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McKenna MC, Sonnewald U, Waageptersen HS, White HS. A tribute to Arne Schousboe's contributions to neurochemistry and his innovative and enduring research in GABA, glutamate, and brain energy metabolism. J Neurochem 2024. [PMID: 39183580 DOI: 10.1111/jnc.16207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2024] [Revised: 08/06/2024] [Accepted: 08/06/2024] [Indexed: 08/27/2024]
Abstract
This is a tribute to Arne Schousboe, Professor Emeritus at the University of Copenhagen, an eminent neurochemist and neuroscientist who was a leader in the fields of GABA, glutamate, and brain energy metabolism. Arne was known for his keen intellect, his wide-ranging expertise in neurochemistry and neuropharmacology of GABA and glutamate and brain energy metabolism. Arne was also known for his strong leadership, his warm and engaging personality and his enjoyment of fine wine and great food shared with friends, family, and colleagues. Sadly, Arne passed away on February 27, 2024, after a short illness. He is survived by his wife Inger Schousboe, his two children, and three wonderful grandchildren. His death is a tremendous loss to the neuroscience community. He will be greatly missed by his friends, family, and colleagues. Some of the highlights of Arne's career are described in this tribute.
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Affiliation(s)
- Mary C McKenna
- Department of Pediatrics and Program in Neuroscience, University of Maryland School of Medicine, Baltimore, Maryland, USA
| | - Ursula Sonnewald
- Department of Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway
| | | | - H Steve White
- Department of Pharmacy, University of Washington, Seattle, Washington, USA
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Metabolic Features of Brain Function with Relevance to Clinical Features of Alzheimer and Parkinson Diseases. Molecules 2022; 27:molecules27030951. [PMID: 35164216 PMCID: PMC8839962 DOI: 10.3390/molecules27030951] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Revised: 01/24/2022] [Accepted: 01/25/2022] [Indexed: 12/04/2022] Open
Abstract
Brain metabolism is comprised in Alzheimer’s disease (AD) and Parkinson’s disease (PD). Since the brain primarily relies on metabolism of glucose, ketone bodies, and amino acids, aspects of these metabolic processes in these disorders—and particularly how these altered metabolic processes are related to oxidative and/or nitrosative stress and the resulting damaged targets—are reviewed in this paper. Greater understanding of the decreased functions in brain metabolism in AD and PD is posited to lead to potentially important therapeutic strategies to address both of these disorders, which cause relatively long-lasting decreased quality of life in patients.
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Song J, Yang X, Zhang M, Wang C, Chen L. Glutamate Metabolism in Mitochondria is Closely Related to Alzheimer's Disease. J Alzheimers Dis 2021; 84:557-578. [PMID: 34602474 DOI: 10.3233/jad-210595] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Glutamate is the main excitatory neurotransmitter in the brain, and its excitatory neurotoxicity is closely related to the occurrence and development of Alzheimer's disease. However, increasing evidence shows that in the process of Alzheimer's disease, glutamate is not only limited to its excitotoxicity as a neurotransmitter but also related to the disorder of its metabolic balance. The balance of glutamate metabolism in the brain is an important determinant of central nervous system health, and the maintenance of this balance is closely related to glutamate uptake, glutamate circulation, intracellular mitochondrial transport, and mitochondrial metabolism. In this paper, we intend to elaborate the key role of mitochondrial glutamate metabolism in the pathogenesis of Alzheimer's disease and review glutamate metabolism in mitochondria as a potential target in the treatment of Alzheimer's disease.
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Affiliation(s)
- Jiayi Song
- Department of Pharmacology, Basic College of Medicine, Jilin University, Changchun, People's Republic of China.,Cadre's Ward, The First Hospital of Jilin University, Changchun, People's Republic of China
| | - Xuehan Yang
- Department of Pharmacology, Basic College of Medicine, Jilin University, Changchun, People's Republic of China
| | - Ming Zhang
- Department of Pharmacology, Basic College of Medicine, Jilin University, Changchun, People's Republic of China
| | - Chunyan Wang
- Cadre's Ward, The First Hospital of Jilin University, Changchun, People's Republic of China
| | - Li Chen
- Department of Pharmacology, Basic College of Medicine, Jilin University, Changchun, People's Republic of China
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Wang T, Suzuki K, Chiba T, Kakisaka K, Takikawa Y. Supplementation with Branched-Chain Amino Acids Induces Unexpected Deleterious Effects on Astrocyte Survival and Intracellular Metabolism with or without Hyperammonemia: A Preliminary In Vitro Study. Int J Hepatol 2021; 2021:7615126. [PMID: 34712496 PMCID: PMC8548177 DOI: 10.1155/2021/7615126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Revised: 08/06/2021] [Accepted: 08/18/2021] [Indexed: 02/08/2023] Open
Abstract
INTRODUCTION Ammonia is a key component in the pathogenesis of hepatic encephalopathy. Branched-chain amino acids (BCAA) have been reported to improve the symptoms of HE induced by hyperammonemia; however, we recently reported that ammonia increases intracellular levels of BCAA and exerts toxic effects on astrocytes. OBJECTIVES This follow-up study was designed to confirm the direct effects of BCAA on human astrocytes and clarify their underlying mechanisms using metabolome analysis and evaluation of associated signaling. METHODS We performed cytotoxicity and cell proliferation tests on astrocytes following BCAA treatment with and without ammonium chloride (NH4Cl) and then compared the results with the effects of BCAA on hepatocytes and neurons. Subsequently, we used metabolomic analysis to investigate intracellular metabolite levels in astrocytes with and without BCAA treatment. RESULTS The astrocytes showed increased leakage of intracellular lactate dehydrogenase and reduced proliferation rate upon BCAA treatment. Interestingly, our analysis showed a BCAA-induced impairment of intracellular glycolysis/glyconeogenesis as well as amino acid and butyric acid metabolism. Furthermore, BCAA treatment was found to cause decreased levels of Glut-1 and phosphorylated GSK-3β and mTOR in astrocytes. CONCLUSIONS Although further investigations of the effect of BCAA on human astrocytes with hyperammonemia are needed, our work demonstrates that BCAA supplementation has direct negative effects on astrocyte survival and intracellular metabolism.
