Glutamine as an immunoenhancing nutrient

Free Amino Acids in Human Milk: A Potential Role for Glutamine and Glutamate in the Protection Against Neonatal Allergies and Infections

Breastfeeding is indicated to support neonatal immune development and to protect against neonatal infections and allergies. Human milk composition is widely studied in relation to these unique abilities, which has led to the identification of various immunomodulating components in human milk, including various bioactive proteins. In addition to proteins, human milk contains free amino acids (FAAs), which have not been well-studied. Of those, the FAAs glutamate and glutamine are by far the most abundant. Levels of these FAAs in human milk sharply increase during the first months of lactation, in contrast to most other FAAs. These unique dynamics are globally consistent, suggesting that their levels in human milk are tightly regulated throughout lactation and, consequently, that they might have specific roles in the developing neonate. Interestingly, free glutamine and glutamate are reported to exhibit immunomodulating capacities, indicating that these FAAs could contribute to neonatal immune development and to the unique protective effects of breastfeeding. This review describes the current understanding of the FAA composition in human milk. Moreover, it provides an overview of the effects of free glutamine and glutamate on immune parameters relevant for allergic sensitization and infections in early life. The data reviewed provide rationale to study the role of free glutamine and glutamate in human milk in the protection against neonatal allergies and infections.

Residual gastric volume evaluation with ultrasonography after ingestion of carbohydrate- or carbohydrate plus glutamine-enriched beverages: a randomized, crossover clinical trial with healthy volunteers

BACKGROUND

- Abbreviation of preoperative fasting to 2 hours with maltodextrin (CHO)-enriched beverage is a safe procedure and may enhance postoperative recovery. Addition of glutamine (GLN) to CHO beverages may include potential benefits to the metabolism. However, by adding a nitrogenous source to CHO beverages, gastric emptying may be delayed and increase the risk of bronchoaspiration during anesthesia.

OBJECTIVE

- In this study of safety, we aimed at investigating the residual gastric volume (RGV) 2 hours after the intake of either CHO beverage alone or CHO beverage combined with GLN.

METHODS

- We performed a randomized, crossover clinical trial. We assessed RGV by means of abdominal ultrasonography (US) in 20 healthy volunteers (10 males and 10 females) after an overnight fast of 8 hours. Then, they were randomized to receive 600 mL (400 mL immediately after US followed by another 200 mL 2 hours afterwards) of either CHO (12.5% maltodextrin) or CHO-GLN (12.5% maltodextrin plus 15 g GLN). Two sequential US evaluations were done at 120 and 180 minutes after ingestion of the second dose. The interval of time between ingestion of the two types of beverages was 2 weeks.

RESULTS

- The mean (SD) RGV observed after 8 hours fasting (13.56±13.25 mL) did not statistically differ (P>0.05) from the RGV observed after ingesting CHO beverage at both 120 (16.32±11.78 mL) and 180 minutes (14.60±10.39 mL). The RGV obtained at 120 (15.63±18.83 mL) and 180 (13.65±10.27 mL) minutes after CHO-GLN beverage also was not significantly different from the fasting condition.

CONCLUSION

- The RGV at 120 and 180 minutes after ingestion of CHO beverage combined with GLN is similar to that observed after an overnight fast.

Glibenclamide impairs responses of neutrophils against Burkholderia pseudomallei by reduction of intracellular glutathione

The major risk factor for melioidosis, an infectious disease caused by B. pseudomallei, is diabetes mellitus. More than half of diabetic melioidosis patients in Thailand were prescribed glibenclamide. Recent evidence demonstrates that glibenclamide reduces pro-inflammatory cytokine production by polymorphonuclear neutrophils (PMNs) of diabetic individuals in response to this bacterial infection. However, the mechanisms by which glibenclamide affects cytokine production are unknown. We found that PMNs from glibenclamide-treated diabetic individuals infected with live B. pseudomallei in vitro showed lower free glutathione (GSH) levels compared with those of healthy individuals. Glibenclamide decreased GSH levels and glutathione peroxidase (GPx) of PMNs after exposed to live B. pseudomallei. Moreover, glibenclamide reduced cytokine production and migration capacity of infected PMNs, whereas GSH could restore these functions. Taken together, our data show a link between the effect of glibenclamide on GSH and PMN functions in response to B. pseudomallei that may contribute to the susceptibility of diabetic individuals to B. pseudomallei infection.

