Increased glycolytic metabolism in cardiac hypertrophy and congestive failure

Perturbations in the gene regulatory pathways controlling mitochondrial energy production in the failing heart

The heart is an omnivore organ that requires constant energy production to match its functional demands. In the adult heart, adenosine-5'-triphosphate (ATP) production occurs mainly through mitochondrial fatty acid and glucose oxidation. The heart must constantly adapt its energy production in response to changes in substrate supply and work demands across diverse physiologic and pathophysiologic conditions. The cardiac myocyte maintains a high level of mitochondrial ATP production through a complex transcriptional regulatory network that is orchestrated by the members of the peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family. There is increasing evidence that during the development of cardiac hypertrophy and in the failing heart, the activity of this network, including PGC-1, is altered. This review summarizes our current understanding of the perturbations in the gene regulatory pathways that occur during the development of heart failure. An appreciation of the role this regulatory circuitry serves in the regulation of cardiac energy metabolism may unveil novel therapeutic targets aimed at the metabolic disturbances that presage heart failure. This article is part of a Special Issue entitled:Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.

Reduction of rat cardiac hypertrophy by osthol is related to regulation of cardiac oxidative stress and lipid metabolism

The objective of this study was to examine the therapeutic effect of osthol, a coumarin compound isolated from the fruit of Cnidium monnieri (L.) Cusson, on cardiac hypertrophy in rats and investigate its potential mechanisms. The rats with cardiac hypertrophy induced by renovascular hypertension were given osthol orally by gavage for 4 weeks. The results showed that in the osthol 20 mg/kg group, the blood pressure, heart weight index and myocardial malondialdehyde content were lowered (p < 0.001, p = 0.002 and p = 0.025, respectively), the myocardial superoxide dismutase and glutathione peroxidase contents were increased (p < 0.001), and the elevated unesterified fatty acids and triacylglycerols in myocardial tissues were decreased (p = 0.017 and p = 0.004, respectively). At the same time, the myocardial peroxisome proliferator-activated receptor (PPAR)-α and carnitine palmitoyltransferase (CPT)-1a mRNA expressions were increased and the myocardial diacylglycerol acyltransferase (DGAT) mRNA expression was decreased in the osthol 20 mg/kg group (p < 0.001). Osthol treatment was associated with a decreased cross-sectional area of cardiomyocytes (p < 0.001). These findings suggest that osthol may exert a therapeutic effect on cardiac hypertrophy in rats, and its mechanisms may be related to the improvement of myocardial oxidative stress and lipid metabolism via regulation of PPARα-mediated target gene expressions including an increase in CPT-1a mRNA expression and a decrease in DGAT mRNA expression.

Cardiac dysfunction in adipose triglyceride lipase deficiency: treatment with a PPARα agonist

BACKGROUND AND PURPOSE

Adipose triglyceride lipase (ATGL) has been identified as a rate-limiting enzyme of mammalian triglyceride catabolism. Deletion of the ATGL gene in mice results in severe lipid accumulation in a variety of tissues including the heart. In the present study we investigated cardiac function in ATGL-deficient mice and the potential therapeutic effects of the PPARα and γ agonists Wy14,643 and rosiglitazone, respectively.

EXPERIMENTAL APPROACH

Hearts isolated from wild-type (WT) mice and ATGL(-/-) mice treated with Wy14,643 (PPARα agonist), rosiglitazone (PPARγ agonist) or vehicle were perfused at a constant flow using the Langendorff technique. Left ventricular (LV) pressure–volume relationships were established, and the response to adrenergic stimulation was determined with noradrenaline (NA).

KEY RESULTS

Hearts from ATGL(-/-) mice generated higher LV end-diastolic pressure and lower LV developed pressure as a function of intracardiac balloon volume compared to those from WT mice. Likewise, passive wall stress was increased and active wall stress decreased in ATGL(-/-) hearts. Contractile and microvascular responses to NA were substantially reduced in ATGL(-/-) hearts. Cardiac contractility was improved by treating ATGL(-/-) mice with the PPARα agonist Wy14,643 but not with the PPARγ agonist rosiglitazone.

CONCLUSIONS AND IMPLICATIONS

Our results indicate that lipid accumulation in mouse hearts caused by ATGL gene deletion severely affects systolic and diastolic function, as well as the response to adrenergic stimulation. The beneficial effects of Wy14,643 suggest that the cardiac phenotype of these mice is partially due to impaired PPARα signalling.

Mitochondrial protein phosphorylation as a regulatory modality: implications for mitochondrial dysfunction in heart failure

Phosphorylation of mitochondrial proteins has been recognized for decades, and the regulation of pyruvate- and branched-chain α-ketoacid dehydrogenases by an atypical kinase/phosphatase cascade is well established. More recently, the development of new mass spectrometry-based technologies has led to the discovery of many novel phosphorylation sites on a variety of mitochondrial targets. The evidence suggests that the major classes of kinase and several phosphatases may be present at the mitochondrial outer membrane, intermembrane space, inner membrane, and matrix, but many questions remain to be answered as to the location, timing, and reversibility of these phosphorylation events and whether they are functionally relevant. The authors review phosphorylation as a mitochondrial regulatory strategy and highlight its possible role in the pathophysiology of cardiac hypertrophy and failure.

Myocardial contractile and metabolic properties of familial hypertrophic cardiomyopathy caused by cardiac troponin I gene mutations: a simulation study

Familial hypertrophic cardiomyopathy (FHC) is an inherited disease that is caused by sarcomeric protein gene mutations. The mechanism by which these mutant proteins cause disease is uncertain. Experimentally, cardiac troponin I (CTnI) gene mutations mainly alter myocardial performance via increases in the Ca(2+) sensitivity of cardiac contractility. In this study, we used an integrated simulation that links electrophysiology, contractile activity and energy metabolism of the myocardium to investigate alterations in myocardial contractile function and energy metabolism regulation as a result of increased Ca(2+) sensitivity in CTnI mutations. Simulation results reproduced the following typical features of FHC: (1) slower relaxation (diastolic dysfunction) caused by prolonged [Ca(2+)](i) and force transients; (2) higher energy consumption with the increase in Ca(2+) sensitivity; and (3) reduced fatty acid oxidation and enhanced glucose utilization in hypertrophied heart metabolism. Furthermore, the simulation indicated that in conditions of high energy consumption (that is, more than an 18.3% increase in total energy consumption), the myocardial energetic metabolic network switched from a net consumer to a net producer of lactate, resulting in a low coupling of glucose oxidation to glycolysis, which is a common feature of hypertrophied hearts. This study provides a novel systematic myocardial contractile and metabolic analysis to help elucidate the pathogenesis of FHC and suggests that the alterations in resting heart energy supply and demand could contribute to disease progression.

