The glucose–fatty acid cycle: a physiological perspective

2003 ◽  
Vol 31 (6) ◽  
pp. 1115-1119 ◽  
Author(s):  
K.N. Frayn
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Glucose Utilization ◽  
Acid Oxidation ◽  
Acid Cycle ◽  
Glucose Fatty Acid Cycle ◽  
High Concentrations ◽  
Glucose Stimulated Insulin Secretion ◽  
Glucose Output ◽  
Carnitine Palmitoyltransferase 1

Glucose and fatty acids are the major fuels for mammalian metabolism and it is clearly essential that mechanisms exist for mutual co-ordination of their utilization. The glucose–fatty acid cycle, as it was proposed in 1963, describes one set of mechanisms by which carbohydrate and fat metabolism interact. Since that time, the importance of the glucose–fatty acid cycle has been confirmed repeatedly, in particular by elevation of plasma non-esterified fatty acid concentrations and demonstration of an impairment of glucose utilization. Since 1963 further means have been elucidated by which glucose and fatty acids interact. These include stimulation of hepatic glucose output by fatty acids, potentiation of glucose-stimulated insulin secretion by fatty acids, and the cellular mechanism whereby high glucose and insulin concentrations inhibit fatty acid oxidation via malonyl-CoA regulation of carnitine palmitoyltransferase-1. The last of these mechanisms, discovered by Denis McGarry and Daniel Foster in 1977, provides an almost exact complement to the mechanism described in the glucose–fatty acid cycle whereby high concentrations of fatty acids inhibit glucose utilization. These additional discoveries have not detracted from the important of the glucose–fatty acid cycle: rather, they have reinforced the importance of mechanisms whereby glucose and fat can interact.

scholarly journals GH replacement causing acute hyperglycaemia and ketonuria in a type 1 diabetic patient

2013 ◽  
Vol 2013 ◽  
Author(s):  
Dominic Cavlan ◽  
Shanti Vijayaraghavan ◽  
Susan Gelding ◽  
William Drake
Keyword(s):  
Insulin Resistance ◽  
Fatty Acids ◽  
Type 1 Diabetes ◽  
Fatty Acid ◽  
Diabetic Patient ◽  
Acid Cycle ◽  
Gh Replacement ◽  
Glucose Fatty Acid Cycle ◽  
Gh Excess

Summary A state of insulin resistance is common to the clinical conditions of both chronic growth hormone (GH) deficiency and GH excess (acromegaly). GH has a physiological role in glucose metabolism in the acute settings of fast and exercise and is the only anabolic hormone secreted in the fasting state. We report the case of a patient in whom knowledge of this aspect of GH physiology was vital to her care. A woman with well-controlled type 1 diabetes mellitus who developed hypopituitarism following the birth of her first child required GH replacement therapy. Hours after the first dose, she developed a rapid metabolic deterioration and awoke with hyperglycaemia and ketonuria. She adjusted her insulin dose accordingly, but the pattern was repeated with each subsequent increase in her dose. Acute GH-induced lipolysis results in an abundance of free fatty acids (FFA); these directly inhibit glucose uptake into muscle, and this can lead to hyperglycaemia. This glucose–fatty acid cycle was first described by Randle et al. in 1963; it is a nutrient-mediated fine control that allows oxidative muscle to switch between glucose and fatty acids as fuel, depending on their availability. We describe the mechanism in detail. Learning points There is a complex interplay between GH and insulin resistance: chronically, both GH excess and deficiency lead to insulin resistance, but there is also an acute mechanism that is less well appreciated by clinicians. GH activates hormone-sensitive lipase to release FFA into the circulation; these may inhibit the uptake of glucose leading to hyperglycaemia and ketosis in the type 1 diabetic patient. The Randle cycle, or glucose–fatty acid cycle, outlines the mechanism for this acute relationship. Monitoring the adequacy of GH replacement in patients with type 1 diabetes is difficult, with IGF1 an unreliable marker.

Effects of blockade of fatty acid oxidation on whole body and tissue-specific glucose metabolism in rats

1993 ◽  
Vol 265 (4) ◽  
pp. E592-E600 ◽  
Author(s):  
A. B. Jenkins ◽  
L. H. Storlien ◽  
G. J. Cooney ◽  
G. S. Denyer ◽  
I. D. Caterson ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Fatty Acid ◽  
Glucose Metabolism ◽  
Fatty Acid Oxidation ◽  
Pyruvate Dehydrogenase ◽  
Glucose Utilization ◽  
Whole Body ◽  
Acid Oxidation ◽  
Tissue Specific ◽  
Glucose Output

