Gastric Mucosal Defense Research Articles

Endogenous bacteria-triggered inducible nitric oxide synthase activation protects the ovariectomized rat stomach

Under experimental circumstances, ovariectomy attenuates gastric mucosal injury where nitric oxide (NO)-mediated pathways are involved. In this study, we have examined the changes in constitutive (cNOS) and inducible NO synthase (iNOS) enzyme activities (assessed by the citrulline assay), and the role of endogenous bacteria in overiectomy-provoked mucosal defence. Gastric lesions were induced by indomethacin (50 mg/kg, s.c.) over a 4 h period in sham-operated and ovariectomized female Wistar rats. Groups of animals received the wide-spectrum antibiotic ampicillin (800 mg/kg/day, p.o., for 3 days), and others were injected with bacterial endotoxin ( E. coli, 3 mg/kg, i.v., 5 h before autopsy). We found that ovariectomy increased iNOS and decreased cNOS activity (resulting an elevated total gastric NOS level), and protected the stomach, effects reversed by ampicillin treatment. In ovary-intact rats, administration of bacterial endotoxin enhanced gastric iNOS activity and reduced lesion-formation. These results suggest that ovariectomy improves gastric mucosal defence perhaps by endogenous bacteria-triggered induction of iNOS.

Activation of central opioid receptors may induce gastric mucosal defence in the rat

The effect of different opioid peptides on acidified ethanol- and indomethacin-induced gastric mucosal lesions was studied following intracerebroventricular (i.c.v.) administration. It was found that both the selective δ opioid receptor agonists—deltorphin II, [D-Ala 2, D-Leu 5]-enkephalin (DADLE), [D-Pen 2, D-Pen 5]-enkephalin (DPDPE)-, μ-opioid receptor agonist — [D-Ala 2, Phe 4, GlyT-ol]-enkephalin (DAGO) — as well as β-endorphin inhibited the mucosal damage induced by both ethanol and indomethacin in pmolar dose range. In contrast, the gastric acid secretion was not influenced by DADLE in the dose of 16 nmol/rat and only a slight reduction (40%) was induced by DAGO in the dose of 1.9 nmol/rat. The protective effect was abolished in both ulcer models by bilateral cervical vagotomy. N G-nitro-L-arginine, an inhibitor of NO synthase, reduced the protective action in ethanol-induced, but not in indomethacin-induced gastric damage. The results suggest that activation of supraspinal δ and μ-opioid receptors resulted in inhibition of gastric mucosal lesions elicited by ethanol or indomethacin. The gastroprotective action is independent from the effect of opioids on acid secretion. Vagal nerve is involved in conveying the central action to the periphery. The mechanism of the gastroprotective effect of opioids is different in ethanol- and indomethacin-ulcer models: prostaglandins and nitric oxide are likely to be involved in the protective action of opioid peptides in ethanol-, but not in the indomethacin-ulcer model.

Gastric mucosal integrity: gastric mucosal blood flow and microcirculation. An overview

The stomach is in a state of continuous exposure to potentially hazardous agents. Hydrochloric acid together with pepsin constitutes a major and serious threat to the gastric mucosa. Reflux of alkaline duodenal contents containing bile and pancreatic enzymes are additional important injurious factors of endogenous origin. Alcohol, cigarette smoking, drugs and particularly aspirin and aspirin-like drugs, and steriods are among exogenous mucosal irritants that can inflict mucosal injury. The ability of the stomach to defend itself against these noxious agents has been ascribed to a number of factors constituting the gastric mucosal defense. These include mucus and bicarbonate secreted by surface epithelial cells, prostaglandins, sulfhydryl compounds and gastric mucosal blood flow. The latter is considered by several researchers to be of paramount importance in maintainig gastric mucosal integrity. The aim of this paper is to review the experimental and clinical data dealing with the role of mucosal blood flow and in particular the microcirculation in both damage and protection of the gastric mucosa.

