Glutamine as an activator of immune cells: how does it work?

Improvements of immune status, intestinal integrity and gain performance in the early-weaned calves parenterally supplemented with L-alanyl-L-glutamine dipeptide

Glutamine (Gln) is an important substrate for the innate immune cells including lymphocytes and macrophages. In this report, the effects of alanyl-glutamine dipeptide (Ala-Gln) on the naïve immune system, intestinal integrity and gain performance of early-weaned calves were investigated. Early-weaned Chinese Holstein calves were intravenously administered different dosages of Ala-Gln. The effects of Ala-Gln administration were ascertained by evaluating the blood for naïve T lymphocyte subpopulations, the concentrations of serum IgG, serum IgA and intestinal mucosal secretory IgA (s-IgA), the intestinal integrity, as well as the gain performance. Results demonstrated that intravenous administration of Ala-Gln dipeptide (1.01 g/kg×d(-1)) for 7 days had a positive effect on gain performance, intestinal integrity and the immune system. Calves administered doses of Ala-Gln displayed an improvement in gain performance and health status concurrent with increases in blood CD2(+) and CD4(+) lymphocytes, the ratio of CD4(+)/CD8(+), serum IgA and IgG, intestinal mucosal s-IgA while decreasing the occurrence of diarrhea. Moreover, we found that animals given the effective dose (1.01 g/kg×d(-1)) of Ala-Gln resulted in improved immune status and intestinal integrity relative to those given a lower (0.49 g/kg×d(-1)) or higher dose (1.99 g/kg×d(-1)) of Ala-Gln. These findings suggest that maintaining a certain concentration of plasma and/or tissue glutamine in the early stages of weaning is an effective alternative approach for improvement of growth performance in early-wean calves.

The effect of L-alanyl-L-glutamine dipeptide supplemented total parenteral nutrition on infectious morbidity and insulin sensitivity in critically ill patients

OBJECTIVE

The aim of this study was to assess the clinical efficacy of alanine-glutamine dipeptide-supplemented total parenteral nutrition defined by the occurrence of nosocomial infections. Secondary parameters included Sequential Organ Failure Assessment score, hyperglycemia and insulin needs, intensive care unit and hospital length of stay, and 6-month mortality.

DESIGN

Multicenter, prospective, double-blind, randomized trial.

SETTING

Twelve intensive care units at Spanish hospitals.

PATIENTS

One hundred twenty-seven patients with Acute Physiology and Chronic Health Evaluation II score >12 and requiring parenteral nutrition for 5-9 days.

INTERVENTION

Patients were randomized to receive an isonitrogenous and isocaloric total parenteral nutrition or alanine-glutamine dipeptide-supplemented total parenteral nutrition. Nutritional needs were calculated: 0.25 g N/kg(-1)/d(-1) and 25 kcal/kg(-1)/d(-1). The study group received 0.5 g/kg(-1)/d(-1) of glutamine dipeptide and the control total parenteral nutrition group a similar amount of amino acids. Hyperglycemia was controlled applying an intensive insulin protocol with a target glycemia of 140 mg/dL.

MEASUREMENTS AND MAIN RESULTS

The two groups did not differ at inclusion for the type and severity of injury or the presence of sepsis or septic shock. Caloric intake was similar in both groups. Preprotocol analysis showed that treated patients with alanine-glutamine dipeptide-supplemented total parenteral nutrition had lesser nosocomial pneumonia, 8.04 vs. 29.25 episodes-‰ days of mechanical ventilation (p = .02), and urinary tract infections, 2.5 vs. 16.7 episodes-‰ days of urinary catheter (p = .04). Intensive care unit, hospital, and 6-month survival were not different. Mean plasmatic glycemia was 149 ± 46 mg/dL in the alanine-glutamine dipeptide-supplemented total parenteral nutrition group and 155 ± 51 mg/dL in the control total parenteral nutrition group (p < .04), and mean hourly insulin dose was 4.3 ± 3.3 IU in the alanine-glutamine dipeptide-supplemented total parenteral nutrition group and 4.7 ± 3.7 IU in control total parenteral nutrition group (p < .001). Multivariate analysis showed a 54% reduction of the amount of insulin for the same levels of glycemia in the alanine-glutamine dipeptide-supplemented total parenteral nutrition group.

CONCLUSIONS

Total parenteral nutrition supplemented with alanine-glutamine in intensive care unit patients is associated with a reduced rate of infectious complications and better glycemic control.

