Beneficial Effect of Eplerenone on Cardiac Remodelling and Electrical Properties of the Failing Heart

Roles of Mineralocorticoid Receptors in Cardiovascular and Cardiorenal Diseases

Mineralocorticoid receptor (MR) activation in the heart and vessels leads to pathological effects, such as excessive extracellular matrix accumulation, oxidative stress, and sustained inflammation. In these organs, the MR is expressed in cardiomyocytes, fibroblasts, endothelial cells, smooth muscle cells, and inflammatory cells. We review the accumulating experimental and clinical evidence that pharmacological MR antagonism has a positive impact on a battery of cardiac and vascular pathological states, including heart failure, myocardial infarction, arrhythmic diseases, atherosclerosis, vascular stiffness, and cardiac and vascular injury linked to metabolic comorbidities and chronic kidney disease. Moreover, we present perspectives on optimization of the use of MR antagonists in patients more likely to respond to such therapy and review the evidence suggesting that novel nonsteroidal MR antagonists offer an improved safety profile while retaining their cardiovascular protective effects. Finally, we highlight future therapeutic applications of MR antagonists in cardiovascular injury.

Type 2 myocardial infarction and myocardial injury: eligibility for novel medical therapy to derisk clinical trials

BACKGROUND

Patients with type 2 myocardial infarction (T2MI) and other mechanisms of nonthrombotic myocardial injury have an unmet therapeutic need. Eligibility for novel medical therapy is generally uncertain.

METHODS

We predefined colchicine, eplerenone and ticagrelor as candidates for repurposing towards novel therapy for T2MI or myocardial injury. Considering eligibility for randomisation in a clinical trial, each drug was classified according to indications and contraindications for therapy and survival for at least 24 hours following admission. Eligibility criteria for prescription were evaluated against the Summary of Medical Product Characteristics. Consecutive hospital admissions were screened to identify patients with ≥1 high-sensitivity troponin-I value >99th percentile. Endotypes of myocardial injury were adjudicated according to the Fourth Universal Definition of MI. Patients' characteristics and medication were prospectively evaluated.

RESULTS

During 1 March to 15 April 2020, 390 patients had a troponin I>URL. Reasons for exclusion: type 1 MI n=115, indeterminate diagnosis n=42, lack of capacity n=14, death <24 hours n=7, duplicates n=2. Therefore, 210 patients with T2MI/myocardial injury and 174 (82.8%) who survived to discharge were adjudicated for treatment eligibility. Patients who fulfilled eligibility criteria initially on admission and then at discharge were colchicine 25/210 (11.9%) and 23/174 (13.2%); eplerenone 57/210 (27.1%) and 45/174 (25.9%); ticagrelor 122/210 (58.1%) and 98/174 (56.3%). Forty-six (21.9%) and 38 (21.8%) patients were potentially eligible for all three drugs on admission and discharge, respectively.

CONCLUSION

A reasonably high proportion of patients may be considered eligible for repurposing novel medical therapy in secondary prevention trials of type 2 MI/myocardial injury.

What an Interventionalist Needs to Know About MI with Non-obstructive Coronary Arteries

MI with non-obstructive coronary arteries (MINOCA) is caused by a heterogeneous group of vascular or myocardial disorders. MINOCA occurs in 5.15% of patients presenting with acute ST-segment elevation MI or non-ST segment elevation MI and prognosis is impaired. The diagnosis of MINOCA is made during coronary angiography following acute MI, where there is no stenosis ≥50% present in an infarct-related epicardial artery and no overt systemic aetiology for the presentation. Accurate diagnosis and subsequent management require the appropriate utilisation of intravascular imaging, coronary function testing and subsequent imaging to assess for myocardial disorders without coronary involvement. Although plaque-related MINOCA is currently managed with empirical secondary prevention strategies, there remains an unmet therapeutic need for targeted and evidence-based therapy for MINOCA patients and increased awareness of the recommended diagnostic pathway.

