Proposed mechanism of induction of gastric carcinoids: the gastrin hypothesis

ICH S1 prospective evaluation study and weight of evidence assessments: commentary from industry representatives

Industry representatives on the ICH S1B(R1) Expert Working Group (EWG) worked closely with colleagues from the Drug Regulatory Authorities to develop an addendum to the ICH S1B guideline on carcinogenicity studies that allows for a weight-of-evidence (WoE) carcinogenicity assessment in some cases, rather than conducting a 2-year rat carcinogenicity study. A subgroup of the EWG composed of regulators have published in this issue a detailed analysis of the Prospective Evaluation Study (PES) conducted under the auspices of the ICH S1B(R1) EWG. Based on the experience gained through the Prospective Evaluation Study (PES) process, industry members of the EWG have prepared the following commentary to aid sponsors in assessing the standard WoE factors, considering how novel investigative approaches may be used to support a WoE assessment, and preparing appropriate documentation of the WoE assessment for presentation to regulatory authorities. The commentary also reviews some of the implementation challenges sponsors must consider in developing a carcinogenicity assessment strategy. Finally, case examples drawn from previously marketed products are provided as a supplement to this commentary to provide additional examples of how WoE criteria may be applied. The information and opinions expressed in this commentary are aimed at increasing the quality of WoE assessments to ensure the successful implementation of this approach.

Correctly identifying the cells of origin is essential for tailoring treatment and understanding the emergence of cancer stem cells and late metastases

Malignancy manifests itself by deregulated growth and the ability to invade surrounding tissues or metastasize to other organs. These properties are due to genetic and/or epigenetic changes, most often mutations. Many aspects of carcinogenesis are known, but the cell of origin has been insufficiently focused on, which is unfortunate since the regulation of its growth is essential to understand the carcinogenic process and guide treatment. Similarly, the concept of cancer stem cells as cells having the ability to stop proliferation and rest in a state of dormancy and being resistant to cytotoxic drugs before "waking up" and become a highly malignant tumor recurrence, is not fully understood. Some tumors may recur after decades, a phenomenon probably also connected to cancer stem cells. The present review shows that many of these questions are related to the cell of origin as differentiated cells being long-term stimulated to proliferation.

Neuroendocrine mechanism of gastric acid secretion: Historical perspectives and recent developments in physiology and pharmacology

The physiology of gastric acid secretion is one of the earliest subjects in medical literature and has been continuously studied since 1833. Starting with the notion that neural stimulation alone drives acid secretion, progress in understanding the physiology and pathophysiology of this process has led to the development of therapeutic strategies for patients with acid-related diseases. For instance, understanding the physiology of parietal cells led to the developments of histamine 2 receptor blockers, proton pump inhibitors (PPIs), and recently, potassium-competitive acid blockers. Furthermore, understanding the physiology and pathophysiology of gastrin has led to the development of gastrin/CCK2 receptor (CCK2 R) antagonists. The need for refinement of existing drugs in patients have led to second and third generation drugs with better efficacy at blocking acid secretion. Further understanding of the mechanism of acid secretion by gene targeting in mice has enabled us to dissect the unique role for each regulator to leverage and justify the development of new targeted therapeutics for acid-related disorders. Further research on the mechanism of stimulation of gastric acid secretion and the physiological significances of gastric acidity in gut microbiome is needed in the future.

The central role of gastrin in gastric cancer

The prevalence of gastric cancer has markedly declined, but due to the high mortality rates associated with gastric cancer, it is still a serious disease. The preferred classification of gastric cancer is according to Lauren into either the intestinal type, which has a glandular growth pattern, or the diffuse type, which does not have glandular structures. Both types have been classified as adenocarcinomas, with the latter type based on periodic acid-Schiff (PAS) positivity presumed to reflect mucin. However, the presence of mucin in the diffuse type, in contrast to neuroendocrine/enterochromaffin-like (ECL) cell markers, has not been confirmed by immunohistochemistry and in situ hybridization. The ECL cells are probably prone to becoming cancerous because they do not express E-cadherin. Gastric cancer is unique in that a bacterium, Helicobacter pylori, is thought to be its main cause. H. pylori predisposes infected individuals to cancer only after having caused oxyntic atrophy leading to gastric hypoacidity and hypergastrinemia. No single H. pylori factor has been convincingly proved to be carcinogenic. It is probable that gastrin is the pathogenetic factor for gastric cancer due to H. pylori, autoimmune gastritis, and long-term prolonged inhibition of gastric acid secretion. Hypergastrinemia induces ECL cell hyperplasia, which develops into neuroendocrine tumors (NETs) and then into neuroendocrine carcinomas in rodents, a sequence that has also been described in humans. During carcinogenesis, the tumor cells lose specific traits, requiring that sensitive methods be used to recognize their origin. Gastric cancer occurrence may hopefully be prevented by H. pylori eradication at a young age, and by the reduced use of inhibitors of acid secretion and use of a gastrin antagonist in those with previous long-term H. pylori infection and those with autoimmune gastritis.

Inflammation and Digestive Cancer

Chronic inflammation is linked to carcinogenesis, particularly in the digestive organs, i.e., the stomach, colon, and liver. The mechanism of this effect has, however, only partly been focused on. In this review, we focus on different forms of chronic hepatitis, chronic inflammatory bowel disease, and chronic gastritis, conditions predisposing individuals to the development of malignancy. Chronic inflammation may cause malignancy because (1) the cause of the chronic inflammation is itself genotoxic, (2) substances released from the inflammatory cells may be genotoxic, (3) the cell death induced by the inflammation induces a compensatory increase in proliferation with an inherent risk of mutation, (4) changes in cell composition due to inflammation may modify function, resulting in hormonal disturbances affecting cellular proliferation. The present review focuses on chronic gastritis (Helicobacter pylori or autoimmune type) since all four mechanisms may be relevant to this condition. Genotoxicity due to the hepatitis B virus is an important factor in hepatocellular cancer and viral infection can similarly be central in the etiology and malignancy of inflammatory bowel diseases. Helicobacter pylori (H. pylori) is the dominating cause of chronic gastritis and has not been shown to be genotoxic, so its carcinogenic effect is most probably due to the induction of atrophic oxyntic gastritis leading to hypergastrinemia.

