Basal protein synthesis rates differ between vastus lateralis and rectus abdominis muscle

BACKGROUND

In vivo muscle protein synthesis rates are typically assessed by measuring the incorporation rate of stable isotope labelled amino acids in skeletal muscle tissue collected from vastus lateralis muscle. It remains to be established whether muscle protein synthesis rates in the vastus lateralis are representative of muscle protein synthesis rates of other muscle groups. We hypothesized that post-absorptive muscle protein synthesis rates differ between vastus lateralis and rectus abdominis, pectoralis major, or temporalis muscle in vivo in humans.

METHODS

Twenty-four patients (62 ± 3 years, 42% female), scheduled to undergo surgery, participated in this study and underwent primed continuous intravenous infusions with l-[ring-¹³ C₆ ]-phenylalanine. During the surgical procedures, serum samples were collected, and muscle tissue was obtained from the vastus lateralis as well as from the rectus abdominis, pectoralis major, or temporalis muscle. Fractional mixed muscle protein synthesis rates (%/h) were assessed by measuring the incorporation of l-[ring-¹³ C₆ ]-phenylalanine into muscle tissue protein.

RESULTS

Serum l-[ring-¹³ C₆ ]-phenylalanine enrichments did not change throughout the infusion period. Post-absorptive muscle protein synthesis rates calculated based upon serum l-[ring-¹³ C₆ ]-phenylalanine enrichments did not differ between vastus lateralis and rectus abdominis (0.032 ± 0.004 vs. 0.038 ± 0.003%/h), vastus lateralis and pectoralis major, (0.025 ± 0.003 vs. 0.022 ± 0.005%/h) or vastus lateralis and temporalis (0.047 ± 0.005 vs. 0.043 ± 0.005%/h) muscle, respectively (P > 0.05). When fractional muscle protein synthesis rates were calculated based upon tissue-free l-[ring-¹³ C₆ ]-phenylalanine enrichments as the preferred precursor pool, muscle protein synthesis rates were significantly higher in rectus abdominis (0.089 ± 0.008%/h) compared with vastus lateralis (0.054 ± 0.005%/h) muscle (P < 0.01). No differences were observed between fractional muscle protein synthesis rates in vastus lateralis and pectoralis major (0.046 ± 0.003 vs. 0.041 ± 0.008%/h) or vastus lateralis and temporalis (0.073 ± 0.008 vs. 0.083 ± 0.011%/h) muscle, respectively.

CONCLUSIONS

Post-absorptive muscle protein synthesis rates are higher in rectus abdominis when compared with vastus lateralis muscle. Post-absorptive muscle protein synthesis rates do not differ between vastus lateralis and pectoralis major or temporalis muscle. Protein synthesis rates in muscle tissue samples obtained during surgery do not necessarily represent a good proxy for appendicular skeletal muscle protein synthesis rates.

Overnight Steady-State Infusions of Parenteral Nutrition on Myosin Heavy Chain Transcripts in Rectus Abdominis Muscle Related to Amino Acid Transporters, Insulin-like Growth Factor 1, and Blood Amino Acids in Patients Aimed at Major Surgery

BACKGROUND

Evaluation of improvements by nutrition support to severely ill patients requires sensitive methods to demonstrate activation of protein synthesis in various tissues from groups with a limited number of patients to be statistically efficient. This study examines effects of standard parenteral nutrition (PN) on abdominal muscle transcripts of amino acid (AA) transporters, myosin heavy chains (MHCs), and the insulin-like growth factor 1 and its receptor (IGF-1/IGF-1R) in patients aimed at major surgery.

METHODS

Twenty-two randomized patients received steady-state PN (0.16 gN/kg/d, 30 kcal/kg/d) or saline infusions for 12 hours before operation. Blood samples and muscle biopsies were obtained at operation start. Muscle messenger RNA (mRNA) levels of AA transporters (solute carrier family members SNAT2, LAT1, LAT3, LAT4, TAUT, PAT1, CD98), IGF-1, IGF-1R, MHC isoforms (MHC1, MHC2A, MHC2X), and LAT3 protein were quantified and related to concentrations of AA, IGF-1, insulin, and metabolic substrates in blood.

RESULTS

Muscle mRNA LAT3, LAT4, IGF-1R, and MHC2A increased by PN infusion, with correlations to specific AA transporters and MHC isoforms (P < .01-.05). TAUT and LAT3 correlated to slow (MHC1) and fast (MHC2A, MHC2X) isoforms (P < .001-.02). Muscle IGF-1 mRNA correlated to plasma essential AAs, whereas IGF-1R mRNA was related to LAT3, MHC2A, and serum IGF-1 (P < .001-.03).

