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Yoshida S, Kohmura M. Comments on "Assessment of changes in the liver of pregnant female rats and their fetuses following monosodium glutamate administration" by Gad El-Hak et al., http://doi.org/10.1007/s11356-021-13,557-7. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2023; 30:16775-16777. [PMID: 36306071 PMCID: PMC9908732 DOI: 10.1007/s11356-022-23858-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 10/21/2022] [Indexed: 06/16/2023]
Affiliation(s)
- Shintaro Yoshida
- International Glutamate Technical Committee (IGTC), National Press Building 529, 14Th Street, Suite 1280, Washington, DC, 20045, USA.
| | - Masanori Kohmura
- International Glutamate Technical Committee (IGTC), National Press Building 529, 14Th Street, Suite 1280, Washington, DC, 20045, USA
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Wang P, Li QQ, Hui J, Xiang QQ, Yan H, Chen LQ. Metabolomics reveals the mechanism of polyethylene microplastic toxicity to Daphnia magna. CHEMOSPHERE 2022; 307:135887. [PMID: 35931252 DOI: 10.1016/j.chemosphere.2022.135887] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 07/04/2022] [Accepted: 07/27/2022] [Indexed: 06/15/2023]
Abstract
Microplastic exposure leads to various toxic effects in Daphnia magna; however, the effects of microplastics on the metabolic processes in D. magna and the corresponding molecular toxicity mechanisms remain unclear. In the present study, the effects of acute exposure to polyethylene microplastics with different particle sizes (20 μm [MPs-20] and 30 μm [MPs-30]) on metabolites in D. magna and the mechanisms of toxicity were investigated by combining metabolomics and traditional toxicology techniques. Exposure to both MPs-20 and MPs-30 resulted in significant accumulation of microplastics in the gut of D. magna and significantly reduced D. magna survival and heart rate. Metabolomics analysis revealed that MPs-20 and MPs-30 induced significant changes in up to 88 and 91 differential metabolites, respectively, and collectively induced significant changes in 75 metabolites in D. magna. Among lipid metabolites, MPs-20 specifically downregulated phosphatidylcholine and upregulated phosphatidylethanolamine, which mainly affected phospholipid metabolism, whereas MPs-30 specifically downregulated amino acid metabolites l-glutamine, l-glutamate and malic acid, which mainly interfered with energy metabolism. The results of this study provide novel insights into the mechanism of effects of microplastics on metabolic processes in D. magna.
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Affiliation(s)
- Peng Wang
- Institute of International Rivers and Eco-security, Yunnan Key Laboratory of International Rivers and Trans-Boundary Eco-security, Yunnan University, Kunming, 650091, People's Republic of China; Yunnan International Joint Research Center for Hydro-Ecology Science & Engineering, Yunnan University, Kunming, 650091, People's Republic of China
| | - Qin-Qin Li
- Institute of International Rivers and Eco-security, Yunnan Key Laboratory of International Rivers and Trans-Boundary Eco-security, Yunnan University, Kunming, 650091, People's Republic of China; Yunnan International Joint Research Center for Hydro-Ecology Science & Engineering, Yunnan University, Kunming, 650091, People's Republic of China
| | - Jin Hui
- Institute of International Rivers and Eco-security, Yunnan Key Laboratory of International Rivers and Trans-Boundary Eco-security, Yunnan University, Kunming, 650091, People's Republic of China; Yunnan International Joint Research Center for Hydro-Ecology Science & Engineering, Yunnan University, Kunming, 650091, People's Republic of China
| | - Qian-Qian Xiang
- Institute of International Rivers and Eco-security, Yunnan Key Laboratory of International Rivers and Trans-Boundary Eco-security, Yunnan University, Kunming, 650091, People's Republic of China; Yunnan International Joint Research Center for Hydro-Ecology Science & Engineering, Yunnan University, Kunming, 650091, People's Republic of China
| | - Hui Yan
- Institute of International Rivers and Eco-security, Yunnan Key Laboratory of International Rivers and Trans-Boundary Eco-security, Yunnan University, Kunming, 650091, People's Republic of China; Yunnan International Joint Research Center for Hydro-Ecology Science & Engineering, Yunnan University, Kunming, 650091, People's Republic of China
| | - Li-Qiang Chen
- Institute of International Rivers and Eco-security, Yunnan Key Laboratory of International Rivers and Trans-Boundary Eco-security, Yunnan University, Kunming, 650091, People's Republic of China; Yunnan International Joint Research Center for Hydro-Ecology Science & Engineering, Yunnan University, Kunming, 650091, People's Republic of China.
