustic cardiography can be used for diagnosis of LV systolic dysfunction in atrial fibrillation.

Cardioprotective signaling by endothelin

The endothelin axis promotes vasoconstriction, suggesting that antagonists of endothelin signaling might be useful in treatment of heart failure. However, promising results from animal trials have not been recapitulated in heart failure patients. Here we review the role of major signaling pathways in the heart that are involved in cell survival initiated by ET-1. These pathways include mitogen-activated protein kinase, phosphatidyl inositol-1,4,5-triphosphate kinase (PI3K-AKT), nuclear factor-kappaB (NF-kappaB), and calcineurin signaling. A better understanding of endothelin-mediated signaling in cardiac cell survival may allow a reevaluation of endothelin receptor antagonists (ETRAs) in the treatment of heart failure.

Decreased FKBP12.6 expression and enhanced endothelin receptor signaling associated with arrhymogenesis in myocardial infarction rats

An increased propensity towards cardiac arrhythmias and aggravated heart function is observed in myocardial infarction (MI), the development of which is associated with the calcium handling system in the myocardium. It was hypothesized that the abnormal changes in the MI model may be a consequence of the abnormal expression and function of the RyR2-FKBP12.6 channel complex and that these abnormalities may be related to an over-activated endothelin (ET) system. Salvianolic acid B is expected to suppress life-threatening arrhythmias and to restore the abnormality of the RyR2-FKBP12.6 complex in rats. MI was produced by ligating the coronary artery for 4 weeks. Salvianolic acid B (100 mg/kg/day, p.o. for 4 weeks) was administered to rats 0.5 h before surgery. Measurements of cardiac arrhythmias, cardiac function, calcium transient, cardiac calcium release channel handling proteins and the endothelin system were conducted. The aggravated arrhythmia and compromised cardiac function in MI rats was accompanied by elevated diastolic Ca(2+) levels in the cytosol and a significant down-regulation of expression of RyR2-FKBP12.6. These were closely linked with an over-activated ET pathway in the myocardium. After a 4-week treatment with salvianolic acid B, all abnormalities were reversed significantly. Salvianolic acid B was capable of normalizing FKBP12.6 expression levels and decreasing the propensity towards arrhythmias by attenuating the up-regulated ET pathway.

Downregulated FKBP12.6 expression and upregulated endothelin signaling contribute to elevated diastolic calcium and arrhythmogenesis in rat cardiomyopathy produced by l-thyroxin

BACKGROUND

Dissociation of FKBP12.6 from RyR2 is considered as an important molecular event resulting in calcium leak and an increased risk in arrhythmogenesis. We hypothesized that augmented ventricular fibrillation (VF) on reperfusion of rat cardiomyopathy induced by l-thyroxin may result from elevated diastolic Ca(2+) levels due to dissociation (downregulation) of FKBP12.6 and upregulation of endothelin (ET-1) signaling pathway.

METHODS

Rats were treated with l-thyroxin (0.4 mg/kg, s.c.) for 10 days. Dajisentan (CPU0213), a dual endothelin receptor antagonist (100 mg/kg p.o.), or propranolol was administered on day 6 to 10. Susceptibility to VF was evaluated on ischemia/reperfusion episode. mRNA expression of FKBP12.6, and ET-1 levels were determined. Calcium transients and FKBP12.6 immunohistochemistry were measured by confocal microscopy in isolated cardiomyocytes from cardiomyopathy.

RESULTS

Cardiomyopathy induced by l-thyroxin resulted in an increased susceptibility to VF on ischemia/reperfusion. Upregulated mRNA expression of RyR2 and PKA in association with downregulated FKBP12.6 expression was found in l-thyroxin-treated rats compared to controls. Calcium transients evoked by field electrical stimulation showed an increase in Ca(2+) by +75% during diastole. An increase in ET-1 (ng/mg protein) (+36.6%) and mRNA abundance of preproET-1 were found in the left ventricle. A decreased mRNA ratio of FKBP12.6 to RyR2 likely reflected dissociation of FKBP12.6 in cardiomyopathy. These changes were normalized by Dajisentan, comparable to propranolol.

CONCLUSION

Increased susceptibility to VF in l-thyroxin-induced cardiomyopathy is related to increase in diastolic Ca(2+) levels, resulting from downregulated FKBP12.6 and upregulated ET system. ET antagonism might be useful in settings of FKBP12.6 dissociation.

Nonselective ETA/ETB-receptor blockade increases systemic blood pressure of Bio 14.6 cardiomyopathic hamstersThis article is one of a selection of papers published in the special issue (part 1 of 2) on Forefronts in Endothelin

To examine the role of endothelin ETA and ETB receptors in congestive heart failure due to cardiomyopathy, the effect of chronic treatment with selective ETA- and ETB-receptor antagonists (atrasentan and A-192621, respectively), alone and in combination, was assessed on functional and biochemical parameters of 52-week-old Bio 14.6 cardiomyopathic hamsters. Compared with control animals, cardiomyopathic hamsters treated for 9 weeks with atrasentan showed no variation in MAP; however, selective ETB- and combined nonselective ETA- and ETB-receptor antagonists increased systemic blood pressure. After selective ETB-receptor blockade, plasma endothelin levels were augmented. Importantly, this increase was highly enhanced (more than 8-fold) by concomitant ETA-receptor antagonism. Furthermore, the left ventricle : body weight ratio of cardiomyopathic hamsters treated with A-192621, alone or in combination with atrasentan, was significantly increased. On the other hand, decreased left ventricular end-diastolic pressure was observed in cardiomyopathic hamsters after selective ETA- or combined nonselective ETA/ETB-receptor antagonism, while only selective ETA-receptor blockade reduced left ventricular endothelin levels. Our results suggest that, in congestive heart failure, ETB receptors are essential to limit circulating endothelin levels, which may argue for improved cardiac benefits after long-term treatment with highly selective ETA-receptor antagonists.

