Helicobacter pylori in vivo causes structural changes in the adherent gastric mucus layer but barrier thickness is not compromised

Tissue remodeling by an opportunistic pathogen triggers allergic inflammation

Different effector arms of the immune system are optimized to protect from different classes of pathogens. In some cases, pathogens manipulate the host immune system to promote the wrong type of effector response-a phenomenon known as immune deviation. Typically, immune deviation helps pathogens to avoid destructive immune responses. Here, we report on a type of immune deviation whereby an opportunistic pathogen, Pseudomonas aeruginosa (P. aeruginosa), induces the type 2 immune response resulting in mucin production that is used as an energy source by the pathogen. Specifically, P. aeruginosa-secreted toxin, LasB, processed and activated epithelial amphiregulin to induce type 2 inflammation and mucin production. This "niche remodeling" by P. aeruginosa promoted colonization and, as a by-product, allergic sensitization. Our study thus reveals a type of bacterial immune deviation by increasing nutrient supply. It also uncovers a mechanism of allergic sensitization by a bacterial virulence factor.

In vitro models to evaluate ingestible devices: Present status and current trends

Orally ingestible medical devices offer significant opportunity in the diagnosis and treatment of gastrointestinal conditions. Their development necessitates the use of models that simulate the gastrointestinal environment on both a macro and micro scale. An evolution in scientific technology has enabled a wide range of in vitro, ex vivo and in vivo models to be developed that replicate the gastrointestinal tract. This review describes the landscape of the existing range of in vitro tools that are available to characterize ingestible devices. Models are presented with details on their benefits and limitations with regards to the evaluation of ingestible devices and examples of their use in the evaluation of such devices is presented where available. The multitude of models available provides a suite of tools that can be used in the evaluation of ingestible devices that should be selected on the functionality of the device and the mechanism of its function.

Interactions between H. pylori and the Gastric Microbiome: Impact on Gastric Homeostasis and Disease

Like many seemingly inhospitable environments on our planet, the highly acidic human stomach harbors a diverse bacterial microflora. The best-known member of the human gastric flora, Helicobacter pylori, causes a number of gastric diseases, including peptic ulcer disease and gastric adenocarcinoma. In the absence of Helicobacter pylori infection, the gastric microbiota displays some features similar to the oral cavity with Firmicutes the most common phylum, followed by Proteobacteria and Bacteroidetes. When present, H. pylori dominates the gastric microbiome and reduces diversity and composition of other taxa. The composition of the gastric microbiome also is altered in the setting of proton pump inhibitor therapy and gastric neoplasia. This review summarizes foundational and recent studies that have investigated the composition of the human gastric microbiome in a variety of patient groups, with a focus on potential mechanisms involved in regulation of gastric microbial community structure.

The role of mucus as an invisible cloak to transepithelial drug delivery by nanoparticles

Mucosal administration of drugs and drug delivery systems has gained increasing interest. However, nanoparticles intended to protect and deliver drugs to epithelial surfaces require transport through the surface-lining mucus. Translation from bench to bedside is particularly challenging for mucosal administration since a variety of parameters will influence the specific barrier properties of the mucus including the luminal fluids, the microbiota, the mucus composition and clearance rate, and the condition of the underlying epithelia. Besides, after administration, nanoparticles interact with the mucosal components, forming a biomolecular corona that modulates their behavior and fate after mucosal administration. These interactions are greatly influenced by the nanoparticle properties, and therefore different designs and surface-engineering strategies have been proposed. Overall, it is essential to evaluate these biomolecule-nanoparticle interactions by complementary techniques using complex and relevant mucus barrier matrices.

Role of Helicobacter pylori infection in gastric carcinogenesis: Current knowledge and future directions

Helicobacter pylori (H. pylori) plays a role in the pathogenesis of gastric cancer. The outcome of the infection depends on environmental factors and bacterial and host characteristics. Gastric carcinogenesis is a multistep process that is reversible in the early phase of mucosal damage, but the exact point of no return has not been identified. Therefore, two main therapeutic strategies could reduce gastric cancer incidence: (1) eradication of the already present infection; and (2) immunization (prior to or during the course of the infection). The success of a gastric cancer prevention strategy depends on timing because the prevention strategy must be introduced before the point of no return in gastric carcinogenesis. Although the exact point of no return has not been identified, infection should be eradicated before severe atrophy of the gastric mucosa develops. Eradication therapy rates remain suboptimal due to increasing H. pylori resistance to antibiotics and patient noncompliance. Vaccination against H. pylori would reduce the cost of eradication therapies and lower gastric cancer incidence. A vaccine against H. pylori is still a research challenge. An effective vaccine should have an adequate route of delivery, appropriate bacterial antigens and effective and safe adjuvants. Future research should focus on the development of rescue eradication therapy protocols until an efficacious vaccine against the bacterium becomes available.

