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Wang G, Weber-Fahr W, Frischknecht U, Hermann D, Kiefer F, Ende G, Sack M. Cortical Glutamate and GABA Changes During Early Abstinence in Alcohol Dependence and Their Associations With Benzodiazepine Medication. Front Psychiatry 2021; 12:656468. [PMID: 34290627 PMCID: PMC8287125 DOI: 10.3389/fpsyt.2021.656468] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Accepted: 06/01/2021] [Indexed: 11/13/2022] Open
Abstract
In this report, we present cross-sectional and longitudinal findings from single-voxel MEGA-PRESS MRS of GABA as well as Glu, and Glu + glutamine (Glx) concentrations in the ACC of treatment-seeking alcohol-dependent patients (ADPs) during detoxification (first 2 weeks of abstinence). The focus of this study was to examine whether the amount of benzodiazepine administered to treat withdrawal symptoms was associated with longitudinal changes in Glu, Glx, and GABA. The tNAA levels served as an internal quality reference; in agreement with the vast majority of previous reports, these levels were initially decreased and normalized during the course of abstinence in ADPs. Our results on Glu and Glx support hyperglutamatergic functioning during alcohol withdrawal, by showing higher ACC Glu and Glx levels on the first day of detoxification in ADPs. Withdrawal severity is reflected in cumulative benzodiazepine requirements throughout the withdrawal period. The importance of withdrawal severity for the study of GABA and Glu changes in early abstinence is emphasized by the benzodiazepine-dependent Glu, Glx, and GABA changes observed during the course of abstinence.
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Affiliation(s)
- Guoying Wang
- Department of Neuroimaging, Central Institute of Mental Health, Mannheim Medical Faculty, University of Heidelberg, Mannheim, Germany
| | - Wolfgang Weber-Fahr
- Department of Neuroimaging, Central Institute of Mental Health, Mannheim Medical Faculty, University of Heidelberg, Mannheim, Germany
| | - Ulrich Frischknecht
- Department of Addiction Medicine and Addictive Behavior, Central Institute of Mental Health, Mannheim Medical Faculty, University of Heidelberg, Mannheim, Germany.,German Institute of Addiction and Prevention Research, Catholic University of Applied Sciences, Cologne, Germany
| | - Derik Hermann
- Department of Addiction Medicine and Addictive Behavior, Central Institute of Mental Health, Mannheim Medical Faculty, University of Heidelberg, Mannheim, Germany.,Therapieverbund Ludwigsmühle, Landau in der Pfalz, Germany
| | - Falk Kiefer
- Department of Addiction Medicine and Addictive Behavior, Central Institute of Mental Health, Mannheim Medical Faculty, University of Heidelberg, Mannheim, Germany
| | - Gabriele Ende
- Department of Neuroimaging, Central Institute of Mental Health, Mannheim Medical Faculty, University of Heidelberg, Mannheim, Germany
| | - Markus Sack
- Department of Neuroimaging, Central Institute of Mental Health, Mannheim Medical Faculty, University of Heidelberg, Mannheim, Germany
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Ferland MC, Therrien-Blanchet JM, Proulx S, Klees-Themens G, Bacon BA, Dang Vu TT, Théoret H. Transcranial Magnetic Stimulation and H 1-Magnetic Resonance Spectroscopy Measures of Excitation and Inhibition Following Lorazepam Administration. Neuroscience 2020; 452:235-246. [PMID: 33246064 DOI: 10.1016/j.neuroscience.2020.11.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 10/16/2020] [Accepted: 11/09/2020] [Indexed: 12/21/2022]
Abstract
This study aimed at better understanding the neurochemistry underlying transcranial magnetic stimulation (TMS) and magnetic resonance spectroscopy (MRS) measurements as it pertains to GABAergic activity following administration of allosteric GABAA receptor agonist lorazepam. Seventeen healthy adults (8 females, 26.0 ± 5.4 years old) participated in a double-blind, crossover, placebo-controlled study, where participants underwent TMS and MRS two hours after drug intake (placebo or lorazepam; 2.5 mg). Neuronavigated TMS measures reflecting cortical inhibition and excitation were obtained in the left primary motor cortex. Sensorimotor cortex and occipital cortex MRS data were acquired using a 3T scanner with a MEGA-PRESS sequence, allowing water-referenced [GABA] and [Glx] (glutamate + glutamine) quantification. Lorazepam administration decreased occipital [GABA], decreased motor cortex excitability and increased GABAA-receptor mediated motor cortex inhibition (short intracortical inhibition (SICI)). Lorazepam intake did not modulate sensorimotor [GABA] and TMS measures of intra-cortical facilitation, long-interval cortical inhibition, cortical silent period, and resting motor threshold. Furthermore, higher sensorimotor [GABA] was associated with higher cortical inhibition (SICI) following lorazepam administration, suggesting that baseline sensorimotor [GABA] may be valuable in predicting pharmacological or neuromodulatory treatment response. Finally, the differential effects of lorazepam on MRS and TMS measures, with respect to GABA, support the idea that TMS measures of cortical inhibition reflect synaptic GABAergic phasic inhibitory activity while MRS reflects extrasynaptic GABA.
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Affiliation(s)
| | | | | | | | | | - Thien Thanh Dang Vu
- Center for Studies in Behavioral Neurobiology and Perform Center, Department of Health, Kinesiology and Applied Physiology, Concordia University, Montreal, QC, Canada; Research Center, Institut Universitaire de Gériatrie de Montréal, Montréal, Qc, Canada
| | - Hugo Théoret
- Département de psychologie, Université de Montréal, Québec, Canada; Centre de recherche du Centre Hospitalier Universitaire de l'Hôpital Sainte-Justine, Montréal, Québec, Canada.
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3
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No evidence of abnormal metabolic or inflammatory activity in the brains of patients with rheumatoid arthritis: results from a preliminary study using whole-brain magnetic resonance spectroscopic imaging (MRSI). Clin Rheumatol 2020; 39:1765-1774. [PMID: 32002761 PMCID: PMC7237391 DOI: 10.1007/s10067-019-04923-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Revised: 12/21/2019] [Accepted: 12/29/2019] [Indexed: 01/15/2023]
Abstract
Introduction/objectives Many individuals with rheumatoid arthritis (RA) report persistent fatigue even after management of peripheral disease activity. This study used whole-brain magnetic resonance spectroscopic imaging (MRSI) to investigate whether abnormal inflammatory activity in the central nervous system may be associated with such symptoms. We hypothesized that RA patients would show higher brain choline (CHO), myo-inositol (MI), and lactate (LAC), and higher brain temperature than healthy controls. We further hypothesized that the metabolite levels would be positively correlated with self-reported fatigue. Method Thirteen women with RA provided fatigue severity ratings and underwent whole-brain MRSI and a joint examination. Thirteen healthy controls (HC) provided comparison imaging and fatigue data. CHO, MI, LAC, and brain temperature in 47 brain regions were contrasted between groups using independent-samples t tests. Significant differences were determined using a false discovery rate (FDR)-adjusted p value threshold of ≤ 0.0023. Secondary analyses obtained correlations between imaging and clinical outcomes in the RA group. Results No brain metabolic differences were identified between the groups. In the RA group, fatigue severity was positively correlated with CHO in several brain regions—most strongly the right frontal lobe (rs = 0.823, p < 0.001). MI was similarly correlated with fatigue, particularly in the right calcarine fissure (rs = 0.829, p < 0.001). CHO in several regions was positively correlated with joint swelling and tenderness. Conclusions We conclude that abnormal brain metabolites are not a common feature of RA, but may been seen in patients with persistent fatigue or disease activity after conventional treatment.Key Points • Whole-brain magnetic resonance spectroscopy revealed no metabolic abnormalities in the brain in patients with rheumatoid arthritis. • Brain choline levels were correlated with fatigue severity reported by RA patients and with peripheral joint swelling and tenderness. • Brain myo-inositol levels were similarly correlated with fatigue severity in RA patients. |
Electronic supplementary material The online version of this article (10.1007/s10067-019-04923-5) contains supplementary material, which is available to authorized users.
