Energy metabolism in the normal and failing heart: potential for therapeutic interventions

Monoamine oxidases (MAO) in the pathogenesis of heart failure and ischemia/reperfusion injury

Recent evidence highlights monoamine oxidases (MAO) as another prominent source of oxidative stress. MAO are a class of enzymes located in the outer mitochondrial membrane, deputed to the oxidative breakdown of key neurotransmitters such as norepinephrine, epinephrine and dopamine, and in the process generate H(2)O(2). All these monoamines are endowed with potent modulatory effects on myocardial function. Thus, when the heart is subjected to chronic neuro-hormonal and/or peripheral hemodynamic stress, the abundance of circulating/tissue monoamines can make MAO-derived H(2)O(2) production particularly prominent. This is the case of acute cardiac damage due to ischemia/reperfusion injury or, on a more chronic stand, of the transition from compensated hypertrophy to overt ventricular dilation/pump failure. Here, we will first briefly discuss mitochondrial status and contribution to acute and chronic cardiac disorders. We will illustrate possible mechanisms by which MAO activity affects cardiac biology and function, along with a discussion as to their role as a prominent source of reactive oxygen species. Finally, we will speculate on why MAO inhibition might have a therapeutic value for treating cardiac affections of ischemic and non-ischemic origin. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.

Clinical correlates of arterial lactate levels in patients with ST-segment elevation myocardial infarction at admission: a descriptive study

Introduction

Blood lactate measurements can be used as an indicator of hemodynamic impairment and relate to mortality in various forms of shock. Little is known at the moment concerning the clinical correlates of systemic lactate in patients with ST-segment elevation myocardial infarction (STEMI).

Methods

To assess the relation of systemic arterial lactate levels in STEMI patients with clinical correlates at presentation in the catheterization laboratory, we measured arterial lactate levels with a rapid point-of-care technique, immediately following femoral sheath insertion. The study population (n= 1,176) was divided into tertiles with lactate levels ≤1.1 (n = 410), 1.2 to 1.7 (n = 398) and ≥1.8 mmol/l (n = 368). We compared both baseline characteristics and outcome measures of the three lactate groups.

Results

Factors independently associated with higher lactate levels were hypotension, heart rate, thrombolysis in myocardial infarction (TIMI) flow 0 to 1, diabetes and non-smoking. Mortality at 30 days in the three groups was 2.0%, 1.5% and 6.5%. The latter group also showed lower blush grades and greater enzymatic infarct sizes. An intra aortic balloon pump (IABP) was used more frequently in patients with higher lactate levels (4.2%, 7.6% and 14.7%).

Conclusions

In STEMI patients, impaired hemodynamics, worse TIMI flow and non-smoking were related to increased arterial lactate levels. Higher lactate levels were independently related with 30-day mortality and an overall worse response to percutaneous coronary intervention (PCI). In particular, acute mortality was related to admission lactates ≥1.8 mmol/L. Point-of-care measurement of arterial lactate at admission in patients with STEMI has the potential to improve acute risk stratification.

Cardioprotective effect of zinc requires ErbB2 and Akt during hypoxia/reoxygenation

Recent literature suggests that exogenous zinc can prevent ischemia reperfusion injury by activating phosphoinositide-3 kinase (PI3K)/Akt and by targeting the mitochondrial permeability transition pore (mPTP). It is known that ErbB2 expression promotes association and activation of PI3-kinase/Akt, resulting in growth and survival of cardiac myocytes. In this study, we found that zinc-induced ErbB2 protein expression and Akt activation are required for preventing reperfusion injury. Neonatal rat cardiac myocytes subjected to 8 h of hypoxia, followed by 16 h of reoxygenation induced cardiomyocyte apoptosis, as assessed by increased caspase-3 activity, annexin V staining and lowered MTT reduction and ATP levels. However, addition of zinc-pyrithione (ZPT) before onset of reoxygenation effectively lowered the apoptotic indices and restored the ATP levels. ZPT induced a significant increase in ErbB2 protein expression and Akt activation. Pretreatment with Hsp 90 inhibitor, geldanamycin or PI3-kinase inhibitor, wortmannin prevented the increase in ATP levels and abrogated the protective effect of zinc-pyrithione. Taken together, these data suggest that zinc prevents reperfusion injury by modulating the ErbB2 protein expression and Akt activation.

PPARs, Cardiovascular Metabolism, and Function: Near- or Far-from-Equilibrium Pathways

Peroxisome proliferator-activated receptors (PPAR α, β/δ and γ) play a key role in metabolic regulatory processes and gene regulation of cellular metabolism, particularly in the cardiovascular system. Moreover, PPARs have various extra metabolic roles, in circadian rhythms, inflammation and oxidative stress. In this review, we focus mainly on the effects of PPARs on some thermodynamic processes, which can behave either near equilibrium, or far-from-equilibrium. New functions of PPARs are reported in the arrhythmogenic right ventricular cardiomyopathy, a human genetic heart disease. It is now possible to link the genetic desmosomal abnormalitiy to the presence of fat in the right ventricle, partly due to an overexpression of PPARγ. Moreover, PPARs are directly or indirectly involved in cellular oscillatory processes such as the Wnt-b-catenin pathway, circadian rhythms of arterial blood pressure and cardiac frequency and glycolysis metabolic pathway. Dysfunction of clock genes and PPARγ may lead to hyperphagia, obesity, metabolic syndrome, myocardial infarction and sudden cardiac death, In pathological conditions, regulatory processes of the cardiovascular system may bifurcate towards new states, such as those encountered in hypertension, type 2 diabetes, and heart failure. Numerous of these oscillatory mechanisms, organized in time and space, behave far from equilibrium and are “dissipative structures”.

Altered spatiotemporal dynamics of the mitochondrial membrane potential in the hypertrophied heart

Chronically elevated levels of oxidative stress resulting from increased production and/or impaired scavenging of reactive oxygen species are a hallmark of mitochondrial dysfunction in left ventricular hypertrophy. Recently, oscillations of the mitochondrial membrane potential (DeltaPsi(m)) were mechanistically linked to changes in cellular excitability under conditions of acute oxidative stress produced by laser-induced photooxidation of cardiac myocytes in vitro. Here, we investigate the spatiotemporal dynamics of DeltaPsi(m) within the intact heart during ischemia-reperfusion injury. We hypothesize that altered metabolic properties in left ventricular hypertrophy modulate DeltaPsi(m) spatiotemporal properties and arrhythmia propensity.

Shedding light on the enigma of myocardial lipotoxicity: the involvement of known and putative regulators of fatty acid storage and mobilization

Excessive fatty acid (FA) uptake by cardiac myocytes is often associated with adverse changes in cardiac function. This is especially evident in diabetic individuals, where increased intramyocardial triacylglycerol (TG) resulting from the exposure to high levels of circulating FA has been proposed to be a major contributor to diabetic cardiomyopathy. At present, our knowledge of how the heart regulates FA storage in TG and the hydrolysis of this TG is limited. This review concentrates on what is known about TG turnover within the heart and how this is likely to be regulated by extrapolating results from other tissues. We also assess the evidence as to whether increased TG accumulation protects against FA-induced lipotoxicity through limiting the accumulations of ceramides and diacylglycerols versus whether it is a maladaptive response that contributes to cardiac dysfunction.

Improvement of mechanical heart function by trimetazidine in db/db mice

AIM

To investigate the influence of trimetazidine, which is known to be an antioxidant and modulator of metabolism, on cardiac function and the development of diabetic cardiomyopathy in db/db mouse.

