Gastrointestinal polyamines and regulation of mucosal growth and function

Ganoderma lucidum polysaccharides reduce methotrexate-induced small intestinal damage in mice via induction of epithelial cell proliferation and migration

AIM

To study the effects of Ganoderma lucidum polysaccharides (Gl-PS) on methotrexate (MTX)-induced small intestinal damage in mice and the underlying mechanisms.

METHODS

BALB/c mice were used for in vivo study. The mice were administered with Gl-PS (50, 100, or 200 mg/kg, ig) for 10 d, and injected with MTX (50 mg/kg, ip) on d 7 and 8 to induce intestinal damage, and then sacrificed on d 11 for morphological study and tissue malondialdehyde (MDA) and superoxide dismutase (SOD) measurements. Before sacrificing, blood samples were collected to analyze immunoglobulin A (IgA). Rat intestinal IEC-6 cells were used for in vitro study. Cell proliferation and migration were assessed using MTT method and an in vitro wounding model, respectively. Transforming growth factor β (TGFβ) protein expression was determined using ELISA assay. Ornithine decarboxylase (ODC) and c-Myc mRNA expression profiles were determined using RT-PCR.

RESULTS

MTX treatment caused severe mucosal damage, significantly increased small intestine MDA levels, and decreased SOD and serum IgA levels in BALB/c mice. Gl-PS (100 and 200 mg/kg) markedly reversed the MTX effects. In IEC-6 cells, Gl-PS (0.1, 1, and 10 μg/mL) significantly stimulated the cell proliferation. Furthermore, Gl-PS (10 μg/mL) significantly stimulated the cell migration. In addition, Gl-PS (10 and 20 μg/mL) significantly increased the expression of ODC and c-Myc mRNAs. However, Gl-PS (up to 20 μg/mL) had no effect on the expression of TGFβ protein.

CONCLUSION

The results suggest that Gl-PS protects small intestine against MTX-induced injury via induction of epithelial cell proliferation and migration.

Amine modification of digested peptide at C-terminal end during protein digestion by protease

We recently reported that C-terminal polyamine modification occurs when proteins are digested with trypsin in the presence of polyamine [Biochem. Biophys. Res. Commun., 356, 159-162 (2007)]. In the present study, the characteristics of this C-terminal modification in the presence of protease and amine were investigated. When hemoglobin (HB) was digested with trypsin in the presence of N-(2-pyridyl)-1,4-diaminobutane (Py4), formation of the modified peptide was dependent on time and on HB or Py4 concentration. When synthetic peptide was treated with trypsin in the presence of Py4, ca. 0.1% of the peptide was modified with Py4. When HB or cytochrome C was treated with a range of serine proteases in the presence of various amines (Py4, N-(2-pyridyl)-1,3-diaminopropane, tranexamic acid, isonicotinic acid hydrazide and ampicillin), the modified peptide was detected in all cases tested, thus suggesting that amine modification widely accompanies digestion by proteases.

Oral polyamine administration modifies the ontogeny of hexose transporter gene expression in the postnatal rat intestine

Gastrointestinal mucosal polyamines influence enterocyte proliferation and differentiation during small intestinal maturation in the rat. Studies in postnatal rats have shown that ornithine decarboxylase (ODC) protein and mRNA peak before the maximal expression of brush-border membrane (BBM) sucrase-isomaltase (SI) and the sugar transporters sodium-dependent glucose transporter 1 (SGLT1) and glucose transporter 2 (GLUT2). This study was undertaken to test the hypothesis that the oral administration of spermidine in postnatal rats upregulates the expression of ODC, thereby enhancing the expression of SI and SGLT1 in the brush-border membrane as well as basolateral membrane-facilitative GLUT2 and Na(+)-K(+)-ATPase. Northern and Western blot analyses were performed with antibodies and cDNA probes specific for SI, SGLT1, GLUT2, alpha(1)- and beta(1)-subunits of Na(+)-K(+)-ATPase, and ODC. Postnatal rats fed 6 mumol spermidine daily for 3 days from days 7 to 9 were killed either on postnatal day 10 (Sp10) or day 13 following a 3-day washout period (Sp13). Sp10 rats showed a precocious increase in the abundance of mRNAs for SI, SGLT1, and GLUT2 and Na(+)-K(+)-ATPase activity and alpha(1)- and beta(1)-isoform gene expression compared with controls. ODC activity and protein and mRNA abundance were also increased in Sp10 animals. The increased expression of these genes was not sustained in Sp13 rats, suggesting that these effects were transient. Thus, 3 days of oral polyamine administration induces the precocious maturation of glucose transporters in the postnatal rat small intestine, which may be mediated by alterations in ODC expression.

