Bacterial lipopolysaccharide protects gastric mucosa against acute injury in rats by activation of genes for cyclooxygenases and endogenous prostaglandins

Spices, herbal xenobiotics and the stomach: Friends or foes?

Spices and herbal remedies have been used since ancient times to treat a variety of disorders. It has been experimentally demonstrated that spices, herbs, and their extracts possess antimicrobial, anti-inflammatory, antirheumatic, lipid-lowering, hepatoprotective, nephroprotective, antimutagenic and anticancer activities, besides their gastroprotective and anti-ulcer activities. Despite a number of reports on the toxicity of herbs and spices, they are generally accepted as safer alternatives to conventional therapy against gastric ulcers. To this end, it is also believed, that excessive consumption of spices may favor the pathogenesis of gastric and duodenal ulcer and some studies have substantiated this common perception. Based on various in vivo experiments and clinical studies, on the effects of spices and herbs on gastric ulcers, it has indeed been shown that certain spices do possess remarkable anti-ulcer properties mediated by antisecretory, cytoprotective, antioxidant, and anti-Helicobacter pylori effects and mechanisms regulated by nitric oxide, prostaglandins, non-protein sulfhydryl molecules and epidermal growth factor expression. Accordingly, their consumption may attenuate and help prevent peptic ulcer disease. In the present review, the beneficial effects of spices and herbal nutritive components on the gastric mucosa are discussed against the paradigm of their deleterious potential.

Pretreatment with the Gram-positive bacterial cell wall molecule peptidoglycan improves bacterial clearance and decreases inflammation and mortality in mice challenged with Staphylococcus aureus

OBJECTIVE

To determine whether tolerance and enhancement of innate immune function can be induced by the Gram-positive cell wall component peptidoglycan.

DESIGN

Controlled, in vivo laboratory study.

SUBJECTS

Male mice, 8-12 wks (C57BL6/J; C3H/HeJ; B6.129-Tlr2/J).

INTERVENTIONS

Mice were given intraperitoneal injections of 1 mg peptidoglycan on two consecutive days. Mice were then challenged with an intravenous injection of live Staphylococcus aureus (1 x 10 colony-forming units) 2 days after the second pretreatment.

MEASUREMENTS AND MAIN RESULTS

Mice pretreated with peptidoglycan had diminished plasma concentrations of tumor necrosis factor-alpha and interferon-gamma in response to the bacterial challenge when compared with untreated controls. Plasma interleukin-10 after bacterial challenge was higher in peptidoglycan-pretreated mice than in controls. Clearance of bacteria after the staphylococcal challenge was improved in mice pretreated with peptidoglycan, and mortality in response to a subsequent Staphylococcus challenge was significantly attenuated. Peptidoglycan pretreatment of mice lacking intact toll-like receptor-4 signaling (C3H/HeJ) or toll-like receptor-2 signaling (toll-like receptor-2 knockouts) had similar effects on plasma cytokine balance, bacterial clearance, and mortality.

CONCLUSIONS

Exposure to peptidoglycan significantly attenuated inflammation and enhanced bacterial clearance after a subsequent challenge with S. aureus. These results show that exposure to Gram-positive bacterial cell wall components can induce tolerance and enhance innate immune function and neither toll-like receptor-2 nor toll-like receptor-4 are necessary for this phenomenon. Further, although the altered cytokine balance is similar to that seen in septic patients, induced tolerance differs importantly from the clinical scenario of sepsis in that bacterial clearance and survival are improved compared with normal control animals.

Pretreatment with the Gram-positive bacterial cell wall molecule peptidoglycan improves bacterial clearance and decreases inflammation and mortality in mice challenged with Pseudomonas aeruginosa

The objective of this study was to determine if inflammatory tolerance and enhancement of innate immune function could be induced by the Gram-positive cell wall component peptidoglycan (PGN). Male mice (C57BL6/J or C3H/HeJ, 8-12 weeks of age) were given intraperitoneal injections of 1mg PGN on 2 consecutive days. The mice were then challenged with lipopolysaccharide (LPS) or live Pseudomonas aeruginosa (1 x 10(8) colony-forming units) 2 days after the second pretreatment. Mice pretreated with PGN had diminished plasma concentrations of TNFalpha and IFNgamma and elevated concentrations of IL-10 in response to a subsequent LPS or Pseudomonas challenge when compared to untreated controls. Bacterial clearance was improved in mice pretreated with PGN, and mortality in response to a subsequent Pseudomonas challenge was significantly attenuated. PGN pretreatment of LPS-unresponsive mice (C3H/HeJ) verified that the effect of PGN pretreatment was not due to any LPS contamination. We have previously demonstrated that PGN pretreatment induced resistance to a Gram-positive bacterial challenge. The present study extends those results by showing that exposure to the Gram-positive bacterial cell wall component peptidoglycan also induces cross-tolerance to LPS and non-specifically enhances innate immune function in that PGN-pretreated mice had increased resistance to Gram-negative bacterial challenge.

ENDOTOXIN PRETREATMENT IMPROVES BACTERIAL CLEARANCE AND DECREASES MORTALITY IN MICE CHALLENGED WITH STAPHYLOCOCCUS AUREUS

We studied the effects of tolerance induced by Escherichia coli-derived LPS on the innate immune response to a subsequent Staphylococcus aureus bacterial challenge. LPS tolerance was induced in wild-type mice by either intraperitoneal or intravenous injection of 2 microg of LPS on 2 consecutive days. Mice were challenged with an intravenous injection of live S. aureus (5 x 10(8) colony-forming units) 2 days after the second LPS dose. LPS-tolerant mice had a diminished serum interferon-gamma response to the bacterial challenge. Bacterial counts in liver and spleen tissues were decreased, and survival was improved after the Staphylococcus challenge in LPS-tolerant mice compared with saline-pretreated control mice. LPS pretreatment by the intravenous route was also associated with a decreased number of bacterial colonies in lung tissue in addition to liver and spleen, suggesting that induction of LPS tolerance was somewhat compartmentalized after intraperitoneal LPS pretreatment. Induction of tolerance seemed to be due to LPS-specific signaling because LPS pretreatment of LPS-nonresponsive C3H/HeJ mice did not provide similar effects after bacterial challenge. Flow cytometric analysis of spleens from LPS-tolerant mice revealed an increase in phagocytic cells (neutrophiles and macrophages) compared with control mice. Ex vivo culture of splenocytes from LPS-tolerant mice demonstrated increased uptake of fluorescein isothiocyanate-tagged ovalbumin, but no difference in either phagocytosis of fluorescein isothiocyanate-labeled Staphylococcus or bactericidal activity could be demonstrated on a per-cell basis. These results show that attenuation of inflammation and mortality during LPS tolerance extends to gram-positive bacterial organisms and suggests that LPS-induced enhancement of the innate immune response may be attributed to increased numbers of phagocytic cells.

