Ginseng, a traditional herbal medicine, may interact with several co-administered drugs in clinical settings, and
ginsenosides, the major active components of ginseng, may be responsible for these ginseng-drug interactions (GDIs).
Results from previous studies on ginsenosides’ effects on human drug-metabolizing P450 enzymes are inconsistent and
confusing. Herein, we first evaluated the inhibitory effects of fifteen ginsenosides and sapogenins on human CYP1A2,
CYP2C9, CYP2C19, CYP2D6 and CYP3A4 enzymes by using commercially available fluorescent probes. The structure-activity
relationship of their effects on the P450s was also explored and a pharmacophore model was established for CYP3A4.
Moreover, substrate-dependent phenomena were found in ginsenosides’ effects on CYP3A4 when another fluorescent
probe was used, and were further confirmed in tests with conventional drug probes and human liver microsomes. These
substrate-dependent effects of the ginsenosides may provide an explanation for the inconsistent results obtained in
previous GDI reports.