Inhibition by 16, 16-dimethyl PGE2 of ethanol-induced gastric mucosal damage and leukotriene B4 and C4 formation

The effects of PGE₂ and its stable analogue, 16, 16 dimethyl PGE₂ (dmPGE₂) were investigated on ethanol-induced gastric mucosal haemorrhagic lesions and leukotriene formation in the rat. Exposure of the rat gastric mucosa to ethanol , produced a concentration-related increase in the mucosal formation of leukotriene B₄ (LTB₄) which was correlated with macroscopically-apparent haemorrhagic damage to the mucosa. Challenge with absolute ethanol likewise enhanced the mucosal formation of LTC₄ whereas the mucosal formation of 6-keto-PGF_1α was unaffected. Challenge of the rat gastric mucosa with ethanol induced a concentration-dependent increase in the formation of LTB₄ and LTC₄, but not 6-keto PGF_1α. Pretreatment with PGE₂ (200–500μg/kg p.o.) prevented the haemorrhagic mucosal damage induced by oral administration of absolute ethanol but not the increased formation of leukotrienes by the mucosa. In contrast, pretreatment with a high dose of dmPGE₂ (20μg/kg p.o.) prevented both the gastric mucosal lesions and the increase mucosal leukotriene formation. The differences in the effects of these prostaglandins may be related to the nature or degree of protection of the gastric mucosa. Thus, high doses of dmPGE₂ but not PGE₂ may protect the cells close the luminal surface of the mucosa and hence reduce the stimulation of leukotriene synthesis by these cells.     

Failure of prostaglandins E1 and E2 to alter canine gastric mucosal cyclic nucleotides

The action of prostaglandins and indomethacin on gastric mucosal cyclic nucleotide concentrations was evaluated in 18 anesthetized mongrel dogs. Prostaglandins E₁ (PGE₁) and E₂ (PGE₂) (25 μg/kg bolus, then 2 μg/kg/min) were administered both intravenously (4 experiments; femoral vein) and directly into the gastric mucosal circulation (10 experiments; superior mesenteric artery). The possible synergistic effect of pre-treatment and continuous arterial infusion of indomethacin (5 mg/kg bolus for 5 min, then 5 mg/min), a prostaglandin synthetase inhibitor, with PGE₂ was studied in 4 experiments. Antral and fundic mucosa were biopsied and measured by radioimmunoassay for cyclic nucleotides. Doses of PGE₁ and PGE₂ which inhibited histamine-stimulated canine gastric acid secretion did not significantly alter antral or fundic mucosal cyclic nucleotide concentrations. Concomitant infusion of PGE₂ with indomethacin did not potentiate the mucosal nucleotide response compared to PGE₂ alone. These studies fail to implicate cyclic nucleotides as mediators of the inhibitory acid response induced by PGE₁ or PGE₂ in intact dog stomach.     

Effects of nimesulide, a preferential cyclooxygenase-2 inhibitor, on carrageenan-induced pleurisy and stress-induced gastric lesions in rats

Intrapleural injection of carrageenan in rats increased prostaglandin E₂ (PGE₂) production and induced newly synthesized cyclooxygenase-2 (COX-2) in pleural exudate cells without affecting COX-1 levels. Nimesulide, a preferential inhibitor of COX-2, reduced pleural PGE₂ production and was almost as active as indomethacin and 10 times more active than ibuprofen. Only COX-1, and no COX-2, was detected in gastric mucosal cells, and PGE₂ concentration of gastric mucosa was significantly decreased by indomethacin and ibuprofen. The decrease in gastric PGE₂ production induced by indomethacin and ibuprofen was enhanced in stressed rats, resulting in aggravation of stress-induced gastric lesions at anti-inflammatory doses. However, nimesulide did not produce stress-induced gastric lesions even at 30 times the anti-inflammatory dose. This supports the hypothesis that inhibition of COX-1 causes unwanted side effects and inhibition of COX-2 produces anti-inflammatory effects.     

