Prevention by mild irritants of gastric necrosis produced in rats by sodium taurocholate

Antioxidant, Gastroprotective, Cytotoxic Activities and UHPLC PDA-Q Orbitrap Mass Spectrometry Identification of Metabolites in Baccharis grisebachii Decoction

The decoction of the local plant Baccharis grisebachii is used as a digestive, gastroprotective, external cicatrizing agent and antiseptic in Argentine. A lyophilized decoction (BLD) from the aerial parts of this plant was evaluated regarding its anti-ulcer, antioxidant and cytotoxic activities and the bioactivities were supported by UHPLC-MS metabolome fingerprinting which revealed the presence of several small bioactive compounds. The antioxidant properties were evaluated by DPPH, TEAC, FRAP and lipoperoxidation inhibition in erythrocytes methods, and the antibacterial activity was evaluated according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. The BLD showed a moderate free radical scavenging activity in the DPPH (EC₅₀ = 106 µg/mL) and lipid peroxidation in erythrocytes assays (67%, at 250 µg/mL). However, the BLD had the highest gastroprotective effect at a dose of 750 mg/kg with a ninety-three percent inhibition of damage through a mechanism that involve NO and prostaglandins using the ethanol-induced gastric damage in a standard rat model. On the other hand, BLD does not induce cytotoxic changes on human tumor and no-tumor cell lines at the concentrations assayed. Regarding the metabolomic analysis, thirty-one compounds were detected and 30 identified based on UHPLC-OT-MS including twelve flavonoids, eleven cinnamic acid derivatives, one coumarin, one stilbene and two other different phenolic compounds. The results support that the medicinal decoction of Baccharis grisebachii is a valuable natural product with gastroprotective effects and with potential to improve human health that opens a pathway for the development of important phytomedicine products.

Investigation of Gastroduodenal Mucosal Injury in Japanese Asymptomatic Antiplatelet Drug Users

Antiplatelet drugs are widely used for the prevention of cardiovascular disease and cerebral vascular disorders. Although there have been several studies on gastroduodenal mucosal injury with gastrointestinal (GI) symptoms such as GI bleeding, in antiplatelet drug users (including low-dose aspirin (LDA)), there have been few reports on the association between antiplatelet drug use and gastroduodenal mucosal injury in asymptomatic antiplatelet drug users. This study was a cross-sectional study elucidating the association between antiplatelet drug use and gastroduodenal mucosal injury in asymptomatic antiplatelet drug users.Subjects were 186 asymptomatic Japanese antiplatelet drug users who underwent a regular health checkup. Subjects were divided into those with and without gastroduodenal mucosal injury endoscopically, and the association between gastroduodenal mucosal injury and other data in asymptomatic antiplatelet drug users was investigated.The prevalence of males and drinkers were significantly higher in subjects with gastroduodenal mucosal injury than in those without. In addition, the prevalence of proton pump inhibitor (PPI) users was significantly lower in subjects with gastroduodenal mucosal injury than in subjects without gastroduodenal mucosal injury. Logistic regression analysis showed PPI (odds ratios: 0.116; 95% confidence intervals: 0.021-0.638; P < 0.05) was a significant predictor of a decreased prevalence of gastroduodenal mucosal injury and closed-type (C-type) atrophy (3.172; 1.322-7.609; P < 0.01) was a significant predictor of an increased prevalence of severe gastroduodenal mucosal injury in asymptomatic antiplatelet drug users.Gender and lifestyle, such as drinking, may have an impact on risk of gastroduodenal mucosal injury in asymptomatic subjects taking antiplatelet drugs. Although PPI is a significant predictor of a decreased prevalence of gastroduodenal mucosal injury, including in asymptomatic antiplatelet drug users, status of gastric atrophy should also be considered against severe gastroduodenal mucosal injury.

"Gastric cytoprotection" is still relevant

Although Andre Robert's historic article on "gastric cytoprotection" in 1979 introduced this new name and concept, gastroprotective drugs (e.g. sofalcone, sucralfate), which prevent and/or accelerate healing of gastric ulcers without inhibiting acid secretion, were known in Japan before or around that time. But since Robert's studies were solely focused on prostaglandins (PG), they became the center of gastrointestinal research for more than 30 years. As endogenous products, PG were implicated in mediating the gastroprotective effect of other drugs such as sofalcone and sucralfate, despite that the cyclooxygenase inhibitor indomethacin diminished but never abolished gastroprotection by other drugs. Another group of endogenous substances, that is, sulfhydryls (SH), investigated in parallel with PG, also seem to play a mechanistic role in gastroprotection, especially since SH alkylators like N-ethylmaleimide counteract virtually any form of gastroprotection. In Robert's terms of "prevention of chemically induced acute mucosal lesions," so far no single mechanism could explain the beneficial effects of diverse protective agents, but I argue that these two endogenous substances (i.e. PG, SH), in addition to histamine, are the main mechanistic mediators of acute gastroprotection: PG and histamine, because as mediators of acute inflammation, they increase vascular permeability (VP), and SH scavenge free radicals. This is contrary to the search for a single mechanism of action, long focused on enhanced secretion of mucus and/or bicarbonate that may contribute but cannot explain all forms of gastroprotection. Nevertheless, based on research work of the last 30 years, in part from our lab, a new mechanistic explanation of gastroprotection may be formulated: it's a complex but orderly and evolution-based physiologic response of the gastric mucosa under pathologic conditions. Namely, one of the first physiologic defense responses of any organ is inflammation that starts with rapid vascular changes (e.g. increased VP and blood flow), followed by cellular events (e.g. infiltration by acute and chronic inflammatory cells). Thus, PG and histamine, by increasing VP create a perivascular edema that dilutes and delays toxic agents reaching the subepithelial capillaries. Otherwise, damaging chemicals may induce severe early vascular injury resulting in blood flow stasis, hypoxia, and necrosis of surrounding epithelial and mesenchymal cells. In this complex response, increased mucus and/or bicarbonate secretion seem to cause luminal dilution of gastrotoxic chemicals that is further reinforced by a perivascular, histodilutional component. This mechanistic explanation would encompass the protective actions of diverse agents as PG, small doses of histamine, motility stimulants, and dilute irritants (i.e. "adaptive cytoprotection"). Thus, although markedly increased VP is pathologic, slight increase in VP seems to be protective, that is, a key element in the complex pathophysiologic response during acute gastroprotection. Over the years, "gastroprotection" was also applied to accelerated healing of chronic gastroduodenal ulcers without reduction of acid secretion. The likely main mechanism here is the binding of angiogenic growth factors (e.g. basic fibroblast growth factor, vascular endothelial growth factor) to the heparin-like structures of sucralfate and sofalcone. Thus, despite intensive research of the last 30 years, gastroprotection is incompletely understood, and we are still far away from effectively treating Helicobacter pylori-negative ulcers and preventing nonsteroidal anti-inflammatory drugs-caused erosions and ulcers in the upper and lower gastrointestinal tract; hence "gastric cytoprotection" research is still relevant.

Moderate ethanol ingestion and cardiovascular protection: from epidemiologic associations to cellular mechanisms

While ethanol intake at high levels (3-4 or more drinks), either in acute (occasional binge drinking) or chronic (daily) settings, increases the risk for myocardial infarction and stroke, an inverse relationship between regular consumption of alcoholic beverages at light to moderate levels (1-2 drinks per day) and cardiovascular risk has been consistently noted in a large number of epidemiologic studies. Although initially attributed to polyphenolic antioxidants in red wine, subsequent work has established that the ethanol component contributes to the beneficial effects associated with moderate intake of alcoholic beverages regardless of type (red versus white wine, beer, spirits). Concerns have been raised with regard to interpretation of epidemiologic evidence for this association including heterogeneity of the reference groups examined in many studies, different lifestyles of moderate drinkers versus abstainers, and favorable risk profiles in moderate drinkers. However, better controlled epidemiologic studies and especially work conducted in animal models and cell culture systems have substantiated this association and clearly established a cause and effect relationship between alcohol consumption and reductions in tissue injury induced by ischemia/reperfusion (I/R), respectively. The aims of this review are to summarize the epidemiologic evidence supporting the effectiveness of ethanol ingestion in reducing the likelihood of adverse cardiovascular events such as myocardial infarction and ischemic stroke, even in patients with co-existing risk factors, to discuss the ideal quantities, drinking patterns, and types of alcoholic beverages that confer protective effects in the cardiovascular system, and to review the findings of recent experimental studies directed at uncovering the mechanisms that underlie the cardiovascular protective effects of antecedent ethanol ingestion. Mechanistic interrogation of the signaling pathways invoked by antecedent ethanol ingestion may point the way towards development of new therapeutic approaches that mimic the powerful protective effects of socially relevant alcohol intake to limit I/R injury, but minimize the negative psychosocial impact and pathologic outcomes that also accompany consumption of ethanol.

