Decrease In Fatty Acid Oxidation Research Articles

Low Levels of Lipopolysaccharide Modulate Mitochondrial Oxygen Consumption in Skeletal Muscle

ObjectiveWe have previously demonstrated that activation of toll-like receptor 4 (TLR4) in skeletal muscle results in an increased reliance on glucose as an energy source and a concomitant decrease in fatty acid oxidation under basal conditions. Herein, we examined the effects of lipopolysaccharide (LPS), the primary ligand for TLR4, on mitochondrial oxygen consumption in skeletal muscle cell culture and mitochondria isolated from rodent skeletal muscle. Materials/methodsSkeletal muscle cell cultures were exposed to LPS and oxygen consumption was assessed using a Seahorse Bioscience extracellular flux analyzer. Mice were also exposed to LPS and oxygen consumption was assessed in mitochondria isolated from skeletal muscle. ResultsAcute LPS exposure resulted in significant reductions in Carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP)-stimulated maximal respiration (state 3u) and increased oligomycin induced state 4 (state 4O) respiration in C2C12 and human primary myotubes. These findings were observed in conjunction with increased mRNA of uncoupling protein 3 (UCP3), superoxide dismutase 2 (SOD2), and pyruvate dehydrogenase activity. The LPS-mediated changes in substrate oxidation and maximal mitochondrial respiration were prevented in the presence of the antioxidants N-acetylcysteine and catalase, suggesting a potential role of reactive oxygen species in mediating these effects. Mitochondria isolated from red gastrocnemius and quadriceps femoris muscle from mice injected with LPS also demonstrated reduced respiratory control ratio (RCR), and ADP- and FCCP-stimulated respiration. ConclusionLPS exposure in skeletal muscle alters mitochondrial oxygen consumption and substrate preference, which is absent when antioxidants are present.

Abstract 12117: The Cardioprotection of Trimetazidine Against Ischemic Injury is Mediated by AMPK and ERK Signaling Pathway

Introduction: Trimetazidine (TMZ) is an anti-anginal drug that has been widely used in Europe and Asia. The TMZ can optimize energy metabolism via inhibition of long-chain 3-ketoacyl CoA thiolase (3-KAT) in the heart, with subsequent decrease in fatty acid oxidation and stimulation of glucose oxidation. However, the mechanism by which TMZ aids in cardioprotection against ischemic injury has not been characterized. Hypothesis: AMP-activated protein kinase (AMPK) is an energy sensor that control ATP supply from substrate metabolism and protect heart from energy stress. TMZ changes the cardiac AMP/ATP ratio via modulating fatty acid oxidation, thereby it may trigger AMPK signaling cascade that contribute to protection heart from ischemia/reperfusion (I/R) injury. Methods: The mouse in vivo regional ischemia and reperfusion by the ligation of the left anterior descending coronary artery (LAD) were used for determination of myocardial infarction. The infarct size was compared between C57BL/6J WT mice and AMPK kinase dead (KD) transgenic mice with or without TMZ treatment. The ex vivo working heart perfusion system was used to monitor the effect of TMZ on glucose oxidation and fatty acid oxidation in the heart. Results: TMZ treatment significantly stimulates cardiac AMPK and extracellular signal-regulated kinase (ERK) signaling pathways (p<0.05 vs. vehicle group). The administration of TMZ reduces myocardial infarction size in WT C57BL/6J hearts, the reduction of myocardial infarction size by TMZ in AMPK KD hearts was significantly impaired versus WT hearts (p<0.05). Intriguingly, the administration of ERK inhibitor, PD 98059, to AMPK KD mice abolished the cardioprotection of TMZ against I/R injury. The ex vivo working heart perfusion data demonstrated that TMZ treatment significantly activates AMPK signaling and modulating the substrate metabolism by shifting fatty acid oxidation to glucose oxidation during reperfusion, leading to reduction of oxidative stress in the I/R hearts. Conclusions: Both AMPK and ERK signaling pathways mediate the cardioprotection of TMZ against ischemic injury. The metabolic benefits of TMZ for angina patients could be due to the activation of energy sensor AMPK in the heart by TMZ administration.

