Corresponding increase in long-chain acyl-CoA and acylcarnitine after exercise in muscle from VLCAD mice

Long-chain acylcarnitines accumulate in long-chain fatty acid oxidation defects, especially during periods of increased energy demand from fat. To test whether this increase in long-chain acylcarnitines in very long-chain acyl-CoA dehydrogenase (VLCAD(-/-)) knock-out mice correlates with acyl-CoA content, we subjected wild-type (WT) and VLCAD(-/-) mice to forced treadmill running and analyzed muscle long-chain acyl-CoA and acylcarnitine with tandem mass spectrometry (MS/MS) in the same tissues. After exercise, long-chain acyl-CoA displayed a significant increase in muscle from VLCAD(-/-) mice [C16:0-CoA, C18:2-CoA and C18:1-CoA in sedentary VLCAD(-/-): 5.95 +/- 0.33, 4.48 +/- 0.51, and 7.70 +/- 0.30 nmol x g(-1) wet weight, respectively; in exercised VLCAD(-/-): 8.71 +/- 0.42, 9.03 +/- 0.93, and 14.82 +/- 1.20 nmol x g(-1) wet weight, respectively (P < 0.05)]. Increase in acyl-CoA in VLCAD-deficient muscle was paralleled by a significant increase in the corresponding chain length acylcarnitine. Exercise resulted in significant lowering of the free carnitine pool in VLCAD(-/-) muscle. This is the first study demonstrating that acylcarnitines and acyl-CoA directly correlate and concomitantly increase after exercise in VLCAD-deficient muscle.     

Lipid oxidation is reduced in obese human skeletal muscle

The purpose of this study was to discern cellular mechanisms that contribute to the suppression of lipid oxidation in the skeletal muscle of obese individuals. Muscle was obtained from obese [body mass index (BMI), 38.3 +/- 3.1 kg/m(2)] and lean (BMI, 23.8 +/- 0.9 kg/m(2)) women, and fatty acid oxidation was studied by measuring (14)CO(2) production from (14)C-labeled fatty acids. Palmitate oxidation, which is at least partially dependent on carnitine palmitoyltransferase-1 (CPT-1) activity, was depressed (P < 0.05) by approximately 50% with obesity (6.8 +/- 2.2 vs. 13.7 +/- 1.4 nmole CO(2).g(-1).h(-1)). The CPT-1-independent event of palmitoyl carnitine oxidation was also depressed (P < 0.01) by approximately 45%. There were significant negative relationships (P < 0.05) for adiposity with palmitate (r = -0.76) and palmitoyl carnitine (r = -0.82) oxidation. Muscle CPT-1 and citrate synthase activity, an index of mitochondrial content, were also significantly (P < 0.05) reduced ( approximately 35%) with obesity. CPT-1 (r = -0.48) and citrate synthase (r = -0.65) activities were significantly (P < 0.05) related to adiposity. These data suggest that lesions at CPT-1 and post-CPT-1 events, such as mitochondrial content, contribute to the reduced reliance on fat oxidation evident in human skeletal muscle with obesity.     

Endothelial t-PA release is impaired in overweight and obese adults but can be improved with regular aerobic exercise

