Sepsis: stimulation of energy-dependent protein breakdown resulting in protein loss in skeletal muscle

Metabolic fingerprint of patients showing responsiveness to treatment of septic shock in intensive care unit

OBJECTIVE

An early metabolic signature associated with the responsiveness to treatment can be useful in the better management of septic shock patients. This would help clinicians in designing personalized treatment protocols for patients showing non-responsiveness to treatment.

METHODS

We analyzed the serum on Day 1 (n = 60), Day 3 (n = 47), and Day 5 (n = 26) of patients with septic shock under treatment using NMR-based metabolomics. Partial least square discriminant analysis (PLS-DA) was performed to generate the list of metabolites that can be identified as potential disease biomarkers having statistical significance (that is, metabolites that had a VIP score > 1, and p value < 0.05, False discovery rate (FDR) < 0.05).

RESULTS

Common significant metabolites amongst the three time points were obtained that distinguished the patients being responsive (R) and non-responsive (NR) to treatments, namely 3 hydroxybutyrate, lactate, and phenylalanine which were lower, whereas glutamate and choline higher in patients showing responsiveness.

DISCUSSION

The study gave these metabolic signatures identifying patients' responsiveness to treatment. The results of the study will aid in the development of targeted therapy for ICU patients.

Identifying potential biomarkers and therapeutic targets for dogs with sepsis using metabolomics and lipidomics analyses

Sepsis is a diagnostic and therapeutic challenge and is associated with morbidity and a high risk of death. Metabolomic and lipidomic profiling in sepsis can identify alterations in metabolism and might provide useful insights into the dysregulated host response to infection, but investigations in dogs are limited. We aimed to use untargeted metabolomics and lipidomics to characterize metabolic pathways in dogs with sepsis to identify therapeutic targets and potential diagnostic and prognostic biomarkers. In this prospective observational cohort study, we examined the plasma metabolomes and lipidomes of 20 healthy control dogs and compared them with those of 21 client-owned dogs with sepsis. Patient data including signalment, physical exam findings, clinicopathologic data and clinical outcome were recorded. Metabolites were identified using an untargeted mass spectrometry approach and pathway analysis identified multiple enriched metabolic pathways including pyruvaldehyde degradation; ketone body metabolism; the glucose-alanine cycle; vitamin-K metabolism; arginine and betaine metabolism; the biosynthesis of various amino acid classes including the aromatic amino acids; branched chain amino acids; and metabolism of glutamine/glutamate and the glycerophospholipid phosphatidylethanolamine. Metabolites were identified with high discriminant abilities between groups which could serve as potential biomarkers of sepsis including 13,14-Dihydro-15-keto Prostaglandin A₂; 12(13)-DiHOME (12,13-dihydroxy-9Z-octadecenoic acid); and 9-HpODE (9-Hydroxyoctadecadienoic acid). Metabolites with higher abundance in samples from nonsurvivors than survivors included 3-(2-hydroxyethyl) indole, indoxyl sulfate and xanthurenic acid. Untargeted lipidomic profiling revealed multiple sphingomyelin species (SM(d34:0)+H; SM(d36:0)+H; SM(d34:0)+HCOO; and SM(d34:1D3)+HCOO); lysophosphatidylcholine molecules (LPC(18:2)+H) and lipophosphoserine molecules (LPS(20:4)+H) that were discriminating for dogs with sepsis. These biomarkers could aid in the diagnosis of dogs with sepsis, provide prognostic information, or act as potential therapeutic targets.

Exogenous Melatonin Alleviates Skeletal Muscle Wasting by Regulating Hypothalamic Neuropeptides Expression in Endotoxemia Rats

To investigate whether exogenous melatonin (MLT) could alleviate skeletal muscle wasting by regulating hypothalamic neuropeptides expression. Adult male Sprague Dawley rats were intraperitoneally injected with lipopolysaccharide (LPS) (10 mg/kg), followed by MLT (30 mg/kg/day) or saline for 3 days. Hypothalamic tissues and skeletal muscle were obtained on day 3. Skeletal muscle wasting was measured by the mRNA expression of two E3 ubiquitin ligases, muscle atrophy F-box and muscle ring finger 1 as well as 3-methylhistidine (3-MH) and tyrosine release. Three hypothalamic neuropeptides (POMC, AgRP, CART) expression were detected in all groups. POMC expression knockdown was achieved by ARC injection of lentiviruses containing shRNA against POMC. Two weeks after ARC viruses injection, rats were i.p. injected with LPS (10 mg/kg) followed by MLT (30 mg/kg/day) or saline for 3 days. Brain tissues were harvested for immunostaining. In septic rats, 3-MH, tyrosine release and muscle atrophic gene expression were significantly decreased in MLT treated group. POMC and CART expression were lower while AgRP expression was higher in MLT treated group. Furthermore, in septic rats treated with MLT, muscle wasting in those with lower expression of neuropeptide POMC did not differ from those with normal POMC expression. Exogenous MLT could alleviate skeletal muscle wasting in septic rats by regulating hypothalamic neuropeptides.

