Expression of inducible nitric oxide synthase activity in human colon epithelial cells: modulation by T lymphocyte derived cytokines

Effect of corticosteroids on nitric oxide production in inflammatory bowel disease: are leukocytes the site of action?

Nitric oxide (NO) production is increased in the human colonic mucosa in intestinal inflammation. We examined the effect of corticosteroids and the role of mononuclear cells in this production. Colonic biopsies from patients with ulcerative colitis and normal controls were cultured with either budesonide or prednisolone in the presence of proinflammatory cytokines. Human mixed mononuclear cells (MMCs) were cocultured with HT-29 cells stimulated with IFN-gamma and LPS in the presence or absence of corticosteroids. Nitrite production was measured in supernatants by a modification of the Griess reaction, and inducible NO synthase (iNOS) mRNA expression was studied in colonic tissue by RT-PCR. Both steroids significantly suppressed the nitrite production and iNOS mRNA expression in inflamed colonic biopsies from ulcerative colitis patients and in cytokine-stimulated normal colonic biopsies but not in cytokine-stimulated HT-29 cells. Nitrite production by HT-29 cells was significantly increased (P < 0.01) in cocultures with MMCs stimulated with IFN-gamma and LPS. The presence of either prednisolone or budesonide significantly (P < 0.01) suppressed nitrite production from cocultures of HT-29 cells and MMCs but not from cultures of HT-29 cells stimulated with conditioned media from activated MMCs. Interestingly, stimulation of HT-29 with conditioned media from MMCs pretreated with steroids before stimulation with LPS and IFN-gamma induced a significantly (P < 0.01) lower nitrite production. These results suggest that the inhibitory effect of corticosteroids on the NO production in the intestinal inflammation might be via the inhibition of MMC-produced mediators responsible for NO production by colonic epithelial cells.

Nitric oxide in inflammatory bowel disease: a universal messenger in an unsolved puzzle

In recent years, nitric oxide (NO), a gas previously considered to be a potentially toxic chemical, has been established as a diffusible universal messenger that mediates cell-cell communication throughout the body. Constitutive and inducible NO production regulate numerous essential functions of the gastrointestinal mucosa, such as maintenance of adequate perfusion, regulation of microvascular and epithelial permeability, and regulation of the immune response. Up-regulation of the production of NO via expression of inducible nitric oxide synthase (iNOS) represents part of a prompt intestinal antibacterial response; however, NO has also been associated with the initiation and maintenance of inflammation in human inflammatory bowel disease (IBD). Recent studies on animal models of experimental IBD have shown that constitutive and inducible NO production seems to be beneficial during acute colitis, but sustained up-regulation of NO is detrimental. This fact is also supported by studies on mice genetically deficient in various NOS isoforms. However, the mechanism by which NO proceeds from being an indispensable homeostatic regulator to a harmful destructor remains unknown. Furthermore, extrapolation of data from animal colitis models to human IBD is questionable. The purpose of this review is to update our knowledge about the role of this universal mediator and the enzymes that generate it in the pathogenesis of IBD.

Relative contributions of NOS isoforms during experimental colitis: endothelial-derived NOS maintains mucosal integrity

The role of nitric oxide (NO) in inflammatory bowel diseases has traditionally focused on the inducible form of NO synthase (iNOS). However, the constitutive endothelial (eNOS) and neuronal (nNOS) isoforms may also impact on colitis, either by contributing to the inflammation or by regulating mucosal integrity in response to noxious stimuli. To date, studies examining the roles of the NOS isoforms in experimental colitis have been conflicting, and the mechanisms by which these enzymes exert their effects remain unclear. To investigate and clarify the roles of the NOS isoforms in gut inflammation, we induced trinitrobenzenesulfonic acid colitis in eNOS, nNOS, and iNOS knockout (KO) mice, assessing the course of colitis at early and late times. Both eNOS and iNOS KO mice developed a more severe colitis compared with wild-type mice. During colitis, iNOS expression dramatically increased on epithelial and lamina propria mononuclear cells, whereas eNOS expression remained localized to endothelial cells. Electron and fluorescence microscopy identified bacteria in the ulcerated colonic mucosa of eNOS KO mice, but not in wild-type, iNOS, or nNOS KO mice. Furthermore, eNOS KO mice had fewer colonic goblet cells, impaired mucin production, and exhibited increased susceptibility to an inflammatory stimulus that was subthreshold to other mice. This susceptibility was reversible, because the NO donor isosorbide dinitrate normalized goblet cell numbers and ameliorated subsequent colitis in eNOS KO mice. These results identify a protective role for both iNOS and eNOS during colitis, with eNOS deficiency resulting in impaired intestinal defense against lumenal bacteria and increased susceptibility to colitis.

Activity of inducible and neuronal nitric oxide synthases in colonic mucosa predicts progression of ulcerative colitis

OBJECTIVE

The present study analyzes inducible and neuronal nitric oxide synthase activity and expression in colonic mucosa of patients with ulcerative colitis, and correlates them with the progression of disease extent.

METHODS

Thirty patients with ulcerative colitis were included. Synthases activity and expression were analyzed both in inflamed and noninflamed mucosa. After 2 yr, disease extent was determined and compared with extent at inclusion.

RESULTS

Ca(2+)-independent activity, expressed as median with (interquartile range), in inflamed mucosa was higher than in noninflamed and control mucosa (102 (165-66), 24 (50-3), 1 (2.5-0.1) pmol.min(-1) mg prot(-1), respectively, p < 0.005), whereas Ca(2+)-dependent activity was significantly lower in inflamed than in noninflamed and control mucosa. Western blot analysis identified inducible and neuronal isoforms and confirmed these differences. Patients with more extended disease after 2 yr had higher levels of Ca(2+)-independent activity in noninflamed mucosa at inclusion and lower levels of Ca(2+)-dependent activity than patients with persistence of similar extent of inflammation (50 (78-29) vs 8 (30-0.1), p < 0.005; 51 (100-36) vs 150 (156-106), p < 0.05, respectively). Values of Ca(2+)-independent activity in noninflamed mucosa greater than 30 pmol. min(-1) mg prot(-1) showed 80% sensitivity and 87.5% specificity in the detection of patients with subsequent progression of disease extent, whereas values of Ca(2+)-dependent activity in noninflamed mucosa greater than 125 pmol. min(-1) mg prot(-1) showed 75% sensitivity and 80% specificity in the detection of patients with stability of disease extent. A ratio of Ca(2+)-independent/Ca(2+)-dependent activities over 0.29 showed 90% sensitivity and 87.5% specificity in the detection of patients with subsequent progression of extent.

CONCLUSIONS

Our results show an up-regulation of inducible nitric oxide synthase and a down-regulation of neuronal isoform not only in inflamed mucosa but also in apparently healthy mucosa of patients with ulcerative colitis. The values of activity of both isoforms in apparently healthy mucosa could predict the disease extent after 2 yr follow-up.

Intestinal interleukin-13 in pediatric inflammatory bowel disease patients

BACKGROUND

Interleukin-13 (IL-13) is a multifunctional cytokine whose net principle action is to diminish inflammatory responses. Dysregulation of IL-13 production has been proposed to contribute to intestinal inflammation in inflammatory bowel disease (IBD) patients. Previous studies implicate IL-13 in IBD pathogenesis; however, they fail to accurately reflect in vivo intestinal IL-13 production. We evaluate IL-13, IL-6, and IL-1beta elaborations from colonic organ cultures of pediatric IBD patients

METHODS

Endoscopic lamina propria biopsies or surgical specimens from pediatric patients with IBD were organ cultured and supernatants evaluated by enzyme-linked immunosorbent assay for IL-1beta, IL-6, and IL-13.

