Carcinogenesis Advance Access originally published online on January 9, 2006
Carcinogenesis 2006 27(7):1358-1368; doi:10.1093/carcin/bgi325
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Enhanced tumorigenesis in p53 knockout mice exposed in utero to high-dose vitamin E
1 Faculty of Pharmacy and 2 Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada, M5S 2S2
* To whom correspondence should be addressed. Tel: +416 978 3221; Fax: +416 267 7797; Email: pg.wells{at}utoronto.ca
The limited antioxidative capacity of the embryo and fetus may increase their risk for cancer initiation and/or promotion by reactive oxygen species (ROS)-mediated oxidative DNA damage and/or signaling. To determine if cancer can originate in utero, a high dietary dose of the antioxidant vitamin E (VE) (10% dl-
-tocopherol-acetate) was given to cancer-prone p53 knockout mice throughout pregnancy. Although reducing fetal death (P < 0.05), in utero exposure to VE enhanced postnatal tumorigenesis in both +/– (P < 0.04) and –/– (P < 0.0008) p53-deficient offspring. VE did not alter maternal weights, offspring p53 genotypic distribution or tumor spectrum. Constitutive embryonic DNA oxidation in untreated –/– p53 embryos [gestational day (GD) 13] was higher than in +/– and +/+ p53 littermates (P < 0.05). VE reduced DNA oxidation in –/– p53 embryos (P < 0.05) without affecting +/– and +/+ p53 littermates. VE had contrasting, tissue-dependent effects on fetal (GD 19) DNA oxidation, with reductions in –/– and +/– p53-deficient fetal brains (P < 0.01), increases in skin (P < 0.05) and no effect in liver and thymus. The 250-fold increase in dietary VE levels produced only 1.6–6.3-fold, tissue-dependent increases in tissue concentrations. The greatest increase, in fetal skin, correlated with increased DNA oxidation in that tissue in –/– and +/– p53-deficient fetuses and enhanced tumorigenesis in these genotypes. These results show that some cancers may originate in utero and the risk can be enhanced by embryonic and fetal exposure to high dietary levels of VE. The elevated DNA oxidation in some tissues of untreated –/– p53 offspring suggests that ROS may contribute to their higher baseline tumor incidence. The limited and tissue-dependent disposition of VE indicates substantial conceptal regulation. The similarly selective and contrasting effects of VE on DNA oxidation may contribute to its controversial protective efficacy and suggest that its effects on tumorigenesis are cell-specific, possibly in high doses involving a pro-oxidative mechanism.
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