Effect of cigarette smoke on ethanol-induced gastric mucosal lesions: the role of nitric oxide and neutrophils

Animal models of gastrointestinal inflammation and cancer

Inflammation and cancer are the two major disorders in the gastrointestinal tract. They are causally related in their pathogenesis. It is important to study animal models' causal relationship and, in particular, to discover new therapeutic agents for such diseases. There are several criteria for these models in order to make them useful in better understanding the etiology and treatment of the said diseases in humans. In this regard, animal models should be similar as possible to human diseases and also be easy to produce and reproducible and also economic to allow a continuous replication in different laboratories. In this review, we summarize the various animal models for inflammatory and cancerous disorders in the upper and lower gastrointestinal tract. Experimental approaches are as simple as by giving a single oral dose of alcohol or other noxious agents or by injections of multiple dosages of ulcer inducing agents or by parenteral administration or in drinking water of carcinogens or by modifying the genetic makeups of animals to produce relatively long-term pathological changes in particular organs. With these methods they could induce consistent inflammatory responses or tumorigenesis in the gastrointestinal mucosa. These animal models are widely used in laboratories in understanding the pathogenesis as well as the mechanisms of action for therapeutic agents in the treatment of gastrointestinal inflammation and cancer.

Evidence for the Involvement of RhoA Signaling in the Ethanol-Induced Increase in Intestinal Epithelial Barrier Permeability

In this work, we investigated the potential role of the small G protein RhoA in ethanol-induced tight junction (TJ) protein disassembly and increased intestinal epithelial barrier (IEB) permeability. Our study used Caco-2 cells as an in vitro IEB model and RhoA short hairpin RNA (shRNA) interference to establish whether RhoA plays a role in ethanol-induced TJ opening. RhoA shRNA interference partially inhibited epithelial leakage and restored normal transepithelial electrical resistance (TEER) values in the IEB. Moreover, RhoA shRNA interference prevented a shift in occludin distribution from insoluble to soluble fractions. Additionally, RhoA shRNA interference inhibited the ethanol-induced expression of zonula occludens-1 (ZO-1). Finally, RhoA shRNA interference inhibited an ethanol-induced increase in RhoA activity. The contributions of RhoA to an ethanol-induced increase in IEB permeability are associated with TJ disassembly.

Role of capsaicin-sensitive primary afferent neurons and non-protein sulphydryl groups on gastroprotective effect of amifostine against ethanol-induced gastric damage in rats

BACKGROUND

Amifostine has been widely tested as a cytoprotective agent against a number of aggressors in different organs. Recently, a gastroprotective effect was observed for this drug in a model of indomethacin-induced gastric injury. Our objective was to investigate the effect of amifostine on ethanol-induced gastric injury and the role played in this mechanism by afferent sensory neurons, non-protein sulfhydryl groups, nitric oxide, ATP-sensitive potassium channels, and cyclooxygenase-2.

METHODS

Rats were treated with amifostine (22.5, 45, 90, or 180 mg/kg, PO or SC). After 30 min, the rats received absolute ethanol (5 ml kg(-1), PO). One hour later, gastric damage was quantified with a planimeter. Samples from the stomach were also taken for histopathological assessment and for assays of non-protein sulfhydryl groups. The other groups were pretreated with L-NAME (10 mg kg(-1), IP), glibenclamide (10 mg kg(-1), PO), or celecoxib (10 mg kg(-1), PO). After 30 min, the animals were given amifostine (90 mg kg(-1), PO or SC), followed 30 min later by gavage with absolute ethanol (5 ml kg(-1)). Other rats were desensitized with capsaicin (125 mg kg(-1), SC) 8 days prior to amifostine treatment.

RESULTS

Amifostine administration PO and SC significantly and dose-dependently reduced ethanol-induced macroscopic and microscopic gastric damage by restoring glutathione levels in the stomach mucosa. Amifostine-promoted gastroprotection against ethanol-induced stomach injury was reversed by pretreatment with neurotoxic doses of capsaicin, but not by L-NAME, glibenclamide, or celecoxib.

CONCLUSIONS

Amifostine protects against ethanol-induced gastric injury by increasing glutathione levels and stimulating the afferent sensory neurons in the stomach.