Effect of acid secretion blockade on acute gastric mucosal lesions induced by Tityus serrulatus scorpion toxin in anaesthetized rats

Scorpion venom (TX) promotes gastric acid and pepsin secretion leading to acute gastric mucosal lesions (AGML), when injected in animals. The goal of the present study was to observe the effects of acid gastric secretion blockers over the incidence of TX-induced AGML in vivo. To verify this model, we used male albino rats, fasted 18-20 h (n=122) and anaesthetized with urethane (1.4 g/kg, i.p.). Their trachea and left femoral vein were both cannulated; the first to avoid airway obstructions during scorpion intoxication and the second for administration of saline, TX and acid blockers. Following the surgical procedure, the animals were divided in 10 groups of at least 10 animals each. Control groups were injected with NaCl 0.9% 1 ml/kg (n=10) or TX 375 microg/kg (n=32). Test groups (n=10, each) received atropine 5 mg/kg, cimetidine 10mg/kg, ranitidine 2.5mg/kg, ranitidine 5mg/kg, omeprazol 1 mg/kg, omeprazol 4 mg/kg, octreotide 80 and octreotide 100 microg/kg 10 min before the TX was injected. After 1h of intoxication, the stomach was resected for macroscopic study and the gastric secretion was collected for volume, pH and acid output assessment. We observed that all blockers were able to completely or partially prevent the TX-induced acid secretion as well as the AGML (p<0.05). Our data suggest the TX-induced AGML can be prevented by different class of acid blockers injected before the intoxication.

Case-control study on the association of upper gastrointestinal bleeding and nonsteroidal anti-inflammatory drugs in Japan

OBJECTIVE

Studies in Western populations have shown the association of nonsteroidal anti-inflammatory drugs (NSAIDs) and upper gastrointestinal bleeding (UGIB). The role of Helicobacter pylori infection in NSAIDs-related UGIB remains to be studied. We conducted a case-control study in Japan to investigate these related topics.

METHODS

Cases of UGIB due to duodenal or gastric ulcer, or gastritis were identified in 14 study hospitals in various areas of Japan. For each case, two controls were identified from population registries in the same district. Information on drugs and other risk factors was obtained from 175 cases and 347 controls by telephone interviews. Anti-H. pylori antibody in the urine was measured in a single laboratory for all the cases and 225 controls.

RESULTS

The odds ratio (OR) of UGIB was 5.5 for aspirin and 6.1 for other NSAIDs (NANSAIDs) (p<0.01). The OR for regular use was higher than for occasional use both for aspirin (7.7 vs 2.0) and NANSAIDs (7.3 vs 4.1). Loxoprofen (5.9), frequently used in Japan as a safe 'prodrug', was significantly associated with UGIB. The odds ratio for H. pylori infection was 4.9 and the relative excess risk due to the interaction between H. pylori and the use of NSAID was 1.2 (95% CI: -5.8-8.1).

CONCLUSION

NSAIDs including loxoprofen increase the risk of UGIB in Japan as in Western countries, with a similar magnitude of association. There was no evidence of biological interaction between NSAIDs and H. pylori infection.

Gastroprotective and ulcer healing effect of ferruginol in mice and rats: assessment of its mechanism of action using in vitro models

The gastroprotective activity of the diterpene ferruginol isolated from Prumnopitys andina wood and bark was determined on HCl/EtOH-induced gastric lesions in mice. The effect of the compound on the healing of subacute gastric lesions in rats was also studied. The mode of action of the diterpene was assessed using human gastric epithelial cells (AGS) and MRC-5 fibroblasts. The effect of ferruginol on the prostaglandin E2 content, protection against sodium taurocholate induced-damage and reduced glutathione content was evaluated on AGS cells as well as on the growth of AGS and fibroblast cultures. The free radical scavenging effect of ferruginol was assessed by the 1,1-diphenyl-2-picryl-hydrazil radical and superoxide anion assays. The effect of ferruginol on human erythrocyte membrane lipoperoxidation was determined. The cytotoxicity of the compound was assessed by means of the neutral red uptake. At 25 mg/kg, ferruginol inhibited the appearance of gastric lesions by 60% showing similar effects than lansoprazole at 20 mg/kg. Additionally, the compound displayed a significant ulcer healing activity in rats at 25 and 50 mg/kg with curative ratios of 36.0% and 92.5%, respectively, while the reference compound ranitidine at 50 mg/kg showed a curative ratio of 79.6%. At 6 and 12 microM, ferruginol increased significantly the prostaglandin E2 content. A strong inhibition of lipoperoxidation was found (IC50: 1.4 microM), but no effect was observed on the sodium taurocholate induced-damage or reduced glutathione content. Ferruginol stimulated cell proliferation at 1-2 microM in AGS cells and at 4-8 microM in fibroblasts, with cytotoxicities (IC50) of 24 and 26 microM, respectively. Our results support that ferruginol acts as gastroprotective increasing the PGs content, protecting the cells against lipid peroxidation and improving the gastric ulcer healing by a stimulating effect on the cell proliferation. These findings encourage further pharmacological studies of ferruginol as a potential new anti-ulcerogenic drug.

Effect of Commiphora opobalsamum (L.) Engl. (Balessan) on experimental gastric ulcers and secretion in rats

The ulcer protective potential of an ethanol extract of Commiphora opobalsamum (L.) Engl. (Burseraceae) 'Balessan' was assessed against different acute gastric ulcer models in rats induced by necrotizing agents (80% ethanol, 0.2M NaOH and 25% NaCl), hypothermic restraint stress, pyloric ligation (Shay) and indomethacin. Balessan, 250 and 500 mg/kg administered orally (intraperitoneally in Shay rat model) showed a dose-dependent ulcer protective effects in all the above ulcer models. Besides, the extract offered protection against ethanol-induced depletion of stomach wall mucus and reduction in nonprotein sulfhydryl (NP-SH) concentration. Ethanol treatment also caused histopathological lesions of the stomach wall. Pretreatment with Balessan extract provided a complete protection of gastric mucosa through supporting both the offensive and defensive factors. Balessan extract was also showed a large margin of safety without any apparent adverse effects in rats.

Mild irritant prevents ethanol-induced gastric mucosal microcirculatory disturbances through actions of calcitonin gene-related peptide and PGI2 in rats

Pretreatment with a mild irritant such as 1 M NaCl prevented ethanol-induced mucosal injury, which was abolished by indomethacin, suggesting involvement of endogenous PGs. With the use of intravital microscopy, we investigated the mechanism in microcirculation whereby a mild irritant prevents ethanol-induced mucosal injury. Microcirculation of the basal part of gastric mucosa in anesthetized rats was observed through a window with transillumination. Diameters of arterioles, collecting venules, and venules were measured with an electric microscaler. One molar NaCl alone caused dilation of arterioles and constrictions of collecting venules and venules, which were inhibited by indomethacin. Ethanol (50%) applied to mucosa constricted collecting venules and venules but dilated arterioles. Constriction of collecting venules resulted in mucosal congestion. Pretreatment with 1 M NaCl inhibited ethanol-induced constrictions of collecting venules and venules, and administration of indomethacin or a calcitonin gene-related peptide (CGRP) antagonist, CGRP-(8-37), abolished elimination of constrictions. Topical application (1 nM-10 microM) of PGE2 or beraprost sodium (a PGI2 analog) to microvasculature markedly and dose-dependently dilated arterioles, whereas that of PGE2, but not beraprost, slightly constricted collecting venules. Pretreatment of microvasculature with a nonvasoactive concentration of PGE2 (100 nM) or beraprost (1 nM) completely inhibited ethanol-induced constriction of collecting venules. The inhibitory effect of beraprost but not of PGE2 was abolished by CGRP-(8-37). Present results suggest that the mechanism whereby 1 M NaCl prevents ethanol-induced injury is elimination of constrictions of collecting venules and venules by CGRP whose release may be enhanced by PGI2 but not by PGE2.

