Gastric adaptation to injury by repeated doses of aspirin strengthens mucosal defence against subsequent exposure to various strong irritants in rats

Effect of Aspirin and ibuprofen either alone or in combination on gastric mucosa and bleeding time and on serum prostaglandin E2 and thromboxane A2 levels in the anaesthetized rats in vivo

There is much evidence that a combination of ibuprofen (IBU) and Aspirin (ASA) can antagonize the irreversible inhibition of platelet function. This study was designed to investigate the degree of gastric damage, bleeding time (BT) and fluctuations in the serum levels of prostaglandin E₂ (PGE₂) and thromboxane A₂ (TXA₂) after oral administration of ASA (200 mg/kg) and IBU (50 mg/kg) either alone or in combination in rats in vivo. The stomach was assessed for any damage either after 6 h, 18 h or 6 days and carboxymethylcellulose (1% CMC) served as a vehicle and control. ELISA was used to measure TXA₂ and PGE₂ in serum. Bleeding time was assessed using tail blood. The results show that ASA and IBU either alone or in combination can cause gastric ulceration in 25-100% of the rats at 6 and 18 h. In contrast, gastric ulceration was seen in 50% of rats with a combination of ASA given before IBU only after 6 days of oral administration. BT was unaffected either by ASA or IBU when administered alone except after 18 h for IBU. In contrast, BT was significantly reduced when IBU was administered before ASA after 18 h and 6 days (P < 0.001). Serum PGE₂ levels decreased significantly after ASA administered either alone or in combination with IBU for 6 h, 18 h and 6 days (P < 0.05). Serum TXA₂ levels were significantly reduced after 6 h, 18 h and 6 days following ASA and IBU administration except for IBU alone which caused a significant increase in serum TXA₂ 6 days after its administration (P < 0.01). It can be concluded that ASA and IBU administered either alone or in combination can cause gastric ulcers in the rat stomach after 6 h and 18 h, but less severe after 6 days. IBU either alone or in combination with ASA reduced BT only after 18 h and 6 days of administration. Together, the results show that gastric ulceration correlated well with the inhibition of serum PGE₂ and TXA₂ levels.

Interaction between endogenous carbon monoxide and hydrogen sulfide in the mechanism of gastroprotection against acute aspirin-induced gastric damage

Acetylsalicylic acid (ASA) is mainly recognized as painkiller or anti-inflammatory drug. However, ASA causes serious side effects towards gastrointestinal (GI) tract which limits its usefulness. Carbon monoxide (CO) and hydrogen sulfide (H₂S) have been described to act as important endogenous messengers and mediators of gastroprotection but whether they can interact in gastroprotection against acute ASA-induced gastric damage remains unknown. In this study male Wistar rats were pretreated with 1) vehicle (saline, i.g.), 2) tricarbonyldichlororuthenium (II) dimer (CORM-2, 5mg/kg i.g.), 3) sodium hydrosulfide (NaHS, 5mg/kg i.g.), 4) zinc protoporphyrin (ZnPP, 10mg/kg i.p.), 5) D,L-propargylglycine (PAG, 30mg/kg i.g.), 6) ZnPP combined with NaHS, 7) PAG combined with CORM-2 or 8) 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10mg/kg i.p.) combined with CORM-2 or NaHS and 30min later ASA was administered i.g. in a single dose of 125mg/kg. After 1h, gastric blood flow (GBF) was determined by H₂ gas clearance technique and gastric lesions were assessed by planimetry and histology. CO content in gastric mucosa and COHb concentration in blood were determined by gas chromatography and H₂S production was assessed in gastric mucosa using methylene blue method. Protein and/or mRNA expression for cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS), 3-mercaptopyruvate sulfurtransferase (3-MST), heme oxygenase (HO)-1, HO-2, hypoxia inducible factor-alpha (HIF)-1α, nuclear factor (erythroid-derived 2)-like 2 (Nrf-2), cyclooxygenase (COX)-1 and COX-2, inducible nitric oxide synthase (iNOS) and interleukin (IL)-1β were determined by Western blot or real-time PCR, respectively. ASA caused hemorrhagic gastric mucosal damage and significantly decreased GBF, H₂S production, CO content, mRNA or protein expression for CSE, 3-MST, HO-2 and increased mRNA and/or protein expression for CBS, HO-1, Nrf-2, HIF-1α, iNOS, IL-1β, COX-2 in gastric mucosa and COHb concentration in blood. Pretreatment with CORM-2 or NaHS but not with PAG decreased ASA-damage and increased GBF. ZnPP reversed protective and hyperemic effect of NaHS but PAG failed to affect CORM-2-induced gastroprotection. CORM-2 elevated CO content, mRNA or protein expression for HO-1, Nrf-2, and decreased expression of CBS, HIF-1α, COX-2, IL-1β, iNOS, the H₂S production in gastric mucosa and COHb concentration in blood. NaHS raised mRNA or protein expression for CSE, COX-1 and decreased mRNA expression for IL-1β and COHb level in blood. We conclude that CO is involved in gastroprotection induced by H₂S while beneficial protective action of CO released from CORM-2 in gastric mucosa seems to be H₂S-independent. In contrast to H₂S, CO ameliorates hypoxia, regulates Nrf-2 expression but similarly to H₂S acts on sGC-dependent manner to restore gastric microcirculation and exhibit anti-inflammatory activity in gastric mucosa compromised by ASA.

