Gastrointestinal luminal polyamines: cellular accumulation and enterohepatic circulation

The Role of the Gallbladder, the Intestinal Barrier and the Gut Microbiota in the Development of Food Allergies and Other Disorders

The microbiota present in the gastrointestinal tract is involved in the development or prevention of food allergies and autoimmune disorders; these bacteria can enter the gallbladder and, depending on the species involved, can either be benign or cause significant diseases. Occlusion of the gallbladder, usually due to the presence of calculi blocking the bile duct, facilitates microbial infection and inflammation, which can be serious enough to require life-saving surgery. In addition, the biliary salts are secreted into the intestine and can affect the gut microbiota. The interaction between the gut microbiota, pathogenic organisms, and the human immune system can create intestinal dysbiosis, generating a variety of syndromes including the development of food allergies and autoimmune disorders. The intestinal microbiota can aggravate certain food allergies, which become severe when the integrity of the intestinal barrier is affected, allowing bacteria, or their metabolites, to cross the intestinal barrier and invade the bloodstream, affecting distal body organs. This article deals with health conditions and severe diseases that are either influenced by the gut flora or caused by gallbladder obstruction and inflammation, as well as putative treatments for those illnesses.

Quantitative input-output dynamics of a c-di-GMP signal transduction cascade in Vibrio cholerae

Bacterial biofilms are multicellular communities that collectively overcome environmental threats and clinical treatments. To regulate the biofilm lifecycle, bacteria commonly transduce sensory information via the second messenger molecule cyclic diguanylate (c-di-GMP). Using experimental and modeling approaches, we quantitatively capture c-di-GMP signal transmission via the bifunctional polyamine receptor NspS-MbaA, from ligand binding to output, in the pathogen Vibrio cholerae. Upon binding of norspermidine or spermidine, NspS-MbaA synthesizes or degrades c-di-GMP, respectively, which, in turn, drives alterations specifically to biofilm gene expression. A long-standing question is how output specificity is achieved via c-di-GMP, a diffusible molecule that regulates dozens of effectors. We show that NspS-MbaA signals locally to specific effectors, sensitizing V. cholerae to polyamines. However, local signaling is not required for specificity, as changes to global cytoplasmic c-di-GMP levels can selectively regulate biofilm genes. This work establishes the input-output dynamics underlying c-di-GMP signaling, which could be useful for developing bacterial manipulation strategies.

Activation of whole body by high levels of polyamine intake in rats

Polyamines are important to the survival and activation of organs and tissues via a homeostatic cell-metabolic process, and the polyamine content in cytoplasm decreases with aging. Decreases in cellular polyamine have been known to augment mutagenesis and cell death. Thus, supplementary polyamine in food is important to the prevention of aging. Here we show the anti-aging effects of oral intake of polyamine using luciferase-transgenic rats. Healthy rats, 10–12 weeks old, were given foods containing 0.01% and 0.1% (w/w) of polyamine, as compared a control food without polyamine, for 4 weeks. Using a bioimaging system, the photon intensities seen in the whole bodies and livers of rats consuming 0.1% of polyamine in food were stronger than those in rats consuming 0.01% and 0% of polyamine. However, there were no differences between groups in other characteristics, such as liver damage and body weight. In conclusion, we found that polyamine intake can activate cells throughout the whole body, providing an anti-aging effect.

Role of agmatine in the application of neural progenitor cell in central nervous system diseases: therapeutic potentials and effects

Agmatine, the primary decarboxylation product of L-arginine, generated from arginine decarboxylase. Since the discovery of agmatine in the mammalian brain in the 1990s, an increasing number of agmatine-mediated effects have been discovered, demonstrating the benefits of agmatine on ischemic strokes, traumatic brain injury and numerous psychological disorders such as depression, anxiety, and stress. Agmatine also has cellular protective effects and contributes to cell proliferation and differentiation in the central nervous system (CNS). Neural progenitor cells are an important component in the recovery and repair of many neurological disorders due to their ability to differentiate into functional adult neurons. Recent data has revealed that agmatine can regulate and increase proliferation and the fate of progenitor cells in the adult hippocampus. This review aims to summarise and discuss the role of agmatine in the CNS; specifically, the effects and relationship between agmatine and neural progenitor cells and how these ideas can be applied to potential therapeutic application.

