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Uematsu S, Ohno S, Tanaka KY, Hatano A, Kokaji T, Ito Y, Kubota H, Hironaka KI, Suzuki Y, Matsumoto M, Nakayama KI, Hirayama A, Soga T, Kuroda S. Multi-omics-based label-free metabolic flux inference reveals obesity-associated dysregulatory mechanisms in liver glucose metabolism. iScience 2022; 25:103787. [PMID: 35243212 PMCID: PMC8859528 DOI: 10.1016/j.isci.2022.103787] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Revised: 12/01/2021] [Accepted: 01/13/2022] [Indexed: 02/07/2023] Open
Abstract
Glucose homeostasis is maintained by modulation of metabolic flux. Enzymes and metabolites regulate the involved metabolic pathways. Dysregulation of glucose homeostasis is a pathological event in obesity. Analyzing metabolic pathways and the mechanisms contributing to obesity-associated dysregulation in vivo is challenging. Here, we introduce OMELET: Omics-Based Metabolic Flux Estimation without Labeling for Extended Trans-omic Analysis. OMELET uses metabolomic, proteomic, and transcriptomic data to identify relative changes in metabolic flux, and to calculate contributions of metabolites, enzymes, and transcripts to the changes in metabolic flux. By evaluating the livers of fasting ob/ob mice, we found that increased metabolic flux through gluconeogenesis resulted primarily from increased transcripts, whereas that through the pyruvate cycle resulted from both increased transcripts and changes in substrates of metabolic enzymes. With OMELET, we identified mechanisms underlying the obesity-associated dysregulation of metabolic flux in the liver. We developed OMELET to infer metabolic flux from label-free multi-omic data Contributions of metabolites, enzymes, and transcripts for flux were inferred Gluconeogenic flux increased in fasting ob/ob mice by increased transcripts Increased pyruvate cycle fluxes were led by increased transcripts and substrates
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Affiliation(s)
- Saori Uematsu
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan
| | - Satoshi Ohno
- Molecular Genetic Research Laboratory, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.,Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Kaori Y Tanaka
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan
| | - Atsushi Hatano
- Department of Omics and Systems Biology, Graduate School of Medical and Dental Sciences, Niigata University, 757 Ichibancho, Asahimachi-dori, Chuo-ku, Niigata City, Niigata 951-8510, Japan
| | - Toshiya Kokaji
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Yuki Ito
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.,Division of Integrated Omics, Research Center for Transomics Medicine, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Hiroyuki Kubota
- Division of Integrated Omics, Research Center for Transomics Medicine, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Ken-Ichi Hironaka
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Yutaka Suzuki
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan
| | - Masaki Matsumoto
- Department of Omics and Systems Biology, Graduate School of Medical and Dental Sciences, Niigata University, 757 Ichibancho, Asahimachi-dori, Chuo-ku, Niigata City, Niigata 951-8510, Japan
| | - Keiichi I Nakayama
- Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Akiyoshi Hirayama
- Institute for Advanced Biosciences, Keio University, 246-2 Mizukami, Kakuganji, Tsuruoka, Yamagata 997-0052, Japan
| | - Tomoyoshi Soga
- Institute for Advanced Biosciences, Keio University, 246-2 Mizukami, Kakuganji, Tsuruoka, Yamagata 997-0052, Japan
| | - Shinya Kuroda
- Department of Computational Biology and Medical Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.,Molecular Genetic Research Laboratory, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan.,Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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Alger JR, Minhajuddin A, Dean Sherry A, Malloy CR. Analysis of steady-state carbon tracer experiments using akaike information criteria. Metabolomics 2021; 17:61. [PMID: 34148138 DOI: 10.1007/s11306-021-01807-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Accepted: 05/29/2021] [Indexed: 11/27/2022]
Abstract
INTRODUCTION Carbon isotope tracers have been used to determine relative rates of tricarboxylic acid cycle (TCA) cycle pathways since the 1950s. Steady-state experimental data are typically fit to a single mathematical model of metabolism to determine metabolic fluxes. Whether the chosen model is appropriate for the biological system has generally not been evaluated systematically. An overly-simple model omits known pathways while an overly-complex model may produce incorrect results due to overfitting. OBJECTIVES The objectives were to develop and study a method that systematically evaluates multiple TCA cycle mathematical models as part of the fitting process. METHODS The problem of choosing overly-simple or overly-complex models was approached by developing software that automatically explores all possible combinations of flux through pyruvate dehydrogenase, pyruvate kinase, pyruvate carboxylase and anaplerosis at propionyl-CoA carboxylase, and equivalent pathways, all relative to TCA cycle flux. Typical TCA cycle metabolic tracer experiments that use 13C nuclear magnetic resonance for detection and quantification of 13C-enriched glutamate products were simulated and analyzed. By evaluating the multiple model fits with both the conventional sum-of-squares residual error (SSRE) and the Akaike Information Criterion (AIC), the software helps the investigator understand the interaction between model complexity and goodness of fit. RESULTS When fitting alternative models of the TCA cycle metabolism, the SSRE may identify more than one model that fits the data well. Among those models, the AIC provides guidance as to which is the simplest of the candidate models is sufficient to describe the observed data. However under some conditions, AIC used alone inappropriately discriminates against necessary metabolic complexity. CONCLUSION In combination, the SSRE and AIC help the investigator identify the model that best describes the metabolism of a biological system.
