The metabolic consequences of critical illness: acute effects on glutamine and protein metabolism

Metabolic Response in Endothelial Cells to Catecholamine Stimulation Associated with Increased Vascular Permeability

Disruption to endothelial cell homeostasis results in an extensive variety of human pathologies that are particularly relevant to major trauma. Circulating catecholamines, such as adrenaline and noradrenaline, activate endothelial adrenergic receptors triggering a potent response in endothelial function. The regulation of the endothelial cell metabolism is distinct and profoundly important to endothelium homeostasis. However, a precise catalogue of the metabolic alterations caused by sustained high catecholamine levels that results in endothelial dysfunction is still underexplored. Here, we uncover a set of up to 46 metabolites that exhibit a dose–response relationship to adrenaline-noradrenaline equimolar treatment. The identified metabolites align with the glutathione-ascorbate cycle and the nitric oxide biosynthesis pathway. Certain key metabolites, such as arginine and reduced glutathione, displayed a differential response to treatment in early (4 h) compared to late (24 h) stages of sustained stimulation, indicative of homeostatic metabolic feedback loops. Furthermore, we quantified an increase in the glucose consumption and aerobic respiration in endothelial cells upon catecholamine stimulation. Our results indicate that oxidative stress and nitric oxide metabolic pathways are downstream consequences of endothelial cell stimulation with sustained high levels of catecholamines. A precise understanding of the metabolic response in endothelial cells to pathological levels of catecholamines will facilitate the identification of more efficient clinical interventions in trauma patients.

Diagnostic Value of 1H NMR-Based Metabolomics in Acute Lymphoblastic Leukemia, Acute Myeloid Leukemia, and Breast Cancer

Cancer refers to a massive number of diseases distinguished by the development of abnormal cells that divide uncontrollably and have the capability of infiltration and destroying the normal body tissue. It is critical to detect biomarkers that are early detectable and noninvasive to save millions of lives. The aim of the present work is to use NMR as a noninvasive diagnostic tool for cancer diseases. This study included 30 plasma and 21 urine samples of patients diagnosed with acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML), 25 plasma and 17 urine samples of patients diagnosed with breast cancer (BC), and 9 plasma and urine samples obtained from healthy individuals as controls. They were prepared for NMR measurements; then, the metabolites were identified and the data were analyzed using multivariate statistical procedures. The OPLS-DA score plots clearly discriminated ALL, AML, and BC from healthy controls. Plots of the PLS-DA loadings and S-line plots showed that all metabolites in plasma were greater in BC than in the healthy controls, whereas lactate, O-acetylcarnitine, pyruvate, trimethylamine-N-oxide (TMAO), and glucose were higher in healthy controls than in ALL and AML. On the other hand, urine samples showed lower amounts of lactate, melatonin, pyruvate, and succinate in all of the studied types of cancer when compared to those of healthy controls. 1H NMR can be a successful and noninvasive tool for the diagnosis of different types of cancer.

Could Exogenous Insulin Ameliorate the Metabolic Dysfunction Induced by Glucocorticoids and COVID-19?

The finding that high-dose dexamethasone improves survival in those requiring critical care due to COVID-19 will mean much greater usage of glucocorticoids in the subsequent waves of coronavirus infection. Furthermore, the consistent finding of adverse outcomes from COVID-19 in individuals with obesity, hypertension and diabetes has focussed attention on the metabolic dysfunction that may arise with critical illness. The SARS coronavirus itself may promote relative insulin deficiency, ketogenesis and hyperglycaemia in susceptible individuals. In conjunction with prolonged critical care, these components will promote a catabolic state. Insulin infusion is the mainstay of therapy for treatment of hyperglycaemia in acute illness but what is the effect of insulin on the admixture of glucocorticoids and COVID-19? This article reviews the evidence for the effect of insulin on clinical outcomes and intermediary metabolism in critical illness.

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.