Endothelial release of tissue-type plasminogen activator (t-PA) regulates fibrinolysis and is considered to be a primary endogenous defense mechanism against thrombosis. Adiposity is associated with an increased risk of atherothrombotic events. We determined the influence of overweight and obesity on the capacity of the vascular endothelium to release t-PA and the effects of regular aerobic exercise on endothelial t-PA release in previously sedentary overweight and obese adults. First, we studied 66 sedentary adults: 28 normal-weight (BMI < 25 kg/m2); 22 overweight (BMI > or = 25 and < 30 kg/m2); and 16 obese (BMI > or = 30 kg/m2). Net endothelial t-PA release was determined in vivo in response to intrabrachial infusions of bradykinin (BK) and sodium nitroprusside. Second, we studied 17 overweight and obese adults who completed a 3-mo aerobic exercise intervention. Net release of t-PA in response to BK was approximately 45% lower (P < 0.01) in overweight (from 0.1 +/- 0.4 to 41.7 +/- 4.9 ng x 100 ml tissue(-1) x min(-1)) and obese (-0.1 +/- 0.6 to 47.7 +/- 5.2 ng x 100 ml tissue(-1) x min(-1)) compared with normal-weight (0.1 +/- 0.8 to 77.5 +/- 6.7 ng x 100 ml tissue(-1) x min(-1)) adults. There was no difference in t-PA release between the overweight and obese groups. Exercise training significantly increased t-PA release capacity in overweight and obese adults (from -0.3 +/- 0.5 to 37.1 +/- 4.9 ng x 100 ml tissue(-1) x min(-1) before training vs. 1.0 +/- 0.9 to 65.4 +/- 6.3 ng x 100 ml tissue(-1) x min(-1) after training) to levels comparable with those of their normal-weight peers. These results indicate that overweight and obesity are associated with profound endothelial fibrinolytic dysfunction. Importantly, however, regular aerobic exercise can increase the capacity of the endothelium to release t-PA in this at-risk population.     

Impaired plasma fatty acid oxidation in extremely obese women

Skeletal muscle from extremely obese individuals exhibits decreased lipid oxidation compared with muscle from lean controls. It is unknown whether this effect is observed in vivo or whether the phenotype is preserved after massive weight loss. The objective of this study was to compare free fatty acid (FFA) oxidation during rest and exercise in female subjects who were either lean [n = 7; body mass index (BMI) = 22.6 +/- 2.2 kg/m(2)] or extremely obese (n = 10; BMI = 40.8 +/- 5.4 kg/m(2)) or postgastric bypass patients who had lost >45 kg (weight reduced) (n = 6; BMI = 33.7 +/- 9.9 kg/m(2)) with the use of tracer ([(13)C]palmitate and [(14)C]acetate) methodology and indirect calorimetry. The lean group oxidized significantly more plasma FFA, as measured by percent fatty acid uptake oxidized, than the extremely obese or weight-reduced group during rest (66.6 +/- 14.9 vs. 41.5 +/- 16.4 vs. 39.9 +/- 15.3%) and exercise (86.3 +/- 11.9 vs. 56.3 +/- 22.1 vs. 57.3 +/- 20.3%, respectively). BMI significantly correlated with percent uptake oxidized during both rest (r = -0.455) and exercise (r = -0.459). In conclusion, extremely obese women and weight-reduced women both possess inherent defects in plasma FFA oxidation, which may play a role in massive weight gain and associated comorbidities.     

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.     

Long-chain acyl-CoA hydrolase in the brain

Summary. Long-chain acyl-CoA hydrolases are a group of enzymes that cleave acyl-CoAs into fatty acids and coenzyme A (CoA-SH). Because acyl-CoAs participate in numerous reactions encompassing lipid synthesis, energy metabolism and regulation, modulating intracellular levels of acyl-CoAs would affect cellular functions. Therefore, acyl-CoA synthetases have been intensively studied. In contrast, acyl-CoA hydrolases have been less investigated, especially in the brain despite the fact that its long-chain acyl-CoA hydrolyzing activity is much higher than that in any other organ in the body. However, recent studies have dissected the multiplicity of this class of enzymes on a genomic basis, and have allowed us to discuss their function. Here, we describe a cytosolic long-chain acyl-CoA hydrolase (referred to as BACH) that is constitutively expressed in the brain, comparing it with other acyl-CoA hydrolases found in peripheral organs that have a role in fatty acid oxidation.     

