Uptake and transport of macromolecules by the intestine: possible role in clinical disorders (an update)

The physicochemical environment of the neonatal intestine

Dietary intake, bacterial metabolites, and the secretion of factors (eg, proteins, electrolytes, lipid-soluble molecules, and water) by the body each contribute to the physicochemical environment of the gastrointestinal tract. Peristalsis regulates the changes along the length of the intestine. However, coordinated peristaltic responses develop as premature infants mature. In addition, the physicochemical environment of the center of the intestinal lumen differs from that of the epithelial surface. The area adjacent to the small intestinal epithelium is more acid than the bulk phase. Na+/H+ exchange antiporters in the epithelial cell apical membrane generate this acidity. Mucus maintains the acid microclimate by preventing free diffusion of hydrogen ions into the bulk phase. Development also affects these mechanisms. Changes in the lumenal environment may alter the synthesis of signaling molecules expressed by the intestinal epithelium. Thus, the epithelium, through changes in gene regulation, may act as an active interface that transmits information about the composition of the intestinal lumen to the mucosal immune system. Premature neonates are at risk of necrotizing enterocolitis, a disease almost exclusively associated with oral feeds. The pathogenesis of this condition may, in part, be due to the immaturity of the interactions between the physicochemical environment of the lumen and intestine.

The role of enterocytes in gut dysfunction

Stem cells in the intestinal epithelium give rise to enterocytes, goblet cells, enteroendocrine cells, and Paneth cells. Each of these cell lines plays a role in cytoprotection of the intestinal mucosa. In particular, it has been demonstrated that mature enterocytes can act as antigen presenting cells. Parenteral and enteral nutrition are used to nourish critically ill patients. However, these regimens are unfortunately associated with gut atrophy. Glutamine, the preferred intestinal nutrient, reverses this gut atrophy and plays a key role in maintaining the barrier function of the gut. Specific nutrients (putrescine, spermidine, spermine) have been used to modulate intestinal adaption. In addition, ornithine has been shown to act as a regulator of intestinal adaption. In this review, we discuss the relationship between the biology of enterocytes and failure of the gut barrier.

Serosal but not mucosal endotoxin exposure increases intestinal permeability in vitro in the rat

BACKGROUND

Microbial endotoxins are normally present in the gut, usually without apparent harmful effects, whereas systemically administered endotoxin impairs the mucosal barrier function. Our aim was to investigate whether in vitro exposure to bacterial lipopolysaccharide (LPS) could affect the intestinal barrier properties of the rat small intestine.

METHODS

Small-intestinal segments from rats were mounted in Ussing diffusion chambers, and the mucosal to serosal permeation of the marker molecules bovine serum albumin (BSA) and 51Cr-ethylenediaminetetraacetic acid (EDTA) was measured after addition of LPS to the mucosal or serosal side.

RESULTS

Mucosal exposure to LPS (0.01, 0.05, 0.25 mg/ml) had no effects on the permeation of BSA and 51Cr-EDTA, whereas when added to the serosal side at 0.05 or 0.25 mg/ml, LPS increased the marker permeation.

CONCLUSION

Serosal LPS exposure in vitro increased the intestinal permeability to the different-sized markers, whereas mucosal LPS did not, indicating that the mechanisms leading to intestinal barrier impairment can be initiated in the intestinal wall itself.

Transforming growth factor-beta levels in maternal milk and expression in postnatal rat duodenum and ileum

After birth, the gastrointestinal tract of the neonate is exposed to food and bacterial and environmental antigens. Maternal milk components may play a role in regulation of mucosal immune activity to luminal antigens. In this study we determine the ontogeny of transforming growth factor (TGF)-beta1-producing cells in the rat pup small intestine and assess maternal milk concentrations of TGF-beta. Intestinal tissue samples of duodenum and ileum were collected, processed, and stained for TGF-beta1, and in situ hybridization for TGF-beta1 mRNA was also performed on the duodenum. TGF-beta levels in milk were assayed by ELISA. TGF-beta2 levels in milk were high at d 6, and declined thereafter at d 10 and 19. TGF-beta1 was not detected. In contrast, the cell number and intensity of staining of TGF-beta1 peptide in the small intestine was low in 3- and 10-d-old rats and increased markedly by 19 d of life. In the duodenum mRNA levels mirrored this trend. TGF-beta1 expression in the lamina propria was absent before d 19, and increased progressively over time. Maternal milk TGF-beta2 levels are high in early milk and decrease during the weaning period. In contrast, endogenous TGF-beta production in the small intestine increases during the weaning period.

Adsorptive-mediated endocytosis of a basic peptide in enterocyte-like Caco-2 cells

The internalization of a basic peptide, 001-C8 [H-MeTyr-Arg-MeArg-D-Leu-NH(CH2)8NH2], into enterocyte-like Caco-2 cells was evaluated. Internalization of 125I-labeled 001-C8 (125I-001-C8) increased time dependently and reached steady state at 60 min. The steady-state internalization of 125I-001-C8 (7.24 +/- 0. 41 microl/mg protein) was temperature and concentration dependent and was significantly decreased by dansylcadaverine (500 microM), protamine (1 mM), poly-L-lysine (1 mM), E-2078 (1 mM), and ebiratide (1 mM), whereas poly-L-glutamic acid (1 mM), tyrosine (1 mM), and glycylglycine (25 mM) were not inhibitory. Predigestion of acid mucopolysaccharides by heparinase I, heparitinase, and chondroitinase ABC also decreased the internalization. The maximal internalization, the half-saturation constant, and the nonsaturable internalization of 125I-001-C8 were 1.13 +/- 0.23 pmol/mg protein, 0. 47 +/- 0.43 microM, and 3.13 +/- 0.19 microl/mg protein, respectively. Confocal microscopy also indicated the internalization of fluorescence-derived 001-C8 [001-C8-4-nitrobenz-2-oxa-1,3-diazole (001-C8-NBD)]. Granular staining seen within the cell, excluding nuclei, indicated the sequestration of 001-C8-NBD within endocytotic vesicles. Dansylcadaverine and protamine strongly decreased the granular distribution of 001-C8-NBD within the cell. These results demonstrate that 001-C8 is taken up by Caco-2 cells via adsorptive-mediated endocytosis.