Examination of mRNA expression in rat hearts and lungs for analysis of effects of exposure to concentrated ambient particles on cardiovascular function

Epidemiological studies have suggested that fine particulate matter (f-PM) is associated with adverse effects on cardiovascular health. However, these effects on the cardiovascular system have not yet been fully elucidated. Using mRNA expression and correlation analyses, we designed the present study to elucidate (1) translocation of chemicals in inhaled f-PM to the heart, (2) induction of oxidative stress, one of the causes of cardiovascular diseases (CVDs), (3) mRNA expression related to CVDs, and (4) correlations among mRNA expression of various molecules and cardiovascular function. Wistar Kyoto male rats were exposed to concentrated ambient particles (CAPs, 0.6-1.5mg/m3) in Yokohama for 4 days (4.5h/day) or to filtered air for 3 days and CAPs for 1 day or to filtered air for 4 days. Messenger RNA expression and cardiovascular function were measured after the 4-day exposure. In samples of heart tissue, the mRNAs of cytochrome P450 (CYP) 1B1, a biomarker of exposure to chemicals; heme oxygenase-1 (HO-1), a marker of oxidative stress; and endothelin A (ET A) receptor, a receptor of vasoconstrictors, were up-regulated by CAPs; their levels were significantly correlated with the cumulative weight of CAPs in the exposure chamber. The up-regulation of ET A receptor mRNA was significantly correlated with the increase in HO-1 mRNA and weakly with the increase in mean blood pressure (Delta MBP). These results suggest the possibility that chemicals in CAPs might be translocated to the heart, where they induce oxidative stress and activate endothelin signaling, resulting in an increase in the blood pressure. The exposure to f-PM might thus affect cardiovascular function through activation of endothelin signaling.

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.

Cardiac sympathetic nerve terminal function in congestive heart failure

Increased cardiac release of norepinephrine (NE) and depleted cardiac stores of NE are two salient features of the human failing heart. Researches from my laboratory have shown that these changes are accompanied by a functional defect of NE uptake in the cardiac sympathetic nerve terminals. Our studies have shown that the decrease of NE uptake is caused by reduction of NE transporter density in the sympathetic nerve endings, and this change is responsible, at least in part, for the increased myocardial interstitial NE, decreased myocardial adrenoceptor density, and increased myocyte apoptosis in experimental cardiomyopathies. We have also provided evidence in both intact animals and cultured PC12 cells that the decrease of NE transporter is induced by the actions of oxidative metabolites of exogenous NE, involving endoplasmic reticulum stress and impaired N-glycosylation of the NE transporter. This change in the cardiac sympathetic NE uptake function, as demonstrated by [123I] metaiodobenzylguanidine in human studies, may not only serve as an important prognostic variable in patients with congestive heart failure, but also be used as a surrogate for the efficacies of various therapeutic interventions for heart failure. Finally, increasing evidence suggests and further studies are needed to show that the cardiac sympathetic nerve terminal function may be a direct target for pharmacologic treatment of congestive heart failure.

Inhibition of free fatty acids metabolism as a therapeutic target in patients with heart failure

Recent studies have evidenced that alterations of cardiac metabolism can be present in several cardiac syndromes. In heart failure, wasting of subcutaneous fat and skeletal muscle is relatively common and suggests an increased utilisation of non-carbohydrate substrates for energy production. In fact, fasting blood ketone bodies as well as fat oxidation during exercise have been shown to be increased in patients with heart failure. This metabolic shift determines a reduction of myocardial oxygen consumption efficiency. A direct approach to manipulate cardiac energy metabolism consists in modifying substrate utilisation by the heart. To date, the most effective metabolic treatments include several pharmacological agents that directly inhibit fatty acid oxidation. Clinical studies have shown that these agents can substantially increase the ischaemic threshold in patients with effort angina. However, the results of current research is also supporting the concept that shifting the energy substrate preference away from fatty acid metabolism and towards glucose metabolism could be an effective adjunctive treatment in patients with heart failure, in terms of left ventricular function and glucose metabolism improvement. In fact, these agents have also been shown to improve overall glucose metabolism in diabetic patients with left ventricular dysfunction. In this paper, the recent literature on the beneficial therapeutic effects of modulation of cardiac metabolic substrates utilisation in patients with heart failure is reviewed and discussed.

Contributory role of VEGF overexpression in endothelin-1-induced cardiomyocyte hypertrophy

Although endothelin-1 (ET-1) stimulates vascular endothelial growth factor (VEGF) expression in a variety of cells, including endothelial cells and vascular smooth muscle cells, the effects of ET-1 on expression of VEGF and its receptors in cardiomyocytes are unknown. In the present study, we found that treatment of neonatal rat cardiomyocytes with ET-1 for 24 h resulted in upregulation of VEGF and its two principal receptors, fetal liver kinase 1 and fms-like tyrosine kinase 1, in a concentration-dependent manner (10(-12) to 10(-6) M). ET-1 treatment also caused significant cardiomyocyte hypertrophy, as indicated by increases in cell surface area and [(14)C]leucine uptake by cardiomyocytes. Treatment with TA-0201 (10(-6) M), an ET(A)-selective blocker, eliminated ET-1-induced overexpression of VEGF and its receptors as well as cardiomyocyte hypertrophy. Treatment with VEGF neutralizing peptides (5-10 mug/ml) partially but significantly inhibited ET-1-induced cardiomyocyte hypertrophy. These results suggest that ET-1 treatment of cardiomyocytes promotes overexpression of VEGF and its receptors via activation of ET(A) receptors, and consequently the upregulated VEGF signaling system appears to contribute, at least in part, to ET-1-induced cardiomyocyte hypertrophy.

