Genotoxicity of 3-methylcholanthrene in liver of transgenic big Blue mice.
Transgenic mice provide a unique tool for studying the tissue specificity and mutagenic potential of chemicals. Because 3-methylcholanthrene (3MC) was found mutagenic in bacteria, clastogenic in bone marrow, and induces DNA adducts in animals, we were interested to determinine whether this xenobiotic provokes (1) cell proliferation, (2) transcriptional activity changes, (3) DNA adducts, and (4) hepatic mutations in transgenic Big Blue mice carrying the lambdaLIZ phage shuttle vector. Big Blue C57/Bl male mice were treated with a single intraperitoneal dose of 80 mg/kg 3MC for 1, 3, 6, 14, or 30 days. Cell proliferation was checked by 5-bromo-2-deoxyuridine labeling and immunohistochemical detection. The maximal increase of the mitotic index was evidenced after 3 days (2.9 times the control value; P < 0.01). The relative nucleus area, reflecting the transcriptional activity, was also the highest in the treated group after 3 days: 1.86 times the control value, on average (P < 0.01). Four major DNA adducts, determined according to the [(32)P]-postlabeling method, were evidenced in liver DNA of treated mice, 6 days after the treatment: the spot intensities increased in a time-dependent manner. The mutant frequency of liver DNA was the highest after 14 days: 20.3 +/- 2.9 x 10(-5) in the treated vs. 7.6 +/- 2.7 x 10(-5) in the control mice (P < 0.01). Sequencing of the lambda lacI mutant plaques showed mainly G:C --> T:A and C:G --> A:T transversions. In conclusion, 3MC at first induced nuclear enlargement and a slight increase of cell proliferation in liver, followed by parallel formation of DNA adducts and mutations. This study shows how transgenic models allow in vivo evaluation of mechanistically simultaneous endpoints.
Rihn
B H
BH
Laboratoire de Cancérogenèse, Institut National de Recherche et de Sécurité, Vandoeuvre, France. rihn@inrs.fr
Bottin
M C
MC
Coulais
C
C
Rouget
R
R
Monhoven
N
N
Baranowski
W
W
Edorh
A
A
Keith
G
G
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002455:Cell Division / Q000187:drug effects; D018736:DNA Adducts; D017931:DNA Primers; D029968:Escherichia coli Proteins; D056968:Lac Repressors; D008099:Liver / Q000166:cytology / Q000187:drug effects*; D008748:Methylcholanthrene / Q000633:toxicity*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009153:Mutagens / Q000633:toxicity*; D009154:Mutation; D009929:Organ Size; D012097:Repressor Proteins / Q000235:genetics
D001426:Bacterial Proteins; D018736:DNA Adducts; D017931:DNA Primers; D029968:Escherichia coli Proteins; D056968:Lac Repressors; D009153:Mutagens; D012097:Repressor Proteins; D008748:Methylcholanthrene