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Denker N, Dringen R. Modulation of Pyruvate Export and Extracellular Pyruvate Concentration in Primary Astrocyte Cultures. Neurochem Res 2024; 49:1331-1346. [PMID: 38376749 PMCID: PMC10991036 DOI: 10.1007/s11064-024-04120-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Revised: 02/02/2024] [Accepted: 02/02/2024] [Indexed: 02/21/2024]
Abstract
Astrocyte-derived pyruvate is considered to have neuroprotective functions. In order to investigate the processes that are involved in astrocytic pyruvate release, we used primary rat astrocyte cultures as model system. Depending on the incubation conditions and medium composition, astrocyte cultures established extracellular steady state pyruvate concentrations in the range between 150 µM and 300 µM. During incubations for up to 2 weeks in DMEM culture medium, the extracellular pyruvate concentration remained almost constant for days, while the extracellular lactate concentration increased continuously during the incubation into the millimolar concentration range as long as glucose was present. In an amino acid-free incubation buffer, glucose-fed astrocytes released pyruvate with an initial rate of around 60 nmol/(h × mg) and after around 5 h an almost constant extracellular pyruvate concentration was established that was maintained for several hours. Extracellular pyruvate accumulation was also observed, if glucose had been replaced by mannose, fructose, lactate or alanine. Glucose-fed astrocyte cultures established similar extracellular steady state concentrations of pyruvate by releasing pyruvate into pyruvate-free media or by consuming excess of extracellular pyruvate. Inhibition of the monocarboxylate transporter MCT1 by AR-C155858 lowered extracellular pyruvate accumulation, while inhibition of mitochondrial pyruvate uptake by UK5099 increased the extracellular pyruvate concentration. Finally, the presence of the uncoupler BAM15 or of the respiratory chain inhibitor antimycin A almost completely abolished extracellular pyruvate accumulation. The data presented demonstrate that cultured astrocytes establish a transient extracellular steady state concentration of pyruvate which is strongly affected by modulation of the mitochondrial pyruvate metabolism.
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Affiliation(s)
- Nadine Denker
- Centre for Biomolecular Interactions Bremen, Faculty 2 (Biology/Chemistry) and Centre for Environmental Research and Sustainable Technologies, University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
| | - Ralf Dringen
- Centre for Biomolecular Interactions Bremen, Faculty 2 (Biology/Chemistry) and Centre for Environmental Research and Sustainable Technologies, University of Bremen, P.O. Box 330440, 28334, Bremen, Germany.
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2
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Harders AR, Arend C, Denieffe SC, Berger J, Dringen R. Endogenous Energy Stores Maintain a High ATP Concentration for Hours in Glucose-Depleted Cultured Primary Rat Astrocytes. Neurochem Res 2023; 48:2241-2252. [PMID: 36914795 PMCID: PMC10182151 DOI: 10.1007/s11064-023-03903-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Revised: 02/24/2023] [Accepted: 02/25/2023] [Indexed: 03/16/2023]
Abstract
Adenosine triphosphate (ATP) is the central energy currency of all cells. Cultured primary rat astrocytes contain a specific cellular ATP content of 27.9 ± 4.7 nmol/mg. During incubation in a glucose- and amino acid-free incubation buffer, this high cellular ATP content was maintained for at least 6 h, while within 24 h the levels of ATP declined to around 30% of the initial value without compromising cell viability. In contrast, cells exposed to 1 mM and 5 mM glucose maintained the initial high cellular ATP content for 24 and 72 h, respectively. The loss in cellular ATP content observed during a 24 h glucose-deprivation was fully prevented by the presence of glucose, fructose or mannose as well as by the mitochondrial substrates lactate, pyruvate, β-hydroxybutyrate or acetate. The high initial specific ATP content in glucose-starved astrocytes, was almost completely abolished within 30 min after application of the respiratory chain inhibitor antimycin A or the mitochondrial uncoupler BAM-15, while these inhibitors lowered in glucose-fed cells the ATP content only to 60% (BAM-15) and 40% (antimycin A) within 5 h. Inhibition of the mitochondrial pyruvate carrier by UK5099 alone or of mitochondrial fatty acid uptake by etomoxir alone hardly affected the high ATP content of glucose-deprived astrocytes during an incubation for 8 h, while the co-application of both inhibitors depleted cellular ATP levels almost completely within 5 h. These data underline the importance of mitochondrial metabolism for the ATP regeneration of astrocytes and demonstrate that the mitochondrial oxidation of pyruvate and fatty acids strongly contributes to the maintenance of a high ATP concentration in glucose-deprived astrocytes.