Formation of polyamine-modified peptides during protein digestion

The effect of polyamines on the digestion of proteins by serine proteases was examined. Based on the mechanism of action of serine proteases, it was anticipated that nucleophilic functionalities such as amino groups in polyamine, rather than hydroxyl ions, would react with peptide bonds during the hydrolysis process. If this were the case, polyamine might be covalently linked to the C-terminus of the product peptides during protein digestion. In order to test this hypothesis, hemoglobin was used as a model protein and was digested with trypsin in the presence of polyamine. The product peptides were separated, collected by HPLC, and analyzed by MALDI-TOF MS using post-source decay. The results showed that some peptides were indeed modified with polyamine at the C-terminus.

Effects of amino acid-derived luminal metabolites on the colonic epithelium and physiopathological consequences

Depending on the amount of alimentary proteins, between 6 and 18 g nitrogenous material per day enter the large intestine lumen through the ileocaecal junction. This material is used as substrates by the flora resulting eventually in the presence of a complex mixture of metabolites including ammonia, hydrogen sulfide, short and branched-chain fatty acids, amines; phenolic, indolic and N-nitroso compounds. The beneficial versus deleterious effects of these compounds on the colonic epithelium depend on parameters such as their luminal concentrations, the duration of the colonic stasis, the detoxication capacity of epithelial cells in response to increase of metabolite concentrations, the cellular metabolic utilization of these metabolites as well as their effects on colonocyte intermediary and oxidative metabolism. Furthermore, the effects of metabolites on electrolyte movements through the colonic epithelium must as well be taken into consideration for such an evaluation. The situation is further complicated by the fact that other non-nitrogenous compounds are believed to interfere with these various phenomenons. Finally, the pathological consequences of the presence of excessive concentrations of these compounds are related to the short- and, most important, long-term effects of these compounds on the rapid colonic epithelium renewing and homeostasis.

Modulation of cell proliferation and polyamine metabolism in rat liver cell cultures by the iron chelator O-trensox

The antiproliferative effects of the iron chelator O-trensox and the ornithine-decarboxylase (ODC) inhibitor alpha-difluoromethylornithine (DFMO) were characterized in the rat hepatoma cell line FAO, the rat liver epithelial cell line (RLEC) and the primary rat hepatocyte cultures stimulated by EGF. We observed that O-trensox and DFMO decreased cell viabilty and DNA replication in the three culture models. The cytostatic effect of O-trensox was correlated to a cytotoxicity, higher than for DFMO, and to a cell cycle arrest in G0/G1 or S phases. Moreover, O-trensox and DFMO decreased the intracellular concentration of spermidine in the three models without changing significantly the spermine level. We concluded that iron, but also polyamine depletion, decrease cell growth. However, the drop in cell proliferation obtained with O-trensox was stronger compared to DFMO effect. Altogether, our data provide insights that, in the three rat liver cell culture models, the cytostatic effect of the iron chelator O-trensox may be the addition of two mechanisms: iron and polyamine depletion.

Gut hormones, and short bowel syndrome: The enigmatic role of glucagon-like peptide-2 in the regulation of intestinal adaptation

Short bowel syndrome (SBS) refers to the malabsorption of nutrients, water, and essential vitamins as a result of disease or surgical removal of parts of the small intestine. The most common reasons for removing part of the small intestine are due to surgical intervention for the treatment of either Crohn's disease or necrotizing enterocolitis. Intestinal adaptation following resection may take weeks to months to be achieved, thus nutritional support requires a variety of therapeutic measures, which include parenteral nutrition. Improper nutrition management can leave the SBS patient malnourished and/or dehydrated, which can be life threatening. The development of therapeutic strategies that reduce both the complications and medical costs associated with SBS/long-term parenteral nutrition while enhancing the intestinal adaptive response would be valuable.

Currently, therapeutic options available for the treatment of SBS are limited. There are many potential stimulators of intestinal adaptation including peptide hormones, growth factors, and neuronally-derived components. Glucagon-like peptide-2 (GLP-2) is one potential treatment for gastrointestinal disorders associated with insufficient mucosal function. A significant body of evidence demonstrates that GLP-2 is a trophic hormone that plays an important role in controlling intestinal adaptation. Recent data from clinical trials demonstrate that GLP-2 is safe, well-tolerated, and promotes intestinal growth in SBS patients. However, the mechanism of action and the localization of the glucagon-like peptide-2 receptor (GLP-2R) remains an enigma. This review summarizes the role of a number of mucosal-derived factors that might be involved with intestinal adaptation processes; however, this discussion primarily examines the physiology, mechanism of action, and utility of GLP-2 in the regulation of intestinal mucosal growth.