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Affiliation(s)
- Ting Wang
- Division of Hepatology, Department of Internal Medicine, Iwate Medical University, Morioka, Iwate, Japan
- Division of Internal Medicine, Department of Oral Medicine, Iwate Medical University, Morioka, Iwate, Japan
| | - Kazuyuki Suzuki
- Division of Hepatology, Department of Internal Medicine, Iwate Medical University, Morioka, Iwate, Japan
| | - Toshimi Chiba
- Division of Internal Medicine, Department of Oral Medicine, Iwate Medical University, Morioka, Iwate, Japan
| | - Keisuke Kakisaka
- Division of Hepatology, Department of Internal Medicine, Iwate Medical University, Morioka, Iwate, Japan
| | - Yasuhiro Takikawa
- Division of Hepatology, Department of Internal Medicine, Iwate Medical University, Morioka, Iwate, Japan
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Andersen JV, Skotte NH, Aldana BI, Nørremølle A, Waagepetersen HS. Enhanced cerebral branched-chain amino acid metabolism in R6/2 mouse model of Huntington's disease. Cell Mol Life Sci 2019; 76:2449-2461. [PMID: 30830240 PMCID: PMC11105563 DOI: 10.1007/s00018-019-03051-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2018] [Revised: 01/23/2019] [Accepted: 02/19/2019] [Indexed: 01/01/2023]
Abstract
Huntington's disease (HD) is a hereditary and fatal disease causing profound neurodegeneration. Deficits in cerebral energy and neurotransmitter metabolism have been suggested to play a central role in the neuronal dysfunction and death associated with HD. The branched-chain amino acids (BCAAs), leucine, isoleucine and valine, are important for cerebral nitrogen homeostasis, neurotransmitter recycling and can be utilized as energy substrates in the tricarboxylic acid (TCA) cycle. Reduced levels of BCAAs in HD have been validated by several reports. However, it is still unknown how cerebral BCAA metabolism is regulated in HD. Here we investigate the metabolism of leucine and isoleucine in the R6/2 mouse model of HD. Acutely isolated cerebral cortical and striatal slices of control and R6/2 mice were incubated in media containing 15N- or 13C-labeled leucine or isoleucine and slice extracts were analyzed by gas chromatography-mass spectrometry (GC-MS) to determine isotopic enrichment of derived metabolites. Elevated BCAA transamination was found from incubations with [15N]leucine and [15N]isoleucine, in both cerebral cortical and striatal slices of R6/2 mice compared to controls. Metabolism of [U-13C]leucine and [U-13C]isoleucine, entering oxidative metabolism as acetyl CoA, was maintained in R6/2 mice. However, metabolism of [U-13C]isoleucine, entering the TCA cycle as succinyl CoA, was elevated in both cerebral cortical and striatal slices of R6/2 mice, suggesting enhanced metabolic flux via this anaplerotic pathway. To support the metabolic studies, expression of enzymes in the BCAA metabolic pathway was assessed from a proteomic resource. Several enzymes related to BCAA metabolism were found to exhibit augmented expression in the R6/2 brain, particularly related to isoleucine metabolism, suggesting an increase in the BCAA metabolic machinery. Our results show that the capacity for cerebral BCAA metabolism, predominantly of isoleucine, is amplified in the R6/2 brain and indicates that perturbations in cerebral BCAA homeostasis could have functional consequences for HD pathology.
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Affiliation(s)
- Jens V Andersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
| | - Niels H Skotte
- Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Blanca I Aldana
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark
| | - Anne Nørremølle
- Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark.
