Immunopathogenesis of IBD: current state of the art

IBD is a chronic inflammatory condition of the gastrointestinal tract encompassing two main clinical entities: Crohn's disease and ulcerative colitis. Although Crohn's disease and ulcerative colitis have historically been studied together because they share common features (such as symptoms, structural damage and therapy), it is now clear that they represent two distinct pathophysiological entities. Both Crohn's disease and ulcerative colitis are associated with multiple pathogenic factors including environmental changes, an array of susceptibility gene variants, a qualitatively and quantitatively abnormal gut microbiota and a broadly dysregulated immune response. In spite of this realization and the identification of seemingly pertinent environmental, genetic, microbial and immune factors, a full understanding of IBD pathogenesis is still out of reach and, consequently, treatment is far from optimal. An important reason for this unsatisfactory situation is the currently limited comprehension of what are the truly relevant components of IBD immunopathogenesis. This article will comprehensively review current knowledge of the classic immune components and will expand the concept of IBD immunopathogenesis to include various cells, mediators and pathways that have not been traditionally associated with disease mechanisms, but that profoundly affect the overall intestinal inflammatory process.

The IBD interactome: an integrated view of aetiology, pathogenesis and therapy

Crohn's disease and ulcerative colitis are prototypical complex diseases characterized by chronic and heterogeneous manifestations, induced by interacting environmental, genomic, microbial and immunological factors. These interactions result in an overwhelming complexity that cannot be tackled by studying the totality of each pathological component (an '-ome') in isolation without consideration of the interaction among all relevant -omes that yield an overall 'network effect'. The outcome of this effect is the 'IBD interactome', defined as a disease network in which dysregulation of individual -omes causes intestinal inflammation mediated by dysfunctional molecular modules. To define the IBD interactome, new concepts and tools are needed to implement a systems approach; an unbiased data-driven integration strategy that reveals key players of the system, pinpoints the central drivers of inflammation and enables development of targeted therapies. Powerful bioinformatics tools able to query and integrate multiple -omes are available, enabling the integration of genomic, epigenomic, transcriptomic, proteomic, metabolomic and microbiome information to build a comprehensive molecular map of IBD. This approach will enable identification of IBD molecular subtypes, correlations with clinical phenotypes and elucidation of the central hubs of the IBD interactome that will aid discovery of compounds that can specifically target the hubs that control the disease.

Expression of lymphocyte-endothelial receptor-ligand pairs, alpha4beta7/MAdCAM-1 and OX40/OX40 ligand in the colon and jejunum of patients with inflammatory bowel disease

BACKGROUND

The interaction between leucocytes and vascular endothelial cells is essential for leucocyte migration into inflammatory sites.

AIMS

To study the local expression of the pairs of complementary molecules, alpha4beta7/mucosal addressin cell adhesion molecule (MAdCAM-1) and OX40/OX40 ligand in the lamina propria of the colon and jejunum of patients with inflammatory bowel disease.

METHODS

Ten patients with active ulcerative colitis (UC), nine with active Crohn's disease (CD), and seven irritable bowel syndrome (IBS) controls were submitted to endoscopic and peroral jejunal biopsies. Specimens were immunostained by indirect alkaline phosphatase using antibodies against CD3, intercellular adhesion molecule (ICAM) 1, alpha4beta7, MAdCAM-1, and OX40. An OX40-mouse-IgG fusion protein was used to detect OX40 ligand on frozen sections. Immunohistological analysis was carried out by optical microscopy using a computer assisted image analyser.

RESULTS

Colonic lamina propria of patients with CD and UC showed increased density of CD3+, alpha4beta7+, and OX40+ cells compared with IBS controls. ICAM-1, MAdCAM-1, and OX40 ligand positive vessels were also increased compared with IBS controls. No significant difference was found in the density of any of these cells in the jejunal mucosa of patients compared with IBS controls.

CONCLUSIONS

The expression of MAdCAM-1 and OX40 ligand on gut endothelial and OX40+ cells is increased in sites of mucosal inflammation in patients with inflammatory bowel disease. No evidence was found for increased lamina propria T cells or increased vascular adhesion molecule expression in the proximal intestine of patients with distal inflammatory bowel disease.

