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PubMed1990

Metabolism of 3-deoxyglucosone, an intermediate compound in the Maillard reaction, administered orally or intravenously to rats.

The Amadori rearrangement compound, the product in the early step of the Maillard reaction of proteins with glucose, is known to be degraded into 3-deoxyglucosone (3DG), a 2-oxoaldehyde. In order to elucidate the metabolic pathway of 3DG, [14C]3DG was synthesized from [14C]-glucose and administered to rats orally and intravenously. 2 h after oral administration of [14C]3DG, the percentages of radioactivity (RaI%) in stomach, small intestine and urine were 3.9, 60 and 6.4%, respectively, while RaI% in liver, kidney, spleen, blood and CO2 were less than 0.5%. The absorption rate of 3DG was obviously lower in comparison with that of glucose. 3 h after intravenous administration of [14C]3DG, the RaI% in urine was 72% and those in liver, kidney, spleen, blood and CO2 were less than 1%. It therefore appeared that the absorbed 3DG was not biologically utilized by the rats, but was rapidly excreted in the urine. Some metabolites of [14C]3DG were detected in urine by TLC-autoradiography. The main metabolite was purified and identified as 3-deoxyfructose by FD-MS and 13C-NMR spectroscopy, indicating that the aldehyde group of 3DG was reduced to an alcohol.

Absorption↗

PubMed2005

Nitric oxide stimulates 18F-FDG uptake in human endothelial cells through increased hexokinase activity and GLUT1 expression.

UNLABELLED: The endothelium constitutes a functionally active organ critically involved in angiogenesis. Nitric oxide (NO) is an important regulator of vascular homeostasis and angiogenesis and stimulates glucose metabolism in certain cells. We thus investigated the effect of exogenous NO on (18)F-FDG transport in human endothelial cells. METHODS: Human umbilical vein endothelial cells (HUVECs) were treated with the NO donors sodium nitroprusside (SNP) or diethylenetriamine (DETA), in concentrations of 1 micromol/L-1 mmol/L for up to 24 h. (18)F-FDG uptake levels corrected for protein content were determined by cellular radioactivity measured after 30-min incubation. Cells were evaluated for total hexokinase activity and plasma membrane glucose transporter 1 (GLUT1) levels, and involvement of potential signaling pathways was investigated by cotreatment with respective protein kinase inhibitors. RESULTS: Both SNP and DETA stimulated HUVEC (18)F-FDG uptake, which began at 16 h and peaked at 24 h. The increase in (18)F-FDG uptake was dose dependent, reaching 464.0% +/- 49.8% and 254.5% +/- 10.8% of control levels at 24 h with 1 mmol/L SNP and DETA, respectively. Exposure of HUVECs to 1 mmol/L SNP resulted in a 3.5 +/- 0.3-fold elevation in hexokinase activity (P < 0.01) and a significant increase in GLUT1 levels. SNP-stimulated (18)F-FDG uptake was abolished by cotreatment with cycloheximide, the tyrosine kinase inhibitor genistein, the phosphatidylinositol-3 kinase (PI3K) inhibitor wortmannin, or the protein kinase C inhibitor staurosporine. CONCLUSION: NO stimulates (18)F-FDG uptake in HUVECs through an increase in GLUT1 expression and hexokinase activity, which appears to involve both protein kinase C and PI3K pathways.

Cells, Cultured↗

PubMed1989

A D-mannose transport system in renal brush-border membranes.

