Pathophysiologie der chronischen Herzinsuffizienz

YB-1 Is a Novel Target for the Inhibition of α-Adrenergic-Induced Hypertrophy

Cardiac hypertrophy resulting from sympathetic nervous system activation triggers the development of heart failure. The transcription factor Y-box binding protein 1 (YB-1) can interact with transcription factors involved in cardiac hypertrophy and may thereby interfere with the hypertrophy growth process. Therefore, the question arises as to whether YB-1 influences cardiomyocyte hypertrophy and might thereby influence the development of heart failure. YB-1 expression is downregulated in human heart biopsies of patients with ischemic cardiomyopathy (n = 8), leading to heart failure. To study the impact of reduced YB-1 in cardiac cells, we performed small interfering RNA (siRNA) experiments in H9C2 cells as well as in adult cardiomyocytes (CMs) of rats. The specificity of YB-1 siRNA was analyzed by a miRNA-like off-target prediction assay identifying potential genes. Testing three high-scoring genes by transfecting cardiac cells with YB-1 siRNA did not result in downregulation of these genes in contrast to YB-1, whose downregulation increased hypertrophic growth. Hypertrophic growth was mediated by PI3K under PE stimulation, as well by downregulation with YB-1 siRNA. On the other hand, overexpression of YB-1 in CMs, caused by infection with an adenovirus encoding YB-1 (AdYB-1), prevented hypertrophic growth under α-adrenergic stimulation with phenylephrine (PE), but not under stimulation with growth differentiation factor 15 (GDF15; n = 10-16). An adenovirus encoding the green fluorescent protein (AdGFP) served as the control. YB-1 overexpression enhanced the mRNA expression of the Gq inhibitor regulator of G-protein signaling 2 (RGS2) under PE stimulation (n = 6), potentially explaining its inhibitory effect on PE-induced hypertrophic growth. This study shows that YB-1 protects cardiomyocytes against PE-induced hypertrophic growth. Like in human end-stage heart failure, YB-1 downregulation may cause the heart to lose its protection against hypertrophic stimuli and progress to heart failure. Therefore, the transcription factor YB-1 is a pivotal signaling molecule, providing perspectives for therapeutic approaches.

Mechanisms in fluid retention - towards a mutual concept

Fluid retention is a common and challenging condition in daily clinical practice. The normal fluid homoeostasis in the human body is based on accurately counter-balanced physiological mechanisms. When compromised fluid retention occurs and is seen in pathophysiologically different conditions such as liver cirrhosis, heart and kidney failure, and in preeclampsia. These conditions may share pathophysiological mechanisms such as functional arterial underfilling, which seems to be a mutual element in cirrhosis, cardiac failure, cardiorenal and hepatorenal syndromes, and in pregnancy. However, there are also distinct differences and it is still unclear whether kidney dysfunction or arterial underfilling is the initiating factor of fluid retention or if they happen simultaneously. This review focuses on similarities and differences in water retaining conditions and points to areas where important knowledge is still needed.

Prevalence of ventricular discordance and its relation to functional capacity in idiopathic dilated cardiomyopathy

INTRODUCTION

Although left ventricular (LV) dilatation is the most distinguishing morphologic feature of idiopathic dilated cardiomyopathy (IDC), right ventricular (RV) dilatation may variably contribute to total cardiac enlargement. The prevalence and functional importance of the relative degree of left and right ventricular dilatation has not been comprehensively studied using cardiac magnetic resonance imaging (MRI).

METHODS

Our prospective study included 58 consecutive IDC patients with a LV ejection fraction <40% and NYHA functional class > or =2. MRI was performed with a 1.5 Tesla scanner for RV and LV dimensional and functional analysis. Cardiopulmonary exercise testing was used for evaluation of exercise capacity. Patients were grouped into tertiles based on the distribution of LV end-diastolic volume.

