Probiotics in inflammatory bowel disease: Pathophysiological background and clinical applications

Ulcerative colitis and Crohn’s disease, collectively termed the inflammatory bowel diseases (IBD), are chronic inflammatory disorders of the gastrointestinal tract. A “dysbiotic” relationship between the commensal gut flora and the intestinal mucosa-associated immune system has been at the core of the pathogenesis of these conditions. Probiotics are “good bacteria” with the ability to benefit the health of the host and their therapeutic application has been studied in IBD. The theoretical basis for such utilization relies upon the ability of probiotic microorganisms to interfere with the dysregulated homeostasis that takes place in IBD and restore the immune-bacterial interaction at the intestinal mucosa. Proposed mechanisms of action include the reconstitution of altered flora composition, enhancement of the integrity of the epithelial barrier, promotion of tolerogenic action by dendritic cells, strengthening of the defensive mechanisms of the innate immunity, and the suppression of pro-inflammatory adaptive immune responses. Despite this abundance of supporting experimental evidence, clinical application of probiotics in IBD has been disappointing. Possible explanations for such discrepancy include the great diversity of microorganisms that fall under the definition of probiotics, the lack of standardization of dosages and administration schemes, the heterogeneity between clinical trials, and the inclusion in the treatment arms of patients with a large variety of clinical phenotypes. Addressing these important issues will be critical for the optimal usage of probiotic-based therapies for patients with IBD.     

Classical and recent advances in the treatment of inflammatory bowel diseases

Crohn''s disease (CD) and ulcerative colitis (UC) are intestinal disorders that comprise the inflammatory bowel diseases (IBD). These disorders have a significant effect on the quality of life of affected patients and the increasing number of IBD cases worldwide is a growing concern. Because of the overall burden of IBD and its multifactorial etiology, efforts have been made to improve the medical management of these inflammatory conditions. The classical therapeutic strategies aim to control the exacerbated host immune response with aminosalicylates, antibiotics, corticosteroids, thiopurines, methotrexate and anti-tumor necrosis factor (TNF) biological agents. Although successful in the treatment of several CD or UC conditions, these drugs have limited effectiveness, and variable responses may culminate in unpredictable outcomes. The ideal therapy should reduce inflammation without inducing immunosuppression, and remains a challenge to health care personnel. Recently, a number of additional approaches to IBD therapy, such as new target molecules for biological agents and cellular therapy, have shown promising results. A deeper understanding of IBD pathogenesis and the availability of novel therapies are needed to improve therapeutic success. This review describes the overall key features of therapies currently employed in clinical practice as well as novel and future alternative IBD treatment methods.     

The RAGE signaling pathway is involved in intestinal inflammation and represents a promising therapeutic target for Inflammatory Bowel Diseases

Inflammatory Bowel Diseases (IBD) are chronic inflammatory conditions of the intestinal tract. IBD are believed to result from an inappropriate immune response against the intestinal flora in genetically predisposed patients. The precise etiology of these diseases is not fully understood, therefore treatments rely on the dampening of symptoms, essentially inflammation, rather than on the cure of the disease. Despite the availability of biologics, such as anti-TNF antibodies, some patients remain in therapeutic failure and new treatments are thus needed. The multiligand receptor for advanced glycation end-products (RAGE) is a pattern recognition receptor implicated in inflammatory reactions and immune system activation. Here, we investigated the role of RAGE in intestinal inflammation and its potential as a therapeutic target in IBD. We showed that RAGE was upregulated in inflamed tissues from IBD patients compared to controls. Rage^−/− mice were less susceptible to intestinal and colonic inflammation development than WT mice. WT mice treated with the RAGE-specific inhibitor FPS-ZM1 experienced less severe enteritis and colitis. We demonstrated that RAGE could induce intestinal inflammation by promoting oxidative stress and endothelial activation which were diminished by FPS-ZM1 treatment. Our results revealed the RAGE signaling pathway as a promising therapeutic target for IBD patients.     

