Comparison of parenteral nutrition supplemented with L-glutamine or glutamine dipeptides

Glutamine, arginine, and leucine signaling in the intestine

Glutamine and leucine are abundant constituents of plant and animal proteins, whereas the content of arginine in foods and physiological fluids varies greatly. Besides their role in protein synthesis, these three amino acids individually activate signaling pathway to promote protein synthesis and possibly inhibit autophagy-mediated protein degradation in intestinal epithelial cells. In addition, glutamine and arginine stimulate the mitogen-activated protein kinase and mammalian target of rapamycin (mTOR)/p70 (s6) kinase pathways, respectively, to enhance mucosal cell migration and restitution. Moreover, through the nitric oxide-dependent cGMP signaling cascade, arginine regulates multiple physiological events in the intestine that are beneficial for cell homeostasis and survival. Available evidence from both in vitro and in vivo animal studies shows that glutamine and arginine promote cell proliferation and exert differential cytoprotective effects in response to nutrient deprivation, oxidative injury, stress, and immunological challenge. Additionally, when nitric oxide is available, leucine increases the migration of intestinal cells. Therefore, through cellular signaling mechanisms, arginine, glutamine, and leucine play crucial roles in intestinal growth, integrity, and function.

Metabolism and nutrition in the surgical neonate

Considerable improvements have been achieved in pediatric surgery during the last two decades: the mortality rate of neonates undergoing major operations has declined to less than 10%, and the morbidity of major operations has become negligible. This considerable improvement can be partly ascribed to a better understanding of the physiological changes that occur after an operation and to more appropriate management and nutrition of the critically ill and "stressed" neonates and children. The metabolic response to an operation is different in neonates from adults: there is a small increase in oxygen consumption and resting energy expenditure immediately after surgery with return to normal by 12-24 hours. The increase in resting energy expenditure is significantly greater in infants having a major operation than in those having a minor procedure. The limited increase in energy expenditure may be due to diversion of energy from growth to tissue repair. During parenteral nutrition, it is not advisable to administer more than 18 g/kg/day of carbohydrate because this intake will be associated with lipogenesis, increased CO(2) production, and increased free radical-mediated lipid peroxide formation. Glutamine intake is potentially beneficial during total parenteral nutrition, although a large, randomized, controlled trial in surgical neonates requiring parenteral nutrition is needed to provide evidence for its benefit.

Glutamine-enriched total parenteral nutrition in patients with inflammatory bowel disease

BACKGROUND

Studies in animal models of inflammatory bowel disease (IBD) suggest that supplementation of total parenteral nutrition with glutamine (gln), a conditionally essential amino acid in catabolic conditions, increases gln plasma concentrations, reduces intestinal damage, improves nitrogen balance and may improve the course of the disease. However, human data supporting this assumption are missing.

METHODS

A total of 24 consecutive patients with an acute exacerbation of IBD (19 Crohn's disease; five ulcerative colitis) and scheduled for total parenteral nutrition (TPN) (>7 days) were randomised. Parallel to a standardised anti-inflammatory therapy, the patients received either a TPN with 1.5 g/kg body weight of a standard amino acid or an isonitrogenic, isocaloric TPN with 1.2 g/kg body weight of a standard amino acid and 0.3 g/kg L-alanine-L-glutamine. Primary end points were gln plasma concentrations and intestinal permeability assessed by urinary lactulose and D-xylose ratio.

RESULTS

Gln plasma levels did not differ significantly in either group throughout the study. Intestinal permeability did not change within 7 days either with or without gln supplementation (Delta-lactulose/xylose ratio: 0.01+/-0.05 (gln+) vs 0.02+/-0.1 (gln-)). The observed changes in inflammatory and nutritional parameters, and also disease activity, length of TPN and hospital stay, were independent of glutamine substitution. Five (41%) patients in the gln+ group and three (25%) patients in the gln- group needed surgical intervention.

CONCLUSION

Although limited by the sample size, these results do not support the hypothesis that glutamine substitution has an obvious biochemical or clinical benefit in patients with active IBD scheduled for total parenteral nutrition.