Myostatin expression and high fat diet effects on skeletal muscle and adipose metabolism in mouse (1102.45)

We explored the effects of myostatin (Mst) expression and high fat diet (HFD) on skeletal muscle (SM) and adipose tissues (AT) metabolic profiles in transgenic mice overexpressing Mst (TG). To investigate the effects of Mst on SM and AT in wild‐type (WT) and TG mice, and the correlation between Mst and insulin resistance, we measured mRNA levels and protein expression of Mst, several intermediates from the insulin signaling pathway and analyzed the metabolic profile of both tissues using METABOLON. Methods: Adult male mice (6 mice/group) were kept on control diet (CD) and HFD for 4 weeks; glucose tolerance was measured before and after the diet; blood, SM and AT were collected. Results: Metabolon heat‐map analysis showed that Mst in TG mice on CD or HFD increased (95%; P<0.05) several glycolytic intermediates in SM suggesting that glycolysis and glucose uptake is elevated by Mst overexpression. TG mice on CD had lower (P>0.05) levels of free fatty acids (FFAs) compared to WT in SM and AT. HFD increased (25%) the levels of FFAs in SM compared to AT in WT and TG. Conclusion: WT‐SM responded to HFD with a rise (62%) in fatty acid oxidation (FAO); TG‐SM with HFD showed no change (P>0.05) in FAO. TG‐AT responded to HFD with a rise in triacylglycerol synthesis (12%) and a decrease in FAO. These data suggest that genetic modification of Mst expression affected primarily SM glucose utilization parallel with decreased FAO in AT in adult mice.Grant Funding Source: NIH/NIGMS: SC1GM089648

Abstract 18701: Activation of PPAR Delta Signaling Corrects Impaired Skeletal Muscle Oxidative Metabolism in Heart Failure

Background Exercise intolerance in heart failure (HF) has been linked to impaired skeletal muscle oxidative capacity. PPARδ signaling regulates oxidative metabolism and exercise capacity. We hypothesized that decreased skeletal muscle oxidative capacity in HF can be reverted by PPARδ agonists. Methods Left ventricular (LV) dysfunction was induced in C57BL/6 mice by left coronary artery ligature and confirmed by echocardiography. At 11 weeks post-MI, mice received the PPARδ agonist GW501516 (5 mg/kg body weight per day for 14 days, n=6) or vehicle (con, n=6). Exercise function was tested by swimming tests. Following sacrifice, skeletal muscle was harvested for RT-PCR, fatty acid (FA) and glucose oxidation assays, and ATP tissue content analysis. Cell culture analysis of signaling pathways was performed in C2C12 myotubes. Results Cardiac function decreased following MI (fractional shortening: 15.9±6.% vs 29.9±6.6% in sham; p<0.001). FA oxidation was reduced in quadriceps muscle in MI mice (2.5±1.0 vs 4.0±0.8 pmol/mg tissue in sham; p=0.04) with a trend in glucose oxidation (-27%; p=0.07). Muscle ATP content decreased following MI (3.3±1.7 vs 6.1±1.1 uM ATP/ug protein in sham; p<0.01). Expression of metabolic marker genes CPT1 (-86%), PDK4 (72%) and PGC1a (-94%) decreased in muscle post-MI (all p<0.05). 2 weeks GW501516 administration increased muscle FA oxidation in animals with LV dysfunction (3.9±1.6 vs 1.8±0.4 pmol oleic acid/mg tissue in con; p=0.04) and also increased CPT1 expression by 309±175% (p<0.001). There was a non-significant increase (+11%) in swimming duration in the GW501516 group. Treatment of C2C12 myotubes with 5 µM GW501516 protected from TNFα (25 ng/ml)-dependent decrease in FA oxidation (129.2±2.5 vs 237.8±6.8 pmol oleic acid/mg protein in TNFα+ GW501516 ; p<0.001) Further, GW501516 prevented TNFα -dependent decrease in CPT1 expression (255±39 vs 58±5 % in TNFα alone, p<0.01). Conclusion Treatment with the PPARδ agonist GW501516 corrects the impaired skeletal muscle oxidative capacity and metabolism in mice with ischemic LV dysfunction. Pharmacologic activation of PPARδ signaling could be an attractive intervention to counteract the progressive skeletal muscle dysfunction in HF.