Polyamines are absorbed through a y+ amino acid carrier in rat intestinal epithelial cells

Due to the similarity in transport characteristics of polyamines and the y+ basic amino acid system, we hypothesized that both substrates could be moving through a common carrier site. Competitive and cross inhibition experiments in intestinal epithelial cells revealed the possibility of a common transport site. N-ethylmalemide (NEM) inhibited both lysine and putrescine transport, confirming that both were carried by a y+ transporter. Overexpressing the y+ transporter CAT-1 in a polyamine transport-deficient cell line, CHO-MG, did not reconstitute polyamine-transport. Thus, polyamines are not traveling through CAT-1. To determine if lysine is carried by a polyamine transport site, an antizyme-overexpressing cell line was used. Antizyme overexpression decreased polyamine uptake by 50%; in contrast, lysine transport was unaffected. Therefore, lysine is not traveling through a polyamine transport site. It appears that polyamines and lysine are likely traveling through a common unknown y+ transport site.

Spermine-induced negative inotropic effect in isolated rat heart, is mediated through the release of ATP

Putrescine, spermidine and spermine are natural compounds found in up to millimolar concentrations in eukaryotic and prokaryotic cells. At physiologic pH, the polyamines are protonated (+2, +3 and +4 charges), their polycationic properties lead to the assumption that they could affect physiological systems by binding to anionic sites of the cellular membrane and/or by modulating ion channels. At the cardiovascular level, their effects are not completely understood. However, these compounds may be able to exert the induction of synthesis and release of cellular mediators. In an attempt to explore this possibility, we used the isolated and perfused rat heart, Langendorff, model in order to evaluate the inotropic effects of these polyamines, putrescine, spermidine and spermine. Dose-response curves (0.1-0.6 mM) for putrescine, spermidine and spermine were constructed; with the finding that spermine had the largest negative effect. The obtained effects were not blocked by nitric oxide synthesis inhibitors (L-NAME), H(1) and H(2) receptor antagonists (Brompheniramine and Cimetidine) or by Glibenclamide, an antagonist of ATP-sensitive K(+) channels. We found that spermine-induced and increased ATP concentration in cardiac effluents. Reactive Blue, a P(2y) purinoreceptor antagonist and Aminophylline, an unspecific adenosine receptor antagonist, blocked the spermine-induced effects. These results showed that ATP, at least in part, is responsible of the spermine cardiovascular effects. Adenosine was shown to also play an important role on those effects.

Fate of orally administered 15N-labeled polyamines in rats bearing solid tumors

We studied absorption, distribution, metabolism, and excretion of polyamines (putrescine, spermidine, and spermine) in the gastrointestinal tract using (15)N-labeled polyamines as tracers and ionspray ionization mass spectrometry (IS-MS). The relatively simple protocol using rats bearing solid tumors provided useful information. Three (15)N-labeled polyamines that were simultaneously administered were absorbed equally from gastrointestinal tract, and distributed within tissues at various concentrations. The uptake of (15)N-spermidine seemed preferential to that of (15)N-spermine since the concentrations of (15)N-spermidine in the liver and tumors were higher, whereas those of (15)N-spermine were higher in the kidney, probably due to the excretion of excess extracellular spermine. Most of the absorbed (15)N-putrescine seemed to be lost, suggesting blood and tissue diamine oxidase degradation. Concentrations of (15)N-spermidine and (15)N-spermine in the tumor were low. We also describe the findings from two rats that were administered with (15)N-spermine. The tissue concentrations of (15)N-spermine were unusually high, and significant levels of (15)N-spermidine were derived from (15)N-spermine in these animals.

Rat colon ornithine and arginine metabolism: coordinated effects after proliferative stimuli

Ornithine decarboxylase (ODC) catalyzes the first step in the polyamine biosynthetic pathway, a highly regulated pathway in which activity increases during rapid growth. Other enzymes also metabolize ornithine, and in hepatomas, rate of growth correlates with decreased activity of these other enzymes, which thus channels more ornithine to polyamine biosynthesis. Ornithine is produced from arginase cleavage of arginine, which also serves as the precursor for nitric oxide production. To study whether short-term coordination of ornithine and arginine metabolism exists in rat colon, ODC, ornithine aminotransferase (OAT), arginase, ornithine, arginine, and polyamine levels were measured after two stimuli (refeeding and/or deoxycholate exposure) known to synergistically induce ODC activity. Increased ODC activity was accompanied by increased putrescine levels, whereas OAT and arginase activity were reduced by either treatment, accompanied by an increase in both arginine and ornithine levels. These results indicate a rapid reciprocal change in ODC, OAT, and arginase activity in response to refeeding or deoxycholate. The accompanying increases in ornithine and arginine concentration are likely to contribute to increased flux through the polyamine and nitric oxide biosynthetic pathways in vivo.

