The stomach in health and disease.

The stomach is traditionally regarded as a hollow muscular sac that initiates the second phase of digestion. Yet this simple view ignores the fact that it is the most sophisticated endocrine organ with unique physiology, biochemistry, immunology and microbiology. All ingested materials, including our nutrition, have to negotiate this organ first, and as such, the stomach is arguably the most important segment within the GI tract. The unique biological function of gastric acid secretion not only initiates the digestive process but also acts as a first line of defence against food-borne microbes. Normal gastric physiology and morphology may be disrupted by Helicobacter pylori infection, the most common chronic bacterial infection in the world and the aetiological agent for most peptic ulcers and gastric cancer. In this state-of-the-art review, the most relevant new aspects of the stomach in health and disease are addressed. Topics include gastric physiology and the role of gastric dysmotility in dyspepsia and gastroparesis; the stomach in appetite control and obesity; there is an update on the immunology of the stomach and the emerging field of the gastric microbiome. H. pylori-induced gastritis and its associated diseases including peptic ulcers and gastric cancer are addressed together with advances in diagnosis. The conclusions provide a future approach to gastric diseases underpinned by the concept that a healthy stomach is the gateway to a healthy and balanced host. This philosophy should reinforce any public health efforts designed to eradicate major gastric diseases, including stomach cancer.

The effect of class II major histocompatibility complex expression on adherence of Helicobacter pylori and induction of apoptosis in gastric epithelial cells: a mechanism for T helper cell type 1-mediated damage.

Helicobacter pylori infection is associated with gastric epithelial damage, including apoptosis, ulceration, and cancer. Although bacterial factors and the host response are believed to contribute to gastric disease, no receptor has been identified that explains how the bacteria attach and signal the host cell to undergo apoptosis. Using H. pylori as "bait" to capture receptor proteins in solubilized membranes of gastric epithelial cells, class II major histocompatibility complex (MHC) molecules were identified as a possible receptor. Signaling through class II MHC molecules leading to the induction of apoptosis was confirmed using cross-linking IgM antibodies to surface class II MHC molecules. Moreover, binding of H. pylori and the induction of apoptosis were inhibited by antibodies recognizing class II MHC. Since type 1 T helper cells are present during infection and produce interferon (IFN)-gamma, which increases class II MHC expression, gastric epithelial cell lines were exposed to H. pylori in the presence or absence of IFN-gamma. IFN-gamma increased the attachment of the bacteria as well as the induction of apoptosis in gastric epithelial cells. In contrast to MHC II-negative cell lines, H. pylori induced apoptosis in cells expressing class II MHC molecules constitutively or after gene transfection. These data describe a novel receptor for H. pylori and provide a mechanism by which bacteria and the host response interact in the pathogenesis of gastric epithelial cell damage.

Expression of B7-1 and B7-2 costimulatory molecules by human gastric epithelial cells: potential role in CD4+ T cell activation during Helicobacter pylori infection.

Human gastric mucosal epithelial cells display class II MHC, the expression of which is increased during Helicobacter pylori infection. These observations suggest that the gastric epithelium may participate as antigen-presenting cells (APC) during local immune responses. The increase in class II MHC expression occurs in parallel with an elevation in gastric CD4+ T cell numbers within and adjacent to the epithelium. Since the expression of either B7-1 (CD80) or B7-2 (CD86) on APC is required for the activation of T cells, it was important to establish human gastric epithelial cells expressed those surface ligands. The expression of B7-1 and B7-2 was detected on human gastric epithelial cell lines and freshly isolated epithelial cells from gastric biopsies with specific antibodies. B7-2 expression was higher than B7-1 at both protein and transcript levels and was increased after crosslinking class II MHC molecules on IFNgamma-treated epithelial cells and in cells pretreated with the combination of IFNgamma and H. pylori. Similarly, B7-2 expression was higher on gastric epithelial cells from H. pylori-infected tissues compared with those from uninfected specimens. To determine the function of these molecules on gastric epithelial cells, antibodies to B7-1 and B7-2 were shown to reduce the ability of the cells to stimulate alloreactive CD4+ T cells. These observations are the first to demonstrate that B7-1 and B7-2 are expressed on mucosal epithelial cells in situ. Thus, the expression of B7-1 and B7-2 by epithelial cells may allow them to act as APC in regulating local responses such as those that occur during infection with H. pylori.

