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Emile Van Schaftingen - One of the best experts on this subject based on the ideXlab platform.
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the glucose 6 phosphatase system
Biochemical Journal, 2002Co-Authors: Emile Van Schaftingen, Isabelle GerinAbstract:Glucose-6-phosphatase (G6Pase), an enzyme found mainly in the liver and the kidneys, plays the important role of providing glucose during starvation. Unlike most phosphatases acting on water-soluble compounds, it is a membrane-bound enzyme, being associated with the endoplasmic reticulum. In 1975, W. Arion and co-workers proposed a model according to which G6Pase was thought to be a rather unspecific phosphatase, with its catalytic site oriented towards the lumen of the endoplasmic reticulum [Arion, Wallin, Lange and Ballas (1975) Mol. Cell. Biochem. 6, 75--83]. Substrate would be provided to this enzyme by a Translocase that is specific for glucose 6-phosphate, thereby accounting for the specificity of the phosphatase for glucose 6-phosphate in intact microsomes. Distinct transporters would allow inorganic phosphate and glucose to leave the vesicles. At variance with this substrate-transport model, other models propose that conformational changes play an important role in the properties of G6Pase. The last 10 years have witnessed important progress in our knowledge of the glucose 6-phosphate hydrolysis system. The genes encoding G6Pase and the glucose 6-phosphate Translocase have been cloned and shown to be mutated in glycogen storage disease type Ia and type Ib respectively. The gene encoding a G6Pase-related protein, expressed specifically in pancreatic islets, has also been cloned. Specific potent inhibitors of G6Pase and of the glucose 6-phosphate Translocase have been synthesized or isolated from micro-organisms. These as well as other findings support the model initially proposed by Arion. Much progress has also been made with regard to the regulation of the expression of G6Pase by insulin, glucocorticoids, cAMP and glucose.
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How many forms of glycogen storage disease type I
European journal of pediatrics, 2000Co-Authors: Maria Veiga Da Cunha, Isabelle Gerin, Emile Van SchaftingenAbstract:Glucose-6-phosphatase is a multicomponent enzymatic system of the endoplasmic reticulum, which catalyses the terminal steps of gluconeogenesis and glycogenolysis by converting Glucose-6-Phosphate to glucose and inorganic phosphate. Glycogen storage diseases type I (GSD I) are a group of metabolic disorders arising from a defect in a component of this enzymatic system, i.e. the Glucose-6-Phosphate hydrolase (GSD Ia), the Glucose-6-Phosphate Translocase (GSD Ib) and possibly also the Translocases for inorganic phosphate (GSD Ic) or glucose (GSD Id). The genes encoding the Glucose-6-Phosphate hydrolase and the Glucose-6-Phosphate Translocase have both been cloned and assigned to human chromosomes 17q21 and 11q23, respectively. Investigation of patients with GSD I shows that those with GSD Ia are mutated in the Glucose-6-Phosphate hydrolase gene, whereas those diagnosed as GSD Ib, GSD Ic or GSD Id are mutated in the Glucose-6-Phosphate Translocase gene, and are therefore GSD Ib patients, in agreement with the fact that they all have neutropenia or neutrophil dysfunction. This suggests that the biochemical assays used to differentiate GSD Ic and GSD Id from GSD Ib are not reliable.
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The putative glucose 6-phosphate Translocase gene is mutated in essentially all cases of glycogen storage disease type I non-a
European Journal of Human Genetics, 1999Co-Authors: Maria Veiga-da-cunha, Isabelle Gerin, Yuan-tsong Chen, Philip J Lee, James V Leonard, Irène Maire, Udo Wendel, Miikka Vikkula, Emile Van SchaftingenAbstract:The purpose of this work was to test the hypothesis that mutations in the putative glucose 6-phosphate Translocase gene would account for most of the cases of GSD I that are not explained by mutations in the phosphohydrolase gene, ie that are not type Ia. Twenty-three additional families diagnosed as having GSD I non-a (GSD Ib, Ic or Id) have now been analysed. The 9 exons of the gene were amplified by PCR and mutations searched both by SSCP and heteroduplex analysis. Except for one family in which only one mutation was found, all patients had two allelic mutations in the gene encoding the putative glucose 6-phosphate Translocase. Sixteen of the mutations are new and they are all predicted to lead to non-functional proteins. All investigated patients had some degree of neutropenia or neutrophil dysfunction and the clinical phenotype of the four new patients who had been diagnosed as GSD Ic and the one diagnosed as GSD Id was no different from the GSD Ib patients. Since these patients, and the four type Ic patients from two families previously studied, shared several mutations with GSD Ib patients, we conclude that their basic defect is in the putative glucose 6-phosphate Translocase and that they should be reclassified as GSD Ib. Isolated defects in microsomal Pi transporter or in microsomal glucose transporter must be very rare or have phenotypes that are not recognised as GSD I, so that in practice there are only two subtypes of GSD I (GSD Ia and GSD Ib).
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Structure of the gene mutated in glycogen storage disease type Ib.
