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Rohm M, Zeigerer A, Machado J, Herzig S. Energy metabolism in cachexia. EMBO Rep 2019; 20:embr.201847258. [PMID: 30890538 DOI: 10.15252/embr.201847258] [Citation(s) in RCA: 94] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Revised: 01/11/2019] [Accepted: 02/05/2019] [Indexed: 12/26/2022] Open
Abstract
Cachexia is a wasting disorder that accompanies many chronic diseases including cancer and results from an imbalance of energy requirements and energy uptake. In cancer cachexia, tumor-secreted factors and/or tumor-host interactions cause this imbalance, leading to loss of adipose tissue and skeletal and cardiac muscle, which weakens the body. In this review, we discuss how energy enters the body and is utilized by the different organs, including the gut, liver, adipose tissue, and muscle, and how these organs contribute to the energy wasting observed in cachexia. We also discuss futile cycles both between the organs and within the cells, which are often used to fine-tune energy supply under physiologic conditions. Ultimately, understanding the complex interplay of pathologic energy-wasting circuits in cachexia can bring us closer to identifying effective treatment strategies for this devastating wasting disease.
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Affiliation(s)
- Maria Rohm
- Institute for Diabetes and Cancer (IDC), Helmholtz Center Munich, Neuherberg, Germany.,Joint Heidelberg-IDC Translational Diabetes Program, Inner Medicine I, Heidelberg University Hospital, Heidelberg, Germany
| | - Anja Zeigerer
- Institute for Diabetes and Cancer (IDC), Helmholtz Center Munich, Neuherberg, Germany.,Joint Heidelberg-IDC Translational Diabetes Program, Inner Medicine I, Heidelberg University Hospital, Heidelberg, Germany
| | - Juliano Machado
- Institute for Diabetes and Cancer (IDC), Helmholtz Center Munich, Neuherberg, Germany.,Joint Heidelberg-IDC Translational Diabetes Program, Inner Medicine I, Heidelberg University Hospital, Heidelberg, Germany
| | - Stephan Herzig
- Institute for Diabetes and Cancer (IDC), Helmholtz Center Munich, Neuherberg, Germany .,Joint Heidelberg-IDC Translational Diabetes Program, Inner Medicine I, Heidelberg University Hospital, Heidelberg, Germany.,Chair Molecular Metabolic Control, Technical University Munich, Munich, Germany
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2
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Identification of a mammalian glycerol-3-phosphate phosphatase: Role in metabolism and signaling in pancreatic β-cells and hepatocytes. Proc Natl Acad Sci U S A 2016; 113:E430-9. [PMID: 26755581 DOI: 10.1073/pnas.1514375113] [Citation(s) in RCA: 73] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Obesity, and the associated disturbed glycerolipid/fatty acid (GL/FA) cycle, contribute to insulin resistance, islet β-cell failure, and type 2 diabetes. Flux through the GL/FA cycle is regulated by the availability of glycerol-3-phosphate (Gro3P) and fatty acyl-CoA. We describe here a mammalian Gro3P phosphatase (G3PP), which was not known to exist in mammalian cells, that can directly hydrolyze Gro3P to glycerol. We identified that mammalian phosphoglycolate phosphatase, with an uncertain function, acts in fact as a G3PP. We found that G3PP, by controlling Gro3P levels, regulates glycolysis and glucose oxidation, cellular redox and ATP production, gluconeogenesis, glycerolipid synthesis, and fatty acid oxidation in pancreatic islet β-cells and hepatocytes, and that glucose stimulated insulin secretion and the response to metabolic stress, e.g., glucolipotoxicity, in β-cells. In vivo overexpression of G3PP in rat liver lowers body weight gain and hepatic glucose production from glycerol and elevates plasma HDL levels. G3PP is expressed at various levels in different tissues, and its expression varies according to the nutritional state in some tissues. As Gro3P lies at the crossroads of glucose, lipid, and energy metabolism, control of its availability by G3PP adds a key level of metabolic regulation in mammalian cells, and G3PP offers a potential target for type 2 diabetes and cardiometabolic disorders.
