Ixiolirion tataricum mucilage/chitosan based antioxidant films activated by free and nanoliposomal fennel essential oil.

Ixiolirion tataricum mucilage (ITM) was characterized and applied in fabrication of ITM/chitosan (CH) blend films activated by Foeniculum vulgare essential oil (FEO) in free and nanoliposomal forms. Uniform smooth surface structure, viscoelastic solid-like behavior and Newtonian nature of ITM were confirmed by morphological and rheological analyses. The prepared FEO nanoliposomes (FEO-NLPs) showed desirable properties in terms of particle size (57.2 nm), polydispersity index (0.243), zeta-potential (-17.6 mV), and encapsulation efficiency (85.2 %). The enhancing effects of FEO-NLPs and the adverse effects of free FEO on the crystalline, morphological and structural properties of films were confirmed by XRD, FE-SEM and ATR-FTIR tests. FEO-NLPs loaded films had better mechanical, thermal, water and gas barrier and antioxidant properties than neat film. Analysis also indicated the high controlled release of FEO from the films containing the nanoliposomal form of FEO. The films containing free FEO showed higher antibacterial activity against E. coli and S. aureus in comparison with FEO-NLPs loaded ones. The results showed the potential of FEO-NLPs loaded ITM/CH films for antioxidant food packaging applications.

Daily protein-polyphenol ingestion increases daily myofibrillar protein synthesis rates and promotes early muscle functional gains during resistance training.

Factors underpinning the time-course of resistance-type exercise training (RET) adaptations are not fully understood. This study hypothesized that consuming a twice-daily protein-polyphenol beverage (PPB; n = 15; age, 24 ± 1 yr; BMI, 22.3 ± 0.7 kg·m-2) previously shown to accelerate recovery from muscle damage and increase daily myofibrillar protein synthesis (MyoPS) rates would accelerate early (10 sessions) improvements in muscle function and potentiate quadriceps volume and muscle fiber cross-sectional area (fCSA) following 30 unilateral RET sessions in healthy, recreationally active, adults. Versus isocaloric placebo (PLA; n = 14; age, 25 ± 2 yr; BMI, 23.9 ± 1.0 kg·m-2), PPB increased 48 h MyoPS rates after the first RET session measured using deuterated water (2.01 ± 0.15 vs. 1.51 ± 0.16%·day-1, respectively; P < 0.05). In addition, PPB increased isokinetic muscle function over 10 sessions of training relative to the untrained control leg (%U) from 99.9 ± 1.8 pretraining to 107.2 ± 2.4%U at session 10 (vs. 102.6 ± 3.9 to 100.8 ± 2.4%U at session 10 in PLA; interaction P < 0.05). Pre to posttraining, PPB increased type II fCSA (PLA: 120.8 ± 8.2 to 109.5 ± 8.6%U; PPB: 92.8 ± 6.2 to 108.4 ± 9.7%U; interaction P < 0.05), but the gain in quadriceps muscle volume was similar between groups. Similarly, PPB did not further increase peak isometric torque, muscle function, or MyoPS measured posttraining. This suggests that although PPB increases MyoPS and early adaptation, it may not influence longer term adaptations to unilateral RET.NEW & NOTEWORTHY Using a unilateral model of resistance training, we show for the first time that a protein-polyphenol beverage increases initial rates of myofibrillar protein synthesis and promotes early functional improvements. Following a prolonged period of training, this strategy also increases type II fiber hypertrophy and causes large individual variation in gains in quadricep muscle cross-sectional area.

Ixiolirion tataricum anthocyanins-loaded biocellulose label: Characterization and application for food freshness monitoring.