CONCLUSIONS

The results confirm that short-term preoperative PN activates transcription of AA transporters and myosin isoforms. Thus, combinations of methods on gene transcription and translation of muscle proteins can be applied to define efficient combinations of nutrition and hormones to catabolic patients in preoperative and postoperative settings.

Nutrition support in hospitalised adults at nutritional risk

BACKGROUND

The prevalence of disease-related malnutrition in Western European hospitals is estimated to be about 30%. There is no consensus whether poor nutritional status causes poorer clinical outcome or if it is merely associated with it. The intention with all forms of nutrition support is to increase uptake of essential nutrients and improve clinical outcome. Previous reviews have shown conflicting results with regard to the effects of nutrition support.

OBJECTIVES

To assess the benefits and harms of nutrition support versus no intervention, treatment as usual, or placebo in hospitalised adults at nutritional risk.

SEARCH METHODS

We searched Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library, MEDLINE (Ovid SP), Embase (Ovid SP), LILACS (BIREME), and Science Citation Index Expanded (Web of Science). We also searched the World Health Organization International Clinical Trials Registry Platform (www.who.int/ictrp); ClinicalTrials.gov; Turning Research Into Practice (TRIP); Google Scholar; and BIOSIS, as well as relevant bibliographies of review articles and personal files. All searches are current to February 2016.

SELECTION CRITERIA

We include randomised clinical trials, irrespective of publication type, publication date, and language, comparing nutrition support versus control in hospitalised adults at nutritional risk. We exclude trials assessing non-standard nutrition support.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane and the Cochrane Hepato-Biliary Group. We used trial domains to assess the risks of systematic error (bias). We conducted Trial Sequential Analyses to control for the risks of random errors. We considered a P value of 0.025 or less as statistically significant. We used GRADE methodology. Our primary outcomes were all-cause mortality, serious adverse events, and health-related quality of life.

MAIN RESULTS

We included 244 randomised clinical trials with 28,619 participants that met our inclusion criteria. We considered all trials to be at high risk of bias. Two trials accounted for one-third of all included participants. The included participants were heterogenous with regard to disease (20 different medical specialties). The experimental interventions were parenteral nutrition (86 trials); enteral nutrition (tube-feeding) (80 trials); oral nutrition support (55 trials); mixed experimental intervention (12 trials); general nutrition support (9 trials); and fortified food (2 trials). The control interventions were treatment as usual (122 trials); no intervention (107 trials); and placebo (15 trials). In 204/244 trials, the intervention lasted three days or more.We found no evidence of a difference between nutrition support and control for short-term mortality (end of intervention). The absolute risk was 8.3% across the control groups compared with 7.8% (7.1% to 8.5%) in the intervention groups, based on the risk ratio (RR) of 0.94 (95% confidence interval (CI) 0.86 to 1.03, P = 0.16, 21,758 participants, 114 trials, low quality of evidence). We found no evidence of a difference between nutrition support and control for long-term mortality (maximum follow-up). The absolute risk was 13.2% in the control group compared with 12.2% (11.6% to 13%) following nutritional interventions based on a RR of 0.93 (95% CI 0.88 to 0.99, P = 0.03, 23,170 participants, 127 trials, low quality of evidence). Trial Sequential Analysis showed we only had enough information to assess a risk ratio reduction of approximately 10% or more. A risk ratio reduction of 10% or more could be rejected.We found no evidence of a difference between nutrition support and control for short-term serious adverse events. The absolute risk was 9.9% in the control groups versus 9.2% (8.5% to 10%), with nutrition based on the RR of 0.93 (95% CI 0.86 to 1.01, P = 0.07, 22,087 participants, 123 trials, low quality of evidence). At long-term follow-up, the reduction in the risk of serious adverse events was 1.5%, from 15.2% in control groups to 13.8% (12.9% to 14.7%) following nutritional support (RR 0.91, 95% CI 0.85 to 0.97, P = 0.004, 23,413 participants, 137 trials, low quality of evidence). However, the Trial Sequential Analysis showed we only had enough information to assess a risk ratio reduction of approximately 10% or more. A risk ratio reduction of 10% or more could be rejected.Trial Sequential Analysis of enteral nutrition alone showed that enteral nutrition might reduce serious adverse events at maximum follow-up in people with different diseases. We could find no beneficial effect of oral nutrition support or parenteral nutrition support on all-cause mortality and serious adverse events in any subgroup.Only 16 trials assessed health-related quality of life. We performed a meta-analysis of two trials reporting EuroQoL utility score at long-term follow-up and found very low quality of evidence for effects of nutritional support on quality of life (mean difference (MD) -0.01, 95% CI -0.03 to 0.01; 3961 participants, two trials). Trial Sequential Analyses showed that we did not have enough information to confirm or reject clinically relevant intervention effects on quality of life.Nutrition support may increase weight at short-term follow-up (MD 1.32 kg, 95% CI 0.65 to 2.00, 5445 participants, 68 trials, very low quality of evidence).

