Endogenous nitric oxide modulates ethanol-induced gastric mucosal injury in rats

Sphaeranthus senegalensis DC: Evaluation of chemical constituents, oral safety, gastroprotective activity, and mechanism of action of its hydroethanolic extract

ETHNOPHARMACOLOGICAL RELEVANCE

Sphaeranthus senegalensis DC is a seasonal herb with a spicy smell that grows wild in wet grounds of tropical Africa and Asia. The plant is used in folk medicine for the treatment of various diseases; that includes its use to treat gastric ulcers.

AIM OF THE STUDY

This study aimed to investigate the chemical constituents of the hydroethanolic extract of Sphaeranthus senegalensis DC and evaluate its oral safety, gastroprotective activity, and mechanisms of action using laboratory models in rats and mice.

MATERIALS AND METHODS

Hydroethanolic extract (70%) of the powdered whole dried material was prepared, and chemical constituents of the resultant extract (denoted HESs) standardized using the high-performance liquid chromatography (HPLC) method. The safety profile of HESs was assessed using 2000 mg/kg, oral (p.o.) for Hippocratic screening in mice, and 800 mg/kg, p.o. for 28 days subchronic toxicity assay in rats. The gastroprotective effect of HESs (25, 100, and 400 mg/kg, p.o.) was investigated using acidified ethanol, piroxicam, water immobilization stress, and acetic acid-induced ulcer models. The gastroprotective mechanisms of HESs were evaluated using its effect on gastric mucus protection, nitric oxide modulation, gastric juice secretory parameters, catalase and myeloperoxidase activities. Histological analysis of the stomach tissues was also carried out.

RESULTS

The HPLC analysis indicated the presence of 25.94% phenolics (gallic acid, caffeic acid, and ferulic acid) and 14.53% flavonoids (rutin, morin, luteolin, quercetin, and apigenin). Hippocratic screening and the 28 days subchronic study indicated that HESs is generally safe. Result shows that oral administration of HESs (25, 100 and 400 mg/kg) alleviated the severity of the gastric ulcers induced by acidified ethanol by 35.65% (p < 0.05), 48.70% (p < 0.05) and 78.02% (p < 0.001) respectively; exhibited gastroprotective effect against the gastric lesions induced by piroxicam by 37.97% (p < 0.05), 53.27% (p < 0.05) and 76.23% (p < 0.001) respectively; and decreased the severity of the water immobilization stress-induced gastric ulcers by 32.43% (p < 0.05), 55.26% (p < 0.01) and 74.05% (p < 0.001) respectively, when compared to the vehicle control group. The mechanisms of action assays indicated that the gastroprotective activity was mediated mainly through gastroprotection, antisecretory, and antioxidant activities. Histological analysis showed it inhibited epithelial cell loss, vascular damage, and leucocyte infiltration.

CONCLUSION

HESs contains useful phytochemicals, is safe, and exhibited significant gastroprotective action. The results provided justification for its claim in the treatment of gastric ulcers and its evaluation for potential application as a gastroprotective agent.

Isolation, characterization, and in silico, in vitro and in vivo antiulcer studies of isoimperatorin crystallized from Ostericum koreanum

CONTEXT

Ostericum koreanum (Maxim.) Kitagawa (Apiaceae) roots are traditionally used as an analgesic and antiulcer agent. However, the antiulcer potential of isoimperatorin isolated from O. koreanum has not yet been explored.

AIM

To evaluate the antiulcer activity of isoimperatorin isolated from the roots of O. koreanum.

MATERIALS AND METHODS

Isoimperatorin was isolated as cubic crystals by repeated column chromatography of the ethyl acetate fraction and structure was verified with 1H NMR, 13C NMR and high-resolution mass spectrometry (HRMS-FAB). The crystals obtained were analyzed with the single crystal X-ray method. The MTT assay was used to determine its cytotoxicity against chondrocytes at different concentrations (0.0-737.74 μM, 24 h). The in vivo antiulcer activity of isoimperatorin (40 mg/kg) was determined against ethanol-, indomethacin- and pyloric ligation-induced ulcers in Sprague-Dawley rats. Furthermore, the effect of isoimperatorin (0.0-737.74 μM, 24 h) on the expression of type II collagen in chondrocytes was determined using western blot method. The in vitro urease inhibitory activity of isoimperatorin (0-80 μM) and molecular docking was also performed against urease.

RESULTS AND DISCUSSION

Isoimperatorin demonstrated significant inhibitory activity (IC50 36.43 μM) against urease as compared to the standard drug thiourea (IC50 33.57 μM) without cytotoxic effects. It provided 70.9%, 67.65% and 54.25% protection in ulcer models induced by ethanol, indomethacin and pyloric ligation, respectively. Isoimperatorin showed the highest expression level of type II collagen at 368.87 μM. The docking results confirmed strong binding affinity with the target protein.

CONCLUSION

Isoimperatorin may be used to develop antiulcer drugs with decreased side effects.

Flavonoids from whole Plant of Euphorbia hirta and their Evaluation against Experimentally induced Gastroesophageal Reflux Disease in Rats

BACKGROUND

Euphorbia hirta possesses antibacterial, anti-inflammatory, galactogenic, antidiarrheal, antioxidant, hypoglycemic, antiasthmatic, antiamebic, antifungal, and antimalarial activities.

OBJECTIVE

The overall objective of the current study was the investigation of the whole plant extract of E. hirta and flavonoids from E. hirta on gastroesophageal reflux disease (GERD) in rats.

MATERIALS AND METHODS

The whole plant extract of E. hirta was characterized by analysis of flavonoids (HPLC: HPLC, UV, IR, MS and ¹HNMR). GERD model was induced surgically in Wistar rats under pentobarbitone sodium anesthesia (50 mg/kg, i.p.) and the tissue esophagus and stomach were removed. The tissues were washed with physiological saline and were examined for GERD. The whole plant extract of E. hirta in doses of 50, 100, and 200 mg/kg were administered orally twice daily at 10:00 and 16:00 hours, respectively, for 5 days and kaempferol (100 mg/kg) or omeprazole (OMZ) in the dose of 30 mg/kg 1 hour prior to the induction of GERD. Control groups received suspension of 1% carboxymethyl cellulose in distilled water (10 mL/kg).

RESULTS

The levels of gastric wall mucus increased and of plasma histamine and H⁺, K⁺ ATPase significantly decreased in groups treated by both the plant extract and flavonoids. Both the plant extract and flavonoids reduced the lipid peroxidation and superoxide dismutase and increased the levels of catalase and reduced glutathione.

CONCLUSIONS

The whole plant extract of E. hirta is attributed to its antisecretory, gastroprotective, and antioxidant potential as that of quercetin, rutin, kaempferol, and proton pump blocker (omeprazole) to treat GERD.

SUMMARY

The aqueous extract of whole plant of Euphorbia hirta revealed the presence of kaempferol (0.0256%), quercetin (0.0557%), and rutin (0.0151%), and the ethyl acetate fraction of whole plant of E. hirta possesses kaempferol (0.0487%), quercetin (0.0789%), and rutin (0.0184%).The levels of gastric wall mucus increased and of plasma histamine and H⁺-K⁺-ATPase significantly decreased in rats groups treated by both the whole plant extract of E. hirta and flavonoids.Both the whole plant extract of E. hirta and flavonoids reduced the lipid peroxidation and superoxide dismutase and increased the levels of catalase and reduced glutathione in rats groups. Abbreviation used: 1HNMR: Proton Nuclear Magnetic Resonance Spectroscopy, CAT: Catalase, EHAE: Aqueous extract of Euphorbia hirta, EHEF: Ethyl Acetate Fractions of Euphorbia hirta, GERD: Gastroesophageal reflux disease, GSH: Reduced Glutathione, HPLC: High performance liquid chromatography, IR: Infrared spectroscopy, LPO: Lipid Peroxidase, MDA: Malondialdehyde, MS: Mass Spectroscopy, OMZ: Omeprazole, ROS: Reactive Oxygen Species, SOD: Superoxide dismutase, TBHQ: tert-Butylhydroquinone, TLC: Thin Layer Chromatography, UV: Ultraviolet, UV: Ultraviolet-Visible Spectroscopy.

