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Baltzer Houlind M, Hansen L, Iversen E, Rasmussen HB, Larsen JB, Jørgensen S, Dalhoff K, Damkier P, Walls AB, Vermehren C, Andersen TRH, Kallemose T, Christrup L, Westergaard N. Pharmacogenetic testing of CYP2D6, CYP2C19 and CYP2C9 in Denmark: Agreement between publicly funded genotyping tests and the subsequent phenotype classification. Basic Clin Pharmacol Toxicol 2024; 134:756-763. [PMID: 38403838 DOI: 10.1111/bcpt.13990] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2023] [Revised: 02/01/2024] [Accepted: 02/06/2024] [Indexed: 02/27/2024]
Affiliation(s)
- Morten Baltzer Houlind
- Department of Clinical Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark
- Emergency Department, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark
- The Capital Region Pharmacy, Herlev, Denmark
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
| | - Luise Hansen
- Department of Clinical Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
| | - Esben Iversen
- Department of Clinical Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark
| | - Henrik Berg Rasmussen
- Institute of Biological Psychiatry, Mental Health Centre Sct. Hans, Roskilde, Denmark
| | | | - Steffen Jørgensen
- Centre for Engineering and Science, University College Absalon, Naestved, Denmark
| | - Kim Dalhoff
- Department of Clinical Pharmacology, Copenhagen University Hospital Bispebjerg and Frederiksberg, Copenhagen, Denmark
- Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Per Damkier
- Department of Clinical Pharmacology, Odense University Hospital, Odense, Denmark
- Department of Clinical Research, University of Southern Denmark, Odense, Denmark
| | - Anne B Walls
- The Capital Region Pharmacy, Herlev, Denmark
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
| | - Charlotte Vermehren
- The Capital Region Pharmacy, Herlev, Denmark
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
| | | | - Thomas Kallemose
- Department of Clinical Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark
| | - Lona Christrup
- Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
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Voss CM, Arildsen L, Nissen JD, Waagepetersen HS, Schousboe A, Maechler P, Ott P, Vilstrup H, Walls AB. Glutamate Dehydrogenase Is Important for Ammonia Fixation and Amino Acid Homeostasis in Brain During Hyperammonemia. Front Neurosci 2021; 15:646291. [PMID: 34220417 PMCID: PMC8244593 DOI: 10.3389/fnins.2021.646291] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2020] [Accepted: 04/19/2021] [Indexed: 01/06/2023] Open
Abstract
Impaired liver function may lead to hyperammonemia and risk for hepatic encephalopathy. In brain, detoxification of ammonia is mediated mainly by glutamine synthetase (GS) in astrocytes. This requires a continuous de novo synthesis of glutamate, likely involving the action of both pyruvate carboxylase (PC) and glutamate dehydrogenase (GDH). An increased PC activity upon ammonia exposure and the importance of PC activity for glutamine synthesis has previously been demonstrated while the importance of GDH for generation of glutamate as precursor for glutamine synthesis has received little attention. We therefore investigated the functional importance of GDH for brain metabolism during hyperammonemia. To this end, brain slices were acutely isolated from transgenic CNS-specific GDH null or litter mate control mice and incubated in aCSF containing [U-13C]glucose in the absence or presence of 1 or 5 mM ammonia. In another set of experiments, brain slices were incubated in aCSF containing 1 or 5 mM 15N-labeled NH4Cl and 5 mM unlabeled glucose. Tissue extracts were analyzed for isotopic labeling in metabolites and for total amounts of amino acids. As a novel finding, we reveal a central importance of GDH function for cerebral ammonia fixation and as a prerequisite for de novo synthesis of glutamate and glutamine during hyperammonemia. Moreover, we demonstrated an important role of the concerted action of GDH and alanine aminotransferase in hyperammonemia; the products alanine and α-ketoglutarate serve as an ammonia sink and as a substrate for ammonia fixation via GDH, respectively. The role of this mechanism in human hyperammonemic states remains to be studied.
