Hypertrophied Human Myocardium Research Articles

Response to a Single Dose of Sildenafil in Single-Ventricle Patients: An Echocardiographic Evaluation

New evidence of increased phosphodiesterase-5 (PDE-5) in hypertrophied human myocardium suggests that sildenafil, a selective PDE-5 inhibitor, may improve muscle contraction and therefore improve ventricular function. The purpose of this study was to compare ventricular function as assessed by echocardiography in 10 surgically palliated single-ventricle patients at baseline and again after a single dose of sildenafil. The velocity time integral of the ventricular outflow tract was increased 2 h after sildenafil administration (p = 0.01), thus suggesting an improvement in cardiac output.

On the Nature of Cell Death During Remodeling of Hypertrophied Human Myocardium

S. Yamamoto, K.-i. Sawada, H. Shimomura, K. Kawamura and T. N. James. On the Nature of Cell Death During Remodeling of Hypertrophied Human Myocardium. Journal of Molecular and Cellular Cardiology (2000) 32, 161–175. Cardiocyte loss during myocardial hypertrophy leads to progressive dysfunction in human hearts with chronic hemodynamic overload. The mechanism for such cell elimination is unknown. We examined lysosomal participation in cardiocytic degradation present in human cardiac biopsies, utilizing electron microscopic cytochemistry (acid phosphatase). Lysosomes were significantly increased in number (t -test, P<0.001) in 50 hemodynamically overloaded hearts (375±69, mean±s.e.m., per 5000 μ m2cardiocytic area; eight controls, 38±11). Secondary lysosomes were prominent near degenerative intracellular organelles in both hypertrophic and atrophic cardiocytes. Increased lysosomal and phagocytic activity in the cytoplasm without typical nuclear apoptosis resembled cytoplasmic degradation in developmental programmed cell death described in different tissues. We also demonstrated cardiocytic DNA degradation (in situ nick-end labeling) in autopsy hearts, including 299 nuclei normalized per 106observed nuclei from five concentrically hypertrophied hearts, 1961 nuclei from five eccentrically hypertrophied hearts, and no positive nuclei in five controls. We postulate a chronic self-controlled cytoplasmic proteolysis in cardiocytes, not initially associated with either nuclear degradation or intercellular dehiscence but later possibly accompanied by apoptotic nuclear elimination, and leading to apoptotic cell death.

Remodeling of the hypertrophied human myocardium by cardiac bHLH transcription factors

The basic helix-loop-helix transcription factors eHAND and dHAND are involved in developmental cardiac growth and differentiation. We investigated HAND gene expression in the normal and in the hypertrophied right and left ventricle of patients with tetralogy of Fallot (ToF) and hypertrophic obstructive cardiomyopathy (HOCM). HAND mRNA was constitutively expressed in the hypertrophied heart and increased in the hypertrophic tissue of both patient groups. HAND genes had a complementary left-right cardiac asymmetry of expression with dHAND predominantly in the right and eHAND in the left ventricle. The two cardiac bHLH factors have the ability to form heterodimers with the ubiquitous bHLH protein E12, subsequently recognizing E-boxes in the promoter region of target genes like ALC-1. We found a highly significant positive correlation between HAND and ALC-1 mRNA. The total ALC-1 protein level in ToF was smaller than in HOCM, although ALC-1 mRNA as well as HAND mRNA levels were significantly higher. ToF patients expressed around four times more ALC-1 mRNA for similar amounts of ALC-1 than HOCM patients. Suggesting disturbed ALC-1 translation in ToF, we found ALC-1 antisense mRNA expression in the hypertrophied, but not in the normal, ventricles. The higher the antisense/sense ALC-1 mRNA ratio, the lower ALC-1 protein was expressed. J. Cell. Biochem. 74:551–561, 1999. © 1999 Wiley-Liss, Inc.

Reduced Myocardial Sarcoplasmic Reticulum Ca2+-ATPase Protein Expression in Compensated Primary and Secondary Human Cardiac Hypertrophy

