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PubMedDate not supplied

Kinetic analysis of hexose transport to determine the mechanism of amygdalin and prunasin absorption in the intestine.

Evidence is accumulating that glucose-conjugated compounds may be carried across the gut mucosa via the epithelial sodium-dependent monosaccharide transporter SGLT1. A modification of the everted intestinal sac technique was utilized to study the transport of the cyanogenic glycoside amygdalin (D-mandelonitrile beta-D-gentiobioside) and its metabolite D-mandelontrile beta-D-glucoside (prunasin). Everted sacs of rat jejunum and ileum were bathed in isotonic oxygenated sodium chloride-potassium phosphate buffer containing 2.8 microCi D-[(3)H]-mannose and 0.187 microCi D-[(14)C]-glucose. For treatment groups, buffers contained phloridzin, galactose, amygdalin or prunasin. The rate constant (k) for the transport process was calculated. Compared with the control (n = 33), phloridzin (n = 25) significantly reduced the rate constants of both D-[(14)C]-glucose and D-[(3)H]-mannose. Substitution of sodium with choline and incremental galactose treatments similarly reduced D-[(14)C]-glucose influx, indicating that a fraction of the transport is carrier-mediated. Treatment with amygdalin did not significantly affect the rate constants of D-[(14)C]-glucose or D-[(3)H]-mannose transport. However, treatment with 1 mM prunasin (n = 16) did reduce the influx of D-[(14)C]-glucose without affecting D-[(3)H]-mannose values. This is consistent with the reports finding that glycoside absorption may be mediated by SGLT1.

Amygdalin↗
PubMed1978

Transport and phosphorylation of hexoses in normal and Rous sarcoma virus-transformed chick embryo fibroblasts.

Effects of transformation by Rous sarcoma virus on sugar uptake and activity and the subcellular distribution of hexokinase isozymes in chick embryo fibroblasts were examined. Transformation caused a several-fold increase in the maximum velocity for uptake of 2-deoxyglucose without a significant change in Km. Cytochalasin B (CB), was used to differentiate between the effects of transformation on facilitated diffusion and the nonsaturable (CB-insensitive) mode. Transformation was found to stimulate 2-deoxyglucose transport by both mechanisms, but the increase in transport by the CB-insensitive mode was greater. Transformation enhances the activity of hexokinase, the enhancement being confined to the particulate fraction of the enzyme. Heat-inactivation and electrophoretic mobility studies showed that although hexokinase Type I is the major form in both normal and transformed fibroblasts, there is a significant increase in the proportion of the Type II isozyme in the transformed cells.

Animals↗
PubMed1990

Regulation of hexose transport in respiration deficient hamster lung fibroblasts.

The transport of [3H]2-deoxy-D-glucose (2DG) and [3H]3-O-methyl-D-glucose (3-OMG) was elevated in a respiration deficient (NADH coenzyme Q [Co Q] reductase deficient) Chinese hamster lung fibroblast cell line (G14). This sugar transport increase was related to an increased Vmax for 2DG transport, 26.9 +/- 4.2 nmoles 2DG/mg protein/30 sec in the G14 cell line vs 9.5 +/- 0.6 nmoles 2DG/mg protein/30 sec in the parental V79 cell line. No differences were observed in their respective Km values for 2DG transport (3.9 +/- .6 vs. 3.0 +/- .13 mM). Factors which increase sugar transport (e.g., glucose deprivation, serum or insulin exposure) or decrease sugar transport (e.g., serum deprivation) in the parental V79 cell line had little effect on sugar transport in the G14 respiration deficient cell lines. Amino acid transport, specific 125I-insulin binding to cells, and insulin-stimulated DNA synthesis, however, were similar in both cell lines. Exposure of both cell lines to varying concentrations of cycloheximide (0.1-50 micrograms/ml) for 4 h resulted in differential effects on 2DG transport. In the parental cell line (V79) low cycloheximide concentrations resulted in decreased 2DG transport, while higher concentrations (greater than or equal to 1 microgram/ml) resulted in elevated 2DG transport. In the G14 cell line, 2DG transport decreased at all concentrations of cycloheximide (up to 50 micrograms/ml). The data indicate that the G14 mutant has been significantly and specifically affected in the expression of sugar transport activity and in the regulatory controls affecting sugar transport activity.

