Showing papers by "David A. Kass published in 2008"

Measurement of cardiac function using pressure–volume conductance catheter technique in mice and rats

Abstract: Ventricular pressure–volume relationships have become well established as the most rigorous and comprehensive ways to assess intact heart function Thanks to advances in miniature sensor technology, this approach has been successfully translated to small rodents, allowing for detailed characterization of cardiovascular function in genetically engineered mice, testing effects of pharmacotherapies and studying disease conditions This method is unique for providing measures of left ventricular (LV) performance that are more specific to the heart and less affected by vascular loading conditions Here we present descriptions and movies for procedures employing this method (anesthesia, intubation and surgical techniques, calibrations) We also provide examples of hemodynamics measurements obtained from normal mice/rats, and from animals with cardiac hypertrophy/heart failure, and describe values for various useful load-dependent and load-independent indexes of LV function obtained using different types of anesthesia The completion of the protocol takes 1–4 h (depending on the experimental design/end points)

Tackling heart failure in the twenty-first century

Abstract: Heart failure, or congestive heart failure, is a condition in which the heart cannot supply the body's tissues with enough blood. The result is a cascade of changes that lead to severe fatigue, breathlessness and, ultimately, death. In the past quarter century, much progress has been made in understanding the molecular and cellular processes that contribute to heart failure, leading to the development of effective therapies. Despite this, chronic heart failure remains a major cause of illness and death. And because the condition becomes more common with increasing age, the number of affected individuals is rising with the rapidly ageing global population. New treatments that target disease mechanisms at the cellular and whole-organ level are needed to halt and reverse the devastating consequences of this disease.

Cardiac Magnetic Resonance Assessment of Dyssynchrony and Myocardial Scar Predicts Function Class Improvement Following Cardiac Resynchronization Therapy

Abstract: Objectives We tested a circumferential mechanical dyssynchrony index (circumferential uniformity ratio estimate [CURE]; 0 to 1, 1 = synchrony) derived from magnetic resonance-myocardial tagging (MR-MT) for predicting clinical function class improvement following cardiac resynchronization therapy (CRT). Background There remains a significant nonresponse rate to CRT. MR-MT provides high quality mechanical activation data throughout the heart, and delayed enhancement cardiac magnetic resonance (DE-CMR) offers precise characterization of myocardial scar. Methods MR-MT was performed in 2 cohorts of heart failure patients with: 1) a CRT heart failure cohort (n = 20; left ventricular ejection fraction of 0.23 ± 0.057) to evaluate the role of MR-MT and DE-CMR prior to CRT; and 2) a multimodality cohort (n = 27; ejection fraction of 0.20 ± 0.066) to compare MR-MT and tissue Doppler imaging septal-lateral delay for assessment of mechanical dyssynchrony. MR-MT was also performed in 9 healthy control subjects. Results MR-MT showed that control subjects had highly synchronous contraction (CURE 0.96 ± 0.01), but tissue Doppler imaging indicated dyssynchrony in 44%. Using a cutoff of Conclusions The MR-MT assessment of circumferential mechanical dyssynchrony predicts improvement in function class after CRT. The addition of scar imaging by DE-CMR further improves this predictive value.

Reversal of Cardiac Hypertrophy and Fibrosis From Pressure Overload by Tetrahydrobiopterin Efficacy of Recoupling Nitric Oxide Synthase as a Therapeutic Strategy

Abstract: Background— Sustained pressure overload induces pathological cardiac hypertrophy and dysfunction Oxidative stress linked to nitric oxide synthase (NOS) uncoupling may play an important role We te

Reversal of global apoptosis and regional stress kinase activation by cardiac resynchronization.

Abstract: Background— Cardiac dyssynchrony in the failing heart worsens global function and efficiency and generates regional loading disparities that may exacerbate stress-response molecular signaling and w...