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Affiliation(s)
- Caroline M Voss
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lene Arildsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jakob D Nissen
- 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
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Pierre Maechler
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Medical Centre, Geneva, Switzerland
| | - Peter Ott
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Hendrik Vilstrup
- Department of Hepatology and Gastroenterology, Aarhus University Hospital, Aarhus, Denmark
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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DiNuzzo M, Walls AB, Öz G, Seaquist ER, Waagepetersen HS, Bak LK, Nedergaard M, Schousboe A. State-Dependent Changes in Brain Glycogen Metabolism. Adv Neurobiol 2019; 23:269-309. [PMID: 31667812 DOI: 10.1007/978-3-030-27480-1_9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
A fundamental understanding of glycogen structure, concentration, polydispersity and turnover is critical to qualify the role of glycogen in the brain. These molecular and metabolic features are under the control of neuronal activity through the interdependent action of neuromodulatory tone, ionic homeostasis and availability of metabolic substrates, all variables that concur to define the state of the system. In this chapter, we briefly describe how glycogen responds to selected behavioral, nutritional, environmental, hormonal, developmental and pathological conditions. We argue that interpreting glycogen metabolism through the lens of brain state is an effective approach to establish the relevance of energetics in connecting molecular and cellular neurophysiology to behavior.
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Affiliation(s)
- Mauro DiNuzzo
- Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Gülin Öz
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA
| | | | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Maiken Nedergaard
- Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Center for Translational Neuromedicine, University of Rochester Medical School, Rochester, NY, USA
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Abstract
The brain contains a fairly low amount of glycogen, mostly located in astrocytes, a fact that has prompted the suggestion that glycogen does not have a significant physiological role in the brain. However, glycogen metabolism in astrocytes is essential for several key physiological processes and is adversely affected in disease. For instance, diminished ability to break down glycogen impinges on learning, and epilepsy, Alzheimer's disease, and type 2 diabetes are all associated with abnormal astrocyte glycogen metabolism. Glycogen metabolism supports astrocytic K+ and neurotransmitter glutamate uptake and subsequent glutamine synthesis-three fundamental steps in excitatory signaling at most brain synapses. Thus, there is abundant evidence for a key role of glycogen in brain function. Here, we summarize the physiological brain functions that depend on glycogen, discuss glycogen metabolism in disease, and investigate how glycogen breakdown is regulated at the cellular and molecular levels.
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Affiliation(s)
- Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark.
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark.
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark
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5
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Affiliation(s)
- Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
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Bak LK, Walls AB. CrossTalk opposing view: lack of evidence supporting an astrocyte-to-neuron lactate shuttle coupling neuronal activity to glucose utilisation in the brain. J Physiol 2018; 596:351-353. [PMID: 29292507 DOI: 10.1113/jp274945] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Affiliation(s)
- Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
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Aldana BI, Waagepetersen HS, Schousboe A, White HS, Bulaj G, Walls AB. The novel anticonvulsant neuropeptide and galanin analogue, NAX-5055, does not alter energy and amino acid metabolism in cultured brain cells. J Neurosci Res 2017; 95:2286-2296. [PMID: 28397993 DOI: 10.1002/jnr.24057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Revised: 02/08/2017] [Accepted: 03/05/2017] [Indexed: 11/09/2022]
Abstract
A large body of evidence suggests that the neuropeptide galanin plays an important role in seizure control. In line with this, it was demonstrated that the galanin analogue, NAX-5055, exerts a potent anticonvulsant activity in animal seizure models. We recently found that the NAX-5055-mediated anticonvulsant action involves modulation of both excitatory and inhibitory neurotransmission. Since homeostasis of neurotransmitters and cerebral energy metabolism are intimately linked, it was investigated whether the effects of NAX-5055 on neurotransmission involve changes in energy metabolism and in particular glucose- and amino acid metabolism. With this aim, cultured neurons from mouse brain were incubated with [U-13 C]glucose in absence or presence of NAX-5055. Since effects of NAX-5055 on neurotransmission were detected during repetitive stimulation, we tested potential metabolic effects while mimicking repetitive bursts of neurotransmitter release as occurring in the intact brain. The metabolic pathways were mapped using gas-chromatography coupled to mass-spectrometry. We found that NAX-5055 does not modify glucose metabolism in glutamatergic and GABAergic neurons. Furthermore, the effect of NAX-5055 on astrocyte-neuron metabolic interactions was investigated by incubating co-cultures of astrocytes and either glutamatergic or GABAergic neurons with [U-13 C]glucose or the glial-selective substrate [1,2-13 C]acetate, with or without NAX-5055. In the presence of NAX-5055, no changes in the metabolic landscape were traced. The findings suggest that the anticonvulsant action of NAX-5055 and the accompanying changes in neurotransmission do not involve alterations in energy and amino acid metabolism. Hence, NAX-5055 appears to be an anti-seizure drug candidate displaying no unwanted side effects concerning brain energy and amino acid homeostasis. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- Blanca I Aldana