Metabolic Remodeling in the Hypertrophic Heart

When it comes to fuel for energy production, it is commonly accepted that the heart is an omnivore, capable of oxidizing a wide range of carbon substrates, and that this metabolic plasticity is necessary to maintain a high and variable workload in the midst of an ever-changing hormonal and nutritional state.1 It is also widely appreciated that shifts in substrate utilization in the heart occur in response to chronic metabolic and hemodynamic stresses.2–5 What is less clear, however, is whether such chronic metabolic shifts should be considered a cause or consequence in the pathogenesis of contractile dysfunction. In the case of diabetes mellitus, the heart exhibits an increased dependence on fatty acids for oxidative energy production, and this increase in lipid metabolism has been proposed to significantly contribute to the etiology of impaired cardiac function.6 Similarly, increased rates of fatty acid oxidation immediately after an ischemic event have been implicated in exacerbation of reperfusion injury.7 However, in both of these pathophysiological settings, compelling data to support a direct causal relationship between contractile abnormalities and metabolic dysregulation remain elusive. Article, see p 728 In response to pressure overload–induced cardiac hypertrophy, the heart reverts more toward a fetal-like metabolic profile, indicative of a decrease in fatty acid oxidation (concomitant with an increased reliance on carbohydrates for oxidative energy metabolism).3 It has been suggested that this substrate shift, which is associated with reactivation of other fetal-like hallmarks (eg, myosin heavy chain isoform switching), contributes to the progression to overt contractile failure.8 Dietary, pharmacological, and genetic strategies have been used in attempts to provide insight regarding the impact that substrate shifts have on pressure overload–induced remodeling; however, mixed results have been reported. …

AMP‐activated protein kinase α2 is an essential signal in the regulation of insulin‐stimulated fatty acid uptake in control‐fed and high‐fat‐fed mice

Owing to its critical role in the regulation of skeletal muscle metabolism, AMP-activated protein kinase (AMPK) remains a central focus of research for the treatment of insulin resistance. The purpose of the present study was to determine the role of AMPKα2 activity in the regulation of glucose uptake and fatty acid (FA) metabolism in insulin-resistant skeletal muscle. Male C57BL/6 mice were divided into groups fed a control diet (CD) or high-fat (60%) diet (HFD) for 6 weeks and were either wild-type (WT) or possessed an AMPKα2 dominant negative transgene (DN). After 6 weeks, hindlimbs of CD (n = 10) and HFD mice (n = 10) were perfused with or without 450 μU ml(-1) insulin. Muscles of CD (n = 8) and HFD mice (n = 8) were used for measurement of basal protein expression. In CD mice, low AMPKα2 activity did not affect basal FA uptake (FAU), but it increased basal FA oxidation (FAO) by 28% and prevented the typical insulin-mediated increase in FAU and decrease in FAO. In HFD-fed mice, low AMPKα2 activity increased basal FAU by 147% (P < 0.05). In both WT and DN mice, HFD abolished the typical insulin-mediated increase in FAU and decrease in FAO. In HFD-fed mice, low AMPKα2 activity increased SIRT1 activity and decreased Protein Tyrosine Phosphatase 1B (PTP1B) expression and Akt(Thr308) phosphorylation (P < 0.05). Adipose tissue protein expression of interleukin-6 and tumour necrosis factor α was increased by HFD in WT mice but not in DN mice (P < 0.05). Skeletal muscle interleukin-15 expression was decreased in both feeding conditions in the DN mice (P < 0.05). The data from this study suggest that in insulin-resistant conditions low AMPKα2 activity impacts the regulation of skeletal muscle FA metabolism via changes in SIRT1 activity, PTP1B expression and Akt phosphorylation and the expression of adipose tissue pro-inflammatory markers.