Gene, 1999Co-Authors: Isabelle Gerin, Maria Veiga-da-cunha, Gaëtane Noël, Emile Van SchaftingenAbstract:We report the structure of the human gene encoding the putative glucose 6-phosphate Translocase that is mutated in glycogen storage disease type Ib. Northern blots showed that the encoded 2.4 kb mRNA is mainly expressed in liver and in kidney, but is also present, although in barely detectable amounts, in leucocytes. The gene contains nine exons, one of which (exon 7) is not present in human liver or leucocyte RNA. RT-PCR analysis of mouse RNA indicates that exon 7, which is 63 bp long compared with 66 bp in man, is not expressed in liver and kidney but well in heart and brain. 5'-RACE and RNase protection assays performed on RNAs from human liver, kidney and leucocytes indicated the presence of two main regions of transcription start at approximately -200 and -100 bp with respect to the initiator ATG.
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Sequence of a putative glucose 6-phosphate Translocase, mutated in glycogen storage disease type Ib.
FEBS letters, 1997Co-Authors: Isabelle Gerin, Maria Veiga-da-cunha, Y Achouri, J F Collet, Emile Van SchaftingenAbstract:We report the sequence of a human cDNA that encodes a 46 kDa transmembrane protein homologous to bacterial transporters for phosphate esters. This protein presents at its carboxy terminus the consensus motif for retention in the endoplasmic reticulum. Northern blots of rat tissues indicate that the corresponding mRNA is mostly expressed in liver and kidney. In two patients with glycogen storage disease type Ib, mutations were observed that either replaced a conserved Gly to Cys or introduced a premature stop codon. The encoded protein is therefore most likely the glucose 6-phosphate Translocase that is functionally associated with glucose-6-phosphatase.
Isabelle Gerin - One of the best experts on this subject based on the ideXlab platform.
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the glucose 6 phosphatase system
Biochemical Journal, 2002Co-Authors: Emile Van Schaftingen, Isabelle GerinAbstract:Glucose-6-phosphatase (G6Pase), an enzyme found mainly in the liver and the kidneys, plays the important role of providing glucose during starvation. Unlike most phosphatases acting on water-soluble compounds, it is a membrane-bound enzyme, being associated with the endoplasmic reticulum. In 1975, W. Arion and co-workers proposed a model according to which G6Pase was thought to be a rather unspecific phosphatase, with its catalytic site oriented towards the lumen of the endoplasmic reticulum [Arion, Wallin, Lange and Ballas (1975) Mol. Cell. Biochem. 6, 75--83]. Substrate would be provided to this enzyme by a Translocase that is specific for glucose 6-phosphate, thereby accounting for the specificity of the phosphatase for glucose 6-phosphate in intact microsomes. Distinct transporters would allow inorganic phosphate and glucose to leave the vesicles. At variance with this substrate-transport model, other models propose that conformational changes play an important role in the properties of G6Pase. The last 10 years have witnessed important progress in our knowledge of the glucose 6-phosphate hydrolysis system. The genes encoding G6Pase and the glucose 6-phosphate Translocase have been cloned and shown to be mutated in glycogen storage disease type Ia and type Ib respectively. The gene encoding a G6Pase-related protein, expressed specifically in pancreatic islets, has also been cloned. Specific potent inhibitors of G6Pase and of the glucose 6-phosphate Translocase have been synthesized or isolated from micro-organisms. These as well as other findings support the model initially proposed by Arion. Much progress has also been made with regard to the regulation of the expression of G6Pase by insulin, glucocorticoids, cAMP and glucose.
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How many forms of glycogen storage disease type I
European journal of pediatrics, 2000Co-Authors: Maria Veiga Da Cunha, Isabelle Gerin, Emile Van SchaftingenAbstract:Glucose-6-phosphatase is a multicomponent enzymatic system of the endoplasmic reticulum, which catalyses the terminal steps of gluconeogenesis and glycogenolysis by converting Glucose-6-Phosphate to glucose and inorganic phosphate. Glycogen storage diseases type I (GSD I) are a group of metabolic disorders arising from a defect in a component of this enzymatic system, i.e. the Glucose-6-Phosphate hydrolase (GSD Ia), the Glucose-6-Phosphate Translocase (GSD Ib) and possibly also the Translocases for inorganic phosphate (GSD Ic) or glucose (GSD Id). The genes encoding the Glucose-6-Phosphate hydrolase and the Glucose-6-Phosphate Translocase have both been cloned and assigned to human chromosomes 17q21 and 11q23, respectively. Investigation of patients with GSD I shows that those with GSD Ia are mutated in the Glucose-6-Phosphate hydrolase gene, whereas those diagnosed as GSD Ib, GSD Ic or GSD Id are mutated in the Glucose-6-Phosphate Translocase gene, and are therefore GSD Ib patients, in agreement with the fact that they all have neutropenia or neutrophil dysfunction. This suggests that the biochemical assays used to differentiate GSD Ic and GSD Id from GSD Ib are not reliable.
