Cytokines and glucocorticoids in the regulation of the "hepato-skeletal muscle axis" in sepsis

Molecular mechanisms of post-burn muscle wasting and the therapeutic potential of physical exercise

After a severe burn injury, a systemic stress response activates metabolic and inflammatory derangements that, among other, leads to muscle mass loss (muscle wasting). These negative effects on skeletal muscle continue for several months or years and are aggravated by short-term and long-term disuse. The dynamic balance between muscle protein synthesis and muscle protein breakdown (proteolysis) is regulated by complex signalling pathways that leads to an overall negative protein balance in skeletal muscle after a burn injury. Research concerning these molecular mechanisms is still scarce and inconclusive, understanding of which, if any, molecular mechanisms contribute to muscle wasting is of fundamental importance in designing of therapeutic interventions for burn patients as well. This review not only summarizes our present knowledge of the molecular mechanisms that underpin muscle protein balance but also summarizes the effects of exercise on muscle wasting post-burn as promising strategy to counteract the detrimental effects on skeletal muscle. Future research focusing on the pathways causing post-burn muscle wasting and the different effects of exercise on them is needed to confirm this hypothesis and to lay the foundation of therapeutic strategies.

Metabolism of Proteins and Amino Acids in Critical Illness: From Physiological Alterations to Relevant Clinical Practice

The clinical impact of nutrition therapy in critically ill patients has been known for years, and relevant guidelines regarding nutrition therapy have emphasized the importance of proteins. During critical illness, such as sepsis or the state following major surgery, major trauma, or major burn injury, patients suffer from a high degree of stress/inflammation, and during this time, metabolism deviates from homeostasis. The increased degradation of endogenous proteins in response to stress hormones is among the most important events in the acute phase of critical illness. Currently published evidence suggests that adequate protein supplementation might improve the clinical outcomes of critically ill patients. The role of sufficient protein supplementation may even surpass that of caloric supplementation. In this review, we focus on relevant physiological alterations in critical illness, the effects of critical illness on protein metabolism, nutrition therapy in clinical practice, and the function of specific amino acids.

Exploring the Inflammatory Metabolomic Profile to Predict Response to TNF-α Inhibitors in Rheumatoid Arthritis

In clinical practice, approximately one-third of patients with rheumatoid arthritis (RA) respond insufficiently to TNF-α inhibitors (TNFis). The aim of the study was to explore the use of a metabolomics to identify predictors for the outcome of TNFi therapy, and study the metabolomic fingerprint in active RA irrespective of patients’ response. In the metabolomic profiling, lipids, oxylipins, and amines were measured in serum samples of RA patients from the observational BiOCURA cohort, before start of biological treatment. Multivariable logistic regression models were established to identify predictors for good- and non-response in patients receiving TNFi (n = 124). The added value of metabolites over prediction using clinical parameters only was determined by comparing the area under receiver operating characteristic curve (AUC-ROC), sensitivity, specificity, positive- and negative predictive value and by the net reclassification index (NRI). The models were further validated by 10-fold cross validation and tested on the complete TNFi treatment cohort including moderate responders. Additionally, metabolites were identified that cross-sectionally associated with the RA disease activity score based on a 28-joint count (DAS28), erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP). Out of 139 metabolites, the best-performing predictors were sn1-LPC(18:3-ω3/ω6), sn1-LPC(15:0), ethanolamine, and lysine. The model that combined the selected metabolites with clinical parameters showed a significant larger AUC-ROC than that of the model containing only clinical parameters (p = 0.01). The combined model was able to discriminate good- and non-responders with good accuracy and to reclassify non-responders with an improvement of 30% (total NRI = 0.23) and showed a prediction error of 0.27. For the complete TNFi cohort, the NRI was 0.22. In addition, 88 metabolites were associated with DAS28, ESR or CRP (p<0.05). Our study established an accurate prediction model for response to TNFi therapy, containing metabolites and clinical parameters. Associations between metabolites and disease activity may help elucidate additional pathologic mechanisms behind RA.

Amino acid supplementation is anabolic during the acute phase of endotoxin-induced inflammation: A human randomized crossover trial

BACKGROUND & AIMS

Inflammation is catabolic and causes muscle loss. It is unknown if amino acid supplementation reverses these effects during the acute phase of inflammation. The aim was to test whether amino acid supplementation counteracts endotoxin-induced catabolism.

METHODS

Eight young, healthy, lean males were investigated three times in randomized order: (i) normal conditions (Placebo), (ii) endotoxemia (LPS), and (iii) endotoxemia with amino acid supplementation (LPS + A). Protein kinetics were determined using phenylalanine, tyrosine, and urea tracers. Each study day consisted of a four-hour non-insulin stimulated period and a two-hour hyperinsulinemic euglycemic clamp period. Muscle biopsies were collected once each period.

RESULTS

Endotoxin administration created a significant inflammatory response (cytokines, hormones, and vital parameters) without significant differences between LPS and LPS + A. Whole body protein breakdown was elevated during LPS compared with Placebo and LPS + A (p < 0.05). Whole body protein synthesis was higher during LPS + A than both Placebo and LPS (p < 0.003). Furthermore, protein synthesis was higher during LPS than during Placebo (p < 0.02). Net muscle phenylalanine release was markedly decreased during LPS + A (p < 0.004), even though muscle protein synthesis and breakdown rates did not differ significantly between interventions. LPS + A increased mammalian target of rapamycin (mTOR) phosphorylation (p < 0.05) and eukaryotic translation factor 4E-binding protein 1 (4EBP1) phosphorylation (p = 0.007) without activating AMPK or affecting insulin signaling through Akt. During insulin stimulation net muscle phenylalanine release and protein degradation were further reduced.