Alpha-Ketoglutarate as a Molecule with Pleiotropic Activity: Well-Known and Novel Possibilities of Therapeutic Use

Alpha-ketoglutarate (AKG), an endogenous intermediary metabolite in the Krebs cycle, is a molecule involved in multiple metabolic and cellular pathways. It functions as an energy donor, a precursor in the amino acid biosynthesis, a signalling molecule, as well as a regulator of epigenetic processes and cellular signalling via protein binding. AKG is an obligatory co-substrate for 2-oxoglutarate-dependent dioxygenases, which catalyse hydroxylation reactions on various types of substrates. It regulates the activity of prolyl-4 hydroxylase, which controls the biosynthesis of collagen, a component of bone tissue. AKG also affects the functioning of prolyl hydroxylases, which, in turn, influences the function of the hypoxia-inducible factor, an important transcription factor in cancer development and progression. Additionally, it affects the functioning of enzymes that influence epigenetic modifications of chromatin: ten-eleven translocation hydroxylases involved in DNA demethylation and the Jumonji C domain containing lysine demethylases, which are the major histone demethylases. Thus, it regulates gene expression. The metabolic and extrametabolic function of AKG in cells and the organism open many different fields for therapeutic interventions for treatment of diseases. This review presents the results of studies conducted with the use of AKG in states of protein deficiency and oxidative stress conditions. It also discusses current knowledge about AKG as an immunomodulatory agent and a bone anabolic factor. Additionally, the regulatory role of AKG and its structural analogues in carcinogenesis as well as the results of studies of AKG as an anticancer agent are discussed.

The effect of glutamine therapy on outcomes in critically ill patients: a meta-analysis of randomized controlled trials

Introduction

Glutamine supplementation is supposed to reduce mortality and nosocomial infections in critically ill patients. However, the recently published reducing deaths due to oxidative stress (REDOX) trials did not provide evidence supporting this. This study investigated the impact of glutamine-supplemented nutrition on the outcomes of critically ill patients using a meta-analysis.

Methods

We searched for and gathered data from the Cochrane Central Register of Controlled Trials, MEDLINE, Elsevier, Web of Science and ClinicalTrials.gov databases reporting the effects of glutamine supplementation on outcomes in critically ill patients. We produced subgroup analyses of the trials according to specific patient populations, modes of nutrition and glutamine dosages.

Results

Among 823 related articles, eighteen Randomized Controlled Trials (RCTs) met all inclusion criteria. Mortality events among 3,383 patients were reported in 17 RCTs. Mortality showed no significant difference between glutamine group and control group. In the high dosage subgroup (above 0.5 g/kg/d), the mortality rate in the glutamine group was significantly higher than that of the control group (relative risk (RR) 1.18; 95% confidence interval (CI), 1.02 to 1.38; P = 0.03). In 15 trials, which included a total of 2,862 patients, glutamine supplementation reportedly affected the incidence of nosocomial infections in the critically ill patients observed. The incidence of nosocomial infections in the glutamine group was significantly lower than that of the control group (RR 0.85; 95% CI, 0.74 to 0.97; P = 0.02). In the surgical ICU subgroup, glutamine supplementation statistically reduced the rate of nosocomial infections (RR 0.70; 95% CI, 0.52 to 0.94; P = 0.04). In the parental nutrition subgroup, glutamine supplementation statistically reduced the rate of nosocomial infections (RR 0.83; 95% CI, 0.70 to 0.98; P = 0.03). The length of hospital stay was reported in 14 trials, in which a total of 2,777 patients were enrolled; however, the patient length of stay was not affected by glutamine supplementation.