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Ucciferri N, Sbrana T, Ahluwalia A. Allometric Scaling and Cell Ratios in Multi-Organ in vitro Models of Human Metabolism. Front Bioeng Biotechnol 2014; 2:74. [PMID: 25566537 PMCID: PMC4269269 DOI: 10.3389/fbioe.2014.00074] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Accepted: 12/04/2014] [Indexed: 11/13/2022] Open
Abstract
Intelligent in vitro models able to recapitulate the physiological interactions between tissues in the body have enormous potential as they enable detailed studies on specific two-way or higher order tissue communication. These models are the first step toward building an integrated picture of systemic metabolism and signaling in physiological or pathological conditions. However, the rational design of in vitro models of cell–cell or cell–tissue interaction is difficult as quite often cell culture experiments are driven by the device used, rather than by design considerations. Indeed, very little research has been carried out on in vitro models of metabolism connecting different cell or tissue types in a physiologically and metabolically relevant manner. Here, we analyze the physiological relationship between cells, cell metabolism, and exchange in the human body using allometric rules, downscaling them to an organ-on-a-plate device. In particular, in order to establish appropriate cell ratios in the system in a rational manner, two different allometric scaling models (cell number scaling model and metabolic and surface scaling model) are proposed and applied to a two compartment model of hepatic-vascular metabolic cross-talk. The theoretical scaling studies illustrate that the design and hence relevance of multi-organ models is principally determined by experimental constraints. Two experimentally feasible model configurations are then implemented in a multi-compartment organ-on-a-plate device. An analysis of the metabolic response of the two configurations demonstrates that their glucose and lipid balance is quite different, with only one of the two models recapitulating physiological-like homeostasis. In conclusion, not only do cross-talk and physical stimuli play an important role in in vitro models, but the numeric relationship between cells is also crucial to recreate in vitro interactions, which can be extrapolated to the in vivo reality.
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Affiliation(s)
- Nadia Ucciferri
- CNR Institute of Clinical Physiology , Pisa , Italy ; Interdepartmental Research Center "E. Piaggio", University of Pisa , Pisa , Italy
| | - Tommaso Sbrana
- Interdepartmental Research Center "E. Piaggio", University of Pisa , Pisa , Italy
| | - Arti Ahluwalia
- CNR Institute of Clinical Physiology , Pisa , Italy ; Interdepartmental Research Center "E. Piaggio", University of Pisa , Pisa , Italy
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Gebauer J, Schuster S, de Figueiredo LF, Kaleta C. Detecting and investigating substrate cycles in a genome-scale human metabolic network. FEBS J 2012; 279:3192-202. [PMID: 22776428 DOI: 10.1111/j.1742-4658.2012.08700.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Substrate cycles, also known as futile cycles, are cyclic metabolic routes that dissipate energy by hydrolysing cofactors such as ATP. They were first described to occur in the muscles of bumblebees and brown adipose tissue in the 1970s. A popular example is the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate and back. In the present study, we analyze a large number of substrate cycles in human metabolism that consume ATP and discuss their statistics. For this purpose, we use two recently published methods (i.e. EFMEvolver and the K-shortest EFM method) to calculate samples of 100,000 and 15,000 substrate cycles, respectively. We find an unexpectedly high number of substrate cycles in human metabolism, with up to 100 reactions per cycle, utilizing reactions from up to six different compartments. An analysis of tissue-specific models of liver and brain metabolism shows that there is selective pressure that acts against the uncontrolled dissipation of energy by avoiding the coexpression of enzymes belonging to the same substrate cycle. This selective force is particularly strong against futile cycles that have a high flux as a result of thermodynamic principles.
