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 aKi of 2.5 μM and akinact of 0.22 min−1 for human liver microsomes and aKi of 0.84 μM and akinact 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.
Footnotes
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Send reprint requests to: Sidney D. Nelson, Ph.D., Department of Medicinal Chemistry, University of Washington, Box 357610, Seattle, WA 98195-7610.
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This research was supported by National Institutes of Health Grants GM25418 and GM32165 (to S.D.N.).
- Abbreviations used are::
- CYP or P450
- cytochrome P450
- TBS
- Tris-buffered saline
- Received September 5, 1997.
- Accepted March 25, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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