Dog renal brush-border membrane vesicles (BBMV) from whole kidney cortex contain both low-affinity, high-capacity and high-affinity, low-capacity Na-dependent D-glucose cotransporters. D-Mannose is an epimer of D-glucose, differing in structure only in the axial, rather than equatorial, orientation of the hydroxyl group at the C-2 position of the pyranose ring. Uptake experiments of radioactive sugars into BBMV by standard Millipore filtration were performed to determine whether D-mannose shares either, or both, of the D-glucose carriers or if it is transported by an independent system. Transport of D-mannose occurs into an osmotically active space and is saturable and sodium dependent with a 1:1 Na:D-mannose stoichiometry, Km of 0.063 mM, Vmax of 3.6 nmol.mg-1.min-1, 25 degrees C, and pH 7.4. When an NaSCN electrochemical gradient was present, an "overshoot" was present, indicating active cotransport. Up to 50 mM D-mannose did not inhibit sodium-dependent D-glucose or alpha-methylglucoside uptake (0.01-20 mM). Sodium-dependent D-mannose uptake was inhibited by the following compounds in order of decreasing effectiveness: fructose greater than mannoheptulose greater than 2-deoxy-D-glucose greater than 2-fluoro-2-deoxy-D-glucose much greater than phloretin, cytochalasin B, galactose, 3-O-methyl-D-glucose, and L-mannose. Phlorizin also inhibited D-mannose uptake, but the high concentration required and the fact that a competitive pattern of inhibition could not be demonstrated contrasted with its effect on D-glucose transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

Identification of genes regulated by glucose in a pancreatic beta-cell line by a new method for subtraction of mRNA.

Various genes are differentially expressed in cells during cell differentiation, development, aging, and in pathological conditions. To identify and isolate the genes that are specifically and differentially expressed in cells, we established a ligation-mediated polymerase chain reaction (PCR)-based method for cDNA subtraction. As this method is PCR-based, when target genes are expressed at high levels relative to the driver (a control pool for subtraction), even a small amount of target genes can be amplified. By this newly developed PCR-based subtraction method, a set of genes regulated by glucose were identified in a mouse insulinoma cell line. This PCR-based and non-radioactive subtraction method will be a powerful tool for identification of novel genes, specifically and differentially expressed in cells.

Animals↗

PubMed1988

Autoradiographic studies on glucose utilization in individual zones of the rat thymus.

Wistar rats were injected intraperitoneally with 2-(14C)deoxyglucose and their thymuses were processed for thaw-mount autoradiography after 5, 10 or 35 min. Highest levels of radioactivity were demonstrated in the thymic medulla (5-fold higher than in the cortex). Scanning of autoradiograms for regional differences in grain densities indicated particularly intense glucose utilization in the cortico-medullary zone. Differences in glucose utilization between individual thymic zones seem to reflect differences in cellular composition, i.e., ratio of stroma cells to thymocytes.

Animals↗

PubMed2002

Altered arachidonic acid biosynthesis and antioxidant protection mechanisms in Schwann cells grown in elevated glucose.

In cultured Schwann cells, elevated glucose induces alterations in arachidonic acid metabolism that cause a decrease in the content of glycerophospholipid arachidonoyl-containing molecular species (ACMS). This could result from decreased de novo arachidonic acid biosynthesis, or increased arachidonic acid release from phospholipids. Incorporation of radioactive 8,11,14-eicosatrienoic acid into ACMS was lower for cells grown in 30 mm versus 5 mm glucose, consistent with a decrease in delta5 desaturase activity. However, neither basal arachidonic acid release from prelabeled cells nor stimulated generation of arachidonic acid in the presence of the reacylation inhibitor, thimerosal, the phosphotyrosine phosphatase inhibitor, bipyridyl peroxovanadium, or both together, were altered by varying the glucose concentrations, indicating that arachidonic acid turnover did not contribute to ACMS depletion. Free cytosolic NAD+ /NADH decreased, whereas NADP+ /NADPH remained unchanged for cells grown in elevated glucose, implying that decreased desaturase activity is a result of metabolic changes other than cofactor availability. Schwann cells in elevated glucose were susceptible to oxidative stress, as shown by increased malondialdehyde, depleted glutathione levels, and reduced cytosolic superoxide dismutase activity. Glutathione-altering compounds had no effect on ACMS levels, in contrast to N -acetylcysteine and alpha-lipoic acid, which partly corrected ACMS depletion in phosphatidylcholine. These findings suggest that in the Schwann cell cultures, a high glucose level elicits oxidative stress and weakens antioxidant protection mechanisms which could decrease arachidonic acid biosynthesis and that this deficit can be partly corrected by treatment with exogenous antioxidants.