High-Dose Folic Acid Pretreatment Blunts Cardiac Dysfunction During Ischemia Coupled to Maintenance of High-Energy Phosphates and Reduces Postreperfusion Injury

Abstract: Background— The B vitamin folic acid (FA) is important to mitochondrial protein and nucleic acid synthesis, is an antioxidant, and enhances nitric oxide synthase activity. Here, we tested whether F...

Phospholamban thiols play a central role in activation of the cardiac muscle sarcoplasmic reticulum calcium pump by nitroxyl.

Abstract: Nitroxyl (HNO) donated by Angeli's salt activates uptake of Ca 2+ by the cardiac SR Ca 2+ pump (SERCA2a). To determine whether HNO achieves this by a direct interaction with SERCA2a or its regulatory protein, phospholamban (PLN), we measured its effects on SERCA2a activation (as reflected in dephosphoryla- tion) using insect cell microsomes expressing SERCA2a with or without PLN (wild-type and Cys f Ala mutant). The results show that activation of SERCA2a dephos- phorylation by HNO is PLN-dependent and that PLN thiols are targets for HNO. We conclude that HNO produces a disulfide bond that alters the conformation of PLN, relieving inhibition of the Ca 2+ pump. Stimulation of the cardiac SR Ca 2+ pump (SERCA2a) 1 in isolated SR vesicles by cAMP/protein kinase A-dependent phosphorylation of phospholamban (PLN) was originally demonstrated by Tada et al. (1). Subsequent studies showed that phosphorylation of PLN at Ser 16 increases the apparent Ca 2+ affinity of SERCA2a (2), the rates of phosphorylation and dephosphorylation (2, 3), and the Vmax of Ca 2+ transport (3, 4). Phosphorylation of Ser 16 induces a change in the conformation of PLN (5, 6), which relieves its inhibition and activates the pump. Recent work with ex- pressed Ca 2+ pump proteins suggests that activation of the cardiac SR Ca 2+ pump following the relief of PLN inhibition involves changes in the kinetic behavior of the Ca 2+ -ATPase consistent with SERCA2a oligomerization (7). These changes include stabilization of the ADP-sensitive phosphoenzyme, E1P, and allosteric activation of dephosphorylation by ATP, resulting in an increased rate of turnover of the ADP- insensitive phosphoenzyme, E2P. We have recently shown that nitroxyl (HNO) donated by Angeli's salt (AS, Na2N2O3) activates the SR Ca 2+ pump in isolated murine cardiac myocytes (8). This effect is inde- pendent of � -adrenergic activation (9) and results from a direct effect of HNO on the SR Ca 2+ pump as evidenced by stimulation of Ca 2+ uptake by HNO in isolated murine heart SR vesicles (8). We hypothesize that HNO stimulates Ca 2+ uptake by covalently modifying critical thiol residues in the SERCA2a pump and/or its regulatory protein, PLN, altering the conformation of these proteins, and relieving the inhibi- tion of the pump. Chemical modification of protein thiols by HNO can proceed by two pathways leading to either (a) the formation of a sulfinamide (RS(O)NH2) when one thiol group is involved or (b) the formation of a disulfide (RSSR) plus hydroxylamine (H2NOH) when two thiols are in the proximity of each other (10, 11). The fact that HNO-induced activation of RyR2 receptors reconstituted in lipid planar bilayers can be reversed by DTT (8) suggests that disulfide bond formation may be important in activating Ca 2+ release. In this study, we investigated the mechanism of activation of the SR Ca 2+ pump by HNO using SERCA2a expressed in the absence or presence of PLN in High Five (HF) insect cell microsomes. To study Ca 2+ pump activation by HNO, we measured the kinetics of dephosphorylation of SERCA2a, which is accelerated by HNO. To test whether thiol residues in PLN are critical for activation, we carried out these experiments in microsomes expressing SERCA2a and null-Cys PLN (PLN(-C)) in which the three transmembrane (TM) domain cysteine residues were replaced with alanine. Immunoblotting with an anti-PLN antibody was used to test whether HNO-induced PLN oligomer formation contributes to the relief of inhibition of SERCA2a by PLN. The results show that PLN is necessary for activation of SERCA2a by HNO and that cysteine residues in the TM domain of PLN play a critical role in PLN-dependent HNO activation of the Ca 2+ pump.

