Effects of caloric restriction on mammary gland gene expression in virgin Sprague-Dawley rats treated with DMBA.

A64

INTRODUCTION: Experimentally-induced mammary tumors in rats constitute one of the most powerful tools for studying the pathogenesis of mammary cancer and, in particular, the molecular mechanisms involved in neoplastic progression. Furthermore, in vivo experimental animal models provide information not otherwise available in human populations. 7,12-dimethylbenz[a] anthracene (DMBA) induced rat mammary carcinomas have several similarities to human breast cancers including: histopathology, origination in the ductal epithelial cells, and hormone dependence. Caloric restriction has been shown to reduce the incidence of both spontaneous and chemically induced mammary tumors; however, the mechanism remains to be established. AIMS: We designed an animal study to: (a) identify early biological alterations in mammary gland carcinogenesis using an integrated genomic, proteomic and metabolomic approach; and (b) understand how a moderate caloric restriction intervention could act interfering with this process. MATERIALS AND METHODS: Two hundred and four 7wk-old virgin female Sprague-Dawley rats were randomized into 4 experimental groups with a single i.g. 40 mg/kg b.w. DMBA exposure and 30% caloric restriction (CR) as the experimental treatment variables: 1) DMBA treated ad libitum-fed (DMBA); 2) DMBA treated and calorie restricted (DMBA-CR); 3) CR fed; and 4) ad libitum fed (Control). Ad libitum fed rats received the standard diet while CR rats were fed 30% less amount of the same formula. In order to identify early alternations associated with mammary tumor development, interim sacrifices were performed. At 2, 4, 6, 8, 13, and 14 weeks after DMBA administration, 7 animals randomly chosen from each experimental group, were sacrificed and necropsied. Urine, blood and tissue samples were collected at each time point. The Affymetrix oligo microarray platform (GeneChip® Rat Genome 230 2.0 Array) was used to examine global gene expression patterns in mRNA isolated from the mammary glands. RESULTS: The CR treatment had a statistically significant effect on animals mean body weight. At various time points, CR treatment was associated with a decline in: tumor incidence, multiplicity, tumor growth and tumor size. Furthermore, the localization of mammary gland tumors differed between DMBA and DMBA+CR groups. The preliminary results obtained from gene expression analysis on thoracic mammary glad samples collected respectively after 2 (T2) and 6 (T4) weeks from DMBA treatment will be presented. The global gene expression patterns of the 4 experimental groups show a distinct trend for time and CR.