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Affiliation(s)
- Juliane Gebauer
- Department of Bioinformatics, School of Biology and Pharmaceutics and JenAge Research Core, Friedrich Schiller University of Jena, Germany
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Vinci B, Murphy E, Iori E, Marescotti MC, Avogaro A, Ahluwalia A. Flow-regulated glucose and lipid metabolism in adipose tissue, endothelial cell and hepatocyte cultures in a modular bioreactor. Biotechnol J 2010; 5:618-26. [PMID: 20518065 DOI: 10.1002/biot.201000009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Static cell culture has serious limitations in its ability to represent cellular behaviour within a live organism. In vivo, cells are constantly exposed to the flow of bodily fluids and contact with other cell types. Bioreactors provide the opportunity to study cells in an environment that more closely resembles the in vivo setting because cell cultures can be exposed to dynamic flow in contact with or in proximity to other cell types. In this study we compared the metabolic profile of a dynamic cell culture system to that of a static cell culture in three different cellular phenotypes: adipocytes, endothelial cells and hepatocytes. Albumin, glucose, free fatty acids, glycerol, and lactate were measured over 48 h. We show that all three cell types have increased glucose uptake in the presence of flow; lactate release was also significantly affected. We provide robust evidence that the presence of flow significantly modifies cellular metabolism. While flow provides a more uniform nutrient distribution and increases metabolite turnover, our results indicate that different cell types have specific metabolic responses to flow, suggesting cell-specific flow-regulated activation of metabolite signalling pathways.
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Affiliation(s)
- Bruna Vinci
- Centro Interdipartimentale di Ricerca E. Piaggio, Faculty of Engineering, University of Pisa, Pisa, Italy
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6
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Sullivan JP, Harris DR, Palmer AF. Convection and hemoglobin-based oxygen carrier enhanced oxygen transport in a hepatic hollow fiber bioreactor. ACTA ACUST UNITED AC 2008; 36:386-402. [PMID: 18649173 DOI: 10.1080/10731190802239065] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Hepatic hollow fiber bioreactors are a promising class of bioartificial liver assist device (BLAD). The development of this type of device is currently hindered by limited oxygen transport to cultured hepatocytes, due to low solubility of oxygen in aqueous media. In order to increase the oxygen spectrum to cultured hepatocytes housed within a hollow fiber bioreactor, several different engineering strategies were explored in this study. These included: supplementing the circulating media stream of the hollow fiber bioreactor with a hemoglobin-based oxygen carrier (bovine red blood cells) with defined oxygen binding and release kinetics and operating the bioreactor with media flow through the hollow fiber membrane into the extracapillary space (ECS). We hypothesize that these two strategies can be used to improve hepatocyte oxygenation and possibly attain an in vivo-like pO(2) spectrum, similar to that observed in vivo in the liver sinusoid. This work is significant, since provision of an in vivo-like pO(2) spectrum should create a fully functional BLAD that could potentially bridge thousands of liver failure patients towards native liver regeneration of damaged tissue or, if necessary, orthotopic liver transplantation.
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Affiliation(s)
- Jesse P Sullivan
- Department of Chemical & Biomolecular Engineering, University of Notre Dame, Notre Dame, IN, USA
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Dubbelhuis PF, Van Sluijters DA, Blommaart EFC, Gustafson LA, Van Woerkom GM, Herling AW, Burger HJ, Meijer AJ. Inhibition of autophagic proteolysis by inhibitors of phosphoinositide 3-kinase can interfere with the regulation of glycogen synthesis in isolated hepatocytes. Biochem J 2002; 368:827-33. [PMID: 12371905 PMCID: PMC1223050 DOI: 10.1042/bj20021340] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2002] [Accepted: 10/08/2002] [Indexed: 12/24/2022]
Abstract
Amino acid-induced cell swelling stimulates conversion of glucose into glycogen in isolated hepatocytes. Activation of glycogen synthase (GS) phosphatase, caused by the fall in intracellular chloride accompanying regulatory volume decrease, and activation of phosphoinositide 3-kinase (PI 3-kinase), induced by cell swelling, have been proposed as underlying mechanisms. Because PI 3-kinase controls autophagic proteolysis, we examined the possibility that PI 3-kinase inhibitors interfere with glycogen production due to their anti-proteolytic action. The PI 3-kinase inhibitor wortmannin inhibited endogenous proteolysis, the production of glycogen from glucose and the activity of active (dephosphorylated) GS (GS a ) in the absence of added amino acids. The stimulation by amino acids of glycogen production and of GS a was only slightly affected by wortmannin. These effects of wortmannin could be mimicked by proteinase inhibitors. A combination of leucine, phenylalanine and tyrosine, which we showed previously to stimulate PI 3-kinase-dependent phosphorylation of ribosomal protein S6, did not stimulate glycogen production from glucose. In contrast with wortmannin, LY294002, another PI 3-kinase inhibitor, strongly inhibited both glycogen synthesis and GS a activity, irrespective of the presence of amino acids. Inhibition of glycogen synthesis by LY294002 could be ascribed in part to increased glycogenolysis and glycolysis. It is concluded that, in hepatocytes, activation of PI 3-kinase may not be responsible for the stimulation of glycogen synthesis by amino acids; LY294002 inhibits glycogen synthesis and stimulates glycogen breakdown by a mechanism that is unrelated to its action as an inhibitor of PI 3-kinase.