CONCLUSIONS

Amino acid supplementation in the acute phase of inflammation reduces whole body and muscle protein loss, and this effect is associated with activation of mTOR and downstream signaling to protein synthesis through mTORC1, suggesting a therapeutic role for intravenous amino acids in inflammatory states.

CLINICAL TRIAL REGISTRY

The Central Denmark Region Ethics Commitee (1-10-71-410-12) www.clinicaltrials.gov (identification number NCT01705782).

Hyperammonemia in cirrhosis induces transcriptional regulation of myostatin by an NF-κB-mediated mechanism

Loss of muscle mass, or sarcopenia, is nearly universal in cirrhosis and adversely affects patient outcome. The underlying cross-talk between the liver and skeletal muscle mediating sarcopenia is not well understood. Hyperammonemia is a consistent abnormality in cirrhosis due to impaired hepatic detoxification to urea. We observed elevated levels of ammonia in both plasma samples and skeletal muscle biopsies from cirrhotic patients compared with healthy controls. Furthermore, skeletal muscle from cirrhotics had increased expression of myostatin, a known inhibitor of skeletal muscle accretion and growth. In vivo studies in mice showed that hyperammonemia reduced muscle mass and strength and increased myostatin expression in wild-type compared with postdevelopmental myostatin knockout mice. We postulated that hyperammonemia is an underlying link between hepatic dysfunction in cirrhosis and skeletal muscle loss. Therefore, murine C2C12 myotubes were treated with ammonium acetate resulting in intracellular concentrations similar to those in cirrhotic muscle. In this system, we demonstrate that hyperammonemia stimulated myostatin expression in a NF-κB-dependent manner. This finding was also observed in primary murine muscle cell cultures. Hyperammonemia triggered activation of IκB kinase, NF-κB nuclear translocation, binding of the NF-κB p65 subunit to specific sites within the myostatin promoter, and stimulation of myostatin gene transcription. Pharmacologic inhibition or gene silencing of NF-κB abolished myostatin up-regulation under conditions of hyperammonemia. Our work provides unique insights into hyperammonemia-induced myostatin expression and suggests a mechanism by which sarcopenia develops in cirrhotic patients.

Tissue dyslipidemia in Salmonella-infected rats treated with amoxillin and pefloxacin

BACKGROUND

This study investigated the effects of salmonella infection and its chemotherapy on lipid metabolism in tissues of rats infected orally with Salmonella typhimurium and treated intraperitoneally with pefloxacin and amoxillin.

METHODS

Animals were infected with Salmonella enterica serovar Typhimurium strain TA 98. After salmonellosis was confirmed, they were divided into 7 groups of 5 animals each. While one group served as infected control group, three groups were treated with amoxillin (7.14 mg/kg body weight, 8 hourly) and the remaining three groups with pefloxacin (5.71 mg/kg body weight, 12 hourly) for 5 and 10 days respectively. Uninfected control animals received 0.1 ml of vehicle. Rats were sacrificed 24h after 5 and 10 days of antibiotic treatment and 5 days after discontinuation of antibiotic treatment. Their corresponding controls were also sacrificed at the same time point. Blood and tissue lipids were then evaluated.

RESULTS

Salmonella infection resulted in dyslipidemia characterised by increased concentrations of free fatty acids (FFA) in plasma and erythrocyte, as well as enhanced cholesterogenesis, hypertriglyceridemia and phospholipidosis in plasma, low density lipoprotein-very low density lipoprotein (LDL-VLDL), erythrocytes, erythrocyte ghost and the organs. The antibiotics reversed the dyslipidemia but not totally. A significant correlation was observed between fecal bacterial load and plasma cholesterol (r=0.456, p<0.01), plasma triacyglycerols (r=0.485, p<0.01), plasma phospholipid (r=0.414, p<0.05), plasma free fatty acids (r=0.485, p<0.01), liver phospholipid (r=0.459, p<0.01) and brain phospholipid (r=0.343, p<0.05).

CONCLUSION

The findings of this study suggest that salmonella infection in rats and its therapy with pefloxacin and amoxillin perturb lipid metabolism and this perturbation is characterised by cholesterogenesis.

Cytokine production by monocytes, neutrophils, and dendritic cells is hampered by long-term intensive training in elite swimmers

Elite level athletes seem to be prone to illness especially during heavy training phases. The aim of this study was to investigate the influence of long term intensive training on the functional features of innate immune cells from high competitive level swimmers, particularly the production of inflammatory mediators and the possible relationship with upper respiratory symptoms (URS) occurrence. A group of 18 swimmers and 11 healthy non athletes was studied. Peripheral blood samples were collected from athletes after 36 h of resting recovery from exercise at four times during the training season and at three times from non athletes. Samples were incubated in the presence or absence of LPS and IFN-γ and the frequency of cytokine-producing cells and the amount produced per cell were evaluated by flow cytometry. In addition, plasma cortisol levels were measured and URS recorded through daily logs. The athletes, but not the controls, showed a decrease in the number of monocytes, neutrophils, and dendritic cell (DC) subsets and in the amount of IL-1β, IL-6, IL-12, TNF-α, and MIP-1β produced after stimulation, over the training season. Differences were most noticeable between the first and second blood collections (initial increase in training volume). Athlete's cortisol plasma levels partially correlated with training intensity and could help explain the reduced in vitro cell response to stimulation. Our results support the idea that long-term intensive training may affect the function of innate immune cells, reducing their capacity to respond to acute challenges, possibly contributing to an elevated risk of infection.

