Omeprazole, Helicobacter pylori status, and alterations in the intragastric milieu facilitating bacterial N-nitrosation

Gastritis and hypergastrinemia due to Acinetobacter lwoffii in mice

In mouse models and humans, Helicobacter pylori is associated with an increase in serum gastrin and gastrin-expressing (G) cells with a concomitant decrease in somatostatin-expressing D cells. Inflammation of the gastric mucosa can progress to metaplastic changes in the stomach and to decreased colonization by H. pylori and increased colonization by non-H. pylori organisms. In addition, about 20% of individuals with chronic gastritis are H. pylori negative, suggesting that other organisms may induce gastritis. Consistent with this hypothesis, we report here that Acinetobacter lwoffii causes the same histologic changes as does H. pylori. Gastric epithelial cells were isolated from the entire stomach by an enzymatic method for quantitation by both flow cytometry and morphometric analysis. Two months after mice were inoculated with H. pylori or A. lwoffii, the mucosal T- and B-cell numbers significantly increased. After 4 months of infection, there was a threefold increase in the number of G cells and a doubling in the number of parietal cells. A threefold decrease in the number of D cells occurred in H. pylori- and A. lwoffii-infected mice. Plasma gastrin levels increased after both H. pylori and A. lwoffii infection. Histology revealed the presence of inflammation in the gastric mucosa with both A. lwoffii and H. pylori infection. A periodic acid-Schiff stain-alcian blue stain revealed mucous gland metaplasia of the corpus. Collectively, the results demonstrate that gastritis and hypergastrinemia are not specific for H. pylori but can be induced by other gram-negative bacteria capable of infecting the mouse stomach.

Genetic or chemical hypochlorhydria is associated with inflammation that modulates parietal and G-cell populations in mice

BACKGROUND & AIMS

Reduced gastric acid predisposes the stomach to colonization by bacteria and inflammation. Therefore, we investigated how the chronic gastritis in mice made hypochlorhydric by either gastrin deficiency or omeprazole treatment modulates epithelial cell function.

METHODS

The gastric pathology of 16-week-old wild-type gastrin-expressing (G+/+) and gastrin-deficient (G-/-) mice maintained in conventional housing was compared. G-/- mice were then treated with antibiotics for 20 days. In a separate experiment, G+/+ mice were treated with omeprazole for 2 months or treated with omeprazole and antibiotics.

RESULTS

Compared with the G+/+ animals, the hypochlorhydric G-/- mice showed significant inflammation that resolved after 20 days of antibiotic treatment and correlated with a decrease in bacterial overgrowth. Elevated G- and parietal-cell numbers in the G-/- mice, quantified by flow cytometry, normalized after antibiotic treatment. G+/+ mice treated with omeprazole had increased bacteria and mucosal lymphocytes that resolved after antibiotic therapy. Quantitation of the gastric cells in these omeprazole-treated mice revealed a significant increase in G- and parietal-cell numbers. On resolution of the gastritis, a decrease in parietal and gastrin-expressing (G) cells was observed despite sustained hypochlorhydria in the presence of omeprazole.

CONCLUSIONS

Genetic or chemical hypochlorhydria predisposes the stomach to bacterial overgrowth resulting in inflammation. The specific changes in parietal and G cells correlate with the presence of inflammation and not directly with gastric acid. Thus, the normal stomach responds to inflammation by increasing the number and function of cell types that are able to maximize gastric acid output.

Helicobacter pylori infection: treatment

Current standard treatment regimens for Helicobacter pylori infection provide eradication rates 80 to 90%. These rates have been achieved with a variety of 1-week triple therapies using two antibiotics and an acid suppressant. Antibiotic resistance, which may develop during failed treatment, is becoming increasingly common and has led to studies of new regimens for primary therapy, and new strategies for salvage of failed therapy. Other regimens have been designed and tested with the aim of decreasing the cost of initial therapy or to improve compliance, but abbreviated regimens have high incidence of failure and may add to the problem of resistance. Increasing attention has been paid to the need for, and timing of, the determination of antibiotic resistance of H. pylori isolates either at the time of initial diagnosis or after treatment failure. New, simpler, and noninvasive methods are offered for follow-up to determine if eradication has been successful. Treatment regimens should be chosen based on local drug susceptibility patterns and the availability of approved therapeutic agents in each country. Established indications for testing for H. pylori and administering therapy include active or inactive peptic ulcer disease, mucosa-associated lymphoid tissue (MALT) lymphoma, as well as hyperplastic polyps, hyperplastic gastropathy, postendoscopic resection for gastric malignancy, and acute H. pylori gastritis. It is now largely accepted that noninvestigated dyspepsia is an indication for testing for and treating H. pylori, but that dyspeptic symptoms shown not to be associated with ulcer (nonulcer dyspepsia) do not now provide an indication for testing. Controversial or unresolved indications for testing and treating include planned use of chronic antisecretory therapy, planned use of nonsteroidal anti-inflammatory drugs, and use as a general approach to the prevention of gastric cancer.

