Apical and basolateral EGF receptors regulate gastric mucosal paracellular permeability.

Previous studies found that monolayers formed from canine oxyntic epithelial cells in primary culture displayed remarkable resistance to apical acidification and both mitogenic and migratory responses to epidermal growth factor (EGF) treatment. In our present studies, we found that EGF increased transepithelial resistance (TER) but not short-circuit current in these monolayers. Parallel effects of EGF on decreasing mannitol flux and increasing TER implicate direct regulation of paracellular permeability. EGF acting at either apical and basolateral receptors rapidly increased TER, but the apical response was sustained whereas the basolateral response was transient. (125)I-labeled EGF binding revealed specific apical binding, but receptor numbers were 25-fold lower than on the basolateral surface. Both apical and basolateral EGF activated tyrosine phosphorylation of EGF receptors (EGFR), beta-catenin, and cellular substrate as evident on confocal microscopy. Although apical EGF activated a lesser degree of receptor autophosphorylation than basolateral EGF, phosphorylation of beta-catenin was equally prominent with apical and basolateral receptor activation. Together, these findings indicate that functional apical and basolateral EGFR exist on primary canine gastric epithelial cells and that these receptors regulate paracellular permeability. The sustained effect of apical EGFR activation and prominent phosphorylation of beta-catenin suggest that apical EGFR may play a key role in this regulation.

Effects of growth factors and trefoil peptides on migration and replication in primary oxyntic cultures.

Restitution, the lateral migration of cells over an intact basement membrane, maintains mucosal integrity. We studied the regulation of migration and proliferation of enzyme-dispersed canine oxyntic mucosa cells in primary culture. Confluent monolayers were wounded and cultured in serum-free medium, and cells migrating into the wound were counted. [3H]thymidine incorporation into DNA was studied using subconfluent cultures. Considerable migration occurred in untreated monolayers; however, epidermal growth factor (EGF), transforming growth factor (TGF)-alpha, basic fibroblast growth factor (bFGF), insulin-like growth factor I (IGF-I), two trefoil peptides, and interleukin (IL)-1beta further enhanced migration. The specific EGF receptor (EGFR) monoclonal antibody, MAb-528, inhibited both basal and TGF-alpha- or IL-1beta-stimulated migration, but not the response to trefoil peptide, bFGF, or IGF-I. Exogenous TGF-beta inhibited cell proliferation but did not alter migration. Immunoneutralization with anti-TGF-beta blocked the response to exogenous TGF-beta and produced a small enhancement of basal thymidine incorporation but did not attenuate basal or TGF-alpha-stimulated migration. In conclusion, endogenous EGFR ligands regulate proliferation and migration. TGF-beta inhibits mitogenesis; it did not upregulate migration in these cultures. Although bFGF, IGF-I, and IL-1beta enhance gastric epithelial migration, only IL-1beta acted in a TGF-alpha-dependent fashion.

Gastroesophageal reflux: practical management of a common, challenging disorder.

Gastroesophageal reflux (GER) occurs in 2 distinct forms that differ in pathophysiology, clinical presentation, natural history, and therapy: mild GER (with no or minimal esophagitis) and classic, severe reflux (at risk for erosive esophagitis). A minority of subjects (< 20%) have the classic, potentially severe pattern of GER caused by reduced lower esophageal sphincter (LES) pressure and prolonged acid reflux, particularly at night, but also during the day. Evaluation and management must be catered to patients with this pattern of reflux. In contrast, symptoms in mild reflux (the majority) often occur during the day after meals in an upright posture (upright reflux); resting LES pressure is usually normal (reflux episodes are related to transient relaxation of the LES) and little reflux occurs at night. Acid reflux, which occurs mostly during the day, overlaps with the normal range and esophagitis is rare; however, symptoms can be distressing. Optimal management is controversial because no outcome trials have been conducted to address management in primary care settings. However, clinical clues can help differentiate mild and severe reflux and guide management decisions. This article provides a detailed approach to current management of GER syndromes.

Peptic ulcer and dyspepsia.

