Gastric inflammation, metaplasia, and tumor development in gastrin-deficient mice

The immune microenvironment in gastric adenocarcinoma

Like most solid tumours, the microenvironment of epithelial-derived gastric adenocarcinoma (GAC) consists of a variety of stromal cell types, including fibroblasts, and neuronal, endothelial and immune cells. In this article, we review the role of the immune microenvironment in the progression of chronic inflammation to GAC, primarily the immune microenvironment driven by the gram-negative bacterial species Helicobacter pylori. The infection-driven nature of most GACs has renewed awareness of the immune microenvironment and its effect on tumour development and progression. About 75-90% of GACs are associated with prior H. pylori infection and 5-10% with Epstein-Barr virus infection. Although 50% of the world's population is infected with H. pylori, only 1-3% will progress to GAC, with progression the result of a combination of the H. pylori strain, host susceptibility and composition of the chronic inflammatory response. Other environmental risk factors include exposure to a high-salt diet and nitrates. Genetically, chromosome instability occurs in ~50% of GACs and 21% of GACs are microsatellite instability-high tumours. Here, we review the timeline and pathogenesis of the events triggered by H. pylori that can create an immunosuppressive microenvironment by modulating the host's innate and adaptive immune responses, and subsequently favour GAC development.

Elevated Protein Kinase A Activity in Stomach Mesenchyme Disrupts Mesenchymal-epithelial Crosstalk and Induces Preneoplasia

BACKGROUND & AIMS

Mesenchymal-epithelial crosstalk (MEC) in the stomach is executed by pathways such as bone morphogenetic protein (BMP) and extracellular signal-regulated kinase (ERK). Mis-regulation of MEC disrupts gastric homeostasis and causes tumorigenesis. Protein Kinase A (PKA) crosstalks with BMP and ERK signaling; however, PKA function(s) in stomach development and homeostasis remains undefined.

METHODS

We generated a novel Six2-Cre^+/-PKAcαR^fl/wt (CA-PKA) mouse in which expression of constitutive-active PKAcαR was induced in gastric mesenchyme progenitors. Lineage tracing determined spatiotemporal activity of Six2-Cre in the stomach. For phenotyping CA-PKA mice histological, co-immunofluorescence, immunoblotting, mRNA sequencing, and bioinformatics analyses were performed.

RESULTS

Lineage tracing showed that Six2-Cre activity in the stomach is restricted to the mesenchymal compartment. CA-PKA mice showed disruption of gastric homeostasis characterized by aberrant mucosal development and epithelial hyperproliferation; ultimately developing multiple features of gastric corpus preneoplasia including decreased parietal cells, mucous cell hyperplasia, spasmolytic peptide expressing metaplasia with intestinal characteristics, and dysplastic and invasive cystic glands. Furthermore, mutant corpus showed marked chronic inflammation characterized by infiltration of lymphocytes and myeloid-derived suppressor cells along with the upregulation of innate and adaptive immune system components. Striking upregulation of inflammatory mediators and STAT3 activation was observed. Mechanistically, we determined there is an activation of ERK1/2 and downregulation of BMP/SMAD signaling characterized by marked upregulation of BMP inhibitor gremlin 1.

CONCLUSIONS

We report a novel role of PKA signaling in gastric MEC execution and show that PKA activation in the gastric mesenchyme drives preneoplasia by creating a proinflammatory and proproliferative microenvironment associated with the downregulation of BMP/SMAD signaling and activation of ERK1/2.

Gastrin and the Moderate Hypergastrinemias

The antral hormone gastrin potently regulates gastric acid secretion and fundic mucosal growth. Consequently, appropriate gastrin secretion and plasma concentrations are important for the early phases of digestion. This review describes as the first premise the normal biogenesis of gastrin in the antral mucosa, but also mentions the extraantral expression. Subsequently, the molecular nature and concentration levels of gastrin in serum or plasma are overviewed. Third, assays for accurate measurements of plasma or serum concentrations are commented. Finally, the problem of moderate hypergastrinemia due to Helicobacter pylori infections and/or treatment with proton-pump inhibitors (PPI) is discussed. The review concludes that accurate measurement of the true concentrations of bioactive gastrins in plasma is important. Moreover, it suggests that moderate hypergastrinemias are also essential health issues that require serious attention.

A New Pyrimidine Schiff Base with Selective Activities against Enterococcus faecalis and Gastric Adenocarcinoma

Enterococcus faecalis is known as a significant nosocomial pathogen due to its natural resistance to many antibacterial drugs. Moreover, it was found that E. faecalis infection causes inflammation, production of reactive oxygen species, and DNA damage to human gastric cancer cells, which can induce cancer. In this study, we synthesized and tested the biological activity of a new Schiff base, 5-[(4-ethoxyphenyl)imino]methyl-N-(4-fluorophenyl)-6-methyl-2-phenylpyrimidin-4-amine (3), and compared its properties with an analogous amine (2). In the biological investigation, 3 was found to have antibacterial activity against E. faecalis 29212 and far better anticancer properties, especially against gastric adenocarcinoma (human Caucasian gastric adenocarcinoma), than 2. In addition, both derivatives were non-toxic to normal cells. It is worth mentioning that 3 could potentially inhibit cancer cell growth by inducing cell apoptosis. The results suggest that the presence of the -C=N- bond in the molecule of 3 increases its activity, indicating that 5-iminomethylpyrimidine could be a potent core for further drug discovery research.

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.

Gastrin secretion in normal subjects and diabetes patients is inhibited by glucagon-like peptide 1: a role in the gastric side effects of GLP-1-derived drugs?

Background: Randomized and controlled trials of glucagon-like peptide-1 (GLP-1) derived drugs have shown that the most frequent adverse symptoms are gastrointestinal. Some of the side effects such as dyspepsia, nausea and upper abdominal pain may well be of gastric origin. Since the antral hormone gastrin regulates gastric secretion of acid and enzymes and contributes to the regulation of gastric motility, we examined the effect of GLP-1 on the secretion of gastrin in normal subjects and diabetes patients.Method: Plasma was sampled from ten healthy subjects and ten patients with diabetes mellitus type 1 with glucose clamped between 6 and 9 mM. GLP-1 or saline were infused for 4 h during and after a meal. Plasma concentrations of gastrin and GLP-1 were measured using specific radioimmunoassays.Results: Basal plasma concentrations of gastrin were similar in controls and patients. After the meal, the gastrin concentrations rose significantly during saline infusion, whereas the GLP-1 infusion suppressed the secretion of gastrin significantly, most pronounced in the diabetes patients.Conclusions: The results show that GLP-1 infusion suppresses the postprandial secretion of gastrin in normal subjects and even more so in the diabetes patients. The results may therefore shed further light on the upper gastrointestinal side effects of GLP-1-derived drugs in diabetic patients.

