Peyer's patches epithelium in the rat: a morphological, immunohistochemical, and morphometrical study

Alginate-Based Oral Delivery Systems to Enhance Protection, Release, and Absorption of Catalase

Oxidative stress, overproduction of reactive oxygen species (ROS), plays an important role in the development of inflammatory bowel diseases. Catalase has great therapeutic potential by scavenging hydrogen peroxide, one of the ROSs produced in cellular metabolisms. However, in vivo application to scavenge ROS is currently limited especially in oral administrations. Here, we introduced an alginate-based oral drug delivery system that effectively protected catalase from the simulated harsh conditions of the gastrointestinal (GI) tract, released it in the small intestine mimicked condition, and enhanced its absorption via M cells, highly specialized epithelium cells in the small intestine. First of all, catalase was encapsulated in alginate-based microparticles with different amounts of polygalacturonic acid or pectin, which achieved an encapsulation efficiency of more than 90%. It was further shown that catalase was released from alginate-based microparticles in a pH-dependent manner. Results indicated that alginate-polygalacturonic acid microparticles (60 wt % Alg:40 wt % Gal) released 79.5 ± 2.4% of encapsulated catalase at pH 9.1 in 3 h, while they only released 9.2 ± 1.5% of encapsulated catalase at pH 2.0. Even when catalase was encapsulated in microparticles (60 wt % Alg:40 wt % Gal) and exposed to pH 2.0 followed by pH 9.1, it still retained 81.0 ± 11.3% enzyme activity compared to that in microparticles prior to the pH treatment. We then investigated the efficiency of RGD conjugation to catalase on the catalase uptake by M-like cells, the coculturing of human epithelial colorectal adenocarcinoma; Caco-2 cells and B lymphocyte; Raji cells. RGD-catalase protected M-cells more efficiently from the cytotoxicity of H₂O₂, a typical ROS. RGD conjugation to catalase enhanced the uptake by M-cells with 87.6 ± 0.8% RGD-catalase, whereas 11.5 ± 9.2% of RGD-free catalase passed across M-cells. From the results of protection, release, and absorption of model therapeutic proteins from the harsh pH conditions, alginate-based oral drug delivery systems will have numerous applications for the controlled release of drugs that are easily degradable in the GI tract.

Mucus properties and goblet cell quantification in mouse, rat and human ileal Peyer's patches

Peyer's patches (PPs) are collections of lymphoid follicles in the small intestine, responsible for scanning the intestinal content for foreign antigens such as soluble molecules, particulate matter as well as intact bacteria and viruses. The immune cells of the patch are separated from the intestinal lumen by a single layer of epithelial cells, the follicle-associated epithelium (FAE). This epithelium covers the dome of the follicle and contains enterocyte-like cells and M cells, which are particularly specialized in taking up antigens from the gut. However, the presence and number of goblet cells as well as the presence of mucus on top of the FAE is controversial. When mouse ileal PPs were mounted in a horizontal Ussing-type chamber, we could observe a continuous mucus layer at mounting and new, easily removable mucus was released from the villi on the patch upon stimulation. Confocal imaging using fluorescent beads revealed a penetrable mucus layer covering the domes. Furthermore, immunostaining of FAE from mice, rats and humans with a specific antibody against the main component of intestinal mucus, the MUC2 mucin, clearly identify mucin-containing goblet cells. Transmission electron micrographs further support the identification of mucus releasing goblet cells on the domes of PPs in these species.

