Myocardial fatty acid metabolism in health and disease.

There is a constant high demand for energy to sustain the continuous contractile activity of the heart, which is met primarily by the beta-oxidation of long-chain fatty acids. The control of fatty acid beta-oxidation is complex and is aimed at ensuring that the supply and oxidation of the fatty acids is sufficient to meet the energy demands of the heart. The metabolism of fatty acids via beta-oxidation is not regulated in isolation; rather, it occurs in response to alterations in contractile work, the presence of competing substrates (i.e., glucose, lactate, ketones, amino acids), changes in hormonal milieu, and limitations in oxygen supply. Alterations in fatty acid metabolism can contribute to cardiac pathology. For instance, the excessive uptake and beta-oxidation of fatty acids in obesity and diabetes can compromise cardiac function. Furthermore, alterations in fatty acid beta-oxidation both during and after ischemia and in the failing heart can also contribute to cardiac pathology. This paper reviews the regulation of myocardial fatty acid beta-oxidation and how alterations in fatty acid beta-oxidation can contribute to heart disease. The implications of inhibiting fatty acid beta-oxidation as a potential novel therapeutic approach for the treatment of various forms of heart disease are also discussed.

Activating PPARα prevents post-ischemic contractile dysfunction in hypertrophied neonatal hearts.

RATIONALE: Post-ischemic contractile dysfunction is a contributor to morbidity and mortality after the surgical correction of congenital heart defects in neonatal patients. Pre-existing hypertrophy in the newborn heart can exacerbate these ischemic injuries, which may partly be due to a decreased energy supply to the heart resulting from low fatty acid ß-oxidation rates. OBJECTIVE: We determined whether stimulating fatty acid ß-oxidation with GW7647, a peroxisome proliferator-activated receptor-α (PPARα) activator, would improve cardiac energy production and post-ischemic functional recovery in neonatal rabbit hearts subjected to volume overload-induced cardiac hypertrophy. METHODS AND RESULTS: Volume-overload cardiac hypertrophy was produced in 7-day-old rabbits via an aorto-caval shunt, after which, the rabbits were treated with or without GW7647 (3 mg/kg per day) for 14 days. Biventricular working hearts were subjected to 35 minutes of aerobic perfusion, 25 minutes of global no-flow ischemia, and 30 minutes of aerobic reperfusion. GW7647 treatment did not prevent the development of cardiac hypertrophy, but did prevent the decline in left ventricular ejection fraction in vivo. GW7647 treatment increased cardiac fatty acid ß-oxidation rates before and after ischemia, which resulted in a significant increase in overall ATP production and an improved in vitro post-ischemic functional recovery. A decrease in post-ischemic proton production and endoplasmic reticulum stress, as well as an activation of sarcoplasmic reticulum calcium ATPase isoform 2 and citrate synthase, was evident in GW7647-treated hearts. CONCLUSIONS: Stimulating fatty acid ß-oxidation in neonatal hearts may present a novel cardioprotective intervention to limit post-ischemic contractile dysfunction.

Treatment with the 3-ketoacyl-CoA thiolase inhibitor trimetazidine does not exacerbate whole-body insulin resistance in obese mice.

There is a growing need to understand the underlying mechanisms involved in the progression of cardiovascular disease during obesity and diabetes. Although inhibition of fatty acid oxidation has been proposed as a novel approach to treat ischemic heart disease and heart failure, reduced muscle fatty acid oxidation rates may contribute to the development of obesity-associated insulin resistance. Our aim was to determine whether treatment with the antianginal agent trimetazidine, which inhibits fatty acid oxidation in the heart secondary to inhibition of 3-ketoacyl-CoA thiolase (3-KAT), may have off-target effects on glycemic control in obesity. We fed C57BL/6NCrl mice a high-fat diet (HFD) for 10 weeks before a 22-day treatment with the 3-KAT inhibitor trimetazidine (15 mg/kg per day). Insulin resistance was assessed via glucose/insulin tolerance testing, and lipid metabolite content was assessed in gastrocnemius muscle. Trimetazidine-treatment led to a mild shift in substrate preference toward carbohydrates as an oxidative fuel source in obese mice, evidenced by an increase in the respiratory exchange ratio. This shift in metabolism was accompanied by an accumulation of long-chain acyl-CoA and a trend to an increase in triacylglycerol content in gastrocnemius muscle, but did not exacerbate HFD-induced insulin resistance compared with control-treated mice. It is noteworthy that trimetazidine treatment reduced palmitate oxidation rates in the isolated working mouse heart and neonatal cardiomyocytes but not C2C12 skeletal myotubes. Our findings demonstrate that trimetazidine therapy does not adversely affect HFD-induced insulin resistance, suggesting that treatment with trimetazidine would not worsen glycemic control in obese patients with angina.