Protein synthesis rates of human PBMC and PMN can be determined simultaneously in vivo by using small blood samples

Immune cell functions can be evaluated in vivo by measuring their specific protein fractional synthesis rates (FSR). Using stable isotope dilution techniques, we describe a new method allowing simultaneous in vivo assessment of FSR in two leukocyte populations in healthy human subjects, using small blood samples. Peripheral blood mononuclear cell (PBMC) and polymorphonuclear neutrophil (PMN) FSR were measured during primed continuous intravenous infusion of l-[1-13C]leucine. Immune cells from 6 ml of whole blood were isolated by density gradient centrifugation. In a first study, we calculated the FSR using plasma [13C]leucine or α-[13C]ketoisocaproate (KIC) enrichments as precursor pools. In a second study, we compared protein FSR in leukocytes, using enrichments of either intracellular or plasma free [13C]leucine as immediate precursor pools. The present approach showed a steady-state enrichment of plasma and circulating immune cell free [13C]leucine precursor pools. The linearity of labeled amino acid incorporation rate within mixed PBMC and PMN proteins also was verified. Postabsorptive protein FSR was 4.09 ± 0.39%/day in PBMC and 1.44 ± 0.08%/day in PMN when plasma [13C]KIC was the precursor pool. The difference between PBMC and PMN FSR was statistically significant, whatever the precursor pool used, suggesting large differences in their synthetic activities and functions. Use of the plasma [13C]KIC pool led to an underestimation of leukocyte FSR compared with the intracellular pool (PBMC: 6.04 ± 0.94%/day; PMN: 2.98 ± 0.30%/day). Hence, the intracellular free amino acid pool must be used as precursor to obtain reliable results. In conclusion, it is possible to assess immune cell metabolism in vivo in humans by using small blood samples to directly indicate their metabolic activity in various clinical situations and in response to regulating factors.

Cost containment through L-alanyl-L-glutamine supplemented total parenteral nutrition after major abdominal surgery: a prospective randomized double-blind controlled study

BACKGROUND & AIMS

Glutamine is recognized as a conditionally essential amino acid. Recent studies indicate that glutamine-containing total parenteral nutrition improves nitrogen economy, enhances gastrointestinal and immune functions and shortens hospital stay.

METHODS

Thirty-seven patients (19 w and 18 m; age 61. 4+/-10.4 years; BMI 23.7+/-2.8 kg/m(2)) following major abdominal surgery receiving an isonitrogenous isoenergetic TPN with or without alanyl-glutamine supplementation (0.5 g/kg BW/day), were evaluated in a double-blind, randomized, controlled trial over a five-day period by measuring nitrogen balance, selected biochemical parameters and length of hospital stay.

RESULTS

Supplemental alanyl-glutamine improved the overall mean (-3.5+/-1.6 vs. -5.5+/-1. 4 g N;P<0.05) and cumulative nitrogen balance (-14.1+/-9.1 vs. -21.7+/-11.4 g N;P<0.05) compared with the isonitrogenous, isoenergetic standard regimen. Alanyl-glutamine normalized plasma glutamine concentration and reduced the length of hospital stay (12.8+/-2.6 vs. 17.5+/-6.4 days;P<0.05).

CONCLUSIONS

The results of the study confirm that supplementation with synthetic alanyl-glutamine dipeptide is associated with cost containment due to shortened hospitalization and improved nitrogen economy.

Aging: a barrier to renutrition? Nutritional and immunologic evidence in rats

BACKGROUND

Previous reports suggest that correcting the malnourished state is more difficult in elderly people than in younger ones and that protein requirements may be higher in elderly than in younger adults.

OBJECTIVE

The aim of this study was to establish whether malnourished old rats respond to protein-supplemented nutritional repletion as do young adult rats.

DESIGN

Adult (3 mo old) and old (22 mo old) rats were submitted to dietary restriction programs that induced similar metabolic and nutritional alterations. Malnourished adult and old rats were then killed (R groups) or refed for 1 wk with a high-protein diet (HPD; 23% protein) or a very-high-protein diet (VHPD; 27% protein). Control groups at both ages were fed ad libitum throughout the experiment. Effects of food repletion were evaluated in terms of protein metabolism, intestinal histomorphometry, and nonspecific immune status.

RESULTS

In adult rats, HPD sufficed to increase body weight and restore basal values of liver weight and protein content (P: < 0.01 compared with the R adult group), nitrogen balance (P: < 0.01 compared with the R adult group), and hydrogen peroxide production by polymorphonuclear neutrophils and monocytes (P: < 0.01 compared with the R group); VHPD had no supplementary effect except on nitrogen balance. In old rats, HPD was less effective and greater benefit was observed with VHPD in terms of body weight gain (10%; P: < 0.01 compared with the old group fed HPD), albuminemia, muscle weight and protein content, plasma arginine concentration, and hydrogen peroxide production by stimulated polymorphonuclear neutrophils and monocytes compared with the old R group (P: < 0.01).

CONCLUSION

Aging is a significant variable affecting the response to nutritional support.

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.

Amino acids with anabolic properties

Experimental studies have clearly demonstrated both the indispensability in stress situations of amino acids, previously considered to be non-essential, and the importance of the specific properties of these same amino acids. Glutamine, arginine and their precursors/metabolites, ornithine and alpha-ketoglutarate, exert anabolic or anticatabolic effects through their involvement in protein metabolism, in the immune response and in cell proliferation. Clinical studies suggest that the supplementation of nutritional therapy with these amino acids can be of significant benefit for injured patients.