Exercise training and sympathetic regulation in experimental heart failure

In this review, we put forth the hypothesis that reduction in sympathetic outflow after exercise training of animals with heart failure is mediated by reductions in angiotensin II and in angiotensin type 1 receptors. Furthermore, we provide evidence that exercise training provides for an upregulation of the neuronal isoform of nitric oxide synthase in the central nervous system that is sympathoinhibitory.

Silent information regulator 2alpha, a longevity factor and class III histone deacetylase, is an essential endogenous apoptosis inhibitor in cardiac myocytes

Yeast silent information regulator 2 (Sir2), a nicotinamide adenine dinucleotide-dependent histone deacetylase (HDAC) and founding member of the HDAC class III family, functions in a wide array of cellular processes, including gene silencing, longevity, and DNA damage repair. We examined whether or not the mammalian ortholog Sir2 affects growth and death of cardiac myocytes. Cardiac myocytes express Sir2alpha predominantly in the nucleus. Neonatal rat cardiac myocytes were treated with 20 mmol/L nicotinamide (NAM), a Sir2 inhibitor, or 50 nmol/L Trichostatin A (TSA), a class I and II HDAC inhibitor. NAM induced a significant increase in nuclear fragmentation (2.2-fold) and cleaved caspase-3, as did sirtinol, a specific Sir2 inhibitor, and expression of dominant-negative Sir2alpha. TSA also modestly increased cell death (1.5-fold) but without accompanying caspase-3 activation. Although TSA induced a 1.5-fold increase in cardiac myocyte size and protein content, NAM reduced both. In addition, NAM caused acetylation and increases in the transcriptional activity of p53, whereas TSA did not. NAM-induced cardiac myocyte apoptosis was inhibited in the presence of dominant-negative p53, suggesting that Sir2alpha inhibition causes apoptosis through p53. Overexpression of Sir2alpha protected cardiac myocytes from apoptosis in response to serum starvation and significantly increased the size of cardiac myocytes. Furthermore, Sir2 expression was increased significantly in hearts from dogs with heart failure induced by rapid pacing superimposed on stable, severe hypertrophy. These results suggest that endogenous Sir2alpha plays an essential role in mediating cell survival, whereas Sir2alpha overexpression protects myocytes from apoptosis and causes modest hypertrophy. In contrast, inhibition of endogenous class I and II HDACs primarily causes cardiac myocyte hypertrophy and also induces modest cell death. An increase in Sir2 expression during heart failure suggests that Sir2 may play a cardioprotective role in pathologic hearts in vivo.

Role of myocardial neuronal nitric oxide synthase-derived nitric oxide in beta-adrenergic hyporesponsiveness after myocardial infarction-induced heart failure in rat

BACKGROUND

An emerging concept is that a neuronal isoform of nitric oxide synthase (NOS1) may regulate myocardial contractility. However, a role for NOS1-derived nitric oxide (NO) in heart failure (HF) has not been defined.

METHODS AND RESULTS

Using a model of myocardial infarction-induced HF, we demonstrated that cardiac NOS1 expression and activity increased in HF rats (P<0.05 and P<0.001 versus shams, respectively). This was associated with translocation of NOS1 from the ryanodine receptor to the sarcolemma through interactions with caveolin-3 in HF hearts. With ex vivo and in vivo pressure-volume analysis, cardiac NOS1-derived NO was found to be negatively inotropic in shams but not HF hearts. Ventricular elastance (E(es)) was significantly reduced in HF rats (P<0.05), and tau, the time constant of left ventricular relaxation, was prolonged (both P<0.05). Acute NOS1 inhibition significantly increased E(es) by 33+/-3% and tau by 17+/-2% (P<0.05) in shams, although these effects were significantly attenuated in HF hearts. beta-Adrenergic stimulation induced a marked increase in systolic performance in sham hearts, with the responses being significantly blunted in HF hearts. E(es) increased by 163+/-42% (P<0.01) in sham hearts and 56+/-9% in HF hearts, and LV +dP/dt increased by 97+/-9% (P<0.01) in shams and 37+/-7% (P<0.05) in the HF group. Interestingly, preferential NOS1 inhibition enhanced the blunted responses of LV +dP/dt and E(es) to beta-adrenergic stimulation in HF rats but had no effect in shams.