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The putative glucose 6-phosphate Translocase gene is mutated in essentially all cases of glycogen storage disease type I non-a
European Journal of Human Genetics, 1999Co-Authors: Maria Veiga-da-cunha, Isabelle Gerin, Yuan-tsong Chen, Philip J Lee, James V Leonard, Irène Maire, Udo Wendel, Miikka Vikkula, Emile Van SchaftingenAbstract:The purpose of this work was to test the hypothesis that mutations in the putative glucose 6-phosphate Translocase gene would account for most of the cases of GSD I that are not explained by mutations in the phosphohydrolase gene, ie that are not type Ia. Twenty-three additional families diagnosed as having GSD I non-a (GSD Ib, Ic or Id) have now been analysed. The 9 exons of the gene were amplified by PCR and mutations searched both by SSCP and heteroduplex analysis. Except for one family in which only one mutation was found, all patients had two allelic mutations in the gene encoding the putative glucose 6-phosphate Translocase. Sixteen of the mutations are new and they are all predicted to lead to non-functional proteins. All investigated patients had some degree of neutropenia or neutrophil dysfunction and the clinical phenotype of the four new patients who had been diagnosed as GSD Ic and the one diagnosed as GSD Id was no different from the GSD Ib patients. Since these patients, and the four type Ic patients from two families previously studied, shared several mutations with GSD Ib patients, we conclude that their basic defect is in the putative glucose 6-phosphate Translocase and that they should be reclassified as GSD Ib. Isolated defects in microsomal Pi transporter or in microsomal glucose transporter must be very rare or have phenotypes that are not recognised as GSD I, so that in practice there are only two subtypes of GSD I (GSD Ia and GSD Ib).
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Structure of the gene mutated in glycogen storage disease type Ib.
Gene, 1999Co-Authors: Isabelle Gerin, Maria Veiga-da-cunha, Gaëtane Noël, Emile Van SchaftingenAbstract:We report the structure of the human gene encoding the putative glucose 6-phosphate Translocase that is mutated in glycogen storage disease type Ib. Northern blots showed that the encoded 2.4 kb mRNA is mainly expressed in liver and in kidney, but is also present, although in barely detectable amounts, in leucocytes. The gene contains nine exons, one of which (exon 7) is not present in human liver or leucocyte RNA. RT-PCR analysis of mouse RNA indicates that exon 7, which is 63 bp long compared with 66 bp in man, is not expressed in liver and kidney but well in heart and brain. 5'-RACE and RNase protection assays performed on RNAs from human liver, kidney and leucocytes indicated the presence of two main regions of transcription start at approximately -200 and -100 bp with respect to the initiator ATG.
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A gene on chromosome 11q23 coding for a putative glucose- 6-phosphate Translocase is mutated in glycogen-storage disease types Ib and Ic.
American journal of human genetics, 1998Co-Authors: Maria Veiga-da-cunha, Isabelle Gerin, Yuan-tsong Chen, Philip J Lee, James V Leonard, Thierry De Barsy, Pascale De Lonlay, Carlo Dionisi-vici, Christiane Fenske, Irène MaireAbstract:Glycogen-storage diseases type I (GSD type I) are due to a deficiency in glucose-6-phosphatase, an enzymatic system present in the endoplasmic reticulum that plays a crucial role in blood glucose homeostasis. Unlike GSD type Ia, types Ib and Ic are not due to mutations in the phosphohydrolase gene and are clinically characterized by the presence of associated neutropenia and neutrophil dysfunction. Biochemical evidence indicates the presence of a defect in Glucose-6-Phosphate (GSD type Ib) or inorganic phosphate (Pi) (GSD type Ic) transport in the microsomes. We have recently cloned a cDNA encoding a putative Glucose-6-Phosphate Translocase. We have now localized the corresponding gene on chromosome 11q23, the region where GSD types Ib and Ic have been mapped. Using SSCP analysis and sequencing, we have screened this gene, for mutations in genomic DNA, from patients from 22 different families who have GSD types Ib and Ic. Of 20 mutations found, 11 result in truncated proteins that are probably nonfunctional. Most other mutations result in substitutions of conserved or semiconserved residues. The two most common mutations (Gly339Cys and 1211-1212 delCT) together constitute approximately 40% of the disease alleles. The fact that the same mutations are found in GSD types Ib and Ic could indicate either that Pi and Glucose-6-Phosphate are transported in microsomes by the same transporter or that the biochemical assays used to differentiate Pi and Glucose-6-Phosphate transport defects are not reliable.
Andreas W Herling - One of the best experts on this subject based on the ideXlab platform.
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Prolonged blood glucose reduction in mrp-2 deficient rats (GY/TR(-)) by the Glucose-6-Phosphate Translocase inhibitor S 3025.
