Dietary Lectins Research Articles

Influence of Diets Containing Native or BoiledPhaseolus vulgarison Segmented Filamentous Bacteria in the Small Intestine of Mice

The hypothesis was tested that the appearance of segmented filamentous bacteria (SFBs) in the small intestine of mice is inhibited by dietary lectins. Mice were fed diets containing either native or boiled (to denature the lectins) Phaseolus vulgaris . Not only was the hypothesis disproved but it was found that native Phaseolus consistently stimulated SFB colonisation. Keywords: Intestinal bacteria; Dietary constituents; Mouse; Segmented filamentous bacteria; Lectins.

Lectins in Food: Their Importance in Health and Disease

Up until about 15 years ago lectins were thought of as laboratory tools, useful for histochemistry and blood transfusion work. The fact that many common foods are rich sources of lectin was not considered by most biomedical scientists. In the last decade, however, there has been a flowering of knowledge about the interactions of lectins with body organs and tissues, and it has become clear that many lectins are resistant to cooking and digestion and are distributed to distant parts of the body after ingestion. There is now abundant evidence that dietary lectins can cause disease in Man and animals. This review will adduce evidence that such hitherto mysterious diseases as inflammatory bowel disease, diabetes mellitus, rheumatoid arthritis, glomerulonephri-tis, psoriasis, multiple sclerosis, retinitis and cataracts in the eye, are all explicable in terms of a lectin aetiology, as are congenital malformations, infertility, IgE-mediated allergies and autoimmune states. Complete proof is still lacking in most...

Repair of microvilli in the rat small intestine after damage with lectins contained in the red kidney bean

That microvilli of intestinal absorptive cells in the duodenum and jejunum are disrupted by acute challenge with lectins contained in raw kidney beans (RKB) was shown nearly 10 yr ago by light microscopy. However, the precise morphologic damage produced by RKB has not been characterized, and it is not known whether microvilli, once damaged, undergo repair. We have examined these issues by challenging rats with suspensions of 300 mg of RKB, boiled beans, or standard laboratory chow by orogastric lavage. Microvillus length was measured in electron micrographs from 6 to 20 h after challenge. Epithelial cell migration was determined by autoradiography after injection of [3H]thymidine. After challenge with RKB, microvilli (a) showed extensive vesiculation along the length of villi 2–4 h after challenge; (b) were reduced significantly in length along the entire villus 6 h after challenge; and (c) were near normal in length by 20 h after challenge. Microvillus length was also reduced significantly 6 h after challenge with boiled beans. The rate of cell migration was not accelerated by treatment with RKB. These data suggest that damage to microvilli caused by 300 mg of RKB is self-limited and reversible; microvilli once damaged by RKB are repaired. Repair of microvilli is due to intrinsic reparative processes rather than accelerated replacement of damaged cells. We speculate that microvilli may be repeatedly damaged and repaired after ingestion of dietary lectins.

Cyclo-oxygenase and oxygen free radical-stimulated fibroblast proliferation

There was no evidence of accumulation of PHA in any particular organ although trichloroacetic acid-precipitable and total counts (not shown) were high in kidneys, particularly when calculated on a tissue weight basis. Only the liver of tomato-lectin-treated rats contained as much radioactivity as that from PHA-intubated animals. It has been shown previously (Pusztai et al., 1986) that the toxicity of dietary PHA is dependent not just on its local disruptive effects on the small intestine but also on ensuing systemic toxic responses to the lectin. This gives an indirect indication that dietary PHA or other lectins might breach the gut absorptive barrier in appreciable quantities. The results presented (Table 1) are, however, the first direct experimental evidence to support the existence of appreciable systemic absorption of a dietary lectin. It is particularly significant that under the same experimental conditions only a small proportion of the non-toxic tomato lectin is absorbed systemically. This was apparently not due to differential survival of the lectins in the gut, but was more probably due to differences in their binding specificity to and extent of endocytosis by small intestinal cells. As recently shown, even lectins less toxic than PHA gain access to the body by passing through the gut wall and thus are good immunogens by the oral route (de Aizapurua & Russell-Jones, 1988). In a recent review on oral drug delivery (Pusztai, 1989) the potential effectiveness of lectins for such an application was explored. The results in the present paper go a long way to underpin such theoretical considerations and form a basis for practical exploration of this potential.

Specific uptake of dietary lectins into the systemic circulation of rats

Specific uptake of dietary lectins into the systemic circulation of rats

Direct effects of wheat germ agglutinin on inositol phosphate formation and cytosolic-free calcium level in intestine 407 cells.