Dysregulation of gastric H,K-ATPase by cigarette smoke extract

AIM

To test whether the expression and activity of H,K-ATPase in parietal cells would be affected by cigarette smoke extract.

METHODS

Extracts of cigarette smoke were administered into mice by gastric gavage (5 mg/kg body weight/day) for 3 d or in drinking water for 7 or 14 d. For the latter, each day a mouse consumed 5 mL water containing extracts of two cigarettes, on average. Control littermate mice received only vehicle. To compare the amount of H,K-ATPase in control and smoke-treated mice, the stomach was processed for Western blotting and immunohistochemical analysis using monoclonal antibodies specific for alpha- or beta-subunits of H,K-ATPase. The p-nitrophenylphosphatase activity assay was used as a measurement for K-dependent H,K-ATPase activity.

RESULTS

Probed transblots showed an increase in the amount of H,K-ATPase in smoke-treated mice which was confirmed by immunohistochemistry and was found to be due to increased amounts of protein per parietal cell rather than an increased parietal cell number. The increase in the amount of H,K-ATPase was associated with an enhancement of its enzymatic activity. K-dependent activity in control and smoke-treated mice was significantly different (respectively, 0.12 micromol/mg vs 0.27 micromol/mg per minute, P < 0.05).

CONCLUSION

Administration of cigarette smoke extract is associated with an increase in the amount and activity of H,K-ATPase and hence, smokers are susceptible to development of peptic ulcer.

Nitric oxide-mediated intestinal injury is required for alcohol-induced gut leakiness and liver damage

BACKGROUND

Alcoholic liver disease (ALD) requires endotoxemia and is commonly associated with intestinal barrier leakiness. Using monolayers of intestinal epithelial cells as an in vitro barrier model, we showed that ethanol-induced intestinal barrier disruption is mediated by inducible nitric oxide synthase (iNOS) upregulation, nitric oxide (NO) overproduction, and oxidation/nitration of cytoskeletal proteins. We hypothesized that iNOS inhibitors [NG-nitro-l-arginine methyl ester (l-NAME), l-N(6)-(1-iminoethyl)-lysine (l-NIL)] in vivo will inhibit the above cascade and liver injury in an animal model of alcoholic steatohepatitis (ASH).

METHODS

Male Sprague-Dawley rats were gavaged daily with alcohol (6 g/kg/d) or dextrose for 10 weeks +/- l-NAME, l-NIL, or vehicle. Systemic and intestinal NO levels were measured by nitrites and nitrates in urine and tissue samples, oxidative damage to the intestinal mucosa by protein carbonyl and nitrotyrosine, intestinal permeability by urinary sugar tests, and liver injury by histological inflammation scores, liver fat, and myeloperoxidase activity.

RESULTS

Alcohol caused tissue oxidation, gut leakiness, endotoxemia, and ASH. l-NIL and l-NAME, but not the d-enantiomers, attenuated all steps in the alcohol-induced cascade including NO overproduction, oxidative tissue damage, gut leakiness, endotoxemia, hepatic inflammation, and liver injury.

CONCLUSIONS

The mechanism we reported for alcohol-induced intestinal barrier disruption in vitro - NO overproduction, oxidative tissue damage, leaky gut, endotoxemia, and liver injury - appears to be relevant in vivo in an animal model of alcohol-induced liver injury. That iNOS inhibitors attenuated all steps of this cascade suggests that prevention of this cascade in alcoholics will protect the liver against the injurious effects of chronic alcohol and that iNOS may be a useful target for prevention of ALD.

Oats supplementation prevents alcohol-induced gut leakiness in rats by preventing alcohol-induced oxidative tissue damage

