Rates Of Protein Breakdown Research Articles

A low postabsorptive whole body protein balance is associated with markers of poor daily physical functioning in Chronic Obstructive Pulmonary Disease

Postabsorptive whole body protein kinetics are related to age, gender, body mass index (BMI), and habitual protein intake level. It is unclear how protein synthesis, breakdown, and postabsorptive protein balance rates are affected in Chronic Obstructive Pulmonary Disease (COPD)) and whether these relate to disease severity, lifestyle characteristics and poor daily functioning. We studied 91 COPD (GOLD 1-4) and 56 age matched control subjects without COPD or other chronic or acute health disease/condition in the postabsorptive state and measured body composition by Dual-energy X-ray Absorptiometry, and disease severity and comorbidities by medical screening, blood analysis and questionnaires. We assessed whole body production rates of phenylalanine and tyrosine by pulse stable isotope tracer infusion to calculate whole body protein breakdown (PB) and hydroxylation of phenylalanine to tyrosine, representative of postabsorptive protein balance. We measured muscle and cognitive function, and physical performance by isokinetic dynamometry, cognitive assessments, and 6-min walk test. We assessed physical activity level, mood and dietary protein intake by questionnaires. We measured plasma enrichments by LC-MS/MS and statistics by Fisher's exact test or analysis of covariance. Data are mean [95% CI]. The COPD patients had moderate to severe airflow obstruction, multiple comorbidities, and elevated values for plasma high sensitivity c-reactive protein (hs-CRP) and glucose. Although PB (3630 [3361, 3900] vs 3504 [3297, 3711] umol/h, p=0.1649) was not different, postabsorptive protein balance was lower in COPD patients (274.2 [242.4, 306.1] vs 212.9 [194.7, 231.0] umol/h, p<0.0001), both compared to control subjects. A lower postabsorptive protein balance was associated with age (p<0.0001) and higher levels for systolic blood pressure (p=0.0051) and hs-CRP (p=0.0046) but not with lung function. Furthermore, a lower postabsorptive protein balance level was associated with a lower intake of total calories and protein (p<0.0001) and lower muscle strength (p=0.0248), while only in COPD with a lower physical performance (p=0.0343). We found no association with cognitive function or mood. For all subjects, a cumulative model that included group, gender, age, BMI, systolic blood pressure, hs-CRP, caloric intake, protein intake, and leg strength was able to explain 55% of the variation in postabsorptive protein balance. These data suggest that systemic inflammation, high blood pressure and low protein intake are risk factors of a lower postabsorptive protein balance in COPD patients. A lower postabsorptive protein balance is associated with markers of poor daily physical functioning.

Ovarian cancer ascites induces skeletal muscle wasting in vitro and reflects sarcopenia in patients.

