A. Slomiany

Campylobacter pyloridis degrades mucin and undermines gastric mucosal integrity

The role of Campylobacter pyloridis, a spiral bacteria associated with gastritis and peptic ulcers in weakening the mucus component of gastric mucosal barrier was investigated. The colonies of bacteria, cultured from antral mucosal biopsies of patients undergoing gastroscopy, were washed with saline, passed through sterilization filter and the filtrate was examined for protease and glycosylhydrolase activities. The obtained results revealed that the filtrate exhibited a strong proteolytic activity not only towards the typical protein substrates such as albumin but also towards gastric mucin. Optimum enzymatic activity for degradation of mucin was attained at pH 7.0 and the protease activity was found in a low m.w. (less than 50K) protein fraction. The filtrate showed little glycosylhydrolase activity and did not cause the hydrolysis of mucin carbohydrates. The data suggest that C pyloridis infection weakens the gastric mucosal defense by causing proteolytic degradation of mucin component of the protective mucus layer.

Salivary mucins in oral mucosal defense.

1. Salivary mucins are well recognized as an important factor in the preservation of the health of the oral cavity. These large glycoproteins play a major role in the formation of protective coatings covering tooth enamel and oral mucosa, which act as a dynamic functional barrier capable of modulating the untoward effects of oral environment, and are of significance to the processes occurring within the epithelial perimeter of mucosal defense. 2. Based on macromolecular characteristics, the mucins in saliva fall into high (> 1000 kDa) and low (200-300 kDa) molecular weight forms. The two forms, although differ with respect to bacterial clearance ability, display virtually identical carbohydrate chain make-up, ranging in size from 3 to 16 sugar units. 3. Of the two mucin forms, the low molecular weight form more efficient in bacterial aggregation, predominates in saliva and oral mucosal mucus coat of caries-resistant individuals, while the level of the high molecular weight form is higher in caries-susceptible subjects. The saliva of caries-resistant individuals also exhibits greater activity of protease capable of conversion of the high molecular weight mucin to the low molecular weight form. 4. The bacterial aggregating activity of salivary mucins appears to be associated with sulfomucins rather than sialomucins. While the removal of sialic acid causes only partial loss in mucin aggregating capacity, a complete loss in the bacterial aggregating activity occurs following mucin desulfation. 5. The mucins in oral mucosal mucus coat interact with the epithelial surfaces through specific membrane receptors. This interaction apparently involves the carbohydrate moiety of mucin molecule and may be rendered vulnerable to disruption by opportunistic bacteria colonizing the oral mucosa. 6. Salivary sulfo- and sialomucins actively participate in the modulation of the oral mucosal calcium channel activity through the inhibition of EGF-stimulated channel protein tyrosine phosphorylation. This function of salivary mucins is of paramount importance to mucosal calcium homeostasis.

Transforming Growth Factor Alpha and Epidermal Growth Factor in Protection and Healing of Gastric Mucosal Injury

Transforming growth factor alpha (TGF) and epidermal growth factor (EGF) present in the gastric mucosa are polypeptides with similar biologic activity. This study compares the activity of TGF and EGF in the protection against injury by 100% ethanol and stress and in healing of acute gastric ulcerations. TGF and EGF (12.5-100 micrograms/kg-h) infused subcutaneously 30 min before and during ethanol or stress decreased mucosal lesions dose-dependently. The ID50 for ethanol- and stress-induced lesions after TGF were 40 and 70 micrograms/kg-h and after EGF 60 and 100 micrograms/kg-h. TGF and EGF infused subcutaneously into intact rats inhibited gastric acid secretion but did not affect the gastric blood flow or mucosal generation of prostaglandin E2 (PGE2). Both TGF and EGF also significantly enhanced the healing of stress-induced lesions and the restoration of DNA synthesis. Ethanol and stress reduced blood flow in the oxyntic mucosa by 68% and 51%, respectively, and this effect was partially reversed by EGF and TGF. Pretreatment with indomethacin (5 mg/kg intraperitoneally), which reduced mucosal generation of PGE2 by 85%, decreased in part the protection by TGF and EGF against ethanol-induced damage and virtually abolished the protective action of these peptides against stress-induced injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of acute gastritis and epithelial apoptosis by Helicobacter pylori lipopolysaccharide.