Inhibition of c-Jun-N-terminal kinase increases cardiac peroxisome proliferator-activated receptor alpha expression and fatty acid oxidation and prevents lipopolysaccharide-induced heart dysfunction

Septic shock results from bacterial infection and is associated with multi-organ failure, high mortality, and cardiac dysfunction. Sepsis causes both myocardial inflammation and energy depletion. We hypothesized that reduced cardiac energy production is a primary cause of ventricular dysfunction in sepsis. The JNK pathway is activated in sepsis and has also been implicated in impaired fatty acid oxidation in several tissues. Therefore, we tested whether JNK activation inhibits cardiac fatty acid oxidation and whether blocking JNK would restore fatty acid oxidation during LPS treatment. LPS treatment of C57BL/6 mice and adenovirus-mediated activation of the JNK pathway in cardiomyocytes inhibited peroxisome proliferator-activated receptor α expression and fatty acid oxidation. Surprisingly, none of the adaptive responses that have been described in other types of heart failure, such as increased glucose utilization, reduced αMHC:βMHC ratio or induction of certain microRNAs, occurred in LPS-treated mice. Treatment of C57BL/6 mice with a general JNK inhibitor (SP600125) increased fatty acid oxidation in mice and a cardiomyocyte-derived cell line. JNK inhibition also prevented LPS-mediated reduction in fatty acid oxidation and cardiac dysfunction. Inflammation was not alleviated in LPS-treated mice that received the JNK inhibitor. We conclude that activation of JNK signaling reduces fatty acid oxidation and prevents the peroxisome proliferator-activated receptor α down-regulation that occurs with LPS.

Longitudinal Evaluation of Fatty Acid Metabolism in Normal and Spontaneously Hypertensive Rat Hearts with Dynamic MicroSPECT Imaging

The goal of this project is to develop radionuclide molecular imaging technologies using a clinical pinhole SPECT/CT scanner to quantify changes in cardiac metabolism using the spontaneously hypertensive rat (SHR) as a model of hypertensive-related pathophysiology. This paper quantitatively compares fatty acid metabolism in hearts of SHR and Wistar-Kyoto normal rats as a function of age and thereby tracks physiological changes associated with the onset and progression of heart failure in the SHR model. The fatty acid analog, ¹²³I-labeled BMIPP, was used in longitudinal metabolic pinhole SPECT imaging studies performed every seven months for 21 months. The uniqueness of this project is the development of techniques for estimating the blood input function from projection data acquired by a slowly rotating camera that is imaging fast circulation and the quantification of the kinetics of ¹²³I-BMIPP by fitting compartmental models to the blood and tissue time-activity curves.

Mitochondrial metabolic adaptation in right ventricular hypertrophy and failure

Right ventricular failure (RVF) is the leading cause of death in pulmonary arterial hypertension (PAH). Some patients with pulmonary hypertension are adaptive remodelers and develop RV hypertrophy (RVH) but retain RV function; others are maladaptive remodelers and rapidly develop RVF. The cause of RVF is unclear and understudied and most PAH therapies focus on regressing pulmonary vascular disease. Studies in animal models and human RVH suggest that there is reduced glucose oxidation and increased glycolysis in both adaptive and maladaptive RVH. The metabolic shift from oxidative mitochondrial metabolism to the less energy efficient glycolytic metabolism may reflect myocardial ischemia. We hypothesize that in maladaptive RVH a vicious cycle of RV ischemia and transcription factor activation causes a shift from oxidative to glycolytic metabolism thereby ultimately promoting RVF. Interrupting this cycle, by reducing ischemia or enhancing glucose oxidation, might be therapeutic. Dichloroacetate, a pyruvate dehydrogenase kinase inhibitor, has beneficial effects on RV function and metabolism in experimental RVH, notably improving glucose oxidation and enhancing RV function. This suggests the mitochondrial dysfunction in RVH may be amenable to therapy. In this mini review, we describe the role of impaired mitochondrial metabolism in RVH, using rats with adaptive (pulmonary artery banding) or maladaptive (monocrotaline-induced pulmonary hypertension) RVH as models of human disease. We will discuss the possible mechanisms, relevant transcriptional factors, and the potential of mitochondrial metabolic therapeutics in RVH and RVF.

Significance of peroxisome proliferator-activated receptors in the cardiovascular system in health and disease

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated nuclear transcription factors that belong to the nuclear receptor superfamily. Three isoforms of PPAR have been identified, alpha, delta and gamma, which play distinct roles in the regulation of key metabolic processes, such as glucose and lipid redistribution. PPARalpha is expressed predominantly in the liver, kidney and heart, and is primarily involved in fatty acid oxidation. PPARgamma is mainly associated with adipose tissue, where it controls adipocyte differentiation and insulin sensitivity. PPARdelta is abundantly and ubiquitously expressed, but as yet its function has not been clearly defined. Activators of PPARalpha (fibrates) and gamma (thiazolidinediones) have been used clinically for a number of years in the treatment of hyperlipidaemia and to improve insulin sensitivity in diabetes. More recently, PPAR activation has been found to confer additional benefits on endothelial function, inflammation and thrombosis, suggesting that PPAR agonists may be good candidates for the treatment of cardiovascular disease. In this regard, it has been demonstrated that PPAR activators are capable of reducing blood pressure and attenuating the development of atherosclerosis and cardiac hypertrophy. This review will provide a detailed discussion of the current understanding of basic PPAR physiology, with particular reference to the cardiovascular system. It will also examine the evidence supporting the involvement of the different PPAR isoforms in cardiovascular disease and discuss the current and potential future clinical applications of PPAR activators.

Altering and analyzing glucose metabolism in perfused hearts of transgenic mice

Glucose metabolism plays an important role in cardiac bioenergetics that changes under various stress conditions including hypertrophy, diabetic cardiomyopathy, and ischemia-reperfusion injury. To understand the role of glycolysis under these conditions, we have altered several steps of the glycolytic pathway specifically in the heart. In this chapter, we describe methods used to produce cardiac-targeted transgenic mice and procedures for measuring various glucose metabolites including glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate, and glycogen. Also, we describe methods for measuring glucose transport and glycolysis in perfused mouse hearts. Using these methods, we show that mice over-expressing cardiac-specific kinase-deficient 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (Mykd-PFK-2) show reduced glucose transport and reduced glycolysis when compared with control. The metabolites glucose-6-phosphate, fructose-6-phosphate, and glycogen were elevated, whereas fructose-1,6-bisphosphate was reduced in the transgenic Mykd-PFK-2 mouse hearts.

