Regional biochemical remodeling in non-infarcted tissue of rat heart post-myocardial infarction

Nkx2.5 enhances the efficacy of mesenchymal stem cells transplantation in treatment heart failure in rats

AIMS

The aim of this study is to determine whether Nkx2.5 transfection of transplanted bone marrow mesenchymal stem cells (MSCs) improves the efficacy of treatment of adriamycin-induced heart failure in a rat model.

MAIN METHODS

Nkx2.5 was transfected in MSCs by lentiviral vector transduction. The expressions of Nkx2.5 and cardiac specific genes in MSCs and Nkx2.5 transfected mesenchymal stem cells (MSCs-Nkx2.5) were analyzed with quantitative real-time PCR and Western blot in vitro. Heart failure models of rats were induced by adriamycin and were then randomly divided into 3 groups: injected saline, MSCs or MSCs-Nkx2.5 via the femoral vein respectively. Four weeks after injection, the cardiac function, expressions of cardiac specific gene, fibrosis formation and collagen volume fraction in the myocardium as well as the expressions of GATA4 and MEF2 in rats were analyzed with echocardiography, immunohistochemistry, Masson staining, quantitative real-time PCR and Western blot, respectively.

KEY FINDINGS

Nkx2.5 enhanced cardiac specific gene expressions including α-MHC, TNI, CKMB, connexin-43 in MSCs-Nkx2.5 in vitro. Both MSCs and MSCs-Nkx2.5 improved cardiac function, promoted the differentiation of transplanted MSCs into cardiomyocyte-like cells, decreased fibrosis formation and collagen volume fraction in the myocardium, as well as increased the expressions of GATA4 and MEF2 in adriamycin-induced rat heart failure models. Moreover, the effect was much more remarkable in MSCs-Nkx2.5 than in MSCs group.

SIGNIFICANCE

This study has found that Nkx2.5 enhances the efficacy of MSCs transplantation in treatment adriamycin-induced heart failure in rats. Nkx2.5 transfected to transplanted MSCs provides a potential effective approach to heart failure.

Coronary flow reserve in the remote myocardium predicts left ventricular remodeling following acute myocardial infarction

PURPOSE

Coronary flow reserve (CFR) in the non-infarcted myocardium is often impaired following acute myocardial infarction (AMI). However, the clinical significance of CFR in the non-infarcted myocardium is not fully understood. The objective of the present study was to assess whether a relationship exists between CFR and left ventricular remodeling following AMI.

MATERIALS AND METHODS

We enrolled 18 consecutive patients undergoing coronary intervention. Heart function was analyzed using real-time myocardial contrast echocardiography at one week and six months after coronary angioplasty. Ten subjects were enrolled as the control group and were examined using the same method at the same time to assess CFR. Cardiac troponin I (cTnI) levels were routinely analyzed to estimate peak concentration.

RESULTS

CFR was 1.55±0.11 in the infarcted zone and 2.05±0.31 in the remote zone (p<0.01) at one week following AMI. According to CFR values in the remote zone, all patients were divided into two groups: Group I (CFR <2.05) and Group II (CFR >2.05). The levels of cTnI were higher in Group I compared to Group II on admission (36.40 vs. 21.38, p<0.05). Furthermore, left ventricular end diastolic volume was higher in Group I compared to Group II at six months following coronary angioplasty.

CONCLUSION

Microvascular dysfunction is commonly observed in the remote myocardium. The CFR value accurately predicts adverse ventricular remodeling following AMI.

A technique for in vivo mapping of myocardial creatine kinase metabolism

ATP derived from the conversion of phosphocreatine to creatine by creatine kinase provides an essential chemical energy source that governs myocardial contraction. Here, we demonstrate that the exchange of amine protons from creatine with protons in bulk water can be exploited to image creatine through chemical exchange saturation transfer (CrEST) in myocardial tissue. We show that CrEST provides about two orders of magnitude higher sensitivity compared to (1)H magnetic resonance spectroscopy. Results of CrEST studies from ex vivo myocardial tissue strongly correlate with results from (1)H and (31)P magnetic resonance spectroscopy and biochemical analysis. We demonstrate the feasibility of CrEST measurement in healthy and infarcted myocardium in animal models in vivo on a 3-T clinical scanner. As proof of principle, we show the conversion of phosphocreatine to creatine by spatiotemporal mapping of creatine changes in the exercised human calf muscle. We also discuss the potential utility of CrEST in studying myocardial disorders.

