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Andersen JV, Schousboe A. Glial Glutamine Homeostasis in Health and Disease. Neurochem Res 2023; 48:1100-1128. [PMID: 36322369 DOI: 10.1007/s11064-022-03771-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2022] [Revised: 08/25/2022] [Accepted: 09/27/2022] [Indexed: 11/05/2022]
Abstract
Glutamine is an essential cerebral metabolite. Several critical brain processes are directly linked to glutamine, including ammonia homeostasis, energy metabolism and neurotransmitter recycling. Astrocytes synthesize and release large quantities of glutamine, which is taken up by neurons to replenish the glutamate and GABA neurotransmitter pools. Astrocyte glutamine hereby sustains the glutamate/GABA-glutamine cycle, synaptic transmission and general brain function. Cerebral glutamine homeostasis is linked to the metabolic coupling of neurons and astrocytes, and relies on multiple cellular processes, including TCA cycle function, synaptic transmission and neurotransmitter uptake. Dysregulations of processes related to glutamine homeostasis are associated with several neurological diseases and may mediate excitotoxicity and neurodegeneration. In particular, diminished astrocyte glutamine synthesis is a common neuropathological component, depriving neurons of an essential metabolic substrate and precursor for neurotransmitter synthesis, hereby leading to synaptic dysfunction. While astrocyte glutamine synthesis is quantitatively dominant in the brain, oligodendrocyte-derived glutamine may serve important functions in white matter structures. In this review, the crucial roles of glial glutamine homeostasis in the healthy and diseased brain are discussed. First, we provide an overview of cellular recycling, transport, synthesis and metabolism of glutamine in the brain. These cellular aspects are subsequently discussed in relation to pathological glutamine homeostasis of hepatic encephalopathy, epilepsy, Alzheimer's disease, Huntington's disease and amyotrophic lateral sclerosis. Further studies on the multifaceted roles of cerebral glutamine will not only increase our understanding of the metabolic collaboration between brain cells, but may also aid to reveal much needed therapeutic targets of several neurological pathologies.
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Affiliation(s)
- Jens V Andersen
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
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2
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Gao Y, Jiang D, Wang C, An G, Zhu L, Cui C. Comprehensive Analysis of Metabolic Changes in Male Mice Exposed to Sodium Valproate Based on GC-MS Analysis. Drug Des Devel Ther 2022; 16:1915-1930. [PMID: 35747443 PMCID: PMC9211130 DOI: 10.2147/dddt.s357530] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Accepted: 05/31/2022] [Indexed: 11/23/2022] Open
Abstract
Purpose Sodium valproate (VPA) is the most widely used broad-spectrum antiepileptic first-line drug in clinical practice and is effective against various types of epilepsy. However, VPA can induce severe cardiotoxicity, nephrotoxicity, hepatotoxicity, and neurotoxicity, which limits its use. Metabolomic studies of VPA-induced toxicity have focused primarily on changes in serum and urine metabolites but have not evaluated changes in major organs or tissues. Methods Central target tissues (intestine, lung, liver, hippocampus, cerebral cortex, inner ear, spleen, kidney, heart, and serum) were analyzed using gas chromatography mass spectrometry to comprehensively evaluate VPA toxicity in mouse models. Results Multivariate analyses, including orthogonal projections of the latent structure and Student’s t test, indicated that depending on the matrix used in the study (the intestine, lung, liver, hippocampus, cerebral cortex, inner ear, spleen, kidney, heart or serum) the number of metabolites differed, the lung being the poorest and the kidney the richest in number. Conclusion These metabolites were closely related and were found to participate in 12 key pathways related to amino acid, fatty acid, and energy metabolism, revealing that the toxic mechanism of VPA may involve oxidative stress, inflammation, amino acid metabolism, lipid metabolism, and energy disorder.