CONCLUSIONS

These results provide the first evidence that increased NOS1-derived NO production may play a role in the autocrine regulation of myocardial contractility in HF.

Natriuretic peptides and the management of heart failure

Hyperactivation of the renin-angiotensin-aldosterone system (RAAS), heightened sympathetic drive and uncontrolled synthesis of inflammatory cytokines, exacerbates ventricular contractile dysfunction in heart failure patients. The pathophysiological consequences include excessive fluid retention, increased peripheral vascular resistance, and endothelial dysfunction. Consequently, the demand for additional work by the failing myocardium in the presence of a greater afterload cannot be sustained. Therapeutically exploiting the natriuretic peptide system may represent a physiological approach to dampen the deleterious effects of the neuroendocrine systems and inflammatory cytokines. In both patients and animal models of heart failure, pharmacologically increasing plasma natriuretic peptide levels ameliorated vascular tone, renal and endothelial function, and ventricular contractility. Based on these observations, the following review will highlight the therapeutic benefits of the natriuretic peptide system in heart failure.

Relation of serum levels of mast cell tryptase of left ventricular systolic function, left ventricular volume or congestive heart failure

BACKGROUND

Activated mast cells (MC) present in the myocardium of patients with cardiomyopathy may contribute to left ventricular dilatation and systolic dysfunction. We sought to determine whether peripheral levels of tryptase, an MC-specific protease, are related to indices of left ventricular size and function, as well as congestive heart failure (CHF) or coronary artery disease (CAD).

METHODS AND RESULTS

Serum tryptase was measured in 85 patients undergoing cardiac catheterization with left ventriculography and coronary angiography and examined in relation to left ventricular ejection fraction (LVEF), left ventricular end-diastolic volume (LVEDV), congestive heart failure (CHF), and angiographically evident CAD. Systemic tryptase levels were lower in patients with increased (>90 mL) LVEDV (6.2 [5.3-8.0] mcg/L versus 8.3 [6.6-10.3] mcg/L, P=.01) and in patients with CHF (6.2 [3.6-7.3] mcg/L versus 8 [6.2-10] mcg/L, P=.02) and tended to be lower in patients with depressed (<55%) LVEF (6.8 [5.2-9] mcg/L versus 8 [6.3-9.9] mcg/L, P=NS). Linear regression did not show a significant relationship between tryptase levels with either LVEF or LVEDV. Finally, tryptase levels were consistently elevated in relation to the presence of CAD.

CONCLUSION

Despite increased numbers of MC in the myocardium of patients with cardiomyopathy, systemic levels of MC tryptase appear to be lower in relation to LV systolic dysfunction, LV dilatation, or clinical CHF. In contrast, the presence of angiographically significant CAD is associated with elevated systemic tryptase levels.

Expression of inducible nitric oxide synthase is increased in patients with heart failure due to ischemic disease

The objective of the present study was to determine the relationship between nitric oxide synthases (NOS) and heart failure in cardiac tissue from patients with and without cardiac decompensation. Right atrial tissue was excised from patients with coronary artery disease (CAD) and left ventricular ejection fraction (LVEF) <35% (N = 10), and from patients with CAD and LVEF >60% (N = 10) during cardiac surgery. NOS activity was measured by the conversion of L-[H(3)]-arginine to L-[H(3)]-citrulline. Gene expression was quantified by the competitive reverse transcription-polymerase chain reaction. Both endothelial NOS (eNOS) activity and expression were significantly reduced in failing hearts compared to non-failing hearts: 0.36 +/- 0.18 vs 1.51 +/- 0.31 pmol mg-1 min-1 (P < 0.0001) and 0.37 +/- 0.08 vs 0.78 +/- 0.09 relative cDNA absorbance at 320 nm (P < 0.0001), respectively. In contrast, inducible NOS (iNOS) activity and expression were significantly higher in failing hearts than in non-failing hearts: 4.00 +/- 0.90 vs 1.54 +/- 0.65 pmol mg-1 min-1 (P < 0.0001) and 2.19 +/- 0.27 vs 1.43 +/- 0.13 cDNA absorbance at 320 nm (P < 0.0001), respectively. We conclude that heart failure down-regulates both eNOS activity and expression in cardiac tissue from patients with LVEF <35%. In contrast, iNOS activity and expression are increased in failing hearts and may represent an alternative mechanism for nitric oxide production in heart failure due to ischemic disease.