Rapid sensing of clinically relevant glutamine concentrations in human serum with metabolically engineered E. coli-based cell-free protein synthesis

Bioavailable glutamine (Gln) is critical for metabolism, intestinal health, immune function, and cell signaling. Routine measurement of serum Gln concentrations could facilitate improved diagnosis and treatment of severe infections, anorexia nervosa, chronic kidney disease, diabetes, and cancer. Current methods for quantifying tissue Gln concentrations rely mainly on HPLC, which requires extensive sample preparation and expensive equipment. Consequently, patient Gln levels may be clinically underutilized. Cell-free protein synthesis (CFPS) is an emerging sensing platform with promising clinical applications, including detection of hormones, amino acids, nucleic acids, and other biomarkers. In this work, in vitro E. coli amino acid metabolism is engineered with methionine sulfoximine to inhibit glutamine synthetase and create a CFPS Gln sensor. The sensor features a strong signal-to-noise ratio and a detection range ideally suited to physiological Gln concentrations. Furthermore, it quantifies Gln concentration in the presence of human serum. This work demonstrates that CFPS reactions which harness the metabolic power of E. coli lysate may be engineered to detect clinically relevant analytes in human samples. This approach could lead to transformative point-of-care diagnostics and improved treatment regimens for a variety of diseases including cancer, diabetes, anorexia nervosa, chronic kidney disease, and severe infections.

Alterations in serum amino-acid profile in the progression of colorectal cancer: associations with systemic inflammation, tumour stage and patient survival

BACKGROUND

Cancer cachexia is a complex wasting syndrome affecting patients with advanced cancer, with systemic inflammation as a key component in pathogenesis. Protein degradation and release of amino acids (AAs) in skeletal muscle are stimulated in cachexia. Here, we define factors contributing to serum AA levels in colorectal cancer (CRC).

METHODS

Serum levels of nine AAs were characterised in 336 CRC patients and their relationships with 20 markers of systemic inflammatory reaction, clinicopathological features of cancers and patient survival were analysed.

RESULTS

Low serum glutamine and histidine levels and high phenylalanine levels associated with indicators of systemic inflammation, including high modified Glasgow Prognostic Score, high blood neutrophil/lymphocyte ratio and high serum levels of CRP, IL-6 and IL-8. Low levels of serum glutamine, histidine, alanine and high glycine levels also associated with advanced cancer stage and with poor cancer-specific survival in univariate analysis.

CONCLUSIONS

In CRC, serum AA levels are associated with systemic inflammation and disease stage. These findings may reflect muscle catabolism induced by systemic inflammation in CRC.

Prevalence of glutamine deficiency in ICU patients: a cross-sectional analytical study

BACKGROUND

Not only is glutamine deficiency an independent predictor of mortality in intensive care unit (ICU) patients, but glutamine supplementation is also recommended for its proven outcome benefits. However, recent data suggest that early glutamine supplementation in certain patient groups increase mortality. The aim of this study was to investigate plasma glutamine levels of adult ICU patients in the South African setting and to determine relationships between glutamine levels, gender, diagnostic categories and selected inflammatory markers. The data from this study will be used as baseline measurement to support a large scale study that will be undertaken in the South African ICU population.

METHODS

This cross-sectional, analytical study included 60 mixed adult ICU patients within 24 h post ICU admission. Plasma glutamine levels were determined on admission. The relationship between glutamine levels, Interleukin-6 (IL-6) and C-reactive protein (CRP); as well as gender- and diagnosis-related differences in glutamine levels were also investigated. A non-parametric ROC curve was computed to determine the CRP concentration cut-off point above which glutamine becomes deficient.

RESULTS

The median plasma glutamine level (497 μmol/L) was in the normal range; however, 38.3 % (n = 23) of patients had deficient (<420 μmol/L) and 6.7 % (n = 4) had supra-normal glutamine levels (>930 μmol/L). No significant difference could be detected between glutamine levels and gender or diagnosis categories as a group. When only the medical and surgical categories were compared, the median plasma glutamine level of the medical patients were significantly lower than that of the surgical patients (p = 0.042). Glutamine showed inverse associations with CRP levels (r = -0.44, p < 0.05) and IL-6 concentrations (r = -0.23, p = 0.08). A CRP cut-off value of 95.5 mg/L was determined above which glutamine levels became deficient.

CONCLUSIONS

About a third of patients (38 %) were glutamine deficient on admission to ICU, whereas some presented with supra-normal levels. While glutamine levels correlated inversely with inflammatory markers, and a CRP value of above 95.5 mg/L indicated potential glutamine deficiency, the clinical application of this finding needs further investigation.