The interaction between dietary lectins, especially wheat germ agglutinin (WGA), and intestinal cells has been implicated in the pathogenesis of celiac disease. The present study was undertaken to investigate the immediate effects following such an interaction. Direct WGA-stimulation of Intestine 407 cells leads to an immediate rise in the cytosolic-free calcium concentration. The major part of this lectin-induced rise is due to an influx of calcium across the plasma membrane into the cytosol. However, WGA-exposure also results in an immediate mobilization of calcium from intracellular stores, most likely mediated via the simultaneous increase of inositol trisphosphate formation in these cells. The transduction mechanism described for WGA in these intestinal cells is not very sensitive towards pertussis toxin, indicating that if a G-protein is involved, it differs from those of most other systems. The suggested role for WGA in changing the functional and structural properties of intestinal cells might involve increases of inositol phosphate and cytosolic-free calcium levels.

Phytohemagglutinin from red kidney bean (Phaseolus vulgaris) inhibits sodium and chloride absorption in the rabbit ileum

Phytohemagglutinin (PHA), derived from red kidney bean (Phaseolus vulgaris), can induce malabsorption and diarrhea when fed to rats. In this study, we determined the effect of PHA on ion transport in the rabbit ileum in vitro. Compared with control tissues, PHA (1 mg/ml) added to the mucosal solution increased short-circuit current (1.1 ± 0.2 μEq/cm2 · h, p < 0.001), decreased net Na (−1.0 ± 0.5 μEq/ cm2 · h, p < 0.02) and Cl (−1.2 ± 0.6 μEq/cm2 · h, p < 0.0250) absorption, and decreased tissue conductance (−1.8 ± 0.5 mS/cm2, p < 0.001). Serosal addition of PHA had no effect on the short-circuit current or tissue conductance. Mucosal PHA did not increase mucosal levels of cyclic adenosine monophosphate or cyclic guanosine monophosphate. Removal of serosal calcium did not affect the increase in short-circuit current induced by mucosal PHA. Utilizing fluorescent microscopy, rhodamine-labeled PHA was found to bind to the luminal border of villus cells, but not to crypt cells, in the ileum. In the descending rabbit colon, PHA did not affect either the short-circuit current or conductance, and rhodaminated PHA did not bind to the epithelial surface. Using the increase in short-circuit current as an indicator of absorption, PHA did not affect Na-coupled glucose or amino acid absorption in the ileum. This study suggests that dietary lectins may play a role in regulating intestinal fluid and electrolyte transport.

Immunosorbent assay of interactions between human parotid immunoglobulin A and dietary lectins

By enzyme-linked immunosorbent assay (ELISA), parotid IgA was found to associate with purified peanut (PNA), pea (PSA) and wheat-germ (WGA) lectins. To determine the effect of eating foods which contained these lectins on the reactivity of IgA with purified lectins, samples of parotid saliva were collected prior to, and after, eating the lectin-containing food and their reactivity determined by ELISA. Four of 5, and 5 of 6 subjects, respectively, gave one or more post-eating samples with increased IgA reactivity to purified PNA or PSA, but not to WGA, a heterologous lectin. Four of 6 subjects had significantly higher IgA reactivity with PSA after they ate raw peas on a single occasion. Absorption experiments with PSA and PNA conjugated to agarose beads showed there were different populations of IgA molecules which reacted with the lectins. One highly-reactive population increased after eating the lectin-containing food and may contain antibodies induced by antigenic determinants in the lectin. The lectins may also bind to saccharide moieties of the IgA molecules.

Morphological changes of rat small intestine after short-time exposure to concanavalin A or wheat germ agglutinin.

Dietary lectins of gluten origin have been suggested to play an important role in the mechanisms leading to the characteristic morphology of the intestine found in patients with celiac disease. To further explore this issue we have used Wheat Germ Agglutinin (WGA) or Concanavalin A (Con A) to challenge rat small intestine and study the ultrastructural changes of such a treatment. Both lectins affected the enterocytes at the base of the villi more than those at the top. The morphological findings included disarrangement of the cytoskeleton, increased endocytosis and shortening of the microvilli. The interrelationship between the observed changes, and their relevance for similar morphological alterations found in patients with celiac disease are discussed. In conclusion, the morphological findings in our rat model resemble early changes in patients with celiac disease, thus supporting the idea that lectins or lectin-like substances are involved in the pathogenesis of this disease.

