Role of acid and duodenogastroesophageal reflux in gastroesophageal reflux disease

BACKGROUND & AIMS

Acid and pepsin are known to cause esophagitis. However, the role of duodenogastroesophageal reflux (DGER) in producing esophageal mucosal injury across the spectrum of gastroesophageal reflux disease (GERD) is controversial.

METHODS

Twenty controls (13 men; mean age, 41 years), 30 patients with GERD (15 men; mean age, 41 years), and 20 patients with Barrett's esophagus (17 men; mean age, 58 years) were studied. Twenty-four-hour ambulatory acid and bilirubin measurements were obtained with Bilitec 2000 using a glass pH electrode and fiberoptic sensor.

RESULTS

Percentage times pH was < 4, bilirubin level was > or = 0.14, and fasting gastric bile acid concentrations showed a graded increase across the GERD spectrum. Esophageal exposure to both acid and DGER was the most prevalent reflux pattern (100% in patients with complicated and 89% in patients with uncomplicated Barrett's esophagus, 79% in patients with esophagitis, and 50% in patients without esophagitis). The majority (70%-91%) of DGER episodes occurred in an acidic environment (pH < 4). Linear regression analysis found a significant correlation (r = 0.73; P < 0.01) between percentage time pH was < 4 and percentage time bilirubin absorbance level was > or = 0.14.

CONCLUSIONS

Both acid and DGER show a graded increase in severity across the GERD spectrum. Acid and DGER occur simultaneously in the majority of the reflux episodes.

Gastric juice: a barrier against infectious diseases

All vertebrates produce gastric acid. Its main function is inactivation of ingested microorganisms. The majority of microbiological pathogens ingested never reaches the intestine because of the gastric barrier. Although gastric hypochlorhydria is fairly common due to atrophic gastritis, gastric surgery or use of inhibitors of gastric acid secretion, the resulting susceptibility to infection has not been studied extensively. Drug-induced blockade of acid secretion leads to gastrointestinal bacterial overgrowth; the clinical significance of this is still controversial. Gastric acidity is known to protect against non-typhoid salmonellosis and cholera and it is suspected that it protects against several parasitic diseases as giardiasis and strongyloides. There is a lack of studies focusing on the impact of the gastric acidic barrier on viral infections. Concerning prion infections only a single study has been performed, demonstrating a possible role of gastric acidity in the protection against foodborne prion disease in mice. The combination of malnutrition and hypochlorhydria may contribute to the high prevalence of gastrointestinal infections in developing countries. Further studies are needed to evaluate the clinical consequences of impaired gastric acidity with respect to susceptibility to infections.

The role of mucus in the protection of the gastroduodenal mucosa

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

The role of pepsin in acid injury to esophageal epithelium

OBJECTIVES

The development of reflux esophagitis in humans is a process resulting from esophageal exposure to refluxed gastric contents. There is no doubt that damage to the esophageal epithelium requires exposure to gastric acid; however, the role of refluxed pepsin as contributor to this damage seems to be underappreciated.

METHODS

The role of physiological concentrations of pepsin was examined in Ussing chambered rabbit esophageal epithelium and in cultured esophageal epithelial cells.

RESULTS

The results of this investigation reaffirmed the ability of pepsin to increase the rate and degree of esophageal cell and tissue damage at acidic pH, although the range of activity was limited to pH < 3.0. Moreover, the increased rate of tissue damage by acidified pepsin rapidly (within 15 min) produced a lesion that was irreversible, whereas, in a similar time frame, acid alone produced a lesion that was completely reversible. This early lesion by acidified pepsin was localized by performance of mannitol fluxes in apparently undamaged esophageal epithelium on light microscopy to the intercellular junctional complex. Further acid produced similar degrees of cell killing as acidified pepsin at pH < 3.0 in rabbit esophageal epithelial cells in suspension but not when growing on coverslips or present within intact epithelium.

CONCLUSIONS

These studies suggest that acidified pepsin plays a key role in the development of reflux esophagitis by producing an early irreversible lesion that results in an increase in paracellular permeability, which indirect evidence suggests is due to damage to the junctional complex. The irreversibility of the increase in paracellular permeability is likely to aid conversion of nonerosive to erosive damage to the epithelium by permitting luminal acid greater access to the basolateral membrane of esophageal epithelial cells, which is known to be acid permeable.

