IMR Press / FBE / Volume 4 / Issue 2 / DOI: 10.2741/e400
Open Access Review

Toxicological significance of azo dye metabolism by human intestinal microbiota

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1 Division of Microbiology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, AR 72079-9502, USA
Academic Editor:King-Thom Chung
Front. Biosci. (Elite Ed) 2012, 4(2), 568–586; https://doi.org/10.2741/e400
Published: 1 January 2012
(This article belongs to the Special Issue Arylamine induced carcinogenesis)
Abstract

Approximately 0.7 million tons of azo dyes are synthesized each year. Azo dyes are composed of one or more R1-N=N-R2 linkages. Studies have shown that both mammalian and microbial azoreductases cleave the azo bonds of the dyes to form compounds that are potentially genotoxic. The human gastrointestinal tract harbors a diverse microbiota comprised of at least several thousand species. Both water-soluble and water-insoluble azo dyes can be reduced by intestinal bacteria. Some of the metabolites produced by intestinal microbiota have been shown to be carcinogenic to humans although the parent azo dyes may not be classified as being carcinogenic. Azoreductase activity is commonly found in intestinal bacteria. Three types of azoreductases have been characterized in bacteria. They are flavin dependent NADH preferred azoreductase, flavin dependent NADPH preferred azoreductase, and flavin free NADPH preferred azoreductase. This review highlights how azo dyes are metabolized by intestinal bacteria, mechanisms of azo reduction, and the potential contribution in the carcinogenesis/mutagenesis of the reduction of the azo dyes by intestinal microbiota.

Keywords
Azo dye
Azoreductase
Degradation
Metabolite
Genotoxicity
Intestinal Microbiota
Review
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