Pathological intracellular calcium handling has been proposed to underlie the alterations of contractile behavior in hypertrophied myocardium. However, the myocardial protein expression of intracellular calcium transport proteins in compensated human left ventricular hypertrophy has not yet been studied. We investigated septal myocardial specimens of patients suffering from hypertrophic obstructive cardiomyopathy (n=14) or from acquired aortic valve stenosis (n=11) undergoing myectomy or aortic valve replacement, respectively. For comparison, we studied non-hypertrophied myocardium of six non-failing hearts which could not be transplanted for technical reasons. The myocardial density of the calcium release channel of the sarcoplasmic reticulum (SR) was determined by3H-ryanodine binding. Myocardial contents of SR Ca2+-ATPase, phospholamban, calsequestrin and Na+/Ca2+-exchanger were analysed by Western blot analysis. The myocardial SR calcium release channel density was not significantly different in hypertrophied and non-failing human myocardium. In both hypertrophic obstructive cardiomyopathy and in aortic valve stenosis, SR Ca2+-ATPase expression was reduced by about 30% compared to non-failing myocardium (P<0.05), whereas the expression of phospholamban, calsequestrin, and the Na+/Ca2+-exchanger was unchanged. The decrease of SR Ca2+-ATPase expression was still observable when related to its regulatory protein phospholamban or to the myosin content of the homogenates (P<0.05). Furthermore, the SR Ca2+-ATPase expression was inversely correlated to the septum thickness assessed by echocardiography, but not to age, cardiac index or outflow tract gradient. In primary as well as in secondary hypertrophied human myocardium, the expression of SR Ca2+-ATPase is reduced and inversely related to the degree of the hypertrophy. The diminished SR Ca2+-ATPase expression might result in reduced Ca2+reuptake into the SR and might contribute to altered contractile behavior in hypertrophied human myocardium.

Remodeling of the hypertrophied human myocardium by cardiac bHLH transcription factors.

The basic helix-loop-helix transcription factors eHAND and dHAND are involved in developmental cardiac growth and differentiation. We investigated HAND gene expression in the normal and in the hypertrophied right and left ventricle of patients with tetralogy of Fallot (ToF) and hypertrophic obstructive cardiomyopathy (HOCM). HAND mRNA was constitutively expressed in the hypertrophied heart and increased in the hypertrophic tissue of both patient groups. HAND genes had a complementary left-right cardiac asymmetry of expression with dHAND predominantly in the right and eHAND in the left ventricle. The two cardiac bHLH factors have the ability to form heterodimers with the ubiquitous bHLH protein E12, subsequently recognizing E-boxes in the promoter region of target genes like ALC-1. We found a highly significant positive correlation between HAND and ALC-1 mRNA. The total ALC-1 protein level in ToF was smaller than in HOCM, although ALC-1 mRNA as well as HAND mRNA levels were significantly higher. ToF patients expressed around four times more ALC-1 mRNA for similar amounts of ALC-1 than HOCM patients. Suggesting disturbed ALC-1 translation in ToF, we found ALC-1 antisense mRNA expression in the hypertrophied, but not in the normal, ventricles. The higher the antisense/sense ALC-1 mRNA ratio, the lower ALC-1 protein was expressed.

Cardiac hypertrophy determines digitalis action on intracellular Ca 2+ in human myocardium

Ventricular hypertrophy alters transporters associated with digitalis action, but the outcome of digitalis treatment on intracellular cations in the hypertrophied human myocardium remains unknown. Using double-barreled Ca 2+-selective microelectrodes, we simultaneously measured Ca 2+ activity and membrane potential in myocardial samples from patients without and with ventricular hypertrophy, prior to and following exposure to strophanthidin, a prototype digitalis. We found that ventricular hypertrophy is associated with greater strophanthidin-induced increase in diastolic Ca 2+ levels compared to that observed in the absence of hypertrophy. Furthermore, in hypertrophied myocardium the magnitude of the increase in Ca 2+ induced by strophanthidin was inversely related to increase in myocardial mass. Thus, the extent of ventricular hypertrophy determines digitalis action on intracellular Ca 2+ within the human myocardium.

Down-regulation of angiotensin II receptors in hypertrophied human myocardium.

1. Specific [125I]-angiotensin II (AngII) binding in normal and hypertrophied human myocardial membranes was saturable and of high affinity. Low concentrations of unlabelled AngII and saralasin competed with [125I]-AngII for the binding sites in these tissues. Thus, saturable [125I]-AngII binding in human myocardium exhibited pharmacological specificity that characterized high affinity receptors for AngII. 2. There was little difference in the apparent dissociation constant (Kd) values for [125I]-AngII binding between normal and hypertrophied human myocardium, whereas the maximal number of binding sites (Bmax) was significantly (51%) lower in the hypertrophied group. Further, PD123177, a selective antagonist of the AT2 receptor subtype, showed three orders of magnitude higher affinity for [125I]-AngII binding sites in both normal and hypertrophied myocardium than losartan, a selective antagonist of the AT1 receptor subtype; the Hill coefficients for these drugs were close to one. 3. A significant decrease in Bmax and Kd values for (-)-[125I]-iodocyanopindolol binding between normal and hypertrophied human myocardium rarely occurred. 4. The present study suggests that both normal and hypertrophied human myocardium predominantly contains the AT2 receptor subtype and that these receptors are down-regulated in hypertrophied tissues.

Hypertrophic cardiomyopathy: a desensitized cardiac beta-adrenergic system in the presence of normal plasma catecholamine concentrations.