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Affiliation(s)
- Peter F Dubbelhuis
- Department of Biochemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands
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Jones ME, Berry MN, Phillips JW. Futile cycles revisited: a markov chain model of simultaneous glycolysis and gluconeogenesis. J Theor Biol 2002; 217:509-23. [PMID: 12234757 DOI: 10.1006/jtbi.2002.3042] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have used a random walk model of glycolysis and gluconeogenesis to investigate the bioenergetic implications of considering the cell cytoplasm to be a uniform well-mixed compartment. Radiotracer studies conducted on hepatocytes harvested from fasted rats and incubated with 40 mM glucose and 10 mM lactate demonstrated simultaneous glycolysis and gluconeogenesis, with net glycolysis. Tracer introduced as glycerol was incorporated both into glucose (via gluconeogenesis) and into pyruvate (via glycolysis). The data allow us to place a lower bound on the energetic cost of futile cycles involving adenosine triphosphate (ATP) hydrolysis in the early phosphorylation steps of glycolysis. Applying the Markov Chain model for glucose undergoing metabolism to pyruvate, the expected number of ATP molecules hydrolysed is not less than 15 ATP molecules per glucose molecule. The data suggest that, in hepatocytes under the circumstances of this experiment, either glycolysis is a net consumer of ATP, or glycolysis and gluconeogenesis are compartmentalized to a greater extent than is generally supposed.
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Affiliation(s)
- M E Jones
- The School of Medicine, 6E-124, Flinders University of South Australia, 2100, Adelaide, 5001, SA, Australia.
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Phillips JW, Jones ME, Berry MN. Implications of the simultaneous occurrence of hepatic glycolysis from glucose and gluconeogenesis from glycerol. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:792-7. [PMID: 11846780 DOI: 10.1046/j.0014-2956.2001.02687.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Glycolysis from [6-(3)H]glucose and gluconeogenesis from [U-(14)C]glycerol were examined in isolated hepatocytes from fasted rats. A 5 mm bolus of glycerol inhibited phosphorylation of 40 mm glucose by 50% and glycolysis by more than 60%, and caused cellular ATP depletion and glycerol 3-phosphate accumulation. Gluconeogenesis from 5 mm glycerol was unaffected by the presence of 40 mm glucose. When nonsaturating concentrations of glycerol (< 200 microm) were maintained in the medium by infusion of glycerol, cellular ATP concentrations remained normal. The rate of uptake of infused glycerol was unaffected by 40 mm glucose, but carbohydrate synthesis from glycerol was inhibited 25%, a corresponding amount of glycerol being diverted to glycolytic products, whereas 10 mm glucose had no inhibitory effect on conversion of infused glycerol into carbohydrate. Glycerol infusion depressed glycolysis from 10 mm and 40 mm glucose by 15 and 25%, respectively; however, the overall rates of glycolysis were unchanged because of a concomitant increase in glycolysis from the infused glycerol. These studies show that exposure of hepatocytes to glucose and low quasi-steady-state concentrations of glycerol result in the simultaneous occurrence, at substantial rates, of glycolysis from glucose and gluconeogenesis from the added glycerol. We interpret our results as demonstrating that, in hepatocytes from normal rats, segments of the pathways of glycolysis from glucose and gluconeogenesis from glycerol are compartmentalized and that this segregation prevents substantial cross-over of phosphorylated intermediates from one pathway to the other. The competition between glucose and glycerol implies that glycolysis and phosphorylation of glycerol take place in the same cells, and that the occurrence of simultaneous glycolysis and gluconeogenesis may indicate channelling within the cytoplasm of individual hepatocytes.
