Ketoconazole (KTZ) has 2 chiral centers with the therapeutically active form being a racemic mixture of 2 cis-enantiomers, namely, (2R,4S)-(+)-KTZ and (2S,4R)-(-)-KTZ. The aims of the present study were to examine the effects of (+)-KTZ, (-)-KTZ, and (±)-KTZ on
aryl hydrocarbon receptor activation and subsequently
CYP1A1 induction in both human HepG2 and murine Hepa1c1c7
hepatoma cells, and to further test their inhibitory effect using recombinant human and mouse
CYP1A1 enzymes. Our results demonstrated that (+)-KTZ induced human
CYP1A1 more than (-)-KTZ, whereas on the other hand (-)-KTZ induced murine
Cyp1a1 more than (+)-KTZ at the
mRNA, and activity levels. Human
CYP1A1 showed higher affinity to 7ER compared with murine
Cyp1a1 (Km values 13.29 nM for human vs. 168.1 nM for murine). The intrinsic clearance values for human and murine
CYP1A1 were 194.1 and 87.6 μL/pmol P450/min, respectively, whereas, Vmax values were 2.58 and 14.73 pmol/pmol P450/min, respectively. (+)-KTZ and (-)-KTZ directly inhibited
CYP1A1 activity by noncompetitive mechanism. The affinity of (-)-KTZ to interact with human
CYP1A1 and murine
Cyp1a1 was significantly different from (+)-KTZ, as the Ki values for human
CYP1A1 and murine
Cyp1a1 were 199.4 and 413.7 nM, respectively, for (+)-KTZ, and 269.3 and 230.8 nM, respectively, for (-)-KTZ.