Protein Kinase Cε Overexpression Alters Myofilament Properties and Composition During the Progression of Heart Failure

We report characterization of a transgenic mouse that overexpresses constitutively active protein kinase Cε in the heart and slowly develops a dilated cardiomyopathy with failure. The hemodynamic, mechanical, and biochemical properties of these hearts demonstrate a series of temporal events that mark the progression of the disease. In the 3-month transgenic (TG) animals, contractile properties and gene expression measurements are normal, but an increase in myofibrillar Ca 2+ sensitivity and thin filament protein phosphorylation is noted. At 6 months, there is a decrease in the myofibrillar Ca 2+ sensitivity, a significant increase in β-myosin heavy chain mRNA and protein, normal cardiac function, but a blunted response to an inotropic challenge. The transition at 9 months is especially interesting because age-related changes appear to contribute to the decline in function seen in the TG heart. At this point, there is a decline in baseline function and maximum tension produced by the myofibrils, which is coincident with the onset of atrial myosin light chain isoform re-expression in the ventricles. In the 12-month TG mice, there is clear hemodynamic and geometric evidence of failure. Alterations in the composition of the myofibrils persist but the phosphorylation of myosin light chain 2v is dramatically different at this age compared with all others. We interpret these data to implicate the disruption of the myofibrillar proteins and their interactions in the propagation of dilated cardiac disease.

Vascular reactivity in heart failure: role of myosin light chain phosphatase

Congestive heart failure (CHF) is a clinical syndrome, which is the result of systolic or diastolic ventricular dysfunction. During CHF, vascular tone is regulated by the interplay of neurohormonal mechanisms and endothelial-dependent factors and is characterized by both central and peripheral vasoconstriction as well as a resistance to nitric oxide (NO)-mediated vasodilatation. At the molecular level, vascular tone depends on the level of regulatory myosin light chain phosphorylation, which is determined by the relative activities of myosin light chain kinase and myosin light chain phosphatase (MLCP). The MLCP is a trimeric enzyme with a catalytic, a 20-kDa and a myosin targeting (MYPT1) subunit. Alternative splicing of a 3' exon produces leucine zipper positive and negative (LZ+/-) MYPT1 isoforms. Expression of a LZ+ MYPT1 has been suggested to be required for NO-mediated smooth muscle relaxation. Thus, we hypothesized that the resistance to NO-mediated vasodilatation in CHF could be attributable to a change in the relative expression of LZ+/- MYPT1 isoforms. To test this hypothesis, left coronary artery ligation was used to induce CHF in rats, and both the dose response relationship of relaxation to 8-Br-cGMP in skinned smooth muscle and the relative expression of LZ+/- MYPT1 isoforms were determined. In control animals, the expression of the LZ+ MYPT1 isoform predominated in both the aorta and iliac artery. In CHF rats, LVEF was reduced to 30+/-5% and there was a significant decrease in both the sensitivity to 8-Br-cGMP and expression of the LZ+ MYPT1 isoform. These results indicate that CHF is associated with a decrease in the relative expression of the LZ+ MYPT1 isoform and the sensitivity to 8-Br-cGMP-mediated smooth muscle relaxation. The data suggest that the resistance to NO-mediated relaxation observed during CHF lies at least in part at the level of the smooth muscle and is a consequence of the decrease in the expression of the LZ+ MYPT1 isoform.

Stress-activated MAP kinases in cardiac remodeling and heart failure; new insights from transgenic studies

Activation of stress-activated mitogen-activated protein kinases (SAPKs), mainly c-Jun N-terminal kinase (JNK) and p38, have long been associated with different forms of cardiac pathology across a wide spectrum of species. However, their specific roles in the development of heart failure are still unclear. Previous studies in neonatal myocytes in culture suggest a critical role for both JNK and p38 in hypertrophy and apoptosis. A far more complex picture has been provided by recent observations from both cellular and transgenic models that have not only challenged their role in hypertrophy and cell death but have also pointed out novel functions of SAPKs in different aspects of cardiac pathology, including contractile function, extracellular matrix remodeling, intercellular communication, and metabolic regulation.

