Nonessential role of leukotrienes as mediators of acute gastric mucosal injury induced by aspirin in rats

Yogurt containing Lactobacillus gasseri OLL 2716 (LG21 yogurt) accelerated the healing of acetic acid-induced gastric ulcer in rats

We have reported that LG21 yogurt containing Lactobacillus gasseri OLL 2716 (LG21 yogurt) inhibits the formation of HCl-induced acute gastric lesions through the generation of prostaglandin E₂. This study aimed to determine the role of viable Lactobacillus in the healing of acetic acid-induced chronic gastric ulcer. LG21 yogurt or γ-ray radiated LG21 yogurt was administered orally twice a day for 10 d at a dose of 5 ml/kg. LG21 yogurt significantly accelerated the healing of the ulcer, but γ-ray radiated LG21 yogurt did not. However, both yogurts significantly inhibited HCl-induced gastric erosive lesions and enhanced the generation of gastric mucosal prostaglandin E₂. From the above results, it was found that viable bacteria are needed to accelerate the healing of chronic gastric ulcer, but not to inhibit gastric lesions.

Yogurt containing Lactobacillus gasseri OLL2716 exerts gastroprotective action against [correction of agaisnt] acute gastric lesion and antral ulcer in rats

Yogurt containing Lactobacillus gasseri OLL2716 (LG21 yogurt) is reported to improve Helicobacter pylori-induced gastric mucosal inflammation in clinical studies. However, other beneficial effects of LG21 yogurt have not been clarified. Therefore, we examined whether LG21 yogurt exhibits a gastroprotective action against acute gastric lesion or antral ulcer in rats. Moreover, the mechanism of gastroprotective action was also evaluated. After fasting, acute gastric lesions were induced by 0.6 M HCl. Gastric mucosal folds were stained by oral administration of methyl violet. Antral ulcers were induced by the combined administration of diethyldithiocarbamate and HCl in refed rats after fasting. LG21 yogurt was orally administered before HCl treatment or staining the mucosal folds. LG21 yogurt significantly and dose-dependently inhibited the formation of acute gastric lesions, and this gastroprotective action was attenuated by pretreatment with indomethacin. LG21 yogurt also significantly increased prostaglandin E2 generation in the gastric mucosa. Stained length of gastric mucosal fold was reduced by LG21 yogurt. Antral ulcer formation was also significantly inhibited by LG21 yogurt. From the above results, it was found that the ingestion of LG21 yogurt is useful for the prevention of gastric ulcer. Moreover, endogenous prostaglandin was suggested to be one of the gastroprotective mechanisms of LG21 yogurt.

Relative contribution of acetylated cyclo-oxygenase (COX)-2 and 5-lipooxygenase (LOX) in regulating gastric mucosal integrity and adaptation to aspirin

In addition to inhibiting formation of prothrombotic eicosanoids, aspirin causes the acetylation of cyclooxygenase (COX)-2. The acetylated COX-2 remains active, and upon cell activation, initiates the generation of 15R-HETE, a lipid substrate for 5-lipoxygenase (LOX) leading to the formation of 15-epi-LXA4 (also termed "aspirin-triggered lipoxin," or ATL). Because ATL potently inhibits polymorphonuclear cell (PMN) function, we assessed the relative contribution of this lipid mediator in conjunction with another 5-LOX product, the leukotriene (LT)B4, to the pathogenesis of acute damage and gastric adaptation to aspirin. Data presented herein indicate that acute injury and gastric adaptation to aspirin is associated with ATL generation. Administration of COX inhibitors (celecoxib, indomethacin, ketoprofen) to aspirin-treated rats exacerbated acute injury and abolished adaptation to aspirin. Moreover, it inhibited ATL formation and caused a four- to fivefold increase in LTB4 synthesis. In contrast, licofelone, a COX/5-LOX inhibitor, did not exacerbate acute gastric injury nor did it interfere with gastric adaptation to aspirin. Although licofelone blocked ATL and LTB4 formation in aspirin-treated rats, it attenuated aspirin-induced gastric PMN margination. These findings indicate that the balance between the production of LTB4 and ATL modulates PMN recruitment/function and gastric mucosal responses to aspirin.

