Increased nitric oxide production in collagenous and lymphocytic colitis

Pathogenesis of Microscopic Colitis: A Systematic Review

BACKGROUND

Whereas the exact aetiology of microscopic colitis [MC] remains unknown, a dysregulated immune response to luminal factors or medications is the most accepted pathogenesis hypothesis.

METHODS

We conducted a systematic review of the pathogenesis of MC. We applied the Joanna Briggs Institute methodologies and the PRISMA statement for the reporting of systematic reviews [PROSPERO Trial Identifier: CRD42020145008]. Populations, Exposure of interest, and Outcome [PEO] questions were used to explore the following topics in MC: 1] intestinal luminal factors; 2] autoimmunity; 3] innate immunity; 4] adaptive immunity; 5] extracellular matrix; 6] genetic risk factors; and 7] mechanism of diarrhoea. A search was done in PubMed, Embase, and Web of Science up to February 2020. A narrative description was performed explaining the findings for each aspect of MC aetiopathogenesis.

RESULTS

Thirty-eight documents provided evidence for PEO1, 100 for PEO2, 72 for PEO3 and 4, 38 for PEO5, 20 for PEO6, and 23 for PEO7. The majority of documents were cohorts, case reports, and case series, with a few case-control and some experimental studies. Consistency among data provided by different studies was considered to support pathogenetic hypotheses. MC is a multifactorial disease believed to involve innate and adaptive immune responses to luminal factors, genetic risk, autoimmunity, and extracellular matrix alterations, all contributing by varied mechanisms to watery diarrhoea.

CONCLUSIONS

This is the first systematic review on the aetiology of MC supporting the notion that MC is a multifactorial disease. However, high-profile studies are lacking, and most evidence derives from small heterogeneous studies.

Diagnosis and Management of Microscopic Colitis

Microscopic colitis (MC) is a relatively common cause of chronic watery diarrhea, especially in older persons. Associated symptoms, including abdominal pain and arthralgias, are common. The diagnosis is based upon characteristic histological findings in the presence of diarrhea. The two types of MC, collagenous and lymphocytic colitis, share similar clinical features, with the main difference being the presence or absence of a thickened subepithelial collagen band. There are several treatment options for patients with MC, although only budesonide has been well studied in multiple controlled clinical trials. This review will describe the clinical features, epidemiology, pathophysiology, diagnostic criteria, and treatment of patients with MC.

Microscopic Colitis: What Do We Know About Pathogenesis?

Microscopic colitis (MC) is a common cause of chronic diarrhea. The 2 most frequent forms of MC are collagenous colitis and lymphocytic colitis. Over the past years, the incidence and prevalence of microscopic colitis are rising and this is largely attributed to a greater awareness, and concomitantly an increasing number of diagnoses. Patients with microscopic colitis report watery, nonbloody diarrhea of chronic course, abdominal pain, weight loss, and fatigue that may impair patient's health-related quality of life. The underlying mechanisms involved in the pathogenesis of microscopic colitis remain unspecified but is probably multifactorial. Collagenous colitis and lymphocytic colitis may represent specific mucosal responses to different luminal agents in predisposed individuals, resulting in an uncontrolled immune response. Genetic predisposition, altered modulation of cytokines and miRNAs, and aberrant response to drugs seem to be involved in the development of MC. Despite the progress of knowledge, still many questions remain unsolved regarding the etiology, pathophysiology, and optimal management of MC. This review gives an update on the immunological aspects of collagenous colitis and lymphocytic colitis.

Diagnosis and management of microscopic colitis: current perspectives

Collagenous colitis and lymphocytic colitis, together constituting microscopic colitis, are common causes of chronic diarrhea. They are characterized clinically by chronic nonbloody diarrhea and a macroscopically normal colonic mucosa where characteristic histopathological findings are seen. Previously considered rare, they now have emerged as common disorders that need to be considered in the investigation of the patient with chronic diarrhea. The annual incidence of each disorder is five to ten per 100,000 inhabitants, with a peak incidence in 60- to 70-year-old individuals and a predominance of female patients in collagenous colitis. The etiology and pathophysiology are not well understood, and the current view suggests an uncontrolled mucosal immune reaction to various luminal agents in predisposed individuals. Clinical symptoms comprise chronic diarrhea, abdominal pain, fatigue, weight loss, and fecal incontinence that may impair the patient's health-related quality of life. An association is reported with other autoimmune disorders, such as celiac disease, thyroid disorders, diabetes mellitus, and arthritis. The best-documented treatment, both short-term and long-term, is budesonide, which induces clinical remission in up to 80% of patients after 8 weeks' treatment. However, after successful budesonide therapy is ended, recurrence of clinical symptoms is common, and the best possible long-term management deserves further study. The long-term prognosis is good, and the risk of complications, including colonic cancer, is low. We present an update of the epidemiology, pathogenesis, diagnosis, and management of microscopic colitis.

Microscopic colitis patients demonstrate a mixed Th17/Tc17 and Th1/Tc1 mucosal cytokine profile

BACKGROUND

Microscopic colitis (MC) is a chronic inflammatory bowel disorder of unknown aetiology comprising collagenous colitis (CC) and lymphocytic colitis (LC). Data on the local cytokine profile in MC is limited. This study investigated the T helper (Th) cell and cytotoxic T lymphocyte (CTL) mucosal cytokine profile at messenger and protein levels in MC patients.

METHODS

Mucosal biopsies from CC (n=10), LC (n=5), and CC or LC patients in histopathological remission (CC-HR, n=4), (LC-HR, n=6), ulcerative colitis (UC, n=3) and controls (n=10) were analysed by real-time PCR and Luminex for expression/production of IL-1β, -4, -5, -6, -10, -12, -17, -21, -22, -23, IFN-γ, TNF-α, T-bet and RORC2.

