Histoplanimetrical study on the relationship between the cell kinetics of villous columnar epithelial cells and the proliferation of indigenous bacteria in rat small intestine

Histological study of diurnal changes in bacterial settlement in the rat alimentary tract

The composition of fecal bacteria is reported to change throughout the day, whereas the circadian rhythmicity of indigenous bacteria that settle on the epithelium is mostly unknown. The present study aimed to clarify the diurnal changes in the settlement of indigenous bacteria in the rat alimentary tract using histological analysis. The settlement of indigenous bacteria on the mucosal epithelium throughout the day and the diurnal changes in settlement levels were observed in the esophagus, the nonglandular area of the stomach, and the ileum. The peak of zeitgeber time (ZT) in the settlement level differed by segment: ZT 12 in the esophagus, ZT 6 in the nonglandular area of the stomach, and ZT 0 in the ileum. Moreover, 16S rRNA amplicon sequencing using tissue sections revealed that the compositions of the indigenous bacteria in the ileum differed among ZT. In the intervillous spaces of the ileum, the formation level of the mucus layer, one of the most fundamental host defenses against bacteria, was lowest at ZT 0. Bacteria were preferentially adjacent to the villous epithelium in the area without coverage by the mucus layer at ZT 0. These findings collectively suggest that the settlement level and possibly the composition of the indigenous bacteria changed diurnally in various segments of the alimentary tract, and the formation of the mucus layer might be the most likely to lead to such diurnal changes in indigenous bacteria, at least in the ileum.

Effects of the expansion of bacterial colonies into the intervillous spaces on the localization of several lymphocyte lineages in the rat ileum

The effect of bacterial colonies expanded into the intervillous spaces on the localization of several lymphocyte lineages was immunohistochemically investigated in two types of mucosa: ordinary mucosa of rat ileum, which consists of mucosa without any mucosal lymphatic tissue; and follicle-associated mucosa (FAM), which accompanies the parafollicular area under the muscularis mucosae in the rat ileal Peyer's patch. The results showed that bacterial colonies in the intervillous spaces induced increased populations of CD8⁺ cells in the epithelium of the intestinal villus in ordinary mucosa (IV) and intestinal villus in FAM (IV-FAM). Bacterial colonies in the intervillous spaces were also associated with increased numbers of IgA⁺ cells, which were mainly localized in the lamina propria of basal portions of IV and IV-FAM, and with expanded localization of IgA⁺ cells into the villous apex in both IV and IV-FAM. Moreover, IgA⁺ cells around the intestinal crypts adjacent to IV or IV-FAM were also increased in response to bacterial colonies. In the IV-FAM, but not IV, L-selectin⁺ cells, which were found to be immunopositive for TCRαβ or CD19, were drastically increased in the lamina propria from the crypt to middle portion of IV-FAM and in the lumen of central lymph vessel of IV-FAM in response to the bacterial colonies in the intervillous spaces. These findings revealed that the expansion of bacterial colonies into the intervillous spaces accompanies the change of histological localization of the lymphocyte lineage in both the ordinary mucosa and FAM.

Ultrastructural and Immunohistochemical Study on the Lamina Propria Cells Beneath Paneth Cells in the Rat Ileum