Pyridine nucleotide regulation of cardiac intermediary metabolism.

The pyridine nucleotides NAD(+) and NADP(+) play a pivotal role in regulating intermediary metabolism in the heart. The intracellular NAD(+)/NADH ratio controls flux through various dehydrogenase enzymes involved in both anaerobic and aerobic metabolism and also regulates posttranslational protein modification. The intracellular NADP(+)/NADPH ratio controls flux through the pentose phosphate pathway (PPP) and the polyol pathway, while also regulating ion channel function and oxidative stress. Not only does the NAD(+)/NADH ratio regulate the rates of ATP production, it can also modify energy substrate preference. For instance, in many forms of heart disease a greater contribution from fatty acids for oxidative energy metabolism increases fatty acid ß-oxidation-derived NADH, which can activate pyruvate dehydrogenase (PDH) kinase isoforms that inhibit PDH and subsequent glucose oxidation. As such, novel therapies that overcome fatty acid ß-oxidation-induced inhibition of PDH improve cardiac efficiency and subsequent function during ischemia/reperfusion and in heart failure. Furthermore, recent studies have implicated a pivotal role for increased PPP-derived NADPH in mediating oxidative stress observed in heart failure. In this article, we review the multiple actions of NAD(+)/NADH and NADP(+)/NADPH in regulating intermediary metabolism in the heart. A better understanding of the roles of NAD(+)/NADH and NADP(+)/NADPH in cellular physiology and pathology could potentially be used to exploit pyridine nucleotide modification in the treatment of a number of different forms of heart disease.

Targeting intermediary metabolism in the hypothalamus as a mechanism to regulate appetite.

The central nervous system mediates energy balance (energy intake and energy expenditure) in the body; the hypothalamus has a key role in this process. Recent evidence has demonstrated an important role for hypothalamic malonyl CoA in mediating energy balance. Malonyl CoA is generated by the carboxylation of acetyl CoA by acetyl CoA carboxylase and is then either incorporated into long-chain fatty acids by fatty acid synthase, or converted back to acetyl-CoA by malonyl CoA decarboxylase. Increased hypothalamic malonyl CoA is an indicator of energy surplus, resulting in a decrease in food intake and an increase in energy expenditure. In contrast, a decrease in hypothalamic malonyl CoA signals an energy deficit, resulting in an increased appetite and a decrease in body energy expenditure. A number of hormonal and neural orexigenic and anorexigenic signaling pathways have now been shown to be associated with changes in malonyl CoA levels in the arcuate nucleus (ARC) of the hypothalamus. Despite compelling evidence that malonyl CoA is an important mediator in the hypothalamic ARC control of food intake and regulation of energy balance, the mechanism(s) by which this occurs has not been established. Malonyl CoA inhibits carnitine palmitoyltransferase-1 (CPT-1), and it has been proposed that the substrate of CPT-1, long-chain acyl CoA(s), may act as a mediator(s) of appetite and energy balance. However, recent evidence has challenged the role of long-chain acyl CoA(s) in this process, as well as the involvement of CPT-1 in hypothalamic malonyl CoA signaling. A better understanding of how malonyl CoA regulates energy balance should provide novel approaches to targeting intermediary metabolism in the hypothalamus as a mechanism to control appetite and body weight. Here, we review the data supporting an important role for malonyl CoA in mediating hypothalamic control of energy balance, and recent evidence suggesting that targeting malonyl CoA synthesis or degradation may be a novel approach to favorably modify appetite and weight gain.

Targeting fatty acid and carbohydrate oxidation--a novel therapeutic intervention in the ischemic and failing heart.