Peptic ulcers are defects in the gastrointestinal mucosa that extend through the muscularis mucosae. They persist as a function of the acid or peptic activity in gastric juice. Twenty years ago, most ulcers were considered idiopathic; but a revolution in knowledge has occurred, so that it is now understood that the great majority of ulcers results from infection with Helicobacter pylori (HP) or use of nonsteroidal anti-inflammatory drugs (NSAIDs). Before this revolution, peptic ulcer disease was a common public health problem, responsible for considerable morbidity, some mortality, and high economic cost. Today, the overall prevalence of ulcers is falling, but complication rates remain relatively stable. These complex trends primarily reflect 3 factors: the rapid decline in the prevalence of HP in the population of developed countries, an increase in consumption of NSAIDs, and change in rates of smoking. Peptic ulcer prevalence is falling in younger individuals because of decreased prevalence of HP, whereas complications are rising in older subjects, largely as the result of increased NSAID use.

NSAID-related gastrointestinal complications.

Despite the common induction of gastrointestinal (GI) complications by nonsteroidal anti-inflammatory drugs (NSAIDs), many aspects of pathogenesis and management remain controversial. The most important complications are bleeding and perforation arising in the esophagus, stomach, and duodenum due to NSAID effects on platelets and on a variety of mucosal lesions. Complications arise from preexisting peptic ulcer, NSAID-induced ulcers and erosions, and other lesions (not caused by NSAIDs) caused to bleed by NSAID-induced platelet dysfunction. Much confusion has arisen from the umbrella term "NSAID gastropathy" used to embrace a variety of pathogenetically distinct mucosal lesions. Failure to discriminate among the different forms of NSAID injury has hampered clinical investigation. This article offers general guidelines for prevention of NSAID complications, but there remain many unresolved issues, including the role of Helicobacter pylori infection. The best approach to management is to remove or reduce exposure to NSAIDs whenever possible. The newer NSAIDs (e.g., cyclo-oxygenase [COX]-2-selective inhibitors) have a much lower risk of endoscopic ulcers and minimal platelet effects, which are likely to translate into lower risk of GI complications. However, this benefit on clinical outcome remains to be established.

H. pylori stimulates gastrin release from canine antral cells in primary culture.

Patients chronically infected with Helicobacter pylori are known to have hypergastrinemia. Previous studies have demonstrated the stimulation of gastrin from isolated G cells by monocytes and cytokines. The aim of this study was to determine if H. pylori can directly stimulate gastrin secretion. The secretion of gastrin from canine G cells in 48-h primary cultures was investigated using either live H. pylori bacteria or various bacterial extracts from three well-characterized strains. Whole bacterial sonic extracts and water-extracted surface proteins, but not PBS extracts, from strains 43579 (CagA+/VacA+), 60190 (CagA+/VacA+), and 60190:v1 (CagA+/VacA-) significantly stimulated gastrin release. Controls demonstrated that gastrin stimulation by the sonic extracts was not due to a direct toxic effect on G cells. We conclude that H. pylori produces a soluble factor(s), which can directly stimulate gastrin release in enriched canine G cell cultures. This stimulatory effect may play an important role in the H. pylori-associated hypergastrinemia and subsequent development of peptic ulcer disease.

Management strategies for Helicobacter pylori-seropositive patients with dyspepsia: clinical and economic consequences.

