Inhibition of Helicobacter pylori infection by bovine milk glycoconjugates in a BAlb/cA mouse model.

The attachment of Helicobacter pylori to the human gastric mucosa is a complex process involving several specific structures recognised by the cell surface receptors. Sialylated multivalent high mol. wt glycoproteins have been shown to inhibit H. pylori sialic acid-specific haemagglutination. This study explored whether sialylated glycoconjugates from bovine milk could inhibit an experimental H. pylori infection in a mouse model. BALB/cA mice (6-8 weeks old) were inoculated with a mouse-passaged H. pylori strain 317p. Four weeks after infection the mice were given lactoferrin (iron-free LF or 20% iron-saturated LF) or bovine milk fat globule membrane fractions (MFGM or defatted MFGM) orally (400 mg/kg body weight) once daily for 10 days and then killed to examine for bacterial colonisation and gastritis. Mice treated with iron-free LF, 20% iron-saturated LF, MFGM or defatted MFGM showed 30%, 10%, 20% or 20% healing rates, respectively, when compared with the H. pylori-infected control. Gastric colonisation by H. pylori was remarkably decreased in all mice treated with bovine milk glycoconjugates and the inflammation score was also significantly lower in treated mice than in infected control animals. The fact that there was no significant difference between iron-free LF and iron-saturated LF or MFGM and defatted MFGM suggested that iron is not crucial for inhibition of H. pylori by lactoferrin and that the lipid part of MFGM is not important for anti-H. pylori activity. In conclusion, bovine milk glycoconjugates showed potencies to inhibit H. pylori infection in this mouse model and, therefore, could be considered as candidates for non-antibiotic strategies against H. pylori infection in man.

Helicobacter pylori interactions with human gastric mucin studied with a resonant mirror biosensor.

Helicobacter pylori, a human pathogen colonizing the gastrointestinal tract, is first interacting with mucus glycoproteins to penetrate the gastric mucus layer and then attach to specific epithelial cell targets. An optical biosensor technique based on the resonant mirror was used to study H. pylori interactions with human gastric mucin. The mucin preparation was immobilized on the sensor surface to set up the experimental model, close to the in vivo situation. Both sialylated and sulphated oligosaccharides interfered with the H. pylori binding to the immobilized mucin by reducing or abolishing the binding of the bacteria. Furthermore, the displacement of the bacteria from immobilized mucin by highly sulphated glycosaminoglycans was observed.

Differentiation of Helicobacter pylori isolates based on lectin binding of cell extracts in an agglutination assay.

Plant and animal lectins with various carbohydrate specificities were used to type 35 Irish clinical isolates of Helicobacter pylori and the type strain NCTC 11637 in a microtiter plate assay. Initially, a panel of eight lectins with the indicated primary specificities were used: Anguilla anguilla (AAA), Lotus tetragonolobus (Lotus A), and Ulex europaeus I (UEA I), specific for alpha-L-fucose; Solanum tuberosum (STA) and Triticum vulgaris (WGA), specific for beta-N-acetylglucosamine; Glycine max (SBA), specific for beta-N-acetylgalactosamine; Erythrina cristagali (ECA), specific for beta-galactose and beta-N-acetylgalactosamine; and Lens culinaris (LCA), specific for alpha-mannose and alpha-glucose. Three of the lectins (SBA, STA, and LCA) were not useful in aiding in strain discrimination. An optimized panel of five lectins (AAA, ECA, Lotus A, UEA I, and WGA) grouped all 36 strains tested into eight lectin reaction patterns. For optimal typing, pretreatment by washing bacteria with a low-pH buffer to allow protein release, followed by proteolytic degradation to eliminate autoagglutination, was used. Lectin types of treated samples were stable and reproducible. No strain proved to be untypeable by this system. Electrophoretic and immunoblotting analyses of lipopolysaccharides (LPSs) indicated that the lectins interact primarily, but not solely, with the O side chain of H. pylori LPS.

Effect on cell surface hydrophobicity and susceptibility of Helicobacter pylori to medicinal plant extracts.