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Loï C, Cynober L. Glutamate: A Safe Nutrient, Not Just a Simple Additive. ANNALS OF NUTRITION AND METABOLISM 2022; 78:133-146. [PMID: 35172302 DOI: 10.1159/000522482] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2021] [Accepted: 02/04/2022] [Indexed: 11/19/2022]
Abstract
BACKGROUND In 2017, an European Food Safety Authority (EFSA) opinion on the use of glutamate and its salts as food additives led to an ADI of 30mg/kg body weight/day. Then, in 2021, an EFSA statement presented a proposal for harmonising the establishment of Health-Based Guidance Values for nutrients that are also regulated substances (including food additives). The present review argues that the 2017 glutamate ADI is unsuitable because safety of glutamate should firstly consider its status as a nutrient and not only as an additive. SUMMARY Glutamate is a non-essential amino acid playing a key role in nitrogen homeostasis. The dietary exposure to glutamate in adults is extensive, due to its ubiquitous presence in foods, under three forms: bound to proteins, naturally free and free form added as an additive. Glutamate naturally included into proteins is the major source of dietary glutamate. Thus, since it plays a role in nitrogen homeostasis, it is a nutrient before being an additive. Its pharmacokinetics is largely impacted by concomitant food intake but the extent to which plasma glutamate concentration must rise to have deleterious effects is never encountered in humans consuming glutamate in their daily diets. This is due to the fact that glutamate is highly metabolized in the splanchnic area. Key Messages: Glutamate should be considered as a safe nutrient before as an additive by risk assessor.
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Affiliation(s)
| | - Luc Cynober
- Laboratoire de Biologie de la Nutrition, URP 4466, Faculté de Pharmacie, Université de Paris, Paris, France
- Service de Biochimie, Hôpital Cochin, AP-HP, Paris, France
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de Bie TH, Witkamp RF, Jongsma MA, Balvers MGJ. Development and validation of a UPLC-MS/MS method for the simultaneous determination of gamma-aminobutyric acid and glutamic acid in human plasma. J Chromatogr B Analyt Technol Biomed Life Sci 2021; 1164:122519. [PMID: 33454439 DOI: 10.1016/j.jchromb.2020.122519] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2020] [Revised: 11/02/2020] [Accepted: 12/22/2020] [Indexed: 11/15/2022]
Abstract
Gamma-aminobutyric acid (GABA) and its precursor glutamic acid are important neurotransmitters. Both are also present in peripheral tissues and the circulation, where abnormal plasma concentrations have been linked to specific mental disorders. In addition to endogenous synthesis, GABA and glutamic acid can be obtained from dietary sources. An increasing number of studies suggest beneficial cardio-metabolic effects of GABA intake, and therefore GABA is being marketed as a food supplement. The need for further research into their health effects merits accurate and sensitive methods to analyze GABA and glutamic acid in plasma. To this end, an ultra-pressure liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for the quantification of GABA and glutamic acid in human plasma. Samples were prepared by a protein precipitation step and subsequent solid phase extraction using acetonitrile. Chromatographic separation was achieved on an Acquity UPLC HSS reversed phase C18 column using gradient elution. Analytes were detected using electrospray ionization and selective reaction monitoring. Standard curve concentrations for GABA ranged from 3.4 to 2500 ng/mL and for glutamic acid from 30.9 ng/mL to 22,500 ng/mL. Within- and between-day accuracy and precision were <10% in quality control samples at low, medium and high concentrations for both GABA and glutamic acid. GABA and glutamic acid were found to be stable in plasma after freeze-thaw cycles and up to 12 months of storage. The validated method was applied to human plasma from 17 volunteers. The observed concentrations ranged between 11.5 and 20.0 ng/ml and 2269 and 7625 ng/ml for respectively GABA and glutamic acid. The reported method is well suited for the measurement of plasma GABA and glutamic acid in pre-clinical or clinical studies.