Inhibition of COX pathway in experimental myocardial infarction

Release of inflammatory mediators within the ischemic myocardium has long been thought to contribute to myocardial damage and dysfunction. Myocardial infarction (MI) and congestive heart failure (CHF) were induced in rats by ligating the left coronary artery. Animals were treated with the selective cyclooxygenase-2 (COX-2) inhibitor-5,5-dimethyl-3-(3-fluorophenyl1)-4-(4-methyl-sulphonyl-2(5H)-fluranone (DFU), low-, high-dose acetyl salicylic acid (aspirin), or vehicle for 3 months. Strong immunoreactivity for COX-2 was detected in the cardiomyocytes, vascular endothelial cells, and macrophages in the infarcted myocardium. Compared to the vehicle, treatment with DFU significantly reduced left ventricular end-diastolic pressure, central venous pressure, lung wet/dry ratio and infarct size, and improved cardiac contractility (P < 0.05). In comparison, treatment with low or high doses of aspirin did not significantly impact any of these parameters. These findings demonstrate that induction of myocardial COX-2 in rats with CHF secondary to MI contributes to the cardiac injury and dysfunction associated with this disease, and that therapy aimed at inhibiting this enzymatic pathway at the onset of the disease may be beneficial in the treatment of MI and CHF.

Changes in skeletal muscle SR Ca2+ pump in congestive heart failure due to myocardial infarction are prevented by angiotensin II blockade

In order to understand the mechanisms of exercise intolerance and muscle fatigue, which are commonly observed in congestive heart failure, we studied sarcoplasmic reticulum (SR) Ca2+-transport in the hind-leg skeletal muscle of rats subjected to myocardial infarction (MI). Sham-operated animals were used for comparison. On one hand, the maximal velocities (Vmax) for both SR Ca2+-uptake and Ca2+-stimulated ATPase activities in skeletal muscle of rats at 8 weeks of MI were higher than those of controls. On the other hand, the Vmax values for both SR Ca2+-uptake and Ca2+-stimulated ATPase activities were decreased significantly at 16 weeks of MI when compared with controls. These alterations in Ca2+-transport activities were not associated with any change in the affinity (1/Ka) of the SR Ca2+-pump for Ca2+. Furthermore, the stimulation of SR Ca2+-stimulated ATPase activity by cyclic AMP-dependent protein kinase was not altered at 8 or 16 weeks of MI when compared with the respective control values. Treatment of 3-week infarcted animals with angiotensin-converting enzyme (ACE) inhibitors such as captopril, imidapril, and enalapril or an angiotensin receptor (AT1R) antagonist, losartan, for a period of 13 weeks not only attenuated changes in left ventricular function but also prevented defects in SR Ca2+-pump in skeletal muscle. These results indicate that the skeletal muscle SR Ca2+-transport is altered in a biphasic manner in heart failure due to MI. It is suggested that the initial increase in SR Ca2+-pump activity in skeletal muscle may be compensatory whereas the depression at late stages of MI may play a role in exercise intolerance and muscle fatigue in congestive heart failure. Furthermore, the improvements in the skeletal muscle SR Ca2+-transport by ACE inhibitors may be due to the decreased activity of renin-angiotensin system in congestive heart failure.Key words: skeletal muscle, sarcoplasmic reticulum, Ca2+-transport, SR Ca2+-pump, congestive heart failure, renin-angiotensin system.

Gene expression of cardiac mast cell chymase and tryptase in a murine model of heart failure caused by viral myocarditis

This study examined the gene expression of mouse mast cell proteases to clarify their role in the pathophysiology of viral myocarditis. Male DBA/2 mice were inoculated intraperitoneally with the encephalomyocarditis virus and the gene expression of mast cell chymase, mouse mast cell protease (mMCP)-4 and -5, and tryptase, mMCP-6, matrix metalloproteinase (MMP)-9 and type-I procollagen was measured by real-time quantitative RT-PCR analysis. The gene expression of mMCP-4, -5 and -6 mRNA was increased at 5 days, and continued to increase to day 14, coinciding with a prominent inflammatory reaction and extensive myocardial necrosis and fibrosis. The gene expression of MMP-9 was also increased, and there was a significant correlation between upregulation of mast cell proteases and MMP-9. The gene expression of type-I procollagen was increased at 5 days and continued to increase to day 14, suggesting that a fibrotic process had already begun during the acute stage of viral myocarditis. These findings suggest that mast cell chymase and tryptase participate in the acute inflammation and remodeling process of viral myocarditis.