RESULTS

Compared to control subjects a considerable heterogeneity in the relative degree of left and right ventricular dilatation was noted in IDC patients. Within the entire patient group, a strong correlation between the degree of ventricular volume discordance and the extent of LV enlargement was observed (r = 0.8; P < 0.001). Tertile analysis revealed that the LV/RV volume ratio significantly differed in the three subgroups of patients (1.0 +/- 0.3 vs. 1.5 +/- 0.4 vs. 2.1 +/- 0.9; P < 0.001). Only weak correlations between MRI data and patients' functional capacity were found. LV ejection fraction was identified as the only independent predictor of maximum oxygen consumption in our setting.

CONCLUSION

In IDC patients the degree of ventricular volume discordance is strongly related to the extent of left ventricular enlargement. However, comprehensive biventricular assessment of cardiac function by MRI adds little to our understanding of the cardiac mechanisms limiting exercise tolerance when compared to exclusive left ventricular measurements.

Prognostic value of heart rate variability and ventricular arrhythmias during 13-year follow-up in patients with mild to moderate heart failure

BACKGROUND

In contrast to patients with moderate to severe chronic heart failure (CHF), data regarding long-term outcome in patients with mild CHF are scarce. We examined the place of Holter monitoring to study the prognostic value of ventricular arrhythmias and heart rate variability (HRV) in patients with mild to moderate CHF during long-term follow-up.

METHODS

We studied 90 patients with mild to moderate CHF and NYHA class II who had been enrolled in the Dutch Ibopamine Multicenter Trial. At baseline their mean age was 60.5 +/- 8.0 years, left ventricular ejection fraction (LVEF) was 0.29 +/- 0.09, and 85% were males. At the start of the study, patients were only using diuretics, while digoxin, and particularly ACE inhibitors and beta-blockers were initiated later. Univariate and multivariate proportional hazard analyses were performed.

RESULTS

At baseline 80% of patients were in NYHA class II, and 20% were in class III; their mean age was 60 years, mean LVEF was 0.29, and 85% were men. During a follow-up of 13 years, 47 patients (53%) died. Cardiovascular (CV) death occurred in 39 patients, of which 28 were sudden cardiac death (SCD). For both CV death and SCD, LVEF <30% and ventricular premature beats/h (>20) were independent risk markers. Of the HRV parameters, total power (>2,500 ms(2)) was an important risk marker for CV death, but not for SCD.

CONCLUSION

The present 13-year follow-up study in 90 patients with mild to moderate CHF showed that ventricular premature beats and HRV may have important value in predicting outcome.

Elevated B-type natriuretic peptide levels in patients with nonischemic cardiomyopathy predict occurrence of arrhythmic events

BACKGROUND

Patients with nonischemic cardiomyopathy (DCM) are at high risk for sudden cardiac death (SCD). However, the predictive value of prophylactic implantation of implantable cardioverter defibrillators (ICD) in this patient cohort is yet unclear.

METHODS AND RESULTS

Whether NT pro BNP levels and/or reproducible non sustained ventricular tachycardias (NSVTs) are predictive for SCD was prospectively tested in 30 patients with DCM and LVEF </= 40%. All patients received Holter-recordings (HR) on three consecutive days and baseline NT-pro BNP levels were determined. Patients were followed for occurrence of ventricular tachyarrhythmias or unexplained syncope. A great degree of variability was found regarding the occurrence of NSVTs (10% had NSVTs in two consecutive HR, 10% in three consecutive HR, 30% in one HR and 50% had no NSVTs). Patients with NSVTs in more than one HR had significantly higher NT-pro BNP levels (first quartile: 715 pg/ml, median 2,176 pg/ml, third quartile 5,755 pg/ml vs. first quartile 273 pg/ml, median 566 pg/ml, third quartile 1,350 pg/ml, P = 0.0388). During a mean follow-up of 21.6 +/- 1.2 months patients with an arrhythmic event had significantly higher NT-pro BNP levels than patients without event (first quartile: 1,002 pg/ml, median 4,075 pg/ml, third quartile 7,777 pg/ml vs. first quartile 173 pg/ml, median 267 pg/ml, third quartile 1,220 pg/ml, P = 0.0135). NT-pro BNP levels of 2,259 pg/ml were identified as optimal cut-off value for the prediction of arrhythmic events (P = 0.0313). In contrast reproducible NSVTs were not predictive for arrhythmic events (P = 0.0960).

