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Distinction of mutagenic carcinogens from a mutagenic noncarcinogen in the big blue transgenic mouse
M L Cunningham1, J J Hayward, B S Shane
1Environmental Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA. cunning1@niehs.nih.gov
Abstract:
The aromatic amines 2,4-diaminotoluene (2,4-DAT) and 2,6-diaminotoluene (2,6-DAT) are structural isomers that have been extensively studied for their mutagenic and carcinogenic characteristics. Both compounds are rapidly absorbed after oral administration and are equally mutagenic in the Ames test; however, 2,4-DAT is a potent hepatocarcinogen, whereas 2,6-DAT does not produce an increased incidence of tumors in rats or mice at similar doses. The Big Blue transgenic B6C3F1 mouse carries multiple copies of the lacl mutational target gene. Our studies were designed to determine whether the Big Blue system could be used to detect differences in the vivo mutagenic activity between the carcinogen-noncarcinogen pair 2,4-DAT and 2,6-DAT and to determine whether the in vivo mutagenesis assay results correspond to the rodent carcinogen bioassay results. Male B6C3F1 transgenic mice were exposed to 2,4-DAT or 2,6-DAT at 0 or 1,000 ppm in the diet for 30 and 90 days or to dimethylnitrosamine as a positive control. Mutant frequencies were nearly identical for all three groups at 30 days, while at 90 days the mutant frequency for the hepatocarcinogen 2,4-DAT (12.1 +/- 1.4 x 10(-5)) was significantly higher (p < 0.01) as compared to both age-matched (spontaneous) controls (5.7 +/- 2.9 x 10(-5)) and the 2,6-DAT-exposed group (5.7 +/- 2.4 x 10(-5)). Results from this study demonstrate that the Big Blue transgenic mutation assay can distinguish differences in vivo between the mutagenic responses of hepatic carcinogens ad a noncarcinogen; is sensitive to mutagens through subchronic dietary exposure; and yields a differential response depending upon the length of time mice are exposed to a mutagen.
Insights
The Big Blue transgenic mouse assay detected higher mutagenicity for 2,4-diaminotoluene (2,4-DAT), a liver carcinogen, compared to non-carcinogen 2,6-diaminotoluene (2,6-DAT) after 90 days of exposure. This demonstrates the assay
Area of Science:
- Toxicology
- Genetics
- Carcinogenesis
Background:
- 2,4-diaminotoluene (2,4-DAT) is a potent hepatocarcinogen, while its isomer 2,6-diaminotoluene (2,6-DAT) is not carcinogenic in rodents.
- Both 2,4-DAT and 2,6-DAT are equally mutagenic in the Ames test, highlighting a discrepancy between in vitro mutagenicity and in vivo carcinogenicity.
- The Big Blue transgenic B6C3F1 mouse model possesses multiple copies of the lacl gene, serving as a target for detecting mutations in vivo.
Purpose of the Study:
- To evaluate the efficacy of the Big Blue transgenic mouse system in differentiating in vivo mutagenic activity between the hepatocarcinogen 2,4-DAT and the non-carcinogen 2,6-DAT.
- To ascertain whether the in vivo mutagenesis assay results correlate with established rodent carcinogen bioassay findings for these compounds.
Main Methods:
- Male B6C3F1 Big Blue transgenic mice were administered diets containing 0 or 1,000 ppm of 2,4-DAT or 2,6-DAT for 30 and 90 days.
- Dimethylnitrosamine was used as a positive control in the study.
- Mutant frequencies in the lacl gene were quantified to assess in vivo mutagenicity.
Main Results:
- At 30 days of exposure, mutant frequencies were comparable across all groups, including controls.
- After 90 days, the mutant frequency in mice exposed to 2,4-DAT (12.1 ± 1.4 x 10^-5) was significantly higher (p < 0.01) than in age-matched controls (5.7 ± 2.9 x 10^-5) and mice exposed to 2,6-DAT (5.7 ± 2.4 x 10^-5).
- The Big Blue assay revealed a differential mutagenic response dependent on the duration of exposure.
Conclusions:
- The Big Blue transgenic mutation assay successfully distinguished the in vivo mutagenic differences between the hepatocarcinogen 2,4-DAT and the non-carcinogen 2,6-DAT.
- The assay demonstrated sensitivity to mutagens following subchronic dietary exposure.
- The findings indicate that the Big Blue system can yield differential responses based on exposure duration, aligning with carcinogenicity data.