Mineralocorticoid receptor antagonists lead to increased adenosine bioavailability and modulate contractile cardiac parameters

Activation of mineralocorticoid receptor antagonists (MRAs) is cardioprotective; however, this property is lost upon blockade or inactivation of adenosine (ADO) receptor A_2b. In this study, we investigated whether the effects of MRAs are mediated by an interaction between cardioprotective ADO receptors A₁ and A₃. Spironolactone (SPI) or eplerenone (EPL) increased ADO levels in the plasma of treated animals compared to control animals. SPI or EPL increased the protein and activity levels of ecto-5'-nucleotidase (NT5E), an enzyme that synthesizes ADO, compared to control. The levels of ADO deaminase (ADA), which degrades ADO, were not affected by SPI or EPL; however, the activity of ADA was reduced in SPI-treated rats compared to control. Using an isolated cardiomyocyte model, we found inotropic and chronotropic effects, and increased calcium transient [Ca²⁺]_i in cells treated with ADO receptor A₁ or A₃ antagonists compared to control groups. Upon co-treatment with MRAs, EPL and SPI fully and partially reverted the effects of receptor A₁ or A₃ antagonism, respectively. Collectively, MRAs in vivo lead to increased ADO bioavailability. In vitro, the rapid effects of SPI and EPL are mediated by an interaction between ADO receptors A₁ and A₃.

Mineralocorticoid Receptor and Cardiovascular Disease

Activation of the mineralocorticoid receptor (MR) in the distal nephron by its ligand, aldosterone, plays an important role in sodium reabsorption and blood pressure regulation. However, expression of the MR goes beyond the kidney. It is expressed in a variety of other tissues in which its activation could lead to tissue injury. Indeed, MR activation in the cardiovascular (CV) system has been shown to promote hypertension, fibrosis, and inflammation. Pharmacological blockade of the MR has protective effects in several animal models of CV disease. Furthermore, the use of MR antagonists is beneficial for heart failure patients, preventing mortality and morbidity. A better understanding of the implications of the MR in the setting of CV diseases is critical for refining treatments and improving patient care. The mechanisms involved in the deleterious effects of MR activation are complex and include oxidative stress, inflammation, and fibrosis. This review will discuss the pathological role of the MR in the CV system and the major mechanisms underlying it.

Emerging Roles of the Mineralocorticoid Receptor in Pathology: Toward New Paradigms in Clinical Pharmacology

The mineralocorticoid receptor (MR) and its ligand aldosterone are the principal modulators of hormone-regulated renal sodium reabsorption. In addition to the kidney, there are several other cells and organs expressing MR, in which its activation mediates pathologic changes, indicating potential therapeutic applications of pharmacological MR antagonism. Steroidal MR antagonists have been used for decades to fight hypertension and more recently heart failure. New therapeutic indications are now arising, and nonsteroidal MR antagonists are currently under development. This review is focused on nonclassic MR targets in cardiac, vascular, renal, metabolic, ocular, and cutaneous diseases. The MR, associated with other risk factors, is involved in organ fibrosis, inflammation, oxidative stress, and aging; for example, in the kidney and heart MR mediates hormonal tissue-specific ion channel regulation. Genetic and epigenetic modifications of MR expression/activity that have been documented in hypertension may also present significant risk factors in other diseases and be susceptible to MR antagonism. Excess mineralocorticoid signaling, mediated by aldosterone or glucocorticoids binding, now appears deleterious in the progression of pathologies that may lead to end-stage organ failure and could therefore benefit from the repositioning of pharmacological MR antagonists.

Cardiac fibrosis as a determinant of ventricular tachyarrhythmias

Animal and emerging clinical studies have demonstrated that increased ventricular fibrosis in a setting of reduced repolarization reserve promotes early afterdepolarizations (EADs) and triggered activity that can initiate ventricular tachycardia and ventricular fibrillation (VT/VF). Increased ventricular fibrosis plays a key facilitatory role in allowing oxidative and metabolic stress-induced EADs to manifest as triggered activity causing VT/VF. The lack of such an arrhythmogenic effect by the same stressors in normal non-fibrotic hearts highlights the importance of fibrosis in the initiation of VT/VF. These findings suggest that antifibrotic therapy combined with therapy designed to increase ventricular repolarization reserve may act synergistically to reduce the risk of sudden cardiac death.