BACKGROUND: Noninvasive testing for Helicobacter pylori is widely available and has been considered as an initial management strategy for uninvestigated dyspepsia. However, data to guide clinicians in the management of patients with dyspepsia who are seropositive for H. pylori are lacking. OBJECTIVE: To examine the economic, clinical, and policy implications of alternative initial management strategies for patients with uninvestigated dyspepsia who are seropositive for H. pylori. DESIGN: Decision analysis comparing the costs and outcomes of initial anti-H. pylori therapy and initial endoscopy. PATIENTS: Helicobacter pylori-seropositive patients with dyspepsia. MEASUREMENTS: Cost estimates were obtained from the Medicare reimbursement schedule and a health maintenance organization pharmacy. Probability estimates were derived from the medical literature. RESULTS: Initial endoscopy costs an average of $1276 per patient, whereas initial anti-H, pylori therapy costs $820 per patient; the average saving is $456 per patient treated. The financial effect of a 252% increase in the use of antibiotics for initial H. pylori therapy is more than offset by reducing the endoscopy workload by 53%. Endoscopy-related costs must be reduced by 96% before the two strategies become equally cost-effective. In patients with nonulcer dyspepsia, the financial benefits of initial anti-H. pylori therapy are not substantially affected by varying the rates of H. pylori eradication, the complications of antibiotics, or the response of symptoms to cure of H. pylori infection. CONCLUSIONS: In H. pylori-seropositive patients with dyspepsia, initial anti-H. pylori therapy is the most cost, effective management strategy. Randomized studies of these strategies that evaluate outcomes and patient preferences are needed to optimize management decisions. In the meantime, unless physicians are concerned about resistance to antimicrobial agents or the lack of proven benefit of anti-H. pylori therapy in nonucler dyspepsia, the strategy outlined in this analysis can be used as a basis for management and policy decisions about H. pylori-seropositive patients with dyspepsia.

Mononuclear cells and cytokines stimulate gastrin release from canine antral cells in primary culture.

Patients with Helicobacter pylori-associated gastritis have an increased release of gastrin. The mechanisms by which H. pylori affects the endocrine cells are unclear. We have used primary cultures containing canine antral G cells to examine the effects of human blood mononuclear cells, purified monocytes and lymphocytes, recombinant cytokines, and NH4Cl on gastrin release. Mononuclear cells and purified monocytes in direct contact with G cells stimulated gastrin release dose dependently. Separating mononuclear cells from G cells by Transwell filters with 0.4-micron pore size still produced a significant increase of gastrin release. Three human recombinant cytokines, interferon-gamma, tumor necrosis factor-alpha, and interleukin-2, but not interleukin-6 and interleukin-1 beta, each produced dose-dependent increases of gastrin stimulation. NH4Cl did not stimulate gastrin release. We conclude that mononuclear cells and purified monocytes prepared from human blood, as well as several cytokines, stimulate gastrin release from antral G cells. These factors may play an important role in the pathogenesis of H. pylori-associated hypergastrinemia.

Consensus conference. Medical treatment of peptic ulcer disease. Practice guidelines. Practice Parameters Committee of the American College of Gastroenterology.

OBJECTIVE: To integrate the realization that peptic ulcer most commonly reflects infection with Helicobacter pylori or use of aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) into a disease management approach. PARTICIPANTS: Guidelines were outlined by the author and presented for review to the American College of Gastroenterology (ACG) Practice Parameters Committee, selected by the president of the ACG, and a panel of experts in peptic ulcer, selected by the committee. EVIDENCE AND CONSENSUS PROCESS: These guidelines were formulated following extensive review of the literature obtained by MEDLINE search and presented for detailed review and revision to unpublicized committee meetings on three occasions and to experts by mail. These recommendations are an official statement of the ACG and have been approved by the American Gastroenterological Association and the American Society for Gastroenterological Endoscopy. Firm recommendations are discriminated from reasonable suppositions pending definitive data. CONCLUSIONS: Since cure of H. pylori infection decreases recurrence rates and facilitates healing, antibiotic therapy is indicated for all H. pylori-infected ulcer patients. No optimal, simple antibiotic regimen has yet emerged. Simultaneous conventional ulcer therapy is recommended to facilitate symptom relief and healing. For refractory ulcers, only maximal acid inhibition offers advantage over continued conventional therapy; cure of H. pylori infection is likely to facilitate healing of refractory ulcers. Only with complicated or refractory ulcers should conventional maintenance therapy be continued, at least until successful H. pylori eradication is confirmed. A search for NSAID use is indicated for all ulcer patients. For NSAID-associated ulcers these drugs should be discontinued if possible and H. pylori, if present, should be cured.

Different effects of indomethacin and nabumetone on prostaglandin-mediated gastric responses to central vagal activation in rats.

