Preparation and anti-influenza A virus activity of κ-carrageenan oligosaccharide and its sulphated derivatives

Carrageenans, the sulphated galactans derived from red algae, are attracting increasing interest in developing potential anti-viral drugs. In this study, low molecular weight κ-carrageenan oligosaccharides (KCO) and their sulphated derivatives (KCO-S) were prepared, and their anti-influenza A virus (IAV) properties were investigated. The results indicated that KCO and KCO-S could effectively inhibit IAV multiplication in MDCK cells in a dose-dependent manner. Furthermore, a structure–activity relationship study showed that the degree of sulphation and molecular weight were the main factors that influenced the anti-IAV activity of κ-carrageenan oligosaccharide. The most active κ-carrageenan oligosaccharide had a sulphate content of 0.8–1.0 mole/mole of disaccharide and a molecular weight of 1–3 kDa. In addition, KCO and KCO-S could significantly improve survival and decrease pulmonary viral titres in IAV-infected mice. Moreover, the antiviral effect of KCO and KCO-S does not seem to be dependent on the interferon system. In conclusion, carrageenan oligosaccharide and its sulphated derivative have good inhibitory actions on IAV replication in vitro and in vivo.