Cardiac ischemia and its consequences including heart failure, which itself has emerged as the leading cause of morbidity and mortality in developed countries are accompanied by complex alterations in myocardial energy substrate metabolism. In contrast to the normal heart, where fatty acid and glucose metabolism are tightly regulated, the dynamic relationship between fatty acid ß-oxidation and glucose oxidation is perturbed in ischemic and ischemic-reperfused hearts, as well as in the failing heart. These metabolic alterations negatively impact both cardiac efficiency and function. Specifically there is an increased reliance on glycolysis during ischemia and fatty acid ß-oxidation during reperfusion following ischemia as sources of adenosine triphosphate (ATP) production. Depending on the severity of heart failure, the contribution of overall myocardial oxidative metabolism (fatty acid ß-oxidation and glucose oxidation) to adenosine triphosphate production can be depressed, while that of glycolysis can be increased. Nonetheless, the balance between fatty acid ß-oxidation and glucose oxidation is amenable to pharmacological intervention at multiple levels of each metabolic pathway. This review will focus on the pathways of cardiac fatty acid and glucose metabolism, and the metabolic phenotypes of ischemic and ischemic/reperfused hearts, as well as the metabolic phenotype of the failing heart. Furthermore, as energy substrate metabolism has emerged as a novel therapeutic intervention in these cardiac pathologies, this review will describe the mechanistic bases and rationale for the use of pharmacological agents that modify energy substrate metabolism to improve cardiac function in the ischemic and failing heart. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.

Cardiac hypertrophy in the newborn delays the maturation of fatty acid ß-oxidation and compromises postischemic functional recovery.

During the neonatal period, cardiac energy metabolism progresses from a fetal glycolytic profile towards one more dependent on mitochondrial oxidative metabolism. In this study, we identified the effects of cardiac hypertrophy on neonatal cardiac metabolic maturation and its impact on neonatal postischemic functional recovery. Seven-day-old rabbits were subjected to either a sham or a surgical procedure to induce a left-to-right shunt via an aortocaval fistula to cause RV volume-overload. At 3 wk of age, hearts were isolated from both groups and perfused as isolated, biventricular preparations to assess cardiac energy metabolism. Volume-overload resulted in cardiac hypertrophy (16% increase in cardiac mass, P < 0.05) without evidence of cardiac dysfunction in vivo or in vitro. Fatty acid oxidation rates were 60% lower (P < 0.05) in hypertrophied hearts than controls, whereas glycolysis increased 246% (P < 0.05). In contrast, glucose and lactate oxidation rates were unchanged. Overall ATP production rates were significantly lower in hypertrophied hearts, resulting in increased AMP-to-ATP ratios in both aerobic hearts and ischemia-reperfused hearts. The lowered energy generation of hypertrophied hearts depressed functional recovery from ischemia. Decreased fatty acid oxidation rates were accompanied by increased malonyl-CoA levels due to decreased malonyl-CoA decarboxylase activity/expression. Increased glycolysis in hypertrophied hearts was accompanied by a significant increase in hypoxia-inducible factor-1α expression, a key transcriptional regulator of glycolysis. Cardiac hypertrophy in the neonatal heart results in a reemergence of the fetal metabolic profile, which compromises ATP production in the rapidly maturing heart and impairs recovery of function following ischemia.

Isoproterenol stimulates 5'-AMP-activated protein kinase and fatty acid oxidation in neonatal hearts.