METHODS

Trimetazidine was administered to db/db mice for eight weeks. Cardiac function was measured by inserting a Millar catheter into the left ventricle, and oxidative stress and AMP-activated protein kinase (AMPK) activity in the myocardium were evaluated.

RESULTS

Untreated db/db mice exhibited a significant decrease in cardiac function compared to normal C57 mice. Oxidative stress and lipid deposition were markedly increased in the myocardium, concomitant with inactivation of AMPK and increased expression of peroxisome proliferator-activated receptor coactivator-1 alpha (PGC-1 alpha). Trimetazidine significantly improved systolic and diastolic function in hearts of db/db mice and led to reduced production of reactive oxygen species and deposition of fatty acid in cardiomyocytes. Trimetazidine also caused AMPK activation and reduced PGC-1 alpha expression in the hearts of db/db mice.

CONCLUSION

The data suggest that trimetazidine significantly improves cardiac function in db/db mice by attenuating lipotoxicity and improving the oxidation status of the heart. Activation of AMPK and decreased expression of PGC-1 alpha were involved in this process. Furthermore, our study suggests that trimetazidine suppresses the development of diabetic cardiomyopathy, which warrants further clinical investigation.

Sensitivity of cardiac carnitine palmitoyltransferase to malonyl-CoA is regulated by leptin: similarities with a model of endogenous hyperleptinemia

Acute leptin increase as well as endogenous hyperleptinemia evoked by high-fat diets (HF) activate fatty acid metabolism in nonadipose tissues. This supports the notion that hyperleptinemia is pivotal to prevent/delay steatosis during periods of positive energy balance. We have previously shown that long-term HF spares ectopic accumulation of lipids specifically in the miocardium. Because carnitine palmitoyltransferase I (CPT-I) allows mitochondrial uptake/oxidation of fatty acids, we have hypothesized that leptin drives cardiac CPT-I activity. In the current study, hyperleptinemia was induced in C57BL/6J mice either by exogenous leptin administration or by means of HF, and the ability of malonyl-coenzyme A (malonyl-CoA) (the main endogenous inhibitor of CPT-I) to inhibit cardiac CPT was analyzed. IC(50) values of malonyl-CoA were 8.1 +/- 1.5 micromol/liter in controls vs. 69.3 +/- 5.2 micromol/liter (P < 0.01) in leptin-treated mice. This effect was also observed in cardiac explants incubated with leptin and was blocked by triciribine, a compound shown to inhibit protein kinase B (Akt) phosphorylation (pAkt). In accordance, acute leptin evoked an increase of cardiac pAkt levels, which correlated with CPT sensitivity to malonyl-CoA. Otherwise, the inhibitory effect of malonyl-CoA was hindered in HF hyperleptinemic mice, and in this case, pAkt levels also correlated with CPT sensitivity to malonyl-CoA. Our data show that leptin reduces the sensitivity of cardiac CPT-I to malonyl-CoA and suggest the involvement of an Akt-related signaling pathway in this effect. This mechanism appears to be sensitive to both acute and chronic hyperleptinemia. We conclude that this action of leptin is pivotal to drive cardiac metabolism under situations associated to hyperleptinemia.

Cardiac and plasma lipid profiles in response to acute hypoxia in neonatal and young adult rats

Background

The physiological and biochemical responses to acute hypoxia have not been fully characterized in neonates. Fatty acids and lipids play an important role in most aspects of cardiac function.

Methods

We performed comprehensive lipid profiling analysis to survey the changes that occur in heart tissue and plasma of neonatal and young adult rats exposed to hypoxia for 2 h, and following 2 h of recovery from hypoxia.

Results

Cardiac and plasma concentrations of short-chain acylcarnitines, and most plasma long-chain fatty acids, were decreased in hypoxic neonates. Following recovery from hypoxia, concentrations of propionylcarnitine, palmitoylcarnitine, stearoylcarnitine were increased in neonatal hearts, while oleylcarnitine and linoleylcarnitine concentrations were increased in neonatal plasma. The concentrations of long-chain fatty acids and long-chain acylcarnitines were increased in the hearts and plasma of hypoxic young adult rats; these metabolites returned to baseline values following recovery from hypoxia.

Conclusion

There are differential effects of acute hypoxia on cardiac and plasma lipid profiles with maturation from the neonate to the young adult rat. Changes to neonatal cardiac and plasma lipid profiles during hypoxia likely allowed for greater metabolic and physiologic flexibility and increased chances for survival. Persistent alterations in the neonatal cardiac lipid profile following recovery from hypoxia may play a role in the development of rhythm disturbances.

An overview of hypoglycemia in the critically ill

Hypoglycemia is a common and serious problem among patients with diabetes mellitus. It is also perceived as the most important obstacle to tight glucose control using intensive insulin therapy in critically ill patients. Because glucose is an obligatory metabolic fuel for the brain, hypoglycemia always represents an emergency that signals the inability of the brain to meet its energy needs. When left untreated, hypoglycemia can result in permanent brain damage and ultimately, death. In the context of critical illness that limits endogenous glucose production and increases glucose utilization, inadequate nutrition, or insufficient provision of glucose, intensive insulin therapy is the most frequent cause of hypoglycemia. Neurogenic and neuroglycopenic symptoms of hypoglycemia can remain unknown because of the underlying critical illness and sedation. Thus, close and reliable monitoring of the glycemic level is crucial in detecting hypoglycemia. In prospective randomized controlled studies comparing the effects of two glucose regimens, intensive insulin therapy aimed to reach strict glucose control (<110 mg/dl) but increased the incidence of severe hypoglycemia (<40 mg/dl) by four- to sixfold. Severe hypoglycemia is statistically associated with adverse outcomes in intensive care unit patients, although a direct causal relationship has not been demonstrated.

Trastuzumab versus lapatinib: the cardiac side of the story

HER2 gene plays a pivotal role in the pathogenesis of 20% of breast cancer patients. At the same time, it is one of the main cardiac survival pathways when subjected to bio-mechanical stress including exposure to anthracyclines. With the emergence of the anti-HER2 targeting agents, concerns raised regarding the potential cardiac toxicities of these drugs. In the early clinical trials with trastuzumab, it was evident that it has a significant cardiac toxicity. The incidence of symptomatic heart failure ranged from 4% to 7% with trastuzumab alone, and 27% when administered concurrently with doxorubicin. On the other hand, available data suggest that lapatinib is much less cardiotoxic. The incidence of symptomatic heart failure has been constantly reported to be less than 0.5%. In this review, we discuss the possible theories behind the differences in the cardiac profile of both agents. We emphasize on the role of cardiac bioenergetics and the effects of trastuzumab and lapatinib on ATP production through the different effects they exert on the cardiac mitochondria.

