Role of P-glycoprotein in the Transport of Tanshinone I, One Active Triterpenoid from Salvia miltiorrhiza

The extracts from the root of Salvia miltiorrhiza are widely used in the treatment of angina and stroke. In this study, we have investigated the role of P-glycoprotein (P-gp) in the transport of tanshinone I (TSI), a major active constituent of S. miltiorrhiza. The TSI transport across Caco-2 monolayers was pH-, energy-, and temperature-dependent, but not sodium-dependent. TSI exhibited a polarized transport in Caco-2 monolayers which was attenuated by P-gp inhibitors. The permeability (Papp) values of TSI in the basolateral to apical direction were significantly higher in MDCK-II cells over-expressing MDR1, as compared to the wild-type control cells. Furthermore, TSI significantly inhibited the transport of digoxin in Caco-2 cells with an IC50 value of 0.53 ± 0.09 μM. TSI also moderately stimulated P-gp ATPase activity with Km and Vmax values of 31.70 ± 7.09 μM and 57.71 ± 5.26 nmol/min/mg protein, respectively. Our findings indicate that TSI is a substrate and inhibitor of Pgp, which has important clinical and toxicological implications.