Eileen M. W. Clarke

The nutritional toxicity of Phaseolus vulgaris lectins.

In rats fed on beans (Phaseolus vulgaris) the poorly digestible lectins were shown to react with intestinal cells in vivo and to cause a disruption of many of the brush borders of duodenal and jejunal enterocytes. Although depressed to a certain extent, absorption still occurred, probably through the non-disrupted cells of the small intestine. In addition, abnormal absorption of potentially harmful substances, lectin-related or of bacterial origin, could also occur, possibly as a direct effect of the disruption caused by the lectins on the enterocytes. It is suggested that toxicity was the result of ensuing systemic effects, such as for example the observed high N excretion possibly through increased tissue catabolism.

The Influence of Diet on the Nitrogenous Components Passing to the Duodenum and through the Lower Ileum of Sheep

Analyses of the alimentary contents flowing to the duodenum of sheep during 24 h show that when the sheep are consuming a low-nitrogen diet more total nitrogen and amino nitrogen pass to the duodenum than are eaten daily in the food whereas when the sheep are eating high nitrogen diets, less total nitrogen and less amino nitrogen pass to the duodenum. The disparity between the total nitrogen and amino nitrogen content of the diets largely disappeared by the time the alimentary contents reached the terminal part of the ileum. From 64 to 68% of the nitrogen entering the duodenum and 54 to 64% of the nitrogen in the ileal contents was in the form of amino nitrogen. Proportionately more of the amino nitrogen was in solution in the ileal contents than in the duodenal contents. Losses of amino acids in the stomach when a high-nitrogen diet was consumed were especially large for glutamic acid, aspartic acid, proline, arginine and leucine. They were least for cystine and threonine. Gains of amino acids in the stomach when low nitrogen diets were consumed were all substantial except for proline, where a loss was found when hay and flaked maize were given. When these changes are considered as proportions of the quantities eaten then trends are similar for all acids. Changes in the molar proportions of the amino acids present in hydrolysates of the duodenal and ileal contents are discussed together with the significance of these changes in relation to the nutrition of the sheep.

Kidney bean (Phaseolus vulgaris) lectin-induced lesions in rat small intestine: 1. Light microscope studies

Abstract The inclusion in rat diets of raw kidney beans (Phaseolus vulgaris, variety “Processor”), containing high levels of lectins, resulted in severe disruption and abnormal development of microvilli in the small intestine. Similar damage occurred when rats were fed on diets containing purified lectin preparations obtained from the same beans. Few or no microvillus abnormalities were detected when the beans fed to rats were of a low-lectin variety (“Pinto III”). It is concluded that the observed depression of appetite, growth and dietary protein utilization of rats fed on diets containing high-lectin kidney beans may be at least partly due to malabsorption of nutrients. However, as many bacteria were associated with the damaged intestinal microvilli of rats which had been fed for several days on the high-lectin beans, the observed decline in the condition of the animals may also be attributed to the effects of bacterial endotoxaemia.

Immunocytochemical localization of ingested kidney bean (Phaseolus vulgaris) lectins in rat gut

SummaryThe binding of ingested kidney bean (Phaseolus vulgaris) lectins to the luminal surface of the rat gut was investigated by an indirect immunofluorescence method in which the primary antiserum was monospecific for kidney bean globulin lectins. The major lectin-positive sites were found to be the non-crypt regions of villi in the proximal region of the small intestine; exactly the same regions displayed extensive disruption of microvilli. Lectins were not localized in the brush border regions of ileal villi and no microvillus abnormalities were detected in this region of the gut. The luminal surface of the caecum was strongly lectin-positive and here also microvillus disruption was evident. Low levels of lectins were detected on the luminal surface of the colon; no microvillus abnormalities were detected in this region.

Kidney bean (Phaseolus vulgaris) lectin-induced lesions in rat small intestine: 3. Ultrastructural studies

Abstract Ultrastructural investigations revealed the extent of disruption of intestinal microvilli which occurred when rats ingested kidney bean lectins. Intracellular changes associated with the disrupted microvilli included disorganization of the terminal web, swelling of the apical cytoplasm and increase in numbers of lysosomes. It is suggested that these changes reflected disturbances in one or more membrane-associated transport processes. Microvilli were often present on the lateral and basal surfaces of enterocytes of rats fed on diets containing kidney bean lectins. Intracellular microvilli-lined cysts were also seen in some of these enterocytes.

Kidney bean (Phaseolus vulgaris) lectin-induced lesions in rat small intestine: 2. Microbiological studies

Abstract The inclusion in rat diets of raw kidney beans ( Phaseolus vulgaris variety “Processor”) containing high levels of lectins resulted in a dramatic overgrowth of Escherichia coli in the small intestine. No overgrowth occurred when the beans fed to rats were of a low-lectin variety. The hypothesis is presented that kidney bean lectins may indirectly or directly enhance the virulence of coliform strains either through aggregation and elimination of competitive strains or by agglutination of certain strains of E. coli to one another and to the mucosal surfaces of the gut. Severe disruption of microvilli precedes and accompanies the proliferation of E. coli and it is possible that malabsorption provides a suitable growth substrate for intestinal bacteria, augmented by cell fragments in the form of microvilli, and possibly also by cellular exudates due to loss of polarization in membrane transport systems.

Recent advances in the study of the nutritional toxicity of kidney bean (Phaseolus vulgaris) lections in rats

The main toxic component isolated from several varieties of kidney bean (Phaseolus vulgaris) is a haemagglutinating lectin. The inclusion in rat diets of raw kidney beans or purified bean lectins results in abnormal development of microvilli in the small intestine. Immunocytochemical investigations have provided evidence that this lesion is associated with the binding of lectins to the luminal surfaces of enterocytes. The lectin-induced disruption of intestinal microvilli may result in interference with the intermediate and final stages of nutrient hydrolysis in the gut. In nitrogen balance studies it was found that rats ingesting pure bean lectins were in negative nitrogen balance. These nitrogen losses may have been partly the result of systemic effects, possibly caused by a selective uptake of lectins by the gut.