Urea synthesis in rats fed diet containing kidney beans

When rats were fed a diet containing kidney bean (Phaesolus vulgaris) urea excretion was increased 3-5 fold. Isolated liver mitochondria from rats fed the kidney bean diet produced 40% more citrulline in the presence of arginine than mitochondria isolated from control rats. Mitochondrial activities of urea cycle enzymes and N-acetylglutamate synthetase were similar in animals fed diets containing kidney bean or lactalbumin. The possible mechanisms causing acute urea production in rats fed with kidney bean are discussed.

Alterations in the level of insulin receptor and GLUT-4 mRNA in skeletal muscle from rats fed a kidney bean (Phaseolus vulgaris) diet

1. A decline in the level of circulating insulin was observed in rats fed a diet containing kidney bean. 2. Consumption of a diet containing kidney bean caused an increase in the level of mRNAs for the insulin receptor (327%) and GLUT-4 (185%) in the gastrocnemius muscle. In contrast there was only a small increase in the amount of actin mRNA (125%). Since the kidney bean-fed rats are euglycaemic the results suggest that insulin receptor and GLUT-4 mRNA levels are regulated in response to circulating insulin concentrations rather than glucose. 3. No increases in the level of insulin receptor and actin mRNA were evident in the soleus muscle of rats fed the diet containing kidney bean; however a decline was observed in the level of GLUT-4 mRNA. 4. It is proposed that a component of kidney beans, most likely the lectin phytohaemagglutinin, has systemic effects which lead to changes in expression of the insulin receptor and GLUT-4 genes and to the sensitivity of muscle to insulin.

Effect of the beta-adrenoceptor agonist clenbuterol and phytohaemagglutinin on growth, protein synthesis and polyamine metabolism of tissues of the rat

1. The kidney bean lectin, phytohaemagglutinin (PHA), induced a marked atrophy of skeletal muscle which was evident from the changes in tissue composition (protein, RNA, DNA and polyamine content) and from the reduction in weight and protein synthesis of hind leg muscles of rats fed on kidney bean-diets for four days. The beta-adrenoceptor agonist, clenbuterol, induced skeletal muscle hypertrophy by transiently stimulating protein synthesis. As a consequence, the muscle loss caused by a short exposure to PHA was, in part, ameliorated by clenbuterol treatment. 2. Cardiac muscle was affected to a lesser extent than skeletal muscle by both clenbuterol and the lectin. However, there was evidence that protein synthesis in heart was reduced by PHA. 3. PHA had opposite effects on the gut, the lectin-induced hyperplasia of the jejunum was accompanied by a large increase in protein synthesis. Clenbuterol alone had no effect on the jejunum whereas a combination of PHA and clenbuterol appeared to exacerbate the effect of the lectin on gut. 4. Both the lectin-induced gut growth and the hypertrophy of skeletal muscle caused by clenbuterol were preceded by the accumulation of polyamines in the respective tissues. Of particular note was the observation that a significant increase in the proportion of the intraperitoneally injected 14C-labelled spermidine or putrescine taken up by the growing tissues could be detected by the second day. Therefore, the measurement of uptake of labelled polyamines may be used as a sensitive indicator of early alterations in tissue metabolism.

Mineral excretion of rats fed on diets containing faba beans (Vicia faba L.) or faba bean fractions

The effects on faecal mineral excretion of two commercial varieties (local cultivar and Troy cultivar) of raw faba beans (Vicia faba L., minor) meal (VFM) and its fractions have been studied in growing rats. Diets contained local-VFM (dark seed coat) and Troy-VFM (light seed coat) at 474-500 g/kg diet, hull (VFH) from both varieties at 65 g/kg diet, and the insoluble cotyledon residue (VFCR) obtained from the Troy variety at 237 g/kg diet. Rats were pair-fed on diets which had been supplemented with amino acids to target requirements and contained similar amounts of zinc, manganese, iron and copper. With VFM diets the apparent absorption of Zn and Mn was significantly reduced. On the other hand, with hulls the apparent absorption of Fe was reduced while that of Cu slightly increased. As the amounts of calcium, phosphorus and magnesium in VFM and VFH diets were higher than in the controls, the increased intake resulted in a significant increase in both the apparent absorption and the faecal excretion of these minerals. The inclusion of VFCR in the diet had no significant effect on the mineral content of faeces. The relatively low concentrations of phytate in the bean seeds of 7.8 and 6.7 g/kg for the local and Troy cultivars respectively, could not adequately account for the increased mineral excretion. The results suggest that other seed constituents, possibly the soluble non-starch polysaccharides, may be involved in the elevated loss of Zn and Mn in rats fed on diets containing faba bean for extended periods, while some insoluble structural hull components may interfere with the absorption of Fe from the gut.

