Whole-body Protein Metabolism Research Articles

Acute Effects of Testosterone on Whole-Body Protein Metabolism in Hypogonadal and Eugonadal Conditions: A Randomized, Placebo-Controlled, Crossover Study.

Chronic testosterone (T) substitution and short-term T administration positively affect protein metabolism, however, data on acute effects in humans are sparse. This study aimed to investigate T's acute effects on whole-body protein metabolism in hypogonadal and eugonadal conditions. We designed a randomized, double-blind, placebo-controlled, crossover study, including twelve healthy young males. Whole-body protein metabolism was evaluated during 1) eugonadism, and after medically-induced hypogonadism, with application of a gel on each trial day containing either 2) placebo, 3) T 50 mg, or 4) T 150 mg; under basal (5h basal period) and insulin-stimulated conditions (3h clamp). The main outcome measure was change in net protein balance. The net protein loss was 62% larger in the placebo-treated hypogonadal state compared with the eugonadal state during the basal period (-5.5 ±3.5 µmol/kg/h versus -3.4 ± 1.2 µmol/kg/h, p=0.038), but not during the clamp (p=0.06). Also, hypogonadism resulted in a 25% increase in whole-body urea flux (p=0.006). However, T did not result in any significant changes in protein breakdown, synthesis, or net balance during either the basal period or clamp (all p > 0.05). Protein breakdown was reduced during clamp compared to the basal period regardless of gonadal status or T exposure (all p≤0.001). In conclusion, the application of transdermal T did not counteract the negative effects of hypogonadism with no effects on protein metabolism within five hours of administration. Insulin (during clamp) mitigated the effects of hypogonadism. This study is the first to investigate acute protein-metabolic effects of T in hypogonadal men.

Quantification and interpretation of postprandial whole-body protein metabolism using stable isotope methodology: a narrative review.

Stable isotopes are routinely applied to determine the impact of factors such as aging, disease, exercise, and feeding on whole-body protein metabolism. The most common approaches to quantify whole-body protein synthesis, breakdown, and oxidation rates and net protein balance are based on the quantification of plasma amino acid kinetics. In the postabsorptive state, plasma amino acid kinetics can easily be assessed using a constant infusion of one or more stable isotope labeled amino acid tracers. In the postprandial state, there is an exogenous, dietary protein-derived amino acid flux that needs to be accounted for. To accurately quantify both endogenous as well as exogenous (protein-derived) amino acid release in the circulation, the continuous tracer infusion method should be accompanied by the ingestion of intrinsically labeled protein. However, the production of labeled protein is too expensive and labor intensive for use in more routine research studies. Alternative approaches have either assumed that 100% of exogenous amino acids are released in the circulation or applied an estimated percentage based on protein digestibility. However, such estimations can introduce large artifacts in the assessment of whole-body protein metabolism. The preferred estimation approach is based on the extrapolation of intrinsically labeled protein-derived plasma bioavailability data obtained in a similar experimental design setting. Here, we provide reference data on exogenous plasma amino acid release that can be applied to allow a more accurate routine assessment of postprandial protein metabolism. More work in this area is needed to provide a more extensive reference data set.

Whole-body and forearm muscle protein metabolism in patients with acromegaly before and after treatment.

Active acromegaly is characterized by increased lean body mass but the mechanisms underlying the protein anabolic effect are unclear. To study if active acromegaly induces reversible changes in whole-body and skeletal muscle protein kinetics. Eighteen patients with acromegaly were investigated before and 47 ± 10 weeks after disease control by surgery (n = 8) and/or medical treatment (n = 10). Labelled phenylalanine and tyrosine tracers were employed to assess whole-body and regional forearm muscle protein kinetics. Intramyocellular protein signaling was assessed in skeletal muscle biopsies, and whole-body DXA scan and indirect calorimetry assessed lean body mass (LBM) and resting energy expenditure, respectively. Disease control induced a 7% decrease in lean body mass (p < 0.000) and a 14% decrease in LBM-adjusted energy expenditure. Whole-body phenylalanine breakdown decreased after disease control (p = 0.005) accompanied by a decrease in the degradation of phenylalanine to tyrosine (p= 0.005) and a decrease in whole-body phenylalanine synthesis (p = 0.030). Skeletal muscle protein synthesis tended to decrease after disease control (p = 0.122), whereas the muscle protein breakdown (p = 0.437) and muscle protein loss were unaltered (p = 0.371). ULK1 phosphorylation, an activator of protein breakdown, increased after disease control (p= 0.042). Active acromegaly represents a reversible high flux state in which both whole-body protein breakdown and synthesis are increased, whereas forearm muscle protein kinetics are unaltered. Future studies are needed to decipher the link between protein kinetics and the structure and function of the associated GH-induced increase in lean body mass.

