Susan Bardocz

Polyamines in food and their consequences for food quality and human health

Polyamines (putrescine, spermidine and spermine) fulfil an array of roles in human cellular metabolism and in the synthesis of protein, RNA and DNA. Only a proportion of polyamines are synthesized in situ according to needs. However, as is the case for semi-essential amino acids, food is an important source of the polyamines required to support cell renewal and growth. Although the bioavailability and the mechanism of the uptake of polyamines in the gastrointestinal tract are not fully established, it is evident that at least some proportion of the polyamines in the diet can be absorbed and utilized by the body.

The importance of dietary polyamines in cell regeneration and growth

The polyamines putrescine, spermidine and spermine are essential for cell renewal and, therefore, are needed to keep the body healthy. It was previously believed that polyamines are synthesized by every cell in the body when required. However, in the present paper evidence is provided to show that, as in the case of the essential amino acids, the diet can supply sufficient amounts of polyamines to support cell renewal and growth. Systematic analysis of different foods was carried out and from the data obtained, the average daily polyamine consumption of British adults was calculated to be in the range 350-500 mumol/person per d. The major sources of putrescine were fruit, cheese and non-green vegetables. All foods contributed similar amounts of spermidine to the diet, although levels were generally higher in green vegetables. Meat was the richest source of spermine. However, only a part of the polyamines supplied by the diet is available for use by the body. Based on experiments with rats it was established that polyamines were readily taken up from the gut lumen, probably by passive diffusion, and were partly metabolized during the process of absorption. More than 80% of the putrescine was converted to other polyamines and non-polyamine metabolites, mostly to amino acids. The enzyme responsible for controlling the bioavailability of putrescine was diamine oxidase (EC 1.4.3.6). For spermidine and spermine, however, about 70-80% of the intragastrically intubated dose remained in the original form. Considering the limitations on bioavailability (metabolism and conversion), the amounts of polyamines supplied by the average daily diet in Britain should satisfy metabolic requirements.

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.

Polyamines in food-implications for growth and health

Abstract Different types of food (fruits, vegetables, meat, and milk products) were analyzed by high pressure liquid chromatography to determine their polyamine (putrescine, spermidine, and spermine) contents. All foods contained some polyamines, although the concentrations in different individual food components were variable. As was established earlier using 14C-labeled putrescine, spermidine, and spermine, polyamines are readily taken up by the gut and enter the systemic circulation. Food appears to constitute a major source of polyamines for humans and animals. The distribution of polyamines in the body, as determined by measuring the accumulation of 14C-spermidine in different tissues of the rat, was correlated with the metabolic activity and growth of particular organs. Thus, phytohemagglutinin induced both extensive hyperplastic growth and the preferential accumulation of labeled spermidine in the gut. Correspondingly, when skeletal muscle growth was promoted by the β-antagonist, clenbuterol, 14C-spermidine was sequestered by the hind leg gastrocnemius muscle. It is concluded that food polyamines are not only necessary for normal body metabolism, but are also used and directed preferentially to tissues and organs that have been stimulated to grow by metabolic signals.

Antinutritive effects of wheat-germ agglutinin and other N-acetylglucosamine-specific lectins

Incorporation of N-acetylglucosamine-specific agglutinins from wheat germ (Triticum aestivum; WGA), thorn apple (Datura stramonium) or nettle (Urtica dioica) rhizomes in the diet at the level of 7 g/kg reduced the apparent digestibility and utilization of dietary proteins and the growth of rats, with WGA being the most damaging. As a result of their binding and endocytosis by the epithelial cells of the small intestine, all three lectins were growth factors for the gut and interfered with its metabolism and function to varying degrees. WGA was particularly effective; it induced extensive polyamine-dependent hyperplastic and hypertrophic growth of the small bowel by increasing its content of proteins, RNA and DNA. Furthermore, an appreciable portion of the endocytosed WGA was transported across the gut wall into the systemic circulation, where it was deposited in the walls of the blood and lymphatic vessels. WGA also induced the hypertrophic growth of the pancreas and caused thymus atrophy. Although the transfer of the gene of WGA into crop plants has been advocated to increase their insect resistance, as the presence of this lectin in the diet may harm higher animals at the concentrations required to be effective against most pests, its use in plants as natural insecticide is not without health risks for man.

