Inhibitory effect of L-glutamine on gastric irritation and back diffusion of gastric acid in response to aspirin in the rat

AMPK/mTOR-driven autophagy & Nrf2/HO-1 cascade modulation by amentoflavone ameliorates indomethacin-induced gastric ulcer

Gastric ulcer (GU) is a worldwide gastrointestinal disorder associated with NSAID use. Recently, amentoflavone proved to be a potent autophagy modulator, antioxidant, anti-inflammatory, and anti-apoptotic agent. Eight-week-old male Wistar rats received amentoflavone orally for 14 days at 25, 50, or 100 mg/kg/day. On day 14 of treatment, GU was induced by a single oral instillation of 100 mg/kg indomethacin, one hour after the last treatment. Amentoflavone dose-dependently alleviated indomethacin-induced GU, as demonstrated by repression of gastric mucosa pathological manifestations (ulcer index, ulcer surface area, histopathological deviations, and score) and increased ulcer inhibition percentage. These protective effects were due to the enhancement of gastric mucosa autophagy, as demonstrated by increased levels of beclin-1, MAP1LC3B, and CTSD, and reduced expression of p62 (SQSTM1). In addition, amentoflavone modulated the AMPK/mTOR pathway by increasing p-AMPK and reducing mTORC1 levels. Moreover, it hindered the redox aberrations by reducing MDA level and enhancing SOD activity, GSH level, and Nrf2/HO-1 cascade. Furthermore, a decrease in caspase-3 levels, Bax/Bcl-2 ratio and an increase in Bcl-2 expression suggest inhibition of the apoptotic process. Additionally, amentoflavone suppressed gastric mucosal inflammation by decreasing IL-1β, TNF-α, IFN-γ levels, IL-4, IL-6 mRNA expressions and MPO activity, and increasing IL-10 mRNA expresion. Therefore, amentoflavone could consider a promising natural agent protecting against indomethacin-induced GU.

New therapeutic strategy for amino acid medicine: prophylactic and healing promoting effect of monosodium glutamate against NSAID-induced enteropathy

We reviewed the effect of monosodium glutamate (MSG) on the development and healing of nonsteroidal anti-inflammatory drug (NSAID)-induced small intestinal lesions in rats. Loxoprofen (60 mg/kg, p.o.) induced lesions in the small intestine within 24 h, accompanied by a decrease of Muc2 expression and an increase in enterobacterial invasion and inducible nitric oxide synthase (iNOS) expression. These lesions were prevented when MSG was given as a mixture of powdered food for 5 days before the loxoprofen treatment. This effect of MSG was accompanied by an increase in Muc2 expression / mucus secretion as well as the suppression of bacterial invasion and iNOS expression. These intestinal lesions healed spontaneously within 6 days, but the process was impaired by the repeated administration of low-dose loxoprofen (30 mg/kg) for 5 days after the ulceration, with the decrease of vascular endothelial derived growth factor (VEGF) expression and angiogenesis. The healing-impairing effect of loxoprofen was prevented by feeding 5% MSG for 5 days after the ulceration. These results suggest that MSG not only prevents loxoprofen-induced small intestinal damage but also promotes a healing of these lesions; the former is functionally associated with the increase in Muc2 expression / mucus secretion and the suppression of bacterial invasion and iNOS expression, while the latter is associated with the stimulation of VEGF expression/angiogenesis.

New frontiers in gut nutrient sensor research: prophylactic effect of glutamine against Helicobacter pylori-induced gastric diseases in Mongolian gerbils

Ammonia is one of the important toxins produced by Helicobacter pylori (H. pylori), the major cause of peptic ulcer diseases. We examined whether glutamine or marzulene (a gastroprotective drug containing 1% sodium azulene and 99% glutamine) protects the gastric mucosa against H. pylori in vivo and investigated the mechanism underlying glutamine-induced mucosal protection against ammonia in gastric epithelial cells in vitro. Mongolian gerbils were fed for 3 months with a diet containing glutamine (2%-20%) or marzulene (20%) starting from 2 weeks or 2 years after H. pylori infection. Then, gastric mucosal changes were evaluated both macro- and microscopically. Cultured gastric epithelial cells were incubated in the presence of ammonia, with or without glutamine; and cell viability, ammonia accumulation, and chemokine production were determined. Gerbils exhibited edema, congestion, and erosion after 3-month infection; and after 2-year infection, they showed cancer-like changes in the gastric mucosa. Glutamine and marzulene significantly suppressed these pathological changes caused in the gastric mucosa by H. pylori infection. Ammonia was accumulated in the cells, resulting in an increase in chemokine production and a decrease in cell viability. These pathological responses were prevented by glutamine. In addition, glutamine decreased chemokine production and cell death through inhibition of cellular accumulation of ammonia, resulting in the prevention of H. pylori-induced gastric diseases in vivo. These results suggest that glutamine/marzulene would be useful for prophylactic treatment of H. pylori-induced gastric diseases in patients.

