Effects of regression of cardiac hypertrophy on myocardial contractility and ventricular myosin isoenzymes

The effects of regression of cardiac hypertrophy on myocardial contractility and ventricular myosin isoenzymes were investigated in rats with renovascular hypertension. Six-week-old male Wistar rats were made hypertensive by constriction of one renal artery with a silver clip. Regression of cardiac hypertrophy was induced following the lowering of blood pressure by nephrectomy on the affected side 5–6 weeks after constriction of the renal artery and was maintained for 5–6 weeks. In contrast, myocardial hypertrophy was induced by 10–11 weeks of the hypertensive state. Isometric developed tension of isolated left ventricular papillary muscles was measured, while they were being perfused with Tyrode solution. Left ventricular myosin isoenzymes were separated by pyrophosphate gel electrophoresis. The ventricular to body weight ratio of the nephrectomized group was significantly lower than that of the hypertensive group, although it was greater than that of age-matched normal control rats. There were no significant differences in the isometric developed tension among three groups, the nephrectomized, hypertensive, and normal control rats. However, dT/dtmax tended to decrease in the hypertensive rats and recovered to normal in the nephrectomized rats. The left ventricular myosin isoenzyme pattern was shifted toward VM-3 in hypertensive rats and was shifted back toward VM-1 again in nephrectomized rats.     

Changes in β-adrenoceptors in heart failure due to myocardial infarction are attenuated by blockade of renin–angiotensin system

Earlier studies have revealed an improvement of cardiac function in animals with congestive heart failure (CHF) due to myocardial infarction (MI) by treatment with angiotensin converting enzyme (ACE) inhibitors. Since heart failure is also associated with attenuated responses to catecholamines, we examined the effects of imidapril, an ACE inhibitor, on the -adrenoceptor (-AR) signal transduction in the failing heart. Heart failure in rats was induced by occluding the coronary artery, and 3 weeks later the animals were treated with 1 mg/(kg·day) (orally) imidapril for 4 weeks. The animals were assessed for their left ventricular function and inotropic responses to isoproterenol. Cardiomyocytes and crude membranes were isolated from the non-ischemic viable left ventricle and examined for the intracellular concentration of Ca²⁺ [Ca²⁺]_i and -ARs as well as adenylyl cyclase (AC) activity, respectively. Animals with heart failure exhibited depressions in ventricular function and positive inotropic response to isoproterenol as well as isoproterenol-induced increase in [Ca²⁺]_i in cardiomyocytes; these changes were attenuated by imidapril treatment. Both ₁-AR receptor density and isoproterenol-stimulated AC activity were decreased in the failing heart and these alterations were prevented by imidapril treatment. Alterations in cardiac function, positive inotropic effect of isoproterenol, ₁-AR density and isoproterenol-stimulated AC activity in the failing heart were also attenuated by treatment with another ACE inhibitor, enalapril and an angiotensin II receptor antagonist, losartan. The results indicate that imidapril not only attenuates cardiac dysfunction but also prevents changes in -AR signal transduction in CHF due to MI. These beneficial effects are similar to those of enalapril or losartan and thus appear to be due to blockade of the renin–angiotensin system. (Mol Cell Biochem 263: 11–20, 2004)     

TNF‐α‐mediated signal transduction pathway is a major determinant of apoptosis in dilated cardiomyopathy

Although J2N-k strain of cardiomyopathic hamsters is an excellent model of dilated cardiomyopathy, the presence and mechanisms of apoptosis in the hearts of these genetically modified animals have not been investigated. This study examined the hypothesis that cardiac dysfunction and apoptosis in the cardiomyopathic hamsters were associated with tumour necrosis factor-alpha (TNF-α)-mediated signalling pathway involving the activation of some pro-apoptotic proteins and/or deactivation of some antiapoptotic proteins. Echocardiographic assessment of 31-week-old hamsters indicated an increase in the internal dimension of the left ventricle as well as decreases in the ejection fraction, fractional shortening and cardiac output without any evidence of cardiac hypertrophy. Increased level of TNF-α and apoptosis in cardiomyopathic hearts were accompanied by increased protein content for protein kinase C (PKC) -α and -ɛ isozymes as well as caspases 3 and 9. Phosphorylated protein content for p38 MAPK and NFκB was increased whereas that for Erk1/2, BAD and Bcl-2 was decreased in cardiomyopathic hearts. These results support the view that TNF-α and PKC isozymes may promote apoptosis due to the activation of p38 MAPK and deactivation of Erk1/2 pathways, and these changes may contribute toward the development of cardiac dysfunction in dilated cardiomyopathy.     

