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

Protein type, protein dose, and age modulate dietary protein digestion and phenylalanine absorption kinetics and plasma phenylalanine availability in humans

This is the final version. Available from the publisher via the DOI in this record.BACKGROUND: Dietary protein ingestion stimulates muscle protein synthesis by providing amino acids to the muscle. The magnitude and duration of the postprandial increase in muscle protein synthesis rates are largely determined by dietary protein digestion and amino acid absorption kinetics. OBJECTIVE: We assessed the impact of protein type, protein dose, and age on dietary protein digestion and amino acid absorption kinetics in vivo in humans. METHODS: We included data from 18 randomized controlled trials with a total of 602 participants [age: 53 ± 23 y; BMI (kg/m2): 24.8 ± 3.3] who consumed various quantities of intrinsically l-[1-13C]-phenylalanine-labeled whey (n = 137), casein (n = 393), or milk (n = 72) protein and received intravenous infusions of l-[ring-2H5]-phenylalanine, which allowed us to assess protein digestion and phenylalanine absorption kinetics and the postprandial release of dietary protein-derived phenylalanine into the circulation. The effect of aging on these processes was assessed in a subset of 82 young (aged 22 ± 3 y) and 83 older (aged 71 ± 5 y) individuals. RESULTS: A total of 50% ± 14% of dietary protein-derived phenylalanine appeared in the circulation over a 5-h postprandial period. Casein ingestion resulted in a smaller (45% ± 11%), whey protein ingestion in an intermediate (57% ± 10%), and milk protein ingestion in a greater (65% ± 13%) fraction of dietary protein-derived phenylalanine appearing in the circulation (P < 0.001). The postprandial availability of dietary protein-derived phenylalanine in the circulation increased with the ingestion of greater protein doses (P < 0.05). Protein digestion and phenylalanine absorption kinetics were attenuated in older when compared with young individuals, with 45% ± 10% vs. 51% ± 14% of dietary protein-derived phenylalanine appearing in the circulation, respectively (P = 0.001). CONCLUSIONS: Protein type, protein dose, and age modulate dietary protein digestion and amino acid absorption kinetics and subsequent postprandial plasma amino acid availability in vivo in humans. These trials were registered at clinicaltrials.gov as NCT00557388, NCT00936039, NCT00991523, NCT01317511, NCT01473576, NCT01576848, NCT01578590, NCT01615276, NCT01680146, NCT01820975, NCT01986842, and NCT02596542, and at http://www.trialregister.nl as NTR3638, NTR3885, NTR4060, NTR4429, and NTR4492

Is Cancer Cachexia Attributed to Impairments in Basal or Postprandial Muscle Protein Metabolism?

Cachexia is a significant clinical problem associated with very poor quality of life, reduced treatment tolerance and outcomes, and a high mortality rate. Mechanistically, any sizeable loss of skeletal muscle mass must be underpinned by a structural imbalance between muscle protein synthesis and breakdown rates. Recent data indicate that the loss of muscle mass with aging is, at least partly, attributed to a blunted muscle protein synthetic response to protein feeding. Whether such anabolic resistance is also evident in conditions where cachexia is present remains to be addressed. Only few data are available on muscle protein synthesis and breakdown rates in vivo in cachectic cancer patients. When calculating the theoretical changes in basal or postprandial fractional muscle protein synthesis and breakdown rates that would be required to lose 5% of body weight within a six-month period, we can define the changes that would need to occur to explain the muscle mass loss observed in cachectic patients. If changes in both post-absorptive and postprandial muscle protein synthesis and breakdown rates contribute to the loss of muscle mass, it would take alterations as small as 1%–2% to induce a more than 5% decline in body weight. Therefore, when trying to define impairments in basal and/or postprandial muscle protein synthesis or breakdown rates using contemporary stable isotope methodology in cancer cachexia, we need to select large homogenous groups of cancer patients (&gt;40 patients) to allow us to measure physiological and clinically relevant differences in muscle protein synthesis and/or breakdown rates. Insight into impairments in basal or postprandial muscle protein synthesis and breakdown rates in cancer cachexia is needed to design more targeted nutritional, pharmaceutical and/or physical activity interventions to preserve skeletal muscle mass and, as such, to reduce the risk of complications, improve quality of life, and lower mortality rates during the various stages of the disease

Ingestion of Wheat Protein Increases In Vivo Muscle Protein Synthesis Rates in Healthy Older Men in a Randomized Trial

