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At least 1,333 records · Page 74Linked to original sources
PubMed1997

19F NMR of 2-deoxy-2-fluoro-D-glucose for tumor diagnosis in mice. An NDP-bound hexose analog as a new NMR target for imaging.

A well-known radiopharmaceutical 2-deoxy-2-fluoro-D-glucose widely used for positron emission tomography diagnosis in terms of glucose utilization, was re-evaluated here as a nuclear magnetic resonance pharmaceutical for cancer detection. The uptake and metabolism of FDG in the experimental tumor, MH134, transplanted to the peritoneum of C3H mice as an ascitic tumor was studied extensively by ex vivo 19F NMR. Prolonged retention of FDG and its metabolites over 2 days was confirmed in the tumor cells as well as in the heart. In these tissues, the 6-phosphate of the injected compound was converted reversibly to its epimer 2-deoxy-2-fluoro-D-mannose and further to their NDP bound forms. The metabolites were almost cleared within a day from the other healthy organs where the formation of NDP-2-deoxy-2-fluoro-D-mannose was low. Thus, the 19F NMR signal of NDP-FDM detected 1 day after the FDG injection could be used as a target signal for tumor detection. Through the use of in vivo 19F NMR spectra and 19F chemical shift images, the feasibility of this proposal was demonstrated. It was concluded that FDG-NMR has a potential for tumor diagnosis in animals.

Animals↗
PubMed1987

Introduction and metabolism of pentose and hexose phosphates in permeabilized Morris hepatoma 5123TC cells.

Metabolism of arabinose 5-P, ribose 5-P and glucose 6-P in permeabilized and resealed Morris hepatoma 5123TC cells was investigated by measuring the contribution of these compounds to nucleic acid biosynthesis. The level of [14C]-arabinose (non-phosphorylated) incorporation into nucleic acids was slight, presumably due to the low activity of the transport system or the absence or low activity of a specific 'kinase' enzyme. The permeabilizing procedure involved the brief treatment of Morris hepatoma 5123TC cells with lysolecithin and resulted in a cell population which was permeable to charged compounds i.e. sugar phosphates and nucleotides, that otherwise could not cross the plasma membrane. The permeabilized (and resealed cells) retained normal cellular morphology and intactness of specific organelles as judged by the maintenance of functional properties. Following permeabilization, these cells resealed when transferred back to normal growth medium, and continued to divide and increase at the same rates as control non-permeabilized cell cultures. The permeabilized cells incorporated deoxyribonucleotides ([methyl -3H]-TTP) into DNA at a linear rate of 0.047 nmol per 10(7) cells min-1, representing 90-100 per cent of the DNA synthesis rate in vivo. The permeabilization technique, when coupled with procedures to establish cell synchrony, permitted the comparative estimate of the contributions of [14C]-labelled arabinose 5-P, ribose 5-P and glucose 6-P to RNA, DNA, amino acids, CO2, lactate and sugar mono- and bisphosphates. The percentage of [14C]-isotope incorporated into total nucleic acids by these three labelled sugar phosphates were 2.3, 4.9 and 6.3 respectively. Possible reasons for the lower incorporation of 14C from arabinose 5-P are given. The results are consistent with the proposal that arabinose 5-P, an intermediate of the L-type pentose pathway activity of 5123TC cells, was incorporated into nucleic acids by its interconversion with ribulose 5-P and ribose 5-P and thus into PRPP. This study represents the first report of sugar phosphate as opposed to free sugar metabolism by tumour cells in culture.

Animals↗
PubMed1980

Hexose uptake enhancing factor released from Rous sarcoma cells.

Conditioned media from Rous sarcoma virus transformed chicken embryo fibroblasts stimulate the uptake of 2-deoxyglucose in normal chicken fibroblasts. The factor responsible for this effect, which is also shed in very low amount by non-transformed fibroblasts, is destroyed by trypsin and not linked to the protease and plasminogen activator activities present in the media. Its apparent molecular weight, determined by gel filtration, is about 20,000 daltons. The factor released by transformed cells might be related to the monomeric form of a family of glucose binding and transport proteins recently reported by Lee and Lipmann ('78) to be detached by detergents from normal and transformed cells.

Animals↗
PubMed1981

The hexose transport system in the human K-562 chronic myelogenous leukemia-derived cell.

Kinetics of glucose transport in K-562 cells was studied using 3-O-methylglucose, a nonmetabolizable analog of glucose. A Km of 3.7 mM and Vmax of 32.0 nmoles/minute/10(6) cells was found for the process. D-Glucose, phloretin, and phlorizin competitively inhibit the transport of 3-O-methylglucose with Ki values of 4.1 mM, 4.1 muM and 225 muM, respectively, whereas L-glucose did not inhibit transport at all. The results indicate that K-562 cells, which are known to have erythropoietic characteristics, possess a glucose carrier system similar to the one in adult human erythrocytes. However, the Vmax data suggest that more copies of the carrier are present in the malignant cell, presumably to support the high rate of anaerobic glycolysis.

Biological Transport↗
PubMed1984

Hexose transport derepressed and refractory to purine regulation in NAD(H)-Depleted Nil cells.