Ectopic expression of eIF2Bepsilon in rat skeletal muscle rescues the sepsis-induced reduction in guanine nucleotide exchange activity and protein synthesis

Eukaryotic initiation factor 2B (eIF2B) is a guanine nucleotide exchange factor (GEF) whose activity is both tightly regulated and rate-controlling with regard to global rates of protein synthesis. Skeletal muscle eIF2B activity and expression of its catalytic epsilon-subunit (eIF2Bepsilon) have been implicated as potential contributors to the altered rates of protein synthesis in a number of physiological conditions and experimental models. The objective of this study was to directly examine the effects of exogenously expressed eIF2Bepsilon in vivo on GEF activity and protein synthetic rates in rat skeletal muscle. A plasmid encoding FLAG-eIF2Bepsilon was transfected into the tibialis anterior (TA) of one leg, while the contralateral TA received a control plasmid. Ectopic expression of eIF2Bepsilon resulted in increased GEF activity in TA homogenates of healthy rats, demonstrating that the expressed protein was catalytically active. In an effort to restore a deficit in eIF2B activity, we utilized an established model of chronic sepsis in which skeletal muscle eIF2B activity is known to be impaired. Ectopic expression of eIF2Bepsilon in the TA rescued the sepsis-induced deficit in GEF activity and muscle protein synthesis. The results demonstrate that modulation of eIF2Bepsilon expression may be sufficient to correct deficits in skeletal muscle protein synthesis associated with sepsis and other muscle-wasting conditions.

Changes in liver function and size after a severe thermal injury

Hepatic homeostasis and metabolism are essential for survival in critically ill and severely burned patients. There is evidence that the liver undergoes hypertrophy after burn. However, the extension and the duration of liver enlargement are not known. The aim of the present study was to determine the changes in liver size, weight, and hepatic protein synthesis in a large prospective clinical trial throughout acute hospitalization and up to 12 months after burn. Liver size was measured by means of ultrasound, and liver weight was calculated weekly during short-term hospital stay and at 6, 9, and 12 months after burn. The liver size was then compared with the predicted liver size for each individual. The levels of hepatic proteins and enzymes were determined by using standard laboratory techniques. One hundred two children were included in the study, with 58% +/- 2% total body surface area and 45% +/- 2% third-degree burn. Liver size and weight significantly increased during the first week after burn (mean +/- SEM, 85% +/- 5%), peaked at 2 weeks after burn (mean +/- SEM, 126% +/- 19%), and, at discharge, increased by 89% +/- 10%. At 6, 9, and 12 months, the liver weight increased by 40% to 50% compared with the predicted liver weight. The hepatic protein synthesis was affected up to 9 months after burn. The liver demonstrates a significant enlargement during short-term hospitalization, accompanied with impairment in the hepatic protein synthesis. The treatment to prevent liver enlargement and the improved impaired function may result in a reduction of complications accompanied with liver hypertrophy and failure.

Hypercortisolemia alters muscle protein anabolism following ingestion of essential amino acids

Debilitating injury is accompanied by hypercortisolemia, muscle wasting, and disruption of the normal anabolic response to food. We sought to determine whether acute hypercortisolemia alters muscle protein metabolism following ingestion of a potent anabolic stimulus: essential amino acids (EAA). A 27-h infusion (80 microg. kg(-1). h(-1)) of hydrocortisone sodium succinate mimicked cortisol (C) levels accompanying severe injury (>30 microg/dl), (C + AA; n = 6). The control group (AA) received intravenous saline (n = 6). Femoral arteriovenous blood samples and muscle biopsies were obtained during a primed (2.0 micromol/kg) constant infusion (0.05 micromol. kg(-1). min(-1)) of l-[ring-(2)H(5)]phenylalanine before and after ingestion of 15 g of EAA. Hypercortisolemia [36.5 +/- 2.1 (C + AA) vs. 9.0 +/- 1.0 microg/dl (AA)] increased postabsorptive arterial, venous, and muscle intracellular phenylalanine concentrations. Hypercortisolemia also increased postabsorptive and post-EAA insulin concentrations. Net protein balance was blunted (40% lower) following EAA ingestion but remained positive for a greater period of time (60 vs. 180 min) in the C + AA group. Thus, although differences in protein metabolism were evident, EAA ingestion improved muscle protein anabolism during acute hypercortisolemia and may help minimize muscle loss following debilitating injury.