Paneth cells secrete bactericidal substances in response to bacterial proliferation on the mucosal surface without directly contacting bacteria. However, the induction mechanism of this transient secretion has not been clarified, although nervous system and/or immunocompetent cells in the lamina propria (LP) might be involved. In this study, we ultrastructurally and immunohistochemically investigated which LP cells are localized beneath Paneth cells and examined the relationship between the Paneth cell-derived cellular processes which extended into the LP and the LP cells. The results showed that various cells-including blood capillary, subepithelial stromal cell, and nerve fiber-were present in the LP beneath Paneth cells. Endothelial cells of blood capillary were the cells most frequently found in this location; they were situated within 1 μm of the Paneth cells and possessed fenestration on the surfaces adjacent to Paneth cells. The Paneth cells rarely extended the cellular processes toward the LP across the basal lamina. Most of the cellular processes of Paneth cells contacted the subepithelial stromal cells. Immunohistochemistry revealed that the CD34⁺ CD31^- αSMA^- stromal cells preferentially localized in the LP beneath the intestinal crypt base, while PDGFRα^hi αSMA⁺ stromal cells mainly localized around the lateral portions of the intestinal crypt and PDGFRα^hi αSMA^- stromal cells localized in the intestinal villus. From these findings, the existence of blood capillaries beneath Paneth cells might reflect the active exocrine function of Paneth cells. Furthermore, subepithelial stromal cells, probably with a CD34⁺ CD31^- αSMA^- PDGFRα^-/lo phenotype, beneath the crypt base might affect Paneth cell activity by interacting with their cellular processes. Anat Rec, 301:1074-1085, 2018. © 2018 Wiley Periodicals, Inc.

Suppression of calpain expression by NSAIDs is associated with inhibition of cell migration in rat duodenum

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used for the alleviation of pain and inflammation, but these drugs are also associated with a suite of negative side effects. Gastrointestinal (GI) toxicity is particularly concerning since it affects an estimated 70% of individuals taking NSAIDs routinely, and evidence suggests the majority of toxicity is occurring in the small intestine. Traditionally, NSAID-induced GI toxicity has been associated with indiscriminate inhibition of cyclooxygenase isoforms, but other mechanisms, including inhibition of cell migration, intestinal restitution, and wound healing, are likely to contribute to toxicity. Previous efforts demonstrated that treatment of cultured intestinal epithelial cells (IEC) with NSAIDs inhibits expression and activity of calpain proteases, but the effects of specific inhibition of calpain expression in vitro or the effects of NSAIDs on intestinal cell migration in vivo remain to be determined. Accordingly, we examined the effect of suppression of calpain protease expression with siRNA on cell migration in cultured IECs and evaluated the effects of NSAID treatment on epithelial cell migration and calpain protease expression in rat duodenum. Our results show that calpain siRNA inhibits protease expression and slows migration in cultured IECs. Additionally, NSAID treatment of rats slowed migration up the villus axis and suppressed calpain expression in duodenal epithelial cells. Our results are supportive of the hypothesis that suppression of calpain expression leading to slowing of cell migration is a potential mechanism through which NSAIDs cause GI toxicity.

Differential expression of Toll-like receptor-2, -4 and -9 in follicle-associated epithelium from epithelia of both follicle-associated intestinal villi and ordinary intestinal villi in rat Peyer's patches

The expressions of Toll-like receptor (TLR) -2, -4 and -9 were immunohistochemically investigated in the follicle-associated epithelium (FAE), and epithelia of the follicle-associated intestinal villus (FAIV) and ordinary intestinal villus (IV) in rat Peyer’s patch regions with no bacterial colonies on the mucous membranes. TLR-2 was expressed in the striated borders of microvillous columnar epithelial cells (MV) in both FAIV and IV except in the apices. However, TLR-2 expression in the striated borders was weaker in the epithelium of the follicular side of FAIV (f-FAIV) than in epithelia of IV and the anti-follicular side of FAIV. TLR-4 and -9 were not expressed in the FAIV and IV. In the FAE, TLR-2, -4 and -9 were not expressed in the striated borders of MV, but the roofs of some typical M-cells were immunopositive for all TLRs. Especially, no TLR-positive MV were found at the FAE sites where M-cells appeared most frequently. In the follicle-associated intestinal crypt (FAIC), immunopositivity for all TLRs was observed in the striated borders of MV and the luminal substances. In conclusion, the lower levels of TLR-2 in both FAE and the epithelium of f-FAIV probably reduce recognition of indigenous bacteria. TLR-2, -4 and -9 appear not to participate directly in differentiation of MV into M-cells, because TLRs were not expressed in any MV in the upstream region of M-cells in FAE with no settlement of indigenous bacteria in the rat Peyer’s patches.