Metabolic and nutritional support of critically ill patients: consensus and controversies

The results of recent large-scale clinical trials have led us to review our understanding of the metabolic response to stress and the most appropriate means of managing nutrition in critically ill patients. This review presents an update in this field, identifying and discussing a number of areas for which consensus has been reached and others where controversy remains and presenting areas for future research. We discuss optimal calorie and protein intake, the incidence and management of re-feeding syndrome, the role of gastric residual volume monitoring, the place of supplemental parenteral nutrition when enteral feeding is deemed insufficient, the role of indirect calorimetry, and potential indications for several pharmaconutrients.

The effects of acute oral glutamine supplementation on exercise-induced gastrointestinal permeability and heat shock protein expression in peripheral blood mononuclear cells

Chronic glutamine supplementation reduces exercise-induced intestinal permeability and inhibits the NF-κB pro-inflammatory pathway in human peripheral blood mononuclear cells. These effects were correlated with activation of HSP70. The purpose of this paper is to test if an acute dose of oral glutamine prior to exercise reduces intestinal permeability along with activation of the heat shock response leading to inhibition of pro-inflammatory markers. Physically active subjects (N = 7) completed baseline and exercise intestinal permeability tests, determined by the percent ratio of urinary lactulose (5 g) to rhamnose (2 g). Exercise included two 60-min treadmill runs at 70 % of VO2max at 30 °C after ingestion of glutamine (Gln) or placebo (Pla). Plasma levels of endotoxin and TNF-α, along with peripheral blood mononuclear cell (PBMC) protein expression of HSP70 and IκBα, were measured pre- and post-exercise and 2 and 4 h post-exercise. Permeability increased in the Pla trial compared to that at rest (0.06 ± 0.01 vs. 0.02 ± 0.018) and did not increase in the Gln trial. Plasma endotoxin was lower at the 4-h time point in the Gln vs. 4 h in the Pla (6.715 ± 0.046 pg/ml vs. 7.952 ± 1.11 pg/ml). TNF-α was lower 4 h post-exercise in the Gln vs. Pla (1.64 ± 0.09 pg/ml vs. 1.87 ± 0.12 pg/ml). PBMC expression of IkBα was higher 4 h post-exercise in the Gln vs. 4 h in the Pla (1.29 ± 0.43 vs. 0.8892 ± 0.040). HSP70 was higher pre-exercise and 2 h post-exercise in the Gln vs. Pla (1.35 ± 0.21 vs. 1.000 ± 0.000 and 1.65 ± 0.21 vs. 1.27 ± 0.40). Acute oral glutamine supplementation prevents an exercise-induced rise in intestinal permeability and suppresses NF-κB activation in peripheral blood mononuclear cells.

A tracer bolus method for investigating glutamine kinetics in humans

Glutamine transport between tissues is important for the outcome of critically ill patients. Investigation of glutamine kinetics is, therefore, necessary to understand glutamine metabolism in these patients in order to improve future intervention studies. Endogenous glutamine production can be measured by continuous infusion of a glutamine tracer, which necessitates a minimum measurement time period. In order to reduce this problem, we used and validated a tracer bolus injection method. Furthermore, this method was used to measure the glutamine production in healthy volunteers in the post-absorptive state, with extra alanine and with glutamine supplementation and parenteral nutrition. Healthy volunteers received a bolus injection of [1-13C] glutamine, and blood was collected from the radial artery to measure tracer enrichment over 90 minutes. Endogenous rate of appearance (endoRa) of glutamine was calculated from the enrichment decay curve and corrected for the extra glutamine supplementation. The glutamine endoRa of healthy volunteers was 6.1±0.9 µmol/kg/min in the post-absorptive state, 6.9±1.0 µmol/kg/min with extra alanyl-glutamine (p = 0.29 versus control), 6.1±0.4 µmol/kg/min with extra alanine only (p = 0.32 versus control), and 7.5±0.9 µmol/kg/min with extra alanyl-glutamine and parenteral nutrition (p = 0.049 versus control). In conclusion, a tracer bolus injection method to measure glutamine endoRa showed good reproducibility and small variation at baseline as well as during parenteral nutrition. Additionally, we showed that parenteral nutrition including alanyl-glutamine increased glutamine endoRa in healthy volunteers, which was not attributable to the alanine part of the dipeptide.

