Muscle glutamine depletion in the intensive care unit

Muscle matters: Prognostic implications of malnutrition and muscle health parameters in patients with cancer. A secondary analysis of a randomised trial

BACKGROUND

Low muscle mass and malnutrition are independently associated with an increased risk of adverse outcomes in patients with cancer. However, it is not yet clear which parameter is most indicative of these risks. This study investigates the prognostic significance of different parameters reflecting malnutrition and muscle health in a well-characterised oncology population at nutritional risk.

METHODS

This preplanned secondary analysis included patients with cancer from a Swiss-wide, randomised-controlled nutritional trial. We investigated associations among malnutrition markers (i.e., malnutrition diagnosis based on modified Global Leadership Initiative on Malnutrition (GLIM) criteria, albumin concentration) and muscle health markers (i.e., hand grip strength, computed tomography (CT)-based muscle mass and radiodensity) with 180-day all-cause mortality (primary outcome).

RESULTS

We included 269 patients with a main admission diagnosis of cancer and available CT scans. In a mutually adjusted model, four parameters contributed to risk assessment including modified malnutrition diagnosis (GLIM) (HR 1.78 (95%CI 1.17 to 2.69), p = 0.007, AUC 0.58), low albumin concentration (HR 1.58 (95%CI 1.08 to 2.31), p = 0.019, AUC 0.62), low handgrip strength (HR 2.05 (95%CI 1.43 to 2.93), p = 0.001, AUC 0.62) and low muscle radiodensity (HR 1.39 (95%CI 0.90 to 2.16), p = 0.139, AUC 0.63). Combining these parameters resulted in a model with high prognostic power regarding 180-day mortality (overall AUC 0.71).

CONCLUSIONS

In this study of inpatients with cancer at nutritional risk, several malnutrition and muscle health parameters emerged as independent prognostic indicators for mortality. The use of these parameters may improve risk stratification and guide nutritional interventions in this vulnerable population.

TRIAL REGISTRATION

ClinicalTrials.gov, number NCT02517476.

Prognostic significance of preoperative osteosarcopenia on patient' outcomes after emergency surgery for gastrointestinal perforation

PURPOSE

Sarcopenia is a prognostic predictor in emergency surgery. However, there are no reports on the relationship between osteopenia and in-hospital mortality. This study clarified the effect of preoperative osteosarcopenia on patients with gastrointestinal perforation after emergency surgery.

METHODS

We included 216 patients with gastrointestinal perforations who underwent emergency surgery between January 2013 and December 2022. Osteopenia was evaluated by measuring the pixel density in the mid-vertebral core of the 11th thoracic vertebra. Sarcopenia was evaluated by measuring the area of the psoas muscle at the level of the third lumbar vertebra. Osteosarcopenia is defined as the combination of osteopenia and sarcopenia.

RESULTS

Osteosarcomas were identified in 42 patients. Among patients with osteosarcopenia, older and female patients and those with an American Society of Anesthesiologists Physical Status of ≥ 3 were significantly more common, and the body mass index, hemoglobin value, and albumin level were significantly lower in these patients than in patients without osteosarcopenia. Furthermore, the osteosarcopenia group presented with more postoperative complications than patients without osteosarcopenia (P < 0.01). In the multivariate analysis, age ≥ 74 years old (P = 0.04) and osteosarcopenia (P = 0.04) were independent and significant predictors of in-hospital mortality.

CONCLUSION

Preoperative osteosarcopenia is a risk factor of in-hospital mortality in patients with gastrointestinal perforation after emergency surgery.

Cathepsin S deficiency improves muscle mass loss and dysfunction via the modulation of protein metabolism in mice under pathological stress conditions

Cathepsin S (CTSS) is a widely expressed cysteinyl protease that has garnered attention because of its enzymatic and non-enzymatic functions under inflammatory and metabolic pathological conditions. Here, we examined whether CTSS participates in stress-related skeletal muscle mass loss and dysfunction, focusing on protein metabolic imbalance. Eight-week-old male wildtype (CTSS^+/+ ) and CTSS-knockout (CTSS^-/- ) mice were randomly assigned to non-stress and variable-stress groups for 2 weeks, and then processed for morphological and biochemical studies. Compared with non-stressed mice, stressed CTSS^+/+ mice showed significant losses of muscle mass, muscle function, and muscle fiber area. In this setting, the stress-induced harmful changes in the levels of oxidative stress-related (gp91^phox and p22^phox ,), inflammation-related (SDF-1, CXCR4, IL-1β, TNF-α, MCP-1, ICAM-1, and VCAM-1), mitochondrial biogenesis-related (PPAR-γ and PGC-1α) genes and/or proteins and protein metabolism-related (p-PI3K, p-Akt, p-FoxO3α, MuRF-1, and MAFbx1) proteins; and these alterations were rectified by CTSS deletion. Metabolomic analysis revealed that stressed CTSS^-/- mice exhibited a significant improvement in the levels of glutamine metabolism pathway products. Thus, these findings indicated that CTSS can control chronic stress-related skeletal muscle atrophy and dysfunction by modulating protein metabolic imbalance, and thus CTSS was suggested to be a promising new therapeutic target for chronic stress-related muscular diseases.

Sarcopenia Is a Prognostic Factor in Patients Undergoing Percutaneous Endoscopic Gastrostomy

(1) Background: Percutaneous endoscopic gastrostomy (PEG) is a widely used long-term enteral nutrition method, but little is known about the associated prognostic factors in patients with PEG. Sarcopenia, a condition characterized by a loss of skeletal muscle mass, increases the risk of developing various gastrointestinal disorders. Yet, the relationship between sarcopenia and the prognosis after PEG remains unclear. (2) Methods: We conducted a retrospective study of patients who underwent PEG consecutively from March 2008 to April 2020. We analyzed preoperative sarcopenia and the prognosis of patients after PEG. We defined sarcopenia as a skeletal muscle index at the level of the third lumbar vertebra of ≤29.6 cm²/m² for women and ≤36.2 cm²/m² for men. Cross-sectional computed tomography images of skeletal muscle at the level of the third lumbar vertebra were evaluated using DICOM image analysis software (OsiriX). The primary outcome was the difference in overall survival after PEG based on the status of sarcopenia. We also performed a covariate balancing propensity score matching analysis. (3) Results: Of 127 patients (99 men, 28 women), 71 (56%) were diagnosed with sarcopenia, and 64 patients died during the observation period. The median follow-up period did not differ between patients with and without sarcopenia (p = 0.5). The median survival time after PEG was 273 days in patients with sarcopenia and 1133 days in those without (p < 0.001). Cox proportional hazard model analyses identified three factors that were significantly associated with overall survival: sarcopenia (adjusted hazard ratio [HR]: 2.9, 95% confidence interval [CI]: 1.6-5.4, p < 0.001), serum albumin level (adjusted HR: 0.34, 95% CI: 0.21-0.55, p < 0.001) and male sex (adjusted HR: 2.0, 95% CI: 1.1-3.7, p = 0.03). Propensity score-matched analysis (n = 37 vs. 37) showed that the survival rate was lower in the sarcopenia group than in the non-sarcopenia group (at 90 days: 77% (95% CI, 59-88) vs. 92% (76-97), at 180 days: 56% (38-71) vs. 92% (76-97), and at one year: 35% (19-51) vs. 81% (63-91), p = 0.0014). (4) Conclusions: Sarcopenia was associated with poor prognosis in patients having undergone PEG.