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Metabolic perturbations after pediatric TBI: It's not just about glucose. Exp Neurol 2019; 316:74-84. [PMID: 30951705 DOI: 10.1016/j.expneurol.2019.03.018] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Revised: 03/13/2019] [Accepted: 03/30/2019] [Indexed: 12/22/2022]
Abstract
Improved patient survival following pediatric traumatic brain injury (TBI) has uncovered a currently limited understanding of both the adaptive and maladaptive metabolic perturbations that occur during the acute and long-term phases of recovery. While much is known about the redundancy of metabolic pathways that provide adequate energy and substrates for normal brain growth and development, the field is only beginning to characterize perturbations in these metabolic pathways after pediatric TBI. To date, the majority of studies have focused on dysregulated oxidative glucose metabolism after injury; however, the immature brain is well-equipped to use alternative substrates to fuel energy production, growth, and development. A comprehensive understanding of metabolic changes associated with pediatric TBI cannot be limited to investigations of glucose metabolism alone. All energy substrates used by the brain should be considered in developing nutritional and pharmacological interventions for pediatric head trauma. This review summarizes post-injury changes in brain metabolism of glucose, lipids, ketone bodies, and amino acids with discussion of the therapeutic potential of altering substrate utilization to improve pediatric TBI outcomes.
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Romeiro FG, Ietsugu MDV, Franzoni LDC, Augusti L, Alvarez M, Santos LAA, Lima TB, Koga KH, Moriguchi SM, Caramori CA, Silva GF, Betting LEGG. Which of the branched-chain amino acids increases cerebral blood flow in hepatic encephalopathy? A double-blind randomized trial. Neuroimage Clin 2018; 19:302-310. [PMID: 30013913 PMCID: PMC6044187 DOI: 10.1016/j.nicl.2018.03.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Revised: 03/07/2018] [Accepted: 03/21/2018] [Indexed: 02/06/2023]
Abstract
Branched-chain amino acids increase the brain perfusion of patients with hepatic encephalopathy (HE), but the amino acid and the mechanisms involved are still unknown. This study compared brain perfusion and clinical improvement during leucine or isoleucine supplementation. After randomization, 27 subjects with cirrhosis and HE received leucine or isoleucine supplements for one year. Brain single Photon Emission Computed Tomography (SPECT) and dynamic brain scintigraphy (DBS) were performed pretreatment and at 1, 8 and 12 months of supplementation. Brain perfusion was increased only in the isoleucine group at 8 months of treatment by both SPECT and DBS (p < 0.001 and p = 0.05, respectively) and by SPECT at the 12th month (p < 0.05). This was associated with hepatic encephalopathy improvement at 8 and 12 months (p = 0.008 and 0.004, respectively), which was not observed in the leucine group (p = 0.313 and 0.055, respectively). Isoleucine supplementation achieved a better impact on brain perfusion restoration in HE.
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Key Words
- AC, arm circumference
- APMT, adductor pollicis muscle thickness
- BCAA, branched-chain amino acids
- BCKA, branched-chain ketoacids
- BMI, body mass index
- Branched-chain amino acids
- CAMA, corrected mid-arm muscle area
- CBF, cerebral blood flow
- Cerebral blood flow
- EEG, electroencephalogram
- FDR, false discovery rate
- GDH, glutamate dehydrogenase
- GLN, glutamine
- GLU, glutamate
- HE, hepatic encephalopathy
- HGS, handgrip strength
- HPLC, high-performance liquid chromatography
- HRQoL, health-related quality of life
- Hepatic encephalopathy
- Liver cirrhosis
- MAMC, mid-arm muscle circumference
- MELD, Model of End-Stage Liver Disease
- NH3, ammonia
- PDH, pyruvate dehydrogenase complex
- ROIs, regions of interest
- ROS, reactive oxygen species
- SF-36, 36-item Short-Form General Health Survey
- SPECT, Single Photon Emission Computed Tomography
- SPM12, Statistical Parametrical Mapping 12
- TCA, tricarboxylic acid
- TSF, triceps skinfold
- α-KG, α-ketoglutarate
- αKGDH, α-ketoglutarate dehydrogenase complex
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Affiliation(s)
- Fernando Gomes Romeiro
- Department of Internal Medicine, Botucatu Medical School, UNESP - Univ Estadual Paulista. Av. Prof. Mário Rubens Guimarães Montenegro, s/n Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil.
| | - Marjorie do Val Ietsugu
- Department of Internal Medicine, Botucatu Medical School, UNESP - Univ Estadual Paulista. Av. Prof. Mário Rubens Guimarães Montenegro, s/n Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil
| | - Letícia de Campos Franzoni
- Department of Internal Medicine, Botucatu Medical School, UNESP - Univ Estadual Paulista. Av. Prof. Mário Rubens Guimarães Montenegro, s/n Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil
| | - Laís Augusti
- Department of Internal Medicine, Botucatu Medical School, UNESP - Univ Estadual Paulista. Av. Prof. Mário Rubens Guimarães Montenegro, s/n Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil
| | - Matheus Alvarez
- Department of Physics and Biophysics, Botucatu Biosciences Institute, UNESP - Univ Estadual Paulista, Rua Prof. Dr. Antonio Celso Wagner Zanin, s/n, Botucatu, São Paulo 18618-689, Brazil.