Association among genetic predisposition,gut microbiota,and host immune response in the etiopathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD), which includes Crohn''s disease (CD) and ulcerative colitis (UC), is a chronic disorder that affects thousands of people around the world. These diseases are characterized by exacerbated uncontrolled intestinal inflammation that leads to poor quality of life in affected patients. Although the exact cause of IBD still remains unknown, compelling evidence suggests that the interplay among immune deregulation, environmental factors, and genetic polymorphisms contributes to the multifactorial nature of the disease. Therefore, in this review we present classical and novel findings regarding IBD etiopathogenesis. Considering the genetic causes of the diseases, alterations in about 100 genes or allelic variants, most of them in components of the immune system, have been related to IBD susceptibility. Dysbiosis of the intestinal microbiota also plays a role in the initiation or perpetuation of gut inflammation, which develops under altered or impaired immune responses. In this context, unbalanced innate and especially adaptive immunity has been considered one of the major contributing factors to IBD development, with the involvement of the Th1, Th2, and Th17 effector population in addition to impaired regulatory responses in CD or UC. Finally, an understanding of the interplay among pathogenic triggers of IBD will improve knowledge about the immunological mechanisms of gut inflammation, thus providing novel tools for IBD control.     

B-cell clonal diversification and gut-lymph node trafficking in ulcerative colitis revealed using lineage tree analysis

In studies of inflammatory bowel diseases (IBD), research has so far focused mainly on the role of T cells. Despite evidence suggesting that B cells and the production of autoantibodies may play a significant role in IBD pathogenesis, the role of B cells in gut inflammation has not yet been thoroughly investigated. In the present study we used the new approach of lineage tree analysis for studying immunoglobulin variable region gene diversification in B cells found in the inflamed intestinal tissue of two ulcerative colitis patients as well as B cells from mucosa-associated lymph nodes (LN) in the same patients. Healthy intestinal tissue of three patients with carcinoma of the colon was used as normal control. Lineage tree shapes revealed active immune clonal diversification processes occurring in ulcerative colitis patients, which were quantitatively similar to those in healthy controls. B cells from intestinal tissues and the associated LN are shown here to be clonally related, thus supplying the first direct evidence supporting B-cell trafficking between gut and associated LN in IBD and control tissues.     

Emerging roles of host and microbial bioactive lipids in inflammatory bowel diseases

The intestinal tract harbors diverse microorganisms, host- and microbiota-derived metabolites, and potentially harmful dietary antigens. The epithelial barrier separates the mucosa, where diverse immune cells exist, from the lumen to avoid excessive immune reactions against microbes and dietary antigens. Inflammatory bowel disease (IBD), such as ulcerative colitis and Crohn's disease, is characterized by a chronic and relapsing disorder of the gastrointestinal tract. Although the precise etiology of IBD is still largely unknown, accumulating evidence suggests that IBD is multifactorial, involving host genetics and microbiota. Alterations in the metabolomic profiles and microbial community are features of IBD. Advances in mass spectrometry–based lipidomic technologies enable the identification of changes in the composition of intestinal lipid species in IBD. Because lipids have a wide range of functions, including signal transduction and cell membrane formation, the dysregulation of lipid metabolism drastically affects the physiology of the host and microorganisms. Therefore, a better understanding of the intimate interactions of intestinal lipids with host cells that are implicated in the pathogenesis of intestinal inflammation might aid in the identification of novel biomarkers and therapeutic targets for IBD. This review summarizes the current knowledge on the mechanisms by which host and microbial lipids control and maintain intestinal health and diseases.     

Endothelial cell autoantibodies are a marker of disease susceptibility in inflammatory bowel disease but apparently not linked to persistent measles virus infection

Intestinal vasculitis caused by persistent measles virus infection of intestinal endothelial cells was described in Crohn's disease. Furthermore, endothelial cell autoantibodies have been demonstrated in inflammatory bowel disease (IBD). Autoantibodies against intestinal endothelial cells were visualized by indirect immunofluorescence in patients with IBD, in their healthy first-degree relatives, in patients with infectious enterocolitis, and in healthy, unrelated controls. In intestinal tissue specimens of 22 antibody-positive IBD patients a search for the measles virus genome was performed. Endothelial cell autoantibodies were significantly more frequent in patients with IBD, in both groups of first-degree relatives, and in patients with infectious enterocolitis than in the healthy controls (P = 0.0002 or less). The measles virus genome was found in none of the intestinal biopsies. Endothelial cell autoantibodies are not a genetic but rather an epigenetic (infectious) marker of disease susceptibility. The expression of these autoantibodies is unlikely to be triggered by a persistent measles virus infection.     