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

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

Cyclooxygenase-1 and cyclooxygenase-2 selectivity of widely used nonsteroidal anti-inflammatory drugs

PURPOSE

Both isoforms of cyclo-oxygenase, COX-1 and COX-2, are inhibited to varying degrees by all of the available nonsteroidal anti-inflammatory drugs (NSAIDs). Because inhibition of COX-1 by NSAIDs is linked to gastrointestinal ulcer formation, those drugs that selectively inhibit COX-2 may have less gastrointestinal toxicity. We measured the extent to which NSAIDs and other anti-inflammatory or analgesic drugs inhibit COX-1 and COX-2 in humans.

SUBJECTS AND METHODS

Aliquots of whole blood from 16 healthy volunteers were incubated ex vivo with 25 antiinflammatory or analgesic drugs at six concentrations ranging from 0 (control) to 100 microM (n = 5 for each). Blood was assayed for serum-generated thromboxane B2 synthesis (COX-1 assay) and for lipopolysaccharide-stimulated prostaglandin E2 synthesis (COX-2 assay). In addition, gastric biopsies from the same volunteers were incubated with each drug ex vivo and mucosal prostaglandin E2 synthesis measured.

RESULTS

Inhibitory potency and selectivity of NSAIDs for COX-1 and COX-2 activity in blood varied greatly. Some NSAIDs (eg, flurbiprofen, ketoprofen) were COX-1 selective, some (eg, ibuprofen, naproxen) were essentially nonselective, while others (eg, diclofenac, mefenamic acid) were COX-2 selective. Inhibitory effects of NSAIDs on gastric prostaglandin E2 synthesis correlated with COX-1 inhibitory potency in blood (P < 0.001) and with COX-1 selectivity (P < 0.01), but not with COX-2 inhibitory potency. Even COX-2 "selective" NSAIDs still had sufficient COX-1 activity to cause potent inhibitory effects on gastric prostaglandin E2 synthesis at concentrations achieved in vivo.

CONCLUSION

No currently marketed NSAID, even those that are COX-2 selective, spare gastric COX activity at therapeutic concentrations. Thus, all NSAIDs should be used cautiously until safer agents are developed.

Non-steroidol anti-inflammatory drug effect on crypt cell proliferation and apoptosis during initiation of rat colon carcinogenesis

Sustained use of non-steroidal anti-inflammatory drugs (NSAIDs) may prevent colorectal cancer. However, the optimal drug, period of efficacy and mechanism(s) of action are unknown. Experiments were undertaken to determine which of several NSAIDs would modulate colon crypt cell proliferation or apoptosis when given during the initiation phase of 1,2-dimethylhydrazine (DMH)-induced rat colon cancer. Colon crypts located both away from and over an aggregate of lymphoid nodules (ALN) were examined. Rats were injected with aspirin, indomethacin, nabumetone, sodium salicylate, 16,16-dimethyl prostaglandin E2 or saline for 3 days and DMH or DMH vehicle on day 4 of each week for 8 weeks, then killed 3 days after the last DMH injection. At the time of killing, DMH had significantly increased crypt cell proliferation but not apoptosis. There was significantly more cell proliferation and apoptosis in crypts over the ALN than away from the ALN. Aspirin and salicylate increased proliferation and apoptosis in crypts over the ALN. Finally, the distributional peaks of cell proliferation and apoptosis were shifted significantly closer together after DMH. Thus, DMH increases proliferation and alters the distribution of proliferating and apoptotic cells in colon crypts early in carcinogenesis. Aspirin may suppress tumour incidence via salicylate by enhancing apoptosis in carcinogen-initiated cells.