Toxicity of kidney bean (Phaseolus vulgaris) in rats: changes in intestinal permeability.

Rats fed on diets containing kidney bean showed increased intestinal permeability to intravenously injected 125I-labelled rat serum proteins after an intragastric challenge with bean proteins. The enhanced accumulation of radioactive serum proteins in the lumen and walls of the small intestine indicated increased vascular permeability. It is suggested that dietary lectins may, at least in part, be responsible for this loss of serum proteins and thus contribute towards the overall toxicity of kidney bean proteins.

Adherent interactions which may affect microbial ecology in the mouth.

Bacteria attach to teeth and oral mucosal surfaces in a surprisingly selective manner, and attachment appears to be the first step in the colonization process. Attachment is thought to involve lectin-like and/or hydrophobic ligands, called adhesins, often present in bacterial surface appendages which interact with receptors on oral tissues. A variety of factors can influence bacterial attachment, and therefore have the potential to affect host-parasite interactions in the mouth. Factors discussed include salivary components, dietary lectins, and sublethal concentrations of antibiotics.

Inhibition of lectin-binding to saliva-treated hydroxy apatite, to buccal epithelial cells, and to erythrocytes by salivary components

The influence of human saliva on the binding of several lectins to saliva-treated hydroxyapatite surfaces which mimic the teeth, to buccal epithelial cells, and to erythrocytes was determined. Clarified whole saliva inhibited binding of3H-labeled concanavalin A, wheat germ, soy bean,Ulex europaeus, and peanut agglutinins to saliva-treated hydroxyapatite by 75 to 95%, depending on lectin concentration used. Different fractions of saliva-inhibited binding of different lectins. For example, salivary mucins reduced the binding of wheat germ agglutinin to salivatreated hydroxyapatite, but they did not significantly affect binding of other lectins studied. Components of saliva also inhibited lectin-mediated hemagglutination. Using an indirect enzymelinked immunoassay, wheat germ and peanut agglutinins were found to bind in a specific manner to human buccal epithelial cells, and this was also greatly reduced by saliva. The data suggest that one of the major functions of salivary and other alimentary secretions may be to reduce the extent of interaction of dietary lectins with mucosal surfaces.

In Vivo Responses of Rat Intestinal Epithelium to Intraluminal Dietary Lectins

Although a variety of plant lectins are consumed as part of the normal human diet and are capable of binding to intestinal cell surfaces in vitro, little information exists on their effects on intact intestine. We have studied the acute effects of intraluminal administration of wheat germ agglutinin and concanavalin A in normal rats. Both lectins caused increased shedding of brush border membrane and, at higher concentrations, reduction in surface area, acceleration of cell loss, and shortening of villi. These changes were prevented by simultaneous administration of the appropriate sugar to inhibit binding, indicating that the effects were related to binding to carbohydrate residues of intestinal cells. Similar changes of brush borders were found after intraluminal administration of antiserum to sucrase-isomaltase, a surface protein of the brush border membrane, suggesting that the lectin effects resulted from cell surface receptor-lectin interaction rather than a primary intracellular effect. Our results suggest that dietary lectins may be in part responsible for normal turnover of brush border membrane, and support, in addition, the possibility that certain intestinal diseases such as celiac sprue may be the consequence of increased levels of lectin receptor allowing a dietary lectin to exert a toxic effect.

The toxicity of Phaseolus vulgaris lectins. Nitrogen balance and immunochemical studies.

AbstractInclusion of pure lectins isolated from the seeds of kidney bean (Phaseolus vulgaris L. cv. Processor) in diets for rats increased both faecal and urinary losses of N and resulted in a negative N balance for the animals. The relationship between total body N change [y (mg)] and lectin concentration [x (g kg−1)] of the diet was: y=421.5‐75.1 x, which was statistically significant (P=0.05). These rats developed circulating antibodies of low avidity to the dietary lectins, while no other proteins of the diet elicited a similar antibody response. Additionally, in several serum samples from rats which had been fed raw beans, the presence of small amounts of a protein reactive with rabbit anti‐lectin antibodies was detected. This protein was isolated from the immune precipitate and was shown by sodium dodecylsulphate‐gel electrophoresis to contain a protein subunit of 30 000, which was very similar to that of pure lectins. It is tentatively suggested that lectin toxicity results from the combined effects of the interference with normal intestinal digestion and/or absorption of N through the damaged enterocytes and of systemic immune (and other) responses of the rat to the internalised lectin.