A new intelligent pH-sensitive colorimetric label was fabricated by immobilizing Ixiolirion tataricum anthocyanins (ITA) into biocellulose (bacterial nanocellulose; BNC) film and was then studied to determine how it can be used as a label for monitoring freshness/spoilage of shrimp during storage at 4 °C. The formation of new interactions between ITA and BNC film and disruption of crystalline structure of BNC after anthocyanins immobilization were approved by FT-IR and XRD analyses, respectively. According to FE-SEM observations, the porosity of the BNC network decreased after ITA incorporation. The fabricated BNC-ITA label showed a distinct color change from violet to green over the pH range of 4-12. The pH, total volatile basic nitrogen (TVB-N), total psychrophiles count (TPC), and the quantity of biogenic amines (histamine, cadaverine, putrescine, and tyramine) in the shrimp samples and their correlation with color changes on the label were measured over a 4-day storage period. Consistent with changes in levels of TVB-N, TPC, pH, and biogenic amines, a visually distinguishable color change occurred on the BNC-ITA label as blue (fresh), dark green (medium fresh), and kelly green (spoiled). This research showed that ITA as a novel pH-sensitive dye is a promising candidate for developing pH labels for seafood intelligent packaging.

Effects of 12-Week Multivitamin and Omega-3 Supplementation on Micronutrient Levels and Red Blood Cell Fatty Acids in Pre-menopausal Women.

The purpose of this study was to validate the efficacy of a customized vitamin-mineral supplement on blood biomarkers in pre-menopausal females. Women (21-40 years old) who were apparently healthy were recruited from the local community (ClinicalTrials.gov trial registration NCT03828097). Pretesting (PRE) occurred in the morning 5 ± 2 days following each participant's menses and involved a fasted blood draw, body mass assessment, and blood pressure assessment. Participants were then randomly assigned in a double-blinded fashion to either the multivitamins (MV) (n = 43) or placebo group (n = 51). Participants consumed two capsules per day with breakfast for 12 weeks. Following the trial, participants reported to the laboratory for POST assessments, which replicated PRE procedures. Red blood cell fatty acid and serum micronutrient analyses were performed in a blinded fashion at hematology laboratories. A group × time interaction was observed for serum vitamin D levels (p < 0.001). MV increased levels from PRE to POST (+43.7%, p < 0.001), whereas no change occurred in the placebo group. Additionally, 78% of MV participants at PRE exhibited inadequate vitamin D levels (<40 ng/dl), whereas only 30% exhibited levels below this threshold at POST. An interaction was also observed for serum folate levels (p < 0.001). MV increased serum folate from PRE to POST (p < 0.001), whereas no change occurred in the placebo group. Red blood cell omega-3 fatty acid content increased from PRE to POST in the MV group (p < 0.001) and placebo group (p < 0.05), although POST values were greater in the MV group (p < 0.001). An interaction was observed for serum HDL cholesterol levels (p = 0.047), and a non-significant increase in this variable from PRE to POST occurred in the MV group (p = 0.060). Four-day food recalls indicated MV increased intake of omega-3 fatty acids, vitamin D, folate, and other micronutrients. In summary, MV supplementation increased serum vitamin D, serum folate, and red blood cell omega-3 fatty acid levels. However, these data are limited to healthy females, and more research is needed to examine if MV can affect metabolic disturbances in individuals with micronutrient deficiencies.

Reducing NF-κB Signaling Nutritionally is Associated with Expedited Recovery of Skeletal Muscle Function After Damage.

