Physiology and pharmacology of the parietal cell

Clinical evaluation of twenty cases of heterotopic gastric mucosa of upper esophagus during five-year observation, using gastroscopy in combination with histopathological and microbiological analysis of biopsies

Aim of the study

Heterotopic gastric mucosa of the upper esophagus (HGMUE) may be connected with disorders of the upper gastrointestinal tract, exacerbated by Helicobacter pylori. Furthermore, HGMUE may be the origin of malignant progression to cervical esophageal carcinoma.

Material and methods

In this work, 20 patients with diagnosed heterotopic gastric mucosa of the upper esophagus (HGMUE) were subjected to 5-year follow-up to determine the extent and structure of histopathological changes within HGMUEs, as well as HGMUE dysplasia and metaplasia, and risk of their malignant transformation. As a diagnostic tool to describe localization, form, size and surface feature of HGMUEs, endoscopy was used. At the same time, the biopsies were collected for histopathological and microbiological analysis.

Results

In examined patients, HGMUEs were associated with inflammation, chronic gastritis, hiatus hernia, duodenal bulb erosion and ulcer and infection of H. pylori. Intestinal metaplasia and low grade dysplasia were also indicated. During 5 years of observation, both the clinical and histopathological image of diagnosed HGMUEs was stable. The patients with detected presence of H. pylori were treated with triple or quadruple therapy.

These results show that HGMUEs may be associated with severe complications in the gastrointestinal tract, such as infection by H. pylori, hiatus hernia or duodenal ulcer. Although dysplasias and metaplasias found in diagnosed HGMUEs were not very numerous and relatively stable both clinically and histopathologically, at the present stage of the study we cannot exclude the possibility of HGMUE malignant transformation.

Loss of parietal cell superoxide dismutase leads to gastric oxidative stress and increased injury susceptibility in mice

Mitochondrial superoxide dismutase (SOD2) prevents accumulation of the superoxide that arises as a consequence of oxidative phosphorylation. However, SOD2 is a target of oxidative/nitrosative inactivation, and reduced SOD2 activity has been demonstrated to contribute to portal hypertensive gastropathy. We investigated the consequences of gastric parietal cell-specific SOD2 deficiency on mitochondrial function and gastric injury susceptibility. Mice expressing Cre recombinase under control of the parietal cell Atpase4b gene promoter were crossed with mice harboring loxP sequences flanking the sod2 gene (SOD2 floxed mice). Cre-positive mice and Cre-negative littermates (controls) were used in studies of SOD2 expression, parietal cell function (ATP synthesis, acid secretion, and mitochondrial enzymatic activity), increased oxidative/nitrosative stress, and gastric susceptibility to acute injury. Parietal cell SOD2 deficiency was accompanied by a 20% (P < 0.05) reduction in total gastric SOD activity and a 93% (P < 0.001) reduction in gastric SOD2 activity. In SOD2-deficient mice, mitochondrial aconitase and ATP synthase activities were impaired by 36% (P < 0.0001) and 44% (P < 0.005), respectively. Gastric tissue ATP content was reduced by 34% (P < 0.002). Basal acid secretion and peak secretagogue (histamine)-induced acid secretion were reduced by 43% (P < 0.0001) and 40% (P < 0.0005), respectively. There was a fourfold (P < 0.02) increase in gastric mucosal apoptosis and 41% (P < 0.001) greater alcohol-induced gastric damage in the parietal cell SOD2-deficient mice. Our findings indicate that loss of parietal cell SOD2 leads to mitochondrial dysfunction, resulting in perturbed energy metabolism, impaired parietal cell function, and increased gastric mucosal oxidative stress. These alterations render the gastric mucosa significantly more susceptible to acute injury.

Marked increase in proton pump inhibitors use in Australia

OBJECTIVES

To examine the trends in the prescribing of subsidized proton pump inhibitors (PPIs) and histamine receptor antagonists (H2RAs), in the Australian population from 1995 to 2006 to encourage discussion regarding appropriate clinical use. PPIs and H2RAs are the second highest drug cost to the publicly subsidized Pharmaceutical Benefits Scheme (PBS).

DESIGN

Government data on numbers of subsidized scripts, quantity and doses for PPIs and H2RAs were analysed by gender and age, dose and indication.

