Assessing the responsiveness of musculoskeletal tissues to protein supplementation in vivo in older adults: an exploratory randomized controlled trial.

IntroductionSkeletal muscle plasticity is reflected by a dynamic balance between protein synthesis and breakdown, with basal muscle protein synthesis rates typically ranging between 0.04 and 0.06 %/h. Though it is evident that other musculoskeletal tissues should also express some level of plasticity, protein synthesis rates of most of these tissues have never been assessed. The present study applies contemporary stable isotope methodology to assess basal muscle, tendon, ligament, bone, as well as cartilage protein synthesis rates in vivo in humans.MethodsSix otherwise healthy patients (62±3 y), scheduled to undergo unilateral total knee arthroplasty, were included in this study. Primed continuous intravenous infusions with L‐[ring‐13C6]‐Phenylalanine were initiated 2.5 h prior to surgery and continued during surgery. Throughout the surgical procedure the following tissue samples were obtained: muscle, tendon, cruciate ligaments, cartilage, bone, menisci, fat and synovium. Tissue‐specific fractional protein synthesis rates (%/h) were assessed by measuring the incorporation of labelled L‐[ring‐13C6]‐Phenylalanine in tissue protein and were compared with muscle tissue protein synthesis rates using a paired t test.ResultsProtein bound L‐[ring‐13C6]‐Phenylalanine enrichments did not differ substantially between the different musculoskeletal tissues and skeletal muscle, except for notch bone tissue (P<0.01). Highest enrichment levels were observed in synovium derived protein (0.029±0.008 MPE) and lowest enrichment levels in patellar bone tissue protein (0.005±0.002 MPE). Tendon, bone, cartilage, fat, anterior cruciate ligament, posterior cruciate ligament, and menisci tissue protein synthesis rates averaged 0.06±0.01, 0.03±0.01, 0.04±0.01, 0.11±0.03, 0.07±0.02, 0.04±0.01, and 0.04±0.01 %/h, respectively, and did not significantly differ from skeletal muscle protein synthesis rates (0.04±0.01 %/h; P>0.05). Synovium derived protein and notch bone tissue protein synthesis rates were respectively higher and lower compared to skeletal muscle protein synthesis rates (P<0.05 and P<0.01, respectively).ConclusionBasal protein synthesis rates in various musculoskeletal tissues are within the same range of skeletal muscle protein synthesis rates, with fractional muscle, tendon, bone, cartilage, ligament and menisci tissue protein synthesis rates ranging between 0.02 and 0.13 % per hour.Support or Funding InformationThis study received no specific grant from any funding agency.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

the progressive loss of muscle mass, commonly termed sarcopenia, accompanies the process of healthy aging ([27][1]). The underlying basis of this condition, in a very simplistic view, would be at a more advanced age skeletal muscle proteins are being lost because of an imbalance between muscle

Skeletal muscle plasticity is reflected by a dynamic balance between protein synthesis and breakdown, with basal muscle tissue protein synthesis rates ranging between 0.02 and 0.09%/h. Though it is evident that other musculoskeletal tissues should also express some level of plasticity, data on protein synthesis rates of most of these tissues in vivo in humans is limited. Six otherwise healthy patients (62±3 y), scheduled to undergo unilateral total knee arthroplasty, were subjected to primed continuous intravenous infusions with L-[ring-13C6]-Phenylalanine throughout the surgical procedure. Tissue samples obtained during surgery included muscle, tendon, cruciate ligaments, cartilage, bone, menisci, fat, and synovium. Tissue-specific fractional protein synthesis rates (%/h) were assessed by measuring the incorporation of L-[ring-13C6]-Phenylalanine in tissue protein and were compared with muscle tissue protein synthesis rates using a paired t test. Tendon, bone, cartilage, Hoffa’s fat pad, anterior and posterior cruciate ligament, and menisci tissue protein synthesis rates averaged 0.06±0.01, 0.03±0.01, 0.04±0.01, 0.11±0.03, 0.07±0.02, 0.04±0.01, and 0.04±0.01%/h, respectively, and did not significantly differ from skeletal muscle protein synthesis rates (0.04±0.01%/h; P>0.05). Synovium derived protein (0.13±0.03%/h) and intercondylar notch bone tissue protein synthesis rates (0.03±0.01%/h) were respectively higher and lower compared to skeletal muscle protein synthesis rates (P<0.05 and P<0.01, respectively). Basal protein synthesis rates in various musculoskeletal tissues are within the same range of skeletal muscle protein synthesis rates, with fractional muscle, tendon, bone, cartilage, ligament, menisci, fat, and synovium protein synthesis rates ranging between 0.02 and 0.13% per hour in vivo in humans.Clinical trial registration: NTR5147

