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De Guingand DL, Ellery SJ, Davies-Tuck ML, Dickinson H. Creatine and pregnancy outcomes, a prospective cohort study in low-risk pregnant women: study protocol. BMJ Open 2019; 9:e026756. [PMID: 30647050 PMCID: PMC6340624 DOI: 10.1136/bmjopen-2018-026756] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
INTRODUCTION The creatine kinase circuit is central to the regulation of high-energy phosphate metabolism and the maintenance of cellular energy turnover. This circuit is fuelled by creatine, an amino acid derivative that can be obtained from a diet containing animal products, and by synthesis in the body de novo. A recent retrospective study conducted in a cohort of 287 pregnant women determined that maternal excreted levels of creatine may be associated with fetal growth. This prospective study aims to overcome some of the limitations associated with the previous study and thoroughly characterise creatine homeostasis throughout gestation in a low-risk pregnant population. METHODS AND ANALYSIS This study is recruiting women with a singleton low-risk pregnancy who are attending Monash Health, in Melbourne, Australia. Maternal blood and urine samples, along with dietary surveys, are collected at five time points during pregnancy and then at delivery. Cord blood and placenta (including membranes and cord) are collected at birth. A biobank of tissue samples for future research is being established. Primary outcome measures will include creatine, creatine kinase and associated metabolites in antenatal bloods and urine, cord bloods and placenta, along with molecular analysis of the creatine transporter (SLC6A8) and synthesising enzymes L - arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT) in placental tissues. Secondary outcome measures include dietary protein intake over pregnancy and any associations with maternal creatine, pregnancy events and birth outcomes. ETHICS AND DISSEMINATION Ethical approval was granted in August 2015 from Monash Health (Ref: 14140B) and Monash University (Ref: 7785). Study outcomes will be disseminated at international conferences and published in peer-reviewed scientific journals. TRIAL REGISTRATION NUMBER ACTRN12618001558213; Pre-results.
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Affiliation(s)
- Deborah L De Guingand
- The Ritchie Centre, Hudson Institute of Medical Research and Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
| | - Stacey J Ellery
- The Ritchie Centre, Hudson Institute of Medical Research and Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
| | - Miranda L Davies-Tuck
- The Ritchie Centre, Hudson Institute of Medical Research and Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
| | - Hayley Dickinson
- The Ritchie Centre, Hudson Institute of Medical Research and Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
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Joncquel-Chevalier Curt M, Bout MA, Fontaine M, Kim I, Huet G, Bekri S, Morin G, Moortgat S, Moerman A, Cuisset JM, Cheillan D, Vamecq J. Functional assessment of creatine transporter in control and X-linked SLC6A8-deficient fibroblasts. Mol Genet Metab 2018; 123:463-471. [PMID: 29478817 DOI: 10.1016/j.ymgme.2018.02.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 02/15/2018] [Accepted: 02/15/2018] [Indexed: 01/01/2023]
Abstract
Creatine transporter is currently the focus of renewed interest with emerging roles in brain neurotransmission and physiology, and the bioenergetics of cancer metastases. We here report on amendments of a standard creatine uptake assay which might help clinical chemistry laboratories to extend their current range of measurements of creatine and metabolites in body fluids to functional enzyme explorations. In this respect, short incubation times and the use of a stable-isotope-labeled substrate (D3-creatine) preceded by a creatine wash-out step from cultured fibroblast cells by removal of fetal bovine serum (rich in creatine) from the incubation medium are recommended. Together, these measures decreased, by a first order of magnitude, creatine concentrations in the incubation medium at the start of creatine-uptake studies and allowed to functionally discriminate between 4 hemizygous male and 4 heterozygous female patients with X-linked SLC6A8 deficiency, and between this cohort of eight patients and controls. The functional assay corroborated genetic diagnosis of SLC6A8 deficiency. Gene anomalies in our small cohort included splicing site (c.912G > A [p.Ile260_Gln304del], c.778-2A > G and c.1495 + 2 T > G), substitution (c.407C > T) [p.Ala136Val] and deletion (c.635_636delAG [p.Glu212Valfs*84] and c.1324delC [p.Gln442Lysfs*21]) variants with reduced creatine transporter function validating their pathogenicity, including that of a previously unreported c.1324delC variant. The present assay adaptations provide an easy, reliable and discriminative manner for exploring creatine transporter activity and disease variations. It might apply to drug testing or other evaluations in the genetic and metabolic horizons covered by the emerging functions of creatine and its transporter, in a way, however, requiring and completed by additional studies on female patients and blood-brain barrier permeability properties of selected compounds. As a whole, the proposed assay of creatine transporter positively adds to currently existing measurements of this transporter activity, and determining on a large scale the extent of its exact suitability to detect female patients should condition in the future its transfer in clinical practice.