Mouse cardiac acyl coenzyme a synthetase 1 deficiency impairs Fatty Acid oxidation and induces cardiac hypertrophy

Long-chain acyl coenzyme A (acyl-CoA) synthetase isoform 1 (ACSL1) catalyzes the synthesis of acyl-CoA from long-chain fatty acids and contributes the majority of cardiac long-chain acyl-CoA synthetase activity. To understand its functional role in the heart, we studied mice lacking ACSL1 globally (Acsl1(T-/-)) and mice lacking ACSL1 in heart ventricles (Acsl1(H-/-)) at different times. Compared to littermate controls, heart ventricular ACSL activity in Acsl1(T-/-) mice was reduced more than 90%, acyl-CoA content was 65% lower, and long-chain acyl-carnitine content was 80 to 90% lower. The rate of [(14)C]palmitate oxidation in both heart homogenate and mitochondria was 90% lower than in the controls, and the maximal rates of [(14)C]pyruvate and [(14)C]glucose oxidation were each 20% higher. The mitochondrial area was 54% greater than in the controls with twice as much mitochondrial DNA, and the mRNA abundance of Pgc1α and Errα increased by 100% and 41%, respectively. Compared to the controls, Acsl1(T-/-) and Acsl1(H-/-) hearts were hypertrophied, and the phosphorylation of S6 kinase, a target of mammalian target of rapamycin (mTOR) kinase, increased 5-fold. Our data suggest that ACSL1 is required to synthesize the acyl-CoAs that are oxidized by the heart, and that without ACSL1, diminished fatty acid (FA) oxidation and compensatory catabolism of glucose and amino acids lead to mTOR activation and cardiac hypertrophy without lipid accumulation or immediate cardiac dysfunction.     

Excess body fat in men decreases plasma fatty acid availability and oxidation during endurance exercise

The effect of relative body fat mass on exercise-induced stimulation of lipolysis and fatty acid oxidation was evaluated in 15 untrained men (5 lean, 5 overweight, and 5 obese with body mass indexes of 21 +/- 1, 27 +/- 1, and 34 +/- 1 kg/m2, respectively, and %body fat ranging from 12 to 32%). Palmitate and glycerol kinetics and substrate oxidation were assessed during 90 min of cycling at 50% peak aerobic capacity (VO2 peak) by use of stable isotope-labeled tracer infusion and indirect calorimetry. An inverse relationship was found between %body fat and exercise-induced increase in glycerol appearance rate relative to fat mass (r2 = 0.74; P < 0.01). The increase in total fatty acid uptake during exercise [(micromol/kg fat-free mass) x 90 min] was approximately 50% smaller in obese (181 +/- 70; P < 0.05) and approximately 35% smaller in overweight (230 +/- 71; P < 0.05) than in lean (354 +/- 34) men. The percentage of total fatty acid oxidation derived from systemic plasma fatty acids decreased with increasing body fat, from 49 +/- 3% in lean to 39 +/- 4% in obese men (P < 0.05); conversely, the percentage of nonsystemic fatty acids, presumably derived from intramuscular and possibly plasma triglycerides, increased with increasing body fat (P < 0.05). We conclude that the lipolytic response to exercise decreases with increasing adiposity. The blunted increase in lipolytic rate in overweight and obese men compared with lean men limits the availability of plasma fatty acids as a fuel during exercise. However, the rate of total fat oxidation was similar in all groups because of a compensatory increase in the oxidation of nonsystemic fatty acids.     

Skeletal muscle lipid oxidation and obesity: influence of weight loss and exercise

Obesity is associated with a decrement in the ability of skeletal muscle to oxidize lipid. The purpose of this investigation was to determine whether clinical interventions (weight loss, exercise training) could reverse the impairment in fatty acid oxidation (FAO) evident in extremely obese individuals. FAO was assessed by incubating skeletal muscle homogenates with [1-(14)C]palmitate and measuring (14)CO(2) production. Weight loss was studied using both cross-sectional and longitudinal designs. Muscle FAO in extremely obese women who had lost weight (decrease in body mass of approximately 50 kg) was compared with extremely obese and lean individuals (BMI of 22.8 +/- 1.2, 50.7 +/- 3.9, and 36.5 +/- 3.5 kg/m(2) for lean, obese, and obese after weight loss, respectively). There was no difference in muscle FAO between the extremely obese and weight loss groups, and FAO was depressed (-45%; P < or = 0.05) compared with the lean subjects. Muscle FAO also did not change in extremely obese women (n = 8) before and 1 yr after a 55-kg weight loss. In contrast, 10 consecutive days of exercise training increased (P < or = 0.05) FAO in the skeletal muscle of lean (+1.7-fold), obese (+1.8-fold), and previously extremely obese subjects after weight loss (+2.6-fold). mRNA content for PDK4, CPT I, and PGC-1alpha corresponded with FAO in that there were no changes with weight loss and an increase with physical activity. These data indicate that a defect in the ability to oxidize lipid in skeletal muscle is evident with obesity, which is corrected with exercise training but persists after weight loss.     