Effects of lipopolysaccharide on gastric stasis: role of cyclooxygenase

This study was done to examine the role of cyclooxygenase (COX) in lipopolysaccharide (LPS)-induced gastroprotection and gastric stasis. In conscious rats, LPS dose and time dependently increased gastric luminal fluid accumulation. LPS decreased blood flow (laser Doppler) and prevented gastric injury from acidified ethanol at time points before significant fluid accumulation occurred. LPS increased COX-2 but not COX-1 expression. In contrast, LPS decreased gastric mucosal prostaglandin synthesis. LPS-induced gastric luminal fluid accumulation was negated by both nonselective COX inhibition with salicylate and selective COX-2 inhibition with NS-398 but not by selective COX-1 inhibition with SC-560. Neither salicylate nor NS-398 blocked LPS-induced gastroprotection. LPS-induced gastroprotection does not depend entirely on accumulation of luminal fluid and is independent of COX-1 and COX-2. However, the ability of LPS to cause gastric stasis and increase gastric luminal fluid accumulation involves COX-2.

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Rat gastric injury after lipopolysaccharide: Role of inducible nitric oxide synthase

BACKGROUND

Short-term treatment with lipopolysaccharide (LPS) causes morphologic, but not macroscopic, gastric injury and decreases gastric injury caused by a subsequent challenge with a luminal irritant. This effect is abrogated by inducible nitric oxide synthase (iNOS) inhibition. The effects of long-term treatment with LPS on gastric injury are unknown as is the role of iNOS. We hypothesized that LPS would cause macroscopic gastric injury at later time points through an iNOS-dependent pathway.

METHODS

Conscious rats were given saline or LPS (1 or 20 mg/kg intraperitoneal) as a single intraperitoneal injection and killed 24 to 72 hours after injection. Macroscopic gastric injury (computerized planimetry), gastric luminal fluid volume and pH, and iNOS protein levels were assessed.

RESULTS

When compared with saline, high-dose but not low-dose LPS caused macroscopic gastric injury, increased gastric luminal fluid and pH, and up-regulated iNOS at 24 and 48 hours. All assessments returned to baseline by 72 hours. Inhibition of iNOS with 1400W (1 mg/kg intraperitoneal) given 15 minutes before saline or LPS (20 mg/kg) attenuated the deleterious effects of LPS on gastric injury and pH, but not fluid accumulation.

CONCLUSIONS

These data suggest that prolonged treatment with high-dose LPS causes gastric injury through an iNOS-mediated pathway.

Acute gastric changes after intracerebral hemorrhage in rats

Severe intracerebral hemorrhage (ICH) produces gastric pathology in about 30% of the patient population, even after the standard treatment of H2 receptor blockers or proton pump inhibitors. This study was undertaken to establish a rat model of ICH-induced gastric ulcer. Adult male Sprague-Dawley rats (300-350 g) were divided into two hemorrhage groups and a sham control group. ICH was produced either by injection of 100 microl of autologous arterial blood or by injection of 4 microl saline containing 0.6 unit of bacterial collagenase VII into the right basal ganglia. Rats were sacrificed at 24, 48, 72 h, and 7 days after ICH to harvest brains and stomachs. Greater degrees of hemorrhage and brain edema were observed in collagenase-induced ICH. Motor behavior decreased significantly after 24 h in both models. The incidence of acute ulceration with destruction of the forestomach epithelium was extremely low at 8.7% in the collagenase injection model and 4.8% in the blood injection rats. Small, pinpoint hemorrhages (petechiae) were noticed in 38% of rats after blood injection and 22% after collagenase injection, in the glandular portion of the gastric mucosa with penetration of red blood cells and inflammatory cells into the gastric mucosa. Enhanced tumor necrosis factor alpha (TNFalpha) and cyclooxygenase 2 (COX-2) expressions were observed in gastric tissues after ICH with more intense staining occurring at 24 and 48 h. Due to the low incidence of ulceration, ICH-induced gastric ulceration in rodents may not appropriate for evaluating the potential human risk of gastric ulceration after ICH.

Ischemic preconditioning of remote organs attenuates gastric ischemia-reperfusion injury through involvement of prostaglandins and sensory nerves

Limitation of the stomach damage by its earlier brief ischemia and reperfusion before prolonged ischemia is defined as gastric ischemic preconditioning but whether such brief ischemia of remote organs like heart or liver can also attenuate the gastric damage caused by longer and severe ischemia-reperfusion remains unknown. The cardiac, hepatic and gastric preconditioning were induced by brief ischemia (occlusion of coronary, hepatic and celiac arteries twice for 5 min) applied 30 min before 3 h of ischemia/reperfusion. Standard 3 h ischemia-reperfusion of the stomach produced numerous gastric lesions, decreased gastric blood flow and mucosal prostaglandin E2 generation and increased expression and plasma release of interleukin-1beta and tumor necrosis factor-alpha (TNF-alpha). These effects were significantly attenuated by brief cardiac, hepatic and gastric preconditioning which upregulated cyclooxygenase-2 mRNA but not cyclooxygenase-1 mRNA. The protective effects of brief gastric, cardiac and hepatic preconditioning were attenuated by selective cyclooxygenase-1 and cyclooxygenase-2 inhibitors and capsaicin denervation. We conclude that brief ischemia of remote preconditioning such as heart or liver protects gastric mucosa against severe ischemia-reperfusion-induced gastric lesions as effectively as local preconditioning of the stomach itself via the mechanism involving prostaglandin derived from cyclooxygenase-1 and cyclooxygenase-2 and the activation of sensory nerves releasing calcitonin gene-related peptide (CGRP) combined with the suppression of interleukin-1beta and TNF-alpha expression and release.