Conclusions

Glutamine supplementation conferred no overall mortality and length of hospital stay benefit in critically ill patients. However, this therapy reduced nosocomial infections among critically ill patients, which differed according to patient populations, modes of nutrition and glutamine dosages.

Pathways involved in alanyl-glutamine-induced changes in neutrophil amino- and α-keto acid homeostasis or immunocompetence

We examined the effects of DON [glutamine-analogue and inhibitor of glutamine-requiring enzymes], alanyl-glutamine (regarding its role in neutrophil immunonutrition) and alanyl-glutamine combined with L-NAME, SNAP, DON, beta-alanine and DFMO on neutrophil amino and alpha-keto acid concentrations or important neutrophil immune functions in order to establish whether an inhibitor of *NO-synthase [L-NAME], an *NO donor [SNAP], an analogue of taurine and a taurine transport antagonist [beta-alanine], an inhibitor of ornithine-decarboxylase [DFMO] as well as DON could influence any of the alanyl-glutamine-induced effects. In summary, irrespective of which pharmacological, metabolism-inhibiting or receptor-mediated mechanisms were involved, our results showed that impairment of granulocytic glutamine uptake, modulation of intracellular glutamine metabolisation and/or de novo synthesis as well as a blockade of important glutamine-dependent metabolic processes may led to significant modifications of physiological and immunological functions of the affected cells.

Effects of glutamic acid and taurine on total parenteral nutrition

BACKGROUND

The objective of the present study was to ascertain whether simultaneous administration of glutamic acid (Glu) and taurine (Tau) to patients on total parenteral nutrition (TPN) could improve intestinal mucosal atrophy and suppress bacterial translocation.

METHODS

A 5-day TPN study was conducted in 5-week-old Sprague-Dawley rats. Commercially available Glu was used for TPN in group G and was enhanced with Tau (500 mg kg(-1) day(-1)) in group GT. Oral nutrition was provided in group C controls. At 5 days, amino acid and cytokine levels in plasma and endotoxin levels in portal blood were measured. The histology of the small intestine, liver, and lung were analyzed.

RESULTS

Mucosal thickness and villus height in the small intestine were lower for group G than for groups C and GT. Taurine level in group GT was higher than in group G. Arginine and citrulline levels in groups G and GT were lower than in group C. Taurine level in the small intestine was greater in group GT than in group G. Citrulline concentration was lower in group G than in groups GT and C. Endotoxin level in portal blood and cytokine (tumor necrosis factor alpha, interleukin-1beta, and interleukin-6) levels in blood tended to be lower for group GT than for group G, but no significant differences were noted. Immunostaining showed strong positive reactions to vascular cell adhesion molecule-1 in the liver and lung for group G, and milder reactions for group GT.

CONCLUSIONS

Simultaneous administration of Glu and Tau improved small intestinal mucosal thickness and villus height during TPN. Levels of Tau in the small intestine and plasma increased, and the level of citrulline in the small intestine improved. Decreased expression of adhesion molecules in the liver and lung and improved microcirculation in the liver were also confirmed.

Intraluminal injection of short chain fatty acids diminishes intestinal mucosa injury in experimental ischemia-reperfusion

PURPOSE: Investigated the effect of intraluminal short-chain fatty acids (SCFA) on the intestinal mucosa in the presence of ischemia-reperfusion injury (IRI). METHODS: Six blind sacs of the small bowel (3at the jejunum and 3 at the ileum) were created in ten Wistar rats. The lateral sacs of both bowel regions were subjected to IRI (15/15 minutes) while the medial sacs were let free to receive blood supply. In the lateral sacs, it was injected either a solution containing SCFA (butyrate, propionate and acetate) or pure saline at the bowel lumen. No fluid was injected in the medial sacs. RESULTS: Both at the jejunum and at the ileum the score of the mucosal injury was higher in saline than in control sacs. SCFA treated sacs showed lesser score at the ileum (p=0.03) but were not significantly different at the jejunum (p=0.83) when compared with saline sacs. It was found a significant greater number of neutrophils (p < 0.01) in the sacs treated with saline than in the other two sacs in both regions. CONCLUSION: SCFA protect the distal small bowel mucosa and diminishes infiltration of neutrophils to the gut lamina propria in IRI.

