Tracey J. Duguid

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.

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.

Purified Pseudomonas aeruginosa PA-I lectin induces gut growth when orally ingested by rats

The effects of PA-I lectin isolated from the human pathogen Pseudomonas aeruginosa upon cellular metabolism in vivo have been studied using the rat gut as a model system. Orally ingested PA-I lectin stimulated metabolic activity and induced polyamine accumulation and growth in the small intestine, caecum and colon. The nature and extent of the changes induced by PA-I lectin were similar to those caused by dietary kidney bean lectin and were likely to lead to impaired epithelial cell function and integrity. This finding contributes to our understanding of the possible roles of these lectins in Pseudomonas aeruginosa infection.

Switching between control and phytohaemagglutinin-containing diets affects growth of Krebs II ascites cells and produces differences in the levels of putrescine, spermidine and spermine

Almost twice as many ascites tumour cells were recovered from mice pre-fed for 3 days on a lactalbumin (La)-based control diet, injected with Krebs II ascites cells and then maintained on the same diet for a further 8 days, when compared with mice fed on a phytohaemagglutinin-containing (PHA) diet for the whole period. A dietary switch on the day of injection of tumour cells produced an intermediate effect; mice switched to the La diet after pre-feeding on PHA for 3 days developed somewhat more tumour cells than when the opposite dietary switch was performed. The polyamine content in the tumour cells was lowest in the mice fed on La, and highest in mice fed PHA for the duration of the experiment, respectively. Since large amounts of extraneous polyamines are required in order to sustain tumour growth, and the hyperplastic growth of the gut which occurs in response to injesting the lectin is a polyamine-dependent process, it is evident that the two growth signals compete with one another for important nutrients/growth factors, including polyamines.

Intracellular levels of polyamines in Krebs II lymphosarcoma cells in mice fed phytohaemagglutinin-containing diets are coupled with altered tumour growth

The number of Krebs II tumour cells recovered from the ascitic fluid of mice fed for 8 days on a lactalbumin (La) control diet was about three times higher than that in animals fed a phytohaemagglutinin-containing (PHA) diet. Feeding a PHA diet for less than 8 days after tumour cell injection also led to a reduction in tumour cell growth. There was an apparent inverse relationship between the total tumour cell count and the intracellular content of putrescine, spermidine and spermine. Hyperplasia of the small intestine occurred in the mice during the development of the ascites. A series of other organs were not affected in the same manner. The results indicate that the polyamine content of Krebs II ascites cells must increase by more than three-fold in order to achieve the intracellular concentration necessary to be able to enter the S-phase. A partial synchronization of the tumour cell population is suggested. Hyperplastic growth of the small intestine would appear to compete with tumour cells for polyamines from a common body pool.

Effect of proteolytic modification and methionine enrichment on the nutritional value of soya albumins for rats

Proteolytic modification, particularly when combined with methionine enrichment, significantly reduced the lectin content and modified the trypsin inhibitor activity of a soya albumin preparation. During both peptic hydrolysis and enzymatic peptide modification, the amount of soya bean agglutinin was reduced. This reduction was verified by the decrease in the intensity of protein staining and immunoblots of the peptic hydrolysate and of the product produced by enzymatic peptide modification, and confirmed by haemagglutination activity measurements and ELISA technique. The functional activity of Kunitz trypsin inhibitor was also partially abolished whereas that of the Bowman-Birk inhibitor was not significantly altered by the enzymatic modifications. In line with the reduction in some of the antinutrients, the nutritional performance of rats fed a diet containing this enzymatically modified product was significantly improved in comparison with that of the control animals fed the original soya albumin but was poorer than the lactalbumin-fed controls. Enzymatic peptide modification of soya albumin fractions by transpeptidation and covalent methionine enrichment is suitable to improve their nutritional value partly by compensating for their methionine deficiency and partly by modifying the structure of the soya antinutrients. Changes in the structure by proteolytic hydrolysis and synthesis of peptide chains can lead to alteration in protein conformation, resulting in modified biological activity and increased nutritional value.

Uptake, inter-organ distribution and metabolism of dietary putrescine in the rat

Abstract The movement of a single dose of 14 C-putrescine in the lumen of the rat gastrointestinal tract was followed for 3 hours after intragastric intubation. Putrescine progressed in the gut lumen in a wave-like fashion and was absorbed in the small bowel. Maximal uptake was observed at 2 hours; therefore, this time-point was selected to measure the concentration dependency of putrescine uptake by the small intestine and distribution between the vital organs in a wide concentration range (1/10 to 100 times the dietary input). Putrescine uptake by the small bowel was likely to be by passive diffusion, because the absorption was in proportion to input. The fate of putrescine was determined in the plasma, small bowel, liver, and skeletal muscle by measuring the radioactivity of the polyamines, their acetyl derivatives, and amino acids at physiologic concentrations. It appears that approximately 10% of the dietary input reaches the putrescine body pool.