Surface hydrophobicity of gastric mucosa in Helicobacter pylori infection: effect of clearance and eradication

Development of the PC-NSAID technology: From contact angle to Vazalore®

We describe strategies in drug development to reduce the gastrointestinal (GI) toxicity of nonsteroidal anti-inflammatory drugs (NSAIDs). We then provide an overview of the experiments that led to the development of PC-NSAIDs, a novel family of NSAIDs associated with phosphatidylcholine (PC) that have reduced GI toxicity and full therapeutic activity. Furthermore, we describe the evidence showing: that the stomach possesses hydrophobic properties that are attributable to phospholipids lining the mucus gel layer; and that NSAIDs chemically associate with intrinsic PC, thereby attenuating the tissue's hydrophobic properties. Further, pre-associating NSAIDs with PC reduces the GI toxicity of these drugs, both in rodent ulcer models and in human subjects, without affecting the drugs' therapeutic activity. Finally, we discuss the commercialization and launch of Aspirin-PC, an over-the-counter (OTC) drug with the brand name Vazalore®.

Structure of the active pharmaceutical ingredient bismuth subsalicylate

Structure determination of pharmaceutical compounds is invaluable for drug development but remains challenging for those that form as small crystals with defects. Bismuth subsalicylate, among the most commercially significant bismuth compounds, is an active ingredient in over-the-counter medications such as Pepto-Bismol, used to treat dyspepsia and H. pylori infections. Despite its century-long history, the structure of bismuth subsalicylate is still under debate. Here we show that advanced electron microscopy techniques, namely three-dimensional electron diffraction and scanning transmission electron microscopy, can give insight into the structure of active pharmaceutical ingredients that are difficult to characterize using conventional methods due to their small size or intricate structural features. Hierarchical clustering analysis of three-dimensional electron diffraction data from ordered crystals of bismuth subsalicylate revealed a layered structure. A detailed investigation using high-resolution scanning transmission electron microscopy showed variations in the stacking of layers, the presence of which has likely hindered structure solution by other means. Together, these modern electron crystallography techniques provide a toolbox for structure determination of active pharmaceutical ingredients and drug discovery, demonstrated by this study of bismuth subsalicylate.

Interface-Mediated Mechanism of Action-The Root of the Cytoprotective Effect of Immediate-Release Omeprazole

Omeprazole is usually administered under an enteric coating. However, there is a Food and Drug Administration-approved strategy that enables its release in the stomach. When locally absorbed, omeprazole shows a higher efficacy and a cytoprotective effect, whose mechanism was still unknown. Therefore, we aimed to assess the effect of the absorption route on the gastric mucosa. 2D and 3D models of dipalmitoylphosphatidylcholine (DPPC) at different pH values (5.0 and 7.4) were used to mimic different absorption conditions. Several experimental techniques, namely, fluorescence studies, X-ray scattering methodologies, and Langmuir monolayers coupled with microscopy, X-ray diffraction, and infrared spectroscopy techniques, were combined with molecular dynamics simulations. The results showed that electrostatic and hydrophobic interactions between omeprazole and DPPC rearranged the conformational state of DPPC. Omeprazole intercalates among DPPC molecules, promoting domain formation with untilted phospholipids. Hence, the local release of omeprazole enables its action as a phospholipid-like drug, which can reinforce and protect the gastric mucosa.

An Additive Effect of Oral N-Acetyl Cysteine on Eradication of Helicobacter pylori

Background. Helicobacter pylori is highly adapted to the gastric environment where it lives within or beneath the gastric mucous layer. The aim of this study was to evaluate whether the addition of N-acetyl cysteine to the treatment regimen of H. pylori infection would affect eradication rates of the disease. Methods. A total of 79 H. pylori positive patients were randomized to two therapeutic groups. Both groups received a 14-day course of three-drug regimen including amoxicillin/clarithromycin/omeprazole. Experimental group (38 subjects) received NAC, and control group (41 subjects) received placebo, besides three-drug regimen. H. pylori eradication was evaluated by urea breath test at least 4 weeks after the cessation of therapy. Results. The rate of H. pylori eradication was 72.9% and 60.9% in experimental and control groups, respectively (P = 0.005). By logistic regression modeling, female gender (OR 3.68, 95% CI: 1.06–5.79; P = 0.040) and treatment including NAC (OR 1.88, 95% CI: 0.68–3.15; P = 0.021) were independent factors associated with H. pylori eradication. Conclusion. The results of the present study show that NAC has an additive effect on the eradication rates of H. pylori obtained with three-drug regimen and appears to be a promising means of eradicating H. pylori infection.

Intestinal uptake and toxicity evaluation of acetazolamide and its multicomponent complexes with hidroxypropyl-β-cyclodextrin in rats

Large oral doses of ACZ lower the intraocular pressure (IOP), but usually lead to a multitude of systemic side effects, including gastrointestinal upset. The present study was undertaken to evaluate the effect of ACZ on the histological structure of rat duodenal mucosa and to assess a possible protective role of the complex formation of ACZ with HP-β-CD, either separately or in combination with a third compound, on the gut epithelial layer by histological and ultrastructural examinations of sections of rat duodenum exposed to ACZ or its formulations. In addition, the transport process of ACZ and its binary or ternary complexes across the duodenal mucosa by means of the single-pass intestinal perfusion (SPIP) method in rats was evaluated. Evidence was found that ACZ alters intestinal permeability and induces damage to the rat small intestine. In contrast, ACZ-induced intestinal injury may be abrogated by ACZ complexation. In addition, the complexation of ACZ with HP-β-CD, alone or in combination with a third compound, facilitated significant levels of ACZ uptake across the rat duodenal segment. Ternary complexes of ACZ with HP-β-CD in combination with TEA (triethanolamine) or calcium ions were found to provide an excellent approach that enabled an increased apparent permeability of ACZ across the duodenal epithelium, with a concomitant ability to preserve the integrity of the gut epithelium from ACZ-induced injury. These results could be useful for the design and development of novel ACZ formulations that can reduce GI toxicity, while still maintaining their essential therapeutic efficacies.

