Adaptive cytoprotection in cultured rat gastric mucus-producing cells. Role of mucus and prostaglandin synthesis

The anti-apoptosis protein, survivin, mediates gastric epithelial cell cytoprotection against ethanol-induced injury via activation of the p34(cdc2) cyclin-dependent kinase

The anti-apoptosis protein, survivin, promotes cell survival and mitosis. Recent studies have demonstrated that survivin is expressed in normal gastric mucosa. Using an in vitro model, we examined whether survivin plays a role in the cytoprotection produced in gastric mucosa by mild irritant ethanol (ETOH) against subsequent exposure to concentrated ETOH. Pre-treatment of rat gastric epithelial cells with 1% ETOH reduced cell death, in response to subsequent incubation with 5% ETOH, by 94% (P < 0.005). This pre-treatment also resulted in increased total and phosphorylated survivin protein levels by 180% (P < 0.0001) and 540% (P < 0.0002), respectively, which required the p34(cdc2) cell cycle-dependent kinase. The cytoprotective effect was abrogated upon siRNA knockdown of survivin protein levels. Further, overexpression of exogenous survivin resulted in significant cytoprotection by 62% (P < 0.02) in the absence of any pre-treatment. We further examined the in vivo relevance of these findings. In fasted rats, administration of 20% ETOH, which we found to be 93% (P < 0.0001) cytoprotective against 50% ETOH challenge, resulted in increased total and phosphorylated survivin protein levels by 234% (P < 0.001) and 214% (P < 0.02), respectively. Administration of 20% ETOH resulted in increased gastric p34(cdc2) activity by 146% (P < 0.01). Inhibition of p34(cdc2) by the potent inhibitor, roscovitine, abolished the increased survivin levels in response to pre-administration of 20% ETOH and reduced the cytoprotection against 50% ETOH challenge by 59% (P < 0.01). These results indicate that survivin is a key mediator of cytoprotection against ETOH-induced gastric injury, acting at the epithelial cell level, by a mechanism that is dependent, in part, on p34(cdc2).

Reduction of ethanol-induced injury in portal hypertensive gastric mucosa of rats by induction of heat shock protein 72 by geranylgeranylacetone

Portal hypertensive (PHT) gastropathy has an increased susceptibility to damage due to noxious factors. Heat shock protein (HSP) 72 has a protective effect against gastric mucosal injury and geranylgeranylacetone (GGA) is an inducer of HSP 72. However, it remains unclear how HSP 72 influences the PHT gastric mucosa. The aim of the present study was to investigate HSP 72 induction by GGA and the protective effect to gastric mucosa in PHT rats. PHT rats were produced by staged portal vein occlusion, and GGA 200 mg/kg was orally administered. Expression of HSP 72 protein in the gastric mucosa was evaluated by enzyme-linked immunosorbent assay, and gastric mucosal damage against 70% ethanol (10 mL/kg) following GGA or vehicle treatment was also estimated. Expression of mucosal HSP 72 after vehicle administration was significantly higher in the PHT rats compared with the sham-operated rats. After GGA treatment, portal pressure did not change but HSP 72 was significantly increased in the gastric mucosa of both groups. Ethanol-induced gastric mucosal damage was significantly decreased due to GGA treatment in the PHT rats, but not in the sham-operated rats. These findings suggest that HSP 72 expression is enhanced in PHT gastric mucosa and plays an important role in gastric mucosal protection. The induction of HSP 72 by GGA may therefore effectively prevent mucosal injury in the PHT stomach.