Gender-specific association of oxidative stress and immune response in septic shock mortality using NMR-based metabolomics

Background: Sepsis and septic shock are still associated with a high mortality rate. The early-stage prediction of septic shock outcomes would be helpful to clinicians for designing their treatment protocol. In addition, it would aid clinicians in patient management by understanding gender disparity in terms of clinical outcomes of septic shock by identifying whether there are sex-based differences in sepsis-associated mortality. Objective: This study aimed to test the hypothesis that gender-based metabolic heterogeneity is associated with sepsis survival and identify the biomarkers of mortality for septic shock in an Indian cohort. Method: The study was performed in an Indian population cohort diagnosed with sepsis/septic shock within 24 hours of admission. The study group was 50 patients admitted to intensive care, comprising 23 females and 27 males. Univariate and multivariate analysis were performed to identify the biomarkers for septic shock mortality and the gender-specific metabolic fingerprint in septic shock-associated mortality. Results: The energy-related metabolites, ketone bodies, choline, and NAG were found to be primarily responsible for differentiating survivors and non-survivors. The gender-based mortality stratification identified a female-specific association of the anti-inflammatory response, innate immune response, and β oxidation, and a male-specific association of the pro-inflammatory response to septic shock. Conclusion: The identified mortality biomarkers may help clinicians estimate the severity of a case, as well as predict the outcome and treatment efficacy. The study underlines that gender is one of the most significant biological factors influencing septic shock metabolomic profiles. This understanding can be utilized to identify novel gender-specific biomarkers and innovative targets relevant for gender medicine.

Single-cell deconstruction of post-sepsis skeletal muscle and adipose tissue microenvironments

BACKGROUND

Persistent loss of skeletal muscle mass and function as well as altered fat metabolism are frequently observed in severe sepsis survivors. Studies examining sepsis-associated tissue dysfunction from the perspective of the tissue microenvironment are scarce. In this study, we comprehensively assessed transcriptional changes in muscle and fat at single-cell resolution following experimental sepsis induction.

METHODS

Skeletal muscle and visceral white adipose tissue from control mice or mice 1 day or 1 month following faecal slurry-induced sepsis were used. Single cells were mechanically and enzymatically prepared from whole tissue, and viable cells were further isolated by fluorescence activated cell sorting. Droplet-based single-cell RNA-sequencing (scRNA-seq; 10× Genomics) was used to generate single-cell gene expression profiles of thousands of muscle and fat-resident cells. Bioinformatics analyses were performed to identify and compare individual cell populations in both tissues.

RESULTS

In skeletal muscle, scRNA-seq analysis classified 1438 single cells into myocytes, endothelial cells, fibroblasts, mesenchymal stem cells, macrophages, neutrophils, T-cells, B-cells, and dendritic cells. In adipose tissue, scRNA-seq analysis classified 2281 single cells into adipose stem cells, preadipocytes, endothelial cells, fibroblasts, macrophages, dendritic cells, B-cells, T-cells, NK cells, and gamma delta T-cells. One day post-sepsis, the proportion of most non-immune cell populations was decreased, while immune cell populations, particularly neutrophils and macrophages, were highly enriched. Proportional changes of endothelial cells, neutrophils, and macrophages were validated using faecal slurry and cecal ligation and puncture models. At 1 month post-sepsis, we observed persistent enrichment/depletion of cell populations and further uncovered a cell-type and tissue-specific ability to return to a baseline transcriptomic state. Differential gene expression analyses revealed key genes and pathways altered in post-sepsis muscle and fat and highlighted the engagement of infection/inflammation and tissue damage signalling. Finally, regulator analysis identified gonadotropin-releasing hormone and Bay 11-7082 as targets/compounds that we show can reduce sepsis-associated loss of lean or fat mass.

CONCLUSIONS

These data demonstrate persistent post-sepsis muscle and adipose tissue disruption at the single-cell level and highlight opportunities to combat long-term post-sepsis tissue wasting using bioinformatics-guided therapeutic interventions.

Nuclear magnetic resonance-based serum metabolomic analysis reveals different disease evolution profiles between septic shock survivors and non-survivors

Background

Septic shock is the most severe phase of sepsis and is associated with high rates of mortality. However, early stage prediction of septic shock outcomes remains difficult. Metabolomic techniques have emerged as a promising tool for improving prognosis.

Methods

Orthogonal projections to latent structures-discriminant analysis (OPLS-DA) models separating the serum metabolomes of survivors from those of non-survivors were established with samples obtained at the intensive care unit (ICU) admission (H0) and 24 h later (H24). For 51 patients with available H0 and H24 samples, multi-level modeling was performed to provide insight into different metabolic evolutions that occurred between H0 and H24 in the surviving and non-surviving patients. Relative quantification and receiver operational characteristic curves (ROC) were applied to estimate the predictability of key discriminatory metabolites for septic shock mortality.

Results

Metabolites that were involved in energy supply and protein breakdown were primarily responsible for differentiating survivors from non-survivors. This was not only seen in the H0 and H24 discriminatory models, but also in the H0-H24 paired models. Reanalysis of extra H0-H24 paired samples in the established multi-level model demonstrated good performance of the model for the classification of samplings. According to the ROC results, nine discriminatory metabolites defined consistently from the unpaired model and the H0-H24 time-trend change (Δ_H24-H0) show good prediction of mortality. These results suggest that NMR-based metabolomic analysis is useful for a better overall assessment of septic shock patients.

Conclusions

Dysregulation of the metabolites identified by this study is associated with poor outcomes for septic shock. Evaluation of these compounds during the first 24 h after ICU admission in the septic shock patient may be helpful for estimating the severity of cases and for predicting outcomes.

Trial registration

All human serum samples were collected and stored, provided by the “center of biologic resources for liver disease”, in Jean Verdier Hospital, Bondy, France (BB-0033-00027).

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2456-z) contains supplementary material, which is available to authorized users.

Human Milk Fortification with Bovine Colostrum Is Superior to Formula-Based Fortifiers to Prevent Gut Dysfunction, Necrotizing Enterocolitis, and Systemic Infection in Preterm Pigs

BACKGROUND

Fortification of donor human milk (DHM) is required for optimal growth of very preterm infants, but there are concerns of more gut dysfunction and necrotizing enterocolitis (NEC) when using formula-based fortifiers (FFs), especially soon after birth. Intact bovine colostrum (BC) is rich in nutrients and bioactive factors, and protects against NEC in preterm pigs. We hypothesized that fortification of DHM with BC is superior to FFs to prevent gut dysfunction and infections when provided shortly after preterm birth.

