Role of oxygen-derived metabolites in the rat gastric mucosal injury induced by nitric oxide donors

Nitric oxide boosters as defensive agents against COVID-19 infection: an opinion

In the prevailing covid times, scientific community is busy in developing vaccine against COVID-19. Under such fascination this article describes the possible role of nitric oxide (NO) releasers in aiding the immune system of a human body against this dreadful pandemic disease. Despite some prodrug antiviral compounds are in practice to recover the patients suffering from covid-19, however, co-morbidity deaths are highest among the total deaths happened so far. This concurrence of a number of diseases in a patient along with this viral infection is indicative of the poor immunity. Literature background supports the use of NO as immunity boosting agent and hence, the nitric oxide releasing compounds could act as lucrative in this context. Some dietary suggestions of NO-containing food items have also been introduced in this article. Also, the profound effect of NO in relieving symptomatic severity of covid-19 has been opined in this work.Communicated by Ramaswamy H. Sarma.

Nitric oxide as a therapeutic option for COVID-19 treatment: a concise perspective

Among several possible therapies applicable for treating COVID-19, nitric oxide therapy has also gained considerable interest. This article describes the same with mechanistic details.

Nitric oxide-releasing molecules at the interface of inorganic chemistry and biology: a concise overview

The useful aspects of nitric oxide (NO) are nowadays widely known. Due to the need for this molecule in the maintenance of homeostasis, NO-releasing compounds are tested every year to optimize its levels in a patient suffering from low NO production. This manuscript is an update of some important historical concerns about nitrosyl complexes having the ability to act as NO-releasing compounds under the influence of different chemically modified environments. At present, the search for efficient and less harmful NO-releasing molecules at desirable targets and concentrations has gained considerable momentum in nitrosyl chemistry. Iron, ruthenium, and manganese nitrosyls have been investigated elitely to disentangle their electronic transition (excitation) under visible light to act as NO donors without harming the healthy cells of a target. There is much evidence supporting the increase of NO lability if amino acids are used as complexing ligands, the design of a reduction center close to an NO grouping, and the development of porphyrin system-based nitrosyl complexes. From the overall survey, it may be concluded that the desirable properties of such scaffolds need to be evaluated further to complement the biological milieu.

Protective effect of rutin against acute gastric mucosal lesions induced by ischemia-reperfusion

CONTEXT

Rutin, a flavonoid commonly present in onions, apples and tea, has been suggested to have a variety of pharmacological activities, including immunomodulator, anti-inflammatory and antioxidant activities.

OBJECTIVES

The present study was to examine the protective effects of rutin on gastric mucosal damage induced by gastric ischemia-reperfusion (I/R) in rats.

MATERIALS AND METHODS

Rutin (50, 100, 200 mg/kg) was administered intragastrically for five consecutive days before ischemia. Sixty minutes after the last administration of rutin, under anesthesia, the celiac artery was clamped for 30 min, and then the clamp was removed for 60 min reperfusion. After reperfusion, the stomach was removed for biochemical and histological examinations.

RESULTS

As compared with the I/R group (116.7 ± 21.5), administration of rutin at doses of 50, 100 and 200 mg/kg significantly prevented the increase of gastric mucosal injury index induced by gastric I/R (73.4 ± 14.8, 65.9 ± 9.6 and 26.9 ± 5.7, respectively). ED50 value was 138.7 mg/kg. Moreover, rutin at doses of 50, 100 and 200 mg/kg showed an inhibition on the increased myeloperoxidase (24.6, 41.3 and 53.1% reduction) activity and malondialdehyde levels (27.4, 40.3 and 50.7% reduction) in gastric mucosa. Also, the elevation of inducible NO synthase (iNOS) activity as well as the decrease of constitutive NO synthase (cNOS) in the gastric mucosa were significantly prevented by rutin pretreatment.

CONCLUSION

These results suggested that rutin has a protective effect against gastric mucosal injury induced by gastric I/R and that the gastroprotection was related to the NOS/NO pathway and its antioxidant activity.

Effect of superoxide on the development and maintenance of mechanical allodynia in a rat model of chronic post-ischemia pain

BACKGROUND

Reactive oxygen species and inflammatory responses contribute to the development of neuropathic pain. Superoxide serves to mediate cell signaling processes and tissue injury during inflammation. We examined the effects of superoxide on the development and maintenance of mechanical allodynia, as well as its contribution to central sensitization in a superoxide-rich animal model of neuropathic pain.

METHODS

Chronic post-ischemia pain (CPIP) was induced via the left hindpaw ischemia for 3 h, followed by reperfusion. Superoxide dismutase (4,000 U/kg, i.p.) was administered either 5 min before ischemia (BI), 5 min before reperfusion (BR), or 3 days after reperfusion (3AR). Withdrawal thresholds of the four paws were measured to assess the mechanical allodynia and the effects of circulating xanthine oxidase (XO)-mediated superoxide production. In addition, we measured the levels of N-methyl D-aspartate receptor subunit 1 phosphorylation (p-NR1) in the ipsilateral and contralateral spinal cord (L4-6), by Western blotting, to examine the superoxide-mediated central sensitization. Superoxide production was assessed by allopurinol-sensitive, XO-mediated lipid peroxidation of the spinal cord and gastrocnemius muscles.

RESULTS

Withdrawal thresholds of forepaws did not vary across the 7 days of testing. In the hindpaws, both ipsilateral and contralateral mechanical allodynia was most attenuated in the BR group, followed by the BI and 3AR groups. The degree of NR1 activation was in contrast to the changes in the withdrawal thresholds.

CONCLUSIONS

These data suggest that superoxide is involved in the development and maintenance of mechanical allodynia, particularly via central sensitization in the spinal cord.

A preliminary study on protective effect of L-citrulline against ischemia-reperfusion induced gastric mucosal lesions in rat

Objectives:

This study was designed to investigate the gastroprotective effect of L-citrulline against gastric ischemia-reperfusion injury.

Materials and Methods:

Sodium pentobarbital-anesthetized rats underwent occlusion of the celiac artery for 30 min, followed by 60 min of reperfusion. Sixty minutes before ischemia, L-citrulline at doses of 300, 600, 900 mg/kg was administered intragastrically. Based on this animal model of gastric ischemia-reperfusion injury, the gastroprotective effect of L-citrulline was assessed by determining and comparing the ulcerative index and the estimation of myeloperoxidase (MPO) activity and malondialdehyde (MDA) level in the gastric mucosal tissues. Moreover, the expression of inducible nitric oxide synthase (iNOS), neuronal nitric oxide synthase (nNOS), and endothelial nitric oxide synthase (eNOS) protein was also determined.