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Affiliation(s)
- Jeffry R Alger
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, USA.
- NeuroSpectroScopics LLC, Sherman Oaks, CA, USA.
- Department of Neurology, Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA.
- Hura Imaging Inc, Calabasas, CA, USA.
| | - Abu Minhajuddin
- Department of Population and Data Sciences, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - A Dean Sherry
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Chemistry, University of Texas at Dallas, Richardson, TX, USA
| | - Craig R Malloy
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Veterans Affairs North Texas Healthcare System, Dallas, TX, USA
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Alger JR, Sherry AD, Malloy CR. tcaSIM: A Simulation Program for Optimal Design of 13C Tracer Experiments for Analysis of Metabolic Flux by NMR and Mass Spectroscopy. ACTA ACUST UNITED AC 2019; 6:176-187. [PMID: 31745452 DOI: 10.2174/2213235x07666181219115856] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Increasingly sophisticated instrumentation for chemical separations and identification has facilitated rapid advancements in our understanding of the metabolome. Since many analyses are performed using either mass spectroscopy (MS) or nuclear magnetic resonance (NMR) spectroscopy, the spin ½ stable 13C isotope is now widely used as a metabolic tracer. There is strong interest in quantitative analysis of metabolic flux through pathways in vivo, particularly in human patients. Although instrumentation advances and scientific interests in metabolism are increasing in parallel, a practical and rational design of a 13C tracer study can be challenging. Prior to planning the details of a tracer experiment, is it important to consider whether the analytical results will be sensitive to flux through the pathways of interest. Here, we briefly summarize the various approaches that have been used to design carbon tracer experiments, outline the sources of complexity, and illustrate the use of a software tool, tcaSIM, to aid in the experimental design of both MS and NMR data in complex systems including patients.
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Affiliation(s)
- Jeffry R Alger
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas.,NeuroSpectroScopics LLC, Sherman Oaks, California
| | - A Dean Sherry
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas.,Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas.,Department of Chemistry, University of Texas at Dallas, Richardson, Texas
| | - Craig R Malloy
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas.,Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas.,Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas.,Veterans Affairs North Texas Healthcare System, Dallas, Texas
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Non-invasive assessment of hepatic mitochondrial metabolism by positional isotopomer NMR tracer analysis (PINTA). Nat Commun 2017; 8:798. [PMID: 28986525 PMCID: PMC5630596 DOI: 10.1038/s41467-017-01143-w] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 08/22/2017] [Indexed: 01/03/2023] Open
Abstract
Hepatic mitochondria play a central role in the regulation of intermediary metabolism and maintenance of normoglycemia, and there is great interest in assessing rates of hepatic mitochondrial citrate synthase flux (VCS) and pyruvate carboxylase flux (VPC) in vivo. Here, we show that a positional isotopomer NMR tracer analysis (PINTA) method can be used to non-invasively assess rates of VCS and VPC fluxes using a combined NMR/gas chromatography-mass spectrometry analysis of plasma following infusion of [3-13C]lactate and glucose tracer. PINTA measures VCS and VPC fluxes over a wide range of physiological conditions with minimal pyruvate cycling and detects increased hepatic VCS following treatment with a liver-targeted mitochondrial uncoupler. Finally, validation studies in humans demonstrate that the VPC/VCS ratio measured by PINTA is similar to that determined by in vivo NMR spectroscopy. This method will provide investigators with a relatively simple tool to non-invasively examine the role of altered hepatic mitochondrial metabolism. Liver mitochondrial metabolism plays an important role for glucose and lipid homeostasis and its alterations contribute to metabolic disorders, including fatty liver and diabetes. Here Perry et al. develop a method for the measurement of hepatic fluxes by using lactate and glucose tracers in combination with NMR spectroscopy.
