Lactobacillus gasseri BNR17 Ameliorates Dexamethasone-Induced Muscle Loss in BALB/c Mice and C2C12 Myotubes.

This study aimed to investigate the effects and mechanism of Lactobacillus gasseri BNR17, a probiotic strain isolated from human breast milk, on dexamethasone-induced muscle loss in mice and cultured myotubes. BALB/c mice were intraperitoneally injected with dexamethasone, and orally administered L. gasseri BNR17 for 21 days. L. gasseri BNR17 treatment ameliorated dexamethasone-induced decline in muscle function, as evidenced by an increase in forelimb grip strength, treadmill running time, and rotarod retention time in both female and male mice. In addition, L. gasseri BNR17 treatment significantly increased the mass of the gastrocnemius and quadriceps muscles. Dual-energy X-ray absorptiometry showed a significant increase in lean body mass and a decrease in fat mass in both whole body and hind limb after treatment with L. gasseri BNR17. It was found that L. gasseri BNR17 treatment downregulated serum myostatin level and the protein degradation pathway composed of muscle-specific ubiquitin E3 ligases, MuRF1 and MAFbx, and their transcription factor FoxO3. In contrast, L. gasseri BNR17 treatment upregulated serum insulin-like growth factor-1 level and Akt-mTOR-p70S6K signaling pathway involved in protein synthesis in muscle. As a result, L. gasseri BNR17 treatment significantly increased the levels of major muscular proteins such as myosin heavy chain and myoblast determination protein 1. Consistent with in vivo results, L. gasseri BNR17 culture supernatant significantly ameliorated dexamethasone-induced C2C12 myotube atrophy in vitro. In conclusion, L. gasseri BNR17 ameliorates muscle loss by downregulating the protein degradation pathway and upregulating the protein synthesis pathway.

Astaxanthin Ameliorates Skeletal Muscle Atrophy in Mice With Cancer Cachexia.

Astaxanthin (AST) is a natural marine carotenoid with a variety of biological activities. This study aimed to demonstrate the possible mechanisms by which AST improves skeletal muscle atrophy in cancer cachexia. In this study, the effects of different doses of AST (30 mg/kg b.w., 60 mg/kg b.w. and 120 mg/kg b.w.) on skeletal muscle functions were explored in mice with cancer cachexia. The results showed that AST (30, 60 and 120 mg/kg b.w.) could effectively protect cachexia mice from body weight and skeletal muscle loss. AST dose-dependently ameliorated the decrease in myofibres cross-sectional area and increased the expression of myosin heavy chain (MHC). AST treatment decreased both the serum and muscle level of IL-6 but not TNF-α in C26 tumor-bearing cachexia mice. Moreover, AST alleviated skeletal muscle atrophy by decreasing the expression of two muscle-specific E3 ligases MAFBx and MuRF-1. AST improved mitochondrial function by downregulating the levels of muscle Fis1, LC3B and Bax, upregulating the levels of muscle Mfn2 and Bcl-2. In conclusion, our study show that AST might be expected to be a nutritional supplement for cancer cachexia patients.

Effect of an immune challenge and two feed supplements on broiler chicken individual breast muscle protein synthesis rate.

Optimization of broiler chicken breast muscle protein accretion is key for the efficient production of poultry meat, whose demand is steadily increasing. In a context where antimicrobial growth promoters use is being restricted, it is important to find alternatives as well as to characterize the effect of immunological stress on broiler chicken's growth. Despite its importance, research on broiler chicken muscle protein dynamics has mostly been limited to the study of mixed protein turnover. The present study aims to characterize the effect of a bacterial challenge and the feed supplementation of citrus and cucumber extracts on broiler chicken individual breast muscle proteins fractional synthesis rates (FSR) using a recently developed dynamic proteomics pipeline. Twenty-one day-old broiler chickens were administered a single 2H2O dose before being culled at different timepoints. A total of 60 breast muscle protein extracts from five experimental groups (Unchallenged, Challenged, Control Diet, Diet 1 and Diet 2) were analysed using a DDA proteomics approach. Proteomics data was filtered in order to reliably calculate multiple proteins FSR making use of a newly developed bioinformatics pipeline. Broiler breast muscle proteins FSR uniformly decreased following a bacterial challenge, this change was judged significant for 15 individual proteins, the two major functional clusters identified as well as for mixed breast muscle protein. Citrus or cucumber extract feed supplementation did not show any effect on the breast muscle protein FSR of immunologically challenged broilers. The present study has identified potential predictive markers of breast muscle growth and provided new information on broiler chicken breast muscle protein synthesis which could be essential for improving the efficiency of broiler chicken meat production. SIGNIFICANCE: The present study constitutes the first dynamic proteomics study conducted in a farm animal species which has characterized FSR in a large number of proteins, establishing a precedent for biomarker discovery and assessment of health and growth status. Moreover, it has been evidenced that the decrease in broiler chicken breast muscle protein following an immune challenge is a coordinated event which seems to be the main cause of the decreased growth observed in these animals.

