The combined effect of quality of dietary protein and 40% dietary restriction during promotion on DMBA-induced mammary tumorigenesis in rats

One hundred twenty-six female Sprague-Dawley weanling rats were fed the AIN-76 diet, ad libitum until 9 weeks of age. At 56 days of age, blood serum was collected from 6 rats and analyzed for the concentrations of total cholesterol (TC), high density lipoprotein-cholesterol (HDL-C), and triacylglycerol (TG). Of the remaining 120 rats, 96 rats were intragastrically administered with DMBA (5 mg/100 g body weight) and 24 rats were given sesame oil alone. At 9 weeks of age, sera from 6 DMBA- and 6 sesame oil-treated rats were analyzed for TC, TG, and HDL-C. The remaining 90 DMBA- and 18 sesame oil-treated rats were then randomly assigned to one of the three dietary treatment groups. The CA group was fed the casein diet, ad libitum. Groups CX and WX were fed the casein restricted diet and wheat gluten restricted diet, respectively, and both groups were given 60% of the intake of the CA group. When the first palpable tumor of the first 10 rats reached 1-2 cm in diameter, the tumors were excised for pathological examination. At the same time, blood was taken for the determination of serum TC, TG, and HDL-C. The remaining rats were fed their respective experimental diets until the termination of the study (26 weeks of age). Sera from 6 rats in each dietary treatment were also analyzed for the concentration of TC, HDL-C, and TG.

At necropsy, palpable tumor incidence for the CA group (90%) was significantly higher than those of the CX (47%) or the WX (30%) groups. The latent period for CA group (9.2 weeks) was significantly shorter (p 0.05) than the CX (12.1 weeks) or the WX (12.7 weeks) groups. Total tumor incidence, tumor count, tumor burden and total multiple tumor incidence were also significantly higher (p 0.05) in the CA group compared to CX or WX group. These data demonstrate a strong beneficial effect of 40% dietary restriction on DMBA-induced mammary tumorigenesis during the promotion period. These results also suggest that the reduction of energy intake was more effective at inhibiting the development of mammary tumor than the quality of dietary protein.

No association was observed between the appearance or the advancement of mammary tumor and the concentrations of serum TC, HDL-C, and TG in the rats receiving DMBA. Serum TC concentration was significantly higher (p 0.05) in CA group than the WX group when the first tumor was 1-2 cm in diameter. Rats in the CX and WX group bearing tumors 1-2 cm in diameter and at termination had lower serum TG concentrations (p 0.05) than the CA group at each period. Dietary restriction resulted in significantly reduced serum TC and TG concentrations. The data indicate that mammary tumor development induced by DMBA was not associated with serum lipid profile of the rats.