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Mondal S, Raja K, Schweizer U, Mugesh G. Chemie und Biologie der Schilddrüsenhormon-Biosynthese und -Wirkung. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201601116] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Santanu Mondal
- Department of Inorganic and Physical Chemistry; Indian Institute of Science; Bangalore Indien
| | - Karuppusamy Raja
- Department of Inorganic and Physical Chemistry; Indian Institute of Science; Bangalore Indien
| | - Ulrich Schweizer
- Rheinische Friedrich-Wilhelms-Universität Bonn; Institut für Biochemie und Molekularbiologie; Nussallee 11 53115 Bonn Deutschland
| | - Govindasamy Mugesh
- Department of Inorganic and Physical Chemistry; Indian Institute of Science; Bangalore Indien
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Mondal S, Raja K, Schweizer U, Mugesh G. Chemistry and Biology in the Biosynthesis and Action of Thyroid Hormones. Angew Chem Int Ed Engl 2016; 55:7606-30. [DOI: 10.1002/anie.201601116] [Citation(s) in RCA: 114] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2016] [Indexed: 12/17/2022]
Affiliation(s)
- Santanu Mondal
- Department of Inorganic and Physical Chemistry; Indian Institute of Science; Bangalore India
| | - Karuppusamy Raja
- Department of Inorganic and Physical Chemistry; Indian Institute of Science; Bangalore India
| | - Ulrich Schweizer
- Rheinische Friedrich-Wilhelms-Universität Bonn; Institut für Biochemie und Molekularbiologie; Nussallee 11 53115 Bonn Germany
| | - Govindasamy Mugesh
- Department of Inorganic and Physical Chemistry; Indian Institute of Science; Bangalore India
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Perry RJ, Borders CB, Cline GW, Zhang XM, Alves TC, Petersen KF, Rothman DL, Kibbey RG, Shulman GI. Propionate Increases Hepatic Pyruvate Cycling and Anaplerosis and Alters Mitochondrial Metabolism. J Biol Chem 2016; 291:12161-70. [PMID: 27002151 PMCID: PMC4933266 DOI: 10.1074/jbc.m116.720631] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2016] [Indexed: 02/03/2023] Open
Abstract
In mammals, pyruvate kinase (PK) plays a key role in regulating the balance between glycolysis and gluconeogenesis; however, in vivo regulation of PK flux by gluconeogenic hormones and substrates is poorly understood. To this end, we developed a novel NMR-liquid chromatography/tandem-mass spectrometry (LC-MS/MS) method to directly assess pyruvate cycling relative to mitochondrial pyruvate metabolism (VPyr-Cyc/VMito) in vivo using [3-(13)C]lactate as a tracer. Using this approach, VPyr-Cyc/VMito was only 6% in overnight fasted rats. In contrast, when propionate was infused simultaneously at doses previously used as a tracer, it increased VPyr-Cyc/VMito by 20-30-fold, increased hepatic TCA metabolite concentrations 2-3-fold, and increased endogenous glucose production rates by 20-100%. The physiologic stimuli, glucagon and epinephrine, both increased hepatic glucose production, but only glucagon suppressed VPyr-Cyc/VMito These data show that under fasting conditions, when hepatic gluconeogenesis is stimulated, pyruvate recycling is relatively low in liver compared with VMito flux and that liver metabolism, in particular pyruvate cycling, is sensitive to propionate making it an unsuitable tracer to assess hepatic glycolytic, gluconeogenic, and mitochondrial metabolism in vivo.
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Affiliation(s)
| | | | | | | | | | - Kitt Falk Petersen
- From the Departments of Internal Medicine, The Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen DK 1017, Denmark
| | - Douglas L Rothman
- Radiology and Biomedical Imaging, and the Department of Biomedical Engineering, Yale University, New Haven, Connecticut 06519, and
| | - Richard G Kibbey
- From the Departments of Internal Medicine, Cellular and Molecular Physiology, and
| | - Gerald I Shulman
- From the Departments of Internal Medicine, The Novo Nordisk Foundation Center for Basic Metabolic Research, University of Copenhagen, Copenhagen DK 1017, Denmark Cellular and Molecular Physiology, and the Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06519,
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Satapati S, Kucejova B, Duarte JAG, Fletcher JA, Reynolds L, Sunny NE, He T, Nair LA, Livingston KA, Fu X, Merritt ME, Sherry AD, Malloy CR, Shelton JM, Lambert J, Parks EJ, Corbin I, Magnuson MA, Browning JD, Burgess SC. Mitochondrial metabolism mediates oxidative stress and inflammation in fatty liver. J Clin Invest 2015; 125:4447-62. [PMID: 26571396 DOI: 10.1172/jci82204] [Citation(s) in RCA: 283] [Impact Index Per Article: 31.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 10/08/2015] [Indexed: 02/06/2023] Open
Abstract
Mitochondria are critical for respiration in all tissues; however, in liver, these organelles also accommodate high-capacity anaplerotic/cataplerotic pathways that are essential to gluconeogenesis and other biosynthetic activities. During nonalcoholic fatty liver disease (NAFLD), mitochondria also produce ROS that damage hepatocytes, trigger inflammation, and contribute to insulin resistance. Here, we provide several lines of evidence indicating that induction of biosynthesis through hepatic anaplerotic/cataplerotic pathways is energetically backed by elevated oxidative metabolism and hence contributes to oxidative stress and inflammation during NAFLD. First, in murine livers, elevation of fatty acid delivery not only induced oxidative metabolism, but also amplified anaplerosis/cataplerosis and caused a proportional rise in oxidative stress and inflammation. Second, loss of anaplerosis/cataplerosis via genetic knockdown of phosphoenolpyruvate carboxykinase 1 (Pck1) prevented fatty acid-induced rise in oxidative flux, oxidative stress, and inflammation. Flux appeared to be regulated by redox state, energy charge, and metabolite concentration, which may also amplify antioxidant pathways. Third, preventing elevated oxidative metabolism with metformin also normalized hepatic anaplerosis/cataplerosis and reduced markers of inflammation. Finally, independent histological grades in human NAFLD biopsies were proportional to oxidative flux. Thus, hepatic oxidative stress and inflammation are associated with elevated oxidative metabolism during an obesogenic diet, and this link may be provoked by increased work through anabolic pathways.
