Inhibition of Helicobacter pylori binding to gastrointestinal epithelial cells by sialic acid-containing oligosaccharides

Abstract

Helicobacterpylori, the ulcer pathogen residing in the human stomach, binds to epithelial cells of the gastric antrum. We have examined binding of 13 bacterial isolates to epithelial cell lines by use of a sensitive microtiter plate method in which measurement of bacterial urease activity provides the means for quantitation of bound organisms. Several established human gastrointestinal carcinoma cell lines grown as monolayers were compared for suitability in these assays, and the duodenum-derived cell line HuTu-80 was selected for testing bacterial binding inhibitors. When bacteria are pretreated with oligosaccharides, glycoproteins, and glycolipids, a complex picture of bacterial-epithelial adherence specificities emerges. Among the monovalent inhibitors tested, 3'-sialyllactose (NeuAc alpha2-3Gal beta1-4Glc; 3'SL) was the most active oligosaccharide, inhibiting adherence for recent clinical isolates of H. pylori with a millimolar 50% inhibitory concentration (IC50). Its alpha2-6 isomer (6'SL) was less active. Most of the recent clinical isolates examined were inhibited by sialyllactose, whereas long-passaged isolates were insensitive. Among the long-passaged bacterial strains whose binding was not inhibited by 3'SL was the strain ATCC 43504, also known as NCTC 11637 and CCUG 17874, in which the proposed sialyllactose adhesin was recently reported to lack surface expression (P. G. O'Toole, L. Janzon, P. Doig, J. Huang, M. Kostrzynska, and T. H. Trust, J. Bacteriol. 177:6049-6057, 1995). Pretreatment of the epithelial monolayer with neuraminidase reduced the extent of binding by those bacteria that are sensitive to inhibition by 3'SL. Other potent inhibitors of bacterial binding are the glycoproteins alpha1-acid glycoprotein, fetuin, porcine gastric and bovine submaxillary mucins, and the glycolipid sulfatide, all of which present multivalent sialylated and/or sulfated galactosyl residues under the conditions of the binding assay. Consistent with this pattern, a multivalent neoglycoconjugate containing 20 mol of 3'SL per mol of human serum albumin inhibited bacterial binding with micromolar IC50. The H. pylori isolate most sensitive to inhibition by 3'SL was least sensitive to inhibition by sulfatide, gastric mucin, and other sulfated oligosaccharides. Bacteria that have been allowed to bind epithelial cells are also effectively detached by 3'SL. These results describe a heterogeneous adherence repertoire for these bacteria, but they also confirm the critical role of the 3'SL structure on human gastric epithelial cells as an adherence ligand for recent isolates of H. pylori.