Combining proteins with n-3 PUFAs (EPA + DHA) and their inflammation pro-resolution mediators for preservation of skeletal muscle mass.

The optimal feeding strategy for critically ill patients is still debated, but feeding must be adapted to individual patient needs. Critically ill patients are at risk of muscle catabolism, leading to loss of muscle mass and its consequent clinical impacts. Timing of introduction of feeding and protein targets have been explored in recent trials. These suggest that "moderate" protein provision (maximum 1.2 g/kg/day) is best during the initial stages of illness. Unresolved inflammation may be a key factor in driving muscle catabolism. The omega-3 (n-3) fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are substrates for synthesis of mediators termed specialized pro-resolving mediators or SPMs that actively resolve inflammation. There is evidence from other settings that high-dose oral EPA + DHA increases muscle protein synthesis, decreases muscle protein breakdown, and maintains muscle mass. SPMs may be responsible for some of these effects, especially upon muscle protein breakdown. Given these findings, provision of EPA and DHA as part of medical nutritional therapy in critically ill patients at risk of loss of muscle mass seems to be a strategy to prevent the persistence of inflammation and the related anabolic resistance and muscle loss.

Pre-heating stress associated with acute oral leucine supplementation effects in rat gastrocnemius muscle: Implications for protein synthesis signaling pathways.

Skeletal muscle is a highly plastic tissue. The role of heat shock protein 72 (Hsp72) in heat stress-induced skeletal muscle hypertrophy has been well demonstrated; however, the precise mechanisms remain unclear. Essential amino acids, such as leucine, mainly mediate muscle protein synthesis. We investigated the effects of pre-heating and increased Hsp72 expression on the mechanistic target of rapamycin (mTOR) signaling and protein synthesis following leucine administration in rat gastrocnemius muscle. To ensure increased Hsp72 expression in both the red and white portions of the muscle, one leg of male Wistar rats (10-week-old, n = 23) was heat-stressed in 43 °C water for 30 min twice at a 48-h-interval (heat-stressed leg, HS leg). The contralateral leg served as a non-heated internal control (CT leg). After the recovery period (48 h), rats were divided into the pre-administration or oral leucine administration groups. We harvested the gastrocnemius muscle (red and white parts) prior to administration and 30 and 90 min after leucine treatment (n = 7-8 per group) and intramuscular signaling responses to leucine ingestion were determined using western blotting. Heat stress significantly upregulated the expression of Hsp72 and was not altered by leucine administration. Although the phosphorylation levels of mTOR/S6K1 and ERK were similar regardless of heating, 4E-BP1 was less phosphorylated in the HS legs than the CT legs after leucine administration in the red portion of the muscles (P < 0.05). Moreover, c-Myc expression differed significantly after leucine administration in both the red and white portions of the muscles. Our findings indicate that following oral leucine administration, pre-heating partially blunted the muscle protein synthesis signaling response in the rat gastrocnemius muscle.

Jakyak-gamcho-tang, a decoction of Paeoniae Radix and Glycyrrhizae Radix et Rhizoma, ameliorates dexamethasone-induced muscle atrophy and muscle dysfunction.