Biotin, folic acid, and vitamin B12 supplementation given in early lactation to Holstein dairy cows: Their effects on whole-body propionate, glucose, and protein metabolism

Biotin (B8), folic acid (B9), and vitamin B12 (B12) play key roles in energy and protein metabolism. The aim of this study was to evaluate the effects of a B8 supplement, administered alone or combined with B9 and B12 during the transition period on glucose, propionate, and protein metabolism. Thirty-two Holstein multiparous cows were assigned to one of the 4 treatments according to an incomplete block design in a 2 × 2 factorial arrangement: 1) 2-mL of weekly intramuscular injections of saline 9 g/L NaCl (B8 −/B9B12 −); 2) 20 mg/d of dietary B8 (unprotected from ruminal degradation) and 2-mL weekly intramuscular injections of saline 9 g/L NaCl (B8 +/B9B12 −); 3) 2.6 g/d of dietary B9 (unprotected) and 2-mL weekly intramuscular injections of 10 mg of B12 (B8 −/B9B12 +); 4) 20 mg/d of dietary B8, 2.6 g/d of dietary B9 and weekly intramuscular injections of 10 mg of B12 (B8 +/B9B12 +). Treatments were given from − 26–45 days relative to calving date. At 43 (SD:3) days in milk (DIM), D-[6,6-2H2]-glucose (23.9 mmol/h; jugular vein) and [1-13C]-sodium propionate (22.7 mmol/h; ruminal vein) were simultaneously infused for 4 h; the following 2 d, respectively, [13C]-sodium bicarbonate (3.0 mmol/h) and L[1-13C]-Leu (3.7 mmol/h) were infused into a jugular vein for 4 h. Blood samples were collected every 15 min during the last 1.5 h of infusions at 43 DIM and every 20 min at 44 and 45 DIM during the last 2 h of infusions. During the infusion week, there were no treatment effects on milk yield and major milk components, on whole-body propionate (1354 ± 116 mmol/h) and glucose (811 ± 34 mmol/h) rates of appearance, and on the proportion of glucose synthesized from propionate (65.1 ± 4.0%). Nevertheless, plasma glucose concentration during the infusions at 43 DIM for cows receiving the B8 supplement was greater when given in combination with B9 and B12, whereas no effect was noted without B8 supplementation. Whole-body Leu rate of appearance, Leu oxidation, and Leu used for protein synthesis and exportation averaged 133 ± 5, 23 ± 2, 111 ± 4, and 53 ± 2 mmol/h, respectively, and were not different among treatments. The present results might indicate that at the time of infusions between 43 and 45 days in milk under the current conditions, supplies of B8, B9, and B12 were sufficient to meet cow requirements. This reinforces the need to better define under which conditions cows would likely benefit from a supplementation caused by an imbalance between supplies and needs.

Gut amino acid absorption in humans: Concepts and relevance for postprandial metabolism