Endogenous glutamine production in critically ill patients: the effect of exogenous glutamine supplementation

Introduction

Glutamine rate of appearance (R_a) may be used as an estimate of endogenous glutamine production. Recently a technique employing a bolus injection of isotopically labeled glutamine was introduced, with the potential to allow for multiple assessments of the glutamine R_a over time in critically ill patients, who may not be as metabolically stable as healthy individuals. Here the technique was used to evaluate the endogenous glutamine production in critically ill patients in the fed state with and without exogenous glutamine supplementation intravenously.

Methods

Mechanically ventilated patients (n = 11) in the intensive care unit (ICU) were studied on two consecutive days during continuous parenteral feeding. To allow the patients to be used as their own controls, they were randomized for the reference measurement during basal feeding without supplementation, before or after the supplementation period. Glutamine R_a was determined by a bolus injection of ¹³C-glutamine followed by a period of frequent sampling to establish the decay-curve for the glutamine tracer. Exogenous glutamine supplementation was given by intravenous infusion of a glutamine containing dipeptide, L-alanyl-L-glutamine, 0.28 g/kg during 20 hours.

Results

A 14% increase of endogenous glutamine R_a was seen at the end of the intravenous supplementation period as compared to the basal measurements (P = 0.009).

Conclusions

The bolus injection technique to measure glutamine R_a to estimate the endogenous production of glutamine in critically ill patients was demonstrated to be useful for repetitive measurements. The hypothesized attenuation of endogenous glutamine production during L-alanyl-L-glutamine infusion given as a part of full nutrition was not seen.

Alterations in glutamine metabolism and its conversion to citrulline in sepsis

In enterocytes, glutamine serves as the major source of energy; another metabolic fate of glutamine is conversion to citrulline. Because sepsis can affect gut function and integrity, alterations in glutamine metabolism may exist and lead to decreased citrulline production. This study aimed to investigate how sepsis affects glutamine metabolism, including its conversion to citrulline, by measuring glutamine and citrulline flux, fractional splanchnic extraction of glutamine and leucine, and the contribution of glutamine nitrogen to citrulline in septic patients and healthy controls. Eight patients with severe sepsis and 10 healthy controls were given primed, constant intravenous infusion of [(2)H2]citrulline and sequential administration of intravenous and enteral [α-(15)N]glutamine and [(13)C]leucine in the postabsorptive state. The results showed that, compared with healthy controls, septic patients had a significantly lower whole body citrulline flux and plasma concentration, higher endogenous leucine flux, and higher glutamine clearance. Fractional splanchnic extraction of leucine was higher in septic patients than in controls, but fractional extraction of glutamine was not different. The majority of the (15)N label transferred from glutamine to citrulline was found at the α-position. These results demonstrate that lower glutamine plasma concentrations in sepsis were a result of increased glutamine clearance. Despite adequate splanchnic uptake of glutamine, there is decreased production of citrulline, suggesting a defect in the metabolic conversion of glutamine to citrulline, decreased uptake of glutamine by the enterocyte but increased uptake by the liver, and/or shunting of glutamine to other metabolic pathways.

Effect of intravenous GLutamine supplementation IN Trauma patients receiving enteral nutrition study protocol (GLINT Study): a prospective, blinded, randomised, placebo-controlled clinical trial

Background Trauma patients are characterised by alterations in the immune system, increased exposure to infectious complications, sepsis and potentially organ failure and death. Glutamine supplementation to parenteral nutrition has been proven to be associated with improved clinical outcomes. However, glutamine supplementation in patients receiving enteral nutrition and its best route are still controversial. Previous trials have been limited by a small sample size, use of surrogate outcomes or a limited period of supplementation. The aim of this trial is to investigate if intravenous glutamine supplementation to trauma patients receiving enteral nutrition is associated with improved clinical outcomes in terms of decreased organ dysfunction, infectious complications and other secondary outcomes. Methods/design Eighty-eight critically ill patients with multiple trauma receiving enteral nutrition will be recruited in this prospective, triple-blind, block-randomised, placebo-controlled clinical trial to receive either 0.5 g/kg/day intravenous undiluted alanyl-glutamine or intravenous placebo by continuous infusion (24 h/day). Both groups will be receiving the same standard enteral nutrition protocol and the same standard intensive care unit care. Supplementation will continue until discharge from the intensive care unit, death or a maximum duration of 3 weeks. The primary outcome will be organ-dysfunction evaluation assessed by the pattern of change in sequential organ failure assessment score over a 10-day period. The secondary outcomes are: the changes in total sequential organ failure assessment score on the last day of treatment, infectious complications during the ICU stay, 60-day mortality, length of stay in the intensive care unit and body-composition analysis. Discussion This study is the first trial to investigate the effect of intravenous alanyl-glutamine supplementation in multiple trauma patients receiving enteral nutrition on reducing severity of organ failure and infectious complications and preservation of lean body mass. Trial registration number This trial is registered at http://www.clinicaltrials.gov. NCT01240291.