We examined the effect of the long-chain fatty acid oxidation blocker methyl palmoxirate (methyl 2-tetradecyloxiranecarboxylate, McN-3716) on glucose metabolism in conscious rats. Fasted animals [5 h with or without hyperinsulinemia (100 mU/l) and 24 h] received methyl palmoxirate (30 or 100 mg/kg body wt po) or vehicle 30 min before a euglycemic glucose clamp. Whole body and tissue-specific glucose metabolism were calculated from 2-deoxy-[3H]-glucose kinetics and accumulation. Oxidative metabolism was assessed by respiratory gas exchange in 24-h fasted animals. Pyruvate dehydrogenase complex activation was determined in selected tissues. Methyl palmoxirate suppressed whole body lipid oxidation by 40-50% in 24-h fasted animals, whereas carbohydrate oxidation was stimulated 8- to 10-fold. Whole body glucose utilization was not significantly affected by methyl palmoxirate under any conditions; hepatic glucose output was suppressed only in the predominantly gluconeogenic 24-h fasted animals. Methyl palmoxirate stimulated glucose uptake in heart in 24-h fasted animals [15 +/- 5 vs. 220 +/- 28 (SE) mumol x 100 g-1 x min-1], with smaller effects in 5-h fasted animals with or without hyperinsulinemia. Methyl palmoxirate induced significant activation of pyruvate dehydrogenase in heart in the basal state, but not during hyperinsulinemia. In skeletal muscles, methyl palmoxirate suppressed glucose utilization in the basal state but had no effect during hyperinsulinemia; pyruvate dehydrogenase activation in skeletal muscle was not affected by methyl palmoxirate under any conditions. The responses in skeletal muscle are consistent with the operation of a mechanism similar to the Pasteur effect.(ABSTRACT TRUNCATED AT 250 WORDS)

135. FATTY ACID OXIDATION IS ESSENTIAL FOR OOCYTE DEVELOPMENTAL COMPETENCE

2009 ◽  
Vol 21 (9) ◽  
pp. 54
Author(s):  
K. R. Dunning ◽  
K. Cashman ◽  
R. J. Norman ◽  
R. L. Robker
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Fatty Acid Oxidation ◽  
Oocyte Maturation ◽  
Dietary Fat ◽  
Fold Increase ◽  
Developmental Competence ◽  
Acid Oxidation ◽  
Oocyte Developmental Competence ◽  
Carnitine Palmitoyltransferase 1

Oocyte lipid composition and developmental competence are influenced by dietary fat yet whether lipids are metabolised by the oocyte or essential for subsequent embryo development is largely unexplored. Fatty acid oxidation (FAO) is largely overlooked as an energy source for the oocyte, despite generating several-fold more energy than glucose oxidation. FAO requires the rate-limiting enzyme carnitine palmitoyltransferase-1 (Cpt1) and the metabolite Carnitine to shuttle fatty acids into mitochondria for energy production. Analysis of Cpt1 mRNA during oocyte maturation showed that Cpt1 expression was hormonally induced (p<0.05) in the cumulus oocyte complex (COC), peaking at 10h following ovulatory hCG treatment. In contrast, Cpt1 was not hormonally regulated in granulosa cells (p>0.05). To investigate the role of Cpt1-mediated FAO during oocyte maturation we measured FAO in oocytes in the presence and absence of Carnitine and inhibited FAO to determine its importance for oocyte developmental competence. Levels of FAO in COCs were assessed as metabolism of the fatty acid 3H-palmitate. During oocyte maturation there was a 2.1-fold increase (p<0.0001) in FAO compared to immature COCs. Carnitine supplementation led to a further 3.7-fold increase (p<0.001), while inhibition of Cpt1 with Etomoxir resulted in a 6.5-fold decrease (p<0.0002) in FAO during oocyte maturation. FAO inhibition had no effect on cumulus expansion. However inhibition of FAO during oocyte maturation followed by IVF and embryo culture in the absence of inhibitor, resulted in significantly decreased numbers of embryos developing ‘on time' (p<0.002). This is the first identification of hormonal induction of Cpt1 and Cpt1 mediated FAO in the COC during oocyte maturation. Further, the results demonstrate that oxidation of fatty acids by the oocyte is essential for oocyte developmental competence and can be modulated by Carnitine. These findings provide a potential mechanism by which dietary fat, obesity or metabolic disorders including CPT deficiency lead to infertility.

