Helicobacter pylori infection does not reduce the viscosity of human gastric mucus gel

The impact of tumor microenvironment: unraveling the role of physical cues in breast cancer progression

Metastasis accounts for the vast majority of breast cancer-related fatalities. Although the contribution of genetic and epigenetic modifications to breast cancer progression has been widely acknowledged, emerging evidence underscores the pivotal role of physical stimuli in driving breast cancer metastasis. In this review, we summarize the changes in the mechanics of the breast cancer microenvironment and describe the various forces that impact migrating and circulating tumor cells throughout the metastatic process. We also discuss the mechanosensing and mechanotransducing molecules responsible for promoting the malignant phenotype in breast cancer cells. Gaining a comprehensive understanding of the mechanobiology of breast cancer carries substantial potential to propel progress in prognosis, diagnosis, and patient treatment.

A slippery slope: On the origin, role and physiology of mucus

The mucosa of the gastrointestinal tract, eyes, nose, lungs, cervix and vagina is lined by epithelium interspersed with mucus-secreting goblet cells, all of which contribute to their unique functions. This mucus provides an integral defence to the epithelium against noxious agents and pathogens. However, it can equally act as a barrier to drugs and delivery systems targeting epithelial passive and active transport mechanisms. This review highlights the various mucins expressed at different mucosal surfaces on the human body, and their role in creating a mucoid architecture to protect epithelia with specialized functions. Various factors compromising the barrier properties of mucus have been discussed, with an emphasis on how disease states and microbiota can alter the physical properties of mucus. For instance, Akkermansia muciniphila, a bacterium found in higher levels in the gut of lean individuals induces the production of a thickened gut mucus layer. The aims of this article are to elucidate the different physiological, biochemical and physical properties of bodily mucus, a keen appreciation of which will help circumvent the slippery slope of challenges faced in achieving effective mucosal drug and gene delivery.

Passive and Active Microrheology of the Intestinal Fluid of the Larval Zebrafish

The fluids of the intestine serve as a physical barrier to pathogens, a medium for the diffusion of nutrients and metabolites, and an environment for commensal microbes. The rheological properties of intestinal mucus have therefore been the subject of many investigations, thus far limited to in vitro studies due to the difficulty of measurement in the natural context of the gut. This limitation especially hinders our understanding of how the gut microbiota interact with the intestinal space, since examination of this calls not only for in vivo measurement techniques, but for techniques that can be applied to model organisms in which the microbial state of the gut can be controlled. We have addressed this challenge with two complementary approaches. We performed passive microrheological measurements using thermally driven nanoparticles and active microrheology using micron-scale ellipsoidal magnetic microparticles, in both cases using light-sheet fluorescence microscopy to optically access the intestinal bulb of the larval zebrafish, a model vertebrate. We present viscosity measurements in germ-free animals (devoid of gut microbes), animals colonized by a single bacterial species, and conventionally reared animals, and find that in all cases, the mucin-rich intestinal liquid is well described as a Newtonian fluid. Surprisingly, despite known differences in the number of secretory cells in germ-free zebrafish and their conventional counterparts, the fluid viscosity for these two groups is very similar, as measured with either technique. Our study provides, to our knowledge, the first in vivo microrheological measurements of the intestinal space in living animals, and we comment on its implications for timescales of host-microbe interactions in the gut.

Hydrodynamics of defecation

Animals discharge feces within a range of sizes and shapes. Such variation has long been used to track animals as well as to diagnose illnesses in both humans and animals. However, the physics by which feces are discharged remain poorly understood. In this combined experimental and theoretical study, we investigate the defecation of mammals from cats to elephants using the dimensions of large intestines and feces, videography at Zoo Atlanta, cone-on-plate rheological measurements of feces and mucus, and a mathematical model of defecation. The diameter of feces is comparable to that of the rectum, but the length is double that of the rectum, indicating that not only the rectum but also the colon is a storage facility for feces. Despite the length of rectum ranging from 4 to 40 cm, mammals from cats to elephants defecate within a nearly constant duration of 12 ± 7 seconds (N = 23). We rationalize this surprising trend by our mathematical model, which shows that feces slide along the large intestine by a layer of mucus, similar to a sled sliding down a chute. Larger animals have not only more feces but also thicker mucus layers, which facilitate their ejection. Our model accounts for the shorter and longer defecation times associated with diarrhea and constipation, respectively. This study may support clinicians use of non-invasive procedures such as defecation time in the diagnoses of ailments of the digestive system.

