Alanyl-glutamine-supplemented total parenteral nutrition improves survival and protein metabolism in rat protracted bacterial peritonitis model

EFFECTS OF INTRAPERITONEAL GLUTAMINE IN THE TREATMENT OF EXPERIMENTAL SEPSIS

Background:

Sepsis is an important public health issue and is associated with high treatment costs and high mortality rates. Glutamine supplementation has proven to be beneficial to the functions of the immune system, acting beneficially in the evolution of patients in severe catabolic states.

Aim:

To evaluate the effect of glutamine supplementation via intraperitoneal in rats, induced sepsis, considering the following organs: intestines, liver, kidneys and lungs.

Methods:

Male Wistar rats subjected to sepsis by ligature and cecal puncture were divided into two groups: control C (n=6) and glutamine G (n=11), in which were administered dipeptiven 20% at a dose of 2 ml/kg/day (equivalent to 0.4g N(2)-L-alanyl-L-glutamine/kg) intraperitoneally 48 h prior to sepsis induction. After 48 h they were euthanized and intestine, liver, lung and kidney were removed for histological analysis.

Results:

Intestinal epithelial desquamation of the control group was more intense compared to the glutamine group (p=0.008). In the kidneys, degenerative tubular epithelial changes were less severe in the animals that received glutamine (p=0.029). Regarding to the liver, glutamine group showed lower levels of cell swelling than the control group (p=0.034). In the lung there were no results with statistical significance.

Conclusion:

Prior intraperitoneal supplementation with glutamine in experimental animals is able to reduce the damage to the intestinal mucosa, to the kidneys and liver’s histoarchitecture.

A RandomizEd trial of ENtERal Glutamine to minimIZE thermal injury (The RE-ENERGIZE Trial): a clinical trial protocol

Background:

Burn injury represents a significant public health problem worldwide. More than in any other injury, the inflammation and catabolism associated with severe burns can exacerbate nutrient deficiencies resulting in impaired immune function and increased risk of developing infection, organ dysfunction and death. Consequently, over the last few decades numerous trials have evaluated the impact of different nutritional strategies in severe burn injury. Glutamine is of particular interest, as it appears vital for a number of key stress-response pathways in serious illness. The purpose of the current manuscript is to provide the rationale and protocol for a large clinical trial of supplemental enteral glutamine in 2700 severe burn-injured patients.

Methods:

We propose a multicentre, double-blind, pragmatic, randomized, clinical trial involving 80 tertiary intensive care unit (ICU) burn centres worldwide. We aim to enrol patients with deep second- and/or third-degree burns at moderate or high risk for death. We will exclude patients admitted > 72 h before screening and patients with advanced liver and kidney disease. The study intervention consists of enteral glutamine 0.5 g/kg/day vs. isocaloric maltodextran control delivered enterally. Primary outcome will be six-month mortality. Key secondary outcomes include time to discharge alive from hospital, ICU and hospital mortality, length of stay and health-related quality of life at six months.

Significance:

This study will be the first large international multicentre trial examining the effects of glutamine in burn patients. Negative or positive, the results of this trial will inform the clinical practice of burns care worldwide.

Clinicaltrials.gov ID #NCT00985205

Patients with severe burns need to recover in a hospital burn unit for a long time and are at high risk of developing infections and dying. Proper nutrition and certain nutrients may improve survival in these patients and shorten their stay in the burn unit. Glutamine is a building block of protein that is normally made in the body and is found in different foods we eat. It is of great interest because it has several beneficial effects on the body during serious illness, such as with burn injury. In this study, we will look at the effect of glutamine supplementation on survival and time spent in hospital. A total of 80 burn units around the world will enrol 2700 patients with 2nd or 3rd degree burns over 4 years. Patients will receive either glutamine powder or a placebo through a feeding tube or mixed with food, from admission to the burn unit, until a week after the burn wound has healed. The main outcome for this study is survival at 6 months. Other outcomes include the time taken to be discharged from hospital alive and duration of stay in the burn unit. This study will be the first large international multicentre trial examining the effects of glutamine in burn patients. Glutamine may lead to better survival and less complications in burn patients, who have a devastating and disabling burn injury. If the trial is positive, the results will be used to inform how nutrition should be given to such patients worldwide.

Alanyl-glutamine but not glycyl-glutamine improved the proliferation of enterocytes as glutamine substitution in vitro

