Glutamine-containing TPN: a question of life and death for intensive care unit-patients?

Pros and cons of L-arginine supplementation in disease

The amino acid arginine and one of its metabolites NO have gathered broad attention in the last decade. Although arginine is regarded as a conditionally essential amino acid in disease, L-arginine supplementation in severe illness has not found its way into clinical practice. This might be due to the invalid interpretation of results from studies with immune-enhancing diets containing L-arginine amongst other pharmaconutrients. However, not much attention is given to research using L-arginine as a monotherapy and the possibility of the alternative hypothesis: that L-arginine supplementation is beneficial in disease. The present review will discuss data from studies in healthy and diseased animals and patients with monotherapy of L-arginine to come to an objective overview of positive and negative aspects of L-arginine supplementation in disease with special emphasis on sepsis, cancer, liver failure and wound healing.

Does acute glutamine depletion enhance the response of glutamine synthesis to fasting in muscle in adult and old rats?

BACKGROUND AND AIMS

In earlier studies, skeletal muscle glutamine synthetase (GS) activity was shown to be enhanced by fasting and glucocorticoids, and inhibited by exogenous glutamine (Gln) supplementation. The current study was designed to determine whether phenylbutyrate (PhiB), a Gln-chelating agent in humans, (1) could trap Gln and produce a decline in plasma Gln in rats, as it does in humans, and (2) if so, whether (Phi)B would further enhance the response of muscle GS activity to fasting in rats.

METHODS

Adult (6-8 months) and aged (20-21 months) rats were fasted for 5 days and received two doses of 0.5 g(Phi)Bby orogastric route at times 0 and 4 h, and were then sacrificed at 5.5 h. Plasma Gln was measured by enzymatic methods, other amino acids were quantified by amino acid analysis. GS activity was measured in soleus (SO) and tibialis anterior (TA) muscles.

RESULTS

(Phi)B treatment was associated with: (1) a 20% decline in plasma Gln concentration from 572+/-54 to 424+/-34 micromol/L (P<0.05) and from 476+/-49 to 360+/-80 micromol/L (P<0.05) in fasted adult and old rats, respectively; and (2) a preservation of GS up-regulation by fasting in TA and SO muscles in both adult and aged rats, with TA muscle GS activities of 198+/-65 vs. 203+/-68 ((Phi)B-treated vs. vehicle-treated, NS), and 244+/-81 vs. 274+/-59 (NS) nmol/h/mg protein in adult and aged rats, respectively.

CONCLUSION

These data suggest that: (1) large doses of (Phi)B deplete plasma Gln in fasted rats, regardless of age, (2) Gln depletion induced by Phi)B does not alter GS activity.

Renal metabolism of amino acids: its role in interorgan amino acid exchange

The kidneys play a role in the synthesis and interorgan exchange of several amino acids. The quantitative importance of renal amino acid metabolism in the body is not, however, clear. We review here the role of the kidney in the interorgan exchange of amino acids, with emphasis on quantitative aspects. We reviewed relevant literature by using a computerized literature search (PubMed) and checking relevant references from the identified articles. Our own data are discussed in the context of the literature. The kidney takes up glutamine and metabolizes it to ammonia. This process is sensitive to pH and serves to maintain acid-base homeostasis and to excrete nitrogen. In this way, the metabolism of renal glutamine and ammonia is complementary to hepatic urea synthesis. Citrulline, derived from intestinal glutamine breakdown, is converted to arginine by the kidney. Renal phenylalanine uptake is followed by stoichiometric tyrosine release, and glycine uptake is accompanied by serine release. Certain administered oligopeptides (eg, glutamine dipeptides) are converted by the kidneys to their constituent components before they can be used in metabolic processes. The kidneys play an important role in the interorgan exchange of amino acids. Quantitatively, for several important amino acids, the kidneys are as important as the gut in intermediary metabolism. The kidneys may be crucial "mediators" of the beneficial effects of specialized, disease-specific feeding solutions such as those enriched in glutamine dipeptides.

L-alanyl-L-glutamine-supplemented parenteral nutrition improves infectious morbidity in secondary peritonitis

BACKGROUND & AIMS

A growing number of randomized clinical trials suggest that glutamine (Gln) supplementation may be beneficial in a selected group of patients and conditions. However, the effects of Gln-enriched total parenteral nutrition (TPN) on recovery from acute intra-abdominal infection have not been thoroughly investigated. Therefore, the aim of this study was to investigate whether the provision of Gln-enriched TPN after surgical and medical treatment of secondary peritonitis improves infectious morbidity.

METHODS

Thirty-three patients with secondary peritonitis were randomly assigned to receive either standard (n=16) TPN or L-alanyl-L-glutamine-supplemented (n=17) TPN, after medical and surgical treatment of the infectious focus. The two TPN formulae were isonitrogenous and isocaloric, which commenced the morning after surgery and ran continuously for 10 consecutive days. The control group received standard TPN, while the treatment group was given L-alanyl-L-glutamine, 0.40 g/kg/d (Dipeptiven, Fresenius Kabi, Bad Homburg, Germany). Infectious morbidity, nitrogen balance, leukocytes, lymphocytes, subpopulations CD(4) and CD(8), Immunoglobulin A (IgA), total proteins, albumin, hospital and intensive care unit (ICU) stays, and mortality were evaluated. Statistical analysis included one-way ANOVA, the unpaired Student's t-test, the Mann-Whitney U-test, chi(2) test, or Fisher's exact test.

RESULTS

Patients in both groups were comparable prior to the operation. Nitrogen balance and the levels of albumin and IgA were significantly better than those in the control group. Also, a significant reduction in the infectious morbidity was found in the Gln-treated group. Lymphocyte counts as well as subpopulations CD(4) and CD(8), and proteins showed a propensity to improvement and a tendency to reduced rates of mortality were observed when comparing the groups. Hospital and ICU stays were similar.

CONCLUSION

L-alanyl-L-glutamine-supplemented TPN improved the infectious morbidity of patients with secondary peritonitis. Gln supplementation to parenteral nutrition may be an alternative for enhancing host defenses and improving infectious morbidity.

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.

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, as a precursor of glutathione, and oxidative stress

Oxidative stress is related to several pathologies and it is also associated with surgical operations. Reactive oxygen species generated during oxidative stress can induce severe damage to biomolecules. To prevent this damage, cells are endowed with both enzymatic and nonenzymatic defenses. One of the most important antioxidant molecules is glutathione. Since glutamine is a precursor of glutathione, its supplementation in the clinical diet can be used to maintain high levels of glutathione and to avoid oxidative stress damage. Here, recent literature concerning this recurrent topic is critically reviewed.

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.