RESULTS

IL-13 concentrations were significantly reduced in ulcerative colitis (UC) patients when compared with normal controls (P = 0.002) and Crohn disease (CD) patients (P = 0.001). End-stage UC patients at colectomy had lower intestinal IL-13 production than all other UC patients (P = 0.002). No significant correlation was found between IL-13 concentration and histologic disease severity (P = 0.134).

CONCLUSIONS

Diminished intestinal IL-13 production is present in UC patients and wanes further with clinical disease progression. These findings suggest that UC patients may be differentiated from CD patients by intestinal IL-13 quantitation, and UC patients may benefit from IL-13 enhancing therapies.

Acidic duodenal pH alters gene expression in the cystic fibrosis mouse pancreas

The duodenum is abnormally acidic in cystic fibrosis (CF) due to decreased bicarbonate ion secretion that is dependent on the CF gene product CFTR. In the CFTR null mouse, the acidic duodenum results in increased signaling from the intestine to the exocrine pancreas in an attempt to stimulate pancreatic bicarbonate ion secretion. Excess stimulation is proposed to add to the stress/inflammation of the pancreas in CF. DNA microarray analysis of the CF mouse revealed altered pancreatic gene expression characteristic of stress/inflammation. When the duodenal pH was corrected genetically (crossing CFTR null with gastrin null mice) or pharmacologically (use of the proton pump inhibitor omeprazole), expression levels of genes measured by quantitative RT-PCR were significantly normalized. It is concluded that the acidic duodenal pH in CF contributes to the stress on the exocrine pancreas and that normalizing duodenal pH reduces this stress.

Interleukin-4 and transforming growth factor beta have opposing regulatory effects on gamma interferon-mediated inhibition of Cryptosporidium parvum reproduction

It was shown previously that enterocytes activated by gamma interferon (IFN-gamma) are efficient effector cells in the killing of Cryptosporidium parvum. How this function is regulated is not clearly understood, but transforming growth factor beta (TGF-beta) and the Th2 regulatory cytokines may play a role. Using an in vitro cell culture system, we investigated how the key regulatory cytokines interleukin-4 (IL-4), IL-10, IL-13, and TGF-beta might modulate the effect of IFN-gamma in inducing resistance to infection in enterocyte cell lines. The results showed that TGF-beta can abolish the inhibitory effect on C. parvum development and that neither IL-13 nor IL-10 influenced the action of IFN-gamma. In contrast, IL-4 cooperated with low concentrations of IFN-gamma (1 and 10 U/ml) to enhance parasite killing. One mechanism that appeared to be involved in the combined activity of IFN-gamma and IL-4 was intracellular Fe(2+) deprivation, but induction of nitric oxide production was not involved. In one cell line, the extents and durations of phosphorylation of STAT1, a transcription factor involved in IFN-gamma signaling, were similar when cells were stimulated with IFN-gamma alone and with IFN-gamma and IL-4 gamma, suggesting that the cooperative effect of the cytokines was not related to STAT1 activation. The effects of the presence of TGF-beta and IL-4 on IFN-gamma function did not appear to involve any alteration in the level of expression of IFN-gamma receptors.

Nitric oxide in inflammatory bowel disease

Nitric oxide (NO) is a pleiotropic free radical messenger molecule. There is a large body of evidence that the inducible form of the NO synthase enzyme (iNOS) that is responsible for high-output production of NO from l-arginine is up-regulated in various forms of mucosal inflammation. Consistent with this, multiple detection strategies have demonstrated that iNOS expression, enzymatic activity, and NO production are increased in human inflammatory bowel disease tissues. There is also evidence that the level of iNOS-derived NO correlates well with disease activity in ulcerative colitis, while for Crohn's disease, the results are more variable. A substantial number of animal studies have assessed the role of inducible NO production. While the majority of studies have shown improvement in experimental inflammatory bowel disease with iNOS inhibition, there are also a significant number of reports of exacerbation of disease with inhibitors. Similarly, studies using iNOS-deficient mice in colitis models have shown improvement, worsening, or no effect on disease. The authors suggest that additional studies to assess the role of the competing biochemical pathway, namely the conversion of l-arginine to polyamines via the actions of arginase and ornithine decarboxylase, may provide important new insights into understanding the regulation of mucosal inflammation and inflammatory bowel disease.

Review article: oxidative stress as a pathogenic factor in inflammatory bowel disease--radicals or ridiculous?

Virtually all inflammatory mediators investigated to date seem to be dysregulated in the inflamed intestinal mucosa of patients with inflammatory bowel disease. However, which of these are actually involved in the initiation and perpetuation of intestinal tissue damage is still not fully understood. Amongst these mediators are the reactive oxygen metabolites, produced in large amounts by the massively infiltrating leucocytes. These reactive oxygen metabolites are believed to constitute a major tissue-destructive force and may contribute significantly to the pathogenesis of inflammatory bowel disease. This paper provides a concise overview of reactive oxygen metabolite biochemistry, the types of cell and tissue damage potentially inflicted by them, and the endogenous antioxidants which should prevent these harmful effects. An up-to-date summary of the available human experimental data suggests that reactive oxygen metabolite-mediated injury is important in both the primary and downstream secondary pathophysiological mechanisms underlying intestinal inflammation. Nonetheless, how the individual components of the mucosal antioxidant enzymatic cascade respond to inflammatory conditions is a neglected area of research. This particular aspect of intestinal mucosal oxidative stress therefore merits further study, in order to provide a sound, scientific basis for the design of antioxidant-directed treatment strategies for inflammatory bowel disease patients.

Modulation of inducible nitric oxide synthase expression by the attaching and effacing bacterial pathogen citrobacter rodentium in infected mice

Citrobacter rodentium belongs to the attaching and effacing family of enteric bacterial pathogens that includes both enteropathogenic and enterohemorrhagic Escherichia coli. These bacteria infect their hosts by colonizing the intestinal mucosal surface and intimately attaching to underlying epithelial cells. The abilities of these pathogens to exploit the cytoskeleton and signaling pathways of host cells are well documented, but their interactions with the host's antimicrobial defenses, such as inducible nitric oxide synthase (iNOS), are poorly understood. To address this issue, we infected mice with C. rodentium and found that iNOS mRNA expression in the colon significantly increased during infection. Immunostaining identified epithelial cells as the major source for immunoreactive iNOS. Finding that nitric oxide (NO) donors were bacteriostatic for C. rodentium in vitro, we examined whether iNOS expression contributed to host defense by infecting iNOS-deficient mice. Loss of iNOS expression caused a small but significant delay in bacterial clearance without affecting tissue pathology. Finally, immunofluorescence staining was used to determine if iNOS expression was localized to infected cells by staining for the C. rodentium virulence factor, translocated intimin receptor (Tir), as well as iNOS. Interestingly, while more than 85% of uninfected epithelial cells expressed iNOS, fewer than 15% of infected (Tir-positive) cells expressed detectable iNOS. These results demonstrate that both iNOS and intestinal epithelial cells play an active role in host defense during C. rodentium infection. However, the selective expression of iNOS by uninfected but not infected cells suggests that this pathogen has developed mechanisms to locally limit its exposure to host-derived NO.