New insights into impairment of mucosal defense in portal hypertensive gastric mucosa

Portal hypertension (PHT) increases susceptibility of the gastric mucosa to injury. The aim of this study was to investigate whether PHT affects rat gastric mucosal defense mechanisms in vivo at the preepithelial, epithelial, and/or post-epithelial levels. PHT was produced in rats by staged portal vein ligation and sham-operated (SO) rats served as controls. The gastric mucosa was exposed, chambered, and continuously superfused with buffers under in vivo microscopy. We measured gastric mucosal gel layer thickness, surface epithelial cell intracellular pH (pH i), mucosal blood flow, and mucosal/serosal oxygenation. In PHT rats, gastric mucosal gel layer thickness was significantly reduced (88 ± 16 μm in PHT rats vs. 135 ± 25 μm in SO rats; P <0.0001), and the surface epithelial cell pH i was significantly decreased (6.80 ± 0.11 in PHT rats vs. 7.09 ± 0.21 in SO rats; P <0.01). Although total gastric mucosal blood flow was significantly increased in PHT rats by 72% ( P <0.05), the oxygenation of the gastric mucosal surface was decreased by 42% ( P <0.05) compared with SO rats. PHT impairs pre-epithelial (mucosal gel layer thickness), epithelial (pH i), and post-epithelial (maldistribution of blood flow) components of the gastric mucosal barrier. These findings can explain the increased susceptibility of portal hypertensive gastric mucosa to injury.

Importance of gap junction in gastric mucosal restitution from acid-induced injury

Evidence is accumulating that gap junctional intercellular communication (GJIC) plays an important role in the gastric mucosal defense system. This study was conducted to determine whether GJIC mediates a restitution process in gastric mucosa. Male Sprague-Dawley rats were fasted and anesthetized. Gastric injury was induced by luminal perfusion with 0.2N HCl for 10 minutes. Mucosal integrity was continuously monitored by measuring the clearance of chromium 51–labeled ethylenediaminetetraacetic acid, which was used for analysis of recovery from the injury. Perfusion with 0.25% octanol (OCT; inhibitor of GJIC) was started after acid injury to assess its effect on restitution. The effect of irsogladine (IG; activator of GJIC) was also tested. Gastric mucosal GJIC was immunohistochemically evaluated with monoclonal antibody gap junction protein (connexin 32). Recovery from acid-induced mucosal injury occurred rapidly when acid perfusion was discontinued (within about 60 minutes). OCT, which didn't cause any injury to normal gastric mucosa, significantly inhibited the restitution. IG reversed this inhibition in a dose-dependent manner. In an immunohistochemical study, OCT-induced damage of gap junction was demonstrated, but not after IG pre-treatment. These findings suggest that GJIC may play a critical role in restitution in rat gastric mucosa and that gap junction function may be one of the important factors for the mucosal defense system. (J Lab Clin Med 2000;136:93-9)

Developmental changes in cyclooxygenase (COX) mRNA expression in gastric mucosa of rats

Background: Developmental changes occur in the gastric mucosal defense mechanism. Experimental mucosal injuries produced by intragastric ethanol or HCl are greatest in newborn rats and decreased with age. Recovery of the mucosa from injury was faster in newborn rats than in older rats. In the present study, to determine if metabolism of prostaglandins is responsible for the physiological characteristics of the mucosal protective mechanisms in developing rats, we studied COX mRNA expression in rats of various age with/without acute mucosal injury by quantitative (kinetic) RT-PCR. The effect of age on endotoxin-induced mRNA expression was also investigated. Methods: Gastric mucosa was excised from male Wistar rats and separated from the muscle layer. mRNA was extracted and converted to cDNA using random primers. The number of copies of cDNA for COX I, COX2, and GAPDH(internal control) was measured using real-time PCR with Taqmann Probes. Mucosal injuries were produced by administrating 0.005 ml/kg of l50mM HCI-60% EtOH through nasogastric tube 60 min prior to the sacrifice. Results:COXl mRNA expression was lowest in l -week-old rats, and highest in 4-week-old rats. Mucosal injury did not increase COXI mRNA expression in any age group. Expression of COX2 mRNA was highest in l-week-old rats and then decreased with age. Mucosal injury increased COX2 mRNA in each age group, mostly in one week old rats (Table). There were no age-related changes in COX2 mRNA expression in response to lipopolysaccharide O,5,lOmg/kg,ip). Conclusion: The high level of COX2 mRNA expression in the gastric mucosa of l-week-old rats might be responsible for the physiological charateristics of gastric mucosal defense in this age group.