Results:

Intragastric administration of L-citrulline (600 and 900 mg/kg) 60 min before ischemia significantly ameliorated the gastric mucosal damage and inhibited the increase in MPO and MDA contents. Also, the increase in expression of iNOS protein was also prevented by L-citrulline. The expression of nNOS and eNOS was not affected significantly by I/R or L-citrulline.

Conclusion:

The results suggest that L-citrulline, administered exogenously, exhibits gastric protection by inhibition of neutrophil infiltration in rats, which may be related in prevention of the increase in iNOS activity.

Oxidative stress, nitric oxide and prostaglandin E2 levels in the gastrointestinal tract of aging rats

Objectives

To evaluate the presence of oxidative stress and alterations in the levels of two cytoprotective agents, prostaglandin E2 and nitric oxide, in the gastrointestinal tract of aging rats.

Methods

The production of superoxide anion, lipid peroxides, levels of superoxide dismutase and catalase, and production of prostaglandin E2 and nitric oxide in the stomach and duodenum of rats were determined at 1.5, 3, 12, 18 and 24 months of age.

Key findings

Oxidative stress was present in the stomach of the old rats (24 months), whereas prostaglandin E2 and nitric oxide production remained stable at 18 and 24 months. In the duodenum, no oxidative stress was observed at 24 months, but at 18 months, an increase in superoxide anion levels was detected. Prostaglandin E2 remained constant in the aged rats but nitric oxide decreased significantly at 24 months.

Conclusions

The absence of macroscopic gastric injury throughout the gastrointestinal tract indicates that the oxidative stress in the stomach and the significant decrease of nitric oxide in the duodenum in the old rats are not sufficient to disrupt the mucosal defence network. The results support the notion that the disruption of the mucosal network is essentially regulated by the cytoprotective agents prostaglandin E2 and nitric oxide, and that injury appears only when both substances are concurrently reduced.

Increased heat-shock protein 90 expression contributes to impaired adaptive cytoprotection in the gastric mucosa of portal hypertensive rats

BACKGROUND AND AIMS

Portal hypertensive (PHT) gastropathy results in an increased susceptibility to damage. Adaptive cytoprotection against ethanol-induced damage is impaired in the gastric mucosa of rats with portal hypertension. Excessive nitric oxide (NO) production occurs in portal hypertension and is mediated in part via heat-shock protein (Hsp)90 production. The aim of this study was to investigate the relation between adaptive cytoprotection after exposure to ethanol and gastric expression of Hsp90 in PHT rats.

METHODS

Portal hypertension was induced in rats by staged portal vein occlusion. Adaptive cytoprotection to 70% ethanol was evaluated by assessing the injury index of the gastric mucosa with or without pretreatment with 10% ethanol. Expression of Hsp90 mRNA was evaluated by real-time polymerase chain reaction, and expression of Hsp90 protein was evaluated by western blotting. The effect of Hsp90 inhibition in PHT rats was evaluated by administration of geldanamycin.

RESULTS

Gastric Hsp90 mRNA expression in PHT rats was significantly less than that in sham-operated (SO) controls. However, after 10% ethanol pretreatment, Hsp90 mRNA expression was significantly greater in PHT rats than in SO controls. In PHT rats, gastric Hsp90 protein expression after 10% ethanol pretreatment was significantly greater than that without the pretreatment. However, the pretreatment had no effect on the injury index compared to SO rats. Administration of geldanamycin prior to 10% ethanol pretreatment significantly decreased the injury index in response to 70% ethanol in the PHT rats.

CONCLUSIONS

These results show that 10% ethanol pretreatment markedly increases gastric Hsp90 expression in PHT rats. Excessive production of Hsp90 may contribute impaired adaptive cytoprotection.

Reactive oxygen species in rats with chronic post-ischemia pain

BACKGROUND

An emerging theme in the study of the pathophysiology of persistent pain is the role of reactive oxygen species (ROS). In the present study, we examined the hypothesis that the exogenous supply of antioxidant drugs during peri-reperfusion would attenuate pain induced by ischemia/reperfusion (IR) injury. We investigated the analgesic effects of three antioxidants administered during peri-reperfusion using an animal model of complex regional pain syndrome-type I consisting of chronic post-ischemia pain (CPIP) of the hind paw.

METHODS

Application of a tight-fitting tourniquet for a period of 3 h produced CPIP in male Sprague-Dawley rats. Low-dose allopurinol (4 mg/kg), high-dose allopurinol (40 mg/kg), superoxide dismutase (SOD, 4000 U/kg), N-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg), or SOD (4000 U/kg)+L-NAME (10 mg/kg) was administered intraperitoneally just after tourniquet application and at 1 and 2 days after reperfusion for 3 days. The effects of antioxidants in rats were investigated using mechanical and cold stimuli. Each group consisted of seven rats.

RESULTS

Allopurinol caused significant alleviation in mechanical and cold allodynia for a period of 4 weeks in rats with CPIP. Both SOD and L-NAME, which were used to investigate the roles of superoxide (O2(-)) and nitric oxide (NO) in pain, also attenuated neuropathic-like pain symptoms in rats for 4 weeks.

CONCLUSIONS

Our findings suggest that O2(-) and NO mediate IR injury-induced chronic pain, and that ROS scavengers administered during the peri-reperfusion period have long-term analgesic effects.

Role of nitric oxide in the gastrointestinal tract

Worldwide osteoarthritis (OA) affects more than 9.6% of men and 18% of women older that 60 years. Treatment for OA often requires chronic use of selective or nonselective nonsteroidal anti-inflammatory drugs (NSAIDs), which have been associated with gastrointestinal and cardiovascular complications. An increased risk for upper gastrointestinal bleeding with NSAIDs alone and when combined with low-dose aspirin has been described in numerous studies. Although cyclo-oxygenase-2 inhibitors have been shown to carry a lower risk for gastrointestinal injury than nonselective NSAIDs, research continues to identify new treatments that not only are effective but also provide an improved benefit/risk profile, including better gastrointestinal tolerability. Nitric oxide (NO) is known to have a protective effect on the gastrointestinal tract. In preclinical studies NO was shown to help maintain gastric mucosal integrity, to inhibit leukocyte adherence to the endothelium, and to repair NSAID-induced damage. In addition, epidemiologic studies have shown that the use of NO-donating agents with NSAIDs or aspirin resulted in reduced risk for gastrointestinal bleeding. Recent studies have shown that cyclo-oxygenase inhibiting NO-donating drugs (CINODs), in which a NO molecule is chemically linked to an NSAID, are effective anti-inflammatory agents and may result in less gastrointestinal damage than is associated with NSAID use. Therefore, these agents provide a potential therapeutic option for patients with arthritis who require long-term NSAID therapy.