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Margari L, De Giacomo A, Craig F, Palumbi R, Peschechera A, Margari M, Picardi F, Caldarola M, Maghenzani MA, Dicuonzo F. Frontal lobe metabolic alterations in autism spectrum disorder: a 1H-magnetic resonance spectroscopy study. Neuropsychiatr Dis Treat 2018; 14:1871-1876. [PMID: 30050301 PMCID: PMC6055909 DOI: 10.2147/ndt.s165375] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
PURPOSE Recently, neuroimaging studies were performed using 1H-magnetic resonance spectroscopy (1H-MRS), revealing a quantitative alteration of neurochemicals (such as neurotransmitters and metabolites) in several brain regions of patients with autism spectrum disorder (ASD). The involvement of the frontal lobe in the neurobiology of ASD has long been documented in the literature. Therefore, the aim of this study was to analyze the alterations of N-acetylaspartate/creatine (NAA/Cr) and choline/Cr (Cho/Cr) ratios in the frontal lobe subcortical white matter (WM) in ASD patients, in order to reveal any alteration of metabolites that might be the expression of specific clinical features of the disorder. PATIENTS AND METHODS An 1H-MRS study of the frontal lobe subcortical WM was performed in 75 children with ASD and in 50 age-matched controls to evaluate the functional activity of this brain region. RESULTS NAA/Cr and Cho/Cr ratios were significantly altered in ASD, compared to control subjects. Moreover, in the ASD group, NAA/Cr was significantly lower in patients with a cognitive impairment. CONCLUSION Results from this study confirm the existence of brain metabolites' alterations in frontal lobe WM in children with ASD, supporting the relevance of this brain region in the clinical expressions of this disorder, including its role in the cognitive impairment. Further 1H-MRS investigations will allow to comprehensively explain the relationship between metabolic alteration in a specific brain region and specific clinical features of ASD.
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Affiliation(s)
- Lucia Margari
- Department of Basic Medical Sciences, Neuroscience and Sense Organs, Child Neuropsychiatry Unit, University of Bari Aldo Moro, Azienda Ospedaliero Universitaria Consorziale Policlinico di Bari, Bari, Italy,
| | - Andrea De Giacomo
- Department of Basic Medical Sciences, Neuroscience and Sense Organs, Child Neuropsychiatry Unit, University of Bari Aldo Moro, Azienda Ospedaliero Universitaria Consorziale Policlinico di Bari, Bari, Italy,
| | - Francesco Craig
- Scientific Institute, IRCCS E. Medea, Unit for Severe Disabilities in Developmental Age and Young Adults, Developmental Neurology and Neurorehabilitation, Brindisi, Italy
| | - Roberto Palumbi
- Department of Basic Medical Sciences, Neuroscience and Sense Organs, Child Neuropsychiatry Unit, University of Bari Aldo Moro, Azienda Ospedaliero Universitaria Consorziale Policlinico di Bari, Bari, Italy,
| | - Antonia Peschechera
- Department of Basic Medical Sciences, Neuroscience and Sense Organs, Child Neuropsychiatry Unit, University of Bari Aldo Moro, Azienda Ospedaliero Universitaria Consorziale Policlinico di Bari, Bari, Italy,
| | - Mariella Margari
- Department of Basic Medical Sciences, Neuroscience and Sense Organs, Child Neuropsychiatry Unit, University of Bari Aldo Moro, Azienda Ospedaliero Universitaria Consorziale Policlinico di Bari, Bari, Italy,
| | - Francesca Picardi
- Department of Basic Medical Sciences, Neuroscience and Sense Organs, Neuroradiology Unit, University of Bari Aldo Moro, Azienda Ospedaliero Universitaria Consorziale Policlinico di Bari, Bari, Italy
| | - Marina Caldarola
- Department of Basic Medical Sciences, Neuroscience and Sense Organs, Neuroradiology Unit, University of Bari Aldo Moro, Azienda Ospedaliero Universitaria Consorziale Policlinico di Bari, Bari, Italy
| | - Marilena Anna Maghenzani
- Emergency Department, Anesthesia and Intensive Care Unit, University of Bari Aldo Moro, Azienda Ospedaliero-Universitaria Policlinico di Bari, Bari, Italy
| | - Franca Dicuonzo
- Department of Basic Medical Sciences, Neuroscience and Sense Organs, Neuroradiology Unit, University of Bari Aldo Moro, Azienda Ospedaliero Universitaria Consorziale Policlinico di Bari, Bari, Italy
