Pathophysiological role of nitric oxide in rat experimental colitis

Therapeutic effect of adenosine on experimentally induced acute ulcerative colitis model in rats

Purpose

To examine the therapeutic effect of external adenosine on an acetic acid-induced acute ulcerative colitis model in rats.

Methods

Thirty male mature rats were divided into three groups as control, acute colitis (AC) and AC+adenosine group (AC+AD). AC was induced by rectal administration of 4% acetic acid (AA). 5mg/kg/day adenosine was performed i.p for 4 weeks to AC+AD group. Rectum and colon were excised for microscopic and histopathological histopathologic evaluations, and immunohistochemical analysis of nuclear factor kappa B (NF-kB). Blood samples were collected for biochemical detection of TNF-α, Pentraxin-3 and malondialdehyde (MDA) levels.

Results

AC group had generalized hyperemia and hemorrhage with increased macroscopic and histopathological scores compared with control (P <0.0001) while adenosine treatment decreased these scores significantly (P <0.001), with reduced distribution of disrupted epithelium, leukocyte infiltrates, and focal hemorrhage. AC group showed significantly increased immunoexpression of NF-kB in rectum, plasma and tissue levels of TNF-α, plasma Pentraxin-3 and MDA levels (P <0.0001) while adenosine reduced these levels (P < 0.05).

Conclusion

Adenosine appears to promote healing of colon and rectum exposed to AA-induced AC, suggesting a boosting effect of adenosine on the intestinal immune system to cure ulcerative colitis.

Lactobacillus plantarum CQPC06 Activity Prevents Dextran Sulfate Sodium-Induced Colitis by Regulating the IL-8 Pathway

Lactobacillus plantarum CQPC06 (LP-CQPC06) is a newly discovered lactic acid bacterial strain. Here, the beneficial effects of this strain on C57BL/6J mice with dextran sulfate sodium-induced colitis were investigated. LP-CQPC06 was more resistant to gastric acid and bile salts than L. delbrueckii subsp. bulgaricus (LB). In the DSS-induced colitis mouse model, LP-CQPC06 treatment decreased the colon weight/length ratio and increased the colon length as compared to untreated mice with DSS-induced colitis. LP-CQPC06 also reduced the serum levels of interleukin 8 (IL-8), IL-1, tumor necrosis factor alpha, and macrophage inflammatory protein-1 alpha, as well as reducing levels of myeloperoxidase (MPO) and nitric oxide (NO) in the colon tissues of mice with DSS-induced colitis. In all cases, the effects of LP-CQPC06 were significantly stronger than those of LB. Quantitative polymerase chain reactions and western blots indicated that LP-CQPC06 increased the mRNA and protein expression levels of neuronal nitric oxide synthase, endothelial nitric oxide synthase, and nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha, while decreasing the expression levels of inducible nitric oxide synthase, nuclear factor kappa-beta, C-X-C motif chemokine receptor 1 (CXCR1), and CXCR2. Thus, L. plantarum CQPC06 had a good protective effect against colitis in a mouse model via the IL-8 pathway. Therefore, L. plantarum CQPC06 might have potential uses as a probiotic for colonic protection.

PRACTICAL APPLICATION

In this study, a newly discovered lactic acid bacteria was investigated. This bacterial strain had a good prophylactic effect against colitis in a mouse model, and might have potential utility as a probiotic.

Anti-Inflammatory and Anti-Oxidant Effects of p-Chloro-phenyl-selenoesterol on TNBS-Induced Inflammatory Bowel Disease in Mice

This study aims to investigate the protective effect of p-chloro-phenyl-selenoesterol [PCS; 0,2 mg/kg; 10 ml/kg i.g.) in colitis induced by 2,4,6-trinitrobenzene sulfonic acid [TNBS; 2 mg/100 µl 50% ethanol; intrarectally) in mice. Several parameters including weight, length, histological analyses determination, thiobarbituric acid reactive species, reactive species levels, superoxide dismutase, catalase, and myeloperoxidase (MPO) activity of colon were evaluated. The serum levels of tumor necrosis factor alpha [TNF-α) and interleukin 6 [IL-6) were also assessed. Treatment with PCS reduced the clinical and histopathologic severity of TNBS-induced colitis, characterized by colon length reduction and increased colon weight and microscopic intestinal inflammation. The therapeutic effects of PCS in this model were associated with significant decrease in proinflammatory cytokines TNF-α and IL-6 and decrease in MPO activity. Furthermore, combined with improvements in inflammatory parameters, treatment with the PCS was able to decrease oxidative stress and to prevent the decrease in antioxidant defenses in animals with TNBS-induced colitis. This finding suggests that PCS can improve experimental colitis in mice and it could be a potential therapeutic agent for the treatment of patients with IBD. J. Cell. Biochem. 118: 709-717, 2017. © 2016 Wiley Periodicals, Inc.

Camel's milk ameliorates TNBS-induced colitis in rats via downregulation of inflammatory cytokines and oxidative stress

Current treatment strategies for inflammatory bowel diseases (IBD) are associated with several adverse effects, and thus, the search for effective agents with minimal side effects merits attention. Camel's milk (CM) is endowed with antioxidant/anti-inflammatory features and has been reported to protect against diabetes and hepatic injury, however, its effects on IBD have not been previously explored. In the current study, we aimed to investigate the potential alleviating effects of CM against TNBS-induced colitis in rats. CM (10 ml/kg b.i.d. by oral gavage) effectively suppressed the severity of colon injury as evidenced by amelioration of macroscopic damage, colon weight/length ratio, histopathological alterations, leukocyte influx and myeloperoxidase activity. Administration of CM mitigated the colonic levels of TNF-α and IL-10 cytokines. The attenuation of CM to colon injury was also associated with suppression of oxidative stress via reduction of lipid peroxides and nitric oxide along with boosting the antioxidant defenses through restoration of colon glutathione and total anti-oxidant capacity. In addition, caspases-3 activity, an apoptotic marker, was inhibited. Together, our study highlights evidences for the promising alleviating effects of CM in colitis. Thus, CM may be an interesting complementary approach for the management of IBD.