Comparison of the mechanisms underlying the relaxation induced by two nitric oxide donors: sodium nitroprusside and a new ruthenium complex

We studied the mechanisms involved in the relaxation induced by nitric oxide (NO) donors, ruthenium complex ([Ru(terpy)(bdq)NO(+)](3+)-TERPY) and sodium nitroprusside (SNP) in denuded rat aorta. Both NO donors induced vascular relaxation independent of the agonist used in the pre-contraction. [Ru(terpy)(bdq)NO(+)](3+) and SNP activated guanylyl cyclase (GC) and K(+) channels. The production of cGMP induced by [Ru(terpy)(bdq)NO(+)](3+) - was higher than that obtained with SNP. The combination of GC inhibitor with K(+)channels blocker almost abolished the relaxation induced by the NO donors. The extracellular NO scavenger oxyhemoglobin reduced the potency without changing the maximum effect (Emax) of both NO donors. By using specific NO species scavengers, hydroxocobalamin and l-cysteine, we have identified the contribution of free radical NO (NO()) and nytroxil anion (NO(-)), respectively, to the rat aorta relaxation induced by both NO donors. The selective scavengers for NO() and NO(-) reduced the potency but not the Emax of [Ru(terpy)(bdq)NO(+)](3+). However, the NO(-) scavenger had no effect on the relaxation induced by SNP and NO() scavenger reduced only the potency to SNP. The inhibition of sarcoplasmic reticulum Ca(2+)-ATPase reduced only the potency of SNP without effect on the relaxation induced by [Ru(terpy)(bdq)NO(+)](3+). Our results demonstrate that both NO donors induce relaxation by activating the GC and K(+) channels. The NO() is the unique NO specie involved in the SNP-relaxation. On the other hand, the relaxant effect of [Ru(terpy)(bdq)NO(+)](3+) involves both NO() and NO(-), that produce higher concentration of cGMP. The inhibition of sarcoplasmic reticulum Ca(2+)-ATPase reduces the relaxation induced by SNP but it did not alter the relaxation induced by [Ru(terpy)(bdq)NO(+)](3+).

The cytoprotective effect of a nitric oxide donor drug on gastric mucous membrane of rats treated with ketoprofen, a non-steroidal anti-inflammatory drug

BACKGROUND: Non-steroidal anti-inflammatory drugs are considered today a very important group of medication, with a wide variety of therapeutic use, in different areas of modern medicine. Despite their beneficial effects on the patient, these drugs show a high incidence of side effects, mainly in the gastrointestinal tract. The physiopathological mechanisms of non-steroidal anti-inflammatory drugs induced lesions and the gastric mucosa defense mechanism became an important source for medical research, especially those which try to evaluate the role of nitric oxide as a cytoprotective agent. AIM: To define a possible cytoprotective effect of a nitric oxide donor, isosorbide dinitrate, on the gastric mucous of rats submitted to non-steroidal anti-inflammatory drugs ketoprofen treatment. METHODS: Adult male Wistar rats, previously submitted to starvation for 24 hours and divided in three groups: group I (standard): animals that received isotonic saline solution intragastric by gavage and intravenous. Group II (control-ketoprofen): animals that received isotonic saline solution intragastric by gavage and ketoprofen intravenous. Group III (nitrate/ketoprofen): animals that received 2mM solution of isosorbide dinitrate intragastric by gavage and ketoprofen intravenous. Later on, these animals were sacrificed and had their stomach removed and submitted to macroscopical, microscopical and biochemical studies. The evaluated parameters were: a) gastric lesion index; b) gastric mucous layer thickness; c) gastric tissue nitrate/nitrite (NOx) concentration and d) gastric tissue malondialdehyde concentration. RESULTS: a) Gastric lesion index evaluation showed a smaller statistically significant incidence on the animals of group III; b) group III showed a thicker mucous layer, which also was statistically significant, when compared to group II; c) the variation on tissue nitrate/nitrite concentration was similar in all three groups, without statistical significance when compared to each other. CONCLUSION: Isosorbide dinitrate has a cytoprotective activity on the gastric mucosa of rats submitted to ketoprofen action.

[Ischemia-reperfusion syndrome associated with liver transplantation: an update]

Ischemia-reperfusion (I/R) injury is the main cause of both initial graft dysfunction and primary failure in liver transplantation. The search for therapeutic strategies to prevent I/R injury has led to research into promising drugs, although most have not been used clinically. Gene therapy requires better transfection techniques, avoiding vector toxicity, and ethical debate before being used clinically. Ischemic preconditioning is the first therapeutic strategy used in clinical practice to reduce I/R injury in hepatectomies for tumors. Future research will provide data on the effectiveness of ischemic preconditioning in reducing I/R injury associated with liver transplantation, and in reducing the vulnerability of steatotic grafts to I/R syndrome so that they can be used in transplantation, thus relieving the organ shortage.

Past and future approaches to ischemia-reperfusion lesion associated with liver transplantation

Ischemia-reperfusion (I/R) injury associated with liver transplantation remains a serious complication in clinical practice, in spite of several attempts to solve the problem. The present review focuses on the complexity of I/R injury, summarizing conflicting results obtained from the literature about the mechanisms responsible for it. We also review the therapeutic strategies designed in past years to reduce I/R injury, attempting to explain why most of them have not been applied clinically. These strategies include improvements in pharmacological treatments, modifications of University of Wisconsin (UW) preservation solution based on a variety of additives, and gene therapy. Finally, we will consider new potential protective strategies using trimetazidine, 5-amino-4-imidazole carboxamide riboside (AICAR), melatonin, modulators of the renin-angiotensin system (RAS) and the phosphatidylinositol-3-OH kinase (PI3K)-Akt and the p42/p44 extracellular signal-regulated kinases (Erk 1/2) pathway. These strategies have shown promising results for I/R injury but have not been tested in experimental liver transplantation to date. Moreover, we will review ischemic preconditioning, taking into account the recent clinical studies that suggest that this surgical strategy could be appropriate for liver transplantation.

Nitric oxide and the gut injury induced by non-steroidal anti-inflammatory drugs

Nitric oxide (NO) can protect the gastrointestinal tract from injury, including that provoked by non-steroidal anti-inflammatory drugs (NSAIDs). This protective profile of NO, which predominantly reflects actions on the microcirculation, is mimicked by NO donors. Moreover, the NO-donating agents know as the NO-NSAIDs or CINODs (cyclo-oxygenase-inhibiting nitric oxide-donating drugs) exhibit reduced gut injury in experimental models, which is considered to reflect these local beneficial actions of NO. NSAIDs cause chronic inflammatory lesions in the small intestine in experimental models. This injury results from initial COX inhibition and other local events, with translocation of indigenous luminal bacteria, leading to induction of NO synthase isoform, iNOS, and subsequent production of the cytotoxic moiety, peroxynitrite from NO and superoxide. Agents that inhibit iNOS or superoxide production can attenuate such intestinal injury. In the absence of reactive oxygen moieties, NO may play a beneficial role in the resolution of inflammatory damage to the gut, thus reconciling the potential opposing properties of NO in tissue inflammation and injury.