CONTEXT: The early events regulating the remodeling program following skeletal muscle damage are poorly understood. OBJECTIVE: The objective of this study was to determine the association between myofibrillar protein synthesis (myoPS) and nuclear factor-kappa B (NF-κB) signaling by nutritionally accelerating the recovery of muscle function following damage. DESIGN, SETTING, PARTICIPANTS, AND INTERVENTIONS: Healthy males and females consumed daily postexercise and prebed protein-polyphenol (PP; n = 9; 4 females) or isocaloric maltodextrin placebo (PLA; n = 9; 3 females) drinks (parallel design) 6 days before and 3 days after 300 unilateral eccentric contractions of the quadriceps during complete dietary control. MAIN OUTCOME MEASURES: Muscle function was assessed daily, and skeletal muscle biopsies were taken after 24, 27, and 36 hours for measurements of myoPS rates using deuterated water, and gene ontology and NF-κB signaling analysis using a quantitative reverse transcription PCR (RT-qPCR) gene array. RESULTS: Eccentric contractions impaired muscle function for 48 hours in PLA intervention, but just for 24 hours in PP intervention (P = 0.047). Eccentric quadricep contractions increased myoPS compared with the control leg during postexercise (24-27 hours; 0.14 ± 0.01 vs 0.11 ± 0.01%·h-1, respectively; P = 0.075) and overnight periods (27-36 hours; 0.10 ± 0.01 vs 0.07 ± 0.01%·h-1, respectively; P = 0.020), but was not further increased by PP drinks (P > 0.05). Protein-polyphenol drinks decreased postexercise and overnight muscle IL1R1 (PLA = 2.8 ± 0.4, PP = 1.1 ± 0.4 and PLA = 1.9 ± 0.4, PP = 0.3 ± 0.4 log2 fold-change, respectively) and IL1RL1 (PLA = 4.9 ± 0.7, PP = 1.6 ± 0.8 and PLA = 3.7 ± 0.6, PP = 0.7 ± 0.7 log2 fold-change, respectively) messenger RNA expression (P < 0.05) and downstream NF-κB signaling compared with PLA. CONCLUSION: Protein-polyphenol drink ingestion likely accelerates recovery of muscle function by attenuating inflammatory NF-κB transcriptional signaling, possibly to reduce aberrant tissue degradation rather than increase myoPS rates.

Improved recovery from skeletal muscle damage is largely unexplained by myofibrillar protein synthesis or inflammatory and regenerative gene expression pathways.

The contribution of myofibrillar protein synthesis (MyoPS) to recovery from skeletal muscle damage in humans is unknown. Recreationally active men and women consumed a daily protein-polyphenol beverage targeted at increasing amino acid availability and reducing inflammation (PPB; n = 9), both known to affect MyoPS, or an isocaloric placebo (PLA; n = 9) during 168 h of recovery from 300 maximal unilateral eccentric contractions (EE). Muscle function was assessed daily. Muscle biopsies were collected for 24, 27, 36, 72, and 168 h for MyoPS measurements using 2H2O and expression of 224 genes using RT-qPCR and pathway analysis. PPB improved recovery of muscle function, which was impaired for 5 days after EE in PLA (interaction P < 0.05). Acute postprandial MyoPS rates were unaffected by nutritional intervention (24-27 h). EE increased overnight (27-36 h) MyoPS versus the control leg (PLA: 33 ± 19%; PPB: 79 ± 25%; leg P < 0.01), and PPB tended to increase this further (interaction P = 0.06). Daily MyoPS rates were greater with PPB between 72 and 168 h after EE, albeit after function had recovered. Inflammatory and regenerative signaling pathways were dramatically upregulated and clustered after EE but were unaffected by nutritional intervention. These results suggest that accelerated recovery from EE is not explained by elevated MyoPS or suppression of inflammation.NEW & NOTEWORTHY The present study investigated the contribution of myofibrillar protein synthesis (MyoPS) and associated gene signaling to recovery from 300 muscle-damaging, eccentric contractions. Measured with 2H2O, MyoPS rates were elevated during recovery and observed alongside expression of inflammatory and regenerative signaling pathways. A nutritional intervention accelerated recovery; however, MyoPS and gene signaling were unchanged compared with placebo. These data indicate that MyoPS and associated signaling do not explain accelerated recovery from muscle damage.

A Randomised, Placebo-Controlled, Crossover Study Investigating the Optimal Timing of a Caffeine-Containing Supplement for Exercise Performance.