Gastroprotective effect of the iridoid fraction from Barleria prionitis leaves on experimentally-induced gastric ulceration

AIM

To study the gastroprotective effect and in vivo antioxidant potential of a standardized iridoid fraction from B. prionitis leaves (BPE) against different gastric ulcer models in rats.

METHOD

The standardized iridoid fraction from BPE at 50, 100, and 200 mg/kg body weight was administered orally, twice daily for 5 days for prevention from aspirin, ethanol, cold-restraint stress (CRS), and pylorus ligation (PL)-induced ulcers. Estimation of the antioxidant enzyme activity was carried out in a CRS-induced ulcer model, and various gastric secretion parameters including volume of gastric juice, acid output, and pH value were estimated in the PL-induced ulcer model.

RESULTS

BPE showed a dose-dependent ulcer protective effect in PL (18.67%-66.26% protection), aspirin (24.65%-63.25% protection), CRS (20.77%-59.42% protection), and EtOH (16.93%-77.04% protection)-induced ulcers. BPE treatment in PL-rats showed a decrease in acid-pepsin secretion, and enhanced mucin and mucosal glycoproteins. However, BPE reduced the ulcer index with significant decrease in LPO (P < 0.01-0.001), SOD (P < 0.01-0.001), and an increase in CAT (P < 0.01-0.001), activity in the CRS-induced model.

CONCLUSION

The data shows that the iridoid fraction from BPE possesses anti-ulcerogenic and antioxidant potential.

Interaction between Helicobacter pylori infection, nonsteroidal anti-inflammatory drugs and/or low-dose aspirin use: Old question new insights

Previous reports clearly demonstrated that Helicobacter pylori (H. pylori) infection, nonsteroidal anti-inflammatory drugs (NSAID) or low dose aspirin (ASA) use significantly and independently increased the risk for the development of peptic ulcer disease. Today, the presence of H. pylori infection associated with low dose ASA and/or NSAID use in the same patient is becoming more frequent and therefore the potential interaction between these factors and the consequences of it has important implications. Whether NSAID intake in the presence of H. pylori infection may further increase the risk of peptic ulcer carried by the presence of only one risk factor is still a matter of debate. Studies on the interaction between the two risk factors yielded conflicting data and no consensus has been reached in the last years. In addition, the interaction between H. pylori infection and low-dose ASA remains even more controversial. In real clinical practice, we can find different clinical scenarios involving these three factors associated with the presence of different gastrointestinal and cardiovascular risk factors. These huge variety of possible combinations greatly hinder the decision making process of physicians.

Reactive increase in gastric mucus secretion is an adaptive defense mechanism against low-dose aspirin-induced gastropathy

BACKGROUND

Gastric mucus is considered to play an essential role in gastric mucosal defense mechanisms, especially when irritants are present in the stomach.

AIM

To investigate the relationship between low-dose aspirin-induced gastropathy and gastric secretory function, especially gastric mucus secretion, in healthy volunteers.

METHODS

Thirty male, asymptomatic, Helicobacter pylori pylori-negative healthy volunteers were asked to take 100 mg of enteric-coated aspirin (Bayaspirin) once a day for 10 days. Endoscopic examination was performed before and 3 and 10 days after drug administration. The extent of endoscopically assessed gastric mucosal injury was semi-quantitatively evaluated according to the modified Lanza score. The pentagastrin-stimulated gastric juice was collected for 10 min during the endoscopic examination and subjected to analysis for gastric acid (mEq/10 min) or mucus (mg hexose/10 min) output.

RESULTS

Overall, the 10-day aspirin treatment significantly increased gastric mucus secretion from 0.8 (interquartile range 1.7) to 1.6 (1.6) mg hexose/10 min (P < 0.05), with a concomitant and significant decrease in the gastric acid/mucus ratio from 4.3 (5.2) to 2.9 (4.7) (P < 0.01). Subsequent analysis of two subgroups of volunteers categorized according to their endoscopic status ("severe gastropathy" vs. "modest gastropathy") revealed that changes in gastric secretory parameters occurred exclusively in those subjects without severe gastric injury; there was no alteration in these parameters in subjects with severe gastric injury.

