A thirty-year odyssey in nitrogen metabolism: from ammonium to dipeptides

Enteral supplementation with glycyl-glutamine improves intestinal barrier function after liver transplantation in rats

BACKGROUND

Most patients after liver transplantation (LT) suffer from intestinal barrier dysfunction. Glycyl-glutamine (Gly-Gln) by parenteral supplementation is hydrolyzed to release glutamine, which improves intestinal barrier function in intestinal injury. This study aimed to investigate the effect of Gly-Gln by enteral supplementation on intestinal barrier function in rats after allogenetic LT under immunosuppressive therapy.

METHODS

Twelve inbred Lewis rats were selected randomly as donors, and 24 inbred Brown Norway (BN) rats as recipients of allogenetic LT. The recipients were divided into a control group (Ala, n=12) and an experimental group (Gly-Gln, n=12). In each group, 6 normal BN rats were sampled for normal parameters on preoperative day 3. The 6 recipients in the control group received alanine (Ala) daily by gastric perfusion for 3 preoperative days and 7 postoperative days, and the 6 recipients in the experimental group were given Gly-Gln in the same manner. The 12 BN recipients underwent orthotopic LT under sterile conditions after a 3-day fast and were given immunosuppressive therapy for 7 days. They were harvested for sampling on postoperative day 8. The following parameters were assessed: intestinal mucosal protein content, mucosal ultrastructure, ileocecal sIgA content, portal plasma levels of endotoxin and TNF-alpha, and bacterial translocation.

RESULTS

All recipients were alive after LT. On preoperative day 3, all parameters were similar in the two groups. On postoperative day 8, all parameters in the two groups were remarkably changed from those on preoperative day 3. However, compared to the Ala group, supplementation with Gly-Gln increased the levels of intestinal mucosal protein and ileocecal sIgA, improved mucosal microvilli, and decreased portal plasma levels of endotoxin and TNF-alpha as well as bacterial translocation.

CONCLUSION

Enteral supplementation with Gly-Gln improved intestinal barrier function after allogenetic LT in rats.

Fish oil after abdominal aorta aneurysm surgery

OBJECTIVE

Fish oil (FO) may attenuate the inflammatory response after major surgery such as abdominal aortic aneurysm (AAA) surgery. We aimed at evaluating the clinical impact and safety aspects of a FO containing parenteral nutrition (PN) after AAA surgery.

METHODS

Intervention consisted in 4 days of either standard (STD: Lipofundin medium-chain triglyceride (MCT): long-chain triglyceride (LCT)50%-MCT50%) or FO containing PN (FO: Lipoplus: LCT40%-MCT50%-FO10%). Energy target were set at 1.3 times the preoperative resting energy expenditure by indirect calorimetry. Blood sampling on days 0, 2, 3 and 4. Glucose turnover by the (2)H(2)-glucose method. Muscle microdialysis.

CLINICAL DATA

maximal daily T degrees, intensive care unit (ICU) and hospital stay.

RESULTS

Both solutions were clinically well tolerated, without any differences in laboratory safety parameters, inflammatory, metabolic data, or in organ failures. Plasma tocopherol increased similarly; with FO, docosahexaenoic and eicosapentaenoic acid increased significantly by day 4 versus baseline or STD. To increased postoperatively, with a trend to lower values in FO group (P=0.09). After FO, a trend toward shorter ICU stay (1.6+/-0.4 versus 2.3+/-0.4), and hospital stay (9.9+/-2.4 versus 11.3+/-2.7 days: P=0.19) was observed.

CONCLUSIONS

Both lipid emulsions were well tolerated. FO-PN enhanced the plasma n-3 polyunsaturated fatty acid content, and was associated with trends to lower body temperature and shorter length of stay.

What are the essential elements needed for the determination of amino acid requirements in humans?