Mechanisms and potential therapeutic targets for folic acid in cardiovascular disease.

Abstract: Folic acid (FA) is a member of the B-vitamin family with cardiovascular roles in homocysteine regulation and endothelial nitric oxide synthase (eNOS) activity. Its interaction with eNOS is thought to be due to the enhancement of tetrahydrobiopterin bioavailability, helping maintain eNOS in its coupled state to favor the generation of nitric oxide rather than oxygen free radicals. FA also plays a role in the prevention of several cardiac and noncardiac malformations, has potent direct antioxidant and antithrombotic effects, and can interfere with the production of the endothelial-derived hyperpolarizing factor. These multiple mechanisms of action have led to studies regarding the therapeutic potential of FA in cardiovascular disease. To date, studies have demonstrated that FA ameliorates endothelial dysfunction and nitrate tolerance and can improve pathological features of atherosclerosis. These effects appear to be homocysteine independent but rather related to their role in eNOS function. Given the growing evidence that nitric oxide synthase uncoupling plays a major role in many cardiovascular disorders, the potential of exogenous FA as an inexpensive and safe oral therapy is intriguing and is stimulating ongoing investigations.

Sustained Soluble Guanylate Cyclase Stimulation Offsets Nitric-Oxide Synthase Inhibition to Restore Acute Cardiac Modulation by Sildenafil

Abstract: Phosphodiesterase type 5 (PDE5) inhibitors are used to treat erectile dysfunction, and growing evidence supports potential cardiovascular utility. Their efficacy declines with reduced nitric-oxide synthase (NOS) activity common to various diseases. We tested whether direct soluble guanylate cyclase (sGC) stimulation restores in vivo cardiovascular modulation by PDE5 inhibition despite acute or chronically suppressed NOS activity. Mice (C57/Bl6; n = 62) were studied by in vivo pressure-volume analysis to assess acute modulation by the PDE5 inhibitor sildenafil (SIL; 100 microg/kg/min) of the cardiac response to isoproterenol (ISO) with or without NOS inhibition [N(omega)-nitro-L-arginine methyl ester (L-NAME)] and cotreatment by the sGC stimulator 2-[1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-5-(4-morpholinyl)pyrimidine-4,6-diamine (BAY 41-8543). SIL induced mild vasodilation but no basal cardiac effects and markedly blunted ISO-stimulated contractility. Acute BAY 41-8543 at a dose lacking cardiovascular effects did not alter ISO responses. However, after acute L-NAME, SIL ceased to influence cardiovascular function, but adding BAY 41-8543 fully restored SIL effects. After 1 week of L-NAME, neither SIL nor SIL + BAY 41-8543 acutely induced vasodilation or blunted ISO responses. However, sustained BAY 41-8543 despite concurrent NOS inhibition restored the cardiovascular efficacy of SIL. The disparity between acute and chronic NOS inhibition related to diffusion of PDE5 away from myocyte z-bands coupled with reduced protein kinase G activation. Both were restored by sustained sGC costimulation. Thus, PDE5 regulation of adrenergic reserve and systemic vasodilation depends upon NOS-induced cGMP/protein kinase G and can be enhanced by sustained low-level stimulation of sGC. This may prove beneficial for enhancing the efficacy of PDE5 inhibitors in conditions with chronically reduced NOS activity.