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Affiliation(s)
- Tessa H de Bie
- Division of Human Nutrition and Health, Wageningen University & Research, P.O. Box 17, 6700 AA Wageningen, the Netherlands; Wageningen Plant Research, Wageningen University & Research, P.O. Box 16, 6700 AA Wageningen, the Netherlands.
| | - Renger F Witkamp
- Division of Human Nutrition and Health, Wageningen University & Research, P.O. Box 17, 6700 AA Wageningen, the Netherlands
| | - Maarten A Jongsma
- Wageningen Plant Research, Wageningen University & Research, P.O. Box 16, 6700 AA Wageningen, the Netherlands
| | - Michiel G J Balvers
- Division of Human Nutrition and Health, Wageningen University & Research, P.O. Box 17, 6700 AA Wageningen, the Netherlands
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Levitt MD, Levitt DG. Use Of Quantitative Modelling To Elucidate The Roles Of The Liver, Gut, Kidney, And Muscle In Ammonia Homeostasis And How Lactulose And Rifaximin Alter This Homeostasis. Int J Gen Med 2019; 12:367-380. [PMID: 31686894 PMCID: PMC6798813 DOI: 10.2147/ijgm.s218405] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Accepted: 09/24/2019] [Indexed: 12/18/2022] Open
Abstract
Humans must eliminate approximately 1M of ammonia per day while maintaining the blood concentration of this potent neurotoxin at a concentration of only about 30 µM. The mechanisms producing such effective ammonia homeostasis are poorly understood by clinicians due to the multiple organs (liver, gut, kidney and muscle) involved in ammonia homeostasis. Based on literature values we present a novel, simplified description of normal and disordered ammonia and the potential mechanisms whereby the drugs used to treat hepatic encephalopathy, lactulose and rifaximin, lower the blood ammonia concentration. Concepts discussed include the following: 1) only about 44 mmol of ammonia/day (4.4% of total production) reaches the peripheral circulation due to the efficient linkage of amino deamination and the urea cycle in hepatic mitochondria; 2) the gut and kidney contribute roughly equally to delivery of this 44 mmol/day to systemic blood; 3) the bulk of gut ammonia production seemingly originates in the small bowel from bacterial deamination of urea by bacteria and mucosal deamination of circulating and ingested glutamine; 4) the apparent production of ammonia in the small bowel markedly exceeds that quantity that enters the portal blood, indicating that ammonia disposal mechanisms in the small bowel play a major role in ammonia homeostasis. With regard to the hyperammonemia of chronic liver disease: 1) shunting of portal blood around the liver, by itself, can account for commonly observed ammonia elevations; 2) severe portal hypertension causes an increased release of ammonia by the kidney; 3) high blood ammonia is associated with an unexplained massive increase in the muscle uptake of ammonia that could play an important role in limiting hyperammonemia; and 4) a major action of lactulose administration may be the enhancement of ammonia uptake by small bowel bacteria, while the mechanism of action of rifaximin is unclear.
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Affiliation(s)
- Michael D Levitt
- Research Service, Veterans Affairs Medical Center, Minneapolis, MN 55417, USA
| | - David G Levitt
- Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, MN 55455, USA
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Zanfirescu A, Ungurianu A, Tsatsakis AM, Nițulescu GM, Kouretas D, Veskoukis A, Tsoukalas D, Engin AB, Aschner M, Margină D. A review of the alleged health hazards of monosodium glutamate. Compr Rev Food Sci Food Saf 2019; 18:1111-1134. [PMID: 31920467 PMCID: PMC6952072 DOI: 10.1111/1541-4337.12448] [Citation(s) in RCA: 83] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 03/15/2019] [Indexed: 12/11/2022]
Abstract
Monosodium glutamate (MSG) is an umami substance widely used as flavor enhancer. Although it is generally recognized as being safe by food safety regulatory agencies, several studies have questioned its long-term safety. The purpose of this review was to survey the available literature on preclinical studies and clinical trials regarding the alleged adverse effects of MSG. Here, we aim to provide a comprehensive overview of the reported possible risks that may potentially arise following chronic exposure. Furthermore, we intend to critically evaluate the relevance of this data for dietary human intake. Preclinical studies have associated MSG administration with cardiotoxicity, hepatotoxicity, neurotoxicity, low-grade inflammation, metabolic disarray and premalignant alterations, along with behavioral changes. Moreover, links between MSG consumption and tumorigenesis, increased oxidative stress and apoptosis in thymocytes, as well as genotoxic effects in lymphocytes have been reported. However, in reviewing the available literature, we detected several methodological flaws, which led us to conclude that these studies have limited relevance for extrapolation to dietary human intakes of MSG risk exposure. Clinical trials have focused mainly on the effects of MSG on food intake and energy expenditure. Besides its well-known impact on food palatability, MSG enhances salivary secretion and interferes with carbohydrate metabolism, while the impact on satiety and post-meal recovery of hunger varied in relation to meal composition. Reports on MSG hypersensitivity, also known as 'Chinese restaurant syndrome', or links of its use to increased pain sensitivity and atopic dermatitis were found to have little supporting evidence. Based on the available literature, we conclude that further clinical and epidemiological studies are needed, with an appropriate design, accounting for both added and naturally occurring dietary MSG. Critical analysis of existing literature, establishes that many of the reported negative health effects of MSG have little relevance for chronic human exposure and are poorly informative as they are based on excessive dosing that does not meet with levels normally consumed in food products.
