Molecular weight of gastric mucus glycoprotein is a determinant of the degree of subsequent aspirin induced chronic gastric ulceration in the rat

Galectin-3 Plays an Important Role in Innate Immunity to Gastric Infection by Helicobacter pylori

We studied the role of galectin-3 (Gal3) in gastric infection by Helicobacter pylori We first demonstrated that Gal3 was selectively expressed by gastric surface epithelial cells and abundantly secreted into the surface mucus layer. We next inoculated H. pylori Sydney strain 1 into wild-type (WT) and Gal3-deficient mice using a stomach tube. At 2 weeks postinoculation, the bacterial cells were mostly trapped within the surface mucus layer in WT mice. In sharp contrast, they infiltrated deep into the gastric glands in Gal3-deficient mice. Bacterial loads in the gastric tissues were also much higher in Gal3-deficient mice than in WT mice. At 6 months postinoculation,H. pylori had successfully colonized within the gastric glands of both WT and Gal3-deficient mice, although the bacterial loads were still higher in the latter. Furthermore, large lymphoid clusters mostly consisting of B cells were frequently observed in the gastric submucosa of Gal3-deficient mice.In vitro, peritoneal macrophages from Gal3-deficient mice were inefficient in killing engulfed H. pylori Furthermore, recombinant Gal3 not only induced rapid aggregation of H. pylori but also exerted a potent bactericidal effect on H. pylori as revealed by propidium iodide uptake and a morphological shift from spiral to coccoid form. However, a minor fraction of bacterial cells, probably transient phase variants of Gal3-binding sugar moieties, escaped killing by Gal3. Collectively, our data demonstrate that Gal3 plays an important role in innate immunity to infection and colonization of H. pylori.

Surface mucus in the non-glandular region of the equine stomach

In horses, ulceration of the non-glandular region of the stomach is common and has been attributed to the lack of a protective mucus covering. This study aimed to determine whether the non-glandular region is covered by a mucus layer. A mixture of antibodies raised against human gastric mucin (MUC 5 AC) showed a tissue distribution in the glandular region of the equine stomach similar to that seen in humans. Dot blots of mucus from the glandular and non-glandular regions showed cross-reactivity with these antibodies. Various histological fixation and processing techniques were compared for their ability to preserve mucus in the non-glandular region. Fixing frozen sections on-slide for 20 seconds in 20 per cent formalin/1 per cent cetylpyridinium chloride was considered the best method. In conclusion, the equine stomach expresses a gene homologous to human MUC 5 AC. Its product is expressed as a neutral mucin, which is present in the mucus that covers both the glandular and non-glandular regions. Future comparison of mucus composition in the healthy and ulcerated stomach will improve our understanding of gastric ulceration in the horse.

Role of mucus reduction and luminal acid elevation in increased susceptibility of stomach to nonsteroidal antiinflammatory drug-induced injury in arthritic rats

We investigated the role of gastric mucus and acid secretion in the increase of nonsteroidal antiinflammatory drug-induced gastric lesions in adjuvant-induced arthritic rats. Both aspirin- and indomethacin-induced gastric injury were remarkably worsened in the arthritic rats. In the arthritic rats, the amounts of mucus glycoprotein in both the mucosa and adherent gel layer were respectively decreased to 70% and 34% of those in normal rats, while gastric acid secretion was augmented to 1.5-fold. The gastroprotective antiulcer agent ecabet sodium, which increased the mucus content in the gel layer but did not affect the luminal acid contents, prevented the increase of both lesions induced by aspirin and indomethacin. Cimetidine also inhibited the formation of aspirin- and indomethacin-induced damage as well as the acid secretion in the arthritic rats. In conclusion, an imbalance between gastric defensive and aggressive systems due to the loss of adherent mucus glycoprotein and the elevation of the luminal acid contents seems to account for the increased susceptibility of the lesion-inducing properties of nonsteroidal antiinflammatory drugs in arthritic rats.

Fasting induces impairment of gastric mucosal integrity in non-insulin-dependent diabetic (db/db) mice

BACKGROUND

Although diabetic patients often have gastrointestinal complications, the gastric mucosal function in diabetes has not been well documented.

AIM

To investigate the effect of fasting on the gastric mucosa in C57BL/KsJ-db +/+ db (db/db) mice, genetically non-insulin-dependent diabetic animals.