Intracisternal injection of a stable thyrotropin-releasing hormone (TRH) analog increases gastric prostaglandins release and mucosal resistance to injury through central vagal pathways. The effects of two nonsteroidal anti-inflammatory drugs, indomethacin (INDO) and nabumetone on intracisternal injection of various doses of TRH-induced gastric acid secretion and changes in mucosal resistance were investigated in urethane-anesthetized rats. Doses of INDO (5 mg/kg) and nabumetone (13.75 mg/kg) producing similar acute anti-inflammatory response in the carrageenin-induced paw edema were injected i.p. in all studies. INDO potentiated the acid secretion induced by intracisternal injection of TRH at 25, 50 and 200 ng by 5.1-, 1.9- and 1.4-fold, respectively, whereas nabumetone did not modify the secretory response to TRH. Moderate erosions were observed in 100% of rats treated with the combination of INDO and TRH (200 ng) whereas no erosions were observed when TRH or INDO were given alone or TRH in combination with nabumetone. TRH at 7 ng reduced mucosal damage induced by intragastric administration of ethanol (60%, 1 ml/kg) by 63%. The mucosal protective action of TRH was abolished by INDO but not altered by nabumetone pretreatment. These data indicate that at comparable anti-inflammatory doses, nabumetone, unlike INDO, neither blocks the protection against ethanol injury induced by low doses of TRH injected intracisternally nor potentiates the gastric acid secretion or lesions induced by higher dose of TRH. We speculate that these differences reflect reduced inhibition of gastric prostaglandins by nabumetone.

Apical acidification induces paracellular injury in canine gastric mucosal monolayers.

We used primary monolayer cultures of enzyme-dispersed canine oxyntic mucosal cells mounted in Ussing chambers to characterize the apical barrier to H+. [3H]mannitol flux (MF) and [14C]inulin flux (IF) were used as size probes for tight junctions. Apical H+ produced a three-phase effect. In phase 1, as the apical pH was decreased from 7 to about 2.5, resistance (R) increased, but short-circuit current (Isc) did not change. In phase 2, an increased paracellular permeability developed at pH below 2.5-1.7, evidenced by decreased R and increased MF but not IF. Size sieving and monolayer integrity were preserved, and this paracellular leak was either fully reversed or stabilized by apical neutralization, depending on the duration of the paracellular leak. In phase 3, after sustained exposure to an apical pH below approximately 2, transepithelial integrity was lost; R decreased to fluid R, and both MF and IF increased. Basolateral acidification below pH 5.5 produced rapid monolayer disruption. Low concentrations of cytochalasin D (CD) decreased R and increased MF but not IF; apical acidification to pH 4 after CD increased R and decreased the MF, indicating reduced paracellular permeability by apical H+. Apical amiloride did not alter Isc; however, after 48 h of treatment with hydrocortisone and insulin, an amiloride-sensitive Isc component became evident. Our data indicate that the increase in R observed with apical acidification reflects decreased paracellular permeability and that the earliest injury with apical acidification is a selective paracellular leak.

Future directions for reductionistic research in gastric secretion and defense.

Our theme centers on the complex processes that constitute and regulate the function of the gastric mucosa. Although some investigators promote the critical importance of a given element, such as acid, blood flow, or mucus, it is clear that both gastric secretory function and mucosal defense and repair mechanisms are multifactorial and are regulated by redundant control circuits. While it is true that critical studies can be performed in vivo with intact mucosa, at the same time it is frequently difficult, using these methods, to define the specific cellular elements involved in the regulation of secretion, defense, and repair. We now recognize that ulcer disease does not occur simply when this balance is thrown off. To the contrary, ulcer disease commonly occurs when the normal mucosal mechanisms are perturbed by Helicobacter pylori-associated gastro-duodenitis or nonsteroidal anti-inflammatory drugs. In the absence of such perturbation, the redundancy of the regulatory mechanisms underlying gastric secretion and the multiple lines of defense and healing would render ulcer disease rare indeed.

Multiple pathways controlling acid secretion.

A simple balance exists between factors that promote ulcer disease (e.g., acid and pepsin secretion) and factors that protect the stomach from ulcer disease (e.g., mucosal defense mechanisms). These factors are regulated and control the integrity of the gastric mucosa. Some of the newest discoveries in the area of regulation of acid secretion are related to the cellular localization of physiologically relevant receptors for acid secretagogues and acid inhibitors. The ability to isolate and culture histamine-containing ECL cells and somatostatin-containing "D" cells, and the ability to clone genes encoding for specific receptors has greatly enhanced our understanding of the physiological role and the regulation of various cell types within the gastric mucosa.