Biochimica et biophysica acta, 2002Co-Authors: Andreas W Herling, Horst Hemmerle, Hansjoerg Burger, Gerrit Schubert, Dietmar Schwab, Jochen Maas, Roland Hammerl, Dietmar Schmidt, Sabine Strohschein, Stefan PetryAbstract:Chlorogenic acid derivatives are potent inhibitors of hepatic glucose production by inhibition of the Glucose-6-Phosphate Translocase component of the hepatic glucose-6-phosphatase system. The pharmacological proof of concept was clearly demonstrated during i.v. infusion of potent derivatives (S 4048, S 3483) in rats. However, the blood glucose lowering effect of S 4048 after bolus i.v. injection lasted only 60-90 min. Plasma clearance of S 4048 was very high, and the parent compound was rapidly and efficiently excreted into the bile of Wistar and GY/TR(-) rats, indicating that mrp-2 was not involved in this hepatobiliary elimination process. About 72% of the total administered radioactivity appeared in the bile within 20 min after i.v. bolus injection of the radiolabeled analogue [(3)H]S 1743 in a Wistar rat. However, in GY/TR(-) rats the dicarboxylic analogue of S 4048, S 3025, was cleared from the plasma less rapidly than its parent compound and its biliary elimination was comparatively low. In contrast, S 3025 exhibited comparable pharmacokinetics and biliary elimination profile as S 4048 in Wistar rats, suggesting that biliary elimination of S 3025 is facilitated by mrp-2, functionally absent in GY/TR(-) rats. Targeting to mrp-2 resulted in a significantly prolonged reduction of blood glucose levels in GY/TR(-) rats after i.v. bolus administration of S 3025.
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Fatty acid and amino acid modulation of glucose cycling in isolated rat hepatocytes.
Biochemical Journal, 2001Co-Authors: Lori A. Gustafson, Hansjoerg Burger, Andreas W Herling, Mies Neeft, Dirk-jan Reijngoud, Folkert Kuipers, Hans P. Sauerwein, Johannes A. Romijn, Alfred J. MeijerAbstract:We studied the influence of glucose/glucose 6-phosphate cycling on glycogen deposition from glucose in fasted-rat hepatocytes using S4048 and CP320626, specific inhibitors of Glucose-6-Phosphate Translocase and glycogen phosphorylase respectively. The effect of amino acids and oleate was also examined. The following observations were made: (1) with glucose alone, net glycogen production was low. Inhibition of Glucose-6-Phosphate Translocase increased intracellular glucose 6-phosphate (3-fold), glycogen accumulation (5-fold) without change in active (dephosphorylated) glycogen synthase (GSa) activity, and lactate production (4-fold). With both glucose 6-phosphate Translocase and glycogen phosphorylase inhibited, glycogen deposition increased 8-fold and approached reported in vivo rates of glycogen deposition during the fasted-->fed transition. Addition of a physiological mixture of amino acids in the presence of glucose increased glycogen accumulation (4-fold) through activation of GS and inhibition of glucose-6-phosphatase flux. Addition of oleate with glucose present decreased glycolytic flux and increased the flux through glucose 6-phosphatase with no change in glycogen deposition. With glucose 6-phosphate Translocase inhibited by S4048, oleate increased intracellular glucose 6-phosphate (3-fold) and net glycogen production (1.5-fold), without a major change in GSa activity. It is concluded that glucose cycling in hepatocytes prevents the net accumulation of glycogen from glucose. Amino acids activate GS and inhibit flux through glucose-6-phosphatase, while oleate inhibits glycolysis and stimulates glucose-6-phosphatase flux. Variation in glucose 6-phosphate does not always result in activity changes of GSa. Activation of glucose 6-phosphatase flux by fatty acids may contribute to the increased hepatic glucose production as seen in Type 2 diabetes.
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Hepatic uptake of synthetic chlorogenic acid derivatives by the organic anion transport proteins.
The Journal of pharmacology and experimental therapeutics, 2001Co-Authors: Dietmar Schwab, Horst Hemmerle, Andreas W Herling, Gerrit Dr Schubert, Bruno Hagenbuch, Hansjoerg BurgerAbstract:Chlorogenic acid derivatives were recently identified as novel, potent, and specific inhibitors of the hepatic glucose 6-phosphate Translocase. Inhibition of the glucose 6-phosphate Translocase leads to a decrease in hepatic glucose production, rendering chlorogenic acid derivatives as potential novel therapeutics in patients with type 2 diabetes. The present study examines the hepatic uptake mechanism of the radiolabeled chlorogenic acid derivative S 1743 into freshly isolated rat hepatocytes. Initial uptake rates were Na + -independent and followed saturation kinetics with no superimposition of facilitated diffusion. Inhibition studies demonstrated that other chlorogenic acid derivatives inhibited uptake of the radiolabeled compound S 1743 into rat hepatocytes in the range of 1.1 to 11 μM, whereas the natural chlorogenic acid (up to 100 μM) had no effect at all. In addition, inhibition of S 1743 uptake into rat hepatocytes was found in the presence of sulfobromophthalein, sulfolithocholyltaurine, estrone-3-sulfate, cholyltaurine, verapamil, bumetanide, probenecide, phenol red, digoxin, and ouabain (in decreasing order) but not with N -methylnicotinamide, α-ketoglutarate, p -aminohippurate, geneticin sulfate, and 5-sulfosalicylate. The observed inhibition pattern suggested that members of the family of the organic anion transporting polypeptides (Oatps) could be involved in hepatic uptake of chlorogenic acid derivatives. Indeed, S 1743 uptake could be demonstrated in Oatp1- and Oatp2-expressing Xenopus laevis oocytes as well as in Oatp1-expressing Chinese hamster ovary cells. A comparison of the inhibition pattern obtained in hepatocytes compared with that obtained in Oatp1-expressing Chinese hamster ovary cells suggests that facilitated uptake by Oatp1 is a major contributor in total hepatic uptake of chlorogenic acid derivatives.