BACKGROUND: Although chronic treatment with glucocorticoids, such as dexamethasone, is frequently associated with muscle atrophy, effective and safe therapeutics for treating muscle atrophy remain elusive. Jakyak-gamcho-tang (JGT), a decoction of Paeoniae Radix and Glycyrrhizae Radix et Rhizoma, has long been used to relieve muscle tension and control muscle cramp-related pain. However, the effects of JGT on glucocorticoid-induced muscle atrophy are yet to be comprehensively clarified. PURPOSE: The objective of the current study was to validate the protective effect of JGT in dexamethasone-induced muscle atrophy models and elucidate its underlying mechanism through integrated in silico - in vitro - in vivo studies. STUDY DESIGN AND METHODS: Differential gene expression was preliminarily analyzed using the RNA-seq data to determine the effects of JGT on C2C12 myotubes. The protective effects of JGT were further validated in dexamethasone-treated C2C12 myotubes by assessing cell viability, myotube integrity, and mitochondrial function or in C57BL/6 N male mice with dexamethasone-induced muscle atrophy by evaluating muscle mass and physical performance. Transcriptomic pathway analysis was also performed to elucidate the underlying mechanism. RESULTS: Based on preliminary gene set enrichment analysis using the RNA-seq data, JGT regulated various pathways related to muscle differentiation and regeneration. Dexamethasone-treated C2C12 myotubes and muscle tissues of atrophic mice displayed substantial muscle protein degradation and muscle loss, respectively, which was efficiently alleviated by JGT treatment. Importantly, JGT-mediated protective effects were associated with observations such as preservation of mitochondrial function, upregulation of myogenic signaling pathways, including protein kinase B/mammalian target of rapamycin/forkhead box O3, inhibition of ubiquitin-mediated muscle protein breakdown, and downregulation of inflammatory and apoptotic pathways induced by dexamethasone. CONCLUSION: To the best of our knowledge, this is the first report to demonstrate that JGT could be a potential pharmaceutical candidate to prevent muscle atrophy induced by chronic glucocorticoid treatment, highlighting its known effects for relieving muscle spasms and pain. Moreover, transcriptomic pathway analysis can be employed as an efficient in silico tool to predict novel pharmacological candidates and elucidate molecular mechanisms underlying the effects of herbal medications comprising diverse biologically active ingredients.

Effects of Whey Protein Combined with Amylopectin/Chromium on the Muscle Protein Synthesis and mTOR Phosphorylation in Exercised Rats.

This study aimed to examine the impact of varying doses of whey protein (WP) and amylopectin/chromium complex (ACr) supplementation on muscle protein synthesis (MPS), amino acid and insulin levels, and the rapamycin (mTOR) signaling pathways in exercised rats. A total of 72 rats were randomly divided into nine groups: (1) Exercise (Ex), (2) Ex + WPI to (5) Ex + WPIV with various oral doses of whey protein (0.465, 1.55, 2.33, and 3.1 g/kg) and (6) Ex + WPI + ACr to (9) Ex + WPIV + ACr with various doses of whey protein combined with 0.155 g/kg ACr. On the day of single-dose administration, the products were given by oral gavage after exercise. To measure the protein fractional synthesis rate (FSR), a bolus dose of deuterium-labeled phenylalanine was given, and its effects were evaluated 1 h after supplementation. Rats that received 3.1 g/kg of whey protein (WP) combined with ACr exhibited the most significant increase in muscle protein synthesis (MPS) compared to the Ex group (115.7%, p < 0.0001). In comparison to rats that received the same dose of WP alone, those given the combination of WP and ACr at the same dosage showed a 14.3% increase in MPS (p < 0.0001). Furthermore, the WP (3.1 g/kg) + ACr group exhibited the highest elevation in serum insulin levels when compared to the Ex group (111.9%, p < 0.0001). Among the different groups, the WP (2.33 g/kg) + ACr group demonstrated the greatest increase in mTOR levels (224.2%, p < 0.0001). Additionally, the combination of WP (2.33 g/kg) and ACr resulted in a 169.8% increase in 4E-BP1 levels (p < 0.0001), while S6K1 levels rose by 141.2% in the WP (2.33 g/kg) + ACr group (p < 0.0001). Overall, supplementation with various doses of WP combined with ACr increased MPS and enhanced the mTOR signaling pathway compared to WP alone and the Ex group.

International Society of Sports Nutrition Position Stand: Effects of essential amino acid supplementation on exercise and performance.

Position Statement: The International Society of Sports Nutrition (ISSN) presents this position based on a critical examination of literature surrounding the effects of essential amino acid (EAA) supplementation on skeletal muscle maintenance and performance. This position stand is intended to provide a scientific foundation to athletes, dietitians, trainers, and other practitioners as to the benefits of supplemental EAA in both healthy and resistant (aging/clinical) populations. EAAs are crucial components of protein intake in humans, as the body cannot synthesize them. The daily recommended intake (DRI) for protein was established to prevent deficiencies due to inadequate EAA consumption. The following conclusions represent the official position of the Society: 1. Initial studies on EAAs' effects on skeletal muscle highlight their primary role in stimulating muscle protein synthesis (MPS) and turnover. Protein turnover is critical for replacing degraded or damaged muscle proteins, laying the metabolic foundation for enhanced functional performance. Consequently, research has shifted to examine the effects of EAA supplementation - with and without the benefits of exercise - on skeletal muscle maintenance and performance. 2. Supplementation with free-form EAAs leads to a quick rise in peripheral EAA concentrations, which in turn stimulates MPS. 3. The safe upper limit of EAA intake (amount), without inborn metabolic disease, can easily accommodate additional supplementation. 4. At rest, stimulation of MPS occurs at relatively small dosages (1.5-3.0 g) and seems to plateau at around 15-18 g. 5. The MPS stimulation by EAAs does not require non-essential amino acids. 6. Free-form EAA ingestion stimulates MPS more than an equivalent amount of intact protein. 7. Repeated EAA-induced MPS stimulation throughout the day does not diminish the anabolic effect of meal intake. 8. Although direct comparisons of various formulas have yet to be investigated, aging requires a greater proportion of leucine to overcome the reduced muscle sensitivity known as "anabolic resistance." 9. Without exercise, EAA supplementation can enhance functional outcomes in anabolic-resistant populations. 10. EAA requirements rise in the face of caloric deficits. During caloric deficit, it's essential to meet whole-body EAA requirements to preserve anabolic sensitivity in skeletal muscle.