Beneficial role of the probiotic mixture Ultrabiotique on maintaining the integrity of intestinal mucosal barrier in DSS-induced experimental colitis

The etiology of inflammatory bowel diseases which include ulcerative colitis (UC) and Crohn disease has not yet been clarified. Several hypotheses suggest a change in composition of gut microflora along with an impaired mucosal barrier that lead to excessive mucosal immunologic responses. Increased production of nitric oxide (NO) contributes greatly to the tissue injury caused by chronic inflammation. Evidence indicates that the mucus layer covering the epithelium is altered during UC and experimental colitis. Our aim in this study was to investigate the potential therapeutic effect of probiotic during DSS-induced colitis by modulating the immune system and colonic mucus production. For that purpose, the probiotic formulation Ultrabiotique(®) (Lactobacillus acidophilus, Bifidobacterium lactis, Lactobacillus plantarum and Bifidobacterium breve) was administered daily for 7 d to mice with colitis. Probiotic supplementation improved clinical symptoms and histological alterations observed during DSS induced colitis. Ultrabiotique(®) treatment down regulated the NO production by peritoneal macrophages of DSS-treated mice and enhanced mucus production in both DSS-treated and healthy mice. In conclusion, the modification of microflora by the Ultrabiotique(®) played a beneficial role in maintaining the integrity of the intestinal mucosal barrier and promoted tissue repair.

IL-23/IL-17A axis correlates with the nitric oxide pathway in inflammatory bowel disease: immunomodulatory effect of retinoic acid

Inflammatory bowel diseases (IBDs) are chronic inflammatory diseases of the gastrointestinal tract, which are clinically present as 1 of the 2 disorders, Crohn's disease (CD) or ulcerative colitis (UC) (Rogler 2004). The immune dysregulation in the intestine plays a critical role in the pathogenesis of IBD, involving a wide range of molecules, including cytokines. The aim of this work was to study the involvement of T-helper 17 (Th17) subset in the bowel disease pathogenesis by the nitric oxide (NO) pathway in Algerian patients with IBD. We investigated the correlation between the proinflammatory cytokines [(interleukin (IL)-17, IL-23, and IL-6] and NO production in 2 groups of patients. We analyzed the expression of messenger RNAs (mRNAs) encoding Th17 cytokines, cytokine receptors, and NO synthase 2 (NOS2) in plasma of the patients. In the same way, the expression of p-signal transducer and activator of transcription 3 (STAT3) and NOS2 was measured by immunofluorescence and immunohistochemistry. We also studied NO modulation by proinflammatory cytokines (IL-17A, IL-6, tumor necrosis factor α, or IL-1β) in the presence or absence of all-trans retinoic acid (At RA) in peripheral blood mononuclear cells (PBMCs), monocytes, and in colonic mucosa cultures. Analysis of cytokines, cytokine receptors, and NOS2 transcripts revealed that the levels of mRNA transcripts of the indicated genes are elevated in all IBD groups. Our study shows a significant positive correlation between the NO and IL-17A, IL-23, and IL-6 levels in plasma of the patients with IBD. Interestingly, the correlation is significantly higher in patients with active CD. Our study shows that both p-STAT3 and inducible NOS expression was upregulated in PBMCs and colonic mucosa, especially in patients with active CD. At RA downregulates NO production in the presence of proinflammatory cytokines for the 2 groups of patients. Collectively, our study indicates that the IL-23/IL-17A axis plays a pivotal role in IBD pathogenesis through the NO pathway.

The sphingosine-1-phosphate analogue FTY720 impairs mucosal immunity and clearance of the enteric pathogen Citrobacter rodentium

The sphingosine-1-phosphate (S1P) analogue FTY720 is therapeutically efficacious in multiple sclerosis and in the prevention of transplant rejection. It prevents the migration of lymphocytes to sites of pathology by trapping them within the peripheral lymph nodes, mesenteric lymph nodes (MLNs), and Peyer's patches. However, evidence suggests that its clinical use may increase the risk of mucosal infections. We investigated the impact of FTY720 treatment on susceptibility to gastrointestinal infection with the mouse enteric pathogen Citrobacter rodentium. This attaching and effacing bacterium induces a transient bacterial colitis in immunocompetent mice that resembles human infection with pathogenic Escherichia coli. FTY720 treatment induced peripheral blood lymphopenia, trapped lymphocytes in the MLNs, and prevented the clearance of bacteria when mice were infected with luciferase-tagged C. rodentium. FTY720-treated C. rodentium-infected mice had enhanced colonic inflammation, with significantly higher colon mass, colon histopathology, and neutrophil infiltration than vehicle-infected animals. In addition, FTY720-treated infected mice had significantly lower numbers of colonic dendritic cells, macrophages, and T cells. Gene expression analysis demonstrated that FTY720-treated infected mice had an impaired innate immune response and a blunted mucosal adaptive immune response, including Th1 cytokines. The data demonstrate that the S1P analogue FTY720 adversely affects the immune response to and clearance of C. rodentium.

Mucosal intestinal alteration in experimental colitis correlates with nitric oxide production by peritoneal macrophages: effect of probiotics and prebiotics

Inflammatory bowel disease (IBD) consists mainly of Ulcerative colitis (UC) and Crohn disease (CD). Although its aetiology is still not clearly established, it is thought to be due to overly aggressive immune response to enteric bacteria in genetically predisposed individuals. Manipulating the microbiota using probiotics or prebiotics is considered as a promising field of new therapeutic strategies used to attenuate immune disorders observed during IBD. The production of nitric oxide (NO) seems to be implicated in IBD pathogenesis. In our study, an acute UC was induced in Swiss mice using 3% Dextran Sulfate Sodium (DSS). The preventive effects of "Ultrabiotique®" (a probiotic) and inulin (a prebiotic) on the colitis were investigated. The production of NO was evaluated in the supernatants of peritoneal macrophages (pMφ) cultures. Colonic mucosa histology was subsequently examined. Results showed severe acute UC after administration of DSS. High levels of NO in pMφ cultures were also observed compared to control samples. These findings correlated with a significant destruction of the colonic mucosa. Oral administration of Ultrabiotique® or inulin decreased the severity of DSS-induced colitis. These treatments lead to a decrease in NO levels in pMφ cultures. A considerable reduction of colonic lesions was also noticed. Our findings suggest the involvement of NO in experimental UC pathogenesis. Pre- and pro-biotics, as discussed herein, seem to have an anti-inflammatory effect.