Background: Muscle mass maintenance is largely regulated by basal muscle protein synthesis and the capacity to stimulate muscle protein synthesis after food intake. The postprandial muscle protein synthetic response is modulated by the amount, source, and type of protein consumed. It has been suggested that plant-based proteins are less potent in stimulating postprandial muscle protein synthesis than animal-derived proteins. However, few data support this contention. Objective: We aimed to assess postprandial plasma amino acid concentrations and muscle protein synthesis rates after the ingestion of a substantial 35-g bolus of wheat protein hydrolysate compared with casein and whey protein. Methods: Sixty healthy older men [mean 6 SEM age: 71 6 1 y; body mass index (in kg/m2 ): 25.3 6 0.3] received a primed continuous infusion of L-[ring-13C6]-phenylalanine and ingested 35 g wheat protein (n = 12), 35 g wheat protein hydrolysate (WPH-35; n = 12), 35 g micellar casein (MCas-35; n = 12), 35 g whey protein (Whey-35; n = 12), or 60 g wheat protein hydrolysate (WPH-60; n = 12). Plasma and muscle samples were collected at regular intervals. Results: The postprandial increase in plasma essential amino acid concentrations was greater after ingesting Whey-35 (2.23 6 0.07 mM) than after MCas-35 (1.53 6 0.08 mM) and WPH-35 (1.50 6 0.04 mM) (P < 0.01). Myofibrillar protein synthesis rates increased after ingesting MCas-35 (P < 0.01) and were higher after ingesting MCas-35 (0.050% 6 0.005%/h) than after WPH-35 (0.032% 6 0.004%/h) (P = 0.03). The postprandial increase in plasma leucine concentrations was greater after ingesting Whey-35 than after WPH-60 (peak value: 580 6 18 compared with 378 6 10 mM, respectively; P < 0.01), despite similar leucine contents (4.4 g leucine). Nevertheless, the ingestion of WPH-60 increased myofibrillar protein synthesis rates above basal rates (0.049% 6 0.007%/h; P = 0.02). Conclusions: The myofibrillar protein synthetic response to the ingestion of 35 g casein is greater than after an equal amount of wheat protein. Ingesting a larger amount of wheat protein (i.e., 60 g) substantially increases myofibrillar protein synthesis rates in healthy older men. This trial was registered at clinicaltrials.gov as NCT0195263

Basal protein synthesis rates differ between vastus lateralis and rectus abdominis muscle

Background In vivo muscle protein synthesis rates are typically assessed by measuring the incorporation rate of stable isotope labelled amino acids in skeletal muscle tissue collected from vastus lateralis muscle. It remains to be established whether muscle protein synthesis rates in the vastus lateralis are representative of muscle protein synthesis rates of other muscle groups. We hypothesized that post-absorptive muscle protein synthesis rates differ between vastus lateralis and rectus abdominis, pectoralis major, or temporalis muscle in vivo in humans. Methods Twenty-four patients (62 ± 3 years, 42% female), scheduled to undergo surgery, participated in this study and underwent primed continuous intravenous infusions with l-[ring-13C6]-phenylalanine. During the surgical procedures, serum samples were collected, and muscle tissue was obtained from the vastus lateralis as well as from the rectus abdominis, pectoralis major, or temporalis muscle. Fractional mixed muscle protein synthesis rates (%/h) were assessed by measuring the incorporation of l-[ring-13C6]-phenylalanine into muscle tissue protein. Results Serum l-[ring-13C6]-phenylalanine enrichments did not change throughout the infusion period. Post-absorptive muscle protein synthesis rates calculated based upon serum l-[ring-13C6]-phenylalanine enrichments did not differ between vastus lateralis and rectus abdominis (0.032 ± 0.004 vs. 0.038 ± 0.003%/h), vastus lateralis and pectoralis major, (0.025 ± 0.003 vs. 0.022 ± 0.005%/h) or vastus lateralis and temporalis (0.047 ± 0.005 vs. 0.043 ± 0.005%/h) muscle, respectively (P > 0.05). When fractional muscle protein synthesis rates were calculated based upon tissue-free l-[ring-13C6]-phenylalanine enrichments as the preferred precursor pool, muscle protein synthesis rates were significantly higher in rectus abdominis (0.089 ± 0.008%/h) compared with vastus lateralis (0.054 ± 0.005%/h) muscle (P < 0.01). No differences were observed between fractional muscle protein synthesis rates in vastus lateralis and pectoralis major (0.046 ± 0.003 vs. 0.041 ± 0.008%/h) or vastus lateralis and temporalis (0.073 ± 0.008 vs. 0.083 ± 0.011%/h) muscle, respectively. Conclusions Post-absorptive muscle protein synthesis rates are higher in rectus abdominis when compared with vastus lateralis muscle. Post-absorptive muscle protein synthesis rates do not differ between vastus lateralis and pectoralis major or temporalis muscle. Protein synthesis rates in muscle tissue samples obtained during surgery do not necessarily represent a good proxy for appendicular skeletal muscle protein synthesis rates

The Muscle Protein Synthetic Response to Whey Protein Ingestion Is Greater in Middle-Aged Women Compared With Men