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Affiliation(s)
- Yahao Gao
- Clinical Medical School, Jining Medical University, Jining, Shandong, People’s Republic of China
| | - Di Jiang
- Cheeloo College of Medicine, Shandong University, Jinan, Shandong, People’s Republic of China
| | - Changshui Wang
- Department of Neurosurgery, Affiliated Hospital of Jining Medical University, Jining, People’s Republic of China
| | - Gang An
- Clinical Medical School, Jining Medical University, Jining, Shandong, People’s Republic of China
| | - Li Zhu
- Department of Clinical Pharmacy, Jining First People’s Hospital, Jining Medical University, Jining, Shandong, People’s Republic of China
| | - Changmeng Cui
- Department of Neurosurgery, Affiliated Hospital of Jining Medical University, Jining, People’s Republic of China
- Correspondence: Changmeng Cui, Department of Neurosurgery, Affiliated Hospital of Jining Medical University, 89 Guhuai Road, Jining, Shandong, 272000, People’s Republic of China, Tel +8617805378911, Email
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Andersen JV, McNair LF, Schousboe A, Waagepetersen HS. Specificity of exogenous acetate and glutamate as astrocyte substrates examined in acute brain slices from female mice using methionine sulfoximine (MSO) to inhibit glutamine synthesis. J Neurosci Res 2017; 95:2207-2216. [DOI: 10.1002/jnr.24038] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Revised: 01/05/2017] [Accepted: 01/26/2017] [Indexed: 12/13/2022]
Affiliation(s)
- Jens Velde Andersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; DK-2100 Copenhagen Denmark
| | - Laura Frendrup McNair
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; DK-2100 Copenhagen Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; DK-2100 Copenhagen Denmark
| | - Helle Sønderby Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; DK-2100 Copenhagen Denmark
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Larive CK, Barding GA, Dinges MM. NMR spectroscopy for metabolomics and metabolic profiling. Anal Chem 2014; 87:133-46. [PMID: 25375201 DOI: 10.1021/ac504075g] [Citation(s) in RCA: 151] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Cynthia K Larive
- Department of Chemistry, University of California-Riverside , Riverside, California 92521, United States
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Kumar V, Nag TC, Sharma U, Mewar S, Jagannathan NR, Wadhwa S. High resolution 1H NMR-based metabonomic study of the auditory cortex analogue of developing chick (Gallus gallus domesticus) following prenatal chronic loud music and noise exposure. Neurochem Int 2014; 76:99-108. [DOI: 10.1016/j.neuint.2014.07.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Revised: 06/16/2014] [Accepted: 07/04/2014] [Indexed: 02/07/2023]
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Nägeli M, Fasshauer M, Sommerfeld J, Fendel A, Brandi G, Stover JF. Prolonged continuous intravenous infusion of the dipeptide L-alanine- L-glutamine significantly increases plasma glutamine and alanine without elevating brain glutamate in patients with severe traumatic brain injury. Crit Care 2014; 18:R139. [PMID: 24992948 PMCID: PMC4227121 DOI: 10.1186/cc13962] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Accepted: 06/02/2014] [Indexed: 01/21/2023] Open
Abstract
INTRODUCTION Low plasma glutamine levels are associated with worse clinical outcome. Intravenous glutamine infusion dose- dependently increases plasma glutamine levels, thereby correcting hypoglutaminemia. Glutamine may be transformed to glutamate which might limit its application at a higher dose in patients with severe traumatic brain injury (TBI). To date, the optimal glutamine dose required to normalize plasma glutamine levels without increasing plasma and cerebral glutamate has not yet been defined. METHODS Changes in plasma and cerebral glutamine, alanine, and glutamate as well as indirect signs of metabolic impairment reflected by increased intracranial pressure (ICP), lactate, lactate-to-pyruvate ratio, electroencephalogram (EEG) activity were determined before, during, and after continuous intravenous infusion of 0.75 g L-alanine-L-glutamine which was given either for 24 hours (group 1, n = 6) or 5 days (group 2, n = 6) in addition to regular enteral nutrition. Lab values including nitrogen balance, urea and ammonia were determined daily. RESULTS Continuous L-alanine-L-glutamine infusion significantly increased plasma and cerebral glutamine as well as alanine levels, being mostly sustained during the 5 day infusion phase (plasma glutamine: from 295 ± 62 to 500 ± 145 μmol/ l; brain glutamine: from 183 ± 188 to 549 ± 120 μmol/ l; plasma alanine: from 327 ± 91 to 622 ± 182 μmol/ l; brain alanine: from 48 ± 55 to 89 ± 129 μmol/ l; p < 0.05, ANOVA, post hoc Dunn's test). CONCLUSIONS High dose L-alanine-L-glutamine infusion (0.75 g/ kg/ d up to 5 days) increased plasma and brain glutamine and alanine levels. This was not associated with elevated glutamate or signs of potential glutamate-mediated cerebral injury. The increased nitrogen load should be considered in patients with renal and hepatic dysfunction. TRIAL REGISTRATION Clinicaltrials.gov NCT02130674. Registered 5 April 2014.
