Whole-body Protein Kinetics Research Articles

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.

A Whole-Grain Diet Increases Whole-Body Protein Balance Compared with a Macronutrient-Matched Refined-Grain Diet.

ABSTRACTBackgroundThere are limited data from randomized control trials to support or refute the contention that whole-grains can enhance protein metabolism in humans.ObjectivesTo examine: 1) the clinical effects of a whole-grain diet on whole-body protein turnover; 2) the cellular effects of whole-grains on protein synthesis in skeletal muscle cells; and 3) the population effects of whole-grain intake on age-related muscle loss.MethodsAdults with overweight/obesity (n = 14; age = 40 ± 7 y; BMI = 33 ± 5 kg/m2) were recruited into a crossover, randomized controlled trial (NCT01411540) in which isocaloric, macronutrient-matched whole-grain and refined-grain diets were fully provisioned for two 8-wk periods. Diets differed only in the presence of whole-grains (50 g/1000 kcal). Whole-body protein kinetics were assessed at baseline and after each diet in the fasted-state (13C-leucine) and integrated over 24 h (15N-glycine). In vitro studies using C2C12 cells assessed global protein synthesis by surface sensing of translation and anabolic signaling by Western blot. Complementary epidemiological assessments using the NHANES database assessed the effect of whole-grain intake on muscle function assessed by gait speed in older adults (n = 2783).ResultsIntegrated 24-h net protein balance was 3-fold higher on a whole-grain diet compared with a refined-grain diet (P = 0.04). A whole-grain wheat extract increased submaximal rates of global protein synthesis (27%, P < 0.05) in vitro. In a large sample of older adults, whole-grain intake was associated with greater muscle function (OR = 0.92; 95% CI: 0.86, 0.98).ConclusionsConsuming 50 g/1000 kcal whole-grains per day promotes greater protein turnover and enhances net protein balance in adults. Whole-grains impact skeletal muscle at the cellular level, and are associated with greater muscle function in older adults. Collectively, these data point to a new mechanism whereby whole-grain consumption favorably enhances protein turnover and improves health outcomes.This clinical trial is registered on clinicaltrials.gov (identifier: NCT01411540).

Whole-body protein kinetic models to quantify the anabolic response to dietary protein consumption

<h2>Summary</h2> Determination of whole body rates of protein synthesis, breakdown and net balance in human subjects still has an important role in nutrition research. Quantifying the anabolic response to dietary protein intake is a particularly important application. There are different models with which to accomplish this goal, each with advantages and limitations. The nitrogen (N)-flux method in which tracer is given orally has distinct advantages in terms of lack of invasiveness. In addition, the calculated results include all aspects of whole-body protein synthesis and breakdown. However, the prolonged timeframe of the method eliminates the possibility of the "pre-post" experimental design whereby each subject serves as their own control in the evaluation of the response to a meal. Models based on the primed-constant infusion of an essential amino acid (EAA) tracer enable the determination of baseline whole-body protein kinetics within 2 h, and can quantify a dynamic change from the basal state. The greatest challenge when using an EAA model is distinguishing exogenous and endogenous sources of the tracee in the blood. One approach is to use an intrinsically-labeled protein. This method has the advantage that the exogenous tracee is clearly distinguished from endogenous tracee. On the other hand, the intrinsically-labeled protein method suffers from unmeasured dilution that is likely to cause the systematic underestimation of the rate of appearance of exogenous tracee and thus overestimate the rate of whole-body protein breakdown. Alternatively, the "bioavailability" approach estimates the contribution of exogenous tracee to the peripheral circulation from the amount of tracee ingested, the true ileal digestibility of the tracee, and the irreversible loss of tracee prior to entry into the peripheral circulation. Errors in assumed values with the bioavailability method can potentially be significant, but are not likely to result in the systematic over- or under-estimations of rates of whole-body protein synthesis and breakdown. The optimal method depends on the degree of uncertainty regarding required assumptions in a particular circumstance. With all methods, it is advisable to calculate upper and lower bounds of whole body protein kinetics, in accord with reasonable maximal and minimal assumed values. Simultaneous use of two methods requiring different assumptions can also serve to confirm the validity of single approach.