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Affiliation(s)
- Anca Zanfirescu
- Faculty of Pharmacy, “Carol Davila” University of Medicine and Pharmacy, Traian Vuia 6, Bucharest 020956, Romania
| | - Anca Ungurianu
- Faculty of Pharmacy, “Carol Davila” University of Medicine and Pharmacy, Traian Vuia 6, Bucharest 020956, Romania
| | - Aristides M. Tsatsakis
- Department of Forensic Sciences and Toxicology, Faculty of Medicine, University of Crete, Heraklion 71409, Crete, Greece
| | - George M. Nițulescu
- Faculty of Pharmacy, “Carol Davila” University of Medicine and Pharmacy, Traian Vuia 6, Bucharest 020956, Romania
| | - Demetrios Kouretas
- Department of Biochemistry and Biotechnology, University of Thessaly, Larissa 41500, Greece
| | - Aris Veskoukis
- Department of Biochemistry and Biotechnology, University of Thessaly, Larissa 41500, Greece
| | - Dimitrios Tsoukalas
- Department of Forensic Sciences and Toxicology, Faculty of Medicine, University of Crete, Heraklion 71409, Crete, Greece
- Metabolomic Medicine Clinic, Athens 10674, Greece
| | - Ayse B. Engin
- Gazi University, Faculty of Pharmacy, Department of Toxicology, Ankara 06330, Turkey
| | - Michael Aschner
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx NY 10463, USA
| | - Denisa Margină
- Faculty of Pharmacy, “Carol Davila” University of Medicine and Pharmacy, Traian Vuia 6, Bucharest 020956, Romania
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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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Glucagon-like peptide-2 (GLP-2) increases net amino acid utilization by the portal-drained viscera of ruminating calves. Animal 2012. [PMID: 23031436 DOI: 10.1017/s17517311120009 5x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucagon-like peptide-2 (GLP-2) increases small intestinal mass and blood flow in ruminant calves, but its impact on nutrient metabolism across the portal-drained viscera (PDV) and liver is unknown. Eight Holstein calves with catheters in the carotid artery, mesenteric vein, portal vein and hepatic vein were paired by age and randomly assigned to control (0.5% bovine serum albumin in saline; n = 4) or GLP-2 (100 μg/kg BW per day bovine GLP-2 in bovine serum albumin; n = 4). Treatments were administered subcutaneously every 12 h for 10 days. Blood flow was measured on days 0 and 10 and included 3 periods: baseline (saline infusion), treatment (infusion of bovine serum albumin or 3.76 μg/kg BW per h GLP-2) and recovery (saline infusion). Arterial concentrations and net PDV, hepatic and total splanchnic fluxes of glucose, lactate, glutamate, glutamine, β-hydroxybutyrate and urea-N were measured on days 0 and 10. Arterial concentrations and net fluxes of all amino acids and glucose metabolism using continuous intravenous infusion of [U13-C]glucose were measured on day 10 only. A 1-h infusion of GLP-2 increased blood flow in the portal and hepatic veins when administered to calves not previously exposed to exogenous GLP-2, but after a 10-day administration of GLP-2 the blood flow response to the 1-h GLP-2 infusion was substantially attenuated. The 1-h GLP-2 infusion also did not appreciably alter nutrient fluxes on either day 0 or 10. In contrast, long-term GLP-2 administration reduced arterial concentrations and net PDV flux of many essential and non-essential amino acids. Despite the significant alterations in amino acid metabolism, glucose irreversible loss and utilization by PDV and non-PDV tissues were not affected by GLP-2. Fluxes of amino acids across the PDV were generally reduced by GLP-2, potentially by increased small intestinal epithelial growth and thus energy and amino acid requirements of this tissue. Increased PDV extraction of glutamine and alterations in PDV metabolism of arginine, ornithine and citrulline support the concept that GLP-2 influences intestine-specific amino acid metabolism. Alterations in amino acid metabolism but unchanged glucose metabolism suggests that the growth effects induced by GLP-2 in ruminants increase reliance on amino acids preferentially over glucose. Thus, GLP-2 increases PDV utilization of amino acids, but not glucose, concurrent with stimulated growth of the small intestinal epithelium in post-absorptive ruminant calves.