Dysbiosis in Inflammatory Bowel Disease: Pathogenic Role and Potential Therapeutic Targets

Microbe-host communication is essential to maintain vital functions of a healthy host, and its disruption has been associated with several diseases, including Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD). Although individual members of the intestinal microbiota have been associated with experimental IBD, identifying microorganisms that affect disease susceptibility and phenotypes in humans remains a considerable challenge. Currently, the lack of a definition between what is healthy and what is a dysbiotic gut microbiome limits research. Nevertheless, although clear proof-of-concept of causality is still lacking, there is an increasingly evident need to understand the microbial basis of IBD at the microbial strain, genomic, epigenomic, and functional levels and in specific clinical contexts. Recent information on the role of diet and novel environmental risk factors affecting the gut microbiome has direct implications for the immune response that impacts the development of IBD. The complexity of IBD pathogenesis, involving multiple distinct elements, suggests the need for an integrative approach, likely utilizing computational modeling of molecular datasets to identify more specific therapeutic targets.

Oxidative stress fuels Trypanosoma cruzi infection in mice

Oxidative damage contributes to microbe elimination during macrophage respiratory burst. Nuclear factor, erythroid-derived 2, like 2 (NRF2) orchestrates antioxidant defenses, including the expression of heme-oxygenase-1 (HO-1). Unexpectedly, the activation of NRF2 and HO-1 reduces infection by a number of pathogens, although the mechanism responsible for this effect is largely unknown. We studied Trypanosoma cruzi infection in mice in which NRF2/HO-1 was induced with cobalt protoporphyrin (CoPP). CoPP reduced parasitemia and tissue parasitism, while an inhibitor of HO-1 activity increased T. cruzi parasitemia in blood. CoPP-induced effects did not depend on the adaptive immunity, nor were parasites directly targeted. We also found that CoPP reduced macrophage parasitism, which depended on NRF2 expression but not on classical mechanisms such as apoptosis of infected cells, induction of type I IFN, or NO. We found that exogenous expression of NRF2 or HO-1 also reduced macrophage parasitism. Several antioxidants, including NRF2 activators, reduced macrophage parasite burden, while pro-oxidants promoted it. Reducing the intracellular labile iron pool decreased parasitism, and antioxidants increased the expression of ferritin and ferroportin in infected macrophages. Ferrous sulfate reversed the CoPP-induced decrease in macrophage parasite burden and, given in vivo, reversed their protective effects. Our results indicate that oxidative stress contributes to parasite persistence in host tissues and open a new avenue for the development of anti-T. cruzi drugs.

Diet and microbiota in inflammatory bowel disease: The gut in disharmony

Bacterial colonization of the gut shapes both the local and the systemic immune response and is implicated in the modulation of immunity in both healthy and disease states. Recently, quantitative and qualitative changes in the composition of the gut microbiota have been detected in Crohn's disease and ulcerative colitis, reinforcing the hypothesis of dysbiosis as a relevant mechanism underlying inflammatory bowel disease (IBD) pathogenesis. Humans and microbes have co-existed and co-evolved for a long time in a mutually beneficial symbiotic association essential for maintaining homeostasis. However, the microbiome is dynamic, changing with age and in response to environmental modifications. Among such environmental factors, food and alimentary habits, progressively altered in modern societies, appear to be critical modulators of the microbiota, contributing to or co-participating in dysbiosis. In addition, food constituents such as micronutrients are important regulators of mucosal immunity, with direct or indirect effects on the gut microbiota. Moreover, food constituents have recently been shown to modulate epigenetic mechanisms, which can result in increased risk for the development and progression of IBD. Therefore, it is likely that a better understanding of the role of different food components in intestinal homeostasis and the resident microbiota will be essential for unravelling the complex molecular basis of the epigenetic, genetic and environment interactions underlying IBD pathogenesis as well as for offering dietary interventions with minimal side effects.

Intraperitoneal but not intravenous cryopreserved mesenchymal stromal cells home to the inflamed colon and ameliorate experimental colitis

BACKGROUND AND AIMS

Mesenchymal stromal cells (MSCs) were shown to have immunomodulatory activity and have been applied for treating immune-mediated disorders. We compared the homing and therapeutic action of cryopreserved subcutaneous adipose tissue (AT-MSCs) and bone marrow-derived mesenchymal stromal cells (BM-MSCs) in rats with trinitrobenzene sulfonic acid (TNBS)-induced colitis.

METHODS

After colonoscopic detection of inflammation AT-MSCs or BM-MSCs were injected intraperitoneally. Colonoscopic and histologic scores were obtained. Density of collagen fibres and apoptotic rates were evaluated. Cytokine levels were measured in supernatants of colon explants. For cell migration studies MSCs and skin fibroblasts were labelled with Tc-99m or CM-DiI and injected intraperitonealy or intravenously.