How microbial community composition regulates coral disease development

Modeling reveals how rapid overgrowth by pathogenic microbes in the mucus layer surrounding corals, which often occurs under temporary stressful conditions, can persist long after environmental conditions return to normal.

Reef coral cover is in rapid decline worldwide, in part due to bleaching (expulsion of photosynthetic symbionts) and outbreaks of infectious disease. One important factor associated with bleaching and in disease transmission is a shift in the composition of the microbial community in the mucus layer surrounding the coral: the resident microbial community—which is critical to the healthy functioning of the coral holobiont—is replaced by pathogenic microbes, often species of Vibrio. In this paper we develop computational models for microbial community dynamics in the mucus layer in order to understand how the surface microbial community responds to changes in environmental conditions, and under what circumstances it becomes vulnerable to overgrowth by pathogens. Some of our model's assumptions and parameter values are based on Vibrio spp. as a model system for other established and emerging coral pathogens. We find that the pattern of interactions in the surface microbial community facilitates the existence of alternate stable states, one dominated by antibiotic-producing beneficial microbes and the other pathogen-dominated. A shift to pathogen dominance under transient stressful conditions, such as a brief warming spell, may persist long after environmental conditions have returned to normal. This prediction is consistent with experimental findings that antibiotic properties of Acropora palmata mucus did not return to normal long after temperatures had fallen. Long-term loss of antibiotic activity eliminates a critical component in coral defense against disease, giving pathogens an extended opportunity to infect and spread within the host, elevating the risk of coral bleaching, disease, and mortality.

An important correlate in bleaching and disease in reef-building corals is a shift in the makeup of the microbial community in the mucus layer surrounding the coral. Resident microbes critical to the healthy functioning of the coral organism are outcompeted by pathogenic microbes, often species of the Vibrio bacteria, and usually in the context of environmental disruptions such as ‘heat waves’ during the warm summer months. In this study we introduce mathematical models for microbial community dynamics in the mucus layer to explore how the surface microbial community responds to changes in environmental conditions, under what circumstances it is vulnerable to pathogen overgrowth, and whether it can recover. Consistent with observations that antibiotic properties in coral mucus did not return to healthy, normal levels for many months after temperatures had fallen, we discover that the shift to pathogen dominance under transient stressful conditions may persist long after environmental conditions return to normal.

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.

Micro- and macrorheology of mucus

Mucus is a complex biological material that lubricates and protects the human lungs, gastrointestinal (GI) tract, vagina, eyes, and other moist mucosal surfaces. Mucus serves as a physical barrier against foreign particles, including toxins, pathogens, and environmental ultrafine particles, while allowing rapid passage of selected gases, ions, nutrients, and many proteins. Its selective barrier properties are precisely regulated at the biochemical level across vastly different length scales. At the macroscale, mucus behaves as a non-Newtonian gel, distinguished from classical solids and liquids by its response to shear rate and shear stress, while, at the nanoscale, it behaves as a low viscosity fluid. Advances in the rheological characterization of mucus from the macroscopic to nanoscopic levels have contributed critical understanding to mucus physiology, disease pathology, and the development of drug delivery systems designed for use at mucosal surfaces. This article reviews the biochemistry that governs mucus rheology, the macro- and microrheology of human and laboratory animal mucus, rheological techniques applied to mucus, and the importance of an improved understanding of the physical properties of mucus to advancing the field of drug and gene delivery.

Barrier properties of mucus

Mucus is tenacious. It sticks to most particles, preventing their penetration to the epithelial surface. Multiple low-affinity hydrophobic interactions play a major role in these adhesive interactions. Mucus gel is also shear-thinning, making it an excellent lubricant that ensures an unstirred layer of mucus remains adherent to the epithelial surface. Thus nanoparticles (NP) must diffuse readily through the unstirred adherent layer if they are to contact epithelial cells efficiently. This article reviews some of the physiological and biochemical properties that form the mucus barrier. Capsid viruses can diffuse through mucus as rapidly as through water and thereby penetrate to the epithelium even though they have to diffuse 'upstream' through mucus that is being continuously secreted. These viruses are smaller than the mucus mesh spacing, and have surfaces that do not stick to mucus. They form a useful model for developing NP for mucosal drug delivery.