Adaptive cytoprotection through modulation of nitric oxide in ethanol-evoked gastritis

AIM: To assess the mechanisms of protective action by different mild irritants through maintenance of gastric mucosal integrity and modulation of mucosal nitric oxide (NO) in experimental gastritis rats.

METHODS: Either 200 mL/L ethanol, 50 g/L NaCl or 0.3 mol/L HCl was pretreated to normal or 800 mL/L ethanol-induced acute gastritis Sprague-Dawley rats before a subsequent challenge with 500 mL/L ethanol. Both macroscopic lesion areas and histological damage scores were determined in the gastric mucosa of each group of animals. Besides, gastric mucosal activities of NO synthase isoforms and of superoxide dismutase, along with mucosal level of leukotriene (LT)C₄ were measured.

RESULTS: Macroscopic mucosal damages were protected by 200 mL/L ethanol and 50 g/L NaCl in gastritis rats. However, although 200 mL/L ethanol could protect the surface layers of mucosal cells in normal animals (protection attenuated by N^G-nitro-L-arginine methyl ester), no cytoprotection against deeper histological damages was found in gastritis rats. Besides, inducible NO synthase activity was increased in the mucosa of gastritis animals and unaltered by mild irritants. Nevertheless, the elevation in mucosal LTC₄ level following 500 mL/L ethanol administration and under gastritis condition was significantly reduced by pretreatment of all three mild irritants in both normal and gastritis animals.

CONCLUSION: These findings suggest that the aggravated 500 mL/L ethanol-evoked mucosal damages under gastritis condition could be due to increased inducible NO and LTC₄ production in the gastric mucosa. Only 200 mL/L ethanol is truly “cytoprotective” at the surface glandular level of non-gastritis mucosa. Furthermore, the macroscopic protection of the three mild irritants involves reduction of LTC₄ level in both normal and gastritis mucosa, implicating preservation of the vasculature.

Protective effect of dietary nitrate on experimental gastritis in rats

Nitrates have long been considered as harmful dietary components and judged responsible for deleterious effects on human health, leading to stringent regulations concerning their levels in food and water. However, recent studies demonstrate that dietary nitrate may have a major role in human health as a non-immune mechanism for host defence, through its metabolism to NO in the stomach. NO is a versatile molecule and although evidence exists showing that administration of low doses of exogenous NO protects against gastrointestinal inflammation, higher NO doses have been shown to exacerbate injury. So, the effect of an ingestion of nitrates in doses corresponding to a normal diet in human consumers on an experimental gastritis induced by iodoacetamide in rats was investigated. During gastritis one of the following compounds was given orally: water; KNO3; the NO donor sodium nitroprusside; the NO scavenger haemoglobin given with either water or KNO3. N(G)-nitro-l-arginine methyl ester (l-NAME), a non-specific NO synthase inhibitor, was administered with either water, iodoacetamide alone, or combined with KNO3. After killing, the stomach was resected and microscopic damage scores, myeloperoxidase and NO synthase activities were determined. Iodoacetamide-induced gastritis was significantly reduced by KNO3 administration, an effect which was reproduced by sodium nitroprusside and reversed by haemoglobin. l-NAME induced gastric mucosal damage in itself, and KNO3 did not prevent the gastritis induced by iodoacetamide associated with l-NAME. In conclusion, dietary nitrate exerts a protective effect against an experimental gastritis in rats by releasing NO in the stomach but such an effect requires the production of endogenous NO.

Modulation of serum cytokine levels by a novel superoxide dismutase mimetic, M40401, in an Escherichia coli model of septic shock: correlation with preserved circulating catecholamines

OBJECTIVES

We have shown previously that inactivation of catecholamines by superoxide anions contributes to the loss of vascular reactivity to norepinephrine and the subsequent hypotension that develops in Gram-negative endotoxic shock. In addition to their vasopressor actions, catecholamines, via beta-adrenoceptor activation, are important regulators of cytokine production. Here we examined if maintenance of serum catecholamine levels by the superoxide dismutase mimetic, M40401, modulates serum cytokine levels and arterial hypotension in an Escherichia coli-infected conscious rat model of septic shock.

DESIGN

Controlled laboratory animal study.

SETTING

University animal research laboratory.

SUBJECTS

Pathogen-free male Sprague-Dawley rats (n = 51).

INTERVENTIONS

Conscious, antibiotic-treated animals with chronic in-dwelling carotid arterial and jugular venous catheters were intravenously infected with 10(10) live E. coli bacteria (O55:B5, n = 51) over 30 mins, ending at time = 0 hrs. At 0.5 or 3 hrs, infected rats were administered an intravenous infusion of either M40401 (n = 33) or 0.9% saline (n = 18) for 6 hrs at a rate of 1 mL/h. In additional experiments, anesthetized animals with catheterized left femoral arteries and veins were administered a dose-range of norepinephrine (0.1-1 microg/kg) as bolus intravenous injections. Thereafter, E. coli lipopolysaccharide (4 mg/kg, n = 6) was administered as a 0.3-mL slow bolus intravenous injection. One hour later, the norepinephrine protocol was repeated, after which the rats were administered an intravenous infusion of either M40401 or 0.9% saline for 15 mins. At 2 hrs, the dose response to norepinephrine was repeated.

MEASUREMENTS AND MAIN RESULTS

Rats infected with live E. coli exhibited a biphasic fall in mean arterial pressure, with mortality reaching 83% by 24 hrs. Rats treated with M40401 (0.25, 2.5, or 25 microg x kg-1 x hr-1 ) 3 hrs after bacteremic sepsis maintained a normal mean arterial pressure, and mortality was dose-dependently reduced to 44, 33, and 22%, respectively, at 24 hrs. Furthermore, serum catecholamine levels were diminished in E. coli-infected rats treated with saline compared with rats treated with M40401. In separate experiments, E. coli-infected rats were administered M40401 (25 microg x kg-1 x hr-1 ) 0.5 hr after bacterial challenge. Blood samples taken at 0, 1.5, 3.5, and 6 hrs were analyzed for tumor necrosis factor-alpha, interleukin (IL)-1 beta, IL-6, and IL-10 and for norepinephrine and epinephrine. Serum levels of tumor necrosis factor-alpha and IL-1 beta were significantly depressed in M40401-treated septic rats, whereas IL-10 was elevated. Moreover, serum catecholamine levels were greater in M40401-treated septic rats at the same time points. IL-6 levels were unaffected by M40401 treatment. Finally we examined whether treatment with M40401 could reverse the hyporeactivity to norepinephrine typifying early septic shock. Using the E. coli lipopolysaccharide (4 mg/kg) challenged anesthetized rat model of shock, we demonstrated that the vasoconstrictor ability of norepinephrine was indeed restored after M40401 treatment (25 microg/kg).