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MESH Headings
- Adolescent
- Brain Diseases, Metabolic, Inborn/genetics
- Brain Diseases, Metabolic, Inborn/metabolism
- Brain Diseases, Metabolic, Inborn/pathology
- Case-Control Studies
- Child
- Child, Preschool
- Cohort Studies
- Creatine/deficiency
- Creatine/genetics
- Creatine/metabolism
- Female
- Fibroblasts/metabolism
- Fibroblasts/pathology
- Follow-Up Studies
- Humans
- Infant
- Male
- Mental Retardation, X-Linked/genetics
- Mental Retardation, X-Linked/metabolism
- Mental Retardation, X-Linked/pathology
- Mutation
- Nerve Tissue Proteins/deficiency
- Nerve Tissue Proteins/genetics
- Plasma Membrane Neurotransmitter Transport Proteins/deficiency
- Plasma Membrane Neurotransmitter Transport Proteins/genetics
- Plasma Membrane Neurotransmitter Transport Proteins/metabolism
- Prognosis
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Affiliation(s)
- Marie Joncquel-Chevalier Curt
- Department of Biochemistry and Molecular Biology, Laboratory of Hormonology, Metabolism-Nutrition & Oncology (HMNO), Center of Biology and Pathology (CBP) Pierre-Marie Degand, CHRU, Lille, France
| | - Marie-Adélaïde Bout
- Department of Biochemistry and Molecular Biology, Laboratory of Hormonology, Metabolism-Nutrition & Oncology (HMNO), Center of Biology and Pathology (CBP) Pierre-Marie Degand, CHRU, Lille, France
| | - Monique Fontaine
- Department of Biochemistry and Molecular Biology, Laboratory of Hormonology, Metabolism-Nutrition & Oncology (HMNO), Center of Biology and Pathology (CBP) Pierre-Marie Degand, CHRU, Lille, France
| | - Isabelle Kim
- Department of Biochemistry and Molecular Biology, Laboratory of Hormonology, Metabolism-Nutrition & Oncology (HMNO), Center of Biology and Pathology (CBP) Pierre-Marie Degand, CHRU, Lille, France
| | - Guillemette Huet
- Cell Culture Department, Center of Biology-Pathology, CHRU Lille, F-59000 Lille, France
| | - Soumeya Bekri
- Inserm U1245, UNIROUEN, Normandie Univ, Normandy Centre for Genomic and Personalized Medicine, France.Department of Metabolic Biochemistry, Rouen University Hospital, Rouen, France
| | - Gilles Morin
- EA 4666, Département de génétique, Université de Picardie-Jules-Verne, CHU d'Amiens, 80054 Amiens, France
| | - Stéphanie Moortgat
- Centre de Génétique Humaine, Institut de Pathologie et de Génétique, Charleroi, Gosselies, Belgium
| | - Alexandre Moerman
- Service de Génétique Clinique Guy Fontaine, Hôpital Jeanne de Flandre, CHRU Lille, 59037 Lille, France
| | - Jean-Marie Cuisset
- Service de Neurologie Infantile, Hôpital Roger Salengro, CHRU Lille, 59037 Lille, France
| | - David Cheillan
- Hospices Civils de Lyon, Service de Biochimie et Biologie Moléculaire Grand Est, Centre de Biologie et de Pathologie Est, 69677 Bron, France and Université de Lyon, INSERM U1060, CarMen; Medical Reference Center for Inherited Metabolic Diseases, Jeanne de Flandre Hospital, CHRU Lille, France
| | - Joseph Vamecq
- Department of Biochemistry and Molecular Biology, Laboratory of Hormonology, Metabolism-Nutrition & Oncology (HMNO), Center of Biology and Pathology (CBP) Pierre-Marie Degand, CHRU, Lille, France; Inserm, Lille, France; Université de Lyon, INSERM U1060 CarMeN, Lyon, France.; Univ. Lille, RADEME - Maladies RAres du Développement et du Métabolisme : du phénotype au génotype et à la Fonction, Lille, EA 7364, France.