Effects of ACE gene insertion/deletion polymorphism on response to spironolactone in patients with chronic heart failure

BACKGROUND

Angiotensin-converting enzyme (ACE) is involved in the pathophysiology of chronic heart failure, and its activity is determined in part by a polymorphism of the ACE gene. We hypothesized that the benefits of spironolactone, which inhibits downstream elements of ACE-mediated abnormalities, may depend on ACE genotype.

METHODS

We randomly assigned 93 chronic heart failure patients to treatment with spironolactone (n = 47) or to a control group (n = 46) and followed them for 12 months. Genotype for the insertion/deletion polymorphism of the ACE gene was determined by polymerase chain reaction. An echocardiographic examination was performed at baseline and at the end of the 12 months.

RESULTS

The mean (+/- SD) age of the 93 patients was 62 +/- 9 years, and the mean New York Heart Association class was 2 +/- 1. The genotype was DD in 26 patients (28%). Forty-seven patients were assigned to spironolactone treatment (mean dose, 32 +/- 16 mg). In the treated group, only patients with a non-DD genotype showed significant improvement in left ventricular ejection fraction (3.0%; 95% confidence interval [CI]: 1.2% to 4.8%; P = 0.002), end-systolic volume (-23 mL; 95% CI: -36 to -11; P = 0.0005), and end-diastolic volume (-27 mL; 95% CI: -43 to -12; P = 0.001). In the multivariate analysis, the estimated net effect of treatment was 29 mL better (95% CI: -20 to 78 mL) for end-diastolic volume, 20 mL better (95% CI: -18 to 58 mL) for end-systolic volume, but 1.4% worse (95% CI: -3.4% to 6.2%) for left ventricular ejection fraction in patients with non-DD versus DD genotypes.

CONCLUSION

The effects of spironolactone treatment on left ventricular systolic function and remodeling may in part depend on ACE genotype.

Cardiac matrix remodelling in congestive heart failure: the role of matrix metalloproteinases

BACKGROUND

Congestive heart failure (CHF), the most frequent reason for hospital admission of elderly patients, is an important and rapidly increasing cause of morbidity and mortality worldwide. Its development is accompanied by left-ventricle (LV) dilatation and pump dysfunction. The extracellular space in the heart is now recognized as an essential element of myocardial structure and function, and a dynamic participant in remodelling. The matrix metalloproteinases (MMPs) are an endogenous enzyme system responsible for extracellular collagen degradation and remodelling.

OBJECTIVES

To evaluate the potential role of several MMPs (MMP-1, MMP-3 and MMP-9) in CHF.

PATIENTS AND METHODS

We recruited 30 consecutive patients with moderate to severe CHF who presented for heart-failure management, along with 15 age- and sex-matched control participants. Two-dimensional and M-mode echocardiographic studies were used to assess LV size and function and hence assess LV remodelling. MMP-1, -3 and -9 concentrations in serum were measured by ELISA at the time of admission and diagnosis.

RESULTS

Serum levels of all 3 metalloproteinases were higher in patients with CHF than in controls; those of MMP-3 were markedly increased in patients with severe CHF.

CONCLUSIONS

The association found between LV performance and MMP levels suggests that MMPs are implicated in CHF, that serum concentrations of MMPs may serve as markers for CHF, and that MMPs are a potential novel therapeutic target.

Sustained Improvement of Cardiac Function and Prevention of Cardiac Remodeling after Long-Term Dual ECE-NEP Inhibition in Rats with Congestive Heart Failure

Acute inhibition of endothelin converting enzyme (ECE) and neutral endopeptidase (NEP) exerts beneficial hemodynamic effects in chronic heart failure (CHF). However, the long-term effects of dual ECE-NEP inhibition are unknown. We evaluated, in rats with CHF, the long-term effects of the dual ECE-NEP inhibitor CGS 26303 (10 mg.kg(-1).day(-1)) on systemic and left ventricular (LV) hemodynamics and LV remodeling, and compared them to those induced by the selective NEP inhibitor CGS 24592 (10 mg.kg(-1).day(-1)), both administered subcutaneously by mini-pump for 30 days starting 7 days after left coronary artery ligation. After 30 days, CGS 26303, but not CGS 24592, reduced systolic blood pressure, while both drugs never affected heart rate. Echocardiographic studies showed that only CGS 26303 diminished LV end-diastolic and systolic diameters and increased LV fractional shortening and cardiac output. Moreover, CGS 26303, but not CGS 24592, reduced LV end-diastolic pressure, while LV dP/dtmax/min was not affected. Both drugs reduced collagen accumulation in the 'viable' part of the LV, but only CGS 26303 reduced LV weight. Thus, long-term treatment with CGS 26303 decreases both preload and afterload, increases cardiac output, and diminishes LV hypertrophy, dilatation, and cardiac fibrosis, suggesting that dual ECE-NEP inhibition might be beneficial in human CHF.

