Gastrointestinal responses to a panel of lectins in rats maintained on total parenteral nutrition

Tepary bean (Phaseolus acutifolius) lectin fraction provokes reversible adverse effects on rats' digestive tract

The Tepary bean (Phaseolus acutifolius) lectin fraction (TBLF) exhibits differential cytotoxicity on colon cancer cells and inhibition of early tumorigenesis in the colon (50 mg/kg, three times per week, for 6 weeks). TBLF showed low toxicity with the ability to activate the immune system; however, some adverse effects are the loss in body weight gain, intestinal atrophy, and pancreatic hyperplasia. After a recovery period of 2 weeks after treatment, reversion of pancreatic hyperplasia but no recovery of intestinal atrophy was observed. As TBLF has shown anticancer effects on the colon, it is important to characterize the adverse effects and how they can be reversed. Sprague Dawley rats were administered with TBLF (50 mg/kg) for 6 weeks, three times per week, and then allowed to recover for 6 weeks post-treatment. After TBLF administration, small intestine atrophy, villus atrophy, and cryptic hyperplasia were confirmed, as well as increased intestinal mucus production, increased permeability and a decrease in the apparent ileal digestibility of crude proteins. The colon showed damage in the simple prismatic tissue and decreased crypt depth, and changes in microbiota and a decrease in the apparent fecal digestibility of crude protein were determined. Our results show that the adverse effects provoked by TBLF were partially reversed after 6 weeks of recovery post-treatment, suggesting that increasing the recovery period it could be possible to reverse all adverse effects observed.

Effects of intragastrically-administered Tepary bean lectins on digestive and immune organs: Preclinical evaluation

Previous work showed that Tepary bean (Phaseolus acutifolius) lectins exhibit differential cytotoxic effects on cancer cell lines by apoptosis induction. In vivo studies using a Tepary bean lectin fraction (TBLF, 50 mg/kg of body weight) after colon cancer induction in rats showed that TBLF inhibited early precancerous lesions without systemic toxicity however, loss of body weight gain and activation of immune cells were observed. In order to know more about the possible adverse effects, we evaluated the administration of TBLF on digestive and immune organs. Sprague Dawley rats were administered TBLF for six weeks and allowed to recover for two weeks. Immune activation was observed through an increased lymphocyte-granulocyte ratio, an increased number of lymphoid follicles in intestinal Peyer's patches and a slight expansion of the splenic white pulp. Atrophy was observed in small intestine villi and crypt foci of the colon without normalization after the recovery period. Pancreas histopathology showed hypertrophy after the six-week administration period, particularly vacuolation and trabecular widening; but after the two-week recovery period atrophy was observed, suggesting a partial compensatory type process. Our results show that TBLF activates the immune system and affects digestive organs through direct interaction with intestinal epithelium, and indirectly by producing pancreatic hyperfunction. Further work will focus in longer recuperation periods after TBLF treatment.

Phaseolus vulgaris lectins: A systematic review of characteristics and health implications

Legume lectins are carbohydrate-binding proteins of non-immune origin. Significant amounts of lectins have been found in Phaseolus vulgaris beans as far back as in the last century; however, many questions about their potential biological roles still remain obscure. Studies have shown that lectins are anti-nutritional factors that can cause intestinal disorders. Owing to their ability to act as toxic allergens and hemagglutinins, the Phaseolus vulgaris lectins are of grave concern for human health and safety. Nonetheless, their potential beneficial health effects, such as anti-cancer, anti-human immunodeficiency virus (anti-HIV), anti-microbial infection, preventing mucosal atrophy, reducing type 2 diabetes and obesity, promoting nutrients absorption and targeting drugs, are of immense interest. The significance of Phaseolus vulgaris lectins in biological researches and the potential biomedical applications have placed tremendous emphasis on the development of purification strategies to obtain the protein in pure and stable forms. These purification strategies entail considerations such as effects of proteolysis, heating, gamma radiation, and high-hydrostatic-pressure that can have crucial outcomes in either eliminating or improving bioactivities of the lectins. Thus, up-to-date research findings of Phaseolus vulgaris lectins on different aspects such as anti-nutritional and health impacts, purification strategies and novel processing trends, are systematically reviewed.

Medium-chain triglycerides enhance mucous secretion and cell proliferation in the rat

BACKGROUND

The specific purpose of this study was to investigate the effects of medium-chain triglycerides (MCTs) on intestinal cell proliferation and mucous secretion of the small intestine in the rat.