Thiazolidinediones upregulate impaired fatty acid uptake in skeletal muscle of type 2 diabetic subjects

We examined the regulation of free fatty acid (FFA, palmitate) uptake into skeletal muscle cells of nondiabetic and type 2 diabetic subjects. Palmitate uptake included a protein-mediated component that was inhibited by phloretin. The protein-mediated component of uptake in muscle cells from type 2 diabetic subjects (78 +/- 13 nmol. mg protein-1. min-1) was reduced compared with that in nondiabetic muscle (150 +/- 17, P < 0.01). Acute insulin exposure caused a modest (16 +/- 5%, P < 0.025) but significant increase in protein-mediated uptake in nondiabetic muscle. There was no significant insulin effect in diabetic muscle (+19 +/- 19%, P = not significant). Chronic (4 day) treatment with a series of thiazolidinediones, troglitazone (Tgz), rosiglitazone (Rgz), and pioglitazone (Pio) increased FFA uptake. Only the phloretin-inhibitable component was increased by treatment, which normalized this activity in diabetic muscle cells. Under the same conditions, FFA oxidation was also increased by thiazolidinedione treatment. Increases in FFA uptake and oxidation were associated with upregulation of fatty acid translocase (FAT/CD36) expression. FAT/CD36 protein was increased by Tgz (90 +/- 22% over control), Rgz (146 +/- 42%), and Pio (111 +/- 37%, P < 0.05 for all 3) treatment. Tgz treatment had no effect on fatty acid transporter protein-1 and membrane-associated plasmalemmal fatty acid-binding protein mRNA expression. We conclude that FFA uptake into cultured muscle cells is, in part, protein mediated and acutely insulin responsive. The basal activity of FFA uptake is impaired in type 2 diabetes. In addition, chronic thiazolidinedione treatment increased FFA uptake and oxidation into cultured human skeletal muscle cells in concert with upregulation of FAT/CD36 expression. Increased FFA uptake and oxidation may contribute to lower circulating FFA levels and reduced insulin resistance in skeletal muscle of individuals with type 2 diabetes following thiazolidinedione treatment.     

Training-induced elevation in FABP(PM) is associated with increased palmitate use in contracting muscle.

To evaluate the effects of endurance training in rats on fatty acid metabolism, we measured the uptake and oxidation of palmitate in isolated rat hindquarters as well as the content of fatty acid-binding proteins in the plasma membranes (FABP(PM)) of red and white muscles from 16 trained (T) and 18 untrained (UT) rats. Hindquarters were perfused with 6 mM glucose, 1,800 microM palmitate, and [1-(14)C]palmitate at rest and during electrical stimulation (ES) for 25 min. FABP(PM) content was 43-226% higher in red than in white muscles and was increased by 55% in red muscles after training. A positive correlation was found to exist between succinate dehydrogenase activity and FABP(PM) content in muscle. Palmitate uptake increased by 64-73% from rest to ES in both T and UT and was 48-57% higher in T than UT both at rest (39.8 +/- 3.5 vs. 26.9 +/- 4. 4 nmol. min(-1). g(-1), T and UT, respectively) and during ES (69.0 +/- 6.1 vs. 43.9 +/- 4.4 nmol. min(-1). g(-1), T and UT, respectively). While the rats were resting, palmitate oxidation was not affected by training; palmitate oxidation during ES was higher in T than UT rats (14.8 +/- 1.3 vs. 9.3 +/- 1.9 nmol. min(-1). g(-1), T and UT, respectively). In conclusion, endurance training increases 1) plasma free fatty acid (FFA) uptake in resting and contracting perfused muscle, 2) plasma FFA oxidation in contracting perfused muscle, and 3) FABP(PM) content in red muscles. These results suggest that an increased number of these putative plasma membrane fatty acid transporters may be available in the trained muscle and may be implicated in the regulation of plasma FFA metabolism in skeletal muscle.     