Gastroprotective effect and mechanism of action of Croton rhamnifolioides essential oil in mice

BACKGROUND

Croton rhamnifolioides Pax is a plant species that have been used in the folk medicine to treat ulcers, inflammations and hypertension. However, despite the relevant data obtained from ethnopharmacological studies, the pharmacological properties endorsing the efficacy of this plant to treat ulcer remain to be elucidated.

HYPOTHESIS/PURPOSE

The present study aimed to characterize the chemical profile and evaluate the gastroprotective activity of the essential oil obtained from C. rhamnifolioides Pax (OECC) in mice.

METHODS

The essential oil of Croton rhamnifolioides was obtained by hydrodistillation and analyzed by gas-phase chromatography coupled to mass spectrometry (GC/MS). The median lethal dose was determined employing an acute toxicity test. The gastroprotective activity of the OECC was investigated using animal models of gastric ulcer induced by the administration of absolute ethanol, acidified ethanol or indomethacin. Mechanisms of action were investigated using the physical barrier test and by in vivo evaluation of the involvement of the following molecular pathways: nitric oxide, ATP - dependent potassium channels, α₂ - noradrenergic receptors, capsaicin - sensitive afferent neurons and opioid receptor.

RESULTS

We identified the presence of 21 compounds in OECC, including spathulenol and 1,8 - cineole as major constituents. In orally administered mice, OECC caused no significant toxicity. OECC significantly prevented gastric lesions in all mice models. The barrier test demonstrated that the gastroprotective activity of OECC occurs in a systemic dimension. Our results demonstrated that the gastroprotective effect of OECC involves mechanisms that are related to modulation of opioid receptors and nitric oxide.

CONCLUSION

In conclusion, OECC demonstrated significant gastroprotective activity associated with low toxicity, providing scientific evidences that C. rhamnifolioides have the potential for the development of new antiulcer drugs.

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

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

Nitric oxide as a mediator of gastrointestinal mucosal injury?-Say it ain't so

Nitric oxide has been suggested as a contributor to tissue injury in various experimental models of gastrointestinal inflammation. However, there is overwhelming evidence that nitric oxide is one of the most important mediators of mucosal defence, influencing such factors as mucus secretion, mucosal blood flow, ulcer repair and the activity of a variety of mucosal immunocytes. Nitric oxide has the capacity to down-regulate inflammatory responses in the gastrointestinal tract, to scavenge various free radical species and to protect the mucosa from injury induced by topical irritants. Moreover, questions can be raised regarding the evidence purported to support a role for nitric oxide in producing tissue injury. In this review, we provide an overview of the evidence supporting a role for nitric oxide in protecting the gastrointestinal tract from injury.

Knock out of neuronal nitric oxide synthase exacerbates intestinal ischemia/reperfusion injury in mice

Recent investigation of the intestine following ischemia and reperfusion (I/R) has revealed that nitric oxide synthase (NOS) neurons are more strongly affected than other neuron types. This implies that NO originating from NOS neurons contributes to neuronal damage. However, there is also evidence of the neuroprotective effects of NO. In this study, we compared the effects of I/R on the intestines of neuronal NOS knockout (nNOS(-/-)) mice and wild-type mice. I/R caused histological damage to the mucosa and muscle and infiltration of neutrophils into the external muscle layers. Damage to the mucosa and muscle was more severe and greater infiltration by neutrophils occurred in the first 24 h in nNOS(-/-) mice. Immunohistochemistry for the contractile protein, α-smooth muscle actin, was used to evaluate muscle damage. Smooth muscle actin occurred in the majority of smooth muscle cells in the external musculature of normal mice but was absent from most cells and was reduced in the cytoplasm of other cells following I/R. The loss was greater in nNOS(-/-) mice. Basal contractile activity of the longitudinal muscle and contractile responses to nerve stimulation or a muscarinic agonist were reduced in regions subjected to I/R and the effects were greater in nNOS(-/-) mice. Reductions in responsiveness also occurred in regions of operated mice not subjected to I/R. This is attributed to post-operative ileus that is not significantly affected by knockout of nNOS. The results indicate that deleterious effects are greater in regions subjected to I/R in mice lacking nNOS compared with normal mice, implying that NO produced by nNOS has protective effects that outweigh any damaging effect of this free radical produced by enteric neurons.

Effect of folic acid supplementation on oxidative gastric mucosa damage and acid secretory response in the rat

Objective:

This study investigated the antioxidative and antisecretory properties of folic acid in the rats’ stomach.

Materials and Methods:

Male Wistar rats were treated with 2 mg/kg diet of folic acid for 21 days. Gastric ulceration was induced by indomethacin, scored, and assayed to determine the concentration of total protein, mucus, malondialdehyde (MDA), catalase (CAT) and superoxide dismutase (SOD) in homogenized samples. Normal saline and Ranitidine treated group served as negative and positive control, respectively. Basal and stimulated acid secretion was measured by continuous perfusion method.

Result:

Indomethacin caused severe damage to the rats’ stomach with an ulcer index of 4.32 ± 0.13, increase in MDA concentration and reduction in the concentration of protein, mucus, catalase and superoxide dismutase (P < 0.001). Pre-treatment with folic acid prevented the formation of ulcers by 32%, and attenuated the inhibition of mucus by 14%, CAT, 51% and SOD, 150%. Ranitidine afforded 56% prevention in ulcer formation with 67%, 55% and 78% attenuation of the inhibition of mucus, CAT and SOD, respectively, by indomethacin. While indomethacin-induced lipid peroxidation was attenuated by 58% reduction in MDA concentration on pretreatment with folic acid, Ranitidine offered 65% reduction. Basal and stimulated acid secretions were significantly reduced in the treated when compared with control animals. Folic acid produced a 21% reduction in the basal acid output when compared with the control animals (P < 0.05), and 140% reduction in histamine-induced acid response.

Conclusion:

The results indicate the gastroprotective activity of folic acid due its antioxidative and anti-secretory properties.

