Gastric mucosal morphological consequences of acid suppression: a balanced view

Best Practice & Research Clinical Gastroenterology Vol. 15, No. 3, pp. 497±510, 2001

doi:10.1053/bega.2001.0189, available online at http://www.idealibrary.com on

11 Gastric mucosal morphological consequences of acid suppression: a balanced view S. G. M. Meuwissen

MD, PhD

Professor of Gastroenterology

M. E. Craanen

MD, PhD

Associate Professor of Gastroenterology Department of Gastroenterology, `Vrije Universiteit' Medical Centre, Amsterdam, The Netherlands

E. J. Kuipers

MD, PhD

Professor of Gastroenterology Department of Gastroenterology and Hepatology, Academic Hospital Dijkzigt, Rotterdam, The Netherlands

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 diculties of classifying gastritis and the new possibilities of quantifying chronic in¯ammation 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. pyloripositive 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 ecacy of H. pylori eradication with regard to the prevention of atrophy. The limited signi®cance 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. Key words: Helicobacter pylori; gastric corpus; gastric antrum; gastric mucosa; atrophic gastritis; proton pump inhibitor; omeprazole; gastro-oesophageal re¯ux disease.

Proton pump inhibitors (PPIs) are at present the most powerful drugs for the treatment of acid-related disorders, in particular for the management of gastro-oesophageal re¯ux disease (GORD) and re¯ux-like symptoms. A Dutch study among 24 general practitioners over the time period 1994±95 showed that 2.1% of their patients were receiving long-term gastric anti-secretory drugs, either H2-receptor antagonists or a PPI.1 It is probable that this percentage has since then increased in favour of PPIs. In the UK, about 5.6% of the National Health Service community drug bill is used for PPIs2, 1521±6918/01/030497‡14 $35.00/00

c 2001 Harcourt Publishers Ltd. *

498 S. G. M. Meuwissen et al

and this ®gure continues to rise, not only because general practitioners are now con®dent in prescribing a PPI, but also because encouraging long-term ecacy and safety data on PPIs are appearing in the literature.3±5 Most patients taking PPIs have a long-term medical indication, such as GORD or re¯ux-like symptoms, and there is now a large cohort of patients who have been taking omeprazole or one of the other PPIs for many years.

EFFECT OF LONG-TERM ACID SUPPRESSION Profound acid suppression a€ects the gastric mucosa, the homeostasis of gastric acid secretion as well as the bacterial ¯ora, with as yet unknown or incompletely understood consequences. It is well known that PPIs not only suppress gastric secretion e€ectively, but also give rise ± as an indirect e€ect ± to a stimulation of the gastrin-secreting cell and serum gastrin levels. Gastrin stimulates the enterochroman-like (ECL) cells, possibly via gastrin/CCKB receptors as well as histamine receptors. In the long run, this may lead to ECL hyperplasia, dysplasia and ®nally carcinoid tumours. Fortunately, no evidence yet exists that this chain occurs in humans; only in rat have carcinoid tumours previously been reported. In addition to their e€ect on serum gastrin and ECL cells, PPIs may decrease the somatostatin messenger RNA, although studies are contradictory. The discussion on the progression of gastric atrophy during PPI therapy needs further comment in light of several studies recently published and in view of some reports on the development of gastric auto-antibodies in Helicobacter pylori-positive patients using PPI maintenance therapy. There is a striking e€ect of PPIs on the function as well as on the morphology of parietal cells, the latter being further discussed in this article.

CLASSIFICATION OF CHRONIC GASTRITIS There have been very been very few topics in pathology that have produced so much confusion as the classi®cation of gastritis, in particular chronic gastritis. Chronic gastritis may be categorized by the presence or absence of atrophy and by the localization of the atrophy, for example the loss of glandular tissue in the gastric mucosa6, such as antralpredominant or pangastritis, which is now called atrophic multifocal gastritis. In autoimmune gastritis (e.g. pernicious anaemia-associated gastritis) atrophy is con®ned to the corpus.6 The original Sydney classi®cation was developed to classify chronic gastritis reproducibly7, but a review was soon necessary, producing the `updated Sydney system'.8 This system uses a visual analogue scale (normal, mild, moderate and severe) for scoring the following parameters: the presence of H. pylori; polymorphonuclear neutrophil activity as a score of acute in¯ammation (neutrophil activity); chronic in¯ammation (an increase in the number of mononuclear cells); glandular atrophy of the antrum and corpus and intestinal metaplasia (all subtypes). In addition to these parameters, other features should also be looked for: foveolar hyperplasia, lymphoid follicles, pseudopyloric metaplasia in the antrum and endocrine cell hyperplasia. This yields information that includes presence of activity, the topography of the in¯amed area (antrum, corpus or both), the severity of the in¯ammation, the presence of atrophy and the aetiology (e.g. H. pylori). For the assessment of mucosal atrophy, corpus as well as

Gastric mucosa in acid suppression 499

antrum biopsies are required from the lesser and greater curvature as well as from the incisura6, and biopsies should preferably be orientated and in any case be apart. In general, the classi®cation appears to be very useful and is at present the standard for the evaluation of gastric mucosal biopsies. Confusion may, however, remain when the gastric mucosa contains a large number of mononuclear cells which by expansion push away the mucosal glands; this may falsely be interpreted as a reduction in the number of glands or atrophy.9 Such discussions have been going on since the appearance of several recently published studies.10±12 Despite the fact that some studies utilizing the Sydney classi®cation have shown a relatively poor interobserver agreement (in terms of kappa values), in particular for atrophy13±15, the Sydney classi®cation currently remains the gold standard. A more quantitative analysis of the gastric mucosa is another valuable, albeit rarely applied technique for approaching the problem of evaluating vanishing mucosal glands in a densely in¯amed area. Volume densities of, for example, parietal and chief cells can be accurately measured. We have recently performed a study in which mucosal biopsies from the corpus in H. pylori-positive patients with atrophic or non-atrophic gastritis were analysed by morphometry. Using a point-counting technique, percentage volumes of glands, stroma and in®ltrate, as well as intestinal metaplasia, were measured.16 First, the optimal number of ®elds of vision was determined as well as the intra- and interobserver variation. Thereafter the mean percentage volume of the tissue components was scored and correlated to the tissue scores. The percentage volume of glands, stroma and in®ltrate correlated very well with the grade of corpus atrophy as scored by the Sydney classi®cation. These results support the qualitative approach of the Sydney classi®cation: with increasingly severe atrophy, there is a demonstrable and quanti®able increase in the stromal component. Another argument in favour of the correct interpretation of the presence of atrophic gastritis has been a functional study in which the degree of chronic corpus gastritis correlated with the serum value of vitamin B12.17 Patients who, according to histological criteria (the modi®ed Sydney classi®cation), developed moderate-to-severe atrophic gastritis during long-term treatment with omeprazole (mean 61 + 25 months) showed a signi®cant decrease in their serum vitamin B12 level, whereas patients without any histological evidence of atrophic gastritis did not show any change in serum level. EFFECT OF LONG-TERM PPI THERAPY ON THE GASTRIC MUCOSA: IS THERE A PROGRESSION OF CORPUS ATROPHY IN H. PYLORIPOSITIVE PATIENTS? There has been ample discussion in the literature on the shift of H. pylori from antrum towards corpus in patients who receive acid-suppressant therapy. Even moderately e€ective acid-suppressant therapy with H2-receptor antagonists or antacids has some e€ect on worsening the degree of corpus activity in patients infected with H. pylori18, the changes in the distribution of H. pylori correlating with the change in pH within the stomach and the gastric pits. This phenomenon is particularly marked in patients receiving PPIs and is caused by the change of corpus pH, whereby the habitat becomes more suitable for H. pylori.10,18±22 The increased in¯ammatory reaction results from a deeper penetration of H. pylori within the gastric pits, leading to closer contact with the individual cells. This increased in¯ammation of the gastric corpus mucosa accelerates the progression of the atrophic gastritis.20,22±24