We reported previously that oats supplementation prevents gut leakiness and alcoholic steatohepatitis (ASH) in our rat model of alcoholic liver disease. Because oxidative stress is implicated in the pathogenesis of both alcohol-induced gut leakiness and ASH, and because oats have antioxidant properties, we tested the hypothesis that oats protect by preventing alcohol-induced oxidative damage to the intestine. Male Sprague-Dawley rats were gavaged for 12 weeks with alcohol (starting dose of 1 g/kg increasing to 6 g/kg/day over the first 2 weeks) or dextrose, with or without oats supplementation (10 g/kg/day). Oxidative stress and injury were assessed by measuring colonic mucosal inducible nitric-oxide synthase (iNOS) (by immunohistochemistry), nitric oxide (colorimetric assay), and protein carbonylation and nitrotyrosination (immunoblotting). Colonic barrier integrity was determined by assessing the integrity of the actin cytoskeleton (immunohistochemistry) and the integrity of tight junctions (electron microscopy). Oats supplementation prevented alcohol-induced up-regulation of iNOS, nitric oxide overproduction in the colonic mucosa, and increases in protein carbonyl and nitrotyrosine levels. This protection was associated with prevention of ethanol (EtOH)-induced disorganization of the actin cytoskeleton and disruption of tight junctions. We conclude that oats supplementation attenuates EtOH-induced disruption of intestinal barrier integrity, at least in part, by inhibiting EtOH-induced increases in oxidative stress and oxidative tissue damage. This inhibition prevents alcohol-induced disruption of the cytoskeleton and tight junctions. This study suggests that oats may be a useful therapeutic agent--a nutraceutical--for the prevention of alcohol-induced oxidative stress and organ dysfunction.

Central ghrelin gastroprotection involves nitric oxide/prostaglandin cross-talk

BACKGROUND AND PURPOSE

Ghrelin, a gut-brain peptide, is considered a gastroprotective factor in gastric mucosa. We investigated the role of prostaglandins (PG) and the possible interplay between PGs and nitric oxide (NO) in ghrelin gastroprotection against ethanol (EtOH)-induced gastric lesions.

EXPERIMENTAL APPROACH

We examined the effects of (1) central ghrelin (4 mug per rat) injection on PGE(2) accumulation in normal or EtOH-lesioned gastric mucosa, (2) pretreatment with indomethacin (10 mg kg(-1), p.o.), a non-selective cyclooxygenase (COX) inhibitor, and with a selective COX-1, SC560 (5 mg kg(-1), p.o.) or COX-2 inhibitor, celecoxib (3.5 mg kg(-1), p.o.) on ghrelin gastroprotection against 50% EtOH (1 mL per rat)-induced gastric lesions, (3) the NO synthase inhibitor, L-NAME (70 mg kg(-1), s.c), on gastric PGE(2) content in ghrelin-treated rats and (4) central ghrelin on the expression of constitutive and inducible NOS and COX mRNA and on the localization of the immunoreactivity for COX-2 in the gastric mucosa exposed to EtOH.

KEY RESULTS

Ghrelin increased PGE(2) in normal mucosa, whereas, it reversed the EtOH-induced PGE(2) surge. Ghrelin had no effect on mucosal COX-1 expression but reduced the EtOH-induced increase in COX-2 expression and immunoreactivity. Indomethacin and SC560, but not celecoxib, removed ghrelin gastroprotection. L-NAME prevented the PGE(2) surge induced by ghrelin and, like indomethacin, reduced EtOH-induced PGE(2) increase. Ghrelin enhanced eNOS expression and reduced iNOS mRNA.

CONCLUSIONS AND IMPLICATIONS

This study shows that COX-1-derived PGs are mainly involved in ghrelin gastroprotection and that the constitutive-derived NO together with PGE(2) are involved in ghrelin gastroprotective activity.

In vivo and in vitro antioxidant activity of ghrelin: Attenuation of gastric ischemic injury in the rat

BACKGROUND AND AIM

Gherlin, an endogenous ligand for the growth hormone secretagogue receptor (GHS-R), is produced by stomach cells. It regulates food intake, gastric secretion and motility. However, its role as a protective agent in gastric ischemia/reperfusion (I/R) injury has not yet been investigated. Therefore, the objectives of the present study were to: (i) test the in vivo effect of peripherally administered ghrelin on gastric I/R-induced lesions in rats; and (ii) investigate in vitro the effect of ghrelin on reactive oxygen species (ROS) production by human polymorphoneuclear (PMN) cells.