Amino acid metabolism, transport and signalling in the liver revisited

The liver controls the systemic exposure of amino acids entering via the gastro-intestinal tract. For most amino acids except branched chain amino acids, hepatic uptake is very efficient. This implies that the liver orchestrates amino acid metabolism and also controls systemic amino acid exposure. Although many amino acid transporters have been identified, cloned and investigated with respect to substrate specificity, transport mechanism, and zonal distribution, which of these players are involved in hepatocellular amino acid transport remains unclear. Here, we aim to provide a review of current insight into the molecular machinery of hepatic amino acid transport. Furthermore, we place this information in a comprehensive overview of amino acid transport, signalling and metabolism.

AMP deamination is sufficient to replicate an atrophy-like metabolic phenotype in skeletal muscle

BACKGROUND

Skeletal muscle atrophy, whether caused by chronic disease, acute critical illness, disuse or aging, is characterized by tissue-specific decrease in oxidative capacity and broad alterations in metabolism that contribute to functional decline. However, the underlying mechanisms responsible for these metabolic changes are largely unknown. One of the most highly upregulated genes in atrophic muscle is AMP deaminase 3 (AMPD3: AMP → IMP + NH3), which controls the content of intracellular adenine nucleotides (AdN; ATP + ADP + AMP). Given the central role of AdN in signaling mitochondrial gene expression and directly regulating metabolism, we hypothesized that overexpressing AMPD3 in muscle cells would be sufficient to alter their metabolic phenotype similar to that of atrophic muscle.

METHODS

AMPD3 and GFP (control) were overexpressed in mouse tibialis anterior (TA) muscles via plasmid electroporation and in C2C12 myotubes using adenovirus vectors. TA muscles were excised one week later, and AdN were quantified by UPLC. In myotubes, targeted measures of AdN, AMPK/PGC-1α/mitochondrial protein synthesis rates, unbiased metabolomics, and transcriptomics by RNA sequencing were measured after 24 h of AMPD3 overexpression. Media metabolites were measured as an indicator of net metabolic flux. At 48 h, the AMPK/PGC-1α/mitochondrial protein synthesis rates, and myotube respiratory function/capacity were measured.

RESULTS

TA muscles overexpressing AMPD3 had significantly less ATP than contralateral controls (-25%). In myotubes, increasing AMPD3 expression for 24 h was sufficient to significantly decrease ATP concentrations (-16%), increase IMP, and increase efflux of IMP catabolites into the culture media, without decreasing the ATP/ADP or ATP/AMP ratios. When myotubes were treated with dinitrophenol (mitochondrial uncoupler), AMPD3 overexpression blunted decreases in ATP/ADP and ATP/AMP ratios but exacerbated AdN degradation. As such, pAMPK/AMPK, pACC/ACC, and phosphorylation of AMPK substrates, were unchanged by AMPD3 at this timepoint. AMPD3 significantly altered 191 out of 639 detected intracellular metabolites, but only 30 transcripts, none of which encoded metabolic enzymes. The most altered metabolites were those within purine nucleotide, BCAA, glycolysis, and ceramide metabolic pathways. After 48 h, AMPD3 overexpression significantly reduced pAMPK/AMPK (-24%), phosphorylation of AMPK substrates (-14%), and PGC-1α protein (-22%). Moreover, AMPD3 significantly reduced myotube mitochondrial protein synthesis rates (-55%), basal ATP synthase-dependent (-13%), and maximal uncoupled oxygen consumption (-15%).

CONCLUSIONS

Increased expression of AMPD3 significantly decreased mitochondrial protein synthesis rates and broadly altered cellular metabolites in a manner similar to that of atrophic muscle. Importantly, the changes in metabolites occurred prior to reductions in AMPK signaling, gene expression, and mitochondrial protein synthesis, suggesting metabolism is not dependent on reductions in oxidative capacity, but may be consequence of increased AMP deamination. Therefore, AMP deamination in skeletal muscle may be a mechanism that alters the metabolic phenotype of skeletal muscle during atrophy and could be a target to improve muscle function during muscle wasting.

Plasma glutamine status at intensive care unit admission: an independent risk factor for mortality in critical illness

Background

A plasma glutamine concentration outside the normal range at Intensive Care Unit (ICU) admission has been reported to be associated with an increased mortality rate. Whereas hypoglutaminemia has been frequently reported, the number of patients with hyperglutaminemia has so far been quite few. Therefore, the association between hyperglutaminemia and mortality outcomes was studied in a prospective, observational study.

Patients and methods

Consecutive admissions to a mixed general ICU were eligible. Exclusion criteria were < 18 years of age, readmissions, no informed consent, or a ‘do not resuscitate’ order at admission. A blood sample was saved within one hour from admission to be analysed by high-pressure liquid chromatography for glutamine concentration. Conventional risk scoring (Simplified Acute Physiology Score and Sequential Organ Failure Assessment) at admission, and mortality outcomes were recorded for all included patients.

Results

Out of 269 included patients, 26 were hyperglutaminemic (≥ 930 µmol/L) at admission. The six-month mortality rate for this subgroup was 46%, compared to 18% for patients with a plasma glutamine concentration < 930 µmol/L (P = 0.002). A regression analysis showed that hyperglutaminemia was an independent mortality predictor that added prediction value to conventional admission risk scoring and age.

Conclusion

Hyperglutaminemia in critical illness at ICU admission was an independent mortality predictor, often but not always, associated with an acute liver condition. The mechanism behind a plasma glutamine concentration outside normal range, as well as the prognostic value of repeated measurements of plasma glutamine during ICU stay, remains to be investigated.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03640-3.

Effects of dietary L-glutamine and glutamic acid combination, and whey powder on the performance and nutrient digestion in weaned piglets that received grain-based diets

Objective

The present study aimed to evaluate the influence of including L-glutamine along with glutamic acid as a supplement in weaned piglets’ diets with and without whey powder.

Methods

Two assays were carried out. A total of 40 piglets ([Landrace×Large White]× Pietrain) weaned at 24 days of age with an initial body weight of 6.6±0.6 kg were used in the first assay, and the following parameters were evaluated: growth performance, the incidence of diarrhea, morphometry, intestinal integrity, and hepatic glycogen index. The animals were then blocked into four groups according to different diets: diet all-grain feeding (G); diet all-grain feeding with whey powder (GW); and with vs without 1% supplementation of the commercial product containing L-glutamine and glutamic acid (A or NA). Whey powder was added according to the stage of life, corresponding to 17%, 10%, and 5%, respectively, in order to meet the need for lactose. The animals were evaluated at 24 to 42 days and at 24 to 55 days of age. The nutrient digestibility for the second assay was carried out by using 24 animals with an average weight of 11.49±1.6 kg, and the same diets were tested.

Results

The supplementation of L-glutamine + glutamic acid or the addition of whey powder in diets for weaned piglets provided (p<0.05) greater feed intake, greater weight gain and improved feed conversion in the initial period (24 to 42 days age). However, in the whole period (24 to 55 days age) only amino acid supplementation affected (p<0.05) growth performance. There was a positive interaction (p<0.05) between the type of diet and L-glutamine + glutamic acid supplementation on villus height, crypt depth and the villus:crypt ratio in the duodenum. In addition, L-glutamine + glutamic acid supplementation reduced (p<0.05) the crypt depth and improved the villus:crypt ratio in the jejunum. The inclusion of whey powder affected (p<0.05) positively the digestibility coefficients analyzed except mineral matter digestibility coeficients. The supplementation of 1% the commercial product composed of L-glutamine and glutamic acid improved (p<0.05) only the digestibility coefficient of crude protein.

