Mechanism-based inhibition of cytochrome P450 (CYP)2A6 by chalepensin in recombinant systems, in human liver microsomes and in mice in vivo.

Article Details

Citation

Copy to clipboard

Ueng YF, Chen CC, Chung YT, Liu TY, Chang YP, Lo WS, Murayama N, Yamazaki H, Soucek P, Chau GY, Chi CW, Chen RM, Li DT

Mechanism-based inhibition of cytochrome P450 (CYP)2A6 by chalepensin in recombinant systems, in human liver microsomes and in mice in vivo.

Br J Pharmacol. 2011 Jul;163(6):1250-62. doi: 10.1111/j.1476-5381.2011.01341.x.

PubMed ID

21418183 [ View in PubMed

]

Abstract

BACKGROUND AND PURPOSE: Chalepensin is a pharmacologically active furanocoumarin compound found in rue, a medicinal herb. Here we have investigated the inhibitory effects of chalepensin on cytochrome P450 (CYP) 2A6 in vitro and in vivo. EXPERIMENTAL APPROACH: Mechanism-based inhibition was studied in vitro using human liver microsomes and bacterial membranes expressing genetic variants of human CYP2A6. Effects in vivo were studied in C57BL/6J mice. CYP2A6 activity was assayed as coumarin 7-hydroxylation (CH) using HPLC and fluorescence measurements. Metabolism of chalepensin was assessed with liquid chromatography/mass spectrometry (LC/MS). KEY RESULTS: CYP2A6.1, without pre-incubation with NADPH, was competitively inhibited by chalepensin. After pre-incubation with NADPH, inhibition by chalepensin was increased (IC(50) value decreased by 98%). This time-dependent inactivation (k(inact) 0.044 min(-1) ; K(I) 2.64 microM) caused the loss of spectrally detectable P450 content and was diminished by known inhibitors of CYP2A6, pilocarpine or tranylcypromine, and by glutathione conjugation. LC/MS analysis of chalepensin metabolites suggested an unstable epoxide intermediate was formed, identified as the corresponding dihydrodiol, which was then conjugated with glutathione. Compared with the wild-type CYP2A6.1, the isoforms CYP2A6.7 and CYP2A6.10 were less inhibited. In mouse liver microsomes, pre-incubation enhanced inhibition of CH activity. Oral administration of chalepensin to mice reduced hepatic CH activity ex vivo. CONCLUSIONS AND IMPLICATIONS: Chalepensin was a substrate and a mechanism-based inhibitor of human CYP2A6. Formation of an epoxide could be a key step in this inactivation. 'Poor metabolizers' carrying CYP2A6*7 or *10 may be less susceptible to inhibition by chalepensin. Given in vivo, chalepensin decreased CYP2A activity in mice.

DrugBank Data that Cites this Article

Drug Enzymes

Drug	Enzyme	Kind	Organism	Pharmacological Action	Actions
Pilocarpine	Cytochrome P450 2A6	Protein	Humans	Unknown	Substrate Inhibitor	Details