Involvement of Capsaicin-Sensitive Afferent Nerves and Cholecystokinin 2/Gastrin Receptors in Gastroprotection and Adaptation of Gastric Mucosa toHelicobacter pylori-Lipopolysaccharide

Lipopolysaccharide (LPS) is one of the virulence factors in the Helicobacter pylori (Hp)-infected stomach, but it remains unknown whether single and prolonged pretreatment with Hp-LPS can affect the course of gastric damage induced by aspirin (ASA). We compared the effects of Hp-LPS with those induced by LPSs isolated from intestinal Bacteroides fragilis, Yersinia enterocolitica, and Campylobacter jejuni applied for 4 days on acute ASA-induced gastric lesions in rats. The area of ASA-induced gastric lesions, gastric blood flow (GBF), expression of mRNA and protein of leptin and plasma leptin, gastrin, interleukin-1beta, and tumor necrosis factor-alpha levels were examined. Single (once) or repeated (five times) i.p. injections of Hp-LPS (1 mg/kg) or intestinal LPSs failed to produce macroscopic gastric damage and did not affect the GBF when compared with vehicle. Hp-LPS injected repeatedly suppressed the gastric acid secretion, up-regulated leptin mRNA and protein, and increased plasma leptin and gastrin levels. Hp-LPS significantly reduced the ASA-induced gastric damage and the accompanying decline in the GBF, and these effects were significantly attenuated by capsaicin denervation and selective antagonism of cholecystokinin-B (CCK2) receptors by RPR-102681 [N-(metoxy-3 phenyl) N-(N-methyl N-phenyl-carbamylmethyl) carbamoylmethyl]-3 ureido]-3 phenyl]-2 propronique] but not by loxiglumide, an antagonist of CCK1 receptors. We conclude that 1) daily application of Hp-LPS enhances gastric mucosal resistance against ASA damage due to the increase of GBF and the expression and release of leptin and gastrin exerting trophic and gastroprotective effects, and 2) this enhanced resistance to ASA damage in Hp-LPS-adapted stomach is mediated by the sensory afferents and specific CCK2/gastrin receptors.

Enhanced resistance of gastric mucosa to damaging agents in the rat stomach adapted to Helicobacter pylori lipopolysaccharide

BACKGROUND AND AIM

Lipopolysaccharide (LPS) has been proposed to act as one of numerous virulence factors in the Helicobacter pylori (HP)-infected stomach. However, little is known as to whether the gastric mucosa can withstand the repeated LPS insult, and how the possible adaptation to this endotoxin influences the damage induced by strong irritants. We determined the effect of a single or repeated parenteral administration of LPS obtained from HP on acute gastric lesions induced by intragastric application of 100% ethanol (1.5 ml) and by water immersion and restraint stress (WRS).

METHODS

The area of the gastric lesions was measured by planimetry, mucosal gastric blood flow (GBF) was determined by H(2) gas clearance, and gastric luminal content was collected for the determination of luminal NO(2)(-)/NO(3)(-) levels by the Griess reaction. Biopsy samples were taken for the measurement of prostaglandin (PG) E(2) by radioimmunoassay and mucosal expression of constitutive and inducible nitric oxide synthase (cNOS and iNOS), constitutive (COX-1) and inducible cyclooxygenase (COX-2), heat shock protein 70 (HSP 70) mRNA and protein were analyzed by RT-PCR and Western blot.

RESULTS

HP LPS (1 mg/kg i.p.) injected once or 5 times produced negligible macroscopic injury and failed to influence GBF significantly compared to the injuries recorded in vehicle-controlled rats. Single and repeated (5 times) administration of HP LPS significantly reduced ethanol- and WRS-induced lesions, these protective effects were accompanied by a rise in GBF and excessive luminal release of NO. The suppression of NOS activity by L-NAME (20 mg/kg i.p.), a nonspecific NOS inhibitor, or L-NIL (30 mg/kg i.g.), a specific iNOS inhibitor, and of COX-2 activity by NS-398 reversed the protective and hyperemic effects of single or repeated LPS administrations against ethanol and WRS damage and the accompanying rise in NO and PGE(2) production. These effects of L-NAME were significantly antagonized by the addition of L-arginine, a substrate for NO synthesis. The signals for cNOS, COX-1 and HSP 70 mRNA were detected by RT-PCR in the vehicle-treated gastric mucosa, whereas gene and protein expression of iNOS, COX-2 and HSP 70 mRNA were significantly increased only in rats treated with 1 or 5 applications of HP LPS.

CONCLUSIONS

Repeated injections of HP LPS enhance gastric mucosal resistance to the mucosal damage induced by ethanol and WRS via a mechanism involving mucosal overexpression of iNOS, COX-2 and HSP 70 with subsequent excessive production of NO and PGE(2).

Effects of lipopolysaccharide and phenylbutazone on gastric contents in the horse

REASONS FOR PERFORMING STUDY

Endotoxaemia causes a disruption of gastrointestinal motility in the horse but there is no information on its effects on gastric secretion. Lipopolysaccharide (LPS) administration is known to affect gastric secretion in other species.

HYPOTHESIS

That LPS, a toxic component of Gram-negative bacteria, would reduce gastric acid secretion and that pretreatment with phenylbutazone (PBZ) would block the effects of LPS.

METHODS

The effects of LPS and PBZ on gastric contents were investigated in fasted, mature horses, with permanent gastric cannulae. Horses were pretreated with either saline or PBZ 15 mins before a 60 min infusion of either LPS or saline. Gastric contents were collected at 15 min intervals for 3 h, beginning 15 mins after the start of the LPS or saline infusion.