Conclusion

These results indicate that supplementation of 1% commercial product containing L-glutamine + glutamic acid in diets for piglets from 24 to 55 days of age, dispenses with the use of whey powder when evaluating growth performance. Amino acid supplementation alone or associated with whey powder affects (p<0.05) positively the indicators of the intestinal integrity.

Sarcopenia discriminates poor prognosis in elderly patients following emergency surgery for perforation panperitonitis

AIM

Sarcopenia has been reported as a prognostic predictor in various conditions; however, it has not been examined in patients with perforation panperitonitis.

METHODS

A total of 103 consecutive patients with perforation panperitonitis who underwent emergency surgery from 2008 to 2016 were retrospectively evaluated. Skeletal muscle index (SMI) was measured as the cross-sectional area (cm2) of skeletal muscle in the L3 region on computed tomography images normalized for height (cm2/m2). Sarcopenia was defined as an SMI of ≤43.75 and ≤41.10 cm2/m2 in men and women, respectively. The impact of sarcopenia on postoperative outcomes was investigated.

RESULTS

Sarcopenia was present in 50 (48.5%) patients. Severe complications (Clavien-Dindo grade ≥IIIb) and in-hospital mortality were more frequently observed in patients with than without sarcopenia (28.0% vs 9.4%, P = .015) (20.0% vs 5.7%, P = .029) respectively. Multivariate analysis showed that age, sarcopenia, and renal dysfunction were independent risk factors for severe complications and in-hospital mortality. The optimal cut-off levels of age and SMI for predicting these were ≥79 years and SMI <38 cm2/m2, respectively. Among the patients aged ≥79 years, those with SMI <38 cm2/m2 had a severe complication rate of 71% and an in-hospital mortality rate of 57%, whereas the rate of those with SMI ≥38 cm2/m2 was 22% (P = .011) and 11% (P = .008), respectively.

CONCLUSION

Sarcopenia is a predictive factor of severe complications and in-hospital mortality following emergency surgery for perforation panperitonitis, especially in elderly patients. Estimation of sarcopenia may identify patients eligible or not eligible for emergency surgery among elderly patients.

Effects of Hypoxia and Bed Rest on Markers of Cardiometabolic Risk: Compensatory Changes in Circulating TRAIL and Glutathione Redox Capacity

In chronic diseases, hypoxia and physical inactivity are associated with atherosclerosis progression. In contrast, a lower mortality from coronary artery disease and stroke is observed in healthy humans residing at high altitude in hypoxic environments. Eleven young, male volunteers completed the following 10-day campaigns in a randomized order: hypoxic ambulatory, hypoxic bed rest and normoxic bed rest. Before intervention, subjects were evaluated in normoxic ambulatory condition. Normobaric hypoxia was achieved in a hypoxic facility simulating 4000 m of altitude. Following hypoxia, either in bed rest or ambulatory condition, markers of cardiometabolic risk shifted toward a more atherogenic pattern consisting of: (a) lower levels of total HDL cholesterol and HDL2 sub-fraction and decreased hepatic lipase; (b) activation of systemic inflammation, as determined by C-reactive protein and serum amyloid A; (c) increased plasma homocysteine; (d) decreased delta-5 desaturase index in cell membrane fatty acids, a marker of insulin sensitivity. Bed rest and hypoxia additively decreased total HDL and delta-5 desaturase index. In parallel to the pro-atherogenic effects, hypoxia activated selected anti-atherogenic pathways, consisting of increased circulating TNF-related apoptosis-inducing ligand (TRAIL), a protective factor against atherosclerosis, membrane omega-3 index and erythrocyte glutathione availability. Hypoxia mediated changes in TRAIL concentrations and redox glutathione capacity (i.e., GSH/GSSG ratio) were greater in ambulatory conditions (+34 ± 6% and +87 ± 31%, respectively) than in bed rest (+17 ± 7% and +2 ± 27% respectively). Hypoxia-induced cardiometabolic risk is blunted by moderate level of physical activity as compared to bed rest. TRAIL and glutathione redox capacity may contribute to the positive interaction between physical activity and hypoxia.

Highlights:

– Hypoxia and bed rest activate metabolic and inflammatory markers of atherogenesis.

– Hypoxia and physical activity activate selected anti-atherogenic pathways.

– Hypoxia and physical activity positive interaction involves TRAIL and glutathione.

TCA cycle rewiring fosters metabolic adaptation to oxygen restriction in skeletal muscle from rodents and humans

In mammals, hypoxic stress management is under the control of the Hypoxia Inducible Factors, whose activity depends on the stabilization of their labile α subunit. In particular, the skeletal muscle appears to be able to react to changes in substrates and O₂ delivery by tuning its metabolism. The present study provides a comprehensive overview of skeletal muscle metabolic adaptation to hypoxia in mice and in human subjects exposed for 7/9 and 19 days to high altitude levels. The investigation was carried out combining proteomics, qRT-PCR mRNA transcripts analysis, and enzyme activities assessment in rodents, and protein detection by antigen antibody reactions in humans and rodents. Results indicate that the skeletal muscle react to a decreased O₂ delivery by rewiring the TCA cycle. The first TCA rewiring occurs in mice in 2-day hypoxia and is mediated by cytosolic malate whereas in 10-day hypoxia the rewiring is mediated by Idh1 and Fasn, supported by glutamine and HIF-2α increments. The combination of these specific anaplerotic steps can support energy demand despite HIFs degradation. These results were confirmed in human subjects, demonstrating that the TCA double rewiring represents an essential factor for the maintenance of muscle homeostasis during adaptation to hypoxia.

Regulation of hepatic stellate cell proliferation and activation by glutamine metabolism

Liver fibrosis is the excessive accumulation of extracellular matrix proteins, which is mainly caused by accumulation of activated hepatic stellate cells (HSCs). The mechanisms of activation and proliferation of HSCs, two key events after liver damage, have been studied for many years. Here we report a novel pathway to control HSCs by regulating glutamine metabolism. We demonstrated that the proliferation of HSCs is critically dependent on glutamine that is used to generate α-ketoglutarate (α-KG) and non-essential amino acid (NEAA). In addition, both culture- and in vivo-activated HSCs have increased glutamine utilization and increased expression of genes related to glutamine metabolism, including GLS (glutaminase), aspartate transaminase (GOT1) and glutamate dehydrogenase (GLUD1). Inhibition of these enzymes, as well as glutamine depletion, had a significant inhibitory effect on HSCs activation. In addition to providing energy expenditure, conversion of glutamine to proline is enhanced. The pool of free proline may also be increased via downregulation of POX expression. Hedgehog signaling plays an important role in the regulation of glutamine metabolism, as well as TGF-β1, c-Myc, and Ras signalings, via transcriptional upregulation and repression of key metabolic enzymes in this pathway. Finally, changes in glutamine metabolism were also found in mouse liver tissue following CCl4-induced acute injury.

CONCLUSION

Glutamine metabolism plays an important role in regulating the proliferation and activation of HSCs. Strategies that are targeted at glutamine metabolism may represent a novel therapeutic approach to the treatment of liver fibrosis.

