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 GlyGln 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-α,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 withGly-Gln increased the levels of intestinal mucosal protein and ileocecal sIgA,improved mucosal microvilli,and decreased portal plasma levels of endotoxin and TNF-α as well as bacterial translocation.CONCLUSION:Enteral supplementation with Gly-Gln improved intestinal barrier function after allogenetic LT in rats.

Enteral feeding of glycyl-glutamine dipeptide improves the structure and absorptive function of the small intestine after allogenetic liver transplantation in rats

BACKGROUND: Recipients of liver transplantation could have postoperative structural injury and declined absorptive function in the gastrointestinal tract. Glutamine (Gln) is a special nutrient of small intestinal mucosa and of various kinds of cells proliferating rapidly. But Gln could form a kind of poisonous pyroglutamic acid in water solution, which is the limitation of Gln in clinical practice. Glycyl-glutamine (Gly-Gln) is highly soluble and can be hydro-lyzed to release glutamine. This study was undertaken to observe the effect of Gly-Gln dipeptide by enteral feeding on the intestinal structure and absorptive function after allogenetic liver transplantation in rats. METHODS: Twelve male inbred Lewis rats were selected randomly as donors, and 24 male inbred BN rats as recipients of allogenetic liver transplantation. The recipients were also randomly divided into two groups; control group (ALA group, n = 12 ) and experimental group ( GLN group , n =12). In each group, 6 normal BN rats were sampled as the normal parameter on the 3rd preoperative day. The 6 recipients in the control group received alanine 0. 6 g/kg daily for 3 days before operation and 7 days after operation by gastric perfusion, and the 6 recipients in the experimental group were given Gly-Gln 0.6 g/kg daily the same way. The 12 BN recipients underwent 3-day fasting (free access to water with 0. 23% sodium chloride) and ortho-topic liver transplantation in aseptic conditions and were given subcutaneous injection of CsA 2 mg/kg daily after the operation. The 12 BN recipients were sampled on the 8th postoperative day. All of the 24 BN rats were subjected to examination of mucosal structure, activities of Na + -K + - ATP and disaccharidase, and D-xylose absorption test. RESULTS: The 12 BN recipients were alive after liver transplantation. On the 3rd preoperative day, mucosal structure , activities of Na + -K -ATP and disaccharidase and D-xylose absorption in the two groups were not significantly different. On the 8th postoperative day, the parameters of the two groups were markedly changed compared with those on the 3rd preoperative day. However, the parameters of GLN group were remarkably higher than those of ALA group. CONCLUSION: Enteral feeding of Gly-Gln could improve the structure and absorptive function of the small intestine after liver transplantation in rats.

The Effect of Glycyl-Glutamine Dipeptide Concentration on Enzyme Activity, Cell Proliferation and Apoptosis of Jejunal Tissues from Weaned Piglets

An experiment was conducted in a singly factorial design to study the effect of glycyl-glutamine dipeptide on enzyme activity, cell proliferation and apoptosis of jejunal tissues from weaned piglets at different glycyl-glutamine concentration levels of 2, 4, 10, 20, and 30 mmol L-1, respectively. The glutaminase activity, diamine oxidase （DAO） activity, cell peoliferation, apoptosis, and perotein metabolism were measured by the tissue culture method in vitro using jejunal tissues. The immunohistochemical method was used to study the cell proliferation and apoptosis of jejunal tissues. The results showed that compared to the blank control, the percentage and MOD value of BrdU-positicve cells incubated with glycyl-glutamine dipeptide solution were significantly （P0.05） increased. Accordingly, the percentage and MOD value of caspase-3-positive cells from tissue incubated with glycyl-glutamine dipeptide were notably lower （P0.05） than that from the control treatment. The glycyl-glutamine dipeptide increased the glutaminase activity, DAO activity and protein content of jejunal tissues, as the dipeptide concentration was on the rise （P0.05）. These results indicated that glycyl-glutamine dipeptide affected the jejunum development and adaptation of weaned piglets, and the function might be fulfilled by enhancing the glutamine-related enzyme activity, thereby increasing the consumption of glutamine, and then improving the jejunal cell proliferation and suppressing cell apoptosis. The effects of glycyl-glutamine dipeptide relied in a dose-dependent manner, and the maximum effect was achieved at 20-30 mmol L-1 glycyl-glutamine dipeptide.

Prokaryotic Expression of Gly-Gln Dipeptide and Its Bioactive Analysis: A Novel Method for Short Peptide Production

Small bioactive peptides, with diverse biological functions, have received increasing attention as physiologically beneficial substances in animal production. The main obstacle to wide application of small bioactive peptides is a lack of costeffective methods for mass production. In this study, we mass-production method for small bioactive peptides. used glycyl-glutamine （Gly-Gln） as a test case to develop a novel The oligonucleotide encoding Gly-Gln pro-peptide （Gpp） was designed and synthesized. Gpp includes 3 Gly-Gln dipeptides and 2 enzymatic sites for pepsin and trypase, allowing direct digestion and absorption of Gly-Gln in the gastrointestinal tract. The Gpp oligonucleotides were linked to generate an oligomeric oligonucleotide segment containing 12 tandem copies of Gpp. This 12Gpp segment was cloned and expressed in Escherichia coli vector pET32a. By optimizing culture conditions [0.1 mmol L^-1 isopropyl-β-D- thiogalactopyranoside （IPTG）, 50 μg mL^-1 ampicillin （Amp）, 30℃ for 12 h], the thioredoxin fusion peptides reached 40% of total bacterial protein. After purification, the fusion protein was fed to Kunming mice to determine its effect on mouse immune function. The results showed that similar to Gly-Gln dipeptide, Gpp polymer protein could significantly suppress the proliferation of T and B lymphocytes in blood and spleen, and additionally could significantly improve interleukin-2 （IL-2） and interleukin-6 （IL-6） secretion of blood and spleen lymphocytes. These effects were not observed in mice fed a 2 amino acids mix （glycine and glutamine）. These evidences indicated that an efficient digestion of Gpp polymer protein could be achieved when ingested into the animal gut. The expression system in this study provides a potential production method for not only Gly-Gln dipeptide but also other short bioactive peptides.