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Imaging of rats with mammary cancer with two 2-deoxy-2-[18F]fluoro-D-hexoses.

Rats with mammary cancer were imaged by scintigraphy: 10 rats with 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) and 10 rats with [18F]F-D-galactose. The uptake of both tracers was similar in the tumors--the tumor-to-normal tissue ratio was 2.7 +/- 1.1 for [18F]FDG and 2.3 +/- 0.9 for [18F]FDGal at 120 min after injection. In addition to the tumors [18F]FDG accumulated in the brain, bladder and heart, [18F]FDGal in the brain, bladder and liver. [18F]FDGal may be useful for tumor imaging in man; further studies should be addressed to elucidate the mechanism of [18F]FDGal uptake into tumors.

9,10-Dimethyl-1,2-benzanthracene↗

Insulin-stimulated phosphatidylcholine hydrolysis, diacylglycerol/protein kinase C signalling, and hexose transport in pertussis toxin-treated BC3H-1 myocytes.

Pertussis toxin was used to block insulin-stimulated phosphatidylinositol (PI)-glycan hydrolysis, consequent de novo synthesis of phosphatidic acid (PA) and the diacylglycerol (DAG) production that results from these two related processes in BC3H-1 myocytes. In contrast, pertussis toxin pretreatment did not inhibit insulin-stimulated hydrolysis of phosphatidylcholine (PC) which was found to be at least partly due to activation of a phospholipase D. Moreover, pertussis toxin-insensitive PC hydrolysis was accompanied by rapid biphasic increases in DAG and translocative activation of protein kinase C (PKC). Insulin-stimulated glucose transport was also insensitive to pertussis toxin pretreatment. Our findings suggest that insulin-stimulated PC hydrolysis pays an important role in DAG/PKC signalling during insulin action.

Animals↗

Evidence from studies of temperature-dependent changes of D-glucose, D-mannose and L-sorbose permeability that different states of activation of the human erythrocyte hexose transporter exist for good and bad substrates.

(1) The inhibition constant of L-sorbose flux from fresh human erythrocytes by D-glucose, Ki(sorbose) increases on cooling from 50 degrees C to 30 degrees C from 5.15 +/- 0.89 mM to 12.24 +/- 1.9 mM; the Ki(sorbose) of D-mannose increases similarly, indicating that the process is endothermic. (2) The activation energy Ea(sorbose) of net L-sorbose exit is 62.9 +/- 3.1 kJ/mol; in the co-presence of 5 mM D-glucose Ea(sorbose) is reduced to 41.7 +/- 1.6 kJ/mol (P < 0.005). (3) Cooling from 35 degrees C to 21 degrees C decreases the Ki(inf, cis) of auto-inhibition of D-glucose net exit from 5.2 +/- 0.3 mM to 1.36 +/- 0.06 mM; the Ki(inf, cis) of D-mannose falls from 10.9 +/- 1.65 mM to 5.7 +/- 0.3 mM. (4) The activation energy of D-glucose zero-trans net exit is 34.7 +/- 2.1 kJ/mol and that of D-mannose exit is 69.4 +/- 3.7 kJ/mol (P < 0.0025). (5) The exothermic and exergonic processes of auto-inhibition of D-glucose net exit are larger than those for D-mannose (P < 0.03). These data are consistent with D-glucose binding promoting an activated transporter state which following dissociation transiently remains; if an L-sorbose molecule binds within the relaxation time after D-glucose dissociation, it will have a higher mobility than otherwise. Cooling slows the relaxation time of the activated state hence raises the probability that L-sorbose will bind to the glucose-activated transporter. D-Glucose donates twice as much energy to the transporter as D-mannose, consequently produces more facilitation of flux. This view is inconsistent with the alternating carrier model of sugar transport in which net flux is considered to be rate-limited by return of the empty carrier, but is consistent with fixed two-site models.

Cell Membrane Permeability↗

Relationship between the rate of erythrocyte hexose monophosphate pathway and the glucose 6-phosphate concentration.