High-energy phosphotransfer in the failing mouse heart: role of adenylate kinase and glycolytic enzymes

AIMS

To measure the activity of the key phosphotransfer enzymes creatine kinase (CK), adenylate kinase (AK), and glycolytic enzymes in two common mouse models of chronic heart failure.

METHODS AND RESULTS

C57BL/6 mice were subjected to transverse aortic constriction (TAC), myocardial infarction induced by coronary artery ligation (CAL), or sham operation. Activities of phosphotransfer enzymes CK, AK, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), 3-phosphoglycerate kinase (PGK), and pyruvate kinase were assessed spectrophotometrically. Mice were characterized by echocardiography or magnetic resonance imaging 5- to 8-week post-surgery and selected for the presence of congestive heart failure. All mice had severe left ventricular hypertrophy, impaired systolic function and pulmonary congestion compared with sham controls. A significant decrease in myocardial CK and maximal CK reaction velocity was observed in both experimental models of heart failure. However, the activity of AK and its isoforms remained unchanged, despite a reduction in its protein expression. In contrast, the activities of glycolytic phosphotransfer mediators GAPDH and PGK were 19 and 12% higher in TAC, and 31 and 23% higher in CAL models, respectively.

CONCLUSION

Chronic heart failure in the mouse is characterized by impaired CK function, unaltered AK, and increased activity of glycolytic phosphotransfer enzymes. This pattern of altered phosphotransfer activity was observed independent of the heart failure aetiology.

Meta-analysis and profiling of cardiac expression modules

Heart failure is a complex, complicated disease that is not yet fully understood. We used the Module Map algorithm to uncover groups of genes that have a similar pattern of expression under various conditions of heart stress. These groups of genes are called modules and may serve as computational predictions of biological pathways for the various clinical situations. The Module Map algorithm allows a large-scale analysis of genes expressed. We applied this algorithm to 700 different mouse experiments downloaded from the Gene Expression Omnibus database, which identified 884 modules. The analysis reconstructed partially known principles that play a role in governing the response of heart to stress, thus demonstrating the strength of the method. We have shown a role of genes related to the immune system in conditions of heart remodeling and failure. We have also shown changes in the expression of genes involved with energy metabolism and changes in the expression of contractile proteins of the heart following myocardial infarction. When focusing on another module we noted a new correlation between genes related to osteogenesis and heart failure, including Runx2 and Ahsg, whose role in heart failure was unknown so far. Despite a lack of prior biological knowledge, the Module Map algorithm has reconstructed known pathways, which demonstrates the strength of this new method for analyzing gene profiles related to clinical phenomenon. The method and the analysis presented are a new avenue to uncover the correlation of clinical conditions to the molecular level.

Creatine uptake in mouse hearts with genetically altered creatine levels

Creatine plays an important role in energy metabolism in the heart. Cardiomyocytes accumulate creatine via a specific creatine transporter (CrT), the capacity of which is reduced in the failing heart, resulting in lower myocardial creatine concentration. Therefore, to gain insight into how the CrT is regulated, we studied two mouse models of severely altered myocardial creatine levels. Cardiac creatine uptake levels were measured in isolated hearts from creatine-free guanidinoacetate-N-methyl transferase knock out (GAMT^−/−) mice and from mice overexpressing the myocardial CrT (CrT-OE) using ¹⁴C-radiolabeled creatine. CrT mRNA levels were measured using real time RT-PCR and creatine levels with HPLC. Hearts from GAMT^−/− mice showed a 7-fold increase in V_max of creatine uptake and a 1.4-fold increase in CrT mRNA levels. The increase in Cr uptake and in CrT mRNA levels, however, was almost completely prevented when mice were fed a creatine supplemented diet, indicating that creatine uptake is subject to negative feedback regulation. Cardiac creatine uptake levels in CrT-OE mice were increased on average 2.7-fold, showing a considerable variation, in line with a similar variation in creatine content. Total CrT mRNA levels correlated well with myocardial creatine content (r = 0.67; p < 0.0001) but endogenous CrT mRNA levels did not correlate at all with myocardial creatine content (r = 0.01; p = 0.96). This study shows that creatine uptake can be massively upregulated in the heart, by almost an order of magnitude and that this upregulation is subject to feedback inhibition. In addition, our results strongly suggest that CrT activity is predominantly regulated by mechanisms other than alterations in gene expression.