Molecular mechanism of adaptive cytoprotection induced by ethanol in human gastric cells

Adaptive cytoprotection is the process by which the pretreatment of cells with low concentrations of a noxious agent prevents the damage caused by a subsequent exposure of those cells to higher concentrations of that same agent. In this study, a human gastric carcinoma cell line was used to examine the molecular mechanism of adaptive cytoprotection induced by ethanol. Pretreatment of cells with 1%-4% ethanol made cells resistant to a subsequent exposure to 8% ethanol. This adaptive cytoprotection was accompanied by an increase in prostaglandin E2 synthesis and was partially inhibited by inhibitors of cyclooxygenase-2, but not by an inhibitor of cyclooxygenase-1. Furthermore, the adaptive cytoprotection was not dependent on newly synthesized proteins and was inhibited by a protein tyrosine kinase inhibitor. Based on these results, it is proposed that the stimulation of cyclooxygenase-2-dependent prostaglandin E2 synthesis, which is regulated post-translationally by protein tyrosine phosphorylation, plays an important role in adaptive cytoprotection induced by ethanol in gastric cells.

Expression of vanilloid receptors in rat gastric epithelial cells: role in cellular protection

Vanilloid receptors subtype 1 (VR1), a nonselective cation channel responsive to capsaicin, protons, and noxious heat, has been recently identified in not only neural but also non-neural cells. In the present study, we demonstrated the peripheral expression of VR1 in gastric mucosal epithelial cells and investigated the role of the receptor in cellular protection. The rat gastric mucosal epithelial cell line was used. The expression of VR1 was examined by Western blotting and RT-PCR. Cell damage was induced by immersion in 10% ethanol or acid (pH 4.0) for 30 min, and cell viability was determined by MTT assay. Capsaicin or resiniferatoxin was added 30 min before the challenge with ethanol or acid, while capsazepine or ruthenium red (a VR1 antagonist) was added simultaneously with capsaicin. The distinct expression of VR1 protein and mRNA was detected in rat gastric mucosal epithelial cell line as well as in the rat stomach and spinal cord by Western blotting and RT-PCR, respectively. The cDNA sequence of the PCR product was found to be almost identical to that of the authentic VR1 (99.8%) when the product was subcloned and sequenced. On the other hand, the cell damage induced by ethanol or acid was dose-dependently prevented by pretreatment with capsaicin. The protective effect of capsaicin was mimicked by resiniferatoxin and almost totally abolished by co-addition of capsazepine or ruthenium red. These findings suggest that VR1 is expressed peripherally in gastric mucosal epithelial cells and plays a cellular protective role.

The intestinal mucosa as a target for dietary polyunsaturated fatty acids

Several studies have reported beneficial effects of dietary polyunsaturated fatty acids (PUFA) on various aspects of both human and animal health, and particular reference has been made to their effects on systemic immune responses. Both immune stimulation and immune suppression have been reported, with the outcome dependent on the type of PUFA, the target cell, as well as the immune competence of the cells before exposure. The systemic and the mucosal immune systems are discrete entities, which have evolved specific approaches in the defense of the host. The latter comprises several interconnected tissues, which communicate with one another through the action of soluble mediators and the trafficking of cellular components. After the oral mucosa, the intestinal epithelium and its associated gut-associated lymphoid tissue are the primary targets of dietary components. Absorption of dietary PUFA and its incorporation into intestinal tissues has been well studied, but the consequences of these events in relation to local immune responses have received little attention. This article describes some of the immune mechanisms operating at this barrier and, where possible, pinpoints areas for which a modulatory role for PUFA has already been demonstrated. Although not an exhaustive treatise of the subject, it is hoped that this review will foster research into the specific interaction between dietary PUFA and cell populations comprising the intestinal barrier.

The role of cyclooxygenase inhibitors in repair of ischaemic-injured jejunal mucosa in the horse

