Species and tissue specificities of I-compounds as contrasted with carcinogen adducts in liver, kidney and skin DNA of Sprague-Dawley rats, ICR mice and Syrian hamsters

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Abstract
I-compounds are age-related bulky DNA modifications that are detected in untreated animals by 32P-postlabeling. To characterize their properties, I-compounds were compared with carcinogen-DNA adducts in liver, kidney and skin of three rodent species. Weanling female Sprague-Dawley rats, ICR mice and Syrian hamsters were fed Tekiad LM485 chow diet for 3 months and raised concurrently and strictly under the same environmental conditions. Animals of each species were treated topically with 24 μmol/kg dibenz [α,j]acridine per day for 3 days, then by gavage once with a mixture of safrole and 7,12-dlmethylbenz[α]anthracene (60 and 80 μmol/kg respectively), or with one of the individual carcinogens, Liver, kidney and skin DNA from carcinogen-exposed (24 h after treatment) and unexposed animals was analyzed by the monophosphate version of the 32P-postlabeling assay. While each of the three carcinogens produced qualitatively identical major adduct patterns in all samples examined, I-compounds in untreated animals showed distinct species- and tissue- dependent profiles. Rats displayed the highest I-compound levels but the lowest adduct levels in both liver and kidney among the three species. These findings demonstrate fundamental differences between I-compounds and carcino gen-DNA adducts, and support the hypothesis that I-compound formation is primarily related to species-specific, i.e. genetically determined, normal metabolic activities rather than exposure to environmental genotoxic carcinogens.

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