Vagal nerve and the gastric mucosal defense

An essential role for an intact vagal nerve has been proven in the development of gastric mucosal cyto- and general protection. On the other hand, chemically-induced (ethanol, HCl, indomethacin) gastric mucosal damage is enhanced after acute surgical vagotomy. The aims of this paper were to study the possible mechanisms of the vagal nerve in the development of gastric mucosal defense. The following questions were addressed: 1) effect of surgical vagotomy on the development of ethanol- (ETOH), HCl-, and indomethacin (IND)-induced gastric mucosal damage; 2) changes in the gastric mucosal defense by scavengers, prostacyclin and other compounds (small doses of atropine and cimetidine: 3) changes in the gastric mucosal vascular permeability due to chemicals; 4) effect of indomethacin in the ETOH and HCl models with and without surgical vagotomy; 5) changes in the gastric mucosal content of prostacyclin and PGE₂ in the ETOH and HCl models after surgical vagotomy; and 6) changes in the role of SH-groups in gastric mucosal defense after surgical vagotomy. It was found that: 1) the gastric mucosal damage produced by chemicals (ETOH, HCl, and indomethacin) was enhanced after surgical vagotomy; 2) the cyto- and general gastric protective effects of β-carotene, prostacyclin, and small doses of atropine and cimetidine disappeared after surgical vagotomy; 3) the vascular permeability due to chemicals (ETOH, HCl, indomethacin) significantly increased after surgical vagotomy in association with an increase in both number and severity of gastric mucosal lesions; 4) IND alone (in animals with an intact vagus) did not produce gastric mucosal lesions (in 1-h experiments), but it aggravated ETOH-induced gastric mucosal damage (both its number and severity); 5) the gastric mucosal levels of prostacyclin and PGE₂ decreased after surgical vagotomy; 6) IND application (after surgical vagotomy) decreased further the tissue levels of prostacyclin and PGE₂ in association with an increase of gastric mucosal damage; and 7) the gastric mucosal protective effects of SH-groups were abolished by surgical vagotomy.     

Acute Toxicity and Gastroprotection Studies with a Newly Synthesized Steroid

Background

Synthetic steroids, such as 9α-bromobeclomethasonedipropionate, have shown gastroprotective activity. For example, the potent glucocorticoid steroid, beclomethasone dipropionate, has been used for treatment of bowel ulcerations. The purpose of the present study was to evaluate the effect of a synthetic steroid, (20S)-22-acetoxymethyl-6β-methoxy-3α,5-dihydro-3′H-cyclopropa[3α,5]-5α-pregnane (AMDCP), on ethanol-induced gastric mucosa injuries in rats.

Methodology/Principal Finding

Rats were divided into 8 groups. The negative control and ethanol control groups were administered Tween 20 (10%v/v) orally. The reference control group, 20 mg/kg omeprazole (10% Tween 20, 5 mL/kg), was administrated orally. The experimental groups received 1, 5, 10, 15 or 20 mg/kg of the AMDCP compound (10% Tween 20, 5 mL/kg). After 60 min, Tween 20 and absolute ethanol was given orally (5 mL/kg) to the negative control group and to the rest of the groups, and the rats were sacrificed an hour later. The acidity of gastric content, gastric wall mucus and areas of mucosal lesions were assessed. In addition, histology and immunohistochemistry of the gastric wall were assessed. Prostaglandin E2 (PGE₂) and malondialdehyde (MDA) content were also measured. The ethanol control group exhibited severe mucosal lesion compared with the experimental groups with fewer mucosal lesions along with a reduction of edema and leukocyte infiltration. Immunohistochemical staining of Hsp70 and Bax proteins showed over-expression and under-expression, respectively, in the experimental groups. The experimental groups also exhibited high levels of PGE₂ as well as a reduced amount of MDA. AMDCP decreased the acidity and lipid peroxidation and increased the levels of antioxidant enzymes.

Conclusion/Significance

The current investigation evaluated the gastroprotective effects of AMDCP on ethanol-induced gastric mucosal lesions in rats. This study also suggests that AMDCP might be useful as a gastroprotective agent.     

