Inhibition of the adhesion of Entamoeba histolytica trophozoites to human erythrocytes by carbohydrates.

We have analyzed the effect of 14 carbohydrates (seven monosaccharides, four disaccharides and three aminosugars) on the adhesion of Entamoeba histolytica HK9 trophozoites to human red blood cells (RBC). Amebal adhesion was significantly inhibited by five of these carbohydrates with the following order of potency: lactose (Lac) greater than N-acetylgalactosamine (GalNac) greater than melibiose (Mel) greater than galactose (Gal) greater than N-acetylglucosamine (GlcNAc). The mean inhibitory concentration of Lac was 2.66 mM. Adhesion increased by 20% in the presence of 5.5 mM glucose (Glc). Inhibition of the adhesion was lower in the absence rather than in the presence of Glc only with Gal-NAc, whereas it was similar with Lac, Mel, Gal, and GlcNAc in both cases. The initial rate of amebal adhesion decreased 27% by RBC fixation, but adhesion to fixed RBC was also inhibited by the same five carbohydrates. Inhibition was higher in mixtures containing Lac, GalNAc, and Mel, than with the same isolated carbohydrates; Lac + Gal-NAc was the most potent mixture. Inhibition decreased when Lac, GalNAc, and Mel were mixed either with Gal or GlcNAc. We conclude that E. histolytica adhesion depends on amebal metabolic energy generated from Glc and on several surface components of RBC, some of which are inactivated with glutaraldehyde whereas others are inhibited by sugars containing Gal, GlcNAc, or Gal-NAc residues.