Hepatic n-3 polyunsaturated fatty acid depletion promotes steatosis and insulin resistance in mice: genomic analysis of cellular targets.

Patients with non-alcoholic fatty liver disease are characterised by a decreased n-3/n-6 polyunsaturated fatty acid (PUFA) ratio in hepatic phospholipids. The metabolic consequences of n-3 PUFA depletion in the liver are poorly understood. We have reproduced a drastic drop in n-3 PUFA among hepatic phospholipids by feeding C57Bl/6J mice for 3 months with an n-3 PUFA depleted diet (DEF) versus a control diet (CT), which only differed in the PUFA content. DEF mice exhibited hepatic insulin resistance (assessed by euglycemic-hyperinsulinemic clamp) and steatosis that was associated with a decrease in fatty acid oxidation and occurred despite a higher capacity for triglyceride secretion. Microarray and qPCR analysis of the liver tissue revealed higher expression of all the enzymes involved in lipogenesis in DEF mice compared to CT mice, as well as increased expression and activation of sterol regulatory element binding protein-1c (SREBP-1c). Our data suggest that the activation of the liver X receptor pathway is involved in the overexpression of SREBP-1c, and this phenomenon cannot be attributed to insulin or to endoplasmic reticulum stress responses. In conclusion, n-3 PUFA depletion in liver phospholipids leads to activation of SREBP-1c and lipogenesis, which contributes to hepatic steatosis.

Myocardial infarction in rats causes partial impairment in insulin response associated with reduced fatty acid oxidation and mitochondrial gene expression

Myocardial infarction leads to contractile dysfunction. In patients with diabetes, impaired contractility has been associated with the loss of insulin effects and mitochondrial dysfunction. We assessed cardiac insulin sensitivity and mitochondrial and contractile function in rats after ligation of the left coronary artery. At 2 weeks after left coronary artery ligation, we performed echocardiography in vivo and assessed the substrate use and insulin response in the isolated working heart and the regulation of insulin (Akt, glucose transporter type 4) and mitochondrial signaling (p38 mitogen-activated protein kinase, peroxisome proliferator-activated receptor-γ coactivator 1α, mitochondrial transcription factor A) using polymerase chain reaction and Western blotting. The infarcted hearts were dilated and had a reduced ejection fraction (ejection fraction<50%). The basal glucose oxidation was preserved, but the fatty acid oxidation was significantly reduced. Insulin's effect on substrate oxidation was significantly impaired for both the decrease in fatty acid oxidation and the increase in glucose oxidation. However, insulin-stimulated glucose uptake was normal in the infarcted hearts, consistent with normal insulin-induced phosphorylation of Akt and unchanged mRNA expression of glucose transporter type 4. The impaired oxidative response to insulin was associated with reduced mRNA expression of the genes regulating fatty acid oxidation (long-chain-acyl-coenzyme A dehydrogenase, carnitine palmitoyltransferase 1, peroxisome proliferator-activated receptor-α) and mitochondrial biogenesis (mitochondrial transcription factor A). Although mRNA expression of the mitochondrial master regulator peroxisome proliferator-activated receptor-γ coactivator 1α was normal in the infarcted hearts, the protein expression of its post-transcriptional activator, p38 mitogen-activated protein kinase, was significantly reduced. Myocardial infarction in rats caused partial insulin resistance at the level of substrate oxidation, which was associated with mitochondrial and cardiac contractile dysfunction. Mitochondrial dysfunction was characterized by a reduced capacity to oxidize fatty acids and might have resulted from impaired mitochondrial biogenesis through the lack of p38 mitogen-activated protein kinase.

