Effects of dietary glutamine supplementation on immune cell polarization and muscle regeneration in diabetic mice with limb ischemia.

PURPOSE: Diabetes is a chronic inflammatory disorder resulting in endothelial dysfunction which contributes to peripheral arterial disease and limb ischemia. Leukocytes play critical roles in vascular and tissue remodelling after ischemia. This study investigated the effects of dietary glutamine (GLN) supplementation on immune cell polarization in diabetic mice subjected to limb ischemia. METHODS: Diabetes was induced by an intraperitoneal injection of streptozotocin for 5 consecutive days in C57BL/6J mice. Diabetic mice were fed the AIN-93 diet or an AIN-93 diet in which a part of the casein was replaced by GLN. After 3 weeks of the dietary intervention, mice were subjected to unilateral femoral artery ligation to induce limb ischemia. RESULTS: GLN supplementation enhanced the proportion of anti-inflammatory monocytes and regulatory T cells in the blood. Expression of C-C motif chemokine receptor 5 by activated CD4+ T cells was promoted and prolonged in the GLN-supplemented group. GLN downregulated the percentage of M1 macrophages in muscle tissues which was correlated with lower levels of C-C motif chemokine ligand 2 in plasma. The muscle M1/M2 ratio was also reduced in the GLN group. Gene expression of interleukin-6 was suppressed by GLN supplementation, while expression levels of the peroxisome proliferator-activated receptor γ and myogenic differentiation 1 genes were elevated in post-ischemic muscles. Histological findings also indicated that muscle regeneration was accelerated in the GLN group. CONCLUSIONS: GLN supplementation in diabetic mice may exert more-balanced polarization of CD4+ T cells, monocytes, and macrophages, thus attenuating inflammatory responses and contributing to muscle regeneration after limb ischemia.

Performance and altitude: Ways that nutrition can help.

High altitudes are a challenge for human physiology and for sports enthusiasts. Several reasons lead to deterioration in performance at high altitudes. Hypoxia owing to high altitude causes a breakdown of homeostasis with imbalance in several physiological systems, including the immune system. The reduction in mucosal immunity and inflammation and the predominance of the humoral immune response causes a condition of immunosuppression and an increased likelihood of infection. In addition, it is known that worsening of the immune response is associated with reduced performance. On the other hand, immunonutrition plays an important role in modulating the effects of physical exercise on the immune system. However, to our knowledge, few studies have evaluated the effect of nutrition on the immune system after exercise in hypoxia. Although the association between exercise and hypoxia has been shown to be more severe for the body owing to the sum of stressful agents, supplementation with carbohydrates and glutamine seems to play a relevant role in mitigating immunosuppressive effects. These findings, although limited by the fact that they are the result of very few studies, shed light on a relevant theme for sports physiology and nutrition and suggest that both supplements may be useful for athletes, visitors, and workers in high-altitude regions. The aim of this review was to discuss the effects of high-altitude hypoxia on the human body from the point of view of exercise immunology because it is known that transient immunosuppression after strenuous exercise and competition should be followed by reduction in training overload and worse performance.

Effect of glutamine supplementation on neutrophil function in male judoists.

Glutamine is an important amino acid for immune function. Though high intensity and prolonged exercise decreases plasma glutamine concentration and causes immune suppression, the relationship between neutrophil functions and glutamine has not yet been found. The purpose of this study was to investigate the impacts of glutamine supplementation on neutrophil function. Twenty-six male university judoists were recruited. Subjects were classified into glutamine and control groups. The glutamine group ingested 3000 mg of glutamine per day and the control group ingested placebo for 2 weeks. Examinations were performed at the start of preunified loading exercise (pre-ULE), then 1 and 2 weeks after ULE (post-ULE). Reactive oxygen species (ROS) production, phagocytic activity, serum opsonic activity and serum myogenic enzymes were measured. Differences between the levels obtained in pre-ULE and post-ULE for the two groups were compared. In the glutamine group, ROS production activity increased 1 week after ULE, whereas it was not observed in the control group (P < 0.001). Though myogenic enzymes increased significantly after ULE (P < 0.001), the glutamine group remained unchanged by supplementation during ULE. Glutamine supplementation has prevented excessive muscle damage and suppression of neutrophil function, especially in ROS production activity, even during an intensive training period.