BackgroundCachexia‐associated skeletal muscle wasting or ‘sarcopenia’ is highly prevalent in ovarian cancer and contributes to poor outcome. Drivers of cachexia‐associated sarcopenia in ovarian cancer remain elusive, underscoring the need for novel and better models to identify tumour factors inducing sarcopenia. We aimed to assess whether factors present in ascites of sarcopenic vs. non‐sarcopenic ovarian cancer patients differentially affect protein metabolism in skeletal muscle cells and to determine if these effects are correlated to cachexia‐related patient characteristics.MethodsFifteen patients with an ovarian mass and ascites underwent extensive physical screening focusing on cachexia‐related parameters. Based on computed tomography‐based body composition imaging, six cancer patients were classified as sarcopenic and six were not; three patients with a benign condition served as an additional non‐sarcopenic control group. Ascites was collected, and concentrations of cachexia‐associated factors were assessed by enzyme‐linked immunosorbent assay. Subsequently, ascites was used for in vitro exposure of C2C12 myotubes followed by measurements of protein synthesis and breakdown by radioactive isotope tracing, qPCR‐based analysis of atrophy‐related gene expression, and NF‐κB activity reporter assays.ResultsC2C12 protein synthesis was lower after exposure to ascites from sarcopenic patients (sarcopenia 3.1 ± 0.1 nmol/h/mg protein vs. non‐sarcopenia 5.5 ± 0.2 nmol/h/mg protein, P < 0.01), and protein breakdown rates tended to be higher (sarcopenia 31.2 ± 5.2% vs. non‐sarcopenia 20.9 ± 1.9%, P = 0.08). Ascites did not affect MuRF1, Atrogin‐1, or REDD1 expression of C2C12 myotubes, but NF‐κB activity was specifically increased in cells exposed to ascites from sarcopenic patients (sarcopenia 2.2 ± 0.4‐fold compared with control vs. non‐sarcopenia 1.2 ± 0.2‐fold compared with control, P = 0.01). Protein synthesis and breakdown correlated with NF‐κB activity (r s = −0.60, P = 0.03 and r s = 0.67, P = 0.01, respectively). The skeletal muscle index of the ascites donors was also correlated to both in vitro protein synthesis (r s = 0.70, P = 0.005) and protein breakdown rates (r s = −0.57, P = 0.04).ConclusionsAscites of sarcopenic ovarian cancer patients induces pronounced skeletal muscle protein metabolism changes in C2C12 cells that correlate with clinical muscle measures of the patient and that are characteristic of cachexia. The use of ascites offers a new experimental tool to study the impact of both tumour‐derived and systemic factors in various cachexia model systems, enabling identification of novel drivers of tissue wasting in ovarian cancer.

204 Awardee Talk: Recent Advances in Protein Nutrition in Horses

Abstract Protein has been recognized as an essential nutrient for animals for well over 100 years. Protein plays many important structural and metabolic roles, and some of its component amino acids have additional functions, including as regulatory molecules, as energy substrates and in the synthesis of other non-protein molecules. Skeletal muscle makes up approximately 50% of body weight in horses, with protein being the major non-water component. As an athletic species, the development and maintenance of muscle mass is of the utmost importance in horses. Because muscle mass is largely determined by the balance of rates of muscle protein synthesis and breakdown, understanding how these pathways are regulated and influenced by dietary protein and amino acid provision is essential. Historically, much research regarding protein nutrition in horses has focused on the protein digestibility of different feed ingredients, and the adequacy of different protein sources in supporting the growth and maintenance of horses. This presentation will focus on some of the current areas of active research relating to protein nutrition in horses: the activation of the signaling pathways that regulate muscle protein synthesis, amino acid supplementation in athletic horses, protein metabolism in aged and horses and those with insulin dysregulation, and amino acid and protein nutrition in predominantly forage-fed horses. There are many exciting opportunities for future research in the area of protein and amino acid nutrition in horses across the lifespan.

Determining the contributions of protein synthesis and breakdown to muscle atrophy requires non-steady-state equations.

