title: Evidence for the bioactivation of 4-nonylphenol to quinone methide and ortho-benzoquinone metabolites in human liver microsomes.
abstract: 4-Nonylphenol (4-NP) is a well-known toxic environmental contaminant. The major objective of the present study was to identify reactive metabolites of 4-NP. Following incubations of 4-NP with NADPH- and GSH-supplemented human liver microsomes, 6 GSH conjugates, along with 19 oxidized metabolites, were detected by UPLC/Q-TOF mass spectrometry utilizing the mass defect filter method. Several authentic key metabolite standards were chemically synthesized for structural identification. Three GSH conjugates were found to derive from quinone methide intermediates, and the other three resulted from ortho-benzoquinone intermediates. Conjugation of the quinone methides with GSH produced benzylic-orientated GSH conjugates by 1,6-addition, while the reaction of the ortho-benzoquinone intermediates offered aromatic-orientated GSH conjugates. The conversion of 4-NP to the quinone methides and ortho-hydroquinones required cytochromes P450, specifically CYPs1A2, 2C19, 2D6, 2E1, and 3A4, while the oxidation of ortho-benzohydroquinones to the corresponding benzoquinones was apparently independent of microsomal enzymes. The ortho-benzoquinone derived from 4-NP was isomerized to the corresponding hydroxyquinone methide, and the former dominated the latter at a rate of approximately 20:1. The findings of the quinone methide and benzoquinone metabolites intensified the concern on the impact of 4-NP exposure on human health.
authors.affiliation: Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Pan
authors.initials: P
authors.lastname: Deng
authors.forename: Dafang
authors.initials: D
authors.lastname: Zhong
authors.forename: Fajun
authors.initials: F
authors.lastname: Nan
authors.forename: Sheng
authors.initials: S
authors.lastname: Liu
authors.forename: Dan
authors.initials: D
authors.lastname: Li
authors.forename: Tao
authors.initials: T
authors.lastname: Yuan
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Chen
authors.forename: Jiang
authors.initials: J
authors.lastname: Zheng
mesh_terms: D016227:Benzoquinones / Q000737:chemistry / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D045563:Indolequinones / Q000737:chemistry / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism*; D009249:NADP / Q000737:chemistry; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D016227:Benzoquinones; D045563:Indolequinones; D010636:Phenols; C068040:quinone methide; C004532:quinone; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D005978:Glutathione; C041594:4-nonylphenol