500 S. G. M. Meuwissen et al

The annual incidence of atrophic gastritis in H. pylori-positive patients without acidsuppressant therapy varies within narrow limits, 1±3%, irrespective of age.25±28 In contrast, the incidence of atrophic gastritis in H. pylori-positive individuals treated with PPIs has repeatedly been shown to be much higher, varying between 3.8% and 8.7%.3,4,10,19,29,30 There are also older studies with high incidence ®gures, albeit without data on H. pylori status.31 Only when di€erent incidence ®gures became available in H. pylori-positive patients, particularly in those individuals with a positive H. pylori status who had received PPIs over a long period, did it become clear that profound acid suppression might facilitate the development of atrophic gastritis. Our study from 1996 was one of the ®rst in GORD patients to compare the e€ect of long-term PPI therapy with the e€ect of surgical treatment (fundoplication) on the development of atrophic gastritis.10 The study concluded that, in H. pylori- negative patients and H. pylori-positive patients undergoing fundoplication, the incidence of atrophic gastritis during the follow-up period remained low (52%), whereas in H. pylori-positive cases treated with omeprazole, the incidence was much higher (6.1%), a conclusion that has been con®rmed by others.4,21,32 Arguments were also put forward against our conclusion that it was not a prospective randomized study, that the study has been performed in di€erent countries and that there was a di€erent mean age of the study groups. Only a randomized prospectively conducted eradication trial with long-term follow-up will provide a de®nite answer to the issue of atrophic gastritis in this patient category. In addition, one issue remains unclear: the increase in intestinal metaplasia in our study has been of limited extent (type I only), types II and III metaplasia not having been observed, even in the recently published international study.4 There is now ample evidence that PPIs can be prescribed safely on a long-term basis, although, in our opinion, a continuing survey in some large centres may be useful to obtain data on serum gastrin level, on mucosal changes in the corpus and antrum and on the possible development of ECL hyperplasia. We have over recent years published two main long-term studies on the use of omeprazole, concerning its ecacy and safety aspects. The ®rst study, published in 1994, described the long-term e€ects of omeprazole in GORD patients, the total follow-up time being 60 months.33 The median serum gastrin level increased from 60 to 162 ng/l, the serum level rising to over 500/ng/l in 11% of patients. Evidence of atrophic gastritis was found in the original biopsies in fewer than 1%, increasing to 25% after 60 months, whereas ECL hyperplasia was noticed in 2.5% and 20% of cases respectively. From this study, we concluded that omeprazole is e€ective and safe for GORD patients, despite the observed mucosal changes. In this study, however, biopsies were not evaluated for H. pylori; it was therefore not known whether atrophy or gastrin level correlated with the presence of this bacterium. It was decided at a later date to try to unravel the signi®cance of these very high serum gastrin levels. A selection was made of those GORD patients with a very high (4400 ng/l) serum gastrin level, these being compared with a control group who had a serum level below 300 ng/ml.34 The two groups di€ered with respect to a longer treatment period with omeprazole in the high-gastrin group, more gastric corpus in¯ammation and evidence of atrophic gastritis as well as a signi®cantly higher prevalence of H. pylori in these patients. No di€erence was noticed with regard to gastric emptying. It is thus probable that both the presence of H. pylori and atrophic gastritis contribute to these high serum gastrin levels. The second long-term study was an open multicentre study in which 230 patients with GORD were followed for a mean study period of 6.5 years while being treated