Temporal nutritional and inflammatory changes in children with severe head injury fed a regular or an immune-enhancing diet: A randomized, controlled trial

OBJECTIVE

To analyze the effect of an immune enhancing (IE) diet on infection and metabolic indices in children with severe head injury fed either an IE or a regular formula.

DESIGN

: Randomized, blinded, controlled study.

SETTING

Pediatric intensive care unit in a university hospital.

PATIENTS

A total of 40 mechanically ventilated children with severe head injury.

INTERVENTIONS

Within 12 hrs of pediatric intensive care unit admission, patients were randomized to receive a masked formula: either IE or regular formula. Feedings were advanced to a target volume of energy intake equal to 0.50%, 100%, 125%, 150%, and 150% of the predicted basal metabolic rate on days 1-5.

MEASUREMENTS AND MAIN RESULTS

Nutritional and metabolic indices; interleukins-1beta, -6, and -8; tumor necrosis factor-alpha; and outcome end points (survival, length of stay, length of mechanical ventilation) were compared between the two groups. Only interleukin-8 levels were lower in the IE group compared with the regular formula group by day 5 (23.6 +/- 1.5 vs. 35.5 +/- 4 pg/mL, p < .04). In multivariate regression analysis, interleukin-8 was also independently negatively correlated with immunonutrition (p < .04). Nitrogen balance became positive in 30.8% of patients in the regular formula group and in 69.2% of patients in the IE group by day 5 (p < .05). Less gastric cultures were positive in the IE group compared with the regular formula group (26.7% vs. 71.4%, p < .02). Nosocomial infections (15% vs. 25%), length of stay (16.7 vs. 12.2 days), length of mechanical ventilation (11 vs. 8 days), and survival (80% vs. 95%) did not differ between groups.

CONCLUSIONS

Although immunonutrition might decrease interleukin-8 and gastric colonization in children with severe head injury, it might not be associated with additional advantage over the one demonstrated by regular early enteral nutrition.

The role of macronutrients in gastrointestinal blood flow

PURPOSE OF REVIEW

The presence of luminal nutrients after a meal increases gastrointestinal blood flow in a phenomenon called postprandial hyperemia. In many conditions related to splanchnic hypoperfusion, enteral nutrition may play a role in counterbalancing the installed splanchnic low-flow state by producing intestinal hyperemia. However, when the gut is hypoperfused there is a chance of enteral nutrition producing a mismatch of the oxygen demand: supply ratio with subsequence gut ischemia. This article aims to review the effects of macronutrients on gastrointestinal blood flow in both health and critical conditions, especially those related to hepatosplanchnic hypoperfusion.

RECENT FINDINGS

Splanchnic blood flow is related not only to the route (intravenous or enteral) and timing of nutritional support (during the course of the insult) but also to the composition of the formula. Critically ill patients with gut hypoperfusion may tolerate enteral nutrition, but this effect may be restricted to the early post-injury phase. During ischaemia reperfusion injury, immune nutrients may promote different outcomes: glutamine may protect whereas arginine may deteriorate the mucosal barrier and enhance permeability.

SUMMARY

Understanding the relationship between macronutrients and gastrointestinal blood flow is a major challenge. Ongoing research in nutritional support in hypoperfused, catecholamine-dependent patients will open the door to optimize the recovery of patients in critical care.