| | - Lívia Alves Amaral Santos
- Department of Internal Medicine, Botucatu Medical School, UNESP - Univ Estadual Paulista. Av. Prof. Mário Rubens Guimarães Montenegro, s/n Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil
| | - Talles Bazeia Lima
- Department of Internal Medicine, Botucatu Medical School, UNESP - Univ Estadual Paulista. Av. Prof. Mário Rubens Guimarães Montenegro, s/n Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil
| | - Kátia Hiromoto Koga
- Department of Tropical Diseases and Imaging Diagnosis, Botucatu Medical School, UNESP - Univ Estadual Paulista, Av. Prof. Mário Rubens Guimarães Montenegro, s/n. Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil.
| | - Sônia Marta Moriguchi
- Department of Tropical Diseases and Imaging Diagnosis, Botucatu Medical School, UNESP - Univ Estadual Paulista, Av. Prof. Mário Rubens Guimarães Montenegro, s/n. Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil
| | - Carlos Antonio Caramori
- Department of Internal Medicine, Botucatu Medical School, UNESP - Univ Estadual Paulista. Av. Prof. Mário Rubens Guimarães Montenegro, s/n Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil
| | - Giovanni Faria Silva
- Department of Internal Medicine, Botucatu Medical School, UNESP - Univ Estadual Paulista. Av. Prof. Mário Rubens Guimarães Montenegro, s/n Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil.
| | - Luiz Eduardo Gomes Garcia Betting
- Department of Neurology, Psychology and Psychiatry, Botucatu Medical School, UNESP - Univ Estadual Paulista, Av. Prof. Mário Rubens Guimarães Montenegro, s/n Distrito de Rubião Jr, Botucatu, São Paulo 18618-687, Brazil.
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Silva LS, Poschet G, Nonnenmacher Y, Becker HM, Sapcariu S, Gaupel AC, Schlotter M, Wu Y, Kneisel N, Seiffert M, Hell R, Hiller K, Lichter P, Radlwimmer B. Branched-chain ketoacids secreted by glioblastoma cells via MCT1 modulate macrophage phenotype. EMBO Rep 2017; 18:2172-2185. [PMID: 29066459 DOI: 10.15252/embr.201744154] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Revised: 09/25/2017] [Accepted: 09/28/2017] [Indexed: 11/09/2022] Open
Abstract
Elevated amino acid catabolism is common to many cancers. Here, we show that glioblastoma are excreting large amounts of branched-chain ketoacids (BCKAs), metabolites of branched-chain amino acid (BCAA) catabolism. We show that efflux of BCKAs, as well as pyruvate, is mediated by the monocarboxylate transporter 1 (MCT1) in glioblastoma. MCT1 locates in close proximity to BCKA-generating branched-chain amino acid transaminase 1, suggesting possible functional interaction of the proteins. Using in vitro models, we demonstrate that tumor-excreted BCKAs can be taken up and re-aminated to BCAAs by tumor-associated macrophages. Furthermore, exposure to BCKAs reduced the phagocytic activity of macrophages. This study provides further evidence for the eminent role of BCAA catabolism in glioblastoma by demonstrating that tumor-excreted BCKAs might have a direct role in tumor immune suppression. Our data further suggest that the anti-proliferative effects of MCT1 knockdown observed by others might be related to the blocked excretion of BCKAs.
