Inhibition of N-nitrosomethylbenzylamine-induced tumorigenesis in the rat esophagus by dietary freeze-dried strawberries

In the present study, we examined the ability of dietary freeze-dried straw berries to inhibit N-nitrosomethylbenzyl-amine (NMBA)-induced tumorigenesis in the rat esophagus, Initially, we conducted a bioassay to determine the effects of dietary freeze-dried strawberries on esophageal tumor developmen t. Two weeks prior to NR IBA treatment, animals were placed on a control di et or diets containing 5 and 10% freeze-dried strawberries. NMBA treatment was once per week for 15 weeks. At 30 weeks, 5 and 10% freeze-dried strawbe rries in the diet caused significant reductions in esophageal tumor multipl icity of 24 and 56%, respectively. Based on these results, we conducted stu dies to determine potential mechanisms by which freeze-dried strawberries i nhibit tumorigenesis, In a short-term bioassay, we evaluated the effects of dietary freeze-dried strawberries on the formation of O-6-methylguanine in the rat esophagus, Animals were placed on control diet or diets containing 5 and 10% freeze-dried strawberries for two weeks. At the end of this peri od, animals received a single subcutaneous dose of NMBA and were killed 24 h later. A significant decrease in O-6-methylguanine levels was observed in the esophageal DNA of animals fed strawberries, suggesting that one or mor e components in strawberries influence the metabolism of NMBA to DNA-damagi ng species. Finally, in order to evaluate post-initiation effects, we condu cted a study where freeze-dried strawberries were administered in the diet only following NMBA treatment. Animals were placed on control diet and dose d with NMBA three times per week for 5 weeks. Immediately following NMBA tr eatment, animals were placed on control diet or diets containing 5 and 10% freeze-dried strawberries. At 25 weeks, 5 and 10% freeze-dried strawberries in the diet significantly reduced tumor multiplicity by 38 and 31%, respec tively. Our data suggest that dietary: freeze-dried strawberries effectivel y inhibit NMBA-induced tumorigenesis in the rat esophagus.