Cdx2 Animal Models Reveal Developmental Origins of Cancers

The Cdx2 homeobox gene is important in assigning positional identity during the finely orchestrated process of embryogenesis. In adults, regenerative responses to tissues damage can require a replay of these same developmental pathways. Errors in reassigning positional identity during regeneration can cause metaplasias-normal tissue arising in an abnormal location-and this in turn, is a well-recognized cancer risk factor. In animal models, a gain of Cdx2 function can elicit a posterior shift in tissue identity, modeling intestinal-type metaplasias of the esophagus (Barrett's esophagus) and stomach. Conversely, loss of Cdx2 function can elicit an anterior shift in tissue identity, inducing serrated-type lesions expressing gastric markers in the colon. These metaplasias are major risk factors for the later development of esophageal, stomach and colon cancer. Leukemia, another cancer in which Cdx2 is ectopically expressed, may have mechanistic parallels with epithelial cancers in terms of stress-induced reprogramming. This review will address how animal models have refined our understanding of the role of Cdx2 in these common human cancers.

Gastric cancer and gastrin: on the interaction of Helicobacter pylori gastritis and acid inhibitory induced hypergastrinemia

Gastric cancer, a disease with a reduced frequency for decades, now appears to be on the rise again in young Americans. The epidemiology of gastric cancer differs between tumors in the cardia and those of the more distal parts of the stomach. The tumors are divided into the intestinal type showing glandular growth pattern and the diffuse type with a different pattern. The latter often expresses neuroendocrine and more specifically ECL-cell markers suggesting that they originate from the ECL cell, the target cell for the antral hormone, gastrin. Helicobacter pylori gastritis is accepted as the major cause of gastric cancer, but only after having induced oxyntic atrophy which reduces gastric acid secretion and thus induces hypoacidity leading to hypergastrinemia. Long-term hypergastrinemia is known to induce malignant neoplasia in the stomach of animals as well as man. Recently treatment with proton pump inhibitor after Helicobacter pylori eradication in patients with gastroesophageal reflux disease, has been reported to predispose to gastric cancer. Since profound acid inhibition is a well-known cause of gastric neoplasia, it is to be expected that Helicobacter pylori infection and profound acid inhibition has an additive or possibly potentiating effect on the development of gastric cancer.

Serum gastrin and cholecystokinin are associated with subsequent development of gastric cancer in a prospective cohort of Finnish smokers

Background

Gastrin, which induces gastric acid secretion, and a structurally similar hormone, cholecystokinin (CCK)-a potent acid inhibitor, may each play a role in gastric cancer. However, few studies have investigated this hypothesis in humans. We therefore investigated whether serum gastrin or CCK concentrations at baseline were associated with the incidence of gastric non-cardia adenocarcinomas (GNCA), oesophagogastric junctional adenocarcinomas (EGJA) or gastric carcinoid tumours over 24 years of follow-up in a study nested within the all-male Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study of Finnish smokers.

Methods

Totals of 283 incident GNCA, 96 EGJA and 10 gastric carcinoid cases, and 778 matched controls, were included in our analysis. Gastrin and CCK were measured using specific radioimmunoassays. Odds ratios (OR) and 95% confidence intervals (95% CI) were estimated by multivariable logistic regression with adjustment for all known or suspected confounding factors, including Helicobacter pylori seropositivity.

Results

Those with high gastrin (Q4 vs Q1), had an increased risk of GNCA (fully adjusted OR: 1.92; 95% CI: 1.21, 3.05) and gastric carcinoids, though the small number of carcinoid cases meant the fully adjusted model was unstable (age-adjusted continuous model OR: 4.67; 95% CI: 2.67, 8.15). CCK was associated with risk of GNCA only for those in Q3 relative to Q1 (OR: 0.56; 95% CI: 0.33, 0.96), and no significant trend was observed.

Conclusions

Our data suggest that high serum concentrations of gastrin may be associated independently with an increased risk of gastric cancer; the role of CCK in cancer risk is less clear.

Genetic ablation of carbonic anhydrase IX disrupts gastric barrier function via claudin-18 downregulation and acid backflux

Aim

This study aimed to explore the molecular mechanisms for the parietal cell loss and fundic hyperplasia observed in gastric mucosa of mice lacking the carbonic anhydrase 9 (CAIX).

Methods

We assessed the ability of CAIX‐knockout and WT gastric surface epithelial cells to withstand a luminal acid load by measuring the pH_i of exteriorized gastric mucosa in vivo using two‐photon confocal laser scanning microscopy. Cytokines and claudin‐18A2 expression was analysed by RT‐PCR.

Results

CAIX‐knockout gastric surface epithelial cells showed significantly faster pH_i decline after luminal acid load compared to WT. Increased gastric mucosal IL‐1β and iNOS, but decreased claudin‐18A2 expression (which confer acid resistance) was observed shortly after weaning, prior to the loss of parietal and chief cells. At birth, neither inflammatory cytokines nor claudin‐18 expression were altered between CAIX and WT gastric mucosa. The gradual loss of acid secretory capacity was paralleled by an increase in serum gastrin, IL‐11 and foveolar hyperplasia. Mild chronic proton pump inhibition from the time of weaning did not prevent the claudin‐18 decrease nor the increase in inflammatory markers at 1 month of age, except for IL‐1β. However, the treatment reduced the parietal cell loss in CAIX‐KO mice in the subsequent months.

Conclusions

We propose that CAIX converts protons that either backflux or are extruded from the cells rapidly to CO₂ and H₂O, contributing to tight junction protection and gastric epithelial pH_i regulation. Lack of CAIX results in persistent acid backflux via claudin‐18 downregulation, causing loss of parietal cells, hypergastrinaemia and foveolar hyperplasia.

hTERT promotes gastric intestinal metaplasia by upregulating CDX2 via NF-κB signaling pathway

Background

hTERT has been reported involved in the proliferation and metastasis of gastric cancer, but the role of hTERT in gastric intestinal metaplasia, a premalignant lesion of the gastric mucosa was unknown. The aim of the present study was to investigate the role of hTERT in GIM and the effect of hTERT on CDX2 expression in gastric cells.

