Comparative Analysis on the Cytotoxicity of Naegleria fowleri and N. gruberi to Macrophages by the Addition of Saccharides

To elucidate the invasion mechanism of pathogenic Naegleria fowleri, especially a receptor-ligand recognition, we investigated the in vitro cytotoxicity of pathogenic N. fowleri and nonpathogenic N. gruberi to murine macrophages, RAW 264.7, by adding four kinds of saccharides, ${\alpha}$-fucose, ${\beta}$-galactose, ${\alpha}$-D-mannopyranoside (${\alpha}$-mannose) and xylose. There was not enough of a difference in the cytotoxicity of N. fowleri treated with 10 mM of each saccharide. In particular, the cytotoxicity of N. fowleri was highly inhibited by 100 mM ${\alpha}$-mannose, which was 62.3% inhibition calculated by the analysis of lactate dehydrogenase (LDH) release assay. Although murine macrophages were not significantly destroyed by nonpathogenic N. gruberi under hematoxylin staining, the cytotoxicity of N. gruberi was inhibited from 31.5% to 14.5% (P<0.01) by 100 mM ${\alpha}$-mannose treatment. The binding of N. fowleri to macrophages was inhibited from 33% to 50% by 100 mM ${\alpha}$-mannose. Furthermore, as results of the adhesion assays which were performed to determine whether binding of Naegleria is mediated by saccharides-binding protein, the binding ability of N. fowleri as well as N. gruberi was inhibited by 100 mM ${\alpha}$-mannose.