Rate Of Protein Synthesis In Tissues Research Articles

Repeated passive heat treatment increases muscle tissue capillarization, but does not affect postprandial muscle protein synthesis rates in healthy older adults.

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 (9males, 5 females; 73 ± 6years) underwent 8weeks of PHT (infrared sauna: 3× per week, 45min 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 POINTS: Repeated exposure to heat has been suggested to trigger skeletal muscle adaptive responses. We investigated the effect of 8weeks of whole-body passive heat treatment (PHT; infrared sauna: 3× per week for 45min 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.

Collagen Peptide Supplementation during Training Does Not Further Increase Connective Tissue Protein Synthesis Rates.

Protein supplementation increases post-exercise muscle protein synthesis rates and, as such, supports exercise-induced muscle conditioning. Collagen protein has been suggested as the preferred protein source to stimulate muscle connective protein synthesis rates during recovery from exercise. Here we assessed the effects of hydrolyzed collagen peptide supplementation on both myofibrillar as well as muscle connective protein synthesis rates during one week of strenuous resistance exercise training. In a randomized, double-blind, parallel design, 25 young men (24 ± 3 y, 76.9 ± 6.4 kg) were selected to perform one week of intense resistance-type exercise training. Subjects were randomly assigned into two groups receiving either 15 g hydrolyzed collagen peptides (COL) or a non-caloric placebo (PLA) twice daily during the intervention. Subjects were administered deuterated water (2H2O) daily, with blood and skeletal muscle tissue samples being collected prior to and after the intervention to determine daily myofibrillar and muscle connective protein synthesis rates. Post-absorptive plasma glycine, proline, and hydroxyproline concentrations increased following collagen peptide supplementation (p < 0.05) and showed higher levels when compared to the placebo group (p < 0.05). Daily muscle connective protein synthesis rates during the intervention period exceeded myofibrillar protein synthesis rates (1.99 ± 0.38 versus 1.34 ± 0.23 %/d, respectively; p < 0.001). Collagen peptide supplementation did not result in higher myofibrillar or muscle connective protein synthesis rates (1.34 ± 0.19 and 1.97 ± 0.47 %/d, respectively) when compared to the placebo group (1.34 ± 0.27 and 2.00 ± 0.27 %/d, respectively; p > 0.05). Collagen peptide supplementation (2 x 15 g daily) does not increase myofibrillar or muscle connective protein synthesis rates during one week of intense resistance exercise training in young, recreational athletes.

A comparative study of tissue protein synthesis rates in an Antarctic, Harpagifer antarcticus and a temperate, Lipophrys pholis teleost

The affect of temperature on tissue protein synthesis rates has been reported in temperate and tropical, but not Antarctic fishes. Previous studies have generally demonstrated low growth rates in Antarctic fish species in comparison to temperate relatives and elevated levels of protein turnover. This study investigates how low temperatures effect tissue protein synthesis and hence tissue growth in a polar fish species. Groups of Antarctic, Harpagifer antarcticus and temperate, Lipophrys pholis, were acclimated to a range of overlapping water temperatures and protein synthesis was measure in white muscle (WM), liver and gastrointestinal tract (GIT). WM protein synthesis rates increased linearly with temperature in both species (H. antarcticus 0.16–0.23%.d−1, L. pholis, 0.31–0.76%.d−1), while liver (H. antarcticus 0.24–0.27%.d−1, L. pholis, 0.44–1.03%.d−1) and GIT were unaffected by temperature in H. antarcticus but increased non-linearly in L.pholis (H. antarcticus 0.22–0.26%.d−1, L. pholis, 0.40–0.86%.d−1). RNA to protein ratios were unaffected by temperature in H. antarcticus but increased weakly, in L.pholis WM and liver. In L.pholis, RNA translational efficiency increased significantly with temperature in all tissues, but only in liver in H. antarcticus. At the overlapping temperature of 3 °C, protein synthesis (WM 26%, Liver, 39%, GIT, 35%) and RNA translational efficiency (WM 273%, Liver, 271%, GIT, 300%) were significantly lower in H. antarcticus than L.pholis, while RNA to protein ratios were significantly higher (WM 270%, Liver 170%, GIT 186%). Tissue specific effects of temperature are detectable in both species. This study provides the first evidence, that tissue protein synthesis rates are constrained in Antarctic fishes.

Trabecular, but not cortical, bone tissue protein synthesis rates are lower in the femoral head when compared to the proximal femur following an intracapsular hip fracture.