Effects of estrogen-deficiency on gastric mucosal defence and nitric oxide synthase activity

Effects of estrogen-deficiency on gastric mucosal defence and nitric oxide synthase activity

Role of heat shock proteins in gastric mucosal protection.

Heat shock proteins (HSP) are crucial for the maintenance of cellular homeostasis during normal cell growth and for survival during and after various cellular stresses. Gastric surface mucous cells are the first line of defence against insults derived from ingested foods and Helicobacter pylori infection. Primary cultures of gastric surface mucous cells from guinea-pig fundic glands exhibited a typical heat shock response after exposure to elevated temperature or metabolic insults, such as ethanol and hydrogen peroxide, and they were able to acquire resistance to these stressors. Restraint and water immersion stress rapidly activated heat shock factor 1 (HSF1) in rat gastric mucosa within 15 min and induced HSP70 mRNA expression and its protein accumulation. The extent of the induction inversely correlated with the severity of mucosal lesions, suggesting an important role of HSP70 in gastric mucosal defence. This heat shock response appeared to be mediated by the alpha1A-adrenoceptor. The HSP70 family functions as a molecular chaperone and reduces stress-induced denaturation and aggregation of intracellular proteins. In addition to its chaperoning activities, HSP70 has been suggested to exert its cytoprotective action by protecting mitochondria and by interfering with the stress-induced apoptotic programme. Recently, we introduced geranylgeranylacetone as a non-toxic HSP70 inducer. This compound weakly stimulated HSP70 induction in cultured gastric mucosal cells and gastric mucosa by directly activating HSF1 and markedly augmented HSP70 induction in response to subsequent exposure to stress. Thus, non-toxic HSP70 inducers may have a potential benefit for the prevention and treatment of stress ulcer.

Does portal hypertension contribute to the pathogenesis of gastric ulcer associated with liver cirrhosis?

The prevalence of gastric ulcers in patients with liver cirrhosis is increased compared with that in the general population, and portal hypertension may contribute to the increased risk of gastric ulcer in cirrhosis patients. Aggressive factors involved in the pathogenesis of gastric ulcer are diminished in association with portal hypertension. In contrast, most of the important gastric mucosal defense mechanisms are shown to be impaired in portal hypertension; many of these mechanisms are also found to be altered in patients with liver cirrhosis. Portal hypotensive treatment with propranolol reduces ethanol-induced gastric mucosal damage in portal hypertensive rats and improves endoscopic signs of portal hypertensive gastropathy in cirrhosis patients. Together, these findings suggest portal hypertension-induced impairment of the gastric mucosal defenses to be an important factor in the pathogenesis of gastric ulcer in patients with liver cirrhosis. Prospective studies of portal pressure-reducing procedures, such as pharmacotherapy with propranolol, and their effect on the incidence of gastric ulcer in cirrhosis patients are needed to confirm this suggestion.

