The production of genotoxic agents from azo dyes

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Sweeney, E.A., 1995. The production of genotoxic agents from azo dyes. PhD, Nottingham Trent University.

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Abstract

Azo dyes are the most common synthetic colourings used in the food, pharmaceutical and cosmetic industry. Also known as coal tar dyes, they contain an aromatic ring linked by an azo bond to a second naphthalene or benzene ring. Although the potential carcinogenicity of food colourings has been assessed (largely by mutagenicity testing), and suspected dyes removed from the approved list, the potential hazard from artificial food colourings has not been fully investigated.

The intestinal flora forms a complex ecosystem that metabolises dietary and endogenous nutrients under primarily anaerobic conditions. The ingestion of azo dyes has been proposed as one source of potential genotoxic agents. Many intestinal bacteria are able to reduce the azo bond (termed azo-fission) liberating the substituted amino compounds.

Following bacterial reduction, the genotoxicity of purified amaranth and sunset yellow correlated well with that of an equimolar amount of the aminonaphthol moiety that would result from azo reduction of these dyes. l-Amino-2-naphthol-3,6-disulphonate and l-amino-2-naphthol-6- sulphonate (end-products of amaranth and sunset yellow respectively) were highly genotoxic. The other cleavage products in each case, l-aminO'naphthalene-4-sulphonate and sulphanilic acid respectively were non-mutagenic, suggesting that mutagenicity was due solely to the presence of an amino-naphthol compound.

Amaranth and sunset yellow were activated by Enterococcus faecalis to a mutagen in Salmonella typhimurium TA102 and TA104, but not in S. typhimurium TA98 or TAIOO. Testing the predicted aminonaphthol azo-fission product of both amaranth and sunset yellow resulted in positive mutagenicity. In contrast, the naphthalene moieties were found to be non-mutagenic in S. typhimurium TA102 and TA104.

Results showed the production of the active oxygen species, hydrogen peroxide and superoxide radical, from azo dyes reduced by either bacterial or chemical means. Catalase and superoxide dismutase were used to identify the formation of these active oxygens. Further examination of the predicted metabolites from azo fission showed that active oxygen species were only generated for those compounds with a hydroxyl substituent ortho to the amino function. The protective affects of desferrioxamine and o-phenanthroline against damage by reduced dyes and amino-naphthols indicated the importance of iron in the mechanism behind their toxicity. Protection by antioxidants also indicated the involvement of active oxygen species in the genotoxicity of these compounds.

Oxidative DNA damage, as expressed by 8-hydroxydeoxyguanosine (8-OHdG), was investigated in both calf thymus DNA and Escherichia coli DNA. Treatment of DNA with reduced azo dyes and aminonaphthol compounds resulted in an increase in 8-OHdG content. The presence of iron enhanced the formation of 8-OHdG, while catalase resulted in a decrease in 8-OHdG production.

These results suggest that various azo dye products maybe mutagenic, not through N-hydroxylation and esterification which is characteristic of many aromatic amines, but rather through a mechanism involving oxygen radicals and the Fenton reaction.

Item Type:

Thesis

Creators:

Sweeney, E.A.

Date:

1995

ISBN:

9781369312850

Identifiers: