RESUMO
Several factors affect muscle protein synthesis (MPS) in the postabsorptive state. Extreme physical inactivity (e.g., bedrest) may reduce basal MPS, whereas walking may augment basal MPS. We hypothesized that outpatients would have a higher postabsorptive MPS than inpatients. To test this hypothesis, we conducted a retrospective analysis. We compared 152 outpatient participants who arrived at the research site the morning of the MPS assessment with 350 Inpatient participants who had an overnight stay in the hospital unit before the MPS assessment the following morning. We used stable isotopic methods and collected vastus lateralis biopsies â¼2 to 3 h apart to assess mixed MPS. MPS was â¼12% higher (P < 0.05) for outpatients than inpatients. Within a subset of participants, we discovered that after instruction to limit activity, outpatients (n = 13) took 800 to 900 steps in the morning to arrive at the unit, seven times more steps than inpatients (n = 12). We concluded that an overnight stay in the hospital as an inpatient is characterized by reduced morning activity and causes a slight but significant reduction in MPS compared with participants studied as outpatients. Researchers should be aware of physical activity status when designing and interpreting MPS results.NEW & NOTEWORTHY The postabsorptive muscle protein synthesis rate is lower in the morning after an overnight inpatient hospital stay compared with an outpatient visit. Although only a minimal amount of steps was conducted by outpatients (â¼900), this was enough to increase postabsorptive muscle protein synthesis rate.
Assuntos
Pacientes Internados , Proteínas Musculares , Humanos , Pacientes Ambulatoriais , Estudos Retrospectivos , Biossíntese de ProteínasRESUMO
BACKGROUND: Higher protein and fiber diets promote weight management and metabolic health. OBJECTIVES: This study aimed to determine if greater weight loss and positive changes in metabolic outcomes could be achieved with twice-daily consumption of a high-protein and fiber-based multi-ingredient nutritional shake (HPF) compared with an isocaloric low-protein, lower fiber-based placebo (LPF). METHODS: Study procedures were conducted by an independent research organization under clinicaltrials.gov registration NCT03057873. Healthy overweight and obese adults [n = 206; BMI (kg/m2): 27-35; 70% female] were randomly assigned to HPF or LPF. All participants were prescribed an energy-restricted diet (500 kcal/d less than energy needs) and consumed a HPF (17 g protein, 6 g fiber) or LPF (1 g protein, 3 g fiber) shake 30 min before breakfast and lunch for 12 wk. Primary outcomes included body weight and total body fat percentage. Blood samples were collected at days (D) 0, 28, 56, and 84 for secondary analyses related to metabolic markers of health. RESULTS: Although weight loss occurred in both groups, HPF had greater weight loss at D84 compared with LPF (-3.3 kg vs. -1.8 kg, P < 0.05). Percentage body fat decreased in both groups (HPF: -1.33%, LPF: -1.09%; P < 0.001) with no differences between groups. Serum total cholesterol, LDL cholesterol, and oxidized LDL decreased between -5.1% to -8.3%, whereas adiponectin increased over time in both groups; these changes occurred to a greater extent in HPF compared with LPF (all P < 0.05). CONCLUSIONS: A multi-ingredient HPF nutritional supplement shake consumed as a preload before breakfast and lunch positively influenced weight management and metabolic outcomes in overweight adults compared with an LPF placebo. These findings suggest that specific nutrient factors (i.e., potentially including protein, fiber, and bioactive content) other than calorie reduction alone influence the success of a weight-loss regimen. This trial was registered at www.clinicaltrials.gov as NCT03057873.
Assuntos
Sobrepeso , Redução de Peso , Adulto , Fibras na Dieta , Suplementos Nutricionais , Método Duplo-Cego , Feminino , Humanos , Masculino , Obesidade/metabolismo , Sobrepeso/tratamento farmacológicoRESUMO
AIMS/HYPOTHESES: Obesity is associated with decreased insulin sensitivity (IS) and elevated plasma branched-chain amino acids (BCAAs). The purpose of this study was to investigate the relationship between BCAA metabolism and IS in overweight (OW) individuals during exercise intervention. METHODS: Whole-body leucine turnover, IS by hyperinsulinaemic-euglycaemic clamp, and circulating and skeletal muscle amino acids, branched-chain α-keto acids and acylcarnitines were measured in ten healthy controls (Control) and nine OW, untrained, insulin-resistant individuals (OW-Untrained). OW-Untrained then underwent a 6 month aerobic and resistance exercise programme and repeated testing (OW-Trained). RESULTS: IS was higher in Control vs OW-Untrained and increased significantly following exercise. IS was lower in OW-Trained vs Control expressed relative to body mass, but was not different from Control when normalised to fat-free mass (FFM). Plasma BCAAs and leucine turnover (relative to FFM) were higher in OW-Untrained vs Control, but did not change on average with exercise. Despite this, within individuals, the decrease in molar sum of circulating BCAAs was the best metabolic predictor of improvement in IS. Circulating glycine levels were higher in Control and OW-Trained vs OW-Untrained, and urinary metabolic profiling suggests that exercise induces more efficient elimination of excess acyl groups derived from BCAA and aromatic amino acid (AA) metabolism via formation of urinary glycine adducts. CONCLUSIONS/INTERPRETATION: A mechanism involving more efficient elimination of excess acyl groups derived from BCAA and aromatic AA metabolism via glycine conjugation in the liver, rather than increased BCAA disposal through oxidation and turnover, may mediate interactions between exercise, BCAA metabolism and IS. TRIAL REGISTRATION: Clinicaltrials.gov NCT01786941.