Results

Experiments showed that expression of hTERT was significantly higher in GIM than in normal gastric mucosa. Moreover, hTERT increased the KLF4 level via NF-κB during GIM. Furthermore, KLF4 is involved in the up-regulation of CDX2 induced by hTERT, and hTERT can interact with p50, thereby increasing the level of CDX2.

Materials and Methods

Immunohistochemistry was used to detect the expression of hTERT in gastric intestinal metaplasia tissue. Then, effect of hTERT on the expression of CDX2 was detected by qRT-PCR, WB and dual luciferase experiment. The role of p65 and p50 in the regulation of CDX2 were further detected by WB, CO-IP and ChIP.

Conclusions

We may conclude that hTERT promotes GIM by up-regulating CDX2 via NF-κB signaling pathway.

Mouse models for gastric cancer: Matching models to biological questions

Gastric cancer is the third leading cause of cancer-related mortality worldwide. This is in part due to the asymptomatic nature of the disease, which often results in late-stage diagnosis, at which point there are limited treatment options. Even when treated successfully, gastric cancer patients have a high risk of tumor recurrence and acquired drug resistance. It is vital to gain a better understanding of the molecular mechanisms underlying gastric cancer pathogenesis to facilitate the design of new-targeted therapies that may improve patient survival. A number of chemically and genetically engineered mouse models of gastric cancer have provided significant insight into the contribution of genetic and environmental factors to disease onset and progression. This review outlines the strengths and limitations of current mouse models of gastric cancer and their relevance to the pre-clinical development of new therapeutics.

Enterococcus faecalis Infection and Reactive Oxygen Species Down-Regulates the miR-17-92 Cluster in Gastric Adenocarcinoma Cell Culture

Chronic inflammation due to bacterial overgrowth of the stomach predisposes to the development of gastric cancer and is also associated with high levels of reactive oxygen species (ROS). In recent years increasing attention has been drawn to microRNAs (miRNAs) due to their role in the pathogenesis of many human diseases including gastric cancer. Here we studied the impact of infection by the gram-positive bacteria Enterococcus faecalis (E. faecalis) on global miRNA expression as well as the effect of ROS on selected miRNAs. Human gastric adenocarcinoma cell line MKN74 was infected with living E. faecalis for 24 h or for 5 days or with E. faecalis lysate for 5 days. The miRNA expression was examined by microarray analysis using Affymetrix GeneChip miRNA Arrays. To test the effect of ROS, MKN74 cells were treated with 100 mM tert-Butyl hydroperoxide (TBHP). Following 5 days of E. faecalis infection we found 91 differentially expressed miRNAs in response to living bacteria and 2 miRNAs responded to E. faecalis lysate. We verified the down-regulation of the miR-17-92 and miR-106-363 clusters and of other miRNAs involved in the oxidative stress-response by qRT-PCR. We conclude that only infection by living E. faecalis bacteria caused a significant global response in miRNA expression in the MKN74 cell culture. E. faecalis infection as well as ROS stimulation down-regulated the expression of the miR-17-92 cluster. We believe that these changes could reflect a general response of gastric epithelial cells to bacterial infections.

Gene expression profiling of gastric mucosa in mice lacking CCK and gastrin receptors

The stomach produces acid, which may play an important role in the regulation of bone homeostasis. The aim of this study was to reveal signaling pathways in the gastric mucosa that involve the acid secretion and possibly the bone metabolism in CCK1 and/or CCK2 receptor knockout (KO) mice. Gastric acid secretion was impaired and the ECL cell signaling pathway was inhibited in CCK2 receptor KO mice but not in CCK1 receptor KO mice. However, in CCK1+2 receptor double KO mice the acid secretion in response to pylorus ligation-induced vagal stimulation and the ECL cell pathway were partially normalized, which was associated with an up-regulated pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1). The basal part of the gastric mucosa expressed parathyroid hormone-like hormone (PTHLH) in a subpopulation of likely ECL cells (and possibly other cells) and vitamin D3 1α hydroxylase probably in trefoil peptide2-immunoreactive cells. In conclusion, mice lacking CCK receptors exhibited a functional shift from the gastrin-CCK pathways to the neuronal pathway in control of the ECL cells and eventually the acid secretion. Taking the present data together with previous findings, we suggest a possible link between gastric PTHLH and vitamin D and bone metabolism.

New insights into the functions and localization of the homeotic gene CDX2 in gastric cancer

Gastric cancer is one of the most frequent cancers, and it ranks the third most common cancer in China. The most recently caudal-related homeobox transcription factor 2 (CDX2) is expressed in a large number of human gastrointestinal cancers. In addition, gastric epithelial cell mutations in CDX2 result in tumor promotion, which is characterized by cellular drug resistance and a high proclivity for developing cancer. A series of publications over the past years suggests a mechanism by which CDX2 overexpression results in multidrug resistance. CDX2 appears to forward control regenerating IV and the multidrug resistance 1 expression signaling pathway for regulation of cell drug resistance.

Helicobacter pylori and gastritis: the role of extracellular matrix metalloproteases, their inhibitors, and the disintegrins and metalloproteases--a systematic literature review

Helicobacter pylori (H. pylori) is the etiologic agent of gastritis; it has been estimated that 50 % of the world's population could be infected by this bacteria. Gastritis may progress to chronic atrophic gastritis, a condition associated with the development of gastric cancer (GC). Several matrix metalloproteases (MMP) and tissue inhibitors of MMPs (TIMP) as well as disintegrins and metalloproteases (ADAM) have been reported as being involved in gastritis. Among other processes, these protein families participate in remodeling the extracellular matrix, cell signaling, immune response, angiogenesis, inflammation and epithelial mesenchymal transition. This systematic review analyzes the scientific evidence surrounding the relationship between members of the MMP, TIMP and ADAM families and infection by H. pylori in gastritis, considering both in vitro and in vivo studies. Given the potential clinical value of certain members of the MMP, TIMP and ADAM families as molecular markers in gastritis and the association of gastritis with GC, the need for further study is highlighted.

Enterococcus faecalis infection causes inflammation, intracellular oxphos-independent ROS production, and DNA damage in human gastric cancer cells

Background

Achlorhydria caused by e.g. atrophic gastritis allows for bacterial overgrowth, which induces chronic inflammation and damage to the mucosal cells of infected individuals driving gastric malignancies and cancer. Enterococcus faecalis (E. faecalis) can colonize achlohydric stomachs and we therefore wanted to study the impact of E. faecalis infection on inflammatory response, reactive oxygen species (ROS) formation, mitochondrial respiration, and mitochondrial genetic stability in gastric mucosal cells.