METHODS

Blood glucose levels, gastric mucosal morphology, and the amount of gastric mucin were examined before and after 18 h of fasting with free access to water in db/db mice and their non-diabetic littermates (db/m).

RESULTS

Although 18 h of fasting reduced the blood glucose levels of both db/db and db/m mice, fasting decreased the amount of gastric adherent mucin and caused haemorrhagic gastric lesions only in db/db mice. After fasting, oral administration of ethanol induced much more severe gastric damage in db/db than in db/m mice. The above fasting-induced gastric damage such as haemorrhagic lesions, loss of the mucin, and the increased sensitivity to ethanol worsened as the duration of diabetes became longer. Glucose ingestion in drinking water during the fasting counteracted the fall in blood glucose and prevented the decrease in the amount of gastric mucin and the formation of gastric mucosal lesions in db/db mice.

CONCLUSION

These findings indicate that fasting-induced glucose deficit causes gastric mucosal lesions and increases the susceptibility of gastric mucosa to noxious agents owing to the loss of mucus glycoprotein in db/db mice. Prolonged diabetes is likely to augment the severity of fasting-induced impairment of the gastric mucosal function.

Ecabet sodium, a novel locally-acting anti-ulcer agent, protects the integrity of the gastric mucosal gel layer from pepsin-induced disruption in the rat

BACKGROUND

Ecabet sodium, a novel non-systemic anti-ulcer agent, possesses high affinity to gastric adherent mucus, which plays an important role in the protection of the gastric epithelium against acid and pepsin.

AIM

To assess the effect of ecabet on pepsin-induced degradation of the structure of the mucus gel layer.

METHODS

Everted sacs of rat stomach were incubated in HCl solution containing pepsin with or without ecabet. Pepsin-induced release of the cleaved peptides and hexosamine from the sacs was determined. Changes in the molecular size of glycoproteins in the adherent mucus (using gel filtration methods) and in the morphology of the epithelium (using both light and scanning electron microscopy) were also examined.

RESULTS

Ecabet reduced the pepsin-induced release of peptides and hexosamine, depending on its content in the adherent mucus. Pepsin treatment partially lowered the molecular weight of native glycoproteins in the adherent mucus, caused exfoliation of the epithelial cells, and degraded the network-like ultrastructure of the mucus layer, giving it a lumpy, globular appearance. Ecabet prevented both the pepsin-induced molecular size shift in mucus glycoproteins, and morphological alteration of the epithelium, including ultrastructural derangement of the mucus gel layer.

CONCLUSION

Ecabet protects the polymeric structure of mucus glycoproteins from proteolytic degradation by pepsin, and thus maintains integrity of the gastric mucus gel layer.

Molecular fractionation of gastric mucus component by high-performance liquid chromatography: application to pig gastric mucus in vitro and to human gastric mucus collected by aspiration during gastric endoscopy

The glycoprotein molecular composition of antral and fundic adherent mucus has been studied by high-performance liquid chromatography on a silica gel column. Preliminary assays with pig gastric mucus allowed us to demonstrate the reproducibility of the method. The mucolytic activity of pepsin on this mucus demonstrates its ability to detect degradation of its glycoprotein components. This method was applied to control the state of pig antral mucosa that has previously been used in an in vitro antacid evaluation procedure, and also study human fundic and antral mucus collected by aspiration from normal and diseased stomachs during upper gastrointestinal endoscopy. Different elution profiles were obtained with these samples, depending on the presence of non-degraded or degraded mucus or due to the lack of mucus on the mucosa.

A separating method for quantifying mucus glycoprotein localized in the different layer of rat gastric mucosa