Metabolic effects of intensive insulin therapy in critically ill patients

Our aim was to investigate the effects of glycemic control and insulin concentration on lipolysis, glucose, and protein metabolism in critically ill medical patients. For our methods, the patients were studied twice. In study 1, blood glucose (BG) concentrations were maintained between 7 and 9 mmol/l with intravenous insulin. After study 1, patients entered one of four protocols for 48 h until study 2: low-insulin high-glucose (LIHG; variable insulin, BG of 7-9 mmol/l), low-insulin low-glucose (LILG; variable insulin of BG 4-6 mmol/l), high-insulin high-glucose [HIHG; insulin (2.0 mU . kg(-1).min(-1) plus insulin requirement from study 1), BG of 7-9 mmol/l], or high-insulin low-glucose [HILG; insulin (2.0 mU.kg(-1).min(-1) plus insulin requirement from study 1), BG of 4-6 mmol/l]. Age-matched healthy control subjects received two-step euglycemic hyperinsulinemic clamps achieving insulin levels similar to the LI and HI groups. In our results, whole body proteolysis was higher in patients in study 1 (P < 0.006) compared with control subjects at comparable insulin concentrations and was reduced with LI (P < 0.01) and HI (P = 0.001) in control subjects but not in patients. Endogenous glucose production rate (R(a)), glucose disposal, and lipolysis were not different in all patients in study 1 compared with control subjects at comparable insulin concentrations. Glucose R(a) and lipolysis did not change in any of the study 2 patient groups. HI increased glucose disposal in the patients (HIHG, P = 0.001; HILG, P = 0.07 vs. study 1), but this was less than in controls receiving HI (P < 0.03). In conclusion, low-dose intravenous insulin administered to maintain BG between 7-9 mmol/l is sufficient to limit lipolysis and endogenous glucose R(a) and increase glucose R(d). Neither hyperinsulinemia nor normoglycemia had any protein-sparing effect.

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.

Metabolic effects of enteral versus parenteral alanyl-glutamine dipeptide administration in critically ill patients receiving enteral feeding: a pilot study

BACKGROUND

Glutamine (Gln) may become conditionally indispensable during critical illness. The short-term metabolic effects of enteral versus parenteral Gln supplementation are unknown in this clinical setting.

OBJECTIVES

We studied metabolic effects of intravenous (i.v.) alanyl-Gln dipeptide (AG) supplementation and enteral (e.n.) AG supplementation on plasma Gln concentration, antioxidant status, plasma lymphocyte subset number, gut permeability and nitrogen balance in adult critically ill patients requiring tube feeding compared to a control group not receiving Gln supplementation.

METHODS

In a double-blind, pilot clinical trial, 44 medical and surgical ICU patients received identical Gln-free tube feedings 24 h/day and were randomized to either isonitrogenous control (n=15), e.n. AG (n=15) or i.v. AG (n=14) groups (AG). Twelve patients were discontinued from the study. The goal AG dose was 0.5 g/kg/day. Biochemical and metabolic endpoints were measured at baseline and on day 9 (plasma Gln, antioxidant indices, lymphocyte subsets; serum IGF-1 and IGF-binding protein-3; intestinal permeability). Nitrogen balance was determined between study days 6 and 8.