The pathways regulating acid secretion: the view from the isolated cell.

Although many aspects of the regulation of acid secretion at the cellular level among different species remains controversial, certain concepts have emerged that span the differences between species, model systems and investigators. The paracrine, endocrine, neural and autocrine pathways mediate acid secretion by acting both directly on the parietal cell and indirectly via modulation of mucosal paracrine cell function. Studies with cells isolated from the acid secreting canine oxyntic mucosa indicate that gastrin and cholinergic receptors are present on parietal cells, somatostatin cells, and the histamine-enterochromaffin-like cell (ECL). Subtypes of these receptors are clearly important; the gastrin receptor on the ECL cell and parietal cell are "B" type CCK/gastrin receptors, whereas the receptor on the somatostatin cell is an A type CCK receptor. From the vantage point of studies in the canine oxyntic mucosa, the challenge is no longer to determine whether parietal, histamine or somatostatin cells have gastrin or muscarinic receptors but to establish the physiologic relevance of the specific actions (secretory, trophic or differentiative) of these receptor subtypes. Furthermore, the mechanisms integrating these paracrine, exocrine and neural elements require elucidation.

Effects of prostaglandins on gastrin release from canine antral mucosal cells in primary culture.

Evidence in vivo indicates that endogenous and exogenous prostaglandins can alter gastrin secretion. We have used primary cultures containing canine antral G-cells to study the cellular actions of prostaglandins on gastrin secretion, comparing the effects of prostaglandin E2 (PGE2) and its synthetic analogue enprostil. Enprostil (10(-10)-10(-6) M) inhibited gastrin secretion in response to bombesin, carbachol, and forskolin, the latter a receptor-independent activator of adenylate cyclase. This inhibition by enprostil was reversed by treatment with pertussis toxin (200 ng/ml, 8 h). However, enprostil did not inhibit the postreceptor stimuli 8-bromoadenosine 3',5'-cyclic monophosphate (10(-3) M), calcium ionophore A-23187 (10(-7) M), or 4 beta-phorbol 12-myristate 13-acetate (10(-8) M). In contrast, whereas PGE2 inhibited forskolin-stimulated gastrin release, PGE2 did not inhibit the response to carbachol or bombesin in control cultures. However, in pertussis toxin-treated cultures, PGE2 inhibition was reversed and, in contrast, the responses to bombesin, carbachol, and possibly forskolin were augmented. Indomethacin at a dose of 10(-5) M did not alter basal or bombesin-stimulated gastrin secretion. However, the somatostatin antibody CURE-S6 enhanced the response to forskolin and enhanced inhibition by PGE2, suggesting that endogenous somatostatin produced an inhibitory tone in these cultures and excluding the possibility that PGE2 acted via release of endogenous somatostatin. Our data suggest that in cultured antral cells gastrin release is regulated by inhibitory and stimulatory prostaglandin mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatostatin is released in response to cholecystokinin by activation of type A CCK receptors.

Cholecystokinin is a principal mediator of intestinal fat-induced inhibition of gastric acid secretion, indicating that it is an important physiological enterogastrone. Cholecystokinin has been shown to inhibit acid secretion by activation of type A CCK receptors and through a mechanism involving somatostatin. In the present study, we investigated the possibility that these two mechanisms are directly related such that activation of type A CCK receptors by CCK causes the release of somatostatin. We tested this hypothesis in vivo in a study of CCK-stimulated release of somatostatin in dogs and in vitro in a study of CCK-stimulated release of somatostatin from an enriched culture of canine fundic D cells. In dogs, IV infusion of CCK (50 pmol/kg/h, IV) significantly increased circulating somatostatin concentrations above basal. Further, systemic administration of somatostatin MAb F(ab)1 fragments of a somatostatin monoclonal antibody prevented most of CCK-induced inhibition of meal-stimulated acid secretion. In canine fundic D cells in culture, CCK-stimulated somatostatin release was blocked in a dose-dependent fashion by application of a type A CCK receptor antagonist. This study indicates that CCK activates type A CCK receptors to release somatostatin from canine fundic mucosal D cells, and accounts for somatostatin-dependent CCK-induced inhibition of acid secretion.