Gastroprotective effects of phenylpropanoids from the rhizomes of Alpinia galanga in rats: structural requirements and mode of action

The effects of 1'S-1'-acetoxychavicol acetate and related phenylpropanoids isolated from the rhizomes of Alpinia galanga on ethanol-induced gastric lesions in rats were examined. Among them, 1'S-1'-acetoxychavicol acetate and 1'S-1'-acetoxyeugenol acetate markedly inhibited the ethanol-induced gastric mucosal lesions (ED(50)=0.61 and ca. 0.90 mg/kg). In addition, 1'S-1'-acetoxychavicol acetate inhibited the lesions induced by 0.6 M HCl (ED(50)=0.73 mg/kg) and aspirin (ED(50)=0.69 mg/kg) but it did not show a significant effect on indomethacin-induced gastric lesions and acid output in pylorus-ligated rats at doses of 0.5-5.0 mg/kg. From the gastroprotective effects of various related compounds, the 1'-acetoxyl group of 1'S-1'-acetoxychavicol acetate and 1'S-1'-acetoxyeugenol acetate was found to be essential for their strong activity. With regard to the mode of action, the gastroprotective effects of 1'S-1'-acetoxychavicol acetate were attenuated by pretreatment with indomethacin and N-ethylmaleimide, and 1'S-1'-acetoxychavicol acetate significantly increased the glutathione levels of gastric mucosa in rats. These findings suggest that endogenous prostaglandins and sulfhydryl compounds are involved in the protective effect of 1'S-1'-acetoxychavicol acetate.

Protective effects of polygodial on gastric mucosal lesions induced by necrotizing agents in rats and the possible mechanisms of action

The effects of polygodial isolated from the leaves of Tasmannia lanceolata on necrotizing agents-induced gastric lesions in rats were compared with capsaicin. Polygodial markedly inhibited the gastric mucosal lesions induced by several necrotizing agents, such as ethanol (ED(50)=0.029 mg/kg, p.o.), 0.6 M HCl (ED(50)=0.26 mg/kg, p.o.), and aspirin (ED(50)=0.38 mg/kg, p.o.), and partly inhibited the gastric mucosal lesions induced by indomethacin, but showed no significant effect on acid output in pylorus-ligated rats at doses of 0.05-0.5 mg/kg. The gastroprotection of polygodial was attenuated by pretreatment with indomethacin (10 mg/kg, s.c.), N(G)-nitro-L-arginine methyl ester (70 mg/kg, i.p.), N-ethylmaleimide (10 mg/kg, s.c.) and ruthenium red (3.5 mg/kg, s.c.). Polygodial (0.2 mg/kg, p.o.) increased the amount of reduced glutathione in gastric mucosa of ethanol-treated group. These results suggested that endogenous prostaglandins, nitric oxide, sulfhydryl compounds and vanilloid receptor-mediated effects are involved in the protective effect of polygodial.

Protective effects of steroid saponins from Paris polyphylla var. yunnanensis on ethanol- or indomethacin-induced gastric mucosal lesions in rats: structural requirement for activity and mode of action

The methanolic extract from the rhizomes of Paris polyphylla SM. var. yunnanensis (FR.) H-M. was found to potently inhibit ethanol-induced gastric lesions in rats. Through bioassay-guided separation, four known spirostanol-type steroid saponins, pennogenin 3-O-alpha-L-rhamnopyranosyl(1-->2)-[alpha-L-arabinofuranosyl(1-->4)]-beta-D-glucopyranoside (1), pennogenin 3-O-alpha-L-rhamnopyranosyl(1-->4)-alpha-L-rhamnopyranosyl(1-->4)-[alpha-L-rhamnopyranosyl(1-->2)]-beta-D-glucopyranoside (2), diosgenin 3-O-alpha-L-rhamnopyranosyl(1-->2)-[alpha-L-arabinofuranosyl(1-->4)]-beta-D-glucopyranoside (3), and diosgenin 3-O-alpha-L-rhamnopyranosyl(1-->4)-alpha-L-rhamnopyranosyl(1-->4)-[alpha-L-rhamnopyranosyl(1-->2)]-beta-D-glucopyranoside (4), and a new furostanol-type steroid saponin, parisaponin I (5), together with two known furostanol-type steroid saponins, trigofoenoside A (6) and protogracillin (7), were isolated from the active fraction. Compounds 1-4 (1.25-10 mg/kg, po) strongly inhibited gastric lesions induced by ethanol and indomethacin. With regard to structural requirement of steroid saponins, the 3-O-glycoside moiety and spirostanol structure were found to be essential for the activity and the 17-hydroxyl group in the aglycon part enhanced the protective effects against ethanol-induced gastric lesions. The protective effects of 1 and 3 against ethanol-induced gastric lesions were attenuated by pretreatment with indomethacin and N-ethylmaleimide. Compounds 1 and 3 weakly inhibited acid secretions in pylorus-ligated rats. These findings suggested that endogenous prostaglandins and sulfhydryl compounds were involved in the protective activity.

Gastroprotective activity of solidagenone on experimentally-induced gastric lesions in rats

The gastroprotective effect of the labdane diterpene solidagenone was assessed on gastric ulcer in rats. The effect of a single oral dose of the compound was evaluated at 50, 100 and 200 mg kg(-1) in the following test systems: pylorus ligature (Shay), aspirin- and ethanol-induced gastric ulcers. In pylorus-ligated rats (Shay model), the ulcerative index decreased by 37% with solidagenone pre-treatment at the three assayed doses. The effect of a single oral dose of 50 mg kg(-1) solidagenone was comparable with ranitidine at the same concentration and similar to higher doses of the compound. A significant effect (P < 0.001) at 100 and 200 mg kg(-1) was observed in the aspirin-induced ulcer model. At both doses, reduction in the number of lesions was approximately 50% compared with controls. The effect was comparable with the reference compound ranitidine (50 mg kg(-1)). With the ethanol-induced gastric ulcers, the effect of solidagenone at 100 and 200 mg kg(-1) was similar to a single oral dose of 20 mg kg(-1) omeprazole with a 50% reduction of the mean number of lesions compared with controls. In acute toxicity tests on mice, intraperitoneal administration of solidagenone showed no toxicity at doses up to 600 mg kg(-1). This is the first report on the gastroprotective activity of a labdane diterpene.

Protective effects of polygodial and related compounds on ethanol-induced gastric mucosal lesions in rats: structural requirements and mode of action

The methanolic extract from the leaves of Tasmannia lanceolata was found to potently inhibit ethanol-induced gastric lesions in rats. Through bioassay-guided separation, three known sesquiterpenes, polygodial, polygodial 12 alpha-acetal, and polygodial 12 beta-acetal, and a new sesquiterpene, methyl isodrimeninol, were isolated as the active constituents. Among them, polygodial showed very potent gastroprotective effects (ED(50)=0.028 mg/kg, po). From the gastroprotective effects of various reduction and oxidation derivatives of polygodial, the dialdehyde or diacetal structure was found to be essential for the strong activity. Since the gastroprotection of polygodial was attenuated by pretreatment with indomethacin, N-ethylmaleimide, N(G)-nitro-L-arginine methyl ester and ruthenium red, endogenous prostaglandins, sulfhydryl compounds, nitric oxide and vanilloid receptors may be involved in the protective activity.