Renal arginine and protein synthesis are increased during early endotoxemia in mice

The kidney has an important function in arginine metabolism, because the kidney is the main endogenous source for de novo arginine production from circulating citrulline. In conditions such as sepsis, nitric oxide (NO) production is increased and is dependent on extracellular arginine availability. To elucidate the adaptive role of renal de novo arginine synthesis in a condition of increased NO production, we studied renal arginine metabolism in a mouse model of endotoxemia. Because arginine flux is largely dependent on protein flux, we also measured protein metabolism in mice. Female mice were injected intraperitoneally with lipopolysaccharide; control mice received 0.9% NaCl. Six hours later, renal blood flow was measured with the use of para-aminohippuric acid. Arginine and protein metabolism were studied using organ-balance, stable-isotope techniques. Systemic NO production was increased in the endotoxin-treated mice. In addition, renal protein synthesis and de novo arginine production from citrulline were increased. However, no effect on renal NO production was observed. In conclusion, increased renal de novo arginine production may serve to sustain systemic NO production. To our knowledge, it was shown for the first time that renal protein synthesis is enhanced in the early response to endotoxemia.

Cancer cachexia: a therapeutic approach

Cancer cachexia is a complex syndrome which occurs in more than two-thirds of patients who die with advanced cancer. The main components of this pathological state are anorexia and metabolic abnormalities such as glucose intolerance, fat depletion, and muscle protein catabolism among others. The aim of the present study is to review the different therapeutic approaches that have been designed to fight and counteract cancer cachexia.

Cytokine hypothesis of overtraining: a physiological adaptation to excessive stress?

Overtraining syndrome (OTS) is a condition wherein an athlete is training excessively, yet performance deteriorates. This is usually accompanied by mood/behavior changes and a variety of biochemical and physiological alterations. Presently, there is no global hypothesis to account for OTS. The present paper will attempt to provide a unifying paradigm that will integrate previous research under the rubric of the cytokine hypothesis of overtraining. It is argued that high volume/intensity training, with insufficient rest, will produce muscle and/or skeletal and/or joint trauma. Circulating monocytes are then activated by injury-related cytokines, and in turn produce large quantities of proinflammatory IL-1beta, and/or IL-6, and/or TNF-alpha, producing systemic inflammation. Elevated circulating cytokines then co-ordinate the whole-body response by: a) communicating with the CNS and inducing a set of behaviors referred to as "sickness" behavior, which involves mood and behavior changes that support resolution of systemic inflammation: b) adjusting liver function, to support the up-regulation of gluconeogenesis, as well as de novo synthesis of acute phase proteins, and a concomitant hypercatabolic state; and c) impacting on immune function. Theoretically, OTS is viewed as the third stage of Selye's general adaptation syndrome, with the focus being on recovery/survival, and not adaptation, and is deemed to be "protective," occurring in response to excessive physical/physiological stress. Recommendations are made for potential markers of OTS, based on a systemic inflammatory condition.

New rationale for glucocorticoid treatment in septic shock

Two recent small randomized trials evaluating a 5- to 12-day course of low dose hydrocortisone in patients with septic shock have reported a significant clinical improvement and a reduction in mortality. Recent studies indicate that an overaggressive and unregulated systemic inflammatory response is a major determinant of outcome in sepsis. In septic shock, nonsurvivors as opposed to survivors have over time: (1) significantly higher NF-kB activity in peripheral mononuclear cells, (2) persistent elevation in circulating inflammatory cytokine levels, and (3) elevated ACTH and cortisol levels. Current research recognizes that cytokines can cause a concentration-dependent resistance to endogenous glucocorticoids (GC). It is postulated that an excess of cytokine-induced transcription factors, such as NF-kB, may form complexes with activated glucocorticoid receptors (GCR), preventing GCR interaction with DNA. When T cells are incubated with a combination of cytokines, GC resistance is induced in a cytokine concentration-dependent fashion and reversed by removal of cytokines. Prolonged treatment with physiological doses of exogenous GCs may be necessary to compensate adequately for the inability of target organs to respond to endogenous cortisol and for the inability of the host to produce appropriately elevated levels of GCs. This hypothesis is supported by the laboratory findings of a recent randomized study of patients with unresolving acute respiratory disease.

Serial experimental and clinical studies on the pathogenesis of multiple organ dysfunction syndrome (MODS) in severe burns

These serial clinical and experimental studies were designed to clarify the pathogenesis of postburn MODS. Both animal and clinical studies were performed. In animal experiments, 46 male cross-bred dogs were cannulated with Swan-Ganz catheters and 39 of them were inflicted with 50% TBSA third degree burns (7 were used as controls). The burned dogs were randomly divided into 4 groups: immediate infusion, delayed infusion, delayed fast infusion and delayed fast infusion combined with ginsenosides. All dogs were kept under constant barbiturate sedation during the whole study period. Hemodynamics, visceral MDA, mitochondrial respiratory control rate (RCR) and ADP/O ratio, ATP, succinic dehydrogenase (SDH), organ water content as well as light and electron microscopy of visceral tissues were determined. In the clinical study, 61 patients with extensive deep burns were chosen, of which 16 sustained MODS. Plasma TXB2/6-keto-PGF1alpha ratio, TNF, SOD, MDA, circulatory platelet aggregate ratio (CPAR), PGE2, interleukin-1, total organ water content and pathological observations of visceral tissues from patients who died of MODS were carried out. Results demonstrated that ischemic-reperfusion damage due to severe shock, sepsis and inhalation injury are three main causes of postburn death. All inflammatory mediators increased markedly in both animals and patients who sustained organ damage or MODS. SDH, RCR, ADP/O and ATP decreased significantly. These findings suggested that ischemic damage and systemic inflammatory response syndrome (SIRS) initiated by mediators or cytokines might be important in the pathogenesis of postburn MODS.