The IFT81-IFT74 complex acts as an unconventional RabL2 GTPase-activating protein during intraflagellar transport.

Cilia are important cellular organelles for signaling and motility and are constructed via intraflagellar transport (IFT). RabL2 is a small GTPase that localizes to the basal body of cilia via an interaction with the centriolar protein CEP19 before downstream association with the IFT machinery, which is followed by initiation of IFT. We reconstituted and purified RabL2 with CEP19 or IFT proteins to show that a reconstituted pentameric IFT complex containing IFT81/74 enhances the GTP hydrolysis rate of RabL2. The binding site on IFT81/74 that promotes GTP hydrolysis in RabL2 was mapped to a 70-amino-acid-long coiled-coil region of IFT81/74. We present structural models for RabL2-containing IFT complexes that we validate in vitro and in cellulo and demonstrate that Chlamydomonas IFT81/74 enhances GTP hydrolysis of human RabL2, suggesting an ancient evolutionarily conserved activity. Our results provide an architectural understanding of how RabL2 is incorporated into the IFT complex and a molecular rationale for why RabL2 dissociates from anterograde IFT trains soon after departure from the ciliary base.

A Comparative Biochemical Study Between L-Carnosine and ß-Alanine in Amelioration of Hypobaric Hypoxia-Induced Skeletal Muscle Protein Loss.

Rathor, Richa, Sukanya Srivastava, and Geetha Suryakumar. A comparative biochemical study between L-carnosine and ß-alanine in amelioration of hypobaric hypoxia-induced skeletal muscle protein loss. High Alt Med Biol. 24:302-311, 2023. Background: Carnosine (CAR; ß-alanyl-L-histidine), a biologically active dipeptide is known for its unique pH-buffering capacity, metal chelating activity, and antioxidant and antiglycation property. ß-Alanine (ALA) is a nonessential amino acid and used to enhance performance and cognitive functions. Hypobaric hypoxia (HH)-induced muscle protein loss is regulated by multifaceted signaling pathways. The present study investigated the beneficial effects of CAR and ALA against HH-associated muscle loss. Methodology: Simulated HH exposure was performed in an animal decompression chamber. Gastric oral administration of CAR (50 mg·kg-1) and ALA (450 mg·kg-1) were given daily for 3 days and at the end of the treatment, hindlimb skeletal muscle tissue was excised for western blot and biochemical assays. Results: Cosupplementation of CAR and ALA alone was able to ameliorate the hypoxia-induced inflammation, oxidative stress (FOXO), ER stress (GRP-78), and atrophic signaling (MuRF-1) in the skeletal muscles. Creatinine phospho kinase activity and apoptosis were also decreased in CAR- and ALA-supplemented rats. However, CAR showed enhanced protection in HH-induced muscle loss as CAR supplementation was able to enhance protein concentration, body weight, and decreased the protein oxidation and ALA administration was not able to restore the same. Conclusions: Hence, the present comprehensive study supports the fact that CAR (50 mg·kg-1) is more beneficial as compared with ALA (450 mg·kg-1) in ameliorating the hypoxia-induced skeletal muscle loss.

The Effect of Omega-3 Fatty Acids on Sarcopenia: Mechanism of Action and Potential Efficacy.