Effect of glutamine on change in early postoperative intestinal permeability and its relation to systemic inflammatory response

AIM: To study the effects of glutamine (Gln) on the change of intestinal permeability and its relationship to systemic inflammatory response in early abdominal postoperative patients.

METHODS: A prospective, randomized, double-blind and controlled trial was taken. Twenty patients undergoing abdominal surgery were randomized into Gln group (oral administration of glutamine, 30 g/d, for 7 d, n = 10) and placebo group (oral administration of placebo, 30 g/d, for 7 d, n = 10). Temperatures and heart rates of all patients were daily recorded. White blood cell counts (WBC) and biochemical variables were measured before operation and 4 and 7 d after drug administration. Serum concentrations of glutamine, endotoxin, diamine oxidase and malondialdehyde and urine lactulose/mannito (L/M) ratio were measured before and 7 d after drug administration.

RESULTS: The patients in the 2 groups were comparable prior to drug administration. Serum Gln concentration was significantly decreased in the placebo group and increased in the Gln group 7 d after drug administration. Urine L/M ratio was significantly increased in the placebo group and decreased in the Gln group. The serum concentration of endotoxin, diamine oxidase and malondialdehyde was significantly decreased in the Gln group compared with those in the placebo group. Temperatures, heart rates and WBC counts were significantly lower in the Gln group than those in the placebo group.

CONCLUSION: Gut is one of the sources of systemic inflammatory response in abdominal postoperative patients and glutamine can decrease intestinal permeability, maintain intestinal barrier and attenuate systemic inflammatory response in early postoperative patients.

The nature of human hazards associated with excessive intake of amino acids

In recent years there has been a large increase in the consumption of individual amino acids as dietary supplements. This has resulted not only from the use of certain amino acids as flavoring agents, but other amino acids are taken for perceived health benefit, for enhancement of physical performance, as well as for psychological effects. Two reviews of the scientific literature exist that mainly deal with effects in animals, and three major reports consider the safety of amino acids for human consumption. This article is a brief summary of the available evidence regarding the safety of individual amino acids when taken in excess relative to the amounts absorbed from dietary protein.

Effects on skeletal muscle of intravenous glutamine supplementation to ICU patients

OBJECTIVE

To evaluate the effect of four doses of intravenous glutamine supplementation on skeletal muscle metabolism.

DESIGN

A prospective, blinded, randomized study.

SETTING

The general Intensive Care Unit (ICU) of a university hospital.

PATIENTS

ICU patients with multiple organ failure (n=40), who were expected to stay in the unit for more than five days.

INTERVENTION

Patients received 0, 0.28, 0.57 or 0.86 g of glutamine per kg bodyweight per day intravenously for five days as part of an isocaloric, isonitrogenous and isovolumetric diet.

RESULTS

Plasma glutamine concentration responded to glutamine supplementation with normalization of plasma levels in a dose-dependent way, while free muscle glutamine concentration, as well as muscle protein synthesis and muscle protein content, did not change significantly.

CONCLUSION

Intravenous glutamine supplementation to ICU patients for a period of five days resulted in normalization of plasma glutamine concentrations in a dose-dependent way whereas muscle glutamine concentrations were unaffected.

Nutritional benefits of enteral alanyl-glutamine supplementation on rat small intestinal damage induced by cyclophosphamide

BACKGROUND

Glutamine is the principal fuel used by the small intestine. Although the parental administration of glutamine promotes intestinal mucosal growth, it is controversial whether enteral glutamine is effective against small intestinal damage caused by chemotherapy. To further evaluate the benefits of enteral supplementation, peptide and amino acid transporter functions must be considered.

METHOD

Rats were given cyclophosphamide (CPM) intraperitoneally (300 mg/kg). Expression of the amino acid transporter, B0 and peptide transporter (PepT1) in the jejunal mucosa was initially examined by northern blot analysis. Rats received a bolus oral supplement of an alanine (1.22 g/kg/day) plus glutamine (2.0 g/kg/day) mixture, alanyl-glutamine (2.972 g/kg/day) or saline as a control, for 7 days after CPM administration.

