Measurement of the surface hydrophobicity of human gastrointestinal mucosa

In vivo analysis of mucosal lipids reveals histological disease activity in ulcerative colitis using endoscope-coupled Raman spectroscopy

The goal of this study is to evaluate endoscopic Raman spectroscopy as a noninvasive technique to determine histological inflammatory status of colitis. Colon mucosal composition was investigated in vivo from patients with ulcerative colitis (UC) and from age- and body mass index (BMI) matched controls using endoscope-coupled Raman spectroscopy. The results were co-registered with histological assessment of inflammatory status at the same locations. Substantial decreases (50-60%) in the content of phosphotidylcholines (PCs) and total lipids were observed in inflamed colon tissue (histology grade 1, 2 and 3) compared to those from the quiescent (histology grade 0) and from the controls. No significant difference was observed in lipids or PC contents between control and grade 0, or among grades 1 - 3. The degree of lipid unsaturation increased in the inflamed tissue regardless of disease severity. The inflammation-associated alterations in lipids and PC are observed independent of BMI or the anatomical locations for data collection. Multivariate analysis using support vector machine (SVM) algorithm classified the spectra of the controls or the inactive colitis from those of inflamed tissue with a sensitivity of 83.5% and 97.1% respectively. Our results showed that mucosal lipid content is related to the microscopic disease activity, and thus could serve as a valuable spectral marker to differentiate active colitis from the quiescent.

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.

Comparative model studies of gastric toxicity of nonsteroidal anti-inflammatory drugs

A high percentage of people treated with a long-term nonsteroidal anti-inflammatory drug (NSAID) therapy suffer NSAID-induced gastrointestinal-tract-related side effects. A current hypothesis states that the side effects are related to the topical action of NSAID molecules on gastric mucus that lowers its resistance to luminal acid. The main lipids in human mucus are palmitoyloleoylphosphatidylcholine (POPC) and cholesterol (Chol). In this study, both X-ray diffraction and molecular dynamics (MD) simulation methods were employed to investigate the effects of selected NSAIDs in protonated and deprotonated states on the structural parameters of a POPC-Chol bilayer. The drugs were three commonly used NSAIDs with apparently different gastric toxicity: ketoprofen (KET), aspirin (ASP), and piroxicam (PXM). Both methods revealed that the effects of the NSAIDs on the POPC-Chol bilayer parameters were moderate and only slightly differentiated among the drugs. Much larger differences among the drugs were noticed in their interactions with interfacial water and Na(+) as well as with the polar groups of POPC and Chol, mainly via H-bonds. Of the three NSAIDs, KET interacted with POPC and water the most extensively, whereas ASP interacted with Chol and Na(+) more than did the other two. Interactions of PXM with POPC and Chol polar groups as well as with water and Na(+) were limited.

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.

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.

Effect of a Hydrophobic Phospholipid Lining of the Gastric Mucosa in Bioadhesion

PURPOSE

The role of a model hydrophobic phospholipid simulating lining of the gastric mucosa, as to adhesion of polymers with different surface functional groups and surface hydrophobicities, was evaluated using an in vitro gastric mucus model.

MATERIALS AND METHOD

Front-faced fluorescence measurement was used to determine adhesion of fluorescent polystyrene microspheres with different surface functional groups. Contact angle measurements and sticking bubble technique were used to measure relative surface hydrophobicity of the polymers.

RESULTS

Adhesion of fluorescent polystyrene microspheres using front-faced fluorescence measurement revealed the hydrophobic phospholipid lining of the in vitro gastric mucus model did not allow adhesion of microspheres with -COOH and -NH(2) functional groups, whereas it did allow adhesion of microspheres with hydrophobic attributes. In addition, in vitro adhesive force studies using diblock copolymers of polystyrene and polyacrylate showed that the in vitro adhesive force between the hydrophobic phospholipid lining of the in vitro gastric mucus model and the polymer increased when the surface hydrophobicity of the polymer increased.

CONCLUSION

The hydrophobic phospholipid acts as an adhesion barrier to hydrophilic bioadhesive polymers and polymers with surface functional groups of carboxylic acid and amine. The hydrophobic phospholipid lining of the gastric mucosa should be taken into considerations for screening and designing of a new gastric bioadhesive polymer.

Gastroduodenal mucus bicarbonate barrier: protection against acid and pepsin

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

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.