Adipose Acyl-CoA Synthetase-1 Directs Fatty Acids toward β-Oxidation and Is Required for Cold Thermogenesis

Long-chain acyl-CoA synthetase-1 (ACSL1) contributes 80% of total ACSL activity in adipose tissue and was believed to be essential for the synthesis of triacylglycerol. We predicted that an adipose-specific knockout of ACSL1 (Acsl1(A-/-)) would be lipodystrophic, but compared to controls, Acsl1(A-/-) mice had 30% greater fat mass when fed a low-fat diet and gained weight normally when fed a high-fat diet. Acsl1(A-/-) adipocytes incorporated [(14)C]oleate into glycerolipids normally, but fatty acid (FA) oxidation rates were 50%-90% lower than in control adipocytes and mitochondria. Acsl1(A-/-) mice were markedly cold intolerant, and beta(3)-adrenergic agonists did not increase oxygen consumption, despite normal adrenergic signaling in brown adipose tissue. The reduced adipose FA oxidation and marked cold intolerance of Acsl1(A-/-) mice indicate that normal activation of FA for oxidation in adipose tissue in vivo requires ACSL1. Thus, ACSL1 has a specific function in directing the metabolic partitioning of FAs toward beta-oxidation in adipocytes.

AMPKα2 deletion leads to marked alterations in SIRT1 activity, CPT1 expression and basal FA muscle metabolism in high‐fat‐fed mice

Because AMPKα2 is a critical signal in the regulation of muscle metabolism, we sought to determine if muscle AMPKα2 deletion would exacerbate the loss of insulin sensitivity, induced by high fat diet (HFD), as it pertains to the regulation of fatty acid (FA) metabolism. Male C57BL/6 mice (8–12 wks), wild‐type (WT) or dominant negative (DN) AMPKα2 in heart and skeletal muscle, were fed control diet (CD; 12%fat) or HFD (60%fat). After 6 wks, hindlimbs of CD (n=10) and HFD (n=10) mice were perfused (550μM palmitate, 6mM glucose, [1‐14C]palmitate) ±450μU insulin (IS). CD (n=8) and HFD (n=8) muscles were used for basal protein expression. In CD, AMPKα2 deletion did not affect basal FA uptake (FAU), but it increased basal FA oxidation (FAO) by 81% and α2 deletion prevented the IS increase in FAU and decrease in FAO. HFD abolished the IS increase in FAU and decrease in FAO in WT. In HFD, α2 deletion increased basal FAU by 139% (P&lt;0.05) but did not affect IS FAU nor FAO (P&gt;0.05). IS SIRT1 activity was higher in HFD‐DN than HFD‐WT (P&lt;0.05). Neither DN nor HFD affected PGC1α content. HFD increased (P&lt;0.05) PTP1b, SIRT1, and CD36 content and α2 deletion prevented the HFD‐induced increases in PTP1b and SIRT1. In HFD, α2 deletion decreased (P&lt;0.05) CPT1 content. These data show that AMPKα2 may be more critical for the regulation of FAU and FAO under basal than IS conditions and that it affects CPT1, PTP1b, and SIRT1 content and IS SIRT1 activity with HFD.

The Role of Interleukin 1 Receptor Associated Kinase 1 (IRAK1) in lipid metabolic alterations associated with endotoxemia

Both inflammatory and metabolic alterations have been established in the pathology of endotoxemia and septic shock, making treatment very difficult. The metabolic alterations associated with endotoxemia contribute to multiple organ failure (MOF) and high mortality rate in septic patients. However, the mechanism behind the shift in metabolism during lipopolysaccharide (LPS) ‐mediated endotoxemia has not been defined. In this study, we examine the role of Interleukin 1 receptor associated kinase 1 (IRAK1), a kinase downstream of the innate LPS receptor Toll‐like receptor 4 (TLR4), in the lipid metabolic alterations associated with LPS. We report a decrease in fatty acid oxidation (FAO) and an increase in plasma levels of free fatty acid (FFA) and triglyceride (TG) in WT but not IRAK1−/− mice injected with a lethal dose of LPS (25mg/kg). Mechanistically, we demonstrate that LPS suppresses FAO by decreasing the expression of mitochondrial β‐oxidation enzymes including carnitine palmitoyl transferase 1□ (CPT1□) and medium chain acyl dehydrogenase (MCAD), as well as pyruvate dehydrogenase kinase 4 (PDK4). Additionally, LPS suppressed the levels of nuclear receptors PPAR□ and PGC‐1□ in tissues from WT but not IRAK1−/− mice after lethal LPS injection. In conclusion, this study establishes that IRAK1 plays a novel role in the lipid metabolic alterations associated with TLR4 stimulation by LPS.Research funded by the NIH T32 Program, mentorship provided by Dr. Liwu Li, member of the ASBMB.