Mineralocorticoid receptor and cardiac arrhythmia

Mineralocorticoid receptor (MR) activation has been shown to play a deleterious role in the development of heart disease in studies using specific MR antagonists (spironolactone, eplerenone) in both experimental models and patients. Pharmacological MR blockade attenuates the transition to heart failure (HF) in models of systolic left ventricular dysfunction and myocardial infarction, as well as diastolic dysfunction, in rats and mice. In humans, MR antagonism is highly beneficial in patients with mild or advanced HF and postinfarct HF. The consequences of aldosterone and MR activation for cardiac arrhythmia and its prevention and/or correction by MR antagonists are often underestimated.  Activation of MR modulates cardiac electrical activity, causing atrial and ventricular arrhythmias. A pro-arrhythmogenic effect of aldosterone (possibly partly dependent on fibrosis) has been suggested by several studies. Cardiac MR activation has important consequences for the control of cellular calcium homeostasis, action potential lengthening, modulation of calcium transients and sarcoplasmic reticulum diastolic leaks, resulting in the promotion of rhythm disorders. Aldosterone and/or MR activation (in both cardiomyocytes and coronary vessels) result in vascular dysfunction and also contribute to pro-arrhythmogenic conditions.  Together, the pro-arrhythmic effects of aldosterone and/or MR may explain the highly beneficial effect of MR antagonism, namely a decrease in the incidence of sudden death, observed in the Randomized Aldactone Evaluation Study (RALES) and Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study (EPHESUS) studies.

Eplerenone: a review of its use in patients with chronic systolic heart failure and mild symptoms

Eplerenone (Inspra®) is a selective mineralocorticoid receptor antagonist (MRA). In the EU, it is approved for use (in addition to standard optimal therapy) to reduce the risk of cardiovascular (CV) mortality and morbidity in adult patients with chronic systolic heart failure (HF) and mild symptoms. This article reviews the efficacy and tolerability of eplerenone in this indication and briefly summarizes its pharmacology. In the EMPHASIS-HF study, relative to placebo, the addition of eplerenone to optimal background therapy significantly reduced the risk of death from CV causes or hospitalization for HF in patients with chronic systolic HF and mild symptoms. Benefits of eplerenone therapy over placebo were also observed in several secondary outcomes, including: death from any cause or hospitalization for HF; death from any cause; hospitalization for any reason; or hospitalization for HF. Eplerenone was generally well tolerated in this study, with the most frequent adverse event being hyperkalaemia, which is a known adverse event of the drug class. Sexual adverse events (e.g. gynecomastia) occurred in <1 % of eplerenone recipients, reflecting the selectivity of eplerenone for mineralocorticoid receptors. Based on these results, European guidelines have been updated and recommend the use of an MRA to reduce the risk of HF hospitalization and premature death in all patients with persisting symptoms (New York Heart Association class II-IV) and a left-ventricular ejection fraction of ≤35 %, despite treatment with ACE inhibitor (or an angiotensin receptor blocker if an ACE inhibitor is not tolerated) and a β-blocker.

Spironolactone enhances the beneficial effect of aliskiren on cardiac structural and electrical remodeling in TGR(mRen2)27 rats

OBJECTIVE

To investigate the influence of simultaneous administration of spironolactone (20 mg/kg per day, intraperitoneal (i.p.)) and aliskiren (50 mg/kg per day, i.p.) for a period of eight weeks on cardiac remodeling in TGR(mRen2)27 rats.

METHODS

Echocardiographic and electrophysiological and histological methods were used to determine the influence of spironolactone and aliskiren on cardiac remodeling.