Sarcopenia, a progressive disease characterized by a decline in muscle strength, quality, and mass, affects aging population worldwide, leading to increased morbidity and mortality. Besides resistance exercise, various nutritional strategies, including omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation, have been sought to prevent this condition. This narrative review summarizes the current evidence on the effect and mechanism of n-3 PUFA on musculoskeletal health. Despite conflicting evidence, n-3 PUFA is suggested to benefit muscle mass and volume, with more evident effects with higher supplementation dose (>2 g/day). n-3 PUFA supplementation likely improves handgrip and quadriceps strength in the elderly. Improved muscle functions, measured by walking speed and time-up-to-go test, are also observed, especially with longer duration of supplementation (>6 months), although the changes are small and unlikely to be clinically meaningful. Lastly, n-3 PUFA supplementation may positively affect muscle protein synthesis response to anabolic stimuli, alleviating age-related anabolic resistance. Proposed mechanisms by which n-3 PUFA supplementation improves muscle health include 1. anti-inflammatory properties, 2. augmented expression of mechanistic target of rapamycin complex 1 (mTORC1) pathway, 3. decreased intracellular protein breakdown, 4. improved mitochondrial biogenesis and function, 5. enhanced amino acid transport, and 6. modulation of neuromuscular junction activity. In conclusion, n-3 PUFAs likely improve musculoskeletal health related to sarcopenia, with suggestive effect on muscle mass, strength, physical performance, and muscle protein synthesis. However, the interpretation of the findings is limited by the small number of participants, heterogeneity of supplementation regimens, and different measuring protocols.

The effect of combined ß-lactoglobulin supplementation and resistance exercise training prior to limb immobilisation on muscle protein synthesis rates in healthy young adults: study protocol for a randomised controlled trial.

BACKGROUND: The decline in skeletal muscle mass experienced following a short-term period (days to weeks) of muscle disuse is mediated by impaired rates of muscle protein synthesis (MPS). Previous RCTs of exercise or nutrition prehabilitation interventions designed to mitigate disuse-induced muscle atrophy have reported limited efficacy. Hence, the aim of this study is to investigate the impact of a complex prehabilitation intervention that combines ß-lactoglobulin (a novel milk protein with a high leucine content) supplementation with resistance exercise training on disuse-induced changes in free-living integrated rates of MPS in healthy, young adults. METHODS/DESIGN: To address this aim, we will recruit 24 healthy young (18-45 years) males and females to conduct a parallel, double-blind, 2-arm, randomised placebo-controlled trial. The intervention group will combine a 7-day structured resistance exercise training programme with thrice daily dietary supplementation with 23 g of ß-lactoglobulin. The placebo group will combine the same training programme with an energy-matched carbohydrate (dextrose) control. The study protocol will last 16 days for each participant. Day 1 will be a familiarisation session and days 2-4 will be the baseline period. Days 5-11 represent the 'prehabilitation period' whereby participants will combine resistance training with their assigned dietary supplementation regimen. Days 12-16 represent the muscle disuse-induced 'immobilisation period' whereby participants will have a single leg immobilised in a brace and continue their assigned dietary supplementation regimen only (i.e. no resistance training). The primary endpoint of this study is the measurement of free-living integrated rates of MPS using deuterium oxide tracer methodology. Measurements of MPS will be calculated at baseline, over the 7-day prehabilitation period and over the 5-day immobilisation period separately. Secondary endpoints include measurements of muscle mass and strength that will be collected on days 4 (baseline), 11 (end of prehabilitation) and 16 (end of immobilisation). DISCUSSION: This novel study will establish the impact of a bimodal prehabilitation strategy that combines ß-lactoglobulin supplementation and resistance exercise training in modulating MPS following a short-term period of muscle disuse. If successful, this complex intervention may be translated to clinical practice with application to patients scheduled to undergo, for example, hip or knee replacement surgery. TRIAL REGISTRATION: NCT05496452. Registered on August 10, 2022. PROTOCOL VERSION: 16-12-2022/1.

The Postprandial Plasma Amino Acid Response Does Not Differ Following the Ingestion of a Solid Versus a Liquid Milk Protein Product in Healthy Adult Females.

Dietary protein digestion and amino acid absorption rates are modulated by numerous factors such as the food matrix. It has been speculated that protein ingested in liquid form is more rapidly digested and absorbed when compared with ingestion in solid form. Here, we assessed the postprandial plasma amino acid availability following ingestion of a single bolus of protein provided in either liquid or solid form. Twelve healthy, young females were included in this randomized cross-over study. On two separate test days, participants ingested 20-g milk protein concentrate in solid form (protein bar) or in liquid form (protein drink). Products were composed of matched ingredients and, thereby, had the same macro- and micronutrient composition. On both test days, arterialized blood samples were collected at regular time intervals for up to 4 hr following protein ingestion to assess the postprandial rise in plasma amino acid concentrations. Protein ingestion robustly elevated circulating plasma amino acid concentrations (p < .001), with no significant differences between treatments (p = .088). The incremental area under the curve of the postprandial rise in total plasma amino acid concentrations did not differ following bar versus drink consumption (160 ± 73 vs. 160 ± 71 mmol·L-1·240 min-1, respectively; 95% confidence interval [-37, 37]; Cohen's dz = 0.003; p = .992). Ingestion of protein in liquid or solid form does not modulate postprandial amino acid availability in healthy, female adults. Any differences in protein digestion and amino acid absorption due to differences in food matrix are not attributed to the protein being consumed as a bar or as a drink.

