Preparation and potential in vivo anti‐influenza virus activity of low molecular‐weight κ‐carrageenans and their derivatives

Degradation of native κ‐carrageenan was performed using acid hydrolysis aided with microwave heating. Combined with nonofiltration membrane (cut‐off molecular weight 250 Da) separation, 1. 400 Da ‐ 50 kDa low‐molecular‐weight (LMW) κ‐carrageenans were obtained. Narrow molecular weight distribution of LMW κ‐carrageenans could be prepared under pH 2.18 during the microwave power range investigated. The in vivo anti‐influenza virus (IV) activity of three kinds of LMW κ‐carrageenans (3, 5, and 10 kDa), their acetylated derivatives (acetylation degree of 1.5), as well as an acetylated and sulfated derivative of 3 kDa carrageenan (acetylation degree of 1.0 and sulfation degree of 2.4), were investigated using FM1‐induced pulmonary oedema model. These LMW κ‐carrageenans showed significant inhibition against FM1‐induced pulmonary oedema as compared with the virus control, although their activities were inferior to that of positive control, Rabivirin. Introduction of acetyl groups greatly increased their anti‐IV activity. The acetylated 3‐kDa κ‐carrageenan exhibited comparative activity with Rabivirin at both doses of 6 and 30 2. mg/kg·d, and the acetylated and sulfated derivative of 3 kDa carrageenan displayed higher activity than Rabivirin at the dose of 30 mg/kg·d. These results disclosed that 3 kDa κ‐carrageenan with proper acetylation degree and sulfation degree was a potential candidate against influenza virus.