Insulin stimulation of glucose uptake fails to decrease palmitate oxidation in muscle if AMPK is activated

Fatty acid oxidation in muscle has been reported to be diminished when insulin and glucose levels are elevated. This study was designed to determine whether activation of AMP-activated protein kinase (AMPK) will prevent inhibitory effects of insulin and glucose on the rate of fatty acid oxidation. Rat hindlimbs were perfused with medium containing 0, 0.3, or 60 nM insulin with or without 2 mM 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR). Glucose uptake was stimulated four- to fivefold by inclusion of insulin in the medium. Insulin attenuated the increase in AMPK caused by AICAR both in perfused hindlimbs and in isolated epitrochlearis muscles. The activation constant for citrate activation of acetyl-CoA carboxylase (ACC) was significantly increased in response to AICAR, and the increase was slightly attenuated if insulin was present in the perfusion medium. Insulin stimulated an increase in malonyl-CoA content of the muscles in the absence of AICAR. Malonyl-CoA was decreased to approximately the same value in AICAR-perfused muscle, regardless of insulin concentration. Muscle glucose 6-phosphate and citrate were significantly increased in response to AICAR and insulin. The rate of palmitate oxidation tended to decrease in response to insulin and in the absence of AICAR. AICAR increased palmitate oxidation to approximately the same level regardless of the insulin concentration or the rate of glucose uptake into the muscle. The rate of palmitate oxidation showed a curvilinear relationship as a function of muscle malonyl-CoA content, with half-maximal inhibition at ∼0.6 nmol/g. We conclude that AMPK activation can prevent high rates of glucose uptake and glycolytic flux from inhibiting palmitate oxidation in predominantly fast-twitch muscle under these conditions.

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An explanation for decreased ketogenesis in the liver of the obese Zucker rat

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1989.257.4.r822 ◽

1989 ◽

Vol 257 (4) ◽

pp. R822-R828 ◽

Cited By ~ 2

Author(s):

M. J. Azain ◽

J. A. Ontko

Keyword(s):

Fatty Acid ◽

Fatty Acid Oxidation ◽

Rat Liver ◽

Intact Cell ◽

Zucker Rats ◽

Acid Oxidation ◽

Palmitate Oxidation ◽

Malonyl Coa ◽

Obese Zucker Rats ◽

Rat Livers

These studies were undertaken to further characterize and explain the differences in hepatic fatty acid metabolism between lean and obese Zucker rats. It was shown that the rate of palmitate or octanoate oxidation and the inhibition of palmitate oxidation by malonyl CoA in mitochondria isolated from lean and obese Zucker rats were similar. Cytochrome oxidase activity was similar in lean and obese rat livers. It was found that the addition of cytosol from the obese rat liver inhibited palmitate oxidation by 20-30% in mitochondria isolated from lean or obese rat livers and thus reproduced the conditions observed in the intact cell. Increased concentrations of metabolites such as malonyl CoA and glycerophosphate in the liver of the obese rat are likely contributors to this inhibitory effect. These results are extrapolated to the intact cell and suggest that decreased hepatic fatty acid oxidation in the obese rat can be accounted for by cytosolic influences on the mitochondria. The decreased rate of fatty acid oxidation observed in the intact hepatocyte or perfused liver cannot be explained by a defect in the capacity of mitochondria to oxidize substrate or by a decrease in mitochondrial number in the obese rat liver.

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AICA riboside increases AMP-activated protein kinase, fatty acid oxidation, and glucose uptake in rat muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1997.273.6.e1107 ◽

1997 ◽

Vol 273 (6) ◽

pp. E1107-E1112 ◽

Cited By ~ 226

Author(s):

G. F. Merrill ◽

E. J. Kurth ◽

D. G. Hardie ◽

W. W. Winder

Keyword(s):