Bio-physical characteristics of gastrointestinal mucosa of celiac patients: comparison with control subjects and effect of gluten free diet-

Background

Intestinal mucosa is leaky in celiac disease (CD), and this alteration may involve changes in hydrophobicity of the mucus surface barrier in addition to alteration of the epithelial barrier. The aims of our study were i) to compare duodenal hydrophobicity as an index of mucus barrier integrity in CD patients studied before (n = 38) and during gluten- free diet (GFD, n = 68), and in control subjects (n = 90), and ii) to check for regional differences of hydrophobicity in the gastro-intestinal tract.

Methods

Hydrophobicity was assessed by measurement of contact angle (CA) (Rame Hart 100/10 goniometer) generated by a drop of water placed on intestinal mucosal biopsies.

Results

CA (mean ± SD) of distal duodenum was significantly lower in CD patients (56° ± 10°)) than in control subjects (69° ± 9°, p < 0.0001), and persisted abnormal in patients studied during gluten free diet (56° ± 9°; p < 0.005). CA was significantly higher (62° ± 9°) in histologically normal duodenal biopsies than in biopsies with Marsh 1-2 (58° ± 10°; p < 0.02) and Marsh 3 lesions (57° ± 10°; p < 0.02) in pooled results of all patients and controls studied. The order of hydrofobicity along the gastrointestinal tract in control subjects follows the pattern: gastric antrum > corpus > rectum > duodenum > oesophagus > ileum.

Conclusions

We conclude that the hydrophobicity of duodenal mucous layer is reduced in CD patients, and that the resulting decreased capacity to repel luminal contents may contribute to the increased intestinal permeability of CD. This alteration mirrors the severity of the mucosal lesions and is not completely reverted by gluten-free diet. Intestinal hydrophobicity exhibits regional differences in the human intestinal tract.

Reduced hydrophobicity of the colonic mucosal surface in ulcerative colitis as a hint at a physicochemical barrier defect

PURPOSE

There is increasing evidence that a defect of the gastrointestinal mucosal barrier is important for the development of inflammatory bowel diseases (IBD). The hydrophobicity of the colonic mucosal surface is a measure of its resistance to luminal antigens, e.g. of bacterial origin. Therefore, the purpose of this study was to determine this parameter in patients suffering from IBD.

METHODS

Nineteen patients with ulcerative colitis (UC), ten patients with Crohn's disease (CD) and 20 controls were examined. All underwent colonic surgery at the University Hospital Heidelberg. Clinical disease activity was determined. From every subject, colonic tissue specimens were obtained, and hydrophobicity of the mucosal surface was determined with a goniometer by multiple plateau contact angle measurements. Histological evaluation of disease activity was performed in directly adjacent tissue specimens.

RESULTS

Hydrophobicity of the colonic mucosal surface, expressed as plateau contact angles, was significantly reduced in patients with UC (mean ± SEM, 47.8° ± 3.4°) compared to those with CD (72.0° ± 5.2°) and controls (72.5° ± 5.6°; over-all P = 0.0004; UC versus controls, P < 0.001; UC versus CD, P < 0.05; CD versus controls, P > 0.05). Between mucosal hydrophobicity and clinical disease activity, as well as mucosal hydrophobicity and histological disease activity, no significant correlation was found.

CONCLUSIONS

The results suggest a defective physicochemical barrier as an essential factor in the pathogenesis of UC, but not CD. The fact that no correlation was found between mucosal hydrophobicity and disease activity may indicate that the loss of mucosal hydrophobicity in UC is not exclusively a secondary effect due to inflammation.

A direct role for secretory phospholipase A2 and lysophosphatidylcholine in the mediation of LPS-induced gastric injury

Endotoxemia from sepsis can injure the gastrointestinal tract through mechanisms that have not been fully elucidated. We have shown that LPS induces an increase in gastric permeability in parallel with the luminal appearance of secretory phospholipase A2 (sPLA2) and its product, lysophosphatidylcholine (lyso-PC). We proposed that sPLA2 acted on the gastric hydrophobic barrier, composed primarily of phosphatidylcholine (PC), to degrade it and produce lyso-PC, an agent that is damaging to the mucosa. In the present study, we have tested whether lyso-PC and/or sPLA2 have direct damaging effects on the hydrophobic barriers of synthetic and mucosal surfaces. Rats were administered LPS (5 mg/kg, i.p.), and gastric contents were collected 5 h later for analysis of sPLA2 and lyso-PC content. Using these measured concentrations, direct effects of sPLA2 and lyso-PC were determined on (a) surface hydrophobicity as detected with an artificial PC surface and with intact gastric mucosa (contact angle analysis) and (b) cell membrane disruption of gastric epithelial cells (AGS). Both lyso-PC and sPLA2 increased significantly in the collected gastric juice of LPS-treated rats. Using similar concentrations to the levels in gastric juice, the contact angle of PC-coated slides declined after incubation with either pancreatic sPLA2 or lyso-PC. Similarly, gastric contact angles seen in control rats were significantly decreased in sPLA2 and lyso-PC-treated rats. In addition, we observed dose-dependent injurious effects of both lyso-PC and sPLA2 in gastric AGS cells. An LPS-induced increase in sPLA2 activity in the gastric lumen and its product, lyso-PC, are capable of directly disrupting the gastric hydrophobic layer and may contribute to gastric barrier disruption and subsequent inflammation.

Phosphatidylcholine as a constituent in the colonic mucosal barrier--physiological and clinical relevance

Phosphatidylcholine (PC) is an important constituent of the gastrointestinal tract. PC molecules are not only important in intestinal cell membranes but also receiving increasing attention as protective agents in the gastrointestinal barrier. They are largely responsible for establishing the hydrophobic surface of the colon. Decreased phospholipids in colonic mucus could be linked to the pathogenesis of ulcerative colitis, a chronic inflammatory bowel disease. Clinical studies revealed that therapeutic addition of PC to the colonic mucus of these patients alleviated the inflammatory activity. This positive role is still elusive, however, we hypothesized that luminal PC has two possible functions: first, it is essential for surface hydrophobicity, and second, it is integrated into the plasma membrane of enterocytes and it modulates the signaling state of the mucosa. The membrane structure and lipid composition of cells is a regulatory component of the inflammatory signaling pathways. In this perspective, we will shortly summarize what is known about the localization and protective properties of PC in the colonic mucosa before turning to its evident medical importance. We will discuss how PC contributes to our understanding of the pathogenesis of ulcerative colitis and how reinforcing the luminal phospholipid monolayer can be used as a therapeutic concept in humans.

