The tumor-preventing effect of a mixture of several lactic acid bacteria on 1,2-dimethylhydrazine-induced colon carcinogenesis in mice.
The anti-tumor effect of a dietary supplement obtained from mixed cultures of several lactic acid bacteria was examined in the colon of tumor-inducing ICR male mice by use of a carcinogen, 1,2-dimethylhydrazine (DMH, 20 mg/kg body weight, 1 intra-muscular injection per week for 10 weeks). The animals were sacrificed either 15 weeks or 24-26 weeks after the first carcinogen injection. Macroscopically, the incidence of colon tumors at a 24-26 week period of tumor induction was apparently lower in mice treated with both the DMH and dietary supplement (76%) than in those treated with DMH alone (100%). Histologically, microadenomas were induced predominantly in the anal half of the total colon, and large lymphoid aggregates were often associated with dysplastic crypts in the distal colon. Apoptotic cell masses were shed into the distended lumen of the involved crypts. The statistical analysis at a 15-week period of tumor induction indicated that the incidence of microadenomas per tumor-induced mouse was lowered significantly by use of the dietary supplement. From the present results, it is suggested that the intake of the dietary supplement inhibits the early development of colon adenomas, and the inhibition of microadenomas results in a reduction of subsequent polyp and tumor yield in the mouse colon.