Nutritional response of growing rats to faba beans (Vicia faba L., minor) and faba bean fractions

The effects of raw faba bean (Vicia faba L., minor) meal (VFM) and its fractions on the growth and nitrogen utilization of rats have been determined in two experiments. Two commercial varieties of VFM were tested, local VFM (409-439 g/kg diet) and Troy VFM (439 g/kg diet). The bean fractions tested were V. faba lectin-depleted protein (VFDP), V. faba lectin (VFL) and V. faba cotyledon residue (VFCR). All diets were supplemented with amino acids to target requirements. Body-weight, body N and lipid contents of rats fed on VFM were reduced significantly in comparison with control rats fed on lactalbumin. This was due, in part, to the lower digestibility of the protein, lipid and dry matter (DM) of VFM diets. As a result, net protein utilization (NPU) and biological value (BV) of faba bean proteins were less than expected. Urine and urea-N outputs of the VFM-fed rats were also elevated in both experiments. Increasing the energy content of local VFM diets led to significantly higher dry body-weight, body N and lipid contents, with the result that the NPU and BV values of the protein also increased. However, the NPU values for VFM-fed rats were still significantly lower than those for the controls in both experiments. In contrast, true N, lipid and DM digestibilities in rats given local VFM were not significantly affected by the difference in the energy content of the diets. The replacement of two-thirds of the lactalbumin in the diet with VFDP (65 g/kg) reduced dry body-weight, N and lipid contents, NPU and BV compared with the control rats, even though N, lipid and DM digestibilities were not significantly different. The nutritional performance of rats fed on lactalbumin-based diets containing 7 g VFL/kg was similar to that of the controls. Similarly, the inclusion of the cotyledon residue (237 g VFCR/kg diet) had no appreciable effect on any of the variables studied. As VFL and VFCR had no antinutritional effects in these rats, it appears that the low nutritional value of VFM for rats (NPU 0.66) results not only from the low digestibility of the bean proteins, but also from disturbances in N metabolism.

Effect of fasting and refeeding on basolateral polyamine uptake and metabolism by the rat small bowel

Fasting reduced the weight, protein, DNA, RNA and polyamine contents of the small intestine of rats, but its effects on the in vivo uptake of intraperitoneally injected 14C-spermidine through the basolateral membrane of the small intestine were small. The uptake of putrescine was nearly doubled by fasting for 48 h. Fasting for 48 h had reduced villus length but was without effects on the crypts. Refeeding for 6 h of rats fasted for 48 h led to hypertrophic growth: the length of both crypts and villi increased by about 50% without changes in cell number. The uptake of spermidine by the small intestine increased above not only that in fasted rats but also that in the controls fed ad libitum. The high putrescine uptake of rats fasted for 48 h was unchanged after refeeding for 6 h, but returned to control values after 12 h. Spermidine in the gut was well conserved, while most of the putrescine was transformed into non-polyamine metabolites. It is concluded that refeeding stimulates basolateral spermidine uptake, and this may be a general mechanism for polyamine accretion in adaptive growth of the small intestine.

