Background : The magnolia bark has been focused on owing to its worldwide usage for various clinical disorders. Despite its extensive use, only a few studies regarding the underlying mechanism of possible interactions of magnolia plant's components with medicines have been reported. In this study, incubation experiments with pooled human liver microsome (HLM) were performed to elucidate the mechanism of the effects of honokiol, a major ingredient of Magnolia officinalis, on human cytochrome P450 (CYP) isoenzymes. Methods and Results : CYP isoenzyme specific substrate was incubated with multiple concentrations of inhibitor, human liver microsome and cofactors. Honokiol demonstrated potent inhibitory effects on CYP1A2, CYP2C9, CYP2C19 and CYP2D6 with IC50 values of 3.73, 4.91, 3.71 and 20.27 μM respectively. For the estimation of inhibition constant (Ki) value and mode of inhibition, incubation studies with various concentrations of each CYP isoenzyme specific probe were performed. Honokiol inhibited CYP1A2, CYP2C9 and CYP2C19 with a competitive mode, indicating Ki values of 1.62, 4.73 and 2.19 μM respectively. In contrast, the inhibition of CYP2D6 by Honokiol was explained by a uncompetitive inhibition mode with Ki value of 14.34 μM. Conclusions : These findings suggest that Honokiol could have inhibitory effects on metabolic activity mediated by CYP1A2, CYP2C9, CYP2C19 and CYP2D6 in humans.

• Jin Kim(Department of Nursing, Gwangju Health University) | 김 진 corresponding author