Enhancement of the mutagenicities of N-methyl-N′-nitro-N-nitrosoguanidine and N-methyl-N-nitrosourea by glucose

The mutagenicity of N-methyl-N′-nitro-N-nitrosoguanidine to Salmonella typhimurium hisG46 was enhanced by pre-incubating the chemical with bacteria in sodium phosphate buffer. Addition of glucose (to 15 mM) to the pre-incubation mixture further enhanced the mutagenicity. Pre-incubation with glucose also increased the mutagenicity of N-methyl-N-nitrosourea. Fructose, galactose, pyruvate and succinate also enhanced the mutagenicity of N-methyl-N′-nitro-N-nitrosoguanidine. The effect of glucose was observed with S. typhimurium strains hisG46, TA1975, TA1950, TA1535 and TA100.     

Effect of glucose and oxygen on β-lactam biosynthesis by Cephalosporium acremonium

The effects of glucose consumption rate (q_s) and oxygen limitation on the control of cephalosporin C (Ceph C) biosynthesis and the activities of deacetoxycephalosporin C synthetase/hydroxylase (DAOC-SH) and acetyl coenzyme A: deacetylcephalosporin C o-acetyltransferase (DAC-AT) were investigated in cultivations of the highly productive Cephalosporium acremonium strain TR87 under conditions similar to those used in industrial production. A carefully optimised time course of q_s during the first part of fed batch cultivations was essential for maximal Ceph C production. The actual glucose concentration in the medium was of secondary importance. A decrease of q_s between 20 and 35 h of cultivation was found to induce the early onset of antibiotic synthesis. By subsequently maintaining q_s at a relatively low level using a controlled feed of glucose and a limiting amount of phosphate, maximal production rates were obtained. Oxygen starvation after the onset of Ceph C production led to a pronounced increase in penicillin N formation, a reduced Ceph C yield (−30%) and a strongly reduced activity of the two enzymes tested. In general, neither the time course nor the absolute levels of the two enzyme activities directly correlated with the actual production rates of Ceph C. This is the first time where an independent parameter (q_s) has been demonstrated to be responsible for triggering the synthesis of an antibiotic.     

Biochemical characteristics and fermentation of glucose and starch by rabbit cæcal strains ofBifidobacterium globosum

Two strains ofBifidobacterium globosum were isolated from cæcal contents of rabbits in a search for potential probiotics. Both strains fermented glucose, galactose, pentoses, maltose, raffinose and starch. Common coccidiostats (monensin, salinomycin) and antimicrobial growth promotors (avoparcin, bacitracin, nitrovin, virginiamycin) supplied at 10 mg/L inhibited their growth in cultures with glucose. Fermentation parameters of bifidobacteria on glucose and starch. When growing on starch, the two strains of bifidobacteria produced 1 mol lactate per 5.6 and 5.7 mol acetate, respectively. Corresponding values during growth on glucose were 17.3 and 8.4 mol of acetate per mol of lactate. Starch-grown cells accumulated more saccharides than cells grown on glucose (1.48vs. 0.41 and 3.12vs. 1.18 mmol glucose units per 1 g of dry matter, respectively).     

Production of γ-linolenic acid by Cunninghamella echinulata cultivated on glucose and orange peel

A newly isolated strain of Cunninghamella echinulata grown on glucose produced significant quantities of biomass and cellular lipids in media with high C/N ratio. The oil yield from glucose consumed increased after nitrogen exhaustion in the growth medium, but gamma-linolenic acid (GLA) content in cellular oil systematically decreased during the lipid accumulation process. When lipid accumulation was completed, GLA concentration in the cellular lipids progressively increased. The highest GLA production (720 mg/l) was achieved in medium with a C/N ratio equal to 163. C. echinulata was also able to grow on orange peel. The C/N ratio in the orange peel decreased from 50 to 26 during solid-state fermentation. Maximum oxygen uptake was observed during assimilation of reducing sugars, whereas a polygalacturonase activity was detected after reducing sugars had been exhausted. The maximum GLA production was 1.2-1.5 mg/g of fermented peel, calculated on a dry weight basis. After enrichment of the pulp with inorganic nitrogen and glucose, an increase in the production of oil and GLA was observed.     