Rationale: Muscle mass maintenance is largely regulated by the postprandial rise in muscle protein synthesis rates. It remains unclear whether postprandial protein handling differs between women and men. Methods: Healthy men (43 ± 3 years; body mass index, 23.4 ± 0.4 kg/m2; n = 12) and women (46 ± 2 years; body mass index, 21.3 ± 0.5 kg/m2; n = 12) received primed continuous infusions of L-[ring-2H5]-phenylalanine and L-[ring-3,5-2H2]-tyrosine and ingested 25 g intrinsically L-[1-13C]-phenylalanine–labeled whey protein. Blood samples and muscle biopsies were collected to assess dietary protein digestion and amino acid absorption kinetics as well as basal and postprandial myofibrillar protein synthesis rates. Results: Plasma phenylalanine and leucine concentrations rapidly increased after protein ingestion (both P < 0.001), with no differences between middle-aged women and men (Time × Sex, P = 0.307 and 0.529, respectively). The fraction of dietary protein–derived phenylalanine that appeared in the circulation over the 5-hour postprandial period averaged 56 ± 1% and 53 ± 1% in women and men, respectively (P = 0.145). Myofibrillar protein synthesis rates increased (Time, P = 0.010) from 0.035 ± 0.004%/h and 0.030 ± 0.002%/h in the postabsorptive state (t test, P = 0.319) to 0.045 ± 0.002%/h and 0.034 ± 0.002%/h in the 5-hour postprandial phase in middle-aged women and men, respectively, with higher postprandial myofibrillar protein synthesis rates in women compared with men (ttest, P = 0.005). Middle-aged women showed a greater increase in myofibrillar protein synthesis rates during the early (0 to 2 hours) postprandial period compared with men (Time × Sex, P = 0.001). Conclusions: There are no differences in postabsorptive myofibrillar protein synthesis rates between middle-aged women and men. The myofibrillar protein synthetic response to the ingestion of 25 g whey protein is greater in women than in men

Habituation to low or high protein intake does not modulate basal or postprandial muscle protein synthesis rates: a randomized trial

Background: Muscle mass maintenance is largely regulated by basal muscle protein synthesis rates and the ability to increase mus-cle protein synthesis after protein ingestion. To our knowledge, no previous studies have evaluated the impact of habituation to either low protein intake (LOW PRO) or high protein intake (HIGH PRO) on the postprandial muscle protein synthetic response. Objective: We assessed the impact of LOW PRO compared with HIGH PRO on basal and postprandial muscle protein synthesis rates after the ingestion of 25 g whey protein. Design: Twenty-four healthy, older men [age: 62 6 1 y; body mass index (in kg/m2): 25.9 6 0.4 (mean 6 SEM)] participated in a parallel-group randomized trial in which they adapted to either aLOWPRO diet(0.7g $kg–1$ d21; n = 12) or a HIGH PRO diet (1.5 g $kg–1$ d–1; n = 12) for 14 d. On day 15, partici-pants received primed continuous L-[ring-2H5]-phenylalanine and L-[1-13C]-leucine infusions and ingested 25 g intrinsically L-[1-13C]-phenylalanine– and L-[1-13C]-leucine–labeled whey pro-tein. Muscle biopsies and blood samples were collected to assess muscle protein synthesis rates as well as dietary protein digestion and absorption kinetics. Results: Plasma leucine concentrations and exogenous phenylala-nine appearance rates increased after protein ingestion (P , 0.01) with no differences between treatments (P . 0.05). Plasma exoge-nous phenylalanine availability over the 5-h postprandial period was greater after LOW PRO than after HIGH PRO (61% 6 1% com-pared with 56% 6 2%, respectively; P , 0.05). Muscle protein synthesis rates increased from 0.031% 6 0.004% compared with 0.039% 6 0.007%/h in the fasted state to 0.062% 6 0.005% com-pared with 0.057% 6 0.005%/h in the postprandial state after LOW PRO compared with HIGH PRO, respectively (P , 0.01), with no differences between treatments (P = 0.25). Conclusion: Habituation to LOW PRO (0.7 g $kg–1$ d–1)compared with HIGH PRO (1.5 g $kg–1$ d–1) augments the postprandial avail-ability of dietary protein–derived amino acids in the circulation and does not lower basal muscle protein synthesis rates or increase postprandial muscle protein synthesis rates after ingestion of 25 g protein in older men. This trial was registered at clinicaltrials.gov as NCT01986842. Am J Clin Nutr 2017;105:332–42