Impact of habituated dietary protein intake on fasting and postprandial whole-body protein turnover and splanchnic amino acid metabolism in elderly men: a randomized, controlled, crossover trial

Efficacy of protein absorption and subsequent amino acid utilization may be reduced in the elderly. Higher protein intakes have been suggested to counteract this. We aimed to elucidate how habituated amounts of protein intake affect the fasted state of, and the stimulatory effect of a protein-rich meal on, protein absorption, whole-body protein turnover, and splanchnic amino acid metabolism. Twelve men (65-70 y) were included in a double-blinded crossover intervention study, consisting of a 20-d habituation period to a protein intake at the RDA or a high amount [1.1 g · kg lean body mass (LBM)-1 · d-1 or >2.1 g · kg LBM-1 · d-1, respectively], each followed by an experimental trial with a primed, constant infusion of D8-phenylalanine and D2-tyrosine. Arterial and hepatic venous blood samples were obtained after an overnight fast and repeatedly 4 h after a standardized meal including intrinsically labeled whey protein concentrate and calcium-caseinate proteins. Blood was analyzed for amino acid concentrations and phenylalanine and tyrosine tracer enrichments from which whole-body and splanchnic amino acid and protein kinetics were calculated. High (compared with the recommended amount of) protein intake resulted in a higher fasting whole-body protein turnover with a resultant mean ± SEM 0.03 ± 0.01 μmol · kg LBM-1 · min-1 lower net balance (P<0.05), which was not rescued by the intake of a protein-dense meal. The mean ± SEM plasma protein fractional synthesis rate was 0.13 ± 0.06%/h lower (P<0.05) after habituation to high protein. Furthermore, higher fasting and postprandial amino acid removal were observed after habituation to high protein, yielding higher urea excretion and increased phenylalanine oxidation rates (P<0.01). Three weeks of habituation to high protein intake (>2.1 g protein · kg LBM-1 · d-1) led to a significantly higher net protein loss in the fasted state. This was not compensated for in the 4-h postprandial period after intake of a meal high in protein.This trial was registered at clinicaltrials.gov as NCT02587156.

Comparison of basal whole-body protein kinetics and muscle protein synthesis between young and older adults.

Significant research has been dedicated to counteracting age‐related muscle loss, but underlying mechanisms have not been clearly established. Previous research examining differences in basal protein kinetics between young and older individuals has been limited by a lack of evaluation of protein breakdown and net balance. The aim of this study was to more comprehensively examine differences in basal protein kinetics between younger and older males and females. Basal whole‐body protein kinetics and muscle fractional synthetic rate (FSR) from 91 younger (18–38 years; 52% female) and 66 older (51–81 years; 53% female) healthy adults were determined using stable isotope tracer techniques (L‐[ring‐2H5]phenylalanine and L‐[ring‐2H2]tyrosine). There were no group × sex interaction effects (p > .05). Older individuals had greater whole‐body protein synthesis (mean difference old‐young (Δ) ± SE: 28.54 ± 8.15 mg/kg LBM/hr; p = .001) and breakdown (Δ: 15.44 ± 7.33 mg/kgLBM/hr; p = .038), but a less negative net balance (Mean ± SD: Young: −31.22 ± 7.42 mg/kg LBM/hr; Old: −18.11 ± 21.60 mg/kg LBM/hr; p < .001) compared to young individuals. Basal FSR was not significantly different between young and older (Δ: 0.007 ± 0.003%/hr; p = .052). Across the age range, females had greater whole‐body protein turnover (PSΔ: 19.10 ± 7.00 mg/kgLBM/hr; PBΔ: 19.22 ± 6.31 mg/kgLBM/hr; p < .01) compared to males. Results demonstrate a difference in basal whole‐body protein kinetics between young and older adults, with older adults having a higher protein turnover rate and a less negative net balance. Across the age range, females were also found to have a higher turnover rate compared to males. Differences may represent a shift in older physiology toward mechanisms that increase the efficiency of amino acid reutilization, especially in women.