PPAR agonists amplify iNOS expression while inhibiting NF-kappaB: implications for mesangial cell activation by cytokines

In acute inflammation, the transcription factor NF-kappaB is activated and increases the expression of multiple pro-inflammatory genes. Agonists of peroxisome proliferator activated receptors (PPAR) have been reported to exert antiinflammatory effects in various systems. In keeping with such an antiinflammatory role, it was found that several PPAR agonists, including Wy14,643, clofibrate, carbaprostacyclin, and ciglitazone inhibited NF-kappaB activity and increased IkappaBalpha levels in cytokine-stimulated mesangial cells (MC). Activation of NF-kappaB has been found to be crucial to the cytokine-elicited expression of inducible nitric oxide synthase (iNOS). Despite the inhibitory effect of PPAR agonists on NF-kappaB activity, this study provides experimental data demonstrating that these agonists amplify cytokine-elicited NO generation in MC, potentiating iNOS protein expression approximately threefold. The upregulation of iNOS expression occurred at the mRNA level and apparently did not result from iNOS mRNA stabilization. Clofibrate and ciglitazone amplified the cytokine-elicited stimulation of a 16-Kb human iNOS promoter construct in stably transfected MC, suggesting that PPAR agonists potentiate iNOS induction through transcriptional mechanisms. MC express all three PPAR proteins. However, iNOS potentiation did not correlate with increased PPAR activity. In addition, Wy14,643-induced amplification of cytokine-elicited iNOS levels also occurred in RAW264.7 macrophages and in human epithelial Caco-2 and HT-29 cells. The observation that these epithelial cell lines express an inactive, truncated PPARalpha variant suggests that a classical PPARalpha agonist, such as Wy14,643, may act through PPARalpha-independent mechanisms. In conclusion, these results show that, despite reducing NF-kappaB activity, PPAR agonists may amplify the expression of certain NF-kappaB-dependent genes that are relevant to the inflammatory process, like iNOS.

Expression of inducible nitric oxide synthase and heat shock proteins in periapical inflammatory lesions

BACKGROUND

The mechanisms responsible for activation and proliferation of lining epithelium involved in inflammatory processes in periapical inflammatory lesions remain unclear. In this study, the expression and distribution of inducible nitric oxide synthase (iNOS) and heat shock proteins (HSPs) were immunohistochemically investigated in periapical inflammatory lesions.

METHODS

Control specimens of periodontal ligaments including Malassez epithelial rests from seven teeth and periapical inflammatory lesions (15 apical granulomas (AGs), 16 radicular cysts (RCs), and 10 residual radicular cysts (RRCs)) were prepared and examined by the standard streptavidin-biotin peroxidase complex method using anti-iNOS rabbit polyclonal antiserum, and anti-HSP27, -HSP60, -HSP70 mouse monoclonal antibodies.

RESULTS

Immunoreactivity for iNOS was detected in macrophages, lymphocytes, and endothelial cells of granulation tissue and in lining epithelium of periapical inflammatory lesions. Malassez epithelial rests showed no or slight staining for iNOS. The epithelial staining intensity of iNOS in RCs was greater than that in Malassez epithelial rests and RRCs. Immunoreactivity for HSP27 was recognized in inflammatory cells, endothelial cells and lining epithelium of periapical inflammatory lesions and in Malassez epithelial rests. HSP60 was detected in some lymphocytes of granulation tissue and in lining epithelium of periapical inflammatory lesions, whereas Malassez epithelial rests showed no staining for HSP60. Epithelial HSP60 reactivity was more intense in RCs than in RRCs. HSP70 was expressed in lymphocytes, endothelial cells and lining epithelium of periapical inflammatory lesions and in Malassez epithelial rests. The staining intensity of HSP70 in Malassez epithelial rests was slightly lower than that in lining epithelium of RCs and RRCs.

CONCLUSIONS

These data demonstrate that the expressions of iNOS, HSP60, and HSP70 are involved in inflammatory processes and might play a role in the activation and proliferation of lining epithelium, leading to progression of periapical inflammatory lesions.

Na+/H+ exchanger blockade inhibits enterocyte inflammatory response and protects against colitis

Na+/H+ exchangers (NHEs) are integral transmembrane proteins found in all mammalian cells. There is substantial evidence indicating that NHEs regulate inflammatory processes. Because intestinal epithelial cells express a variety of NHEs, we tested the possibility that NHEs are also involved in regulation of the epithelial cell inflammatory response. In addition, since the epithelial inflammatory response is an important contributor to mucosal inflammation in inflammatory bowel disease (IBD), we examined the role of NHEs in the modulation of disease activity in a mouse model of IBD. In human gut epithelial cells, NHE inhibition using a variety of agents, including amiloride, 5-(N-methyl-N-isobutyl)amiloride, 5-(N-ethyl-N-isopropyl)- amiloride, harmaline, clonidine, and cimetidine, suppressed interleukin-8 (IL-8) production. The inhibitory effect of NHE inhibition on IL-8 was associated with a decrease in IL-8 mRNA accumulation. NHE inhibition suppressed both activation of the p42/p44 mitogen-activated protein kinase and nuclear factor-kappaB. Finally, NHE inhibition ameliorated the course of IBD in dextran sulfate-treated mice. Our data demonstrate that inhibition of NHEs may be an approach worthy of pursuing for the treatment of IBD.

Evaluation of Th1, Th2 and immunosuppressive cytokine mRNA expression within the colonic mucosa of dogs with idiopathic lymphocytic-plasmacytic colitis

The objective of this study was to evaluate the expression of the immunoregulatory and pro-inflammatory cytokines interleukin (IL)-2, IL-4, IL-6, IL-12p35, IL-12p40, interferon-gamma (IFN-gamma), and tumour necrosis factor-alpha (TNF-alpha), and the expression of the predominantly immunosuppressive cytokines transforming growth factor-beta (TGF-beta) and IL-10 in canine idiopathic lymphocytic-plasmacytic colitis (LPC). Semi-quantitative reverse transcriptase-polymerase chain reactions were performed using specific primers on RNA isolated from the colonic mucosa of healthy dogs, dogs with clinical signs of large intestinal disease but normal histopathology of the colon, and dogs with LPC. Canine LPC was associated with over-expression of IL-2 compared to healthy colonic mucosa (p<0.01) and the mucosa of dogs with large intestinal diarrhoea but normal histopathology (p<0.05). Higher levels of TNF-alpha mRNA were also seen in LPC compared to healthy mucosa (p<0.05). These results indicate that LPC is associated with activation of CD4+ T-helper lymphocytes and increased production of T-helper-1-type cytokines.

The role of cytokines in the pathogenesis of Cryptosporidium infection

First described in 1912, the importance of the coccidian parasite Cryptosporidium parvum as an enteropathogen in humans was not recognized until the early 1980s, when it was found to be a common opportunistic infection in AIDS. Infection with this organism triggers a complex array of innate and cell-mediated immune responses within the intestinal mucosa. How cytokines and chemokines interact to regulate these responses in order to achieve clearance of the parasite yet preserve the integrity of the intestinal mucosa is still being unravelled. T helper type 1 cytokines, and particularly interferon-gamma, have long been considered to be the main orchestrators of the immune response to this infection, but recent studies suggest that T helper type 2 cytokines may also be involved. In addition, transforming growth factor-beta 1, although having little effect on parasite development, is an important modulator of the immune response and plays a role in protecting the epithelial integrity from the effects of the inflammatory process.

Effect of L-NAME on nitric oxide and gastrointestinal motility alterations in cirrhotic rats

AIM

To investigate the effect of L-NAME on nitric oxide and gastrointestinal motility alterations in cirrhotic rats.

METHODS

Rats with cirrhosis induced by carbon tetrachloride were randomly divided into two groups, one n =13 receiving 0.5mg.kg(-1) per day of N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, for 10 days, whereas the other group (n =13) and control (n =10) rats were administrated the same volume of 9g.L(-1) saline. Half gastric emptying time and 2h residual rate were measured by SPECT, using (99m)Tc-DTPA-labeled barium sulfate as test meal. Gastrointestinal transition time was recorded simultaneously. Serum concentration of nitric oxide (NO) was determined by the kinetic cadmium reduction and colorimetric methods. Immunohistochemical SABC method was used to observe the expression and distribution of three types of nitric oxide synthase (NOS) isoforms in the rat gastrointestinal tract. Western blot was used to detect expression of gastrointestinal NOS isoforms.