RESULTS

Mucosal mRNA but not protein levels of IFN-γ and IL-12 were significantly up regulated in CC, LC as well as UC patients compared to controls. Transcription of the Th1 transcription factor T-bet was significantly enhanced in CC but not LC patients. mRNA levels for IL-17A, IL-21, IL-22 and IL-6 were significantly up regulated in CC and LC patients compared to controls, albeit less than in UC patients. Significantly enhanced IL-21 protein levels were noted in both CC and LC patients. IL-6 protein and IL-1β mRNA levels were increased in CC and UC but not LC patients. Increased mucosal mRNA levels of IFN-γ, IL-21 and IL-22 were correlated with higher clinical activity, recorded as the number of bowel movements per day, in MC patients. Although at lower magnitude, IL-23A mRNA was upregulated in CC and LC, whereas TNF-α protein was increased in CC, LC as well as in UC patients. Neither mRNA nor protein levels of IL-4, IL-5 or IL-10 were significantly changed in any of the colitis groups. LC-HR and especially CC-HR patients had normalized mRNA and protein levels of the above cytokines compared to LC and CC patients. No significant differences were found between LC and CC in cytokine expression/production.

CONCLUSION

LC and CC patients demonstrate a mixed Th17/Tc17 and Th1/Tc1 mucosal cytokine profile.

Clinical presentation, diagnosis, pathogenesis and treatment options for lymphocytic colitis (Review)

Lymphocytic colitis (LC) is characterized by chronic or relapsing non-bloody watery diarrhea and a macroscopically normal colon. However, histopathological examination of colonic biopsy samples reveals an increased intraepithelial infiltration of lymphocytes (≥20/100 enterocytes), and increased inflammatory cells within the lamina propria, but with a normal mucosal architecture. The reported prevalence of LC varies from 14.2 to 45 per 100,000 individuals, while its reported incidence is between 0.6 and 16 per 100,000 individuals. LC has a high rate of spontaneous symptomatic remission and is not associated with an increased risk of colon cancer or inflammatory bowel disease. The diagnosis is based on the histopathological findings. The density of colonic chromogranin A-positive cells provides an effective diagnostic tool with high sensitivity and specificity in both the right and left colon. Gastrointestinal infections, drugs, and/or autoimmunity may trigger chronic colonic low-grade inflammation. Colonic nitric oxide, serotonin and peptide YY (PYY) cell densities are markedly increased in patients with LC. It has been hypothesized that the low-grade inflammation in LC through the endocrine-immune axis causes this increase. It has been postulated further that these abnormalities in the neuroendocrine system of the colon are responsible for the diarrhea observed in patients with LC. The benign course and rate of spontaneous remission of LC denotes that drugs with severe side-effects should be avoided if possible. The drug cost and drug coverage may also be limiting factors for some patients. These aspects should be taken into account when making decisions regarding treatment options.

Review of the microscopic colitides

Microscopic colitis is a common cause of chronic diarrhea in predominantly older adults. Incidence rates of microscopic colitis (including lymphocytic and collagenous colitis) have increased over time to levels comparable to other forms of inflammatory bowel disease. The possibility of drug-induced microscopic colitis is an important consideration when evaluating these patients, although this concept requires further investigation. There are few controlled treatment trials in microscopic colitis, with much of the data on treatment coming from retrospective studies. In patients with microscopic colitis, a systematic approach to therapy often leads to satisfactory control of symptoms. In this review, we will provide an updated assessment of the epidemiology, diagnosis, and treatment of microscopic colitis.

Review of the microscopic colitides

Microscopic colitis is a common cause of chronic diarrhea in predominantly older adults. Incidence rates of microscopic colitis (including lymphocytic and collagenous colitis) have increased over time to levels comparable to other forms of inflammatory bowel disease. The possibility of drug-induced microscopic colitis is an important consideration when evaluating these patients, although this concept requires further investigation. There are few controlled treatment trials in microscopic colitis, with much of the data on treatment coming from retrospective studies. In patients with microscopic colitis, a systematic approach to therapy often leads to satisfactory control of symptoms. In this review, we will provide an updated assessment of the epidemiology, diagnosis, and treatment of microscopic colitis.

Review article: Microscopic colitis--lymphocytic, collagenous and 'mast cell' colitis

BACKGROUND

Microscopic colitis is a relatively common cause of chronic diarrhoea in predominantly older adults, traditionally termed lymphocytic colitis and collagenous colitis. Increased mast cells found in the colonic biopsies of some patients with chronic diarrhoea may represent a distinct type of microscopic colitis.

AIM

To provide an updated review of the epidemiology, diagnosis and treatment of microscopic colitis, and to discuss the role of mast cells in the gastrointestinal tract and their potential role in cases of functional diarrhoea.

METHOD

A MEDLINE literature search was performed to identify pertinent articles. Relevant clinical abstracts were also reviewed.

RESULTS

Incidence rates of microscopic colitis (lymphocytic and collagenous colitis) have increased over time, to levels comparable with other forms of inflammatory bowel disease. The possibility of drug-induced microscopic colitis and concomitant coeliac sprue are important considerations when evaluating these patients. There are few controlled treatment trials in microscopic colitis, with much of the data on treatment coming from retrospective studies. Mast cells have been implicated in functional bowel disorders, with increased mast cells possibly contributing to cases of otherwise unexplained chronic diarrhoea, although this concept requires further investigation.

CONCLUSIONS

In patients with microscopic colitis, a systematic approach to therapy often leads to satisfactory control of symptoms. The role of mast cells in chronic diarrhoea represents an evolving field, with the potential to offer alternative treatment pathways in patients with otherwise unexplained functional diarrhoea.

Microscopic colitis

Microscopic colitis is a common cause of chronic watery diarrhea, especially among older persons. Diagnosis requires histologic analysis of colon biopsy samples in the appropriate clinical setting. Recent studies have shown an increase in the incidence of microscopic colitis, and several have addressed potential mechanisms. We review recent findings about the clinical features, diagnosis, epidemiology, pathophysiology, and treatment of microscopic colitis.

Diagnosis and management of microscopic colitis

Microscopic colitis, comprising collagenous and lymphocytic colitis, is characterized clinically by chronic watery diarrhea, and a macroscopically normal colonic mucosa where diagnostic histopathological features are seen on microscopic examination. The annual incidence of each disorder is 4-6/100,000 inhabitants, with a peak incidence in 60-70-year-old individuals and a noticeable female predominance for collagenous colitis. The etiology is unknown. Chronic diarrhea, abdominal pain, weight loss, fatigue and fecal incontinence are common symptoms, which impair the health-related quality of life of the patient. There is an association with other autoimmune disorders such as celiac disease, diabetes mellitus, thyroid disorders and arthritis. Budesonide is the best-documented short-term treatment, but the optimal long-term strategy needs further study. The long-term prognosis is good and the risk of complications including colonic cancer is low.