Detection of Helicobacter Pylori Infection in Dyspeptic Patients by Different Sero-Bacteriological Methods

To evaluate invasive (biopsy related) tests and noninvasive (serological) tests in the diagnosis of H.pylori, ninety-two adults (54 male, 38 female) presenting with dyspepsia were studied after classification into two groups on the basis of endoscopical diagnosis; 46 patients with erosive diseases (gastroduodenal ulcers or gastroduodenal erosions) and 46patients with non-erosive diseases (gastritis or gastroduodenitis). Sera were testedfor anti-H.pylori IgG and IgM by an immunochromatography card test and ELISA respectively. Three antral biopsies were taken for biopsy urease test (BUT), bacterial culture and histological examination. Stool samples were obtained from only 30 dyspeptic cases for H.pylori antigen detection (HpSA) by an ELISA method.

H. pylori was detected in 81 of 92 cases; these were positive by one or more of the gold standard tests (culture, histology and biopsy-urease test). Histological examination yielded the highest frequency of microorganism detection (71.7%), followed by BUT (68.5%) and then bacterial culture (26.1%). In erosive disorders the BUT gave the highest frequency ofpositivity (78.3%),followed by histological examination (67.4%), and then bacterial culture (41.3%) but in non-erosive disorders histological examination gave the highest positive results (76.1%) followed by BUT (58.7%) and bacterial culture (10.9%). The overall sensitivities of BUT, histology and bacterial culture of H.pylori were 77.8%, 81.5% and 29.6% respectively. Serologically the anti-H.pylori IgG test yielded the highest frequency of positive results (80.4%), followed by HpSA test (66.7%) and the least positive was anti-H.pylori IgM test (65.2%). In the light of the gold standard tests used (biopsy-related tests), the validity of anti-H.pylori IgG test, anti-H.pylori IgM test and HpSA test were determined; the sensitivities being 79%, 65.4% and 75% respectively and their specificities were 9.1%, 36.4% and 66.7% respectively. The positive and negative predictive values, the positive and negative likelihood ratios of serological tests were also evaluated.

Conclusion: The most sensitive invasive test (biopsy related) and noninvasive (serological) tests were histological examination and IgG immunochromatography card tests respectively.

Quantitative determination of gland mucous cells-type mucin using a monoclonal antibody, HIK1083: its pathophysiological changes in human gastric juice

BACKGROUND

Pathological alteration in gastric mucosa is caused by Helicobacter pylori infection and is detectable by histological analysis. In particular, the alteration of gland mucous cells (GMCs)-type mucin, which plays a protective role against H. pylori infection, is critical in the pathogenesis of H. pylori-related gastritis. We established an assay for GMCs-type mucin and quantitatively assessed the pathophysiological changes in its content in human gastric juice samples.

METHODS

The assay method for GMCs-type mucin was based on ELISA using a monoclonal antibody (HIK1083), and was used it to measure GMCs-type mucin in gastric juice obtained from patients with or without H. pylori infection.

RESULTS

All the basic characteristics of the current method were satisfactory to quantify the GMCs-type mucin content in gastric juice. The GMCs-type mucin content, but not total mucin content, was significantly higher in patients with H. pylori infection (n=17; 437+/-476 U, mean+/-SD) than in those without H. pylori infection (n=55; 168+/-322 U, p<0.05).

CONCLUSIONS

The current method is suitable for the quantitative analysis of GMCs-type mucin in gastric juice. The change in GMCs-type mucin content in gastric juice may be possibly implicated in the pathophysiology of the gastric mucosa and in the patient's gastric mucosal lesions.

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.