RESULTS

Intraperitoneal injection of AT-MSCs or BM-MSCs reduced the endoscopic and histopathologic severity of colitis, the collagen deposition, and the epithelial apoptosis. Levels of TNF-α and interleukin-1β decreased, while VEGF and TGF-β did not change following cell-therapy. Scintigraphy showed that MSCs migrated towards the inflamed colon and the uptake increased from 0.5 to 24 h. Tc-99m-MSCs injected intravenously distributed into various organs, but not the colon. Cm-DiI-positive MSCs were detected throughout the colon wall 72 h after inoculation, predominantly in the submucosa and muscular layer of inflamed areas.

CONCLUSIONS

Intraperitoneally injected cryopreserved MSCs home to and engraft into the inflamed colon and ameliorate TNBS-colitis.

Sulfate-reducing bacteria stimulate gut immune responses and contribute to inflammation in experimental colitis

The intestinal microbiota is critical for mammalian immune system development and homeostasis. Sulfate-reducing bacteria (SRB) are part of the normal gut microbiota, but their increased levels may contribute to colitis development, likely in association with hydrogen sulfide (H2S) production. Here, we investigated the effects of SRB in the gut immune response in germ-free mice, and in experimental colitis. After 7days of colonization with Desulfovibrio indonesiensis or with a human SRB consortium (from patients with colitis), germ-free mice exhibited alterations in the colonic architecture, with increased cell infiltration in the lamina propria. SRB colonization upregulated the Th17 and Treg profiles of cytokine production/cell activation, in T cells from mesenteric lymph nodes. These alterations were more pronounced in mice colonized with the human SRB consortium, although D. indonesiensis colonization produced higher levels of H2S. Importantly, the colon of C57BL/6 mice with colitis induced by TNBS or oxazolone had increased SRB colonization, and the administration of D. indonesiensis to mice with TNBS-induced colitis clearly exacerbated the alterations in colonic architecture observed in the established disease, and also increased mouse weight loss. We conclude that SRB contribute to immune response activation in the gut and play an important role in colitis development.

Cell death and inflammatory bowel diseases: apoptosis, necrosis, and autophagy in the intestinal epithelium

Cell death mechanisms have been associated with the development of inflammatory bowel diseases in humans and mice. Recent studies suggested that a complex crosstalk between autophagy/apoptosis, microbe sensing, and enhanced endoplasmic reticulum stress in the epithelium could play a critical role in these diseases. In addition, necroptosis, a relatively novel programmed necrosis-like pathway associated with TNF receptor activation, seems to be also present in the pathogenesis of Crohn's disease and in specific animal models for intestinal inflammation. This review attempts to cover new data related to cell death mechanisms and inflammatory bowel diseases.

Apoptosis in the intestinal mucosa of patients with inflammatory bowel disease: evidence of altered expression of FasL and perforin cytotoxic pathways

BACKGROUND AND AIMS

Abnormal apoptosis may result in the persistence of activated intestinal T-cells in inflammatory bowel disease (IBD). We investigated apoptosis in distinct mucosal compartments, and the expression of Fas/Fas ligand and perforin in the inflamed and non-inflamed intestinal mucosa of patients with IBD.

METHODS

Colon specimens from 15 patients with ulcerative colitis (UC) and inflamed and non-inflamed mucosa from 15 patients with Crohn's disease (CD) were analysed for densities and distribution of apoptotic cells determined by the terminal deoxynucleotidyltransferase-mediated dUDP-biotin nick-end labelling (TUNEL) method. Fas, FasL, and perforin-expressing cells were assessed by immunoperoxidase, and with anti-CD3, anti-CD20 and anti-CD68, by double immunofluorescence with confocal microscopy. Quantitative analysis was performed using a computer-assisted image analyser.

RESULTS

Colonic lamina propria (LP) and epithelium from patients with UC showed higher rates of apoptosis than controls, but no difference was shown regarding patients with CD. In LP, co-expression of Fas was reduced with T-cells in inflamed CD mucosa, and with macrophages in all patients with IBD. No difference was found in the expression of Fas on B-cells. Rates of FasL-expressing cells in LP were higher in IBD than in controls, with no correlation with the rates of apoptosis. Rates of perforin-expressing cells in LP were greater in UC than in controls, and correlated to the rates of apoptosis. No difference was shown regarding the inflamed and non-inflamed CD mucosa. Rates of FasL and perforin-expressing intra-epithelial lymphocytes showed no difference among groups.

