Dissociation between regional dysfunction and beta-adrenergic receptor signaling in heart failure

Continuous hemodiafiltration as a rescue therapy for patients with cardiopulmonary failure caused by enterovirus-71: a retrospective observational study in a PICU

Background

Hand, foot and mouth disease (HFMD) remains a burdensome health issue in mainland China. Enterovirus71 (EV-A71) is the main pathogen of severe HFMD. Continuous hemofiltration improves fluid overload, restores kidney function and alleviates inflammatory reactions. The aim of the present study was to evaluate the effects of continuous veno-venous hemodiafiltration (CVVHDF) on severe HFMD caused by EV-A71(EV-A71-HFMD) in a pediatric intensive care unit (PICU).

Methods

A retrospective observational study was performed in a tertiary university PICU from January 2012 to December 2016. Children with severe EV-A71-HFMD complicated by cardiopulmonary failure were included. The patients were divided into a CVVHDF group and a conventional therapy (control) group (non-CVVHDF). The demographics, characteristics, and outcomes between the groups were collected and analyzed.

Results

Twenty-nine patients with severe EV-A71-HFMD were enrolled. The 28-day mortality was 17.6% (3/17) in the CVVHDF group and 33.3% (4/12) in the non-CVVHDF group, with no statistical significance between the two groups (P = 0.403). The median interval between CVVHDF initiation and PICU admission was 6 (4,8.5) hrs, and the median duration of CVVHDF was 48 (36, 64) hrs. The left ventricular ejection fraction (LVEF) and cardiac index (CI) in the CVVHDF group were improved after treatment. The plasma levels of catecholamines and renin-angiotensin-aldosterone system (RAAS) substances in the CVVHDF group were significantly decreased after treatment. The decreased catecholamines and RAAS substances included adrenalin (169.8 [145.5, 244.6] vs. 148.0 [109.0, 208.1] ng/L, P = 0.033), dopamine (152.7 [97.0, 191.1] vs. 96.0 [68.0, 160.9] ng/L, P = 0.026), angiotensin II (185.9 [125.2, 800.0] vs. 106.0 [90.8, 232.5] ng/L, P = 0.047), aldosterone (165.7 [94.0, 353.3] vs. 103.3 [84.3, 144.3] ng/L, P = 0.033), and renin (1.12 [0.74, 3.45] vs. 0.79 [0.52, 1.25] μg/L/h, P = 0.029),

Conclusions

CVVHDF reduced the levels of catecholamines and RAAS substances and improved cardiovascular function. Continuous hemodiafiltration may represent a potential therapy in patients with severe EV-A71-HFMD complicated with cardiopulmonary failure.

Cell-to-cell variability in troponin I phosphorylation in a porcine model of pacing-induced heart failure

We tested the hypothesis that myocardial contractile protein phosphorylation and the Ca²⁺ sensitivity of force production are dysregulated in a porcine model of pacing-induced heart failure (HF). The level of protein kinase A (PKA)-dependent cardiac troponin I (TnI) phosphorylation was lower in the myocardium surrounding the pacing electrode (pacing site) of the failing left ventricle (LV) than in the controls. Immunohistochemical assays of the LV pacing site pointed to isolated clusters of cardiomyocytes exhibiting a reduced level of phosphorylated TnI. Flow cytometry on isolated and permeabilized cardiomyocytes revealed a significantly larger cell-to-cell variation in the level of TnI phosphorylation of the LV pacing site than in the opposite region in HF or in either region in the controls: the interquartile range (IQR) on the distribution histogram of relative TnI phosphorylation was wider at the pacing site (IQR = 0.53) than that at the remote site of HF (IQR = 0.42; P = 0.0047) or that of the free wall of the control animals (IQR = 0.36; P = 0.0093). Additionally, the Ca²⁺ sensitivities of isometric force production were higher and appeared to be more variable in single permeabilized cardiomyocytes from the HF pacing site than in the healthy myocardium. In conclusion, the level of PKA-dependent TnI phosphorylation and the Ca²⁺ sensitivity of force production exhibited a high cell-to-cell variability at the LV pacing site, possibly explaining the abnormalities of the regional myocardial contractile function in a porcine model of pacing-induced HF.

Chronic sympathetic activation promotes downregulation of β-adrenoceptor-mediated effects in the guinea pig heart independently of structural remodeling and systolic dysfunction

It is uncertain if downregulation of β-adrenoceptor signaling pathway is promoted by an enhanced adrenergic tone at an early stage of cardiac disease, or it develops secondary to detrimental local myocardial changes in advanced heart failure. We examined the integrity of β-adrenoceptor signaling pathway upon chronic infusion of isoproterenol, a β-adrenoceptor agonist, at a dose producing no structural left ventricular (LV) remodeling and systolic dysfunction. Subcutaneous isoproterenol infusion (400 μg kg(-1) h(-1) over 16 days) to guinea pigs using osmotic minipumps produced no change in cardiac weights, LV internal dimensions, myocyte cross-sectional area, extent of interstitial fibrosis, and basal contractile function. Isolated, perfused heart preparations from isoproterenol-treated guinea pigs exhibited attenuated responsiveness to acute β-adrenoceptor stimulation, as evidenced by reduced LV developed pressure increase, less shortening of LV epicardial monophasic action potential and effective refractory period, and less myocardial cyclic adenosine monophosphate elevation, in response to isoproterenol exposure, when compared to saline-treated controls. Pharmacological responses to forskolin, an activator of the adenylate cyclase catalytic subunit, were well preserved in isoproterenol-treated hearts. Downregulation of β-adrenoceptor-mediated effects upon chronic isoproterenol infusion was associated with markedly reduced stimulatory G-protein α-subunit (G(sα)) myocardial expression levels. No change in expression levels of β-adrenoceptors, G-protein-coupled receptor kinase 2, inhibitory G-protein α-subunit (G(iα2)), and Ca(v)1.2 and K(v)7.1 ion channels was determined in isoproterenol-treated hearts. We therefore conclude that sustained adrenergic overstimulation may promote downregulation of myocardial β-adrenoceptor-mediated effects independently of structural LV remodeling and systolic failure, an effect attributed to β-adrenoceptor uncoupling from adenylate cyclase due to reduced G(sα)-protein expression.