RESULTS

1) the beneficial effect of aliskiren on SBP was enhanced by simultaneous administration of spironolactone; 2) echocardiographic studies showed that the left ventricle diameter (LVD), the left ventricle end diastolic volume (LVEDV) and the left ventricle posterior wall thickness (LVPW) were significantly reduced by the combination of both drugs when compared with aliskiren alone; 3) the ejection fraction was also increased; 4) histological studies indicated a greater decline in perivascular and interstitial fibrosis when both drugs were used; 5) the decrease of electrical remodeling of the left ventricle caused by aliskiren was further reduced by simultaneous administration of spironolactone; 6) the cardiac refractoriness increased by aliskiren was further incremented by spironolactone. Spironolactone (20 mg/kg per day) alone increased the ejection fraction and reduced LVD, LVEDV and LVPW but its effect was smaller than that achieved with the combination spironolactone plus aliskiren.

CONCLUSION

The combination of an aldosterone inhibitor with a direct renin inhibitor proved to be of greater benefit for cardiac structural and electrical remodeling in this experimental model of hypertension than aliskiren alone.

Systematic approach: an evidence management strategy for better decision-making

Evidence-based medicine aims to apply best evidences to medical decision making. Although evidence are established using the scientific method, decision making has received less priority. Decision making is a mental process requiring a systematic analysis of evidences for a specific use, leading to a final choice of action. In many scientific disciplines involving decision and control, this process has been significantly improved by making it as a system (a set of interacting entities forming an integrated whole). Hypothesizing that most medical decisions can be described as a system, we present a schematic systematic loop, based on four traditional medical steps (nosology, semeiology, pathophysiology, and therapy), and on the four transitions between these steps. Steps are evaluated by reproducibility, transitions are evaluated by predictability. This leads to formulate eight basic questions for testing the reliability of any loop. We applied this approach to a specific study (EPHESUS) to show its interest in the control of the medical knowledge provided by a study and in indicating where evidence is missing. A systematic approach helps evidence-based medicine in structuring evidences for better medical decisions and in determining which research needs priority.

RU28318, an aldosterone antagonist, in combination with an ACE inhibitor and angiotensin receptor blocker attenuates cardiac dysfunction in diabetes

AIMS

We evaluated the effects of RU28318 (RU), a selective mineralocorticoid receptor (MR) antagonist, Captopril (Capt), an angiotensin converting enzyme inhibitor, and Losartan (Los), an angiotensin receptor blocker, alone or in combination with ischemia/reperfusion- (I/R-) induced cardiac dysfunction in hearts obtained from normal and diabetic rats.

METHODS

Isolated hearts were perfused for 30 min and then subjected to 30 min of global ischemia (I) followed by a period of 30 min of reperfusion (R). Drugs were administered for 30 min either before or after ischemia. Drug regimens tested were RU, Capt, Los, RU + Capt, RU + Los, Capt + Los, and RU + Capt + Los (Triple). Recovery of cardiac hemodynamics was evaluated.

RESULTS

Recovery of cardiac function was up to 5-fold worse in hearts obtained from diabetic animals compared to controls. Treatment with RU was generally better in preventing or reversing ischemia-induced cardiac dysfunction in normal hearts compared to treatment with Capt or Los alone. In diabetic hearts, RU was generally similarly effective as Capt or Los treatment.

CONCLUSIONS

RU treatment locally might be considered as an effective therapy or preventative measure in cardiac I/R injury. Importantly, RU was the most effective at improving -dP/dt (a measure of diastolic function) when administered to diabetic hearts after ischemia.

Effect of spironolactone on ventricular arrhythmias in patients with left ventricular systolic dysfunction and implantable cardioverter defibrillators

AIMS/OBJECTIVES

Patients with implantable cardioverter defibrillators (ICD) often receive an adjunctive anti-arrhythmic therapy. We propose that an addition of spironolactone will reduce the number of clinically significant ventricular arrhythmias and ICD-related therapies.