Changes in gastric mucosa and luminal environment during acid-suppressive therapy: a review in depth

Acid-suppressive therapy and subsequent changes in gastric mucosa and luminal environment rank highly amongst the investigated issues in gastroenterology over the past two to three decades. Herewith, we present an overview of these intragastric changes, particularly during long-term administration of acid-suppresive medication and concurrent infection with Helicobacter pylori. Current evidence indicates that: i) Long-term acid suppression facilitates the development of fundic ECL cell hyperplasia, especially in the presence of Helicobacter pylori. No neoplastic changes directly attributable to acid suppression have so far been demonstrated in humans. ii) Acid-suppressive therapy increases the risk of enteric infections. iii) Acid-suppressive therapy does not alter fat and mineral bioavailability, but may decrease the absorption of protein-bound vitamin B12. iv) Acid suppression invariably results in intragastric overgrowth of non-Helicobacter pylori bacterial species. The concurrent infection with Helicobacter pylori may promote this bacterial overgrowth and the intragastric formation of N-nitrosamines. v) Acid-suppressive therapy alters the natural course of Helicobacter pylori gastritis, transforming the antral-predominant pattern into a body-predominant pattern, which in turn may progress to body gland atrophy. The pathophysiology of this phenomenon is currently under investigation. vi) In view of the potential adverse effects of acid suppression in the presence of Helicobacter pylori, the screen-and-treat strategy is advocated for Helicobacter pylori in subjects considered for long-term treatment.

Intragastric volatile N-nitrosamines, nitrite, pH, and Helicobacter pylori during long-term treatment with omeprazole

BACKGROUND & AIMS

This study evaluated the effect of long-term gastric acid suppressive therapy with omeprazole on intragastric levels of carcinogenic N-nitrosamines and related parameters.

METHODS

Forty-five patients on long-term omeprazole medication (mean, 35 months) and 13 healthy subjects without medication participated. Volatile N-nitrosamines were determined in gastric juice and urine. Intragastric pH, nitrite, nitrate, and H. pylori status were determined. DNA isolated from gastric biopsy specimens was analyzed for precarcinogenic alkyl-DNA adducts.

RESULTS

The intragastric pH in patients was significantly higher compared with controls (P = 0.0001). Gastric nitrite levels in patients were nonsignificantly higher. There was no difference in total levels of intragastric volatile N-nitrosamines between patients and controls, however, urinary N-nitrosodimethylamine excretion was higher in patients (P = 0.001). On omeprazole, Helicobacter pylori-positive vs. -negative patients had a nonsignificantly higher intragastric nitrite level and higher urinary N-nitrosodimethylamine excretion. No alkyl-DNA adducts could be detected in gastric epithelium.

CONCLUSIONS

Increased intragastric pH caused by long-term treatment with omeprazole does not result in increased intragastric levels of nitrite and volatile N-nitrosamines. The significantly higher urinary N-nitrosamine excretion implies the risk of increased endogenous formation of N-nitrosamines during long-term omeprazole treatment. This risk may be higher in H. pylori-positive patients.

Double gastric infection with Helicobacter pylori and non-Helicobacter pylori bacteria during acid-suppressive therapy: increase of pro-inflammatory cytokines and development of atrophic gastritis

BACKGROUND

Long-term acid suppression may accelerate the development of atrophic gastritis in Helicobacter pylori-positive subjects. The pathogenetic mechanism remains unclear.

AIM

To test the hypothesis that gastric double infection with H. pylori and non-H. pylori bacterial species-during acid suppression-may result in an enhanced inflammatory response, contributing to the development of atrophic gastritis.

PATIENTS AND METHODS

A consecutive series of patients with gastro-oesophageal reflux disease undergoing treatment with proton pump inhibitors (n=113) or histamine2-receptor antagonists (H2-RAs) (n=37), and 76 non-treated dyspeptic controls were investigated. Gastric mucosal H. pylori and non-H. pylori bacteria, histological gastritis, H. pylori serology, and circulating interleukin (IL)-1beta, IL-6, and IL-8 were examined.

RESULTS

Patients on acid suppression with either proton pump inhibitors or H2-RAs had a similar prevalence of H. pylori infection to the controls, but a higher prevalence of non-H. pylori bacteria (61% and 60% vs. 29%, P < 0.0001 and P < 0.002). Both the presence of H. pylori and non-H. pylori bacteria were independent risk factors of atrophic gastritis (antrum: relative risks (RRs), 10.1 and 5.07; corpus: RRs, 11.74 and 6.38). A simultaneous presence of H. pylori and non-H. pylori bacteria was associated with a markedly increased risk of atrophic gastritis (antrum: RR, 20.25; corpus: RR, 20.38), compatible with a synergistic effect. Furthermore, the simultaneous presence of both types of bacteria was associated with higher cytokine levels than in patients without any type of bacteria. This increase was also greater than in patients with H. pylori infection alone (P < 0.001, for both IL-1beta and IL-8).