Effect of physical activity on glutamine metabolism.

PURPOSE OF REVIEW: Glutamine is largely synthesized in skeletal muscles and provides fuel to rapidly dividing cells of the immune system and precursors to gluconeogenesis in the liver. Physical exercise is known to affect glutamine synthesis and to modulate glutamine uptake. Overtraining is frequently associated with reduced availability of glutamine and decreased immunocompetence. Inactivity affects glutamine metabolism, but this subject was poorly investigated. RECENT FINDINGS: Strenuous physical exercise as well as exhaustive training programs lead to glutamine depletion due to lowered synthesis and enhanced uptake by liver and immune cells. Evidence suggests that postexercise glutamine depletion is associated with immunodepression. Counterwise, moderate training leads to improved glutamine availability due to a positive balance between muscle synthesis and peripheral clearance. Physical inactivity, as investigated by experimental bed rest in healthy volunteers, reduced glutamine synthesis and availability. SUMMARY: After exercise, a reduced glutamine availability may be considered as a marker of overtraining. An increased glutamine availability may contribute to decreased inflammation and health benefits associated with optimal training. Thus, glutamine supplementation may enhance immunocompetence after strenuous exercise. The potential of glutamine supplementation during physical inactivity needs to be explored.

Nonnutritive effects of glutamine.

Glutamine is the most abundant free amino acid of the human body. Besides its role as a constituent of proteins and its importance in amino acid transamination, glutamine has regulatory capacity in immune and cell modulation. Glutamine deprivation reduces proliferation of lymphocytes, influences expression of surface activation markers on lymphocytes and monocytes, affects the production of cytokines, and stimulates apoptosis. Moreover, glutamine administration seems to have a positive effect on glucose metabolism in the state of insulin resistance. Glutamine influences a variety of different molecular pathways. Glutamine stimulates the formation of heat shock protein 70 in monocytes by enhancing the stability of mRNA, influences the redox potential of the cell by enhancing the formation of glutathione, induces cellular anabolic effects by increasing the cell volume, activates mitogen-activated protein kinases, and interacts with particular aminoacyl-transfer RNA synthetases in specific glutamine-sensing metabolism. Glutamine is applied under clinical conditions as an oral, parenteral, or enteral supplement either as the single amino acid or in the form of glutamine-containing dipeptides for preventing mucositis/stomatitis and for preventing glutamine-deficiency in critically ill patients. Because of the high turnover rate of glutamine, even high amounts of glutamine up to a daily administration of 30 g can be given without any important side effects.

Dosing and efficacy of glutamine supplementation in human exercise and sport training.

Some athletes can have high intakes of l-glutamine because of their high energy and protein intakes and also because they consume protein supplements, protein hydrolysates, and free amino acids. Prolonged exercise and periods of heavy training are associated with a decrease in the plasma glutamine concentration and this has been suggested to be a potential cause of the exercise-induced immune impairment and increased susceptibility to infection in athletes. However, several recent glutamine feeding intervention studies indicate that although the plasma glutamine concentration can be kept constant during and after prolonged strenuous exercise, the glutamine supplementation does not prevent the postexercise changes in several aspects of immune function. Although glutamine is essential for lymphocyte proliferation, the plasma glutamine concentration does not fall sufficiently low after exercise to compromise the rate of proliferation. Acute intakes of glutamine of approximately 20-30 g seem to be without ill effect in healthy adult humans and no harm was reported in 1 study in which athletes consumed 28 g glutamine every day for 14 d. Doses of up to 0.65 g/kg body mass of glutamine (in solution or as a suspension) have been reported to be tolerated by patients and did not result in abnormal plasma ammonia levels. However, the suggested reasons for taking glutamine supplements (support for immune system, increased glycogen synthesis, anticatabolic effect) have received little support from well-controlled scientific studies in healthy, well-nourished humans.

Dietary glutamine supplementation affects macrophage function, hematopoiesis and nutritional status in early weaned mice.