CONCLUSION

The present study demonstrates that in patients with DCM the value of reproducible NSVTs in predicting arrhythmic events is low. In contrast raised NT-pro BNP levels significantly correlated with occurrence of symptomatic ventricular arrhythmias. Larger prospective trials are required to confirm these results.

Reversal of isoproterenol-induced downregulation of phospholamban and FKBP12.6 by CPU0213-mediated antagonism of endothelin receptors

AIM

The downregulation of phospholamban (PLB) and FKBP12.6 as a result of beta- receptor activation is involved in the pathway(s) of congestive heart failure. We hypothesized that the endothelin (ET)-1 system may link to downregulated PLB and FKBP12.6.

METHODS

Rats were subjected to ischemia/reperfusion (I/R) to cause heart failure (HF). 1 mg/kg isoproterenol (ISO) was injected subcutaneously (sc) for 10 d to worsen HF. 30 mg/kg CPU0213 (sc), a dual ET receptor (ETAR/ETBR) antagonist was given from d 6 to d 10. On d 11, cardiac function was assessed together with the determination of mRNA levels of ryanodine receptor 2, calstabin-2 (FKBP12.6), PLB, and sarcoplasmic reticulum Ca2+-ATPase. Isolated adult rat ventricular myocytes were incubated with ISO at 1X10(-6) mol/L to set up an in vitro model of HF. Propranolol (PRO), CPU0213, and darusentan (DAR, an ETAR antagonist) were incubated with cardiomyocytes at 1X10(-5) mol/L or 1X10(-6) mol/L in the presence of ISO (1X10(-6) mol/L). Immunocytochemistry and Western blotting were applied for measuring the protein levels of PLB and FKBP12.6.

RESULTS

The worsened hemodynamics produced by I/R were exacerbated by ISO pretreatment. The significant downregulation of the gene expression of PLB and FKBP12.6 and worsened cardiac function by ISO were reversed by CPU0213. In vitro ISO 1X10(-6) mol/L produced a sharp decline of PLB and FKBP12.6 proteins relative to the control. The downregulation of the protein expression was significantly reversed by the ET receptor antagonist CPU0213 or DAR, comparable to that achieved by PRO.

CONCLUSION

This study demonstrates a role of ET in mediating the downregulation of the cardiac Ca2+-handling protein by ISO.

Left atrial remodelling contributes to the progression of asymptomatic left ventricular systolic dysfunction to chronic symptomatic heart failure

Systolic heart failure (HF) is a progressive disorder that often begins with asymptomatic left ventricular (LV) systolic dysfunction and culminates in symptoms from fluid overload and poor end-organ perfusion. The progression to symptomatic HF is accompanied by marked activation of neurohormonal and cytokine systems, as well as a series of adaptive LV anatomical and functional changes, collectively referred to as LV remodelling. However, the mechanisms underlying symptom appearance have not been delineated and the weight of experimental and clinical evidence suggests that the development of symptomatic HF occurs independently of the haemodynamic status of the patient. The left atrium is a muscular chamber strategically located between the left ventricle and the pulmonary circulation with important mechanical function (modulation of LV filling), which is closely coupled with its endocrine (atrial natriuretic peptide synthesis and secretion) and regulatory (contribution to the control of sympathetic activity and vasopressin release) functions. In this narrative review we provide evidence supporting the concept that left atrial dilation and systolic dysfunction (left atrial remodelling) contributes to the progression of asymptomatic LV dysfunction to chronic symptomatic systolic HF as it is a prerequisite for the development of the pulmonary congestion and marked neuronhormoral activity that characterize the symptomatic state.