AUTHORS' CONCLUSIONS

There is low-quality evidence for the effects of nutrition support on mortality and serious adverse events. Based on the results of our review, it does not appear to lead to a risk ratio reduction of approximately 10% or more in either all-cause mortality or serious adverse events at short-term and long-term follow-up.There is very low-quality evidence for an increase in weight with nutrition support at the end of treatment in hospitalised adults determined to be at nutritional risk. The effects of nutrition support on all remaining outcomes are unclear.Despite the clinically heterogenous population and the high risk of bias of all included trials, our analyses showed limited signs of statistical heterogeneity. Further trials may be warranted, assessing enteral nutrition (tube-feeding) for different patient groups. Future trials ought to be conducted with low risks of systematic errors and low risks of random errors, and they also ought to assess health-related quality of life.

Preoperative overnight parenteral nutrition (TPN) improves skeletal muscle protein metabolism indicated by microarray algorithm analyses in a randomized trial

Loss of muscle mass is associated with increased risk of morbidity and mortality in hospitalized patients. Uncertainties of treatment efficiency by short‐term artificial nutrition remain, specifically improvement of protein balance in skeletal muscles. In this study, algorithmic microarray analysis was applied to map cellular changes related to muscle protein metabolism in human skeletal muscle tissue during provision of overnight preoperative total parenteral nutrition (TPN). Twenty‐two patients (11/group) scheduled for upper GI surgery due to malignant or benign disease received a continuous peripheral all‐in‐one TPN infusion (30 kcal/kg/day, 0.16 gN/kg/day) or saline infusion for 12 h prior operation. Biopsies from the rectus abdominis muscle were taken at the start of operation for isolation of muscle RNA. RNA expression microarray analyses were performed with Agilent Sureprint G3, 8 × 60K arrays using one‐color labeling. 447 mRNAs were differently expressed between study and control patients (P < 0.1). mRNAs related to ribosomal biogenesis, mRNA processing, and translation were upregulated during overnight nutrition; particularly anabolic signaling S6K1 (P < 0.01–0.1). Transcripts of genes associated with lysosomal degradation showed consistently lower expression during TPN while mRNAs for ubiquitin‐mediated degradation of proteins as well as transcripts related to intracellular signaling pathways, PI3 kinase/MAPkinase, were either increased or decreased. In conclusion, muscle mRNA alterations during overnight standard TPN infusions at constant rate altered mRNAs associated with mTOR signaling; increased initiation of protein translation; and suppressed autophagy/lysosomal degradation of proteins. This indicates that overnight preoperative parenteral nutrition is effective to promote muscle protein metabolism.

Myosin heavy chain 2A and α-actin expression in human and murine skeletal muscles at feeding; particularly amino acids

BACKGROUND

Protein dynamics during non-steady state conditions as feeding are complex. Such studies usually demand combinations of methods to give conclusive information, particularly on myofibrillar proteins with slow turnover. Therefore, time course transcript analyses were evaluated as possible means to monitor changes in myofibrillar biosynthesis in skeletal muscles in conditions with clinical nutrition; i.e. long term exposure of nutrients.

METHODS

Muscle tissue from overnight intravenously fed surgical patients were used as a model combined with muscle tissue from starved and refed mice as well as cultured L6 muscle cells. Transcripts of acta 1 (α-actin), mhc2A (myosin) and slc38 a2/Snat 2 (amino acid transporter) were quantified (qPCR) as markers of muscle protein dynamics.

RESULTS

Myosin heavy chain 2A transcripts decreased significantly in skeletal muscle tissue from overnight parenterally fed patients but did not change significantly in orally refed mice. Alpha-actin transcripts did not change significantly in muscle cells from fed patients, mice or cultured L6 cells during provision of AA. The AA transporter Snat 2 decreased in L6 cells refed by all AA and by various combinations of AA but did not change during feeding in muscle tissue from patients or mice.

CONCLUSION

Our results confirm that muscle cells are sensitive to alterations in extracellular concentrations of AA for induction of protein synthesis and anabolism. However, transcripts of myofibrillar proteins and amino acid transporters showed complex alterations in response to feeding with provision of amino acids. Therefore, muscle tissue transcript levels of actin and myosin do not reflect protein accretion in skeletal muscles at feeding.