Absence Of D-glucose Research Articles

The effect of ionic redistributions on the microwave dielectric response of cytosol water upon glucose uptake.

The sensitivity of cytosol water's microwave dielectric (MD) response to D-glucose uptake in Red Blood Cells (RBCs) allows the detailed study of cellular mechanisms as a function of controlled exposures to glucose and other related analytes like electrolytes. However, the underlying mechanism behind the sensitivity to glucose exposure remains a topic of debate. In this research, we utilize MDS within the frequency range of 0.5-40 GHz to explore how ionic redistributions within the cell impact the microwave dielectric characteristics associated with D-glucose uptake in RBC suspensions. Specifically, we compare glucose uptake in RBCs exposed to the physiological concentration of Ca2+ vs. Ca-free conditions. We also investigate the potential involvement of Na+/K+ redistribution in glucose-mediated dielectric response by studying RBCs treated with a specific Na+/K+ pump inhibitor, ouabain. We present some insights into the MD response of cytosol water when exposed to Ca2+ in the absence of D-glucose. The findings from this study confirm that ion-induced alterations in bound/bulk water balance do not affect the MD response of cytosol water during glucose uptake.

CAMP signaling factors regulate carbon catabolite repression of hemicellulase genes in Aspergillus nidulans

Carbon catabolite repression (CCR) enables preferential utilization of easily metabolizable carbon sources, implying the presence of mechanisms to ensure discriminatory gene repression depending on the ambient carbon sources. However, the mechanisms for such hierarchical repression are not precisely understood. In this report, we examined how deletion of pkaA and ganB, which encode cAMP signaling factors, and creA, which encodes a well-characterized repressor of CCR, affects CCR of hemicellulase genes in the filamentous fungus Aspergillus nidulans. β-Xylanase production increased not only in ΔcreA but also in ΔpkaA and ΔganB, with the highest level observed in their double deletants, irrespective of the presence or absence of d-glucose. Expression of the β-xylanase genes in the presence of d-glucose was de-repressed in all the deletion mutants, with significantly higher tolerance against d-glucose repression in ΔpkaA and ΔganB than in ΔcreA. In the presence of galactomannan and d-glucose, partial de-repression of β-mannanase production was detected in ΔcreA, but not in ΔpkaA and ΔganB. The double deletion of creA/pkaA and creA/ganB led to earlier production. Release from d-glucose repression of the β-mannanase genes was partial in the single deletants, while nearly full de-repression was observed in ΔcreAΔpkaA and ΔcreAΔganB. The contribution of PkaA and GanB to CCR by d-xylose of the β-mannanase genes was very minor compared to that of CreA. Consequently, the present study revealed that cAMP signaling plays a major role in CCR of hemicellulase gene expression in a manner that is clearly independent from CreA.

Electrophysiology of the pancreatic islet β-cell sweet taste receptor TIR3.

Over recent years, the presence of the sweet taste receptor TIR3 in rodent and human insulin-producing pancreatic islet β-cells was documented. The activation of this receptor by sweet-tasting sucralose mimics several biochemical and functional effects of D-glucose in the β-cells. The present study extends this analogy to the bioelectrical response of β-cells. In this respect, sucralose was inefficient in the absence of D-glucose, but induced on occasion electrical activity in mouse β-cells exposed to low non-stimulatory concentrations of the hexose and potentiated, in a concentration-related manner, the response to stimulatory concentrations of D-glucose. These data indicate that sucralose, acting as an agonist of the TIR3 receptor, exerts an excitatory effect upon pancreatic β-cell bioelectrical activity.

TP53 mutation hits energy metabolism and increases glycolysis in breast cancer.

