Preparation and Inhibitory Activity on Influenza Virus Neuraminidase of Low Molecular Weight Fucoidan from Laminaria japonica

Low molecular weight fucoidan was prepared by free radical oxygen degradation and ultrafiltration technology from high molecular weight fucoidan extracted from Laminaria japonica.The molecular weight and chemical composition of low molecular weight fucoidan fractions obtained by different degradation conditions were compared and the optimum degradation condition to yield highly sulfated low molecular weight fucoidan was 4.5% H2O2 and 0.0267mol/L Cu2+ from 4.5 g crude fucoidan.Two highly sulfated fractions Fa3(Mw 7.68 kDa)and Fb3(Mw 3.89 kDa)were obtained with the sulfated ester content of 30.32% and 32.48% respectively.Low molecular weight fraction Fa3 was mainly made up of fucose(64.25%) and galactose(30.74%),while the fucose content of fraction Fb3 decreased to 46.94%,though it had a higher content of sulfated ester.When the concentration of H2O2 increased to 9%,the molecular weight and content of sulfated ester and fucose of low molecular weight fucoidan fractions decreased significantly.The antiviral effect on influenza virus of low molecular weight fucoidan was assessed by fluorometric assay of influenza virus neuraminidase in vitro.Low molecular weight fucoidan exhibited significantly inhibitory effect on the activity of neuraminidase in vitro,especially fraction Fa3 with Mw 7.68 kDa had better inhibitory activity than Fb3 and Fc3.The results revealed that molecular weight played a more important role on determining the inhibitory activity of low molecular weight fucoidan on neuraminidase in vitro than sulfated ester content.The homogeneous neutral sugar composition may also contribute to the inhibitory activity on influenza virus neuraminidase of Fa3.