Intrinsic and extrinsic factors in muscle aging

The regenerative potential of skeletal muscle, and overall muscle mass, decline with age. This regenerative potential may be influenced by autocrine growth factors intrinsic to the muscle itself. Extrinsic host factors that may influence muscle regeneration include hormones, growth factors secreted in a paracrine manner by accessory cells, innervation, and antioxidant mechanisms. Unaccustomed exercise, which involves mechanical overload of myofibers, provides a convenient method for studying muscle regeneration in both humans and animal models. An inflammatory response ensues in which distinctive populations of macrophages infiltrate the affected tissue: some of these macrophages are involved in phagocytosis of damaged fibers; other macrophages arriving at later times may deliver growth factors or cytokines that promote regeneration. These include fibroblast growth factor and insulin-like growth factor, which are important regulators of muscle precursor cell growth and differentiation, as well as nerve growth factor, which is essential for maintenance or reestablishment of neuronal contact. Other cytokines, including interleukin-1, tumor necrosis factor, interleukin-15, and ciliary neurotrophic factor, have a strong influence on the balance between muscle protein synthesis and breakdown. The functional activity of invading macrophages can be influenced by age, by factors in myofibers and extracellular matrix, and can be influenced systemically by the antioxidant status of the host.

Effect of a chimeric antibody to tumor necrosis factor-alpha on cytokine and physiologic responses in patients with severe sepsis--a randomized, clinical trial

OBJECTIVES

Tumor necrosis factor (TNF)-alpha appears central to the pathogenesis of severe sepsis, but aspects of the cytokine cascade and the link to physiologic responses are poorly defined. We hypothesized that a monoclonal antibody to TNF-alpha given early in the course of severe sepsis would modify the pattern of systemic cytokine release and, as a consequence, resuscitation fluid requirements, net proteolysis, and hypermetabolism would be reduced.

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

Critical Care Unit and University Department of Surgery in a single tertiary care center.

PATIENTS

Fifty-six patients (from 92 eligible patients) with severe sepsis. Twenty-eight patients were randomized to treatment, and were comparable with the placebo group for age, gender, race, Acute Physiology and Chronic Health Evaluation II score, and site and type of infection.

INTERVENTIONS

A 300-mg single dose of cA2 (a chimeric neutralizing antibody to TNF-alpha) was given intravenously within 12 hrs of the onset of severe sepsis. Standard surgical and intensive care therapy was otherwise delivered.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of TNF-alpha, interleukin (IL)-1beta IL-6, IL-8, IL-10, soluble 75-kilodalton TNF-alpha receptor (sTNFR-75), and IL-1beta receptor antagonist (IL-1ra) were measured by sandwich enzyme-linked immunosorbent assay before cA2 infusion, 8 hrs later, and then daily for a minimum of 4 days. Sequential changes in total body protein, body water spaces, and resting energy expenditure over 21 days were measured, as soon as patients achieved hemodynamic stability, by in vivo neutron activation analysis, tritium and bromide dilution, and indirect calorimetry, respectively. Twenty-one patients died, ten having received cA2. Suppression of measurable TNF-alpha was observed at 8 hrs with subsequent rebound by 24 hrs after cA2 treatment. The concentrations of other cytokines were high, were not reduced by intervention, and decreased logarithmically over 5 days. Both groups reached hemodynamic stability at similar times (57.5 +/- 11.8 hrs in controls vs. 58.6 +/- 9.2 hrs in the cA2 group) and following similar volumes of infused fluids (29.1 +/- 3.4 L vs. 28.9 +/- 4.4 L). No differences in net proteolysis, resolution of body water expansion, or alteration in resting energy expenditure were demonstrated.

CONCLUSION

A single dose of cA2 did not alter the overall pattern of cytokine activation or the profound derangements in physiologic function that accompany severe sepsis.

Regulation of the spatiotemporal pattern of expression of the glutamine synthetase gene

Glutamine synthetase, the enzyme that catalyzes the ATP-dependent conversion of glutamate and ammonia into glutamine, is expressed in a tissue-specific and developmentally controlled manner. The first part of this review focuses on its spatiotemporal pattern of expression, the factors that regulate its levels under (patho)physiological conditions, and its role in glutamine, glutamate, and ammonia metabolism in mammals. Glutamine synthetase protein stability is more than 10-fold reduced by its product glutamine and by covalent modifications. During late fetal development, translational efficiency increases more than 10-fold. Glutamine synthetase mRNA stability is negatively affected by cAMP, whereas glucocorticoids, growth hormone, insulin (all positive), and cAMP (negative) regulate its rate of transcription. The signal transduction pathways by which these factors may regulate the expression of glutamine synthetase are briefly discussed. The second part of the review focuses on the evolution, structure, and transcriptional regulation of the glutamine synthetase gene in rat and chicken. Two enhancers (at -6.5 and -2.5 kb) were identified in the upstream region and two enhancers (between +156 and +857 bp) in the first intron of the rat glutamine synthetase gene. In addition, sequence analysis suggests a regulatory role for regions in the 3' untranslated region of the gene. The immediate-upstream region of the chicken glutamine synthetase gene is responsible for its cell-specific expression, whereas the glucocorticoid-induced developmental appearance in the neural retina is governed by its far-upstream region.

