title: Metabolism of (+)- and (-)-limonenes to respective carveols and perillyl alcohols by CYP2C9 and CYP2C19 in human liver microsomes.
abstract: Limonene, a monocyclic monoterpene, is present in orange peel and other plants and has been shown to have chemopreventive activities. (+)- and (-)-Limonene enantiomers were incubated with human liver microsomes and the oxidative metabolites thus formed were analyzed using gas chromatography-mass spectrometry. Two kinds of metabolites, (+)- and (-)-trans-carveol (a product by 6-hydroxylation) and (+)- and (-)-perillyl alcohol (a product by 7-hydroxylation), were identified, and the latter metabolites were found to be formed more extensively, the former ones with liver microsomes prepared from different human samples. Sulfaphenazole, flavoxamine, and antibodies raised against purified liver cytochrome P450 (P450) 2C9 that inhibit both CYP2C9- and 2C19-dependent activities, significantly inhibited microsomal oxidations of (+)- and (-)-limonene enantiomers. The limonene oxidation activities correlated well with contents of CYP2C9 and activities of tolbutamide methyl hydroxylation in liver microsomes of 62 human samples, whereas these activities did not correlate with contents of CYP2C19 and activities of S-mephenytoin 4-hydroxylation. Of 11 recombinant human P450 enzymes (expressed in Trichoplusia ni cells) tested, CYP2C8, 2C9, 2C18, 2C19, and CYP3A4 catalyzed oxidations of (+)- and (-)-limonenes to respective carveols and perillyl alcohol. Interestingly, human CYP2B6 did not catalyze limonene oxidations, whereas rat CYP2B1 had high activities in catalyzing limonene oxidations. These results suggest that both (+)- and (-)-limonene enantiomers are oxidized at 6- and 7-positions by CYP2C9 and CYP2C19 in human liver microsomes. CYP2C9 may be more important than CYP2C19 in catalyzing limonene oxidations in human liver microsomes, since levels of the former protein are more abundant than CYP2C19 in these human samples. Species-related differences exist in the oxidations of limonenes in CYP2B subfamily in rats and humans.
authors.affiliation: Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University, Kowakae, Higashiosaka, Osaka, Japan. miyazawa@apch.kindai.ac.jp
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Miyazawa
authors.forename: Masaki
authors.initials: M
authors.lastname: Shindo
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Shimada
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D002478:Cells, Cultured; D000081005:Cyclohexane Monoterpenes; D053138:Cyclohexenes; D065731:Cytochrome P-450 CYP2C19; D065727:Cytochrome P-450 CYP2C8; D065729:Cytochrome P-450 CYP2C9; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D066298:In Vitro Techniques; D007313:Insecta / Q000166:cytology; D000077222:Limonene; D008862:Microsomes, Liver / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D039821:Monoterpenes; D010084:Oxidation-Reduction; D020011:Protective Agents / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D013237:Stereoisomerism; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013729:Terpenes / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000081005:Cyclohexane Monoterpenes; D053138:Cyclohexenes; D039821:Monoterpenes; D020011:Protective Agents; D011994:Recombinant Proteins; D013729:Terpenes; C032208:perillyl alcohol; D003577:Cytochrome P-450 Enzyme System; C075856:carveol; D000077222:Limonene; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; C450259:CYP2C8 protein, human; D065731:Cytochrome P-450 CYP2C19; D065727:Cytochrome P-450 CYP2C8; D039181:Steroid 16-alpha-Hydroxylase