Nutritional support of the critically ill and injured patient

The understanding of the importance of nutrition, particularly in the critically ill patient, is based on the known physiologic consequences of malnutrition. It includes respiratory muscle function, cardiac function, the coagulation cascade balance, electrolyte and hormonal balance, and renal function. Nutrition affects emotional and behavioral responses, functional recovery, and the overall cost of health care. The need to identify and treat the malnourished or potentially malnourished patient is a critical aspect of patient management. Much is known of catabolic and hypermetabolic state caused by trauma and burns. The response to injury needs to be mediated. There is much to learn about the intervention of that response through adjuvant nutritional therapy.

Glutamine supplementation in vitro and in vivo, in exercise and in immunodepression

In situations of stress, such as clinical trauma, starvation or prolonged, strenuous exercise, the concentration of glutamine in the blood is decreased, often substantially. In endurance athletes this decrease occurs concomitantly with relatively transient immunodepression. Glutamine is used as a fuel by some cells of the immune system. Provision of glutamine or a glutamine precursor, such as branched chain amino acids, has been seen to have a beneficial effect on gut function, on morbidity and mortality, and on some aspects of immune cell function in clinical studies. It has also been seen to decrease the self-reported incidence of illness in endurance athletes. So far, there is no firm evidence as to precisely which aspect of the immune system is affected by glutamine feeding during the transient immunodepression that occurs after prolonged, strenuous exercise. However, there is increasing evidence that neutrophils may be implicated. Other aspects of glutamine and glutamine supplementation are also addressed.

Healing responses of skin and muscle in critical illness

OBJECTIVE

Many aspects of the care and underlying pathologies in patients suffering critical illness can detrimentally influence the normal healing processes of skin and soft tissues. Although a great diversity of pathologies exists, some aspects of the diseases and their treatments are common in critically ill patients. We aimed to identify some features, both common and specific, that could influence wound healing and the mechanisms by which they may do so.

DESIGN

In this review, we first outline the biology of normal skin and muscle healing and then explore how critical illness may influence the normal healing cascade.

FINDINGS

The healing of skin and skeletal muscle in critical illness is influenced by both underlying disease processes and the intensive care environment. Local and systemic factors can contribute to impaired healing, with the potential to prolong functional disability and increase the likelihood of wound complications. The frequency and number of soft tissue injuries derived from accidental injury, surgical intervention, and the need for invasive monitoring and therapies in the intensive care unit setting are likely to compromise the innate immunity and potentially further jeopardize the patient's ability to heal. Alterations in coagulation, tissue perfusion, inflammation, immune functioning, metabolism, nutrition, and drug therapies will influence healing responses by modifying the biological responses to tissue disruption. Locally, wound contamination, sepsis, tissue hypoxia, edema, and excessive or prolonged local pressure all have the potential to compromise soft tissue healing. One or more of these factors may be present at any time.

CONCLUSION

The skin and soft tissues are vulnerable to both injury and compromised healing when a patient is critically ill and exposed to a critical care environment. The identification of risk factors may aid in forming and modifying treatment strategies when caring for the critically ill patient with soft tissue injuries.

Nutrition support of the trauma patient

Hypercatabolism after trauma may lead to acute protein malnutrition, ultimately resulting in multiple organ failure. Nutrition support may prevent this sequence. This review addresses the need for early nutrition support, the preferred route of substrate delivery, and the potential advantages of "immune-enhancing" diets.

Immune-enhancing enteral diet selectively augments ileal blood flow in the rat

BACKGROUND

Clinical studies show that immune-enhancing enteral diets (IED; with L-arginine, fish oil, and RNA fragments) decrease the rate of sepsis and shorten the length of hospital stay after the start of enteral feeding. These beneficial effects are dependent on the route of administration (enteral vs parenteral) and on the nutrient composition (IED vs standard diets). Gut exposure to an IED seems to preserve and/or augment intestinal mucosal immunity. However, nutrient absorption stimulates gut blood flow in a nutrient-specific manner (i.e., postprandial hyperemia). We hypothesized that an IED would initiate a different pattern of whole organ blood flow compared to a standard diet. This suggests that a mechanism for the protective effect of IED might be the preferential augmentation of gut blood flow to gut-associated lymphoid tissue (GALT) or mucosa-associated lymphoid tissue (MALT).