More than one disease process in chronic sinusitis based on mucin fragmentation patterns and amino Acid analysis

Objective. To characterise fragmentation patterns and amino acid composition of MUC2 and MUC5AC in chronic sinusitis. Methods. Antigenic identity of purified sinus mucins was determined by ELISA. Fragmentation patterns of a MUC5AC rich sample mucin were analysed by Sepharose CL-2B gel chromatography. Samples, divided into one MUC2 rich and one MUC5AC rich group, were subjected to sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and their amino acid contents were analysed. Results. Reduction, trypsin digestion, and papain digestion produced progressively smaller mucin species. On SDS-PAGE, digested MUC5AC rich mucin produced four distinct products. Amino acid analysis was characteristic of mucins with high serine, threonine, and proline contents and reduction and proteolysis increased relative proportions of these amino acids. MUC5AC rich mucins contained more protein than MUC2 rich mucins. Conclusion. Sinus mucin fragmentation produced mucin subunits and glycopeptide units of smaller molecular sizes which are likely to have lower viscoelastic properties. Applying this in vivo could alter mucus physical properties and biologic functions. Amino acid contents of MUC2 and MUC5AC mucins are different. This could be contributing to biological properties and functions of sinus mucins. These data suggest that there may be different pathological processes occurring at the cellular level on chronic sinusitis.

The Influence of Mucus Microstructure and Rheology in Helicobacter pylori Infection

The bacterium Helicobacter pylori (H. pylori), has evolved to survive in the highly acidic environment of the stomach and colonize on the epithelial surface of the gastric mucosa. Its pathogenic effects are well known to cause gastritis, peptic ulcers, and gastric cancer. In order to infect the stomach and establish colonies on the mucus epithelial surface, the bacterium has to move across the gel-like gastric mucus lining of the stomach under acidic conditions. In this review we address the question of how the bacterium gets past the protective mucus barrier from a biophysical perspective. We begin by reviewing the molecular structure of gastric mucin and discuss the current state of understanding concerning mucin polymerization and low pH induced gelation. We then focus on the viscoelasticity of mucin in view of its relevance to the transport of particles and bacteria across mucus, the key first step in H. pylori infection. The second part of the review focuses on the motility of H. pylori in mucin solutions and gels, and how infection with H. pylori in turn impacts the viscoelastic properties of mucin. We present recent microscopic results tracking the motion of H. pylori in mucin solutions and gels. We then discuss how the biochemical strategy of urea hydrolysis required for survival in the acid is also relevant to the mechanism that enables flagella-driven swimming across the mucus gel layer. Other aspects of the influence of H. pylori infection such as, altering gastric mucin expression, its rate of production and its composition, and the influence of mucin on factors controlling H. pylori virulence and proliferation are briefly discussed with references to relevant literature.

Contribution of secretory antibodies to intestinal mucosal immunity against Helicobacter pylori

The natural immune response to Helicobacter pylori neither clears infection nor prevents reinfection. However, the ability of secretory antibodies to influence the course of H. pylori infection has not been determined. We compared the natural progression of H. pylori infection in wild-type C57BL/6 mice with that in mice lacking the polymeric immunoglobulin receptor (pIgR) that is essential for the secretion of polymeric antibody across mucosal surfaces. H. pylori SS1-infected wild-type and pIgR knockout (KO) mice were sampled longitudinally for gastrointestinal bacterial load, antibody response, and histological changes. The gastric bacterial loads of wild-type and pIgR KO mice remained constant and comparable at up to 3 months postinfection (mpi) despite SS1-reactive secretory IgA in the intestinal contents of wild-type mice at that time. Conversely, abundant duodenal colonization of pIgR KO animals contrasted with the near-total eradication of H. pylori from the intestine of wild-type animals by 3 mpi. H. pylori was cultured only from the duodenum of those animals in which colonization in the distal gastric antrum was of sufficient density for immunohistological detection. By 6 mpi, the gastric load of H. pylori in wild-type mice was significantly lower than in pIgR KO animals. While there was no corresponding difference between the two mouse strains in gastric pathology results at 6 mpi, reductions in gastric bacterial load correlated with increased gastric inflammation together with an intestinal secretory antibody response in wild-type mice. Together, these results suggest that naturally produced secretory antibodies can modulate the progress of H. pylori infection, particularly in the duodenum.