Assuntos
Aminoácidos de Cadeia Ramificada/metabolismo , Exercício Físico/fisiologia , Glicina/metabolismo , Resistência à Insulina/fisiologia , Sobrepeso/metabolismo , Treinamento Resistido , Adulto , Glicemia/metabolismo , Técnica Clamp de Glucose , Humanos , Fígado/metabolismo , Masculino , Pessoa de Meia-Idade , Músculo Esquelético/metabolismo , Sobrepeso/terapia , Resultado do TratamentoRESUMO
In humans, essential amino acids (EAAs) stimulate muscle protein synthesis (MPS) with no effect on muscle protein breakdown (MPB). Insulin can stimulate MPS, and carbohydrates (CHOs) and insulin decrease MPB. Net protein balance (NB; indicator of overall anabolism) is greatest when MPS is maximized and MPB is minimized. To determine whether adding CHO or a gluconeogenic amino acid to EAAs would improve NB compared with EAA alone, young men and women (n = 21) ingested 10 g EAA alone, with 30 g sucrose (EAA+CHO), or with 30 g alanine (EAA+ALA). The fractional synthetic rate and phenylalanine kinetics (MPS, MPB, NB) were assessed by stable isotopic methods on muscle biopsies at baseline and 60 and 180 min following nutrient ingestion. Insulin increased 30 min postingestion in all groups and remained elevated in the EAA+CHO and EAA+ALA groups for 60 and 120 min, respectively. The fractional synthetic rate increased from baseline at 60 min in all groups (P < 0.05; EAA = 0.053 ± 0.018 to 0.090 ± 0.039% · h(-1); EAA+ALA = 0.051 ± 0.005 to 0.087 ± 0.015% · h(-1); EAA+CHO = 0.049 ± 0.006 to 0.115 ± 0.024% · h(-1)). MPS and NB peaked at 30 min in the EAA and EAA+CHO groups but at 60 min in the EAA+ALA group and NB was elevated above baseline longer in the EAA+ALA group than in the EAA group (P < 0.05). Although responses were more robust in the EAA+CHO group and prolonged in the EAA+ALA group, AUCs were similar among all groups for fractional synthetic rate, MPS, MPB, and NB. Because the overall muscle protein anabolic response was not improved in either the EAA+ALA or EAA+CHO group compared with EAA, we conclude that protein nutritional interventions to enhance muscle protein anabolism do not require such additional energy.
Assuntos
Alanina/farmacologia , Aminoácidos Essenciais/farmacologia , Sacarose Alimentar/farmacologia , Proteínas Musculares/metabolismo , Músculo Esquelético/efeitos dos fármacos , Biossíntese de Proteínas/efeitos dos fármacos , Sacarose/farmacologia , Adulto , Alanina/metabolismo , Aminoácidos Essenciais/metabolismo , Área Sob a Curva , Biópsia , Dieta , Feminino , Humanos , Insulina/metabolismo , Masculino , Músculo Esquelético/metabolismoRESUMO
The relationship between mammalian target of rapamycin complex 1 (mTORC1) signaling and muscle protein synthesis during instances of amino acid surplus in humans is based solely on correlational data. Therefore, the goal of this study was to use a mechanistic approach specifically designed to determine whether increased mTORC1 activation is requisite for the stimulation of muscle protein synthesis following L-essential amino acid (EAA) ingestion in humans. Examination of muscle protein synthesis and signaling were performed on vastus lateralis muscle biopsies obtained from 8 young (25 ± 2 y) individuals who were studied prior to and following ingestion of 10 g of EAA during 2 separate trials in a randomized, counterbalanced design. The trials were identical except during 1 trial, participants were administered a single oral dose of a potent mTORC1 inhibitor (rapamycin) prior to EAA ingestion. In response to EAA ingestion, an ~60% increase in muscle protein synthesis was observed during the control trial, concomitant with increased phosphorylation of mTOR (Ser(2448)), ribosomal S6 kinase 1 (Thr(389)), and eukaryotic initiation factor 4E binding protein 1 (Thr(37/46)). In contrast, prior administration of rapamycin completely blocked the increase in muscle protein synthesis and blocked or attenuated activation of mTORC1-signaling proteins. The inhibition of muscle protein synthesis and signaling was not due to differences in either extracellular or intracellular amino acid availability, because these variables were similar between trials. These data support a fundamental role for mTORC1 activation as a key regulator of human muscle protein synthesis in response to increased EAA availability. This information will be useful in the development of evidence-based nutritional therapies targeting mTORC1 to counteract muscle wasting associated with numerous clinical conditions.