Early bacterial dependent induction of inducible nitric oxide synthase (iNOS) in epithelial cells upon transfer of CD45RB(high) CD4(+) T cells in a model for experimental colitis

BACKGROUND

Both the role of inducible nitric oxide synthase (iNOS) in the development of inflammatory bowel disease (IBD) as well as the molecular details governing its mucosal induction remain unclear.

METHODS

In the present study we evaluated the role of the residing intestinal microflora in the induction of epithelial iNOS upon transfer of CD45RB(high) CD4(+) T cells to SCID mice. CB-17 SCID mice were reared with conventional flora (CNV) or germfree CB-17 SCID mice were monoassociated with Helicobacter muridarum, act A(-) mutant Listeria monocytogenes, segmented filamentous bacteria (SFB), or Ochrobactrum anthropi.

RESULTS

Within 2 weeks CNV SCID mice injected with CD45RB(high) CD4(+) T cells showed a focal, epithelial iNOS expression on the apical site of villi that preceded the infiltration of CD4(+) T cells and cytokine production followed by extension of this expression to the entire surface along the whole crypt axis as the colitis progressed. SCID mice monoassociated with H. muridarum developed a severe colitis and showed high epithelial iNOS expression. CNV-SCID mice without T cells and SCID mice monoassociated with SFB did not show any iNOS expression, whereas SCID mice monoassociated with act A(-) mutant L. monocytogenes and O. anthropi showed some scattered epithelial iNOS staining on the apical site of a few villi, but none of these mice developed colitis.

CONCLUSIONS

These findings demonstrate that the expression of epithelial iNOS is highly bacterium-specific and correlates with the severity of disease, suggesting an important role for this enzyme in the development of IBD.

Rectal nitric oxide and fecal calprotectin in inflammatory bowel disease

OBJECTIVE

The assessment of intestinal inflammation in patients with inflammatory bowel disease (IBD) remains a difficult challenge. Both rectal nitric oxide (NO) and fecal calprotectin can be measured using non-invasive methods and are emerging as promising inflammatory markers in IBD. In this study the aim was to compare calprotectin and NO levels in IBD patients.

MATERIAL AND METHODS

Rectal NO was measured tonometrically in 23 healthy volunteers and 32 patients with IBD. In addition, we collected stool samples from all subjects for measurement of fecal calprotectin and nitrate/nitrite (NO metabolites).

RESULTS

Patients with IBD had greatly increased NO and calprotectin levels compared to healthy volunteers (p <0.001). In addition, the nitrate levels were slightly increased in IBD patients. A weak correlation was found between rectal NO levels, disease activity and number of loose stools in IBD patients (Spearman's rho 0.37 and 0.51, respectively; p <0.05). Fecal calprotectin correlated only with age (Spearman's rho 0.51; p <0.01). However, no correlation was found between NO and calprotectin.

CONCLUSIONS

Both rectal NO and fecal calprotectin are greatly increased during bowel inflammation, but they may reflect different parts of the inflammatory process. Future studies will elucidate the clinical usefulness of these two markers.

Early changes in rectal nitric oxide and mucosal inflammatory mediators in Crohn's colitis in response to infliximab treatment

BACKGROUND

Treatment with tumor necrosis factor-alpha monoclonal antibody (infliximab) reduces clinical activity and intestinal inflammation in Crohn's disease.

AIM

To study the time-course of the effects of infliximab with reference to mucosal cytokine and inducible nitric oxide synthase expression.

METHODS

Thirty-two patients with Crohn's disease were treated with single dose infliximab (5 mg/kg). Disease activity was assessed days 1, 3, 7 and 28 using Harvey-Bradshaw index. Rectal nitric oxide levels were determined and rectal biopsies collected before treatment, 1 h after infusion and on days 3, 7 and 28. Immunohistochemical staining against inducible nitric oxide synthase, tumor necrosis factor-alpha, interleukin-1beta and interferon-gamma were performed.

RESULTS

Clinical response was seen in 14 patients with down-regulation of global immunohistochemistry expression, reaching nadir day 3. Rectal nitric oxide was increased at baseline (3578 +/- 1199 parts per billion, ppb) compared with controls (89 +/- 13 ppb) (P < 0.001). In patients with clinical response, rectal nitric oxide decreased from 3926 +/- 1687 ppb to 1050 +/- 428 ppb day 28 (P < 0.05).

CONCLUSIONS

Down-regulation of mucosal inflammatory mediators occurs after infliximab. Rectal nitric oxide levels parallel down-regulation of inducible nitric oxide synthase, tumor necrosis factor-alpha, interleukin-1beta and interferon-gamma and may serve as a quantitative biomarker of intestinal inflammation.

Budesonide treatment and expression of inducible nitric oxide synthase mRNA in colonic mucosa in collagenous colitis

OBJECTIVE

In collagenous colitis, the production of nitric oxide in the colon is found to be 50 to 100-fold higher than in healthy controls. The role of nitric oxide in collagenous colitis is debated and it has been suggested that nitric oxide has a causative role in diarrhoea. The aim of this study was to examine the possible effect of budesonide treatment on the level of inducible nitric oxide synthase mRNA.

METHODS

In 20 patients with collagenous colitis, clinical activity was assessed by registration of the daily stool frequency and stool weight. Sigmoidoscopy was performed and biopsies for histological examination and one biopsy for determination of inducible nitric oxide synthase mRNA was obtained in 16 patients.

RESULTS

Budesonide treatment was followed by a significant reduction of inducible nitric oxide synthase mRNA (P<0.01) whereas no change was observed after placebo treatment. Significant correlations between inducible nitric oxide synthase mRNA and the grade of inflammation (rho=0.47; P<0.01), the daily stool weight (rho=0.51; P<0.005) and the daily stool frequency (rho=0.49; P<0.005) were observed. No significant association was observed between inducible nitric oxide synthase mRNA and the thickness of the collagen layer.