Cardiac metabolic compensation to hypertension requires lipoprotein lipase

Fatty acids (FAs) are acquired from free FA associated with albumin and lipoprotein triglyceride that is hydrolyzed by lipoprotein lipase (LpL). Hypertrophied hearts shift their substrate usage pattern to more glucose and less FA. However, FAs may still be an important source of energy in hypertrophied hearts. The aim of this study was to examine the importance of LpL-derived FAs in hypertensive hypertrophied hearts. We followed cardiac function and metabolic changes during 2 wk of angiotensin II (ANG II)-induced hypertension in control and heart-specific lipoprotein lipase knockout (hLpL0) mice. Glucose metabolism was increased in ANG II-treated control (control/ANG II) hearts, raising it to the same level as hLpL0 hearts. FA uptake-related genes, CD36 and FATP1, were reduced in control/ANG II hearts to levels found in hLpL0 hearts. ANG II did not alter these metabolic genes in hLpL0 mice. LpL activity was preserved, and mitochondrial FA oxidation-related genes were not altered in control/ANG II hearts. In control/ANG II hearts, triglyceride stores were consumed and reached the same levels as in hLpL0/ANG II hearts. Intracellular ATP content was reduced only in hLpL0/ANG II hearts. Both ANG II and deoxycorticosterone acetate-salt induced hypertension caused heart failure only in hLpL0 mice. Our data suggest that LpL activity is required for normal cardiac metabolic compensation to hypertensive stress.

Cardiac phosphatase-deficient 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase increases glycolysis, hypertrophy, and myocyte resistance to hypoxia

During ischemia and heart failure, there is an increase in cardiac glycolysis. To understand if this is beneficial or detrimental to the heart, we chronically elevated glycolysis by cardiac-specific overexpression of phosphatase-deficient 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2) in transgenic mice. PFK-2 controls the level of fructose-2,6-bisphosphate (Fru-2,6-P2), an important regulator of phosphofructokinase and glycolysis. Transgenic mice had over a threefold elevation in levels of Fru-2,6-P2. Cardiac metabolites upstream of phosphofructokinase were significantly reduced, as would be expected by the activation of phosphofructokinase. In perfused hearts, the transgene caused a significant increase in glycolysis that was less sensitive to inhibition by palmitate. Conversely, oxidation of palmitate was reduced by close to 50%. The elevation in glycolysis made isolated cardiomyocytes highly resistant to contractile inhibition by hypoxia, but in vivo the transgene had no effect on ischemia-reperfusion injury. Transgenic hearts exhibited pathology: the heart weight-to-body weight ratio was increased 17%, cardiomyocyte length was greater, and cardiac fibrosis was increased. However, the transgene did not change insulin sensitivity. These results show that the elevation in glycolysis provides acute benefits against hypoxia, but the chronic increase in glycolysis or reduction in fatty acid oxidation interferes with normal cardiac metabolism, which may be detrimental to the heart.

Ventricle-specific metabolic differences in the newborn piglet myocardium in vivo and during arrested global ischemia

Ventricular dysfunction is reported greater in the left (LV) versus right ventricle (RV) in infants following surgically induced ischemia. Ventricle-specific differences in baseline metabolism may alter response to ischemia thus affecting postischemic functional recovery. This study identifies ventricle-specific metabolic differences in the newborn (piglet) heart at baseline (working) and during ischemia (arrested). Baseline LV citrate synthase (CS) and hydroxyacyl-CoA dehydrogenase (HAD) activities were 15% and 18% lower (p < 0.02), whereas creatine kinase (CK) and phosphofructokinase (PFK) activities were 40% and 23% higher (p < 0.04) than the RV. Baseline LV glycogen reserves were also 55% higher (p = 0.004). By 15 min of ischemia, LV ATP was 20% lower (p < 0.05), lactate was 51% higher (p = 0.001), and hydrogen ions (H) were 43% higher (p = 0.03) compared with the RV. These differences persisted for the entire ischemic period (p < 0.02). After 45 min of ischemia, the LV used 58% less (p < 0.05) glycogen than the RV. These findings demonstrate that the enhanced glycolytic capacity of the newborn LV was accompanied by greater anaerobic end-product accumulation and lower energy levels during ischemia. This profile may offer one explanation for greater LV-dysfunction relative to the RV in children following ischemia.

The absence of endogenous lipid oxidation in early stage heart failure exposes limits in lipid storage and turnover

Intramyocardial lipid handling in pressure-overload-induced heart failure remains poorly understood, and the balance between endogenous and exogenous lipid utilization for mitochondrial ATP production is essentially unknown. In this study, we determined the contribution of endogenous triacylglycerols (TAG) to mitochondrial oxidation relative to that of exogenous palmitate, glucose, and endogenous glycogen in the failing, pressure-overloaded rat heart. TAG content and turnover were also assessed to determine if lipid availability and mobility were altered. Dynamic-mode (13)C NMR was performed in intact hearts from aortic banded and sham operated Spraque-Dawley rats perfused with (13)C-labeled palmitate or glucose to assess TAG turnover rate and palmitate oxidation rate. The fractional contributions from palmitate, glucose, glycogen, and TAG to mitochondrial ATP production were determined from NMR analysis of heart extracts. TAG oxidation was not evident in HF, whereas the contribution of TAG to oxidative ATP production was significant in shams. TAG content was 39% lower in HF compared to sham, and TAG turnover rate was 60% lower in HF. During adrenergic challenge, TAG sources were again not oxidized in the HF group. In early cardiac failure, endogenous TAG oxidation was reduced in parallel to increased carbohydrate oxidation, with no change in exogenous palmitate oxidation. This finding was consistent with reduced TAG storage and mobilization. These data further elucidate the role of intermediary and lipid metabolism in the progression of LVH to failure, and contribute to emerging evidence linking the disruption of myocardial substrate use to cardiomyopathies.