RESULTS

Illness severity indices, clinical demographics, enteral energy and nitrogen intake and major biochemical indices were similar between groups during study. Plasma Gln was higher in the i.v. AG (565+/-119 microM, mean+/-SEM) vs the e.n. AG (411+/-27 microM) group by day 9 (p=0.039); however, subjects in the i.v. AG group received a higher dose of AG (i.v. AG 0.50 versus e.n. AG 0.32+/-0.02 g/kg/day; p<0.001). E.n. AG subjects showed a significant increase in plasma alpha-tocopherol levels over time and maintained plasma gamma-tocopherol concentrations. There were no differences between groups for plasma concentrations of vitamin C, glutathione, malondialdehyde (MDA), T-lymphocyte subsets, intestinal permeability or nitrogen balance.

CONCLUSIONS

This study showed that alanyl-Gln administration by enteral or parenteral routes did not appear to affect antioxidant capacity or oxidative stress markers, T-lymphocyte subset (CD-3, CD-4, CD-8) number, gut barrier function or whole-body protein metabolism compared to unsupplemented ICU patients requiring enteral tube feeding. Enteral Gln appeared to maintain plasma tocopherol levels in this pilot metabolic study.

Corticosteroids increase glutamine utilization in human splanchnic bed

Glutamine is the most abundant amino acid in the body and is extensively taken up in gut and liver in healthy humans. To determine whether glucocorticosteroids alter splanchnic glutamine metabolism, the effect of prednisone was assessed in healthy volunteers using isotope tracer methods. Two groups of healthy adults received 5-h intravenous infusions of l-[1-(14)C]leucine and l-[(2)H(5)]glutamine, along with q. 20 min oral sips of tracer doses of l-[1-(13)C]glutamine in the fasting state, either 1) at baseline (control group; n = 6) or 2) after a 6-day course of 0.8 mg.kg(-1).day(-1) prednisone (prednisone group; n = 8). Leucine and glutamine appearance rates (Ra) were determined from plasma [1-(14)C]ketoisocaproate and [(2)H(5)]glutamine, respectively, and leucine and glutamine oxidation from breath (14)CO(2) and (13)CO(2), respectively. Splanchnic glutamine extraction was estimated by the fraction of orally administered [(13)C]glutamine that failed to appear into systemic blood. Prednisone treatment 1) did not affect leucine Ra or leucine oxidation; 2) increased plasma glutamine Ra, mostly owing to enhanced glutamine de novo synthesis (medians +/- interquartiles, 412 +/- 61 vs. 280 +/- 190 mumol.kg(-1).h(-1), P = 0.003); and 3) increased the fraction of orally administered glutamine undergoing extraction in the splanchnic territory (means +/- SE 64 +/- 6 vs. 42 +/- 12%, P < 0.05), without any change in the fraction of glutamine oxidized (means +/- SE, 75 +/- 4 vs. 77 +/- 4%, not significant). We conclude that high-dose glucocorticosteroids increase in splanchnic bed the glutamine requirements. The role of such changes in patients receiving chronic corticoid treatment for inflammatory diseases or suffering from severe illness remains to be determined.

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.

Critical illness myopathy: what is happening?

PURPOSE OF REVIEW

The current review focuses on recent studies, both clinical and from basic sciences, which approach possible pathomechanisms of critical illness myopathy in order to better derive potential clinical strategies for a preventive or curative clinical setting. Trends and concepts of clinical diagnosis and handling will be evaluated and their implications for muscle physiology and nutritional/metabolic intervention discussed.

RECENT FINDINGS

Conventional electrophysiology was combined with direct muscle stimulation to better differentiate critical illness myopathy from other neuromuscular disorders in critical illness. Muscle weakness was the result of impaired excitation-contraction-coupling at the level of the sarcolemma and the sarcoplasmic reticulum membrane. Critical illness may alter sodium and ryanodine receptor calcium-release channels. Also, increased muscle proteolysis contributes to weakness in critical illness myopathy. Myosin loss is due to the risk factors systemic inflammatory response syndrome/sepsis, steroids and neuromuscular blocking agents. Steroids can also induce necrosis and apoptosis in muscle. Inflammatory mediators aggravated muscle metabolic failure in critical illness myopathy. Ubiquitin-proteasome pathways, cyclooxygenase activation, altered glucose transporter expression, MyoD suppression, impaired respiratory chain enzymes, ATP depletion, glucose toxicity and insulin resistance can all contribute to the critical illness myopathy pathomechanism.