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Vatner DF, Snikeris J, Popov V, Perry RJ, Rahimi Y, Samuel VT. 3,5 Diiodo-L-Thyronine (T2) Does Not Prevent Hepatic Steatosis or Insulin Resistance in Fat-Fed Sprague Dawley Rats. PLoS One 2015; 10:e0140837. [PMID: 26485433 PMCID: PMC4618341 DOI: 10.1371/journal.pone.0140837] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Accepted: 09/29/2015] [Indexed: 01/21/2023] Open
Abstract
Thyroid hormone mimetics are alluring potential therapies for diseases like dyslipidemia, nonalcoholic fatty liver disease (NAFLD), and insulin resistance. Though diiodothyronines are thought inactive, pharmacologic treatment with 3,5- Diiodo-L-Thyronine (T2) reportedly reduces hepatic lipid content and improves glucose tolerance in fat-fed male rats. To test this, male Sprague Dawley rats fed a safflower-oil based high-fat diet were treated with T2 (0.25 mg/kg-d) or vehicle. Neither 10 nor 30 days of T2 treatment had an effect on weight, adiposity, plasma fatty acids, or hepatic steatosis. Insulin action was quantified in vivo by a hyperinsulinemic-euglycemic clamp. T2 did not alter fasting plasma glucose or insulin concentration. Basal endogenous glucose production (EGP) rate was unchanged. During the clamp, there was no difference in insulin stimulated whole body glucose disposal. Insulin suppressed EGP by 60% ± 10 in T2-treated rats as compared with 47% ± 4 suppression in the vehicle group (p = 0.32). This was associated with an improvement in hepatic insulin signaling; insulin stimulated Akt phosphorylation was ~2.5 fold greater in the T2-treated group as compared with the vehicle-treated group (p = 0.003). There was no change in expression of genes thought to mediate the effect of T2 on hepatic metabolism, including genes that regulate hepatic lipid oxidation (ppara, carnitine palmitoyltransferase 1a), genes that regulate hepatic fatty acid synthesis (srebp1c, acetyl coa carboxylase, fatty acid synthase), and genes involved in glycolysis and gluconeogenesis (L-pyruvate kinase, glucose 6 phosphatase). Therefore, in contrast with previous reports, in Sprague Dawley rats fed an unsaturated fat diet, T2 administration failed to improve NAFLD or whole body insulin sensitivity. Though there was a modest improvement in hepatic insulin signaling, this was not associated with significant differences in hepatic insulin action. Further study will be necessary before diiodothyronines can be considered an effective treatment for NAFLD and dyslipidemia.
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Affiliation(s)
- Daniel F. Vatner
- Department of Internal Medicine,Yale University School of Medicine, New Haven, CT, United States of America
| | - Jaclyn Snikeris
- Department of Internal Medicine,Yale University School of Medicine, New Haven, CT, United States of America
| | - Violeta Popov
- Department of Internal Medicine,Yale University School of Medicine, New Haven, CT, United States of America
| | - Rachel J. Perry
- Department of Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, CT, United States of America
| | - Yasmeen Rahimi
- Department of Internal Medicine,Yale University School of Medicine, New Haven, CT, United States of America
| | - Varman T. Samuel
- Department of Internal Medicine,Yale University School of Medicine, New Haven, CT, United States of America
- West Haven VAMC, West Haven, CT, United States of America
- * E-mail:
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Previs SF, Kelley DE. Tracer-based assessments of hepatic anaplerotic and TCA cycle flux: practicality, stoichiometry, and hidden assumptions. Am J Physiol Endocrinol Metab 2015; 309:E727-35. [PMID: 26330343 DOI: 10.1152/ajpendo.00216.2015] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Accepted: 08/24/2015] [Indexed: 11/22/2022]
Abstract
Two groups recently used different tracer methods to quantify liver-specific flux rates. The studies had a similar goal, i.e., to characterize mitochondrial oxidative function. These efforts could have a direct impact on our ability to understand metabolic abnormalities that affect the pathophysiology of fatty liver and allow us to examine mechanisms surrounding potential therapeutic interventions. Briefly, one method couples the continuous infusion of [(13)C]acetate with direct real-time measurements of [(13)C]glutamate labeling in liver; the other method administers [(13)C]propionate, in combination with other tracers, and subsequently measures the (13)C labeling of plasma glucose and/or acetaminophen-glucuronide. It appears that a controversy has arisen, since the respective methods yielded different estimates of the anaplerotic/TCA flux ratio (VANA:VTCA) in "control" subjects, i.e., the [(13)C]acetate- and [(13)C]propionate-derived VANA:VTCA flux ratios appear to be ∼1.4 and ∼5, respectively. While the deep expertise in the respective groups makes it somewhat trivial for each to perform the tracer studies, the data interpretation is inherently difficult. The current perspective was undertaken to examine potential factors that could account for or contribute to the apparent differences. Attention was directed toward 1) matters of practicality, 2) issues surrounding stoichiometry, and 3) hidden assumptions. We believe that the [(13)C]acetate method has certain weaknesses that limit its utility; in contrast, the [(13)C]propionate method likely yields a more correct answer. We hope our discussion will help clarify the differences in the recent reports. Presumably this will be of interest to investigators who are considering tracer-based studies of liver metabolism.