BACKGROUND & AIMS: To investigate the effect that early weaning associated with the ingestion of either a glutamine-free or supplemented diet has on the functioning of peritoneal macrophages, hematopoiesis and nutritional status of mice. METHODS: Swiss Webster mice were early weaned on their 14th day of life and distributed to two groups, being fed either a glutamine-free diet (-GLN) or a glutamine-supplemented diet (+GLN). Animals belonging to a control group (CON) were weaned on their 21st day of life. RESULTS: The -GLN and +GLN groups had a lower lean body mass, carcass protein and ash content, plasma glutamine concentration and lymphocyte counts both in the peripheral blood and bone marrow when compared to the CON group (P<0.05). Dietary supplementation with glutamine reversed both the lower concentrations of protein and DNA in the muscle and liver, as well as the reduced capacity of spreading and synthesizing nitric oxide, hydrogen peroxide, TNF-alpha, IL-1 beta and IL-6 in cultures of peritoneal macrophages obtained from the -GLN group (P<0.05). CONCLUSION: These data indicate that the ingestion of glutamine modulates the function of peritoneal macrophages in early weaned mice. However, a glutamine-supplemented diet cannot substitute maternal milk in respect to immunological and metabolic parameters.

Strategies to enhance immune function for marathon runners : what can be done?

Marathoners are at an increased risk of developing upper respiratory tract infections (URTIs) following races and periods of hard training, which are associated with temporary changes in the immune system. The majority of the reported changes are decreases in function or concentration of certain immune cells. During this period of immune suppression, by some referred to as an 'open window' in immune function, it has been hypothesised that viruses and bacteria might gain a foothold, which would increase the risk of infections. In light of this, nutritional interventions that can enhance immune function and reduce the risk of URTIs have been sought. This paper focuses on the effect of glutamine, vitamin C, bovine colostrum and glucose. Although, some of these supplements can affect the physiological and immune changes associated with marathon racing, none of the supplements discussed have consistently been shown to reduce the risk of URTIs and therefore cannot be recommended for use as enhancers of immune function in marathon runners.

Immunomodulation. Part IV: Glutamine.

Glutamine, a nonessential amino acid that appears to be conditionally essential during periods of physiologic stress, plays important physiologic roles in the immune system. However, neither enteral nor parenteral glutamine supplementation makes a difference in the rate of systemic infection or of NEC in very low birth weight infants. Thus, the search for agents to enhance the neonate's immune system and to serve as safe and effective adjuvants to antibiotics continues. Part V, the final article in this immunomodulation series, will explore the use of probiotics to support the neonatal immune system.

Glutamine depletion potentiates leucocyte-dependent inflammatory events induced by carrageenan or Clostridium difficile toxin A in rats.

This research investigated the effect of glutamine (Gln) depletion on leucocyte-dependent inflammatory events. Rats were treated intraperitoneally, 16 hr prior to the peak of every parameter evaluated, with either 0.9% NaCl, methionine-sulphoximine (MSO, an inhibitor of endogenous Gln synthesis, 25 mg/kg) or with MSO + Gln (MSO as above plus Gln 3 g/kg in three doses). MSO-induced Gln depletion increased paw oedema induced both by carrageenan (Cg) and by Clostridium difficile toxin A (TxA) (66.2% and 45.5%, respectively; P < 0.05). In dextran-injected animals, oedema and myeloperoxidase (MPO) activity were not modified by Gln depletion. In Cg-treated paws, Gln depletion increased MPO activity by 44% (P < 0.05), interleukin-1beta (IL-1beta) and tumour necrosis factor-alpha (TNF-alpha) concentrations by 47% and 52%, respectively (P < 0.05), and immunostaining for TNF-alpha in paw tissue. In TxA-injected paws, Gln depletion increased MPO activity (46%; P < 0.05). Gln depletion increased Cg- and TxA-induced neutrophil migration to subcutaneous air pouches by 56% and 77% (P < 0.05), respectively, but did not affect migration induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP). Gln infusions reversed all the effects of MSO. Leucocyte counts did not differ between groups. Gln depletion potentiates acute inflammation, possibly by increasing neutrophil migration through resident cell activation and production of IL-1beta and TNF-alpha. Gln supplementation reverses these effects and may be useful during inflammatory catabolic stress.

Immune-enhancing enteral nutrients differentially modulate the early proinflammatory transcription factors mediating gut ischemia/reperfusion.

