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INDUCTION OF CYP1A1 AD CYP1B1 AND FORMATION OF DNA ADDUCTS IN C57BL/6, BALB/C, AND F1 MICE FOLLOWING IN UTERO EXPOSURE TO 3-METHYLCHOLANTHRENE
Citation:
XU, M., G. B. NELSON, J. E. MOORE, T. P. MCCOY, J. DAI, R. A. MANDERVILLE, J. A. ROSS, AND M. S. MILLER. INDUCTION OF CYP1A1 AD CYP1B1 AND FORMATION OF DNA ADDUCTS IN C57BL/6, BALB/C, AND F1 MICE FOLLOWING IN UTERO EXPOSURE TO 3-METHYLCHOLANTHRENE. TOXICOLOGY AND APPLIED PHARMACOLOGY. Elsevier Online, New York, NY, online(online):online, (2005).
Description:
Fetal mice are more sensitive to chemical carcinogens than are adults. Previous studies from our laboratory demonstrated differences in the mutational spectrum induced in the Ki-ras gene from lung tumors isolated from [D2 x B6D2F1]F2 mice and Balb/c mice treated in utero with 3�methylcholanthrene (MC). We thus determined if differences in metabolism, adduct formation, or adduct repair influence strain-specific responses to transplacental MC exposure in C57BL/6 (B6), Balb/c (BC), and reciprocal F l crosses between these two strains of mice. The induction of Cyp1a1 and Cyp1b1 in fetal lung and liver tissue was determined by quantitative fluorescent real time PCR. MC treatment caused maximal induction of Cyplal and Cyplbl RNA 2 to 8 hr after injection in both organs. RNA levels for both genes then declined in both fetal organs, but a small biphasic, secondary increase in Cypla1 was observed specifically in the fetal lung 24 to 48 hr after MC exposure in all 4 strains. Cyplal induction by MC at 4 hr was 2 to 5 times greater in fetal liver (7,000 to 16,000-fold) than fetal lung (2,000 to 6000-fold). Cyplbl induction in both fetal lung and liver were similar and much lower than that observed for Cyplal, with induction ratios of 8 to 18-fold in fetal lung and 10 to 20-fold in fetal liver. The overall kinetics and patterns of induction were thus very similar across the 4 strains of mice. The only significant strain-specific effect appeared to be the relatively poor induction of Cyplbl in parental B6 mice, especially in fetal lung tissue. We also measured the levels of MC adducts and their disappearance from lung tissue by the P32post�labeling assay on gestation days 18 and 19 and postnatal days 1, 4, 11, and 18. Few differences were seen between the different strains of mice; the parental B6 mice had nominally higher levels of DNA adducts 2 (gestation day 19) and 4 (postnatal day 1) days after injection, although this was not statistically significant. These results indicate that differences in Phase I metabolism of MC and formation of MC-DNA adducts are unlikely to account for the marked differences observed in the Ki-ras mutational spectrum seen in previous studies. Further, the results suggest that other genetic factors may interact with chemical carcinogens in determining individual susceptibility to these agents during development.