Treatment with agmatine inhibits Cryptosporidium parvum infection in infant mice

Cryptosporidium parvum is an intracellular protozoan parasite that causes enteric infection and diarrhea in a wide range of mammalian hosts, including humans and economically important livestock species. There are no effective vaccines or drug treatments available for cryptosporidiosis. Cryptosporidium parvum utilizes a unique metabolic pathway for the synthesis of polyamines, forming agmatine as an intermediary metabolite. We treated infant mice with oral doses of agmatine for 2 days before, the day of, and 5 days following experimental infection with C. parvum. Mice treated with agmatine were significantly less infected with C. parvum than were control mice receiving phosphate-buffered saline. Mice treated with agmatine only on the day of experimental infection with C. parvum were also significantly less infected than were control mice. These data suggest that exogenous agmatine alters the metabolism of C. parvum sufficient to interfere with its ability to colonize the mammalian intestine.

Polyamines in human and animal milk

Polyamines are highly regulated polycations which are essentially involved in cell growth and differentiation. Polyamines in food significantly contribute to the polyamine body pool. Dietary polyamines exert various direct and indirect trophic effects on the rat's immature intestine and play an important role during intestinal maturation. Human milk and that of other mammalians contain relatively high levels of polyamines which are essential luminal growth and maturation factors. The polyamines spermidine and spermine as well as their diamine precursor putrescine are ubiquitous normal constituents of all prokaryotic and eukaryotic cells and are essentially involved in various processes of cell growth and differentiation (Pegg & McCann, 1982; Tabor & Tabor, 1984; Seiler, 1990).

Polyamines in the gastro-intestinal tract of goat kids and in the regenerating ruminal epithelium of sheep

The aim of the present study was to investigate whether temporal changes in polyamine concentration and synthesis could be found in the luminal content and wall tissue of the rumen and abomasum, two organs which have entirely different growth patterns during the first month of life. In the abomasal mucosa there was a marked gradual decrease in the ornithine decarboxylase (ODC) activity during the first month of life, while the ODC activity in the ruminal mucosa was low during the whole experimental period. However, injury of the rumen wall was followed by increased ODC activity. The ODC activity in duodenal mucosa was about 10 times higher than in the ileal mucosa and the ruminal epithelium. In ruminal liquid a clear peak in ODC activity was observed during the period 51-70 days after birth. The polyamine concentration did not parallel the ODC activity, in either the ruminal epithelium or the ruminal liquid. Of the polyamines, the spermine concentration was always highest, and with the exception of duodenal mucosa, the putrescine concentration was lowest. In liver a clear decrease in spermidine concentration from day 1 to about day 60 after birth was observed. Otherwise no marked temporal changes in tissue polyamine concentrations were observed. Two and a half hours after oral administration of 14C-labelled spermine, nearly all of the radioactivity was found in the lumen of the gastrointestinal tract. On the other hand, 1 h after intravenous injection of polyamines the walls of the gastrointestinal tract were strongly labelled. In conclusion, the polyamines needed for ruminal epithelial development seem to come from sources other than the ruminal epithelium itself or the ruminal lumen.

Ontogeny of intestinal nutrient transport

Children born prematurely lack the ability to digest and to absorb nutrients at rates compatible with their nutritional needs. As a result, total parenteral nutrition may need to be given. While this nutritional support may be life-saving, the baby who receives this therapy is exposed to the risks of possible sepsis, catheter dysfunction, and liver disease. The rodent model of postnatal development provides a useful framework to investigate some of the cellular features of human intestinal development. The up-regulation of intestinal gene expression and precocious development of intestinal nutrient absorption can be achieved by providing growth factor(s) or by modifying the composition of the maternal diet during pregnancy and nursing or the weaning diet of the infant. Accelerating the digestive and absorptive functions of the intestine would thereby allow for the maintenance of infant nutrition through oral food intake, and might possibly eliminate the need for, and risks of, total parenteral nutrition. Accordingly, this review was undertaken to focus on the adaptive processes available to the intestine, to identify what might be the signals for and mechanisms of the modified nutrient absorption, and to speculate on approaches that need to be studied as means to possibly accelerate the adaptive processes in ways which would be beneficial to the newborn young.Key words: absorption, adaptation, diet, peptides.