MAIN OUTCOME MEASURE

Drug utilisation as DDD [defined daily dose]/1000 population/day.

RESULTS

The use of combined PPIs increased by 1318%. Utilisation increased substantially after the relaxation of the subsidized indications for PPIs in 2001. Omeprazole had the largest market share but was substituted by its S-enantiomer esomeprazole after its introduction in 2002. There was considerable use in the elderly with the peak use being in those aged 80 years and over. The utilisation of H2RAs declined 72% over 12 years.

CONCLUSIONS

PPI use has increased substantially, not only due to substitution of H2RAs but to expansion in the overall market. Utilisation does not appear to be commensurate with prevalence of gastro-oesophageal reflux disease (GORD) nor with prescribing guidelines for PPIs, with significant financial costs to patients and PBS. This study encourages clinical discussion regarding quality use of these medicines.

Characterization of tissue autofluorescence in Barrett's esophagus by confocal fluorescence microscopy

High grade dysplasia and early cancer in Barrett's esophagus can be distinguished in vivo by endoscopic autofluorescence point spectroscopy and imaging from non-dysplastic Barrett's mucosa. We used confocal fluorescence microscopy for ex vivo comparison of autofluorescence in non-dysplastic and dysplastic Barrett's esophagus. Unstained frozen sections were obtained from snap-frozen Barrett's esophagus biopsy samples and scanned with confocal fluorescence microscopy (458 nm excitation; 505-550 nm [green] and > 560 nm [red] emission). Digital micrographs were taken from areas with homogenous and specific histopathology. Visual inspection and statistical analysis were used to evaluate the image datasets. Dysplastic and non-dysplastic Barrett's esophagus epithelia fluoresced mainly in the green spectrum and the main sources of autofluorescence were the cytoplasm and lamina propria. High-grade dysplasia was differentiated from non-dysplastic Barrett's esophagus by microstructural tissue changes. However, there were no specific changes in either the locations or average intensities of intrinsic green and red autofluorescence at the epithelial level that could differentiate between dysplastic and non-dysplastic Barrett's esophagus epithelia, ex vivo. Detectable differences in autofluorescence between BE and dysplasia/cancer in vivo are probably not caused by specific changes in epithelial fluorophores but are likely due to other inherent changes (e.g. mucosal thickening and increased microvascularity) attenuating autofluorescence from the collagen-rich submucosa. Furthermore, confocal fluorescence microscopy provides 'histology-like' imaging of Barrett's tissues and may offer a unique opportunity to exploit microstructural tissue changes occurring during neoplastic transformation for in vivo detection of high-grade dysplasia in Barrett's patients using newly developed confocal fluorescence microendoscopy devices.

Acid transport through gastric mucus

The gastric mucosa is frequently exposed to endogenously secreted hydrochloric acid of high acidity. Gastric mucosal defense mechanisms are arranged at different levels of the gastric mucosa and must work in unison to maintain its integrity. In this work, several mechanisms underlying gastric mucosal resistance to strong acid were investigated in anesthetized rats and mice. The main findings were as follows: Only when acid secretion occurred did the pH gradient in the mucus gel withstand back-diffusion of luminal acid (100 mM or 155 mM HCl), and keep the juxtamucosal pH (pH(jm)) neutral. Thus, with no on-going acid secretion and low luminal pH, the pH gradient was destroyed. Bicarbonate ions, produced concomitant with hydrogen ions in the parietal cells during acid secretion and transported by the blood to the surface epithelium, were carried transepithelially through a DIDS-sensitive transport. Prostaglandin-dependent bicarbonate secretion seemed to be less important in maintaining a neutral pH(jm). Removal of the loosely adherent mucus layer did not influence the maintenance of the pH(jm). Hence, only the firmly adherent mucus gel layer, approximately 80 microm thick, seemed to be important for the pH(jm). Staining of the mucus gel with a pH-sensitive dye revealed that secreted acid penetrated the mucus gel from the crypt openings toward the gastric lumen only in restricted paths (channels). One crypt opening was attached to one channel, and the channel was irreversibly formed during acid secretion. Gastric mucosal blood flow increased on application of strong luminal acid (155 mM HCl). This acid-induced hyperemia involved the inducible but not the neural isoform of nitric oxide synthase. These results suggest a novel role for iNOS in gastric mucosal protection and indicate that iNOS is constitutively expressed in the gastric mucosa.