Animal models of gastroduodenal ulcer disease

Animal models have played a significant role in research that aims to understand peptic ulceration. Firstly, they have helped define basic mechanisms of gastric mucosal defence and repair. The basis for gastric injury following NSAID administration was facilitated by animal models that correlated well with disease in humans. In early studies, ulceration was induced by grossly damaging insults to the gastric mucosa that were unphysiological. With refinement these models provided a clearer appreciation of stress ulceration. The discovery of Helicobacter pylori(H. pylori), as the cause of most ulcers, resulted in a need to re-evaluate the early literature and to look for new models. To date, these have contributed little to our understanding of the pathogenesis of H. pylori -induced ulcer. A major aim of this chapter is to suggest that thorough understanding of the animal models of Helicobacter infection may provide important new insights, in particular the factors controlling gastritis, the essential precursor lesion of ulceration. Available models include primates, cats, guinea pigs, ferrets and pigs. The mouse models provide opportunity for identifying both essential bacterial and host factors. The most severe pathologies are seen in the H. pylori -infected Mongolian gerbil with ulcers being formed in most animals. This is likely to become the standard animal model for investigation of peptic ulcer disease.

Selective Inhibitors of COX-2 - Are They Safe for the Stomach?

NSAIDs are widely used and beneficial for patients with inflammatory pain. However, NSAIDs cause significant adverse upper gastrointestinal effects, including increased mortality from serious ulcer complications. NSAIDs exert their anti-inflammatory effects by inhibiting the activity of the COX enzyme, which was recently shown to exist in two isoforms, a constitutive COX-1 and an inducible COX-2. The latter isoform is induced in inflammation, while the former is responsible for prostaglandin effects on platelet function and gastric mucosal defense. Two specific COX-2 inhibitors have recently been introduced into the market. The available data from clinical trials indicate that these new drugs have anti-inflammatory and analgesic effects similar to those of conventional NSAIDs, but reduced rates of adverse upper gastroduodenal effects, which are similar to those observed with placebo. This difference in rates of adverse effects might imply improved safety for patients requiring anti-inflammatory treatment. It has, however, to be kept in mind that specific COX-2 inhibitors lack cardiovascular protective effects. Considering the high consumption rate of NSAIDs to achieve pain relief in arthritis and other musculo-sceletal diseases, the reduced risk of gastrointestinal ulcers and ulcer complications may have a positive impact on population health and health economy.

Capsaicin-sensitive afferent sensory nerves in modulating gastric mucosal defense against noxious agents

In the rat stomach, evidence has been provided that capsaicin-sensitive sensory nerves (CSSN) are involved in a local defense mechanism against gastric ulcer. In the present study capsaicin or resiniferatoxin (RTX), a more potent capsaicin analogue, was used to elucidate the role of these sensory nerves in gastric mucosal protection, mucosal permeability, gastric acid secretion and gastrointestinal blood flow in the rat. In the rat stomach and jejunum, intravenous RTX or topical capsaicin or RTX effected a pronounced and long-lasting enhancement of the microcirculation at these sites, measured by laser Doppler flowmetry technique. Introduction of capsaicin into the rat stomach in very low concentrations of ng–μg.mL –1 range protected the gastric mucosa against damage produced by topical acidified aspirin, indomethacin, ethanol or 0.6 N HCl. Resiniferatoxin exhibited acute gastroprotective effect similar to that of capsaicin and exerted marked protective action on the exogenous HCl, or the secretagogue-induced enhancement of the indomethacin injury. The ulcer preventive effect of both agents was not prevented by atropine or cimetidine treatment. Capsaicin given into the stomach in higher desensitizing concentrations of 6.5 mM markedly enhanced the susceptibility of the gastric mucosa and invariably aggravated gastric mucosal damage evoked by later noxious challenge. Such high desensitizing concentrations of capsaicin, however, did not reduce the cytoprotective effect of prostacyclin (PGI 2) or β-carotene. Capsaicin or RTX had an additive protective effect to that of atropine or cimetidine. In rats pretreated with cysteamine to deplete tissue somatostatin, capsaicin protected against the indomethacin-induced mucosal injury. Gastric acid secretion of the pylorus-ligated rats was inhibited with capsaicin or RTX given in low non-desensitizing concentrations, with the inhibition being most marked in the first hour following pylorus-ligation. Low intragastric concentrations of RTX reduced gastric hydrogen ion back-diffusion evoked by topical acidified salicylates. It is concluded that the gastropotective effect of capsaicin-type agents involves primarily an enhancement of the microcirculation effected through local release of mediator peptides from the sensory nerve terminals. A reduction in gastric acidity may contribute to some degree in the gastric protective action of capsaicin-type agents. The vasodilator and gastroprotective effects of capsaicin-type agents do not depend on vagal efferents or sympathetic neurons, involve prostanoids, histaminergic or cholinergic pathways.