Animal models of dilated cardiomyopathy for translational research

Animal models of cardiovascular disease have proved critically important for the discovery of pathophysiological mechanisms and for the advancement of diagnosis and therapy. They offer a number of advantages, principally the availability of adequate healthy controls and the absence of confounding factors such as marked differences in age, concomitant pathologies and pharmacological treatments. Dilated cardiomyopathy (DCM) is the third cause of heart failure (HF) and is characterized by progressive ventricular dilation and functional impairment in the absence of coronary lesions and/or hypertension. Over the past thirty years, investigators have developed numerous small and large animal models to study this very complex syndrome. Genetically modified mice are the most widely and intensively utilized research animals and allow high throughput studies on DCM. However, to translate discoveries from basic science into medical applications, research in large animal models becomes a necessary step. An accurate large animal model of DCM is pacing-induced HF. It is obtained by continuous cardiac pacing at a frequency three- to fourfold higher than the spontaneous heart rate and is mostly applied to dogs, but also to pigs, sheep and monkeys. To date, this model can still be considered a gold standard in HF research.

Myocardial distribution and regulation of GRK and beta-arrestin isoforms in congestive heart failure in rats

Myocardial G protein-coupled receptor kinase 2 (GRK2) has been shown to be involved in the pathophysiology of congestive heart failure (CHF). However, the cellular distribution of this isoform, as well as the other isoforms of the GRK-arrestin system, has not been studied in myocardial tissue. Thus myocardial expression and cellular distribution of the different GRK and arrestin isoforms were investigated in a rat model of CHF. Rats subjected to ligation of the left coronary artery or sham operation were euthanized 2, 7, or 42 days after the surgical procedure. Myocardial GRK2, GRK5, beta-arrestin-1, and beta-arrestin-2 mRNA levels, but not that of GRK3, were induced in the failing hearts. Consistently, Western blot analysis of tissue extracts from the nonischemic region of the left ventricle revealed 3.0-, 2.6-, and 1.5-fold elevations of GRK2, GRK5, and beta-arrestin-1, respectively, 7 days after induction of myocardial infarction compared with the sham-operated rats (P < 0.05). Immunohistochemical analysis of myocardial tissue sections and Western blot analysis of isolated cells revealed localization of GRK2 and beta-arrestin-1 predominantly in endothelial cells. Conversely, GRK3 was confined to cardiac myocytes. GRK5 immunostaining appeared to be homogeneously distributed in the cellular elements of the myocardium. In conclusion, myocardial mRNA and protein levels of GRK2, GRK5, and beta-arrestin-1 are induced in postinfarction failure in rats. The immunohistochemical analysis suggests that GRK2 and beta-arrestin-1 may act as primary regulators of endothelial function. Conversely, the cellular distribution of GRK3 and GRK5 implicates these isoforms as putative regulators of cardiac myocyte function.

Functional desensitization to isoproterenol without reducing cAMP production in canine failing cardiocytes

To corroborate alterations in the functional responses to beta-adrenergic receptor (beta-AR) stimulation with changes in beta-AR signaling in failing cardiomyocytes, contractile and L-type Ca(2+) current responses to isoproterenol along with stimulated cAMP generation were compared among cardiomyocytes isolated from canines with tachycardia-induced heart failure or healthy hearts. The magnitude of shortening of failing cardiomyocytes was significantly depressed (by 22 +/- 4.4%) under basal conditions, and the maximal response to isoproterenol was significantly reduced (by 45 +/- 18%). Similar results were obtained when the responses in the rate of contraction and rate of relaxation to isoproterenol were considered. The L-type Ca(2+) current amplitude measured in failing cardiomyocytes under basal conditions was unchanged, but the responses to isoproterenol were significantly reduced compared with healthy cells. Isoproterenol-stimulated cAMP generation was similar in sarcolemmal membranes derived from the homogenates of failing (45 +/- 6.8) and healthy cardiomyocytes (52 +/- 8.5 pmol cAMP. mg protein(-1). min(-1)). However, stimulated cAMP generation was found to be significantly reduced when the membranes were derived from the homogenates of whole tissue (failing: 67 +/- 8.1 vs. healthy: 140 +/- 27.8 pmol cAMP. mg protein(-1). min(-1)). Total beta-AR density was not reduced in membranes derived from either whole tissue or isolated cardiomyocyte homogenates, but the beta(1)/beta(2) ratio was significantly reduced in the former (failing: 45/55 vs. healthy: 72/28) without being altered in the latter (failing: 72/28, healthy: 77/23). We thus conclude that, in tachycardia-induced heart failure, reduction in the functional responses of isolated cardiomyocytes to beta-AR stimulation may be attributed to alterations in the excitation-contraction machinery rather than to limitation of cAMP generation.