METHODS

Two FF products, Enfamil (ENF; intact protein, vegetable oil) and PreNAN+Nutrilon (NAN; extensively hydrolyzed protein, maltodextrin), were compared with BC as fortifier to DHM fed to preterm pigs for 5 days.

RESULTS

Relative to the DHM+BC group, DHM+FF groups had higher diarrhea score and lower hexose uptake and lactase activity, and specifically the DHM+NAN group showed higher gut permeability, NEC score, more mucosa-adherent bacteria with altered gut microbiota structure (ie, lower diversity, increased Enterococcus, decreased Staphylococcus abundance). Both DHM+FF groups showed higher expression of intestinal cytokine and inflammation-related genes, more gut-derived bacteria in the bone marrow, lower density of mucin-containing goblet cells, and slightly higher colon lactate, stomach pH and acetate, and blood neutrophil-to-lymphocyte levels than the DHM+BC group.

CONCLUSIONS

Used as a fortifier to DHM, BC is superior to FFs to support gut function, nutrient absorption, and bacterial defense mechanisms in preterm pigs. It is important to optimize the composition of nutrient fortifiers for preterm infants fed human milk.

Amelioration of energy metabolism by melatonin in skeletal muscle of rats with LPS induced endotoxemia

In the literature, few studies have investigated the effects of melatonin on energy metabolism in skeletal muscle in endotoxemia. We investigated the effects of melatonin on tissue structure, energy metabolism in skeletal muscle, and antioxidant level of rats with endotoxemia. We divided rats into 4 groups, control, lipopolysaccharide (LPS) (20 mg/kg, i.p., single dose), melatonin (10 mg/kg, i.p., three times), and melatonin + LPS. Melatonin was injected i.p. 30 min before and after the 2nd and 4th hours of LPS injection. Antioxidant status was determined by glutathione (GSH) measurement in the blood. Muscle tissue was stained using modified Gomori trichrome (MGT), succinic dehydrogenase (SDH), and cytochrome oxidase (COX) and histological scored. Also the sections were then stained with hematoxylin and eosin. The stained sections were visualized and photographed. Creatine, creatine phosphate, adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP) levels were investigated using high performance liquid chromatography (HPLC) in muscle tissue. In the Melatonin + LPS group, blood GSH levels were increased compared with the LPS group (P<0.01). Melatonin reduced myopathic changes in the LPS group according to the histopathologic findings. In addition, ATP values were increased compared with the LPS group (P<0.05). Our findings showed melatonin treatment prevented muscle damage by increasing ATP and GSH levels in rats with LPS induced endotoxemia.

Protein Requirements of the Critically Ill Pediatric Patient

This article includes a review of protein needs in children during health and illness, as well as a detailed discussion of protein metabolism, including nitrogen balance during critical illness, and assessment and prescription/delivery of protein to critically ill children. The determination of protein requirements in children has been difficult and challenging. The protein needs in healthy children should be based on the amount needed to ensure adequate growth during infancy and childhood. Compared with adults, children require a continuous supply of nutrients to maintain growth. The protein requirement is expressed in average requirements and dietary reference intake, which represents values that cover the needs of 97.5% of the population. Critically ill children have an increased protein turnover due to an increase in whole-body protein synthesis and breakdown with protein degradation leading to loss of lean body mass (LBM) and development of growth failure, malnutrition, and worse clinical outcomes. The results of protein balance studies in critically ill children indicate higher protein needs, with infants and younger children requiring higher intakes per body weight compared with older children. Monitoring the side effects of increased protein intake should be performed. Recent studies found a survival benefit in critically ill children who received a higher percentage of prescribed energy and protein goal by the enteral route. Future randomized studies should evaluate the effect of protein dosing in different age groups on patient outcomes, including LBM, muscle structure and function, duration of mechanical ventilation, intensive care unit and hospital length of stay, and mortality.

Application of LC-MS-based metabolomics method in differentiating septic survivors from non-survivors

Septic shock is the most severe form of sepsis, which is still one of the leading causes of death in the intensive care unit (ICU). Even though early prognosis and diagnosis are known to be indispensable for reaching an optimistic outcome, pathogenic complexities and the lack of specific treatment make it difficult to predict the outcome individually. In the present study, serum samples from surviving and non-surviving septic shock patients were drawn before clinical intervention at admission. Metabolic profiles of all the samples were analyzed by liquid chromatography-mass spectrometry (LC-MS)-based metabolomics. One thousand four hundred nineteen peaks in positive mode and 1878 peaks in negative mode were retained with their relative standard deviation (RSD) below 30 %, in which 187 metabolites were initially identified by retention time and database in the light of the exact molecular mass. Differences between samples from the survivors and the non-survivors were investigated using multivariate and univariate analysis. Finally, 43 significantly varied metabolites were found in the comparison between survivors and non-survivors. Concretely, metabolites in the tricarboxylic acid (TCA) cycle, amino acids, and several energy metabolism-related metabolites were up-regulated in the non-survivors, whereas those in the urea cycle and fatty acids were generally down-regulated. Metabolites such as lysine, alanine, and methionine did not present significant changes in the comparison. Six metabolites were further defined as primary discriminators differentiating the survivors from the non-survivors at the early stage of septic shock. Our findings reveal that LC-MS-based metabolomics is a useful tool for studying septic shock. Graphical abstract ᅟ.

