Adherent Mucus Research Articles

Stabilization of Pre-Epithelial Mucus Gel in Cryostat Sections from Rat Colon with Celloidin

Gastrointestinal mucus occurs partly as a stable, translucent water-insoluble gel adherent to the mucosal surface, and partly in a water soluble form in the lumen (Allen and Carroll 1985). The adherent pre-epithelial mucus gel (PMG) has been shown in unfixed sections of rat stomach as a continuous layer of median thickness 80 μm (Kerss et al. 1982), and 145 μm (Sandzen et al. 1988), respectively.

Effect of sialoadenectomy on adaptive cytoprotection in the rat

In the present study we have investigated the effect of sialoadenectomy in the rat on adaptive cytoprotection induced by intragastric instillation of an irritant concentration of ethanol (10% wt/vol). Gastric mucosae were examined 1 h after oral administration of 100% ethanol. In animals with intact salivary glands, pretreatment with saline was followed 15 min later by 100% ethanol. This treatment was associated with a significant degree of mucosal damage. However, prior administration of 10% ethanol in place of saline reduced the area of ulceration. In sialoadenectomized rats, the irritant concentration of ethanol did not protect the gastric mucosa from the damaging actions of absolute ethanol. The effect was partially restored if sialoadenectomized rats were treated for 3 days with an aqueous extract of rat salivary gland tissue. Histologic examination revealed no differences in the extent of epithelial damage or adherent mucus between rats with intact salivary glands and sialoadenectomized rats following pretreatment with either saline or 10% ethanol. Although adaptive cytoprotection in animals with intact salivary glands was not associated with increases in mucosal capacities for prostaglandin E2 or 6-keto prostaglandin F1α biosynthesis, sialoadenectomy resulted in a reduction in the mucosal biosynthetic capacities for both prostanoids. Salivary gland extract administration to sialoadenectomized rats did not significantly alter mucosal prostaglandin biosynthesis levels. These data suggest that salivary gland factors affected adaptive cytoprotection induced by an irritant dose of ethanol. Although endogenous prostaglandin biosynthesis capabilities do not appear to be altered in adaptive cytoprotection, salivary factors appear to influence mucosal generation of prostaglandins.

Augmentation of the gastric mucosal defense mechanism induced by KW-5805, a novel antiulcer agent.

KW-5805 (a new antiulcer agent), given p. o. at 30 mg/kg to rats, significantly increased the amount of gastric adherent mucus and mucosal glycoproteins. Gastric mucosal glucosamine synthetase activity was significantly enhanced by KW-5805 (30 mg/kg, p. o.). KW-5805 (10, 30 mg/kg, p. o.) significantly suppressed the decrease of gastric mucosal blood volume and oxygen sufficiency induced by hemorrhagic shock. The agent also significantly inhibited the extravasation of Evans blue into the gastric mucosa after ischemia-reinfusion. In conclusion, KW-5805 increased biosynthesis, storage and secretion of gastric mucus and improved the gastric mucosal hemodynamics.

Nature of the Enhancement of the Protective Qualities of Gastric Mucus by Sucralfate

The effects of intragastric administration of an antiulcer drug, sucralfate, on the content, composition and physical properties of the mucus component of gastric mucosal barrier were investigated. The experiments were conducted with two groups of rats in which one group received twice daily for five consecutive days a dose of 100 mg sucralfate, while the control group received daily doses of saline. The animals were sacrificed 16 h after the last dose, their stomachs dissected and the mucosa subjected to measurements of the adherent mucus gel dimension and mucin content, evaluation of its viscosity, H+ retardation capacity and hydrophobicity, and analysis of its components and molecular form distribution of elaborated mucin. The results revealed that sucralfate elicited only a minor (8%) increase in mucus gel dimension, while sulfo- and sialomucin contents of the gel increased by 63 and 81%, respectively. The changes in mucus gel mucin content with sucralfate were accompanied by a slight (9.5%) increase in mucus H+ retardation capacity, 1.9-fold increase in viscosity, and a 60% increase in the gel hydrophobicity. Chemical analyses indicated that the mucus elaborated in the presence of sucralfate exhibited 14% lower protein content and 62% higher content of carbohydrate than that of control, displayed similar levels of total lipids and covalently bound fatty acids, but its neutral lipid content was significantly higher. Furthermore, the gastric mucus of the sucralfate group showed a marked increase in the proportion of the high-molecular-weight form of mucin, while the low-molecular-weight form predominated in the control group. The results indicate that the protective qualities of sucralfate lie mainly in its ability to enhance the gastric mucus gel viscosity, hydrophobicity, content of mucin and its proportion in the high-molecular-weight form.