METHODS

Male Sprague-Dawley rats (200-225 g) were anesthetized and cannulated for colorimetric microsphere determination of blood flow distribution (with the phantom organ technique). Animals received gastric gavage (2 ml) of an IED (Impact; Novartis) or an isocaloric, isonitrogenous control diet (Boost; Mead-Johnson). Blood flow to the antrum, duodenum, jejunum, ileum, colon, liver, kidneys, and spleen was determined at baseline and 30, 60, 90, and 120 min after gavage.

RESULTS

Baseline blood flows to the left and right kidneys were within 10%, indicating the technical integrity of the microsphere technique and assay. Control diet augmented blood flow compared to IED in the antrum, duodenum, jejunum, and spleen. Conversely, IED gavage stimulated a delayed and sustained hyperemic response in the ileum. IED also increased hepatic blood flow early (30 min). IED increased blood glucose levels compared to control diet at 30, 60, and 90 min, suggesting enhanced nutrient absorption.

CONCLUSIONS

These data show that blood flow distribution depends on nutrient composition and that IED preferentially augments blood flow to the ileum. Since the terminal jejunum and ileum contain much of the GALT, our data suggest that a mechanism for enterally stimulated mucosal immunity involves selective perfusion of the terminal ileum during IED nutrient absorption.

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.

Oral glutamine does not prevent bacterial translocation in rats subjected to intestinal obstruction and Escherichia coli challenge but reduces systemic bacteria spread

OBJECTIVE

We investigated whether oral glutamine prevents bacterial translocation.

METHODS

Male Wistar rats were fed with isocaloric and isoproteic standard rat chow and randomly assigned to receive glutamine (GLN) or glycine administered through an orogastric tube at 1.5 g.kg(-1).d(-1) for 7 d. On day 8 of the study, the animals were anesthetized and intestinal obstruction was produced by ligature of the terminal ileum. A suspension containing 10(9) colony-forming units per milliliter of Escherichia coli ATCC 25992 was injected into the lumen of the ileum. Twenty-four hours later, blood was withdrawn, and mesenteric lymph nodes and fragments of spleen, liver, and lung were sent for microbiological analysis. Cultures were done on blood agar and MacConkey agar. Student's t test and analysis of variance between two proportions were used. P < 0.05 was considered significant.

RESULTS

Rats in both groups lost body weight during the experiment (not significant). Mesenteric lymph node cultures were positive in both groups. The GLN group had a smaller percentage of E. coli in blood and organ cultures (65.45% versus 82.67% in the glycine group; P = 0.027). Positive cultures of blood, spleen, liver and lung also were higher on glycine group, although not significantly.

CONCLUSIONS

Oral GLN does not prevent bacterial translocation in rats after intestinal obstruction and E. coli challenge. No specific organ was protected by GLN. Nevertheless, its use was associated with a reduced number of positive E. coli cultures in blood and remote organs, and thus diminished bacteria spread. This association suggests a role for GLN in gut barrier protection, possibly by immune system enhancement.

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.

Glutamine utilization in activated lymphocytes from rats receiving endotoxin

BACKGROUND

A beneficial effect of supplemental glutamine for lymphocyte function in patients under metabolic stress has been suggested. Nevertheless, it is not clear how glutamine is used by lymphocytes when under stress. This time course study investigated the effect of endotoxin-induced stress on in vitro glutamine utilization and glutamine-dependent proliferation of activated lymphocytes.