Targeted beta-adrenergic receptor kinase (betaARK1) inhibition by gene transfer in failing human hearts

BACKGROUND

Failing human myocardium is characterized by an attenuated contractile response to beta-adrenergic receptor (betaAR) stimulation due to changes in this signaling cascade, including increased expression and activity of the beta-adrenergic receptor kinase (betaARK1). This leads to desensitization and downregulation of betaARs. Previously, expression of a peptide inhibitor of betaARK1 (betaARKct) has proven beneficial in several animal models of heart failure (HF).

METHODS AND RESULTS

To test the hypothesis that inhibition of betaARK1 could improve beta-adrenergic signaling and contractile function in failing human myocytes, the betaARKct was expressed via adenovirus-mediated (AdbetaARKct) gene transfer in ventricular myocytes isolated from hearts explanted from 10 patients with end-stage HF undergoing cardiac transplantation. AdbetaARKct also contained the marker gene, green fluorescent protein, and successful gene transfer was confirmed via fluorescence and immunoblotting. Compared with uninfected failing myocytes (control), the velocities of both contraction and relaxation in the AdbetaARKct-treated cells were increased in response to the beta-agonist isoproterenol (contraction: 57.5+/-6.6% versus 37.0+/-4.2% shortening per second, P<0.05; relaxation: 43.8+/-5.5% versus 27.5+/-3.9% lengthening per second, P<0.05). Fractional shortening was similarly enhanced (12.2+/-1.2% versus 8.0+/-0.9%, P<0.05). Finally, adenylyl cyclase activity in response to isoproterenol was also increased in AdbetaARKct-treated myocytes.

CONCLUSIONS

These results demonstrate that as in animal models of HF, expression of the betaARKct can improve contractile function and beta-adrenergic responsiveness in failing human myocytes. Thus, betaARK1 inhibition may represent a therapeutic strategy for human HF.

Activation of matrix metalloproteinases precedes left ventricular remodeling in hypertensive heart failure rats: its inhibition as a primary effect of Angiotensin-converting enzyme inhibitor

BACKGROUND

Matrix metalloproteinases (MMPs) are activated in dilated failing hearts, and angiotensin-converting enzyme (ACE) inhibition prevents left ventricular (LV) dilatation. However, it remains unclear whether activation of MMPs precedes or is secondary to LV remodeling, and an effect of ACE inhibition on MMPs is unknown.

METHODS AND RESULTS

Dahl salt-sensitive rats fed a high-salt diet from 8 weeks served as the hypertensive heart failure (HF) model. LV echo, histological study, measurement of mRNA levels, and gelatin zymography were performed before (at 23 weeks) and after (at 26 weeks) the development of LV dilatation and pulmonary edema. The same procedures were conducted in the HF model rats treated with a subdepressor dose of ACE inhibitor (enalapril 5 mg x kg(-1) x d(-1)) from 9 weeks. Rats fed on normal chow served as age-matched controls. In the untreated HF model rats, gene expression of MMP-2 and MMP-9 and tissue gelatinase activity were elevated at 23 weeks without LV dilatation. LV dilatation, LV systolic dysfunction, and pulmonary edema occurred at 26 weeks, with further enhancement of the expression and activity of MMPs. ACE inhibition prevented such geometrical and functional deterioration. The gene expression and activity of MMPs were suppressed by ACE inhibition at 23 weeks without a decrease in blood pressure, and the suppressive effects continued at 26 weeks.

CONCLUSIONS

MMPs are likely to trigger and promote LV remodeling, and ACE inhibition directly exerts inhibitory effect on MMPs, leading to the prevention of LV remodeling and dysfunction.

Mechanical unloading of the failing human heart fails to activate the protein kinase B/Akt/glycogen synthase kinase-3beta survival pathway

BACKGROUND

Left ventricular assist device (LVAD) support of the failing human heart improves myocyte function and increases cell survival. One potential mechanism underlying this phenomenon is activation of the protein kinase B (PKB)/Akt/glycogen synthase kinase-3beta (GSK-3beta) survival pathway.