Assuntos
Aminoácidos Essenciais/metabolismo , Ativação Enzimática , Proteínas Musculares/biossíntese , Músculo Esquelético/metabolismo , Proteínas/metabolismo , Transdução de Sinais , Serina-Treonina Quinases TOR/metabolismo , Regulação para Cima , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Adulto , Aminoácidos Essenciais/sangue , Biópsia por Agulha , Proteínas de Ciclo Celular , Ativação Enzimática/efeitos dos fármacos , Feminino , Humanos , Cinética , Masculino , Alvo Mecanístico do Complexo 1 de Rapamicina , Complexos Multiproteicos , Músculo Esquelético/efeitos dos fármacos , Fosfoproteínas/metabolismo , Fosforilação/efeitos dos fármacos , Inibidores de Proteínas Quinases/farmacologia , Processamento de Proteína Pós-Traducional/efeitos dos fármacos , Músculo Quadríceps/efeitos dos fármacos , Músculo Quadríceps/metabolismo , Proteínas Quinases S6 Ribossômicas 90-kDa/metabolismo , Transdução de Sinais/efeitos dos fármacos , Sirolimo/farmacologia , Serina-Treonina Quinases TOR/antagonistas & inibidores , Regulação para Cima/efeitos dos fármacos , Adulto JovemRESUMO
Essential amino acids (EAA) stimulate skeletal muscle mammalian target of rapamycin complex 1 (mTORC1) signaling and protein synthesis. It has recently been reported that an increase in amino acid (AA) transporter expression during anabolic conditions is rapamycin-sensitive. The purpose of this study was to determine whether an increase in EAA availability increases AA transporter expression in human skeletal muscle. Muscle biopsies were obtained from the vastus lateralis of seven young adult subjects (3 male, 4 female) before and 1-3 h after EAA ingestion (10 g). Blood and muscle samples were analyzed for leucine kinetics using stable isotopic techniques. Quantitative RT-PCR, and immunoblotting were used to determine the mRNA and protein expression, respectively, of AA transporters and members of the general AA control pathway [general control nonrepressed (GCN2), activating transcription factor (ATF4), and eukaryotic initiation factor (eIF2) alpha-subunit (Ser(52))]. EAA ingestion increased blood leucine concentration, delivery of leucine to muscle, transport of leucine from blood into muscle, intracellular muscle leucine concentration, ribosomal protein S6 (Ser(240/244)) phosphorylation, and muscle protein synthesis. This was followed with increased L-type AA transporter (LAT1), CD98, sodium-coupled neutral AA transporter (SNAT2), and proton-coupled amino acid transporter (PAT1) mRNA expression at 1 h (P < 0.05) and modest increases in LAT1 protein expression (3 h post-EAA) and SNAT2 protein expression (2 and 3 h post-EAA, P < 0.05). Although there were no changes in GCN2 expression and eIF2 alpha phosphorylation, ATF4 protein expression reached significance by 2 h post-EAA (P < 0.05). We conclude that an increase in EAA availability upregulates human skeletal muscle AA transporter expression, perhaps in an mTORC1-dependent manner, which may be an adaptive response necessary for improved AA intracellular delivery.
Assuntos
Sistemas de Transporte de Aminoácidos/metabolismo , Aminoácidos Essenciais/administração & dosagem , Aminoácidos Essenciais/metabolismo , Músculo Quadríceps/metabolismo , Fatores de Transcrição/metabolismo , Adulto , Sistemas de Transporte de Aminoácidos/genética , Análise de Variância , Transporte Biológico , Western Blotting , Ingestão de Alimentos , Feminino , Humanos , Masculino , Alvo Mecanístico do Complexo 1 de Rapamicina , Complexos Multiproteicos , Biossíntese de Proteínas , Proteínas , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Serina-Treonina Quinases TOR , Fatores de Transcrição/genéticaRESUMO
Muscle protein breakdown (MPB) is increased following resistance exercise, but ingestion of carbohydrate during postexercise recovery can decrease MPB with no effect on muscle protein synthesis (MPS). We sought to determine whether a combination of essential amino acids (EAA) with low carbohydrate or high carbohydrate could effectively reduce MPB following resistance exercise and improve muscle protein net balance (NB). We hypothesized that higher levels of carbohydrate and resulting increases in circulating insulin would inhibit MPB and associated signaling, resulting in augmented NB. Thirteen male subjects were assigned to one of two groups receiving equivalent amounts of EAA (approximately 20 g) but differing carbohydrate levels (low = 30, high = 90 g). Groups ingested nutrients 1 h after an acute bout of leg resistance exercise. Leg phenylalanine kinetics (e.g., MPB, MPS, NB), signaling proteins, and mRNA expression were assessed on successive muscle biopsies using stable isotopic techniques, immunoblotting, and real-time quantitative PCR, respectively. MPB tended to decrease (P < 0.1) and MPS increased (P < 0.05) similarly in both groups following nutrient ingestion. No group differences were observed, but muscle ring finger 1 (MuRF1) protein content and MuRF1 mRNA expression increased following resistance exercise and remained elevated following nutrient ingestion, while autophagy marker (light-chain 3B-II) decreased after nutrient ingestion (P < 0.05). Forkhead box-O3a phosphorylation, total muscle atrophy F-box (MAFbx) protein, and MAFbx and caspase-3 mRNA expression were unchanged. We conclude that the enhanced muscle protein anabolic response detected when EAA+carbohydrate are ingested postresistance exercise is primarily due to an increase in MPS with minor changes in MPB, regardless of carbohydrate dose or circulating insulin level.