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Affiliation(s)
- Lidia Santos Silva
- Division of Molecular Genetics, German Cancer Research Center (DKFZ), Heidelberg, Germany.,German Cancer Consortium (DKTK), Heidelberg, Germany
| | - Gernot Poschet
- Center for Organismal Studies Heidelberg, Heidelberg University, Heidelberg, Germany
| | - Yannic Nonnenmacher
- Department of Bioinfomatics and Biochemistry and Braunschweig Integrated Center of Systems Biology (BRICS), Technische Universität Braunschweig, Braunschweig, Germany.,Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-Belval, Luxembourg
| | - Holger M Becker
- Division of General Zoology, Department of Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Sean Sapcariu
- Department of Bioinfomatics and Biochemistry and Braunschweig Integrated Center of Systems Biology (BRICS), Technische Universität Braunschweig, Braunschweig, Germany.,Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-Belval, Luxembourg
| | - Ann-Christin Gaupel
- Division of Molecular Genetics, German Cancer Research Center (DKFZ), Heidelberg, Germany.,German Cancer Consortium (DKTK), Heidelberg, Germany
| | - Magdalena Schlotter
- Division of Molecular Genetics, German Cancer Research Center (DKFZ), Heidelberg, Germany.,German Cancer Consortium (DKTK), Heidelberg, Germany
| | - Yonghe Wu
- Division of Molecular Genetics, German Cancer Research Center (DKFZ), Heidelberg, Germany.,German Cancer Consortium (DKTK), Heidelberg, Germany
| | - Niclas Kneisel
- Division of Molecular Genetics, German Cancer Research Center (DKFZ), Heidelberg, Germany.,German Cancer Consortium (DKTK), Heidelberg, Germany
| | - Martina Seiffert
- Division of Molecular Genetics, German Cancer Research Center (DKFZ), Heidelberg, Germany.,German Cancer Consortium (DKTK), Heidelberg, Germany
| | - Rüdiger Hell
- Center for Organismal Studies Heidelberg, Heidelberg University, Heidelberg, Germany
| | - Karsten Hiller
- Department of Bioinfomatics and Biochemistry and Braunschweig Integrated Center of Systems Biology (BRICS), Technische Universität Braunschweig, Braunschweig, Germany.,Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-Belval, Luxembourg
| | - Peter Lichter
- Division of Molecular Genetics, German Cancer Research Center (DKFZ), Heidelberg, Germany.,German Cancer Consortium (DKTK), Heidelberg, Germany
| | - Bernhard Radlwimmer
- Division of Molecular Genetics, German Cancer Research Center (DKFZ), Heidelberg, Germany .,German Cancer Consortium (DKTK), Heidelberg, Germany
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Yudkoff M. Interactions in the Metabolism of Glutamate and the Branched-Chain Amino Acids and Ketoacids in the CNS. Neurochem Res 2017; 42:10-18. [PMID: 27696119 PMCID: PMC5285401 DOI: 10.1007/s11064-016-2057-z] [Citation(s) in RCA: 87] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 08/29/2016] [Accepted: 09/01/2016] [Indexed: 01/17/2023]
Abstract
Glutamatergic neurotransmission entails a tonic loss of glutamate from nerve endings into the synapse. Replacement of neuronal glutamate is essential in order to avoid depletion of the internal pool. In brain this occurs primarily via the glutamate-glutamine cycle, which invokes astrocytic synthesis of glutamine and hydrolysis of this amino acid via neuronal phosphate-dependent glutaminase. This cycle maintains constancy of internal pools, but it does not provide a mechanism for inevitable losses of glutamate N from brain. Import of glutamine or glutamate from blood does not occur to any appreciable extent. However, the branched-chain amino acids (BCAA) cross the blood-brain barrier swiftly. The brain possesses abundant branched-chain amino acid transaminase activity which replenishes brain glutamate and also generates branched-chain ketoacids. It seems probable that the branched-chain amino acids and ketoacids participate in a "glutamate-BCAA cycle" which involves shuttling of branched-chain amino acids and ketoacids between astrocytes and neurons. This mechanism not only supports the synthesis of glutamate, it also may constitute a mechanism by which high (and potentially toxic) concentrations of glutamate can be avoided by the re-amination of branched-chain ketoacids.
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Affiliation(s)
- Marc Yudkoff
- Department of Pediatrics, Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA.
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Multifactorial Effects on Different Types of Brain Cells Contribute to Ammonia Toxicity. Neurochem Res 2016; 42:721-736. [PMID: 27286679 DOI: 10.1007/s11064-016-1966-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2016] [Revised: 05/20/2016] [Accepted: 05/24/2016] [Indexed: 12/12/2022]
Abstract
Effects of ammonia on astrocytes play a major role in hepatic encephalopathy, acute liver failure and other diseases caused by increased arterial ammonia concentrations (e.g., inborn errors of metabolism, drug or mushroom poisoning). There is a direct correlation between arterial ammonia concentration, brain ammonia level and disease severity. However, the pathophysiology of hyperammonemic diseases is disputed. One long recognized factor is that increased brain ammonia triggers its own detoxification by glutamine formation from glutamate. This is an astrocytic process due to the selective expression of the glutamine synthetase in astrocytes. A possible deleterious effect of the resulting increase in glutamine concentration has repeatedly been discussed and is supported by improvement of some pathologic effects by GS inhibition. However, this procedure also inhibits a large part of astrocytic energy metabolism and may prevent astrocytes from responding to pathogenic factors. A decrease of the already low glutamate concentration in astrocytes due to increased synthesis of glutamine inhibits the malate-aspartate shuttle and energy metabolism. A more recently described pathogenic factor is the resemblance between NH4+ and K+ in their effects on the Na+,K+-ATPase and the Na+,K+, 2 Cl- and water transporter NKCC1. Stimulation of the Na+,K+-ATPase driven NKCC1 in both astrocytes and endothelial cells is essential for the development of brain edema. Na+,K+-ATPase stimulation also activates production of endogenous ouabains. This leads to oxidative and nitrosative damage and sensitizes NKCC1. Administration of ouabain antagonists may accordingly have therapeutic potential in hyperammonemic diseases.