Inhibition of Kv channel expression by NSAIDs depolarizes membrane potential and inhibits cell migration by disrupting calpain signaling

Clinical use of non-steroidal anti-inflammatory drugs (NSAIDs) is well known to cause gastrointestinal ulcer formation via several mechanisms that include inhibiting epithelial cell migration and mucosal restitution. The drug-affected signaling pathways that contribute to inhibition of migration by NSAIDs are poorly understood, though previous studies have shown that NSAIDs depolarize membrane potential and suppress expression of calpain proteases and voltage-gated potassium (Kv) channel subunits. Kv channels play significant roles in cell migration and are targets of NSAID activity in white blood cells, but the specific functional effects of NSAID-induced changes in Kv channel expression, particularly on cell migration, are unknown in intestinal epithelial cells. Accordingly, we investigated the effects of NSAIDs on expression of Kv1.3, 1.4, and 1.6 in vitro and/or in vivo and evaluated the functional significance of loss of Kv subunit expression. Indomethacin or NS-398 reduced total and plasma membrane protein expression of Kv1.3 in cultured intestinal epithelial cells (IEC-6). Additionally, depolarization of membrane potential with margatoxin (MgTx), 40mM K(+), or silencing of Kv channel expression with siRNA significantly reduced IEC-6 cell migration and disrupted calpain activity. Furthermore, in rat small intestinal epithelia, indomethacin and NS-398 had significant, yet distinct, effects on gene and protein expression of Kv1.3, 1.4, or 1.6, suggesting that these may be clinically relevant targets. Our results show that inhibition of epithelial cell migration by NSAIDs is associated with decreased expression of Kv channel subunits, and provide a mechanism through which NSAIDs inhibit cell migration and may contribute to NSAID-induced gastrointestinal (GI) toxicity.

Ultrastructural study on the morphological changes in indigenous bacteria of mucous layer and chyme throughout the rat intestine

Indigenous bacteria in the alimentary tract are exposed to various bactericidal peptides and digestive enzymes, but the viability status and morphological changes of indigenous bacteria are unclear. Therefore, the present study aimed to ultrastructurally clarify the degeneration and viability status of indigenous bacteria in the rat intestine. The majority of indigenous bacteria in the ileal mucous layer possessed intact cytoplasm, but the cytoplasm of a few bacteria contained vacuoles. The vacuoles were more frequently found in bacteria of ileal chyme than in those of ileal mucous layer and were found in a large majority of bacteria in both the mucous layer and chyme throughout the large intestine. In the dividing bacteria of the mucous layer and chyme throughout the intestine, the ratio of area occupied by vacuoles was almost always less than 10%. Lysis or detachment of the cell wall in the indigenous bacteria was more frequently found in the large intestine than in the ileum, whereas bacterial remnants, such as cell walls, were distributed almost evenly throughout the intestine. In an experimental control of long-time-cultured Staphylococcus epidermidis on agar, similar vacuoles were also found, but cell-wall degeneration was never observed. From these findings, indigenous bacteria in the mucous layer were ultrastructurally confirmed to be the source of indigenous bacteria in the chyme. Furthermore, the results suggested that indigenous bacteria were more severely degenerated toward the large intestine and were probably degraded in the intestine.

Meta-analysis of the turnover of intestinal epithelia in preclinical animal species and humans