CONCLUSIONS

The results of this study suggest that the reactive increase in gastric mucus secretion is an adaptive defense mechanism against low-dose aspirin-induced gastropathy. In some individuals, such a response may be insufficient to prevent the development of severe mucosal injury and even ulcers and their complications.

Gastric acid secretion level modulates the association between Helicobacter pylori infection and low-dose aspirin-induced gastropathy

BACKGROUND

The relative contribution of gastric acid secretion and Helicobacter pylori infection to low-dose aspirin-induced gastropathy remains to be clarified. This is partly because the capability of the infection to modify gastric acid secretion complicates the interaction. The aim of this study was to estimate the association of aspirin-induced mucosal injury, as well as H. pylori infection, with gastric acid output.

METHODS

A total of 186 male outpatients, comprising 60 aspirin takers, on 100 mg of enteric-coated aspirin daily and 126 non-aspirin takers were prospectively enrolled in this study. Gastrin-stimulated acid output was estimated by the endoscopic gastrin test. The grade of gastric mucosal injury was assessed endoscopically according to the modified Lanza score. Multiple logistic regression analyses were used to adjust for potential confounders.

RESULTS

The gastric acid secretion level, with an odds ratio (OR) (95% confidence interval [CI]) of 10.5 (3.0-36.9) and aspirin administration, with an OR (95% CI) of 7.4 (3.0-18.3) were independently associated with gastric mucosal injury, and the co-existence of both factors greatly elevated the risk of mucosal injury, with an OR (95% CI) of 77.0 (13.5-440.0). H. pylori infection, itself, did not show any significant effect on the aspirin-induced mucosal injury after adjusting for gastric acid secretion.

CONCLUSIONS

This study has demonstrated that aspirin-induced gastropathy is directly associated with gastric acid secretion. In addition, it also suggested that the gastric acid secretion level modulates the association between H. pylori infection and aspirin-induced gastropathy.

Effect of fish oil on offensive and defensive factors in gastric ulceration in rats

The effect of fish oil (FO) derived from Scomberoides commersonianus containing omega-3 polyunsaturated fatty acids was studied on gastric ulcers and as well as on offensive and defensive factors in gastric mucosal damage, following experimental gastric ulceration. FO significantly reduced the severity of ulceration in gastric ulcers induced by aspirin, cold-restraint stress (CRS), alcohol, and pylorus ligation. The results also indicated the potentiality of FO in maintaining the integrity of gastric mucosa by virtue of its effect on both offensive and defensive gastric mucosal factors. It decreased the offensive acid-pepsin secretion and augmented the defensive factors like mucin secretion, cellular mucus and life span of mucosal cells following pylorus ligation. FO significantly increased activity of anti-oxidant enzymes (catalase and glutathione peroxidase) and decreased lipid peroxidation in gastric mucosa of CRS rats. The study indicates the beneficial role of FO in gastric ulceration by inhibition of offensive mucosal factors and oxidative stress, and augmentation of defensive mucosal factors.

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.

Gastrointestinal tolerability of metamizol, acetaminophen, and diclofenac in subchronic treatment in rats

The gastrointestinal tolerability of metamizol and acetaminophen [weak cyclooxygenase (COX) inhibitors] in comparison with diclofenac (nonselective cyclooxygenase inhibitor) was evaluated in subchronic treatments in rats. Wistar rats received 60 mg/kg body weight of metamizol and acetaminophen, and 3 mg/kg body weight of diclofenac by oral route twice daily for 14 days. Myeloperoxidase activity, an index of neutrophil infiltration, COX expression and the effects on blood parameters used as indicators of liver and renal functions were also studied. Metamizol and acetaminophen did not cause apparent gastrointestinal lesions; in contrast diclofenac showed swelling and an increased thickness on the distal intestinal mucosa. Myeloperoxidase activity was significantly increased in the small bowel with diclofenac treatment. In gastric mucosa the expression of the cyclooxygenase-1 was not affected and the expression of cyclooxygenase-2 was not observed. Diclofenac treatment significantly diminished hematocrit, hemoglobin, and corpuscular volume and increased the number of platelets. Aspartate aminotransferase and gamma-glutamyltransferase activity were also altered and, regarding the renal biochemical parameters, the animals treated with diclofenac had increased urea values. In contrast, acetaminophen treatment did not affect either of these parameters and metamizol increased only the alanine aminotransferase activity. Under our experimental conditions, metamizol and acetaminophen seem to be safe drugs. In contrast, with diclofenac treatment blood loss and anemia are observed which could stem from the small intestinal injury. Moreover, this drug could to impair kidney function.