All musculoskeletal tissues are in a constant state of turnover, with a dynamic equilibrium between tissue protein synthesis and breakdown rates. The synthesis of protein allows musculoskeletal tissues to heal following injury. Yet, impaired tissue healing is observed following certain injuries, such as geriatric hip fractures. It is assumed that the regenerative properties of femoral head bone tissue are compromised following an intracapsular hip fracture and therefore hip replacement surgery is normally performed. However, the actual impact on in vivo bone protein synthesis rates has never been determined. In the present study, 10 patients (age: 79±10 y, BMI: 24±4kg/m2) with an acute (<24h) intracapsular hip fracture received a primed continuous intravenous infusion of L-[ring-13C6]-phenylalanine before and throughout their hip replacement surgery. Trabecular and cortical bone tissue from both the femoral head and proximal femur were sampled during surgery to assess protein synthesis rates of affected (femoral head) and unaffected (proximal femur) bone tissue, respectively. In addition, tissue samples of gluteus maximus muscle, synovium, ligamentum teres, and femoral head cartilage were collected. Tissue-specific protein synthesis rates were assessed by measuring L-[ring-13C6]-phenylalanine incorporation in tissue protein. Femoral head trabecular bone protein synthesis rates (0.056 [0.024-0.086] %/h) were lower when compared to proximal femur trabecular bone protein synthesis rates (0.081 [0.056-0.118] %/h; P=0.043). Cortical bone protein synthesis rates did not differ between the femoral head and proximal femur (0.041 [0.021-0.078] and 0.045 [0.028-0.073] %/h, respectively; P>0.05). Skeletal muscle, synovium, ligamentum teres, and femoral head cartilage protein synthesis rates averaged 0.080 [0.048-0.089], 0.093 [0.051-0.130], 0.121 [0.110-0.167], and 0.023 [0.015-0.039] %/h, respectively. In contrast to the general assumption that the femoral head is avital after an intracapsular displaced hip fracture in the elderly, our data show that bone protein synthesis is still ongoing in femoral head bone tissue during the early stages following an intracapsular hip fracture in older patients. Nonetheless, trabecular bone protein synthesis rates are lower in the femoral head when compared to the proximal femur in older patients following an acute intracapsular hip fracture. Trial register no: NL9036.

Exercise Plus Presleep Protein Ingestion Increases Overnight Muscle Connective Tissue Protein Synthesis Rates in Healthy Older Men.

Protein ingestion and exercise stimulate myofibrillar protein synthesis rates. When combined, exercise further increases the postprandial rise in myofibrillar protein synthesis rates. It remains unclear whether protein ingestion with or without exercise also stimulates muscle connective tissue protein synthesis rates. The authors assessed the impact of presleep protein ingestion on overnight muscle connective tissue protein synthesis rates at rest and during recovery from resistance-type exercise in older men. Thirty-six healthy, older men were randomly assigned to ingest 40g intrinsically L-[1-13C]-phenylalanine and L-[1-13C]-leucine-labeled casein protein (PRO, n = 12) or a nonprotein placebo (PLA, n = 12) before going to sleep. A third group performed a single bout of resistance-type exercise in the evening before ingesting 40g intrinsically-labeled casein protein prior to sleep (EX+PRO, n = 12). Continuous intravenous infusions of L-[ring-2H5]-phenylalanine and L-[1-13C]-leucine were applied with blood and muscle tissue samples collected throughout overnight sleep. Presleep protein ingestion did not increase muscle connective tissue protein synthesis rates (0.049 ± 0.013 vs. 0.060 ± 0.024%/hr in PLA and PRO, respectively; p = .73). Exercise plus protein ingestion resulted in greater overnight muscle connective tissue protein synthesis rates (0.095 ± 0.022%/hr) when compared with PLA and PRO (p < .01). Exercise increased the incorporation of dietary protein-derived amino acids into muscle connective tissue protein (0.036 ± 0.013 vs. 0.054 ± 0.009 mole percent excess in PRO vs. EX+PRO, respectively; p < .01). In conclusion, resistance-type exercise plus presleep protein ingestion increases overnight muscle connective tissue protein synthesis rates in older men. Exercise enhances the utilization of dietary protein-derived amino acids as precursors for de novo muscle connective tissue protein synthesis during overnight sleep.

Comprehensive assessment of post-prandial protein handling by the application of intrinsically labelled protein in vivo in human subjects.

