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Anand SK, Governale TA, Zhang X, Razani B, Yurdagul A, Pattillo CB, Rom O. Amino Acid Metabolism and Atherosclerotic Cardiovascular Disease. THE AMERICAN JOURNAL OF PATHOLOGY 2024; 194:510-524. [PMID: 38171450 PMCID: PMC10988767 DOI: 10.1016/j.ajpath.2023.12.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Revised: 11/09/2023] [Accepted: 12/06/2023] [Indexed: 01/05/2024]
Abstract
Despite significant advances in medical treatments and drug development, atherosclerotic cardiovascular disease (ASCVD) remains a leading cause of death worldwide. Dysregulated lipid metabolism is a well-established driver of ASCVD. Unfortunately, even with potent lipid-lowering therapies, ASCVD-related deaths have continued to increase over the past decade, highlighting an incomplete understanding of the underlying risk factors and mechanisms of ASCVD. Accumulating evidence over the past decades indicates a correlation between amino acids and disease state. This review explores the emerging role of amino acid metabolism in ASCVD, uncovering novel potential biomarkers, causative factors, and therapeutic targets. Specifically, the significance of arginine and its related metabolites, homoarginine and polyamines, branched-chain amino acids, glycine, and aromatic amino acids, in ASCVD are discussed. These amino acids and their metabolites have been implicated in various processes characteristic of ASCVD, including impaired lipid metabolism, endothelial dysfunction, increased inflammatory response, and necrotic core development. Understanding the complex interplay between dysregulated amino acid metabolism and ASCVD provides new insights that may lead to the development of novel diagnostic and therapeutic approaches. Although further research is needed to uncover the precise mechanisms involved, it is evident that amino acid metabolism plays a role in ASCVD.
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Affiliation(s)
- Sumit Kumar Anand
- Department of Pathology and Translational Pathobiology, Louisiana State University Health Sciences Center-Shreveport, Shreveport, Louisiana
| | - Theresea-Anne Governale
- Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center-Shreveport, Shreveport, Louisiana
| | - Xiangyu Zhang
- Division of Cardiology and Vascular Medicine Institute, Department of Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania
| | - Babak Razani
- Division of Cardiology and Vascular Medicine Institute, Department of Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania
| | - Arif Yurdagul
- Department of Pathology and Translational Pathobiology, Louisiana State University Health Sciences Center-Shreveport, Shreveport, Louisiana; Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center-Shreveport, Shreveport, Louisiana; Center for Cardiovascular Diseases and Sciences, Louisiana State University Health Sciences Center-Shreveport, Shreveport, Louisiana
| | - Christopher B Pattillo
- Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center-Shreveport, Shreveport, Louisiana; Center for Cardiovascular Diseases and Sciences, Louisiana State University Health Sciences Center-Shreveport, Shreveport, Louisiana.
| | - Oren Rom
- Department of Pathology and Translational Pathobiology, Louisiana State University Health Sciences Center-Shreveport, Shreveport, Louisiana; Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center-Shreveport, Shreveport, Louisiana; Center for Cardiovascular Diseases and Sciences, Louisiana State University Health Sciences Center-Shreveport, Shreveport, Louisiana.
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Hsieh CH, Huang CT, Cheng YS, Hsu CH, Hsu WM, Chung YH, Liu YL, Yang TS, Chien CY, Lee YH, Huang HC, Juan HF. Homoharringtonine as a PHGDH inhibitor: Unraveling metabolic dependencies and developing a potent therapeutic strategy for high-risk neuroblastoma. Biomed Pharmacother 2023; 166:115429. [PMID: 37673018 DOI: 10.1016/j.biopha.2023.115429] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Revised: 08/22/2023] [Accepted: 08/30/2023] [Indexed: 09/08/2023] Open
Abstract
Neuroblastoma, a childhood cancer affecting the sympathetic nervous system, continues to challenge the development of potent treatments due to the limited availability of druggable targets for this aggressive illness. Recent investigations have uncovered that phosphoglycerate dehydrogenase (PHGDH), an essential enzyme for de novo serine synthesis, serves as a non-oncogene dependency in high-risk neuroblastoma. In this study, we show that homoharringtonine (HHT) acts as a PHGDH inhibitor, inducing intricate alterations in cellular metabolism, and thus providing an efficient treatment for neuroblastoma. We have experimentally verified the reliance of neuroblastoma on PHGDH and employed molecular docking, thermodynamic evaluations, and X-ray crystallography techniques to determine the bond interactions between HHT and PHGDH. Administering HHT to treat neuroblastoma resulted in effective cell elimination in vitro and tumor reduction in vivo. Metabolite and functional assessments additionally disclosed that HHT treatment suppressed de novo serine synthesis, initiating intricate metabolic reconfiguration and oxidative stress in neuroblastoma. Collectively, these discoveries highlight the potential of targeting PHGDH using HHT as a potent approach for managing high-risk neuroblastoma.
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Affiliation(s)
- Chiao-Hui Hsieh
- Department of Life Science, National Taiwan University, Taipei, Taiwan, ROC; Center for Computational and Systems Biology, National Taiwan University, Taipei, Taiwan, ROC
| | - Chen-Tsung Huang
- Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, ROC
| | - Yi-Sheng Cheng
- Department of Life Science, National Taiwan University, Taipei, Taiwan, ROC; Institute of Plant Biology, National Taiwan University, Taipei, Taiwan, ROC; Genome and Systems Biology Degree Program, National Taiwan University and Academia Sinica, Taipei, Taiwan, ROC
| | - Chun-Hua Hsu
- Genome and Systems Biology Degree Program, National Taiwan University and Academia Sinica, Taipei, Taiwan, ROC; Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan, ROC
| | - Wen-Ming Hsu
- Department of Surgery, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan, ROC
| | - Yun-Hsien Chung
- Department of Life Science, National Taiwan University, Taipei, Taiwan, ROC
| | - Yen-Lin Liu
- Department of Pediatrics, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan, ROC
| | - Tsai-Shan Yang
- Department of Surgery, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan, ROC
| | - Chia-Yu Chien
- Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan, ROC
| | - Yu-Hsuan Lee
- Department of Life Science, National Taiwan University, Taipei, Taiwan, ROC
| | - Hsuan-Cheng Huang
- Institute of Biomedical Informatics, National Yang Ming Chiao Tung University, Taipei, Taiwan, ROC.