Effects on aqueous extracts of medicinal plants on ten Helicobacter pylori strains were studied by the salt aggregation test to determine the possibility to modulate their cell surface hydrophobicity and by an agar diffusion assay for detection of antimicrobial activity. It was established that aqueous extracts of bearberry and cowberry leaves enhance cell aggregation of all H. pylori strains tested by the salt aggregation test, and the extract of bearberry possessed a remarkable bacteriostatic activity. Pure tannic acid showed a result similar to that of bearberry and cowberry extracts which contained a large amount of tannins. In contrast, extracts of wild camomile and pineapple-weed, which blocked aggregation of H. pylori, contained small amounts of tannins and did not reveal any antimicrobial activity. Tannic acid seems to be the component of bearberry and cowberry aqueous extracts with the highest activity to decrease cell surface hydrophobicity as well as in antibacterial activity against H. pylori.

Inhibition of Helicobacter pylori sialic acid-specific haemagglutination by human gastrointestinal mucins and milk glycoproteins.

Helicobacter pylori, a human gastric pathogen causing chronic gastritis and duodenal ulcer disease, has been found in large amounts in gastric mucous gel layer. Mucin preparations, separated from human gastric juices and isolated from different colon regions, were examined for their ability to inhibit haemagglutination of H. pylori with the emphasis on evaluating the role of sialic acid-dependent haemagglutinins of the bacteria in colonisation of the stomach. The mucins showed high inhibitory activity for H. pylori, which was significantly decreased after the removal of sialic acids from the mucins. The inhibitory potencies using high molecular mass mucin-like components from bovine milk were comparable with those obtained for gastric mucins, suggesting their possible role in the prevention of H. pylori infection.

Characterization of Helicobacter pylori interactions with sialylglycoconjugates using a resonant mirror biosensor.

A new optical biosensor technique based on the resonant mirror was used to characterize Helicobacter pylori strains according to their sialic acid binding, demonstrating the suitability of using intact bacteria in real-time measurements and classifying strains based on their binding abilities. Results obtained from both competition and displacement assays using different glycoconjugates confirmed that several, but not all, H.pylori strains express sialic acid-binding adhesin(s), specific for alpha-2,3-sialyllactose. The adhesin, removable from the bacterial surface by water extraction, is not related to other reported H.pylori cell surface proteins with binding ability to sialylated compounds such as sialylglycoceramides.

Biochemical aspects of H. pylori adhesion.

In analogy with Vibrio cholerae and other toxigenic enteropathogens such as Yersinia enterocolitica it seems most likely today that H. pylori by specific surface proteins binds to epithelial cell receptors (Table 1) allowing the pathogen to deliver urease, vacuolating toxin and other toxic metabolites to cause tissue damage and inflammation (1-3). H. pylori as well as animal gastric pathogens as H. mustelae and H. felis have developed an efficient flagellar apparatus allowing rapid and efficient penetration of the gastric mucus layer (3). Most interestingly, flagellae seems to be synthesized in the late stage of growth before the switch of spiral-shaped organisms to coccoidal forms in a liquid medium.

Sulfatides inhibit binding of Helicobacter pylori to the gastric cancer Kato III cell line.

Helicobacter pylori adhere to Kato III and Hela S3 cells in monolayer cultures. To explore whether cell surface glycoconjugates on these two cell lines mediate binding of H. pylori, various carbohydrates, glycoproteins, and glycolipids were tested to inhibit H.pylori cell adhesion. The adhesion was measured (i) with a urease-based assay and (ii) by cells stained with fluorescein. Sodium periodate and sialidase treatment (but not alpha- or beta-galactosidase, heparitinase,lysozyme, or trypsin) inhibited H. pylori binding to both cell lines. Sulfatides and sulfated glycoconjugates (50 microg/ml) but not heparin or a number of simple carbohydrates inhibited binding (1 mg/ml). The two H.pylori strains studied (CCUG 17874 and strain 25) showed high binding of soluble 125I-labeled heparin and other sulfated carbohydrate compounds.

Lack of evidence for sialidase activity in Helicobacter pylori.

The role of sialic acid for the adhesion of Helicobacter pylori to gastric mucosa cells and/or to the mucin layer is still under debate. Several but not all H. pylori strains express a sialic acid-binding adhesin, specific for terminal alpha-2,3-sialic acid residues. Recently, the production of sialidase by H. pylori was reported [Dwarakanath, A.D. et al. (1995) FEMS Immunol. Med. Microbiol. 12,213 216]. We analysed several strains isolated from gastric biopsies cultivated both in liquid media and on agar plates for sialidase. Activity of this enzyme was first assayed using the fluorigenic substrate 4-methylumbelliferyl-alpha-D-N-acetylneuraminic acid. Since the fluorimetric assay can give false-positive results caused by non-specific interactions with umbelliferyl-tagged substances, we used also the more sensitive and specific assay with sialyl-[3H]lactitol as a substrate. No evidence for sialidase activity of H. pylori strains, cultivated under both inducible and non-inducible conditions, was obtained.