Cyclooxygenase inhibitors are administered to horses to prevent endotoxin-induced elaboration of prostaglandins. However, PGE2 and PGI2 stimulate repair of injured intestine. There are 2 isoforms of cyclooxygenase: COX-1, which constitutively produces prostaglandins and COX-2, which is induced by inflammation. We hypothesised that the nonspecific cyclooxygenase inhibitor flunixin meglumine would retard repair of ischaemic intestinal injury by preventing production of reparative prostaglandins, whereas the selective COX-2 inhibitor, etodolac, would permit repair as a result of continued COX-1 prostaglandin production. Segments of equine jejunum were subjected to ischaemia for 1 h, and recovered for 4 h in Ussing chambers. In ischaemic tissue, treated with the nonspecific cyclooxygenase inhibitor, flunixin meglumine (2.7 x 10(-5) mol/l), production of PGE2 and PGI2 was inhibited, and there was no evidence of recovery based on measurements of transepithelial resistance. Conversely, untreated ischaemic tissues or tissues treated with the specific COX-2 inhibitor etodolac (2.7 x 10(-5) mol/l) had significant elevations in PGE2 and PGI2, and significant recovery of transepithelial resistance. These studies suggest that specific COX-2 inhibitors may provide an advantageous alternative to nonspecific cyclooxygenase inhibitors in horses with colic.

Adaptive cytoprotection induced by ethanol in human intestinal cells: role of prostaglandins and calcium homeostasis

OBJECTIVE

To determine whether adaptive cytoprotection exists in human intestinal cells under in vitro conditions and what role, if any, endogenous prostaglandins or calcium may play in mediating this protective response.

SUMMARY BACKGROUND DATA

Adaptive cytoprotection can be defined as that process whereby the administration of a low concentration of a damaging agent, termed a "mild irritant," which by itself is not injurious, can attenuate gastrointestinal mucosal injury subsequently induced by the application of higher concentrations of the same or other necrotizing agents. Despite substantial investigation, the mediator or mediators of adaptive cytoprotection remain poorly understood.

METHODS

Postconfluent Caco-2 cells were used in all experiments. Cellular death was quantitated using a dual-component fluorescent assay. Changes in intracellular calcium concentration were quantitated by measuring fluorescent signal changes of the single wavelength calcium indicator (Fluo-3). Finally, prostaglandin E2 release into the media was quantitated by radioimmunoassay.

RESULTS

Pretreatment of Caco-2 cells with low concentrations of ethanol (mild irritant) significantly attenuated injury induced by higher damaging concentrations of ethanol. The protection conferred by the mild irritant was directly dependent on both the concentration of the irritant used and the duration of exposure and was abrogated when cells were pretreated with an endogenous prostaglandin inhibitor (indomethacin) or if the mild irritant was administered in calcium-free media. Cells exposed to ethanol had a significant and concentration-dependent increase in intracellular calcium concentration, an effect that was highly related to cellular injury. Pretreatment with a mild irritant significantly decreased intracellular calcium increases induced by not only ethanol but also by a calcium ionophore (A23187). Cells treated with low concentrations of ethanol demonstrated no significant elevation in prostaglandin E2 release.

CONCLUSIONS

Adaptive cytoprotection induced by ethanol exists in human colonocytes under in vitro conditions independent of mucosal blood flow, neural innervation, or circulating humoral factors. The authors' data suggest that this response does not require endogenous prostaglandin synthesis but may involve processes whereby intracellular calcium accumulation is prevented.

Intragastric distribution of nonsteroidal anti-inflammatory drug-related ulcers in patients without collagen diseases

During the long-term administration of nonsteroidal anti-inflammatory drugs (NSAIDs), approximately 3% of patients have gastric ulcers develop in each year. Although much is known about the endoscopic characteristics of NSAID-induced gastric ulcers in patients with rheumatoid arthritis (RA), it is not clear where in the stomach NSAIDs induce ulcers in patients without RA. We looked at that question. During the 1-year study period, 29 patients with gastric ulcer, who had been taking NSAIDs regularly for more than 4 weeks mainly for osteoarthritis, were identified. Seventy-five patients with gastric ulcers who had not taken NSAID also were found. The sites of gastric ulcers of these two groups were quite different. The NSAID-induced ulcers mainly were found in the gastric antrum, whereas the majority of NSAID-unrelated ulcers were in the gastric corpus. We conclude that NSAID-induced ulcers in non-RA patients mainly are formed in the gastric antrum.