METHODS

The present study was carried out on three groups of rats (six per group): control (sham-operated), I/R (clamping of celiac artery for 30 min and reperfusion for 1 h), and I/R + ghrelin (200 ng/kg i.v., 15 min before ischemia and before reperfusion, respectively). Histological assessment of hematoxylin and eosin stained sections was performed and immunostaining with inducible nitric oxide (iNOS) antibody were performed on a gastric paraffin embedded section. Oxidative stress markers thiobarbituric acid reactive substance (TBARS) and glutathione (GSH) were measured in gastric tissue homogenates. Serum lactic acid dehydrogenase (LDH) was determined. Tumor necrosis factor-alpha (TNF-alpha) was assayed in gastric tissue homogenate. Gastric permeability was assessed calorimetrically using Evans blue dye. In vitro studies were carried out on isolated human PMN cells incubated with ghrelin and tested for ROS generation as measured by chemiluminecence (CL).

RESULTS

Peripheral administration of ghrelin attenuated gastric injury by reducing ulceration, tissue congestion, cellular infiltration and vascular permeability. Serum level of LDH and tissue content of TNF-alpha were markedly reduced. A decrement in TBARS and an increment in GSH were observed. Ghrelin treatment attenuated iNOS protein expression which was upregulated by gastric ischemic injury. In vitro studies showed for the first time that ghrelin inhibited ROS generation by human PMN in a dose-dependent manner.

CONCLUSIONS

These results provide evidence that peripherally administered ghrelin protects against gastric I/R injury. We also demonstrated that this protection is possibly accomplished through the antioxidant activity of ghrelin observed in vivo and in vitro.

Constituents and antiulcer effect of Alchornea glandulosa: activation of cell proliferation in gastric mucosa during the healing process

Alchornea glandulosa (Euphorbiaceae) is a plant used in folk medicine as an antiulcer agent. Rats pretreated with methanolic extract obtained from the leaves of A. glandulosa (AG) showed a dose-dependent effect and significant reduction of gastric ulcers induced by absolute ethanol at the doses of 500 (57%) and 1000 mg/kg (85%) in relation to the control group. Pretreatment of mice with AG (500, 1000 mg/kg, p.o.) showed dose-dependent activity and significantly decreased the severity of lesions caused by HCl/ethanol and by non steroidal anti inflammatory drug-induced gastric lesions. Pretreatment with AG also induced antisecretory action via local and systemic routes and a significant decrease in the total gastric acid content. The gastroprotective effects of AG involved the participation of nitric oxide and increased levels of endogenous sulfhydryl compounds, which are defensive mechanisms of the gastrointestinal mucosa against aggressive factors. The ability of AG to heal gastric ulcers was evaluated after 14 consecutive days of treatment. The results showed that single oral administrations of AG (250 mg/kg/once daily) potently stimulates gastric epithelial cell proliferation that contributes to the accelerated healing of gastric ulcers induced by acetic acid. In addition, no subacute toxicity (body weight gain, vital organs, and serum biochemical parameters) was observed during treatment with AG. Phytochemical investigation of AG led to the isolation of myricetin-3-O-alpha-L-rhamnopyranoside, quercetin-3-O-alpha-L-arabinopyranoside, quercetin-3-O-beta-D-galactopyranoside, quercetin, amentoflavone, methyl gallate, gallic acid, and pterogynidine. We also established the phytochemical profile of AG with the quantification of total phenolic compounds. These compounds may contribute to the observed antiulcerogenic effects of AG.

The effects of chronic exposure to ethanol and cigarette smoke on the formation of peroxynitrite, level of nitric oxide, xanthine oxidase and myeloperoxidase activities in rat kidney