BACKGROUND: Pre-exercise supplements containing low doses of caffeine improve endurance exercise performance, but the most efficacious time for consumption before intense endurance exercise remains unclear, as does the contribution of caffeine metabolism. METHODS: This study assessed the timing of a commercially available supplement containing 200 mg of caffeine, 1600 mg of ß-alanine and 1000 mg of quercetin [Beachbody Performance Energize, Beachbody LLC, USA] on exercise performance, perception of effort and plasma caffeine metabolites. Thirteen cyclists (V̇O2max 64.5 ± 1.4 ml kg- 1 min- 1 (± SEM)) completed four experimental visits consisting of 30 min of steady-state exercise on a cycle ergometer at 83 ± 1% V̇O2max followed by a 15-min time trial, with perceived exertion measured regularly. On three of the visits, participants consumed caffeine either 35 min before steady-state exercise (PRE), at the onset of steady-state (ONS) or immediately before the time trial (DUR) phases, with a placebo consumed at the other two time points (i.e. three drinks per visit). The other visit (PLA) consisted of consuming the placebo supplement at all three time points. The placebo was taste-, colour- and calorie-matched. RESULTS: Total work performed during the time trial in PRE was 5% greater than PLA (3.53 ± 0.14 vs. 3.36 ± 0.13 kJ kg- 1 body mass; P = 0.0025), but not ONS (3.44 ± 0.13 kJ kg- 1; P = 0.3619) or DUR (3.39 ± 0.13 kJ kg- 1; P = 0.925), which were similar to PLA. Perceived exertion was lowest during steady-state exercise in the PRE condition (P < 0.05), which coincided with elevated plasma paraxanthine in PRE only (P < 0.05). CONCLUSION: In summary, ingestion of a pre-exercise supplement containing 200 mg caffeine 35 min before exercise appeared optimal for improved performance in a subsequent fatiguing time trial, possibly by reducing the perception of effort. Whether this was due to increased circulating paraxanthine requires further investigation. TRIAL REGISTRATION: ClinicalTrials.Gov, NCT02985606 ; 10/26/2016.

Effect of a High-Protein, High-Fiber Beverage Preload on Subjective Appetite Ratings and Subsequent Ad Libitum Energy Intake in Overweight Men and Women: A Randomized, Double-Blind Placebo-Controlled, Crossover Study.

BACKGROUND: Dietary protein and fiber have been shown to independently improve subjective measures of appetite control. OBJECTIVE: The aim of this study was to determine the acute effects of a high-protein, high-fiber (HP/HFb) beverage taken as a preload compared with an isocaloric lower-protein, lower-fiber (LP/LFb) placebo beverage on subjective appetite ratings and subsequent energy intake at an ad libitum meal in healthy adults. METHODS: A total of 50 overweight/obese men and women [n = 25 men, 25 women; age 30 ± 2 y; body mass index (BMI) 29.6 ± 0.3 kg/m2] received a 160 kcal HP/HFb beverage containing 17 g protein and 6 g fiber on one occasion and an isocaloric LP/LFb placebo beverage containing 1 g protein and 3 g fiber on another occasion in a randomized, double-blind, crossover design. Thirty min after consumption of the beverage preload, an ad libitum pizza meal was provided to be consumed over a 30-min period. Visual analog scales (VAS) were used to assess subjective appetite ratings throughout the testing period. The Revised Restraint Scale (RRS) was used to classify participants as restrained or unrestrained eaters. RESULTS: HP/HFb led to greater reductions in postprandial desire to eat and hunger compared with LP/LFb (both, P < 0.05) but did not significantly affect postprandial fullness or prospective food consumption. Subsequent meal energy intake tended to be lower after HP/HFb compared with LP/LFb (P = 0.09). A subanalysis showed lower energy intake after HP/HFb in older participants (≥25 y) compared with LP/LFb, which was not observed in the younger participants (<25 y). CONCLUSIONS: Compared with LP/LFb, a HP/HFb beverage preload reduced hunger, desire to eat, and tended to reduce subsequent food intake. Dietary restraint and age appear to influence subsequent energy intake and should be taken into account when designing nutrition interventions for weight reduction and/or maintenance. This trial was registered at clinicaltrials.gov as NCT02979717.