Helicobacter pylori infection up-regulates gland mucous cell-type mucins in gastric pyloric mucosa

BACKGROUND

Two types of mucous cell are present in gastric mucosa: surface mucous cells (SMCs) and gland mucous cells (GMCs), which consist of cardiac gland cells, mucous neck cells, and pyloric gland cells. We have previously reported that the patterns of glycosylation of SMC mucins are reversibly altered by Helicobacter pylori infection. In this study, we evaluated the effects of H. pylori infection on the expression of GMC mucins in pyloric gland cells.

METHODS

Gastric biopsy specimens from the antrums of 30 H. pylori-infected patients before and after eradication of H. pylori and 10 normal uninfected volunteers were examined by immunostaining for MUC6 (a core protein of GMC mucins), alpha1,4-N-acetyl-glucosaminyl transferase (alpha4GnT) (the glycosyltransferase which forms GlcNAcalpha1-4Galbeta-R), and GlcNAcalpha1-4Galbeta-R (a GMC mucin-specific glycan).

RESULTS

MUC6, alpha4GnT, and HIK1083-reactive glycan were expressed in the cytoplasm, supranuclear region, and secretory granules in pyloric gland cells, respectively. The immunoreactivity of MUC6 and alpha4GnT, but not of GlcNAcalpha1-4Galbeta-R, in the pyloric gland increased in H. pylori-associated gastritis, and after the eradication of H. pylori, the increased expression of MUC6 and alpha4GnT in the gastric mucosa of H. pylori-infected patients decreased to almost normal levels. This up-regulation was correlated with the degree of inflammation.

CONCLUSIONS

In addition to the synthesis of GMC mucins increasing reversibly, their metabolism or release may also increase reversibly in H. pylori-associated gastritis. The up-regulation of the expression of gastric GMC mucins may be involved in defense against H. pylori infection in the gastric surface mucous gel layer and on the gastric mucosa.

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.

Helicobacter pylori vaccines and mechanisms of effective immunity: is mucus the key?

In this theoretical article, the hypothesis is proposed that immunization against gastric helicobacter infection is mediated by CD4+ T-cell induced changes in mucus production. Vaccine development for the gastric pathogen Helicobacter pylori has encountered several problems. Resolving these problems is impeded by our lack of understanding of the mechanisms by which the immune response influences bacterial colonization. Protective immunity requires CD4+ T cells, but the majority of helicobacters are located in the mucus of the gastric lumen, away from the epithelial surface. Evidence suggests that this mechanism functions independently of antibodies, so how this is achieved is unknown. Clues to this mechanism may be provided by immune clearance of nematode infection. Similar to H. pylori, expulsion of the intestinal nematode, Nippostrongylus brasiliensis, in rodents is mediated by CD4+ T-cell changes in the numbers of goblet cells and the type of mucins secreted into the gut. Immune-mediated changes in secretion of gastric mucins could similarly be responsible for the reductions in helicobacter colonization seen in immunized animals. Helicobacter pylori are highly motile bacteria that have evolved to inhabit their specialized niche. Alterations in their mucus environment could influence their motility, such that the bacteria cannot remain efficiently within the mucus and are flushed away.

Virulence and pathogenicity of Helicobacter pylori

Bacterial and host response factors play significant roles in the pathogenicity of H. pylori-related disease manifestations. The complete DNA sequences for two H. pylori strain genomes have been published. The differences in the sequences between these two unrelated strains may enable clinicians to identify rapidly other conserved and potentially virulent genes and products. Whether these two DNA sequences are sufficient representation of the H. pylori genetic heterogeneity is unknown. The host immune response and the cascade of events that occurs with H. pylori infection are being clarified rapidly. Understanding the role of this gastric bacterium in apoptosis and cellular proliferation would enable clinicians to understand its relationship to ulcerogenesis and gastric malignancy. Piecing together many observations related to H. pylori would result in understanding the interaction of H. pylori factors and host responses that lead to the variety of disease manifestations associated with this chronic infection. The development of animal models with H. pylori and other Helicobacter species has set the stage in which in vitro observations can be tested in the in vivo model.