Mucosal protective effect of leminoprazole on reflux esophagitis induced in rats

We examined the effect of leminoprazole (an acid pump inhibitor) on reflux esophagitis induced in rats. Intragastrically administered leminoprazole significantly and dose-dependently protected the esophageal mucosa against the reflux of gastric contents, without affecting gastric acid secretion. However, it had no effect on the esophagitis when administered intraduodenally, despite its significant inhibition (about 40%) of gastric acid secretion. Omeprazole significantly prevented the development of esophagitis, most probably through potent inhibition of gastric acid secretion. Indomethacin significantly reduced the synthesis of prostaglandin E2 in the esophagus. Since indomethacin pretreatment had no effect on the esophageal protection by leminoprazole, omeprazole or sucralfate, the involvement of endogenous prostaglandins can be ruled out as a possible underlying mechanism. Intragastrically, but not intraduodenally, administered sucralfate significantly prevented the esophagitis even at a dose not affecting gastric acid secretion. These results strongly suggest that both leminoprazole and sucralfate protect the esophageal mucosa directly.

ML 3000 reduces gastric prostaglandin synthesis without causing mucosal injury

In this study we characterized the effects of a novel anti-inflammatory drug, ML 3000 ([2,2-dimethyl-6-(4-chlorophenyl)-7-phenyl-2,3-dihydro-1H-pyrrolizine- 5-yl]-acetic acid), on the gastric mucosa and attempted to determine the mechanism responsible for its apparent stomach-sparing properties. Acute gastric damaging properties of ML 3000 versus indomethacin were examined in the rat, while chronic-type gastric ulcer was examined in the rabbit. At doses of up to 100 mg/kg p.o., ML 3000 did not produce significant acute gastric injury, while indomethacin at 5-20 mg/kg p.o. caused mucosal necrosis and bleeding. ML 3000 significantly inhibited gastric and blood prostaglandin E2 synthesis, with the higher doses tested (30 and 100 mg/kg) producing comparable effects to that seen with indomethacin at 10 or 20 mg/kg. Gastric and blood leukotriene B4 synthesis were not significantly affected by either drug. While indomethacin caused a significant increase in leukocyte adherence to mesenteric venules, ML 3000 did not. When administered repeatedly to rabbits, diclofenac caused penetrating ulcer formation in the gastric antrum of the majority of the animals. ML 3000 did not produce any detectable damage at doses of 10 or 30 mg/kg, but an ulcer was observed in one of five rabbits given the 100 mg/kg dose. Prior administration of ML 3000 (10-100 mg/kg) did not significantly affect the extent of gastric damage induced by subsequent oral administration of ethanol. These studies demonstrate that ML 3000 spares the gastric mucosa despite significantly suppressing gastric prostaglandin synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related reductions in gastric mucosal prostaglandin levels increase susceptibility to aspirin-induced injury in rats

BACKGROUND/AIMS

Aspirin and other nonsteroidal anti-inflammatory drugs are known to cause gastrointestinal mucosal injury in humans and animals. The present study was designed to determine the effect of aging on gastric mucosal eicosanoid formation and aspirin-induced injury in Fischer 344 rats.

METHODS

In part 1 of the study, rats of three different age groups (3, 12, and 21 months) were killed after an overnight fast, and gastric mucosal formation of prostaglandins and leukotrienes was determined. In part 2, rats of various ages were killed 3 hours after receiving aspirin (100 mg/kg intragastrically) or vehicle (for controls). Gastric mucosal eicosanoid formation and gross mucosal injury were assessed.

RESULTS

Gastric mucosal prostaglandin formation decreased with aging, whereas no significant changes in mucosal leukotriene formation were noted in any age groups. No gastric mucosal lesions were present in any rats treated with vehicle alone. In contrast, aspirin caused significant mucosal injury in all age groups, but significantly more mucosal lesions were noted in the older rats.

CONCLUSIONS

These observations indicate that gastric mucosal prostaglandin synthesis decreases with aging in rats and that aged animals are more susceptible to aspirin-induced acute gastric mucosal injury.

Leukotrienes do not contribute to the pathogenesis of indomethacin-induced ulceration of the gastric antrum in the re-fed rat

The potential involvement of leukotrienes in the pathogenesis of indomethacin-induced ulceration of the rat gastric antrum has been studied. Pretreatment with the leukotriene biosynthesis inhibitor, MK886 (30 mg/kg p.o.), inhibited the increases in blood and antral leukotriene B4 release ex vivo associated with the evolution of antral ulceration. Despite this, however, there was no significant reduction in either the area of antral ulceration, or in the associated blood neutrophilia and neutrophil infiltration into the gastric antrum. Similarly, pretreatment with the leukotriene B4 antagonist, SC41930 (50 mg/kg p.o.) or the peptidyl leukotriene antagonist ICI198,615 (50 mg/kg p.o.) did not inhibit the area of antral ulceration induced by indomethacin. Thus, in contrast to published reports studying fundic ulceration, our results suggest that leukotrienes do not play a major role either in the pathogenesis of indomethacin-induced ulceration of the rat gastric antrum or neutrophil infiltration into the damaged antrum.