BackgroundAgeing and cachexia cause a loss of muscle mass over time, indicating that protein breakdown exceeds protein synthesis. Deuterium oxide (D2O) is used for studies of protein turnover because of the advantages of long‐term labelling, but these methods introduce considerations that have been largely overlooked when studying conditions of protein gain or loss. The purpose of this study was to demonstrate the importance of accounting for a change in protein mass, a non‐steady state, during D2O labelling studies while also exploring the contribution of protein synthesis and breakdown to denervation‐induced muscle atrophy.MethodsAdult (6 months) male C57BL/6 mice (n = 14) were labelled with D2O for a total of 7 days following unilateral sciatic nerve transection to induce denervation of hindlimb muscles. The contralateral sham limb and nonsurgical mice (n = 5) were used as two different controls to account for potential crossover effects of denervation. We calculated gastrocnemius myofibrillar and collagen protein synthesis and breakdown assuming steady‐state or using non‐steady‐state modelling. We measured RNA synthesis rates to further understand ribosomal turnover during atrophy.ResultsGastrocnemius mass was less in denervated muscle (137 ± 9 mg) compared with sham (174 ± 15 mg; P < 0.0001) or nonsurgical control (162 ± 5 mg; P < 0.0001). With steady‐state calculations, fractional synthesis and breakdown rates (FSR and FBR) were lower in the denervated muscle (1.49 ± 0.06%/day) compared with sham (1.81 ± 0.09%/day; P < 0.0001) or nonsurgical control (2.27 ± 0.04%/day; P < 0.0001). When adjusting for change in protein mass, FSR was 4.21 ± 0.19%/day in denervated limb, whereas FBR was 4.09 ± 0.22%/day. When considering change in protein mass (ksyn), myofibrillar synthesis was lower in denervated limb (2.44 ± 0.14 mg/day) compared with sham (3.43 ± 0.22 mg/day; P < 0.0001) and non‐surgical control (3.74 ± 0.12 mg/day; P < 0.0001), whereas rate of protein breakdown (kdeg, 1/t) was greater in denervated limb (0.050 ± 0.003) compared with sham (0.019 ± 0.001; P < 0.0001) and nonsurgical control (0.023 ± 0.000; P < 0.0001). Muscle collagen breakdown was completely inhibited during denervation. There was a strong correlation (r = 0.83, P < 0.001) between RNA and myofibrillar protein synthesis in sham but not denervated muscle.ConclusionsWe show conflicting results between steady‐ and non‐steady‐state calculations on myofibrillar protein synthesis and breakdown during periods of muscle loss. We also found that collagen accumulation was largely from a decrease in collagen breakdown. Comparison between sham and non‐surgical control demonstrated a crossover effect of denervation on myofibrillar protein synthesis and ribosomal biogenesis, which impacts study design for unilateral atrophy studies. These considerations are important because not accounting for them can mislead therapeutic attempts to maintain muscle mass.

Anemic hypoxemia reduces myoblast proliferation and muscle growth in late-gestation fetal sheep.

Fetal skeletal muscle growth requires myoblast proliferation, differentiation, and fusion into myofibers in addition to protein accretion for fiber hypertrophy. Oxygen is an important regulator of this process. Therefore, we hypothesized that fetal anemic hypoxemia would inhibit skeletal muscle growth. Studies were performed in late-gestation fetal sheep that were bled to anemic and therefore hypoxemic conditions beginning at ∼125 days of gestation (term = 148 days) for 9 ± 0 days (n = 19) and compared with control fetuses (n = 16). A metabolic study was performed on gestational day ∼134 to measure fetal protein kinetic rates. Myoblast proliferation and myofiber area were determined in biceps femoris (BF), tibialis anterior (TA), and flexor digitorum superficialis (FDS) muscles. mRNA expression of muscle regulatory factors was determined in BF. Fetal arterial hematocrit and oxygen content were 28% and 52% lower, respectively, in anemic fetuses. Fetal weight and whole body protein synthesis, breakdown, and accretion rates were not different between groups. Hindlimb length, however, was 7% shorter in anemic fetuses. TA and FDS muscles weighed less, and FDS myofiber area was smaller in anemic fetuses compared with controls. The percentage of Pax7+ myoblasts that expressed Ki67 was lower in BF and tended to be lower in FDS from anemic fetuses indicating reduced myoblast proliferation. There was less MYOD and MYF6 mRNA expression in anemic versus control BF consistent with reduced myoblast differentiation. These results indicate that fetal anemic hypoxemia reduced muscle growth. We speculate that fetal muscle growth may be improved by strategies that increase oxygen availability.

A Novel Stable Isotope Approach Demonstrates Surprising Degree of Age-Related Decline in Skeletal Muscle Collagen Proteostasis.