The human gut bacteria Bacteroides thetaiotaomicron and Fusobacterium varium produce putrescine and spermidine in cecum of pectin-fed gnotobiotic rats

Pectin is a soluble indigestible polysaccharide that stimulates cecal polyamine formation in rats. Bacteroides and fusobacteria, two numerically dominant bacterial population groups in the large intestine, were found to synthesize in vitro high amounts of spermidine and putrescine. The purpose of this study was to elucidate the effect of pectin on the polyamine production by defined bacterial species in vivo. Germfree male Wistar rats (n = 18) were randomly assigned to one of three treatments: (i) monoassociation with Bacteroides thetaiotaomicron + fiber-free diet; (ii) diassociation with B. thetaiotaomicron + Fusobacterium varium + fiber-free diet or (iii) diassociation with B. thetaiotaomicron + F. varium + fiber-free diet + 10% pectin. The cecal contents of monoassociated rats fed fiber-free diet contained large amounts (1.51+/-0.21 micromol/dry total cecum content) of spermidine which was the major polyamine. The cecum of diassociated rats fed the fiber-free diet contained even higher concentrations of spermidine (2.53+/-0.21 micromol/dry total cecum content) and also putrescine, which was now the dominant polyamine (putrescine 0.32+/-0.28 vs. 3.01+/-0.28 micromol/dry total cecum content; monoassociation vs. diassociation). Pectin consumption by diassociated rats led to an additional increase in the cecal concentrations of all polyamines: putrescine, spermidine and spermine were 40, 37 and 100%, respectively, higher in the diassociated rats consuming the pectin diet than in those consuming the pectin-free diet. Since the microbial counts in the cecum did not differ in the diassociated treatment groups, the elevated concentrations of polyamines observed in the pectin group must have been due to stimulated bacterial polyamine synthesis. The decline of individual polyamines from cecum to feces detected at the end of the study in all treatment groups and the high microbial counts in the cecum and in feces suggest that bacterial polyamines are absorbed in cecum and colon. Pectin stimulates intestinal microbes to synthesize large amounts of polyamines which may be utilized by the host.

Spermidine-induced glycoprotein fucosylation in immature rat intestine

In rat small intestine, during postnatal development, the glycoprotein fucosylation is markedly increased at weaning. At the same time, a rise in the intestinal spermidine level was observed, partly due to the increase in the spermidine content of solid food given to animals at this period as compared to the spermidine content of milk. In order to mimic the spermidine increase observed in weanling rat intestines, we had treated suckling rats with spermidine by oral ingestion to study its role as maturation factor of the small intestine. In spermidine-treated suckling rats, the spermidine and N-acetyl-spermidine contents were highly increased. Spermidine treatment induced the rise in alpha-1,2-fucosyltransferase activity and the precocious appearance in the brush-border membrane of some alpha-1,2-fucoproteins in weaned rats. Such results indicate that spermidine could be a maturation factor implicated in the appearance of alpha-1,2-fucoproteins naturally observed at weaning time.

Spermine affects intestinal in vitro permeability to different-sized molecules in rats

The gut epithelial lining is normally an effective barrier to entry of luminal bacteria and macromolecules into the body and dietary polyamines may influence its function. Therefore, the effects of spermine on regional intestinal permeability to different-sized marker molecules in rats were investigated in Ussing diffusion chambers. Mucosal exposure to 1 mM spermine reduced the permeation of the marker Na-fluorescein in jejunum, expressed as the apparent permeability coefficient (Papp). In contrast, Papp for Na-fluorescein was increased by 10 mM spermine in ileum and by 50 mM spermine in both jejunum and ileum. No effects were observed on [51Cr]-EDTA permeability in any of the intestinal regions. For the larger marker molecules, bovine serum albumin (BSA) and FITC-dextran 71200 (FITC-D), mucosal exposure to 0.5 mM spermine reduced Papp in colon. Spermine (10 mM), increased Papp for FITC-D in all regions and for BSA only in ileum, while Papp for BSA was increased by 50 mM spermine in both jejunum and ileum. The effects of spermine on the intestinal permeability to different-sized molecules generally seemed to depend on the intestinal region and on the polyamine concentration; higher spermine concentrations (10-50 mM) enhanced, while lower (0.5-1 mM) decreased the permeability. These findings may be important when trying to modulate epithelial barrier functions, especially during barrier dysfunction.