Omeprazole Treatment Ameliorates Oxyntic Atrophy Induced by DMP-777

Atrophic gastritis, characterized as parietal cell loss or oxyntic atrophy, is the primary event in the evolution of the spectrum of metaplastic and hyperplastic lineage changes thought to predispose to gastric neoplasia. A number of animal models have provided insights into the lineage changes induced by oxyntic atrophy. Recently, we have reported a model for pharmacological induction of oxyntic atrophy with DMP-777. DMP-777 ablates parietal cells selectively and leads to the gastric cell lineage changes including foveolar hyperplasia and spasmolytic polypeptide expressing metaplasia (SPEM). Previous investigations showed that DMP-777 dissipated a gastric tubulovesicle proton gradient without impairing the H/K-ATPase activity, consistent with its pharmacological action as a parietal cell-specific protonophore which could induce parietal cell necrosis through backwash of luminal acid into actively secreting cells. We hypothesized that, if DMP-777 was acting as a parietal cell protonophore, then suppression of acid secretion should protect parietal cells from the toxic effects of the drug. In this study, we pretreated and coadministered the proton pump inhibitor omeprazole with DMP-777 to determine the effect of active acid secretion inhibition on the DMP-777-induced histologic changes in the stomachs of male rats. Omeprazole pretreatment ameliorated DMP-777-induced parietal cell loss as well as foveolar hyperplasia. These results indicate that active acid secretion is required for DMP-777 cytotoxicity, consistent with its suggested behavior as a parietal cell-specific protonophore.     

Foveolar hyperplasia following partial gastrectomy results from expansion of surface mucous cell compartment

Antrectomy with gastroenterostomy reconstruction is often associated with the development of foveolar hyperplasia and oxyntic atrophy. While a role for bile reflux in the etiology of foveolar hyperplasia is well established, the identity of the mucous cell lineages responsible for this condition have not been well characterized. We have studied three patients who demonstrated foveolar hyperplasia in their gastric remnant following antrectomy and gastroenterostomy. Mucosal samples were stained with antibodies against the trefoil peptides pS2 and hSP, to identify surface mucous and mucous neck cell lineages, respectively. Postoperative biopsies from all three patients showed oxyntic atrophy as documented by staining of parietal cells with antibodies against H/K-ATPase. All three patients demonstrated an exclusive expansion of pS2 immunoreactive mucous cells. The hSP staining cells were located deep in the expanded foveolar region. The results suggest that foveolar hyperplasia following antrectomy with gastroenterostomy results from a reactive hyperplasia of surface mucous cells. This pattern of surface cell hyperplasia is more consistent with a reactive expansion of mucous cells than with a response to chronic injury.     

Potentiation of oxyntic atrophy-induced gastric metaplasia in amphiregulin-deficient mice

BACKGROUND & AIMS: The loss of parietal cells from the gastric mucosa (oxyntic atrophy) is a critical step in the pathogenesis of chronic gastritis and gastric adenocarcinoma. Parietal cells are known to secrete epidermal growth factor receptor (EGFR) ligands, which are critical regulators of differentiation in the gastric mucosa. Although all of the actions of EGFR ligands are mediated through a common EGFR protein, individual ligands may produce different physiologic responses. Previous investigations have suggested that a deficit in EGFR signaling in waved-2 mice accelerates the emergence of metaplasia after induction of acute oxyntic atrophy. We sought to determine whether specific EGFR ligands regulate the metaplastic response to oxyntic atrophy. METHODS: To induce spasmolytic polypeptide-expressing metaplasia (SPEM), amphiregulin (AR) and transforming growth factor-alpha-deficient mice and their wild-type littermates were treated with DMP-777 for 0-14 days and for 14 days followed by 14 days of recovery off drug. We evaluated the gastric mucosal response to oxyntic atrophy using cell lineage-specific markers. RESULTS: Although loss of transforming growth factor-alpha did not influence the induction of SPEM, loss of AR caused an acceleration and amplification in the induction of SPEM after acute oxyntic atrophy. Trefoil factor family 2/spasmolytic polypeptide and intrinsic factor dual-immunostaining cells significantly increased in the SPEM of AR-deficient mice. At the bases of glands, intrinsic factor immunoreactive cells also were costained for 5-bromo-2'-deoxyuridine, suggesting their re-entry into the cell cycle. CONCLUSIONS: The absence of AR promoted the rapid emergence of SPEM in response to oxyntic atrophy.     