Melatonin inhibits Prevotella intermedia lipopolysaccharide-induced production of nitric oxide and interleukin-6 in murine macrophages by suppressing NF-κB and STAT1 activity

Although a range of biological and pharmacological activities of melatonin have been reported, little is known about its potential anti-inflammatory efficacy in periodontal disease. In this study, we investigated the effects of melatonin on the production of inflammatory mediators by murine macrophages stimulated with lipopolysaccharide (LPS) from Prevotella intermedia, a major cause of inflammatory reactions in the periodontium, and sought to determine the underlying mechanisms of action. Melatonin suppressed the production of nitric oxide (NO) and interleukin-6 (IL-6) at both gene transcription and translation levels in P. intermedia LPS-activated RAW264.7 cells. P. intermedia LPS-induced NF-κB-dependent luciferase activity was significantly inhibited by melatonin. Melatonin did not reduce NF-κB transcriptional activity at the level of IκB-α degradation. Melatonin blocked NF-κB signaling through the inhibition of nuclear translocation and DNA-binding activity of NF-κB p50 subunit and suppressed STAT1 signaling. Although further research is required to clarify the detailed mechanism of action, we conclude that melatonin may contribute to blockade of the host-destructive processes mediated by these two proinflammatory mediators and could be a highly efficient modulator of host response in the treatment of inflammatory periodontal disease.

Effects of luteolin on the release of nitric oxide and interleukin-6 by macrophages stimulated with lipopolysaccharide from Prevotella intermedia

BACKGROUND

Although a range of biologic and pharmacologic activities of luteolin has been reported, little is known about its potential as an agent to treat periodontal disease. In the present study, we investigated whether luteolin could downregulate the production of proinflammatory mediators in murine macrophage-like RAW264.7 cells stimulated with lipopolysaccharide (LPS) from Prevotella intermedia (Pi), a major cause of inflammatory periodontal disease, and we attempted to elucidate the possible mechanisms of action.

METHODS

LPS was prepared from lyophilized Pi ATCC 25611 cells by the standard hot phenol-water method. Culture supernatants were collected and assayed for nitric oxide (NO) and interleukin (IL)-6. We used real-time polymerase chain reaction to detect inducible NO synthase (iNOS) and IL-6 mRNA expression. iNOS expression, phosphorylation of JNK and p38, IκB-α degradation, nuclear translocation of nuclear factor-kappaB (NF-κB) subunits, and signal transducer and activator of transcription-1 (STAT1) phosphorylation were characterized via immunoblotting. DNA-binding of NF-κB was also analyzed.

RESULTS

Luteolin strongly suppressed the production of NO and IL-6 at both gene transcription and translation levels in Pi LPS-activated RAW264.7 cells. Mitogen-activated protein kinase pathways were not involved in the inhibition of Pi LPS-induced NO and IL-6 release by luteolin. Luteolin did not reduce NF-κB transcriptional activity at the level of IκB-α degradation. Luteolin blocked NF-κB signaling through inhibition of nuclear translocation and DNA binding activity of NF-κB p50 subunit and suppressed STAT1 signaling.

CONCLUSIONS

Although further research is encouraged to clarify the detailed mechanism of action, flavonoid luteolin may contribute to blockade of the host-destructive processes mediated by these two proinflammatory mediators and could have potential use in the treatment of inflammatory periodontal disease.

The pathogenicity of an enteric Citrobacter rodentium Infection is enhanced by deficiencies in the antioxidants selenium and vitamin E

The pathogenesis of a Citrobacter rodentium infection was evaluated in mice fed diets with a single deficiency in either selenium or vitamin E or with a double deficiency in both selenium and vitamin E compared to mice on nutritionally adequate diets. Mice fed the selenium- and vitamin E-deficient diet for 6 weeks had increased loads of C. rodentium in the colon and spleen, which were not observed in mice fed either of the singly deficient diets or the adequate diet. Infected mice fed the doubly deficient diet had increased colon crypt hyperplasia and an influx of infiltrating cells along with gross changes to crypt architecture, including ulceration and denuding of the epithelial layer. Cytokine and chemokine mRNA levels in the colon were measured by real-time PCR. Expression of proinflammatory cytokines and chemokines was upregulated on day 12 after infection with C. rodentium in mice fed the doubly deficient diet compared to mice fed the control diet. Heme oxygenase 1, an enzyme upregulated by oxidative stress, also was more highly induced in infected mice fed the doubly deficient diet. Production of C. rodentium antigen-specific IgM and IgG antibodies was not affected by feeding the doubly deficient diet. The results indicated that selenium and vitamin E play an important role in host resistance and in the pathology induced by C. rodentium, an infection that mimics disease caused by common food-borne bacterial pathogens in humans.

Crucial involvement of the CX3CR1-CX3CL1 axis in dextran sulfate sodium-mediated acute colitis in mice

Ingestion of DSS solution can induce in rodents acute colitis with a massive infiltration of neutrophils and macropahges, mimicking pathological changes observed in the acute phase of UC patients. Concomitantly, DSS ingestion enhanced the expression of a potent macrophage-tropic chemokine, CX3CL1/fractalkine, and its receptor, CX3CR1, in the colon. WT but not CX3CR1-deficient mice exhibited marked body weight loss and shortening of the colon after DSS ingestion. Moreover, inflammatory cell infiltration was attenuated in CX3CR1-deficient mice together with reduced destruction of glandular architecture compared with WT mice. DSS ingestion enhanced intracolonic iNOS expression by macrophages and nitrotyrosine generation in WT mice, but iNOS expression and nitrotyrosine generation were attenuated in CX3CR1-deficient mice. The analysis on bone marrow chimeric mice revealed that bone marrow-derived but not non-bone marrow-derived CX3CR1-expressing cells were a major source of iNOS. These observations would indicate that the CX3CL1-CX3CR1 axis can regulate the expression of iNOS, a crucial mediator of DSS-induced colitis. Thus, targeting the CX3CL1-CX3CR1 axis may be effective for the treatment of IBDs such as UC.

The effects of caffeic acid phenethyl ester (CAPE) on TNBS-induced colitis in ovariectomized rats

AIM

The aim of this investigation was to examine the effects of caffeic acid phenethyl ester (CAPE) on the development of colitis and antioxidant parameters in bilateral ovariectomized rats subjected to trinitrobenzene sulfonic acid (TNBS)-induced colitis.

MATERIALS AND METHODS

Twenty-one Wistar Albino ovariectomized female rats were divided into four subgroups (n = 5 or 6) (colitis control, vehicle control, CAPE 10 and 30 mg/kg, respectively). Colitis was induced using an enema of TNBS and ethanol, following which CAPE was administrated for 3 days to induce colitis and effect of CAPE was subsequently evaluated.