Improved left and right ventricular functions with trimetazidine in patients with heart failure: a tissue Doppler study

Downregulation of glucose and fatty acid oxidation occurs in heart failure (HF). Trimetazidine reduces fatty acid oxidation and increases glucose oxidation. In this single-blind study, trimetazidine, 20 mg three times per day (n = 51) or placebo (n = 36) was added to treatment of 87 HF patients receiving optimal HF therapy. Etiology of heart failure was coronary artery disease in 35 patients (68.6%) in the trimetazidine group and 22 (62.9%) in the placebo group. Fourteen (27.5%) patients in the trimetazidine group and 11 (31.4%) patients in the placebo group had diabetes. Peak systolic velocity (Vs), and the peak early diastolic (Vd) and late diastolic (Va) velocities of various segments left and right ventricles (RV) were obtained with tissue Doppler imaging (TDI) and averaged. Patients were re-evaluated three months later. Significant increases in mean left ventricular ejection fraction (LVEF) (33.3% +/- 5.6% to 42.4% +/- 6.3%, P < 0.001 and 30.6% +/- 8.2% to 33.2% +/- 6.6%, P = 0.021) and LV and RV myocardial velocities and mitral and tricuspid annular TDI velocities were observed in both groups. However, compared to placebo, increments in LVEF (9.1% +/- 4.2% vs. 2.5% +/- 1.4%, P < 0.001) and myocardial velocities were significantly higher with trimetazidine (P < 0.001 for LV Vs, Vd, Va; P = 0.035 for RV Vd; and P < 0.001 for RV Va and Vs). Increase in LVEF with trimetazidine was significantly correlated with presence of diabetes (r = 0.524, P < 0.001). With trimetazidine LVEF increased significantly more in diabetic patients compared to nondiabetics (P < 0.001). Also, patients having both diabetes and ischemic HF tended to have greater improvement in LVEF compared to ischemic HF patients without diabetes (P = 0.063). Addition of trimetazidine to current treatment of HF, especially for those who are diabetic, may improve LV and RV functions.

Anticipating anticipation: pursuing identification of cardiomyocyte circadian clock function

Diurnal rhythms in myocardial physiology (e.g., metabolism, contractile function) and pathophyiology (e.g., sudden cardiac death) are well establish and have classically been ascribed to time-of-day-dependent alterations in the neurohumoral milieu. Existence of an intramyocellular circadian clock has recently been exposed. Circadian clocks enable the cell to anticipate environmental stimuli, facilitating a timely and appropriate response. Generation of genetically modified mice with a targeted disruption of the cardiomyocyte circadian clock has provided an initial means for deciphering the functions of this transcriptionally based mechanism and allowed predictions regarding which environmental stimuli the heart anticipates (i.e., "anticipating anticipation"). Recent studies show that the cardiomyocyte circadian clock influences myocardial gene expression, beta-adrenergic signaling, transcriptional responsiveness to fatty acids, triglyceride metabolism, heart rate, and cardiac output, as well as ischemia-reperfusion tolerance. In addition to reviewing current knowledge regarding the roles of the cardiomyocyte circadian clock, this article highlights putative frontiers in this field. The latter includes establishing molecular links between the cardiomyocyte circadian clock with identified functions, understanding the pathophysiological consequences of disruption of this mechanism, targeting resynchronization of the cardiomyocyte circadian clock for prevention/treatment of cardiovascular disease, linking the circadian clock with the cardiobeneficial effects of caloric restriction, and determining whether circadian clock genes are subject to epigenetic regulation. Information gained from studies investigating the cardiomyocyte circadian clock will likely translate to extracardiac tissues, such as skeletal muscle, liver, and adipose tissue.

Cardiac expression of microsomal triglyceride transfer protein is increased in obesity and serves to attenuate cardiac triglyceride accumulation

Obesity causes lipid accumulation in the heart and may lead to lipotoxic heart disease. Traditionally, the size of the cardiac triglyceride pool is thought to reflect the balance between uptake and β-oxidation of fatty acids. However, triglycerides can also be exported from cardiomyocytes via secretion of apolipoproteinB-containing (apoB) lipoproteins. Lipoprotein formation depends on expression of microsomal triglyceride transfer protein (MTP); the mouse expresses two isoforms of MTP, A and B. Since many aspects of the link between obesity-induced cardiac disease and cardiac lipid metabolism remain unknown, we investigated how cardiac lipoprotein synthesis affects cardiac expression of triglyceride metabolism-controlling genes, insulin sensitivity, and function in obese mice. Heart-specific ablation of MTP-A in mice using Cre-loxP technology impaired upregulation of MTP expression in response to increased fatty acid availability during fasting and fat feeding. This resulted in cardiac triglyceride accumulation but unaffected cardiac insulin-stimulated glucose uptake. Long-term fat-feeding of male C57Bl/6 mice increased cardiac triglycerides, induced cardiac expression of triglyceride metabolism-controlling genes and attenuated heart function. Abolishing cardiac triglyceride accumulation in fat-fed mice by overexpression of an apoB transgene in the heart prevented the induction of triglyceride metabolism-controlling genes and improved heart function. The results suggest that in obesity, the physiological increase of cardiac MTP expression serves to attenuate cardiac triglyceride accumulation albeit without major effects on cardiac insulin sensitivity. Nevertheless, the data suggest that genetically increased lipoprotein secretion prevents development of obesity-induced lipotoxic heart disease.

The effects of trimetazidine on p-wave duration and dispersion in heart failure patients

BACKGROUND

P-wave duration and dispersion (PWD) have been shown to be noninvasive predictors for development of atrial fibrillation. Thus, it may be possible to attenuate atrial fibrillation risk through normalization of P-wave duration and dispersion. Trimetazidine, a metabolic modulator, has been reported to improve cardiac function in heart failure (HF) patients.

METHODS

Thirty-six HF patients being treated with angiotensin inhibitors, carvedilol, spironolactone, and furosemide were prescribed trimetazidine, 20 mg three times a day. Electrocardiographic and echocardiographic examinations were obtained before and 6 months after addition of trimetazidine in HF patients and 36 healthy control group patients having normal echocardiographic examination.

RESULTS

Maximum P-wave duration (Pmax) (106.7 +/- 15.8 vs. 91.7 +/- 12.7 ms) and PWD (57.2 +/- 15.4 vs. 37.9 +/- 16.7 ms) were significantly longer in HF patients compared to the control group. There were significant correlations of Pmax and PWD with left atrial diameter (r = 0.508, P = < 0.001 and r = 0.315, P = 0.029), left ventricular ejection fraction (LVEF) (r = 0.401, p = 0.005 and r = 0.396, P = 0.005), deceleration time (r = 0.296, P = 0.032 and r = 0.312, P = 0.035), and isovolumetric relaxation time (r = 0.265, P = 0.038 and r = 0.322, P = 0.015). There were significant improvements in LVEF (32.7 +/- 6.5% to 37.2 +/- 5.5%, P = 0.036), left atrial diameter (41.5 +/- 6.7 to 40.3 +/- 6.1 mm, P < 0.001), and Pmax (106.7 +/- 15.8 to 102.2 +/- 11.5 ms, P = 0.006) and PWD (57.2 +/- 15.4 to 48.9 +/- 10.1 ms, P < 0.001) during follow-up.

CONCLUSIONS

Trimetazidine added to optimal medical therapy in HF may improve Pmax and PWD in association with improved left ventricular function. Longer-term and larger studies are necessary to evaluate whether these findings may have clinical implications on prevention of atrial fibrillation.