Inverse regulation of Vibrio cholerae biofilm dispersal by polyamine signals

The global pathogen Vibrio cholerae undergoes cycles of biofilm formation and dispersal in the environment and the human host. Little is understood about biofilm dispersal. Here, we show that MbaA, a periplasmic polyamine sensor, and PotD1, a polyamine importer, regulate V. cholerae biofilm dispersal. Spermidine, a commonly produced polyamine, drives V. cholerae dispersal, whereas norspermidine, an uncommon polyamine produced by vibrios, inhibits dispersal. Spermidine and norspermidine differ by one methylene group. Both polyamines control dispersal via MbaA detection in the periplasm and subsequent signal relay. Our results suggest that dispersal fails in the absence of PotD1 because endogenously produced norspermidine is not reimported, periplasmic norspermidine accumulates, and it stimulates MbaA signaling. These results suggest that V. cholerae uses MbaA to monitor environmental polyamines, blends of which potentially provide information about numbers of ‘self’ and ‘other’. This information is used to dictate whether or not to disperse from biofilms.

Health-Promoting Effects of Dietary Polyamines

The purpose of this paper is to summarize the latest information on the various aspects of polyamines and their health benefits. In recent years, attempts to treat cancer by reducing elevated polyamines levels in cancer cells have been made, with some advancing to clinical trials. However, it has been reported since 2009 that polyamines extend the healthy life span of animals by inducing autophagy, protecting the kidneys and liver, improving cognitive function, and inhibiting the progression of heart diseases. As such, there is conflicting information regarding the relationship between polyamines and health. However, attempts to treat cancer by decreasing intracellular polyamines levels are a coping strategy to suppress the proliferation-promoting effects of polyamines, and a consensus is being reached that polyamine intake does not induce cancer in healthy individuals. To provide further scientific evidence for the health-promoting effects of polyamines, large-scale clinical studies involving multiple groups are expected in the future. It is also important to promote basic research on polyamine intake in animals, including elucidation of the polyamine balance between food, intestinal bacteria, and biosynthesis.

Analysis of interaction between intracellular spermine and transient receptor potential canonical 4 channel: multiple candidate sites of negatively charged amino acids for the inward rectification of transient receptor potential canonical 4

Transient receptor potential canonical 4 (TRPC4) channel is a nonselective calcium-permeable cation channels. In intestinal smooth muscle cells, TRPC4 currents contribute more than 80% to muscarinic cationic current (mIcat). With its inward-rectifying current-voltage relationship and high calcium permeability, TRPC4 channels permit calcium influx once the channel is opened by muscarinic receptor stimulation. Polyamines are known to inhibit nonselective cation channels that mediate the generation of mIcat. Moreover, it is reported that TRPC4 channels are blocked by the intracellular spermine through electrostatic interaction with glutamate residues (E728, E729). Here, we investigated the correlation between the magnitude of channel inactivation by spermine and the magnitude of channel conductance. We also found additional spermine binding sites in TRPC4. We evaluated channel activity with electrophysiological recordings and revalidated structural significance based on Cryo-EM structure, which was resolved recently. We found that there is no correlation between magnitude of inhibitory action of spermine and magnitude of maximum current of the channel. In intracellular region, TRPC4 attracts spermine at channel periphery by reducing access resistance, and acidic residues contribute to blocking action of intracellular spermine; channel periphery, E649; cytosolic space, D629, D649, and E687.