Infection decreases fatty acid oxidation and nuclear hormone receptors in the diaphragm

Respiratory failure is a major cause of mortality during septic shock and is due in part to decreased ventilatory muscle contraction. Ventilatory muscles have high energy demands; fatty acid (FA) oxidation is an important source of ATP. FA oxidation is regulated by nuclear hormone receptors; studies have shown that the expression of these receptors is decreased in liver, heart, and kidney during sepsis. Here, we demonstrate that lipopolysaccharide (LPS) decreases FA oxidation and the expression of lipoprotein lipase (LPL), FA transport protein 1 (FATP-1), CD36, carnitine palmitoyltransferase beta, medium chain acyl-CoA dehydrogenase (MCAD), and acyl-CoA synthetase, key proteins required for FA uptake and oxidation, in the diaphragm. LPS also decreased mRNA levels of PPARalpha and beta/delta, RXRalpha, beta, and gamma, thyroid hormone receptor alpha and beta, and estrogen related receptor alpha (ERRalpha) and their coactivators PGC-1alpha, PGC-1beta, SRC1, SRC2, Lipin 1, and CBP. Zymosan resulted in similar changes in the diaphragm. Finally, in PPARalpha deficient mice, baseline CPT-1beta and FATP-1 levels were markedly decreased and were not further reduced by LPS suggesting that a decrease in the PPARalpha signaling pathway plays an important role in inducing some of these changes. The decrease in FA oxidation in the diaphragm may be detrimental, leading to decreased diaphragm contraction and an increased risk of respiratory failure during sepsis.

Muscle acylcarnitines during short-term fasting in lean healthy men

The transition from the fed to the fasted resting state is characterized by, among other things, changes in lipid metabolism and peripheral insulin resistance. Acylcarnitines have been suggested to play a role in insulin resistance, as well as other long-chain fatty acid metabolites. Plasma levels of long-chain acylcarnitines increase during fasting, but this is unknown for muscle long-chain acylcarnitines. In the present study we investigated whether muscle long-chain acylcarnitines increase during fasting and we investigated their relationship with glucose/fat oxidation and insulin sensitivity in lean healthy humans. After 14 h and 62 h of fasting, glucose fluxes, substrate oxidation, and plasma and muscle acylcarnitines were measured before and during a hyperinsulinaemic-euglycaemic clamp. Hyperinsulinaemia decreased long-chain muscle acylcarnitines after 14 h of fasting, but not after 62 h of fasting. In both the basal state and during the clamp, glucose oxidation was lower and fatty acid oxidation was higher after 62 h compared with 14 h of fasting. Absolute changes in glucose and fatty acid oxidation in the basal compared with hyperinsulinaemic state were not different. Muscle long-chain acylcarnitines did not correlate with glucose oxidation, fatty acid oxidation or insulin-mediated peripheral glucose uptake. After 62 h of fasting, the suppression of muscle long-chain acylcarnitines by insulin was attenuated compared with 14 h of fasting. Muscle long-chain acylcarnitines do not unconditionally reflect fatty acid oxidation. The higher fatty acid oxidation during hyperinsulinaemia after 62 h compared with 14 h of fasting, although the absolute decrease in fatty acid oxidation was not different, suggests a different set point.

