The over-all objective of this study is to determine the biologic mechanism(s) involved with the increased mammary tumor burden in rats fed an enriched casein diet supplemented with methionine.
Specific aim of this experiment is to determine in mammary epithelial tissue whether the metabolic pathways associated with polyamine biosynthesis and transmethylation metabolism are modified in rats fed exogenous methionine and enriched protein diet. Induction of ornithine decarboxylase (ODC) and increased polyamine synthesis (putrescine, spermidine and spermine) is associated with increased cell proliferation. Conversely studies have demonstrated that diets deficient in methyl donors (i.e. methionine and/or choline) enhance hepatocarcinogenesis. Varying levels of dietary methionine could affect the synthesis of S-adenosylmethionine (Ado Met) an important intermediate in these pathways. Utilizing the 2-generation animal model, our preliminary studies have indicated increased ODC activity in normal and carcinogen treated mammary epithelial tissue in rats fed an enriched casein diet supplemented with methionine. The increased activity correlated positively to increased mammary tumor burden. However a reported study utilizing a post-lactation model and a high methionine diet showed no effect on tumor burden. The experiments have been designed to determine the interactive effect of varying concentration of dietary methionine-casein and animal model on the concentration of selected intermediates in these metabolic pathways. Selected intermediates will include the following: ornithine decarboxylase, putrescine, spermidine and spermine, methionine, S- adenosylmethionine, adenosylhomocysteine, decarboxylated adenosylmethionine, methionine adenosyltransferase and S- adenosylmethionine decarboxylase. In addition, tissue samples will be analyzed for DNA, RNA and protein concentration and at selected ages DNA index, ploidy and S-phase fraction will be determined. These intermediates will be measured as a function of age in normal developing mammary epithelial and liver tissues. Following treatment with the carcinogen N-nitrosomethylurea (NMU), metabolites will be analyzed in mammary and liver tissue throughout the tumor initiation phase. Diet formulations will be evaluated for their influence on mammary tumor burden, tumor histologic characteristics and concentration of metabolites. Tumor burden will be related to metabolic pathway, animal model and dietary protein-casein concentration.