Dietary and Gut Microbiota Polyamines in Obesity- and Age-Related Diseases

The polyamines putrescine, spermidine, and spermine are widely distributed polycationic compounds essential for cellular functions. Intracellular polyamine pools are tightly regulated by a complex regulatory mechanism involving de novo biosynthesis, catabolism, and transport across the plasma membrane. In mammals, both the production of polyamines and their uptake from the extracellular space are controlled by a set of proteins named antizymes and antizyme inhibitors. Dysregulation of polyamine levels has been implicated in a variety of human pathologies, especially cancer. Additionally, decreases in the intracellular and circulating polyamine levels during aging have been reported. The differences in the polyamine content existing among tissues are mainly due to the endogenous polyamine metabolism. In addition, a part of the tissue polyamines has its origin in the diet or their production by the intestinal microbiome. Emerging evidence has suggested that exogenous polyamines (either orally administrated or synthetized by the gut microbiota) are able to induce longevity in mice, and that spermidine supplementation exerts cardioprotective effects in animal models. Furthermore, the administration of either spermidine or spermine has been shown to be effective for improving glucose homeostasis and insulin sensitivity and reducing adiposity and hepatic fat accumulation in diet-induced obesity mouse models. The exogenous addition of agmatine, a cationic molecule produced through arginine decarboxylation by bacteria and plants, also exerts significant effects on glucose metabolism in obese models, as well as cardioprotective effects. In this review, we will discuss some aspects of polyamine metabolism and transport, how diet can affect circulating and local polyamine levels, and how the modulation of either polyamine intake or polyamine production by gut microbiota can be used for potential therapeutic purposes.

Beneficial effects of spermidine on cardiovascular health and longevity suggest a cell type-specific import of polyamines by cardiomyocytes

Recent and exciting in vivo studies show that supplementation with the polyamine spermidine (Spd) is cardioprotective and prolongs lifespan in both mice and humans. The mechanisms behind Spd-induced cardioprotection are supposed to involve Spd-evoked stimulation of autophagy, mitophagy and mitochondrial respiration and improved the mechano-elastical function of cardiomyocytes. Although cellular uptake of Spd was not characterized, these results suggest that Spd is imported by the cardiomyocytes and acts intracellularly. In the light of these new and thrilling data, we discuss in the present review cellular polyamine import with a special focus on mechanisms that may be relevant for Spd uptake by electrically excitable cells such as cardiomyocytes.

Personalizing protein nourishment

Proteins are not equally digestible-their proteolytic susceptibility varies by their source and processing method. Incomplete digestion increases colonic microbial protein fermentation (putrefaction), which produces toxic metabolites that can induce inflammation in vitro and have been associated with inflammation in vivo. Individual humans differ in protein digestive capacity based on phenotypes, particularly disease states. To avoid putrefaction-induced intestinal inflammation, protein sources, and processing methods must be tailored to the consumer's digestive capacity. This review explores how food processing techniques alter protein digestibility and examines how physiological conditions alter digestive capacity. Possible solutions to improving digestive function or matching low digestive capacity with more digestible protein sources are explored. Beyond the ileal digestibility measurements of protein digestibility, less invasive, quicker and cheaper techniques for monitoring the extent of protein digestion and fermentation are needed to personalize protein nourishment. Biomarkers of protein digestive capacity and efficiency can be identified with the toolsets of peptidomics, metabolomics, microbial sequencing and multiplexed protein analysis of fecal and urine samples. By monitoring individual protein digestive function, the protein component of diets can be tailored via protein source and processing selection to match individual needs to minimize colonic putrefaction and, thus, optimize gut health.