Modulation of lipid peroxidation and antioxidant defense systems in rat intestine by subchronic fluoride and ethanol administration

Excessive consumption of fluoride and ethanol has been identified as injurious to human health. Fluoride and ethanol co-exposures are commonly seen among the alcoholics residing in endemic fluoride areas worldwide. This study was undertaken to examine the modulation of lipid peroxidation and antioxidant defense systems in rat intestine by subchronic fluoride and ethanol administration. Female Sprague-Dawley rats were divided into four groups: group I (control), group II (fluoride was given orally at a dose of 25 mg/kg body weight), group III (30% ethanol was given orally at a dose of 1 mL/kg body weight), and group IV (a combination of fluoride and ethanol was administered orally at the dose described for groups II and III). Lipid peroxidation was elevated (P<.05) in intestine of rats by fluoride or ethanol treatments for 20 or 40 days. However, glutathione content was reduced by fluoride (32 and 44%) and ethanol (21 and 40%) treatments after 20 and 40 days, respectively. Fluoride-exposed animals showed reduction (P<.05) in the activities of superoxide dismutase (22 and 42%), catalase (30 and 37%), glutathione peroxidase (22 and 35%), glutathione reductase (32 and 34%), and glutathione-S-transferase (24 and 30%) after 20 and 40 days. A similar decrease (P<.05) in the activities of these enzymes was also noticed in animals exposed to ethanol for 20 or 40 days. The observed changes in lipid peroxidation, reduced glutathione levels, and enzyme systems were further augmented in intestine of rats exposed to fluoride and ethanol together. Intestinal histology showed large reactive lymphoid follicles along with mild excess of lymphocytes in lamina propria of villi, villous edema, focal ileitis, and necrosis of villi in animals exposed to fluoride and ethanol for 40 days. These findings suggest that fluoride and ethanol exposure induces considerable changes in lipid peroxidation, antioxidant defense, and morphology of rat intestine, which may affect its functions.

Asymmetric dimethylarginine: A novel biomarker of gastric mucosal injury?

Nitric oxide (NO), a multifunctional endogenous gas molecule, is metabolized from L-arginine by enzymatic reaction in the presence of nitric oxide synthase. NO, an important gas signaling molecule, is a gastric mucosa protective factor that contributes significantly to maintain normal gastric mucosa integrity. NO increases gastric mucosa blood flow, regulates the secretion of mucus and bicarbonate, and inhibits the secretion of gastric juice. Asymmetric dimethylarginine (ADMA) has been identified as the major endogenous inhibitor of nitric oxide synthase. The function of ADMA is to decrease NO production via inhibiting nitric oxide synthase activity. Besides inhibiting NO synthesis, ADMA also directly induces oxidative stress and cell apoptosis, and participates in inflammation reaction. Its systemic accumulation was observed in conjunction with several cardiovascular and metabolic diseases. ADMA also mediates gastric ulcer injury induced by ethanol, stress, helicobacter pylori and indomethacin. The mechanism of ADMA directly producing adverse effect in gastric mucosa is incompletely understood. It is widely accepted that NO bioavailability decrease is the majority reason. Promotion of apoptosis and aggravation of inflammation may be other important mechanisms of ADMA-induced gastric injury. ADMA might be a novel clinical and experimental biomarker related to gastric mucosa disorder. Although therapeutic tool targeting to ADMA is available in multiple cardiovascular diseases, it is unknown in gastrointestinal disease. The strategy to inhibit ADMA is beneficial to gastric ulcer induced by ethanol in rats. Thus, ADMA might be a candidate of therapeutic target in gastric mucosa damage.

The NMDA receptor/nitric oxide pathway: a target for the therapeutic and toxic effects of lithium

Although lithium has largely met its initial promise as the first drug discovered in the modern era of psychopharmacology, to date no definitive mechanism for its effects has been established. It has been proposed that lithium exerts its therapeutic effects by interfering with signal transduction through G-protein-coupled receptor (GPCR) pathways or direct inhibition of specific targets in signaling systems, including inositol monophosphatase and glycogen synthase kinase-3 (GSK-3). Recently, increasing evidence has suggested that N-methyl-D-aspartate receptor (NMDAR)/nitric oxide (NO) signaling could mediate some lithium-induced responses in the brain and peripheral tissues. However, the probable role of the NMDAR/NO system in the action of lithium has not been fully elucidated. In this review, we discuss biochemical, preclinical/behavioral and physiological evidence that implicates NMDAR/NO signaling in the therapeutic effect of lithium. NMDAR/NO signaling could also explain some of side effects of lithium.

Pharmacological mechanisms underlying the anti-ulcer activity of methanol extract and canthin-6-one of Simaba ferruginea A. St-Hil. in animal models

RELEVANCE

Simaba ferruginea A. St-Hil. (Simaroubaceae) is a subshrub typical of the Brazilian Cerrado, whose rhizomes are popularly used as infusion or decoction for the treatment of gastric ulcers, diarrhea and fever.

AIM OF THE STUDY

To evaluate the pharmacological mechanism(s) of action of the antiulcer effects of the methanol extract of Simaba ferruginea and its alkaloid canthin-6-one.

MATERIALS AND METHODS

Rhizome of Simaba ferruginea was macerated with methanol to obtain the methanol extract (MESf) from which was obtained, the chloroform fraction. Canthin-6-one alkaloid (Cant) was purified and then isolated from the chloroform fraction (CFSf). The isolated Cant was identified by HPLC. Anti-ulcer assays were determined using ethanol and indomethacin-induced ulcer models in mice and rats respectively. In order to determine the probable mechanisms of actions of MESf and Cant animals were pretreated with l-NAME prior to anti-ulcer agent treatments and ulcer induction and nitric oxide (NO) level determined in order to assess NO involvement in the gastroprotective effects. Assays of malondialdehyde (MDA), myeloperoxidase (MPO), pro-inflammatory cytokines: interleukin 8 (IL-8) and tumor necrosis factor-alpha (TNF-α) and prostaglandin E(2) (PGE(2)) were also carried out according to previously described methods.

RESULTS

The results indicate that the antiulcerogenic effects of MESf and Cant in ethanol-induced ulcer is mediated in part through increase in the production of protective endogenous NO as the antiulcerogenic activity of MESf and Cant was reduced in animals pre-treated with l-NAME. In indomethacin-induced ulcer pre-treatment with MESf and Cant showed reduction in the levels of MPO and MDA in the gastric tissue, thus indicating the participation of the antioxidant mechanisms on the gastroprotective effects. The plasma levels of IL-8 in ulcerated rats with indomethacin were also reduced by Cant, but not by MESf, indicating that inhibition of this cytokine contributes to the gastroprotective effect of Cant. However MESf and Cant had no effect on the mucosal membrane levels of PGE(2), indicating that the gastroprotective effects of these agents is independent of PGE(2) modulation.

CONCLUSION

The results obtained in this study with MESf and Cant added insights into the pharmacological mechanisms involved in their mode of antiulcer action. The results indicate that Cant is one of the compounds responsible for these effects. Such findings are of extreme importance in the strive for future development of potent, safer and effective antiulcer agent. The efficacy of MESf and Cant in gastroprotection shows that Simaba ferruginea might be a promising antiulcer herbal medicine, in addition to confirming the popular use of this plant against gastric ulcer models utilised in this study.

Mechanism of Cytosolic Phospholipase A(2) Activation in Ghrelin Protection of Salivary Gland Acinar Cells against Ethanol Cytotoxicity

Ghrelin, a peptide hormone, newly identified in oral mucosal tissues, has emerged recently as an important mediator of the processes of mucosal defense. Here, we report on the mechanism of ghrelin protection against ethanol cytotoxicity in rat sublingual salivary gland cells. The protective effect of ghrelin was associated with the increase in NO and PGE2, and upregulation in cytosolic phospholipase A₂ (cPLA₂) activity and arachidonic acid (AA) release. The loss in countering effect of ghrelin occurred with cNOS inhibitor, L-NAME, as well as indomethacin and COX-1 inhibitor, SC-560, while COX-2 inhibitor, NS-398, and iNOS inhibitor, 1400W, had no effect. The effect of L-NAME was reflected in the inhibition of ghrelin-induced cell capacity for NO production, cPLA₂ activation and PGE2 generation, whereas indomethacin caused only the inhibition in PGE2. Moreover, the ghrelin-induced up-regulation in AA release was reflected in the cPLA₂ phosphorylation and S-nitrosylation. Inhibition in ghrelin-induced S-nitrosylation was attained with L-NAME, whereas the ERK inhibitor, PD98059, caused the blockage in cPLA₂ protein phosphorylation as well as S-nitrosylation. Thus, ghrelin protection of salivary gland cells against ethanol involves cNOS-derived NO induction of cPLA₂ activation through S-nitrosylation for the increase in AA release at the site of COX-1 action for PGE2 synthesis.