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Affiliation(s)
- John W Phillips
- Departments of Medical Biochemistry, Anatomy and Histology and Human Physiology, School of Medicine, The Flinders University of South Australia, Adelaide, South Australia, Australia
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Atlante A, Gagliardi S, Marra E, Calissano P, Passarella S. Glutamate neurotoxicity in rat cerebellar granule cells involves cytochrome c release from mitochondria and mitochondrial shuttle impairment. J Neurochem 1999; 73:237-46. [PMID: 10386976 DOI: 10.1046/j.1471-4159.1999.0730237.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To gain some insight into the mechanism by which glutamate neurotoxicity takes place in cerebellar granule cells, two steps of glucose oxidation were investigated: the electron flow via respiratory chain from certain substrates to oxygen and the transfer of extramitochondrial reducing equivalents via the mitochondrial shuttles. However, cytochrome c release from intact mitochondria was found to occur in glutamate-treated cells as detected photometrically in the supernatant of the cell homogenate suspension. As a result of cytochrome c release, an increase of the oxidation of externally added NADH was found, probably occurring via the NADH-b5 oxidoreductase of the outer mitochondrial membrane. When the two mitochondrial shuttles glycerol 3-phosphate/dihydroxyacetone phosphate and malate/oxaloacetate, devoted to oxidizing externally added NADH, were reconstructed, both were found to be impaired under glutamate neurotoxicity. Consistent early activation in two NADH oxidizing mechanisms, i.e., lactate production and plasma membrane NADH oxidoreductase activity, was found in glutamate-treated cells. In spite of this, the increase in the cell NADH fluorescence was found to be time-dependent, an index of the progressive damage of the cell.
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Affiliation(s)
- A Atlante
- Centro di Studio sui Mitocondri e Metabolismo Energetico, CNR, Bari, Italy
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11
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Shangraw RE, Rabkin JM, Lopaschuk GD. Hepatic pyruvate dehydrogenase activity in humans: effect of cirrhosis, transplantation, and dichloroacetate. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:G569-77. [PMID: 9530159 DOI: 10.1152/ajpgi.1998.274.3.g569] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The liver is the major site for lactate clearance, and liver disease exacerbates lactic acidosis during orthotopic liver transplantation (OLT). This study assessed pyruvate dehydrogenase (PDH) activity in control, cirrhotic, and graft liver to test the hypotheses that 1) liver disease decreases hepatic PDH activity, 2) graft PDH activity is inhibited due to protracted ischemia, and 3) dichloroacetate (DCA) reverses functional PDH inhibition in cirrhotic and graft liver. After having given their informed consent, 43 patients received either DCA (80 mg/kg) or aqueous 5% glucose during OLT. Six patients without apparent liver dysfunction that were undergoing subtotal hepatic resection served as controls. Liver biopsy PDH activity was assayed by measuring [14C]citrate synthesis from [14C]oxaloacetate and PDH-derived acetyl-CoA. PDH in the active form (PDHa) in cirrhotic and control liver was 5.6 +/- 1.3 (SE) and 57 +/- 10 nmol.g wet wt-1.min-1, respectively (P < 0.001). Total PDH activity (PDHt) was 21.5 +/- 3.6 and 264 +/- 27 nmol.g wet wt-1.min-1, respectively (P < 0.001). DCA increased PDHa in cirrhotic liver to 22.3 +/- 4.1 nmol.g wet wt-1.min-1 (P < 0.05 vs. no DCA) without altering PDHt. Graft liver PDHa was 166 +/- 19 nmol.g wet wt-1.min-1, which was not altered by DCA. We conclude that decreased hepatic PDH activity secondary to decreased content may underlie lactic acidosis during OLT, which can be partially compensated by DCA administration. There is no apparent inhibition of graft liver PDH activity after reperfusion.