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9
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Glucagon-like peptide-2 (GLP-2) increases net amino acid utilization by the portal-drained viscera of ruminating calves. Animal 2012; 6:1985-97. [PMID: 23031436 DOI: 10.1017/s175173111200095x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Glucagon-like peptide-2 (GLP-2) increases small intestinal mass and blood flow in ruminant calves, but its impact on nutrient metabolism across the portal-drained viscera (PDV) and liver is unknown. Eight Holstein calves with catheters in the carotid artery, mesenteric vein, portal vein and hepatic vein were paired by age and randomly assigned to control (0.5% bovine serum albumin in saline; n = 4) or GLP-2 (100 μg/kg BW per day bovine GLP-2 in bovine serum albumin; n = 4). Treatments were administered subcutaneously every 12 h for 10 days. Blood flow was measured on days 0 and 10 and included 3 periods: baseline (saline infusion), treatment (infusion of bovine serum albumin or 3.76 μg/kg BW per h GLP-2) and recovery (saline infusion). Arterial concentrations and net PDV, hepatic and total splanchnic fluxes of glucose, lactate, glutamate, glutamine, β-hydroxybutyrate and urea-N were measured on days 0 and 10. Arterial concentrations and net fluxes of all amino acids and glucose metabolism using continuous intravenous infusion of [U13-C]glucose were measured on day 10 only. A 1-h infusion of GLP-2 increased blood flow in the portal and hepatic veins when administered to calves not previously exposed to exogenous GLP-2, but after a 10-day administration of GLP-2 the blood flow response to the 1-h GLP-2 infusion was substantially attenuated. The 1-h GLP-2 infusion also did not appreciably alter nutrient fluxes on either day 0 or 10. In contrast, long-term GLP-2 administration reduced arterial concentrations and net PDV flux of many essential and non-essential amino acids. Despite the significant alterations in amino acid metabolism, glucose irreversible loss and utilization by PDV and non-PDV tissues were not affected by GLP-2. Fluxes of amino acids across the PDV were generally reduced by GLP-2, potentially by increased small intestinal epithelial growth and thus energy and amino acid requirements of this tissue. Increased PDV extraction of glutamine and alterations in PDV metabolism of arginine, ornithine and citrulline support the concept that GLP-2 influences intestine-specific amino acid metabolism. Alterations in amino acid metabolism but unchanged glucose metabolism suggests that the growth effects induced by GLP-2 in ruminants increase reliance on amino acids preferentially over glucose. Thus, GLP-2 increases PDV utilization of amino acids, but not glucose, concurrent with stimulated growth of the small intestinal epithelium in post-absorptive ruminant calves.
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Lutgens L, Lambin P. Biomarkers for radiation-induced small bowel epithelial damage: An emerging role for plasma Citrulline. World J Gastroenterol 2007; 13:3033-42. [PMID: 17589917 PMCID: PMC4172608 DOI: 10.3748/wjg.v13.i22.3033] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Reduction of cancer treatment-induced mucosal injury has been recognized as an important target for improving the therapeutic ratio as well as reducing the economic burden associated with these treatment related sequellae. Clinical studies addressing this issue are hampered by the fact that specific objective parameters, which enable monitoring of damage in routine clinical practice, are lacking. This review summarizes pros and cons of currently available endpoints for intestinal injury. The metabolic background and characteristics of plasma citrulline, a recently investigated biomarker specifically for small intestinal injury, are discussed in more detail.
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Affiliation(s)
- Ludy Lutgens
- Department of Radiation Oncology (Maastro), GROW Research Institute, University of Maastricht, Tanslaan 12, 6202 AZ Maastricht, The Netherlands.
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Abstract
PURPOSE OF REVIEW This review reports recent findings on the effect of enterally fed protein and amino acids on metabolism, function, and clinical outcome, particularly during the neonatal period. RECENT FINDINGS Splanchnic tissues metabolize significant proportions of some enteral amino acids and this likely contributes to the higher requirement for these amino acids when they are provided enterally versus parenterally. Splanchnic tissues are particularly key in the provision of nutrition to preterm infants, who possess an exceedingly high protein anabolic drive, but limited tolerance to aggressive enteral feeding. The protein anabolic response to specific proteins is influenced by the rate of digestion and the pattern of feeding, as well as the amino acid composition of the proteins. The post-prandial rise in amino acids and insulin stimulates neonatal tissue protein synthesis by modulation of the nutrient and insulin signaling pathways that lead to translation initiation. A flurry of investigations into the metabolic response and clinical impact of individual amino acids suggests that leucine, glutamine, and arginine, in particular, have specific roles in regulating protein synthesis and immune function. SUMMARY Recent findings suggest that enteral nutrition support that provides an optimum combination of proteins and amino acids can have a beneficial impact on the clinical outcome of patients.