3-O-Methylglucose↗
PubMed1994

Evidence that modulation of glucose transporter intrinsic activity is the mechanism involved in the allose-mediated depression of hexose transport in mammalian cells.

In serum starved V79 Chinese hamster lung fibroblast cells, replacement of D-glucose with D-allose resulted in a significant 38 +/- 18% (P < 0.05) reduction of 2-deoxy-D-glucose (2-DG) transport. Similarly, in a respiration-deficient mutant cell line (V79-G14), which has elevated 2-DG transport activity, D-allose reduced 2-DG transport by 59 +/- 18% (P < 0.05). [3H]D-allose uptake by V79 cells occurred slowly and was not inhibited by cytochalasin B, suggesting diffusion as the mode of D-allose entry. Western blot analysis using a rabbit polyclonal antibody to the human erythrocyte glucose transporter (GT) demonstrated that, in both cell lines, GT content and GT subcellular distribution were not significantly different in D-glucose vs. D-allose-treated cells. delta-Antibody, which has been shown to bind to exofacial epitopes of the GT (Harrison et al., 1990, J. Biol. Chem., 265:5793-5801), did not demonstrate any differences in surface binding to D-glucose vs. D-allose-treated intact V79 cells. D-allose treatment of 3T3 fibroblasts resulted in a similar decrease (72%) of 2-DG transport, however D-allose had no apparent effect on basal sugar transport in 3T3 adipocytes. These results suggest that D-allose reduces sugar transport through a modulation of the intrinsic activity of the GT, and that D-allose may act in a tissue-specific manner.

3T3 Cells↗
PubMed2005

MRS reveals additional hexose N-acetyl resonances in the brain of a mouse model for Sandhoff disease.

Sandhoff disease, one of several related lysosomal storage disorders, results from the build up of N-acetyl-containing glycosphingolipids in the brain and is caused by mutations in the genes encoding the hexosaminidase beta-subunit. Affected individuals undergo progressive neurodegeneration in response to the glycosphingolipid storage. (1)H magnetic resonance spectra of perchloric acid extracts of Sandhoff mouse brain exhibited several resonances ca 2.07 ppm that were not present in the corresponding spectra from extracts of wild-type mouse brain. High-performance liquid chromatography and mass spectrometry of the Sandhoff extracts post-MRS identified the presence of N-acetylhexosamine-containing oligosaccharides, which are the likely cause of the additional MRS resonances. MRS of intact brain tissue with magic angle spinning also showed additional resonances at ca 2.07 ppm in the Sandhoff case. These resonances appeared to increase with disease progression and probably arise, for the most part, from the stored glycosphingolipids, which are absent in the aqueous extracts. Hence in vivo MRS may be a useful tool for detecting early-stage Sandhoff disease and response to treatment.

Animals↗
PubMed1996

Hexose metabolism in pancreatic islets: apparent dissociation between the secretory and metabolic effects of D-fructose.

In rat pancreatic islets, D-fructose causes a concentration-related shift to the left of the sigmoidal relationship between insulin release and D-glucose concentration. For instance, when D-fructose is tested at a 80 mM concentration, which is close to the threshold value for stimulation of insulin release by the ketohexose in the absence of D-glucose, a close-to-maximal secretory response is recorded in islets concomitantly exposed to as little as 6.0 to 8.3 mM D-glucose. Under these conditions, however, D-fructose fails to affect the utilization of D-[5-3H]glucose, the oxidation of D-[U-14C]glucose, or its conversion to either 14C-labeled acidic metabolites or amino acids. Under the same experimental conditions, the oxidation of D-[U-14C]fructose and its conversion to 14C-labeled amino acids represent no more than 80-85% of the corresponding values found with 6 mM D-[U-14C]glucose. Actually, the total output of 14CO2 attributable to the oxidation of both D-[U-14C]glucose (6 mM) and D-[U-14C]fructose (80 mM) remains lower than that found in the sole presence of 8.3 mM D-[U-14C]glucose, despite the much higher rate of insulin secretion found in the former compared to the latter situation. These findings suggest that the insulinotropic action of D-fructose cannot be fully accounted for by its capacity to act as a fuel in islet cells, as if it were to involve the generation of a second messenger distinct from those coupling factors currently implied in the process of nutrient-stimulated insulin release.

Animals↗