The inhibitory effect of lyophilized cultures of Bifidobacterium longum on 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-induced carcinogenesis was investigated in male and female F344 rats. Beginning at 5 weeks of age, male and female rats were divided into various experimental groups and fed one of the high-fat, semipurified diets containing 0 and 0.5% lyophilized cultures of B. longum with or without 125 ppm IQ in the diet. All animals were continued on this regimen until the termination of the study. All animals were necropsied during the 58th week. The results indicated that dietary B. longum significantly inhibited the IQ-induced incidence (percentage of animals with tumors) of colon (100% inhibition) and liver (80% inhibition) tumors and multiplicity (tumors/animal) of colon, liver, and small intestinal tumors in male rats. In female rats, dietary supplementation of Bifidobacterium cultures also suppressed the IQ-induced mammary carcinogenesis to 50% and liver carcinogenesis to 27% of those observed in animals fed the control diet, but the differences did not reach a statistical significance at P < 0.05; however, the mammary tumor multiplicity (tumors/animal) was significantly (P < 0.05) inhibited in female rats fed the diet containing Bifidobacterium cultures. These findings suggest that Bifidobacterium supplements in the diet inhibit IQ-induced colon and liver tumors and to a lesser extent mammary tumors in F344 rats.
Supported by USPHS Grant CA 17613 from the National Cancer Institute.