Spermine inhibits Vibrio cholerae biofilm formation through the NspS-MbaA polyamine signaling system

The aquatic bacterium and human intestinal pathogen, Vibrio cholerae, senses and responds to a variety of environment-specific cues to regulate biofilm formation. Specifically, the polyamines norspermidine and spermidine enhance and repress V. cholerae biofilm formation, respectively. These effects are relevant for understanding V. cholerae pathogenicity and are mediated through the periplasmic binding protein NspS and the transmembrane bis-(3'-5') cyclic diguanosine monophosphate (c-di-GMP) phosphodiesterase MbaA. However, the levels of spermidine required to inhibit biofilm formation through this pathway are unlikely to be encountered by V. cholerae in aquatic reservoirs or within the human host during infection. We therefore hypothesized that other polyamines in the gastrointestinal tract may control V. cholerae biofilm formation at physiological levels. The tetramine spermine has been reported to be present at nearly 50 μm concentrations in the intestinal lumen. Here, we report that spermine acts as an exogenous cue that inhibits V. cholerae biofilm formation through the NspS-MbaA signaling system. We found that this effect probably occurs through a direct interaction of spermine with NspS, as purified NspS protein could bind spermine in vitro Spermine also inhibited biofilm formation by altering the transcription of the vps genes involved in biofilm matrix production. Global c-di-GMP levels were unaffected by spermine supplementation, suggesting that biofilm formation may be regulated by variations in local rather than global c-di-GMP pools. Finally, we propose a model illustrating how the NspS-MbaA signaling system may communicate exogenous polyamine content to the cell to control biofilm formation in the aquatic environment and within the human intestine.

A new piece of the Shigella Pathogenicity puzzle: spermidine accumulation by silencing of the speG gene [corrected]

The genome of Shigella, a gram negative bacterium which is the causative agent of bacillary dysentery, shares strong homologies with that of its commensal ancestor, Escherichia coli. The acquisition, by lateral gene transfer, of a large plasmid carrying virulence determinants has been a crucial event in the evolution towards the pathogenic lifestyle and has been paralleled by the occurrence of mutations affecting genes, which negatively interfere with the expression of virulence factors. In this context, we have analysed to what extent the presence of the plasmid-encoded virF gene, the major activator of the Shigella regulon for invasive phenotype, has modified the transcriptional profile of E. coli. Combining results from transcriptome assays and comparative genome analyses we show that in E. coli VirF, besides being able to up-regulate several chromosomal genes, which potentially influence bacterial fitness within the host, also activates genes which have been lost by Shigella. We have focused our attention on the speG gene, which encodes spermidine acetyltransferase, an enzyme catalysing the conversion of spermidine into the physiologically inert acetylspermidine, since recent evidence stresses the involvement of polyamines in microbial pathogenesis. Through identification of diverse mutations, which prevent expression of a functional SpeG protein, we show that the speG gene has been silenced by convergent evolution and that its inactivation causes the marked increase of intracellular spermidine in all Shigella spp. This enhances the survival of Shigella under oxidative stress and allows it to better face the adverse conditions it encounters inside macrophage. This is supported by the outcome of infection assays performed in mouse peritoneal macrophages and of a competitive-infection assay on J774 macrophage cell culture. Our observations fully support the pathoadaptive nature of speG inactivation in Shigella and reveal that the accumulation of spermidine is a key determinant in the pathogenicity strategy adopted by this microrganism.

The mechanisms by which polyamines accelerate tumor spread

Increased polyamine concentrations in the blood and urine of cancer patients reflect the enhanced levels of polyamine synthesis in cancer tissues arising from increased activity of enzymes responsible for polyamine synthesis. In addition to their de novo polyamine synthesis, cells can take up polyamines from extracellular sources, such as cancer tissues, food, and intestinal microbiota. Because polyamines are indispensable for cell growth, increased polyamine availability enhances cell growth. However, the malignant potential of cancer is determined by its capability to invade to surrounding tissues and metastasize to distant organs. The mechanisms by which increased polyamine levels enhance the malignant potential of cancer cells and decrease anti-tumor immunity are reviewed. Cancer cells with a greater capability to synthesize polyamines are associated with increased production of proteinases, such as serine proteinase, matrix metalloproteinases, cathepsins, and plasminogen activator, which can degrade surrounding tissues. Although cancer tissues produce vascular growth factors, their deregulated growth induces hypoxia, which in turn enhances polyamine uptake by cancer cells to further augment cell migration and suppress CD44 expression. Increased polyamine uptake by immune cells also results in reduced cytokine production needed for anti-tumor activities and decreases expression of adhesion molecules involved in anti-tumor immunity, such as CD11a and CD56. Immune cells in an environment with increased polyamine levels lose anti-tumor immune functions, such as lymphokine activated killer activities. Recent investigations revealed that increased polyamine availability enhances the capability of cancer cells to invade and metastasize to new tissues while diminishing immune cells' anti-tumor immune functions.