Arginase II Plays a Central Role in the Sexual Dimorphism of Arginine Metabolism in C57BL/6 Mice

Sex differences in plasma concentration of arginine and arginase activity of different tissues have been reported in mice. In addition, male but not female C57BL/6 mice have a dietary arginine requirement for growth. The goal of this research was to test the hypothesis that arginase II is a key factor in the sexual dimorphism of arginine metabolism. Young adult male and female wild type (WT), and heterozygous and arginase II knockout mice on a C57BL/6 background mice were infused with labeled citrulline, arginine, ornithine, phenylalanine, and tyrosine to determine the rates of appearance and interconversion of these amino acids. Tissue arginase activity was measured in the liver, heart, jejunum, kidney, pancreas, and spleen with an arginine radioisotope. The effect of genotype, sex, and their interaction was tested. Female mice produced ∼36% more citrulline than their male littermates, which translated into a greater arginine endogenous synthesis, flux, and plasma concentration (42, 6, and 27%, respectively; P< 0.001). Female mice also had a greater phenylalanine flux (10%) indicating a greater rate of whole protein breakdown; however, they had a lower protein synthesis rate than males (18%; P< 0.001). The ablation of arginase II reduced the production of citrulline and the de novo synthesis of arginine in females and increased the rate of appearance of arginine and plasma arginine concentration in male mice (16 and 22%, respectively; P< 0.001). No effect of arginase II deletion, however, was observed for whole-body protein kinetics. Arginase II activity was present in the pancreas, kidney, jejunum, and spleen; WT females had a ∼2-fold greater renal arginase activity than their WT counterparts. A clear sexual dimorphism exists in the endogenous synthesis of arginine and its disposal. Female mice have a greater arginine availability than their male littermates. The ablation of arginase II increases arginine availability in male mice.

The Anabolic Response to Dietary Protein Is Not Limited by the Maximal Stimulation of Protein Synthesis in Healthy Older Adults: A Randomized Crossover Trial

We have recently demonstrated in young adults that an anabolic response with mixed meal protein intake above ~35 g/meal, previously recognized as an “optimal” protein dose, was further stimulated. However, it is unknown if this applies to older adults. We therefore examined anabolic response to a mixed meal containing either 35 g (MOD, moderate amount of protein) or 70 g (HIGH, high amount of protein) in a randomized cross-over metabolic study in older adults (n = 8). Primed continuous infusions of L-[2H5] phenylalanine and L-[2H2]tyrosine were performed to determine whole-body protein kinetics and muscle protein fractional synthesis rate (MPS) in basal fasted and fed states. Whole-body protein kinetics (NB, net protein balance; PS, protein synthesis; PB, protein breakdown) and MPS was expressed as changes from the baseline post-absorptive state. Consistent with our previous findings in young adults, both feedings resulted in a positive NB, with HIGH being more positive than MOD. Furthermore, NB (expressed as g protein∙240 min) increased linearly with an increasing amount of protein intake, expressed relative to lean body mass. The positive NB was achieved due mainly to the suppression of PB in both MOD and to a greater extent HIGH, while PS was only increased in HIGH. Consistent with the whole-body data, MPS was significantly higher in HIGH than MOD. Plasma concentrations of essential amino acids and insulin were greater in HIGH vs. MOD. We conclude that in the context of mixed meals, whole-body anabolic response linearly increases with increasing protein intake primarily through the suppression of PB, and MPS was further stimulated with protein intake above the previously considered “optimal” protein dose in older adults.

Whole-body protein kinetics in critically ill patients during 50 or 100% energy provision by enteral nutrition: A randomized cross-over study.