Influence of long-term 16,16-dimethyl prostaglandin E2 treatment on the rat gastrointestinal mucosa

We performed acid secretory and histomorphometric studies in rats treated intragastrically with a regimen of 100 micrograms/kg or 5 micrograms/kg of 16,16-dimethyl prostaglandin E2, or of saline every 8 h for 21 days. All animals given the high-dose treatment developed a macroscopically visible enlargement of the ridge at the corpus-forestomach border, due to an increase in connective tissue and epithelial cell layer. Mucosal thickness was significantly increased in all parts of the stomach, the duodenum, and the proximal colon, but most markedly in the gastric antrum (+115%), where it was accompanied by a higher mitotic rate and hyperplasia of surface and foveolar mucous cells. Within the oxyntic area (corpus), high-dose prostaglandin treatment led to an increase in the number of surface and foveolar mucous cells and chief cells. In contrast, both the number of parietal cells and maximal acid output were not influenced. It is unlikely that the hyperplasia of gastric mucosa is mediated by gastrin since gastrin has no trophic effects on the rat antrum and disproportionally increases the parietal cell number of the oxyntic gastric glands.     

Evaluation of the trophic effect of longterm treatment with the histamine H2 receptor antagonist loxtidine on rat oxyntic mucosa by differential counting of dispersed cells.

To evaluate whether the general trophic effect of gastrin on the oxyntic mucosa is an indirect effect mediated by histamine H2 receptors, sustained 24 hour hypergastrinaemia was induced in Sprague-Dawley rats by treatment with the long acting and potent histamine H2 antagonist loxtidine for five months. The trophic effect was assessed by weight, enumeration of total mucosal cells, parietal cells, and enterochromaffin like cells in smears stained for the actual cells after enzymatic dispersion of the mucosa, and by biochemical analysis of oxyntic mucosal homogenates. The weight of the whole stomach and the oxyntic mucosa increased by 12.7% (p = 0.016) and 27.5% (p = 0.006), respectively. Total oxyntic mucosal protein content increased by 28.7% (p = 0.058). Total numbers of mucosal cells and parietal cells increased by 11.9% (NS) and 24.1% (NS), respectively. The amount of the parietal cell specific enzyme H+,K(+)-ATPase was unchanged. On the other hand, the number of enterochromaffin like cells and related parameters, histidine decarboxylase activity and histamine content of the oxyntic mucosa, showed a pronounced and significant increase. It is concluded that the general trophic effect of gastrin on the oxyntic mucosa is not mediated by the histamine H2 receptor. The tropic effect of gastrin on the parietal cell seems, in contrast with that on the enterochromaffin like cell, not to be specific but only reflecting the general trophic effect on the oxyntic mucosa.     

Effects of some gastrointestinal peptides on isolated human and rabbit gastric glands.

The isolated gastric gland preparation, with aminopyrine accumulation as an index of the parietal cell response, has been used to study the effects of somatostatin (S-14), gastrin-releasing peptide (GRP), cholecystokinin (CCK-8), vasoactive intestinal peptide (VIP), and peptide YY (PYY) on the in vitro acid secretion in human and rabbit oxyntic mucosa. Somatostatin was able to inhibit the parietal cell response to histamine in both human and rabbit isolated gastric glands (maximal inhibition, 22% and 34%, respectively) but failed to inhibit the parietal cell response to db-cAMP. However, other peptides capable of inhibiting gastric acid secretion in vivo, such as CCK, VIP, and PYY, were unable to induce any inhibition of the parietal cell response to db-cAMP or histamine in the isolated gastric gland preparation irrespective of the species studied. GRP was not able to induce a parietal cell response, a finding that is in accord with the assumption that the stimulatory effect of GRP on gastric acid secretion in vivo is by releasing gastrin from antral G-cells.     