Luminal and basolateral polyamine uptake by rat small intestine stimulated to grow by Phaseolus vulgaris lectin phytohaemagglutinin in vivo

Luminal and basolateral uptake of polyamines by the rat small intestine was studied in vivo. In the concentration range studied (0.1-5 mg per rat) 23-47% of the individual polyamines given intragastrically were found in the body after 1 h, with the small intestine retaining 4-12% of the dose. With spermidine or spermine, labelled polyamines accounted for 85-96% of the counts in the small intestine and between 72-82% were in the form given. However, with putrescine only 29-39% of the label found in the tissue remained in polyamine form and even less, 11-15%, as putrescine. Luminal uptake of polyamines was linear, non-saturable and was not stimulated when small intestinal growth was stimulated by phytohaemagglutinin (PHA). On the basolateral side of the gut, polyamine uptake was stimulated by PHA in a time-dependent way in advance of detectable growth. Overall polyamine recoveries were high (89-99%) with intraperitoneally administered spermidine and spermine. Moreover, a large proportion of the counts in the tissue (63-89%) were still in the original form. Even with putrescine, total recoveries of polyamines (72-88%) and putrescine (24-33%) were elevated in comparison with those from the lumen. Treatment of rats with alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, reduced tissue polyamine content, although it had slight effects only on basolateral polyamine transport. The PHA-stimulated increase of polyamine uptake was not abolished in the presence of DFMO.

Relationship between survival and binding of plant lectins during small intestinal passage and their effectiveness as growth factors

The effects on the small intestine and the growth of rats of six pure plant lectins: PHA (Phaseolus vulgaris); SBL (Glycine maxima); SNA-I and SNA-II (Sambucus nigra); GNA (Galanthus nivalis) and VFL (Vicia faba), covering most sugar specificities found in nature, were studied in vivo. Variable amounts, 25% (VFL) to 100% (PHA, GNA) of the lectins administered intragastrically, remained in immunochemically intact form in the small intestine after 1 h. All lectins, except GNA, showed binding to the brush border on first exposure, although this was slight with VFL. Thus, binding to the gut wall was not obligatory for resistance to proteolysis. Exposure of rats to lectins, except VFL, for 10 days, retarded their growth but induced hyperplastic growth of their small intestine. The two activities were directly related. PHA and SNA-II, whose intestinal binding and endocytosis was appreciable after 10 days of feeding the rats with diets containing these lectins and similar to that found on acute (1 h) exposure, were powerful growth factors for the small intestine. GNA, which did not bind at the start but was reactive after 10 days, and SNA-I, which behaved in the opposite way, induced changes in receptor expression in the gut. As they were bound to the brush border transiently, they were less effective growth factors. VFL was not bound or endocytosed, was non-toxic and did not promote gut growth.

Polyamine metabolism and uptake during Phaseolus vulgaris lectin, PHA-induced growth of rat small intestine

Kidney bean lectin, PHA, stimulated the hyperplastic and hypertrophic growth of rat small intestine. This growth was preceded by a rapid accumulation of polyamines in the small intestine. However, since the lectin had little effect on in situ polyamine biosynthesis, most of the polyamines must have been of extracellular origin. To investigate the source of polyamines, both the luminal uptake and basolateral transport of polyamines by the rat small intestine were measured in vivo. Luminal polyamine uptake was apparently by passive diffusion, non-saturable, linearly dependent on concentration and its extent was not stimulated by PHA. In contrast, 14C-polyamines injected intraperitoneally were probably taken up by a transport system(s). Moreover, basolateral polyamine transport was stimulated in a time-dependent manner when small intestinal growth was stimulated by PHA. However, in keeping with the finding of polyamine accumulation prior to demonstrable growth of the tissue, stimulation by PHA of the polyamine transport system also preceded small intestinal growth. Stimulation of polyamine transport by luminal factors is possibly a general mechanism involved in intestinal adaptation.