Enteral nutrition (EN) is a ubiquitous intervention in ICU patients but there is uncertainty regarding the optimal dose, timing and importance for patient-centered outcomes during critical illness. Our research group has previously found an improved protein balance during normocaloric versus hypocaloric parenteral nutrition in neurosurgical ICU patients. We now wanted to investigate if this could be demonstrated in a general ICU population with established enteral feeding, including patients on renal replacement therapy. Patients with EN >80% of energy target as determined by indirect calorimetry were randomized to or 50% or 100% of current EN rate. After 24 hours, whole-body protein kinetics were determined by enteral and parenteral stable isotope tracer infusions. Treatment allocation was then switched, and tracer investigations repeated 24 hours later in a crossover design with patients serving as their own controls. Six patients completed the full protocol. During feeding with 100% EN all patients received >1.2 g/kg/day of protein. Mean whole-body protein balance increased from -6.07 to 2.93 µmol phenylalanine/kg/h during 100% EN as compared to 50% (p = 0.044). The oxidation rate of phenylalanine was unaltered (p = 0.78). It is possible to assess whole-body protein turnover using a stable isotope technique in critically ill patients during enteral feeding and renal replacement therapy. Our results also suggest a better whole-body protein balance during full dose as compared to half dose EN. As the sample size was smaller than anticipated, this finding should be confirmed in larger studies.

Net protein balance correlates with expression of autophagy, mitochondrial biogenesis, and fat metabolism-related genes in skeletal muscle from older adults.

The mechanisms leading to sarcopenia, the main cause for frailty in older adults, are still unclear. Autophagy and the ubiquitin‐proteasome system (UPS) may play a role in mediating muscle protein breakdown related to sarcopenia. In addition to loss of muscle mass, compromised muscle performance observed in sarcopenic patients has been linked to muscle mitochondria dysfunction. Increased fat deposition and fat cell infiltration in muscle frequently seen in skeletal muscle of older adults may play an additional role for the pathogenesis of sarcopenia. Therefore, the first objective of this study was to understand differences in expression of genes related to autophagy, UPS, mitochondrial biogenesis, and fat metabolism in skeletal muscle of older adults compared with young adults. Our second objective was to determine the correlation between whole body protein kinetics (WBPK) and gene expression with age. Real‐time quantitative PCR was used to determine the relative expression of targeted genes, and hierarchical regression analysis was used to determine if age had a moderating effect on the correlation between expression of targeted genes and WBPK. Increases in the expression of autophagy‐related genes and fat metabolism‐related genes were observed in muscle of older adults compared with young adults. In addition, age enhanced the negative correlations between mitochondrial biogenesis genes and net protein balance. These results suggest that dysregulated gene expression of mitochondrial biogenesis could play a role in muscle loss in older adults.

Muscle Protein Synthesis and Whole-Body Protein Turnover Responses to Ingesting Essential Amino Acids, Intact Protein, and Protein-Containing Mixed Meals with Considerations for Energy Deficit.

Protein intake recommendations to optimally stimulate muscle protein synthesis (MPS) are derived from dose-response studies examining the stimulatory effects of isolated intact proteins (e.g., whey, egg) on MPS in healthy individuals during energy balance. Those recommendations may not be adequate during periods of physiological stress, specifically the catabolic stress induced by energy deficit. Providing supplemental intact protein (20–25 g whey protein, 0.25–0.3 g protein/kg per meal) during strenuous military operations that elicit severe energy deficit does not stimulate MPS-associated anabolic signaling or attenuate lean mass loss. This occurs likely because a greater proportion of the dietary amino acids consumed are targeted for energy-yielding pathways, whole-body protein synthesis, and other whole-body essential amino acid (EAA)-requiring processes than the proportion targeted for MPS. Protein feeding formats that provide sufficient energy to offset whole-body energy and protein-requiring demands during energy deficit and leverage EAA content, digestion, and absorption kinetics may optimize MPS under these conditions. Understanding the effects of protein feeding format-driven alterations in EAA availability and subsequent changes in MPS and whole-body protein turnover is required to design feeding strategies that mitigate the catabolic effects of energy deficit. In this manuscript, we review the effects, advantages, disadvantages, and knowledge gaps pertaining to supplemental free-form EAA, intact protein, and protein-containing mixed meal ingestion on MPS. We discuss the fundamental role of whole-body protein balance and highlight the importance of comprehensively assessing whole-body and muscle protein kinetics when evaluating the anabolic potential of varying protein feeding formats during energy deficit.

