The high parenteral toxicity of mistletoe lectin ML-1, a type-2 RIP (ribosome inactivating protein), with LD
50 values of 5 to 10 μg/kg BW, seriously limits its use as a cytotoxic agent in cancer ...therapy. As RIP proteins are generally better tolerated when given orally, we investigated the effects of ML-1 on growth, gut and body metabolism and composition by feeding rats diets containing 67 or 200 mg ML-1 kg
−1 BW for 10 days. Although ML-1 depressed voluntary feed intake and reduced growth rate, none of the rats lost weight during the experiment. ML-1 had no effect on the digestibility of proteins and other components of the diet but because of increased urinary nitrogen losses, the overall N balance and total body N content were reduced, particularly at the higher dose of ML-1. Body fat was also reduced, probably due to the depression of circulating insulin levels. Some organs were affected by oral ML-1: there was hypertrophy of the pancreas and lungs and, most importantly, a dramatic dose-dependent hyperplastic growth of the small intestine, probably due to the avid binding and endocytosis of ML-1 by gut epithelial cells. The plasma level of tumour necrosis factor-α was significantly increased by oral ML-1 and there was a similar, though not significant, rise in Interleukin-1β levels. These similarities in cytokine release by oral and intraperitoneal ML-1 suggest that the oral route may be as effective in tumor suppression as the parenteral. As orally given ML-1 was well tolerated by rats with an extended nontoxic dose range over that of parenteral ML-1, the possible advantages in therapy offered by this route could now be profitably explored.
With increasing use of lectin genes in crop plants to improve insect resistance, the dietary exposure of humans to lectins will rise and it is necessary to assess whether the presently most favored ...insecticidal lectin,
Galanthus nivalis agglutinin, would be harmful for mammals. Effects of
Galanthus nivalis agglutinin on gut and brush border enzymes were studied in rats over a 10-day dietary exposure and compared with those of a known antinutrient, phytohaemagglutinin. At a level that provides insecticidal protection for plants but did not reduce the growth of young rats,
Galanthus nivalis agglutinin had negligible effects on the weight and length of the small intestine even though there was a slight, but significant hypertrophy of this tissue. However, the activities of brush border enzymes were affected; sucrase-isomaltase activity was nearly halved and those of alkaline phosphatase and aminopeptidase were significantly increased. Although most of the changes in gut metabolism caused by the incorporation of
Galanthus nivalis agglutinin in the diet were less extensive than those found with toxic phytohaemagglutinin, some of them may be potentially deleterious. Thus, further and longer animal studies are needed to establish whether it is safe to use
Galanthus nivalis agglutinin in transgenic plants destined for human consumption.
In short-term feeding experiments, about 78% of the phaseolin administered to rats was degraded regardless of the amounts of phaseolin intubated. In contrast, the total N found in the feces increased ...rapidly and exceeded the original administered amounts. The bulk of N output was not immunologically related to the glycoprotein. The effects of phaseolin on the stimulation of endogenous N secretion in the small intestine were confirmed from the results of acute experiments. Phaseolin fragments, derived from the breakdown of the native protein, when reapplied intragastrically to rats, were broken down further and to a similar extent as the original glycoprotein and were even more potent related to stimulation of N secretion. It is suggested that this secretagogue biological activity of phaseolin and not its resistance to gut proteolysis, is the main reason for the poor nutritional value of this glycoprotein.
Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB and *Bacterial Diseases Department, Veterinary Laboratories Agency (Weybridge) Addlestone, Surrey KT15 3NB
Corresponding ...author: Dr P. J. Naughton. Present address: School of Biomedical Sciences, University of Ulster, Cromore Road, Coleraine, Co. Londonderry, Northern Ireland BT52 1SA (e-mail: PJ.Naughton{at}ulst.ac.uk ).
Received 1 Dec. 2000; revised version accepted 15 May 2001.
Abstract
Rats were dosed for 6 days with purified SEF 21 fimbriae of Salmonella enterica serovar Enteritidis 10360. The levels of fimbriae in gut contents associated with tissues and in the faeces were quantified by direct non-competitive ELISA. SEF 21 was distributed throughout the gut. The majority was found in the large intestine where it was primarily in the luminal contents. In contrast, a high proportion of SEF 21 detected in the ileum, the main site of salmonella colonisation and invasion, was tissue-bound. Thus, purified SEF 21 survived intestinal passage and associated with the stomach and gastrointestinal tract in a pattern similar to that found with whole Salmonella cells.
