Multiple antiviral activities in extracts of seaweeds from British Columbia

Sixteen extracts of British Columbian seaweeds, previously shown to have antiviral activity, were investigated in more detail. In all cases except one (Analipus japonicus) the antiviral activity was predominantly virucidal (direct virus-killing effect). The A. japonicus extract showed replication-inhibition as well as virucidal activity. All extracts, with the exception of A. japonicus again, required light for maximum activity, indicating the presence of antiviral photosensitizers. In some cases light was absolutely required, whereas in others light enhanced the antiviral activity, and furthermore different extracts showed a preference for either visible light or long-wave ultraviolet (UVA). These results taken together indicate the presence of different antiviral compounds with distinct modes of action, and argue strongly against the hypothesis that antiviral activities in seaweeds are due to common ingredients such as polysaccharides. This was further substantiated by the finding that in most cases the anti-viral activity could be adsorbed by polyvinyl-polypyrrolidone, which indicates the presence of phenolic compounds. In view of the presence of many different antiviral compounds among these extracts, we believe BC seaweeds may provide a source of potentially useful antivirals, and are worthy of further study.