Long-term proton pump inhibitors use and its association with premalignant gastric lesions: a systematic review and meta-analysis

Background: Long-term maintenance therapy with proton pump inhibitors (PPIs) is a common treatment strategy for acid-related gastrointestinal diseases. However, concerns have been raised about the potential increased risk of gastric cancer and related precancerous lesions with long-term PPI use. This systematic review and meta-analysis aimed to evaluate this potential risk. Methods: We searched PubMed, Embase, and the Cochrane Central Register of Controlled Trials for randomised controlled trials published before 1 March 2023, with no language restrictions. The primary endpoint was the occurrence and progression of gastric mucosal atrophy, intestinal metaplasia, Enterochromaffin-like (ECL) cell hyperplasia, gastric polyps, and gastric cancer during the trial and follow-up. Data were analysed using a random effects model. Results: Of the 4,868 identified studies, 10 met the inclusion criteria and were included in our analysis, comprising 27,283 participants. Compared with other treatments, PPI maintenance therapy for more than 6 months was associated with an increased risk of ECL cell hyperplasia (OR 3.01; 95% CI 1.29 to 7.04; p = 0.01). However, no significant increase was found in the risk of gastric mucosal atrophy (OR 1.01; 95% CI 0.55 to 1.85; p = 0.97), intestinal metaplasia (OR 1.14; 95% CI 0.49 to 2.68; p = 0.76), gastric polyps (OR 1.13; 95% CI 0.68 to 1.89; p = 0.64), or gastric cancer (OR 1.06; 95% CI 0.79 to 1.43; p = 0.71). Conclusion: This systematic review and meta-analysis does not support an increased risk of gastric cancer or related precancerous lesions with long-term PPI maintenance therapy. However, long-term PPI use should be monitored for potential complications such as ECL cell hyperplasia. Further studies are needed to confirm these findings and evaluate the safety of PPI maintenance therapy for acid-related gastrointestinal diseases. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/, Identifier: PROSPERO (CRD42022379692).

Proton Pump Inhibitors and Gastric Cancer

Concerns have been raised regarding the long-term use of proton pump inhibitors (PPIs) as an important risk factor for gastric cancer in clinical practice. PPIs can cause hypergastrinemia at clinical doses, and hypergastrinemia has been reported to induce malignant neoplasms in the stomach in previous animal studies. In humans, the proliferation of enterochromaffin-like (ECL) cells induced by hypergastrinemia is suspected as a potential mechanism of gastric cancer. Meanwhile, persistent Helicobacter pylori (H. pylori) infection causes gastric atrophic change, which itself is a major cause of gastric cancer, and it can further increase the risk of gastric cancer by strengthening corpus atrophy through interaction with PPIs. Recent epidemiologic studies have reported an important link between long-term PPI intake and gastric cancer risk even after successful eradication of H. pylori. However, due to the methodological limitations of observational clinical studies, the causal relationship is still not clear, and a recent big data-based study reported that long-term PPI use was not related to gastric cancer incidence. Taken together, despite the potential detrimental effects of PPIs, it is currently difficult to draw a definite conclusion about its association with gastric cancer. To minimize the possibility of gastric cancer in H. pylori-infected patients or precancerous lesions in long-term PPI users, long-term PPI administration should be limited to the minimum effective dose, and antibacterial treatment for H. pylori should be considered.

Towards Understanding of Gastric Cancer Based upon Physiological Role of Gastrin and ECL Cells

Simple Summary

Generally, we know that cancers represent genetic changes in tumour cells, but we most often do not know the causes of cancers or how they develop. Our knowledge of the regulation of gastric acid secretion is well known, with the gastric hormone gastrin maintaining gastric acidity by stimulation of the enterochromaffin-like (ECL) cell to release histamine, which subsequently augments acid secretion. Furthermore, it seems to be a general principle that stimulation of function (which, for the ECL cell, is release of histamine) in a parallel way stimulates the proliferation of the same cell. Long-term hyperstimulation of cell division predisposes to genetic changes and, thus, development of tumours. All conditions with reduced gastric acidity result in an increased risk of gastric tumours due to elevated gastrin in order to restore gastric acidity. It is probable that Helicobacter pylori infection (the most important cause of gastric cancer), as well as drugs inhibiting gastric acid secretion induce gastric cancer in the long-term, due to an elevation of gastrin caused by reduced gastric acidity. Gastric carcinomas have been shown to express ECL cell markers, further strengthening this relationship.

Abstract

The stomach is an ideal organ to study because the gastric juice kills most of the swallowed microbes and, thus, creates rather similar milieu among individuals. Combined with a rather easy access to gastric juice, gastric physiology was among the first areas to be studied. During the last century, a rather complete understanding of the regulation of gastric acidity was obtained, establishing the central role of gastrin and the histamine producing enterochromaffin-like (ECL) cell. Similarly, the close connection between regulation of function and proliferation became evident, and, furthermore, that chronic overstimulation of a cell with the ability to proliferate, results in tumour formation. The ECL cell has long been acknowledged to give rise to neuroendocrine tumours (NETs), but not to play any role in carcinogenesis of gastric adenocarcinomas. However, when examining human gastric adenocarcinomas with the best methods presently available (immunohistochemistry with increased sensitivity and in-situ hybridization), it became clear that many of these cancers expressed neuroendocrine markers, suggesting that some of these tumours were of neuroendocrine, and more specifically, ECL cell origin. Thus, the ECL cell and its main regulator, gastrin, are central in human gastric carcinogenesis, which make new possibilities in prevention, prophylaxis, and treatment of this cancer.

Sacubitril/valsartan increases postprandial gastrin and cholecystokinin in plasma

AIMS

Neprilysin degrades natriuretic peptides in circulation and is also suggested to degrade the gut hormones gastrin and cholecystokinin. Neprilysin inhibition has become a therapeutic strategy and thus a regimen in need of further testing in terms of other hormonal axes besides natriuretic peptides. The aim of this study was to examine whether acute inhibition of neprilysin affects meal-induced responses in gastrin and cholecystokinin concentrations in healthy individuals.

METHODS AND RESULTS

Nine healthy young men were included in an open-labelled, randomized cross-over clinical trial. The participants received a standardized meal (25 g fat, 26 g protein, 42 g carbohydrate) on two separate days with or without a one-time dosage of sacubitril ((194 mg)/valsartan (206 mg)). Blood pressure, heart rate and blood samples were measured and collected during the experiment. Statistical differences between groups were assessed using area under the curve together with an ANOVA with a Bonferroni post hoc test. Sacubitril/valsartan increased the postprandial plasma concentrations of both gastrin and cholecystokinin (80% (AUC0-270 min, P = 0.004) and 60% (AUC0-270 min, P = 0.003), respectively) compared with the control meal. No significant hemodynamic effects were noted (blood pressure, AUC0-270 min, P = 0.86, heart rate, AUC0-270 min, P = 0.96).

CONCLUSION

Our study demonstrates that sacubitril/valsartan increases the postprandial plasma concentrations of gastrin and cholecystokinin in healthy individuals. The results thus suggest that neprilysin-mediated degradation of gastrin and cholecystokinin is physiologically relevant and may have a role in heart failure patients treated with sacubitril/valsartan.