METHODS

Rats were fed chow diet and given MCTs or the same weight of corn oil (5 g/kg per day) by gavage daily for 2 weeks, and then tissue samples of the small intestines were harvested. Leptin concentration in the small intestine was measured. Cell proliferation and apoptosis in the small intestine was determined by immunohistochemistry. Diamine oxidase (DAO) activity was measured by colorimetric assay.

RESULTS

In rats fed only chow diet (normal rats), the number of goblet cells per villi was 14.2 +/- 0.75 in the jejunum and 15.2 +/- 1.12 in the ileum. The number of goblet cells increased significantly in rats given MCTs compared with rats given corn oil or normal rats. Ki-67-positive cells were detected on the entire villi and the crypts in the small intestine. Furthermore, the proliferative index and the apoptotic index were also significantly greater in rats given MCTs than rats given corn oil or normal rats. Moreover, DAO activity and leptin concentration in the small intestine were significantly greater in rats given MCTs than rats given corn oil or normal rats.

CONCLUSIONS

MCTs enhance cell proliferation of the intestinal epithelium and mucous secretion from goblet cells in the small intestine. These effects may protect the gut in patients suffering from inflammatory bowel disease or enterogenous infection.

Probiotic Lactobacillus plantarum 299v does not counteract unfavorable phytohemagglutinin-induced changes in the rat intestinal microbiota

Application of phytohemagglutinin (PHA) in weaning feed has been suggested to stimulate intestinal epithelium maturation. In this study, PHA strongly affected the fecal bacterial population structure of rats. Escherichia coli overgrowth was not prevented by probiotic mannose-adhering Lactobacillus plantarum 299v. Therefore, use of PHA in weaning feed deserves careful evaluation.

Peanut lectin stimulates proliferation of colon cancer cells by interaction with glycosylated CD44v6 isoforms and consequential activation of c-Met and MAPK: functional implications for disease-associated glycosylation changes

Peanut agglutinin lectin (PNA) binds the Thomsen-Friedenreich (TF) oncofetal carbohydrate antigen (galactose beta1-3N-acetylgalactosamine alpha) that shows increased expression in colon cancer, adenomas, and inflammatory bowel disease. PNA is mitogenic, both in vitro and in vivo, for colon epithelial cells. In these cells, PNA binds predominantly to cell-surface TF antigen expressed by high molecular weight isoforms of the transmembrane glycoprotein CD44 that are generated in inflamed and neoplastic colonic epithelia by altered RNA splicing. Our aim was to identify the signaling mechanism underlying the proliferative response to PNA. This was investigated in HT29, T84, and Caco2 colon cancer cells. Parallel lectin and immunoblotting of PNA affinity-purified HT29 cell membrane extracts showed PNA binding to high molecular weight CD44v6 isoforms. Within 5 min, PNA (25 microg/mL) caused a 6-fold increase in phosphorylation of hepatocyte growth factor receptor c-Met, known to co-associate with CD44v6. This was followed by the downstream activation of p44/p42 mitogen-activated protein kinase (MAPK) over 15-20 min. The presence of 100 microg/mL asialofetuin, a TF antigen-expressing glycoprotein, blocked both PNA-induced c-Met and MAPK activation. A similar PNA-induced c-Met and MAPK phosphorylation was also seen in T84 cells that express CD44v6 but not in Caco2 cells that lack CD44v6. PNA-induced cell proliferation was completely blocked by 1 microM PD98059, an inhibitor of MAPK activation (p < 0.0001). The expression of TF antigen by CD44 isoforms in colonic epithelial cells allows lectin-induced mitogenesis that is mediated by phosphorylation of c-Met and MAPK. It provides a mechanism by which dietary, microbial, or endogenous galactose-binding lectins could affect epithelial proliferation in the cancerous and precancerous colon.

The effects of lectins on indomethacin-induced small intestinal ulceration

Growth factors, such as epidermal growth factor and keratinocyte growth factor, have considerable therapeutic potential for repairing mucosal injury in the intestine when given systemically. Recently, several lectins have been shown to have trophic effects on the intestine when given orally. We examined the effects of phytohaemagglutinin (PHA) and concanavalin A (Con-A) on indomethacin-induced intestinal injury in rat. Five-week-old rats were randomized to four groups (n=5), and intestinal injury was induced by indomethacin injection in three of these groups. Elemental diet (ED) feeding was then commenced. The groups were thus ED feeding/indomethacin untreated (control group), ED feeding/indomethacin treated (ED group), 0.1% PHA-supplemented ED feeding/indomethacin treated (PHA group) and 0.1% Con-A-supplemented ED feeding/indomethacin treated (Con-A group). After 7 days of feeding, macroscopic inflammatory scores, mucosal permeability, myeloperoxidase (MPO) activities and cell proliferation were determined. Macroscopic inflammatory scores, mucosal permeability and MPO activities were significantly lower in both lectin groups than that in control group. Twenty-four hour excretion rate of phenolsulphonphthalein was significantly lower in both lectin groups than that in ED group. Cell proliferation of the small intestine was significantly increased by both lectins. Lectin supplementation can induce ulcer healing following indomethacin-induced damage.