Membrane-bound ß-catenin degradation is enhanced by ETS2-mediated Siah1 induction in Helicobacter pylori-infected gastric cancer cells.

ß-catenin has two different cellular functions: intercellular adhesion and transcriptional activity. The E3 ubiquitin ligase Siah1 causes ubiquitin-mediated degradation of the cytosolic ß-catenin and therefore, impairs nuclear translocation and oncogenic function of ß-catenin. However, the effect of Siah1 on the cell membrane bound ß-catenin has not been studied. In this study, we identified that the carcinogenic bacterium H. pylori increased ETS2 transcription factor-mediated Siah1 protein expression in gastric cancer cells (GCCs) MKN45, AGS and Kato III. Siah1 protein level was also noticeably higher in gastric adenocarcinoma biopsy samples as compared to non-cancerous gastric epithelia. Siah1 knockdown significantly decreased invasiveness and migration of H. pylori-infected GCCs. Although, Siah1 could not increase degradation of the cytosolic ß-catenin and its nuclear translocation, it enhanced degradation of the membrane-bound ß-catenin in the infected GCCs. This loss of membrane-bound pool of ß-catenin was not associated with the proteasomal degradation of E-cadherin. Thus, this work delineated the role of Siah1 in increasing invasiveness of H. pylori-infected GCCs.

Review article: the global emergence of Helicobacter pylori antibiotic resistance.

BACKGROUND: Helicobacter pylori is one of the most prevalent global pathogens and can lead to gastrointestinal disease including peptic ulcers, gastric marginal zone lymphoma and gastric carcinoma. AIM: To review recent trends in H. pylori antibiotic resistance rates, and to discuss diagnostics and treatment paradigms. METHODS: A PubMed literature search using the following keywords: Helicobacter pylori, antibiotic resistance, clarithromycin, levofloxacin, metronidazole, prevalence, susceptibility testing. RESULTS: The prevalence of bacterial antibiotic resistance is regionally variable and appears to be markedly increasing with time in many countries. Concordantly, the antimicrobial eradication rate of H. pylori has been declining globally. In particular, clarithromycin resistance has been rapidly increasing in many countries over the past decade, with rates as high as approximately 30% in Japan and Italy, 50% in China and 40% in Turkey; whereas resistance rates are much lower in Sweden and Taiwan, at approximately 15%; there are limited data in the USA. Other antibiotics show similar trends, although less pronounced. CONCLUSIONS: Since the choice of empiric therapies should be predicated on accurate information regarding antibiotic resistance rates, there is a critical need for determination of current rates at a local scale, and perhaps in individual patients. Such information would not only guide selection of appropriate empiric antibiotic therapy but also inform the development of better methods to identify H. pylori antibiotic resistance at diagnosis. Patient-specific tailoring of effective antibiotic treatment strategies may lead to reduced treatment failures and less antibiotic resistance.

Regulation of the mucosal immune response.

Infectious diseases continue to exact an extensive toll on populations living closest to the equatorial regions of the globe. A substantial proportion of these infections gain access to the host via the mucosal tissues. Thus, the development of new vaccines that enhance mucosal immunity is considered to be of paramount importance in order to prevent or limit the impact of these infections. Mucosal immune responses must discriminate between commensal flora within the lumen and potential pathogens. These responses are highly adapted to induce protection without excessive amounts of inflammation. The balances that regulate mucosal immune and inflammatory responses have to be understood if effective mucosal immunity is to be induced through local immunization. This review will summarize some of the unique properties of mucosal immune responses and focus on recent advances that have significantly influenced our understanding of the regulation of immune and inflammatory responses following infection.