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.

Abstract 653: Muscle Ring Finger-1 (MuRF1) Expression Shifts Cardiomyocyte Substrate Utilization from Fatty Acids to Glucose

Previous work has suggested that MuRF1, a cardiac-specific protein, regulates metabolism by its interactions with proteins that regulate ATP transport, glycolysis, and the electron transport chain. We recently identified that MuRF1 is cardioprotective in ischemia reperfusion injury. In the current study, we investigated the effects of MuRF1 expression on metabolic substrate utilization and found that MuRF1 shifts substrate utilization from fatty acids to glucose in a dose-dependent manner. Isolated neonatal ventricular cardiomyocytes were treated with an adenovirus expressing MuRF1 (Ad.MuRF1) or GFP (Ad.GFP) at a range of 0–25 MOI (Multiplicity Of Infection). 14C-Oleate or 14C-glucose were added to cells for 1 hour and 14C-CO2 release was determined using the CO2-trapping method. Trapped 14CO2 and acid soluble metabolites were used to calculate total fatty acid oxidation. Cardiomyocytes treated with 5–25 MOI Ad.MuRF1 demonstrated a dose dependent decrease in fatty acid oxidation of 10.5 +/− 2.3(5 MOI), 8.5 +/− 1.9 (10 MOI), 6.6 +/− 1.6 (15 MOI), and 5.1 +/− 1.3 (25 MOI) nmol oleate/mg protein/h. Compared with control cardiomyocytes treated with 5–25 MOI Ad.GFP (average of 5–25 MOI=13.5 +/− 0.7 nmol oleate/mg protein/h), this represents a 22.2%– 62.2% decrease in fatty acid oxidation. Inversely, glucose oxidation increased with increasing MuRF1 expression. Cardiomyocytes infected with 25 MOI Ad.MuRF1 oxidized 184% more glucose (28.9 +/− 4.6 nmol glucose/mg protein/h) compared to control cells treated with 25 MOI Ad.GFP (15.7 +/− 1.3 nmol glucose/mg protein/h). Increasing MuRF1 expression resulted in no net gain or loss of calculated ATP production (1699 +/− 157 vs. 1480 +/− 188 nmol ATP/mg protein/h). The co-utilization of glucose and fatty acids as substrates for the production of ATP allows the heart to adapt to both environmental stress and disease. Increasing the relative proportion of glucose oxidation in relationship to fatty acids is a known protective mechanism during cardiac stress, and may represent one mechanism by which MuRF1 is cardioprotective.

On substrate selection for ATP synthesis in the failing human myocardium

the heart is an omnivore, able to oxidize a variety of substrates to support ATP synthesis: fatty acids, glucose, lactate, and even some amino acids ([Fig. 1][1]). Substrate selection is a highly dynamic process. For example, the uptake and utilization of substrates change from being primarily

Lipids and the Heart

The role of serum lipids in cardiovascular disease risk is well established, and reduction of serum lipid levels is now a cornerstone in the treatment of coronary artery disease. Dysregulation of lipid metabolism is also thought to play a role in the development of heart failure, although the mechanisms behind this are incompletely understood.1 Under normal conditions, the heart is primarily dependent on energy production derived from the β-oxidation of fatty acids and, to a lesser extent, glycolysis. However, in heart failure, fatty acid use seems to be reduced.2 The decrease in fatty acid oxidation and subsequent reduction in energy availability have been proposed to contribute to decreased contractile function of the heart. On the other hand, there is growing evidence that overaccumulation of fatty acid or triglyceride in the heart may be directly toxic to the myocyte, contributing to a process called cardiac lipotoxicity.1 Because the heart depends on fatty acid oxidation for energy, the transport and storage of lipids in the myocyte are tightly regulated. Although precise quantification of lipid levels within the myocyte is technically difficult, triglyceride and free fatty acid levels are thought to be low under normal physiological conditions. As noted above, there is evidence to suggest that exaggerated accumulation of triglyceride or free fatty acid within the myocyte is linked to the development of cardiomyopathy (ie, cardiac lipotoxicity). In diabetic and obese …