RESULTS

Half gastric emptying time and trans-gastrointestinal time were significantly prolonged(124.0 +/- 26.4 min; 33.7 +/- 8.9 min; 72.1 +/- 15.3 min; P<0.01), (12.4 +/- 0.5h; 9.5 +/- 0.3h; 8.2 +/- 0.8h; P<0.01), 2h residual rate was raised in cirrhotic rats than in controls and cirrhotic rats treated with L-NAME (54.9 +/- 7.6%,13.7 +/- 3.2%, 34.9 +/- 10.3%, P<0.01). Serum concentration of NO was significantly increased in cirrhotic rats than in the other groups (8.20 +/- 2.48) micromol.L(-1), (5.94 +/-1.07) micromol.L(-1) and control (5.66 +/- 1.60 micromol.L(-1), P<0.01. NOS staining intensities which were mainly located in the gastrointestinal tissues were markedly lower in cirrhotic rats than in the controls and cirrhotic rats after treated with L-NAME.

CONCLUSION

Gastrointestinal motility was remarkably inhibited in cirrhotic rats, which could be alleviated by L-NAME. Nitric oxide may play an important role in the inhibition of gastrointestinal motility in cirrhotic rats.

Depletion of non specific esterase activity in the colonic mucosa of patients with ulcerative colitis

BACKGROUND

Non specific esterases (NSE) are a group of cellular carboxylesterases, enzyme markers of monocytes/macrophages, whose tissue distribution in the human body and changes in various disease states have not been adequately studied. We investigate the presence and localization of NSE, in the normal and inflamed human colonic mucosa.

DESIGN

NSE were studied histochemically and biochemically using alpha-naphthyl acetate as the substrate, in the colonic mucosa from 67 patients with colitis of various aetiologies and 10 normal controls. In addition, esterase activity was studied biochemically in serum from colitic patients and normal controls.

RESULTS

Histochemical study of the colonic tissue demonstrated that NSE were localised in the epithelial brush border, the goblet cells of the glands and a macrophage population of the lamina propria in the colonic mucosa of normal controls and patients with non specific colitis. In active ulcerative colitis, esterase depletion and esterase negative macrophages were identified in parallel with goblet cell disappearance. Gradual reappearance of esterase activity was found after successful treatment. Biochemical study of NSE activity showed that serum and colonic tissue esterase levels were greatly (P < 0.001) reduced in active ulcerative colitis compared to the normal controls or non specific colitis patients and they were increased after successful treatment. Despite this increase, the esterase activity in the colonic tissue from ulcerative colitis patients after treatment was significantly reduced compared to the normal controls. Interestingly, the enzyme levels from non-inflamed areas of the bowel of patients with ulcerative colitis were also significantly (P < 0.01) decreased compared to the normal controls.

CONCLUSIONS

These data suggest that esterase reduction in ulcerative colitis is not a simple result of the inflammatory process but rather it precedes its development. This enzyme depletion might have an important pathogenetic implication in the inflammatory process.

Expression of nitric oxide synthase 2 and tumor necrosis factor alpha in swine naturally infected with Actinobacillus pleuropneumoniae

Nitric oxide synthase 2 (NOS2) and tumor necrosis factor alpha (TNF-alpha) were detected and localized in 15 pigs with naturally occurring pleuropneumonia by use of in situ hybridization with a nonradioactive digoxigenin-labeled cDNA probe. Two cDNA probes 491 and 219 base pairs for NOS2 and TNF-alpha, respectively, were generated by reverse transcription polymerase chain reaction. All 15 pigs infected with Actinobacillus pleuropneumoniae had distinct positive hybridization signals for NOS2 and TNF-alpha. Strong hybridization signals for both NOS2 and TNF-alpha were evident in degenerate alveolar leukocytes bordering zones of coagulative necrosis and in alveolar spaces. NOS2 nucleic acids were detected in neutrophils and macrophages. In situ hybridization of serial sections of lung tissue revealed numerous cells positive for NOS2 and TNF-alpha, suggesting that NOS2 and TNF-alpha expression may play a role in the pathophysiology of pleuropneumonia.

Regulation of murine intestinal inflammation by reactive metabolites of oxygen and nitrogen: divergent roles of superoxide and nitric oxide

Several reports have implicated reactive oxygen and nitrogen metabolites (RONS) in the initiation and/or progression of inflammatory bowel diseases (IBDs). We have investigated the role of three key RONS-metabolizing enzymes (inducible nitric oxide synthase [iNOS], superoxide dismutase [SOD], nicotinamide adenine dinucleotide phosphate [NADPH] oxidase) in a murine model of IBD. Mice genetically deficient ((-/-)) in either iNOS or the p47phox subunit of NADPH oxidase, transgenic (Tg) mice that overexpress SOD, and their respective wild-type (WT) littermates were fed dextran sulfate sodium (DSS) in drinking water for 7 days to induce colitis. In addition, the specific iNOS inhibitor 1400W was used in DSS-treated WT and p47phox(-/-) mice. WT mice responded to DSS feeding with progressive weight loss, bloody stools, elevated serum NO(X) and colonic mucosal injury with neutrophil infiltration. Both the onset and severity of colitis were significantly attenuated in iNOS(-/-) and 1400W-treated WT mice. While the responses to DSS did not differ between WT and p47phox(-/-) mice, enhanced protection was noted in 1400W-treated p47phox(-/-) mice. Interestingly, SOD(Tg) mice exhibited more severe colitis than their WT littermates. These findings reveal divergent roles for superoxide and iNOS-derived NO in intestinal inflammation.

Reduced sensitivity of inducible nitric oxide synthase-deficient mice to chronic colitis

BACKGROUND

Overproduction of nitric oxide by the inducible form of nitric oxide synthase (iNOS) has been implicated in colitis. Different authors have postulated both toxic and protective effects of nitric oxide (NO) in the pathophysiology of active inflammation. The objective of this study was to examine the role of iNOS in experimental chronic colitis using iNOS-deficient mice.

METHODS

For induction of colitis, mice received three cycles of 2% of dextran sodium sulfate (DSS) (M.W. 40,000) treatment in drinking water. The degree of colonic inflammation, leukocyte infiltration, and the expression of cell adhesion molecules were determined. INOS expression and nitrotyrosine were also determined by immunohistochemistry.

RESULTS

After DSS treatment, a moderate colitis with marked cell infiltration was observed. Intense expression of iNOS was observed on infiltrating cells as well as on the colonic mucosal epithelium in these animals. In the iNOS-deficient mice, tissue damage was significantly diminished. No iNOS or nitrotyrosine staining was found in iNOS-deficient mice. The number of infiltrating cells and the expression of mucosal adressin cell adhesion molecule-1 were significantly attenuated in the DSS-treated colon of iNOS-deficient mice.

CONCLUSION

Induction of iNOS seems to act as a critical toxic effector molecule in the pathogenesis of chronic colonic inflammation.

Evidence of an Inflammatory Pathologic Condition in “Normal” Appendices Following Emergency Appendectomy

Background.—Appendices removed from patients with suspected appendicitis often appear normal on histologic examination.

Objective.—To study appendix specimens for the expression of inflammatory markers as an indicator of presence of an inflammatory response in this subgroup of patients.

Methods.—Cyclooxygenase 1 and 2, prostaglandin E2, inducible nitric oxide synthase, and major histocompatibility complex class II were investigated by immunofluorohistochemistry using confocal laser microscopy in 15 acutely inflamed appendix specimens, 39 histologically classified “normal” appendices, and 11 negative control specimens.

Results.—Strong expressions of all the inflammatory mediators were found in the mucosa of inflamed appendices, in approximately 50% of histologically normal appendices from patients with a clinical diagnosis of appendicitis, and in none of the normal control specimens.

Conclusion.—This study confirms the existence of a subgroup of appendicitis within the so-called histologically normal appendices in which evidence of an inflammatory pathologic condition is only obvious at a molecular level. The initiating signal for this and all other forms of clinical appendicitis still remains elusive.