Promising new hallmarks of cancer is alteration of energy metabolism that involves molecular mechanisms shifting cancer cells to aerobe glycolysis. Our goal was to evaluate the correlation between mutation in the commonly mutated tumor suppressor gene TP53 and metabolism. We established a database comprising mutation and RNA-seq expression data of the TCGA repository and performed receiver operating characteristics (ROC) analysis to compare expression of each gene between TP53 mutated and wild type samples. All together 762 breast cancer samples were evaluated of which 215 had TP53 mutation. Top up-regulated metabolic genes include glycolytic enzymes (e.g. HK3, GPI, GAPDH, PGK1, ENO1), glycolysis regulator (PDK1) and pentose phosphate pathway enzymes (PGD, TKT, RPIA). Gluconeogenesis enzymes (G6PC3, FBP1) were down-regulated. Oxygen consumption and extracellular acidification rates were measured in TP53 wild type and mutant breast cell lines with a microfluorimetric analyzer. Applying metabolic inhibitors in the presence and absence of D-glucose and L-glutamine in cell culture experiments resulted in higher glycolytic and mitochondrial activity in TP53 mutant breast cancer cell lines. In summary, TP53 mutation influences energy metabolism at multiple levels. Our results provide evidence for the synergistic activation of multiple hallmarks linking to these the mutation status of a key driver gene.

Influence of P-Glycoprotein Inhibition or Deficiency at the Blood-Brain Barrier on (18)F-2-Fluoro-2-Deoxy-D-glucose ( (18)F-FDG) Brain Kinetics.

The fluorinated D-glucose analog (18)F-2-fluoro-2-deoxy-D-glucose ((18)F-FDG) is the most prevalent radiopharmaceutical for positron emission tomography (PET) imaging. P-Glycoprotein's (P-gp, MDR1, and ABCB1) function in various cancer cell lines and tumors was shown to impact (18)F-FDG incorporation, suggesting that P-gp function at the blood-brain barrier may also modulate (18)F-FDG brain kinetics. We tested the influence of P-gp inhibition using the cyclosporine analog valspodar (PSC833; 5μM) on the uptake of (18)F-FDG in standardized human P-gp-overexpressing cells (MDCKII-MDR1). Consequences for (18)F-FDG brain kinetics were then assessed using (i) (18)F-FDG PET imaging and suitable kinetic modelling in baboons without or with P-gp inhibition by intravenous cyclosporine infusion (15mgkg(-1)h(-1)) and (ii) in situ brain perfusion in wild-type and P-gp/Bcrp (breast cancer resistance protein) knockout mice and controlled D-glucose exposure to the brain. In vitro, the time course of (18)F-FDG uptake in MDR1 cells was influenced by the presence of valspodar in the absence of D-glucose but not in the presence of high D-glucose concentration. PET analysis revealed that P-gp inhibition had no significant impact on estimated brain kinetics parameters K 1, k 2, k 3, V T , and CMRGlc. The lack of P-gp effect on in vivo (18)F-FDG brain distribution was confirmed in P-gp/Bcrp-deficient mice. P-gp inhibition indirectly modulates (18)F-FDG uptake into P-gp-overexpressing cells, possibly through differences in the energetic cell level state. (18)F-FDG is not a P-gp substrate at the BBB and (18)F-FDG brain kinetics as well as estimated brain glucose metabolism are influenced by neither P-gp inhibition nor P-gp/Bcrp deficiencies in baboon and mice, respectively.

Characterization of a Novel β-Glucosidase from a Compost Microbial Metagenome with Strong Transglycosylation Activity

The β-glucosidase encoded by the td2f2 gene was isolated from a compost microbial metagenomic library by functional screening. The protein was identified to be a member of the glycoside hydrolase family 1 and was overexpressed in Escherichia coli, purified, and biochemically characterized. The recombinant β-glucosidase, Td2F2, exhibited enzymatic activity with β-glycosidic substrates, with preferences for glucose, fucose, and galactose. Hydrolysis occurred at the nonreducing end and in an exo manner. The order of catalytic efficiency for glucodisaccharides and cellooligosaccharides was sophorose > cellotetraose > cellotriose > laminaribiose > cellobiose > cellopentaose > gentiobiose, respectively. Intriguingly, the p-nitrophenyl-β-D-glucopyranoside hydrolysis activity of Td2F2 was activated by various monosaccharides and sugar alcohols. At a D-glucose concentration of 1000 mM, enzyme activity was 6.7-fold higher than that observed in the absence of D-glucose. With 31.3 mM D-glucose, Td2F2 catalyzed transglycosylation to generate sophorose, laminaribiose, cellobiose, and gentiobiose. Transglycosylation products were detected under all activated conditions, suggesting that the activity enhancement induced by monosaccharides and sugar alcohols may be due to the transglycosylation activity of the enzyme. These results show that Td2F2 obtained from a compost microbial metagenome may be a potent candidate for industrial applications.