CONCLUSIONS

Increased expression of FasL in IBD colonic LP not parallelled by Fas on T-cells and macrophages may indicate a reduced susceptibility to the Fas/FasL-mediated apoptosis of lymphoid cells. Expression of perforin is correlated to the tissue damage, and may represent the enhancement of a distinct cytotoxic pathway in UC.

Overexpression of ATP-activated P2X7 receptors in the intestinal mucosa is implicated in the pathogenesis of Crohn's disease

BACKGROUND

Extracellular nucleotides released in conditions of cell stress alert the immune system from tissue injury or inflammation. We hypothesized that the P2X7 receptor (P2X7-R) could regulate key elements in inflammatory bowel disease pathogenesis.

METHODS

Colonoscopy samples obtained from patients with Crohn's disease (CD), ulcerative colitis, and controls were used to analyze P2X7-R expression by RT and real-time PCR, immunohistochemistry, and confocal microscopy. Inflammatory response was determined by the levels of cytokines by enzyme-linked immunosorbent assay in cultures of intestinal explants. Apoptosis was determined by the TUNEL assay. P2X7-R C57BL/6 mice were treated with trinitrobenzene sulfonic acid or dextran sulfate sodium (DSS) for inducing colitis.

RESULTS

P2X7-R was expressed in higher levels in inflamed CD epithelium and lamina propria, where it colocalizes more with dendritic cells and macrophages. Basal levels of P2X7-R mRNA were higher in CD inflamed mucosa compared with noninflamed CD and controls and were upregulated after interferon-γ in controls. Apoptotic rates were higher in CD epithelium and lamina propria compared with ulcerative colitis and controls. Levels of tumor necrosis factor-α, interleukin (IL)-1β, and IL-17 were higher, whereas IL-10 was lower in CD compared with controls. Levels of tumor necrosis factor-α-α and interleukin-1β increased after adenosine-triphosphate and decreased after KN62 treatment in CD. P2X7-R animals did not develop trinitrobenzene sulfonic acid or DSS colitis.

CONCLUSIONS

The upregulation of P2X7-R in CD inflamed mucosa is consistent with the involvement of purinoceptors in inflammation and apoptosis. These observations may implicate purinergic signaling in the pathogenesis of intestinal inflammation, and the P2X7-R may represent a novel therapeutic target in CD.

Immunohistochemical study of intestinal eosinophils in inflammatory bowel disease

BACKGROUND

Eosinophil accumulation and activation are characteristic features of inflammation in allergic diseases and in host defense against parasites.

GOALS

To investigate the involvement of eosinophils in inflamed and noninflamed mucosa of patients with inflammatory bowel disease (IBD).

STUDY

Specimens of inflamed colonic mucosa from 15 patients with ulcerative colitis (UC) and inflamed and noninflamed colonic mucosa from 15 patients with Crohn's disease (CD) were submitted to histologic and immunohistochemical studies. Twelve patients with irritable bowel syndrome were studied as controls. Sirius red was used to label eosinophils in tissue. EG1, EG2, and anti-hIL-5 were used as primary antibodies in an indirect alkaline phosphatase-labeled immunostaining protocol. Both positive and negative lamina propria cells were assessed by a quantitative grading system and the results expressed as cell numbers per mm.

RESULTS

Increased proportions of eosinophils stained with Sirius red, EG1, EG2, and anti-hIL-5+ cells were found in the colon of patients with UC and in inflamed and noninflamed colon of CD patients as compared with controls. Crohn's disease patients showed increased proportions of EG1+ and EG2+ cells as compared with those with UC. Increased proportions of IL-5+ cells were detected in UC patients as compared with those with CD.

CONCLUSION

Quantitative eosinophil alterations and IL-5+ cells may indicate enhanced cellular activation with degranulation, which is implicated in the pathogenesis of IBD. Increase in IL-5+ cells may reflect a predominant local Th2 response in UC as compared with CD.

IL-13Rα2-bearing, type II NKT cells reactive to sulfatide self-antigen populate the mucosa of ulcerative colitis

OBJECTIVE

Previous studies have shown that ulcerative colitis (UC) is associated with the presence of lamina propria non-invariant (Type II) NKT cells producing IL-13 and mediating epithelial cell cytotoxicity. Here we sought to define the antigen(s) stimulating the NKT cells and to quantitate these cells in the UC lamina propria.