Suppression of atrogin-1 and MuRF1 prevents dexamethasone-induced atrophy of cultured myotubes.

OBJECTIVE: The mechanistic role of the ubiquitin ligases atrogin-1 and MuRF1 in glucocorticoid-induced muscle wasting is not fully understood. Here, we tested the hypothesis that glucocorticoid-induced muscle atrophy is at least in part linked to atrogin-1 and MuRF1 expression and that the ubiquitin ligases are regulated by compensatory mechanisms. METHODS: The expression of atrogin-1 and MuRF1 was suppressed individually or in combination in cultured L6 myotubes by using siRNA technique. Myotubes were treated with dexamethasone followed by determination of mRNA and protein levels for atrogin-1 and MuRF1, protein synthesis and degradation rates, and myotube morphology. RESULTS: Suppression of atrogin-1 resulted in increased expression of MuRF1 and vice versa, suggesting that the ubiquitin ligases are regulated by compensatory mechanisms. Simultaneous suppression of atrogin-1 and MuRF1 resulted in myotube hypertrophy, mainly reflecting stimulated protein synthesis, and prevented dexamethasone-induced myotube atrophy, mainly reflecting inhibited protein degradation. CONCLUSIONS: The results provide evidence for a link between upregulated atrogin-1 and MuRF1 expression and glucocorticoid-induced muscle atrophy. The study also suggests that atrogin-1 and MuRF1 levels are regulated by compensatory mechanisms and that inhibition of both ubiquitin ligases may be needed to prevent glucocorticoid-induced muscle proteolysis and atrophy.

PPARß/δ regulates glucocorticoid- and sepsis-induced FOXO1 activation and muscle wasting.

FOXO1 is involved in glucocorticoid- and sepsis-induced muscle wasting, in part reflecting regulation of atrogin-1 and MuRF1. Mechanisms influencing FOXO1 expression in muscle wasting are poorly understood. We hypothesized that the transcription factor peroxisome proliferator-activated receptor ß/δ (PPARß/δ) upregulates muscle FOXO1 expression and activity with a downstream upregulation of atrogin-1 and MuRF1 expression during sepsis and glucocorticoid treatment and that inhibition of PPARß/δ activity can prevent muscle wasting. We found that activation of PPARß/δ in cultured myotubes increased FOXO1 activity, atrogin-1 and MuRF1 expression, protein degradation and myotube atrophy. Treatment of myotubes with dexamethasone increased PPARß/δ expression and activity. Dexamethasone-induced FOXO1 activation and atrogin-1 and MuRF1 expression, protein degradation, and myotube atrophy were inhibited by PPARß/δ blocker or siRNA. Importantly, muscle wasting induced in rats by dexamethasone or sepsis was prevented by treatment with a PPARß/δ inhibitor. The present results suggest that PPARß/δ regulates FOXO1 activation in glucocorticoid- and sepsis-induced muscle wasting and that treatment with a PPARß/δ inhibitor may ameliorate loss of muscle mass in these conditions.

Acetylation and deacetylation--novel factors in muscle wasting.