Nil hamster fibroblasts depleted of NAD(H) by growth in medium devoid of nicotinamide (NAm-MEM) exhibit up to 2-3-fold higher rates of glucose transport. Derepression of glucose transport is observed only when Nil cells have become severely depleted of both intracellular NAD(H) and ATP, despite the continued presence of 5.5 mM D-glucose in the growth medium. Neither the initial rate of transport, approximated from 3-O-methylglucose uptake, nor accumulation of D-glucose itself is repressed upon restoring nicotinamide to the medium. Exposure of the cells to NAD+ (10(-5) M), however, leads to a sharp curtailment of transport within 2 to 3 hours. The purines, hypoxanthine and guanine, that sharply reduce glucose transport capacity of normal cells, have no significant effect upon transport activity of NAD(H)-depleted cells.

Adenosine Triphosphate↗
PubMed1985

Stimulation of hexose uptake by haemopoietic cell growth factor occurs in WEHI-3B myelomonocytic leukaemia cells: a possible mechanism for loss of growth control.

WEHI-3B myelomonocytic leukaemia cells secrete a haemopoietic cell growth factor (HCGF) which facilitates the proliferation and development of multipotential stem cells and committed progenitor cells. Several cloned, nonleukaemic cell lines (FDC-P cells) are absolutely dependent on HCGF and die in the absence of it. In these cell lines, factor dependence is associated with the ability of HCGF to increase glucose uptake, thereby controlling glycolytic flux and intracellular ATP levels. We have now investigated the effects of HCGF on glucose uptake in WEHI-3B cells. At 20 degrees C 2-deoxyglucose uptake could be stimulated by the addition of HCGF to the extracellular medium. L-glucose uptake was markedly lower than 2-deoxyglucose uptake and did not respond to the addition of HCGF. At 37 degrees C no HCGF stimulation of 2-deoxyglucose uptake was found. However, at this temperature HCGF release from WEHI-3B cells was markedly higher than at 20 degrees C. Our experiments indicate that HCGF stimulates the glucose transport system in both WEHI-3 cells and FDC-P cells. The similarities between the WEHI-3B cell and FDC-P2 cell polypeptide phenotype were investigated using two-dimensional isoelectric focussing/poly-acrylamide gel electrophoresis. This revealed a high degree of correlation between the two cell types in their protein constituents, indicating a close relationship between the normal and leukaemic cells. These similarities between WEHI-3B cells and FDC-P2 cells are considered and their relevance to haemopoiesis and leukaemogenesis is discussed.

Animals↗
PubMed1989

Pathways for the synthesis of sorbitol from 13C-labeled hexoses, pentose, and glycerol in renal papillary tissue.

Suspensions of rabbit renal papillary tissue were incubated with D-[6-13C]glucose, D-[1-13C]fructose, D-[1-13C]ribose, and [2-13C]glycerol. The perchloric acid extracts of the above incubations were investigated with 13C NMR spectroscopy. All 13C-labeled substrates give rise to 13C-labeled D-sorbitol. D-[6-13C]Glucose and D-[1-13C]fructose are converted directly into D-sorbitol via the aldose reductase and sorbitol dehydrogenase pathway, respectively, whereas D-[1-13C]ribose and [2-13C]glycerol give rise to labeling of the D-glyceraldehyde pool which on its turn causes a labeling of D-sorbitol. Label exchanges observed from incubations with glycerol and D-ribose indicate that the pentose shunt plays a role in this synthesis of D-sorbitol.

Animals↗
PubMed1994

Hexose metabolism in pancreatic islets: glycogen synthase and glycogen phosphorylase activities.

The activity of glycogen synthase and glycogen phosphorylase was measured in rat pancreatic islet homogenates. For this purpose, the sensitivity of current radioisotopic procedures for the assay of these enzymes in liver extracts was increased by about two orders of magnitude. Even so, the measurement of glycogen synthase and phosphorylase in islet homogenates was hampered by a potent amylase-like activity, resulting in the hydrolysis of preformed or newly formed 14C-labeled glycogen. Acarbose suppressed the latter phenomenon which was found attributable to both minute contamination of isolated islets by acinar cells and genuine alpha-amylase activity in purified islet beta-cells. As measured by the more sensitive method in the presence of acarbose, the a/(a+b) ratio for glycogen synthase activity in islet homogenates was increased in islets preincubated in the presence as distinct from absence of D-glucose and decreased after preincubation with forskolin. These changes represented a mirror image of those evoked by D-glucose and forskolin in the a/(a+b) ratio for glycogen phosphorylase activity. It is concluded that glycogen synthesis and breakdown are regulated in the endocrine pancreas in a manner qualitatively comparable to that prevailing in hepatocytes, the possible participation of an amylase-like activity to glycogen metabolism in intact islet beta-cells requiring further investigation.

Acarbose↗
PubMed1995

Hexose metabolism in pancreatic islets: regulation of the mitochondrial NADH/NAD+ ratio.