Gastric mucosal fibrosis: a novel explanation for dyspepsia

The etiology of functional dyspepsia has not been discerned yet which has led to inadequate treatment of this disease. It remains a common disorder with expensive and yet often ineffective therapy. We propose that the pathogenesis of this disease lies in the histological and ultrastructural changes inflicted on the gastric mucosa in chronic gastritis and fibrosis. This hypothesis, if substantiated will provide for therapy which will be based on the pathogenesis of the disease and which will be cheaper and easily available to most. It will also add impetus to the early eradication of Helicobacter pylori, which would prevent chronic gastritis and hence gastric fibrosis.

The chemotherapeutic effects of H+/K+ inhibitors on Helicobacter pylori infection

Helicobacter pylori's powerful urease enzyme is essential for colonisation and adaptation to the acid milieu of the stomach. Eradication of infection with "standard triple therapy" abolishes the chronic immunological and inflammatory responses to H. pylori and, thus, cures gastritis and peptic ulcer. In vitro, proton pump inhibitors (PPI) are active against H. pylori with minimum inhibitory concentrations that compare favourably with bismuth salts. PPIs are also potent urease inhibitors, but because PPIs are also active against urease-negative mutant Helicobacter spp., it is unlikely that urease inhibition alone accounts for their anti-H. pylori activity. Early reports suggested that omeprazole monotherapy was able to eradicate H. pylori. This has not been confirmed by more comprehensive studies, which have shown that treatment with omeprazole is associated with a shift of infection from the antrum to the corpus. The explanation for this observation is unclear, but does not appear to be due to bacterial overgrowth. Raising the intragastric pH with a PPI lowers the minimum inhibitory concentration of the many antimicrobials, while decreasing the acid storage pool increases the intramucosal concentration. Dual therapy (omeprazole with either amoxycillin or clarithromycin) is a more logical and highly effective alternative to standard triple therapy, with fewer side effects and better patient compliance. However, H. pylori eradication regimens based on a PPI and two antimicrobials will be the first-line treatment for H. pylori gastritis and peptic ulcer in the future.

Carbonic anhydrase II in rat acid secreting cells: comparison of osteoclasts with gastric parietal cells and kidney intercalated cells

Location of carbonic anhydrase II, an important enzyme involved in acid production, was studied using an immunogold method on ultracryosections. Its distribution in osteoclasts was compared with that in gastric parietal cells and kidney intercalated cells of the inner stripe of outer medulla. It is shown that the distribution of carbonic anhydrase II is much similar in all of these acid producing cells: most of the enzyme is cytoplasmic and nucleoplasmic and only a small fraction of the enzyme is associated with the apical plasma membrane. It seems likely that carbonic anhydrase II has a similar role in all of these acid producing cells.

Structure and function of rat parietal cells during treatment with omeprazole, SCH 28080, SCH 32651, or ranitidine

For 2 weeks four groups of adult female rats were given daily peroral doses of 400 mumols/kg of one of the following inhibitors of gastric acid secretion: omeprazole, SCH 28080, SCH 32651, or ranitidine; additional control rats were given vehicle only. Six rats in each group were killed 2 h after the last dose and another six in each group at 48 h. Samples of the gastric corpus wall were processed for light and electron microscopy. The maximal reduction of stimulated acid secretion in parallel gastric fistula rats was 100%, 90%, 40%, and 85%, respectively. Forty-eight hours after the last dose only SCH 28080 produced significant inhibition of acid secretion. 'Vacuolation' of parietal cells was occasionally observed in paraffin sections. Such 'vacuoles', which were not found in plastic sections, probably represent dilated secretory canaliculi. A small number of lucid parietal cells--presumably in the process of desquamation--were seen in all groups of rats; their proportion was significantly higher 2 h after the last dose of ranitidine, SCH 28080, or SCH 32651 than in the controls. Forty-eight hours after the last dose the proportion of such degenerating parietal cells was about the same in all groups.