Morphological changes of cell proliferation and apoptosis in rat jejunal mucosa at different ages

AIM: To study the changes of cell proliferation and apoptosis in rat jejunal epithelium at different ages.

METHODS: Cell proliferation and apoptosis of the jejunal mucosal and glandulous epithelia from birth to postnatal 12^th month were observed using immunocytochemistry (ICC), and TUNEL method. The height of villus, the thickness of muscle layer and the number of goblet cells in jejunal mucosal and glandulous epithelia were measured by BeiHang analytic software and analyzed by STAT.

RESULTS: (1) Proliferating cell nuclear antigen (PCNA) positive cells of jejunal glandulous recess were found and increased in number from birth to the postnatal 3^rd month. The number of PCNA positive cells peaked in the postnatal 3^rd month, and decreased from then on. (2) The number of apoptotic cells also peaked in the postnatal 3^rd month, showing a similar trend to that of the PCNA positive cells. (3) The height of jejunal villus increased after birth, peaked in the postnatal 3^rd month and decreased from then on. The jejunal muscle layer became thicker in the postnatal 3^rd week and the postnatal 12^th month. The number of goblet cells of the jejunal mucosal and glandulous epithelia had a linear correlation with age.

CONCLUSION: (1) PCNA positive cells are distributed in the jejunal glandulous recess. (2) Apoptotic cell number peaks in the postnatal 3^rd month, indicating that cell proliferation and apoptosis are developed with the formation of digestive metabolism as rat grows to maturity. (3) The thickness of jejunal muscle layer increases to a maximum in the postnatal 3^rd week, which may be related to the change in diet from milk to solid food. (4) The number of goblet cells increases rapidly in the postnatal 3^rd week, probably due to ingestion of solid food.

Acidomucin goblet cell expansion induced by parenteral nutrition in the small intestine of piglets

Total parenteral nutrition (TPN) impairs small intestine development and is associated with barrier failure, inflammation, and acidomucin goblet cell expansion in neonatal piglets. We examined the relationship between intestinal goblet cell expansion and molecular and cellular indices of inflammation in neonatal piglets receiving TPN, 80% parenteral + 20% enteral nutrition (PEN), or 100% enteral nutrition (control) for 3 or 7 days. Epithelial permeability, T cell numbers, TNF-alpha and IFN-gamma mRNA expression, and epithelial proliferation and apoptosis were compared with goblet cell numbers over time. Epithelial permeability was similar to control in the TPN and PEN jejunum at day 3 but increased in the TPN jejunum by day 7. By day 3, intestinal T cell numbers were increased in TPN but not in PEN piglets. However, goblet cell expansion was established by day 3 in both the TPN and PEN ileum. Neither TNF-alpha nor IFN-gamma mRNA expression in the TPN and PEN ileum correlated with goblet cell expansion. Thus goblet cell expansion occurred independently of overt inflammation but in association with parenteral feeding. These data support the hypothesis that goblet cell expansion represents an initial defense triggered by reduced epithelial renewal to prevent intestinal barrier failure.

Dietary lectins can stimulate pancreatic growth in the rat

Lectins are proteins or glycoproteins of nonimmune origin, which bind specifically to carbohydrate structures. They are widespread in the human diet, and many are resistant to digestion. High doses of lectins have been shown to stimulate intestinal and pancreatic growth. The aim of the present study was to investigate the long-term actions of low doses of lectins on the rat intestine and pancreas. A long-term carcinogenesis study was performed using low levels (40 micro g/rat/day) of peanut (PNA) or mushroom lectin (ABA) which bind to O-linked (mucin-type) oligosaccharides in the gut. While this was primarily designed as a colon carcinogenesis study, the pancreas was also investigated. No significant changes in colon carcinogenesis were seen, however, the colons were slightly heavier in the lectin treated groups. The weight of the pancreas was significantly greater (by 18 and 23%) in both lectin treated groups (P < 0.03/0.001). The weights of the acini and septal tissue were also increased by 39-46% in PNA and ABA fed animals, respectively (P < 0.002); there was no significant change in the endocrine pancreas. In conclusion, long-term feeding of low doses of lectin can influence pancreatic growth, and this trophic action may have potential adverse implications for the development of pancreatic cancer in humans.