Time dependent changes in cytoplasmic proteins of the right ventricle during prolonged pressure overload

In many forms of congenital heart disease, the right ventricle (RV) is subject to abnormal loading conditions resulting in RV hypertrophy and remodeling. We determined the alterations in RV cytoplasmic proteomic phenotype that occur during prolonged periods of RV pressure overload. We performed a differential proteomic profiling study on RV hypertrophy using an animal model of various durations of pulmonary artery banding (PAB) in parallel with hemodynamic characterization. This hemodynamic evaluation showed that after 6, 12 and 20 weeks of PAB, the RV is in a compensated state of hypertrophy. Overall, the majority of protein changes were metabolism related indicating a shift towards the glycolytic pathway at the expense of beta-oxidation in the RV of the PAB animals. The changes in proteins related to the glycolytic pathway, exemplified by enolase and creatine kinase B-chain, tended to precede changes in beta-oxidation. In parallel, increases in stress chaperones, exemplified by several phosphorylated HSP-27 species, are present from the 6 week time point, whereas increases in antioxidant proteins, exemplified by peroxiredoxin 2 and 6, appear to be restricted to the 12 week time point. The p38 MAPK signal transduction pathway appears not to be activated. Observed protein changes are likely part of a protective mechanism against the development of RV failure.

Antihypertensive effects of Gynura procumbens extract in spontaneously hypertensive rats

Aqueous extracts of Gynura procumbens (Lour.) Merr. were orally administered to spontaneously hypertensive (SHR) rats for 4 weeks, and antihypertensive effects were determined. Oral administration of 500 mg/kg of G. procumbens (Lour.) Merr. extract (GPE) resulted in significantly lower blood pressure in SHR rats compared with SHR rats not given GPE (P < .05). Furthermore, GPE-administered rats had significantly lower serum lactate dehydrogenase, creatine phosphate kinase, and increased nitric oxide (NO), a known vasodilator, compared with the non-GPE-administered SHR group (P < .05). These results suggest that oral administration of aqueous GPE may be useful for prevention and treatment of hypertension through increasing NO production in blood vessels.

Roles of PPARs on regulating myocardial energy and lipid homeostasis

Myocardial energy and lipid homeostasis is crucial for normal cardiac structure and function. Either shortage of energy or excessive lipid accumulation in the heart leads to cardiac disorders. Peroxisome proliferator-activated receptors (PPARalpha, -beta/delta and -gamma), members of the nuclear receptor transcription factor superfamily, play important roles in regulating lipid metabolic genes. All three PPAR subtypes are expressed in cardiomyocytes. PPARalpha has been shown to control transcriptional expression of key enzymes that are involved in fatty acid (FA) uptake and oxidation, triglyceride synthesis, mitochondrial respiration uncoupling, and glucose metabolism. Similarly, PPARbeta/delta is a transcriptional regulator of FA uptake and oxidation, mitochondrial respiration uncoupling, and glucose metabolism. On the other hand, the role of PPARgamma on transcriptional regulation of FA metabolism in the heart remains obscure. Therefore, both PPARalpha and PPARbeta/delta are important transcriptional regulators of myocardial energy and lipid homeostasis. Moreover, it appears that the heart needs to have two PPAR subtypes with seemingly overlapping functions in maintaining myocardial lipid and energy homeostasis. Further studies on the potential distinctive roles of each PPAR subtype in the heart should provide new therapeutic targets for treating heart disease.

AMPK and metabolic adaptation by the heart to pressure overload

Accelerated glycolysis in hypertrophied hearts may be a compensatory response to reduced energy production from long-chain fatty acid oxidation with 5′-AMP-activated protein kinase (AMPK) functioning as a cellular signal. Therefore, we tested the hypothesis that enhanced fatty acid oxidation improves energy status and normalizes AMPK activity and glycolysis in hypertrophied hearts. Glycolysis, fatty acid oxidation, AMPK activity, and energy status were measured in isolated working hypertrophied and control hearts from aortic-constricted and sham-operated male Sprague-Dawley rats. Hearts from halothane (3–4%)-anesthetized rats were perfused with KH solution containing either palmitate, a long-chain fatty acid, or palmitate plus octanoate, a medium-chain fatty acid whose oxidation is not impaired in hypertrophied hearts. Compared with control, fatty acid oxidation was lower in hypertrophied hearts perfused with palmitate, whereas it increased to similar values in both groups with octanoate plus palmitate. Glycolysis was accelerated in palmitate-perfused hypertrophied hearts and was normalized in hypertrophied hearts by the addition of octanoate. AMPK activity was increased three- to sixfold with palmitate alone and was reduced to control values by octanoate plus palmitate. Myocardial energy status improved with the addition of octanoate but did not differ between groups. Our findings, particularly the correspondence between glycolysis and AMPK activity, provide support for the view that activation of AMPK is responsible, in part, for the acceleration of glycolysis in cardiac hypertrophy. Additionally, they indicate myocardial AMPK is activated by energy state-independent mechanisms in response to pressure overload, demonstrating AMPK is more than a sensor of the heart's energy status.

Causes and characteristics of diabetic cardiomyopathy

Type 1 and type 2 diabetic patients are at increased risk of cardiomyopathy and heart failure is a major cause of death for these patients. Cardiomyopathy in diabetes is associated with a cluster of features including decreased diastolic compliance, interstitial fibrosis and myocyte hypertrophy. The mechanisms leading to diabetic cardiomyopathy remain uncertain. Diabetes is associated with most known risk factors for cardiac failure seen in the overall population, including obesity, dyslipidemia, thrombosis, infarction, hypertension, activation of multiple hormone and cytokine systems, autonomic neuropathy, endothelial dysfunction and coronary artery disease. In light of these common contributing pathologies it remains uncertain whether diabetic cardiomyopathy is a distinct disease. It is also uncertain which factors are most important to the overall incidence of heart failure in diabetic patients. This review focuses on factors that can have direct effects on diabetic cardiomyocytes: hyperglycemia, altered fuel use, and changes in the activity of insulin and angiotensin. Particular attention is given to the changes these factors can have on cardiac mitochondria and the role of reactive oxygen species in mediating injury to cardiomyocytes.