Isoproterenol increases phosphorylation of LKB, 5'-AMP-activated protein kinase (AMPK), and acetyl-CoA carboxylase (ACC), enzymes involved in regulating fatty acid oxidation. However, inotropic stimulation selectively increases glucose oxidation in adult hearts. In the neonatal heart, fatty acid oxidation becomes a major energy source, while glucose oxidation remains low. This study tested the hypothesis that increased energy demand imposed by isoproterenol originates from fatty acid oxidation, secondary to increased LKB, AMPK, and ACC phosphorylation. Isolated working hearts from 7-day-old rabbits were perfused with Krebs solution (0.4 mM palmitate, 11 mM glucose, 0.5 mM lactate, and 100 mU/l insulin) with or without isoproterenol (300 nM). Isoproterenol increased myocardial O(2) consumption (in J·g dry wt(-1)·min(-1); 11.0 ± 1.4, n = 8 vs. 7.5 ± 0.8, n = 6, P < 0.05), and the phosphorylation of LKB (in arbitrary density units; 0.87 ± 0.09, n = 6 vs. 0.59 ± 0.08, n = 6, P < 0.05), AMPK (0.82 ± 0.08, n = 6 vs. 0.51 ± 0.06, n = 6, P < 0.05), and ACC-ß (1.47 ± 0.14, n = 6 vs. 0.97 ± 0.07, n = 6, P < 0.05), with a concomitant decrease in malonyl-CoA levels (in nmol/g dry wt; 0.9 ± 0.9, n = 8 vs. 7.5 ± 1.3, n = 8, P < 0.05) and increase in palmitate oxidation (in nmol·g dry wt(-1)·min(-1); 272 ± 45, n = 8 vs. 114 ± 9, n = 6, P < 0.05). Glucose and lactate oxidation were increased (in nmol·g dry wt(-1)·min(-1); 253 ± 75, n = 8 vs. 63 ± 15, n = 9, P < 0.05 and 246 ± 43, n = 8 vs. 82 ± 11, n = 6, P < 0.05, respectively), independent of alterations in pyruvate dehydrogenase phosphorylation, but occurred secondary to a decrease in acetyl-CoA content and acetyl-CoA-to-free CoA ratio. As acetyl-CoA levels decrease in response to isoproterenol, despite an acceleration of the rates of palmitate and carbohydrate oxidation, these data suggest net rates of acetyl-CoA utilization exceed the net rates of acetyl-CoA generation.

High levels of fatty acids increase contractile function of neonatal rabbit hearts during reperfusion following ischemia.

In the neonatal heart the transition from using carbohydrates to using fatty acids has not fully matured and oxidative metabolism/ATP generation may be limiting contractile function after ischemia. This study tested the hypothesis that increasing fatty acid availability increases recovery of left ventricular (LV) work by increasing palmitate oxidation, tricarboxylic acid (TCA) cycle activity, and ATP generation. Isolated working hearts from 7-day-old rabbits were perfused with Krebs solution containing low (0.4 mM) or high (2.4 mM) palmitate and 5.5 mM glucose. Hearts were subjected to 35-min global ischemia before 40-min reperfusion, and rates of glycolysis, glucose oxidation, and palmitate oxidation were assessed. LV work was similar before ischemia but was greater during reperfusion in hearts perfused with 2.4 mM palmitate compared with hearts perfused with 0.4 mM palmitate [6.98 +/- 0.14 (n = 15) vs. 3.01 +/- 0.23 (n = 16) mJ.beat(-1).g dry wt(-1); P < 0.05]. This was accompanied by increased LV energy expenditure during reperfusion [35.98 +/- 0.16 (n = 8) vs. 19.92 +/- 0.18 (n = 6) mJ.beat(-1).g dry wt(-1); P < 0.05]. During reperfusion the rates of palmitate oxidation [237.5 +/- 28.10 (n = 7) vs. 86.0 +/- 9.7 (n = 6) nmol.g dry wt(-1).min(-1); P < 0.05], total TCA cycle activity [2.65 +/- 0.39 (n = 7) vs. 1.36 +/- 0.14 (n = 6) micromol acetyl-CoA.g dry wt(-1).min(-1); P < 0.05], and ATP generation attributable to palmitate oxidation [26.6 +/- 3.1 (n = 7) vs. 12.6 +/- 1.7 (n = 6) micromol.g dry wt(-1).min(-1); P < 0.05] were greater in hearts perfused with 2.4 mM palmitate. These data indicate that the neonatal heart has decreased energy reserve, and, in contrast to the mature heart, increasing availability of fatty acid substrate increases energy production and improves recovery of function after ischemia.

Energy metabolic phenotype of the cardiomyocyte during development, differentiation, and postnatal maturation.