Pepsin-mediated processing of the cytoplasmic histone H2A to strong antimicrobial peptide buforin I

The intestinal epithelium forms a first line of innate host defense by secretion of proteins with antimicrobial activity against microbial infection. Despite the extensive studies on the antimicrobial host defense in many gastrointestinal tracts, little is known about the antimicrobial defense system of the stomach. The potent antimicrobial peptide buforin I, consisting of 39 aa, was isolated recently from the stomach tissue of an Asian toad, Bufo bufo gargarizans. In this study we examined the mechanism of buforin I production in toad stomach tissue. Buforin I is produced by the action of pepsin isozymes, named pepsin Ca and Cb, cleaving the Tyr39-Ala40 bond of histone H2A. Immunohistochemical analysis revealed that buforin I is present extracellularly on the mucosal surface, and unacetylated histone H2A, a precursor of buforin I, is localized in the cytoplasm of gastric gland cells. Furthermore, Western blot analysis showed that buforin I is also present in the gastric fluids, and immunoelectron microscopy detected localization of the unacetylated histone H2A in the cytoplasmic granules of gastric gland cells. The distinct subcellular distribution of the unacetylated histone H2A and the detection of the unacetylated buforin I both on the mucosal surface and in the lumen suggest that buforin I is produced from the cytoplasmic unacetylated histone H2A secreted into the gastric lumen and subsequently processed by pepsins. Our results indicate that buforin I along with pepsins in the vertebrate stomach may contribute to the innate host defense of the stomach against invading microorganisms.

Cleavage and inactivation of alpha 1-antitrypsin by metalloproteinases released from neutrophils

Human neutrophils, when stimulated with phorbol myristate acetate or fMet-Leu-Phe in the presence or absence of cytochalasin B, released metalloproteinases that catalytically inactivated the plasma serine proteinase inhibitor, alpha 1-antitrypsin. Inactivation, measured as loss of elastase inhibitory capacity, was accompanied by cleavage of a Mr 4,000 peptide from the COOH-terminus. Cleavage of alpha 1-antitrypsin by cell supernatants was inhibited by EDTA, o-phenanthroline, and DTT, but not by inhibitors of serine or thiol proteinases. Gelatinase and collagenase were separated from the medium of stimulated neutrophils. Both preparations cleaved and inactivated alpha 1-antitrypsin, with cleavage occurring close to the reactive center, at the Phe-Leu bond between positions P7 and P6. Cleavage by purified gelatinase was very slow and could account for only a minor fraction of the activity of neutrophil supernatants. The collagenase preparation was more active. However, the unusual cleavage site, and the ability of fMet-Leu-Phe-stimulated neutrophils to cleave alpha 1-antitrypsin without releasing collagenase, suggests that collagenase is not responsible for cleavage by the cells, which, by implication, is due to an as yet uncharacterized metalloenzyme. Our results demonstrate that by releasing metalloproteinases, neutrophils could proteolytically inactivate alpha 1-antitrypsin at sites of inflammation. This provides an alternative to the previously documented mechanism of inactivation by neutrophil-derived oxidants.

Experimental esophagitis in a rabbit model. Clinical relevance

Esophagitis occurs in patients with excessive acid and/or alkaline gastroesophageal reflux. This observation prompted us to develop a continuously perfused in vivo rabbit esophageal model to examine the potential for different endogenous injurious agents to cause H+ back diffusion and morphologic evidence of esophagitis. We found that HCl at physiologic pH values did not break the mucosal barrier to H+ back diffusion or cause esophagitis. Bile salts at physiologic concentrations in both an acid or alkaline perfusate broke the mucosal barrier and caused H+ back diffusion, but failed to cause a morphologic injury consistent with clinical reflux esophagitis. Instead, proteolytic enzymes, such as pepsin in an acid environment and trypsin in an alkaline environment, caused a severe hemorrhagic erosive esophagitis consistent with that seen clinically. We feel new therapeutic strategies for the treatment of reflux esophagitis should be directed at proteolytic enzymes rather than only HCl or bile salts. Finally, we showed sucralfate to be a mucosal protectant against the acid-pepsin injury.

