The interaction of alkaloids in Coptis chinensis Franch -Tetradium ruticarpum (A. Juss.) T.G. Hartley with hOCT1 and hOCT2.

ETHNOPHARMACOLOGICAL RELEVANCE: Zuojin Pill, a traditional poly-herbal drug, comprises Coptis chinensis Franch - Tetradium ruticarpum (A. Juss.) T.G. Hartley (6:1). The significant quantity of alkaloids found in the participating herbs is a key aspect of the Zuojin Pill. According to traditional Chinese medicine (TCM), these numerous alkaloidal compounds within Zuojin Pill have various essential therapeutic effects. AIM OF THE STUDY: The alkaloids in Tetradium are mainly indole alkaloids, while the alkaloids in Coptis are mostly isoquinoline alkaloids with low bioavailability. Alkaloids and their metabolites are nitrogen-containing compounds or weakly alkaline substances that can be partially ionized under physiological pH conditions. Fortunately, organic cation transporters (OCTs) play a crucial role in the cellular uptake of weakly alkaline compounds. Therefore, we speculated that the alkaloidal compounds might interact with liver cation transporters hOCT1 and kidney cation transporters hOCT2 to alter cell drug disposal. In order to clarify our hypothesis, a series of alkaloids-OCTs interaction experiments were conducted. MATERIALS AND METHODS: HEK293 cells stably expressing hOCT1 and hOCT2 were modeled and evaluated. Afterward, high-content screening (HCS) was conducted to analyze whether the main alkaloids and their metabolites of Coptis - Tetradium were inhibitors of hOCT1 and hOCT2 transporters. Meanwhile, LC-MS/MS was used to investigate whether the alkaloidal compounds were substrates of hOCT1 and hOCT2 transporters. Finally, drug interactions at the cellular level were assessed by LC-MS/MS after co-administration of berberine and rutacorine. RESULTS: Berberine, jateorhizine, coptisine, epiberberine, columbamine, demethyleneberberine, and berberrubine could significantly inhibit hOCT1 and hOCT2 activity. Isoquinoline alkaloids, including berberine, jateorhizine, coptisine, epiberberine, columbamine, and palmatine, were substrates of hOCT1 and hOCT2, but not the indole alkaloids evodiamine and rutaecarpine. Furthermore, evodiamine at a concentration of 20 µmol/L had a trivial effect on berberine accumulation in HEK293-hOCT2 cells. CONCLUSIONS: These results support the idea that alkaloidal compounds within Coptis and Tetradium have hOCT1 and hOCT2 inhibitory activity or be their substrates, and the increased oral bioavailability of berberine in vivo was closely related to the potential interactions of small molecules in Coptis- Tetradium. Overall, our study provides a framework for investigating the potential interactions of small molecules in Coptis- Tetradium.