The creatine kinase energy transport system in the failing mouse heart

Characteristic alterations of the creatine kinase (CK) system occur in heart failure and may contribute to contractile dysfunction. We examined two mouse models of chronic cardiac stress, transverse aortic constriction (TAC) and coronary artery ligation (CAL), and examined the relationship of CK system changes with hypertrophy and heart failure development. C57Bl/6 mice were subjected to TAC or sham surgery and sacrificed after 2-10 weeks according to echocardiographic criteria of myocardial hypertrophy and function to create four groups representing progressive dysfunction from normal, through compensated hypertrophy, to heart failure. Only mice with congestive heart failure had LV total creatine concentration and total CK activity significantly lower than sham values (11% and 30% lower, respectively). However for all aortic banded mice, a linear relationship was observed between ejection fraction and estimated maximal CK reaction velocity. Mice with heart failure also had corresponding decreases in the activities of the Mito-, MM-, and MB-CK isoenzymes, while the BB isoform remained unchanged. To determine whether these changes were model specific, mice were subjected to CAL or sham operation and followed for 7 weeks. Quantitative changes in total creatine, total CK activity, Mito-CK and MM-CK activities were similar for CAL and TAC mice. We conclude that alterations in the creatine kinase system occur during heart failure in mice qualitatively similar to those occurring in larger animals and humans, suggesting that mice are a suitable model for studying the role of such changes in the pathogenesis of heart failure.

Xanthine oxidase inhibitors improve energetics and function after infarction in failing mouse hearts

After myocardial infarction, ventricular geometry and function, as well as energy metabolism, change markedly. In nonischemic heart failure, inhibition of xanthine oxidase (XO) improves mechanoenergetic coupling by improving contractile performance relative to a reduced energetic demand. However, the metabolic and contractile effects of XO inhibitors (XOIs) have not been characterized in failing hearts after infarction. After undergoing permanent coronary ligation, mice received a XOI (allopurinol or oxypurinol) or matching placebo in the daily drinking water. Four weeks later, 1H MRI and 31P magnetic resonance spectroscopy (MRS) were used to quantify in vivo functional and metabolic changes in postinfarction remodeled mouse myocardium and the effects of XOIs on that process. End-systolic (ESV) and end-diastolic volumes (EDV) were increased by more than sixfold after infarction, left ventricle (LV) mass doubled ( P < 0.005), and the LV ejection fraction (EF) decreased (14 ± 9%) compared with control hearts (59 ± 8%, P < 0.005) at 1 mo. The myocardial phosphocreatine (PCr)-to-ATP ratio (PCr/ATP) was also significantly decreased in infarct remodeled hearts (1.4 ± 0.6) compared with control animals (2.1 ± 0.5, P < 0.02), in agreement with prior studies in larger animals. The XOIs allopurinol and oxypurinol did not change LV mass but limited the increase in ESV and EDV of infarct hearts by 50%, increased EF (23 ± 9%, P = 0.01), and normalized cardiac PCr/ATP (2.0 ± 0.5, P < 0.04). We conclude that XOIs improve ventricular function after infarction and normalize high-energy phosphate ratio in heart failure. Thus XOI therapy offers a new and potentially complementary approach to limit the adverse contractile and metabolic consequences after infarction.