SUMMARY

The search for pathomechanisms is an important task for both clinical and basic sciences. Targets for treatment or prevention of critical illness myopathy include systemic inflammatory response, increased proteolysis and reduced antioxidative capacitance in critically ill patients.

Cerebral interstitial levels of glutamate and glutamine after intravenous administration of nutritional amino acids in neurointensive care patients

After severe trauma or disease glutamine (GLN) is mobilised from all muscles, including the heart and smooth muscles. The result is weakness and fatigue which affects recovery. The breakdown of muscle tissue can be counteracted by external GLN supply. There are concerns, however, that increasing the blood glutamine (Blood-GLN) concentration in patients with acute brain diseases is harmful by elevating the CNS interstitial (IS) concentration of glutamate (CNS-GLT), and that this may result in a secondary excitotoxic injury. We therefore studied the IS CNS-GLN and CNS-GLT when a commercially available nutritional amino acid solution was given intravenously. Ten NICU patients were included. The IS concentrations of amino acids in the brain were measured using intracerebral microdialysis. Blood concentrations of amino acids were measured before and after the amino acid infusion. The change in Blood-GLN was 2.14 (median; range 1.34-3.22) times the basal levels and Blood-GLT increased 1.37 (median; range 0.93-3.45) times basal levels. Both changes were statistically significant. The changes in CNS-GLN was 1.21 (median; range 0.72-1.92) and for CNS-GLT 0.96 (median; range 0.45-1.53) times the basal levels. This was statistically significant for CNS-GLN but not for CNS-GLT. A high initial CNS-GLT (55.3 micromol/l) in one patient increased even further to 84.4 micromol/l after infusion of amino acid solution. We submit that nutritional amino acid solutions can be administrated to some patients with acute brain disease without increasing the CNS-GLT values. However, since BBB function was not quantified in our study, further evaluation of this issue is warranted.

Myopathies in critical illness: characterization and nutritional aspects

Myopathies related to critical illness have received increasing recognition over the past decade and are common in patients even after a brief period in the intensive care unit. Recent studies have revealed that myopathies in the critically ill may in fact be more prevalent than neuropathies and that morbidity and mortality may be greater. Protein catabolism, an increase in urinary nitrogen loss, and muscle wasting are observed in critical illness myopathy. Muscle biopsies in critically ill patients demonstrate low glutamine levels, low protein/DNA levels, and high concentrations of extracellular water. The increased flux of glutamine in muscle in these patients is thought to be insufficient to meet the body's requirement for glutamine, and thus in critical illness this amino acid may be classified as "conditionally essential." Three subtypes of critical illness myopathy have been described that are often grouped together as acute quadriplegic myopathy: thick-filament myopathy, critical illness myopathy, and necrotizing myopathy. These can be differentiated based on clinical features and muscle biopsy. Treatments for critical illness myopathies range from primary prevention, i.e., avoiding myopathy-inducing drugs, to novel nutritional therapies, such as glutamine and glutathione supplementation. One should be particularly vigilant for the development of myopathies in critically ill alcoholic patients, who may have a chronic alcoholic myopathy at baseline. In the past decade, advances have been made in characterizing and identifying patients with myopathies due to critical illness. However, additional studies must be performed in order to develop appropriate therapies for this potentially devastating disorder.

Combined growth hormone/insulin-like growth factor I in addition to glutamine-supplemented TPN results in net protein anabolism in critical illness

