Anti-influenza virus activity of crude extract of Ribes nigrum L

This experiment was designed to detect the antiviral activities of crude fruit extracts of wild Ribes nigrum L. (Kurokarin extract) against influenza virus types A and B. Kurokarin extract was prepared as follows: fruits of Ribes nigrum L. were heated at 50 degrees C in a heating tank, and then ground under anaerobic conditions. The extracts were centrifuged, and the supernatant fluid was filtered and sterilized by infrared rays. The crude extract was diluted with Eagle's minimum essential medium (MEM) and the solution was adjusted to a pH 7.2 with 0.1 N or 1 N NaOH. Proven anti-influenza virus effects of the extracts were shown. The concentration of extract required to inhibit the plaque formation of both IVA and IVB by 50% (IC(50)) was 3.2 microgram/mL. Both IVA and IVB were directly inactivated up to 99% by 10 microgram/mL of the extract at pH 2.8, and 95% to 98% by this dose at pH 7.2. The growth of IVA in cells treated with 10 and 100 microgram/mL of the extract for 6 h after infection was completely suppressed. Virus titres in culture fluids of the cells treated with 100 microgram/mL of Kurokarin extract for 1 h at 8 to 9 h after infection, were completely suppressed, indicating that the extract inhibited the virus release from the infected cells.