METHODS AND RESULTS

In a multicentre retrospective study, 64 patients with ischaemic and non-ischaemic dilated cardiomyopathy whose left ventricular ejection fraction (LVEF) was <35% and with ICD were selected. Amongst these patients, 28 patients were on spironolactone and 36 were not taking spironolactone. The ICD interrogation data were analysed for a maximum of 12 months. Wilcoxon Rank Sum test was used to compare the study and control groups. The outcomes were: (1) the number of shocks/anti-tachycardia pacing (ATP) episodes and (2) the number of episodes of ventricular tachycardia (VT) requiring ATP, non-sustained VT (NSVT), and ventricular fibrillation (VF) over the study period. The spironolactone group had fewer monthly, VTs (P=0.027) (requiring ATP). The two groups did not differ in the number of NSVT or VF per month.

CONCLUSION

Addition of spironolactone as an adjunct to ICD therapy in patients with congestive heart failure (CHF) reduces VT requiring ATP, but does not affect NSVT or VF per month.

Aldosterone, mineralocorticoid receptor, and heart failure

Several large clinical studies have demonstrated the important benefit of mineralocorticoid receptor (MR) antagonists in patients with heart failure, left ventricular dysfunction after myocardial infarction, hypertension or diabetic nephropathy. Aldosterone adjusts the hydro-mineral balance in the body, and thus participates decisively to the control of blood pressure. This traditional view of the action of aldosterone restricted to sodium reabsorption in epithelial tissues must be revisited. Clinical and experimental studies indicated that chronic activation of the MR in target tissues induces structural and functional changes in the heart, kidneys and blood vessels. These deleterious effects include cardiac and renal fibrosis, inflammation and vascular remodeling. It is important to underscore that these effects are due to elevated MR activation that is inadequate for the body salt requirements. Aldosterone is generally considered as the main ligand of MR. However, this is a matter of debate especially in heart. Complexity arises from the glucocorticoids with circulating concentrations much higher than those of aldosterone, and the fact that the MR has a high affinity for 11β-hydroxyglucocorticoids. Nevertheless, the beneficial effects of MR inhibition in patients with heart failure emphasize the importance of this receptor in cardiovascular tissue. Diverse experimental models and strains of transgenic mice have allowed to dissect the effects of aldosterone and the MR in the heart. Taken together experimental and clinical data clearly highlight the deleterious cardiovascular effects of MR stimulation.

The effect of aldosterone antagonists for ventricular arrhythmia: a meta-analysis

BACKGROUND

Sudden cardiac death (SCD) from cardiac arrest, one of the most common types of cardiac-related death, is most often triggered by ventricular arrhythmia (VA). It has been reported that aldosterone antagonists (AAs) have the benefit of reducing SCD in patients with heart failure (HF). It also has been indicated in animal experiments and clinical trials that AAs may have an antiarrhythmic effect.

HYPOTHESIS

AAs have an effect on VA in patients with HF or coronary artery disease.

METHODS

We searched the Cochrane Central Register of Controlled Trials, PubMed, Current Controlled Trials, and the National Research Register, and identified randomized controlled trials on the effect of AAs on VA.

RESULTS

All together, 7 trials with a total of 8635 patients were identified and extracted. AAs reduced the risk of SCD in patients with HF by 21% (relative risk [RR]: 0.79, 95% confidence interval [CI]: 0.67-0.93). AAs significantly reduced the episodes of ventricular premature complexes (mean difference 705 ± 646 episodes per 24 hours). Risk of ventricular tachycardia was reduced by 72% (RR: 0.28, 95% CI: 0.10-0.77).

CONCLUSIONS

The additional administration of AAs in patients with HF or coronary artery disease shows a benefit in reducing the risk of SCD and may also be effective for reducing episodes of ventricular premature complexes and ventricular tachycardia.

Aldosterone Antagonists in Heart Failure

Aldosterone antagonists represented by nonselective spironolactone and mineralocorticoid-selective eplerenone are approved for treatment of symptomatic heart failure with reduced systolic function. Their cardioprotective, antifibrotic, and antiarrhythmic effects have been proven in animal experiments, and their effects on morbidity and mortality have been demonstrated in randomized clinical trials. Yet, they remain the most underutilized of all classes of medications for heart failure, primarily because of fear of hyperkalemia. Thorough patient screening and selection is the key for minimizing risks and optimizing benefits from these drugs. Ongoing trials will demonstrate whether the indication for aldosterone antagonists can be expanded to less severe heart failure or patients with preserved systolic function.