Assuntos
Aminoácidos Essenciais/administração & dosagem , Carboidratos da Dieta/administração & dosagem , Proteínas Alimentares/administração & dosagem , Contração Muscular , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Treinamento Resistido , Adulto , Biópsia , Glicemia/metabolismo , Caspase 3/metabolismo , Estudos Transversais , Carboidratos da Dieta/sangue , Proteínas Alimentares/sangue , Proteínas Alimentares/farmacocinética , Proteína Forkhead Box O3 , Fatores de Transcrição Forkhead/metabolismo , Regulação da Expressão Gênica , Humanos , Insulina/sangue , Masculino , Proteínas Associadas aos Microtúbulos/metabolismo , Proteínas Musculares/genética , Fosforilação , Período Pós-Prandial , RNA Mensageiro/metabolismo , Proteínas Ligases SKP Culina F-Box/metabolismo , Transdução de Sinais , Proteínas com Motivo Tripartido , Ubiquitina-Proteína Ligases/metabolismoRESUMO
Essential amino acids (EAA) stimulate skeletal muscle protein synthesis (MPS) in humans. Leucine may have a greater stimulatory effect on MPS than other EAA and/or decrease muscle protein breakdown (MPB). To determine the effect of 2 different leucine concentrations on muscle protein turnover and associated signaling, young men (n = 6) and women (n = 8) ingested 10 g EAA in 1 of 2 groups: composition typical of high quality proteins (CTRL; 1.8 g leucine) or increased leucine concentration (LEU; 3.5 g leucine). Participants were studied for 180 min postingestion. Fractional synthetic rate and leg phenylalanine and leucine kinetics were assessed on muscle biopsies using stable isotopic techniques. Signaling was determined by immunoblotting. Arterial leucine concentration and delivery to the leg increased in both groups and was significantly higher in LEU than in CTRL; however, transport into the muscle and intracellular availability did not differ between groups. MPS increased similarly in both groups 60 min postingestion. MPB decreased at 60 min only in LEU, but net muscle protein balance improved similarly. Components of mammalian target of rapamycin (mTOR) signaling were improved in LEU, but no changes were observed in ubiquitin-proteasome system signaling. Changes in light chain 3 and mTOR association with Unc-51-like kinase 1 indicate autophagy decreased more in LEU. We conclude that in 10 g of EAA, the leucine content typical of high quality proteins (~1.8 g) is sufficient to induce a maximal skeletal muscle protein anabolic response in young adults, but leucine may play a role in autophagy regulation.
Assuntos
Leucina/administração & dosagem , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Transdução de Sinais , Adulto , Autofagia , Biomarcadores/sangue , Biomarcadores/metabolismo , Biópsia , Isótopos de Carbono , Feminino , Humanos , Infusões Intravenosas , Cinética , Leucina/sangue , Leucina/metabolismo , Masculino , Alvo Mecanístico do Complexo 1 de Rapamicina , Complexos Multiproteicos , Fenilalanina/administração & dosagem , Fenilalanina/metabolismo , Complexo de Endopeptidases do Proteassoma/metabolismo , Proteínas , Músculo Quadríceps/irrigação sanguínea , Músculo Quadríceps/metabolismo , Fluxo Sanguíneo Regional , Serina-Treonina Quinases TOR , Fatores de Transcrição/metabolismo , Ubiquitina/metabolismoRESUMO
Muscle protein synthesis and mTORC1 signalling are concurrently stimulated following muscle contraction in humans. In an effort to determine whether mTORC1 signalling is essential for regulating muscle protein synthesis in humans, we treated subjects with a potent mTORC1 inhibitor (rapamycin) prior to performing a series of high-intensity muscle contractions. Here we show that rapamycin treatment blocks the early (1-2 h) acute contraction-induced increase ( approximately 40%) in human muscle protein synthesis. In addition, several downstream components of the mTORC1 signalling pathway were also blunted or blocked by rapamycin. For instance, S6K1 phosphorylation (Thr421/Ser424) was increased post-exercise 6-fold in the control group while being unchanged with rapamycin treatment. Furthermore, eEF2 phosphorylation (Thr56) was reduced by approximately 25% post-exercise in the control group but phosphorylation following rapamycin treatment was unaltered, indicating that translation elongation was inhibited. Rapamycin administration prior to exercise also reduced the ability of raptor to associate with mTORC1 during post-exercise recovery. Surprisingly, rapamycin treatment prior to resistance exercise completely blocked the contraction-induced increase in the phosphorylation of ERK1/2 (Thr202/Tyr204) and blunted the increase in MNK1 (Thr197/202) phosphorylation. However, the phosphorylation of a known target of MNK1, eIF4E (Ser208), was similar in both groups (P > 0.05) which is consistent with the notion that rapamycin does not directly inhibit MAPK signalling. We conclude that mTORC1 signalling is, in part, playing a key role in regulating the contraction-induced stimulation of muscle protein synthesis in humans, while dual activation of mTORC1 and ERK1/2 stimulation may be required for full stimulation of human skeletal muscle protein synthesis.