Gastric Peptides-Gastrin and Somatostatin

Gastric acid secretion (i) facilitates digestion of protein as well as absorption of micronutrients and certain medications, (ii) kills ingested microorganisms, including Helicobacter pylori, and (iii) prevents bacterial overgrowth and enteric infection. The principal regulators of acid secretion are the gastric peptides gastrin and somatostatin. Gastrin, the major hormonal stimulant for acid secretion, is synthesized in pyloric mucosal G cells as a 101-amino acid precursor (preprogastrin) that is processed to yield biologically active amidated gastrin-17 and gastrin-34. The C-terminal active site of gastrin (Trp-Met-Asp-Phe-NH₂ ) binds to gastrin/CCK₂ receptors on parietal and, more importantly, histamine-containing enterochromaffin-like (ECL) cells, located in oxyntic mucosa, to induce acid secretion. Histamine diffuses to the neighboring parietal cells where it binds to histamine H₂ -receptors coupled to hydrochloric acid secretion. Gastrin is also a trophic hormone that maintains the integrity of gastric mucosa, induces proliferation of parietal and ECL cells, and is thought to play a role in carcinogenesis. Somatostatin, present in D cells of the gastric pyloric and oxyntic mucosa, is the main inhibitor of acid secretion, particularly during the interdigestive period. Somatostatin exerts a tonic paracrine restraint on gastrin secretion from G cells, histamine secretion from ECL cells, and acid secretion from parietal cells. Removal of this restraint, for example by activation of cholinergic neurons during ingestion of food, initiates and maximizes acid secretion. Knowledge regarding the structure and function of gastrin, somatostatin, and their respective receptors is providing novel avenues to better diagnose and manage acid-peptic disorders and certain cancers. Published 2020. Compr Physiol 10:197-228, 2020.

The Enterochromaffin-like [ECL] Cell-Central in Gastric Physiology and Pathology

Background: Studies on the regulation of gastric and pancreatic secretion began more than 100 years ago. Secretin was the first hormone postulated to exist, initiating the field of endocrinology. Gastrin produced in the antral mucosa was the second postulated hormone, and together with histamine and acetylcholine, represent the three major gastric acid secretagogues known since 1920. For a long time, the mast cell was the only recognized histamine-producing cell in the oxyntic mucosa and, in the mid-1980s, the ECL cell was recognized as the cell producing histamine, taking part in the regulation of gastric acid secretion. Methods: This review is based upon literature research and personal knowledge. Results: The ECL cell carries the gastrin receptor, and gastrin regulates its function (histamine release) as well as proliferation. Long-term hypergastrinemia results in gastric neoplasia of variable malignancies, implying that gastric hypoacidity resulting in increased gastrin release will induce gastric neoplasia, including gastric cancer. Conclusions: The trophic effect of gastrin on the ECL cell has implications to the treatment with inhibitors of acid secretion.

Not only stem cells, but also mature cells, particularly neuroendocrine cells, may develop into tumours: time for a paradigm shift

Stem cells are considered the origin of neoplasms in general, and malignant tumours in particular, and the stage at which the stem cells stop their differentiation determines the degree of malignancy. However, there is increasing evidence supporting an alternative paradigm. Tumours may develop by dedifferentiation from mature cells able to proliferate. Studies of gastric carcinogenesis demonstrate that mature neuroendocrine (NE) cells upon long-term overstimulation may develop through stages of hyperplasia, dysplasia, and rather benign tumours, into highly malignant carcinomas. Dedifferentiation of cells may change the histological appearance and impede the identification of the cellular origin, as seen with gastric carcinomas, which in many cases are dedifferentiated neuroendocrine tumours. Finding the cell of origin is important to identify risk factors for cancer, prevent tumour development, and tailor treatment. In the present review, we focus not only on gastric tumours, but also evaluate the role of neuroendocrine cells in tumourigenesis in two other foregut-derived organs, the lungs and the pancreas, as well as in the midgut-derived small intestine.

Neuroendocrine pathology of the stomach: the Parma contribution

The current knowledge on gastric neuroendocrine pathology essentially developed in the last four decades. The historical evolution of the concepts and of the relevant clinical implications is described from the perspective of a group actively participating in this research domain. The histamine-producing enterochromaffin-like (ECL) cells have been recognized as the leading cell type involved in the most significant alterations of gastric neuroendocrine cells. The trophic stimulus exerted by circulating gastrin has been demonstrated to have a crucial role on proliferative changes of ECL cells through a sequence of hyperplasia-dysplasia-neoplasia described by Solcia et al. (Digestion 41:185-200,1988). The development of ECL cell tumors in rats treated with toxicological doses of inhibitors of gastric acid secretion prompted appropriate anatomoclinical investigations proving the lack of tumor risk in humans when therapeutic dosages of the drugs are used. Moving from the comprehensive concept of gastric carcinoid, different types of neuroendocrine tumors have been identified in the stomach with substantial variations in prognosis and treatment options. In general, ECL cell tumors developed in hypergastrinemic conditions were found to behave better than those originating outside the setting of hormonal stimulation. Pathological features highly predictive of patient survival have been described. The genetic changes involved in tumor development and progression have revealed substantial overlapping with those of neuroendocrine tumors of other foregut derivatives (i.e., pancreas, duodenum, lung) delineating a family of neuroendocrine tumors genetically distinct from those of the distal parts of the digestive system.

Ultrastructure of ECL cells in Mastomys after long-term treatment with H2 receptor antagonist loxtidine

Gastric ECL-cell hyperplasia and carcinoids (ECLoma) develop after 1 year in rats treated with omeprazole or 2 months in Mastomys treated with loxtidine. The aim of this study was to examine the ultrastructure of ECL cells in Mastomys after loxtidine treatment with an attempt to evaluate whether an impairment of autophagy was involved in the tumorigenesis. Mastomys were given loxtidine for 8 or 27 weeks. Morphological analysis of ECL cells showed that (1) cell size was not increased after 8 or 27 weeks; (2) secretory vesicles, a hallmark feature of welldifferentiated ECL cells, were unchanged after 8 weeks but reduced after 27 weeks; (3) granules were reduced after 8 or 27 weeks; (4) microvesicles were unchanged after the treatment; and (5) vacuoles and lipofuscin bodies were found occasionally after 8 weeks but not at 27 weeks. In addition, the appearance of ECL-cell ultrastructure differed between loxtidine-treated Mastomys and rats treated with omeprazole or subjected to antrectomy, but was similar between Mastomys treated with loxtidine for 27 weeks and mice deficient in CCK(2) receptor. We suggest that the ultrastructure of ECL cells in Mastomys after long-term treatment with loxtidine displayed an impaired formation of vacuoles and lipofuscin bodies, markers of the autophagic pathway.

