Functional Morphology of Epithelium of the Small Intestine

THE ISSUE OF HISTOLOGICAL IDENTIFICATION OF М-CELLS IN THE PEYER'S PATCHES OF ALBINO RAT SMALL INTESTINE

OBJECTIVE

The aim: Based on the above cytological signs of M-cells, we set the goal of more detailed clarification of some of their topological relationships with other enterocytes in the follicle-associated epithelium of Peyer's patches of albino rat small intestine.

PATIENTS AND METHODS

Materials and methods: 10 mature albino male rats weighted 200,0±20,0 g were involved into the study. Anatomical dissection with the sampling of the sections of the small intestine containing Peyer's patches was carried out with subsequent embedment of the latter into paraffin blocks and making of serial histological sections of 4 μm thick in the cross-section of the small intestine, followed with hematoxylin-eosin staining. The specimens were studied and documented on the "Konus" light microscope equipped. Morphometric characteristics of the specimen tissue structures were studied using the Sigeta X 1 mm/100 Div.x0.01mm stage micrometer.

RESULTS

Results: The findings of the study revealed enterocytes with phagocytic properties found in the lymphoid-associated epithelium of Peyer's patches of the small intestine of albino rats. Moreover, if they are clearly visualized at the light-optical level, then M-cells are poorly recognizable, which is consistent with a similar assessment made by other authors.

CONCLUSION

Conclusions: Given this, the issue on the topology and functional purpose of M-cells remains uncertain to date and, thereby, the prospect of further research is being outlined, which, in our opinion, can be successful using the method of stereomorphological analysis. For this purpose, multilayer plastic reconstruction methods can be used for serial semi-thin sections of Peyer's patches embedded in epoxy resin, according to the requirements of transmission electron microscopy.

Changes of the glutathione redox system during the weaning transition in piglets, in relation to small intestinal morphology and barrier function

Background

Weaning is known to result in barrier dysfunction and villus atrophy in the immediate post-weaning phase, and the magnitude of these responses is hypothesized to correlate with changes in the glutathione (GSH) redox system. Therefore, these parameters were simultaneously measured throughout the weaning phase, in piglets differing in birth weight category and weaning age, as these pre-weaning factors are important determinants for the weaning transition. Low birth weight (LBW) and normal birth weight (NBW) littermates were assigned to one of three weaning treatments; i.e. weaning at 3 weeks of age (3w), weaning at 4 weeks of age (4w) and removal from the sow at 3 d of age and fed a milk replacer until weaning at 3 weeks of age (3d3w). For each of these treatments, six LBW and six NBW piglets were euthanized at 0, 2, 5, 12 or 28 d post-weaning piglets, adding up 180 piglets.

Results

Weaning increased the glutathione peroxidase activity on d 5 post-weaning in plasma, and duodenal and jejunal mucosa. Small intestinal glutathione-S-transferase activity gradually increased until d 12 post-weaning, and this was combined with a progressive rise of mucosal GSH up till d 12 post-weaning. Oxidation of the GSH redox status (GSH/GSSG E_h) was only observed in the small intestinal mucosa of 3d3w weaned piglets at d 5 post-weaning. These piglets also demonstrated increased fluorescein isothiocyanate dextran (FD4) and horseradish peroxidase fluxes in the duodenum and distal jejunum during the experiment, and specifically demonstrated increased FD4 fluxes at d 2 to d 5 post-weaning. On the other hand, profound villus atrophy was observed during the weaning transition for all weaning treatments. Finally, LBW and NBW piglets did not demonstrate notable differences in GSH redox status, small intestinal barrier function and histo-morphology throughout the experiment.

Conclusion

Although moderate changes in the GSH redox system were observed upon weaning, the GSH redox status remained at a steady state level in 3w and 4w weaned piglets and was therefore not associated with weaning induced villus atrophy. Conversely, 3d3w weaned piglets demonstrated GSH redox imbalance in the small intestinal mucosa, and this co-occurred with a temporal malfunction of their intestinal barrier function.

The impact of apical and basolateral albumin on intestinal zinc resorption in the Caco-2/HT-29-MTX co-culture model

The molecular mechanisms of intestinal zinc resorption and its regulation are still topics of ongoing research. To this end, the application of suitable in vitro intestinal models, optimized with regard to their cellular composition and medium constituents, is of crucial importance. As one vital aspect, the impact of cell culture media or buffer compounds, respectively, on the speciation and cellular availability of zinc has to be considered when investigating zinc resorption. Thus, the present study aims to investigate the impact of serum, and in particular its main constituent serum albumin, on zinc uptake and toxicity in the intestinal cell line Caco-2. Furthermore, the impact of serum albumin on zinc resorption is analyzed using a co-culture of Caco-2 cells and the mucin-producing goblet cell line HT-29-MTX. Apically added albumin significantly impaired zinc uptake into enterocytes and buffered its cytotoxicity. Yet, undigested albumin does not occur in the intestinal lumen in vivo and impairment of zinc uptake was abrogated by digestion of albumin. Interestingly, zinc uptake, as well as gene expression studies of mt1a and selected intestinal zinc transporters after zinc incubation for 24 h, did not show significant differences between 0 and 10% serum. Importantly, the basolateral application of serum in a transport study significantly enhanced fractional apical zinc resorption, suggesting that the occurrence of a zinc acceptor in the plasma considerably affects intestinal zinc resorption. This study demonstrates that the apical and basolateral medium composition is crucial when investigating zinc, particularly its intestinal resorption, using in vitro cell culture.