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Affiliation(s)
- R E Shangraw
- Department of Anesthesiology, Oregon Health Sciences University, Portland, USA
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Matsushita M, Ohashi I, Becker GL, Pohorecki R. Isoflurane Preserves Adenosine Triphosphate Levels in Anoxic Isolated Rat Hepatocytes by Stimulating Glycolytic Adenosine Triphosphate Formation. Anesth Analg 1996. [DOI: 10.1213/00000539-199606000-00028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Matsushita M, Ohashi I, Becker GL, Pohorecki R. Isoflurane preserves adenosine triphosphate levels in anoxic isolated rat hepatocytes by stimulating glycolytic adenosine triphosphate formation. Anesth Analg 1996; 82:1261-7. [PMID: 8638802 DOI: 10.1097/00000539-199606000-00028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The hypothesis that general anesthetics protect energy reserves by decreasing energy demand is widely accepted but poorly substantiated. Isoflurane at clinical doses preserved adenosine triphosphate (ATP) levels in anoxic isolated hepatocytes. Specific inhibitors were used to block mitochondrial and/or glycolytic ATP formation to ascertain whether pathways of energy supply or demand, or both, were involved in ATP preservation by isoflurane. Hepatocytes were isolated from fed adult male rats after perfusing livers with Krebs buffer containing collagenase. Cells were incubated in Krebs buffer for 0-30 min at 25 degrees C under N2/CO2 (95%/5%) +/- isoflurane 0.63 mM in liquid phase. Oligomycin, iodoacetate, or fasting were used to block mitochondrial and glycolytic ATP formation. Under anoxia alone, ATP levels declined more slowly in the presence than in the absence of isoflurane, confirming the ATP-protective effect of isoflurane reported previously. With oligomycin plus iodoacetate blocking all ATP formation, ATP decline (representing pure ATP consumption) was not slowed by isoflurane. Isoflurane's protective effect recurred when glycolytic ATP supply was restored by incubating with oligomycin only. The protective effect was accompanied by increased lactate accumulation, and both effects-ATP preservation and lactate formation-were similarly dependent on isoflurane concentration. We conclude that the protective effect of isoflurane on energy status in anoxic isolated hepatocytes was not associated with reduced ATP demand but with enhanced ATP supply via stimulation of glycolysis.
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Affiliation(s)
- M Matsushita
- Department of Anesthesiology, University of Nebraska Medical Center, Omaha 68198-4455, USA
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Henly DC, Phillips JW, Berry MN. Suppression of glycolysis is associated with an increase in glucose cycling in hepatocytes from diabetic rats. J Biol Chem 1996; 271:11268-71. [PMID: 8626677 DOI: 10.1074/jbc.271.19.11268] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Rates of cycling between glucose and glucose 6-phosphate and between glucose and pyruvate, and the effects of these cycles on glucose metabolism, were compared in hepatocytes isolated from fasted normal or streptozotocin-induced diabetic rats. In diabetic hepatocytes the rate of glucose phosphorylation was 30% lower than that in normal hepatocytes, and there was a doubling of the rate of glucose/glucose 6-phosphate cycling. In addition, the rate of glycolysis was 60% lower in diabetic hepatocytes. This inhibition of glycolysis and stimulation of glucose/glucose 6-phosphate cycling appeared to be a consequence of the elevated rates of endogenous fatty acid oxidation observed in diabetic hepatocytes. The proportion of glycolytically derived pyruvate that was recycled to glucose was more than doubled in hepatocytes from diabetic rats compared with normal animals. This increase also appeared to be linked to the high rates of endogenous fatty acid oxidation in diabetic cells. As a consequence of the increased rates of both these cycles, 85% of all glucose molecules taken up by diabetic hepatocytes were recycled to glucose, compared with only 50% in normal hepatocytes. Glucose cycling is therefore likely to make a substantial contribution to the hyperglycemia of diabetes.