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Befroy DE, Kibbey RG, Perry RJ, Petersen KF, Rothman DL, Shulman GI. Response to burgess. Nat Med 2015; 21:109-10. [PMID: 25654597 DOI: 10.1038/nm.3790] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Douglas E Befroy
- 1] Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, USA. [2] Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Richard G Kibbey
- 1] Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA. [2] Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Rachel J Perry
- 1] Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA. [2] Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Kitt Falk Petersen
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Douglas L Rothman
- 1] Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, USA. [2] Department of Biomedical Engineering, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Gerald I Shulman
- 1] Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA. [2] Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA. [3] Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
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Sridharan GV, Ullah E, Hassoun S, Lee K. Discovery of substrate cycles in large scale metabolic networks using hierarchical modularity. BMC SYSTEMS BIOLOGY 2015; 9:5. [PMID: 25884368 PMCID: PMC4349670 DOI: 10.1186/s12918-015-0146-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Accepted: 01/26/2015] [Indexed: 11/10/2022]
Abstract
BACKGROUND A substrate cycle is a set of metabolic reactions, arranged in a loop, which does not result in net consumption or production of the metabolites. The cycle operates by transforming a cofactor, e.g. oxidizing a reducing equivalent. Substrate cycles have been found experimentally in many parts of metabolism; however, their physiological roles remain unclear. As genome-scale metabolic models become increasingly available, there is now the opportunity to comprehensively catalogue substrate cycles, and gain additional insight into this potentially important motif of metabolic networks. RESULTS We present a method to identify substrate cycles in the context of metabolic modules, which facilitates functional analysis. This method utilizes elementary flux mode (EFM) analysis to find potential substrate cycles in the form of cyclical EFMs, and combines this analysis with network partition based on retroactive (cyclical) interactions between reactions. In addition to providing functional context, partitioning the network into modules allowed exhaustive EFM calculations on smaller, tractable subnetworks that are enriched in metabolic cycles. Applied to a large-scale model of human liver metabolism (HepatoNet1), our method found not only well-known substrate cycles involving ATP hydrolysis, but also potentially novel substrate cycles involving the transformation of other cofactors. A key characteristic of the substrate cycles identified in this study is that the lengths are relatively short (2-13 reactions), comparable to many experimentally observed substrate cycles. CONCLUSIONS EFM computation for large scale networks remains computationally intractable for exhaustive substrate cycle enumeration. Our algorithm utilizes a 'divide and conquer' strategy where EFM analysis is performed on systematically identified network modules that are designed to be enriched in cyclical interactions. We find that several substrate cycles uncovered using our approach are not identified when the network is partitioned in a more generic manner based solely on connectivity rather than cycles, demonstrating the value of targeting motif searches to sub-networks replete with a topological feature that resembles the desired motif itself.
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Affiliation(s)
- Gautham Vivek Sridharan
- Department of Chemical and Biological Engineering, Tufts University, 4 Colby Street, Medford, MA, 02155, USA.
| | - Ehsan Ullah
- Department of Computer Science, Tufts University, 161 College Avenue, Medford, MA, 02155, USA.
| | - Soha Hassoun
- Department of Computer Science, Tufts University, 161 College Avenue, Medford, MA, 02155, USA.
| | - Kyongbum Lee
- Department of Chemical and Biological Engineering, Tufts University, 4 Colby Street, Medford, MA, 02155, USA.
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Befroy DE, Perry RJ, Jain N, Dufour S, Cline GW, Trimmer JK, Brosnan J, Rothman DL, Petersen KF, Shulman GI. Direct assessment of hepatic mitochondrial oxidative and anaplerotic fluxes in humans using dynamic 13C magnetic resonance spectroscopy. Nat Med 2014; 20:98-102. [PMID: 24317120 PMCID: PMC3947269 DOI: 10.1038/nm.3415] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Accepted: 10/29/2013] [Indexed: 12/11/2022]
Abstract
Despite the central role of the liver in the regulation of glucose and lipid metabolism, there are currently no methods to directly assess hepatic oxidative metabolism in humans in vivo. By using a new (13)C-labeling strategy in combination with (13)C magnetic resonance spectroscopy, we show that rates of mitochondrial oxidation and anaplerosis in human liver can be directly determined noninvasively. Using this approach, we found the mean rates of hepatic tricarboxylic acid (TCA) cycle flux (VTCA) and anaplerotic flux (VANA) to be 0.43 ± 0.04 μmol g(-1) min(-1) and 0.60 ± 0.11 μmol g(-1) min(-1), respectively, in twelve healthy, lean individuals. We also found the VANA/VTCA ratio to be 1.39 ± 0.22, which is severalfold lower than recently published estimates using an indirect approach. This method will be useful for understanding the pathogenesis of nonalcoholic fatty liver disease and type 2 diabetes, as well as for assessing the effectiveness of new therapies targeting these pathways in humans.