An update on the use of benzoate, phenylacetate and phenylbutyrate ammonia scavengers for interrogating and modifying liver nitrogen metabolism and its implications in urea cycle disorders and liver disease

INTRODUCTION

Ammonia-scavenging drugs, benzoate and phenylacetate (PA)/phenylbutyrate (PB), modulate hepatic nitrogen metabolism mainly by providing alternative pathways for nitrogen disposal. Areas covered: We review the major findings and potential novel applications of ammonia-scavenging drugs, focusing on urea cycle disorders and liver disease. Expert opinion: For over 40 years, ammonia-scavenging drugs have been used in the treatment of urea cycle disorders. Recently, the use of these compounds has been advocated in acute liver failure and cirrhosis for reducing hyperammonemic-induced hepatic encephalopathy. The efficacy and mechanisms underlying the antitumor effects of these ammonia-scavenging drugs in liver cancer are more controversial and are discussed in the review. Overall, as ammonia-scavenging drugs are usually safe and well tolerated among cancer patients, further studies should be instigated to explore the role of these drugs in liver cancer. Considering the relevance of glutamine metabolism to the progression and resolution of liver disease, we propose that ammonia-scavenging drugs might also be used to non-invasively probe liver glutamine metabolism in vivo. Finally, novel derivatives of classical ammonia-scavenging drugs with fewer and less severe adverse effects are currently being developed and used in clinical trials for the treatment of acute liver failure and cirrhosis.

Simultaneous Infusion of Glutamine and Branched-Chain Amino Acids (BCAA) to Septic Rats Does Not Have More Favorable Effect on Protein Synthesis in Muscle, Liver, and Small Intestine Than Separate Infusions

BACKGROUND

Glutamine and branched-chain amino acids (BCAA; valine, leucine, and isoleucine) are used as nutrition supplements in the treatment of proteocatabolic illness. We hypothesized that simultaneous administration of BCAA and glutamine affects protein metabolism more significantly than separate administration. In the present study, we evaluated their effect on protein synthesis in skeletal muscle, liver, and jejunum of septic rats.

METHODS

Twenty-four hours after induction of sepsis by subcutaneous injection of turpentine, the rats were infused for 6 hours with 5 mL of 1.75% glutamine, 1.75% BCAA, 1.75% glutamine+BCAA, or saline solution. The control group consisted of intact rats infused with saline. Protein synthesis was measured at the end of infusion by a "flooding method" with [3,4,5-(3)H]phenylalanine.

RESULTS

In turpentine-treated animals, we observed a decrease in glutamine concentration in blood plasma and skeletal muscle, a decrease in BCAA concentration in liver and jejunum, and a decrease in protein synthesis in all tissues. Glutamine or glutamine+BCAA infusion increased glutamine concentration in plasma and muscle and stimulated protein synthesis in the liver. The BCAA infusion enhanced concentrations of BCAA in plasma and tissues, but the effect of BCAA on protein synthesis was insignificant. Synergistic effect of simultaneous infusion of glutamine and BCAA on protein synthesis was not observed.

CONCLUSIONS

We conclude that glutamine infusion to rats with septic injury may significantly improve impaired protein synthesis in the liver and that there is no synergistic effect of glutamine and BCAA infusion on protein synthesis in skeletal muscle, liver, and jejunum.

Pivotal role of glutamine synthetase in ammonia detoxification

Glutamine synthetase (GS) catalyzes condensation of ammonia with glutamate to glutamine. Glutamine serves, with alanine, as a major nontoxic interorgan ammonia carrier. Elimination of hepatic GS expression in mice causes only mild hyperammonemia and hypoglutaminemia but a pronounced decrease in the whole-body muscle-to-fat ratio with increased myostatin expression in muscle. Using GS-knockout/liver and control mice and stepwise increments of enterally infused ammonia, we show that ∼35% of this ammonia is detoxified by hepatic GS and ∼35% by urea-cycle enzymes, while ∼30% is not cleared by the liver, independent of portal ammonia concentrations ≤2 mmol/L. Using both genetic (GS-knockout/liver and GS-knockout/muscle) and pharmacological (methionine sulfoximine and dexamethasone) approaches to modulate GS activity, we further show that detoxification of stepwise increments of intravenously (jugular vein) infused ammonia is almost totally dependent on GS activity. Maximal ammonia-detoxifying capacity through either the enteral or the intravenous route is ∼160 μmol/hour in control mice. Using stable isotopes, we show that disposal of glutamine-bound ammonia to urea (through mitochondrial glutaminase and carbamoylphosphate synthetase) depends on the rate of glutamine synthesis and increases from ∼7% in methionine sulfoximine-treated mice to ∼500% in dexamethasone-treated mice (control mice, 100%), without difference in total urea synthesis.

CONCLUSIONS

Hepatic GS contributes to both enteral and systemic ammonia detoxification. Glutamine synthesis in the periphery (including that in pericentral hepatocytes) and glutamine catabolism in (periportal) hepatocytes represents the high-affinity ammonia-detoxifying system of the body. The dependence of glutamine-bound ammonia disposal to urea on the rate of glutamine synthesis suggests that enhancing peripheral glutamine synthesis is a promising strategy to treat hyperammonemia. Because total urea synthesis does not depend on glutamine synthesis, we hypothesize that glutamate dehydrogenase complements mitochondrial ammonia production. (Hepatology 2017;65:281-293).

Glutamine dipeptide-supplemented parenteral nutrition improves the clinical outcomes of critically ill patients: A systematic evaluation of randomised controlled trials

BACKGROUND & AIMS

Early randomised controlled trials (RCTs) testing whether parenteral nutrition regimens that include glutamine dipeptides improves the outcomes of critically ill patients demonstrated convincingly that this regimen associates with reduced mortality, infections, and hospital stays. However, several new RCTs on the same question challenged this. To resolve this controversy, the present meta-analysis was performed. Stringent eligibility criteria were used to select only those RCTs that tested the outcomes of critically ill adult patients without hepatic and/or renal failure who were haemodynamically and metabolically stabilised and who were administered glutamine dipeptide strictly according to current clinical guidelines (via the parenteral route at 0.3-0.5 g/kg/day; max. 30% of the prescribed nitrogen supply) in combination with adequate nutrition.

METHODS

The literature research (PubMed, Embase, Cochrane Central Register of Controlled Trials) searched for English and German articles that had been published in peer-review journals (last entry March 31, 2015) and reported the results of RCTs in critically ill adult patients (major surgery, trauma, infection, or organ failure) who received parenteral glutamine dipeptide as part of an isoenergetic and isonitrogenous nutrition therapy. The following data were extracted: infectious complications, lengths of stay (LOS) in the hospital and intensive care unit (ICU), duration of mechanical ventilation, days on inotropic support, and ICU and hospital mortality rates. The selection of and data extraction from studies were performed by two independent reviewers.

RESULTS

Fifteen RCTs (16 publications) fulfilled all selection criteria. They involved 842 critically ill patients. None had renal and/or hepatic failure. The average study quality (Jadad score: 3.8 points) was well above the predefined cut-off of 3.0. Common effect estimates indicated that parenteral glutamine dipeptide supplementation significantly reduced infectious complications (relative risk [RR] = 0.70, 95% CI 0.60, 0.83, p < 0.0001), ICU LOS (common mean difference [MD] -1.61 days, 95% CI -3.17, -0.05, p = 0.04), hospital LOS (MD -2.30 days, 95% CI -4.14, -0.45, p = 0.01), and mechanical ventilation duration (MD -1.56 days, 95% CI -2.88, -0.24, p = 0.02). It also lowered the hospital mortality rate by 45% (RR = 0.55, 95% CI 0.32, 0.94, p = 0.03) but had no effect on ICU mortality. Visual inspection of funnel plots did not reveal any potential selective reporting of studies.