The Mucus Barrier

A layer of water-insoluble mucus gel has been shown to form a continuous cover over the gastroduodenal mucosal surfaces, of median thickness of 180 micron in stomach in humans. This adherent mucus is the first line in mucosal defence against the natural aggressors, acid and pepsin, in the lumen. Mucus gel provides a stable unstirred layer that supports surface neutralisation of acid by mucosal bicarbonate. Mucus gel is a diffusion barrier to pepsin in the lumen, preventing proteolysis of the underlying epithelial cells. There is, however, a dynamic balance between digestion by pepsin of the mucus layer at its luminal aspect and secretion of new mucus by the epithelium. There is evidence that, in peptic ulcer disease, the rate of peptic degradation of the mucus barrier is increased. Exogenous damaging agents such as ethanol and aspirin permeate the gel matrix of the mucus barrier, rapidly damaging the underlying epithelium. The subsequent reepithelialisation process is protected by a gelatinous coat over ten times thicker than the original adherent mucus layer. This gelatinous coat is primarily a fibrin-based gel with necrotic cells and mucus.

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'.

Protection against Alcohol-Induced Gastric Mucosal Injury by Geranylgeranylacetone: Effect of Indomethacin

The mechanism of gastric mucosal protection by an antiulcer agent, geranylgeranylacetone (GGA), against ethanol-induced injury was investigated. The experiments were conducted with groups of rats with and without intraperitoneal indomethacin pretreatment. Animals received intragastrically either a dose of GGA (200 mg/kg) or a vehicle, followed 30 min later by 1 ml of absolute ethanol. The rats were sacrificed after 30 min and the gastric mucosa was subjected to macroscopic and histologic assessment and the measurements of adherent mucus, its dimension and chemical composition. In the absence of GGA, ethanol produced advanced macroscopic necrosis (greater than 38%) and the extensive necrotic lesions were visible upon histologic examination. Pretreatment with GGA significantly reduced (p less than 0.001) the extent and depth of mucosal necrotic lesions caused by ethanol, and this protection was not thwarted by indomethacin. Evaluation of the adherent mucus and its dimension by Alcian blue uptake and inverted microscope technique revealed that GGA was also capable of preventing the untoward effect of indomethacin on the adherent gastric mucus gel and its thickness. Results of chemical analyses established that in the absence of GGA indomethacin caused an increase in mucus protein (15%) and a decrease in its covalently bound fatty acids (67%) and lipids (36%). The decrease in lipids was particularly reflected in the content of phospholipids. Indomethacin, however, had no apparent effect on the composition of gastric mucus elaborated in the presence of GGA. The results suggest that gastric mucosal protective action of GGA is not mediated by endogenous prostaglandins but rather appears to involve the metabolism of mucosal lipids.

Enhancement of the lipid content and physical properties of gastric mucus by geranylgeranylacetone

The effects of intragastric administration of geranylgeranylacetone (GGA) on the content, composition and physical properties of the mucus component of the gastric mucosal barrier were investigated. One group of rats received twice daily for 3 consecutive days a dose of 100 mg/kg body weight of GGA, while the control group was subjected to daily doses of the vehicle. Sixteen hours following the last dose, the animals were killed, and their stomach was cut open and subjected to measurements of the adherent mucus gel content, analysis of its lipids and molecular forms of elaborated mucin, and evaluation of the viscosity and H + retardation capacity. The results revealed that GGA elicited a 62% increase in the adherent mucus gel and caused a marked decrease in the proportion of the lower molecular weight mucin. Furthermore, the mucus of the GGA group exhibited a 67% higher content of covalently bound fatty acids and contained 46% more total lipids which were greatly (143%) enriched in phospholipids. The physical measurements demonstrated that mucus elaborated in the presence of GGA also exhibited 2.3 times higher viscosity and had a 32% greater ability to retard the diffusion of H + than the mucus of the control group. The results suggest that GGA exerts a profound effect on the lipid content and the properties of gastric mucus associated with the maintenance of the mucosal integrity.

