Inhibition of adhesion of Plasmodium falciparum-infected erythrocytes by structurally defined hyaluronic acid dodecasaccharides

Abstract

We recently reported that Plasmodium falciparum-infected erythrocytes (IRBCs) can adhere to hyaluronic acid (HA), which appears to be a receptor, in addition to chondroitin sulfate A (CSA), for parasite sequestration in the placenta. Further investigations of the nature and specificity of this interaction indicate that HA oligosaccharide fragments competitively inhibit parasite adhesion to immobilized purified HA in a size-dependent manner, with dodecasaccharides being the minimum size for maximum inhibition. Rigorously purified and structurally defined HA dodecasaccharides, free of contamination by CSA or other glycosaminoglycans, effectively inhibited IRBC adhesion to HA but not CSA, providing compelling evidence of a specific interaction between IRBCs and HA.

FIG. 1

HPLC profiles of HA dodecasaccharides A12 (A) and B12 (B).

FIG. 2

Inhibition of adhesion of CS2 IRBCs by HA oligosaccharides. (A) Dodecasaccharides A12-b (from testicular hyaluronidase digests) and B12-b (from Streptomyces hyaluronate lyase digests) effectively inhibited adhesion to immobilized HA-BVH or HA-HUC, but not CSA, at 200 μg/ml. The error bars indicate standard deviation. (B) Adhesion to HA was effectively inhibited by increasing concentrations of HA polysaccharide (polysacc.) or dodecasaccharides A12-b and B12-b but not by tetrasaccharide A4 (P < 0.01). Differences in inhibitory activity among polysaccharide, A12-b, and B12-b were of borderline statistical significance.

FIG. 3

Negative-ion electrospray mass spectra of HPLC-purified dodecasaccharides A12-b (A) and B12-b (B). The acquired spectra showing multiply charged molecular species (A3 to A6, denoting three to six negative charges, respectively) are shown at the bottom of each panel, and transformed spectra showing the molecular mass are shown at the top of each panel.

FIG. 4

1D ¹H NMR spectra of A12-b (A) and B12-b (B). Anomeric and other structural reporter proton resonances are indicated by roman numerals corresponding to the position of the residue in the sequence as shown in the formulae.