Serine Protease Inhibitory Activity of Kampo Medicines: One of the Mechanisms Against Cold Syndrome
Yukiko Matsuo, Reina Akaiwa, Miku Yanagioka, Mishizu Kikuchi, Yuuna Kawahara, Takuma Yoshida, Hidemasa Nakaminami, Niro Inaba, Yoshihiro MimakiABSTRACT
Aim
Serine proteases play a key role in coronavirus viral entry into host cells and in viral replication. To explore one of the mechanisms underlying the effectiveness of Kampo medicines against cold syndrome, we focused on the serine protease‐mediated cell entry process of coronaviruses.
Methods
We evaluated 50 clinically approved Kampo extract products for trypsin inhibitory activity as a preliminary screening of serine protease inhibition. Among them, four Kampo extracts were selected for evaluation of TMPRSS2 inhibitory activity. In vivo enzyme inhibitory examination was demonstrated using serum samples from mice orally administered Kampo extract products. Analyses of trypsin inhibitory activity of the individual crude drug component extracts of Kampo were assessed. Finally, antiviral activity of the Kampo extract products was evaluated by a plaque assay.
Results
In the preliminary screening, 11 Kampo extract products inhibited trypsin activity. Jiinkokato, keishikakakkonto, keishikakobokukyoninto, and ryokankyomishingeninto inhibited over 70% of trypsin activity and showed potent TMPRSS2 inhibitory activity (IC 50 0.25–2.88 mg/mL). The jiinkokato (1.0 g/kg) or ryokankyomishingeninto (0.1 and 1.0 g/kg) extract products inhibited more than 70% of serine protease activity in vivo. Asiasari Radix, Glycyrrhizae Radix, Pinelliae Tuber, and Schisandrae Fructus contribute to the trypsin inhibitory activity of ryokankyomishingeninto. The ryokankyomishingeninto extract product showed antiviral activity against SARS‐CoV‐2 entry in VeroE6/TMPRSS2 cells.
Conclusion
Inhibition of serine protease may be involved in the mechanism of Kampo medicines used for treating common cold symptoms. The findings suggest ryokankyomishingeninto has the potential to prevent virus‐cell fusion by inhibiting serine protease activity.