On the wettability of soft tissues in the human oral cavity

In this study, the wettability of gingival surfaces in the human oral cavity was assessed by the measurement of intra-oral water contact angles. Intra-oral water contacts angles were measured in the morning prior to tooth brushing, immediately after tooth brushing and prior to and after lunch in order to reveal the influences of toothpaste and dietary components on the wettability of the gingiva. Within a group of 10 volunteers, gingival surfaces were hydrophobic, with water contact angles ranging from 72 to 79 degrees, which is high as compared with other soft tissues in the human body. Gingival contact angles were not affected by most commercial toothpastes involved in this study, but decreased slightly to 65 degrees after brushing with a hexametaphosphate containing toothpaste. During the day, however, the hydrophobicity readily recovered and after lunch contact angles on the gingival surfaces were higher than early in the morning, now ranging from 76 to 83 degrees. It is generally known that soft tissues in the human body involved in adsorptive and exchange functions and requiring lubrication are more hydrophilic than tissues with more protective functions. This study shows that gingival surfaces classify as the most hydrophobic soft tissue in the human body, attesting to their important protective role in the oral cavity.

Lipopolysaccharide-induced gastrointestinal injury in rats: role of surface hydrophobicity and bile salts

Sepsis of gastrointestinal origin can lead to life-threatening complications in vital organs due to bacterial overgrowth and/or translocation from the lumen into the blood. In a rat model of endotoxemia, changes in surface hydrophobicity (associated with barrier integrity) of the gastrointestinal mucosa were examined. Rats were treated with Escherichia coli lipopolysaccharide (LPS), and gastric and ileal tissue were collected for determination of surface hydrophobicity by contact angle analysis. A role for bile salts in hydrophobicity changes was tested by quantifying bile salts in the lumen of both the stomach and ileum after LPS and by the administration of LPS to bile duct-ligated rats. A single intraperitoneal dose of LPS induced a dose- and time-dependent reduction in hydrophobicity of both the stomach and ileum, with the stomach showing greater sensitivity at an earlier time than the ileum. LPS also induced gastric bleeding, reflux of bile acid into the gastric lumen, and decreased levels of bile salt in the ileum. The LPS-induced reductions in surface hydrophobicity of the stomach were prevented by prior bile duct ligation. We conclude that LPS disrupts gastrointestinal barrier integrity, in part by mechanisms involving bile constituents and an attenuation in the mucosa's hydrophobic characteristics.

Epidermal growth factor increases surface hydrophobicity and resistance to acid in the rat duodenum

Epidermal growth factor (EGF) is produced in Brunner's glands and plays a role in healing and repair of duodenal ulcers. We examined the participation of zwitterionic phospholipids of mucus in the effects of EGF. Under anesthesia, groups of rats received an intraduodenal bolus of either saline or EGF. Some rats received subcutaneous indomethacin followed by EGF or EGF followed by a detergent (5% Brij 35, a nonionic detergent that solubilizes luminal phospholipids). Thirty minutes after treatment, mucosal surface hydrophobicity and phospholipid concentration in the mucus layer were measured. Matched groups of rats were challenged with 0.5 M HCl, instilled intraduodenally 30 min after treatment, and mucosal damage was assessed 1 h after acid challenge. Exogenous EGF significantly increased surface hydrophobicity and phosphatidylcholine concentration in the mucus layer. EGF treatment also reduced mucosal damage induced by acid. However, indomethacin pretreatment or detergent administration after EGF abolished both protection against acid and changes in the mucus layer. These data suggest that EGF increases duodenal resistance to luminal acid via stimulation of mucosal zwitterionic phospholipids.

Where is the evidence that cyclooxygenase inhibition is the primary cause of nonsteroidal anti-inflammatory drug (NSAID)-induced gastrointestinal injury? Topical injury revisited

In this commentary, we take a critical look at the concept that the gastrointestinal (GI) side-effects of nonsteroidal anti-inflammatory drugs (NSAIDs) are due to the ability of these drugs to inhibit cyclooxygenase-1 (COX-1) that is constitutively expressed in the GI mucosa. Indeed, development of the new "super aspirins," such as Celebrex and Vioxx, that selectively inhibit the inducible COX-2, expressed in areas of inflammation, is a direct outgrowth of this concept. We discuss evidence from both the laboratory and the clinic that appears to be inconsistent with the above concept, and cite a number of examples where the depletion of mucosal prostaglandin levels and the development of GI injury can be dissociated. Instead, we revisit the possibility that NSAID-induced GI side-effects are mostly due to the ability of these drugs to topically injure the GI mucosa. We devote the remainder of the commentary to presenting evidence from our and other laboratories that NSAIDs can directly attenuate the surface hydrophobic barrier of the GI mucosa due to their ability to bind to zwitterionic phospholipids, and that even systemically administered NSAIDs that are secreted into the bile may induce GI ulceration and/or bleeding due to phospholipid interactions and the development of topical mucosal injury.