METHODS AND RESULTS

Left ventricular tissue was obtained both at the time of implantation and explantation of the LVAD (n = 11). Six patients were diagnosed with idiopathic dilated cardiomyopathy, 4 patients with ischemic cardiomyopathy and 1 patient with peripartum cardiomyopathy. The mean duration of LVAD support was 205 +/- 35 days. Myocyte diameter and phosphorylation of ERK were used as indices for reverse remodeling. Transcript levels of genes required for the activation of PKB/Akt (insulin-like growth factor-1, insulin receptor substrate-1) were measured by quantitative RT-PCR. In addition, we measured the relative activity of PKB/Akt and GSK-3beta, and assayed for molecular and histological indices of PKB/Akt activation (cyclooxygenase mRNA levels and glycogen levels). Myocyte diameter and phosphorylation of ERK decreased with LVAD support. In contrast, none of the components of the PKB/Akt/GSK-3beta pathway changed significantly with mechanical unloading.

CONCLUSION

The PKB/Akt/GSK-3beta pathway is not activated during LVAD support. Other signaling pathways must be responsible for the improvement of cellular function and cell survival during LVAD support.

Matrix Metalloproteinases: Pathways of Induction by Bioactive Molecules

Regulation of the extracellular matrix (ECM) is an important therapeutic target that can potentially attenuate the adverse ventricular remodeling seen in the progression of heart failure. Matrix metalloproteinases (MMPs) degrade numerous ECM proteins. Importantly, the activation of MMPs and their endogenous inhibitors (TIMPs) are associated with ventricular remodeling. Bioactive-molecules (vasoactive peptides) become activated in proportion to the magnitude of heart failure and have been demonstrated to affect directly collagen degradation as well as collagen synthesis in the myocardium. Pro-fibrotic factors such as norepinephrine, angiotensin II, and endothelin-1 stimulate fibrosis by modulating collagen synthesis and MMP/TIMP activity. Antagonism of these bioactive-molecules has produced improved hemodynamic performance concomitant with modulation of MMP/TIMP activity and in association with reverse remodeling. The natriuretic peptides and nitric oxide, both of which function via the second messenger cGMP, demonstrate anti-fibrotic actions by inhibiting collagen synthesis and by stimulating MMP activity. Furthermore, bioactive-molecules along with certain cytokines are reported to amplify MMP activity, suggesting that different signaling systems work together to modulate ECM turnover. Taken together, the evidence supports an important functional role for bioactive-molecules in the regulation of ECM turnover and suggests that pharmacological intervention at the level of such bioactive molecules may provide potential therapeutic strategies for attenuation of the adverse ventricular remodeling associated with the progression of heart failure.

Carnitine palmitoyltransferase-I, a new target for the treatment of heart failure: perspectives on a shift in myocardial metabolism as a therapeutic intervention

Although the heart is capable of extracting energy from different types of substrates such as fatty acids and carbohydrates, fatty acids are the preferred fuel under physiological conditions. In view of the presence of diverse defects in myocardial metabolism in the failing heart, changes in metabolism of glucose and fatty acids are considered as viable targets for therapeutic modification in the treatment of heart failure. One of these changes involves the carnitine palmitoyltransferase (CPT) enzymes, which are required for the transfer of long chain fatty acids into the mitochondrial matrix for oxidation. Since CPT inhibitors have been shown to prevent the undesirable effects induced by mechanical overload, e.g. cardiac hypertrophy and heart failure, it was considered of interest to examine whether the inhibition of CPT enzymes represents a novel approach for the treatment of heart disease. A shift from fatty acid metabolism to glucose metabolism due to CPT-I inhibition has been reported to exert beneficial effects in both cardiac hypertrophy and heart failure. Since the inhibition of fatty acid oxidation is effective in controlling abnormalities in diabetes mellitus, CPT-I inhibitors may also prove useful in the treatment of diabetic cardiomyopathy. Accordingly, it is suggested that CPT-I may be a potential target for drug development for the therapy of heart disease in general and heart failure in particular.

Unchanged G-protein-coupled receptor kinase activity in the aging human heart

OBJECTIVES

We sought to find out whether G-protein-coupled receptor kinase (GRK) activity is also increased in the aging human heart.