The production and role of gastrin-17 and gastrin-17-gly in gastrointestinal cancers

The gastrointestinal peptide hormone gastrin is responsible for initiating the release of gastric acid in the stomach in response to the presence of food and/or humoral factors such as gastrin releasing peptide. However, it has a role in the growth and maintenance of the gastric epithelium, and has been implicated in the formation and growth of gastric cancers. Hypergastrinemia resulting from atrophic gastritis and pernicious anemia leads to hyperplasia and carcinoid formation in rats, and contributes to tumor formation in humans. Additionally, gastrin has been suspected to play a role in the formation and growth of cancers of the colon, but recent studies have instead implicated gastrin processing intermediates, such as gastrin-17-Gly, acting upon a putative, non-cholecystokinin receptor. This review summarizes the production and chemical structures of gastrin and of the processing intermediate gastrin-17-Gly, as well as their activities in the gastrointestinal tract, particularly the promotion of colon cancers.

Chemical carcinogenesis of the gastrointestinal tract in rodents: an overview with emphasis on NTP carcinogenesis bioassays

Cancers of the stomach and large intestine (LI) are the second and fourth leading causes of human cancer mortality. A review of the National Toxicology Program (NTP) database and the Carcinogenic Potency Database (CPDB) reveals that chemically induced neoplasms of the gastrointestinal tract (GIT) are relatively common. Within the GIT, epithelial tumors of the forestomach in mice and rats and LI of the rat are most common. Generally, there is a high species concordance for forestomach with at least 26 chemicals inducing tumors in both species. Glandular stomach tumors are rare, and the few reported are usually neuroendocrine tumors (carcinoids) originating from the enterochromaffin-like (ECL) cells. Of 290 carcinogenic agents identified by the NTP, 19 (7%) caused intestinal neoplasia, 14 in the rat and 5 in the mouse. Neoplasms occurred in both males and females, exclusively in the small intestine (SI) of the mouse and in the LI or both SI and LI in the rat. Enteric carcinogens (NTP) frequently induced neoplasms at other alimentary sites (oral cavity, esophagus, and stomach). In conclusion, the most common induced GIT tumors are squamous neoplasms of the forestomach, glandular neoplasms of the stomach are rare, and rats appear more prone to developing LI (colorectal) cancer compared to mice.

Achlorhydria is associated with gastric microbial overgrowth and development of cancer: Lessons learned from the gastrin knockout mouse

Gastrin and gastrin receptor-deficient mice have been used for genetic dissection of the role of gastrins in maintaining gastric homeostasis and control of acid secretion. The gastrin knockout mice are achlorhydric due to inactivation of the ECL and parietal cells. Moreover, this achlorhydria is associated with intestinal metaplasia and bacterial overgrowth, which ultimately leads to the development of gastric tumours. The association between progastrin, progastrin-derived processing intermediates and colorectal carcinogenesis has also been examined through genetic or chemical cancer induction in several mouse models, although the clinical relevance of these studies remains unproven. While others have focused on models of increased gastrin production, the present review describes the lessons learned from gastrin-deficient mice. Study of these mice helps our understanding of how dysregulation of gastrin secretion may be implicated in human disease.

Low gastric acid and high plasma gastrin in high-anxiety Wistar Kyoto rats

OBJECTIVE

Wistar Kyoto (WKY) rats are more susceptible to stress-evoked ulcerations than Sprague-Dawley (SPD) rats. We have already demonstrated that gastrin cells are more active and ghrelin cells less active in WKY rats than in SPD rats. The purpose of this study was to compare endocrine cell activity and gastric acid output in WKY and SPD rats.

MATERIAL AND METHODS

Gastric acid output was determined in conscious rats with gastric fistula. Plasma gastrin and ghrelin levels were measured after an overnight fast. Acid secretagogues (gastrin, histamine and carbachol) were given by continuous subcutaneous infusion.

RESULTS

The volume of gastric juice, and the acidity and acid output were all significantly lower (p <0.05) in fasted WKY rats than in fasted SPD rats. Gastrin evoked a 4-fold (p <0.01) and 3-fold (p <0.05) increase in gastric acid output in SPD rats and WKY rats, respectively. Histamine raised the acid output 1.6-fold in SPD rats (p=0.06) and 3-fold in WKY rats (p <0.05), while carbachol failed to affect the acid output (weak increase, p >0.05). Fasting plasma ghrelin levels were 2-fold higher in SPD rats than in WKY rats (p <0.01) while fasting gastrin levels were 10-fold higher in WKY rats than in SPD rats (p <0.05). Neither the parietal-cell density nor the oxyntic mucosal thickness differed between the two strains.

CONCLUSIONS

The results of the present study suggest that a high gastrin cell activity in WKY rats is secondary to a low gastric acidity. Whether the high gastrin cell activity is linked to susceptibility to stress ulcer in WKY rats warrants further investigation.

Octreotide induces apoptosis in the oxyntic mucosa

Previous studies show that octreotide LAR causes regression of gastric ECL-cell carcinoids, reducing both number and size of tumours. This study examines the molecular mechanisms behind the antiproliferative effect of octreotide on the oxyntic mucosa. Female rats received octreotide LAR for 21 days. Serum gastrin was measured and tissue samples for RNA extraction and histology collected from the oxyntic mucosa. Affymetrix analysis showed regulated genes related to apoptosis and proliferation, and a large group of regulated growth-related transcription factors. Verification by real time qRT-PCR showed a high degree of consistency to the microarray results. Supporting the molecular results, histomorphometry showed significant decreases in the number of gastric glands, cells per gland and length of glands, and a tendency towards increased apoptosis and decreased proliferation. Thus, octreotide exerts a negative effect on oxyntic mucosal growth, and induces extensive gene expression changes relevant to growth regulation.

Ciprofibrate stimulates the gastrin-producing cell by acting luminally on antral PPAR-alpha

The lipid-lowering drug ciprofibrate stimulates gastrin-producing cells in the rat stomach without lowering gastric acidity. Although suggested to be a luminal action on antral peroxisome proliferator-activated receptor-alpha (PPAR-alpha), the mechanism is still not fully elucidated. Gastric bypass was surgically prepared in male Sprague-Dawley rats. Gastric-bypassed and sham-operated rats were either given ciprofibrate (50 mg.kg(-1).day(-1) in methocel) or vehicle alone for 7 wk. PPAR-alpha knockout (KO) and wild-type (WT) mice were either given ciprofibrate (500 mg.kg(-1).day(-1) in methocel) or vehicle alone for 2 wk. The concentration of gastrin in blood was analyzed. Antral G cell density and gastrin mRNA abundance were determined by using immunostaining and Northern blot analysis. Ciprofibrate did not raise plasma gastrin or G cell density in gastric-bypassed rats, although the gastrin mRNA level was slightly increased. In contrast, ciprofibrate induced hypergastrinemia, a 50% increase in G cell density, and a threefold increase in gastrin mRNA in sham-operated rats. In PPAR-alpha KO mice, ciprofibrate did not raise G cell density or the gastrin mRNA level. The serum gastrin level was reduced by ciprofibrate. In WT mice, ciprofibrate induced hypergastrinemia, a doubling of G cell density, and a threefold increase in gastrin mRNA. Comparing animals dosed with vehicle only, PPAR-alpha KO mice had higher serum gastrin concentration than WT mice. We conclude that the main effects of ciprofibrate on G cells are mediated from the antrum lumen, and the mechanism is dependent on PPAR-alpha. The results indicate that PPAR-alpha may have a role in the physiological regulation of gastrin release.