The effect of subdiaphragmatic vagotomy on the gastric mucus barrier in rats.

1. Little information exists on the quantitation of mucus barrier and its vagal control; hence, the effect of vagotomy on the two components of the mucus barrier was studied in the glandular regions of rat stomach. 2. Bilateral subdiaphragmatic vagotomy was carried out by cutting both vagus nerves at the level of the lower end of the oesophagus. After 14 days, the glycoproteins in mucosal epithelial cells were identified by periodic acid Schiff's (PAS) staining technique and were assessed by calculating the ratio of the mucosal height to that of the thickness of PAS-positive materials in it. The adherent mucus was estimated by the Alcian blue binding technique and the results were compared with control animals subjected to mock vagotomy. 3. The bilateral subdiaphragmatic vagotomy caused a significant reduction in mucosal epithelial PAS-stainable materials content in oxyntic and pyloric gland areas. 4. The operation also caused a decrease in Alcian blue binding capacity of both the glandular regions. 5. The data suggest that the absence of vagal influence causes weakening of both the lines of mucus barrier. The findings support the hypothesis that the vagal system must be intact in the rat in order to maintain gastric mucus glycoproteins and thereby mucosal integrity.

Formation of a fibrin based gelatinous coat over repairing rat gastric epithelium after acute ethanol damage: interaction with adherent mucus.

A gelatinous coat, heterogeneous in appearance, was formed over damaged rat gastric mucosa recovering from acute ethanol injury. This coat, in places 1.6 mm thick (median thickness 680 microns), was 10 times thicker than the translucent layer of adherent mucus (median thickness 70 microns) covering the undamaged mucosa. Immunohistochemistry and periodic acid Schiff staining showed this gelatinous coat to be predominantly a fibrin gel with an exterior layer rich in mucus and necrotic cells. The plasma clotting time was significantly decreased in vitro by pig gastric mucus gel and soluble mucus glycoprotein (90% and 13% respectively) suggesting that in vivo the mucus layer remaining after epithelial damage could act as a template for fibrinogen-fibrin conversion. These results show that a fibrin based gelatinous coat, quite distinct from the adherent mucus layer and with considerable protective potential could be formed over the repairing rat gastric mucosa after acute ethanol damage.

Gastric mucosal defence mechanism during stress of pyloric obstruction in albino rats.

1. The integrity of the gastric mucosa and its ability to secrete mucus are believed to be essential for protection of gastric mucosa against ulceration induced by aggressive factors active in any stress situation. This study involves a three-compartmental analysis of gastric mucosal barrier in pylorus-ligated albino rats. 2. Quantitative analyses of histologically identifiable gastric mucosal epithelial neutral glycoproteins and gastric adherent mucus from oxyntic and pyloric gland areas, and components of non-dialysable mucosubstances in gastric secretion were made under stress of pyloric obstruction for 4, 8, and 16 h durations. Epithelial mucin was identified by periodic acid-Schiff (PAS) staining technique and assessed from the ratio of gastric mucosal thickness to the depth of PAS positive materials in it. The remaining visible mucus adhered to the gastric mucosa was estimated by Alcian blue binding technique. The results were compared with that of identical control groups. 3. A significant reduction in mucosal epithelial PAS positive materials after 8 or 16 h of pylorus ligation was observed. 4. The Alcian blue binding capacity of the pyloric gland area was increased significantly after 4 h of pylorus ligation, while after 8 or 16 h it was reduced in both oxyntic and pyloric gland areas. 5. Significant reductions in the rate of gastric secretion and volume, as well as concentration of the components of non-dialysable mucosubstances, were observed, indicating decreased synthesis of mucus glycoproteins. 6. Disruption of the mucosal barrier may have occurred due to decreased mucus synthesis and acid-pepsin accumulation; both could be due to stress associated with gastric distension. 7. The present findings confirm the role of mucus in protecting the underlying gastric epithelium during stress. The adherent mucus offers a first line of defence and epithelial mucus a second line of defence.