CONCLUSIONS

In patients with collagenous colitis, treatment with budesonide results in a reduction of inducible nitric oxide synthase mRNA. The level of inducible nitric oxide synthase mRNA in colonic mucosa correlates with the inflammatory and clinical activity. The results support that nitric oxide is a central factor in the pathogenesis of collagenous colitis.

Systematic review: microscopic colitis

BACKGROUND

Collagenous and lymphocytic colitis are fairly common causes of chronic non-bloody diarrhoea, especially in elderly female.

AIM

To present a systematic review of microscopic colitis.

METHODS

A PubMed search using the MeSH terms microscopic colitis, collagenous colitis, lymphocytic colitis and chronic diarrhoea was performed.

RESULTS

Annual incidence of each disorder is 4-6/100,000 inhabitants. The aetiology is unknown. Clinical characteristics are well described and there is an association with autoimmune diseases. Budesonide is the best-documented short-term treatment of collagenous colitis. In meta-analysis pooled odds ratio for clinical response after 6-8 weeks of treatment was 12.3 (95% CI: 5.5-27.5) in comparison with placebo. The evidence for bismuth subsalicylate is weaker and the effectiveness of other alternatives such as loperamide, cholestyramine, aminosalicylates, probiotics, or Boswellia serrata extract is unknown. Although unproven, in unresponsive severe disease azathioprine or methotrexate may be tried. No controlled trials have been carried out in lymphocytic colitis. The long-term prognosis of microscopic colitis is good, serious complications are rare and there is no increased mortality.

CONCLUSIONS

Clinical and epidemiological aspects of microscopic colitis are well described. Budesonide is the best-documented short-term therapy in collagenous colitis, but the optimal long-term strategy needs further study. Controlled treatment data of lymphocytic colitis are awaited for.

Technology insight: calprotectin, lactoferrin and nitric oxide as novel markers of inflammatory bowel disease

Distinguishing patients with inflammatory bowel disease from those with irritable bowel syndrome can be difficult. A simple and reliable test that detects intestinal inflammation would therefore be very useful in the clinic. If such a test parameter correlated with the intensity of the inflammatory reaction it could also be used to monitor disease activity. Calprotectin, lactoferrin and nitric oxide are produced and released locally in much greater quantities in the inflamed gut than in the noninflamed gut. These compounds can be readily measured in fecal samples (calprotectin and lactoferrin) or directly in the intestinal lumen (nitric oxide gas). Here, we discuss what is known about these markers, how they could be used in clinical practice and how they can complement existing techniques used for the diagnosis and monitoring of inflammatory bowel disease.

Workgroup report: Drinking-water nitrate and health--recent findings and research needs

Human alteration of the nitrogen cycle has resulted in steadily accumulating nitrate in our water resources. The U.S. maximum contaminant level and World Health Organization guidelines for nitrate in drinking water were promulgated to protect infants from developing methemoglobinemia, an acute condition. Some scientists have recently suggested that the regulatory limit for nitrate is overly conservative; however, they have not thoroughly considered chronic health outcomes. In August 2004, a symposium on drinking-water nitrate and health was held at the International Society for Environmental Epidemiology meeting to evaluate nitrate exposures and associated health effects in relation to the current regulatory limit. The contribution of drinking-water nitrate toward endogenous formation of N-nitroso compounds was evaluated with a focus toward identifying subpopulations with increased rates of nitrosation. Adverse health effects may be the result of a complex interaction of the amount of nitrate ingested, the concomitant ingestion of nitrosation cofactors and precursors, and specific medical conditions that increase nitrosation. Workshop participants concluded that more experimental studies are needed and that a particularly fruitful approach may be to conduct epidemiologic studies among susceptible subgroups with increased endogenous nitrosation. The few epidemiologic studies that have evaluated intake of nitrosation precursors and/or nitrosation inhibitors have observed elevated risks for colon cancer and neural tube defects associated with drinking-water nitrate concentrations below the regulatory limit. The role of drinking-water nitrate exposure as a risk factor for specific cancers, reproductive outcomes, and other chronic health effects must be studied more thoroughly before changes to the regulatory level for nitrate in drinking water can be considered.

Collagenous mucosal inflammatory diseases of the gastrointestinal tract

Collagenous mucosal inflammatory diseases involve the columnar-lined gastric and intestinal mucosa and have become recognized increasingly as a significant cause of symptomatic morbidity, particularly in middle-aged and elderly women, especially with watery diarrhea. Still, mechanisms involved in the pathogenesis of this diarrhea remain poorly understood and require further elucidation. The prognosis and long-term outcome of these disorders has been documented only to a limited extent. Recent clinical and pathologic studies have indicated that collagenous mucosal inflammatory disease is a more extensive pathologic process that concomitantly may involve several sites in the gastric and intestinal mucosa. The dominant pathologic lesion is a distinct subepithelial hyaline-like deposit that has histochemical and ultrastructural features of collagen overlying a microscopically defined inflammatory process. An intimate relationship with other autoimmune connective tissue disorders is evident, particularly celiac disease. This is intriguing because these collagenous disorders have not been shown to be gluten dependent. Collagenous mucosal inflammatory disorders may represent a relatively unique but generalized inflammatory response to a multitude of causes, including celiac disease, along with a diverse group of pharmacologic agents. Some recent reports have documented treatment success but histopathologic reversal has been more difficult to substantiate owing to the focal, sometimes extensive nature, of this pathologic process.

Birth-related increase in intracolonic hydrogen gas and nitric oxide as indicator of host-microbial interactions

BACKGROUND

Bacterial colonization of the intestine early in life might have implications for allergy development. We studied early host-bacterial interactions in the gut by simultaneous measurements of hydrogen gas (H(2)) and faecal short chain fatty acid pattern (SCFAs), i.e. bacterial products, as well as of nitric oxide (NO), a marker of mucosal immune activation.

METHODS

A novel minimally invasive technique was used for repeated measurements of luminal colonic H(2) and NO in 32 healthy newborn infants delivered vaginally or by Caesarean section. Luminal gas was sampled and analysed at five occasions: immediately after birth, day 1, days 3-5, 1 and 5-6 months after birth.

RESULTS

Colonic H(2), NO and faecal SCFAs were undetectable at birth. The H(2) and SCFAs appeared within 24 h and continued to increase during the 6 months follow-up. Nitric oxide remained very low until 3-5 days after birth at which time it markedly increased. In some apparently healthy infants NO transiently reached levels similar to those seen in adults with inflammatory bowel disease.