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.

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.

Effects of Protein Quality on Post-exercise Skeletal Muscle and Whole-body Protein Kinetics During Energy Deficit

Effects of Protein Quality on Post-exercise Skeletal Muscle and Whole-body Protein Kinetics During Energy Deficit

Timing and pattern of postexercise protein ingestion affects whole-body protein balance in healthy children: a randomized trial.

The dose and timing of postexercise protein ingestion can influence whole-body protein balance (WBPB) in adults, although comparable data from children are scarce. This study investigated how protein intake (both amount and distribution) postexercise can affect WBPB in physically active children. Thirty-five children (26 males; 9-13 years old) underwent a 5-day adaptation diet, maintaining a protein intake of 0.95 g·kg-1·day-1. Participants consumed [15N]glycine (2 mg·kg-1) before performing 3 × 20 min of variable-intensity cycling, and whole-body protein kinetics were assessed over 6 and 24 h of recovery. Fifteen grams of protein was distributed across 2 isoenergetic carbohydrate-containing beverages (15 and 240 min postexercise) containing reciprocal amounts of protein (i.e., 0 + 15 g, 5 + 10 g, 10 + 5 g, and 15 + 0 g for Groups A-D, respectively). Over the 6 h that included the exercise bout and consumption of the first beverage at 15 min postexercise, WBPB (i.e., synthesis - breakdown) demonstrated a linear increase of 0.647 g·kg-1·day-1 per 1 g protein intake (P < 0.001). Over 24 h, robust regression revealed that WBPB was best modeled by a parabola (P < 0.05), suggesting that a maximum in WBPB was achieved between groups B and C. In conclusion, despite a dose response early in recovery, a periodized protein intake with multiple smaller doses after physical activity may be more beneficial than a single bolus dose in promoting daily WBPB in healthy active children.

High dose amino acid administration achieves an anabolic response in type 2 diabetic patients that is independent of glycaemic control: A randomized clinical trial

Surgical stress provokes protein catabolism and hyperglycaemia that is enhanced in patients with type 2 diabetes (T2DM), and increases perioperative morbidity. This study hypothesized that perioperative administration of high dose intravenous (IV) amino acids (AA) will augment protein balance in T2DM patients receiving tight plasma glucose control via continuous IV insulin compared to standard plasma glucose control via subcutaneous (SC) insulin sliding scale. Eighteen patients with well-controlled T2DM (HbA1C%<7.1) undergoing colorectal surgery were assigned randomly to receive standard glucose control (6-10mmol/l, SC insulin, n=9) or tight glucose control (4-6mmol/l, IV insulin, n=9). Both groups received general anaesthesia and epidural analgesia. AA (1ml/kgh Aminoven™ 10%, ∼2.4g/kgd) were infused via a peripheral vein for two 3-hperiods: at the beginning of surgery and in the post-operative care unit. Whole-body protein and glucose kinetics were assessed by stable isotope tracers, L-[1-13C]leucine and [6,6-2H2]glucose. Whole-body protein balance was positive after surgery in all patients. Since protein synthesis, breakdown and leucine oxidation were comparable in both groups, whole body protein balance was not different (p=0.605). Tight glucose control suppressed endogenous glucose production (EGP, p<0.001) and increased glucose clearance (p<0.001) compared to standard glucose control during both study periods. No episode of hypoglycaemia occurred in either group. High-dose perioperative AA administration under optimal anti-catabolic care with epidural analgesia was effective in achieving a positive protein balance in T2DM patients undergoing surgery that was independent of glycaemic control strategy. Continuous IV insulin maintained normoglycaemia by inhibiting EGP and increasing glucose clearance. Improved glucose control, without a pronounced increase in protein balance with the intravenous insulin regimen, suggests perioperative protein metabolism may be less sensitive to insulin than is glucose.

