title: Metabolism of mequindox and its metabolites identification in chickens using LC-LTQ-Orbitrap mass spectrometry.
abstract: Mequindox (MEQ), 3-methyl-2-quinoxalinacetyl-1,4-dioxide, is widely used in Chinese veterinary medicine as an antimicrobial and feed additive. Its toxicities have been reported to be closely related to its metabolism. To understand more clearly the metabolic pathways of MEQ, its metabolism in chickens was studied using liquid chromatography coupled with electrospray ionization hybrid linear trap quadrupole orbitrap (LC-LTQ-Orbitrap) mass spectrometry. The structures of the MEQ metabolites and their product ions were easily and reliably characterized based on the accurate MS-squared spectra and known structure of MEQ. Twenty-four metabolites were detected in chicken plasma, bile, faeces, and tissues, of which 12 were detected in vivo for the first time. The major metabolic pathways reported previously for in vitro metabolism of MEQ in chicken microsomes were confirmed in this study, including N→O group reduction, carbonyl reduction, and methyl mono-hydroxylation. In addition, deacetylation and acetyl-hydroxylation of MEQ were shown to be important metabolic pathways. Collectively, these data contribute to our understanding of the in vivo metabolism of MEQ.
authors.affiliation: College of Veterinary Medicine, National Reference Laboratory of Veterinary Drug Residues (SCAU), South China Agricultural University, Guangzhou 510642, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Shan
authors.forename: Yiming
authors.initials: Y
authors.lastname: Liu
authors.forename: Limin
authors.initials: L
authors.lastname: He
authors.forename: Huanzhong
authors.initials: H
authors.lastname: Ding
authors.forename: Xianhui
authors.initials: X
authors.lastname: Huang
authors.forename: Fan
authors.initials: F
authors.lastname: Yang
authors.forename: Yafei
authors.initials: Y
authors.lastname: Li
authors.forename: Zhenling
authors.initials: Z
authors.lastname: Zeng
mesh_terms: D000818:Animals; D001646:Bile / Q000737:chemistry; D002645:Chickens; D002853:Chromatography, Liquid / Q000379:methods*; D005243:Feces / Q000737:chemistry; D005260:Female; D008297:Male; D055442:Metabolome; D011810:Quinoxalines / Q000032:analysis / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D014018:Tissue Distribution; D019155:Veterinary Drugs / Q000032:analysis / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics
chemical_list: C545385:Mequindox; D011810:Quinoxalines; D019155:Veterinary Drugs