CONCLUSIONS

This meta-analysis clearly confirms that when critically ill patients are supplemented with parenteral glutamine dipeptide according to clinical guidelines as part of a balanced nutrition regimen, it significantly reduces hospital mortality, infectious complication rates, and hospital LOS. The latter two effects indicate that glutamine dipeptide supplementation also confers economic benefits in this setting. The present analysis indicates the importance of delivering glutamine dipeptides together with adequate parenteral energy and nitrogen so that the administered glutamine serves as precursor in various biosynthetic pathways rather than simply as a fuel.

Glutamine metabolism in advanced age

Glutamine, reviewed extensively in the last century, is a key substrate for the splanchnic bed in the whole body and is a nutrient of particular interest in gastrointestinal research. A marked decrease in the plasma glutamine concentration has recently been observed in neonates and adults during acute illness and stress. Although some studies in newborns have shown parenteral and enteral supplementation with glutamine to be of benefit (by decreasing proteolysis and activating the immune system), clinical trials have not demonstrated prolonged advantages such as reductions in mortality or risk of infections in adults. In addition, glutamine is not able to combat the muscle wasting associated with disease or age-related sarcopenia. Oral glutamine supplementation initiated before advanced age in rats increases gut mass and improves the villus height of mucosa, thereby preventing the gut atrophy encountered in advanced age. Enterocytes from very old rats continuously metabolize glutamine into citrulline, which allowed, for the first time, the use of citrulline as a noninvasive marker of intestinal atrophy induced by advanced age.

Oncogenic Myc Induces Expression of Glutamine Synthetase through Promoter Demethylation

c-Myc is known to promote glutamine usage by upregulating glutaminase (GLS), which converts glutamine to glutamate that is catabolized in the TCA cycle. Here we report that in a number of human and murine cells and cancers, Myc induces elevated expression of glutamate-ammonia ligase (GLUL), also termed glutamine synthetase (GS), which catalyzes the de novo synthesis of glutamine from glutamate and ammonia. This is through upregulation of a Myc transcriptional target thymine DNA glycosylase (TDG), which promotes active demethylation of the GS promoter and its increased expression. Elevated expression of GS promotes cell survival under glutamine limitation, while silencing of GS decreases cell proliferation and xenograft tumor growth. Upon GS overexpression, increased glutamine enhances nucleotide synthesis and amino acid transport. These results demonstrate an unexpected role of Myc in inducing glutamine synthesis and suggest a molecular connection between DNA demethylation and glutamine metabolism in Myc-driven cancers.

Skeletal Muscle Depletion Predicts the Prognosis of Patients with Advanced Pancreatic Cancer Undergoing Palliative Chemotherapy, Independent of Body Mass Index

Introduction

Body composition has emerged as a prognostic factor in cancer patients. We investigated whether sarcopenia at diagnosis and loss of skeletal muscle during palliative chemotherapy were associated with survival in patients with pancreatic cancer.

Methods

We retrospectively reviewed the clinical outcomes of pancreatic cancer patients receiving palliative chemotherapy between 2003 and 2010. The cross-sectional area of skeletal muscle at L3 by computed tomography was analyzed with Rapidia 3D software. We defined sarcopenia as a skeletal muscle index (SMI)< 42.2 cm²/m² (male) and < 33.9 cm²/m² (female) using ROC curve.

Results

Among 484 patients, 103 (21.3%) patients were sarcopenic at diagnosis. Decrease in SMI during chemotherapy was observed in 156 (60.9%) male and 65 (40.6%) female patients. Decrease in body mass index (BMI) was observed in 149 patients (37.3%), with no gender difference. By multivariate analysis, sarcopenia (P< 0.001), decreasedBMI and SMI during chemotherapy (P = 0.002, P = 0.004, respectively) were poor prognostic factors for overall survival (OS). While the OS of male patients was affected with sarcopenia (P< 0.001) and decreased SMI (P = 0.001), the OS of female patients was influenced with overweight at diagnosis (P = 0.006), decreased BMI (P = 0.032) and decreased SMI (P = 0.014). Particularly, while the change of BMI during chemotherapy did not have impact on OS within the patients with maintained SMI (P = 0.750), decrease in SMI was associated with poor OS within the patients with maintained BMI (HR 1.502; P = 0.002).

Conclusions

Sarcopenia at diagnosis and depletion of skeletal muscle, independent of BMI change, during chemotherapy were poor prognostic factors in advanced pancreatic cancer.

Glutamine: an obligatory parenteral nutrition substrate in critical care therapy

Critical illness is characterized by glutamine depletion owing to increased metabolic demand. Glutamine is essential to maintain intestinal integrity and function, sustain immunologic response, and maintain antioxidative balance. Insufficient endogenous availability of glutamine may impair outcome in critically ill patients. Consequently, glutamine has been considered to be a conditionally essential amino acid and a necessary component to complete any parenteral nutrition regimen. Recently, this scientifically sound recommendation has been questioned, primarily based on controversial findings from a large multicentre study published in 2013 that evoked considerable uncertainty among clinicians. The present review was conceived to clarify the most important questions surrounding glutamine supplementation in critical care. This was achieved by addressing the role of glutamine in the pathophysiology of critical illness, summarizing recent clinical studies in patients receiving parenteral nutrition with intravenous glutamine, and describing practical concepts for providing parenteral glutamine in critical care.

Improving rehabilitation after critical illness through outpatient physiotherapy classes and essential amino acid supplement: A randomized controlled trial

PURPOSE

Patients recovering from critical illness may be left with significant muscle mass loss. This study aimed to evaluate whether a 6-week program of enhanced physiotherapy and structured exercise (PEPSE) and an essential amino acid supplement drink (glutamine and essential amino acid mixture [GEAA]) improves physical and psychological recovery.

MATERIALS AND METHODS

Intensive care patients aged 45 years or older, with a combined intensive care unit stay/pre-intensive care unit stay of 5 days or more were recruited to a randomized controlled trial examining the effect of PEPSE and GEAA on recovery. The 2 factors were tested in a 2 × 2 factorial design: (1) GEAA drink twice daily for 3 months and (2) 6-week PEPSE in first 3 months. Primary efficacy outcome was an improvement in the 6-minute walking test at 3 months.

RESULTS

A total of 93 patients were randomized to the study. Patients receiving the PEPSE and GEA had the biggest gains in distance walked in 6-minute walking test (P < .0001). There were also significant reductions in rates of anxiety in study groups control supplement/PEPSE (P = .047) and GEAA supplement/PEPSE (P = .036) and for GEAA supplement/PEPSE in depression (P = .0009).

CONCLUSION

Enhanced rehabilitation combined with GEAA supplement may enhance physical recovery and reduce anxiety and depression.

Activity of MMP1 and MMP13 and amino acid metabolism in patients with alcoholic liver cirrhosis

Background

Alcoholic liver disease remains one of the most common causes of chronic liver disease worldwide.

The aim of this study was to assess the usefulness of metalloproteinases (MMP1 and MMP13) as diagnostic markers of alcoholic liver disease and to determine the changes in free amino acid profile in the patients with alcoholic liver cirrhosis.