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Affiliation(s)
- Antonia Regina Harders
- Centre for Biomolecular Interactions Bremen Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany.,Centre for Environmental Research and Sustainable Technologies, University of Bremen, Bremen, Germany
| | - Christian Arend
- Centre for Biomolecular Interactions Bremen Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany.,Centre for Environmental Research and Sustainable Technologies, University of Bremen, Bremen, Germany
| | - Sadhbh Cynth Denieffe
- Centre for Biomolecular Interactions Bremen Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
| | - Julius Berger
- Centre for Biomolecular Interactions Bremen Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
| | - Ralf Dringen
- Centre for Biomolecular Interactions Bremen Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany. .,Centre for Environmental Research and Sustainable Technologies, University of Bremen, Bremen, Germany.
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3
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β-lapachone-mediated WST1 Reduction as Indicator for the Cytosolic Redox Metabolism of Cultured Primary Astrocytes. Neurochem Res 2023; 48:2148-2160. [PMID: 36811754 PMCID: PMC10182120 DOI: 10.1007/s11064-023-03878-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 01/25/2023] [Accepted: 01/26/2023] [Indexed: 02/24/2023]
Abstract
Electron cycler-mediated extracellular reduction of the water-soluble tetrazolium salt 1 (WST1) is frequently used as tool for the determination of cell viability. We have adapted this method to monitor by determining the extracellular WST1 formazan accumulation the cellular redox metabolism of cultured primary astrocytes via the NAD(P)H-dependent reduction of the electron cycler β-lapachone by cytosolic NAD(P)H:quinone oxidoreductase 1 (NQO1). Cultured astrocytes that had been exposed to β-lapachone in concentrations of up to 3 µM remained viable and showed an almost linear extracellular accumulation of WST1 formazan for the first 60 min, while higher concentrations of β-lapachone caused oxidative stress and impaired cell metabolism. β-lapachone-mediated WST1 reduction was inhibited by the NQO1 inhibitors ES936 and dicoumarol in a concentration-dependent manner, with half-maximal inhibition observed at inhibitor concentrations of about 0.3 µM. β-lapachone-mediated WST1 reduction depended strongly on glucose availability, while mitochondrial substrates such as lactate, pyruvate or ketone bodies allowed only residual β-lapachone-mediated WST1 reduction. Accordingly, the mitochondrial respiratory chain inhibitors antimycin A and rotenone hardly affected astrocytic WST1 reduction. Both NADH and NADPH are known to supply electrons for reactions catalysed by cytosolic NQO1. Around 60% of the glucose-dependent β-lapachone-mediated WST1 reduction was prevented by the presence of the glucose-6-phosphate dehydrogenase inhibitor G6PDi-1, while the glyceraldehyde-3-phosphate dehydrogenase inhibitor iodoacetate had only little inhibitory potential. These data suggest that pentose phosphate pathway-generated NADPH, and not glycolysis-derived NADH, is the preferred electron source for cytosolic NQO1-catalysed reductions in cultured astrocytes.
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4
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Consumption and Metabolism of Extracellular Pyruvate by Cultured Rat Brain Astrocytes. Neurochem Res 2022; 48:1438-1454. [PMID: 36495387 PMCID: PMC10066139 DOI: 10.1007/s11064-022-03831-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 11/14/2022] [Accepted: 11/17/2022] [Indexed: 12/14/2022]
Abstract
AbstractBrain astrocytes are considered as glycolytic cell type, but these cells also produce ATP via mitochondrial oxidative phosphorylation. Exposure of cultured primary astrocytes in a glucose-free medium to extracellular substrates that are known to be metabolised by mitochondrial pathways, including pyruvate, lactate, beta-hydroxybutyrate, alanine and acetate, revealed that among the substrates investigated extracellular pyruvate was most efficiently consumed by astrocytes. Extracellular pyruvate was consumed by the cells almost proportional to time over hours in a concentration-dependent manner with apparent Michaelis–Menten kinetics [Km = 0.6 ± 0.1 mM, Vmax = 5.1 ± 0.8 nmol/(min × mg protein)]. The astrocytic consumption of pyruvate was strongly impaired in the presence of the monocarboxylate transporter 1 (MCT1) inhibitor AR-C155858 or by application of a 10-times excess of the MCT1 substrates lactate or beta-hydroxybutyrate. Pyruvate consumption by viable astrocytes was inhibited in the presence of UK5099, an inhibitor of the mitochondrial pyruvate carrier, or after application of the respiratory chain inhibitor antimycin A. In contrast, the mitochondrial uncoupler BAM15 strongly accelerated cellular pyruvate consumption. Lactate and alanine accounted after 3 h of incubation with pyruvate for around 60% and 10%, respectively, of the pyruvate consumed by the cells. These results demonstrate that consumption of extracellular pyruvate by astrocytes involves uptake via MCT1 and that the velocity of pyruvate consumption is strongly modified by substances that affect the entry of pyruvate into mitochondria or the activity of mitochondrial respiration.