We review recent evidence that acetylation and deacetylation of cellular proteins, including transcription factors and nuclear cofactors, may be involved in the regulation of muscle mass. The level of protein acetylation is balanced by histone acetyltransferases (HATs) and histone deacetylases (HDACs) and studies suggest that this balance is perturbed in muscle wasting. Hyperacetylation of transcription factors and nuclear cofactors regulating gene transcription in muscle wasting may influence muscle mass. In addition, hyperacetylation may render proteins susceptible to degradation by different mechanisms, including intrinsic ubiquitin ligase activity exerted by HATs and by dissociation of proteins from cellular chaperones. In recent studies, inhibition of p300/HAT expression and activity and stimulation of SIRT1-dependent HDAC activity reduced glucocorticoid-induced catabolic response in skeletal muscle, providing further evidence that hyperacetylation plays a role in muscle wasting. It should be noted, however, that although several studies advocate a role of hyperacetylation in muscle wasting, apparently contradictory results have also been reported. For example, muscle atrophy caused by denervation or immobilization may be associated with reduced, rather than increased, protein acetylation. In addition, whereas hyperacetylation results in increased degradation of certain proteins, other proteins may be stabilized by increased acetylation. Thus, the role of acetylation and deacetylation in the regulation of muscle mass may be both condition- and protein-specific. The influence of HATs and HDACs on the regulation of muscle mass, as well as methods to modulate protein acetylation, is an important area for continued research aimed at preventing and treating muscle wasting.

CaMKII activity is reduced in skeletal muscle during sepsis.

Exercise-induced muscle hypertrophy is associated with increased calcium/calmodulin-dependent protein kinase II (CaMKII) expression and activity. In contrast, the influence of muscle atrophy-related conditions on CaMKII is poorly understood. Here, we tested the hypothesis that sepsis-induced muscle wasting is associated with reduced CaMKII expression and activity. Sepsis, induced by cecal ligation and puncture in rats, and treatment of rats with TNFα, resulted in reduced total CaMKII activity in skeletal muscle whereas autonomous CaMKII activity was unaffected. The expression of CaMKIIδ, but not ß and γ, was reduced in septic muscle. In additional experiments, treatment of cultured myotubes with TNFα resulted in reduced total CaMKII activity and decreased levels of phosphorylated glycogen synthase kinase (GSK)-3ß, a downstream target of CaMKII. The present results suggest that sepsis-induced muscle wasting is associated with reduced CaMKII activity and that TNFα may be involved in the regulation of CaMKII activity in skeletal muscle. Decreased phosphorylation (consistent with activation) of GSK-3ß may be a consequence of reduced CaMKII activity, indicating that inhibited CaMKII activity may be involved in the catabolic response to sepsis.

Loss of muscle strength during sepsis is in part regulated by glucocorticoids and is associated with reduced muscle fiber stiffness.

Sepsis is associated with impaired muscle function but the role of glucocorticoids in sepsis-induced muscle weakness is not known. We tested the role of glucocorticoids in sepsis-induced muscle weakness by treating septic rats with the glucocorticoid receptor antagonist RU38486. In addition, normal rats were treated with dexamethasone to further examine the role of glucocorticoids in the regulation of muscle strength. Sepsis was induced in rats by cecal ligation and puncture, and muscle force generation (peak twitch and tetanic tension) was determined in lower extremity muscles. In other experiments, absolute and specific force as well as stiffness (reflecting the function of actomyosin cross bridges) were determined in isolated skinned muscle fibers from control and septic rats. Sepsis and treatment with dexamethasone resulted in reduced maximal twitch and tetanic force in intact isolated extensor digitorum longus muscles. The absolute and specific maximal force in isolated muscle fibers was reduced during sepsis together with decreased fiber stiffness. These effects of sepsis were blunted (but not abolished) by RU38486. The results suggest that muscle weakness during sepsis is at least in part regulated by glucocorticoids and reflects loss of contractility at the cellular (individual muscle fiber) level. In addition, the results suggest that reduced function of the cross bridges between actin and myosin (documented as reduced muscle fiber stiffness) may be involved in sepsis-induced muscle weakness. An increased understanding of mechanisms involved in loss of muscle strength will be important for the development of new treatment strategies in patients with this debilitating consequence of sepsis.

ß-Hydroxy-ß-methylbutyrate (HMB) prevents dexamethasone-induced myotube atrophy.