DESIGN

Detection of Type II NKT cells in UC lamina propria mononuclear cells (LPMC) with lyso-sulfatide loaded tetramer and quantum dot-based flow cytometry and staining. Culture of UC LPMCs with lyso-sulfatide glycolipid to determine sulfatide induction of epithelial cell cytotoxicity, IL-13 production and IL-13Rα2 expression. Blinded quantum dot-based phenotypic analysis to assess UC LPMC expression of IL-13Rα2, CD161 and IL-13.

RESULTS

Approximately 36% of UC LPMC were lyso-sulfatide tetramer positive, whereas few, if any, control LPMCs were positive. When tested, the positive cells were also CD3 and IL-13Rα2 positive. Culture of UC LPMC with lyso-sulfatide glycolipid showed that sulfatide stimulates UC LPMC production of IL-13 and induces UC CD161 LPMC-mediated cytotoxicity of activated epithelial cells; additionally, lyso-sulfatide induces enhanced expression of IL-13Rα2. Finally, blinded phenotypic analysis of UC LP MC using multicolour quantum dot-staining technology showed that approximately 60% of the LPMC bear both IL-13Rα2 and CD161 and most of these cells also produce IL-13.

CONCLUSIONS

These studies show that UC lamina propria is replete with Type II NKT cells responsive to lyso-sulfatide glycolipid and bearing IL-13Rα2. Since lyso-sulfatide is a self-antigen, these data suggest that an autoimmune response is involved in UC pathogenesis.

Prophylactic systemic P2X7 receptor blockade prevents experimental colitis

BACKGROUND

The P2X7 receptor (P2X7-R) is a non-selective adenosine triphosphate-gated cation channel present in epithelial and immune cells, and involved in inflammatory response. Extracellular nucleotides released in conditions of cell stress or inflammation may function as a danger signal alerting the immune system from inflammation. We investigated the therapeutic action of P2X7-R blockade in a model of inflammatory bowel disease.

METHODS

Rats with trinitrobenzene sulfonic (TNBS) acid-induced colitis were treated with the P2X7-R antagonists A740003 or brilliant blue G (BBG) through intra-peritoneal (IP) or intra-colonic (IC) injection prior to colitis induction. Clinical and endoscopic follow-up, histological scores, myeloperoxidase activity, densities of collagen fibers and goblet cells were evaluated. P2X7-R expression, NF-kappa B and Erk activities, and densities of T-cells and macrophages were analyzed by immunoperoxidase. The inflammatory response was determined by measuring inflammatory cytokines in cultures of colon explants, by enzyme-linked immunosorbent assay. Colonic apoptosis was determined by the TUNEL assay.

RESULTS

IP-BBG significantly attenuated the severity of colitis, myeloperoxidase activity, collagen deposition, densities of lamina propria T-cells and macrophages, while maintaining goblet cell densities. IP-BBG inhibited the increase in P2X7-R expression in parallel with apoptotic rates. TNF-α and interleukin-1β stabilized in low levels, while TGF-β and interleukin-10 did not change following IP-BBG-therapy. Colonic NF-kappa-B and Erk activation were significantly lower in IP-BBG-treated animals. Prophylactic IP-A740003 also protected rats against the development of TNBS-colitis.

CONCLUSIONS

Prophylactic systemic P2X7-R blockade is effective in the prevention of experimental colitis, probably due to a systemic anti-inflammatory action, interfering with a stress-inflammation amplification loop mediated by P2X7-R.

Enhanced recruitment of CX3CR1+ T cells by mucosal endothelial cell-derived fractalkine in inflammatory bowel disease

BACKGROUND & AIMS

Fractalkine (FKN/CX3CL1) is a unique chemokine combining adhesive and chemotactic properties. We investigated FKN production by the mucosal microvasculature in inflammatory bowel disease (IBD), its capacity for leukocyte recruitment into the gut, and the number of CX3CR1+ cells in the circulation and mucosa of IBD patients.

METHODS

The expression of FKN by human intestinal microvascular endothelial cells (HIMECs) and CX3CR1 by circulating cells was evaluated by flow cytometry, and mucosal CX3CR1+ cells were enumerated by immunohistochemistry. The capacity of FKN to mediate leukocyte binding to HIMECs was assessed by immunoblockade, and to induce HIMEC transmigration by a Transwell system.