Recent advances in the molecular biology of metazoan polyamine transport

Very limited molecular knowledge exists about the identity and protein components of the ubiquitous polyamine transporters found in animal cells. However, a number of reports have been published over the last 5 years on potential candidates for metazoan polyamine permeases. We review the available evidence on these putative polyamine permeases, as well as establish a useful "identikit picture" of the general polyamine transport system, based on its properties as found in a wide spectrum of mammalian cells. Any molecular candidate encoding a putative "general" polyamine permease should fit that provided portrait. The current models proposed for the mechanism of polyamine internalization in mammalian cells are also briefly reviewed.

Drug interactions

Drugs for allergy are often taken in combination with other drugs, either to treat allergy or other conditions. In common with many pharmaceuticals, most such drugs are subject to metabolism by P450 enzymes and to transmembrane transport. This gives rise to considerable potential for drug-drug interactions, to which must be added consideration of drug-diet interactions. The potential for metabolism-based drug interactions is increasingly being taken into account during drug development, using a variety of in silico and in vitro approaches. Prediction of transporter-based interactions is not as advanced. The clinical importance of a drug interaction will depend upon a number of factors, and it is important to address concerns quantitatively, taking into account the therapeutic index of the compound.

Conditioning of uropathogenic Escherichia coli for enhanced colonization of host

While in transit within and between hosts, uropathogenic Escherichia coli (UPEC) encounters multiple stresses, including substantial levels of nitric oxide and reactive nitrogen intermediates. Here we show that UPEC, the primary cause of urinary tract infections, can be conditioned to grow at higher rates in the presence of acidified sodium nitrite (ASN), a model system used to generate nitrosative stress. When inoculated into the bladder of a mouse, ASN-conditioned UPEC bacteria are far more likely to establish an infection than nonconditioned bacteria. Microarray analysis of ASN-conditioned bacteria suggests that several NsrR-regulated genes and other stress- and polyamine-responsive factors may be partially responsible for this effect. Compared to K-12 reference strains, most UPEC isolates have increased resistance to ASN, and this resistance can be substantially enhanced by addition of the polyamine cadaverine. Nitrosative stress, as generated by ASN, can stimulate cadaverine synthesis by UPEC, and growth of UPEC in cadaverine-supplemented broth in the absence of ASN can also promote UPEC colonization of the bladder. These results suggest that UPEC interactions with polyamines or stresses such as reactive nitrogen intermediates can in effect reprogram the bacteria, enabling them to better colonize the host.

Activities of DL-alpha-difluoromethylarginine and polyamine analogues against Cryptosporidium parvum infection in a T-cell receptor alpha-deficient mouse model

The in vivo effectiveness of a series of conformationally restricted polyamine analogues alone and selected members in combination with DL-alpha-difluoromethylarginine against Cryptosporidium parvum infection in a T-cell receptor alpha-deficient mouse model was tested. Polyamine analogues were selected from the extended bis(ethyl)-sym-homospermidine or bis(ethyl)-spermine backbone having cis or trans double bonds at the center of the molecule. The cis isomers were found to have significantly greater efficacy in both preventing and curing infection in a mouse model than the trans polyamine analogues when tested in a T-cell receptor alpha-deficient mouse model. When tested in combination with DL-alpha-difluoromethylarginine, the cis-restricted analogues were found to be more effective in preventing oocyst shedding. This study demonstrates the potential of polyamine analogues as anticryptosporidial agents and highlights the presence of multiple points in polyamine synthesis by this parasite that are susceptible to inhibition resulting in growth inhibition.