Apoptosis at a distance: Remote activation of caspase-3 occurs early after myocardial infarction

OBJECTIVE

After an acute myocardial infarction, the viable myocardium remote from the infarct zone is subjected to ventricular remodeling. Besides hypertrophy, processes of apoptosis may contribute to these remodeling processes. Reports on apoptosis in this area have been doubted because they were mainly based on in-situ nick-end DNA labeling (TUNEL) measurements, with questionable specifity. Moreover, the time course of initiation of these processes has not been characterized. Therefore the goals of this study were to (1) reliably determine if in the remote area of the infarcted heart apoptosis may be initiated using highly specific biochemical markers and (2) evaluate the time course of such an activation.

METHODS

A well-defined model, regional myocardial infarction induced by ligation of the left anterior coronary artery in rats in vivo, was used. Heart and lung wet weights, the left ventricular end-diastolic pressure (LVEDP), and the serum level of the atrial natriuretic propeptide (proANP) were determined from 1 day up to 4 weeks as indicators of developing heart failure. In transmural biopsies from the non-ischemic left ventricular wall of the infarcted heart, the activation of caspase-3, the bcl-2/bax ratio (Western blot analysis), and the DNA laddering (LM-PCR) were determined.

RESULTS

Although heart- and lung weights did not increase before 1 week after infarction, proANP levels were elevated already 1 day after myocardial infarction suggesting early sub-clinical heart failure. The activity of caspase-3 increased significantly to 160+/- 20% compared to sham operated controls as early as 1 day after ligation and remained elevated over the entire time course. In parallel, the bcl-2/bax ratio shifted toward the pro-apoptotic bax. Moreover, these clear and specific biochemical indicators of apoptosis in the remote area of the infarcted heart were paralleled by the fragmentation of genomic DNA.

CONCLUSION

These data demonstrate that apoptotic markers are activated in the surviving zone of the heart remote from the infarct area as early as 1 day after myocardial infarction with persistence for up to 4 weeks. This activation coincides with early markers of heart failure. The exact regulation of this apoptotic process remains to be elucidated.

Bioenergetic protection of failing atrial and ventricular myocardium by vasopeptidase inhibitor omapatrilat

Deficient bioenergetic signaling contributes to myocardial dysfunction and electrical instability in both atrial and ventricular cardiac chambers. Yet, approaches capable to prevent metabolic distress are only partially established. Here, in a canine model of tachycardia-induced congestive heart failure, we compared atrial and ventricular bioenergetics and tested the efficacy of metabolic rescue with the vasopeptidase inhibitor omapatrilat. Despite intrinsic differences in energy metabolism, failing atria and ventricles demonstrated profound bioenergetic deficiency with reduced ATP and creatine phosphate levels and compromised adenylate kinase and creatine kinase catalysis. Depressed phosphotransfer enzyme activities correlated with reduced tissue ATP levels, whereas creatine phosphate inversely related with atrial and ventricular load. Chronic treatment with omapatrilat maintained myocardial ATP, the high-energy currency, and protected adenylate and creatine kinase phosphotransfer capacity. Omapatrilat-induced bioenergetic protection was associated with maintained atrial and ventricular structural integrity, albeit without full recovery of the creatine phosphate pool. Thus therapy with omapatrilat demonstrates the benefit in protecting phosphotransfer enzyme activities and in preventing impairment of atrial and ventricular bioenergetics in heart failure.

“Energenetics” of Heart Failure

It has been postulated that the failing heart suffers from chronic energy starvation, and that the derangements in cardiac energy production contribute to the inevitable transition from compensated hypertrophy to decompensated heart failure. Although the existence of metabolic alterations is hardly disputed anymore, the molecular mechanisms driving this "metabolic remodeling" process and its significance for the development of cardiac failure are still open to discussion. Next to changes in mitochondrial function, the hypertrophied heart is characterized by a marked change in substrate preference away from fatty acids toward glucose. Several lines of evidence suggest that these metabolic adaptations are brought about, at least in part, by alterations in the rate of transcription of genes encoding for proteins involved in substrate transport and metabolism. Here, we present an overview of the principal metabolic changes and discuss the various mechanisms that are likely to play a role, with special emphasis on gene regulatory mechanisms. In addition, the significance of these changes for the etiology of heart failure is discussed.