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.

Adaptive cytoprotection mediated by prostaglandin I(2) is attributable to sensitization of CRGP-containing sensory nerves

BACKGROUND & AIMS

The phenomenon by which the gastric mucosa is protected in response to mild irritants has been called adaptive cytoprotection, a mechanism believed to be related to production of endogenous prostaglandins (PGs). We tested whether PGs generated by mild irritant prevent injury through the release of calcitonin gene-related peptide (CGRP) from the sensory nerves using prostanoid receptor-knockout mice.

METHODS

The stomach was doubly cannulated and perfused with 1 mol/L NaCl or 50% ethanol. CGRP levels in the perfusate were determined by enzyme immunoassay, and the injured area was estimated at the end of perfusion.

RESULTS

Preperfusion with mildly hypertonic saline (1 mol/L NaCl) increased generation of gastric PGE(2) and PGI(2) and reduced ethanol-induced mucosal damage. Exposure of ethanol after 1 mol/L NaCl increased intragastric CGRP levels from 166 +/- 27 to 713 +/- 55 pg/2 min (n = 4, P < 0.05), and the protective action of 1 mol/L NaCl was inhibited by indomethacin treatment. CGRP antagonist blocked 1 mol/L NaCl-induced protective effect. Intragastric perfusion of 50% ethanol after administration of PGI(2), but not of PGE(2), increased CGRP levels. Application of 1 mol/L NaCl to IP receptor-knockout mice (IP(-/-)) did not elicit the protective effects seen in the wild-type on ethanol-induced gastric mucosal lesions. Protective effect of 1 mol/L NaCl was observed in EP3 receptor-knockout mice (EP3(-/-)). CGRP level during ethanol perfusion was not increased in IP(-/-) but was increased in EP3(-/-) and wild-type counterparts after preperfusion of 1 mol/L NaCl.

CONCLUSIONS

These results indicate that the endogenous PGI(2) generated by 1 mol/L NaCl may have a protective role in gastric mucosal injury through enhancement of CGRP release from gastric mucosa. This mechanism may explain the adaptive cytoprotection observed after treatment with mild irritants.

Roles of capsaicin-sensitive sensory nerves, endogenous nitric oxide, sulfhydryls, and prostaglandins in gastroprotection by momordin Ic, an oleanolic acid oligoglycoside, on ethanol-induced gastric mucosal lesions in rats

The roles of capsaicin-sensitive sensory nerves (CPSN), endogenous nitric oxide (NO), sulfhydryls (SHs), prostaglandins (PGs) in the gastroprotection by momordin Ic, an oleanolic acid oligoglycoside isolated from the fruit of Kochia scoparia (L.) SCHRAD., on ethanol-induced gastric mucosal lesions were investigated in rats. Momordin Ic (10 mg/kg, p.o.) potentially inhibited ethanol-induced gastric mucosal lesions. The effect of momordin Ic was markedly attenuated by the pretreatment with capsaicin (125 mg/kg in total, s.c., an ablater of CPSN), N(G)-nitro-L-arginine methyl ester (L-NAME, 70 mg/kg, i.p., an inhibitor of NO synthase), N-ethylmaleimide (NEM, 10 mg/kg, s.c., a blocker of SHs), or indomethacin (10 mg/kg, s.c., an inhibitor of PGs biosynthesis). The attenuation of L-NAME was abolished by L-arginine (300 mg/kg, i.v., a substrate of NO synthase), but not by D-arginine (300 mg/kg, i.v., the enatiomer of L-arginine). The effect of the combination of capsaicin with indomethacin, NEM, or L-NAME was not more potent than that of capsaicin alone. The combination of indomethacin and NEM, indomethacin and L-NAME, or indomethacin and NEM and L-NAME increased the attenuation of each alone. These results suggest that CPSN play an important role in the gastroprotection by momordin Ic on ethanol-induced gastric mucosal lesions, and endogenous PGs, NO, and SHs interactively participate, in rats.

Activation of VEGF and Ras genes in gastric mucosa during angiogenic response to ethanol injury

Our previous studies demonstrated that ethanol injury triggers the angiogenic response in gastric mucosa bordering necrosis. The present study was aimed to determine whether vascular endothelial growth factor (VEGF) (a potent angiogenic peptide selectively acting on endothelial cells) and Ras (a mediator of cell proliferation and a putative regulator of VEGF expression) are involved in gastric angiogenesis after ethanol injury. We studied the angiogenic response and expression of VEGF and Ras in gastric mucosa after ethanol injury. Ethanol damage triggered 1) angiogenesis in the gastric mucosa bordering necrosis, 2) significant increases in VEGF mRNA and protein expression, and 3) significant increases in the expression of Ki-ras mRNA and Ras proteins. Neutralizing anti-VEGF antibody significantly reduced (by greater than threefold) the angiogenic response to ethanol-induced injury. Moreover, mevastatin, an inhibitor of Ras activation, completely blocked the induction of VEGF expression in cultured primary endothelial cells. Because, in other tissues, VEGF is one of the most potent angiogenic factors and VEGF expression is dependent on Ras, our data indicate that Ras and VEGF are involved in gastric mucosal angiogenesis after ethanol injury.

Gastroprotections of escins Ia, Ib, IIa, and IIb on ethanol-induced gastric mucosal lesions in rats

Effects of escins Ia, Ib, IIa, and IIb isolated from horse chestnuts on ethanol-induced gastric mucosal lesions and the roles of capsaicin-sensitive afferent neurons, endogenous nitric oxide (NO), sulfhydryls, prostaglandins, as well as gastric secretion and the sympathetic nervous system, were investigated in rats. Test samples were given orally to fasted rats 1 h before ethanol (1.5 ml/rat, p.o.) treatment or ligation of the pylorus. Escins Ia-IIb (10-50 mg/kg) potently inhibited ethanol-induced gastric mucosal lesions, whereas desacylescins I and II (50 mg/kg) showed no such effect. These active saponins (10 and 20 mg/kg) did not decrease the gastric secretion. The gastroprotections of escins Ia-IIb were attenuated by the pretreatment with capsaicin, N(G)-nitro-L-arginine methyl ester, and indomethacin, but not by N-ethylmaleimide. The effects of escins Ia-IIb were also attenuated in streptozotocin-induced diabetic rats, in which the activity of the sympathetic nervous system was abnormal. These results suggest that the gastroprotections of escins Ia-IIb on ethanol-induced gastric mucosal lesions are acid-independent, whereas endogenous prostaglandins, NO, capsaicin-sensitive afferent neurons, and the sympathetic nervous system participate.

Indomethacin increases susceptibility to injury in human gastric cells independent of PG synthesis inhibition

Indomethacin and other nonsteroidal anti-inflammatory drugs are commonly used to indirectly deduce the possible role of PGs in a process being studied. The objective of this study was to determine if indomethacin, at concentrations comparable to plasma and tissue levels obtained in humans taking therapeutic doses, predisposes human gastric cells to injury through inhibition of PGs or acts through an alternate mechanism. The role of intracellular Ca2+ in this damaging process was also assessed. Indomethacin pretreatment, although by itself nondamaging, was associated with elevated intracellular Ca2+ concentrations and an increased cellular permeability, an effect that was dependent on extracellular Ca2+. Furthermore, indomethacin pretreatment significantly predisposed AGS cells to injury induced by two dissimilar agents (deoxycholate and A-23187), both of which are associated with intracellular Ca2+ accumulation. The addition of exogenous PGs did not reverse the predisposition to injury induced by indomethacin. The observed effects of indomethacin were dependent on concentration and not on ability to inhibit PG synthesis. Similar effects were not observed with equipotent concentrations of ibuprofen or aspirin. Finally, the exacerbation of deoxycholate-induced injury induced by indomethacin was not observed when extracellular Ca2+ was removed. Indomethacin, by disturbing intracellular Ca2+ homeostasis, predisposes human gastric cells to injury through mechanisms independent of PG synthesis. The current study suggests that data resulting from studies employing only indomethacin as a PG synthesis inhibitor should be interpreted with caution.