RESULTS

Lipopolysaccharide significantly decreased gastric acid output, [K+] and potassium output and increased [Na+] and sodium output. Phenylbutazone did not affect basal gastric acid secretion but decreased LPS-induced changes in the secreted volume, [Na+] and sodium output.

CONCLUSIONS

This study provides evidence that LPS affects gastric acid secretion in the horse and that these LPS-induced changes are mediated, in part, by prostaglandins.

POTENTIAL RELEVANCE

Lipopolysaccharide administration can induce changes in the composition of gastric contents in the horse but further work is needed to determine the source of these changes.

Functional and morphological aspects of Helicobacter pylori-induced gastric cancer in Mongolian gerbils

BACKGROUND

Helicobacter pylori infection of Mongolian gerbils is an established model of gastric carcinogenesis, but gastric secretory aspects of this carcinogenesis have not been studied.

METHODS

The effects of single intragastric inoculation of gerbils with H. pylori strain (cagA+ vacA+, 5 x 10(6) CFU/ml) or vehicle (saline) were examined at 1, 2, 4, 6, 9, 12 and 30 weeks from inoculation. Gastric morphology, the presence of H. pylori using the rapid urease test, the density of H. pylori and 16S rRNA and the plasma gastrin and somatostatin were determined.

RESULTS

H. pylori was detected in gastric mucosa in all infected animals. Basal gastric acid in gerbils was reduced by about 50% after H. pylori inoculation. Early lesions seen at 4 weeks after H. pylori inoculation consisted of chronic gastritis with thickened mucosal folds, oedema, congestion and mucosal lymphocytic infiltration. Adenomatous hyperplasia with cellular atypia with increased mitotic activity and the formation of apoptotic bodies and visible erosions and ulcerations were observed at 12-30 weeks after inoculation. The atypical gastric glands were situated 'back-to-back', suggesting gastric pre-cancer. The gastric blood flow in H. pylori-infected gerbils was significantly lower than that in the controls. Six- to seven-fold increase in plasma gastrin levels combined with significant fall in gastric somatostatin contents and the intraepithelial neoplasia were noticed in gerbils at all tested periods.

CONCLUSION

H. pylori-infection in gerbils resulted in gastric pre-cancer associated with functional changes, such as suppression of gastric secretion and impairment of both gastric mucosal microcirculation and the gastrin-somatostatin link.

Effect of local application of growth factors on gastric ulcer healing and mucosal expression of cyclooxygenase-1 and -2

BACKGROUND/AIMS

Ulcer healing involves expression of various growth factors such as epidermal growth factor (EGF), hepatocyte growth factor (HGF) and basic fibroblast growth factor (bFGF) at the ulcer margin, but the influence of EGF, HGF and bFGF applied locally with or without neutralizing anti-EGF, HGF and bFGF antibodies or cyclooxygenase (COX)-1 and COX-2 inhibitors on ulcer healing and the expression of COX-1 and COX-2 during ulcer healing have only been studied a little.

METHODS

Rats with gastric ulcers induced by serosal application of acetic acid (ulcer area 28 mm2 received a submucosal injection of either (1) vehicle (saline), (2) EGF, (3) HGF, and (4) bFGF with or without antibodies against EGF, HGF and bFGF or indomethacin (2 mg/kg/day i.p.), a nonspecific inhibitor of COX, or NS-398 (10 mg/kg/day i.g.) and Vioxx (5 mg/kg/day i.g.), both highly specific COX-2 inhibitors. A separate group of animals with chronic gastric fistulas was also used to assess gastric secretion during ulcer healing with and without growth factors. Each growth factor and specific antibody against EGF, HGF and bFGF (100 ng/100 microl each) were injected just around the ulcer immediately after ulcer induction and this local injection was repeated on day 2 following anesthesia and laparotomy. On days 13 and 21, the ulcer area was determined by planimetry, gastric blood flow (GBF) at the ulcer margin was examined by the H2-gas clearance technique, and mucosal generation of PGE2 and the gene expression of COX-1 and COX-2 in the non-ulcerated and ulcerated gastric mucosa were assessed. Gastric ulcers healed progressively within 21 days after induction and this effect was accompanied by a significant increase in GBF at the ulcer margin and in the expression of COX-2 in the ulcer area. Local treatment with EGF, HGF and bFGF produced a significant decrease in gastric acid secretion and significantly accelerated the rate of ulcer healing and raised GBF at the ulcer margin causing further significant upregulation of COX-2 but not COX-1 expression in the ulcerated mucosa. The acceleration of ulcer healing and hyperemia at the ulcer margin exhibited by locally applied EGF, HGF and bFGF were similar to those obtained with systemic administration of these growth factors. HGF applied submucosally, upregulated COX-2 expression and this was significantly attenuated by concurrent treatment with antibody against this peptide. Anti-EGF and anti-bFGF antibodies completely abolished the acceleration of the ulcer healing and hyperemia at the ulcer margin induced by these growth factors. Indomethacin and both COX-2 inhibitors significantly prolonged ulcer healing, while suppressing the generation of PGE2 in non-ulcerated and ulcerated gastric mucosa and GBF at the ulcer margin. The acceleration of ulcer healing by EGF, HGF and bFGF and the accompanying rise in GBF at the ulcer margin were significantly attenuated by the concurrent treatment with indomethacin or NS-398 and Vioxx.

CONCLUSIONS

(1) Growth factors accelerate ulcer healing due to enhancement in the microcirculation around the ulcer and these effects are specific because they can be abolished by neutralization with antibodies; (2) COX-2-derived prostaglandins and suppression of gastric secretion may play an important role in the acceleration of ulcer healing by various growth factors, and (3) the local effects of EGF, HGF and bFGF on ulcer healing can be reproduced by their systemic application indicating the high efficacy of growth factors to accelerate this healing.