Methods

To separate the changes induced by bacteria from those of the inflammatory cells we established an in vitro E. faecalis infection model system using the gastric carcinoma cell line MKN74. Total ROS and superoxide was measured by fluorescence microscopy. Cellular oxygen consumption was characterized non-invasively using XF24 microplate based respirometry. Gene expression was examined by microarray, and response pathways were identified by Gene Set Analysis (GSA). Selected gene transcripts were verified by quantitative real-time polymerase chain reaction (qRT-PCR). Mitochondrial mutations were determined by sequencing.

Results

Infection of MKN74 cells with E. faecalis induced intracellular ROS production through a pathway independent of oxidative phosphorylation (oxphos). Furthermore, E. faecalis infection induced mitochondrial DNA instability. Following infection, genes coding for inflammatory response proteins were transcriptionally up-regulated while DNA damage repair and cell cycle control genes were down-regulated. Cell growth slowed down when infected with viable E. faecalis and responded in a dose dependent manner to E. faecalis lysate.

Conclusions

Infection by E. faecalis induced an oxphos-independent intracellular ROS response and damaged the mitochondrial genome in gastric cell culture. Finally the bacteria induced an NF-κB inflammatory response as well as impaired DNA damage response and cell cycle control gene expression.

Transcript profiling

Array Express accession number E-MEXP-3496.

Omission of breakfast and risk of gastric cancer in Mexico

AIM

To investigate factors associated with gastric cancer (GC) in the Mexican population using a validated questionnaire.

METHODS

We designed and validated in Spanish a Questionnaire to Find Factors Associated with Diseases of the Digestive Tract using GC as a model. A cross-sectional study using 49 subjects, with confirmed histopathological GC diagnosis, and 162 individuals without GC participated. Odds ratio and 95% CIs were estimated in univariate and multivariate analysis adjusted for possible confounding factors. In order to match age groups, a multivariate sub-analysis was performed in subjects ≥ 39 years of age and in females and males separately.

RESULTS

In the univariate analysis, we found an association between GC and education to primary level or below, low socioeconomic status, the use of dental prostheses, omission of breakfast, consumption of very hot food and drink, addition of salt to prepared foods, consumption of salt-preserved foods and the pattern of alcohol consumption. We found protection against GC associated with the use of mouthwash, food refrigeration and regular consumption of fruit and vegetables. In the multivariate sub-analysis with subjects of ≥ 39 years, the omission of breakfast was identified as a risk factor for GC.

CONCLUSION

Our study suggests an association between the omission of breakfast and the failure to refrigerate food with GC in the Mexican population.

microRNA-146a inhibits G protein-coupled receptor-mediated activation of NF-κB by targeting CARD10 and COPS8 in gastric cancer

BACKGROUND

Gastric cancer is the second most common cause of cancer-related death in the world. Inflammatory signals originating from gastric cancer cells are important for recruiting inflammatory cells and regulation of metastasis of gastric cancer. Several microRNAs (miRNA) have been shown to be involved in development and progression of gastric cancer. miRNA-146a (miR-146a) is a modulator of inflammatory signals, but little is known about its importance in gastric cancer. We therefore wanted to identify targets of miR-146a in gastric cancer and examine its biological roles.

RESULTS

The expression of miR-146a was evaluated by quantitative PCR (qPCR) and found up-regulated in the gastrin knockout mice, a mouse model of gastric cancer, and in 73% of investigated human gastric adenocarcinomas. Expression of miR-146a by gastric cancer cells was confirmed by in situ hybridization. Global analysis of changes in mRNA levels after miR-146a transfection identified two transcripts, caspase recruitment domain-containing protein 10 (CARD10) and COP9 signalosome complex subunit 8 (COPS8), as new miR-146a targets. qPCR, Western blotting and luciferase assays confirmed these transcripts as direct miR-146a targets. CARD10 and COPS8 were shown to be part of the G protein-coupled receptor (GPCR) pathway of nuclear factor-kappaB (NF-kappaB) activation. Lysophosphatidic acid (LPA) induces NF-kappaB activation via this pathway and over-expression of miR-146a inhibited LPA-induced NF-kappaB activation, reduced LPA-induced expression of tumor-promoting cytokines and growth factors and inhibited monocyte attraction.

CONCLUSIONS

miR-146a expression is up-regulated in a majority of gastric cancers where it targets CARD10 and COPS8, inhibiting GPCR-mediated activation of NF-kappaB, thus reducing expression of NF-kappaB-regulated tumor-promoting cytokines and growth factors. By targeting components of several NF-kappaB-activating pathways, miR-146a is a key component in the regulation of NF-kappaB activity.

Gastric intestinal metaplasia revisited: function and regulation of CDX2

Intestinal metaplasia of the stomach is a preneoplastic lesion that appears following Helicobacter pylori infection and confers increased risk for gastric cancer development. However, the molecular networks connecting infection to lesion formation and the cellular origin of this lesion remain largely unknown. A more comprehensive understanding of how intestinal metaplasia arises and is maintained will be a major breakthrough towards developing novel therapeutic interventions. Furthermore, after ascertaining the pivotal role of CDX2 in establishing and maintaining intestinal metaplasia, it becomes important to decipher the upstream molecular pathways leading to its ectopic expression. Here, we review the pathophysiology of intestinal metaplasia in the context of the molecular network involved in its establishment and maintenance, with emphasis on CDX2 function and regulation.

Genetic Mechanisms and Aberrant Gene Expression during the Development of Gastric Intestinal Metaplasia and Adenocarcinoma

Gastric adenocarcinoma occurs via a sequence of molecular events known as the Correa’s Cascade which often progresses over many years. Gastritis, typically caused by infection with the bacterium H. pylori, is the first step of the cascade that results in gastric cancer; however, not all cases of gastritis progress along this carcinogenic route. Despite recent antibiotic intervention of H. pylori infections, gastric adenocarcinoma remains the second most common cause of cancer deaths worldwide. Intestinal metaplasia is the next step along the carcinogenic sequence after gastritis and is considered to be a precursor lesion for gastric cancer; however, not all patients with intestinal metaplasia develop adenocarcinoma and little is known about the molecular and genetic events that trigger the progression of intestinal metaplasia into adenocarcinoma. This review aims to highlight the progress to date in the genetic events involved in intestinal-type gastric adenocarcinoma and its precursor lesion, intestinal metaplasia. The use of technologies such as whole genome microarray analysis, immunohistochemical analysis and DNA methylation analysis has allowed an insight into some of the events which occur in intestinal metaplasia and may be involved in carcinogenesis. There is still much that is yet to be discovered surrounding the development of this lesion and how, in many cases, it develops into a state of malignancy.