Inhibitory effect of DS-4574, a peptidoleukotriene antagonist with mast cell stabilizing action, on compound 48/80-induced gastric mucosal lesions in rats

We evaluated the inhibitory effect of DS-4574, a peptidoleukotriene antagonist with mast cell stabilizing action, on rat gastric mucosal lesions induced by compound 48/80 (C48/80: a mast cell degranulator), in comparison with those of disodium cromoglycate (DSCG: a mast cell stabilizer), LY171883 (a peptidoleukotriene antagonist) and cimetidine (a histamine H2 receptor antagonist). Subcutaneous administration of C48/80 (1 mg/kg) once daily for four consecutive days produced extensive gastric lesions in the fundic mucosa. DS-4574 (20, 50 and 100 mg/kg/day, oral) and DSCG (200 mg/kg/day, intraperitoneal) treatment markedly inhibited formation of these mucosal lesions, but LY171883 (100 and 200 mg/kg/day, oral) and cimetidine (400 mg/kg/day, oral) treatment did not. Moreover, DS-4574 and DSCG significantly suppressed both hyperhistaminemia and histamine release from rat peritoneal mast cells induced by C48/80. These results indicate that the inhibitory effect of DS-4574 on gastric lesions induced by C48/80 may be related to its mast cell stabilizing action, but to neither its antisecretory nor its peptidoleukotriene antagonistic activity.

Tissue-selective inhibition of prostaglandin synthesis in rat by tepoxalin: anti-inflammatory without gastropathy?

BACKGROUND

Inhibition of prostaglandin synthesis is likely a primary mechanism for both the anti-inflammatory and ulcerogenic effects of nonsteroidal anti-inflammatory drugs (NSAIDs). The present study examined the mechanism underlying the ability of a novel anti-inflammatory drug, tepoxalin, to suppress prostaglandin synthesis without inducing gastric mucosal injury.

METHODS

The effects on prostaglandin synthesis by various tissues of tepoxalin, diclofenac, and indomethacin were examined in vivo and in vitro. These compounds were also studied in two inflammation models. The capacity of indomethacin and tepoxalin to induced antral ulceration in the rabbit was compared.

RESULTS

In most tissues, tepoxalin was a weaker inhibitor of prostaglandin synthesis than the two NSAIDs. However, at a site of peripheral inflammation, tepoxalin was comparable with the NSAIDs in suppressing prostaglandin synthesis and in exerting anti-inflammatory effects. Indomethacin induced penetrating antral ulcers in rabbits whereas tepoxalin produced no detectable mucosal injury.

CONCLUSIONS

The ability of tepoxalin to suppress inflammation without causing gastric mucosal injury appears to be related to its differential suppression of prostaglandin synthesis in various tissues. Compounds that selectively inhibit prostaglandin synthesis at sites of inflammation may represent a class of anti-inflammatory drugs without detrimental effects on the stomach.

Importance of gastric acid in gastric ulcer formation in rabbits with antibody-induced prostaglandin deficiency

The role of gastric acid in the development of gastroduodenal ulcers in prostaglandin-deficient conditions is unclear. In the current study, the effect of the proton pump inhibitor omeprazole on the formation of gastric ulcers was examined in a previously validated rabbit model of antibody-induced prostaglandin deficiency. Intragastric administration of 20 mg/kg omeprazole every 12 hours caused a profound suppression of gastric acidity (i.e., pH above 5 continuously). This same dose of omeprazole significantly reduced gastric ulcer formation induced by passive immunization with 6-keto-prostaglandin F1 alpha antibodies. It is concluded from these observations that gastric acid plays a critical role in the formation of gastric ulcers in rabbits with antibody-induced prostaglandin deficiency.