Peptic ulcer disease

Peptic ulcer disease had a tremendous effect on morbidity and mortality until the last decades of the 20th century, when epidemiological trends started to point to an impressive fall in its incidence. Two important developments are associated with the decrease in rates of peptic ulcer disease: the discovery of effective and potent acid suppressants, and of Helicobacter pylori. With the discovery of H pylori infection, the causes, pathogenesis, and treatment of peptic ulcer disease have been rewritten. We focus on this revolution of understanding and management of peptic ulcer disease over the past 25 years. Despite substantial advances, this disease remains an important clinical problem, largely because of the increasingly widespread use of non-steroidal anti-inflammatory drugs (NSAIDs) and low-dose aspirin. We discuss the role of these agents in the causes of ulcer disease and therapeutic and preventive strategies for drug-induced ulcers. The rare but increasingly problematic H pylori-negative NSAID-negative ulcer is also examined.

Gastrointestinal safety and therapeutic efficacy of parenterally administered phosphatidylcholine-associated indomethacin in rodent model systems

BACKGROUND AND PURPOSE

Indomethacin is a non-steroidal anti-inflammatory drug (NSAID) that is limited in its enteral or parenteral use by side effects of gastroduodenal bleeding and ulceration. We have investigated the ability of phosphatidylcholine associated with indomethacin to form a therapeutically effective drug (INDO-PC) with reduced gastrointestinal (GI) toxicity for parenteral use.

EXPERIMENTAL APPROACH

Rats were treated acutely by intravenous or chronically with subcutaneous injection of vehicle, indomethacin or INDO-PC using three related protocols. We then evaluated the following properties of these parenterally administered test drugs: (i) GI toxicity (luminal and faecal haemoglobin; intestinal perforations and adhesions; and haematocrit); (ii) bioavailability (plasma indomethacin); and (iii) therapeutic efficacy (analgesia from sensitivity to pressure; anti-inflammatory from ankle thickness; cyclo-oxygenase (COX) inhibition from synovial fluid prostaglandin E(2) concentration) in rats with adjuvant-induced joint inflammation.

KEY RESULTS

Acute and chronic dosing with INDO-PC produced less GI bleeding and intestinal injury than indomethacin alone, whereas the bioavailability, analgesic, anti-inflammatory and COX inhibitory activity of INDO-PC were comparable to indomethacin.

CONCLUSIONS AND IMPLICATIONS

The chemical association of phosphatidylcholine with indomethacin appears to markedly reduce the GI toxicity of the NSAID while providing equivalent therapeutic efficacy in a parenteral INDO-PC formulation.

Hydrophobicity of mucosal surface and its relationship to gut barrier function

Loss of the gut barrier has been implicated in the pathogenesis of the multiple organ dysfunction syndrome, and, thus, understanding the intestinal barrier is of potential clinical importance. An important, but relatively neglected, component of the gut barrier is the unstirred mucus layer, which through its hydrophobic and other properties serves as an important barrier to bacterial and other factors within the gut lumen. Thus, the goal of this study was to establish a reproducible method of measuring mucosal hydrophobicity and test the hypothesis that conditions that decrease mucosal hydrophobicity are associated with increased gut permeability. Hydrophobicity was measured in various segments of normal gut by measuring the contact angle of an aqueous droplet placed on the mucosal surface using a commercial goniometer. Second, the effect of the mucolytic agent N-acetyl cysteine on mucosal hydrophobicity and gut permeability was measured, as was the effects of increasing periods of in vivo gut ischemia on these parameters. Gut ischemia was induced by superior mesenteric artery occlusion, and gut permeability was measured by the mucosal-to-serosal passage of fluoresceine isothiocyanate-dextran (4.3 kDa) (FD4) across the everted sacs of ileum. Intestinal mucosal hydrophobicity showed a gradual increase from the duodenum to the end of the ileum and remained at high level in the cecum, colon, and rectum. Both N-acetyl cysteine treatment and ischemia caused a dose-dependent decrease in mucosal hydrophobicity, which significantly correlated increased gut permeability. Mucosal hydrophobicity of the intestine can be reproducibly measured, and decreases in mucosal hydrophobicity closely correlate with increased gut permeability. These results suggest that mucosal hydrophobicity can be a reliable method of measuring the barrier function of the unstirred mucus layer and a useful parameter in evaluating the pathogenesis of gut barrier dysfunction.

N-acetylcysteine, a novel treatment for Helicobacter pylori infection

N-Acetylcysteine (NAC), being both a mucolytic agent and a thiol-containing antioxidant, may affect the establishment and maintenance of H. pylori infection within the gastric mucus layer and mucosa. Agar and broth dilution susceptibility tests determined the MIC of H. pylori strain SSI to NAC. H. pylori load in SSI strain-infected C57BL mice was determined as colony forming units per gram of gastric tissue. Gastritis assessment was scored and gastric surface hydrophobicity was determined by contact angle measurement. MICs of NAC were 5 to 10 and 10 to 15 mg/ml using the agar dilution and broth dilution methods, respectively. NAC (120 mg per day for 14 days) reduced the H. pylori load in mice by almost 1 log compared with sham treatment. Pretreatment with NAC (40 mg/day) also significantly reduced the H. pylori load but did not prevent H. pylori colonization. Both H. pylori infection and NAC reduced the surface hydrophobicity of murine gastric mucosa. No significant differences were observed in the gastritis scores of H. felis- or H. pylori-infected mice receiving either NAC or sham treatments. This study demonstrates that NAC inhibits the growth of H. pylori in both agar and broth susceptibility tests and in H. pylori-infected mice. NAC did not alter the severity of H. pylori- or H. felis-induced gastritis.

Meta-analysis: the relationship between Helicobacter pylori infection and gastro-oesophageal reflux disease

BACKGROUND

The relationship between Helicobacter pylori infection and its treatment and gastro-oesophageal reflux disease (GERD) is controversial.

AIMS

To establish if H. pylori infection is associated with the presence of GERD and if anti-H. pylori treatment leads to de novo GERD or rebound/exacerbation of GERD.

