A double-blind, prospective, randomized study of glutamine-enriched compared with standard peptide-based feeding in critically ill patients

The Renal Safety of L-Carnitine, L-Arginine, and Glutamine in Athletes and Bodybuilders

One of the major concerns about taking amino acid supplements is their potential adverse effects on the kidney as a major organ involved in the metabolism and excretion of exogenous substances. The aim of this study is to review available data about renal safety of the most prominent amino acid supplements including L-arginine, glutamine and also L-carnitine as well as creatine (as amino acid derivatives) in athletes and bodybuilders. The literature was searched by keywords such as "L-carnitine", "L-arginine", "glutamine", and "kidney injury" in databases such as Scopus, Medline, Embase, and ISI Web of Knowledge. Articles published from 1950 to December 2017 were included. Among 3171, 5740, and 1608 records after primary search in the relevant databases, 8, 7, and 5 studies have been finally included, respectively, for L-carnitine, L-arginine, and glutamine in this review. Arginine appears to have both beneficial and detrimental effects on kidney function. However, adverse effects are unlikely to occur with the routine doses (from 3 to >100 g/day). The risks and benefits of L-carnitine on the athletes' and bodybuilders' kidney have not been evaluated yet. However, L-carnitine up to 6000 mg/day is generally considered to be a safe supplement at least in healthy adults. Both short-term (20-30 g within a few hours) and long-term (0.1 g/kg four times daily for 2 weeks) glutamine supplementation in healthy athletes were associated with no significant adverse effects, but it can cause glomerulosclerosis and serum creatinine level elevation in the setting of diabetic nephropathy. Creatine supplementation (ranged from 5 to 30 g/day) also appears to have no detrimental effects on kidney function of individuals without underlying renal diseases. More clinical data are warranted to determine the optimal daily dose and intake duration of common supplemental amino acids associated with the lowest renal adverse effects in sportsmen and sports women.

Nutritional Aspects of Acute Pancreatitis

The goal of nutritional support in acute pancreatitis is to reduce inflammation, prevent nutritional depletion, correct a negative nitrogen balance, and improve outcomes. Enteral nutrition (EN) in severe acute pancreatitis (SAP) should be preferred to parenteral nutrition. It maintains the integrity of the gut barrier, decreases intestinal permeability, downregulates the systemic inflammatory response, maintains intestinal microbiota equilibrium, and reduces the complications of the early phase of SAP, improving morbidity and possibly improving mortality, and it is less expensive. Further studies to understand optimal timing of nutrition, route of delivery of EN, and the type of nutrition and nutrients are necessary.

Enteral Nutrition and Bone Marrow Transplantation

This retrospective study evaluated the efficacy of enteral nutrition for pediatric patients undergoing the challenging treatment of allogeneic bone marrow transplantation. During the period from January 1999 to May 2000, 15 patients were transplant recipients. On admission to the hospital, 87% of patients were above the 50th percentile for weight for age. Nasogastric tubes were inserted while platelet counts remained greater than 50 × 10 9 mL/L. A specialized elemental formula for pediatric patients was commenced. These feeds were administered continuously and were titrated until caloric requirement or tolerance level had been achieved. During hospitalization for bone marrow transplantation, enteral nutrition was the major form of nutritional support for all patients. Enteral feeds continued even during maximal gut toxicity and were supported with antiemetics and analgesia. There were insignificant weight fluctuations during hospitalization, with 80% of children above the 50th percentile weight for age being discharged. Enteral nutrition via a nasogastric tube was effective in the provision of nutrition during bone marrow transplantation and continues to have an important role in this unit.

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.

Enteral glutamine supplementation in critically ill patients: a systematic review and meta-analysis

Introduction

Glutamine (GLN) has been suggested to have a beneficial influence on outcomes of critically ill patients. However, recent large-scale trials have suggested harm associated with GLN supplementation. Recently, systematic reviews on the use of parenteral GLN have been published; however, less information is available on the role of enteral GLN. Therefore, the aim of this systematic review was to study the effects of enteral GLN supplementation in patients with critical illness.

Methods

We identified randomized controlled trials conducted from 1980 to 2014 with enterally administered GLN in adult critically ill patients. Studies of parenteral GLN only or combined enteral-parenteral GLN were excluded. The methodological quality of studies was scored, and trial data were statistically combined. We examined a priori the treatment effects in subgroups of trials of burn and trauma patients.

Results

A total of 11 studies involving 1079 adult critically ill patients and enteral GLN supplementation were identified. Enteral GLN supplementation was not associated with a reduction of hospital mortality (risk ratio [RR] 0.94, 95 % confidence interval [CI] 0.65–1.36; p =0.74), infectious complications (RR 0.93, 95 % CI 0.79–1.10; p =0.39) or stay in the intensive care unit (weighted mean difference [WMD] −1.36 days, 95 % CI −5.51 to 2.78; p =0.52). However, there was a significant reduction in hospital stay (WMD 4.73 days, 95 % CI −8.53 to −0.90; p =0.02). In the subset of studies of patients with burns, enteral GLN supplementation was associated with significant reductions in hospital mortality (RR 0.19, 95 % 0.06–0.67; p =0.010) and hospital stay (WMD −9.16, 95 % CI −15.06 to −3.26; p =0.002). There was no effect in trauma patients.