Modulation of the transient outward K+ current by inhibition of endothelin-A receptors in normal and hypertrophied rat hearts

Inhibition of endothelin-A (ET(A)) receptors has been shown to reduce ventricular electrical abnormalities associated with cardiac failure. In this study, we investigate the effect of ET(A)-receptor inhibition on the development of regional alterations of the transient outward K(+) current (I (to)) in the setting of pressure-induced left ventricular (LV) hypertrophy. Cardiac hypertrophy was induced in female Sprague-Dawley rats by stenosis of the ascending aorta (AS) for 7 days. Treatment with the selective ET(A)-receptor antagonist darusentan (LU135252, 35 mg [kg body weight](-1) day(-1)) was started 1 day before the surgery. AS induced a 46% increase in the relative LV weight (p < 0.001) and caused a significant reduction in I (to) (at +40 mV) in epicardial myocytes (19.5 +/- 1.2 pA pF(-1), n = 32 vs 23.2 +/- 1.2 pA pF(-1), n = 35, p < 0.05). Darusentan further reduced I (to) in AS (15.4 +/- 1.3 pA pF(-1), n = 37, p < 0.05) and sham-operated animals (19.8 +/- 1.6 pA pF(-1), n = 48, ns.). The effects of AS and darusentan on I (to) were significant and independent as tested by two-way analysis of variance. I (to) was not affected in endocardial myocytes. These results indicate that endothelin-1 may exert a tonic effect on the magnitude of I (to) in the epicardial region of the left ventricle but that ET(A)-receptor activation is not necessary for the development of electrical alterations associated with pressure-induced hypertrophy.

ETBreceptor dependent alteration in aortic responses to ET-1 in the cardiomyopathic hamsterThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference

The aim of this study was to verify whether an alteration in the aortic endothelin-1 (ET-1) response takes place in UM-X7.1 cardiomyopathic hamsters. Our results showed that ET-1 (10−12– 10−5 mol/L) induces dose-dependent sustained increases in tension in the intact and endothelium denuded aortas from both normal and cardiomyopathic hamsters. The EC50values of ET-1 of both intact and endothelium denuded aortas of normal hamsters were similar (2.2 × 10−9 mol/L and 1.8 × 10−9 mol/L, respectively). However, in cardiomyopathic hamsters, the EC50of ET-1 in intact aortas was higher (1.5 × 10−8 mol/L) than that of the endothelium denuded preparations (2.7 × 10−9 mol/L). The EC50of ET-1 in normal and cardiomyopathic hamster denuded aortas were similar. However, the EC50of ET-1 in intact aortas of cardiomyopathic hamster was higher (1.5 × 10−8 mol/L) than that of normal hamsters (2.2 × 10−9 mol/L). Pre-treatment with the ETAreceptor antagonist ABT-627 (10−5 mol/L) of intact and endothelium denuded aortas from both normal and cardiomyopathic hamsters significantly prevented ET-1 (10−7 mol/L) from inducing an increase in tension. Pre-treatment with the ETBreceptor antagonist A-192621 (10−5 mol/L) had no effect on the ET-1-induced increase in tension in endothelium denuded aortas of both normal and cardiomyopathic hamsters, as well as in intact preparations of normal animals. However, blockade of the ETBreceptors in intact aortas of cardiomyopathic hamsters significantly (p < 0.001) potentiated the ET-1-induced increase in tension. In summary, an attenuation of the contraction response to ET-1 was found in UM-X7.1 cardiomyopathic hamsters when compared with normal age-matched hamsters. This alteration of the ET-1 effect in the aortas of cardiomyopathic hamsters seems to be dependent on the presence of the endothelium and could be due, in part, to an increase in the contribution of endothelial ETBreceptors to relaxation, which in turn acts as a physiological depressor of ET-1 vasoconstriction. Our results suggest that an increase in the endothelium ETBreceptor density may play a role in the development of hypotension in UM-X7.1 cardiomyopathic hamsters.

Endothelin receptor antagonists

Endothelin receptor antagonists (ERAs) have been developed to block the effects of endothelin-1 (ET-1) in a variety of cardiovascular conditions. ET-1 is a powerful vasoconstrictor with mitogenic or co-mitogenic properties, which acts through the stimulation of 2 subtypes of receptors [endothelin receptor subtype A (ETA) and endothelin receptor subtype B (ETB) receptors]. Endogenous ET-1 is involved in a variety of conditions including systemic and pulmonary hypertension (PH), congestive heart failure (CHF), vascular remodeling (restenosis, atherosclerosis), renal failure, cancer, and cerebrovascular disease. The first dual ETA/ETB receptor blocker, bosentan, has already been approved by the Food and Drug Administration for the treatment of pulmonary arterial hypertension (PAH). Trials of endothelin receptor antagonists in heart failure have been completed with mixed results so far. Studies are ongoing on the effects of selective ETA antagonists or dual ETA/ETB antagonists in lung fibrosis, cancer, and subarachnoid hemorrhage. While non-peptidic ET-1 receptor antagonists suitable for oral intake with excellent bioavailability have become available, proven efficacy is limited to pulmonary hypertension, but it is possible that these agents might find a place in the treatment of several cardiovascular and non-cardiovascular diseases in the coming future.

Walnuts reduce aortic ET-1 mRNA levels in hamsters fed a high-fat, atherogenic diet