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Affiliation(s)
- Douglas G Burrin
- USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030, USA
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Le Bacquer O, Laboisse C, Darmaun D. Glutamine preserves protein synthesis and paracellular permeability in Caco-2 cells submitted to "luminal fasting". Am J Physiol Gastrointest Liver Physiol 2003; 285:G128-36. [PMID: 12799310 DOI: 10.1152/ajpgi.00459.2002] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
This study used polarized cell line Caco-2 as a model of human enterocytes to determine: 1) whether deprivation of nutrients on the apical (luminal) side of the epithelium (fasting) alters protein synthesis in enterocytes; 2) if so, whether glutamine can attenuate the effects of fasting; and 3) whether the effects of glutamine depend on its route (i.e., apical vs. basolateral) of supply. Caco-2 cells were submitted to nutrient deprivation on the apical side to mimic the effects of fasting, whereas the basolateral side of the epithelium remained exposed to regular medium. Cells were then incubated with [2H3]leucine with or without glutamine, and the fractional synthesis rate (FSR) of total cell protein was determined from [2H3]leucine enrichments in protein-bound and intracellular free leucine measured by gas chromatography/mass spectrometry. A 24-h apical nutrient deprivation (luminal fasting) was associated with a decline in intracellular glutamine, glutamate, and glutathione concentrations (-38, -40, and -40%, respectively), protein FSR (-20%), and a rise in passage of dextran, an index of transepithelial permeability. In fasted cells, basolateral or luminal glutamine supplementation did not alter the glutathione pool, but it restored protein FSR and improved permeability. The effects of glutamine were abolished by 6-diazo-oxo-l-norleucine, an inhibitor of glutaminase, and was mimicked by glutamate. We conclude that in Caco-2 cells, protein synthesis depends on nutrient supply on the apical side, and glutamine regardless of the route of supply corrects some of the deleterious effects of fasting in a model of human enterocytes through its deamidation into glutamate.
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Affiliation(s)
- Olivier Le Bacquer
- INSERM U.539, Centre de Recherche en Nutrition Humaine Groupe Métabolisme, Hotel-Dieu, 3ème étage aile nord, 44093 Nantes cedex 1, France
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Mourtzakis M, Graham TE. Glutamate ingestion and its effects at rest and during exercise in humans. J Appl Physiol (1985) 2002; 93:1251-9. [PMID: 12235022 DOI: 10.1152/japplphysiol.00111.2002] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Glutamate is central to several transamination reactions that affect the production of ammonia, alanine, glutamine, as well as TCA cycle intermediates during exercise. To further study glutamate metabolism, we administered 150 mg/kg body wt of monosodium glutamate (MSG) and placebo to seven male subjects who then either rested or exercised (15-min cycling at approximately 85% maximal oxygen consumption). MSG ingestion resulted in elevated plasma glutamate, aspartate, and taurine, both at rest and during exercise (P < 0.05), whereas most other amino acids were unchanged. Neither plasma alanine nor ammonia was altered at rest. During exercise and after glutamate ingestion, alanine was increased (P < 0.05) and ammonia was attenuated (P < 0.05). Glutamine was also elevated after glutamate ingestion during rest and exercise trials. MSG administration also resulted in elevated insulin levels (P < 0.05), which were parallel to the trend in C-peptide levels. Thus MSG can successfully elevate plasma glutamate, both at rest and during exercise. The plasma amino acid responses suggest that increased glutamate availability during exercise alters its distribution in transamination reactions within active muscle, which results in elevated alanine and decreased ammonia levels.