Ten days after subcutaneous injection of MPC-11 cells, plasmacytoma tumours which developed in female Balb/c mice fed on a diet containing the kidney bean lectin phytohaemagglutinin (PHA) at a ...concentration of 7.0 mg g
−1 diet, weighed only about 38% of those fed a lactalbumin (La) control diet. The reduction in growth caused by the lectin appeared to occur in a dose-dependent manner but the values did not reach significance before PHA was at a concentration of 7.0 mg g
− diet. Pre-feeding with the lectin caused a further 50% reduction in tumour weight. In contrast to the reduction in tumour size the inclusion of PHA in the diet elevated the mean dry weight of the small intestine in a dose-dependent manner, values reaching significance at 3.5 mg g
− diet. The results showed that gut hyperplasia was able to occur even in the presence of the developing tumour. A lypolytic effect of PHA occurred at high concentration. The observations suggest that PHA itself does not have a direct effect on the tumour cells, but an inter-relationship between gut hyperplasia and decreased tumour growth is indicated.
In the hypertrophic pancreas, we studied the oxidative degradation of polyamines, which are endogenous polycations important for cell division, growth and differentiation. To induce pancreatic ...hypertrophy, rats were fed on a semi-synthetic diet containing a daily dose of 42 mg phytohaemagglutinin per rat for 5 or 10 days. In the model, the activities of polyamine oxidase (the enzyme that degrades spermidine, spermine and mainly their acetyl derivatives) and diamine oxidase (the key enzyme of terminal catabolism of polyamines in vivo) increased by 100–180% and 90–100%, respectively, parallel to an elevation in polyamine content (40–100%). The results suggest that in pancreas hypertrophy, which does not exhibit stimulation of spermidine/spermine
N
1-acetyltransferase activity, increases in the activity of polyamine and diamine oxidases are related events that lead to putrescine formation and removal of excess polyamines.
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.
Mice injected intraperitoneally with Krebs II cells and then fed on a diet containing the lectin phytohaemagglutinin (PHA) developed ascites tumours more slowly than mice fed on a control diet. After ...an 8-day period following injection the number of cells recovered from mice maintained on the PHA diet was half that from those fed the control diet. A switch of diet from control to PHA on day 4 after injection resulted in a large decrease in number of tumour cells recovered. Mice injected s.c. also developed tumours at later times when fed on the PHA diet. A quantitative of ribosomes in polysome-containing fractions showed no major differences in protein synthesis in control mice and those fed the PHA diet.
Characterization of the lectins from onion (Allium cepa), shallot (A. ascalonicum) and leek (A. porrum) has shown that these lectins differ from previously isolated Alliaceae lectins not only in ...their molecular structure but also in their ability to inhibit retrovirus infection of target cells. cDNA libraries constructed from poly(A)-rich RNA isolated from young shoots of onion, shallot and leek were screened for lectin cDNA clones using colony hybridization. Sequence analysis of the lectin cDNA clones from these three species revealed a high degree of sequence similarity both at the nucleotide and at the amino acid level. Apparently the onion, shallot and leek lectins are translated from mRNAs of ca. 800 nucleotides. The primary translation products are preproproteins (ca. 19 kDa) which are converted into the mature lectin polypeptides (12.5-13 kDa) after post-translational modifications. Southern blot analysis of genomic DNA has shown that the lectins are most probably encoded by a family of closely related genes which is in good agreement with the sequence heterogeneity found between different lectin cDNA clones of one species.
The behaviour of the activity of tissue transglutaminase, a calcium-dependent enzyme, and the levels of polyamines, which are physiological substrates for the enzyme, were studied in rat small ...intestine induced to grow by lectin phytohaemagglutinin. Transglutaminase activity greatly increased in the homogenates and the cytosolic fractions of the intestinal mucosa of lectin-treated rats compared to that of untreated animals. The measurement of enzyme activity in the presence of monodansylcadaverine, a competitive inhibitor of transglutaminase, testified that the assayed enzyme activity was authentic transglutaminase. As regards polyamines, the level of spermine did not change, whereas putrescine and spermidine contents were enhanced. The activation of transglutaminase, which was probably due to Ca
2+ accumulation in enterocytes, could have a role in maintaining enterocyte adhesion and intestinal cell homeostasis, and/or repairing lectin-induced damages of microvilli of the gut epithelium.
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