Changes in beta-adrenoceptors in heart failure due to myocardial infarction are attenuated by blockade of renin-angiotensin system

Earlier studies have revealed an improvement of cardiac function in animals with congestive heart failure (CHF) due to myocardial infarction (MI) by treatment with angiotensin converting enzyme (ACE) inhibitors. Since heart failure is also associated with attenuated responses to catecholamines, we examined the effects of imidapril, an ACE inhibitor, on the beta-adrenoceptor (beta-AR) signal transduction in the failing heart. Heart failure in rats was induced by occluding the coronary artery, and 3 weeks later the animals were treated with g/(kg x day) (orally) imidapril for 4 weeks. The animals were assessed for their left ventricular function and inotropic responses to isoproterenol. Cardiomyocytes and crude membranes were isolated from the non-ischemic viable left ventricle and examined for the intracellular concentration of Ca2+ [Ca2+]i and beta-ARs as well as adenylyl cyclase (AC) activity, respectively. Animals with heart failure exhibited depressions in ventricular function and positive inotropic response to isoproterenol as well as isoproterenol-induced increase in [Ca2+]i in cardiomyocytes; these changes were attenuated by imidapril treatment. Both beta1-AR receptor density and isoproterenol-stimulated AC activity were decreased in the failing heart and these alterations were prevented by imidapril treatment. Alterations in cardiac function, positive inotropic effect of isoproterenol, beta1-AR density and isoproterenol-stimulated AC activity in the failing heart were also attenuated by treatment with another ACE inhibitor, enalapril and an angiotensin II receptor antagonist, losartan. The results indicate that imidapril not only attenuates cardiac dysfunction but also prevents changes in beta-AR signal transduction in CHF due to MI. These beneficial effects are similar to those of enalapril or losartan and thus appear to be due to blockade of the renin-angiotensin system.     

Differential changes in cardiac myofibrillar and sarcoplasmic reticular gene expression in alloxan-induced diabetes

In order to examine the relationship between heart dysfunction and subcellular abnormalities as well as molecular mechanisms during the development of diabetes, we studied changes in cardiac performance, myofibrillar as well as sarcoplasmic reticular (SR) activities, and cardiac gene expression at different time intervals upon inducing diabetes in rats by an injection of alloxan (65 mg/kg; i.v.). Cardiac dysfunction was associated with a depression in myofibrillar Ca²⁺-stimulated ATPase and changes in myosin isozyme composition at 2-12 weeks of inducing diabetes. A reduction in SR Ca²⁺-uptake and Ca²⁺-pump (SERCA2) activities was evident at 10 days to 12 weeks of inducing diabetes. Alterations in cardiac function during 2-12 weeks of diabetes show a linear relationship with changes in myofibrils and SR membranes. Furthermore, alterations in cardiac function as well as myofibrillar and SR activities in 4 week diabetic animals were normalized upon treatment with insulin for 4 weeks. The steady-state mRNA abundance for -myosin heavy chain in the heart was decreased at 2 and 3 weeks but was unchanged at 5 and 6 weeks, whereas mRNA levels for -myosin heavy chain remained elevated during 2-6 weeks after inducing diabetes. SERCA2 mRNA abundance in diabetic heart was significantly increased at 3 and 5 weeks but was unaltered at 2 and 6 weeks. These results support the view that heart dysfunction in diabetes may be a consequence of myofibrillar and SR abnormalities; however, defects in myofibrillar proteins, unlike those in the SR membranes, appear to be due to changes in their gene expression.     

Effect of an ACE inhibitor and an AT1 receptor antagonist on cardiac hypertrophy

The effect of long-term administration of delapril, an angiotensin converting enzyme inhibitor, and candesartan, an angiotensin II receptor blocker, on cardiac hypertrophy was investigated in spontaneously hypertensive rats (SHR). Delapril (2 mg/kg/day) and candesartan (2 mg/kg/day) were administered for 5 weeks to 15-week-old male SHR. Echocardiographic estimation of cardiac morphology and function revealed cardiac hypertrophy in SHR compared with Wistar-Kyoto rats (WKY) which were used as normal controls. Both treated groups revealed regression of cardiac hypertrophy estimated by echocardiography. Heart to body weight ratio of treated SHR was also smaller than that of untreated SHR. Plasma BNP and ANP concentrations were increased in untreated SHR and decreased in the treated groups. Histological examination was performed using light microscopy and the area of fibrosis was estimated by computer. Reduction of the fibrotic area was observed in SHR treated with delapril and candesartan, although the latter was not statistically significant. Immunohistochemical examination using anti-collagen monoclonal antibody showed a decrease of type I collagen in treated SHR as compared with untreated SHR. It is concluded that both angiotensin converting enzyme inhibitor and angiotensin II receptor blocker sufficiently reduce blood pressure in SHR associated with regression of cardiac remodeling.     

