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Persistence, gestation stage-dependent formation and interrelationship of benzo[a]pyrene-induced DNA adducts in mothers, placentae and fetuses of Erythrocebus patas monkeys
Divisions of Environmental Toxicology and Epidemiology and Biostatistics, Department of Preventive Medicine and Community Health, The University of Texas Medical Branch Galveston, TX 77555
1Laboratory of Comparative Carcinogenesis, Division of Cancer Etiology, National Cancer Institute, Frederick Cancer Research and Development Center Frederick, MD 21702
2BioQual, Inc. Rockville, MD 20850, USA
Since DNA adducts have been detected in the placentae of pregnant women who smoke cigarettes, the importance of these adducts as biomarkers of fetal exposure and risk has been evaluated using a non-human primate as a model. Pregnant Erythrocebus patas monkeys on days 50, 100 or 150 of gestation (term = 160 ± 5 days) were treated once with 5–50 mg/kg benzo[a]pyrene (B[a]P), p.o. Fetuses were removed by Cesarean section 1–50 days after treatment and analyzed for DNA adducts by the nuclease P1 version of the 32P-postlabeling method. B[a]P induced high levels of DNA adducts in all fetal organs, placentae and maternal livers in all three trimesters of gestation. DNA adduct levels were higher in mid-gestation compared to early and late gestation. The major adduct detected was 10ß-(deoxyguanosin)-N2-yl-7ß,8
,9-trihydroxy-7,8,9,10-tetrahydro-B[a]P. The adduct levels in fetal tissues increased with B[a]P dose, but at a much lower rate than in placenta or maternal livers. Preference in binding to DNA of various fetal organs was more apparent in early gestation compared to late gestation and at lower doses compared to higher doses. During early gestation and at low doses, B[a]P produced a similar level of DNA adducts in fetal lung, fetal liver, maternal liver and placenta. Individual fetal organ adduct levels correlated significantly with placental adduct levels, indicating placental and/or maternal contribution to genotoxic injuries in fetuses. However, the slopes of linear regression lines of correlation analyses varied among organs and among gestation stages at treatment, indicating fetal contribution to its own genotoxic injuries. DNA adduct levels in fetal skin were the lowest of all fetal organs tested and less affected by gestational stages at time of treatment. In contrast, DNA adduct levels in fetal liver exhibited distinct gestation stage specificity with higher adduct levels attained during mid-gestation compared to other stages of gestation. Adduct levels decreased at a much faster rate during the first 10–15 days compared to 15–50 days after B[a]P treatment. However, 10% of DNA adducts persisted 50 days after treatment in all organs studied. Together, the results suggest that placental adduction accurately indicates fetal exposure. Toxicokinetics of B[a]P and its metabolites as well as maternal, placental and fetal competence in activation and deactivation of B[a]P may be critical determinants in overall fetal risk to genetic damage. Importantly, maximal sensitivity to transplacental DNA damage may be during mid-gestation.
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