Erythrocytes of individuals with increased (+ 50%) or reduced (-35%) hexokinase activity contain respectively 70 and 17 nmole/ml RBC of glucose-6-phosphate (normal concentration 30 +/- 5nmole/ml RBC) and show comparable rates of the HMP (60 +/- 5nmole/hr/ml RBC). Similarly, in RBC of different ages, obtained by density gradient ultracentrifugation, the glucose-6-phosphate concentration range from 57 (young cells) to 18 (old cells) nmole/ml RBC but the rate at which glucose is utilized in the HMP is unchanged. These data exclude a regulatory role of glucose 6-phosphate in the HMP even if its concentration is under that required for maximal G6PD activity.

Chromosomes, Human, 6-12 and X↗

Role of hexokinase in the regulation of erythrocyte hexose monophosphate pathway under oxidative stress.

Human erythrocytes overloaded with homogeneous human hexokinase (up to 15-times the activity of normal RBC) show almost unmodified rates of glucose metabolized in the HMP, however hexokinase-loaded RBC are able to metabolize 1.5 fold more glucose than controls through the HMP when an oxidizing agent like methylene blue (5 to 100 microM) is present. Similarly, RBC loaded with inactivating anti-hexokinase IgG (12 +/- 3% residual hexokinase activity) show HMP rates unchanged under resting conditions, but only 12% of the HMP rate found in normal controls under oxidative stress. These data provide clear evidence that the HMP rate under conditions of oxidative stress is controlled by hexokinase activity and suggest that RBC from patients with hexokinase deficiency are not able to increase the HMP rate under oxidative stress like erythrocytes from individuals with G6PD deficiency.

Erythrocytes↗

Synthesis of 1-deoxy-D-erythro-hexo-2,3-diulose, a major hexose Maillard intermediate.

1-Deoxy-D-erythro-hexo-2,3-diulose (1-DG) was prepared by the reaction of ethoxyvinyllithium with an erythronolactone derivative. Characterization by 1H and 13C NMR spectroscopy and NOE difference experiments revealed the 2C5-chair beta-pyranose as the major isomer in solution. Experiments assessing browning and polymerization reactivity proved 1-DG to be a much more potent protein modifier than 3-deoxy-D-erythro-hexos-2-ulose.

Food Analysis↗

A preparative synthesis of 3-amino-2,3,6-trideoxy-L-lyxo-hexose (daunosamine) hydrochloride from D-mannose.

A simple, preparative route in nine steps from methyl alpha-D-mannopyranoside (1) is described that affords, in 40% overall yield, the title amino sugar 11, the sugar constituent of the antitumor antibiotics adriamycin and daunorubicin. The 2,3:4,5-dibenzylidene acetal (2) of 1 is converted by butyllithium into the 2-deoxy-3-ketone 3, whose oxime 4 is reduced with high stereoselectivity to the D-ribo amine, isolated as its N-acetyl derivative 5 and converted by action of N-bromosuccinimide into the 4-O-benzoyl-6-bromide 7. Dehydrohalogenation of gives the 5,6-unsaturated glycoside 8, which, after O-debenzoylation to 9, undergoes stereospecific reduction by hydrogen with net C-5 inversion to give the crystalline, N-acetylated methyl beta-glycoside (10) of daunosamine, readily converted into daunosamine hydrochloride (11) and into the crystalline N-benzoyl (14) and N-acetyl(15) derivatives. No chromatographic procedures for isolation are required in any of the steps.

Deoxy Sugars↗

Regulation of hexose transport in cultured bovine retinal microvessel endothelium by insulin.

In microvessel endothelium obtained from young calf retinas, insulin stimulated the uptake of 2-deoxy-D-glucose in a dose-dependent manner. The maximal level of glucose uptake (50-100% over basal values) was observed at 1 ng ml-1 insulin. The effects of insulin on glucose uptake were time-dependent, with optimum stimulation of glucose transport observed after 90 min of insulin treatment. The effects of insulin were prevented by 15 min pretreatment with 2 micrograms ml-1 cycloheximide or by 2 micrograms ml-1 actinomycin D, suggesting a role for new protein synthesis in the actions of insulin on glucose transport in this cell type. These results demonstrate that cultured retinal microvessel endothelial cells exhibit an insulin-sensitive glucose transport system.

3-O-Methylglucose↗