A review of stress-related mucosal disease

OBJECTIVE

To review and summarize the human and veterinary literature regarding stress-related mucosal disease (SRMD) pathogenesis, patient risk factors, and therapeutic options for prophylaxis and treatment.

ETIOLOGY

SRMD is a common sequela of critical illness in human patients. Development of SRMD results from splanchnic hypoperfusion, reperfusion injury, and exposure of the gastric mucosa to acid, pepsin, and bile acids following breakdown of the gastric mucosal defense system. Human patients with the highest risk of stress ulceration include those with respiratory failure necessitating mechanical ventilation greater than 48 h or coagulopathy. Currently, little is known about the incidence and pathophysiology of SRMD in critically ill veterinary patients.

DIAGNOSIS

A presumptive diagnosis can be made in high-risk patient populations following detection of occult or gross blood in nasogastric tube aspirates, hematemesis, or melena. Definitive diagnosis is achieved via esophagogastroduodenoscopy. Lesions are localized to the acid-producing portions of the stomach, the fundus, and body.

THERAPY

Therapy is aimed at optimization of tissue perfusion and oxygenation. Pharmacologic interventions are instituted to increase intraluminal pH and augment natural gastric defenses. Histamine(2)-receptor antagonists, proton pump inhibitors, and sucralfate are the mainstays of therapy. In people, clinically significant bleeding may necessitate additional interventions (eg, packed red blood cell transfusions, endoscopic, or surgical hemostasis).

PROGNOSIS

Mortality is increased in people with clinically significant bleeding compared to those patients who do not bleed. Institution of prophylaxis is recommended in high-risk patients. However, no consensus exists regarding initiation of prophylaxis, preference of frontline drug class, or indication for discontinuation of therapy. The prognosis of veterinary patients with SRMD remains unknown at this time.

Helicobacter pylori moves through mucus by reducing mucin viscoelasticity

The ulcer-causing gastric pathogen Helicobacter pylori is the only bacterium known to colonize the harsh acidic environment of the human stomach. H. pylori survives in acidic conditions by producing urease, which catalyzes hydrolysis of urea to yield ammonia thus elevating the pH of its environment. However, the manner in which H. pylori is able to swim through the viscoelastic mucus gel that coats the stomach wall remains poorly understood. Previous rheology studies on gastric mucin, the key viscoelastic component of gastric mucus, indicate that the rheology of this material is pH dependent, transitioning from a viscous solution at neutral pH to a gel in acidic conditions. Bulk rheology measurements on porcine gastric mucin (PGM) show that pH elevation by H. pylori induces a dramatic decrease in viscoelastic moduli. Microscopy studies of the motility of H. pylori in gastric mucin at acidic and neutral pH in the absence of urea show that the bacteria swim freely at high pH, and are strongly constrained at low pH. By using two-photon fluorescence microscopy to image the bacterial motility in an initially low pH mucin gel with urea present we show that the gain of translational motility by bacteria is directly correlated with a rise in pH indicated by 2',7'-Bis-(2-Carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF), a pH sensitive fluorescent dye. This study indicates that the helicoidal-shaped H. pylori does not bore its way through the mucus gel like a screw through a cork as has previously been suggested, but instead achieves motility by altering the rheological properties of its environment.

Effects of a novel histamine H2-receptor antagonist, lafutidine, on the mucus barrier of human gastric mucosa

BACKGROUND AND AIM

Lafutidine is a novel histamine H(2)-receptor antagonist used primarily as an antisecretory agent in Japan. Previous human studies have not assessed its gastroprotective effects. The purpose of the present study was to determine the effects of lafutidine on the human gastric mucus layer using both histological and biochemical methods.

METHODS

Of the 14 patients scheduled for gastrectomy who consented to participate, seven were given 14 days of lafutidine 20 mg/day (lafutidine group) and the others received no medication (control group). The surface mucus gel layer in Carnoy-fixed tissue sections was examined immunohistochemically. Both the thickness of the mucus layer and its mucin content were measured in gastric corpus mucosa.