All human tissues are in a constant state of remodelling, regulated by the balance between tissue protein synthesis and breakdown rates. It has been well-established that protein ingestion stimulates skeletal muscle and whole-body protein synthesis. Stable isotope-labelled amino acid methodologies are commonly applied to assess the various aspects of protein metabolism in vivo in human subjects. However, to achieve a more comprehensive assessment of post-prandial protein handling in vivo in human subjects, intravenous stable isotope-labelled amino acid infusions can be combined with the ingestion of intrinsically labelled protein and the collection of blood and muscle tissue samples. The combined application of ingesting intrinsically labelled protein with continuous intravenous stable isotope-labelled amino acid infusion allows the simultaneous assessment of protein digestion and amino acid absorption kinetics (e.g. release of dietary protein-derived amino acids into the circulation), whole-body protein metabolism (whole-body protein synthesis, breakdown and oxidation rates and net protein balance) and skeletal muscle metabolism (muscle protein fractional synthesis rates and dietary protein-derived amino acid incorporation into muscle protein). The purpose of this review is to provide an overview of the various aspects of post-prandial protein handling and metabolism with a focus on insights obtained from studies that have applied intrinsically labelled protein under a variety of conditions in different populations.

Assessing the whole-body protein synthetic response to feeding in vivo in human subjects.

All tissues are in a constant state of turnover, with a tightly controlled regulation of protein synthesis and breakdown rates. Due to the relative ease of sampling skeletal muscle tissue, basal muscle protein synthesis rates and the protein synthetic responses to various anabolic stimuli have been well defined in human subjects. In contrast, only limited data are available on tissue protein synthesis rates in other organs. Several organs such as the brain, liver and pancreas, show substantially higher (basal) protein synthesis rates when compared to skeletal muscle tissue. Such data suggest that these tissues may also possess a high level of plasticity. It remains to be determined whether protein synthesis rates in these tissues can be modulated by external stimuli. Whole-body protein synthesis rates are highly responsive to protein intake. As the contribution of muscle protein synthesis rates to whole-body protein synthesis rates is relatively small considering the large amount of muscle mass, this suggests that other organ tissues may also be responsive to (protein) feeding. Whole-body protein synthesis rates in the fasted or fed state can be quantified by measuring plasma amino acid kinetics, although this requires the production of intrinsically labelled protein. Protein intake requirements to maximise whole-body protein synthesis may also be determined by the indicator amino acid oxidation technique, but the technique does not allow the assessment of actual protein synthesis and breakdown rates. Both approaches have several other methodological and inferential limitations that will be discussed in detail in this paper.

Casein Ingestion Does Not Increase Muscle Connective Tissue Protein Synthesis Rates.

This study aimed to assess the effect of dietary protein ingestion on intramuscular connective tissue protein synthesis rates during overnight recovery from a single bout of resistance exercise. Thirty-six healthy, young males were randomly assigned to one of three treatments. One group ingested 30 g intrinsically L-[1-C]-phenylalanine-labeled casein protein before sleep (PRO, n = 12). The other two groups performed a bout of resistance exercise in the evening and ingested either placebo (EX, n = 12) or 30 g intrinsically L-[1-C]-phenylalanine-labeled casein protein before sleep (EX + PRO, n = 12). Continuous intravenous infusions of L-[ring-H5]-phenylalanine and L-[1-C]-leucine were applied, and blood and muscle tissue samples were collected to assess connective tissue protein synthesis rates and dietary protein-derived amino acid incorporation in the connective tissue protein fraction. Resistance exercise resulted in higher connective tissue protein synthesis rates when compared with rest (0.086 ± 0.017%·h [EX] and 0.080 ± 0.019%·h [EX + PRO] vs 0.059 ± 0.016%·h [PRO]; P < 0.05). Postexercise casein protein ingestion did not result in higher connective tissue protein synthesis rates when compared with postexercise placebo ingestion (P = 1.00). Dietary protein-derived amino acids were incorporated into the connective tissue protein fraction at rest, and to a greater extent during recovery from exercise (P = 0.002). Resistance exercise increases intramuscular connective tissue protein synthesis rates during overnight sleep, with no further effect of postexercise protein ingestion. However, dietary protein-derived amino acids are being used as precursors to support de novo connective tissue protein synthesis.

Protein synthesis rates of muscle, tendon, ligament, cartilage, and bone tissue in vivo in humans.

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

Tumour-specific and organ-specific protein synthesis rates in patients with pancreatic cancer.

