Effects of Traditional Kampo Drugs and Their Constituent Crude Drugs on Influenza Virus Replication In Vitro: Suppression of Viral Protein Synthesis by Glycyrrhizae Radix

An influenza virus epidemic is an important issue in public hygiene, and continuous development on an effective drug is required. Kampo medicine is a traditional medicine that is used clinically for treatment of various diseases in Japan and other East Asian countries. We evaluated the effects of the Kampo drugs maoto, kakkonto, senkyuchachosan, jinkokato, and bakumondoto, which are prescribed for treatment of respiratory symptoms including symptoms caused by influenza, on influenza virus replication in cultured cells. Culture media of influenza virus-infected MDCK(+) cells were tested for hemagglutination and infectivity at 24 h after the addition of Kampo drugs at various concentrations, and four of the five Kampo drugs were found to inhibit virus release to the culture media. These drugs inactivated virus infectivity not by acting on virus particles but by acting on virus-infected cells. In addition, when six crude drugs (Atractylodis lanceae rhizome, Citri unshiu pericarpium, Cnidii rhizome, Glycyrrhizae radix, Rehmanniae radix, and Saposhnikoviae radix) that constitute the effective Kampo drugs were examined, the strongest activity was found for Glycyrrhizae radix (IC(50) = 0.27 mg/ml), which selectively suppressed viral protein synthesis. Since Glycyrrhizae radix is contained in many Kampo drugs, it may give anti-influenza virus activity to a broad range of Kampo drugs.