The purpose of this study was to determine whether ornithine affects the rate of tissue protein synthesis in male rats. Two experiments were done on five or two groups of young rats (5 wk) given diets containing 0.15, 0.3, 0.5 or 0.7% ornithine-HCl added to a 20% casein diet for 1 d (only one 3 h period) (Experiment 1), and given a diet containing 0 or 0.7% ornithine-HCl added to a 20% casein diet for 10 d (Experiment 2). The plasma concentration of growth hormone (GH) was the highest in rats fed 0.5 and 0.7% ornithine added to the 20% casein diet. The fractional rates of protein synthesis in brain regions, liver and gastrocnemius muscle increased significantly with the 20% casein+0.7% ornithine diet compared with the 20% casein diet. In brain regions, liver and gastrocnemius muscle, the RNA activity [g protein synthesized/(g RNA·d)] significantly correlated with the fractional rate of protein synthesis. The RNA concentration (mg RNA/g protein) was not related to the fractional rate of protein synthesis in any organ. The present results suggest that the treatment of young rats with ornithine is likely to increase the concentration of plasma GH and the rate of protein synthesis in the tissues, and that RNA activity is at least partly related to the fractional rate of tissue protein synthesis.

In order to elucidate the physiological function of circulating IGF-I on muscle protein synthesis in the chicken under malnutritional conditions, we administrated recombinant chicken IGF-I using a osmotic mini pump to fasted young chickens and measured the rate of muscle protein synthesis and plasma metabolite. The pumps delivered IGF-I at the rate of 22 µg/d {300 µg⋅(kg body weight⋅d) -1 }. Fractional rate of protein synthesis in the muscle was measured using a large dose injection of L-(2,6- 3 H)phenylalanine. Constant infusion of chicken IGF-I did not affect plasma glucose level. Significant interaction between dietary treatment and IGF-I infusion was observed in plasma NEFA and total cholesterol concentrations. When chicks were fasted, IGF-I infusion decreased plasma NEFA and total cholesterol concentrations. On the other hand, IGF-I administration did not affect plasma levels of both metabolites. Fasting reduced plasma triglyceride concentration significantly. IGF-I infusion also decreased the level of plasma triglyceride. Plasma IGF-I concentration of young chickens was halved by fasting for 1 d. IGF-I infusion using an osmotic minipump for 1 d increased plasma IGF-I concentration in fasted chicks to the level of fed chicks. Fasting decreased body weight and the loss of body weight was significantly ameliorated by IGF-I infusion. There was a significant interaction between dietary treatment and IGF-I infusion in the fractional rate of breast muscle protein synthesis. There was no effect of IGF-I infusion on muscle protein synthesis in fed chicks. Muscle protein synthesis reduced by fasting was ameliorated by IGF-I infusion, but did not reach to the level of fed control. Muscle weight of fasted chicks infused with IGF-I was similar to fasted birds without IGF-I infusion, which suggests that muscle protein degradation would be increased by IGF-I infusion as well as protein synthesis in fasted chicks. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 12 : 1760-1764)

Muscle protein turnover during early development in chickens divergently selected for growth rate

1. The fractional synthesis rate of protein is commonly measured by either the constant infusion method or the flooding dose method. The two methods often give different results. 2. An underlying assumption of the traditional flooding dose formula is that the protein synthesis rate is not stimulated by the flooding dose. A new formula for calculation of the fractional synthesis rate is derived with the alternative assumption that the protein synthesis rate is stimulated by an amount proportional to the change in the intracellular concentration of the infused amino acid. The alternative formula is: Fractional synthesis rate = [formula: see text] where EB and EF are the enrichments of bound and free amino acid, respectively (atom per cent excess), and C = 1-(EF/EI), where EI is the enrichment of the infusate. This approach defines the lowest possible value for the fractional synthesis rate. The traditional equation gives a maximal value for the fractional synthesis rate. 3. When data from the literature are considered, the fractional synthesis rate of muscle protein as calculated by the constant infusion technique falls between the values of fractional synthesis rate calculated by the two flooding dose formulae when leucine is the tracer, suggesting that a flooding dose of leucine exerts a stimulatory effect on the rate of protein synthesis, but that the increase is not as great as the increase in the intracellular concentration of leucine.(ABSTRACT TRUNCATED AT 250 WORDS)