Metalloproteinases and tissue inhibitor of metalloproteinases in mesothelial cells. Cellular differentiation influences expression

Mesothelial cells play a critical role in the remodeling process that follows serosal injury. Although mesothelial cells are known to synthesize a variety of extracellular matrix components including types I, III, and IV collagens, their potential to participate in matrix degradation has not been explored. We now report that human pleural and peritoneal mesothelial cells express interstitial collagenase, 72- and 92-kD gelatinases (type IV collagenases), and the counterregulatory tissue inhibitor of metalloproteinases (TIMP). Our initial characterization of the mesothelial cell metalloenzymes and TIMP has revealed: (a) they are likely identical to corresponding molecules secreted by other human cells; (b) they are secreted rather than stored in an intracellular pool; (c) a primary site of regulation occurs at a pretranslational level; (d) phorbol myristate acetate, via activation of protein kinase C, upregulates expression of collagenase, 92-kD gelatinase, and TIMP, but has no effect on expression of 72-kD gelatinase; and (e) lipopolysaccharide fails to upregulate the biosynthesis of either metalloproteinases or TIMP. Of particular interest is the observation that the state of cellular differentiation has a striking influence on the expression of metalloenzymes and TIMP, such that epitheloid cells display a more matrix-degradative phenotype (increased 92-kD gelatinase and decreased TIMP) than their fibroblastoid counterparts. We speculate that mesothelial cells directly participate in the extracellular matrix turnover that follows serosal injury via elaboration of metalloproteinases and TIMP. Additionally, the reactive cuboidal mesothelium which is characteristic of the early response to serosal injury may manifest a matrix-degenerative phenotype favoring normal repair rather than fibrosis.

The physiology of excystment of the metacercaria of Fasciola hepatica L

Excystment of the metacercaria ofFasciola hepaticais an active process and occurs in two stages—activation and emergence. Activation is initiated by high concentrations of carbon dioxide, reducing conditions and a temperature about 39 °C. The reducing conditions increase the rate of action of the other two stimuli. The carbon dioxide stimulus need only be applied for 5 min, but the exposure time to the reducing conditions has to be of the order of 30 min. Changes in the order of application of the stimuli carbon dioxide and redox potential have no effect.

The second phase, emergence, is triggered by bile. Metacercariae were held in an activated condition for 24 h, and when bile was added emergence took place normally.

During excystment the metacercariae exhibit a complex behaviour pattern. After activation there is an initial period of rotatory activity, but after about 20 min a quiescent phase ensues when the metacercariae contract away from the cyst wall at an imperceptible rate. This behaviour occurs in response to stimulus from a high concentration of carbon dioxide and a temperature about 39 °C. When the metacercariae are exposed to bile the second phase of activity is initiated, consisting of antero-posterior thrusting movements directed against the ventral side of the cyst wall. Within about 15 min the juvenile flukes escape through a small circular hole in the ventral surface of the cyst wall which corresponds to the ventral plug region.

A matrix effect in pectin-rich fruits hampers digestion of allergen by pepsin in vivo and in vitro

BACKGROUND

It is a general belief that a food allergen should be stable to gastric digestion. Various acidic plant polysaccharides, including pectin, are ubiquitous in fruit matrixes and can form hydrogels under low-pH conditions.

OBJECTIVE

The purpose of this study was to investigate the effect of hydrogel forming polysaccharide-rich fruit matrixes on in vivo gastric and in vitro pepsic digestion of fruit allergens.

METHODS

Fruit extract proteins (kiwi, banana, apple and cherry) and a purified major kiwi allergen Act c 2 were digested with simulated gastric fluid in accordance with the US Pharmacopeia. In vivo experiments on kiwi fruit digestion were performed on four healthy non-atopic volunteers by examining the gastric content 1 h after ingestion of kiwi fruit. The Act c 2 and kiwi proteins were detected in immunoblots using monoclonal anti-Act c 2 antibodies and rabbit polyclonal antisera.

RESULTS

Crude fruit extracts were resistant to digestion by pepsin when compared with commonly prepared extracts. In the gastric content of all volunteers, following kiwi fruit ingestion and immunoblotting, intact Act c 2 was detected with anti-Act c 2 monoclonal antibodies, while kiwi proteins of higher molecular weights were detected using rabbit polyclonal antisera. Addition of apple fruit pectin (1.5% and 3%) to the purified kiwi allergen was able to protect it from pepsin digestion in vitro.

CONCLUSION

The matrix effect in pectin-rich fruits can influence the digestibility of food proteins and thereby the process of allergic sensitization in atopic individuals.