Isolation of soybean trypsin inhibitors by affinity chromatography on anhydrotrypsin-Sepharose 4B

By repeated treatments of trypsin with phenylmethylsulfonyl fluoride (PMSF), followed by base elimination of PMS from the PMS-trypsin, a catalytically inactive anhydrotrypsin preparation of low (less than 1%) active trypsin content was obtained. Inactive material was removed by affinity chromatography on trypsin inhibitor-Sepharose 4B and the purified anhydrotrypsin with full binding capacity for trypsin inhibitors was coupled to cyanogen bromide-activated Sepharose 4B. When used below its maximum capacity for trypsin inhibitors the anhydrotrypsin-Sepharose-4B affinity column absorbed both classes of inhibitors present in soybean. When overloaded, the Kunitz type was bound preferentially. Based on this observation, conditions for the partial separation of the two types of inhibitors were worked out.

Immunogold localization of ingested kidney bean (Phaseolus vulgaris) lectins in epithelial cells of the rat small intestine

The interactions between dietary kidney bean (Phaseolus vulgaris) lectins and the epithelial cells of the rat small intestine were investigated by immunogold electron microscopy. The results demonstrated that the lectins bind to the glycocalyx of duodenal and jejunal microvilli and that some of these dietary constituents are endocytosed into lysosomal pathways within both absorptive and secretory gut cells. It is concluded that the lysosomal response serves to limit the absorption of nutritionally significant levels of these dietary toxins.

Effect of kidney bean (Phaseolus vulgaris) toxin on tissue weight and composition and some metabolic functions of rats

Inclusion of raw kidney bean (Phaseolus vulgaris) proteins in the diet for rats was shown to affect the weight of some internal organs. Of these, in addition to the well-known hypertrophy of the pancreas attributable to dietary trypsin inhibitors, the observed atrophy of the thymus and the doubling in weight of the small intestine are related to the protein or lectin content of the bean diet, or both. Changes in tissue composition of the small intestine were also recorded. Its protein content increased by about 40-50% and carbohydrate content doubled suggesting the occurrence of increased mucinous glycoprotein secretion. Increased DNA content (by about 30-40%) however also indicated mucosal hyperplasia. Changes were also observed in mineral content, urea concentration and some enzyme activities in sera and urine, possibly as a result of disturbances in systemic metabolism or hormone levels, or both. The results gave further support to previous suggestions that the oral toxicity of kidney-bean lectins involves local reactions in the small intestine in combination with their effects on the systemic immune system and general metabolism.

Tomato lectin resists digestion in the mammalian alimentary canal and binds to intestinal villi without deleterious effects

Experiments were designed to investigate whether orally consumed tomato lectin could resist the digestive process and function as a lectin within the alimentary canal. Rats fed on a tomato lectin-rich diet passed faeces containing serologically detectable tomato lectin, and the lectin could be shown by immunoperoxidase staining bound to intestinal villi. Moreover, radioactivity was mainly recovered from the alimentary canal 3h after 125I-labelled tomato lectin administration with only traces in the circulation or internal organs. Radioactivity absorbed into the human circulation after consumption of 125I-labelled tomato lectin was also less than that expected for a digestable protein.

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.

The complete amino acid sequence of the major alpha subunit of the lectin from the seeds of Dioclea grandiflora (Mart)

The complete amino acid sequence of the major alpha subunit of the lectin from seeds of Dioclea grandiflora was determined. The sequence was deduced from analysis of peptides derived from the native alpha subunit by digestion with trypsin, chymotrypsin, the Staphylococcus aureus V8 protease, and pepsin; and from larger peptides produced by digestion of the citraconylated protein with trypsin. The alpha subunit consists of a single polypeptide chain of 237 amino acids which differs from the sequence of concanavalin in 53 positions. Significant levels of heterogeneity were observed in five positions in the sequence.