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5
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Jaszczyk A, Juszczak GR. Glucocorticoids, metabolism and brain activity. Neurosci Biobehav Rev 2021; 126:113-145. [PMID: 33727030 DOI: 10.1016/j.neubiorev.2021.03.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 03/04/2021] [Accepted: 03/07/2021] [Indexed: 12/17/2022]
Abstract
The review integrates different experimental approaches including biochemistry, c-Fos expression, microdialysis (glutamate, GABA, noradrenaline and serotonin), electrophysiology and fMRI to better understand the effect of elevated level of glucocorticoids on the brain activity and metabolism. The available data indicate that glucocorticoids alter the dynamics of neuronal activity leading to context-specific changes including both excitation and inhibition and these effects are expected to support the task-related responses. Glucocorticoids also lead to diversification of available sources of energy due to elevated levels of glucose, lactate, pyruvate, mannose and hydroxybutyrate (ketone bodies), which can be used to fuel brain, and facilitate storage and utilization of brain carbohydrate reserves formed by glycogen. However, the mismatch between carbohydrate supply and utilization that is most likely to occur in situations not requiring energy-consuming activities lead to metabolic stress due to elevated brain levels of glucose. Excessive doses of glucocorticoids also impair the production of energy (ATP) and mitochondrial oxidation. Therefore, glucocorticoids have both adaptive and maladaptive effects consistently with the concept of allostatic load and overload.
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Affiliation(s)
- Aneta Jaszczyk
- Department of Animal Behavior and Welfare, Institute of Genetics and Animal Biotechnology, Polish Academy of Sciences, 05-552 Jastrzebiec, 36a Postepu str., Poland
| | - Grzegorz R Juszczak
- Department of Animal Behavior and Welfare, Institute of Genetics and Animal Biotechnology, Polish Academy of Sciences, 05-552 Jastrzebiec, 36a Postepu str., Poland.
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6
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Ehrke E, Steinmeier J, Stapelfeldt K, Dringen R. The Menadione-Mediated WST1 Reduction by Cultured Astrocytes Depends on NQO1 Activity and Cytosolic Glucose Metabolism. Neurochem Res 2021; 46:88-99. [PMID: 31902045 DOI: 10.1007/s11064-019-02930-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 12/03/2019] [Accepted: 12/05/2019] [Indexed: 01/07/2023]
Abstract
The reduction of water-soluble tetrazolium salts (WSTs) is frequently used to determine the metabolic integrity and the viability of cultured cells. Recently, we have reported that the electron cycler menadione can efficiently connect intracellular oxidation reactions in cultured astrocytes with the extracellular reduction of WST1 and that this menadione cycling reaction involves an enzyme. The enzymatic reaction involved in the menadione-dependent WST1 reduction was found strongly enriched in the cytosolic fraction of cultured astrocytes and is able to efficiently use both NADH and NADPH as electron donors. In addition, the reaction was highly sensitive towards dicoumarol with Kic values in the low nanomolar range, suggesting that the NAD(P)H:quinone oxidoreductase 1 (NQO1) catalyzes the menadione-dependent WST1 reduction in astrocytes. Also, in intact astrocytes, dicoumarol inhibited the menadione-dependent WST1 reduction in a concentration-dependent manner with half-maximal inhibition observed at around 50 nM. Moreover, the menadione-dependent WST1 reduction by viable astrocytes was strongly affected by the availability of glucose. In the absence of glucose only residual WST1 reduction was observed, while a concentration-dependent increase in WST1 reduction was found during a 30 min incubation with maximal WST1 reduction already determined in the presence of 0.5 mM glucose. Mannose could fully replace glucose as substrate for astrocytic WST1 reduction, while other hexoses, lactate and the mitochondrial substrate β-hydroxybutyrate failed to provide electrons for the cell-dependent WST1 reduction. These results demonstrate that the menadione-mediated WST1 reduction involves cytosolic NQO1 activity and that this process is strongly affected by the availability of glucose as metabolic substrate.
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Affiliation(s)
- Eric Ehrke
- Center for Biomolecular Interactions Bremen (CBIB), Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
- Center for Environmental Research and Sustainable Technology (UFT), University of Bremen, Bremen, Germany
| | - Johann Steinmeier
- Center for Biomolecular Interactions Bremen (CBIB), Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
- Center for Environmental Research and Sustainable Technology (UFT), University of Bremen, Bremen, Germany
| | - Karsten Stapelfeldt
- Center for Biomolecular Interactions Bremen (CBIB), Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany
- Institute for Biophysics, University of Bremen, Bremen, Germany
| | - Ralf Dringen
- Center for Biomolecular Interactions Bremen (CBIB), Faculty 2 (Biology/Chemistry), University of Bremen, P.O. Box 330440, 28334, Bremen, Germany.
- Center for Environmental Research and Sustainable Technology (UFT), University of Bremen, Bremen, Germany.