Conclusions

Enteral GLN supplementation does not confer significant clinical benefit in critically ill patients, with the exception of reduced hospital stay. There may be a significant benefit in patients with burns, but data are sparse and larger randomized trials are warranted to confirm this effect.

The relationship between fasting plasma citrulline concentration and small intestinal function in the critically ill

Introduction

In this study, we aimed to evaluate whether fasting plasma citrulline concentration predicts subsequent glucose absorption in critically ill patients.

Methods

In a prospective observational study involving 15 healthy and 20 critically ill subjects, fasting plasma citrulline concentrations were assayed in blood samples immediately prior to the administration of a liquid test meal (1 kcal/ml; containing 3 g of 3-O-methylglucose (3-OMG)) that was infused directly into the small intestine. Serum 3-OMG concentrations were measured over the following 4 hours, with the area under the 3-OMG concentration curve (AUC) calculated as an index of glucose absorption.

Results

The groups were well matched in terms of age, sex and body mass index (BMI) (healthy subjects versus patients, mean (range) values: age, 47 (18 to 88) versus 49 (21 to 77) years; sex ratio, 60% versus 80% male; BMI, 25.2 (18.8 to 30.0) versus 25.5 (19.4 to 32.2) kg/m²). Compared to the healthy subjects, patients who were critically ill had reduced fasting citrulline concentration (26.5 (13.9 to 43.0) versus 15.2 (5.7 to 28.6) μmol/L; P < 0.01) and glucose absorption (3-OMG AUC, 79.7 (28.6 to 117.8) versus 61.0 (4.5 to 97.1) mmol/L/240 min; P = 0.05). There was no relationship between fasting citrulline concentration and subsequent glucose absorption (r = 0.28; P = 0.12).

Conclusions

Whereas both plasma citrulline concentrations and glucose absorption were reduced in critical illness, fasting plasma citrulline concentrations were not predictive of subsequent glucose absorption. These data suggest that fasting citrulline concentration does not appear to be a marker of small intestinal absorptive function in patients who are critically ill.

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 administration in patients undergoing cardiac surgery and the influence on blood glutathione levels

BACKGROUND

Cardiac surgery with an extracorporeal circulation cardiopulmonary bypass (CPB) is characterized by an oxidative stress response. Glutathione (GSH) belongs to the major antioxidative defense. In metabolic stress, glutamine (GLN) may be the rate-limiting factor of GSH synthesis. Decreased GLN plasma levels were observed after various critical states. We evaluated, in patients undergoing open heart surgery with CPB, the effects of a peri-operative GLN supplementation on GSH in whole blood and assessed their influence on the Sequential Organ Failure Assessment score and the intensive care unit length of stay.

METHODS

In this prospective, randomized, double-blinded study, we included 60 patients (age older than 70 years, ejection fraction <40% or mitral valve replacement) undergoing an elective cardiac surgery with CPB. We randomly assigned each subject to receive an infusion with either GLN (0.5 g/kg/day, group 1) or an isonitrogeneous, isocaloric, isovolemic amino acids solution (group 2) or saline (group 3).

RESULTS

From the first post-operative day GLN plasma levels in group 1 were significantly increased compared with the other groups. With saline GSH the levels decreased significantly post-operatively compared with GLN. We observed a significant correlation between GLN delivery and GSH levels.

CONCLUSIONS

A peri-operative high-dose GLN infusion increased plasma GLN concentrations and maintained the GSH levels after cardiac surgery with CPB.

Immunonutrition in surgical and critically ill patients

Surgery, trauma, burns and injury induce an inflammatory response that can become excessive and damaging in some patients. This hyperinflammation can be followed by an immunosuppressed state which increases susceptibility to infection. The resulting septic syndromes are associated with significant morbidity and mortality. A range of nutrients are able to modulate inflammation (and the associated oxidative stress) and to maintain or improve immune function. These include several amino acids, antioxidant vitamins and minerals, long-chain n-3 fatty acids and nucleotides. Experimental studies support a role for each of these nutrients in surgical, injured or critically ill patients. There is good evidence that glutamine influences immune function in such patients and that this is associated with clinical improvement. Evidence is also mounting for the use of long-chain n-3 fatty acids in surgical and septic patients, but more evidence of clinical efficacy is required. Mixtures of antioxidant vitamins and minerals are also clinically effective, especially if they include selenium. Their action appears not to involve improved immune function, although an anti-inflammatory mode of action has not been ruled out. Enteral immunonutrient mixtures, usually including arginine, nucleotides and long-chain n-3 fatty acids, have been used widely in surgical and critically ill patients. Evidence of efficacy is good in surgical patients. However whether these same mixtures are beneficial, or should even be used, in critically ill patients remains controversial, since some studies show increased mortality with such mixtures. There is a view that this is due to a high arginine content driving nitric oxide production.