CONCLUSION

Intracolonic measurements of H(2) and NO may be useful to monitor the developmental colonization process as well as mucosal responses.

Microscopic colitis: an update

Microscopic colitis is an increasingly common cause of chronic diarrhea, and often causes abdominal pain and weight loss. The colonic mucosa appears normal or nearly normal endoscopically, and the diagnosis is made in the appropriate clinical setting when there is intraepithelial lymphocytosis and a mixed lamina propria inflammatory infiltrate. The 2 subtypes, collagenous and lymphocytic colitis, are similar clinically and histologically, and are distinguished by the presence or absence of a thickened subepithelial collagen band. Many potential pathophysiologic mechanisms have been proposed, but no convincing unifying mechanism has been identified. There are many anecdotal reports on treatment, but few controlled trials have been performed in these patients, although a systematic approach to therapy often leads to the satisfactory control of symptoms.

Rectal nitric oxide gas and stool cytokine levels during the course of infectious gastroenteritis

Nitric oxide (NO) is known to be an important inflammatory mediator with a potential role in gastrointestinal diseases. We prospectively studied the luminal NO levels in 51 patients with infectious gastroenteritis, 35 patients with nonenteric bacterial infections, and 11 healthy control subjects. The levels of proinflammatory cytokines were simultaneously measured in the stools of patients with gastroenteritis. Rectal gas was sampled with balloon catheters made of silicone and was analyzed for NO levels by chemiluminescence. The median rectal NO level was 2,450 ppb in the acute phase of gastroenteritis and gradually decreased to 225 ppb after 3 to 8 weeks, whereas the median NO values were 150 ppb in patients with nonenteric bacterial infections and 100 ppb in healthy control subjects. Patients with Salmonella, Shigella, and Campylobacter infections generally had more severe symptoms and a higher median NO level (17,250 ppb) than patients with Clostridium difficile-associated diarrhea (median NO value, 275 ppb). Interleukin-1 beta levels were elevated in 82% of the patients at disease onset and decreased during the convalescent phase. In contrast, gamma interferon was detected in only 16% of the patients and was predominantly collected in stool samples collected during the subacute and convalescent stages. Our data point to the possibility of using this easy, minimally invasive method for luminal NO measurement as a diagnostic tool, among others, to evaluate the degree of intestinal inflammation in patients with infectious gastroenteritis.

Effect of intravenous L-NMMA on nitric oxide production in collagenous colitis

BACKGROUND

Nitric oxide (NO) is greatly increased in the colon of patients with inflammatory bowel disease of different aetiology, including collagenous colitis. In man, NO can be generated from NO synthases as well as from non-enzymatic sources. The source of the NO found in luminal intestinal gas has not been exactly pinpointed. We investigated the effect of the NO synthase inhibitor L-NMMA on intestinal concentrations of NO in patients with clinically active collagenous colitis. In addition, we measured NO levels from the respiratory tract.

METHODS

Ten patients with active collagenous colitis were studied. NO levels were measured from the respiratory tract and in the rectum before and after i.v. administration of L-NMMA (7.5 mg/kg) using a chemiluminescence method.

RESULTS

Airway NO release decreased markedly, and mean arterial blood pressure increased in all patients following L-NMMA treatment. Basal rectal NO levels were high (median > 10000 ppb) and decreased markedly in 5 patients after L-NMMA. In contrast, NO levels remained completely unchanged or even increased in the other 5 patients.

CONCLUSION

Rectal levels of NO are greatly increased in patients with symptomatic collagenous colitis. Intravenous administration of an NO synthase inhibitor reduced rectal NO only in half of the patients despite clear evidence of effective systemic NO synthase inhibition. This could indicate alternative NOS-independent sources of intestinal NO in this disease.

Paradoxical roles of different nitric oxide synthase isoforms in colonic injury

Nitric oxide (NO) is a free radical that is largely produced by three isoforms of NO synthase (NOS): neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). NO regulates numerous processes in the gastrointestinal tract; however, the overall role that NO plays in intestinal inflammation is unclear. NO is upregulated in both ulcerative colitis and Crohn's disease as well as in animal models of colitis. There have been conflicting reports on whether NO protects or exacerbates injury in colitis or is simply a marker of inflammation. To determine whether the site, timing, and level of NO production modulate the effect on the inflammatory responses, the dextran sodium sulfate model of colitis was assessed in murine lines rendered deficient in iNOS, nNOS, eNOS, or e/nNOS by targeted gene disruption. The loss of nNOS resulted in more severe disease and increased mortality, whereas the loss of eNOS or iNOS was protective. Furthermore, concomitant loss of eNOS reversed the susceptibility found in nNOS-/- mice. Deficiencies in specific NOS isoforms led to distinctive alterations of inflammatory responses, including changes in leukocyte recruitment and alterations in colonic lymphocyte populations. The present studies indicate that NO produced by individual NOS isoforms plays different roles in modulating an inflammatory process.

Blockade of NF-kappaB activation and donation of nitric oxide: new treatment options in inflammatory bowel disease?

BACKGROUND

Inhibition of NF-kappaB activation has been suggested as an anti-inflammatory treatment strategy in inflammatory bowel disease (IBD). However, NF-kappaB regulated genes like inducible nitric oxide synthase (iNOS) are also involved in cell survival mechanisms.

METHODS

Review of the literature on NF-kappaB activation and iNOS induction in IBD.

RESULTS

In patients with IBD the mucosal immune response is derailed. The nuclear transcription factor NF-kappaB is a key regulator of the inducible expression of many genes involved in immune and inflammatory responses in the gut. Stimuli like oxidative stress, cytokines (IL-1, IL-6, TNF-alpha), bacteria and viruses can release NF-kappaB from their inactive cytoplasmatic form to the nucleus. Drugs like corticosteroids, sulphasalazine, mesalazine and inhibitory cytokines (e.g. IL-10, IL-11) can prevent the activation of NF-kappaB. New, more potent and selective treatment strategies with anti-sense p65, proteasome inhibitors and viral IkappaBalpha expression vectors aim at the prevention of NF-kappaB activation in mucosal macrophages and T lymphocytes. However, NF-kappaB regulated genes are also involved in survival responses of epithelial cells. For example, inhibition of the NF-kappaB mediated induction of iNOS in epithelial cells could block important anti-apoptotic and anti-microbial survival mechanisms. Nitric oxide may also serve in a negative feedback loop to antagonize prolonged activation of NF-kappaB, thereby limiting chronic inflammation.