| | - Hsueh-Fen Juan
- Department of Life Science, National Taiwan University, Taipei, Taiwan, ROC; Center for Computational and Systems Biology, National Taiwan University, Taipei, Taiwan, ROC; Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, ROC; Genome and Systems Biology Degree Program, National Taiwan University and Academia Sinica, Taipei, Taiwan, ROC; Center for Advanced Computing and Imaging in Biomedicine, Taipei, Taiwan, ROC.
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Chen CT, Shao Z, Fu Z. Dysfunctional peroxisomal lipid metabolisms and their ocular manifestations. Front Cell Dev Biol 2022; 10:982564. [PMID: 36187472 PMCID: PMC9524157 DOI: 10.3389/fcell.2022.982564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 08/17/2022] [Indexed: 11/13/2022] Open
Abstract
Retina is rich in lipids and dyslipidemia causes retinal dysfunction and eye diseases. In retina, lipids are not only important membrane component in cells and organelles but also fuel substrates for energy production. However, our current knowledge of lipid processing in the retina are very limited. Peroxisomes play a critical role in lipid homeostasis and genetic disorders with peroxisomal dysfunction have different types of ocular complications. In this review, we focus on the role of peroxisomes in lipid metabolism, including degradation and detoxification of very-long-chain fatty acids, branched-chain fatty acids, dicarboxylic acids, reactive oxygen/nitrogen species, glyoxylate, and amino acids, as well as biosynthesis of docosahexaenoic acid, plasmalogen and bile acids. We also discuss the potential contributions of peroxisomal pathways to eye health and summarize the reported cases of ocular symptoms in patients with peroxisomal disorders, corresponding to each disrupted peroxisomal pathway. We also review the cross-talk between peroxisomes and other organelles such as lysosomes, endoplasmic reticulum and mitochondria.
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Affiliation(s)
- Chuck T. Chen
- Department of Nutritional Sciences, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada
| | - Zhuo Shao
- Post-Graduate Medical Education, University of Toronto, Toronto, ON, Canada
- Division of Clinical and Metabolic Genetics, the Hospital for Sick Children, University of Toronto, Toronto, ON, Canada
- The Genetics Program, North York General Hospital, University of Toronto, Toronto, ON, Canada
| | - Zhongjie Fu
- Department of Ophthalmology, Boston Children’s Hospital, Harvard Medical School, Boston, MA, United States
- *Correspondence: Zhongjie Fu,
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Swanson MA, Miller K, Young SP, Tong S, Ghaloul‐Gonzalez L, Neira‐Fresneda J, Schlichting L, Peck C, Gabel L, Friederich MW, Van Hove JLK. Cerebrospinal fluid amino acids glycine, serine, and threonine in nonketotic hyperglycinemia. J Inherit Metab Dis 2022; 45:734-747. [PMID: 35357708 PMCID: PMC9543955 DOI: 10.1002/jimd.12500] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Revised: 03/24/2022] [Accepted: 03/28/2022] [Indexed: 01/30/2023]
Abstract
Nonketotic hyperglycinemia (NKH) is caused by deficient glycine cleavage enzyme activity and characterized by elevated brain glycine. Metabolism of glycine is connected enzymatically to serine through serine hydroxymethyltransferase and shares transporters with serine and threonine. We aimed to evaluate changes in serine and threonine in NKH patients, and relate this to clinical outcome severity. Age-related reference values were developed for cerebrospinal fluid (CSF) serine and threonine from 274 controls, and in a cross-sectional study compared to 61 genetically proven NKH patients, categorized according to outcome. CSF d-serine and l-serine levels were stereoselectively determined in seven NKH patients and compared to 29 age-matched controls. In addition to elevated CSF glycine, NKH patients had significantly decreased levels of CSF serine and increased levels of CSF threonine, even after age-adjustment. The CSF serine/threonine ratio discriminated between NKH patients and controls. The CSF glycine/serine aided in discrimination between severe and attenuated neonates with NKH. Over all ages, the CSF glycine, serine and threonine had moderate to fair correlation with outcome classes. After age-adjustment, only the CSF glycine level provided good discrimination between outcome classes. In untreated patients, d-serine was more reduced than l-serine, with a decreased d/l-serine ratio, indicating a specific impact on d-serine metabolism. We conclude that in NKH the elevation of glycine is accompanied by changes in l-serine, d-serine and threonine, likely reflecting a perturbation of the serine shuttle and metabolism, and of one-carbon metabolism. This provides additional guidance on diagnosis and prognosis, and opens new therapeutic avenues to be explored.
