Potential detoxification effect of active ingredients in liquorice by upregulating efflux transporter

Background: As one of most widely used herbal medicine, liquorice exhibits diverse pharmacological activities, for instance, analgesic, antitussive, antiarrhythmic, anti-inflammatory, and immune regulation. Additionally, detoxification effects were observed in combination of liquorice with other herbal drugs. The mechanism of detoxification of liquorice has been extensively investigated through material basis and interference with CYPs though, investigations of its effect on transporters were very limited, according to the literature. Purpose: The objective of this study was attempt to investigate the effect of active ingredients existing in liquorice on the efflux transporters as to clarify the potential mechanism of detoxification of liquorice. Methods: Multiple analytical approaches have been explored, including flow cytometry, fluorescent detection, RT-PCR, Western blot to measure the function, activity as well as mRNA/protein expression of efflux transporters on LS-180 cell model after treatments with active compounds of liquorice. Additionally, Caco-2 cell model was utilized to further investigate the potential impact of those ingredients on efflux transporter. Results: The resulting data indicated that those active ingredients, including flavonoids (liquiritin, liquiritigenin, isoliquiritin, isoliquiritigenin and licochalcone A) and pentacyclic triterpene saponin (glycyrrhetinic acid) were able to upregulate the expression of efflux transporters, for example P-gp, BCRP and MRP2. The gene expressions were approximately over 2.5 folds by comparison with that of control, and up to 13 folds and 16 folds for BCRP by isoliquiritin and isoliquiritigenin, and further confirmed by Western blot. The functional assay also supported up-regulation of efflux transporter by those ingredients. Flow cytometry study showed that the level of rhodamine123 as probe substrate in LS-180 cells decreased to approximately 50% after treatment with active ingredients of liquorice, compared with that of control. The fluorescent assay confirmed that change of rhodamine 123 was correlated with the concentrations of active ingredients given. The efflux transport of rhodamine 123 was enhanced in Caco-2 cell models as well. Conclusion: The study clarified potential detoxification mechanism of liquorice by up-regulating efflux transporter as to reduce absorption of xenobiotics across small intestinal membrane, which provided a new insight into pharmacological function of liquorice.