RESULTS

There was no detectable difference between the groups in the grade of gastritis or the immunohistochemical staining characteristics. The laminated structure of the surface mucus gel layer was retained after administration of lafutidine and it was thicker than the layer in the control group. The surface layer in the lafutidine group had three-fold more mucin than that in the control group. There was no difference between the two groups in the mucin content of the deep mucosa.

CONCLUSION

Lafutidine, given at clinical dosages, not only inhibits acid secretion but also strengthens the mucus barrier of the human gastric mucosa.

Impaired mucus-bicarbonate barrier in Helicobacter pylori-infected mice

To resist the harsh intrinsic milieu, several lines of defense exist in the stomach. The aim of this study was to investigate the effect of the gastric pathogen Helicobacter pylori on these mechanisms in vivo. We used FVB/N mice expressing human alpha-1,3/4-fucosyl transferase (producing Lewis b epitopes) and inoculated with H. pylori 1. Mice were anesthetized with isoflurane or Hypnorm-midazolam, the stomach was exteriorized, and the surface of the corpus mucosa was exposed. Mucus thickness was measured with micropipettes, juxtamucosal pH (pH(jm)) was measured with pH-sensitive microelectrodes, blood flow was measured with laser-Doppler flowmetry, and mRNA levels of the bicarbonate transporter SLC26A9 were quantified with real-time PCR. The increase in mucosal blood flow seen in response to luminal acid (pH 1.5) in control animals (140 +/- 9% of control) was abolished in infected mice. The firmly adherent mucus layer was significantly thinner in infected mice (31 +/- 2 microm) than in control mice (46 +/- 5 microm), and no mucus accumulation occurred in infected mice. pH(jm) decreased significantly more on exposure to luminal acid in infected mice (luminal pH 1.5, pH(jm) 2.4 +/- 0.7) than in control mice (pH(jm) 6.4 +/- 0.5). Despite reduced pH(jm), SLC26A9 mRNA expression was significantly, by increased 1.9-fold, in infected mice. The reduction in pH(jm) by infection with H. pylori might be due to a reduced firmly adherent mucus layer, increased mucus permeability to H(+), and/or inhibition of bicarbonate transport. The upregulation of SLC26A9 in H. pylori-infected epithelium might be a result of continuous inhibition of the transporter, e.g., by ammonium, a H. pylori product, which has been previously shown to inhibit SLC26A9.

Gastroretentive dosage forms: Overview and special case of Helicobacter pylori

The challenge to develop efficient gastroretentive dosage forms began about 20 years ago, following the discovery of Helicobacter pylori by Warren and Marshall. In order to understand the real difficulty of increasing the gastric residence time of a dosage form, we have first summarized the important physiologic parameters, which act upon the gastric residence time. Afterwards, we have reviewed the different drug delivery systems designed until now, i.e. high-density, intragastric floating, expandable, superporous hydrogel, mucoadhesive and magnetic systems. Finally, we have focused on gastroretentive dosage forms especially designed against H. pylori, including specific targeting systems against this bacterium.

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Topographic expression of MUC5AC and MUC6 in the gastric mucosa infected by Helicobacter pylori and in associated diseases

We investigated the topographic expression of MUC5AC and MUC6 in relationship with gastric diseases. The immunoexpression of MUC5AC and MUC6 was evaluated in 75 adults presenting Helicobacter pylori gastritis (n = 22; 11 cagA positive), duodenal ulcer (DU, n = 11), gastric ulcer (GU, n = 9), gastric carcinoma (GC, n = 20), and normal mucosa (H. pylori negative, n = 13). Five gastric areas (antral and corporeal lesser and greater curvatures and incisura) were studied. H. pylori was detected by carbolfuchsin, urease, and culture; cagA was determined by PCR. All patients with DU (eight with GU and 13 with GC) were H. pylori-positive. In H. pylori gastritis, MUC5AC expression was higher in the antrum than in the corpus; no difference was observed with respect to cagA status. MUC5AC expression was higher in the antrum of gastritis than in DU, and it was lower in the incisura among GU patients compared to DU. MUC6 expression was higher in the antrum of H. pylori gastritis compared to DU and to uninfected patients. No difference was observed in the topographic pattern of expression of MUC5AC and MUC6 among GC cases. The topographic over- and under-expression of mucins in H. pylori-associated gastritis and peptic disease suggest a role for these mucins in the pathogenesis of H. pylori infection and associated diseases.

