title: Metabolism of α-thujone in human hepatic preparations in vitro.
abstract: This study aims to characterize the metabolism of α-thujone in human liver preparations in vitro and to identify the role of cytochrome P450 (CYP) and possibly other enzymes catalyzing α-thujone biotransformations. With a liquid chromatography-mass spectrometry (LC-MS) method developed for measuring α-thujone and four potential metabolites, it was demonstrated that human liver microsomes produced two major (7- and 4-hydroxy-thujone) and two minor (2-hydroxy-thujone and carvacrol) metabolites. Glutathione and cysteine conjugates were detected in human liver homogenates, but not quantified. No glucuronide or sulphate conjugates were detected. Major hydroxylations accounted for more than 90% of the primary microsomal metabolism of α-thujone. Screening of α-thujone metabolism with CYP recombinant enzymes indicated that CYP2A6 was principally responsible for the major 7- and 4-hydroxylation reactions, although CYP3A4 and CYP2B6 participated to a lesser extent and CYP3A4 and CYP2B6 catalyzed minor 2-hydroxylation. Based on the intrinsic efficiencies of different recombinant CYP enzymes and average abundances of these enzymes in human liver microsomes, CYP2A6 was calculated to be the most active enzyme in human liver microsomes, responsible for 70-80% of the metabolism on average. Inhibition screening indicated that α-thujone inhibited both CYP2A6 and CYP2B6, with 50% inhibitory concentration values of 15.4 and 17.5 µM, respectively.
authors.affiliation: Pharmacology and Toxicology Unit, Institute of Biomedicine, FI-90014 University of Oulu, Oulu, Finland. khaled.megahed@oulu.fi
authors.forename: Khaled
authors.initials: K
authors.lastname: Abass
authors.forename: Petri
authors.initials: P
authors.lastname: Reponen
authors.forename: Sampo
authors.initials: S
authors.lastname: Mattila
authors.forename: Olavi
authors.initials: O
authors.lastname: Pelkonen
mesh_terms: D000328:Adult; D000081008:Bicyclic Monoterpenes; D002853:Chromatography, Liquid; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D020128:Inhibitory Concentration 50; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D008875:Middle Aged; D039821:Monoterpenes / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D055815:Young Adult
chemical_list: D000081008:Bicyclic Monoterpenes; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D039821:Monoterpenes; D011994:Recombinant Proteins; C005790:beta-thujone; D003577:Cytochrome P-450 Enzyme System