BACKGROUND The preservation of gastric mucosal homeostasis is a complex biologic process, controlled by a dynamic equilibrium of cell loss by apoptosis with that of cellular proliferation, and its abrogation is a prominent feature of Helicobacter pylori-associated gastritis. In this report, we show that H. pylori lipopolysaccharide induces histologic lesions typical of acute gastritis and that these changes are reflected in the increased epithelial cell apoptosis. METHODS The experiments were conducted with groups of rats subjected to intragastric surface epithelial application of the lipopolysaccharide at 50 and 200 micrograms per animal. The histologic assessment of the mucosal tissue and quantification of apoptotic epithelial cells was performed 2 and 10 days after the lipopolysaccharide treatment. RESULTS Histologic examination showed that H. pylori lipopolysaccharide at both doses within 2 days induced infiltration of lamina propria with lymphocytes and plasma cells, edema, hyperemia, and hemorrhage extending from the lamina propria to the surface of mucosa, and the effect persisted beyond the 10 days. The in situ DNA fragmentation assay showed that lipopolysaccharide caused a marked increase in epithelial cell apoptosis, with the numerous apoptotic cells present not only in the superficial epithelium but also deeper in the glands. The mean apoptotic index in the mucosa was 59% when assessed 2 days after the administration of the 50-microgram lipopolysaccharide dose and 71.9% after the 200-microgram dose, whereas in the sections assessed 10 days after the lipopolysaccharide treatment the apoptotic index averaged 46% for a 50-microgram dose and 76.8% for a 200-microgram dose. Moreover, the apoptotic index showed positive correlation (r = 0.71) with the grade of the induced inflammatory changes. CONCLUSIONS Our findings demonstrate that H. pylori lipopolysaccharide can cause gastric mucosal responses typical of acute gastritis and identify the lipopolysaccharide as a virulence factor responsible for the induction of gastric epithelial cell apoptosis by H. pylori.

Effect of lipids and proteins on the viscosity of gastric mucus glycoprotein

The effect of associated lipids and covalently bound fatty acids, and the contribution of serum albumin and secretory IgA to the viscosity of dog gastric mucus glycoprotein was investigated. Using a cone/plate viscometer at shear rates between 1.15 - 230s -1, it was found that extraction of associated lipids from the glycoprotein lead to 80-85% decrease in the viscosity. Further loss (39%) in viscosity of the delipidated glycoprotein occurred following removal of covalently bound fatty acids. Reassociation of the delipidated glycoprotein with its neutral lipids increased the viscosity 3-fold, a 2.5-fold increase was obtained with glycolipids, and 2-fold with phospholipids. Preincubation of purified mucus glycoprotein with albumin or IgA resulted in the increase in viscosity. This increase in viscosity was proportional to albumin concentration up to 10%, and to IgA concentration up to 5%. The results show that interaction of lipids and proteins with mucus glycoprotein contributes significantly to the viscosity of gastric mucus.

Hydrogen ion diffusion in dog gastric mucus glycoprotein: Effect of associated lipids and covalently bound fatty acids

The effect of neutral lipids, glycolipids and phospholipids associated with dog gastric mucus glycoprotein, and that of covalently bound fatty acids on the ability of glycoprotein to retard the diffusion of hydrogen ion was investigated. Purified mucus glycoprotein in its native form, placed between equimolar (0.155M) solutions of HCl and NaCl in a specially designed two-compartment chamber, caused a 90% reduction in permeability to hydrogen ion when compared with a layer of NaCl. Extraction of associated lipids lead to a 68% increase in permeability of the glycoprotein to hydrogen ion, while removal of the covalently bound fatty acids increased further the diffusion rate by 6%. Reassociation of the delipidated glycoprotein with its neutral lipids reduced the permeability to hydrogen ion by 34%, an 11% reduction was obtained with glycolipids, and 23% with phospholipids. Since neutral lipids account for 47% of the glycoprotein lipids, glycolipids 41.1% and phospholipids 11.9%, the quantitative decrease in permeability of the delipidated glycoprotein following its reassociation with phospholipids is 2.7 times greater than that of neutral lipids and 7.3 times greater than that of glycolipids.