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7
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Metabolism of Mannose in Cultured Primary Rat Neurons. Neurochem Res 2017; 42:2282-2293. [DOI: 10.1007/s11064-017-2241-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Revised: 03/16/2017] [Accepted: 03/17/2017] [Indexed: 10/19/2022]
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8
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The Protein Tyrosine Kinase Inhibitor Tyrphostin 23 Strongly Accelerates Glycolytic Lactate Production in Cultured Primary Astrocytes. Neurochem Res 2016; 41:2607-2618. [PMID: 27278759 DOI: 10.1007/s11064-016-1972-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Revised: 05/29/2016] [Accepted: 06/01/2016] [Indexed: 02/07/2023]
Abstract
Tyrphostin 23 (T23) is a well-known inhibitor of protein tyrosine kinases. To investigate potential acute effects of T23 on the viability and the glucose metabolism of brain cells, we exposed cultured primary rat astrocytes to T23 for up to 4 h. While the viability and the morphology of the cultured astrocytes were not acutely affected by the presence of T23 in concentrations of up to 300 µM, this compound caused a rapid, time- and concentration-dependent increase in glucose consumption and lactate release. Maximal effects on glycolytic flux were found for incubations with 100 µM T23 for 2 h which doubled both glucose consumption and lactate production. The stimulation of glycolytic flux by T23 was reversible, completely abolished upon removal of the compound and not found in presence of other known inhibitors of endocytosis. Structurally related compounds such as tyrphostin 25 and catechol or modulators of AMP kinase activity did neither affect the basal nor the T23-stimulated lactate production by astrocytes. In contrast, the presence of the phosphatase inhibitor vanadate completely abolished the stimulation by T23 of astrocytic lactate production in a concentration-dependent manner. These data suggest that T23-sensitive phosphorylation/dephosphorylation events are involved in the regulation of astrocytic glycolysis.
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9
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Westhaus A, Blumrich EM, Dringen R. The Antidiabetic Drug Metformin Stimulates Glycolytic Lactate Production in Cultured Primary Rat Astrocytes. Neurochem Res 2015; 42:294-305. [PMID: 26433380 DOI: 10.1007/s11064-015-1733-8] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Revised: 09/25/2015] [Accepted: 09/26/2015] [Indexed: 12/11/2022]
Abstract
Metformin is the most frequently used drug for the treatment of type 2 diabetes in humans. However, only little is known about effects of metformin on brain metabolism. To investigate potential metabolic consequences of an exposure of brain cells to metformin, we incubated rat astrocyte-rich primary cultures with this compound. Metformin in concentrations of up to 30 mM did not acutely compromise the viability of astrocytes, but caused a time- and concentration-dependent increase in cellular glucose consumption and lactate production. For acute incubations in the hour range, the presence of 10 mM metformin doubled the glycolytic flux, while already 1 mM metformin doubled glycolytic flux during incubation for 24 h. In addition to metformin, also other guanidino compounds increased astrocytic lactate production. After 4 h of incubation, half-maximal stimulation of glycolysis was observed for metformin, guanidine and phenformin at concentrations of around 3 mM, 3 mM and 30 µM, respectively. The acute stimulation of glycolytic lactate production by metformin was persistent after removal of extracellular metformin and was also observed, if glucose was absent from the incubation medium or replaced by other hexoses. The metformin-induced stimulation of glycolytic flux was not prevented by compound C, an inhibitor of AMP-dependent protein kinase, nor was it additive to the stimulation of glycolytic flux caused by respiratory chain inhibitors. These data demonstrate that the antidiabetic drug metformin has the potential to strongly activate glycolytic lactate production in brain astrocytes.
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Affiliation(s)
- Adrian Westhaus
- Centre for Biomolecular Interactions Bremen, University of Bremen, PO. Box 330440, 28334, Bremen, Germany
| | - Eva Maria Blumrich
- Centre for Biomolecular Interactions Bremen, University of Bremen, PO. Box 330440, 28334, Bremen, Germany.,Centre for Environmental Research and Sustainable Technology, Leobener Strasse, 28359, Bremen, Germany
| | - Ralf Dringen
- Centre for Biomolecular Interactions Bremen, University of Bremen, PO. Box 330440, 28334, Bremen, Germany. .,Centre for Environmental Research and Sustainable Technology, Leobener Strasse, 28359, Bremen, Germany.