Regional differences in the effect of cholera toxin and enterotoxigenic Escherichia coli infection on electrolyte and fluid transport in the porcine small intestine

The regional differences in secretory and absorptive responses to cholera toxin (CT) and to infection by enterotoxigenic Escherichia coli (ETEC), producing heat-stable enterotoxins, were studied in the porcine small intestine. Proximal, mid and distal small intestine from newly weaned piglets were used. Na+ and Cl- fluxes and electrical parameters in CT-stimulated and ETEC-infected intestine were measured by the Ussing chamber technique. In addition, CT-induced fluid accumulation in ligated loops was measured. CT induced fluid accumulation, which was highest in the proximal segment and decreased in the aboral direction of the small intestine. In addition, CT induced a net Cl- secretion in the proximal and mid segments, while net Na+ absorption was reduced only in the proximal segment. The ETEC-infected intestine showed a net increase in Cl- secretion in the proximal part and abolished the net Na+ absorption in the distal segment. These results demonstrate segmental differences in the epithelial transport responses to enterotoxin from Vibrio cholerae and to ETEC infection. This needs to be taken into consideration in relation to oral rehydration studies.

The Influence of Mast Cells on Pathways of Transepithelial Antigen Transport in Rat Intestine

Luminal Ag challenge of intestinal segments from sensitized rats results in a rapid (∼3 min) secretory response. We previously showed in horseradish peroxidase (HRP)-sensitized rats that the initial phase of transepithelial Ag transport occurred via a transcellular route and was enhanced by sensitization. However, following the hypersensitivity reaction, Ag also crossed between epithelial cells. The aim of this study was to determine the role of mast cells in the altered transepithelial Ag transport. White spotting mast cell-deficient rats and +/+ littermate controls were sensitized to HRP. After 10 to 14 days, jejunal segments were resected, mounted in Ussing chambers, and challenged with HRP on the luminal side. Electron microscopy of jejunum fixed at 2 min showed a similarly enhanced endocytic transport of HRP in sensitized +/+ and Ws/Ws rats compared with naive controls. In sensitized +/+ rats, a secretory response occurred ∼3 min after challenge, and tissue conductance increased thereafter. Naive +/+ and sensitized Ws/Ws rats did not demonstrate a secretory response to HRP challenge, and conductance remained at baseline levels. The flux of HRP was elevated across tissue from sensitized +/+ rats but not across tissue from naive controls or sensitized Ws/Ws rats. The results indicate that sensitization enhances the initial phase of transepithelial uptake of Ag by transcytosis in a mast cell-independent manner. However, subsequent recruitment of the paracellular pathway for Ag transport in sensitized rats is dependent upon the presence of mast cells and occurs after the activation of such cells.

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.

Functional food science and gastrointestinal physiology and function

The gut is an obvious target for the development of functional foods, acting as it does as the interface between diet and the metabolic events which sustain life. The key processes in digestive physiology which can be regulated by modifying diet are satiety, the rate and extent of macronutrient breakdown and absorption from the small bowel, sterol metabolism, the colonic microflora, fermentation, mucosal function and bowel habit, and the gut immune system. The intestinal microflora is the main focus of many current functional foods. Probiotics are foods which contain live bacteria which are beneficial to health whilst prebiotics, such as certain non-digestible oligosaccharides which selectively stimulate the growth of bifidobacteria in the colon, are already on the market. Their claimed benefits are to alleviate lactose maldigestion, increase resistance to invasion by pathogenic species of bacteria in the gut, stimulate the immune system and possibly protect against cancer. There are very few reports of well-designed human intervention studies with prebiotics as yet. Certain probiotic species have been shown to shorten the duration of rotavirus diarrhoea in children but much more work is needed on the mechanism of immunomodulation and of competitive exclusion and microflora modification. The development of functional foods for the gut is in its infancy and will be successful only if more fundamental research is done on digestive physiology, the gut microflora, immune system and mucosal function.

Kinetics of particle uptake in the domes of Peyer's patches

Uptake of particulate antigenic matter, including microorganisms and vaccine-bearing microspheres, by the intestinal mucosa takes place in the domes of the gut-associated lymphoid tissues and is achieved by membranous (M) cells, which continuously transport particles from the lumen to the underlying tissue where some particle components initiate immune reactions. Using yeast as tracer, we investigated the kinetics of particle uptake in the Peyer's patches of pigs. A suspension of baker's yeast (Saccharomyces cerevisiae) was injected into the gut lumen of anesthetized minipigs; the position of yeast cells in the tissue was determined after 1, 2.5, 4, and 24 h using fluorescence light- and thin-section electron microscopy. After 1 h, 18.5% of all M cells had taken up or were in close contact with yeast cells. The intercellular space of the epithelium contained a maximum of 60.8% of all yeast cells found in the tissue after 2.5 h, but only 1.3% had been phagocytosed by macrophages. After 4 h most yeast cells (77.8%) were found beneath the basal lamina, and most of these (89%) were found in macrophages. No yeast cells were detected in the Peyer's patch domes 24 h after application. The data show that transcytosis of yeast particles (3.4 +/- 0.8 micron in diameter) by M cells takes <1 h. Without significant phagocytosis by intraepithelial macrophages, the particles migrate down to and across the basal lamina within 2.5-4 h, where they quickly get phagocytosed and transported out of the Peyer's patch domes.

In situ expression of interleukin-10 in noninflamed human gut and in inflammatory bowel disease

A dysregulated secretion of contra-inflammatory cytokines such as interleukin-10 (IL-10) could play a role in the pathogenesis of inflammatory bowel disease (IBD). We have investigated the expression of IL-10 in gut tissues from patients with Crohn's disease (CD), ulcerative colitis (UC) and controls by mRNA in situ hybridization and immunohistochemistry. Intestinal epithelial cells were found to express IL-10 mRNA and IL-10 protein in all of the tissues investigated without any major differences in the expression patterns. However, compared with noninflamed gut, significantly increased numbers of mononuclear cells (MNCs) producing IL-10 were present in inflamed gut, both in CD and UC. This cytokine was expressed most prominently by inflammatory infiltrates enriched in macrophages, although T cells seem to contribute to its production as well. Elevated IL-10 expression in IBD was mainly detected in the submucosa, whereas IL-10 production by lamina propria cells remained comparably low. In contrast, the expression of IL-1beta mRNA was preferentially increased in the lamina propria. Our data argue against a general deficiency in IL-10 production in IBD. The results suggest rather that the local production of IL-10 by mucosal MNCs in IBD is insufficient to down-regulate pro-inflammatory cytokines such as IL-1beta in the lamina propria compartment.