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Affiliation(s)
- Mirjam Nägeli
- Surgical Intensive Care Medicine, University Hospital Zuerich, Raemistrasse 100, Zuerich 8091, Switzerland
| | - Mario Fasshauer
- Surgical Intensive Care Medicine, University Hospital Zuerich, Raemistrasse 100, Zuerich 8091, Switzerland
| | - Jutta Sommerfeld
- Surgical Intensive Care Medicine, University Hospital Zuerich, Raemistrasse 100, Zuerich 8091, Switzerland
| | - Angela Fendel
- Surgical Intensive Care Medicine, University Hospital Zuerich, Raemistrasse 100, Zuerich 8091, Switzerland
| | - Giovanna Brandi
- Surgical Intensive Care Medicine, University Hospital Zuerich, Raemistrasse 100, Zuerich 8091, Switzerland
| | - John F Stover
- Surgical Intensive Care Medicine, University Hospital Zuerich, Raemistrasse 100, Zuerich 8091, Switzerland
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Purwaha P, Silva L, Hawke DH, Weinstein JN, Lorenzi PL. An artifact in LC-MS/MS measurement of glutamine and glutamic acid: in-source cyclization to pyroglutamic acid. Anal Chem 2014; 86:5633-7. [PMID: 24892977 PMCID: PMC4063328 DOI: 10.1021/ac501451v] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2014] [Accepted: 06/03/2014] [Indexed: 02/06/2023]
Abstract
Advances in metabolomics, particularly for research on cancer, have increased the demand for accurate, highly sensitive methods for measuring glutamine (Gln) and glutamic acid (Glu) in cell cultures and other biological samples. N-terminal Gln and Glu residues in proteins or peptides have been reported to cyclize to pyroglutamic acid (pGlu) during liquid chromatography (LC)-mass spectrometry (MS) analysis, but cyclization of free Gln and Glu to free pGlu during LC-MS analysis has not been well-characterized. Using an LC-MS/MS protocol that we developed to separate Gln, Glu, and pGlu, we found that free Gln and Glu cyclize to pGlu in the electrospray ionization source, revealing a previously uncharacterized artifact in metabolomic studies. Analysis of Gln standards over a concentration range from 0.39 to 200 μM indicated that a minimum of 33% and maximum of almost 100% of Gln was converted to pGlu in the ionization source, with the extent of conversion dependent on fragmentor voltage. We conclude that the sensitivity and accuracy of Gln, Glu, and pGlu quantitation by electrospray ionization-based mass spectrometry can be improved dramatically by using (i) chromatographic conditions that adequately separate the three metabolites, (ii) isotopic internal standards to correct for in-source pGlu formation, and (iii) user-optimized fragmentor voltage for acquisition of the MS spectra. These findings have immediate impact on metabolomics and metabolism research using LC-MS technologies.
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Affiliation(s)
- Preeti Purwaha
- Department of Bioinformatics and
Computational Biology and Proteomics and
Metabolomics Facility, Department of Pathology, MD Anderson Cancer
Center, University of Texas, Houston, Texas 77054, United States
| | - Leslie
P. Silva
- Department of Bioinformatics and
Computational Biology and Proteomics and
Metabolomics Facility, Department of Pathology, MD Anderson Cancer
Center, University of Texas, Houston, Texas 77054, United States
| | - David H. Hawke
- Department of Bioinformatics and
Computational Biology and Proteomics and
Metabolomics Facility, Department of Pathology, MD Anderson Cancer
Center, University of Texas, Houston, Texas 77054, United States
| | - John N. Weinstein
- Department of Bioinformatics and
Computational Biology and Proteomics and
Metabolomics Facility, Department of Pathology, MD Anderson Cancer
Center, University of Texas, Houston, Texas 77054, United States
| | - Philip L. Lorenzi
- Department of Bioinformatics and
Computational Biology and Proteomics and
Metabolomics Facility, Department of Pathology, MD Anderson Cancer
Center, University of Texas, Houston, Texas 77054, United States
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Propofol compared with isoflurane inhibits mitochondrial metabolism in immature swine cerebral cortex. J Cereb Blood Flow Metab 2014; 34:514-21. [PMID: 24398942 PMCID: PMC3948133 DOI: 10.1038/jcbfm.2013.229] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Revised: 11/13/2013] [Accepted: 11/23/2013] [Indexed: 01/19/2023]
Abstract
Anesthetics used in infants and children are implicated in the development of neurocognitive disorders. Although propofol induces neuroapoptosis in developing brain, the underlying mechanisms require elucidation and may have an energetic basis. We studied substrate utilization in immature swine anesthetized with either propofol or isoflurane for 4 hours. Piglets were infused with 13-Carbon-labeled glucose and leucine in the common carotid artery to assess citric acid cycle (CAC) metabolism in the parietal cortex. The anesthetics produced similar systemic hemodynamics and cerebral oxygen saturation by near-infrared spectroscopy. Compared with isoflurane, propofol depleted ATP and glycogen stores. Propofol decreased pools of the CAC intermediates, citrate, and α-ketoglutarate, while markedly increasing succinate along with decreasing mitochondrial complex II activity. Propofol also inhibited acetyl-CoA entry into the CAC through pyruvate dehydrogenase, while promoting glycolytic flux with marked lactate accumulation. Although oxygen supply appeared similar between the anesthetic groups, propofol yielded a metabolic phenotype that resembled a hypoxic state. Propofol impairs substrate flux through the CAC in the immature cerebral cortex. These impairments occurred without systemic metabolic perturbations that typically accompany propofol infusion syndrome. These metabolic abnormalities may have a role in the neurotoxity observed with propofol in the vulnerable immature brain.