Effect of 1-year daily protein supplementation and physical exercise on muscle protein synthesis rate and muscle metabolome in healthy older Danes: a randomized controlled trial.

BACKGROUND: The skeletal muscle mass decreases with age and the responsiveness of aging muscles' protein synthesis rate (MPS) to protein intake seems to deteriorate. OBJECTIVE: This study investigated the impact of 12 months of protein supplementation with or without physical exercise training on the basal and postprandial MPS and the skeletal muscle metabolome of healthy older Danes (> 65 years, 29 females/37 males). METHODS: Subjects were randomized to follow one of five intervention groups: (1) carbohydrate, (2) collagen protein, (3) whey protein, (4) home-based light resistance training with whey protein, and (5) center-based heavy-load resistance training with whey protein. Before and after the intervention, a tracer infusion trial was conducted to measure basal and postprandial MPS in response to intake of a cocktail consisting of 20 g whey hydrolysate + 10 g glucose. In addition, the skeletal muscle metabolome was measured using gas chromatography-mass spectrometry (GC-MS) at basal state and 4 h after the intake of the cocktail. RESULTS: One year of daily protein or carbohydrate supplementation did not alter the basal and protein-stimulated postprandial muscle protein synthesis rate or the muscle metabolome of healthy older Danes. Basal MPS (%/h) at baseline for all subjects were 0.0034 ± 0,011 (mean ± SD). In contrast to previous studies, no difference was observed in basal MPS between males and females (p = 0.75). With the developed untargeted GC-MS methodology, it was possible to detect and tentatively annotate > 70 metabolites from the human skeletal muscle samples. CONCLUSION: One year of protein supplementation in comparison to an isocaloric-control supplement seems to affect neither the MPS at basal or postprandial state nor the skeletal muscle metabolome. CLINICAL TRIAL REGISTRY: Number: NCT02115698, clinicaltrials.gov/ct2/show/NCT02115698.

Vicia faba Peptide Network Supplementation Does Not Differ From Milk Protein in Modulating Changes in Muscle Size During Short-Term Immobilization and Subsequent Remobilization, but Increases Muscle Protein Synthesis Rates During Remobilization in Healthy Young Men.

BACKGROUND: Muscle mass and strength decrease during short periods of immobilization and slowly recover during remobilization. Recent artificial intelligence applications have identified peptides that appear to possess anabolic properties in in vitro assays and murine models. OBJECTIVES: This study aimed to compare the impact of Vicia faba peptide network compared with milk protein supplementation on muscle mass and strength loss during limb immobilization and regain during remobilization. METHODS: Thirty young (24 ± 5 y) men were subjected to 7 d of one-legged knee immobilization followed by 14 d of ambulant recovery. Participants were randomly allocated to ingest either 10 g of the Vicia faba peptide network (NPN_1; n = 15) or an isonitrogenous control (milk protein concentrate; MPC; n = 15) twice daily throughout the study. Single-slice computed tomography scans were performed to assess quadriceps cross-sectional area (CSA). Deuterium oxide ingestion and muscle biopsy sampling were applied to measure myofibrillar protein synthesis rates. RESULTS: Leg immobilization decreased quadriceps CSA (primary outcome) from 81.9 ± 10.6 to 76.5 ± 9.2 cm2 and from 74.8 ± 10.6 to 71.5 ± 9.8 cm2 in the NPN_1 and MPC groups, respectively (P < 0.001). Remobilization partially recovered quadriceps CSA (77.3 ± 9.3 and 72.6 ± 10.0 cm2, respectively; P = 0.009), with no differences between the groups (P > 0.05). During immobilization, myofibrillar protein synthesis rates (secondary outcome) were lower in the immobilized leg (1.07% ± 0.24% and 1.10% ± 0.24%/d, respectively) than in the non-immobilized leg (1.55% ± 0.27% and 1.52% ± 0.20%/d, respectively; P < 0.001), with no differences between the groups (P > 0.05). During remobilization, myofibrillar protein synthesis rates in the immobilized leg were greater with NPN_1 than those with MPC (1.53% ± 0.38% vs. 1.23% ± 0.36%/d, respectively; P = 0.027). CONCLUSION: NPN_1 supplementation does not differ from milk protein in modulating the loss of muscle size during short-term immobilization and the regain during remobilization in young men. NPN_1 supplementation does not differ from milk protein supplementation in modulating the myofibrillar protein synthesis rates during immobilization but further increases myofibrillar protein synthesis rates during remobilization.