Effects of selective cyclooxygenase-2 inhibitor and non-selective NSAIDs on Helicobacter pylori-induced gastritis in Mongolian gerbils

Background. It is still a point of controversy whether Helicobacter pylori‐infected patients are more likely to develop mucosal damage while taking NSADIs. Selective cyclooxygenase (COX‐2) inhibitors may be associated with less severe gastric mucosal damage than conventional NSAIDs, but this association is undefined in H. pylori‐induced gastritis. The aim of this study was to evaluate the effects of selective COX‐2 and nonselective NSAIDs on H. pylori‐induced gastritis. Methods. After intragastric administration of indomethacin, NS‐398 or vehicle alone, once daily for 5 days in H. pylori‐infected and uninfected Mongolian gerbils, we evaluated gastric mucosal damage, inflammatory cell infiltration and prostaglandin E₂ (PGE₂) concentration. We investigated whether H. pylori infection induced the COX‐2 expression. Results. In H. pylori‐uninfected groups, the indomethacin‐treated group showed the highest mucosal damage score and the lowest PGE₂ concentration. There was no difference in mucosal damage scores and PGE₂ concentration between NS‐398 and vehicle‐alone treated group. In H. pylori‐infected groups, there was no difference in mucosal damage scores, irrespective of the type of drugs administered. The indomethacin‐treated group showed the lowest PGE₂ concentration, similar to that of the NS‐398 and vehicle‐alone treated groups, both without H. pylori infection. Gastric neutrophil and monocyte infiltration scores were higher in H. pylori‐infected groups than in uninfected groups. However, there was no difference in these scores according to the type of drugs administered, within H. pylori‐infected or uninfected groups. COX‐2 protein expression was observed in H. pylori‐infected Mongolian gerbils but not in uninfected ones. Conclusions. Our animal study showed that H. pylori infection induced COX‐2 expression and increased prostaglandin concentration. Administration of NSAIDs decreased the prostaglandin concentration, but did not increase mucosal damage in H. pylori‐induced gastritis. Selective COX‐2 inhibitors, instead of conventional NSIADs, had no beneficial effect on preventing mucosal damage in H. pylori‐induced gastritis.     

Effect of selenium and grape seed extract on indomethacin-induced gastric ulcers in rats

Indomethacin (IND) is a non-steroid anti-inflammatory agent that is known to induce severe gastric mucosal lesions. In this study, we investigated the protective effect of selenium (SEL), grape seed extract (GSE), and both on IND-induced gastric mucosal ulcers in rats. Sprague–Dawley rats (200–250 g) were given SEL, GSE, and both by oral gavage for 28 days, and then gastric ulcers were induced by oral administration of 25 mg/kg IND. Malondialdehyde (MDA), non-enzymatic (reduced glutathione, GSH) and enzymatic (superoxide dismutase, catalase, and glutathione peroxidase) antioxidants, prostaglandin E₂ (PGE₂) in gastric mucosa, and serum tumor necrosis factor alpha (TNF-α) were measured. Moreover, gastric ulcer index and preventive index were determined. Indomethacin increased the gastric ulcer index, MDA, TNF-α, and decreased PGE₂ and non-enzymatic (GSH) and enzymatic (superoxide dismutase, catalase, and glutathione peroxidase) antioxidants. Pretreatment with SEL, GSE, and both significantly decreased the gastric ulcer index, MDA, and TNF and increased antioxidants and PGE₂. Histopathological observations confirm the gastric ulcer index and biochemical parameters. Selenium and GSE have a protective effect against IND-induced gastric ulcers through prevention of lipid peroxidation, increase of GSH, activation of radical scavenging enzymes, PGE₂ generation, and anti-inflammatory activity. Co-administration of GSE and SEL is more effective than GSE or SEL alone.     

Actions of prostacyclin (PGI2) and its product, 6-oxo-PGF1α on the rat gastric mucosa in vivo and in vitro

The effects of prostacyclin (PGI₂) and its breakdown product 6-oxo-PGF_1α on various aspects of gastric function were investigated in the rat. PGI₂ increased mucosal blood flow when infused intravenously. PGI₂ was a more potent inhibitor of gastric acid secretion in vivo than PGE₂. Like PGE₂, PGI₂ inhibited acid secretion from the rat stomach in vitro. PGI₂ had comparable activity to PGE₂ in inhibiting indomethacin-induced gastric erosions. Thus prostacyclin shares several of the activities of PGE₂, and may be involved in the regulation of gastric mucosal function.     