Gastric mucosa in acid suppression 501

with omeprazole.4 With regard to the ecacy of the PPI, no di€erence was observed between H. pylori-positive and negative patients, although it was noticed that the annual incidence of atrophy (by the Sydney classi®cation) in the H. pylori-negative group was 0.7% and that in the H. pylori-positive patients 4.7%. The development of intestinal metaplasia remained very limited although no biopsies had been taken from the incisure from the stomach. Gastrin serum levels increased during the study and were higher in the H. pylori-positive group. The data on the development of atrophic gastritis were comparable to those from previous studies.10,21 Eissele et al showed, in a long-term follow-up study of 42 cases with di€erent peptic disorders treated with lansoprazole, that only in H. pylori-positive patients did chronic in¯ammation, as well as atrophy of the corpus mucosa, worsen.21 During the followup, more than 25% of the H. pylori- positive patients developed linear or micronodular argyrophil cell hyperplasia, a ®gure comparable to the percentage seen in the longterm study by Klinkenberg-Knol et al.33 One recent publication from Scandinavia claimed to show no di€erence in results with respect to the progression of atrophic gastritis. In this study, 155 patients were included for anti-re¯ux surgery and 139 for PPI (omeprazole) therapy, an interim analysis being carried out after 3 years.11 A confounding variable in the study was that pre-operative patients could be treated with a PPI, usually for a period of 4±8 weeks or at the most 16 months before surgery. After 3 years, 139 and 131 cases respectively were evaluable. With regard to in¯ammation and atrophy, the study results are, in our opinion, rather dicult to interpret because gastric mucosal biopsies were taken only at the time of inclusion in the study, i.e. after pre-treatment with omeprazole. In¯ammation of the oxyntic mucosa was found at the start in 2 patients and and at the end of the study in 37 PPI-treated patients and 31 surgically treated cases. Moderate or severe corpus atrophy in H. pylori-positive cases was observed in 7 out of 40 patients treated with omeprazole (17.5%) and 2 out of 44 surgically treated cases (4.5%). The annual progression rate to atrophy should therefore be 17.5/3 ˆ 5.8% and 4.5/3 ˆ 1.5%, the di€erence not being signi®cant. The number of patients studied was, however, too small to reach sucient power. In Kuipers et al's study, percentages were 18.6 and 0%, ®gures that are almost identical.10,35 Another point of relevance is that, in the surgical arm of the Swedish study, 10 patients also underwent a vagotomy and 17 cases continued omeprazole therapy because of a relapse of re¯ux symptoms. These patients were included in the histological evaluation: 3 out of 40 controls (7.5%) without vagotomy or post-operative omeprazole treatment showed an increase in atrophy score, in contrast to 4 out of 13 patients (31%) receiving vagotomy or omeprazole.11,35 In addition, the original data, as presented during the Digestive Disease Week (DDW) meeting in 1997, were di€erent with regard to atrophy development, no particular explanation being given for this discrepancy.36 In the recent DDW meeting (May, 2000, San Diego), the Swedish study was further expanded, but data on inclusion were not given, and therefore their ®nal results at 5-year follow-up are still awaited.37 Others have also interpreted the Scandinavian study di€erently.38 Two other studies are of importance in the analysis of development of atrophic gastritis in H. pylori-positive patients treated with a PPI. In one study, 114 patients with a duodenal ulcer were treated with lansoprazole (N ˆ 62) or ranitidine (N ˆ 52) over a year.39 Endoscopy was performed before the study and at 6 and 12 months. However, no initial biopsies were taken, and therefore the evaluation of atrophy progression was incomplete. As in other studies, a signi®cant increase in gastritis activity of the oxyntic mucosa occurred when patients were taking lansoprazole, with

502 S. G. M. Meuwissen et al

a decrease of the density of H. pylori in the antrum, while changes did not occur with ranitidine. No alteration in the degree of atrophy was seen after 1 year, but the number of patient years was too limited to study this phenomenon. The second study from the same German group was performed in GORD patients (N ˆ 111) treated for 1 year with omeprazole or lansoprazole.40 Again, an increase of the degree of gastritis activity was observed in the corpus, in addition to a greater degree of H. pylori colonization, while the H. pylori colonization density decreased in the antrum. No change in the degree of atrophy or intestinal metaplasia was seen in a limited population. The German investigators advised eradication in H. pylori-positive patients in order to prevent a progression towards corpus-predominant gastritis and a risk of argyrophil cell hyperplasia.21,40 Even moderately e€ective acid-suppression therapy with H2-receptor antagonists or antacids may have some e€ect on worsening of the degree of corpus activity in H. pylori-positive patients18, these changes correlating with the changing pattern in pH within the stomach and the gastric pits. Can H. pylori eradication prevent the development of atrophic gastritis during PPI therapy? Several authors have suggested that eradication may prevent or minimize the development of atrophic gastritis40,41, but hard data are limited. A prospective and randomized eradication case control study was recently published, studying H. pyloripositive GORD patients receiving PPI therapy.42 All the patients were treated with omeprazole during 12 months; in one arm, H. pylori was eradicated, the other arm serving as a control. In the patient group that remained H. pylori positive, a decrease of in¯ammation occurred in the antrum while an increase was observed in the corpus. In those patients who had successful H. pylori eradication, both corpus and antrum in¯ammation decreased signi®cantly. With regard to atrophy, only antral atrophic gastritis decreased somewhat, while corpus atrophy scores after 1 year were no di€erent between the patients with or without eradication. This study demonstrates again that a shift occurs of H. pylori-induced mucosal in¯ammation towards the corpus, but an increase in mucosal corpus atrophy was not substantiated. The number of patients may have been too low to provide a de®nite answer; alternatively, the treatment period may not have been long enough to notice the gradual change from chronic in¯ammation towards mucosal gland loss. Another recent study has con®rmed the ®nding in GORD patients treated with a PPI that a shift towards the corpus is prevented when H. pylori is eradicated.43 A ®nal answer on whether a preventative e€ect arises from eradicating H. pylori infection may be provided by a large international study that has for 2 years been studying GORD patients during PPI therapy, but no data are yet available. OTHER GASTRIC MUCOSAL CHANGES Omeprazole has a hypertrophic e€ect on parietal cells: the height and cell mass of acidsecreting cells increases, and in ultrastructural studies, parietal cells have been seen to be enlarged, with a prominence of the cytoplasmic tubulovesicles with sparse secretory canaliculi44, although previous studies have been negative in this respect. These intracellular features correspond to the protrusions of parietal cells into the lumen of the gland, providing a `serrated' appearance.45±47 Similar observations have been made by several other groups on patients with or without acid-suppressant therapy.46,48 The development of fundic gland cysts may possibly be related to a raised fundic gland luminal pressure, as shown in rat and explainable by a swelling of gland cells in the neck region, creating out¯ow resistance.49 A further enlargement of cysts

