Inhibitory effects of dimethyllirioresinol, epimagnolin a, eudesmin, fargesin, and magnolin on cytochrome P450 enzyme activities in human liver microsomes

Magnolin, epimagnolin A, dimethyllirioresinol, eudesmin, and fargesin are pharmacologically active tetrahydrofurofuranoid lignans found in Flos Magnoliae. The inhibitory potentials of dimethyllirioresinol, epimagnolin A, eudesmin, fargesin, and magnolin on eight major human cytochrome P450 (CYP) enzyme activities in human liver microsomes were evaluated using liquid chromatography-tandem mass spectrometry to determine the inhibition mechanisms and inhibition potency. Fargesin inhibited CYP2C9-catalyzed diclofenac 4ʹ-hydroxylation with a K_i value of 16.3 μM, and it exhibited mechanism-based inhibition of CYP2C19-catalyzed [S]-mephenytoin 4ʹ-hydroxylation (K_i, 3.7 μM; k_inact, 0.102 min^-1), CYP2C8-catalyzed amodiaquine N-deethylation (K_i, 10.7 μM; k_inact, 0.082 min^-1), and CYP3A4-catalyzed midazolam 10-hydroxylation (K_i, 23.0 μM; k_inact, 0.050 min^-1) in human liver microsomes. Fargesin negligibly inhibited CYP1A2-catalyzed phenacetin O-deethylation, CYP2A6-catalyzed coumarin 7-hydroxylation, CYP2B6-catalyzed bupropion hydroxylation, and CYP2D6-catalyzed bufuralol 1ʹ-hydroxylation at 100 μM in human liver microsomes. Dimethyllirioresinol weakly inhibited CYP2C19 and CYP2C8 with IC₅₀ values of 55.1 and 85.0 μM, respectively, without inhibition of CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2D6, and CYP3A4 activities at 100 μM. Epimagnolin A, eudesmin, and magnolin showed no the reversible and time-dependent inhibition of eight major CYP activities at 100 μM in human liver microsomes. These in vitro results suggest that it is necessary to investigate the potentials of in vivo fargesin-drug interaction with CYP2C8, CYP2C9, CYP2C19, and CYP3A4 substrates.