Association between intestinal microbiota and inflammatory bowel disease

Inflammatory bowel disease (IBD), which includes Crohn''s disease (CD) and ulcerative colitis (UC), has emerged as a global disease with high incidence, long duration, devastating clinical symptoms, and low curability (relapsing immune response and barrier function defects). Mounting studies have been performed to investigate its pathogenesis to provide an ever‐expanding arsenal of therapeutic options, while the precise etiology of IBD is not completely understood yet. Recent advances in high‐throughput sequencing methods and animal models have provided new insights into the association between intestinal microbiota and IBD. In general, dysbiosis characterized by an imbalanced microbiota has been widely recognized as a pathology of IBD. However, intestinal microbiota alterations represent the cause or result of IBD process remains unclear. Therefore, more evidences are needed to identify the precise role of intestinal microbiota in the pathogenesis of IBD. Herein, this review aims to outline the current knowledge of commonly used, chemically induced, and infectious mouse models, gut microbiota alteration and how it contributes to IBD, and dysregulated metabolite production links to IBD pathogenesis.     

Guanylin ligand protects the intestinal immune barrier by activating the guanylate cyclase-C signaling pathway

Inflammatory bowel disease (IBD) impacts patient quality of life significantly. The dysfunction of intestinal immune barrier is closely associated with IBD. The guanylate cyclase-C (GC-C) signaling pathway activated by the guanylin (Gn) ligand is involved in the occurrence and development of IBD. However, how it regulates the intestinal immune barrier is still unclear. To investigate the effect of the GC-C pathway on intestinal mucosal immunity and provide experimental basis for seeking new therapeutic strategies for IBD, we focused on Caco-2 cells and intestinal intra-epithelial lymphocytes (IELs), which displayed inflammatory responses induced by lipopolysaccharide (LPS). GC-C activity was modulated by transfection with Gn overexpression or GC-C shRNA plasmid. Levels of Gn, GC-C, and CFTR; transepithelial electrical resistance (TER); paracellula r permeability; and levels of IL-2, IFN-γ, and secretory IgA (sIgA) were examined. The study found that after stimulation with LPS, Gn, GC-C, CFTR, TER, and sIgA levels were all significantly reduced, IL-2 and IFN-γ levels as well as paracellular permeability were significantly increased. These indicators changed inversely and significantly after transfection with the Gn overexpression vector. Compared to the vector controls, GC-C-silenced cells displayed significantly decreased levels of GC-C, CFTR, and TER and increased levels of IL-2, IFN-γ, and paracellular permeability stimulated by LPS. The results show that Gn ligand can protect the intestinal immune barrier by activating the GC-C signaling pathway, which may be helpful for the development of new treatments for IBD.Data availability statementThe data used to support the findings of this study are available from the corresponding author upon request.     

Targeting desmosomal adhesion and signalling for intestinal barrier stabilization in inflammatory bowel diseases—Lessons from experimental models and patients

Inflammatory bowel diseases (IBD) such as Crohn’s disease (CD) and Ulcerative colitis (UC) have a complex and multifactorial pathogenesis which is incompletely understood. A typical feature closely associated with clinical symptoms is impaired intestinal epithelial barrier function. Mounting evidence suggests that desmosomes, which together with tight junctions (TJ) and adherens junctions (AJ) form the intestinal epithelial barrier, play a distinct role in IBD pathogenesis. This is based on the finding that desmoglein (Dsg) 2, a cadherin‐type adhesion molecule of desmosomes, is required for maintenance of intestinal barrier properties both in vitro and in vivo, presumably via Dsg2‐mediated regulation of TJ. Mice deficient for intestinal Dsg2 show increased basal permeability and are highly susceptible to experimental colitis. In several cohorts of IBD patients, intestinal protein levels of Dsg2 are reduced and desmosome ultrastructure is altered suggesting that Dsg2 is involved in IBD pathogenesis. In addition to its adhesive function, Dsg2 contributes to enterocyte cohesion and intestinal barrier function. Dsg2 is also involved in enterocyte proliferation, barrier differentiation and induction of apoptosis, in part by regulation of p38MAPK and EGFR signalling. In IBD, the function of Dsg2 appears to be compromised via p38MAPK activation, which is a critical pathway for regulation of desmosomes and is associated with keratin phosphorylation in IBD patients. In this review, the current findings on the role of Dsg2 as a novel promising target to prevent loss of intestinal barrier function in IBD patients are discussed.     