Adaptive evolution and functional divergence of pepsin gene family

In vertebrates, a large proportion of genes is organized in gene families. Paralogous gene groups generated by gene duplication are related by homology, high degree of sequence identity and similar structural architecture of their products. Aspartic proteinases form a widely distributed protein superfamily including cathepsins, pepsins, renin and napsin. In the present study, the nucleotide sequences coding for various pepsins in 30 vertebrate species have been used to derive a gene phylogeny. Gene duplication and losses have been inferred from a reconciled tree, reconstructed by combining information from gene tree and species tree. Our findings based on the results of the relative rate ratio test and maximum likelihood analysis suggest that each round of gene duplication is characterized by adaptive evolution, although instances of evolution under positive selection have been found also long after divergence of gene families. The results of functional divergence analysis provided statistical evidence for shifted evolutionary rate after gene duplication.

The gastroduodenal mucus barrier and its role in protection against luminal pepsins: the effect of 16,16 dimethyl prostaglandin E2, carbopol-polyacrylate, sucralfate and bismuth subsalicylate

Mucus and bicarbonate secretions have been widely implicated as an important pre-epithelial protective barrier against autodigestion of the gastric mucosa by acid and pepsin. Evidence from several independent studies shows there is a continuous layer of resilient viscoelastic mucus gel adherent to the surface of the gastroduodenal mucosa. The median thickness of the adherent gastric mucus layer in humans is 180 microns, range 50-450 microns. The epithelial bicarbonate secretion permeates the unstirred matrix of mucus gel neutralizing luminal acid and establishing a pH gradient within the gel. In the duodenum, evidence supports the mucus bicarbonate barrier as a major protective mechanism against acid aggression. The adherent mucus gel, by acting as an effective 'permeability' barrier to pepsin, protects the underlying sensitive mucosa from digestion. However, pepsin slowly digests mucus gel at its luminal surface to produce soluble degraded mucin. In a rat gastric damage model in vivo, pepsin in excess digests the gastric mucus barrier sufficiently rapidly to outweigh new mucus secretion and lead to breaching of the mucus barrier with the formation of small punctate ulcers in the epithelium accompanied by mucosal haemorrhage. The mucus secretagogue 16,16 dimethyl prostaglandin E2 and the muco-adhesive carbopol-polyacrylate both fully protected the mucosa against pepsin damage by enhancing the protective properties of the mucus barrier. Sucralfate and bismuth subsalicylate were partially effective in protection against pepsin damage but this protection was mainly mediated at the level of the mucosa. In peptic ulcer disease, there is increased mucolytic (mucus degrading) activity in gastric juice and this is associated with an impaired mucin polymeric structure and a weaker mucus barrier.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspartic proteinases in fishes and aquatic invertebrates

1. The literature on molecular properties and physiological role of aspartic proteinases in fishes and aquatic invertebrates has been reviewed. 2. Pepsins have not been detected in invertebrates, and apparently cathepsin D, as well as other cathepsins, act both as digestive and lysosomal enzymes in many of these animals. The molecular properties of invertebrate cathepsin D correspond with cathepsin D in fishes and mammalians. 3. Fishes with a true stomach have pepsinogen secretion. Fish pepsins have higher pH optimum and are less stable in strong acid conditions than mammalian pepsins. They are very efficient at low temperatures, but less thermostable than mammalian pepsins. 4. Many fishes have two significantly different pepsins: Pepsin I and Pepsin II, which digest haemoglobin at a maximal rate in the pH ranges 3-4 and 2-3 respectively. Usually the pI of Pepsin I is in the range 6.5-7, whereas pI of Pepsin II is about 4. 5. Fish Pepsin I and cathepsin D have very similar molecular properties, and a hypothesis proposing that cathepsin D is the ancestor enzyme of aspartic proteinases in higher animals is presented.

Essential role of pepsin in pathogenesis of acid reflux esophagitis in rats

Pepsin, a protease activated by gastric acid, is a component of the refluxate, yet the role of pepsin in the pathogenesis of reflux esophagitis has not been well studied. In the present study, we examined the effect of pepstatin, a specific inhibitor of pepsin, on acid reflux esophagitis. Acid reflux esophagitis was induced in rats by ligating both the pylorus and the forestomach for 3 or 4 hr. Pepstatin, ecabet Na (the anti-ulcer drug), and L-glutamine were administered intragastrically after the ligation. Pepstatin or ecabet Na, given intragastrically, significantly prevented esophageal lesions, even though they did not affect basal acid secretion in pylorus-ligated rats. Pepstatin significantly inhibited pepsin activity in vivo and in vitro, while ecabet Na inhibited this activity in vitro. By contrast, L-glutamine given intragastrically aggravated the lesions in a dose-dependent manner, but even in the presence of L-glutamine the development of esophageal lesions was totally prevented by coadministration of pepstatin or ecabet Na. L-Glutamine increased the pH of gastric contents to approximately 2.0, the optimal pH for the proteolytic activity of pepsin in vitro. In addition, intragastric administration of exogenous pepsin worsened the severity of esophageal damage. These results suggest that pepstatin is highly effective against acid reflux esophagitis, without influencing acid secretion, while L-glutamine aggravated these lesions by increasing the pepsin activity by shifting the intraluminal pH to the optimal pH range for proteolytic action. It is assumed that pepsin plays a major pathogenic role in the development of acid reflux esophagitis.