Studies of mucus in mouse stomach, small intestine, and colon. I. Gastrointestinal mucus layers have different properties depending on location as well as over the Peyer's patches

Colon has been shown to have a two-layered mucus system where the inner layer is devoid of bacteria. However, a complete overview of the mouse gastrointestinal mucus system is lacking. We now characterize mucus release, thickness, growth over time, adhesive properties, and penetrability to fluorescent beads from stomach to distal colon. Colon displayed spontaneous mucus release and all regions released mucus in response to carbachol and PGE2, except the distal colon and domes of Peyer's patches. Stomach and colon had an inner mucus layer that was adherent to the epithelium. In contrast, the small intestine and Peyer's patches had a single mucus layer that was easily aspirated. The inner mucus layer of the distal colon was not penetrable to beads the size of bacteria and the inner layer of the proximal colon was only partly penetrable. In contrast, the inner mucus layer of stomach was fully penetrable, as was the small intestinal mucus. This suggests a functional organization of the intestinal mucus system, where the small intestine has loose and penetrable mucus that may allow easy penetration of nutrients, in contrast to the stomach, where the mucus provides physical protection, and the colon, where the mucus separates bacteria from the epithelium. This knowledge of the mucus system and its organization improves our understanding of the gastrointestinal tract physiology.

Challenges in translational research on probiotic lactobacilli: from in vitro assays to clinical trials

Beneficial effects of certain probiotic strains have been established in the treatment and prevention of various immune and intestinal disorders in humans, including allergic diseases, chronic inflammatory diseases and diarrhoea. The proposed mechanisms underlying the immunomodulatory effects of probiotics in humans are not understood in precise detail but include enhancement of intestinal barrier function, altered epithelial signalling, competition with pathogens and effects on immune cells and immunity depending on the probiotic strain. The publication of controversial or inconclusive probiotic studies in humans highlights the need for a better understanding of the mechanisms and improved strain selection criteria. This review focuses on the immunomodulatory properties of lactobacilli and bifidobacteria in vitro and in vivo, current knowledge concerning the mechanisms in vivo and challenges in translational research on probiotics. A better understanding of the molecular mechanisms of probiotics, the effect of probiotic mixtures versus single strains, the effect of formulation of probiotics and the fate of ingested probiotics should help to clarify the value of immune assays as selection criteria for probiotics.

Immunochemical, biomolecular and biochemical characterization of bovine epithelial intestinal primocultures

BACKGROUND

Cultures of enterocytes and colonocytes represent valuable tools to study growth and differentiation of epithelial cells. In vitro models may be used to evaluate passage or toxicity of drugs, interactions of enteropathogenes bacteria strains with intestinal epithelium and other physiologic or pathologic phenomenon involving the digestive tract.

RESULTS

Cultures of bovine colonocytes and jejunocytes were obtained from organoid-enriched preparations, using a combination of enzymatic and mechanical disruption of the intestine epithelium, followed by an isopicnic centrifugation discarding most single cells. Confluent cell monolayers arising from plated organoids exhibited epithelium typical features, such as the pavement-like structure, the presence of apical microvilli and tight junctions. Accordingly, cells expressed several markers of enterocyte brush border (i.e. maltase, alkaline phosphatase and fatty acid binding protein) as well as an epithelial cytoskeleton component (cytokeratin 18). However, enterocyte primocultures were also positive for the vimentin immunostaining (mesenchyme marker). Vimentin expression studies showed that this gene is constitutively expressed in bovine enterocytes. Comparison of the vimentin expression profile with the pattern of brush border enzymes activities, suggested that the decrease of cell differentiation level observed during the enterocyte isolation procedure and early passages of the primoculture could result from a post-transcriptional de-repression of vimentin synthesis. The low differentiation level of bovine enterocytes in vitro could partly be counteracted adding butyrate (1-2 mM) or using a glucose-deprived culture medium.

CONCLUSION

The present study describes several complementary approaches to characterize bovine primary cultures of intestinal cells. Cultured cells kept their morphologic and functional characteristics during several generations.