Due to the rapid turnover of the small intestinal epithelia, the rate at which enterocyte renewal occurs plays an important role in determining the level of drug-metabolizing enzymes in the gut wall. Current physiologically based pharmacokinetic (PBPK) models consider enzyme and enterocyte recovery as a lumped first-order rate. An assessment of enterocyte turnover would enable enzyme and enterocyte renewal to be modeled more mechanistically. A literature review together with statistical analysis was employed to establish enterocyte turnover in human and preclinical species. A total of 85 studies was identified reporting enterocyte turnover in 1602 subjects in six species. In mice, the geometric weighted combined mean (WX) enterocyte turnover was 2.81 ± 1.14 days (n = 169). In rats, the weighted arithmetic mean enterocyte turnover was determined to be 2.37 days (n = 501). Humans exhibited a geometric WX enterocyte turnover of 3.48 ± 1.55 days for the gastrointestinal epithelia (n = 265), displaying comparable turnover to that of cytochrome P450 enzymes in vitro (0.96-4.33 days). Statistical analysis indicated humans to display longer enterocyte turnover as compared with preclinical species. Extracted data were too sparse to support regional differences in small intestinal enterocyte turnover in humans despite being indicated in mice. The utilization of enterocyte turnover data, together with in vitro enzyme turnover in PBPK modeling, may improve the predictions of metabolic drug-drug interactions dependent on enzyme turnover (e.g., mechanism-based inhibition and enzyme induction) as well as absorption of nanoparticle delivery systems and intestinal metabolism in special populations exhibiting altered enterocyte turnover.

Peculiar composition of epithelial cells in follicle-associated intestinal crypts of Peyer's patches in the rat small intestine

The epithelial cell composition was investigated in the follicle-associated intestinal crypt (FAIC) of rat Peyer’s patches. The epithelium of the FAIC mainly consisted of columnar epithelial cells, goblet cells and Paneth cells. The characteristics of secretory granules in Paneth cells and goblet cells of both the FAIC and ordinary intestinal crypts (IC) were almost the same in periodic acid-Schiff (PAS) reaction, Alcian blue (AB) staining and the immunohistochemical detection of lysozymes and soluble phospholipase A2. Both goblet cells and Paneth cells were markedly less frequent on the follicular sides than on the anti-follicular sides of the FAIC. Goblet cells were also markedly less frequent in the follicle-associated epithelium (FAE) than in the ordinary intestinal villi (IV). Indigenous bacteria were more frequently adhered to FAE than to follicle-associated intestinal villi or IV. These findings suggest that the host defense against indigenous bacteria is inhibited on the follicular sides of FAIC, which might contribute to the preferential settlement of indigenous bacteria on the FAE; they also suggest that differentiation into secretory cells is inhibited in the epithelium of the follicular sides of FAIC, so that differentiation into M cells might be admitted in the FAE of rat Peyer’s patches. Furthermore, intermediate cells possessing characteristics of both Paneth cells and goblet cells were rarely found in the FAIC, but not in the IC. This finding suggests that the manner of differentiation into Paneth cells in the FAIC differs from that in the IC.

Histoplanimetrical study on the relationship between invasion of indigenous bacteria into intestinal crypts and proliferation of epithelial cells in rat ascending colon

The relationship between the invasion of indigenous bacteria into intestinal crypts and the proliferation of epithelial cells was histoplanimetrically investigated in the rat ascending colon. Indigenous bacteria preferentially adhered to the intestinal superficial epithelial cells in the mesenterium-attached mucosa (MAM) compared to those in the mesenterium-non-attached mucosa (MNM). Intestinal crypts with indigenous bacteria were also significantly more frequently found in MAM than in MNM. Total epithelial cells, columnar epithelial cells and goblet cells were significantly more abundant in the intestinal crypts with no-indigenous bacteria in MAM (MAM-C) than those in MNM (MNM-C), whereas the columnar epithelial cells were less abundant in MAM-C than in the intestinal crypts with indigenous bacteria in MAM (MAM-C-B). Columnar epithelial cells and goblet cells immuno-positive for proliferating cell nuclear antigen (PCNA) in MAM-C were more abundant than those in MNM-C, but less abundant than those in MAM-C-B. Toll-like receptor (TLR)-2, -4 and -9 were immuno-positive in the striated borders of the intestinal superficial epithelial cells, but their positive intensities were weaker in MAM than in MNM. From these findings, indigenous bacteria were confirmed to preferentially settle on the intestinal superficial epithelium of MAM in the rat ascending colon, and low TLRs-expression might contribute to the preferential settlement of indigenous bacteria in MAM. The increase of proliferating epithelial cells is probably induced by the invasion of indigenous bacteria into the intestinal crypts of MAM.