BACKGROUND: Recent reports suggest that enteral diets enriched with arginine may be harmful by enhancing inflammation. This is consistent with our gut ischemia/reperfusion (I/R) model in which arginine induced the proinflammatory mediator inducible nitric oxide synthase and resulted in injury and inflammation whereas glutamine was protective. We now hypothesize that arginine and glutamine differentially modulate the early proinflammatory transcription factors activated by gut I/R. METHODS: At laparotomy, jejunal sacs were filled with either 60 mmol/L glutamine, arginine, or an iso-osmotic control followed by 60 minutes of superior mesenteric artery occlusion and 6 hours of reperfusion and compared with shams. Jejunum was harvested for nuclear factor (NF)-kappaB and activator protein-1 (AP-1) measured by electrophoretic mobility shift assay and c-jun and c-fos (AP-1 family) by supershift. RESULTS: Both NF-kappaB and AP-1 were activated by gut I/R. Arginine and glutamine had no differential effect on NF-kappaB, whereas AP-1 expression (c-jun but not c-fos) was markedly enhanced by arginine and significantly lessened by glutamine. CONCLUSION: Arginine enhanced expression of the early proinflammatory transcription factor AP-1 but not NF-kappaB. This represents a novel mechanism by which arginine may be harmful when administered to critically ill patients.

The pharmacological effects of novel nutrients on the immune system.

The role of novel nutrients that appear to have pharmacological effects on the immune system has been studied over the past 20 years. This area of research has been termed immunonutrition. This paper provides an overview of particular novel nutrients--argtnine, glutamine, omega-3 fatty acids, and nucleotides--and examines some of the evidence for the effects that they may have on immune function. The benefits to particular patient groups are also considered (Box 1).

Glutamine: recent developments in research on the clinical significance of glutamine.

PURPOSE OF REVIEW: The aim of this review is to describe the clinical relevance of supplementation of glutamine from the recent literature. First, new basic research is examined and subsequently recent clinical trials and a metaanalysis are illustrated. RECENT FINDINGS: Glutamine has a major impact on the functionality of the immune system. It has recently been established that glutamine not only has a protective effect on cells of the immune system, but also on other cells of the body, for instance cardiomyocytes. Evidence is accumulating for an effect of glutamine via glutathione, heat shock proteins as well as taurine. Another area of interest is the way glutamine enhances gut barrier function. More and more research is concentrating on the positive effect of glutamine on the gut-associated lymphoid tissue. SUMMARY: Based on a recent meta-analysis and up-to-date clinical trials, we may conclude that glutamine has a beneficial effect on infectious complications and reduces hospital stay. In critically ill patients glutamine supplementation may reduce morbidity and mortality. The greatest effect was observed in patients receiving high dose parenteral glutamine. A recent study with high dose enteral glutamine demonstrated a reduced mortality in the glutamine supplemented group. In the future more trials with larger numbers of participants are needed, especially with high dose enteral glutamine in the perioperatively and the intensive care unit setting.

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.

Immunosuppression in undernourished rats: the effect of glutamine supplementation.

OBJECTIVE: The aim of our study is to determine the effect of a 30-day-period caloric restriction (CR) upon the immune response of rats and the influence of glutamine upon mononuclear cells proliferation and cytokine production. METHODS: Male albino Wistar rats were submitted to CR receiving an amount of food equivalent to 50% of the mean amount consumed by the control animals. We measured the incorporation of [2-14C]-thymidine by lymphocytes obtained from the spleen and mesenteric lymph nodes, plasma glucose and glutamine concentration, as well as cytokine production by cultivated cells, in the presence of glutamine. RESULTS: Rats submitted to CR presented reduced body weight (49%) and decreased splenic leukocyte number. CR led to a reduction in the proliferative response of lymphocyte. Spleenocytes from CR animals produced less gamma-interferon and interleukins 1, 4 and 10 in 48 h culture than did those from control rats. The same pattern is observed in cells obtained from the mesenteric lymph nodes. The addition of glutamine 2mM to the culture medium restored spleen and mesenteric lymph node cells' proliferative response and the production of interleukin 2 by cells obtained from the spleen and from the mesenteric lymph nodes. CONCLUSIONS: The present data reinforce that undernutrition decreases in vitro immune cell function and indicates that, in such circumstances, glutamine supplementation could reverse some of the changes observed in the functionality of cultured immune cells. The presence of the amino acid at physiological concentration, however, reinforces the diversion of the immune response towards a Th(1)-like response.