Selective β1-blockade attenuates post-infarct remodelling without improvement in myocardial energy metabolism and function in rats with heart failure

OBJECTIVE

To investigate in vivo effects of long-term selective beta1-blockade on cardiac energy metabolism, remodelling, function and plasma cytokines in a rat model of post-infarct congestive heart failure (CHF).

METHODS

Myocardial infarction (MI) was induced in male rats by ligation of the left coronary artery. Three different groups of rats were studied, MI rats treated with metoprolol (n=17), MI rats treated with saline (n=14) and sham-operated rats (n=12). The treatment with metoprolol 1 mg/kg/h was initiated in the third week post-infarct for a period of 6 weeks. All rats were investigated non-invasively with volume-selective 31P magnetic resonance spectroscopy and echocardiography for evaluation of left ventricular (LV) energy metabolism, morphology and function. Plasma concentration of IL-1beta and IL-6 and density of beta-adrenergic receptors were analyzed.

RESULTS

Metoprolol attenuated the increase in LV dimensions and volumes. Treatment with metoprolol had no effect on PCr/ATP and LV function. Plasma level of IL-1beta was higher and IL-6 was lower in the metoprolol group. Density of beta-adrenergic receptors was similar in all three groups.

CONCLUSION

Selective beta1-blockade in rats with chronic CHF attenuates post-infarct structural remodelling, without concomitant improvement in myocardial energy metabolism and function. Improvements in myocardial energy metabolism and function do not precede and are not a prerequisite for an anti-remodelling effect of beta1-blockade in the setting of chronic CHF.

Time course of right ventricular remodeling in rats with experimental myocardial infarction

Right ventricular (RV) weight increases dependent on time after myocardial infarction (MI) and on MI size. The sequential changes in RV volume and hemodynamics and their relations to left ventricular (LV) remodeling after MI are unknown. We therefore examined the time course of RV remodeling in rats with LV MI. MI was produced by left coronary artery ligation. Four, eight, and sixteen weeks later, LV and RV hemodynamic measurements were performed and pressure-volume curves were obtained. For serial measurement of RV volumes and performance, cine-MRI was performed 2 and 8 wk after MI. The ratios of beta-myosin heavy chain (MHC) to alpha-MHC and skeletal to cardiac alpha-actin were determined for the RV and LV after large MI or sham operation. RV weight increased in rats with MI, as did RV volume. RV pressure-volume curves were shifted toward larger volumes 16 wk after large MI. RV systolic pressure increased gradually over time; however, the gain in RV weight was always in excess of RV systolic pressure. The ratios of skeletal to cardiac alpha-actin and beta-MHC to alpha-MHC were increased after MI in both ventricles in a similar fashion. Because RV wall stress was not increased after infarction, mechanical factors may not conclusively explain hypertrophy, which maintained balanced loading conditions for the RV even after large LV infarction.

Acute changes of myocardial creatine kinase gene expression under beta-adrenergic stimulation

Creatine kinase (CK) plays a crucial role in myocardial energy metabolism. Alterations in CK gene expression are found in hypertrophied and failing heart, but the mechanisms behind these changes are unclear. This study tests the hypothesis that increased adrenergic stimulation, which is observed in heart failure, induces changes of myocardial CK-activity, -isoenzyme distribution and -gene expression that are characteristic of the failing and hypertrophied heart. Isolated rat hearts were perfused (constant pressure of 80 mmHg) with red cell suspensions. Following a 20-min warm-up period, perfusion for 3 h with 10(-8) M (iso 3 h) or without (control 3 h) isoproterenol was started or experiments were immediately terminated (control 0 h). Left ventricular tissue was analyzed for total CK-activity, CK-isoenzyme distribution and, by use of quantitative RT-PCR, for B-CK, M-CK, mito-CK and GAPDH- (as internal standard) mRNA. After beta-adrenergic stimulation (iso 3 h) but not after control perfusion (control 3 h) a roughly threefold increase in B-CK mRNA levels and a decrease in M-CK mRNA levels by 18% was found. There were no significant differences among the three groups in total CK-activity and in distribution of CK-MM, CK-BB, CK-MB and mito-CK. Thus, beta-adrenergic stimulation induces a switch in CK gene expression from M-CK to B-CK, which is characteristic for the hypertrophied and failing heart. This may be interpreted as an adaptive mechanism making energy transduction via CK more efficient at times of increased metabolic demand.