Expression of inducible and endothelial nitric oxide synthases in pouchitis

To study the induction of nitric oxide synthase (NOS) in different forms of pouchitis, we divided patients in five groups: 1) ulcerative colitis, no pouch; 2) no-pouchitis; 3) chronic asymptomatic pouchitis; 4) chronic active pouchitis; and 5) acute pouchitis. Ileal biopsies were scored for NOS-2 (inducible) and NOS-3 (endothelial) immunoreactivity and acute inflammation. In group 1, most specimens lacked NOS-2 immunoreactivity. In group 2, some specimens showed NOS-2 immunoreactive epithelium. In group 3, areas of NOS-2-immunoreactive epithelium were consistently observed in most specimens. In groups 4 and 5, most specimens showed moderate-to-extensive epithelial NOS-2 staining. NOS-2 immunoreactivity scores of groups 1-5 were 0.25 +/- 0.16, 0.67 +/- 0.19, 1.19 +/- 0.40, 2.0 +/- 0.23, and 2.18 +/- 0.12, respectively. Corresponding acute inflammation scores were 0, 0.53 + 0.17, 1.00 +/- 0.33, 1.80 +/- 0.20, and 1.64 +/- 0.15. NOS-2 score correlated with acute inflammation score (p < 0.0001), indicating that NOS-2 induction correlates with both the clinical degree of pouchitis and the severity of acute inflammation. NOS-3 immunoreactivity increased in all pouchitis groups.

Upregulation of Reg 1alpha and GW112 in the epithelium of inflamed colonic mucosa

BACKGROUND AND AIMS

Colonic epithelium is involved in the regulation of intestinal function and mucosal immune responses, and its function is altered in inflammatory bowel disease (IBD). However, a comprehensive analysis of the genetic alterations in inflamed colonic epithelium is not available at present. The aim of our study was to detect genes that are preferentially expressed in inflamed colonic epithelia and clarify the biochemical responses of epithelial cells in inflamed colonic mucosa.

METHODS

cDNA representation difference analysis was used to identify candidate genes selectively expressed in inflamed colonic epithelia. Selective expression of these genes in the epithelium of inflamed colonic mucosa, including IBD and non-IBD tissues, was examined by real time polymerase chain reaction and in situ hybridisation. The effect of cell confluence and inflammatory mediators on Reg 1alpha gene expression was examined using a colon cancer cell line (HT29).

RESULTS

We identified seven candidate genes that were presumed to be upregulated in the inflamed colonic epithelium. Of these, Reg 1alpha and GW112 were the dominant species and expression of these genes was confined to the crypt epithelium. In vitro studies using a colonic epithelial cell line suggested that cell confluence regulates Reg 1alpha gene expression.

CONCLUSIONS

Selective expression of Reg 1alpha and GW112 genes in the crypt epithelium of inflamed colonic mucosa suggests the important regulatory functions of these genes.

The physiological expression of inducible nitric oxide synthase (iNOS) in the human colon

BACKGROUND

Inducible nitric oxide synthase (iNOS) is expressed in the colonic epithelium in both inflammatory bowel disease and colorectal cancer. Nitric oxide (NO), the product of this enzyme, has been implicated in the pathogenesis of both conditions. However, there are conflicting data on whether iNOS is expressed in the normal, uninflamed human colon.

AIMS

To evaluate the expression of iNOS in histologically normal, non-inflamed human colonic mucosa.

PATIENTS/METHODS

Reverse transcription polymerase chain reaction (RT-PCR), immunoblotting, and immunohistochemistry were used to investigate the expression of iNOS in 17 histologically normal specimens obtained at colectomy performed for colorectal neoplasia. In addition, 16 endoscopic mucosal biopsies, taken from normal individuals, were also evaluated. Eleven surgical specimens and 16 endoscopic biopsies from patients with refractory ulcerative colitis were used as inflammatory controls.

RESULTS

All types of specimens expressed iNOS mRNA. Immunoblotting revealed a protein of approximately 130 kDa consistent with iNOS in mucosal extracts of 77% of normal individuals, and 85% of diseased controls. Immunolabelling localised this protein to the surface epithelium in most of the normal specimens and also to the crypt epithelium and inflammatory cells in the diseased controls.

CONCLUSIONS

These findings provide evidence that iNOS is often expressed in the surface epithelium of non-inflamed human colon, suggesting that it is induced by local luminal factors, such as bacterial lipopolysaccharide (endotoxin). The resultant NO produced at this site might act as an oxidative barrier, reducing bacterial translocation and providing a means of defence against pathogenic microorganisms.

Recent advances in inflammatory bowel disease

The last decade has seen tremendous advances in our knowledge, which has led to genuine improvements in our understanding of the pathogenesis and management of inflammatory bowel disease (IBD). The combined power of cellular and molecular biology has begun to unveil the enigmas of IBD, and, consequently, substantial gains have been made in the treatment of IBD. Refinements in drug formulation have provided the ability to target distinct sites of delivery, while enhancing the safety and efficacy of older agents. Simultaneous progress in biotechnology has fostered the development of new agents that strategically target pivotal processes in disease pathogenesis. This article addresses our current understanding of the pathogenesis of IBD, including the latest developments in animal models and covers agents currently used in the treatment of IBD as well as emerging therapies.

In situ generation of nitric oxide by myenteric neurons but not by mononuclear cells of the human colon

1. Production of nitric oxide (NO) is implicated in the pathogenesis of inflammatory bowel disease. However, the cells responsible for the production of NO in situ in the human colon remain unknown. 2. Surgical samples from 12 patients with ulcerative colitis, eight patients with Crohn's disease and 10 controls were studied. Possible generation of NO was visualized by reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activity in human colon. Immunohistological staining for various NO synthase (NOS) isoforms (endothelial, neuronal and inducible), nitrotyrosine and interleukin-2 was also performed. 3. Reduced NADPH diaphorase activity was not found in lamina propria mononuclear cells, but was found in colonic epithelium, endothelium and myenteric neurons and their processes. 4. The NADPH-diaphorase activity positive processes were significantly less common in colon from patients with Crohn's disease compared with control colon. 5. Endothelial NOS was constitutively expressed on colonic endothelium. 6. Neuronal NOS was constitutively expressed on myenteric neurons. 7. Expression of inducible NOS (iNOS) was increased in the epithelium and endothelium of the colon of patients with ulcerative colitis. 8. No correlation was found between expression of iNOS and NADPH diaphorase activity. 9. Nitrotyrosine was expressed by lamina propria leucocytes, but not by epithelium. 10. Interleukin-2 was expressed on both leucocytes and myenteric neurons. 11. Colonic epithelium, endothelium and myenteric neurons synthesize NO. Myenteric neurons were principally responsible for NO production and NO may act as a neurotransmitter in the enteric nervous system.

Regulated production of interferon-inducible T-cell chemoattractants by human intestinal epithelial cells

BACKGROUND & AIMS

Human intestinal epithelial cells inducibly express neutrophil and monocyte chemoattractants, yet little is known about the regulated production of T-cell chemoattractants by the intestinal epithelium. IP-10, Mig, and I-TAC are 3 CXC chemokines that are known to act as CD4(+) T-cell chemoattractants.

METHODS

We studied constitutive chemokine expression in human colon, and defined the regulated expression of these chemokines by reverse-transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and immunohistology using cultured human intestinal epithelial cell lines and a novel adaptation of an in vivo human intestinal xenograft model.