METHODS

A search of MEDLINE and EMBASE databases was made. Pooled odds ratios (OR) were calculated for de novo GERD and rebound/exacerbated GERD after anti-H. pylori therapy in case-control studies and in therapeutic trials.

RESULTS

Fourteen case-control studies and 10 clinical trials were included. Among case-control studies, pooled OR for the association between H. pylori negative status and GERD was 1.34 [95% confidence interval (CI) 1.15-1.55]. Among therapeutic trials, pooled OR for the association anti-H. pylori therapy - GERD was 2.54 (95% CI 1.92-3.37). The OR for de novo GERD was 3.25 (95% CI 2.09-5.33), and for rebound/exacerbated GERD was 2.39 (95% CI 1.75-3.34). Associations were higher among Asian studies than among North American and European studies.

CONCLUSIONS

This meta-analysis shows significant association between absence of H. pylori infection and GERD symptoms, and a positive association between anti-H. pylori therapy and occurrence of both de novo and rebound/exacerbated GERD. The significance of these associations appears to have been inflated by the effect of single trials and by geographical variations.

Normalization of phospholipids concentration of the gastric mucosa was observed in patients with peptic ulcer after eradication of Helicobacter pylori

BACKGROUND

Phospholipids concentration in the gastric mucosa decreased in patients with Helicobacter pylori infection. The aim of this study is to examine the effects of eradication of H. pylori on decreasing the phospholipids concentration in the gastric mucosa in patients with gastric or duodenal ulcer.

MATERIALS AND METHODS

Phospholipids (phosphatidylcholine, phosphatidylethanolamine, and sphingonomyeline) were measured in biopsy specimens from the antrum and corpus using thin-layer chromatography. In H. pylori positive patients with gastric ulcer (n = 26) and duodenal ulcer (n = 13), and H. pylori negative controls (n = 20), the biopsy specimens were obtained before and 3 months after eradication. Eradication was performed using lansoprazole, amoxycillin, and clarithromycin.

RESULTS

Compared with the H. pylori negative control group, the concentrations of phosphatidylcholine and phosphatidylethanolamine decreased significantly in the gastric ulcer group in both antrum and corpus mucosa, and in the duodenal ulcer group in antrum mucosa. This decrease returned to the control level after eradication.

CONCLUSIONS

This study demonstrates that the eradication of H. pylori in patients with peptic ulcer normalized the decrease of phosphatidylcholine and phosphatidylethanolamine in the gastric mucosa.

Expression of mucosal cyto-chemokine mRNAs in patients with Helicobacter pylori infection

BACKGROUND

Helicobacter pylori-induced destruction of the gastroduodenal mucosal barrier is initiated with mucosal infiltration of inflammatory cells. Cytokines and chemokines have been suggested to play important roles in the migration and activation of these inflammatory cells into the mucosa. The present study aimed to investigate expression rates of cyto-chemokine mRNAs using gastric mucosal biopsy specimens.

METHODS

In 98 patients infected with Helicobacter pylori, mucosal mRNA expression rates of cytokines (IL-1 beta, IL-6, and IL-10), C-C chemokines (macrophage inflammatory protein 1 alpha (MIP-1 alpha), and macrophage inflammatory protein 1 beta (MIP-1 beta), monocyte chemotactic and activating factor (MCAF), regulated on activation, normal T cell expressed and presumably secreted (RANTES)) and C-X-C chemokines (IL-8 and growth regulated a (GRO-alpha)) were examined using reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

The expression rates of mRNA for IL-8, GRO-alpha, MIP-1 alpha and RANTES were significantly more increased in H. pylori-positive patients than in H. pylori-negative patients. However, the expressions of IL-1 beta, IL-6 and IL-10 mRNA were statistically not different between two groups. After eradication of H. pylori, expressions of mRNA for three cytokines (IL-1 beta, IL-6 and IL-10), four C-C chemokines (MIP-1 alpha, MIP-1 beta, MCAF and RANTES) and two C-X-C chemokines (IL-8 and GRO-alpha) were significantly decreased.

CONCLUSION

These results suggest that C-X-C chemokines and some C-C chemokines play important roles in H. pylori-associated peptic ulcer diseases.

Effect of Helicobacter pylori eradication on gastric mucosal phospholipid content and its fatty acid composition

BACKGROUND AND AIMS

Whether Helicobacter pylori eradication alters gastric mucosal phospholipid contents and their fatty acid composition remains unclear. The aim of the present study was to clarify the effect of H. pylori eradication on gastric mucosal phosphatidylcholine (PC) content and its fatty acid composition.

METHODS

Endoscopic biopsy specimens were taken from the antrum and body of each of 19 asymtomatic male volunteers for detection of H. pylori, histopathological assessment of gastritis, phospholipid determination and fatty acid analysis. All the subjects with H. pylori infection were treated with eradication therapy. Endoscopy and tissue sampling were repeated again 1 and 6 months after all treatment.

RESULTS

In eight subjects, H. pylori infection was evident and was successfully eradicated. Pretreatment degrees of lymphocytes and plasma cells (inflammation) and polymorphonuclear neutrophils (activity) were greater in H. pylori-positive subjects compared with H. pylori-negative subjects (P<0.001), whereas the degree of inflammation decreased (P<0.001), and neutrophils had completely disappeared at 6 months after eradication. Moreover, the gastric mucosal PC contents at the antrum and body were unchanged within 1 month after cessation of treatment, but increased at 6 months after eradication (P<0.05). At 6 months after cessation of treatment, H. pylori-eradicated subjects had an increase (+30% at antrum, +18% at body) in linoleic acid composition and a decrease (-37%, -43%) in arachidonic acid composition of PC at the antrum and body, respectively.

CONCLUSIONS

These findings suggest that H. pylori eradication reduces the production of various eicosanoids, resulting in the normalization of gastric mucosal PC content and its fatty acid composition, which may consequently cause the gastric mucosal hydrophobicity to be normalized.