Functionalized Vesicles Based on Amphiphilic Boronic Acids: A System for Recognizing Biologically Important Polyols

We report on a new approach for creating water-soluble functionalized vesicles employing N-alkyl-3-boronopyridinium triflates (alkyl = Me, C12H25, C16H33) as sensors for monosaccharides. The nanoaggregate properties were studied by means of DLS, TEM, high-resolution (1)H NMR, and the solvatochromic dyes Reichardt's betaine and Methyl Orange. The vesicles were shown to have 30-200 nm diameters depending on the amphiphile chain length. Diol binding to the vesicles was studied by steady-state fluorescence and UV-vis using Alizarin Red S as a probe in the solution at pH 7.4 in the presence and in the absence of D-glucose and D-fructose. Strong sensing ability of boronic acid functional moieties in the order D-fructose > D-glucose was demonstrated, and apparent binding constants were estimated.

Validation of a new metabolic marker to assess the vascular viability of vitrified whole sheep ovaries

Whole ovary cryopreservation has been suggested as a means to preserve fertility. In animal models, autologous cryopreserved ovary transplants frequently undergo thrombosis and a method to assess the vascular viability of cryopreserved ovaries would be valuable. We developed a staining method using methylthiazolyl blue tetrazolium (MTT, a metabolic marker) to assess the pedicle metabolism of whole ovaries vitrified using cryoprotectant called 'VS4'. Whole sheep ovaries were perfused with MTT (1 g/l). In one group, ovarian tissue lesions were induced by immersing the ovarian pedicle in medium at 53°C or 65°C or in liquid nitrogen prior to MTT perfusion. In the second group, several metabolic substrates (d-glucose, l-glucose and pyruvic acid) and inhibitors [2-deoxy-d-glucose for d-glucose metabolism, azide for mitochondrial respiration and diphenyleneiodonium (DPI) for NADPH oxidase (an effector of the pentose phosphate pathway)] were added to the MTT stain. The third group was subjected to VS4 ± vitrification/warming prior to MTT perfusion. Pedicle MTT staining was assessed qualitatively by histological examination of frozen sections or quantified at 564 nm after solubilization in alcohol. MTT strongly and reproducibly stained the vascular smooth muscle. Heating at 53°C or 65°C or cooling in liquid nitrogen significantly diminished MTT staining by 48% (P = 0.001, n = 10), 94% (P = 0.0002, n = 10) and 94% (P = 0.0002, n = 10), respectively. MTT staining was affected by d-glucose metabolism: absence of d-glucose, substitution of unmetabolized l-glucose for d-glucose or addition of 2-deoxy-d-glucose significantly decreased MTT staining by 44% (P < 0.01, n = 10), 45% (P < 0.01, n = 10) and 29% (P < 0.01, n = 10), respectively. Pyruvic acid failed to correct the MTT staining decrease induced by d-glucose deprivation and azide did not decrease MTT staining, suggesting that MTT staining could be independent of mitochondrial metabolism. Adding DPI significantly inhibited MTT staining by 25% (P < 0.001, n = 10), suggesting involvement of the pentose phosphate pathway's effectors. Compared with controls, VS4-vitrified/warmed pedicles showed significantly less MTT staining (-30%, P < 0.005, n = 10), with unstained foci, whereas unvitrified VS4-exposed pedicles showed no difference. MTT can serve as a qualitative and quantitative vascular viability marker.VS4 vitrification caused alterations in ovarian vascular metabolism. MTT staining should allow accurate comparisons of whole-organ cryoprotection protocols.