Age-related deterioration in turnover of collagen proteins accelerates extracellular matrix fibrosis and hinders adaptation to external stimuli. This project sought to understand factors that increase skeletal muscle fibrosis with age by studying what we term the dynamic protein pool. We hypothesized that the dynamic protein pool size of muscle collagen decreases with age, thus indicating a decrease in proteostatic maintenance (ie, ability to maintain proteostasis), and that failure to account for these changes impacts the interpretation of tracer-measured synthesis rates. We used deuterium oxide (D2O) labeling for up to 60 days in adult (6 months) and old (23 months) mice. The dynamic protein pool in adult skeletal muscle was 65% in tibialis anterior (TA), but only 28% in gastrocnemius (Gastroc). In aged muscle, the dynamic protein pool was further decreased to only 35% and 14% for TA and Gastroc, respectively. We showed that this loss in dynamic pool size was associated with increases in markers of fibrosis and decreased proteostatic maintenance. We demonstrate that aged muscle has higher rates of collagen protein synthesis and lower rates of collagen protein breakdown, which causes collagen accumulation. We further demonstrated that the normal assumption of complete protein renewal and the standard practice of taking a single sample with isotope labeling have profound impacts on interpretation of the genesis of fibrosis. Strategies to maintain muscle function with aging should focus on the dynamic protein pool with attention to methodological strategies to assess those changes.

Anabolic Resistance of Muscle Protein Turnover Comes in Various Shapes and Sizes.

Anabolic resistance is defined by a blunted stimulation of muscle protein synthesis rates (MPS) to common anabolic stimuli in skeletal muscle tissue such as dietary protein and exercise. Generally, MPS is the target of most exercise and feeding interventions as muscle protein breakdown rates seem to be less responsive to these stimuli. Ultimately, the blunted responsiveness of MPS to dietary protein and exercise underpins the loss of the amount and quality of skeletal muscle mass leading to decrements in physical performance in these populations. The increase of both habitual physical activity (including structured exercise that targets general fitness characteristics) and protein dense food ingestion are frontline strategies utilized to support muscle mass, performance, and health. In this paper, we discuss anabolic resistance as a common denominator underpinning muscle mass loss with aging, obesity, and other disease states. Namely, we discuss the fact that anabolic resistance exists as a dimmer switch, capable of varying from higher to lower levels of resistance, to the main anabolic stimuli of feeding and exercise depending on the population. Moreover, we review the evidence on whether increased physical activity and targeted exercise can be leveraged to restore the sensitivity of skeletal muscle tissue to dietary amino acids regardless of the population.

Understanding the effects of nutrition and post-exercise nutrition on skeletal muscle protein turnover: Insights from stable isotope studies

Understanding the effects of nutrition and post-exercise nutrition on skeletal muscle protein turnover: Insights from stable isotope studies

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.

Stable isotope approaches to study muscle mass outcomes in clinical populations

Both low muscle mass and muscle loss are associated with reduced physical function, mobility, independence, and quality of life, and are characteristic of a number of clinical conditions including diabetes, cardiovascular disease (CVD), chronic obstructive pulmonary disease (COPD), and critical illness. The accurate measurement of muscle mass is critical to assess the efficacy of an intervention or therapy. Stable isotope amino acid approaches can be used to quantify specific aspects of whole-body and muscle protein turnover, including synthesis and breakdown, which play distinctive roles in muscle mass maintenance in direct response to therapies. This review aims to elucidate whether acute responses measured using stable isotope amino acid tracers relate to changes in muscle mass in vulnerable clinical populations. Experimental studies quantifying whole-body protein synthesis and breakdown rates in clinical populations have been conducted to determine the response to nutritional interventions or to compare disease with health; however, these studies show limited potential to translate to expected muscle mass outcomes. In addition, clinical studies that have assessed both muscle mass and acute changes in whole-body or muscle protein turnover are lacking. We argue that the assessment of both muscle protein synthesis and breakdown rates, or simply limb net balance, obtains the most complete picture in relation to muscle-specific outcomes. While stable isotope amino acid tracer experiments provide meaningful mechanistic insight into the acute response to clinical interventions, they should be combined with, and/or followed-up by, longer-term studies incorporating measurements of muscle mass to ascertain the impact of an intervention on muscle mass maintenance in clinical populations.