Effectiveness of an experimental consensus phytase in improving dietary phytate-phosphorus utilization by weanling pigs.

Consensus phytase is a new biosynthetic, heat-stable enzyme derived from the sequences of multiple homologous phytases. Two experiments were conducted to determine its effectiveness, relative to inorganic P and a mutant enzyme of Escherichia coli phytase (Mutant-EP), in improving dietary phytate-P availability to pigs. In Exp. 1, 36 pigs (3 wk old, 7.00 +/- 0.24 kg of BW) were fed a low-P corn-soybean meal basal diet plus consensus phytase at 0, 250, 500, 750, 1,000, or 1,250 U/kg of feed for 5 wk. Plasma inorganic P concentration, plasma alkaline phosphatase activity, bone strength, and overall ADG and gain:feed ratio of pigs were improved (P < 0.05) by consensus phytase in both linear (R2 = 0.20 to 0.70) and quadratic (R2 = 0.30 to 0.70) dose-dependent fashions. In Exp. 2, 36 pigs (4 wk old, 9.61 +/- 0.52 kg BW) were fed the basal diet + inorganic P at 0.1 or 0.2%, consensus phytase at 750 or 450 U/kg of feed, Mutant-EP at 450 U/kg of feed, or 225 U consensus + 225 U Mutant-EP/kg of feed. Pigs fed 750 U of consensus phytase or 450 U of Mutant-EP/kg feed had plasma inorganic concentrations and bone strength that fell between those of pigs fed 0.1 or 0.2% inorganic P. These two measures were 16 to 29% lower (P < 0.05) in pigs fed 450 U of consensus phytase/kg of feed than those of pigs fed 0.2% inorganic P. Plasma inorganic P concentrations were 14 to 29% higher (P < 0.05) in pigs fed Mutant-EP vs. consensus phytase at 450 U/kg at wk 2 and 3. In conclusion, the experimental consensus phytase effectively releases phytate P from the corn-soy diet for weanling pigs. The inorganic P equivalent of 750 U of consensus phytase/kg of feed may fall between 0.1 and 0.2%, but this requires further determination.

The role of the local immune response in the pathogenesis of peptic ulcer formation.

Mucosal immune responses are designed to provide local protection against infection, without inducing excessive amounts of inflammation that would alter epithelial integrity or function. It has become clear that the epithelium not only serves as a barrier to exclude pathogens, but also initiates host responses to infection. Gastric epithelial cells infected with Helicobacter pylori can respond within hours to produce inflammatory mediators that recruit and activate neutrophils. The gastric epithelium can also be recognized by local T-cells, resulting in their activation and ability to induce epithelial damage. During infection with H. pylori, there is a remarkable increase in the level of local IgG antibodies, which may also recognize and damage the epithelium. Thus, activated neutrophils, T-cells and auto-antibodies may contribute to a weakened epithelial barrier that allows luminal acid and other factors to contribute to peptic ulceration. The epithelium appears to play a key role in the initiation of the local inflammatory and immune responses that may contribute to the more serious sequelae associated with H. pylori infection.

Synaptic deficits in layer 5 neurons precede overt structural decay in 5xFAD mice.

Synaptic decay and neurodegeneration are hallmarks of Alzheimer's disease that are thought to precede dementia. Recently, we have reported that the first signs of neuritic dystrophy in a new transgenic mouse model of familial Alzheimer's disease (FAD) called the "5xFAD" are axonal dystrophy followed by loss of spines on basal dendrites. The 5xFAD mouse has profound loss of layer 5 neurons by 12months, and these initial structural insults appear between 4 and 6months of age. Here, we test, for the first time, if synaptic failure of layer 5 neurons in the 5xFAD mouse precedes these structural changes. We used longitudinal, in vivo two-photon fluorescence imaging of bigenic 5xFAD/YFP mice to assess the overall structural stability of layer 5 neurons in young mice (age less than 14weeks). We found these neurons to be structurally and morphologically sound. In parallel, we used in vitro, whole-cell patch clamp electrophysiology of layer 5 pyramidal neurons, from mice aged 8-12weeks, to reveal significant pre- and postsynaptic defects in these cells. Thus our data suggest that layer 5 neurons in the 5xFAD mouse model have synaptic deficits at an early time point, before any overt structural dystrophy, and that such synaptic failure, with co-temporal biochemical changes, may be an early step in neuronal loss.