Effects of ammonia solution on the gastric mucosa in cirrhotic rats and therapeutic effects of geranylgeranylacetone.

We designed an animal model in order to clarify whether Helicobacter pylori infection causes the gastric mucosal lesion frequently seen in cirrhotic patients. Ammonia (NH3) solution was given to rats with carbon tetrachloride-induced cirrhosis. The gastric mucosal hexosamine (Hx) content and histopathological findings in the cirrhotic rats were analysed and compared with those of the intact liver rats. Moreover, the usefulness of geranylgeranylacetone (GGA) was investigated in both rat groups. Both rat groups were subdivided according to the treatment as follows: a control group, an NH3 (0.02% solution) group, and an NH3 + GGA (400 mg/kg per day) group; and fed for 4 weeks. The gastric mucosal Hx content of the control group of the cirrhotic rats (16.7 +/- 5.2 microg/mg) was significantly lower than that of the control group of the intact liver rats (26.6 +/- 4.5 microg/mg, P < 0.05). In the cirrhotic rats, the Hx content of both the NH3 (31.9 +/- 13.1 microg/mg) and the NH3 + GGA group (31.9 +/- 9.8 microg/mg) was significantly higher than the Hx content of the control group (P < 0.05). Microscopically, in the cirrhotic rats, while scattered mucosal erosions were recognized in three of five rats of the NH3 group, there were no erosions in any rats of the NH3 + GGA group. These data suggest that the gastric mucosal defence mechanism is defective in liver cirrhosis and that NH3 enhances this defensive mechanism by acting as mild irritant; however, in some cirrhotics this results in gastric erosion due to excessive irritation. Geranylgeranylacetone protects the gastric mucosa against NH3 irritation in cirrhotics without enhancing the Hx content. Thus, H. pylori infection may be a possible cause of the gastric mucosal lesion in patients with liver cirrhosis. The mechanism of the therapeutic effect of GGA is not due to an enhancement of the gastric mucosal Hx content.

Molecular stress response in the stomach

Stress response is mediated by a number of stress-related gene products and is crucial for maintenance of homeostasis during and after various cellular stresses. Exposure of rats to restraint and water-immersion stress rapidly and transiently activated heart shock factor 1 (HSF1) and caused rapid HSP70 mRNA expression and HSP70 accumulation in gastric mucosa. Using protein-malnourished, bilateral adrenalectomized, and subdiaphragmatically vagotomized rats, we showed that this heat shock response was regulated by the hypothalamic-pituitary-adrenocortical or the sympathoadrenal systems. Experiments with inhibitors for adrenoceptor subtypes and glucocorticoids suggested that the alpha 1A-adrenergic receptor appeared to mediate the HSP70 induction. The extent of HSP70 induction inversely correlated to the severity of mucosal damage, suggesting an important role of the heat shock response in gastric mucosal defense under conditions of stress. Recently, we found that gastric surface mucous cells possessed a phagocyte NADPH oxidase-like system and secreted abundant superoxide anion (O2.-). Helicobactor pylori lipopolysaccharide markedly up-regulated this secretion. The enhanced O2.- production activated nuclear factor kappa B by autocrine/paracrine mechanisms, resulting in activation of proinflammatory cytokine gene expressions. These results suggest that surface mucous cells may actively regulate stress responses of Helicobacter pylori-infected gastric mucosa through a phagocyte NADPH oxidase-like activity.