In rat pancreatic islets, D-glucose in concentrations exceeding 5.6 mM caused a concentration-related decrease of the mitochondrial NADH/NAD+ ratio, as judged from the changes in the islet content of glutamate, NH4+, and 2-ketoglutarate, and assuming that the glutamate dehydrogenase reaction is near equilibrium with the mitochondrial NAD system. The concentration dependency of the response to D-glucose was vastly different in islet and parotid cells, respectively. L-Leucine, 2-ketoisocaproate, BCH (a nonmetabolized but insulinotropic analog of L-leucine) and 3-phenylpyruvate also lowered the mitochondrial NADH/NAD+ ratio. In the presence of D-glucose, the latter ratio was also decreased by NH4+ or the absence of extracellular Ca2+, but dramatically increased by aminooxyacetate. Taking into account prior metabolic findings, the nutrient-induced fall in the mitochondrial redox state is thought to reflect an increased clearance of mitochondrial NADH through both the respiratory chain and malate-aspartate shuttle. The nutrient-induced decrease in the mitochondrial NADH/NAD+ ratio might favor both the circulation of metabolites in the Krebs cycle and the exit of Ca2+ from the mitochondria.

Amino Acids↗
PubMed1990

Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates: isotopic discrimination between hydrogen and deuterium.

The discrimination between the isotopes of hydrogen in the reaction catalyzed by yeast phosphoglucoisomerase is examined by NMR, as well as by spectrofluorometric or radioisotopic methods. The monodirectional conversion of D-glucose 6-phosphate to D-fructose 6-phosphate displays a lower maximal velocity with D-[2-2H]glucose 6-phosphate than unlabelled D-glucose 6-phosphate, with little difference in the affinity of the enzyme for these two substrates. About 72% of the deuterium located on the C2 of D-[1-13C,2-2H]glucose 6-phosphate is transferred intramolecularly to the C1 of D-[1-13C,1-2H]fructose 6-phosphate. The velocity of the monodirectional conversion of D-[U-14C]glucose 6-phosphate (or D-[2-3H]glucose 6-phosphate) to D-fructose 6-phosphate is virtually identical in H2O and D2O, respectively, but is four times lower with the tritiated than 14C-labelled ester. In the monodirectional reaction, the intramolecular transfer from the C2 of D-[2-3H]glucose 6-phosphate is higher in the presence of D2O than H2O. Whereas prolonged exposure of D-[1-13C]glucose 6-phosphate to D2O, in the presence of phosphoglucoisomerase, leads to the formation of both D-[1-13C,2-2H]glucose 6-phosphate and D-[1-13C,1-2H]fructose 6-phosphate, no sizeable incorporation of dueterium from D2O on the C1 of D-[1-13C]fructose 1,6-bisphosphate is observed when the monodirectional conversion of D-[1-13C]glucose 6-phosphate occurs in the concomitant presence of phosphoglucoisomerase and phosphofructokinase. The latter finding contrasts with the incorporation of hydrogen from 1H2O or tritium from 3H2O in the monodirectional conversion of D-[2-3H]glucose 6-phosphate and unlabelled D-glucose 6-phosphate, respectively, to their corresponding ketohexose esters.

Carbon Isotopes↗
PubMed1989

Phosphoglucoisomerase-catalyzed interconversion of hexose-phosphates. Isotopic discrimination between hydrogen and tritium.

The rate of conversion of D-glucose 6-phosphate to D-fructose 6-phosphate as catalyzed by yeast phosphoglucoisomerase is about fourfold lower when 3H, rather than 1H, is present on the C2 of D-glucose 6-phosphate. This difference appears to be due mainly to a change in maximal velocity, rather than affinity. Phosphoglucoisomerase also distinguishes between 1H and 3H in terms of either their intramolecular transfer from C2 to C1 or their incorporation from water on the C1 of D-fructose 6-phosphate.

Carbon Radioisotopes↗
PubMed1986

Regulation of liver and brain hexose monophosphate dehydrogenases by insulin and dietary intake in the female rat.

Liver glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities were significantly decreased in both diabetic and fasted rats. Treatment of diabetic rats with insulin resulted in liver glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities that were significantly greater than controls. Insulin promoted an increase in food consumption that was blocked by adrenaline. Insulin, when administered together with adrenaline, restored hepatic glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities of diabetic animals to control values, without altering food consumption. Brain glucose 6-phosphate dehydrogenase and phosphogluconate dehydrogenase activities were not significantly altered by either dietary restriction, diabetes or insulin treatment. These results demonstrate a dissociation between the action of insulin on hepatic glucose 6-phosphate dehydrogenase activity and its action to increase food intake.

Animals↗
PubMed1991

Hexose metabolism in pancreatic islets: the glucose-6-phosphatase riddle.

Glucose-6-phosphatase activity was measured in rat liver or pancreatic islet crude homogenates and microsomes. The data recorded in the liver were comparable to those reported in prior studies. However, in the islets, the hydrolysis of D-glucose 6-phosphate by disrupted microsomes represented, when expressed relative to the protein content, less than 2% of the value recorded in liver microsomes. Moreover, no phosphotransferase activity was detected in the islets. These findings impose reservation on both the presence of glucose-6-phosphatase in rat islets and its participation to stimulus-secretion coupling.

Animals↗