CONCLUSION

Postinfection treatment with the superoxide dismutase mimetic M40401 protects against hypotension, vascular hyporeactivity to catecholamines, and mortality associated with septic shock. Such beneficial effects correlate with both reduced oxidative inactivation of serum catecholamines and a reduction in canonical cytokine mediators of inflammation.

Pharmacological action of melatonin in shock, inflammation and ischemia/reperfusion injury

A vast amount of circumstantial evidence implicates oxygen-derived free radicals (especially, superoxide and hydroxyl radical) and high-energy oxidants (such as peroxynitrite) as mediators of inflammation, shock and ischemia/reperfusion injury. The aim of this review is to describe recent developments in the field of oxidative stress research. The first part of the review focuses on the roles of reactive oxygen species in shock, inflammation and ischemia/reperfusion injury. The second part of the review described the pharmacological action of melatonin in shock, ischemia/reperfusion, and inflammation. The role of reactive oxygen species: Immunohistochemical and biochemical evidence demonstrate the production of reactive oxygen species in shock, inflammation and ischemia/reperfusion injury. Reactive oxygen species can initiate a wide range of toxic oxidative reactions. These include the initiation of lipid peroxidation, direct inhibition of mitochondrial respiratory chain enzymes, inactivation of glyceraldehyde-3 phosphate dehydrogenase, inhibition of membrane sodium/potassium ATP-ase activity, inactivation of membrane sodium channels, and other oxidative modifications of proteins. All these toxicities are likely to play a role in the pathophysiology of shock, inflammation and ischemia and reperfusion. Treatment with melatonin has been shown to prevent in vivo the delayed vascular decompensation and the cellular energetic failure associated with shock, inflammation and ischemia/reperfusion injury. Reactive oxygen species (e.g., superoxide, peroxynitrite, hydroxyl radical and hydrogen peroxide) are all potential reactants capable of initiating DNA single-strand breakage, with subsequent activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS), leading to eventual severe energy depletion of the cells, and necrotic-type cell death. Recently, it has been demonstrated that melatonin inhibits the activation of poly (ADP-ribose) synthetase, and prevents the organ injury associated with shock, inflammation and ischemia and reperfusion.

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.

Nitric oxide donors

Nitric oxide (NO) donors are pharmacologically active substances that release NO in vivo or in vitro. NO has a variety of functions such as the release of prostanoids, inhibition of platelet aggregation, effect on angiogenesis, and production of oxygen free radicals. This report discusses the chemical and pharmacological characteristics of NO donors, their effect on platelet function and cyclooxygenase, their cardiac action including myocardial infarction, and release of superoxide anions. This review stresses NO tolerance and the effect of NO donors on angiogenesis in myocardial infarction and in solid tumors.

Effects of iron and iron chelation in vitro on mucosal oxidant activity in ulcerative colitis

BACKGROUND

Reactive oxygen species may be pathogenic in ulcerative colitis. Oral iron supplements anecdotally exacerbate inflammatory bowel disease and iron levels are elevated in the inflamed mucosa. Mucosal iron may enhance hydroxyl ion production via Fenton chemistry. Conversely, the iron chelator, desferrioxamine, is reportedly beneficial in Crohn's disease.

AIMS

To assess the in vitro effects of exogenous iron and of iron chelators on the production of reactive oxygen species by colonic biopsies from normal control subjects and patients with ulcerative colitis.

METHODS

Luminol-amplified chemiluminescence was used to measure mucosal reactive oxygen species production both before and after addition in vitro of ferric citrate (100 microM), desferrioxamine (1 mM) and 1,10-phenanthroline (1 mM).

RESULTS

Ferric citrate had no effect on the chemiluminescence produced by human colonic mucosa. However, desferrioxamine and phenanthroline reduced chemiluminescence by 47% (n=7, P=0.018) and by 26% (n=10, P=0.005), respectively, in inactive ulcerative colitis, and by 44% (n=9, P=0. 008) and 42% (n=11, P=0.006) in active disease.

CONCLUSION

The lack of effect of ferric citrate suggests that sufficient free iron is already present in inflamed biopsies to drive the Fenton reaction maximally. The effects of desferrioxamine and 1,10-phenanthroline on the chemiluminescence of biopsies from patients with ulcerative colitis suggest that a clinical trial of topical iron chelation in active disease is indicated.

Inactivation of catecholamines by superoxide gives new insights on the pathogenesis of septic shock

A major feature of septic shock is the development of a vascular crisis characterized by nonresponsiveness to sympathetic vasoconstrictor agents and the subsequent irreversible fall in blood pressure. In addition, sepsis, like other inflammatory conditions, results in a large increase in the production of free radicals, including superoxide anions (O(2)) within the body. Here we show that O(2) reacts with catecholamines deactivating them in vitro. Moreover, this deactivation would appear to account for the hyporeactivity to exogenous catecholamines observed in sepsis, because administration of a superoxide dismutase (SOD) mimetic to a rat model of septic shock to remove excess O(2) restored the vasopressor responses to norepinephrine. This treatment with the SOD mimetic also reversed the hypotension in these animals; suggesting that deactivation of endogenous norepinephrine by O(2) contributes significantly to this aspect of the vascular crisis. Indeed, the plasma concentrations of both norepinephrine and epinephrine in septic rats treated with the SOD mimetic were significantly higher than in untreated rats. Interestingly, the plasma concentrations for norepinephrine and epinephrine were inversely related to the plasma concentrations of adrenochromes, the product of the autoxidation of catecholamines initiated by O(2). We propose, therefore, that the use of a SOD mimetic represents a new paradigm for the treatment of septic shock. By removing O(2), exogenous and endogenous catecholamines are protected from autoxidation. As a result, both hyporeactivity and hypotension are reversed, generation of potentially toxic adrenochromes is reduced, and survival rate is improved.

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.

Involvement of superoxide and/or nitric oxide in renal tissue injury

We examined the influence of superoxide (O2-) and/or nitric oxide (NO) on renal tissue injury estimated from the levels of lipid peroxidation and sulfhydryl (SH) oxidation. Pyrogallol, an O2- generator and precursor of hydrogen peroxide, produced marked tissue injury, but this was prevented by superoxide dismutase (SOD)/catalase (CAT). Hemoglobin (Hb), a NO scavenger, provided protection from tissue injury caused by sodium nitroprusside (SNP). The tissue injury produced by 3-morpholinosydnonimine (SIN-1), which is thought to form peroxynitrite (ONOO-) as a simultaneous O2- and NO generator, was blocked by SOD/CAT or Hb. On the other hand, protein-SH and nonprotein-SH were significantly increased by addition of SOD/CAT or Hb. These data suggest that the renal tissue injury induced by O2-, NO and ONOO- can be blocked by SH, suggesting an important protective role against these reactive oxygen species in the mechanism of tissue defense.