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

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

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

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

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.

Androgen depletion alters the diurnal patterns to signals that regulate autophagy in the limb skeletal muscle.

Hypogonadism contributes to limb skeletal muscle atrophy by increasing rates of muscle protein breakdown. Androgen depletion increases markers of the autophagy protein breakdown pathway in the limb muscle that persist throughout the diurnal cycle. However, the regulatory signals underpinning the increase in autophagy markers remain ill-defined. The purpose of this study was to characterize changes to autophagy regulatory signals in the limb skeletal muscle following androgen depletion. Male mice were subjected to a castration surgery or a sham surgery as a control. Seven weeks post-surgery, a subset of mice from each group was sacrificed every 4hr over a 24hr period. Protein and mRNA from the Tibialis Anterior (TA) were subjected to Western blot and RT-PCR. Consistent with an overall increase in autophagy, the phosphorylation pattern of Uncoordinated Like Kinase 1 (ULK1) (Ser555) was elevated throughout the diurnal cycle in the TA of castrated mice. Factors that induce the progression of autophagy were also increased in the TA following androgen depletion including an increase in the phosphorylation of c-Jun N-terminal Kinase (JNK) (Thr183/Tyr185) and an increase in the ratio of BCL-2 Associated X (BAX) to B-cell lymphoma 2 (BCL-2). Moreover, we observed an increase in the protein expression pattern of p53 and the mRNA of the p53 target genes Cyclin-Dependent Kinase Inhibitor 1A (p21) and Growth Arrest and DNA Damage Alpha (Gadd45a), which are known to increase autophagy and induce muscle atrophy. These data characterize novel changes toautophagy regulatory signals in the limb skeletal muscle following androgen deprivation.

Skeletal Muscle Recovery from Disuse Atrophy: Protein Turnover Signaling and Strategies for Accelerating Muscle Regrowth.

Skeletal muscle fibers have a unique capacity to adjust their metabolism and phenotype in response to alternations in mechanical loading. Indeed, chronic mechanical loading leads to an increase in skeletal muscle mass, while prolonged mechanical unloading results in a significant decrease in muscle mass (muscle atrophy). The maintenance of skeletal muscle mass is dependent on the balance between rates of muscle protein synthesis and breakdown. While molecular mechanisms regulating protein synthesis during mechanical unloading have been relatively well studied, signaling events implicated in protein turnover during skeletal muscle recovery from unloading are poorly defined. A better understanding of the molecular events that underpin muscle mass recovery following disuse-induced atrophy is of significant importance for both clinical and space medicine. This review focuses on the molecular mechanisms that may be involved in the activation of protein synthesis and subsequent restoration of muscle mass after a period of mechanical unloading. In addition, the efficiency of strategies proposed to improve muscle protein gain during recovery is also discussed.

Changes in Whole-Body Amino Acid Metabolism in Response to 2 Weeks of the Very-Low Calorie Diet Are Not Affected by Gender