Effects of cagA+ and cagA- strains of Helicobacter pylori on the human gastric mucus layer thickness

BACKGROUND

Infection with cytotoxin-associated gene A (cagA) Helicobacter pylori is associated with severe gastric diseases, with contradictory views being expressed concerning the effect of H. pylori on the gastric mucus thickness. The aim of the present study was to differentiate between the effect of cagA+ and cagA- strains on gastric mucus thickness.

METHODS

Ninety-nine patients without peptic ulcers who were not on medication were randomly recruited from consecutive endoscopy clinics: six biopsies (five antral, one body) were obtained from each patient. Cryostat sections (18 microm) were cut and stained using the modified periodic acid-Schiff/Alcian blue technique. Mucus thickness was measured using computer-assisted light microscopy. The H. pylori status was assessed by histology, Campylobacter-like organism (CLO)test and culture, and cagA+ status determined by polymerase chain reaction (PCR).

RESULTS

There was no significant difference (P = 0.784) in mean mucus thickness between cagA+ (52.7 +/- 1.2 microm, n = 10), cagA- (46.6 +/- 1.1 microm, n = 18) or H. pylori-negative patients (51.3 +/- 1.1 microm, n = 30). In cagA- patients, mucus thickness was significantly reduced with increased H. pylori colonization density, Spearman (r(s)) = -0.805, P < 0.0001. In contrast, in cagA+ patients there was a weak positive, but not significant, association between mucus thickness and H. pylori colonization density, r(s) = 0.333, P = 0.381.

CONCLUSIONS

The human gastric mucus thickness is not affected by infection with cagA+ or cagA- strains of H. pylori compared with uninfected. Although a trend of increased mucus thickness with cagA+ infection was observed.

Infection with Helicobacter pylori affects all major secretory cell populations in the human antrum

We have investigated how gastric H. pylori infection affects antrum secretory cell types by studying the expression of secretory proteins in antrum epithelium. Antrum biopsy specimens were prospectively collected from 102 individuals (49 H. pylori-infected). Immunohistochemistry was performed for secretory mucins (MUC5AC, MUC5B, MUC6), Trefoil factor family (TFF)-peptides (TFF1, TFF2), endocrine peptides (gastrin, chromogranin A), and proliferating cells (Ki-67). Protein expression was quantified morphometrically. H. pylori infection was significantly correlated to mucosal inflammation and to epithelial atrophy and proliferation. In H. pylori-infected patients the number of proliferating cells increased significantly, and the zone of proliferating cells shifted toward the surface epithelium of the antral glands. Infection was correlated with decreased MUC5AC, TFF1, and TFF2 expression and increased MUC6 and MUC5B expression. Endocrine cells expressing chromagranin A and gastrin shifted toward the surface epithelium of the antral glands in H. pylori-infected patients. H. pylori infection and concomitant inflammation induced increased epithelial proliferation and triggered coordinate deregulation of secretory cell populations in the antrum. In particular, infection led to a coordinated increase in cells expressing MUC6 and MUC5B at the expense of MUC5AC-producing cells.

Gastroduodenal mucus bicarbonate barrier: protection against acid and pepsin

Secretion of bicarbonate into the adherent layer of mucus gel creates a pH gradient with a near-neutral pH at the epithelial surfaces in stomach and duodenum, providing the first line of mucosal protection against luminal acid. The continuous adherent mucus layer is also a barrier to luminal pepsin, thereby protecting the underlying mucosa from proteolytic digestion. In this article we review the present state of the gastroduodenal mucus bicarbonate barrier two decades after the first supporting experimental evidence appeared. The primary function of the adherent mucus gel layer is a structural one to create a stable, unstirred layer to support surface neutralization of acid and act as a protective physical barrier against luminal pepsin. Therefore, the emphasis on mucus in this review is on the form and role of the adherent mucus gel layer. The primary function of the mucosal bicarbonate secretion is to neutralize acid diffusing into the mucus gel layer and to be quantitatively sufficient to maintain a near-neutral pH at the mucus-mucosal surface interface. The emphasis on mucosal bicarbonate in this review is on the mechanisms and control of its secretion and the establishment of a surface pH gradient. Evidence suggests that under normal physiological conditions, the mucus bicarbonate barrier is sufficient for protection of the gastric mucosa against acid and pepsin and is even more so for the duodenum.