RESULTS

Based on microscopic damage scores, there was no difference between rats of the TNBS-colitis and the vehicle-treated groups, whereas treatment with CAPE 10 and 30 mg/kg, respectively, caused a significant reduction in colon injury compared to that observed in rats of the TNBS-colitis and vehicle-treated groups. The histologies of both treatment groups were not significantly different. In terms of the biochemical analyses, myeloperoxidase levels in rats from the CAPE 10 and 30 mg/kg groups were significantly different from that of the colitis control rats; however, the levels of malondialdehyde (MDA), catalase and reduced glutathione (GSH) were only significantly different from the levels found colitis control rats in rats administered 10 mg/kg. The levels of MDA, GSH and SOD in rats given CAPE were also significantly different from those of rats in the vehicle control group. These results were consistent with histological findings.

CONCLUSION

CAPE may have a positive effect on the inflammatory bowel disease treatment process and could, therefore, be used as an adjunct therapy in colitis. These effects of CAPE may occur through antiinflammatory and antioxidant mechanisms.

Effectiveness of mesalamine and propolis in experimental colitis

This study was conducted to investigate the effects of propolis and mesalamine on experimental colitis in rats. Distal colitis was induced in rats by intracolonic instillation of 2 mL of 4% acetic acid. The animals were randomly assigned to 5 groups: group 1, control, (n=8); group 2, colitis, received no treatment (n=8); group 3, colitis+mesalamine, 2 mL once a day via an enema (n=8); group 4, colitis+propolis, 600 mg/kg once a day via intragastric lavage (n=8); and group 5, colitis+mesalamine+propolis for 1 wk (n=8). Levels of nitric oxide were statistically significantly different in comparisons between groups 1 and 2, groups 2 and 3, and groups 4 and 5. Malondialdehyde levels were significantly different when group 2 was compared with groups 3, 4, and 5. A significant difference was observed when group 3 was compared with group 4 for myeloperoxidase. Most propolis-treated rats had normal histology; mesalamine-treated and propolis+mesalamine-treated rats had inflammatory cell infiltration at rates of 50% and 33%, respectively. The investigators concluded that propolis and mesalamine are efficient independently and in combination, but that their combined effect was not observed to be additive in experimental colitis.

Lipid A-associated proteins from Porphyromonas gingivalis stimulate release of nitric oxide by inducing expression of inducible nitric oxide synthase

BACKGROUND AND OBJECTIVE

The purpose of this study was to examine the effects of lipid A-associated proteins from Porphyromonas gingivalis, a major cause of inflammatory periodontal disease, on the production of nitric oxide and expression of inducible nitric oxide synthase in the murine macrophage cell line, RAW264.7. We also attempted to throw light on the signaling mechanisms involved in P. gingivalis lipid A-associated protein-induced nitric oxide production.

MATERIAL AND METHODS

The lipid A-associated proteins from P. gingivalis 381 were prepared by standard hot phenol-water extraction of endotoxin isolated by the butanol method. Nitric oxide production was assayed by measuring the accumulation of nitrite in culture supernatants. Western blot analysis of inducible nitric oxide synthase and analysis of reverse transcription-polymerase chain reaction products were carried out.

RESULTS

We found that P. gingivalis lipid A-associated proteins can induce inducible nitric oxide synthase expression and stimulate the release of nitric oxide without additional stimuli, and we demonstrated that multiple signaling pathways, such as nuclear factor-kappaB, microtubule polymerization, protein tyrosine kinase, protein kinase C, and mitogen-activated protein kinase cascades, are involved in P. gingivalis lipid A-associated protein-stimulated nitric oxide production. The production of nitric oxide required l-arginine.

CONCLUSION

The present study clearly shows that P. gingivalis lipid A-associated proteins fully induced inducible nitric oxide synthase expression and nitric oxide production in RAW264.7 cells in the absence of other stimuli. The ability of P. gingivalis lipid A-associated proteins to promote the production of nitric oxide may be important in the pathogenesis of inflammatory periodontal disease.

Pure compound from Boswellia serrata extract exhibits anti-inflammatory property in human PBMCs and mouse macrophages through inhibition of TNFα, IL-1β, NO and MAP kinases

The aim of the present study is to probe the anti-inflammatory potential of the plant Boswellia serrata by studying the effect of the crude extract and the pure compound isolated from it on key inflammatory mediators like TNFalpha, IL-1beta, and NO thus enabling the understanding of the key signaling events involved. The crude methanolic extract and the pure compound were analysed for their inhibitory effect on TNFalpha, IL-1beta and IL-6. The results demonstrated that all three cytokines are down regulated when PBMCs are cultured in the presence of crude extract or the pure compound at various time points. Observations on Th1/Th2 cytokines revealed marked down regulation of Th1 cytokines IFNgamma and IL-12 while the Th2 cytokines IL-4 and IL-10 were up regulated upon treatment with crude extract and pure compound. The extract and the pure compound isolated also showed considerable inhibition of NO production in activated RAW 264.7 cells, possibly via suppression of inducible NO synthase mRNA expression. Further to elucidate the underlying mechanism of action the effect of 12-ursene 2-diketone on LPS-induced activation of MAPK has also been examined. Our results demonstrated that 12-ursene 2-diketone inhibits the expression of pro-inflammatory cytokines and mediators via inhibition of phosphorylation of the MAP kinases JNK and p38 while no inhibition was seen in ERK phosphorylation in LPS-stimulated PBMCs. The above study therefore indicates that the crude methanolic extract and the isolated pure compound are capable of carrying out a natural anti-inflammatory activity at sites where chronic inflammation is present by switching off the pro-inflammatory cytokines and mediators, which initiate the process.

Ameliorative effect of pyrrolidinedithiocarbamate on acetic acid-induced colitis in rats

Ulcerative colitis is a chronically recurrent inflammatory bowel disease of unknown origin. The present study examined the effect of NF-kappaB inhibitor and antioxidant, pyrrolidinedithiocarbamate (PDTC) on experimental ulcerative colitis in rats. Animals were randomly divided into 4 groups, each consisting of 6 animals; normal control group, acetic acid group, PDTC-treated group and sulfasalazine-treated group as a positive control group. Induction of colitis by intracolonic administration of 3% acetic acid produced severe macroscopic inflammation in the colon 24 h after acetic acid administration as assessed by the colonic damage score. Microscopically, colonic tissues showed ulceration, oedema and inflammatory cells infiltration. Biochemical studies revealed increased serum levels of lactate dehydrogenase (LDH), and nitrite/nitrate and colonic concentrations of tumor necrosis factor-alpha (TNF-alpha) and the neutrophil infiltration index, myeloperoxidase (MPO). Oxidative stress was indicated by elevated lipid peroxides formation and depleted reduced glutathione concentrations (GSH) in colonic tissues. Immunohistochemical studies of colonic sections revealed upregulation of inducible nitric oxide synthase (iNOS). Pretreatment with PDTC at a dose of (200 mg/kg/day, i.p.), three days before induction of colitis decreased serum LDH, nitrite/nitrate and TNF-alpha levels, colonic concentrations of MPO and lipid peroxides while increased colonic GSH concentration. Moreover, PDTC pretreatment attenuated colonic iNOS expression. Finally, histopathological changes were nearly restored by PDTC pretreatment. The findings of the present study provide evidence that PDTC may be beneficial in patients with inflammatory bowel disease.

