Detection of oxidative DNA damage, cell proliferation and in vivo mutagenicity induced by dicyclanil, a non-genotoxic carcinogen, using gpt delta mice.
To ascertain whether measurement of possible contributing factors to carcinogenesis concurrently with the transgenic mutation assay is useful to understand the mode of action underlying tumorigenesis of non-genotoxic carcinogens, male and female gpt delta mice were given dicyclanil (DC), a mouse hepatocarcinogen showing all negative results in various genotoxicity tests, at a carcinogenic dose for 13 weeks. Together with gpt and Spi(-) mutations, thiobarbituric acid-reactive substances (TBARS), 8-hydroxydeoxyguanosine (8-OHdG) and bromodeoxyuridine labeling indices (BrdU-LIs) in the livers were examined. Whereas there were no changes in TBARS levels among the groups, significant increases in 8-OHdG levels and centrilobular hepatocyte hypertrophy were observed in the treated mice of both genders. In contrast, BrdU-LIs and liver weights for the treated females, but not the males were significantly higher than those for the controls. Likewise, the gpt mutant frequencies (MFs) in the treated females were significantly elevated, GC:TA transversion mutations being predominant. No significant alterations were found in the gpt MFs of the males and the Spi(-) MFs of both sexes. The results for the transgenic mutation assays were consistent with DC carcinogenicity in terms of the sex specificity for females. Considering that 8-OHdG induces GC:TA transversion mutations by mispairing with A bases, it is likely that cells with high proliferation rates and a large amounts of 8-OHdG come to harbor mutations at high incidence. This is the first report demonstrating DC-induced genotoxicity, the results implying that examination of carcinogenic parameters concomitantly with reporter gene mutation assays is able to provide crucial information to comprehend the underlying mechanisms of so-called non-genotoxic carcinogenicity.
Umemura
Takashi
T
Divisions of Pathology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan. umemura@nihs.go.jp
Kuroiwa
Yuichi
Y
Tasaki
Masako
M
Okamura
Toshiya
T
Ishii
Yuji
Y
Kodama
Yukio
Y
Nohmi
Takehiko
T
Mitsumori
Kunitoshi
K
Nishikawa
Akiyoshi
A
Hirose
Masao
M
D000818:Animals; D001973:Bromodeoxyuridine / Q000378:metabolism; D049109:Cell Proliferation; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured / Q000187:drug effects; D004249:DNA Damage / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D029968:Escherichia coli Proteins / Q000235:genetics / Q000502:physiology*; D005260:Female; D007605:Juvenile Hormones / Q000633:toxicity; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009152:Mutagenicity Tests; D009154:Mutation / Q000187:drug effects* / Q000235:genetics; D010430:Pentosyltransferases / Q000235:genetics / Q000502:physiology*; D017392:Thiobarbituric Acid Reactive Substances
D029968:Escherichia coli Proteins; D007605:Juvenile Hormones; D017392:Thiobarbituric Acid Reactive Substances; C121718:dicyclanil; D010430:Pentosyltransferases; C071962:Gpt protein, E coli; D001973:Bromodeoxyuridine