Critical illness myopathy in a cervical spine-injured patient

Neuromuscular weakness acquired in the intensive care unit (ICU) causes significant impairment in critically ill patients. The spectrum of critical illness neuromuscular disease includes critical illness myopathy, critical illness polyneuropathy or both, and occurs in approximately one-third of patients admitted to the ICU and those who are ventilated for at least 7 days. Recognized risk factors include sepsis, systemic inflammatory response syndrome, multi-organ failure, neuromuscular blocking agents and corticosteroids, however the absence of predisposing factors should not preclude critical illness neuromuscular disease. A 23-year-old male suffered a cervical spine injury and was admitted to the ICU. Two weeks post admission, he lost all power in his upper limbs, neck and face. Nerve conduction studies and needle electromyography were performed 4 weeks and 3 months after the injury, suggesting that myopathy was the likely cause of weakness. The definitive diagnosis of critical illness myopathy was based on muscle biopsy demonstrating myosin filament loss. Evaluation of new-onset weakness in ICU patients is essential to distinguish neurological causes from complications of critical illness. Signs and symptoms of critical illness neuromuscular disease must be identified early to encourage recovery, promote rehabilitation, and reduce morbidity and mortality.

Wound-healing ability is conserved during periods of chronic stress and costly life history events in a wild-caught bird

Chronic stress, potentially through the actions of corticosterone, is thought to directly impair the function of immune cells. However, chronic stress may also have an indirect effect by influencing allocation of energy, ultimately shifting resources away from the immune system. If so, the effects of chronic stress on immune responses may be greater during energetically-costly life history events. To test whether the effects of chronic stress on immune responses differ during expensive life history events we measured wound healing rate in molting and non-molting European starlings (Sturnus vulgaris) exposed to control or chronic stress conditions. To determine whether corticosterone correlated with wound healing rates before starting chronic stress, we measured baseline and stress-induced corticosterone and two estimates of corticosterone release and regulation, negative feedback (using dexamethasone injection), and maximal capacity of the adrenals to secrete corticosterone (using adrenocorticotropin hormone [ACTH] injection). After 8days of exposure to chronic stress, we wounded both control and chronically stressed birds and monitored healing daily. We monitored nighttime heart rate, which strongly correlates with energy expenditure, and body mass throughout the study. Measures of corticosterone did not differ with molt status. Contrary to work on lizards and small mammals, all birds, regardless of stress or molt status, fully-healed wounds at similar rates. Although chronic stress did not influence healing rates, individuals with low baseline corticosterone or strong negative feedback had faster healing rates than individuals with high baseline corticosterone or weak negative feedback. In addition, wound healing does appear to be linked to energy expenditure and body mass. Non-molting, chronically stressed birds decreased nighttime heart rate during healing, but this pattern did not exist in molting birds. Additionally, birds of heavier body mass at the start of the experiment healed wounds more rapidly than lighter birds. Finally, chronically stressed birds lost body mass at the start of chronic stress, but after wounding all birds regardless of stress or molt status started gaining weight, which continued for the remainder of the study. Increased body mass could suggest compensatory feeding to offset energetic or resource demands (e.g., proteins) of wound healing. Although chronic stress did not inhibit healing, our data suggest that corticosterone may play an important role in mediating healing processes and that molt could influence energy saving tactics during periods of chronic stress. Although the experiment was designed to test allostasis, interpretation of data through reactive scope appears to be a better fit.

High phosphoserine in sepsis: panel of clinical and plasma amino acid correlations

The determination of plasma phosphoserine concentration in sepsis is uncommon, and the clinical and metabolic correlations of abnormally high phosphoserine are basically unknown. We analyzed 430 determinations of phosphoserine, other amino acid (AA) levels and ancillary variables obtained in 18 septic patients, in order to assess the biochemical and clinical correlations of changes in phosphoserine. Phosphoserine ranged between 5 and 55 micromol/L (n.v. < 12). Increasing phosphoserine was associated with higher severity of illness and death, and its best AA correlates were increasing cystathionine, 3-methylhistidine, histidine, hydroxyproline and tyrosine (r > 0.65, p < 0.001 for all). High phosphoserine seemed to cumulatively reflect kidney and liver dysfunction and enhanced proteolysis. As a collateral finding, 3-methylhistidine (a best correlate of phosphoserine) was also inversely related to nutritional AA dose (p < 0.001). These data suggest that in septic patients the determination of plasma phosphoserine may provide useful information on severity of septic illness and prognosis. The observed correlations also indirectly evidenced an impact of nutritional AA dose in moderating proteolysis.

Muscle wasting in animal models of severe illness

Muscle wasting is a serious complication of various clinical conditions that significantly worsens the prognosis of the illnesses. Clinically relevant models of muscle wasting are essential for understanding its pathogenesis and for selective preclinical testing of potential therapeutic agents. The data presented here indicate that muscle wasting has been well characterized in rat models of sepsis (endotoxaemia, and caecal ligation and puncture), in rat models of chronic renal failure (partial nephrectomy), in animal models of intensive care unit patients (corticosteroid treatment combined with peripheral denervation or with administration of neuromuscular blocking drugs) and in murine and rat models of cancer (tumour cell transplantation). There is a need to explore genetically engineered mouse models of cancer. The degree of protein degradation in skeletal muscle is not well characterized in animal models of liver cirrhosis, chronic heart failure and chronic obstructive pulmonary disease. The major difficulties with all models are standardization and high variation in disease progression and a lack of reflection of clinical reality in some of the models. The translation of the information obtained by using these models to clinical practice may be problematic.