Bovine prion is endocytosed by human enterocytes via the 37 kDa/67 kDa laminin receptor

Some forms of transmissible spongiform encephalopathies result from oral infection. We have thus analyzed the early mechanisms that could account for an uptake of infectious prion particles by enterocytes, the major cell population of the intestinal epithelium. Human Caco-2/TC7 enterocytes cultured on microporous filters were incubated with different prion strains and contaminated brain homogenates in the apical compartment. Internalization of infectious particles was analyzed by Western blotting and immunofluorescence. We observed internalization by enterocytes of prion particles from bovine spongiform encephalopathy brain homogenates but not from mouse-adapted scrapie-strain brain homogenates or purified bovine spongiform encephalopathy scrapie-associated fibrils. Bovine prion particles were internalized via endocytosis within minutes of infection and were associated with subapical vesicular structures related to early endosomes. The endocytosis of the infectious bovine PrP(Sc) was reduced by preincubating the cells with an anti-LRP/LR blocking antibody, identifying the 37 kDa/67 kDa laminin receptor (LRP/LR), which is apically expressed in Caco-2/TC7 cells, as the receptor for the infectious prion protein. Altogether, our results underscore a potential role of enterocytes in the absorption of bovine prions during oral infection through specific LRP/LR-dependent endocytosis.

The cellular prion protein PrPc is expressed in human enterocytes in cell-cell junctional domains

The physiological function of PrPc, the cellular isoform of prion protein, still remains unclear, although it has been established, in vitro or by using nerve cells, that it can homodimerize, bind copper, or interact with other proteins. Expression of PrPc was demonstrated as necessary for prion infection propagation. Considering the importance of the intestinal barrier in the process of oral prion infectivity, we have analyzed the expression of PrPc in enterocytes, which represent the major cell population of the intestinal epithelium. Our study, conducted both on normal human intestinal tissues and on the enterocytic cell line Caco-2/TC7, shows for the first time that PrPc is present in enterocytes. Interestingly, we found that this glycosylphosphatidylinositol-anchored glycoprotein was localized in cholesterol-dependent raft domains of the upper lateral membranes of enterocytes, beneath tight junctions, in cell-cell junctional domains. We observed that PrPc, E-cadherin, and Src co-localized in adherens junctions and that PrPc was co-immunoprecipitated with Src kinase but not with E-cadherin. Alteration of cell polarity after cholesterol depletion or loosening of the cell-cell junctions after EGTA treatment rapidly impaired membrane targeting of PrPc. Overall, our results point out the signaling of cell-cell contacts as a putative role for PrPc in epithelial cells.

Peyer's patches: organized lymphoid structures for the induction of mucosal immune responses in the intestine

Peyer's patches (PP) comprise transmucosal clusters of lymphoid follicles overlaid with a specialized lympho-epithelium and consequently play a central role in the induction of mucosal immune responses in the gut. Despite considerable achievements in the last 3 decades, in our understanding of how PP are involved in the induction of immune responses, much remains to be learned about these major organized lymphoid organs. The history and current status of PP termed 'the major inductive site of immune responses' is reviewed. The present understanding of PP biology and function, taking into account their preferential and unique retention of immune competent cells at specific sites, is discussed.

Regional peptide uptake study in the rat intestinal mucosa: glatiramer acetate as a model drug

PURPOSE

To identify regions of the rat intestine that are able to internalize from the lumen oligopeptides, using the model drug glatiramer acetate (GA).

METHODS

GA was introduced into rat intestinal sacs and the integrity of GA during uptake was monitored using antibody detection. Sodium docecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting of intestinal homogenates that had been exposed to GA were performed to identify GA presence. An enzyme-linked immunosorbent assay (ELISA) protocol was adapted for GA quantification. Immunohistochemistry was undertaken to examine the rat colonic wall for GA uptake, and confocal microscopy was used to differentiate adsorbed and internalized peptide in cultured colorectal adenocarcinoma cells.

RESULTS

The colon and the ileum, respectively, were identified to be the intestinal regions in which GA was maximally preserved during uptake from the lumen. GA was identified to cross the colonic wall from the epithelium to the serosa. Internalization of GA into cultured colonic epithelial cells was demonstrated.

CONCLUSIONS

The rat colonic wall was identified to be less proteolytically active toward GA compared to the wall of the more proximal regions of the small intestine. GA has the capacity to penetrate from the lumen into the colonic wall. The maintenance of GA integrity within the wall of the colon offers the potential for local biological activity of the drug.