Effects of a 15% orange-pulp diet on tumorigenesis and immune response in rats with colon tumors

This study evaluated whether the feeding of rats with a 15% orange-pulp die t affects the lymphatic system and the tumorigenic response in rats exposed to a high dose of carcinogen. Five-week-old Sprague Dawley rats were divid ed into 2 groups fed a control chow diet or the same diet with 15% orange p ulp. All rats were injected with 1,2-dimethylhydrazine (DMH) (20 mg/kg) wee kly for 6 weeks. At 8 months, tumors, spleens and descending colon were tak en from each group for analyses. Feeding rats the 15% orange-pulp diet did not reduce the tumor number but modified the number of adenocarcinomas foun d in the orange-pulp group compared to controls: 66.7% vs. 93.7%. The numbe r of endophytic tumors was also significantly lower in the experimental gro up: 6.3% vs. 32.3% in controls. DMH affected the size of the splenic struct ures. The size of follicles and germinal centers decreased significantly in tumor-bearing rats compared to tumor-free rats. This effect was changed in rats fed the orange-pulp diet. In tumor-bearing rats from this group, only the area of the marginal zone decreased and the red pulp increased compare d to tumor-free rats. The size of germinal centers significantly increased compared to tumor-bearing rats in controls. The total number of lymphoid ce lls decreased in germinal centers of spleens obtained from control tumor-be aring rats compared to tumor-free rats. DMH alone significantly increased t he total number of cells in the colon mucosa of the rats fed the control di et. In tumor-bearing rats exposed to the carcinogen and fed the 15% orange- pulp diet, the total number of cells and the number of Ki-67(+) cells incre ased in the depth of tumors whereas the number of CD8(+) T cells increased in the colon mucosa, at the border of tumors and its depth. The caspase-3 p rotein a cysteine protease was elevated in tumors from rats fed the orange- pulp diet. Although the 15% orange-pulp diet did not change the number of t umors in the tumor-bearing rats, feeding rats orange pulp significantly dec reased the number of endophytic tumors and increased the number of exophyti c tumors. Increased activity of T cell killers in tumors and higher level o f proteins involved with apoptosis following consumption of the orange pulp indicate a clear tumor suppressor effect of these dietary fibers.