Further studies on the effects of intracrine and extracellular angiotensin II on the regulation of heart cell volume. On the influence of aldosterone and spironolactone

The influence of extracellular and intracellular angiotensin II (Ang II) on the cell volume in the failing heart of cardiomyopathic hamsters (TO2) was further investigated as well as the influence of aldosterone and spironolactone on the Ang II action on cell volume. Measurements of cell width and area of quiescent ventricular cardiomyocytes were performed using a video camera and computer analysis and the relative cell volume was calculated. All measurements of cell volume were performed in the same cell before and after the administration of Ang II (10⁻⁸M). The results indicated that: a) the increase in cell volume caused by extracellular Ang II(10⁻⁸ M) was enhanced in cells incubated with aldosterone (100 nM) for 48 h; b) the effect of aldosterone was abolished by spironolactone (10⁻⁸ M); c) the decline in cell volume elicited by intracellular administration of Ang II (10⁻⁸ M) was increased by aldosterone and inhibited by spironolactone; d) the effects of aldosterone and spironolactone were related, in part, to a change in expression of AT1 receptors; and e) the intracellular administration of Ang II reduced the swelling-dependent chloride current (I(Clswell)). The implications of these findings to the failing heart and myocardial ischemia are discussed.

Reduction of fibrosis-related arrhythmias by chronic renin-angiotensin-aldosterone system inhibitors in an aged mouse model

Myocardial fibrosis increases arrhythmia vulnerability of the diseased heart. The renin-angiotensin-aldosterone system (RAAS) governs myocardial collagen synthesis. We hypothesized that reducing cardiac fibrosis by chronic RAAS inhibition would result in reduced arrhythmia vulnerability of the senescent mouse heart. Wild-type mice (52 wk old) were treated for 36 wk: 1) untreated control (C); 2) eplerenone (E); 3) losartan (L); and 4) cotreatment with eplerenone and losartan (EL). Ventricular epicardial activation mapping was performed on Langendorff-perfused hearts. Arrhythmia inducibility was tested by one to three premature stimuli and burst pacing. Longitudinal and transverse conduction velocity and dispersion of conduction were determined during pacing at a basic cycle length of 150 ms. Sirius red staining (collagen) was performed. As a result, in the RV of mice in the E, L, and EL groups, transverse conduction velocity was significantly increased and anisotropic ratio was significantly decreased compared with those values of mice in the C group. Anisotropic reentrant arrhythmias were induced in 52% of untreated mice and significantly reduced to 22%, 26%, and 16% in the E, L, and EL groups, respectively. Interstitial fibrosis was significantly decreased in both the RV and LV of all treated groups. Scattered patches of replacement fibrosis were found in 90% of untreated hearts, which were significantly reduced in the E, L, and EL groups. A strong correlation between the abundance of patchy fibrosis and arrhythmia inducibility was found. In conclusion, chronic RAAS inhibition limited aging-related interstitial fibrosis. The lower arrhythmogeneity of treated mice was directly correlated to the reduced amount of patchy fibrosis.

Upstream therapy of atrial fibrillation

Failure of current pharmacological therapy for atrial fibrillation in maintaining sinus rhythm may be due to structural atrial remodeling caused by inflammation and fibrosis. Upstream therapy that interferes in the structural remodeling process may be effective in maintaining sinus rhythm. This article reviews upstream therapy in atrial fibrillation. Various prospective and retrospective studies demonstrate that upstream therapy, consisting of angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, statins, fish oils, glucocorticoids, or moderate physical activity, is associated with a reduced incidence of new-onset atrial fibrillation (i.e., primary prevention) and with a reduced recurrence of atrial fibrillation (i.e., secondary prevention). Larger clinical trials are required to further elucidate the position of upstream therapy in the primary and secondary prevention of atrial fibrillation.