Radiation-induced molecular imprinting of d-glucose onto poly(2-hydroxyethyl methacrylate) matrices using various crosslinking agents

Radiation-induced molecular imprinting of d-glucose onto poly(2-hydroxyethyl methacrylate) matrix was achieved to create three-dimensional cavities to recognize and bind d-glucose. The optimization of imprinting capability of matrices was achieved by investigating the effects of various parameters such as the type and amount of crosslinking agent, type of solvent, template to monomer ratio and total absorbed dose. Crosslinking agents with increasing chain lengths and different flexibilities were used in an attempt to elucidate the impact of relevant imprint parameters on the effectiveness of imprinting technique. The absorbed dose varied from 1 to 15 kGy. Cavity sizes of MIPs were measured by positron annihilation lifetime (PAL) experiments. Control matrices were synthesized with exactly the same composition in the absence of d-glucose. Separation of d-glucose has been shown to be successfully achieved in HPLC columns filled with MIPs whereas no separation was observed for non-imprint matrices.

Glucose-induced Remodeling of Intermediary and Energy Metabolism in Procyclic Trypanosoma brucei

The procyclic form of Trypanosoma brucei is a parasitic protozoan that normally dwells in the midgut of its insect vector. In vitro, this parasite prefers d-glucose to l -proline as a carbon source, although this amino acid is the main carbon source available in its natural habitat. Here, we investigated how l -proline is metabolized in glucose-rich and glucose-depleted conditions. Analysis of the excreted end products of (13)C-enriched l -proline metabolism showed that the amino acid is converted into succinate or l -alanine depending on the presence or absence of d-glucose, respectively. The fact that the pathway of l -proline metabolism was truncated in glucose-rich conditions was confirmed by the analysis of 13 separate RNA interference-harboring or knock-out cell lines affecting different steps of this pathway. For instance, RNA interference studies revealed the loss of succinate dehydrogenase activity to be conditionally lethal only in the absence of d-glucose, confirming that in glucose-depleted conditions, l -proline needs to be converted beyond succinate. In addition, depletion of the F(0)/F(1)-ATP synthase activity by RNA interference led to cell death in glucose-depleted medium, but not in glucose-rich medium. This implies that, in the presence of d-glucose, the importance of the F(0)/F(1)-ATP synthase is diminished and ATP is produced by substrate level phosphorylation. We conclude that trypanosomes develop an elaborate adaptation of their energy production pathways in response to carbon source availability.

L‐glutamine and palmitate catabolism in pancreatic islets from rats depleted in long‐chain polyunsaturated ω3 fatty acids

The catabolism of D-glucose was recently found to be impaired in pancreatic islets from rats depleted in long-chain polyunsaturated omega3 fatty acids. The specificity of this alteration was now investigated by characterizing the oxidative fate of endogenous nutrients in islets preincubated with either L-[U-14C]glutamine or [U-14C]palmitate and then incubated variously in the absence of D-glucose, presence of the hexose or presence of metabolic poisons. Relative to their radioactive content after preincubation, the production of 14CO2 by islets prelabelled with [U-14C]glutamine was higher in omega3-depleted rats than control animals. The enhancing action of D-glucose upon such production was impaired, however, in the omega3-depleted rats. The net uptake of 14C-palmitate and absolute value for 14CO2 output were both increased in omega3-depleted rats, whilst the ratio between 14CO2 output and islet radioactive content was decreased in the same animals. The inhibition of 14CO2 production by metabolic poisons was comparable in all cases. These results are consistent with recent findings on such items as the availability of endogenous amino acids and uptake of unesterified fatty acids in extrapancreatic sites of the omega3-depleted rats. They also support the view that the alteration of D-glucose metabolism in the islets of the latter animals may be attributable, in part at least, to alteration of glucokinase kinetics by high intracellular acyl-CoA levels.