Morphologic alterations of the gastric mucosa following vagotomy (author's transl)

A progression in the development of gastritis is not observed following selective proximal vagotomy. Morphometrically, a moderate compensatory foveolar hyperplasia can be noticed in addition to a reduction of parietal cells. Paralleles can be found concerning the ultrastructural alterations of parietal cells following vagotomy or after anticholinergic treatment. They consist in an increase of lamellar osmiophilic bodies, reduction of tubulovesicles, a narrow canalicular lumen and sparse mitochondria. A few years after vagotomy, the parietal cells appear rather unstimulated. After vagotomy, numerous antral G-cells can be demonstrated, with ultrastructural features of increased secretory activity in correlation to raised plasma gastrin levels. This moderate G-cells hyperplasia may, however, already exist preoperatively with the duodenal ulcer. 5 years after vagotomy, there is no pronounced alteration concerning the number of granular or agranular vesicles inside the terminal axons. Experimentally, a degeneration of sympathetic nerves has been described a few days after vagotomy.     

Physiology and pharmacology of the parietal cell

The parietal cells possess the unique capacity to produce large quantities of acid at a high concentration, and this is reflected in unique properties at the cellular level. The cells are comparatively large, and they are equipped with secretory canaliculi, a multitude of mitochondria, and cytoplasmic tubulovesicles. During secretion many of the tubulovesicles merge with the secretory canaliculi, which then expand. In the process H+, K+-ATPase is transferred from the tubulovesicular membrane to the secretory membrane. This enzyme catalyses the final step in the production of HCl. Parietal cell activity is regulated through receptors on the basolateral cell surfaces. In the isolated gland and in the isolated parietal-cell fractions, stimulation of receptors for histamine evokes higher secretion than receptor stimulation with cholinergic compounds or with gastrin. In these experimental models, specific inhibitors are required to block acid secretion; for example histamine H2-receptor antagonists will block histamine-induced secretion but will be inactive when secretion is evoked by gastrin or by cholinergic stimulation. These stimuli cause a more or less marked increase in the intracellular levels of Ca2+, which acts as a second messenger, leading to the activation of phosphokinases and, ultimately, to morphological transformation of the parietal cells and acid secretion. Another such intracellular messenger is cAMP, which is formed in response to histamine stimulation only; prostaglandins may prevent this process and block acid secretion. The final step in the production of acid requires K+ and Cl- channels in the secretory membrane and the H+, K+-ATPase-catalysed exchange of K+ for H+ across this membrane. This reaction consumes large amounts of energy and depends on the aerobic production of ATP by the parietal cells. Substituted benzimidazoles, such as omeprazole, accumulate in the acid compartments of the parietal cells and inhibit the H+, K+-ATPase, thereby blocking acid production.     

Alterations in Gastric Mucosal Lineages Before or After Acute Oxyntic Atrophy in Gastrin Receptor and H2 Histamine Receptor-Deficient Mice

Spasmolytic polypeptide (SP/TFF2)-expressing metaplasia (SPEM) is induced by oxyntic atrophy and is known as a precancerous or paracancerous lesion. We seek to determine whether the gastrin receptor or H₂ histamine receptor influence the development of SPEM. DMP-777 was administered to gastrin receptor and/or H₂ receptor-deficient mice and wild-type mice. Gastric mucosal lineage changes were analyzed. The mucosa from double knockout mice and H₂ receptor knockout mice contained elevated numbers of dual TFF2 and intrinsic factor immunoreactive cells even before DMP-777 treatment. All genotypes of mice showed SPEM after 7-day treatment. In all types of knockout mice, the number of TFF2 immunoreactive cells remained elevated after cessation of treatment. The H₂ receptor and gastrin receptor do not affect emergence of SPEM. However, it is suggested that the absence of H₂ receptor signaling causes a delay in the maturation of chief cells from mucous neck cells.     

对链脲佐菌素诱导的糖尿病大鼠壁细胞和G细胞的体视学研究

采用ＨＥ染色和免疫组化方法结合生物体视学技术，对链脲佐菌素诱导的糖尿病大鼠在胃底腺的壁细胞和幽门部胃粘膜的Ｇ细胞进行立体计量研究。结果显示：糖尿病状态的早期，壁细胞和Ｇ细胞的体积均明显增大，数量却显著减少。根据正常情况下壁细胞和Ｇ细胞的细胞动力学变化、胃泌素的生物学作用和上述实验结果，认为大鼠胃底腺峡部的干细胞向壁细胞分化成熟的功能及Ｇ细胞的分裂增殖活动，在胰岛素缺乏的情况下受到一定程度的抑制，而这种功能的抑制是糖尿病状态下易出现胃粘膜萎缩、胃酸分泌减少和胃轻瘫的重要原因之一。     

Antrectomy does not accelerate reversal of omeprazole-induced trophic effects in the rat stomach.