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Upregulation of hepatic glucose 6-phosphatase gene expression in rats treated with an inhibitor of Glucose-6-Phosphate Translocase.
Archives of biochemistry and biophysics, 2000Co-Authors: Caecilia Simon, Andreas W Herling, Gerald Preibisch, Hansjoerg BurgerAbstract:The multicomponent hepatic glucose 6-phosphatase (Glc-6-Pase) system catalyzes the terminal step of hepatic glucose production and plays a key role in the regulation of blood glucose. We used the chlorogenic acid derivative S 3483, a reversible inhibitor of the Glucose-6-Phosphate (Glc-6-P) Translocase component, to demonstrate for the first time upregulation of Glc-6-Pase expression in rat liver in vivo after inhibition of Glc-6-P Translocase. In accordance with its mode of action, S 3483-treatment of overnight-fasted rats induced hypoglycemia and increased blood lactate, hepatic Glc-6-P, and glycogen. The metabolic changes were accompanied by rapid and marked increases in Glc-6-Pase mRNA (above 35-fold), protein (about 2-fold), and enzymatic activity (about 2-fold). Maximal mRNA levels were reached after 4 h of treatment. Glycemia, blood lactate, and Glc-6-Pase mRNA levels returned to control values, whereas Glc-6-P and glycogen levels decreased but were still elevated 2 h after S 3483 withdrawal. The capacity for Glc-6-P influx was only marginally increased after 8.5 h of treatment. Prevention of hypoglycemia by euglycemic clamp did not abolish the increase in Glc-6-Pase mRNA induced by S 3483 treatment. A similar pattern of hypoglycemia and possibly of associated counterregulatory responses elicited by treatment with the phosphoenolpyruvate carboxykinase inhibitor 3-mercaptopicolinic acid could account for only a 2-fold induction of Glc-6-Pase mRNA. These findings suggest that the significant upregulation of Glc-6-Pase gene expression observed after treatment of rats in vivo with an inhibitor of Glc-6-P Translocase is caused predominantly either by S 3483 per se or by the compound-induced changes of intracellular carbohydrate metabolism.
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Alterations of carbohydrate and lipid intermediary metabolism during inhibition of glucose-6-phosphatase in rats.
European journal of pharmacology, 1999Co-Authors: Andreas W Herling, Horst Hemmerle, Hansjoerg Burger, Gerrit Dr Schubert, Hans-ludwig Schaefer, Werner KramerAbstract:S 4048 (1-[2-(4-Chloro-phenyl)-cyclopropylmethoxy]-3,4-dihydroxy-5-(3-imidazo[4,5-b]pyridin-1-yl-3-phenyl-acryloyloxy)-cyclohexanecarboxylic acid), a derivative of chlorogenic acid, specifically inhibits the Glucose-6-Phosphate translocating component T1 of the glucose-6-phosphatase system. Its pharmacological effect was studied on carbohydrate and lipid parameters in rats. In starved and fed rats, S 4048 caused a dose-dependent reduction of blood glucose levels with a corresponding increase in hepatic and renal glycogen and Glucose-6-Phosphate. The major quantitative route of carbon flux in the liver during S 4048-induced inhibition of the glucose-6-phosphatase activity seemed to be glycogenesis. Plasma free fatty acids were increased secondarily due to the S 4048-induced hypoglycemia. Hepatic triglycerides were increased possibly due to increased re-esterification of the readily available free fatty acids. Glucose-6-Phosphate Translocase inhibitors may be useful for experimentally studying aspects of type 1 glycogen storage disease in laboratory animals as well as for the therapeutic modulation of inappropriately high rates of hepatic glucose production in type 2 diabetes.
Hansjoerg Burger - One of the best experts on this subject based on the ideXlab platform.
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Prolonged blood glucose reduction in mrp-2 deficient rats (GY/TR(-)) by the Glucose-6-Phosphate Translocase inhibitor S 3025.