Dietary Leucine Supplementation Decreases Whole-Body Protein Turnover before, but Not during, Immune System Stimulation in Pigs

Immune system stimulation (ISS) adversely affects protein metabolism and reduces pig productivity. Leu has a regulatory role in skeletal muscle and whole-body protein turnover, which may be affected by ISS. We sought to determine the effect of supplemental Leu intake on whole-body protein turnover in pigs before and during ISS. Pigs [mean ± SD initial body weight (BW): 10.6 ± 1.1 kg] were surgically fitted with jugular vein catheters and assigned to 1 of 3 treatments: 1.36% standardized ileal-digestible (SID) Leu (CON; n = 13); 2.04% SID Leu (LEU-M; n = 8); and 2.72% SID Leu (LEU-H; n = 7). Pigs were infused continuously with 0.66 ± 0.05 mmol 15N ⋅ kg BW-1 ⋅ d-1 to determine whole-body protein kinetics. The study consisted of a 72-h prechallenge period followed by a 36-h challenge period. At the start of the challenge period, ISS was induced in all LEU-M and LEU-H pigs and half of the CON pigs with LPS (ISS+); the remaining CON pigs were administered saline (ISS-). Whole-body protein synthesis (309, 273, and 260 ± 14 mmol N ⋅ kg BW-1 ⋅ d-1 for CON, LEU-M, and LEU-H pigs, respectively) and protein degradation (233, 203, and 185 ± 14 mmol N ⋅ kg BW-1 ⋅ d-1 for CON, LEU-M, and LEU-H pigs, respectively) were reduced with increasing Leu intake during the prechallenge period (P < 0.05). ISS reduced whole-body protein synthesis (203 compared with 169 ± 12 mmol N ⋅ kg BW-1 ⋅ d-1 for ISS- and ISS+ pigs fed CON, respectively; P < 0.05) and protein deposition (PD) (64.9 compared with 45.0 ± 2.9 mmol N ⋅ kg BW-1 ⋅ d-1 for ISS- and ISS+ pigs fed CON, respectively; P < 0.01), whereas ISS did not affect whole-body protein degradation. Leu intake did not affect whole-body protein synthesis or degradation in ISS+ pigs. Our results indicate that supplemental Leu intake improves the efficiency of PD rather than PD directly in healthy pigs but did not affect whole-body protein turnover during ISS.

Insulin resistance of protein anabolism accompanies that of glucose metabolism in lean, glucose-tolerant offspring of persons with type 2 diabetes

ObjectiveTo test whether protein anabolic resistance is an early defect in type 2 diabetes (T2D).Research design and methodsSeven lean, normoglycemic T2D offspring (T2D-O) and eight matched participants without family history...

Dietary Methyl Donors Contribute to Whole-Body Protein Turnover and Protein Synthesis in Skeletal Muscle and the Jejunum in Neonatal Piglets

Background: The neonatal methionine requirement must consider not only the high demand for rapid tissue protein expansion but also the demands as the precursor for a suite of critical transmethylation reactions. However, methionine metabolism is inherently complex because upon transferring its methyl group during transmethylation, methionine can be reformed by the dietary methyl donors choline (via betaine) and folate.Objective: We sought to determine whether dietary methyl donors contribute to methionine availability for protein synthesis in neonatal piglets.Methods: Yucatan miniature piglets aged 4–8 d were fed a diet that provided 38 μg folate/(kg·d), 60 mg choline/(kg·d), and 238 mg betaine/(kg·d) [methyl-sufficient (MS); n = 8] or a diet devoid of these methyl precursors [methyl-deficient (MD); n = 8]. After 5 d, dietary methionine was reduced from 0.30 to 0.20 g/(kg·d) in both groups. On day 6, piglets received a constant [1-13C]phenylalanine infusion to measure whole-body protein kinetics, and on day 8 they received a constant [3H-methyl]methionine infusion to measure tissue-specific protein synthesis in skeletal muscle, the liver, and the jejunum.Results: Whole-body phenylalanine flux, protein synthesis, and protein breakdown were 13%, 12%, and 22% lower, respectively, in the MD group than in the MS group (P < 0.05). Reduced whole-body protein synthesis in the MD piglets was attributed to 50% lower protein synthesis in skeletal muscle and the jejunum than in the MS piglets (P < 0.05). Furthermore, methionine availability in skeletal muscle was halved in piglets fed the MD diet (P < 0.05), and the specific radioactivity of methionine was doubled in the jejunum of MD piglets (P < 0.05), suggesting lower intestinal remethylation. Liver protein synthesis did not significantly differ between the groups, but secreted proteins were not measured.Conclusions: Dietary methyl donors can affect whole-body and tissue-specific protein synthesis in neonatal piglets and should be considered when determining the methionine requirement.