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Affiliation(s)
- Michael A. Swanson
- Section of Clinical Genetics and Metabolism, Department of PediatricsUniversity of ColoradoAuroraColoradoUSA
| | - Kristen Miller
- Department of Pediatrics, Child Health Biostatistics CoreUniversity of Colorado and Children's Hospital ColoradoAuroraColoradoUSA
| | - Sarah P. Young
- Division of Medical Genetics, Department of PediatricsDuke University School of MedicineDurhamNorth CarolinaUSA
| | - Suhong Tong
- Department of Pediatrics, Child Health Biostatistics CoreUniversity of Colorado and Children's Hospital ColoradoAuroraColoradoUSA
| | - Lina Ghaloul‐Gonzalez
- Division of Genetic and Genomic Medicine, Department of PediatricsUniversity of Pittsburgh School of MedicinePittsburghPennsylvaniaUSA
- Department of Human GeneticsGraduate School of Public Health, University of PittsburghPittsburghPennsylvaniaUSA
| | | | - Lisa Schlichting
- Department of Pathology and Laboratory MedicineChildren's Hospital ColoradoAuroraColoradoUSA
| | - Cheryl Peck
- Department of Pathology and Laboratory MedicineChildren's Hospital ColoradoAuroraColoradoUSA
| | - Linda Gabel
- Department of Pathology and Laboratory MedicineChildren's Hospital ColoradoAuroraColoradoUSA
| | - Marisa W. Friederich
- Section of Clinical Genetics and Metabolism, Department of PediatricsUniversity of ColoradoAuroraColoradoUSA
- Department of Pathology and Laboratory MedicineChildren's Hospital ColoradoAuroraColoradoUSA
| | - Johan L. K. Van Hove
- Section of Clinical Genetics and Metabolism, Department of PediatricsUniversity of ColoradoAuroraColoradoUSA
- Department of Pathology and Laboratory MedicineChildren's Hospital ColoradoAuroraColoradoUSA
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Anshuman Gogoi, Linkon Bharali. Conversion of Glycine to Oxalate in Presence of CuSO4⋅5H2O and Isonicotinamide. RUSS J INORG CHEM+ 2022. [DOI: 10.1134/s0036023622050072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Zhang Q, Hou Y, Bazer FW, He W, Posey EA, Wu G. Amino Acids in Swine Nutrition and Production. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1285:81-107. [PMID: 33770404 DOI: 10.1007/978-3-030-54462-1_6] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Amino acids are the building blocks of proteins in animals, including swine. With the development of new analytical methods and biochemical research, there is a growing interest in fundamental and applied studies to reexamine the roles and usage of amino acids (AAs) in swine production. In animal nutrition, AAs have been traditionally classified as nutritionally essential (EAAs) or nutritionally nonessential (NEAAs). AAs that are not synthesized de novo must be provided in diets. However, NEAAs synthesized by cells of animals are more abundant than EAAs in the body, but are not synthesized de novo in sufficient amounts for the maximal productivity or optimal health (including resistance to infectious diseases) of swine. This underscores the conceptual limitations of NEAAs in swine protein nutrition. Notably, the National Research Council (NRC 2012) has recognized both arginine and glutamine as conditionally essential AAs for pigs to improve their growth, development, reproduction, and lactation. Results of recent work have also provided compelling evidence for the nutritional essentiality of glutamate, glycine, and proline for young pigs. The inclusion of so-called NEAAs in diets can help balance AAs in diets, reduce the dietary levels of EAAs, and protect the small intestine from oxidative stress, while enhancing the growth performance, feed efficiency, and health of pigs. Thus, both EAAs and NEAAs are needed in diets to meet the requirements of pigs. This notion represents a new paradigm shift in our understanding of swine protein nutrition and is transforming pork production worldwide.
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Affiliation(s)
- Qian Zhang
- Hubei International Scientific and Technological Cooperation Base of Animal Nutrition and Gut Health, Wuhan Polytechnic University, Wuhan, China
| | - Yongqing Hou
- Hubei International Scientific and Technological Cooperation Base of Animal Nutrition and Gut Health, Wuhan Polytechnic University, Wuhan, China.
| | - Fuller W Bazer
- Department of Animal Science, Texas A&M University, College Station, TX, USA
| | - Wenliang He
- Department of Animal Science, Texas A&M University, College Station, TX, USA
| | - Erin A Posey
- Department of Animal Science, Texas A&M University, College Station, TX, USA
| | - Guoyao Wu
- Department of Animal Science, Texas A&M University, College Station, TX, USA.
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Tan YL, Sou NL, Tang FY, Ko HA, Yeh WT, Peng JH, Chiang EPI. Tracing Metabolic Fate of Mitochondrial Glycine Cleavage System Derived Formate In Vitro and In Vivo. Int J Mol Sci 2020; 21:ijms21228808. [PMID: 33233834 PMCID: PMC7699879 DOI: 10.3390/ijms21228808] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Revised: 11/04/2020] [Accepted: 11/05/2020] [Indexed: 02/07/2023] Open
Abstract
Folate-mediated one-carbon (1C) metabolism is a major target of many therapies in human diseases. Studies have focused on the metabolism of serine 3-carbon as it serves as a major source for 1C units. The serine 3-carbon enters the mitochondria transferred by folate cofactors and eventually converted to formate and serves as a major building block for cytosolic 1C metabolism. Abnormal glycine metabolism has been reported in many human pathological conditions. The mitochondrial glycine cleavage system (GCS) catalyzes glycine degradation to CO2 and ammonium, while tetrahydrofolate (THF) is converted into 5,10-methylene-THF. GCS accounts for a substantial proportion of whole-body glycine flux in humans, yet the particular metabolic route of glycine 2-carbon recycled from GCS during mitochondria glycine decarboxylation in hepatic or bone marrow 1C metabolism is not fully investigated, due to the limited accessibility of human tissues. Labeled glycine at 2-carbon was given to humans and primary cells in previous studies for investigating its incorporations into purines, its interconversion with serine, or the CO2 production in the mitochondria. Less is known on the metabolic fate of the glycine 2-carbon recycled from the GCS; hence, a model system tracing its metabolic fate would help in this regard. We took the direct approach of isotopic labeling to further explore the in vitro and in vivo metabolic fate of the 2-carbon from [2-13C]glycine and [2-13C]serine. As the 2-carbon of glycine and serine is decarboxylated and catabolized via the GCS, the original 13C-labeled 2-carbon is transferred to THF and yield methyleneTHF in the mitochondria. In human hepatoma cell-lines, 2-carbon from glycine was found to be incorporated into deoxythymidine (dTMP, dT + 1), M + 3 species of purines (deoxyadenine, dA and deoxyguanine, dG), and methionine (Met + 1). In healthy mice, incorporation of GCS-derived formate from glycine 2-carbon was found in serine (Ser + 2 via cytosolic serine hydroxy methyl transferase), methionine, dTMP, and methylcytosine (mC + 1) in bone marrow DNA. In these experiments, labeled glycine 2-carbon directly incorporates into Ser + 1, A + 2, and G + 2 (at C2 and C8 of purine) in the cytosol. It is noteworthy that since the serine 3-carbon is unlabeled in these experiments, the isotopic enrichments in dT + 1, Ser + 2, dA + 3, dG + 3, and Met + 1 solely come from the 2-carbon of glycine/serine recycled from GCS, re-enters the cytosolic 1C metabolism as formate, and then being used for cytosolic syntheses of serine, dTMP, purine (M + 3) and methionine. Taken together, we established model systems and successfully traced the metabolic fate of mitochondrial GCS-derived formate from glycine 2-carbon in vitro and in vivo. Nutritional supply significantly alters formate generation from GCS. More GCS-derived formate was used in hepatic serine and methionine syntheses, whereas more GCS-derived formate was used in dTMP synthesis in the bone marrow, indicating that the utilization and partitioning of GCS-derived 1C unit are tissue-specific. These approaches enable better understanding concerning the utilization of 1C moiety generated from mitochondrial GCS that can help to further elucidate the role of GCS in human disease development and progression in future applications. More studies on GCS using these approaches are underway.