Dedifferentiation of enterochromaffin-like cells in gastric cancer of hypergastrinemic cotton rats

The role of enterochromaffin-like (ECL) cells in gastric carcinogenesis is not fully understood. Spontaneous tumours developing in hypergastrinemic female cotton rats have an adenocarcinoma phenotype, but numerous cells in the dysplastic mucosa as well as in the carcinomas are positive for neuroendocrine markers. In the present study of female cotton rats with 2 and 8 months' hypergastrinemia, the oxyntic mucosa of the stomach was examined histologically and immunolabelled for histidine decarboxylase (HDC) and pancreastatin, and hyperplastic and neoplastic ECL cells were evaluated by electron microscopy. These animals developed hyperplasia of the oxyntic mucosa in general and of the ECL cells in particular after 2 months and dysplasia and carcinomas after 8 months. The immunoreactivity of the ECL cells in the oxyntic mucosa was increased at 2 months and declined at 8 months. These histological changes were associated with progressive loss of secretory vesicles and granules in ECL cells. We suggest that ECL cells in hypergastrinemic cotton rats dedifferentiate with time and that the gastric carcinomas may develop from ECL cells.

Regression of type II gastric carcinoids in multiple endocrine neoplasia type 1 patients with Zollinger-Ellison syndrome after surgical excision of all gastrinomas

Enterochromaffin-like (ECL) tumors are documented in patients with hypergastrinemia secondary to chronic atrophic gastritis or with Zollinger-Ellison syndrome and multiple endocrine neoplasia type 1 (ZES-MEN-1). In patients with ECL tumors and atrophic gastritis, normogastrinemia after antrectomy has resulted in resolution, regression, or stabilization of ECL tumors. The natural history of ECL tumors associated with ZES-MEN-1 following normalization of gastrin levels after gastrinoma resection has not been previously reported. The purpose of this study was to determine the course of ECL tumors in patients with ZES-MEN-1 following normalization of serum gastrin levels after gastrinoma resection. Two patients with ZES-MEN-1 had biopsy-proven ECL tumors on endoscopic evaluation. They then underwent surgical exploration that included distal pancreatectomy, enucleation of pancreatic head tumors, duodenotomy with excision of submucosal tumors, and peripancreatic lymphadenectomy. Gastric ECL tumors larger than 1.0 cm were locally excised. Patients underwent long-term follow-up with biochemical and endoscopic surveillance. Normogastrinemia was achieved and sustained following gastrinoma resection in two patients with ZES-MEN-1. Periodic endoscopic surveillance over a 6-year period showed complete resolution of the ECL tumors. The development of ECL tumors associated with ZES-MEN-1 is multifactorial. Studies identified a genetic influence on tumor growth with loss of heterozygosity at the MEN-1 gene locus in ECL tumors. The resolution of ECL tumors in ZES-MEN-1 patients who are normogastrinemic indicates that an elevated gastrin level is a primary initiator for development of these tumors. Therefore both genetic defects and hypergastrinemia are causative agents. Normalization of serum gastrin levels is critical for the prevention of aggressive forms of ECL tumors.

New molecular targets for treatment of peptic ulcer disease

Most patients with peptic ulcer disease are currently treated with proton pump inhibitors or histamine H(2) receptor antagonists. The long-term use of these compounds has been associated with two potential problems. Firstly, proton pump inhibitors may induce enterochromaffin-like (ECL) cell hyperplasia. Secondly, ulcers may relapse despite maintenance therapy with histamine H(2) antagonists. This has been the rationale for the development of new antisecretory agents, including antagonists against gastrin and gastrin releasing peptide (GRP), as well as ligands to histamine H(3) receptors. Several potent, high affinity cholecystokinin (CCK)-2 receptor antagonists have recently been identified such as L-365260, YM-022, RP-73870, S-0509, spiroglumide and itriglumide (CR-2945). Current data suggest that they all have antisecretory and anti-ulcer effects. In addition to reducing acid production, CCK-2 receptor antagonists may possibly also accelerate gastric emptying, a combination of functions which could potentially be beneficial in patients with functional dyspepsia. Receptors for bombesin and its mammalian counterpart GRP have been localised in the brain, spinal cord and enteric nerve fibres of the gut as well as on secretory cells and smooth muscle cells of the intestinal tract. Current data clearly indicate that endogenous GRP is involved in the regulation of basal and postprandial acid secretion. However, at this stage it is not clear whether GRP agonists or GRP antagonists can be developed into useful drugs. The peptide has a wide range of biological effects and it is likely that analogues of GRP or antagonists of the peptide affect not only gastric acid secretion but also induce considerable side effects. Histamine plays a central role in the stimulation of acid secretion. After their detection in the brain, H(3) receptors have been identified in a variety of tissues including perivascular nerve terminals, enteric ganglia of the ileum and lung, and ECL cells. Despite many studies, the role of H(3) receptors in the regulation of gastric acid secretion is still unclear. Controversial data have been presented, and study results largely depend on the species and experimental models. It seems unlikely that proton pump inhibitors or H(2) receptor antagonists will be replaced in the near future by new antisecretory agents. The current shortcomings of the new compounds include mainly their reduced clinical effectiveness and pharmacological limitations. However, the development of these new antisecretory compounds provides interesting tools to assess the physiological and pharmacological role of different receptors within the gastrointestinal tract. The use of CCK-2 receptor antagonists in patients with functional dyspepsia and Zollinger-Ellison syndrome should be examined in randomised, controlled trials.