Intestinal absorption of fluorescence-derivatized cationic peptide 001-C8-NBD via adsorptive-mediated transcytosis

The intestinal absorption of an intact oligopeptide was investigated in rats using a synthetic cationic peptide, 001-C8 (H-MeTyr-Arg-MeArg-D-Leu-NH(CH2)8NH2). The peptide was coupled with 4-nitrobenzo-2-oxa-1,3-diazole (NBD) to prepare a fluorescence-labeled derivative 001-C8-NBD (H-MeTyr-Arg-MeArg-D-Leu-NH(CH2)8NH-NBD) for the purpose of quantification. The degradation half-life of 001-C8-NBD in jejunal homogenate (1 mg/mL) was 99.5 min, which was significantly longer than that of natural leucine enkephalin (1.14 min). The absorption of 001-C8-NBD was evaluated by the vascular-perfusion method. Intact 001-C8-NBD appeared in the blood time-dependently and the absorption volume at 30 min (2.75 +/- 0.14 microL/cm intestine) was significantly larger than that of [3H]PEG 900 (0.88 +/- 0.13 microL/cm intestine), of which membrane permeability is very low. The absorption of 001-C8-NBD was greatly reduced by an adsorptive-mediated endocytosis inhibitor, protamine (10 mM). No inhibition of the absorption of [3H]PEG 900 by protamine was observed. The intestinal absorption was also measured by an in vivo loop method. The absorption clearance of 001-C8-NBD measured by this method (0.083 +/- 0.008 microL/min/cm intestine) was comparable to that obtained by the vascular perfusion method (0.092 +/- 0.005 microL/min/cm intestine). All of these data suggested that 001-C8-NBD was absorbed as the intact oligopeptide in the intestine in vivo. Adsorptive-mediated transcytosis is suggested to have enormous potential as an oral delivery system for peptide and/or protein drugs.

Mucosal immunity in the female genital tract

Immunoglobulin (Ig)-producing cells in mucosal tissues represent quantitatively the most important humoral immune system of the body. All exocrine tissue sites contain immunocytes (B-cell blasts and plasma cells) that mainly synthesize dimers and larger polymers of IgA (collectively called pIgA) with incorporated J chain. Such pIgA is actively transported to external secretions as secretory IgA (SIgA) by the polymeric Ig receptor (pIgR), a transmembrane epithelial glycoprotein also called the secretory component (SC). The same transport mechanism includes pentameric IgM to generate SIgM. Although the most active SIgA system occurs in the gut, secretory immunity also operates in the female genital tract, with considerable pIgA production in the cervical mucosa and fallopian tubes. The origin of these local IgA immunocytes remains undefined. In mice, both lymphoid tissue in the large bowel (GALT) and nasopharynx (NALT) have been suggested as inductive sites for B cells homing to the urogenital tract. It is well established that integrin alpha 4 beta 7 is used by primed lymphoid cells to enter the intestinal lamina propria through interactions with mucosal addressin cell adhesion molecule (MAdCAM)-1 expressed on venule endothelium. However, alpha 4 beta 7 does not appear to be an important homing molecule in the airways, and the same might be true for the urogenital tract; this could explain that high levels of IgA antibodies occur in cervicovaginal secretions of mice after nasal immunization. The endometrium can likewise perform pIgR-mediated external translocation of pIgA that in this tissue appears to be mainly derived from serum, partly under hormonal regulation. In addition, paracellular diffusion of serum-derived and locally produced IgG through epithelia is an important part of humoral immunity in the female genital tract.

Mechanisms of gastrointestinal reactions to food

Much of the genetic information that modulates mucosal immune responses was encoded several million years ago and has subsequently been subjected to modifications selected by the impact of microorganisms and food antigens. Confronted with these challenges, the intestinal immune system has developed two arms: (1) immune exclusion performed mainly by secretory IgA antibodies to inhibit colonization of pathogenic microorganisms and penetration of harmful antigens; and (2) down-regulatory mechanisms to avoid local and peripheral overreaction (hypersensitivity) towards innocuous substances. The latter phenomenon is called oral tolerance and apparently explains why most individuals show no adverse immune reactions food. When the mucosal barrier function is insufficient, tolerance to dietary antigens is abrogated in genetically susceptible individuals. This is most likely to occur during the vulnerable period after birth before the immunoregulatory network has been established. Breast-feeding appears to be immunologically important during this period, not only to substitute for the infant's lacking secretory antibodies but also because of its immune-modulating effects.

Diet and gene expression in the intestine

Gene expression is central to the pathogenesis of many disorders. An ability to alter the expression of genes would, if their relationship to disease processes were fully understood, constitute a new modality of treatment. This review examines the evidence that nutritional factors can regulate genes in the gastrointestinal epithelium and it discusses the physiological relevance of such alterations in gene expression. Dietary regulation of the genes expressed by the epithelium confers three fundamental advantages for mammals. It enables the epithelium to adapt to the luminal environment to digest and absorb food better; it provides the means whereby mother's milk can influence the development of the gastrointestinal tract; when the proteins expressed by the epithelium act on the immune system, it constitutes a signalling mechanism from the intestinal lumen to the body's defences. Each of these mechanisms is amenable to manipulation for therapeutic purposes.

Intestinal inflammation and barrier function in HLA-B27/beta 2-microglobulin transgenic rats

BACKGROUND

Since intestinal inflammation is correlated with impaired barrier functions, transgenic HLA-B27/human beta 2-microglobulin rats that spontaneously develop intestinal inflammation were used to investigate whether onset of inflammation or impaired barrier function was the initial event.

METHODS

During the age period of 9-14 weeks, transgenic and non-transgenic (control) rats were gavaged weekly with the marker molecules, 51Cr-ethylenediaminetetraacetic acid, 1-deamino-8-D-arginine vasopressin, and albumin, which were quantified in blood or urine.

RESULTS

At 12 weeks of age the first signs of inflammation appeared with decreased body weight gain, decreased urine production, and onset of diarrhea. By 14-15 weeks of age all transgenic rats had developed intestinal inflammation, as confirmed by histology and increased myeloperoxidase content, whereas no inflammation was observed in controls. Intestinal passage of the markers did, however, not differ between transgenic and control rats over the studied period.

CONCLUSIONS

The results suggest that intestinal inflammation precedes altered intestinal barrier function in this inflammation model.

Dot blot chemiluminescence assay for studying food protein binding to small intestinal brush border membranes in vitro

Interactions of food proteins with the apical membrane of small intestinal epithelial cells can influence enterocytic antigen handling. For studying these interactions in vitro, isolated brush border membrane vesicles are a widely accepted model. In order to improve measurement of food protein binding, we developed a sensitive dot blot chemiluminescence assay. This assay comprises immobilization of membrane vesicles on nitrocellulose, detection of bound biotinylated food proteins by a peroxidase-catalyzed chemiluminescence reaction, and densitometric quantitation of signal intensities. By using this assay, saturation of brush border membrane binding of food proteins (gliadin peptides, alpha-casein, beta-lactoglobulin, ovalbumin) was demonstrated. Inhibition studies indicated components of specific membrane binding of gliadin peptides, alpha-casein and beta-lactoglobulin, whereas aggregation tendency of ovalbumin interfered with inhibition experiments. Maximal binding intensities of gliadin peptides (22.2 +/- 1.2 densitometric units (d.u.)/microgram membrane protein), alpha-casein (27.9 +/- 1.7 d.u./microgram) and ovalbumin (21.3 +/- 1.6 d.u./microgram) were comparable to sugar-specific lectin binding (range from 23.4 to 35.1 d.u./microgram), in contrast to significantly less binding of beta-lactoglobulin (6.8 +/- 0.6 d.u./microgram). The dot blot chemiluminescence assay is appropriate for characterizing interactions between food proteins and brush border membranes. Its sensitivity makes investigation of pathological membrane alterations possible. Besides, it might be useful for any studies defining ligand-membrane interactions.