The aims of this introductory article are to survey and critically evaluate the concepts and approaches that have been used to assess amino acid adequacy and to hypothesize about possible future directions of research. The issue in question is extensive, consequently this article will be limited to: 1) definitions of amino acid requirements; 2) available techniques to assess amino acid requirements; 3) actual recommendations for healthy adults; 4) factors influencing requirements; and 5) requirements in acute and chronic wasting diseases. Recommendations for amino acid intakes for healthy adults were proposed by the FAO/WHO expert committee in 2001. They have not yet been published. The major factors affecting amino acid requirements are the stage of development, reproductive state, environmental factors, digestibility of dietary proteins, genotype of the individual, and pathological conditions. Remarkably, there are no conclusive data relative to changes in requirements induced by infection, injury, trauma, and renal or liver failure. Future research using modern methods to evaluate requirements must thus receive a high priority. Wasting diseases are associated with deficiencies and imbalances of particular amino acids causing specific changes in requirements. Consequently, a new approach has been used to categorize amino acids as conditionally indispensable according to their functional and physiological properties. Kinetic measurements of plasma amino acids might help to estimate qualitative requirements. Measurement of tissue intracellular free amino acid deficiencies or excesses is another method to estimate qualitative requirements. Based on these measurements tentative values for conditionally indispensable amino acids during disease are given in the article.

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.

Glycyl-glutamine-supplemented long-term total parenteral nutrition selectively improves structure and function in heterotopic small-bowel autotransplantation in the pig

Marked atrophy and impaired absorptive and barrier function occur in transplanted small intestinal graft during total parenteral nutrition (TPN), TPN is required by all the patients after small bowel transplantation (SBT). Glutamine (Gln) is a conditional indispensable amino acid that is not included in regimens for parenteral nutrition because of its chemical instability in aqueous solution. Glutamine-containing dipeptide, however, is heat-stable. With this study, we determine whether the glycyl-glutamine-supplemented long-term TPN improves mucosal structure and function in heterotopic transplanted small intestinal graft in the pig. Ten outbred pigs, randomly divided into two groups, underwent heterotopic small bowel autotransplantation. In the STPN group, the animals received standard TPN without glycyl-glutamine (Gly-Gln) and in the GTPN group, the animals received isonitrogenous (0.3g kg day(-1)) and isocalories (nonprotein calories, 30 kcal kg day(-1)) TPN with Gly-Gln (3% Gln) for 28 days. At the end of TPN, there was no significant difference in the body weight loss between two groups ( P>0.05). The mucosal contents of Gln and protein were significantly higher in the GTPN group than in the STPN group ( P<0.05). The mucosal disaccharidase activities in the homogenate of the graft mucosa of the GTPN group were significantly higher than that of the STPN group ( P<0.05). The villous height, surface area, mucosal thickness were significantly higher in the GTPN group than in the STPN group ( P<0.05). There was no significant difference in crypt depth between the two groups ( P>0.05). These results suggest that glycyl-glutamine-supplemented long-term TPN improves graft mucosal structure in heterotopic autotransplanted small bowel grafts in the pig. Long-term (4 weeks) TPN supplemented with Gln could alleviate small intestinal graft atrophy, but could not completely eliminate atrophy.

New developments in glutamine delivery

Numerous studies demonstrate that free glutamine can be added to commercially available crystalline amino acid-based preparations before their administration. Instability during heat sterilization and prolonged storage and limited solubility (35 g/L at 20 degrees C) hamper the use of free glutamine in the routine clinical setting. Indeed, there are many well-controlled and valuable trials with free glutamine, yet its use is restricted to clinical research. The obvious limitations of using free glutamine initiated an intensive search for alternative substrates. Synthetic glutamine dipeptides are stable under heat sterilization and highly soluble; these properties qualify the dipeptides as suitable constituents of nutritional preparations. Industrial production of these dipeptides at a reasonable price is an essential prerequisite for implications of dipeptide-containing solutions in clinical practice. Recent development of novel synthesis procedures allows increased capacity in industrial-scale production. Basic studies with synthetic glutamine-containing short-chain peptides provide convincing evidence that these new substrates are cleared rapidly from plasma after parenteral administration, without being accumulated in tissues and with negligible loss in urine. The presence of membrane-bound as well as tissue-free extracellular hydrolase activity facilitates a prompt and quantitative peptide hydrolysis, the liberated amino acids being available for protein synthesis and/or generation of energy. In the clinical setting, glutamine dipeptide nutrition beneficially influences outcome (nitrogen balance, immunity, gut integrity, hospital stay, morbidity and mortality). The provision of conditionally indispensable glutamine should be considered a necessary replacement of a deficiency rather than a supplementation. The beneficial effects observed with glutamine dipeptide nutrition should be seen simply as a correction of disadvantages produced by the inadequacy of conventional clinical nutrition. The availability of stable dipeptide preparations certainly facilitates, for the first time, adequate amino acid nutrition of critically ill, malnourished or stressed patients in the routine clinical setting and, thus, represents a new dimension in artificial nutrition.