Interferon-γ inhibits ghrelin expression and secretion via a somatostatin-mediated mechanism

AIM: To investigate if and how the proinflammatory cytokine interferon γ (IFNγ) affects ghrelin expression in mice.

METHODS: The plasma concentration of ghrelin, and gastric ghrelin and somatostatin expression, were examined in wild-type mice and mice infected with Helicobacter pylori (H. pylori). Furthermore, ghrelin expression was examined in two achlorhydric mouse models with varying degrees of gastritis due to bacterial overgrowth. To study the effect of IFNγ alone, mice were given a subcutaneous infusion of IFNγ for 7 d. Finally, the influence of IFNγ and somatostatin on the ghrelin promoter was characterized.

RESULTS: H. pylori infection was associated with a 50% reduction in ghrelin expression and plasma concentration. Suppression of ghrelin expression was inversely correlated with gastric inflammation in achlorhdyric mouse models. Subcutaneous infusion of IFNγ suppressed fundic ghrelin mRNA expression and plasma ghrelin concentrations. Finally, we showed that the ghrelin promoter operates under the control of somatostatin but not under that of IFNγ.

CONCLUSION: Gastric infection and inflammation is associated with increased IFNγ expression and reduced ghrelin expression. IFNγ does not directly control ghrelin expression but inhibits it indirectly via somatostatin.

miR-449 inhibits cell proliferation and is down-regulated in gastric cancer

BACKGROUND

Gastric cancer is the fourth most common cancer in the world and the second most prevalent cause of cancer related death. The development of gastric cancer is mainly associated with H. Pylori infection leading to a focus in pathology studies on bacterial and environmental factors, and to a lesser extent on the mechanistic development of the tumour. MicroRNAs are small non-coding RNA molecules involved in post-transcriptional gene regulation. They are found to regulate genes involved in diverse biological functions and alterations in microRNA expression have been linked to the pathogenesis of many malignancies. The current study is focused on identifying microRNAs involved in gastric carcinogenesis and to explore their mechanistic relevance by characterizing their targets.

RESULTS

Invitrogen NCode miRNA microarrays identified miR-449 to be decreased in 1-year-old Gastrin KO mice and in H. Pylori infected gastric tissues compared to tissues from wild type animals. Growth rate of gastric cell lines over-expressing miR-449 was inhibited by 60% compared to controls. FACS cell cycle analysis of miR-449 over-expressing cells showed a significant increase in the sub-G1 fraction indicative of apoptosis. ß-Gal assays indicated a senescent phenotype of gastric cell lines over-expressing miR-449. Affymetrix 133v2 arrays identified GMNN, MET, CCNE2, SIRT1 and CDK6 as miR-449 targets. Luciferase assays were used to confirm GMNN, MET, CCNE2 and SIRT1 as direct targets. We also show that miR-449 over-expression activated p53 and its downstream target p21 as well as the apoptosis markers cleaved CASP3 and PARP. Importantly, qPCR analyses showed a loss of miR-449 expression in human clinical gastric tumours compared to normal tissues.

CONCLUSIONS

In this study, we document a diminished expression of miR-449 in Gastrin KO mice and further confirmed its loss in human gastric tumours. We investigated the function of miR-449 by identifying its direct targets. Furthermore we show that miR-449 induces senescence and apoptosis by activating the p53 pathway.

Gastrins, iron homeostasis and colorectal cancer

The peptide hormone gastrin has been identified as a major regulator of acid secretion and a potent mitogen for normal and malignant gastrointestinal cells. The importance of gastric acid in the absorption of dietary iron first became evident 50 years ago when iron deficiency anemia was recognized as a long-term consequence of partial gastrectomy. This review summarizes the connections between circulating gastrins, iron status and colorectal cancer. Gastrins bind two ferric ions with micromolar affinity and, in the case of non-amidated forms of the hormone, iron binding is essential for biological activity in vitro and in vivo. The demonstration of an interaction between gastrin and transferrin by biochemical techniques led to the proposal that gastrins catalyze the loading of transferrin with iron. Several lines of evidence, including the facts that the concentrations of circulating gastrins are increased in mice and humans with the iron overload disease hemochromatosis and that transferrin saturation positively correlates with circulating gastrin concentration, suggest the potential involvement of gastrins in iron homeostasis. Conversely, recognition that ferric ions play an unexpected role in the biological activity of gastrins may assist in the development of useful therapies for colorectal carcinoma and other disorders of mucosal proliferation in the gastrointestinal tract. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Animal models to study the role of long-term hypergastrinemia in gastric carcinogenesis

Patients with chronic hypergastrinemia due to chronic atrophic gastritis or gastrinomas have an increased risk of developing gastric malignancy, and it has been questioned whether also patients with hypergastrinemia caused by long-term use of acid inhibiting drugs are at risk. Gastric carcinogenesis in humans is affected by numerous factors and progresses slowly over years. When using animal models with the possibility of intervention, a complex process can be dissected by studying the role of hypergastrinemia in carcinogenesis within a relatively short period of time. We have reviewed findings from relevant models where gastric changes in animal models of long-term hypergastrinemia have been investigated. In all species where long-term hypergastrinemia has been induced, there is an increased risk of gastric malignancy. There is evidence that hypergastrinemia is a common causative factor in carcinogenesis in the oxyntic mucosa, while other cofactors may vary in the different models.

