4-Chloro-o-phenylenediamine induces a dose-related increase in G : C -> T : A transversions and one major DNA adduct in the liver of Big Blue (R) mice after 26 weeks in feed treatment

The monocyclic aromatic amine 4-chloro-o-phenylenediamine (4-C-o-PDA), a kn own mutagen and mouse hepatocarcinogen, was tested for its in vivo mutageni c potential in the Big Blue(R) transgenic mouse assay system. Genomic DNA w as isolated from liver tissue of control and treated animals and lacI mutan ts were recovered. In an initial 2-week study 4-C-o-PDA was administered da ily per os to groups of male and female C57BL/6 Big Blue(R) mice at doses o f 0 and 200 mg/kg for 2 weeks (on working days) followed by a treatment fre e expression time of 10 days. Only a weak increase in the mutant frequencie s in females was observed. In a 26-week study, where 4-C-o-PDA was given to groups of male and female Big Blue(R) mice in feed at dietary concentratio ns of 0, 5000 and 10,000 ppm, 4-C-o-PDA was found to induce a pronounced do se-dependent increase in mutant frequencies in either sex. In the present w ork, we analyzed the mutation spectrum by automated DNA sequencing of lacI mutants from both studies. Following the 2-week administration of 4-C-o-PDA by oral gavage, no treatment-related changes were observed, whereas after 26 weeks in feed administration, there was a clear dose-dependent increase in the incidence of G:C > T:A transversions in both sexes. In addition, upo n 26-week treatment with 4-C-o-PDA, one major DNA adduct was detected by P- 33 postlabelling and subsequent multidimensional thin layer chromatography. It is concluded that 4-C-o-PDA is strongly mutagenic in the liver of mice inducing predominantly G:C > T:A transversions after 26 weeks in feed treat ment. This result indicates that the sensitivity of the Big Blue(R) transge nic assay system, in detecting a unique chemically induced mutation spectru m, is dependent on experimental parameters, such as treatment time. The dat a suggest that the formation of one major DNA adduct upon 4-C-o-PDA treatme nt may be critical for its mutagenicity. (C) 1999 Elsevier Science B.V. All rights reserved.