Impaired fatty acid metabolism in type 2 diabetic skeletal muscle cells is reversed by PPARgamma agonists

The impact of type 2 diabetes on the ability of muscle to accumulate and dispose of fatty acids and triglycerides was evaluated in cultured muscle cells from nondiabetic (ND) and type 2 diabetic (T2D) subjects. In the presence of 5 microM palmitate, T2D muscle cells accumulated less lipid than ND cells (11.5 +/- 1.2 vs. 15.1 +/- 1.4 nmol/mg protein, P < 0.05). Chronic treatment (4 days) with the peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist troglitazone increased palmitate accumulation, normalizing uptake in T2D cells. There were no significant differences between groups with regard to the relative incorporation of palmitate into neutral lipid species. This distribution was also unaffected by troglitazone treatment. beta-Oxidation of both long-chain (palmitate) and medium-chain (octanoate) fatty acids in T2D muscle cells was reduced by approximately 40% compared with ND cells. Palmitate oxidation occurred primarily in mitochondrial ( approximately 40-50% of total) and peroxisomal (20-30%) compartments. The diabetes-related defect in palmitate oxidation was localized to the mitochondrial component. Both palmitate and octanoate oxidation were stimulated by a series of thiazolidinediones. Oxidation in T2D muscle cells was normalized after treatment. Troglitazone increased the mitochondrial component of palmitate oxidation. Skeletal muscle cells from T2D subjects express defects in free fatty acid metabolism that are retained in vitro, most importantly defects in beta-oxidation. These defects can be corrected by treatment with PPARgamma agonists. Augmentation of fatty acid disposal in skeletal muscle, potentially reducing intramyocellular triglyceride content, may represent one mechanism for the lipid-lowering and insulin-sensitizing effects of thiazolidinediones.     

Insulin fails to alter plasma LCFA metabolism in muscle perfused at similar glucose uptake

Insulin has been shown to alter long-chain fatty acid (LCFA) metabolism and malonyl-CoA production in muscle. However, these alterations may have been induced, in part, by the accompanying insulin-induced changes in glucose uptake. Thus, to determine the effects of insulin on LCFA metabolism independently of changes in glucose uptake, rat hindquarters were perfused with 600 microM palmitate and [1-(14)C]palmitate and with either 20 mM glucose and no insulin (G) or 6 mM glucose and 250 microU/ml of insulin (I). As dictated by our protocol, glucose uptake was not significantly different between the G and I groups (10.3 +/- 0.6 vs. 11.0 +/- 0.5 micromol x g(-1) x h(-1); P > 0.05). Total palmitate uptake and oxidation were not significantly different (P > 0.05) between the G (10.1 +/- 1.0 and 0.8 +/- 0.1 nmol x min(-1) x g(-1)) and I (10.2 +/- 0.6 and 1.1 +/- 0.2 nmol. min(-1) x g(-1)) groups. Preperfusion muscle triglyceride and malonyl-CoA levels were not significantly different between the G and I groups and did not change significantly during the perfusion (P > 0.05). Similarly, muscle triglyceride synthesis was not significantly different between groups (P > 0.05). These results demonstrate that the presence of insulin under conditions of similar glucose uptake does not alter LCFA metabolism and suggest that cellular mechanisms induced by carbohydrate availability, but independent of insulin, may be important in the regulation of muscle LCFA metabolism.     

Peroxisomal beta-oxidation of long-chain fatty acids possessing different extents of unsaturation.