Bispecific antibodies: The next generation of targeted inflammatory bowel disease therapies

Targeting various disease pathways using monoclonal antibodies (mAbs) has transformed the treatment paradigm for inflammatory bowel disease (IBD), with these agents exhibiting improved efficacy over corticosteroids or immunosuppressive therapies. Antibodies targeting tumor necrosis factor α (TNF-α) were the first approved biologics for IBD, followed by the more recent approval of antibodies targeting the α4β7 integrin heterodimer and ustekinumab, which targets the p40 subunit of interleukin-23. Current efforts are focused on the development of additional biologics targeting these known and other newly discovered pathways. Still significant unmet needs remain, as a large proportion of patients either fail to achieve remission or fail to respond altogether. Both Crohn's disease and ulcerative colitis are complex and heterogeneous diseases with several molecular pathways involved in disease pathophysiology. We propose an additional therapeutic approach to the treatment of IBD, bispecific antibodies (BsAbs), which combine two distinct binding specificities within a single biologic to allow the simultaneous targeting of multiple disease-causing cytokines or pathways. Although primarily used in oncology thus far, the unique combinatorial mechanism of action of BsAbs may provide new therapeutic options for a broad range of clinical applications, including autoimmune and inflammatory diseases. This review will discuss the current status of BsAb development in general and potentially therapeutic application in IBD.     

PTPN2 is associated with Crohn's disease and its expression is regulated by NKX2-3

PTPN2 is a risk gene for Crohn's disease (CD). We investigated whether PTPN2 genetic variants (rs2542151 and rs2542152) were associated with CD in a familial IBD registry. Both rs2542151 and rs2542152 are associated with CD, but not ulcerative colitis (UC). mRNA expression levels of PTPN2 were significantly increased in intestinal tissues (p=0.0493), and nearly significantly increased in B cells (p=0.0889) from CD patients, but not significantly altered in UC. cDNA microarray results found that PTPN2 was down-regulated by NKX2-3 knockdown in human cells. We confirmed this observation by RT-PCR analyses in NKX2-3 knockdown in B cells from IBD patients and human intestinal microvascular endothelial cells (HIMEC). In addition, we found that mRNA expression of another IBD-associated gene, NKX2-3, was increased in intestinal tissues and B cells from CD patients, but not significantly increased in UC patients. A positive correlation was observed between mRNA expression of PTPN2 and NKX2-3 in B cells and in intestinal tissues from both CD and UC patients. These results suggest that PTPN2 may have an important role in CD pathogenesis and may represent a potential diagnostic and therapeutic target for IBD.     

CCR5在炎症性肠病患者肠黏膜的表达及其与β-arrestin 2表达的关系

 目的: 通过分析CCR5在炎症性肠病(IBD)患者活检肠黏膜的表达及其与β-arrestin 2表达的相关性,探讨CCR5与β-arrestin 2在IBD发病中的作用。方法: IBD活动期组53例、IBD缓解期组26例和正常对照组30例纳入研究,用EnVision二步免疫组化方法检测活检肠黏膜CCR5和β-arrestin 2的表达。结果: IBD活动期组CCR5阳性表达率及免疫组化评分均高于正常对照组和IBD缓解期组(P<0.05),CCR5表达与IBD活动期组的临床严重程度、病变范围及内镜下分级无明显关联性;β-arrestin 2在IBD活动期组的阳性表达率均明显低于IBD缓解期组和正常对照组(P<0.05),并且在IBD活动期β-arrestin 2表达与CCR5表达呈负相关性(P<0.05)。结论: 在IBD活动期组肠黏膜CCR5呈高表达,β-arrestin 2呈明显低表达,CCR5与β-arrestin 2表达呈负相关性。     

CXCR1-binding chemokines in inflammatory bowel diseases: down-regulated IL-8/CXCL8 production by leukocytes in Crohn's disease and selective GCP-2/CXCL6 expression in inflamed intestinal tissue