The association between cagA+ H. pylori infection and distal gastric cancer: a proposed model

Cytotoxin-associated gene A (cagA)+ infection is associated with an increased risk of distal gastric cancer. The aim was to determine the effect of Helicobacter pylori (HP) on gastric mucus thickness, hydrophobicity, and PGE2 and their relation to colonization density. Ninety-nine patients were recruited (69 HP- and 30 HP+: 10 cagA+, 18 cagA-, 2 undetermined) and six biopsies were obtained from each patient. Mucus thickness, hydrophobicity, PGE2, and colonization density were determined. HP status was assessed by histology and culture; cagA+ was determined by PCR. In age- and sex-matched patients, PGE2 was greater in PH+ than HP- (P = 0.04), with cagA+ having higher PGE2 than HP- patients (P = 0.031). No differences were observed in mucus thickness (P = 0.717) or hydrophobicity (P = 0.27) between HP+ and HP- patients. However, cagA+ showed a nonsignificant trend of increase in mucus thickness (P = 0.784) and hydrophobicity (P = 0.30) compared to cagA- and HP- patients. cagA+ colonization density was weakly correlated with increased thickness (r = 0.333, P = 0.381), whereas cagA- density was inversely correlated with thickness (r = -0.805, P = 0.0001). A model suggesting the possible changes induced by cagA+ infection is proposed which explains the high association of cagA+ with distal gastric cancer. If supported by large multicenter studies, this could form the basis for the development of new therapies directed at the mucous layer to eradicate HP and thus reduce the risk of gastric cancer.

The diurnal profile of gastric pepsin activity is reduced with Helicobacter pylori infection

Both Helicobacter pylori and pepsin are proven mucosal damaging agents and implicated in the aetiology of peptic ulcer disease. Historically studies of pepsin over time have proved methodologically difficult, and as a result little work has been done on the effect of H. pylori on luminal pepsin secretion. Our objectives were to determine pepsin activity over 24 hr in normal human subjects and to examine luminal pepsin activity in relation to H. pylori infection. Twenty-seven healthy volunteers had gastric juice samples aspirated every 2 hr for 24 hr. All subjects had H. pylori status determined by C13 urea breath test and serology. Meals were standardized throughout the study period. Gastric juice samples were measured for pH, diluted, and frozen in acetate buffer pH 4.1 for up to 1 month, conditions shown to cause no loss of activity. Individual samples were measured for pepsin activity by assaying for new N-terminal peptide formation. Mean pepsin activity (microg enzyme/ml) in 21 normal H. pylori-negative subjects ranged from 114 to 1030 microg/ml, with a characteristic diurnal profile of increasing activity to maximum after the evening meal. Mean pepsin activity in subjects with H. pylori was consistently below that for age-matched H. pylori-negative subjects at each time point. Overall mean pepsin activity was significantly lower in those with H. pylori compared to those without (P < 0.001). There is significant pepsin activity in the stomach throughout the 24-hr period, with a trend for the highest activity through the night. Subjects with H. pylori infection have lower luminal pepsin activity.

Removal of mucus for ultrastructural observation of the surface of human gastric epithelium using pronase

BACKGROUND

Helicobacter pylori adhering to the human gastric epithelium causes gastric diseases such as ulcer, carcinoma and lymphoma. It is thus important to observe in detail both the surface of the epithelial cells and the H. pylori that adhered to it for the elucidation of H. pylori-induced diseases by scanning electron microscopy (SEM). Since the thick mucus layer blocks the observation of the cell surface and the bacteria, it is generally eliminated during the processing for SEM by roughly mechanical methods, but these treatments also demolish the ultrastructure of the cells. We studied the nonmechanical method for removal of mucus layer of gastric epithelium using pronase.

MATERIALS AND METHODS

To determine the optimal concentration of pronase, mucin was used as a substrate for inhibition of the viscosity. Pronase was added in 2% mucin at the concentration of 10, 50, 100, 500, 1000, 2000 or 5000 unit/ml and the flowing time of the mixture was measured. Based on the digestion experiment, biopsied specimens from 24 patients with dyspepsic symptoms were fixed in glutaraldehyde and then washed in rolling with different concentration of pronase. After the pretreatment by pronase, the specimens were treated according to the standard process for SEM.

RESULTS

We succeeded in removing the mucus layer on the surface of epithelial cells from the biopsied specimens fixed in glutaraldehyde by rinsing with 2000 unit/ml pronase for 24 hours.

CONCLUSIONS

Using our digestive method without destroying the ultrastructure, the earliest stage which H. pylori has adhered onto the human gastric epithelium can be observed for the investigation of H. pylori-induced gastric disorders by SEM.