Gastric mucosa in acid suppression 503

will ®nally lead to fundic gland polyps. Intramucosal cysts have also been found in high frequency in corpus biopsies from patients with Zollinger-Ellison syndrome, the severity of the cystic change being closely correlated to the height of serum gastrin level and the duration of PPI therapy but not to the dose of omeprazole.50 Fundic gland polyps have been recognised for more than 20 years in patients with familial polyposis coli and more recently in patients treated with PPIs.45,51,52 No major clinical studies on the e€ect of PPIs on gastric mucosa appeared until 1998. Fundic gland polyps were searched for in a retrospective study of 231 patients with GORD and treated with a PPI for a mean of 32 months.53 In 7.3% of the patients, polyps were found as small sessile weak elevations of the corpus mucosa, mainly at the greater curvature. Histology showed a fundic gland-type or a hyperplastic-type lesion, without dysplastic features. A possible mechanism of development of fundic gland polyps may be a raised serum gastrin level (present in about 10±20% of patients on long-term PPI therapy). Japanese workers observed, in H. pylori-positive patients with enlarged corpus mucosa folds, that parietal cell hyperplasia with dilated canaliculi and vacuoles occurs; these changes disappeared after H. pylori eradication.54 Others have considered fundic gland polyps to be hamartomas.55 To investigate the e€ect of PPIs on the morphology of the parietal cell in a prospective double-blind fashion, we studied patients with GORD who were treated during 1 year with omeprazole. H. pylori-positive patients were treated with eradication therapy or placebo.56 The prevalence of protrusions of parietal cells or fundic gland cysts at the start of the study was no di€erent between H. pylori-positive or negative patients but increased strikingly at 3 and 12 months irrespective of the H. pylori status. Fundic gland cysts developed signi®cantly more often in the H. pylorieradicated patients in comparison to the persistently H. pylori-positive patients. A correlation was found between the increase in parietal cell protrusions and fundic gland cysts and the serum gastrin level, and to a lesser extent with the serum pepsinogen-A level. This study suggests that PPIs do indeed interfere with the function of the parietal cell, based on the aforementioned intracellular alterations. In daily practice, it appears, however, unlikely that the cascade protrusions of parietal cells ! fundic gland cysts ! fundic gland polyps has clinical signi®cance. Long-term studies are not yet available, and it is not known whether, in the long run, the immune properties and membrane receptors of the parietal cells may undergo a change, making them more liable to autoimmune attack. There is evidence that the morphological changes are reversible after stopping the PPI57, but this process takes some months, and temporary hypersecretion may be explained by the presence of hypertrophic and hyperplastic parietal cells, which return to their normal morphological and functional state only after a considerable time delay. These morphological changes ± which return to normal at only a slow pace ± may be responsible for the well-known rebound acid secretion after stopping PPI therapy.58 DO PPIs HAVE A ROLE IN THE DEVELOPMENT OF H. PYLORIINDUCED AUTOIMMUNE GASTRITIS? In a recent case report, a H. pylori-positive male patient with GORD was described who had been treated with omeprazole over a period of 4 years. He developed a severe `autoaggressive' gastritis with progressive atrophy, hypochlorhydria and nodular ECL-cell hyperplasia.59 Helicobacter pylori eradication therapy induced a considerable improvement of in¯ammation (low-grade inactive gastritis), and 10 months

504 S. G. M. Meuwissen et al

later the glands appeared normal. Anti-parietal and intrinsic factor antibodies were found to be negative, and it was therefore thought that anti-canalicular antibodies induced by H. pylori could be responsible for this.60,61 The authors could not, however, demonstrate anti-canalicular antibodies, and therefore the mechanisms responsible for gland destruction in this patient were not elucidated. This case shows how incomplete our evidence remains with regard to the role of PPIs in the development of autoimmune gastritis and whether a long-term high intragastric pH facilitates the development of anti-parietal cell antibodies. We know that molecular mimicry is present in H. pylori infection: the lipopolysaccharide of the majority of H. pylori strains expresses Lex, Ley, Lea or Leb, antigens similar to those expressed by gastric epithelium.62 As discussed in a recent editorial, an expression of Lewis antigens may be involved in the chronic in¯ammatory process via one of the following processes: the induction of auto-antibodies, the adaptation of the bacterium to the host (a host expressing Lex produces antibodies not against H. pylori Lex but against Ley) and ®nally the possible promotion of adhesion and colonization by Lewis antibodies.63 There are, however, almost no data on the interrelationship between the development of antigastric mucosal antibodies and long-term raised intragastric pH, as induced by longterm PPI therapy. The topic has far from been elucidated, and discussion reaches outside the scope of this review; further reading is contained in the reference list.61,63±67 PPIs AND CHANGES OF INTRAGASTRIC pH AND INTRAGASTRIC BACTERIAL FLORA The composition of the intragastric bacterial ¯ora depends mainly on the intragastric pH, the number of non-H. pylori bacteria rapidly increasing above a pH of 3±4. Above pH 4, for example, Lactobacilli spp. and Streptococci spp. will grow, and above pH 5 several other species will proliferate.68 If the pH is below 4.0 for a few hours during each 24 hours, an inhibition of bacterial growth occurs.69 A relatively high pH and consequent bacterial colonization will occur if an individual is receiving long-term H2receptor antagonist therapy.70±72 PPI therapy may provide a persistent high intragastric pH, with, as a consequence, an increased number of intragastric bacteria after short-term therapy in healthy subjects73±75 as well as in patients being treated for peptic disorders.76±79 The shortterm consequences of PPI therapy for the development of acute infectious enteritis or colitis are well known and may provide a de®nite risk for the frequent traveller who is on PPI therapy. Much more complicated is the problem of long-term PPI use: does the patient run a risk of, for years, harbouring nitrate-reducing bacteria, which will lead to raised intragastric concentrations of nitrite and N-nitroso compounds, which are known to be carcinogenic in the experimental animal and human.80 An important recent study adds new data to the issue of safety of omeprazole and the importance of the H. pylori status.81 Healthy volunteers were treated with omeprazole after collecting gastric acid, the gastric juice pH, nitrite, ascorbic acid and total vitamin C concentrations being measured, and bacterial analysis being carried out. After 6 weeks treatment, H. pylori-positive individuals had a higher bacterial count (of nitrate- reducing bacteria, such as Gram-positive facultative Streptococci, usually from the oropharynx), a higher gastric pH and a lower intragastric vitamin C concentration than did the H. pylori-negative individuals. This study stresses that H. pylori-positive cases will run the greatest risk of metabolic changes that have the potential to induce a dysplasia cascade. A low intragastric