[Intensive care unit-acquired weakness in the critically ill : critical illness polyneuropathy and critical illness myopathy]

Intensive care unit-acquired weakness (ICUAW) is a severe complication in critically ill patients which has been increasingly recognized over the last two decades. By definition ICUAW is caused by distinct neuromuscular disorders, namely critical illness polyneuropathy (CIP) and critical illness myopathy (CIM). Both CIP and CIM can affect limb and respiratory muscles and thus complicate weaning from a ventilator, increase the length of stay in the intensive care unit and delay mobilization and physical rehabilitation. It is controversially discussed whether CIP and CIM are distinct entities or whether they just represent different organ manifestations with common pathomechanisms. These basic pathomechanisms, however, are complex and still not completely understood but metabolic, inflammatory and bioenergetic alterations seem to play a crucial role. In this respect several risk factors have recently been revealed: in addition to the administration of glucocorticoids and non-depolarizing muscle relaxants, sepsis and multi-organ failure per se as well as elevated levels of blood glucose and muscular immobilization have been shown to have a profound impact on the occurrence of CIP and CIM. For the diagnosis, careful physical and neurological examinations, electrophysiological testing and in rare cases nerve and muscle biopsies are recommended. Nevertheless, it appears to be difficult to clearly distinguish between CIM and CIP in a clinical setting. At present no specific therapy for these neuromuscular disorders has been established but recent data suggest that in addition to avoidance of risk factors early active mobilization of critically ill patients may be beneficial.

Development aggravates the severity of skeletal muscle catabolism induced by endotoxemia in neonatal pigs

Accretion rates of muscle protein are elevated in normal neonates, but this anabolic drive decreases with maturation. As this change occurs, it is not known whether development also influences muscle protein catabolism induced by sepsis. We hypothesize that protein degradation in skeletal muscle induced by endotoxemia becomes more severe as the neonate develops. Fasted 7- and 26-day-old pigs were infused for 8 h with LPS (0 and 10 μg·kg(-1)·h(-1)), while plasma amino acids (AA), 3-methylhistidine (3-MH), and α-actin concentrations and muscle protein degradation signal activation were determined (n = 5-7/group/age). Plasma full-length α-actin was greater in 7- than 26-day-old pigs, suggesting a higher baseline protein turnover in neonatal pigs. LPS increased plasma total AA, 3-MH, and full-length and cleaved α-actin in 26- than in 7-day-old pigs. In muscle of both age groups, LPS increased AMPK and NF-κB phosphorylation, the abundances of activated caspase 3 and E-3 ligases MuRF1 and atrogin1, as well as the abundance of cleaved α-actin, suggesting activation of muscle proteolysis by endotoxin in muscle. LPS decreased Forkhead box 01 (Fox01) and Fox04 phosphorylation and increased procaspase 3 abundance in muscle of 26-day-old pigs despite the lack of effect of LPS on PKB phosphorylation. The results suggest that skeletal muscle in healthy neonatal pigs maintains high baseline degradation signal activation that cannot be enhanced by endotoxin, but as maturation advances, the effect of LPS on muscle protein catabolism manifests its severity.

Sepsis and development impede muscle protein synthesis in neonatal pigs by different ribosomal mechanisms

In muscle, sepsis reduces protein synthesis (MPS) by restraining translation in neonates and adults. Even though protein accretion decreases with development as neonatal MPS rapidly declines by maturation, the changes imposed by development on the sepsis-associated decrease in MPS have not been described. Pigs at 7 and 26 d of age were infused for 8 h with lipopolysaccharide (LPS, endotoxin, 0 and 10 μg · kg⁻¹ · h⁻¹). Fractional MPS rates and translation eukaryotic initiation factor (eIF) activation in muscle were examined (n = 5-7/group). The LPS-induced decrease in MPS was associated with reduced ribosomal and translational efficiency, whereas the age-induced decrease in MPS occurred by decreasing ribosome number. Abundances of mammalian target of rapamycin (mTOR) and S6 decreased, and that of the repressor eIF4E · 4E-binding protein 1 (4EBP1) association increased in 26-d-old pigs--compared with 7-d-old pigs. LPS decreased the abundance of the active eIF4E ·eIF4G association and the phosphorylation of eIF4G across ages, whereas the abundance of eIF4G declined and eIF2α phosphorylation increased with age. Therefore, when lacking anabolic stimulation, the decrease in MPS induced by LPS is associated with reduced ribosomal efficiency and decreased eIF4E ·eIF4G assembly, whereas that induced by development involves reduced ribosomal number, translation factor abundance, and increased eIF2α phosphorylation.

Mycobacterium ulcerans infections cause progressive muscle atrophy and dysfunction, and mycolactone impairs satellite cell proliferation

Clinical observations from Buruli ulcer (BU) patients in West Africa suggest that severe Mycobacterium ulcerans infections can cause skeletal muscle contracture and atrophy leading to significant impairment in function. In the present study, male mice C57BL/6 were subcutaneously injected with M. ulcerans in proximity to the right biceps muscle, avoiding direct physical contact between the infectious agent and the skeletal muscle. The histological, morphological, and functional properties of the muscles were assessed at different times after the injection. On day 42 postinjection, the isometric tetanic force and the cross-sectional area of the myofibers were reduced by 31% and 29%, respectively, in the proximate-infected muscles relative to the control muscles. The necrotic areas of the proximate-infected muscles had spread to 7% of the total area by day 42 postinjection. However, the number of central nucleated fibers and myogenic regulatory factors (MyoD and myogenin) remained stable and low. Furthermore, Pax-7 expression did not increase significantly in mycolactone-injected muscles, indicating that the satellite cell proliferation is abrogated by the toxin. In addition, the fibrotic area increased progressively during the infection. Lastly, muscle-specific RING finger protein 1 (MuRF-1) and atrogin-1/muscle atrophy F-box protein (atrogin-1/MAFbx), two muscle-specific E3 ubiquitin ligases, were upregulated in the presence of M. ulcerans. These findings confirmed that skeletal muscle is affected in our model of subcutaneous infection with M. ulcerans and that a better understanding of muscle contractures and weakness is essential to develop a therapy to minimize loss of function and promote the autonomy of BU patients.

