Anti-herpes simplex virus activity of polysaccharides from Eucheuma gelatinae

Acyclovir is a commonly-used drug for treating herpes simplex virus (HSV) infections, but with its wide clinical application, more and more resistant strains have been found. Therefore, seeking a drug that can act against acyclovir-resistant virus has become an important goal of drug screening and development. In this study, plaque reduction assay, real-time PCR, Western blot, and immunofluorescence technique were used to investigate the antiviral effect of Eucheuma gelatinae polysaccharide (EGP) on HSV and to preliminarily clarify the in vitro anti-HSV mechanism of EGP. EGP was found to significantly inhibit HSV infection in vitro and displayed a good inhibitory effect on acyclovir-resistant strains. More detailed experiments have shown that EGP prevented early HSV-1 infection through directly inactivating HSV-1 particles and impairing virus attachment, but without effect on viral penetration. EGP also inhibited the RNA synthesis of HSV-1 early gene and late gene as well as viral DNA replication; no effect on immediate-early gene synthesis was observed. Besides, through immunofluorescence and western blot, we found that EGP significantly affected the protein synthesis of HSV-1. Taken together, these results demonstrate that EGP exerts its anti-HSV activity mainly through impeding early HSV-1 infection and inhibiting viral RNA and DNA syntheses. The weak cytotoxicity, strong viral inactivation as well as attachment inhibition activity enable EGP to be a virucide candidate for HSV therapy, especially for drug-resistant strains.