title: Carbonyl reduction of mequindox by chicken and porcine cytosol and cloned carbonyl reductase 1.
abstract: Mequindox (MEQ) is a novel synthetic quinoxaline 1,4-dioxides derivative, which is widely used as a veterinary drug and animal feed additive. However, the metabolic mechanism of MEQ is rarely reported. The N-oxide reduction mechanism of MEQ was reported in our previous work. In this article, the toxicity and the reduction of the carbonyl of MEQ were studied. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assays demonstrated that the carbonyl-reduced MEQ, 2-isoethanol MEQ was much less toxic than MEQ. High-performance liquid chromatography analysis showed that the cytosol extracts of chicken and pig livers were able to reduce MEQ to 2-isoethanol MEQ and the reaction was NADPH-dependent. Further study via enzyme-inhibitory experiment revealed that carbonyl reductase 1 (CBR1) participated in this metabolism. The enzyme activity analysis showed that both chicken CBR1 (cCBR1) and porcine CBR1 (pCBR1) were capable of catalyzing the carbonyl reduction of MEQ and its N-oxide reductive metabolite, 1-deoxymequindox. By comparison of the kinetic constants, we observed that the activity of cCBR1 was higher than pCBR1 to MEQ and the standard substrate of CBR1, menadione. On the other hand, both CBR1s exhibited higher activity to 1-deoxymequindox than MEQ. Mutation analysis suggested that the difference of amino acid at position 141/142 may be one possible reason that caused the activity difference between cCBR1 and pCBR1. Thus far, CBR1 was first reported to participate in the carbonyl reduction of MEQ. Our results will be helpful to recognize the metabolic pathways of quinoxaline drugs deeply and to provide a theoretical basis for controlling the negative effects of these drugs.
authors.affiliation: College of Life Sciences, South China Agricultural University, 483 Wushan Road, Tianhe District, Guangzhou 510642, China.
authors.forename: Xianqing
authors.initials: X
authors.lastname: Tang
authors.forename: Peiqiang
authors.initials: P
authors.lastname: Mu
authors.forename: Jun
authors.initials: J
authors.lastname: Wu
authors.forename: Jun
authors.initials: J
authors.lastname: Jiang
authors.forename: Caihui
authors.initials: C
authors.lastname: Zhang
authors.forename: Ming
authors.initials: M
authors.lastname: Zheng
authors.forename: Yiqun
authors.initials: Y
authors.lastname: Deng
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001711:Biotransformation; D002470:Cell Survival / Q000187:drug effects; D002645:Chickens / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D003600:Cytosol / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D056945:Hep G2 Cells; D006801:Humans; D008099:Liver / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011810:Quinoxalines / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D016415:Sequence Alignment; D013045:Species Specificity; D034421:Sus scrofa / Q000378:metabolism
chemical_list: C545385:Mequindox; D011810:Quinoxalines; D000429:Alcohol Oxidoreductases