Effect of Helicobacter pylori on delay in ulcer healing induced by aspirin in rats

Helicobacter pylori and nonsteroidal anti-inflammatory drugs (NSAIDs) are major pathogenic factors in peptic ulcer disease but whether these two factors exert synergistic or antagonistic effects on ulcer healing has been a subject of controversy. We compared the effect of aspirin alone with that of aspirin combined with H. pylori on gastric acid secretion and healing of acetic acid gastric ulcers in rats. The H. pylori colonization of gastric mucosa was determined by viable H. pylori culture, histology and assessment of bacterial DNA using polymerase chain reaction (PCR). The area of ulcers, gastric blood flow, mucosal generation of prostaglandin E(2) and plasma gastrin levels and expression of cyclooxygenase-1, cyclooxygenase-2 and growth factors was determined. Aspirin delayed significantly the healing of chronic gastric ulcers, decreased the gastric blood flow at the ulcer margin and gastric mucosal prostaglandin E(2) generation being without significant influence on gastric acid output. H. pylori acquisition that produced moderate gastric inflammation at the ulcer margin delayed significantly the healing of gastric ulcers, decreased significantly both the gastric blood flow at the ulcer margin and the gastric secretion while raising significantly the gastric mucosal prostaglandin E(2) generation and plasma gastrin levels. H. pylori infection attenuated the aspirin-induced inhibition of ulcer healing and accompanying fall in the gastric blood flow. Both aspirin and H. pylori up-regulated significantly cyclooxygenase-2 messenger RNA (mRNA) and protein but not that of cyclooxygenase-1 at the ulcer margin. Aspirin reduced significantly the transforming growth factor alpha- and vascular endothelial growth factor mRNAs, but these effects were significantly attenuated by H. pylori. We conclude that H. pylori antagonizes, in part, aspirin-induced delay of ulcer healing due to suppression of acid secretion, the enhancement in prostaglandin E(2) possibly derived from cyclooxygenase-2 and the overexpression of transforming growth factor alpha and vascular endothelial growth factor in the ulcer area.

Effect of psychogenic stress on gastrointestinal function

This review summarizes the studies published over the last twenty years on the effects of psychogenic stress on gastrointestinal function, using animal models. The effects of stress on gastric ulceration have received wide attention and the central and local mechanisms of mucosal damage have been, for the most part, clearly delineated. In comparison, relatively few studies have focused on the impact of stress on intestinal and colonic physiology, even though its influence on intestinal motility, mucosal permeability and inflammation has been established. More work is necessary in this field, especially considering the importance of irritable bowel syndrome in modern society.

Activation of genes for superoxide dismutase, interleukin-1beta, tumor necrosis factor-alpha, and intercellular adhesion molecule-1 during healing of ischemia-reperfusion-induced gastric injury

BACKGROUND

Ischemia followed by reperfusion (I/R) induces gastric lesions, probably due to excessive formation of free radicals, but the role of the scavenger of these radicals, proinflammatory cytokines such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), in the healing of these lesions has not been extensively studied. It is also unknown whether expression of intercellular adhesion molecule-1 (ICAM-1), which mediates neutrophil-induced injury and neutrophil infiltration, is involved in the recovery from I/R lesions.

METHODS

I/R lesions were induced in Wistar rats by applying a small clamp to the celiac artery for 30 min (ischemia phase), followed by the removal of the clamp for 60 min (reperfusion phase). The influence of I/R on gastric secretion was also tested in rats equipped with a gastric fistula (GF) without or with the exposure to a standard period of I/R. Two series of rats (A and B) were used to determine the effects of exogenous and endogenous superoxide dismutase SOD (series A) and allopurinol, a xanthine oxidase inhibitor (series B), on the mucosal recovery from the gastric lesions induced by I/R. The animals were killed immediately after the exposure to I/R (0 h) and at 3 h, 24 h, or 3, 5, or 10 days after this I/R, the area of gastric lesions being measured by planimetry, and the gastric blood flow (GBF) determined by the H2 gas clearance method. Blood was withdrawn for measurement of plasma IL-1beta and TNF-alpha levels with enzyme-linked immunosorbent assay, and plasma gastrin with radioimmunoassay. Biopsy samples of oxyntic mucosa were taken for the assessment of SOD, IL-1beta, TNF-alpha, and ICAM-1 mRNAs by reverse-transcription polymerase chain reaction and Southern blot.