Divergent effects of irritants on the gastric mucosa in rats during various stages after bile duct ligation

BACKGROUND AND AIM

Controversy exists as to whether rats after bile duct ligation (BDL) are more susceptible to gastric mucosal damage (GMD) induced by irritants. In the present study we characterize GMD after intragastric instillation of either ethanol or hydrochloric acid (HCL), 3 and 21 days after the surgical procedure.

METHODS

Bile duct ligation and sham operated (SO) rats were studied.

RESULTS

Three days after surgery, BDL rats exhibited a reduction in gastric mucosal nitric oxide synthase (NOS) activity but an increase in ethanol-induced GMD. Twenty-one days after surgery gastric mucosal prostaglandin (PG) E(2) generation in BDL rats was increased while NOS activity in both groups was similar. Ethanol-induced GMD in SO rats was higher. Pretreatment with NG-nitro-L-arginine methyl ester, prior to ethanol administration was associated with an increase in gastric mucosal PGE(2) generation: (147% in SO and 104% in BDL rats) and in GMD (176% in SO and 303% in BDL rats). HCL induced GMD was of similar magnitude in both groups in both time periods.

CONCLUSIONS

The gastric resistance to damage by irritants in rats with BDL is not a static phenomenon. This may result from sequential changes that occur in the gastric mucosal defense mechanisms during the evolution of liver disease.

Involvement of constitutive nitric oxide synthase in ghrelin-induced cytosolic phospholipase A(2) activation in gastric mucosal cell protection against ethanol cytotoxicity

Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, is an important regulator of nitric oxide synthase (NOS) and cyclooxygenase (COX) enzyme systems, the products of which are of major significance to the processes of gastric mucosal defense and repair. Here, using primary culture of rat gastric mucosal cells, we report on the mechanism of ghrelin protection against ethanol cytotoxicity. We show that the protective effect of ghrelin was associated with the increase in NO and PGE2 production, and characterized by a marked up-regulation in cytosolic phospholipase A(2) (cPLA(2)) activity and arachidonic acid (AA) release. The loss in countering effect of ghrelin on the ethanol cytotoxicity was attained with constitutive NOS (cNOS) inhibitor, L-NAME, as well as indomethacin and a specific COX-1 inhibitor, SC-560, while specific COX-2 inhibitor, NS-398, and a selective inducible NOS (iNOS) inhibitor, 1400W, had no effect. The effect of L-NAME was reflected in the inhibition of ghrelin-induced mucosal cell capacity for NO production, cPLA(2) activation, and PGE2 generation, whereas indomethacin caused only the inhibition in PGE2 generation. Moreover, the ghrelin-induced up-regulation in AA release was reflected in the cPLA(2) enzyme protein phosphorylation and S-nitrosylation. Preincubation with L-NAME resulted in the inhibition of the ghrelin-induced S-nitrosylation, whereas the ERK inhibitor, PD98059, caused the blockage in cPLA(2) protein phosphorylation as well as S-nitrosylation. The findings demonstrate that ghrelin protection of gastric mucosa against ethanol cytotoxicity involves cNOS-derived NO induction of cPLA(2) activation for the increase in PGE2 synthesis. This activation process apparently includes the cPLA(2) phosphorylation followed by S-nitrosylation.

Gastroprotective activity of isopulegol on experimentally induced gastric lesions in mice: investigation of possible mechanisms of action

The present study investigated whether isopulegol, a monoterpene present in essential oils of several aromatic plants, would be able to promote some gastroprotective effect and also verified the possible mechanisms involved in this action. For this study, ethanol- and indomethacin-induced gastric ulcer models in mice and histopathological assessment were used. The roles of NO, sulfhydryls (glutathione, GSH), ATP-sensitive K(+) channels (K(ATP) channels), and prostaglandins were also investigated. Isopulegol exhibited a dose-related gastroprotective effect against ethanol-induced lesions, while the pretreatment with glibenclamide and indomethacin [but not with N(G)-nitro-L-arginine methyl ester] were able to reverse this action. The pretreatment with isopulegol also restored GSH levels to normal levels and exhibited dose-related gastroprotective effect against indomethacin-induced ulcer. The results suggested that isopulegol presents significant gastroprotective effects in both ethanol- and indomethacin-induced ulcer models, which appear to be mediated, at least in part, by endogenous prostaglandins, K(ATP) channel opening, and antioxidant properties.

Taurocholate-induced nitric oxide signaling and the ensuing production of reactive oxygen species lead to an increase in epithelial permeability in cultivated mouse gastric epithelium

We have here elucidated whether ulcerogenic agents affect the production of NO and reactive oxygen species (ROS). The ulcerogenic agents dose dependently induced NO and ROS production in mouse gastric epithelial cells. Taurocholate (TC, 5 mM) exposure did not affect cell viability, but it increased inducible nitric oxide synthase (iNOS) expression, NO production, ROS production, and epithelial permeability. Epithelial permeability was inhibited with NOS inhibitors or antioxidants. Oxidative stress induced by acetylsalicylic acid (ASA) and ethanol was not inhibited with NOS inhibitors. ASA induced ROS production even at low concentrations (1 mM), which did not affect cell viability. Ethanol-induced ROS production was linked to cell viability, suggesting direct oxidative stress caused by ethanol. Taurocholate-induced NO signaling and the ensuing production of ROS might contribute to initiation of defensive or adaptive cellular mechanisms. ASA-induced ROS signaling might have similar effects, whereas ethanol induced direct oxidative stress, having an influence on cell viability.

Capsaicin-sensitive afferent fibers mediate the protective effect of electrical stimulation of paraventricular nucleus against gastric ischemia-reperfusion injury in rats

AIM: To elucidate the role of capsaicin-sensitive afferent fibers in mediating the effect of electrical stimulation (ES) of paraventricular nucleus (PVN) against rat gastric ischemia-reperfusion (GI-R) injury.

METHODS: GI-R injury was induced in rats by clamping the celiac artery for 30 min and then reperfusing for 1 h. The methods of nuclear electric stimulation to excite the PVN and pretreatment with a high dose of capsaicin to ablate the capsaicin-sensitive afferent fibers were used to explore the role of capsaicin-sensitive afferent fibers in the regulation of PVN on GI-R injury.

RESULTS: Pretreament with a high dose of capsaicin to ablate afferent fibers partly abolished the protective effect of PVN against GI-R injury and the injury was increased by 54.85% as compared with that in the PVN stimulation group (P < 0.01); Pretreament with L-nitro-L-arginine methyl ester (L-NAME) significantly abolished the protective effect of PVN against GI-R injury and the injury was increased by 72.98% as compared with that in the PVN stimulation group (P < 0.01).

CONCLUSION: Capsaicin-sensitive afferent fibers and endogenous NO are involved in the protective effect of PVN stimulation against GI-R injury.

