Dietary effects of 2% curcumin supplementation with two types of protein on NMU-induced mammary carcinogenesis in Sprague-Dawley rats
The objectives of this study were to investigate the effects of AIN-93G diets with protein provided as either casein or soy with (2%w/w) or without curcumin, on N-nitroso-N-methylurea (NMU)-induced mammary carcinogenesis and on biochemical indices of hepatic and renal functions in female Sprague-Dawley rats. One hundred female Sprague-Dawley rats (7-wk-old) were injected with NMU (50 mg/kg body weight) via the tail vein. At 9 weeks of age they were randomly assigned to one of the four experimental diets (n = 25) containing 20% casein (C) or soy protein isolate (S) with or without curcumin (U) supplementation. At the end of study period (22 weeks post NMU), the tumor incidence for groups C, CU, S and SU were 56%, 87%, 64% and 56%, respectively. These results indicate that curcumin supplementation significantly increased the tumor incidence when casein was the protein (87%) but not when soy (56%) was used. There were no differences in the tumor burden, tumor latency or tumor multiplicity. Histopathological diagnoses of the tumor specimens revealed that both palpable and non-palpable tumors from all the groups were adenocarcinomas. Curcumin levels could not be detected in either the serum or the liver. The lipid profile was analyzed by detecting the serum total-cholesterol, HDL-cholesterol and triacylglycerol levels. There were no significant differences found between the groups. To investigate the different effects of curcumin supplementation due to protein type, biochemical indices of hepatic (aspartate amino transferase, AST) and renal (blood urea nitrogen, BUN and serum creatinine) functions were performed. The results showed that AST was significantly lower in group S than group C. Serum creatinine level was not affected by either curcumin supplementation or protein type; however, BUN level was significantly higher in the rats fed soy-based diets than in those fed casein-based diets regardless of curcumin supplementation. These results indicate that 2% curcumin supplementation does not inhibit mammary tumor incidence and is higher when casein is the protein source. It does not influence normal hepatic and renal function in rats fed casein or soy-based diets. Neither the protein type nor the curcumin supplementation had any lipid lowering effect (This study was funded by Human Nutrition Research Fund, Texas Woman's University).