Role of calcium in adaptive cytoprotection and cell injury induced by deoxycholate in human gastric cells

We have developed an in vitro model of adaptive cytoprotection induced by deoxycholate (DC) in human gastric cells and have shown that pretreatment with a low concentration of DC (mild irritant, 50 microM) significantly attenuates injury induced by a damaging concentration of DC (250 microM). This study was undertaken to assess the effect of the mild irritant on changes in intracellular Ca2+ and to determine if these perturbations account for its protective action. Protection conferred by the mild irritant was lost when any of its effects on intracellular Ca2+ were prevented: internal Ca2+ store release via phospholipase C and inositol 1,4, 5-trisphosphate sustained Ca2+ influx through store-operated Ca2+ channels or eventual Ca2+ efflux. We also investigated the relationship between Ca2+ accumulation and cellular injury induced by damaging concentrations of DC. In cells exposed to high concentrations of DC, sustained Ca2+ accumulation as a result of extracellular Ca2+ influx, but not transient changes in intracellular Ca2+ content, appeared to precede and induce cellular injury. We propose that the mild irritant disrupts normal Ca2+ homeostasis and that this perturbation elicits a cellular response (involving active Ca2+ efflux) that subsequently provides a protective action by limiting the magnitude of intracellular Ca2+ accumulation.

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.

Bosentan, a novel synthetic mixed-type endothelin receptor antagonist, attenuates acute gastric mucosal lesions induced by indomethacin and HCl in the rat: role of endogenous endothelin-1

Endothelin-1 has been reported to be responsible for gastric mucosal damage in various experimental models. We evaluated the role of endogenous endothelin-1 in the pathogenesis of gastric mucosal damage induced by indomethacin and HCl in the rat. Rats were given indomethacin (25 mg/kg) subcutaneously, and 15 min later, 0.2N HCl intragastrically. Gastric mucosal damage, gastric endogenous endothelin-1, and gastric mucosal hemodynamics were measured. The effects of bosentan, a mixed endothelin receptor antagonist, on gastric mucosal integrity and hemodynamics were assessed. Gastric endogenous endothelin-1 was significantly elevated at 20 min, gastric mucosal blood flow began to decrease significantly at 25 min, and gastric damage occupied 52.2% of the total glandular mucosa at 135 min after injection of indomethacin. Intragastric pretreatment with bosentan (5, 10, 30, and 60 mg/kg) significantly attenuated gastric damage, to 26.1%, 7.7%, 3.6%, and 1.6%, respectively, of the total glandular mucosa. Bosentan (60 mg/kg) prevented the initial decrease of blood flow and, even at 135 min, improved blood flow and hemoglobin oxygen saturation significantly. We suggest that indomethacin-induced endogenous endothelin-1 diminishes gastric mucosal blood flow and tissue oxygenation and ultimately causes gastric damage. Endogenous endothelin-1 may play an important role in the pathogenesis of the acute gastric mucosal lesions induced by indomethacin and HCl.

Inhibition of MNNG-induced gastroduodenal carcinoma in rats by synchronous application of wine or 11% ethanol

There are divergent opinions on the effect of ethanol in the carcinogenesis of gastroduodenal tumors. The effect of the synchronous application of 11% ethanol or wine (11% ethanol) and N-methyl-N'-nitro-N-nitrosoguanidine (100 micrograms/ml, MNNG) in a drinking solution on the incidence of gastroduodenal tumors was evaluated. Sixty outbred male Wistar rats were distributed among three groups. The animals drank MNNG and ethanol or wine for six months and consumed the same quantity of MNNG. Then they consumed a normal diet until the 13th month, when the experiment was terminated. The stomach and duodenum were examined histologically. In the stomach, 15 tumors (2 squamous paillomas, 4 squamous carcinomas, 1 sarcoma, and 8 adenocarcinomas) and 4 cases of dysplasia were found; in the duodenum, there were four cases of adenocarcinoma. There were 6 cases of multiple tumors. Incidence of forestomach tumors did not differ among the groups, whereas the incidence of glandular stomach carcinoma and duodenal carcinoma was significantly lower in the groups treated with 11% ethanol or wine than in the control group. MNNG was not inactivated by ethanol in the drinking solutions. We concluded that the inhibitory effect on gastroduodenal carcinogenesis is the result of 11% ethanol ingestion and its protective action on the mucosa and not of the wine's nonethanol components.

The importance of gastric emptying and mucosal folds in the adaptive cytoprotection of mild irritants in rats

This study examines the involvement of gastric emptying and mucosal folds in the adaptive cytoprotection of different mild irritants against 100% ethanol-induced gastric mucosal damage. Pre-exposure to either 20% ethanol, 5% NaCl or 0.3M HCl significantly reduced the gastric mucosal damage caused by 100% ethanol in rats. Administration of either one of the three mild irritants increased the basal gastric residual volume and decreased the area occupied by gastric mucosal folds, but only 20% ethanol reduced the gastric emptying rate. Indomethacin (5 mg/kg, s.c.) pretreatment did not affect ethanol ulceration and gastric emptying rate when given by itself, but reversed the flattening of mucosal folds produced by the three mild irritants, and abolished the protective effect of 20% ethanol. These results suggest that the gastric adaptive cytoprotection induced by the three mild irritants acts through luminal dilution of the noxious agent, possibly caused by gastric retention. The reduction of mucosal folds could also contribute to the anti-lesion action of 20% ethanol. It is therefore suggested that the protective actions of the three mild irritants act through different mechanisms.

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

In cultured gastric mucosal cells, we investigated whether: (1) adaptive cytoprotection was associated with stimulation of endogenous prostaglandin synthesis; (2) prostaglandins given exogenously were cytoprotective against ethanol-induced gastric mucosal cell damage; and (3) a relationship existed between cytoprotection and mucus release. Cytolysis was quantified by measuring 51Cr release from prelabeled cells. Mucus release was determined by measurement of [3H]glucosamine release. Concentrations of ethanol > 12% caused cell damage and increased 51Cr release dose dependently. Pretreatment with low concentrations of ethanol (0.5-1.5%) decreased ethanol-induced 51Cr release, but also decreased prostaglandin E2 synthesis. Prostaglandin E2 and 16,16-dimethyl prostaglandin E2 given exogenously were cytoprotective against ethanol-induced gastric mucosal cell damage. Treatment with low concentrations of ethanol (1.5%) increased mucus release from cultured gastric mucosal cells. However, prostaglandin E2 and 16,16-dimethyl prostaglandin E2 did not affect mucus release. We conclude that in cultured gastric mucus-producing cells: (1) adaptive cytoprotection occurs without stimulation of endogenous prostaglandin synthesis but with increase in mucus release; and (2) exogenous prostaglandins are cytoprotective against ethanol-induced gastric mucosal cell damage without stimulating mucus release in vitro. We postulate that adaptive cytoprotection in cultured gastric mucus-producing cells is not mediated by prostaglandin, but by mucus released in response to a mild irritant.