Lectins : biomedical perspectives

1. Lectins and Pathology : An Overview 2. Carrier-immobilized Carbohydrate Ligands: Design of the Lectin-detecting Tools and their Applications with Focus on Histopatholgy 3. Lectins, Microglia and Alzheimers Disease 4. The Role of Galectin-3 in Inflammation 5. The Role of Galectin-3 in Tumor Metastasis 6. Laminin-binding Lectins during Cancer Invasion and Metastasis 7. Lectins as Diagnostic Tools and Endogenous Targets in AIDS and Prion Diseases 8. Protein-carbohydrate Interactions in the Attachement of Enterotoxigenic Escherichia Coli to the Intestinal Mucosa 9. Lectin-carbohydrate Interactions in Bacterial Pathogenesis 10. Lectin-Mediated Interaction of Parasites with Host Cells

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.

Reversible effect of phytohaemagglutinin on the growth and metabolism of rat gastrointestinal tract.

The lectin, phytohaemagglutinin, present in beans survives passage through the gastrointestinal tract in a biologically and immunologically intact form. It is known that by binding to the brush border membranes of the small intestine phytohaemagglutinin induces its hyperplastic growth. However, its effect on the other parts of the gut are not known. This study considered the dose and time dependent changes in the gastrointestinal tract exposed to phytohaemagglutinin. Lectin binding was detected by polyclonal antibodies using PAP staining to the surface and the parietal cell region of the stomach, the brush border epithelium of the small intestine and to the surface membrane of the caecum and colon. To characterise the metabolic changes in the gut organ weights, protein, RNA, DNA, and polyamine contents were measured. While phytohaemagglutinin induced a dose and time dependent growth of the small intestine by lengthening the tissue and thickening the gut wall by increasing the number of crypt cells, the lectin also changed the size and metabolism of the large intestine and pancreas, but this growth was by hypertrophy. Phytohaemagglutinin in the diet influences the size, metabolism, and function of the entire digestive tract. The lectin induced changes were fully or partially reversed within three days.

LECTINS AND ALSO BACTERIA MODIFY THE GLYCOSYLATION OF GUT SURFACE RECEPTORS IN THE RAT

Oral exposure to lectins or the presence or absence of bacteria in the rat small intestine were shown by histological methods using anti-lectin antibodies or digoxigenin-labelled lectins to have major effects on the state of glycosylation of lumenal membranes and cytoplasmic glycoconjugates of epithelial cells. Taken together with the dramatic effects of exposure to lectins on gut function, metabolism and bacterial ecology, this can be used as a basis for new perspectives of biomedical manipulations to improve health.

The effect of phytohaemagglutinin at different dietary concentrations on the growth, body composition and plasma insulin of the rat

Young growing rats weighing approximately 83 g were fed on diets containing kidney bean (Phaseolus vulgaris) lectin (phytohaemagglutinin, PHA) in the range of 0-0.45 g/kg body weight for 10 d to ascertain whether there was a minimum dose below which the lectin had no significant effect on body and skeletal muscle weights in comparison with pair-fed lectin-free controls. Averaged over all experiments, PHA doses of less than 10 mg/d (0.12 g/kg body weight) reduced body dry by 1.14 (SE 0.25) g when compared with controls. Between 10 and 27 mg/d (0.12-0.32 g/kg body weight) a further reduction of 0.64 (SE 0.21) g occurred, suggesting a slight but steady decline of body dry weight with increasing dose. However, above 27 mg/d the depression of growth and changes in body composition accelerated. The difference between the proportional losses of skeletal muscle and body weight was not significant at doses of PHA below 10 mg/d (0.12 g/kg body weight) but the ratio of these losses rose to 1.5-2.0 at doses above this. The proportional decrease in lipid weight exceeded that of both body and skeletal muscle weights at all lectin doses, suggesting that lipid catabolism was the first target of the PHA effect. Plasma insulin level was depressed at the PHA dose of 0.02 g/kg body weight at which growth depression and muscle atrophy were minimal but, contrary to expectations, plasma glucose levels remained stable over the whole PHA dose range. It appears that despite a PHA-induced lowering of blood insulin, glucose catabolism is elevated by an unknown, possibly hormonal, compensatory mechanism. Thus, because low insulin levels facilitate the mobilization and catabolism of lipids, it may be possible to use low doses of PHA to reduce hyperglycaemia and body fat.