Protein deficiency and nematode infection during pregnancy and lactation reduce maternal bone mineralization and neonatal linear growth in mice

Using a 2 x 2 factorial design, we investigated the combined impact of protein deficiency (PD) and gastrointestinal nematode infection during late pregnancy and lactation on resting metabolic rate (RMR), body composition and bone mineralization, neonatal growth, and the regulatory hormones [corticosterone, leptin, and insulin-like growth factor-1 (IGF-1)] and proinflammatory cytokines [interleukin (IL)-1 beta and IL-6] that may drive these processes. Pregnant CD1 mice, fed either a protein-sufficient (PS; 24%) or protein-deficient (PD; 6%) isocaloric diet, were infected 4 times with either 0 (sham) or 100 Heligmosomoides bakeri larvae beginning on d 14 of pregnancy. Dams were killed on d 20 postpartum and pups on d 2, 7, 14, and 21. Diet and infection had largely independent effects. The PD diet elevated corticosterone and upregulated leptin concentration in maternal serum, which was associated with reduced food intake leading to lower body mass, RMR, and body temperature. Infection reduced food intake but elevated maternal serum IL-1 beta and IL-6 and did not affect corticosterone, leptin, RMR, or body temperature. The PD diet decreased maternal bone area and bone mineral content. Infection lowered maternal bone mineral density, consistent with elevated IL-1 beta and IL-6. The elevated serum IL-1 beta and lower IGF-1 in pups of PD dams and lower serum leptin and IGF-1 in pups of infected dams were both consistent with the lower pup body mass and shorter crown-rump length. This mouse model provides a novel framework to study the impact of diet and nematode infection on bone.

Critical illness polyneuropathy and myopathy in the intensive care unit

Critical illness polyneuropathy (CIP) and critical illness myopathy (CIM) are major complications that occur in severely ill patients who require intensive care treatment. CIP and CIM affect the limb and respiratory muscles, and, as a consequence, they characteristically complicate weaning from the ventilator, increase the length of stay on the intensive care unit, and prolong physical rehabilitation. The basic pathophysiology of both disorders is complex and involves metabolic, inflammatory and bioenergetic alterations. It is unclear at present whether CIP and CIM are distinct entities, or whether they just represent different 'organ' manifestations of a common pathophysiological mechanism. This article provides an overview of the clinical and diagnostic features of CIP and CIM and discusses current pathophysiological and therapeutic concepts relating to these neuromuscular disorders.

Critical illness myopathy: sepsis-mediated failure of the peripheral nervous system

With better survival of critically ill patients, 'de novo' arising neuromuscular complications like critical illness myopathy or polyneuropathy have been increasingly observed. Prolonged hospitalization not only imposes risks like pneumonia or thrombosis on patients but also represents a real budget threat to modern intensive-care medicine. Clinical symptoms like muscle weakness and weaning failure are common to critical illness myopathy and critical illness polyneuropathy and do not allow for distinction. Specific therapies are not yet available, and the quest for the pathomechanisms has proved more complicated than anticipated. Especially for critical illness myopathy, multiple sites of disturbances to the excitation-contraction coupling cascade are possible causes of muscle weakness. The present review summarizes the epidemiological, clinical and diagnostic features of critical illness myopathy and then focuses on current concepts of the presumed pathomechanisms of critical illness myopathy. Sepsis was shown to be a major cause of critical illness myopathy and special emphasis will be placed on how sepsis and inflammatory mediators influence (i) the membrane excitability at the level of voltage-gated ion channels and (ii) the intracellular protein signalling that results in selective loss of myosin protein content and muscle wasting. For (i), critical illness myopathy represents a new type of acquired channelopathy affecting the inactivation properties of Na+ channels. For (ii), both protein proteolysis and protein build up at the transcriptional level seem to be involved. Findings from different studies are put into a common context to propose a model for cytokine-mediated failure of muscle in severe sepsis. This can open a series of new possible trials to test specific therapeutic strategies in the future.

Alterations in intracellular Ca2+-homeostasis of skeletal muscle fibers during sepsis

OBJECTIVE

To investigate changes in intracellular Ca2+-regulation and Ca2+-sensitivity of the contractile apparatus in murine skeletal muscle fibers during sepsis.

DESIGN AND SETTING

Animal study in a university-based research laboratory.

SUBJECTS

Isolated muscle fibers (M. extensor digitorum longus) of septic mice.

INTERVENTIONS

In one group, sepsis was induced in "black six" mice using cecal ligation and puncture (CLP). In a second group, laparotomy (SHAM), and in a third group, general anesthesia (GA) was performed. Saponin-skinned skeletal muscle fibers were examined 2, 3, 5, and 7 days after treatment, and caffeine-induced Ca2+-release from the sarcoplasmic reticulum (SR) as well as Ca2+-sensitivity of the contractile apparatus were assessed.

MEASUREMENTS AND RESULTS

In the CLP group, Ca2+-release significantly decreased over 5 days and increased again after 7 days. In the SHAM group, Ca2+-release decreased at days 2 and 3, whereas no changes were observed in the GA group. Ca2+-sensitivity significantly increased over 5 days in the CLP group and decreased again at day 7. In the SHAM group, Ca2+-sensitivity increased at days 2 and 3, and no changes were seen in the GA group.

CONCLUSIONS

In murine skeletal muscle fibers, Ca2+-release from the SR decreases during sepsis, with effects being most pronounced 2-3 days after CLP. In parallel, Ca2+-sensitivity of the contractile apparatus is increased, and all changes are reversible. Thus, these effects might be involved in skeletal muscle dysfunction during sepsis as corresponding changes are less pronounced or absent in control groups.