Effect of glutamine on intestinal mucosal integrity and bacterial translocation after abdominal radiation

This study evaluates the effect of oral glutamine on intestinal mucosal integrity and bacterial translocation in rats. 80 animals were randomised into four groups: group 1 (chow diet and water), group 2 (chow diet and glutamine 3%), group 3 (radiation, chow diet and water), group 4 (radiation, chow diet and glutamine 3%). Groups 1 and 2 were fed for 5 days, then sacrificed. Groups 3 and 4 were fed for 12 days, irradiated on the 5th day and sacrificed on 1st, 3rd and 7th post-radiation days. Cultures from the mesenteric lymph nodes (MLN), portal vein (PV) and aorta (A) were taken and two tissue samples were also taken from the terminal ileum for light and electron microscopic examination. In non-radiated rats glutamine did not alter the histologic parameters of villous height (VH), mitoses per crypt (M/C) and muscle thickness (MT). Group 3 rats had severe mucosal damage associated with a significant decrease of VH (p < 0.0001) and M/C (p < 0.01) on 1st and 3rd post-radiation days respectively. In contrast, group 4 rats maintained their mucosal structure and had a significant increase of VH and M/C (p < 0.0001) on post-radiation days 1 and 3. Bacterial translocation in MLN was 87.5% (p < 0.002) and 75% (p < 0.04) on 1st and 3rd post-radiation days respectively in group 3, and fell significantly to 12.5% (p < 0.002) in group 4. The data demonstrate that glutamine helps maintain the integrity of the intestinal mucosa and thereby reduces the incidence of bacterial translocation following abdominal irradiation.

Inflammation and foveolar hyperplasia are reduced by supplemental dietary glutamine during Helicobacter pylori infection in mice

We recently showed that L-Gln protects cultured gastric cells from ammonia-induced cell death and predicted that Gln may also protect during Helicobacter pylori infection in vivo. Thus, the aim of this study was to test whether supplemental dietary Gln protects against H. pylori-associated pathology. For this, C57BL/6 mice were fed a purified diet consisting of 20.3% protein (1.9% Gln), 66% carbohydrate, and 5% fat or 25.3% protein (5% supplemental L-Gln; 6.9% total Gln), 61% carbohydrate, and 5% fat. After a 2-wk prefeeding period, mice were divided into sham-(uninfected) or H. pylori-infected groups. Body weight and food consumption were recorded weekly. Tissue histopathology, H. pylori colonization, serum IgG, and pro- and antiinflammatory cytokine mRNA expression were determined at 6, 12, and 20 wk postinfection (wkPI). Inflammation, antiinflammatory cytokine, and interleukin-1beta mRNA expression were significantly greater at 6 wkPI in H. pylori-infected mice fed supplemental Gln compared with those fed the control diet. At 20 wkPI, however, inflammation and foveolar hyperplasia were significantly lower in H. pylori-infected mice fed supplemental Gln compared with those fed the control diet. Body weight gain, food consumption, H. pylori colonization, and serum IgG did not differ in H. pylori-infected mice fed supplemental Gln compared with the control diet. Our data demonstrate that H. pylori-infected mice fed supplemental dietary Gln have reduced H. pylori-associated pathology in vivo that is accompanied by beneficial changes in the immune response to H. pylori early in infection. Thus, Gln supplementation may be an alternative therapy for reducing H. pylori-associated pathology.

Effect of glutamine on the intestinal permeability changes induced by indomethacin in humans

BACKGROUND

Long-term non-steroidal anti-inflammatory drug (NSAID) intake may induce increased intestinal permeability, eventually resulting in enteropathy. Because increased permeability might be related to cell damage resulting from energy depletion, it was hypothesized that glutamine--the major energy source of the intestinal mucosal cell--might prevent permeability changes.

METHODS

The 6-h urinary excretion of 51Cr-EDTA after an oral load of 51Cr-EDTA was used in this study as a measure for intestinal permeability. Healthy volunteers underwent a series of permeability tests: (i) basal test; (ii) test following NSAID (indomethacin); (iii) test following NSAID in combination with glutamine and/or misoprostol.