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Affiliation(s)
- Douglas E Befroy
- 1] Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, USA. [2] Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA. [3]
| | - Rachel J Perry
- 1] Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA. [2] Department of Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA. [3]
| | - Nimit Jain
- Department of Biomedical Engineering, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Sylvie Dufour
- Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Gary W Cline
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
| | | | | | - Douglas L Rothman
- 1] Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, USA. [2] Department of Biomedical Engineering, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Kitt Falk Petersen
- 1] Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA. [2] Novo Nordisk Foundation Center for Basic Metabolic Research, Copenhagen, Denmark
| | - Gerald I Shulman
- 1] Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA. [2] Department of Cellular & Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA. [3] Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA. [4] Novo Nordisk Foundation Center for Basic Metabolic Research, Copenhagen, Denmark
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14
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Vatner DF, Weismann D, Beddow SA, Kumashiro N, Erion DM, Liao XH, Grover GJ, Webb P, Phillips KJ, Weiss RE, Bogan JS, Baxter J, Shulman GI, Samuel VT. Thyroid hormone receptor-β agonists prevent hepatic steatosis in fat-fed rats but impair insulin sensitivity via discrete pathways. Am J Physiol Endocrinol Metab 2013; 305:E89-100. [PMID: 23651850 PMCID: PMC3725564 DOI: 10.1152/ajpendo.00573.2012] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Liver-specific thyroid hormone receptor-β (TRβ)-specific agonists are potent lipid-lowering drugs that also hold promise for treating nonalcoholic fatty liver disease and hepatic insulin resistance. We investigated the effect of two TRβ agonists (GC-1 and KB-2115) in high-fat-fed male Sprague-Dawley rats treated for 10 days. GC-1 treatment reduced hepatic triglyceride content by 75%, but the rats developed fasting hyperglycemia and hyperinsulinemia, attributable to increased endogenous glucose production (EGP) and diminished hepatic insulin sensitivity. GC-1 also increased white adipose tissue lipolysis; the resulting increase in glycerol flux may have contributed to the increase in EGP. KB-2115, a more TRβ- and liver-specific thyromimetic, also prevented hepatic steatosis but did not induce fasting hyperglycemia, increase basal EGP rate, or diminish hepatic insulin sensitivity. Surprisingly, insulin-stimulated peripheral glucose disposal was diminished because of a decrease in insulin-stimulated skeletal muscle glucose uptake. Skeletal muscle insulin signaling was unaffected. Instead, KB-2115 treatment was associated with a decrease in GLUT4 protein content. Thus, although both GC-1 and KB-2115 potently treat hepatic steatosis in fat-fed rats, they each worsen insulin action via specific and discrete mechanisms. The development of future TRβ agonists must consider the potential adverse effects on insulin sensitivity.
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Affiliation(s)
- Daniel F Vatner
- Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520, USA
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15
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Song Y, Yao X, Ying H. Thyroid hormone action in metabolic regulation. Protein Cell 2011; 2:358-68. [PMID: 21614672 DOI: 10.1007/s13238-011-1046-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2011] [Accepted: 04/24/2011] [Indexed: 12/19/2022] Open
Abstract
Thyroid hormone plays pivotal roles in growth, differentiation, development and metabolic homeostasis via thyroid hormone receptors (TRs) by controlling the expression of TR target genes. The transcriptional activity of TRs is modulated by multiple factors including various TR isoforms, diverse thyroid hormone response elements, different heterodimeric partners, coregulators, and the cellular location of TRs. In the present review, we summarize recent advance in understanding the molecular mechanisms of thyroid hormone action obtained from human subject research, thyroid hormone mimetics application, TR isoform-specific knock-in mouse models, and mitochondrion study with highlights in metabolic regulations. Finally, as future perspectives, we share our thoughts about current challenges and possible approaches to promote our knowledge of thyroid hormone action in metabolism.
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Affiliation(s)
- Yiyun Song
- Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Graduate School of the Chinese Academy of Sciences, Shanghai, China
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16
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17
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Mitchell CS, Savage DB, Dufour S, Schoenmakers N, Murgatroyd P, Befroy D, Halsall D, Northcott S, Raymond-Barker P, Curran S, Henning E, Keogh J, Owen P, Lazarus J, Rothman DL, Farooqi IS, Shulman GI, Chatterjee K, Petersen KF. Resistance to thyroid hormone is associated with raised energy expenditure, muscle mitochondrial uncoupling, and hyperphagia. J Clin Invest 2010; 120:1345-54. [PMID: 20237409 PMCID: PMC2846038 DOI: 10.1172/jci38793] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Accepted: 01/13/2010] [Indexed: 01/07/2023] Open
Abstract
Resistance to thyroid hormone (RTH), a dominantly inherited disorder usually associated with mutations in thyroid hormone receptor beta (THRB), is characterized by elevated levels of circulating thyroid hormones (including thyroxine), failure of feedback suppression of thyrotropin, and variable tissue refractoriness to thyroid hormone action. Raised energy expenditure and hyperphagia are recognized features of hyperthyroidism, but the effects of comparable hyperthyroxinemia in RTH patients are unknown. Here, we show that resting energy expenditure (REE) was substantially increased in adults and children with THRB mutations. Energy intake in RTH subjects was increased by 40%, with marked hyperphagia particularly evident in children. Rates of muscle TCA cycle flux were increased by 75% in adults with RTH, whereas rates of ATP synthesis were unchanged, as determined by 13C/31P magnetic resonance spectroscopy. Mitochondrial coupling index between ATP synthesis and mitochondrial rates of oxidation (as estimated by the ratio of ATP synthesis to TCA cycle flux) was significantly decreased in RTH patients. These data demonstrate that basal mitochondrial substrate oxidation is increased and energy production in the form of ATP synthesis is decreased in the muscle of RTH patients and that resting oxidative phosphorylation is uncoupled in this disorder. Furthermore, these observations suggest that mitochondrial uncoupling in skeletal muscle is a major contributor to increased REE in patients with RTH, due to tissue selective retention of thyroid hormone receptor alpha sensitivity to elevated thyroid hormone levels.