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 thioredoxin system of Helicobacter pylori

This paper describes the purification of thioredoxin reductase (TR) and the characterization, purification, and cloning of thioredoxin (Trx) from Helicobacter pylori. Purification, amino acid sequence analysis, and molecular cloning of the gene encoding thioredoxin revealed that it is a 12-kDa protein which possesses the conserved redox active motif CGPC. The gene encoding Trx was amplified by polymerase chain reaction and inserted into a pET expression vector and used to transform Escherichia coli. Trx was overexpressed by induction with isopropyl-1-thio-beta-D-galactopyranoside as a decahistidine fusion protein and was recovered from the cytoplasm as a soluble and active protein. The redox activity of this protein was characterized using several mammalian proteins of different architecture but all containing disulfide bonds. H. pylori thioredoxin efficiently reduced insulin, human immunoglobulins (IgG/IgA/sIgA), and soluble mucin. Subcellular fractionation analysis of H. pylori revealed that thioredoxin was associated largely with the cytoplasm and inner membrane fractions of the cell in addition to being recovered in the phosphate-buffered saline-soluble fraction of freshly harvested cells. H. pylori TR was purified to homogeneity by chromatography on DEAE-52, Cibacron blue 3GA, and 2',5'-ADP-agarose. Gel filtration revealed that the native TR had a molecular mass of 70 kDa which represented a homodimer composed of two 35-kDa subunits, as determined by SDS-polyacrylamide gel electrophoresis. H. pylori TR (NADPH-dependent) efficiently catalyzed the reduction of 5,5'-dithiobis(nitrobenzoic acid) in the presence of either native or recombinant H. pylori Trx. H. pylori Trx behaved also as a stress response element as broth grown bacteria secreted Trx in response to chemical, biological, and environmental stresses. These observations suggest that Trx may conceivably assist H. pylori in the process of colonization by inducing focal disruption of the oligomeric structure of mucin while rendering host antibody inactive through catalytic reduction.

The relationship between Helicobacter pylori motility, morphology and phase of growth: implications for gastric colonization and pathology

To explore the relationship between Helicobacter pylori motility, morphology and phase of growth, bacteria were isolated from antral biopsies of patients with duodenal ulcer or non-ulcer dyspepsia, and grown in liquid medium in batch and continuous culture systems. Motilities and morphologies of H. pylori in different phases of growth were examined with a Hobson BackTracker and by transmission electron microscopy. Morphologies of bacteria grown in vitro were also compared with those of bacteria in antral biopsies from patients with non-autoimmune gastritis. H. pylori had poor motility in lag phase, became highly motile in mid-exponential phase and lost motility in the decline phase of growth. Motilities of bacteria in the same phase of growth from patients with duodenal ulcer or non-ulcer dyspepsia were not significantly different. In the mid/late-exponential phase of growth bacteria had helical morphologies and multiple polar flagella, typical of H. pylori in the gastric mucus layer. In the decline phase of growth bacteria shed flagella, and had precoccoidal or coccoidal morphologies. These findings support the view that helical and coccoidal H. pylori are in different phases of growth with different roles in gastric colonization, indicate that bacterial motility per se is unlikely to be a determinant of H. pylori pathology, and suggest that H. pylori in the antral mucus layer is in a state of continuous (exponential phase) growth.

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

BACKGROUND

It has been proposed that a pathogenic effect of Helicobacter pylori is a weakening of the protective mucus barrier; however, this remains controversial.

AIMS

To clarify the effects of H pylori infection on the mucus gel barrier in vivo.

METHODS

Mucus gel polymeric structure and the thickness of the adherent mucus barrier were measured in endoscopic biopsy samples in subjects with and without H pylori infection.

RESULTS

There was a significant 18% reduction in the proportion of polymeric gel forming mucin in the adherent mucus layer in H pylori positive compared with negative subjects. There was no change in the adherent mucus thickness between H pylori positive and negative subjects without gastric atrophy (mean (SD): 104 (26) micron, 106 (30) micron, respectively). There was however a significant reduction in mucus thickness in those H pylori positive subjects with underlying gastric atrophy (84 (13) micron, p=0.03) compared with those without atrophy.

CONCLUSIONS

A partial breakdown in gel forming structure of the gastric mucus barrier does occur in H pylori infection per se but this is insufficient to cause a collapse of the mucus barrier.