Skeletal muscle protein turnover responses to parenteral nutrition in patients with alcoholic liver cirrhosis and sarcopenia.

Alcoholic liver cirrhosis (ALC) is accompanied by sarcopenia. The aim of this study was to investigate the acute effects of balanced parenteral nutrition (PN) on skeletal muscle protein turnover in ALC. Eight male patients with ALC and seven age- and sex-matched healthy controls were studied for 3 h of fasting followed by 3 h of intravenous PN (SmofKabiven 1,206 mL: amino acid = 38 g, carbohydrates = 85 g, and fat = 34 g) 4 mL/kg/h. We measured leg blood flow and sampled paired femoral arteriovenous concentrations and quadriceps muscle biopsies while providing a primed continuous infusion of [ring-2d5]-phenylalanine to quantify muscle protein synthesis and breakdown. Patients with ALC exhibited shorter 6-min walking distance (ALC: 487 ± 38 vs. controls: 722 ± 14 m, P < 0.05), lower hand-grip strength (ALC: 34 ± 2 vs. controls: 52 ± 2 kg, P < 0.05), and computed tomography (CT)-verified leg muscle loss (ALC: 5,922 ± 246 vs. controls: 8,110 ± 345 mm2, P < 0.05). Net leg muscle phenylalanine uptake changed from negative (muscle loss) during fasting to positive (muscle gain) in response to PN (ALC: -0.18 ± +0.01 vs. 0.24 ± 0.03 µmol/kg muscle·min-1; P < 0.001 and controls: -0.15 ± 0.01 vs. 0.09 ± 0.01 µmol/kg muscle·min-1; P < 0.001) but with higher net muscle phenylalanine uptake in ALC than controls (P < 0.001). Insulin concentrations were substantially higher in patients with ALC during PN. Our results suggest a higher net muscle phenylalanine uptake during a single infusion of PN in stable patients with ALC with sarcopenia compared with healthy controls.NEW & NOTEWORTHY Muscle protein turnover responses to parenteral nutritional (PN) supplementation have not previously been studied in stable alcoholic liver cirrhosis (ALC). We applied stable isotope tracers of amino acids to directly quantify net muscle protein turnover responses to PN in sarcopenic males with ALC and healthy controls. We found a higher net muscle protein gain in ALC during PN, thereby providing the physiological rationale for future clinical trials of PN as a potential countermeasure to sarcopenia.

Evaluation of pea/rice and amylopectin/chromium as an alternative protein source to improve muscle protein synthesis in rats.

BACKGROUND: A preclinical study reported that the combination of an amylopectin/chromium complex (ACr) of branched-chain amino acids (BCAA) significantly enhanced muscle protein synthesis (MPS). This study was conducted to determine the effects of the addition of ACr complex to a pea/rice (PR) protein on MPS, insulin, muslin levels, and the mTOR pathway in exercised rats. METHODS: Twenty-four rats were divided into three groups: (i) exercise (Ex); (ii) Ex + PR 1:1 blend (0.465 g/kg BW); (iii) Ex + PR + ACr (0.155 g/kg BW). On the day of single-dose administration, after the animals were exercised at 26/m/min for 2 h, the supplement was given by oral gavage. The rats were injected with a bolus dose (250 mg/kg BW, 25 g/L) of deuterium-labeled phenylalanine to determine the protein fractional synthesis rate (FSR) one h after consuming the study product. RESULTS: The combination of PR and ACr enhanced MPS by 42.55% compared to the Ex group, while Ex + PR alone increased MPS by 30.2% over the Ex group (p < 0.0001) in exercised rats. Ex + PR plus ACr significantly enhanced phosphorylation of mTOR and S6K1 (p < 0.0001), and 4E-BP1 (p < 0.001) compared to the Ex (p < 0.0001). PR to ACr also significantly increased insulin and musclin levels (p < 0.0001) in exercised rats. Additionally, compared to Ex + PR alone, Ex + PR + ACr enhanced mTOR (p < 0.0001) and S6K1 (p < 0.0001) levels. CONCLUSION: These data suggested that PR + ACr may provide an alternative to animal proteins for remodeling and repairing muscle by stimulating MPS and mTOR signaling pathways in post-exercised rats. More preclinical and clinical human studies on combining pea/rice and amylopectin/chromium complex are required.

PK1 from Drosophila obscurin is an inactive pseudokinase with scaffolding properties.

