Preservation of mucus in situ in rat colon

Methacarn preserves mucus integrity and improves visualization of amoebae in gills of Atlantic salmon (Salmo salar L.)

Two aqueous fixation methods (modified Davidson's solution and modified Davidson's solution with 2% (w/v) Alcian blue) were compared against two non-aqueous fixation methods (methacarn solution and methacarn solution with 2% (w/v) Alcian blue) along with the standard buffered formalin fixation method to (a) improve preservation of the mucous coat on Atlantic salmon, Salmo salar L., gills and (b) to examine the interaction between the amoebae and mucus on the gill during an infection with amoebic gill disease. Aqueous fixatives demonstrated excellent cytological preservation but failed to deliver the preservation of the mucus when compared to the non-aqueous-based fixatives; qualitative and semi-quantitative analysis revealed a greater preservation of the gill mucus using the non-aqueous methacarn solution. A combination of this fixation method and an Alcian blue/Periodic acid-Schiff staining was tested in gills of Atlantic salmon infected with amoebic gill disease; lectin labelling was also used to confirm the mucus preservation in the methacarn-fixed tissue. Amoebae were observed closely associated with the mucus demonstrating that the techniques employed for preservation of the mucous coat can indeed avoid the loss of potential mucus-embedded parasites, thus providing a better understanding of the relationship between the mucus and parasite.

Chronic stress induces mast cell-dependent bacterial adherence and initiates mucosal inflammation in rat intestine

BACKGROUND & AIMS

Chronic psychological stress is an important factor in relapses of intestinal disorders, but it remains unclear if stress can induce primary gut inflammation in a previously healthy host.

METHODS

Mast cell-deficient (Ws/Ws) rats and wild-type control (+/+) rats were submitted to water avoidance stress or sham stress (1 h/day) for 10 consecutive days, as a model of ongoing life stress.

RESULTS

Both rat groups had similar systemic responses to stress, as assessed by changes in weight, corticosterone levels, and defecation. In +/+ rats, chronic stress induced barrier dysfunction in the ileum and colon (increased macromolecular permeability and depletion of mucus) and ultrastructural changes in epithelial cells (enlarged mitochondria and presence of autophagosomes) associated with bacterial adhesion and penetration into enterocytes. Moreover, hyperplasia and activation of mast cells, infiltration of neutrophils and mononuclear cells, and increased myeloperoxidase (MPO) activity were documented in the mucosa. In intestine of Ws/Ws rats, epithelial function and morphology were unchanged by chronic stress, bacterial-epithelial cell interaction was not demonstrated, and there was no evidence of inflammatory cell infiltration.

CONCLUSIONS

These findings suggest that chronic psychological stress can be an initiating factor in intestinal inflammation by impairing mucosal defenses against luminal bacteria and highlight the importance of mast cells in this process.

Role of intestinal mucus on the uptake of latex beads by Peyer's patches and on their transport to mesenteric lymph nodes in rats

BACKGROUND

The effects of N-acetylcysteine (NAC) as a mucolytic agent on the uptake of fluorescent polystyrene microparticles by Peyer's patches, on intestinal permeability, and on subsequent transport to mesenteric lymph nodes (MLNs) were investigated to establish the role of mucus gel layer in this process.

METHODS

Twenty rats were divided into two groups: control (n = 10) and NAC (n = 10). Fluorescent polystyrene latex beads of 3.2+/-0.2 microm in diameter were used as a probe for measuring the previously mentioned parameters. The solution of latex beads (0.1 mL) was injected into a 2-cm length of ileal loop containing Peyer's patches, with 0.1 mL of saline (control group) or with 0.1 mL of NAC solution (NAC group) within 10 cm proximal from the ileocaecal valve. Intestinal loops, portal blood, and neighboring MLNs were taken within 1 hour of injection. Intestinal sections were stained by periodic acid-Schiff reagent. Peyer's patches and MLNs were analyzed for the count of particles by image analysis using a confocal laser scanning microscope.

RESULTS

Morphologically, periodic acid-Schiff positive uniform mucus gel was present in front of Peyer's patches of the control group, and mucus gel layer was disrupted and noncontinuous in the NAC group. The number of particles within Peyer's patches and MLNs in the NAC group was significantly higher than that in the control group (p<.001). Intestinal permeability of latex beads in the NAC group was significantly higher than that in the control group (p<.001).

CONCLUSIONS

These data suggest that the mucus gel layer located in front of Peyer's patches is one of the important factors for the uptake of noxious macromolecules, and this in turn plays a major role on small intestinal permeability and subsequent translocation to MLNs.