Gastric mucosal high-energy phosphate metabolism. Influence of ethanol and PGE2

This study investigated potential alterations in gastric mucosal energy metabolism following exposure to the damaging agent 50% ethanol (50% EtOH) alone and after pretreatment with either 16,16-dimethyl (dmPGE2) or the mild irritant 25% ethanol (25% EtOH). Fasted rats (n = 12-26/group) were orally given 1 ml of normal saline (NS), dmPGE2 in a dose of 5 micrograms/kg, or 25% EtOH. Fifteen minutes later, they randomly received 1 ml of NS or 50% EtOH. After 5 min, rats were anesthetized and their stomachs rapidly excised, frozen in liquid nitrogen, and lyophyllized. Once dried, the surface area (in square millimeters) of mucosal lesions was quantitated. Mucosa was then scraped off the underlying muscularis. Tissue metabolites (ATP, ADP, AMP, lactate, pyruvate, glucose, and glucose-6-phosphate) were measured in deproteinized, neutralized samples by enzymatic methods. In conjunction with the development of mucosal lesions involving an average of 45 mm2, ATP was significantly (P < 0.05) lower and AMP significantly higher in 50% EtOH-treated animals (indicating dephosphorylation) when compared with NS controls. Although both 25% EtOH and dmPGE2 prevented these lesions, only 25% EtOH prevented the ATP and AMP alterations. Fifty percent EtOH also significantly increased the tissue content of glucose and lactate over control values while glucose-6-phosphate was significantly decreased. With both protective agents pyruvate levels were significantly reduced, while glucose and lactate levels were not affected. In contrast to dmPGE2, the mild irritant (25% EtOH) significantly increased glucose-6-phosphate levels over control.(ABSTRACT TRUNCATED AT 250 WORDS)

The gastric cytoprotective action of adenosine and prostaglandin E2 in rabbits

The direct protective action of adenosine and prostaglandin E2 (PGE2) was examined in an isolated gastric gland preparation in rabbits. Ethanol (8%, v/v) incubation markedly increased the release of lactate dehydrogenase (LDH) and number of non-viable glands in the preparation. Both effects were prevented by PGE2 preincubation in a concentration (10(-6), 1.4 x 10(-5) or 2.8 x 10(-5) M)-dependent manner. The protective action was smaller in adenosine-treated groups, and yet the highest concentration (10(-4) M) of the compound also significantly inhibited the cytotoxic effects of ethanol. These findings indicate that both adenosine and PGE2 possess cytoprotective action on gastric glands in rabbits, but the former compound exerts its action beyond physiological concentrations. It is concluded that endogenous PGE2, but not adenosine may act as an ulcer modulator in the stomach.

Protection against necrotizing agents-induced gastric lesions in rats. Unrelated to inhibition of gastric motility

Effects of necrotizing agents, blockers of gastric motility, and mild irritants on gastric mucosa and gastric motility were investigated in conscious rats. Gastric motor activity was recorded using a miniature balloon placed in the glandular part of the stomach, which was connected to a pressure transducer and polygraph. Necrotizing agents, such as 96% ethanol, 0.6 N hydrochloric acid, 0.2 N sodium hydroxide, or 4 M sodium chloride, were given intragastrically through a fistula on the forestomach. One milliliter of these agents produced hemorrhagic bandlike lesions in the corpus mucosa along the long axis of the stomach with the occurrence of a complete inhibition of gastric motility (smooth muscle relaxation). Blockers of gastric motility alone, such as subcutaneous papaverine HCl (50 mg/kg), and intraperitoneal verapamil (20 mg/kg), or mild irritants (1 ml/rat, orally) such as 20% ethanol or 1 M NaCl, which by themselves suppressed gastric motility, have no effect on gastric mucosa and on the inhibited gastric motility induced by necrotizing agents. Bandlike lesions were significantly prevented by pretreatment with 20% ethanol or 1 M NaCl but not with papaverine HCl or verapamil administered 30 min before necrotizing agents. The gastroprotection offered by 20% ethanol or 1 M NaCl was significantly diminished by pretreatment with subcutaneous indomethacin (30 mg/kg), but the inhibited gastric motility was not reversed by indomethacin. These results indicate that it seems unlikely that gastric contractile activity would play a major role in the development and prevention of gastric lesions after the administration of necrotizing agents.

Stimulation of prostaglandin E2 release from cultured rabbit gastric cells by sodium deoxycholate

Although bile salts are irritants in the gastric mucosa, their effects on prostaglandin (PG) release have not been well studied. We investigated the effects of bile salts on PGE2 release and the possible mechanisms involved. Cultured rabbit gastric mucous epithelial cells were studied. PGE2 was measured by radioimmunoassay. Intracellular free Ca2+ concentration was measured with Ca2+ fluorescent dye indo-1 AM. Dihydroxy bile salts, such as chenodeoxycholate and deoxycholate (DC), dose-dependently increased PGE2 release, while non-dihydroxy bile salts did not. Since agents involved in the cellular signal transduction system have been reported to play important roles in PG release, the possible involvement of Ca2+, calmodulin, and protein kinase C (PKC) in DC-induced PGE2 release was studied. Deprivation of Ca2+ from the medium blocked DC-induced PGE2 release. Lanthanum (La3+), which displaced surface-bound Ca2+, suppressed DC-induced PGE2. However, BAPTA (a chelator of intracellular Ca2+) did not decrease it. Neither calmodulin inhibitors nor PKC inhibitors altered DC-induced PGE2 release. DC increased intracellular free Ca2+ concentrations. This effect was blocked by deprivation of Ca2+ from the medium. Quinacrine (a phospholipase A2 inhibitor) blocked DC-induced PGE2 release. These results suggest that in cultured rabbit gastric cells, deoxycholate stimulates PGE2 release mainly through the influx of extracellular Ca2+.

The differential mechanisms of mild irritants on adaptive cytoprotection

The protective action of mild irritants has been established. However, the mechanisms as to how they antagonize the injurious action produced by the subsequent challenge with an ulcerogenic stimulus are still unclear. The present study examined the different protective mechanisms of an oral administration of the three mild irritants, 20% ethanol, 0.3 mol/L HCl or 5% NaCl against the gastric injurious actions of absolute ethanol in rats. In an attempt to clarify the pathways and mediators involved in the adaptive cytoprotection, [D-Pro2, D-Trp7,9]-substance P (substance P antagonist), Nw-nitro-L-arginine methyl ester (L-NAME), indomethacin, capsaicin, lidocaine, atropine or hexamethonium was given. The protective action of 20% ethanol but not the other two mild irritants, was antagonized by L-NAME, indomethacin and capsaicin, which are the inhibitors of nitric oxide (NO) and prostaglandins (PG) synthesis, and afferent sensory neuron blocker, respectively. Substance P antagonist, lidocaine or atropine given alone, prevented mucosal damage; however, only substance P antagonist enhanced the anti-lesion action of 20% ethanol, while atropine and lidocaine increased the protective effect of NaCl and HCl. The three mild irritants increased the residual gastric secretion. Only 20% ethanol and 5% NaCl but not 0.3% HCl significantly increased the basal adherent mucus and also attenuated the mucus depletion by absolute ethanol. It is concluded that the cytoprotective action of either ethanol or NaCl seems to be mediated through the increase of residual gastric secretion and adherent mucus. In the ethanol-treated group, these actions could act through the afferent sensory fibres, with NO and PG as the possible mediators.(ABSTRACT TRUNCATED AT 250 WORDS)

Adverse effects of vagotomy on ethanol-induced gastric injury in the rat. Absence of a role for glutathione redox cycle

Truncal vagotomy is known to aggravate the damaging effects of alcohol-induced gastric injury and prevent the occurrence of adaptive cytoprotection against such injury by a mild irritant. This study was undertaken to determine whether aberrations in glutathione (GSH) metabolism were responsible for these vagotomy-induced effects. Fasted rats (6-8/group) were subjected to truncal vagotomy and pyloroplasty or sham vagotomy and pyloroplasty. One week later they were given 2 ml of oral saline or the mild irritant, 25% ethanol (EtOH). Thirty minutes following such treatment, animals were either sacrificed or orally received 2 ml of 100% EtOH and then were sacrificed 5 min later. At sacrifice, in each experimental group, stomachs were removed and either evaluated macroscopically for the degree of injury involving the glandular gastric epithelium or samples of the mucosa were prepared for measurement of total GSH levels or GSH peroxidase (GPX) and GSH reductase (GRT) activity. In nonvagotomized animals, saline treatment prior to 100% EtOH exposure resulted in injury to the glandular epithelium involving approximately 18%. Treatment with 25% EtOH prior to 100% EtOH exposure virtually abolished this injury. In vagotomized animals, 100% EtOH elicited almost three times the amount of injury observed in the nonvagotomized state and the protective effect of 25% EtOH pretreatment was prevented. Effects of the various treatment modalities on GPX and GRT activity were not significantly different from control values. When mucosal GSH results were plotted against the presence or absence of gastric injury among the various groups studied, no significant correlation was apparent.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple mediators and mechanisms are involved in the adaptive cytoprotection provided by certain mild irritants

