Bile Acid-Related Regulation of Mucosal Inflammation and Intestinal Motility: From Pathogenesis to Therapeutic Application in IBD and Microscopic Colitis.

Inflammatory bowel diseases (IBD) and microscopic colitis are chronic immune-mediated inflammatory disorders that affect the gastroenterological tract and arise from a complex interaction between the host's genetic risk factors, environmental factors, and gut microbiota dysbiosis. The precise mechanistic pathways interlinking the intestinal mucosa homeostasis, the immunological tolerance, and the gut microbiota are still crucial topics for research. We decided to deeply analyze the role of bile acids in these complex interactions and their metabolism in the modulation of gut microbiota, and thus intestinal mucosa inflammation. Recent metabolomics studies revealed a significant defect in bile acid metabolism in IBD patients, with an increase in primary bile acids and a reduction in secondary bile acids. In this review, we explore the evidence linking bile acid metabolites with the immunological pathways involved in IBD pathogenesis, including apoptosis and inflammasome activation. Furthermore, we summarize the principal etiopathogenetic mechanisms of different types of bile acid-induced diarrhea (BAD) and its main novel diagnostic approaches. Finally, we discuss the role of bile acid in current and possible future state-of-the-art therapeutic strategies for both IBD and BAD.

Quantifying intraepithelial lymphocytes and subepithelial collagen band in microscopic colitis, extracting insights into the interrelationship of lymphocytic and collagenous colitis.

Microscopic colitis (MC) is the umbrella term for the conditions termed lymphocytic colitis (LC) and collagenous colitis (CC). LC with thickening of the subepithelial collagen band or CC with increased number of intraepithelial T- lymphocytes (IELs) is often seen in MC and may lead to difficulties in correct histological classification. We investigated the extent of overlapping features of CC and LC in 60 cases of MC by measuring the exact thickness of the subepithelial collagen band in Van Gieson stained slides and quantifying number of IELs in CD3 stained slides by digital image analysis. A thickened collagen band was observed in nine out of 29 cases with LC (31%) and an increased number of IELs in all 23 cases of CC (100%). There was no correlation between the thickness of the collagen band and number of IELs. Due to the increased number of IELs in all cases of CC we consider the lymphocytic inflammatory infiltration of the mucosa to be the essential histopathological feature of MC. However, although LC and CC are related due to the lymphocytic inflammation, the non-linear correlation of number of IELs and thickness of the collagenous band indicate differences in their pathogenesis.

Microscopic Colitis Evolved Into Inflammatory Bowel Diseases Is Characterized by Increased Th1/Tc1 Cells in Colonic Mucosal Lamina Propria.

BACKGROUND: An association between microscopic colitis (MC), i.e., lymphocytic colitis (LC) and collagenous colitis (CC), and inflammatory bowel diseases (IBD) has been noticed. A subset of MC cases may evolve into IBD, and IBD in remission may present as MC in a histologic pattern. Moreover, MC and IBD may coexist in different regions of the bowel. A link between MC and IBD in their pathogenesis is, therefore, suggested. Abnormal mucosal immunity is likely the key. METHODS: We reviewed 2324 MC cases in Calgary over 14 years and identified 20 cases evolved into IBD (IBD transformers). 13 of them were further investigated for colonic mucosal lamina propria mononuclear cells (LPMNCs), as opposed to 22 cases whose MC resolved. On their index colonic biopsy immunohistochemistry was performed to detect major T cell subsets characterized by key cytokines and master transcription factors (IFNγ and T-bet for Th1/Tc1, GATA-3 for Th2/Tc2, IL-17 and RORc for Th17/Tc17, FoxP3 for Treg/Tcreg) as well as TNFα+ cells (partly representing Th1). LPMNCs positive for each marker were counted (average number per high-power field). RESULTS: IBD transformers had increased IFNγ+, T-bet+, TNF-α+, and GATA-3+ LPMNCs compared to the MC-resolved cases. The LC-to-IBD subgroup had increased IFNγ+ and GATA-3+ cells compared to the LC-resolved subgroup. The CC-to-IBD subgroup had increased T-bet+, TNF-α+, and GATA-3+ cells compared to the CC-resolved subgroup. Among MC-resolved patients, more TNF-α+ and RORc+ cells were seen in LC than in CC. CONCLUSION: Th1/Tc1- and TNFα-producing cells, and likely a subset of Th2/Tc2 cells as well, may be involved in the MC-to-IBD transformation.