Post-prandial protein handling: You are what you just ate

Background Protein turnover in skeletal muscle tissue is highly responsive to nutrient intake in healthy adults. Objective To provide a comprehensive overview of post-prandial protein handling, ranging from dietary protein digestion and amino acid absorption, the uptake of dietary protein derived amino acids over the leg, the post-prandial stimulation of muscle protein synthesis rates, to the incorporation of dietary protein derived amino acids in de novo muscle protein. Design 12 healthy young males ingested 20 g intrinsically [1-13C]-phenylalanine labeled protein. In addition, primed continuous L-[ring-2H5]-phenylalanine, L-[ring-2H2]-tyrosine, and L-[1-13C]-leucine infusions were applied, with frequent collection of arterial and venous blood samples, and muscle biopsies throughout a 5 h post-prandial period. Dietary protein digestion, amino acid absorption, splanchnic amino acid extraction, amino acid uptake over the leg, and subsequent muscle protein synthesis were measured within a single in vivo human experiment. Results 55.3±2.7% of the protein-derived phenylalanine was released in the circulation during the 5 h post-prandial period. The post-prandial rise in plasma essential amino acid availability improved leg muscle protein balance (from -291±72 to 103±66 μM·min-1·100 mL leg volume-1; P < 0.001). Muscle protein synthesis rates increased significantly following protein ingestion (0.029±0.002 vs 0.044±0.004%·h-1 based upon the muscle protein bound L-[ring-2H5]-phenylalanine enrichments (P < 0.01)), with substantial incorporation of dietary protein derived L-[1-13C]-phenylalanine into de novo muscle protein (from 0 to 0.0201±0.0025 MPE). Conclusion Ingestion of a single meal-like amount of protein allows ~55% of the protein derived amino acids to become available in the circulation, thereby improving whole-body and leg protein balance. About 20% of the dietary protein derived amino acids released in the circulation are taken up in skeletal muscle tissue following protein ingestion, thereby stimulating muscle protein synthesis rates and providing precursors for de novo muscle protein synthesis

Increasing Insulin Availability Does Not Augment Postprandial Muscle Protein Synthesis Rates in Healthy Young and Older Men

Context: Skeletal muscle protein synthesis is highly responsive to food intake. It has been suggested that the postprandial increase in circulating insulin modulates the muscle protein synthetic response to feeding. Objective: The objective of the study was to investigate whether a greater postprandial rise in circulating insulin level increases amino acid uptake in muscle and augments postprandial muscle protein synthesis rates. Participants and Design: Forty-eight healthy young ( age 22 ± 1 y; body mass index 22.0 ± 0.3 kg/m2 ) and older males ( age 68 ± 1 y; body mass index 26.3 ± 0.4 kg/m2 ) ingested 20 g intrinsically L-[1-13C]-leucine- and L-[1-13C]-phenylalanine-labeled casein protein with or without local insulin infusion. Primed continuous infusions of L-[1-13C]-leucine and L-[ring-2H5]-phenylalanine were applied, with arterial and venous blood samples and muscle biopsies being collected during a 5-hour postprandial period. Results: Insulin administration did not increase overall leg blood flow ( P = .509 ) but increased amino acid uptake over the leg in both young and older subjects ( P = .003 ). The greater amino acid uptake over the leg did not further increase postprandial muscle protein synthesis rates ( 0.050% ± 0.006% and 0.037% ± 0.004% per hour vs 0.044% ± 0.004% and 0.037% ± 0.002% per hour in the insulin-stimulated vs control condition in the young and older groups, respectively; P = .804 ) and did not affect postprandial deposition of dietary protein-derived amino acids in de novo muscle protein ( P = .872 ). Conclusion: Greater postprandial plasma insulin availability stimulates amino acid uptake over the leg but does not further augment postprandial muscle protein synthesis rates or stimulate the postprandial deposition of protein derived amino acids into de novo muscle protein in healthy young and older men

Whey protein supplementation does not accelerate recovery from a single bout of eccentric exercise

The current double blind, randomized, placebo-controlled trial with two parallel groups aimed to assess the impact of whey protein supplementation on recovery of muscle function and muscle soreness following eccentric exercise. During a 9-day period, forty recreationally active males received twice daily supplementation with either whey protein (PRO; 60 g/day) or an iso-energetic amount of carbohydrate (CON). Muscle function and soreness were assessed before, and 0, 3, 24, 48, and 72 h after performing 100 drop jumps. Recovery of isometric maximal voluntary contraction (MVC) did not significantly differ between groups (timextreatment, P = 0.56). In contrast, the recovery of isokinetic MVC at 90°·s−1 was faster in CON as opposed to PRO (timextreatment interaction, P = 0.044). Recovery of isokinetic MVC at 180°·s−1 was also faster in CON as opposed to PRO (timextreatment interaction, P = 0.011). Recovery of countermovement jump performance did not differ between groups (timextreatment interaction, P = 0.52). Muscle soreness, CK and CRP showed a transient increase over time (P < 0.001), with no differences between groups. In conclusion, whey protein supplementation does not accelerate recovery of muscle function or attenuate muscle soreness and inflammation during 3 days of recovery from a single bout of eccentric exercise