Limited functional and metabolic improvements in hypertrophic and healthy rat heart overexpressing the skeletal muscle isoform of SERCA1 by adenoviral gene transfer in vivo

Adenoviral gene transfer of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA)2a to the hypertrophic heart in vivo has been consistently reported to lead to enhanced myocardial contractility. It is unknown if the faster skeletal muscle isoform, SERCA1, expressed in the whole heart in early failure, leads to similar improvements and whether metabolic requirements are maintained during an adrenergic challenge. In this study, Ad.cmv.SERCA1 was delivered in vivo to aortic banded and sham-operated Sprague-Dawley rat hearts. The total SERCA content increased 34%. At 48-72 h posttransfer, echocardiograms were acquired, hearts were excised and retrograded perfused, and hemodynamics were measured parallel to NMR measures of the phosphocreatine (PCr)-to-ATP ratio (PCr/ATP) and energy substrate selection at basal and high workloads (isoproterenol). In the Langendorff mode, the rate-pressure product was enhanced 27% with SERCA1 in hypertrophic hearts and 10% in shams. The adrenergic response to isoproterenol was significantly potentiated in both groups with SERCA1. 31P NMR analysis of PCr/ATP revealed that the ratio remained low in the hypertrophic group with SERCA1 overexpression and was not further compromised with adrenergic challenge. 13C NMR analysis revealed fat and carbohydrate oxidation were unaffected at basal with SERCA1 expression; however, there was a shift from fats to carbohydrates at higher workloads with SERCA1 in both groups. Transport of NADH-reducing equivalents into the mitochondria via the alpha-ketoglutamate-malate transporter was not affected by either SERCA1 overexpression or adrenergic challenge in both groups. Echocardiograms revealed an important distinction between in vivo versus ex vivo data. In contrast to previous SERCA2a studies, the echocardiogram data revealed that SERCA1 expression compromised function (fractional shortening) in the hypertrophic group. Shams were unaffected. While our ex vivo findings support much of the earlier cardiomyocyte and transgenic data, the in vivo data challenge previous reports of improved cardiac function in heart failure models after SERCA intervention.

PPARalpha-mediated remodeling of repolarizing voltage-gated K+ (Kv) channels in a mouse model of metabolic cardiomyopathy

Diabetes is associated with increased risk of diastolic dysfunction, heart failure, QT prolongation and rhythm disturbances independent of age, hypertension or coronary artery disease. Although these observations suggest electrical remodeling in the heart with diabetes, the relationship between the metabolic and the functional derangements is poorly understood. Exploiting a mouse model (MHC-PPARalpha) with cardiac-specific overexpression of the peroxisome proliferator-activated receptor alpha (PPARalpha), a key driver of diabetes-related lipid metabolic dysregulation, the experiments here were aimed at examining directly the link(s) between alterations in cardiac fatty acid metabolism and the functioning of repolarizing, voltage-gated K(+) (Kv) channels. Electrophysiological experiments on left (LV) and right (RV) ventricular myocytes isolated from young (5-6 week) MHC-PPARalpha mice revealed marked K(+) current remodeling: I(to,f) densities are significantly (P<0.01) lower, whereas I(ss) densities are significantly (P<0.001) higher in MHC-PPARalpha, compared with age-matched wild type (WT), LV and RV myocytes. Consistent with the observed reductions in I(to,f) density, expression of the KCND2 (Kv4.2) transcript is significantly (P<0.001) lower in MHC-PPARalpha, compared with WT, ventricles. Western blot analyses revealed that expression of the Kv accessory protein, KChIP2, is also reduced in MHC-PPARalpha ventricles in parallel with the decrease in Kv4.2. Although the properties of the endogenous and the "augmented" I(ss) suggest a role(s) for two pore domain K(+) channel (K2P) pore-forming subunits, the expression levels of KCNK2 (TREK1), KCNK3 (TASK1) and KCNK5 (TASK2) in MHC-PPARalpha and WT ventricles are not significantly different. The molecular mechanisms underlying I(to,f) and I(ss) remodeling in MHC-PPARalpha ventricular myocytes, therefore, are distinct.

Measuring regional changes in the diastolic deformation of the left ventricle of SHR rats using microPET technology and hyperelastic warping

The objective of this research was to assess applicability of a technique known as hyperelastic warping for the measurement of local strains in the left ventricle (LV) directly from microPET image data sets. The technique uses differences in image intensities between template (reference) and target (loaded) image data sets to generate a body force that deforms a finite element (FE) representation of the template so that it registers with the target images. For validation, the template image was defined as the end-systolic microPET image data set from a Wistar Kyoto (WKY) rat. The target image was created by mapping the template image using the deformation results obtained from a FE model of diastolic filling. Regression analysis revealed highly significant correlations between the simulated forward FE solution and image derived warping predictions for fiber stretch (R (2) = 0.96), circumferential strain (R (2) = 0.96), radial strain (R (2) = 0.93), and longitudinal strain (R (2) = 0.76) (p < 0.001 for all cases). The technology was applied to microPET image data of two spontaneously hypertensive rats (SHR) and a WKY control. Regional analysis revealed that, the lateral freewall in the SHR subjects showed the greatest deformation compared with the other wall segments. This work indicates that warping can accurately predict the strain distributions during diastole from the analysis of microPET data sets.

Diurnal variations in myocardial metabolism

The heart is challenged by a plethora of extracellular stimuli over the course of a normal day, each of which distinctly influences myocardial contractile function. It is therefore not surprising that myocardial metabolism also oscillates in a time-of-day dependent manner. What is becoming increasingly apparent is that the heart exhibits diurnal variations in its intrinsic properties, including responsiveness to extracellular stimuli. This article summarizes our current knowledge regarding the mechanism(s) mediating diurnal variations in myocardial metabolism. Particular attention is focused towards the intramyocardial circadian clock, a cell autonomous molecular mechanism that appears to regulate myocardial metabolism both directly (e.g. triglyceride and glycogen metabolism) and indirectly (through modulation of the responsiveness of the myocardium to workload, insulin, and fatty acids). In doing so, the circadian clock within the cardiomyocyte allows the heart to anticipate environmental stimuli (such as changes in workload, feeding status) prior to their onset. This synchronization between the myocardium and its environment is enhanced by regular feeding schedules. Conversely, loss of synchronization may occur through disruption of the circadian clock and/or diurnal variations in neurohumoral factors (as observed during diabetes mellitus). Here, we discuss the possibility that loss of synchronization between the heart and its environment predisposes the heart to metabolic maladaptation and subsequent myocardial contractile dysfunction.

The concentration of oxygen, lactate and glucose in the central veins, right heart, and pulmonary artery: a study in patients with pulmonary hypertension

INTRODUCTION

Decreases in oxygen saturation (SO2) and lactate concentration [Lac] from superior vena cava (SVC) to pulmonary artery have been reported. These gradients (Delta SO2 and Delta[Lac]) are probably created by diluting SVC blood with blood of lower SO2 and [Lac]. We tested the hypothesis that Delta SO2 and Delta[Lac] result from mixing SVC and inferior vena cava (IVC) blood streams.

METHODS

This was a prospective, sequential, observational study of hemodynamically stable individuals with pulmonary artery hypertension (n = 9) who were about to undergo right heart catheterization. Catheters were advanced under fluoroscopic guidance into the IVC, SVC, right atrium, right ventricle, and pulmonary artery. Samples were obtained at each site and analyzed for SO2, [Lac], and glucose concentration ([Glu]). Analysis of variance with Tukey HSD test was used to compare metabolite concentrations at each site.

RESULTS

There were no differences in SO2 or [Lac] between IVC and SVC, both being greater than their respective pulmonary artery measurements (P < 0.01 for SO2 and P < 0.05 for [Lac]). SO2 and [Lac] in right atrium, right ventricle, and pulmonary artery were similar. Delta SO2 was 4.4 +/- 1.4% (mean +/- standard deviation) and Delta[Lac] was 0.16 +/- 0.11 mmol/l (both > 0; P < 0.001). Delta[Glu] was -0.19 +/- 0.31 mmol/l, which was not significantly different from zero, with SVC [Glu] being less than IVC [Glu].

CONCLUSION

Mixing of SVC with IVC blood does not account for the development of Delta SO2 and Delta[Lac] in hemodynamically stable individuals with pulmonary artery hypertension. An alternate mechanism is mixing with coronary sinus blood, implying that Delta SO2 and Delta[Lac] may reflect changes in coronary sinus SO2 and [Lac] in this patient population.