The aim of this study was to investigate the effects of chronic ethanol intake and cigarette smoke exposure on rat kidney. The animals were divided into four experimental groups: (1) the control group (C), (2) the ethanol group (E), (3) the cigarette smoke group (CS), and (4) the cigarette smoke plus ethanol group (CS+E). Rats in E, CS and CS+E groups were treated with ethanol and/or cigarette smoke for 6 months. The animals were killed and the kidneys were removed to determine the activity of xanthine oxidase (XO), myeloperoxidase (MPO) and the levels of nitric oxide (NO). Histopathological and immunohistochemical analysis were performed in kidney tissues. The activity of XO/g protein were 2.8 +/- 0.3, 5.2 +/- 0.3, 3.2 +/- 0.1, and 7.4 +/- 0.7 U for C, E, CS and CS+E groups, respectively. In groups E, and CS+E, the XO values were significantly higher than in group C (P < 0.05). The increase in XO activity of CS was not significantly different from group C (P > 0.05). There was a significant increase in XO activity of group CS+E as compared to CS and E groups (P < 0.05), and also a significant difference in XO activity between E and CS was observed (P < 0.05). The activity of MPO/g protein were 13.5 +/- 0.6, 16.2 +/- 1.1, 14.7 +/- 1.1, 23.8 +/- 0.9 U for C, E, CS, and CS+E groups, respectively. While MPO activity of kidneys from group CS+E were significantly higher as compared to C, CS, and E groups (P < 0.05), there was no significant difference among the groups of C, CS, E (P > 0.05). The levels of NO/g wet tissue were 347.7 +/- 8.5, 261.1 +/- 4.8, 329.8 +/- 5.6, and 254.2 +/- 3.8 nmol for C, E, CS, and CS+E groups, respectively. In groups of E and CS+E, the NO values were significantly lower than that of group C animals (P < 0.05). Although we detected lower NO levels in the E and CS+E groups than in CS group (P < 0.05), a significant difference in NO levels between CS+E and E groups was not observed. In the histopathological analysis of the kidney slices, severe degenerations in kidney tissues of group CS, E, CS+E were observed. Generally, the histological changes in kidney of CS+E and E groups were more severe than those observed in CS alone. While we observed a strong immunoreactivity for anti-nitrotyrosine antibody in kidneys of group CS+E, examination of sections from rat kidneys in group E revealed moderate staining. On the other hand, group CS had very little immunostaining. There was no immunostaining in group C. We concluded that chronic ethanol administration and cigarette smoke exposure may cause oxidative and nitrosative stress which lead to rat kidney damage.

Effects of hexarelin against acid-independent and acid-dependent ulcerogens in the rat

The effects of intracerebroventricular (icv) or subcutaneous (sc) hexarelin (Hexa) administration, against gastric ulcers induced by ethanol (50%, 1 ml/rat/os) or Indomethacin (20 mg/kg/os) were examined in conscious rats. Hexa at 1 nmol/rat, icv or 10 nmol/kg, sc reduced ethanol-induced ulcers by 47% and 32% respectively. Hexa, but not ghrelin significantly worsened (+40%) Indomethacin-induced ulcers when injected sc. Hexa-gastroprotection against ethanol-induced ulcers was removed by the GHS-R antagonist (D-Lys3)-GRPR-6 and by the inhibitor of NO-synthase (NOS) Nomega-nitro-L-arginine methyl ester. Semiquantitative RT-PCR assay of gastric NOS mRNA isoforms revealed that the reduction in iNOS-derived NO and the increase of constitutive-derived NO are relevant for the gastroprotection of Hexa against ethanol-induced gastric damage.

Rebamipide binds to iNOS-positive cells in acetic acid-treated but not in ethanol-treated rat gastric mucosa

BACKGROUND

Rebamipide is a gastroprotective agent to stimulate prostaglandin generation in gastric mucosa and attenuate the activity of neutrophils, but direct evidence for the effector sites of this agent has remained to be clarified.

AIM

The present study was undertaken to show the effector sites of rebamipide in control and ulcer-provoked rats.

METHODS

The rats were divided into control, acetic acid- and ethanol-treated rats. In the acetic acid-treated group, 100% acetic acid was attached to the serosal surface of the stomach for 30 s, 7 days before the experiments. In the ethanol-treated group, a dose of 0.5 mL/100 g body weight of 50% ethanol was administered through orogastric intubation 2 h before the experiments. Using the unfixed cryostat sections, aqueous solution of 3H-rebamipide was applied and the localization of the binding sites of rebamipide was investigated by autoradiography.

RESULTS

In the control rats, rebamipide was found to bind to the surface epithelial cells. In the ethanol-treated group, few binding sites were observed in the damaged gastric mucosa. In the acetic acid-treated group, the marked accumulation of the binding sites of 3H-rebamipide was observed in the mesenchymal cells in the lamina propria mucosae between the regenerated gastric epithelial cells. Combination of autoradiography and immunohistochemistry has revealed that iNOS-immunoreactive cells had the strong binding of rebamipide in the acetic acid-treated group. Some of these cells were CD68-positive macrophages, while others were CD68-negative, corresponding to polymorphonuclear leucocytes. In the ethanol-treated acute gastric mucosal injury group, few binding sites were observed in the damaged gastric mucosa.

