PT  - JOURNAL ARTICLE
AU  - Mao, Xu
AU  - Wang, Jian
AU  - Wang, Qian
AU  - Yang, Lan
AU  - Li, Yilin
AU  - Lin, Hao
AU  - Peng, Ying
AU  - Zheng, Jiang
TI  - Nitidine Chloride–Induced CYP1 Enzyme Inhibition and Alteration of Estradiol Metabolism
AID  - 10.1124/dmd.119.086892
DP  - 2019 Aug 01
TA  - Drug Metabolism and Disposition
PG  - 919--927
VI  - 47
IP  - 8
4099  - http://dmd.aspetjournals.org/content/47/8/919.short
4100  - http://dmd.aspetjournals.org/content/47/8/919.full
SO  - Drug Metab Dispos2019 Aug 01; 47
AB  - The cytochrome P450 (P450) 1 family is an important phase I enzyme involved in carcinogen activation. Nitidine chloride (NC) is a pharmacologically active alkaloid with polyaromatic hydrocarbon found in the roots of Zanthoxylum nitidum (Roxb.) DC, a traditional medicinal herb widely used in China. We examined the inhibitory effects of NC on CYP1A1, 1B1, and 1A2. NC significantly inhibited CYP1A1- and 1B1-catalyzed ethoxyresorufin O-deethylation activity (IC50 = 0.28 ± 0.06 and 0.32 ± 0.02 μM, respectively) in a concentration-dependent manner, but only showed slight inhibition of CYP1A2 activity (IC50 > 50 μM). Kinetic analysis revealed that NC competitively inhibited CYP1B1 with a Ki value of 0.47 ± 0.05 μM, whereas NC caused a mixed type of inhibition on CYP1A1 with Ki and KI values of 0.14 ± 0.04 and 0.19 ± 0.09 μM, respectively. The observed enzyme inhibition neither required NADPH nor revealed time dependency. Molecular docking manifested the generation of strong hydrogen-bonding interactions of Ser116 in CYP1A1 and Ser127 in CYP1B1 with methoxy moiety of NC. Additionally, NC-induced alteration of estradiol (E2) metabolism was also investigated in the present study. Hydroxyestradiols, including 2-hydroxyestradiol [(2-OHE2) nontoxic] and 4-hydroxyestradiol [(4-OHE2) genotoxic] generated in recombinant enzyme incubation systems and cultured MCF-7 cells were analyzed, and NC was found to preferentially inhibit the nontoxic 2-hydroxylation activity of E2 mediated by CYP1A1. In conclusion, NC was a mixed type inhibitor of CYP1A1 and a competitive inhibitor of CYP1B1. The remarkable inhibition on E2 2-hydroxylation might increase the risk of 4-OHE2–induced genotoxicity.SIGNIFICANCE STATEMENT CYP1 enzymes catalyze oxidative metabolism of a variety of compounds and are known to play a crucial role in the development of cancer. CYP1A1 and CYP1A2 are responsible for hydroxylation of estradiol (E2) at the C-2 position, resulting in the formation of 2-OHE2, which is proposed to be a detoxification pathway. However, CYP1B1-mediated hydroxylation of E2 at the C-4 position has been suggested to be a tumor initiator. The present study found that nitidine chloride is a mixed type inhibitor of CYP1A1 and a competitive inhibitor of CYP1B1. NC preferentially inhibited the nontoxic E2 2-hydroxylation pathway mediated by CYP1A1, which might increase the risk of 4-OHE2–induced genotoxicity and cause severe drug-drug interactions.