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Affiliation(s)
- Marina Mourtzakis
- Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
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van Goudoever JB, Stoll B, Henry JF, Burrin DG, Reeds PJ. Adaptive regulation of intestinal lysine metabolism. Proc Natl Acad Sci U S A 2000; 97:11620-5. [PMID: 11016965 PMCID: PMC17250 DOI: 10.1073/pnas.200371497] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The metabolism of dietary essential amino acids by the gut has a direct effect on their systemic availability and potentially limits growth. We demonstrate that, in neonatal pigs bearing portal and arterial catheters and fed a diet containing 23% protein [high protein (HP) diet], more than half the intake of essential amino acids is metabolized by the portal-drained viscera (PDV). Intraduodenal or i.v. infusions of [U-(13)C]-lysine were used to measure the appearance across and the use of the tracer by the PDV. In HP-fed pigs, lysine use by the PDV was derived almost entirely from the arterial input. In these animals, the small amount of dietary lysine used in first pass was oxidized almost entirely. Even so, intestinal lysine oxidation (24 micromol/kg per h) accounted for one-third of whole-body lysine oxidation (77 micromol/kg per h). Total lysine use by the PDV was not affected by low protein (LP) feeding (HP, 213 micromol/kg per h; LP,186 micromol/kg per h). In LP-fed pigs, the use of lysine by the PDV accounted for more than 75% of its intake. In contrast to HP feeding, both dietary and arterial lysines were used by the PDV of LP-fed pigs in nearly equal amounts. Intestinal lysine oxidation was suppressed completely. We conclude that the PDV are key organs with respect to amino acid metabolism and that the intestines use a disproportionately large amount of the dietary supply of amino acids during protein restriction.
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Affiliation(s)
- J B van Goudoever
- United States Department of Agriculture/Agricultural Research Service (DOA) Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, 1100 Bates Street, Houston, TX 77030, USA
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Forslund AH, Hambraeus L, van Beurden H, Holmbäck U, El-Khoury AE, Hjorth G, Olsson R, Stridsberg M, Wide L, Akerfeldt T, Regan M, Young VR. Inverse relationship between protein intake and plasma free amino acids in healthy men at physical exercise. Am J Physiol Endocrinol Metab 2000; 278:E857-67. [PMID: 10780942 DOI: 10.1152/ajpendo.2000.278.5.e857] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effect of a "normal" (n = 8) and "high" (n = 6) protein intake (1 and 2.5 g x kg(-1) x day(-1), respectively) and of exercise on plasma amino acid (AA) concentrations, insulin, and glucagon concentrations was followed throughout a continuous 24-h period in adult male subjects at energy balance after six days on a standardized diet and exercise program. Subjects were fasting from 2100 on day 6 to 1200 on day 7 and then fed 10 identical meals hourly until 2100. Physical exercise was performed (46% maximal oxygen uptake) between 0830 and 1000 (fasting) and in a fed state (1600-1730) on each day. The normal-protein group showed fasting plasma AA concentrations that were higher (P < 0.05) than those for the high-protein group, except for leucine, methionine, and tyrosine. Glutamine, glycine, alanine, taurine, and threonine concentrations were distinctly higher ( approximately 30% or greater) throughout the 24-h period in subjects consuming the normal- vs. the high-protein diets. Exercise appeared to increase, although not profoundly, the plasma concentrations of amino acids except for glutamate, histidine, ornithine, and tryptophan. The profound diet-related differences in plasma AA concentrations are only partially explained by differences in the renal clearance of the amino acids. We speculate on the possible metabolic basis for these findings.
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Affiliation(s)
- A H Forslund
- Department of Medical Sciences, Nutrition and Clinical Chemistry, Uppsala University, SE-75237 Uppsala, Sweden
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Metges CC, Yu YM, Cai W, Lu XM, Wong S, Regan MM, Ajami A, Young VR. Oxoproline kinetics and oxoproline urinary excretion during glycine- or sulfur amino acid-free diets in humans. Am J Physiol Endocrinol Metab 2000; 278:E868-76. [PMID: 10780943 DOI: 10.1152/ajpendo.2000.278.5.e868] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
L-5-oxoproline (L-5-OP) is an intermediate in glutathione synthesis, possibly limited by cysteine availability. Urinary 5-OP excretion has been proposed as a measure of glycine availability. We investigated whether 5 days of dietary sulfur amino acid (SAA-free) or glycine (Gly-free) restriction affects plasma kinetics of 5-OP and urinary excretion of L- and D-5-OP in 6 healthy men. On day 6, L-5-[1-(13)C]oxoproline and [3,3-(2)H(2)]cysteine were infused intravenously for 8 h (3 h fast/5 h fed). In a control study (adequate amino acid mixture), plasma oxoproline fluxes were 37.8 +/- 13.8 (SD) and 38.4 +/- 14.8 micromol x kg(-1) x h(-1); oxidation accounted for 85% of flux. Cysteine flux was 47.9 +/- 8.5 and 43.2 +/- 8.5 micromol x kg(-1) x h(-1) for fast and fed phases, respectively. Urinary excretion of L- and D-5-OP was 70 +/- 34 and 31.1 +/- 13.3 micromol/mmol creatinine, respectively, during days 3-5, and 46.4 +/- 13.9 and 22.4 +/- 8.3 micromol/mmol over the 8-h tracer study. The 5-OP flux for the Gly-free diet was higher (P = 0. 018) and tended to be higher for the SAA-free diet (P = 0.057) when compared with the control diet. Oxidation rates were higher on the Gly-free (P = 0.005) and SAA-free (P = 0.03) diets. Cysteine fluxes were lower on the the Gly-free (P = 0.01) and the SAA-free diets (P = 0.001) compared with the control diet. Rates of L-5-OP excretion were unchanged by withdrawal of SAA or Gly for 5 days but increased on day 6 (P = 0.005 and P = 0.019, respectively). Thus acute changes in the dietary availability of SAA and Gly alter oxoproline kinetics and urinary 5-OP excretion.