Circulating lipids are lowered but pancreatic islet lipid metabolism and insulin secretion are unaltered in exercise-trained female rats

2007 ◽  
Vol 32 (2) ◽  
pp. 241-248 ◽  
Author(s):  
Julien Lamontagne ◽  
Pellegrino Masiello ◽  
Mariannick Marcil ◽  
Viviane Delghingaro-Augusto ◽  
Yan Burelle ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Insulin Secretion ◽  
Fatty Acid ◽  
Lipid Metabolism ◽  
Free Fatty Acids ◽  
Fatty Acid Oxidation ◽  
Female Rats ◽  
Acid Oxidation ◽  
Β Cell ◽  
Glucose Stimulated Insulin Secretion

Deteriorating islet β-cell function is key in the progression of an impaired glucose tolerance state to overt type 2 diabetes (T2D), a transition that can be delayed by exercise. We have previously shown that trained rats are protected from heart ischemia–reperfusion injury in correlation with an increase in cardiac tissue fatty-acid oxidation. This trained metabolic phenotype, if induced in the islet, could also prevent β-cell failure in the pathogenesis of T2D. To assess the effect of training on islet lipid metabolism and insulin secretion, female Sprague–Dawley rats were exercised on a treadmill for 90 min/d, 4 d/week, for 10 weeks. Islet fatty-acid oxidation, the expression of key lipid metabolism genes, and glucose-stimulated insulin secretion were determined in freshly isolated islets from trained and sedentary control rats after a 48 h rest period from the last exercise. Although this moderate training reduced plasma glycerol, free fatty acids, and triglyceride levels by about 40%, consistent with reduced lipolysis from adipose tissue, it did not alter islet fatty-acid oxidation, nor the islet expression of key transcription factors and enzymes of lipid metabolism. The training also had no effect on glucose-stimulated insulin secretion or its amplification by free fatty acids. In summary, chronic exercise training did not cause an intrinsic change in islet lipid metabolism. Training did, however, substantially reduce the exposure of islets to exogenous lipid, thereby providing a potential mechanism by which exercise can prevent islet β-cell failure leading to T2D.

scholarly journals Effects of pent-4-enoate on cellular redox state, glycolysis and fatty acid oxidation in isolated perfused rat heart

1978 ◽  
Vol 170 (2) ◽  
pp. 235-240 ◽  
Author(s):  
J. Kalervo Hiltunen ◽  
V. Pekka Jauhonen ◽  
Markku J. Savolainen ◽  
Ilmo E. Hassinen
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Citric Acid ◽  
Redox State ◽  
Citric Acid Cycle ◽  
Beating Heart ◽  
Acid Oxidation ◽  
O2 Consumption ◽  
Cellular Redox ◽  
Acid Cycle

The metabolic effects of pent-4-enoate were studied in beating and potassium-arrested perfused rat hearts. The addition of 0.8mm-pent-4-enoate to the fluid used to perfuse a potassium-arrested heart resulted in a 70% increase in the O2 consumption and a 66% decrease in the glycolytic flux as measured in terms of the de-tritiation of [3-3H]glucose, although the proportion of the O2 consumption attributable to glucose oxidation decreased from an initial 30% to 10%. The pent-4-enoate-induced increase in O2 consumption was only 15% in the beating heart. In the potassium-arrested heart, pent-4-enoate stimulated palmitate oxidation by more than 100% when measured in terms of the production of 14CO2 from [1-14C]palmitate, but in the beating heart palmitate oxidation was inhibited. Perfusion of the heart with pent-4-enoate had no effect on the proportion of pyruvate dehydrogenase found in the active form, in spite of large changes in the CoASH and acetyl-CoA concentrations and changes in their concentration ratios. The effects of pent-4-enoate on the cellular redox state were dependent on the ATP consumption of the heart. In the beating heart, pent-4-enoate caused a rapid mitochondrial NAD+ reduction that subsequently faded out, so that the final state was more oxidized than the initial state. The arrested heart, however, remained in a more reduced state than initially, even after the partial re-oxidation that followed the initial rapid NAD+ reduction. The ability of pent-4-enoate to increase or decrease fatty acid oxidation can be explained on the basis of the differential effects of pent-4-enoate on the concentration of citric acid-cycle intermediates under conditions of high or low ATP consumption of the myocardial cell. The proportion of the fatty acids in the fuel consumed by the heart is probably primarily determined by the regulatory mechanisms of glycolysis. When pent-4-enoate causes an increase in the citric acid-cycle intermediates, feedback inhibition of glycolysis results in an increase in the oxidation of fatty acids.

Glucose and insulin-induced inhibition of fatty acid oxidation: the glucose-fatty acid cycle reversed

1996 ◽  
Vol 270 (4) ◽  
pp. E733-E738 ◽  
Author(s):  
L. S. Sidossis ◽  
R. R. Wolfe
Keyword(s):  
Fatty Acid ◽  
Fatty Acid Oxidation ◽  
Indirect Calorimetry ◽  
Plasma Insulin ◽  
Human Subjects ◽  
Substrate Oxidation ◽  
Acid Oxidation ◽  
Acid Cycle ◽  
Hyperglycemic Clamp ◽  
Glucose Fatty Acid Cycle