Alanyl-glutamine-supplemented parenteral nutrition increases luminal mucus gel and decreases permeability in the rat small intestine

BACKGROUND

Effect of supplemental alanyl-glutamine in standard TPN (S-TPN) on luminal mucus gel and small intestinal permeability was investigated.

METHODS

Thirty Sprague-Dawley rats were divided into group I (n = 10), receiving standard rat diet; group II (n = 10), receiving S-TPN; and group III (n = 10), receiving alanyl-glutamine-supplemented TPN for 1 week. After 1 week, fluorescein isothiocyanate (FITC)-dextran was injected into the small intestine of the rats, and they were killed. A small intestinal sample and portal blood were obtained for morphologic and functional analysis of mucus gel and intestinal permeability.

RESULTS

In group II, thickness and optical density of mucus gel per millimeter serosal length of intestine were significantly lower than group I (p<.001) and were significantly higher in group III than in group II (p<.001). The number of goblet cells in the villi and in the crypt of the small intestine was significantly lower in group II than in group I (p<.001) and was significantly higher in group III than in group II (p<.001), with the exception of the villi of jejunum. Villous and crypt surface area per millimeter serosal length of intestine was significantly lower in group II than in group I (p<.001) and was significantly higher in group III than in group II (p<.001). Small intestinal permeability to FITC-dextran was significantly higher in group II than in group I (p<.001) and was significantly lower in group III than in group II (p<.001). Glucosamine synthetase level was significantly higher in group III than in group I and ileum of group II (p<.001).

CONCLUSIONS

Alanyl-glutamine-supplemented TPN prevents a decrease in mucus gel and an increase in small intestinal permeability associated with S-TPN.

Adaptation of a fluorocarbon-based non-aqueous fixation regime for the ultrastructural study of the teleost epithelial mucous coat

Studies on the microanatomy of the mucus-rich biofilm surface of normal or damaged teleost skin tissue have been limited because conventional fixation regimes do not effectively retain mucus during tissue preparation. A non-aqueous fixation method, based on a technique devised to retain airway mucous for ultrastructural study, and consisting of the use of an inert perfluorocarbon solvent with osmium teroxide 1%, was successfully used to prepare skin tissues of healthy juvenile rainbow trout. The skin's mucous coat was examined by transmission electron microscopy and the results were compared with those obtained with tissues prepared by a conventional glutaraldehyde-based method. In samples fixed with glutaraldehyde, the cell-surface structures retained were limited to microridges and a poorly discernible glycocalyx layer. In contrast, those fixed by the non-aqueous method had a more clearly demonstrated glycocalyx layer, and a second fibrillar layer, resembling mucus, which was separated from the glycocalyx layer by an electron-lucent zone.

Developmental changes in distribution of the mucous gel layer and intestinal permeability in rat small intestine

BACKGROUND

From the developmental aspects, the distribution of fluorescein isothiocyanate dextran 70,000 (FTTC-dextran) and mucous gel across the lumen of small intestine was observed as an investigation into the role of mucous gel on intestinal permeability. Furthermore, the effect of N-acetyl cysteine (NAC), a mucolytic agent, on intestinal permeability was examined.

METHODS

In suckling and weaned rats, FTTC-dextran (750 mg/kg body wt) was gavage-fed. After 3 hours, blood samples were taken by cardiac puncture to analyze plasma FTTC-dextran by fluorescence spectrometry. Samples of small intestine with luminal contents were frozen and sectioned in a cryostat for fluorescence microscopy; the same sections were placed in a 0.2% celloidin solution to preserve mucous gel and were stained by periodic acid-Schiff reaction for light microscopy. In weaned rats, intestinal permeability was examined with different concentrations of intraluminally instilled NAC.

RESULTS

The plasma level of FTTC-dextran showed a significant increase (p < .01) in suckling rats compared with the weaned rats. Morphologic findings were similar in both the jejunum and ileum: The spaces between villi were not entirely filled with mucus but filled with FTTC-dextran in suckling rats, whereas the spaces were filled with mucus and not filled with FTTC-dextran in weaned rats. Intestinal permeability in groups with NAC were significantly higher (p < .01) than that in group without NAC.

CONCLUSIONS

These results suggest that an increase in the mucous gel layer that coats the epithelial lining according to the maturation of the gastrointestinal tract is one of the most important factors for a restriction in intestinal permeability.

