Selective inhibitory effects of machilin A isolated from Machilus thunbergii on human cytochrome P450 1A and 2B6

Background: The bark of Machilus thunbergii (Lauraceae) has been used as a folk medicine to treat abdominal pain and distension, and leg edema in Korea. Machilin A (MA), a lignan isolated from Machilus thunbergii, exhibits several biological activities including anti-oxidant and stimulatory effects on cell differentiation and proliferation.

Purpose: Potential drug-interactions with MA via inhibition of cytochrome P450 (CYP) activity in human liver microsomes (HLMs), have not been investigated.

Study design: The inhibitory effects of MA on the activities of CYPs were investigated using cocktail probe substrates in pooled HLMs and on human recombinant cDNA-expressed CYP isoforms.

Methods: The nine CYP-specific substrates were incubated in HLM or recombinant cDNA-expressed CYP 1A1, 1A2 and 2B6 with MA. After incubation, the samples were injected onto a C18 column for liquid chromatography-tandem mass spectrometry analysis. To investigate the binding poses between MA and CYP, we carried out structure-based docking simulations by using software and scripts written in-house (ALIS-DOCK; Automatic pLatform for Iterative Structure-based DOCKing).

Results: MA strongly inhibited CYP1A2-mediated phenacetin O-deethylation and CYP2B6-mediated bupropion hydroxylation with IC50 values of 3.0 and 3.9 µM, respectively, while it did not significantly inhibit other CYPs. A Dixon plot indicated that MA competitively inhibits CYP1A2 and CYP2B6 with Ki values of 0.71 and 4.1 µM, respectively.

Conclusion: Overall, this was the first investigation of the inhibitory effects of MA on CYP1A2 and CYP2B6 in HLMs, and it has identified that MA acts via competitive inhibition.