Prospects for future development in the pharmacology of gastric ulcer models and of gastric acid secretion in experimental animals

Prospects for future development in the field of gastrointestinal pharmacology were briefly discussed on the base of the present progress in our own research on animal models of gastric ulcer and the mechanism of gastric acid secretion. We established a few novel methods to induce extensive ulceration restricted to the gastric antral area in rats by a combination of drug-induced vagal stimulation with necrotizing agents or anti-inflammatory drugs, as well as with ammonia in relation to the etiological role of Helicobacter pilori. In these models, it was found that the gastric antral area become sensitive to mucosal aggression under vagal stimulation and refeeding after starvation and that the mucosal primary afferent nervous system was involved in the integration of gastric mucosal defense mechanisms. Among many experimental gastric ulcer models, the gastric antral ulcer is important for future study because of its unique analogy with human ulcer in its location of incidence and pathology. We also established methods to measure gastric acid secretion in the isolated gastric mucosa or whole stomach of rat or mouse, as well as acid secretion in anesthetized rats. By using these methods, the signal transduction route of vagus nerve stimulation to parietal cells was studied. The importance of mediation of enterochromaffin cells in gastric acid secretion was clearly confirmed. In the studies on receptor mechanisms in the central nervous system regulating gastric acid secretion, critical roles of GABA, barbiturate, glutamate, neurosteroids and opioid receptors were clarified. From these results, several remaining problems were suggested and these must be resolved in future research.

Evaluation of possible mechanism of anti-ulcerogenic activity of UL-409, a herbal preparation

UL-409, a herbal preparation was investigated for its anti-ulcerogenic activity and possible mechanism of action in different experimental models. Oral administration of UL-409 at a dose of 600 mg/kg significantly reduced the volume of gastric secretion, total acidity and free acidity in aspirin+pylorus-ligated rats. The drug appeared to strengthen the gastric mucosal defense mechanism by significantly increasing the total carbohydrate:protein ratio in aspirin+pylorus-ligated rats. The major mechanism involved appears to be due to promotion of mucosal protection by augmenting gastric mucin activity. Pre-treatment with UL-409 showed inhibition of alcohol-induced contraction of isolated rat fundus preparation which was reversed by indomethacin suggesting a possible involvement of the cyclo-oxygenase system.

Gastroprotective actions of bombesin, L-DOPA, and mild irritants: Roles of prostaglandins and sensory neurons

Background: Bombesin and dopamine prevent gastric injury by an unknown mechanism. Sensory neurons and endogenous prostaglandins play an important role in gastric mucosal defense. This study was designed to assess the role of these two local defense mechanisms in bombesin and dopamine-induced gastroprotection, as well as mild irritant-induced adaptive cytoprotection. Methods: Conscious, fasted rats were given either capsaicin (125 mg/kg subcutaneously) to ablate sensory neurons or indomethacin (5 mg/kg intraperitoneally) to inhibit prostaglandin synthesis, 2 weeks and 30 minutes, respectively, before administration of bombesin (100 μg/kg subcutaneously), the dopamine precursor L-DOPA (25 mg/kg intraperitoneally), or the mild irritant 25% ethanol (1 mL orogastric). A 1-mL orogastric bolus of acidified ethanol (150 mmol/L HCl/50% ethanol) was given 30 minutes after pretreatment with these peptides and 15 minutes after administration of the mild irritant. Rats were killed 5 minutes later and the total area of macroscopic gastric injury quantified. Results: Ablation of sensory neurons with capsaicin negated the protective actions of bombesin but failed to reverse gastroprotection by L-DOPA or 25% ethanol. Cyclooxygenase inhibition with indomethacin partially reversed bombesin and mild irritant-induced gastroprotection but did not diminish the protective actions of L-DOPA. Conclusions: Bombesin requires intact sensory neurons to exert its protective actions through a mechanism mediated, at least in part, by endogenous prostaglandins. Adaptive cytoprotection by the mild irritant 25% ethanol requires the presence of endogenous prostaglandins but not sensory neurons. L-DOPA–induced gastroprotection is independent of both local defense mechanisms. (Surgery 1998; 124:864-70.)