Effect of gamma-interferon on binding of gliadin and other food peptides to the human intestinal cell line HT-29

gamma-Interferon is one of the main cytokines released during activation of intestinal lymphocytes in coeliac patients. The question has never been addressed whether gamma-interferon influences binding of gliadin and other food peptides to human enterocytes. Therefore, the human intestinal epithelial cell line HT-29 was cultured with gliadin, casein, beta-lactoglobulin and ovalbumin, with or without gamma-interferon, and peptide binding to cells was determined by flow cytometry and fluorescence microscopy. gamma-Interferon stimulated gliadin binding by a factor of 4. Binding was saturable with half maximal binding at 0.15 mg/ml. For maximal binding, an incubation of at least 24 h was necessary. gamma-Interferon increased binding of beta-lactoglobulin and casein, too, but inhibited that of ovalbumin. Binding of gliadin was inhibited by the other peptides. Under the conditions of ongoing mucosal inflammatory reactions and release of gamma-interferon, enhanced binding may trigger intestinal lymphocytes, increase secretion of cytokines and thus induce a vicious circle.

beta-(1-->3, 1-->4) oat glucan enhances resistance to Eimeria vermiformis infection in immunosuppressed mice

The effect of intragastrically or parenterally administered beta-glucan, extracted from oats, on the enhancement of disease resistance to Eimeria vermiformis was studied in C57BL/6 mice. Groups of mice were immunosuppressed with dexamethasone (DXM), infected with oocysts of E. vermiformis and treated with oat beta-glucan by the intragastric (i.g.) or subcutaneous (s.c.) routes. Faecal oocyst shedding was reduced in the beta-glucan-treated groups compared to the non-treated group. Immunosuppressed mice which received no beta-glucan treatment showed more severe clinical signs of the disease and a 50% mortality, while minimal clinical signs and no mortality were recorded in the beta-glucan-treated groups. Total IgG, IgG1, IgG2a, IgM and IgA immunoglobulins in the serum of beta-glucan-treated groups were overall higher than those in the non-treated group. Specific IgG anti-sporozoite and merozoite immunoglobulins in serum were significantly higher in the beta-glucan-treated groups than in the non-treated animals. No significant differences were found in the levels of intestinal IgA anti-sporozoite and anti-merozoite immunoglobulins. IFN-gamma- and IL-4-secreting cells, in response to sporozoite antigen, were detected in the spleen and mesenteric lymph nodes of the beta-glucan-treated groups only. In conclusion, the i.g. and s.c. oat beta-glucan treatment increased the resistance to E. vermiformis infection in immunosuppressed mice.

Effects of nucleosides and a nucleotide mixture on gut mucosal barrier function on parenteral nutrition in rats

BACKGROUND

We have previously reported that the addition of nucleosides and a nucleotide mixture (OG-VI) to total parenteral nutrition (TPN) prevents TPN-induced intestinal mucosal atrophy and results in increased intestinal cathepsin activities under TPN. The aims of the present study are to examine the effects of OG-VI on mucosal barrier functions and to clarify whether the intestinal cathepsins can be used as a new marker of mucosal barrier function.

METHODS

Male Wistar rats were divided into three groups: FED (food ad libitum), TPN (a standard TPN solution), and OG (OG-VI in addition to the TPN solution). Mucosal barrier functions were analyzed by the lactulose/mannitol (L/M) test, mucosal ZO-1 messenger RNA level, and electron micrographs in the gut. Intestinal cathepsin B, H, and L activities were also measured.

RESULTS

The L/M ratio for TPN was much higher than that for FED. Only lactulose excretion was significantly reduced by OG-VI. The intercellular spaces of the mucosal cells for TPN were significantly wider than those for FED, but were reduced in size by the addition of OG-VI. All cathepsin activities of the ileum were higher for TPN than for FED, whereas OG showed no increase.

CONCLUSION

OG-VI contributes to the improvement of gut mucosal barrier function. Intestinal cathepsin activities can be used as a new marker of mucosal barrier function.

The oral absorption of micro- and nanoparticulates: neither exceptional nor unusual

This mini-review covers some of the historical and recent arguments over the experimental evidence on the uptake by and translocation from the intestinal mucosa of microparticulates after oral administration. It is concluded that there is now no dispute over the fact that this is a normal occurrence. Particulate uptake does take place, not only via the M-cells in the Peyer's patches and the isolated follicles of the gut-associated lymphoid tissue, but also via the normal intestinal enterocytes. Factors affecting uptake include particle size, surface charge and hydrophobicity and the presence or absence of surface ligands. The covalent attachment of lectin or invasion molecules to the surface of carrier particles leads to greater systemic uptake. Whether or not the route can be utilized for the routine administration of therapeutic agents which are not normally absorbed from the gut is not yet proven. Many studies show that 2-3% of the ingested dose of submicron particles can be absorbed. The increasing diversity of carrier systems, which includes dendrimers and liposomes, needs to be exploited fully. More also must be learned about the inter- and intra-subject variability of lymphoid tissue so that appropriate selectivity can be achieved through the design of specific carriers.

IFN-gamma enhances macromolecular transport across Peyer's patches in suckling rats: implications for natural immune responses to dietary antigens early in life

BACKGROUND

The capacity to generate (interferon-gamma) IFN-gamma, a potent immunoregulatory and inflammatory cytokine, is low in neonates and deficient in patients with food allergy.

METHODS

We investigated the effect of IFN-gamma on antigen transport in the gut. In experiment I rat pups were randomized into two groups at the age of 14 days i.e., before gut maturation: Group IFN was given intraperitoneally recombinant rat IFN-gamma on days 14, 16, 18, 20. In experiment II, rats were randomized into two groups at the age of 26 days, i.e., after gut maturation: Group IFN received the IFN-gamma treatment on days 26, 28, 30, 32. Controls in both experiments received sterile saline. The absorption of horseradish peroxidase (HRP) across jejunal segments with and without Peyer's patches was studied in Ussing chambers on days 21 and 33 for experiments I and II, respectively.