Endotoxemia causes a paradoxical intracellular pH recovery in exercising rat skeletal muscle

In resting skeletal muscle, endotoxemia causes disturbances in energy metabolism that could potentially disturb intracellular pH (pH(i)) during muscular activity. We tested this hypothesis using in situ (31)P-magnetic resonance spectroscopy in contracting rat gastrocnemius muscle. Endotoxemia was induced by injecting rats intraperitoneally at t(0) and t(0) + 24 h with Klebsiella pneumoniae endotoxin (lipopolysaccharides at 3 mg/kg) or saline vehicle. Muscle function was investigated strictly noninvasively at t(0) + 48 h through a transcutaneous electrical stimulation protocol consisting of 5.7 minutes of repeated isometric contraction at 3.3 HZ, and force production was measured with an ergometer. At rest, endotoxin treatment did not affect pH(i) and adenosine triphosphate concentration, but significantly reduced phosphocreatine and glycogen contents. Endotoxemia produced both a reduction of isometric force production and a marked linear recovery (0.08 +/- 0.01 pH unit/min) of pH(i) during the second part of the stimulation period. This recovery was not due to any phenomenon of fiber inactivation linked to development of muscle fatigue, and was not associated with any change in intracellular proton buffering, net proton efflux from the cell, or proton turnovers through creatine kinase reaction and oxidative phosphorylation. This paradoxical pH(i) recovery in exercising rat skeletal muscle under endotoxemia is likely due to slowing of glycolytic flux following the reduction in intramuscular glycogen content. These findings may be useful in the follow-up of septic patients and in the assessment of therapies.

Amino acids augment muscle protein synthesis in neonatal pigs during acute endotoxemia by stimulating mTOR-dependent translation initiation

In skeletal muscle of adults, sepsis reduces protein synthesis by depressing translation initiation and induces resistance to branched-chain amino acid stimulation. Normal neonates maintain a high basal muscle protein synthesis rate that is sensitive to amino acid stimulation. In the present study, we determined the effect of amino acids on protein synthesis in skeletal muscle and other tissues in septic neonates. Overnight-fasted neonatal pigs were infused with endotoxin (LPS, 0 and 10 microg.kg(-1).h(-1)), whereas glucose and insulin were maintained at fasting levels; amino acids were clamped at fasting or fed levels. In the presence of fasting insulin and amino acids, LPS reduced protein synthesis in longissimus dorsi (LD) and gastrocnemius muscles and increased protein synthesis in the diaphragm, but had no effect in masseter and heart muscles. Increasing amino acids to fed levels accelerated muscle protein synthesis in LD, gastrocnemius, masseter, and diaphragm. LPS stimulated protein synthesis in liver, lung, spleen, pancreas, and kidney in fasted animals. Raising amino acids to fed levels increased protein synthesis in liver of controls, but not LPS-treated animals. The increase in muscle protein synthesis in response to amino acids was associated with increased mTOR, 4E-BP1, and S6K1 phosphorylation and eIF4G-eIF4E association in control and LPS-infused animals. These findings suggest that amino acids stimulate skeletal muscle protein synthesis during acute endotoxemia via mTOR-dependent ribosomal assembly despite reduced basal protein synthesis rates in neonatal pigs. However, provision of amino acids does not further enhance the LPS-induced increase in liver protein synthesis.

Reduced protein degradation rates and low expression of proteolytic systems support skeletal muscle hypertrophy in transgenic mice overexpressing the c-ski oncogene

We have investigated the protein turnover modulations involved in the hypertrophic muscle phenotype of c-ski overexpressing transgenic mice. In these animals, the body weight is increased and all the muscles examined show a definite hypertrophy. The protein degradation rate is significantly reduced in the fast twitch muscles of c-ski transgenic animals with respect to controls; in contrast, there are no detectable differences in the synthesis rates. The down-regulation of protein breakdown is paralleled by decreased expression of genes belonging to the lysosomal as well as to the ATP-ubiquitin-dependent proteolytic pathways.

Muscle wasting

The loss of lean body mass (muscle wasting) is initiated by cascades or events that precipitate increased proteolysis. Muscle wasting is stimulated by internal and external factors. Humorally related feedback loops stimulated by disease states, e.g., cancer, inflammatory myopathies, leukemia, or sepsis, and initiated as a response to systemic inflammatory response syndrome can cause a downward progression of events, resulting in chronic illness or even death. This article discusses the pathogenesis of muscle wasting, which is often referred to as cachexia.

Inhibition of interleukin-6-activated janus kinases/signal transducers and activators of transcription but not mitogen-activated protein kinase signaling in liver of endotoxin-treated rats

OBJECTIVES

Endotoxin-induced cytokines, such as interleukin-6, mediate systemic inflammatory responses through multiple cellular signaling pathways. Interleukin-6 is also responsible for the synthesis of acute phase proteins. Recent studies have shown that endotoxin can inhibit signal transducers and activators of transcription (STAT)-3 tyrosine phosphorylation in cultured cells, suggesting that this effect may limit the synthesis of acute phase proteins. The purpose of this study was to examine the effects of endotoxin on interleukin-6 activation of STATs and mitogen-activated protein (MAP) kinase pathways in rat liver in vivo.

DESIGN

Controlled laboratory study.

SETTING

Medical school laboratory.

SUBJECTS

Specific pathogen-free male Sprague Dawley rats.

INTERVENTIONS

Under anesthesia, interleukin-6 was injected into the portal vein of rats 4 hrs after the bolus intravenous administration of endotoxin (1 mg/kg) or saline. The effects of interleukin-6 on key intermediates in early steps of the interleukin-6 signaling pathway, including janus kinase-1, gp 130, the interleukin-6 receptor, STAT1, and STAT3, were examined in both saline and endotoxin-treated rats.