Eplerenone inhibits the intracrine and extracellular actions of angiotensin II on the inward calcium current in the failing heart. On the presence of an intracrine renin angiotensin aldosterone system

The influence of chronic administration of eplerenone on the intracrine as well as on the extracellular action of angiotensin II (Ang II) on L-type inward calcium current was investigated in the failing heart of cardiomyopathic hamsters (TO-2).For this, eplerenone (200 mg/kg/day) was administered orally to 2 month-old cardiomyopathic hamsters for a period of 3 months. Measurements of the peak inward calcium current (I(Ca)) was performed in single cells under voltage clamp using the whole cell configuration. The results indicated that eplerenone suppressed the intracrine action of Ang II (10(-)(8) M) on peak I(Ca) density. Moreover, the intracellular dialysis of the peptide did not change the time course of I(Ca) inactivation in animals treated chronically with eplerenone. The extracellular administration of Ang II (10(-)(8) M) incremented the peak I(Ca) density by only 20+/-8% (n=30) compared with 38+/-4% (n=35) (P<0.05) obtained in age-matched cardiomyopathic hamsters not exposed to eplerenone. Interestingly, the inhibitory of eplerenone (10(-7) M) on the intracrine action of Ang II was also found, in vitro, but required an incubation period of, at least, 24 h. The inhibitory action of eplerenone on the intracellular action of Ang II was partially reversed by exposing the eplerenone-treated cells to aldosterone (10 nM) for a period of 24 h what supports the view that: a) the mineralocorticoid receptor(MR) was involved in the modulation of the intracrine action of the peptide; b) the effect of eplerenone on the intracrine as well as on the extracellular action of Ang II was related ,in part, to a decreased expression of membrane-bound and intracellular AT1 receptors.

IN CONCLUSION

a) eplerenone inhibits the intracrine action of Ang II on inward calcium current and reduces drastically the effect of extracellular Ang II on I(Ca); b) aldosterone is able to revert the effect of eplerenone; c) the mineralocorticoid receptor is an essential component of the intracrine renin angiotensin aldosterone system.

Differences in distribution of fibrosis in the ventricles underlie dominant arrhythmia vulnerability of the right ventricle in senescent mice

Mutations that are supposed to affect right (RV) and left ventricular (LV) electrophysiology equally, often reveal dominant conduction slowing and arrhythmia vulnerability in RV. In this study we investigated the mechanism of dominant arrhythmia vulnerability of RV in senescent mice. We performed epicardial ventricular activation mapping on adult and senescent Langendorff perfused hearts. Longitudinal and transversal conduction velocity, as well as arrhythmia inducibility were determined. Subsequently, hearts were processed for immunohisto-chemistry and Picro Sirius Red staining. Senescent mice revealed decreased conduction velocity, increased aniso-tropic ratio and reduced excitation wavelength in RV, but not in LV. Arrhythmias were mainly induced in RV of senescent hearts. No arrhythmias were induced in adult hearts. Immunohistochemistry revealed that the amount of Connexin 43 and cardiac sodium channel Nav1 .5 were equally decreased, and that collagen content was equally increased in senescent RV and LV. However, patches of replacement fibrosis were found throughout the RV wall, but only in the sub-endocardium and mid-myocardium of LV. The study shows that the dominant arrhythmia vulnerability in RV of senescent mice is caused by the distribution of replacement fibrosis which involves the entire RV but only part of the LV. (Neth Heart J 2008;16:356-8.).

Plasma concentrations of matrix metalloproteinase-2, tissue inhibitor of metalloproteinase-1 and osteopontin reflect severity of heart failure in DOCA-salt hypertensive rat