RESULTS

In experiment I, the absorption of intact HRP across both types of segments was significantly increased in Group IFN compared to controls. The mean (95% confidence interval) rate of degraded HRP absorption across patch-containing segments in Group IFN was significantly greater than in controls, 4420 (3162-6179) ng.h-1.cm-2 in comparison to 1550 (633-3790) ng.h-1.cm-2; F = 8.96, p = 0.009.

CONCLUSION

IFN-gamma increases macromolecular transport before gut maturation particularly across Peyer's patches. This Peyer's patch-targeted effect can be important eliciting mucosal immune responses against dietary antigens early in life and aiding their immune exclusion.

Review: Peyer's patches

The function of Peyer's patches as antigenic sampling sites involves the complex interplay of a variety of mechanisms that aim to recognize luminal antigens, induce an immunological response and decrease the incidence of antigen translocation across the mucosal epithelium. This is achieved by M cells, which facilitate the uptake of luminal antigens, a vascular architecture that promotes the retention of absorbed antigens within the patch interstitium (allowing for maximal antigenic activation of lymphocytes) and the presence of lymphoid follicles that contain antigen-presenting cells and lymphocytes. Lymphocytes encountering antigen in the Peyer's patches proliferate, differentiate into fully mature antigen-specific effector cells and migrate to the mesenteric lymph nodes where they undergo final maturation. The mature lymphocytes then enter the systemic circulation and migrate throughout the other mucosa-associated lymphoid tissues of the body and "home' into the gut via high endothelial venules and gut-associated lymphoid tissue-specific adhesion molecules, providing antigen-specific lymphocytes at sites likely to re-encounter the antigen.

Effect of running intensity on intestinal permeability

Enhanced intestinal permeability has been associated with gastrointestinal disorders in long-distance runners. The primary purpose of this study was to evaluate the effect of running intensity on small intestinal permeability by using the lactulose and rhamnose differential urinary excretion test. Secondary purposes included assessing the relationship between small intestinal permeability and gastrointestinal symptoms and evaluating gastric damage by using sucrose as a probe. Six healthy volunteers [5 men, 1 woman; age = 30 +/- 2 yr; peak O2 uptake (VO2peak) = 57.7 +/- 2.1 ml.kg-1.min-1] rested or performed treadmill exercise at 40, 60, or 80% VO2peak for 60 min in a moderate environment (22 degrees C, 50% relative humidity). At 30 min into rest or exercise, the permeability test solution (5 g sucrose, 5 g lactulose, 2 g rhamnose in 50 ml water, approximately 800 mosM) was ingested. Urinary excretion rates (6 h) of the lactulose-to-rhamnose ratio were used to assess small intestinal permeability, and concentrations of each probe were determined by using high-performance liquid chromatography. Running at 80% VO2peak increased (P < 0.05) small intestinal permeability compared with rest, 40, and 60% VO2peak with mean values expressed as percent recovery of ingested dose of 0.107 +/- 0.021 (SE), 0.048 +/- 0.009, 0.056 +/- 0.005, and 0.064 +/- 0.010%, respectively. Increases in small intestinal permeability did not result in a higher prevalence of gastrointestinal symptoms, and urinary recovery of sucrose did not reflect increased gastric permeability. The significance and mechanisms involved in increased small intestinal permeability after high-intensity running merit further investigation.

Regulation of metal absorption in the gastrointestinal tract

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Clinical uses of probiotics for stabilizing the gut mucosal barrier: successful strains and future challenges

Probiotic bacteria are used to treat disturbed intestinal microflora and increased gut permeability which are characteristic to many intestinal disorders. Examples include children with acute rotavirus diarrhoea, subjects with food allergy, subjects with colonic disorders and patients undergoing pelvic radiotherapy and sometimes changes associated with colon cancer development. In all such disease states altered intestinal microflora, impaired gut barrier and different types of intestinal inflammation are present. Successful probiotic bacteria are able to survive gastric conditions and colonize the intestine, at least temporarily, by adhering to the intestinal epithelium. Such probiotic microorganisms appear to be promising candidates for the treatment of clinical conditions with abnormal gut microflora and altered gut mucosal barrier functions. They are also promising ingredients to future functional foods and clinical foods for specific disease states provided that basic requirements for strains and clinical studies are carefully followed.

Antigen presentation in the intestine

The intestinal mucosa is the largest surface area in the body which is continually exposed to an enormous amount of food antigens, viruses, bacteria, parasites or the by-products of these organisms. In such an antigen-loaded environment, specialized defence mechanisms must exist. There is clear evidence that the function of lymphocytes in the intestinal mucosa (IELs or LPLs) is different from that of lymphocytes of the peripheral blood, lymph node or spleen (these are antigen-free organs). The basic processes of these reactions are not completely understood. The role of differential antigen handling and presentation, and the non-random distribution of responsibilities between the professional and non-professional APC in this regard, have not been characterized. Thus, much remains to be learned about the basic mechanisms of antigen uptake, processing and presentation in the intestine which are necessary to induce an immune response. Diversity in APC function is a natural requirement for the maintenance of homeostasis in the intestine. Subpopulations of professional and non-professional APC may have been programmed to function in such a way that non-professional APCs may play a dominant role. It is anticipated that in vivo model systems will be developed and that eventually a clearer understanding will be gained in this rapidly evolving field.

Influnce of oat saponins on intestinal permeability in vitro and in vivo in the rat

The aim of the present study was to investigate whether oat saponins (avenacosides A and B) have any effect on the permeability of the rat intestine to actively and passively transported markers in vitro and in vivo. Intestinal segments were mounted in modified Ussing chambers, and the passage of the different marker compounds from the mucosal to the serosal side was measured for 120 min. Avenacosides (1 mg/ml) gave a significantly higher passage of the macromolecule ovalbumin and there was a tendency to increased passage of [14C]D-mannitol and [51Cr]EDTA. On the other hand, the saponins did not affect the active transport of [3H]methyl glucose. When rats were given saponins (40 mg/kg body weight) together with markers by gastric intubation, the passage of [51Cr]EDTA into blood and urine was somewhat reduced. For the macromolecule bovine serum albumin, no evident effect on the passage was observed in the presence of saponins. Thus, in contrast to the in vitro results, the in vivo marker passage seemed to be unaffected or even reduced in the presence of avenacosides. The study shows that saponins can affect the permeability of the rat intestine. However, this effect needs further investigation in vivo, especially regarding proteins.