- 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
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - H Steve White
- Anticonvulsant Drug Development Program, Department of Pharmacology and Toxicology, College of Pharmacy, University of Utah, Salt Lake City, Utah, USA.,Department of Pharmacy, School of Pharmacy, University of Washington, Seattle, Washington, USA
| | - Grzegorz Bulaj
- University of Utah, Department of Medicinal Chemistry, College of Pharmacy, Salt Lake City, Utah, USA
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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McNair LF, Kornfelt R, Walls AB, Andersen JV, Aldana BI, Nissen JD, Schousboe A, Waagepetersen HS. Metabolic Characterization of Acutely Isolated Hippocampal and Cerebral Cortical Slices Using [U-13C]Glucose and [1,2-13C]Acetate as Substrates. Neurochem Res 2016; 42:810-826. [DOI: 10.1007/s11064-016-2116-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Revised: 11/11/2016] [Accepted: 11/16/2016] [Indexed: 12/21/2022]
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Brekke E, Morken TS, Walls AB, Waagepetersen H, Schousboe A, Sonnewald U. Anaplerosis for Glutamate Synthesis in the Neonate and in Adulthood. Adv Neurobiol 2016; 13:43-58. [PMID: 27885626 DOI: 10.1007/978-3-319-45096-4_3] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A central task of the tricarboxylic acid (TCA, Krebs, citric acid) cycle in brain is to provide precursors for biosynthesis of glutamate, GABA, aspartate and glutamine. Three of these amino acids are the partners in the intricate interaction between astrocytes and neurons and form the so-called glutamine-glutamate (GABA) cycle. The ketoacids α-ketoglutarate and oxaloacetate are removed from the cycle for this process. When something is removed from the TCA cycle it must be replaced to permit the continued function of this essential pathway, a process termed anaplerosis. This anaplerotic process in the brain is mainly carried out by pyruvate carboxylation performed by pyruvate carboxylase. The present book chapter gives an introduction and overview into this carboxylation and additionally anaplerosis mediated by propionyl-CoA carboxylase under physiological conditions in the adult and in the developing rodent brain. Furthermore, examples are given about pathological conditions in which anaplerosis is disturbed.
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Affiliation(s)
- Eva Brekke
- Department of Pediatrics, Nordland Hospital Trust, Bodo, Norway
| | - Tora Sund Morken
- Department of Ophthalmology, Trondheim University Hospital, Trondheim, 7006, Norway.,Department of Laboratory Medicine, Children's and Women's Health, Norwegian University of Science and Technology (NTNU), Trondheim, 7489, Norway
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Helle Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Ursula Sonnewald
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, 2100, Denmark. .,Department of Neuroscience, Norwegian University of Science and Technology (NTNU), Postboks 8905, Trondheim, 7489, Norway.
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10
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Affiliation(s)
- Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark,
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Müller MS, Pedersen SE, Walls AB, Waagepetersen HS, Bak LK. Isoform-selective regulation of glycogen phosphorylase by energy deprivation and phosphorylation in astrocytes. Glia 2014; 63:154-62. [PMID: 25130497 DOI: 10.1002/glia.22741] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Accepted: 07/29/2014] [Indexed: 11/07/2022]
Abstract
Glycogen phosphorylase (GP) is activated to degrade glycogen in response to different stimuli, to support both the astrocyte's own metabolic demand and the metabolic needs of neurons. The regulatory mechanism allowing such a glycogenolytic response to distinct triggers remains incompletely understood. In the present study, we used siRNA-mediated differential knockdown of the two isoforms of GP expressed in astrocytes, muscle isoform (GPMM), and brain isoform (GPBB), to analyze isoform-specific regulatory characteristics in a cellular setting. Subsequently, we tested the response of each isoform to phosphorylation, triggered by incubation with norepinephrine (NE), and to AMP, increased by glucose deprivation in cells in which expression of one GP isoform had been silenced. Successful knockdown was demonstrated on the protein level by Western blot, and on a functional level by determination of glycogen content showing an increase in glycogen levels following knockdown of either GPMM or GPBB. NE triggered glycogenolysis within 15 min in control cells and after GPBB knockdown. However, astrocytes in which expression of GPMM had been silenced showed a delay in response to NE, with glycogen levels significantly reduced only after 60 min. In contrast, allosteric activation of GP by AMP, induced by glucose deprivation, seemed to mainly affect GPBB, as only knockdown of GPBB, but not of GPMM, delayed the glycogenolytic response to glucose deprivation. Our results indicate that the two GP isoforms expressed in astrocytes respond to different physiological triggers, therefore conferring distinct metabolic functions of brain glycogen.
