Carcinogenesis Advance Access originally published online on July 28, 2007
Carcinogenesis 2007 28(11):2419-2425; doi:10.1093/carcin/bgm170
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ß-Glucuronidase in human intestinal microbiota is necessary for the colonic genotoxicity of the food-borne carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline in rats
1 UR910 Ecology and Physiology of the Digestive Tract, Institut National de la Recherche Agronomique, F-78352 Jouy-en-Josas Cedex, France
2 Department of Food Chemistry and Technology, Graz University of Technology, Petersgasse 12/2, A-8010 Graz, Austria
3 Present address: UR106 Nutrition, Food, Societies, Institut de Recherche pour le Developpement, BP 64501, 911 avenue Agropolis, F-34394 Montpellier Cedex 05, France
4 Present address: UR888 Dairy Research and Applied Genetics, Institut National de la Recherche Agronomique, F-78352 Jouy-en-Josas Cedex, France
* To whom correspondence should be addressed. Tel: +33 1 3465 2465; Fax: +33 1 3465 2462;Email: sylvie.rabot{at}jouy.inra.fr
2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) is a genotoxic/carcinogenic compound formed in meat and fish during cooking. Following absorption in the upper part of the gastrointestinal tract, IQ is mainly metabolized in the liver by xenobiotic-metabolizing enzymes. Among them, UDP-glucuronosyl transferases lead to harmless glucuronidated derivatives that are partly excreted via the bile into the digestive lumen, where they come into contact with the resident microbiota. The purpose of this study is to investigate if microbial ß-glucuronidase could contribute to IQ genotoxicity by releasing reactive intermediates from IQ glucuronides. We constructed a ß-glucuronidase-deficient isogenic mutant from a wild-type Escherichia coli strain carrying the gene uidA encoding this enzyme and compared the genotoxicity of IQ in gnotobiotic rats monoassociated with the wild-type or the mutant strain. The Comet assay performed on colonocytes and hepatocytes showed that the presence of ß-glucuronidase in the digestive lumen dramatically increased (3-fold) the genotoxicity of IQ in the colon. This deleterious effect was paralleled by slight modifications of the pharmacokinetics of IQ. The urinary and faecal excretion of the parent compound and its conjugated derivatives reached a maximum 24–48 h after gavage in rats harbouring the ß-glucuronidase-deficient strain. In rats associated with the wild-type strain, the kinetics of urinary excretion showed a biphasic curve with a second, smaller peak after 144 h. This is the first in vivo demonstration that bacterial ß-glucuronidase plays a pivotal role in the genotoxicity of a common food-borne carcinogen.
Abbreviations: ANOVA, analysis of variance; HA, heterocyclic aromatic amine; IQ, 2-amino-3-methylimidazo[4,5-f]quinoline; IQ-N-glucuronide, N2-(ß-1-glucosiduronyl)-2-amino-3-methylimidazo[4,5-f]quinoline; IQ-sulphamate, N-(3-methylimidazo[4,5-f]quinolin-2-yl)sulphamic acid; IQ-5-O-glucuronide, 2-amino-5-(ß-1-glucosiduronyloxy)-3-methylimidazo[4,5-f]quinoline; IQ-5-O-sulphate, 2-amino-3-methylimidazo[4,5-f]quinolin-5-yl sulphate; p.a., peak area; PhIP, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine
Received March 10, 2007; revised July 19, 2007; accepted July 20, 2007.