A survey of the nutritional and haemagglutination properties of legume seeds generally available in the UK

Eighty-five samples from fifteen different legume seed lines generally available in the UK were examined by measurements of their net protein utilization by rats and by haemagglutination tests with erythrocytes from a number of different animal species. From these results the seeds were classified into four broad groups. Group a seeds from most varieties of kidney (Phaseolus vulgaris), runner (Phaseolus coccineus) and tepary (Phaseolus acutifolius) beans showed high reactivity with all cell types and were also highly toxic. Group b, which contained seeds from lima or butter beans (Phaseolus lunatus) and winged bean (Psophocarpus tetragonolobus), agglutinated only human and pronase-treated rat erythrocytes. These seeds did not support proper growth of the rats although the animals survived the 10 d experimental period. Group c consisted of seeds from lentils (Lens culinaris), peas (Pisum sativum), chick-peas (Cicer arietinum), blackeyed peas (Vigna sinensis), pigeon peas (Cajanus cajan), mung beans (Phaseolus aureus), field or broad beans (Vicia faba) and aduki beans (Phaseolus angularis). These generally had low reactivity with all cells and were non-toxic. Group d, represented by soya (Glycine max) and pinto (Phaseolus vulgaris) beans, generally had low reactivity with all cells but caused growth depression at certain dietary concentrations. This growth depression was probably mainly due to antinutritional factors other than lectins. Lectins from group a seeds showed many structural and immunological similarities. However the subunit composition of the lectin from the tepary bean samples was different from that of the other bean lectins in this or any other groups.

Isolation and characterization of a lectin from the seeds of Dioclea grandiflora (Mart.)

By a combination of solubility fractionation, affinity and molecular-sieve chromatography, a lectin preparation containing several closely related lectin components of different isoelectric point was isolated from the seeds of Dioclea grandiflora Mart. The lectins showed a carbohydrate specificty for D-mannose (D-glucose)-binding and had a requirement for the presence of Ca(2+) and Mn(2+). The results of preliminary characterization studies showed that the D. grandiflora lectins had similar properties to those of concanavalin A, the lectin from the seeds of Canavalia ensiformis, a plant also belonging to the tribe Diocleae. Thus the D. grandiflora lectins contained no covalently bound carbohydrate and had an amino-acid composition characterized by a low content of methionine and the virtual absence of cysteine. Above pH 4.8 they had molecular weight of about 100,000, while below pH 3.1 they were dissociated to half-molecules. Between these two pH values there was a fast association-dissociation equilibrium for the two species. In dissociating solvents, three subunits were obtained of the approximate size of 25-26,000, 13-14,000 and 8-9,000. The lectins from C. grandiflora similar to concanavalin A were more distantly related to the lectins obtained from the members of the tribe Vicieae although these were also specific for D-mannose (D-glucose)-binding.

Immunocytochemical localisation of lectins in cells of Phaseolus vulgaris L. seeds

Antibodies against pure E4- and L4-lectins from the seeds of Phaseolus vulgaris L. raised in rabbits were made monospecific by immunoaffinity chromatography on E4- or L4-lectin Sepharose 4B columns. Localisation of lectins in bean seeds was investigated by indirect immunofluorescence and by electron microscopy on sections stained with colloidal gold particles coated with monospecific anti-E4- and anti-L4-IgG. In parenchyma cells from the cotyledons both E- and L-type lectins were found inside the protein bodies. Apparently the matrix of all protein bodies contained both types of lectins. On the other hand in vascular and in axis cells the two types of lectins were localised in the cytoplasm, outside the protein bodies. Thus these findings suggest different roles for the lectins: in cotyledons this may be a specific form of N storage, while in vascular and axis cells lectins may have a more direct metabolic part to play.

Recent advances in the study of the nutritional toxicity of kidney bean (Phaseolus vulgaris) lectins 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.

Characterization of C-reactive protein from the eggs of the marine teleost. Cyclopterus lumpus L

Further evidence is presented for the existence in teleost fish of proteins homologous with mammalian C-reactive protein. The amino acid composition is given for a C-reactive protein isolated from the eggs of a marine teleost, Cyclopterus lumpus, by extraction with lecithin in the presence of Ca2+, followed by electrofocusing. A molecular weight of 150,000 was calculated from gel filtration and electrophoresis at different polyacrylamide gel concentrations, while the s20,w was 7.4 S. The 1.5-S subunit had an apparent Mr of 20,000 by SDS-polyacrylamide gel electrophoresis and 21,000 by computer analysis based on amino acid composition. Comparison is made with the physicochemical properties of mammalian C-reactive protein.