Control of pancreatic β cell regeneration by glucose metabolism

Recent studies revealed a surprising regenerative capacity of insulin-producing β cells in mice, suggesting that regenerative therapy for human diabetes could in principle be achieved. Physiologic β cell regeneration under stressed conditions relies on accelerated proliferation of surviving β cells, but the factors that trigger and control this response remain unclear. Using islet transplantation experiments, we show that β cell mass is controlled systemically rather than by local factors such as tissue damage. Chronic changes in β cell glucose metabolism, rather than blood glucose levels per se, are the main positive regulator of basal and compensatory β cell proliferation in vivo. Intracellularly, genetic and pharmacologic manipulations reveal that glucose induces β cell replication via metabolism by glucokinase, the first step of glycolysis, followed by closure of K(ATP) channels and membrane depolarization. Our data provide a molecular mechanism for homeostatic control of β cell mass by metabolic demand.     

Batch production of high-content fructo-oligosaccharides from sucrose by the mixed-enzyme system of β-fructofuranosidase and glucose oxidase

The production of high-content fructo-oligosaccharides from sucrose by the mixed-enzyme system of β-fructofuranosidase and glucose oxidase was investigated. The mixed-enzyme reaction was carried out in a stirred tank reactor containing 0.7 l of sucrose solution with coupled β-fructofuranosidase and glucose oxidase for 25 h. The optimum conditions for the mixed-enzyme reaction were as follows: pH, 5.5; temperature, 40°C; sucrose concentration, 400 g/l; agitation speed, 550 rpm; oxygen flow rate, 0.7 l/min; enzyme dosage, 10 units of β-fructofuranosidase with the combination of 15 units of glucose oxidase per gram sucrose. Under optimum conditions, high-content fructo-oligosaccharides up to 98% were obtained with complete consumption of sucrose and glucose by the mixed-enzyme system. Compared with the fructo-oligosaccharides produced by the β-fructofuranosidase, the high-content fructo-oligosaccharides produced by the mixed-enzyme system showed a significant difference with respect to sugar composition; i.e., a higher content of nystose was accumulated and only a trace amount of fructofuranosyl nystose was detected.     

Are diabetic neuropathy,retinopathy and nephropathy caused by hyperglycemic exclusion of dehydroascorbate uptake by glucose transporters?

Vitamin C exists in two major forms. The charged form, ascorbic acid (AA), is taken up into cells via sodium-dependent facilitated transport. The uncharged form, dehydroascorbate (DHA), enters cells via glucose transporters (GLUT) and is then converted back to AA within these cells. Cell types such as certain endothelial and epithelial cells as well as neurons that are particularly prone to damage during diabetes tend to be those that appear to be dependent on GLUT transport of DHA rather than sodium-dependent AA uptake. We hypothesize that diabetic neuropathies, nephropathies and retinopathies develop in part by exclusion of DHA uptake by GLUT transporters when blood glucose levels rise above normal. AA plays a central role in the antioxidant defense system. Exclusion of DHA from cells by hyperglycemia would deprive the cells of the central antioxidant, worsening the hyperglycemia-induced oxidative stress level. Moreover, AA participates in many cellular oxidation-reduction reactions including hydroxylation of polypeptide lysine and proline residues and dopamine that are required for collagen production and metabolism and storage of catecholamines in neurons. Increase in the oxidative stress level and metabolic perturbations can be expected in any tissue or cell type that relies exclusively or mainly on GLUT for co-transport of glucose and DHA including neurons, epithelial cells, and vascular tissues. On the other hand, since DHA represents a significant proportion of total serum ascorbate, by increasing total plasma ascorbate concentrations during hyperglycemia, it should be possible to correct the increase in the oxidative stress level and metabolic perturbations, thereby sparing diabetic patients many of their complications.     

Ultra performance liquid chromatography-mass spectrometric determination of the site specificity of modification of β-casein by glucose and methylglyoxal

Modification of protein by carbonyl compounds under in vitro physiological conditions is site-directed. There are few reports of the site specificity of glycation of proteins using heating conditions of relevance to food processing. The aim of this study was to determine the site specificity of modification of β-casein (βCN) by glucose and methylglyoxal (MGO). βCN (1.33 M, 3.2%) was heated with either glucose (1.345 M, 4.6%) or MGO (1 mM) at 95°C for up to 4 h. Tryptic digests were prepared and analysed by ultra performance liquid chromatography electrospray ionisation mass spectrometry (UPLC-ES/MS). The sites of formation of the Amadori product, N ^ε -(fructosyl)lysine (FL), and the advanced glycation end-products, N ^ε -(carboxymethyl)lysine (CML), MGO-derived dihydroxyimidazolidine (MG-DH) and MGO-derived hydroimidazolone (MG-HI), were located. FL and CML were detected at K107 and K176 residues in βCN/glucose incubations. Indigenous N ^ε -(lactulosyl)lysine was detected at K107 only. MG-DH and MG-HI were detected at R202 and possibly R183 residues in both βCN/glucose and βCN/MGO incubations. Glycation of βCN by glucose and MGO resulted in similar site specificity for MG-DH and MG-HI formation.     