A method was devised for separating rat gastric mucosa into three layers each containing a different mucin species. The mucus gel (first layer) was removed by stirring the gastric mucosa in a solution of phosphate-buffered saline containing 2% N-acetylcysteine. The surface mucosa (second layer), rich in surface mucus cells, was then separated from the deep mucosa (third layer) containing mucus neck cells, by scraping with forceps. The effectiveness of this method was confirmed by light microscopical observation after GOCTS-PCS (dual staining by the galactose oxidase-cold thionin Schiff method and paradoxical concanavalin A method) and AB-PAS staining (dual staining with alcian blue and the periodic acid Schiff method). The fixed specimen of scraped mucus and cell debris was rich in AB-PAS and GOCTS positive mucus, but was hardly stained by PCS, indicating mucus derived from surface mucus cells to have been efficiently recovered from this preparation. The residual mucosa could be stained by PCS but hardly at all by AB-PAS or GOCTS. The lyophilized powder specimens obtained from the three different layers of rat gastric mucosa were used to extract and quantify mucus glycoprotein (mucin). This was done to examine changes in mucin content in the three layers of gastric mucosa one hour following the oral administration of 20% ethanol or 0.35 N hydrochloric acid, both mild irritants. Mucin content was noted to significantly increase in the first layer but hardly at all in the second layer. In the third layer, it decreased significantly by 0.35 N hydrochloric acid, but changed only slightly by 20% ethanol administration.(ABSTRACT TRUNCATED AT 250 WORDS)

A new method of separation and quantitation of mucus glycoprotein in rat gastric mucus gel layer and its application to mucus secretion induced by 16,16-dimethyl PGE2

A method was established for recovering the mucus gel layer of rat gastric mucosa without damage to underlying surface epithelium. The mucus gel was solubilized by stirring the gastric mucosa in a solution of N-acetylcysteine (NAC), a mucolytic agent. Optimal mucus gel solubilization was possible by treatment with 2% NAC for 5 minutes at room temperature. Mucus glycoprotein was quantitatively extracted and measured from the mucus gel sample obtained by the NAC treatment. This treatment caused no damage to surface epithelial cells, as observed by a light microscope. Besides NAC, pronase solution was also adequate for solubilizing the mucus gel layer without any damage to the surface epithelium. However, extraction and measurement of mucus glycoprotein from the pronase-treated mucus gel sample was not possible due to contamination by high molecular hexose-containing substances which were eluted along with the mucus glycoprotein from the column of Bio-Gel A-1.5m. This NAC method was used to examine changes in mucus glycoprotein content in the mucus gel at one hour following the oral administration of 16,16-dimethyl prostaglandin E2. A significant increase in mucus glycoprotein of the gel was brought about by the prostaglandin treatment. Thus, the present method was suitable for estimating the amount of mucus secreted in to the mucus gel layer.

Enhancement of the protective qualities of gastric mucus by sucralfate: role of phosphoinositides

The effects of intragastric administration of sucralfate on the physicochemical properties of gastric mucus, and the mechanism of its protective action against alcohol-induced mucosal injury were investigated using in vivo and in vitro models. The experiments in vivo were conducted with groups of rats receiving a dose of 100 mg sucralfate twice daily for 5 consecutive days. The animals were sacrificed 16 hours after the last dose, their stomachs dissected, and the mucosa subjected to physicochemical measurements. In the in vitro studies, gastric mucosa was cultured in the presence of sucralfate, ethanol, or both. The in vivo results revealed that sucralfate elicited an 8% increase in mucus gel dimension, while its sulfo- and sialomucin content increased by 63% and 81%, respectively. The changes in mucus gel mucin content with sucralfate were accompanied by a 9.5% increase in mucus hydrogen ion (H+) retardation capacity, 1.9-fold increase in viscosity, and a 60% increase in the gel hydrophobicity. The mucus elaborated in the presence of sucralfate exhibited 14% lower protein content and 62% higher content of carbohydrate than that of control, and contained more neutral lipids. Furthermore, the gastric mucus of the sucralfate group showed a marked increase in mucus glycoprotein polymeric form. The data obtained with gastric mucosal culture demonstrated that sucralfate elicited a significant increase in mucin synthesis, which was reflected in the enhanced metabolism of mucosal phosphoinositides. In contrast, ethanol, which exhibited detrimental effects on mucin synthesis, also caused alterations in the phosphoinositide signal pathway. The changes in mucin and phosphoinositide distribution patterns evoked by ethanol were prevented by sucralfate. Our results suggest that the mucosal strengthening action of sucralfate occurs through the stimulation of the metabolism of phosphoinositide-derived messenger molecules.