Gastroduodenal Mucosal Defence Mechanisms and the Action of Non-steroidal Anti-inflammatory Agents

This review summarises gastroduodenal protective mechanisms, the actions of non-steroidal anti-inflammatory (NSAI) agents on mucus and HCO3 secretions, and the basis of gastric mucosal injury induced by acetylsalicylic and salicylic acids (ASA and SA). Resistance to autodigestion by acid and pepsin present in gastric juice is multifactorial involving pre-epithelial (mucus-bicarbonate barrier) and post-epithelial (blood flow, acid-base balance) factors in addition to properties of the surface cell layer per se. The latter includes mucosal re-epithelialisation, a property which appears particularly important with respect to recovery from acute injury. A range of NSAI agents (ASA, fenclofenac, ibuprofen and indomethacin) inhibit gastric HCO3 transport in isolated mucosal preparations. Inhibition of duodenal HCO3 transport has been demonstrated in response to indomethacin in vitro and in vivo. These effects on secretion can be antagonised by exogenous prostaglandins of the E series. The layer of secreted mucus gel overlying the epithelial surface is not affected by NSAI drugs in the short term. However a number of these agents have been shown to inhibit glycoprotein biosynthesis by the epithelial cells. Thus loss of this protective coat could be anticipated during chronic drug exposure since erosion of adherent mucus by luminal shear and proteolysis would not be compensated by continued secretion. Detailed analysis of the gastric mucosal injury induced by salicylates both in vitro and in vivo reveals that much of the damage previously attributed to ASA is in fact due to the metabolic product SA. In this respect it is concluded that mucosal injury caused by ASA is due to a combination of two factors.(ABSTRACT TRUNCATED AT 250 WORDS)

The gastric mucosal epithelial barrier: role of mucus and fibrin.

A continuous layer of insoluble mucus gel is adherent to the luminal surface of the gastric epithelium. The true thickness of the gel and its continuity can only be observed on unfixed sections of mucosa since histological fixatives cause dehydration and denaturation of mucus. The mucus:bicarbonate barrier can protect the undamaged epithelium from the endogenous luminal aggressors acid and pepsin but does not appear to offer much protection against exogenous damaging agents such as topical alcohol. Following acute ethanol injury, damaged epithelium is replaced by cells migrating from the gastric pits. In rat gastric mucosa this process of re-epithelialisation is protected by a gelatinous coat ten times thicker than the normal adherent mucus layer. Our studies now show this coat to be a fibrin gel with mucus and necrotic cells. Evidence suggests that the existing mucus layer can act as a template for the fibrinogen--fibrin conversion. These results demonstrate that a fibrin based gelatinous coat, quite distinct from the adherent mucus layer and with considerable protective potential, can be formed over the repairing damaged gastric mucosa.

Antibacterial immunity to Vibrio cholerae in rats.

Blind loops prepared in the small intestines of fasted, MgSO4-treated rats were shown to provide a simple, consistent and inexpensive means of studying mucosal colonisation by Vibrio cholerae serogroup O1. When c. 2000 cfu were injected, the number of mucosa-associated V. cholerae in each loop increased by c. 5-6 orders of magnitude in 10-14 h, without enterotoxin-induced fluid production. Scanning electronmicroscopy and culture suggested that most surface-associated organisms were present in the adherent surface mucus. V. cholerae strains varied in terms of surface-colonising capacity. Immunisation with V. cholerae given intra-intestinally greatly reduced the rate of increase and final number of mucosa-associated vibrios within the 14-h period after challenge. The method could be used to compare the immunity induced by various immunising regimens. Immunity was sometimes accompanied by intestinal mucus-borne antibody against V. cholerae lipopolysaccharide but was sometimes demonstrated in the absence of such antibody or of mucus-borne antibody to heat-sensitive surface protein.

