薬理と治療

Abstract

Background　Kuromoji（Lindera umbellata Thunb.）is a deciduous shrub with aroma and has long been used as a gastrointestinal herbal medicine. Previous studies have shown that a hot-water extract of stem branches of Kuromoji （Kuromoji extract）inhibits the adsorption and entry of influenza virus into target cells and suppresses infection. Human coronavirus OC43（OC43） is classified in the genus β-coronavirus, the same as SARS-CoV-2, and is spreading worldwide as a causative virus of the common cold. In this study, we evaluated the effect of Kuromoji extract on OC43 infection in vitro. Methods　Human rhabdomyosarcoma-derived RD cell line was used as the target of OC43 infection. The effect of addition of Kuromoji extract simultaneously with OC43 infection to RD culture system on the expression of nucleocapsid protein（N）was evaluated by quantitative RT-PCR and immunofluorescent staining. In addition, the infectious titer of the culture supernatant of RD after OC43 infection was evaluated by the quantification of cytopathic effect shown by viruses. Results　Kuromoji extract significantly decreased the mRNA expression of N, and decreased the amount of protein of N under microscopic observation in a dose-dependent manner. Kuromoji extract also significantly decreased the infectious titer of the culture supernatant 17 hours after infection in a dose-dependent manner. Conclusions　Kuromoji extract inhibited the expression of N after infection of OC43. Infectious titer of culture supernatant shown by the infection-established viruses was also significantly reduced by the treatment with Kuromoji extract. We believe that Kuromoji extract may be useful as a food material to prevent OC43 infection.