NHE-1 inhibition improves cardiac mitochondrial function through regulation of mitochondrial biogenesis during postinfarction remodeling

We have recently demonstrated that mitochondrial respiratory dysfunction and mitochondrial permeability transition pore opening during postinfarction remodeling are prevented by the Na+/H+ exchange-1 (NHE-1)-specific inhibitor EMD-87580 (EMD). One of the mechanisms underlying the beneficial effect of NHE-1 inhibition on mitochondria could result from the drug's ability to regulate transcriptional factors responsible for mitochondrial function. In the present study, the effect of EMD on the expression of nuclear factors involved in mitochondrial biogenesis and expression of nuclear (COXNUCSUB IV) and mitochondrial (COXMITSUB I) encoded cytochrome c oxidase subunits has been studied in rat hearts subjected to either 12 or 18 wk of coronary artery ligation (CAL). Remodeling induced an increase in expression of the hypertrophic marker gene atrial natriuretic peptide, especially 12 wk after CAL. The mRNA level of the peroxisome proliferator-activated receptor-γ coactivator-1α and its downstream factors, including nuclear respiratory factor 1 and 2, mitochondrial transcription factor A, COXNUCSUB IV, and COXMITSUB I, were significantly reduced in hearts both 12 and 18 wk after ligation compared with sham-operated hearts. Dietary EMD provided immediately after ligation attenuated downregulation of mitochondrial transcription factors with a parallel decrease of hypertrophic marker gene expression. Regression analysis demonstrated a strong positive correlation between the transcription factors and mitochondrial respiratory function. Thus our study shows that the downregulation of mitochondrial transcription factors induced by postinfarction remodeling can be significantly attenuated by NHE-1 inhibition with a further improvement of mitochondrial function in these hearts.

Cardiac PPARα expression in patients with dilated cardiomyopathy

BACKGROUND

The peroxisome proliferator-activated receptor alpha (PPARalpha) is a central regulator of myocardial fatty acid (FA) metabolism implicated in the pathogenesis of heart failure.

AIMS

To characterize PPARalpha regulation in human dilated cardiomyopathy (DCM), we studied the expression of cardiac PPARalpha, cardiac carnitine palmitoyl-transferase I (CPT-1), a major PPARalpha target gene, and of the cardiac glucose transporter GLUT-4 in patients with DCM.

METHODS

Left ventricular biopsies were taken from patients with DCM (n=16) and control subjects (n=15), and mRNA expression was quantitated using real-time PCR (SYBR((R))Green) and protein expression was measured by Western immunoblotting.

RESULTS

Left ventricular PPARalpha mRNA levels were significantly increased in the DCM group compared to the control group (136+/-25.4% vs. control, p<0.01). Consistently, DCM patients had a significantly higher cardiac CPT-1 mRNA expression (147+/-51% vs. control, p<0.05) compared to the control group. Cardiac GLUT-4 expression was similar in both groups.

CONCLUSION

Elevated cardiac PPARalpha levels followed by an induction of cardiac CPT-1 expression may result in increased fatty acid metabolism for cardiac energy production in DCM, suggesting a specific cardiac metabolic program in human DCM compared to other types of cardiomyopathy.

Gender and post-ischemic recovery of hypertrophied rat hearts

Background

Gender influences the cardiac response to prolonged increases in workload, with differences at structural, functional, and molecular levels. However, it is unknown if post-ischemic function or metabolism of female hypertrophied hearts differ from male hypertrophied hearts. Thus, we tested the hypothesis that gender influences post-ischemic function of pressure-overload hypertrophied hearts and determined if the effect of gender on post-ischemic outcome could be explained by differences in metabolism, especially the catabolic fate of glucose.

Methods

Function and metabolism of isolated working hearts from sham-operated and aortic-constricted male and female Sprague-Dawley rats before and after 20 min of no-flow ischemia (N = 17 to 27 per group) were compared. Parallel series of hearts were perfused with Krebs-Henseleit solution containing 5.5 mM [5-³H/U-¹⁴C]-glucose, 1.2 mM [1-¹⁴C]-palmitate, 0.5 mM [U-¹⁴C]-lactate, and 100 mU/L insulin to measure glycolysis and glucose oxidation in one series and oxidation of palmitate and lactate in the second. Statistical analysis was performed using two-way analysis of variance. The sequential rejective Bonferroni procedure was used to correct for multiple comparisons and tests.

Results

Female gender negatively influenced post-ischemic function of non-hypertrophied hearts, but did not significantly influence function of hypertrophied hearts after ischemia such that mass-corrected hypertrophied heart function did not differ between genders. Before ischemia, glycolysis was accelerated in hypertrophied hearts, but to a greater extent in males, and did not differ between male and female non-hypertrophied hearts. Glycolysis fell in all groups after ischemia, except in non-hypertrophied female hearts, with the reduction in glycolysis after ischemia being greatest in males. Post-ischemic glycolytic rates were, therefore, similarly accelerated in hypertrophied male and female hearts and higher in female than male non-hypertrophied hearts. Glucose oxidation was lower in female than male hearts and was unaffected by hypertrophy or ischemia. Consequently, non-oxidative catabolism of glucose after ischemia was lowest in male non-hypertrophied hearts and comparably elevated in hypertrophied hearts of both sexes. These differences in non-oxidative glucose catabolism were inversely related to post-ischemic functional recovery.

Conclusion

Gender does not significantly influence post-ischemic function of hypertrophied hearts, even though female sex is detrimental to post-ischemic function in non-hypertrophied hearts. Differences in glucose catabolism may contribute to hypertrophy-induced and gender-related differences in post-ischemic function.

Metabolic Energetics and Genetics in the Heart

From the first stages of differentiation in the embryo to the end of life, energy substrate metabolism and function are inextricably linked features of the heart. The principle of energy substrate metabolism is simple. For a given developmental stage and for a given environment, the heart oxidizes the most efficient fuel on the path to ATP. The "multitasking" of energy substrate metabolism in the heart entails more than the generation of reducing equivalents for oxidative phosphorylation of ADP in the respiratory chain. In the postnatal heart, substrate switching and metabolic flexibility are features of normal function. In the stressed heart, metabolic remodeling precedes, triggers, and sustains functional and structural remodeling. This manuscript reviews the pleiotropic actions of metabolism in energy transfer, signal transduction, cardiac growth, gene expression, and viability. Examples are presented to illustrate that metabolic signals of stressed and failing heart are the product of complex cellular processes. An early feature of the maladapted heart is a loss of metabolic flexibility. The example of lipotoxic heart failure illustrates the concept of sustained metabolic dysregulation as a cause of contractile dysfunction of the heart. Thus, a paradigm emerges in which metabolic signals not only regulate fluxes through enzyme catalyzed reactions in existing metabolic pathways, but also regulate transcriptional, translational, and post-translational signaling in the heart. As new insights are gained into metabolic adaptation and maladaptation of the heart, metabolic modulation may become an effective strategy for the treatment of heart failure.