Enhanced absorption of macromolecules. A secondary factor in Crohn's disease

We explored the function of the intestine's mucosal barrier to foreign antigen entry in Crohn's disease. Macroscopically and microscopically uninvolved areas of the small intestines of patients with Crohn's disease were examined. We studied 27 endoscopic biopsy samples from 17 patients with Crohn's disease and 14 samples from nine controls. The absorption and degradation of horseradish peroxidase (molecular weight 40,000 Da) were studied in Ussing chambers. The absorption of intact horseradish peroxidase was significantly increased in patients with moderate or severe Crohn's disease: 271 (95% confidence interval 119-616) ng/hr/cm2, but not in those with slight disease activity: 42 (18-98), compared with controls: 45 (32-64); F = 10.90, P = 0.0002. The transport rates of degraded horseradish peroxidase were comparable in the Crohn's disease samples and controls. Our results indicate that enhanced absorption of macromolecules is associated with clinical activation of Crohn's disease, and impairment of the mucosal barrier function is a secondary phenomenon in Crohn's disease.

Effects of luminal antigen on intestinal albumin and hyaluronan permeability and ion transport in atopic patients

BACKGROUND

Increased luminal transport of proteins and fluid is part of the inflammatory reaction in inflammatory disease of the bowel and of the airways in allergic diseases and asthma. The objective of this study was to determine intestinal appearance rates of albumin and hyaluronan in vivo in atopic patients allergic to birch, as well as changes in net jejunal transport of monovalent ions and water induced by the antigen.

METHODS

Secretion studies were performed with the use of a segmental jejunal perfusion system with a small two-balloon, six-channel tube. The intestinal mucosa was challenged with birch allergen in patients allergic to birch and in matched control subjects (n = 12 in both groups).

RESULTS

In patients, but not in control subjects, the luminal antigen induced a net increase in albumin of 2689 +/- 567 micrograms/cm/hr and in hyaluronan of 2609 +/- 737 ng/cm/hr (p < 0.01 vs control subjects in both cases). Furthermore, basal net absorption of Cl- ions, Na+ ions, and water was converted to a net secretion after antigen challenge.

CONCLUSION

Exposure to antigen normally acting on the respiratory tract induced increased permeability of the gastrointestinal mucosa. This would suggest less organ specificity and more general allergic recognition shared by several immunocompetent tissues in the body, probably mediated by circulating IgE antibodies.

Effects of a dietary and environmental prevention programme on the incidence of allergic symptoms in high atopic risk infants: three years' follow-up

A prospective case-control study is presented to assess an allergy prevention programme in children up to 36 months of age. Infants born at three maternity hospitals were followed from birth: 279 infants with high atopic risk (intervention group) were compared with 80 infants with similar atopic risk but no intervention (non-intervention group). The intervention programme included dietary measures (exclusive and prolonged milk feeding diet followed by a hypoantigenic weaning diet) and environmental measures (avoidance of parental smoking in the presence of the babies, day care > 2 years of life). Mothers in this group who had insufficient breast milk were randomly assigned to one of two coded formulas: either a hydrolysed milk formula (Nidina HA, Nestlé) or a conventional adapted formula (Nan, Nestlé). Other environmental measures remained the same as for the breastfeeding mothers. The non-intervention group were either breastfed or received the usual Italian milk feeding and weaning diet, without environmental advice. The main outcome measures were anthropometric measurements and allergic disease manifestations. Normal anthropometric data were observed both in the intervention group and in the non-intervention group. The incidence of allergic manifestations was much lower in the intervention group than in the non-intervention group at 1 year (11.5 versus 54.4%, respectively) and at 2 years (14.9 versus 65.6%) and 3 years (20.6 versus 74.1%). Atopic dermatitis and recurrent wheezing were found in both the intervention group and the non-intervention group from birth up to the second year of life, while urticaria and gastrointestinal disorders were only present in the non-intervention group in the first year of life. Conjunctivitis and rhinitis were present after the second year in both the intervention group and the non-intervention group. Relapse of the same allergic symptom was less in the intervention group (13.0%) than in the non-intervention group (36.9%). In comparison to the non-intervention group, there were fewer intervention group cases with two or more different allergic symptoms (8.7 versus 32.6%), and they were more likely to avoid steroid treatment (0 versus 10.8%) and hospital admission (0 versus 6.5%). Babies in the non-intervention group fed with adapted formula were more likely to develop allergies than breastfed babies in the same group. In the intervention group the breastfed infants had the lowest incidence of allergic symptoms, followed by the infants fed the hydrolysed formula (ns). Infants in the intervention group fed the adapted formula had significantly more allergies than the breastfed and hydrolysed milk fed infants, although less than their counterparts in the non-intervention group. Of the affected subjects in the intervention group, 80.4% were RAST and/or Prick positive to food or inhalant allergens. Total serum IgE values detected at birth in the intervention group were not predictive, but at 1 and 2 years of age, IgE values more than 2 SD above the mean in asymptomatic babies were found to predictive for later allergy. In breastfed babies the total IgE level at 1 and 2 years of age was lower than in the other two feeding groups. Of the various factors tested in the non-intervention group, the following were the most important in the pathogenesis of allergic symptoms: (i) formula implementation begun in the first week of life; (ii) early weaning (< 4 months); (iii) feeding beef (< 6 months); (iv) early introduction of cow's milk (< 6 months); and (v) parental smoking in the presence of the babies and early day care admission (< 2 years of life). All the preventive measures used in this study (exclusive breastfeeding and/or hydrolysed milk feeding, delayed and selective introduction of solid foods, and environmental advice) were effective at the third year of follow-up, greatly reducing allergic manifestations in high atopic risk babies in comparison with those not receiving these interventions

Development of immune function in the intestine and its role in neonatal diseases

This review has traced the ontogeny of the human mucosal immune system, speculating that appropriate gut immune responses are essential in preventing many significant neonatal enteric diseases. Because the gastrointestinal tract serves as the portal of entry for many potential antigens, its mucosal immune function is essential in controlling antigenic responses and ensuring systemic tolerance. A thorough under standing of the development of the entire immune system is essential in defining intestinal mucosal immune function. From the protective barrier covering the enterocyte to the intraepithelial T lymphocytes, these components work together to limit antigen passage from the gut lumen to the underlying immune cells and, thus, promote normal immunity and tolerance. When abnormalities exist or when this immune barrier has not matured fully, conditions afflicting newborns, especially preterm infants, occur. Necrotizing enterocolitis, milk-protein enteropathy, and enteric bacterial infections are only three clinical examples of how aberrant gut immune-mediated defenses may have a significant role in their pathogenesis. In clinical practice, it is not only important to recognize these conditions at their onset but also to understand the basis for the underlying illness and identify newborns who are at an increased risk of acquiring them.