Dramatic maturational changes occur in cardiac energy metabolism during cardiac development, differentiation, and postnatal growth. These changes in energy metabolism have important impacts on the ability of the cardiomyocyte to proliferate during early cardiac development, as well as when cardiomyocytes terminally differentiate during later development. During early cardiac development, glycolysis is a major source of energy for proliferating cardiomyocytes. As cardiomyocytes mature and become terminally differentiated, mitochondrial oxidative capacity increases, with fatty acid beta-oxidation becoming a major source of energy for the heart. The increase in mitochondrial oxidative capacity seems to coincide with a decrease in the proliferative ability of the cardiomyocyte. The switch from glycolysis to mitochondrial oxidative metabolism during cardiac development includes both alterations in the transcriptional control and acute alterations in the control of each pathway. Interestingly, if a hypertrophic stress is placed on the adult heart, cardiac energy metabolism switches to a more fetal phenotype, which includes an increase in glycolysis and decrease in mitochondrial fatty acid beta-oxidation. In this article, we review the impact of alterations in energy substrate metabolism on cardiomyocyte proliferation, differentiation, and postnatal maturation.

Role of the atypical protein kinase Czeta in regulation of 5'-AMP-activated protein kinase in cardiac and skeletal muscle.

During metabolic stress, phosphorylation and activation of 5'-AMP-activated protein kinase (AMPK) becomes a major regulator of cellular energy metabolism in heart and skeletal muscle. Despite this, the upstream regulation of AMPK in both heart and muscle is poorly understood. Recent work has implicated the atypical protein kinase Czeta (PKCzeta) as a regulator of AMPK in endothelial cells via phosphorylation of LKB1, an upstream AMPK kinase (AMPKK). Our goal was to determine the potential role PKCzeta plays in regulating AMPK in cardiac and skeletal muscle. Cultures of H9c2 myocytes (cardiac) and C(2)C(12) myotubes (skeletal muscle) were pretreated with a selective PKCzeta pseudosubstrate peptide inhibitor and treated with various AMPK activating agents to determine whether PKCzeta regulates AMPK. PKCzeta activity was also examined in isolated working rat hearts subjected to ischemia. We show that PKCzeta is not involved in regulating threonine 172 AMPK phosphorylation induced by metformin or phenformin in either cardiac or skeletal muscle cells but is involved in 5-aminoimidazole-4-carboxamine-1-beta-D-ribofuranoside (AICAR)-induced AMPK phosphorylation in cardiac muscle cells. Activation of PKCzeta with high palmitate concentrations is also insufficient to increase AMPK phosphorylation. Furthermore, we show that the ischemia-induced activation of AMPK is not accompanied by increased PKCzeta activity. Finally, we show that PKCzeta may actually be a downstream target of AMPK in skeletal muscle, since adenoviral expression of a dominant-negative mutant of AMPK prevented metformin- and AICAR-induced phosphorylation of PKCzeta. We conclude that PKCzeta plays a very minor role in the regulation of AMPK in cardiac and skeletal muscle and may actually be a downstream target of AMPK in skeletal muscle.

Myocardial hypertrophy and the maturation of fatty acid oxidation in the newborn human heart.

After birth dramatic decreases in cardiac malonyl CoA levels result in the rapid maturation of fatty acid oxidation. We have previously demonstrated that the decrease in malonyl CoA is due to increased activity of malonyl CoA decarboxylase (MCD), and decreased activity of acetyl CoA carboxylase (ACC), enzymes which degrade and synthesize malonyl CoA, respectively. Decreased ACC activity corresponds to an increase in the activity of 5'-AMP activated protein kinase (AMPK), which phosphorylates and inhibits ACC. These alterations are delayed by myocardial hypertrophy. As rates of fatty acid oxidation can influence the ability of the heart to withstand an ischemic insult, we examined the expression of MCD, ACC, and AMPK in the newborn human heart. Ventricular biopsies were obtained from infants undergoing cardiac surgery. Immunoblot analysis showed a positive correlation between MCD expression and age. In contrast, a negative correlation in both ACC and AMPK expression and age was observed. All ventricular samples displayed some degree of hypertrophy, however, no differences in enzyme expression were found between moderate and severe hypertrophy. This indicates that increased expression of MCD, and the decreased expression of ACC and AMPK are important regulators of the maturation of fatty acid oxidation in the newborn human heart.

Genetic and Pharmacological Inhibition of Malonyl CoA Decarboxylase Does Not Exacerbate Age-Related Insulin Resistance in Mice.