Active trypsin and reflux oesophagitis: an experimental study in rats

In order to clarify the role of active trypsin, bile acids and pepsin in reflux oesophagitis, a comparable series of experiments was performed in rats before and after reflux-inducing operations. Three control procedures were used--laparotomy (n = 10), oesophageal transection and reanastamosis (n = 7) and a Roux-en-Y reconstruction (n = 9)--and seven experimental procedures in order to produce gastric, bile and pancreatic reflux (G + B + P) (n = 9), gastric and pancreatic reflux (B + B) (n = 8), bile and pancreatic reflux (B + P) (n = 10), pancreatic reflux alone (P) (n = 9), gastric reflux alone (G) (n = 8), bile reflux alone (B) (n = 9) and gastric with bile reflux (G + B) (n = 9). Macroscopic and histologically confirmed oesophagitis was produced in groups G + B + P, G + P, B + P and P. The trypsin levels were significantly elevated in these groups, compared to both the control and other experimental groups (P less than 0.01). Bile acid levels were insignificantly different between the groups. Because these experiments involved vagal transection, no oesophagitis was found in the gastric juice reflux group. This study has shown for the first time a correlation between the presence of active trypsin in the oesophagus and the occurrence of oesophagitis. It is possible that active components of duodenal juice may contribute to the development of reflux oesophagitis in man.

Pathogenetic factors in erosive gastritis

Under physiologic conditions, luminal acid and pepsin are absolute requirements in the development of erosive gastritis and ulceration. Even the injurious effects of most drugs are potentiated by acid and pepsin. Although the importance of luminal acid has long been recognized, only in the last 10 years has evidence accrued showing the detrimental effects of tissue acidosis in producing injury to the gastric mucosa. It now seems clear that by whatever means it is produced, e.g., through reduced mucosal blood flow, metabolic or respiratory acidosis, or inhibition of acid secretion with subsequent decreased "alkaline tide," tissue acidosis plays a profound role in the pathogenesis of erosive gastritis and ulceration. The gastric mucosal barrier is now recognized as the anatomic integrity of the surface epithelium, rather than as an ethereal physiologic barrier. This barrier is maintained as an intact layer under physiologic conditions by a newly described rapid repair process called restitution.

Gelatinase expression in generalized epidermolysis bullosa simplex fibroblasts

The use of gelatinase expression in dermal fibroblast cultures as a marker for generalized epidermolysis bullosa simplex (D-EBS-Köbner) has been tested. None of the 6 Köbner patients tested (from 3 families) produced reduced amounts of gelatinase compared with their healthy relatives and other control groups. This shows that a reduced production of gelatinase from dermal fibroblasts is not uniformly a marker for D-EBS-K.

Effect of Acid and Pepsin on Gene Expression in Laryngeal Fibroblasts

The aim of this study was to determine changes that momentary low pH with or without pepsin causes in gene expression in laryngeal fibroblasts. Cell cultures were established from human false vocal fold (FVF) and postcricoidal (PC) mucosae. Using a real-time polymerase chain reaction, we analyzed messenger RNA gene expression of growth factors (transforming growth factor β1, vascular endothelial growth factor, fibroblast growth factor 2), matrix metalloproteinases (MMP-1, MMP-2), and decorin in normal media, pH 4 media, and pH 5 media with and without pepsin. The FVF fibroblast gene expression differed substantially from the PC fibroblast gene expression. No significant interaction effects for acid and pepsin were found in the FVF culture, but in PC cultures we found a significant overexpression interaction effect for vascular endothelial growth factor, fibroblast growth factor 2, MMP-1, MMP-2, and decorin. These results imply that PC tissue is more sensitive than FVF tissue to the noxious effects of gastric contents. Furthermore, there appears to be a synergistic effect for acid and pepsin exposure in the posterior larynx.