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Affiliation(s)
- Catherine S. Mitchell
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - David B. Savage
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Sylvie Dufour
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Nadia Schoenmakers
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Peter Murgatroyd
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Douglas Befroy
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - David Halsall
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Samantha Northcott
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Philippa Raymond-Barker
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Suzanne Curran
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Elana Henning
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Julia Keogh
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Penny Owen
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - John Lazarus
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Douglas L. Rothman
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - I. Sadaf Farooqi
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Gerald I. Shulman
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Krishna Chatterjee
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
| | - Kitt Falk Petersen
- University of Cambridge Metabolic Research Laboratories, Institute of Metabolic Science, Addenbrooke’s Hospital, Cambridge, United Kingdom.
Howard Hughes Medical Institute and
Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
Department of Clinical Biochemistry, Addenbrooke’s Hospital.
Department of Medicine, University of Cardiff, United Kingdom.
Department of Diagnostic Radiology and
Department of Cellular and Molecular Physiology, Yale University School of Medicine
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18
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Thyroid hormone mimetics: potential applications in atherosclerosis, obesity and type 2 diabetes. Nat Rev Drug Discov 2009; 8:308-20. [PMID: 19337272 DOI: 10.1038/nrd2830] [Citation(s) in RCA: 174] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Thyroid hormones influence heart rate, serum lipids, metabolic rate, body weight and multiple aspects of lipid, carbohydrate, protein and mineral metabolism. Although increased thyroid hormone levels can improve serum lipid profiles and reduce fat, these positive effects are counterbalanced by harmful effects on the heart, muscle and bone. Thus, attempts to use thyroid hormones for cholesterol-lowering and weight loss purposes have so far been limited. However, over the past decade, thyroid hormone analogues that are capable of uncoupling beneficial effects from deleterious effects have been developed. Such drugs could serve as powerful new tools to address two of the largest medical problems in developed countries--atherosclerosis and obesity.
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19
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Grant N. The role of triiodothyronine-induced substrate cycles in the hepatic response to overnutrition: thyroid hormone as an antioxidant. Med Hypotheses 2006; 68:641-9. [PMID: 17023119 DOI: 10.1016/j.mehy.2006.07.045] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2006] [Accepted: 07/29/2006] [Indexed: 01/11/2023]
Abstract
Overnutrition, by generating reactive oxygen species (ROS), produces oxidative stress - an important cause of cellular injury. In the liver, overnutrition begins in the perivenous hepatocytes. To prevent injury, cells must protect themselves against ROS accumulation. Overnutrition also activates the enzyme deiodinase-1 (D1), which catalyzes the conversion of T4 to T3. D1 is primarily located in the PV region of the liver. Thyroid hormone is known to generate substrate cycling. The hypothesis of this paper is that a nutrient-induced increase in intracellular T3 acts as an antioxidant by inducing substrate cycles that reduce ROS accumulation. These cycles do this by: (i) reducing ROS formation by hydrolyzing excess ATP, thus enhancing oxidative phosphorylation and reducing the proton motive force on the electron transport chain (ETC), and; (ii) enhancing the removal (reduction) of ROS by producing the NADPH required for regeneration of reduced glutathione, a potent endogenous antioxidant. Oxidative stress is an important factor in the etiology of a number of hepatic injuries, including nonalcoholic steatohepatitis (NASH) and hepatocarcinogenesis. In the latter, the frequency of mutations in thyroid hormone receptors (TRs) supports the concept that thyroid hormone acts as a tumor suppressor by reducing oxidative stress. This paper reviews the substrate cycles involved in this process. It also describes other mechanisms that permit rapid availability of T3 to cells undergoing oxidative stress.
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Affiliation(s)
- Neville Grant
- Department of Medicine, Washington University School of Medicine, David P Wohl Jr., Hospital, 4960 Children's Pl sixth floor, St. Louis, MO, USA.
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20
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Jin ES, Burgess SC, Merritt ME, Sherry AD, Malloy CR. Differing mechanisms of hepatic glucose overproduction in triiodothyronine-treated rats vs. Zucker diabetic fatty rats by NMR analysis of plasma glucose. Am J Physiol Endocrinol Metab 2005; 288:E654-62. [PMID: 15562253 DOI: 10.1152/ajpendo.00365.2004] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The metabolic mechanism of hepatic glucose overproduction was investigated in 3,3'-5-triiodo-l-thyronine (T3)-treated rats and Zucker diabetic fatty (ZDF) rats (fa/fa) after a 24-h fast. 2H2O and [U-13C3]propionate were administered intraperitoneally, and [3,4-13C2]glucose was administered as a primed infusion for 90 min under ketamine-xylazine anesthesia. 13C NMR analysis of monoacetone glucose derived from plasma glucose indicated that hepatic glucose production was twofold higher in both T3-treated rats and ZDF rats compared with controls, yet the sources of glucose overproduction differed significantly in the two models by 2H NMR analysis. In T3-treated rats, the hepatic glycogen content and hence the contribution of glycogenolysis to glucose production was essentially zero; in this case, excess glucose production was due to a dramatic increase in gluconeogenesis from TCA cycle intermediates. 13C NMR analysis also revealed increased phosphoenolpyruvate carboxykinase flux (4x), increased pyruvate cycling flux (4x), and increased TCA flux (5x) in T3-treated animals. ZDF rats had substantial glycogen stores after a 24-h fast, and consequently nearly 50% of plasma glucose originated from glycogenolysis; other fluxes related to the TCA cycle were not different from controls. The differing mechanisms of excess glucose production in these models were easily distinguished by integrated 2H and 13C NMR analysis of plasma glucose.