Animals↗

PubMed1997

Stable isotope techniques for the study of gluconeogenesis in man.

Glucose is produced by gluconeogenesis from pyruvate and its precursors and from glycerol and by glycogenolysis (Fig.1). We introduced a technique using 2H2O to quantitate the contribution of gluconeogenesis to glucose production in the fasted state (1,2). The method removes the uncertainty in older methods using radioactive or stable isotopes of knowing 1) the enrichment or specific activity of the gluconeogenic precursor being traced, 2) the contribution to gluconeogenesis of that precursor compared to contributions by the other precursors, and 3) the extent of dilution of label of that precursor in the Krebs cycle during the course of its conversion to glucose.

Blood Glucose↗

PubMed1988

Non-enzymic glycosylation (glycation) of lens proteins by galactose and protection by aspirin and reduced glutathione.

Radioactive galactose becomes attached covalently to lens proteins in the same way as glucose. Simultaneous incubation with aspirin inhibits the reaction with galactose in a dose-related manner. Incubation with aspirin before incubation with galactose in the absence of aspirin showed that aspirin can modify crystallins permanently to prevent the binding of galactose. The galactosylation was also inhibited by glutathione at physiological concentrations. All major groups of lens proteins reacted with galactose but a higher level of modification of protein in the material of high molecular weight may indicate that galactosylation has induced aggregation of the proteins. The modification of all major crystallin groups was confirmed by isolating the galactosylated proteins by affinity chromatography. The results are discussed in relation to glycosylation of lens proteins in diabetes and galactosaemia and the role of glycosylation in cataract.

Acetylation↗

PubMed1996

Effects of stress and hypophysectomy on the uptake of [3H]2-deoxy-D-glucose in the mouse adrenal medulla: an autoradiographic study.

Effects of immobilization stress and hypophysectomy on the uptake of [3H] 2-deoxy-D-glucose (2DG) in the adrenal medulla of the mouse was examined by autoradiography. Radioactivity due to [3H]2DG in both adrenaline-storing and noradrenaline-storing cells was markedly increased by acute immobilization stress. Under immobilization stress, adrenaline-storing cells incorporated more 2DG than noradrenaline-storing cells. Adrenal denervation did not change the uptake of 2DG either in control or in stressed adrenal medulla. The uptake of [3H]2DG was also increased by hypophysectomy. Since withdrawal of cortical steroid hormones enhanced the uptake of 2DG and the adrenal denervation did not change the uptake, it is suggested that certain substances, such as bradykinin or histamine, which are released on immobilization stress from certain tissues other than sympathetic nerve endings in the medulla, enhanced the uptake of [3H]2DG. This phenomenon occurs mainly in adrenaline-storing cells.

Adrenal Medulla↗

PubMed1968

The redistribution of carbon label by the reactions involved in glycolysis, gluconeogenesis and the tricarboxylic acid cycle in rat liver.

A scheme is presented that shows how the reactions involved in gluconeogenesis, glycolysis and the tricarboxylic acid cycle are linked in rat liver. Equations are developed that show how label is redistributed in aspartate, glutamate and phosphopyruvate when it is introduced as specifically labelled pyruvate or glucose either at a constant rate (steady-state theory) or at a variable rate (non-steady-state theory). For steady-state theory the fractions of label introduced as specifically labelled pyruvate that are incorporated into glucose and carbon dioxide are also given, and for both theories the specific radioactivities of aspartate and glutamate relative to the specific radioactivity of the substrate. The theories allow for entry of label into the tricarboxylic acid cycle via both oxaloacetate and acetyl-CoA, for (14)CO(2) fixation and for loss of label from the tricarboxylic acid cycle in glutamate, but not for losses in citrate. They also allow for incomplete symmetrization of label in oxaloacetate due to incomplete equilibration with fumarate both in the extramitochondrial part of the cell and in the mitochondrion on entry of oxaloacetate into the tricarboxylic acid cycle. In the latter case failure both of oxaloacetate to equilibrate with malate and of malate to equilibrate with fumarate are considered.