RESULTS

The NSAID induced increased permeability in all volunteers. Pre-treatment with glutamine (3x7 g daily, 1 week before NSAID-dosing) did not prevent the NSAID-induced increase in permeability. Multiple doses of glutamine close in time to NSAID-dosing resulted in significantly lower permeability compared to the NSAID without glutamine. Co-administration of misoprostol with the multiple-dose scheme of glutamine resulted in a further reduction in the NSAID-induced increase in permeability.

CONCLUSIONS

Glutamine decreases the permeability changes caused by NSAID-dosing when it is administered close in time, and misoprostol has a synergistic effect.

Glutamine metabolism in the gastrointestinal tract of the rat assess by the relative activities of glutaminase (EC 3.5.1.2) and glutamine synthetase (EC 6.3.1.2)

The activities of the two key enzyme involved in glutamine metabolism, glutaminase (EC 3.5.1.2) and glutamine synthetase (EC 6.3.1.2), have been measured in the various tissues of the gastrointestinal (GI) tract of the rat, from the mouth to the rectum. Glutaminase activity was particularly high in the mucosa of the small intestine, where its activity accounted for more than 80% of the total activity of the GI tract. In contrast, the mouth and oesophagus had very low activities, accounting for less than 2% of the total. Glutamine synthetase was mainly confined to the lower part of the stomach, which accounted for almost 90% of the total activity of the GI tract. Activity in the small intestine was very low, accounting for less than 2% of the total, and similarly low levels were found in the mouth and oesophagus. The data provide the most complete information on the distribution of these enzymes in the GI tract of the rat and suggest: (a) that the mucosa of the small intestine has the highest capacity for glutamine breakdown but the lowest capacity for its synthesis, and so requires an external source of this amino acid; (b) that there is little potential for glutamine synthesis or breakdown in the mouth and oesophagus: and (c) that the lower stomach has a substantial capacity to synthesize glutamine, in contrast to the rest of the GI tract. The results of the investigation are relevant to sites of glutamine metabolism in therapeutic studies involving glutamine administration discussed with reference to reports of the effects of glutamine administration on GI tract injury.

The use of glutamine in the treatment of gastrointestinal disorders in man

The human gastrointestinal tract (GIT) is a major site of glutamine utilisation accounting for more than half of the net splanchnic utilisation (approximately 15 g/day) of glutamine obtained from the systemic circulation. Dietary glutamine (approximately 5 g/day) is less important than circulating glutamine, especially in disease conditions associated with substantial reduction in food intake. Glutamine has multiple effects on the structure and function of the GIT, and effects in improving morbidity and mortality in animal models of GIT damage has led to a series of studies in man, which have produced variable results. Glutamine administration to treat mucositis of the upper GIT (mouth, oesophagus) due to cytotoxic drug therapy, has produced no evidence of benefit. Early studies suggested improved healing, as do recent studies of small intestinal mucositis resulting from chemotherapy. Investigations in colitis are lacking although in experimental rat models of colitis no benefit has been reported. Multiple explanations can be put forward to explain the overall results, including the GIT distribution of enzymes involved in glutamine metabolism. Apart from the lower stomach in man (upper stomach in the rat) there is very little weak activity of glutamine synthetase, suggesting that the gut derives glutamine formed in other tissues and from the diet. The activity of glutaminase, which is key flux generating enzyme involved in glutaminolysis is very weak in mucosa with stratified squamous epithelium (oesophagus), where intermediate in the same intestine, and highest in the small intestinal mucosa which accounts for about 80% of the total glutaminase in the entire human GIT mucosa.

Effect of enteral glutamine on intestinal permeability and bacterial translocation after abdominal radiation injury in rats

We investigated the effect of enteral glutamine on intestinal permeability and bacterial translocation after whole abdominal radiation in rats. Rats irradiated with 10 Gy to the abdomen were randomly divided into a glutamine-free diet group and a glutamine-rich diet (2% glutamine) group. After 3 days of feeding of each diet, the 6-h urinary recovery of polyethylene glycol 4000 was significantly decreased in the glutamine-rich diet group compared to that in the glutamine-free diet group. The 6-h urinary recovery of phenolsulfonphthalein was also decreased in the glutamine-rich diet group, but the difference was not significant. Plasma endotoxin concentration was significantly lower in the glutamine-rich diet group. Twenty-four hour after gavage with 14C-labeled Escherichia coli, the detection rate of 14C-labeled bacteria in the mesenteric lymph nodes of rats was significantly lower in the glutamine-rich diet group. The adherence of 14C-labeled E. coli in the jejunal mucosa was significantly lower in the glutamine-rich diet group than in the glutamine-free diet group, but there were no significant differences in the ileal mucosa. These findings suggest that in rats with intestinal injury induced by irradiation, enteral glutamine maintains the intestinal barrier and reduces bacterial translocation.