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Affiliation(s)
- Margit S Müller
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, 2100, Denmark
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Walls AB, Eyjolfsson EM, Schousboe A, Sonnewald U, Waagepetersen HS. A subconvulsive dose of kainate selectively compromises astrocytic metabolism in the mouse brain in vivo. J Cereb Blood Flow Metab 2014; 34:1340-6. [PMID: 24824917 PMCID: PMC4126094 DOI: 10.1038/jcbfm.2014.88] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2014] [Revised: 04/09/2014] [Accepted: 04/16/2014] [Indexed: 11/09/2022]
Abstract
Despite the well-established use of kainate as a model for seizure activity and temporal lobe epilepsy, most studies have been performed at doses giving rise to general limbic seizures and have mainly focused on neuronal function. Little is known about the effect of lower doses of kainate on cerebral metabolism and particularly that associated with astrocytes. We investigated astrocytic and neuronal metabolism in the cerebral cortex of adult mice after treatment with saline (controls), a subconvulsive or a mildly convulsive dose of kainate. A combination of [1,2-(13)C]acetate and [1-(13)C]glucose was injected and subsequent nuclear magnetic resonance spectroscopy of cortical extracts was employed to distinctively map astrocytic and neuronal metabolism. The subconvulsive dose of kainate led to an instantaneous increase in the cortical lactate content, a subsequent reduction in the amount of [4,5-(13)C]glutamine and an increase in the calculated astrocytic TCA cycle activity. In contrast, the convulsive dose led to decrements in the cortical content and (13)C labeling of glutamate, glutamine, GABA, and aspartate. Evidence is provided that astrocytic metabolism is affected by a subconvulsive dose of kainate, whereas a higher dose is required to affect neuronal metabolism. The cerebral glycogen content was dose-dependently reduced by kainate supporting a role for glycogen during seizure activity.
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Affiliation(s)
- Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Elvar M Eyjolfsson
- Department of Neuroscience, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Ursula Sonnewald
- Department of Neuroscience, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Walls AB, Bak LK, Sonnewald U, Schousboe A, Waagepetersen HS. Metabolic Mapping of Astrocytes and Neurons in Culture Using Stable Isotopes and Gas Chromatography-Mass Spectrometry (GC-MS). Brain Energy Metabolism 2014. [DOI: 10.1007/978-1-4939-1059-5_4] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Brekke EMF, Walls AB, Schousboe A, Waagepetersen HS, Sonnewald U. Quantitative importance of the pentose phosphate pathway determined by incorporation of 13C from [2-13C]- and [3-13C]glucose into TCA cycle intermediates and neurotransmitter amino acids in functionally intact neurons. J Cereb Blood Flow Metab 2012; 32:1788-99. [PMID: 22714050 PMCID: PMC3434630 DOI: 10.1038/jcbfm.2012.85] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The brain is highly susceptible to oxidative injury, and the pentose phosphate pathway (PPP) has been shown to be affected by pathological conditions, such as Alzheimer's disease and traumatic brain injury. While this pathway has been investigated in the intact brain and in astrocytes, little is known about the PPP in neurons. The activity of the PPP was quantified in cultured cerebral cortical and cerebellar neurons after incubation in the presence of [2-(13)C]glucose or [3-(13)C]glucose. The activity of the PPP was several fold lower than glycolysis in both types of neurons. While metabolism of (13)C-labeled glucose via the PPP does not appear to contribute to the production of releasable lactate, it contributes to labeling of tricarboxylic acid (TCA) cycle intermediates and related amino acids. Based on glutamate isotopomers, it was calculated that PPP activity accounts for ~6% of glucose metabolism in cortical neurons and ~4% in cerebellar neurons. This is the first demonstration that pyruvate generated from glucose via the PPP contributes to the synthesis of acetyl CoA for oxidation in the TCA cycle. Moreover, the fact that (13)C labeling from glucose is incorporated into glutamate proves that both the oxidative and the nonoxidative stages of the PPP are active in neurons.
