title: Metabolism and Bioactivation of Fluorochloridone, a Novel Selective Herbicide, in Vivo and in Vitro.
abstract: Fluorochloridone (FLC) is a herbicide used worldwide that is thought to be safe. However, due to its potential genotoxicity, cytotoxicity, and even systematic toxicity, there are increasing concerns about human exposure to this compound. Thus, the metabolism and bioactivation of FLC was investigated. After oral administration to mice, 27 metabolites were identified by ultrahigh performance liquid chromatography-electrospray ionization-quadrupole time-of-flight-mass spectrometry and with further structural identification by nuclear magnetic resonance spectroscopy. Hydroxylation and oxidative dechlorination were the major phase I pathways, while glutathione (GSH) and N-acetylcysteine conjugations were two major phase II pathways, indicating the formation of a reactive intermediate. In vitro microsomal and cytosolic studies revealed that a GSH conjugate (M13) was the predominant metabolite of FLC formed through a nucleophilic SN2 substitution of 3-Cl by GSH; this pathway is NADPH independent and accelerated by glutathione S-transferase (GST). Further, a kinetic study showed that M13 formation in both human liver microsomes and cytosols obeyed typical Michaelis-Menten kinetics. The maximum clearance (Vmax/Km) of GSH conjugation in human liver microsomes was approximately 5.5-fold higher than human liver cytosol, thus implying that microsomal GST was mainly responsible for M13 formation. These findings are important for understanding the potential hazard of human exposure to FLC.
authors.affiliation: Pharmacology and Toxicology, Department/Center for Drug Safety Evaluation, Shanghai Institute for Food and Drug Control , Shanghai 201203, PR China.
authors.forename: Jingmin
authors.initials: J
authors.lastname: Shi
authors.forename: Cen
authors.initials: C
authors.lastname: Xie
authors.forename: Hongbing
authors.initials: H
authors.lastname: Liu
authors.forename: Kristopher W
authors.initials: KW
authors.lastname: Krausz
authors.forename: Carole A
authors.initials: CA
authors.lastname: Bewley
authors.affiliation: Pharmacology and Toxicology, Department/Center for Drug Safety Evaluation, Shanghai Institute for Food and Drug Control , Shanghai 201203, PR China.
authors.forename: Suhui
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Pharmacology and Toxicology, Department/Center for Drug Safety Evaluation, Shanghai Institute for Food and Drug Control , Shanghai 201203, PR China.
authors.forename: Liming
authors.initials: L
authors.lastname: Tang
authors.affiliation: School of Public Health, Fudan University , Shanghai 200032, PR China.
authors.forename: Zhijun
authors.initials: Z
authors.lastname: Zhou
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Gonzalez
mesh_terms: D000818:Animals; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006540:Herbicides / Q000378:metabolism; D006801:Humans; D051379:Mice; D008862:Microsomes, Liver / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D006540:Herbicides; D005982:Glutathione Transferase; D005978:Glutathione