Surface-associated material from Porphyromonas gingivalis stimulates the release of nitric oxide by inducing expression of inducible nitric oxide synthase

The purpose of this study was to examine the effects of surface-associated material (SAM) from Porphyromonas gingivalis, a major cause of inflammatory periodontal disease, on the production of nitric oxide (NO) and expression of inducible nitric oxide synthase (iNOS) in the murine macrophage cell line RAW264.7. We also attempted to throw light on the signaling mechanisms involved in P. gingivalis SAM-induced NO production. SAM from P. gingivalis 381 was obtained by saline extraction. NO production was assayed by measuring the accumulation of nitrite in culture supernatants. Western blot analysis of iNOS and analysis of reverse transcription-polymerase chain reaction (RT-PCR) products were carried out. We found that P. gingivalis SAM can induce iNOS expression and stimulate the release of NO without additional stimuli and demonstrated an important role of the transcription factor NF-kappaB and microtubule polymerization in NO production. The production of NO required L-arginine, protein tyrosine kinase, and protein kinase C. The ability of P. gingivalis SAM to promote the production of NO may be important in the pathogenesis of inflammatory periodontal disease.

Inducible nitric oxide synthase involvement in the mechanism of action of Saccharomyces boulardii in castor oil-induced diarrhoea in rats

The biotherapeutic agent Saccharomyces boulardii has been shown to inhibit castor oil-induced diarrhoea in rats in a dose-response fashion, and one of the suggested mechanisms of action included involvement of the nitric oxide pathway. The present study was designed to address this mechanism of action by firstly measuring the effects of S. boulardii on the inducible nitric oxide synthase (iNOS) isoform activity in vitro. Second, the effects of S. boulardii on the increase in colonic citrulline level associated with castor oil treatment were examined. In vitro, S. boulardii showed a dose-dependent inhibition of iNOS activity with an IC50 of 0.89 mg/ml. In the rat diarrhoea model, the antidiarrhoeal effect of S. boulardii was confirmed using a single oral dose of 12 x 10(10) CFU/kg (viable cells). In this model, castor oil significantly elevated citrulline level from 2526+/-164 to 3501+/-193 nmol/g in the colon. When the rats were treated with the same antidiarrhoeal single dose of S. boulardii, no increase in citrulline level was observed. Moreover, the iNOS inhibitor 1400 W at 10 mg/kg and the inhibitor of iNOS expression dexamethasone at 1 mg/kg, administered subcutaneously, blocked the citrulline production induced by the laxative. Taken together, these findings confirm the involvement of inhibition of the inducible isoform of nitric oxide synthase in the mechanism of action of S. boulardii in diarrhoea.

Nitric oxide production and inducible nitric oxide synthase expression induced byPrevotella nigrescenslipopolysaccharide

We have examined the effects of lipopolysaccharide (LPS) from Prevotella nigrescens, one of the causative agents of inflammatory periodontal disease and endodontic infections, on the production of nitric oxide (NO) and expression of inducible nitric oxide synthase (iNOS) in the murine macrophage cell line RAW264.7. We also attempted to throw light on the signaling mechanisms involved in P. nigrescens LPS-induced NO production. We found that P. nigrescens LPS can induce iNOS expression and stimulate the release of NO without additional stimuli and demonstrated an important role of the transcription factor NF-kappaB and microtubule polymerization in NO production. The production of NO required l-arginine and protein tyrosine kinase but not activation of protein kinase C. The ability of P. nigrescens LPS to promote the production of NO may be important in the pathogenesis of inflammatory periodontal disease and endodontic infections.

Effects of intrarectal and intraperitoneal N(G)-nitro-L-arginine methyl ester treatment in 2,4,6-trinitrobenzenesulfonic acid induced colitis in rats

Inflammatory bowel disease (IBD) has been associated with an increased generation of nitric oxide (NO). Different authors have shown that NO in IBD can be either harmful or protective. The aim of this study was to investigate the efficiency of intrarectal (i.r.) and intraperitoneal (i.p.) application of N(G)-nitro-L-arginine methyl ester (L-NAME), a non-specific nitric oxide synthase inhibitor, in experimental acute colitis in the rats. Acute colitis was induced in rats by 2,4,6-trinitrobenzenesulfonic acid (TNBS) and ethanol. Twenty-eight rats were divided into four groups. L-NAME (50 mg/kg/day) was administered i.p. (Group 1) and i.r. (Group 2) for 7 days following the day when colitis was induced. Group 3 rats were not given any treatment after induction of colitis. Control group rats were given saline solution i.r. instead of TNBS. The presence of hyperemia, inflammation and ulcer was evaluated to score of macroscopic morphologic damage. The severity of colitis was assessed by microscopic criteria including ulceration, mucus cell depletion, crypt abscesses, inflammatory cysts, mucosal atrophy, edema, inflammatory cell infiltration, and vascular dilatation. Rectal tissue myeloperoxidase (MPO) activity and serum-rectal tissue nitrite levels were measured. Serum and rectal tissue nitrite levels increased in Group 3 rats. Both i.p. and i.r. L-NAME treatment significantly reduced serum and rectal tissue nitrite levels, but no effect on MPO activity and histologic damage score was observed. Under the present conditions we concluded i.r. and i.p. L-NAME treatment, applied at the dosage of 50 mg/kg/day, does not have any protective effect on the colonic injury.

Inhibition of inducible nitric-oxide synthase by activators of AMP-activated protein kinase: a new mechanism of action of insulin-sensitizing drugs

AMP-activated protein kinase (AMPK), an energy-sensing enzyme that is activated in response to cellular stress, is a critical signaling molecule for the regulation of multiple metabolic processes. AMPK has recently emerged as an attractive novel target for the treatment of obesity and type 2 diabetes because its activation increases fatty acid oxidation and improves glucose homeostasis. Here we show that pharmacological activation of AMPK by insulin-sensitizing drugs markedly inhibits inducible nitric-oxide synthase (iNOS), a proinflammatory mediator in endotoxic shock and in chronic inflammatory states including obesity-linked diabetes. AMPK-mediated iNOS inhibition was observed in several cell types (myocytes, adipocytes, macrophages) and primarily resulted from post-transcriptional regulation of the iNOS protein. AMPK activation in vivo also blunted iNOS induction in muscle and adipose tissues of endotoxin-challenged rats. Reduction of AMPK expression by small interfering RNA reversed the inhibitory effects of AMPK activators on iNOS expression and nitric oxide production in myocytes. These results indicate that AMPK is a novel anti-inflammatory signaling pathway and thus represents a promising therapeutic target for immune-inflammatory disorders.