Emergence of diverse Helicobacter species in the pathogenesis of gastric and enterohepatic diseases

Since Helicobacter pylori was first cultivated from human gastric biopsy specimens in 1982, it has become apparent that many related species can often be found colonizing the mucosal surfaces of humans and other animals. These other Helicobacter species can be broadly grouped according to whether they colonize the gastric or enterohepatic niche. Gastric Helicobacter species are widely distributed in mammalian hosts and are often nearly universally prevalent. In many cases they cause an inflammatory response resembling that seen with H. pylori in humans. Although usually not pathogenic in their natural host, these organisms serve as models of human disease. Enterohepatic Helicobacter species are an equally diverse group of organisms that have been identified in the intestinal tract and the liver of humans, other mammals, and birds. In many cases they have been linked with inflammation or malignant transformation in immunocompetent hosts and with more severe clinical disease in immunocompromised humans and animals. The purpose of this review is to describe these other Helicobacter species, characterize their role in the pathogenesis of gastrointestinal and enterohepatic disease, and discuss their implications for our understanding of H. pylori infection in humans.

Evidence for surfactant contributing to the gastric mucosal barrier of the horse

This study was undertaken to determine the hydrophobicity of the luminal surface of the equine stomach and to elucidate the ultrastructure of the lining imparting that property. Gastric and duodenal mucosal samples from 5 horses were collected immediately after euthanasia and subjected to surface contact angle measurement using a goniometer. Gastric mucosal samples from 4 horses and a foal were examined by electron microscopy following a fixation procedure known to preserve phospholipids and oligolamellar structures. Contact angles for the equine gastric glandular mucosal surface (mean +/- s.e. 78.0 +/- 11.0 degrees) were greater than for the duodenum (33.4 +/- 8.7 degrees), (P = 0.003). The contact angles for gastric squamous tissue (50.4 +/- 4.5 degrees) tended to be greater than for duodenum (P = 0.15). Electron microscopy revealed the existence of surfactant as abundant osmiophilic phospholipid material within both squamous and glandular gastric mucosae. These results indicate the hydrophobic nature of the equine gastric mucosae. We propose that the water-repellent nature of the stomach contributes to the 'gastric mucosal barrier' and is imparted by surface-active phospholipid adsorbed to the surface. Phospholipids may also be utilised as a physical barrier to back-diffusion of acid by lining intracellular canaliculi and oxyntic ducts where other defence mechanisms are absent.

Effect of bisphosphonates on surface hydrophobicity and phosphatidylcholine concentration of rodent gastric mucosa

Bisphosphonates are a family of chemically related zwitterionic molecules that are used clinically to retard bone resorption in individuals with osteoporosis and associated skeletal diseases. Inflammation and ulceration of the upper gastrointestinal tract by a mechanism that relates to a topical irritant action is associated with the consumption of some bisphosphonates. In the present study, we investigated the effects of three bisphosphonate molecules, pamidronate, alendronate, and risedronate on the surface hydrophobicity and phosphatidylcholine (PC) concentration of the antral mucosa. We also examined how these surface changes related to mucosal injury in an established rat model, in which the test compounds were administered in combination with indomethacin. We initially determined that a combination of pamidronate (300 mg/kg) and indomethacin (40 mg/kg) induced a significant reduction in mucosal surface hydrophobicity and macroscopic lesion formation by 15 min and mucosal PC concentration by 30 min, with the magnitude of these changes increasing over the 4-hr study period. An equivalent dose of alendronate or risedronate in combination with indomethacin produced modest or no macroscopic injury, respectively, to the antral mucosa over the 4-hr study, although the bisphosphonates clearly induced surface injury and some glandular necrosis when examined at the light microscopic level. These bisphosphonates also induced modest decreases in antral surface hydrophobicity and mucosal PC concentration that appeared to be related to their injurious potential. In conclusion, the variable toxicity of bisphosphonates to the antral mucosa appears to be associated with their ability to compromise the surface hydrophobic phospholipid barrier of the tissue, with pamidronate > > > alendronate > risedronate. This bisphosphonate effect on the surface barrier may trigger the development of mucosal injury and possible ulceration.

A comprehensive review of the natural history of Helicobacter pylori infection in children

Across populations of children, Helicobacter pylori prevalence ranges from under 10% to over 80%. Low prevalence occurs in the U.S., Canada, and northern and western Europe; high prevalence occurs in India, Africa, Latin America, and eastern Europe. Risk factors include socioeconomic status, household crowding, ethnicity, migration from high prevalence regions, and infection status of family members. H. pylori infection is not associated with specific symptoms in children; however, it is consistently associated with antral gastritis, although its clinical significance is unclear. Duodenal ulcers associated with H. pylori are seldom seen in children under 10 years of age. H. pylori-infected children demonstrate a chronic, macrophagic, and monocytic inflammatory cell infiltrate and a lack of neutrophils, as compared with the response observed in adults. The effect of H. pylori infection on acid secretion in children remains poorly defined. The events that occur during H. pylori colonization in children should be studied more thoroughly and should include urease activity, motility, chemotaxis, adherence, and downregulation of the host response. The importance of virulence determinants described as relevant for disease during H. pylori infection has not been extensively studied in children. Highly sensitive and specific methods for the detection of H. pylori in children are needed, especially in younger pediatric populations in which colonization is in its early phases. Criteria for the use of eradication treatment in H. pylori-infected children need to be established. Multicenter pediatric studies should focus on the identification of risk factors, which can be used as prognostic indicators for the development of gastroduodenal disease later in life.

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.

Phospholipid association reduces the gastric mucosal toxicity of aspirin in human subjects

OBJECTIVE

In previous studies on rats, we have shown that aspirin (ASA)-induced injury to the gastric mucosa is markedly reduced or completely abolished if ASA is chemically associated with the phospholipid, phosphatidylcholine (PC). We have also shown that the protective effect of PC does not influence the ability of ASA to inhibit mucosal cyclooxygenase (COX) activity in the stomach and other tissues. We therefore sought to assess the effect of PC-associated ASA (ASA/PC) on the gastric mucosa of normal volunteers and to compare the results with the use of ASA alone.

METHODS

Sixteen normal healthy subjects were administered ASA or ASA/PC in a randomized, double-blind, crossover study. The subjects received ASA in a dose of 650 mg three times a day for 3 days or an equivalent dose of ASA chemically associated with PC. Endoscopy was performed at baseline and again on the morning of day 4, after the subjects had taken the final dose of the test drug. On both occasions, antral biopsy specimens were obtained for the assessment of mucosal COX activity and prostaglandin concentration.