RESULTS

The spontaneously low HIMEC FKN expression was enhanced markedly by tumor necrosis factor-alpha plus interferon-gamma stimulation, or direct leukocyte contact. This effect was significantly stronger in IBD than control HIMECs. Up-regulation of HIMEC FKN expression was dependent on p38 and extracellular signal-regulated kinase phosphorylation, as was abrogated by selective mitogen-activated protein kinase inhibitors. Circulating T cells contained significantly higher numbers of CX3CR1+ cells in active IBD than inactive IBD or healthy subjects, and IBD mucosa contained significantly more CX3CR1+ cells than control mucosa. Antibody-blocking experiments showed that FKN was a major contributor to T- and monocytic-cell adhesion to HIMECs. Finally, FKN enhanced the expression of active beta1 integrin on leukocytes and mediated leukocyte HIMEC transmigration.

CONCLUSIONS

In view of the capacity of FKN to mediate leukocyte adhesion, chemoattraction, and transmigration, its increased production by mucosal microvascular cells and increased numbers of circulating and mucosal CX3CR1+ cells in IBD point to a significant role of FKN in disease pathogenesis.

Extracellular ATP induces cell death in human intestinal epithelial cells

BACKGROUND

Extracellular ATP is an endogenous signaling molecule released by various cell types and under different stimuli. High concentrations of ATP released into the extracellular medium activate the P2X7 receptor in most inflammatory conditions. Here, we seek to characterize the effects of ATP in human intestinal epithelial cells and to evaluate morphological changes in these cells in the presence of ATP.

METHODS

We treated human intestinal epithelial cells with ATP and evaluated the effects of this nucleotide by scanning and transmission electron microscopy analysis and calcium measurements. We used flow cytometry to evaluate apoptosis. We collected human intestinal explants for immunohistochemistry, apoptosis by the TUNEL approach and caspase-3 activity using flow cytometry analyses. We also evaluated the ROS production by flow cytometry and NO secretion by the Griess technique.

RESULTS

ATP treatment induced changes characteristic of cell death by apoptosis and autophagy but not necrosis in the HCT8 cell line. ATP induced apoptosis in human intestinal explants that showed TUNEL-positive cells in the epithelium and in the lamina propria. The explants exhibited a significant increase of caspase-3 activity when the colonic epithelial cells were incubated with IFN-gamma followed by ATP as compared to control cells. In addition, it was found that antioxidants were able to inhibit both the ROS production and the apoptosis induced by ATP in epithelial cells.

GENERAL SIGNIFICANCE

The activation of P2X7 receptors by ATP induces apoptosis and autophagy in human epithelial cells, possibly via ROS production, and this effect might have implications for gut inflammatory conditions.

The Rise of Gastrointestinal Cancers as a Global Phenomenon: Unhealthy Behavior or Progress?

The overall burden of cancer is rapidly increasing worldwide, reflecting not only population growth and aging, but also the prevalence and spread of risk factors. Gastrointestinal (GI) cancers, including stomach, liver, esophageal, pancreatic, and colorectal cancers, represent more than a quarter of all cancers. While smoking and alcohol use are the risk factors most commonly associated with cancer development, a growing consensus also includes dietary habits as relevant risk factors for GI cancers. Current evidence suggests that socioeconomic development results in several lifestyle modifications, including shifts in dietary habits from local traditional diets to less-healthy Western diets. Moreover, recent data indicate that increased production and consumption of processed foods underlies the current pandemics of obesity and related metabolic disorders, which are directly or indirectly associated with the emergence of various chronic noncommunicable conditions and GI cancers. However, environmental changes are not restricted to dietary patterns, and unhealthy behavioral features should be analyzed with a holistic view of lifestyle. In this review, we discussed the epidemiological aspects, gut dysbiosis, and cellular and molecular characteristics of GI cancers and explored the impact of unhealthy behaviors, diet, and physical activity on developing GI cancers in the context of progressive societal changes.

Unfractionated heparin and new heparin analogues from ascidians (chordate-tunicate) ameliorate colitis in rats

The anti-inflammatory effect of mammalian heparin analogues, named dermatan sulfate and heparin, isolated from the ascidian Styela plicata was accessed in a TNBS-induced colitis model in rats. Subcutaneous administration of the invertebrate compounds during a 7-day period drastically reduced inflammation as observed by the normalization of the macroscopic and histological characteristics of the colon. At the molecular level, a decrease in the production of TNF-alpha, TGF-beta, and VEGF was observed, as well as a reduction of NF-kappaB and MAPK kinase activation. At the cellular level, the heparin analogues attenuated lymphocyte and macrophage recruitment and epithelial cell apoptosis. A drastic reduction in collagen-mediated fibrosis was also observed. No hemorrhagic events were observed after glycan treatment. These results strongly indicate the potential therapeutic use of these compounds for the treatment of colonic inflammation with a lower risk of hemorrhage when compared with mammalian heparin.