Assuntos
Exercício Físico , Contração Muscular , Proteínas Musculares/biossíntese , Músculo Esquelético/efeitos dos fármacos , Biossíntese de Proteínas/efeitos dos fármacos , Inibidores de Proteínas Quinases/administração & dosagem , Proteínas Quinases/metabolismo , Transdução de Sinais/efeitos dos fármacos , Sirolimo/administração & dosagem , Administração Oral , Adulto , Aminoácidos/sangue , Humanos , Hidrocortisona/sangue , Insulina/sangue , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Masculino , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Músculo Esquelético/enzimologia , Músculo Esquelético/metabolismo , Fator 2 de Elongação de Peptídeos/metabolismo , Fosforilação , Inibidores de Proteínas Quinases/sangue , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Quinases S6 Ribossômicas/metabolismo , Sirolimo/sangue , Serina-Treonina Quinases TOR , Fatores de TempoRESUMO
Essential amino acids (EAA) stimulate muscle protein synthesis in humans. However, little is known about whether microRNAs (miRNA) and genes associated with muscle growth are expressed differently following EAA ingestion. Our purpose in this experiment was to determine whether miRNA and growth-related mRNA expressed in skeletal muscle are up- or downregulated in humans following the ingestion of EAA. We hypothesized that EAA would alter miRNA expression in skeletal muscle as well as select growth-related genes. Muscle biopsies were obtained from the vastus lateralis of 7 young adult participants (3 male, 4 female) before and 3 h after ingesting 10 g of EAA. Muscle samples were analyzed for muscle miRNA (miR-499, -208b, -23a, -1, -133a, and -206) and muscle-growth related genes [MyoD1, myogenin, myostatin, myocyte enhancer factor C (MEF2C), follistatin-like-1 (FSTL1), histone deacytylase 4, and serum response factor mRNA] before and after EAA ingestion using real-time PCR. Following EAA ingestion, miR-499, -208b, -23a, -1, and pri-miR-206 expression increased (P < 0.05). The muscle-growth genes MyoD1 and FSTL1 mRNA expression increased (P < 0.05), and myostatin and MEF2C mRNA were downregulated following EAA ingestion (P < 0.05). We conclude that miRNA and growth-related genes expressed in skeletal muscle are rapidly altered within hours following EAA ingestion. Further work is needed to determine whether these miRNA are post-transcriptional regulators of growth-related genes following an anabolic stimulus.
Assuntos
Aminoácidos Essenciais/farmacologia , Proteínas de Domínio MADS/genética , MicroRNAs/genética , Músculo Esquelético/fisiologia , Fatores de Regulação Miogênica/genética , Miostatina/genética , RNA Mensageiro/genética , Adulto , Aminoácidos/sangue , Glicemia/metabolismo , Primers do DNA , DNA Complementar/genética , Regulação para Baixo/efeitos dos fármacos , Ácidos Graxos não Esterificados/sangue , Feminino , Humanos , Insulina/sangue , Fatores de Transcrição MEF2 , Masculino , MicroRNAs/efeitos dos fármacos , Músculo Esquelético/efeitos dos fármacos , Reação em Cadeia da Polimerase , RNA Mensageiro/efeitos dos fármacosRESUMO
In this review we discuss current findings in the human skeletal muscle literature describing the acute influence of nutrients (leucine-enriched essential amino acids in particular) and resistance exercise on muscle protein synthesis and mammalian target of rapamycin complex 1 (mTORC1) signaling. We show that essential amino acids and an acute bout of resistance exercise independently stimulate human skeletal muscle protein synthesis. It also appears that ingestion of essential amino acids following resistance exercise leads to an even larger increase in the rate of muscle protein synthesis compared with the independent effects of nutrients or muscle contraction. Until recently the cellular mechanisms responsible for controlling the rate of muscle protein synthesis in humans were unknown. In this review, we highlight new studies in humans that have clearly shown the mTORC1 signaling pathway is playing an important regulatory role in controlling muscle protein synthesis in response to nutrients and/or muscle contraction. We propose that essential amino acid ingestion shortly following a bout of resistance exercise is beneficial in promoting skeletal muscle growth and may be useful in counteracting muscle wasting in a variety of conditions such as aging, cancer cachexia, physical inactivity, and perhaps during rehabilitation following trauma or surgery.
Assuntos
Proteínas Musculares/biossíntese , Músculo Esquelético/metabolismo , Músculo Esquelético/fisiologia , Fenômenos Fisiológicos da Nutrição/fisiologia , Transdução de Sinais/fisiologia , Fatores de Transcrição/fisiologia , Envelhecimento/fisiologia , Exercício Físico/fisiologia , Expressão Gênica , Humanos , Alvo Mecanístico do Complexo 1 de Rapamicina , Complexos Multiproteicos , Contração Muscular/fisiologia , Biossíntese de Proteínas , Proteínas , Serina-Treonina Quinases TORRESUMO
Ingestion of an essential amino acid-carbohydrate (EAA + CHO) solution following resistance exercise enhances muscle protein synthesis during postexercise recovery. It is unclear whether EAA + CHO ingestion before resistance exercise can improve direct measures of postexercise muscle protein synthesis (fractional synthetic rate; FSR). We hypothesized that EAA + CHO ingestion before a bout of resistance exercise would prevent the exercise-induced decrease in muscle FSR and would result in an enhanced rate of muscle FSR during postexercise recovery. We studied 22 young healthy subjects before, during, and for 2 h following a bout of high-intensity leg resistance exercise. The fasting control group (n = 11) did not ingest nutrients, and the EAA + CHO group (n = 11) ingested a solution of EAA + CHO 1 h before beginning the exercise bout. Stable isotopic methods were used in combination with muscle biopsies to determine FSR. Immunoblotting procedures were utilized to assess cell signaling proteins associated with the regulation of FSR. We found that muscle FSR increased in the EAA + CHO group immediately following EAA + CHO ingestion (P < 0.05), returned to basal values during exercise, and remained unchanged at 1 h postexercise. Muscle FSR decreased in the fasting group during exercise and increased at 1 h postexercise (P < 0.05). However, the 2 h postexercise FSR increased by approximately 50% in both groups with no differences between groups (P > 0.05). Eukaryotic elongation factor 2 phosphorylation was reduced in both groups at 2 h postexercise (EAA + CHO: 39 +/- 7%; fasting: 47 +/- 9%; P < 0.05). We conclude that EAA + CHO ingestion before resistance exercise does not enhance postexercise FSR compared with exercise without nutrients.