RESULTS

The number (mean +/- SD) of gastric erosions seen with the ASA/PC formulation was significantly less than when ASA was used alone (8.7 +/- 10.7 vs 2.9 +/- 4.3; p < 0.025). A similar trend was seen in the duodenum but the difference was statistically not significant. The antral mucosal COX activity, as well as the level of prostaglandin 6-keto PGF1alpha, were reduced significantly (80-88%) and to a similar extent by both ASA and ASA/PC.

CONCLUSIONS

The present study shows that acute aspirin-induced damage to the gastric mucosa can be reduced by chemically associating ASA with PC. The mechanism of mucosal protection provided by this compound is not related to any alteration in the ability of ASA to inhibit mucosal COX activity. We believe this protection is attributable to the maintenance of the defensive hydrophobic barrier of the gastric mucosa.

Effect of ranitidine bismuth citrate on the phospholipase A2 activity of Naja naja venom and Helicobacter pylori: a biochemical analysis

BACKGROUND

Helicobacter pylori has become recognized as a fundamental pathogen in the development of gastritis and peptic ulcer disease. Bismuth compounds in combination with antibiotics are widely used to treat H. pylori associated peptic ulcer disease.

METHODS

In this study we measured and analysed the inhibitory effect of ranitidine bismuth citrate (RBC, Pylorid, Tritec) on the activity and kinetics of phospholipase A2 (PLA2) (E.C.3.1.1.4) of commercial cobra (Naja naja) venom and H. pylori (French press lysates) using L-alpha-dipalmitoyl-(2[1-14C]palmitoyl)-phosphatidylcholine as substrate.

RESULTS

Our data suggest that RBC might exert a dose-dependent uncompetitive inhibition on PLA2 activity of both H. pylori and Naja naja venom. the inhibitory effect of RBC on the PLA2 activity cannot be abolished by the optimal concentration of calcium (10 mM), indicating its mechanism to be unrelated to the displacement of calcium from the activation site of the enzyme.

CONCLUSION

Our results suggest that one of the mechanisms by which bismuth compounds are therapeutically effective in the treatment of H. pylori associated gastritis is by inhibiting the activity of the degradative PLA2 enzyme secreted by H. pylori. As a consequence of the inhibitory action of RBC on PLA2 of the bacteria, the extracellular and/or intracellular phospholipid components of the gastric mucosal barrier are preserved.

Identification of two genes, cpsX and cpsY, with putative regulatory function on capsule expression in group B streptococci

Two divergently transcribed open reading frames: cpsX and cpsY separated by a common regulatory region was identified upstream of the cpsA-D genes involved in polysaccharide capsule biosynthesis in group B streptococci (GBS). We suggest that these genes are involved in the regulation of capsule expression in GBS, since the CpsX protein shares sequence similarities with LytR of Bacillus subtilis, an attenuator of transcription while CpsY has similarity to a wide variety of members of the LysR family of transcriptional regulators. No deletions, insertions, DNA rearrangements, or apparent differences were discovered in the postulated regulatory genes when the gene region was compared in GBS with different capsule phenotypes. Thus, other yet unidentified gene loci may control capsule phase variation in GBS.

Antibody-secreting cells in the stomachs of symptomatic and asymptomatic Helicobacter pylori-infected subjects

In this study we analyzed whether infection with Helicobacter pylori gives rise to specific B-cell responses against a number of putative virulence factors of H. pylori, e.g., urease, flagellin, and different bacterial surface antigens, locally in the gastric mucosa. This was studied in antrum and corpus biopsies collected from 11 H. pylori-infected patients with duodenal ulcers, 11 asymptomatic H. pylori carriers, and 13 noninfected, healthy controls. Mononuclear cells were isolated from the biopsies and assayed for frequencies of total and H. pylori-specific antibody-secreting cells (ASCs) by means of the enzyme-linked immunospot technique. The H. pylori-infected subjects had remarkably higher frequencies of total immunoglobulin A (IgA)- and IgM-secreting cells than the noninfected subjects, while the frequencies of IgG-secreting cells were virtually the same in the different groups. In addition, most of the infected subjects had IgA ASCs reacting with H. pylori membrane proteins, flagellin, and urease, while none of the noninfected subjects had any detectable H. pylori-reactive ASCs. Furthermore, half of the infected subjects also had ASCs reacting with a Helicobacter-specific 26-kDa protein, while only a few of them had ASCs reacting with neutrophil-activating protein, the neuraminyllactose-binding hemagglutinin HpaA, or lipopolysaccharides purified from different H. pylori strains. The frequencies of H. pylori-specific ASCs in the antrum and corpus were almost identical, and no differences in either antigen specificity or magnitude of the B-cell response in the stomach could be detected between the ulcer patients and the asymptomatic H. pylori carriers. This study demonstrates that H. pylori infection induces strong antibody responses in the human gastric mucosa, both in asymptomatic carriers and in duodenal ulcer patients. However, the outcome of infection could not be explained by differences in the local B-cell response to any of the antigens used in this study.

Effect of Helicobacter pylori infection on gastric mucosal phospholipid contents and their fatty acid composition

To investigate the effect of Helicobacter pylori infection on the 'gastric mucosal barrier', phospholipid contents and the fatty acid composition of endoscopic biopsy specimens of the gastric mucosa were analysed in healthy volunteers with and without H. pylori infection. The gastric corporeal phosphatidylcholine (PC) content of H. pylori-positive healthy volunteers was less than that of H. pylori-negative healthy volunteers (P < 0.05). Moreover, H. pylori-positive healthy volunteers had a decrease in linoleic acid composition (P < 0.0001) and an increase in arachidonic acid composition (P < 0.0001) and in the arachidonic acid/linoleic acid ratio (P < 0.0001) of antral and corporeal PC compared with H. pylori-negative healthy volunteers. These findings suggest that H. pylori infection enhances production of various eicosanoids, resulting in changes in the gastric mucosal phospholipid contents and their fatty acid composition, that may consequently cause the gastric mucosal barrier to be weakened.

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.

