Chemical characterization and evaluation of antiviral activity of two fucoidans extracted from Mediterranean brown seaweeds, <i>Padina pavonica</i> and <i>Dictyopteris membranacea</i>

Brown seaweeds are known for their bioactive compounds, particularly sulfated polysaccharides such as fucoidans, which have demonstrated antiviral properties. However, limited studies have focused on the antiviral potential of fucoidans extracted from Mediterranean brown seaweeds. In this study, two brown seaweeds Padina pavonica and Dictyopteris membranacea (Fuc-Pad and Fuc-Dic, respectively) were collected from monastir coasts, Tunisia, and a specific extraction protocol was employed to obtain fucoidans. The main objective of this study was to evaluate their antiviral activity against Herpes simplex virus type 2 (HSV-2) and coxsackievirus B3 (CVB-3). Fuc-Pad and Fuc-Dic exhibited potent antiviral activity with high selectivity indexes (>158 780 and 3125 for Fuc-Pad and 6101 and 84 for Fuc-Dic against HSV-2 and CVB-3, respectively). On the other hand, the two brown algae demonstrated different mechanisms of antiviral action according to virus type since they inhibited HSV-2 during the adsorption and penetration stages likely through interaction with cellular receptors that block viral binding while directly inhibiting CVB-3 by blocking specific viral ligands, preventing their attachment to host cell receptors. This antiviral activity seems to be associated with the high degree of sulfating of the fucoidans. These results may suggest the possibility of developing new antiviral drugs.