The synthetic dipeptides alanyl-glutamine (Ala-Gln) and glycyl-glutamine (Gly-Gln) are used as Gln substitution to provide energy source in the gastrointestinal tract due to their high solubility and stability. This study aimed to investigate the effects of Gln, Ala-Gln and Gly-Gln on mitochondrial respiration and protein turnover of enterocytes. Intestinal porcine epithelial cells (IPEC-J2) were cultured for 2 days in Dulbecco's modified Eagle's-F12 Ham medium (DMEM-F12) containing 2.5 mM Gln, Ala-Gln or Gly-Gln. Results from 5-ethynyl-2'-deoxyuridine incorporation and flow cytometry analysis indicated that there were no differences in proliferation between free Gln and Ala-Gln-treated cells, whereas Gly-Gln treatment inhibited the cell growth compared with Gln treatment. Significantly lower mRNA expressions of Sp1 and PepT1 were also observed in Gly-Gln-treated cells than that of Ala-Gln treatment. Ala-Gln treatment increased the basal respiration and ATP production, compared with free Gln and Gly-Gln treatments. There were no differences in protein turnover between free Gln and Ala-Gln-treated cells, but Gly-Gln treatment reduced protein synthesis and increased protein degradation. Ala-Gln treatment stimulated mTOR activation whereas Gly-Gln decreased mTOR phosphorylation and increased the UB protein expression compared with free Gln treatment. These results indicate that Ala-Gln has the very similar functional profile to free Gln in porcine enterocytes in vitro and can be substituted Gln as energy and protein sources in the gastrointestinal tract.

Addition of Alanyl-Glutamine to Dialysis Fluid Restores Peritoneal Cellular Stress Responses - A First-In-Man Trial

BACKGROUND

Peritonitis and ultrafiltration failure remain serious complications of chronic peritoneal dialysis (PD). Dysfunctional cellular stress responses aggravate peritoneal injury associated with PD fluid exposure, potentially due to peritoneal glutamine depletion. In this randomized cross-over phase I/II trial we investigated cytoprotective effects of alanyl-glutamine (AlaGln) addition to glucose-based PDF.

METHODS

In a prospective randomized cross-over design, 20 stable PD outpatients underwent paired peritoneal equilibration tests 4 weeks apart, using conventional acidic, single chamber 3.86% glucose PD fluid, with and without 8 mM supplemental AlaGln. Heat-shock protein 72 expression was assessed in peritoneal effluent cells as surrogate parameter of cellular stress responses, complemented by metabolomics and functional immunocompetence assays.

RESULTS

AlaGln restored peritoneal glutamine levels and increased the primary outcome heat-shock protein expression (effect 1.51-fold, CI 1.07-2.14; p = 0.022), without changes in peritoneal ultrafiltration, small solute transport, or biomarkers reflecting cell mass and inflammation. Further effects were glutamine-like metabolomic changes and increased ex-vivo LPS-stimulated cytokine release from healthy donor peripheral blood monocytes. In patients with a history of peritonitis (5 of 20), AlaGln supplementation decreased dialysate interleukin-8 levels. Supplemented PD fluid also attenuated inflammation and enhanced stimulated cytokine release in a mouse model of PD-associated peritonitis.

CONCLUSION

We conclude that AlaGln-supplemented, glucose-based PD fluid can restore peritoneal cellular stress responses with attenuation of sterile inflammation, and may improve peritoneal host-defense in the setting of PD.

Liver regeneration with l-glutamine supplemented diet: experimental study in rats

OBJECTIVE

To assess liver regeneration in rats after 60% hepatectomy with and without supplementation of L-glutamine through liver weight changes, laboratory parameters and histological study.

METHODS

36 male rats were divided into two groups: glutamine group and control group. Each group was subdivided into three subgroups, with death in 24h, 72h and seven days. The glutamine group received water and standard diet supplemented with L-glutamine, and the control recieved 0.9% saline. In all subgroups analysis of liver regeneration was made by the Kwon formula, study of liver function (AST, ALT, GGT, total bilirubin, indirect and indirect bilirubin and albumin) and analysis of cell mitosis by hematoxylin-eosin.

RESULTS

In both groups there was liver regeneration by weight gain. Gamma-GT increased significantly in the control group (p < 0.05); albumin increased in the glutamine group. The other indicators of liver function showed no significant differences. Histological analysis at 72h showed a higher number of mitoses in the glutamine group, with no differences in other subgroups.

CONCLUSION

Diet supplementation with L glutamine is beneficial for liver regeneration.

The effect of supplemental glutamine on growth performance, development of the gastrointestinal tract, and humoral immune response of broilers

Two experiments were conducted to evaluate the effect of supplemental Gln on growth performance, development of the gastrointestinal tract, and humoral immune response of broilers. Immediately after hatch 6 replicate pens of 6 chicks were randomly assigned to 1 of 7 (experiment 1) or 5 (experiment 2) dietary treatments for 21 d. On d 4, 7, 14, and 21, twelve chicks per treatment (2 chicks/pen) were killed for thymus, spleen, bursa, duodenum, jejunum, ileum, bile, and blood sample collections and weights. In experiment 1, the effect of 1 or 4% Gln addition to the feed, water, or both was compared with a corn-soybean meal (SBM) control diet. All diets were formulated to be isocaloric and isonitrogenous. Weight gain improved significantly (P < 0.05) when chicks were fed diets with 1% Gln as compared with chicks fed the control diet (11% average improvement). The addition of 4% Gln to the diet or water depressed (P < 0.05) growth performance. Based on the results from experiment 1, 1% Gln supplementation to the diet was determined to be ample and most practical. Thus in experiment 2, diets supplemented with 1% Gln were fed for 4, 7, 14, or 21 d after which time chicks were fed the corn-SBM control diet until the experiment was terminated at 21 d. Weight gain improved significantly (P < 0.05) when chicks were fed diets supplemented with 1% Gln throughout the 21-d study. In both experiments, chicks fed diets supplemented with 1% Gln for 21 d had higher concentrations of bile, intestinal, and sera IgA and sera IgG (P < 0.05). Chicks fed diets with 1% Gln had heavier intestinal relative weights and longer intestinal villi (P < 0.05) as compared with the chicks fed the corn-SBM diet. Our results indicate that the addition of 1% Gln to the diet of broiler chicks improves growth performance and may stimulate development of the gastrointestinal tract and humoral immune response.