The Pathogenic Role of NLRP3 Inflammasome Activation in Inflammatory Bowel Diseases of Both Mice and Humans.

BACKGROUND AND AIMS: NLRP3 inflammasome is known to be involved in inflammatory bowel diseases. However, it is controversial whether it is pathogenic or beneficial. This study evaluated the roles of NLRP3 inflammasome in the pathogenesis of inflammatory bowel disease in IL-10-/- mice and humans. METHODS: NLRP3 inflammasome in colonic mucosa, macrophages, and colonic epithelial cells were analysed by western blotting. The NLRP3 inflammasome components were studied by sucrose density gradient fractionation, chemical cross-linking, and co-immunoprecipitation. The role of NLPR3 inflammasome in the pathogenesis of colitis was extensively evaluated in IL-10-/- mice, using a specific NLPR3 inflammasome inhibitor glyburide. RESULTS: NLRP3 inflammasome was upregulated in colonic mucosa of both IL-10-/- mice and Crohn's patients. NLRP3 inflammasome activity in IL-10-/- mice was elevated prior to colitis onset; it progressively increased as disease worsened and peaked as macroscopic disease emerged. NLRP3 inflammasome was found in both intestinal epithelial cells and colonic macrophages, as a large complex with a molecular weight of ≥ 360 kDa in size. In the absence of IL-10, NLRP3 inflammasome was spontaneously active and more robustly responsive when activated by LPS and nigericin. Glyburide markedly suppressed NLRP3 inflammasome expression/activation in IL-10-/- mice, leading to not only alleviation of ongoing colitis but also prevention/delay of disease onset. Glyburide also effectively inhibited the release of proinflammatory cytokines/chemokines by mucosal explants from Crohn's patients. CONCLUSIONS: Abnormal activation of NLRP3 inflammasome plays a major pathogenic role in the development of chronic colitis in IL-10-/- mice and humans. Glyburide, an FDA-approved drug, may have great potential in the management of inflammatory bowel diseases.

[Evolution of ideas on microscopic colitis].

The literature review gives the present-day views of the definition, etiology, pathogenesis, diagnosis, and treatment of microscopic colitis (MC). In the present view, MC is an inflammatory bowel disease of unknown etiology, which is characterized by chronic watery diarrhea, no macroscopic signs of large bowel involvement in the presence of specific pathomorphological changes. There are two major forms of MC, which are similar in its clinical picture, yet, heterogeneous in histological criteria: collagenous colitis (CC) and lymphocytic colitis (LC). As of now, the prevalence of MC is about 100 cases per 100,000 population, which is similar with that in other inflammatory bowel diseases, such as ulcerative colitis and Crohn's disease. MC generally prevails in women aged over 50 years. The etiology and pathogenesis of MC have not fully investigated. Watery diarrhea is as a predominant pathognomonic symptom in all the patients with MC. The major histological criterion for the diagnosis of CC is subepithelial collagen lining thickening (more than 10 pm) and that for LC is higher intraepithelial lymphocyte counts (more than 20 intraepithelial lymphocytes/100 epitheliocytes). The topical glucocorticosteroid budesonide is currently the only agent, the efficacy of which has been proven in both inducing and maintaining remission in patients with MC in many clinical trials.

Enhanced levels of chemokines and their receptors in the colon of microscopic colitis patients indicate mixed immune cell recruitment.