Material/Methods

Sixty patients with alcoholic liver cirrhosis treated in various hospitals of the Lublin region were randomly enrolled. The control group consisted of 10 healthy individuals without liver disease, who did not drink alcohol. Additionally, a group of alcoholics (22 persons) without liver cirrhosis was included in the study. The activity of MMP-1 and MMP-13 in blood plasma of patients and controls was measured using the sandwich enzyme immunoassay technique with commercially available quantitative ELISA test kits. Amino acids were determined by automated ion-exchange chromatography.

Results

No significant differences were observed in the activity of MMP-1 in alcoholics with or without liver cirrhosis or in controls. Increased serum MMP-13 was found in patients with liver cirrhosis (stage A, B, C) compared to the control group. Patients with alcoholic liver cirrhosis (stage A, B, C) demonstrated reduced concentrations of glutamic acid and glutamine compared to the control group. Plasma levels of valine, isoleucine, leucine, and tryptophan were significantly lower in patients with alcoholic liver cirrhosis (stage C) than in controls.

Conclusions

MMP-13 can be useful to confirm the diagnosis of alcoholic liver cirrhosis, but levels of MMP-1 are not significantly increased in patients with liver cirrhosis compared to controls. The serum branched-chain amino acid (BCAA) is markedly reduced in patients with stage C alcoholic liver cirrhosis.

Sarcopenia is a prognostic factor in living donor liver transplantation

The aims of this study were to investigate sarcopenia as a novel predictor of mortality and sepsis after living donor liver transplantation (LDLT) and to evaluate the effects of early enteral nutrition on patients with sarcopenia. Two hundred four patients undergoing preoperative computed tomography within the month before LDLT were retrospectively evaluated. The lengths of the major and minor axes of the psoas muscle were simply measured at the caudal end of the third lumbar vertebra, and the area of the psoas muscle was calculated. A psoas muscle area lower than the 5th percentile for healthy donors of each sex was defined as sarcopenia. Ninety-six of the 204 patients (47.1%), including 58.3% (60/103) of the male patients and 35.6% (36/101) of the female patients, were diagnosed with sarcopenia. Sarcopenia was independently and significantly associated with overall survival: there was an approximately 2-fold higher risk of death for patients with sarcopenia versus patients without sarcopenia (hazard ratio = 2.06, P = 0.047). Sarcopenia was an independent predictor of postoperative sepsis (hazard ratio = 5.31, P = 0.009). Other independent predictors were a younger recipient age (P < 0.001) and a higher body mass index (P = 0.02). Early enteral nutrition within the first 48 hours after LDLT was performed for 24.2% in 2003-2007 and for 100% in 2008-2011, and the incidence of postoperative sepsis for patients with sarcopenia (n = 96) was 28.2% (11/39) in 2003-2007 and 10.5% (6/57) in 2008-2011 (P = 0.03). In conclusion, sarcopenia is an independent predictor of mortality and sepsis after LDLT. The incidence of postoperative sepsis was reduced even in patients with sarcopenia after the routine application of early enteral nutrition.

Antioxidant strategies in neurocritical care

An increase in oxidative stress and overproduction of oxidizing reactive species plays an important role in the pathophysiology of several conditions encountered in the neurocritical care setting including: ischemic and hemorrhagic strokes, traumatic brain injury, acute respiratory distress syndrome, sepsis, and organ failure. The presence of oxidative stress in these conditions is supported by a large body of pre-clinical and clinical studies, and provides a rationale to support a potential therapeutic role for antioxidants. The purpose of this article is to briefly review the basic mechanisms and molecular biology of oxidative stress, summarize its role in critically ill neurological patients, and review available data regarding the potential role of antioxidant strategies in neurocritical care and future directions.

Assessment of Small Bowel Function in Critical Illness: Potential Role of Citrulline Metabolism

Small intestinal function in critically ill patients should ideally be assessed in order to determine the preferred feeding route, timing, and composition of enteral nutrition. Additionally, evaluation of small bowel function may lead to new insights aimed to maintain enterocyte integrity. Critically ill patients are likely to have impaired enterocyte function mainly as a consequence of diminished splanchnic blood flow associated with mucosal hyperpermeability and bacterial translocation, a pathological state believed to be pivotal in the development of sepsis and multiple organ dysfunction syndrome (MODS). However, feasible and validated clinical tools to reliably assess enterocyte function are lacking. This explorative review discusses the promising role of citrulline, a nonprotein amino acid almost exclusively generated by the enterocyte, as a biomarker reflecting enterocyte function in critically ill patients. Citrulline metabolism, its potential as enterocyte biomarker, and literature on citrulline in critically illness will be discussed. Finally, a novel test for enterocyte function, the citrulline generation test (enterocytic citrulline production upon stimulation with enteral or intravenous glutamine) will be considered briefly.

Glutamine depletion induces murine neonatal melena with increased apoptosis of the intestinal epithelium

AIM: To investigate the possible biological outcome and effect of glutamine depletion in neonatal mice and rodent intestinal epithelial cells.

METHODS: We developed three kinds of artificial milk with different amounts of glutamine; Complete amino acid milk (CAM), which is based on maternal mouse milk, glutamine-depleted milk (GDM), and glutamine-rich milk (GRM). GRM contains three-fold more glutamine than CAM. Eighty-seven newborn mice were divided into three groups and were fed with either of CAM, GDM, or GRM via a recently improved nipple-bottle system for seven days. After the feeding period, the mice were subjected to macroscopic and microscopic observations by immunohistochemistry for 5-bromo-2’-deoxyuridine (BrdU) and Ki-67 as markers of cell proliferation, and for cleaved-caspase-3 as a marker of apoptosis. Moreover, IEC6 rat intestinal epithelial cells were cultured in different concentrations of glutamine and were subject to a 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate cell proliferation assay, flow cytometry, and western blotting to examine the biological effect of glutamine on cell growth and apoptosis.

RESULTS: During the feeding period, we found colonic hemorrhage in six of 28 GDM-fed mice (21.4%), but not in the GRM-fed mice, with no differences in body weight gain between each group. Microscopic examination showed destruction of microvilli and the disappearance of glycocalyx of the intestinal wall in the colon epithelial tissues taken from GDM-fed mice. Intake of GDM reduced BrdU incorporation (the average percentage of BrdU-positive staining; GRM: 13.8%, CAM: 10.7%, GDM: 1.14%, GRM vs GDM: P < 0.001, CAM vs GDM: P < 0.001) and Ki-67 labeling index (the average percentage of Ki-67-positive staining; GRM: 24.5%, CAM: 22.4% GDM: 19.4%, GRM vs GDM: P = 0.001, CAM vs GDM: P = 0.049), suggesting that glutamine depletion inhibited cell proliferation of intestinal epithelial cells. Glutamine deprivation further caused the deformation of the nuclear membrane and the plasma membrane, accompanied by chromatin degeneration and an absence of fat droplets from the colonic epithelia, indicating that the cells underwent apoptosis. Moreover, immunohistochemical analysis revealed the appearance of cleaved caspase-3 in colonic epithelial cells of GDM-fed mice. Finally, when IEC6 rat intestinal epithelial cells were cultured without glutamine, cell proliferation was significantly suppressed after 24 h (relative cell growth; 4 mmol/L: 100.0% ± 36.1%, 0 mmol/L: 25.3% ± 25.0%, P < 0.05), with severe cellular damage. The cells underwent apoptosis, accompanied by increased cell population in sub-G0 phase (4 mmol/L: 1.68%, 0.4 mmol/L: 1.35%, 0 mmol/L: 5.21%), where dying cells are supposed to accumulate.

