Age influences on intestinal sugar absorption

Intestinal absorption of sugars show differences depending on animals age. This is demonstrated using in vivo and in vitro techniques. The age dependence relationship is present in animals of different species such as avian, rodents and ruminants. In chicken the intestinal sugar transport increases after hatching and attains its maximum capacity by the first week of life. The D-glucose and D-galactose uptake is greater in young rats, maximum at 21 days, while it decreases thereafter. The total capacity of the small intestine of adult sheep for sugar absorption was approx. 25% of that for lambs less than 1 week of age. The differences observed in intestinal absorption of sugars at different ages could be attributed to differences in sodium and calcium transport. Other authors assume that it is induced by morphological differentiation during intestinal development.     

Sugar sensing by enterocytes combines polarity, membrane bound detectors and sugar metabolism

Sugar consumption and subsequent sugar metabolism are known to regulate the expression of genes involved in intestinal sugar absorption and delivery. Here we investigate the hypothesis that sugar-sensing detectors in membranes facing the intestinal lumen or the bloodstream can also modulate intestinal sugar absorption. We used wild-type and GLUT2-null mice, to show that dietary sugars stimulate the expression of sucrase-isomaltase (SI) and L-pyruvate kinase (L-PK) by GLUT2-dependent mechanisms, whereas the expression of GLUT5 and SGLT1, did not rely on the presence of GLUT2. By providing sugar metabolites, sugar transporters, including GLUT2, fuelled a sensing pathway. In Caco2/TC7 enterocytes, we could disconnect the sensing triggered by detector from that produced by metabolism, and found that GLUT2 generated a metabolism-independent pathway to stimulate the expression of SI and L-PK. In cultured enterocytes, both apical and basolateral fructose could increase the expression of GLUT5, conversely, basolateral sugar administration could stimulate the expression of GLUT2. Finally, we located the sweet-taste receptors T1R3 and T1R2 in plasma membranes, and we measured their cognate G alpha Gustducin mRNA levels. Furthermore, we showed that a T1R3 inhibitor altered the fructose-induced expression of SGLT1, GLUT5, and L-PK. Intestinal gene expression is thus controlled by a combination of at least three sugar-signaling pathways triggered by sugar metabolites and membrane sugar receptors that, according to membrane location, determine sugar-sensing polarity. This provides a rationale for how intestine adapts sugar delivery to blood and dietary sugar provision.     

Role of -SH groups in rat sugar intestinal transport in vivo.

The effect of p-chloromercuribenzoic acid (pCMB), either alone or in the presence of 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), on the 1 mM galactose absorption by in vivo perfused rat intestine has been studied. At 0.25 mM concentration, pCMB inhibits galactose absorption in about 32% but it does not modify the absorption of this sugar when the transport is blocked by 0.5 mM phlorizin, or that of the non-transportable monosaccharide derivative 2-deoxy-D-glucose. This shows that only the active transport component of galactose absorption is inhibited. A 2 min preexposure period is required for the inhibition to appear. The inhibition was not reversed by washing with saline solution even when it contained 0.5 mM dithioerythritol, 10 mM cysteine or 5 and 10 mM EDTA. The simultaneous exposure to 0.25 pCMB and 0.25 mM DTNB inhibits the total galactose entry in about 50%, an effect higher than the one exerted by each reagent separately and close to the one obtained with 0.5 mM phlorizin. Our results, in vivo, confirm the importance of the thiol groups in the cotransport of Na+ and sugar. As DTNB is an SH-reagent of lesser liposolubility than pCMB, the existence of two populations of sulfhydryl groups related to sugar transport which differ in their location within the brushborder membrane and in accessibility from the intestinal lumen, is suggested.     

Uranyl action on sugar transport across rat jejunum

The effect of uranyl on sugar transport across rat jejunum has been studied in vitro and in vivo. D-glucose and D-galactose accumulation in jejunum rings at pH 6.0 is inhibited about 40-65% by 1 mM uranyl nitrate. This inhibition is lower than that produced by 0.5 mM phlorizin. The effect was very similar when the incubation of the rings with the sugar was made in the absence of uranyl, after preincubation with the inhibitor. Washing with 10 mM EDTA reverted uranyl inhibition only slightly. D-fructose entry was weakly inhibited by uranyl. Glucose absorption in vivo along perfusion periods of 1 min was not affected by the presence of uranyl (0.001 to 1 mM) in the sugar solution, but the exposure of the mucosa to 0.1 mM uranyl at pH 6.5 for 10 min inhibited sugar absorption at the same pH in the subsequent periods of perfusion. Results suggest that uranyl impairs sugar transport by binding to protein chemical groups at the surface or in deeper sites of enterocyte membranes, a process that requires some minutes to be accomplished.     