Esophageal mucin: an adherent mucus gel barrier is absent in the normal esophagus but present in columnar-lined Barrett's esophagus

OBJECTIVES

The presence of a protective adherent mucus gel barrier against gastric reflux in the healthy esophagus is uncertain. The aim was to characterize the surface mucin composition and determine the extent of any adherent mucus gel layer on the normal esophagus, and compare this with that in Barrett's esophagus.

METHODS

Isolated surface mucins were characterized by density centrifugation, gel filtration chromatography, and chemical composition. Adherent surface mucus was visualized in situ on unfixed and cryostat sections of mucosa and biopsies using a method that preserves mucus layer thickness.

RESULTS

There was a complete absence of adherent mucus gel layers on normal human, pig, and rat esophagi. This was in contrast to the thick adherent mucous layer (median thickness = 100-200 microm) seen on the corresponding gastric mucosa. Small quantities of glycoprotein with a composition characteristic of a secretory mucin were isolated from the pig esophagus surface. The mucin, density range between 1.44 and 1.48 g x ml(-1), contained 80% carbohydrate and was rich in serine, threonine, and proline. The mucin fragmented into smaller glycoprotein units on proteolysis and partially on reduction. Cryostat sections from columnar-lined esophageal biopsies had a substantial adherent surface mucous layer (median thickness = 90 microm, interquartile range = 84-94 microm) staining for neutral mucins (gastric-type epithelium) and acidic mucins (intestinal metaplasia).

CONCLUSIONS

A secretory mucin, with an analysis distinct from that of gastric or salivary mucin, is present in very small quantities on the esophageal mucosa and in amounts insufficient to form an adherent gel layer. It is unlikely that mucus has a role in protecting the normal esophagus against reflux. However, an adherent mucous layer was observed over columnar-lined esophagus, and this may protect against reflux.

Altered mucin expression in the gastrointestinal tract: a review

Early studies of changes in mucin expression in disorders of the gastrointestinal tract focused on alterations in the carbohydrate chain. This review briefly considers the various mechanisms by which such alterations may come about: (a) normal variation, (b) sialic acid alterations, (c) defective assembly of carbohydrate side-chains, (d) changed expression of core proteins and (e) epithelial metaplasia. The availability of monoclonal antibodies to mucin core proteins adds a new dimension to mucin histochemistry. It is now possible to offer explanations for traditional mucin histochemical findings on the basis of lineage-specific patterns of mucin core protein expression. Changes in core protein expression are described in inflammatory, metaplastic and neoplastic disorders of the gastrointestinal tract. The possibility that mucin change could be important in the aetiology of some diseases such as ulcerative colitis and H. pylori gastritis is considered. It is more probable, however, that changes in mucin expression are secondary to reprogramming of cellular differentiation and altered cell turnover. As such they may serve as markers to explain pathogenesis and provide novel diagnostic and prognostic information.

The adherent gastrointestinal mucus gel layer: thickness and physical state in vivo

Divergent results from in vitro studies on the thickness and appearance of the gastrointestinal mucus layer have previously been reported. With an in vivo model, we studied mucus gel thickness over time from stomach to colon. The gastrointestinal tissues of Inactin-anesthetized rats were mounted luminal side up for intravital microscopy. Mucus thickness was measured with a micropipette before and after mucus removal by suction. The mucus layer was translucent and continuous; it was thickest in the colon (approximately 830 microm) and thinnest in the jejunum (approximately 123 microm). On mucus removal, a continuous, firmly adherent mucus layer remained attached to the epithelial surface in the corpus (approximately 80 microm), antrum (approximately 154 microm), and colon (approximately 116 microm). In the small intestine, this layer was very thin (approximately 20 microm) or absent. After mucus removal, there was a continuous increase in mucus thickness with the highest rate in the colon and the lowest rate in the stomach. In conclusion, the adherent gastrointestinal mucus gel in vivo is continuous and can be divided into two layers: a loosely adherent layer removable by suction and a layer firmly attached to the mucosa.