Effect of obesity and type 2 diabetes on protein anabolic response to insulin in elderly women

Obesity and type 2 diabetes have been shown to alter the insulin sensitivity of glucose and protein metabolism in middle-aged women. We aimed to determine whether these findings translate to the elderly who are at increased risk of muscle loss. We assessed whole-body protein (1-13C-leucine) and glucose (3-3H-glucose) kinetics in 10 healthy (age: 71.6±1.8years; BMI: 23.2±0.8kg/m2), 8 obese (age: 72.9±1.3; BMI: 33.1±1.0) and 8 obese well-controlled type 2 diabetic (age: 69.8±1.6; BMI: 34.4±1.5) elderly women in the postabsorptive state and during a hyperinsulinemic, euglycemic, isoaminoacidemic clamp. All subjects followed an isoenergetic, protein-controlled diet for 6days preceding the clamp. The net protein anabolic response to hyperinsulinemia was similarly blunted in obese (0.08±0.06) and obese type 2 diabetic women (0.06±0.04) compared to healthy women (0.24±0.05μmol·kg fat free mass−1·min−1; ANOVA p=0.018). In contrast, the insulin-mediated glucose disposal (healthy: 9.72±0.67) was decreased with obesity (6.96±0.86) and further with diabetes (5.23±0.27mg·kg fat free mass−1·min−1; ANOVA p<0.001). Endogenous glucose production was not completely suppressed during the clamp only in diabetic women. Thus, the glucose infusion rate was the lowest in this group. Obese elderly women with and without type 2 diabetes have a similar degree of insulin resistance of protein anabolism, despite worse glucose metabolism in type 2 diabetes. Similar to previous findings in middle-aged women, obesity exerted a blunting effect on protein anabolism, which may contribute to the development of sarcopenic obesity. Our results suggest that the presence of type 2 diabetes at an advancing age does not further aggravate this effect.

Dietary crude protein intake influences rates of whole-body protein synthesis in weanling horses

The objective of this study was to measure whole-body protein kinetics in weanling horses receiving forage and one of two different concentrates: (1) commercial crude protein (CCP) concentrate, which with the forage provided 4.1 g CP/kg bodyweight (BW)/day (189 mg lysine (Lys)/kg BW/day), and (2) recommended crude protein (RCP) concentrate which, with the same forage, provided 3.1 g CP/kg BW/day (194 mg Lys/kg BW/day). Blood samples were taken to determine the response of plasma amino acid concentrations to half the daily concentrate allocation. The next day, a 2 h-primed, constant infusion of [13C]sodium bicarbonate and a 4 h-primed, constant infusion of [1-13C]phenylalanine were used with breath and blood sampling to measure breath 13CO2 and blood [13C]phenylalanine enrichment.Horses on the CCP diet showed an increase from baseline in plasma isoleucine, leucine, lysine, threonine, valine, alanine, arginine, asparagine, glutamine, ornithine, proline, serine, and tyrosine at 120 min post-feeding. Baseline plasma amino acid concentrations were greater with the CCP diet for histidine, isoleucine, leucine, threonine, valine, asparagine, proline, and serine. Phenylalanine, lysine, and methionine were greater in the plasma of horses receiving the RCP treatment at 0 and 120 min. Phenylalanine intake was standardized between groups; however, horses receiving the RCP diet had greater rates of phenylalanine oxidation (P = 0.02) and lower rates of non-oxidative phenylalanine disposal (P = 0.04). Lower whole-body protein synthesis indicates a limiting amino acid in the RCP diet.