Helicobacter pylori factors involved in the development of gastroduodenal mucosal damage and ulceration

Many putative virulence determinants of Helicobacter pylori are believed to trigger and worsen the gastroduodenal mucosa damage observed in infected patients. H. pylori urease reacts with the gastric urea and generates ammonia; ammonia combines with water and yields ammonium hydroxide, which is cytotoxic. Ammonia may also inhibit cell proliferation and cause indirect mucosal injury by stimulating neutrophils. Phospholipases may damage the gastric mucosa by degrading phospholipids and generating precursors of ulcerogenic components. Other enzymes, such as protease, neuraminidase, fucosidase, and alcohol dehydrogenase, can contribute to damage of the gastric epithelium by destroying the integrity of mucus or by inducing lipid peroxidation. Infection by vacuolating cytotoxic (VacA+) H. pylori strains is considered to constitute increased risk for development of peptic ulcer and gastric cancer. Exploration of the vacA gene structure has shown the existence of strongly toxigenic strains, and has confirmed at the molecular level the increased ulcerogenic potential of VacA+ H. pylori strains. A pathogenicity island called cag has been recently described in Type 1 H. pylori strains (VacA+/CagA+).cag contains the cagA gene (whose expression is associated with toxigenicity) and many genes, some of which are highly homologous to virulence genes of other virulent bacteria, that account for the enhanced pathogenic potential of CagA+ organisms.

Identifiable Helicobacter pylori strains or factors important in the development of duodenal ulcer disease

BACKGROUND

Helicobacter pylori is a primary pathogen as its presence in the stomach almost always is associated with a strong mucosal and systemic immune response. Putative virulence factors of H. pylori are numerous. In this article, we evaluate whether currently available evidence supports the existence of factors important in the development of duodenal ulcer disease.

METHODS

The evaluation is conducted by a review of the literature on H. pylori toxins and virulence factors.

RESULTS

Most putative H. pylori virulence factors are present in all isolates examined, though some are present only in, or are expressed more intensively by, determined strains. Urease is the main virulence determinant of H. pylori. It generates ammonia from the gastric urea, which in turn injures the gastric mucosa either directly by forming ammonium hydroxide or indirectly by stimulating polymorphonuclear leukocytes and inhibiting cell proliferation. Other enzymes (e.g., mucinase, phospholipases, alcohol dehydrogenase, neuraminidase) could promote tissue erosion and ulceration by destroying the integrity of mucus, by inducing lipid peroxidation, and the like. H. pylori strains that express the vacuolating toxin vacA and the associated protein cagA are called type I and are considered to be endowed with increased ulcerogenic and inflammatory potential. Exploration of the structure of the vacA gene has shown that the degree of toxicity is regulated at the molecular level. Type I H. pylori strains carry a 40-kb genomic fragment called cag that is absent from type II strains (vacA- and cagA-negative). cag is considered a pathogenicity island because it contains numerous genes that are highly homologous to virulence genes of classic bacterial pathogens and because it has been suggested that it is acquired through recombination events. CagA is part of the pathogenicity island. CagA-positive strains are more likely to be isolated from patients with duodenal ulcer and other severe digestive pathological processes.

CONCLUSIONS

The use of simple serological tests to identify patients infected with type I H. pylori strains could help to calculate the risk of development of severe gastroduodenal diseases and, possibly, to prevent such severe diseases.

Increased motility of Helicobacter pylori by methylcellulose could upregulate the expression of proinflammatory cytokines in human gastric epithelial cells