Rates of peroxisomal beta-oxidation were measured as fatty acyl-CoA-dependent NAD+ reduction, by using solubilized peroxisomal fractions isolated from livers of rats treated with clofibrate. Medium- to long-chain saturated fatty acyl-CoA esters as well as long-chain polyunsaturated fatty acyl-CoA esters were used. Peroxisomal beta-oxidation shows optimal specificity towards long-chain polyunsaturated acyl-CoA esters. Eicosa-8,11,14-trienoyl-CoA, eicosa-11,14,17-trienoyl-CoA and docosa-7,10,13,16-tetraenoyl-CoA all gave Vmax. values of about 150% of that obtained with palmitoyl-CoA. The Km values obtained with these fatty acyl-CoA esters were 17 +/- 6, 13 +/- 4 and 22 +/- 3 microM respectively, which are in the same range as the value for palmitoyl-CoA (13.8 +/- 1 microM). Myristoyl-CoA gave the higher Vmax. (110% of the palmitoyl-CoA value) of the saturated fatty acyl-CoAs tested. Substrate inhibition was mostly observed with acyl-CoA esters giving Vmax. values higher than 50% of that given by palmitoyl-CoA.     

Plasma FFA utilization and fatty acid-binding protein content are diminished in type 2 diabetic muscle

In this study, we investigated the hypothesis that impairments in forearm skeletal muscle free fatty acid (FFA) metabolism are present in patients with type 2 diabetes both in the overnight fasted state and during beta-adrenergic stimulation. Eight obese subjects with type 2 diabetes and eight nonobese controls (Con) were studied using the forearm balance technique and indirect calorimetry during infusion of the stable isotope tracer [U-(13)C]palmitate after an overnight fast and during infusion of the nonselective beta-agonist isoprenaline (Iso, 20 ng. kg lean body mass(-1) x min(-1)). Additionally, activities of mitochondrial enzymes and of cytoplasmatic fatty acid-binding protein (FABP) were determined in biopsies from the vastus lateralis muscle. Both during fasting and Iso infusion, the tracer balance data showed that forearm muscle FFA uptake (Con vs. type 2: fast 449+/-69 vs. 258 +/-42 and Iso 715+/-129 vs. 398+/-70 nmol. 100 ml tissue(-1) x min(-1), P<0.05) and FFA release were lower in type 2 diabetes compared with Con. Also, the oxidation of plasma FFA by skeletal muscle was blunted during Iso infusion in type 2 diabetes (Con vs. type 2: Iso 446 +/- 274 vs. 16+/-70 nmol. 100 ml tissue(-1) x min(-1), P<0.05). The net forearm glycerol release was increased in type 2 diabetic subjects (P< 0.05), which points to an increased forearm lipolysis. Additionally, skeletal muscle cytoplasmatic FABP content and the activity of muscle oxidative enzymes were lowered in type 2 diabetes. We conclude that the uptake and oxidation of plasma FFA are impaired in the forearm muscles of type 2 diabetic subjects in the overnight fasted state with and without Iso stimulation.     

Overexpression of acyl-CoA synthetase-1 increases lipid deposition in hepatic (HepG2) cells and rodent liver in vivo

Accumulation of intracellular lipid in obesity is associated with metabolic disease in many tissues including liver. Storage of fatty acid as triglyceride (TG) requires the activation of fatty acids to long-chain acyl-CoAs (LC-CoA) by the enzyme acyl-CoA synthetase (ACSL). There are five known isoforms of ACSL (ACSL1, -3, -4, -5, -6), which vary in their tissue specificity and affinity for fatty acid substrates. To investigate the role of ACSL1 in the regulation of lipid metabolism, we used adenoviral-mediated gene transfer to overexpress ACSL1 in the human hepatoma cell-line HepG2 and in liver of rodents. Infection of HepG2 cells with the adenoviral construct AdACSL1 increased ACSL activity >10-fold compared with controls after 24 h. HepG2 cells overexpressing ACSL1 had a 40% higher triglyceride (TG) content (93 +/- 3 vs. 67 +/- 2 nmol/mg protein in controls, P < 0.05) after 24-h exposure to 1 mM oleate. Furthermore, ACSL1 overexpression produced a 60% increase in cellular LCA-CoA content (160 +/- 6 vs. 100 +/- 6 nmol/g protein in controls, P < 0.05) and increased [(14)C]oleate incorporation into TG without significantly altering fatty acid oxidation. In mice, AdACSL1 administration increased ACSL1 mRNA and protein more than fivefold over controls at 4 days postinfection. ACSL1 overexpression caused a twofold increase in TG content in mouse liver (39 +/- 4 vs. 20 +/- 2 mumol/g wet wt in controls, P < 0.05), and overexpression in rat liver increased [1-(14)C]palmitate clearance into liver TG. These in vitro and in vivo results suggest a pivotal role for ACSL1 in regulating TG synthesis in liver.     