<h2>Summary</h2> Dietary amino acid absorption kinetics are an important determinant of protein quality. The term "amino acid digestibility" is commonly used to refer to the amount of ingested amino acids that become available following absorption. However, one should differentiate between the subsequent processes of converting protein into smaller constituents (protein digestion) and luminal amino acid uptake (amino acid absorption). Amino acid "absorbability" or "bioavailability" is assessed by quantifying the disappearance of amino acids across (part of) the gastrointestinal tract. The assessment of fecal, apparent ileal (AID), standardized ileal (SID), and true ileal disappearance (TID), reflect amino acid absorbability with increasing accuracy, due to correction for microbial metabolism in the large intestine, basal gut endogenous amino acid losses, and total gut endogenous amino acids losses, respectively. A substantial amount of absorbed amino acids undergo first-pass splanchnic extraction, but the majority is immediately released in the circulation and becomes available for peripheral tissues. The assessment of amino acid "bioavailability" or "absorbability" is used in protein quality ranking systems such as the Digestible Indispensable Amino Acid Score (DIAAS). However, such scores neglect that the rate of absorption is also an important determinant of postprandial metabolism. In addition, amino acid absorption and/or its rate are highly dependent on factors such as the duration of the postprandial assessment period. Therefore, amino acid absorption kinetics should be assessed under the relevant experimental conditions. To this end, an oral-intravenous dual tracer approach can be applied to assess dietary protein derived amino acid release into the circulation and allows the assessment of the subsequent impact on postprandial whole-body protein metabolism.

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.

The impact of Hayward green kiwifruit on dietary protein digestion and protein metabolism

PurposeThe purpose of the study was to determine if an actinidin protease aids gastric digestion and the protein anabolic response to dietary protein.MethodsHayward green kiwifruit (containing an actinidin protease) and Hort 16A gold kiwifruit (devoid of actinidin protease) were given in conjunction with a beef meal to healthy older subjects. Twelve healthy older males (N = 6) and females (N = 6) were studied with a randomized, double-blinded, crossover design to assess muscle and whole-body protein metabolism before and after ingestion of kiwifruit and 100 g of ground beef. Subjects consumed 2 of each variety of kiwifruit daily for 14 d prior to each metabolic study, and again during each study with beef intake.ResultsHayward green kiwifruit consumption with beef resulted in a more rapid increase in peripheral plasma essential amino acid concentrations. There were significant time by kiwifruit intake interactions for plasma concentrations of EAAs, branched chain amino acids (BCAAs), and leucine (P < 0.01). However, there was no difference in the total amount of EAAs absorbed. As a result, there were no differences between kiwifruit in any of the measured parameters of protein kinetics.ConclusionConsumption of Hayward green kiwifruit, with a beef meal facilitates protein digestion and absorption of the constituent amino acids as compared to Hort 16A gold kiwifruit.Clinical trialNCT04356573, April 21, 2020 “retrospectively registered”.

Dose-response effects of dietary protein on muscle protein synthesis during recovery from endurance exercise in young men: a double-blind randomized trial

ABSTRACTBackgroundProtein ingestion increases skeletal muscle protein synthesis rates during recovery from endurance exercise.ObjectivesWe aimed to determine the effect of graded doses of dietary protein co-ingested with carbohydrate on whole-body protein metabolism, and skeletal muscle myofibrillar (MyoPS) and mitochondrial (MitoPS) protein synthesis rates during recovery from endurance exercise.MethodsIn a randomized, double-blind, parallel-group design, 48 healthy, young, endurance-trained men (mean ± SEM age: 27 ± 1 y) received a primed continuous infusion of l-[ring-2H5]-phenylalanine, l-[ring-3,5-2H2]-tyrosine, and l-[1-13C]-leucine and ingested 45 g carbohydrate with either 0 (0 g PRO), 15 (15 g PRO), 30 (30 g PRO), or 45 (45 g PRO) g intrinsically l-[1-13C]-phenylalanine and l-[1-13C]-leucine labeled milk protein after endurance exercise. Blood and muscle biopsy samples were collected over 360 min of postexercise recovery to assess whole-body protein metabolism and both MyoPS and MitoPS rates.ResultsProtein intake resulted in ∼70%–74% of the ingested protein-derived phenylalanine appearing in the circulation. Whole-body net protein balance increased dose-dependently after ingestion of 0, 15, 30, or 45 g protein (mean ± SEM: −0.31± 0.16, 5.08 ± 0.21, 10.04 ± 0.30, and 13.49 ± 0.55 μmol phenylalanine · kg−1 · h−1, respectively; P < 0.001). 30 g PRO stimulated a ∼46% increase in MyoPS rates (%/h) compared with 0 g PRO and was sufficient to maximize MyoPS rates after endurance exercise. MitoPS rates were not increased after protein ingestion; however, incorporation of dietary protein–derived l-[1-13C]-phenylalanine into de novo mitochondrial protein increased dose-dependently after ingestion of 15, 30, and 45 g protein at 360 min postexercise (0.018 ± 0.002, 0.034 ± 0.002, and 0.046 ± 0.003 mole percentage excess, respectively; P < 0.001).ConclusionsProtein ingested after endurance exercise is efficiently digested and absorbed into the circulation. Whole-body net protein balance and dietary protein–derived amino acid incorporation into mitochondrial protein respond to increasing protein intake in a dose-dependent manner. Ingestion of 30 g protein is sufficient to maximize MyoPS rates during recovery from a single bout of endurance exercise.This trial was registered at trialregister.nl as NTR5111.