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Baharom S, De Matteo R, Ellery S, Della Gatta P, Bruce CR, Kowalski GM, Hale N, Dickinson H, Harding R, Walker D, Snow RJ. Does maternal-fetal transfer of creatine occur in pregnant sheep? Am J Physiol Endocrinol Metab 2017; 313:E75-E83. [PMID: 28325734 DOI: 10.1152/ajpendo.00450.2016] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 03/17/2017] [Accepted: 03/18/2017] [Indexed: 01/03/2023]
Abstract
Our aim was to determine the disposition of creatine in ovine pregnancy and whether creatine is transferred across the placenta from mother to fetus. Pregnant ewes received either 1) a continuous intravenous infusion of creatine monohydrate or saline from 122 to 131 days gestation, with maternal and fetal arterial blood and amniotic fluid samples collected daily for creatine analysis and fetal tissues collected at necropsy at 133 days for analysis of creatine content, or 2) a single systemic bolus injection of [13C]creatine monohydrate at 130 days of gestation, with maternal and fetal arterial blood, uterine vein blood, and amniotic fluid samples collected before and for 4 h after injection and analyzed for creatine, creatine isotopic enrichment, and guanidinoacetic acid (GAA; precursor of creatine) concentrations. Presence of the creatine transporter-1 (SLC6A8) and l-arginine:glycine amidinotransferase (AGAT; the enzyme synthesizing GAA) proteins were determined by Western blots of placental cotyledons. The 10-day creatine infusion increased maternal plasma creatine concentration three- to fourfold (P < 0.05) without significantly changing fetal arterial, amniotic fluid, fetal tissues, or placental creatine content. Maternal arterial 13C enrichment was increased (P < 0.05) after bolus [13C]creatine injection without change of fetal arterial 13C enrichment. SLC6A8 and AGAT proteins were identified in placental cotyledons, and GAA concentration was significantly higher in uterine vein than maternal artery plasma. Despite the presence of SLC6A8 protein in cotyledons, these results suggest that creatine is not transferred from mother to fetus in near-term sheep and that the ovine utero-placental unit releases GAA into the maternal circulation.