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.

Role of intestinal surfactant-like particles as a potential reservoir of uropathogenic Escherichia coli

The binding of uropathogenic Escherichia coli is mediated at the tips of pili by the PapG adhesin, which recognizes the Galalpha(1-4)Gal disaccharide on the uroepithelial surface. These receptors have been identified unequivocally in the human and murine urinary tracts but not in intestinal epithelium, yet uropathogenic E. coli strains are commonly found in normal colonic microflora. The gastrointestinal tract from duodenum to rectum elaborates a phospholipid-rich membrane particle with surfactant-like properties. In these studies, we report that purified murine particles contain a receptor recognized by the class I PapG adhesin because: (1) PapD-PapG complexes and class I pili bound to surfactant-like particles in a solid-phase assay, whereas binding was not detected in microvillous membranes derived from the same tissues, (2) purified PapD-PapG complex bound to a glycolipid receptor detectable in lipid extracts from the particles, and (3) soluble Galalpha(1-4)Gal inhibited the adhesin by 72% from binding to surfactant-like particles. The Galalpha(1-4)Gal receptor present in the intestinal surfactant-like particle which overlies the intestinal mucosa could provide one means to establish an intestinal habitat for uropathogenic E. coli.

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.

Investigation of surface properties of some polymers by a thermodynamic and mechanical approach: possibility of predicting mucoadhesion and biocompatibility

Mucoadhesive properties of several polymers, such as sodium alginate, hydroxypropylmethyl cellulose, scleroglucan, xanthan gum, polyacrylic acid (Carbopol), and poly co-(methyl vinyl ether-maleic anhydride) (Gantrez), have been investigated by comparing a thermodynamical and a mechanical approach. Surface properties of polymers in the dry state have been studied by contact angle measurements and thermodynamical parameters derived by using different equations. This tensile adhesive strength of polymers in hydration conditions was measured by a modified DuNoy tensiometer. Comparison of the two different approaches has allowed us to conclude that thermodynamical consideration on surface energy can be used to evaluate mucoadhesive properties of materials. Data obtained with the two methods yielded a good linear correlation. Calculation of surface free energy of the considered materials also allowed a prediction of the water-polymer interface free energy: biocompatibility, defined according to the minimal interfacial free energy concept, could consequently be evaluated.

Oesophageal surfactant: evidence for a possible mucosal barrier on oesophageal epithelium

BACKGROUND

There is a growing body of evidence to indicate that the gastric mucosa is protected against the back-diffusion of acid by a physical barrier comprising surface-active phospholipid (SAPL) otherwise known as gastric surfactant on account of its similarity to pulmonary surfactant in composition and behaviour.

AIMS

To determine whether this form of mucosal protection might extend into the oesophagus to offer some degree of protection against the reflux of gastric contents.

METHODS

Oesophageal epithelium was tested for the same hydrophobicity which is characteristically imparted to gastric mucosa by SAPL. A morphological study was also performed to visualise any barrier, purposely avoiding conventional fixatives for electron microscopy which destroy hydrophobic surfaces.

RESULTS

Oesophageal epithelium in the vicinity of the cardiac sphincter was found to be appreciably hydrophobic, although not as hydrophobic as gastric mucosa. This hydrophobicity was eliminated by bile salts selected as a known 'barrier breaker' and one which reacts with any lining of SAPL. The morphological study revealed much evidence of SAPL, especially that lining epithelial cells, while its source is probably the lamellar bodies also visualised.

CONCLUSIONS

These findings indicate a physical barrier of oesophageal surfactant which could offer some degree of protection against gastro-oesophageal reflux but one which is particularly prone to attack by bile.

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.