Modulation of Intestinal Paracellular Transport by Bacterial Pathogens

The passive and regulated movement of ions, solutes, and water via spaces between cells of the epithelial monolayer plays a critical role in the normal intestinal functioning. This paracellular pathway displays a high level of structural and functional specialization, with the membrane-spanning complexes of the tight junctions, adherens junctions, and desmosomes ensuring its integrity. Tight junction proteins, like occludin, tricellulin, and the claudin family isoforms, play prominent roles as barriers to unrestricted paracellular transport. The past decade has witnessed major advances in our understanding of the architecture and function of epithelial tight junctions. While it has been long appreciated that microbes, notably bacterial and viral pathogens, target and disrupt junctional complexes and alter paracellular permeability, the precise mechanisms remain to be defined. Notably, renewed efforts will be required to interpret the available data on pathogen-mediated barrier disruption in the context of the most recent findings on tight junction structure and function. While much of the focus has been on pathogen-induced dysregulation of junctional complexes, commensal microbiota and their products may influence paracellular permeability and contribute to the normal physiology of the gut. Finally, microbes and their products have become important tools in exploring host systems, including the junctional properties of epithelial cells. © 2018 American Physiological Society. Compr Physiol 8:823-842, 2018.

Reversible Toxic Effects of the Dietary Supplement Indole-3-Carbinol in an Immune Compromised Rodent Model: Intestine as the Main Target

Dietary supplements are widely used in the United States, but the safety issue remains unresolved. Immuno-deficient or immuno-compromised patients, estimated to exceed 10 million in the United States, are known to use dietary supplements. This population potentially may be susceptible to supplements' adverse effects. The cruciferous vegetable-derived indole-3-carbinol (I3C) is known for its possible protective effects against a number of chronic diseases and is commercially available as a dietary supplement. However, the safety of orally consumed I3C in the general population and particularly in immuno-compromised individuals remains unknown. In this study, rodent model of immune-deficient male BALB/c nu/nu athymic mice were given diets supplemented with 0-100 μmoles I3C/g diet for 4 weeks. We found that BALB/c nu/nu mice were not viable after three days on a 100 μmoles I3C/g supplemented diet. Switching to the control diet (without I3C) after first detection of stress resulted in a 75% recovery of mice. Mice fed with 10-50 μmoles I3C/g supplemented diet survived but showed concentration-dependent adverse effects. More importantly, the intestine appeared to be the target of I3C toxicity. Number and width of intestinal villi were significantly altered by I3C, which associated with a dose-dependent reduction in cell proliferation and increase in apoptosis. Other molecular effects observed for I3C include activation of multiple xenobiotic metabolism pathways. This is the first study to report hazardous effects of I3C supplementation that are specific to the gastrointestinal tract in an immuno-compromised model and should serve as a caution in using I3C as dietary supplements.

Leakiness and size exclusion of paracellular channels in cultured epithelial cell monolayers-interlaboratory comparison

PURPOSE

To determine and compare the paracellular characteristics of permeability (Papp) of Caco (-2), MDCK, and 2/4/A1 cell lines.

METHODS

The Papp data from 14 studies were analyzed by weighted nonlinear regression in terms of the paracellular parameters: porosity-pathlength (epsilon/delta), pore radius (R), and electrostatic potential drop (deltaphi). Aqueous diffusivities, Daq, for the analysis, were empirically determined. The required hydrodynamic radii, rHYD, were estimated without knowledge of compound density. Mannitol iso-paracellular profiles allowed comparisons of "leakiness" across labs.

RESULTS

Daq (37 degreeC) was predicted as 9.9x10(-5) MW(-0.453); rHYD=(0.92+21.8 MW(-1))xrSE, where rSE is the Stokes-Einstein radius. Values of pore radius ranged from 4.0(+/-0.1) to 18(+/-3) A, with the 2/4/A1 indicating the largest pores. The epsilon/delta capacity factor ranged from 0.2 (+/-0.1) to 69 (+/-5) cm(-1), with most values <1.5 cm(-1). The average potential drop for Caco-2 models was deltaphi(wt avg) Caco(-2)=(-43)+/-20 mV. The paracellular model predicted measured log Papp values with pooled r2=0.93 and s=0.17 (n=108).

CONCLUSION

R and epsilon/delta are negatively correlated to a large extent. Papp can be rate-limited by either factor, with a wide range of possible combinations still indicating nearly constant leakiness for a given marker.