Usefulness of algal polysaccharides for viral infectious diseases

Edible algae have been attracted as multifunctional foods since they were revealed to produce various bioactive metabolites. Among them, acidic polysaccharides such as fucan sulfates and rhamnnan sulfates were reported to exhibit antiviral, antitumor, antiulcer, anticoagulant, immunostimulatory effects and so on. So far, we succeeded in isolation of several types of antiviral polysaccharides from algae (fucan sulfates or fucoidans from Sargassum horneri, S. trichophllum and Undaria pinnatifida; rhamnan sulfates from Monostroma nitidum and Spirulina platensis; acidic polysaccharide containing glucuronic acid from Nostoc flagelliforme) [1–4]. Thus, we wish to report the results of evaluation of polysaccharides isolated from algae for their usefulness toward viral infectious diseases.

All isolated acidic polysaccharides exhibited inhibitory effects on enveloped viruses including herpes simplex virus, human cytomegalovirus, influenza A virus and human immunodeficiency virus type 1 in vitro. Their antiviral targets were found to be early stages such as virus adsorption to and penetration into host cells. Moreover, some polysaccharides inhibited replication stages of progeny virus after penetration. The structural factors regulating antiviral potency by algal polysaccharides were suggested to be molecular size, content of acidic groups and counter metal ion species of sulfate group. Therefore, three dimensional structure of the molecule might be important for its exhibition of antiviral effect. Rhamnan sulfate from S. platensis, fucoidan from U. pinnatifida and nostoflan from N. flagelliforme were also proved to be effective in animal tests. In addition, the polysaccharides from U. pinnatifida and N. flagelliforme were found to be useful for treatment of influenza type A in vivo, and they were indicated to stimulate signal transduction by immunosystem such as activation of NO production as well as production of neutral antibody against infected viruses. Combination of these polysaccharides with clinically used antiviral drugs such as acylclovir or oseltamivir showed synergistic effects on virus titres and production of antibody, indicating their usefulness for viral infectious diseases.

References: 1. Hayashi K, et al. (1996) AIDS Res. Human Retroviruses 12:1463. 2. Hoshino et al. (1998) Biol. Pharm. Bull. 21: 730.

3. Lee, J-B. et al. (2004) Chem. Pharm. Bull. 52: 1091. 4. Kanekiyo et al. (2005)J. Nat. Prod. 68: 1037.