Biochimica et biophysica acta, 2002Co-Authors: Andreas W Herling, Horst Hemmerle, Hansjoerg Burger, Gerrit Schubert, Dietmar Schwab, Jochen Maas, Roland Hammerl, Dietmar Schmidt, Sabine Strohschein, Stefan PetryAbstract:Chlorogenic acid derivatives are potent inhibitors of hepatic glucose production by inhibition of the Glucose-6-Phosphate Translocase component of the hepatic glucose-6-phosphatase system. The pharmacological proof of concept was clearly demonstrated during i.v. infusion of potent derivatives (S 4048, S 3483) in rats. However, the blood glucose lowering effect of S 4048 after bolus i.v. injection lasted only 60-90 min. Plasma clearance of S 4048 was very high, and the parent compound was rapidly and efficiently excreted into the bile of Wistar and GY/TR(-) rats, indicating that mrp-2 was not involved in this hepatobiliary elimination process. About 72% of the total administered radioactivity appeared in the bile within 20 min after i.v. bolus injection of the radiolabeled analogue [(3)H]S 1743 in a Wistar rat. However, in GY/TR(-) rats the dicarboxylic analogue of S 4048, S 3025, was cleared from the plasma less rapidly than its parent compound and its biliary elimination was comparatively low. In contrast, S 3025 exhibited comparable pharmacokinetics and biliary elimination profile as S 4048 in Wistar rats, suggesting that biliary elimination of S 3025 is facilitated by mrp-2, functionally absent in GY/TR(-) rats. Targeting to mrp-2 resulted in a significantly prolonged reduction of blood glucose levels in GY/TR(-) rats after i.v. bolus administration of S 3025.
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Fatty acid and amino acid modulation of glucose cycling in isolated rat hepatocytes.
Biochemical Journal, 2001Co-Authors: Lori A. Gustafson, Hansjoerg Burger, Andreas W Herling, Mies Neeft, Dirk-jan Reijngoud, Folkert Kuipers, Hans P. Sauerwein, Johannes A. Romijn, Alfred J. MeijerAbstract:We studied the influence of glucose/glucose 6-phosphate cycling on glycogen deposition from glucose in fasted-rat hepatocytes using S4048 and CP320626, specific inhibitors of Glucose-6-Phosphate Translocase and glycogen phosphorylase respectively. The effect of amino acids and oleate was also examined. The following observations were made: (1) with glucose alone, net glycogen production was low. Inhibition of Glucose-6-Phosphate Translocase increased intracellular glucose 6-phosphate (3-fold), glycogen accumulation (5-fold) without change in active (dephosphorylated) glycogen synthase (GSa) activity, and lactate production (4-fold). With both glucose 6-phosphate Translocase and glycogen phosphorylase inhibited, glycogen deposition increased 8-fold and approached reported in vivo rates of glycogen deposition during the fasted-->fed transition. Addition of a physiological mixture of amino acids in the presence of glucose increased glycogen accumulation (4-fold) through activation of GS and inhibition of glucose-6-phosphatase flux. Addition of oleate with glucose present decreased glycolytic flux and increased the flux through glucose 6-phosphatase with no change in glycogen deposition. With glucose 6-phosphate Translocase inhibited by S4048, oleate increased intracellular glucose 6-phosphate (3-fold) and net glycogen production (1.5-fold), without a major change in GSa activity. It is concluded that glucose cycling in hepatocytes prevents the net accumulation of glycogen from glucose. Amino acids activate GS and inhibit flux through glucose-6-phosphatase, while oleate inhibits glycolysis and stimulates glucose-6-phosphatase flux. Variation in glucose 6-phosphate does not always result in activity changes of GSa. Activation of glucose 6-phosphatase flux by fatty acids may contribute to the increased hepatic glucose production as seen in Type 2 diabetes.
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Hepatic uptake of synthetic chlorogenic acid derivatives by the organic anion transport proteins.
The Journal of pharmacology and experimental therapeutics, 2001Co-Authors: Dietmar Schwab, Horst Hemmerle, Andreas W Herling, Gerrit Dr Schubert, Bruno Hagenbuch, Hansjoerg BurgerAbstract:Chlorogenic acid derivatives were recently identified as novel, potent, and specific inhibitors of the hepatic glucose 6-phosphate Translocase. Inhibition of the glucose 6-phosphate Translocase leads to a decrease in hepatic glucose production, rendering chlorogenic acid derivatives as potential novel therapeutics in patients with type 2 diabetes. The present study examines the hepatic uptake mechanism of the radiolabeled chlorogenic acid derivative S 1743 into freshly isolated rat hepatocytes. Initial uptake rates were Na + -independent and followed saturation kinetics with no superimposition of facilitated diffusion. Inhibition studies demonstrated that other chlorogenic acid derivatives inhibited uptake of the radiolabeled compound S 1743 into rat hepatocytes in the range of 1.1 to 11 μM, whereas the natural chlorogenic acid (up to 100 μM) had no effect at all. In addition, inhibition of S 1743 uptake into rat hepatocytes was found in the presence of sulfobromophthalein, sulfolithocholyltaurine, estrone-3-sulfate, cholyltaurine, verapamil, bumetanide, probenecide, phenol red, digoxin, and ouabain (in decreasing order) but not with N -methylnicotinamide, α-ketoglutarate, p -aminohippurate, geneticin sulfate, and 5-sulfosalicylate. The observed inhibition pattern suggested that members of the family of the organic anion transporting polypeptides (Oatps) could be involved in hepatic uptake of chlorogenic acid derivatives. Indeed, S 1743 uptake could be demonstrated in Oatp1- and Oatp2-expressing Xenopus laevis oocytes as well as in Oatp1-expressing Chinese hamster ovary cells. A comparison of the inhibition pattern obtained in hepatocytes compared with that obtained in Oatp1-expressing Chinese hamster ovary cells suggests that facilitated uptake by Oatp1 is a major contributor in total hepatic uptake of chlorogenic acid derivatives.