Amino acids in surgical nutrition. Principles and practice

Amino acids will always be an integral part of nutritional support in all patients. The use of specific amino acids in pharmacologic doses may be beneficial to certain critically ill patients, indicating that such compounds are conditionally essential. As our knowledge of the altered regulation of amino acid metabolism in surgical patients improves, the design of more effective feeding regimens will follow. The goal should be to provide the best nutrition to all patients at all times.

Glutamine nutrition: theoretical considerations and therapeutic impact

In critically ill surgical patients, nutritional therapy is an important component of overall care. As our knowledge increases, "tailor-made" diets designed to meet specific nutritional requirements in specific patients may play an important role. Although the data reviewed here suggest that glutamine-supplemented diets may have a significant impact in some clinical settings, it should be emphasized that additional carefully designed studies are necessary before the use of glutamine-enriched nutrition in critically ill patients should be advocated. It is clear, however, that the concept that the intestine is an organ of inactivity during critical illness merits reconsideration.

Gut glutamine metabolism

The gut plays a key role in interorgan glutamine metabolism in normal and catabolic states. During critical illness, the gut responds to prevailing metabolic pressures that may result in a temporary "reset" in interorgan glutamine flow. As the body recovers from the disease process, the alterations in gut glutamine metabolism revert to normal, which helps restore glutamine homeostasis. Overwhelming stresses, such as severe systemic infection, may lead to permanent organ dysfunction and further adaptive changes in glutamine metabolism.

The role of glutamine in maintaining a healthy gut and supporting the metabolic response to injury and infection

In the critically ill surgical patient a variety of therapeutic maneuvers is required to maintain a "healthy gut." Provision of adequate amounts of glutamine to the gastrointestinal mucosa appears to be just one of these maneuvers. Other methods utilized to protect the gut from becoming a wound include: (a) minimizing additional systemic insults (such as hypotension, sepsis, multiple operative procedures); (b) aggressive pulmonary care; (c) the judicious use of antibiotics; and (d) aggressive enteral or parenteral feedings. The concept that the gut is an organ of quiescence following surgical stress merits reconsideration. The intestinal tract plays a central role in interorgan glutamine metabolism and is a key regulator of nitrogen handling following surgical stress. Critically ill patients are susceptible to developing gut-origin sepsis, the incidence of which will be diminished by instituting measures and providing treatments which support intestinal structure, function, and metabolism. Provision of glutamine-enriched diets to such patients may be one of these therapies.

Oral glutamine reduces bacterial translocation following abdominal radiation

The effect of dietary glutamine on bacterial translocation was studied in rats following administration of a single dose of abdominal radiation (1000 rad) that causes a reproducible mucosal injury and results in a high incidence of culture-positive mesenteric lymph nodes after radiation (XRT). Following XRT, rats received only the amino acid glutamine (3%, +GLN) in their drinking water or a control nonessential amino acid (glycine, -GLN). Diets were isonitrogenous and isovolumetric. Four days after XRT, rats were anesthetized and a laparotomy was performed. Mesenteric lymph nodes were sterilely excised and cultured. Arterial blood was also obtained for whole blood glutamine determination. Control rats received no XRT but received identical diets. In XRT rats who received the GLN-free diet, the incidence of culture-positive mesenteric lymph nodes was 89% (eight of nine rats) while in the radiated rats receiving the GLN-enriched diet, the incidence fell to 20% (P less than 0.05). In non-radiated control rats receiving GLN-enriched and GLN-depleted diets for 4 days, bacterial translocation occurred in zero of eight and one of eight rats, respectively (NS). Provision of glutamine to XRT rats resulted in higher blood levels of glutamine (408 +/- 25 microM in XRT +GLN vs 311 +/- 19 microM in XRT -GLN, P less than 0.05). In addition, provision of GLN maintained mucosal mass and reduced weight loss (P less than 0.05). The data lend further support to the hypothesis that glutamine helps maintain the gut mucosal barrier and thereby decreases the incidence of bacterial translocation following bowel injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Interorgan glutamine metabolism in the tumor-bearing rat