Pretreatment with SR48692 has different effects on central neurotensin-induced gastric mucosal defense and inhibition of gastric acid secretion in rats

Neurotensin is a tridecapeptide present in the brain and gastrointestinal tract. Administration of neurotensin into the brain results in responses in the gastrointestinal tract, suggesting a role for neurotensin in the interrelationships that comprise the brain–gut axis. Intracerebroventricular (i.c.v.) administration of neurotensin protects the gastric mucosa against injury caused by cold water restraint (CWR) and also inhibits gastrin-stimulated gastric acid secretion. The hypothesis tested was that these two actions of neurotensin are mediated via its high-affinity receptor. Rats were given neurotensin (60 μg, i.c.v.) prior to CWR or pylorus ligation after pretreatment with SR48692, a nonpeptide antagonist of the high-affinity neurotensin receptor (0.25 or 2.5 μg, i.c.v., or 10, 100, or 500 μg kg −1, i.p.). Neurotensin reduced cold water restraint (CWR)-induced gastric mucosal injury and inhibited gastrin-stimulated acid secretion. Pretreatment with SR48692 (2.5 μg, i.c.v., or 100 μg kg −1, i.p.) prior to CWR blocked neurotensin's protection of the gastric mucosa against injury. In contrast, pretreatment with 2.5 μg SR48692, i.c.v., did not block neurotensin-induced inhibition of acid secretion, whereas 500 μg kg −1, i.p., partially blocked the inhibition. SR48692 (2.5 μg, i.c.v.) inhibited acid secretion, suggesting that SR48692 has agonist activity in this system. These results suggest that central neurotensin protects the gastric mucosa against CWR-induced injury via its high-affinity receptor. The receptor that mediates central neurotensin-induced inhibition of gastric acid secretion does not appear to be the high-affinity receptor since the neurotensin receptor antagonist SR48692, when given i.c.v., had agonist activity, inhibiting stimulated acid secretion. High-affinity neurotensin receptors in the periphery appear to play a role in inhibition of stimulated gastric acid secretion.

Age and Helicobacter pylori decrease gastric mucosal surface hydrophobicity independently

Background—Gastric mucosal surface hydrophobicity (GMSH) is an essential component of the mucosal defence system that is decreased by Helicobacter pylori and non-steroidal anti-inflammatory drugs (NSAIDs). Gastric ulcers occur predominantly in...

Glutathione depletion inhibits oxidant-induced activation of nuclear factor-kappa B, AP-1, and c-Jun/ATF-2 in cultured guinea-pig gastric epithelial cells.

The aim of this study was to reveal the role of intracellular glutathione in the oxidative stress responses of gastric epithelial cells. Metabolic radiolabeling with L-[35S]methionine and analysis of synthesized proteins by gel electrophoresis and fluorography showed that upon exposure to hydrogen peroxide (H2O2) or diamide, primary cultures of guinea-pig gastric epithelial cells rapidly induced several undefined proteins, as well as heat shock proteins. When intracellular glutathione was depleted to less than 10% of the control value by treatment with buthionine-[S,R]-sulfoximine, these inductions were completely inhibited. Gel mobility shift assay demonstrated that H2O2 and diamide rapidly activated nuclear factor-kappa B (NF-kappaB), and diamide activated activator protein (AP)-1, and c-Jun/activating transcription factor (ATF)-2, suggesting that the response may be coupled to these reduction-oxidation (redox)-sensitive transcription factors, as well as heat shock transcription factor 1. The activations of NF-kappaB, AP-1, and c-Jun/ATF-2 by the oxidants did not occur in glutathione-depleted cells. Northern blot analysis showed that glutathione depletion markedly or completely suppressed the diamide-induced expression of c-fos and c-jun mRNAs. These results suggest that intracellular glutathione redox may participate in the initiation of oxidative stress responses; thereby, it plays an important role in gastric mucosal defense.