We investigated the participation of prostaglandins (PG) and nitric oxide (NO) in adaptive cytoprotection using 0.6 N HCl-induced gastric lesions in the rat stomach. Indomethacin reversed the protective effect of 0.2 N HCl more strongly than that of 0.35 N HCl, both of which markedly inhibited HCl ulcer. NG-Nitro-L-arginine (L-NNA) did not affect the protective effect afforded by either 0.2 N HCl or 0.35 N HCl. Combined pretreatment with indomethacin and L-NNA did not diminish the protective action induced by 0.35 N HCl, but almost completely abolished the indomethacin-resistant protection afforded by 0.1 N NaOH. Acid mild irritant increased the gastric fluid volume concentration-dependently, whereas alkaline mild irritant had little or no effect on the volume. These results suggest that: 1) The mediators involved in adaptive cytoprotection afforded by 0.1 N NaOH may be fully ascribed to PG and NO; 2) PG is a major mediator in the protection induced by 0.2 N HCl; 3) In the case of 0.35 N HCl, the mediators remain to be determined since increased gastric fluid volume could contribute to the protection through dilution. These findings thus may indicate that multiple mediators and mechanisms are implicated in adaptive cytoprotection.

Effects of chronic superficial injury on the rat gastric mucosa

The effects of chronic superficial injury on the stomach were studied in rats dosed with a mild irritant (2 mol/L NaCl intragastrically) every 48 hours for 1 month followed by 1-month recovery. A single exposure to this mild irritant induced gross protection against 6 mol/L NaCl for 1 but not 2 days. Leukotriene C4 (LTC4) levels increased slightly. Prostaglandin E2 (PGE2) concentration was unchanged. After 2-week dosing, protection was concomitant with markedly elevated PGE2 concentration. LTC4 values remained unchanged. Superficial epithelial cells were more resistant to damage. After 4-week dosing, protection occurred at 1 but not 2 days after the dose with an inverse correlation of PGE2. LTC4 concentration increased significantly at both times. Chronic injury for 1 month did not alter rapid epithelial restitution or PGE2 and LTC4 released 15 minutes after challenge with 6 mol/L NaCl. The recovery period showed loss of protection. PGE2 values returned to control levels but LTC4 values remained slightly elevated. It is concluded that short- or long-term (4-week) "adaptive cytoprotection" is not mediated by endogenous PGE2. Only extremely high levels of LTC4 correlated with loss of protection. The role of the more resistant superficial epithelium remains unknown.

Protective effect of dimethylthiourea against mucosal injury in rat stomach. Implications for hydroxyl radical mechanism

The present study was undertaken to determine whether dimethylthiourea (DMTU), a hydroxyl radical scavenger, could prevent gastric injury in the rat stomach induced by various noxious agents. Fasted rats (N = 6-8/group) were given a 1-ml oral bolus of saline or DMTU over the dose range 10-500 mg/kg. After 30 min, animals received 1 ml of 100% ethanol orally and were sacrificed 5 min later. At sacrifice, stomachs were harvested and the degree of macroscopic damage was assessed by planimetry. In selected animals, specimens of gastric mucosa were also processed for histology. Saline pretreatment prior to ethanol exposure resulted in 22.5% injury to the glandular epithelium when assessed macroscopically. DMTU pretreatment prevented such injury in a dose-related fashion with only 2% of the mucosa showing injury with a 500 mg/kg dose (P less than 0.01 vs control). Although the superficial injury involving surface mucous cells induced by ethanol was not altered by DMTU, the deep damage to gastric glands was almost completely prevented. Other experiments in which DMTU was given intraperitoneally demonstrated similar protective effects against ethanol injury. Additional studies showed that indomethacin did not prevent the protective effects of oral or intraperitoneal DMTU, excluding a role for endogenous prostaglandins, and that DMTU was equally protective when administered within minutes or as long as 2 hr prior to ethanol exposure. Furthermore, DMTU was also shown to be protective against gastric injury induced by concentrated acid or base. In in vitro studies in which hydroxyl radicals were actually generated, DMTU was noted to scavenge the hydroxyl radical in a dose-related fashion. The ability of DMTU to prevent gastric injury by three different damaging agents suggests that the hydroxyl radical may play a major role in the pathogenesis of such injury and that DMTU mediated its protective action by scavenging this radical species.

Effect of capsaicin on gastric mucosal injury and blood flow following bile acid exposure

Topical bile acid at low pH stimulates gastric mucosal blood flow (GMBF), thereby limiting injury to surface epithelial cells (SEC). Capsaicin-sensitive afferent neurons (ASN) are possible mediators of the GMBF response and, therefore, of mucosal protection. In order to investigate the effect of topical capsaicin (ASN stimulant) and topical lidocaine (ASN inhibitor) on SEC exfoliation and GMBF, vascularized wedges of canine gastric corpus were mounted in lucite chambers. Mucosae were pretreated for 15 min with saline (NSS), 160 microM capsaicin (CAP), 4% lidocaine (LIDO), or CAP and LIDO, followed by a 30-min exposure to acid test solution (ATS; pH 1.2). The same mucosae were then pretreated in an identical fashion followed by a second 30-min exposure to 5 mM taurocholate (5 TC; pH 1.2). Parameters evaluated during both ATS and 5 TC periods were the luminal accumulation of DNA (DNAE, a sensitive marker of SEC exfoliation) and GMBF measured using radiolabeled microspheres. It was found that, relative to NSS pretreatment, CAP pretreatment increased GMBF and decreased DNAE during exposure to both ATS and 5 TC. LIDO blocked the CAP effect on GMBF but not on DNAE. Thus, ASN stimulation by CAP enhances GMBF and is protective. ANS inhibition blocks CAP's GMBF increase but not its protective capabilities. Therefore, augmentation of GMBF is not the only mechanism by which ASNs blunt SEC exfoliation.

Increased production of transforming growth factor alpha following acute gastric injury

Transforming growth factor alpha (TGF-alpha) production recently has been found in normal mammalian gastric mucosa. Inasmuch as TGF-alpha and epidermal growth factor (EGF) both stimulate epithelial cell migration and proliferation and suppress gastric acid secretion, the authors of the current study proposed that these growth factors may participate in tissue repair after acute gastric mucosal injury. Consequently, TGF-alpha and EGF production were examined after orogastric administration of either acidified taurocholate or 0.6 mol/L HCl to rats. TGF-alpha messenger RNA (mRNA) expression increased in a dose- and time-dependent manner after administration of taurocholate, whereas EGF mRNA expression was not detected. Radioimmunoassay of gastric mucosal scrapings obtained 6 hours after gastric injury induced by 0.6 mol/L HCl showed a 2.1-fold increase in immunoreactive TGF-alpha but no increase in immunoreactive EGF. In addition, there was a 68-fold increase in immunoreactive TGF-alpha in gastric juice within 30 minutes of gastric instillation of HCl and, again, no increase in immunoreactive EGF. There is a rapid appearance of TGF-alpha in the gastric juice within 30 minutes of injury, which is followed by increased expression of TGF-alpha mRNA and protein in the gastric mucosa. These studies suggest that locally produced TGF-alpha may participate in gastric mucosal repair following acute gastric injury to rats.