BackgroundLiving tissues maintain a fine balance between protein synthesis and protein breakdown rates. Animal studies indicate that protein synthesis rates are higher in organs when compared with skeletal muscle tissue. As such, organ and tumour protein synthesis could have major effects on whole‐body protein metabolism in wasting disorders such as cancer cachexia. We aimed to assess protein synthesis rates in pancreatic tumour tissue and healthy pancreas, liver, and skeletal muscle tissue in vivo in humans.MethodsIn eight patients with pancreatic cancer undergoing pancreaticoduodenectomy, primed continuous infusions with L‐[ring‐13C6]phenylalanine and L‐[3,5‐2H2]tyrosine were started prior to surgery and continued throughout the surgical procedures. During surgery, plasma samples and biopsies from the pancreas, pancreatic tumour, liver, and vastus lateralis muscle were taken. Post‐absorptive fractional protein synthesis rates were determined by measuring incorporation of labelled L‐[ring‐13C6]phenylalanine in tissue protein using the weighed plasma L‐[ring‐13C6]phenylalanine enrichments as the precursor pool.ResultsFive male patients and three female patients with a mean age of 67 ± 2 years were included into this study. Plasma L‐[ring‐13C6]phenylalanine enrichments (6–9 mole per cent excess) did not change during surgery (P = 0.60). Pancreatic tumour protein synthesis rates were 2.6‐fold lower than surrounding pancreatic tissue protein synthesis rates (0.268 ± 0.053 vs. 0.694 ± 0.228%/h, respectively; P = 0.028) and 1.7‐fold lower than liver protein synthesis rates (0.268 ± 0.053 vs. 0.448 ± 0.043%/h, respectively; P = 0.046). Among healthy organ samples, protein synthesis rates were 20‐fold and 13‐fold higher in pancreas and liver, respectively, compared with skeletal muscle tissue (0.694 ± 0.228 and 0.448 ± 0.043 vs. 0.035 ± 0.005%/h, respectively; P < 0.05).ConclusionsLiver and pancreas tissue protein synthesis rates are higher when compared with pancreatic tumour and skeletal muscle tissue protein synthesis rates and can, therefore, strongly impact whole‐body protein metabolism in vivo in humans.

Measurement of Muscle, Tendon, Ligament, Cartilage, and Bone Protein Synthesis Rates In Vivo in Humans

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&lt;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&gt;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&lt;0.05 and P&lt;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.

Brain tissue plasticity: protein synthesis rates of the human brain.

All tissues undergo continuous reconditioning via the complex orchestration of changes in tissue protein synthesis and breakdown rates. Skeletal muscle tissue has been well studied in this regard, and has been shown to turnover at a rate of 1-2% per day in vivo in humans. Few data are available on protein synthesis rates of other tissues. Because of obvious limitations with regard to brain tissue sampling no study has ever measured brain protein synthesis rates in vivo in humans. Here, we applied stable isotope methodology to directly assess protein synthesis rates in neocortex and hippocampus tissue of six patients undergoing temporal lobectomy for drug-resistant temporal lobe epilepsy (Clinical trial registration: NTR5147). Protein synthesis rates of neocortex and hippocampus tissue averaged 0.17 ± 0.01 and 0.13 ± 0.01%/h, respectively. Brain tissue protein synthesis rates were 3-4-fold higher than skeletal muscle tissue protein synthesis rates (0.05 ± 0.01%/h; P < 0.001). In conclusion, the protein turnover rate of the human brain is much higher than previously assumed.

Creatine supplementation to total parenteral nutrition improves creatine status and supports greater liver and kidney protein synthesis in neonatal piglets.

BackgroundCreatine is not included in commercial pediatric parenteral products; the entire creatine requirement must be met by de novo synthesis from arginine during parenteral nutrition (PN). Poor arginine status is common during PN in neonates, which may compromise creatine accretion. We hypothesized that creatine supplementation will improve creatine status and spare arginine in PN-fed piglets.MethodsPiglets (3-5-day (d) old) were provided PN with or without creatine for 14 d. Tissue concentrations of creatine metabolites and activities of creatine-synthesizing enzymes, as well as tissue protein synthesis rates and liver lipid parameters, were measured.ResultsCreatine provision lowered kidney and pancreas L-arginine:glycine amidinotransferase (AGAT, EC number 2.1.4.1) activities and plasma guanidinoacetic acid (GAA) concentration, suggesting the downregulation of de novo creatine synthesis. Creatine increased plasma creatine concentrations to sow-fed reference levels and increased the creatine concentrations in most tissues, but not in the brain. PN creatine resulted in greater protein synthesis in the liver and the kidney, but not in the pancreas, skeletal muscle, or gut. Creatine supplementation also reduced liver cholesterol concentrations, but not triglyceride or total fat.ConclusionThe addition of creatine to PN may optimize the accretion of creatine and reduce the metabolic burden of creatine synthesis in rapidly growing neonates.