The effect of glucose on 11β- and 19-hydroxylation of reichstein's substance S by Pellicularia filamentosa

Summary Experiments in batch-fermenters have demonstrated that the 11- and 19-hydroxylation of Reichstein's Substance S by Pellicularia filamentosa ceases in the absence of glucose. The effects of glucose consumption rate and growth rate on hydroxylation have been investigated using chemostat cultures. With glucose-limited cultures, increased hydroxylation rates were observed with increased glucose consumption rates. With nitrogen-limited cultures, however, some form of glucose-repression exists. The maximum rate of hydroxylation occurred at a glucose consumption rate at which the culture was just nitrogen-limited. The growth rate had no major importance.     

Is the hepatic metabolism of glucose and linoleic acid influenced by species in overfed ducks?

There are genetic differences in the hepatic glucose and linoleic acid metabolisms between Muscovy and Pekin ducks ad libitum-fed. To understand the effect of overfeeding on the hepatic metabolisms in these two species of ducks, we compared the different pathways of glucose and linoleic acid reaching the liver of Muscovy (Cairina moschata) (n = 6) and Pekin (Anas platyrhynchos) (n = 6) ducks overfed for 1 week and sacrificed 2–4 h after their last meal by using the ex vivo method of liver slices incubated for 16 h with [U-¹⁴C]-glucose, [1-¹⁴C]-linoleic acid and [³⁵S]-methionine added to the survival medium. The glucose was the main precursor of triacylglycerol synthesis in the liver of these two species and its hepatic metabolism was similar between species. The hepatic uptake of linoleic acid was 1.7-fold higher (P = 0.020) in the Muscovy duck than in the Pekin duck leading to a 1.9-fold higher (P = 0.017) esterification of this fatty acid in the liver of the Muscovy duck than in that of the Pekin duck. Finally, both species after 1 week of overfeeding exhibited the same capacity to secrete VLDL remaining insufficient to avoid hepatic steatosis.     

Rate of utilization of glucose and `compartmentation'' of α-oxoglutarate and glutamate in rat brain

1. The rate of incorporation of ¹⁴C into pyruvate, α-oxoglutarate, lactate and glucose of rat tissues was measured after the subcutaneous injection of uniformly labelled glucose. 2. In rat brain the specific radioactivities of lactate and glucose were similar to that of alanine. In liver the specific radioactivity of glucose was considerably higher than that of lactate or alanine. 3. The specific radioactivities of α-oxo acids of rat brain were lower than those of corresponding amino acids, alanine and glutamate. These findings have been explained in relation to metabolic compartments in vivo. 4. The approximate estimated rate of glucose utilization in rat brain in vivo is 0·96μmole/g. of brain/min.     

Metabolic amplification of insulin secretion by glucose is independent of β-cell microtubules

Glucose-induced insulin secretion (IS) by β-cells is controlled by two pathways. The triggering pathway involves ATP-sensitive potassium (K(ATP)) channel-dependent depolarization, Ca(2+) influx, and rise in the cytosolic Ca(2+) concentration ([Ca(2+)](c)), which triggers exocytosis of insulin granules. The metabolic amplifying pathway augments IS without further increasing [Ca(2+)](c). After exclusion of the contribution of actin microfilaments, we here tested whether amplification implicates microtubule-dependent granule mobilization. Mouse islets were treated with nocodazole or taxol, which completely depolymerized and polymerized tubulin. They were then perifused to measure [Ca(2+)](c) and IS. Metabolic amplification was studied during imposed steady elevation of [Ca(2+)](c) by tolbutamide or KCl or by comparing [Ca(2+)](c) and IS responses to glucose and tolbutamide. Nocodazole did not alter [Ca(2+)](c) or IS changes induced by the three secretagogues, whereas taxol caused a small inhibition of IS that is partly ascribed to a decrease in [Ca(2+)](c). When [Ca(2+)](c) was elevated and controlled by KCl or tolbutamide, the amplifying action of glucose was unaffected by microtubule disruption or stabilization. Both phases of IS were larger in response to glucose than tolbutamide, although triggering [Ca(2+)](c) was lower. This difference, due to amplification, persisted in nocodazole- or taxol-treated islets, even when IS was augmented fourfold by microfilament disruption with cytochalasin B or latrunculin B. In conclusion, metabolic amplification rapidly augments first and second phases of IS independently of insulin granule translocation along microtubules. We therefore extend our previous proposal that it does not implicate the cytoskeleton but corresponds to acceleration of the priming process conferring release competence to insulin granules.     