the more we learn about skeletal muscle biology the more it becomes clear how important muscle tissue is for maintaining overall health. Specifically, muscle is important to provide sufficient strength/force production for locomotion and performing regular activities associated with daily living. In

Prolonged passive heat treatment (PHT) has been suggested to trigger skeletal muscle adaptations that may improve muscle maintenance in older individuals. To assess the effects of PHT on skeletal muscle tissue capillarization, perfusion capacity, protein synthesis rates, hypertrophy and leg strength, 14 older adults (9 males, 5 females; 73 ± 6 years) underwent 8 weeks of PHT (infrared sauna: 3× per week, 45 min at ∼60°C). Before and after PHT we collected muscle biopsies to assess skeletal muscle capillarization and fibre cross‐sectional area (CSA). Basal and postprandial muscle tissue perfusion kinetics and protein synthesis rates were assessed using contrast‐enhanced ultrasound and primed continuous l‐[ring‐13C6]phenylalanine infusions, respectively. One‐repetition maximum (1RM) leg strength and vastus lateralis muscle CSA were assessed. Type I and type II muscle fibre capillarization strongly increased following PHT (capillary‐to‐fibre perimeter exchange index: +31 ± 18 and +33 ± 30%, respectively; P < 0.001). No changes were observed in basal (0.24 ± 0.27 vs. 0.18 ± 0.11 AU; P = 0.266) or postprandial (0.20 ± 0.12 vs. 0.18 ± 0.14 AU; P = 0.717) microvascular blood flow following PHT. Basal (0.048 ± 0.014 vs. 0.051 ± 0.019%/h; P = 0.630) and postprandial (0.041 ± 0.012 vs. 0.051 ± 0.024%/h; P = 0.199) muscle protein synthesis rates did not change in response to prolonged PHT. Furthermore, no changes in vastus lateralis muscle CSA (15.3 ± 4.6 vs. 15.2 ± 4.6 cm2; P = 0.768) or 1RM leg strength (46 ± 12 vs. 47 ± 12 kg; P = 0.087) were observed over time. In conclusion, prolonged PHT increases muscle tissue capillarization but this does not improve muscle microvascular blood flow or increase muscle protein synthesis rates in healthy, older adults. Prolonged PHT does not induce skeletal muscle hypertrophy or increase leg strength in healthy, older adults.Key pointsRepeated exposure to heat has been suggested to trigger skeletal muscle adaptive responses.We investigated the effect of 8 weeks of whole‐body passive heat treatment (PHT; infrared sauna: 3× per week for 45 min at ∼60°C) on skeletal muscle tissue capillarization, perfusion capacity, basal, and postprandial muscle protein synthesis rates, muscle (fibre) hypertrophy, and leg strength in healthy, older adults.Prolonged PHT increases muscle tissue capillarization, but this does not improve muscle microvascular blood flow or increase muscle protein synthesis rates.Despite increases in muscle tissue capillarization, prolonged PHT does not suffice to induce skeletal muscle hypertrophy or increase leg strength in healthy, older adults.

The purpose of this study was to determine whether recombinant human growth hormone (GH) administration enhances muscle protein anabolism in experienced weight lifters. The fractional rate of skeletal muscle protein synthesis and the whole body rate of protein breakdown were determined during a constant intravenous infusion of [13C]leucine in 7 young (23 +/- 2 yr; 86.2 +/- 4.6 kg) healthy experienced male weight lifters before and at the end of 14 days of subcutaneous GH administration (40 microgram.kg-1 x day-1). GH administration increased fasting serum insulin-like growth factor-I (from 224 +/- 20 to 589 +/- 80 ng/ml, P = 0.002) but did not increase the fractional rate of muscle protein synthesis (from 0.034 +/- 0.004 to 0.034 +/- 0.002%/h) or reduce the rate of whole body protein breakdown (from 103 +/- 4 to 108 +/- 5 mumol.kg-1 x h-1). These findings suggest that short-term GH treatment does not increase the rate of muscle protein synthesis or reduce the rate of whole body protein breakdown, metabolic alterations that would promote muscle protein anabolism in experienced weight lifters attempting to further increase muscle mass.