Effects of glutamine supplementation on innate immune response in rats with gut-derived sepsis

The present study examined the effect of glutamine (Gln)-enriched diets before sepsis or Gln-containing total parenteral nutrition (TPN) after sepsis, or both, on the phagocytic activity and blood lymphocyte subpopulation in rats with gut-derived sepsis. Rats were assigned to a control group or one of four experimental groups. The control group and groups 1 and 2 were fed a semipurified diet; groups 3 and 4 had part of casein replaced by Gln. After feeding the diets for 10d, sepsis was induced by caecal ligation and puncture (CLP); TPN was maintained for 3d after CLP. The control group and groups 1 and 3 were infused with conventional TPN and groups 2 and 4 were supplemented with Gln in the TPN solution. All rats were killed 3d after CLP or sham operation to examine their immune responses. The results showed that compared with the control group, the phagocytic activities of peritoneal macrophages were enhanced in groups 3 and 4, but not in groups 1 and 2. The proportion of CD3+ cells in group 1 was significantly lower (P<0·05) than that of the control group, whereas no differences were observed among the control and Gln-supplemented groups. The CD4+ cell proportion was significantly lower (P<0·05) in group 1 compared with the control group and groups 3 and 4. These findings suggest that Gln-enriched diets before CLP significantly enhanced peritoneal macrophage phagocytic activity, preserved CD4+ cells and maintained blood total T lymphocytes in gut-derived sepsis. However, parenteral Gln administration after caecal ligation and puncture had no favourable effects on modulating immune response in septic rats.

REducing Deaths due to OXidative Stress (The REDOXS Study): Rationale and study design for a randomized trial of glutamine and antioxidant supplementation in critically-ill patients

Critically-ill patients experience an extent of hyperinflammation, cellular immune dysfunction, oxidative stress and mitochondrial dysfunction. Supplementation with key nutrients, such as glutamine and antioxidants, is most likely to have a favourable effect on these physiological derangements, leading to an improvement in clinical outcomes. The results of two meta-analyses suggest that glutamine and antioxidants may be associated with improved survival. The purpose of the present paper is to report the background rationale and study protocol for the evaluation of the effect of high-dose glutamine and antioxidant supplementation on mortality in a large-scale randomized trial in 1200 mechanically-ventilated, critically-ill patients. Patients admitted to an intensive care unit (ICU) with clinical evidence of severe organ dysfunction will be randomized to one of four treatments in a 2 x 2 factorial design: (1) glutamine; (2) antioxidant therapy; (3) glutamine and antioxidant therapy; (4) placebo. The primary outcome for this study is 28 d mortality. The secondary outcomes are duration of stay in ICU, adjudicated diagnosis of infection, multiple organ dysfunction, duration of mechanical ventilation, length of stay in hospital and health-related quality of life at 3 and 6 months. A novel design feature is the combined use of parenteral and enteral study nutrients dissociated from the nutrition support. The therapeutic strategies tested in the randomized trial may lead to less morbidity and improved survival in critically-ill patients. The trial will be conducted in approximately twenty tertiary-care ICU in Canada and the first results are expected in 2009.

Aspects of Protein and Amino Acid Metabolism in a Model of Severe Glutamine Deficiency in Sepsis

BACKGROUND/AIMS

Growth hormone (GH) could have the potential to improve protein metabolism in sepsis but glutamine deficiency has been reported after GH treatment. The aim was to investigate the effects of glutamine deficiency in sepsis with and without GH treatment on protein and amino acid metabolism.

METHODS

Cecal ligation and puncture (CLP) was used as a model of sepsis. Serious glutamine deficiency was induced by administration of glutamine synthetase inhibitor, methionine sulfoximine (MSO). Young Wistar rats were divided into 5 groups: control; CLP; CLP+MSO; CLP+GH, and CLP+MSO+GH. Parameters of protein metabolism were measured on incubated soleus and extensor digitorum longus muscles: [1-14C]leucine was used to estimate protein synthesis and leucine oxidation, tyrosine release was used to evaluate protein breakdown. Amino acid concentrations in plasma, skeletal muscle and incubation media were measured by HPLC.

RESULTS/CONCLUSIONS

A reduced muscle glutamine concentration after MSO treatment is not associated with changes in the rates of protein synthesis or breakdown. MSO treatment decreased glutamine release from skeletal muscle and plasma glutamine concentration. Severe glutamine deficiency in GH-treated septic rats resulted in increased release of branched-chain amino acids from skeletal muscle.