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Affiliation(s)
- Yee-Ling Tan
- Food Science and Biotechnology, National Chung Hsing University (NCHU), Taichung 402, Taiwan; (Y.-L.T.); (N.-L.S.); (H.-A.K.); (W.-T.Y.); (J.-H.P.)
| | - Nga-Lai Sou
- Food Science and Biotechnology, National Chung Hsing University (NCHU), Taichung 402, Taiwan; (Y.-L.T.); (N.-L.S.); (H.-A.K.); (W.-T.Y.); (J.-H.P.)
- Innovation and Development Center of Sustainable Agriculture (IDCSA), National Chung Hsing University (NCHU), Taichung 402, Taiwan
| | - Feng-Yao Tang
- Department of Nutrition, China Medical University, Taichung 402, Taiwan;
| | - Hsin-An Ko
- Food Science and Biotechnology, National Chung Hsing University (NCHU), Taichung 402, Taiwan; (Y.-L.T.); (N.-L.S.); (H.-A.K.); (W.-T.Y.); (J.-H.P.)
| | - Wei-Ting Yeh
- Food Science and Biotechnology, National Chung Hsing University (NCHU), Taichung 402, Taiwan; (Y.-L.T.); (N.-L.S.); (H.-A.K.); (W.-T.Y.); (J.-H.P.)
| | - Jian-Hau Peng
- Food Science and Biotechnology, National Chung Hsing University (NCHU), Taichung 402, Taiwan; (Y.-L.T.); (N.-L.S.); (H.-A.K.); (W.-T.Y.); (J.-H.P.)
- Innovation and Development Center of Sustainable Agriculture (IDCSA), National Chung Hsing University (NCHU), Taichung 402, Taiwan
- Microbial Genomics Ph.D. Graduate Program, National Chung Hsing University (NCHU), Taichung 402, Taiwan
| | - En-Pei Isabel Chiang
- Food Science and Biotechnology, National Chung Hsing University (NCHU), Taichung 402, Taiwan; (Y.-L.T.); (N.-L.S.); (H.-A.K.); (W.-T.Y.); (J.-H.P.)
- Department of Nutrition, China Medical University, Taichung 402, Taiwan;
- Microbial Genomics Ph.D. Graduate Program, National Chung Hsing University (NCHU), Taichung 402, Taiwan
- Department of Food Science and Biotechnology, National Chung Hsing University, Taichung 402, Taiwan
- Correspondence: ; Tel.: +886-4-22853049; Fax: +886-4-22876211
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Zaric BL, Radovanovic JN, Gluvic Z, Stewart AJ, Essack M, Motwalli O, Gojobori T, Isenovic ER. Atherosclerosis Linked to Aberrant Amino Acid Metabolism and Immunosuppressive Amino Acid Catabolizing Enzymes. Front Immunol 2020; 11:551758. [PMID: 33117340 PMCID: PMC7549398 DOI: 10.3389/fimmu.2020.551758] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Accepted: 08/25/2020] [Indexed: 02/05/2023] Open
Abstract
Cardiovascular disease is the leading global health concern and responsible for more deaths worldwide than any other type of disorder. Atherosclerosis is a chronic inflammatory disease in the arterial wall, which underpins several types of cardiovascular disease. It has emerged that a strong relationship exists between alterations in amino acid (AA) metabolism and the development of atherosclerosis. Recent studies have reported positive correlations between levels of branched-chain amino acids (BCAAs) such as leucine, valine, and isoleucine in plasma and the occurrence of metabolic disturbances. Elevated serum levels of BCAAs indicate a high cardiometabolic risk. Thus, BCAAs may also impact atherosclerosis prevention and offer a novel therapeutic strategy for specific individuals at risk of coronary events. The metabolism of AAs, such as L-arginine, homoarginine, and L-tryptophan, is recognized as a critical regulator of vascular homeostasis. Dietary intake of homoarginine, taurine, and glycine can improve atherosclerosis by endothelium remodeling. Available data also suggest that the regulation of AA metabolism by indoleamine 2,3-dioxygenase (IDO) and arginases 1 and 2 are mediated through various immunological signals and that immunosuppressive AA metabolizing enzymes are promising therapeutic targets against atherosclerosis. Further clinical studies and basic studies that make use of animal models are required. Here we review recent data examining links between AA metabolism and the development of atherosclerosis.