Plasma and muscle amino acid levels in relation to resting energy expenditure and inflammation in stable chronic obstructive pulmonary disease

In patients with chronic obstructive pulmonary disease (COPD), muscle wasting can occur independently of fat loss, suggesting disturbances in protein metabolism. In order to provide more insight in amino-acid (AA) metabolism in patients with stable COPD, we examined arterial plasma and anterior tibialis muscle AA levels, comparing 12 COPD patients with eight age-matched healthy control subjects. We also studied relationships between AA levels, the acute phase response as measured by lipopolysaccharide-binding protein (LBP), and resting energy expenditure (REE). In contrast to findings in acute diseases associated with muscle wasting, we found increased muscle glutamine (GLN) levels in our patient group (mean +/- SEM = 10,782 +/- 770 versus 7,844 +/- 293 micromol/kg wet weight, p < 0. 01). Furthermore, muscle arginine, ornithine, and citrulline were significantly increased in the patient group, whereas glutamic acid was decreased. In plasma, the sum of all AA (SumAA) was decreased in the patient group (2,595 +/- 65 versus 2,894 +/- 66 micromol/L, p < 0.01), largely because of decreased levels of alanine (254 +/- 10 versus 375 +/- 25 micromol/L, p < 0.0001), GLN (580 +/- 17 versus 641 +/- 17 micromol/L, p < 0.05), and glutamic acid (91 +/- 5 versus 130 +/- 10 micromol/L, p < 0.01). LBP levels were increased in COPD patients as compared with controls (11.7 +/- 4.5 versus 8.6 +/- 1.0 mg/L, p < 0.05), and showed a positive correlation with REE (r = 0. 49, p = 0.03), a negative correlation with the SumAA in plasma (r = -0.76, p < 0.0001), and no correlation with muscle AA levels. In conclusion, various disturbances in plasma and muscle AA levels were found in COPD patients. A relationship between the observed decreased plasma AA levels and inflammation was suggested.

Cytokines in exertion-induced skeletal muscle injury

Cytokines are a diverse family of intercellular signaling proteins that influence the movement, proliferation, differentiation, metabolism and membrane processes of target cells. Synthesis and release of cytokines from leukocytes in response to microbial stimuli are well known. This review, however, will present evidence that non-infectious stimuli can induce cytokine secretion from leukocytes and other cells (including muscle cells) following myocellular injury. The biological actions and potential adaptive values of these cytokines through the course of muscle necrosis and regeneration will be described.

Endocrine neuromyopathies

The myopathies associated with endocrine disorders range in clinical presentation from the relatively nonspecific pattern of proximal muscle weakness of glucocorticoid excess states to specific presentations of contractions produced in tetany. All endocrine neuromyopathies emphasize the role of skeletal muscle in protein, carbohydrate, and electrolyte metabolism. Hormonal abnormalities tend to compromise muscle force generation by indirect effects on muscle function. The recognition and effective treatment of all these disorders require the identification of the underlying hormonal imbalances and awareness of general medical problems produced by the endocrine disorders.

Sequential changes in insulin-like growth factor 1, plasma proteins, and total body protein in severe sepsis and multiple injury

BACKGROUND

Our group wanted to test the hypothesis that plasma levels of insulin-like growth factor 1 (IGF-1), transferrin, and prealbumin are useful markers of nutritional progress in severe sepsis and multiple injury.

METHODS

Measurements of IGF-1 and plasma proteins were made in critically ill patients as soon as they were hemodynamically stable and 5, 10, 15, and 21 days later. The magnitude and direction of the measured changes were compared with the magnitude and direction of the change in total body protein in the same time period.

RESULTS

Fourteen patients with severe sepsis and 10 multiply injured patients were studied. As a group they had an increased metabolic expenditure that peaked at 153% of normal and lost approximately 12.0% of total body protein. An early fall in IGF-1 and plasma proteins accompanied a marked acute phase response, and recovery occurred while hypermetabolism and net proteolysis continued. No correlation existed between changes in IGF-1 or plasma proteins and the change in total body protein.

CONCLUSIONS

Plasma levels of IGF-1, transferrin, and prealbumin are not useful for following changes in protein stores early in the course of critical illness.

Inhibition of liver RNA breakdown during acute inflammation in the rat

Liver RNA- and protein-degradation rates were measured after the induction of acute inflammation in the rat. A preliminary study determined changes in hepatic RNA and protein content 12, 18 and 24 h after a turpentine oil injection. The RNA content in turpentine-treated rats compared with pair-fed animals increased significantly and sharply from 12 h (+ 11%) to 18 h (+ 32%) and slightly thereafter (+ 37% at 24 h). The liver protein content was significantly enhanced only at 24 h (+ 11%) in response to inflammation. RNA-degradation rates were determined in livers perfused cyclically in situ for 15 min by measuring the accumulation of radioactive cytidine in the medium 60 h after in vivo labelling of RNA by [5-3H]cytidine instead of [6-14C]orotic acid, the most commonly used radioactive marker. Several validation procedures showed that the method employed was a valid alternative to the use of radioactive orotic acid. RNA-degradation rates, which mainly reflect rRNA breakdown, were significantly lower in the turpentine-treated rats than in respective pair-fed animals at 18 and 24 h (57 and 45% decrease respectively). Proteolysis rates measured at 24 h together with RNA breakdown by valine accumulation in the perfusion medium were not modified after turpentine treatment. The main factors known to regulate RNA degradation (amino acids, insulin/glucagon ratio) were measured in the portal blood 24 h after induction of acute inflammation. Of the known regulatory amino acids, only glutamine and to a lesser extent methionine were increased in the turpentine-treated rats as compared with their pair-fed counterparts. The insulin/glucagon molar ratio was similar in both groups. In conclusion, the reduced breakdown of RNA, especially rRNA, is largely responsible for the accumulation of hepatic RNA during acute inflammation. This inhibition of RNA degradation could possibly be related to the increase in glutamine.