Molecular mechanisms of glutamine action

Glutamine is the most abundant free amino acid in the body and is known to play a regulatory role in several cell specific processes including metabolism (e.g., oxidative fuel, gluconeogenic precursor, and lipogenic precursor), cell integrity (apoptosis, cell proliferation), protein synthesis, and degradation, contractile protein mass, redox potential, respiratory burst, insulin resistance, insulin secretion, and extracellular matrix (ECM) synthesis. Glutamine has been shown to regulate the expression of many genes related to metabolism, signal transduction, cell defense and repair, and to activate intracellular signaling pathways. Thus, the function of glutamine goes beyond that of a simple metabolic fuel or protein precursor as previously assumed. In this review, we have attempted to identify some of the common mechanisms underlying the regulation of glutamine dependent cellular functions.

Glutamine supplementation enhances mucosal immunity in rats with Gut-Derived sepsis

OBJECTIVE

Supplemental glutamine (Gln) has been demonstrated to improve the immunologic response and reduce mortality in rodents with sepsis. However, the effects of Gln on gut-associated lymphoid tissue function after infection and sepsis are not clear. We investigated the effects of Gln-supplemented diets before sepsis, Gln-enriched total parenteral nutrition (TPN) after sepsis, or both on the intestinal immunity in rats with gut-derived sepsis.

METHODS

Male Wistar rats were assigned to control and four experimental groups. The control and experimental groups 1 and 2 were fed a semi-purified diet; in experimental groups 3 and 4, part of the casein in the diets was replaced with Gln. After feeding rats the respective diets for 10 d, sepsis was induced by cecal ligation and puncture (CLP) in the experimental groups, whereas the control group underwent a sham operation; at the same time, the internal jugular vein of all rats was cannulated. All rats were maintained on TPN for 3 d. The control group and groups 1 and 3 were infused with conventional TPN, and groups 2 and 4 were given a TPN solution supplemented with Gln, which provided 25% of total amino acid nitrogen. All rats were killed 3 d after the sham operation or CLP. Intestinal immunoglobin A levels, total lymphocyte yields, and lymphocyte subpopulations in Peyer's patches were analyzed.

RESULTS

Total Peyer's patch lymphocyte numbers were significantly higher in the Gln-supplemented groups than in the control group. Distributions of CD3+ and CD4+ in group 1 were significantly lower than those in the control group, whereas no differences were observed among the control and Gln-supplemented groups. Plasma immunoglobulin A levels were higher in the Gln-supplemented groups than the control group and group 1. Intestinal immunoglobulin A levels were significantly higher in groups 2 and 4 than in the control group and group 1.

CONCLUSIONS

Preventive use of a Gln-supplemented enteral diet before CLP or intravenous Gln supplementation after CLP have similar effects in promoting proliferation of total lymphocyte in gut-associated lymphoid tissue, enhancing IgA secretion, and maintaining T-lymphocyte populations in Peyer's patches. Gln administered before and after CLP did not seem to have a synergistic effect on enhancing mucosal immunity in rats with gut-derived sepsis.

Effect of glutamine dipeptide on hepatic regeneration in partially hepatectomized malnourished rats

Glutamine promotes hepatic regeneration in nourished (N) rats. The aim of the present study was to evaluate the effects of glutamine-enriched total parenteral nutrition (TPN) on liver regeneration in malnourished (MN) rats.Seventy-two male Wistar rats ( congruent with 270 g) were assigned to one of two groups: N and MN. Each group was then subdivided into three groups: the first underwent partial hepatectomy (PH) and received standard TPN enriched with L-alanyl-L-glutamine (Ala-Gln); the second also underwent PH and received standard TPN, but enriched with a solution containing proline and alanine (Ala-Pro); and the third underwent no surgical procedure (control group). All experimental groups received isocaloric (188 kcal. kg(-1). d(-1)) and isonitrogenous (1.12 g of nitrogen. kg(-1). d(-1)) TPN for 96 h. All animals were injected with bromodeoxyuridine 2 h before death. The hepatic regeneration index (HRI), hepatic growth percentage (HG) and hepatic morphology were analyzed. In MN rats, HRI and HG were higher with glutamine enrichment (HRI = 81 and HG = 190) than with proline-containing TPN (HRI = 66 and HG = 154; P < 0.05) and HRI was 100 times higher in animals that underwent PH than in control animals. Morphologic analysis of hepatic tissue showed no difference among the six groups.Glutamine-enriched TPN promoted growth of the remnant liver in MN rats after PH, maintained cellular proliferation in the various experimental groups after surgery, and maintained hepatic morphology of MN rats after surgery.

Glutamine supplementation in serious illness: a systematic review of the evidence

OBJECTIVE

To examine the relationship between glutamine supplementation and hospital length of stay, complication rates, and mortality in patients undergoing surgery and experiencing critical illness.

DATA SOURCES

Computerized search of electronic databases and search of personal files, abstract proceedings, relevant journals, and review of reference lists.