Adhesive mucous gel layer and mucus release as intestinal barrier in rats

BACKGROUND

Although it has been reported that total parenteral nutrition induces an increased intestinal permeability and a decreased mucous gel layer covering the intestinal epithelium, the role of mucous gel on intestinal permeability has not been well understood. We examined the in vivo effects of N-acetyl cysteine (NAC) as mucolytic agent and colchicine as suppressant of the mucus production on the intestinal transmission of fluorescein isothiocyanate dextran 70,000 (FITC-dextran).

METHODS

Rats were divided into four groups. In each group, FITC-dextran (750 mg/kg) with or without NAC (3000 mg/kg) was injected into the small intestinal lumen 3 hours after intraperitoneal injection of saline or colchicine (Col, 10 mg/kg). Thirty minutes after injection of FITC-dextran, blood samples were taken from portal vein to analyze plasma fluorescein concentration by fluorescence spectrometry. Samples of small intestine were sectioned in a cryostat for fluorescence microscopy, and the identical sections were stained by periodic acid-Schiff reaction.

RESULTS

Plasma FITC-dextran level in NAC group was higher than that in control group (p < .01), that in Col + NAC group was higher than that in Col group (p < .01) and that in Col + NAC group was higher than that in NAC group (p < .05). The spaces between villi were filled with mucous gel in the control and Col groups, whereas those were not entirely filled with mucous gel in NAC and Col + NAC groups. FITC-dextran and mucous gel showed complementary distribution in all rats. The villous interstitial edema was recognized in NAC group and the villi were disrupted in Col + NAC group.

CONCLUSIONS

These results suggest that intestinal permeability is possibly affected not only by the mucous gel covering the intestinal epithelium but also by mucus release from goblet cells of the small intestine.

Total parenteral nutrition decreases luminal mucous gel and increases permeability of small intestine

The distribution of fluorescein isothiocyanate dextran 70,000 (FITC-dextran) and mucous gel across the lumen of small intestine was observed as an investigation into the role of mucous gel on permeability in total parenteral nutrition (TPN). Thirty-two rats were randomly divided into two groups fed with either TPN or oral rat food. On day 4 or 7, FITC-dextran (750 mg/kg body weight) was given through the gastroduodenal tube. After 1 hour, blood samples were taken by aortic puncture to analyze plasma FITC-dextran by fluorescence spectrometry. Samples of small intestine with luminal contents were frozen and sectioned in a cryostat for fluorescence microscopy; the same sections were placed in a 0.2% celloidin solution for 3 minutes to preserve mucous gel and stained by periodic acid-Schiff reaction for light microscopy. The plasma level of FITC-dextran after 1 hour of this marker injection showed a significant increase (p < .01) in the TPN group compared with the rat food group on days 4 and 7. Morphologic findings on days 4 and 7 were similar in both the jejunum and ileum: The mucous gel filled the spaces between villi and FITC-dextran centered in the lumen in the rat food group, whereas the mucous gel decreased and FITC-dextran filled the spaces between villi in the TPN group. FITC-dextran and mucous gel showed complementary distributions in both groups. These data suggest that TPN decreases luminal mucous gel and increases permeability of small intestine in rats.

Thickness of adherent mucus gel on colonic mucosa in humans and its relevance to colitis

The thickness of adherent mucus gel on the surface of colonic mucosa was measured in surgically resected specimens from 46 'control' patients most of whom had carcinoma of the colon; 12 were from right colon, 17 left colon, and 21 from rectum. In addition specimens were examined from 17 patients with ulcerative colitis and 15 patients with Crohn's disease. In controls a continuous layer of mucus was readily seen on specially prepared sections viewed by phase contrast illumination. Mean values for right and left colon and rectum were 107 (48), 134 (68), and 155 (54) microns respectively with a significant difference between right colon and rectum (p = 0.015). Values in ulcerative colitis showed greater variation and in those areas with acute inflammation mucosa was denuded of the mucus layer. In contrast, values for Crohn's disease were normal or greater than normal in thickness--right colon 190 (83) microns compared with 107 48 microns, p = 0.0093. A series of validation experiments are described for the method used to measure mucus thickness. The possible role of mucus in the pathogenesis of inflammatory bowel disease is discussed.