In this study we have investigated a hypothesis that proposes the reverse of the so-called "glucose-fatty acid cycle, " i.e., that accelerated carbohydrate metabolism directly inhibits fatty acid oxidation. We studied normal volunteers in the basal state and during a hyperinsulinemic, hyperglycemic clamp (plasma insulin = 1,789 +/- 119 pmol/l, plasma glucose = 7.7 +/- 0.2 mmol/l). We quantified fat oxidation using indirect calorimetry and stable isotopes ([1-13C]oleate). Plasma oleate enrichment and free fatty acid (FFA) concentration were kept constant by means of infusion of lipids and heparin. Glucose oxidation increased from basal 6.2 +/- 0.8 to 22.3 +/- 1.4 mumol.kg-1.min-1 during the clamp (P < 0.01). Total (indirect calorimetry) and plasma fatty acid oxidation (isotopic determination) decreased from 2.6 +/- 0.2 to 0.4 +/- 0.3 (P < 0.01) and 2.2 +/- 0.2 to 1.4 +/- 0.1 mumol.kg-1.min-1 (P <0.05), respectively. We conclude that under the conditions of the present experiment, glucose and/or insulin directly inhibits fatty acid oxidation. Our findings suggest that, contrary to the prediction of the glucose-fatty acid cycle, the intracellular availability of glucose (rather than FFA) determines the nature of substrate oxidation in human subjects.

scholarly journals Palmitate inhibits liver glycolysis. Involvement of fructose 2,6-bisphosphate in the glucose/fatty acid cycle

1988 ◽  
Vol 251 (2) ◽  
pp. 541-545 ◽  
Author(s):  
L Hue ◽  
L Maisin ◽  
M H Rider
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Ketone Bodies ◽  
Acid Cycle ◽  
Glucose Fatty Acid Cycle ◽  
Inhibition Of Glycolysis ◽  
Beta Hydroxybutyrate ◽  
Fasted Rats

In hepatocytes from overnight-fasted rats incubated with glucose, palmitate decreased the production of lactate, the detritiation of [2-3H]- and [3-3H]-glucose, and the concentration of fructose 2,6-bisphosphate. Similarly, perfusion of hearts from fed rats with beta-hydroxybutyrate resulted in an inhibition of the detritiation of [3-3H]glucose and a fall in fructose 2,6-bisphosphate concentration. This fall could result from an increase in citrate (hepatocytes and heart) and sn-glycerol 3-bisphosphate concentration. It is suggested that a fall in fructose 2,6-bisphosphate concentration participates in the inhibition of glycolysis by fatty acids and ketone bodies.

Malonyl-CoA regulation in skeletal muscle: its link to cell citrate and the glucose-fatty acid cycle

1997 ◽  
Vol 272 (4) ◽  
pp. E641-E648 ◽  
Author(s):  
A. K. Saha ◽  
D. Vavvas ◽  
T. G. Kurowski ◽  
A. Apazidis ◽  
L. A. Witters ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Fatty Acid ◽  
Pancreatic Beta Cell ◽  
Acid Oxidation ◽  
Atp Citrate Lyase ◽  
Acetyl Coa ◽  
Acid Cycle ◽  
Citrate Lyase ◽  
Malonyl Coa ◽  
Glucose Fatty Acid Cycle

Malonyl-CoA is an inhibitor of carnitine palmitoyltransferase I, the enzyme that controls the oxidation of fatty acids by regulating their transfer into the mitochondria. Despite this, knowledge of how malonyl-CoA levels are regulated in skeletal muscle, the major site of fatty acid oxidation, is limited. Two- to fivefold increases in malonyl-CoA occur in rat soleus muscles incubated with glucose or glucose plus insulin for 20 min [Saha, A. K., T. G. Kurowski, and N. B. Ruderman. Am. J. Physiol. 269 (Endocrinol. Metab. 32): E283-E289, 1995]. In addition, as reported here, acetoacetate in the presence of glucose increases malonyl-CoA levels in the incubated soleus. The increases in malonyl-CoA in all of these situations correlated closely with increases in the concentration of citrate (r2 = 0.64) and to an even greater extent the sum of citrate plus malate (r2 = 0.90), an antiporter for citrate efflux from the mitochondria. Where measured, no increase in the activity of acetyl-CoA carboxylase (ACC) was found. Inhibition of ATP citrate lyase with hydroxycitrate markedly diminished the increases in malonyl-CoA in these muscles, indicating that citrate was the major substrate for the malonyl-CoA precursor, cytosolic acetyl-CoA. Studies with enzyme purified by immunoprecipitation indicated that the observed increases in citrate could have also allosterically activated ACC. The results suggest that in the presence of glucose, insulin and acetoacetate acutely increase malonyl-CoA levels in the incubated soleus by increasing the cytosolic concentration of citrate. This novel mechanism could complement the glucose-fatty acid cycle in determining how muscle chooses its fuels. It could also provide a means by which glucose acutely modulates signal transduction in muscle and other cells (e.g., the pancreatic beta-cell) in which its metabolism is determined by substrate availability.

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