Carbohydrate supplementation during intense exercise and the immune response of cyclists.

OBJECTIVE: To evaluate the effect of carbohydrate supplementation upon some aspects of the immune function in athletes during intense indoor cycling. METHODS: Twelve male athletes cycled for 20 min at a velocity corresponding to 90% of that obtained at the anaerobic threshold and rested for 20 min. This protocol was repeated six times. The athletes received, during the trial, water ad libitum, or a solution of carbohydrate (95% glucose polymers and 5% fructose) at 10% (w/v), 1 g kg h every 20 min, starting at the 10th minute of the first exercise period, plus extra water ad libitum. RESULTS: Exercise induced a reduction in peripheral blood mononuclear cell proliferation (37%) as well as in the production of cytokines by cultured cells (interleukin-1 (IL-1), interleukin-2 (IL-2), tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), by 37%, 35%, 26% and 16%, respectively). All of these changes were prevented by the ingestion of a carbohydrate drink by the athletes, except that in IFN-gamma production, which was equally decreased (17%) after the second trial. The concentration of plasma glutamine, an important fuel for immune cells, was decreased in the placebo group but maintained in the group that received carbohydrate. CONCLUSION: Carbohydrate supplementation affects positively the immune response of cyclists by avoiding or minimizing changes in plasma glutamine concentration.

Immunonutrition.

Nutrition and immunology are interrelated. Several nutrients like arginine, glutamine, omega-3-fatty acids and nucleotides enhance cellular immunity, modulate tumor cell metabolism and improve clinical outcome in stress situations. Glutamine supplementation has been shown to decrease incidence of sepsis and to reduce length of hospital stay in bone marrow transplant patients, low birth weight infants, surgical and multiple trauma patients. Studies with arginine have shown a reduction in infectious complications and lower mortality, however a better understanding of the biology of arginine is needed. Omega-3-fatty acid supplimentation as in fish oil stimulates the immune system. The beneficial effects of immunonutrition in surgical patients has been demonstrated in several studies. It significantly reduces infectious complications and length of hospital stay. In critically ill patients immunonutrition may decrease infectious complications but it is not associated with a mortality advantage. Pediatric experience is limited, but the future is promising.

Influence of enteral diets supplemented with key nutrients on lymphocyte subpopulations in Peyer's patches of endotoxin-boostered mice.

BACKGROUND AND AIMS: This study was undertaken to compare the effect of different key nutrients on lymphocyte subsets of Peyer's patches (PP) and spleen in endotoxemic mice. METHODS: Female Balb/c mice were fed over a period of 10 days either with an isocaloric and isonitrogenous control diet (Control), a glutamine enriched diet (Diet I) or a diet containing glutamine, arginine, glycine, and n-3 fatty acids (Diet II). On day 7 the mice were challenged intraperitoneally with 25 microg LPS. The lymphocyte subpopulations (B cells, T cells, CD4+ and CD8+) of PP and spleen were analysed by flow cytometry. Glutathione content of small intestinal mucosa and spleen was determined by HPLC and luminal small intestinal IgA by ELISA. RESULTS: Both experimental diets increased the number of B and T cells in the PP and that of T cells in the spleen (P<0.01). Glutathione content in PP and spleen was higher under administration of key nutrients (P<0.05). Diet II reduced luminal small intestinal IgA content in comparison to the two other groups. CONCLUSION: The addition of arginine, glycine and n-3 fatty acids to a glutamine supplemented diet does not enhance lymphocyte numbers in PP and spleen, but reduces intestinal IgA content.

Immunonutrition - fact or fad.

Suggestions that modifications to the diet may have a beneficial effect on health are not new. recent work demonstrates that nutritional supplements may effect immune function. This review examines the evidence for the effects of these supplements including arginine, glutamine, nucleotides and omega - 3 fatty acids. In particular, clinical trials with patients in multiple organ failure are discussed. The evidence published thus far suggests that immunonutrition, if absorbed in adequate amounts both pre- and post-operatively, reduces septic complications and improves surrogate measures of ourcome, including length of stay and requirements for mechanical ventilation.