Aging is associated with the development of chronic diseases such as insulin resistance and type 2 diabetes. A reduction in mitochondrial fat oxidation is postulated to be a key factor contributing to the progression of these diseases. Our aim was to investigate the contribution of impaired mitochondrial fat oxidation toward age-related disease. Mice deficient for malonyl CoA decarboxylase (MCD(-/-)), a mouse model of reduced fat oxidation, were allowed to age while life span and a number of physiological parameters (glucose tolerance, insulin tolerance, indirect calorimetry) were assessed. Decreased fat oxidation in MCD(-/-) mice resulted in the accumulation of lipid intermediates in peripheral tissues, but this was not associated with a worsening of age-associated insulin resistance and, conversely, improved longevity. This improvement was associated with reduced oxidative stress and reduced acetylation of the antioxidant enzyme superoxide dismutase 2 in muscle but not the liver of MCD(-/-) mice. These findings were recapitulated in aged mice treated with an MCD inhibitor (CBM-3001106), and these mice also demonstrated improvements in glucose and insulin tolerance. Therefore, our results demonstrate that in addition to decreasing fat oxidation, MCD inhibition also has novel effects on protein acetylation. These combined effects protect against age-related metabolic dysfunction, demonstrating that MCD inhibitors may have utility in the battle against chronic disease in the elderly.

Effect of fatty acids on human bone marrow mesenchymal stem cell energy metabolism and survival.

Successful stem cell therapy requires the optimal proliferation, engraftment, and differentiation of stem cells into the desired cell lineage of tissues. However, stem cell therapy clinical trials to date have had limited success, suggesting that a better understanding of stem cell biology is needed. This includes a better understanding of stem cell energy metabolism because of the importance of energy metabolism in stem cell proliferation and differentiation. We report here the first direct evidence that human bone marrow mesenchymal stem cell (BMMSC) energy metabolism is highly glycolytic with low rates of mitochondrial oxidative metabolism. The contribution of glycolysis to ATP production is greater than 97% in undifferentiated BMMSCs, while glucose and fatty acid oxidation combined only contribute 3% of ATP production. We also assessed the effect of physiological levels of fatty acids on human BMMSC survival and energy metabolism. We found that the saturated fatty acid palmitate induces BMMSC apoptosis and decreases proliferation, an effect prevented by the unsaturated fatty acid oleate. Interestingly, chronic exposure of human BMMSCs to physiological levels of palmitate (for 24 hr) reduces palmitate oxidation rates. This decrease in palmitate oxidation is prevented by chronic exposure of the BMMSCs to oleate. These results suggest that reducing saturated fatty acid oxidation can decrease human BMMSC proliferation and cause cell death. These results also suggest that saturated fatty acids may be involved in the long-term impairment of BMMSC survival in vivo.

Lowering body weight in obese mice with diastolic heart failure improves cardiac insulin sensitivity and function: implications for the obesity paradox.

Recent studies suggest improved outcomes and survival in obese heart failure patients (i.e., the obesity paradox), although obesity and heart failure unfavorably alter cardiac function and metabolism. We investigated the effects of weight loss on cardiac function and metabolism in obese heart failure mice. Obesity and heart failure were induced by feeding mice a high-fat (HF) diet (60% kcal from fat) for 4 weeks, following which an abdominal aortic constriction (AAC) was produced. Four weeks post-AAC, mice were switched to a low-fat (LF) diet (12% kcal from fat; HF AAC LF) or maintained on an HF (HF AAC HF) for a further 10 weeks. After 18 weeks, HF AAC LF mice weighed less than HF AAC HF mice. Diastolic function was improved in HF AAC LF mice, while cardiac hypertrophy was decreased and accompanied by decreased SIRT1 expression, increased FOXO1 acetylation, and increased atrogin-1 expression compared with HF AAC HF mice. Insulin-stimulated glucose oxidation was increased in hearts from HF AAC LF mice, compared with HF AAC HF mice. Thus lowering body weight by switching to LF diet in obese mice with heart failure is associated with decreased cardiac hypertrophy and improvements in both cardiac insulin sensitivity and diastolic function, suggesting that weight loss does not negatively impact heart function in the setting of obesity.