Gastrin induces the interaction between human mononuclear leukocytes and endothelial cells through the endothelial expression of P-selectin and VCAM-1

Gastric mucosal inflammation is frequently associated with hypergastrinemia, and a correlation exists between the level of gastrin and degree of gastritis. We have previously observed that gastrin promotes leukocyte-endothelial interactions and contributes to Helicobacter-induced inflammation in the rat mesentery. In the present study, we aimed to evaluate a possible proinflammatory activity of gastrin in humans. The interaction between human leukocytes [U-937 cells, peripheral blood polymorphonuclear (PMN), and peripheral blood mononuclear (PBMC) cells] and human umbilical vein endothelial cells (HUVEC) was analyzed in static and dynamic conditions. The endothelial expression of adhesion molecules [P-selectin, E-selectin, intercellular adhesion molecule-1, vascular cell adhesion molecule (VCAM)-1] was analyzed by flow cytometry and fluorescent microscopy screening. Gastrin increased the static adhesion of U-937 cells to HUVEC (1 h; 10(-9) M: 122 +/- 9%; 10(-8) M: 143 +/- 17%; 10(-7) M: 162 +/- 14% vs. control, all P < 0.05). Incubation of HUVEC with gastrin (4 h) also increased PBMC rolling (vehicle: 63 +/- 12; 10(-9) M: 109 +/- 29; 10(-8) M: 141 +/- 24; 10(-7) M: 261 +/- 16 leukocytes/min, P < 0.05) and adhesion (vehicle: 3 +/- 2, 10(-9) M: 11 +/- 4, 10(-8) M: 17 +/- 5, 10(-7) M: 15 +/- 5 leukocytes/mm(2), all P < 0.05) in the parallel-plate flow chamber. Treatment of PBMC with gastrin had no effects. The cholecystokinin (CCK)-2 receptor antagonist (L-365,260, 10(-7) M) prevented the effects of gastrin. P-selectin and VCAM-1 expression were enhanced by gastrin, and neutralizing antibodies against these molecules prevented PBMC rolling and adhesion. Gastrin did not affect the interactions between HUVEC and PMN. Gastrin induces interactions between human mononuclear leukocytes and endothelial cells through the activation of CCK-2 receptors and the enhancement of endothelial P-selectin and VCAM-1.

Nature meets nurture: molecular genetics of gastric cancer

The immensity of genes and molecules implicated in gastric carcinogenesis is overwhelming and the relevant importance of some of these molecules is too often unclear. This review serves to bring us up-to-date with the latest findings as well as to look at the larger picture in terms of how to tackle the problem of solving this multi-piece puzzle. In this review, the environmental nurturing of intestinal cancer is discussed, beginning with epidemiology (known causative factors for inducing molecular change), an update of H. pylori research, including the role of inflammation and stem cells in premalignant lesions. The role of E-cadherin in the nature (genotype) of diffuse gastric cancer is highlighted, and finally the ever growing discipline of SNP analysis (including IL1B) is discussed.

Nature meets nurture: molecular genetics of gastric cancer

The immensity of genes and molecules implicated in gastric carcinogenesis is overwhelming and the relevant importance of some of these molecules is too often unclear. This review serves to bring us up-to-date with the latest findings as well as to look at the larger picture in terms of how to tackle the problem of solving this multi-piece puzzle. In this review, the environmental nurturing of intestinal cancer is discussed, beginning with epidemiology (known causative factors for inducing molecular change), an update of H. pylori research, including the role of inflammation and stem cells in premalignant lesions. The role of E-cadherin in the nature (genotype) of diffuse gastric cancer is highlighted, and finally the ever growing discipline of SNP analysis (including IL1B) is discussed.

Definition of the residues required for the interaction between glycine-extended gastrin and transferrin in vitro

Transferrin is the main iron transport protein found in the circulation, and the level of transferrin saturation in the blood is an important indicator of iron status. The peptides amidated gastrin(17) (Gamide) and glycine-extended gastrin(17) (Ggly) are well known for their roles in controlling acid secretion and as growth factors in the gastrointestinal tract. Several lines of evidence, including the facts that transferrin binds gastrin, that gastrins bind ferric ions, and that the level of expression of gastrins positively correlates with transferrin saturation, suggest the possible involvement of the transferrin-gastrin interaction in iron homeostasis. In the present work, the interaction between gastrins and transferrin has been characterized by surface plasmon resonance and covalent crosslinking. First, an interaction between iron-free apo-transferrin and Gamide or Ggly was observed. The fact that no interaction was observed in the presence of the chelator EDTA suggested that the gastrin-ferric ion complex was the interacting species. Moreover, removal of ferric ions with EDTA reduced the stability of the complex between apo-transferrin and gastrins, and no interaction was observed between Gamide or Ggly and diferric transferrin. Second, some or all of glutamates at positions 8-10 of the Ggly molecule, together with the C-terminal domain, were necessary for the interaction with apo-transferrin. Third, monoferric transferrin mutants incapable of binding iron in either the N-terminal or C-terminal lobe still bound Ggly. These findings are consistent with the hypothesis that gastrin peptides bind to nonligand residues within the open cleft in each lobe of transferrin and are involved in iron loading of transferrin in vivo.

Gastrin is an essential cofactor for helicobacter-associated gastric corpus carcinogenesis in C57BL/6 mice

We have previously described a synergistic interaction between hypergastrinemia and Helicobacter felis infection on gastric corpus carcinogenesis in FVB/N mice housed under specific-pathogen-free conditions. However, gastrin-deficient (GAS-KO) mice on a mixed C57BL/6/129Sv genetic background maintained in conventional housing were reported to develop spontaneous gastric antral tumors. Therefore, we investigated the role of gastrin in Helicobacter-associated gastric carcinogenesis in H. felis-infected mice on a uniform C57BL/6 background housed in specific-pathogen-free conditions. Hypergastrinemic transgenic (INS-GAS) mice, GAS-KO mice, and C57BL/6 wild-type mice were infected with H. felis for either 12 or 18 months. At 12 months postinfection, INS-GAS mice had mild corpus dysplasia, while B6 wild-type mice had either severe gastritis or metaplasia, and GAS-KO mice had only mild to moderate gastritis. At 18 months postinfection, both INS-GAS and B6 wild-type mice had both severe atrophic gastritis and corpus dysplasia, while GAS-KO mice had severe gastritis with mild gastric atrophy, but no corpus dysplasia. In contrast, both GAS-KO and B6 wild-type mice had mild to moderate antral dysplasia, while INS-GAS mice did not. H. felis antral colonization remained stable over time among the three groups of mice. These results point to a distinct effect of gastrin on carcinogenesis of both the gastric corpus and antrum, suggesting that gastrin is an essential cofactor for gastric corpus carcinogenesis in C57BL/6 mice.

