Dysregulation of Mitochondrial Dynamics and the Muscle Transcriptome in ICU Patients Suffering from Sepsis Induced Multiple Organ Failure

BACKGROUND: Septic patients treated in the intensive care unit (ICU) often develop multiple organ failure including persistent skeletal muscle dysfunction which results in the patient's protracted recovery process. We have demonstrated that muscle mitochondrial enzyme activities are impaired in septic ICU patients impairing cellular energy balance, which will interfere with muscle function and metabolism. Here we use detailed phenotyping and genomics to elucidate mechanisms leading to these impairments and the molecular consequences. METHODOLOGY/PRINCIPAL FINDINGS: Utilising biopsy material from seventeen patients and ten age-matched controls we demonstrate that neither mitochondrial in vivo protein synthesis nor expression of mitochondrial genes are compromised. Indeed, there was partial activation of the mitochondrial biogenesis pathway involving NRF2alpha/GABP and its target genes TFAM, TFB1M and TFB2M yet clearly this failed to maintain mitochondrial function. We therefore utilised transcript profiling and pathway analysis of ICU patient skeletal muscle to generate insight into the molecular defects driving loss of muscle function and metabolic homeostasis. Gene ontology analysis of Affymetrix analysis demonstrated substantial loss of muscle specific genes, a global oxidative stress response related to most probably cytokine signalling, altered insulin related signalling and a substantial overlap between patients and muscle wasting/inflammatory animal models. MicroRNA 21 processing appeared defective suggesting that post-transcriptional protein synthesis regulation is altered by disruption of tissue microRNA expression. Finally, we were able to demonstrate that the phenotype of skeletal muscle in ICU patients is not merely one of inactivity, it appears to be an actively remodelling tissue, influenced by several mediators, all of which may be open to manipulation with the aim to improve clinical outcome. CONCLUSIONS/SIGNIFICANCE: This first combined protein and transcriptome based analysis of human skeletal muscle obtained from septic patients demonstrated that losses of mitochondria and muscle mass are accompanied by sustained protein synthesis (anabolic process) while dysregulation of transcription programmes appears to fail to compensate for increased damage and proteolysis. Our analysis identified both validated and novel clinically tractable targets to manipulate these failing processes and pursuit of these could lead to new potential treatments

Muscle protein synthesis : Effects of metabolic stress and feeding

Surgical trauma and critical illness are pathophysiological conditions where the metabolic stress leads to an imbalance between protein synthesis and protein breakdown, resulting in a net loss of body proteins. A major part of the protein losses comes from skeletal muscle. Muscle depletion is associated with a high morbidity and mortality. To understand the changes that occur during critical illness and following trauma it is therefore necessary to study protein metabolism on the tissue level. The aim of this thesis work was to investigate the impact of metabolic stress and feeding on muscle protein synthesis. Healthy patients undergoing elective surgery and critically ill patients in the intensive care unit were investigated by the flood technique, employing L-[2H5] phenylalanine, for quantification of muscle protein synthesis rate. The effect of continuous and ongoing total parenteral nutrition was investigated in healthy patients scheduled for elective abdominal surgery of medium size. Muscle protein synthesis rate was determined before surgery and 24 hours after surgery with continuous and ongoing total parenteral nutrition. Conventional TPN could not prevent the decrease in muscle protein synthesis rate as compared to a control group receiving saline. Whereas conventional total parenteral nutrition is not effective in the immediate postoperative period it is shown that provision of glutamine can attenuate the decrease in muscle protein synthesis. However, glutamine is only marginally effective on muscle protein synthesis in ICU patients. To evaluate if a large enough dose of intravenous glutamine supplementation would influence muscle protein synthesis, ICU patients were randomized to receive 0, 20, 40 or 60 g of glutamine per kg body weight and day for a five-day study period. The main result was that plasma glutamine concentrations were normalized in all glutamine treated groups. No increase was seen in muscle glutamine concentration and therefore glutamine had no effect on muscle protein synthesis rate. The effect of difference size of trauma on muscle protein synthesis rate was investigated in patients undergoing elective minor surgery and major surgery before and immediately after surgery. Minor surgery did not have an impact on muscle protein synthesis rate, as expected. However, muscle protein synthesis rate following major surgery was also unaltered. Intensive care patients have an on average normal muscle protein synthesis rate but with a larger variation than in healthy individuals. In order to evaluate if artefacts or muscle tissue heterogeneity can explain this large scatter, muscle protein synthesis rate was determined simultaneously in both legs of ICU patients. Muscle protein synthesis rate was on average normal, and similar in the two legs. The variation between the legs was smaller than the variation between individuals and muscle morphology revealed no local differences. In summary the immediate effect of surgical trauma on muscle protein synthesis rate was not demonstrated to be size dependent. The decrease in muscle protein synthesis rate observed following medium size abdominal surgery could not be prevented by continuous and ongoing conventional total parenteral nutrition. In ICU patients glutamine supplemented TPN normalized plasma glutamine concentrations but muscle glutamine concentrations were not affected and no effect were seen on muscle protein synthesis. No local differences were found in leg muscle morphology of ICU patients, confirming earlier results showing a large variation in muscle protein synthesis rate between individuals. ICU patients have an on average normal muscle protein synthesis rate with a low intra-individual variation

Protein metabolism and gene expression in skeletal muscle of critically ill patients with sepsis. Clin Sci (Lond)