Effect of an immunonutrient mix on human colorectal adenocarcinoma cell growth and viability

OBJECTIVE

L-Glutamine, L-arginine, RNA, and omega-3 polyunsaturated fatty acids (PUFAs) have been incorporated into nutritional formulas to improve immunity of patients with gastrointestinal cancer. We therefore examined the individual and net effects of these immunonutrients on four different human colorectal adenocarcinoma cell lines.

METHODS

LS174T, HT-29, CO112, and Caco-2 cells were exposed to dilutions of 1:50, 1:100, and 1:1000 of a mix or individual components of a mix of 15 g/L of L-glutamine, 16.3 g/L of L-arginine, 1.6 g/L of RNA, and 2.7 g/L of omega-3 PUFAs. Cell growth kinetic was assessed using cell count with a flow cytometer. Cell cycle and apoptosis were evaluated with double fluorescence-activated cell sorter analyses using bromodeoxyuridine labeling index and annexin V staining, respectively. One-way analysis of variance and Student's t tests were used for comparison.

RESULTS

Evaluation of the cell growth kinetic over an 18-d period showed that the immunonutrient mix stimulated cancer cell growth only when diluted > or =100 times. Individual component evaluation indicated that the cell growth stimulation was mainly due to the presence of L-glutamine and to a lesser extent RNA in the mix. L-Arginine had no effect. At a lower dilution of 1:50, omega-3 PUFA concentrations were sufficient to induce cell cycle arrest and massive cell death in part through apoptosis.

CONCLUSION

These results suggest that cancer cell growth stimulation by current immunonutrient formulas is unlikely due to predominant cytotoxic effect of omega-3 PUFAs.

ESPEN Guidelines on Enteral Nutrition: Intensive care

Enteral nutrition (EN) via tube feeding is, today, the preferred way of feeding the critically ill patient and an important means of counteracting for the catabolic state induced by severe diseases. These guidelines are intended to give evidence-based recommendations for the use of EN in patients who have a complicated course during their ICU stay, focusing particularly on those who develop a severe inflammatory response, i.e. patients who have failure of at least one organ during their ICU stay. These guidelines were developed by an interdisciplinary expert group in accordance with officially accepted standards and are based on all relevant publications since 1985. They were discussed and accepted in a consensus conference. EN should be given to all ICU patients who are not expected to be taking a full oral diet within three days. It should have begun during the first 24h using a standard high-protein formula. During the acute and initial phases of critical illness an exogenous energy supply in excess of 20-25 kcal/kg BW/day should be avoided, whereas, during recovery, the aim should be to provide values of 25-30 total kcal/kg BW/day. Supplementary parenteral nutrition remains a reserve tool and should be given only to those patients who do not reach their target nutrient intake on EN alone. There is no general indication for immune-modulating formulae in patients with severe illness or sepsis and an APACHE II Score >15. Glutamine should be supplemented in patients suffering from burns or trauma.

Glutamine: do the data support the cause for glutamine supplementation in humans?

This review examines the preclinical rationale for using glutamine supplements and reviews the prospective randomized trials using glutamine to improve outcomes in patients. A special role for glutamine in gut physiology and in management of a variety of serious illnesses has been suggested, because it is the most abundant extracellular amino acid, and is used at high rates by the gut, liver, central nervous system, and immune cells. A state of relative Gln deficiency has been postulated in humans based on the decrease in plasma Gln in acute critical illness, but the decrease in plasma Gln is not specific for that amino acid, predicts only poorer outcome, and has not been validated to identify a deficiency state. Current evidence does not necessarily predict a special need or role for Gln in critical illness. Clinical efficacy of supplemental Gln has been difficult to demonstrate, possibly related to the lack of a Gln deficiency state, the wide range of end points used that reflect the lack of certainty of the predicted effect of supplementation, the heterogeneous patient populations studied, the lack of stable clinical course during the study, the lack of adequate power, and the relatively short follow-up period. Prospective randomized clinical trials of Gln supplementation were reviewed in patients with short-bowel syndrome, during cancer chemotherapy and in bone marrow transplantation, and in surgical, burn, and intensive care unit patients. No firm recommendation can be made at this time. Future studies should seek to develop a more standard and stable design for intervention in sufficiently powered studies.

Short-term enteral glutamine does not enhance protein accretion in burned children: a stable isotope study

OBJECTIVE

Glutamine is a nonessential amino acid that, in recent years, has been found to play important roles in several metabolic and immunologic processes. It has been theorized that, in a stressed state, it may become "conditionally essential" because the patient's ability to manufacture glutamine may not be adequate to meet their needs under this condition. We chose to evaluate the ability of 48 hours of enteral glutamine to enhance immediate nitrogen accretion in stressed pediatric burn patients.

METHODS

Nine children with serious burns who were tolerating tube feedings were enrolled in a human studies committee-approved protocol in which they received 48 hours of enteral feedings with glutamine replacing 20% of essential and nonessential amino acids and 48 hours of isonitrogenous, isocaloric standard enteral feedings. This interval was chosen to help ensure that the study periods were comparable from a metabolic perspective. At the end of each period, protein kinetics were determined by a primed constant infusion of L-[1-(13)C] leucine tracer. The order of the studies was randomized. Seven children completed both phases of the study. Results were compared by paired t test and are presented as mean +/- standard error of the mean.

