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32P-postlabelling analysis of DNA adducts from Fischer-344 rats administered 2,4-diaminotoluene
1Department of Environmental Health Sciences, School of Public Health, University of California, Los Angeles 90024.
Abstract:
Using 32P-postlabelling and thin layer chromatography, DNA adduct formation by the potent animal carcinogen 2,4-diaminotoluene in Fischer-344 rats was investigated. DNA from four different organs, liver, mammary gland, kidney and lung, were examined for adducts following single administration of this compound. DNA binding was detected in all four organs, with each producing one major and two minor adduct spots on autoradiograms. The adducts induced were qualitatively identical among the different organs, but quantitative differences were observed. The two target organs of 2,4-diaminotoluene induced carcinogenesis, the liver and mammary gland produced higher adduct yields, with levels up to 30-times higher than those for the two non-target organs. Since the liver is the principal target for 2,4-diaminotoluene induced carcinogenesis, we further examined DNA adducts from this site for the effects of different doses and time points. DNA binding in liver was detected following doses as low as 4.1 mumol/kg. At the highest concentration examined (2046 mumol/kg), the level of the major adduct was 29.2 adducted nucleotides per 10(7) total nucleotides. The yields for the two minor adducts were approximately one-tenth that for the major adduct. Following a 410 mumol/kg dose, DNA adduct removal over time was examined. DNA adduct removal exhibited biphasic kinetics, with a rapid initial phase followed by a slower rate of elimination. Up to 60% of maximum adduct levels persisted after 2 weeks. DNA binding by 2,4-diaminotoluene was also compared to that by its weakly carcinogenic analog, 2,4-dinitrotoluene. The two compounds produced identical adduct patterns, suggesting that they share common metabolites and adducts. Adduct yields from 2,4-dinitrotoluene, however, were lower. The results of our studies suggest that the differences in carcinogenic potency between 2,4-diaminotoluene and 2,4-dinitrotoluene, as well as the organotropic effects of 2,4-diaminotoluene may be explained, in part, by quantitative differences in the extent of DNA adduct formation.
Insights
2,4-diaminotoluene forms DNA adducts in rat organs, with higher levels in target tissues like the liver and mammary gland. These adducts persist, potentially explaining its carcinogenic potency compared to related compounds.
Area of Science:
- Toxicology and Carcinogenesis
- Molecular Biology and Biochemistry
Background:
- 2,4-diaminotoluene (2,4-DAT) is a potent animal carcinogen.
- Understanding its DNA adduct formation is crucial for explaining its organ-specific toxicity.
Purpose of the Study:
- To investigate DNA adduct formation by 2,4-DAT in Fischer-344 rats.
- To compare adduct levels across different organs and doses.
- To examine adduct persistence and compare 2,4-DAT with 2,4-dinitrotoluene (2,4-DNT).
Main Methods:
- 32P-postlabeling assay combined with thin-layer chromatography.
- Analysis of DNA from liver, mammary gland, kidney, and lung tissues.
- Dose-response and time-course studies in the liver.
Main Results:
- DNA adducts were detected in all four organs, with identical adduct patterns but quantitative differences.
- Target organs (liver, mammary gland) showed up to 30-fold higher adduct levels than non-target organs.
- Adducts were detected at low doses, showed biphasic removal kinetics, and persisted for at least 2 weeks.
Conclusions:
- Quantitative differences in DNA adduct formation correlate with the organotropic effects and carcinogenic potency of 2,4-DAT.
- Shared adduct patterns between 2,4-DAT and 2,4-DNT suggest common metabolites.
- DNA adduct levels and persistence are key factors in 2,4-DAT-induced carcinogenesis.