Animals↗

PubMed1977

Blood-brain barrier during electroshock seizures in the rat.

The effect of electrically induced seizures on the permeability of the rat blood-brain barrier was investigated. The small radioactive tracers sodium (24Na+), chloride (36Cl-) carbon labelled thiourea (14C-thiourea) and glucose (14C-D-glucose) were studied in indicator dilution experiments with indium labelled diethylenetriaminepenta-acetic acid (113mIn-DTPA) as reference substance. This method allows a quantitative estimate of the transcapillary loss of solutes, the extraction (E), during a single passage through the brain. Passage of macromolecules was studied using as marker substance Evans Blue which binds to plasma albumin. In the resting state ENa, ECl, Ethiourea and Eglucose were 2.9, 4.8, 9.3 and 12.5%, respectively. During seizures and during shortlasting hypercapnia E glucose decreased while E for the other tracers was unchanged. As cerebral blood flow increased, there must be an increased transfer of test substances into the brain. This finding is in agreement with recent human studies [15]. When Evans Blue was injected intravenously prior to electroshock, there was no staining of brain tissue after one electroshock but following repeated electroshocks some staining was observed. In an attempt quantify this transcapillary loss of albumin by means of indicator dilution, 51Cr-labelled erythrocytes were used as intravascular reference substance against 113mIn-DTPA (a plasma tracer). However, the albumin loss (by pinocytosis or otherwise) occurring after ten electroshocks could not be detected during a single passage through the brain.

Animals↗

PubMed1984

Mobilization of 45Ca from insulin-producing RINm5F cells attached to microcarriers.

A technique was designed allowing studies of 45Ca efflux from insulin-releasing cells of a clonal cell line (RINm5F) attached to fibronectin-coated plastic beads. Supporting the existence of Ca2+-Ca2+ and Na+-Ca2+ exchange mechanisms, the efflux of 45Ca in a Ca2+-deficient perifusion medium was increased after introduction of Ca2+ and decreased after removal of Na+. The washout of radioactivity was similar to that from pancreatic islets in also being inhibited by glucose in the presence of low concentrations of extracellular Ca2+. During perifusion with a medium containing 2.56 mM Ca2+, increasing the K+ concentration resulted in an increased 45Ca efflux, a process counteracted by D-600. Also, exposure to tolbutamide resulted in a distinct stimulatory peak. Glucose was a poor stimulator of 45Ca efflux, suggesting that this sugar lacks the ability to depolarize the RINm5F cells sufficiently to induce normal opening of the voltage-dependent channels in the plasma membrane. Such a defect might well explain why the RINm5F cells do not respond to glucose with stimulation of insulin release.

Animals↗

PubMed2000

Prognostic value of [18F]fluorodeoxyglucose positron emission tomographic scanning in patients with thyroid cancer.

Poorly differentiated thyroid cancer lesions often lose the ability to concentrate radioactive [131I]iodine (RAI) and exhibit increased metabolic activity, as evidenced by enhanced glucose uptake. We incorporated [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET) scanning into the routine follow-up of a cohort of thyroid cancer patients undergoing annual evaluations. One hundred and twenty-five patients who had previous thyroidectomies were included. They had diagnostic RAI whole body scans, serum thyroglobulin measurements, and additional imaging studies as clinically indicated. During 41 months of follow-up, 14 patients died. Univariate analysis demonstrated that survival was reduced in those with age over 45 yr, distant metastases, PET positivity, high rates of FDG uptake, and high volume of the FDG-avid disease (>125 mL). Survival did not correlate with gender, RAI uptake, initial histology, or grade. Multivariate analysis demonstrated that the single strongest predictor of survival was the volume of FDG-avid disease. The 3-yr survival probability of patients with FDG volumes of 125 mL or less was 0.96 (95% confidence interval, 0.91, 1.0) compared with 0.18 (95% confidence interval, 0.04, 0.85) in patients with FDG volume greater than 125 mL. Only 1 death (of leukemia) occurred in the PET-negative group (n = 66). Of the 10 patients with distant metastases and negative PET scans, all were alive and well. Patients over 45 yr with distant metastases that concentrate FDG are at the highest risk. Once distant metastases are discovered in patients with differentiated thyroid carcinoma, FDG-PET can identify high and low risk subsets. Subjects with a FDG volume greater than 125 mL have significantly reduced short term survival.

Adult↗

PubMed1975

[Correlation of some nitrogenous compounds in the blood and tissues of tumor-bearing rabbits in hyperglycemia].

In rabbits transplanted Brown-Pearce carcinoma the content of nitrous compounds in tissues is changed in a different way: in the liver and kidneys -- nitrous compounds are accumulated, while in cardiac and skeletal muscles their concentration is diminished. It is found that tumor cells in mice with Ehrlich carcinoma accumulate radioactive aminoacid considerably faster than adjacent tissues not involved by neoplasma. A continuous glucose administration in tumor-bearing rabbits renders a marked nitrogen-saving effect by means of attenuation of catabolism of myoproteins, as a result of it the balance between the processes of synthesis and catabolism in host tissues is shifted toward synthesis.

Amino Acids↗

PubMed1994

Evaluation of cerebral metabolism and quantitative electroencephalography after hypothermic circulatory arrest and low-flow cardiopulmonary bypass at different temperatures.

Although widely used for repair of complex cardiovascular pathologic conditions, long intervals of hypothermic circulatory arrest and low flow cardiopulmonary bypass may both result in cerebral injury. This study examines cerebral hemodynamics, metabolism, and electrical activity to evaluate the risks of cerebral injury after 60 minutes of hypothermic circulatory arrest at 8 degrees C, 13 degrees C, and 18 degrees C, compared with 60 minutes of low flow cardiopulmonary bypass at 18 degrees C. Thirty-two puppies were randomly assigned to one of four experimental groups and centrally cooled to the appropriate temperature. Serial evaluations of quantitative electroencephalography, radioactive microsphere determinations of cerebral blood flow, calculations of cerebral oxygen consumption, cerebral glucose consumption, cerebral vascular resistance, cerebral oxygen extraction, systemic oxygen metabolism, and systemic vascular resistance were done. Measurements were obtained at baseline (37 degrees C), at the end of cooling, at 30 degrees C during rewarming, and at 2, 4, and 8 hours after hypothermic circulatory arrest or low flow cardiopulmonary bypass. At the end of cooling, cerebral vascular resistance remained at baseline levels in all groups, but systemic vascular resistance was increased in all groups. Cerebral oxygen consumption became progressively lower as temperature was reduced: it was only 5% of baseline at 8 degrees C; 20% at 13 degrees C; and 34% and 39% at 18 degrees C. Quantitative electroencephalography was silent in the 8 degrees C and 13 degrees C groups, but significant slow wave activity was present at 18 degrees C. Systemic vascular resistance and cerebral oxygen consumption returned to baseline values in all groups by 2 hours after hypothermic circulatory arrest or low flow cardiopulmonary bypass, but cerebral vascular resistance remained elevated at 2 and 4 hours, not returning to baseline until 8 hours after hypothermic circulatory arrest or low flow cardiopulmonary bypass. All but two of the long-term survivors (27 of 32) appeared neurologically normal; after hypothermic circulatory arrest at 8 degrees and 18 degrees C two animals had an unsteady gait. Comparison of quantitative electroencephalography before operation and 6 days after operation showed a significant increase in slow wave activity (delta activity) after hypothermic circulatory arrest and low flow cardiopulmonary bypass at 18 degrees C, a change that suggests possible cerebral injury. Although undetected after operation by simple behavioral and neurologic assessment, significant differences in cerebral metabolism, vasomotor responses, and quantitative electroencephalography do exist during and after hypothermic circulatory arrest and low flow cardiopulmonary bypass at various temperatures and may be implicated in the occurrence of cerebral injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of Variance↗

PubMedDate not supplied

[Metabolism of methionine in tissues of cattle in vitro].