Gastric mucosa in acid suppression 505

concentration of vitamin C has been found by various authors82±89, and is in part explainable by the oxidation of ascorbic acid by increased free radicals from the in¯amed corpus mucosa. This situation is worrying because nitrite cannot be converted to nitrite oxide gas and therefore damage may occur.81 The authors suggest that the pangastritis seen in H. pylori-positive patients may be responsible for the metabolic changes related to vitamin C. Long-term studies are therefore needed in which a correlation is sought between the degree of, or progression of degree of, atrophic gastritis, the vitamin C concentration during long-term PPI therapy and molecular markers detectable in dysplastic or malignant tissue. How nitrate-reducing bacteria induce a carcinogenic cascade with the ultimate development of dysplastic and/or malignant gastric tissue remains unclear as the ®nal molecular mechanisms responsible for (pre)neoplastic changes in the gastric mucosa have not yet been unravelled.75,90±94 The Mowat studies may provide new and important arguments in favour of eradication therapy for H. pylori in positive patients, as also suggested by ourselves and others.10,28,94±99 THE ECL CELL STORY ECL cells are, by means of their gastrin (CCK-B) receptors, sensitive to changes in the serum gastrin level, an increase leading to histamine secretion and the stimulation of parietal cells. A long-term raised serum level of gastrin will therefore permanently stimulate the ECL cells and induce ECL cell hyperplasia and ®nally carcinoid tumours. The increased ECL mass may also be responsible for acid rebound hypersecretion.100,101 ECL cell carcinoid tumours are well known in patients with Zollinger±Ellison syndrome or as part of the multiple endocrine neoplasia but have so far fortunately not been described in patients on long-term PPI therapy. Waldum has repeatedly stressed that PPI users may run a risk as the more benign ECL cell carcinoids may eventually develop into more malignant ECL cell neuroendocrine carcinomas.100,102,103 Such a change in patients taking PPIs has not to our knowledge been documented, and the interpretation of the clinical data in the Haga103a case report provides insucient support for Waldum's extreme caution. A high serum gastrin level has repeatedly been found during omeprazole use33 but now appears to be associated with H. pylori status rather than with abnormalities of gastric emptying or vagal nerve damage.34 In other studies, normal or slightly raised values have usually been found.4,104 What then is wisdom in the clinical management of GORD patients? Should we withhold PPIs (especially in young patients) for fear of carcinoid tumour development? The reader is referred to Yeomans and Dent105 for a balanced discussion of and a reassuring answer to this problem. We would like to add here that monitoring using long-term serum gastrin measurements appears to have clinical value. In those patients (fewer than 10%) who develop a high (4400 ng/l) gastrin level and who are H. pylori positive, eradication should de®nitely be considered. CONCLUSION During the past 5 years, many important studies have been published clarifying the safety of PPIs as used in patients with acid-related disorders, in particular GORD. The impressive increase in the prescription of PPIs for these disorders makes it imperative

506 S. G. M. Meuwissen et al

Practice Points . long-term prescription of PPI's to Helicobacter pylori positive patients is safe . there is no proof, that ECL-cell carcinoids develop during long-term PPItherapy (in other words: the `Waldum sequence' has generally not been accepted) . development of atrophic gastritis in Helicobacter pylori positive patients is accelerated, when long-term PPI therapy is given. Helicobacter pylori eradication is therefore advisable . Helicobacter pylori positive patients develop during long-term PPI therapy lower intragastric vitamin C concentrations, bacterial colonization is induced and higher numbers of nitrate reducing bacteria are observed. These observations are important additional arguments for Helicobacter pylori eradication

Research Agenda . the classi®cation of chronic gastritis remains unsatisfactory and rather confusing, therefore additional criteria are needed for a more accurate de®nition. Additional quantitative (morphometric) assessment of atrophic gastritis may be of value to improve the classi®cation . the process of development of atrophic changes in the gastric mucosa in Helicobacter pylori positive patients is likely to take many years. To de®ne the e€ect of PPI's any better, long-term studies with sucient power are needed . the molecular events show Helicobacter pylori a€ects the corpus mucosa are not understood and need intensive study . how does Helicobacter pylori-induced autoimmune gastritis develop? What is hereby the role of PPIs? that safety aspects relating to long-term profound acid suppression are continuously studied. A high serum gastrin level is exceptional during PPI therapy and may be, according to some authors, related to H. pylori positivity; in such patients, eradication has to be considered. No evidence exists that ECL cell carcinoids develop in patients receiving long-term PPI therapy. There is, in our opinion, sucient evidence to suggest that gastric acid suppression accelerates the onset of atrophic gastritis in H. pylori-positive patients; long-term studies are now in progress to solve the ®nal issue of whether eradication will reduce or stop the progression to atrophy. There are no data available on the sequence of chronic atrophic gastritis towards dysplasia and this will be much more dicult to prove, at least in patients on long-term PPI therapy. The arguments for eradicating H. pylori in this patient group seem to be supported by the observation that a low vitamin C level and the induction of bacterial colonization and N-nitrosation may occur. REFERENCES 1. Hurenkamp GJB, Grundmeyer HGLM, Bindels PJE et al. Chronic use of stomach acid inhibitor medication in family practice in the region of Amsterdam. Nederlands Tijdschrift voor Geneeskunde 1999; 143: 410±413.

