Showing papers by "David A. Kass published in 2010"

Monoamine Oxidase A–Mediated Enhanced Catabolism of Norepinephrine Contributes to Adverse Remodeling and Pump Failure in Hearts With Pressure Overload

Abstract: Rationale: Monoamine oxidases (MAOs) are mitochondrial enzymes that catabolize prohypertrophic neurotransmitters, such as norepinephrine and serotonin, generating hydrogen peroxide. Because excess reactive oxygen species and catecholamines are major contributors to the pathophysiology of congestive heart failure, MAOs could play an important role in this process. Objective: Here, we investigated the role of MAO-A in maladaptive hypertrophy and heart failure. Methods and Results: We report that MAO-A activity is triggered in isolated neonatal and adult myocytes on stimulation with norepinephrine, followed by increase in cell size, reactive oxygen species production, and signs of maladaptive hypertrophy. All of these in vitro changes occur, in part, independently from α- and β-adrenergic receptor–operated signaling and are inhibited by the specific MAO-A inhibitor clorgyline. In mice with left ventricular dilation and pump failure attributable to pressure overload, norepinephrine catabolism by MAO-A is increased accompanied by exacerbated oxidative stress. MAO-A inhibition prevents these changes, and also reverses fetal gene reprogramming, metalloproteinase and caspase-3 activation, as well as myocardial apoptosis. The specific role of MAO-A was further tested in mice expressing a dominant-negative MAO-A (MAO-A neo ), which were more protected against pressure overload than their wild-type littermates. Conclusions: In addition to adrenergic receptor–dependent mechanisms, enhanced MAO-A activity coupled with increased intramyocardial norepinephrine availability results in augmented reactive oxygen species generation, contributing to maladaptive remodeling and left ventricular dysfunction in hearts subjected to chronic stress.

Ultrastructure and Regulation of Lateralized Connexin43 in the Failing Heart

Abstract: Rationale: Gap junctions mediate cell-to-cell electric coupling of cardiomyocytes. The primary gap junction protein in the working myocardium, connexin43 (Cx43), exhibits increased localization at the lateral membranes of cardiomyocytes in a variety of heart diseases, although the precise location and function of this population is unknown. Objective: To define the subcellular location of lateralized gap junctions at the light and electron microscopic level, and further characterize the biochemical regulation of gap junction turnover. Methods and Results: By electron microscopy, we characterized gap junctions formed between cardiomyocyte lateral membranes in failing canine ventricular myocardium. These gap junctions were varied in structure and appeared to be extensively internalizing. Internalized gap junctions were incorporated into multilamellar membrane structures, with features characteristic of autophagosomes. Intracellular Cx43 extensively colocalized with the autophagosome marker GFP-LC3 when both proteins were exogenously expressed in HeLa cells, and endogenous Cx43 colocalized with GFP-LC3 in neonatal rat ventricular myocytes. Furthermore, a distinct phosphorylated form of Cx43, as well as the autophagosome-targeted form of LC3 (microtubule-associated protein light chain 3) targeted to lipid rafts in cardiac tissue, and both were increased in heart failure. Conclusions: Our data demonstrate a previously unrecognized pathway of gap junction internalization and degradation in the heart and identify a cellular pathway with potential therapeutic implications.

Modulation of mitochondrial proteome and improved mitochondrial function by biventricular pacing of dyssynchronous failing hearts.

Abstract: Background— Cardiac resynchronization therapy (CRT) improves chamber mechanoenergetics and morbidity and mortality of patients manifesting heart failure with ventricular dyssynchrony; however, litt...

PDE5A suppression of acute β-adrenergic activation requires modulation of myocyte beta-3 signaling coupled to PKG-mediated troponin I phosphorylation

Abstract: Phosphodiesterase type 5A (PDE5A) inhibitors acutely suppress beta-adrenergic receptor (beta-AR) stimulation in left ventricular myocytes and hearts. This modulation requires cyclic GMP synthesis via nitric oxide synthase (NOS)-NO stimulation, but upstream and downstream mechanisms remain un-defined. To determine this, adult cardiac myocytes from genetically engineered mice and controls were studied by video microscopy to assess sarcomere shortening (SS) and fura2-AM fluorescence to measure calcium transients (CaT). Enhanced SS from isoproterenol (ISO, 10 nM) was suppressed >or=50% by the PDE5A inhibitor sildenafil (SIL, 1 microM), without altering CaT. This regulation was unaltered despite co-inhibition of either the cGMP-stimulated cAMP-esterase PDE2 (Bay 60-7550), or cGMP-inhibited cAMP-esterase PDE3 (cilostamide). Thus, the SIL response could not be ascribed to cGMP interaction with alternative PDEs. However, genetic deletion (or pharmacologic blockade) of beta3-ARs, which couple to NOS signaling, fully prevented SIL modulation of ISO-stimulated SS. Importantly, both PDE5A protein expression and activity were similar in beta3-AR knockout (beta3-AR(-/-)) myocytes as in controls. Downstream, cGMP stimulates protein kinase G (PKG), and we found contractile modulation by SIL required PKG activation and enhanced TnI phosphorylation at S23, S24. Myocytes expressing the slow skeletal TnI isoform which lacks these sites displayed no modulation of ISO responses by SIL. Non-equilibrium isoelectric focusing gel electrophoresis showed SIL increased TnI phosphorylation above that from concomitant ISO in control but not beta3-AR(-/-) myocytes. These data support a cascade involving beta3-AR stimulation, and subsequent PKG-dependent TnI S23, S24 phosphorylation as primary factors underlying the capacity of acute PDE5A inhibition to blunt myocardial beta-adrenergic stimulation.