Walnut consumption is associated with reduced coronary vascular disease (CVD) risk; however, the mechanisms responsible remain incompletely understood. Recent clinical studies suggested that these mechanisms involve non-plasma lipid-related effects on endothelial function. Male Golden Syrian hamsters (12 groups, n=10-15) were fed for 26 wk atherosclerotic, high-fat, hyperlipidemic diets with increasing concentrations of whole walnuts (61-150 g/kg diet), or alpha-tocopherol (alpha-T, 8.1-81 mg/kg diet) and single diets with either walnut oil (32 g/kg diet) or pure gamma-tocopherol (gamma-T; 81 mg/kg diet) added. Aortic endothelin 1 (ET-1), an important endothelial regulator, was assayed as mRNA. Aortic cholesterol ester (CE) concentration along with other vascular stress markers (Cu/Zn and Mn superoxide dismutase, biliverdin reductase) and plasma lipid concentrations were determined. Hyperlipidemia (plasma LDL cholesterol approximately 6 times normal) occurred in all groups. Aortic CE concentration, a measure of atherosclerotic plaque, was highest in the lowest alpha-T only group and declined significantly with increasing alpha-T. The aortic CE of all walnut groups was decreased significantly relative to the lowest alpha-T only group but showed no dose response. The diets did not produce changes in the other vascular stress markers, whereas aortic ET-1 mRNA levels declined dramatically with increasing dietary walnuts (to a 75% reduction in the highest walnut content group compared with the lowest alpha-T group) but were unaltered in the alpha-T groups or gamma-T group. The study results are consistent with those of human walnut feeding studies and suggest that the mechanisms underlying those results are mediated in part by ET-1-dependent mechanisms. The contrasting results between the alpha-tocopherol or gamma-tocopherol diets and the walnut diets also make it unlikely that the non-plasma lipid-related CVD effects of walnuts are due to their alpha-tocopherol or gamma-tocopherol content. Finally, the results indicate that the walnut fat compartment is a likely location for the components responsible for the reduced aortic CE concentration.

Characterizing the role of endothelin-1 in the progression of cardiac hypertrophy in aryl hydrocarbon receptor (AhR) null mice

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor characterized to play a role in detection and adaptation to environmental stimuli. Genetic deletion of AhR results in hypertension, and cardiac hypertrophy and fibrosis, associated with elevated plasma angiotensin II (Ang II) and endothelin-1 (ET-1), thus AhR appears to contribute to cardiovascular homeostasis. In these studies, we tested the hypothesis that ET-1 mediates cardiovascular pathology in AhR null mice via ETA receptor activation. First, we determine the time courses of cardiac hypertrophy, and of plasma and tissue ET-1 expression in AhR wildtype and null mice. AhR null mice exhibited increases in heart-to-body weight ratio and age-related expression of cardiac hypertrophy markers, beta-myosin heavy chain (beta-MHC), and atrial natriuretic factor (ANF), which were significant at 2 months. Similarly, plasma and tissue ET-1 expression was significantly elevated at 2 months and increased further with age. Second, AhR null mice were treated with ETA receptor antagonist, BQ-123 (100 nmol/kg/day), for 7, 28, or 58 days and blood pressure, cardiac fibrosis, and cardiac hypertrophy assessed, respectively. BQ-123 for 7 days significantly reduced mean arterial pressure in conscious, catheterized mice. BQ-123 for 28 days significantly reduced the histological appearance of cardiac fibrosis. Treatment for 58 days significantly reduced cardiac mass, assessed by heart weight, echocardiography, and beta-MHC and ANF expression; and reduced cardiac fibrosis as determined by osteopontin and collagen I mRNA expression. These findings establish ET-1 and the ETA receptor as primary determinants of hypertension and cardiac pathology in AhR null mice.

Concomitant antagonism of endothelial and vascular smooth muscle cell ETB receptors for endothelin induces hypertension in the hamster

In the vascular system, endothelin (ET) type B (ET(B)) receptors for ET-1 are located on endothelial and on venous and arterial smooth muscle cells. In the present study, we investigated the hemodynamic effects of chronic ET(B) receptor blockade at low and high doses in the Syrian Golden hamster. After 16 days of gavage with A-192621 (0.5 or 30 mg.kg(-1).day(-1)), a selective ET(B) receptor antagonist, hamsters were anesthetized with a mixture of ketamine and xylazine (87 and 13 mg/kg im, respectively), and basal mean arterial blood pressure (MAP) and pressor responses to exogenous ET-1 were evaluated. The lower dose of A-192621 (0.5 mg.kg(-1).day(-1)) did not modify basal MAP, whereas the higher dose (30 mg.kg(-1).day(-1)) increased MAP and plasma ET levels. Radio-telemetry recordings confirmed the increase in MAP induced by the higher dose of A-192621 in conscious hamsters. On the other hand, although the lower dose of A-192621 was devoid of intrinsic pressor effects, it markedly reduced the transient hypotensive phase induced by intravenously injected IRL-1620, a selective ET(B) receptor agonist. Finally, A-192621 (0.5 mg.kg(-1).day(-1)) alone or A-192621 (30 mg.kg(-1).day(-1)) + atrasentan (6 mg.kg(-1).day(-1)), a selective ET(A) receptor antagonist, potentiated the pressor response to exogenous ET-1. Our results suggest that, in the hamster, ET(B) receptors on vascular smooth muscle cells are importantly involved in the clearance of endogenous ET-1, whereas the same receptor type on the endothelium is solely involved in the vasodilatory responses to the pressor peptide. Blockade of endothelial and vascular smooth muscle cell ET(B) receptors triggers a marked potentiation of ET(A)-dependent increases in systemic resistance.

Clinical effects of endothelin receptor antagonism with bosentan in patients with severe chronic heart failure: results of a pilot study

BACKGROUND

Endothelin receptor antagonism produces favorable short-term hemodynamic effects in heart failure, but the clinical effects of longer term therapy have not been evaluated.

METHODS AND RESULTS

Three hundred and seventy patients with symptoms of heart failure at rest or on minimal exertion and a left ventricular ejection fraction <35% were randomly assigned (double-blind) to placebo (n = 126) or the endothelin receptor antagonist bosentan, titrated slowly (n = 121) or rapidly (n = 123) to a target dose of 500 mg twice daily. Treatment with the study drug was to be maintained for 26 weeks, whereas background medications for heart failure were kept constant. Safety concerns led to early termination of the trial when only 174 patients had had an opportunity to complete 26 weeks of therapy. Bosentan exerted no apparent benefit when all randomized patients were analyzed (P = .709). However, in the first 174 patients who were recruited at least 26 weeks before study termination and who could therefore be followed for the planned duration of the trial, patients in the bosentan groups were more likely to be improved (26% versus 19%) and were less likely to be worse (28% versus 43%), P = .045. When compared with placebo-treated patients, bosentan-treated patients had a increased risk of heart failure during the first month of treatment but a decreased risk of heart failure during the fourth, fifth, and sixth months of therapy. The major noncardiac adverse effects of bosentan included an increase in hepatic transaminases (in 15.6% of patients) and a decrease in hemoglobin (of about 1 g/L).