STUDY SELECTION

We reviewed 550 titles, abstracts, and articles. Primary studies were included if they were randomized trials of critically ill or surgical patients that evaluated the effect of glutamine vs. standard care on clinical outcomes. DATA EXTRACTION We abstracted relevant data on the methodology and outcomes of primary studies in duplicate, independently. DATA SYNTHESIS There were 14 randomized trials comparing the use of glutamine supplementation in surgical and critically ill patients. When the results of these trials were aggregated, with respect to mortality, glutamine supplementation was associated with a risk ratio (RR) of 0.78 (95% confidence interval [CI], 0.58-1.04). Glutamine supplementation was also associated with a lower rate of infectious complications (RR, 0.81; 95% CI, 0.64-1.00) and a shorter hospital stay (-2.6 days; 95% CI, -4.5 to -0.7). We examined several -specified subgroups. Although there were no statistically significant subgroup differences detected, there were some important trends. With respect to mortality, the treatment benefit was observed in studies of parenteral glutamine (RR, 0.71; 95% CI, 0.51-0.99) and high-dose glutamine (RR, 0.73; 95% CI, 0.53-1.00) compared with studies of enteral glutamine (RR, 1.08; 95% CI, 0.57-2.01) and low-dose glutamine (RR, 1.02; 95% CI, 0.52-2.00). With respect to hospital length of stay, all of the treatment benefit was observed in surgical patients (-3.5 days; 95% CI, -5.3 to -1.7) compared with critically ill patients (0.9 days; 95% CI, -4.9 to 6.8).

CONCLUSION

In surgical patients, glutamine supplementation may be associated with a reduction in infectious complication rates and shorter hospital stay without any adverse effect on mortality. In critically ill patients, glutamine supplementation may be associated with a reduction in complication and mortality rates. The greatest benefit was observed in patients receiving high-dose, parenteral glutamine.

Effects of glutamine-supplemented total parenteral nutrition on cytokine production and T cell population in septic rats

BACKGROUND

This study was designed to investigate the effects of total parenteral nutrition (TPN) enriched with glutamine (GLN) on in vivo cytokine production and cellular immune response in early and late septic stages of rats.

METHODS

Male Wistar rats were divided into 2 experimental groups and received TPN solution at an energy level of 270 kcal/kg body weight. The TPN solutions were isonitrogenous and identical in nutrients composition except for differences in amino acid content. One group received 2% GLN, whereas the other group received glycine (Gly) instead. TPN was maintained for 5 or 6 days according to the sacrifice schedule of the rats. On day 5, sepsis was induced by cecal ligation and puncture (CLP). Respective groups of rats were sacrificed 2, 4, 6, and 24 hours after CLP.

RESULTS

Sepsis resulted in a negative nitrogen balance in both groups, and nitrogen loss was significantly lower in the GLN than the Gly group. Interleukin (IL)-2 and interferon (IFN)-gamma in most of the samples collected at various time points were not detectable in plasma or peritoneal lavage fluid. No differences in plasma IL-6 and TNF-alpha concentrations were observed between the GLN and Gly groups. Also, there were no significant differences in IL-1beta, IL-6, and TNF-alpha concentrations in peritoneal lavage fluid between the 2 groups at various time points. The CD4+/CD8+ ratio was significantly higher in the GLN group than in the Gly group only at 4 hours after CLP, and no difference was observed at 24 hours after CLP.

CONCLUSIONS

TPN preinfused with a GLN-supplemented solution had a beneficial effect in ameliorating the extent of negative nitrogen balance in septic rats. However, parenterally administered GLN did not reduce the production of inflammatory mediators systemically or at the site of injury, and the influence on enhancing cellular immunity was not obvious.

Alanyl-glutamine dipeptide does not affect hemodynamics despite a greater increase in myocardial heat shock protein 72 immunoreactivity in endotoxemic sheep

The possible beneficial effect of supplemental glutamine (Gln) in critically ill patients has been suggested to be mediated by the induction of the cytoprotective heat shock proteins (HSP)32 and HSP72. There is evidence that HSP72 and HSP32 have opposite effects on the hemodynamic situation during endotoxemia. Therefore, the effect of Gln supplementation on the cardiovascular system is not clear. We investigated the effect of alanyl-Gln (Ala-Gln) dipeptide on cardiovascular function in healthy and endotoxemic sheep. Ten sheep catheterized for chronic studies received Ala-Gln 700 mg/(kg x d) [equal to 470 mg/(kg x d)Gln] on 4 consecutive days, and 10 sheep received NaCl (9 g/L) as the control solution. On d 4, four sheep of each group were killed and myocardial samples were taken for immunohistochemistry. The remaining sheep received a continuous infusion of endotoxin [Salmonella typhosa, 10 ng/(kg x min)]. Hemodynamic parameters were measured before application of Ala-Gln or the control solution, and during endotoxemia. Myocardial HSP72 immunoreactivity was determined by immunohistochemistry. After 24 h of endotoxemia, the sheep exhibited a hyperdynamic circulation. No difference was found in the hemodynamic parameters between treatment and control group. Ala-Gln treated sheep had a greater increase in myocardial HSP72 immunoreactivity compared with controls after (P < 0.05) but not before endotoxemia. In summary, Ala-Gln increased HSP72 immunoreactivity after endotoxemia, but did not alter hemodynamic parameters. Thus, Ala-Gln supplementation does not seem to aggravate the hyperdynamic circulation in endotoxemic shock.