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Frischknecht U, Hermann D, Tunc-Skarka N, Wang GY, Sack M, van Eijk J, Demirakca T, Falfan-Melgoza C, Krumm B, Dieter S, Spanagel R, Kiefer F, Mann KF, Sommer WH, Ende G, Weber-Fahr W. Negative Association Between MR-Spectroscopic Glutamate Markers and Gray Matter Volume After Alcohol Withdrawal in the Hippocampus: A Translational Study in Humans and Rats. Alcohol Clin Exp Res 2017; 41:323-333. [DOI: 10.1111/acer.13308] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Accepted: 11/21/2016] [Indexed: 01/03/2023]
Affiliation(s)
- Ulrich Frischknecht
- Department of Addictive Behavior and Addiction Medicine ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Derik Hermann
- Department of Addictive Behavior and Addiction Medicine ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Nuran Tunc-Skarka
- Department of Neuroimaging ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Guo-Ying Wang
- Department of Neuroimaging ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Markus Sack
- Department of Neuroimaging ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Julia van Eijk
- Department of Neuroimaging ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Traute Demirakca
- Department of Neuroimaging ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Claudia Falfan-Melgoza
- Research Group for Translational Imaging ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Bertram Krumm
- Department of Biostatistics ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Sandra Dieter
- Institute of Psychopharmacology ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Rainer Spanagel
- Institute of Psychopharmacology ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Falk Kiefer
- Department of Addictive Behavior and Addiction Medicine ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Karl F. Mann
- Department of Addictive Behavior and Addiction Medicine ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Wolfgang H. Sommer
- Department of Addictive Behavior and Addiction Medicine ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
- Institute of Psychopharmacology ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Gabriele Ende
- Department of Neuroimaging ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
| | - Wolfgang Weber-Fahr
- Research Group for Translational Imaging ; Central Institute for Mental Health; Medical Faculty Mannheim, Heidelberg University; Mannheim Germany
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Aydin B, Yurt A, Gökmen N, Renshaw P, Olson D, Yildiz A. Trait-related alterations of N-acetylaspartate in euthymic bipolar patients: A longitudinal proton magnetic resonance spectroscopy study. J Affect Disord 2016; 206:315-320. [PMID: 27662572 PMCID: PMC5077644 DOI: 10.1016/j.jad.2016.09.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Revised: 07/27/2016] [Accepted: 09/08/2016] [Indexed: 12/25/2022]
Abstract
BACKGROUND Neurochemical changes are responsible for bipolar disorder (BD) pathophysiology. Despite current progress in BD research, mood- and trait-related alterations in BD continue to elicit further investigation. METHODS In this study, we report a longitudinal proton magnetic resonance spectroscopy study evaluating dorsomedial prefrontal cortex (DMPFC) metabolites N-acetylaspartate (NAA), creatine plus phosphocreatine (total creatine [tCr]), phosphorylcholine plus glycerophosphocholine, myo-inositol, and glutamate plus glutamine levels of manic and euthymic adult BD type I patients (n=48) treated with standard antimanic medicines, compared to matching healthy controls (n=44). RESULTS DMPFC NAA values and NAA/tCr ratio were significantly lower in euthymic BD patients when compared with healthy controls with similar levels of other metabolites in all groups, indicating a trait-related NAA abnormality in euthymic BD patients. LIMITATIONS of our study include a relatively low (1.5T) magnetic resonance field strength and variable drugs administered to achieve euthymia despite the best efforts to standardize the open fashion treatment. CONCLUSIONS Our study contributes to the integrating models of trait-related metabolite alterations observed in euthymia since NAA is considered as a marker of neuronal viability and mitochondrial energy metabolism. In light of supporting and conflicting results reported previously, future studies with longitudinal designs and larger patient groups are warranted to better define both state- and trait-related cerebral metabolic alterations associated with BD pathophysiology.