RESULTS

Exposure to I/R resulted in acute gastric erosions, with the maximal increase of the area of these lesions observed 3 h after the end of I/R. This effect was accompanied by a decrease in the GBF, a significant increase in blood free radicals and plasma gastrin increments, and almost complete suppression of gastric secretion. Starting 24 h after I/R, the gastric superficial lesions progressed into deeper ulcers that healed progressively within 10 days, and this was accompanied by gradual restoration of the gastric secretion and the GBF. Treatment with SOD and allopurinol accelerated significantly the healing of I/R erosions, and this effect was accompanied by a significant increase in the GBF and the attenuation of blood free radicals. At 0, 3, and 12 h after I/R a significant decrease in SOD mRNA was observed, whereas expression of TNF-alpha, IL-1beta, and ICAM-1 showed a progressive increase starting immediately after I/R, reaching a maximum on day 3. The plasma level of TNF-alpha and IL-1beta started to increase on day 3 and peaked on day 5 after I/R, being still significantly higher at day 10 than that measured in the vehicle-treated control gastric mucosa. On day 10 the gastric ulcers were almost completely healed, and a decrease in the expression for TNF-alpha, IL-1beta, and ICAM-1 mRNA and an increase in the expression of SOD mRNA were observed.

CONCLUSIONS

1) exposure to I/R produces gastric lesions mediated by the excessive formation of free radicals, resulting in suppression of both gastric microcirculation and secretory activity of the stomach; 2) SOD and allopurinol accelerate the healing of I/R lesions, probably due to suppression of oxygen free radicals and improvement of gastric microcirculation; and 3) the upregulation of SOD mRNA, with subsequent increase in the SOD production and local release of IL-1beta and TNF-alpha, may activate ICAM-1 expression and neutrophil infiltration, which appear to play an important role in the progression of I/R-induced acute gastric erosions into chronic ulcers.

Effect of naproxen on the hamster gastric antrum: ulceration, adaptation and efficacy of anti-ulcer drugs

BACKGROUND

Various animal models of non-steroidal anti-inflammatory drug (NSAID)-induced gastric ulceration exist. These models have limitations, which make them less relevant to the human situation.

AIM

: To develop a more simple and more relevant model of NSAID-induced gastric ulceration and adaptation.

METHODS

Gastric ulceration was evaluated following the orogastric administration of naproxen (80 mg/kg b.d.) to hamsters. The effects of misoprostol and famotidine on gastric acid secretion and ulceration were also determined. Gastric adaptation was evaluated by proliferating cell nuclear antigen (PCNA) immunohistochemistry, in hamsters given naproxen for 3 weeks. Antral resistance to acute injury by NSAIDs and ethanol was also determined in these animals.

RESULTS

Naproxen caused primarily gastric antral ulceration, which decreased from day 3 to day 21. This gastric adaptation was accompanied by an increase in PCNA positive cells, particularly on days 7 and 14. The adapted gastric antral mucosa was resistant to acute damage by various agents. Misoprostol (1 or 100 microg/kg) prevented antral ulceration, without affecting gastric acid secretion. Despite decreasing acid output by> 90%, famotidine (30 mg/kg) failed to prevent ulceration.

CONCLUSION

The administration of naproxen (80 mg/kg b.d.) to hamsters is a simple, reliable and relevant method for evaluating NSAID-induced gastric antral ulceration and adaptation.

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.

Involvement of endogenous cholecystokinin and somatostatin in gastroprotection induced by intraduodenal fat

Duodenal fat such as oleate is known to influence gut functions by release of cholecystokinin (CCK), but the contribution of CCK endogenously released by duodenal fat or by diversion of pancreatic juice from the duodenum in the mechanism of mucosal integrity and gastroprotection has been little studied. This study was designed to compare the effect of CCK-8 and intraduodenal (i.d.) instillation of sodium oleate, or diversion of the pancreatic biliary secretions that are known to release CCK, on the gastric mucosal lesions induced by topical application of 100% ethanol or acidified aspirin (ASA) in rats with or without the pretreatment with a CCK-A receptor antagonist, loxiglumide, or with L-365,260 to block CCK-B receptors. In addition, the effect of suppression of prostaglandin (PG) biosynthesis by indomethacin (5 mg/kg i.p.), inhibition of nitric oxide (NO)-synthase by L-NAME (5 mg/kg i.v.), or blockade of sensory nerves by capsaicin (125 mg/kg s.c.) on the protective activity of sodium oleate was determined. Sodium oleate (50-200 mM i.d.), or diversion of pancreatic juice from the duodenum for 3 h that produced significant rise in plasma CCK levels, significantly reduced gastric lesions induced by 100% ethanol to an extent similar to that induced by exogenous CCK-8 (5 nmol/kg s.c.). The protective effect of oleate or diversion of pancreatic juice was accompanied by an increase in gastric blood flow (GBF). Both protection and accompanying hyperemia were completely abolished by blockade of CCK-A receptors with loxiglumide, whereas L-365,260, an antagonist of CCK-B receptors, had no effect. Oleate given i.d. significantly attenuated acidified ASA-induced gastric lesions and gastric secretion while increasing the luminal concentration of somatostatin. These effects were significantly reduced by loxiglumide but not by L-365,260. In contrast, CCK-8, which stimulated gastric acid secretion, failed to affect the lesions induced by acidified ASA and the decrease in the GBF produced by this ulcerogen. Indomethacin, which suppressed PG generation by approximately 90%, failed to influence the protective activity of oleate or CCK-8 against ethanol-induced lesions, whereas L-NAME, vagotomy, or sensory denervation significantly attenuated this protection and accompanying hyperemia. Addition to L-NAME of L-arginine, but not D-arginine, restored the protective and hyperemic effects of CCK-8 and duodenal oleate against gastric lesions induced by ethanol or acidified ASA. We conclude that endogenous CCK released by oleate or diversion of pancreatic secretion exerts a potent gastroprotective action on the stomach involving predominantly CCK-A receptors and depending on vagal activity, and hyperemia mediated by NO and sensory nerves but unrelated to acid secretory effects and endogenous PG.