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Central Role of Glutamate Metabolism in the Maintenance of Nitrogen Homeostasis in Normal and Hyperammonemic Brain. Biomolecules 2016; 6:biom6020016. [PMID: 27023624 PMCID: PMC4919911 DOI: 10.3390/biom6020016] [Citation(s) in RCA: 111] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Revised: 03/10/2016] [Accepted: 03/15/2016] [Indexed: 12/21/2022] Open
Abstract
Glutamate is present in the brain at an average concentration—typically 10–12 mM—far in excess of those of other amino acids. In glutamate-containing vesicles in the brain, the concentration of glutamate may even exceed 100 mM. Yet because glutamate is a major excitatory neurotransmitter, the concentration of this amino acid in the cerebral extracellular fluid must be kept low—typically µM. The remarkable gradient of glutamate in the different cerebral compartments: vesicles > cytosol/mitochondria > extracellular fluid attests to the extraordinary effectiveness of glutamate transporters and the strict control of enzymes of glutamate catabolism and synthesis in well-defined cellular and subcellular compartments in the brain. A major route for glutamate and ammonia removal is via the glutamine synthetase (glutamate ammonia ligase) reaction. Glutamate is also removed by conversion to the inhibitory neurotransmitter γ-aminobutyrate (GABA) via the action of glutamate decarboxylase. On the other hand, cerebral glutamate levels are maintained by the action of glutaminase and by various α-ketoglutarate-linked aminotransferases (especially aspartate aminotransferase and the mitochondrial and cytosolic forms of the branched-chain aminotransferases). Although the glutamate dehydrogenase reaction is freely reversible, owing to rapid removal of ammonia as glutamine amide, the direction of the glutamate dehydrogenase reaction in the brain in vivo is mainly toward glutamate catabolism rather than toward the net synthesis of glutamate, even under hyperammonemia conditions. During hyperammonemia, there is a large increase in cerebral glutamine content, but only small changes in the levels of glutamate and α-ketoglutarate. Thus, the channeling of glutamate toward glutamine during hyperammonemia results in the net synthesis of 5-carbon units. This increase in 5-carbon units is accomplished in part by the ammonia-induced stimulation of the anaplerotic enzyme pyruvate carboxylase. Here, we suggest that glutamate may constitute a buffer or bulwark against changes in cerebral amine and ammonia nitrogen. Although the glutamate transporters are briefly discussed, the major emphasis of the present review is on the enzymology contributing to the maintenance of glutamate levels under normal and hyperammonemic conditions. Emphasis will also be placed on the central role of glutamate in the glutamine-glutamate and glutamine-GABA neurotransmitter cycles between neurons and astrocytes. Finally, we provide a brief and selective discussion of neuropathology associated with altered cerebral glutamate levels.
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12
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Rapid adaptation of rat brain and liver metabolism to a ketogenic diet: an integrated study using (1)H- and (13)C-NMR spectroscopy. J Cereb Blood Flow Metab 2015; 35:1154-62. [PMID: 25785828 PMCID: PMC4640267 DOI: 10.1038/jcbfm.2015.29] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Revised: 12/11/2014] [Accepted: 01/22/2015] [Indexed: 11/08/2022]
Abstract
The ketogenic diet (KD) is an effective alternative treatment for refractory epilepsy in children, but the mechanisms by which it reduces seizures are poorly understood. To investigate how the KD modifies brain metabolism, we infused control (CT) and 7-day KD rats with either [1-(13)C]glucose (Glc) or [2,4-(13)C2]β-hydroxybutyrate (β-HB). Specific enrichments of amino acids (AAs) measured by (1)H- and (13)C-NMR in total brain perchloric acid extracts were similar between CT and KD rats after [1-(13)C]Glc infusion whereas they were higher in KD rats after [2,4-(13)C2]β-HB infusion. This suggests better metabolic efficiency of ketone body utilization on the KD. The relative rapid metabolic adaptation to the KD included (1) 11%-higher brain γ-amino butyric acid (GABA)/glutamate (Glu) ratio versus CT, (2) liver accumulation of the ketogenic branched-chain AAs (BCAAs) leucine (Leu) and isoleucine (ILeu), which were never detected in CT, and (3) higher brain Leu and ILeu contents. Since Glu and GABA are excitatory and inhibitory neurotransmitters, respectively, higher brain GABA/Glu ratio could contribute to the mechanism by which the KD reduces seizures in epilepsy. Increased BCAA on the KD may also contribute to better seizure control.