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Upregulation of hepatic glucose 6-phosphatase gene expression in rats treated with an inhibitor of Glucose-6-Phosphate Translocase.
Archives of biochemistry and biophysics, 2000Co-Authors: Caecilia Simon, Andreas W Herling, Gerald Preibisch, Hansjoerg BurgerAbstract:The multicomponent hepatic glucose 6-phosphatase (Glc-6-Pase) system catalyzes the terminal step of hepatic glucose production and plays a key role in the regulation of blood glucose. We used the chlorogenic acid derivative S 3483, a reversible inhibitor of the Glucose-6-Phosphate (Glc-6-P) Translocase component, to demonstrate for the first time upregulation of Glc-6-Pase expression in rat liver in vivo after inhibition of Glc-6-P Translocase. In accordance with its mode of action, S 3483-treatment of overnight-fasted rats induced hypoglycemia and increased blood lactate, hepatic Glc-6-P, and glycogen. The metabolic changes were accompanied by rapid and marked increases in Glc-6-Pase mRNA (above 35-fold), protein (about 2-fold), and enzymatic activity (about 2-fold). Maximal mRNA levels were reached after 4 h of treatment. Glycemia, blood lactate, and Glc-6-Pase mRNA levels returned to control values, whereas Glc-6-P and glycogen levels decreased but were still elevated 2 h after S 3483 withdrawal. The capacity for Glc-6-P influx was only marginally increased after 8.5 h of treatment. Prevention of hypoglycemia by euglycemic clamp did not abolish the increase in Glc-6-Pase mRNA induced by S 3483 treatment. A similar pattern of hypoglycemia and possibly of associated counterregulatory responses elicited by treatment with the phosphoenolpyruvate carboxykinase inhibitor 3-mercaptopicolinic acid could account for only a 2-fold induction of Glc-6-Pase mRNA. These findings suggest that the significant upregulation of Glc-6-Pase gene expression observed after treatment of rats in vivo with an inhibitor of Glc-6-P Translocase is caused predominantly either by S 3483 per se or by the compound-induced changes of intracellular carbohydrate metabolism.
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Alterations of carbohydrate and lipid intermediary metabolism during inhibition of glucose-6-phosphatase in rats.
European journal of pharmacology, 1999Co-Authors: Andreas W Herling, Horst Hemmerle, Hansjoerg Burger, Gerrit Dr Schubert, Hans-ludwig Schaefer, Werner KramerAbstract:S 4048 (1-[2-(4-Chloro-phenyl)-cyclopropylmethoxy]-3,4-dihydroxy-5-(3-imidazo[4,5-b]pyridin-1-yl-3-phenyl-acryloyloxy)-cyclohexanecarboxylic acid), a derivative of chlorogenic acid, specifically inhibits the Glucose-6-Phosphate translocating component T1 of the glucose-6-phosphatase system. Its pharmacological effect was studied on carbohydrate and lipid parameters in rats. In starved and fed rats, S 4048 caused a dose-dependent reduction of blood glucose levels with a corresponding increase in hepatic and renal glycogen and Glucose-6-Phosphate. The major quantitative route of carbon flux in the liver during S 4048-induced inhibition of the glucose-6-phosphatase activity seemed to be glycogenesis. Plasma free fatty acids were increased secondarily due to the S 4048-induced hypoglycemia. Hepatic triglycerides were increased possibly due to increased re-esterification of the readily available free fatty acids. Glucose-6-Phosphate Translocase inhibitors may be useful for experimentally studying aspects of type 1 glycogen storage disease in laboratory animals as well as for the therapeutic modulation of inappropriately high rates of hepatic glucose production in type 2 diabetes.
Ann Burchell - One of the best experts on this subject based on the ideXlab platform.
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Rat liver glucose-6-phosphatase system: light scattering and chemical characterization.
Archives of biochemistry and biophysics, 2002Co-Authors: Eric Clottes, Claire Middleditch, Ann BurchellAbstract:Abstract Glucose-6-phosphatase is a multicomponent system located in the endoplasmic reticulum, involving both a catalytic subunit (G6PC) and several substrate and product carriers. The Glucose-6-Phosphate carrier is called G6PT1. Using light scattering, we determined K D values for phosphate and glucose transport in rat liver microsomes (45 and 33 mM, respectively), G6PT1 K D being too low to be estimated by this technique. We provide evidence that phosphate transport may be carried out by an allosteric multisubunit Translocase or by two distinct proteins. Using chemical modifications by sulfhydryl reagents with different solubility properties, we conclude that in G6PT1, one thiol group important for activity is facing the cytosol and could be Cys 121 or Cys 362 . Moreover, a different Glucose-6-Phosphate Translocase, representing 20% of total Glucose-6-Phosphate transport and insensitive to N -ethylmaleimide modification, could coexist with liver G6PT1. In the G6PC protein, an accessible thiol group is facing the cytosol and, according to structural predictions, could be Cys 284 .