The purpose of this study was to determine the acute in vivo response of human muscle protein to stress. Prior animal and human in vitro studies have suggested that physiologic stress increases muscle protein turnover. In contrast, recent publications using a polyribosomal methodology have demonstrated a reduction in human muscle protein synthesis in vivo after surgery. Five healthy volunteers were given a stable isotopic infusion of 1,2(13)C leucine that allowed for determination of the fractional rate of muscle protein synthesis by measuring the rate of incorporation of 13C label into vastus lateralis muscle biopsies. Simultaneous infusion of 15N lysine and quantitation of leg blood flow by indocyanine green dye dilution allowed for estimation of leg muscle protein breakdown rate (Lys Ra) and synthesis rate (Lys Rd). These measurements were performed before and then at the conclusion of a 4-hour femoral arterial infusion of the catabolic hormones epinephrine, cortisol, and glucagon. The catabolic hormone infusion elicited a significant (65%) increase in the leg muscle protein breakdown rate and a significant but less marked increase in the rate of muscle protein synthesis, as assessed by both an increase in the fractional rate of muscle protein synthesis of 48.5% and in lysine uptake within the leg of 32%. This study conclusively demonstrates that a hormonally induced stress results in a net catabolism of human muscle protein by increasing the rate of protein breakdown in excess of an increased protein synthetic rate.

Physical activity and eating are two major physiological muscle growth stimuli. Although muscle protein turnover rates are not different in young and middle-aged men and women, we recently found that the basal rate of muscle protein synthesis is greater and the anabolic response to mixed-meal intake is blunted in 65- to 80-yr-old women compared with men of the same age. Whether older women are also resistant to the anabolic effect of exercise is not known. We measured the rate of muscle protein synthesis (both during basal, postabsorptive conditions and during mixed-meal intake) before and after 3 months of exercise training in obese, 65- to 80-yr-old men and women. At the beginning of the study (before training) the basal, postabsorptive muscle protein fractional synthesis rate (FSR) was significantly greater in women than in men (0.064 ± 0.006%·h(-1) vs 0.039 ± 0.006%·h(-1), respectively, P < 0.01), whereas the meal-induced increase in the muscle protein FSR was greater in men than in women (P < 0.05). In men, exercise training approximately doubled the basal muscle protein FSR (P = 0.001) but had no effect on the meal-induced increase in muscle protein FSR (P = 0.78). In women, exercise training increased the muscle protein FSR by ~40% (P = 0.03) and also had no effect on the meal-induced increase in muscle protein FSR (P = 0.51). These results suggest that there is significant sexual dimorphism not only in the basal, postabsorptive rate of muscle protein synthesis but also in the anabolic response to feeding and exercise training in obese, older adults.

In Vivo Rates of Skeletal Muscle Protein Synthesis in Rats Are Decreased by Acute Ethanol Treatment but Are Not Ameliorated by Supplemental α-Tocopherol

MRI appearances of the infrapatellar fat pad in occult traumatic patellar dislocation

Skeletal muscle is the largest organ of the human body and plays a pivotal role in whole-body homeostasis through the maintenance of physical and metabolic health. Establishing strategies aimed at increasing the amount, and minimising loss, of muscle mass are of upmost importance. Muscle mass is primarily dictated by the meal-to-meal fluctuations in muscle protein synthesis (MPS) and muscle protein breakdown (MPB), each of which can be quantified through the use of stable isotopically labelled tracers. Importantly, both MPS and MPB can be influenced by external factors such as nutritional manipulation, specifically protein ingestion, and changes in loading via exercise. To date, research involving stable isotopic tracers has focused on determining the optimal dose, timing surrounding bouts of exercise, distribution and composition of protein to maximally stimulate MPS and inhibit MPB, both at rest and following exercise. In this review we focus on the use of these stable isotopically-labeled tracers to unravel the intricacies of skeletal muscle protein turnover in response to specific nutritional interventions.