CONCLUSION

Luminal donation of nitric oxide could block NF-kappaB activation. Selective inhibition of NF-kappaB activation in inflammatory cells could be a treatment option in IBD.

Hyperbaric oxygen treatment of active cluster headache: a double-blind placebo-controlled cross-over study

Sixteen patients, 12 with episodic and four with chronic cluster headache (CH) according to the International Headache Society criteria (1), participated in the study. They were randomly selected to start with one out of two different hyperbaric treatments in a double-blind, placebo-controlled, cross-over study design. Both gases were administered by mask inside a multiplace hyperbaric chamber for 70 min at 250 kPa (2.5 ATA) in two sessions 24 h apart. Active treatment was 100% oxygen (HBO treatment), while placebo treatment was 10% oxygen in nitrogen (hyperbaric normoxic placebo = sham treatment) corresponding to breathing air at sea level. All patients were decompressed on air. The patients documented the number of headache attacks and their degree of severity according to a modified VAS scale (level 0-4, where level 0 = no headache and level 4 = very severe headache). A headache index (HI = sum of (number of attacks times degree of severity)) was calculated for the run-in week prior to and the week after each separate treatment. A treatment was regarded as effective if it reduced the HI by>50%. Blood samples were taken from the external jugular vein before and during hyperbaric treatment (after 30 and 70 min), 1 day and 1 week after each treatment for analyses of calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) and in a few patients also endotheline and nitrate. No difference between HBO and sham treatment on the HI or the prophylactic effect was observed in our study. However, 83% of the episodic CH patients and 25% of the chronic ones responded to either of the two treatments with at least 50% reduction of HI or remission for shorter or longer periods. This response rate exceeds an expected high placebo response due to the study procedure. Two episodic CH patients still experienced remission on follow-up 1 year after sham treatment. Five patients reported mild or moderate CH attacks during the sham treatment, and none during the HBO treatment. Changes in neuropeptides, endotheline and nitrate levels did not differ systematically when comparing the two different hyperbaric treatments or with respect to responders and non-responders. We conclude that two HBO sessions were not more effective than two sham treatments in reducing the HI and interrupting the CH period when given in a well-established cluster period or in chronic CH. The hyperbaric condition itself seems effective in reducing the HI, at least in patients with episodic CH, although a powerful placebo response can not be ruled out.

Nitric oxide supplementation ameliorates dextran sulfate sodium-induced colitis in mice

Nitric oxide (NO) synthesis is up-regulated in inflammatory bowel disease. However, its role in the pathophysiology of this condition is controversial. The aims of this study were to assess whether nitric oxide administration ameliorates experimental colitis and to determine the possible mechanisms underlying its effects on intestinal inflammation. For this purpose, the NO donor diethylamine NONOate (DETA/NO; 0.01, 0.1, 1, 5, or 10 mg/kg/day), or the DETA moiety, was administered daily to mice with dextran sulfate sodium-induced colitis. Daily body weight and colonic pathologic alterations at Day 10 were determined. Leukocyte endothelial cell interactions in colonic venules were assessed with intravital microscopy, and expression of endothelial cell adhesion molecules was determined using radiolabeled antibodies. IL-12 and IFN-gamma production were measured in intestinal tissue. Colitis induced a significant loss of body weight, reduction of colon length, and increase in colon weight and myeloperoxidase activity. Administration of 1 mg/kg/day DETA/NO significantly attenuated these pathologic changes. The marked increase in leukocyte rolling and adhesion in colonic venules of colitic mice were significantly reduced by administration of 1 mg/kg/day DETA/NO. Development of colitis was associated with a marked increase in endothelial expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and P-selectin. Supplementation with NO significantly attenuated the up-regulation of endothelial intercellular adhesion molecule-1 and P-selectin, but not vascular cell adhesion molecule-1, in colonic tissue. NO abrogated the increase in IL-12 and IFN-gamma mRNA expression in the colon of colitic mice. The DETA moiety alone did not have any effect on any of the parameters studied. In conclusion, exogenous NO supplementation significantly ameliorates dextran sulfate sodium-induced colitis. This effect is related to a reduction in leukocyte recruitment and proinflammatory cytokine production.

Microscopic colitis: a review

Microscopic colitis is a relatively common cause of chronic watery diarrhea, often accompanied by abdominal pain and weight loss. The colonic mucosa appears normal grossly, and the diagnosis is made when there is an intraepithelial lymphocytosis and a mixed inflammatory infiltrate in the lamina propria. The two main subtypes, collagenous and lymphocytic colitis, are similar clinically and histologically, distinguished by the presence or absence of a thickened subepithelial collagen band. Many potential pathophysiological mechanisms have been described, although none have been conclusively proved. There is a paucity of randomized treatment trials in these patients, although a rational approach to therapy often leads to satisfactory control of symptoms.

Microscopic colitis

Microscopic colitis is an umbrella term used to include two idiopathic inflammatory bowel disorders that present with chronic watery diarrhea, normal endoscopic findings and characteristic inflammatory changes on histology. Collagenous colitis and lymphocytic colitis are distinguished by the presence of a thickened subepithelial collagen table. It is likely that they are a spectrum of one disease, but this is yet to be proven. The majority of cases tend to undergo spontaneous remission within a few years of onset, and their clinical course is benign, with no increase in risk of colorectal cancer. Sufficient evidence exists to suggest that microscopic colitis occurs as a response to one or more luminal antigens. A variety of medications have been reported in the treatment of this condition, but only colloidal bismuth and budesonide have thus far been shown to be effective in randomized controlled trials.

Increased rectal nitric oxide in children with active inflammatory bowel disease

BACKGROUND

Luminal nitric oxide increases in ulcerative colitis and Crohn disease. The authors have previously used a minimally invasive method to demonstrate increased luminal nitric oxide in ulcerative colitis and Crohn disease of the colon. The aim of the current study was to determine whether this method could be applied to identify inflammatory activity in ulcerative colitis and Crohn disease in children.