The oxyntic mucosa in the rat stomach is under the influence of circulating gastrin. The histamine-producing enterochromaffin-like (ECL) cells constitute the major endocrine cell population in the oxyntic mucosa. They are notably sensitive to changes in the serum gastrin concentration and respond to long-term hypergastrinemia with hyperplasia, whereas hypogastrinemia induces hypoplasia. In the present study long-term, sustained hypergastrinemia was induced by daily treatment with a high dose of the proton pump inhibitor omeprazole. After 10 weeks omeprazole-treated and control rats were antrectomized, resulting in prompt hypogastrinemia. Antrectomy was followed by a rapid reduction of the thickness of the oxyntic mucosa and a somewhat slower reduction of the ECL cell number in both omeprazole-treated and control rats. The percentage decrease in the ECL cell number with time was similar in both groups; after 2-3 weeks the ECL cell number was half of that before antrectomy in both groups. Interestingly, however, 12 weeks after antrectomy the ECL cell number in the omeprazole-pretreated rats remained elevated compared with untreated rats. The histamine concentration of the oxyntic mucosa was markedly lowered within a week after antrectomy in both omeprazole-treated and control rats. Although antrectomy induces hypogastrinemia and although atrophy develops rapidly in the oxyntic mucosa, the omeprazole-induced ECL cell hyperplasia was not completely reversed by antrectomy during the 12 weeks of examination.     

Antrectomy Does Not Accelerate Reversal of Omeprazole-Induced Trophic Effects in the Rat Stomach

The oxyntic mucosa in the rat stomach is under the influence of circulating gastrin. The histamine-producing enterochromaffin-like (ECL) cells constitute the major endocrine cell population in the oxyntic mucosa. They are notably sensitive to changes in the serum gastrin concentration and respond to long-term hypergastrinemia with hyperplasia, whereas hypogastrinemia induces hypoplasia. In the present study long-term, sustained hypergastrinemia was induced by daily treatment with a high dose of the proton pump inhibitor omeprazole. After 10 weeks omeprazoie-treated and control rats were antrectomized, resulting in prompt hypogastrinemia. Antrectomy was followed by a rapid reduction of the thickness of the oxyntic mucosa and a somewhat slower reduction of the ECL cell number in both omeprazoie-treated and control rats. The percentage decrease in the ECL cell number with time was similar in both groups; after 2-3 weeks the ECL cell number was half of that before antrectomy in both groups. Interestingly, however, 12 weeks after antrectomy the ECL cell number in the omeprazole-pretreated rats remained elevated compared with untreated rats. The histamine concentration of the oxyntic mucosa was markedly lowered within a week after antrectomy in both omeprazoie-treated and control rats. Although antrectomy induces hypogastrinemia and although atrophy develops rapidly in the oxyntic mucosa, the omeprazole-induced ECL cell hyperplasia was not completely reversed by antrectomy during the 12 weeks of examination.     

Effects of proximal gastric vagotomy and antrectomy on parietal cell function in humans

Both proximal gastric vagotomy and antrectomy reduce maximal gastric acid secretion in vivo by about 60%. The combination of vagotomy and antrectomy reduces the maximal acid secretion by about 80%. This additive effect indicates that these surgical procedures differ in their mode of action. The function of isolated human oxyntic glands was studied before and after vagotomy and antrectomy, respectively, using radioactively labeled aminopyrine as a marker of parietal cell response. The basal accumulation increased after vagotomy, suggesting a vagally controlled inhibitory component. The carbachol response disappeared and the maximal response induced by histamine or dibutyryl-cyclic adenosine monophosphate was reduced by 60% (p less than 0.01) after vagotomy. This reduction could not be overcome by increasing the dose of dibutyryl-cyclic adenosine monophosphate. This indicates an intracellular effect of vagotomy peripheral to dibutyryl-cyclic adenosine monophosphate point of action. Antrectomy did not induce any statistically significant change at the glandular level, indicating that the reduced gastric acid secretion in vivo may be caused by a reduction in the number of oxyntic glands due to a removal of a trophic effect of antral gastrin.     