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El Hage M, Baverel G, Conjard-Duplany A, Martin G. Effect of glucose on glutamine metabolism in rat brain slices: a cellular metabolomic study with Effect of glucose ¹³C NMR. Neuroscience 2013; 248:243-51. [PMID: 23769890 DOI: 10.1016/j.neuroscience.2013.05.064] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Revised: 05/27/2013] [Accepted: 05/29/2013] [Indexed: 11/30/2022]
Abstract
To examine the effect of glucose on the cerebral metabolism of glutamine, rat brain slices were incubated with 5mM [3-(13)C]glutamine without and with 5mM unlabeled glucose. Tissue plus medium extracts were analyzed by using enzymatic and (13)C NMR techniques and fluxes through the enzymatic steps involved were calculated with a mathematical model. We demonstrate that glucose increased alanine, pyruvate and glutamate accumulations and decreased ammonium ions accumulation, aspartate accumulation and labeling, and GABA labeling. In order to determine the participation of glutamine synthetase when glucose was added to the incubation medium, we incubated rat brain slices with 5mM [3-(13)C]glutamine plus 5mM unlabeled glucose without and with 2mM methionine sulfoximine (MSO). The results indicate that 77% of the newly appeared glutamine was formed via glutamine synthetase and 23% from endogenous sources; the stimulation of [3-(13)C]glutamine removal by MSO also strongly suggests the existence of a cycle between [3-(13)C]glutamine and [3-(13)C]glutamate. This work also demonstrates that glucose increased fluxes through hexokinase, pyruvate kinase, lactate dehydrogenase, alanine aminotransferase, pyruvate carboxylase, pyruvate dehydrogenase, citrate synthase, flux from α-ketoglutarate to glutamate and flux through glutamine synthetase whereas it inhibited fluxes through aspartate aminotransferase, glutamic acid decarboxylase and GABA aminotransferase.
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Affiliation(s)
- M El Hage
- Metabolys Inc., Laennec Faculty of Medicine, 69372 Lyon Cedex 08, France.
| | - G Baverel
- Metabolys Inc., Laennec Faculty of Medicine, 69372 Lyon Cedex 08, France
| | - A Conjard-Duplany
- EA 4611, Biochimie et Physiopathologie Métaboliques, Laennec Faculty of Medicine, 69372 Lyon Cedex 08, France
| | - G Martin
- EA 4611, Biochimie et Physiopathologie Métaboliques, Laennec Faculty of Medicine, 69372 Lyon Cedex 08, France
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El Hage M, Masson J, Conjard-Duplany A, Ferrier B, Baverel G, Martin G. Brain slices from glutaminase-deficient mice metabolize less glutamine: a cellular metabolomic study with carbon 13 NMR. J Cereb Blood Flow Metab 2012; 32:816-24. [PMID: 22373647 PMCID: PMC3345920 DOI: 10.1038/jcbfm.2012.22] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
In the brain, glutaminase is considered to have a key role in the provision of glutamate, a major excitatory neurotransmitter. Brain slices obtained from wild-type (control) and glutaminase-deficient (GLS1+/-) mice were incubated without glucose and with 5 or 1 mmol/L [3-(13)C]glutamine as substrate. At the end of the incubation, substrate removal and product formation were measured by both enzymatic and carbon 13 nuclear magnetic resonance ((13)C-NMR) techniques. Slices from GLS1+/- mice consumed less [3-(13)C]glutamine and accumulated less [3-(13)C]glutamate. They also produced less (13)CO(2) but accumulated amounts of (13)C-aspartate and (13)C-gamma-aminobutyric acid (GABA) that were similar to those found with brain slices from control mice. The newly formed glutamine observed in slices from control mice remained unchanged in slices from GLS1+/- mice. As expected, flux through glutaminase in slices from GLS1+/- mice was found diminished. Fluxes through all enzymes of the tricarboxylic acid cycle were also reduced in brain slices from GLS1+/- mice except through malate dehydrogenase with 5 mmol/L [3-(13)C]glutamine. The latter diminutions are consistent with the decreases in the production of (13)CO(2) also observed in the slices from these mice. It is concluded that the genetic approach used in this study confirms the key role of glutaminase for the provision of glutamate.