CONCLUSION

Although bosentan exerted no favorable effects in the overall study, our findings suggest that the clinical responses to endothelin antagonism with bosentan in patients with severe chronic heart failure may be dependent on the duration of treatment.

Selective Endothelin ETB Receptor Antagonist Improves Left Ventricular Function but Exaggerates Degeneration of Cardiomyocytes in J2N-k Hamsters

BACKGROUND

Endothelin-1 (ET-1) receptor antagonist is expected to improve the prognosis of patients with heart failure, but the role of the ET(B) receptor in cardiac function and structure is complicated. In the present study the NADPH diaphorase activity and ET-1 content in the failing heart treated with ET(A) or ET(B) receptor antagonist were evaluated in a model of dilated cardiomyopathy.

METHODS AND RESULTS

Selective ET(A) receptor antagonist, ABT-627 (10 mg/kg per day), or selective ET(B) antagonist, A-192621 (30 mg/kg per day), was given to 22-week-old J2N-k cardiomyopathic hamsters for 8 weeks. The effects of ABT-627 and A-192621 on cardiac function, left ventricular (LV) histology, ET-1 content and NADPH diaphorase activity in the LV were evaluated. Treatment with ABT-627, but not A-192621, significantly decreased ET-1 content and NADPH diaphorase activity. Although the improvement of LV function was modest, ABT-627 prevented tissue damage in J2N-k hamsters. In contrast, A-192621 worsened the degeneration of cardiomyocytes despite improving hemodynamic parameters.

CONCLUSIONS

Selective ET(A) antagonist, but not ET(B) antagonist, reduced the ET-1 content as well as the NADPH diaphorase activity, and preserved the fine structure of LV myocardium in cardiomyopathic hamsters. Long-term blockade of ET(B) receptor might worsen the degeneration of cardiomyocytes through the ET-1/ET(A) system even if LV function could be improved.

The role of endothelin-1 in myocarditis and inflammatory cardiomyopathy: old lessons and new insights

Endothelin-1 has emerged as an important participant in the pathophysiology of a variety of cardiovascular diseases, where it may act on endocrine, paracrine and autocrine bases. Here we review its regulated biosynthesis, receptor-mediated signaling, and functional consequences in the heart, with particular emphasis on cardiac development and disease. Exploring published data employing molecular genetic mouse models of endothelin dysregulation, we highlight its heretofore underappreciated role as a pro-inflammatory cytokine. We also present novel micro-array data from one such mouse model, which implicate the specific downstream pathways that may mediate endothelin-1's effects.Key words: endothelin-1, cardiac development, inflammation, transgenic mice, gene expression profiling.

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.

Myocardial fibrosis and diastolic dysfunction in deoxycorticosterone acetate-salt hypertensive rats is ameliorated by the peroxisome proliferator-activated receptor-alpha activator fenofibrate, partly by suppressing inflammatory responses associated with the nuclear factor-kappa-B pathway

OBJECTIVES

We sought to clarify that a peroxisome proliferator-activated receptor-alpha (PPAR-alpha) activator inhibits myocardial fibrosis and its resultant diastolic dysfunction in hypertensive heart disease, as well as to investigate whether inflammatory mediators through the nuclear factor (NF)-kappa-B pathway are involved in the effects.

BACKGROUND

Patients with hypertensive heart disease often have diastolic heart failure without systolic dysfunction. Meanwhile, it has been well established in atherosclerosis that PPAR-alpha activation negatively regulates early inflammation. In hypertensive hearts, however, it is still unclear whether PPAR-alpha activation inhibits inflammation and fibrosis.

METHODS

Twenty-one rats were randomly separated into the following three groups: deoxycorticosterone acetate (DOCA)-salt hypertensive rats treated with a PPAR-alpha activator, fenofibrate (80 mg/kg/day for 5 weeks); DOCA-salt rats treated with vehicle only; and uni-nephrectomized rats as normotensive controls.

RESULTS

Fenofibrate significantly inhibited the elevation of left ventricular end-diastolic pressure and the reduction of the magnitude of the negative maximum rate of left ventricular pressure rise and decline, corrected by left ventricular pressure (-dP/dt(max)/P), which are indicators of diastolic dysfunction. Next, fenofibrate prevented myocardial fibrosis and reduced the hydroxyproline content and procollagen I and III messenger ribonucleic acid expression. Finally, inflammatory gene expression associated with NF-kappa-B (interleukin-6, cyclooxygenase-2, vascular cell adhesion molecule-1, and monocyte chemoattractant protein-1), which is upregulated in DOCA-salt rats, was significantly suppressed by fenofibrate. Activation of NF-kappa-B and expression of I-kappa-B-alpha in DOCA-salt rats were normalized by fenofibrate.

CONCLUSIONS

A PPAR-alpha activator reduced myocardial fibrosis and prevented the development of diastolic dysfunction in DOCA-salt rats. The effects of a PPAR-alpha activator may be mediated partly by prevention of inflammatory mediators through the NF-kappa-B pathway. These results suggest that treatment with PPAR-alpha activators will improve diastolic dysfunction in hypertensive heart disease.