RESULTS

Levels of B0 mRNA remained unchanged at both 3 and 7 days after CPM administration. Conversely, PepT1 mRNA increased significantly after CPM administration, and reached 200% of the initial level 7 days later. In rats given alanyl-glutamine, the mucosal wet weight and protein content increased significantly with increasing villus height at 3 and 7 days, compared with the alanine plus glutamine mixture. The plasma glutamine concentration in the alanyl-glutamine group, but not the alanine plus glutamine mixture group, increased significantly compared with that in the saline group.

CONCLUSION

Enteral supplementation with an alanyl-glutamine but not alanine plus glutamine mixture prevents intestinal damage, as demonstrated by increased peptide transport expression and an elevated plasma glutamine concentration after CPM administration.

Metabolism and nutritional support in the surgical neonate

Various factors can influence the metabolism of surgical neonates. These include prematurity, operative stress, critical illness, and sepsis. The nutritional management of surgical infants with congenital or acquired intestinal abnormalities has improved after the introduction of parenteral nutrition. This article is focused on the energy and protein metabolism of surgical neonates with particular reference to the metabolic response to operative trauma and sepsis. The metabolic utilization of intravenous nutrients also is discussed. The metabolic response to operative trauma is different between neonates and adults. Infants have high rates of protein turnover and are avid retainers of nitrogen. Energy expenditure increases only transiently (4 to 6 hours) after major surgery in neonates. Protein turnover and catabolism seems not to be affected by major operative procedures in neonates. In neonates on parenteral nutrition, carbohydrate and fat have an equivalent effect on protein metabolism. The main determinants of fat utilization are carbohydrate intake and resting energy expenditure. Parenteral nutrition in surgical neonates is associated with increased production of oxygen-free radicals. This seems to be related to intravenous fat administration. Promoting fat utilization by reducing the carbohydrate to fat ratio in the intravenous diet reduces free radical activity to a similar extent as fat exclusion. Glutamine appears to be safe for use in neonates and infants and is "conditionally essential" in very-low birth weight infants and in septic neonates. Enteral glutamine supplementation in very-low birth weight infants reduces the risk of sepsis. The metabolism of surgical neonates is affected by operative trauma, critical illness, and sepsis. Nutritional support in surgical neonates has a profound impact on outcome. Exogenous glutamine can modulate immune, metabolic, and inflammatory responses. Further investigations are needed to clarify the clinical benefit of parenteral or enteral glutamine administration in surgical neonates.

The impact of alanyl-glutamine on clinical safety, nitrogen balance, intestinal permeability, and clinical outcome in postoperative patients: a randomized, double-blind, controlled study of 120 patients

PURPOSE

To evaluate the impact of alanyl-glutamine (Ala-Gln)-supplemented parenteral nutrition (PN) on clinical safety, nitrogen balance, intestinal permeability, and clinical outcome in postoperative patients.

METHODS

One hundred twenty patients undergoing major abdominal surgery were enrolled. Protocol was approved and informed consent obtained. A double-blind protocol was designed as used in Europe. The clinical safety and outcome were observed for 60 patients in 2 centers (30 each). Sixty patients from 2 additional centers (30 each) were observed for clinical safety, nitrogen balance, intestinal permeability, and clinical outcome. All patients received isonitrogenous (0.20 g/kg body wt per day) and isocaloric (30 kcal/kg body wt per day) parenteral nutrition. The study group received Ala-Gln (Dipeptiven, Fresenius Kabi, Bad Homberg, Germany) 0.50 g/kg per day. Clinical chemistry variables, plasma amino acids profile, nitrogen balance, intestinal permeability (lactulose/mannitol ratio [L/M ratio]) were measured; hospital stay and infection rate were monitored. Statview was used for analysis of variance (ANOVA) or chi2 tests. Data were expressed as means +/- SD, and the significance level was p < .05.