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Affiliation(s)
- Eunsook S Jin
- The Mary Nell and Ralph B. Rogers Magnetic Resonance Center, 5801 Forest Park Road, Dallas, TX 75235-9085, USA.
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21
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Carbone MA, Robinson BH. Expression and characterization of a human pyruvate carboxylase variant by retroviral gene transfer. Biochem J 2003; 370:275-82. [PMID: 12437512 PMCID: PMC1223164 DOI: 10.1042/bj20021397] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2002] [Revised: 10/24/2002] [Accepted: 10/30/2002] [Indexed: 11/17/2022]
Abstract
Type A pyruvate carboxylase (PC) deficiency presents mainly in the Amerindian population, specifically the Ojibwa, Cree and Micmac tribes of the Algonquin-speaking peoples. The gene for PC contains a homozygous founder mutation (G1828-->A) that results in an Ala610-->Thr amino acid substitution in Ojibwa with Type A PC deficiency. The mutation is located in the highly conserved pyruvate-binding domain of PC. The present paper describes a retroviral expression system for human PC used to analyse the effects of this mutation. We show, through immunoblot analysis, PC enzyme activity assays, reverse-transcription PCR and mitochondrial-import experiments, that this mutation is disease-causing in the Ojibwa population owing to its decreased catalytic activity, decreased steady-state levels of expression and inefficient import into the mitochondria. Our data suggest that this mutation may affect the stability of the protein, resulting in decreased steady-state levels of expression, and that it may also affect the secondary structure of the protein during the import process, thereby inhibiting proper translocation into the mitochondria, where PC is active.
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Affiliation(s)
- Mary Anna Carbone
- Research Institute, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada M5G 1X8
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22
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Astroglial contribution to brain energy metabolism in humans revealed by 13C nuclear magnetic resonance spectroscopy: elucidation of the dominant pathway for neurotransmitter glutamate repletion and measurement of astrocytic oxidative metabolism. J Neurosci 2002. [PMID: 11880482 DOI: 10.1523/jneurosci.22-05-01523.2002] [Citation(s) in RCA: 259] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Increasing evidence supports a crucial role for glial metabolism in maintaining proper synaptic function and in the etiology of neurological disease. However, the study of glial metabolism in humans has been hampered by the lack of noninvasive methods. To specifically measure the contribution of astroglia to brain energy metabolism in humans, we used a novel noninvasive nuclear magnetic resonance spectroscopic approach. We measured carbon 13 incorporation into brain glutamate and glutamine in eight volunteers during an intravenous infusion of [2-13C] acetate, which has been shown in animal models to be metabolized specifically in astroglia. Mathematical modeling of the three established pathways for neurotransmitter glutamate repletion indicates that the glutamate/glutamine neurotransmitter cycle between astroglia and neurons (0.32 +/- 0.07 micromol x gm(-1) x min(-1)) is the major pathway for neuronal glutamate repletion and that the astroglial TCA cycle flux (0.14 +/- 0.06 micromol x gm(-1) x min(-1)) accounts for approximately 14% of brain oxygen consumption. Up to 30% of the glutamine transferred to the neurons by the cycle may derive from replacement of oxidized glutamate by anaplerosis. The further application of this approach could potentially enlighten the role of astroglia in supporting brain glutamatergic activity and in neurological and psychiatric disease.
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23
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McCarty MF. Peroxisome proliferators as adjuvants for the reverse-electron-transport therapy of obesity: an explanation for the large increase in metabolic rate of MEDICA 16-treated rats. Med Hypotheses 1999; 53:272-6. [PMID: 10608261 DOI: 10.1054/mehy.1998.0757] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The efficacy of reverse-electron-transport therapy of obesity should be promoted by agents which up-regulate hepatocyte enzymes that are potentially rate-limiting for mitochondrial fatty acid oxidation and electron shuttles. Peroxisome proliferator drugs, including the fibrates used to treat hyperlipidemia, may be useful in this regard, as they induce malic enzyme, the mitochondrial glycerol-3-phosphate dehydrogenase, and carnitine palmitoyl transferase I in rodent hepatocytes. An agent of this class, MEDICA 16, has the additional property of potently inhibiting both citrate lyase and acetyl-CoA carboxylase. As a result, methyl-substituted diacarboxylic acids (MEDICA) 16 can be expected to disinhibit hepatic fatty acid oxidation while up-regulating electron shuttle mechanisms, and thus should stimulate reverse electron transport. This may explain the remarkable 40% increase in basal metabolic rate observed in normal rats ingesting MEDICA 16--an effect not associated with any compensatory increase in food intake. Relative to controls, the MEDICA 16-treated rats achieved a 50% reduction in body fat and a modest increase in lean mass, such that weight and growth were not changed. In other rodent strains, MEDICA 16 has prevented obesity diabetes and atherogenesis. However, whether MEDICA 16 and other peroxisome proliferator drugs will have clinical utility in reverse-electron-transport therapy may hinge on their ability to induce key enzymes in human hepatocytes; cell culture studies to evaluate this are required.
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