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.
Footnotes
This work was supported by the National Basic Research Program of China (973 Program) [Grant 2009CB118802]; the National Natural Science Foundation of China [Grant 31172087]; the Program for New Century Excellent Talents in University [Grant NCET-08-0643]; and the Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme (2009).
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material.
ABBREVIATIONS:
- MEQ
- mequindox
- MTT
- 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
- HPLC
- high-performance liquid chromatography
- IPTG
- isopropyl-β-d-(−)thiogalactoside
- CBR1
- carbonyl reductase 1
- cCBR1
- chicken carbonyl reductase 1
- pCBR1
- porcine carbonyl reductase 1
- MEN
- menadione
- QUE
- quercetin
- IPTG
- isopropyl β-d-thiogalactoside.
- Received November 1, 2011.
- Accepted January 19, 2012.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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