Integration of in vivo genotoxicity and short-term carcinogenicity assays using F344 gpt delta transgenic rats: in vivo mutagenicity of 2,4-diaminotoluene and 2,6-diaminotoluene structural isomers.
An important trend in current toxicology is the replacement, reduction, and refinement of the use of experimental animals (the 3R principle). We propose a model in which in vivo genotoxicity and short-term carcinogenicity assays are integrated with F344 gpt delta transgenic rats. Using this model, the genotoxicity of chemicals can be identified in target organs using a shuttle vector lambda EG10 that carries reporter genes for mutations; short-term carcinogenicity is determined by the formation of glutathione S-transferase placenta form (GST-P) foci in the liver. To begin validating this system, we examined the genotoxicity and hepatotoxicity of structural isomers of 2,4-diaminotoluene (2,4-DAT) and 2,6-diaminotoluene (2,6-DAT). Although both compounds are genotoxic in the Ames/Salmonella assay, only 2,4-DAT induces tumors in rat livers. Male F344 gpt delta rats were fed diet containing 2,4-DAT at doses of 125, 250, or 500 ppm for 13 weeks or 2,6-DAT at a dose of 500 ppm for the same period. The mutation frequencies of base substitutions, mainly at G:C base pairs, were significantly increased in the livers of 2,4-DAT-treated rats at all three doses. In contrast, virtually no induction of genotoxicity was identified in the kidneys of 2,4-DAT-treated rats or in the livers of 2,6-DAT-treated rats. GST-P-positive foci were detected in the livers of rats treated with 2,4-DAT at a dose of 500 ppm but not in those treated with 2,6-DAT. Integrated genotoxicity and short-term carcinogenicity assays may be useful for early identifying genotoxic and nongenotoxic carcinogens in a reduced number of experimental animals.
Toyoda-Hokaiwado
Naomi
N
Division of Genetics and Mutagenesis, National Institute of Health Sciences, Setagaya-ku, Tokyo 158-8501, Japan.
Inoue
Tomoki
T
Masumura
Kenichi
K
Hayashi
Hiroyuki
H
Kawamura
Yuji
Y
Kurata
Yasushi
Y
Takamune
Makiko
M
Yamada
Masami
M
Sanada
Hisakazu
H
Umemura
Takashi
T
Nishikawa
Akiyoshi
A
Nohmi
Takehiko
T
D000818:Animals; D015197:Carcinogenicity Tests / Q000379:methods*; D029968:Escherichia coli Proteins / Q000235:genetics; D008099:Liver / Q000187:drug effects; D008297:Male; D009152:Mutagenicity Tests / Q000379:methods*; D009153:Mutagens / Q000633:toxicity*; D010430:Pentosyltransferases / Q000235:genetics; D010655:Phenylenediamines / Q000633:toxicity*; D051381:Rats; D011916:Rats, Inbred F344; D055647:Rats, Transgenic
D029968:Escherichia coli Proteins; D009153:Mutagens; D010655:Phenylenediamines; D010430:Pentosyltransferases; C071962:Gpt protein, E coli; C025235:2,6-diaminotoluene; C010914:2,4-diaminotoluene