The inflammatory reaction in the human gastric mucosa to Helicobacter pylori could be initially triggered by an array of cytokines expressed in infected gastric epithelial cells. The spiral morphology and flagella of these organisms could increase their velocity in a viscous environment such as methylcellulose solution. The goal of this study was to determine whether modification of H. pylori motility could influence the expression of cytokine genes from gastric epithelial cells infected with H. pylori. Adherent human gastric epithelial cells were cultured and overlaid with methylcellulose solutions of varying viscosity. These epithelial cell layers covered with methylcellulose solution were inoculated with H. pylori. RNAs were then extracted from the gastric epithelial cells. Various cytokine gene expressions were assessed and quantified by reverse transcription-polymerase chain reaction (RT-PCR) and standard synthetic RNA. Cytokine proteins were also measured by enzyme-linked immunosorbent assay (ELISA). Expression of mRNA for interleukin(IL)-8 was upregulated in H. pylori-infected gastric epithelial cells overlaid with methylcellulose of 15 centipoise (cp) viscosity. The expression of mRNA for IL-1 alpha, IL-8, monocyte chemotactic protein (MCP)-1 and granulocyte macrophage colony-stimulating factor (GM-CSF) was also upregulated in H. pylori-infected gastric epithelial cells overlaid with methylcellulose solution of the same viscosity. The number of molecules of the expressed cytokine transcripts also paralleled the amounts of protein secreted from gastric epithelial cells infected with H. pylori. These results suggest that methylcellulose solution (simulating the mucus layer in vivo) could increase contact of H. pylori with gastric epithelial cells by increasing its motility. This could result in the upregulation of mRNA for proinflammatory cytokines in gastric epithelial cells, therefore enhancing inflammatory reaction at H. pylori-infected sites.

The effect of omeprazole on gastric juice viscosity, pH and bacterial counts

BACKGROUND

In vitro studies have shown that pH is an important determinant of mucus structure and function, but the relationship in vivo is unclear. Omeprazole increases intragastric pH and also allows bacterial overgrowth. In this study we have assessed the effect of omeprazole on gastric juice viscosity and examined the influence of pH and bacterial overgrowth on the resulting change.

METHODS

Gastric juice specific viscosity, pH and total bacterial counts were measured in nine healthy male volunteers before and after omeprazole 20 mg twice daily for 1 week. The effect of incubation at pH 2 and 7 was also determined. Viscosity changes were compared with changes in pH and bacterial counts.

RESULTS

Mean viscosity fell (P < 0.05) following treatment, though there was a wide range in viscosity both before and after treatment. The decrease was reproduced by incubation of pre-treatment juice at pH 7 but not pH 2. The fall in viscosity was correlated (P < 0.05) with change pH.

CONCLUSION

Omeprazole decreases gastric juice, and hence gastric mucus, viscosity by increasing intragastric pH. This could be important if it allows improved penetration of antimicrobials to Helicobacter pylori within the mucus layer.

Histological responses to Helicobacter pylori infection: gastritis, atrophy and preneoplasia

It is interesting that the principal histological features of acute H. pylori gastritis, surface epithelial degeneration and neutrophil polymorph infiltration, remain as the most sensitive indicators of the 'activity' of infection in the chronic phase. It is not surprising therefore that these are the first features to resolve after successful H. pylori eradication therapy. In one of the earliest studies of histological response to eradication, McNulty et al (1986) endoscoped patients immediately after a three-week treatment regime and found a highly significant decline in polymorph scores. The response was even more striking four weeks after the end of treatment, as at that time biopsies from responders were virtually devoid of polymorphs (Valle et al, 1991). Indeed the disappearance of polymorphs from a post-treatment biopsy is a useful indicator of successful eradication. Less attention has been paid to the recovery of the surface epithelium yet this is an impressive feature when comparing pre- and post-treatment biopsies. Using subjective grading of surface epithelial lesions, Solcia et al (1994) found a dramatic and highly significant improvement in mean grade immediately after anti-H. pylori treatment. Recently a morphometric approach was used to demonstrate a significant increase in surface epithelial cell height corresponding to the recovery that accompanies successful H. pylori eradication (Hassan et al, 1993). Chronic inflammatory cell infiltrate resolution is much slower. There is only a gradual reduction in cell density so that even 6 months after eradication treatment the mean score had only fallen by 50% of pre-treatment values (Solcia et al, 1994). In the author's experience, a minor increase in such cells persists for many months and may never completely resolve, in that more lymphocytes and plasma cells are seen than in a truly normal (pre-infection) stomach. Valle et al (1991) found resolution of chronic inflammation in only 15% of subjects at 6 months and in 51% at one year after eradication. The long delay in disappearance of lymphocytes and plasma cells poses a question over continuing antigenic stimulation in the absence of infection. Possible answers could involve persistence of antigenic moieties in dendritic cells of the lamina propria, or sensitization to host antigens brought about by infection so that an element of autoimmunity persists after eradication. Unravelling these mechanisms will add important new elements to our understanding of the long-term consequences of this fascinating infection.