CONCLUSION: Glutamine is an important alimentary component for the maintenance of intestinal mucosa. Glutamine deprivation can cause instability of the intestinal epithelial alignment by increased apoptosis.

Glutamine synthetase in muscle is required for glutamine production during fasting and extrahepatic ammonia detoxification

The main endogenous source of glutamine is de novo synthesis in striated muscle via the enzyme glutamine synthetase (GS). The mice in which GS is selectively but completely eliminated from striated muscle with the Cre-loxP strategy (GS-KO/M mice) are, nevertheless, healthy and fertile. Compared with controls, the circulating concentration and net production of glutamine across the hindquarter were not different in fed GS-KO/M mice. Only a approximately 3-fold higher escape of ammonia revealed the absence of GS in muscle. However, after 20 h of fasting, GS-KO/M mice were not able to mount the approximately 4-fold increase in glutamine production across the hindquarter that was observed in control mice. Instead, muscle ammonia production was approximately 5-fold higher than in control mice. The fasting-induced metabolic changes were transient and had returned to fed levels at 36 h of fasting. Glucose consumption and lactate and ketone-body production were similar in GS-KO/M and control mice. Challenging GS-KO/M and control mice with intravenous ammonia in stepwise increments revealed that normal muscle can detoxify approximately 2.5 micromol ammonia/g muscle.h in a muscle GS-dependent manner, with simultaneous accumulation of urea, whereas GS-KO/M mice responded with accumulation of glutamine and other amino acids but not urea. These findings demonstrate that GS in muscle is dispensable in fed mice but plays a key role in mounting the adaptive response to fasting by transiently facilitating the production of glutamine. Furthermore, muscle GS contributes to ammonia detoxification and urea synthesis. These functions are apparently not vital as long as other organs function normally.

Relationship among plasma amino acids, C-reactive protein, illness severity, and outcome in critically ill dogs

BACKGROUND

Alterations in circulating amino acids have been documented in animal models and in critically ill people but have not been evaluated in dogs with spontaneously occurring disease.

HYPOTHESIS/OBJECTIVES

To compare amino acid concentrations in critically ill dogs and healthy controls and to investigate potential relationships among amino acids, markers of inflammation, illness severity, and clinical outcome.

ANIMALS

Forty-eight critically ill dogs and 24 healthy control dogs.

METHODS

Plasma was analyzed for amino acids and C-reactive protein (CRP) was measured in serum. The Fischer ratio (the molar ratio of branched chain amino acids [BCAA] to aromatic amino acids [AAA]) and survival prediction index (SPI2) were calculated.

RESULTS

Median CRP concentrations were significantly higher in the critically ill dogs compared with controls (P < .001). Critically ill dogs had significantly lower concentrations of alanine (P= .001), arginine (P < .001), citrulline (P < .001), glycine (P < .001), methionine (P < .001), proline (P < .001), and serine (P= .001) but significantly higher concentrations of lysine (P= .02) and phenylalanine (P < .001; Table 1). This pattern resulted in a significantly lower Fischer ratio (P= .001) in the critically ill group. Median SPI2 score was significantly higher in dogs that survived (P= .03). Concentrations of arginine (P= .02), isoleucine (P= .01), leucine (P= .04), serine (P= .04), valine (P= .04), total BCAA (P= .03), and the Fischer ratio (P= .03) were significantly higher in survivors compared with nonsurvivors.

CONCLUSIONS AND CLINICAL IMPORTANCE

Critically ill dogs have altered amino acid profiles and additional research to investigate potential benefits of amino acid supplementation is warranted.

Glutamine metabolism and function in relation to proline synthesis and the safety of glutamine and proline supplementation

At normal intakes, dietary glutamine and glutamate are metabolized by the small intestine and essentially all glutamine within the body is synthesized de novo through the action of glutamine synthetase. The major sites of net glutamine synthesis are skeletal muscle, lung, and adipose tissue and, under some conditions, the liver. In addition to the small intestine, where glutamine is the major respiratory fuel, other sites of net glutamine utilization include the cells of the immune system, the kidneys, and the liver. The intestine expresses pyrroline 5-carboxylate (P5C) synthase, which means that proline is an end product of intestinal glutamine catabolism. Proline can also be synthesized from ornithine and the exact contribution of the 2 pathways is not certain. Infusion of proline i.v. to increase circulating concentrations is associated with increased proline oxidation and decreased proline synthesis. In contrast, conditions of proline insufficiency, after feeding low-proline diets or in response to high rates of proline catabolism in burn patients, do not result in increased proline synthesis. Glutamine supplementation is widespread and up to 0.57-0.75 g.kg(-1).d(-1) is well tolerated. Similarly, the only study of proline supplementation, in which patients with gyrate atrophy were given 488 mg.kg(-1).d(-1), reported no deleterious side effects. In the absence of controlled trials, it is currently not possible to estimate a safe upper limit for either of these 2 amino acids.

Glutamine deprivation causes enhanced plating efficiency of a herpes simplex virus type 1 ICP0-null mutant

Isoleucine deprivation of cellular monolayers prior to infection has been reported to result in partial complementation of a herpes simplex virus type 1 (HSV-1) ICP0 null (ICP0(-)) mutant. We now report that glutamine deprivation alone is able to enhance the plating efficiency of an ICP0(-) virus and that isoleucine deprivation has little or no effect. Because a low glutamine level is associated with stress and because stress is known to induce reactivation, low levels of glutamine may be relevant to the reactivation of HSV-1 from latency. Additionally, we demonstrate that arginine and methionine deprivation result in partial complementation of the ICP0(-) virus.

Physical inactivity decreases whole body glutamine turnover independently from changes in proteolysis

Glutamine synthesis and utilization are strictly linked to energy metabolism and physical activity. To investigate the interaction between bed rest and moderate energy restriction on whole body glutamine kinetics in healthy volunteers, we performed a four-period study in which each subject randomly underwent a bed rest or ambulatory 14 day period both in eucaloric or hypocaloric (-20% of energy requirement) conditions. Glutamine kinetics were measured by l-[5-(15)N]glutamine and l-[1-(13)C]leucine primed continuous infusions in the postabsorptive state and during a 3 h infusion of a glutamine-free amino acid mixture (0.13 g amino acids (kg lean body mass (LBM))(-1) h(-1)). Bed rest decreased glutamine de novo synthesis in the postabsorptive state both in eucaloric (from 4.17 +/- 0.14 to 3.56 +/- 0.13 micromol (kg LBM)(-1) min(-1); P < 0.001) and in hypocaloric (from 3.79 +/- 0.19 to 3.49 +/- 0.14 micromol (kg LBM)(-1) min(-1); P < 0.001) conditions, independently of changes in whole body proteolysis. Bed rest did not affect glutamine clearance. We failed to detect either significant effects of energy intake or energy x activity interactions on glutamine kinetics. Bed rest significantly decreased postabsorptive plasma glutamine concentrations (P < 0.05). Amino acid infusion increased glutamine de novo synthesis rate and plasma glutamine concentrations in all conditions, without significant effects of bed rest or energy levels. We conclude that inactivity is associated with decreased whole body glutamine availability due to down-regulated de novo synthesis.

Does long-term intermittent treatment with glutamine improve the well-being of fed and fasted very old rats?