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

Surface hydrophobicity of the gastric mucosa is reduced in peptic ulcer disease and Helicobacter pylori infection. This abnormality may be caused by H. pylori or may be an inherent defect. The aim of the present study was to clarify the relationship between H. pylori infection and mucosal hydrophobicity by examining the effect of eradication of the organism. H. pylori-positive patients with (n = 42) or without (n = 42) duodenal ulcer were randomized to receive ranitidine, bismuth, or bismuth plus antibiotics. Surface hydrophobicity of gastric mucosa was assessed by measurement of plateau-advancing contact angle. Measurements were performed at presentation, end of treatment, and 1 month later. Contact angle was unchanged after ranitidine (55 degrees vs. 56 degrees) but increased with bismuth (57 degrees-62 degrees; P < 0.05) and bismuth plus antibiotics (56 degrees-67 degrees; P < 0.0001). One month after treatment ended, contact angles in patients in whom H. pylori was not eradicated were not different from those before treatment (56 degrees vs. 56 degrees) but increased to a value similar to H. pylori-negative controls in patients in whom H. pylori was eradicated (56 degrees-69 degrees; P < 0.0001). It is concluded that reduced mucosal hydrophobicity in peptic ulcer disease is secondary to H. pylori infection and that this impaired mucosal defense provides a possible mechanism whereby H. pylori infection predisposes to acid/peptic digestion.

Gastric mucosal barrier: intergranular matrix of gastric surfactant in the mucous lining

Transmission electron microscopy of rat gastric mucosa fixed by a novel procedure designed for barriers to water-soluble solutes has shown that the intergranular matrix material of gastric mucus is oligolamellar surface-active phospholipid. It is a gastric surfactant similar to that seen on deeper mucus-free surfaces also exposed to acid.

A surface energy analysis of mucoadhesion: contact angle measurements on polycarbophil and pig intestinal mucosa in physiologically relevant fluids

The possible role of surface energy thermodynamics in mucoadhesion was investigated with Polycarbophil and pig intestinal mucosa. In separate experiments, the surface energy parameters of the substrate (mucosa) and the adhesive (polymer film) were determined by contact angle measurements on captive air/octane bubbles in three physiologically relevant test fluids (isotonic saline, artificial gastric fluid, and artificial intestinal fluid). Whereas the swollen Polycarbophil films were relatively hydrophilic as indicated by small water contact angles (22, 23, and 16 degrees), the water contact angles measured on mucosal tissue were significantly larger (61, 48, and 57 degrees). Hence, mucus was found to possess an appreciable hydrophobicity. The measured adhesive performance (force of detachment) between Polycarbophil and pig small intestinal mucosa was highest in nonbuffered saline medium, intermediate in gastric fluid, and minimal in intestinal fluid. In agreement with this trend, the mismatch in surface polarities between substrate and adhesive, calculated from the contact angle data, increased in the same order.

In vitro surface properties of the newly recognized gastric pathogen Helicobacter pylori

There appears to be a particular association between Helicobacter pylori and the gastric antrum, but the mechanisms by which the organism adheres to and colonizes the gastric mucosa are unclear. Surface hydrophobicity and surface charge mediate the adherence of other bacterial pathogens to mucosal epithelial cell surfaces. Therefore, in this study we characterized both the surface hydrophobicity and the surface charge of 10 H. pylori strains grown in broth culture. Four complementary methods were used to determine hydrophobicity: hydrophobic interaction chromatography, the salt aggregation test, comparison of bacterial adherence to polystyrene with adherence to sulfonated polystyrene, and measurement of contact angle with droplets of water. Three of the methods (salt aggregation test, adherence to polystyrene, and contact angles) indicated that each of the 10 strains expressed a relatively hydrophilic cell surface. In contrast, hydrophobic interaction chromatography determinations with both phenyl- and octyl-Sepharose suggested that the H. pylori strains were relatively hydrophobic. However, tetramethyl urea (0.4 M) did not reduce the binding of H. pylori to phenyl-Sepharose columns. DEAE-cellulose ion-exchange chromatography showed that each of the 10 strains of H. pylori had a surface which, overall, was highly negatively charged. We conclude that H. pylori expresses an overall relatively hydrophilic and negatively charged surface in vitro.