Distribution of prostaglandin E2 in gastric and duodenal mucosa: possible role in the pathogenesis of peptic ulcer

BACKGROUND

Prostaglandin E which is present abundantly in the gastric mucosa is a powerful inhibitor of gastric acid secretion and a stimulus to gastric mucus production. In addition, prostaglandin E2 inhibits ulcer formation in animals, and the synthetic analogues of prostaglandin E have successfully been used in the treatment of patients with gastric and duodenal ulcer disease. To evaluate the role of endogenous prostaglandin E2 in the pathogenesis of the peptic ulcer disease, we measured mucosal prostaglandin E2 levels in patients with gastric and duodenal ulcer disease and compared with that of non-ulcer control persons.

METHODS

The study population was made up of 44 non-ulcer persons, 36 patients with a benign gastric ulcer, and 48 with a duodenal ulcer. Every mucosal specimen, taken from the antrum and from the duodenal bulb, were homogenized, mixed with 1 M HCl, and centrifuged. After removal of the supernatant, precipitate was eluted with ethyl acetate in the Amprep C18 minicolumn. Then the extracted prostaglandin E2 in the ethyl acetate fractions was converted into its methyl oximate derivatives, and the prostaglandin E2 level was measured by radioimmunoassay. During the procedure any homogenized specimen which was looking grossly bloody was removed from the assay in order to avoid any possible contamination or prostaglandin E2 in blood.

RESULTS

In non-ulcer persons, the mean values was 258.17 +/- 127.03 pg/mg. tissue in antrum and 121.07 +/- 67.46 pg/mg. tissue in duodenal bulb. The corresponding values were 186.42 +/- 70.51 pg/mg. tissue, 79.44 +/- 39.04 pg/mg. tissue in gastric ulcer patients and 204. 94 92.03 pg/mg. tissue, 99.66 +/- 56.10 pg/mgl. tissue in duodenal ulcer patients respectively. Gastric ulcer patients have the significantly lower level of the antral and duodenal prostaglandin E2 (p < 0.005). Those levels of duodenal ulcer patients were also significantly lower than those of non-ulcer persons (p < 0.025 & 0.05). Antral prostaglandin E2 level increased to 305.21 +/- 104.91 pg/mg. tissue in the gastric ulcer patients (p < 0.005) and to 271.02 +/- 93. 23 pg/mg. tissue in the duodenal ulcer (p < 0.005) when the ulcer crater was healed. The duodenal bulb prostaglandin E2 level was also increased in the healed stage of ulcer, e. g., 128.84 +/- 57.62 (p < 0.005) and 112.60 +/- 42.25 pg/mg. tissue, respectively.

CONCLUSION

These results suggest that prostaglandin deficiency in the antral and duodenal bulb mucosa may have an important role in the pathogenesis of peptic ulcer disease.

Effects of a polysaccharide fraction from the roots of Bupleurum falcatum L. on experimental gastric ulcer models in rats and mice

Effects of an acidic polysaccharide fraction, BR-2, from the roots of Bupleurum falcatum L., on HCl-ethanol, ethanol and water immersion stress-induced gastric lesions in mice and pylorus-ligated ulcers in rats have been studied. Oral administration of BR-2 at doses of 50 to 200 mg kg-1 inhibited the formation of the gastric lesions induced by necrotizing agents such as HCl-ethanol and ethanol, in a dose dependent manner. This protective effect was observed after oral, intraperitoneal, and subcutaneous administration of BR-2 (25-100 mg kg-1). BR-2 also inhibited the formation of gastric ulcers which were induced by water immersion stress or pylorus-ligation. Prostaglandin E2 in gastric juice from rats and in gastric mucosa from mice was not influenced by oral administration of BR-2. The protective action of BR-2 against HCl-ethanol-induced gastric lesions was not abolished by pretreatment with indomethacin (20 mg kg-1, i.p.). The amount of alcian blue binding to mucosa also increased after administration of BR-2 (100 mg kg-1, p.o.); however, the amount of hexosamine and N-acetylneuraminic acid in mucosa did not change significantly.

Role of acid milieu in the gastroprotective and ulcer-healing activity of sucralfate

Sucralfate prevents the formation of acute gastric lesions induced by various ulcerogens and enhances the healing of chronic gastroduodenal ulcerations, but the mechanism of these effects has not been fully explained. This study was designed to determine the importance of intragastric pH in the sucralfate-induced gastroprotection against 100% ethanol, acidified aspirin, taurocholate, or stress, and in the healing of chronic gastroduodenal ulcerations induced by acetic acid. Sucralfate acidified to pH 2.0 showed significantly stronger protective activity against all four irritants, its protective potency against 100% ethanol being about eight times greater and the duration of the protection about four times longer than those obtained with sucralfate at its pH of 5.0. Pretreatment with indomethacin to suppress mucosal generation of prostaglandin or the removal of salivary glands to eliminate the endogenous source of epidermal growth factor failed to affect sucralfate-induced gastroprotection. In contrast, the rate of healing of chronic gastric ulcerations was significantly delayed by indomethacin or sialoadenectomy; but sucralfate enhanced the healing, and a marked inhibition of gastric acid secretion by ranitidine did not eliminate this enhancement. We conclude that the protective activity of sucralfate depends on the presence of acid milieu in the stomach, but that the ulcer-healing effects of this drug occur even after a marked inhibition of gastric acid secretion.

Adaptive cytoprotection against alcohol injury in the rat stomach is not due to increased prostanoid synthesis

This study evaluated the effects of 25% ethanol, a mild irritant, on endogenous prostanoid synthesis in the rat stomach before and after exposure to oral 100% ethanol. Rats received water or 25% ethanol orally. After 15 min, a portion of each group was sacrificed and the remaining animals treated with 100% ethanol prior to sacrifice one minute later. Microsomal membrane fractions were prepared from the glandular gastric mucosa in all groups and incubated with 14C arachidonic acid in the presence of cofactors. Endogenous mucosal prostanoid synthesis was analyzed by radiochromatography and results correlated with the presence or absence of gastric injury macroscopically. Prostanoids measured included PGI2, PGF2 alpha, PGE2, PGD2, PGA2, and thromboxane A2. Additional experiments were performed in like manner to those just described with the exception that indomethacin (5 mg/kg intraperitoneally) pretreatment was rendered. Stomachs exposed to water or 25% ethanol alone demonstrated a modest and equivalent level of synthesis of all prostanoids measured. Exposure to 100% ethanol (with and without mild irritant pretreatment) significantly increased prostanoid synthesis (especially PGI2, PGF2 alpha, and PGE2) compared with stomachs exposed to water or 25% ethanol alone; only mild irritant treated mucosa was protected from injury by 100% ethanol. Indomethacin pretreatment reversed the increased prostanoid synthesis in mucosa exposed to 100% ethanol, with or without mild irritant pretreatment, and partially reversed the protective effect of 25% ethanol. Other experiments using tissue slices in which perturbations in mucosal levels of prostanoids were measured by radioimmunoassay under identical experimental conditions exhibited similar results. These data dispute the notion that adaptive cytoprotection is mediated by increased endogenous prostanoid synthesis. The partial reversal of this process by indomethacin was most likely secondary to some other action of this agent, such as a reduction in gastric blood flow, rather than direct effects on prostanoid synthesis.

Acute gastric mucosal injury induced by toxins from Tityus serrulatus scorpion venom: a novel experimental model in the rat

The effect of a partially purified fraction (T1) and toxin gamma purified from Tityus serrulatus scorpion venom, on gastric mucosa were investigated in anesthetized rats. The animals were injected i.v. with the T1 fraction (37.5 micrograms/100 g) or with saline and 60 min later were sacrificed and the stomachs resected. The gastric juice was measured and stereoscopic examination of the stomachs made. In animals injected with the T1 fraction there was an increase in volume, acidity and pepsin output of rat stomach. The T1 fraction also induced acute gastric injuries in the glandular mucosa, consisting of circular or linear ulcers, and punctiform lesions. Intravenous injection of 20 micrograms/100 g of a pure toxin obtained from Tityus serrulatus scorpion venom (toxin gamma) also induced similar lesions in the rat stomach. Our data indicate that the injection of T1 fraction or toxin gamma are good models to induce acute gastric ulcers in a short period of time in anesthetized rats.