CONCLUSIONS

Autoradiography has made it clear that rebamipide binds to iNOS-positive cells in the gastric mucosa 7 days after acetic acid-treatment.

Involvement of bcl-2 and caspase-3 in apoptosis induced by cigarette smoke extract in the gastric epithelial cell

Previous studies have shown that short-term passive cigarette smoking can increase apoptosis in rat gastric mucosa. However, the mechanism is not yet defined. Chloroform and ethanol extracts were used to investigate whether cigarette smoke could induce apoptosis in a human gastric epithelial cell line (AGS) as well as the roles of bcl-2, caspase-3, and cytochrome c in this process. AGS cell lines were treated with either chloroform extract (CE) or ethanol extract (EE) for 5 hours, and the level of bcl-2, the activity of caspase-3, and the level of cytosolic cytochrome c in these cells were determined. Time course studies on the effects of cigarette smoke extracts (CSEs) on DNA fragmentation and cytochrome c relocalization were also performed. Data showed that only CE induced apoptosis in a dose- and time-dependent manner in AGS cells, along with a decrease of bcl-2 and an increase of caspase-3 activity. Pretreatment with Z-DEVD-FMK (specific inhibitor of caspase-3) dose-dependently blocked the DNA fragmentation induced by the CE. Moreover, CE could time- and dose-dependently increase the level of cytochrome c in the cytoplasm, which might activate caspase-3. In conclusion, CSE triggers apoptosis in AGS cells through the inhibition of bcl-2 and the activation of a mitochondria-related pathway.

Effect of acute cigarette smoking, alone or with alcohol, on gastric barrier function in healthy volunteers

BACKGROUND

Smoking is a risk factor for gastroduodenal ulcer and gastric adenocarcinoma. However, the pathophysiological mechanisms induced by acute cigarette smoking in the human gastric mucosa are poorly understood.

AIM

To evaluate the effect of acute cigarette smoking, alone or with alcohol, on the gastric permeability to sucrose, a specific marker of mucosal damage in the stomach.

SUBJECTS AND METHODS

Twenty healthy volunteers (8 smokers/12 non-smokers) were studied. Each fasted subject ingested 500 ml of a 20% sucrose solution and the amount of sucrose excreted in a 5-hour urine collection was measured by gas chromatography Four sucrose permeability tests were carried out: 1. basal, 2. while smoking 5 cigarettes, 3. after drinking 50 ml of a 40 degrees alcoholic beverage, 4. a combination of 2+3.

RESULTS

Sucrose excretion increased after alcohol ingestion (40.5 +/- 6.0 mg vs 143.1 +/- 28.9 mg, p = 0.002), but was not modified by acute cigarette smoking (34.4 +/- 5.9 mg). When alcohol and cigarettes were simultaneously consumed, the increase in alcohol-induced sucrose excretion was significantly reduced (73.1 +/- 16.6 mg, p = 0.03). Basal sucrose excretion was similar in smokers and non-smokers. However, in acute cigarette smoking, a decrease in sucrose excretion was observed in smokers (p = 0.02) but not in non-smokers.

CONCLUSIONS

These results indicate that acute cigarette smoking may tighten the gastric mucosa in habitual smokers and this is associated with a smaller increase of gastric permeability induced by alcohol.

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.

Protective role of heme oxygenase-1 on trinitrobenzene sulfonic acid-induced colitis in rats

Preliminary studies showed that the inducible form of heme oxygenase (HO-1) was induced and played a protective role in the process of inflammation. The present study investigated the possible role of HO-1 in 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats. We measured HO-1 activity in TNBS-induced colitis in rats and analyzed the severity of colitis along with altered HO activity by assessing lesion area and myeloperoxidase activity. HO-1 mRNA and protein expressions were determined at different time points after TNBS induction. Free radical production and inducible nitric oxide synthase (iNOS), which participate in oxidative injury, were also assayed. HO activity and HO-1 gene expression increased markedly after TNBS induction. Administration with tin mesoporphyrin (SnMP), a HO inhibitor, potentiated the colonic damage along with a reduction in HO-1 activity. Furthermore, the reduction of HO-1 expression by SnMP also enhanced reactive oxygen species and iNOS expression, both of which were dramatically increased after the TNBS enema. L-Arginine pretreatment further aggravated the injurious action of SnMP. Our results indicate that HO-1 plays a protective role in the colonic damage induced by the TNBS enema, and the preventive effects probably result from decreased free radical production and inhibition of iNOS expression in colonic tissues.