Upstream stimulatory factor 1 transactivates the human gene promoter of the cardiac isoform of acetyl-CoA carboxylase

E-box cis-elements act as binding sites for upstream stimulatory factors (USFs), putative glucose-responsive transcriptional modulators. Since four E-boxes were identified on the human ACCbeta promoter, we hypothesized that USF1 induces ACCbeta expression in a glucose-dependent manner. Here, murine cardiac ACCbeta expression was significantly increased in response to high carbohydrate re-feeding after fasting. However, transfection studies showed no difference in ACCbeta promoter activity in neonatal cardiomyocytes and CV-1 fibroblasts after low (5.5mM) and high (25 mM) glucose exposure. USF1 overexpression significantly increased ACCbeta promoter activity in both cell lines under low glucose conditions. With high glucose exposure, USF1 further induced ACCbeta promoter activity only in CV-1 fibroblasts. USF1-induced ACCbeta promoter responsiveness was markedly attenuated when co-transfecting cardiomyocytes with a -93/+65 or -38/+65 promoter deletion construct (lacking E-boxes 1-3). Thus, USF1 transactivates the human ACCbeta promoter in the heart, likely through an E-box cis-element located close to the transcription start site.

Proteomic changes in the pressure overloaded right ventricle after 6 weeks in young rats: Correlations with the degree of hypertrophy

Right ventricular (RV) hypertrophy is an important problem in congenital heart disease. We determined the alterations in phenotype that occur in the initial phase of RV hypertrophy and their possible correlations with the degree of hypertrophy. Therefore, we performed a differential proteomic profiling study on RV hypertrophy using an animal model of pulmonary artery banding (PAB) in parallel with hemodynamic characterization. The RV homogenates were subfractionated in myofilament and cytoplasmic proteins, which subsequently were separated by two-dimensional gel electrophoresis (2-DE), excised, and analyzed by mass spectrometry (MS). The cytoplasmic fraction showed expression changes in metabolic proteins, indicative of a shift from fatty acid to glucose as a substrate for energy supply. Up-regulation of three HSP-27s (1.9-, 1.7-, and 3.5-fold) indicated an altered stress response in RV hypertrophy. Detailed analysis by immunoblotting and MS showed that two of these HSP-27s were at least phosphorylated on Ser15. The myofilament fraction showed up-regulation of desmin and alpha-B-crystallin (1.4-and 1.3-fold, respectively). This alteration in desmin was confirmed by 1-DE immunoblots. Certain differentially expressed proteins, such as HSP-27, showed a significant correlation with the RV weight to the body weight ratio in the PAB rats, suggesting an association with the degree of hypertrophy.

Mitochondrial energy metabolism in heart failure: a question of balance

The mitochondrion serves a critical role as a platform for energy transduction, signaling, and cell death pathways relevant to common diseases of the myocardium such as heart failure. This review focuses on the molecular regulatory events and downstream effector pathways involved in mitochondrial energy metabolic derangements known to occur during the development of heart failure.

Mitochondrial energy metabolism in heart failure: a question of balance

The mitochondrion serves a critical role as a platform for energy transduction, signaling, and cell death pathways relevant to common diseases of the myocardium such as heart failure. This review focuses on the molecular regulatory events and downstream effector pathways involved in mitochondrial energy metabolic derangements known to occur during the development of heart failure.

Is the failing heart energy starved? On using chemical energy to support cardiac function

The requirement of chemical energy in the form of ATP to support systolic and diastolic work of the heart is absolute. Because of its central role in cardiac metabolism and performance, the subject of this review on energetics in the failing heart is ATP. We briefly review the basics of myocardial ATP metabolism and describe how this changes in the failing heart. We present an analysis of what is now known about the causes and consequences of these energetic changes and conclude by commenting on unsolved problems and opportunities for future basic and clinical research.

Cardiac Expression of Kinase-deficient 6-Phosphofructo-2-kinase/Fructose-2,6-bisphosphatase Inhibits Glycolysis, Promotes Hypertrophy, Impairs Myocyte Function, and Reduces Insulin Sensitivity

Glycolysis is important to cardiac metabolism and reduced glycolysis may contribute to diabetic cardiomyopathy. To understand its role independent of diabetes or hypoxic injury, we modulated glycolysis by cardiac-specific overexpression of kinase-deficient 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (kd-PFK-2). PFK-2 controls the level of fructose 2,6-bisphosphate (Fru-2,6-P(2)), an important regulator of glycolysis. Transgenic mice had over 2-fold reduced levels of Fru-2,6-P(2). Heart weight/body weight ratio indicated mild hypertrophy. Sirius red staining for collagen was significantly increased. We observed a 2-fold elevation in glucose 6-phosphate and fructose 6-phosphate levels, whereas fructose 1,6-bisphosphate was reduced 2-fold. Pathways branching off of glycolysis above phosphofructokinase were activated as indicated by over 2-fold elevated UDP-N-acetylglucosamine and glycogen. The kd-PFK-2 transgene significantly inhibited glycolysis in perfused hearts. Insulin stimulation of metabolism and Akt phosphorylation were sharply reduced. In addition, contractility of isolated cardiomyocytes was impaired during basal and hypoxic incubations. The present study shows that cardiac overexpression of kinase-deficient PFK-2 reduces cardiac glycolysis that produced negative consequences to the heart including hypertrophy, fibrosis, and reduced cardiomyocyte function. In addition, metabolic and signaling responses to insulin were significantly decreased.

Mechanisms for increased glycolysis in the hypertrophied rat heart

Glycolysis increases in hypertrophied hearts but the mechanisms are unknown. We studied the regulation of glycolysis in hearts with pressure-overload LV hypertrophy (LVH), a model that showed marked increases in the rates of glycolysis (by 2-fold) and insulin-independent glucose uptake (by 3-fold). Although the V(max) of the key glycolytic enzymes was unchanged in this model, concentrations of free ADP, free AMP, inorganic phosphate (P(i)), and fructose-2,6-bisphosphate (F-2,6-P2), all activators of the rate-limiting enzyme phosphofructokinase (PFK), were increased (up to 10-fold). Concentrations of the inhibitors of PFK, ATP, citrate, and H+ were unaltered in LVH. Thus, our findings show that increased glucose entry and activation of the rate-limiting enzyme PFK both contribute to increased flux through the glycolytic pathway in hypertrophied hearts. Moreover, our results also suggest that these changes can be explained by increased intracellular free [ADP] and [AMP], due to decreased energy reserve in LVH, activating the AMP-activated protein kinase cascade. This, in turn, results in enhanced synthesis of F-2,6-P2 and increased sarcolemma localization of glucose transporters, leading to coordinated increases in glucose transport and activation of PFK.