A Whole-Grain Diet Improves Whole-Body Protein Turnover Compared to a Macronutrient-Matched Refined-Grain Diet in Adults with Overweight/Obesity

Abstract Objectives We investigated the effect of consuming a whole-grain diet on whole-body protein metabolism compared to a macronutrient-matched refined-grain diet in adults with overweight/obesity using labelled amino acids (ClinicalTrials.gov Identifier: NCT01411540). Methods We conducted a randomized, controlled crossover trial in 14 adults with overweight/obesity (age: 40 ± 7 yrs, BMI: 33 ± 5 kg/m2) in which isocaloric, macronutrient-matched whole-grain (WG) and refined-grain (RG) diets were fully provided for two 8-week periods (with a 10-week washout period). Diets differed only in the inclusion of whole grains (50 g/1000 kcal). Body composition was measured via DEXA. Whole-body protein kinetics were assessed before and after each diet in the fasted state (13C-Leucine, primed, constant infusion) and over 24 hours (15N-Glycine, bolus). Protein kinetics were normalized to fat-free mass (FFM). Results Both diets resulted in mild weight loss (WG: −2.0 ± 2.5 kg; RG: −2.9 ± 3.3 kg; both P = 0.01 compared to baseline). Fasted-state leucine kinetics revealed greater protein synthesis (WG: 205 ± 61 µmol/kgFFM/hr; RG: 178 ± 36 µmol/kgFFM/hr; P = 0.04) and protein breakdown (WG: 235 ± 68 µmol/kgFFM/hr; RG: 203 ± 40 µmol/kgFFM/hr, P = 0.03) on a WG vs RG diet. This resulted in a more negative fasted-state net balance on a WG diet (WG: −30 ± 8 µmol/kg/hr; RG: −25 ± 6 µmol/kg/hr, P = 0.02). In contrast, 24-hour whole-body protein turnover measured by the end-product method (15N-Glycine), revealed greater protein synthesis (WG: 316 ± 135 mg protein/kgFFM/hr; RG: 250 ± 94 mg protein/kgFFM/hr) with no difference in protein breakdown, yielding a more positive 24-hr net balance on a WG diet (WG: 31 ± 21 mg protein/kgFFM/hr; RG: 10 ± 34 mg protein/kgFFM/hr). Conclusions A whole-grain diet increases whole-body leucine flux and results in a greater 24-hr net protein balance in adults with overweight/obesity compared to a refined-grain diet. This trial suggests whole-grains have an independent effect on protein metabolism and may benefit adults with overweight/obesity. Funding Sources This research was supported by the NIH (UL1 RR024989, T32DK007319 (JPK); T32AT004094 (JTM – trainee)) and an investigator-initiated grant from Nestle (JPK). Nestle Product Technology Center and Cereal Partners Worldwide provided the study meals and foods.

In Vitro, In Vivo, and In Silico Methods for Assessment of Muscle Size and Muscle Growth Regulation.