NSAIDs counteract H. pylori VacA toxin-induced cell vacuolation in MKN 28 gastric mucosal cells

The relationship between nonsteroidal anti-inflammatory drugs (NSAIDs) and Helicobacter pylori-induced gastric mucosal injury is still under debate. VacA toxin is an important H. pylori virulence factor that causes cytoplasmic vacuolation in cultured cells. Whether and how NSAIDs affect VacA-induced cytotoxicity is unclear. This study was designed to evaluate the effect of NSAIDs on H. pylori VacA toxin-induced cell vacuolation in human gastric mucosal cells in culture (MKN 28 cell line). Our data show that 1) NSAIDs (indomethacin, aspirin, and NS-398) inhibit VacA-induced cell vacuolation independently of inhibition of cell proliferation and prostaglandin synthesis; 2) NSAIDs impair vacuole development/maintenance without affecting cell binding and internalization of VacA; and 3) NSAIDs, as well as the chloride channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid, also inhibit cell vacuolation induced by ammonia. We thus hypothesize that NSAIDs might protect MKN 28 cells against VacA-induced cytotoxicity by inhibiting VacA channel activity required for vacuole genesis.

Developmental changes in cyclooxygenase mRNA expression in the gastric mucosa of rats

BACKGROUND

In newborn rats, gastric mucosa is more susceptible to various damaging agents and recovers from injury more quickly than in older animals. To determine whether metabolism of prostaglandins is responsible for this mucosal protective mechanism in developing rats, we studied cyclooxygenase (COX) mRNA expression in the mucosa using quantitative real-time polymerase chain reaction (PRC).

METHODS

Cyclooxygenase-1 and COX-2 mRNA was extracted from the gastric mucosa of rats of various ages and quantitatively analyzed using real-time PCR with dual-labeled fluorogenic probes. The copy numbers of cDNA for COX-1 and COX-2 were standardized to glyceraldehyde-3-phosphate dehydrogenase from the same sample.

RESULTS

Cyclooxygenase-1 mRNA expression was lowest in 1-week-old rats and highest in 4-week-old rats. Mucosal damage produced by 150 mmol/L HCl and 60% ethyl alcohol did not increase COX-1 mRNA expression in any age group. Cyclooxygenase-2 mRNA expression increased significantly with age. Mucosal injury increased COX-2 mRNA in each age group, especially in 1-week-old rats. Intraperitoneal lipopolysaccharide also increased COX-2 mRNA in both 1- and 4-week old rats.

CONCLUSION

The high level of COX-2 mRNA expression in the gastric mucosa of 1-week-old rats may be responsible for the physiologic characteristics of gastric mucosal defenses in this age group.

Ischemic preconditioning, the most effective gastroprotective intervention: involvement of prostaglandins, nitric oxide, adenosine and sensory nerves

Various organs, including heart, kidneys, liver or brain, respond to brief exposures to ischemia with an increased resistance to severe ischemia/reperfusion and this phenomenon is called "preconditioning". No study so far has been undertaken to check whether such short, repeated gastric ischemic episodes protect gastric mucosa against severe damage caused by subsequent prolonged ischemia/reperfusion and, if so, what could be the mechanism of this phenomenon. The ischemic preconditioning was induced by short episodes of gastric ischemia (occlusion of celiac artery from one to five times, for 5 min each) applied 30 min before prolonged (30 min) ischemia followed by 3 h of reperfusion or 30 min before topical application of strong mucosal irritants, such as 100% ethanol, 25% NaCl or 80 mM taurocholate. Exposure to regular 30-min ischemia, followed by 3-h reperfusion, produced numerous severe gastric lesions and significant fall in the gastric blood flow and prostaglandin E(2) generation. Short (5-min) ischemic episodes (1-5 times) by itself failed to cause any gastric lesions, but significantly attenuated those produced by ischemia/reperfusion. This protection was accompanied by a reversal of the fall in the gastric blood flow and prostaglandin E(2) generation and resembled that induced by classic gastric mild irritants. These protective and hyperemic effects of standard preconditioning were significantly attenuated by pretreatment with cyclooxygenase-2 and cyclooxygenase-1 inhibitors, such as indomethacin, Vioxx, resveratrol and nitric oxide (NO)-synthase inhibitor, N(G)-nitro-L-arginine (L-NNA). The protective and hyperemic effects of standard preconditioning were restored by addition of 16,16 dm prostaglandin E(2) or L-arginine, a substrate for NO synthase, respectively. Gastroprotective and hyperemic actions of standard ischemic preconditioning were abolished by pretreatment with capsaicin-inactivating sensory nerves, but restored by the administration of exogenous CGRP to capsaicin-treated animals. Gene and protein expression of cyclooxygenase-1, but not cyclooxygenase-2, were detected in intact gastric mucosa and in that exposed to ischemia/reperfusion with or without ischemic preconditioning, whereas cyclooxygenase-2 was overexpressed only in preconditioned mucosa. We conclude that: (1) gastric ischemic preconditioning represents one of the most powerful protective interventions against the mucosal damage induced by severe ischemia/reperfusion as well as by topical mucosal irritants in the stomach; (2) gastric ischemic preconditioning resembles the protective effect of "mild irritants" against the damage by necrotizing substances in the stomach acting via "adaptive cytoprotection" and involves several mediators, such as prostaglandin derived from cyclooxygenase-1 and cyclooxygenase-2, NO originating from NO synthase and sensory nerves that appear to play a key mechanism of gastric ischemic preconditioning.