RESULTS

IP-10 and Mig were constitutively expressed by normal human colon epithelium, and their cognate receptor, CXCR3, was expressed by mucosal mononuclear cells. Interferon (IFN)-gamma stimulation increased mRNA expression and the polarized basolateral secretion of these chemokines by human colon epithelial cell lines; infection with enteroinvasive bacteria, or stimulation with the proinflammatory cytokines tumor necrosis factor alpha and interleukin 1alpha, strongly potentiated IFN-gamma-induced epithelial cell IP-10, Mig, and I-TAC production. Epithelial cell mRNA and protein expression of IP-10, Mig, and I-TAC were rapidly up-regulated in human intestinal xenografts in response to stimulation with IFN-gamma alone or in combination with IL-1.

CONCLUSIONS

The constitutive and regulated production of the IFN-gamma-inducible chemokines IP-10, Mig, and I-TAC by human intestinal epithelium, and the expression of their cognate receptor, CXCR3, by mucosal mononuclear cells, suggest that the intestinal epithelium can play a role in modulating physiologic and pathologic T cell-mediated mucosal inflammation.

Interferon gamma induces enterocyte resistance against infection by the intracellular pathogen Cryptosporidium parvum

BACKGROUND & AIMS

Interferon (IFN)-gamma plays an important role in the immunologic control of infection by the protozoan enteropathogen Cryptosporidium parvum. We tested the hypothesis that IFN-gamma may directly inhibit infection of enterocytes by this pathogen.

METHODS

HT-29, Caco-2, and H4 human enterocyte cell lines were grown in monolayers and incubated with IFN-gamma before exposure with C. parvum. IFN-gamma receptor expression in the cell lines was determined by Western blot analysis.

RESULTS

IFN-gamma inhibited C. parvum infection of both HT-29 and Caco-2 cells but not H4 cells. Response to IFN-gamma was related to the expression of the IFN-gamma receptor in the respective cell lines. The effect of IFN-gamma was partially reversed by inhibition of the JAK/STAT signaling pathway. IFN-gamma mediated its action by at least 2 mechanisms: (1) inhibition of parasite invasion and (2) by modification of intracellular Fe(2+) concentration. No role for tryptophan starvation or nitric oxide synthase activity was found. TNF-alpha and IL-1beta also had anti-C. parvum activity but had no synergistic effect with IFN-gamma.

CONCLUSIONS

IFN-gamma directly induces enterocyte resistance against C. parvum infection; this observation may have important consequences for our understanding of the mucosal immune response to invasive pathogens.

Colonic expression and synthesis of interleukin 13 and interleukin 15 in inflammatory bowel disease

A dysregulated local immune reaction with unbalanced cytokine expression seems essential in inflammatory bowel disease (IBD), i.e. ulcerative colitis (UC) and Crohn's disease (CD). Since the roles of interleukin (IL-)13 and IL-15 remain unclear, this study aimed at studying intestinal expression of IL-13 and IL-15 in IBD.

METHODS

In colonic biopsies from 24 UC, 18 CD, and 12 controls IL-13 and IL-15 were measured using ELISA, and their gene expressions were assessed by RT-PCR. Leukocytes were visualised histochemically.

RESULTS

Concentrations of IL-13 were decreased in UC (median 56 pg/mg tissue; interquartile range 30-99 pg/mg) compared to CD (82 pg/mg tissue; 41-122;P=0.004) and controls (83 pg/mg tissue; 18-134;P>0.05), and lower in active UC (53 pg/mg tissue; 33-96) than in inactive UC (80 pg/mg tissue; 65-99;P=0.02). IL-15 concentrations were higher in CD patients (34 pg/mg tissue; 24-53) as compared to controls (20 pg/mg tissue; 15-21;P=0.001) whilst being 22 pg/mg tissue (15-32) in UC. IL-13 mRNA and IL-15 mRNA were detected in 20% and 15%, respectively. Infiltration of leukocytes correlated inversely with IL-13 levels (P=0.02).

CONCLUSION

Active UC is associated with decreased colonic IL-13 suggesting that IL-13 levels are diminished as a part of UC exacerbations, or that exacerbations follow active downregulation of IL-13.

Spontaneously developing chronic colitis in IL-10/iNOS double-deficient mice

Mice deficient in both inducible nitric oxide synthase (iNOS) and interleukin (IL)-10 (iNOS(-/-)/IL-10(-/-)) were created to examine the role of iNOS in spontaneously developing intestinal inflammation. IL-10(-/-)/iNOS(-/-) mice were compared with IL-10(-/-) (iNOS(+/+)) littermates over 6 mo. RT-PCR, Western blot analysis, and immunohistochemistry were performed to measure iNOS message and protein levels. Plasma nitrate/nitrite (NO(x)) levels were assessed by HPLC. Damage scores (macroscopic and microscopic) and granulocyte infiltration were assessed. At 3-4 wk, IL-10(-/-) and IL-10(-/-)/iNOS(-/-) mice had no signs of colonic inflammation or granulocyte infiltration. Plasma NO(x) levels were not different from controls. By 3-4 mo, IL-10(-/-) mice had increased damage scores and granulocyte infiltration concurrent with increased mRNA and protein synthesis (restricted to the epithelium) for iNOS in intestinal tissues but not other tissues. Plasma NO(x) levels increased fivefold. Interestingly, in the absence of iNOS induction or increased plasma NO(x), iNOS(-/-)/IL-10(-/-) mice had damage and granulocyte infiltration equivalent to those observed in IL-10(-/-) littermates. These data suggest that iNOS does not impact on the development or severity of spontaneous chronic inflammation in IL-10-deficient mice.

Role of nitric oxide in wound healing

Nitric oxide is a short-lived free radical, that is capable of multiple effects at the molecular, cellular, and physiologic levels. Over the past several years, nitric oxide has been proved to play an important role in the healing of various types of wounds. The present review examines some of the recently defined roles of nitric oxide in normal and pathologic healing.

Tonometric assessment of jejunal mucosal nitric oxide formation in anaesthetized pigs

Nitric oxide (NO) in the gut has attracted increasing interest as a regulatory factor for a wide variety of intestinal functions. This study was performed to evaluate some methodological aspects and jejunal sources for NO synthesis. Bench side evaluations and an animal model using chloralose-anaesthetized pigs were used. Immunohistochemistry was performed on samples from pig intestine and direct measurements of intestinal NO formation were performed using intraluminal tonometry. Tonometric measurements were quantitatively accurate and with high reproducibility. A substantial NO formation was assessed which was markedly inhibited by luminal administration of the non-selective NOS inhibitor L-NAME. Intravenous administration of L-NAME also reduced jejunal NO formation but to a lesser extent. Immunohistochemistry revealed staining for the inducible type of NOS in the mucosal surface epithelium whereas endothelial and neuronal subtypes were located in deeper layers of the jejunal wall. The study argues for that the source of jejunal NO production, as measured by intraluminal tonometry, is located in close proximity with the intestinal mucosa. The NOS in this compartment is predominantly of the inducible type.

The I kappa B/NF-kappa B system: a key determinant of mucosalinflammation and protection

The ubiquitous transcription factor NF-kappa B is a central regulator of the transcriptional activation of a number of genes involved in cell adhesion, immune and proinflammatory responses, apoptosis, differentiation, and growth. Induction of these genes in intestinal epithelial cells (IECs) by activated NF-kappa B profoundly influences mucosal inflammation and repair. NF-kappa B activation requires the removal of I kappa B from NF-kappa B by inducible proteolysis, which liberates this transcription factor for migration to the nucleus, where it binds to kappa B-regulatory elements and induces transcription. I kappa B alpha degradation is incomplete and delayed in IECs, resulting in buffered responses to luminal stimuli. The stimulatory environment partially determines whether the effect of NF-kappa B is protective or deleterious for the host. kappa B-dependent proinflammatory gene expression, particularly chemokines, major histocompatibility complex class II antigens, and adhesion molecules may be extremely important in early protective responses to mucosal pathogens but, when dysregulated, could lead to the development of chronic inflammation, as seen in inflammatory bowel diseases. The key role of NF-kappa B in regulating expression of a number of proinflammatory genes makes this protein an attractive target for selective therapeutic intervention.