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10
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Ehrke E, Arend C, Dringen R. 3-bromopyruvate inhibits glycolysis, depletes cellular glutathione, and compromises the viability of cultured primary rat astrocytes. J Neurosci Res 2014; 93:1138-46. [DOI: 10.1002/jnr.23474] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Revised: 07/29/2014] [Accepted: 08/01/2014] [Indexed: 01/29/2023]
Affiliation(s)
- Eric Ehrke
- Center for Biomolecular Interactions Bremen, Faculty 2 (Biology/Chemistry); University of Bremen; Bremen Germany
| | - Christian Arend
- Center for Biomolecular Interactions Bremen, Faculty 2 (Biology/Chemistry); University of Bremen; Bremen Germany
| | - Ralf Dringen
- Center for Biomolecular Interactions Bremen, Faculty 2 (Biology/Chemistry); University of Bremen; Bremen Germany
- Center for Environmental Research and Sustainable Technology; University of Bremen; Bremen Germany
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11
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Schmidt MM, Rohwedder A, Dringen R. Effects of Chlorinated Acetates on the Glutathione Metabolism and on Glycolysis of Cultured Astrocytes. Neurotox Res 2010; 19:628-37. [DOI: 10.1007/s12640-010-9209-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 06/29/2010] [Accepted: 07/01/2010] [Indexed: 01/05/2023]
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12
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Liddell JR, Zwingmann C, Schmidt MM, Thiessen A, Leibfritz D, Robinson SR, Dringen R. Sustained hydrogen peroxide stress decreases lactate production by cultured astrocytes. J Neurosci Res 2010; 87:2696-708. [PMID: 19382228 DOI: 10.1002/jnr.22093] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Oxidative stress and disrupted energy metabolism are common to many pathological conditions of the brain. Because astrocytes play an important role in the glucose metabolism of the brain, we have investigated whether sustained oxidative stress affects astroglial glucose metabolism with cultured primary rat astrocytes as a model system. Cultured astrocytes were exposed to a sustained concentration of approximately 50 muM H(2)O(2) in the presence of [U-(13)C]glucose, and cellular and extracellular contents of lactate and glucose were analysed by enzymatic assays and NMR spectroscopy. Exposure of the cells to sustained H(2)O(2) stress for up to 120 min significantly lowered the rate of lactate accumulation in the media to 61% +/- 14% of that in cultures incubated without peroxide. In addition, the ratio of lactate release to glucose consumption was lowered in peroxide-treated astrocytes to 77% +/- 13% of that in control cells, and the specific activity of glyceraldehyde-3-phosphate dehydrogenase had declined to about 10% of control cells within 90 min. In addition, the (13)C enrichment of intracellular and extracellular [(13)C]lactate was about 30% and 95%, respectively, and was not affected by the presence of peroxide, demonstrating that two metabolic pools of lactate are present in cultured astrocytes. The decreased rate of lactate production by astrocytes that have been exposed to peroxide stress is a new example of an alteration by oxidative stress of an important metabolic pathway in astrocytes. Such alterations could contribute to the pathological conditions that have been connected with oxidative stress and disrupted energy metabolism in the brain.
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Affiliation(s)
- Jeff R Liddell
- School of Psychology, Psychiatry, and Psychological Medicine, Monash University, Clayton, Victoria, Australia
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13
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Glucose and lactate supply to the synapse. ACTA ACUST UNITED AC 2009; 63:149-59. [PMID: 19879896 DOI: 10.1016/j.brainresrev.2009.10.002] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2009] [Revised: 10/19/2009] [Accepted: 10/25/2009] [Indexed: 11/23/2022]
Abstract
The main source of energy for the mammalian brain is glucose, and the main sink of energy in the mammalian brain is the neuron, so the conventional view of brain energy metabolism is that glucose is consumed preferentially in neurons. But between glucose and the production of energy are several steps that do not necessarily take place in the same cell. An alternative model has been proposed that states that glucose preferentially taken by astrocytes, is degraded to lactate and then exported into neurons to be oxidized. Short of definitive data, opinions about the relative merits of these competing models are divided, making it a very exciting field of research. Furthermore, growing evidence suggests that lactate acts as a signaling molecule, involved in Na(+) sensing, glucosensing, and in coupling neuronal and glial activity to the modulation of vascular tone. In the present review, we discuss possible dynamics of glucose and lactate in excitatory synaptic regions, focusing on the transporters that catalyze the movement of these molecules.
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14
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Tomás M, Fornas E, Megías L, Durán JM, Portolés M, Guerri C, Egea G, Renau-Piqueras J. Ethanol impairs monosaccharide uptake and glycosylation in cultured rat astrocytes. J Neurochem 2002; 83:601-12. [PMID: 12390522 DOI: 10.1046/j.1471-4159.2002.01167.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Astrocyte and glial-neuron interactions have a critical role in brain development, which is partially mediated by glycoproteins, including adhesion molecules and growth factors. Ethanol affects the synthesis, intracellular transport, subcellular distribution and secretion of these glycoproteins, suggesting alterations in glycosylation. We analyzed the effect of long-term exposure to low doses of ethanol (30 mm) on glycosylation process in growing cultured astrocytes in vitro. Cells were incubated for short (5 min) and long (90 min) periods with several radioactively labeled carbohydrate precursors. The uptake, kinetics and metabolism of these precursors, as well as the radioactivity distribution in protein gels were analyzed. The levels of GLUT1 and mannosidase II were also determined. Ethanol increased the uptake of monosaccharides and the protein levels of GLUT1 but decreased those of mannosidase II. It altered the carbohydrate moiety of proteins and increased cell surface glycoproteins containing terminal non-reduced mannose. These results indicate that ethanol impairs glycosylation in rat astrocytes, thus disrupting brain development.