Polyamine depletion inhibits irradiation-induced apoptosis in intestinal epithelia

Our group has previously shown that polyamine depletion delays apoptosis in rat intestinal epithelial (IEC-6) cells (Ray RM, Viar MJ, Yuan Q, and Johnson LR, Am J Physiol Cell Physiol 278: C480-C489, 2000). Here, we demonstrate that polyamine depletion inhibits gamma-irradiation-induced apoptosis in vitro and in vivo. Pretreatment of IEC-6 cells with 5 mM alpha-difluoromethylornithine (DFMO) for 4 days significantly reduced radiation-induced caspase-3 activity and DNA fragmentation. This protective effect was prevented by the addition of 10 muM exogenous putrescine. Radiation exposure to mice resulted in a high frequency of apoptosis over cells positioned fourth to seventh in crypt-villus units. Pretreatment of mice with 2% DFMO in drinking water significantly reduced apoptotic cells from approximately 2.75 to 1.61 per crypt-villus unit, accompanied by significant decreases in caspase-3 levels. Further examination showed that DFMO pretreatment inhibited the radiation-induced increase in the proapoptotic protein Bax. Moreover, DFMO pretreatment significantly enhanced the intestinal crypt survival rate by 2.1-fold subsequent to radiation and ameliorated mucosal structural damage. We conclude that polyamine depletion by DFMO inhibits gamma-irradiation-induced apoptosis of intestinal epithelial cells both in vitro and in vivo through inhibition of Bax and caspase-3 activity, which leads to attenuation of radiation-inflicted intestinal injury. These data indicate that DFMO may be therapeutically useful to counteract the gastrointestinal toxicity caused by chemoradiotherapy. This is the first demonstration that polyamines are required for apoptosis in vivo.

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.

Effects of polyamines on the muscarinic receptor-operated cation current in guinea-pig ileal smooth muscle myocytes

The effects of extracellular and intracellular polyamines (PAs), spermine and putrescine, on the cation current (mI(CAT)) evoked either by activating muscarinic receptors with carbachol or by intracellularly applied GTPgammaS (in the absence of carbachol) were studied using patch-clamp recording techniques in single guinea-pig ileal myocytes. Extracellular spermine and putrescine rapidly and reversibly inhibited mI(CAT) in a concentration- and voltage-dependent manner with the IC(50) values at -40 mV of about 1 and 5 mM, respectively. Membrane depolarization relieved the blocking action of PAs although cation conductance activation curve remained N-shaped. The inhibition was similar for both carbachol- and GTPgammaS-evoked currents, suggesting that the cation channel rather than the muscarinic receptor was the primary site of the PA action. In outside-out membrane patches, both cation channel unitary conductance and open probability were reduced. In perforated-patch experiments used to retain cytoplasmic PAs sustained 100 microM carbachol-induced mI(CAT) was significantly smaller (478 +/- 76 pA, n = 7) compared to that recorded using conventional whole-cell configuration with nominally PA-free pipette solution (1314 +/- 76 pA, n = 12), but comparable in size to mI(CAT) with 0.3 mM spermine in the pipette solution (509 +/- 41 pA, n = 19). Intracellular putrescine inhibited mI(CAT) less potently compared to spermine. In conclusion, these results show a novel role of intestinal PAs in mI(CAT) inhibition, which can contribute to their well-known suppressing effect on the gastrointestinal smooth muscle excitability and contractility.

Transepithelial transport of putrescine across monolayers of the human intestinal epithelial cell line, Caco-2

AIM: To study the transepithelial transport characteristics of the polyamine putrescine in human intestinal Caco-2 cell monolayers to elucidate the mechanisms of the putrescine intestinal absorption.

METHODS: The transepithelial transport and the cellular accumulation of putrescine was measured using Caco-2 cell monolayers grown on permeable filters.