P2X7 receptor promotes intestinal inflammation in chemically induced colitis and triggers death of mucosal regulatory T cells

P2X7 receptor activation contributes to inflammation development in different pathologies. We previously reported that the P2X7 receptor is over-expressed in the gut mucosa of patients with inflammatory bowel disease, and that P2X7 inhibition protects against chemically induced colitis. Here, we investigated in detail the role of the P2X7 receptor in inflammatory bowel disease development, by treating P2X7 knockout (KO) and WT mice with two different (and established) colitis inductors. P2X7 KO mice were protected against gut inflammation induced by 2,4,6-trinitrobenzenesulfonic acid or oxazolone, with no weight loss or gut histological alterations after treatment. P2X7 receptor knockout induced regulatory T cell accumulation in the colon, as evaluated by qRT-PCR for FoxP3 expression and immunostaining for CD90/CD45RBlow. Flow cytometry analysis of mesenteric lymph node cells showed that P2X7 activation (by ATP) triggered regulatory T cell death. In addition, such cells from P2X7 KO mice expressed more CD103, suggesting increased migration of regulatory T cells to the colon (relative to the WT). Our results show that the P2X7 has a key role during inflammation development in inflammatory bowel disease, by triggering the death and retention in the mesenteric lymph nodes of regulatory T cells that would otherwise promote immune system tolerance in the gut.

Etiopathogenesis of inflammatory bowel disease: today and tomorrow

PURPOSE OF REVIEW

Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD), represent chronic diseases of unknown cause, and they are regarded as prototypical complex diseases. Despite all the recent advances, a complete appreciation of the pathogenesis of IBD is still limited. In this review, we present recent information contributing to a better understanding of mechanisms underlying IBD.

RECENT FINDINGS

Here, we attempt to highlight novel environmental triggers, data on the gut microbiota, its interaction with the host, and the potential influence of diet and food components. We discuss recent findings on defective signaling pathways and the potential effects on the immune response, and we present new data on epigenetic changes, inflammasome, and damage-associated molecular patterns associated with IBD.

SUMMARY

The continuing identification of several epigenetic, transcriptomic, proteomic, and metabolomic alterations in patients with IBD reflects the complex nature of the disease and suggests the need for innovative approaches such as systems biology for identifying novel relevant targets in IBD.

CXCR4 and MIF are required for neutrophil extracellular trap release triggered by Plasmodium-infected erythrocytes

Neutrophil extracellular traps (NETs) evolved as a unique effector mechanism contributing to resistance against infection that can also promote tissue damage in inflammatory conditions. Malaria infection can trigger NET release, but the mechanisms and consequences of NET formation in this context remain poorly characterized. Here we show that patients suffering from severe malaria had increased amounts of circulating DNA and increased neutrophil elastase (NE) levels in plasma. We used cultured erythrocytes and isolated human neutrophils to show that Plasmodium-infected red blood cells release macrophage migration inhibitory factor (MIF), which in turn caused NET formation by neutrophils in a mechanism dependent on the C-X-C chemokine receptor type 4 (CXCR4). NET production was dependent on histone citrullination by peptidyl arginine deiminase-4 (PAD4) and independent of reactive oxygen species (ROS), myeloperoxidase (MPO) or NE. In vitro, NETs functioned to restrain parasite dissemination in a mechanism dependent on MPO and NE activities. Finally, C57/B6 mice infected with P. berghei ANKA, a well-established model of cerebral malaria, presented high amounts of circulating DNA, while treatment with DNAse increased parasitemia and accelerated mortality, indicating a role for NETs in resistance against Plasmodium infection.

Use of butyrate or glutamine in enema solution reduces inflammation and fibrosis in experimental diversion colitis

AIM

To investigate whether butyrate or glutamine enemas could diminish inflammation in experimental diversion colitis.

METHODS

Wistar specific pathogen-free rats were submitted to a Hartmann's end colostomy and treated with enemas containing glutamine, butyrate, or saline. Enemas were administered twice a week in the excluded segment of the colon from 4 to 12 wk after the surgical procedure. Follow-up colonoscopy was performed every 4 wk for 12 wk. The effect of treatment was evaluated using video-endoscopic and histologic scores and measuring interleukin-1β, tumor necrosis factor-alpha, and transforming growth factor beta production in organ cultures by enzyme linked immunosorbent assay.