A B S T R A C T Muscle wasting negatively affects morbidity and mortality in critically ill patients. This progressive wasting is accompanied by, in general, a normal muscle PS (protein synthesis) rate. In the present study, we investigated whether muscle protein degradation is increased in critically ill patients with sepsis and which proteolytic enzyme systems are involved in this degradation. Eight patients and seven healthy volunteers were studied. In vivo muscle protein kinetics was measured using arteriovenous balance techniques with stable isotope tracers. The activities of the major proteolytic enzyme systems were analysed in combination with mRNA expression of genes related to these proteolytic systems. Results show that critically ill patients with sepsis have a variable but normal muscle PS rate, whereas protein degradation rates are dramatically increased (up to 160 %). Of the major proteolytic enzyme systems both the proteasome and the lysosomal systems had higher activities in the patients, whereas calpain and caspase activities were not changed. Gene expression of several genes related to the proteasome system was increased in the patients. mRNA levels of the two main lysosomal enzymes (cathepsin B and L) were not changed but, conversely, genes related to calpain and caspase had a higher expression in the muscles of the patients. In conclusion, the dramatic muscle wasting seen in critically ill patients with sepsis is due to increased protein degradation. This is facilitated by increased activities of both the proteasome and lysosomal proteolytic systems

A supplemental intravenous amino acid infusion sustains a positive protein balance for 24 hours in critically ill patients

Abstract Background Providing supplemental amino acids to ICU patients during a 3-h period results in improved whole-body net protein balance, without an increase in amino acid oxidation. The primary objective was to investigate if a 24-h intravenous amino acid infusion in critically ill patients has a sustained effect on whole-body protein balance as was seen after 3 h. Secondary objectives were monitoring of amino acid oxidation rate, urea and free amino acid plasma concentrations. Methods An infusion of [1-13C]-phenylalanine was added to ongoing enteral nutrition to quantify the enteral uptake of amino acids. Primed intravenous infusions of [ring-2H5]-phenylalanine and [3,3-2H2]-tyrosine were used to assess whole-body protein synthesis and breakdown, to calculate net protein balance and to assess amino acid oxidation at baseline and at 3 and 24 hours. An intravenous amino acid infusion was added to nutrition at a rate of 1 g/kg/day and continued for 24 h. Results Eight patients were studied. The amino acid infusion resulted in improved net protein balance over time, from -1.6 ± 7.9 μmol phe/kg/h at 0 h to 6.0 ± 8.8 at 3 h and 7.5 ± 5.1 at 24 h (p = 0.0016). The sum of free amino acids in plasma increased from 3.1 ± 0.6 mmol/L at 0 h to 3.2 ± 0.3 at 3 h and 3.6 ± 0.5 at 24 h (p = 0.038). Amino acid oxidation and plasma urea were not altered significantly. Conclusion We demonstrated that the improvement in whole-body net protein balance from a supplemental intravenous amino acid infusion seen after 3 h was sustained after 24 h in critically ill patients. Trial registration This trial was prospectively registered at Australian New Zealand Clinical Trials Registry. ACTRN, 12615001314516. Registered on 1 December 2015

Variability in Skeletal Muscle Protein Synthesis Rates in Critically Ill Patients

International audience(1) Background: Muscle protein synthesis in critically ill patients is, on average, normal despite dramatic muscle loss, but the variation is much larger than in controls. Here, we evaluate if this variation is due to 1) heterogeneity in synthesis rates, 2) morphological variation or infiltrating cells, or 3) heterogeneity in the synthesis of different protein fractions. (2) Methods: Muscle biopsies were taken from both legs of critically ill patients (n = 17). Mixed and mitochondrial protein synthesis rates and morphologies were evaluated in both legs. Synthesis rates of myosin and actin were determined in combined biopsies and compared with controls. (3) Results: Muscle protein synthesis rates had a large variability in the patients (1.4–10.8%/day). No differences in mixed and mitochondrial protein synthesis rates between both legs were observed. A microscopic examination revealed no morphological differences between the two legs or any infiltrating inflammatory cells. The synthesis rates for myosin were lower and for actin they were higher in the muscles of critically ill patients, compared with the controls. (4) Conclusions: The large variation in muscle protein synthesis rates in critically ill patients is not the result of heterogeneity in synthesis rates, nor due to infiltrating cells. There are differences in the synthesis rates of different proteins, but these do not explain the larger variations

Plasma Glutamine Concentrations in Liver Failure.

Higher than normal plasma glutamine concentration at admission to an intensive care unit is associated with an unfavorable outcome. Very high plasma glutamine levels are sometimes seen in both acute and chronic liver failure. We aimed to systematically explore the relation between different types of liver failure and plasma glutamine concentrations.Four different groups of patients were studies; chronic liver failure (n = 40), acute on chronic liver failure (n = 20), acute fulminant liver failure (n = 20), and post-hepatectomy liver failure (n = 20). Child-Pugh and Model for End-stage Liver Disease (MELD) scores were assessed as indices of liver function. All groups except the chronic liver failure group were followed longitudinally during hospitalisation. Outcomes were recorded up to 48 months after study inclusion.All groups had individuals with very high plasma glutamine concentrations. In the total group of patients (n = 100), severity of liver failure correlated significantly with plasma glutamine concentration, but the correlation was not strong.Liver failure, regardless of severity and course of illness, may be associated with a high plasma glutamine concentration. Further studies are needed to understand whether high glutamine levels should be regarded as a biomarker or as a contributor to symptomatology in liver failure