RESULTS: Transepithelial transport of putrescine in physiological concentrations ( > 0.5 mM) from the apical to basolateral side was linear. Intracellular accumulation of putrescine was higher in confluent than in fully differentiated Caco-2 cells, but still negligible (less than 0.5%) of the overall transport across the monolayers in apical to basolateral direction.EGF enhanced putrescine accumulation in Caco-2 cells by four fold, as well as putrescine conversion to spermidine and spermine by enhancing the activity of S adenosylmethionine decarboxylase. However, EGF did not have any significant influence on putrescine flux across the Caco- 2 cell monolayers. Excretion of putrescine from Caco-2 cells into the basolateral medium did not exceed 50 picomoles, while putrescine passive flux from the apical to the basolateral chamber, contributed hundreds of micromoles polyamines to the basolateral chamber.

CONCLUSION: Transepithelial transport of putrescine across Caco-2 cell monolayers occurs in passive diffusion, and is not influenced when epithelial cells are stimulated to proliferate by a potent mitogen such as EGF.

Dietary polyamines are essential luminal growth factors for small intestinal and colonic mucosal growth and development

BACKGROUND

Polyamines are essential for cell growth. Dietary and probably gut bacterial derived polyamines contribute significantly to the polyamine body pool.

AIMS

To evaluate the influence of dietary, luminal polyamines on growth and development of different gastrointestinal organs in normally growing rats.

METHODS

Male suckling Wistar rats were randomly allocated to four treatment groups: polyamine deficient diet (PDD); PDD plus antibiotics (neomycin 2 g/kg and metronidazole 34 mg/kg); PDD plus polyamine supplementation at normal concentrations; or normal standard laboratory chow. After a six month feeding period 7-10 animals/group were sacrificed.

RESULTS

No differences in body weight gain, food consumption, or general behaviour could be observed between the four groups of animals. Feeding of PDD alone or PDD plus antibiotics resulted in a highly significant decrease in organ weight, protein content, and DNA content in small intestinal and colonic mucosa whereas no alterations were found in the liver.

CONCLUSIONS

Long term feeding of polyamine deficient diets resulted in a significant hypoplasia of small intestinal and colonic mucosa. Dietary, luminal polyamines are important local factors for growth and the development of small intestinal and colonic mucosa.

Dependence of mammalian putrescine and spermidine transport on plasma-membrane potential: identification of an amiloride binding site on the putrescine carrier

The mechanism of mammalian polyamine transport is poorly understood. We have investigated the role of plasma-membrane potential (DeltaPsipm) in putrescine and spermidine uptake in ZR-75-1 human breast cancer cells. The rate of [3H]putrescine and [3H]spermidine uptake was inversely correlated to extracellular [K+] ([K+]o) and to DeltaPsipm, as determined by the accumulation of [3H]tetraphenylphosphonium bromide (TPP). Inward transport was unaffected by a selective decrease in mitochondrial potential (DeltaPsimit) induced by valinomycin at low [K+]o, but was reduced by approximately 60% by the rheogenic protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP), which rapidly (<=15 min) collapsed both DeltaPsipm and DeltaPsimit. Plasma-membrane depolarization by high [K+]o or CCCP did not enhance putrescine efflux in cells pre-loaded with [3H]putrescine, suggesting that decreased uptake caused by these agents did not result from a higher excretion rate. On the other hand, the electroneutral K+/H+ exchanger nigericin (10 microM) co-operatively depressed -3H-TPP, [3H]putrescine and [3H]spermidine uptake in the presence of ouabain. Suppression of putrescine uptake by nigericin+ouabain was Na+-dependent, suggesting that plasma-membrane repolarization by the electrogenic Na+ pump was required upon acidification induced by nigericin, due to the activation of the Na+/H+ antiporter. The sole addition of 5-N, N-hexamethylene amiloride, a potent inhibitor of the Na+/H+ antiporter, strongly inhibited putrescine uptake in a competitive fashion -Ki 4.0+/-0.9 (S.D.) microM-, while being a weaker antagonist of spermidine uptake. The potency of a series of amiloride analogues to inhibit putrescine uptake was clearly different from that of the Na+/H+ antiporter, and resembled that noted for Na+ co-transport proteins. These data demonstrate that putrescine and spermidine influx is mainly unidirectional and strictly depends on DeltaPsipm, but not DeltaPsimit. This report also provides first evidence for a high-affinity amiloride-binding site on the putrescine carrier, which provides new insight into the biochemical properties of this transporter.