Monoclonal antibody to the gastrin receptor on parietal cells recognizes a 78-kDa protein.

Four monoclonal antibodies reactive by immunofluorescence and by flow microfluorimetry with canine and porcine gastric parietal cell membranes were produced by fusion of mouse NS-1 myeloma cells with splenocytes from mice immunized with a population of canine gastric mucosal cells containing 60-70% parietal cells. One of these, an IgM antibody designated 2C1, reacted with the surface membranes of parietal cells by immunofluorescence, flow microfluorimetry, and immunogold electron microscopy; competed with 125I-labeled gastrin for binding to gastric cells; and inhibited by 56% maximal gastrin stimulation of [14C]aminopyrine uptake in parietal cells. The antibody immunoprecipitated 125I-labeled samples of a 78-kDa gastrin-binding protein purified from membrane extracts of porcine gastrin mucosa but did not recognize the same protein labeled covalently with 125I-labeled gastrin-(2-17)-hexadecapeptide. These observations suggest that the previously identified 78-kDa gastrin-binding protein is the gastrin receptor and that the antibody 2C1 is directed against the gastrin binding site of the gastrin receptor.     

Trefoil factor 1 is required for the commitment programme of mouse oxyntic epithelial progenitors

BACKGROUND: Trefoil factor 1 (TFF1/pS2) is a major secretory product of the stomach and TFF1 knockout mice constantly develop adenomas and occasional carcinomas in the pyloric antrum. AIM: To analyse the role of TFF1 in the differentiation of gastric epithelial cell lineages using oxyntic mucosae from normal and TFF1 knockout mice. METHODS: The various cell lineages were labelled using specific markers of pit, neck, parietal, and enteroendocrine cells. Patterns of TFF1, TFF2, and TFF3 expressions were defined using western blotting, immunohistochemistry, and/or immunogold electron microscopy. RESULTS: In normal mice, starting from postnatal day 1 (P1), TFF1 and TFF2 were produced by mucus secreting cells of the developing epithelium. At P7, TFF3 expression occurred in pit and parietal cells. When oxyntic glands were compartmentalised, at P21 and in older mice, TFF1 and TFF2 were expressed in pit and neck cells, respectively, and TFF3 was no longer in parietal cells but became a feature of zymogenic cells. In TFF1 deficient mice, alteration of oxyntic epithelial differentiation became obvious at P21, showing significant amplification of pit cells at the expense of parietal cells. At the molecular level, lack of TFF1 induced dramatic inhibition of TFF2 expression and more precocious TFF3 expression. CONCLUSION: In the oxyntic mucosa, all three TFFs are produced in a lineage specific manner and TFF1 is essential in maintaining the normal commitment programme of epithelial progenitors.     

Control of gastric acid secretion in somatostatin receptor 2 deficient mice: shift from endocrine/paracrine to neurocrine pathways

The gastrin-enterochromaffin-like (ECL) cell-parietal cell axis is known to play an important role in the regulation of gastric acid secretion. Somatostatin, acting on somatostatin receptor type 2 (SSTR(2)), interferes with this axis by suppressing the activity of the gastrin cells, ECL cells, and parietal cells. Surprisingly, however, freely fed SSTR(2) knockout mice seem to display normal circulating gastrin concentration and unchanged acid output. In the present study, we compared the control of acid secretion in these mutant mice with that in wild-type mice. In SSTR(2) knockout mice, the number of gastrin cells was unchanged; whereas the numbers of somatostatin cells were reduced in the antrum (-55%) and increased in the oxyntic mucosa (35%). The ECL cells displayed a reduced expression of histidine decarboxylase and vesicle monoamine transport type 2 (determined by immunohistochemistry), and an impaired transformation of the granules to secretory vesicles (determined by electron microscopic analysis), suggesting low activity of the ECL cells. These changes were accompanied by an increased expression of galanin receptor type 1 in the oxyntic mucosa. The parietal cells were found to respond to pentagastrin or to vagal stimulation (evoked by pylorus ligation) with increased acid production. In conclusion, the inhibitory galanin-galanin receptor type 1 pathway is up-regulated in the ECL cells, and the direct stimulatory action of gastrin and vagal excitation is enhanced on the parietal cells in SSTR(2) knockout mice. We suggest that there is a remodeling of the neuroendocrine mechanisms that regulate acid secretion in these mutant mice.     