Microscopic colitis (MC), comprising collagenous colitis (CC) and lymphocytic colitis (LC), is a common cause of chronic diarrhea. Various immune cell infiltrations in the epithelium and lamina propria are seen in MC immunopathology. We compared gene and protein expressions of different immune cell attracting chemokines and their receptors in colon biopsies from MC patients in active disease or histopathological remission (CC/LC-HR) with controls, using qRT-PCR and Luminex, respectively. CC and LC patients with active disease demonstrated a mixed chemokine profile with significantly enhanced gene and/or protein expressions of the chemokines CCL2, CCL3, CCL4, CCL5, CCL7, CCL22, CXCL8, CXCL9, CXCL10, CXCL11, and CX3CL1 and the receptors CCR2, CCR3, CCR4, CXCR1, CXCR2, and CX3CR1. Enhanced chemokine/chemokine receptor gene and protein levels in LC-HR patients were similar to LC patients, whereas CC-HR patients demonstrated almost normalized levels. These findings expand the current understanding of the involvement of various immune cells in MC immunopathology and endorse chemokines as potential diagnostic markers as well as therapeutic candidates. Moreover, this study further supports the hypothesis that CC and LC are two different entities due to differences in their immunoregulatory responses.

Cytokine expression of microscopic colitis including interleukin-17.

BACKGROUND/AIMS: Microscopic colitis is characterized by chronic watery diarrhea with specific pathological changes that can be diagnosed by microscopic examination. We performed immunohistochemical analysis of proinflammatory cytokines to investigate the pathogenic mechanism of microscopic colitis. METHODS: This study consisted of six patients with lymphocytic colitis, six patients with collagenous colitis, and six patients with functional diarrhea but normal pathology. We performed an immunohistochemical analysis of the colonic mucosal biopsies to assess the expression of cyclo-oxygenase-2, interleukin-17, nuclear factor-κB, interferon-γ, inducible nitric oxide synthase, and tumor necrosis factor-α. We compared the quantity score of immunohistochemical staining among the groups. RESULTS: The microscopic colitis group showed significantly higher expression of cyclo-oxygenase-2, interleukin-17, nuclear factor-κB, and interferon-γ compared with the control group. Cytokine expression was similar between collagenous colitis and lymphocytic colitis. However, the expression of cyclo-oxygenase-2 was higher in collagenous colitis. CONCLUSIONS: Proinflammatory cytokines, including interleukin-17 and interferon-γ, are highly expressed in microscopic colitis. The expression of cyclo-oxygenase-2 was higher in collagenous colitis than in lymphocytic colitis. This study is the first on interleukin-17 expression in microscopic colitis patients.

Cytokine Expression of Microscopic Colitis Including Interleukin-17

BACKGROUND/AIMS: Microscopic colitis is characterized by chronic watery diarrhea with specific pathological changes that can be diagnosed by microscopic examination. We performed immunohistochemical analysis of proinflammatory cytokines to investigate the pathogenic mechanism of microscopic colitis. METHODS: This study consisted of six patients with lymphocytic colitis, six patients with collagenous colitis, and six patients with functional diarrhea but normal pathology. We performed an immunohistochemical analysis of the colonic mucosal biopsies to assess the expression of cyclo-oxygenase-2, interleukin-17, nuclear factor-kappaB, interferon-gamma, inducible nitric oxide synthase, and tumor necrosis factor-alpha. We compared the quantity score of immunohistochemical staining among the groups. RESULTS: The microscopic colitis group showed significantly higher expression of cyclo-oxygenase-2, interleukin-17, nuclear factor-kappaB, and interferon-gamma compared with the control group. Cytokine expression was similar between collagenous colitis and lymphocytic colitis. However, the expression of cyclo-oxygenase-2 was higher in collagenous colitis. CONCLUSIONS: Proinflammatory cytokines, including interleukin-17 and interferon-gamma, are highly expressed in microscopic colitis. The expression of cyclo-oxygenase-2 was higher in collagenous colitis than in lymphocytic colitis. This study is the first on interleukin-17 expression in microscopic colitis patients.

Differential expression of miR-31 between inflammatory bowel disease and microscopic colitis.