Alterations in carbohydrate metabolism and its regulation in PPARalpha null mouse hearts

Although a shift from fatty acids (FAs) to carbohydrates (CHOs) is considered beneficial for the diseased heart, it is unclear why subjects with FA beta-oxidation defects are prone to cardiac decompensation under stress conditions. The present study investigated potential alterations in the myocardial utilization of CHOs for energy production and anaplerosis in 12-wk-old peroxisome proliferator-activating receptor-alpha (PPARalpha) null mice (a model of FA beta-oxidation defects). Carbon-13 methodology was used to assess substrate flux through energy-yielding pathways in hearts perfused ex vivo at two workloads with a physiological substrate mixture mimicking the fed state, and real-time RT-quantitative polymerase chain reaction was used to document the expression of selected metabolic genes. When compared with that from control C57BL/6 mice, isolated working hearts from PPARalpha null mice displayed an impaired capacity to withstand a rise in preload (mimicking an increased venous return as it occurs during exercise) as reflected by a 20% decline in the aortic flow rate. At the metabolic level, beyond the expected shift from FA (5-fold down) to CHO (1.5-fold up; P < 0.001) at both preloads, PPARalpha null hearts also displayed 1) a significantly greater contribution of exogenous lactate and glucose and/or glycogen (2-fold up) to endogenous pyruvate formation, whereas that of exogenous pyruvate remained unchanged and 2) marginal alterations in citric acid cycle-related parameters. The lactate production rate was the only measured parameter that was affected differently by preloads in control and PPARalpha null mouse hearts, suggesting a restricted reserve for the latter hearts to enhance glycolysis when the energy demand is increased. Alterations in the expression of some glycolysis-related genes suggest potential mechanisms involved in this defective CHO metabolism. Collectively, our data highlight the importance of metabolic alterations in CHO metabolism associated with FA oxidation defects as a factor that may predispose the heart to decompensation under stress conditions even in the fed state.

Metoprolol improves cardiac function and modulates cardiac metabolism in the streptozotocin-diabetic rat

The effects of diabetes on heart function may be initiated or compounded by the exaggerated reliance of the diabetic heart on fatty acids and ketones as metabolic fuels. beta-Blocking agents such as metoprolol have been proposed to inhibit fatty acid oxidation. We hypothesized that metoprolol would improve cardiac function by inhibiting fatty acid oxidation and promoting a compensatory increase in glucose utilization. We measured ex vivo cardiac function and substrate utilization after chronic metoprolol treatment and acute metoprolol perfusion. Chronic metoprolol treatment attenuated the development of cardiac dysfunction in streptozotocin (STZ)-diabetic rats. After chronic treatment with metoprolol, palmitate oxidation was increased in control hearts but decreased in diabetic hearts without affecting myocardial energetics. Acute treatment with metoprolol during heart perfusions led to reduced rates of palmitate oxidation, stimulation of glucose oxidation, and increased tissue ATP levels. Metoprolol lowered malonyl-CoA levels in control hearts only, but no changes in acetyl-CoA carboxylase phosphorylation or AMP-activated protein kinase activity were observed. Both acute metoprolol perfusion and chronic in vivo metoprolol treatment led to decreased maximum activity and decreased sensitivity of carnitine palmitoyltransferase I to malonyl-CoA. Metoprolol also increased sarco(endo)plasmic reticulum Ca(2+)-ATPase expression and prevented the reexpression of atrial natriuretic peptide in diabetic hearts. These data demonstrate that metoprolol ameliorates diabetic cardiomyopathy and inhibits fatty acid oxidation in streptozotocin-induced diabetes. Since malonyl-CoA levels are not increased, the reduction in total carnitine palmitoyltransferase I activity is the most likely factor to explain the decrease in fatty acid oxidation. The metabolism changes occur in parallel with changes in gene expression.

Contrast between cardiac left ventricle and diaphragm muscle in expression of genes involved in carbohydrate and lipid metabolism

The heart and diaphragm both need appropriate metabolic machinery to ensure long-term energy supplies, as they must contract rhythmically without cessation for the entire lifetime of the organism to ensure homeostasis of oxygen and carbon dioxide exchange. However, their energy requirements differ due to disparities in mechanical loads. Understanding how these two muscles converge and diverge in their approaches to meeting their metabolic demands may suggest novel strategies for improving cardiac and skeletal muscle long-term performance in health and disease. To assess this at a transcriptional level, expression of genes involved in carbohydrate and lipid metabolism was assessed using microarrays in rats. There were 594 genes with >2-fold differential expression between left ventricle of the heart and diaphragm; 307 were expressed heart>diaphragm and 287 diaphragm>heart. Assignment to gene ontology groups revealed over-representation for "carbohydrate metabolism" (P=0.005, n=32 genes or 5.4% of all genes with differential expression) and "lipid metabolism" (P=0.0012, n=48 genes or 8.1% of all genes with differential expression). For carbohydrate there were 14 genes with heart>diaphragm and 18 genes with diaphragm>heart, and for lipid there were 30 genes with heart>diaphragm and 18 genes with diaphragm>heart. The magnitude of differential expression between heart and diaphragm ranged up to 30-fold for carbohydrate and up to 59-fold for lipid. Carbohydrate-related genes were almost all involved in energy metabolism (e.g. Pfkm, Pgm1, Pgam1, Pfkfb1, Pfkfb2), whereas lipid-related genes were involved in energetics as well as other cellular processes; for both groups this included genes involved in rate-limiting metabolic steps. Data thus indicate that diaphragm and heart have both shared and differential transcriptional strategies for ensuring long-term energy supplies, with a relative favoring of lipid metabolism in the heart and carbohydrate metabolism in the diaphragm.

Altered myocardial gene expression reveals possible maladaptive processes in heterozygous and homozygous cardiac myosin-binding protein C knockout mice

Familial hypertrophic cardiomyopathy (FHC) is an autosomal dominant disease characterized by left ventricular hypertrophy (LVH) predominantly affecting the interventricular septum. Cardiac myosin-binding protein C (cMyBP-C) mutations are common causes of FHC. Gene expression profiling was performed in left ventricles of 9-week-old wild-type mice, heterozygous cMyBP-C KO mice displaying asymmetric septal hypertrophy, and homozygous mice developing eccentric LVH. Knocking out one or two cMyBP-C genes leads primarily to gene expression changes indicating an increased energy demand, activation of the JNK and p38 parts of the MAPK pathway and deactivation of the ERK part, and induction of apoptosis. Altered gene expression for processes related to cardiac structure, contractile proteins, and protein turnover was also identified. Many of the changes were more pronounced in the homozygous KO mice. These alterations point to physiological and pathological adaptations in the prehypertrophic heterozygous KO mice and the hypertrophic homozygous mice.

Mitochondrial uncoupling protein 3 and its role in cardiac- and skeletal muscle metabolism

Uncoupling protein 3 (UCP3), is primarily expressed in skeletal muscle mitochondria and has been suggested to be involved in mediating energy expenditure via uncoupling, hereby dissipating the mitochondrial proton gradient necessary for adenosine triphosphate (ATP) synthesis. Although some studies support a role for UCP3 in energy metabolism, other studies pointed towards a function in fatty acid metabolism. Thus, the protein is up regulated or high when fatty acid supply to the mitochondria exceeds the capacity to oxidize fatty acids and down regulated or low when oxidative capacity is high or improved. Irrespective of the exact operating mechanism, UCP3 seems to protect mitochondria against lipid-induced oxidative stress, which makes this protein a potential player in the development of type 2 diabetes mellitus. Next to skeletal muscle, UCP3 is also expressed in cardiac muscle where its role is relatively unexplored. Interestingly, energy deficiency in cardiac muscle is associated to heart failure and UCP3 might contribute to this energy deficiency. It has been suggested that UCP3 decreases energy status via uncoupling of mitochondrial respiration, but the available data does not provide a unified answer. In fact, the results obtained regarding cardiac UCP3 are very similar as in skeletal muscle, implying that its physiological function can be extrapolated. Therefore, cardiac UCP3 can just as well serve to protect the heart against lipid-induced oxidative stress, similar to the function described for skeletal muscle UCP3. The present review will deal with the available literature on both skeletal muscle- and cardiac UCP3 to elucidate its physiological function in these tissues.