Relationship between inositol 1,4,5-trisphosphate mass level and [14C]aminopyrine uptake in gastrin-stimulated parietal cells.

The relationship between gastrin-stimulated inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) content and [14C]aminopyrine ([14C]AP) uptake (an index of in vitro acid secretion) was investigated in a population of highly enriched rabbit parietal cells (90 +/- 5%). Gastrin induced a rapid rise in Ins(1,4,5)P3 content which was maximal within 15 s of stimulation (2- to 2.5-fold basal level) followed by a rapid decrease within 30 s; a high Ins(1,4,5)P3 level could also be observed after a longer time of hormone stimulation (180 s). Gastrin dose-dependently induced Ins(1,4,5)P3 accumulation and [14C]AP uptake; both dose-response curves were similar (EC50 approximately 0.1 nM). Furthermore, L-365,260 (3-(acylamino)benzodiazepine), a selective gastrin/CCK-B receptor antagonist, dose-dependently inhibited Ins(1,4,5)P3 production and [14C]AP accumulation induced by 10 nM gastrin with a similar potency (IC50 approximately 1-2 nM). These results led us to conclude that Ins(1,4,5)P3 is involved in gastrin-stimulated acid secretory activity of gastric parietal cells.     

The CCK-2 Receptor is Located on the ECL Cell,But Not on the Parietal Cell

Background: The interrelationship between histamine and gastrin in the physiological regulation of gastric acid secretion is still a matter of dispute. CCK-2 receptors are located on enterochromaffin-like (ECL) cells in corpus mucosa and gastrin stimulates acid production by releasing histamine from the ECL cells, which in turn stimulates the parietal cells. Whether parietal cells also possess gastrin receptors of physiological significance is unclear. The aim of the present study was to localize the CCK-2 receptor cellularly and concomitantly demonstrate a gastrin receptor response (histamine release). Methods: Fluorescein labelled cholecystokinin-8 (Fluo-CCK-8) was added to the arterial infusion to totally isolated, vascularly perfused rat stomachs to a final concentration of 130 pmol L -1 for 1 min, either alone or along with 520 nmol -1 CCK-8 after 10-min pre-perfusion with CCK-8. Immediately after the FluoCCK-8 had reached the oxyntic mucosa, biopsies were taken and the binding sites were localized by double immunohistochemistry combined with the tyramide signal amplification (TSA) technique. Venous histamine was measured before and during stimulation. Results: Fluo-CCK-8 (130 pM) evoked histamine release, and binding sites were found in the basal part of corpus mucosa, co-localized with histidine decarbocylase (HDC) immunoreactive ECL cells. No binding of Fluo-CCK was found in the midglandular region of corpus, dominated by parietal cells. Binding of Fluo-CCK-8 was abolished by concomitant perfusion with excess CCK-8. Conclusion: Fluo-CCK-8 given to isolated rat stomachs in a physiological concentration binds to CCK-2 receptors on ECL cells and causes histamine release, whereas no binding of Fluo-CCK-8 to parietal cells was found.     

Studies on Serum Gastrin of the Patients with Gastric Cancer

In patients with gastric cancer who were to undergo gastrectomy, the fasting serum gastrin concentration in the peripheral vein was estimated by radioimmunoassay. The blood samples were also collected from the gastric veins and artery during the time of operations. These gastrin values were compared with morphological findings in the resected stomach.
No significant differences in serum gastrin concentration was found between the patients of gastric cancer and normal subjects. In the patients with mucosal atrophy in the oxyntic gland area but with no atrophy in the pyloric gland area, however, significant increase in serum gastrin concentration was observed. In cases where fundal atrophy was accompanied by atrophy in the pyloric gland area, the increase was not observed. The amount of gastrin content in cancer tissue was negligible.
These results indicate that the increase in serum gastrin concentration in some patients with gastric cancer might be due to the accompanied atrophy of oxyntic glands in the stomach.