ABSTRACTTrauma, burn injury, sepsis, and ischemia lead to acute and chronic loss of skeletal muscle mass and function. Healthy muscle is essential for eating, posture, respiration, reproduction, and mobility, as well as for appropriate function of the senses including taste, vision, and hearing. Beyond providing support and contraction, skeletal muscle also exerts essential roles in temperature regulation, metabolism, and overall health. As the primary reservoir for amino acids, skeletal muscle regulates whole-body protein and glucose metabolism by providing substrate for protein synthesis and supporting hepatic gluconeogenesis during illness and starvation. Overall, greater muscle mass is linked to greater insulin sensitivity and glucose disposal, strength, power, and longevity. In contrast, low muscle mass correlates with dysmetabolism, dysmobility, and poor survival. Muscle mass is highly plastic, appropriate to its role as reservoir, and subject to striking genetic control. Defining mechanisms of muscle growth regulation holds significant promise to find interventions that promote health and diminish morbidity and mortality after trauma, sepsis, inflammation, and other systemic insults. In this invited review, we summarize techniques and methods to assess and manipulate muscle size and muscle mass in experimental systems, including cell culture and rodent models. These approaches have utility for studies of myopenia, sarcopenia, cachexia, and acute muscle growth or atrophy in the setting of health or injury.

Glucose and protein metabolic responses to an energy- but not protein- restricted diet in type 2 diabetes.

To test the effect of energy restriction with maintained protein intake on body composition and on insulin sensitivity of glucose and protein metabolism in adults with type 2 diabetes (T2D). After 3 days of an isoenergetic diet with 1.2 g/kg/d protein, obese adults with T2D (three women, two men) followed a 5-week diet providing 60% of energy requirements with 45% carbohydrate, and with protein maintained at pre-intervention level. Isotopic tracers were used to quantify whole-body glucose (3-3 H-glucose) and protein (13 C-leucine) metabolism pre- (day 4) and post-intervention (day 39), in the postabsorptive state and during a hyperinsulinaemic, isoglycaemic, isoaminoacidaemic clamp. Body composition was measured using dual-energy x-ray absorptiometry. After energy restriction, 6% weight loss occurred via total body (11%) and visceral fat losses (25%), but lean mass was preserved. Fasting glucose level, serum insulin level, homeostatic model assessment of insulin resistance index and C-peptide level decreased significantly (29%, 38%, 54% and 38%, respectively) as did other cardiometabolic risk factors. Between clamp studies, postabsorptive protein turnover and oxidation rates decreased (12% and 32%), resulting in less negative net balance, consistent with protein conservation. The rates of glucose turnover decreased, and glucose metabolic clearance rate improved (24%). During the clamp, protein flux was lower (9%) and breakdown suppressed (12%), and net balance became less negative but not different. Although glucose turnover did not differ, metabolic clearance improved by 47%. In obese adults with T2D, an energy-restricted diet with maintained protein intake of ~1.2 g/kg/d improved the kinetics of protein metabolism (particularly in the postabsorptive state), and preserved lean body mass and increased glucose metabolic clearance rate.

New advances in stable tracer methods to assess whole-body protein and amino acid metabolism.

Stable isotope methods have been used for many years to assess whole-body protein and amino acid kinetics in healthy conditions and in response to aging, exercise and (clinically stable) disease states. In recent years, tracer research expanded to the anabolic response to feeding in critical illness and its use during acute metabolic stressors. Furthermore, new isotope approaches and tracer insights have been obtained. In the postabsorptive state, the novel tracer pulse approach has several advantages above the established continuous tracer approach because of the metabolic information that can be obtained, easy applicability, and low tracer costs. The use of bolus versus sip-feeding approaches to assess the anabolic response to a meal is dependent on the research question and its feasibility. Promising new tracer approaches have been developed to measure the anabolic capacity, and protein digestibility and absorption. Advances have been made in the field of mass spectrometry in low enrichment analysis. Novel tracer approaches are available that can more readily be used in critical illness and during acute metabolic stressors. Besides the use of tracer application in various clinical conditions, more research is needed on how to incorporate isotopes on an individual level.

Effect of forage type and ration balancer protein content on measures of whole-body protein metabolism in growing horses consuming a predominantly forage diet

Effect of forage type and ration balancer protein content on measures of whole-body protein metabolism in growing horses consuming a predominantly forage diet

A potent liver-mediated mechanism for loss of muscle mass during androgen deprivation therapy.

