Effect of Phaseolus vulgaris lectins on glucose absorption, transport, and metabolism in rat everted intestinal sacs

Abstract

Many legume seeds contain lectins. Some of these lectins are toxic when fed to humans or laboratory animals. Although the mechanism for such toxicity has not been clearly elucidated, lectin binding to the intestinal mucosa is an obligatory step. Therefore, the interaction of lectin and enterocytes may interfere with the digestive process. Lectins from toxic (red kidney bean) and non-toxic (mountaineer half runner) Phaseolus vulgaris varieties were tested for their effect on the intestinal absorption, transport, and metabolism of glucose. Both lectins were purified by affinity chromatography on Con A-Sepharose 4B. Everted sacs, 5 cm long, from the first third of the small intestine were incubated for 20 min in the presence of 10 mmol/L glucose in both the luminal and serosal media. Pre-incubation (15 min) of the everted sacs with increasing concentrations of the red kidney bean lectin (50–200 μg/mL mucosal solution) before glucose addition reduced both the absorption and transport of the sugar from the luminal to the serosal side. Glucose metabolism as judged by lactate formation was not affected. At a concentration of 100 μg/mL of red kidney bean lectin, absorption, and transport were inhibited by 40% and 72%, respectively. Lactate production was decreased by only 5%. Under the same conditions (100 μg/mL) mountaineer half runner lectin inhibited glucose absorption and transport by less than 10%. Interference of lectins with the absorption and transport of nutrients could partially explain the toxic effect of lectins from some Phaseolus vulgaris varieties.