Helicobacter-based mouse models of digestive system carcinogenesis

Animal models are necessary to reproduce the complex host, microbial and environmental influences associated with infectious carcinogenesis of the digestive system. Today, mouse models are preferred by most researchers because of cost efficiencies, rapid reproduction, choice of laboratory reagents, and availability of genetically engineered mutants to study specific gene functions in vivo. Mouse models have validated the once-provocative hypothesis that Helicobacter pylori infection is a major risk factor for gastric carcinoma, dispelling early skepticism over the pathogenic nature of this organism in the human stomach. Enterohepatic Helicobacter spp. induce inflammatory bowel disease and colorectal carcinoma in susceptible mouse strains, permitting study of host immunity and microbial factors at the cellular and molecular level. H. hepaticus is the only proven infectious hepatocarcinogen of mice and has been used to explore mechanisms of inflammation-associated liver cancer as seen in human chronic viral hepatitis. For example, this model was used to identify for the first time a potential mechanism for male-predominant liver cancer risk independent of circulating sex hormones. Helicobacter-based mouse models of digestive system carcino-genesis are used to investigate the basic biology of inflammation-associated human cancers and to evaluate therapeutic interventions at the discovery level. Because of exciting advances in genetic engineering of mice, in vivo imaging, and system-wide genomics and proteomics, these models will provide even more information in the future. This chapter introduces the mouse as a model species; summarizes important models of inflammation-associated cancer incited by murine Helicobacter infection; and describes methods for the collection, sampling, and histologic grading of mouse digestive system tissues.

Importance of gastrin in the pathogenesis and treatment of gastric tumors

In addition to regulating acid secretion, the gastric antral hormone gastrin regulates several important cellular processes in the gastric epithelium including proliferation, apoptosis, migration, invasion, tissue remodelling and angiogenesis. Elevated serum concentrations of this hormone are caused by many conditions, particularly hypochlorhydria (as a result of autoimmune or Helicobacter pylori (H pylori)-induced chronic atrophic gastritis or acid suppressing drugs) and gastrin producing tumors (gastrinomas). There is now accumulating evidence that altered local and plasma concentrations of gastrin may play a role during the development of various gastric tumors. In the absence of H pylori infection, marked hypergastrinemia frequently results in the development of gastric enterochromaffin cell-like neuroendocrine tumors and surgery to remove the cause of hypergastrinemia may lead to tumor resolution in this condition. In animal models such as transgenic INS-GAS mice, hypergastrinemia has also been shown to act as a cofactor with Helicobacter infection during gastric adenocarcinoma development. However, it is currently unclear as to what extent gastrin also modulates human gastric adenocarcinoma development. Therapeutic approaches targeting hypergastrinemia, such as immunization with G17DT, have been evaluated for the treatment of gastric adenocarcinoma, with some promising results. Although the mild hypergastrinemia associated with proton pump inhibitor drug use has been shown to cause ECL-cell hyperplasia and to increase H pylori-induced gastric atrophy, there is currently no convincing evidence that this class of agents contributes towards the development of gastric neuroendocrine tumors or gastric adenocarcinomas in human subjects.

Interrelationships between circulating gastrin and iron status in mice and humans

The observations that the peptide hormone gastrin interacts with transferrin in vitro and that circulating gastrin concentrations are increased in the iron-loading disorder hemochromatosis suggest a possible link between gastrin and iron homeostasis. This study tested the hypothesis that gastrin and iron status are interrelated by measurement of iron homeostasis in mice and humans with abnormal circulating gastrin concentrations. Intestinal iron absorption was determined by (59)Fe uptake following oral gavage, and concentrations of duodenal divalent metal transporter-1 (DMT-1) and hepatic hepcidin mRNAs were determined by quantitative real-time PCR in agastrinemic (GasKO), hypergastrinemic cholecystokinin 2 receptor-deficient (CCK2RKO), or wild-type mice. Iron status was measured by standard methods in the same mice and in hypergastrinemic humans with multiple endocrine neoplasia type 1 (MEN-1). Iron absorption was increased sixfold and DMT-1 mRNA concentration fourfold, and transferrin saturation was reduced 0.8-fold and hepcidin mRNA expression 0.5-fold in juvenile GasKO mice compared with age-matched wild-type mice. In mature mice, few differences were observed between the strains. Juvenile CCK2RKO mice were hypergastrinemic and had a 5.4-fold higher DMT-1 mRNA concentration than wild-type mice without any increase in iron absorption. In contrast to juvenile GasKO mice, juvenile CCK2RKO mice had a 1.5-fold greater transferrin saturation, which was reflected in a twofold increase in liver iron deposition at maturity compared with wild-type mice. The correlation between transferrin saturation and circulating gastrin concentration observed in mutant mice was also observed in human patients with MEN, in whom hypergastrinemia correlated positively (P = 0.004) with an increased transferrin saturation. Our data indicate that, in juvenile animals when iron demand is high, circulating gastrin concentrations may alter iron status by a CCK2R-independent mechanism.

Translational research in gastric malignancy

This article discusses recent advances in gastric cancer research that have improved treatment and outcomes of gastric malignancy, or have the potential to do so. The significance of Helicobacter pylori infection and eradication, immunology, host genetics, proto-oncogenes, and epigenetic alterations in gastric cancer are discussed. Abnormal signaling through growth factor pathways (tyrosine kinases and gastrointestinal peptides) presents ample opportunities for therapeutic intervention that are currently being tested in clinical trials. Drugs targeting abnormal epigenetic changes, such as DNA hypermethylation and histone deacetylation, are also on the horizon, although most of this research is still in the preclinical phase. The potential prognostic implications of genetics and immunology in gastric cancer prognosis are also reviewed.

Changes in gene expression of gastric mucosa during therapeutic acid inhibition

BACKGROUND

Long-term therapy with potent acid inhibitors is a common treatment for gastro-esophageal reflux disease. Administration of proton pump inhibitors (PPIs) causes profound and continuous hypochlorhydria by inhibition of the proton pump in gastric parietal cells. Long-term hypergastrinaemia increases mucosal thickness and enterochromaffin-like cell density in oxyntic mucosa.

OBJECTIVE

The aim of this study was to see whether this very common clinical intervention induces significant changes in the gastric mucosal gene expression pattern.

METHODS

Seven patients suffering from gastro-esophageal reflux disease were included in this study. Endoscopic biopsies were taken from the corpus mucosa before and toward the end of a 3-month treatment with the PPI esomeprazole.

RESULTS

Microarray analysis identified 186 differentially expressed genes. A high proportion of genes with changed gene expression levels during PPI treatment are involved in proliferation, apoptosis, and stress response.

CONCLUSION

This study identified many genes that were not previously known to be affected by inhibition of gastric acid secretion. Further characterization of the functional roles of genes whose expression is modulated by potent acid inhibition may give new insight into the biological responses to potent acid inhibition, including the mucosal response to the moderately increased gastrin levels encountered in clinical practice.