Carcinoid tumors of the stomach

Interest in gastric carcinoid tumors has in recent time amplified considerably as the understanding of both their biological background and clinical significance has developed. The increase in identification associated with the widespread availability of upper gastrointestinal endoscopy has facilitated diagnosis. In addition concern related to the consequences of long-standing hypergastrinemia generated by the use of potent acid-suppressive medications has augmented both clinical and scientific focus on gastric neuro endocrine issues. The elucidation of the regulatory mechanisms of the progenitor cell (ECL cell) of the gastric carcinoid tumor, the refinement of a pathological grading system for ECL cell proliferation, and the availability of specific immunohistologic identification techniques have further amplified the characterization of this lesion. Although the putative malignant potential of gastric carcinoids may ultimately be of only modest concern in a background of hypergastrinemia its relationship to gastric adenocarcinoma is still enigmatic and worthy of further consideration. This review will describe the molecular interrelationship between low-acid states, gastrin, and ECL cell proliferation and will discuss the pathological classification of the distinct types of gastric carcinoid tumors. In addition, the clinical rationale of current diagnostic and therapeutic strategies will be examined, providing a logical basis for the formulation of appropriate management strategies for patient care.

Gastric acid secretion in L-histidine decarboxylase-deficient mice

BACKGROUND & AIMS

Histamine, gastrin, and acetylcholine are known to be the primary secretagogues of gastric acid secretion, but how the roles are shared among these secretagogues remains to be fully clarified. To evaluate the cooperation between histamine and the other secretagogues, acid secretion responses induced by each secretagogue were measured in L-histidine decarboxylase (HDC)-deficient mice.

METHODS

Acid secretion was measured by the titration of acid under anesthesia. The expression of selected genes involved in acid secretion was determined by Northern blot and/or immunoblot analysis. Histamine-2 (H(2)) receptor binding in the gastric mucosa was investigated using [(3)H]tiotidine.

RESULTS

HDC-deficient mice showed low basal and high exogenous histamine-stimulated acid secretion. The mutant mice showed hypergastrinemia and did not undergo acid secretion upon treatment with exogenous gastrin. However, carbachol stimulated weak and transient acid secretion in the mutants. The Bmax values for H(2) and the expression of Gs alpha in gastric mucosal membranes were higher in the mutants than in the wild-type mice.

CONCLUSIONS

This study confirms the concept that histamine production is essential for gastric acid secretion induced by gastrin, but not for that induced by carbachol. HDC-deficient mice should be a suitable model for further functional analyses of the correlation between histamine and the other acid secretagogues.

Review article: potential gastrointestinal effects of long-term acid suppression with proton pump inhibitors

This review examines the evidence for the development of adverse effects due to prolonged gastric acid suppression with proton pump inhibitors. Potential areas of concern regarding long-term proton pump inhibitor use have included: carcinoid formation; development of gastric adenocarcinoma (especially in patients with Helicobacter pylori infection); bacterial overgrowth; enteric infections; and malabsorption of fat, minerals, and vitamins. Prolonged proton pump inhibitor use may lead to enterochromaffin-like cell hyperplasia, but has not been demonstrated to increase the risk of carcinoid formation. Long-term proton pump inhibitor treatment has not been documented to hasten the development or the progression of atrophic gastritis to intestinal metaplasia and gastric cancer, although long-term studies are required to allow definitive conclusions. At present, we do not recommend that patients be tested routinely for H. pylori infection when using proton pump inhibitors for prolonged periods. Gastric bacterial overgrowth does increase with acid suppression, but important clinical sequelae, such a higher rate of gastric adenocarcinoma, have not been seen. The risk of enteric infection may increase with acid suppression, although this does not seem to be a common clinical problem with prolonged proton pump inhibitor use. The absorption of fats and minerals does not appear to be significantly impaired with chronic acid suppression. However, vitamin B12 concentration may be decreased when gastric acid is markedly suppressed for prolonged periods (e.g. Zolllinger-Ellison syndrome), and vitamin B12 levels should probably be assessed in patients taking high-dose proton pump inhibitors for many years. Thus, current evidence suggests that prolonged gastric acid suppression with proton pump inhibitors rarely, if ever, produces adverse events. Nevertheless, continued follow-up of patients taking proton pump inhibitors for extended periods will provide greater experience regarding the potential gastrointestinal adverse effects of long-term acid suppression.

Lessons from genetically engineered animal models. III. Lessons learned from gastrin gene deletion in mice

Gastrin is the principal hormonal inducer of gastric acid secretion. Chronic hypergastrinemia, leading to hypersecretion of gastric acid and increased proliferation of parietal and enterochromaffin-like (ECL) cells, has been well described. In contrast, the physiological consequences of chronic gastrin deficiency had been poorly understood until the recent genetic engineering of mouse mutants containing a gastrin gene deletion by homologous recombination in embryonic stem cells. This themes article describes the consequences of constitutive gastrin deficiency on the development and physiology of the stomach. A lack of gastrin disrupts basal gastric acid secretion and renders the acid secretory system unresponsive to acute histaminergic, cholinergic, and gastrinergic stimulation. The defect in acid secretion is greater than would have been predicted from previous studies in which gastrin action was acutely blocked. Cellular changes include thinning of the gastric mucosa in the gastrin-deficient mice, with a reduction in parietal cells and reduced expression of markers of parietal and ECL cell-differentiated functions. The results suggest that gastrin is required for the functional maturation of the acid-secretory system.

Serum gastrin and chromogranin A during medium- and long-term acid suppressive therapy: a case-control study

BACKGROUND

Serum chromogranin A (CgA) is regarded as a reliable marker of neuroendocrine proliferation. We previously described increased serum CgA levels during short-term profound gastric acid inhibition.

AIM

To investigate serum gastrin and CgA levels in dyspeptic patients during continuous medium- (6 weeks to 1 year), or long-term (1-8 years) gastric acid suppressive therapy.

PATIENTS AND METHODS

114 consecutive dyspeptic patients referred for upper gastrointestinal endoscopy were enrolled in a cross-sectional, case-control study [62 patients on continuous antisecretory therapy, either with proton pump inhibitors (n = 47) or H2-receptor antagonists (H2RA) (n = 15) for gastro-oesophageal reflux disease with or without Barrett's oesophagus or functional dyspepsia, and 52 age- and sex-matched patients without medical acid inhibition and with normal endoscopic findings (control group)]. Omeprazole doses ranged from 20 mg to 80 mg daily and ranitidine from 150 mg to 450 mg daily. Fasting serum CgA and serum gastrin levels were measured by radioimmunoassay (reference values: serum CgA < 4.0 nmol/L; serum gastrin < 85 ng/L).