Implications of inducible nitric oxide synthase expression and enzyme activity

We summarize here our current knowledge about inducible nitric oxide synthase (NOS) activity in human diseases and disorders. As basic research discovers more and more effects of low or high concentrations of NO toward molecular and cellular targets, successful therapies involving inhibition of NO synthesis or application of NO to treat human diseases are still lacking. This is in part due to the fact that the impact of NO on cell function or death are complex and often even appear to be contradictory. NO may be cytotoxic but may also protect cells from a toxic insult; it is apoptosis-inducing but also exhibits prominent anti-apoptotic activity. NO is an antioxidant but may also compromise the cellular redox state via oxidation of thiols like glutathione. NO may activate specific signal transduction pathways but is also reported to inhibit exactly these, and NO may activate or inhibit gene transcription. The situation may even be more complicated, because NO, depending on its concentration, may react with oxygen or the superoxide anion radical to yield reactive species with a much broader chemical reaction spectrum than NO itself. Thus, the action of NO during inflammatory reactions has to be considered in the context of timing and duration of its synthesis as well as stages and specific events in inflammation.

Role of inducible nitric oxide synthase in trinitrobenzene sulphonic acid induced colitis in mice

BACKGROUND

Studies using inhibitors of nitric oxide synthase (NOS) to date are inconclusive regarding the role of inducible NOS (iNOS) in intestinal inflammation.

AIMS

(1) To examine the role of iNOS in the development of chronic intestinal inflammation; (2) to identify the cellular source(s) of iNOS.

METHODS

Colitis was induced by an intrarectal instillation of trinitrobenzene sulphonic acid (TNBS, 60 mg/ml, 30% ethanol), in wild type (control) or iNOS deficient mice. Mice were studied over 14 days; the colons were scored for injury and granulocyte infiltration was quantified. Blood to lumen leakage of (51)Cr-EDTA was measured as a quantitative index of mucosal damage.

RESULTS

At 24 and 72 hours, iNOS deficient mice had significantly increased macroscopic inflammation compared with wild type mice. Granulocyte infiltration increased significantly at 24 hours and remained elevated in iNOS deficient mice at 72 hours, but significantly decreased in controls. However, by seven days post-TNBS macroscopic damage, microscopic histology, granulocyte infiltration, and mucosal permeability did not differ between wild type and iNOS deficient mice. A four- to fivefold increase in iNOS mRNA was observed in wild type mice at 72 hours and seven days post-TNBS and was absent in iNOS deficient mice. Immunohistochemistry techniques showed that iNOS expression was predominantly localised in neutrophils, with some staining also in macrophages.

CONCLUSIONS

These results suggest that leucocyte derived iNOS ameliorates the early phase, but does not impact on the chronic phase of TNBS induced colitis despite the presence of iNOS.

Expression and function of inducible nitric oxide synthase during rat colon anastomotic healing

Nitric oxide plays a significant but incompletely understood role in fibroblast function and cutaneous wound collagen synthesis; however, the participation of inducible nitric oxide synthase (iNOS) in gastrointestinal anastomotic healing has not been studied. Male Sprague-Dawley rats underwent single-layer left colonic anastomosis. Animals were killed at 24-hour intervals postoperatively and the anastomosis was excised. Parallel uninjured colon tissue samples were also analyzed. Reverse transcriptase-polymerase chain reaction confirmed the absence of iNOS messenger RNA in control colon and expression of the gene in anastomotic tissue on all study days. Northern hybridization demonstrated maximal iNOS messenger RNA transcription on day 1 with decreased levels on days 3 and 5. iNOS enzyme activity, measured biochemically by the conversion of [(3) H-arginine to [(3) H]-citrulline ex vivo, was also maximal on day 1 (7.35 +/- 1.34 pmol/mg protein/min [+/- standard error of the mean], n = 10) and decreased on days 3 (4.37 +/- 2.32 pmol/mg protein/min; n = 6) and 5 (2.80 +/- 0.92 pmol/mg protein/min; n = 6). Immunohistochemical staining demonstrated that (1) iNOS expression is confined to a discrete cell population in the region of the anastomosis containing inflammatory cells; (2) those cells assume a highly conserved position on the luminal edge of the proliferating scar; and (3) the iNOS-expressing cells are present throughout the fibroplastic phase of healing. To functionally assess the role of iNOS in colonic healing, rats were treated with a continuous intravenous infusion of S-methylisothiourea (a selective inhibitor of iNOS) at a dosage of 200 mg/kg/day for 5 days after anastomosis. There was a significantly reduced anastomotic bursting pressure in rats treated with the inhibitor as compared to rats treated with intravenous normal saline solution (108.4 +/- 13.2 mm Hg vs. 148.4 +/- 10.3 mm Hg; P <0.05). These results suggest that iNOS gene expression is induced during colonic anastomotic healing, that it is present through all phases of healing but is maximal through the inflammatory phase, and that iNOS activity is required for optimal anastomotic healing.

Nitric oxide synthesis in patients with infective gastroenteritis

BACKGROUND

There is evidence that endogenous nitrate synthesis is notably increased in patients with infective gastroenteritis.

AIMS

To determine whether this is due to nitric oxide (NO) production via the L-arginine/NO pathway.

METHODS

Seven male patients with community acquired bacterial gastroenteritis and 15 healthy male volunteers participated in this study. All patients had stool culture positive infective gastroenteritis. A bolus of 200 mg L-[(15)N](2)-arginine was administered intravenously after an overnight fast. Urine was collected for the next 36 hours. Urinary [(15)N:(14)N]nitrate ratio was assessed by dry combustion in an isotope ratio mass spectrometer.

RESULTS

Mean 36 hour total urinary nitrate excretion in the gastroenteritis group was 5157 (577) micromol compared with 2594 (234) micromol in the control group (p<0.001). Thirty six hour urinary [(15)N]nitrate excretion was considerably higher in the gastroenteritis group compared with the control group (13782 (1665) versus 1698 (98) etamol; p<0.001). These values represent 1.129 (0.139)% and 0.138 (0.007)% of [(15)N]nitrogen administered (p<0.001), respectively. Corrected 36 hour urinary [(15)N]nitrate excretion for urinary creatinine was also significantly higher in the patient compared with the control group (1934 (221) versus 303 (35) etamol/mmol; p<0.001).

CONCLUSION

Results show notably enhanced nitrate synthesis due to increased activity of the L-arginine/NO pathway in patients with infective gastroenteritis.

Potentiation of cytokine induced iNOS expression in the human intestinal epithelial cell line, DLD-1, by cyclic AMP

BACKGROUND

Nitric oxide production by the inducible isoform of nitric oxide synthase (iNOS) is thought to play a role in the pathogenesis of inflammatory bowel disease along with other proinflammatory mediators.

AIMS

To examine the effects of cAMP, an intracellular mediator of several proinflammatory mediators, on iNOS expression in the human intestinal epithelial cell line, DLD-1.

METHODS

iNOS activity was assessed by measuring the NO stable oxidative product NO(2)(-). iNOS protein expression and iNOS mRNA levels were determined by western blotting and northern blotting, respectively.

RESULTS

iNOS activity, protein, and mRNA were induced by a combination of interleukin 1beta (0.5-5 ng/ml), interferon gamma (20-200 u/ml), and tumour necrosis factor alpha (10-100 ng/ml). The cytokine induced NOS activity was potentiated by N(6), 2'-O-dibutyryladenosine 3':5'-cyclic monophosphate and 8-bromoadenosine 3':5'-cyclic monophosphate (0.1-1 mM), and the adenylate cyclase activator, forskolin (1-100 microM). This activity was inhibited by the selective iNOS inhibitor, 1400W (0.1-100 microM). These agents increased iNOS protein. The cAMP analogues potentiated iNOS at the transcriptional level as shown by effects of actinomycin D (5 microgram/ml) and northern blot analyses; the nuclear factor (NF) kappaB inhibitor, pyrrolidine dithiocarbamate (10-200 microM), significantly reduced this potentiation. The cAMP potentiated iNOS activity was inhibited by the tyrosine kinase inhibitor, A25 (10-200 microM) and the Janus activated kinase 2 inhibitor, B42 (10-200 microM).