The effects of progressive malignant disease on gut/liver glutamine metabolism were studied in order to gain further insight into the altered glutamine metabolism that characterizes the host with cancer and to further elucidate the causes and consequences of glutamine depletion in tumor-bearing rats. Rats were inoculated on Day 0 with 2 X 10(6) viable fibrosarcoma cells and blood glutamine was measured every 6 days. On Day 24 the animals underwent laparotomy and sampling of arterial, portal venous, and hepatic venous blood. Arterial glutamine fell by more than one-third in tumor-bearing rats and the arterial-portal venous concentration difference for glutamine across the intestinal tract was diminished by 50% (P less than 0.01). Simultaneously the fractional extraction of glutamine by the gut was reduced from 21 to 15% (P less than 0.05). The liver switched from an organ of near glutamine balance in control rats to one of marked glutamine output in tumor-bearing rats (P less than 0.01). The wet weight of the small intestine was diminished by 15% in tumor-bearing rats and villous height was uniformly decreased in tumor-bearing rats with an average reduction in villous height of 26% (P less than 0.05). The causes of glutamine depletion in this tumor-bearing rat model remain unclear. The growing tumor may behave as a glutamine trap but also appears to alter glutamine metabolism in vital metabolic processing centers such as the gut and liver. Malignant cells may compete with gut mucosal cells for glutamine resulting in a diminished gut glutamine utilization and detrimental changes in mucosal architecture.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of gastric mucosal hexosamine in aspirin-induced ulcers

In order to elucidate the role of gastric tissue hexosamine, used as an index of mucopolysaccharide content, in the development and healing process of peptic ulcers, the distribution of hexosamine and the changes of gastric hexosamine content in the development and healing of aspirin-induced ulcers in rats were studied. In addition, the effects of proglumide and L-glutamine on gastric hexosamine were also studied. The hexosamine content was found to be the highest in the antrum, followed by the corpus and then the forestomach. The mucosa contained significantly higher hexosamine than the smooth muscle layer in both the antrum and the corpus. Prior treatment with proglumide significantly increased the mucosal hexosamine to the extent of 10.3--18.1% in the glandular stomach. Administration of aspirin decreased the gastric mucosal hexosamine and induced the onset of ulcer, while administration of proglumide suppressed the gastric lesions in proportion to dosage and correspondingly prevented a decrease of the hexosamine. In contrast, L-glutamine showed an anti-ulcerogenic effect without suppressing a decrease of the hexosamine. In the process of curing gastric lesions, proglumide accelerated the healing of the ulcers and simultaneously returned the total hexosamine content to its original level. These results suggest that the gastric mucosal hexosamine is closely related to the onset and healing of aspirin-induced ulcer in rats, and that proglumide contributes to both the prevention and healing of ulcers by increasing gastric mucosal hexosamine.

Strain differences in aspirin-induced gastric ulceration in rats

We found that there are strain differences in aspirin-induced ulceration in pylorus-ligated rats; the ulcer indices varied, from high to low, in the following order: Donryu greater than Sprague-Dawley greater than Wistar. Several experiments including analysis of gastric contents or ionic flux, determination of serum aspirin esterase activity, absorption of aspirin from the stomach, prothrombin time and hexosamine content in gastric mucosa and juice were performed to elucidate the origin of the differences. A significantly higher acid output in Donryu rats, and higher hexosamine content in the gastric mucosa of Wistar rats were noted. However, it appears unlikely that these factors only contribute to the marked strain difference in aspirin-induced ulcers. The possible different sensitivity of gastric mucosal cell itself to aspirin must be considered.

Effects of L-glutamine on acetylsalycylic acid induced gastric lesions and acid back diffusion in dogs

Effects of L-glutamine on acetylsalicylic acid (ASA)-induced gastric mucosal lesions were studied in mongrel dogs. It was confirmed that when oral ASA at 1.0 or 2.0 g per dog is given in two divided doses, there is severe and consistent dose-dependent mucosal damage in the glandular portion of the stomach in fasted dogs. However, when L-glutamine 2.0 or 4.0 g per dog in two divided doses is given concomitantly with ASA 2.0 g per dog orally, the gastric irritation is significantly inhibited. Instillation of 20 mM of ASA in 100 mM HCl solution into the Heidenhain pouch of Beagle dogs produced a significant loss of H+ from the pouch and a gain of Na+ in the lumen compared with ASA-free controls. When L-glutamine (100 mM) was given concomitantly with ASA (20 mM) into the pouch, changes of electrolyte fluxes in response to ASA alone were significantly suppressed. However, 50 mM of L-glutamine had no appreciable effect on acid back diffusion caused by ASA 20 mM. The amino acid itself had little effect on the ionic movement in the pouch. Gross bleeding from the pouch treated with ASA was never observed with the concomitant dosing of ASA and L-glutamine 50 or 100 mM.