Skeletal muscle mitochondrial FAT/CD36 content and palmitate oxidation are not decreased in obese women

A reduction in fatty acid oxidation has been associated with lipid accumulation and insulin resistance in the skeletal muscle of obese individuals. We examined whether this decrease in fatty acid oxidation was attributable to a reduction in muscle mitochondrial content and/or a dysfunction in fatty acid oxidation within mitochondria obtained from skeletal muscle of age-matched, lean [body mass index (BMI) = 23.3 +/- 0.7 kg/m2] and obese women (BMI = 37.6 +/- 2.2 kg/m2). The mitochondrial marker enzymes citrate synthase (-34%), beta-hydroxyacyl-CoA dehydrogenase (-17%), and cytochrome c oxidase (-32%) were reduced (P < 0.05) in obese participants, indicating that mitochondrial content was diminished. Obesity did not alter the ability of isolated mitochondria to oxidize palmitate; however, fatty acid oxidation was reduced at the whole muscle level by 28% (P < 0.05) in the obese. Mitochondrial fatty acid translocase (FAT/CD36) did not differ in lean and obese individuals, but mitochondrial FAT/CD36 was correlated with mitochondrial fatty acid oxidation (r = 0.67, P < 0.05). We conclude that the reduction in fatty acid oxidation in obese individuals is attributable to a decrease in mitochondrial content, not to an intrinsic defect in the mitochondria obtained from skeletal muscle of obese individuals. In addition, it appears that mitochondrial FAT/CD36 may be involved in regulating fatty acid oxidation in human skeletal muscle.

Decrease in fatty acid oxidation increases tolerance of the ageing heart to ischaemic injury

Decrease in fatty acid oxidation increases tolerance of the ageing heart to ischaemic injury

Ranolazine for the Treatment of Chronic Angina and Potential Use in Other Cardiovascular Conditions

Chronic angina, a condition that impairs quality of life and is associated with decreased life expectancy, affects &6.4 million Americans.1 Current therapies that reduce angina frequency and nitrate consumption and increase the threshold at which demand-induced myocardial ischemic symptoms become evident include drugs (nitrates, β-blockers, calcium antagonists), exercise conditioning, enhanced external counterpulsation, and coronary revascularization.1–3 Several new investigational drugs are being tested for the treatment of chronic angina.4–9 This review will focus on sustained-release ranolazine, a drug that reduces angina symptoms, with a mechanism of action different from that of currently available pharmacological therapies.8–29 Ranolazine was approved on January 27, 2006, in the United States for use in patients with chronic angina who continue to be symptomatic on β-blockers, calcium antagonists, or nitrates. Ranolazine ([(+) N -(2,6-dimethylphenyl)-4(2-hydroxy-3-(2-methoxyphenoxy)-propyl)-1-piperazine acetamide dihydrochloride]) is an active piperazine derivative that was patented in 1986 and is available in an oral and intravenous form (Figure 1). The immediate-release ranolazine (not in current use) had an average terminal elimination half-life ranging from 1.4 to 1.9 hours and a 10-fold peak/trough difference with dosing of 240 to 400 mg 3 times per day.19 Early studies with immediate-release ranolazine provided evidence of antiischemic/antianginal properties in patients with chronic angina without clinically significant changes in heart rate or blood pressure and are reviewed elsewhere.20–24 Unless otherwise stated, the remainder of this review refers to sustained-release ranolazine. Figure 1. Chemical structure and metabolism of ranolazine. Reprinted with permission from J Clin Pharmacol . 2005;45:422–433.17 Ranolazine (Ranexa; CV Therapeutics Inc, Palo Alto, Calif) is manufactured in a sustained-release form that has a prolonged absorption phase with maximal plasma concentrations (Cmax) typically seen 4 to 6 hours after administration. The average terminal elimination half-life is &7 hours after multiple dosing to steady state, and the …