Effects of melatonin on the expression of iNOS and COX-2 in rat models of colitis

AIM: To investigate the effects of melatonin (MT) on the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in rat models of colitis.

METHODS: Healthy adult Sprague-Dawlay (SD) rats of both sexes, weighing 280 ± 30 g, were employed in the present study. The rat models of colitis were induced by either acetic acid or 2, 4, 6-trinitrobenzene sulfonic acid (TNBS) enemas. The experimental animals were randomly divided into melatonin treatment and model control group that were intracolicly treated daily with melatonin at doses of 2.5, 5.0, 10.0 mg•kg^-1 and equal amount of saline respectively from 24 h following induction of colitis in rats inflicted with acetic acid enema and the seventh day in rats with TNBS to the end of study. A normal control group of rats treated with neither acetic acid nor TNBS but saline enema was also included in the study. On the 28^th day of the experiment, the rat colon mucosal damage index (CDMI) was calculated, and the colonic prostaglandin E₂ (PGE₂), nitric oxide (NO), as well as the iNOS and COX-2 expression were also determined biochemically or immunohistochemically.

RESULTS: CDMI increased to 2.87 ± 0.64 and 3.12 ± 1.12 respectively in rats treated with acetic acid and TNBS enema, which was in accordance with the significantly elevated colonic NO and PGE₂ contents, as well as the up-regulated colonic iNOS and COX-2 expression in both of the two rat models of colitis. With treatment by melatonin at the doses of 5.0 and 10.0 mg•kg^-1, CDMI in both models of rat colitis was significantly decreased (P < 0.05-0.01), which accorded synchronously and unanimously with the reduced colonic NO and PGE₂ content, as well as the down-regulated expression of colonic iNOS and COX-2.

CONCLUSION: Melatonin has a protective effect on colonic injury induced by both acetic acid and TNBS enemas, which is probably via a mechanism of local inhibition of iNOS and COX-2 expression in colonic mucosa.

PACAP in immunity and inflammation

The pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide belonging to the VIP/secretin/glucagon family of peptides, produced by the lymphoid cells, which exerts a wide spectrum of immunological functions controlling the homeostasis of immune system through different receptors expressed in various immunocompetent cells. In the last decade, PACAP has been clearly identified as a potent anti-inflammatory factor that exerts its function by regulating the production of both anti- and proinflammatory mediators. In this sense, PACAP prevents death by septic shock, an acute inflammatory disease with a high mortality. In addition, PACAP regulates the expression of costimulatory molecules, inasmuch as this related to the modulation in the shift from Th1 towards Th2 differentiation. We recently reported that PACAP prevents the deleterious effects of arthritis by downregulating both inflammatory and autoimmune components of the disease. Therefore, PACAP and analogs have been proposed as very promising candidates, alternative to other existing treatments, for treating acute and chronic inflammatory and autoimmune diseases, such as septic shock, arthritis, multiple sclerosis, Crohn's disease, or autoimmune diabetes.

Disruption of bladder epithelium barrier function after spinal cord injury

Neural-epithelial interactions are hypothesized to play an important role in bladder function. We determined whether spinal cord injury (SCI) altered several indicators of urinary bladder epithelium barrier function, including continuity of the surface umbrella cell layer, transepithelial resistance (TER), and urea and water permeability. Within 2 h of SCI, significant changes in uroepithelium were noted, including disruption of the surface umbrella cells and an approximately 50% decrease in TER. By 24 h, TER reached a minimum and was accompanied by significant increases in water and urea permeability. Regeneration of the surface uroepithelium was accomplished by 14 days after SCI and was accompanied by a return to normal TER and urea and water permeabilities. This early disruption of the uroepithelial permeability and accompanying changes in uroepithelial morphology were prevented by pretreatment with hexamethonium (a blocker of ganglion transmission), indicating involvement of sympathetic or parasympathetic input to the urinary bladder. In addition, prior treatment with capsaicin worsened the effect of SCI on uroepithelial permeability, suggesting that capsaicin-sensitive afferents may play a protective role in the process. These results demonstrate that SCI results in a significant disruption of the urinary bladder uroepithelium and that these changes may be mediated in part by an interaction with bladder nerves.

Zinc as a potential enteroprotector in oral rehydration solutions: its role in nitric oxide metabolism

Zinc has been recognized as an antioxidant with potential for chronic and acute effects. Oxidative damage produced by free radicals, including nitric oxide (NO), is responsible for certain types of intestinal malabsorption syndromes and diarrhea. Under physiologic or mildly stimulatory conditions for NO synthesis, the small intestine characteristically is in a proabsorptive state; however, an excessive production of NO triggers formation of cyclic nucleotides, which cause secretion and malabsorption. In this study, we hypothesized that low-molecular-weight, soluble zinc chelates could modulate the effects of induced NO excess on the small intestine. In vitro experiments demonstrated that zinc-citrate or zinc-histidine at > or =0.66 mM, as well as a known NO scavenger, 2-[carboxyphenyl]-4,4,4,4-tetramethylimidazoline-1-oxyl-3-oxide, at 2 microM, were effective at removing chemically generated NO. In vivo jejunal perfusions, conducted in healthy rats under anesthesia, showed that c-PTIO reduced the proabsorptive effects produced by 1 mM L-arginine, the precursor of NO. In a standard oral rehydration solution, 1 mM zinc-citrate partially reversed the antiabsorptive effects on potassium caused by an excess of NO generated from 20 mM L-arginine but did not alter sodium or water absorption. The data are consistent with the view that soluble zinc compounds incorporated into an oral rehydration solution may deserve further attention as a means to scavenge NO with fluids used for the treatment of chronic or acute diarrhea, especially in malnourished children who are often zinc deficient.

