INHIBITION OF HELICOBACTER-PYLORI BINDING TO GASTROINTESTINAL EPITHELIAL-CELLS BY SIALIC ACID-CONTAINING OLIGOSACCHARIDES

Helicobacter pylori, the ulcer pathogen residing in the human stomach, binds to epithelial cells of the gastric antrum. We have examined bin ding of 13 bacterial isolates to epithelial cell lines by use of a sen sitive microtiter plate method in which measurement of bacterial ureas e activity provides the means for quantitation of bound organisms, Sev eral established human gastrointestinal carcinoma cell lines grown as monolayers were compared for suitability in these assays, and the duod enum-derived cell line HuTu-80 was selected for testing bacterial bind ing inhibitors. When bacteria are pretreated with oligosaccharides, gl ycoproteins, and glycolipids, a complex picture of bacterial-epithelia l adherence specificities emerges. Among the monovalent inhibitors tes ted, 3'-sialyllactose (NeuAc alpha 2-3Gal beta 1-4Glc; 3'SL) was the m ost active oligosaccharide, inhibiting adherence for recent clinical i solates of H. pylori with a millimolar 50% inhibitory concentration (I C50). Its alpha 2-6 isomer (6'SL) was less active. Most of the recent clinical isolates examined were inhibited by sialyllactose, whereas lo ng-passaged isolates were insensitive. Among the long-passaged bacteri al 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 expressio n (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 epi thelial 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 alpha(1)-acid gl ycoprotein, fetuin, porcine gastric and bovine submaxillary mucins, an d the glycolipid sulfatide, all of which present multivalent sialylate d and/or sulfated galactosyl residues under the conditions of the bind ing assay, Consistent with this pattern, a multivalent neoglycoconjuga te containing 20 mol of 3'SL per mol of human serum albumin inhibited bacterial binding with micromolar IC50. The H. pylori isolate most sen sitive to inhibition by 3'SL was least sensitive to inhibition by sulf atide, gastric mucin, and other sulfated oligosaccharides. Bacteria th at have been allowed to bind epithelial cells are also effectively det ached by 3'SL. These results describe a heterogeneous adherence repert oire for these bacteria, but they also confirm the critical role of th e 3'SL structure on human gastric epithelial cells as an adherence lig and for recent isolates of H. pylori.