Pathology of the mucous coat of trout skin during an erosive bacterial dermatitis: a technical advance in mucous coat stabilization for ultrastructural examination

A fixation regime which combined cryopreservation, freeze drying and vapour fixation with osmium tetroxide, was found to preserve the mucous coat of trout skin for ambient temperature scanning electron microscopy. The regime was used to study changes to the mucous coat of trout skin during a spontaneous outbreak of "columnaris" disease--a common dermatitis of commercial salmonids associated with the bacterial pathogen Cytophaga columnaris. Infected and damaged regions of skin were covered by a mucous coat which differed from that which covered adjacent unaffected areas. In unaffected areas, the mucous coat topography was smooth and relatively featureless. In contrast, the mucous coat which covered damaged areas was fissured, cratered and contained exfoliated epithelial cells. Nevertheless, this study showed that even sites of extensive dermal ulceration, in which mucous cells had been destroyed, retained a partial mucous coat. This suggests that mucus, after secretion, flows over the skin surface, rather than functioning only near the site of production. Because of the various protective functions attributed to the mucous coat, its partial presence over areas of skin damage would contribute to defence against secondary pathogens and to the prevention of excess movement of ions and water at these sites. The technical development in mucous stabilization, described in this paper, will provide a means for examining morphological changes to the mucous coat of fish skin in response to a range of stimuli in future studies.

The ion exchange properties of human post-mortem caecal and colonic mucus: the effect of sodium butyrate

This study examined Na+/H+ ion exchange of caecal and colonic mucus. Two distinct Na+/H+ ion exchange populations of caecal mucus were identified, one group being a cation exchanger and the other an anion exchanger, suggesting that caecal mucus has ampholyte properties responsive to changing physical and chemical properties of luminal contents. Mucus from the colon was consistently an anionic exchanger--this may aid water and electrolyte absorption in the colon. When mucus was incubated with sodium butyrate, the Na+/H+ ion exchange properties of the mucus were decreased.

The rheology of pig small intestinal and colonic mucus: weakening of gel structure by non-mucin components

Mechanical spectroscopy has been used to study the structure and properties of pig small intestinal and colonic adherent mucus gel. Both mucus secretions had properties of viscoelastic gels, but that from the small intestine was substantially weaker in quality. Small intestinal mucus gel was disrupted by acid (pH 1), detergents (bile) and protein denaturants while that from the colon remained stable following these treatments. Concentration of purified colonic mucin produced a gel with the same rheological properties as the native secretion. Purified small intestinal mucin when concentrated produced a stronger gel than the native secretion and, in contrast to the latter, one which was not disrupted by acid or denaturants. The instability of native small intestinal mucus was shown not to be a function of the mucin components (which alone could account for the gel-forming properties), but to arise from the presence of insoluble material largely from sloughed mucosal cells. These studies show (1) that mucus gels from the colon and small intestine have similar mechanical behaviour and properties to those from the stomach and duodenum, and (2) emphasise the caution that should be exercised when interpreting the rheological properties of mucus preparations, particularly with respect to their content of mucosal cellular material.

The adherent gastric mucus gel barrier in man and changes in peptic ulceration

The mucus barrier is a layer of water-insoluble gel adherent to the gastroduodenal epithelium. In man most previous studies have focused on luminal mucus or histological assessment of presecreted, intracellular mucus--neither of which can be directly correlated with the protective capacity of the adherent mucus barrier. We here describe direct observation of adherent mucus thickness in man, and changes in peptic ulceration. Adherent mucus gel on human antral mucosa is a continuous homogeneous layer of variable thickness, in the range 50-450 microns (median 180 microns), comprising 67% polymeric mucin. In gastric ulcer patients, adherent antral mucus is significantly increased in thickness (median 240 microns), but is very heterogeneous and structurally a substantially weaker gel, comprising only 35% polymeric mucin. Adherent antral mucus from duodenal ulcer patients is homogeneous, significantly thinner (median 110 microns), and structurally a weaker gel, comprising 50% polymeric mucin. The adherent mucus layer from patients with gastric carcinoma resembled that from subjects with gastric ulcer in that it was very heterogeneous, of significantly increased thickness (median 240 microns) and structurally a very weak gel (23% polymeric mucin). These results are discussed in the context of gastroduodenal mucosal protection against acid and pepsin in the gastric juice.

Tightly spiral shaped bacteria in the human stomach: another cause of active chronic gastritis?

Tightly spiral shaped Gram negative bacteria were seen in the gastric biopsies obtained from two patients undergoing gastroscopy. Active chronic gastritis was present in both patients and one patient also had gastric ulceration. Attempts to culture the organism by a number of methods were unsuccessful but positive urease results were obtained in both patients. Both patients were treated with colloidal bismuth subcitrate. Biopsies taken after treatment showed resolution of infection and histological gastritis. These results suggest that Helicobacter pylori is not the only organism associated with chronic active gastritis in man.