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Affiliation(s)
- Burç Aydin
- Department of Medical Pharmacology, School of Medicine, Dokuz Eylul University, Balcova 35340, Izmir, Turkey.
| | - Ayşegül Yurt
- Department of Medical Physics, Health Sciences Institute, Dokuz Eylul University, İzmir, Turkey
| | - Necati Gökmen
- Department of Anesthesiology and Reanimation, School of Medicine, Dokuz Eylul University, Izmir, Turkey
| | - Perry Renshaw
- University of Utah, The Brain Institute & Department of Psychiatry, Salt Lake City, UT, USA
| | - David Olson
- Harvard Medical School, McLean Hospital, Brain Imaging Center, Belmont, MA, USA
| | - Ayşegül Yildiz
- Department of Psychiatry, School of Medicine, Dokuz Eylul University, Izmir, Turkey,International Consortium for Bipolar Disorder Research & Psychopharmacology Program, McLean Division of Massachusetts General Hospital, Boston, MA, USA
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Yildiz A, Aydin B, Gökmen N, Yurt A, Cohen B, Keskinoglu P, Öngür D, Renshaw P. Antimanic Treatment With Tamoxifen Affects Brain Chemistry: A Double-Blind, Placebo-Controlled Proton Magnetic Resonance Spectroscopy Study. BIOLOGICAL PSYCHIATRY: COGNITIVE NEUROSCIENCE AND NEUROIMAGING 2016; 1:125-131. [PMID: 27231722 DOI: 10.1016/j.bpsc.2015.12.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
BACKGROUND The antimanic efficacy of a protein kinase C (PKC) inhibitor, tamoxifen, has been tested in several clinical trials, all reporting positive results. However, mechanisms underlying the observed clinical effects requires further confirmation through studies of biological markers. METHODS We investigated the effect of tamoxifen versus placebo on brain metabolites via a proton (1H) magnetic resonance spectroscopy (MRS) study. Forty-eight adult bipolar I manic patients (mean Young Mania Rating Scale (YMRS) score of 37.8±5.8) were scanned at baseline and following 3 weeks of double-blind treatment. We hypothesized that manic symptom alleviation would improve the levels of markers associated with brain energy metabolism (creatine plus phosphocreatine [total creatine; tCr]) and neuronal viability (N-acetylaspartate [NAA]). RESULTS The YMRS scores decreased from 38.6±4.5 to 20.0±11.1 in the tamoxifen group and increased from 37.0±6.8 to 43.1±7.8 in the placebo group (p<0.001). 1H MRS measurements revealed a 5.5±13.8% increase in the dorsomedial prefrontal cortex (DMPFC) tCr levels in the tamoxifen group and a 5.3±13.1% decrease in tCr in the placebo group (p=0.027). A significant correlation between the YMRS score change and tCr percent change was observed in the whole group (Spearman ρ=0.341, p=0.029). Both tCr and NAA levels in the responder group were increased by 9.4±15.2% and 6.1±11.7%, whereas levels in the non-responder group were decreased by 2.1±13.2% and 6.5±10.5%, respectively (p<0.05). CONCLUSIONS Tamoxifen effectively treated mania while it also increased brain tCr levels, consistent with involvement of both excessive PKC activation and impaired brain energy metabolism in the development of bipolar mania. CLINICAL TRIAL REGISTRATION Registry name: ClinicalTrials.gov URL: https://clinicaltrials.gov/ct2/show/NCT00411203?term=NCT00411203&rank=1 Registration number: NCT00411203.