Glutamine and the immune system

Glutamine is utilised at a high rate by cells of the immune system in culture and is required to support optimal lymphocyte proliferation and production of cytokines by lymphocytes and macrophages. Macrophage-mediated phagocytosis is influenced by glutamine availability. Hydrolysable glutamine dipeptides can substitute for glutamine to support in vitro lymphocyte and macrophage functions. In man plasma and skeletal muscle glutamine levels are lowered by sepsis, injury, burns, surgery and endurance exercise and in the overtrained athlete. The lowered plasma glutamine concentrations are most likely the result of demand for glutamine (by the liver, kidney, gut and immune system) exceeding the supply (from the diet and from muscle). It has been suggested that the lowered plasma glutamine concentration contributes, at least in part, to the immunosuppression which accompanies such situations. Animal studies have shown that inclusion of glutamine in the diet increases survival to a bacterial challenge. Glutamine or its precursors has been provided, usually by the parenteral route, to patients following surgery, radiation treatment or bone marrow transplantation or suffering from injury. In most cases the intention was not to stimulate the immune system but rather to maintain nitrogen balance, muscle mass and/or gut integrity. Nevertheless, the maintenance of plasma glutamine concentrations in such a group of patients very much at risk of immunosuppression has the added benefit of maintaining immune function. Indeed, the provision of glutamine to patients following bone marrow transplantation resulted in a lower level of infection and a shorter stay in hospital than for patients receiving glutamine-free parenteral nutrition.

Dietary glutamine enhances cytokine production by murine macrophages

To examine the effects of dietary glutamine on cytokine production by macrophages, mice were fed for 2 wk on a control diet that included 200.0 g casein/kg providing 19.6 g glutamine/kg or a glutamine-enriched diet that provided 54.8 g glutamine/kg partly at the expense of casein. There were no differences in weight gain between animals fed the two diets. The plasma concentrations of a number of amino acids differed according to the diet fed; this variation largely reflected the variation in the levels of the different amino acids in the diets. Plasma glutamine concentration was not significantly affected by dietary glutamine level. The production of three cytokines, tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6, was greater for lipopolysaccharide-stimulated macrophages from mice fed the glutamine-enriched diet. Thus, increasing the amount of glutamine in the murine diet enhances the ability of macrophages to respond to stimulation, at least in terms of cytokine production. These observations suggest that increasing the availability of glutamine orally could promote immune responses involving macrophage-derived cytokines.

Glutamine as an immunoenhancing nutrient

New strategies for immunonutritional support include administration of special nutrients such as glutamine. Glutamine is important in several key metabolic processes of immune cells and enterocytes. Exogenous glutamine augments the functions of lymphocytes and macrophages. Neutrophils also reportedly utilize glutamine at a significant rate. Our recent studies demonstrated that glutamine enhances neutrophil function. This article focuses on the effects of glutamine on neutrophil function in surgical stress. Enteral glutamine administration enhanced peritoneal and hepatic bacterial clearance in our rat peritonitis model. Furthermore, IV glutamine supplementation improved the outcome of animals with severe surgical stress. Our in vitro study revealed that supplemental glutamine augmented the bacterial killing function of neutrophils from postoperative patients. Glutamine increased phagocytosis of the neutrophils. In addition, glutamine dose-dependently increased production of reactive oxygen intermediates (ROI) by neutrophils. Thus, our studies suggest that glutamine supplementation may improve bactericidal function of neutrophils by increasing both phagocytosis and ROI production. In conclusion, glutamine plays an important role in neutrophil function. Glutamine may be useful for the prevention, and treatment, of severe infection in critical illness and trauma.

Dietary glutamine enhances murine T-lymphocyte responsiveness

To examine the effects of dietary glutamine on lymphocyte function, male mice aged 6 wk were fed for 2 wk one of three isonitrogenous, isocaloric diets, which varied in glutamine concentration. The control diet included 200 g casein/kg, providing 19.6 g glutamine/kg; the glutamine-enriched diet provided 54.8 g glutamine/kg partly at the expense of casein; and the alanine + glycine-enriched diet provided 13.3 g glutamine/kg. The plasma concentrations of a number of amino acids varied because of the diet fed. The plasma glycine concentration was greater in mice fed the alanine + glycine-enriched diet (380 +/- 22 micromol/L) than in mice fed the control (177 +/- 17 micromol/L) or the glutamine-enriched (115 +/- 18 micromol/L) diets. The plasma glutamine concentration was greater in mice fed the glutamine-enriched diet (945 +/- 117 micromol/L) than in those fed the diet enriched with alanine + glycine (561 +/- 127 micromol/L), but was not different from that in mice fed the control diet (791 +/- 35 micromol/L). There was a significant linear relationship between the amount of glutamine in the diet and plasma glutamine concentration (r = 0.655, P = 0.015). Plasma alanine concentration was unaffected by diet. The reason for the lack of effect of increasing the amount of alanine in the diet upon its concentration in the circulation may relate to its use by the liver. Thymidine incorporation (56 +/- 18 kBq/well versus <10 kBq/well), expression of the alpha-subunit of the interleukin-2 receptor (62 versus 30% receptor positive cells) and interleukin-2 production [189 +/- 28 versus 106 +/- 5 (control) or 61 +/- 13 (alanine + glycine enriched) ng/L] were greater for concanavalin A-stimulated spleen lymphocytes from mice fed the glutamine-enriched diet compared to those from mice fed the other two diets. Thus, increasing the amount of glutamine in the murine diet enhances the ability of T lymphocytes to respond to mitogenic stimulation. Taken together, these observations suggest that increasing the oral availability of glutamine could promote the T-cell driven, cell-mediated immune response.