Abstract Objectives Very Low-Calorie Diet (VLCD) is an approved method to safely achieve substantial short-term weight loss in obese patients. We previously reported that two weeks of the VLCD maintains whole-body protein and amino acid turnover despite a large reduction in lean body mass. Since the observed effects on body weight (BW) and composition differed between men and women, we hypothesized that the changes in amino acid metabolism in a response to the calorie-restricted diet is gender-specific. Methods 34 morbidly obese adults (BMI: 42 ± 0.9 kg/m2, 10 males and 24 females) underwent a VLCD for 2 weeks consisting of 820 kcal/day and 105-grams protein/day. Before the start of the VLCD (baseline), the whole-body production (WBP) rates of multiple amino acids involved in protein metabolism (e.g., glycine (GLY), glutamine (GLN), phenylalanine (PHE), tyrosine (TYR), and arginine (ARG)) were measured after IV pulse administration of their stable isotopes. Weight loss and body composition by dual-energy X-ray absorptiometry were assessed after 2 weeks of the VLCD. Baseline plasma enrichments were measured by LC-MS/MS. Data are presented as mean ± SE. Statistics are performed by Pearson correlation tests. Results The magnitude of the BW loss after 2 weeks of the VLCD differed between males and females (7.0 ± 0.7 kg vs. 4.1 ± 0.2 kg, P &amp;lt; 0.0001, respectively) with a higher reduction in lean body mass observed in men than women (4.3 ± 0.8 kg vs. 2.7 ± 0.4 kg, P &amp;lt; 0.05). Although, females had significantly reduced baseline WBP of ARG (7.3% vs. 2%, P = 0.0027), GLY (22.8% vs. 3.6%, P &amp;lt; 0.001), and PHE (4.8% vs. 3.1%, P = 0.018) in comparison to men, two weeks of the VLCD had a comparable effect on multiple amino acid WBP in both genders. Suppressed contractile myofibrillar protein breakdown rate was observed in both groups (13% vs. baseline, P = 0.02) with no gender difference in net protein breakdown (PHE to TYR conversion rate). Hence, increased catabolism in men cannot be explained by a different response to the 2 weeks of a calorie-restricted diet. Conclusions Despite gender differences in body weight loss and changes in composition in response to a Very Low-Calorie Diet, changes in whole-body amino acid kinetics are not differently affected in men and women. Funding Sources CTRAL Internal Funds.

Nutritional Strategies to Offset Disuse-Induced Skeletal Muscle Atrophy and Anabolic Resistance in Older Adults: From Whole-Foods to Isolated Ingredients.

Preserving skeletal muscle mass and functional capacity is essential for healthy ageing. Transient periods of disuse and/or inactivity in combination with sub-optimal dietary intake have been shown to accelerate the age-related loss of muscle mass and strength, predisposing to disability and metabolic disease. Mechanisms underlying disuse and/or inactivity-related muscle deterioration in the older adults, whilst multifaceted, ultimately manifest in an imbalance between rates of muscle protein synthesis and breakdown, resulting in net muscle loss. To date, the most potent intervention to mitigate disuse-induced muscle deterioration is mechanical loading in the form of resistance exercise. However, the feasibility of older individuals performing resistance exercise during disuse and inactivity has been questioned, particularly as illness and injury may affect adherence and safety, as well as accessibility to appropriate equipment and physical therapists. Therefore, optimising nutritional intake during disuse events, through the introduction of protein-rich whole-foods, isolated proteins and nutrient compounds with purported pro-anabolic and anti-catabolic properties could offset impairments in muscle protein turnover and, ultimately, the degree of muscle atrophy and recovery upon re-ambulation. The current review therefore aims to provide an overview of nutritional countermeasures to disuse atrophy and anabolic resistance in older individuals.

Expression of genes related to autophagy and protein breakdown are positively correlated with protein synthesis and protein breakdown in skeletal muscle of healthy adults after a bout of resistance exercise