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Affiliation(s)
- Ayşegül Yildiz
- Department of Psychiatry, School of Medicine, Dokuz Eylul University, Izmir, Turkey
| | - Burç Aydin
- Department of Medical Pharmacology, School of Medicine, Dokuz Eylul University, Izmir, Turkey
| | - Necati Gökmen
- Department of Anesthesiology and Reanimation, School of Medicine, Dokuz Eylul University, Izmir, Turkey
| | - Ayşegül Yurt
- Department of Medical Physics, Health Sciences Institute, Dokuz Eylul University, İzmir, Turkey
| | - Bruce Cohen
- Schizophrenia and Bipolar Disorder Program, Mclean Hospital, Belmont, MA, USA
| | - Pembe Keskinoglu
- Department of Biostatistics, School of Medicine, Dokuz Eylul University, Izmir, Turkey
| | - Dost Öngür
- Schizophrenia and Bipolar Disorder Program, Mclean Hospital, Belmont, MA, USA
| | - Perry Renshaw
- Brain Institute, University of Utah, Salt Lake City, UT, USA
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Fu H, Li B, Hertz L, Peng L. Contributions in astrocytes of SMIT1/2 and HMIT to myo-inositol uptake at different concentrations and pH. Neurochem Int 2012; 61:187-94. [PMID: 22564531 DOI: 10.1016/j.neuint.2012.04.010] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Revised: 04/09/2012] [Accepted: 04/11/2012] [Indexed: 12/21/2022]
Abstract
myo-Inositol is important for cell signaling both in cytoplasm and in intracellular organelles. It is required in the plasma membrane and cytoplasm for maintained synthesis of the second messengers, inositoltrisphosphate (IP(3)) and diacylglycerol (DAG) from phosphatidylinositol bisphosphate (PIP(2)), and in organelles as precursor for synthesis of complex signaling phospholipids and inositolphosphates from IP(3) and PIP(2). myo-Inositol must be taken up into the cell where its is used, because neither neurons nor astrocytes synthesize it. It is also an osmolyte, taken up in response to surrounding hyperosmolarity and released during hypo-osmolarity. There are three myo-inositol transporters, the Na(+)-dependent SMIT1 and SMIT2, and HMIT, which co-transports myo-inositol with H(+). Their relative expressions in astrocytes and neurons are unknown. Uptake kinetics for myo-inositol in astrocytes has repeatedly been determined, but always on the assumption of only one component, leaving kinetics for the individual transporters unknown. This paper demonstrates that astrocytes obtained directly from the brain express SMIT1 and HMIT, but little SMIT2, and that all three transporters are expressed in neurons. Cultured mouse astrocytes show a high-affinity/low-capacity myo-inositol uptake (V(max): 60.0 ± 3.0 pmol/min per mg protein; K(m): 16.7 ± 2.6 μM), mediated by SMIT1 and perhaps partly by SMIT2. It was determined in cells pre-treated with HMIT-siRNA and confirmed by specific inhibition of SMIT. However at physiologically relevant myo-inositol concentrations most uptake is by a lower-affinity/higher-capacity uptake, mediated by HMIT (V(max): 358 ± 60 pmol/min per mg protein; K(m): 143 ± 36 μM) and determined by subtraction of SMIT-mediated from total uptake. At high myo-inositol concentrations, its uptake is inhibited by incubation in medium with increased pH, and increased during intracellular acidification with NH(4)Cl. This is in agreement with literature data for HMIT alone. At low concentration, where SMIT1/2 activity gains importance, myo-inositol uptake is reduced by ammonia-induced intracellular acidification, consistent with the transporter's pH sensitivity reported in the literature.
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Affiliation(s)
- Hui Fu
- Department of Clinical Pharmacology, College of Basic Medical Sciences, China Medical University, Shenyang, PR China
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