Immunohistochemical detection of toll-like receptor-2, -4 and -9 in exocrine glands associated with rat alimentary tract

Localization of Toll-like receptors (TLRs) in the exocrine glands associated with the rat alimentary tract was immunohistochemically studied using anti-TLR antibodies. TLR-2, -4 and -9 were detected in the secretory granules of acinar cells or the luminal substances of the gustatory gland, extraorbital lacrimal gland, Harderian gland, proper gastric gland and pancreas. TLR-2 and -9 were also detected in the mucous acinar cells of the sublingual gland. Positivity for all TLRs was found in the striated borders of columnar epithelial cells and the luminal substances of the intestinal crypts throughout the small intestine, and also in the goblet cells throughout the large intestine. Only TLR-4 was detected in the secretory granules of Paneth cells. A reduction of TLR-4-positive secretory granules and the formation of TLR-4-positive vacuoles were found in the ileal Paneth cells under the hyper-proliferation of indigenous bacteria. In the apical to middle intervillous portions of the ileum, Gram-positive bacterial colonies were significantly more abundant than Gram-negative bacterial colonies, whereas this difference disappeared in the basal intervillous portions. These findings suggest that there are distribution differences in the secretory sources of soluble TLRs that possibly neutralize their luminal ligands, in the rat alimentary tract. Therefore, the bacterial ligand-recognition system composed of the membranous TLRs of villous columnar epithelial cells and soluble TLRs from crypt epithelial cells might contribute to host defense mechanisms for the selective elimination of Gram-positive bacteria rather than Gram-negative bacteria in the rat small intestine.

Alteration in the apoptosis process of rat esophageal epithelium with hyperproliferation of indigenous bacteria under a physiological condition

The apoptosis process in rat esophageal epithelium was investigated using enzyme-immunohistochemistry and transmission electron microscopy. As a result, Fas and Fas-L were expressed in the epithelial cell membrane and cytoplasm from the stratum spinosum (SS) to the stratum granulosum (SG). No TNF-R1 show immunopositivity in the cell membranes. TNF-α and caspase-8 were not observed in any layer. Caspase-10, cleaved caspase-3, XIAP and DNase-1 were found in the epithelial cytoplasm from the SS to the SG, whereas Bid, Apaf-1 and cleaved caspase-9 were detected only in the SG. Cytochrome c was observed as cytoplasmic granular positivity from the stratum basale (SB) and altered into homogeneous immunopositivity in the SG. Bcl-2 and Bcl-X immunopositivity was detected in cytoplasm from the SB to the SG. Immunoreactions of Bak in the cytoplasm and Bax beneath the cell membrane were observed from the upper portion of the SS with increasing intensity toward the SG. In the sites with the hyperproliferation of indigenous bacteria, TNF-R1, TNF-α and caspase-8 were detected in the SG and the immunopositive intensities of Bid, Apaf-1 and cleaved caspase-9 were altered to be strong. Prominently swollen cells and decreased mitochondria were ultrastructurally confirmed in the uppermost layers of stratum corneum. These findings suggest that the Fas-Fas-L-interaction initially induces apoptosis through a mitochondria-independent pathway and secondarily through a mitochondria-dependent pathway, leading to eventual epithelial cell death in the rat esophageal epithelium. The bacterial stimuli probably enhance the mitochondria-dependent pathway through the TNF-R1-TNF-α interaction.

Immunohistochemical and histoplanimetrical study on the spatial relationship between the settlement of indigenous bacteria and the secretion of bactericidal peptides in rat alimentary tract