Mouse model of gastric infection with cytotoxin-expressing strain of Helicobacter pylori in studying of pathogenesis of chronic gastric ulcer

Helicobacter pylori is a major risk factor for peptic ulcer, but studies on the role of H. pylori infection in gastric pathology are limited due to lack of convenient models resembling H. pylori infection in humans. We studied the effects of inoculation of conventional BALB/c mice with a toxigenic (cytotoxin associated gene A (cagA)+ and vacuolating cytotoxin gene A (vacA+) H. pylori strain on the course of healing of gastric ulcers. Following inoculation of toxigenic H. pylori or vehicle, gastric ulcers were produced in mice, which were then killed either at day 0 or after 2, 4, 7, 14 or 28 days and ulcer area and gastric blood flow (GBF) were determined. Gastric secretions from mice with chronic gastric fistulae were studied before and after inoculation with toxigenic H. pylori or vehicle (saline). The area (7 mm² ) of ulcers in control mice decreased gradually and disappeared almost completely after 14 or 28 days. The ulcers in H. pylori-infected mice were present at all test days, showing a larger area than in vehicle control animals. The GBF in control mice rose gradually with decreasing ulcer size, being significantly higher at the ulcer margin than the ulcer crater. In contrast, the GBF in H. pylori-infected mice was significantly lower at the ulcer area than that in the vehicle controls but, again, the GBF at the ulcer margin was always higher than at the ulcer crater. Gastric acid output was reduced by more than 50% immediately after H. pylori inoculation and was accompanied by a significant increase in plasma gastrin release and a fall in gastric luminal somatostatin content. These secretory changes persisted at all test days. Oedema/congestion of surface epithelium appeared after 7 days and mucosal inflammatory infiltration appeared after 14 days, to further increase after 28 days, upon the induction of ulcer. Plasma interleukin (IL)-Iß and IL-12 were significantly elevated above the initial values compared with controls. Conventional mice with gastric ulcers can be successfully infected with an H. pylori strain expressing cagA and vacA cytotoxin and this infection markedly delays healing of the ulcers, probably due to the fall in GBF in the ulcer area, mucosal inflammation, cytokine release and impairment of the gastrin-somatostatin link.

Activation of genes for spasmolytic peptide, transforming growth factor alpha and for cyclooxygenase (COX)-1 and COX-2 during gastric adaptation to aspirin damage in rats

BACKGROUND

NSAIDs, such as aspirin (ASA), cause widespread mucosal damage, but repeated ASA insults appear to induce mucosal tolerance (adaptation) to this injury. The mechanism of the gastric adaptation to the damage induced by ASA has not been fully explained.

AIM

To determine the role of the mucosal gene expression for spasmolitic peptide (SP) (a member of trefoil peptides) and transforming growth factor alpha (TGF alpha) as well as for cyclooxygenase (COX)-1 and COX-2 during gastric adaptation to ASA in rats.

METHODS

Gastric lesions were produced by ASA (100 mg/kg in 1.5 mL of 0.2 M HCl) applied intragastrically (i.g.) as a single dose. every day for 5 days. Control rats were given 1.5 mL of vehicle (0.2 M HCl i.g.) as a single dose, during 5 consecutive days. Gastric blood flow (GBF) was measured by H2-gas clearance technique and gastric mucosal specimens were taken for the assessment of cell proliferation rate in gastric mucosa by bromodeoxyuridine (BrdU) uptake, mucosal generation of prostaglandin E2 measured by radioimmunoassay, and for expression of SP, TGF alpha COX-1 and COX-2 mRNA as determined by RT-PCR. To quantify the relative amounts of mRNA for SP and TGF alpha, southern blotting analysis of the PCR products was performed and the intensity of PCR products was compared with that of beta-actin used as a standard.