RESULTS

Fasting serum CgA levels positively correlated with serum gastrin in the entire study population (r = 0. 55, P = 0.0001). Median serum CgA values were higher in patients treated with a proton pump inhibitor than H2RA [2.8 (2.0-5.9) nmol/L vs. 2 (1.9-2.3) nmol/L, P < 0.002] and controls [2.8 (2.0-5.9) nmol/L vs. 1.8 (1.5-2.2) nmol/L, P < 0.0001) and did not differ between patients treated with H2RA or controls. Serum gastrin and CgA levels in patients on proton pump inhibitor therapy positively correlated with the degree and duration of acid inhibition. Patients on long-term proton pump inhibitor therapy had significantly higher fasting serum gastrin and CgA than those on medium-term proton pump inhibitor therapy [127 (73-217) ng/L vs. 49 (29-78) ng/L, P < 0.0001 and 4.8 (2.8-8) ng/L vs. 2.1 (1.9-2.6) ng/L, P < 0.001]. No such relation was found in patients on medium- vs. long-term H2RA. Overall, patients with positive Helicobacter pylori serology had higher serum gastrin and CgA levels than those with negative H. pylori serology [51 (27-119) ng/L vs. 27 (14-79) ng/L, P = 0.01, 2.4 (1.9-3.4) nmol/L vs. 2.0 (1.7-2.5) nmol/L, P = 0.05].

CONCLUSIONS

During long-term continuous proton pump inhibitor treatment, serum gastrin and CgA levels are significantly elevated compared to H2RA treatment and nontreated dyspeptic controls. H. pylori infection seems to affect gastric ECL cell secretory function. Increased serum CgA values during long-term profound gastric acid inhibition could reflect either gastric enterochromaffin-like cell hyperfunction or proliferative changes.

Impaired gastric acid secretion in gastrin-deficient mice

To further understand the role of the peptide hormone gastrin in the development and function of the stomach, we have generated gastrin-deficient mice by gene targeting in embryonic stem cells. Mutant mice were viable and fertile, without obvious visible abnormalities. However, gastric function was severely affected by the loss of gastrin. Basal gastric acid secretion was abolished and could not be induced by histamine, carbachol, or gastrin. Histological analysis revealed alterations in the two cell types primarily involved in acid secretion, parietal and enterochromaffin-like (ECL) cells. Parietal cells were reduced in number with an accumulation of immature cells lacking H(+)-K(+)-adenosinetriphosphatase (H(+)-K(+)-ATPase). ECL cells were positioned closer to the base of the gastric glands, with markedly lower expression of histidine decarboxylase. Gastrin administration for 6 days reversed the effects of the gastrin deficiency, leading to an increase in the number of mature, H(+)-K(+)-ATPase-positive parietal cells and a partial restoration of acid secretion. The results show that gastrin is critically important for the function of the acid secretory system.

Gastrin inhibits secretin-induced ductal secretion by interaction with specific receptors on rat cholangiocytes

We assessed the effect of gastrin on ductal secretion in normal and bile duct-ligated (BDL) rats. The effect of gastrin on ductal secretion was examined in the presence of proglumide, a specific antagonist for gastrin receptor (GR). We isolated pure cholangiocytes from normal and BDL rats and assessed gastrin effects on secretin receptor (SR) gene expression and intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels. We examined the presence of GR mRNA in cholangiocytes by reverse transcription polymerase chain reaction (RT-PCR). In normal or BDL rats, gastrin produced no changes in spontaneous bile secretion. Simultaneous infusion of gastrin inhibited secretin-induced choleresis and bicarbonate output in BDL rats. In the presence of proglumide gastrin did not inhibit secretin-induced choleresis in BDL rats. Gastrin decreased in cholangiocytes from BDL rats 1) SR gene expression and 2) secretin-induced cAMP levels. With the use of RT-PCR, GR mRNA was detected in cholangiocytes. Similar to what is shown for secretin and somatostatin, we propose that the opposing effects of secretin and gastrin on cholangiocyte secretory activity regulate ductal secretion in rats.

Evidence that rat stomach ECL cells represent the main source of circulating pancreastatin

Recently, we showed that the ECL cells in the oxyntic mucosa of the rat stomach are an important source of circulating pancreastatin, a fragment of chromogranin A. The present study examined how much the ECL cells contribute to the circulating levels of pancreastatin during omeprazole-evoked hypergastrinemia. Rats received omeprazole (400 mumol kg-1 day-1) by the oral route for 3 weeks. Two weeks after the start of the treatment, the rats were subjected to a sham operation or fundectomy. The concentrations of gastrin and pancreastatin in serum were monitored before and after the operations. The ECL cells were visualized by pancreastatin immunostaining and their number was determined. The activity of oxyntic mucosal histidine decarboxylase (HDC) was measured before and after 2 weeks of omeprazole treatment. Omeprazole-induced hypergastrinemia resulted in elevated serum pancreastatin and increased oxyntic mucosal HDC activity. Pancreastatin-immunoreactive cells were equally numerous before and after 2 weeks of omeprazole treatment. After surgical removal of the ECL cells by fundectomy, the serum gastrin concentration remained high whereas the serum pancreastatin concentration decreased by 90%. We conclude that the ECL cells in omeprazole-treated rats are responsible for 90% of circulating pancreastatin.

The role of gastrin and cholecystokinin in normal and neoplastic gastrointestinal growth

Gastrin and cholecystokinin (CCK) act as growth factors for the gastric mucosa and the pancreas, respectively. CCK is also responsible, via the CCK-A receptor, for the pancreatic hyperplasia observed following the feeding of protease inhibitors or pancreaticobiliary diversion. Hypergastrinaemia does not increase the incidence of spontaneous gastrointestinal carcinoma, but does stimulate the proliferation of gastric enterochromaffin-like cells via the gastrin/CCK-B receptor, with a consequent increase in the incidence of gastric carcinoids. Whether gastrin influences mutagen-induced gastrointestinal carcinogenesis is still controversial, but CCK clearly enhances the induction by carcinogens of acinar tumours in the pancreas. While gastrin increases xenograft growth of 50% of gastrointestinal tumours tested, effects on the proliferation of gastrointestinal tumour cell lines in vitro have been more difficult to demonstrate, perhaps because many cell lines are already maximally stimulated by autocrine gastrin. Gastrin mRNA and progastrin, but not mature amidated gastrin, have been detected in all gastrointestinal cell lines tested. Although cell proliferation is inhibited by gastrin/CCK receptor antagonists, the spectrum of antagonist affinities is not consistent with binding to either CCK-A or gastrin/CCK-B receptors. Definition of the molecular structure of the receptor involved in the autocrine loop may lead to novel therapies for gastrointestinal cancer.