Thermodynamic effects of bile acids in the stomach

The surface thermodynamic effects of bile acids in the stomach were assessed in 48 subjects who had undergone gastric surgery for peptic ulcer disease and in 52 controls with medically healed ulcers. We derived values for surface tension of gastric mucosa from contact angle using a goniometer and measured the surface tension of gastric juice by the drop-weight method. Subjects with gastric surgery had higher median fasting bile acid concentrations than controls (1.2 vs. 0.1 mmol/L; P less than 0.0001), higher mean mucosal surface tension (51.9 vs. 47.9 mN/m; P less than 0.0001), and lower mean surface tension of gastric juice (43.2 vs. 51.7 mN/m; P less than 0.0001). Subjects who had had a Billroth II gastrectomy (n = 19) had higher bile acid concentrations (5.8 vs. 0.6 mmol/L; P less than 0.01), higher mucosal surface tension (53.7 vs. 50.3 mN/m; P less than 0.05), and lower gastric juice surface tension (41.3 vs. 47.1 mN/m; P less than 0.05) than those who had a vagotomy and drainage procedure (n = 17). Overall, intragastric bile acid concentration correlated directly with surface tension of gastric mucosa (r = 0.51, P less than 0.0001) and inversely with that of gastric juice (r = -0.60, P less than 0.0001). In conclusion, the interfacial energy barrier at the surface of the gastric mucosa is overcome in the presence of intragastric bile acids.

A physical identity for the gastric mucosal barrier

An oligolamellar lining which is probably phospholipid has been demonstrated on the gastric mucosal surface of the rat by transmission electron microscopy using fixation procedures specially developed to avoid the destruction of hydrophobic surfaces. This structure is unlikely to be an artefact since the use of two hydrophobic probes in epifluorescence microscopy gave emissions characteristic of oligolamellar phospholipid prepared in vitro. Moreover, lipid solvents almost eliminated both the fluorescence and the hydrophobicity. An oligolamellar lining was seen also on deeper structures, including oxyntic ducts and canaliculi in parietal cells, and it might offer a physical basis for the hitherto elusive gastric mucosal barrier. Parietal cells were also found to contain multilamellar bodies which, in the lung at least, represent phospholipid (surfactant) in a particularly surface-active form and one conducive to its deposition on tissue surfaces. This suggests that the parietal cell could gear the protection (surfactant) to the potential insult (acid) by secreting both together. The demonstration of a simple physical barrier preventing the stomach from digesting itself is discussed in regard to suggesting the use of certain surface-active foods which could be beneficial in preventing gastric ulcers and their recurrence after the acute phase has been treated using conventional therapies.

Surface hydrophobicity of gastric mucosa in peptic ulcer disease. Relationship to gastritis and Campylobacter pylori infection

The hydrophobicity of biopsy specimens of gastric mucosa in 228 dyspeptic subjects undergoing diagnostic endoscopy was assessed by measuring the plateau-advancing contact angle of saline drops using a goniometer. Subjects with duodenal ulcers (n = 49) and gastric ulcers (n = 17) had significantly lower mean contact angles than controls (n = 124) without ulcer (57 degrees in duodenal ulcer, 59 degrees in gastric ulcer vs. 66 degrees in controls; p less than 0.0001). There was no change in contact angle after healing with H2-receptor antagonists by comparison with pretreatment (59 degrees vs. 56 degrees for duodenal ulcer, n = 15; 57 degrees vs. 59 degrees for gastric ulcer, n = 5). Controls with gastritis had lower contact angles than those without (61 degrees, n = 50, vs. 70 degrees, n = 63; p less than 0.0001). The presence of Campylobacter pylori was associated with a significant decrease in contact angle in controls (59 degrees, n = 39, vs. 70 degrees, n = 75; p less than 0.0001).

Acid and barriers. Current research and future developments for peptic ulcer therapy

Medical therapy for peptic ulcer disease has been targeted at inhibiting acid secretion based on the belief that ulcers occur due to an imbalance between aggressive and protective factors. New antisecretory agents are unlikely to show any dramatic improvement over the success and safety of histamine H2 receptor antagonists or the recently introduced H+K+ATPase proton pump antagonist omeprazole. The development of specific muscarinic M3 and gastrin receptor antagonists will provide useful agents to suppress acid and pepsinogen secretion by alternative means and may prevent the associated hypergastrinaemia seen with anti-secretory therapy. Enhancement of mucosal defence by site protective agents will be based on a better understanding of the vascular and immune factors involved in maintaining mucosal integrity and the growth factors that regulate wound healing. Molecular techniques are likely to produce the 'model anti-ulcer' agent which will effectively inhibit acid secretion and also enhance wound healing thus providing a cure for this chronic disease.