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Affiliation(s)
- Bozidarka L. Zaric
- Department of Radiobiology and Molecular Genetics, “VINČA” Institute of Nuclear Sciences - National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - Jelena N. Radovanovic
- Department of Radiobiology and Molecular Genetics, “VINČA” Institute of Nuclear Sciences - National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia
| | - Zoran Gluvic
- Department of Endocrinology and Diabetes, Faculty of Medicine, University Clinical-Hospital Centre Zemun-Belgrade, University of Belgrade, Belgrade, Serbia
| | - Alan J. Stewart
- School of Medicine, University of St Andrews, St Andrews, United Kingdom
| | - Magbubah Essack
- Computer, Electrical and Mathematical Sciences and Engineering Division (CEMSE), Computational Bioscience Research Center, Computer (CBRC), King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
| | - Olaa Motwalli
- College of Computing and Informatics, Saudi Electronic University (SEU), Medina, Saudi Arabia
| | - Takashi Gojobori
- Computer, Electrical and Mathematical Sciences and Engineering Division (CEMSE), Computational Bioscience Research Center, Computer (CBRC), King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
- Biological and Environmental Sciences and Engineering Division (BESE), King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
| | - Esma R. Isenovic
- Department of Radiobiology and Molecular Genetics, “VINČA” Institute of Nuclear Sciences - National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia
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Multifarious Beneficial Effect of Nonessential Amino Acid, Glycine: A Review. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2017; 2017:1716701. [PMID: 28337245 PMCID: PMC5350494 DOI: 10.1155/2017/1716701] [Citation(s) in RCA: 109] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 02/07/2017] [Accepted: 02/07/2017] [Indexed: 02/06/2023]
Abstract
Glycine is most important and simple, nonessential amino acid in humans, animals, and many mammals. Generally, glycine is synthesized from choline, serine, hydroxyproline, and threonine through interorgan metabolism in which kidneys and liver are the primarily involved. Generally in common feeding conditions, glycine is not sufficiently synthesized in humans, animals, and birds. Glycine acts as precursor for several key metabolites of low molecular weight such as creatine, glutathione, haem, purines, and porphyrins. Glycine is very effective in improving the health and supports the growth and well-being of humans and animals. There are overwhelming reports supporting the role of supplementary glycine in prevention of many diseases and disorders including cancer. Dietary supplementation of proper dose of glycine is effectual in treating metabolic disorders in patients with cardiovascular diseases, several inflammatory diseases, obesity, cancers, and diabetes. Glycine also has the property to enhance the quality of sleep and neurological functions. In this review we will focus on the metabolism of glycine in humans and animals and the recent findings and advances about the beneficial effects and protection of glycine in different disease states.
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Glycine metabolism in animals and humans: implications for nutrition and health. Amino Acids 2013; 45:463-77. [PMID: 23615880 DOI: 10.1007/s00726-013-1493-1] [Citation(s) in RCA: 432] [Impact Index Per Article: 39.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2013] [Accepted: 04/02/2013] [Indexed: 01/01/2023]
Abstract
Glycine is a major amino acid in mammals and other animals. It is synthesized from serine, threonine, choline, and hydroxyproline via inter-organ metabolism involving primarily the liver and kidneys. Under normal feeding conditions, glycine is not adequately synthesized in birds or in other animals, particularly in a diseased state. Glycine degradation occurs through three pathways: the glycine cleavage system (GCS), serine hydroxymethyltransferase, and conversion to glyoxylate by peroxisomal D-amino acid oxidase. Among these pathways, GCS is the major enzyme to initiate glycine degradation to form ammonia and CO2 in animals. In addition, glycine is utilized for the biosynthesis of glutathione, heme, creatine, nucleic acids, and uric acid. Furthermore, glycine is a significant component of bile acids secreted into the lumen of the small intestine that is necessary for the digestion of dietary fat and the absorption of long-chain fatty acids. Glycine plays an important role in metabolic regulation, anti-oxidative reactions, and neurological function. Thus, this nutrient has been used to: (1) prevent tissue injury; (2) enhance anti-oxidative capacity; (3) promote protein synthesis and wound healing; (4) improve immunity; and (5) treat metabolic disorders in obesity, diabetes, cardiovascular disease, ischemia-reperfusion injuries, cancers, and various inflammatory diseases. These multiple beneficial effects of glycine, coupled with its insufficient de novo synthesis, support the notion that it is a conditionally essential and also a functional amino acid for mammals (including pigs and humans).