CONCLUSIONS

Increased intracellular cAMP is a potent stimulus of iNOS expression in combination with cytokines in DLD-1 cells, acting at the transcriptional level and involving NF-kappaB and the JAK-STAT pathways. Thus, proinflammatory mediators that increase cAMP levels may augment iNOS expression and NO production.

Reduced oxidative and nitrosative damage in murine experimental colitis in the absence of inducible nitric oxide synthase

BACKGROUND

Oxidative and nitrosative stress have been implicated in the pathogenesis of inflammatory bowel diseases.

AIMS

To study the role of nitric oxide (NO) derived from inducible NO synthase (iNOS) in an experimental model of murine enterocolitis.

METHODS

Trinitrobenzene sulphonic acid (TNBS) was instilled per rectum to induce a lethal colitis in iNOS deficient mice and in wild type controls. The distal colon was evaluated for histological evidence of inflammation, iNOS expression and activity, tyrosine nitration and malondialdehyde formation (as indexes of nitrosative and oxidative stress), myeloperoxidase activity (as index of neutrophil infiltration), and tissue localisation of intercellular adhesion molecule 1 (ICAM-1).

RESULTS

TNBS administration induced a high mortality and weight loss associated with a severe colonic mucosal erosion and ulceration, increased myeloperoxidase activity, increased concentrations of malondialdehyde, and an intense staining for nitrotyrosine and ICAM-1 in wild type mice. Genetic ablation of iNOS gene conferred to mice a significant resistance to TNBS induced lethality and colonic damage, and notably reduced nitrotyrosine formation and concentrations of malondialdehyde; it did not, however, affect neutrophil infiltration and intestinal ICAM-1 expression in the injured tissue.

CONCLUSION

Data show that activation of iNOS is required for nitrosative and oxidative damage in experimental colitis.

Cytokine-induced apoptosis in epithelial HT-29 cells is independent of nitric oxide formation. Evidence for an interleukin-13-driven phosphatidylinositol 3-kinase-dependent survival mechanism

A combination of the pro-inflammatory cytokines interleukin (IL)-1alpha, interferon (IFN)-gamma, and tumor necrosis factor (TNF)-alpha induces nitric oxide synthase mRNA expression and nitric oxide (NO) generation in the human colon carcinoma cell line HT-29. This can be inhibited by pretreatment with IL-13 via a phosphatidylinositol (PI) 3-kinase-dependent mechanism (Wright, K., Ward, S. G., Kolios, G., and Westwick, J. (1997) J. Biol. Chem. 272, 12626-12633). Since NO has been implicated in regulating mechanisms leading to cell death, while activation of PI 3-kinase-dependent signaling cascades are thought to be involved with promoting cell survival events, we have investigated the outcome of these cytokine treatments on apoptosis and cell survival of HT-29 cells. Initiation of apoptosis can be achieved by the combinations of IFN-gamma/TNF-alpha, IFN-gamma/CD95, IL-1alpha/IFN-gamma, and IL-1alpha/IFN-gamma/TNF-alpha to varying extents. Induction of apoptotic markers by HT-29 cells in response to cytokine treatment is not dependent on NO production. Pretreatment with IL-13 protects against IL-1alpha/IFN-gamma/TNF-alpha- and IFN-gamma/TNF-alpha- as well as IFN-gamma/CD95-induced (but not IL-1alpha/IFN-gamma-induced) cell death. In addition, IFN-gamma/TNF-alpha and IL-1alpha/IFN-gamma/TNF-alpha stimulate activation of caspase-8 and caspase-3, which IL-13 pretreatment was able to partially inhibit and delay. IL-13 also stimulates activation of the major PI 3-kinase effector, protein kinase B. The PI 3-kinase inhibitors wortmannin and LY294002 inhibit IL-13 stimulation of protein kinase B as well as the cell survival effects of IL-13. These data demonstrate that cytokine-induced apoptosis of HT-29 cells is NO-independent and that the activation of a PI 3-kinase-dependent signaling cascade by IL-13 is a key signal responsible for the inhibition of apoptosis.

Differential regulation of inducible nitric oxide synthase gene expression by ethanol in the human intestinal epithelial cell line DLD-1

We have examined the regulation of inducible nitric oxide synthase (iNOS) gene expression by ethanol in monolayers of DLD-1 cells, an epithelial cell line derived from human intestinal adenocarcinoma. Optimum induction of iNOS mRNA in these cells was obtained with IFN-gamma and IL-1beta treatment, while further addition of TNF-alpha did not have significant effect. In a set of experiments to study ethanol effects, DLD-1 monolayers were pretreated with ethanol for 24 h and were then treated with IFN-gamma + IL-1beta for an additional 24 h. Cells pretreated with ethanol showed decreased iNOS mRNA levels, indicating that ethanol may inhibit cytokine-induced iNOS transcription or affect mRNA destabilization. The suppression was ethanol-dose dependent with an IC50 of 50 mM. In another set of experiments to study ethanol effects, DLD-1 monolayers were pretreated with 66 mM ethanol for 24 h. These cells showed significant upregulation of IL-1beta mRNA and protein as detected in the supernatants. Aliquoted supernatants from these cells (i.e., conditioned media) were added to naive DLD-1 monolayers together with IFN-gamma. Conditioned medium from ethanol-treated cells increased the IFN-gamma-induced iNOS mRNA of naive cells by threefold. Two different effects of ethanol are now reported: (a) ethanol inhibits IFN-gamma + IL-1beta-induced iNOS mRNA of the same DLD-1 cells and (b) ethanol induces cellular paracrine signals by releasing IL-1beta into the medium, which in combination with IFN-gamma increases iNOS mRNA levels of the recipient naive DLD-1 cells. Because IFN-gamma and IL-1beta are produced by intestinal immune cells, these findings may have implications for differential in vivo regulation of epithelial iNOS genes by ethanol, depending on the inflammatory and immune status of the host.

C-X-C and C-C chemokine expression and secretion by the human colonic epithelial cell line, HT-29: differential effect of T lymphocyte-derived cytokines

Differential chemokine production by colonic epithelial cells is thought to contribute to the characteristic increased infiltration of selected population of leukocytes cells in inflammatory bowel disease. We have previously demonstrated that IL-13 enhances IL-1alpha-induced IL-8 secretion by the colonic epithelial cell line HT-29. We have now explored the C-C chemokine expression and modulation in this system. The combination of TNF-alpha and IFN-gamma was the minimal stimulation required for regulated on activation, normal T cell expressed and secreted (RANTES) and monocyte chemoattractant protein (MCP-1) mRNA expression and secretion by HT-29 cells. The same stimulation induced a stronger IL-8 mRNA expression and secretion. Pretreatment with IL-13 or IL-4, reduced significantly the RANTES, and MCP-1, but not IL-8 mRNA expression and secretion. In contrast, IL-10 had no effect on either MCP-1, or RANTES, or IL-8 generation. Pretreatment of HT-29 cells with wortmannin suggested that the IL-13-induced inhibition of C-C chemokine expression is via activation of a wortmannin-sensitive phosphatidylinositol 3-kinase. These data demonstrate that colonic epithelial cell chemokine production can be differentially regulated by T cell-derived cytokines and suggest an interplay between epithelial cells and T lymphocytes potentially important in the intestinal inflammation.