Effects of boron on nitrogen metabolism and sugar levels of sugar beet

Summary The effects of deficient and toxic levels of boron on various aspects of nitrogen metabolism in sugar beet are studied. Plant analysis shows a nitrate ion accumulation, a decrease in the activity of the nitrate reductase enzyme and a lower molybdenum absorption.The effect of boron levels on the plant and root sugar concentration has also been studied.     

Effect of adrenomedullin and proadrenomedullin N-terminal 20 peptide on sugar transport in the rat intestine

Previous studies have shown immunostaining of adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) throughout the gastrointestinal tract. Based on these data, we decided to investigate the effect of these peptides on intestinal sugar absorption using everted rings from Wistar rat intestine. PAMP increases alpha-methylglucoside (MG) uptake at concentrations ranging from 10(-12) to 10(-7) M. AM shows a dual effect inhibiting sugar absorption at low concentrations (10(-12) to 10(-11) M) and increasing MG uptake at higher concentrations (10(-8) to 10(-6) M). In all cases, the effect is phloridzin-sensitive, indicating that the peptides alter SGLT1 function without modifying the non-mediated component of absorption. The enhancing effect of 10(-8) M AM and PAMP seems to be mediated by elevation of cAMP and is accompanied by an increase on SGLT1 expression in the brush-border membrane of the enterocytes. The inhibitory effect of 10(-12) M AM could be mediated by either cAMP reduction or, more probably, by other second messenger able to inhibit sugar absorption. PKC is not involved in the action of either AM or PAMP. These results demonstrate that both peptides play a role in the regulation of the active transport of sugars in the intestine.     

Interaction of rubidium or sodium with potassium in absorption by intact sugar beet plants

This study concerns the selective absorption of K and Rb or of K and Na by intact sugar beet (Beta vulgaris) plants from modified conventional nutrient solutions over an extended period of plant growth. Long term results agreed with those of short term experiments by other investigators using excised root systems and simple salt solutions. Potassium and Rb were mutually competitive in their absorption. High selectivity of K relative to Na absorption was observed. Sodium was excluded during the early growth period of sugar beets.     

Effects of dietary fibre on the intestinal absorption of dextrin, blood sugar level and growth of tilapia, Oreochromis niloticm × O. aureus

The roles of five different dietary fibres (cellulose, agar, guar gum, carrageenan and carboxy-methylcellulose) each as 10% wt/wt added into the diet, affecting the intestinal sugar absorption, blood sugar level and utilization of dextrin were studied in hybrid tilapia, Oreochromis niloticus × O. aureus ; dextrin and glucose were also included in the study as controls for comparison. There were seven dietary groups: each diet was fed to three aquaria each containing 15 fish. The experiment was carried out in a closed circulation, filtered, rearing system for 2 months. The results indicated that the weight gain percentage and food conversion ratio were significantly (P<0.05) lower in tilapia fed fibre-containing diets than those of tilapia fed dextrin or glucose diet. The intestinal absorption of carbohydrate and the blood sugar content of tilapia were low when diets contained fibre, regardless of the source.     

The Asn-420-linked sugar chain in human epidermal growth factor receptor suppresses ligand-independent spontaneous oligomerization. Possible role of a specific sugar chain in controllable receptor activation

To elucidate a role(s) of Asn-linked sugar chain(s) in the function of epidermal growth factor receptor (EGFR), a series of the EGFR mutants were prepared in which potential glycosylation sites in the domain III were eliminated by site-directed mutagenesis. Although the wild-type and mutants of Asn-328, Asn-337, and Asn-389 underwent autophosphorylation in response to epidermal growth factor (EGF), the Asn-420 --> Gln mutant was found to be constitutively tyrosine-phosphorylated. This abnormal ligand-independent phosphorylation of the mutant appears to be due to a ligand-independent spontaneous oligomer formation, as shown by a cross-linking experiment using the purified soluble extracellular domain (sEGFR). As revealed by the dissociation of the Asn-420 --> Gln sEGFR oligomer by simple dilution, it seems likely that the equilibrium is shifted toward oligomer formation to an unusual degree. Furthermore, it was also found that the mutation caused a loss of the ability to bind EGF. These findings suggest that the sugar chain linked to Asn-420 plays a crucial role in EGF binding and prevents spontaneous oligomerization of the EGFR, which may otherwise lead to uncontrollable receptor activation, and support the view of a specific role of an Asn-linked sugar chain in the function of a glycoprotein.     