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Marx MC, Billups D, Billups B. Maintaining the presynaptic glutamate supply for excitatory neurotransmission. J Neurosci Res 2015; 93:1031-44. [PMID: 25648608 DOI: 10.1002/jnr.23561] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Revised: 01/04/2015] [Accepted: 01/05/2015] [Indexed: 01/09/2023]
Abstract
Glutamate released from synapses during excitatory neurotransmission must be rapidly recycled to maintain neuronal communication. This review evaluates data from physiological experiments at hippocampal CA3 to CA1 synapses and the calyx of Held synapse in the brainstem to analyze quantitatively the rates of release and resupply of glutamate required to sustain neurotransmission. We calculate that, without efficient recycling, the presynaptic glutamate supply will be exhausted within about a minute of normal synaptic activity. We also discuss replenishment of the presynaptic pool by diffusion from the soma, direct uptake of glutamate back into the presynaptic terminal, and uptake of glutamate precursor molecules. Diffusion of glutamate from the soma is calculated to be fast enough to resupply presynaptic glutamate in the hippocampus but not at the calyx of Held. However, because the somatic cytoplasm will also quickly run out of glutamate and synapses can function continually even if the presynaptic axon is severed, mechanisms other than diffusion must be present to resupply glutamate for release. Direct presynaptic uptake of glutamate is not present at the calyx of Held but may play a role in glutamate recycling in the hippocampus. Alternatively, glutamine or tricarboxylic acid cycle intermediates released from glia can serve as a precursor for glutamate in synaptic terminals, and we calculate that the magnitude of presynaptic glutamine uptake is sufficient to supply enough glutamate to sustain neurotransmission. The nature of these mechanisms, their relative abundance, and the co-ordination between them remain areas of intensive investigation.
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Affiliation(s)
- Mari-Carmen Marx
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, Canberra, Australian Capital Territory, Australia
| | - Daniela Billups
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, Canberra, Australian Capital Territory, Australia
| | - Brian Billups
- Eccles Institute of Neuroscience, The John Curtin School of Medical Research, The Australian National University, Canberra, Australian Capital Territory, Australia
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Sturgeon JP, Shawcross DL. Recent insights into the pathogenesis of hepatic encephalopathy and treatments. Expert Rev Gastroenterol Hepatol 2014; 8:83-100. [PMID: 24236755 DOI: 10.1586/17474124.2014.858598] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Hepatic encephalopathy (HE) encompasses a spectrum of neuropsychiatric disorders related to liver failure. The development of HE can have a profound impact on mortality as well as quality of life for patients and carers. Ammonia is central in the disease process contributing to alteration in neurotransmission, oxidative stress, and cerebral edema and astrocyte swelling in acute liver failure. Inflammation in the presence of ammonia coactively worsens HE. Inflammation can result from hyperammonemic responses, endotoxemia, innate immune dysfunction or concurrent infection. This review summarizes the current processes implicated in the pathogenesis of HE, as well as current and potential treatments. Treatments currently focus on reducing inflammation and/or blood ammonia levels and provide varying degrees of success. Optimization of current treatments and initial testing of novel therapies will provide the basis of improvement of care in the near future.
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Affiliation(s)
- Jonathan P Sturgeon
- Institute of Liver Studies, King's College London School of Medicine at King's College Hospital, Denmark Hill, London, SE5 9RS, UK
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15
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Schousboe A, Scafidi S, Bak LK, Waagepetersen HS, McKenna MC. Glutamate metabolism in the brain focusing on astrocytes. ADVANCES IN NEUROBIOLOGY 2014; 11:13-30. [PMID: 25236722 DOI: 10.1007/978-3-319-08894-5_2] [Citation(s) in RCA: 245] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Metabolism of glutamate, the main excitatory neurotransmitter and precursor of GABA, is exceedingly complex and highly compartmentalized in brain. Maintenance of these neurotransmitter pools is strictly dependent on the de novo synthesis of glutamine in astrocytes which requires both the anaplerotic enzyme pyruvate carboxylase and glutamine synthetase. Glutamate is formed directly from glutamine by deamidation via phosphate activated glutaminase a reaction that also yields ammonia. Glutamate plays key roles linking carbohydrate and amino acid metabolism via the tricarboxylic acid (TCA) cycle, as well as in nitrogen trafficking and ammonia homeostasis in brain. The anatomical specialization of astrocytic endfeet enables these cells to rapidly and efficiently remove neurotransmitters from the synaptic cleft to maintain homeostasis, and to provide glutamine to replenish neurotransmitter pools in both glutamatergic and GABAergic neurons. Since the glutamate-glutamine cycle is an open cycle that actively interfaces with other pathways, the de novo synthesis of glutamine in astrocytes helps to maintain the operation of this cycle. The fine-tuned biochemical specialization of astrocytes allows these cells to respond to subtle changes in neurotransmission by dynamically adjusting their anaplerotic and glycolytic activities, and adjusting the amount of glutamate oxidized for energy relative to direct formation of glutamine, to meet the demands for maintaining neurotransmission. This chapter summarizes the evidence that astrocytes are essential and dynamic partners in both glutamatergic and GABAergic neurotransmission in brain.