TRP-ing up heart and vessels: canonical transient receptor potential channels and cardiovascular disease.

Abstract: Transient receptor potential channels are a large superfamily of non-selective and non-voltage-gated ion channels that convey signaling information linked to a broad range of sensory inputs. In the cardiovascular system, the canonical transient receptor potential (TRPC) family has been particularly found to play a role in vascular and cardiac disease, responding to neurohormonal and mechanical load stimulation. TRPC1, TRPC3, and TRPC6 are often upregulated in models of cardiovascular disease, and their inhibition ameliorates the associated pathophysiology. Studies in gene deletion models and overexpression models of wild-type and dominant-negative proteins supports a direct role of these channels, which likely act together as heterotetramers to influence signaling. Recent evidence has further revealed the importance of protein kinase G phosphorylation as a mechanism to suppress TRPC6 channel current and dependent signaling in vascular and cardiac myocytes. This suggests a novel mechanism underlying benefits of drugs such as sildenafil, a phosphodiesterase type 5 inhibitor, nitrates, and atrial natriuretic peptides. This review describes new evidence supporting a pathophysiologic role of these three TRPC channels, and the potential utility of inhibition strategies to treat cardiovascular disease.

Nitroxyl enhances myocyte Ca2+ transients by exclusively targeting SR Ca2+-cycling.

Abstract: Nitroxyl (HNO), the 1-electron reduction product of nitric oxide, improves myocardial contraction in normal and failing hearts. Here we test whether the HNO donor Angeli's salt (AS) will change myocyte action potential (AP) waveform by altering the L-type Ca2+ current (ICa) and contrast the contractile effects of HNO with that of the hydroxyl radical (.OH) and nitrite (NO2-), two potential breakdown products of AS. We confirmed the positive effect of AS/HNO on basal cardiomyocyte function, as opposed to the detrimental effect of .OH and the negligible effect of NO2-. Upon examination of the myocyte AP, we observed no change in resting membrane potential or AP duration to 20 per cent repolarization with AS/HNO, whereas AP duration to 90 per cent repolarization was slightly prolonged. However, perfusion with AS/HNO did not elicit a change in basal ICa, but did hasten ICa inactivation. Upon further examination of the SR, the AS/HNO-induced increase in cardiomyocyte Ca2+ transients was abolished with inhibition of SR Ca2+-cycling. Therefore, the HNO-induced increase in Ca2+ transients results exclusively from changes in SR Ca2+-cycling, and not from ICa.

Protective role of PI3-kinase/Akt/eNOS signaling in mechanical stress through inhibition of p38 mitogen-activated protein kinase in mouse lung

Abstract: To test the hypothesis that PI3K/Akt/eNOS signaling has a protective role in a murine model of ventilation associated lung injury (VALI) through down-regulation of p38 MAPK signaling. Male C57BL/J6 (wild-type, WT) or eNOS knockout mice (eNOS−/−) were exposed to mechanical ventilation (MV) with low (LVT, 7 mL/kg) and high tidal volume (HVT, 20 mL/kg) for 0−4 h. A subset of WT mice was administered the specific inhibitors of PI3K (100 nmol/L Wortmannin [Wort], ip) or of p38 MAPK (SB203580, 2 mg/kg, ip) 1 h before MV. Cultured type II alveolar epithelial cells C10 were exposed to 18% cyclic stretch for 2 h with or without 20 nmol/L Wort pretreatment. At the end of the experiment, the capillary leakage in vivo was assessed by extravasation of Evans blue dye (EBD), wet/dry weight ratio and lung lavage protein concentration. The lung tissue and cell lysate were also collected for protein and histological review. MV decreased PI3K/Akt phosphorylation and eNOS expression but increased phospho-p38 MAPK expression along with a lung leakage of EBD. Inhibitions of phospho-Akt by Wort worsen the lung edema, whereas inhibition of p38 MAPK kinase restored activation of Akt together with alleviated capillary leakage. eNOS−/− mice showed an exacerbated lung edema and injury. The stretched C10 cells demonstrated that Wort diminished the activation of Akt, but potentiated phosphorylation of MAPK p38. Our results indicate that PI-3K/Akt/eNOS pathway has significant protective effects in VALI by preventing capillary leakage, and that there is a cross-talk between PI3K/Akt and p38 MAPK pathways in vascular barrier dysfunction resulting from VALI.

