A novel stable isotope tracer method to measure muscle protein fractional breakdown rate during a physiological non-steady state condition.
ABSTRACT The measurement of the fractional breakdown rate (FBR) of muscle proteins during physiological non-steady state of amino acids (AAs) presents some challenges. Therefore, the goal of the present experiment was to modify the bolus stable isotope tracer injection approach to determine both fractional synthesis rate (FSR) and FBR of leg muscle protein during a physiological non-steady state of AAs. The approach uses the traditional precursor-product principle, but is modified with the assumption that inward transport of AAs is proportional to their plasma concentrations. The FBR value calculated from the threonine tracer served as a reference to evaluate the validity of the FBR measurement from the phenylalanine tracer, which was under a non-steady state condition due to the concomitant injection of unlabeled phenylalanine. Plasma phenylalanine concentration increased more than 4-fold after the bolus injection, and thereafter decreased exponentially, while the threonine concentration remained stable. FBR values were similar with the two tracers (0.133±0.003 and 0.148±0.003 %/hr (Mean±SE) for phenylalanine and threonine tracers, respectively (p > 0.05). In addition, FSR values for the two tracers were similar (0.069±0.002 and 0.067±0.001 %/hr for phenylalanine and threonine tracers, respectively, p>0.05), indicating that the traditional FSR approach can also be used in the non-steady state. Accordingly, net balance (NB) values were similar -0.065±0.002 and -0.081±0.002 %/hr for phenylalanine and threonine tracers, respectively (p>0.05). This new method of measuring muscle protein FBR during physiological non-steady state gives reliable results and allows simultaneous measurement of muscle protein FSR and thus a calculation of NB.
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ABSTRACT: The main purpose of this review is to discuss novel methodological advances in the assessment of muscle protein synthesis (MPS) in response to protein feeding and resistance exercise.Current Opinion in Clinical Nutrition and Metabolic Care 09/2014; 17(5):412-417. DOI:10.1097/MCO.0000000000000083 · 3.97 Impact Factor
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ABSTRACT: Background. The systemic inflammatory response syndrome (SIRS) is characterized by a hypercatabolic state induced by inflammatory mediators. Continuous venovenous hemofiltration (CVVH) stabilizes the internal environment but also aggravates loss of amino acids. The effect of CVVH on protein dynamics is largely unknown. We adopted the stable isotopic tracer technology to investigate how CVVH changed serum albumin metabolism. Methods. Twenty SIRS patients were randomized into low- (2000 mL/h) and high- (4000 mL/h) volume CVVH groups according to the rate of replacement fluid. Eight patients with abdominal infection matched for age, sex, and laboratory index served as controls. Consecutive arterial blood samples were drawn during a primed-constant infusion of two stable isotopes to determine the albumin fractional synthesis rate (FSR) and fractional breakdown rate (FBR). Results. Before treatment, there was no significant difference of FSR and FBR among 3 groups. After CVVH, the albumin FSR in high- and low-volume groups was 7.75 ± 1.08% and 7.30 ± 0.89%, respectively, both higher than in the control (5.83 ± 0.94%). There was no significant difference in albumin FBR after treatment. Conclusions. Protein dynamic indicators could reflect protein synthesis and breakdown state directly and effectively. CVVH increased albumin synthesis, while the breakdown rate remained at a high level independently of the CVVH rate.BioMed Research International 01/2015; 2015:917674. DOI:10.1155/2015/917674 · 2.71 Impact Factor
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ABSTRACT: Skeletal muscle proteolysis is highly regulated, involving complex intramuscular proteolytic systems that recognize and degrade muscle proteins, and recycle free amino acid precursors for protein synthesis and energy production. Autophagy-lysosomal, calpain, and caspase systems are contributors to muscle proteolysis, although the ubiquitin proteasome system (UPS) is the primary mechanism by which actomyosin fragments are degraded in healthy muscle. The UPS is sensitive to mechanical force and nutritional deprivation, as recent reports have demonstrated increased proteolytic gene expression and activity of the UPS in response to resistance and endurance exercise, and short-term negative energy balance. However, consuming dietary protein alone (or free amino acids), or as a primary component of a mixed meal, may attenuate intramuscular protein loss by down-regulating proteolytic gene expression and the catabolic activity of the UPS. Although these studies provide novel insight regarding the intramuscular regulation of skeletal muscle mass, the role of proteolysis in the regulation of skeletal muscle protein turnover in healthy human muscle is not well described. This article provides a contemporary review of the intramuscular regulation of skeletal muscle proteolysis in healthy muscle, methodological approaches to assess proteolysis, and highlights the effects of nutrition and exercise on skeletal muscle proteolysis. © 2014 IUBMB Life, 2014International Union of Biochemistry and Molecular Biology Life 07/2014; 66(7). DOI:10.1002/iub.1291 · 2.79 Impact Factor