Obscurins are large filamentous proteins with crucial roles in the assembly, stability and regulation of muscle. Characteristic of these proteins is a tandem of two C-terminal kinase domains, PK1 and PK2, that are separated by a long intrinsically disordered sequence. The significance of this conserved domain arrangement is unknown. Our study of PK1 from Drosophila obscurin shows that this is a pseudokinase with features typical of the CAM-kinase family, but which carries a minimalistic regulatory tail that no longer binds calmodulin or has mechanosensory properties typical of other sarcomeric kinases. PK1 binds ATP with high affinity, but in the absence of magnesium and lacks detectable phosphotransfer activity. It also has a highly diverged active site, strictly conserved across arthropods, that might have evolved to accommodate an unconventional binder. We find that PK1 interacts with PK2, suggesting a functional relation to the latter. These findings lead us to speculate that PK1/PK2 form a pseudokinase/kinase dual system, where PK1 might act as an allosteric regulator of PK2 and where mechanosensing properties, akin to those described for regulatory tails in titin-like kinases, might now reside on the unstructured interkinase segment. We propose that the PK1-interkinase-PK2 region constitutes an integrated functional unit in obscurin proteins.

Chronic Fetal Leucine Infusion Increases Rate of Leucine Oxidation but Not of Protein Synthesis in Late Gestation Fetal Sheep.

BACKGROUND: Leucine increases protein synthesis rates in postnatal animals and adults. Whether supplemental leucine has similar effects in the fetus has not been determined. OBJECTIVE: To determine the effect of a chronic leucine infusion on whole-body leucine oxidation and protein metabolic rates, muscle mass, and regulators of muscle protein synthesis in late gestation fetal sheep. METHODS: Catheterized fetal sheep at ∼126 d of gestation (term = 147 d) received infusions of saline (CON, n = 11) or leucine (LEU; n = 9) adjusted to increase fetal plasma leucine concentrations by 50%-100% for 9 d. Umbilical substrate net uptake rates and protein metabolic rates were determined using a 1-13C leucine tracer. Myofiber myosin heavy chain (MHC) type and area, expression of amino acid transporters, and abundance of protein synthesis regulators were measured in fetal skeletal muscle. Groups were compared using unpaired t tests. RESULTS: Plasma leucine concentrations were 75% higher in LEU fetuses compared with CON by the end of the infusion period (P < 0.0001). Umbilical blood flow and uptake rates of most amino acids, lactate, and oxygen were similar between groups. Fetal whole-body leucine oxidation was 90% higher in LEU (P < 0.0005) but protein synthesis and breakdown rates were similar. Fetal and muscle weights and myofiber areas were similar between groups, however, there were fewer MHC type IIa fibers (P < 0.05), greater mRNA expression levels of amino acid transporters (P < 0.01), and a higher abundance of signaling proteins that regulate protein synthesis (P < 0.05) in muscle from LEU fetuses. CONCLUSIONS: A direct leucine infusion for 9 d in late gestation fetal sheep does not increase protein synthesis rates but results in higher leucine oxidation rates and fewer glycolytic myofibers. Increasing leucine concentrations in the fetus stimulates its own oxidation but also increases amino acid transporter expression and primes protein synthetic pathways in skeletal muscle.

Effects of carboxymethyl cellulose on the emulsifying, gel and digestive properties of myofibrillar protein-soybean oil emulsion.

Improving the qualities of vegetable oil replaced animal fat meat products is particularly fascinating for the development of healthy meat products. This work was designed to investigate the effects of different carboxymethyl cellulose (CMC) concentrations (0.01 %, 0.05 %, 0.1 %, 0.2 %, and 0.5 %) on the emulsifying, gelation, and digestive properties of myofibrillar protein (MP)-soybean oil emulsions. The changes in MP emulsion characteristics, gelation properties, protein digestibility, and oil release rate were determined. Results demonstrated that CMC addition decreased the average droplet size and increased the apparent viscosity, storage modulus, and loss modulus of MP emulsions, and a 0.5 % CMC addition significantly increased the storage stability during 6 weeks. Lower CMC addition (0.01 % to 0.1 %) increased the hardness, chewiness, and gumminess of emulsion gel especially for the 0.1 % CMC addition, while higher CMC (0.5 %) content decreased the texture properties and water holding capacity of emulsion gels. The addition of CMC decreased protein digestibility during the gastric stage, and 0.01 % and 0.05 % CMC addition significantly decreased the free fatty acid release rate. In summary, the addition of CMC could improve the stability of MP emulsion and the texture properties of the emulsion gels, and decrease protein digestibility during the gastric stage.