Stimulatory effect of enprostil, an anti-ulcer prostaglandin, on gastric mucus secretion

Enprostil, a synthetic analogue of prostaglandin E2, is known to be a potent inhibitor of gastric acid secretion, and has marked anti-ulcer activity in rodents. Enprostil was administered in doses ranging from 15 to 250 micrograms/kg to rats prepared using the Shay procedure. Three hours later, the rats' stomachs were removed and processed either for the chemical determination of mucus, or for scanning electron microscopy. For the chemical determination, the secreted gastric juice was removed and the adherent gastric mucus was eluted with 2 M sodium chloride. The anthrone method was used to determine the mucus present. Enprostil was found to significantly increase gastric mucus at a dose of 60 micrograms/kg when measured by the anthrone test. Enprostil administered by the oral route was most effective in stimulating mucus secretion, suggesting a local or topical action of enprostil on mucus-secreting cells. Scanning electron microscopy of rat fundic mucosa after enprostil administration (50 to 100 micrograms/kg) revealed the presence of thin veil-like layers covering the epithelial surface, which was interpreted as an increase in mucus secretion. Higher magnifications (X 2,000) clearly showed the layers of mucus covering the surface epithelial cells. Enprostil's apparent increase of gastric mucus secretion may contribute to its anti-ulcer activity and may promote gastric healing.

Misoprostol-induced increases in adherent gastric mucus thickness and luminal mucus output.

Gastroduodenal mucus can be separated into two phases: insoluble mucus gel adherent to the mucosal surface, and luminal mucus, which is removed by washing out the lumen. The adherent mucus gel is part of the mucosal protective barrier to acid and pepsin in the gastric juice. Luminal mucus, which is mobile, probably does not significantly protect against gastric juice, but functions as a lubricant, protecting the adherent mucus layer and underlying mucosa from mechanical damage. Adherent mucus is observed on the mucosal surface as a thin, continuous, gelatinous layer of variable thickness, about 50-450 microns (median, 180 microns) in man and 10-230 microns (median 80 microns) in the rat. Thickness of this adherent mucus layer in the rat stomach is increased significantly (up to threefold) following topical administration of misoprostol in vivo 1 hr before measurement. Simultaneous increases are observed in the content of luminal mucus following misoprostol administration. Seventy percent of maximum response is observed within 5 min of topical prostaglandin administration, compatible with the release of preformed mucus. Such prostaglandin-stimulated increases in mucus thickness will improve the protective capacity of the adherent mucus gel. The thickness of the adherent mucus layer is not changed following topical exposure, in vivo 1 hr before measurement, to exogenous mucosal-damaging agents (eg, ethanol, indomethacin and taurocholate. However, since such damaging agents permeate the mucus gel, it appears to offer little initial protection to the underlying epithelium. The mucus barrier primarily guards against the natural aggressors acid and pepsin, protecting the epithelium and its repair following acute mucosal damage.

The role of mucus in the protection of the gastroduodenal mucosa.

There is good evidence that the adherent mucus plays an important role in the protection of gastroduodenal mucosa from the endogenous aggressors acid and pepsin. Adherent mucus provides a stable unstirred layer which supports surface neutralization of acid by mucosal bicarbonate output and acts as a permeability barrier to luminal pepsin. The adherent mucus layer is continuous. True thickness of the mucus layer and its continuity can only be observed on unfixed sections of mucosa, since histological fixatives and preparation for electron microscopy can cause dehydration and shrinkage of the mucus gel. The structure of adherent gastric mucus is deficient in patients with peptic ulcer disease because of decreased polymerization of the component glycoproteins. This impairment of the mucus barrier is associated with raised amounts of pepsin 1, which digests the mucus layer more aggressively than the major pepsin, pepsin 3, under conditions that pertain both in the stomach (pH 2) and duodenum (pH 4-5). Adherent mucus does not appear to offer much protection against exogenous damaging agents, e.g. alcohol and aspirin. These agents permeate the mucus barrier, damaging the underlying epithelium. The subsequent epithelial repair process is protected by a gelatinous coat over ten times thicker and distinct from the normal adherent mucus layer. Our recent studies show this gelatinous coat to be primarily a fibrin-based gel with mucus and necrotic cells.