The endothelin receptor antagonist ameliorates the hypertensive phenotypes of transgenic hypertensive mice with renin-angiotensin genes and discloses roles of organ specific activation of endothelin system in transgenic mice

Endothelin (ET)-1 and ET-2 are potent vasoconstrictor peptides with mitogenic activity. In this study, we investigated roles of ET system in renin-angiotensin system (RAS)-mediated hypertension, using transgenic hypertensive mice (THM) with over-expression of both human renin and angiotensinogen genes. In the first step, it was revealed that expression of ET system was locally enhanced, i.e. increases in cardiac preproET-1 mRNA and renal preproET-2 mRNA in THM, compared with the control (wild type) mice. In the next step, we studied the chronic effects of an ET antagonist (SB209670) on THM. Blood pressure (BP) in THM was significantly higher than that in the normal mice during the investigation. However, in the later phase of the study, from 12 to 20 weeks of treatment, THM receiving SB 209670 showed significantly lower BP than that in THM receiving saline. SB 209670 treatment for 20 weeks significantly attenuated phenotypes of cardiac hypertrophy, vascular wall thickening and hypertensive nephropathy observed in THM, suggesting that the ETA/B receptor antagonist is also effective even in the extraordinarily activated RAS condition. These findings suggest that organ specifically activated ET system in THM develops the phenotypes, hypertension, cardiac hypertrophy, and hypertensive nephropathy.

An antidiabetic thiazolidinedione induces eccentric cardiac hypertrophy by cardiac volume overload in rats

1. To assess the involvement of volume overload in the development of cardiac hypertrophy during treatment with an antidiabetic thiazolidinedione, changes in cardiac anatomy and parameters of cardiac volume overload were evaluated in female Sprague-Dawley rats treated with the thiazolidinedione derivative T-174. 2. Two week administration of T-174 (13 and 114 mg/kg per day) increased absolute and relative heart weights by 11-24%, demonstrating the development of cardiac hypertrophy. There was no evidence of oedema in hearts from treated rats. 3. Both plasma and blood volumes were increased in T-174-treated rats without any changes in systolic blood pressure and heart rate, whereas haematocrit was decreased. In accordance with the existence of volume overload, both left ventricular end-diastolic pressure and right atrial pressure were increased. Morphometric analysis of hearts revealed that T-174 induced eccentric heart hypertrophy, as characterized by a small increase in wall thickness and a large increase in the chamber volume, which is characteristic of volume overload. Volume overload is suggested as the possible trigger mechanism because blood volume expansion preceded cardiac hypertrophy and there was a high correlation between heart weight and blood volume. 4. T-174-treated streptozotocin-induced diabetic rats also exhibited blood volume expansion and cardiac hypertrophy. 5. These findings suggest that cardiac volume overload is induced by plasma volume expansion and contributes to the development of eccentric cardiac hypertrophy during treatment with antidiabetic thiazolidinediones. Although thiazolidinediones are insulin-sensitizing agents, these cardiac effects are likely to be mediated independently of insulin.

Cardiomyocyte-specific endothelin A receptor knockout mice have normal cardiac function and an unaltered hypertrophic response to angiotensin II and isoproterenol

Even though endothelin is recognized as an important vasoregulatory molecule, the roles of endothelin receptors in specific cell types are not yet fully understood. Mice with a null mutation in endothelin A receptor gene (ET(A)) or in the gene of its ligand (endothelin 1) die neonatally due to craniofacial and cardiac abnormalities. This early lethality has in the past hindered studies on the role of endothelin in cardiovascular physiology and pathophysiology. To overcome this obstacle, we utilized the cre/loxP technology to generate mice in which the ET(A) gene could be deleted specifically in cardiomyocytes. The cre recombinase transgene driven by the alpha-myosin heavy-chain promoter deleted the floxed ET(A) allele specifically in the hearts of these mice, resulting in a 78% reduction in cardiac ET(A) mRNA level compared to wild-type controls. Cardiomyocyte-specific ET(A) knockout animals are viable and exhibit normal growth, cardiac anatomy, and cardiac contractility, as assessed by echocardiography. In addition, these animals exhibit hypertrophic and contractile responses to 10-day infusion of angiotensin II or isoproterenol similar to those observed in control animals. These results indicate that in adult mice cardiac ET(A) receptors are not necessary for either baseline cardiac function or stress-induced response to angiotensin II or isoproterenol.

The endothelin system and its role in acute myocardial infarction

Immediately after an acute myocardial infarction (AMI) or in models of ischemia-reperfusion injury, cardiac endothelin (ET) system is markedly activated, and plasma levels of ET are increased. In the heart, expression of the main components of the ET system (ET-1 peptide, both receptor subtypes ETA and ETB, though not endothelin converting enzyme) are increased both at the gene level and protein level, in the viable myocardium, and--even more substantially--in the necrotic area. Despite these conspicuous abnormalities, the role of ET in this setting remains unclear. In the absence of human data, most short-term studies in animals (in terms of hours to up to 8 days post-AMI) and in the reperfused ischemic heart, have found beneficial effects of ET receptor blockade on survival rate, incidence of arrhythmias, cardiac function, and morphology. In contrast, many studies in which a long-term ET inhibition was started immediately post-infarction and the late effects were examined in animals with ensuing chronic heart failure (14-100 days postinfarction), adverse effects were also observed, such as scar thinning, further ventricular dilation, or even a worse survival rate. It appears that the ET system plays a dual role during the early post-AMI period. At present, it is not clear whether the short-term beneficial effects or long-term adverse effects of ET receptor blockade would prevail. Acute use of short-acting ET receptor antagonists in patients with AMI complicated by an acute heart failure is an attractive possibility that also remains to be investigated.

Role of endothelins in congestive heart failure

Despite major advances in conventional medical therapy, patients with heart failure continue to experience significant morbidity and mortality. Endothelin-1 (ET-1) is a potent vasocontrictor and mitogenic peptide that is activated in heart failure. There is increasing experimental and clinical evidence in support of an important role of ET-1 in the pathophysiology of heart failure. Manipulation of the activity of ET-1, especially using endothelin receptor blockers, has allowed for the further elucidation of the role of this neurohormonal system and development of novel therapeutic strategies in heart failure. Published clinical studies of these agents to date have involved relatively small numbers of patients with severe heart failure, followed for a relatively short period of time, and have mainly examined surrogate endpoints. Large-scale trials that address to hard clinical outcomes are ongoing and their results forthcoming. A key question that remains concerns whether selective ETA or dual ETA-ETB receptor blockade will be more effective.