Skeletal Muscle ◽

Fatty Acid ◽

Protein Kinase ◽

Glucose Uptake ◽

Fatty Acid Oxidation ◽

Fold Increase ◽

Acid Oxidation ◽

Acetyl Coa Carboxylase ◽

Malonyl Coa ◽

Amp Activated Protein Kinase

5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR) has previously been reported to be taken up into cells and phosphorylated to form ZMP, an analog of 5′-AMP. This study was designed to determine whether AICAR can activate AMP-activated protein kinase (AMPK) in skeletal muscle with consequent phosphorylation of acetyl-CoA carboxylase (ACC), decrease in malonyl-CoA, and increase in fatty acid oxidation. Rat hindlimbs were perfused with Krebs-Henseleit bicarbonate containing 4% bovine serum albumin, washed bovine red blood cells, 200 μU/ml insulin, and 10 mM glucose with or without AICAR (0.5–2.0 mM). Perfusion with medium containing AICAR was found to activate AMPK in skeletal muscle, inactivate ACC, and decrease malonyl-CoA. Hindlimbs perfused with 2 mM AICAR for 45 min exhibited a 2.8-fold increase in fatty acid oxidation and a significant increase in glucose uptake. No difference was observed in oxygen uptake in AICAR vs. control hindlimb. These results provide evidence that decreases in muscle content of malonyl-CoA can increase the rate of fatty acid oxidation.

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Regulation of fatty acid oxidation and glucose metabolism in rat soleus muscle: effects of AICAR

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.2001.281.2.e335 ◽

2001 ◽

Vol 281 (2) ◽

pp. E335-E340 ◽

Cited By ~ 58

Author(s):

Virendar K. Kaushik ◽

Martin E. Young ◽

David J. Dean ◽

Theodore G. Kurowski ◽

Asish K. Saha ◽

...

Keyword(s):

Fatty Acid ◽

Protein Kinase ◽

Glucose Uptake ◽

Fatty Acid Oxidation ◽

Glucose Oxidation ◽

Acid Oxidation ◽

Malonyl Coa ◽

Rat Soleus Muscle ◽

Amp Activated Protein Kinase ◽

Fasted Rats

Previous studies have shown that 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), a cell-permeable activator of AMP-activated protein kinase, increases the rate of fatty acid oxidation in skeletal muscle of fed rats. The present study investigated the mechanism by which this occurs and, in particular, whether changes in the activity of malonyl-CoA decarboxylase (MCD) and the β-isoform of acetyl-CoA carboxylase (ACCβ) are involved. In addition, the relationship between changes in fatty acid oxidation induced by AICAR and its effects on glucose uptake and metabolism was examined. In incubated soleus muscles isolated from fed rats, AICAR (2 mM) increased fatty acid oxidation (90%) and decreased ACCβ activity (40%) and malonyl-CoA concentration (50%); however, MCD activity was not significantly altered. In soleus muscles from overnight-fasted rats, AICAR decreased ACCβ activity (40%), as it did in fed rats; however, it had no effect on the already high rate of fatty acid oxidation or the low malonyl-CoA concentration. In keeping with its effect on fatty acid oxidation, AICAR decreased glucose oxidation by 44% in fed rats but did not decrease glucose oxidation in fasted rats. It had no effect on glucose oxidation when fatty acid oxidation was inhibited by 2-bromopalmitate. Surprisingly, AICAR did not significantly increase glucose uptake or assayable AMP-activated protein kinase activity in incubated soleus muscles from fed or fasted rats. These results indicate that, in incubated rat soleus muscle, 1) AICAR does not activate MCD or stimulate glucose uptake as it does in extensor digitorum longus and epitrochlearis muscles, 2) the ability of AICAR to increase fatty acid oxidation and diminish glucose oxidation and malonyl-CoA concentration is dependent on the nutritional status of the rat, and 3) the ability of AICAR to diminish assayable ACC activity is independent of nutritional state.

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Influence of malonyl-CoA and palmitate concentration on rate of palmitate oxidation in rat muscle

Journal of Applied Physiology ◽

10.1152/jappl.1998.85.5.1909 ◽

1998 ◽

Vol 85 (5) ◽

pp. 1909-1914 ◽

Cited By ~ 32

Author(s):

G. F. Merrill ◽

E. J. Kurth ◽

B. B. Rasmussen ◽

W. W. Winder

Keyword(s):

