Prevention of Oxidative DNA Damage by Bioactive Berry Components

Abstract

The hormone 17ß-estradiol (E₂) causes oxidative DNA damage via redox cycling of its metabolites such as 4-hydroxy estradiol (4E₂). In this study, ACI rats (8 wk old) were fed either AIN-93M diet or diets supplemented with 0.5% each of mixed berries (strawberry, blueberry, blackberry, and red and black raspberry), blueberry alone (BB; 2.5%), or ellagic acid (EA; 400 ppm) from 2 wk prior to and up to 12 wk of E₂ treatment. The liver DNA was analyzed for the presence of 8-oxo-7,8-dihydroguanine (8-oxodG) and other polar adducts by ³²P-postlabeling. Compared to sham treatment, E₂ significantly increased the levels of both 8-oxodG and P-1 subgroup (259% and 214%, respectively; P< 0.05). EA diet significantly reduced E₂-induced levels of 8-oxodG, P-1, P-2, and PL-1 by 79, 63, 44, and 67%, respectively (P< 0.001). BB diet also significantly reduced the levels of P-1, P-2, and PL-1 subgroups by 77, 43, and 68%, respectively (P< 0.001). Mixed berries were, however, ineffective. In addition, aqueous extracts of berries (2%) and EA (100 μM) were tested for their efficacy in diminishing oxidative DNA adducts induced by redox cycling of 4E₂ catalyzed by copper chloride in vitro. EA was the most efficacious (90%), followed by extracts of red raspberry (70%), blueberry, and strawberry (50% each; P< 0.001).

ACKNOWLEDGMENTS

The authors would like to thank Drs. Manicka Vadhanam and Srivani Ravoori for their help with the ACI rat implants. Contributions of Isabelle Jean, a visiting summer student from Dijon, France, in preparing the berry extracts is gratefully acknowledged. This work was supported by grants from U.S. Public Health Service CA-90892 and CA-114118. H. S. Aiyer was supported, in part, by a Graduate School Fellowship from the University of Kentucky, Lexington, Kentucky. Part of the work was conducted at the authors' previous affiliation: Department of Preventive Medicine and Environmental Health and The Graduate Center for Toxicology, University of Kentucky, Lexington, Kentucky.

Notes

^a Calculated from ellagic acid contents described in Daniel et al. (29).

^b Anthocyanin contents described in Wu et al. (30).

^a Adducts were separated by 2-directional polyethyleneimine thin-layer chromatography using solvent composition as described in Materials and Methods and visualized using a Packard InstantImager®. Each subgroup of adduct was individually measured and quantified using the formula relative adduct labeling = counts per minute (cpm) adducts/cpm normal nucleotides × 1/dilution factor as described (26). The values represented are the mean of 3 separate analyses. All groups were compared to E₂ + control diet using 1-way analysis of variance followed by a Tukey's post hoc test.