Effects of trimetazidine on acetic acid-induced colitis in female Swiss rats

Induction of colitis by acetic acid (AA) in the rat is widely used experimental model of inflammatory bowel disease (IBD) and ulcerations. AA as an irritant induces colitis involving infiltration of colonic mucosa with neutrophils and increased production of inflammatory mediators, such as hydrogen peroxide (H2O2), nitric oxide (NO), myeloperoxidase activity (MPO), and tumor necrosis factor (TNF-alpha). Trimetazidine (TMZ), an antianginal compound, was administered to investigate if its cytoprotective features in cardiac tissue are also effective in AA colitis where ischemic injury contributes to colitis. Administration of TMZ intraperitoneally improved the macroscopic and microscopic score alterations produced by AA. AA administration significantly elevated colonic MPO activity; however, treatment with TMZ significantly lowered this enzyme activity compared to AA. AA administration significantly enhanced superoxide dismutase (SOD) activities, except for AA + TMZ given rectally. TMZ treatment significantly lowered nitrate levels, but AA increased these levels. AA administration markedly lowered TNF-alpha levels, but TMZ treatment elevated these levels to control. These findings indicate that overproduction of NO may be involved in the immunosuppression observed during acute AA-induced rat colitis. In conclusion, TMZ treatment was more effective via the intraperitoneal than rectal route, and may be beneficial in therapy of colitis.

Irsogladine Prevents Monochloramine-Induced Gastric Mucosal Lesions by Improving the Decrease in Mucosal Blood Flow Due to the Disturbance of Nitric Oxide Synthesis in Rats

The inhibitory effect of an anti-ulcer drug irsogladine [2,4-diamino-6-(2,5-dichlorophenyl)-s-triazine maleate] on monochloramine (NH(2)Cl)-induced gastric mucosal lesions and its mechanisms of action were clarified in rats. Irsogladine dose-dependently prevented the formation of gastric mucosal lesions induced by 60 mM NH(2)Cl. The mucosal protective effect of irsogladine was not influenced by capsaicin-sensitive sensory defunctionalization. On the other hand, its protective effect was diminished by the inhibitor of nitric oxide synthase N(G)-nitro-L-arginine methylester (L-NAME), but not by the inducible nitric oxide synthase selective inhibitor aminoguanidine. Irsogladine restored the NH(2)Cl-induced decrease in the gastric cGMP formation as an index of nitric oxide synthesis, while it alone had no influence on the cGMP formation in intact tissues. Pretreatment with L-NAME abolished the recovery of cGMP by irsogladine. Furthermore, irsogladine ameliorated the NH(2)Cl-induced decrease in gastric mucosal blood flow, which was also reversed by pretreatment with L-NAME. These findings suggest that the improvement of the decrease in mucosal blood flow subsequent to the disturbance of gastric nitric oxide synthesis is involved in the protective effect of irsogladine on gastric mucosal lesions caused by NH(2)Cl.

Nutritional aspects of nitric oxide: human health implications and therapeutic opportunities

Nitric oxide (NO), the most potent natural vasorelaxant known, has close historical ties to cardiovascular physiology, despite NO's rich physiologic chemistry as an ubiquitous, signal-transducing radical. Aspects of NO biology critical to gastrointestinal health and, consequently, nutritional status are increasingly being recognized. Attempts are underway to exploit the gastrointestinal actions of NO for therapeutic gain. Cross-talk between NO and micronutrients within and outside the gastrointestinal system affects the establishment or progression of several diseases with pressing medical needs. These concepts imply that NO biology can influence nutrition and be nutritionally modulated to affect mammalian (patho)physiology. At least four nutritional facets of NO biology are at the forefront of contemporary biomedical research: 1) NO as modulator of feeding behavior and mediator of gastrointestinal homeostasis; 2) NO supplementation as a therapeutic modality for preserving gastrointestinal health; 3) interactions among elemental micronutrients (e.g., zinc), NO, and inflammation as potential contributors to diarrheal disease; and 4) vitamin micronutrients (e.g., vitamins E and C) as protectors of NO-dependent vascular function. Discussion of extant data on these topics prompts speculation that future research will broaden NO's nutritional role as an integrative signaling molecule supporting gastrointestinal and nutritional well-being.

NO-mesalamine protects colonic epithelial cells against apoptotic damage induced by proinflammatory cytokines

The activation of a self-amplifying cascade of caspases, of which caspase-8 is the apical protease, mediates Fas-, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-, and TNF-alpha-induced apoptosis in colon cell lines. Nitric oxide (NO) protects from apoptosis induced by Fas and TNF-alpha. We examined whether NCX-456, an NO-releasing derivative of mesalamine, protects colon epithelial cells from cytokine-induced apoptosis. Caco-2 and HT-29 cell lines express death factor receptors and are driven to apoptosis in response to incubation with Fas-agonistic antibody, TNF-alpha/interferon-gamma, and TRAIL. The two novel observations reported here are that 1) cotreatment of cells with NCX-456, but not mesalamine, resulted in concentration-dependent protection against death factor-induced apoptosis and inhibition of caspase activity, and 2) exposure to dithiothreitol, an agent that effectively removes NO from thiol groups, resulted in a 70% recovery of caspase activity, which is consistent with S-nitrosation as a major mechanism for caspase inactivation. These data suggest that caspase S-nitrosation represents a mechanism for protection of colonic mucosal epithelial cells from death factor-induced death.

Thalidomide impairment of trinitrobenzene sulphonic acid-induced colitis in the rat - role of endothelial cell-leukocyte interaction

1. Immune response-modulating drugs such as thalidomide may be of therapeutic value in the treatment of chronic inflammatory bowel diseases including Crohn's disease (CD). In the present study, we have investigated whether thalidomide exerts this effect by impairing endothelial cell-leukocyte interaction through down-regulation of the expression of pro-inflammatory gene products in these cells. 2. Transient CD-like colitis was induced in male Wistar rats by single enema with trinitrobenzene sulphonic acid (TNBS) in ethanol followed by macroscopic scoring, histology, intravital microscopy, RT - PCR and immunohistochemistry (IHC) analyses. Thalidomide or its analogue supidimide were administered in olive oil by intragastric instillation 6 h prior to the induction of colitis and then daily for one week. 3. Both thalidomide and supidimide (200 mg kg(-1) d(-1)) significantly attenuated TNBS-induced colitis as compared to vehicle-treated control animals (44 and 37% inhibition, respectively), and this effect persisted for 7 days post cessation of thalidomide treatment (46% inhibition). 4. Moreover, thalidomide significantly reduced leukocyte sticking to postcapillary venular endothelial cells in the submucosa (by 45%), improved functional capillary density and perfusion, and attenuated endothelial interleukin-8 expression, as judged by IHC analysis. According to RT - PCR analysis, both thalidomide and supidimide also significantly reduced vascular cell adhesion molecule-1 mRNA expression in the affected part of the descending colon. 5. These findings suggest that thalidomide and one of its derivatives impairs CD-like TNBS-induced colitis in the rat by down-regulating endothelial adhesion molecule and chemokine expression and, as a consequence, the interaction of these cells with circulating leukocytes.