Deferiprone, an oral iron chelator, ameliorates experimental colitis and gastric ulceration in rats

Iron is pivotal is producing tissue-damaging reactive oxygen metabolites. Our aim is to determine the antiinflammatory activity of deferiprone, an oral iron chelator, in experimental colitis and gastritis. Colitis was induced by intraceccal administration of 2 ml 5% acetic acid or by intracolonic administration of 0.1 ml 3% iodoacetamide, with or without cotreatment with deferiprone. Gastritis was induced by intragastric administration of ethanol or hydrochloric acid (HCl) and by subcutaneous injection of indomethacin, with and without deferiprone. Rats were killed 24 hours after acetic acid and iodoacetamide, 30 minutes after ethanol, one hour after HCl, and three hours after indomethacin administration. The colon or stomach was isolated, macroscopic damage was measured, and mucosal samples were obtained for determination of eicosanoid generation, myeloperoxidase (MPO), and nitric oxide synthase (NOS) activities. Deferiprone decreased iodoacetamide and acetic acid-induced macroscopic colonic damage by 67% and 69%, respectively, and macroscopic gastric damage by 91%, 68%, and 46% induced by ethanol, HCl, and indomethacin, respectively. The effect of deferiprone was accompanied by significant decrease in colonic and gastric, MPO and NOS activities, and colonic prostaglandin E2 (PGE2) generation, in acetic acid, ethanol, and indomethacin models, whereas in the iodoacetamide and HCl models attenuation of the decrease in PGE2 generation was seen. Deferiprone is protective in experimental colitis and gastritis, probably due to decreased production of iron-dependent oxygen-free radicals. Oral iron chelators may constitute a novel approach to ameliorate gastrointestinal inflammatory disorders.

Effects of nitric oxide donors GEA 3162 and SIN-1 on ethanol-induced gastric ulceration in rats

Low doses of the intragastrically (i.g.) administered nitric oxide (NO) donors, 1,2,3,4-oxatriazolium,5-amino-3-(3,4-dichlorophenyl)-chloride (GEA 3162; 0.3 mg/kg) and 3-morpholino-sydnonimine (SIN-1; 1 mg/kg), inhibited gastric ulceration induced by ethanol (94%) in anesthetized rats. In contrast, higher doses of these NO donors administered i.g. exacerbated the damage. When administered intravenously, the NO donors had no effect on ethanol-induced gastric lesions although a clear blood pressure-lowering effect was seen. Neither the inhibition nor the exacerbation of ulceration was correlated with changes in blood pressure or prostaglandin E2 release from the mucosal tissue. The relatively small difference between the gastroprotective and damaging doses suggests that orally administered NO donors, especially in the case of GEA 3162, may have a narrow gastric safety margin.

Mechanisms of gastroprotection by transdermal nitroglycerin in the rat

Nitric oxide (NO) donors prevent experimentally-induced gastric mucosal damage, but their clinical utility is limited by short duration of action or unsuitability of the pharmaceutical form employed. This study analyses the gastroprotection elicited by a clinically used mode of continuous administration of an NO donor, namely the nitroglycerin patch. Application to rats of a transdermal patch that releases doses of nitroglycerin comparable to those used in man (40, 80, 160 and 400 ng min(-1) rat(-1)) reduced gastric damage induced by indomethacin (25 mg kg(-1), p.o. or s.c.). The nitroglycerin patch (160 ng min(-1) rat(-1)) also diminished damage by oral administration (1 ml) of acidified bile salts (100 mg kg(-1) taurocholic acid in 150 mM HCl) or 50% ethanol. Transdermal nitroglycerin (160 ng min(-1) rat(-1)) did not influence basal gastric blood flow, as measured by lasser-doppler flowmetry, but prevented its reduction by indomethacin. Transdermal nitroglycerin (160 ng min(-1) rat(-1)) prevented in vivo leukocyte rolling and adherence in the rat mesentery microvessels superfused with indomethacin, as evaluated by intravital microscopy. The transdermal nitroglycerin patch protects the gastric mucosa from damage by mechanisms that involve maintenance of mucosal blood flow and reduction of leukocyte-endothelial cell interaction.

Protective effects of a superoxide dismutase mimetic and peroxynitrite decomposition catalysts in endotoxin-induced intestinal damage

1. The relative contributions of superoxide anion (O2-) and peroxynitrite (PN) were evaluated in the pathogenesis of intestinal microvascular damage caused by the intravenous injection of E. coli lipopolysaccharide (LPS) in rats. The superoxide dismutase mimetic (SODm) SC-55858 and the active peroxynitrite decomposition catalysts 5,10,15,20-tetrakis(2,4,6-trimethyl-3,5-disulphonatophenyl)-por phyrinato iron (III) and 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)-porphyrinato iron (III) (FeTMPS, FeTMPyP respectively) were used to assess the roles of O2- and PN respectively. 2. The intravenous injection of LPS elicited an inflammatory response that was characterized by a time-dependent infiltration of neutrophils, lipid peroxidation, microvascular leakage (indicative of microvascular damage), and epithelial cell injury in both the duodenum and jejunum. 3. Administration of the SODm SC-55858, FeTMPS or FeTMPyP at 3 h post LPS reduced the subsequent increase in microvascular leakage, lipid peroxidation and epithelial cell injury. Inactive peroxynitrite decomposition catalysts exhibited no protective effects. Only, SC-55858 inhibited neutrophil infiltration. 4. Our results suggest that O2 and peroxynitrite play a significant role in the pathogenesis of duodenal and intestinal injury during endotoxaemia and that their remoyal by SODm and peroxynitrite decomposition catalysts offers a novel approach to the treatment of septic shock or clinical conditions of gastrointestinal inflammation. Furthermore, the remarkable protection of the intestinal epithelium by these agents suggests their use during chemo- and radiation therapy, cancer treatments characterized by gastrointestinal damage. Potential mechanisms through which these radicals evoke damage are discussed.