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Three Thiol Groups Are Important for the Activity of the Liver Microsomal Glucose-6-phosphatase System UNUSUAL BEHAVIOR OF ONE THIOL LOCATED IN THE Glucose-6-Phosphate Translocase
The Journal of biological chemistry, 1998Co-Authors: Eric Clottes, Ann BurchellAbstract:Abstract Liver microsomal glucose-6-phosphatase (Glc-6-Pase) is a multicomponent system involving both substrate and product carriers and a catalytic subunit. We have investigated the inhibitory effect of N-ethylmaleimide (NEM), a rather specific sulfhydryl reagent, on rat liver Glc-6-Pase activity. Three thiol groups are important for Glc-6-Pase system activity. Two of them are located in the Glucose-6-Phosphate (Glc-6-P) Translocase, and one is located in the catalytic subunit. The other transporters (phosphate and glucose) are not affected by NEM treatment. The NEM alkylation of the catalytic subunit sulfhydryl residue is prevented by preincubating the disrupted microsomes with saturating concentrations of substrate or product. This suggests either that the modified cysteine is located in the protein active site or that substrate binding hides the thiol group via a conformational change in the enzyme structure. Two other thiols important for the Glc-6-Pase system activity are located in the Glc-6-P Translocase and are more reactive than the one located in the catalytic subunit. The study of the NEM inhibition of the Translocase has provided evidence of the existence of two distinct areas in the protein that can behave independently, with conformational changes occurring during Glc-6-P binding to the transporter. The recent cloning of a human putative Glc-6-P carrier exhibiting homologies with bacterial phosphoester transporters, such as Escherichia coli UhpT (a Glc-6-P Translocase), is compatible with the fact that two cysteine residues are important for the bacterial Glc-6-P transport.
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Multiple transport protein defects in a patient with glycogen storage disease type 1: GSD 1b/1cβ
Journal of Inherited Metabolic Disease, 1995Co-Authors: R. A. Hawkins, K. R. Kamath, H. M. Scott, Ann BurchellAbstract:A male child presented at 5 months of age with vomiting, diarrhoea, hypoglycaemia and hepatomegaly. Histology on a frozen liver biopsy suggested glycogen storage disease (GSD), while biochemical analyses confirmed an elevated glycogen content and normal activities of the GSD enzymes with the proviso that a variant of GSD 1 should be considered. The patient presented at 9 months of age with severe lactic acidosis and hypoglycaemia. A glucagon tolerance test and galactose load test on the patient produced no glycaemic response. A second biopsy was obtained and appropriately handled for the investigation of variants of the glucose-6-phosphatase enzyme (G6Pase) complex. Results showed that the patient had a deficiency of two transport proteins of the G6Pase complex, namely Glucose-6-Phosphate Translocase and pyrophosphate Translocase, i.e. GSD 1b/1cβ. These results were confirmed by additional kinetic analyses which provided confirmation of the double Translocase deficiency. Evidence for inhibitors to these Translocases was not found. The patient's treatment has resulted in the hypoglycaemia now being well controlled; however, at 3 years of age, height and weight are markedly lagging and he is moderately developmentally delayed. Neutropenia has not been found and neutrophil function is normal. Double enzyme deficiencies are very rare and possible explanations which might lead to this phenotype are considered. This, to the authors' knowledge, is the first report of a double Translocase deficiency causing GSD type 1.
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Fatty acyl-CoA esters inhibit glucose-6-phosphatase in rat liver microsomes.
Biochemical Journal, 1995Co-Authors: Rosella Fulceri, Ann Burchell, H. M. Scott, Alessandra Gamberucci, Roberta Giunti, Angelo BenedettiAbstract:In native rat liver microsomes glucose 6-phosphatase activity is dependent not only on the activity of the glucose-6-phosphatase enzyme (which is lumenal) but also on the transport of Glucose-6-Phosphate, phosphate and glucose through the respective Translocases T1, T2 and T3. By using enzymic assay techniques, palmitoyl-CoA or CoA was found to inhibit glucose-6-phosphatase activity in intact microsomes. The effect of CoA required ATP and fatty acids to form fatty acyl esters. Increasing concentrations (2-50 microM) of CoA (plus ATP and 20 microM added palmitic acid) or of palmitoyl-CoA progressively decreased glucose-6-phosphatase activity to 50% of the control value. The inhibition lowered the Vmax without significantly changing the Km. A non-hydrolysable analogue of palmitoyl-CoA also inhibited, demonstrating that binding of palmitoyl-CoA rather than hydrolysis produces the inhibition. Light-scattering measurements of osmotically induced changes in the size of rat liver microsomal vesicles pre-equilibrated in a low-osmolality buffer demonstrated that palmitoyl-CoA alone or CoA plus ATP and palmitic acid altered the microsomal permeability to glucose 6-phosphate, but not to glucose or phosphate, indicating that T1 is the site of palmitoyl-CoA binding and inhibition of glucose-6-phosphatase activity in native microsomes. The type of inhibition found suggests that liver microsomes may comprise vesicles heterogeneous with respect to Glucose-6-Phosphate Translocase(s), i.e. sensitive or insensitive to fatty acid ester inhibition.