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Lamers Y, Williamson J, Gilbert LR, Stacpoole PW, Gregory JF. Glycine turnover and decarboxylation rate quantified in healthy men and women using primed, constant infusions of [1,2-(13)C2]glycine and [(2)H3]leucine. J Nutr 2007; 137:2647-52. [PMID: 18029478 PMCID: PMC5833992 DOI: 10.1093/jn/137.12.2647] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Glycine plays several roles in human metabolism, e.g. as a 1-carbon donor, in purine synthesis, and as a component of glutathione. Glycine is decarboxylated via the glycine cleavage system (GCS) that yields concurrent generation of a 1-carbon unit as 5,10-methylenetetrahydrofolate (methyleneTHF). Serine hydroxymethyltransferase (SHMT) catalyzes the interconversion of glycine and serine, another 1-carbon donor. The quantitative role of glycine in human 1-carbon metabolism has received little attention. The aim of this protocol was to quantify whole body glycine flux, glycine to serine flux, and rate of glycine cleavage in humans. A primed, constant infusion with 9.26 micromol x kg(-1) x h(-1) [1,2-(13)C2]glycine and 1.87 micromol x kg(-1) x h(-1) [(2)H3]leucine was used to quantify the kinetic behavior of glycine in young, healthy volunteers (n = 5) in a fed state. The isotopic enrichment of infused tracers and metabolic products in plasma, as well as breath (13)CO2 enrichment, were determined for use in kinetic analysis. Serine synthesis by direct conversion from glycine via SHMT occurred at 193 +/- 28 micromol x kg(-1) x h(-1) (mean +/- SEM), which comprised 41% of the 463 +/- 55 micromol x kg(-1) x h(-1) total glycine flux. Nearly one-half (46%) of the glycine-to-serine conversion occurred using GCS-derived methyleneTHF 1-carbon units. Based on breath (13)CO2 measurement, glycine decarboxylation (190 +/- 41 micromol x kg(-1) x h(-1)) accounted for 39 +/- 6% of whole body glycine flux. This study is the first to our knowledge to quantify human glycine cleavage and glycine-to-serine SHMT kinetics. GCS is responsible for a substantial proportion of whole body glycine flux and constitutes a major route for the generation of 1-carbon units.
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Affiliation(s)
- Yvonne Lamers
- Food Science and Human Nutrition Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL
| | - Jerry Williamson
- Food Science and Human Nutrition Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL
| | - Lesa R Gilbert
- Division of Endocrinology and Metabolism, Department of Medicine, University of Florida, Gainesville, FL
| | - Peter W Stacpoole
- Division of Endocrinology and Metabolism, Department of Medicine, University of Florida, Gainesville, FL,Department of Biochemistry and Molecular Biology, College of Medicine, University of Florida, Gainesville, FL
| | - Jesse F Gregory
- Food Science and Human Nutrition Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL
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Narkewicz MR, Jones G, Thompson H, Kolhouse F, Fennessey PV. Folate cofactors regulate serine metabolism in fetal ovine hepatocytes. Pediatr Res 2002; 52:589-94. [PMID: 12357055 DOI: 10.1203/00006450-200210000-00020] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The fetal liver is the primary site of fetal serine production. The regulation of this unique fetal hepatic serine production is unknown. We hypothesized that serine production would be responsive to folate cofactor supply or hormonal regulation. To test this hypothesis, we determined the effect of key folate cofactors and insulin and glucagon on serine and glycine metabolism in primary culture of fetal ovine hepatocytes. Hepatocytes were cultured in serum-free, low-folate media [5 nM 5-methyl-tetrahydrofolate (THF)] with or without 50 nM 5,10-methylene-THF (MTHF) or 5-formyl-THF (FTHF). Serine and glycine production (P) and utilization (U) were determined by stable isotope dilution with [1-(13)C]serine and [1-(13)C]glycine for 24 h. The effect of insulin (1 microM) or glucagon (1 micro M) was determined in a similar manner. Under basal conditions, serine P (43.2 +/- 5.1 micromol/mg DNA per 24 h) is greater than serine U (24.1 +/- 3.1 micromol/mg DNA per 24 h), whereas glycine U (27.3 +/- 3.0 micromol/mg DNA per 24 h) exceeds glycine P (16.7 +/- 1.9 micromol/mg DNA per 24 h). MTHF results in a significant decrease in serine U (16.0 +/- 2.7 micromol/mg DNA per 24 h; p = 0.02 versus low folate), with no change in serine P. FTHF reduces serine P (36.2 +/- 4.9 micromol/mg DNA per 24 h; p = 0.01), but does not alter serine U. There were no effects on glycine metabolism with 50 nM MTHF or FTHF. Serine P and U were inversely correlated whereas glycine P and U were directly correlated with the media concentration of MTHF or FTHF. Glucagon treatment increased serine U by 260 +/- 65% versus low folate (p = 0.0004) but did not change serine P. Insulin treatment led to parallel increases in both serine P and U. Both folate cofactor availability and hormone concentrations regulate serine metabolism in the fetal liver. We speculate that serine metabolism may be a marker of fetal hepatic folate cofactor supply.
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Affiliation(s)
- Michael R Narkewicz
- Department of Pediatrics, Section of Pediatric Gastroenterology, University of Colorado School of Medicine and The Children's Hospital, Denver, Colorado 80218, USA.
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13
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Thompson HR, Jones GM, Narkewicz MR. Ontogeny of hepatic enzymes involved in serine- and folate-dependent one-carbon metabolism in rabbits. Am J Physiol Gastrointest Liver Physiol 2001; 280:G873-8. [PMID: 11292595 DOI: 10.1152/ajpgi.2001.280.5.g873] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Serine occupies a central position in folate-dependent, one-carbon metabolism through 5,10-methylenetetrahydrofolate (MTHF) and 5-formyltetrahydrofolate (FTHF). We characterized the ontogeny of the specific activity of key enzymes involved in serine, 5,10-MTHF, and 5-FTHF metabolism: methenyltetrahydrofolate synthetase (MTHFS), MTHF reductase (MTHFR), the glycine cleavage system (GCS), methionine synthase (MS), and serine hydroxymethyltransferase (SHMT) in rabbit liver, placenta, brain, and kidney. In liver, MTHFS activity is low in the fetus (0.36 +/- 0.07 nmol. min(-1). mg protein(-1)), peaks at 3 wk (1.48 +/- 0.50 nmol. min(-1). mg protein(-1)), and then decreases to adult levels (1.13 +/- 0.32 nmol. min(-1). mg protein(-1)). MTHFR activity is highest early in gestation (24.9 +/- 2.4 nmol. h(-1). mg protein(-1)) and declines rapidly by birth (4.7 +/- 1.3 nmol. h(-1). mg protein(-1)). MS is highest during fetal life and declines after birth. Cytosolic SHMT activity does not vary during development, but mitochondrial SHMT peaks at 23 days. GCS activity is high in the fetus and the neonate, declining after weaning. In placenta and brain, all activities are low throughout gestation. Cytosolic and mitochondrial SHMT activities are low in kidney and rise after weaning, whereas MTHFS is low throughout development. These data suggest that the liver is the primary site of activity for these enzymes. Throughout development, there are multiple potential sources for production of 5,10-MTHF, but early in gestation high MTHFR activity and low MTHFS activity could reduce 5,10-MTHF availability.