Alanyl-glutamine-supplemented parenteral nutrition increases luminal mucus gel and decreases permeability in the rat small intestine

BACKGROUND

Effect of supplemental alanyl-glutamine in standard TPN (S-TPN) on luminal mucus gel and small intestinal permeability was investigated.

METHODS

Thirty Sprague-Dawley rats were divided into group I (n = 10), receiving standard rat diet; group II (n = 10), receiving S-TPN; and group III (n = 10), receiving alanyl-glutamine-supplemented TPN for 1 week. After 1 week, fluorescein isothiocyanate (FITC)-dextran was injected into the small intestine of the rats, and they were killed. A small intestinal sample and portal blood were obtained for morphologic and functional analysis of mucus gel and intestinal permeability.

RESULTS

In group II, thickness and optical density of mucus gel per millimeter serosal length of intestine were significantly lower than group I (p<.001) and were significantly higher in group III than in group II (p<.001). The number of goblet cells in the villi and in the crypt of the small intestine was significantly lower in group II than in group I (p<.001) and was significantly higher in group III than in group II (p<.001), with the exception of the villi of jejunum. Villous and crypt surface area per millimeter serosal length of intestine was significantly lower in group II than in group I (p<.001) and was significantly higher in group III than in group II (p<.001). Small intestinal permeability to FITC-dextran was significantly higher in group II than in group I (p<.001) and was significantly lower in group III than in group II (p<.001). Glucosamine synthetase level was significantly higher in group III than in group I and ileum of group II (p<.001).

CONCLUSIONS

Alanyl-glutamine-supplemented TPN prevents a decrease in mucus gel and an increase in small intestinal permeability associated with S-TPN.

Rate at which glutamine enters TCA cycle influences carbon atom fate in intestinal epithelial cells

Glutamine carbon entry into the tricarboxylic acid (TCA) cycle was assessed in small intestinal epithelial cells by measuring CO2 production from [1-14C]glutamine, and these data together with [U-14C]glutamine data were used to calculate fractional oxidation rates for glutamine. CO2 production from either [1-14C]glutamine or [U-14C]glutamine showed saturation kinetics, and the concentration needed to achieve the half-maximal rate of CO2 production was 0.7 and 0.4 mmol/l, respectively. Maximal rate for [1-14C]glutamine was twice that for [U-14C]glutamine. Increasing glutamine concentration did not cause proportional increases in glutamine entry into the TCA cycle and glutamine oxidation. Consequently, fractional oxidation of glutamine decreased with increasing glutamine concentration. Fractional oxidation could be predicted from the rate at which glutamine carbon entered the TCA cycle. (Aminooxy)acetic acid, an aminotransferase inhibitor, reduced entry of glutamine into the TCA cycle and increased fractional oxidation of glutamine. Glutamate carbon entered the TCA cycle at about one-half the rate of glutamine-derived glutamate carbon and had a higher fractional oxidation rate when provided at equivalent concentrations to glutamine. These differences in the rate of entry predictably account for the differences in the metabolic fate of glutamine vs. glutamate carbon.

Role of glutamine in immunologic responses

Glutamine has traditionally been thought of as a nonessential amino acid, but laboratory and clinical data suggests that it may be essential during certain inflammatory conditions, such as infection and injury. Glutamine is a necessary nutrient for cell proliferation, serves as a specific fuel for inflammatory cells and enterocytes, and, when present in appropriate concentrations, enhances cell function. During inflammatory states, glutamine consumption may outstrip endogenous production and a relative glutamine deficiency state may exist. Animal and clinical studies suggest that improved outcome may be possible by providing the appropriate dose of this nutrient by the appropriate route to achieve adequate tissue concentrations. Such an approach prevents patients from being exposed to some of the inadequacies of present day conventional nutrition. The overall benefit of providing an appropriate glutamine-supplemented diet to all metabolically compromised patients arises from the multiple anabolic and host protective effects of this amino acid, of which immunomodulation is only one important facet of glutamine's essential nature.

Effects of endotoxin challenge on hepatic amino acid transport during cancer

BACKGROUND

The hepatic uptake of amino acids is increased in both sepsis and cancer, and this response appears to be both global and essential in the catabolic host. Because immunocompromised cancer patients are susceptible to episodes of gram-negative sepsis, we examined the capacity of hepatocytes from normal and tumor-influenced livers to respond to the additional challenge of endotoxemia via increases in the Na+-dependent uptake of glutamine and zwitterionic amino acids by System N and System A, respectively.