Starvation and endotoxin act independently and synergistically to coordinate hepatic glutamine transport

OBJECTIVE

Because hepatic glutamine transport is markedly enhanced during critical illness, we tested the hypothesis that nutrient starvation and endotoxemia act coordinately to augment transport activity.

DESIGN

Fed or starved (48 hours) rats received Escherichia coli endotoxin (LPS, 10 mg/kg of body weight, intraperitoneally) or saline before hepatocyte isolation for measurement of glutamine transport.

MATERIALS AND METHODS

Hepatocytes were isolated from fed or fasted rats 4 hours after LPS treatment. [3H]glutamine uptake was measured and normalized to cellular protein. Data (mean +/- standard deviation, three separate determinations) were analyzed by Student's t test and analysis of variance.

MAIN RESULTS

Starvation induced a 1.6-fold increase in glutamine transport, while LPS treatment of fed rats increased transport activity 2.6-fold. Treatment of fasted animals with LPS induced a sixfold increase in glutamine transport. Kinetically, this effect in endotoxemic starved rats was mediated by both an increase in System N Vmax and the induction of a high affinity System A amino acid carrier which transports glutamine.

CONCLUSIONS

Starvation and endotoxemia regulate hepatocyte glutamine transport independently and synergistically. This hepatic response provides glutamine and other amino acids to support key metabolic pathways in the liver during critical illness.

Oxidative metabolism in sepsis and sepsis syndrome

The high mortality associated with sepsis syndrome and multiple organ dysfunction syndrome has persisted despite extraordinary research efforts in the laboratory and the intensive care unit. These syndromes produce systemic tissue damage that is likely to result from widespread inflammation and subsequent endothelial injury. This article reviews the oxidative metabolic effects and responses to sepsis syndrome at several levels: the oxygen transport system, the cell, and the mitochondrion. Specifically, aerobic metabolism of carbon substrates and oxygen is altered in sepsis. As a result of systemic inflammation and nonmetabolic oxygen use, oxidative stress may occur both outside and inside the cell. The consequences of these oxidative processes during sepsis may be ongoing cell damage mediated by reactive oxygen and nitrogen oxide species that culminates in multisystem organ failure.

Amino acid uptake in skeletal muscle of rats bearing the Yoshida AH-130 ascites hepatoma

Rats bearing the Yoshida AH-130 ascites hepatoma show decreased activity of neutral amino acid transport in skeletal muscle measured in vivo as the tissue accumulation of the analogue alpha-amino [1-14C]isobutyrate (AIB). The decreased accumulation of AIB observed is not merely a consequence of the hypoinsulinaemia present in these animals (as a result of tumour burden) since in vitro experiments carried out using incubations of isolated soleus muscles also showed a decreased uptake of neutral amino acids. In these preparations the addition of insulin results in similar increases in uptake both in the pair-fed controls and the tumour-bearing animals, thus suggesting similar insulin sensitivities. The decrease in amino acid uptake in soleus muscle is associated with a decrease in the activity of system A, while systems L and ASC show no particular changes as a result of the tumour growth. The kinetic characterisation of system A in the Yoshida-bearing rats shows a decrease in Vmax together with a decrease in KM in relation with the pair-fed animals.

Sepsis and septic shock. II. Treatment

Mortality from septic shock is considerable despite the advantages of cardiovascular support and antibiotic therapy. This article reviews current therapy of septic shock including immunotherapy and further possibilities of septic shock treatment. The role of cytokines, their inhibitors and antibodies to endotoxin is mentioned. Although these treatments hold much promise for the future, careful evaluation of both the benefits and complications of therapy is needed before widespread clinical use can be recommended.

Acute phase proteins and recombinant IL-2 therapy: prediction of response and survival in patients with colorectal cancer

Twenty-four patients with metastatic colorectal cancer were treated with recombinant IL-2 (rIL-2) by continuous intravenous infusion for 5 days (18 x 10(6) U/m2 per 24 h), followed by three injections of 5-fluorouracil (600 mg/m2) and folinic acid (25 mg/m2) at weekly intervals. The response to treatment was assessed using standard UICC criteria (partial or complete response, stasis or progression of disease). The serum concentrations of the acute phase proteins; C-reactive protein (CRP), retinol binding protein (RBP), alpha 1-antitrypsin (alpha 1-AT), transferrin (TF) and albumin were measured. A response to therapy occurred in the tumours of seven (29%) of the 24 patients (two complete and five partial responses). All patients who demonstrated a response to treatment had a serum albumin level of > 37 g/l and a CRP level of < or = 10 mg/l. In contrast, of the 17 patients who did not respond to therapy, 12 (71%) had a serum albumin of less than 37 g/dl and a CRP of greater than 10 mg/l. Examination of the survival times of the 12 patients who had a pretreatment serum albumin level of less than 37 g/l revealed that all had died within 12 months of cessation of therapy. However, 58% of patients with pretreatment serum albumin levels of greater than 37 g/l survived for longer than 12 months. These results have shown that (i) patients who respond to rIL-2-based therapy and (ii) those patients who have prolonged survival times, can be identified by pretreatment measurement of serum levels of acute phase proteins.

