The mutagenic activity of select azo compounds in MutaMouse target tissues in vivo and primary hepatocytes in vitro
- DOI
- Language of the publication
- English
- Date
- 2019-07-17
- Type
- Article
- Author(s)
- Cox, Julie A.
- White, Paul A.
- Publisher
- Elsevier
Abstract
The mutagenicity of Direct Black 38, Sudan I, and Para Red were evaluated in the in vivo MutaMouse assay and the in vitro MutaMouse primary hepatocyte (PH) assay. Direct Black 38 is an International Agency for Research on Cancer (IARC) Group 1 carcinogen and a prototypical benzidine-based azo compound that requires azo-reduction to yield a DNA-reactive metabolite. Sudan I and Para Red are structurally related azo compounds that have been detected as illegal contaminants in foods. Sudan I is an in vivo mutagen, and both it and Para Red are known to be mutagenic in vitro. Sudan I is oxidized by hepatic and/or bladder enzymes to yield a mutagenic metabolite, but little is known about Para Red. In the present study, Direct Black 38 elicited a significant mutagenic response in the bone marrow, glandular stomach, small intestine and colon in vivo, and in PHs in vitro. Sudan I elicited a weak positive response in the bone marrow and a marginally significant treatment effect in the bladder (p = 0.059); it did not elicit a significant response in PHs in vitro. Para Red elicited a positive response in the colon, as well as in PHs in vitro, albeit at a cytotoxic concentration. The findings are well aligned with the known mechanisms of action of Direct Black 38 and Sudan I; they suggest that intestinal azo-reduction plays an important role in the activation of Para Red. The MutaMouse pH results illustrate the ability of this assay to detect chemicals requiring azo-reduction; however, they also demonstrate a gap in applicability domain, as MutaMouse PHs elicit a negative response following exposure to Sudan I. Elucidation of the mechanisms underlying this gap will require further study.
Plain language summary
This study evaluates the utility of a novel gene mutation test using cultured liver cells (i.e., the MutaMouse primary hepatocyte [PH] assay) to assess genetic damage caused by select azo compounds through the comparison of the results of this test with results obtained in the MutaMouse animal exposure gene mutation test. Azo compounds comprise a large and diverse class of synthetic chemicals used extensively as dyes and pigments in a variety of industrial and commercial applications, including paints, textiles, personal care products, and inks. Some azo compounds are capable of causing genetic damage (i.e., genetic toxicity) after being metabolized in mammals, including humans. The main mechanism of action for azo compounds, such as Direct Black 38, appears to involve cleavage of the molecule by gut bacteria. Sudan I, another azo compound, is thought to require metabolism in the liver and/or bladder via a separate reaction. Para Red is similar to Sudan I and is known to cause genetic damage, but its mechanism is unknown. In this study, we found that the MutaMouse animal exposure gene mutation test results supported the proposed mechanisms of action of Direct Black 38 and Sudan I, respectively. Interestingly, the results suggest that the mechanism of action of Para Red is more similar to Direct Black 38 than to Sudan I. Both Direct Black 38 and Para Red yielded positive results in the in vitro MutaMouse PH assay. Sudan I yielded a negative result in the MutaMouse PH assay, although it is known to cause genetic damage. Overall, the results illustrate the ability of the MutaMouse PH assay to detect genetic damage following azo chemical cleavage, but also indicate an inability to detect genetic damage caused by Sudan I. Further research is required to better understand the lack of sensitivity for this chemical.
Subject
- Health,
- Health and safety