Mechanisms underlying gastric antiulcerative activity of nitroxides in rats

Reactive oxygen-derived species and redox-active metals are implicated in mediation of the pathogenesis of gastric mucosal damage and ulceration. Therefore, common strategies of intervention employ metal chelators, antioxidative enzymes, and low-molecular-weight antioxidants (LMWA). The aim of the present study was to elaborate the mechanism(s) responsible for the protection provided by nitroxide radicals in the experimental model of gastric ulceration. Fasted male rats were treated ig with 1 ml 96% ethanol, with or without ig pretreatment with nitroxide or hydroxylamine. In several experiments, rats were injected ip or iv with iron(III) or iron(II) prior to ethanol administration. Rats were sacrificed 10 min after ethanol administration, the stomach was removed, washed and lesion area measured. Pretreatment with iron(III) complexed to nitrilotriacetate or citrate, aggravated the extent of the gastric injury. Conversely, iron(II) inhibited the formation of lesions. The nitroxides were rapidly reduced to their respective hydroxylamines and demonstrated antiulcerative activity for rats treated with iron. However, injecting the hydroxylamine resulted in a similar tissue distribution of nitroxide/hydroxylamnine but did not provide protection. The results show that: (a) the nitroxide radicals, rather than their respective non-radical reduced form, are the active species responsible for protection; (b) nitroxides protect by dismutating O2*- and possibly indirectly increasing the NO level; (c) unlike classical LMWA which are reducing agents, nitroxides inhibit gastric damage by acting as mild oxidants, oxidizing reduced metals and pre-empting the Fenton reaction; and (d) the nitroxides act catalytically as recycling antioxidants.

Application of authentic peroxynitrite to biological materials

A method to expose cultured cardiac myocytes to authentic ONOO- by using a constant perfusion system was described. The perfusion apparatus is linked to a microscope equipped with video and fluorescence measurement systems, which enable the evaluation of myocardial contraction, [Ca2+]i, [pH]i, and membrane fluidity. Special care is needed to adjust the pH of the solution appropriately and to obtain a constant concentration of ONOO-.

Oxidant stress, anti-oxidants, nitric oxide and essential fatty acids in peptic ulcer disease

In patients with duodenal ulcer (DU), the plasma levels of nitrite and lipid peroxides, the anti-oxidant content of red cells and plasma phospholipid fatty acid analysis were performed both before and after healing of the ulcer following treatment with lansoprazole, a proton pump inhibitor. These results showed that during the phase of active DU, the concentrations of antioxidants (superoxide dismutase, SOD, catalase and glutathione peroxidase) in red cells were low where as those of lipid peroxides and nitric oxide were high. Of the fatty acids measured, the concentration of palmitic acid (16:0) was increased during the active ulcer phase whereas those of arachidonic acid, alpha-linolenic acid and docosahexaenoic acid were low. These biochemical abnormalities reverted to normal following healing of the ulcer with lansoprazole. These results coupled with the observation that polyunsaturated fatty acids (PUFAs) can inhibit the growth of Helicobacterpylori and heal the ulcer suggest that free radicals, anti-oxidants, nitric oxide and PUFAs may play a significant role in the pathogenesis of DU. If this is true, it suggests that PUFAs can be exploited as potential anti-peptic ulcer drugs.

Nitric oxide donor-induced hyperpermeability of cultured intestinal epithelial monolayers: role of superoxide radical, hydroxyl radical, and peroxynitrite

Many of the cytopathic effects of nitric oxide (NO*) are mediated by peroxynitrite (PN), a product of the reaction between NO* and superoxide radical (O2*-). In the present study, we investigated the role of PN, O2*- and hydroxyl radical (OH*) as mediators of epithelial hyperpermeability induced by the NO* donor, S-nitroso-N-acetylpenicillamine (SNAP), and the PN generator, 3-morpholinosydnonimine (SIN-1). Caco-2BBe enterocytic monolayers were grown on permeable supports in bicameral chambers. Epithelial permeability, measured as the apical-to-basolateral flux of fluorescein disulfonic acid, increased after 24 h of incubation with 5.0 mM SNAP or SIN-1. Addition of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, an NO* scavenger, or Tiron, an O2*- scavenger, reduced the increase in permeability induced by both donor compounds. The SNAP-induced increase in permeability was prevented by allopurinol, an inhibitor of xanthine oxidase (a source of endogenous O2*-). Diethyldithiocarbamate, a superoxide dismutase inhibitor, and pyrogallol, an O2* generator, potentiated the increase in permeability induced by SNAP. Addition of the PN scavengers deferoxamine, urate, or glutathione, or the OH* scavenger mannitol, attenuated the increase in permeability induced by both SNAP and SIN-1. Both donor compounds decreased intracellular levels of glutathione and protein-bound sulfhydryl groups, suggesting the generation of a potent oxidant. These results support a role for PN, and possibly OH*, in the pathogenesis of NO* donor-induced intestinal epithelial hyperpermeability.

Peroxynitrite formation in focal cerebral ischemia-reperfusion in rats occurs predominantly in the peri-infarct region

Peroxynitrite (ONOO-) exhibits potent neurotoxicity and plays an important role in neuronal death, but no evidence shows that it is formed in the brain during ischemia or subsequent reperfusion. To detect the formation of ONOO-, we used a hydrolysis/HPLC procedure to measure the formation of 3-nitro-L-tyrosine (NO2-Tyr), which is considered to reflect attack of ONOO- on L-tyrosine residues of cellular components in the brain. Focal ischemia was produced by occluding the right common carotid and right middle cerebral arteries for 2 hours, and the ischemic area was reperfused by reopening the middle cerebral artery. After 2 hours of ischemia, the values of the ratio of NO2-Tyr to L-tyrosine were 0% +/- 0%, 0.42% +/- 0.13% and 0.29% +/- 0.10% in the noninfarct, periinfarct, and core-of-infarct regions, respectively. After 3 hours of reperfusion following 2 hours of ischemia, the ratio in the periinfarct region reached 0.89 +/- 0.22%, which was significantly higher than that in the core-of-infarct region (0.35 +/- 0.09%). The NO2-Tyr was not detected in 50 mg/kg of N-monomethyl-L-arginine-treated or sham-operated rats. Regional CBF in the periinfarct region decreased to 30.8 +/- 15.9 mL/100 g/min during occlusion, but recovered more rapidly than did that in the core-of-infarct region.

Role of endogenous endothelin-1 in stress-induced gastric mucosal damage and acid secretion in rats

In rats subjected to 8 h water-immersion stress, gastric and duodenal mucosal hemorrhage and erosions were detected by macroscopic and histopathological examination. Moreover, plasma and gastric mucosal endothelin-1 (ET-1) levels rose appreciably in a time-related manner during water immersion, with a higher concentration detected in gastric mucosa. Thus, the percentage increases in plasma (gastric mucosal) ET-1, relative to basal levels, after 1, 4 and 8 h of water immersion were 86(172), 169(322) and 210(391)%, respectively. Likewise, a marked increase of gastric acid output was demonstrated 30 min after water immersion and lasted for 3 h. Pretreatment with the endothelin ET(A)/ET(B) receptor blocker, bosentan (30 and 100 mg kg(-1)), orally, dose-dependently antagonized gastric and duodenal mucosal damage as indicated by reductions in lesion lengths of 67 and 80%, respectively. Similar protective effects on mucosa were observed when bosentan was given by the intramuscular route. On the other hand, bosentan suppressed the rate of acid output by 30.3+/-2.1% in the stressed rats, but had no such effect in non-stressed animals. Taken together, results from this study implicate the endogenous peptide, ET-1, as a powerful mediator of stress-evoked gastro-duodenal mucosal damage and, moreover, present bosentan as a potential protector against hyperacidity and mucosal erosion that occur as a consequence of stress.

