Antiviral effect of red microalgal polysaccharides on Herpes simplex and Varicella zoster viruses

The cell-wall sulphated polysaccharide of the red microalga Porphyridium sp. has impressive antiviral activity against Herpes simplex viruses types 1 and 2 (HSV 1, 2) and Varicella zoster virus (VZV). Treatment of cells with 1 mug mL(-1) polysaccharide resulted in 50% inhibition of HSV-infection as measured by the plaque assay. Inhibition of the production of new virus particles was also shown when pre-infected cell cultures were treated with the polysaccharide. In addition, there was indirect evidence for a strong interaction between the polysaccharide and HSV and a weak interaction with the cell surface. Depending on the concentration, the polysaccharide completely inhibited or slowed down the development of the cytopathic effect in HSV or VZV preinfected cells, but did not show any cytotoxic effects on Vero cells even when a concentration as high as 250 mug mL(-1) was used. It seems therefore that the polysaccharide is able to inhibit viral infection by preventing adsorption of virus into the host cells and/or by inhibiting the production of new viral particles inside the host cells. Thus, this alga seems to be a good candidate for the development of an antiviral drug.