Positron annihilation lifetime spectroscopy of molecularly imprinted hydroxyethyl methacrylate based polymers

Radiation-induced molecular imprinting of d-glucose onto poly(2-hydroxyethyl methacrylate) (HEMA) matrix was achieved to create three-dimensional cavities to recognize and bind glucose. Molecularly imprinted polymers (MIPs) were synthesized with different types of crosslinkers and varying amounts of template molecule in an attempt to elucidate the impact of imprint quantities on the effectiveness of imprinting technique. The crosslinking agents used in this study were diethylene glycol diacrylate (DEGDA), triethylene glycol dimethacrylate (TEGDMA) and polypropylene glycol dimethacrylate (PPGDMA) in the order of increasing chain length. Crosslinking agent concentration in the polymerization mixture (monomer, crosslinking agent and template) covered a range of 10, 20, 30, and 70 mol%. The mole ratio of template molecule, d-glucose to functional monomer, HEMA, was kept either as 1:3 or 1:6. The absorbed dose varied from 1 to 15 kGy. Control polymers were synthesized with exactly the same composition in the absence of d-glucose. Cavity sizes of MIPs were investigated by positron annihilation lifetime (PAL) measurements. A sandwich arrangement (sample–source–sample) was used. PAL experiments were carried out using a conventional fast–fast coincidence system having a time resolution (FWHM) of about 280 ps. Free-volume hole radii of samples were investigated in their dry and fully water swollen state. The results obtained from a systematic study of the effects of concentration and molecular size of the crosslinking agents, template to monomer ratio and irradiation dose experiments suggest that control of cavity size is feasible in nanometer scale by the optimization of these parameters revealed by means of (PAL) spectroscopy technique.

Opposite effects of d-fructose on total versus cytosolic ATP/ADP ratio in pancreatic islet cells

d-fructose (10 mM) augments, in rat pancreatic islets, insulin release evoked by 10 mM d-glucose. Even in the absence of d-glucose, d-fructose (100 mM) displays a positive insulinotropic action. It was now examined whether the insulinotropic action of d-fructose could be attributed to an increase in the ATP content of islet cells. After 30–60 min incubation in the presence of d-glucose and/or d-fructose, the ATP and ADP content was measured by bioluminescence in either rat isolated pancreatic islets (total ATP and ADP) or the supernatant of dispersed rat pancreatic islet cells exposed for 30 s to digitonine (cytosolic ATP and ADP). d-fructose (10 and 100 mM) was found to cause a concentration-related decrease in the total ATP and ADP content and ATP/ADP ratio below the basal values found in islets deprived of exogenous nutrient. Moreover, in the presence of 10 mM d-glucose, which augmented both the total ATP content and ATP/ADP ratio above basal value, d-fructose (10 mM) also lowered these two parameters. The cytosolic ATP/ADP ratio, however, was increased in the presence of d-glucose and/or d-fructose. Under the present experimental conditions, a sigmoidal relationship was found between such a cytosolic ATP/ADP ratio and either 86Rb net uptake by dispersed islet cells or insulin release from isolated islets. These data provide, to our knowledge, the first example of a dramatic dissociation between changes in total ATP content or ATP/ADP ratio and insulin release in pancreatic islets exposed to a nutrient secretagogue. Nevertheless, the cationic and insulinotropic actions of d-glucose and/or d-fructose were tightly related to the cytosolic ATP/ADP ratio.

Stimulative effects of insulin on Toxoplasma gondii replication in 3T3‐L1 cells

The influence of insulin and 2-deoxy-glucose (D-glucose) on the intracellular protozoan Toxoplasma gondii replication in 3T3-L1 cells was investigated. Insulin and D-glucose had a dose-responsive mitogenic effect on intracellular T. gondii replication and development in 3T3-L1 cells. Insulin concentrations between 10(-2) and 10(-1) microg/ml combination of 4.5 g/l D-glucose in DMEM medium gave maximum stimulus to T. gondii replication. The number of tachyzoites increased rapidly, with the growth peaking typically on day 3 or 4 of culture, and then declining quickly. However, insulin, in the absence of d-glucose, had comparably less effect on T. gondii growth than two of their combination. d-glucose concentrations significantly affected the tachyzoite replication and appear to be indispensable for maintaining the host 3T3-L1 cells.

Conformational stability and domain coupling in D-glucose/D-galactose-binding protein from Escherichia coli.