Current roles of nitric oxide in gastrointestinal disorders

It has been confusing as to what roles nitric oxide (NO) has in different physiological and pathological mechanisms in various diseases. In the gastrointestinal tract, NO can be either protective or deleterious in different disorders. This depends on what type of nitric oxide synthase (NOS) is involved in these pathological conditions. Constitutive NOS (cNOS) is responsible for production of NO in physiological context. In contrast, inducible NOS (iNOS) produces NO in pathophysiological circumstances. NO is implicated in mechanisms maintaining the integrity of the gastric epithelium. In this connection, it regulates gastric blood flow and directly stimulates gastric mucus secretion by activating soluble guanylate cyclase. A blockade of NO production resulted in an impairment of the vascular response and the subsequent alkaline flux in the lumen. This would impair the restitution process. Endogenous NO also contributes to the inhibition of acid secretion in the stomach. Indeed the adverse action of cigarette smoking on ulcer healing is largely dependent on the deficiency of cNOS and a subsequent depression of gastric blood flow and angiogenesis. To this end, NO may act as a crucial signal to promote endothelial cell differentiation into vascular tubes. In experimental colitis, NO derived from iNOS, together with other free radicals contribute significantly to the inflammatory response in the colon. It is also involved in the ulcerogenic effect of passive smoking on colitis. The mechanism is likely mediated through the interaction with superoxide to produce peroxynitrite, a strong oxidizing agent that initiates lipid peroxidation. In conclusion, NO in low concentration derived from cNOS is cytoprotective by directly acting as an inducer of defense responses in the gastrointestinal tract. However, higher concentrations of NO from iNOS exhibit toxic effects through nitrosative and oxidative stress.

Involvement of neutrophils and free radicals in the potentiating effects of passive cigarette smoking on inflammatory bowel disease in rats

BACKGROUND & AIMS

Cigarette smoking is associated with inflammatory bowel diseases (IBDs), particularly Crohn's disease, in humans. The aim of this study was to examine whether passive cigarette smoking aggravates experimental IBD in rats and to clarify the underlying mechanisms.

METHODS

Rats were exposed to cigarette smoke (CS) for 1 hour once daily for 4 days before induction of IBD by 2,4, 6-trinitrobenzene sulfonic acid (TNBS)-ethanol enema and were then killed at 2, 6, or 24 hours later.

RESULTS

Preexposure to CS significantly potentiated colonic damage induced by TNBS. TNBS-ethanol enema caused a pronounced increase in colonic myeloperoxidase activity, leukotriene B(4) level, and also inducible nitric oxide synthase activity, its protein, and messenger RNA expression. These parameters were all significantly increased further by exposure to CS. In contrast, increased colonic superoxide dismutase activity after TNBS-ethanol enema was attenuated by CS exposure. The potentiating effects of CS exposure on TNBS-induced IBD were significantly alleviated after pretreatment with cyclosporin A (an immunosuppressant), N (G)-nitro-L-arginine methylester (a nitric oxide synthase inhibitor), and dimethyl sulfoxide (a hydroxyl radical scavenger).

CONCLUSIONS

The results show that promotion of neutrophil infiltration and free radical production contributed significantly to the potentiating effect of passive cigarette smoking on experimental IBD.

Effects of cigarette smoking on gastric ulcer formation and healing: possible mechanisms of action

Epidemiologic studies have shown that cigarette smoking is closely related to peptic ulcer disease. The mechanisms by which cigarette smoking adversely affects gastric mucosa have been suggested and elucidated. This article reviews some of the mechanisms involved in cigarette smoking-related gastric ulceration and healing. Experimental findings suggest that cigarette smoking increases xanthine oxidase activity, leukotrienes, and nitric oxide production and also neutrophil infiltration in the gastric mucosa. On the other hand, it reduces blood flow, prostaglandin production, epithelial cell proliferation, and formation of blood vessels in the tissue. These actions are important for ulcer formation and healing. The evidence thus far available strengthens the hypothesis that cigarette smoke is indeed harmful to gastric mucosa through defined mechanisms.