METHODS

Metabolic stress was modeled by intraperitoneal (ip) administration of endotoxin (5 mg/kg body wt) to rats. Control animals were injected with sterile saline. Cervical lymph node lymphocytes collected from animals 6, 12, 24, and 48 h following injection were activated with concanavalin A. Proliferation of these activated lymphocytes in the presence of 0.1-2 mM glutamine was determined. The glutamine utilization rate and glutaminase activity in the activated lymphocytes were also determined.

RESULTS

The proliferation rate of lymphocytes was not affected by ip administration of endotoxin 6 h following the insult, however, 12, 24, and 48 h following the insult, the maximal response was suppressed (P < 0.05). In addition, at 12, 24, and 48 h, the concentration of glutamine for the maximal response of lymphocytes was lower than that for the control group (P < 0.05). Throughout the investigation period, both the glutamine utilization rate and glutaminase activity in the activated lymphocytes were decreased time-dependently.

CONCLUSION

The present study demonstrates that glutamine utilization by lymphocytes under a mitogenic challenge in vitro is significantly decreased in the late period after endotoxin injection. This is at least partly due to decreased glutaminase activity and is associated with decreased proliferation rate of mitogen-activated lymphocytes.

Nutrition in chronic critical illness

Nutritional management of patients with respiratory failure can be a model of nutritional management in chronically critically ill patients. This model requires recognition of the differing metabolic states of starvation and hypermetabolism. Starvation can result in malnutrition, with adverse effect on respiratory muscle strength, ventilatory drive, and immune defense mechanisms. General nutritional goals include preservation of lean body mass by providing adequate energy and positive nitrogen balance. General nutritional prescriptions for both states include a substrate mix of 20% protein, 60% to 70% carbohydrates, and 20% to 30% fat. Positive nitrogen balance is difficult to attain in hypermetabolic patients and energy requirements are increased compared with starved patients. Enteral nutrition should be the mode of initial nutrient delivery unless the gastrointestinal tract is nonfunctional. Monitoring of nutritional support is essential. Complications of nutritional support are multiple. Nutritional hypercapnia is an important complication in a chronically critically ill patient. Outcomes of selected long-term acute patients are poor, with only 8% of patients fully functional 1 year after discharge. Appropriate nutritional therapy is one aspect of management of these patients that has the possibility of optimizing function and survival.

Nutrition support for individuals with liver failure

The prevalence of liver diseases is increasing in the United States, particularly as a result of the recent hepatitis C epidemic. In the past, patients who developed fulminant hepatic failure or cirrhosis owing to a chronic liver disease were likely to expire. During the last 15-20 years, liver transplantation has given these patients a chance at survival. Progressive nutrition deficiencies and muscle wasting are universal problems in these patients. Left untreated, the progressive wasting of liver disease leads to infection and an increased risk of death owing to infection both before and after transplantation. Aggressive nutritional support is essential to optimize the care of these patients and to enable them to obtain and survive a liver transplant and gain access to a new life following a successful liver engraftment.

The metabolic and nutritional response to critical illness

The metabolic response to critical illness promotes catabolism, which mobilizes substrates for energy. Initially the hypothalamic-pituitary-adrenal axis is stimulated, but later there appears to be anterior pituitary depression. Despite this, the early increase in plasma cortisol levels is usually maintained by means independent of (falling) corticotropin levels. Some patients, however, develop acute adrenal insufficiency and appear to benefit from replacement exogenous glucocorticoid. However, identifying such patients is often difficult. The replacement of other deficiencies may not be in the patients' interests. For example, leptin, a stress-related hormone, has multiple effects, some seemingly advantageous and others detrimental in critical illness. Its overall influence and significance remains unclear.The health of gut mucosa and the inflammatory response might be improved or influenced to the (presumed) benefit of the patient by agents such as glutamine, arginine, some eicosanoids, and exogenous nucleic acids. Such "immunonutrition" appears to improve mortality and other measures of outcome in surgical intensive care unit patients and those with sepsis.