Helicobacter pylori infection upregulates endothelial nitric oxide synthase expression and induces angiogenesis in gastric mucosa of dyspeptic patients

BACKGROUND

Helicobacter pylori (H. pylori) infection induces nitric acid (NO) overproduction through inducible NO synthase (NOS) expression, subsequent DNA damage and enhanced antiapoptosis signal transduction sequence in the human gastric mucosa, whereas its possible effect on endothelial nitric oxide synthase (eNOS) expression has not as yet been investigated. The aim of this study was to evaluate the effect of H. pylori infection in the expression of eNOS in gastric mucosa.

PATIENTS AND METHODS

We prospectively studied 30 nonsmoking dyspeptic patients (12 men, 18 women, mean age 54.26+/-12.89 years). The diagnosis of H. pylori infection was based mainly on histology. The histological grading of H. pylori infection was evaluated according to the modified Sydney classification. Histological grading of eNOS expression and microvessel density as estimated by CD34 expression were determined by immunohistochemistry (degree 0-3) and correlated with H. pylori infection and histological degree of gastritis.

RESULTS

Twelve patients were H. pylori-positive and 18 patients were H. pylori-negative. The two groups were matched for age (P=0.139), sex (P=0.342) and similar degree of gastritis. Intensity of eNOS and CD34 expression in the corpus and antrum were significantly correlated (P<0.001). eNOS expression was correlated with H. pylori infection in the mucosa of the body and antrum (P=0.013 and 0.037, respectively) but not with gastric inflammation and activity (P=0.848 and 0.871, respectively, for the corpus and P=0.565 and 0.793, respectively, for the antrum). H. pylori-positive patients showed higher expression of CD34-positive blood vessels in the mucosa of the antrum (P=0.048). CD34 expression was correlated with gastric inflammation and activity (P=0.03 and 0.044, respectively) in the mucosa of the antrum of H. pylori-positive patients.

CONCLUSION

H. pylori infection upregulates eNOS, and induces angiogenesis, contributing to H. pylori-associated pathophysiology in gastric mucosa.

Lead exposure increases oxidative stress in the gastric mucosa of HCl/ethanol-exposed rats

AIM: To investigate the role of reactive oxygen species in the ulcer-aggravating effect of lead in albino rats.

METHODS: Albino Wistar rats were randomly divided into three groups and treated orally with 100 mg/L (low dose) or 5000 mg/L (high dose) of lead acetate for 15 wk. A third group received saline and served as control. At the end of wk 15, colorimetric assays were applied to determine the concentrations of total protein and nitrite, the activities of the oxidative enzymes catalase and superoxide dismutase, and lipid peroxidation in homogenized gastric mucosal samples.

RESULTS: Exposure of rats to lead significantly increased the gastric mucosal damage caused by acidified ethanol. Although the basal gastric acid secretory rate was not significantly altered, the maximal response of the stomach to histamine was significantly higher in the lead-exposed animals than in the unexposed control group. Exposure to low and high levels of lead significantly increased gastric lipid peroxidation to 183.2% ± 12.7% and 226.1% ± 6.8% of control values respectively (P < 0.0). On the other hand, lead exposure significantly decreased catalase and superoxide dismutase (SOD) activities and the amount of nitrite in gastric mucosal samples.

CONCLUSION: Lead increases the formation of gastric ulcers by interfering with the oxidative metabolism in the stomach.

Sphincter of Oddi function in the Australian brush-tailed possum is inhibited by intragastric ethanol

The role of sphincter of Oddi (SO) function in alcoholic acute pancreatitis (AP) is unclear. We aimed to compare the effect of i.v. and intragastric (IG) ethanol on SO function (i.e. trans-sphincteric flow; TSF) and investigate possible neural mechanisms. The involvement of gastric mucosal damage was also investigated by pretreatment with pantoprazole. In anaesthetized Australian possums, blood pressure (BP), TSF and blood ethanol concentrations were measured after i.v. or IG ethanol. Possums were subjected to acute vagotomy, atropine, L-nitro arginine methyl ester (L-NAME) or pantoprazole pretreatment prior to IG ethanol. BP was not significantly altered by ethanol. Ethanol decreased TSF in a dose and route-dependent manner. The lowest dose of IG ethanol reduced TSF but this response was not duplicated by i.v. ethanol producing the same blood ethanol concentrations. Acute vagotomy, atropine or L-NAME pretreatment blocked the ethanol-induced decrease in TSF and simultaneously suppressed the blood ethanol concentration. Pantoprazole pretreatment reduced the TSF response and blood ethanol concentrations implicating mechanisms induced by gastric mucosal damage. We conclude that ethanol (and/or its metabolites) reduces TSF via humoral and neural mechanisms involving vagal pathways, muscarinic receptors and nitric oxide. Reduced TSF could contribute to the onset of AP.

Gastroprotective effect of fructus evodiae water extract on ethanol-induced gastric lesions in rats

Fructus Evodiae is a widely used herbal medicine with anti-inflammatory and analgetic activities in China. The present study was designed to investigate the effect of Fructus Evodiae water extract (FE) on ethanol-induced gastric lesions in rats. Three hours before ethanol challenge, animals were intraperitoneally treated with FE (424.8 mg/kg, 141.6 mg/kg, and 47.6 mg/kg). Subsequently, we employed ex-vivo chamber technique to examine the effect of FE on gastric transmucosal potential difference (PD) changes. NO(x) (nitrate and nitrite) in gastric perfusate and gastric lesion index of whole glandular stomach were determined by intubation. The results showed that FE dose-dependently accelerated the recovery of PD reduction by ethanol, and increased NO(x) production in gastric perfusate. FE also inhibited gastric lesion formation in a dose-dependent manner. These results suggested that FE prevented ethanol-induced gastric mucosal lesions by strengthening the mucosal barrier integrity and increasing gastric mucosal nitric oxide (NO) synthesis.

Gastric mucosal protection via enhancement of MUC5AC and MUC6 by geranylgeranylacetone

The mucus layer that covers gastric mucosa is a powerful barrier that protects tissues from the hazardous gastric environment; however, the role of each gastric MUC type, such as MUC1, MUC5AC, and MUC6, has not been evaluated. The purpose of this study is to identify the MUC type, which plays a predominant role in this protective process by use of geranylgeranylacetone (GGA), a promising cytoprotective agent. In addition, the mechanism of mucus secretion promoted by GGA was investigated. Rat gastric mucosal damage was provoked using ethanol, and GGA was pretreated 1 hour before ethanol. GGA was found to significantly protect rats from ethanol-induced gastric damage by increasing mucus levels, MUC5AC and MUC6, especially at ethanol-induced ulcer margins, but not by MUC1. When expression of heat shock protein 70 (HSP70) and neuronal nitric oxide synthase (nNOS) was evaluated by Western blotting, both were found to be increased in GGA-treated ethanol rats. In addition, the cytoprotective effect of GGA was blocked by L-NMMA, a nonspecific NOS inhibitor, but not blocked by aminoguanidine, a specific inducible nitric oxide synthase inhibitor, thus indicating the participation of nNOS. In conclusion, GGA protected ethanol-induced gastric damage by upregulating MUC5AC and MUC6 rather than MUC1. In addition, HSP70 and nNOS were found to be involved in GGA cytoprotection, probably by increasing mucus production or secretion.