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Affiliation(s)
- Syed Baharom
- The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Australia
- Department of Anatomy and Developmental Biology, Monash University, Melbourne, Australia
- Faculty of Medicine, Universiti Teknologi MARA, Sungai Buloh, Selangor, Malaysia
| | - Robert De Matteo
- Department of Anatomy and Developmental Biology, Monash University, Melbourne, Australia
| | - Stacey Ellery
- The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Australia
| | - Paul Della Gatta
- Institute for Physical Activity and Nutrition, Deakin University, Melbourne, Australia
| | - Clinton R Bruce
- Institute for Physical Activity and Nutrition, Deakin University, Melbourne, Australia
| | - Greg M Kowalski
- Institute for Physical Activity and Nutrition, Deakin University, Melbourne, Australia
| | - Nadia Hale
- The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Australia
| | - Hayley Dickinson
- The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Australia
| | - Richard Harding
- Department of Anatomy and Developmental Biology, Monash University, Melbourne, Australia
| | - David Walker
- The Ritchie Centre, Hudson Institute of Medical Research, Clayton, Australia
- Department of Obstetrics and Gynaecology, Monash University, Melbourne, Australia; and
| | - Rodney J Snow
- Institute for Physical Activity and Nutrition, Deakin University, Melbourne, Australia;
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Ellery SJ, Della Gatta PA, Bruce CR, Kowalski GM, Davies-Tuck M, Mockler JC, Murthi P, Walker DW, Snow RJ, Dickinson H. Creatine biosynthesis and transport by the term human placenta. Placenta 2017; 52:86-93. [PMID: 28454702 DOI: 10.1016/j.placenta.2017.02.020] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Revised: 02/22/2017] [Accepted: 02/23/2017] [Indexed: 10/20/2022]
Abstract
INTRODUCTION Creatine is an amino acid derivative that is involved in preserving ATP homeostasis. Previous studies suggest an important role for the creatine kinase circuit for placental ATP turnover. Creatine is obtained from both the diet and endogenous synthesis, usually along the renal-hepatic axis. However, some tissues with a high-energy demand have an inherent capacity to synthesise creatine. In this study, we determined if the term human placenta has the enzymatic machinary to synthesise creatine. METHODS Eleven placentae were collected following elective term caesarean section. Samples from the 4 quadrants of each placenta were either fixed in formalin or frozen. qPCR was used to determine the mRNA expression of the creatine synthesising enzymes arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT), and the creatine transporter (SLC6A8). Protein expression of AGAT and GAMT was quantified by Western blot, and observations of cell localisation of AGAT, GAMT and SLC6A8 made with immunohistochemistry. Synthesis of guanidinoacetate (GAA; creatine precursor) and creatine in placental homogenates was determined via GC-MS and HPLC, respectively. RESULTS AGAT, GAMT and SLC6A8 mRNA and protein were detected in the human placenta. AGAT staining was identified in stromal and endothelial cells of the fetal capillaries. GAMT and SLC6A8 staining was localised to the syncytiotrophoblast of the fetal villi. Ex vivo, tissue homogenates produce both GAA (4.6 nmol mg protein-1h-1) and creatine (52.8 nmol mg protein-1h-1). DISCUSSION The term human placenta has the capacity to synthesise creatine. These data present a new understanding of placental energy metabolism.
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Affiliation(s)
- Stacey J Ellery
- The Ritchie Centre, Hudson Institute of Medical Research, Department of Obstetrics and Gynaecology, Monash University, Melbourne, Australia
| | - Paul A Della Gatta
- Institute for Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Burwood Campus, Melbourne, Australia
| | - Clinton R Bruce
- Institute for Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Burwood Campus, Melbourne, Australia
| | - Greg M Kowalski
- Institute for Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Burwood Campus, Melbourne, Australia
| | - Miranda Davies-Tuck
- The Ritchie Centre, Hudson Institute of Medical Research, Department of Obstetrics and Gynaecology, Monash University, Melbourne, Australia
| | - Joanne C Mockler
- Department of Obstetrics and Gynaecology, Monash University & Monash Health, Melbourne, Australia
| | - Padma Murthi
- The Ritchie Centre, Hudson Institute of Medical Research, Department of Obstetrics and Gynaecology, Monash University, Melbourne, Australia; Department of Medicine, School of Clinical Sciences, Monash University, Monash Medical Centre, Clayton, Australia
| | - David W Walker
- The Ritchie Centre, Hudson Institute of Medical Research, Department of Obstetrics and Gynaecology, Monash University, Melbourne, Australia
| | - Rod J Snow
- Institute for Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Burwood Campus, Melbourne, Australia
| | - Hayley Dickinson
- The Ritchie Centre, Hudson Institute of Medical Research, Department of Obstetrics and Gynaecology, Monash University, Melbourne, Australia.