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Affiliation(s)
- Eva M F Brekke
- Department of Neuroscience, Faculty of Medicine, Norwegian University of Science and Technology, NTNU, Trondheim, Norway
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15
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Obel LF, Müller MS, Walls AB, Sickmann HM, Bak LK, Waagepetersen HS, Schousboe A. Brain glycogen-new perspectives on its metabolic function and regulation at the subcellular level. Front Neuroenergetics 2012; 4:3. [PMID: 22403540 PMCID: PMC3291878 DOI: 10.3389/fnene.2012.00003] [Citation(s) in RCA: 137] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Accepted: 02/13/2012] [Indexed: 11/14/2022]
Abstract
Glycogen is a complex glucose polymer found in a variety of tissues, including brain, where it is localized primarily in astrocytes. The small quantity found in brain compared to e.g., liver has led to the understanding that brain glycogen is merely used during hypoglycemia or ischemia. In this review evidence is brought forward highlighting what has been an emerging understanding in brain energy metabolism: that glycogen is more than just a convenient way to store energy for use in emergencies—it is a highly dynamic molecule with versatile implications in brain function, i.e., synaptic activity and memory formation. In line with the great spatiotemporal complexity of the brain and thereof derived focus on the basis for ensuring the availability of the right amount of energy at the right time and place, we here encourage a closer look into the molecular and subcellular mechanisms underlying glycogen metabolism. Based on (1) the compartmentation of the interconnected second messenger pathways controlling glycogen metabolism (calcium and cAMP), (2) alterations in the subcellular location of glycogen-associated enzymes and proteins induced by the metabolic status and (3) a sequential component in the intermolecular mechanisms of glycogen metabolism, we suggest that glycogen metabolism in astrocytes is compartmentalized at the subcellular level. As a consequence, the meaning and importance of conventional terms used to describe glycogen metabolism (e.g., turnover) is challenged. Overall, this review represents an overview of contemporary knowledge about brain glycogen and its metabolism and function. However, it also has a sharp focus on what we do not know, which is perhaps even more important for the future quest of uncovering the roles of glycogen in brain physiology and pathology.
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Affiliation(s)
- Linea F Obel
- Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology, University of Copenhagen Copenhagen, Denmark
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Brekke E, Walls AB, Nørfeldt L, Schousboe A, Waagepetersen HS, Sonnewald U. Direct measurement of backflux between oxaloacetate and fumarate following pyruvate carboxylation. Glia 2011; 60:147-58. [PMID: 22052553 DOI: 10.1002/glia.21265] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2011] [Accepted: 10/11/2011] [Indexed: 12/17/2022]
Abstract
Pyruvate carboxylation (PC) is thought to be the major anaplerotic reaction for the tricarboxylic acid cycle and is necessary for de novo synthesis of amino acid neurotransmitters. In the brain, the main enzyme involved is pyruvate carboxylase, which is predominantly located in astrocytes. Carboxylation leads to the formation of oxaloacetate, which condenses with acetyl coenzyme A to form citrate. However, oxaloacetate may also be converted to malate and fumarate before being regenerated. This pathway is termed the oxaloacetate-fumarate-flux or backflux. Carbon isotope-based methods for quantification of activity of PC lead to underestimation when backflux is not taken into account and critical errors have been made in the interpretation of results from metabolic studies. This study was conducted to establish the degree of backflux after PC in cerebellar and neocortical astrocytes. Astrocyte cultures from cerebellum or neocortex were incubated with either [3-(13) C] or [2-(13) C]glucose, and extracts were analyzed using mass spectrometry or nuclear magnetic resonance spectroscopy. Substantial PC compared with pyruvate dehydrogenase activity was observed, and extensive backflux was demonstrated in both types of astrocytes. The extent of backflux varied between the metabolites, reaffirming that metabolism is highly compartmentalized. By applying our calculations to published data, we demonstrate the existence of backflux in vivo in cat, rat, mouse, and human brain. Thus, backflux should be taken into account when calculating the magnitude of PC to allow for a more precise evaluation of cerebral metabolism.