Mitochondrial DNA deletion in human myocardium

Mutation of myocardial mitochondrial DNA was investigated in human left ventricles obtained at autopsy using the polymerase chain reaction (PCR). Seventeen autopsy cases were examined, including patients with diabetes mellitus, myocardial infarction, cardiomyopathy, cancer, and other diseases. Two cases of diabetes mellitus, 2 of myocardial infarction, and 1 of pulmonary fibrosis showed a 7.4 kb deletion of myocardial mitochondrial DNA. Primer shift PCR confirmed that an amplified DNA fragment had not been obtained by misannealing of the primers. It is unclear how much these findings are related to the severity or prognosis of the various diseases, but they indicate that mutation of myocardial mitochondrial DNA can occur in other diseases besides cardiomyopathy, although the influence of aging could not be excluded.     

Increased expression of protein kinase C isoforms in heart failure due to myocardial infarction

The activities of cardiac protein kinase C (PKC) were examined in hemodynamically assessed rats subsequent to myocardial infarction (MI). Both Ca(2+)-dependent and Ca(2+)-independent PKC activities increased significantly in left ventricular (LV) and right ventricular (RV) homogenates at 1, 2, 4, and 8 wk after MI was induced. PKC activities were also increased in both LV and RV cytosolic and particulate fractions from 8-wk infarcted rats. The relative protein contents of PKC-alpha, -beta, -epsilon, and -zeta isozymes were significantly increased in LV homogenate, cytosolic (except PKC-alpha), and particulate fractions from the failing rats. On the other hand, the protein contents of PKC-alpha, -beta, and -epsilon isozymes, unlike the PKC-zeta isozyme, were increased in RV homogenate and cytosolic fractions, whereas the RV particulate fraction showed an increase in the PKC-alpha isozyme only. These changes in the LV and RV PKC activities and protein contents in the 8-wk infarcted animals were partially corrected by treatment with the angiotensin-converting enzyme inhibitor imidapril. No changes in protein kinase A activity and its protein content were seen in the 8-wk infarcted hearts. The results suggest that the increased PKC activity in cardiac dysfunction due to MI may be associated with an increase in the expression of PKC-alpha, -beta, and -epsilon isozymes, and the improvement of heart function in the infarcted animals by imidapril may be due to partial prevention of changes in PKC activity and isozyme contents.     

Modification of sarcolemmal Na+-K+-ATPase and Na+/Ca2+ exchanger expression in heart failure by blockade of renin-angiotensin system

The activities of both sarcolemmal (SL) Na(+)-K(+)-ATPase and Na(+)/Ca(2+) exchanger, which maintain the intracellular cation homeostasis, have been shown to be depressed in heart failure due to myocardial infarction (MI). Because the renin-angiotensin system (RAS) is activated in heart failure, this study tested the hypothesis that attenuation of cardiac SL changes in congestive heart failure (CHF) by angiotensin-converting enzyme (ACE) inhibitors is associated with prevention of alterations in gene expression for SL Na(+)-K(+)-ATPase and Na(+)/Ca(2+) exchanger. CHF in rats due to MI was induced by occluding the coronary artery, and 3 wk later the animals were treated with an ACE inhibitor, imidapril (1 mg.kg(-1).day(-1)), for 4 wk. Heart dysfunction and cardiac hypertrophy in the infarcted animals were associated with depressed SL Na(+)-K(+)-ATPase and Na(+)/Ca(2+) exchange activities. Protein content and mRNA levels for Na(+)/Ca(2+) exchanger as well as Na(+)-K(+)-ATPase alpha(1)-, alpha(2)- and beta(1)-isoforms were depressed, whereas those for alpha(3)-isoform were increased in the failing heart. These changes in SL activities, protein content, and gene expression were attenuated by treating the infarcted animals with imidapril. The beneficial effects of imidapril treatment on heart function and cardiac hypertrophy as well as SL Na(+)-K(+)-ATPase and Na(+)/Ca(2+) exchange activities in the infarcted animals were simulated by enalapril, an ACE inhibitor, and losartan, an angiotensin receptor antagonist. These results suggest that blockade of RAS in CHF improves SL Na(+)-K(+)-ATPase and Na(+)/Ca(2+) exchange activities in the failing heart by preventing changes in gene expression for SL proteins.     

Detection of hepatitis C virus RNA in the hearts of patients with hepatogenic cardiomyopathy

We examined the Hepatitis C virus (HCV) genome in the myocardium and liver obtained at autopsy from seven patients with HCV-positive liver cirrhosis and hepatocellular carcinoma (HCC) by in situ hybridization and histopathological studies. The HCV virus genome was detected in the myocardium of one patient as well as in the liver in three out of seven patients. However, Epstein-Barr (EB) virus genome could not be detected in liver or myocardium. In the patient who showed positive reaction to HCV in myocardium, both serum HCV and Hepatitis B virus (HBV) antibodies were positive. It is unknown whether this was related to an immunological abnormality of the host or to an interaction between RNA and DNA viruses. In conclusion, we could identify the HCV genome in the myocardium of a patient with hepatogenic myocardosis.