Oxidation of 1,8-cineole, the monoterpene cyclic ether originated from eucalyptus polybractea, by cytochrome P450 3A enzymes in rat and human liver microsomes.
1,8-Cineole, the monoterpene cyclic ether known as eucalyptol, is one of the components in essential oils from Eucalyptus polybractea. We investigated the metabolism of 1,8-cineole by liver microsomes of rats and humans and by recombinant cytochrome P450 (P450 or CYP) enzymes in insect cells in which human P450 and NADPH-P450 reductase cDNAs had been introduced. 1,8-Cineole was found to be oxidized at high rates to 2-exo-hydroxy-1,8-cineole by rat and human liver microsomal P450 enzymes. In rats, pregenolone-16alpha-carbonitrile (PCN) and phenobarbital induced the 1,8-cineole 2-hydroxylation activities by liver microsomes. Several lines of evidence suggested that CYP3A4 is a major enzyme involved in the oxidation of 1,8-cineole by human liver microsomes: (1), 1,8-cineole 2-hydroxylation activities by liver microsomes were inhibited very significantly by ketoconazole, a CYP3A inhibitor, and anti-CYP3A4 immunoglobulin G; (2), there was a good correlation between CYP3A4 contents and 1,8-cineole 2-hydroxylation activities in liver microsomes of eighteen human samples; and (3), of various recombinant human P450 enzymes examined, CYP3A4 had the highest activities for 1,8-cineole 2-hydroxylation; the rate catalyzed by CYP3A5 was about one-fourth of that catalyzed by CYP3A4. Kinetic analysis showed that K(m) and V(max) values for the oxidation of 1,8-cineole by liver microsomes of human sample HL-104 and rats treated with PCN were 50 microM and 91 nmol/min/nmol P450 and 20 microM and 12 nmol/min/nmol P450, respectively. The rates observed using human liver microsomes and recombinant CYP3A4 were very high among other CYP3A4 substrates reported so far. These results suggest that 1,8-cineole, a monoterpenoid present in nature, is one of the effective substrates for CYP3A enzymes in rat and human liver microsomes.
Miyazawa
M
M
Department of Applied Chemistry, Faculty of Science and Engineering, Kinki University, Kowakae, Higashiosaka, Osaka 577-8502, Japan. miyazawa@apch.kindai.ac.jp
Shindo
M
M
Shimada
T
T
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D016367:Baculoviridae / Q000235:genetics; D003511:Cyclohexanols; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D004790:Enzyme Induction / Q000187:drug effects; D000077591:Eucalyptol; D006801:Humans; D006900:Hydroxylation; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D008297:Male; D008610:Menthol / Q000031:analogs & derivatives* / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D039821:Monoterpenes; D009036:Moths / Q000821:virology; D010084:Oxidation-Reduction; D010089:Oxidoreductases, N-Demethylating / Q000096:biosynthesis / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D013729:Terpenes
D003511:Cyclohexanols; D007527:Isoenzymes; D039821:Monoterpenes; D011994:Recombinant Proteins; D013729:Terpenes; D008610:Menthol; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating; D000077591:Eucalyptol