title: Metabolism of 1,8-cineole by human cytochrome P450 enzymes: identification of a new hydroxylated metabolite.
abstract: Human metabolism of the monoterpene cyclic ether 1,8-cineole was investigated in vitro and in vivo. In vitro, the biotransformation of 1,8-cineole was investigated by human liver microsomes and by recombinant cytochrome P450 enzymes coexpressed with human CYP-reductase in Escherichia coli cells. Besides the already described metabolite 2alpha-hydroxy-1,8-cineole we found another metabolite produced at high rates. The structure was identified by a comparison of its mass spectrum and retention time with the reference compounds as 3alpha-hydroxy-1,8-cineole. There was a clear correlation between the concentration of the metabolites, incubation time and enzyme content, respectively. CYP3A4/5 antibody significantly inhibited the 2alpha- and 3alpha-hydroxylation catalyzed by pooled human liver microsomes. Further kinetic analysis revealed that the Michaelis-Menten K(m) and V(max) for oxidation of 1,8-cineole in position three were 19 microM and 64.5 nmol/min/nmol P450 for cytochrome P450 3A4, and 141 microM and 10.9 nmol/min/nmol P450 for cytochrome P450 3A5, respectively. To our knowledge, this is the first time that 3alpha-hydroxy-1,8-cineole is described as a human metabolite of 1,8-cineole. We confirmed these in vitro results by the investigation of human urine after the oral administration of cold medication containing 1,8-cineole. In human urine we found by GC-MS analysis the described metabolites, 2alpha-hydroxy-1,8-cineole and 3alpha-hydroxy-1,8-cineole.
authors.affiliation: Institute of Hygiene and Environmental Medicine, RWTH Aachen, Pauwelsstrasse 30, 52074 Aachen, Germany.
authors.forename: Mike
authors.initials: M
authors.lastname: Duisken
authors.forename: Frank
authors.initials: F
authors.lastname: Sandner
authors.forename: Brunhilde
authors.initials: B
authors.lastname: Blömeke
authors.forename: Juliane
authors.initials: J
authors.lastname: Hollender
mesh_terms: D000284:Administration, Oral; D003511:Cyclohexanols / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D000077591:Eucalyptol; D005260:Female; D006801:Humans; D006900:Hydroxylation; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism; D039821:Monoterpenes / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D003511:Cyclohexanols; D039821:Monoterpenes; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; D000077591:Eucalyptol