BACKGROUND

Glutamine is known to have a specific role in very old rats (>25 months of age). For this reason, we have orally supplemented female rats with glutamine (20% of diet protein) intermittently. The treatment started before animals became very old and lasted 5 months. Very old rats were studied in fed state or after 5-day fasting after the last glutamine cure. The aim of this study was to determine whether this in vivo pretreatment improves the well-being of very old rats (muscle sarcopenia decrease, gut integrity improvement, decrease of the known up-regulated glutamine synthetase observed regardless of nutrition state).

METHODS

Protein turnover was measured in epitrochlearis muscle, whereas glutamine synthetase (GS) activities were assessed in tibialis anterior muscle from fed and 5-days-fasted female Wistar adult (6 months) and very old (27 months) rats, pretreated or not with glutamine. Furthermore, gut was dissected and weighed.

RESULTS

Long-term treatment with glutamine had positive effects on very old rats: (1) it prevented the loss of body weight, but, (2) it did not prevent the inevitable sarcopenia regardless of nutrition state, and (3) it maintained the gut mass. Surprisingly, the muscle up-regulated GS activity observed in fed and fasted very old rats was only decreased in the fed state when rats were supplemented, without change in plasma and muscle glutamine concentrations.

CONCLUSIONS

Long-term treatment with glutamine started before advanced age had essentially a beneficial role on the gut. It may play a role in maintaining intestine integrity and intestinal immune function. Further investigations would be warranted to explore these mechanisms.

Nutrition and Polymyositis and Dermatomyositis

• Chronic muscle inflammation in polymyositis or dermatomyositis causes muscle weakness and fatigue.

• The chronic inflammation could lead to a catabolic state and additional loss of muscle mass.

• The chronic muscle inflammation could induce a metabolic myopathy.

• Body weight may not be reliable to measure muscle loss, rather measurement of body composition is recommended.

•For patients with polymyositis or dermatomyositis it is important to provide the body with the right amount of macronutrients and trace elements for maintenance and improvement of body functions.

• One recommendation is supplementation with calcium and vitamin D.

• Another recommendation is regular physical exercise that during limited periods can be combined with supplements such as creatine, if done under the care of a physician.

Exogenous glutamine: The clinical evidence

We know that critically ill patients suffering from undernutrition with a limited nutritional reserve have a poorer outcome. Furthermore, having a low body mass index has been shown to be an independent predictor of excess mortality in multiple organ failure. Therefore, nutritional support has gained increasing interest in critical illness with the hope of preventing or attenuating the effects of malnutrition. A negative nitrogen balance is the characteristic metabolic feature in critical illness, with the major protein loss derived from skeletal muscle. In particular, glutamine concentrations are rapidly reduced in plasma and muscle. Over the last 20 yrs or so, increasing evidence is emerging to support the use of glutamine supplementation in critical illness. Clinical trials have found a mortality and morbidity advantage with glutamine supplementation. The advantage appears to be greater the more glutamine is given and greater again when given parenterally. Various modes of action have been postulated. Glutamine seems to have an effect on the immune system, antioxidant status, glucose metabolism, and heat shock protein response. However, the benefit of exogenous glutamine on morbidity and mortality is not universally accepted. This review critically appraises the current clinical evidence regarding glutamine supplementation in critical illness.

Does glutamine supplementation decrease the response of muscle glutamine synthesis to fasting in muscle in adult and very old rats?

BACKGROUND

Glutamine synthetase (GS), a key enzyme in the production of glutamine, is preserved in rat skeletal muscle during aging but is increased with advanced age in vivo. The aim of this study was to determine whether glutamine supplementation affects up-regulation of GS by fasting in vivo in adult and very old female rats.

METHODS

Muscle GS activities were assessed in 5-day-fasted female Wistar adult (6 months) and very old (27 months) rats refed and supplemented with glutamine or other amino acids (alanine or glycine). Fed rats were used to investigate the possible effect of glutamine supplementation in the fed state.

RESULTS

After 5 days' fasting, the up-regulated GS activity was decreased whatever the type of amino acid supplementation (glutamine, alanine, and glycine) in adults, whereas it was only decreased by glutamine supplementation in very old rats). In the fed state, no effect of glutamine supplementation was observed even if GS activity remained up-regulated whatever the age and the period of supplementation.

CONCLUSIONS

These results confirm that glutamine has a specific role in very old rats. The up-regulated GS activity was decreased by an exogenous supply of glutamine only if intramuscular glutamine was depleted; this was confirmed by studies in the fed state. The up-regulated GS activity in both fed and fasted rats may be associated with increased glutamine requirements in the whole body.

Alterations in glutamine synthetase activity in rat skeletal muscle are associated with advanced age

OBJECTIVE

Glutamine synthetase (GS), a key enzyme in the production of glutamine, is preserved in skeletal muscle during early aging (<24 mo). Because the effects of advanced age on GS are unknown, we investigated the effect of advanced age (>24 mo) on GS activity in skeletal muscle. We hypothesized that advanced age would enhance muscle GS activity.

METHODS

Muscle GS activities were assessed in adult (8 mo), mature adult (15 mo), aged (20-22 mo), advanced age (25-27 mo), or very advanced age (29-32 mo) female Wistar rats. Male Wistar (6-27 mo) were used to investigate the effect of gender on this activity.

RESULTS

Glutamine synthetase activity remained low and unaltered in rats from 8 to 22 mo of age, as previously demonstrated. In contrast, GS activity was high ( approximately 75% of individual values were higher than the low value mean) in 25-mo to 27-mo-old rats. In very-old-aged rats (29-32 mo), approximately 55% of GS activity data points exhibited low values. Changes in GS protein content paralleled those in GS activities. In male rats, GS activity was also high ( approximately 80% of individual values were higher than the mean value of 6-mo to 19-mo-old rats) at the upper limit of life expectancy (27 mo).

CONCLUSION

There is enhanced GS activity in old female and male rats suggesting a greater need for glutamine. In some very old rats, low GS activity may be associated with longevity or reflect a limitation in glutamine production due to extremely advanced age per se.

The effect of glutamine-supplemented total parenteral nutrition on nutrition and intestinal absorptive function in a rat model

The aim of the present study was to evaluate the effect of short-term (7 days) glycyl-glutamine-supplemented total parenteral nutrition (TPN) on nutrition and intestinal absorptive function in a rat model. Thirty Wistar rats, weighting 140-180 g, were divided into three groups (n=10) randomly. The animals received isonitrogenous and isocaloric TPN solutions for 7 days. The nitrogen was supplied by glycyl-glutamine dipeptide-supplemented amino acid solution (group G), and two standard amino acid solutions (group V, group N), respectively. Body weight, plasma glutamine level, nitrogen balance, total tissue water and intestinal absorptive function, assessed by (15-N)-glycine absorption, were investigated. Body weight decreased in three groups at the end of TPN; there was no significant difference in relative body-weight changes. There was a significant improvement of cumulative nitrogen balance and nitrogen retention in group G compared to other groups (P<0.05). There was no significant difference in intestinal glycine absorption (P>0.05) among the three groups. Total tissue water of left thigh muscle was significantly higher in group V and group N than that in group G (P<0.05). The results indicated that short-term (7 days) TPN supplemented with glycyl-glutamine improved plasma glutamine level and nitrogen balance, decreased water content of muscle, but had no beneficial effect on absorptive function in a rat model.