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Ardon O, Procter M, Mao R, Longo N, Landau Y, Shilon-Hadass A, Gabis L, Hoffmann C, Tzadok M, Heimer G, Sada S, Ben-Zeev B, Anikster Y. Creatine transporter deficiency: Novel mutations and functional studies. Mol Genet Metab Rep 2016; 8:20-3. [PMID: 27408820 PMCID: PMC4932609 DOI: 10.1016/j.ymgmr.2016.06.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2016] [Revised: 06/24/2016] [Accepted: 06/24/2016] [Indexed: 12/31/2022] Open
Abstract
X-linked cerebral creatine deficiency (MIM 300036) is caused by deficiency of the creatine transporter encoded by the SLC6A8 gene. Here we report three patients with this condition from Israel. These unrelated patients were evaluated for global developmental delays and language apraxia. Borderline microcephaly was noted in one of them. Diagnosis was prompted by brain magnetic resonance imaging and spectroscopy which revealed normal white matter distribution, but absence of the creatine peak in all three patients. Biochemical testing indicated normal plasma levels of creatine and guanidinoacetate, but an increased urine creatine/creatinine ratio. The diagnosis was confirmed by demonstrating absent ([14])C-creatine transport in fibroblasts. Molecular studies indicated that the first patient is hemizygous for a single nucleotide change substituting a single amino acid (c.619 C > T, p.R207W). Expression studies in HeLa cells confirmed the causative role of the R207W substitution. The second patient had a three base pair deletion in the SLC6A8 gene (c.1222_1224delTTC, p.F408del) as well as a single base change (c.1254 + 1G > A) at a splicing site in the intron-exon junction of exon 8, the latter occurring de novo. The third patient, had a three base pair deletion (c.1006_1008delAAC, p.N336del) previously reported in other patients with creatine transporter deficiency. These three patients are the first reported cases of creatine transporter deficiency in Israel.
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Affiliation(s)
- O. Ardon
- Research and Development, ARUP Laboratories, Salt Lake City, UT, USA
- Division of Medical Genetics, Department of Pediatrics, University of Utah, Salt Lake City, UT, USA
- Department of Pathology, University of Utah, Salt Lake City, UT, USA
| | - M. Procter
- Research and Development, ARUP Laboratories, Salt Lake City, UT, USA
| | - R. Mao
- Research and Development, ARUP Laboratories, Salt Lake City, UT, USA
- Division of Medical Genetics, Department of Pediatrics, University of Utah, Salt Lake City, UT, USA
- Department of Pathology, University of Utah, Salt Lake City, UT, USA
| | - N. Longo
- Research and Development, ARUP Laboratories, Salt Lake City, UT, USA
- Division of Medical Genetics, Department of Pediatrics, University of Utah, Salt Lake City, UT, USA
- Department of Pathology, University of Utah, Salt Lake City, UT, USA
- Corresponding author at: Division of Medical Genetics, Department of Pediatrics, University of Utah, 295 Chipeta Way, Salt Lake City, UT 84108, USA.Division of Medical GeneticsDepartment of PediatricsUniversity of Utah295 Chipeta WaySalt Lake CityUT84108USA
| | - Y.E. Landau
- Edmond and Lily Safra Children's hospital and Sackler Faculty of Medicine, TAU, Sheba Medical Center, Israel
| | - A. Shilon-Hadass
- Edmond and Lily Safra Children's hospital and Sackler Faculty of Medicine, TAU, Sheba Medical Center, Israel
| | - L.V. Gabis
- Edmond and Lily Safra Children's hospital and Sackler Faculty of Medicine, TAU, Sheba Medical Center, Israel
| | - C. Hoffmann
- Edmond and Lily Safra Children's hospital and Sackler Faculty of Medicine, TAU, Sheba Medical Center, Israel
| | - M. Tzadok
- Edmond and Lily Safra Children's hospital and Sackler Faculty of Medicine, TAU, Sheba Medical Center, Israel
| | - G. Heimer
- Edmond and Lily Safra Children's hospital and Sackler Faculty of Medicine, TAU, Sheba Medical Center, Israel
- Pediatric Neurology Unit, Edmond and Lily Safra Children's Hospital and The Dr. Pinchas Borenstein Talpiot Medical Leadership Program, Sheba Medical Center, Tel-Hashomer, Israel
| | - S. Sada