Altered expression of proteins of metabolic regulation during remodeling of the left ventricle after myocardial infarction

Non-infarcted myocardium after coronary occlusion undergoes progressive morphological and functional changes. The purpose of this study was to determine whether non-infarcted myocardium exhibits (1) alteration of the substrate pattern of myocardial metabolism and (2) concomitant changes in the expression of regulatory proteins of glucose and fatty acid metabolism. Myocardial infarction was induced in rats by ligation of the left coronary artery. One day and eight weeks after coronary occlusion, glucose and palmitate oxidation were measured. Expression of selected proteins of metabolism were determined one day to 12 weeks after infarction. One day after coronary occlusion no difference of glucose and palmitate oxidation was detectable, whereas after eight weeks, glucose oxidation was increased (+84%, P<0.05) and palmitate oxidation did not change significantly (-19%, P=0.07) in infarct-containing hearts, compared with hearts from sham-operated rats. One day after coronary occlusion, myocardial mRNA expression of the glucose transporter GLUT-1 was increased (+86%, P<0.05) and the expression of GLUT-4 was decreased (-28%, P<0.05) in surviving myocardium of infarct-containing hearts. Protein level of GLUT-1 was increased (+81%, P<0.05) and that of GLUT-4 slightly, but not significantly, decreased (-16%, P=NS). mRNA expressions of heart fatty acid binding protein (H-FABP), and of medium chain acyl-CoA dehydrogenase (MCAD), were decreased by 36% (P<0.05) and 35% (P=0. 07), respectively. Eight weeks after acute infarction, the left ventricle was hypertrophied and, at this time-point, there was no difference in the expression of GLUT-1 and GLUT-4 between infarcted and sham-operated hearts. However, myocardial mRNA and protein content of MCAD were decreased by 30% (P<0.01) and 27% (P<0.05), respectively. In summary, in surviving myocardium, glucose oxidation was increased eight weeks after coronary occlusion. Concomitantly, mRNA and protein expression of MCAD were decreased, compatible with a role of altered expression of regulatory proteins of metabolism in post-infarction modification of myocardial metabolism.

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

Beneficial effects of MET-88, a gamma-butyrobetaine hydroxylase inhibitor in rats with heart failure following myocardial infarction

Myocardial ischemia can cause myocardial infarction and as a consequence, heart failure. 3-(2,2,2-trimethylhydrazinium) propionate (MET-88) inhibits gamma-butyrobetaine hydroxylase and has cardioprotective effects on the ischemic heart. We now examined the effects of MET-88 in rats with congestive heart failure following myocardial infarction. Congestive heart failure was produced by left coronary artery ligation in rats. MET-88 at 100 mg/kg/day was orally administered from the 2nd day after surgery. We performed a survival study for 181 days, and measured ventricular remodeling, cardiac function, and myocardial high-energy phosphate levels after treatment for 20 days. MET-88 prolonged survival with a median 50% survival of 103 days compared to 79 days for the heart-failure control rats. The expansion of the left ventricular cavity (ventricular remodeling) in heart-failure rats was prevented by treatment with MET-88, and the effect of MET-88 was similar to that of captopril at 20 mg/kg. MET-88 attenuated the rise in right atrial pressure in heart-failure rats and augmented cardiac functional adaptability against an increased load. Also, MET-88 improved the myocardial energy state in heart-failure rats. The present results indicate that MET-88 improves the pathosis in rats with heart failure induced by myocardial infarction.