Role of L-arginine in ibuprofen-induced oxidative stress and neutrophil infiltration in gastric mucosa

It has been proposed that neutrophil and oxygen dependent microvascular injuries may be important prime events in gastrointestinal (GI) toxicity of non-steroidal antiinflammatory drugs (NSAIDs). L-arginine (L-ARG) is an essential amino acid which participates in many important biochemical reactions associated to the normal physiology of the organism. In these experimentations, we studied the role of L-ARG, aminoacid precursor of NO synthesis, on ibuprofen (IB) induced gastric lesions, and also on the inflammatory and oxidative mechanisms related to mucosal damage. Oral administration of IB (100 mg kg(-1)), produced severe damage on gastric mucosa, which was more important after 6 h test-period, and was accompanied by a significant increment in myeloperoxidase (MPO) activity, as index of neutrophil activation, as well as lipid peroxidation (LP) levels and xanthine oxidase (XO) activity. However, no changes were observed in total mucosal glutathione (tGSH), nor glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) activity. Simultaneous treatment with equimolar doses of L-ARG (oral and i.p.), considerably reduced the number and intensity of lesions, and at the same time (6 h) the maximum protection was also observed. In addition, L-ARG inhibited the IB-induced LP and XO enhancement, but did not produce changes in leukocyte infiltration, tGSH, GSH-Px and SOD activity. These findings suggest that (1) L-ARG protective effect on gastric mucosa against IB-induced mucosal lesions could be explained by a local effect and also might be due to the systemic action of the aminoacid; (2) the active oxygen species, derived both from XO and activated neutrophils, could play a role in the pathogenesis of gastric injury induced by IB, (3) L-ARG exhibit a protective effect against IB-induced mucosal damage, probably through the inhibition of oxidative stress derived via xanthine-XO, but it does not block the oxygen free radical production through polymorphe nuclear leukocytes.

Investigation of the mechanisms involved in the central effects of glucagon-like peptide-1 on ethanol-induced gastric mucosal lesions

The aim of this study was to investigate the effects of intracerebroventricularly injected glucagon-like peptide-1 (GLP-1) on ethanol-induced gastric mucosal damage and to elucidate the mechanisms involved. Absolute ethanol was administered through an orogastric cannula 5 min before GLP-1 (1 microg/10 microl) injection. One hour later, the rats were decapitated, their stomachs were removed and scored for mucosal damage. GLP-1 inhibited the ethanol-induced gastric mucosal damage by 92%. Centrally injected atropine sulphate, a muscarinic receptor antagonist (5 microg/10 microl), prevented the gastroprotective effect of GLP-1, while mecamylamine, a nicotinic receptor antagonist (25 microg/10 microl), was ineffective. Peripherally injected atropine methyl nitrate (1 mg/kg) did not change the effect of GLP-1, but mecamylamine (5 mg/kg) blocked it. Cysteamine, a somatostatin depletor (280 mg/kg, s.c.), did not affect the protective activity of GLP-1, while inhibition of nitric oxide (NO) synthesis by L-NAME (3 mg/kg, i.v.) significantly abolished the protective effect of GLP-1 on ethanol-induced gastric mucosal lesions. We conclude that central muscarinic and peripheral nicotinic cholinergic receptors and NO, but not somatostatin, contribute to the protective effect of intracerebroventricularly injected GLP-1 on ethanol-induced gastric mucosal damage.

Bombesin-induced gastroprotection

Bombesin is an endogenous gut peptide that is prominent in the stomach. In addition to its effects on modulating acid and gut peptide secretion, recent evidence indicates that bombesin is a potent gastroprotective agent. This review article examines the ability of bombesin to prevent gastric injury. Its protective actions appear to be mediated primarily via the release of endogenous gastrin, as gastroprotection is negated by blockade of gastrin receptors. Bombesin-induced gastroprotection and gastrin release are modified by somatostatin. Immunoneutralization of endogenous somatostatin increases the ability of bombesin to prevent gastric injury by increasing gastrin release. In mechanistic studies, ablation of capsaicin-sensitive afferent neurons abolishes bombesin-induced gastroprotection while cyclo-oxygenase inhibition partially reverses this effect. Nitric oxide synthase inhibition also negates bombesin-induced gastroprotection as well as the ability of bombesin to increase gastric mucosal blood flow. Taken together, the available evidence indicates that bombesin causes release of endogenous gastrin that activates sensory neurons located in the gastric mucosa. Activation of sensory neurons causes increased production of nitric oxide through activation of constitutive nitric oxide synthase, which leads to a resultant increase in gastric mucosal blood flow and renders the stomach less susceptible to damage from luminal irritants.

Overexpression of inducible nitric oxide synthase in gastric mucosa of rats with portal hypertension: correlation with gastric mucosal damage

BACKGROUND

An increased biosynthesis of nitric oxide (NO) has been implicated in the hyperdynamic circulation and development of collaterals of portal hypertension (PHT) because of its potent vasodilatory effects. NO is synthesized from L-arginine by three different isozymes of nitric oxide synthase (nNOS, iNOS and eNOS). Thus, the expression of inducible NOS (iNOS) might account for NO overproduction in PHT. However, in previous investigations, the role of iNOS in the pathogenesis of PHT gastropathy remained controversial. Our current study was in both molecular and protein levels to determine whether the expression of iNOS is responsible for PHT gastropathy.

MATERIALS AND METHODS

PHT was induced experimentally by partial ligation of the portal vein. Fourteen days after partial ligation of the portal vein, the rats were randomly assigned to receive either vehicle or L-NAME (NOS inhibitor) at doses of 5 mg/kg/day, 10 mg/kg/day, or 25 mg/kg/day by gastric lavage twice a day for 1 week. Sham operated rats served as controls. Northern hybridization and in situ hybridization are used to compare the expression of gastric mucosa iNOS mRNA in the PHT rats and the controls. NO was measured by the Griess method after reduction of nitrate to nitrite with nitrate reductase. Immunohistochemical staining was carried out to detect the iNOS protein. In addition, the severity of gross gastric mucosal lesions was evaluated macroscopically by a gross ulcer index.

RESULTS

The iNOS expression at both mRNA and protein was prominently increased in PHT rats, accompanied with the enhanced NO production. The gastric mucosa iNOS mRNA and serum NO levels were significantly decreased after L-NAME administration (P < 0.05). However, the markedly reduced gastric mucosal damage in PHT rats was observed only at high does of L-NAME (25 mg/kg/day) administration.

CONCLUSION

PHT triggers overexpression of iNOS mRNA and proteins in rat gastric mucosa, but that this alone does not account for PHT gastropathy.

Somatostatin-induced gastric protection against ethanol: involvement of nitric oxide and effects on gastric mucosal blood flow

BACKGROUND/AIMS

The mechanisms of somatostatin-mediated gastroprotection are not fully understood. Aims of this study were to determine in the rat the role of nitric oxide (NO) in somatostatin-induced effects on gastric mucosal protection and blood flow (GMBF) in the absence and in the presence of intraluminal ethanol.

METHODS

Ethanol (70% v/v)-induced gastric mucosal injury after orogastric dosing was quantitated at 30 min and GMBF determined in an ex vivo gastric chamber preparation.

RESULTS

Somatostatin (4 microg/kg; i.p.) protection against ethanol-induced ulceration was prevented by the NO inhibitor L-NNA and restored by L-arginine, but not D-arginine. Somatostatin (1-8 microg/kg; i.p.) did not effect basal GMBF. The gastroprotective dose of somatostatin (4 microg/kg; i.p.) prevented the decrease in GMBF caused by ethanol. L-NNA reversed this vascular effect of somatostatin.

CONCLUSION

Somatostatin-induced gastroprotection and restoration of GMBF during ethanol exposure involve mechanisms which are dependent on NO generation.