Gastric mucosa in acid suppression 507

*

*

* *

2. Hungin AP, Rubin G & O'Flanagan H. Factors in¯uencing compliance in long-term proton pump inhibitor therapy in general practice. British Journal of General Practice 1999; 49: 463±464. 3. Klinkenberg-Knol EC, Festen HPM, Jansen JBMJ et al. Ecacy and safety of long-term treatment with omeprazole for refractory re¯ux esophagitis. Annals of Internal Medicine 1994; 121: 161±167. 4. Klinkenberg-Knol EC, Nelis F, Dent J et al. Long-term omeprazole treatment in resistant gastroesophageal re¯ux disease: ecacy, safety, and in¯uence on gastric mucosa [see comments]. Gastroenterology 2000; 118: 661±669. 5. Armstrong D. Long-term safety and ecacy of omeprazole in gastro-oesophageal re¯ux disease. Lancet 2000; 356: 610±612. 6. Dixon M. The components of gastritis. In Graham D, Genta RM & Dixon MF (eds) Gastritis, pp 51±66. Philadelphia: Lippincott, Williams & Wilkins, 1999. 7. Price AB. The Sydney system: histological division. Journal of Gastroenterology and Hepatology 1991; 6: 209±222. 8. Dixon MF, Genta RM, Yardley JH & Correa P. Classi®cation and grading of gastritis. The up-dated Sydney system. American Journal of Surgical Pathology 1996; 20: 1161±1181. 9. Genta RM. Recognizing atrophy: another step toward a classi®cation of gastritis. American Journal of Surgical Pathology 1996; 20: S23±S30. 10. Kuipers EJ, Lundell L, Klinkenberg-Knol EC et al. Atrophic gastritis and Helicobacter pylori infection in patients with re¯ux esophagitis treated with omeprazole or fundoplication. New England Journal of Medicine 1996; 334: 1018±1022. 11. Lundell L, Miettinen P, Myrvold HE et al. Lack of e€ect of acid suppression therapy on gastric atrophy. Gastroenterology 1999; 117: 319±326. 12. Genta RM. Atrophy, acid suppression and Helicobacter pylori infection: a tale of two studies. European Journal of Gastroenterology and Hepatology 1999; 11 (supplement 2): 29±33. 13. Andrew A, Wyatt JI & Dixon MF. Observer variation in the assessment of chronic gastritis according to the Sydney system. Histopathology 1994; 25: 317±322. 14. El-Zimaity HMT, Graham DY, Al-Assi MT et al. Interobserver variation in the histopathological assessment of Helicobacter pylori. Human Pathology 1996; 27: 35±41. 15. Guarner J, Herrera-Goepfert R, Mohar A et al. Interobserver variability in application of the revised Sydney classi®cation for gastritis. Human Pathology 1999; 30: 1431±1434. 16. Grieken van N, Weiss MM, Meijer G et al. Rapid quantitative assessment of gastric corpus atrophy in tissue sections. Journal of Pathology 2000; 192: 301±306. 17. Schenk BE, Kuipers EJ, Klinkenberg-Knol EC et al. Atrophic gastritis during long-term omeprazole therapy a€ects serum vitamin B12 levels. Alimentary Pharmacology and Therapeutics 1999; 13: 1343±1346. 18. Meining A, Bossecker H, Capsary WF et al. H2-receptor antagonists and antacids have an aggravating e€ect on Helicobacter pylori gastritis in duodenal ulcer patients. Alimentary Pharmacology and Therapeutics 1997; 11: 729±734. 19. Lamberts R, Creutzfeldt W, StruÈber HG et al. Long-term omeprazole therapy in peptic ulcer disease: gastrin, endocrine cell growth, and gastritis. Gastroenterology 1993; 104: 1356±1370. 20. Kuipers EJ, Uyterlinde AM, Pena AS et al. Increase of Helicobacter pylori-associated corpus gastritis during acid suppressive therapy: implications for long-term safety. American Journal of Gastroenterology 1995; 90: 1401±1406. 21. Eissele R, Brunner G, Simon B et al. Gastric mucosa during treatment with lansoprazole: Helicobacter pylori is a risk factor for argyrophil-cell hyperplasia. Gastroenterology 1997; 112: 707±717. 22. Berstad AE, Hatlebakk JG, Maartmann-Moe H et al. Helicobacter pylori gastritis and epithelial cell proliferation in patients with re¯ux oesophagitis after treatment with lansoprazole. Gut 1997; 41: 740±747. 23. Solcia E, Villani L, Fiocca R et al. E€ects of eradication of Helicobacter pylori on gastritis in duodenal ulcer patients. Scandinavian Journal of Gastroenterology 1994; 29: 28±34. 24. Logan RPH, Walker MM, Misiewicz JJ et al. Changes in the intragastric distribution of Helicobacter pylori during treatment with omeprazole. Gut 1995; 36: 12±16. 25. Correa P, Haenszel W, Cuello C et al. Gastric precancerous process in a high risk population: crosssectional studies. Cancer Research 1990; 50: 4731±4736. 26. Sipponen P, Helske T, JaÈrvinen P et al. Fall in the prevalence of chronic gastritis over 15 years: analysis of outpatient series in Finland from 1977, 1985 and 1992. Gut 1994; 35: 1167±1171. 27. Kawaguchi H, Haruma K, Komoto K et al. Helicobacter pylori infection is the major risk factor for atrophic gastritis. American Journal of Gastroenterology 1996; 91: 959±962. 28. Kuipers EJ. Review article: Relationship between Helicobacter pylori, atrophic gastritis and gastric cancer. Alimentary Pharmacology and Therapeutics 1998; 12: 25±36. 29. Solcia E, Fiocca R, Havu N et al. Gastric endocrine cells and gastritis in patients receiving long-term omeprazole treatment. Digestion 1992; 51: 82±92.

508 S. G. M. Meuwissen et al 30. Kuipers EJ, Lee A, Klinkenberg-Knol EC & Meuwissen SGM. Review article: The development of atrophic gastritis ± Helicobacter pylori and the e€ects of acid suppressive therapy. Alimentary Pharmacology and Therapeutics 1995; 9: 331±340. 31. Maaroos HI, Salupere V, Uibo R et al. Seven-year follow-up study of chronic gastritis in gastric ulcer patients. Scandinavian Journal of Gastroenterology 1985; 20: 198±204. 32. Berstad AE, Hatlebakk JG, Maartmann-Moe H et al. Helicobacter pylori gastritis and epithelial cell proliferation in patients with re¯ux oesophagitis after treatment with lansoprazole. Gut 1997; 41: 740±747. 33. Klinkenberg-Knol EC, Festen HP, Jansen JB et al. Long-term treatment with omeprazole for refractory re¯ux esophagitis: ecacy and safety. Annals of Internal Medicine 1994; 121: 161±167. 34. Schenk BE, Kuipers EJ, Klinkenberg-Knol EC et al. Hypergastrinaemia during long-term omeprazole therapy: in¯uences of vagal nerve function, gastric emptying and Helicobacter pylori infection. Alimentary Pharmacology and Therapeutics 1998; 12: 605±612. 35. Kuipers EJ, Klinkenberg-Knol EC & Meuwissen SG. Omeprazole and accelerated onset of atrophic gastritis. Gastroenterology 2000; 118: 239±240. 36. Lundell L, Havu N, Andersson A et al. Gastritis development and acid suppression therapy revisited. Results of a randomized clinical study with long-term follow-up. Gastroenterology 1997; 112: A771. 37. Lundell L, Havu N, Miettinen P et al. No e€ect of acid suppression therapy over ®ve years on gastric glandular atrophy. Results of a randomised clinical study. Gastroenterology 2000; 118: A214. 38. McColl KE, Murray LS & Gillen D. Omeprazole and accelerated onset of atrophic gastritis. Gastroenterology 2000; 118: 239 (letter). * 39. Meining A, Kiel G & Stolte M. Changes in Helicobacter pylori-induced gastritis in the antrum and corpus during and after 12 months of treatment with ranitidine and lansoprazole in patients with duodenal ulcer disease. Alimentary Pharmacology and Therapeutics 1998; 12: 735±740. 40. Stolte M, Meining A, Schmitz JM et al. Changes in Helicobacter pylori-induced gastritis in the antrum and corpus during 12 months of treatment with omeprazole and lansoprazole in patients with gastrooesophageal re¯ux disease. Alimentary Pharmacology and Therapeutics 1998; 12: 247±253. 41. Malfertheiner P. Current European concepts in the management of Helicobacter pylori infection: the Maastricht consensus report. Gut 1997; 41: 8±13. * 42. Schenk BE, Kuipers EJ, Nelis GF et al. E€ect of Helicobacter pylori eradication on chronic gastritis during omeprazole therapy. Gut 2000; 46: 615±621. 43. Moayyedi P, Morrow S, Peacock R et al. Changing patterns of H. pylori gastritis in longstanding acid suppression. Gastroenterology 1999; 116: A257. 44. Driman DK, Wright C, Tougas G & Riddell RH. Omeprazole produces parietal cell hypertrophy and hyperplasia in humans. Digestive Diseases and Sciences 1996; 41: 2039±2047. 45. Stolte M, Bethke B, Ruhl G & Ritter M. Omeprazole-induced pseudohypertrophy of gastric parietal cells. Zeitschrift fuÈr Gastroenterologie 1992; 30: 134±138. 46. Riddell RH. The biopsy diagnosis of gastroesophageal re¯ux disease, carditis, and Barrett's esophagus, and sequelae of therapy. American Journal of Surgical Pathology 1996; 20 (supplement 1): S31±S50. 47. Stolte M, Meining A, Seifert E & Alexandridis T. Treatment with lansoprazole also induces hypertrophy of the parietal cells of the stomach. Pathology Research and Practice 2000; 196: 9±13. 48. Krishnamuthy S & Dayal Y. Parietal cell protrusions in gastric ulcer disease. Human Pathology 1997; 28: 1126±1130. 49. Synnerstad I & Holm L. Omeprazole induces high intraglandular pressure in the rat gastric mucosa. Gastroenterology 1997; 112: 1221±1230. 50. Aprile MR, Azzoni C, Gibril F et al. Intramucosal cysts in the gastric body of patients with Zollinger± Ellison syndrome. Human Pathology 2000; 31: 140±148. 51. Graham JR. Gastric polyposis: onset during long-term therapy with omeprazole. Medical Journal of Australia 1992; 157: 287±288. 52. Graham JR. Omeprazole and gastric polyposis in humans. Gastroenterology 1993; 104: 1584 (letter). 53. Choudhry U, Boyce HW Jr & Coppola D. Proton pump inhibitor-associated gastric polyps: a retrospective analysis of their frequency, and endoscopic, histologic, and ultrastructural characteristics. American Journal of Clinical Pathology 1998; 110: 615±621. 54. Murayama Y, Miyagawa J, Shinomura Y et al. Morphological and functional restoration of parietal cells in helicobacter pylori associated enlarged fold gastritis after eradication. Gut 1999; 45: 653±661. 55. Odze RD, Marcial MA & Antonioli D. Gastric fundic gland polyps: a morphological study including mucin histochemistry, stereometry, and MIB-1 immunohistochemistry [see comments]. Human Pathology 1996; 27: 896±903. 56. Cats A, Schenk E, Bloemena E et al. Parietal cell protrusions and fundic gland cysts during omeprazole maintenance treatment. Human Pathology 2000; 31: 684±690.

