Distinction of mutagenic carcinogens from a mutagenic noncarcinogen in the big blue transgenic mouse.

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.

Evaluation of In Vivo Mutagenicity by 2,4-Diaminotoluene and 2,6-Diaminotoluene in Liver of F344 gpt delta Transgenic Rat Dosed for 28 Days: A Collaborative Study of the gpt delta Transgenic Rat Mutation Assay

“…Thus, the results obtained in this study agreed with the previous reports as follows: 2,6-DAT give only negative results in TGR mutagenicity assays using Big Blue TM , Muta TM Mouse transgenic mice (20,21) and F344 gpt delta transgenic rats (6). Approximately 1.8 times increase was observed in the total MF in 2,6-DAT-treated group in this study; however, we speculate that this slight increase in total MF in the 2,6-DAT-treated group may have been caused by the MF (i.e., 12.82×10 -6 ) from one animal at Lab D3, which had a low colony count (i.e., 156,000) (Appendix 3).…”

“…This negative result was consistent with the results of carcinogenicity study (8) and the other in vivo genotoxicity assays (6,(17)(18)(19)(20)(21). However, weakly positive result of 2,6-DAT in the rat bone marrow micronucleus study is present (22).…”

“…2,4-DAT induces DNA damage (comets) in the mouse liver, while 2,6-DAT does not (18). 2,4-DAT induces LacI, LacZ and gpt mutations in the liver of Big Blue TM mice (19,20), Muta TM Mouse transgenic mice (21) and F344 gpt delta transgenic rats (6), respectively, while 2,6-DAT does not (6,20,21). Both 2,4-DAT and 2,6-DAT weakly induce micronuclei in rat bone marrow (22), while neither 2,4-DAT nor 2,6-DAT in peripheral blood of F344 gpt delta transgenic rat (6).…”

“…In particular, the results of TGR assays using the liver are correlated with those of the bioassays for carcinogenicity of 2,4-DAT and 2,6-DAT; however, the MF is not increased when the treatment period (19) and the sampling time (20) are not appropriate. Thus, the treatment period and the sampling time are important factors in the TGR assay protocol.…”

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

“…2,6-DAT is not carcinogenic in mice and rats, regardless of their sex ( NTP, 1980 ). Previous studies with MutaMouse ( Kirkland and Beevers, 2006 ) and Big Blue mouse ( Cunningham et al , 1996 ) indicate that 2,4-DAT is mutagenic in the liver, while 2,6-DAT is not. However, the transgenic mice employed for these studies were males, in which the hepatocarcinogenicity of 2,4-DAT is not observed.…”