Characterisation of inorganic microparticles in pigment cells of human gut associated lymphoid tissue

Macrophages at the base of human gut associated lymphoid tissue (GALT), become loaded early in life with dark granular pigment that is rich in aluminium, silicon, and titanium. The molecular characteristics, intracellular distribution, and source of this pigment is described. Laser scanning and electron microscopy showed that pigmented macrophages were often closely related to collagen fibres and plasma cells in GALT of both small and large intestine and contained numerous phagolysosomes, previously described as granules, that are rich in electron dense submicron sized particles. Morphological assessment, x ray microanalysis, and image electron energy loss spectroscopy showed three distinct types of microparticle: type I - spheres of titanium dioxide, 100-200 nm diameter, characterised as the synthetic food-additive polymorph anatase; type II - aluminosilicates, < 100-400 nm in length, generally of flaky appearance, often with adsorbed surface iron, and mostly characteristic of the natural clay mineral kaolinite; and type III - mixed environmental silicates without aluminium, 100-700 nm in length and of variable morphology. Thus, this cellular pigment that is partly derived from food additives and partly from the environment is composed of inert inorganic microparticles and loaded into phagolysosomes of macrophages within the GALT of all human subjects. These observations suggest that the pathogenicity of this pigment should be further investigated since, in susceptible individuals, the same intracellular distribution of these three types of submicron particle causes chronic latent granulomatous inflammation.

Intestinal inflammation in children with atopic eczema: faecal eosinophil cationic protein and tumour necrosis factor-alpha as non-invasive indicators of food allergy

BACKGROUND

Food allergy is contemplated in atopic eczema. Early recognition of food allergies is difficult and the diagnosis is often missed because of the non-specificity of symptoms. New non-invasive tests are clearly needed.

OBJECTIVE AND METHODS

We measured the concentrations of tumour necrosis factor-alpha, eosinophil cationic protein and alpha-1 antitrypsin in faeces as indicators of intestinal inflammation induced by double-blind placebo-controlled oral cow's milk challenge in infants and young children with atopic eczema.

RESULTS

An increased alpha-1 antitrypsin concentration (> 2 mg/g) after cow's milk challenge was detected in 43% of the infants positive as compared with 11% of the infants negative to challenge, P = 0.02. The concentration of eosinophil cationic protein in faeces increased after cow's milk challenge in patients positive to challenge (P = 0.02) but not in those negative to challenge (P = 0.79). The concentration of eosinophil cationic protein was enhanced particularly in patients manifesting immediate-type reactions to the cow's milk challenge. The concentration of tumour necrosis factor-alpha increased after cow's milk challenge in patients positive to challenge (P = 0.005) but not in those negative to challenge (P = 0.25). The concentration of tumour necrosis factor-alpha in faeces was enhanced particularly in patients manifesting delayed-type reactions to the cow's milk challenge.

CONCLUSION

We conclude that in children with atopic eczema food allergy is associated with intestinal inflammation indicating that more general immunologic disturbances than previously thought take place in these patients. We further suggest that faecal eosinophil cationic protein, tumour necrosis factor-alpha and alpha-1 antitrypsin distinctly indicate various reaction types of food allergy. Parallel testing with eosinophil cationic protein and tumour necrosis factor-alpha may significantly enhance the accuracy in diagnosis of food allergy in patients with atopic eczema.

Combined skin prick and patch testing enhances identification of food allergy in infants with atopic dermatitis

BACKGROUND

Early recognition of dietary allergies in infants with atopic dermatitis is essential for avoidance of unnecessary elimination diets, amelioration of the skin disease, and secondary prevention of the development of multiple food allergies. Simple and accurate methods of identifying provocative foods are urgently needed.

METHODS

The usefulness of skin prick and patch tests as indicators of cow milk allergy was evaluated in 183 patients ranging in age from 2 to 36 months with double-blind, placebo-controlled (n = 118) or open (n = 65) cow milk challenges.

RESULTS

The oral cow milk challenges were interpreted as positive in 54% of both challenge types. Positive challenge rapidly elicited pruritus, urticaria, and/or exanthema in 49% of cases and delayed-onset eczematous lesions in 51%. The skin prick and patch tests gave markedly discrepant results; prick tests were positive in 67% of the cases with acute-onset reactions to milk challenge, whereas patch tests tended to be negative. Patch tests were positive in 89% of those with delayed-onset reactions, although prick tests were frequently negative.

CONCLUSIONS

The observations indicate that IgE and T cell-mediated responses to cow milk can be distinguished in atopic dermatitis. Parallel skin testing with combined prick and patch tests can significantly enhance the accuracy in diagnosis of specific dietary allergies in patients with atopic dermatitis.

M cells in Peyer's patches of the intestine

M cells are specialized epithelial cells of the mucosa-associated lymphoid tissues. A characteristic of M cells is that they transport antigens from the lumen to cells of the immune system, thereby initiating an immune response or tolerance. Soluble macromolecules, small particles, and also entire microorganisms are transported by M cells. The interactions of these substances with the M cell surface, their transcytosis, and the role of associated lymphoid cells are reviewed in detail. The ultrastructure and several immuno- and lectin-histochemical properties of M cells vary according to species and location along the intestine. We present updated reports on these variations, on identification markers, and on the origin and differentiation of M cells. The immunological significance of M cells and their functional relationship to lymphocytes and antigenpresenting cells are critically reviewed. The current knowledge on M cells in mucosa-associated lymphoid tissues outside the gut is briefly outlined. Clinical implications for drug deliver, infection, and vaccine development are discussed.

Sodium deoxycholate facilitates systemic absorption of verotoxin 2e from pig intestine

Injection of verotoxin 2e together with sodium deoxycholate, which increases intestinal permeability to macromolecules, into the intestine of pigs resulted in fluid accumulation, intestinal damage, and signs and lesions of edema disease. Intragastric administration of verotoxin 2e to newborn piglets, who normally absorb protein nonspecifically, resulted in systemic verotoxemia. These results suggest that development of natural edema disease requires a state of increased intestinal permeability.

Crypt-villus differentiation reflected by lectin and protein binding to rat small intestinal brush border membranes

To compare differentiation along the crypt-villus axis in adult rats with changes observed in postnatal maturation with respect to binding capacities for lectins and food proteins, crypts and villi were isolated by in vivo perfusion and in vitro incubation. Brush border membranes were prepared from adults and newborns, and binding of 125I-labeled lectins and food proteins was assessed by airfuge ultracentrifugation. Crypt and villus membrane protein patterns looked almost identical, unlike newborn membranes. Considerable shifts in lectin binding to membranes were observed during postnatal maturation, but not in crypt-villus differentiation. For instance, fucose-specific lectin binding patterns in both preparations resembled the general adult mode. Contrary to differences in food protein binding between newborn and adult membranes, food protein binding did not show a consistent significant difference between membranes of crypt and villus origin in adult animals. In conclusion, membrane differentiation along the crypt-villus axis was found to follow a pattern dissimilar from neonatal maturation as far as protein and carbohydrate composition and food protein binding were concerned.