Brain Plasticity: Measuring Protein Synthesis Rates in the Human Brain

IntroductionBrain plasticity is a term typically used to refer to the ability of the brain to reorganize itself throughout life. Though the term is often applied in neuroscience to express synaptic or non‐synaptic plasticity, information on whether neuroplasticity is also accompanied by a high brain tissue protein turnover rate is scarce. Because of obvious limitations with regard to brain tissue sampling no study has ever directly measured brain protein synthesis rates in vivo in humans. In this study, we applied contemporary stable isotope methodology to assess protein synthesis rates in vivo in human brain tissue of patients operated for drug‐resistant epilepsy.MethodsSix otherwise healthy patients (47±6 y), scheduled to undergo resective surgery for treatment of drug‐resistant temporomesial epilepsy, were included in this study. Primed continuous intravenous infusions with L‐[ring‐13C6]‐Phenylalanine and L‐[3,5‐2H2]‐Tyrosine were initiated 2.5 h prior to surgery and continued during surgery. Throughout the surgical procedure the following tissue samples were obtained: temporal neocortex, hippocampus, temporalis muscle, and vastus lateralis muscle. 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 between the different tissues using a paired t test.ResultsSerum L‐[ring‐13C6]‐Phenylalanine enrichments averaged 8.1±0.7 MPE throughout the surgical procedure. Protein synthesis rates of temporal neocortex and hippocampus tissue averaged 0.17±0.01 and 0.13±0.01 %/h, respectively, with a significant difference between both tissues (P&lt;0.05). Brain tissue protein synthesis rates were 3–4 fold higher compared to skeletal muscle protein synthesis rates (0.05±0.01 %/h; P&lt;0.001).ConclusionThis is the first study to present protein synthesis rates in vivo in the human brain. With brain protein synthesis rates being several‐fold higher compared to skeletal muscle protein synthesis rates, the human brain displays a degree of tissue plasticity much higher than generally assumed.

Comparison of different mass spectrometry techniques in the measurement of L‐[ring‐13C6]phenylalanine incorporation into mixed muscle proteins

Precise measurement of low enrichment of stable isotope labeled amino-acid tracers in tissue samples is a prerequisite in measuring tissue protein synthesis rates. The challenge of this analysis is augmented when small sample size is a critical factor. Muscle samples from human participants following an 8 h intravenous infusion of L-[ring-(13)C(6)]phenylalanine and a bolus dose of L-[ring-(13)C(6)]phenylalanine in a mouse were utilized. Liquid chromatography tandem mass spectrometry (LC/MS/MS), gas chromatography (GC) MS/MS and GC/MS were compared to the GC-combustion-isotope ratio MS (GC/C/IRMS), to measure mixed muscle protein enrichment of [ring-(13)C(6)]phenylalanine enrichment. The sample isotope enrichment ranged from 0.0091 to 0.1312 molar percent excess. As compared with GC/C/IRMS, LC/MS/MS, GC/MS/MS and GC/MS showed coefficients of determination of R(2)= 0.9962 and R(2) = 0.9942, and 0.9217 respectively. However, the precision of measurements (coefficients of variation) for intra-assay are 13.0%, 1.7%, 6.3% and 13.5% and for inter-assay are 9.2%, 3.2%, 10.2% and 25% for GC/C/IRMS, LC/MS/MS, GC/MS/MS and GC/MS, respectively. The muscle sample sizes required to obtain these results were 8 µg, 0.8 µg, 3 µg and 3 µg for GC/C/IRMS, LC/MS/MS, GC/MS/MS and GC/MS, respectively. We conclude that LC/MS/MS is optimally suited for precise measurements of L-[ring-(13)C(6)]phenylalanine tracer enrichment in low abundance and in small quantity samples.

Dietary Ornithine Affects the Tissue Protein Synthesis Rate in Young Rats

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.