Sodium absorption by intact sugar beet plants

Sodium absorption by intact sugar beet plants (Beta vulgaris) was found to be mediated by at least two distinct mechanisms when uptake was studied over a wide range of Na and K concentrations. The first mechanism operates at low Na concentrations (<1 milliequivalent per liter); presence of K completely blocks this mechanism for Na. The second mechanism operates at high Na concentrations (>1 milliequivalent per liter), transporting Na as well as K; but apparently this mechanism is not active for Na absorption in young sugar beet plants up to the 10-leaf stage.     

Adenylate patterns of autumn-sown sugar beet differ from spring-sown sugar beet. Implications for root quality

Sugar beet ( Beta vulgaris L) is generally cultivated using two different planting and harvest patterns. In northern zones, spring sugar beet is sown in spring and harvested in autumn, whereas in subtropical latitudes, autumn sugar beet is sown in autumn and harvested in summer. The industrial quality of the root is frequently higher in spring-sown sugar beet crops. In order to explore physiological changes associated with this fact, this study has been focused on the seasonal changes of adenosine 5'-triphosphate and adenosine 5'-diphosphate levels in the storage roots of sugar beet plants, as an index of its metabolic status. The results obtained correspond to a different metabolic status of spring and autumn sugar beet at the moment of harvest. The adenylate patterns of autumn beets suggested a functional and active respiratory system. On the contrary, the patterns shown by spring beets corresponded to those we would expect to see in plants becoming dormant. The proline and glucose contents, which decrease the industrial quality of the root, and the respiratory rate measured in autumn-sown sugar beets, were nearly twice those of spring-sown sugar beets. The combination of an active respiratory system, which allows the carbohydrate catabolism and the synthesis of stress molecules, with the environmental factors at the time of the harvest, could be the underlying physiological mechanism causing some of the differences between spring- and autumn-sown sugar beet crops.     

Conversion of pyridylamino sugar chains to corresponding reducing sugar chains

Pyridylamino sugar chains were converted to the corresponding reducing sugar chains by first converting them to 1-amino-1-deoxy derivatives using the method previously reported [S. Hase, J. Biochem. 112, 266-268 (1992)] and then converting the products to the corresponding reducing sugar chains using the Sommlet reaction. The reaction conditions were optimized so as to obtain the maximal product yield using 1-amino-1-deoxylactose and 1-amino-1-deoxy-N-acetylglucosamine. When the established procedure was successively applied to pyridylamino high-mannose and complex-type sugar chains, the corresponding reducing sugar chains were obtained in yields of 30%.     

Vitamin C interaction with cobalt-ammine cations. Synthesis, spectroscopic and structural characterization of cobalt-pentammine and cobalt-tetrammine sugar complexes containing L-ascorbate anion

Interaction between [Co(NH3)5Cl]Cl2, [Co(NH3)4Cl2]Cl and L-ascorbic acid has been investigated in aqueous solution and solid complexes of the type [Co(NH3)5 ascorbate]Cl2 X H2O and [Co(NH3)4 ascorbate]Cl2 X H2O have been isolated and characterized by 13C-NMR, FT-IR and electron absorption spectroscopy. Spectroscopic and other evidence suggested that the sugar anion binds monodentately in the [Co(NH3)5 ascorbate]2+ cation via the ionized O3 oxygen atom and bidentately in [Co(NH3)4 ascorbate]2+ through the O1 and O4 oxygen atoms, resulting in a six-coordinate geometry around the Co(III) ion. The intermolecular sugar hydrogen-bonding network is perturbed upon sugar metalation and the sugar moiety shows a similar conformation to that of the sodium ascorbate compound in these series of cobalt-ammine complexes.     

Stereoselective degradation of benalaxyl in tomato, tobacco, sugar beet, capsicum, and soil

The stereoselective degradation of the racemic benalaxyl in vegetables such as tomato, tobacco, sugar beet, capsicum, and the soil has been investigated. The two enantiomers of benalaxyl in the matrix were extracted by organic solvent and determined by validated chiral high-performance liquid chromatography with a cellulose-tris-(3, 5-dimethylphenylcarbamate)-based chiral column. Rac-benalaxyl was fortified into the soil and foliar applied to vegetables. The assay method was linear over a range of concentrations (0.5-50 microg ml(-1)) and the mean recoveries in all the samples were more than 70% for the two enantiomers. The limit of detection for both enantiomers was 0.05 microg g(-1). The results in soil showed that R-(-)-enantiomer dissipated faster than S-(+)-enantiomer and the stereoselectivity might be caused by microorganisms. In tomato, tobacco, sugar, beet, and capsicum plants, there was significantly stereoselective metabolism. The preferential absorption and degradation of S-(+)-enantiomer resulted an enrichment of the R-(-)-enantiomer residue in all the vegetables.     

