title: (R)-(+)-Menthofuran is a potent, mechanism-based inactivator of human liver cytochrome P450 2A6.
abstract: (R)-(+)-Menthofuran is a potent, mechanism-based inactivator of human liver cytochrome P450 (CYP or P450) 2A6. Menthofuran caused a time- and concentration-dependent loss of CYP2A6 activity. The inactivation of CYP2A6 was characterized by a Ki of 2.5 microM and a kinact of 0.22 min-1 for human liver microsomes and a Ki of 0.84 microM and a kinact of 0.25 min-1 for purified expressed CYP2A6. Addition of various nucleophiles, a chelator of iron, or scavengers of reactive oxygen species or extensive dialysis failed to protect CYP2A6 from inactivation. An antibody to metallothionein conjugates of a suspected reactive metabolite of menthofuran was used to detect reactive menthofuran metabolite adducts with CYP2A6. These adducts were formed only in the presence of NADPH-P450 reductase and NADPH. Glutathione, methoxylamine, and semicarbazide did not prevent adduction of reactive menthofuran metabolites to CYP2A6, however. The menthofuran metabolite formation/CYP2A6 inactivation partition ratio was determined to be 3.5 +/- 0.6 nmol/nmol of P450. Menthofuran was unable to inactivate CYP1A2, CYP2D6, CYP2E1, or CYP3A4 in a time- and concentration-dependent manner.
authors.affiliation: Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195-7610, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: Khojasteh-Bakht
authors.forename: L L
authors.initials: LL
authors.lastname: Koenigs
authors.forename: R M
authors.initials: RM
authors.lastname: Peter
authors.forename: W F
authors.initials: WF
authors.lastname: Trager
authors.forename: S D
authors.initials: SD
authors.lastname: Nelson
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D065637:Cytochrome P-450 CYP2A6; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors*; D039821:Monoterpenes; D009249:NADP / Q000494:pharmacology; D011817:Rabbits; D013729:Terpenes / Q000494:pharmacology*
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D039821:Monoterpenes; D013729:Terpenes; C054487:menthofuran; D009249:NADP; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C585710:CYP2A6 protein, human; D065637:Cytochrome P-450 CYP2A6