Gastric mucosa in acid suppression 509 57. Weinstein W, Ippoliti A, Lee S et al. Acid hypersecretion parietal cell hyperplasia and endoscopic changes after withdrawal of long term high dose omeprazole therapy: a prospective study. Gastroenterology 1996; 110: A294. 58. McColl KE, el-Omar E & Gillen D. Interactions between H. pylori infection, gastric acid secretion and anti-secretory therapy. British Medical Bulletin 1998; 54: 121±138. 59. Stolte M, Meining A, Koop H & Seifert E. Eradication of Helicobacter pylori heals atrophic corpus gastritis caused by long-term treatment with omeprazole. Virchows Archives 1999; 434: 91±94. 60. Faller G, Steininger H, Eck M et al. Antigastric autoantibodies in Helicobacter pylori gastritis: prevalence, in-situ binding sites and clues for clinical relevance. Virchows Archives 1996; 427: 483±486. 61. Negrini R, Savio A, Poiesi C et al. Antigenic mimicry between Helicobacter pylori and gastric mucosa in the pathogenesis of body atrophic gastritis. Gastroenterology 1996; 111: 655±665. 62. Appelmelk BJ, Simoons-Smit I, Negrini R et al. Molecular mimicry between Helicobacter pylori lipopolysaccharide and host Lewis blood group antigens. Role in autoimmunity. Infection and Immunity 1996; 64: 2031±2040. * 63. Appelmelk BJ & Vandenbroucke-Grauls CM. H. pylori and Lewis antigens. Gut 2000; 47: 10±11. 64. Negrini R. Is autoimmunity involved in the relationship between Helicobacter pylori infection, atrophic gastritis and gastric cancer? Italian Journal of Gastroenterology and Hepatology 1999; 31: 842±845. 65. Faller G & Kirchner T. Role of antigastric autoantibodies in chronic Helicobacter pylori infection. Microscopic Research and Technique 2000; 48: 321±326. 66. Claeys D, Faller G, Appelmelk BJ et al. The gastric H‡,K ‡ -ATPase is a major autoantigen in chronic Helicobacter pylori gastritis with body mucosa atrophy. Gastroenterology 1998; 115: 340±347. 67. Appelmelk BJ, Faller G, Claeys D et al. Bugs on trial: the case of Helicobacter pylori and autoimmunity. Immunology Today 1998; 19: 296±299. 68. Jonkers D. The intragastric bacterial ¯ora in relation to gastric malignancy, thesis, University of , Maastricht, The Netherlands, 1997 (Ph thesis). 69. Hill M. Normal and pathological microbial ¯ora of the upper gastro-intestinal tract. Scandinavian Journal of Gastroenterology 1984; 20 (supplement 111): 111±115. 70. Meyrick Thomas J, Misiewicz J & Cook A. E€ects of one year's treatment with ranitidine and of truncal vagotomy on gastric contents. Gut 1987; 28: 726±738. 71. Ruddell WS, Axon AT, Findlay JM et al. E€ect of cimetidine on the gastric bacterial ¯ora. Lancet 1980; 1: 672±674. 72. Stockbrugger RW, Cotton PB, Eugenides N et al. Intragastric nitrites, nitrosamines, and bacterial overgrowth during cimetidine treatment. Gut 1982; 23: 1048±1054. 73. Sharma B, Santana I & Wood E. Intragastric bacterial activity and nitrosation during and after treatment with omeprazole. British Medical Journal 1984; 289: 717±719. 74. Verdu E, Viani F, Armstrong D et al. E€ect of omeprazole on intragastric bacterial counts, nitrates, nitrites, and N-nitroso compounds. Gut 1994; 35: 455±460. 75. Viani F, Siegrist HH, Pignatelli B et al. The e€ect of intra-gastric acidity and ¯ora on the concentration of N-nitroso compounds in the stomach. European Journal of Gastroenterology and Hepatology 2000; 12: 165±173. 76. Karmeli Y, Stainikowitz R, Eliakim R & Rahav G. Conventional dose of omeprazole alters gastric ¯ora. Digestive Diseases and Sciences 1995; 40: 2070±2073. 77. Fried M, Siegrist H & Frei R. Duodenal bacterial overgrowth during treatment in outpatients with omeprazole. Gut 1994; 35: 23±26. 78. Houben G, Hooi J, Hameeteman W et al. Intragastric bacterial growth, nitrite and nitrosamines after short term treatment of healthy subjects with various doses of acid reducing drugs. Gastroenterology 1994; 106: A96. 79. Thorens J, Froehlich F, Schwizer W et al. Bacterial overgrowth during treatment with omeprazole compared with cimetidine: a prospective randomised double blind study. Gut 1996; 39: 54±59. 80. Pignatelli B, Malaveille C, Rogatko A et al. Mutagens, N-nitroso compounds and their precursors in gastric juice from patients with and without precancerous lesions of the stomach. European Journal of Cancer 1993; 14: 2031±2039. * 81. Mowat C, Williams C, Gillen D et al. Omeprazole, Helicobacter pylori status, and alterations in the intragastric milieu facilitating bacterial N-nitrosation. Gastroenterology 2000; 119: 339±347. 82. Rokkas T, Papatheodorou G, Karameris A et al. Helicobacter pylori infection and gastric juice vitamin C levels. Impact of eradication. Digestive Diseases and Sciences 1995; 40: 615±621. 83. Rokkas T, Liatsos C, Petridou E et al. Relationship of Helicobacter pylori CagA(‡) status to gastric juice vitamin C levels. European Journal of Clinical Investigation 1999; 29: 56±62. 84. Ruiz B, Rood JC, Fontham ET et al. Vitamin C concentration in gastric juice before and after antiHelicobacter pylori treatment. American Journal of Gastroenterology 1994; 89: 533±539.