Comparative study of myocardial high energy phosphate substrate content in slow and fast growing chicken and in chickens with heart failure and ascites

In order to explain the biochemical mechanisms associated with deteriorating heart function in broiler chickens, this study compared myocardial high energy phosphate substrates in leghorns, feed restricted (Broilers-Res) broilers, ad libitum fed broilers (Broilers-AL), and in broilers that developed heart failure and ascites. The profile of adenine nucleotide content in the heart tissue did not differ between leghorns and Broilers-Res, but there were significant differences among Broilers-Res, Broilers-AL, and broilers with ascites. During intensive growth periods, leghorns and Broilers-Res showed increasing trends in heart ATP levels, whereas in fast growing broilers the heart ATP declined (p<0.021). ATP:ADP and ATP:CrP ratios increased with age in both leghorn and Broilers-Res, declined in fast growing broilers, and were the lowest in broilers that developed heart failure. The changes in heart high energy phosphate profile in broilers suggest that the energy demand of the heart during a rapid growth phase may exceed the bird's metabolic capacity to supply adequate levels of high energy phosphate substrate. The insufficiency of energy substrate likely contributes to the declining heart rate. In some individuals this may lead to impaired heart pump function, and in more severe cases may progress to heart pump failure.

Circadian rhythms in myocardial metabolism and contractile function: influence of workload and oleate

Multiple extracardiac stimuli, such as workload and circulating nutrients (e.g., fatty acids), known to influence myocardial metabolism and contractile function exhibit marked circadian rhythms. The aim of the present study was to investigate whether the rat heart exhibits circadian rhythms in its responsiveness to changes in workload and/or fatty acid (oleate) availability. Thus, hearts were isolated from male Wistar rats (housed during a 12:12-h light-dark cycle: lights on at 9 AM) at 9 AM, 3 PM, 9 PM, and 3 AM and perfused in the working mode ex vivo with 5 mM glucose plus either 0.4 or 0.8 mM oleate. Following 20-min perfusion at normal workload (i.e., 100 cm H(2)O afterload), hearts were challenged with increased workload (140 cm H(2)O afterload plus 1 microM epinephrine). In the presence of 0.4 mM oleate, myocardial metabolism exhibited a marked circadian rhythm, with decreased rates of glucose oxidation, increased rates of lactate release, decreased glycogenolysis capacity, and increased channeling of oleate into nonoxidative pathways during the light phase. Rat hearts also exhibited a modest circadian rhythm in responsiveness to the workload challenge when perfused in the presence of 0.4 mM oleate, with increased myocardial oxygen consumption at the dark-to-light phase transition. However, rat hearts perfused in the presence of 0.8 mM oleate exhibited a markedly blunted contractile function response to the workload challenge during the light phase. In conclusion, these studies expose marked circadian rhythmicities in myocardial oxidative and nonoxidative metabolism as well as responsiveness of the rat heart to changes in workload and fatty acid availability.

Effect of aging and caloric restriction on the mitochondrial proteome

The rat mitochondrial proteome was analyzed using two-dimensional polyacrylamide gel electrophoresis (2-D PAGE), and proteins altered by age or caloric restriction (CR) were identified using mass spectrometry. Of 2061 mitochondrial proteins analyzed in the three tissues, a significant change with age occurred in 25 liver proteins (19 increased, 6 decreased), 3 heart proteins (1 increased, 2 decreased), and 5 skeletal muscle proteins (all increased). CR prevented the age-related change in the level of one liver mitochondrial protein, altered the levels of four proteins (one increased, three decreased) from heart, and one protein (decreased) from skeletal muscle. Identification of the proteins that changed with age or CR revealed that they were varied among the three tissues, that is, not one mitochondrial protein was changed, in common, by age or CR in any tissue studied. Thus, the effect of age on the mitochondrial proteome appears to be tissue-specific, and CR has a minor effect on age-related protein changes.

Hyperglycemia during acute myocardial infarction in patients who are treated by primary percutaneous coronary intervention: impact on long-term prognosis

BACKGROUND

Transient hyperglycemia is common during acute myocardial infarction in non-diabetic patients and is associated with a worse outcome. There is limited data on the outcome of patients who undergo primary percutaneous coronary intervention and have transient hyperglycemia.

METHODS

Fasting plasma glucose was measured in 431 consecutive acute myocardial infarction patients who underwent primary percutaneous coronary interventions. Patients were classified into three groups: non-diabetics/non-hyperglycemic (NDNH, glucose < 126 mg/dL; n=224); non-diabetics/hyperglycemic (NDH, glucose > or = 126 mg/dL; n=119); and diabetics (n=88). Data were analyzed according to the different groups and according to exact glucose levels.

RESULTS

In-hospital mortality was significantly lower in NDNH (1%) compared to NDH (8%) and diabetic (5%) patients (p=0.01). One-year cumulative mortality was highest (10%) in patients with NDH (p<0.001). One year target lesion revascularization rates were identical in NDNH and NDH patients (6% vs. 8%) and higher in diabetic patients (19%, p=0.001). In a multivariate model, a striking increase in the risk of death (0.6%, p=0.05) and target lesion revascularization (2%, p<0.0001) was found for every increment of 1 mg/dL in glucose level.

CONCLUSIONS

Transient hyperglycemia in non-diabetic acute myocardial infarction patients who undergo primary percutaneous coronary interventions is associated with high one-year mortality. One year target lesion revascularization rates were significantly higher in diabetics compared to non-diabetics with normoglycemia or transient hyperglycemia.

Optimizing cardiac fatty acid and glucose metabolism as an approach to treating heart failure

Despite the recent introduction of new therapeutic approaches to treat heart failure, mortality from heart failure remains high, and patients still frequently experience progression of contractile dysfunction and ongoing left ventricular enlargement. Therefore, new treatments are needed for heart failure that work independently of mechanisms already targeted. Emerging evidence suggests that the failure of the myocardium in heart failure is affected by alterations in the energy substrate metabolism. In particular, there is now evidence that in the failing heart, shifting metabolism away from a preference for fatty acids toward more carbohydrate oxidation can improve contractile function and slow the progression of pump failure.

Ranolazine for the management of coronary artery disease

BACKGROUND

Despite coronary revascularization and standard antianginal therapy, many patients continue to experience symptoms of stable angina and progression of their disease. Ranolazine is a new class of antianginal agent. Unlike standard antianginal agents, it alters glucose and fatty acid metabolism for a different approach to the management of coronary artery disease.

OBJECTIVE

This article discusses the clinical pharmacology of ranolazine and its use in the management of chronic stable angina.

METHODS

Peer-reviewed articles and abstracts were identified from MEDLINE and the Current Contents database (both from 1966 to September 20, 2006) using the search terms ranolazine, angina, pharmacokinetics, and pharmacology. Citations from available articles were reviewed for additional references. Abstracts presented at recent professional meetings were also reviewed.