Only few data are available concerning the biochemical and functional state of the beta-adrenergic system in hypertrophied human myocardium. The present study was to investigate the myocardial beta-adrenergic signal transduction system in hypertrophic obstructive cardiomyopathy (HOCM). Thin myocardial strips were prepared from surgically excised, septal myocardium from 7 patients with HOCM and their force of contraction was measured in vitro. The positive inotropic effects of calcium and dihydro-ouabain, both acting independently of beta-adrenoceptors and cAMP, were similar in these preparations to those, previously published, seen with nonfailing myocardium. In contrast, the beta-adrenoceptor agonist isoprenaline and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) had reduced positive inotropic effects. Their EC50-values were about 10 fold higher than the respective EC50-values published for nonfailing myocardium. The positive inotropic potencies of isoprenaline and IBMX were reduced in HOCM by as much as they were in the additionally investigated myocardium from 6 patients with severe mitral regurgitation (MR, NYHA III). In order to clarify whether the functional alterations are related to changes in the beta-adrenoceptors, beta-adrenoceptor density and beta 1: beta 2-adrenoceptor subtype distribution were determined in the same myocardium using 125I-Iodocyanopindolol saturation binding. Myocardial beta-adrenoceptor density was reduced to 68% in HOCM and to 56% in MR compared to nonfailing myocardium controls (NF: 64.8 +/- 6.5 fmol/mg protein). In HOCM, this reduction was due to a selective down regulation of beta 1-adrenoceptors (24.9 +/- 3.7 fmol/mg protein vs NF: 46.4 +/- 6.8 fmol/mg protein, P < 0.05), whereas beta 2-adrenoceptor density was unchanged (19.0 +/- 1.9 fmol/mg protein vs NF: 18.4 +/- 3.3 fmol/mg protein, n.s.). In MR both beta-adrenoceptor subtypes were reduced (beta 1: 26.9 +/- 1.4 fmol/mg protein, beta 2: 9.6 +/- 1.7 fmol/mg protein; both P < 0.05 vs NF). Electrochemically determined plasma catecholamine levels were elevated in MR. However, plasma catecholamine levels were normal or slightly below normal in HOCM. In summary, myocardial beta-adrenoceptors are downregulated and their function is impaired in HOCM. This desensitization is not caused by a negative feedback regulation due to increased plasma catecholamines. The present results show that the desensitizations of the beta-adrenergic system associated with HOCM has characteristics that indicate a major deviation in its development from that of the beta-adrenergic desensitization previously described to occur in congestive heart failure.

Detection of low phosphocreatine to ATP ratio in failing hypertrophied human myocardium by 31P magnetic resonance spectroscopy

Phosphorus-31 magnetic resonance spectroscopy can be used to study intracellular biochemistry non-invasively by measuring the relative proportions of high energy phosphates. Study of deteriorating cardiac metabolism might be useful in the management of hypertrophy and heart failure. 31P magnetic resonance spectroscopy was carried out in fourteen patients with aortic valve disease (six with aortic stenosis, eight with aortic incompetence). Six patients were receiving treatment for symptoms of heart failure. The phosphocreatine (PCr) to ATP ratio in these patients (1·1 [SD 0·32]) was significantly lower than that in thirteen controls (1·5 [0·2], p<0·001 ) or in the eight patients who did not have symptoms of heart failure (1·56 [0·15], p<0·0035). These findings indicate that heart failure in aortic valve disease is associated with low PCr, which could be due to loss of intracellular creatine. The measurement could eventually have a role in helping to determine the optimum timing for aortic valve replacement.

Myosin type distribution in normal and hypertrophied human myocardium : S. Schiaffino, L. Gorza and S. Sartore. Institute of General Pathology, University of Padova, Italy

Myosin type distribution in normal and hypertrophied human myocardium : S. Schiaffino, L. Gorza and S. Sartore. Institute of General Pathology, University of Padova, Italy

Fibrillolysis and electrophoretic determination of actin and myosin in hypertrophied human myocardium.

Destructive myofibrillar lesions, particularly degenerative fibrillolysis in hypertrophied hearts, were studied with the electron microscope in left ventricular myocardium samples obtained from autopsies with post mortem periods not exceeding 195 min. The contractile protein composition of these samples was determined electrophoretically. 18 cases were studied, grouped as follows: Group I, composed of 5 cases showing normal hearts which were employed in the determination of normal electrophoretic values. Group II: 10 cases with hypertrophic hearts, 1 of them showing contraction bands and decreased myosin, 6 others with fibrillolytic lesions of which 3 presented a decrease in myosin and 3 possessed normal myosin values. None of the cases showed a decrease in actin values. Group III was composed of 3 cases of hearts with normal weights that showed ultrastructural alterations of the myofibrils: 1 with myofibrillar disarray and normal electrophoretic values, 1 with incomplete contraction bands and normal protein values and 1 with focal myofibrillar disgregation and myosin decrease. It is concluded that in some cases of degenerative fibrillolytic lessions a decrease of myosin occurs. The method employed does not rule out that apparently normal actin and myosin values might be due to the presence of contractile proteins in a denatured state that does not affect their electrophoretic mobility.