Skeletal Muscle ◽

Fatty Acid ◽

Protein Kinase ◽

Fatty Acid Oxidation ◽

Acid Oxidation ◽

Acetyl Coa Carboxylase ◽

Acetyl Coa ◽

Palmitate Oxidation ◽

Malonyl Coa ◽

Amp Activated Protein Kinase

5-Aminoimidazole-4-carboxamide 1-β-d-ribofuranoside (AICAR) is taken up by perfused skeletal muscle and phosphorylated to form 5-aminoimidazole-4-carboxamide-1-β-d-ribofuraosyl-5′-monophosphate (analog of 5′-AMP) with consequent activation of AMP-activated protein kinase, phosphorylation of acetyl-CoA carboxylase, decrease in malonyl-CoA, and increase in fatty acid oxidation. This study was designed to determine the effect of increasing levels of palmitate on the rate of fatty acid oxidation. Malonyl-CoA concentration was manipulated with AICAR at different palmitate concentrations. Rat hindlimbs were perfused with Krebs-Henseleit bicarbonate containing 4% bovine serum albumin, washed bovine red cells, 200 μU/ml insulin, 10 mM glucose, and different concentrations of palmitate (0.1–1.0 mM) without or with AICAR (2.0 mM). Perfusion with medium containing AICAR was found to activate AMP-activated protein kinase in skeletal muscle, inactivate acetyl-CoA carboxylase, and decrease malonyl-CoA at all concentrations of palmitate. The rate of palmitate oxidation increased as a function of palmitate concentration in both the presence and absence of AICAR but was always higher in the presence of AICAR. These results provide additional evidence that malonyl-CoA is an important regulator of the rate of fatty acid oxidation at palmitate concentrations in the physiological range.

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Flexibility of zonation of fatty acid oxidation in rat liver

Biochemical Journal ◽

10.1042/bj3110853 ◽

1995 ◽

Vol 311 (3) ◽

pp. 853-860 ◽

Cited By ~ 27

Author(s):

M Guzmán ◽

C Bijleveld ◽

M J H Geelen

Keyword(s):

Fatty Acid ◽

Fatty Acid Oxidation ◽

Carnitine Palmitoyltransferase ◽

Physiological Status ◽

Acid Oxidation ◽

Acetyl Coa Carboxylase ◽

Acetyl Coa ◽

Palmitate Oxidation ◽

Malonyl Coa ◽

Carnitine Palmitoyltransferase I

Periportal and perivenous hepatocytes were isolated from rats subjected to different treatments that induce (starvation, cold exposure) or depress (refeeding after starvation) hepatic fatty acid oxidation. These experiments were designed to determine factors that may be involved in creating and maintaining the asymmetrical distribution of this metabolic pathway in the acinus of the liver. The uneven distribution of mitochondrial [14C]-palmitate oxidation within the acinus (i) was very flexible and changed markedly with the physiological status of the animal (periportal/perivenous ratio: 1.5, 2.0, 1.0 and 0.4 for fed, starved, refed and cold-exposed animals respectively), (ii) coincided with a similar zonation of carnitine palmitoyltransferase I activity in fed as well as in cold-exposed animals, (iii) was paralleled by a comparable zonation of mitochondrial 3-hydroxy-3-methyl-glutaryl-CoA synthase activity in starved animals, and (iv) was not determined by zonal differences in any of the following parameters: sensitivity of carnitine palmitoyltransferase I to malonyl-CoA, intracellular concentration of malonyl-CoA, fatty acid synthesizing capacity, acetyl-CoA carboxylase activity, fatty acid synthase activity or relative content of the two hepatic acetyl-CoA carboxylase isoforms. Unlike mitochondrial oxidation, peroxisomal [14C]palmitate oxidation was always zonated towards the perivenous zone of the liver irrespective of the physiological status of the animal. The data presented show that changes in the acinar distribution of mitochondrial long-chain fatty acid oxidation involve specific long-term mechanisms under different physiological conditions.

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

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00949.2007 ◽

2008 ◽

Vol 294 (4) ◽

pp. H1609-H1620 ◽

Cited By ~ 33

Author(s):

Vijay Sharma ◽

Pavan Dhillon ◽

Richard Wambolt ◽

Hannah Parsons ◽

Roger Brownsey ◽

...

Keyword(s):

Fatty Acid ◽

Cardiac Function ◽

Fatty Acid Oxidation ◽

Heart Function ◽

Carnitine Palmitoyltransferase ◽

Acid Oxidation ◽

Protein Kinase Activity ◽

Palmitate Oxidation ◽

Malonyl Coa ◽

Carnitine Palmitoyltransferase I

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. β-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 Ca2+-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.

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