RESULTS

ASA applied once produced numerous gastric erosions, but with repeated ASA doses the adaptation to this NSAID developed, the area of gastric lesions being reduced by 86% after six consecutive ASA insults. This adaptation to ASA was accompanied by approximately a 90% reduction in prostaglandin E2 biosynthesis, by a significant rise in BrdU uptake by glandular cells predominantly in the neck region of gastric glands and by expression of SP (SP/beta-actin ratio; 0.96 +/- 0.08 in ASA-adapted mucosa vs. 0.38 +/- 0.05 in the control mucosa) and TGF alpha (TGF alpha/beta-actin ratio: 0.97 +/- 0.07 in ASA-adapted mucosa vs. 0.77 +/- 0.06 in the control mucosa). COX-1 expression was detected in vehicle-control gastric mucosa and after single exposure to ASA or after six consecutive ASA insults, while COX-2 mRNA was not detected in vehicle-control gastric mucosa, but appeared after single ASA insult and was sustained after subsequent ASA doses.

CONCLUSIONS

(i) Gastric adaptation to aspirin injury involves enhanced cell proliferation which appears to be mediated by increased expression of SP and TGF alpha, and (ii) rapid upregulation of COX-2 expression following single and repeated ASA insults may represent a compensatory response to suppression of prostaglandin generation by this NSAID.

The role of melatonin and L-tryptophan in prevention of acute gastric lesions induced by stress, ethanol, ischemia, and aspirin

Melatonin, a pineal hormone, synthesized from L-tryptophan, is known to exist in the gut and to scavenge oxygen free radicals but its role in gastroprotection against acute lesions induced by various strong irritants has been little studied. In this study, we determined the effects of melatonin and L-tryptophan on gastric secretion and the formation of acute gastric lesions induced by absolute ethanol, acidified aspirin (ASA), stress, and ischemia-reperfusion (I/R). Area of gastric lesions was determined by planimetry, gastric blood flow (GBF) was measured using a H2-gas clearance technique, and blood was withdrawn for the measurement of free radicals, plasma gastrin, and melatonin concentration by specific radioimmunoassay. Intragastric (i.g.) administration of melatonin (2.5-10 mg/kg) or L-tryptophan (25-200 mg/kg) failed to affect gastric lesions by ethanol and ASA but dose-dependently reduced the lesions provoked by stress and I/R; this protective effect was accompanied by a significant rise in plasma melatonin level, GBF, and DNA synthesis and by a marked fall in blood free radicals. L-tryptophan, which significantly elevated the plasma melatonin by about 3-5-fold, also reduced the stress and I/R-induced lesions and blood levels of free radicals, while increasing the GBF, DNA synthesis, and plasma gastrin levels. Inhibition of mucosal generation of PGE2 by indomethacin abolished the protection and the rise of GBF afforded by melatonin and L-tryptophan, whereas pretreatment with N(G)-nitro-L-arginine (L-NNA), to suppress nitric oxide (NO) synthase, was without any effect. We conclude that melatonin applied exogenously in pharmacological doses and that released by the administration of its precursor, L-tryptophan, protect gastric mucosa from the damage induced by stress and I/R possibly by a mechanism involving the scavenging of free radicals and gastric hyperemia probably mediated by endogenous prostaglandin but not NO.

Mucosal expression and luminal release of epidermal and transforming growth factors in patients with duodenal ulcer before and after eradication of Helicobacter pylori

BACKGROUND

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF alpha) are potent gastric acid inhibitors and stimuli of mucosal growth and protection but their involvement in Helicobacter pylori associated duodenal ulcer has been little examined.

AIM

To assess gastric acid secretion, plasma gastrin concentrations, mucosal content of EGF and TGF alpha, and mucosal expression of these peptides and their receptor (EGFr) as well as salivary and gastric luminal release of EGF under basal conditions and after pentagastrin stimulation in 10 healthy subjects and in 25 H pylori positive patients with duodenal ulcer before and after two weeks of triple anti-H pylori therapy and four weeks after the termination of this therapy.

RESULTS

Pentagastrin stimulation caused a significant increase in salivary and gastric release of EGF both in healthy controls and patients with duodenal ulcers but in the patients, the eradication of H pylori resulted in several fold higher gastric luminal (but not salivary) EGF release than before the anti-H pylori therapy. Mucosal contents of immunoreactive EGF and TGF alpha and mucosal expression of EGF, TGF alpha, and EGFr in H pylori positive patients with duodenal ulcer were significantly higher than those in healthy H pylori negative controls and this increase persisted after eradication of H pylori. Basal plasma gastrin was significantly reduced after two weeks of triple therapy and four weeks after the H pylori eradication all ulcers were completely healed.