Identification of neutral and acidic sphingomyelinases in Helicobacter pylori

We demonstrated for the first time the presence of sphingomyelinase (SMase) in Helicobacter pylori. Activation of SMase has been implicated as the cause of elevation of cellular ceramide levels and consequently of apoptosis. The data indicate that there are two classes of SMase, defined by their optimal pHs and cellular locations, existing in H. pylori. One is an Mg(2+)-dependent membrane-bound enzyme with an optimal activity at pH 7, and the other is an Mg(2+)-independent cytosolic enzyme with an optimal activity at pH 5. Bisalumin, a bismuth salt, was found to inhibit the activities of both forms of SMase regardless of the presence of Mg2+. By Western blot analysis, the membrane-bound SMases of H. pylori and Bacillus cereus were shown to be antigenically related and to have a similar denatured molecular mass of 28 kDa.

Clarification of the link between polyunsaturated fatty acids and Helicobacter pylori-associated duodenal ulcer disease: a dietary intervention study

Epidemiological evidence has suggested that the declining prevalence of duodenal ulcer disease may be attributable to rising consumption of polyunsaturated fatty acids, a hypothesis supported by in vitro evidence of toxicity of such substances to Helicobacter pylori. The objective of the present study was to establish whether this association is causal. Forty patients with proven infection with H. pylori and endoscopic evidence of past or present duodenal ulcer disease were randomized to receive either polyunsaturated fatty acids (PUFA group), in the form of capsules and margarine, or a placebo (control). Both groups received concurrent H2 antagonist therapy. Efficacy of therapy was determined endoscopically by assessment of ulcer healing while H. pylori status was determined by antral biopsy, urease (EC 3.5.1.5) culture and histological assessment of the severity of H. pylori infection. Antral levels of prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) were quantified. Compliance was monitored. Before treatment, both groups were comparable for severity of H. pylori infection, smoking status and levels of LTB4 and PGE2. Despite a significant difference in consumption of linoleic acid (19.9 (SE 1.6) g for PUFA group v. 6.7 (SE 0.8) g for controls (P < 0.01) and linolenic acid (2.6 (SE 0.2) g v. 0.6 (SE 0.03) g (P < 0.01) there was no significant change in either the severity of H. pylori infection or prostaglandin levels in either group at 6 weeks. Consumption of a considerable amount of PUFA does not inhibit the colonization of the stomach by H. pylori nor does this alter the inflammatory changes characteristic of H. pylori gastritis. We conclude that the association between duodenal ulceration and a low level of dietary PUFA is likely to be spurious, probably reflecting the effect of confounding factors such as affluence, social class or smoking.

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.

Helicobacter colonization of biopsy specimens cultured in vitro is dependent on both mucosal type and bacterial strain

BACKGROUND

Colonization by Helicobacter pylori is strictly tissue-specific. We have previously reported on an in vitro adhesion model for pig and human gastric mucosa, in which biopsy specimens were successfully infected and cultured for 72h. The aim of this study was to compare H. pylori colonization of different mucosae and by different Helicobacter strains.

METHODS

Specimens from pig, rabbit, and rat antrum, pig urinary bladder, and pig duodenum were inoculated with two H. pylori strains and one H. mustelae strain. Four additional strains, including one mutant lacking flagella, were compared on pig antral specimens.

RESULTS

The viability of all mucosae was comparable at 48h of culture. The percentage adhering bacteria increased with time in all mucosae, reaching 17%, 11%, and 2% in pig, rabbit and rat antral mucosa, 11% in pig bladder, and 3% in duodenum at 48h. The type of H. pylori strain was a strong determinant for adhesion in pig antrum. Strain SVA40 had the highest adhesion; the mutant lacking flagella colonized very poorly. H. mustelae adhered to all types of mucosae in a more unspecific manner.

CONCLUSIONS

On the basis of tissue viability, bacterial colonization, and adhesion, pig antral mucosa is clearly superior. H. pylori strains differ in their ability to adhere to and colonize cultured mucosa.

Pathogenic mechanisms

Research is asking how H. pylori causes diseases, and also why the same bacteria produces different conditions in different persons. The process involves bacterial factors and the host's response. Some bacterial factors such as urease are produced by all strains of H. pylori. This enzyme may damage the gastric epithelium by practically releasing ammonia. Other bacterial factors such as vacuolating toxin are only produced by some strains, and these strains are more likely to cause ulcers or cancer. The host's response has been studied by physiologists, immunologists, and histologists, but the separation of systems is artificial. For example, physiologists find that H. pylori stops gastric D-cells from expressing somatostatin normally, which impairs reflex inhibition of acid secretion, but the D-cell malfunction is probably due to inflammatory factors. In H. pylori gastritis, the gastric epithelial cells behave like immunocytes and express class II molecules and cytokines such as interleukin-8. The patient's histological response to H. pylori is quite closely related to the disease outcome. Patients who respond by developing gastric atrophy are more likely to get gastric ulcers or stomach cancer, but patients whose gastric corpus remains healthy tend to secrete more acid and develop duodenal ulcers, particularly if they have gastric metaplasia in their duodenum. Studies of disease mechanisms provide a valuable insight into the development of these common diseases, and may enable us to identify at-risk groups who particularly merit eradication therapy.

Lipids of human gastric mucosa: effect of Helicobacter pylori infection and nonalcoholic cirrhosis

BACKGROUND/AIMS

Gastric mucosa phospholipids play an important protective role against exogenous and endogenous toxic agents. Recently, we described a significant alteration of phospholipid profile in patients with chronic atrophic gastritis without Helicobacter pylori infection. The aim of the present study was to assess the phospholipid composition of gastric biopsy specimens in 41 subjects with chronic gastritis in relation to H. pylori infection (no. 26) and nonalcoholic cirrhosis (no. 18).

METHODS

Phospholipids were extracted from homogenate mucosal samples using Folch's method, purified, and separated by thin-layer chromatography, while bound fatty acids were analyzed by gas liquid chromatography.

RESULTS

The amounts of five gastric phospholipid classes, their rank order, and percent distribution of the principal ones (phosphatidylcholine [PC] 58%, phosphatidylethanolamine [PE] 26%, and phosphatidylinositol 11% vs. values of 49, 19, and 14, respectively, in the earlier study) were confirmed in chronic gastritis without H. pylori infection. H. pylori infection induced a dramatic reduction (about 30%) in the absolute amount of total phospholipids (24.2 micrograms/mg protein versus 35.1 of the H. pylori-negative group; P < 0.01), PC and PE being the most affected (-36% and -26%, respectively), while bound fatty acids remained unchanged. There was no difference in cirrhotic vs. noncirrhotic subjects.

