Protein turnover in the whole body

Waterlow, J. C.

doi:10.1038/253157a0

Cited by 135 publications

(208 citation statements)

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“…Theoretically, protein breakdown in tissues and individual proteins can be measured from the rate of loss of tracer enrichment in prelabelled proteins. However, reutilization of the tracer released by protein breakdown for protein synthesis leads to artificially-low rates, and the data critically depend on the time period over which the measurements are made (Waterlow et al 1978a). Another difficulty, which has prevented the routine use of this technique in human subjects, is that several biopsies are required in periods of hours to many days, depending on the turnover rate, and that in some tissues, e.g.…”

Section: Amino Acid Incorporation Methods To Measure Protein Synthesimentioning

confidence: 99%

“…In early studies (Waterlow et al 1978a) the tracer was given as a continuous intragastric infusion (infusion rate i) until after 2-3 d a plateau had been reached in the labelling of urea in the urine. The enrichment in the urea pool was assumed to reflect the 15 N enrichment in a single 'N metabolic pool' in which all free amino acids and urea eventually reached the same enrichment and from which exchange occurs with whole-body protein (Fig.…”

Section: Whole-body Protein Turnovermentioning

confidence: 99%

“…The contribution of whole-body methodology (without parallel organ balances, biopsies, or protein separations) to the future gain of knowledge is expected to be limited due to the fact that most physiological disturbances have been investigated extensively (see Waterlow et al 1978a;Waterlow, 1984;Rennie, 1985;Hasselgren, 1995;Wagenmakers & Soeters, 1995;Rooyakers & Nair, 1997;Wagenmakers, 1998a,b), and due to the lack of information on the relative contribution of various tissues and proteins to whole-body changes (e.g. an increase in protein synthesis in the liver may be compensated for by a decrease in protein synthesis in muscle).…”

Section: Whole-body Protein Turnovermentioning

confidence: 99%

“…The present paper will describe how the use of tracer amino acids has contributed to the present knowledge on the regulation of protein and amino acid metabolism in human subjects, where the limitations and uncertainties of the existing methods lie, and finally which methodological developments will be necessary and which complimentary research methodologies should be used in parallel to gain new knowledge in future research on protein metabolism in vivo in human subjects. For reviews describing the current physiological knowledge of the regulation of protein and amino acid metabolism by hormones, nutrition, disease and exercise (see Waterlow et al 1978a;Waterlow, 1984;Rennie, 1985;Hasselgren, 1995;Wagenmakers & Soeters, 1995;Rooyackers & Nair, 1997;Wagenmakers, 1998a,b).…”

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Tracers to investigate protein and amino acid metabolism in human subjects

Wagenmakers

1999

Proc. Nutr. Soc.

110

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Abbreviations: FSR, fractional synthesis rate; IRMS, isotope-ratio mass spectrometry; α-KIC, α-ketoisocaproic acid; MS, mass spectrometry; nb, net balance of tracer; NB, net balance of tracee; Ra, rate of appearance; Rd, rate of disappearance. The contribution of whole-body methods to the future gain of knowledge is expected to be limited due to the fact that most physiological disturbances have been investigated extensively, and due to the lack of information on the relative contribution of various tissues and proteins to whole-body changes.Tracer amino acid-incorporation methods are most suited to investigate these latter aspects of protein metabolism. These methods have shown that some tissues (liver and gut) have much higher turnover rates and deposit much more protein than others (muscle). Massive differences also exist between the fractional synthesis rates of individual proteins. The incorporation methods have been properly validated, although minor disagreements remain on the identity of the true precursor pool (the enrichment of which should be used in the calculations). Arterio-venous organ balance studies have shown that little protein is deposited in skeletal muscle following a proteincontaining meal, while much more protein is deposited in liver and gut. The amount deposited in the feeding period in each of these tissues is released again during overnight fasting. The addition of tracers to organ balance studies allows the simultaneous estimation of protein synthesis and protein breakdown, and provides information on whether changes in net protein balance are caused primarily by a change in protein synthesis or in protein breakdown. In the case of a small arterio-venous difference in a tissue with a high blood flow, estimates of protein synthesis and breakdown become very uncertain, limiting the value of using the tracer. An additional measurement of the intracellular free amino acid pool enrichment allows a correction for amino acid recycling and quantification of the inward and outward transmembrane transport. However, in order to obtain reliable estimates of the intramuscular amino acid enrichment and, therefore, of muscle protein synthesis and breakdown in this so-called three-pool model, the muscle should be freeze-dried and the resulting fibres should be freed from connective tissue and small blood clots under a dissection microscope. Even when optimal precautions are taken, the calculations in these tracer balance methods use multiple variables and, therefore, are bound to lead to more variability in estimates of protein synthesis than the tracer amino acid incorporation methods. In the future, most studies should focus on the measurement of protein synthesis and breakdown in specific proteins in order to understand the mechanisms behind tissue adaptation in response to various stimuli (feeding, fasting, exercise, trauma, sepsis, disuse and disease). The tracer laboratories, therefore, should improve the methodology to allow the measurement of low tracer amino acid enrichments in small amount...

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Section: Amino Acid Incorporation Methods To Measure Protein Synthesimentioning

confidence: 99%

Section: Whole-body Protein Turnovermentioning

confidence: 99%

Section: Whole-body Protein Turnovermentioning

confidence: 99%

mentioning

confidence: 99%

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Tracers to investigate protein and amino acid metabolism in human subjects

Wagenmakers

1999

Proc. Nutr. Soc.

110

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“…15 Because leucine is an essential amino acid in humans, leucine enters the plasma-free amino acid pool by only 2 sources: from the breakdown of endogenous protein stores (B) and from PN (I) as all subjects were fed exclusively with PN. Leucine exits the plasma amino acid pool by incorporation into body protein (S) or through leucine oxidation (O).…”

Section: Calculations For Leucine Kineticsmentioning

confidence: 99%

Intravenous insulin decreases protein breakdown in infants on extracorporeal membrane oxygenation

Agus

Javid

Ryan

et al. 2004

Journal of Pediatric Surgery

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The determination of amino acid pool sizes and turnover rates by gas chromatographic mass spectrometric analysis of stable isotope enrichment

Irving

Nissim

Lapidot

1978

Biol. Mass Spectrom.

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Gas chromatography mass spectrometry has been used to determine the 15N enrichment of plasma glycine of rabbits at various times following the intravenous administration of 15N-glycine. These data were used to prepare isotope enrichment time decay curves for eleven individual animals. The slopes and intercepts of least squares lines that describe the decay curves were considerably more accurately than those reported in similar studies employing radioactive tracers. Individual glycine pool sizes (13.8-37.4 micronmoles per 100 g body wt), turnovers rates (2.66-3.36 pools h-1) and flux (50.4-99.7 micronmoles h-1 per 100 g body wt) were estimated from these parameters in a group of animals and compared with the literature values. These results demonstrate that low risk non-radioactive stable isotopes can be substituted for radioactive tracers in studies of human amino acid metabolism, with considerable saving in time and without loss in accuracy, when gas chromatography mass spectrometry is used to determine plasma amino acid and stable isotope enrichment.

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Protein turnover in the whole body

Cited by 135 publications

References 0 publications

Tracers to investigate protein and amino acid metabolism in human subjects

Tracers to investigate protein and amino acid metabolism in human subjects

Intravenous insulin decreases protein breakdown in infants on extracorporeal membrane oxygenation

The determination of amino acid pool sizes and turnover rates by gas chromatographic mass spectrometric analysis of stable isotope enrichment

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