After incubation of homogenates of liver, kidney, brain, skeletal muscles mucosa of rumen and empty intestine of cattle in Krebs-Ringer's phosphate buffer with [2-14C]methionine 25.8-43.4% radioactive label was found in protein; 28.1-42.0%, in CO2; 12.0-18.6%, in glucose; 8.2-14.9%, in glycogen; 3.1-6.3%, in lipids. The highest level of [2-14C]methionine utilization in protein synthesis was found in skeletal muscle; in energetical processes, in liver; in the process of gluconeogenesis, in skeletal muscles and liver; in lipid synthesis, in brain; the lowest level of [2-14C]methionine utilisation in above-mentioned process was found in skin.

Animals↗

PubMed2000

L-[U-14C] lactate binding to a 43 kDa protein in plasma membranes of Candida utilis.

To identify the putative lactate transporter protein of Candida utilis, plasma membranes from cells grown either on lactic acid (presence of lactate proton symport) or glucose (absence of lactate proton symport) were incubated with L-[U-14C]lactic acid and the membrane proteins were then separated by SDS-PAGE. A well-defined peak of radioactivity occurred in the lane of the gel containing plasma membrane proteins from lactic-acid-grown cells but not from glucose-grown cells. Binding was inhibited by unlabelled pyruvate and lactate, whereas succinate and citrate were not inhibitory. The monocarboxylate transporter inhibitor of animal cells, 4,4'-diisothiocyanatostilbene-2,2'-disulfonate, competitively inhibited the lactate proton symport in the whole yeast and also inhibited lactate binding to proteins of isolated plasma membranes. The polypeptide pattern of plasma membranes from lactic-acid-grown cells revealed a 43 kDa polypeptide associated with the peak of labelled lactate. Altogether the results suggest that this polypeptide is either the lactate transporter or a component of it.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1976

Differences in free fatty acid and glucose metabolism of human blood neutrophils and lymphocytes.

Comparison of isolated human neutrophils and lymphocytes in short-term tissue culture revealed marked differences in their rates of lipid biosynthesis. Ficoll-Hypaque gradients were used to separate lymphocytes and neutrophils from the blood of normal subjects. Neutrophils incorporated more palmitate into cell lipids (151.0 +/- 16.6 nmole/hr/10(8) cells) than lymphocytes (41.6 +/- 4.1). By contrast, the lymphocytes oxidized more palmitate (8.3 +/- 0.5 nmole/hr/10(8) cells) as compared to neutrophils (1.1 +/- 0.1). The greater fatty acid uptake by the neutrophils was due to a sixfold greater rate of incoporation of palmitate into their triglyceride fraction. Triglyceride synthesis by neutrophils increased as the molar ratio of free fatty acid to albumin was raised, whereas incorporation into phospholipids remained relatively constant; there was preferential labeling of neutrophil triglycerides throughout the physiologic range. Studies using linoleate and oleate gave similar results. The distribution of radioactivity into various phospholipids determined by thin-layer chromatography was similar for the two cell types. When labeled glucose was used as a substrate to measure incorporation primarily into the glycerol backbone of the cell lipids, neutrophils incorporated more radioactivity into total lipids and triglycerides than lymphocytes. These results indicate that neutrophils take up much more fatty acid than lymphocytes primarily because they synthesize much larger quantities of triglycerides, a storage form. Since cellular triglycerides may act as a source of fatty acid for lecithin synthesis during phagocytosis, the greater rate of fatty acid incorporation in the neutrophil may reflect a metabolic pattern that permits efficient phagocytosis.

Blood Glucose↗