Adhesion of Helicobacter pylori strains to alpha-2,3-linked sialic acids.

Helicobacter pylori is a human pathogen associated with gastritis and peptic ulcer. Adhesion properties of H. pylori to various structures have been described in the literature, including evidence for sialic acid-binding. To study the specificity and frequency of sialic acid-binding, fourteen H. pylori strains were investigated using haemagglutination with derivatized erythrocytes carrying sialic acids only on defined glycans and using haemagglutination inhibition assays. From these studies H. pylori strains can be grouped into sialic acid-dependent and sialic acid-independent classes. The sialic acid-dependent strains require alpha-2,3-linked sialic acid for haemagglutination. The potential roles of sialic acid-dependent adhesions for H. pylori-related infections are discussed.

A particle agglutination assay for rapid identification of heparin binding to coagulase-negative staphylococci.

The heparin-binding properties of six different species of coagulase-negative staphylococci were examined by a particle agglutination assay. Heparin (mol. wt 4000-6000), mildly treated with sodium periodate, was covalently coupled to amino-modified latex beads (0.72 micron diameter). The particle agglutination assay was validated by comparing results with the adhesion (percentage binding of adherent cells) of coagulase-negative staphylococcal strains to heparinised microtitration plates. Of 38 different coagulase-negative staphylococcal strains tested, 30 showed agglutination reactivity with heparin-coated latex beads. Strains of different coagulase-negative staphylococcal species agglutinated heparin-coated latex beads to various extents (e.g., cells of Staphylococcus haemolyticus strains reacted more strongly than cells of S. epidermidis strains). The agglutination reaction was significantly inhibited by fucoidan, suramin, lambda-carrageenan and other sulphated compounds, but not by non-sulphated carbohydrate polymers such as hyaluronic acid. Agglutination of staphylococcal cells with heparin-coated latex beads was completely blocked by a cell-surface extract. These results suggest that structures responsible for heparin binding are exposed on the cell surface.

Biochemical aspects of Helicobacter pylori colonization of the human gastric mucosa.

Unlike Helicobacter felis and other Helicobacter species of animal origin, Helicobacter pylori colonizes the lower gastric mucin layer of the stomach and adheres to human gastric epithelial cells. It is still an open question if H. pylori can interact with specific glycoconjugates in the gastric mucin layer. It is possible that colonization of the oral cavity is a first step of a complex infectious process. Most likely resting or slow growing cells of H. pylori interact with Lewis blood group substances in the gastric mucin layer and on the epithelium. This initial colonization is probably followed by binding to specific cell surface glycoconjugates (glycoproteins and glycolipids such as GM3) and specific sialylated or highly sulphated molecules such as cell surface sulphatides and heparan sulphate. H. pylori may also bind to specific phospholipid molecules such as phosphatidylethanolamine on the gastric cells. The adhesion process of certain strains can stimulate 'close' cell adhesion including pedestal formation similar to the phenomenon typical for a special class of enterovirulent Escherichia coli called attaching effacing E. coli. After gastric cell destruction by ammonia and H. pylori toxins (such as the vacuolating toxin) H. pylori may colonize the extracellular matrix (ECM). This phenomenon seems to include binding of cell surface sialic acid specific haemagglutinin to one ECM component, i.e. laminin. It is also likely that H. pylori may use similar events to penetrate intercellular junctions of gastric epithelial cells. These adhesion-penetration phenomena also involve coating of the microbe with host proteins to escape the host immune system and initiate a chronic lifelong infection process.

Inhibition of heparan sulphate and other glycosaminoglycans binding to Helicobacter pylori by various polysulphated carbohydrates.

Heparan sulphate binding to Helicobacter pylori at pH 4 to 5 was inhibited with various sulphated polysaccharides (heparin and chondroitin sulphates, fucoidan, carrageenans and some others), but not by carboxylated or nonsulphated compounds. Heparin binding proteins are exposed on the cell surface.