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Affiliation(s)
- Maha El Hage
- Metabolys, Faculté de Médecine R.T.H. Laennec, 7–11 rue G. Paradin, Lyon Cedex 08, France.
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El Hage M, Baverel G, Martin G. Effects of valproate on glutamate metabolism in rat brain slices: A 13C NMR study. Epilepsy Res 2012; 99:94-100. [DOI: 10.1016/j.eplepsyres.2011.10.028] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 07/18/2011] [Accepted: 10/18/2011] [Indexed: 11/27/2022]
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Bauer DE, Jackson JG, Genda EN, Montoya MM, Yudkoff M, Robinson MB. The glutamate transporter, GLAST, participates in a macromolecular complex that supports glutamate metabolism. Neurochem Int 2012; 61:566-74. [PMID: 22306776 DOI: 10.1016/j.neuint.2012.01.013] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Revised: 01/11/2012] [Accepted: 01/12/2012] [Indexed: 01/25/2023]
Abstract
GLAST is the predominant glutamate transporter in the cerebellum and contributes substantially to glutamate transport in forebrain. This astroglial glutamate transporter quickly binds and clears synaptically released glutamate and is principally responsible for ensuring that synaptic glutamate concentrations remain low. This process is associated with a significant energetic cost. Compartmentalization of GLAST with mitochondria and proteins involved in energy metabolism could provide energetic support for glutamate transport. Therefore, we performed immunoprecipitation and co-localization experiments to determine if GLAST might co-compartmentalize with proteins involved in energy metabolism. GLAST was immunoprecipitated from rat cerebellum and subunits of the Na(+)/K(+) ATPase, glycolytic enzymes, and mitochondrial proteins were detected. GLAST co-localized with mitochondria in cerebellar tissue. GLAST also co-localized with mitochondria in fine processes of astrocytes in organotypic hippocampal slice cultures. From these data, we hypothesized that mitochondria participate in a macromolecular complex with GLAST to support oxidative metabolism of transported glutamate. To determine the functional metabolic role of this complex, we measured CO(2) production from radiolabeled glutamate in cultured astrocytes and compared it to overall glutamate uptake. Within 15 min, 9% of transported glutamate was converted to CO(2). This CO(2) production was blocked by inhibitors of glutamate transport and glutamate dehydrogenase, but not by an inhibitor of glutamine synthetase. Our data support a model in which GLAST exists in a macromolecular complex that allows transported glutamate to be metabolized in mitochondria to support energy production.
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Affiliation(s)
- Deborah E Bauer
- Children's Hospital of Philadelphia Research Institute, University of Pennsylvania, Philadelphia, PA 19104, United States
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Rat brain slices oxidize glucose at high rates: a (13)C NMR study. Neurochem Int 2011; 59:1145-54. [PMID: 22067134 DOI: 10.1016/j.neuint.2011.10.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Revised: 10/11/2011] [Accepted: 10/21/2011] [Indexed: 11/24/2022]
Abstract
Since glucose is the main cerebral substrate, we have characterized the metabolism of various (13)C glucose isotopomers in rat brain slices. For this, we have used our cellular metabolomic approach that combines enzymatic and carbon 13 NMR techniques with mathematical models of metabolic pathways. We identified the fate and the pathways of the conversion of glucose carbons into various products (pyruvate, lactate, alanine, aspartate, glutamate, GABA, glutamine and CO(2)) and determined absolute fluxes through pathways of glucose metabolism. After 60 min of incubation, lactate and CO(2) were the main end-products of the metabolism of glucose which was avidly metabolized by the slices. Lactate was also used at high rates by the slices and mainly converted into CO(2). High values of flux through pyruvate carboxylase, which were similar with glucose and lactate as substrate, were observed. The addition of glutamine, but not of acetate, stimulated pyruvate carboxylation, the conversion of glutamate into succinate and fluxes through succinate dehydrogenase, malic enzyme, glutamine synthetase and aspartate aminotransferase. It is concluded that, unlike brain cells in culture, and consistent with high fluxes through PDH and enzymes of the tricarboxylic acid cycle, rat brain slices oxidized both glucose and lactate at high rates.
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