Classic NSAID and selective cyclooxygenase (COX)-1 and COX-2 inhibitors in healing of chronic gastric ulcers

Prostaglandins (PG) derived from COX-1 are essential for the maintenance of mucosal integrity but COX-2 isoform synthesizes PG at a site of inflammation. Recently, COX-2 mRNA expression was demonstrated at the ulcer edge during healing of chronic gastric ulcers but the role for expression of COX-2 and its products such as PGE(2) and cytokines including interleukin (IL-1beta) and tumor necrosis factor alpha (TNFalpha) in ulcer healing remains unknown. In this study, Wistar rats with gastric ulcers produced by serosal application of acetic acid (ulcer area 28 mm(2)) received daily treatment either with: (1) vehicle (saline); (2) NS-398 (10 mg/kg-d i.g.) and Vioxx (5 mg/kg-d i.g.), both, highly specific COX-2 inhibitors; (3) meloxicam (5 mg/kg-d i.g.), a preferential inhibitor of COX-2; (4) resveratrol (10 mg/kg-d i.g.), a specific COX-1 inhibitor; (5) indomethacin (5 mg/kg-d i.g); and (6) aspirin (ASA; 50 mg/kg-d i.g.), non-selective inhibitors of both COX-1 and COX-2. At day 3, 7, and 14 after ulcer induction, the animals were sacrificed and the area of gastric ulcers was determined by planimetry and histology, gastric blood flow (GBF) at ulcer base and margin was measured by H(2) clearance technique, and blood was withdrawn for measurement of plasma IL-1beta and TNFalpha levels. The mucosal biopsy samples were taken for the determination of PGE(2) generation by RIA and expression of COX-1, COX-2, IL-1beta, and TNFalpha mRNA by RT-PCR. In vehicle-treated rats, gastric ulcers healed progressively and at day 14 the healing was completed, accompanied by a significant rise in the GBF at ulcer margin. The IL-1beta, TNFalpha, and COX-1 mRNA were detected in intact and ulcerated gastric mucosa, whereas COX-2 mRNA were upregulated only in ulcerated mucosa with peak observed at day 3 after ulcer induction. The plasma IL-1beta level was significantly increased at day 3 and 7 but then declined at day 14 to that measured in vehicle-controls. Indomethacin and ASA, which suppressed PGE(2) generation both in the non-ulcerated and ulcerated gastric mucosa, significantly delayed the rate of ulcer healing and this was accompanied by the fall in GBF at ulcer margin and further elevation of plasma IL-1beta and TNFalpha levels, which was sustained up to the end of the study. Treatment with NS-398 and Vioxx, which caused only a moderate decrease in the PGE(2) generation in the non-ulcerated gastric mucosa, delayed ulcer healing and attenuated significantly the GBF at ulcer margin and PGE(2) generation in the ulcerated tissue, while raising the plasma IL-1beta and TNFalpha similarly to those observed in indomethacin- and ASA-treated rats. Resveratrol, which suppressed the PGE(2) generation in both non-ulcerated and ulcerated gastric mucosa, prolonged ulcer healing and this was accompanied by the fall in the GBF at the ulcer margin and a significant increase in plasma IL-1beta and TNFalpha levels. We conclude that (1) classic NSAID delay ulcer healing due to suppression of endogenous PG, impairment in GBF at ulcer area, and excessive cytokine expression and release, and (2) this deleterious effect of classic NSAID on the healing of pre-existing ulcers can be reproduced by selective COX-1 and COX-2 inhibitors, suggesting that both COX isoforms are important sources of PG that appear to contribute to ulcer healing.

Water extracts of Helicobacter pylori suppress the expression of histidine decarboxylase and reduce histamine content in the rat gastric mucosa

BACKGROUND

Acute Helicobacter pylori (Hp) infection in humans may be associated with markedly reduced gastric acid secretion, but the mechanism of this hypochlorhydria has not been fully explained.

AIMS

This study was designed to investigate how water extracts (WE) of Hp applied on rat gastric mucosa affect gastric secretion and mucosal histamine concentration as well as the gene expression for histamine decarboxylase (HDC), the key enzyme converting histidine to histamine and for interleukin-1beta (IL-1beta), the important proinflammatory cytokine.

MATERIALS AND METHODS

Wistar rats were surgically equipped with small cannulas to form gastric fistulas (GF). Four weeks after formation of GF, rats received either saline (control group) or WE obtained from type I Hp strain expressing CagA/VacA proteins and from type II Hp strain negative for CagA/VacA. Hp-WE was applied intragastrically (i.g.) in a volume of 1 ml at days 0, 2, 4 and 6 (total 4 times). At days 7 and 14, the secretory tests were performed during which basal gastric acid and pepsin secretion was examined and acid and pepsin outputs were measured. After secretory tests, the rats were sacrificed, the stomachs removed and the damage to the gastric mucosa was assessed by measuring the lesion area planimetrically and by histology, the gene expression in gastric mucosa for HDC and interleukin-1beta (IL-1beta) was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blot. Additionally, somatostatin concentration in gastric juice, gastric mucosal histamine content and plasma gastrin and IL-1beta levels were determined using radioimmunoassay (RIA).

RESULTS

Administration of Hp-WE failed to induce gross mucosal damage but microscopic examination revealed partial denudation of gastric surface epithelium without causing deep necrosis. In secretory tests, Hp-WE produced marked hypochlorhydria but type I Hp-WE induced significantly stronger inhibition of acid and pepsin secretion than type II Hp-WE, both at days 7 and 14. Both, type I and type II Hp-WE suppressed significantly the gene expression for HDC mRNA and lowered significantly gastric mucosal histamine content as compared to respective values in vehicle-treated control gastric mucosa. Furthermore, Hp-WE, resulted in a significant increase in expression of IL-1beta mRNA and a significant fall in luminal somatostatin concentration as well as a insignificant elevation of plasma gastrin level, the type I Hp-WE being more effective in these alterations than type II Hp-WE.

CONCLUSIONS

(1) Ability of Hp-WE to induce superficial damage, the reduction in HDC mRNA and accompanying fall in gastric histamine release, contribute, at least in part, to marked hypochlorhydria observed in the stomach exposed to repeated Hp-WE treatments, and (2) the deleterious effect of Hp-WE on the gastric mucosa involves an impairment of gastrin-somatostatin link possibly resulting from the action of Hp-derived toxins and the induction in mucosal cells of proinflammatory cytokine such as IL-1beta.