RESULTS

The patients in both groups were comparable prior to the operation. Vital signs and clinical chemical parameters were similar between groups. L/M ratio was 0.047+/-0.029 in control and 0.058+/-0.049 in study group before the operation (AOD-3). The L/M ratio was 0.132+/-0.081 in the control group, and 0.097+/-0.063 in study group on the seventh postoperative day. The difference of L/M ratio between groups was significant (p = .02). The cumulative nitrogen balance values were -5+/-162 mg/kg for 6 days in control and 144+/-145 mg/kg for 6 days in study group (p = .0004). All the patients recovered without incision infection. However, there were 3 cases that had infection-related complications in the control group; the difference was not significant between groups. The hospital stay in the study group was 12.5 days, which was 4 days less than that of the control group (p = .02).

CONCLUSIONS

Ala-Gln-supplemented PN was clinically safe, had better nitrogen balance, and maintained intestinal permeability in postoperative patients. The clinical outcome of the patients in study group was better; it was significantly different from the control group.

Glutamine: a precursor of glutathione and its effect on liver

AIM:To investigate the relationship between alanyl-glutamine (ALA-GLN) and glutathione (GSH) biosynthesis in hepatic protection.METHODS:Twenty male Wistar rats were randomly divided into two groups:one receiving standard parenteral nutrition (STD) and the other supplemented with or without ALA-GLN for 7 days. The blood and liver tissue samples were examined after 5-fluorouracil (5-FU) was injected peritoneally.RESULTS:The concentration measurements were significantly higher in ALA-GLN group than in STD group in serum GLN (687&mgr;mol/L plus minus 50&mgr;mol/L vs 505&mgr;mol/L plus minus 39&mgr;mol/L, P < 0.05), serum GSH (14&mgr;mol/L plus minus 5&mgr;mol/L vs 7&mgr;mol/L plus minus 3&mgr;mol/L, P <0.01) and in liver GSH content (6.9&mgr;mol/g plus minus 2.5&mgr;mol/g vs 4.4&mgr;mol/g plus minus 1.6&mgr;mol/g liver tissue, P <0.05). Rats in ALA-GLN group had lesser elevations in hepatic enzymes after 5-FU administration.CONCLUSION:The supplemented nutrition ALA-GLN can protect the liver function through increasing the glutathione biosynthesis and preserving the glutathione stores in hepatic tissue.

Glutamine dipeptides in clinical nutrition

Glutamine is a conditional indispensable amino acid during stress. However, limited solubility and instability of glutamine prevent its addition to presently available nutritional preparations. To overcome these drawbacks, we propose the dipeptide concept by which stable and highly soluble synthetic glutamine containing dipeptides are used. The synthetic dipeptides fulfill all chemical/physical properties to be considered as parenteral substrates. Numerous experimental studies show rapid clearance of parenteral supplied glutamine containing dipeptides without accumulation in tissues; the loss via the urine being inconsequential. Differences related to the dipeptide structure are not observed. There is overwhelming evidence existent that a nutritional support with supplemental glutamine dipeptide positively influences nitrogen excretion, immune status, gut integrity, morbidity, rehabilitation and outcome. Consequently, omission of glutamine from conventional TPN and its subsequent administration should be considered as a replacement of a deficiency rather than a supplementation. It might thus be conceivable that the beneficial effects observed with glutamine nutrition are simply a correction of disadvantages produced by an inadequacy of conventional amino acid solutions. The availability of stable glutamine containing preparations will certainly facilitate an adequate amino acid nutrition in routine clinical setting during episodes of stress and malnutrition.

Effects of alanyl-glutamine on intestinal adaptation and bacterial translocation in rats after 60% intestinal resection

The effects of alanyl-glutamine dipeptide (Ala-Gln)-enriched parenteral nutrition on intestinal mucosa and gut barrier function were investigated. Wistar rats were studied. After moderate surgical stress was induced by 60% resection of the small intestine, the rats were randomized to three groups: the chow group was given standard rat chow; the PN group received standard parenteral nutrition (PN); and the Ala-Gln group received glutamine dipeptide-enriched parenteral nutrition (3% Ala-Gln). Rats were maintained on their respective diets for 8 days. The chow and Ala-Gln groups maintained serum glutamine concentrations, intestinal mucosal thickness and villus height. Bacterial translocation rates in the chow and Ala-Gln groups were 20%, which was significantly less than that in the PN group (70%, P < 0.05). The results indicated that Ala-Gln-enriched parenteral nutrition maintains intestinal adaptation and gut barrier function after massive intestinal resection and parenteral nutrition.