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Affiliation(s)
- Arne Schousboe
- Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology, University of Copenhagen, 2100, Copenhagen, Denmark
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Cooper AJL. Quantitative analysis of neurotransmitter pathways under steady state conditions - a perspective. Front Endocrinol (Lausanne) 2013; 4:179. [PMID: 24302920 PMCID: PMC3831341 DOI: 10.3389/fendo.2013.00179] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Accepted: 11/04/2013] [Indexed: 11/29/2022] Open
Abstract
In a contribution to this Research Topic Erkki Somersalo and Daniela Calvetti carried out a mathematical analysis of neurotransmitter pathways in brain, modeling compartmental nitrogen flux among several major participants - ammonia, glutamine, glutamate, GABA, and selected amino acids. This analysis is important because cerebral nitrogen metabolism is perturbed in many diseases, including liver disease and inborn errors of the urea cycle. These diseases result in an elevation of blood ammonia, which is neurotoxic. Here, a brief description is provided of the discovery of cerebral metabolic compartmentation of nitrogen metabolism - a key feature of cerebral glutamate-glutamine and GABA-glutamine cycles. The work of Somersalo and Calvetti is discussed as a model for future studies of normal and pathological cerebral ammonia metabolism.
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Affiliation(s)
- Arthur J. L. Cooper
- Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY, USA
- *Correspondence: Arthur J. L. Cooper, Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY 10520, USA e-mail:
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Gluud LL, Dam G, Borre M, Les I, Cordoba J, Marchesini G, Aagaard NK, Risum N, Vilstrup H. Oral branched-chain amino acids have a beneficial effect on manifestations of hepatic encephalopathy in a systematic review with meta-analyses of randomized controlled trials. J Nutr 2013; 143:1263-8. [PMID: 23739310 DOI: 10.3945/jn.113.174375] [Citation(s) in RCA: 80] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Supplements with branched-chain amino acid (BCAA) have cerebral, metabolic, and nutritional effects that may benefit patients with hepatic encephalopathy (HE). We therefore conducted a systematic review on the effects of oral BCAAs compared with control supplements or placebo for patients with cirrhosis and recurrent overt or minimal HE. The quantitative analyses included data from 8 trials (n = 382 patients). Individual patient data were retrieved from 4 trials to recalculate outcomes (n = 255 patients). The mean dose of the oral BCAA supplements was 0.25 g/(kg body weight · d). Random effects meta-analysis showed that improvements in HE manifestations were registered for 87 of 172 patients in the BCAA group compared with 56 of 210 controls [risk ratio = 1.71 (95% CI: 1.17, 2.51) number needed to treat = 5 patients]. The effect of BCAAs differed (P = 0.04) for patients with overt [risk ratio = 3.26 (95% CI: 1.47, 7.22)] and minimal HE [risk ratio = 1.32 (95% CI: 0.97, 1.79)]. Subgroup, sensitivity, regression, and sequential analyses found no other sources of heterogeneity or bias. BCAA supplements had no effect on mortality or markers of nutritional status and did not induce adverse events. In conclusion, oral BCAA supplements improve manifestations of HE but have no effect on survival.
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Affiliation(s)
- Lise L Gluud
- Department of Medicine, Copenhagen University Hospital Gentofte, Hellerup, Denmark.
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Schousboe A, Bak LK, Waagepetersen HS. Astrocytic Control of Biosynthesis and Turnover of the Neurotransmitters Glutamate and GABA. Front Endocrinol (Lausanne) 2013; 4:102. [PMID: 23966981 PMCID: PMC3744088 DOI: 10.3389/fendo.2013.00102] [Citation(s) in RCA: 193] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 07/31/2013] [Indexed: 01/20/2023] Open
Abstract
Glutamate and GABA are the quantitatively major neurotransmitters in the brain mediating excitatory and inhibitory signaling, respectively. These amino acids are metabolically interrelated and at the same time they are tightly coupled to the intermediary metabolism including energy homeostasis. Astrocytes play a pivotal role in the maintenance of the neurotransmitter pools of glutamate and GABA since only these cells express pyruvate carboxylase, the enzyme required for de novo synthesis of the two amino acids. Such de novo synthesis is obligatory to compensate for catabolism of glutamate and GABA related to oxidative metabolism when the amino acids are used as energy substrates. This, in turn, is influenced by the extent to which the cycling of the amino acids between neurons and astrocytes may occur. This cycling is brought about by the glutamate/GABA - glutamine cycle the operation of which involves the enzymes glutamine synthetase (GS) and phosphate-activated glutaminase together with the plasma membrane transporters for glutamate, GABA, and glutamine. The distribution of these proteins between neurons and astrocytes determines the efficacy of the cycle and it is of particular importance that GS is exclusively expressed in astrocytes. It should be kept in mind that the operation of the cycle is associated with movement of ammonia nitrogen between the two cell types and different mechanisms which can mediate this have been proposed. This review is intended to delineate the above mentioned processes and to discuss quantitatively their relative importance in the homeostatic mechanisms responsible for the maintenance of optimal conditions for the respective neurotransmission processes to operate.
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Affiliation(s)
- Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- *Correspondence: Arne Schousboe, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark e-mail:
| | - Lasse K. Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Helle S. Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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