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Affiliation(s)
- M Tomás
- Centro de Investigación, Department of Biology and Cellular Pathology, Hospital Universitario La Fe, Avda. Campenar 21, E-46009 Valencia, Spain
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15
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Brown AM, Wender R, Ransom BR. Metabolic substrates other than glucose support axon function in central white matter. J Neurosci Res 2001; 66:839-43. [PMID: 11746409 DOI: 10.1002/jnr.10081] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We tested the hypothesis that non-glucose energy sources can support axon function in the rat optic nerve. Axon function was assessed by monitoring the stimulus-evoked compound action potential (CAP). CAP was maintained at full amplitude for 2 hr in 10 mM glucose. 20 mM lactate, 20 mM pyruvate, 10 mM fructose, or 10 mM mannose supported axon function as effectively as did glucose, and 10 mM glutamine provided partial support, but beta-hydroxybutyrate, octanoate, sorbitol, alanine, aspartate, and glutamate failed to support axon function. Our results indicated that a variety of compounds can sustain function in CNS myelinated axons. Axons probably use lactate, pyruvate, and glutamine directly as energy substrates, whereas mannose and fructose could be shuttled through astrocytes to lactate, which is then exported to axons.
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Affiliation(s)
- A M Brown
- Department of Neurology, Box 356465, University of Washington School of Medicine, Seattle, WA 98195, USA.
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16
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Prothmann C, Wellard J, Berger J, Hamprecht B, Verleysdonk S. Primary cultures as a model for studying ependymal functions: glycogen metabolism in ependymal cells. Brain Res 2001; 920:74-83. [PMID: 11716813 DOI: 10.1016/s0006-8993(01)03021-9] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Ependymal cells form a single-layered, ciliated epithelium at the interface between the cerebrospinal fluid and the brain parenchyma. Although their morphology has been studied in detail, ependymal functions remain largely speculative. We have established and characterized a previously described cell culture model to investigate ependymal glycogen metabolism. During growth in minimal medium lacking many non-essential amino acids including L-glutamate, but containing glucose at physiological concentration, the cells contained negligible amounts of glycogen (7+/-3 nmol glucosyl residues/mg protein) despite the presence of insulin. However, during a period of 24 h, the cells accumulated glycogen to very high levels after transferal to a medium containing insulin, glucose at a 5-fold higher concentration, and all proteinogenic amino acids except L-asparagine and L-serine (990+/-112 nmol glucosyl residues/mg protein). Omission of insulin resulted in a 50% reduction in glycogen accumulation. Upon glucose deprivation, glycogen was degraded with a half-life of 21 min. The ependymal primary cultures contained 80+/-5 mU glycogen phosphorylase (Pho)/mg protein and stained positively with antibodies raised against this enzyme. Astroglial cultures built up less glycogen and had less Pho activity under identical conditions. Ependymal glycogen was mobilized by noradrenaline and serotonin. Our results indicate that ependymal cells maintain glycogen as a functional energy store, subject to rapid turnover dependent on the availability of energy substrates and the presence of appropriate signal molecules. Thus ependymocytes appear to be active players in the multitude of processes resulting in normal brain function, and ependymal primary cultures are suggested as a suitable model for studying the role of ependymal cells in these processes.
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Affiliation(s)
- C Prothmann
- Physiologisch-chemisches Institut der Universität, Hoppe-Seyler-Str. 4, D-72076, Tübingen, Germany
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Weber MH, de Oliveira KR, Valle SC, Schweigert ID, Rotta LN, Fagundes I, Krüger AH, Souza K, Souza DO, Perry ML. Study of developmental changes on hexoses metabolism in rat cerebral cortex. Neurochem Res 2001; 26:161-6. [PMID: 11478743 DOI: 10.1023/a:1011050913448] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We have studied the developmental changes of glucose, mannose, fructose and galactose metabolism in rat cerebral cortex. As the animals aged, glucose, mannose and fructose oxidation to CO2 increased, whereas galactose oxidation decreased. Lipid synthesis from glucose and fructose also increased with age, that from mannose decreased and galactose did not change. Cytochalasin B, a potent non-competitive inhibitor of sodium-independent glucose transport, significantly impaired glucose, mannose and galactose metabolism, but had no effect on fructose metabolism. Both galactose or fructose did not change, whereas mannose declined the glucose metabolism. Glucose decreased fructose, galactose and mannose metabolism. Our results show that besides glucose, the metabolism of mannose, galactose and fructose present developmental changes from fetal to adult age, and reinforce the literature data indicating that mannose and galactose are transported by glucose carriers, while fructose is not.