MATERIALS AND METHODS

Fischer 344 rats were implanted with methylcholanthrene-induced fibrosarcomas. Control rats were sham-operated and pair-fed. Animal pairs (tumor burden = 8-32% carcass weight) were injected intraperitoneally with either Escherichia coli endotoxin (10 mg/kg) or PBS, and after 4 h, hepatocytes were isolated from the livers of the animals via collagenase perfusion and placed in primary culture. Three hours later, amino acid transport rates were measured using radiolabeled glutamine for System N and alpha-methylaminoisobutyric acid (MeAIB), a nonmetabolizable substrate specific for System A.

RESULTS

Cancer-independent of tumor size-and endotoxin each elicited similar 1.5- to 2-fold inductions of System N activity. When combined, their effects were additive rather than synergistic. In contrast, endotoxin induced an insignificant increase in System A activity, whereas cancer stimulated this carrier 2-fold in either the absence or the presence of endotoxin.

CONCLUSIONS

The primary glutamine and alanine carriers in hepatocytes are differentially influenced during catabolic states, and the tumor-influenced liver is competent to further increase glutamine uptake in response to additional catabolic insults.

Nutrition support in patients with multiple organ failure

The problem with any attempt to feed patients in multiple organ failure is that, because of an ongoing inflammatory process, the conventional techniques of supplying energy and protein do not maintain lean tissue mass. In addition, the conventional markers of nutritional status, both anthropometric (body mass and composition, arm circumference, etc.) and visceral protein (albumin, prealbumin) as well as immunological markers (delayed reactive skin hypersenstivity to common antigens and lymphocyte counts) are confounded by fluid retention (5-15 l) and the metabolic response to the illness. Recent research has focussed on the nature and origin of this inflammatory response, the problems of trying to feed an individual undergoing such a response, the details of the protein breakdown observed in sepsis and multiple organ failure and methods of modifying the response favourably.

Nutritional and pathophysiological modulation of body protein

This review deals with recent developments in methodology and the effects of nutrition, hormonal modulation and muscular activity on changes in lean body mass and protein turnover in the whole body and in muscle. It also deals with organ-specific protein metabolism of the splanchnic region, particularly the gut, liver and kidney.

Glutamine-enriched enteral diet enhances bacterial clearance in protected bacterial peritonitis, regardless of glutamine form

BACKGROUND

The effects of glutamine (Gln)-enriched enteral diets on bacterial clearance were investigated in a rat protracted peritonitis model. The effects of the Gln form, peptide-based vs free amino acid-based, were also compared.

METHODS

Twenty-three rats underwent gastrostomy. An osmotic pump was implanted in the peritoneal cavity. The rats received a continuous intragastric infusion of one of three diets: Gln-depleted (Gln 0), Gln-enriched with the Gln in free amino acid form (Gln F), or Gln-enriched with the Gln in oligopeptide form (Gln P). The three formulas were isocaloric and isonitrogenous. The pumps delivered a continuous infusion of Escherichia coli, starting at 48 hours after implantation, for 24 hours. Then, the animals were killed.

RESULTS

Bacterial numbers in peritoneal lavaged fluid (PLF) and the liver were significantly lower in the Gln P and Gln F groups than in the Gln 0 group. The bacterial number in PLF correlated with that in the liver. Neither the number nor the population of peritoneal exudative cells differed among groups. Plasma levels of proline, alanine and citrulline were significantly higher in the Gln P and Gln F groups than in the Gln 0 group. Both Gln supplemented groups showed significantly greater villous height, crypt depth, and numbers of mitoses per crypt in the small intestine than the Gln 0 group.

CONCLUSIONS

Supplemental Gln enhances peritoneal and hepatic bacterial clearance, regardless of Gln form. Gln-enriched may be more beneficial than Gln-depleted enteral diets in peritonitis.

Alanylglutamine-enriched total parenteral nutrition improves protein metabolism more than branched chain amino acid-enriched total parenteral nutrition in protracted peritonitis

Branched chain amino acids (BCAAs) and glutamine are both recommended in catabolic states. The object of this study was to compare the efficacies of alanylglutamine (Ala-Gln)-enriched and BCAA-enriched total parenteral nutrition (TPN) on the protein kinetics in peritonitis. Rats were divided into Ala-Gln and BCAA groups after intraperitoneal implantation of an osmotic pump, delivering a continuous infusion of Escherichia coli. Glutamine composed 30.0% (w/v) of the total amino acids in the Ala-Gln group, and BCAA composed 30.5% (w/v) of the total amino acids in the BCAA group. The two solutions were isocaloric and isonitrogenous. Whole body protein turnover and organ fractional protein synthetic rates (FSR) were measured on days 3 and 5. Serum amino acid levels and mucosal morphology were determined. Ala-Gln group had higher rates of whole body protein turnover, and hepatic FSR on both days. Serum glutamine levels correlated with hepatic and muscle FSR. Ala-Gln TPN group had greater mucosal thickness, numbers of mitoses per crypt, and FSR in distal intestine. Ala-Gln-enriched TPN may be a useful nutritional treatment modality in sepsis.