A new strategy for evaluation of the eradication treatment of Helicobacter pylori: validation of the analysis of mucin composition in human gastric juice

The change in the mucin composition of human gastric juice has been investigated in patients before and after the eradication of the Helicobacter pylori (H. pylori) infection. We confirmed the successful eradication of H. pylori in all 17 patients. The gastric luminal mucins were divided into three fractions by ion-exchange chromatography using a discontinuous salt gradient with three salt steps. Although there was a significant variation in the proportion of the mucin content in each fraction among the individual patients, a decrease in the acidic mucin content after the eradication of H. pylori was commonly observed in all the patients. These results indicate that the mucin compositional analysis in the gastric luminal mucin may be a very useful tool for the assessment of H. pylori eradication.

Inhibition of gastric mucin synthesis by Helicobacter pylori

BACKGROUND & AIMS

Mucins are high-molecular-weight glycoproteins that protect the gastric epithelium. Previous data suggested that gastric surface-type mucin is decreased in Helicobacter pylori-infected patients and restored after eradication of the infection. Our aim was to determine the effect of H. pylori on mucin synthesis in cultured gastric epithelial cells.

METHODS

Mucin synthesis was measured by labeling with [(3)H]glucosamine and size-exclusion chromatography. Expression of MUC5AC and MUC1 mucin protein antigens was quantitated by Western blot analysis.

RESULTS

Mucin synthesis was inhibited more than 80% when KATO III cells were incubated with H. pylori, with no effect on mucin secretion or degradation. Inhibition was rapid (4 hours), partially reversible, dependent on concentration of bacteria, and associated with the insoluble membrane fraction. H. pylori decreased levels of MUC5AC and MUC1 mucins. MUC1 inhibition was half-maximal by 4 hours and partially reversed by 24 hours, but the decrease in MUC5AC was less rapid and not reversible within 24 hours.

CONCLUSIONS

H. pylori inhibits total mucin synthesis in vitro and decreases the expression of MUC5AC and MUC1. A decrease in gastric mucin synthesis in vivo may disrupt the protective surface mucin layer.

The human trefoil peptide, TFF1, is present in different molecular forms that are intimately associated with mucus in normal stomach

BACKGROUND

TFF1 is a 6.5 kDa secreted protein that is expressed predominantly in normal gastric mucosa. It is coexpressed with mucins and it can form dimers via a free carboxy terminal cysteine residue.

AIMS

To investigate the molecular forms of TFF1 that are present in normal human stomach and the association of the different molecular forms with mucus.

SUBJECTS

All subjects had macroscopically normal stomachs at gastroscopy. None had a significant past medical history.

METHODS

TFF1 was detected in normal gastric mucosa and adherent mucus by western transfer analysis after electrophoresis on reducing and non-reducing polyacrylamide gels. In some instances, proteins were fractionated by caesium chloride density gradient centrifugation prior to detection of TFF1. The location of TFF1 in gastric mucosa with an intact adherent mucus layer was assessed by immunohistochemistry.

RESULTS

Three different molecular forms of TFF1 were detected: TFF1 monomer, TFF1 dimer, and a TFF1 complex with an apparent molecular mass of about 25 kDa. TFF1 was present at higher concentrations than realised previously. The TFF1 complex was present in the adherent mucus gel layer but while its interaction with mucin was destabilised by caesium chloride, the interaction between mucin and the TFF1 dimer was resistant to caesium chloride.

CONCLUSIONS

Most of TFF1 in normal human gastric mucosa is present in a complex that is stabilised by a disulphide bond. TFF1 is intimately associated with mucus. The high concentration, colocalisation, and binding of TFF1 to gastric mucus strongly implicate TFF1 in gastric mucus function.

Gastroduodenal mucosal defense

Research performed in the laboratory and the clinic over the past several years has added to our understanding of the mechanisms that are operative in protecting the epithelial lining of the stomach and duodenum from injury and ulceration, most frequently caused by necrotic agents in the lumen. The defensive mechanism of the gastroduodenal mucosa comprises a series of physical, chemical, biologic, and immunologic barriers or mechanisms that act in concert to either prevent or limit cellular injury or transformation. The field of gastroduodenal defense can be subdivided into the following four areas: extracellular mucus barrier properties; membrane and ion transport properties; cellular factors promoting growth and restitution; and vascular, neural, and inflammatory factors ensuring optimal tissue perfusion and immune responsiveness, respectively. In addition, a great deal can be learned about gastroduodenal defense by studying the effects of ulcerogenic factors and conditions on the defensive mechanisms described here and specifically how they may be compromised by nonsteroidal anti-inflammatory drugs and Helicobacter pylori infection. This review presents interesting and noteworthy findings impacting on these properties contributing to gastroduodenal defense since the prior review article on this subject appearing in this journal.