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Affiliation(s)
- M H Weber
- Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil
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18
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Rahman B, Kussmaul L, Hamprecht B, Dringen R. Glycogen is mobilized during the disposal of peroxides by cultured astroglial cells from rat brain. Neurosci Lett 2000; 290:169-72. [PMID: 10963890 DOI: 10.1016/s0304-3940(00)01369-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Regeneration of reduced nicotinamide adenine dinucleotide phosphate (NADPH) is essential for the activity of glutathione redox cycling during cellular peroxide detoxification. In order to test for a function of astroglial glycogen to serve as endogenous precursor for glucose-6-phosphate, the substrate for the regeneration of NADPH by the pentose phosphate pathway, the content of glycogen in astroglia-rich primary cultures derived from the brains of newborn rats was determined after application of peroxides. In the presence of hydrogen peroxide or cumene hydroperoxide in concentrations of 200 microM glycogen was mobilized with a half-life of 16 min in incubation medium containing 20 mM glucose, whereas in the absence of peroxides the glycogen content decreased more slowly with a half-life of 42 min. After 30 min of incubation with or without peroxides 30 and 73%, respectively, of the initial glycogen content was found. The degree of glycogen mobilization was reduced by lowering the initial concentration of the peroxides. These results demonstrate that in astroglial cells (i) glucosyl residues of glycogen are mobilized after application of peroxides despite the presence of exogenous glucose, and (ii) that the demand for glucose-6-phosphate as substrate for NADPH regeneration via the pentose phosphate pathway can, at least partially, be met by mobilization of glycogen.
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Affiliation(s)
- B Rahman
- Physiologisch-chemisches Institut der Universität, Hoppe-Seyler-Strasse 4, D-72076, Tübingen, Germany
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Kussmaul L, Hamprecht B, Dringen R. The detoxification of cumene hydroperoxide by the glutathione system of cultured astroglial cells hinges on hexose availability for the regeneration of NADPH. J Neurochem 1999; 73:1246-53. [PMID: 10461918 DOI: 10.1046/j.1471-4159.1999.0731246.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The ability of astroglia-rich primary cultures derived from the brains of newborn rats to detoxify exogenously applied cumene hydroperoxide (CHP) was analyzed as a model to study glutathione-mediated peroxide detoxification by astrocytes. Under the conditions used, 200 microM CHP disappeared from the incubation buffer with a half-time of approximately 10 min. The half-time of CHP in the incubation buffer was found strongly elevated (a) in cultures depleted of glutathione by a preincubation with buthionine sulfoximine, an inhibitor of glutathione synthesis, (b) in the presence of mercaptosuccinate, an inhibitor of glutathione peroxidase, and (c) in the absence of glucose, a precursor for the regeneration of NADPH. The involvement of glutathione peroxidase in the clearance of CHP was confirmed by the rapid increase in the level of GSSG after application of CHP. The restoration of the initial high ratio of GSH to GSSG depended on the presence of glucose during the incubation. The high capacity of astroglial cells to clear CHP and to restore the initial ratio of GSH to GSSG was fully maintained when glucose was replaced by mannose. In addition, fructose and galactose at least partially substituted for glucose, whereas exogenous isocitrate and malate were at best marginally able to replace glucose during peroxide detoxification and regeneration of GSH. These results demonstrate that CHP is detoxified rapidly by astroglial cells via the glutathione system. This metabolic process strongly depends on the availability of glucose or mannose as hydride donors for the regeneration of the NADPH that is required for the reduction of GSSG by glutathione reductase.
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Affiliation(s)
- L Kussmaul
- Physiologisch-chemisches Institut der Universität, Tübingen, Germany
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20
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Martin A, Rambal C, Berger V, Perier S, Louisot P. Availability of specific sugars for glycoconjugate biosynthesis: a need for further investigations in man. Biochimie 1998; 80:75-86. [PMID: 9587665 DOI: 10.1016/s0300-9084(98)80059-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We review the metabolism of specific sugars used for protein glycosylation, focusing on the fate of exogenously provided sugars. Theoretically, all glycoprotein sugars can derive from glucose, but previous studies show that other exogenous sugars can be incorporated into glycoproteins. From data obtained in congenital galactosemia, exogenous galactose may be important for correct glycosylation. Contrary to galactose, the metabolism of other sugars seems to depend on insulin regulation: stimulation of their endogenous production in diabetic subjects might participate in some diabetic complications, precluding the need for an exogenous supply. The metabolic fate of these sugars is different according to the administration route and exogenous supply may be important either in enteral nutrition or in some clinical situations as has been suggested for sialic acid in the newborn. Data in man are too sparse to reach firm conclusions, implying a need for further investigations. Our preliminary results in animals and man demonstrate that stable isotope methodology allows one to trace glycoprotein sugar metabolism in nutritionally relevant conditions with accuracy and sensitivity, using doses of specific sugars well below toxic levels.