Gastric cancer: Animal studies on the risk of hypoacidity and hypergastrinemia

Gastric hypoacidity and hypergastrinaemia are seen in several conditions associated with an increased risk of gastric malignancy. Hypoacidity and hypergastrinaemia are closely related and their long-term effects are difficult to study separately in patients. Studies using animal models can provide valuable information about risk factors and mechanisms in gastric cancer development as the models allow a high degree of intervention when introducing or eliminating factors possibly affecting carcinogenesis. In this report, we briefly review findings from relevant animal studies on this topic. Animal models of gastric hypoacidity and hypergastrinaemia provide evidence hypergastrinaemia is a common causative factor in many otherwise diverse settings. In all species where sufficient hypoacidity and hypergastrinaemia have been induced, a proportion of the animals develop malignant lesions in the gastric oxyntic mucosa.

Microbial flora of the stomach after gastric bypass for morbid obesity

BACKGROUND

The normal stomach is virtually sterile but the effect of Roux-en-Y gastric bypass (RYGBP) on bacterial flora in the used (very small proximal pouch) and unused (large bypassed) gastric chambers is not known. In a prospective study, this variable was documented.

METHODS

Bariatric subjects (n=37) were submitted to endoscopic examination of both gastric reservoirs via FUJINON enteroscope model EN-450P5, 7.3 +/- 1.4 years after RYGBP. Age was 42.4 +/- 9.9 years (70.2% females), preoperative BMI was 53.5 +/- 10.6, and current BMI was 32.6 +/- 7.8 kg/m2. Methods included quantitative culture of gastric secretion along with gastric pH and lactulose/hydrogen breath test.

RESULTS

None of the subjects displayed diarrhea, malabsorption or other complaints suggestive of GI bacterial overgrowth. Elevated counts of bacteria and fungi were identified in both chambers, with predominance of aerobes and anaerobes, but not molds and yeasts, in the proximal stomach. Gram-positive cocci, bacilli and coccobacilli represented the majority of the isolates. Gastric pH was neutral (pH 7.0 +/- 0.2) in the proximal pouch, whereas the distal chamber mostly but not always conserved the expected acidity (pH 3.3 +/- 2.2, P<0.001). The breath test for bacterial overgrowth was positive in 40.5% of the population.

CONCLUSIONS

1) Frequent colonization of both gastric chambers was detected; 2) Aerobes, anaerobes and fungi were represented in both situations; 3) Gastric pH as well as bacterial count was higher in the functioning proximal stomach; 4) Breath test was positive in 40.5% of the subjects; 5) Clinical manifestation such as diarrhea, malabsorption or pneumonia were not demonstrated; 6) Further histologic and microbiologic studies of both the stomach and the small bowel are recommended.

Genetically engineered mice: a new paradigm to study gastric physiology

PURPOSE OF REVIEW

To summarize key aspects from recent research as well as review articles on the topic of genetic mouse models, particularly in knockout mice, that have considerably contributed to understanding the pathways and mechanisms underlying gastric physiology.

RECENT FINDINGS

A series of knockout mouse models has proven to be invaluable in elucidating the mechanism and validating the current model of acid secretion. The interaction between the gastrin-histamine and cholecystokinin-somatostatin pathways was identified using the genetic approach as being critical in regulating acid secretion. Curiously, neither ghrelin nor ghrelin receptor knockout mice displayed the expected lean phenotype. Importantly, the study of obestatin in GPR39 knockout mice could be misleading, as zinc rather than obestatin is the endogenous ligand for GPR39. The physiological roles of ghrelin and obestatin have yet to be confirmed using knockout mouse models.

SUMMARY

The knockout mouse continues to serve as an excellent model to dissect the complexity of the mechanism of gastric acid secretion and to study the physiological importance of gastric ghrelin.

Gastric secretion

PURPOSE OF REVIEW

This review summarizes the past year's literature regarding the regulation of gastric exocrine and endocrine secretion.

RECENT FINDINGS

Gastric acid secretion is tightly regulated by overlapping neural, hormonal, paracrine, and intracellular pathways in order to achieve the correct amount of acid secretion required by the specific situation. Too little acid can interfere with the absorption of iron, calcium, vitamin B12, and certain drugs as well as predispose to enteric infection, bacterial overgrowth, and gastric malignancy. Too much acid can induce esophageal, gastric, and duodenal injury. Gastrin, histamine, acetylcholine, and ghrelin stimulate whereas somatostatin, cholecystokinin, atrial natriuretic peptide, and nitric oxide inhibit acid secretion. Most patients infected with Helicobacter pylori manifest a pangastritis and produce less than normal amounts of acid; those with antral predominant gastritis, however, are hypergastrinemic and produce increased amounts of acid. Improved understanding of the channels and receptors that are required for and regulate H+K+-ATPase activity should lead to the development of novel antisecretory agents.

SUMMARY

A better understanding of the pathways regulating gastric secretions should lead to new strategies to prevent and treat a variety of gastric disorders such as gastroesophageal reflux disease, autoimmune gastritis, gastric cancer, and functional dyspepsia.

Transcriptional profiling of gastrin-regulated genes in mouse stomach

Gastrin, a potent stimulator of gastric acid secretion, primarily targets the acid-secreting parietal cells and histamine-secreting enterochromaffin-like (ECL) cells in the stomach. Accordingly, gastrin-deficient (GAS-KO) mice have a severe impairment in acid secretion. The aim of this study was to characterize changes in gene expression in GAS-KO mice to identify gastrin-regulated genes and to gain insight into how gastric cell types are regulated by gastrin and acid secretion. Affymetrix microarray analysis of GAS-KO and wild-type mice identified numerous differentially expressed transcripts. The results were compared with GAS-KO mice treated with gastrin to identify genes that were gastrin responsive. Finally, genes that were primarily changed due to gastrin and not hypochlorhydria were identified by comparison to mice that are deficient in both gastrin and cholecystokinin (GAS/CCK-KO), since these mice have restored basal acid secretion. The data were validated by quantitative reverse transcriptase polymerase chain reaction analysis. Interestingly, a number of inflammatory response genes were induced in GAS-KO mice and normalized in GAS/CCK-KO mice, suggesting that they were increased in response to low gastric acid. Moreover, a number of parietal cell transcripts that were downregulated in GAS-KO mice were similarly restored in GAS/CCK-KO mice, suggesting that parietal cell changes were also primarily associated with hypochlorhydria. In contrast, ECL cell genes that were markedly downregulated in GAS-KO mice continued to be reduced in GAS/CCK-KO mice, demonstrating that gastrin coordinately regulates a number of ECL cell genes, including several involved in histamine synthesis and secretion.