510 S. G. M. Meuwissen et al 85. Reed PL. Vitamin C, Helicobacter pylori infection and gastric carcinogenesis. International Journal for Vitamin and Nutrition Research 1999; 69: 220±227. 86. Phull PS, Price AB, White KL et al. Gastroduodenal mucosal vitamin-C levels in Helicobacter pylori infection. Scandinavian Journal of Gastroenterology 1999; 34: 361±366. 87. Jarosz M, Dzieniszewski J, Dabrowska-Ufniarz E et al. E€ects of high dose vitamin C treatment on Helicobacter pylori infection and total vitamin C concentration in gastric juice. European Journal of Cancer Prevention 1998; 7: 449±454. 88. Sobala GM, Schorah CJ, Shires S et al. E€ect of eradiation of Helicobacter pylori on gastric juice ascorbic acid concentrations. Gut 1993; 34: 1038±1041. 89. Webb PM, Bates CJ, Palli D & Forman D. Gastric cancer, gastritis and plasma vitamin C: results from an international correlation and cross-sectional study. The Eurogast Study Group. International Journal of Cancer 1997; 73: 684±689. 90. Craanen ME, Blok P, Dekker W et al. Chronolgy of p53 protein accumulation in gastric carcinogenesis. GUT 1995; 36: 848±852. 91. Craanen ME, Blok P, Top B et al. Absence of ras gene mutations in early gastric carcinomas. Gut 1995; 37: 758±762. 92. Cats A, Meuwissen SGM, Forman D et al. Helicobacter pylori: a true carcinogen? European Journal of Gastroenterology and Hepatology 1998; 10: 447±450. 93. Moncur PH & Heatley RV. Safety of proton-pump inhibitors: the acid test. European Journal of Gastroenterology and Hepatology 2000; 12: 145±147. 94. Ebert MP, Yu J, Sung JJ & Malfertheiner P. Molecular alterations in gastric cancer: the role of Helicobacter pylori [in process citation]. European Journal of Gastroenterology and Hepatology 2000; 12: 795±798. 95. Lynch DAF, Mapstone NP, Clarke AMT et al. Cell proliferation in Helicobacter pylori associated gastritis and the e€ect of eradication therapy. Gut 1995; 36: 346±350. 96. Kuipers EJ, Lee A, Klinkenberg-Knol EC & Meuwissen SG. Review article: The development of atrophic gastritis ± Helicobacter pylori and the e€ects of acid suppressive therapy. Alimentary Pharmacology and Therapeutics 1995; 9: 331±340. 97. Kuipers EJ & Meuwissen SGM. Helicobacter pylori and gastric carcinogenesis. Scandinavian Journal of Gastroenterology 1996; 218 (supplement 31): 103±105. 98. Kuipers EJ, Schenk BE, Klinkenberg-Knol EC & Meuwissen SG. Helicobacter pylori and omeprazole therapy in GORD. American Journal of Gastroenterology 1999; 94: 3378±3379 (letter; comment). 99. Nardone G, Staibano S, Rocco A et al. E€ect of Helicobacter pylori infection and its eradication on cell proliferation, DNA status, and oncogene expression in patients with chronic gastritis. Gut 1999; 44: 789±799. 100. Waldum HL, Arnestad JS, Brenna E et al. Marked increase in gastric acid secretory capacity after omeprazole treatment. Gut 1996; 29: 649±653. 101. Gillen D, Wirz AA, Ardill JE & McColl KE. Rebound hypersecretion after omeprazole and its relation to on-treatment acid suppression and Helicobacter pylori status. Gastroenterology 1999; 116: 239±247. 102. Rindi G, Luinetti O, Cornaggia M et al. Three subtypes of gastric argyrophil carcinoid and the gastric neuroendocrine carcinoma: a clinicopathologic study. Gastroenterology 1993; 104: 994±1006. *103. Waldum HL & Brenna E. Personal review: Is profound acid inhibition safe? Alimentary Pharmacology and Therapeutics 2000; 14: 15±22. 103a. Haga Y, Nakatsura T, Shibata Y et al. Human gastric carcinoid detected during long-term anticular therapy of H2 receptor antagonist and proton pump inhibitor. Digestive Diseases and Sciences 1998; 43: 253±257. 104. Freston JW, Rose PA, Heller CA & Haber CM. Safety pro®le of lansoprazole: the US experience. Drug Safety 1999; 20: 195±205. 105. Yeomans ND & Dent J. Personal review: Alarmism or legitimate concerns about long-term suppression of gastric acid secretion? Alimentary Pharmacology and Therapeutics 2000; 14: 267±271.