Effects of ACE inhibition and beta-receptor blockade on energy metabolism in rats postmyocardial infarction

Chronic treatment with beta-receptor blockers or angiotensin-converting enzyme (ACE) inhibitors in heart failure can reduce mortality and improve left ventricular function, but the mechanisms involved in their beneficial action remain to be fully defined. Our hypothesis was that these agents prevent the derangement of cardiac energy metabolism. Rats were subjected to myocardial infarction (MI) or sham operation. Thereafter, animals were treated with bisoprolol, captopril, or remained untreated. Two months later, cardiac function was measured in the isolated heart by a left ventricular balloon (pressure-volume curves), and energy metabolism of residual intact myocardium was analyzed in terms of total and isoenzyme creatine kinase (CK) activity, steady-state levels (ATP, phosphocreatine), and turnover rates (CK reaction velocity) of high-energy phosphates (31P nuclear magnetic resonance) and total creatine content (HPLC). Bisoprolol and partially captopril prevented post-MI hypertrophy and partially prevented left ventricular contractile dysfunction. Residual intact failing myocardium in untreated, infarcted hearts showed a 25% decrease of the total, a 26% decrease of MM-, and a 37% decrease of the mitochondrial CK activity. Total creatine was reduced by 15%, phosphocreatine by 21%, and CK reaction velocity by 41%. Treatment with bisoprolol or captopril largely prevented all of these changes in infarcted hearts. Thus the favorable functional effects of beta-receptor blockers and ACE inhibitors post-MI are accompanied by substantial beneficial effects on cardiac energy metabolism.

Functional and energetic consequences of chronic myocardial creatine depletion by beta-guanidinopropionate in perfused hearts and in intact rats

Oral feeding with the creatine analogue beta-guanidinopropionate (beta-GP) reduces myocardial phosphocreatine and creatine concentrations by about 80%in vitro, this is accompanied by reduced contractile performance. We hypothesized, thus, that beta-GP feeding leads to hemodynamic changes in vivo characteristic of heart failure. beta-GP was fed to Wistar rats for up to 8 weeks. In isolated hearts, function was measured isovolumically, myocardial energetics were followed with (31)P-NMR spectroscopy. In vivo hemodynamics were measured with Millar-Tip-catheters and an electromagnetic flow probe. Beta-GP feeding did not alter heart weight. In vitro, diastolic pressure-volume curves indicated structural left ventricular dilatation, and a 36% reduction of left ventricular developed pressure was found; phosphocreatine was reduced by approximately 80%, ATP unchanged and creatine kinase reaction velocity ((31)P-MR saturation transfer) decreased by approximately 90%. The total creatine pool (high-pressure liquid chromatography) was reduced by up to approximately 70%. In contrast to in vitro findings, in vivo cardiac hemodynamics (including left ventricular developed pressure, d P/d t(max), cardiac output and peripheral vascular resistance) at rest and during acute volume loading showed no alterations after beta-GP feeding. The only functional impairment observed in vivo was a 14% reduction of maximum left ventricular developed pressure during brief aortic occlusion. In the intact rat, cardiac and/or humoral compensatory mechanisms are sufficient to maintain normal hemodynamics in spite of a 90% reduction of creatine kinase reaction velocity. However, chronic beta-GP feeding leads to structural left ventricular dilatation.

Bioenergetic, functional and morphological consequences of postinfarct cardiac remodeling in the rat

Despite recent advances in the treatment, severe chronic heart failure (CHF) remains a syndrome associated with high mortality. Therefore, the search for new agents to improve both patient symptoms and survival, as well as the pursuit for detailed knowledge about pathophysiology of the failing heart, will continue to depend on relevant animal models. Large acute myocardial infarction (MI) initiates complex changes in the geometrical, structural, and biochemical architecture of both infarcted and non-infarcted regions of ventricular myocardium, which can profoundly affect left ventricular function and prognosis. In this paper we present a new model for non-invasive cardiac (31)P MRS in the rat. Volume-selective (31)P magnetic resonance spectroscopy and echocardiography were used for evaluation of myocardial energy metabolism, cardiac morphology and function in rats 3 days and 3 weeks after induction of large MI. The phosphocreatine:adenosine triphosphate (PCr:ATP) ratio was decreased in rats with MI comparing with controls both at 3 days (1.6+/-0.06 vs 2.7+/-0.04; mean+/-s.e.m. P<0.0001) and 3 weeks (1.6+/-0.07 v 2.7+/-0.02 P<0.0001) postinfarct. The results from the study demonstrate that postinfarct cardiac remodeling is a rapid process of changes not only in cardiac geometry, structure and function but also in myocardial energy metabolism after large transmural MI in the rat.