Prevention of Japanese encephalitis virus infections by low-degree-polymerisation sulfated saccharides from Gracilaria sp. and Monostroma nitidum

► Sulfated saccharides inhibit Japanese encephalitis virus (JEV) infection by blocking virus entry into cells. ► The direct binding of the low-DP sulfated saccharides with JEV was spotted by transmission electron microscopy. ► Low-DP sulfated saccharides can enhance survival rates of JEV-infected mice. ► Antiviral effects of sulfated saccharides correlate to the length of polysaccharide. Many researchers have utilised undigested sulfated polysaccharides as effective in vitro antiviral agents; however, their in vivo activity remains controversial. Here we report the utility of novel low-degree-polymerisation (low-DP) sulfated saccharides from two algae, Gracilaria sp. and Monostroma nitidum, in the prevention of Japanese encephalitis virus (JEV) infection both in vitro and in vivo. During in vitro studies performed by MTT or plaque assays, low-DP sulfated saccharides have slightly lower antiviral activities than their undigested polysaccharides (PS). However low-DP sulfated saccharides bind to the JEV envelope protein at least as strongly as PS. In addition, the low-DP sulfated saccharides have a distinctly higher positive effect on survivability in JEV-infected C3H/HeN mice in comparison to PS. The in vivo antiviral activity seems to be connected with better absorption of low-DP sulfated saccharides than undigested PS. Our results point out that the low-DP sulfated saccharides are promising candidates for further development as antiviral agents.