Pharmacological characterization of TA-0201, an endothelin receptor antagonist, with recombinant and human prostate endothelin receptors

The pharmacological profile of N-(6-(2-(5-bromopyrimidine-2-yloxy)ethoxy)-5-(4-methylphenyl)pyrimidin-4-yl)-4-(2-hydroxy-1,1-dimethylethyl) benzensulfonamide sodium salt sesquihydrate (TA-0201), a new antagonist of endothelin receptors, was examined, using human recombinant and prostate endothelin receptors. In binding experiments with [125I]endothelin-1, TA-0201 showed extremely high affinity for recombinant endothelin ET(A) receptors (pK(i)=10.7), as compared with that for recombinant endothelin ET(B) receptors (pK(i)=7.8). Endothelin ET(A) and ET(B) receptors coexisted in human prostate with different proportions (endothelin ET(A) receptor: approximately 70%), which were distinguished by TA-0201 in the same manner as with recombinant receptors. Human prostate strips contracted in response to endothelin-1 and sorafotoxin S6c, but the maximum contraction induced by endothelin-1 was approximately three times greater than that induced by sarafotoxin S6c. The response to endothelin-1, but not to sarafotoxin S6c, was inhibited by TA-0201 and cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ123) (endothelin ET(A) receptor antagonist) but not by BQ788 (endothelin ET(B) receptor antagonist). These results suggest that TA-0201 is a highly selective endothelin ET(A) receptor antagonist and will be useful for understanding the physiological and pathological roles of the endothelin ET(A) receptor in human prostate and other tissues.

[New expansion of endothelin research: perspectives for clinical application of endothelin-receptor antagonists]

Three isopeptides of endothelin (ET-1, -2, and -3) exert various actions through stimulation of two sub-types of receptor (ETA and ETB). Vascular endothelial cells produce only ET-1. In addition to its powerful vasoconstrictor action, ET-1 has direct mitogenic actions on cardiovascular tissues, as well as comitogennic actions with a wide variety of growth factors and vasoactive substances. ET-1 also promotes the synthesis and secretion of growth factors and various substances, including extracellular constituents. These effects of endogenous ET-1 would naturally be thought to be concerned with the development and/or aggravation of chronic cardiovascular diseases; e.g., hypertension, pulmonary hypertension, vascular remodeling (stenosis, atherosclerosis), renal failure, and heart failure. A large number of peptide and orally active non-peptide endothelin receptor antagonists have been developed, and utilized to analyze physiological and pathophysiological roles of endogenous ET-1. These antagonists have been shown to exert excellent therapeutic effects in animal models of various kinds of diseases by either acute or chronic treatment. Therapeutic treatment of patients suffering from the above-mentioned cardiovascular diseases with ET-receptor antagonists have also been taking place, and bosentan (ETA/ETB antagonist) was recently approved by the FDA as a formal therapeutic drug for pulmonary hypertension. In this review, perspectives for therapeutic applicability of ET-receptor antagonists will be explored.

Isradipine prevents the development of spontaneously occurring cardiac necrosis in cardiomyopathic hamster

Recent studies on the heart necrotizing process at the early stages of hamster polymyopathy have led us to believe that this hereditary disease derives from an anomalous transmembrane ion flux due to the presence of slow Na+ channels that contribute to intracellular Na+ accumulation which promote intracellular Ca2+ overload via the Ca2+ influx through the Na+-Ca2+ exchanger. In the present study, we investigated the potential beneficial effect of chronic treatment with a dual L-type Ca2+ and slow Na+ channel blockers isradipine, on the development of necrosis in myopathic hamster hearts. Young cardiomyopathic (CM) hamsters (CMH) were treated with isradipine (0.1 mg x kg(-1) x day(-1)) and nifedipine (1 mg x kg(-1) x day(-1)) for 4 consecutive weeks. Microscopic assessments were carried out in staged serial paraffin sections of heart ventricles from tissues freshly dissected at autopsy. In comparison with control nontreated hearts, which exhibited numerous necrotic calcific foci, myolytic lesions, and dilated right ventricle, isradipine treatment prevented, in a significant manner, all the above spontaneous pathological changes, while nifedipine had no effect. Our present observations provide evidence for the first time that in vivo treatment with a DHP Ca2+ channel blocker, isradipine, is cardioprotective against the development of necrosis in hereditary cardiomyopathy in the hamster. It is possible that the protective effect of isradipine in CMH could be largely due to the indirect blockade of Ca2+ influx through the Na+-Ca2+ exchanger as well as to possible direct blockade of Ca2+ influx through the T-type Ca2+ channel.

A combination of oral endothelin-A receptor antagonist and oral prostacyclin analogue is superior to each drug alone in ameliorating pulmonary hypertension in rats

OBJECTIVES

We sought to investigate whether the combination of an oral endothelin (ET)A receptor antagonist and an oral prostacyclin (PGI(2)) analogue is superior to the single use of each drug alone for treating pulmonary hypertension (PH).

BACKGROUND

Treatment with intravenous PGI(2) or an ET(A) receptor antagonist was effective for PH; however, the effect of both agents is unclear.

METHODS

We administered the oral ET(A) receptor antagonist TA-0201 and/or the oral PGI(2) analogue beraprost sodium (BPS) to rats with monocrotaline-induced PH for 19 days. The groups were: normal rats with vehicle treatment (Control group), PH rats with vehicle treatment (PH group), PH rats with TA-0201 treatment (PH + TA group), PH rats with BPS treatment (PH + BPS group) and PH rats with TA-0201 and BPS treatment (PH + TA + BPS group).

