Examination of the molecular mechanism of the mutual inhibitory effect of each cytotoxicity caused by the combined extraction of Coptidis Rhizoma and Rhei Rhizoma: An example of providing evidence for ‘herbal pair’ theory

Abstract

Aim: Kampo medicines are effective depending on the combination of crude drugs. In addition, the basis is a combination of two crude drugs, which is defined as a 'herbal pair'. However, there are very few studies from this point of view. We found that Rhei Rhizoma (RR) may interact with Coptidis Rhizoma (CR). Methods: Component profiles were analyzed by three-dimensional high-performance liquid chromatography (3D-HPLC). Cell viability in N18TG-2 cells was determined by morphology observation and a '3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, yellow tetrazole (MTT)' assay. Results: When RR and CR were extracted together, the color of the extract was lighter than the colors of the individual extracts. In addition, precipitation occurred by simply combining the extracts of both in vitro. When each component profile was analyzed by 3D-HPLC, at least the amount of berberine, which is contained in a large amount in CR, was strongly decreased in combined extracts with RR. Although CR and RR each have a cytotoxic effect, when both were extracted together, their cytotoxicity almost disappeared. However, cytotoxicity remained in the supernatant when both extracts were combined in vitro, and also in the suspension of the resulting precipitate. Conclusion: From these results, when CR and RR are extracted together, their cytotoxicity is suppressed by some unknown mechanism. Whether this is due to the synthesis of new compounds by co-extraction or the detoxification of toxic components by interaction needs further investigation. This result suggests the importance of 'herbal pair' research.