MEASUREMENTS AND MAIN RESULTS

In endotoxin-treated rats, there was significant inhibition of interleukin-6 activation of janus kinase-1, gp 130, the interleukin-6 receptor, STAT1, and STAT3. These signaling changes were associated with decreased tissue abundance of interleukin-6 receptors and STAT3. In contrast to its effects on the janus kinase/STAT pathways, interleukin-6 activation of MAP kinases (extracellular signal-regulated kinase-1, extracellular signal-regulated kinase-2, and p38) was unaffected by endotoxin.

CONCLUSIONS

The pathway-specific inhibition of interleukin-6 signaling responses in the liver may be an important determinant of the pathophysiologic consequences of endotoxin exposure.

IGF-I/IGFBP-3 binary complex modulates sepsis-induced inhibition of protein synthesis in skeletal muscle

The present study evaluated the ability of insulin-like growth factor I (IGF-I) complexed with IGF binding protein-3 (IGFBP-3) to modulate the sepsis-induced inhibition of protein synthesis in gastrocnemius. Beginning 16 h after the induction of sepsis, either the binary complex or saline was injected twice daily via a tail vein, with measurements made 3 and 5 days later. By day 3, sepsis had reduced plasma IGF-I concentrations approximately 50% in saline-treated rats. Administration of the binary complex provided exogenous IGF-I to compensate for the sepsis-induced diminished plasma IGF-I. Sepsis decreased rates of protein synthesis in gastrocnemius relative to controls by limiting translational efficiency. Treatment of septic rats with the binary complex for 5 days attenuated the sepsis-induced inhibition of protein synthesis and restored translational efficiency to control values. Assessment of potential mechanisms regulating translational efficiency showed that neither the sepsis-induced change in gastrocnemius content of eukaryotic initiation factor 2B (eIF2B), the amount of eIF4E associated with 4E binding protein-1 (4E-BP1), nor the phosphorylation state of 4E-BP1 or eIF4E were altered by the binary complex. Overall, the results are consistent with the hypothesis that decreases in plasma IGF-I are partially responsible for enhanced muscle catabolism during sepsis.

Metabolic derangements in sepsis and septic shock

This article examines the spectrum of metabolic alterations in sepsis and septic shock. The clinical manifestations, neuroendocrine control, and bioenergetics of the "ebb" and "flow" phases of sepsis are reviewed. Characteristic alterations in carbohydrate, fat, and protein metabolism induced by sepsis are outlined. Finally, the implications of these metabolic alterations for the nutritional support of patients with sepsis are discussed.

[Pathophysiology of catabolism in undernurished elderly patients]

Malnutrition is a common finding amongst our elders. The causes of malnutrition are multifactorial and although they have been extensively studied, they are not entirely understood. Both physiological and pathological processes of aging put this population at a higher risk of being undernourished. These may be related to social, financial, psychological and/or physiological changes directly or indirectly associated to growing old. Age associated changes increase the risk of malnutrition in older individuals. These alterations range from problems in taste and smell perception, which were previously thought to be the main cause of anorexia in this population, to alterations in either the concentration or efficacy of the previously mentioned feeding modulators. Increased intestinal malabsorption together with an altered pancreatic exocrine response to different diets, further contributing to subclinical malabsorption in the elderly population aged and may account in part for the malnutrition observed in this group. Although not directly caused by the aging process, several conditions such as anorexia nervosa, cancer, infectious conditions, and inflammatory processes are associated with decreased food intake and weight loss. These conditions present with elevated levels of immunoregulatory substances known as cytokines. Each of these cytokines has multiple effects and play a leading role in the pathophysiology and maintainance of malnutrition in these situations.

Inflammation nutritional state and outcome in end stage renal disease

Hypoalbuminemia and reduction in lean body mass are potentially a reflection of malnutrition and portend a poor prognosis in patients with end stage renal disease (ESRD). The classic understanding of this relationship has been that ESRD patients receive insufficient dialysis, reduce dietary intake and become malnourished. Inflammation also causes many of the same changes in serum protein composition and in body morphometry as malnutrition does even with adequate calorie and protein intake. It has recently been recognized that this, the acute phase response, occurs with frequency in ESRD patients and that both the physical attributes of malnutrition and reduction in the serum concentration of albumin, transferrin, prealbumin and apolipoprotein A-I all may lack a nutritional base. The serum concentration of the acute phase proteins, C reactive protein (CRP) and serum amyloid A (SAA), as well as the cytokines orchestrating the acute phase response, predict albumin concentration as well as a number of clinically important outcomes: specifically, erythropoietin resistance rejection of renal transplant and survival. ESRD per se does not cause the acute phase response, and indeed may blunt the response to infection. Activation of the acute phase response may be a consequence of the interaction of mononuclear cells with dialysis membranes, especially cuprophane, with endotoxin in dialysate, or represents either clinically evident or obscure infection. Evaluation of the acute phase response by measurement of CRP is advisable in the evaluation of hypoalbuminemia or other stigmata of malnutrition in dialysis patients.

Inter-organ protein and carbohydrate metabolic relationships during sepsis: necessary evils or uncanny coincidences?

Sepsis alters the dynamic flux of metabolic substrates between skeletal muscle and liver. Derangements in skeletal muscle glucose metabolism evoked by sepsis to a certain extent determine the rate of gluconeogenesis in the liver. In contrast, accelerated rates of gluconeogenesis do not drive net catabolism in skeletal muscle, nor does the upregulation of hepatic protein metabolism in sepsis or inflammation appear to be contingent or dependent upon the catabolism of muscle proteins during sepsis.