Crohn's disease (CD) and ulcerative colitis (UC) are inflammatory bowel diseases (IBD) that are characterized by chronic intestinal inflammation and a constant influx of leukocytes mediated by pro-inflammatory cytokines and chemokines. The intestinal expression of the CXCR1-binding chemokines IL-8/CXCL8 and GCP-2/CXCL6 and the participation of immunocompetent cells in IBD were evaluated. IL-8 production by peripheral blood mononuclear cells (PBMC) from IBD patients, stimulated with endotoxin, plant lectin or double-stranded RNA, was significantly lowered in patients with CD, but not in UC patients or healthy subjects. The reduced chemokine production by PBMC from IBD patients was both IL-8 and CD specific, but not inducer dependent. In serum, most chemokines remained undetectable, while the levels of those that were measurable remained unaltered in IBD patients. GCP-2, but not ENA-78/CXCL5, nor IL-8, were highly expressed by endothelial cells in inflamed intestinal tissue of IBD patients. In contrast, stimulated endothelial cell cultures produced more IL-8 than GCP-2. The selective GCP-2 staining of endothelial cells at sites of ulcerations suggests that GCP-2, despite its low production capacity in vitro, plays a role in IBD that is different from that of structurally (ENA-78) and functionally (IL-8) related ELR(+) CXC chemokines. Thus, the chemokine network shows complementarity rather than redundancy.     

Immunological mechanisms underpinning faecal microbiota transplantation for the treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic gastrointestinal disease that results from a dysregulated immune response against specific environmental triggers in a genetically predisposed individual. Increasing evidence has indicated a causal role for changes in gut microbiota (dysbiosis) contributing to this immune-mediated intestinal inflammation. These mechanisms involve dysregulation of multiple facets of the host immune pathways that are potentially reversible. Faecal microbiota transplantation (FMT) is the transfer of processed stool from a healthy donor into an individual with an illness. FMT has shown promising results in both animal model experiments and clinical studies in IBD in the resolution of intestinal inflammation. The underlying mechanisms, however, are unclear. Insights from these studies have shown interactions between modulation of dysbiosis via changes in abundances of specific members of the gut microbial community and changes in host immunological pathways. Unravelling these causal relationships has promising potential for a translational therapy role to develop targeted microbial therapies and understand the mechanisms that underpin IBD aetiopathogenesis. In this review, we discuss current evidence for the contribution of gut microbiota in the disruption of intestinal immune homeostasis and immunoregulatory mechanisms that are associated with the resolution of inflammation through FMT in IBD.     

Identification of disease-associated DNA methylation in intestinal tissues from patients with inflammatory bowel disease

Lin Z, Hegarty JP, Cappel JA, Yu W, Chen X, Faber P, Wang Y, Kelly AA, Poritz LS, Peterson BZ, Schreiber S, Fan J‐B, Koltun WA. Identification of disease‐associated DNA methylation in intestinal tissues from patients with inflammatory bowel disease. Overwhelming evidence supports the theory that inflammatory bowel disease (IBD) is caused by a complex interplay between genetic predispositions of multiple genes, combined with an abnormal interaction with environmental factors. It is becoming apparent that epigenetic factors can have a significant contribution in the pathogenesis of disease. Changes in the methylation state of IBD‐associated genes could significantly alter levels of gene expression, potentially contributing to disease onset and progression. We have explored the role of DNA methylation in IBD pathogenesis. DNA methylation profiles (1505 CpG sites of 807 genes) of matched diseased (n = 26) and non‐diseased (n = 26) intestinal tissues from 26 patients with IBD [Crohn's disease (CD) n = 9, ulcerative colitis (UC) n = 17] were profiled using the GoldenGate? methylation assay. After an initial identification of a panel of 50 differentially methylated CpG sites from a training set (14 non‐diseased and 14 diseased tissues) and subsequent validation with a testing set (12 non‐diseased and 12 diseased tissues), we identified seven CpG sites that are differentially methylated in intestinal tissues of IBD patients. We have also identified changes in DNA methylation associated with the two major IBD subtypes, CD and UC. This study reports IBD‐associated changes in DNA methylation in intestinal tissue, which may be disease subtype‐specific.