Protein loss leading to reduced lean body mass is recognized to contribute to the high levels of morbidity and mortality seen in critical illness. This prospective, randomized, controlled study compared the effects of conventional parenteral nutrition (TPN), glutamine-supplemented (0.4 g.kg-1.day-1) TPN (TPNGLN), and TPNGLN with combined growth hormone (GH, 0.2 IU.kg-1.day-1) and IGF-I (160 microg.kg-1.day-1) on protein metabolism in critical illness. Nineteen mechanically ventilated subjects [64 +/- 3 yr, body mass index (BMI) 23.8 +/- 1.3, kg/m2] were initially studied in the fasting state (study 1) and subsequently after 3 days of nutritional with/without hormonal support (study 2). All had recently been admitted to the ICU and the majority were postemergency abdominal surgery (APACHE II 17.5 +/- 1.0). Protein metabolism was assessed using a primed constant infusion of [1-13C]leucine. Conventional TPN contained mixed amino acids, Intralipid, and 50% dextrose. TPNGLN, unlike TPN alone, resulted in an increase in plasma glutamine concentration ( approximately 50%, P < 0.05). Both TPN and TPNGLN decreased the rate of protein breakdown (TPN 15%, P < 0.002; TPNGLN 16%, P < 0.05), but during these treatments the patients remained in a net negative protein balance. Combined treatment with TPNGLN + GH/IGF-I increased plasma IGF-I levels (10.3 +/- 0.8 vs. 48.1 +/- 9.1 nmol/l, study 1 vs. study 2, P < 0.05), and in contrast to therapy with nutrition alone, resulted in net protein gain (-0.75 +/- 0.14 vs. 0.33 +/- 0.12 g protein.kg-1.day-1, study 1 vs. study 2, P < 0.05). Therapy with GH/IGF-I + TPNGLN, unlike nutrition alone, resulted in net positive protein balance in a group of critically ill patients.

Amino acid kinetics during the anhepatic phase of liver transplantation

Alanine and glutamine are interorgan nitrogen/carbon carriers for ureagenesis and gluconeogenesis, which are mainly but not necessarily only hepatic. The liver is central to alanine and glutamine metabolism, but most organs can produce and use them. We studied amino acid kinetics after liver removal to depict initial events of liver failure and to provide a model to study extrahepatic gluconeogenesis and nitrogen disposal in humans. We measured amino acid kinetics with [5,5,5-(2)H(3)]leucine and [3-(13)C]alanine or [1,2-(13)C(2)]glutamine tracers in 21 subjects during and after the anhepatic phase of liver transplantation: 12 were at 7 months posttransplantation, and 7 were healthy control subjects. Anhepatic leucine kinetics, including proteolysis, was unchanged. Alanine plasma and whole-body contents increased 3x and 2x, with a halved metabolic clearance and a doubled production, 2% greater than disposal. Free whole-body glutamine decreased 25% but increased 50% in plasma. Glutamine clearance was halved, and the production decreased by 25%, still 2% greater than disposal. Liver replacement decreased alanine and glutamine concentrations, leaving leucine unchanged. Liver removal caused doubled alanine fluxes, minor changes in glutamine, and no changes in leucine. The initial events after liver removal are an accumulation of three-carbon compounds, an acceleration of alanine turnover, and limited nitrogen storage in alanine and glutamine.

Effects of glutamine supplementation, GH, and IGF-I on glutamine metabolism in critically ill patients

During critical illness glutamine deficiency may develop. Glutamine supplementation can restore plasma concentration to normal, but the effect on glutamine metabolism is unknown. The use of growth hormone (GH) and insulin-like growth factor I (IGF-I) to prevent protein catabolism in these patients may exacerbate the glutamine deficiency. We have investigated, in critically ill patients, the effects of 72 h of treatment with standard parenteral nutrition (TPN; n = 6), TPN supplemented with glutamine (TPNGLN; 0.4 g x kg(-1) x day(-1), n = 6), or TPNGLN with combined GH (0.2 IU. kg(-1). day(-1)) and IGF-I (160 microg x kg (-1) x day(-1)) (TPNGLN+GH/IGF-I; n = 5) on glutamine metabolism using [2-(15)N]glutamine. In patients receiving TPNGLN and TPNGLN+GH/IGF-I, plasma glutamine concentration was increased (338 +/- 22 vs. 461 +/- 24 micromol/l, P < 0.001, and 307 +/- 65 vs. 524 +/- 71 micromol/l, P < 0.05, respectively) and glutamine uptake was increased (5.2 +/- 0.5 vs. 7.4 +/- 0.7 micromol x kg(-1) x min(-1), P < 0.05 and 5.2 +/- 1.1 vs. 7.6 +/- 0.8 micromol x kg(-1) x min(-1), P < 0.05). Glutamine production and metabolic clearance rates were not altered by the three treatments. These results suggest that there is an increased requirement for glutamine in critically ill patients. Combined GH/IGF-I treatment with TPNGLN did not have adverse effects on glutamine metabolism.