ContextAndrogen deprivation therapy (ADT) in prostate cancer results in muscular atrophy, due to loss of the anabolic actions of testosterone. Recently, we discovered that testosterone acts on the hepatic urea cycle to reduce amino acid nitrogen elimination. We now hypothesize that ADT enhances protein oxidative losses by increasing hepatic urea production, resulting in muscle catabolism. We also investigated whether progressive resistance training (PRT) can offset ADT-induced changes in protein metabolism.ObjectiveTo investigate the effect of ADT on whole-body protein metabolism and hepatic urea production with and without a home-based PRT program.DesignA randomized controlled trial.Patients and interventionTwenty-four prostate cancer patients were studied before and after 6 weeks of ADT. Patients were randomized into either usual care (UC) (n = 11) or PRT (n = 13) starting immediately after ADT.Main outcome measuresThe rate of hepatic urea production was measured by the urea turnover technique using 15N2-urea. Whole-body leucine turnover was measured, and leucine rate of appearance (LRa), an index of protein breakdown and leucine oxidation (Lox), a measure of irreversible protein loss, was calculated.ResultsADT resulted in a significant mean increase in hepatic urea production (from 427.6 ± 18.8 to 486.5 ± 21.3; P < 0.01) regardless of the exercise intervention. Net protein loss, as measured by Lox/Lra, increased by 12.6 ± 4.9% (P < 0.05). PRT preserved lean body mass without affecting hepatic urea production.ConclusionAs early as 6 weeks after initiation of ADT, the suppression of testosterone increases protein loss through elevated hepatic urea production. Short-term PRT was unable to offset changes in protein metabolism during a state of profound testosterone deficiency.

Dose-Dependent Increases in Whole-Body Net Protein Balance and Dietary Protein-Derived Amino Acid Incorporation into Myofibrillar Protein During Recovery from Resistance Exercise in Older Men

ABSTRACTBackgroundAge-related decline in skeletal muscle mass is at least partly attributed to anabolic resistance to food intake. Resistance exercise sensitizes skeletal muscle tissue to the anabolic properties of amino acids.ObjectiveThe present study assessed protein digestion and amino acid absorption kinetics, whole-body protein balance, and the myofibrillar protein synthetic response to ingestion of different amounts of protein during recovery from resistance exercise in older men.MethodsForty-eight healthy older men [mean ± SEM age: 66 ± 1 y; body mass index (kg/m2): 25.4 ± 0.3] were randomly assigned to ingest 0, 15, 30, or 45 g milk protein concentrate after a single bout of resistance exercise consisting of 4 sets of 10 repetitions of leg press and leg extension and 2 sets of 10 repetitions of lateral pulldown and chest press performed at 75–80% 1-repetition maximum. Postprandial protein digestion and amino acid absorption kinetics, whole-body protein metabolism, and myofibrillar protein synthesis rates were assessed using primed, continuous infusions of l-[ring-2H5]-phenylalanine, l-[ring-2H2]-tyrosine, and l-[1-13C]-leucine combined with ingestion of intrinsically l-[1-13C]-phenylalanine and l-[1-13C]-leucine labeled protein.ResultsWhole-body net protein balance showed a dose-dependent increase after ingestion of 0, 15, 30, or 45 g of protein (0.015 ± 0.002, 0.108 ± 0.004, 0.162 ± 0.008, and 0.215 ± 0.009 μmol Phe · kg−1 · min−1, respectively; P < 0.001). Myofibrillar protein synthesis rates were higher after ingesting 30 (0.0951% ± 0.0062%/h, P = 0.07) or 45 g of protein (0.0970% ± 0.0062%/h, P < 0.05) than after 0 g (0.0746% ± 0.0051%/h). Incorporation of dietary protein–derived amino acids (l-[1-13C]-phenylalanine) into de novo myofibrillar protein showed a dose-dependent increase after ingestion of 15, 30, or 45 g protein (0.0171 ± 0.0017, 0.0296 ± 0.0030, and 0.0397 ± 0.0026 mole percentage excess, respectively; P < 0.05).ConclusionsDietary protein ingested during recovery from resistance exercise is rapidly digested and absorbed. Whole-body net protein balance and dietary protein-derived amino acid incorporation into myofibrillar protein show dose-dependent increases. Ingestion of ≥30 g protein increases postexercise myofibrillar protein synthesis rates in older men. This trial was registered at Nederlands Trial Register as NTR4492.