Pathophysiology of the hypertrophied heart in man.

Increase in sympathetic drive, the Frank-Starling effect and myocardial hypertrophy represent the three compensatory mechanisms in chronic mechanical overloading of the heart. Chronic pressure overload is associated with concentric and chronic volume overload with eccentric hypertrophy. The changes in ventricular geometry have an important influence on the ejection dynamics of the heart; the magnitude of fiber shortening is the predominant mechanism for systolic reduction of cavity size in eccentric hypertrophy whereas in concentric hypertrophy the contribution of systolic wall thickening to ejection becomes very important. The main abnormality of diastolic function in patients with left ventricular (LV) hypertrophy is the increase of chamber stiffness indicated by the steepened slope of the diastolic pressure-volume relationship. In contrast LV diastolic myocardial stiffness as evaluated from the stress-strain relationship remains relatively unaltered in hypertrophy unless there is massive admixture of fibrosis in the LV wall (congestive cardiomyopathy). Finally LV relaxation (rate of pressure decay) is often impaired in hypertrophied states although the relationship of abnormalities of relaxation to alterations of systolic function remains to be established. There has been considerable debate whether in secondary LV hypertrophy from chronic pressure or volume overload myocardial contractility is normal or depressed. We have recently shown that in patients with myocardial hypertrophy from aortic stenosis ejection phase indexes of contractility are correlated inversely to peak systolic wall stress and that this relationship is modulated according to the actual inotropic state. The patients on the downward shifted curve (depressed contractile state) had a significantly increased LV angiographic mass. Thus advanced LV hypertrophy in chronic pressure overload appears to be associated with compromised contractile state. The structural and metabolic abnormalities which may be ultimately responsible for the depression of contractility of the hypertrophied human myocardium encompass the following findings: reduced intracellular volume fraction of myofibrils; massive increase of the average fiber diameter and increased variability of the thickness of the individual fibers and reduced activity of the myofibrillar ATPase.

Intermyofibrillar and nuclear-myofibrillar connections in human and canine myocardium an ultrastructural study

Cytoplasmic filaments, which measure 100 Å in diameter, and which differ morphologically from actin and myosin filaments, are described in normal canine myocardium and in normal and hypertrophied human myocardium. These filaments were found between Z bands, near the sarcolemma, in regions of intercalated discs, and in the vicinity of nuclear membranes. The 100 Å filaments appeared to form transverse connections between adjacent Z bands and between Z bands and outer nuclear membranes. These filaments probably function as a cytoskeleton.

Antero-Lateral Myocardial Infarction: Peri-Infarction Block

Pathological intracellular calcium handling has been proposed to underlie the alterations of contractile behavior in hypertrophied myocardium. However, the myocardial protein expression of intracellular calcium transport proteins in compensated human left ventricular hypertrophy has not yet been studied. We investigated septal myocardial specimens of patients suffering from hypertrophic obstructive cardiomyopathy (n=14) or from acquired aortic valve stenosis (n=11) undergoing myectomy or aortic valve replacement, respectively. For comparison, we studied non-hypertrophied myocardium of six non-failing hearts which could not be transplanted for technical reasons. The myocardial density of the calcium release channel of the sarcoplasmic reticulum (SR) was determined by3H-ryanodine binding. Myocardial contents of SR Ca2+-ATPase, phospholamban, calsequestrin and Na+/Ca2+-exchanger were analysed by Western blot analysis. The myocardial SR calcium release channel density was not significantly different in hypertrophied and non-failing human myocardium. In both hypertrophic obstructive cardiomyopathy and in aortic valve stenosis, SR Ca2+-ATPase expression was reduced by about 30% compared to non-failing myocardium (P<0.05), whereas the expression of phospholamban, calsequestrin, and the Na+/Ca2+-exchanger was unchanged. The decrease of SR Ca2+-ATPase expression was still observable when related to its regulatory protein phospholamban or to the myosin content of the homogenates (P<0.05). Furthermore, the SR Ca2+-ATPase expression was inversely correlated to the septum thickness assessed by echocardiography, but not to age, cardiac index or outflow tract gradient. In primary as well as in secondary hypertrophied human myocardium, the expression of SR Ca2+-ATPase is reduced and inversely related to the degree of the hypertrophy. The diminished SR Ca2+-ATPase expression might result in reduced Ca2+reuptake into the SR and might contribute to altered contractile behavior in hypertrophied human myocardium.