Alanine metabolism in rats bearing the Yoshida AH-130 ascites hepatoma

Rats bearing the Yoshida AH-130 ascites hepatoma, a cachectic rat tumour, showed signs of important muscle wasting with reduced muscle weights. This phenomenon was associated with a decreased rate of in vivo alanine oxidation as measured by the production of 14CO2 from [U-14C]alanine intragastrically administered. It was later found that the decreased amino acid oxidation was associated with a reduced uptake in skeletal muscle as measured in incubated soleus muscles, thus suggesting that the decreased in vivo oxidation is basically due to a reduced oxidation of the amino acid in skeletal muscle. The decrease in alanine oxidation in the tumour-bearing animals was also associated with higher circulating alanine concentrations in their blood. In addition, tumour-bearing rats presented a lower (26%) protein synthetic rate in skeletal muscle, as measured by the incorporation of [14C]phenylalanine into muscle protein. The addition of insulin to the incubation medium abolished the lower rate of protein synthesis, thus suggesting a greater response to this hormone by the muscle of tumour-bearing rats. In conjunction with a reduced protein synthesis, tumour-bearing rats showed a clearly enhanced rate of protein degradation in isolated skeletal muscles. The results presented confirm previous observations suggesting that the skeletal muscle of tumour bearing animals is in a profound negative nitrogen balance which partially accounts for the wasting observed in the tissue. In addition, the present study allows us to conclude that, in spite of the increased alanine utilization for both gluconeogenesis and tumour growth, the oxidation of alanine by the whole animal is decreased in the tumour-bearing rats. This seems to be associated with a decreased ability of skeletal muscle to handle this amino acid.

Reduced muscle protein breakdown in septic rats following treatment with interleukin-1 receptor antagonist

1. The role of interleukin-1 (IL-1) in sepsis-induced muscle proteolysis was assessed by treating septic rats with recombinant IL-1 receptor antagonist (rIL-1ra). 2. In initial experiments, we tested the effectiveness of IL-1ra in preventing muscle proteolysis induced by administration of IL-1. 3. When normal rats were treated with rIL-1 alpha (three intraperitoneal doses of 100 micrograms/kg body weight each over 16 hr), total and myofibrillar muscle protein breakdown rates, measured as release of tyrosine and 3-methylhistidine, respectively, by incubated extensor digitorum longus muscles, were significantly increased. 4. This metabolic response to IL-1 alpha was completely abolished by rIL-1ra, administered as three intraperitoneal doses of 3 mg/kg body weight each over 16 hr. 5. In subsequent experiments, sepsis was induced in rats by cecal ligation and puncture (CLP); non-septic rats were sham-operated. 6. Treatment of septic rats over 16 hr with a total dose of 25 mg/kg body weight of rIL-1ra reduced, but did not normalize, the increased muscle protein breakdown rates seen during sepsis. 7. When the dose of rIL-1ra was more than doubled and given as a constant infusion at a rate of 4.2 mg/kg body weight/hr for 16 hr, the increased rate of muscle proteolysis in septic rats was normalized. 8. The present study offers the first direct evidence that IL-1 is involved in the regulation of muscle proteolysis during sepsis.

Cytokine mediators of malnutrition: clinical implications

During the past decade, the relationships that exist between inflammatory cytokines and the metabolic changes associated with critical illness have been the focus of extensive research efforts. Alterations in protein metabolism, characterized by increased peripheral protein catabolism and increased hepatic synthesis of acute-phase proteins, have been reported with tumor necrosis factor, interleukin-1, and interleukin-6 administration in animals and humans. Hyperlipoproteinemia has also been observed, particularly in association with increases in very-low-density lipoproteins and hepatic fatty acid synthesis. The release of counter-regulatory hormones in response to cytokine activity contributes to these metabolic changes as well. An understanding of the complex interactions of cytokines as mediators of intermediary metabolism is important to clinicians caring for critically ill patients.

Increased intestinal protein synthesis during sepsis and following the administration of tumour necrosis factor alpha or interleukin-1 alpha

The influence of sepsis on intestinal protein synthesis was studied in rats. Sepsis was induced by caecal ligation and puncture (CLP); control rats were sham-operated. Protein synthesis was measured in vivo in the jejunum and ileum following a flooding dose of [14C]leucine. At 8 h after CLP the protein synthesis rate was increased by approx. 15% in jejunal mucosa, and at 16 h after CLP, the protein synthesis rate was increased by 50-60% in the mucosa and seromuscular layer of both jejunum and ileum. In a second series of experiments, rats were treated with recombinant tumour necrosis factor alpha (rTNF alpha) or recombinant interleukin-1 alpha (rIL-1 alpha) administered at a total dose of 300 micrograms/kg body weight over 16 h. Control rats received corresponding volumes of solvent. Treatment with rTNF alpha resulted in an approx. 25% increase in mucosal protein synthesis in jejunum. Following treatment with rIL-1 alpha, protein synthesis increased by 25% in jejunal mucosa and almost doubled in ileal mucosa. The results suggest that sepsis stimulates intestinal protein synthesis and that this response may, at least in part, be mediated by TNF and/or IL-1.