While it is well‐established that exercise increases muscle protein synthesis rate, it is still unclear that what role of protein breakdown plays in muscle after exercise. Therefore, the objective of this study was to determine if rates of protein synthesis and breakdown correlate with expression of genes related autophagy and protein degradation in skeletal muscle of healthy adults after a bout of resistance exercise. This is a secondary analysis of a previous published study ( Kim et al., 2016). In total, twenty‐three subjects were divided into two groups, rest (n = 12) and exercised (n = 11). Real‐time PCR was used for analyzing gene expression of baseline muscle samples from both groups, and student t test was used to compare significance (p &lt; 0.05) between two groups. Relationships between variables were assessed using Pearson’s Product‐Moment Correlation, and p value lower than 0.05 was considered as significant. Autophagy‐related genes p62, p53, ATG3, ATG5, LC3B, Beclin1, ATF4, and GADD54A, were significantly upregulated (p &lt; 0.05) in skeletal muscle from exercised subjects versus subjects at rest. Two genes involved in ubiquitin‐proteasome pathway, MuRF1 and Atrogin1, were also upregulated (p &lt; 0.05) after exercise. Neither protein synthesis nor protein breakdown rate was correlated with gene expression in skeletal muscle from subjects at rest. However, protein synthesis rate was positively correlated (p &lt; 0.05) with increased expression of p62, p53, ATG3, ATG5, ATG7, LC3B, Beclin1, ATF4, GADD54A, Atrogin‐1 and MuRF1 in exercised muscle. Protein breakdown rates were positively associated (p &lt; 0.05) with increased expression of ATF4, ATG5, and p62 in exercised skeletal muscle. In conclusion, the results provide preliminary evidence that genes related to autophagy and protein breakdown are upregulated after exercise in skeletal muscle from healthy adults and are positively correlated with muscle protein synthesis rate.Support or Funding InformationThis study is funded by an Arkansas Biosciences Institute grant, we would like to thank thegenerous contribution of muscle samples by Dr. Wolfe.

Extending the Shelf Life of Ready-to-Eat Spiced Chicken Meat: Garlic Aqueous Extracts-Carboxymethyl Chitosan Ultrasonicated Coating Solution

Edible crude nano-coating solutions were prepared via ultrasonic treatment using carboxymethyl chitosan (CMCS) and garlic aqueous extracts as raw materials, and these were used to extend the shelf life of ready-to-eat (RTE) spiced chicken meat. First, the chemical composition of garlic aqueous extracts and the properties of the ultrasonicated coating solutions (particle size, ZETA potential, bacteriostasis, and mechanical properties) were determined. The results showed that the main chemical component was diallyl disulfide, and the most suitable coating solution (solution A) was produced by the addition of the garlic aqueous extracts after ultrasonic treatment of the CMCS solution. Subsequently, solution A was applied to the preservation experiment of the RTE chicken meat. According to microbial index (total viable count, TVC) and physical and chemical indicators, including total volatile base nitrogen (TVB-N), thiobarbituric acid reactive substances (TBARS), water distribution, and sensory evaluation, it was determined that this method effectively inhibited the growth of microorganisms and could delay the rate of protein breakdown and lipid oxidation in the RTE chicken meat. Moreover, there were no side effects regarding the appearance or taste of the products. Therefore, the garlic aqueous extracts-CMCS ultrasonicated coating method could be used as a potential fresh-keeping method for RTE chicken meat.

Muscle Protease Activities in Salmo Trutta L. Inhabiting the Krivoi Ruchey River

The effects of size, age, and smoltification on muscle protein breakdown systems were studied in wild brown trout Salmo trutta L. inhabiting the Krivoi Ruchey River of the White Sea basin, Kola Peninsula. Activities of autophagy-related proteases including cathepsin B and D, calpains, and proteasome were assayed in the skeletal muscle of brown trout parr and smolt of different age group. Youngest fish group consisted of the most actively growing individuals possessed the higher rate of protein breakdown compared to older groups. Different patterns of muscle protein breakdown inherent to brown trout parr and smolts were shown to be associated with calpain system and cathepsin D activities. Thus, increased activity of these proteases in smoltifying individuals obviously results in amino acid accumulation that could be a mechanism of seawater tolerance required for seaward migration. This study is the first to show the age- and stage-related dynamics in protease activities in skeletal muscle of brown trout inhabiting the Krivoi Ruchey River. Growth- and smoltification-related patterns of protease activities were quite similar in brown trout from the Krivoi Ruchey River and previously studied rivers of the White Sea basin, however, some habitat-related differences were observed.