BACKGROUND: Idiopathic inflammatory bowel disease (IBD) and microscopic colitis (MC) are distinct entities. However, patients with intermittent episodes of IBD and MC that are encountered in a clinical setting puzzle clinicians and pathologists. This study examined whether microRNA assisted in the classification of IBD and MC. DESIGN: Small RNA was extracted from formalin-fixed, paraffin-embedded (FFPE) colon tissue and qRT-PCR was performed from cohorts of normal control (n=38), ulcerative colitis (n=36), Crohns disease (n=26), collagenous colitis (n=36), lymphocytic colitis (n=30), and patients with intermittent features of IBD and MC (n=6). RESULTS: Differential expression of miR-31 distinguished IBD (ulcerative colitis and Crohns disease) from MC (collagenous colitis and lymphocytic colitis), confirming the specificity of miR-31 expression in IBD (P=0.00001). In addition, expression of miR-31 was increased in collagenous colitis compared to that of lymphocytic colitis (P=0.010). Among 6 patients with alternating episodes of IBD and MC, one patient had matching miR-31 expression in different phases (lymphocytic colitis to ulcerative colitis, and then back to collagenous colitis). The other 5 patients had MC-like expression patterns in both MC and IBD episodes. CONCLUSION: In summary, IBD and MC have distinct miR-31 expression pattern. Therefore, miR-31 might be used as a biomarker to distinguish between IBD and MC in FFPE colonic tissue. In addition, miR-31 is differentially expressed in colonic tissue between lymphocytic colitis and collagenous colitis, suggesting them of separate disease processes. Finally, patients with alternating IBD and MC episodes represent a diverse group. Among them, the majority demonstrates MC-like miR-31 expression pattern in MC phases, which seems unlikely to support the speculation of MC as an inactive form of IBD. Although the mechanisms deserve further investigation, microRNA is a potentially useful biomarker to differentiate IBD and MC.

Urine sugars for in vivo gut permeability: validation and comparisons in irritable bowel syndrome-diarrhea and controls.

Mucosal barrier dysfunction contributes to gastrointestinal diseases. Our aims were to validate urine sugar excretion as an in vivo test of small bowel (SB) and colonic permeability and to compare permeability in patients with irritable bowel syndrome-diarrhea (IBS-D) to positive and negative controls. Oral lactulose (L) and mannitol (M) were administered with (99m)Tc-oral solution, (111)In-oral delayed-release capsule, or directly into the ascending colon (only in healthy controls). We compared L and M excretion in urine collections at specific times in 12 patients with IBS-D, 12 healthy controls, and 10 patients with inactive or treated ulcerative or microscopic colitis (UC/MC). Sugars were measured by high-performance liquid chromatography-tandem mass spectrometry. Primary endpoints were cumulative 0-2-h, 2-8-h, and 8-24-h urinary sugars. Radioisotopes in the colon at 2 h and 8 h were measured by scintigraphy. Kruskal-Wallis and Wilcoxon tests were used to assess the overall and pairwise associations, respectively, between group and urinary sugars. The liquid in the colon at 2 h and 8 h was as follows: health, 62 ± 9% and 89 ± 3%; IBS-D, 56 ± 11% and 90 ± 3%; and UC/MC, 35 ± 8% and 78 ± 6%, respectively. Liquid formulation was associated with higher M excretion compared with capsule formulation at 0-2 h (health P = 0.049; IBS-D P < 0.001) but not during 8-24 h. UC/MC was associated with increased urine L and M excretion compared with health (but not to IBS-D) at 8-24 h, not at 0-2 h. There were significant differences between IBS-D and health in urine M excretion at 0-2 h and 2-8 h and L excretion at 8-24 h. Urine sugars at 0-2 h and 8-24 h reflect SB and colonic permeability, respectively. IBS-D is associated with increased SB and colonic mucosal permeability.

Microscopic colitis with giant cells: a clinico-pathological review of 11 cases and comparison with microscopic colitis without giant cells.