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Affiliation(s)
- Eva Brekke
- Faculty of Medicine, Department of Neuroscience, Norwegian University of Science and Technology, Trondheim, Norway
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Walls AB, Nilsen LH, Eyjolfsson EM, Vestergaard HT, Hansen SL, Schousboe A, Sonnewald U, Waagepetersen HS. GAD65 is essential for synthesis of GABA destined for tonic inhibition regulating epileptiform activity. J Neurochem 2010; 115:1398-408. [PMID: 21039523 DOI: 10.1111/j.1471-4159.2010.07043.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
GABA is synthesized from glutamate by glutamate decarboxylase (GAD), which exists in two isoforms, that is, GAD65 and GAD67. In line with GAD65 being located in the GABAergic synapse, several studies have demonstrated that this isoform is important during sustained synaptic transmission. In contrast, the functional significance of GAD65 in the maintenance of GABA destined for extrasynaptic tonic inhibition is less well studied. Using GAD65-/- and wild type GAD65+/+ mice, this was examined employing the cortical wedge preparation, a model suitable for investigating extrasynaptic GABA(A) receptor activity. An impaired tonic inhibition in GAD65-/- mice was revealed demonstrating a significant role of GAD65 in the synthesis of GABA acting extrasynaptically. The correlation between an altered tonic inhibition and metabolic events as well as the functional and metabolic role of GABA synthesized by GAD65 was further investigated in vivo. Tonic inhibition and the demand for biosynthesis of GABA were augmented by injection of kainate into GAD65-/- and GAD65+/+ mice. Moreover, [1-(13) C]glucose and [1,2-(13) C]acetate were administered to study neuronal and astrocytic metabolism concomitantly. Subsequently, cortical and hippocampal extracts were analyzed by NMR spectroscopy and mass spectrometry, respectively. Although seizure activity was induced by kainate, neuronal hypometabolism was observed in GAD65+/+ mice. In contrast, kainate evoked hypermetabolism in GAD65-/- mice exhibiting deficiencies in tonic inhibition. These findings underline the importance of GAD65 for synthesis of GABA destined for extrasynaptic tonic inhibition, regulating epileptiform activity.
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Affiliation(s)
- Anne B Walls
- Department of Neuroscience, Faculty of Medicine, Norwegian University of Science and Technology, Norway
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Schousboe A, Sickmann HM, Walls AB, Bak LK, Waagepetersen HS. Functional importance of the astrocytic glycogen-shunt and glycolysis for maintenance of an intact intra/extracellular glutamate gradient. Neurotox Res 2010; 18:94-9. [PMID: 20306167 DOI: 10.1007/s12640-010-9171-5] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2009] [Revised: 01/10/2010] [Accepted: 03/05/2010] [Indexed: 11/24/2022]
Abstract
It has been proposed that a considerable fraction of glucose metabolism proceeds via the glycogen-shunt consisting of conversion of glucose units to glycogen residues and subsequent production of glucose-1-phosphate to be metabolized in glycolysis after conversion to glucose-6-phosphate. The importance of this as well as the significance of ATP formed in glycolysis versus that formed by the concerted action of the tricarboxylic acid (TCA) cycle processes and oxidative phosphorylation for maintenance of glutamate transport capacity in astrocytes is discussed. It is argued that glycolytically derived energy in the form of ATP may be of particular functional importance in this context.
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Affiliation(s)
- Arne Schousboe
- Faculty of Pharmaceutical Sciences, Department of Pharmacology and Pharmacotherapy, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark.
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Bak LK, Walls AB, Schousboe A, Ring A, Sonnewald U, Waagepetersen HS. Neuronal glucose but not lactate utilization is positively correlated with NMDA-induced neurotransmission and fluctuations in cytosolic Ca2+ levels. J Neurochem 2009; 109 Suppl 1:87-93. [PMID: 19393013 DOI: 10.1111/j.1471-4159.2009.05943.x] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Although the brain utilizes glucose for energy production, individual brain cells may to some extent utilize substrates derived from glucose. Thus, it has been suggested that neurons consume extracellular lactate during synaptic activity. However, the precise role of lactate for fueling neuronal activity is still poorly understood. Recently, we demonstrated that glucose metabolism is up-regulated in cultured glutamatergic neurons during neurotransmission whereas that of lactate is not. Here, we show that utilization of glucose but not lactate correlates with NMDA-induced neurotransmitter glutamate release in cultured cerebellar neurons from mice. Pulses of NMDA at 30, 100, and 300 microM, leading to a progressive increase in both cytosolic [Ca2+] and release of glutamate, increased uptake and metabolism of glucose but not that of lactate as evidenced by mass spectrometric measurement of 13C incorporation into intracellular glutamate. In this manuscript, a cascade of events for the preferential neuronal utilization of glucose during neurotransmission is suggested and discussed in relation to our current understanding of neuronal energy metabolism.