A2A adenosine receptor (AR) activation inhibits pro-inflammatory cytokine production by human CD4+ helper T cells and regulates Helicobacter-induced gastritis and bacterial persistence.

Helicobacter pylori causes a lifelong infection and provides a model of bacterial adaptation and persistent colonization. Adenosine is an anti-inflammatory mediator that limits tissue damage during inflammation. We studied the role of adenosine in the T-cell-mediated regulation of gastritis and bacterial persistence. After 4 h of activation, human T helper (Th) cells increased A(2A) adenosine receptor (A(2A)AR) mRNA level (sevenfold). A(2A)AR was the predominant subtype expressed in resting and stimulated gastric or peripheral Th cells. Stimulation with ATL313, an A(2A)AR agonist, increased cyclic AMP (cAMP) accumulation and reduced interleukin-2 (IL-2) production by 20-50%. ATL313 also attenuated tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) production, which was inhibited by an A(2A)AR antagonist. Infection of IL-10-deficient mice with H. pylori is cleared spontaneously due to the marked inflammation. Administration of ATL313 during infection reduced gastritis and pro-inflammatory cytokine responses while bacterial load increased. In contrast, infection of A(2A)AR-deficient mice enhanced gastritis. Thus, A(2A)AR limits the pro-inflammatory effects of Th cells and favor chronic Helicobacter infection.

Gastrointestinal food allergies: do they exist?

Gastrointestinal (GI) symptoms are often attributed to adverse reactions to foods (ARF), but it is not always clear whether such reactions are caused by food allergy. A reaction to food proteins that is mediated by immunologic events is referred to as food allergy or food hypersensitivity. One of the most common types of food allergy is the IgE-mediated immediate hypersensitivity reaction to foods, which can give rise to dermatologic and respiratory tract symptoms in addition to GI complaints. Other GI forms of food allergy include food protein-induced enterocolitis or gastroenteropathy, celiac disease, and some cases of eosinophilic gastroenteritis. Because most patients complaining of adverse reactions to food have non-immune mechanisms for their complaints, it is important to distinguish the various types of ARF, as their management may differ substantially. Recent advances in the field of food allergy provide opportunities to improve diagnostic methods and develop new modalities for management that will complement the current practice of allergen avoidance.

Gastrointestinal food hypersensitivity: basic mechanisms of pathophysiology.

Gastrointestinal symptoms occur in a large number of patients with food allergies. Immediate hypersensitivity mechanisms may give rise to the nausea, vomiting, abdominal pain, and diarrhea experienced by these patients. However, there are limited human data about the pathophysiological basis for these symptoms. Most of the available information comes from a variety of animal models. This article reviews the literature using models of intestinal food hypersensitivity, as well as human studies, that have contributed to our understanding of the pathophysiological mechanisms in gastrointestinal food hypersensitivity.

Functional abnormalities in the intestine associated with mucosal mast cell activation.

Mast cells are a significant component of the mucosa in the gastrointestinal tract. There is increasing evidence that these cells are involved in the pathophysiology of various intestinal disorders ranging from food allergy to inflammatory bowel disease. When activated, mast cells release a host of potent mediators and cytokines which are capable of inducing pathophysiology. The bulk of the evidence has come from hypersensitivity studies in experimental animals sensitized either by parasitic infection or by active immunization to an antigen using adjuvants which stimulate IgE production. Subsequent antigen challenge of the gut results in mast cell activation associated with alterations in intestinal functions including ion transport and epithelial permeability. Intestinal secretory transport responses are inhibited by antagonists of mast cell mediators and neurotoxins, implicating mast cell-nerve interactions with the epithelium. In genetically mast cell-deficient mice, antigen-induced secretion is reduced approximately 70% and this component is not affected by neural or mast cell inhibitors; adoptive transfer of bone marrow containing mast cell precursors derived from congenic normal mice restores the complete antigen response. These results provide more direct proof that mast cell activation causes abnormal gut function. Recently, we have begun studies which indicate that activation of mast cells induces ion secretion in surgically resected human intestine. Reduced secretory responses in specimens from patients with IBD suggest that mast cells may play a role in the pathophysiology of inflammatory bowel disease.