Adherent and soluble mucus in the stomach and duodenum.

Gastroduodenal mucus is present as a water insoluble gel adherent to the mucosal surface and as a viscous mobile solution in the lumen. The protective properties of the mucus against acid (with bicarbonate), pepsin (diffusion barrier) and mechanical damage depend on the quality (structure) and quantity (thickness) of the adherent mucus gel layer. Adherent mucus is a viscoelastic gel which is 95% (v/v) water. It is permeable to ions and smaller molecules (Mr c. 1000), but is impermeable to large proteins (Mr c. 17,000) including pepsins. However, mucus is solubilized rapidly by pepsin, more slowly (greater than or equal to 1 h) by thiol agents, and is unchanged following exposure to bile, acid and ethanol (less than 40%). Glycoprotein macromolecules (Mr greater than or equal to 2 X 10(6] are the structural components of the mucus gel and have a polymeric structure of glycoprotein subunits (Mr c. 5 X 10(5), for gastric mucus) joined by disulphide bridges between their protein cores. This glycoprotein polymerization, which is essential for gel formation and hence function, is the site of action of proteolytic enzymes and thiol agents. The glycoprotein polymeric structure is deficient in antral mucus from patients with peptic ulcer disease. In vivo, adherent mucus forms a thin but continuous cover of variable thickness (50-450 micron in man, about two-fold less in rat) over the gastroduodenal mucosa. Pepsin in gastric juice will rapidly dissolve this mucus cover and can be active up to luminal pH values of 5.(ABSTRACT TRUNCATED AT 250 WORDS)

Properties of Gastric and Duodenal Mucus: Effect of Proteolysis, Disulfide Reduction, Bile, Acid, Ethanol, and Hypertonicity on Mucus Gel Structure

Small deformation oscillatory rheologic measurements have been used to investigate the structure of human and pig gastric mucus and pig duodenal mucus. All three secretions had viscoelastic properties characteristic of water-insoluble, viscoelastic gels. Mucus will flow and anneal if damaged, due to the making and breaking of its elastic structure, the measured lifetime of which was 10-120 min. Mucus reconstituted by concentration of the purified glycoprotein (pig gastric and duodenal mucus) had the same viscoelastic properties as the fresh mucus, giving evidence that the glycoprotein alone will reproduce the rheologic characteristics of the mucus. The structure of fresh mucus gel was unaffected by prolonged exposure to the following mucosal damaging agents: undiluted pig bile, 20 mM sodium taurocholate or 20 mM sodium glycocholate (all at pH 2, 6, and 8), HCl at pH 1, 2 M NaCl, and ethanol less than 40% (vol/vol). Higher concentrations of ethanol greater than 40% (vol/vol), caused dehydration and denaturation of mucus. Proteolysis by pepsin and other enzymes resulted in solubilization of the mucus gel with a complete change in the properties from an "elastic" gel to those of a "viscous" liquid. A similar collapse of mucus gel structure was observed after reduction of disulfide bonds in 0.2 M mercaptoethanol, but only after incubation for at least 50 min. This study demonstrates the stability of mucus to several mucosal damaging agents. It is proposed in vivo that although adherent gastroduodenal mucus allows penetration of these agents to the underlying mucosa, it can remain in situ and continue to protect against acid (with HCO3-) and pepsin, thus minimizing mucosal damage and maximizing repair.

Washout versus non-washout (picolax) preparation for double-contrast barium enemas

A non-washout preparation using Picolax in 40 patients, compared with a standard method using washouts in 38 patients, showed no significant difference in the contamination by residual formed or semiliquid faeces, although Picolax was associated with significantly more contamination due to adherent faeces and mucus. The overall differences in contamination were most marked in the transverse colon. Picolax also affected the smooth muscle tone of the bowel wall, causing an increase in 'mucosal crinkling'.