Magnolol is one of the most important bioactive neolignans of Magnolia obovata Thunberg (Magnoliaceae) which has been used for crude drug prescriptions in Asian countries. Magnolol has been extensively used as an ingredient of traditional crude drugs, yet little is known of its possible interactions with medicines. To ascertain the influence of magnolol on medicines, an in vitro incubation test concerning human cytochrome P450 (CYP) isoenzymes was performed. The CYP isoenzyme specific substrate was incubated with different concentrations of magnolol, human liver microsome (HLM) and cofactors. Magnolol showed potent inhibitory effects on CYP2C9, CYP1A2, CYP2C19 and CYP2D6 with IC50 values of 5.75, 3.88, 3.62 and 109.18 μM respectively. Tests to estimate the inhibition constant (Ki) value and mode of inhibition were carried out to investigate the mechanism underlying the interactions of magnolol-CYP with various concentrations of each CYP isoenzyme specific probe. Magnolol exhibited a competitive inhibitory effect on CYP1A2 with a Ki value of 1.28 μM. In contrast, magnolol inhibited CYP2C9, CYP2C19 and CYP2D6 noncompetitively with Ki values of 7.41, 4.49 and 83.31 μM, respectively. These in vitro data indicate that magnolol might have potential to cause the pharmacokinetic changes of drug metabolism in vivo.
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