Metabolism of (+)-Fenchone by CYP2A6 and CYP2B6 in Human Liver Microsomes

Abstract

Among numerous groups of naturally occurring compounds examined so far, volatile monoterpenes have long been used as fragrances and flavouring agents. (ϩ)-Fenchone, a bicyclic monoterpene, is widely distributed in plants and found in essential oils from Foeniculum vulgare.1) This component has camphoraceous fragrance. (ϩ)-Fenchone is used as a food flavour and in perfumes. Although, there are report that (ϩ)-fenchone have toxic.2) P450 enzymes are shown to detoxify and/or toxify these compounds to metabolites more polar and sometimes more reactive metabolites. 3-7)There is no literature on the absorption, excretion of the (ϩ)-fenchone in human body. Therefore, it is interesting to examine how (ϩ)-fenchone is metabolized by P450 in human liver microsomes.There are several reports on the biotransformation of (ϩ)-fenchone by microorganisms, insect and mammals, e.g. Baeyer-Villiger type oxidation by Corynebacterium sp. 5-exo and 6-exo hydroxylation by Absidia orchidis, 8) 5-exo, 6-exo and H-7 glucosylation by cultured plant cells of Eucalyptus perriniana, 9) 5-endo, 6-endo hydroxylation by Aspergillus niger, 10) 5-exo, 6-exo, 6-endo, 10-hydroxylation by Spodoptera litura 11) and hydroxylation of methyl groups by rabbits. 12) However, there is no report on the biotransformation of (ϩ)-fenchone by the human body.Our previous studies have demonstrated that several terpenes, 1,4-cineole, 1,8-cineole, (ϩ)-and (Ϫ)-limonenes and (Ϫ)-verbenone are catalyzed by cytochrome P450 enzymes to their respective oxidation products in human liver microsomes. [13][14][15][16] The metabolite from monoterpene esthers have determined to be oxidized at the 2-position of the molecules (1,4-cineole and 1,8-cineole) by human CYP3A4 enzyme. 13,14) Limonene enatiomers are metabolized to their respective carveols and perillyl alcohols in human liver. 13,14) (Ϫ)-Verbenone has found to be oxidized at the 10-position of the molecules by human CYP2A6 and 2B6. 16) In this study, we examined oxidations of (ϩ)-fenchone by P450 enzymes in liver microsomes prepared from different human samples. The metabolites thus formed were analyzed on GC-MS. To determine which P450s are the major enzymes in the oxidations of (ϩ)-fenchone, we used specific P450 inhibitors and antibodies raised against purified human liver P450 enzymes. Catalytic rates with eleven forms of human P450 enzymes expressed in Trichoplusia ni cells in the oxidations of (ϩ)-fenchone are also reported. MATERIALS AND METHODSChemicals (ϩ)-Menthofuran, thioTEPA, NADP, glucose 6-phosphate, and glucose 6-phosphate dehydrogenase were purchased from Sigma Chemical Co. (St. Louis, MO, U.S.A.). (ϩ)-Fenchone (purity, Ͼ99%) was purchased from Fluka. 6-exo-Hydroxyfenchone, 6-endo-hydroxyfenchone and 10-hydroxyfenchone (purity, Ͼ99%) were isolated with Spodoptera litura.11) Other reagents and chemicals used in this study were obtained from sources as described previously or were of the highest quality commercially available. (3H, s, H-9), 1.16 (3H, s, H-10), 1.62 (1H, dd, Jϭ1.7, 11.0 Hz, H B -7; nearly C...

Essential oil components and cytochrome P450 enzymes: a review

“…(+)-Fenchone was reported to be metabolized by CYP2A6, which was determined in human liver microsomes and Salmonella typhimurium cells expressing human CYP2A6. 45,46 Furthermore, CYP2B6 contributes to the (+)-fenchone metabolism, which was tested in human liver microsomes. 45 Further reports about the biotransformation of (-)-fenchone showed similar results.…”

“…45,46 Furthermore, CYP2B6 contributes to the (+)-fenchone metabolism, which was tested in human liver microsomes. 45 Further reports about the biotransformation of (-)-fenchone showed similar results. CYP2A6 and CYP2B6 are the principle enzymes in (-)-fenchone metabolism, which was also tested in human liver microsomes and recombinant enzymes.…”

Terpene Bioconversion – How does its Future Look?

“…was likewise capable to hydroxylate (+)-camphor to 5-exo-hydroxycamphor [119]. The disposition of human liver microsomes derived cytochromes P450 (CYP2A6 and CYP2B6) expressed in cells of the Ni moth Trichoplusia ni for terpenoid biotransformation was demonstrated by means of (+)-fenchone hydroxylation to endo/exo-6hydroxy and 10-hydroxyfenchone [120][121][122] 3.3. Integrated bioprocesses: State of the art industrial aroma production with micro-organisms and enzymes are batch processes with subsequent product recovery by means of distillation [123].…”

In Vitro Regio- and Stereoselective Oxidation of β-Ionone by Human Liver Microsomes

“…For this reason, investigations of β-ionone metabolic pathways, patterns of metabolite and intermediate formation, and kinetics are often studied using CYP human liver microsomes (HLMs). Studies of HLM metabolism indicate that CYP is a major enzyme in the metabolism of monoterpenes 1,8-cineole, (+)-and (−)-limonenes, (+)-fenchone, and (−)-camphor [12][13][14][15]. The major pathways used for the metabolism of these compounds involve CYP-dependent hydroxylation or oxidation.…”