The effect of freeze-dried blueberries on N-nitrosomethylbenzylamine tumorigenesis in the rat esophagus

Previous studies in our laboratory have demonstrated the inhibitory effects of freeze-dried strawberries and black raspberries on N-nitrosomethylbenzylamine (NMBA)-induced tumorigenesis in the rat esophagus. In addition, organic extracts from strawberries and black raspberries were shown to inhibit benzo[a]pyrene-induced transformation of Syrian hamster embryo (SHE) cells in vitro. In the present study, we evaluated blueberries for their ability to inhibit NMBA tumorigenesis in the rat esophagus. Blueberries, like strawberries and black raspberries, contain multiple cancer preventive agents, and are among the most heavily consumed berries in the American diet. They differ from strawberries and black raspberries, however, in that they contain only small amounts of the chemopreventive agent ellagic acid. Two weeks prior to NMBA treatment, animals were placed on a control diet or diets containing 5 and 10% freeze-dried blueberries. The animals were fed berry diets or control diets for the duration of the study. NMBA treatment was once per week for 15 weeks. At 25 weeks, 5 and 10% blueberries produced no significant differences in tumor incidence, multiplicity, or size when compared to NMBA-treated controls. In addition, blueberries did not reduce the formation of NMBA-induced O-6-methylguanine adducts in esophageal DNA when fed at 10% of the diet. Blueberries appear to lack components that inhibit the initiation and progression of NMBA-induced tumorigenesis in the rat esophagus.