CONCLUSIONS

(1) The development of gastritis is characterized by an alteration of the lipid mucosal pattern that can change with the different etiologies, the most dramatic variations being observed in the presence of H. pylori infection; and (2) cirrhosis does not affect further the alteration in the phospholipid profile of the antral mucosa caused by chronic gastritis.

Gastric mucosal defensive factors: the therapeutic strategy

There are several interesting approaches to augmenting defence or repair mechanisms that can be used already or may find a place in therapy for ulcer disease. Factors such as epidermal growth factor and basic fibroblast growth factor show potential. Alternative strategies might be to stimulate mucosal blood flow with agents that release nitric oxide (NO), or to scavenge free radicals in the inflamed or ischaemic mucosa. If such approaches are to find a role in therapy, it is likely that it will be restricted: perhaps for the treatment of refractory ulcers, or for prophylaxis of stress ulceration. This is because most ulcers in future are likely to be healed with tolerable and high efficacy acid-inhibiting drugs then have their recurrence prevented by regimens that eradicate Helicobacter pylori. The most important current indication for concentrating on enhancing mucosal defences is for managing non-steroidal anti-inflammatory drug (NSAID)-induced ulcers. There is no clear advantage in using a defence-enhancing agent (rather than an acid suppressant) to heal an NSAID ulcer if the NSAID can be stopped. The main value of prostaglandins is for prophylaxis of NSAID ulcers in those patients who need ongoing treatment with NSAID. For cost-benefit reasons, prostaglandins should probably be used mainly for those at high risk of NSAID complications, and there has been progress in identifying these. Another interesting approach is aimed at clarifying mechanisms of gastric adaptation to NSAID, so that we might be able to design drugs and dosing regimens to maximize this phenomenon.

Effect of ammonium ion on the hydrophobic and barrier properties of the gastric mucus gel layer: implications on the role of ammonium in H. pylori-induced gastritis

Infection with the bacterium Helicobacter pylori is associated with both the development of gastritis and an attenuation in the hydrophobic properties of the stomach. In order to better understand the effect of ammonium, one of the major products of H. pylori urease on these properties, a series of in vivo and in vitro experiments was performed. In the in vivo studies rats were intragastrically administered NH4Cl alone and in combination with the mucolytic agent, Muco-Mist, in various dosing strategies and concentrations. It was determined that the intragastric administration of four consecutive doses of a NH4Cl/Muco-Mist mixture (20 mmol/L/5%) was capable of converting the stomach from a hydrophobic to hydrophilic state as determined by contact angle analysis. Further, the treated rats became more susceptible to the injurious effect of luminal acid as determined by measuring the haemoglobin concentration of a collected gastric perfusate. In the in vitro studies it was determined that exposure of the hydrophobic surface of a synthetic mucus gel layer to increasing concentrations of NH4Cl (0-20 mmol/L) resulted in a rapid transition to a hydrophilic state and an associated increase in the flux of H+ across its surface. Helicobacter pylori may induce an attenuation in both mucosal hydrophobicity and barrier properties by producing high concentrations of NH4+ in the mucus gel layer. The molecular mechanism of this action may be related to the chemical similarities of NH4+ and choline-based phospholipids which contribute to the stomach's hydrophobic surface.

Demonstration of a phospholipid-rich zone in the human gastric epithelium damaged by Helicobacter pylori

BACKGROUND

Recently, a hydrophobic layer has been shown by the contact angle method in human gastric biopsy specimens. The aim of this study was to show the existence of a phospholipid-rich layer in the human gastric epithelium and to investigate the influence of Helicobacter pylori on these structures.

METHODS

Biopsy specimens from the gastric antrum were obtained during gastroscopy from patients with normal gastric mucosa as well as from patients with H. pylori-positive gastritis for electron microscopical and histological examination. Structures reacting with a phospholipid-selective stain, iodoplatinate were analyzed by electron microscopy and electron-dispersive x-ray microanalysis.

RESULTS

Both methods revealed the morphological existence of a phospholipid-rich zone covering the human gastric epithelial layer. Reaction products could be localized within the cells, at the epithelium closely associated with the surface, and in connection with the mucus. In infected tissue, H. pylori affects iodoplatinate-reactive material within the mucous layer and material covering the epithelium.

CONCLUSIONS

The phospholipid-rich zone in the apical region of surface mucous cells is likely to represent an important factor of the gastric protective system in humans. The destruction of this hydrophobic layer may result in a reduction of hydrophobicity giving access to gastric acid.

Phospholipase activity of Helicobacter pylori and its inhibition by bismuth salts. Biochemical and biophysical studies

In this study we measured phospholipase A (PLA) and C (PLC) activity of media filtrates and French Press lysates of the gastritis-inducing bacteria Helicobacter pylori. We report here that both H. pylori lysates and filtrates contain PLA1, PLA2, and C enzymes, which readily hydrolyze a radiolabeled dipalmitoylphosphatidylcholine (DPPC) and phosphorylcholine substrates, respectively. The specific activity of both PLA and C enzymes were greatest in the 6.5-7.0 and 8.4-8.8 pH ranges, respectively. Colloidal bismuth subcitrate (CBS) induced a dose-dependent inhibition of PLA2 and C activity of both H. pylori lysates and filtrates. This inhibitory effect of CBS on PLA2 was antagonized in a dose-dependent fashion by the addition of CaCl2 to the incubation mixture, suggesting that calcium and bismuth may be competing for the same site on the enzyme. In contrast, the ability of bismuth salts to inhibit PLC activity of H. pylori lysates was not antagonized by CaCl2. Employing a biophysical assay system for surface wettability, it was determined that H. pylori lysates had the capacity to remove a synthetic phospholipid monolayer off a glass in a dose-dependent fashion. This ability of the bacterial lysates to catalyze the transformation of a hydrophobic surface to a wettable state was significantly attenuated in the presence of bismuth salts. Our experimental results are, therefore, consistent with the possibility that H. pylori colonization compromises the stomach's barrier to acid by eroding a phospholipid lining, possibly a monolayer, on the surface of the gastric mucus gel and that this process is blocked in response to bismuth therapy.