Effects of non-steroidal anti-inflammatory drugs on prostaglandin E2 production by cyclooxygenase-2 from endogenous and exogenous arachidonic acid in rat peritoneal macrophages stimulated with lipopolysaccharide

Lipopolysaccharide (LPS) stimulated prostaglandin E₂ (PGE₂) formation and induction of cyclooxygenase-2 (COX-2) expression without changing the levels of COX-1 protein in rat peritoneal macrophages. Non-steroidal anti-inflammatory drugs (NSAIDs) (nimesulide, indomethacin and ibuprofen) strongly inhibited LPS-stimulated PGE₂ production without any effect on COX-2 protein expression, suggesting that NSAIDs are active in inhibiting the ability of COX-2 to convert arachidonic acid (AA) endogenously released in response to LPS stimulation. Exogenous AA can be converted to PGE₂ by both COX isoforms even in LPS-stimulated macrophages. NSAIDs inhibited PGE₂ production from exogenous AA mediated by both COX-1 and COX-2. However, the two isoforms interacted differentially with different NSAIDs. Furthermore, NSAIDs were distinctly more active in inhibiting PGE₂ production from endogenous AA than that from exogenous AA. These data suggest that PGE₂ production through COX-2 from exogenous AA may not be subject to the same regulatory processes as that from endogenous AA and the two metabolic processes may be differentially sensitive to different NSAIDs.     

Prostaglandin production in cultured gastric mucosal cells: Role of cAMP on its modulation

The effect of cAMP on prostaglandin production may depend on cell types. To clarify the relationship between PG and cAMP, we examined arachidonate's effects on PG synthesis and intracellular cAMP accumulation in monolayers of rat gastric mucosal cells. These cells produced PGE₂, PGI₂ and thromboxaneA₂ (TXA₂) in amounts of 316±18, 100±7 and 30±5 pg per 10⁵ cells in 10 min, respectively, in response to 10μM arachidonic acid (AA). The production of these PG, however, leveled off subsequently. Cells initially exposed to AA responded poorly to a subsequent stimulation by AA. AA simultaneously stimulated intracellular cAMP accumulation; this stimulatory effect on cAMP production was abolished by the pretreatment with indomethacin. Nevertheless, the pretreatments with dibutyryl cAMP (0.1–5mM) did not alter the amount of subsequent AA-induced PGE₂ production. Furthermore, the preincubation with 1mM isobutyl methyl xanthine also failed to affect PGE₂ synthesis, while it increased intracellular cAMP accumulation. Our studies suggest (1) AA stimulates intracellular cAMP formation in cultured gastric mucosal cells, linked with conversion of AA to cyclooxygenase metabolites, (2) AA-induced PG production is limited in these cells, and (3) it seems, however, unlikely that intracellular cAMP modulates AA metabolism to PG.     

PGE2 secretion from organ cultured gastric mucosa: Correlation with cyclooxygenase activity and endogenous substrate release

In gastrointestinal research the in vitro release of prostaglandins from incubated or cultured biopsies is a widely used method to estimate prostaglandin synthesis. We therefore investigated the rate limiting mechanisms of PGE₂ release in organ cultured gastric mucosa of the rabbit, determining PGE₂ secretion from organ cultured mucosal biopsies by radioimmunoassay and prostaglandin synthesizing capacity by in vitro incubation of mucosal homogenate or microsomes with [¹⁴C]-arachidonic acid.Freshly taken biopsies secreted PGE₂ at an initial high rate, that decreased during the following 4 hrs of culture. This PGE₂ release was dose dependently reduced by inhibitors of the prostaglandin cyclooxygenase. 5mM acetylsalicylic acid (ASA) maximally suppressed PGE₂ secretion to 7% of controls, and the inhibition by ASA was quantitatively similar at every given culture period. PGE₂ release was markedly increased by carbenoxolone but was only slightly activated by extracellular calcium and the Ca⁺⁺-ionophore A23187. However, Ca⁺⁺/A23187 were unable to maintain PGE₂ secretion at the initial rate.PGE₂ secretion was undisturbed in calcium-free medium but was reduced to 50–60% of controls by excess EDTA. The intracellular calcium chelator 1,2-bis-(2-aminophenoxy)-ethane-N,N,N′,N′,-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) similarly inhibited PGE₂ release to 72% of controls. In contrast, PGE₂ release was unaffected by the intracellular calcium antagonist 3,4,5-trimethylene-bis(4-formylpyridinium bromide) dioxime (TMB-8), the calmodulin antagonists N-(6-aminohexyl)-1-5-chloro-1-naphthalenesulfonamide (W-7) and calmidazolium (compound R24571) or various direct inhibitors of endogenous arachidonic acid release like tetracaine, bromophenacyl bromid, neomycine or low dose quinacrine, indicating that the reduction of PGE₂ release by EDTA or BAPTA may be mediated by mechanisms different from substrate release. In contrast, an inhibition of PGE₂ secretion by quinacrine at high concentrations (≥ 0.8mM) was attributed to a direct inhibition of the prostaglandin cyclooxygenase, similar to ASA. Finally, the reduction of the prostaglandin synthesizing capacity by ASA was strongly correlated with the inhibition of PGE₂ secretion, also at low concentrations and minor degrees of inhibition.From these data we conclude, that the activity of the prostaglandin cyclooxygenase is rate limiting for PGE₂ secretion from organ cultured mucosal biopsies rather than arachidonic acid release by a phospholipase A₂. This should be considered for interpretation of studies based on prostaglandin release from cultured mucosa.     