RESULTS

Ranolazine is a cell membrane inhibitor of the late sodium current. Extended-release ranolazine was recently approved in the United States for the treatment of chronic angina. Ranolazine is metabolized in the liver by the cytochrome P-450 (CYP) 3A4 system. Because of its potential to prolong corrected QT (QTc) intervals, ranolazine should not be used in patients with hepatic impairment, those with QTc prolongation, or those taking drugs known to prolong QTc intervals or drugs that are potent CYP 3A4 inhibitors. Other adverse effects of ranolazine include dizziness, headache, constipation, and nausea. Placebo-controlled clinical studies performed to date have found that sustained-release ranolazine 500 to 1500 mg PO BID was associated with significantly increased time to onset of angina (range of increase, 27.0-144.0 s; P < 0.05 [varied among studies]), exercise duration (range of increase, 23.8-99.0 s; P < 0.05 [varied among studies] ), and time to 1-mm ST depression (range of increase, 27.6-146.2 s; P < 0.05 [varied among studies]). In addition, exercise duration was found to be significantly longer with ranolazine compared with atenolol (453 vs 430 s; P = 0.006).

CONCLUSIONS

Ranolazine is a new antianginal agent that is effective in the management of chronic angina. Its unique mechanism of action warrants further study in other cardiovascular conditions such as heart failure and arrhythmias. Ongoing studies will address whether ranolazine can reduce clinical end points such as cardiovascular death and myocardial infarction.

CVT-4325 Inhibits Myocardial Fatty Acid Uptake and Improves Left Ventricular Systolic Function without Increasing Myocardial Oxygen Consumption in Dogs with Chronic Heart Failure

BACKGROUND

Inhibition of myocardial fatty acid oxidation has been suggested as a therapeutic approach for improving cardiac function in chronic heart failure (HF). The novel piperazine derivative CVT-4325 was shown to inhibit fatty acid oxidation in cardiac mitochondria and in isolated perfused rat hearts. In the present study, we tested the hemodynamic and metabolic effects of acute intravenous CVT-4325 in dogs with HF.

METHODS AND RESULTS

HF (LV ejection fraction <or=35%) was created in eight dogs by multiple sequential intracoronary microembolizations. Treatment with CVT-4325 administered intravenously as 0.5 mg/kg bolus followed by a continuous infusion of 0.8 mg/kg/h for 40 min reduced free fatty acid (FFA) uptake (4.51+/-0.96 to 1.65+/-0.32 micromols/min, p<0.04), coronary blood flow (56+/-3 to 46+/-4 ml/min, p<0.01), and myocardial oxygen consumption (MVO2) (240+/-23 to 172+/-7 micromols/min, p<0.03), and increased LV ejection fraction (30+/-2 to 37+/-1%, p<0.0001). In the same study, but on a different day, the same dogs were treated with an inactive analogue of CVT-4325 (CVT-2540), and no hemodynamic or metabolic effects were observed.

CONCLUSIONS

In dogs with HF, acute intravenous infusion of CVT-4325 reduces FFA uptake and improves LV systolic function without increasing MVO2. The improvement in LV systolic function in the absence of an increase in MVO2 and a lower FFA uptake is consistent with the concept that inhibition of myocardial fatty acid oxidation may be an effective treatment for HF.

Alterations in oxidative phosphorylation complex proteins in the hearts of transgenic mice that overexpress the p38 MAP kinase activator, MAP kinase kinase 6

Ischemia-reperfusion (I/R) has critical consequences in the heart. Recent studies on the functions of I/R-activated kinases, such as p38 mitogen-activated protein kinase (MAPK), showed that I/R injury is reduced in the hearts of transgenic mice that overexpress the p38 MAPK activator MAPK kinase 6 (MKK6). This protection may be fostered by changes in the levels of many proteins not currently known to be regulated by p38. To examine this possibility, we employed the multidimensional protein identification technology MudPIT to characterize changes in levels of proteins in MKK6 transgenic mouse hearts, focusing on proteins in mitochondria, which play key roles in mediating I/R injury in the heart. Of the 386 mitochondrial proteins identified, the levels of 58 were decreased, while only 2 were increased in the MKK6 transgenic mouse hearts. Among those that were decreased were 21 mitochondrial oxidative phosphorylation complex proteins, which was unexpected because p38 is not known to mediate such decreases. Immunoblotting verified that proteins in each of the five oxidative phosphorylation complexes were reduced in MKK6 mouse hearts. On assessing functional consequences of these reductions, we found that MKK6 mouse heart mitochondria exhibited 50% lower oxidative respiration and I/R-mediated reactive oxygen species (ROS) generation, both of which are predicted consequences of decreased oxidative phosphorylation complex proteins. Thus the cardioprotection observed in MKK6 transgenic mouse hearts may be partly due to decreased electron transport, which is potentially beneficial, because damaging ROS are known to be generated by mitochondrial complexes I and III during reoxygenation.

Competition between acetate and oleate for the formation of malonyl-CoA and mitochondrial acetyl-CoA in the perfused rat heart

We previously showed that, in the perfused rat heart, the capacity of n-fatty acids to generate mitochondrial acetyl-CoA decreases as their chain length increases. In the present study, we investigated whether the oxidation of a long-chain fatty acid, oleate, is inhibited by short-chain fatty acids, acetate or propionate (which do and do not generate mitochondrial acetyl-CoA, respectively). We perfused rat hearts with buffer containing 4 mM glucose, 0.2 mM pyruvate, 1 mM lactate, and various concentrations of either (i) [U-(13)C]acetate, (ii) [U-(13)C]acetate plus [1-(13)C]oleate, or (iii) unlabeled propionate plus [1-(13)C]oleate. Using mass isotopomer analysis, we determined the contributions of the labeled substrates to the acetyl moiety of citrate (a probe of mitochondrial acetyl-CoA) and to malonyl-CoA. We found that acetate, even at low concentration, markedly inhibits the oxidation of [1-(13)C]oleate in the heart, without change in malonyl-CoA concentration. We also found that propionate, at a concentration higher than 1 mM, decreases (i) the contribution of [1-(13)C]oleate to mitochondrial acetyl-CoA and (ii) malonyl-CoA concentration. The inhibition by acetate or propionate of acetyl-CoA production from oleate probably results from a competition for mitochondrial CoA between the CoA-utilizing enzymes.

Mitochondrial uncoupling: a key contributor to reduced cardiac efficiency in diabetes

Cardiovascular disease is the primary cause of death in individuals with obesity and diabetes. However, the underlying mechanisms for cardiac dysfunction are partially understood. Studies have suggested that altered cardiac metabolism may play a role. The diabetic heart is characterized by increased fatty acid oxidation, increased myocardial oxygen consumption, and reduced cardiac efficiency. Here, we review possible mechanisms for reduced cardiac efficiency in obesity and diabetes by focusing on the potential role of mitochondrial uncoupling.