Anti-immunoglobulin E-stimulated ion transport in human large and small intestine.

BACKGROUND: Mast-cell regulation of intestinal ion transport, previously shown in animals and cultured cells, was examined in surgically resected human bowel in this study. METHODS: Changes in short-circuit current (Isc) in response to rabbit anti-human immunoglobulin (Ig) E or control serum, histamine, and electrical stimulation were measured in muscle-stripped, noninflamed segments of intestine mounted in Ussing chambers. Chloride-free buffer, pyrilamine, piroxicam, sodium cromoglycate, and tetrodotoxin were examined for their effect on Isc responses to these stimuli. RESULTS: Within 1-2 minutes of adding anti-IgE serum, a specific monophasic rise in Isc (peaking at 7-10 minutes) was observed in large and small intestine. This response was reduced approximately 80% in chloride-free buffer and inhibited by the histamine1-receptor antagonist, pyrilamine, and the cyclo-oxygenase inhibitor, piroxicam, implicating histamine and prostaglandins as mediators of the ion transport changes. The mast-cell stabilizer, sodium cromoglycate, reduced anti-IgE responses in the small, but not large, intestine. Approximately 50% inhibition of anti-IgE responses in colon by the neurotoxin, tetrodotoxin, indicated that nerves were involved. CONCLUSIONS: These results suggest that activation of mast cells releases mediators that stimulate intestinal ion transport through direct epithelial action and via nerves. This study provides important evidence that immunoregulation of intestinal ion transport does occur in humans.

Virulence and pathogenicity of Helicobacter pylori.

Bacterial and host response factors play significant roles in the pathogenicity of H. pylori-related disease manifestations. The complete DNA sequences for two H. pylori strain genomes have been published. The differences in the sequences between these two unrelated strains may enable clinicians to identify rapidly other conserved and potentially virulent genes and products. Whether these two DNA sequences are sufficient representation of the H. pylori genetic heterogeneity is unknown. The host immune response and the cascade of events that occurs with H. pylori infection are being clarified rapidly. Understanding the role of this gastric bacterium in apoptosis and cellular proliferation would enable clinicians to understand its relationship to ulcerogenesis and gastric malignancy. Piecing together many observations related to H. pylori would result in understanding the interaction of H. pylori factors and host responses that lead to the variety of disease manifestations associated with this chronic infection. The development of animal models with H. pylori and other Helicobacter species has set the stage in which in vitro observations can be tested in the in vivo model.

How does Helicobacter pylori cause mucosal damage? The inflammatory response.

The role for Helicobacter pylori in the pathogenesis of disease provides the conundrum that only a subset of subjects infected with H. pylori will ever develop peptic ulcer or gastric cancer. Thus, variation in strain as well as environmental or host factors converge in the gastroduodenal milieu and control the final outcome of infection. The host immune and inflammatory response is emerging as an important element in the pathogenesis of these gastric diseases. The ideal host response provides protection to clear an infection without causing excessive amounts of inflammation that could compromise the integrity and function of host cells. This review will cover four main questions: (1) What are the mucosal immune/inflammatory responses that confer protection without damaging the host? (2) How do the gastric immune responses during infection with H. pylori differ from this ideal scenario? (3) Do these responses contribute to autoimmune-mediated damage to gastric tissue? (4) Can immunomodulation through vaccination enhance protective, nondestructive responses that prevent or treat infection or, at least, attenuate inflammation?