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Affiliation(s)
- A Martin
- INSERM-CNRS U189, Lyon-Sub Medical School, Oullins, France
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21
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Panneerselvam K, Freeze HH. Mannose enters mammalian cells using a specific transporter that is insensitive to glucose. J Biol Chem 1996; 271:9417-21. [PMID: 8621609 DOI: 10.1074/jbc.271.16.9417] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The concentration of D-mannose in serum is 20-50 micron, but its physiological significance for glycoprotein synthesis is unknown. Here, we show that the uptake of D-mannose by different mammalian cell lines involves a mannose-specific transporter(s) with a K(uptake) of about 30-70 micron and a V(max) which is probably sufficient to account for the bulk of mannose needed for glycoprotein synthesis. Mannose uptake appears to be through a facilitated transport process since it is not inhibited by cyanide. Phloretin completely inhibits mannose uptake, but phloridzin inhibits only 25-30%. Both of these inhibitors can block 2-deoxyglucose uptake in fibroblasts which occurs through the typical glucose transporters. None of 9 other sugars tested inhibited mannose transport. Most importantly, 5 mM D-glucose only inhibits mannose uptake by 50% showing that it is not an efficient competitor. These results suggest that this transporter(s) may use serum mannose for glycoprotein synthesis.
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Affiliation(s)
- K Panneerselvam
- La Jolla Cancer Research Foundation, La Jolla, California 92037, USA
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Abstract
The regulation of H+ in nervous systems is a function of several processes, including H+ buffering, intracellular H+ sequestering, CO2 diffusion, carbonic anhydrase activity and membrane transport of acid/base equivalents across the cell membrane. Glial cells participate in all these processes and therefore play a prominent role in shaping acid/base shifts in nervous systems. Apart from a homeostatic function of H(+)-regulating mechanisms, pH transients occur in all three compartments of nervous tissue, neurones, glial cells and extracellular spaces (ECS), in response to neuronal stimulation, to neurotransmitters and hormones as well as secondary to metabolic activity and ionic membrane transport. A pivotal role for H+ regulation and shaping these pH transients must be assigned to the electrogenic and reversible Na(+)-HCO3-membrane cotransport, which appears to be unique to glial cells in nervous systems. Activation of this cotransporter results in the release and uptake of base equivalents by glial cells, processes which are dependent on the glial membrane potential. Na+/H+ and Cl-/HCO3-exchange, and possibly other membrane carriers, accomplish the set of tools in both glial cells and neurones to regulate their intracellular pH. Due to the pH dependence of a great variety of processes, including ion channel gating and conductances, synaptic transmission, intercellular communication via gap junctions, metabolite exchange and neuronal excitability, rapid and local pH transients may have signalling character for the information processing in nervous tissue. The impact of H+ signalling under both physiological and pathophysiological conditions will be discussed for a variety of nervous system functions.
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Affiliation(s)
- J W Deitmer
- Abteilung für Allgemeine Zoologie, Universität Kaiserslautern, Germany
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Abstract
A convenient physiology of the nervous system closely depends on the availability of glucose, the lack of which quickly results in syncope and death. Carbohydrate metabolism in the brain was long thought of as being specific and different from liver carbohydrate metabolism. The present report tries to summarize current data and advances in our knowledge about carbohydrate metabolism. Glucose is brought to the brain by blood flowing through a special network of arteries and is quickly catabolized by the glycolytic and tricarboxylic acid cycle pathways to synthesize energy. It is also used in the synthesis of numerous amino acids, nucleotides and NADPH. Glucose can be polymerized into glycogen in the brain. The nerve tissue is capable of synthesizing glucose-6-phosphate in the gluconeogenic pathway since the fructose-1,6-bisphosphatase, the key enzyme believed to be absent, is actually active and has been purified up to electrophoretic homogeneity. Moreover, the possibility of free glucose synthesis by astrocytes exists. Although the exact role of glycogen in the brain is not totally clear, it is known that the polysaccharide content generally decreases when the functioning of the brain is stimulated and increases in sedative state. This carbohydrate can therefore serve as an indicator for the level of brain activity. Through the administration of methionine sulfoximine, it is possible to increase the amount of glycogen in the brain massively and obtain particles similar to those found in the liver. These in vivo findings have been confirmed by studies based on cultured astrocytes. It has been shown with cultured astrocytes that glutamate increases glycogen synthesis in a pathway which still remains to be elucidated. Brain carbohydrate metabolism is thus in many ways similar to liver carbohydrate metabolism. The astrocyte constitutes the main cell implicated in this metabolism. Improvement in our knowledge about brain carbohydrate metabolism should spread the use of brain glucose metabolism in the diagnosis of certain diseases.
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Affiliation(s)
- T K Hevor
- Laboratoire de Physiologie animale, Université d'Orléans, France
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