Effects of alanyl-glutamine on gut barrier function

Traditional parenteral nutrition (PN) and chemotherapy may lead to changes of mucosal morphology and gut barrier function. This study investigated the effect of alanyl-glutamine (Ala-Gln) on intestinal morphology and gut barrier function in PN-fed rats challenged with 5-fluorouracil (5-FU). Male Wistar rats were centrally catheterized and then randomized to receive PN devoid of glutamine (control group; n = 10) or 3% Ala-Gln-supplemented PN (study group; n = 10) for 7 d. Intestinal permeability to lactulose and mannitol was measured before and 72 h post 5-FU administration on day 4. Serum glutamine concentration and jejunal mucosal structure were maintained in the study group compared with the control group (P < 0.05). The bacterial translocation rates of mesenteric lymph nodes in the study group were significantly lower than the control (30% versus 90%; P < 0.05). No significant differences was found between the control and study groups with respect to ratio of lactulose and mannitol excreted in urine (L/M) (0.026 +/- 0.005575 versus 0.022 +/- 0.03079; P > 0.05) on day 3. On day 7, L/M was unaltered in the study group, whereas it increased in the control (0.042 +/- 0.004634 versus 0.029 +/- 0.002020; P < 0.05). We concluded that glutamine dipeptide maintained intestinal mucosal morphology and barrier function in PN-fed rats challenged with 5-FU.

Alanyl-glutamine preserves hepatic glutathione storesafter 5-FU treatment

Glutathione (GSH) is a major antioxidant that protects tissues from free radical injury. 5-fluorouracil (5-FU) considered the most active antineoplastic agent in the treatment of advanced gastrointestinal malignancies, causes hepatic GSH depletion. Glutamine (GLN) augments host defenses and may be important in GSH synthesis. We hypothesized that alanyl-glutamine (ALA-GLN) may protect liver cells from oxidant injury, like GLN, by increasing hepatic GSH stores. Two rat groups received standard parenteral nutrition (STD) supplemented with or without ALA-GLN for 7 days. After the antineoplastic agent 5-FU was injected, the concentration measurements were significantly different in ALA-GLN group compared with STD animals for serum GLN (687.3 +/- 49.8 vs. 504.9 +/- 38.6 uMol/L, P < 0.05), serum GSH (14.37 +/- 5.16 vs. 7.08 +/- 3.16 uMol/L, P < 0.01) and in liver GSH content (6.86 +/-2.46 vs. 4.38 +/-1.63 uMol/g liver tissue, P < 0.05). Rats in ALA-GLN group had lower elevations in hepatic enzymes induced by 5-FU. The experiment demonstrated that the supplemented nutrition ALA-GLN, like glutamine, protected the liver function and improved survival during 5-FU treatment by increasing GSH biosynthesis and by preserving the GSH stores of hepatic tissue.

Cerebrospinal and plasma amino acid concentrations after administration of i.v. glycyl-glutamine and glycyl-tyrosine containing amino acid solutions in humans

BACKGROUND

Glycyl-glutamine and glycyl-tyrosine may supply adequate glutamine and tyrosine in amino acid solutions for parenteral nutrition. However, plasma peptides may be transported into the cerebrospinal fluid, exerting effects on the neuronal tissue. Cerebrospinal fluid (CSF) and plasma amino acid concentrations after administration of a glycyl-glutamine/glycyltyrosine supplemented amino acid solution were therefore evaluated in a randomized controlled comparison with a conventional amino acid infusion.

METHODS

Dipeptide/amino acid solutions (0.60 mL/h/kg; 82.2 mg total dipeptides/amino acids/h/kg) or conventional amino acid solutions (0.73 mL/h/kg; 83.2 mg total amino acids/h/kg) were infused in 15 patients per group scheduled to undergo spinal anesthesia for urologic surgery over a 12-hour period preoperatively. Plasma amino acids were measured before the infusion was started. CSF and venous concentrations were analyzed simultaneously before the infusion was stopped. CSF samples were drawn through the spinal needle for anesthesia.