SUMMARY AND CONCLUSIONS

H. pylori-positive patients on long-term acid inhibition displayed three features: non-H. pylori bacterial growth; increased cytokine levels; and a higher risk of atrophic gastritis. We suggest that double infection with H. pylori and non-H. pylori bacteria is a major factor in the development of atrophic gastritis during gastric acid inhibition.

Gastric mucosal morphological consequences of acid suppression: a balanced view

In the chapter, an analysis of the literature on the relationship between Helicobacter pylori, the use of proton pump inhibitors and the development of atrophic gastritis is presented, and the difficulties of classifying gastritis and the new possibilities of quantifying chronic inflammation by morphometric analysis are discussed. The issue surrounding the necessity of eradicating H. pylori in H. pylori-positive patients has still not been solved. Most studies have now accepted that proton pump inhibitors indeed accelerate the onset of atrophic gastritis in H. pylori-positive patients, but evidence against such an association was published in one recent (Scandinavian) study; conclusions from this study have, however, been challenged by several groups. Some data are available on the efficacy of H. pylori eradication with regard to the prevention of atrophy. The limited significance of the development of parietal cell protrusions and fundic gland cysts is better understood, but much less is known of the development and long-term consequence of H. pylori-induced autoimmune gastritis. Finally, recent studies in H. pylori-positive patients indicate that treatment with proton pump inhibitors may promote bacterial N-nitrosation formation. These data taken together suggest that the eradication of H. pylori may be based not only on morphological arguments, but also on bacterial alterations in the gastric milieu.

Current role of acid suppressants in Helicobacter pylori eradication therapy

Helicobacter pylori induces chronic active gastritis that may progress to atrophy. Serious clinical consequences are peptic ulcer disease and gastric malignancies. Today, treatment of the infection is an appropriate option and is strongly recommended in various clinical situations. Although many antibiotics are effective against H. pylori in vitro, few substances are suitable for use in vivo. This is because H. pylori lives in a unique environment in which several factors may affect the pharmacokinetic and pharmacodynamic properties of the anti-microbial agents. One of the most important factors is gastric acidity. This article reviews the effects of acid suppression on H. pylori and the associated gastritis, the potential mechanisms by which anti-secretory drugs such as proton pump inhibitors might enhance the activity of anti-microbials in vivo, and the results of clinical trials supporting the current view that proton pump inhibitors are a mainstay in the treatment of this infection.

Occurrence and significance of gastric colonization during acid-inhibitory therapy

There are now a wide variety of drugs available that are able profoundly to reduce the production of gastric acid. These drugs are currently widely prescribed for the treatment of peptic ulceration and gastro-oesophageal reflux disease. One of the main functions of gastric acid is to kill ingested bacteria. Colonization of the gastric lumen occurs in patients on anti-secretory medication, the degree of bacterial overgrowth depending upon the degree of elevation of the pH. There have been concerns that these bacteria may produce carcinogenic nitrosamines and increase the risk of gastric cancer, but there is at present no definitive evidence in support of this. A profound suppression of gastric acid may also facilitate the colonization of the upper small intestine, leading to deconjugation of the bile salts and malabsorption. There is some evidence that profound gastric acid suppression may decrease the number of ingested pathogens required to produce enteric disease. This chapter discusses these potential bacterial complications of therapeutic acid suppression and the evidence for them.

Alterations in intragastric nitrite and vitamin C levels during acid inhibitory therapy

Most nitrite entering the healthy acid-secreting stomach is derived from dietary nitrate. The latter is absorbed from the small intestine, 25% then being secreted by the salivary glands into the mouth. Buccal organisms subsequently convert 20% of this nitrate to nitrite. When this nitrite is swallowed, the ascorbic acid in the acidic gastric juice reduces it to nitric oxide, which is absorbed by the mucosa. In the process, the ascorbic acid is oxidized to dehydroascorbic acid. When the intragastric pH is elevated by powerful anti-secretory agents, this gastric chemistry is profoundly modified. At a neutral pH, the swallowed nitrite does not react with ascorbic acid but accumulates in the stomach. The level of nitrite in the gastric juice during treatment with anti-secretory medication is particularly high after a nitrate-containing meal. Powerful anti-secretory medication also lowers the intragastric concentration of ascorbic acid and total vitamin C, probably because of the relative instability of the vitamin at a higher pH. These changes in the intragastric concentrations of nitrite and ascorbic acid are most marked in Helicobacter pylori -infected subjects on proton pump inhibitor therapy. It is recognized that an elevated nitrite-to-ascorbic acid ratio predisposes to the formation of potentially carcinogenic N -nitroso compounds. It is, however, unclear at present whether such compounds are formed within the human stomach.