Histamine as an intermediate growth factor in genesis of gastric ECLomas associated with hypergastrinemia in mastomys

Profound and sustained inhibition of gastric acid secretion has been associated with development of carcinoid tumors of the fundic enterochromaffin-like (ECL) cells in rodents. While ECL cell hyperplasia has been recognized in humans, the development of carcinoid tumors is rare and often confined to patients under treatment for gastrinoma related to the multiple endocrine neoplasia type I (MEN1) syndrome. The Mastomys was utilized as a model for the rapid induction of ECLomas by insurmountable acid secretory blockade induced by the pharmacologically irreversible H2-receptor antagonist, loxtidine. Loxtidine-induced ECL cell hyperplasia and neoplasia were compared in the absence of presence of cyproheptadine (0.5 mg/kg), an H1-receptor antagonist. Loxtidine administration resulted in a significant increase in ECL cell hyperplasia and neoplasia as well as an increase in ECL cell number, mucosal thickness, plasma gastrin levels, and stomach weight. Cyproheptadine ameliorated loxtidine-induced ECL cell hyperplasia and neoplasia and significantly decreased loxtidine-stimulated increases in ECL cell number. Nevertheless, cyproheptadine failed to alter the loxtidine-induced increase in plasma gastrin, stomach weight or mucosal height. The results indicate that cyproheptadine, an H1-receptor antagonist, inhibits loxtidine-induced ECL cell hyperplasia independent of any effects on serum gastrin.

Hyperplastic manifestations of enterochromaffin-like cells in the stomach of rats with congenital moderate hypergastrinemia

The effect of moderate congenital hypergastrinemia on the enterochromaffin-like (ECL) cells was investigated in Zucker rats 4 and 18 months of age by combining autoradiography after tritiated thymidine injection and selective immunocytochemistry. In both age groups the serum gastrin concentration was 200% higher in obese (fa/fa) than in lean (Fa/Fa; Fa/fa) littermates. In 4-month-old obese rats there was a 120% increase (p < 0.05) in the ECL cell labeling index and also a moderate increase in the ECL cell density (p < 0.05) compared with lean controls. In 18-month-old obese rats the hyperplasia was quantitatively more prominent, with both linear and micronodular ECL cell hyperplasia. At this stage, the ECL cell labeling indices in obese and in lean animals were similar. These data support the hypothesis that moderate hypergastrinemia initially accelerates the ECL cell proliferation rate, leading to diffuse ECL cell hyperplasia. In similar conditions, at the latter stage, linear and micronodular ECL cell hyperplasia also develop in most of the hypergastrinemic animals.

A new look at an old hormone gastrin

The origin of gastrin from the G cell has been identified, as have a number of mechanisms regulating both secretion and processing of the peptide. Little, however, is known of the intracellular regulation of processing and secretion. Gastrin receptors have been identified and cloned, although the exact relationship to the cholecystokinin receptor remains to be clarified. The gene for the peptide has been sequenced and various promoters identified. Up- and downstream sequences have been demonstrated to be interrelated with epidermal growth factor and somatostatin, and the existence of a complex gastric-based molecular regulatory system is apparent. The dynamic role of gastrin in the regulation of acid secretion has been delineated by its action on multiple targets in gastric parietal cells and endocrine enterochromaffinlike cells. Similarly, its trophic effects on gastrointestinal tissue have been explored, resulting in its identification as a common denominator of gastric fundic hyperplasia and microcarcinoid evolution in conditions of hypergastrinemia.

Reversibility of the cell kinetic changes induced by omeprazole in the rat oxyntic mucosa. An autoradiographic study using tritiated thymidine

Both oxyntic mucosal progenitor cells and enterochromaffin-like (ECL) cells are under the trophic control of gastrin. We studied the effect of discontinuing omeprazole-induced hypergastrinemia on cell proliferation and ECL cell function in the rat oxyntic mucosa. All rats had hypergastrinemia after 16 days' omeprazole administration, and the proliferation rate of both progenitor and ECL cells was increased, whereas it was decreased 5 days after withdrawal of omeprazole. Circulating gastrin had normalized by then. The proliferative activity of the progenitor cells returned to normal within 10 days, whereas that of the ECL cells remained suppressed for at least 20 days. The histidine decarboxylase activity of the ECL cells changed in parallel with their proliferative activity. These data suggest either a down-regulation of membrane receptors or the involvement of still unknown inhibitors of mitotic activity and ECL cell function in the oxyntic mucosa.

Unilateral vagal denervation suppresses omeprazole-induced trophic effects on the denervated side of the rat stomach

In several experimental animals treatment with large doses of the proton pump inhibitor omeprazole leads to hypergastrinemia and with time to trophic effects in the acid-producing part of the stomach, most notably an increased density of the histamine-producing enterochromaffin-like (ECL) cells. The trophic effects are thought to reflect the increase in circulating gastrin. In the present study unilateral vagal denervation in the rat partly suppressed the tropic effects seen in the denervated side of the stomach but not those in the intact side after treatment with omeprazole for 10 weeks. Unilateral vagal denervation significantly reduced the proliferative stimulus of omeprazole on the ECL cells in the denervated part of the stomach. Thus, an intact vagal innervation appears to be essential for the capacity of the oxyntic mucosa, including the ECL cells, to respond to elevations in serum gastrin. We suggest that gastrin and the vagus interact to maintain trophic control of the oxyntic glands.

The effect of omeprazole-induced hypergastrinemia on the oxyntic mucosa of mastomys

Mastomys is a rodent with a high incidence of spontaneous carcinoids in the acid-producing part of the stomach. The present study was conducted to examine whether hypergastrinemia could promote tumor formation in this species. Mastomys, 4 months of age, were treated for 5 months with omeprazole subcutaneously, 100 mumol/kg body weight daily, and compared with mastomys given the vehicle only. The plasma gastrin concentration and the number of antral gastrin cells were increased in the omeprazole-treated group. The hypergastrinemia was associated with elevated histidine decarboxylase activity and histamine content in the oxyntic mucosa and with a trophic effect on the oxyntic mucosa and the enterochromaffin-like cells. However, no carcinoid tumors were observed, possibly because the strain of mastomys studied does not produce carcinoids spontaneously.

The neuroendocrine system of the gut--an update

During the last few years the endocrine stomach has come into focus much due to the side-effects produced by powerful acid blockers. A sustained and marked inhibition of acid secretion in the rat results in hypergastrinemia, with gastrin cell hyperplasia, and a consequent hyperplasia of the ECL cells. This response of the ECL cells was predictable in view of previous observations that sustained hypergastrinemia causes ECL cell hyperplasia. While the gastrin cell hyperplasia levels off at about twice the normal cell density a few weeks after start of treatment, the ECL cells continue to proliferate for months to reach a five-fold higher density than normally. Evidence is accumulating that ECL cells proliferate through self replication. After life-long inhibition of acid production (high doses of ranitidine or omeprazole) or after extirpation of 75% of the acid-producing part of the stomach, ECL cell carcinoids develop. Endocrine cells in the gut often contain more than one putative messenger. Thus, gastrin cells in many species store GABA and peptide YY; in e.g. cat and man they store in addition a xenopsin-like peptide. Neuromedin U and pituitary adenylate cyclase activating peptide (PACAP) have recently been demonstrated in gut nerves. Their role in gut physiology remains to be identified.