Structural characterization and antiviral activity of two fucoidans from the brown algae Sargassum henslowianum

Purified fucoidans SHAP-1 and SHAP-2 with apparent molecular weights of 6.55 × 10⁵ and 5.89 × 10⁵, respectively, were isolated from Sargassum henslowianum by ion-exchange and gel-filtration column chromatography. They are both composed of fucose and galactose at a ratio of around 3:1 and 31.9% sulfate. The backbone of two fucoidans consists of α-(1→3)-linked L-Fucp residues which are mainly sulfated on the C-2 and C-4 positions. Side chains composed of terminally linked α-L-Fucp and α-D-Galp residues, and (1→2)-, (1→6)-, and (1→2,6)-linked β-D-Galp residues attach mainly at O-4 position of backbone residues. Antiviral test showed that the IC₅₀ values of SHAP-1 and SHAP-2 against HSV-1 were estimated to be 0.89 and 0.82 μg/mL by plaque reduction assay, respectively, whereas both as low as 0.48 μg/mL against HSV-2. The antiviral mechanism of the fucoidans might be at least through blocking HSV-2 virion adsorption to host cells. These results suggest that the fucoidans have potential clinical applications.