RESULTS

During the glutamine feeding period, the leucine flux and leucine oxidation rate were significantly lower than those in the conventional feeding period. This reflects a reduction in total leucine intake from 80 +/- 11 to 62 +/- 10 micromol/kg per hour. However, there was no significant difference in the net balance of leucine accretion into proteins between these 2 dietary periods, which indicated that enriched glutamine feeding for 48 hours did not result in an immediate whole body protein gain in this group of pediatric patients. In addition, plasma glutamine concentration showed a moderate increase after 48 hours of supplementation but did not reach significance.

CONCLUSION

Rapid protein accretion does not occur with short-term enteral glutamine supplementation. Several days of glutamine supplementation may be required to restore plasma glutamine levels and stimulate protein synthesis.

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.

Gut mucosal and plasma concentrations of glutamine: a comparison between two enriched enteral feeding solutions in critically ill patients

Background

Addition of glutamine to enteral nutrition formulas is consistently associated with a significant decrease in septic morbidity in critically ill patients, possibly related to the attenuation of gut dysfunction. This pilot study was undertaken to compare the effects of enteral administration of two glutamine-enriched formulas containing either additional free glutamine or glutamine-rich proteins, with a standard solution on plasma and mucosal concentrations of glutamine in patients admitted in the Department of Intensive Care.

Methods

Following randomization, glutamine concentration was determined in endoscopically sampled duodenal biopsies and plasma, before and after a 7-day period of continuous administration of the designated solution.

Results

The mucosal concentration of glutamine increased in the duodenal biopsies sampled from patients randomized to the solution containing the glutamine-rich proteins (from 3.6 ± 2.2 to 6.7 ± 5.2 micro-mol/g protein), but not from the others. There were no differences between the 3 groups in the plasma concentrations of glutamine, which remained stable over time.

Conclusion

The source of supplemental glutamine can influence gut mucosal glutamine concentrations, suggesting differences in its availability or utilization.

A randomised clinical trial to assess the effect of total enteral and total parenteral nutritional support on metabolic, inflammatory and oxidative markers in patients with predicted severe acute pancreatitis (APACHE II > or =6)

BACKGROUND

Total enteral nutrition (TEN) within 48 h of admission has recently been shown to be safe and efficacious as part of the management of severe acute pancreatitis. Our aim was to ascertain the safety of immediate TEN in these patients and the effect of TEN on systemic inflammation, psychological state, oxidative stress, plasma glutamine levels and endotoxaemia.

METHODS

Patients admitted with predicted severe acute pancreatitis(APACHE II score >5) were randomised to total enteral (TEN; n = 8) or total parenteral nutrition (TPN; n = 9). Measurements of systemic inflammation (C-reactive protein), fatigue (visual analogue scale), oxidative stress (plasma thiobarbituric acid-reactive substances), plasma glutamine and anti-endotoxin IgG and IgM antibody concentrations were made on admission and repeated on days 3 and 7 thereafter. Clinical progress was monitored using APACHE II score. Organ failure and complications were recorded.

RESULTS

All patients tolerated the feeding regime well with few nutrition-related complications. Fatigue improved in both groups but more rapidly in the TEN group. Oxidative stress was high on admission and rose by similar amounts in both groups. Plasma glutamine concentrations did not change significantly in either group. In the TPN group, 3 patients developed respiratory failure and 3 developed non-respiratory single organ failure. There were no such complications in the TEN group. Hospital stay was shorter in the TEN group [7(4-14) vs. 10 (7-26) days; p = 0.05] as was time to passing flatus and time to opening bowels [1 (0-2) vs. 2 (1-5)days; p = 0.01]. The cost of TEN was considerably less than of TPN.

CONCLUSION

Immediate institution of nutritional support in the form of TEN is safe in predicted severe acute pancreatitis. It is as safe and as efficacious as TPN and may be beneficial in the clinical course of this disease.

Clinical evidence for enteral nutritional support with glutamine: a systematic review

OBJECTIVE

The purpose of this systematic review was to locate and assess the quality of scientific evidence to establish a graded recommendation based on the effectiveness of glutamine-enriched enteral nutrition in different medical and surgical conditions. We were concerned with the following topics: 1) benefits of enteral administration of glutamine in different pathologic conditions, and 2) dose, duration, and time of initiation of glutamine-enriched diets.

METHODS

The sources consulted for the search were MEDLINE, EMBASE, Cochrane Database of Systematic Reviews, Healthstar and HSTAT. Ninety-one studies were assessed; after a methodologic review (primary review), only 16 studies met the inclusion criteria for analysis by a group of experts (secondary review). The coordinators supervised all data, and a final consensus was reached among the coordinators, experts, and methodologists.

