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 μmol/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.
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 nutritional effects in the rat of raw lentil meal or its fractions have been evaluated in three feeding trials. Growth, gain/feed ratio, apparent N digestibility, and N retention were ...significantly (p < 0.05) reduced by the inclusion of whole lentil meal, dehulled lentil meal, or ethanol-extracted lentil meal as the sole source of protein in the diet. Pure lentil lectin and lectin-depleted albumin proteins had no significant negative effect on nutritional performance. In contrast, growth, gain/feed ratio, protein conversion efficiency, N digestibility, and N retention were significantly (p < 0.05) reduced by diets containing lentil globulins or lentil hulls. The poor nutritional quality of raw lentil meal for rats is therefore likely to be primarily due to the combined effects of these two components. Keywords: Lentils; nutritional utilization; lentil fractions; lentil lectin; rat
New research directions in the last decade have led to major developments in the uses of plant lectins in bioscience and biomedicine. Major advances have been made in our understanding how lectins in ...the diet can act on the gastrointestinal tract and the physiological consequences of their actions, and how they can modulate body- and organ metabolism, the immune system and the gut microflora. Particularly striking progress has been made in unravelling the effects, often beneficial, of both orally- and parenterally administered lectins, including lectins of Viscum album-, Phaseolus vulgaris-, Robinia pseudoacacia, Agaricus bisporus, etc on tumours and in cancer therapy. Results have also made it possible to devise and try out other beneficial applications of plant lectins as gut-, metabolic- and hormonal regulators, immune reagents, probiotic/prebiotic oral supplements and to develop methods based on the oral application of lectins to protect the intestines against the often lethally harmful effects of chemo- and radiotherapy. With the development of genetically modified (GM) plants by transferring the genes of some of the natural insecticidal lectins such as the various Bacillus thuringiensis lectin-Cry toxins or some insecticidal plant lectins to major crop plants, a possible new avenue in plant protection may have opened up.
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 activities of diamine and polyamine oxidases, two enzymes of polyamine catabolism, were studied in hyperplastic growth of rat small intestine induced by phytohaemagglutinin. This growth, ...evaluated by the elongation of Lieberkühn's crypts, was more extensive in the proximal than in the distal parts of the gut. The activity of diamine oxidase was significantly reduced in the proximal (70%), medial (45%) and the distal (25%) parts. The activity of polyamine oxidase was doubled. The concentrations of putrescine, cadaverine and spermidine were significantly elevated in the three intestinal parts studied, whereas those of histamine and spermine were unchanged. It appears that changes in the activities of diamine and polyamine oxidases may contribute to the increased putrescine content, which is necessary to maintain active polyamine turnover for sustaining growth of the gut.
The growth of a murine non-Hodgkin lymphoma (NHL) tumour, either as an intraperitoneal ascites tumour or as a solid subcutaneous tumour, has been shown to be greatly reduced by including ...phytohaemagglutinin (PHA), a lectin present in raw kidney bean (Phaseolus vulgaris) in the diet. The reduced rate of growth occurred in a dose-dependent manner. Based on the experimental observations it has been suggested that a competition occurs between the gut tissue undergoing hyperplasia and the developing tumour for nutrients (including polyamines) from a common body pool. This may be an important factor with regard to the observed initial low level of tumour growth following the feeding of a PHA-containing diet. Results showing that the level of hyperplasia of the small intestine in response to feeding the PHA diets was higher in non-injected mice compared to those which had been injected with tumour cells substantiated the concept of competition between gut and tumour for nutrients etc. required for growth. The observations suggest that lectins, which exhibit growth-promoting effects on the gut, may have interesting applications in the formulation of new approaches with respect to cancer treatment.
Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB and *Department of Bacterial Diseases, Veterinary Laboratories Agency (Weybridge), Addlestone, Surrey KT15 3NB
Corresponding ...author: Dr P.J. Naughton (e-mail: Patrick.Naughton{at}agrsci.dk ). Present address: Department of Animal Nutrition and Physiology, Danish Institute of Agricultural Sciences, Research Centre Foulum, PO Box 50, DK-8830, Denmark.
Received 5 May 2000; revised version accepted 25 June 2000.
Abstract
The involvement of type 1 fimbriae in colonisation of the rat gastrointestinal tract in vivo was investigated with Salmonella enterica serotype Enteritidis LA5 and a mutant of LA5 denoted EAV3 unable to elaborate type 1 fimbriae (SEF 21). Rats were given a single dose of LA5 or EAV3 or a 1:1 mixture of both. LA5 was found in higher numbers in the stomach and small intestine than EAV3 at 6 h after infection with a single strain, but not after 6 days. LA5 did not out-compete EAV3 when the strains were administered together. Indeed, after 6 and 21 days, EAV3 was found in the distal small intestine and large intestine in far higher numbers than LA5. These findings suggest that SEF 21 have an important role(s) in the early stages of infection in vivo . However, SEF 21 expression may disadvantage the pathogen in the longer term as indicated by EAV3 out- competing LA5 in the gut at 21 days.
The growth of a non-Hodgkin lymphoma, developing subcutaneously as a solid tumour in NMRI mice, is markedly diminished by including phytohaemagglutinin (PHA), a lectin present in raw kidney bean (
...Phaseolus vulgaris), in the diet. In the experiment described in this communication the effect of first allowing tumours to develop for 5 days before switching the mice to a diet containing PHA at different concentrations was tested to establish whether or not feeding the lectin at late times also resulted in reducing tumour growth. This switch of diet indeed proved to be effective in slowing down growth of the lymphoma tumour. The reduced rate of growth occurs in a dose-dependent manner. We have suggested that a competition between the gut epithelium undergoing PHA-stimulated hyperplasia and the developing tumour may occur for polyamines and other nutrients from a common body pool and this could be an important contributory factor with regard to the observed low level of tumour growth following the feeding of PHA-containing diet. Recent data which showed that the level of hyperplasia of the small bowel in response to feeding the PHA diets was higher in non-injected mice compared to those which had been injected with tumour cells substantiated the concept of competition between gut and tumour for nutrients and other requirements for growth.
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