RESULTS

Right ventricular (RV) systolic pressure and the ratio of RV systolic pressure to systemic systolic blood pressure (Pp/Ps) were markedly higher in the PH group than in the Control group. The increased RV systolic pressure and Pp/Ps were significantly and comparably depressed in the PH + TA and PH + BPS groups; it was more greatly depressed in the PH + TA + BPS group than in the groups with each drug alone. The indexes of RV hypertrophy showed the same tendency as the increase in RV systolic pressure among the five groups. The expression of beta-myosin heavy chain messenger ribonucleic acid in the RV was markedly augmented in the PH group; the enhancement was inhibited in the PH + TA + BPS group to the greatest degree. Medial wall thickness of the pulmonary artery was markedly increased in the PH group; the increase was depressed in the PH + TA + BPS group. Combined treatment also ameliorated PH, even if it started after the onset of PH.

CONCLUSIONS

The combination of an oral ETA receptor antagonist and an oral PGI(2) analogue is superior to the single use of each drug alone in inhibiting the progression of PH.

T-1032, a novel phosphodiesterase type 5 inhibitor, increases the survival of cardiomyopathic hamsters

To evaluate the influence of T-1032 (methyl2-(4-aminophenyl)-1,2-dihydro-1-oxo-7-(2-pyridylmethoxy)-4-(3,4,5-trimethoxyphenyl)-3-isoquinoline carboxylate sulfate), a potent and relatively selective phosphodiesterase 5 inhibitor, on chronic heart failure, we examined the acute hemodynamic profile of T-1032 and its chronic effect on the survival of Bio 14.6 cardiomyopathic hamsters. In the acute study, T-1032 (1, 10, 100 microg/kg) was administered intravenously by means of a dose-escalating procedure in 55-week-old hamsters. T-1032 significantly reduced both the right and left ventricular end-diastolic pressure in a dose-dependent manner. T-1032 modestly reduced the systemic arterial pressure at the highest dose (100 microg/kg i.v.). T-1032 did not change the heart rate or left ventricular dp/dt(max). In the survival study, chronic administration of T-1032 (50 and 500 ppm in a diet) increased survival, and the survival rate was 24.2%, 45.4% and 48.5% in the control, 50 and 500 ppm-treated groups, respectively. The median survival was 55, 58 and 58 weeks in control, 50 and 500 ppm-treated groups, respectively. Analysis of the survival curves revealed that T-1032 (500 ppm) significantly increased the survival of these hamsters (P<0.05 vs. control). It was concluded that T-1032 had beneficial hemodynamic effects on heart failure in Bio 14.6 cardiomyopathic hamsters, and the favorable hemodynamic changes induced by T-1032 were partly related to the increase in the survival of these hamsters. Phosphodiesterase type 5 inhibitors may have therapeutic potential for the treatment of chronic heart failure.

Prevention of diastolic heart failure by endothelin type A receptor antagonist through inhibition of ventricular structural remodeling in hypertensive heart

OBJECTIVES

Despite the clinical frequency of diastolic heart failure, its therapeutic strategy has not been established. Our recent study demonstrated activation of the endothelin (ET) system in a diastolic heart failure model with hypertension. Several studies have reported that ET type A (ETA) receptor antagonist improves systolic function and prevents systolic heart failure; however, its effects on diastolic heart failure are unknown. We investigated the effects of chronic administration of ET(A) receptor antagonist in diastolic heart failure.

DESIGN AND METHODS

Dahl-Iwai salt-sensitive rats fed on a high-salt diet from 7 weeks of age, in which congestive heart failure develops following hypertension without cardiac chamber dilatation or systolic dysfunction, were divided into groups with and without administration of a subdepressor dose of ET(A) receptor antagonist.

RESULTS

Hypertension induced compensatory left ventricular (LV) hypertrophy at 13 weeks in six untreated rats. Persistent pressure overload developed progressive LV hypertrophy and fibrosis from 13 to 19 weeks, resulting in elevated LV filling pressure and increased lung weight. Chronic ET(A) receptor blockade did not restrain compensatory LV hypertrophy at 13 weeks; however, it attenuated LV hypertrophy and fibrosis thereafter (n = 6). These beneficial effects resulted in the maintenance of normal LV filling pressure without changes in LV end-diastolic diameter, indicating prevention of LV stiffening.

CONCLUSIONS

Chronic ET(A) receptor blockade is likely to exert beneficial effects in diastolic failure through attenuation of the progression of LV hypertrophy and fibrosis.

Role of endothelin in cardiovascular disease

Endothelins are a family of peptides, which comprises endothelin-1 (ET-1), endothelin-2 (ET-2) and endothelin-3 (ET-3), each containing 21 amino-acids. ET-1 is a peptide secreted mostly by vascular endothelial cells, the predominant isoform expressed in vasculature and the most potent vasoconstrictor currently known. ET-1 also has inotropic, chemotactic and mitogenic properties. In addition, it influences salt and water homeostasis through its effects on the renin-angiotensin-aldosterone system (RAAS), vasopressin and atrial natriuretic peptide and stimulates the sympathetic nervous system. The overall action of endothelin is to increase blood pressure and vascular tone. Therefore, endothelin antagonists may play an important role in the treatment of cardiac, vascular and renal diseases associated with regional or systemic vasoconstriction and cell proliferation, such as essential hypertension, pulmonary hypertension, chronic heart failure and chronic renal failure. Long-term anti-endothelin therapy may improve symptoms and favourably alter the progression of heart failure. Endothelin appears to participate in induction and progression of sclerotic renal changes, leading to progression to end-stage renal disease. Anti-endothelin therapy might offer additional benefits in the prevention of progression of chronic renal failure in addition to the known benefits of RAAS inhibition. Clinical trials have demonstrated potentially important benefits of endothelin antagonists for patients with essential hypertension, pulmonary hypertension and heart failure. Further studies are necessary to determine the role of anti-endothelin therapy in the treatment of cardiovascular diseases and determine the different roles of selective receptor antagonism vs. mixed ET(A/B)-receptor antagonism in human diseases.