Nuclear receptor signaling and cardiac energetics

The heart has a tremendous capacity for ATP generation, allowing it to function as an efficient pump throughout the life of the organism. The adult myocardium uses either fatty acid or glucose oxidation as its main energy source. Under normal conditions, the adult heart derives most of its energy through oxidation of fatty acids in mitochondria. However, the myocardium has a remarkable ability to switch between carbohydrate and fat fuel sources so that ATP production is maintained at a constant rate in diverse physiological and dietary conditions. This fuel selection flexibility is important for normal cardiac function. Although cardiac energy conversion capacity and metabolic flux is modulated at many levels, an important mechanism of regulation occurs at the level of gene expression. The expression of genes involved in multiple energy transduction pathways is dynamically regulated in response to developmental, physiological, and pathophysiological cues. This review is focused on gene transcription pathways involved in short- and long-term regulation of myocardial energy metabolism. Much of our knowledge about cardiac metabolic regulation comes from studies focused on mitochondrial fatty acid oxidation. The genes involved in this key energy metabolic pathway are transcriptionally regulated by members of the nuclear receptor superfamily, specifically the fatty acid-activated peroxisome proliferator-activated receptors (PPARs) and the nuclear receptor coactivator, PPARgamma coactivator-1alpha (PGC-1alpha). The dynamic regulation of the cardiac PPAR/PGC-1 complex in accordance with physiological and pathophysiological states will be described.

Promoting angiogenesis protects severely hypertrophied hearts from ischemic injury

BACKGROUND

Myocardial hypertrophy is associated with progressive contractile dysfunction, increased vulnerability to ischemia-reperfusion injury, and is, therefore, a risk factor in cardiac surgery. During the progression of hypertrophy, a mismatch develops between the number of capillaries and cardiomyocytes per unit area, suggesting an increase in diffusion distance and the potential for limited supply of oxygen and nutrients. We hypothesized that promoting angiogenesis in hypertrophied hearts increases microvascular density, thereby improves tissue perfusion and substrate availability, maintains myocardial function, and improves postischemic recovery.

METHODS

Left ventricular hypertrophy was created in 10-day-old rabbits by aortic banding and progression was monitored by echocardiography. At 4 weeks (compensated hypertrophy), 2 microg of vascular endothelial growth factor (VEGF) or placebo was administered intrapericardially. After 2 weeks, microvascular density, coronary flow (CF), and glucose uptake (GU) were measured. Tolerance to ischemia was determined by cardiac function measurements before and after ischemia-reperfusion using an isolated heart preparation.

RESULTS

Microvascular density increased significantly following VEGF treatment (1.43 +/- 0.08/nuclei/field vs 1.04 +/- 0.06/nuclei/field untreated hypertrophy). Concomitantly, there was an increase in CF (7 +/- 0.5 vs 5 +/- 0.4 mL/min/g) and GU (1.24 +/- 0.2 vs 0.69 +/- 0.2 micromoles/g/30 minutes; p <or= 0.05). In vivo contractile function (-0.08 +/- 0.48 vs -1.39 +/- 0.35 untreated hypertrophy; p <or= 0.05) and postischemic myocardial recovery (% recovery: 93 +/- 2.0 vs 73 +/- 6.8 untreated hypertrophy; p <or= 0.05) were significantly improved in VEGF-treated hearts compared to untreated hypertrophied hearts.

CONCLUSIONS

Treatment of hypertrophied hearts with VEGF resulted in an increase of microvascular density, improved tissue perfusion, and glucose delivery. Promoting angiogenesis proved useful in preserving myocardial function in late hypertrophy and improving postischemic recovery of contractile function.

Transcriptional regulation of energy substrate metabolism in normal and hypertrophied heart

Impaired myocardial energy metabolism in cardiac hypertrophy and failure is characterized by decreased fatty-acid oxidation and increased glucose utilization. Mechanisms involving deactivation of peroxisome proliferator-activated receptor alpha/relinoid X receptor alpha (PPARalpha/RXRalpha),and activation of chicken ovalbumin upstream promoter transcription factor (COUP-TF), and transcription factors Sp1 and Sp3, lead to decreased capacity for fatty acid utilization in hypertrophied hearts. Furthermore, impaired myocardial energetic status stimulates glucose uptake and glycolysis, which, in combination with the permissive effect due to decreased fatty acid oxidation, promotes increases in glucose utilization in hypertrophied hearts. Finally, shifting substrate utilization toward glucose is likely adaptive and has the potential to delay transition to heart failure.

Glycolysis and pyruvate oxidation in cardiac hypertrophy--why so unbalanced?

Cardiac hypertrophy, induced by chronic pressure or volume overload, is associated with abnormalities in energy metabolism as well as characteristic increases in muscle mass and alterations in the structure of the heart. Hypertrophied hearts display increased rates of glycolysis and overall glucose utilization, but rates of pyruvate oxidation do not rise in step with rates of pyruvate generation. Glycolysis and glucose oxidation, therefore, become markedly less 'coupled' in hypertrophied hearts than in non-hypertrophied hearts. Because the pyruvate dehydrogenase complex (PDC) contributes so powerfully to the control of glucose oxidation, we set out to test the hypothesis that the function of PDC is impaired in cardiac hypertrophy. In this review we describe evidence indicating that the alterations in glucose metabolism in hypertrophied hearts cannot be explained simply by changes in PDC expression or control. Additional mechanisms that may lead to an altered balance of pyruvate metabolism in cardiac hypertrophy are discussed, with commentaries on possible changes in pyruvate transport, NADH shuttles, lactate dehydrogenase, and amino acid metabolism.

Oxidative capacity in failing hearts

Although high-energy phosphate metabolism is abnormal in failing hearts [congestive heart failure (CHF)], it is unclear whether oxidative capacity is impaired. This study used the mitochondrial uncoupling agent 2,4-dinitrophenol (DNP) to determine whether reserve oxidative capacity exists during the high workload produced by catecholamine infusion in hypertrophied and failing hearts. Left ventricular hypertrophy (LVH) was produced by ascending aortic banding in 21 swine; 9 animals developed CHF. Basal myocardial phosphocreatine (PCr)/ATP measured with 31P NMR spectroscopy was decreased in both LVH and CHF hearts (corresponding to an increase in free [ADP]), whereas ATP was decreased in hearts with CHF. Infusion of dobutamine and dopamine (each 20 microg. kg-1. min-1 iv) caused an approximate doubling of myocardial oxygen consumption (MVO2) in all groups and decreased PCr/ATP in the normal and LVH groups. During continuing catecholamine infusion, DNP (2-8 mg/kg iv) caused further increases of MVO2 in normal and LVH hearts with no change in PCr/ATP. In contrast, DNP caused no increase in MVO2 in the failing hearts; the associated decrease of PCr/ATP suggests that DNP decreased the mitochondrial proton gradient, thereby causing ADP to increase to maintain adequate ATP synthesis.