Gastroprotective effect of epoxy clerodane diterpene isolated from Tinospora cordifolia Miers (Guduchi) on indomethacin-induced gastric ulcer in rats

The present study evaluated the gastroprotective effect of epoxy clerodane diterpene (ECD), isolated from Tinospora cordifolia on indomethacin-induced gastric ulcer in rats. Administration of indomethacin exhibits extreme levels of ulcer index (UI) and myeloperoxidase (MPO) activity. Indomethacin down regulated PGE₂, anti-inflammatory cytokines (IL-4, IL-10) and pro-angiogenic factors (VEGF and EGF). The ECD pretreatment considerably increased the levels of PGE₂, anti-inflammatory cytokines and pro-angiogenic factors. The ulcer-healing activity of ECD was inhibited by pre-administration of the specific COX-1 inhibitor (SC560) and nonspecific NOS inhibitor (l-NAME), which indicates the involvement of PGE₂ and NOS in ECD induced ulcer healing activity. These findings suggest that ECD exerts its antiulcer activity by reinforcement of defensive elements and diminishing the offensive elements.     

Comparative behavioral effects of dibutyryl cyclic AMP and prostaglandin E1 in mice

Three behavioral tests, spontaneous locomotor activity (SLMA), exploratory behavior (EB) and rotarod performance (RP), a measure of neuromuscular coordination, were used to study the interaction of PGE₁ (1 mg/kg i.p., 10 min. pretreatment) with DBcAMP (25 mg/kg i.p., 25 min. pretreatment) in mice. A dose-response relationship of PGE₁ (0.01–5.0 mg/kg) to SLMA was determined, with a significant decrease in SLMA produced by a dose of 0.1 mg/kg. Decreases in SLMA were produced by PGE₁ (79%), DBcAMP (41%) and DBcAMP-PGE₁ combination (71%). Similar decreases in EB were observed. Although no significant difference between controls and DBcAMP was observed in RP, 52% of mice tested were RP failures following PGE₁ and a 100% failure rate was induced by the combination. Mice were treated with a second injection of DBcAMP or PGE₁ or the combination 24 hr following the first injection. Behavioral activity of these mice was observed 25 min (DBcAMP) or 10 min (PGE₁) after the second dose was administered. A second injection of DBcAMP failed to decrease SLMA and EB from controls; moreover, SLMA began to return towards control levels as early as 2 hr between injections. The second injection of PGE₁ or DBcAMP+PGE₁ produced the same behavior as that produced by the first injection. On the basis of these results, the relationship of cyclic nucleotides and PGs to behavioral activity is discussed.     

Methylated analogues of prostaglandin E2 and the gastric mucosal barrier

15(R)-methyl PGE₂ methyl ester (15MPG) and 16,16-dimethyl PGE₂ methyl ester (16DMPG) were assessed for their effect on gastric mucosal permeability to Na⁺ and H⁺ in dogs prepared by antrectomy and vagally-denervated fundic pouches. 15MPG did not increase mucosal permeability to either ion when given topically (18.75 – 300 μg) or parenterally (30 μg), and did not affect permeability increases induced by topical 5mM sodium taurocholate in acid solution. 16DMPG caused significant increases in net Na⁺ gain when given topically (18.75 – 75 μg) but did not affect net H⁺ loss from the pouch lumen. Attempts to use higher doses of 16DMPG were abandoned because of bleeding from the pouch, and perforation in one animal. It is conceivable that 16DMPG could cause adverse effects on the gastric mucosal barrier if used to suppress gastric secretion therapeutically. 15MPG does not share this potentially harmful property and remains worthy of further study as an inhibitor of gastric secretion with therapeutic promise.     

