Oral toxicity of Kintoki bean (Phaseolus vulgaris) lectin

There are several antinutritive factors in the Kintoki bean such as lectin, trypsin inhibitor, lack of methionine etc. The present experiment has revealed that lectin is mainly responsible for the growth impairment of experimental animals orally fed raw Kintoki bean. Mice fed raw Kintoki bean as the only protein source lost their body weight and died in 8 days, while mice fed the heated bean grew normally. When mice on a 10% albumin diet ingested 20 mg or 40 mg or 60 mg Kintoki bean lectin by daily stomach-feeding, their body weights were reduced to 84%, 74%, 71% of the control group after 5 days respectively and some of them could not live to complete the experiment. The apparent rates of the intestinal absorption of carbohydrate, lipid, and protein were considerably reduced, when rats were fed a diet containing 0.4% lectin. Especially, the rate of protein absorption was decreased to 26.3% from 55.5% of the control rate. The main tissues of mice that had ingested Kintoki bean lectin by stomach-feeding were subjected to microscopic observation. No changes were observed in the liver, kidney, spleen and pancreas. But in the small intestine, the epithelial cells lining the villi were considerably disordered and conspicuously disrupted. These results indicate that the Kintoki bean lectin is one of the most promoting factors for growth impairment in experimental animals and that the first target organ in the case of oral feeding is the small intestine.