Intestinal absorptive capacity, intestinal permeability and jejunal histology in HIV and their relation to diarrhoea

Intestinal function is poorly defined in patients with HIV infection. Absorptive capacity and intestinal permeability were assessed using 3-O-methyl-D-glucose, D-xylose, L-rhamnose, and lactulose in 88 HIV infected patients and the findings were correlated with the degree of immunosuppression (CD4 counts), diarrhoea, wasting, intestinal pathogen status, and histomorphometric analysis of jejunal biopsy samples. Malabsorption of 3-O-methyl-D-glucose and D-xylose was prevalent in all groups of patients with AIDS but not in asymptomatic, well patients with HIV. Malabsorption correlated significantly (r = 0.34-0.56, p < 0.005) with the degree of immune suppression and with body mass index. Increased intestinal permeability was found in all subgroups of patients. The changes in absorption-permeability were of comparable severity to those found in patients with untreated coeliac disease. Jejunal histology, however, showed only mild changes in the villus height/crypt depth ratio as compared with subtotal villus atrophy in coeliac disease. Malabsorption and increased intestinal permeability are common in AIDS patients. Malabsorption, which has nutritional implications, relates more to immune suppression than jejunal morphological changes.

Basal secretion and anaphylactic release of rat mast cell protease-II (RMCP-II) from ex vivo perfused rat jejunum: translocation of RMCP-II into the gut lumen and its relation to mucosal histology

The kinetics of the release of rat mast cell protease-II (RMCP-II) from mucosal mast cells in the jejunum of Nippostrongylus brasiliensis primed (immune) rats was investigated using ex vivo perfusion of a segment of jejunum through the cranial mesenteric artery. The aim of the study was to assess the role of the protease in anaphylaxis and in particular to ascertain whether it is responsible for the histological changes, which include widespread epithelial shedding, seen in the mucosa in in vivo models of anaphylaxis. Perfusion of the jejunal vasculature with a Krebs-Ringer buffer showed that there was basal secretion of RMCP-II by jejunal mast cells in all rats studied. The baseline concentration of RMCP-II was significantly greater (p < 0.05) in immune rats (> 7 ng/ml) previously exposed to nippostrongylus infection than in control, naive animals (< 2 ng/ml). Challenge of immune rats with 100 or 400 worm equivalents of whole worm antigen resulted in an immediate (within 40 seconds) and significant (p < 0.02) increase in the concentration of RMCP-II (to > 3 micrograms/ml) in the vascular perfusate, which was not seen in naive rats or immune rats challenged with an irrelevant antigen. Greater amounts of RMCP-II were also recovered from the jejunal lumen of immune rats compared with naive rats after challenge of both groups with worm antigen. Despite the release of microgram quantities of RMCP-II into the gut lumen and vascular perfusate, however, there were no significant changes seen in the mucosal histology. These results suggest that RMCP-II alone is not responsible fore the loss of gut epithelium seen during anaphylaxis in the rat.

Intestinal permeability: an overview

The noninvasive assessment of intestinal permeability in humans has a 20-year history. Because the tests are increasingly used in clinical practice and research and because there is much controversy, we reviewed the literature and outlined the potential and possible shortcomings of these procedures. Data was obtained from personal files and from a systemic search through MEDLINE and EMBASE. The principle of the differential urinary excretion of orally administered test markers is explained with reference to the desired physicochemical properties of the markers and how the principle can be exploited to allow assessment of various other gastrointestinal functions. The use of intestinal permeability tests for diagnostic screen for small bowel disease and assessment of responses to treatment, the pathogenesis of disease, normal intestinal physiology, and the effect of drugs and toxins on the intestine is described and reviewed. The controversy surrounding the anatomic location of the permeation pathways that the markers use is highlighted. Noninvasive tests of intestinal permeability have fulfilled early promises of usefulness in clinical practice and research. There is now a need for integrated research into the basic mechanisms of regulatory control of the intestinal barrier function.

Interrelation of intracellular proteases with total parenteral nutrition-induced gut mucosal atrophy and increase of mucosal macromolecular transmission in rats

Total parenteral nutrition (TPN) is known to induce mucosal atrophy and to increase macromolecular transmission of the small intestine. The potential participation of various proteases in that process was investigated. Male Wistar rats were randomly divided into two groups: the TPN group (n = 11) received a standard TPN (250 kcal/kg per day, 1.78 g nitrogen/kg per day) and the FED group (n = 10) received a standard rat food for 1 week. This was followed by an examination of gut macromolecular transmission of fluorescein isothiocyanate dextran 70,000 (FITC-dextran) after intragastric injection and of the activities of gut mucosal cathepsins B, H, and L and of proteasome. Mucosal wet weight and protein content decreased significantly by TPN for 1 week. In both groups, the activities of all proteases in the ileum were significantly greater than in the jejunum. In the TPN group, cathepsin L and H activities in the ileum, and cathepsin B activity in both the jejunum and the ileum, were greater than those in the FED group. The portal concentration of FITC-dextran was higher than arterial and venous concentrations in the both groups. In the TPN group, the portal FITC-dextran concentration increased significantly compared with the FED group. In conclusion, active proteolysis is not associated with TPN-induced mucosal atrophy. Cathepsins activities in the ileum increase as a result of TPN. Interrelationship is implicated between increase of lysosomal protease activity and the deterioration of the intestinal barrier function, which permits macromolecular transmission.

Ultrastructure and protein transport of M cells in the rabbit cecal patch

BACKGROUND

The gut-associated lymphoid tissue of the rabbit cecum includes a single lymphoid patch located close to the ileocecal orifice. Vimentin immunoreactivity, which can now be regarded as a marker for M cells in rabbits, has identified a subpopulation of epithelial cells as M cells in the domes of this patch. The aim of the present study was to demonstrate that these M cells are capable of antigen transport and to characterize their ultrastructure.

METHODS

M cells of the rabbit cecal lymphoid patch were studied by scanning, thin section, and freeze-fracture electron microscopy. The transcytosis across these M cells was investigated using horseradish peroxidase as a soluble tracer protein.

RESULTS

The M cells were concentrated at the flanks of the domes and had long, thick, branched microvilli, a well-developed terminal web, and a deep invagination of their apical membrane. Numerous small vesicles lay beneath the terminal web in close vicinity to the base of the invagination. These vesicles transported the luminally applied horseradish peroxidase through the M cells. In contrast to adjacent enterocytes, the glycocalyx of M cells was thin, stub-like, and had very few glycocalyceal bodies. Bacteria adhered to the surface of M cells and were also found in the apical invagination.

CONCLUSIONS

The M cells of the rabbit cecal lymphoid patch differ from those of Peyer's patches of the small intestine in their ultrastructure and route of antigen transport. These differences might be related to the situations resulting from differences in the microbial populations at these locations.