Assuntos
Aminoácidos Essenciais/administração & dosagem , Carboidratos da Dieta/administração & dosagem , Exercício Físico/fisiologia , Proteínas Musculares/biossíntese , Músculo Esquelético/efeitos dos fármacos , Adulto , Aminoácidos Essenciais/química , Feminino , Privação de Alimentos , Humanos , Leucina/administração & dosagem , Leucina/análise , Leucina/metabolismo , Masculino , Músculo Esquelético/metabolismo , Fenilalanina/administração & dosagem , Fenilalanina/análise , Fenilalanina/metabolismo , Proteínas Quinases/metabolismo , Fluxo Sanguíneo Regional/efeitos dos fármacos , Transdução de Sinais , Serina-Treonina Quinases TOR , Adulto JovemRESUMO
Ribosomal S6 kinase 1 (S6K1) is a downstream component of the mammalian target of rapamycin (mTOR) signaling pathway and plays a regulatory role in translation initiation, protein synthesis, and muscle hypertrophy. AMP-activated protein kinase (AMPK) is a cellular energy sensor, a negative regulator of mTOR, and an inhibitor of protein synthesis. The purpose of this study was to determine whether the hypertrophy/cell growth-associated mTOR pathway was downregulated during muscle atrophy associated with chronic paraplegia. Soleus muscle was collected from male Sprague-Dawley rats 10 wk following complete T(4)-T(5) spinal cord transection (paraplegic) and from sham-operated (control) rats. We utilized immunoprecipitation and Western blotting techniques to measure upstream [AMPK, Akt/protein kinase B (PKB)] and downstream components of the mTOR signaling pathway [mTOR, S6K1, SKAR, 4E-binding protein 1 (4E-BP1), and eukaryotic initiation factor (eIF) 4G and 2alpha]. Paraplegia was associated with significant soleus muscle atrophy (174 +/- 8 vs. 240 +/- 13 mg; P < 0.05). There was a reduction in phosphorylation of mTOR, S6K1, and eIF4G (P < 0.05) with no change in Akt/PKB or 4E-BP1 (P > 0.05). Total protein abundance of mTOR, S6K1, eIF2alpha, and Akt/PKB was decreased, and increased for SKAR (P < 0.05), whereas 4E-BP1 and eIF4G did not change (P > 0.05). S6K1 activity was significantly reduced in the paraplegic group (P < 0.05); however, AMPKalpha2 activity was not altered (3.5 +/- 0.4 vs. 3.7 +/- 0.5 pmol x mg(-1) x min(-1), control vs. paraplegic rats). We conclude that paraplegia-induced muscle atrophy in rats is associated with a general downregulation of the mTOR signaling pathway. Therefore, in addition to upregulation of atrophy signaling during muscle wasting, downregulation of muscle cell growth/hypertrophy-associated signaling appears to be an important component of long-term muscle loss.
Assuntos
Músculo Esquelético/metabolismo , Atrofia Muscular/metabolismo , Paraplegia/complicações , Proteínas Quinases/metabolismo , Proteínas Quinases S6 Ribossômicas/metabolismo , Transdução de Sinais , Traumatismos da Medula Espinal/complicações , Proteínas Quinases Ativadas por AMP , Animais , Western Blotting , Proteínas de Transporte/metabolismo , Doença Crônica , Modelos Animais de Doenças , Regulação para Baixo , Fator de Iniciação 2 em Eucariotos/metabolismo , Fator de Iniciação Eucariótico 4G/metabolismo , Imunoprecipitação , Peptídeos e Proteínas de Sinalização Intracelular , Masculino , Complexos Multienzimáticos/metabolismo , Músculo Esquelético/enzimologia , Músculo Esquelético/patologia , Atrofia Muscular/enzimologia , Atrofia Muscular/etiologia , Atrofia Muscular/patologia , Paraplegia/enzimologia , Paraplegia/etiologia , Paraplegia/metabolismo , Paraplegia/patologia , Fosfoproteínas/metabolismo , Fosforilação , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Ratos , Ratos Sprague-Dawley , Traumatismos da Medula Espinal/enzimologia , Traumatismos da Medula Espinal/metabolismo , Traumatismos da Medula Espinal/patologia , Serina-Treonina Quinases TOR , Fatores de TempoRESUMO
Akt substrate of 160 kDa (AS160/TBC1D4) is associated with insulin and contraction-mediated glucose uptake. Human skeletal muscle AS160 phosphorylation is increased during aerobic exercise but not immediately following resistance exercise. It is not known whether AS160 phosphorylation is altered during recovery from resistance exercise. Therefore, we hypothesized that muscle AS160/TBC1D4 phosphorylation and glucose uptake across the leg would be increased during recovery following resistance exercise. We studied 9 male subjects before, during, and for 2 h of postexercise recovery. We utilized femoral catheterizations and muscle biopsies in combination with indirect calorimetry and immunoblotting to determine whole body glucose and fat oxidation, leg glucose uptake, muscle AMPKalpha2 activity, and the phosphorylation of muscle Akt and AS160/TBC1D4. Glucose oxidation was reduced while fat oxidation increased ( approximately 35%) during postexercise recovery (P Assuntos
Exercício Físico/fisiologia
, Proteínas Ativadoras de GTPase/metabolismo
, Glucose/metabolismo
, Perna (Membro)/fisiologia
, Músculo Esquelético/metabolismo
, Aptidão Física/fisiologia
, Absorciometria de Fóton
, Adulto
, Western Blotting
, Eletroforese em Gel de Poliacrilamida
, Humanos
, Imunoprecipitação
, Insulina/sangue
, Perna (Membro)/irrigação sanguínea
, Metabolismo dos Lipídeos/fisiologia
, Masculino
, Músculo Esquelético/irrigação sanguínea
, Oxirredução
, Fosforilação
, Fluxo Sanguíneo Regional/fisiologia
RESUMO
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.