Effects of inhibition of myocardial extracellular-responsive kinase and P38 mitogen-activated protein kinase on mechanical function of rat hearts after prolonged hypothermic ischemia.

BACKGROUND: Mitogen-activated protein kinases (MAPKs), including extracellular-responsive kinase (ERK) and p38 MAPK, are activated by stresses associated with hypothermia-rewarming and ischemia-reperfusion. Their activation in heart is associated with beneficial (preconditioning) and adverse effects (apoptosis and impaired contractility). This study determined whether ERK and p38 MAPK activities are altered by hypothermic ischemia and normothermic reperfusion and the consequences of their inhibition on recovery of myocardial function. METHODS: Left ventricular work (L x min(-1) x mm Hg) was assessed during normothermic perfusion (30 min) of isolated rat hearts that were either freshly excised or previously subjected to hypothermic storage (8 hr, 3 degrees C) and rewarming (10 min, 37 degrees C) before normothermic reperfusion (30 min). Phospho-specific immunoblot analysis of p38 MAPK was performed in hearts and various cultured cells. RESULTS: Compared with fresh hearts, hearts subjected to hypothermia and rewarming demonstrated impaired left ventricular work (1.96+/-0.53, n=12 vs. 8.37+/-0.46, n=4, <0.05) during reperfusion. The ERK inhibitor, PD98059 (20 microM), present during storage and rewarming, caused modest improvement (3.66+/-0.75, n=9, <0.05). The p38 MAPK inhibitor, SB202190 (10 microM), when present during reperfusion, improved recovery (to 6.12+/-0.75, n=6, <0.05); it was ineffective if present only during rewarming (1.52+/-0.88, n=4). In rat2 fibroblasts, hypothermia and rewarming activated p38 MAPK and its downstream kinase MAPK-activated protein kinase 2, but not c-Jun N-terminal kinase/stress-activated protein kinase. CONCLUSIONS: Myocardial p38 MAPK and MAPK-activated protein kinase 2 are stimulated by hypothermia, ischemia, and rewarming and are detrimental to recovery of mechanical function of hearts subjected to prolonged hypothermic storage. Inhibition of p38 MAPK may be useful in protocols to improve the recovery of mechanical function of cold-stored hearts.

Trimetazidine therapy prevents obesity-induced cardiomyopathy in mice.

Obesity is a significant risk factor for the development of cardiovascular disease. Inhibiting fatty acid oxidation has emerged as a novel approach for the treatment of ischemic heart disease. Our aim was to determine whether pharmacologic inhibition of 3-ketoacyl-coenzyme A thiolase (3-KAT), which catalyzes the final step of fatty acid oxidation, could improve obesity-induced cardiomyopathy. A 3-week treatment with the 3-KAT inhibitor trimetazidine prevented obesity-induced reduction in both systolic and diastolic function. Therefore, targeting cardiac fatty acid oxidation may be a novel therapeutic approach to alleviate the growing burden of obesity-related cardiomyopathy.

Failing mouse hearts utilize energy inefficiently and benefit from improved coupling of glycolysis and glucose oxidation.

AIMS: To determine whether post-infarction LV dysfunction is due to low energy availability or inefficient energy utilization, we compared energy metabolism in normal and failing hearts. We also studied whether improved coupling of glycolysis and glucose oxidation by knockout of malonyl CoA decarboxylase (MCD-KO) would have beneficial effects on LV function and efficiency. METHODS AND RESULTS: Male C57BL/6 mice were subjected to coronary artery ligation (CAL) or sham operation (SHAM) procedure. After 4 weeks and echocardiographic evaluation, hearts were perfused (working mode) to measure LV function and rates of energy metabolism. Similar protocols using MCD-KO mice and wild-type (WT) littermates were used to assess consequences of MCD deficiency. Relative to SHAM, CAL hearts had impaired LV function [lower % ejection fraction (%EF, 49%) and LV work (46%)]. CAL hearts had higher rates (expressed per LV work) of glycolysis, glucose oxidation, and proton production. LV work per ATP production from exogenous sources was lower in CAL hearts, indicative of inefficient exogenous energy substrate utilization. Fatty acid oxidation rates, ATP, creatine, and creatine phosphate contents were unaffected. Utilization of endogenous substrates, triacylglycerol and glycogen, was similar in CAL and SHAM hearts. MCD-KO CAL hearts had 31% higher %EF compared with that of WT-CAL, and lower rates of glycolysis, glucose oxidation, proton production, and ATP production, indicative of improved efficiency. CONCLUSION: CAL hearts are inefficient in utilizing energy for mechanical function, possibly due to higher proton production arising from mismatched glycolysis and glucose oxidation. MCD deficiency lessens proton production, LV dysfunction, and inefficiency of exogenous energy substrate utilization.

