Inhibitory effects of freeze-dried milk fermented by selected Lactobacillus bulgaricus strains on carcinogenesis induced by 1,2-dimethylhydrazine in rats and by diethylnitrosamine in hamsters

Fermented milk products might be used for cancer chemoprevention due to the ir putative anticarcinogenic and antitumor activities. The diet was supplem ented with freeze-dried milk fermented by Lactobacillus bulgaricus strain L BB.B144 (product FFM.B144) added throughout the experiment at doses of 1.3 g and 2.5 g per rat, 5 times a week starting 3 weeks before the first carci nogen injection. This treatment significantly inhibited, by 26.2-28.6% and by 34.2%, the total intestinal carcinogenesis induced by 1,2-dimethylhydraz ine (DMH, 21 mg/kg, s.c., once per week for 20 weeks) in male and female BD 6 rats, respectively. FFM.B144 decreased the tumor incidence and multiplici ty in large bowel, caecum, and duodenum. Protective effects were better exp ressed in female animals, with exception of that observed in duodenum. Supp lementation of diet with freeze-dried milk fermented by Lactobacillus bulga ricus strain LBB.B5 (product FFM.B5) inhibited DMH-induced carcinogenesis o nly in the large bowel, but had no significant protective effect when all i ntestinal tumors were taken into account. However, both freeze-dried produc ts favorably shifted the differentiation of large bowel tumors by increasin g the proportion of benign and highly differentiated malignant tumors and d ecreasing in parallel the number of poorly differentiated carcinomas withou t influencing the tumor size. A lower number of cases with visible mesenter ial metastasis was also observed in FFM-treated rats. In addition, both FFM .B144 and FFM.B5 significantly inhibited, by 26-33%, the induction in the s ame rats of ear-duct tumors. FFM.B144 but not FFM.B5 was also effective in inhibiting the tracheal carcinogenesis induced in Syrian golden hamsters by diethylnitrosamine (DEN, 100 mg/kg, two s.c. injections), the protective e ffect being better expressed in female animals. The anticarcinogenic potent ial of some fermented milk products might be exploited in chemoprevention o f cancer in humans. (C) 1999 Elsevier Science Ireland Ltd. All rights reser ved.