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Affiliation(s)
- H R Thompson
- Department of Pediatrics, Section of Pediatric Gastroenterology, Hepatology, and Nutrition, University of Colorado School of Medicine, Denver, CO 80218, USA
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14
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Gregory JF, Cuskelly GJ, Shane B, Toth JP, Baumgartner TG, Stacpoole PW. Primed, constant infusion with [2H3]serine allows in vivo kinetic measurement of serine turnover, homocysteine remethylation, and transsulfuration processes in human one-carbon metabolism. Am J Clin Nutr 2000; 72:1535-41. [PMID: 11101483 DOI: 10.1093/ajcn/72.6.1535] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND One-carbon metabolism involves both mitochondrial and cytosolic forms of folate-dependent enzymes in mammalian cells, but few in vivo data exist to characterize the biochemical processes involved. OBJECTIVE We conducted a stable-isotopic investigation to determine the fates of exogenous serine and serine-derived one-carbon units in homocysteine remethylation in hepatic and whole-body metabolism. DESIGN A healthy man aged 23 y was administered [2,3,3-(2)H(3)]serine and [5,5,5-(2)H(3)]leucine by intravenous primed, constant infusion. Serial plasma samples were analyzed to determine the isotopic enrichment of free glycine, serine, leucine, methionine, and cystathionine. VLDL apolipoprotein B-100 served as an index of liver free amino acid labeling. RESULTS [(2)H(1)]Methionine and [(2)H(2)]methionine were labeled through homocysteine remethylation. We propose that [(2)H(2)]methionine occurs by remethylation with [(2)H(2)]methyl groups (as 5-methyltetrahydrofolate) formed only from cytosolic processing of [(2)H(3)]serine, whereas [(2)H(1)]methionine is formed with labeled one-carbon units from mitochondrial oxidation of C-3 serine to [(2)H(1)]formate to yield cytosolic [(2)H(1)]methyl groups. The labeling pattern of cystathionine formed from homocysteine and labeled serine suggests that cystathionine is derived mainly from a serine pool different from that used in apolipoprotein B-100 synthesis. CONCLUSIONS The appearance of both [(2)H(1)]- and [(2)H(2)]methionine forms indicates that both cytosolic and mitochondrial metabolism of exogenous serine generates carbon units in vivo for methyl group production and homocysteine remethylation. This study also showed the utility of serine infusion and indicated functional roles of cytosolic and mitochondrial compartments in one-carbon metabolism.
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Affiliation(s)
- J F Gregory
- Department of Nutritional Sciences, University of California Berkeley, Berkeley, CA, USA.
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15
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D'Souza DC, Gil R, Cassello K, Morrissey K, Abi-Saab D, White J, Sturwold R, Bennett A, Karper LP, Zuzarte E, Charney DS, Krystal JH. IV glycine and oral D-cycloserine effects on plasma and CSF amino acids in healthy humans. Biol Psychiatry 2000; 47:450-62. [PMID: 10704956 DOI: 10.1016/s0006-3223(99)00133-x] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND The amino acid glycine, modulates neurotransmission via actions at GLY-A receptor and GLY-B receptor. The latter are coagonist sites associated with N-Methyl-D-Aspartate (NMDA) glutamate receptors. The central bioavailability of peripherally administered glycine has not been adequately characterized in humans. METHODS Healthy human subjects were administered either oral D-cycloserine (50 mg or placebo) and intravenous glycine (saline, 100 mg/kg or 200 mg/kg) in random order over 4 test days under double-blind conditions. Cerebrospinal fluid was collected by lumbar puncture performed on the first test day was analyzed to determine amino acid levels. The acoustic startle response was measured on the second test day. RESULTS Intravenous glycine dose-dependently increased both serum and CSF glycine and serine levels. Neither glycine nor DCS produced any significant effects on behavior, cognition or the acoustic startle response. Neither IV glycine nor DCS were associated with any toxicity. CONCLUSIONS Thus, peripheral glycine administration raised CSF glycine levels without producing any clear central nervous system effects. Glycine and D-cycloserine did not worsen cognitive test performance and did not induce behavioral symptoms on their own. The possibility that glycine and D-cycloserine enhanced cognitive test performance cannot be excluded given the psychometric limitations of the test battery.
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Affiliation(s)
- D C D'Souza
- Schizophrenia Biological Research Center, West Haven Veterans Affairs Medical Center, West Haven, CT, USA
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Narkewicz MR, Moores RR, Battaglia FC, Frerman FF. Ontogeny of serine hydroxymethyltransferase isoenzymes in fetal sheep liver, kidney, and placenta. Mol Genet Metab 1999; 68:473-80. [PMID: 10607477 DOI: 10.1006/mgme.1999.2932] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Serine is an amino acid that is not transported from the placenta to the ovine fetus. Thus, fetal plasma serine levels may be controlled by flux through their relevant biosynthetic pathways. This study was designed to determine, in fetal sheep tissues, the ontogeny of the three key enzymes in the biosynthetic pathway for serine, the cytosolic (c) and mitochondrial (m) isoforms of serine hydroxymethyltransferase (SHMT), phosphoglycerate dehydrogenase (PGD), and phosphoserine aminotransferase (PSAT). PGD and PSAT activity did not vary during gestation in either liver (PSAT, 9.4 +/- 1.3 nmol/min/mg cytosolic protein; and PGD, 76 +/- 10 mU/mg protein) or placenta (PGD, 8.0 +/- 3.6 mU/mg protein). In the liver, cSHMT activity was low early in gestation (0.6 +/- 0.5 nmol/min/mg protein at 45 days), rose in the last one-third of gestation, and peaked in the newborn period (25 +/- 3 nmol/min/mg protein at 1 week of age). Hepatic cSHMT RNA levels parallel the activity pattern. Mitochondrial SHMT was stable throughout gestation and with low constant mSHMT RNA levels. In contrast, the kidney and placenta had high mSHMT and steady low cSHMT activity throughout gestation. These data support the possible role of SHMT in the fetal control of plasma serine levels. While cSHMT may contribute to fetal hepatic serine production, its activity pattern does not support a primary role in the control of fetal hepatic serine biosynthesis. In the placenta, mSHMT may be important for glycine production from serine.