Serum and testicular testosterone and nitric oxide products in aluminum-treated mice

The present investigation aimed to elucidate possible mechanisms of aluminum (Al)-induced reproductive toxicity in male mice. Daily intraperitoneal administrations of Al chloride (0, 1/8 and 1/3 LD(50)) were conducted for 12 or 16 days, followed by a 2-week withdrawal period. Serum Al levels significantly increased in Al-treated animals, compared to controls, whereas serum testosterone concentrations were markedly decreased. In addition, significant increases in nitric oxide products (NO(x)) were also observed during Al injection. Similar trends were found for testicular Al, NO(x) and testosterone levels. However, during the withdrawal period, when diminished testicular Al levels were observed, the changes in NO(x) and testosterone levels were indistinguishable from control values. It was concluded that: (i) Al exerted a significant adverse effect on the steroidogenesis; (ii) the process was reversible; and (iii) increased production of NO(x), induced by excessive Al, might inhibit testosterone levels.

The inducible nitric oxide synthase inhibitor ONO-1714 blunts dextran sulfate sodium colitis in mice

In mice with acute dextran sulfate sodium colitis, we examined the effect of inducible nitric oxide synthase inhibition by (1S,5S,6R,7R)-7chloro-3-amino-5methyl-2-azabicyclo[4.1.0]heptane hydrochloride (ONO-1714) on colonic biochemistry, injury, and inflammation. Colonic luminal nitrate and nitrite were measured by the Griess reaction; inducible nitric oxide synthase messenger RNA expression by reverse transcription-polymerase chain reaction; and nitrotyrosine by immunohistochemistry. Mice with colitis showed increases in nitrate and nitrite, inducible nitric oxide synthase messenger RNA, and numbers of cells staining for nitrotyrosine. Colonic inflammation was severe. ONO-1714 inhibited increases in nitrate and nitrite and numbers of nitrotyrosine-positive cells; injury and inflammation also were reduced. Dextran sulfate sodium-induced increases in thiobarbituric acid-reactive substances, a lipid peroxidation marker, were blunted by ONO-1714, which also inhibited increases in mucosal inflammatory cytokines. Nitric oxide produced by inducible nitric oxide synthase may contribute to colonic inflammation by nitrosation, oxidative damage, and enhanced inflammatory cytokines.

Nitric oxide augments release of chemokines from monocytic U937 cells: modulation by anti-inflammatory pathways

Nitric oxide (NO) appears to act as an inflammatory mediator on monocytic cells. Exogenous NO augmented release of chemokines from human promonocytic U937 cells and peripheral blood mononuclear cells. Pharmacological strategies aiming at modulation of NO-induced release of interleukin-8 (IL-8) were investigated in U937 cells in detail. Release of IL-8 was down-regulated by transforming growth factor beta2 (TGF-beta2), by the protein tyrosine-kinase inhibitor genistein, and via rises in intracellular cyclic AMP, generated by prostaglandin E(2), rolipram, pentoxifylline, forskolin, or dibutyryl-cyclic AMP. In addition, incubation with the synthetic glucocorticoid dexamethasone or suppression of activity of p38 mitogen-activated protein (MAP) kinases by SB-203580 modulated release of IL-8. Activation of p38 MAP kinases was confirmed by the demonstration of an augmented appearance of phosphorylated p38 in the presence of NO. The present data suggest that exposure to exogenous NO resembles activation of U937 cells by proinflammatory stimuli. The anti-inflammatory cytokine TGF-beta2, as well as anti-inflammatory or immunosuppressive agents such as genistein, pentoxifylline, rolipram, dexamethasone, and SB-203580 modulate inflammatory, chemokine-inducing actions of NO.

Zinc deficiency, malnutrition and the gastrointestinal tract

Recent clinical and experimental findings have reinforced the link among zinc deficiency, malnutrition and diarrheal disease. Because there is a strong association between protein and zinc content in virtually all types of foods, insufficient protein intake may often be the cause of zinc deficiency. Compensatory mechanisms operating in monogastric species during malnutrition are less effective for the absorption of transition divalent elements such as zinc, which remain bound to ligands of dietary or endogenous origin. Both protein and zinc deficiencies are strong negative determinants for normal cellular immunity. In zinc deficiency, the organism is more susceptible to toxin-producing bacteria or enteroviral pathogens that activate guanylate and adenylate cyclases, stimulating chloride secretion, producing diarrhea and diminishing absorption of nutrients, thus exacerbating an already compromised mineral status. In addition, zinc deficiency may impair the absorption of water and electrolytes, delaying the termination of normally self-limiting gastrointestinal disease episodes. The gastrointestinal tract may be one of the first target areas where zinc insufficiency may be manifested. A prolonged low zinc intake deprives the organism of the local potential beneficial effects of zinc, including interactions with oxidative free radicals and nitric oxide metabolism. Nitric oxide is a second messenger that plays an important part in the triggering of diarrheal disease. The possible interrelationship among infection, inflammation, free radical damage and its quenching by potential scavengers, such as zinc, in the intestinal lumen or within the enterocyte should be more extensively studied.

Nitric Oxide. V. therapeutic potential of nitric oxide donors and inhibitors

Nitric oxide is a crucial mediator of gastrointestinal mucosal defense, but, paradoxically, it also contributes to mucosal injury in several situations. Inhibitors of nitric oxide synthesis and compounds that release nitric oxide have been useful pharmacological tools for evaluating the role of nitric oxide in gastrointestinal physiology and pathophysiology. Newer inhibitors with selectivity for one of the isoforms of nitric oxide synthase are even more powerful tools and may have utility as therapeutic agents. Also, agents that can scavenge nitric oxide or peroxynitrite are promising as drugs to prevent nitric oxide-associated tissue injury. Compounds that release nitric oxide in small amounts over a prolonged period of time may also be very useful for prevention of gastrointestinal injury associated with shock and with the use of drugs that have ulcerogenic effects. Indeed, the coupling of a nitric oxide-releasing moiety to nonsteroidal anti-inflammatory drugs has proven to be a valid means of substantially reducing the gastrointestinal toxicity of these drugs without decreasing their efficacy.