Aspirin inhibits lipopolysaccharide-induced COX-2 expression and PGE2 production in porcine alveolar macrophages by modulating protein kinase C and protein tyrosine phosphatase activity

Aspirin has been demonstrated to be effective in inhibiting COX-2 and PGE₂ in Alveolar macrophages (AMs). However, the mechanisms have not been fully understood. In the present study, we found that pretreatment with aspirin inhibited LPS-induced COX-2 and PGE₂ upregulation, IκBα degradation, NFκB activation and the increase of PKC activity, but elevated LPS-induced the decrease of PTP activity. The PKC inhibitor calphostin C dramatically reduced the COX-2 mRNA and PGE₂ levels, but the PTP inhibitor peroxovanadium (POV) significantly increased the COX-2 mRNA and PGE₂ levels. Furthermore, the PTP inhibitor mitigated the inhibitory effect of aspirin on COX-2 and PGE₂ upregulation and NF-κB activation, whereas the PKC inhibitor enhanced the inhibitory effects of aspirin on the production of COX-2 and PGE₂. Our data indicate a novel mechanism by which aspirin acts as a potent anti-inflammatory agent in alveolus macrophages and ALI. [BMB Reports 2014; 47(1): 45-50]     

Diosmin Protects against Ethanol-Induced Gastric Injury in Rats: Novel Anti-Ulcer Actions

Alcohol consumption has been commonly associated with gastric mucosal lesions including gastric ulcer. Diosmin (DIO) is a natural citrus flavone with remarkable antioxidant and anti-inflammatory features that underlay its protection against cardiac, hepatic and renal injuries. However, its impact on gastric ulcer has not yet been elucidated. Thus, the current study aimed to investigate the potential protective effects of DIO against ethanol-induced gastric injury in rats. Pretreatment with DIO (100 mg/kg p.o.) attenuated the severity of ethanol gastric mucosal damage as evidenced by lowering of ulcer index (UI) scores, area of gastric lesions, histopathologic aberrations and leukocyte invasion. These actions were analogous to those exerted by the reference antiulcer sucralfate. DIO suppressed gastric inflammation by curbing of myeloperoxidase (MPO) and tumor necrosis factor-α (TNF-α) levels along with nuclear factor kappa B (NF-κB) p65 expression. It also augmented the anti-inflammatory interleukin-10 (IL-10) levels. Meanwhile, DIO halted gastric oxidative stress via inhibition of lipid peroxides with concomitant enhancement of glutathione (GSH), glutathione peroxidase (GPx) and the total antioxidant capacity (TAC). With respect to gastric mucosal apoptosis, DIO suppressed caspase-3 activity and cytochrome C (Cyt C) with enhancement of the anti-apoptotic B cell lymphoma-2 (Bcl-2) in favor of cell survival. These favorable actions were associated with upregulation of the gastric cytoprotective prostaglandin E₂ (PGE₂) and nitric oxide (NO). Together, these findings accentuate the gastroprotective actions of DIO in ethanol gastric injury which were mediated via concerted multi-pronged actions, including suppression of gastric inflammation, oxidative stress and apoptosis besides boosting of the antioxidant and the cytoprotective defenses.     

16, 16 Dimethyl prostaglandin E2 reduces histamine release from the stomach and protects the gastric mucosal barrier altered by ethanol in neutral solution

Damage to the gastric mucosal barrier results in histamine release from intramucosal stores. Previous reports have shown that 16, 16 dimethyl prostaglandin E₂ (dm PGE₂) protects the stomach from injury by various damaging agents in either acidic or neutral solution. Furthermore histamine released in response to a damaging drug in an acidic medium was reduced by dm PGE₂. Using the Heidenhain pouch dog preparation, the present study examined the action of dm PGE₂ on ethanol-induced barrier breaking and histamine release in neutral solution. Topical ethanol treatment (15% w/v) damaged the gastric mucosal barrier as evidenced by increased net fluxes of Na+ and K+ and an increase in the histamine content of the fluid irrigating the Heidenhain pouch. Intravenous injection of dm PGE₂ in the doses of 0.01, 0.10 and 1.00 μg/kg one-half hour before ethanol administration significantly reduced the appearance of Na+, K+ and histamine. It is concluded that dm PGE₂ effectively protects the canine gastric mucosa from damaging agents in neutral solution as evidenced by a reduction in the luminal appearance of Na+, K+ and histamine.     