RESUMO
Current obesity interventions suffer from lack of durable effects and undesirable complications. Fumagillin, an inhibitor of methionine aminopeptidase-2, causes weight loss by reducing food intake, but with effects on weight that are superior to pair-feeding. Here, we show that feeding of rats on a high-fat diet supplemented with fumagillin (HF/FG) suppresses the aggressive feeding observed in pair-fed controls (HF/PF) and alters expression of circadian genes relative to the HF/PF group. Multiple indices of reduced energy expenditure are observed in HF/FG but not HF/PF rats. HF/FG rats also exhibit changes in gut hormones linked to food intake, increased energy harvest by gut microbiota, and caloric spilling in the urine. Studies in gnotobiotic mice reveal that effects of fumagillin on energy expenditure but not feeding behavior may be mediated by the gut microbiota. In sum, fumagillin engages weight loss-inducing behavioral and physiologic circuits distinct from those activated by simple caloric restriction.
Assuntos
Bactérias/isolamento & purificação , Cicloexanos/administração & dosagem , Metabolismo Energético/efeitos dos fármacos , Ácidos Graxos Insaturados/administração & dosagem , Microbioma Gastrointestinal/efeitos dos fármacos , Obesidade/tratamento farmacológico , Aminopeptidases/antagonistas & inibidores , Animais , Bactérias/efeitos dos fármacos , Bactérias/metabolismo , Comportamento Animal/efeitos dos fármacos , Peso Corporal/efeitos dos fármacos , Dieta Hiperlipídica/efeitos adversos , Modelos Animais de Doenças , Fezes/microbiologia , Comportamento Alimentar/efeitos dos fármacos , Microbioma Gastrointestinal/fisiologia , Vida Livre de Germes/efeitos dos fármacos , Vida Livre de Germes/fisiologia , Glicoproteínas/antagonistas & inibidores , Humanos , Masculino , Metionil Aminopeptidases , Camundongos , Camundongos Endogâmicos C57BL , Obesidade/etiologia , Obesidade/metabolismo , Ratos , Ratos Wistar , Sesquiterpenos/administração & dosagem , Resultado do Tratamento , Redução de Peso/efeitos dos fármacosRESUMO
The rate of muscle loss with aging is higher in men than women. However, women have smaller muscles throughout the adult life. Protein content is a major determinant of skeletal muscle size. This study was designed to determine if age and sex differentially impact basal muscle protein synthesis and mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling. We performed a secondary data analysis on a cohort of 215 healthy, non-obese (BMI<30kg·m(-2)) young (18-40y; 74 men, 52 women) and older (60-87y; 57 men, 32 women) adults. The database contained information on physical characteristics, basal muscle protein fractional synthetic rate (FSR; n=215; stable isotope methodology) and mTORC1 signaling (n=125, Western blotting). FSR and mTORC1 signaling were measured at rest and after an overnight fast. mTORC1 and S6K1 phosphorylation were higher (p<0.05) in older subjects with no sex differences. However, there were no age or sex differences or interaction for muscle FSR (p>0.05). Body mass index, fat free mass, or body fat was not a significant covariate and did not influence the results. We conclude that age and sex do not influence basal muscle protein synthesis. However, basal mTORC1 hyperphosphorylation in the elderly may contribute to insulin resistance and the age-related anabolic resistance of skeletal muscle protein metabolism to nutrition and exercise.
Assuntos
Envelhecimento/fisiologia , Complexos Multiproteicos/metabolismo , Proteínas Musculares , Músculo Esquelético/fisiologia , Proteínas Quinases S6 Ribossômicas 70-kDa/metabolismo , Serina-Treonina Quinases TOR/metabolismo , Adulto , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Masculino , Alvo Mecanístico do Complexo 1 de Rapamicina , Pessoa de Meia-Idade , Contração Muscular/fisiologia , Proteínas Musculares/biossíntese , Proteínas Musculares/metabolismo , Fosforilação/fisiologia , Fatores Sexuais , Transdução de Sinais/fisiologiaRESUMO
BACKGROUND: The loss of skeletal muscle mass and strength during aging, sarcopenia, increases the risk for falls and dependency. Resistance exercise (RE) training is effective at improving muscle mass and strength in older adults; however, aging is associated with reduced training-induced hypertrophy. Recent research has illustrated an impaired muscle protein synthetic response following an acute bout of RE in older adults but much less is known regarding the effect of acute RE on muscle protein breakdown (MPB). We hypothesize that the ubiquitin proteasome system and the autophagosomal-lysosomal system may regulate the overall rate of MPB during postexercise recovery. METHODS: Muscle biopsies of the vastus lateralis were sampled from 16 older (age = 70±2 years) and 16 younger (age = 27±2 years) participants at baseline and at 3, 6, and 24 hours following an acute bout of RE. In conjunction with stable isotopic techniques to measure MPB, we utilized immunoblotting and RT-PCR to examine protein and mRNA expression for key signaling molecules in both the ubiquitin proteasome system and the autophagosomal-lysosomal system. RESULTS: MuRF1 mRNA expression increased, whereas GABARAP mRNA decreased after RE in both younger and older adults (p < .05). The LC3B-II/LC3B-I protein ratio decreased in both groups after RE (p < .05), but MPB was not different 24 hour post-RE in either group (p > .05). CONCLUSIONS: Aging does not influence skeletal MPB, autophagy, or the ubiquitin proteasome system following an acute bout of RE. Therefore, targeting the muscle protein synthesis response to exercise may hold more promise in the prevention of sarcopenia.