Usefulness of Soluble Endoglin as a Noninvasive Measure of Left Ventricular Filling Pressure in Heart Failure

Abstract: Progressive left ventricular (LV) dysfunction induces expression of the cytokine transforming growth factor-β1. Endoglin (CD105) is a transforming growth factor-β1 co-receptor that is released into the circulation as soluble endoglin (sEng). The objective of the present study was to assess the serum levels of sEng in patients with heart failure and to identify the predictive value of sEng for detecting elevated left ventricular end-diastolic pressures (LVEDPs). We measured the sEng levels in 82 consecutive patients with suspected LV dysfunction referred for determination of left heart filling pressures using cardiac catheterization. Among these subjects, the sEng levels correlated with the LVEDP (R = 0.689; p <0.0001), irrespective of the LV ejection fraction. Using a receiving operating characteristic curve, the sEng levels predicted an LVEDP of ≥16 mm Hg with an area under the curve of 0.85, exceeding the measured area under the curves for both atrial and brain natriuretic peptide, currently used biomarkers for heart failure diagnosis (atrial natriuretic peptide 0.68 and brain natriuretic peptide 0.65; p <0.01 vs sEng). In 10 subjects receiving medical therapy guided by invasive hemodynamic monitoring for heart failure, decreased a pulmonary capillary wedge pressure was associated with a reduced sEng level (R = 0.75, p = 0.008). Finally, compared to 25 healthy controls, the sEng levels were elevated in subjects with suspected LV dysfunction (3,589 ± 588 vs 4,257 ± 966 pg/ml, respectively, p <0.005) and correlated directly with the New York Heart Association class (R = 0.501, p<0.001). In conclusion, circulating levels of sEng are elevated in patients with increased LVEDP and New York Heart Association class, irrespective of the LV ejection fraction. sEng levels also decreased in association with a reduced cardiac filling pressure after diuresis. These findings have identified circulating sEng as a sensitive measure of elevated left heart filling pressures.

Analysis of Isovolumic Relaxation in Failing Hearts by Monoexponential Time Constants Overestimates Lusitropic Change and Load-dependence: Mechanisms and Advantages of Alternative Logistic Fit

Abstract: Background— Failing hearts display slow relaxation with apparent increased load sensitivity. However, inaccuracies of monoexponential analysis can contribute to these observations, and different qualitative and quantitative results might be obtained by alternative models. We tested whether pressure relaxation of failing hearts consistently deviates from a monoexponential waveform, leading to overestimations of lusitropic change and load sensitivity by monoexponential-derived time constants.Methods and Results— Fourteen dogs were studied before and after tachycardia pacing-induced heart failure. Relaxation time constants were derived by monoexponential fits (τE) with zero or nonzero asymptotes and by a logistic fit (τL). τL assumes nonlinear relations between pressure and its first derivative, whereas τE assumes a linear dependence. Load sensitivity of τ was tested by comparing beats during vena caval occlusion. τE prolonged by 75% to 80% with heart failure, 3 times more than τL (P<0.01). τE displayed mark...

Hemodynamic Improvement in Cardiac Resynchronization Does Not Require Improvement in Left Ventricular Rotation Mechanics: Three-Dimensional Tagged MRI Analysis

Abstract: BACKGROUND: Earlier studies have yielded conflicting evidence on whether or not cardiac resynchronization therapy (CRT) improves left ventricular (LV) rotation mechanics. METHODS AND RESULTS: In dogs with left bundle branch block and pacing-induced heart failure (n=7), we studied the effects of CRT on LV rotation mechanics in vivo by 3-dimensional tagged magnetic resonance imaging with a temporal resolution of 14 ms. CRT significantly improved hemodynamic parameters but did not significantly change the LV rotation or rotation rate. LV torsion, defined as LV rotation of each slice with respect to that of the most basal slice, was not significantly changed by CRT. CRT did not significantly change the LV torsion rate. There was no significant circumferential regional heterogeneity (anterior, lateral, inferior, and septal) in LV rotation mechanics in either left bundle branch block with pacing-induced heart failure or CRT, but there was significant apex-to-base regional heterogeneity. CONCLUSIONS: CRT acutely improves hemodynamic parameters without improving LV rotation mechanics. There is no significant circumferential regional heterogeneity of LV rotation mechanics in the mechanically dyssynchronous heart. These results suggest that LV rotation mechanics is an index of global LV function, which requires coordination of all regions of the left ventricle, and improvement in LV rotation mechanics appears to be a specific but insensitive index of acute hemodynamic response to CRT.