The monomeric D-glucose/D-galactose-binding protein (GGBP) from Escherichia coli (M(r) 33000) is a periplasmic protein that serves as a high-affinity receptor for the active transport and chemotaxis towards both sugars. The effect of D-glucose binding on the thermal unfolding of the GGBP protein at pH 7.0 has been measured by differential scanning calorimetry (DSC), far-UV CD and intrinsic tryptophanyl residue fluorescence (Trp fluorescence). All three techniques reveal reversible, thermal transitions and a midpoint temperature (T(m)) increase from 50 to 63 degrees C produced by 10 mM D-glucose. Both in the absence and presence of D-glucose a single asymmetric endotherm for GGBP is observed in DSC, although each endotherm consists of two transitions about 4 degrees C apart in T(m) values. In the absence of D-glucose, the protein unfolding is best described by two non-ideal transitions, suggesting the presence of unfolding intermediates. In the presence of D-glucose protein, unfolding is more co-operative than in the absence of the ligand, and the experimental data are best fitted to a model that assumes two ideal (two-state) sequential transitions. Thus D-glucose binding changes the character of the GGBP protein folding/unfolding by linking the two domains such that protein unfolding becomes a cooperative, two two-state process. A K(A)' value of 5.6x10(6) M(-1) at 63 degrees C for D-glucose binding is estimated from DSC results. The domain with the lower stability in DSC measurements has been identified as the C-terminal domain of GGBP from thermally induced Trp fluorescence changes.

Reduction and uptake of methylene blue by human erythrocytes.

A thiazine dye reductase has been described in endothelial cells that reduces methylene blue (MB), allowing its uptake into cells. Because a different mechanism of MB uptake in human erythrocytes has been proposed, we measured MB uptake and reduction in this cell type. Oxidized MB (MB(+)) stimulated reduction of extracellular ferricyanide in a time- and concentration-dependent manner, reflecting extracellular reduction of the dye. Reduced MB was then taken up by the cells and partially oxidized to MB(+). Both forms were retained against a concentration gradient, and their redox cycling induced an oxidant stress in the cells. Whereas concentrations of MB(+) <5 microM selectively oxidized NAD(P)H, higher concentrations also oxidized both glutathione (GSH) and ascorbate, especially in the absence of d-glucose. MB(+)-stimulated ferricyanide reduction was inhibited by thiol reagents with different mechanisms of action. Phenylarsine oxide, which is selective for vicinal dithiols in proteins, inhibited MB(+)-dependent ferricyanide reduction more strongly than it decreased cell GSH and pentose phosphate cycle activity, and it did not affect cellular NADPH. Open erythrocyte ghost membranes facilitated saturable NAD(P)H oxidation by MB(+), which was abolished by pretreating ghosts with low concentrations of trypsin and phenylarsine oxide. These results show that erythrocytes sequentially reduce and take up MB(+), that both reduced and oxidized forms of the dye are concentrated in cells, and that the thiazine dye reductase activity initially responsible for MB(+) reduction may correspond to MB(+)-dependent NAD(P)H reductase activity in erythrocyte ghosts.

Anomeric Specificity of the Stimulatory Effect ofd-Glucose on d-Fructose Phosphorylation by Human Liver Glucokinase

D-Glucose was recently reported to stimulate d-fructose phosphorylation by human B-cell glucokinase. The present study aims at investigating the anomeric specificity of such a positive cooperativity. The alpha-anomer of D-glucose was found to increase much more markedly than beta-D-glucose the phosphorylation of D-fructose by human liver glucokinase. Such an anomeric preference diminished at high concentrations of the D-glucose anomers, i.e. when the effect of the aldohexose upon d-fructose phosphorylation became progressively less marked. A comparison between the effects of the two anomers of D-glucose and those of equilibrated D-glucose upon D-fructose phosphorylation by human liver glucokinase indicated that the results obtained with the equilibrated aldohexose were not significantly different from those expected from the combined effects of each anomers of D-glucose. In isolated rat islets incubated for 60 min at 4 degrees C, alpha-D-glucose (5.6 mm), but not beta-D-glucose (also 5.6 mm), augmented significantly the conversion of D-[U-(14)C]fructose (5.0 mm) to acidic radioactive metabolites. Likewise, in islets prelabeled with (45)Ca and perifused at 37 degrees C, D-fructose (20.0 mm) augmented (45)Ca efflux and provoked a biphasic stimulation of insulin release from islets exposed to alpha-D-glucose (5.6 mm), while inhibiting (45)Ca efflux and causing only a sluggish and modest increase in insulin output from islets exposed to beta-D-glucose (also 5.6 mm). The enhancing action of D-glucose upon D-fructose phosphorylation by glucokinase thus displays an obvious anomeric preference for alpha-D-glucose, and such an anomeric specificity remains operative in intact pancreatic islets.

