The effect of an oral administration of Lactobacillus casei strain Shirotaon azoxymethane-induced colonic aberrant crypt foci and colon cancer in the rat

The preventive effect of oral administration of viable Lactobacillus casei strain Shirota (LcS) on azoxymethane (AOM)-induced colonic aberrant crypt f oci (ACF) and colon cancers in the rat was investigated. The study consiste d of two experiments; in a short-term experiment (Exp-I), the inhibitory ef fect of 8- and 12-week treatments with LcS. Forty rats each received weekly a subcutaneous injection of AOM at a dose of 15 mg/kg of body weight for 5 weeks. Eight and twelve weeks after the start of the carcinogen treatment, each subgroup of rats were sacrificed, and the colon and the mesenteric ly mph nodes (MLN) were removed. The number of ACFs and the surface marker of lymphocytes derived from the MLN were investigated. The large ACF (those co mprising four or more aberrant crypts per focus) had significantly decrease d in the rats which had consumed the LcS diet. And oral administration of v iable LcS significantly recovered CD8 positive lymphocytes to the levels in the control group. In a long-term experiment (Exp-II), 30 rats each receiv ed weekly a subcutaneous injection of AOM at a dose of 7.4 mg/kg of body we ight for 10 weeks. Twenty-five weeks after the start of the carcinogen trea tment, each subgroup of rats were sacrificed, and the colon were removed. T he number and incidence of colon cancers were investigated. The number of r ats with colon cancers and the number of colon cancers per rat, were signif icantly decreased in the rats which had consumed the LcS diet. LcS inhibite d chemically-induced colon carcinogenesis in the rat. CD8 positive T lympho cytes may play a key role in the preventive effect against colon carcinogen esis.