Assuntos
Autofagia , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Treinamento Resistido , Fatores Etários , Idoso , Feminino , Humanos , Masculino , Músculo Esquelético/fisiologiaRESUMO
BACKGROUND: Nutrient stimulation of muscle protein anabolism is blunted with aging and may contribute to the development and progression of sarcopenia in older adults. This is likely due to insulin resistance of protein metabolism and/or endothelial dysfunction with a reduction in nutritive flow, both of which can be improved by aerobic exercise. OBJECTIVE: Our objective was to determine whether increasing physical activity can enhance the muscle protein anabolic effect of essential amino acid (EAA) + sucrose intake in older subjects by improving nutritive flow and/or insulin signaling. DESIGN: Using a randomized crossover design, we measured in older subjects [n = 6, 70 ± 3 y of age, BMI (in kg/m2) of 25 ± 1] the acute effects of increasing physical activity with aerobic exercise, as compared with normal sedentary lifestyle, on the response of blood flow, microvascular perfusion, insulin signaling, and muscle protein kinetics to EAA+sucrose intake. RESULTS: No differences between treatment groups were found in the basal state. The change from the basal state in blood flow, muscle perfusion, phenylalanine delivery, net balance, and muscle protein synthesis during the consumption of EAA+sucrose was significantly higher after the exercise than after the control treatment (P < 0.05). Insulin signaling increased during EAA+sucrose ingestion in both groups (P < 0.05). CONCLUSIONS: Our data indicate that a prior bout of aerobic exercise increases the anabolic effect of nutrient intake in older adults. This effect appears to be mediated by an exercise-induced improvement in nutrient-stimulated vasodilation and nutrient delivery to muscle rather than to improved insulin signaling. This trial was registered at clinicaltrials.gov as NCT00690534.
Assuntos
Aminoácidos Essenciais/metabolismo , Dieta , Metabolismo Energético/fisiologia , Exercício Físico/fisiologia , Proteínas Musculares/biossíntese , Músculo Esquelético/metabolismo , Sarcopenia/prevenção & controle , Idoso , Circulação Sanguínea , Índice de Massa Corporal , Estudos Cross-Over , Sacarose Alimentar/metabolismo , Ingestão de Energia , Terapia por Exercício , Feminino , Humanos , Insulina/metabolismo , Masculino , Músculo Esquelético/irrigação sanguínea , Fenilalanina/metabolismo , Sarcopenia/metabolismo , Comportamento Sedentário , Transdução de Sinais , Sacarose/metabolismoRESUMO
Amino acid transporters and mammalian target of rapamycin complex 1 (mTORC1) signaling are important contributors to muscle protein anabolism. Aging is associated with reduced mTORC1 signaling following resistance exercise, but the role of amino acid transporters is unknown. Young (n = 13; 28 ± 2 yr) and older (n = 13; 68 ± 2 yr) subjects performed a bout of resistance exercise. Skeletal muscle biopsies (vastus lateralis) were obtained at basal and 3, 6, and 24 h postexercise and were analyzed for amino acid transporter mRNA and protein expression and regulators of amino acid transporter transcription utilizing real-time PCR and Western blotting. We found that basal amino acid transporter expression was similar in young and older adults (P > 0.05). Exercise increased L-type amino acid transporter 1/solute-linked carrier (SLC) 7A5, CD98/SLC3A2, sodium-coupled neutral amino acid transporter 2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, and cationic amino acid transporter 1/SLC7A1 mRNA expression in both young and older adults (P < 0.05). L-type amino acid transporter 1 and CD98 protein increased only in younger adults (P < 0.05). eukaryotic initiation factor 2 α-subunit (S52) increased similarly in young and older adults postexercise (P < 0.05). Ribosomal protein S6 (S240/244) and activating transcription factor 4 nuclear protein expression tended to be higher in the young, while nuclear signal transducer and activator of transcription 3 (STAT3) (Y705) was higher in the older subjects postexercise (P < 0.05). These results suggest that the rapid upregulation of amino acid transporter expression following resistance exercise may be regulated differently between the age groups, but involves a combination of mTORC1, activating transcription factor 4, eukaryotic initiation factor 2 α-subunit, and STAT3. We propose an increase in amino acid transporter expression may contribute to enhanced amino acid sensitivity following exercise in young and older adults. In older adults, the increased nuclear STAT3 phosphorylation may be indicative of an exercise-induced stress response, perhaps to export amino acids from muscle cells.