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Affiliation(s)
- Lasse K Bak
- Department of Pharmacology and Pharmacotherapy, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark.
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Sickmann HM, Walls AB, Schousboe A, Bouman SD, Waagepetersen HS. Functional significance of brain glycogen in sustaining glutamatergic neurotransmission. J Neurochem 2009; 109 Suppl 1:80-6. [DOI: 10.1111/j.1471-4159.2009.05915.x] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Walls AB, Sickmann HM, Brown A, Bouman SD, Ransom B, Schousboe A, Waagepetersen HS. Characterization of 1,4-dideoxy-1,4-imino-d-arabinitol (DAB) as an inhibitor of brain glycogen shunt activity. J Neurochem 2008; 105:1462-70. [PMID: 18221367 DOI: 10.1111/j.1471-4159.2008.05250.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The pharmacological properties of 1,4-dideoxy-1,4-imino-d-arabinitol (DAB), a potent inhibitor of glycogen phosphorylase and synthase activity in liver preparations, were characterized in different brain tissue preparations as a prerequisite for using it as a tool to investigate brain glycogen metabolism. Its inhibitory effect on glycogen phosphorylase was studied in homogenates of brain tissue and astrocytes and IC50-values close to 400 nM were found. However, the concentration of DAB needed for inhibition of glycogen shunt activity, i.e. glucose metabolism via glycogen, in intact astrocytes was almost three orders of magnitude higher. Additionally, such complete inhibition required a pre-incubation period, a finding possibly reflecting a limited permeability of the astrocytic membrane. DAB did not affect the accumulation of 2-deoxyglucose-6-phosphate indicating that the transport of DAB is not mediated by the glucose transporter. DAB had no effect on enzymes involving glucose-6-phosphate, i.e. glucose-6-phosphate dehydrogenase, phosphoglucoisomerase and hexokinase. Furthermore, DAB was evaluated in a functional preparation of the isolated mouse optic nerve, in which its presence severely reduced the ability to sustain evoked compound action potentials in the absence of glucose, a condition in which glycogen serves as an important energy substrate. Based on the experimental findings, DAB can be used to evaluate glycogen shunt activity and its functional importance in intact brain tissue and cells at a concentration of 300-1000 muM and a pre-incubation period of 1 h.
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Affiliation(s)
- Anne B Walls
- Department of Pharmacology and Pharmacotherapy, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark
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Caesar K, Hashemi P, Douhou A, Bonvento G, Boutelle MG, Walls AB, Lauritzen M. Glutamate receptor-dependent increments in lactate, glucose and oxygen metabolism evoked in rat cerebellum in vivo. J Physiol 2008; 586:1337-49. [PMID: 18187464 DOI: 10.1113/jphysiol.2007.144154] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Neuronal activity is tightly coupled with brain energy metabolism. Numerous studies have suggested that lactate is equally important as an energy substrate for neurons as glucose. Lactate production is reportedly triggered by glutamate uptake, and independent of glutamate receptor activation. Here we show that climbing fibre stimulation of cerebellar Purkinje cells increased extracellular lactate by 30% within 30 s of stimulation, but not for briefer stimulation periods. To explore whether lactate production was controlled by pre- or postsynaptic events we silenced AMPA receptors with CNQX. This blocked all evoked rises in postsynaptic activity, blood flow, and glucose and oxygen consumption. CNQX also abolished rises in lactate concomitantly with marked reduction in postsynaptic currents. Rises in lactate were unaffected by inhibition of glycogen phosphorylase, suggesting that lactate production was independent of glycogen breakdown. Stimulated lactate production in cerebellum is derived directly from glucose uptake, and coupled to neuronal activity via AMPA receptor activation.
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Affiliation(s)
- Kirsten Caesar
- Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark
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