CONCLUSIONS

(1) H pylori infection in patients with duodenal ulcer was accompanied by enhanced plasma gastrin and increased mucosal content and expression of TGF alpha, EGF, and EGFr; (2) H pylori eradication resulted in ulcer healing, reduction in plasma gastrin, and enhancement of gastric (but not salivary) luminal release of EGF, particularly after pentagastrin stimulation; and (3) enhanced mucosal content and expression of TGF alpha, EGF, and EGFr and increased luminal release of EGF may contribute to ulcer healing after eradication of H pylori.

Expression of epidermal growth factor and transforming growth factor alpha during ulcer healing. Time sequence study

BACKGROUND

Growth factors such as epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) have been shown to share common receptor (EGFR) and to accelerate ulcer healing due to stimulation of cell proliferation, but the time sequence of expression of EGF and TGF alpha during ulcer healing has not been investigated. In this study the rate of cell proliferation and the gastric secretion and gene expression of mRNA for EGF and TGF alpha were determined during ulcer healing.

METHODS

Gastric ulcers were induced in 150 Wistar rats by serosal application of 100% acetic acid (ulcer area, 14 mm2). Some of these animals were also equipped with a gastric fistula for the assessment of gastric secretion during ulcer healing. The animals were killed 0, 2, 4, 6, or 8 days after ulcer induction, and the ulcer area was determined. The mucosal sections with gastric ulcer were immunostained for proliferating cell nuclear antigen (PCNA) and for immunoexpression of EGF, TGF alpha, and EGFR. The expression of mRNA EGF and mRNA TGF alpha was also determined in the ulcer margin by reverse transcriptase (RT) polymerase chain reaction (PCR) using specific primers.

RESULTS

Two, 4, 6, and 8 days after ulcer induction the gastric ulcer area was gradually reduced from the initial size (day 0) by 47%, 70%, 80%, and 87%, respectively, and this was accompanied by an increase in PCNA with its maximum on day 4. The gastric acid and pepsin secretion was significantly reduced by 75% and 79%, respectively, on day 2 after ulcer induction but then the secretion tended to return to normal value by day 8. The expression of EGF, TGF alpha, and EGFR was negligible on day 0 but increased significantly during the healing, reaching maximum on day 4. Expression of EGF mRNA was detected on days 2, 4, and 6, and that of TGF alpha mRNA on days 2, 4, 6, and 8 after ulcer induction, with the most intense signals for both transcripts observed on day 2.

CONCLUSIONS

1) The enhancement in cell proliferation during ulcer healing may be mediated by increased release of EGF and TGF alpha; 2) the expression of EGF and TGF alpha mRNA precedes the overexpression of these growth factors at the ulcer margin during ulcer healing; and 3) the overexpression of growth factors coincides with the inhibition of gastric secretion and increased blood flow at the ulcer margin, indicating that these factors affect gastric secretion and blood flow in the course of ulcer healing.

Mucosal irritation, adaptive cytoprotection, and adaptation to topical ammonia in the rat stomach

BACKGROUND

The urease-ammonia (NH4OH) system has been proposed to play a major role in the pathogenesis of the Helicobacter pylori-associated gastritis, but the mechanism of the mucosal damage has not been fully explained. This study was designed to examine possible adaptive cytoprotection and the adaptation of rat gastric mucosa to the irritant action of NH4OH and urease.

METHODS AND RESULTS

Single application of NH4OH alone in various concentrations (15-500 mM) caused concentration-dependent mucosal damage starting with 30 mM and reaching a maximum at 250 mM NH4OH, similar to that obtained with 100% ethanol; it was accompanied by a decrease in gastric blood flow (GBF) to approximately 30% of the normal value. When the mucosa was first exposed to the low, non-damaging concentration (15 mM) of NH4OH and then insulted with 100% ethanol, the extent of ethanol damage was greatly attenuated as compared with that caused by ethanol alone. This adaptive cytoprotection was accompanied by the rise in GBF and reversed, in part, by the pretreatment with indomethacin, an inhibitor of prostaglandin (PG)-cyclooxygenase; with L-NAME, a blocker of NO-synthase; or with capsaicin deactivating the sensory nerves. Damaging concentrations of NH4OH (125 mM) caused widespread mucosal damage after the first application, but with repeated insults with 125 mM NH4OH a gradual reduction in the mucosal lesions, accompanied by enhanced mucosal cell proliferation and over-expression of epidermal growth factor (EGF) (using immunocytochemistry) and mRNA of EGF (using trans-reverse polymerase chain reaction), were observed.

CONCLUSIONS

NH4OH alone damages gastric mucosa only at the concentration exceeding that found in H. pylori-infected stomachs, whereas at lower concentrations it acts as 'mild' irritant to induce adaptive cytoprotection. This adaptive cytoprotection appears to be mediated, in part, by endogenous PG, sensory nerves, and an arginine-NO-dependent pathway, and repeated applications of NH4OH induce gastric adaptation, probably mediated by enhanced expression of EGF and its receptors and by an increased cell proliferation.