title: Dynamic profiling of the glucose metabolic network in fasted rat hepatocytes using [1,2-13C2]glucose.
abstract: Recent studies in metabolic profiling have underscored the importance of the concept of a metabolic network of pathways with special functional characteristics that differ from those of simple reaction sequences. The characterization of metabolic functions requires the simultaneous measurement of substrate fluxes of interconnecting pathways. Here we present a novel stable isotope method by which the forward and reverse fluxes of the futile cycles of the hepatic glucose metabolic network are simultaneously determined. Unlike previous radio-isotope methods, a single tracer [1,2-13C2]D-glucose and mass isotopomer analysis is used. Changes in fluxes of substrate cycles, in response to several gluconeogenic substrates, in isolated fasted hepatocytes from male Wistar rats were measured simultaneously. Incubation with these substrates resulted in a change in glucose-6-phosphatase/glucokinase and glycolytic/gluconeogenic flux ratios. Different net redistributions of intermediates in the glucose network were observed, resulting in distinct metabolic phenotypes of the fasted hepatocytes in response to each substrate condition. Our experimental observations show that the constraints of concentrations of shared intermediates, and enzyme kinetics of intersecting pathways of the metabolic network determine substrate redistribution throughout the network when it is perturbed. These results support the systems-biology notion that network analysis provides an integrated view of the physiological state. Interaction between metabolic intermediates and glycolytic/gluconeogenic pathways is a basic element of cross-talk in hepatocytes, and may explain some of the difficulties in genotype and phenotype correlation.
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Martí i Franquès 1, Barcelona 08028, Spain.
authors.forename: Silvia
authors.initials: S
authors.lastname: Marin
authors.forename: W-N Paul
authors.initials: WN
authors.lastname: Lee
authors.forename: Sara
authors.initials: S
authors.lastname: Bassilian
authors.forename: Shu
authors.initials: S
authors.lastname: Lim
authors.forename: Laszlo G
authors.initials: LG
authors.lastname: Boros
authors.forename: Josep J
authors.initials: JJ
authors.lastname: Centelles
authors.forename: Josep Maria
authors.initials: JM
authors.lastname: FernAndez-Novell
authors.forename: Joan J
authors.initials: JJ
authors.lastname: Guinovart
authors.forename: Marta
authors.initials: M
authors.lastname: Cascante
mesh_terms: D000818:Animals; D002247:Carbon Isotopes / Q000378:metabolism; D002952:Citric Acid Cycle / Q000235:genetics / Q000502:physiology; D005215:Fasting / Q000502:physiology*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods / Q000706:statistics & numerical data; D005838:Genotype; D005941:Glucokinase / Q000378:metabolism; D005943:Gluconeogenesis / Q000235:genetics / Q000502:physiology; D005947:Glucose / Q000737:chemistry / Q000378:metabolism*; D005952:Glucose-6-Phosphatase / Q000378:metabolism; D006003:Glycogen / Q000096:biosynthesis / Q000737:chemistry; D006019:Glycolysis / Q000235:genetics / Q000502:physiology; D022781:Hepatocytes / Q000737:chemistry* / Q000201:enzymology / Q000378:metabolism*; D019344:Lactic Acid / Q000096:biosynthesis / Q000737:chemistry; D008297:Male; D010641:Phenotype; D051381:Rats; D017208:Rats, Wistar; D015219:Substrate Cycling / Q000235:genetics / Q000502:physiology
chemical_list: D002247:Carbon Isotopes; D019344:Lactic Acid; D006003:Glycogen; D005941:Glucokinase; D005952:Glucose-6-Phosphatase; D005947:Glucose