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Affiliation(s)
- C C Metges
- Laboratory of Human Nutrition, School of Science and Clinical Research Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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17
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Abstract
[1,2-(13)C(2)]glutamine and [ring-(2)H(5)]phenylalanine were infused for 7 h into five postabsorptive healthy subjects on two occasions. On one occasion, the tracers were infused intravenously for 3.5 h and then by a nasogastric tube for 3.5 h. The order of infusion was reversed on the other occasion. From the plasma tracer enrichment measurements at plateau during the intravenous and nasogastric infusion periods, we determined that 27 +/- 2% of the enterally delivered phenylalanine and 64 +/- 2% of the glutamine were removed on the first pass by the splanchnic bed. Glutamine flux was 303 +/- 8 micromol. kg(-1). h(-1). Of the enterally delivered [(13)C]glutamine tracer, 73 +/- 2% was recovered as exhaled CO(2) compared with 58 +/- 1% of the intravenously infused tracer. The fraction of the enterally delivered tracer that was oxidized specifically on the first pass by the splanchnic bed was 53 +/- 2%, comprising 83% of the total tracer extracted. From the appearance of (13)C in plasma glucose, we estimated that 7 and 10% of the intravenously and nasogastrically infused glutamine tracers, respectively, were converted to glucose. The results for glutamine flux and first-pass extraction were similar to our previously reported values when a [2-(15)N]glutamine tracer [Matthews DE, Morano MA, and Campbell RG, Am J Physiol Endocrinol Metab 264: E848-E854, 1993] was used. The results of [(13)C]glutamine tracer disposal demonstrate that the major fate of enteral glutamine extraction is for oxidation and that only a minor portion is used for gluconeogenesis.
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Affiliation(s)
- M Haisch
- Departments of Medicine and Chemistry, University of Vermont, Burlington, Vermont 05405, USA
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Graham TE, Sgro V, Friars D, Gibala MJ. Glutamate ingestion: the plasma and muscle free amino acid pools of resting humans. Am J Physiol Endocrinol Metab 2000; 278:E83-9. [PMID: 10644540 DOI: 10.1152/ajpendo.2000.278.1.e83] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Monosodium glutamate (MSG) ingestion is known to increase plasma glutamate concentration, and MSG infusion stimulates insulin secretion. We investigated the impact of MSG ingestion on both the plasma and intramuscular amino acid pools. Nine postprandial adults ingested MSG (150 mg/kg) and rested for 105 min. Venous blood was sampled preingestion and then every 15 min; vastus lateralis muscle biopsies were taken preingestion and at 45, 75, and 105 min postingestion. Venous plasma glutamate and aspartate concentrations increased (P </= 0.05) approximately 700-800 and 300-400%, respectively, after 30-45 min. Although several other plasma amino acids increased modestly, the rise in glutamate accounted for approximately 80% of the increase in total plasma amino acids. In addition, plasma insulin increased threefold after 15 min; this occurred before a significant increase in plasma glutamate, indicating a feed-forward stimulation from the gastrointestinal tract. The intramuscular amino acid pool was remarkably constant, with only glutamate increasing (P </= 0.05) by 3.56 mmol/kg dry wt. By 105 min, the plasma and muscle amino acids had returned to resting concentrations. This increase in muscle glutamate concentration could account for approximately 40% of the MSG ingested; we propose that resting skeletal muscle is a major sink for the glutamate and metabolizes it to aspartate.
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Affiliation(s)
- T E Graham
- Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph N1G 2W1, Canada L85 4L8.
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