The matrix metalloproteinases (MMPs) and their endogenous inhibitors, the tissue inhibitors of metalloproteinases (TIMPs) play a key role in extracellular matrix maintenance and are altered in the failing heart, both in experimental models and in chronic end-stage heart failure in humans. As the common diagnostic markers of heart failure, atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) primarily reflect increased pressure loading, determination of soluble, heart-derived MMPs and TIMPs in plasma, as well as the determination of the emerging fibrosis marker osteopontin (OPN) might be valuable tools for detecting heart fibrosis. In this study the effect of spironolactone treatment on plasma MMP-2, TIMP-1 and OPN levels was assessed in a heart failure animal model. Unilaterally nephrectomized Sprague Dawley rats received subcutaneous injection of 100 mg deoxycorticosterone acetate (DOCA) once a week and 1% (w/v) NaCl in drinking water. Blood pressure was monitored weekly and blood samples were collected after 1, 2 and 4 weeks. After 6 weeks, left ventricular contractility (LVC) and heart weight-to-body weight ratio (HW/BW) were assessed. DOCA treatment increased plasma MMP-2, TIMP-1 and OPN concentrations. Alterations of plasma marker levels were correlated with changes of HW/BW and paralleled impaired LVC. Furthermore, beneficial effects of spironolactone treatment were observed. In DOCA-salt hypertensive rats, plasma concentrations of MMP-2, TIMP-1 and OPN reflected heart failure associated with haemodynamic, functional and morphological changes. Based on these findings, it appears reasonable to use plasma markers of fibrosis to monitor the development of heart failure.

Drug Insight: eplerenone, a mineralocorticoid-receptor antagonist

Increasing recognition of the role of aldosterone in cardiovascular disease has been supported by a significant body of evidence from animal models. This evidence has been translated into clinical practice, and large-scale, randomized, placebo-controlled trials have confirmed the beneficial effects of mineralocorticoid blockade in patients with heart failure. As a consequence, there has been a resurgence in the use of mineralocorticoid-receptor antagonists in clinical practice that has prompted the search for a potent and specific antagonist without the sexual side effects of spironolactone. Eplerenone, a mineralocorticoid-receptor antagonist with minimal binding to the progesterone and androgen receptors, is now licensed for treatment of heart failure in Europe and heart failure and hypertension in the US; it has also been proposed as a treatment for a variety of cardiovascular conditions. This article reviews the current concepts of the actions of aldosterone at a cellular level. Recent findings regarding its role as a cardiovascular hormone, both in animal models and human studies, are discussed. We also describe the development of mineralocorticoid-receptor blockers following the isolation of aldosterone and discuss the subsequent search for a specific mineralocorticoid antagonist. In addition we detail the effects of eplerenone in a number of clinical situations and outline its potential future applications.

Dominant arrhythmia vulnerability of the right ventricle in senescent mice

BACKGROUND

Several cardiac disorders affect the right ventricle (RV) and left ventricle (LV) equally, but nevertheless, RV vulnerability to conduction slowing and arrhythmias exceeds that of the LV.

OBJECTIVE

This study sought to assess the mechanism of dominant RV arrhythmia vulnerability in senescent mice as a model of general reduced myocardial integrity.

METHODS

Epicardial ventricular activation mapping was performed on senescent (22 months) and adult (3 months) Langendorff perfused mouse hearts. Arrhythmia inducibility was tested by programmed stimulation. Conduction velocity longitudinal and transversal (CVT) to fiber orientation, conduction heterogeneity, and effective refractory period were determined. Subsequently, hearts were processed for immunohistochemistry, Western blotting, and Sirius red staining.

RESULTS

In senescent RV, but not LV, CVT was reduced and wavelength decreased, whereas anisotropic ratio and conduction heterogeneity increased. Arrhythmias, based on anisotropic reentry, were induced in 55% of senescent hearts only and predominantly in RV. In senescent mice, Connexin 43 (Cx43) and Cardiac Sodium Channel (Nav1.5) were decreased and interstitial fibrosis increased comparably in RV and LV. However, in senescent mice, heterogeneously distributed patches of replacement fibrosis were present throughout the entire RV myocardium, but only in midendocardium and subendocardium of LV. Cx43 expression in these areas was disrupted.

CONCLUSION

Widespread presence of replacement fibrosis in senescent RV compared with LV, combined with Cx43 and Nav1.5 disruption, potentiate shorter wavelength, conduction slowing, and conduction heterogeneity in RV, resulting in greater vulnerability of senescent RV to arrhythmias.