- Department of Pathology, University of Utah, Salt Lake City, UT, USA
- Edmond and Lily Safra Children's hospital and Sackler Faculty of Medicine, TAU, Sheba Medical Center, Israel
| | - B. Ben-Zeev
- Edmond and Lily Safra Children's hospital and Sackler Faculty of Medicine, TAU, Sheba Medical Center, Israel
| | - Y. Anikster
- Edmond and Lily Safra Children's hospital and Sackler Faculty of Medicine, TAU, Sheba Medical Center, Israel
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Whole body creatine and protein kinetics in healthy men and women: effects of creatine and amino acid supplementation. Amino Acids 2015; 48:677-687. [PMID: 26480831 DOI: 10.1007/s00726-015-2111-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Accepted: 10/01/2015] [Indexed: 01/27/2023]
Abstract
Creatine kinetics were measured in young healthy subjects, eight males and seven females, age 20-30 years, after an overnight fast on creatine-free diet. Whole body turnover of glycine and its appearance in creatine was quantified using [1-(13)C] glycine and the rate of protein turnover was quantified using L-ring [(2)H5] phenylalanine. The creatine pool size was estimated by the dilution of a bolus [C(2)H3] creatine. Studies were repeated following a five days supplement creatine 21 g.day(-1) and following supplement amino acids 14.3 g day(-1). Creatine caused a ten-fold increase in the plasma concentration of creatine and a 50 % decrease in the concentration of guanidinoacetic acid. Plasma amino acids profile showed a significant decrease in glycine, glutamine, and taurine and a significant increase in citrulline, valine, lysine, and cysteine. There was a significant decrease in the rate of appearance of glycine, suggesting a decrease in de-novo synthesis (p = 0.006). The fractional and absolute rate of synthesis of creatine was significantly decreased by supplemental creatine. Amino acid supplement had no impact on any of the parameters. This is the first detailed analysis of creatine kinetics and the effects of creatine supplement in healthy young men and women. These methods can be applied for the analysis of creatine kinetics in different physiological states.
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Abstract
Creatine synthesis is required in adult animals to replace creatine that is spontaneously converted to creatinine and excreted in the urine. Additionally, in growing animals it is necessary to provide creatine to the expanding tissue mass. Creatine synthesis requires three amino acids: glycine, methionine and arginine, and three enzymes: L-arginine:glycine amidinotransferase (AGAT), methionine adenosyltransferase (MAT) and guanidinoacetate methyltransferase (GAMT). The entire glycine molecule is consumed in creatine synthesis but only the methyl and amidino groups, respectively, from methionine and arginine. Creatinine loss averages approximately 2 g (14.6 mmol) for 70 kg males in the 20- to 39-year age group. Creatinine loss is lower in females and in older age groups because of lower muscle mass. Approximately half of this creatine lost to creatinine can be replaced, in omnivorous individuals, by dietary creatine. However, since dietary creatine is only provided in animal products, principally in meat and fish, virtually all of the creatine loss in vegetarians must be replaced via endogenous synthesis. Creatine synthesis does not appear to place a major burden on glycine metabolism in adults since this amino acid is readily synthesized. However, creatine synthesis does account for approximately 40% of all of the labile methyl groups provided by S-adenosylmethionine (SAM) and, as such, places an appreciable burden on the provision of such methyl groups, either from the diet or via de novo methylneogenesis. Creatine synthesis consumes some 20-30% of arginine's amidino groups, whether provided in the diet or synthesized within the body. Creatine synthesis is, therefore, a quantitatively major pathway in amino acid metabolism and imposes an appreciable burden on the metabolism of methionine and of arginine.
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