Obesity-induced lysine acetylation increases cardiac fatty acid oxidation and impairs insulin signalling.

AIMS: Lysine acetylation is a novel post-translational pathway that regulates the activities of enzymes involved in both fatty acid and glucose metabolism. We examined whether lysine acetylation controls heart glucose and fatty acid oxidation in high-fat diet (HFD) obese and SIRT3 knockout (KO) mice. METHODS AND RESULTS: C57BL/6 mice were placed on either a HFD (60% fat) or a low-fat diet (LFD; 4% fat) for 16 or 18 weeks. Cardiac fatty acid oxidation rates were significantly increased in HFD vs. LFD mice (845 ± 76 vs. 551 ± 87 nmol/g dry wt min, P < 0.05). Activities of the fatty acid oxidation enzymes, long-chain acyl-CoA dehydrogenase (LCAD), and ß-hydroxyacyl-CoA dehydrogenase (ß-HAD) were increased in hearts from HFD vs. LFD mice, and were associated with LCAD and ß-HAD hyperacetylation. Cardiac protein hyperacetylation in HFD-fed mice was associated with a decrease in SIRT3 expression, while expression of the mitochondrial acetylase, general control of amino acid synthesis 5 (GCN5)-like 1 (GCN5L1), did not change. Interestingly, SIRT3 deletion in mice also led to an increase in cardiac fatty acid oxidation compared with wild-type (WT) mice (422 ± 29 vs. 291 ± 17 nmol/g dry wt min, P < 0.05). Cardiac lysine acetylation was increased in SIRT3 KO mice compared with WT mice, including increased acetylation and activity of LCAD and ß-HAD. Although the HFD and SIRT3 deletion decreased glucose oxidation, pyruvate dehydrogenase acetylation was unaltered. However, the HFD did increase Akt acetylation, while decreasing its phosphorylation and activity. CONCLUSION: We conclude that increased cardiac fatty acid oxidation in response to high-fat feeding is controlled, in part, via the down-regulation of SIRT3 and concomitant increased acetylation of mitochondrial ß-oxidation enzymes.

Inhibition of carnitine palmitoyltransferase-1 activity alleviates insulin resistance in diet-induced obese mice.

Impaired skeletal muscle fatty acid oxidation has been suggested to contribute to insulin resistance and glucose intolerance. However, increasing muscle fatty acid oxidation may cause a reciprocal decrease in glucose oxidation, which might impair insulin sensitivity and glucose tolerance. We therefore investigated what effect inhibition of mitochondrial fatty acid uptake has on whole-body glucose tolerance and insulin sensitivity in obese insulin-resistant mice. C57BL/6 mice were fed a high-fat diet (60% calories from fat) for 12 weeks to develop insulin resistance. Subsequent treatment of mice for 4 weeks with the carnitine palmitoyltransferase-1 inhibitor, oxfenicine (150 mg/kg i.p. daily), resulted in improved whole-body glucose tolerance and insulin sensitivity. Exercise capacity was increased in oxfenicine-treated mice, which was accompanied by an increased respiratory exchange ratio. In the gastrocnemius muscle, oxfenicine increased pyruvate dehydrogenase activity, membrane GLUT4 content, and insulin-stimulated Akt phosphorylation. Intramyocellular levels of lipid intermediates, including ceramide, long-chain acyl CoA, and diacylglycerol, were also decreased. Our results demonstrate that inhibition of mitochondrial fatty acid uptake improves insulin sensitivity in diet-induced obese mice. This is associated with increased carbohydrate utilization and improved insulin signaling in the skeletal muscle, suggestive of an operating Randle Cycle in muscle.