METHODS

Thirty-six children (18 of whom had active disease) with inflammatory bowel disease localized to the colon were studied. The control group comprised 12 healthy children. To measure nitric oxide, a silicon catheter with an inflatable balloon was inserted into the rectum and inflated with 10 mL of nitric oxide-free air. After a 10-minute incubation time, the air was withdrawn and nitric oxide concentrations were immediately analyzed using a chemiluminescence technique.

RESULTS

Children with active ulcerative colitis and Crohn disease of the colon had greatly increased luminal nitric oxide concentrations in the rectum (8,840 +/- 5,120 and 15,170 +/- 4,757 parts per billion [ppb], respectively) compared with controls (77 +/- 17 ppb) (P < 0.001). Children with nonactive ulcerative colitis or Crohn disease displayed low concentrations of rectal nitric oxide (356 +/- 110 and 188 +/- 55 ppb, respectively), which was not different from that of healthy controls.

CONCLUSION

Rectal nitric oxide measurement is a feasible and useful method for monitoring disease activity in inflammatory bowel disease, especially in children.

Rectal nitric oxide assessment in children with Crohn disease and ulcerative colitis. Indicator of ileocaecal and colorectal affection

BACKGROUND

Nitric oxide (NO) production is increased in inflammatory bowel disease (IBD). Measurements of luminal NO in Crohn disease and ulcerative colitis have revealed that levels are increased during active disease. We aim to evaluate whether rectal measurements of NO can reveal active disease of the colon as well as ileum.

METHODS

Sixteen children with active Crohn disease in the ileocaecal or colorectal regions of the gut and 6 children with active ulcerative colitis were compared to a group of 14 healthy children. Gaseous samples for analysis of luminal NO were collected using a Foley catheter inserted into rectum. The balloon of the catheter was filled with NO-free air and incubated for 10 min. After aspiration, samples were analysed using chemiluminescence. Values are expressed as median and range.

RESULTS

In healthy children, rectal NO values were 60 (0-275) ppb. In children with Crohn disease of the colorectal region, NO concentrations were 5,675 (300-49,350) ppb (P < 0.001), while those with Crohn disease of the ileocaecal region had NO levels of 2,625 (300-15,000) ppb (P < 0.01). In children with ulcerative colitis, NO values of 5,500 (950-34,000) ppb were found (P < 0.001).

CONCLUSION

Rectal NO levels are greatly increased in children with IBD. Highest values were found in patients with colorectal engagement, but rectal NO was increased also in ileocaecal disease. Rectal sampling of luminal NO is a simple and minimally invasive method and should be considered a diagnostic tool for intestinal inflammatory activity in children regardless of primary disease location.

Nitrite and nitrate measurement in human urine by capillary electrophoresis

Nitrite and nitrate have been widely used as markers for nitric oxide (NO) formation in vivo and represent the major NO oxidation products in biological fluids. In the present study, the use of capillary electrophoresis (CE) in the measurement of nitrite and nitrate in human urine is described. Urine samples were electrophoresed in an extended light path fused-silica capillary (104 cm; 75 microm ID) at an applied negative potential of 30 kV, and UV detection at 214 nm. Using electrokinetic sample injection (-6 kV x 20 s), we found that urine concentration, pH, sodium and chloride interfered with nitrite and nitrate detection. The detection of nitrite and nitrate was decreased when hydrodynamic sample injection was used (30 mbar x 60 s). However, basal levels of urinary nitrite (0.25 +/- 0.05 microM) and nitrate (591 +/- 115 microM) were detected and no interference by variations in urine concentration and pH was noted when hydrodynamic sample injection was used. Thus, hydrodynamic sample injection is convenient for the measurement of urinary nitrite and nitrate and avoids the effect of variations in urine matrices and pH on nitrite and nitrate detection.

Increased presence of eosinophilic granulocytes expressing transforming growth factor-beta1 in collagenous colitis

BACKGROUND

Collagenous colitis is a disease characterized by chronic watery diarrhea, and on microscopic examination of colonic tissue, a typical thickening of the subepithelial collagen layer is seen. The etiology and pathophysiology behind this disease state are largely unknown.

METHODS

We have used in situ hybridization and immunohistochemistry to study the expression of transforming growth factor (TGF) -beta1, a growth factor with the capacity to cause accumulation of collagen in tissues, in collagenous colitis. Colonic pinch biopsy specimens from a total of 34 patients were investigated: 17 patients with collagenous colitis and 17 controls.

RESULTS

In patients with collagenous colitis there was increased expression of the TGF-beta1 gene compared with controls, as visualized by in situ hybridization. The vast majority of the TGF-beta1-expressing cells were eosinophils, both in collagenous colitis and controls, but there were also scattered fibroblastic and histiocytic stromal cells. Immunohistochemistry showed the presence of TGF-beta1, mainly in eosinophils, in the colonic mucosa. Morphometric quantification showed 603 +/- 192 eosinophils/mm2, (mean +/- standard error of the mean) in the colonic mucosa of patients with collagenous colitis compared with 30 +/- 7 eosinophils/mm2 in the controls.

CONCLUSIONS

The present results suggest that eosinophils expressing TGF-beta1 may be of pathophysiologic importance in the connective tissue remodeling seen in collagenous colitis.

Collagenous colitis and lymphocytic colitis

The most recently recognized and least understood forms of inflammatory bowel disease are two types of idiopathic microscopic colitis-collagenous colitis and lymphocytic colitis. These disorders share many clinical and histologic features, but they have a few notable differences. Whether these are two distinct entities or different presentations of the same disease remains controversial. Bismuth subsalicylate is effective in some patients and treatment is symptomatic and empirical in others. Unlike ulcerative colitis and Crohn's disease, these forms of inflammatory bowel disease rarely require surgery. Ileostomy with or without colectomy is curative for the rare patient with severe symptoms that are refractory to medical measures. Collagenous and lymphocytic colitis are not associated with an increased risk of malignancy.

