High susceptibility of mouse hepatic Cyp2a to the inactivation by oral imperatorin: isoform sensitivity and tissue specificity.

The natural furanocoumarin, imperatorin, is a potent time-dependent inhibitor of human cytochrome P450 (P450, CYP) 2A6, whose coumarin 7-hydroxylation (COH) activity can be observed in mouse Cyp2a. Because of the time-dependent property, the oral effects of imperatorin (0.15‒5 mg/kg) on P450s, NAD(P)H-quinone oxidoreductase 1 (NQO1), UDP-glucuronosyltransferase (UGT), and glutathione S-transferase (GST) were studied in male C57BL/6JNarl mice after acute (3 h) administration. Studies on the time-dependent inhibition and imperatorin oxidation aimed to clarify the different sensitivities of P450 isoforms to oral imperatorin. Among hepatic P450 activities, COH suppression required the lowest dose of 0.15 mg/kg imperatorin, indicating the high susceptibility of Cyp2a. Hepatic protein and mRNA levels of Cyp2a4/5 remained unchanged. Imperatorin decreased renal and pulmonary COH activities in vitro, whereas these activities remained unchanged in imperatorin-treated mice. Imperatorin treatment had no effects on hepatic, renal, and pulmonary NQO1, UGT, and GST activities. Among P450 activities of liver microsomes, imperatorin irreversibly inhibited COH, exhibiting the lowest IC50 value after pre-incubation and the greatest IC50 shift. Multiple P450s participated in mouse hepatic imperatorin oxidation, in which Cyp2a and Cyp3a were primarily involved in the epoxidation. However, imperatorin did not cause an IC50 shift in the Cyp3a inhibition. In summary, Cyp2a is highly sensitive to the inactivation by oral treatment with imperatorin, being attributed to the irreversible time-dependent inhibition by imperatorin through epoxidation. For future use of imperatorin-containing natural products, their oral effects on the metabolism of human CYP2A6 substrates should be carefully considered and investigated.