Distinct transcriptional regulation of long-chain acyl-CoA synthetase isoforms and cytosolic thioesterase 1 in the rodent heart by fatty acids and insulin

The molecular mechanism(s) responsible for channeling long-chain fatty acids (LCFAs) into oxidative versus nonoxidative pathways is (are) poorly understood in the heart. Intracellular LCFAs are converted to long-chain fatty acyl-CoAs (LCFA-CoAs) by a family of long-chain acyl-CoA synthetases (ACSLs). Cytosolic thioesterase 1 (CTE1) hydrolyzes cytosolic LCFA-CoAs to LCFAs, generating a potential futile cycle at the expense of ATP utilization. We hypothesized that ACSL isoforms and CTE1 are differentially regulated in the heart during physiological and pathophysiological conditions. Using quantitative RT-PCR, we report that the five known acsl isoforms ( acsl1, acsl3, acsl4, acsl5, and acsl6) and cte1 are expressed in whole rat and mouse hearts, as well as adult rat cardiomyocytes (ARCs). Streptozotocin-induced insulin-dependent diabetes (4 wk) and fasting (≤24 h) both dramatically induced cte1 and repressed acsl6 mRNA, with no significant effects on the other acsl isoforms. In contrast, high-fat feeding (4 wk) induced cte1 without affecting expression of the acsl isoforms in the heart. Investigation into the mechanism(s) responsible for these transcriptional changes uncovered roles for peroxisome proliferator-activated receptor-α (PPARα) and insulin as regulators of specific acsl isoforms and cte1 in the heart. Culturing ARCs with oleate (0.1–0.4 mM) or the PPARα agonists WY-14643 (1 μM) and fenofibrate (10 μM) consistently induced acsl1 and cte1. Conversely, PPARα null mouse hearts exhibited decreased acsl1 and cte1 expression. Culturing ARCs with insulin (10 nM) induced acsl6, whereas specific loss of insulin signaling within the heart (cardiac-specific insulin receptor knockout mice) caused decreased acsl6 expression. Our data expose differential regulation of acsl isoforms and cte1 in the heart, where acsl1 and cte1 are PPARα-regulated genes, whereas acsl6 is an insulin-regulated gene.

Metabolic modulation of myocardial ischemia

The metabolic pathways of the heart during normoxia and ischemia have been well studied. High plasma fatty acid concentrations and the myocardial accumulation of long-chain fatty acyl metabolites during ischemia correlate with increased morbidity and mortality. However, enhanced glucose use can maintain cell homeostasis, diminish ischemic injury, and be clinically beneficial. Metabolic modulators represent a new class of drugs with the potential to treat myocardial ischemia. They are ideal as adjunctive anti-ischemic therapy because they lack the hemodynamic consequences of traditional therapy and treat the underlying metabolic dysfunction that leads to contractile failure and arrhythmias. Clinical studies have demonstrated their efficacy in acute and chronic settings. It is anticipated that there will be greater utilization of this new class of agents in the near future.

Metabolic therapeutics in angina pectoris: history revisited with perhexiline

The ever-increasing burden of ischaemic heart disease and its common manifestation chronic angina pectoris calls for the exploration of other treatment options for those patients who despite the maximum conventional pharmacological and surgical interventions continue to suffer. Such exploration has led to the increasing use of new metabolically acting antianginal agents and the re-emergence of an old and somewhat forgotten pharmacological agent, perhexiline maleate. This review aims to update the cardiac nurse with knowledge to manage the care a patient receiving perhexiline maleate treatment and provide a brief review of three new metabolic agents: trimetazidine, ranolazine and etomoxir.

Glycolytic enzyme activities are decreased during acute rejection in transplanted rat hearts

Metabolic alterations have been characterized in various heart diseases. However, no data are available concerning metabolic changes during acute rejection episodes. Heterotopic heart transplantations in rats were done using Lewis rats as donors and recipients as a control group. The rejection group included Brown-Norway rat donors to Lewis rat recipients. Nonoperated hearts were also studied. Enzyme activities were determined for phosphofructokinase, pyruvate kinase, and lactate dehydrogenase. There were no alterations in the control group compared to nonoperated hearts. However, the rejection cohort of hearts showed decreased glycolytic enzymes. Although lactate dehydrogenase maintained similar levels compared to the control group, phosphofructokinase showed only 50% activity, and pyruvate kinase showed less than 10% of the activity compared with controls. These results suggested that metabolic alterations in rejected hearts differ from other cardiomyopathies.

Loss of lipoprotein lipase-derived fatty acids leads to increased cardiac glucose metabolism and heart dysfunction

Long-chain fatty acids (FAs) are the predominant energy substrate utilized by the adult heart. The heart can utilize unesterified FA bound to albumin or FA obtained from lipolysis of lipoprotein-bound triglyceride (TG). We used heart-specific lipoprotein lipase knock-out mice (hLpL0) to test whether these two sources of FA are interchangeable and necessary for optimal heart function. Hearts unable to obtain FA from lipoprotein TG were able to compensate by increasing glucose uptake, glycolysis, and glucose oxidation. HLpL0 hearts had decreased expression of pyruvate dehydrogenase kinase 4 and increased cardiomyocyte expression of glucose transporter 4. Conversely, FA oxidation rates were reduced in isolated perfused hLpL0 hearts. Following abdominal aortic constriction expression levels of genes regulating FA and glucose metabolism were acutely up-regulated in control and hLpL0 mice, yet all hLpL0 mice died within 48 h of abdominal aortic constriction. Older hLpL0 mice developed cardiac dysfunction characterized by decreased fractional shortening and interstitial and perivascular fibrosis. HLpL0 hearts had increased expression of several genes associated with transforming growth factor-beta signaling. Thus, long term reduction of lipoprotein FA uptake is associated with impaired cardiac function despite a compensatory increase in glucose utilization.

Plasma free fatty acids and peroxisome proliferator-activated receptor alpha in the control of myocardial uncoupling protein levels

Diabetic patients have abnormal cardiac energy metabolism associated with high plasma free fatty acid (FFA) concentrations. We investigated whether high plasma FFAs increase mitochondrial uncoupling protein (UCP) levels in the mouse heart by activating the nuclear transcription factor peroxisome proliferator-activated receptor (PPAR)alpha. We used Western blotting to measure UCP protein levels in isolated cardiac mitochondria from PPARalpha-/- and diabetic mice. Cardiac UCP2 and UCP3 were significantly lower in the PPARalpha-/- mouse than in the wild type. Treatment with the PPARalpha-specific agonist, WY-14,643, increased cardiac UCP2 and UCP3 levels in wild-type mice but did not alter UCP levels in PPARalpha-/- mice. Inhibition of beta-oxidation with etomoxir increased cardiac UCP2 and UCP3 levels in wild-type mice and UCP2 levels in PPARalpha-/- mice but did not alter UCP3 levels in PPARalpha-/- mice. Streptozotocin treatment, which increased circulating FFAs by 91%, did not alter cardiac UCP2 levels in wild-type or PPARalpha-/- mice but increased UCP3 levels in wild-type, and not in PPARalpha-/-, mice. The diabetic db/db mouse had 50% higher plasma FFA concentrations and elevated cardiac UCP2 and UCP3 protein levels. We conclude that high plasma FFAs activated PPARalpha to increase cardiac UCP3 levels, but cardiac UCP2 levels changed via PPARalpha-dependent and -independent mechanisms.

Genome-wide expression dynamics during mouse embryonic development reveal similarities to Drosophila development

Gene transcription mediates many vital aspects of mammalian embryonic development. A comprehensive characterization and analysis of the dynamics of gene transcription in the embryo is therefore likely to provide significant insights into the basic mechanisms of this process. We used microarrays to map transcription in the mouse embryo in the important period from embryonic day 8 (e8.0) to postnatal day 1 (p1) during which the bulk of the differentiation and development of organ systems takes place. Analysis of these expression profiles revealed distinct patterns of gene expression which correlate with the differentiation of organs including the nervous system, liver, skin, lungs, and digestive system, among others. Statistical analysis of the data based on Gene Ontology (GO) group annotation showed that specific temporal sequence patterns in gene class utilization across development are very similar to patterns seen during the embryonic development of Drosophila, suggesting conservation of the temporal progression of these processes across 550 million years of evolution. The temporal profiles of gene expression and activation of processes revealed here provide intriguing insights into the mechanisms of mammalian development, embryogenesis, and organogenesis, as well as into the evolution of developmental processes.