AIM: To document clinical and pathological features of microscopic colitis with giant cells (MCGC) which is one of a number of atypical variants of microscopic colitis. METHODS: Cases of microscopic colitis were assessed for giant cells during routine reporting and retrieved from the slide file at a private laboratory. The histological features and clinical data were assessed. Histochemistry (trichome and haematoxylin van Gieson) and immunohistochemistry (CD68) was performed to characterise the nature of the giant cells. RESULTS: Giant cells were identified in 11 cases of microscopic colitis. The histological features of MCGC are not significantly different from usual MC except for the presence of multinucleated giant cells in the superficial lamina propria. Apart from the common but not unexpected association with autoimmune disease, no unique clinical features of the MCGC group were identified versus those described in the literature for ordinary MC. Immune disorders included gluten-sensitive enteropathy, systemic lupus erythematosus and raised titres of antinuclear antibodies. CONCLUSIONS: The giant cells have the same immunohistochemical characteristics as histiocytes and appear to form through histiocyte fusion. The presence of giant cells does not appear to confer any further clinical significance and remains a histological curiosity.

Reduced CD1d expression in colonic epithelium in microscopic colitis.

CD1d is a member of a major histocompatibility complex class I-like molecule family. Its function may involve presenting microbial nonpeptide or lipidic antigens to T lymphocytes, therefore to serve as an important factor in normal mucosal immunity of the gastrointestinal tract. In this study, the expression level of CD1d in microscopic colitis (ie, collagenous and lymphocytic colitis) was examined, and compared with that in normal colonic mucosa. Formalin-fixed, paraffin-embedded colon biopsies with diagnosis of lymphocytic colitis (19 cases), collagenous colitis (6 cases), and no pathologic change (20 cases) were studied immunohistochemically using monoclonal antibodies against human CD1d, CD3, CD4, and CD8. CD1d staining in the epithelium and lamina propria was graded along a scale of 0 to 4. Intraepithelial CD3-positive lymphocytes were counted in an area of 300 epithelial cells for each specimen. The results show that CD1d was expressed in normal colonic epithelial cells, primarily on the basolateral membranes with a concentrated intracellular pool in the subnuclear region. The expression level was markedly reduced in both lymphocytic colitis (P<0.001) and collagenous colitis (P<0.001), along with a significant increase in the number of intraepithelial CD3/CD8 lymphocytes (P<0.001). These findings suggest that microscopic colitis is associated with decreased epithelial expression of CD1d, an important immunoregulatory molecule in the gastrointestinal tract.

Expression of inducible nitric oxide synthase and effects of L-arginine on colonic nitric oxide production and fluid transport in patients with "minimal colitis".

OBJECTIVE: Some patients with idiopathic, chronic diarrhoea have minimal, non-specific colonic inflammation. As nitric oxide (NO) acts as a secretagogue in the colon, we studied the expression of inducible NO synthase (iNOS) in mucosal biopsies and the effects of NOS stimulation on colonic transfer of fluid and output of NO in patients with "minimal colitis". MATERIAL AND METHODS: Twelve patients with idiopathic, chronic diarrhoea and "minimal colitis" and 6 healthy volunteers were included in the study. Expression of iNOS in colonic mucosal biopsies was quantified by Western blot analysis and localized by immunohistochemistry. The effects of topical L-arginine or placebo on colonic net fluid transfer and nitrite/nitrate (NOx) output were assessed during "steady state" perfusion of the whole colon. Concentrations of NOx were measured by Griess' assay. RESULTS: The expression of iNOS was increased 10-fold (p<0.01) in patients with "minimal colitis" compared with that in healthy volunteers and localized to the colonic epithelium. Colonic absorption of fluid was impaired (mean (SEM) 1.5 (0.2) versus 3.0 (0.2) ml/min, p<0.001) and the output of NOx was increased (47 (4) nmol/min versus <37 nmol/min, p<0.05) in patients with "minimal colitis" compared with that in healthy volunteers. Luminal L-arginine (20 mM) reduced colonic absorption of fluid in both groups (95% confidence intervals (CIs) 21-50% in patients with "minimal colitis" versus 4-18% in healthy volunteers), but an increase in NOx output was detectable only in the group of patients (8-106%). In time control experiments, colonic net transfer rates of fluid and outputs of NOx were unaffected by placebo. CONCLUSIONS: In patients with idiopathic, chronic diarrhoea and histopathological evidence of "minimal colitis", colonic absorption of fluid is impaired, while epithelial expression of iNOS and mucosal production of NO is enhanced. It could be speculated that NO in excess contributes to the diarrhoea observed in "minimal colitis".