Role of mast cells, neutrophils and nitric oxide in endotoxin-induced damage to the neonatal rat colon

1. The mechanisms involved in mediating bacterial endotoxin lipopolysaccharide (LPS)-induced injury in the colon of neonatal rat pups aged 10-12 days was examined. 2. Administration of LPS (3 mg kg(-1), i.p.) caused a time-related increase in the plasma concentration of rat mast cell protease-II (RMCP-II) which was attenuated dose-dependently, by the non-selective mast cell stabilizer doxantrazole (0.05-5 mg kg(-1), i.p.). The selective connective tissue mast cell stabilizer ketotifen (5-25 mg kg(-1), i.p.) was without effect at the lower dose and had only a limited inhibitory effect at the higher dose. 3. In addition, doxantrazole (5 mg kg(-1), i.p.) inhibited mast cell degranulation in response to LPS in sections of neonatal rat colon, but ketotifen (5 mg kg(-1), i.p.) was without effect. 4. The increase in plasma RMCP-II concentration in response to LPS treatment preceded increases in tissue myeloperoxidase (MPO) activity, inducible nitric oxide synthase (iNOS) activity and tissue lipid peroxidation. These events were all attenuated by pretreatment with doxantrazole (5 mg kg(-1), i.p.), antineutrophil serum (100 microl kg(-1), i.p.), dexamethasone (2 mg kg(-1), i.p.) and the selective iNOS inhibitor, aminoguanidine (25 mg kg(-1), i.p.). 5. In addition, lipid peroxidation was inhibited by pre-administration of the antioxidant enzymes superoxide dismutase (2000 u kg(-1), i.p.) and catalase (2000 u kg(-1), i.p.), the xanthine oxidase inhibitor allopurinol (100 mg kg(-1), i.p.) and the peroxyl scavenger deferoxamine (10 mg kg(-1), i.p.), suggesting the involvement of reactive oxygen metabolites in the colonic injury. 6. These findings suggest that the sequence of events resulting in colonic damage in the neonatal rat following administration of LPS include mast cell degranulation, neutrophil infiltration, elevation in iNOS activity and subsequent lipid peroxidation.

Involvement of peroxynitrite in the lipid peroxidation induced by nitric oxide in rat gastric mucosa

Local intra-arterial infusion of high doses of nitric oxide (NO) donors, such as S-nitroso-N-acetyl-penicillamine or nitroprusside cause extensive gastric mucosal damage. The involvement of lipid peroxidation of mucosal tissue in the mechanism of such gastric damage has been investigated in the pentobarbitone-anaesthetised rat. Local intra-arterial infusion of nitroprusside (40 micrograms.kg-1.min-1) or S-nitroso-N-acetyl-penicillamine (40 micrograms.kg-1.min-1) induced macroscopically apparent injury and provoked a dose-dependent peroxidation of lipid in gastric tissue. By contrast, endothelin-1 infusion provoked mucosal injury of the mucosa, yet did not produce lipid peroxidation. Local co-infusion of superoxide dismutase (2000-4000 IU.kg-1) reduced both the lipid peroxidation and the mucosal damage provoked by S-nitroso-N-acetyl-penicillamine and nitroprusside. These findings indicate that lipid peroxidation accompanies the mucosal tissue damage induced by NO donors, while the action of superoxide dismutase implicates the involvement of peroxynitrite, formed from superoxide and NO, in this process.

DNA strand breakage and activation of poly-ADP ribosyltransferase: a cytotoxic pathway triggered by peroxynitrite

Peroxynitrite is a reactive oxidant produced from nitric oxide (NO) and superoxide. Although its reactivity and decomposition are very much dependent on the constituents of the cellular environment, peroxynitrite is considered a potent oxidant that reacts with proteins, lipids, and DNA. Inasmuch as peroxynitrite is formed in many pathophysiological conditions that are associated with NO and/or superoxide overproduction, the investigation of the cytotoxic pathways triggered by peroxynitrite is of major importance. Here we review the evidence that peroxynitrite is a potent initiator of DNA strand breakage, which is an obligatory stimulus for the activation of the nuclear enzyme poly ADP ribosyl synthetase (PARS). We present an overview of experimental data that demonstrate or suggest that the peroxynitrite-PARS pathway, by leading to cell necrosis or apoptosis, contributes to cellular injury in a number of pathophysiological conditions including shock and inflammation, pancreatic islet cell destruction, and diabetes, stroke, and neurodegenerative disorders, as well as the toxic effects of various environmental oxidants or cytotoxic drugs.

Involvement of superoxide and xanthine oxidase in neutrophil-independent rat gastric damage induced by NO donors

1. Nitric oxide (NO) and the superoxide anion can interact to form the cytotoxic moiety, peroxynitrite. The involvement and potential source of superoxide in the gastric mucosal damage induced by local infusion of NO donors, has now been investigated in the pentobarbitone-anaesthetized rat. 2. Local intra-arterial infusion of the NO donor, sodium nitroprusside (40 micrograms kg-1 min-1) for 10 min induced macroscopically apparent gastric mucosal injury. 3. This mucosal damage was dose-dependently reduced by prior administration of a systemically acting form of superoxide dismutase conjugated with polyethylene glycol (500-2000 iu kg-1, i.v.). 4. Likewise, the mucosal damage induced by nitroprusside was dose-dependently reduced by prior administration of the xanthine oxidase inhibitor, allopurinol (20-100 mg kg-1, i.p. or 100 mg kg-1, p.o.). 5. Pretreatment with allopurinol (100 mg kg-1, i.p.) also reduced the mucosal injury induced by local intra-arterial infusion of the nitrosothiol, S-nitroso-N-acetyl-penicillamine (40 micrograms kg-1 min-1), but not that induced by local infusion of endothelin-1 (5 pmol kg-1 min-1), indicating specificity of action. 6. Prior administration (4h) of rabbit anti-rat neutrophil serum (0.4 ml kg-1, i.p.), which reduced circulating neutrophils by 90%, did not significantly protect against mucosal injury induced by nitroprusside. 7. Intravenous administration of the platelet-activating factor receptor antagonists, WEB 2086 (1 mg kg-1) or BN 52021 (10 mg kg-1), or the thromboxane synthase inhibitor, OKY 15181 (25 mg kg-1), did not modify mucosal damage induced by nitroprusside, showing lack of involvement of these neutrophil-derived mediators. 8. These findings indicate the involvement of superoxide in the injurious actions of the NO donors, implicating a cytotoxic role of peroxynitrite. Xanthine oxidase, but not neutrophils, appears to be a source of the superoxide.