Tracers To Investigate Protein And Amino Acid Metabolism In Human Subjects Pdf

tracers to investigate protein and amino acid metabolism in human subjects pdf

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Muscle proteins turn over slowly and there are minimal diurnal changes in the size of the muscle protein pool in response to feeding and fasting. An imbalance between muscle protein synthesis and degradation does exist during one leg knee extensor exercise and during two legged cycling in patients with glycogen Phosphorylase deficiency.

The investigation of protein metabolism under various nutritional and physiological conditions has been made possible by the use of indirect, principally tracer-based methods. Most studies were conducted at the whole-body level, mainly using steady-state isotopic techniques and equations based on simple two-pool models, in which amino acids are either free or protein bound. Because whole-body methods disregard regional contributions to protein metabolism, some regional approaches have tried to distinguish the distribution of protein kinetics in the different tissues. The organ-balance tracer technique, involving the arteriovenous catheterization of regions or organs with concomitant isotopic tracer infusion, distinguishes between amino acid uptake and release in the net amino acid balance and measures protein synthesis and degradation under steady-state conditions. Last, the importance has become clear of the difference in dietary and endogenous amino acids recycled from proteolysis for anabolic and catabolic pathways.

Critical Assessment of Methods Used to Measure Protein Synthesis In Human Subjects

The association between albuminuria and altered whole body protein turnover in T2DM is currently unknown. To assess whole body protein degradation and synthesis in type 2 diabetes with and without albuminuria. Phe and Tyr Ra were not different among the groups. On the basis of the kinetics of the essential amino acid phenylalanine, T2DM subjects with increased AER exhibit a catabolic pattern of whole body protein turnover. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Amino Acid Metabolism in the Human Fetus at Term: Leucine, Valine, and Methionine Kinetics

Metrics details. Skeletal muscle protein synthesis has generally been determined by the precursor:product labeling approach using labeled amino acids e. Although reliable for determining rates of protein synthesis, this methodological approach requires experiments to be conducted in a controlled environment, and as a result, has limited our understanding of muscle protein renewal under free-living conditions over extended periods of time i. An alternative tracer, 2 H 2 O, has been successfully used to measure rates of muscle protein synthesis in mice, rats, fish and humans. Moreover, perturbations such as feeding and exercise have been included in these measurements without exclusion of common environmental and biological factors.

Protein turnover in skeletal muscle tissue is highly responsive to nutrient intake in healthy adults. To provide a comprehensive overview of post-prandial protein handling, ranging from dietary protein digestion and amino acid absorption, the uptake of dietary protein derived amino acids over the leg, the post-prandial stimulation of muscle protein synthesis rates, to the incorporation of dietary protein derived amino acids in de novo muscle protein. In addition, primed continuous L-[ring- 2 H 5 ]-phenylalanine, L-[ring- 2 H 2 ]-tyrosine, and L-[1- 13 C]-leucine infusions were applied, with frequent collection of arterial and venous blood samples, and muscle biopsies throughout a 5 h post-prandial period. Dietary protein digestion, amino acid absorption, splanchnic amino acid extraction, amino acid uptake over the leg, and subsequent muscle protein synthesis were measured within a single in vivo human experiment. Muscle protein synthesis rates increased significantly following protein ingestion 0. This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

Tracers to investigate protein and amino acid metabolism in human subjects. Published online by Cambridge University Press: 12 June Anton J. M.

Critical Assessment of Methods Used to Measure Protein Synthesis In Human Subjects

Regulation of glucose homeostasis by insulin is modified during aging, but whether this alteration is associated with changes in protein metabolism is less defined. Insulin dose responses of whole body glucose, leucine, and albumin metabolism have been investigated using isotopic dilution of d -[6, 6- 2 H 2 ]glucose and l -[1- 13 C]leucine in 14 young Y; Despite significantly higher plasma insulin in E than in Y, the glucose disposal rate was lower in E than in Y at both insulin levels, whereas glucose production was normally suppressed. The albumin synthesis rate was identical and stimulated to the same extent by insulin in groups Y and E.

Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Three tracer methods have been used to measure protein synthesis, protein breakdown and protein oxidation at whole-body level.

Tracers to investigate protein and amino acid metabolism in human subjects.

The ingestion of intact protein or essential amino acids EAA stimulates mechanistic target of rapamycin complex-1 mTORC1 signaling and muscle protein synthesis MPS following resistance exercise. Ten young Myofibrillar-MPS was measured during exercise recovery with a primed, constant infusion of L-[ring 13 C 6 ] phenylalanine and collection of muscle biopsies pre and 4 h-post drink ingestion.

Protein and Amino Acid Metabolism in Human Muscle

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Human fetal metabolism is largely unexplored. Understanding how a healthy fetus achieves its fast growth rates could eventually play a pivotal role in improving future nutritional strategies for premature infants. To quantify specific fetal amino acid kinetics, eight healthy pregnant women received before elective cesarean section at term, continuous stable isotope infusions of the essential amino acids [1- 13 C, 15 N]leucine, [U- 13 C 5 ]valine, and [1- 13 C]methionine.

The loss of body protein that frequently accompanies illness occurs through changes in protein synthesis and degradation. In human tissues, rates of protein synthesis can be assessed with stable isotopic tracer techniques and mass spectrometry. The basic principles of these methods are explained, and the advantages and drawbacks of the two main approaches, the constant infusion method and the flooding method, are described. Examples are given of the use of these methods to investigate protein synthesis and surgical trauma, pathologies of the gastrointestinal tract and the response of tumor growth to amino acid supplements. Full text is available as a scanned copy of the original print version. Get a printable copy PDF file of the complete article 1. Links to PubMed are also available for Selected References.

Protein depletion is a major determinant of clinical outcome in a number of catabolic states. Hence, assessment of protein metabolism is necessary to understand these conditions as well as to evaluate treatment. Since the regulation of synthesis and breakdown of proteins differs between tissues, it is preferable to study the parameters of protein metabolism separately, and at the organ level. In this chapter we will discuss techniques developed to study liver protein metabolism in man. A technique for liver tissue sampling was established during laparoscopic surgery in order to investigate some parameters of human liver protein metabolism, free amino acid concentrations ion exchange chromatography , and synthesis rates of total liver protein and albumin stable isotope technique and gas chromatography-mass spectrometry GC-MS as well as ribosome analysis. The impact on these parameters of intravenous nutrition, of growth hormone and of the surgical procedure are also discussed. Unable to display preview.

Tracers to investigate protein and amino acid metabolism in human subjects.


Over a century ago, Frederick Soddy provided the first evidence for the existence of isotopes; elements that occupy the same position in the periodic table are essentially chemicall y identical but differ in mass due to a different number of neutrons within the atomic nucleus. Allied to the discovery of isotopes was the development of some of the first forms of mass spectrometers, driven forward by the Nobel laureates JJ Thomson and FW Aston, enabling the accurate separation, identification, and quantification of the relative abundance of these isotopes. As a result, within a few years, the number of known isotopes both stable and radioactive had greatly increased and there are now over stable or radioisotopes presently known. From this important breakthrough, the age of the isotope tracer was born. This historical review details the development of stable isotope tracers as metabolic tools, with particular reference to their use in monitoring protein metabolism, highlighting the unique array of tools that are now available for the investigation of protein metabolism in vivo at a whole body down to a single protein level.

John's Research Institute, Bengaluru, India. Indians have a poor protein intake in terms of quantity as well as quality because of their predominantly cereal-based diet. However, there is limited information on circulatory amino acid levels in healthy Indians. Herein, we evaluated the acute effect of a protein supplement on the plasma levels of essential amino acids EAAs in healthy Indian adults, using targeted EAA analysis. After 7 days, the participants returned for the crossover treatment.


Elodia V.


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