To clarify the regulatory mechanism by bactericidal peptides secretion, the secretion of bactericidal peptides was immunohistochemically and histoplanimetrically compared with the degree of Gram-positive/negative bacterial colonization throughout the rat alimentary tract. In the associated exocrine glands from the oral cavity to the stomach, no comparable differences were observed under the changes of development of indigenous bacterial colonies. In the small intestine, immunopositive granules for lysozyme and secretory phospholipase A2 (sPLA2) were markedly decreased, whereas immunopositive vacuoles in the Paneth cells were more increased at sites with hyper-development of indigenous bacterial colonies in the intervillous spaces than at sites with no or less development. No changes in exocrine glands were observed in the large intestine because of the constant existence of large quantities of bacteria. Gram-positive bacterial colonies on the mucosal surfaces were dominant from the oral cavity to the stomach. Gram-negative bacteria were dominant in the large intestine, and the distributions of both Gram-positive and negative bacteria were intermediate in the small intestine. These findings suggest that lysozyme and sPLA2 secreted from the Paneth cells contribute to the regulation of the proliferation of indigenous bacteria in the intervillous spaces of the small intestine, and that the inversion of distributions of Gram-positive and -negative bacteria in the alimentary tract might be caused by the secretion of lysozyme and sPLA2 in the small intestine.

Lectin histochemical detection of special sugars on the mucosal surfaces of the rat alimentary tract

Surfaces of the most luminal positions of mucosae are fundamental settlement sites of indigenous bacteria throughout the rat alimentary tract. In these positions, also epithelial cell-shedding sites, the special sugar expression in the glycocalyx is very important as it provides possible ligands of bacterial lectins for attachment to epithelial cells. Therefore, the sugar expression in glycocalyx of epithelial cells was lectin-histochemically surveyed using 21 lectins throughout the rat alimentary tract. From the tongue to the nonglandular part of the stomach, α-D-Man, α-D-Glc and α-D-GalNAc were detected on the surface of the keratinized stratified squamous epithelium. In the glandular part of the stomach, α-D-Man, β-D-Gal-4GlcNAc, D-Gal, D-GalNAc, D-GlcNAc, α-L-Fuc- α-D-Gal-β(1-4)GlcNAc and bisected triantennary N-glycans were detected on the surface of gastric superficial epithelial cells. From the duodenum to the ileum, (GlcNAc)(2-4) was expressed exclusively on the epithelial cells in the apical portions of the intestinal villi. From the cecum to the rectum, α-D-Man, β-D-Gal-4GlcNAc, D-Gal, D-GalNAc, α-D-Gal(1-3)D-GalNAc, (GalNAc)(n) and NeuNAc were expressed on the intestinal superficial epithelial cells. These results suggest that special sugars are expressed on the most luminal portions of mucosae as exclusive epithelial cell-shedding sites, and that sugar expression differs among the various segments of the alimentary tract. These site differences might reflect differences in resident bacterial species in the rat alimentary tract.

Histoplanimetrical study on the relationship between cellular kinetics of epithelial cells and proliferation of indigenous bacteria in the rat colon

The aim of this study was to clarify the regulatory effects of epithelial kinetics on indigenous bacterial proliferation in the large intestine. The lifespan, migration speed and proliferation rate of crypt epithelial cells in the initial 20% of the colon (proximal colon) and the 50% of the colon (middle colon) in bromodeoxyuridine-administrated rats were histoplanimetrically and chronologically compared. The proximal colon possessed well-developed mucosal folds and a large amount of indigenous bacteria which filled the crypt lumen, whereas no folds or bacteria were found to occupy the crypt lumen in the middle colon. The cell lifespans were 32.2, 42.5 and 33.6 hr in the apical and the basal parts of the mucosal folds of the proximal colon, and in the middle colon, respectively. The migration speeds were 4.2, 2.1 and 3.3 microm/hr, respectively, while the appearance frequencies of proliferating cell nuclear antigen (PCNA)-positive crypt epithelial cells were 35.0, 24.6 and 33.8%. These findings suggest that the lifespan was shortened and the migration speed increased in the most luminal mucosa of colon, contributing to the elimination of the adhered bacteria from the most luminal mucosa. By contrast, the elongation of the lifespan and deceleration of the migration of epithelial cells in the basal parts of the mucosal folds might contribute to reliable settlement of indigenous bacteria, resulting in the maintenance of a large amount of indigenous bacteria in the lumen of the proximal colon.