Evidence for Weakening of Gastric Mucus Integrity by Campylobacter pylori

The role of Campylobacter pylori in weakening the mucus component of the gastric mucosal barrier was investigated. The extracellular material elaborated by C. pylori, cultured from antral mucosal biopsy specimens of patients undergoing gastroscopy, caused a rapid degradation of mucus glycoprotein polymer to glycopeptides comparable in size to those produced by the action of pepsin. Viscosity measurements showed that incubation of C. pylori filtrate with gastric mucus led to a gradual loss in mucus viscosity, which at the end of 48 h decreased by 36%. The C. pylori filtrate also had a detrimental effect on the ability of mucus to retard the diffusion of H+. After 12 h of incubation the permeability of mucus to H+ increased by 10%, whereas a 32% increase in permeability was observed after 48 h. The results suggest that the degenerative changes produced in gastric mucus gel by C. pylori may be a contributing factor in the pathogenesis of gastritis and peptic ulcer.

Role of salivary epidermal growth factor in the maintenance of physicochemical characteristics of oral and gastric mucosal mucus coat.

The involvement of salivary epidermal growth factor (EGF) in the maintenance of oral and gastric mucosal mucus coat dimension and chemical characteristics was investigated using sialoadenectomized rats. Examination of the oral and gastric mucosal surface by phase contrast microscopy and Alcian blue uptake revealed that deprivation of salivary EGF caused a 31-36% reduction in mucus coat thickness and a 38-43% reduction in adherent mucin content. Chemical analyses indicated that the mucus coat of sialoadenectomized group exhibited a 21-28% increase in protein and a 67% decrease in covalently bound fatty acids, a 30% decrease in carbohydrates, and a 32-37% decrease in lipids. Sialoadenectomy also evoked changes in the chemical composition of mucus glycoprotein component of oral and gastric mucus coat reflected in the lower content of sulfate (25-26%), associated lipids (24-25%), and covalently bound fatty acids (67-75%). Intragastric supplementation of EGF had no effect on the physicochemical changes caused by sialoadenectomy in the oral mucosal mucus coat, while nearly complete restoration to normal characteristics occurred in the gastric mucosal mucus coat. The results suggest that salivary EGF is essential for the maintenance of mucus coat dimension and quality needed in the protection of alimentary tract epithelium.

Adsorption of human salivary mucins to hydroxyapatite

The interactions between low (MG2) and high (MG1) molecular-weight human submandibular-sublingual mucin and hydroxyapatite (OHAp) were compared using a quantitative assay. Data obtained appeared to empirically fit the Langmuir adsorption isotherm. Apparent affinity constants derived from this isotherm indicated that MG1 had a greater affinity for OHAp than did MG2. Inhibition studies revealed that salivary glycolipids inhibited the interaction of MG1 and OHAp without influencing MG2 adsorption. In contrast, MG2 adsorption to OHAp was markedly inhibited by cysteine-containing salivary phosphoprotein fractions. Collectively, the data indicate MG1 and MG2 differ in their interaction with OHAp.

Tooth surface-pellicle lipids and their role in the protection of dental enamel against lactic-acid diffusion in man

The lipid content and composition of the enamel pellicle from caries-resistant (CR) and caries-susceptible (CS) subjects and their effect on its ability to retard the diffusion of lactic acid were investigated. Lipids accounted for 22.2 per cent of the dry weight of CR pellicle and 23.7 per cent of CS pellicle. The content of glycolipids in both groups was similar but CR pellicle contained 42 per cent less neutral lipids and 31 per cent less phospholipids. CR lipids had a higher content of cholesterol, cholesterol esters and sphingomyelin, whereas CS pellicle was richer in free fatty acids and phosphatidylethanolamine. Retardation of lactic-acid diffusion by CR pellicle was 45 per cent higher than by CS. Removal of lipids caused 50 per cent reduction in retardation by CR pellicle and 35 per cent by CS pellicle.