Conversion of O species by cellobiose dehydrogenase (cellobiose oxidase) and glucose oxidase – a comparison

Cellobiose dehydrogenase from Phanerochaete chrysosporium produces HO by electron transfer between cellobiose and O with a lower yield than the 1:1:1 molar ratio displayed by Aspergillus niger. glucose oxidase in the similar reaction between glucose and O. The discrepancy could best be explained if both a FentonÕs reaction and the spontaneous reactivity of the oxygen species formed were taken into account.     

Autocrine modulation of glucose transporter SGLT2 by IL-6 and TNF-α in LLC-PK1 cells

We determined in cultured kidney epithelial cells (LLC-PK(1)) the effects of high glucose, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) on mRNA and protein expression of the renal glucose transporters SGLT1 and SGLT2. Cultured monolayers were incubated with similar concentrations of IL-6 and TNF-α to those produced by LLC-PK(1) in the presence of 20 mM glucose. Confluent monolayers with either 5 (controls, C) or 20 mM glucose (high glucose, HG) were incubated in the presence of 5 mM glucose, 20 mM glucose, 10 pg/ml IL-6, or TNF-α alone or in combination. Separate groups with IL-6 and TNF-α were incubated with antibodies to their respective receptors. HG induced an increased SGLT1 mRNA at 48 h (p<0.05 vs. C) and protein expression in 120 h (p<0.05 vs. C). HG also induced an increased SGLT2 mRNA at 72 and 96 h (P<0.05 vs. C) and SGLT2 protein expression at 120 h (p<0.05 vs. C). In C, 10 pg/ml IL-6 or TNF-α did not modify SGLT1 mRNA (n.s vs. in the absence of cytokines). In contrast, cytokines induced an increased expression of SGLT1 protein at 120 h (p<0.05 vs. in the absence of cytokines), and SGLT2 mRNA and protein were increased at 96 and 120 h, respectively (p<0.05 vs. in absence of cytokines). No changes were observed when cells were incubated with cytokines and HG (n.s vs. C). In conclusion, this study showed that SGLT2 increased in the presence of IL-6 and TNF-α, indicating an autocrine modulation of the expression of this transporter by cytokines.     

Subcellular shifts of trimeric G-proteins following activation of Baker’s yeast by glucose

Addition of glucose to a resting cell suspension of the yeastSaccharomyces cerevisiae was accompanied by marked shifts of the Gα-protein subunits from the plasma membrane to the cell interior. This process was rapid with half-times between <10 and 20 s. The decrease of the plasma membrane pool of the G_iα/G_oα- and G_qα/G₁₁α-protein subunits correlated with an increase in acid-sensitive forms of these proteins which was recovered in the mitochondrial and/or lysosomal membrane fraction. In contrast to cells from higher organisms glucose-stimulated yeast exhibits an extremely rapid type of the redistribution (internalization). The question remains’open as to the functional significance of the internalized forms of the G-proteins as these remain sequestered from the plasma membrane. well after glucose has been consumed.     

Synthesis of tetracyclic oxindoles and evaluation of their α-glucosidase inhibitory and glucose consumption-promoting activity

A series of tetracyclic oxindole derivatives was synthesized by asymmetric 1, 3-dipole reaction in 2–4 steps in 57–86% overall yields. These compounds were evaluated for α-glucosidase inhibitory and glucose consumption-promoting activity in vitro. Compound 4l competitively and reversibly inhibited α-glucosidase (IC₅₀ = 3.64 μM) with activity 14-fold higher than that of acarbose. Docking analysis substantiated these findings. In addition, compound 4l exhibited significant glucose consumption promoting activity at 1 μM.     

Distribution of L-tryptophan in normal and glucose — loaded mice

Summary L-tryptophan is an essential amino acid in food, but is also widely used as a drug on the basis of several physiological actions. Lately, tryptophan's uses as a drug and as a food supplement have been discontinued in several countries due to its severe side-effects.In the present study, the distribution of tryptophan in mice was studied with special attention on the target organs, where the drug has been shown to have pathological or physiological effects.The results showed that several organs took up tryptophan and that glucose loading increased the accumulation. An interesting finding was that the highest concentration of tryptophan was found in the pancreas. The hypophysis and adrenal glands were also sites of accumulation. Within the brain the highest accumulation was found in the cerebrum. High concentrations were also seen in the gastrointestinal tract and bone marrow.The connection between the accumulation of tryptophan and its normal and pathophysiological effects is discussed.