Capillary Electrophoresis of Free Amino Acids in Physiological Fluids Without Derivatization Employing Direct or Indirect Absorbance Detection.

Whole blood and/or plasma amino acids are useful for monitoring whole-body protein and amino acid metabolism in an organism under various physiological and pathophysiological conditions. Various methodological procedures are in use for their measurement in biological fluids. From the time when capillary electrophoresis was introduced as a technology offering rapid separation of various ionic and/or ionizable compounds with low sample and solvent consumption, there were many attempts to use it for the measurement of amino acids present in physiological fluids. As a rule, these methods require derivatization procedures for detection purposes.Here, we present two protocols for the analysis of free amino acids employing free zone capillary electrophoresis. Main advantage of both methods is an absence of any derivatization procedures that permits the analysis of free amino acid in physiological fluids. The method using direct detection and carrier electrolyte consisting of disodium monophosphate (10mM at pH2.90) permits determination of compounds that absorb in UV region (aromatic and sulfur containing amino acids, as well as some peptides such as carnosine, reduced, and oxidized glutathione). The other method use indirect absorbance detection, employing 8mM p-amino salicylic acid buffered with sodium carbonate at pH10.2 as running electrolyte. It permits quantification of 30 underivatized physiological amino acids and peptides. In our experience factorial design represents a useful tool for final optimization of the electrophoretic conditions if it is necessary.

Dicarbonyl Stress and Glyoxalase-1 in Skeletal Muscle: Implications for Insulin Resistance and Type 2 Diabetes.

Glyoxalase-1 (GLO1) is a ubiquitously expressed cytosolic protein which plays a role in the natural maintenance of cellular health and is abundantly expressed in human skeletal muscle. A consequence of reduced GLO1 protein expression is cellular dicarbonyl stress, which is elevated in obesity, insulin resistance and type 2 diabetes (T2DM). Both in vitro and pre-clinical models suggest dicarbonyl stress per se induces insulin resistance and is prevented by GLO1 overexpression, implicating a potential role for GLO1 therapy in insulin resistance and type 2 diabetes (T2DM). Recent work has identified the therapeutic potential of novel natural agents as a GLO1 inducer, which resulted in improved whole-body metabolism in obese adults. Given skeletal muscle is a major contributor to whole-body glucose, lipid, and protein metabolism, such GLO1 inducers may act, in part, through mechanisms in skeletal muscle. Currently, investigations examining the specificity of dicarbonyl stress and GLO1 biology in human skeletal muscle are lacking. Recent work from our lab indicates that dysregulation of GLO1 in skeletal muscle may underlie human insulin resistance and that exercise training may impart therapeutic benefits. This minireview will summarize the existing human literature examining skeletal muscle GLO1 and highlight the emerging therapeutic concepts for GLO1 gain-of-function in conditions such as insulin resistance and cardiometabolic disease.

Effects of alfalfa hay cubes versus timothy hay cubes on measures of whole-body protein metabolism in mature horses

Effects of alfalfa hay cubes versus timothy hay cubes on measures of whole-body protein metabolism in mature horses

Whey Protein Supplementation Enhances Whole Body Protein Metabolism and Recovery of Performance after Resistance Exercise: A Double‐blind Crossover Study