Epidermal growth factor and prostaglandin E2 accelerate mucosal recovery from stress-induced gastric lesions via inhibition of apoptosis

The repair of damaged gastric mucosa is a complex process involving prostaglandins (PG) and mucosal growth factors such as epidermal growth factor (EGF). Recently, we postulated that the increased occurence of apoptosis in the gastric epithelium might be of pathophysiological importance in the development of stress lesions. The aim of the present study was to assess the effect of the pretreatment of rats, exposed to 3.5 h of water immersion and restraint stress (WRS), with EGF and PG (16,16 dmPGE₂) on the number of stress lesions, recovery of gastric mucosa from stress and the expression of apoptosis related genes such as caspase-3 and antiapoptotic bcl-2. Rats were divided in following groups: (1) vehicle; (2) EGF 100 μg/kg i.p.; (3) 16,16 dm-PGE₂ (5 μg/kg i.g.) and caspase-1 inhibitor (ICE-I; 100 μg/kg i.p.). One hour later, the rats were exposed to 3.5 h of WRS and then sacrificed immediately (0 h) or at 6, 12, or 24 h after WRS. The number of acute gastric lesions was determined. Gastric epithelial apoptosis was assessed by TUNEL staining. In addition, mRNA expression of caspase-3, Bcl-2 and proinflammatory cytokines (IL-1β, TNFα) was assessed by RT-PCR. PGE₂ generation in gastric mucosa and luminal EGF were determined by RIA. Exposure to WRS resulted in the development of multiple acute stress erosions (18) which almost completely healed during 24 h. The gastric blood flow was significantly reduced (70% of intact mucosa) immediately after WRS. The expression of mRNA for IL-1β and TNFα reached their peak at 12 h after stress exposure. The apoptosis rate was highest at 6 h after WRS and was accompanied by the highest caspase-3 expression. In rats pretreated with EGF or 16,16 dm-PGE₂, a significant decrease in caspase-3 mRNA and upregulation of bcl-2 mRNA as observed as compared to vehicle controls. Caspase-1 inhibitor significantly reduced the number of stress lesions. We conclude that EGF and PGE₂ accelerate healing of stress-induced lesions due to the attenuation of apoptosis via upregulation of bcl-2 in gastric mucosa. Inhibitors of apoptosis accelerate healing of stress lesions and may be potentially effective agents in the healing of damaged gastric mucosa.     

Alterations of matrix metalloproteinases,gastric mucin and prostaglandin E2 levels by pectic polysaccharide of swallow root (Decalepis hamiltonii) during ulcer healing

Gastric ulcer is a multi-step disease caused due to imbalance between mucosal defense and aggressive factors. Available anti-ulcer drugs although effective at various steps of ulcer pathogenecity, pose adverse effects. Pectic polysaccharide (SRPP) from swallow root (Decalepis hamiltonii) – previously shown to possess ulcer preventive effect against swim stress and ethanol induced gastric ulcers. In the current study, alteration of matrix metalloproteinases, gastric mucin and prostaglandin E₂ levels during polysaccharide mediated ulcer healing was determined in acetic acid induced gastric ulcer model in Wistar albino rats. Results indicated the potential ulcer healing effect of SRPP as evidenced by ∼90% reduction in ulcer index; improvement in the antioxidant defense such as increase of glutathione levels together with significant reduction in lipid and protein oxidation and protection to damaged gastric mucin. Further, histological studies substantiated the result of the recovery of mucin that was eroded during ulceration, rejuvenation of mucosal epithelium and enhancement of high molecular mass mucin as opposed to the degraded ∼55 kDa mucin that appeared only during ulcer condition. Matrix metalloproteinases (MMPs) that are involved in tissue injury was found to be modulated by SRPP treatment in addition to increased cytoprotectivity due to enhanced synthesis of PGE₂ that necessitates the active proliferation of gastric mucin cells. Further, reduction in ∼3 folds of galectin-3, an inflammatory marker suggests gastro protection against acid induced inflammation and gastric wall damages. Overall, studies show the effectiveness of SRPP in inhibiting MMPs and galectin-3 levels which were up-regulated during ulcer conditions. In addition SRPP ensured cytoprotectivity and rejuvenation of mucosal barrier via PGE₂ trigger leading to ulcer healing.