Carcinogenesis Advance Access originally published online on April 30, 2009
Carcinogenesis 2009 30(7):1202-1208; doi:10.1093/carcin/bgp093
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Vitamin C and 
-naphthoflavone prevent estrogen-induced mammary tumors and decrease oxidative stress in female ACI rats
Department of Environmental Health Sciences, Mailman School of Public Health, Columbia University, 60 Haven Avenue, B106, New York, NY 10032, USA
1 Department of Pathology, Columbia University Medical Center, New York, NY 10032, USA
2 Department of Biostatistics, Mailman School of Public Health, Columbia University, New York, NY 10032, USA
* To whom correspondence should be addressed. Tel: +1 212 305 0528; Fax: +1 212 342 0450; Email: hb2009{at}columbia.edu
The mechanisms underlying the pathogenesis of estrogen-induced breast carcinogenesis remain unclear. The present study investigated the roles of estrogen metabolism and oxidative stress in estrogen-mediated mammary carcinogenesis in vivo. Female August Copenhagen Irish (ACI) rats were treated with 17β-estradiol (E2), the antioxidant vitamin C, the estrogen metabolic inhibitor 
-naphthoflavone (ANF), or cotreated with E2 + vitamin C or E2 + ANF for up to 8 months. E2 (3 mg) was administered as an subcutaneous implant, ANF was given via diet (0.2%) and vitamin C (1%) was added to drinking water. At necropsy, breast tumor incidence in the E2, E2 + vitamin C and E2 + ANF groups was 82, 29 and 0%, respectively. Vitamin C and ANF attenuated E2-induced alterations in oxidative stress markers in breast tissue, including 8-iso-prostane F2 formation and changes in the activities of antioxidant enzymes superoxide dismutase and glutathione peroxidase. Quantification of 2-hydroxyestradiol (2-OHE2) and 4-hydroxyestradiol (4-OHE2) formation in breast tissue confirmed that ANF inhibited 4-hydroxylation of E2 and decreased formation of the highly carcinogenic 4-OHE2. These results demonstrate that antioxidant vitamin C reduces the incidence of estrogen-induced mammary tumors, increases tumor latency and decreases oxidative stress in vivo. Further, our data indicate that ANF completely abrogates breast cancer development in ACI rats. The present study is the first to demonstrate the inhibition of breast carcinogenesis by antioxidant vitamin C or the estrogen metabolic inhibitor ANF in an animal model of estrogen-induced mammary carcinogenesis. Taken together, these results suggest that E2 metabolism and oxidant stress are critically involved in estrogen-induced breast carcinogenesis.
Abbreviations: ACI, August Copenhagen Irish; ANF, -naphthoflavone; CAT, catalase; E2, 17β-estradiol; ER, estrogen receptor; GPx, glutathione peroxidase; 8-isoPGF2, 8-iso-prostane F2; 2-OHE2, 2-hydroxyestradiol; 4-OHE2, 4-hydroxyestradiol; SOD, superoxide dismutase
Received February 27, 2009; revised April 9, 2009; accepted April 10, 2009.