Efflux system for pyridoxine in Schizosaccharomyces pombe.

Pyridoxine-charged Schizosaccharomyces pombe released pyridoxine rapidly at 30 degrees C: very low amounts of three other B6 vitamers were also released. The rate of efflux was temperature-dependent. The initial rate of efflux was dependent on the concentration of pyridoxine in the cells: the rate was almost zero at lower than 0.02 mM and became saturated at higher than 0.2 mM. Na+, sodium azide, and dinitrophenol increased the rate in both the presence and absence of D-glucose. Mg++, thiamine, and menadione inhibited the efflux. The intracellular concentration of ATP did not significantly affect the efflux rate. The system may be dependent on a membrane potential of the yeast cells. It was found that the fission yeast cells have a gate or carrier system for efflux of pyridoxine, which was distinct from that in Saccharomyces cerevisiae.

Insulinotropic Action of the Monoethyl Ester of Succinic Acid

1. Selected esters of succinic acid are currently under investigation as potential insulinotropic tools in the treatment of non-insulin-dependent diabetes. At variance with the methyl esters of succinic acid used in most of the work so far conducted from this perspective, the monoethyl ester of succinic acid (EMS) offers the advantage of avoiding the undesirable generation of methanol by intracellular hydrolysis. In the present study, the metabolism and functional effects of EMS were investigated, therefore, in rat pancreatic islets. 2. At a 10 mM concentration, EMS enhanced insulin release from islets stimulated by 7–17 mM D-glucose but failed to do so at lower concentrations of the hexose. EMS was efficiently metabolized, as judged from the generation of 14CO 2 by islets exposed to the monoethyl ester of either [1,4- 14C] or [2,3- 14C]succinic acid. D-Glucose (6 mM) failed to affect the metabolism of EMS (10 mM), which itself failed to affect the metabolism of D-[5- 3H]glucose or D-[U- 14C]glucose. EMS also stimulated biosynthetic activity in the islets. It inhibited 86Rb and 45Ca outflow from prelabeled islets perfused in the absence of D-glucose but enhanced the efflux of the two cationic tracers in the presence of the hexose (7 mM). 3. It is concluded that the insulinotropic action of EMS is attributable, to a large extent, to its capacity to act as a nutrient in islet cells.

Synergistic insulinotropic action of succinate, acetate, and glucose esters in islets from normal and diabetic rats.

Succinic acid esters are currently under investigation as possible insulinotropic tools in the treatment of noninsulin-dependent diabetes mellitus. The present article introduces three novel nutrient esters and aims mainly to explore, in both normal and GK rats, the secretory response to such esters when tested alone or in combination. It documents that in pancreatic islets from normal rats, methyl acetate (10 mM), which fails to augment basal insulin output, potentiates the secretory response to succinate dimethyl ester (also 10 mM). It also reveals that alpha-D-glucose pentaacetate (alpha GPA) (1.7 mM) stimulates insulin release in the absence of any other exogenous nutrient and even more so in the presence of succinate methyl ester. Moreover, the methyl esters of succinic acid (10 mM), when used together with either methyl acetate or alpha GPA, provoked insulin secretion in islets from diabetic GK rats incubated in the absence of D-glucose, although no significant secretory response of such islets could be detected when each of these agents was tested separately. These findings thus draw attention to the insulinotropic potential in type 2 diabetes of selected combinations of nutrient esters, including a D-glucose ester presumably able to enter into islet cells without requiring the intervention of a hexose carrier.