Nitric oxide donors retard wound healing in cultured rabbit gastric epithelial cell monolayers

Effects of nitric oxide (NO) on gastric wound healing were investigated in primary rabbit gastric epithelial cell cultures. We analyzed the speed of cell migration, proliferation, and apoptosis after creating a round wound on the cell cultures. The monolayers were incubated with or without the NO donor sodium nitroprusside, oxatriazolimine 1,2,3,4-oxatriazolium, 5amino-3-(3,4-dichlorophenylchloride), or the peroxynitrite generator 3-morpholinosydnomine-N-ethylcarbamide. The possible role of cGMP as a second messenger of NO was investigated with 8-bromo-cGMP. The role of O2(-*) was evaluated using diethyldithiocarbamate and pyrogallol. The effects of superoxide dismutase and allopurinol were also investigated. NO inhibited the speed of cell migration and proliferation and induced cell apoptosis in a dose- and time-dependent manner. The effects were augmented with O2(-*) generators and ameliorated by O2-(8) scavengers, whereas cGMP had no significant effect on wound healing. NO donors retard gastric wound healing by inhibiting migration and proliferation and inducing cell apoptosis. These effects do not seem to be mediated via cGMP, but O2(-*). or peroxynitrites may be involved.

Nitric oxide: relation to integrity, injury, and healing of the gastric mucosa

Nitric oxide (NO) plays a multifaceted role in mucosal integrity. The numerous functions of NO and the double-edged role played by NO in most of them provide a great complexity to the NO action. The three enzymatic sources of NO, neuronal NO-synthase (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS), have been characterised in the gastrointestinal tract. The protective properties of the NO derived from constitutive NO-synthases (eNOS and nNOS) have already been well established. Less clear is the role assigned to iNOS. The simplistic initial view of low levels of NO synthesised by constitutive NOS being protective while exaggerated NO levels after iNOS induction leading irremediably to cytotoxicity is being questioned by new evidence. As initially reported for constitutive NOS, iNOS activity may be associated to reduced leukocyte-endothelium interaction and platelet aggregation as well as protection of mucosal microcirculation. Moreover, iNOS activity may be important to resolve inflammation by increasing apoptosis in inflammatory cells. It is entirely possible that a low level of expression of iNOS will reflect a positive host-defense response to challenge, but that exaggerated or uncontrolled expression of iNOS itself becomes detrimental. There is no doubt about the protective role of NO in physiological conditions. However, when the mucosa is threatened, the role of NO becomes multiple and the final effect will probably depend on the nature of the insult, the environment involved, and the interaction with other mediators.

Induction of nitric oxide synthesis by probiotic Lactobacillus rhamnosus GG in J774 macrophages and human T84 intestinal epithelial cells

BACKGROUNDS AND AIMS

Probiotic Lactobacillus rhamnosus GG (LGG) has proved to be beneficial in the treatment of viral- and antibiotic-associated diarrhea but the mechanisms of action remain unknown. Nitric oxide (NO) is involved in the protective mechanisms in the gastrointestinal tract and may contribute to some of the beneficial effects of probiotics. The aim of the present study was to investigate if induction of NO synthesis is involved in the cellular actions of LGG.

METHODS

NO synthesis and its regulation were measured in cultures of J774 murine macrophages and human T84 colon epithelial cells. NO production was measured as its metabolite nitrite accumulated into the culture medium. Inducible nitric oxide synthase (iNOS) protein and iNOS mRNA were detected by Western blot and RT-PCR, respectively.

RESULTS

In J774 macrophages, LGG induced a low level production of NO in the presence of gamma interferon (IFNgamma) and it was inhibited by NOS inhibitors, cycloheximide and by a NF-kappa B inhibitor pyrrolidinedithiocarbamate. Accordingly, LGG and IFNgamma-stimulation increased iNOS mRNA and protein levels. T84 cells produced NO in response to LGG when first primed with a combination of IL-1beta, TNFalpha and IFNgamma. Lipoteichoic acid (LA), an antigenic structure in gram-positive bacteria, also induced NO formation in J774 cells in the presence of IFNgamma suggesting that LA may be the active component in LGG.

CONCLUSIONS

LGG induces NO production in J774 macrophages and in human T84 colon epithelial cells through induction of iNOS by a mechanism involving activation of transcription factor NF-kappaB. Induction of iNOS and low-level synthesis of NO may be involved in the protective actions of LGG in the gastrointestinal tract.

Nitric oxide synthase inhibition negates bombesin-induced gastroprotection

BACKGROUND

Bombesin prevents gastric injury primarily by the release of endogenous gastrin. Gastroprotection by exogenous gastrin is negated by nitric oxide synthase inhibition, which implicates a role for nitric oxide as a protective mediator. Because both endothelial and inducible isoforms of this enzyme can play a role in mucosal defense, this study was done to examine the contrasting effects of 2 nitric oxide synthase inhibitors on bombesin-induced gastroprotection.

METHODS

Rats were given subcutaneous saline or bombesin (10-100 microg/kg) 30 minutes before they received a 1-mL orogastric bolus of acidified ethanol (150 mmol/L of hydrochloric acid/50% ethanol) and rats were killed 5 minutes later for assessment of macroscopic injury (mm(2)). Gastric mucosal blood flow was measured by laser Doppler. Endothelial, neural, and inducible nitric oxide synthase were assessed by using Western immunoblot.

RESULTS

Bombesin decreased gastric mucosal damage, and dose-dependently increased blood flow when compared with saline-treated rats. Endothelial but not neural or inducible nitric oxide synthase immunoreactivity was increased by bombesin. In additional studies, intraperitoneal administration of N(G)-nitro-l-arginine methyl ester (l-NAME, 5-10 mg/kg), a nonselective nitric oxide synthase inhibitor, negated bombesin-induced gastroprotection and hyperemia, whereas the selective inducible inhibitor aminoguanidine (45 mg/kg) did not. Subcutaneous (SC) l-arginine (300 mg/kg), but not d-arginine, abolished the effects of l-NAME.

CONCLUSIONS

Taken together, these data suggest that nitric oxide produced by the endothelial isoform of nitric oxide synthase plays an important role in mediating the gastroprotective and hyperemic actions associated with bombesin.

Nonsteroidal anti-inflammatory drugs

NSAID-associated dyspeptic symptoms are common and can be managed empirically with an H2-receptor antagonist or a proton-pump inhibitor. Treatment of established gastroduodenal ulcers is accomplished best by withholding the offending drugs. Proton-pump inhibitors appear to heal ulcers at the same rate whether or not NSAID therapy is continued. After the ulcer is healed and if NSAID therapy must be continued, prophylaxis is accomplished best by the concomitant use of proton-pump inhibitors, misoprostol (at least 200 micrograms 3 times a day), or a NSAID that preferentially inhibits COX-2. The future development of newer, safer NSAID preparations, including highly selective COX-2 inhibitors and nitric oxide-releasing NSAIDs, should provide better treatment options for the increasing number of individuals requiring anti-inflammatory agents.