Breakdown of gastric mucus in presence of Helicobacter pylori

The potential of Helicobacter pylori to degrade gastric mucus was examined. Colonies of H pylori cultured from antral mucosal biopsy specimens of patients with non-autoimmune gastritis were washed with sterile saline, passed through a sterilisation filter, and the filtrate examined for urease, protease, and mucolytic activity. The filtrate failed to hydrolyse bovine serum albumin, or to degrade stable mucus glycoprotein structures of high particle weight that had been separated from human gastric mucus on Sepharose 2B. The high particle weight mucus glycoprotein was, however, extensively degraded when incubated with H pylori filtrate (which possessed urease activity) in the presence of 2 M urea, to release fragments of Mr approximately 2 X 10(6). The high particle weight mucus glycoprotein was also broken down to a comparable extent when incubated with Jack bean urease in the presence of 2 M urea, or 1 M ammonium carbonate, or 40 mM carbonate-bicarbonate buffer (pH 8.7), but not when treated with 4 M urea alone, or Jack bean urease alone. These results indicate that the loss of high particle weight mucus glycoprotein in gastric mucus from patients with gastritis and gastric ulcers is unlikely to be due to the mucolytic action of an extra-cellular protease produced by H pylori, but it may result from the destabilising effects of a carbonate-bicarbonate buffer, generated at the mucosal surface when H pylori urease hydrolyses transuded plasma urea.

Hypothesis: Helicobacter pylori, urease, mucus, and gastric ulcer

Ammonia, released in the gastric mucosa by the action of Helicobacter pylori urease on transuded plasma urea, curtails the biosynthesis of mucus and/or causes the mucus to be disassembled at the mucosal surface. These changes facilitate colonisation by H pylori and may promote gastric ulcer formation.

Experimental pathogenesis: drugs and chemical lesions in the gastric mucosa

The goals of this article are to review the similarities and differences in the pathogenesis of acute gastric mucosal injury induced by alcohol, exemplified mostly by ethanol, and aspirin, as a representative of nonsteroidal anti-inflammatory drugs, and to deduce implications from pathogenetic studies for a better understanding of the concept of gastric cytoprotection. The main similarity between the hemorrhagic erosions caused by ethanol and aspirin is their localization in the acid-producing glandular stomach, the rate-limiting step in their pathogenesis being the extent of microvascular injury in the gastric mucosa. The major differences include the fast healing and low probability of transition into chronic gastritis after a single exposure to aspirin. On the other hand, perforated ulcer may develop, especially in the elderly, after chronic aspirin but not ethanol consumption. The main implications of pathogenetic investigations include the relative nature of gastroprotection: that is, initially, the superficial epithelial layer is not protected against concentrated luminal solutions, but it is rapidly replaced by migrating, adjacent, surviving cells if blood flow is maintained and the basement membrane is relatively intact. Vascular changes thus seem to be the rate-limiting step both in the pathogenesis and prevention of chemically induced acute gastric mucosal injury. The ultimate biochemical mechanisms of gastroprotection seem to include an effect on structural and enzymic proteins, and vascular mediators which influence vascular permeability and, indirectly, the extent of tissue injury.

Mechanisms of nonsteroidal anti-inflammatory drug-induced gastric damage

The effects of nonsteroidal anti-inflammatory drugs (NSAIDs) on the gastric mucosa are well documented. The complex mechanisms of gastric damage, however, are not fully understood. This review examines current knowledge about the normal function of the gastric mucosal barrier; the role of prostaglandins in cytoprotection and repair; the mechanisms by which aspirin and other weak organic acids are absorbed by the stomach; and the subsequent cascade of events--including ion trapping and back diffusion of hydrogen ions--that leads to gastric erosion and bleeding. A hypothesis describing NSAIDs' dual insult on the stomach is advanced.

Peptic erosion of gastric mucus in the rat

1. The effect of pepsin on the loss of mucus glycoprotein from the gastric epithelial mucus layer was studied in the rat. 2. Pepsin was instilled into the gastric lumen, and luminal contents were subsequently assayed. 3. Glycoprotein loss increased with luminal pepsin, up to a concentration of 1 mg pepsin/ml. 4. Luminal glycoprotein had a molecular size distribution intermediate between subunit, and native mucus glycoprotein of the epithelial mucus layer. 5. Incubation of gastric epithelial scrapings with pepsin demonstrated that insoluble, native mucus glycoprotein was rapidly degraded to soluble glycoprotein of similar molecular size distribution to that found in vivo in the lumen.