Inhibition of diamine oxidase promotes uptake of putrescine from rat small intestine

In blood from the portal vein of anaesthetized rats the levels of histamine and putrescine were 2-3-fold lower compared to arterial blood. Putrescine concentration was increased severalfold and the difference between portal and arterial blood abolished in animals pretreated with the specific diamine oxidase inhibitor aminoguanidine. Histamine concentration was 40% lower in portal compared to arterial blood in animals treated with the mast cell degranulator compound 48/80. In animals pretreated with aminoguanidine, compound 48/80 enhanced the level of histamine and no difference was observed between arterial and portal blood. The amounts of intravenously injected [14C]-labeled histamine was about 15% lower in portal compared to arterial blood. The uptake of [14C]-putrescine from the small intestine was estimated. In urine from animals pretreated with aminoguanidine the concentration of [14C]-putrescine was more than 40-times higher than in control animals corresponding to a calculated uptake of about 7% in aminoguanidine treated animals. Our results suggest that intestinal diamine oxidase clears the blood from diamines and prevents luminal uptake of putrescine.

Substrate protection against inactivation of the mammalian polyamine-transport system by 1-ethyl-3-(3-dimethylaminopropyl)carbodi-imide

Mammalian polyamine transporters have not thus far been biochemically characterized. Since essential carboxy groups in the polyamine carrier might participate in the transport process, the ability of two different carbodi-imides to affect [3H]spermidine uptake was assessed in Chinese hamster ovary cells. Both the hydrophobic 1,3-dicyclohexylcarbodi-imide (DCC) and the more polar 1-ethyl-3-(3-dimethylaminopropyl)carbodi-imide (EDC) irreversibly inhibited spermidine transport with EC50 values of 11 +/- 4 and 96 +/- 16 microM after 30 min at 22 degrees C respectively. Prior treatment with EDC in the absence of substrate decreased both the Vmax and K(m) for spermidine uptake in a time- and concentration-dependent manner. Spermidine-transport inactivation by EDC (1 mM) was temperature-dependent, with 60 and 90% inhibition observed after 10 min at 22 and 37 degrees C respectively. Spermine (10 microM) almost fully protected against spermidine-transport inactivation by EDC at 22 degrees C, and decreased the rate of inactivation at 37 degrees C by about 80%. Putrescine, spermidine and spermine were all effective in protecting against EDC-mediated inactivation of [3H]spermidine and [3H]putrescine uptake at 22 degrees C with EC50 values estimated at 10, 1 and less than 1 microM respectively. The nucleophile glycine ethyl ester (up to 50 mM) prevented the inhibition brought about by 1 mM EDC. Inhibition by 1 mM EDC was greater at pH 7.2 than at pH 5.8 (89 +/- 3 compared with 44 +/- 5%), whereas the converse was true for 100 microM DCC (81 +/- 3 compared with 92 +/- 5%). On the other hand, spermine did not protect against inactivation of spermidine uptake by DCC. Moreover, DCC, but not EDC, inhibited Na(+)-dependent amino acid uptake. The present data indicate that (i) EDC and DCC inhibit polyamine transport through distinct mechanisms, (ii) substrate binding occludes one or several carboxy groups lying in a polar environment of the carrier and (iii) these carboxyl residues might be activated by EDC to crosslink a neighbouring nucleophile side group, resulting in a conformation of the polyamine carrier which is inactive for transport.