Regulation and role of myocyte cyclic GMP-dependent protein kinase-1

Abstract: We were intrigued with the study by Lukowski et al. (1), which investigated mice lacking cGMP-activated kinase (cGK1α and cGK1β) in all cells except those with smooth muscle (sm22) promoter activity (cGK1β-rescue) and concluded that cardiomyocyte cGK1 does not modify hypertrophic responses to β-adrenergic or pressure stress. As this study appears to counter prior work suggesting cGK1 suppresses myocyte hypertrophy, we felt it was important to point out some alternative interpretations to the readers. For example, their conclusions presume that cGK1 activity rose sufficiently in wild-type controls with their stress models, but this was not confirmed. Basal myocyte cGK1 activity is low, yet it may confer potent brake-like effects if sufficiently activated. The authors did not test if antihypertrophic effects of nitric oxide, natriuretic peptides, or other methods to stimulate cGMP levels are myocyte cGK1-independent, which is unlikely. Antihypertrophic action also requires that relevant cGK1 targets (e.g., calcineurin and Gαq cascades) be stimulated, which depends on the mode and extent of stress. Sildenafil [phosphodiesterase type 5 (PDE5) inhibitor] augments cGK1 activity similarly in moderate and severe pressure overload but suppresses hypertrophy more in severe overload where cGK1-targeted signaling is activated (2). In Lukowski et al. (1), isoproterenol and pressure overload yielded modest 20–40% increases in left ventricular mass (figures showed higher values because of an unexplained decline in body weight), suggesting that cGK1-targeted cascades may not have been activated. Last, cardiac characteristics of the genetic model were not fully described, although it displays time-dependent increased mortality by 1 year. This is especially relevant, because the rescue model is created in mice harboring a complete cGK1 deletion that cannot be bred because of early mortality and the mice are rescued in the vasculature only.

Clinical Trials: Methods and Design The Restoration of Chronotropic CompEtence in Heart Failure PatientS with Normal Ejection FracTion (RESET) Study: Rationale and Design

Abstract: Background: Heart failure with preserved ejection fraction (HFpEF) is the predominant form of heart failure among the elderly and in women. However, there are few if any evidence-based therapeutic options for HFpEF. The chief complaint of HFpEF is reduced tolerance to physical exertion. Recent data revealed that 1 potential mechanism of exertional intolerance in HFpEF patients is inadequate chronotropic response. Although there is considerable evidence demonstrating the benefits of rate-adaptive pacing (RAP) provided from implantable cardiac devices in patients with an impaired chronotropic response, the effect of RAP in HFpEF is unknown. Methods and Results: The Restoration of Chronotropic CompEtence in Heart Failure PatientS with Normal Ejection FracTion (RESET) study is a prospective, multicenter, double-blind, randomized with stratification, study assessing the effect of RAP on peak oxygen consumption and quality of life. RAP therapy will be evaluated in a crossover paired fashion for each patient within each study stratum. Study strata are based on patient b-blocker usage at time of enrollment. The study is powered to assess the impact of pacing independently in both strata. Conclusions: The RESET study seeks to evaluate the potential benefit of RAP in patients with symptomatic mild to moderate HFpEF and chronotropic impairment. Study enrollment began in July 2008. (J Cardiac Fail 2010;16:17e24)

Beta 3-Adrenoreceptor Agonists for the Treatment of Cardiac Hypertrophy and Heart Failure

Abstract: The present invention relates to the field of cardiology. More specifically, the present invention relates to the use of β3 adrenoreceptor agonists to treat cardiac hypertrophy and heart failure. In a specific embodiment, a method for treating cardiac hypertrophy comprises the step of administering a therapeutically effective amount of a β3 adrenoreceptor agonist to a patient diagnosed with cardiac hypertrophy. In a more specific embodiment, the method for treating cardiac hypertrophy comprises the step of administering a therapeutically effective amount of the β3 adrenoreceptor agonist BRL 26830A to a patient diagnosed with cardiac hypertrophy. In a further embodiment, the present invention provides a method for treating a cardiovascular disease or condition associated with cardiac hypertrophy comprising the step of administering a therapeutically effective amount of a β3 adrenoreceptor agonist to a patient diagnosed with cardiac hypertrophy.