RESULTS

Colonoscopies of the diverted segment showed mucosa with hyperemia, increased number of vessels, bleeding and mucus discharge. Treatment with either glutamine or butyrate induced significant reductions in both colonoscopic (P < 0.02) and histological scores (P < 0.01) and restored the densities of collagen fibers in tissue (P = 0.015; P = 0.001), the number of goblet cells (P = 0.021; P = 0.029), and the rate of apoptosis within the epithelium (P = 0.043; P = 0.011) to normal values. The high levels of cytokines in colon explants from rats with diversion colitis significantly decreased to normal values after treatment with butyrate or glutamine.

CONCLUSION

The improvement of experimental diversion colitis following glutamine or butyrate enemas highlights the importance of specific luminal nutrients in the homeostasis of the colonic mucosa and supports their utilization for the treatment of human diversion colitis.

Inflammasome in intestinal inflammation and cancer

The activation of specific cytosolic pathogen recognition receptors, the nucleotide-binding-oligomerization-domain- (NOD-) like receptors (NLRs), leads to the assembly of the inflammasome, a multimeric complex platform that activates caspase-1. The caspase-1 pathway leads to the upregulation of important cytokines from the interleukin (IL)-1 family, IL-1β , and IL-18, with subsequent activation of the innate immune response. In this review, we discuss the molecular structure, the mechanisms behind the inflammasome activation, and its possible role in the pathogenesis of inflammatory bowel diseases and intestinal cancer. Here, we show that the available data points towards the importance of the inflammasome in the innate intestinal immune response, being the complex involved in the maintenance of intestinal homeostasis, correct intestinal barrier function and efficient elimination of invading pathogens.

Mucosal T cell proliferation and apoptosis in inflammatory bowel disease

Both forms of inflammatory bowel disease (IBD), Crohn's disease (CD) and ulcerative colitis (UC), represent prototypical conditions whose most salient features are the presence of chronic inflammation involving various parts of the intestinal tract and an increased risk of cancer, which is a complication directly related to the duration and activity of gut inflammation. Several factors have been implicated in the unrelenting mucosal inflammation of IBD, prominent among them being the presence of a persistently elevated number of activated T cells in the mucosa of CD and UC patients. These T cells display various defects of proliferation and apoptosis, and these abnormalities are credited with directly contributing to the pathogenesis of IBD and possibly the progression to colon cancer. This notion is supported by the observation that T cells are also prominently found infiltrating most tumors and are functionally impaired compared to T cells in the circulation. This establishes a parallel that may constitute a link between chronic intestinal inflammation and the development of malignancies in the inflamed intestine. This article will review some of the basic features of human intestinal mucosal T cells, examine the mechanisms underlying the processes of cell cycling and cell death, describe the defective proliferative and apoptotic function detected in CD and UC, and discuss the implications of modulating T cell apoptosis in IBD for therapeutic purposes and eventually decreasing the risk of cancer development.

The role of innate immunity receptors in the pathogenesis of inflammatory bowel disease

Innate immunity constitutes the first line of defense, fundamental for the recognition and the initiation of an inflammatory response against microorganisms. The innate immune response relies on the sensing of microbial-associated molecular patterns through specialized structures such as toll-like receptors (TLRs) and the nucleotide oligomerization domain- (NOD-) like receptors (NLRs). In the gut, these tasks are performed by the epithelial barrier and the presence of adaptive and innate immune mechanisms. TLRs and NLRs are distributed throughout the gastrointestinal mucosa, being more expressed in the epithelium, and in lamina propria immune and nonimmune cells. These innate immunity receptors exhibit complementary biological functions, with evidence for pathways overlapping. However, as tolerance is the predominant physiological response in the gastrointestinal mucosa, it appears that the TLRs are relatively downregulated, while NLRs play a critical role in mucosal defense in the gut. Over the past two decades, genetic polymorphisms have been associated with several diseases including inflammatory bowel disease. Special emphasis has been given to the susceptibility to Crohn's disease, in association with abnormalities in the NOD2 and in the NLRP3/inflammasome. Nevertheless, the mechanisms underlying innate immune receptors dysfunction that result in the persistent inflammation in inflammatory bowel disease remain to be clarified.