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Affiliation(s)
- D C Henly
- Department of Medical Biochemistry, School of Medicine, Flinders University of South Australia, Adelaide, Australia
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Abstract
The effects of alterations in thyroid status on glucose metabolism have been investigated in rat hepatocytes. Addition of 10 or 40 mmol/L glucose induced increases in respiration rate that were significantly larger in cells from hyperthyroid rats than from hypothyroid animals. The responses of hepatocytes from euthyroid rats were intermediate. In cells from hyperthyroid rats, most of the increase occurred upon addition of 10 mmol/L glucose, with only a further small stimulation resulting when glucose concentration was increased to 40 mmol/L. For a given glucose concentration, glycolytic rates, determined by measuring release of tritium from [6-3H]glucose, were comparable in all thyroid states. Studies with 10 mmol/L [2-3H]glucose showed that cycling between glucose-6-phosphate and glucose was almost twofold higher in euthyroid and hyperthyroid states as compared with the hypothyroid state, although the magnitude of the increase in cycling rate was only approximately 0.2 mumol glucose.min-1.g-1. When 40 mmol/L [2-3H]glucose was added, over 44% of the glucose that was phosphorylated to glucose-6-phosphate was cycled back to glucose, but this cycling was independent of thyroid status. Cycling between fructose-1,6-bisphosphate and fructose-6-phosphate was negligible in all thyroid states. Rates of glycogen synthesis were comparable in hypothyroid and hyperthyroid states and slightly less than in the euthyroid state. Glycolytically formed pyruvate was cycled back to glucose in hepatocytes from hypothyroid, euthyroid, and hyperthyroid rats. During a 60-minute incubation period, cycling to glucose in the presence of 10 mmol/L or 40 mmol/L glucose was up to twofold higher in cells from euthyroid and hyperthyroid rats than in hepatocytes from hypothyroid animals. The measured increases in cycling rates induced by thyroid hormone were small and in theory could have been satisfied by a much smaller increase in respiration rate than was observed.
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Affiliation(s)
- R B Gregory
- Department of Medical Biochemistry, School of Medicine, Flinders University of South Australia, Adelaide, Australia
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Abstract
Energy metabolism in liver has to cope with the special tasks of this organ in intermediary metabolism. Main ATP-generating processes in the liver cell are the respiratory chain and glycolysis, whereas main ATP-consuming processes are gluconeogenesis, urea synthesis, protein synthesis, ATPases and mitochondrial proton leak. Mitochondrial respiratory chain in the intact liver cell is subject to control mainly by substrate (hydrogen donors, ADP, oxygen) transport and supply and proton leak/slip. Whereas hormonal control is mainly on substrate supply to mitochondria, proton leak/slip is supposed to play an important role in the modulation of the efficiency of oxidative phosphorylation.
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Affiliation(s)
- S Soboll
- Institut für Physiologische Chemie I, Heinrich Heine-Universität Düsseldorf, Germany
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Gregory RB, Berry MN. The influence of thyroid state on hepatic glycolysis. EUROPEAN JOURNAL OF BIOCHEMISTRY 1995; 229:344-8. [PMID: 7744057 DOI: 10.1111/j.1432-1033.1995.0344k.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The effects of thyroid status on glycolysis using 10, 20, and 40 mM glucose have been examined in hepatocytes derived from hypothyroid, euthyroid, and hyperthyroid rats. For any given concentration of added glucose, total glycolytic rates, as measured by the release of tritium from [6-3H]glucose, were similar in all thyroid states. The aerobic component of glycolysis, where cytoplasmically generated reducing equivalents are transferred to the mitochondria for oxidation, was the major component in the hyperthyroid state, at all concentrations of glucose. In contrast, the aerobic proportion of glycolysis in the hypothyroid and euthyroid states decreased with increasing concentration of added glucose and the anaerobic component became dominant above 20 mM glucose. Cytoplasmic reducing equivalents generated during aerobic glycolysis were transferred to the mitochondria via both the glycerol 1-phosphate and malate/aspartate shuttles in each thyroid state, even though the former shuttle was considerably depressed in the livers of hypothyroid rats. Both asparagine and aminooxyacetate had only minor effects on the rate of glycolysis, but aminooxyacetate depressed the contribution of aerobic glycolysis whereas asparagine had relatively little influence. The respiration rate in the presence of 40 mM glucose was twice as high in hepatocytes from hyperthyroid rats as in cells from hypothyroid animals, and 1.4 times as high as in hepatocytes from euthyroid rats. Smaller stimulations were observed with lower concentrations of added glucose. Furthermore, the increase in respiratory rate over the endogenous value, induced by 10 mM glucose, was six times higher in cells from hyperthyroid rats than in hepatocytes from hypothyroid animals and 2.7 times higher than that observed with cells from euthyroid rats. The insensitivity of glycolysis to thyroid status in contrast to the marked response of respiration provides additional support for the view that the stimulation of metabolism by thyroid hormone is mediated primarily by its action on mitochondrial processes.
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Affiliation(s)
- R B Gregory
- Department of Medical Biochemistry, School of Medicine, Flinders University of South Australia
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