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Affiliation(s)
- M R Narkewicz
- Department of Pediatrics, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA
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Verleysdonk S, Martin H, Willker W, Leibfritz D, Hamprecht B. Rapid uptake and degradation of glycine by astroglial cells in culture: synthesis and release of serine and lactate. Glia 1999; 27:239-48. [PMID: 10457370 DOI: 10.1002/(sici)1098-1136(199909)27:3<239::aid-glia5>3.0.co;2-k] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Free glycine is known to have vital functions in the mammalian brain, where it serves mainly as both neurotransmitter and neuromodulator. Despite its importance, little is known about the metabolic pathways of glycine synthesis and degradation in the central nervous system. In this study, the pathway of glycine metabolism in astroglia-rich primary cultures from rat brain was examined. The cells were allowed to degrade glycine in the presence of [U-(14)C]glycine, [U-(13)C]glycine or [(15)N]glycine. The resulting intra- and extracellular metabolites were analyzed both by high-performance liquid chromatography and by (13)C/(15)N nuclear magnetic resonance spectroscopy. Glycine was rapidly consumed in a process obeying first-order kinetics. The initial glycine consumption rate was 0.47 nmol per mg protein. The half-life of glycine radiolabel in the incubation medium was shorter than that of glycine mass. This suggests that glycine is produced from endogenous sources and released simultaneously with glycine uptake and metabolism. As the main metabolites of the glycine carbon skeleton in astroglia-rich primary cultures from rat brain, serine and lactate were released during glycine consumption. The main metabolite containing the glycine amino nitrogen was glutamine. To establish a metabolic pathway from glycine to serine in neural tissue, homogenates of rat brain and of neural primary cultures were assayed for their content of serine hydroxymethyltransferase (SHMT) and glycine cleavage system (GCS). SHMT activity was present in homogenates of rat brain as well as of astroglia-rich and neuron-rich primary cultures, whereas GCS activity was detectable only in homogenates of rat brain and astroglia-rich primary culture. Of the two known SHMT isoenzymes, only the mitochondrial form was found in rat brain homogenate. It is proposed that, in neural tissue, glycine is metabolized by the combined action of SHMT and the GCS. Owing to the absence of the GCS from neurons, astrocytes appear to be the only site of this part of glycine metabolism in brain. However, neurons are able to utilize as energy source the lactate formed by astroglial cells in this metabolic pathway.
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Affiliation(s)
- S Verleysdonk
- Physiologisch-chemisches Institut der Universität, Tübingen, Germany
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18
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Narkewicz MR, Thureen PJ, Sauls SD, Tjoa S, Nikolayevsky N, Fennessey PV. Serine and glycine metabolism in hepatocytes from mid gestation fetal lambs. Pediatr Res 1996; 39:1085-90. [PMID: 8725274 DOI: 10.1203/00006450-199606000-00025] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Using stable isotopes of serine, glycine, and glutamine, the metabolism of serine and glycine was investigated in primary hepatocytes from six mid-gestation fetal lambs (mean gestational age = 81 +/- 6 d, normal gestation = 145 d). Serine production was 6.84 +/- 1.22 mumol/24 h/mg of DNA and exceeded serine utilization (3.76 +/- 1.44 mumol/24 h/mg of DNA) with a resultant net increase in medium serine of 2.58 +/- 1.70 mumol/24 h/mg of DNA. In contrast, glycine production (6.84 +/- 1.16 mumol/24 h/mg of DNA) was less than glycine utilization (12.10 +/- 1.78 mumol/24 h/mg of DNA) with a net decline in medium glycine of -5.44 +/- 2.03 mumol/24 h/mg of DNA. Of the serine produced, 50.4 +/- 4.3% was derived from glycine via the action of serine hydroxymethyltransferase (SHMT) and the glycine cleavage enzyme complex (GCS). Increasing the medium serine concentration resulted in an increase in serine utilization and sparing of the utilization of other amino acids. Biosynthesis of glycine from serine accounts for only 18.1 +/- 5.6% of glycine production, and this percentage is not affected by changes in medium serine concentration. Using 2.5-[15N2]glutamine as the tracer, an estimated 18 +/- 7% of serine production was derived from transamination reactions. The specific activity of both cytosolic and mitochondrial SHMT was constant for the duration of the cultures. We conclude that, in mid-gestation fetal ovine hepatocytes, there is net production of serine (with glycine as the primary metabolic source of this serine biosynthesis) and net glycine utilization. These data suggest that flux through SHMT and GCS accounts for 50% of serine biosynthesis in mid-gestation fetal ovine hepatocytes. The sparing of the utilization of other amino acids by serine suggests that serine a conditionally essential amino acid for the mid-gestation fetal liver.
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Affiliation(s)
- M R Narkewicz
- Department of Pediatrics, University of Colorado Health Sciences Center, Denver 80262, USA
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