Mast cell mediated ion transport in intestine from patients with and without inflammatory bowel disease.

BACKGROUND: Mast cells have been shown to regulate intestinal ion transport in animal models and normal human colon but their physiological role in human intestinal inflammatory disorders is unknown. AIMS: To examine mast cell regulation of ion transport in inflammatory bowel disease (IBD). SUBJECTS AND METHODS: Small and large intestine was obtained from patients with and without IBD undergoing surgical resection. Short circuit current (Isc) responses to rabbit antihuman IgE, histamine, and electrical stimulation were measured in Ussing chambers. Specimens were also examined for mast cell numbers and degree of inflammation. RESULTS: Isc responses to anti-IgE and histamine were smaller in magnitude in IBD compared with non-IBD tissues. In all tissues, anti-IgE Isc responses were reduced by about 80% in chloride free buffer. The histamine H1 receptor antagonist, pyrilamine, decreased anti-IgE responses in non-IBD tissues. Greater inhibition with pyrilamine was seen in IBD small intestine but its effect was less in IBD colon. Histamine pretreatment of non-IBD control tissues reduced anti-IgE responses to levels seen in IBD colon but had no effect in small intestine. Mast cell numbers were greater in IBD compared with non-IBD small intestine while no differences were observed between the colonic groups. Isc responses to anti-IgE were not correlated with the degree of mucosal inflammation. CONCLUSIONS: This study provides further evidence that mast cells are capable of mediating alterations of ion transport in human gut but that this regulatory role may be altered in IBD. The data suggest that prior activation of mast cells with release of histamine may account for the reduced secretory response to anti-IgE observed in IBD colonic tissues.

Allergic reactions of rat jejunal mucosa. Ion transport responses to luminal antigen and inflammatory mediators.

This study examined the electrophysiological responses to antigen and to various stimuli in jejunal mucosa from rats sensitized to egg albumin with alum and pertussis adjuvants. Luminal antigen caused an immediate increase in short-circuit current, a measure of net ion transport, which was one of three different patterns. All were inhibited by the chloride channel blocker diphenyl-2-carboxylate, by chloride-free buffer, and by doxantrazole, a mast cell stabilizer. Depending on the pattern, the histamine-1 antagonist diphenhydramine, the 5-hydroxytryptamine-2 antagonist ketanserin, and the cyclooxygenase inhibitor piroxicam also reduced the responses. A neural component was indicated by inhibition of the responses to luminal antigen by the neurotoxin tetrodotoxin and by neonatal capsaicin treatment, which depletes substance P-containing nerves. In the absence of antigen, histamine and substance P caused increases in short-circuit current; the magnitude of these changes was significantly greater in tissues from sensitized animals than in controls. These data suggest that sensitization itself may result in hypersecretory responses to some inflammatory mediator and neurotransmitter substances.

Helicobacter pylori infection as a model for gastrointestinal immunity and chronic inflammatory diseases.

Approximately 50% of humanity is infected with Helicobacter pylori. It is a life-long infection that elicits a marked host inflammatory response; however, natural infection fails to yield protective immunity. Rather than providing protection, the chronic inflammatory response associated with natural infection contributes to tissue damage and the pathogenesis of gastroduodenal disease, including atrophic gastritis, peptic ulcer, and gastric cancer. While bacterial factors are important triggers of inflammation, many subjects infected with strains bearing putative virulence factors remain free from disease. Recent genetic studies have implicated the host's immune and inflammatory responses, suggesting that disease results from an interaction between bacterial and environmental factors in genetically susceptible hosts. Other digestive diseases, including celiac disease and inflammatory bowel disease, mimic this paradigm, where it appears that luminal triggers only manifest disease in subjects with the right combination of host and environmental factors. Since infection with H. pylori is relatively common, it is possible to study the impact of a specific etiologic agent on the pathogenesis of disease in humans. This approach has illuminated the complexity of the pathogenic mechanisms, but the advances achieved to date may provide some hints regarding the pathogenesis of chronic inflammatory diseases elsewhere in the digestive tract.