Method of treating ischemia/reperfusion injury with nitroxyl donors

Abstract: Nitroxyl donating compounds are administered prior to the onset of ischemia for the prevention and/or reduction of ischemia/reperfusion injury in subjects at risk for ischemia. Nitroxyl donors also are administered to organs to be transplanted for the prevention and/or reduction of ischemia/reperfusion injury upon reperfusion in a recipient. Nitroxyl donors include any nitroxyl donating compound. In particular cases the nitroxyl donor is a nitroxyl-donating diazeniumdiolate, such as Angeli's salt or IPA/NO.

Phosphodiesterase 5 inhibition blocks pressure overload-induced cardiac hypertrophy independent of the calcineurin pathway

Abstract: Aims Cyclic GMP (cGMP)-specific phosphodiesterase 5 (PDE5) inhibition by sildenafil (SIL) activates myocardial cGMP-dependent protein kinase G (PKG) and blunts cardiac hypertrophy. To date, the only documented target of PKG in myocardium is the serine–threonine phosphatase calcineurin (Cn), which is central to pathological cardiac hypertrophy. We tested whether Cn suppression is necessary in order to observe anti-hypertrophic effects of SIL. Methods and results Mice lacking the Cn-Aβ subunit ( CnA β−/−) and wild-type (WT) controls were subjected to transverse aorta constriction (TAC) with or without SIL (200 mg/kg/day, p.o.) for 3 weeks. TAC-induced elevation of Cn expression and activity in WT was absent in CnA β−/− hearts, and the latter accordingly developed less cardiac hypertrophy (50 vs. 100% increase in heart weight/tibia length, P < 0.03) and chamber dilation. SIL remained effective in CnA β−/− mice, increasing PKG activity similarly as in WT, suppressing hypertrophy and fetal gene expression, and enhancing heart function without altering afterload. TAC-stimulated calcium–calmodulin kinase II, Akt, and glycogen synthase kinase 3β in both groups (the first rising more in CnA β−/− hearts), and SIL also suppressed these similarly. Activation of extracellular signal-regulated kinase observed in WT-TAC but not CnA β−/− hearts was also suppressed by SIL. Conclusion PDE5A inhibition and its accompanying PKG activation blunt hypertrophy and improve heart function even without Cn activation. This occurs by its modulation of several alternative pathways which may result from concomitant distal targeting, or activity against a common proximal node.

Key pathways associated with heart failure development revealed by gene networks correlated with cardiac remodeling

Abstract: Heart failure (HF) is the leading cause of morbidity and mortality in the industrialized world. While the transcriptomic changes in end-stage failing myocardium have received much attention, no inf...

Message delivered: how myocytes control cAMP signaling.

Abstract: See related article, pages 1091–1100 Despite the vast array of specific receptors and ligands through which cells receive information from their outside environment, the first line of messengers that relay this onto internal signaling cascades is more limited. Yet, somehow, the purpose of the original message is conveyed (ie, we know who knocked on the front door), and the message ends up influencing just the right proteins to produce the desired effect. A striking example of this selectivity is the cyclic nucleotides for which only 2 basic types exist; cAMP and cGMP. Despite this limited cast, these molecules precisely regulate many complex and disparate cellular activities. Their trick is to be in the right place at the right time and with the right amount of signal. It is now well established that cyclic nucleotides are spatially compartmentalized to enable different external triggers to vary the internal cellular response.1–5 This can be achieved by localizing the cyclases that synthesize cAMP or cGMP in different parts of the cell, parking the effector kinase protein kinase (PK)A in particular regions by means of anchoring proteins (AKAPs)6 (may apply to PKG though still unclear), and targeting phosphodiesterases to one area or another and/or providing them with hierarchical control.1 The latter is thought to be particularly important by limiting diffusion of a cyclic nucleotide from its site of generation to other parts of the cell. There are eleven 3′,5′-phosphodiesterase (PDE) subfamily members with approximately 50 isoforms, targeting cAMP, cGMP, or in some instances both.7 Given that many of these PDEs can themselves be activated by cyclic nucleotides and/or their effector kinases, the system has substantial built-in complexity for localized regulation. Compartmental signaling was first …