Excessive Energy Intake Does Not Modify Fed‐state Tissue Protein Synthesis Rates in Adult Rats

The impact of chronic excessive energy intake on protein metabolism is still controversial. Male Wistar rats were fed ad libitum during 5 weeks with either a high-fat high-sucrose diet (HF: n = 9) containing 45% of total energy as lipids (protein 14%; carbohydrate 40% with 83.5% sucrose) or a standard diet (controls: n = 10). Energy intake and body weight were recorded. At the end of the experiment, we measured body composition, metabolic parameters (plasma amino acid, lipid, insulin, and glucose levels), inflammatory parameter (plasma alpha2-macroglobulin), oxidative stress parameters (antioxidant enzyme activities, lipoperoxidation (LPO), protein carbonyl content in liver and muscle), and in vivo fed-state fractional protein synthesis rates (FSRs) in muscle and liver. Energy intake was significantly higher in HF compared with control rats (+28%). There were significant increases in body weight (+8%), body fat (+21%), renal (+41%), and epidydimal (+28%) fat pads in HF compared with control rats. No effect was observed in other tissue weights (liver, muscle, spleen, kidneys, intestine). Liver and muscle FSRs, plasma levels of lipids, glucose, insulin and alpha2-macroglobulin, soleus and liver glutathione reductase and peroxidase activities, MnSOD activity, LPO, and protein carbonyl content were not altered by the HF diet. Only soleus muscle and liver Cu/ZnSOD activity and soleus muscle catalase activities were reduced in HF rats compared with control rats. Thus, chronic excessive energy intake and increased adiposity, in the absence of other metabolic alterations, do not stimulate fed-state tissue protein synthesis rates.

Characterisation of the high-protein-induced effects on tissue protein synthesis rates and accretion in rats

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Incorporating turnover in estimates of protein retention efficiency for different body tissues

Formulated in terms of protein synthesis (PS) and protein retention (PR), a definition of turnover-related protein retention efficiency (kP) allows the expression kP=[1+(PS/PR)/6](-1), 6 representing the ratio of the energy equivalent of protein to the cost of synthesis. By combining plausible hormonal and cellular control mechanisms of protein (P) growth, it is possible to derive (PS/PR)=[Q{(P/alpha)(-(4/9)Y)-1}](-1)+1, allowing the calculation of kP by substitution. The symbol alpha represents the limit value of protein growth, while the term 4/9 derives from the power in the relationship between the concentration of growth factor-related activator in the nucleus and cell volume (cv). Y is the power in the relationship between cv and total tissue protein, and Q represents the proportion of growth factor-activated nuclei in a tissue. The proportion Q can be estimated from simple functions of intake rates or blood growth factor concentrations. Estimates of Y are derived from histological considerations or calculated from experimental observations; Y=1 for multinucleated skeletal muscle fibres and Y=1/3, 1/2, 1/6 on average for mononucleated cell tissues, skin or bone and viscera, respectively. To apply kP to the whole body, an average value of Y=1/2 can be taken. Experimental observations on tissue protein synthesis and breakdown rates yield direct estimates of kP in satisfactory agreement with comparable theoretical predictions.

Dietary protein and lactose increase translation initiation factor activation and tissue protein synthesis in neonatal pigs

Protein synthesis and eukaryotic initiation factor (eIF) activation are increased in muscle and liver of pigs parenterally infused with amino acids and insulin. To examine the effects of enteral protein and carbohydrate on protein synthesis, pigs (n = 42, 1.7 kg body wt) were fed isocaloric milk diets containing three levels of protein (5, 15, and 25 g x kg body wt(-1) x day(-1)) and two levels of lactose (low = 11 and high = 23 g x kg body wt(-1) x day(-1)) from 1 to 6 days of age. On day 7, pigs were gavage fed after 4-h food deprivation, and tissue protein synthesis rates and biomarkers of mRNA translation were assessed. Piglet growth and protein synthesis rates in muscle and liver increased with dietary protein and plateaued at 15 g x kg body wt(-1) x day(-1) (P < 0.001). Growth tended to be greater in high-lactose-fed pigs (P = 0.07). Plasma insulin was lowest in pigs fed 5 g x kg body wt(-1) x day(-1) protein (P < 0.0001). Plasma branched-chain amino acids increased as protein intake increased (P < 0.0001). Muscle (P < 0.001) and liver (P < or = 0.001) ribosomal protein S6 kinase-1 and eIF4E-binding protein phosphorylation increased with protein intake and plateaued at 15 g x kg body wt(-1) x day(-1). The results indicate that growth and protein synthesis rates in neonatal pigs are influenced by dietary protein and lactose intake and might be mediated by plasma amino acids and insulin levels. However, feeding protein well above the piglet's requirement does not further stimulate the activation of translation initiation or protein synthesis in skeletal muscle and liver.