High levels of glucocorticoids result in muscle wasting and weakness. ß-hydroxy-ß-methylbutyrate (HMB) attenuates the loss of muscle mass in various catabolic conditions but the influence of HMB on glucocorticoid-induced muscle atrophy is not known. We tested the hypothesis that HMB prevents dexamethasone-induced atrophy in cultured myotubes. Treatment of cultured L6 myotubes with dexamethasone resulted in increased protein degradation and expression of atrogin-1 and MuRF1, decreased protein synthesis and reduced myotube size. All of these effects of dexamethasone were attenuated by HMB. Additional experiments provided evidence that the inhibitory effects of HMB on dexamethasone-induced increase in protein degradation and decrease in protein synthesis were regulated by p38/MAPK- and PI3K/Akt-dependent cell signaling, respectively. The present results suggest that glucocorticoid-induced muscle wasting can be prevented by HMB.

Multiple muscle wasting-related transcription factors are acetylated in dexamethasone-treated muscle cells.

Recent studies suggest that the expression and activity of the histone acetyltransferase p300 are upregulated in catabolic muscle allowing for acetylation of cellular proteins. The function of transcription factors is influenced by posttranslational modifications, including acetylation. It is not known if transcription factors involved in the regulation of muscle mass are acetylated in atrophying muscle. We determined cellular levels of acetylated C/EBPß, C/EBPδ, FOXO1, FOXO3a, and NF-kB/p65 in dexamethasone-treated L6 muscle cells, a commonly used in vitro model of muscle wasting. The role of p300 in dexamethasone-induced transcription factor acetylation and myotube atrophy was examined by transfecting muscle cells with p300 siRNA. Treatment of L6 myotubes with dexamethasone resulted in increased cellular levels of acetylated C/EBPß and δ, FOXO1 and 3a, and p65. Downregulation of p300 with p300 siRNA reduced acetylation of transcription factors and decreased dexamethasone-induced myotube atrophy and expression of the ubiquitin ligase MuRF1. The results suggest that several muscle wasting-related transcription factors are acetylated supporting the concept that posttranslational modifications of proteins regulating gene transcription may be involved in the loss of muscle mass. The results also suggest that acetylation of the transcription factors is at least in part regulated by p300 and plays a role in glucocorticoid-induced muscle atrophy. Targeting molecules that regulate acetylation of transcription factors may help reduce the impact of muscle wasting.

Resveratrol prevents dexamethasone-induced expression of the muscle atrophy-related ubiquitin ligases atrogin-1 and MuRF1 in cultured myotubes through a SIRT1-dependent mechanism.

Resveratrol (3,5,4'-trihydroxystilbene) has been ascribed multiple beneficial biological effects but the influence of resveratrol on glucocorticoid-induced muscle atrophy is not known. We examined the effects of resveratrol on dexamethasone-induced atrogin-1 and MuRF1 expression, FOXO1 acetylation, protein degradation and atrophy in cultured L6 myotubes. In addition, the role of the deacetylase SIRT1 in the effects of resveratrol was determined by transfecting myotubes with SIRT1 siRNA. The catabolic effects of dexamethasone were prevented by resveratrol and the protective effects of resveratrol on dexamethasone-induced atrogin-1 and MuRF1 expression were abolished in myotubes transfected with SIRT1 siRNA. Results suggest that resveratrol can prevent glucocorticoid-induced muscle wasting and that this effect is at least in part SIRT1-dependent.

Molecules modulating gene transcription during muscle wasting in cancer, sepsis, and other critical illness.