Nitric oxide effect on colonocyte metabolism: co-action of sulfides and peroxide

Luminal levels of nitric oxide/nitrite are high in colitis. Whether nitric oxide is injurious or protective to human colonocytes is unknown and the role of nitric oxide in the genesis of colitis unclear. The aims were to establish whether nitric oxide was injurious to oxidation of substrates (n-butyrate and D-glucose) in isolated human and rat colonocytes both alone and in the presence of hydrogen sulfide and hydrogen peroxide, agents implicated in cell damage of colitis. Nitric oxide generation from S-nitrosoglutathione was measured by nitrite appearance. Colonocytes were isolated and incubated with [1-14C] butyrate or [6-14C] glucose and 2.6 microM nitric oxide, 1.5 mM sodium hydrogen sulfide or 2.5 mM hydrogen peroxide. Acyl-CoA esters were measured by high performance liquid chromatography, 14CO2 radiochemically and lactate/ketones by enzymic methods. Results indicate that nitric oxide very significantly (p < .001) reduced acyl-CoA formation but did not impair 14CO2 generation. Peroxide and sulfide with nitric oxide resulted in significant reduction (p < 0.01) of substrate oxidation to CO2. Sulfide significantly stimulated release of nitric oxide from S-nitrosoglutathione. The principal conclusion is that nitric oxide diminishes CoA metabolism in colonocytes. CoA depletion has been observed in chronic human colitis for which a biochemical explanation has been lacking. For acute injurious action in human colonocytes nitric oxide requires co-action of peroxide and sulfide to impair oxidation of substrates in cells. From current observations treatment of colitis should aim to reduce simultaneously nitric oxide, peroxide and sulfide generation in the colon.

Budesonide for the treatment of collagenous colitis: first results of a pilot trial

OBJECTIVE

Collagenous colitis is a chronic watery diarrhea disorder characterized by a subepithelial collagen layer and a lymphoplasmacytic infiltration within the lamina propria. However, no standard treatment has been introduced by controlled clinical trials. Aim of the present pilot trial was to investigate the clinical effects of orally administered budesonide (3 mg t.i.d.) in 7 patients with collagenous colitis. In addition, the histomorphological changes after budesonide treatment were described in a group of 3 patients.

METHODS

The study was performed as an open label pilot trial. Study end point was the clinical remission of collagenous colitis defined by stool frequency and stool consistency.

RESULTS

The results indicate a rapid and sustained clinical response in all patients. Stool frequency significantly decreased (p < 0.001) from 10.43 +/- 5.56 per day (4-20 per day) to 3.3 +/- 1.2 (1-5 per day) after 10 days and to 1.86 +/- 0.69 per day (1-3 per day) after 10 wk. Moreover stool consistency changed from watery (6 patients) or soft (1 patient) to soft (1 patient) or solid (6 patients). Clinical improvement was achieved within the first 10 days in all patients and maintained after dose reduction. In 3 patients no diarrhea recurred within 7, 12, or 15 months after treatment with budesonide was terminated. In these patients control biopsies were taken and showed a marked regression of both characteristics, the collagen band and the lymphoplasmacytic infiltration.

CONCLUSIONS

With respect to the preliminary data from this pilot trial, budesonide with its high topical and low systemic effects seems to be of therapeutic clinical benefit in collagenous colitis. A therapeutic effect could be demonstrated for both therapeutic goals, the clinical response and morphological changes. Further studies on the effects of budesonide on mucosal collagen metabolism and long-term follow-up are warranted.

Review article: the potential role of nitric oxide in chronic inflammatory bowel disorders

The aetiology of the chronic inflammatory bowel diseases-ulcerative colitis and Crohn's disease-as well as 'microscopic colitis'-both collagenous (COC) and lymphocytic colitis (LC)-remains unknown. Autoimmune mechanisms, cytokine polymorphism, commensal bacteria, infectious agents and vascular impairment have all been proposed as playing important roles in the pathogenesis of this spectrum of diseases. A variety of proinflammatory mediators, including tumour necrosis factor alpha, interleukin-1beta, interferon gamma, leukotriene B4 and platelet activating factor, promote the adherence of phagocytes to the venular endothelium and extravasation of these cells into the colonic mucosa. In addition to large amounts of nitric oxide (NO), injurious peroxynitrite may be formed in the epithelium by the inducible nitric oxide synthase (iNOS), which is considered to elicit cytotoxicity by the generation of superoxide with reduced L-arginine availability. In active ulcerative colitis, and to a lesser extent in Crohn's disease, a greatly increased production of NO has been demonstrated by indirect and direct measurements. Surprisingly, even higher rates of production have been observed in COC-a condition which is never associated with injurious inflammation. The latter observation favours the notion that NO promotes mucosal integrity. Further evidence for a protective role of NO in chronic inflammatory bowel disorders is provided by the observation of increased susceptibility to the induction of experi mental colitis in 'knock-out' mice deficient in iNOS. Selective inhibitors of iNOS activity, as well as topical L-arginine, may therefore prove beneficial in inflammatory bowel disease by reducing the production of superoxide by iNOS, while only the former option may be expected to reduce diarrhoea in chronic inflammatory bowel disorders. Clearly, further experimental work needs to be done before testing topical L-arginine in human inflammatory bowel disease.

Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).

Increased luminal nitric oxide in inflammatory bowel disease as shown with a novel minimally invasive method

BACKGROUND

The production of nitric oxide (NO) is increased in ulcerative colitis, as shown by bioassays of NO synthase activity in mucosal biopsy specimens. We wanted to develop a less invasive method for measurement of NO directly in the rectum in patients with inflammatory bowel disease (IBD).

METHODS

We studied 10 patients with active ulcerative colitis, 6 with active Crohn's disease, 6 with non-active ulcerative colitis, and 24 controls without inflammation A tonometer balloon catheter was inserted in the rectum and inflated with 5 ml of NO-free air. After 15 min of incubation the sample was extracted, and the NO concentration was immediately analysed with a chemiluminescence technique.

RESULTS

Patients with active disease had greatly increased concentrations of NO in the rectum as compared with controls and patients with non-active disease.

CONCLUSIONS

During inflammation in the large intestine increased amounts of NO are released from the mucosa. Measurements of NO directly in the rectum could be of help in further understanding the role of this gas in IBD. Moreover, it is tempting to speculate that this minimally invasive method could be clinically useful as a diagnostic tool and in monitoring the effect of therapy.