Effect of endurance training on lipid metabolism in women: a potential role for PPARalpha in the metabolic response to training

Endurance training increases fatty acid oxidation (FAO) and skeletal muscle oxidative capacity. However, the source of the additional fat and the mechanisms for increasing FAO capacity in muscle are not clear. We measured whole body and regional lipolytic activity and whole body and plasma FAO in six lean women during 90 min of bicycling exercise (50% pretraining peak O(2) consumption) before and after 12 wk of endurance training. We also assessed skeletal muscle content of peroxisome proliferator-activated receptor-alpha (PPARalpha) and its target proteins that regulate FAO [medium-chain and very long chain acyl-CoA dehydrogenase (MCAD and VLCAD)]. Despite a 25% increase in whole body FAO during exercise after training (P < 0.05), training did not alter regional adipose tissue lipolysis (abdominal: 0.56 +/- 0.26 and 0.57 +/- 0.10 micromol x 100 g(-1) x min(-1); femoral: 0.13 +/- 0.07 and 0.09 +/- 0.02 micromol x 100 g(-1) x min(-1)), whole body palmitate rate of appearance in plasma (168 +/- 18 and 150 +/- 25 micromol/min), and plasma FAO (554 +/- 61 and 601 +/- 45 micromol/min). However, training doubled the levels of muscle PPARalpha, MCAD, and VLCAD. We conclude that training increases the use of nonplasma fatty acids and may enhance skeletal muscle oxidative capacity by PPARalpha regulation of gene expression.     

AMPK activation is not critical in the regulation of muscle FA uptake and oxidation during low-intensity muscle contraction

To determine the role of AMP-activated protein kinase (AMPK) activation on the regulation of fatty acid (FA) uptake and oxidation, we perfused rat hindquarters with 6 mM glucose, 10 microU/ml insulin, 550 microM palmitate, and [14C]palmitate during rest (R) or electrical stimulation (ES), inducing low-intensity (0.1 Hz) muscle contraction either with or without 2 mM 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR). AICAR treatment significantly increased glucose and FA uptake during R (P < 0.05) but had no effect on either variable during ES (P > 0.05). AICAR treatment significantly increased total FA oxidation (P < 0.05) during both R (0.38 +/- 0.11 vs. 0.89 +/- 0.1 nmol x min(-1) x g(-1)) and ES (0.73 +/- 0.11 vs. 2.01 +/- 0.1 nmol x min(-1) x g(-1)), which was paralleled in both conditions by a significant increase and significant decrease in AMPK and acetyl-CoA carboxylase (ACC) activity, respectively (P < 0.05). Low-intensity muscle contraction increased glucose uptake, FA uptake, and total FA oxidation (P < 0.05) despite no change in AMPK (950.5 +/- 35.9 vs. 1,067.7 +/- 58.8 nmol x min(-1) x g(-1)) or ACC (51.2 +/- 6.7 vs. 55.7 +/- 2.0 nmol x min(-1) x g(-1)) activity from R to ES (P > 0.05). When contraction and AICAR treatment were combined, the AICAR-induced increase in AMPK activity (34%) did not account for the synergistic increase in FA oxidation (175%) observed under similar conditions. These results suggest that while AMPK-dependent mechanisms may regulate FA uptake and FA oxidation at rest, AMPK-independent mechanisms predominate during low-intensity muscle contraction.