RESULTS AND CONCLUSIONS

Glutamine-enriched diets showed good overall tolerance, improvement of immunologic aspects in multiple trauma patients, cost reduction in critically ill patients, and improvement of mucositis in post-chemotherapy patients (grade B recommendations). The doses given and the duration of therapy varied widely depending on the pathologic condition. Intake of 20 to 30 g/d, early initiation of diet, and maintenance for 5 d or longer are recommended (grade C recommendations).

Enteral glutamine supplementation and morbidity in low birth weight infants

OBJECTIVE

To determine if glutamine-supplemented enteral nutrition decreased the incidence of nosocomial sepsis in neonates.

METHODS

In a multicenter (n = 20) clinical trial, we randomly allocated infants (n = 649) with birth weight between 500 and 1250 g, who were <7 days of age, and had no major anomalies to receive enteral glutamine supplementation (0.3 g/kg/day) or sterile water (placebo) for the first 28 days. The primary outcome variable was the number of infants who had blood culture-proven nosocomial sepsis between 7 days' and 36 weeks' postmenstrual age.

RESULTS

Infants were assigned to placebo (n = 335) or to glutamine supplementation (n = 314). Neonates assigned to glutamine were similar to those assigned placebo for demographic characteristics and nutritional support during the first week. There was no difference in the occurrence of culture-proven nosocomial sepsis (33.7% vs 30.9%) or suspected sepsis (51.6% vs 47.1%) between the placebo and glutamine groups; however, neonates treated with glutamine less often had gastrointestinal dysfunction (7.5% vs 2.5%, P <.01) and severe neurologic sequelae (15.1% vs 10.4%, P =.08).

CONCLUSIONS

At a dose of 0.3 g/kg/day, enteral glutamine does not appear to reduce nosocomial sepsis in premature neonates.

Infection, multiple organ failure, and survival in the intensive care unit: influence of glutamine-supplemented parenteral nutrition on acquired infection

OBJECTIVE

We investigated the effect of a glutamine-supplemented parenteral nutrition on intensive-care-acquired infection (ICAI) and its relation to outcome.

METHODS

We analyzed new data prospectively collected during a double-blind, randomized, and controlled trial in an adult general intensive care unit previously reported (Nutrition 1997;13:295). Eighty-four patients were randomized to receive glutamine-supplemented total parenteral nutrition or an isonitrogenous, isoenergetic control. Sepsis was present on admission in 71% of the patients. Clinical and microbiological data were collected on all new infective episodes and associated treatment decisions. Data were analyzed blind to the randomization and study outcome.

RESULTS

There was no significant difference in the number of patients developing new infections or in the number occurring during the first 5 d. There was a non-significant trend to increased numbers of infections in those patients receiving the control feed for at least 5 d. In these patients the glutamine recipients showed significantly fewer catheter-related infections: 21 versus 12 (P = 0.026). The difference in overall 6-mo mortality was almost completely described by those patients fed for at least 5 d: 9 of 25 versus 18 of 27 using the control nutrition (P = 0.05). Of the deaths in the intensive care unit due to multiple organ failure, 8 of 8 in the glutamine group and 14 of 16 in the control group sustained one or more ICAI and accounted for 38% versus 74%, respectively, of the ICAIs occurring in those patients. In those patients, despite a similar high incidence of colonization with Candida, those receiving glutamine developed fewer Candida infections and none died, whereas six control patients who developed Candida infections died from multiple organ failure (P = 0.02). Survival was not related to the reduced occurrence of the first acquired infection; however, binary logistic regression analysis of glutamine and the incidence of ICAI after starting total parenteral nutrition to outcome showed that only glutamine was significantly associated with improved 6-mo survival (P = 0.027).

CONCLUSIONS

In these severely ill patients, parenteral nutrition containing glutamine may not reduce the overall incidence of ICAI, but it may reduce the risk of dying from acquired infections. The improved survival seen at 6 mo appeared related mostly to reduced mortality in the intensive care unit from multiple organ failure in those patients in whom acquired infections are common.

Protective nutrients and functional foods for the gastrointestinal tract

Epithelial and other cells of the gastrointestinal mucosa rely on both luminal and bloodstream sources for their nutrition. The term functional food is used to describe nutrients that have an effect on physiologic processes that is separate from their established nutritional function, and some of these nutrients are proposed to promote gastrointestinal mucosal integrity. We review the recent in vitro, animal, and clinical experiments that evaluated the role of several types of gastrointestinal functional foods, including the amino acids glutamine and arginine, the essential micronutrients vitamin A and zinc, and 2 classes of food additives, prebiotics and probiotics. Many of the data from preclinical studies support a strong role for enteral nutrients in gastrointestinal health; in comparison, the data from human studies are limited. In some cases, impressive data from in vitro and animal studies have not been replicated in human trials. Other clinical trials have shown positive health benefits, but some of those studies were plagued by flaws in study design or analysis. The methods available to detect important changes in human gastrointestinal function and structure are still limited, but with the development of more sensitive measures of gastrointestinal function, the effects of specific nutrients may be more easily detected. This may facilitate the development of phase 3 clinical trials designed to more rigorously evaluate the effects of a particular nutrient by focusing on valid and reliable outcome measures. Regulatory changes in the way in which health claims can be made for dietary supplements should also be encouraged.