Post‐exercise protein consumption enhances muscle and whole body anabolism for up to 24h by providing amino acids to support increased rates of protein synthesis. However, little research has addressed if high quality protein consumption may concomitantly facilitate the acute recovery of exercise performance. We aimed to determine if a whey protein supplement enhances whole body net protein balance during overnight and 24h recovery and whether supplementation supported greater recovery of exercise performance over this same period. In a double‐blind crossover design, 12 healthy resistance‐trained men (76 ± 8 kg, 24 ± 4 y, 14 ± 5% body fat; means ± SD) performed a strenuous bout of whole body resistance exercise in the evening prior to consuming either 25g of MuscleTech 100% Whey protein (REx+PRO) or an energy‐matched placebo (REx+CHO) immediately after exercise as well as the following morning (i.e., after 10h recovery). A third randomized trial involving no exercise or supplement served as a control trial (Rest). Participants ingested 2 mg [15N]glycine/kg to determine whole body nitrogen turnover, protein synthesis, breakdown, and net balance over 10 and 24h of recovery. Exercise performance was assessed before and immediately, 10h, and 24h after exercise using the following tests: i) knee extension repetitions‐to‐failure (REP) and maximal isometric strength (MVC); ii) peak (PP) and mean (MP) anaerobic power via Wingate, and; iii) countermovement jump as an indicator of neuromuscular fatigue. Data were analyzed using two‐way repeated measures ANOVA and, using Cohen's d effect size (ES), by calculating the Probability of REx+PRO Superiority (PS) versus REx+CHO (50% = no effect). There was a trend (P = 0.064; ES = 0.61; PS = 67%) toward an effect of condition on net protein balance during 10‐h overnight recovery. Over 24h, net protein balance was enhanced in REx+PRO (P = 0.036 vs. Rest; ES = 0.69; PS = 69%) but not in REx+CHO (P = 0.84 vs. Rest), which was mediated primarily through a reduction in protein breakdown (REx+PRO &lt; REx+CHO; P &lt; 0.01). Exercise decreased REP, MVC, PP, MP, and CMJ in post‐testing (all P &lt; 0.05, Pre vs. Post). At 10h recovery, REx+PRO tended to enhance recovery of MVC (ES = 0.56; PS = 65%), MP (ES = 0.49; PS = 64%), and markers of neuromuscular function including jump height (ES = 0.49; PS = 64%), peak velocity (ES = 0.27; PS = 58%) and kinetic energy at take‐off (ES = 0.30; PS = 58%). At 24h, potential benefits to neuromuscular fatigue were negligible (ES for CMJ variables = −0.09 to −0.38; PS = 41–49%) whereas protein supplementation appeared to be beneficial for the recovery of MVC (ES = 1.15; PS = 79%), REP (ES = 0.44; PS = 62%), and PP (ES = 0.55; PS = 65%). There was no correlation between recovery in performance tests and whole body net balance at 10 or 24h (all P &gt; 0.05, r &lt; 0.3). In conclusion, whey protein supplementation enhances whole body net protein balance after an acute bout of whole body resistance exercise. The improvement in select exercise tasks suggests whey protein supplementation enhances the rate of performance recovery in trained young men.Support or Funding InformationSupported by Iovate Health Sciences Int. and Mitacs

Testosterone prevents protein loss via the hepatic urea cycle in human.

The urea cycle is a rate-limiting step for amino acid nitrogen elimination. The rate of urea synthesis is a true indicator of whole-body protein catabolism. Testosterone reduces protein and nitrogen loss. The effect of testosterone on hepatic urea synthesis in humans has not been studied. To determine whether testosterone reduces hepatic urea production. An open-label study. Eight hypogonadal men were studied at baseline, and after two weeks of transdermal testosterone replacement (Testogel, 100 mg/day). The rate of hepatic urea synthesis was measured by the urea turnover technique using stable isotope methodology, with 15N2-urea as tracer. Whole-body leucine turnover was measured, from which leucine rate of appearance (LRa), an index of protein breakdown and leucine oxidation (Lox), a measure of irreversible protein loss, were calculated. Testosterone administration significantly reduced the rate of hepatic urea production (from 544.4 ± 71.8 to 431.7 ± 68.3 µmol/min; P < 0.01), which was paralleled by a significant reduction in serum urea concentration. Testosterone treatment significantly reduced net protein loss, as measured by percent Lox/LRa, by 19.3 ± 5.8% (P < 0.05). There was a positive association between Lox and hepatic urea production at baseline (r2 = 0.60, P < 0.05) and after testosterone administration (r2 = 0.59, P < 0.05). Testosterone replacement reduces protein loss and hepatic urea synthesis. We conclude that testosterone regulates whole-body protein metabolism by suppressing the urea cycle.