RESULTS

The dipeptide-containing solution did not increase either dipeptide to detectable levels in the CSF (detection limit < 5.0 nmol/mL). Venous glycyl-glutamine increased from below detection limits up to 308 +/- 111 nmol/mL (p < .05), whereas glycyl-tyrosine could not be found. In the dipeptide group, venous glutamine and tyrosine were higher (p < .05) but only tyrosine appeared in small amounts (p < .05) in the cerebrospinal fluid.

CONCLUSIONS

This study provides no evidence to support a CSF entry of IV glycyl-tyrosine and glycyl-glutamine under conditions of a normal blood-brain barrier in the adult (detection limit 5 nmol/mL). The data suggest that amino acid solutions containing these dipeptides may be used in parenteral solutions for nutrition support.

Glutamine

Glutamine is the most abundant free amino acid in the circulation. It is a primary fuel for rapidly dividing cells and plays a key role in the transport of nitrogen between organs. Although glutamine is absent from conventional regimens aimed at nutritional support, glutamine deficiency can occur during periods of metabolic stress; this has led to the reclassification of glutamine as a conditionally essential amino acid. Experiments with various animal models have demonstrated that the provision of glutamine can result in better nitrogen homoeostasis, with conservation of skeletal muscle. There is also considerable evidence that glutamine can enhance the barrier function of the gut. This review concludes by discussing the clinical evidence that supports the inclusion of stable forms of glutamine in solutions of nutrients.

Glutamine dipeptide-supplemented parenteral nutrition reverses gut atrophy, disaccharidase enzyme activity, and absorption in rats

BACKGROUND

Total parenteral nutrition (TPN) is associated with intestinal atrophy and dysfunction possibly attributed to the absence of the nonessential amino acid glutamine from commercially available TPN solutions because of the instability of the monoamino acid during heat sterilization and storage. The use of stable dipeptides may overcome this problem. In this study we tested the hypothesis that glutamine dipeptide supplementation with alanyl-L-glutamine during TPN for 10 days would reverse small bowel atrophy and TPN-induced dysfunction in rats.

METHODS

A conventional TPN solution (250 kcal/kg bw) was compared with an isocaloric and isonitrogenous TPN supplemented with alanyl-L-glutamine dipeptide. A food-fed control group was included (n = 6 each group). Jejunum mucosal architecture, absorption of water and glucose, and disaccharidase activity of maltase and alkaline phosphatase were evaluated.

RESULTS

TPN-induced villous atrophy, significantly reduced absorption rate, and decreased activity of villous enzymes, compared with the TPN group, could be reversed by supplementation of glutamine dipeptide alanyl-L-glutamine to parenteral nutrition solutions with no difference to the control group.

CONCLUSIONS

Glutamine dipeptide-enriched parenteral nutrition preserves mucosal structure and reversed atrophy-associated dysfunction.

Arginine-enriched solution induces a marked increase in muscle glutamine concentration and enhances muscle protein synthesis in tumor-bearing rats

Using a transplantable Yoshida sarcoma in a rat model of total parenteral nutrition (TPN), we measured the effectiveness of an arginine-enriched amino acid solution (AI-82) on muscle glutamine concentration and muscle protein synthesis compared with that of a conventional amino acid solution (Proteamin12). After tumor-bearing rats had been given one of two isocaloric TPN regimens for 6 days, [15N]glycine (99 atom %) containing TPN solution was infused into animals at a constant rate of 8 mg of [15N]glycine per hour for 18 hours, after which the liver, skeletal muscle (gastrocnemius muscle), and tumor protein synthesis rates were measured. A significantly increased whole muscle protein synthesis rate was observed in the AI-82 group; there was no difference in the whole liver and tumor protein synthesis rates between the two groups. When each TPN solution was administered for 1 week, muscle concentrations of arginine, ornithine, glutamine, and glutamate were considerably higher in the AI-82 group than in the Proteamin12 group, and these differences were also accompanied by a decrease in the plasma branched-chain amino acid (BCAA) (leucine, isoleucine, and valine) levels in the AI-82 group. The high levels of muscle glutamine concentration in the AI-82 group were investigated in connection with the high use of exogenous branched-chain amino acids.