Nitric oxide and intestinal inflammation

Inflammation of the intestinal tract remains a very serious concern in the clinical setting. Unfortunately, to date, the mechanisms underlying many inflammatory conditions such as sepsis or inflammatory bowel diseases are poorly understood and our therapeutic interventions are less than ideal. Over the past decade, an abundance of research has been directed toward the role of nitric oxide (NO) in intestinal inflammation. It has become apparent that NO might have a dichotomous role as both a beneficial and detrimental molecule. Nitric oxide is a weak radical produced from L-arginine via the enzyme nitric oxide synthase (NOS). NOS exists in three distinct isoforms; constitutively (cNOS) expressed neuronal NOS (NOS1 or nNOS) and endothelial NOS (NOS3 or eNOS) or an inducible isoform (NOS2 or iNOS) capable of high production output of NO during inflammation. Constitutively expressed NOS has been shown to be critical to normal physiology and inhibition of these enzymes (nNOS or eNOS) caused damage. It has been proposed that the high output production of NO from iNOS causes injury, perhaps through the generation of potent radicals such as peroxynitrite and hence may explain the apparent dichotomous role of NO. However, recent studies have challenged this simple paradigm providing evidence that iNOS may have some protective role in some inflammatory models. Moreover, the importance of peroxynitrite has been questioned. In this review we discuss the role of cNOS and iNOS in intestinal inflammation and provide an overview of peroxynitrite in intestinal inflammation, highlighting some of the controversy that exists.

L-Arginine protects and exacerbates ethanol-induced rat gastric mucosal injury

BACKGROUND AND AIMS

We have previously demonstrated that 60% ethanol (EtOH) increases macromolecular leakage and induces focal lesion formation in areas of permanent flow stasis within gastric mucosal vessels. Nitric oxide (NO) may prevent lesion formation by inhibiting leakage. This study used fluorescent in vivo microscopy to investigate (i) whether L-arginine (NO precursor) prevented EtOH induced injury and (ii) the mechanisms of protection.

METHODS

Experiments were carried out on anaesthetized rats (hypnorm/diazepam) receiving either intra-arterial fluorescein isothiocyanate-bovine serum albumin (0.2 mL/100 g), a marker for quantitating leakage, or Acridine red (0.1 mL/100 g) which labels leukocytes. Animals then received 100, 300 or 500 mg/kg L-arginine (i.a.) followed by 60% EtOH or distilled water, topically applied to the gastric mucosa (n = 6 for each group). Vessel diameter, macromolecular leakage of labelled albumin from post capillary venules (PCV) and capillaries and leukocyte activity were quantitated using image analysis.

RESULTS

L-Arginine (100 mg/kg) did not increase vessel diameter or prevent EtOH-induced lesion formation and leakage. Both 300 mg/kg and 500 mg/kg alone induced significant and sustained increases in PCV diameter after 15 (P< 0.01) and 5 min (P< 0.001), respectively. Lesion formation was only prevented by 300 mg/kg L-arginine, whereas 500 mg/kg exacerbated haemorrhagic lesion formation over the entire exposed mucosa. Neither 300 mg/kg nor 500 mg/kg L-arginine prevented leakage following EtOH. No leukocyte activity was observed following EtOH with or without L-arginine pretreatment.

CONCLUSION

L-Arginine (300 mg/kg) prevented lesion formation. The mechanism of protection probably involved the increased blood flow in the dilated PCV and not the inhibition of leakage. The combined effects of EtOH and the possible high NO levels exacerbate gastric mucosal damage despite the increases observed in vessel diameter.

Nitric oxide (NO)-related pharmaceuticals: contemporary approaches to therapeutic NO modulation

The biologically important gaseous radical, nitric oxide (NO), is a versatile chemical entity that enters into regulatory, protective, and adverse interactions with biomolecules and cells, in some cases through NO-derived nitrogen oxide species. Both excess tissue NO and its insufficiency have been implicated in the genesis or evolution of several important disease states. The associated medical needs and commercial opportunities have fostered attempts to modulate tissue NO tone for symptomatic benefit or therapeutic gain. State-of-the-art strategies for NO modulation in contemporary drug discovery and development encompass sexual dysfunction, cardiovascular, and antiinflammatory indications. Increased understanding of NO's physiological chemistry and ways to target its pharmacology appear critical to the successful clinical exploitation of NO's diverse properties. Integration of research on both the basic science of NO's mechanistic biology and the applied science of drug discovery and development represents a millennium mandate to the pharmaceutical industry in the area of NO-related therapeutics.

Protective role of intracellular glutathione against nitric oxide-induced necrosis in rat gastric mucosal cells

BACKGROUND

Nitric oxide synthase activity is increased in the stomach in association with Helicobacter pylori infection and portal hypertension, but the mechanism by which nitric oxide contributes to mucosal damage remains unclear.

AIM

To examine whether nitric oxide injures gastric mucosal cells and whether cellular glutathione affects nitric oxide-induced cytotoxicity.

METHODS

A confluent monolayer of RGM-1 gastric mucosal cells was exposed to nitric oxide donors (NOC5 or NOC12). Cell viability was determined by trypan blue dye exclusion, lactate dehydrogenase release and supravital staining with Hoechst 33342 and propidium iodide. The kinetics of the reduced/oxidized forms of glutathione were also measured, as well as the effect of glutathione-depletion or glutathione-precursor treatment on nitric oxide-induced cytotoxicity.

RESULTS

Excess exogenous nitric oxide produced by NOC5 or NOC12 induced necrosis in RGM-1 cells in a time- and concentration-dependent manner. The level of reduced glutathione drastically decreased prior to the loss of cell viability and remained low, but oxidized glutathione was not affected. Glutathione depletion increased necrosis of both NOCs in an NOC-concentration-related fashion, while pre-treatment with gamma-glutamylcysteine ethyl ester reduced their necrotic susceptibility.

CONCLUSION

Exogenous nitric oxide induced necrosis in gastric mucosal cells, and intracellular reduced glutathione protects gastric mucosal cells from damage by nitric oxide.

Investigation on the mechanism involved in the effects of agmatine on ethanol-induced gastric mucosal injury in rats

Effects of agmatine, an endogenous metabolite formed by decarboxylation of L-arginine, on ethanol-induced gastric mucosal injury were investigated in rats. Agmatine at 1 and 10 mg/kg i.p doses significantly increased ethanol-induced gastric mucosal injury. This effect of agmatine was abolished completely by pretreatment with idazoxan, an imidazoline receptor-antagonist and alpha2 receptor- antagonist, (0.5 mg/kg i.p), partly by yohimbine, an alpha2 receptor- antagonist, (1 mg/kg i.p) but not by L-arginine, a precursor of nitric oxide, (500 mg/kg i.p). Our results suggest that agmatine had a potent ulcerogenic effect mediated, at least in part, by both alpha2-adrenoceptors and imidazoline receptors.

Role of mucosal blood flow: a conceptional review in gastric mucosal injury and protection

The present article overviews the role of gastric mucosal blood flow (MBF) in gastric mucosal injury and protection. The MBF maintains the structure and function of the stomach and, thereby, is closely associated with the pathogenesis and the healing of gastrointestinal lesions. Gastric blood flow was regulated and modified by systemic and also local metabolic factors, such as prostaglandin, leukotrienes and other endogenous chemical mediators, in the mucosa. In the present article, we review the role of endothelin (ET) and nitric oxide (NO) in the development of gastric mucosal injury and protection via mucosal microcirculation. Endothelin-1 was increased under various stressful conditions and caused microcirculatory disturbances resulting in mucosal injury. Inhibitors of NO aggravated mucosal injury induced by ethanol, which produced mucosal congestion. Thus, regionally disturbed gastric circulation is closely associated with the pathogenesis of ethanol- and non-steroidal anti-inflammatory drug-induced gastric lesions. The endothelium-derived vasoactive substances ET and NO regulate gastric mucosal microcirculation and an imbalance of endothelium-derived factors may play an important pathophysiological role in the development of gastric lesions.