BACKGROUND

In the aging and failing human heart, cardiac beta-adrenoceptors (beta-AR) are desensitized. In heart failure (HF), an increase in cardiac GRK activity considerably contributes to this beta-AR desensitization.

METHODS

We assessed GRK activity (by in vitro rhodopsin phosphorylation) in the right atria (RA) from 16 children (mean age 9 +/- 2 years) and 17 elderly patients (mean age 67 +/- 2 years) without apparent HF and in the RA from four patients with end-stage HF.Cytosolic and membranous GRK activities in the RA from children were not significantly different from those in elderly patients; in contrast, cytosolic and membranous GRK activities in the RA from patients with end-stage HF were significantly increased.

CONCLUSIONS

In contrast to the failing human heart, in the aging human heart, GRK activity is not increased. Thus, GRK activity appears to not play an important role in beta-AR desensitization in the aging human heart.

Maximum rate of oxygen consumption related to succinate dehydrogenase activity in skeletal muscle fibres of chronic heart failure patients and controls

Previous studies indicate that the low maximum rate of oxygen consumption (VO2max) of chronic heart failure (CHF) patients is not because of impaired pump function of the heart. We hypothesize that VO2 during maximum exercise is determined by the total oxidative capacity of skeletal muscle. VO2max of six controls and 14 CHF patients, New York Heart Association class I-III, was determined using an incremental bicycle ergometer test. Cryostat sections of a biopsy from the quadriceps femoris muscle were incubated for succinate dehydrogenase (SDH) using quantitative histochemistry. VO2max (range: 29 ml O2 kg muscle(-1) min(-1) in a class III patient to 118 ml O2 kg muscle(-1) min(-1) in a control subject) correlates with the mean SDH activity of skeletal muscle fibres (r=0.79 or r=0.81, including or excluding oxygen uptake at rest, respectively; P<0.001). The relationship between VO2max and SDH activity is similar to that determined previously using isolated single muscle fibres and myocardial trabeculae under hyperoxic conditions. From the product of SDH activity and the cross-sectional area of the fibre (i.e. spatially integrated SDH activity), it is possible to calculate the maximum oxygen uptake rate per unit muscle fibre length. This uptake rate is linearly related to the number of capillaries per fibre (r=0.76, P<0.001) in all subjects, suggesting that oxidative capacity of skeletal muscle fibres in CHF patients decreases in proportion to the oxygen supply capacity of the microcirculation.

Phosphoinositide 3-kinase gamma-deficient mice are protected from isoproterenol-induced heart failure

BACKGROUND

We have recently shown that genetic inactivation of phosphoinositide 3-kinase gamma (PI3Kgamma), the isoform linked to G-protein-coupled receptors, results in increased cardiac contractility with no effect on basal cell size. Signaling via the G-protein-coupled beta-adrenergic receptors has been implicated in cardiac hypertrophy and heart failure, suggesting that PI3Kgamma might play a role in the pathogenesis of heart disease.

METHODS AND RESULTS

To determine the role for PI3Kgamma in hypertrophy induced by G-protein-coupled receptors and cardiomyopathy, we infused isoproterenol, a beta-adrenergic receptor agonist, into PI3Kgamma-deficient mice. Compared with controls, isoproterenol infusion in PI3Kgamma-deficient mice resulted in an attenuated cardiac hypertrophic response and markedly reduced interstitial fibrosis. Intriguingly, chronic beta-adrenergic receptor stimulation triggered impaired heart functions in wild-type mice, whereas PI3Kgamma-deficient mice retained their increased heart function and did not develop heart failure. The lack of PI3Kgamma attenuated the activation of Akt/protein kinase B and extracellular signal-regulated kinase 1/2 signaling pathways in cardiac myocytes in response to isoproterenol. beta1- and beta2-adrenergic receptor densities were decreased by similar amounts in PI3Kgamma-deficient and control mice, suggesting that PI3Kgamma isoform plays no role in the downregulation of beta-adrenergic receptors after chronic beta-adrenergic stimulation.

CONCLUSIONS

Our data show that PI3Kgamma is critical for the induction of hypertrophy, fibrosis, and cardiac dysfunction function in response to beta-adrenergic receptor stimulation in vivo. Thus, PI3Kgamma may represent a novel therapeutic target for the treatment of decreased cardiac function in heart failure.