The red blood cell glucose transporter presents multiple, nucleotide-sensitive sugar exit sites.

At any instant, the human erythrocyte sugar transporter presents at least one sugar export site but multiple sugar import sites. The present study asks whether the transporter also presents more than one sugar exit site. We approached this question by analysis of binding of [3H]cytochalasin B (an export conformer ligand) to the human erythrocyte sugar transporter and by analysis of cytochalasin B modulation of human red blood cell sugar uptake. Phloretin-inhibitable cytochalasin B binding to human red blood cells, to human red blood cell integral membrane proteins, and to purified human red blood cell glucose transport protein (GluT1) displays positive cooperativity at very low cytochalasin B levels. Cooperativity between sites and K(d(app)) for cytochalasin B binding are reduced in the presence of intracellular ATP. Red cell sugar uptake at subsaturating sugar levels is inhibited by high concentrations of cytochalasin B but is stimulated by lower (<20 nM) concentrations. Increasing concentrations of the e1 ligand forskolin also first stimulate then inhibit sugar uptake. Cytochalasin D (a cytochalasin B analogue that does not interact with GluT1) is without effect on sugar transport over the same concentration range. Cytochalasin B and ATP binding are synergistic. ATP (but not AMP) enhances [3H]cytochalasin B photoincorporation into GluT1 while cytochalasin B (but not cytochalasin D) enhances [gamma-32P]azidoATP photoincorporation into GluT1. We propose that the red blood cell glucose transporter is a cooperative tetramer of GluT1 proteins in which each protein presents a translocation pathway that alternates between uptake (e2) and export (e1) states but where, at any instant, two subunits must present uptake (e2) and two subunits must present exit (e1) states.     

Synthesis of sugar fatty acid esters by modified lipase.

A simple synthesis of sugar fatty acid esters was developed in a nonaqueous solution using lipase modified by synthetic detergent. Esterification of sugar was accelerated by continuous removal of water from the reaction mixture with a molecular sieve. When glucose and palmitic acid (1:1 by mole) were used as the starting substrates, more than 90% of glucose was converted to its ester in this system. The resultant product was 6-O-palmitoylglucose. Other mono- or disaccharides were also esterified by the modified lipase with high yield. It was shown that the modified lipase might act as a catalyst for the synthesis of sugar fatty acid esters.     

Effect of enteric micro-organisms on intestinal sugar and fatty acid absorption

The effect of micro-organisms contaminating the upper intestinal contents of malnourished children on intestinal absorption of 3-0 methyl-alpha-D-glucopyranose (3-M.G.) and oleic acid was studied in rats in vivo. Oleci acid absorption was unaffected by non-pathogenic E. coli but decreased by E. coli 0111, Salmonella paratyphi B., Shigella sonnei and Candida sp. This effect was probably explained by intestinal secretion diluting the test solution leading to a decreased diffusion gradient for solubilised fatty acid. Inhibition of sugar absorption occurred with bacterial suspensions of Staphylococcus aureus, Streptococcus faecalis, E. coli and Candida sp. and cell-free preparations of Staphylococcus aureus, Streptococcus faecalis, a non-pathogenic E. coli, Proteus sp., Klebsiella sp., Pseudomonas sp. and Candida sp. These effects were not explained by dilution of the test solution. This indicates that numerous micro-organisms and, in some instances, their cell-free preparations can interfere with intestinal active sugar transport. These findings may be relevant to the production of malabsorption in malnourished children who have a wide variety of micro-organisms contaminating their upper intestinal contents.     

Structural analysis of N-linked sugar chains of human blood clotting factor IX

The structures of N-glycans of human blood clotting factor IX were studied. N-Glycans liberated by hydrazinolysis were N-acetylated and the reducing-end sugar residues were tagged with 2-aminopyridine. The pyridylamino (PA-) sugar chains thus obtained were purified by HPLC. Each PA-sugar chain was analyzed by two-dimensional sugar mapping combined with glycosidase digestion. The major structures of the N-linked sugar chains of human factor IX were found to be sialotetraantennary and sialotriantennary chains with or without fucose residues. These highly sialylated sugar chains are located on the activation peptide of the protein.