Antiviral activities of selected Hong Kong marine algae against herpes simplex viruses and other viruses and their possible antiviral mechanisms

Initially, aqueous extracts from eight species of Hong Kong marine algae were screened for their antiviral activity against herpes simplex viruses type 1 (HSV-1) and type 2 (HSV-2) by cytopathogenic effect (CPE) inhibition assay. Two kinds of the extracts were found to have potent anti-HSV activities. An anti-HSV polysaccharide fraction (Fr2a) was isolated from the brown alga Sargassum patens by bioactivity-guided fractionation. The analysis on the chemical and physical characterizations of Fr2a demonstrated that the active compound is a sulfated polysaccharide with molecular weight of 424 kDa.; Fr2a exhibited very low cellular toxicity to Vero cells with CC ₅₀ greater than 2,500 μg/ml by MTT assay and LDH assay. The EC ₅₀ values of Fr2a against HSV-2 standard strain (8702) and clinical strain were 1.3 and 1.65 μg/ml respectively by plaque reduction assay. The selective index of Fr2a against HSV-2 was estimated to be higher than 1923. Fr2a also significantly inhibited the replication of HSV-1 acyclovir resistant strain and sensitive strain in vitro in a dose-dependent manner with EC₅₀ of 1.5 to 5.3 μg/ml.; Treatment of host cells with Fr2a before infection showed no inhibitory effect against HSV-2 replication. Fr2a did not protect the cells from virus infection. But Fr2a exhibited an extracellular virucidal effect against HSV-2 in high concentration with EC₅₀ of 50 μg/ml. In low concentration, Fr2a could not inactivate the viral particles. The virus inactivation by Fr2a was temperature-dependent and time-independent.; The pretreatment of host cells with Fr2a for 24 h could not cause inhibition against HSV-1 in viral yield. Fr2a had weak virucidal activity against HSV-1 ACV sensitive strain at the concentration of 100 μg/ml. However, it did not show any virucidal activity against HSV-1 acyclovir resistant strain at this concentration. In viral replication cycle of HSV-1 assay, Fr2a was found not to decrease the virus yield of ACV resistant strain when it was added after 1 h adsorption. However, it could inhibit ACV sensitive strain replication to some extent. (Abstract shortened by UMI.)...