A novel oral tracer procedure for measurement of habitual myofibrillar protein synthesis

MacDonald, A.J., Small, A.C., Greig, C.A., Husi, H., Ross, J.A., Stephens, N.A., Fearon, K.C.H. and Preston, T. (2013) A novel oral tracer procedure for measurement of habitual myofibrillar protein synthesis. Rapid Communications in Mass Spectrometry, 27(15), pp. 1769-1777. (doi: 10.1002/rcm.6622)

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Abstract

RATIONALE: Conventionally, myofibrillar protein synthesis is measured over time periods of hours. In clinical studies, interventions occur over weeks. Functional measures over such periods may be more representative. We aimed to develop a novel method to determine myofibrillar protein fractional synthetic rate (FSR) to estimate habitual rates, while avoiding intravenous tracer infusions. METHODS: Four healthy males were given 100 g water enriched to 70 Atom % with 2H2O as a single oral bolus. Vastus-lateralis needle biopsies were performed and plasma samples collected, 3–13 days post-dose. 2H enrichment in body water was measured in plasma using continuous flow isotope ratio mass spectrometry (IRMS). Myofibrillar protein was isolated from muscle biopsies and acid hydrolysed. 2H enrichment of protein-bound and plasma-free alanine was measured by gas chromatography (GC)/pyrolysis/IRMS. Myofibrillar protein FSR was calculated (% day–1). RESULTS: The tracer bolus raised the initial enrichment of body water to 1514 ppm 2H excess. Water elimination followed a simple exponential. The average elimination half-time was 8.3 days. Plasma alanine, labelled during de novo synthesis, followed the same elimination kinetics as water. The weighted average myofibrillar protein FSR from the four subjects was 1.38 % day–1 (range, 1.0–1.9 % day–1). CONCLUSIONS: Myofibrillar protein FSR was measured in free-living healthy individuals over 3–13 days. Using a single oral 2H2O bolus, endogenous labelling of alanine occurred in a predictable manner giving estimates of synthesis comparable with published values. Furthermore, the protocol does not compromise the ability to measure other important metabolic processes such as total energy expenditure.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Preston, Professor Tom and Small, Mrs Sandra and Husi, Dr Holger
Authors: MacDonald, A.J., Small, A.C., Greig, C.A., Husi, H., Ross, J.A., Stephens, N.A., Fearon, K.C.H., and Preston, T.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
College of Medical Veterinary and Life Sciences > School of Cardiovascular & Metabolic Health
Journal Name:Rapid Communications in Mass Spectrometry
ISSN:0951-4198
ISSN (Online):1097-0231

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