Glutamine alimentation in catabolic state

Glutamine should be reclassified as a conditionally essential amino acid in the catabolic state because the body's glutamine expenditures exceed synthesis and low glutamine levels in plasma are associated with poor clinical outcome. After severe stress, several amino acids are mobilized from muscle tissue to supply energy and substrate to the host. Glutamine is one of the most important amino acids that provide this function. Glutamine acts as the preferred respiratory fuel for lymphocytes, hepatocytes and intestinal mucosal cells and is metabolized in the gut to citrulline, ammonium and other amino acids. Low concentrations of glutamine in plasma reflect reduced stores in muscle and this reduced availability of glutamine in the catabolic state seems to correlate with increased morbidity and mortality. Adding glutamine to the nutrition of clinical patients, enterally or parenterally, may reduce morbidity. Several excellent clinical trials have been performed to prove efficacy and feasibility of the use of glutamine supplementation in parenteral and enteral nutrition. The increased intake of glutamine has resulted in lower septic morbidity in certain critically ill patient populations. This review will focus on the efficacy and the importance of glutamine supplementation in diverse catabolic states.

Why is L-glutamine metabolism important to cells of the immune system in health, postinjury, surgery or infection?

Glutamine is normally considered to be a nonessential amino acid. However, recent studies have provided evidence that glutamine may become "conditionally essential" during inflammatory conditions such as infection and injury. It is now well documented that under appropriate conditions, glutamine is essential for cell proliferation, that it can act as a respiratory fuel and that it can enhance the function of stimulated immune cells. Studies thus far have determined the effect of extracellular glutamine concentration on lymphocyte proliferation and cytokine production, macrophage phagocytic plus secretory activities and neutrophil bacterial killing. Other cells of the immune system remain to be studied. The high rate of glutamine utilization and its importance to the function of lymphocytes, macrophages and neutrophils have raised the question "why glutamine?" because these cells have access to a variety of metabolic fuels both in vivo and in vitro. I have attempted to answer this question in this article. Additionally, knowledge of the rate of utilization and the pathway of metabolism of glutamine by cells of the immune system raises some intriguing questions concerning therapeutic manipulation of utilization of this amino acid such that the proliferative, phagocytic and secretory capacities of cells of the defense system may be beneficially altered. Evidence to support the hypothesis that glutamine is beneficially immunomodulatory in animal models of infection and trauma, as well as trauma in humans, is provided.

The evidence for glutamine use in the critically-ill

Research into the metabolic role of glutamine in trauma and sepsis brings evidence to suggest a conditional deficiency occurs because increased and altered tissue demands exceed endogenous production. Such a deficiency has functional implications, and the restorative provision of parenteral glutamine has been shown to offer improved clinical outcomes in a variety of conditions. In the critically-ill it is associated with improvements in immune function, and improved survival from infection leading to an overall improved outcome.

Glutamine: commercially essential or conditionally essential? A critical appraisal of the human data

Glutamine is a nonessential amino acid that can be synthesized from glutamate and glutamic acid by glutamate-ammonia ligase. Glutamine is an important fuel source for the small intestine. It was proposed that glutamine is necessary for the maintenance of normal intestinal morphology and function in the absence of luminal nutrients. However, intestinal morphologic and functional changes related to enteral fasting and parenteral nutrition are less significant in humans than in animal models and may not be clinically significant. Therefore, it is unclear whether glutamine is necessary for the preservation of normal intestinal morphology and function in humans during parenteral nutrition. It was suggested that both glutamine-supplemented parenteral nutrition and enteral diets may pre-vent bacterial translocation via the preservation and augmentation of small bowel villus morphology, intestinal permeability, and intestinal immune function. However, it is unclear whether clinically relevant bacterial translocation even occurs in humans, much less whether there is any value in the prevention of such occurrences. Results of the therapeutic use of glutamine in humans at nonphysiologic doses indicate limited efficacy. Although glutamine is generally recognized to be safe on the basis of relatively small studies, side effects in patients receiving home parenteral nutrition and in those with liver-function abnormalities have been described. Therefore, on the basis of currently available clinical data, it is inappropriate to recommend glutamine for therapeutic use in any condition.

Free and protein-bound glutamine have identical splanchnic extraction in healthy human volunteers

The objectives of the present study were to determine the splanchnic extraction of glutamine after ingestion of glutamine-rich protein ((15)N-labeled oat proteins) and to compare it with that of free glutamine and to determine de novo glutamine synthesis before and after glutamine consumption. Eight healthy adults were infused intravenously in the postabsorptive state with L-[1-(13)C]glutamine (3 micromol x kg(-1) x h(-1)) and L-[1-(13)C]lysine (1.5 micromol x kg(-1) x h(-1)) for 8 h. Four hours after the beginning of the infusion, subjects consumed (every 20 min) a liquid formula providing either 2.5 g of protein from (15)N-labeled oat proteins or a mixture of free amino acids that mimicked the oat-amino acid profile and contained L-[2,5-(15)N(2)]glutamine and L-[2-(15)N]lysine. Splanchnic extraction of glutamine reached 62.5 +/- 5.0% and 66.7 +/- 3.9% after administration of (15)N-labeled oat proteins and the mixture of free amino acids, respectively. Lysine splanchnic extraction was also not different (40.9 +/- 11.9% and 34.9 +/- 10.6% for (15)N-labeled oat proteins and free amino acids, respectively). The main conclusion of the present study is that glutamine is equally bioavailable when given enterally as a free amino acid and when protein bound. Therefore, and taking into consideration the drawbacks of free glutamine supplementation of ready-to-use formulas for enteral nutrition, protein sources naturally rich in this amino acid are the best option for providing stable glutamine.