Endogenous somatostatin inhibits histamine release from canine gastric mucosal cells in primary culture.

The effects of somatostatin on histamine release were studied using primary cultures of canine oxyntic mucosal cells in which mast cell content was reduced by density gradient. The S6 monoclonal antibody to somatostatin, but not control antibodies, enhanced gastrin-stimulated histamine release. In the presence of S6, the somatostatin analogue SMS-201-995 (10(-7) M) inhibited gastrin-stimulated histamine release by 95%. The dose producing 50% inhibition for this inhibition was approximately 3 x 10(-10) M and was completely reversed by pertussis toxin treatment. In contrast to somatostatin, epinephrine failed to inhibit this gastrin stimulation. However, the lectin concanavalin A (ConA) also stimulated histamine release from these cultures, and this response was inhibited by epinephrine but not by somatostatin. Thus somatostatin selectively inhibited the gastrin-responsive histamine pool, which presumably is stored in oxyntic mucosal endocrine cells. In contrast, epinephrine selectively inhibits histamine release from the ConA-sensitive pool, which is presumably stored in mast cells. Furthermore, enhancement of gastrin-stimulated histamine release by immunoneutralization of somatostatin indicates an important role for endogenous somatostatin as a paracrine inhibitor of non-mast cell histamine release.

Paracrine control of gastric epithelial cell growth in culture by transforming growth factor-alpha.

Studying primary cultures of replicating canine oxyntic mucosal cells, we found evidence for modulation of cell growth by endogenous factors. [3H]thymidine incorporation into DNA was rapid with cells cultured in medium free of serum or added growth factors, and growth rates of these cultures were markedly dependent on plating density, indicating mitogenic control by soluble endogenous growth factors. Data indicated that endogenous transforming growth factor-alpha (TGF-alpha) exerted mitogenic control under the following conditions. 1) TGF-alpha was detected in the cultured cells by radioimmunoassay and immunohistochemistry. 2) TGF-alpha-like immunoreactivity and receptor reactivity were present in the medium in concentrations sufficient to exert mitogenic control. 3) Receptors for TGF-alpha and epidermal growth factor (EGF) were present in the cultures. 4) Immunoabsorption by a TGF-alpha-specific antisera reduced [3H]thymidine incorporation. TGF-alpha was localized to parietal cells by immunohistochemistry and cell separation. In contrast, combined [3H]thymidine autoradiography and immunohistochemistry with anti-TGF-alpha did not detect TGF-alpha in dividing cells. We conclude that parietal cell TGF-alpha exerts paracrine control of mucosal cell growth in vitro, and we speculate that this is an important paracrine mechanism in vivo.

Regulation of histamine release from oxyntic mucosa.

The regulation of histamine release from oxyntic mucosa is complex because of two potential sources of histamine: mast cells and enterochromaffin-like (ECL) cells. A gastrin-responsive histamine pool was identified in the rat oxyntic mucosa two decades ago, but these ECL cells from the rat have not yet been isolated or characterized in vitro. In vivo studies in canine and human mucosa have been more difficult because of the high content of histamine in mast cells. Using enzyme-dispersed canine oxyntic mucosal cells, we have studied regulation of histamine release from a mast cell-depleted fraction prepared by sequential elutriation and density gradient. Histamine-like immunoreactivity was demonstrated, using peroxidase-anti-peroxidase immunohistochemistry. After short-term culture, histamine was released in response to gastrin, cholecystokinin, carbachol, and forskolin. Somatostatin potently and effectively inhibited the response to gastrin. The cultures used for these studies also contained somatostatin cells, and, furthermore, the response to gastrin was enhanced by incubation with monoclonal antibodies to somatostatin. The latter findings suggested that somatostatin was acting in these cultures by a paracrine route. This pattern contrasts with that obtained in previous studies of canine oxyntic mucosal mast cells.