Sucralfate interactions with gastric mucus

Sucralfate protects the stomach against a number of experimental damaging agents and is efficacious in the treatment of peptic ulcer disease. It binds with acidity to the base of an ulcer to form a protective barrier. Sucralfate also enhances prostaglandin synthesis and release in the mucosa. In this study, the rat stomach was examined to determine sucralfate's interaction with gastric mucus. Mucus in the rat stomach forms a distinct and continuous blanket. In snap-frozen samples, pretreatment with phosphate-buffered saline as a control shows a layer of mucus of homogeneous structure thinner than the homogeneous layer after pretreatment with antibodies developed against rat gastric mucus. Pretreatment with the surface protective agent sucralfate shows some increase in the thickness of mucus with a thin dense sublayer adjacent to the epithelium and a less dense-appearing outer zone of variable thickness. Analysis of x-rays generated by the electron beam on windows of mucus and epithelium showed the expected gradients of sodium, potassium, chloride, and sulfur. The percentage of aluminum and sulfur in the mucus was higher in sucralfate-treated samples than in controls. Interaction between sucralfate and gastric mucus needs further investigation.

Distribution of Campylobacter pylori in the human stomach obtained at postmortem

The distribution of Campylobacter pylori, its prevalence, and its relationship to gastritis and urease activity have been studied in 54 postmortem stomachs. Infection was confirmed by finding C. pylori in a Gram-stained smear of gastric mucus harvested from the entire stomach. Eight tissue specimens were obtained from predetermined sites from each stomach and examined for histologic gastritis and urease activity. Thirty-seven per cent of stomachs were infected, and of these 80% had widespread histologic gastritis. The detection of urease activity provided information on the distribution of the organism and had a high correlation with histologic gastritis. The organism is capable of infecting any area of the stomach. Infection is common and is more prevalent in Polynesian subjects (60%) than in Caucasians (19%).

Pepsins and the mucus barrier in peptic ulcer disease

Studies show that the gastroduodenal mucosal barrier is damaged by pepsin under conditions in which it is resistant to acid alone. The continuous layer of adherent mucus gel provides a diffusion barrier to luminal pepsin, preventing its access to the underlying epithelium. Pepsin has mucolytic activity and will progressively digest the adherent mucus layer at its luminal surface, although normally this is balanced by secretion of new mucus to maintain a continuous barrier. In peptic ulcer disease the proportion of peptic activity in gastric juice attributable to pepsin type 1 is significantly raised (four to five-fold). Pepsin 1 has increased mucolytic activity compared with the major component, pepsin 3, both at the optimal pH of 2 (twofold increase in activity) and at higher pH values up to pH 5 (sixfold increase in activity at pH 4). Structural studies show that the gel forming polymeric mucin of the antral adherent mucus barrier is deficient in peptic ulcer disease. This breakdown of the mucus barrier in peptic ulcer patients can be attributed to the increased pepsin activity of gastric juice seen in this disease, although other explanations are also possible. The increased pepsin activity of gastric juice in peptic ulcer patients is compatible with the concept 'no acid, no pepsin, no ulcer'.

The anatomical basis for the immune function of the gut

The barrier function of the gut wall can be divided into different histotopographically defined lines of defence. These consist not only of lymphoid cells but also of goblet cells, entero-endocrine cells, macrophages and mast cells. Subsets of lymphoid cells are found preferentially within the epithelium (T suppressor) or in the lamina propria (T helper). Most plasma cells produce IgA. Peyer's patches are described in detail as typical organized lymphoid structures of the gut. In man, they are present well before birth and are found in large numbers even in old age. They are not only typical for the ileum but are also present in the duodenum and jejunum. The four compartments in Peyer's patches, i.e. follicle, corona, interfollicular area and the dome, are defined by the typical localization of lymphocyte subsets and by their different functions. Typical features of the epithelium of the dome are the lack of villi and goblet cells and the presence of specialized epithelial cells (M cells) which are important for the uptake of particulate antigen from the gut lumen. Precursor cells of IgA producing plasma cells leave the intestinal wall via the lymphatics and return preferentially to the gut mucosa, and this is summarized by the term gut-associated lymphoid tissue (GALT). Other organs with mucous membranes, such as mammary and salivary glands, bronchial and genital tract, are also included in this circulatory route and this is expressed by the term mucosa-associated lymphoid tissue (MALT). Mast cells in the gut mucosa can be classified as connective tissue or mucosa mast cells. These differ in their sensitivity to formaldehyde as a fixative, contain different granules and mediators, have different origins, and show major differences in the effectiveness of antiallergic compounds on the stabilizing of the cell membrane. Mucosa mast cells have also been demonstrated in the human gut. The histotopographical relationship of many cell types such as goblet and M cells in addition to cells of the immune system such as lymphoid cells, macrophages and mast cells, is essential in the understanding of the barrier function of the gut wall.