Muscle wasting in patients with sepsis, severe injury, and cancer is associated with increased transcription of several genes regulating different proteolytic pathways. The involvement of gene activation in muscle wasting suggests that transcription factors and nuclear cofactors play important roles in the regulation of muscle mass. Among transcription factors, NF-κB, C/EBPß, and FOXO transcription factors are activated in atrophying muscle and stimulate the transcription of genes in the ubiquitin-proteasome proteolytic pathway, as well as genes regulating authophagy/lysosomal proteolysis. Changes in the expression and activity of several nuclear cofactors, including the histone acetyltransferase p300, histone deacetylases (HDACs), such as HDAC3, HDAC6, and SIRT1, as well as the nuclear cofactors PGC-1α and ß, contribute to loss of muscle mass in various catabolic conditions. The activity of transcription factors and nuclear cofactors involved in the regulation of muscle mass is influenced not only by their abundance, but also by posttranslational modifications as well, including ubiquitination, phosphorylation, and acetylation. Transcription factors and nuclear cofactors involved in muscle wasting interact with each other at multiple levels, supporting the concept that the molecular regulation of muscle mass in various catabolic conditions is complex. An increased understanding of molecules that modulate gene transcription in catabolic muscle may make it possible to develop treatments targeting transcription factors and nuclear cofactors in the prevention and treatment of muscle wasting.

C/EBPß regulates dexamethasone-induced muscle cell atrophy and expression of atrogin-1 and MuRF1.

Muscle wasting in catabolic patients is in part mediated by glucocorticoids and is associated with increased expression and activity of the transcription factor C/EBPß. It is not known, however, if C/EBPß is causally linked to glucocorticoid-induced muscle atrophy. We used dexamethasone-treated L6 myoblasts and myotubes to test the role of C/EBPß in glucocorticoid-induced expression of the muscle-specific ubiquitin ligases atrogin-1 and MuRF1, protein degradation, and muscle atrophy by transfecting cells with C/EBPß siRNA. In myoblasts, silencing C/EBPß expression with siRNA inhibited dexamethasone-induced increase in protein degradation, atrogin-1 and MuRF1 expression, and muscle cell atrophy. Similar effects of C/EBPß siRNA were seen in myotubes except that the dexamethasone-induced increase in MuRF1 expression was not affected by C/EBPß siRNA in myotubes. In additional experiments, overexpressing C/EBPß did not influence atrogin-1 or MuRF1 expression in myoblasts or myotubes. Taken together, our observations suggest that glucocorticoid-induced muscle wasting is at least in part regulated by C/EBPß. Increased C/EBPß expression alone, however, is not sufficient to upregulate atrogin-1 and MuRF1 expression.

Sepsis downregulates myostatin mRNA levels without altering myostatin protein levels in skeletal muscle.

Myostatin is a negative regulator of muscle mass and has been reported to be upregulated in several conditions characterized by muscle atrophy. The influence of sepsis on myostatin expression and activity is poorly understood. Here, we tested the hypothesis that sepsis upregulates the expression and downstream signaling of myostatin in skeletal muscle. Because sepsis-induced muscle wasting is at least in part regulated by glucocorticoids, we also determined the influence of glucocorticoids on myostatin expression. Sepsis was induced in rats by cecal ligation and puncture and control rats were sham-operated. In other experiments, rats were injected intraperitoneally with dexamethasone (10 mg/kg) or corresponding volume of vehicle. Surprisingly, myostatin mRNA levels were reduced and myostatin protein levels were unchanged in muscles from septic rats. Muscle levels of activin A, follistatin, and total and phosphorylated Smad2 (p-Smad2) were not influenced by sepsis, suggesting that myostatin downstream signaling was not altered during sepsis. Interestingly, total and p-Smad3 levels were increased in septic muscle, possibly reflecting altered signaling through pathways other than myostatin. Similar to sepsis, treatment of rats with dexamethasone reduced myostatin mRNA levels and did not alter myostatin protein levels. Fasting, an additional condition characterized by muscle wasting, reduced myostatin mRNA and activin A protein levels, increased myostatin protein, and did not influence follistatin and p-Smad2 levels. Of note, total and p-Smad3 levels were reduced in muscle during fasting. The results suggest that sepsis and glucocorticoids do not upregulate the expression and activity of myostatin in skeletal muscle. The role of myostatin may vary between different conditions characterized by muscle wasting. Downstream signaling through Smad2 and 3 is probably regulated not only by myostatin but by other mechanisms as well.