Increased susceptibility of hypertrophied hearts to ischemic injury

Cardiac hypertrophy is an adaptive response that compensates for increased workload by normalizing wall stress and preserving cardiac contractile function. In advanced stages, however, clinical and experimental studies have shown that when the high workload is maintained, hypertrophy progresses to ventricular dilatation, contractile dysfunction, and decreased tolerance to ischemia/reperfusion. Development of hypertrophy is accompanied by distinct qualitative and quantitative changes in contractile protein expression and isoform switching, cytosolic calcium regulation, and substrate delivery and use. We have focused our investigations on changes in substrate delivery and capillary density in pressure overload hypertrophy and on the effects that these changes have on tolerance to ischemia/reperfusion. This report summarizes our work in this area using a model of aortic banding in 10-day-old rabbits, which exhibits the same pattern of concentric hypertrophy early, followed by ventricular dilatation and contractile dysfunction that is clinically apparent.

Cardiac Hypertrophy by Hypertension and Exercise Training Exhibits Different Gene Expression of Enzymes in Energy Metabolism

Hypertension-induced pathological cardiac hypertrophy (hypertensive heart) and exercise training-induced physiological cardiac hypertrophy (athletic heart) have differences in cardiac properties. We hypothesized that gene expression of energy metabolic enzymes differs between these two types of cardiac hypertrophy. To investigate whether mRNA expression of key enzymes in the long-chain fatty acid (FA), glucose, and lactic acid metabolic pathways differs between these two types of cardiac hypertrophy, we used the hearts of spontaneously hypertensive rats (SHR; 19 weeks old) as a model of the hypertensive heart, swim-trained rats (Trained; 19 weeks old, swimming training for 15 weeks) as a model of the athletic heart, and sedentary Wistar-Kyoto rats (Control; 19 weeks old). SHR developed hypertensive cardiac hypertrophy, of which cardiac function was deteriorated, whereas Trained rats developed an athletic heart, of which cardiac function was enhanced. The mRNA expression of CD36, which involved in uptake of long-chain FA, in the heart was almost never detected in the SHR group. Furthermore, the mRNA expression of key enzymes in the long-chain FA metabolic pathway (acyl CoA synthase [ACoAS], carnitine palmitoyl transferase [CPT]-I, CPT-II, and isocitrate dehydrogenase [ISCD]) in the heart was significantly higher in the SHR group compared with the Control group. The mRNA expression of ACoAS, CPT-I, ISCD, and CD36 in the heart did not differ between Trained group and Control group, whereas that of CPT-II in the Trained group was significantly higher compared with the Control group. The mRNA expression of key enzymes (phosphofructokinase and lactate dehydrogenase) in glycolytic metabolic pathway in the heart was markedly higher in the SHR group compared with the Control group, whereas these mRNA expressions did not differ between Trained group and Control group. These findings suggest that the molecular phenotypes in the energy metabolic system differ in hypertension-induced pathological and exercise training-induced physiological cardiac hypertrophy, and these differences may participate in the differences in cardiac function.

Cardiac-specific overexpression of GLUT1 prevents the development of heart failure attributable to pressure overload in mice

BACKGROUND

Increased rates of glucose uptake and glycolysis have been repeatedly observed in cardiac hypertrophy and failure. Although these changes have been considered part of the fetal gene reactivation program, the functional significance of increased glucose utilization in hypertrophied and failing myocardium is poorly understood.

METHODS AND RESULTS

We generated transgenic (TG) mice with cardiac-specific overexpression of insulin-independent glucose transporter GLUT1 to recapitulate the increases in basal glucose uptake rate observed in hypertrophied hearts. Isolated perfused TG hearts showed a greater rate of basal glucose uptake and glycolysis than hearts isolated from wild-type littermates, which persisted after pressure overload by ascending aortic constriction (AAC). The in vivo cardiac function in TG mice, assessed by echocardiography, was unaltered. When subjected to AAC, wild-type mice exhibited a progressive decline in left ventricular (LV) fractional shortening accompanied by ventricular dilation and decreased phosphocreatine to ATP ratio and reached a mortality rate of 40% at 8 weeks. In contrast, TG-AAC mice maintained LV function and phosphocreatine to ATP ratio and had <10% mortality.

CONCLUSIONS

We found that increasing insulin-independent glucose uptake and glycolysis in adult hearts does not compromise cardiac function. Furthermore, we demonstrate that increasing glucose utilization in hypertrophied hearts protects against contractile dysfunction and LV dilation after chronic pressure overload.

Altered myocardial fatty acid and glucose metabolism in idiopathic dilated cardiomyopathy

OBJECTIVES

The purpose of this study was to determine whether patients with idiopathic dilated cardiomyopathy (IDCM) exhibit alterations in myocardial fatty acid and glucose metabolism.

BACKGROUND

Alterations in myocardial metabolism have been implicated in the pathogenesis of heart failure (HF); however, studies of myocardial metabolic function in human HF have yielded conflicting results. Animal models of HF have shown a downregulation of the expression of enzymes of fatty acid beta-oxidation that recapitulates the fetal energy metabolic program, in which fatty acid metabolism is decreased and glucose metabolism is increased.

METHODS

Seven patients with IDCM (mean left ventricular ejection fraction 27 +/- 8%) and 12 normal controls underwent positron emission tomography for measurements of myocardial blood flow (MBF), myocardial oxygen consumption (MVO(2)), myocardial glucose utilization (MGU), myocardial fatty acid utilization (MFAU) and myocardial fatty acid oxidation (MFAO).

RESULTS

The systolic and diastolic blood pressures, plasma substrates and insulin levels, MBF and MVO(2), were similar between groups. The rates of MFAU and MFAO were significantly lower in IDCM than in the normal control group (MFAU: 134 +/- 44 vs. 213 +/- 49 nmol/g/min, p = 0.003; and MFAO: 113 +/- 50 vs. 205 +/- 49 nmol/g/min, p = 0.001) and the rates of MGU were significantly higher in IDCM than the normal control group (MGU: 247 +/- 63 vs. 125 +/- 64 nmol/g/min, p < 0.001).

CONCLUSIONS

Patients with IDCM exhibit alterations in myocardial metabolism characterized by decreased fatty acid metabolism and increased myocardial glucose metabolism, a pattern similar to that shown in animal models of HF. Whether alterations in myocardial metabolism constitute an adaptive response or mediate the development of HF remains to be determined.