Whole body and skeletal muscle glutamine metabolism in healthy subjects

We measured glutamine kinetics using L-[5-15N]glutamine and L-[ring-2H5]phenylalanine infusions in healthy subjects in the postabsorptive state and during ingestion of an amino acid mixture that included glutamine, alone or with additional glucose. Ingestion of the amino acid mixture increased arterial glutamine concentrations by approximately 20% (not by 30%; P < 0.05), irrespective of the presence or absence of glucose. Muscle free glutamine concentrations remained unchanged during ingestion of amino acids alone but decreased from 21.0 +/- 1.0 to 16.4 +/- 1.6 mmol/l (P < 0.05) during simultaneous ingestion of glucose due to a decrease in intramuscular release from protein breakdown and glutamine synthesis (0.82 +/- 0.10 vs. 0.59 +/- 0.06 micromol x 100 ml leg(-1) x min(-1); P < 0.05). In both protocols, muscle glutamine inward and outward transport and muscle glutamine utilization for protein synthesis increased during amino acid ingestion; leg glutamine net balance remained unchanged. In summary, ingestion of an amino acid mixture that includes glutamine increases glutamine availability and uptake by skeletal muscle in healthy subjects without causing an increase in the intramuscular free glutamine pool. Simultaneous ingestion of glucose diminishes the intramuscular glutamine concentration despite increased glutamine availability in the blood due to decreased glutamine production.

Glutamine and arginine: immunonutrients for improved health

There is considerable literature demonstrating that specific nutrients can influence immune function in health and disease. This review will examine the literature and the rational for classifying two amino acids, glutamine (gln) and arginine (arg), as "immunonutrients" during infections. An understanding of immune defenses during infections (virus, parasite, bacteria, protozoa) and metabolism of gln and arg by immune cells is necessary to understand how these nutrients can influence specific functions of the immune system. This review focuses on several key clinical studies in immunosuppressed individuals (burn patients, individuals with cancer and HIV infection, and those undergoing surgery or who have experienced major traumas) that have tested the hypothesis that the provision of gln and/or arg is beneficial to immune function and clinical outcome. These clinical studies support the dietary "essentiality" of these two nutrients for improving immune responses in most immunosuppressive states associated with high rates of infection. However, the role of these nutrients in modulating the immune changes that occur with exercise in healthy athletes demands additional experiments.

Conseqüências do exercício para o metabolismo da glutamina e função imune

Para o atleta, o objetivo do treinamento é aperfeiçoar sua capacidade física para obtenção do melhor desempenho em competições. Isso o leva a procurar os mais novos e eficientes métodos de treinamento. Um aspecto importante do programa de treinamento é o período de recuperação entre as sessões de exercícios, imprescindível para que ocorram as adaptações fisiológicas, como as alterações morfológicas e a supercompensação das reservas energéticas. A liberação de glutamina pelos músculos esqueléticos é aumentada durante o exercício. Como conseqüência, o conteúdo muscular de glutamina diminui após um exercício extenuante. Este aminoácido, entretanto, é muito importante para a funcionalidade dos leucócitos (linfócitos, macrófagos e neutrófilos). Portanto, após um exercício intenso, a concentração plasmática de glutamina diminui, suprimindo a função imune e tornando o indivíduo mais suscetível a infecções respiratórias. Nesta revisão são discutidas as implicações do exercício sobre o metabolismo dos músculos esqueléticos e leucócitos.

Evolution of nutritional support in acute pancreatitis

BACKGROUND

Acute pancreatitis is a catabolic illness and patients with the severe form have high metabolic and nutrient demands. Artificial nutritional support should therefore be a logical component of treatment. This review examines the evidence in favour of initiating nutritional support in these patients and the effects of such support on the course of the disease.

METHODS

Medline and Science Citation Index searches were performed to locate English language publications on nutritional support in acute pancreatitis in the 25 years preceding December 1999. Manual cross-referencing was also carried out. Letters, editorials, older review articles and most case reports were excluded.

RESULTS AND CONCLUSION

There is no evidence that nutritional support in acute pancreatitis affects the underlying disease process, but it may prevent the associated undernutrition and starvation, supporting the patient while the disease continues and until normal and sufficient eating can be resumed. The safety and feasibility of enteral nutrition in acute pancreatitis have been established; enteral nutrition may even be superior to parenteral nutrition. Some patients, however, cannot tolerate enteral feeding and this route may not be practical in others. Parenteral nutrition still has a role, either on its own or in combination with the oral and enteral routes, depending on the stage of the illness and the clinical situation.