Involvement of gastrin in gastric secretory and protective actions of N-alpha-methyl histamine

N alpha-methylhistamine (N alpha-MH) is one of an unusual metabolite of histamine that was found in Helicobacter pylori-infected stomachs and is believed to interact with specific histamine H(1), H(2) and H(3)-receptors to stimulate gastric acid secretion and gastrin release from isolated G-cells but the effects of N alpha-MH on gastric mucosal integrity have been little studied. This study was designed; (1) to compare the effect of exogenous N alpha-MH with that of standard histamine on gastric secretion and plasma gastrin levels in rats equipped with gastric fistula (series A); and (2) to assess the action of N alpha-MH on gastric lesions induced by 100% ethanol (series B) in rats with or without removal of antral portion of the stomach (antrectomy). Rats of series B were pretreated intragastrically (i.g.) or intraperitoneally (i.p.) with N alpha-MH or histamine (0.1-2 mg/kg) 30 min prior to 100% ethanol (1.5 ml, i.g.) with or without: (1) vehicle (saline); (2) RPR 102681 (30 mg/kg i.p.), to block CCK-B/gastrin receptors; and (3) ranitidine (40 mg/kg s.c.) to inhibit histamine H(2)-receptors. The area of gastric lesions was determined planimetrically, gastric blood flow (GBF) was assessed by H(2)-gas clearance method and venous blood was collected for determination of plasma gastrin levels by radioimmunoassay (RIA). N alpha-MH and histamine dose-dependently increased gastric acid output (series A); the dose increasing this secretion by 50% (ED(50)) being 2 and 5 mg/kg i.g or i.p., respectively, and this effect was accompanied by a significant rise in plasma gastrin levels. Both, N alpha-MH and histamine attenuated dose-dependently the area of gastric lesions induced by 100% ethanol (series B) while producing significant rise in the GBF and plasma immunoreactive gastrin increments. These secretory, protective, hipergastrinemic and hyperemic effects of N alpha-MH and histamine were completely abolished by antrectomy, whereas pretreatment with RPR 102681 attenuated significantly the N alpha-MH and histamine-induced protection against ethanol damage and accompanying hyperemia. Ranitidine, that produced achlorhydria and a further increase in plasma gastrin levels, failed to influence the N alpha-MH- and histamine-induced protection and accompanying rise in the GBF. We conclude that (1) N alpha-MH stimulates gastric acid secretion and exhibit gastroprotective activity against acid-independent noxious agents in the manner similar to that afforded by histamine; and (2) this protection involves an enhancement in the gastric microcirculation and release of gastrin acting via specific CCK-B/gastrin receptors but unexpectedly, appears to be unrelated to histamine H(2)-receptors.

Role of gastric acid secretion in progression of acute gastric erosions induced by ischemia-reperfusion into gastric ulcers

Ischemia followed by reperfusion is known to produce gastric lesions due to oxidative stress, but the role of gastric H(+) secretion in the formation of this mucosal injury remains unknown. We studied alterations in gastric acid secretion and gastric histamine content, as well as the expression of histidine-decarboxylase and interleukin-1beta during the mucosal recovery from ischemia-reperfusion erosions. Gastric secretion was studied in rats (series A) with gastric fistula before, during and after the ischemia induced by clamping of celiac artery for 0.5 h followed by reperfusion in animals pretreated with vehicle (saline), omeprazole, a proton pump inhibitor, or ranitidine, a histamine (H(2)) receptor antagonist. In series B, the animals were submitted to 0.5 h of ischemia followed by 1 h of reperfusion and then anesthetized at 0, 3, 12 and 24 h or 3, 5, 10 or 15 days after the end of ischemia-reperfusion to determine gastric blood flow by H(2)-gas clearance technique, area of gastric lesions, plasma gastrin and interleukin-1beta levels, histamine content by radioimmunoassay (RIA) and expression of histidine-decarboxylase and interleukin-1beta mRNA by reverse transcription polymerase chain reaction. Clamping of celiac artery caused cessation of gastric blood flow and almost complete suppression of basal gastric acid secretion (series A) that returned gradually to the control value at day 3 after ischemia-reperfusion, accompanied by the rise in plasma gastrin levels, pronounced expression of histidine-decarboxylase mRNA and increased mucosal histamine content. Ischemia, followed by 1 h of reperfusion, produced gastric erosions (series B) that reached maximum at 12 h, but then declined at 24 h. These erosions progressed at day 3 into deeper ulcers whose area declined progressively within the next 5-15 days. The gastric blood ceased to flow (series B) during 30 min of clamping and was reduced throughout the period of healing of acute erosions, being accompanied by a gradual rise in mucosal interleukin-1beta mRNA content and in plasma interleukin-1beta levels. Treatment with omeprazole or ranitidine, which completely suppressed gastric acid secretion and significantly raised plasma gastrin level, greatly reduced the formation of erosive lesions preventing the progression of these lesions to chronic gastric ulcers, and this was accompanied by the rise in gastric blood flow and plasma gastrin levels and the significant attenuation of plasma interleukin-1beta levels. The ranitidine and omeprazole-induced suppression of ischemia-reperfusion erosions were abolished by the instillation of exogenous 0.2 N HCl into the stomach of these rats. The histidine-decarboxylase was faintly expressed in the intact gastric mucosa, but strongly upregulated during mucosal recovery from the damage induced by ischemia-reperfusion. We conclude that following ischemia-reperfusion: (1) gastric acid secretion, gastric microcirculation and histamine production markedly decline, while interleukin-1beta release significantly increases, probably playing an important role in the progression of acute lesions into chronic gastric ulcerations; (2) the suppression of gastric acid secretion by omeprazole and ranitidine, that induces hypergastrinemia, prevents the progression of gastric erosions into ulcers; and (3) the addition of exogenous acid restores the progression of the acute lesions into gastric ulcers, indicating that gastric acid plays a key role in ulcerogenesis induced by ischemia-reperfusion.

Role of prostaglandins generated by cyclooxygenase-1 and cyclooxygenase-2 in healing of ischemia-reperfusion-induced gastric lesions

In this study, ischemia-reperfusion produced in rats by clamping the celiac artery for 0.5 h followed by 1 h of reperfusion was used to develop a new model of superficial gastric erosions progressing to deeper ulcers. Ischemia alone resulted in an immediate fall in gastric blood flow but no gross mucosal lesions were observed. When ischemia was followed by reperfusion, gastric erosive lesions occurred, reached a maximum at 12 h and then declined after 24 h. These acute erosions progressed into deeper lesions 24 h after ischemia-reperfusion and reached a peak after 3 days. Gastric blood flow and the mucosal generation of prostaglandin E(2) were significantly suppressed immediately following ischemia-reperfusion, but with the healing of deeper gastric ulcers, both gastric blood flow and prostaglandin E(2) generation were gradually restored. Cyclooxygenase-1 mRNA was detected by reverse transcription-polymerase chain reaction in intact gastric mucosa and throughout the recovery of the mucosa from acute ischemia-reperfusion lesions, whereas cyclooxygenase-2 mRNA, was recorded only after ischemia-reperfusion. NS-398 and rofecoxib, selective inhibitors of cyclooxyganase-2, failed to affect prostaglandin E(2) generation in the non-ulcerated gastric mucosa but inhibited it significantly in the ulcer area. The two cyclooxygenase-2 inhibitors as well as resveratrol, a specific cyclooxygenase-1 inhibitor and indomethacin and meloxicam, non-specific inhibitors of cyclooxygenase, augmented acute gastric erosions induced by ischemia-reperfusion and delayed significantly the progression of these lesions into deeper ulcers at each time interval after ischemia-reperfusion. We conclude that prostaglandins generated by both cyclooxygenase-1 and cyclooxygenase-2 contribute to the healing of gastric lesions induced by ischemia-reperfusion.

Inducible types of cyclooxygenase and nitric oxide synthase in adaptive cytoprotection in rat stomachs

Roles of cyclooxygenases (COX-1 and COX-2) and nitric oxide (NO) synthases (nNOS and iNOS) in adaptive cytoprotection induced by 20 mM taurocholate dissolved in 50 mM HCl (TC) were investigated in rat stomachs. Intragastric administration of 0.6 N HCl caused haemorrhagic damage in the stomach. These lesions were prevented by pretreatment of the animals with TC p.o. 0.5 h before 0.6 N HCl, and a significant protection persisted for more than 5 h. The protection afforded by TC given 0.5 h before HCl was almost totally reversed by indomethacin and slightly mitigated by N(G)-nitro-L-arginine methyl ester (L-NAME) but not affected by NS-398 or aminoguanidine. By contrast, the mucosal protective action of TC given 5 h before HCl was significantly reversed by NS-398, L-NAME and aminoguanidine as well as indomethacin. Mucosal prostaglandin E2 (PGE2) contents were significantly increased for over 5 h after TC, while luminal NOx output tended to elevate at 0.5 h and be significantly increased at 5 h after TC. The increased PGE2 generation observed 0.5 h after TC was attenuated only by indomethacin, while that observed 5 h after TC was inhibited by NS-398 as well as indomethacin. On the other hand, the NOx output determined at 5 h after TC was significantly reduced by both L-NAME and aminoguanidine. The expression of mRNA for both COX-2 and iNOS was apparently detected in the stomach from 3 h after TC treatment. These results suggest that TC induced adaptive cytoprotection in the rat stomach against 0.6 N HCl, the effect lasting for over 5 h, and the underlying mechanism differs depending on the period after the irritation. The early phase is mediated mainly by COX-1/PGs, while the later phase is mediated by iNOS/NO, in addition to prostaglandins (PGs) produced by both COX-1 and COX-2.

Mouse model of Helicobacter pylori infection: studies of gastric function and ulcer healing

BACKGROUND

Helicobacter pylori infection in humans is a major risk factor for peptic ulcer, but studies on the relation between H. pylori infection and gastric pathology are limited due to a deficiency of convenient animal models resembling this infection in humans.

METHODS

We studied the effects of inoculation of conventional BALB/c mice with CagA and VacA positive (type I) H. pylori or CagA and VacA negative H. pylori (type II) strains on gastric secretion and healing of chronic acetic acid-induced ulcers in mouse stomachs. The ulcer area, gastric blood flow, plasma interleukin (IL)-1beta and IL-12, as well as plasma gastrin and gastric luminal somatostatin were determined. Gastric mucosal biopsy samples were also taken for assessment of the presence of viable H. pylori using a rapid urease test, H. pylori-culture and the RT-PCR analysis of the signal for H. pylori CagA.

RESULTS

Gastric acid and pepsin secretion was reduced by over 50% immediately after H. pylori inoculation and accompanied by a significant increment in plasma gastrin and fall in gastric luminal somatostatin content observed over all test days, particularly in mice infected with type I H. pylori. The area of ulcers in vehicle-treated controls decreased significantly starting from day 2 after ulcer induction and then continued to decline for a further 14 days to heal almost completely after 28 days. In contrast, the ulcers were present until day 28 in all mice infected with type I or type II H. pylori strains, being significantly larger, especially with type I H. pylori infection. The gastric blood flow at the ulcer margin and ulcer crater in vehicle-treated mice gradually increased with decreasing ulcer size, after 14 and 28 days reaching a value which was not significantly different from that in vehicle-administered mice. In contrast, the gastric blood flow in type I H. pylori and, to a lesser extent, in type II H. pylori infected mice was significantly lower than in vehicle controls, both at the margin and at the crater of ulcers at all tested days. Histological changes such as oedema or congestion of surface epithelium were found after 7 days whereas mucosal inflammatory infiltration appeared after 14 days with a further increase after 28 days, especially in type I H. pylori and to a lesser extent in type II H. pylori infected mice. Plasma IL-1beta and IL-12 were significantly elevated at all tested days of ulcer healing and their increments were significantly higher in type I than in type II H. pylori infection.

CONCLUSIONS

Conventional mice with gastric ulcers can be successfully infected by both toxigenic and nontoxigenic H. pylori strains, and this infection causes an immediate suppression of gastric secretion and markedly delays the healing of ulcers due to the fall in mucosal microcirculation in the ulcer region, cytokine release and an impairment in the gastrin-somatostatin link that appears to be independent of gastritis and more pronounced with infection of toxigenic than nontoxigenic strains.