Protein metabolism in the extremely low-birth weight infant

Although extensive data are available on the impact of nutrient and protein administration on growth, plasma amino acids, and nitrogen balance in the newborn and growing infants, relatively few studies have carefully examined the dynamic aspects of protein metabolism in vivo and particularly in the micropremie or ELBW infant. These studies show that the very preterm infants, either because of immaturity or because of the intercurrent illness, have high rates of protein turnover and protein breakdown. This high rate of proteolysis is not as responsive to nutrient administration. Intervention strategies aimed at promoting nitrogen accretion, such as insulin, human growth hormone, or glutamine, have not thus far resulted in enhanced protein accretion and growth. This may be, in part, due to limitations in delivery of adequate calorie and nitrogen.

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.

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.

[Protein requirements in children during states of stress. Committee on Nutrition of the French Society of Pediatrics]

Acute and chronic stress conditions affecting critically ill children are characterized by severe protein breakdown and growth failure. This paper describes the disorders of protein metabolism, and gives recommendations for protein and energy intakes during stress conditions in children.

Oral and parenteral glutamine in bone marrow transplantation: a randomized, double-blind study

BACKGROUND

Total parenteral nutrition (TPN) supplemented with glutamine (GLN) has been reported to be effective for patients with bone marrow transplantation (BMT). Our aim was to evaluate enteral and parenteral glutamine in patients undergoing BMT.

METHODS

For evaluation of GLN in BMT, 66 patients with 43 hematologic and 23 solid malignancies (21 breast carcinomas), were randomized, double-blinded, to either oral GLN (n = 35) or glycine-control (GLY) (n = 31), 10 g three times daily. When TPN became necessary, patients who received GLN orally were given TPN with GLN (0.57 g/kg). Those who received GLY received standard TPN, isocaloric and isonitrogenous. Patients with hematologic malignancies received high-dose chemotherapy, total body irradiation, and either allogeneic (ALLO) BMT (n = 18) or autologous (AUTO) stem cell transplantation (n = 25). Patients with solid malignancies (n = 23) received AUTO.

RESULTS

There were 14 in-hospital deaths without relationship to GLN administration. For respective comparisons of ALLO and AUTO transplants in the GLN and GLY hematologic groups and AUTO in the solid tumor groups, there were no significant differences in hospital stay, duration of stay after BMT, TPN days, neutrophil recovery >500/mm3, incidence of positive blood cultures, sepsis, mucositis, and diarrhea. Acute graft us host disease occurred in 1 of 10 hematologic patients receiving GLN and in 3 of 8 patients receiving GLY placebo (p > .05). Possible reduction in need for TPN and a suggestion of improved long-term survival were associated with GLN.

CONCLUSIONS

Oral and parenteral GLN seemed to be of limited benefit for patients having AUTO or ALLO BMT for hematologic or solid malignancies. Further study of long-term effects of GLN in BMT seems warranted.

Glutamine: establishing clinical indications

Glutamine, a non-essential amino acid, is abundant in the human body and in the food we eat; it is mainly produced in skeletal muscle and acts as a major inter-organ nitrogen and carbon transporter. Its importance to the metabolism is evident during stress, when it becomes a conditionally essential amino acid when endogenous supply fails to meet increased demands. During the past 2 years, an increased understanding has been gained into the role of glutamine in metabolism. A number of new clinical studies of glutamine supplementation have shown interesting outcomes that should be influencing clinical decision-making.

Randomized clinical outcome study of critically ill patients given glutamine-supplemented enteral nutrition

Glutamine is normally an abundant amino acid in the body. It has many important metabolic roles, which may protect or promote tissue integrity and enhance the immune system. Low plasma and tissue levels of glutamine in the critically ill suggest that demand may exceed endogenous supply. A relative deficiency of glutamine could compromise recovery, resulting in prolonged illness and an increase in late mortality, morbidity, and consequently hospital costs. Using a prospective block-randomized, double-blind treatment study design, we tested whether a glutamine-containing enteral feed compared with an isonitrogenous, isoenergetic control feed would influence outcome. The study endpoints were morbidity, mortality, and hospital cost at 6 mo postintervention. In one general intensive care unit (ICU), to ensure consistency of management policies, 78 critically ill adult patients with Acute Physiological and Chronic Health Evaluation (APACHE) II score of 11 and greater and who were considered able to tolerate introduction of enteral nutrition were studied. Fifty patients successfully received enteral nutrition (26 glutamine, 24 control). There was no mortality difference between those patients receiving glutamine-containing enteral feed and the controls. However, there was a significant reduction in the median postintervention ICU and hospital patient costs in the glutamine recipients $23,000 versus $30,900 in the control patients (P = 0.036). For patients given glutamine there was a reduced cost per survivor of 30%. We conclude that in critically ill ICU patients enteral feeds containing glutamine have significant hospital cost benefits.